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Posts Tagged ‘osteoporosis’


Parathyroids and Bone Metabolism

Writer and Curator: Larry H. Bernstein, MD, FCAP 

 

 

Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the thyroid gland) acts to decrease calcium concentration. PTH acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor (high levels in bone and kidney) and the parathyroid hormone 2 receptor (high levels in the central nervous system, pancreas, testis, and placenta). PTH half-life is approximately 4 minutes.[2] It has a molecular mass of 9.4 kDa.

hPTH-(1-34) crystallizes as a slightly bent, long helical dimer. Analysis reveals that the extended helical conformation of hPTH-(1-34) is the likely bioactive conformation.[4] The N-terminal fragment 1-34 of parathyroid hormone (PTH) has been crystallized and the structure has been refined to 0.9 Å resolution.

The_ribbon_cartoon_structure - hPTH helical dimer

The_ribbon_cartoon_structure – hPTH helical dimer

http://upload.wikimedia.org/wikipedia/commons/1/1e/The_ribbon_cartoon_structure.png

Regulation of serum calcium

PTH was one of the first hormones to be shown to use the G-protein, adenylyl cyclase second messenger system.

Normal total plasma calcium level ranges from 8.5 to 10.2 mg/dL (2.12 mmol/L to 2.55 mmol/L).

Region Effect
bone It enhances the release of calcium from the large reservoir contained in the bones.[7] Bone resorption is the normal destruction of bone by osteoclasts, which are indirectly stimulated by PTH. Stimulation is indirect since osteoclasts do not have a receptor for PTH; rather, PTH binds to osteoblasts, the cells responsible for creating bone. Binding stimulates osteoblasts to increase their expression of RANKL and inhibits their expression of Osteoprotegerin (OPG). OPG binds to RANKL and blocks it from interacting with RANK, a receptor for RANKL. The binding of RANKL to RANK (facilitated by the decreased amount of OPG available for binding the excess RANKL) stimulates these osteoclast precursors to fuse, forming new osteoclasts, which ultimately enhances bone resorption
kidney It enhances active reabsorption of calcium and magnesium from distal tubules and the thick ascending limb. As bone is degraded, both calcium and phosphate are released. It also decreases the reabsorption of phosphate, with a net loss in plasma phosphate concentration. When the calcium:phosphate ratio increases, more calcium is free in the circulation
intestine via kidney It enhances the absorption of calcium in the intestine by increasing the production of activated vitamin D. Vitamin D activation occurs in the kidney. PTH up-regulates25-hydroxyvitamin D3 1-alpha-hydroxylase, the enzyme responsible for 1-alpha hydroxylation of 25-hydroxy vitamin D, converting vitamin D to its active form (1,25-dihydroxy vitamin D). This activated form of vitamin D increases the absorption of calcium (as Ca2+ ions) by the intestine via calbindin.

http://en.wikipedia.org/wiki/Parathyroid_hormone

Development of Present Concepts of the Parathyroid –
The Parathyroids – Progress, problems and practice,
in Current Problems in Surgery, 1971; 8(8): 3-64.
Leon Goldman, Gilbert Gordon, Betty S. Roof
http://dx.doi.org/10.1016/S0011-3840(71)80008-4

The parathyroid gland first achieved clinical significance because of hypoparathyroid tetany. Tetany: a syndrome manifested by painful muscle spasms or rigors; is derived from the Greek:  tetanos, past participle of the verb teinein, meaning “to stretch,” Tetany : stretched, or spastic, in modern terms “up tight.,’ When the word was used by Hippocrates, no differentiation was made between the types of muscular spasms caused by neurotoxins (e.g., lockjaw) and those of metabolic causes. The word ~ went through the Latin, tetanus, and to French. Te’tanie, where the attribute of intermittent muscular spasm was added.

Owea's drawing of parathyroid gland of Indian rhinoceros

Owea’s drawing of parathyroid gland of Indian rhinoceros

Owea’s drawing of parathyroid gland of Indian rhinoceros

According to file Oxford English Dictionary, the relation of tetany to surgical operations was noted in tile year 1805 in The Medical Journal XIV, 304: “tetanie affections very often to|low the great operations. . .” It is not clear from this reference what type of operations were invo]ved.  The relationship of tetany to thyroidectomy was recognized as early as 1878 when WoIfler described convulsions in one of the patients on whom Billroth had performed a total thyroidectomy. The great surgeon WilIiam Stewart Halsted suggested that postoperative hypoparathyroidism had not been reported earlier because before that time total thyroidectomy had always been fatal, leaving insufficient time for tetany to develop. In 1883 Weiss collected 13 cases of tetany, all following total thyroidcctomy. The relation to total thyroidectomy became historically significant later when postoperative tetany was misinterpreted as the acute form of thyroid insufficiency, while myxedema was correctly recognized as the chronic form.
Anatomically, the parathyroid glands had been noted fleetingly by Remak (1855), by Virchow (1863) and probably by others in the course of human dissection. Perhaps better publicized was the description by Sir Richard Owen, published in 1852. As Hunterian Professor and Conservator of the Museum in the Royal College of Surgeons, Owen anatomized animals that died at the London Zoo. In 1849, while performing an autopsy on tile Great Indian rhinoceros, Owen clearly noted, drew and named the parathyroid gland (Fig. 1). However, microscopic examination was not reported, and it was not known at that time whether the parathyroid gland was separate.
The causal relationship of the parathyroid gland to post-thyroidectomy tetany was clarified by the French physiologist Eugdne Gley in 1891. He showed that, in the rabbit, removal of the thyroid gland was not responsible for these seizures but that removal of the parathyroid glands caused fatal convulsions.
Very soon after this, a parallel discovery was made in Berkeley, California, by Jacques Loeb.  Loeb noticed that the rhythmic contractions of a frog muscle in a saline medium were stopped by the addition of calcium. He concluded that calcium has the important function of inhibiting excessive neuromuscular
irritability.  Loeb’s studies led MacCallum, in 1909, to investigate the possibility that a low blood calcium level might be responsible for the increased excitability of the muscles, in hypoparathyroid tetany.  He and Voegtlin removed the parathyroids from dogs and showed that tetany ensued when the serum calcium level fell. They also showed that administration of calcium promptly relieved tetany. Less well known is their publication in the following
year, which entirely recanted the earlier view. Their observations that calcium, magnesium and strontium immediately abolish tetany, and the report of Joseph and Sleltzer that infusion of hypertonic sodium chloride slowly relieves this kind of tetany, led MacCallum to believe that the effect of calcium was nonspecific.
By this time thyroid surgery was being performed widely. The Reverdin brothers in Geneva noted what they considered complex nervous manifestations following total thyroidectomv, Moussu’ s observations in animals were confirmed in patients; post-thyroidectomy convulsions were not necessarily fatal.
Thyroid surgery was now sufficiently improved so that Kocher was able to find symptoms of tetany–and these were transient ….. in only 1 of his 18 cases of total thyroidectomy. How many more would have been identified as victims of hypoparathyroidism by appropriate chemical examination can only be conjectured. By 1907 Halsted had recognized the importance of the parathyroids and how essential the intimate knowledge of their anatomy is to the goiter surgeon. Halsted put a bright young medical student to work on this project as a penalty for delinquent attendance at lectures. The sketch of the beautiful dissection by the student, Herbert McLean Evans, was used by Halsted to illustrate his monograph on The Operative History of Goiter. On the basis of this knowledge, of anatomy, it was established that the parathyroids are usually related to the posterior capsule and that leaving this capsule intact greatly reduces the risk of tetany.
In 1923 the distinguished Norwegian physician-physiologist, Harald Salvesen published beautiful, imaginative and thorough studies in which he showed, that complete parathyroid ablation invariably lowered the blood calcium, that the blood sugar level was not altered and that guanidine accumulation occurred only terminally during agonal convulsions. He further found that parathyroid tetany could be prevented by calcium feeding and confirmed MacCallum’s earlier observation that it could be promptly corrected by calcium infusion. He also noted that one of his dogs with parathyroid tetany developed a cataract. In our opinion, the relation of the parathyroid gland to calcium metabolism was first firmly established by Salvesen in 1923.
Consider the knowledge and use of endocrines in 1923. Desiccated thyroid, which Osler had praised as the miracle of modern metabolic therapy, was the only orally effective endocrine preparation. ]nsulin had just been discovered. Another potent preparation was the hydrochloric acid extract of parathyroid glands made by Adolph Hanson. That it was an effective preparation is perhaps best attested by the fact that it is still used, under the name Parathyroid Extract USP, and that much of the work on the actions of parathyroid hormone has been carried out with this crude extract. In 1925 Collip, who had been of such immeasurable help to Banting, Best and McLeod in preparing a clean, potent insulin extract from normal pancreas, applied his genius to the parathyroid with an equally satisfactory result. His relatively clean parathyroid extract  made it possible for the first time to elucidate the actions of the parathyroid glands in man.
Using this preparation, Albright and Ellsworth in 1929 clarified the two fundamental actions of parathyroid hormone (PTH) identical with those obtained nowadays with the most highly purified preparations. These two actions are:
(1) elevation of serum calcium and
(2) excretion of phosphate by the kidneys, with a consequent lowering of the serum phosphate.
It will later be shown that the action that raises serum calcium levels is, for the most part, an increase in the rate of bone breakdown. It remained for Copp and associates to show in 1961 that another horrnone, calcitonin, with an opposite action, is necessary for maintenance of calcium homeostasis. And still later Chase and Aurbach showed in 1968 that the phosphaturic action of PTH is mediated by the enzyme adenyl cyclase, which stimulates production of cyclic 3’5′-adenosine monophosphate (AMP).
It is now clear that hypophosphatemia predisposes to hyperealcemia and that hyperphosphatemia can actually abolish hypercalcemia. However, numerous experiments, one of them by Albright’s collaborators, Ellsworth and Futeher in 1935 showed that parathyroid extract raised the serum calcium level in the absence of the kidneys.  Clearly, therefore, the calcium-mobilizing effect of PTH is not the result of the phosphate diuretic action only. Conclusive evidence was obtained by Barnicot of Cambridge in 1948. …
The brilliant group at the Massachusetts General Hospital, led by Aub and including two young men destined to make brilliant records in American medicine Fuller Albright and Waiter Bauer soon showed that the kind of hyperparathyroidism described by Recklinghausen, Mandl and Askanazy is, in fact, the end stage of a series of chemical events predictable from the known actions of PTH. Starting with the famous case of Captain Charles Martell, a mariner with severe bone disease, who shrank in stature in 10 years, Albright soon clarified the most significant feature of hyperparathyroidism: the hypercalcemia that is found in at least 99% of patients with proved primary hyperparathyroidism.
It was not until 1953 that Jonas Shota directly demonstrated the other action of excess PTH in hyperparathyroidism: a low rate of tubular reabsorption of phosphate (TRP), as fifteen years later, in 1968, Chase and Aurbach would show that this action is mediated by renal adenyl cyclase and cyclic AMP. Meanwhile, in 1935, Pappenheimer and Wilens had described another form of hyperparathyroidism arising not as a primary tumor, but as a secondary or compensatory response to the metabolic abnormalities of uremia. Goldman independently described this phenomenon. It .is noteworthy that hyperparathyroidism secondary to lack of dietary calcium had already been described by Erdheiqm and that  these 2 causes of secondary hyperparathyroidism, Uremia and intestinal malabsorption, have subsequently been shown, to have in comrnon inadequate intestinal absorption of calcium.
Since the classic studies of Sandstrom, Gley, Loeb, Salvesen, Cotlip, Aub, Bauer and Albright, enormous strides have advanced our knowledge of parathyroid physiology. Isolation, purification, and characterization of  the hormone and development of a highly sensitive  radioimmunoassay for PTH.  Almost slmultaneously in1959, Aurbach, Rasmussen and Craig obtained a purified bovine PTH. These two groups of investigators identified a similar peptide with a molecular weight of about 8,500 and with biological activity of about 3.000 units/mg. This peptide contains 84 amino acid residfies the first 30-45 are necessary for biologic and immunologic activity. A tentative molecular structure reported by Potts, Aurbach and Sherwood in 1965 has subsequently been modified by Brewer and Ronan, with confirmation by Niall et aI. in Potts’s laboratory. The heterogeneous  nature of circulating PTH was first: shown by Berson and Yalow using two antisera prepared from beef PTH but showing quantitative differences in reaction to circulating PTH. They were able  to detect two parathormones, one with a half-life of only 10-20 minutes, and another with a half-life of about 1.5 hours.
The parathyroid hormone-regulated transcriptome in osteocytes: Parallel actions with 1,25-dihydroxyvitamin D3 to oppose gene expression changes during differentiation and to promote mature cell function

Hillary C. St. John, MB Meyer, NA Benkusky, AH Carlson, M Prideaux, et al.
Bone 72 (2015) 81–91
http://dx.doi.org/10.1016/j.bone.2014.11.010

Although localized to the mineralized matrix of bone, osteocytes are able to respond to systemic factors such as the calciotropic hormones 1, 25-(OH)2 D3 and PTH. In the present studies, we examined the transcriptomic response to PTH in an osteocyte cell model and found that this hormone regulated an extensive panel of genes. Surprisingly, PTH uniquely modulated two cohorts of genes, one that was expressed and associated with the osteoblast to osteocyte transition and the other a cohort that was expressed only in the mature osteocyte. Interestingly, PTH’s effects were largely to oppose the expression of differentiation-related genes in the former cohort, while potentiating the expression of osteocyte-specific genes in the latter cohort. A comparison of the transcriptional effects of PTH with those obtained previously with 1, 25-(OH)2 D3 revealed a subset of genes that was strongly overlapping. While 1, 25-(OH)2 D3 potentiated the expression of osteocyte-specific genes similar to that seen with PTH, the overlap between the two hormones was more limited. Additional experiments identified the PKA-activated phospho-CREB (pCREB) cistrome, revealing that while many of the differentiation-related PTH regulated genes were apparent targets of a PKA-mediated signaling pathway, a reduction in pCREB binding at sites associated with osteocyte-specific PTH targets appeared to involve alternative PTH activation pathways. That pCREB binding activities positioned near important hormone-regulated gene cohorts were localized to control regions of genes was reinforced by the presence of epigenetic enhancer signatures exemplified by unique modifications at histones H3 and H4. These studies suggest that both PTH and 1, 25-(OH)2 D3 may play important and perhaps cooperative roles in limiting osteocyte differentiation from its precursors while simultaneously exerting distinct roles in regulating mature osteocyte function. Our results provide new insight into transcription factor-associated mechanisms through which PTH and 1, 25-(OH)2 D3 regulate a plethora of genes important to the osteoblast/osteocyte lineage.

Bone, a dynamic and integrating tissue

The guest editors Bram C.J. van der Eerden, Anna Teti, Willian F. Zambuzzi
Archives of Biochemistry and Biophysics 561 (2014) 1–2
http://dx.doi.org/10.1016/j.abb.2014.08.012

The special issue ‘Bone, a dynamic and integrating tissue’ provides the most recent information regarding the interacting nature of bone cells with their immediate neighboring cells within the skeleton as well as with distant target cells in other organs, using different types of both cellular and non-cellular communication. It should appeal to any scientist or clinician in the field, given the wide variety of topics, covering molecular, experimental cell and animal biology, biomechanics and -physics, genetics and medicine.

This special issue arose from a collaboration between the guest editors within ‘INTERBONE’, a European Union funded Marie Curie Actions – People – International Research Staff Scheme (PIRSESGA-2011-295181) on the interplay among bone cells, matrices and systems.

Over the recent years, many developments have paved new avenues to study signaling pathways and mechanisms in bone in much greater detail. Genetic progress has been made, which has provided us with novel genes behind already known as well as hitherto idiopathic bone diseases. The enormous expansion of specific animal models has enabled us to study new mechanisms and pathways in vivo in great spatial and temporal detail. As a consequence, novel treatment modalities have seen the light, which are predominantly focusing on bone anabolic therapies. These advances will not cease to exist and an exciting biological era lies ahead of us, with many discoveries to be made.

In this special issue of Archives in Biochemistry and Biophysics, experts in the field of bone metabolism have addressed the recent developments in which special attention is paid to the concept that bone is not just a static, isolated organ, but a dynamic and integrating tissue. Over the last decade, discoveries have led to the notion that bone cells are interacting with many other cell types within bone. Besides this intraskeletal communication, bone cells produce factors that are capable of controlling cell types and organs elsewhere in the organism, which are now being recognized as bona fide hormones.

All contributors have explored the recent advances made in their research area. The latest progress in osteoblast/osteocyte and osteoclast biology is revisited with special focus on bone morphogenetic proteins, microRNAs and extracellular vesicles as illustrative examples of different levels of communication between cell types. In separate chapters, the interaction of osteoblasts and osteoclasts, as well as their cross-talk with endothelial cells, fat cells, immune cells, hematopoietic stem cells and different types of cancer cells is discussed extensively, further emphasizing the interactive nature of bone cells in their microenvironment. Beside cell–cell interaction, attention has been paid to the osteointegration of bone cells in a non-cellular context, including extracellular matrix and metal devices, combining main components for bone bioengineering. Finally, the endocrine role of bone is discussed in great detail by several contributors, focusing on the control of bone cell function by the brain as well as the role of bone-produced factors in, amongst others, phosphate homeostasis, energy metabolism and fertility.

The Great Beauty of the osteoclast

Alfredo Cappariello, Antonio Maurizi, Vimal Veeriah, Anna Teti
Archives of Biochemistry and Biophysics 561 (2014) 13–21
http://dx.doi.org/10.1016/j.abb.2014.08.009

Much has been written recently on osteoclast biology, but this cell type still astonishes scientists with its multifaceted functions and unique properties. The last three decades have seen a change in thinking about the osteoclast, from a cell with a single function, which just destroys the tissue it belongs to, to an ‘‘orchestrator’’ implicated in the concerted regulation of bone turnover. Osteoclasts have unique morphological features, organelle distribution and plasma membrane domain organization. They require polarization to cause extracellular bone breakdown and release of the digested bone matrix products into the circulation. Osteoclasts contribute to the control of skeletal growth and renewal. Alongside other organs, including kidney, gut, thyroid and parathyroid glands, they also affect calcemia and phosphatemia. Osteoclasts are very sensitive to pro-inflammatory stimuli, and studies in the ‘00s ascertained their tight link with the immune system, bringing about the question why bone needs a cell regulated by the immune system to remove the extracellular matrix components. Recently, osteoclasts have been demonstrated to contribute to the hematopoietic stem cell niche, controlling local calcium concentration and regulating the turnover of factors essential for hematopoietic stem cell mobilization. Finally, osteoclasts are important regulators of osteoblast activity and angiogenesis, both by releasing factors stored in the bone matrix, and secreting ‘‘clastokines’’ that regulate the activity of neighboring cells. All these facets will be discussed in this review article, with the aim of underscoring The Great Beauty of the osteoclast.

Osteoclasts: more than ‘bone eaters’

Julia F. Charles and Antonios O. Aliprantis
Trends in Molecular Medicine, Aug 2014; 20(8): 449-459
http://dx.doi.org/10.1016/j.molmed.2014.06.001

As the only cells definitively shown to degrade bone, osteoclasts are key mediators of skeletal diseases including osteoporosis. Bone-forming osteoblasts, and hematopoietic and immune system cells, each influence osteoclast formation and function, but the reciprocal impact of osteoclasts on these cells is less well appreciated. We highlight here the functions that osteoclasts perform beyond bone resorption.
First, we consider how osteoclast signals may contribute to bone formation by osteoblasts and to the pathology of bone lesions such as fibrous dysplasia and giant cell tumors.
Second, we review the interaction of osteoclasts with the hematopoietic system, including the stem cell niche and adaptive immune cells. Connections between osteoclasts and other cells in the bone microenvironment are discussed within a clinically relevant framework.

Bone is a composite tissue of protein and mineral which undergoes continual remodeling to grow, heal damage, and regulate calcium and phosphate metabolism. This remodeling process is executed by the concerted and sequential effort of bone-resorbing osteoclasts and bone-forming osteoblasts, acting in what has been termed the basic multicellular unit (BMU) (Figure 1A). Osteocytes, long-lived osteoblast-derived cells that reside within the bone matrix, monitor bone quality and stress, and coordinate remodeling through membrane-bound and secreted factors. Skeletal integrity is maintained throughout the life-span by matching bone formation and resorption, a process referred to as osteoclast:osteoblast  ‘coupling.’ Coupling is thoroughly summarized in recent excellent reviews and in Figure 1.

Coupling: how osteoclasts ‘talk back’ to cells of the osteoblast lineage Coupling of bone formation to resorption is likely achieved through multiple mechanisms, including signals that stimulate the proliferation of pre-osteoblasts, their recruitment to resorption lacunae, and their differentiation into bone-forming cells. Cellular mediators of coupling include osteoclasts, osteoblasts, osteocytes, macrophages, and T cells, which produce a variety of factors including Wnt pathway regulators, such as sclerostin, and cytokines such as oncostatin M

Osteoclasts–osteoblast interactions in the basic multicellular unit (BMU).

Osteoclasts–osteoblast interactions in the basic multicellular unit (BMU).

Osteoclasts–osteoblast interactions in the basic multicellular unit (BMU).
Cell–cell contact mechanisms may also mediate OC-OB communication. Bidirectional signaling from OC ephrins and OB Eph receptors, and reverse signaling through RANKL on OBs, have both been invoked.

Box 1. Usurping local resources: osteoclasts feed bone invaders

Liberation of growth factors embedded in bone matrix by osteoclasts may promote metastatic tumor growth in bone. Reciprocal stimulation of osteoclasts by cancer cell derived parathyroid hormone related protein (PTHrP), and other factors, could potentiate growth factor release in what has been termed the ‘vicious cycle’ ]. Xenograft experiments utilizing breast cancer cells expressing a TGFβ responsive reporter demonstrated osteolytic metastases had high TGFβ activity. Inhibition of osteoclastic bone resorption with pamidronate reduced TGFβ activity and osteolytic lesions, suggesting that matrix resorption is a relevant source of TGFβ for skeletal metastasis in vivo. Although prophylactic pamidronate treatment decreased frequency of bone metastasis, the drug did not decrease disease progression if administered after tumor cell inoculation. Thus, whether inhibiting the release of matrix growth factors by osteoclasts has a substantive effect on tumor growth is unclear. Several bisphosphonates, as well as the anti-RANKL antibody denosumab, reduce skeletal events in metastatic cancer, but data on whether they prevent bone metastasis are inconsistent.

Immunoregulation by osteoclasts. Osteoclast precursors (OCPs) and osteoclasts (OCs) inhibit CD4 and CD8 T cell proliferation via nitric oxide (NO) production in response to T cell derived interferon g (IFNg). IFNg in turn inhibits differentiation of OCPs into mature OCs. OCs also present antigen through major histocompatibility complex class I (MHCI) to skew CD8+ T cells toward an induced Treg phenotype termed OC-iTcreg. OC-iTcreg cells in turn inhibit OCP differentiation to mature OC through IFNg, interleukin 10 (IL10), and IL6.

In mouse models, we suggest that systems for the temporal deletion of conditional alleles in osteoclasts and their precursors be established. Moreover, clinical research in humans with emerging therapeutics which specifically target key regulators of bone remodeling, such as RANKL, cathepsin K, and sclerostin, could include nested translational studies that specifically address their effects on the immune system, HSCs, and tumor growth, where appropriate. In these ways, a clear picture of osteoclast biology beyond their role as ‘bone eaters’ will emerge.

Leukemia inhibitory factor: A paracrine mediator of bone metabolism

Natalie A. Sims & Rachelle W. Johnson
Growth Factors, April 2012; 30(2): 76–87
http://dx.doi.org:/10.3109/08977194.2012.656760

Leukemia inhibitory factor (LIF) is a soluble interleukin-6 family cytokine that regulates a number of physiologic functions, including normal skeletal remodeling. LIF signals through the cytokine co-receptor glycoprotein-130 in complex with its cytokine-specific receptor [LIF receptor (LIFR)] to activate signaling cascades in cells of the skeletal system, including stromal cells, chondrocytes, osteoblasts, osteocytes, adipocytes, and synovial fibroblasts. LIF action on skeletal cells is cell-type specific, and frequently dependent on the state of cell differentiation. This review describes the expression patterns of LIF and LIFR in bone, their regulation by physiological and inflammatory agents, as well as cell-specific influences of LIF on osteoblast, osteoclast, chondrocyte, and adipocyte differentiation. The actions of LIF in normal skeletal growth and maintenance, in pathological states (e.g. autocrine tumor cell signaling and growth in bone) and inflammatory conditions (e.g. arthritis) will be discussed, as well as the signaling pathways activated by LIF and their importance in bone formation and resorption.

In vivo evidence of IGF-I–estrogen crosstalk in mediating the cortical bone response to mechanical strain

Subburaman Mohan, CG Bhat, JE Wergedal and C Kesavan
Bone Research (2014) 2, 14007 http://dx.doi.org:/10.1038/boneres.2014.7

Although insulin-like growth factor-I (IGF-I) and estrogen signaling pathways have been shown to be involved in mediating the bone anabolic response to mechanical loading, it is not known whether these two signaling pathways crosstalk with each other in producing a skeletal response to mechanical loading. To test this, at 5 weeks of age, partial ovariectomy (pOVX) or a sham operation was performed on heterozygous IGF-I conditional knockout (HIGF-I KO) and control mice generated using a Cre-loxP approach. At 10 weeks of age, a 10 N axial load was applied on the right tibia of these mice for a period of 2 weeks and the left tibia was used as an internal non-non-loaded control. At the cortical site, partial estrogen loss reduced total volumetric bone mineral density (BMD) by 5% in control pOVX mice (P50.05, one-way ANOVA), but not in the H IGF-I KO pOVX mice. At the trabecular site, bone volume/total volume (BV/TV) was reduced by 5%–6% in both control pOVX (P,0.05) and H IGF-I KO pOVX (P50.05) mice. Two weeks of mechanical loading caused a 7%–8% and an 11%–13%(P,0.05 vs. non-loaded bones) increase in cortical BMD and cortical thickness (Ct.Th), respectively, in the control sham, control pOVX and H IGF-I KO sham groups. By contrast, the magnitude of cortical BMD (4%, P50.13) and Ct.Th (6%, P,0.05) responses were reduced by 50% in the H IGF-I KO pOVX mice compared to the other three groups. The interaction between genotype and estrogen deficiency on the mechanical loading-induced cortical bone response was significant (P,0.05) by two-way ANOVA. Two weeks of axial loading caused similar increases in trabecular BV/TV (13%–17%) and thickness (17%–23%) in all four groups of mice. In conclusion, partial loss of both estrogen and IGF-I significantly reduced cortical but not the trabecular bone response to mechanical loading, providing in vivo evidence of the above crosstalk in mediating the bone response to loading.

Role of FGF/FGFR signaling in skeletal development and homeostasis: learning from mouse models

Nan Su, Min Jin and Lin Chen
Bone Research (2014) 2, 14003; http://dx.doi.org:/10.1038/boneres.2014.3

Fibroblast growth factor (FGF)/fibroblast growth factor receptor (FGFR) signaling plays essential roles in bone development and diseases. Missense mutations in FGFs and FGFRs in humans can cause various congenital bone diseases, including chondrodysplasia syndromes, craniosynostosis syndromes and syndromes with dysregulated phosphate metabolism. FGF/FGFR signaling is also an important pathway involved in the maintenance of adult bone homeostasis. Multiple kinds of mouse models, mimicking human skeleton diseases caused by missense mutations in FGFs and FGFRs, have been established by knock-in/out and transgenic technologies. These genetically modified mice provide good models for studying the role of FGF/FGFR signaling in skeleton development and homeostasis. In this review, we summarize the mouse models of FGF signaling-related skeleton diseases and recent progresses regarding the molecular mechanisms, underlying the role of FGFs/FGFRs in the regulation of bone development and homeostasis. This review also provides a perspective view on future works to explore the roles of FGF signaling in skeletal development and homeostasis.

Osteoporosis in men: a review

Robert A Adler
Bone Research (2014) 2, 14001; http://dx.doi.org:/10.1038/boneres.2014.1

Osteoporosis and consequent fracture are not limited to postmenopausal women. There is increasing attention being paid to osteoporosis in older men. Men suffer osteoporotic fractures about 10 years later in life than women, but life expectancy is increasing faster in men than women. Thus, men are living long enough to fracture, and when they do the consequences are greater than in women, with men having about twice the 1-year fatality rate after hip fracture, compared to women. Men at high risk for fracture include those men who have already had a fragility fracture, men on oral glucocorticoids or those men being treated for prostate cancer with androgen deprivation therapy. Beyond these high risk men, there are many other risk factors and secondary causes of osteoporosis in men. Evaluation includes careful history and physical examination to reveal potential secondary causes, including many medications, a short list of laboratory tests, and bone mineral density testing by dual energy X-ray absorptiometry (DXA) of spine and hip. Recently, international organizations have advocated a single normative database for interpreting DXA testing in men and women. The consequences of this change need to be determined. There are several choices of therapy for osteoporosis in men, with most fracture reduction estimation based on studies in women.

From skeletal to non skeletal: The intriguing roles of BMP-9: A literature review

  1. Leblanc, G. Drouin, G. Grenier, N. Faucheux, R. Hamdy
    Advances in Bioscience and Biotechnology, 2013; 4: 31-46
    http://dx.doi.org/10.4236/abb.2013.410A4004

In the well-known superfamily of transforming growth factors beta (TGF-), bone morphogenetic proteins (BMPs) are one of the most compelling cytokines for their major role in regulation of cell growth and differentiation in both embryonic and adult tissues. This subfamily was first described for its ability of potentiating bone formation, but nowadays, the power of BMPs is well beyond the bone healing scope. Some of the BMPs have been well studied and described in the literature, but the BMP9 is still worthy of attention. It has been shown by many authors that it is the most potent osteogenic BMP. Moreover, it has been de- scribed as one of the rare circulating BMPs. In this paper, we will review the recent literature on BMP9 and the different avenues for future research in that field. Our primary scope is to review its relation to bone formation and to elaborate on the available literature on other systems.

Fong et al. recently demonstrated in vitro that rhBMP9 can also augment bone resorption. This increase was shown to be functional and not related to osteoclast formation. Furthermore, rhBMP9 could alter the intrinsic apoptosis pathway and increase survival of osteoclasts. The effect of rhBMP9 on osteoclast was explained by the presence of ALK1 and BMPRII co-receptors and their activation of the Smad 1/5/8 and non-smad MAPK/ERK pathways. These results show for the first time that BMP9 can directly affect human osteoclasts, acting on their function and their survival.

Insulin resistance is a systemic multifactorial impairment of glucose uptake. Muscle, a glucose consuming organ, needs Akt2 to be able to activate insulin-induced glucose uptake and this pathway seems to be severely impaired in insulin resistance. Interestingly, a combination of bioinformatic and high- throughput functional analyses have shown BMP9 to be the first hepatic factor to regulate blood glucose concencentration. Moreover, this effect was thought to be mediated by activation of Akt kinase in differentiated myotubes. Then, it has been demonstrated that recombinant BMP9 (1 and 5 mg/kg) improves glucose homeostasis in vivo in diabetic and non-diabetic rodents. The mechanism relied on the upregulation of Smad5 and Akt2 in differentiated rats myotubes. On the opposite side, Smad5 was downregulated in myotubes by de xamethasone, a well known hyperglycemia inducer and Smad5 knockdown in rats decreased Akt2 expression and phosphorylation leading to a decrease in insulin-induced glucose uptake by myotubes. It was then hypothesized that Smad5 regulated glucose uptake in skeletal muscle through Akt2 expression and phosphorylation. These findings also revealed Smad5 as a potential target for the treatment of type 2 diabetes. Hence, BMP9 could be seen as a potential activator of Smad5 for that purpose.

BMP9 is a major member of the TGF- superfamily that is implied in many fundamental developmental and pa- thologic processes. Future research will certainly bring answers to the many questions left open, and those an- swers will unquestionably lead to clinical applications.

Understanding Bone Loss

Max Stanley Chartrand, PhD.
DigiCare® Behavioral Research

During their lifetimes, at least half of those over age 50 will be at risk of developing osteoporosis. When we speak of bone loss we are primarily speaking of three diagnostic stages: Osteoarthritis (1-2% loss per annum), Osteopenia (3% per annum), and Osteoporosis (4-5%+ per annum) that are caused almost entirely by diet, hydration, lifestyle, medications, and environ-mental stressors.

Human bones are highly vascularized and mineralized tissues that are constantly being shaped and developed by cells called osteoblasts and torn down and resorbed by cells called osteoclasts. Recent research confirms that throughout one’s lifespan it is osteoblast activity that controls and dictates osteoclast activity as long as the body receives the nutrients it requires to maintain homeostasis. Growing children, for instance, have a far greater abundance of osteoblasts than of osteoclasts. By the time they reach young adulthood (at about age 26 for men, 22 for women) osteoclasts increase while osteoblasts slow down. Even so, humans of any age can increase osteoblast activity and slow the formation of osteoclasts through weight bearing exercise and other methods.

Long bone

Long bone

Long bone
The problem of bone shrinkage and decline in strength presents most often in health states involving:

  1. Sedentary Lifestyle, making weight bearing exercise a frontline defense against bone loss for everyone.
  2. Acidosis (low pH), from a diet that is nutritionally lacking, genetically modified, degerminated, irradiated, laden with toxins & over-processed.
  3. Chronic dehydration from too much caffeine and high fructose corn syrup (a GMO) and not enough water that is both ionized and alkalized.
  4. Lacking in calcium that is live, ionically charged, as well as phosphorus, magnesium, boron, and other minerals comprised in human bones. On the other hand, commercially available calcium causes atherosclerosis, kidney stones, bone spurs, cataracts, and yet MORE bone loss!
  5. Taking prescription medications, especially acid reflux meds, NSAIs and steroids. These and more interfere with osteoblast activity and weaken immunology. Osteoporosis meds prevent living bone mass!
  6. Unhealed injuries and deterioration of the spine, such as compression fractures (>50% of the US adult population), spinal stenosis, kyphosis, and scoliosis. These cause even more rapid loss of bone mass.
  7. Subclinical infections: tooth and gum sepsis, around artificial joints, keratosis obturans, kidney and bladder infections, neuropathies, and osteomyelitis as a result of injuries and/or shock to the bones.
  8. Heavy metal accumulations: lead, mercury, cadmium, arsenic, formaldehyde, cyanide, etc. found in the drinking water, fresh foods, cosmetics, paints, fuels, and a host of commonly used products.
  9.  Lifestyle Substances– Smoking, alcohol, excess coffee, marijuana, opium (including opiate pain killers), diet sodas, caffeine drinks.

The Kinetics of Skeletal Remodeling

Jan 1, 1966  by Lent C. Johnson
Semin Musculoskelet Radiol. 2000;4(1):1-15.

Bone tumor dynamics: an orthopedic pathology perspective.
Johnson LC1, Vinh TN, Sweet DE.

The diagnosis and classification of primary bone tumors remains as much a challenge today as it has for the last 80 plus years. Although pathology is invariably equated with the image of a diagnostic microscope, the vast majority of diagnoses are made grossly with the unaided eye, as are the tissue specimens selected for microscopic “confirmation.” Radiologic studies, particularly plain radiographs, remain the gold standard in gross pathologic diagnosis of the skeleton. Today, confirmation and final classification continue as the pathologist’s domain, but perhaps not for long, considering the evolving ancillary imaging techniques and progressive sophistication of magnetic resonance (MR) imaging. The bone tumor cases collected and compiled by Ernest Codman, M.D. during the second through fourth decades of this century formed the basis of the first tumor registry. The Codman Bone Sarcoma Registry demonstrated among other things the importance of radiographic/pathologic correlation, underscoring the reliability of a bone tumor’s location, margin (host bone/tumor interface), periosteal reaction, and matrix patterns as an accurate guide to classification and likely future biologic behavior. “A General Theory of Bone Tumors,” written by Lent C. Johnson nearly 50 years ago and published in the Bulletin of The New York Academy of Medicine (February 1953, second series, vol. 29, no. 2, pp. 164-171), provided a conceptual cellular approach to the understanding bone tumor dynamics reinforcing radiologic/pathologic correlation as a reliable diagnostic tool. At the time of Dr. Lent C. Johnson’s death (1910-1998), he was literally working on an updated version of his original article, the latter of which is being reprinted as the core of this illustrated revision. Our continued experience with bone tumors over the past five decades has only served to validate, on a daily basis, the fundamental principles outlined in Johnson’s original article. In like fashion, it is important to keep in mind that terminology and nomenclature has also evolved since 1953, despite a continued inability to achieve complete consensus.
PMID:  11061688    http://www.ncbi.nlm.nih.gov/pubmed/11061688

Interactions between adrenal-regulatory and calcium-regulatory hormones in human health

Brown, J.M., Vaidya, A.

Curr Opinion in Endocr, Diabetes and Obesity 2014; 21 (3), pp. 193-201

Purpose of review: To summarize the evidence characterizing the interactions between adrenal-regulating and calcium-regulating hormones, and the relevance of these interactions to human cardiovascular and skeletal health. Recent findings: Human studies support the regulation of parathyroid hormone (PTH) by the renin-angiotensin-aldosterone system (RAAS): angiotensin II may stimulate PTH secretion via an acute and direct mechanism, whereas aldosterone may exert a chronic stimulation of PTH secretion.
Studies in primary aldosteronism, congestive heart failure, and chronic
kidney disease have identified associations between hyperaldosteronism, hyperparathyroidism, and bone loss, which appear to improve when
inhibiting the RAAS. Conversely, elevated PTH and insufficient vitamin D
status have been associated with adverse cardiovascular outcomes, which
may be mediated by the RAAS. Studies of primary hyperparathyroidism implicate PTH-mediated stimulation of the RAAS, and recent evidence shows that the vitamin D-vitamin D receptor complex may negatively regulate renin expression and RAAS activity. Ongoing human interventional studies are evaluating the influence of RAAS inhibition on PTH and the influence of vitamin D receptor agonists on RAAS activity. Summary: Although previously considered independent endocrine systems, emerging evidence supports a complex web of interactions between adrenal-regulating and calcium-regulating hormones, with implications for human cardiovascular and
skeletal health.

Backbone modification of a polypeptide drug alters duration of action in vivo

Cheloha, R.W., Maeda, A., Dean, T., Gardella, T.J., Gellman, S.H.

Nature Biotechnology 2014; 32 (7), pp. 653-655 http://dx.doi.org/doi:10.1038/nbt.2920

Systematic modification of the backbone of bioactive polypeptides through amino acid residue incorporation could provide a strategy for generating molecules with improved drug properties, but such alterations can result in lower receptor affinity and potency. Using an agonist of parathyroid hormone receptor-1 (PTHR1), a G protein-coupled receptor in the B-family, we present an approach for residue replacement that enables both high activity and improved pharmacokinetic properties in vivo.

Mouse and human BAC transgenes recapitulate tissue-specific expression
of the vitamin D receptor in mice and rescue the VDR-null phenotype

Lee, S.M., Bishop, K.A., Goellner, J.J., O’Brien, C.A., Pike, J.W.
Endocrinology 2014; 155 (6), pp. 2064-2076
http://dx.doi.org/10.1210/en.2014-1107

The biological actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the vitamin D receptor (VDR), which is expressed in numerous target tissues in a cell type-selective manner. Recent studies using genomic analyses and recombined bacterial artificial chromosomes (BACs) have defined the specific features of mouse and human VDR gene loci in vitro. In the current study, we introduced recombined mouse and human VDR BACs as transgenes into mice and explored their expression capabilities in vivo. Individual transgenic mouse strains selectively expressed BAC derived mouse or human VDR proteins in appropriate vitamin D target tissues, thereby recapitulating the tissue-specific expression of endogenous mouse VDR. The mouse VDR transgene was also regulated by 1,25(OH)2D3 and dibutyryl-cAMP. When crossed into a VDR-null mouse background, both transgenes restored wild-type basal as well as 1,25(OH)2D3-inducible gene expression patterns in the appropriate tissues. This maneuver resulted in the complete rescue of the aberrant phenotype noted in the VDR-null mouse, including systemic features associated with altered calcium and phosphorus homeostasis and disrupted production of parathyroid hormone and fibroblast growth factor 23, and abnormalities associated with the skeleton, kidney, parathyroid gland, and the skin. This study suggests that both mouse and human VDR transgenes are capable of recapitulating basal and regulated expression of the VDR in the appropriate mouse tissues and restore 1,25(OH)2D 3 function. These results provide a baseline for further dissection of mechanisms integral to mouse and human VDR gene expression and offer the potential to explore the consequence of selective mutations in VDR proteins in vivo.

The sclerostin-independent bone anabolic activity of intermittent PTH treatment is mediated by T-cell-produced Wnt10β

Li, J.-Y., Walker, L.D., Tyagi, A.M., (…), Neale Weitzmann, M., Pacifici, R
Journal of Bone and Mineral Research 2014; 29 (1), pp. 43-54
http://onlinelibrary.wiley.com/doi/10.1002/jbmr.2044/pdf

Both blunted osteocytic production of the Wnt inhibitor sclerostin (Scl) and increased T-cell production of the Wnt ligand Wnt10b contribute to the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. However, the relative contribution of these mechanisms is unknown. In this study, we modeled the repressive effects of iPTH on Scl production in mice by treatment with a neutralizing anti-Scl antibody (Scl-Ab) to determine the contribution of T-cell-produced Wnt10b to the Scl-independent modalities of action of iPTH. We report that combined treatment with Scl-Ab and iPTH was more potent than either iPTH or Scl-Ab alone in increasing stromal cell production of OPG, osteoblastogenesis, osteoblast life span, bone turnover, bone mineral density, and trabecular bone volume and structure in mice with T cells capable of producing Wnt10b. In T-cell-null mice and mice lacking T-cell production of Wnt10b, combined treatment increased bone turnover significantly more than iPTH or Scl-Ab alone. However, in these mice, combined treatment with Scl-Ab and iPTH was equally effective as Scl-Ab alone in increasing the osteoblastic pool, bone volume, density, and structure. These findings demonstrate that the Scl-independent activity of iPTH on osteoblasts and bone mass is mediated by T-cell-produced Wnt10b. The data provide a proof of concept of a more potent therapeutic effect of combined treatment with iPTH and Scl-Ab than either alone.

N-cadherin restrains PTH activation of Lrp6/β-catenin signaling and osteoanabolic action

Revollo, L., Kading, J., Jeong, S.Y., (…), Mbalaviele, G., Civitelli, R.
Journal of Bone and Mineral Research 2015; 30 (2), pp. 274-28

Interaction between parathyroid hormone/parathyroid hormone-related peptide receptor 1 (PTHR1) and low-density lipoprotein receptor-related protein 6 (Lrp6) is important for parathyroid hormone (PTH) signaling and anabolic action. Because N-cadherin has been shown to negatively regulate canonical Wnt/β-catenin signaling, we asked whether N-cadherin alters PTH signaling and stimulation of bone formation. Ablation of the N-cadherin gene (Cdh2) in primary osteogenic lineage cells resulted in increased Lrp6/PTHR1 interaction in response to PTH1-34, associated with enhanced PTH-induced PKA signaling and PKA-dependent β-catenin C-terminus phosphorylation, which promotes β-catenin transcriptional activity. β-catenin C-terminus phosphorylation was abolished by Lrp6 knockdown. Accordingly, PTH1-34 stimulation of Tcf/Lef target genes, Lef1 and Axin2, was also significantly enhanced in Cdh2-deficient cells. This enhanced responsiveness to PTH extends to the osteo-anabolic effect of PTH, as mice with a conditional Cdh2 deletion in Osx+ cells treated with intermittent doses of PTH1-34 exhibited significantly larger gains in trabecular bone mass relative to control mice, the result of accentuated osteoblast activity. Therefore, N-cadherin modulates Lrp6/PTHR1 interaction, restraining the intensity of PTH-induced β-catenin signaling, and ultimately influencing bone formation in response to intermittent PTH administration.

EphrinB2 signaling in osteoblasts promotes bone mineralization by preventing apoptosis

Tonna, S., Takyar, F.M., Vrahnas, C., (…), Martin, T.J., Sims, N.A.
FASEB Journal 2014; 28 (10), pp. 4482-4496 10.1096/fj.14-254300

Cells that form bone (osteoblasts) express both ephrinB2 and EphB4, and previous work has shown that pharmacological inhibition of the ephrinB2/ EphB4 interaction impairs osteoblast differentiation in vitro and in vivo. The purpose of this study was to determine the role of ephrinB2 signaling in the osteoblast lineage in the process of bone formation. Cultured osteoblasts from mice with osteoblast-specific ablation of ephrinB2 showed delayed expression of osteoblast differentiation markers, a finding that was reproduced by ephrinB2, but not EphB4, RNA interference. Microcomputed tomography, histomorphometry, and mechanical testing of the mice lacking ephrinB2 in osteoblasts revealed a 2-fold delay in bone mineralization, a significant reduction in bone stiffness, and a 50% reduction in osteoblast differentiation induced by anabolic parathyroid hormone (PTH) treatment, compared to littermate sex- and age-matched controls. These defects were associated with significantly lower mRNA levels of late osteoblast differentiation markers and greater levels of osteoblast and osteocyte apoptosis, indicated by TUNEL staining and transmission electron microscopy of bone samples, and a 2-fold increase in annexin V staining and 7-fold increase in caspase 8 activation in cultured ephrinB2 deficient osteoblasts. We conclude that osteoblast differentiation and bone strength are maintained by antiapoptotic actions of ephrinB2 signaling within the osteoblast lineage.-
Bone involvement in primary hyperparathyroidism and changes after parathyroidectomy

Rolighed, L., Rejnmark, L., Christiansen, P.
European Endocrinology 2014; 10 (1), pp. 84-87

Parathyroid hormone (PTH) is produced and secreted by the parathyroid glands and has primary effects on kidney and bone. During the pathological growth of one or more parathyroid glands, the plasma level of PTH increases and causes primary hyperparathyroidism (PHPT). This disease is normally characterized by hyperparathyroid hypercalcemia. In PHPT a continuously elevated PTH stimulates
the kidney and bone causing a condition with high bone turnover, elevated plasma calcium and increased fracture risk. If bone resorption is not followed by a balanced formation of new bone, irreversible bone loss may occur in these patients. Medical treatment can help to minimize the loss of bone but the cure of PHPT is by parathyroidectomy. After operation, bone mineral density increases during the return to normal bone metabolism. Supplementation with calcium and vitamin D after operation may improve the normalization to normal bone metabolism with a secondary reduction in fracture risk.

Primary hyperparathyroidism and the skeleton

Mosekilde, L.
Clinical Endocrinology 2008; 69 (1), pp. 1-19
http://dx.doi.org:/10.1111/j.1365-2265.2007.03162.x

Today, primary hyperparathyroidism (PHPT) in the developed countries is typically a disease with few or no obvious clinical symptoms. However, even in the asymptomatic cases the endogenous excess of PTH increases bone turnover leading to an insidious reversible loss of cortical and trabecular bone because of an expansion of the remodelling space and an irreversible loss of cortical bone due to increased endocortical resorption. In contrast trabecular bone structure and integrity to a large extent is maintained and there may be a slight periosteal expansion. Most studies have reported decreased bone mineral density (BMD) in PHPT mainly located at cortical sites, whereas sites rich in trabecular bone only show a modest reduction or even a slight increase in BMD. The frequent occurrence of vitamin D insufficiency and deficiency in PHPT and increased plasma FGF23 levels may also contribute to the decrease in BMD. The effect of smoking is unsolved. Epidemiological studies have shown that the relative risk of spine and nonspine fractures is increased in untreated PHPT starting up to 10 years before the diagnosis is made. Successful surgery for PHPT normalizes bone turnover, increases BMD and decreases fracture risk based on larger epidemiological studies. However, 10 years after surgery fracture risk appears to increase again due to an increase in forearm fractures. There are no randomized controlled studies (RCTs) demonstrating a protective effect of medical treatment on fracture risk in PHPT. Less conclusive studies suggest that vitamin D supplementation may have a beneficial effect on plasma PTH and BMD in vitamin D deficient PHPT patients. Hormone replacement therapy (HRT) and maybe SERM appear to reduce bone turnover and increase BMD. However, their nonskeletal side-effects preclude their use for this purpose. Bisphosphonates reduce bone turnover and increase BMD in PHPT as in osteoporosis and may be a therapeutical option in selected patients with low BMD. Obviously, there is a need for larger RCTs with fractures as end-points that appraise this possibility. Calcimimetics reduce plasma calcium and PTH in PHPT but has no beneficial effect on bone turnover or BMD. In symptomatic hypercalcemic PHPT with low BMD where curative surgery is impossible or contraindicated a combination of a calcimimetic and a bisphosphonate may be an undocumented therapeutical option that needs further evaluation.

Current Issues in the Presentation of Asymptomatic Primary Hyperparathyroidism: Proceedings of the Fourth International Workshop

Shonni J. Silverberg, Bart L. Clarke, Munro Peacock, Francisco Bandeira, et al. The Journal of Clinical Endocrinology & Metabolism 2014; 99(10) http://dx.doi.org/10.1210/jc.2014-1415

Objective: This report summarizes data on traditional and nontraditional manifestations of primary hyperparathyroidism (PHPT) that have been published since the last International Workshop on PHPT.

Participants: This subgroup was constituted by the Steering Committee to address key questions related to the presentation of PHPT. Consensus was established at a closed meeting of the Expert Panel that followed.

Evidence: Data from the 5-year period between 2008 and 2013 were
presented and discussed to determine whether they support changes in recommendations for surgery or nonsurgical follow-up.

Consensus Process: Questions were developed by the International Task
Force on PHPT. A comprehensive literature search for relevant studies was undertaken. After extensive review and discussion, the subgroup came to agreement on what changes in the recommendations for surgery or nonsurgical follow-up of asymptomatic PHPT should be made to the Expert Panel.

Conclusions:

1) There are limited new data available on the natural history of
asymptomatic PHPT. Although recognition of normocalcemic PHPT
(normal serum calcium with elevated PTH concentrations; no secondary
cause for hyperparathyroidism) is increasing, data on the clinical
presentation and natural history of this phenotype are limited.
2) Although there are geographic differences in the predominant
phenotypes of PHPT (symptomatic, asymptomatic, normocalcemic),
they do not justify geography-specific management guidelines.
3) Recent data using newer, higher resolution imaging and analytic
methods have revealed that in asymptomatic PHPT, both trabecular
bone and cortical bone are affected.
4) Clinically silent nephrolithiasis and nephrocalcinosis can be detected
by renal imaging and should be listed as a new criterion for surgery.
5) Current data do not support a cardiovascular evaluation or surgery
for the purpose of improving cardiovascular markers, anatomical or
functional abnormalities.
6) Some patients with mild PHPT have neuropsychological complaints
and cognitive abnormalities, and some of these patients may benefit
from surgical intervention. However, it is not possible at this time to
predict which patients with neuropsychological complaints or cognitive
issues will improve after successful parathyroid surgery.

Sclerosing Bone Dysplasias: Leads Toward Novel Osteoporosis Treatments

Igor Fijalkowski, Eveline Boudin, Geert Mortier, Wim Van Hul
Current Osteoporosis Reports Sept 2014; 12(3), pp 243-251
http://dx.doi.org:/10.1007/s11914-014-0220-5

Sclerosing bone dysplasias are a group of rare, monogenic disorders characterized by increased bone density resulting from the disturbance in the fragile equilibrium between bone formation and resorption. Over the last decade, major contributions have been made toward better understanding of the pathogenesis of these conditions. These studies provided us with important insights into the bone biology and yielded the identification of numerous drug targets for the prevention and treatment of osteoporosis. Here, we review this heterogeneous group of disorders focusing on their utility in the development of novel osteoporosis therapies.

Clinical development of neridronate: potential for new applications

Gatti D, Rossini M, Viapiana O, Idolazzi L, Adami S
Ther & Clin Risk Manag Apr 2013; 2013(9): Pages 139—147

Neridronate is an aminobisphosphonate, licensed in Italy for the treatment
of osteogenesis imperfecta (OI) and Paget’s disease of bone (PDB).  A characteristic property of neridronate is that it can be administered both intravenously and intramuscularly, providing a useful system for administration in homecare. In this review, we discuss the latest clinical results of neridronate administration in OI and PDB, as well as in osteoporosis and other conditions. We will focus in particular on the latest evidence of the effect of neridronate on treatment of complex regional pain syndrome type I.

Disorders of bone remodeling

Feng, X., McDonald, J.M.
Ann Rev of Pathol: Mechanisms of Disease 2011; 6, pp. 121-145
http://dx.doi.org:/10.1146/annurev-pathol-011110-130203

The skeleton provides mechanical support for stature and locomotion, protects vital organs, and controls mineral homeostasis. A healthy skeleton must be maintained by constant bone modeling to carry out these crucial functions throughout life. Bone remodeling involves the removal of old or damaged bone by osteoclasts (bone resorption) and the subsequent replacement of new bone formed by osteoblasts (bone formation). Normal bone remodeling requires a tight coupling of bone resorption to bone formation to guarantee no alteration in bone mass or quality after each remodeling cycle. However, this important physiological process can be derailed by a variety of factors, including menopause-associated hormonal changes, age-related factors, changes in physical activity, drugs, and secondary diseases, which lead to the development of various bone disorders in both women and men. We review the major diseases of bone remodeling, emphasizing our current understanding of the underlying pathophysiological mechanisms.

Paget’s disease and hypercalcemia: Coincidence or causal relationship?

Green, I., Altman, A.
Harefuah 2009; 148 (10), pp. 708-710

Paget’s disease is a chronic disease in which osteoclast mediated bone resorption precedes imperfect osteoblast mediated bone repair. Symptoms include bone pain, pathological fractures, osteoarthritis and neurological symptoms. There is evidence that genetic and viral component are involved in the etiology. Hypercalcemia is rare and when it is diagnosed, primary hyperparathyroidism should be ruled out. The authors present a patient with Paget’s disease and concomitant hypercalcemia. Evaluation for hypercalcemia revealed an adenoma of the parathyroid. However, despite the removal of the adenoma, the symptoms persisted. Previous studies
showed that hyperparathyroidism causes hypercalcemia in Paget’s disease patients. Removal of the adenoma led to improvement in calcium and alkaline phosphatase (ALP) levels but clinical improvement is seen only in patients with high calcium level prior to the operation. This leads to the assumption that symptoms of Paget’s disease are due to osteoclast hypersensitivity to parathyroid hormone (PTH) and by removing the adenoma the osteoclast activity is also reduced. In summary, the most common cause of hypercalcemia in Paget’s disease patients is hyperparathyroidism and adenectomy may improve the biochemical and sometimes also the clinical symptoms of Paget’s disease.

Signaling networks that control the lineage commitment and differentiation of bone cells

Soltanoff, C.S., Yang, S., Chen, W., Li, Y.-P.
Critical Reviews in Eukaryotic Gene Expression 2009; 19 (1), pp. 1-46

Osteoblasts and osteoclasts are the two major bone cells involved in the bone remodeling process. Osteoblasts are responsible for bone formation while osteoclasts are the bone-resorbing cells. The major event that triggers osteogenesis and bone remodeling is the transition of mesenchymal stem cells into differentiating osteoblast cells and monocyte/macrophage precursors into differentiating osteoclasts. Imbalance in differentiation and function of these two cell types will result in skeletal diseases such as osteoporosis, Paget’s disease, rheumatoid arthritis, osteopetrosis, periodontal disease, and bone cancer metastases.
Osteoblast and osteoclast commitment and differentiation are controlled by complex activities involving signal transduction and transcriptional regulation of gene expression. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of the multiple factors and signaling networks that control the differentiation process at a molecular level.
This review summarizes recent advances in studies of signaling transduction pathways and transcriptional regulation of osteoblast and osteoclast cell lineage commitment and differentiation. Understanding the signaling networks that control the commitment and differentiation of bone cells will not only expand our basic understanding of the molecular mechanisms of skeletal development but will also aid our ability to develop therapeutic means of intervention in skeletal diseases.

Salmon calcitonin: a review of current and future therapeutic indications

  1. H. Chesnut III, M. Azria, S. Silverman, M. Engelhardt, M. Olson, L. Mindeholm Osteoporosis International 2008; 19(4), pp 479-491
    http://dx.doi.org:/10.1007/s00198-007-0490-1

Salmon calcitonin, available as a therapeutic agent for more than 30 years, demonstrates clinical utility in the treatment of such metabolic bone diseases as osteoporosis and Paget’s disease, and potentially in the treatment of osteoarthritis. This review considers the physiology and pharmacology of salmon calcitonin, the evidence based research demonstrating efficacy and safety of this medication in postmenopausal osteoporosis with potentially an effect on bone quality to explain its abilities to reduce the risk of spine fracture, the development of an oral salmon calcitonin preparation, and the therapeutic rationale for this preparation’s chondroprotective effect in osteoarthritis.

Pharmacotherapies to Manage Bone Loss-Associated Diseases:  A Quest for the Perfect Benefit-to-Risk Ratio

Valverde

Current Medicinal Chemistry : 15 (3): Pages 284-304
http://dx.doi.org:/10.2174/092986708783497274

In this review, benefits and side-effects of current and emerging therapies to treat and prevent pathological bone loss are described. Bisphosphonates are the antiresorptive compounds most widely used in the treatment of bone-loss associated diseases. They are generally well-tolerated although have recently been associated with osteonecrosis of the jaw and other complications. Therapies modulating estrogen receptor activation are indicated in the prevention and treatment of either breast cancer or osteoporosis in postmenopausal women. Thus, hormone replacement therapy is effective in prevention of osteoporosis, but its long-term use can increase the risk of breast cancer, stroke and embolism. Tamoxifen benefits all stages of breast cancer, but its use may lead to uterine cancer and thromboembolism. Raloxifene is approved in prevention of breast cancer and treatment of postmenopausal osteoporosis, but its use can increase the risk of fatal stroke. Aromatase inhibitors are superior to tamoxifen at advanced stages of disease and as adjuvants, but their use increase fracture incidence. Fulvestrant is as effective as aromatase inhibitors in the treatment of advanced breast cancer and does not cause bone fractures. Another antiresorptive available for the treatment of postmenopausal osteoporosis, Pagets disease and hypercalcemia is calcitonin, which also exhibits analgesic effects. A promising antiresorptive agent currently in clinical trials is denosumab. Aditional therapies for osteoporosis that decrease fracture risk consist of PTH-like anabolic agents and the dual action bone agent strontium ranelate. Antiseptics and antibiotics are used extensively in periodontal disease intervention to target bacterial biofilm, although hostdirected therapies are also being developed. – See more at: http://www.eurekaselect.com/66301/article#sthash.EGNCH4Eu.dpuf

Parathyroid Hormone An Anabolic Treatment for Osteoporosis

Paul Morley, James F. Whitfield and Gordon E. Willick
Current Pharmaceutical Design Pages 671-687
http://dx.doi.org:/10.2174/1381612013397780

Osteoporosis is a disease characterised by low bone mass, structural deterioration of bone and increased risk of fracture. The prevalence, and cost, of osteoporosis is increasing dramatically with our ageing population and the World Health Organization now considers it to be the second-leading healthcare problem. All currently approved therapies for osteoporosis (eg., estrogen, bisphosphonates, calcitonin and selective estrogen receptor modulators) are anti-resorptive agents that act on osteoclasts to prevent further bone loss. A new class of bone anabolic agent capable of building mechanically strong new bone in patients with established osteoporosis is
in development. While the parathyroid hormone (PTH) is classically considered to be a bone catabolic agent, when delivered intermittently at low doses PTH potently stimulates cortical and trabecular bone growth in animals humans. The native hPTH-(1-84) and its osteogenic fragment, hPTH-(1-34), have already entered Phase III clinical trials. Understanding the mechanism of PTHs osteogenic actions has led to the development of smaller PTH analogues which can also build mechanically normal bone in osteopenic rats. These new PTH analogues are promising candidates for treating osteoporosis in humans as they are as efficacious as hPTH-(1-84) and hPTH-(1-34), but there is evidence that they may have considerably less ability to induce hypercalcemia, the major side effect of PTH therapy. In addition to treating osteoporosis, PTHs may be used to promote fracture healing, to restore bone loss in immobilized patients, or following excessive glucocorticoid or prolonged spaceflight, and to treat psoriasis. http://www.eurekaselect.com/65008/article#sthash.FWa67NrB.dpuf

Effects of Parathyroid Hormone on Cancellous Bone Mass and Structure in Osteoporosis

Naohisa Miyakoshi
Current Pharmaceutical Design  ;10(21): Pages 2615-2627
http://dx.doi.org:/10.2174/1381612043383737

Parathyroid hormone (PTH) is the major hormonal regulator of calcium homeostasis. PTH is a potent stimulator of bone formation and can restore bone to an osteopenic skeleton, when administered intermittently. Osteoblasts are the primary target cells for the anabolic effects of PTH in bone tissue. Anabolic effects of PTH on bone have been demonstrated in animals and humans, by numerous measurement techniques including bone mineral density and bone histomorphometry. Clinically, the most important aspect of treatment for osteoporosis is prevention of fractures. Microstructural alterations, such as loss of trabecular connectivity, have been implicated in increased propensity for fracture. Recent two-dimensional (2D) and three-dimensional (3D) assessments of cancellous bone structure have shown that PTH can re-establish lost trabecular connectivity in animals and humans.
These results provide new insight into the positive clinical effects of PTH in osteoporosis. In recent randomized controlled clinical trials of intermittent
PTH treatment, PTH decreased incidence of vertebral and non-vertebral fractures
in postmenopausal women. Thus, PTH shows strong potential as therapy for osteoporosis. However, 2D and 3D structural analysis of advanced osteopenia in animals has shown that there is a critical limit of trabecular connectivity and bone strength below which PTH cannot completely reverse the condition. Given that PTH treatment fails to completely restore trabecular connectivity and bone strength in animals with advanced osteopenia, early treatment of osteoporosis appears important and efficacious for preventing fractures caused by decreased bone strength resulting from decreased trabecular connectivity. – See more at: http://www.eurekaselect.com/62780/article#sthash.OnoaRPyh.dpuf

Clinical applications of RANK-ligand inhibition

Romas, E.
Internal Medicine Journal 2009; 39 (2), pp. 110-116
http://dx.doi.org:/10.1111/j.1445-5994.2008.01732.x

An enhanced rate of bone remodelling fuelled by osteoclastogenesis mediates diseases such as osteoporosis, arthritic bone destruction, Paget’s disease and malignancy-induced bone loss. Thus, the control of osteoclastogenesis is of major clinical importance. The receptor activator of nuclear factor κB (RANK); its ligand, RANKL and decoy receptor, osteoprotegerin, are critical determinants of osteoclastogenesis, and increased RANK signalling is involved in several bone diseases, providing the rationale for RANKL inhibition. The effects of RANKL inhibition are being witnessed in clinical trials of neutralizing fully human monoclonal antibodies that target RANKL (e.g. denosumab) and which induce profound and sustained inhibition of bone resorption. The relative efficacy, cost-effectiveness and side-effects of targeted RANKL inhibition compared with conventional antiresorptive drugs (i.e. bisphosphonates) should be resolved by clinical trials in coming years.

Clinical development of neridronate: potential for new applications

Davide Gatti, M Rossini, O Viapiana, L Idolazzi, SAdami
Therapeutics and Clinical Risk Management 2013:9 139–147
http://dx.doi.org/10.2147/TCRM.S35788

Neridronate is an aminobisphosphonate, licensed in Italy for the treatment of osteogenesis imperfecta (OI) and Paget’s disease of bone (PDB). A characteristic property of neridronate is that it can be administered both intravenously and intramuscularly, providing a useful system for administration in homecare. In this review, we discuss the latest clinical results of neridronate administration in OI and PDB, as well as in osteoporosis and other conditions. We will focus in particular on the latest evidence of the effect of neridronate on treatment of complex regional pain syndrome type I.

The Sclerostin‐Independent Bone Anabolic Activity of Intermittent PTH Treatment Is Mediated by T‐Cell–Produced Wnt10β

Jau‐Yi Li, Lindsey D Walker, Abdul Malik Tyagi, Jonathan Adams, et al.
Journal of Bone and Mineral Research, Jan 2014; 29(1): pp 43–54
http://dx.doi.org:/10.1002/jbmr.2044

Both blunted osteocytic production of the Wnt inhibitor sclerostin (Scl) and increased T‐cell production of the Wnt ligand Wnt10β contribute to the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. However, the relative contribution of these mechanisms is unknown. In this study, we modeled the repressive effects of iPTH on Scl production in mice by treatment with a neutralizing anti‐Scl antibody (Scl‐Ab) to determine the contribution of T‐cell–produced Wnt10β to the Scl‐independent modalities of action of iPTH. We report that combined treatment with Scl‐Ab and iPTH was more potent than either iPTH or Scl‐Ab alone in increasing stromal cell production of OPG, osteoblastogenesis, osteoblast life span, bone turnover, bone mineral density, and trabecular bone volume and structure in mice with T cells capable of producing Wnt10β. In T‐cell–null mice and mice lacking T‐cell production of Wnt10β, combined treatment increased bone turnover significantly more than iPTH or Scl‐Ab alone. However, in these mice, combined treatment with Scl‐Ab and iPTH was equally effective as Scl‐Ab alone in increasing the osteoblastic pool, bone volume, density, and structure. These findings demonstrate that the Scl‐independent activity of iPTH on osteoblasts and bone mass is mediated by T‐cell–produced Wnt10β. The data provide a proof of concept of a more potent therapeutic effect of combined treatment with iPTH and Scl‐Ab than either alone.

Treatment of Paget’s disease with hypercalcemia

Donald H. Gutteridge – Letter to the Editor
Bone 12 Jan 2006; 39(668)
http://dx.doi.org:/10.1016/j.bone.2006.01.165

Selby et al. [7] “Guidelines on the management of Paget’s disease of bone” produced a very helpful review, with 139 references. I take issue however with their approach to the clinical problem of concurrent Paget’s and hypercalcemia.
Firstly, the combination is not rare. Of 1836 literature and personally reported unselected patients with Paget’s disease, 90 had concurrent hypercalcemia due to primary hyperparathyroidism [PHPT], i.e., 4.9% [4]. The number with unspecified hypercalcemia would have exceeded 5%.                                     Secondly, the authors give similar weight to immobilization and PHPT as causes. Immobilization as a cause of hypercalcemia in Paget’s disease is rare [4,3]. The former paper studied 184 consecutive new referrals with Paget’s disease over 15 years. Hypercalcemia was present in 21: two had malignancy (multiple myeloma, secondary cancer); the remaining 19 had biochemical PHPT with most confirmed by neck exploration; none had hypercalcemia of immobilization. Gillespie [3] reported two patients who died following pagetic fractures with immobilization. One was diagnosed and treated as immobilization hypercalcemia; both had large parathyroid adenomas at autopsy.
Thirdly, they have recommended that “patients with Paget’s disease and hypercalcemia should be treated with bisphosphonate”. Since most patients with this combination have PHPT, since bisphosphonate treatment of Paget’s disease is associated with parathyroid hormone (PTH) stimulation [5] and since activation of Paget’s disease occurs with increased PTH [2], it seems reasonable to exclude PHPT (and other causes— e.g., milk alkali syndrome and vitamin D toxicity) and consider neck exploration before bisphosphonate treatment. The response to parathyroidectomy can be profound—and is predictable. In those with PHPT there is a significant linear relationship between preoperative severity (plasma calcium corrected for plasma albumin) and postoperative improvement in bone turnover (%fall in plasma alkaline phosphatase) [4]. In those 7 patients with a preoperative calcium >3.0 mmol/l, the postoperative mean fall in plasma alkaline phosphatase was 68%. Bisphosphonate treatment may be an option in those with PHPT and mild asymptomatic hypercalcemia; likewise following a reasonable interval (say 6 months) after successful neck exploration, should increased bone turnover and pagetic symptoms persist.

In those rare cases with the combination of Paget’s disease, hypercalcemia and immobilized pagetic fracture, where other causes of hypercalcemia have been excluded [1,6], bisphosphonate treatment is eminently reasonable.

[1] Bannister P, Roberts M, Sheridan P. Recurrent hypercalcaemia in a young man with mono-ostotic Paget’s disease. Postgrad Med J 1986;62:481–3.
[2] Genuth SM, Klein L. Hypoparathyroidism and Paget’s disease: the effect of parathyroid hormone administration. J Clin Endocrinol Metab 1972;35: 693–9.
[3] Gillespie WJ. Hypercalcaemia in Paget’s disease of bone. Aust N Z J Surg 1979;49:84–6.
[4] Gutteridge DH, Gruber HE, Kermode DG, Worth GK. Thirty cases of concurrent Paget’s disease and primary hyperparathyroidism: sex distribution, histomorphometry, and prediction of the skeletal response to parathyroidectomy. Calcif Tissue Int 1999;65:427–35.
[5] Harinck HIJ, Bijvoet OLM, Blanksma HJ, Dahlinghaus-Nienhuys PJ. Efficacious management with aminobisphosphonate (APD) in Paget’s disease of bone. Clin Orthop Relat Res 1987;217:79–98.
[6] Nathan AW, Ludlam HA, Wilson DW, Dandona P. Hypercalcaemia due to immobilization of a patient with Paget’s disease of bone. Postgrad Med J 1982;58:714–5.
[7] Selby PL, Davie MWJ, Ralston SH, Stone MD. Guidelines on the management of Paget’s disease of bone. Bone 2002;31:10–9.

The authors of the article entitled “Guidelines on the management of Paget’s disease of bone” published in BONE 2002:31:10–9, have elected not to respond to the above letter to the Editor.

Safety of Bisphosphonates in the Treatment of Osteoporosis

Robert R. Recker, E. Michael Lewiecki, Paul D. Miller, James Reiffel
The American Journal of Medicine (2009) 122, S22–S32
http://dx.doi.org:/10.1016/j.amjmed.2008.12.004

In this review 4 experts consider the major safety concerns relating to bisphosphonate therapy for osteoporosis. Specific topics covered are skeletal safety (particularly with respect to atypical fractures and delayed healing), gastrointestinal intolerance, hypocalcemia, acute-phase (i.e., postdose) reactions, chronic musculoskeletal pain, renal safety, and cardiovascular safety (specifically, atrial fibrillation).

The bone-remodeling cycle

The bone-remodeling cycle

The bone-remodeling cycle.
Remodeling of bone in a multicellular bone unit starts with osteoblastic activation of osteoclast differentiation, fusion, and activation (A and B).
When resorption lacunae are formed, the osteoclasts leave the area and mononucleated cells of uncertain origin appear and “clean up” the organic matrix remnants left by the osteoclast, also possibly forming the cement line (dotted line) at the bottom of the lacunae
(C). During the resorption process, coupling factors, including insulin-like growth factor–I and transforming growth factor–β, are released from the bone-extracellular matrix, and these growth factors contribute to the recruitment of osteoblasts to the resorption lacunae and their activation.
(D). The osteoblasts will then fill the lacunae with new bone; when the same amount of bone is formed as is being resorbed, the remodeling process is finished, and the mineralized extracellular matrix will be covered by osteoid and a single-cell layer of osteoblasts
(E). (Reprinted with permission from J Dent Res.6)

SUMMARY

Persistent, long-term antifracture efficacy has been demonstrated for bisphosphonates, and there is no evidence that the antifracture efficacy declines during treatment periods lasting as long as 10 years. Bisphosphonate-induced oversuppression of remodeling and return of fracturing remains a theoretical possibility.
It is likely that a few patients who are potential candidates for bisphosphonate treatment have preexisting oversuppression of bone remodeling. Treatment with a bisphosphonate in these cases would not be helpful and might even be harmful. The problem when encountering a patient with fractures and deciding whether to recommend treatment with a bisphosphonate is that no reliable diagnostic method exists that allows detection of the rare instance of preexisting oversuppression of remodeling.  When pretreatment BMD is not particularly low, that is, not lower than normal or mildly osteopenic, the persistence of fracturing during treatment may mean that oversuppression of remodeling was already present and a change in medication would be appropriate. There is no evidence that bisphosphonate treatment impairs fracture healing. Indeed, there are a substantial number of reports involving animal models, as well as a few human case reports, to suggest that bisphosphonate treatment actually improves fracture healing. In general, it is important to bear in mind the positive benefit-to-risk ratio for this therapeutic class when making treatment recommendations for patients with osteoporosis.

Bisphosphonate Safety:

1.               Gastrointestinal Intolerance,2.               Hypocalcemia,

3.               Acute-Phase Reaction, and

4.               Chronic Bone and Muscle Pain

PTH: Potential role in management of heart failure

  1. Gruson, A. Buglioni, J.C. Burnett Jr.
    Clinica Chimica Acta 433 (2014) 290–296
    http://dx.doi.org/10.1016/j.cca.2014.03.029

Biomarkers play an important role for the diagnosis and prognosis of heart failure (HF), a disease with high morbidity and mortality as well as a huge impact on healthcare budgets. Parathyroid hormone (PTH) is a major systemic calcium-regulating hormone and an important regulator of bone and mineral homeostasis. PTH testing is important for differential diagnosis of calcemia related disorders and for the management of patients with chronic kidney disease. As secondary hyperparathyroidism has been evidenced in HF patients, PTH testing might be relevant in HF patients for risk stratification and more personalized selection of treatment.

Heart failure and neurohormonal activation

Heart failure is a syndrome characterized by increasing prevalence, high morbidity, elevated hospital readmission rate and high mortality. The continuing improvement of diagnosis, prognosis, treatment and management of HF requires a better understanding of the different sub-phenotypes and heterogeneity of this syndrome at the cellular, organ, and systemic level. Neurohormonal activation, one of the hallmarks of HF, plays a significant role in the myocardial and multi-organ adaptation. The comprehensive understanding of neurohormonal activation has allowed the identification of several biomarkers, such as natriuretic peptides, which are now playing an important role in HF management. Beside their contribution to the diagnosis of HF, natriuretic peptides are also relevant for follow-up and prognosis of HF patients.  Nevertheless, natriuretic peptides are more related to ventricular stretch, and biomarkers from other biological pathways like cardiac remodeling might provide additional value for the risk stratification of HF patients. The integration of biomarkers from several pathophysiological pathways along with imaging and genetic testing, might therefore be used to define HF subtypes, responding differently to specific therapeutic actions and contributing to more tailored based approaches.
Abnormalities of bone and mineral metabolism are also found in HF.  Secondary hyperparathyroidism has been evidenced in this context and several recent reports have documented the potential use of parathyroid hormone (PTH) testing for a more personalized management of HF patients. The aim of this article is therefore to review some of the cardiac effects of PTH and the potential role of PTH testing in HF.

Parathyroid hormone: biology and cardiac effects
PTH is one of the major regulators of the bone and mineral metabolism and its secretion is modulated by changes in concentration of calcium in the blood; decreased calcium concentrations stimulating PTH secretion via calcium-sensing receptors in the parathyroid gland. In response to hypocalcemia,
PTH has different targets to increase circulating calcium concentration. A fundamental target is the renal tubule where PTH will increase phosphorus excretion in the proximal tract and will enhance calcium reabsorption from the ascending limb of the loop of Henle to the collecting duct. The proximal renal tubule is also a target where PTH will stimulate the 1-α hydroxylation of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D: this biologically active form of vitamin D acts on the gut to increase absorption of both dietary calcium and phosphorus. Another target of PTH is the osteoclasts, leading to increased bone resorption with release of phosphorus and calcium in the blood.
PTH is a polypeptide containing 84 amino acids secreted by the parathyroid glands after cleavage from preproparathyroid hormone to proparathyroid hormone to the mature hormone. However, it displays several circulating forms and related fragments. PTH is secreted predominantly as an intact molecule, but it is rapidly cleaved in peripheral tissues to amino terminus and carboxy terminus fragments. The amino terminus fragment is biologically active and has a relatively short circulating half-life. The carboxy-terminal species include a 7-84 peptide and a variety of shorter fragments. These fragments can have a longer half-life and accumulate in renal failure. PTH assays measure not only the full-length form of PTH but also isoforms as well as fragments and differences can be observed between assays depending on the antibody specificities.

Cardiac effects of PTH
Primary hyperparathyroidism has been associated with heart diseases, underlying the potential cardiac consequences of increased circulating levels of PTH. Furthermore, as the heart is one of the target organs of PTH, the involvement of this hormone in the pathogenesis of cardiovascular diseases was previously suggested. PTH has different effects on the heart and can stimulate hypertrophy, arrhythmias and a pro-oxidative state. PTH has a direct hypertrophic action on cardiomyocytes. PTH is able, through a direct effect mediated through its receptors, to activate protein kinase C which further stimulates hypertrophic growth and reexpression of fetal type proteins in cardiomyocytes. PTH was also reported as a potent activator of protein kinase A (PKA) and several other downstream effectors related to cardiomyocyte hypertrophy. The hypertrophic effect of PTH on cardiac cells is also reinforced by its ability to stimulate an anti-hypertrophic response, including the natriuretic peptide gene transcription and by the increased of plasma concentrations of N-terminal pro-B-type natriuretic peptide (NT-proBNP) observed in patients with primary hyperparathyroidism. The hypertrophic effect of PTH on the heart was also evidence by a close relation between PTH levels and left ventricular mass.
In addition to its hypertrophic action, PTH can stimulate cardiac arrhythmias. PTH was documented as a chronotropic agent able to cause early death ofmyocytes in rat. Importantly, Bogin et al. showed in cultured heart cells of rat, that both amino-terminal PTH 1–34 and intact PTH 1–84 produced an immediate, sustained and significant rise in beats per minute and that the cells died earlier than control cardiomyocytes. Similar bservations were obtained by Shimoyama et al. In human, recent data showed that chronic renal failure and hyperparathyroidism are associated with a sympathetic over-activity. In that case, PTH 1–34 was able to facilitate norepinephrine release in human heart atria by activating the PTH-receptors. Therefore, highly increased PTH levels that can be observed in HF patients can participate to the elevated sympathetic nerve activity and the associated cardiovascular mortality.
The cardiac impact of PTH is also related to calcium overloading in myocardial cells. This cytoplasmic calcium overloading induced by PTH in myocardial cells appears as a paradox for hyperparathyroidism states. The mechanisms behind the increase of intracellular calcium involve a receptor-mediated rise in L-type calcium channel at the plasma membrane level leading to a secondary entry of calcium into cardiomyocyte and mobilization of calcium from sarcoplasmic reticulum. Both PTH 1–34 and PTH 1–84 produced such a dose dependent increase of intracellular calcium in cardiomyocytes. This increase of cytosolic calcium can be prevented by the calcium channel blocker verapamil.
Hyperparathyroidism has also been documented to trigger oxidative stress. When PTH levels are increased, a higher H2O2 production is observed in peripheral blood mononuclear cells. The increase in intracellular calcium induced by PTH might impair the mitochondrial function and ATP production, inducing the production of reactive oxygen species and leading to oxidative stress as well as inflammation and, at the end, to cardiomyocyte necrosis.
Lastly, increased circulating concentrations of PTH might stimulate adrenal aldosterone synthesis, initiating a vicious circle between hyperparathyroidism and hyperaldosteronism and leading to more proinflammatory, pro-oxidant and pro-fibrotic actions.

The rise of PTH in HF
Through its cardiac effects PTH can participate to the pathophysiology of cardiovascular diseases and a chronic excess to high circulating levels of PTH can have some deleterious consequences for the HF patients. Several factors might explain the increase of circulating PTH levels in HF patients.
First of all, impaired cation homeostasis and calcium loss should be considered.   Alteration in electrolyte equilibrium is frequent in HF patients as a consequence of hormonal changes in this pathological condition (hyperadrenergic state and secondary hyperaldosteronism). Calcium wasting is also triggered by diuretics, used to treat HF patients.
A second important factor can be a deficiency of vitamin D. Low vitamin D levels are frequently observed in HF patients and can lead to a rise in PTH levels.
Another documented factor is the interrelationship between hemodynamic state and serum intact PTH levels in patients with HF. Indeed, in a cross-sectional study including 105 patients with chronic HF, log-transformed intact PTH levels were positively and significantly correlated with pulmonary capillary wedge pressure and inversely correlated with stroke volume index after adjusting for variables associated with PTH.

The cross talk between PTH and aldosterone
The cross talk between PTH and FGF-23
Circulating levels of PTH and heart failure
PTH levels in HF patients
PTH testing and heart failure: conclusions and perspectives
PTH testing: assay matters

secondary hyperparathyroidism

secondary hyperparathyroidism

Potential involvement of secondary hyperparathyroidism in the worsening course of heart failure significant correlations were observed, through generation assays, between PTH and natriuretic peptides aswell as galectin-3. Importantly, the different immunoreactivities might impact on the value of PTH testing in treatment and prognosis of HF.

The measurement of PTH concentrations in HF can, like in patients with chronic kidney disease, help to monitor the efficiency of the treatment (drugs as well as medical devices). The use of PTH testing in HF patients might also allow the selection of more personalized and tailored therapies. HF patients with higher PTH levels could be relevant candidates for vitamin D supplementation or other pharmacological treatment. Based on the positive relationship between aldosterone and PTH, higher PTH levels can be an additional reason to use aldosterone blockers in HF patients.

Parathyroid hormone and cardiovascular disease events: A systematic review and meta-analysis of prospective studies

Adriana J. van Ballegooijen, I Reinders, M Visser, and IA Brouwer
Am Heart J 2013;165:655-664.e5
http://dx.doi.org/10.1016/j.ahj.2013.02.014

The parathyroid hormone (PTH) is a key hormone for the maintenance of calcium homeostasis. Low serum calcium triggers the secretion of PTH from the parathyroid glands.1 This results in a raise in serum calcium by promoting the release of calcium from bone, reduces calcium excretion by the kidneys, and increases the calcium absorption by the small intestine. In turn, the increase in calcium inhibits PTH secretion from the parathyroid glands.
In addition to traditionally known target organs, PTH is of interest for its potential impact on cardiovascular disease (CVD) risk. Observational studies have demonstrated that chronic PTH elevation is linked to hypertension, cardiac hypertrophy, and myocardial dysfunction. Furthermore, PTH receptors are present in the myocardium and exert hypertrophic effects on cardiomyocytes. Taken together, these associations suggest plausible mechanisms whereby elevated PTH concentrations may be involved in pathological processes that lead to CVD.

Background Parathyroid hormone (PTH) excess might play a role in cardiovascular health. We therefore conducted a systematic review and meta-analysis to evaluate the association between PTH and cardiovascular disease (CVD) events, and intermediate outcomes.
Methods We conducted a systematic and comprehensive database search using MEDLINE and Embase between 1947 and October 2012. We included English-language prospective studies that reported risk estimates for PTH and CVD events, and intermediate outcomes. The characteristics of study populations, exposure, and outcomes of total CVD events, fatal and non-fatal CVD events were reported, and a quality assessment was conducted. Results were extracted for the highest versus lowest PTH concentrations, and meta-analyses were carried out using random effects models.
Results The systematic literature search yielded 5770 articles, and 15 studies were included. Study duration ranged between 2 and 14 years. All studies were performed primarily in whites with a mean age between 55 and 75 years. The metaanalyses included 12 studies, of which 10 investigated total CVD events; 7, fatal CVD events; and 3, non-fatal CVD events. PTH excess indicated an increased risk for total CVD events: pooled HR (95% CI), 1.45 (1.24-1.71). The results for fatal CVD events and non-fatal CVD events were: HR 1.50 (1.18-1.91) and HR 1.48 (1.14-1.92). Heterogeneity was moderately present; however, sensitivity analyses for follow-up duration, prior CVD, or PTH as dichotomous values showed similar results.
Conclusions The meta-analysis indicates that higher PTH concentrations are associated with increased risk of CVD events.

Impact of estrogen on mechanically stimulated cells in vitro

Jörg Neunzehn, Ulrich Meyer and Hans-Peter Wiesman
Int.J.Curr.Microbiol.App.Sci (2014) 3(5) 898-906
Estrogen deficiency and decreased exercise known to be major causes for osteoporosis in elderly patients are assumed on important role in implant failure. Hormone replacement therapy and exercise are established methods to prevent the accompanying bone loss, thereby improving the conditions for implant osseointegration. Whereas the clinical effects of estrogen on bone are well documented, less is known about estrogen effects on loaded and unloaded osteoblasts on a cellular level. This study was aimed at investigating the effects of estrogen on mechanically stimulated osteoblast like cells in culture. Mechanically unstimulated cultures served as controls. Our investigations revealed that estrogen had a suppressive effect on the proliferative response of osteoblasts towards mechanical strain. Estrogen increased the synthesis of bone specific proteins in mechanically stimulated cultures whereas estrogen had no effect on unstimulated cells. The differentiation effects significant altered at estrogen doses of 10nmol and 10 μmol. Our data suggest a positive effect of hormone substitution on the composition of the extracellular matrix in loaded bones. In the context of implant dentistry, hormone repaints therapy should be regarded as a medical tool to improve the conditions for an undisturbed implant healing.

Normal bone physiology, remodelling and its hormonal regulation

Jennifer S Walsh
Surgery 2014; 33:1

The skeleton has structural and locomotor functions, and is a mineral reservoir. Bone turnover by osteoclasts and osteoblasts is a lifelong process, incorporating growth, modelling and remodeling to repair microdamage and access the mineral reservoir.
Bone formation and resorption are the basis of growth, modeling and remodeling. The bone remodeling cycle is an ongoing process that renews bone to repair microdamage and maintain strength. It also maintains serum calcium in the normal physiological range by release of mineral from the bone matrix as required. About 5-10% of the adult skeleton is replaced by remodeling each year.
On trabecular bone and at the endocortical surface, remodeling takes place on the surface of bone, but within cortical bone the osteoclasts form a cutting cone through the bone matrix. The signal to initiate remodeling may be endocrine (such as increased parathyroid hormone (PTH) in response to hypocalcaemia), which leads to generalized increases in osteoclast activation. Localized remodeling is initiated in response to microdamage, probably by signals from osteocytes. During a remodeling cycle, osteoclasts on the bone surface become activated and resorb bone matrix, creating a defect which is filled in by osteoblasts. The cycle usually takes about 200 days to complete. The bone remodeling cycle is highly regulated, and resorption and formation are closely coupled.
Signaling between bone cells is essential for the coordination of these processes. Osteoblasts regulate osteoclast activity through the receptor activator of nuclear factor-kB (RANK)/RANK ligand/osteoprotegerin system, and osteocytes regulate osteoblast activity through sclerostin secretion. If resorption and formation are balanced there is no net change in bone mass after each cycle, but with ageing and some disease states resorption exceeds formation leading to remodeling imbalance, decreased bone mass and loss of microstructural integrity. The rate of remodeling is determined by loading and endocrine influences. The most important endocrine regulator of bone turnover is probably estrogen, but other hormones regulating bone metabolism include insulin-like growth factor-1, parathyroid hormone and gut and adipocyte hormones.

Differential Diagnosis, Causes, and Management of Hypercalcemia

Fredriech K. W. Chan, et al.
Current Problems In Surgery June 1997; 34(6)

Hypercalcemia is a challenging clinical syndrome, both in diagnosis and therapy. The two most common causes of hypercalcemia, primary hyperparathyroidism and malignancy, account for approximately 90% of all patients with an elevated calcium level. In the general population, primary hyperparathyroidism is more common than malignancy. In a hospitalized population, malignancy is by far the more common. The differential diagnosis of hypercalcemia should be focused initially on the distinction between primary hyperparathyroidism and malignancy.

Primary hyperparathyroidism is caused by excessive, abnormally regulated secretion of parathyroid hormone from one or more adenomatous or hyperplastic parathyroid glands. In 80% of cases, primary hyperparathyroidism is due to a single adenoma. In 15% to 20% of patients, all four glands are enlarged as a result of hyperplasia. Parathyroid hyperplasia is also encountered in patients with Multiple Endocrine Neoplasia, Type I or II. Rarely, in fewer than 0.5% of patients, primary hyperparathyroidism is due to parathyroid carcinoma. The clinical features of primary hyperparathyroidism result from the hypercalcemia and the excessive output of parathyroid hormone (PTH).
The major target organs are the bones and the kidneys. The classic but rare bone disease of primary hyperparathyroidism is osteitis fibrosa cystica. Since the advent of the multichannel autoanalyzer in the early 1970s, an era marked by a great increase in incidence of primary hyperparathyroidism, the prevalence of radiologically apparent bone disease in patients with primary hyperparathyroidism has declined from 10% to 15% to a vanishingly small 1% to 2%. Sensitive technologies such as bone densitometry and bone histomorphometry, however, have revealed skeletal involvement with preferential reduction of cortical bone mass and relative preservation of cancellous bone mass. Although the incidence of nephrolithiasis in primary hyperparathyroidism has also decreased markedly, from approximately 60% in the 1940s and 1950s to 15% to 20% now, nephrolithiasis is still the most frequent complication of primary hyperparathyroidism.
Primary hyperparathyroidism also can be associated with neuropsychiatric, gastrointestinal, and cardiovascular manifestations. However, evidence that these features are pathophysiologically linked to the hyperparathyroid process or are reversible after successful parathyroidectomy is not compelling.

Management of Skeletal Health in Patients With Asymptomatic Primary Hyperparathyroidism

  1. Michael Lewiecki
    J Clin Densitometry: Assessment of Skeletal Health, 2010; 13(4), 324e334.
    http://dx.doi.org:/10.1016/j.jocd.2010.06.004

Asymptomatic primary hyperparathyroidism (PHPT) may cause adverse skeletal effects that include high bone remodeling, reduced bone mineral density (BMD), and increased fracture risk. Parathyroid surgery, the definitive treatment for PHPT, has been shown to increase BMD and appears to reduce fracture risk. Current guidelines recommend parathyroid surgery for patients with symptomatic PHPT or asymptomatic PHPT with serum calcium > 1 mg/dL above the upper limit of normal, calculated creatinine clearance < 60 mL/min, osteoporosis, previous fracture, or age > 50 yr. The type of operation performed (parathyroid exploration or minimally invasive procedure) and localizing studies to identify the abnormal parathyroid glands preoperatively should be individualized according to the skills of the surgeon and the resources of the institution. In patients who choose not to be treated surgically or who have contraindications for surgery, medical therapy should include a daily calcium intake of at least 1200 mg and maintenance of serum 25-hydroxyvitamin D levels of at least 20 ng/mL (50 nmol/L). Bisphosphonates and estrogens have been shown to provide skeletal benefits that appear to be similar to parathyroid surgery. Cinacalcet reduces serum calcium in PHPT patients with intractable hypercalcemia but has not been shown to improve BMD. It is not known whether any medical intervention reduces fracture risk in patients with PHPT. There are insufficient data on the natural history and treatment of normocalcemic PHPT to make recommendations for management of this disorder.

Hyperparathyroidism

William D Fraser
thelancet July 11, 2009; 374: 145-158 – Seminar

Hyperparathyroidism is due to increased activity of the parathyroid glands, either from an intrinsic abnormal change altering excretion of parathyroid hormone (primary or tertiary hyperparathyroidism) or from an extrinsic abnormal change affecting calcium homoeostasis stimulating production of parathyroid hormone (secondary hyperparathyroidism). Primary hyperparathyroidism is the third most common endocrine disorder, with the highest incidence in postmenopausal women. Asymptomatic disease is common, and severe disease with renal stones and metabolic bone disease arises less frequently now than it did 20–30 years ago. Primary hyperparathyroidism can be cured by surgical removal of an adenoma, increasingly by minimally invasive parathyroidectomy. Medical management of mild disease is possible with bisphosphonates, hormone replacement therapy, and calcimimetics. Vitamin D deficiency is a common cause of secondary hyperparathyroidism, particularly in elderly people. However, the biochemical definition of vitamin D deficiency and its treatment are subject to much debate. Secondary hyperparathyroidism as the result of chronic kidney disease is important in the genesis of renal bone disease, and several new treatments could help achieve the guidelines set out by the kidney disease outcomes quality initiative.

Table 1: Changing clinical presentation of primary hyperparathyroidism
1930–1970 1970–2000
Nephrolithiasis 51–57% 17–37%
Hypercalciuria 36% 40%
Overt skeletal disease 10–23% 4–14%
Asymptomatic 6–18% 22–80%
Modified from reference 12
Panel 1: Recommendations for surgery from the National Institutes of Health
consensus conference on primary hyperparathyroidism in 1990 and 2002• Serum albumin-adjusted calcium greater than 0·25 mmol/L
above the upper limit of local laboratory reference range

• Urine calcium greater than 10 mmol per 24 h

• Creatinine clearance reduced by 30% or more

• Bone mineral density T score less than –2·5 (at any site)

• Age younger than 50 years

• Patient request; adequate follow-up unlikely

Aldosterone and parathyroid hormone interactions as mediators of metabolic and cardiovascular disease

Andreas Tomaschitz, Eberhard Ritz, Burkert Pieske, Jutta Rus-Machan
Metabolism Clinical and  Experimental 2014; 63: 20 31
http://dx.doi.org/10.1016/j.metabol.2013.08.016

Several studies demonstrated a strong link between dysregulation of the aldosterone and parathyroid hormone (PTH) axes on the one hand and CV pathology on the other hand. Such evidence documents clinically relevant interactions between aldosterone and PTH and a resulting impact on CV health. This review provides an up to date overview discussing the mechanisms and the clinical relevance underlying the interactions between aldosterone and PTH.

Inappropriate aldosterone and parathyroid hormone (PTH) secretion is strongly linked with development and progression of cardiovascular (CV) disease. Accumulating evidence suggests a bidirectional interplay between parathyroid hormone and aldosterone. This interaction may lead to a disproportionally increased risk of CV damage, metabolic and bone diseases.

This review focuses on mechanisms underlying the mutual interplay between aldosterone and PTH as well as their potential impact on CV, metabolic and bone health. PTH stimulates aldosterone secretion by increasing the calcium concentration in the cells of the adrenal zona glomerulosa as a result of binding to the PTH/PTH-rP receptor and indirectly by potentiating angiotensin 2 induced effects. This may explain why after parathyroidectomy lower aldosterone levels are seen in parallel with improved cardiovascular outcomes.

Aldosterone mediated effects are inappropriately pronounced in conditions such as chronic heart failure, excess dietary salt intake (relative aldosterone excess) and primary aldosteronism.

PTH is increased as a result of
(1) the MR (mineralocorticoid receptor)mediated calciuretic and magnesiuretic effects with a trend of hypocalcemia and hypomagnesemia; the resulting secondary hyperparathyroidism causes myocardial fibrosis and disturbed bone metabolism; and

(2) direct effects of aldosterone on parathyroid cells via binding to the MR. This adverse sequence is interrupted by mineralocorticoid receptor blockade and adrenalectomy.

Hyperaldosteronism due to klotho deficiency results in vascular calcification, which can be mitigated by spironolactone treatment. In view of the documented reciprocal interaction between aldosterone and PTH as well as the potentially ensuing target organ damage, studies are needed to evaluate diagnostic and therapeutic strategies to address this increasingly recognized pathophysiological phenomenon.

The classical view that aldosterone acts exclusively on the electrolyte transport in epithelial cells has been broadened after the mineralocorticoid receptor (MR) has been identified in non-epithelial cells as well, e.g. vascular smooth muscle cells and cardiomyocytes. Apart from classical genomic effects, non-genomic aldosterone mediated effects have been identified in various tissues and organs outside of the kidneys and colon, e.g. inner ear, choroid plexus, endothelial cells and cardiomyocytes.

In the past it had been documented that primary aldosteronism (PA; absolute aldosterone excess) contributed to the development of CVD. Several studies suggested, however, that “absolute aldosterone excess” is only the tip of the iceberg leading to the concept of “relative aldosterone excess” . Several large cross-sectional and prospective studies demonstrated a consistent relationship between circulating aldosterone levels, CV risk factors and mortality risk.

Such recent studies also document that even circulating aldosterone concentrations in the “normal” range may result in inappropriate aldosterone–MR interaction which may be reversed by MR blockade.
The identification of PTH receptors within the CV system e.g. in cardiomyocytes, vascular smooth muscle, and endothelial cells, indicates that inappropriate PTH secretion may impact on the CV health beyond the dysregulation of calcium and phosphate homeostasis.

Application of PTH after myocardial infarction attenuates ischaemic cardiomyopathy by increasing migration of bone marrow-derived stem cells to the ischaemic myocardium. On the other hand the PTH excess in primary hyperparathyroidism (pHPT) is linked in the long-term to a spectrum of adverse effects e.g. bone loss and increased fracture risk, coronary microvascular dysfunction, derangement of lipid and glucose metabolism, subclinical aortic valve calcification, increased aortic stiffness, endothelial dysfunction and arterial hypertension.

Interactions between vitamin D, klotho and aldosterone
Increased activity of systemic or local renin–angiotensin systems (RAS) is linked to increased target organ damage. The organ and tissue protective effects of vitamin D have in part been explained by vitamin D induced modulation of RAS activity.

In landmark experiments Li et al. documented markedly elevated renin mRNA expression in the juxtaglomerular apparatus of vitamin D receptor (VDR) knock-out mice compared to wild type mice. Furthermore, 1,25-dihydroxy vitamin D (1,25(OH2)D3) modulated renin gene transcription and renin synthesis and this was independent of serum calcium, PTH and angiotensin 2. Angiotensin 2 in turn reduces renal klotho expression resulting in modulations of FGF-23-signaling and of 1-α hydroxylase activity. Klotho is a membrane (and circulating) protein which is highly expressed in the kidney and modulates the inhibitory effects of FGF-23 on calcitriol formation; klotho contributes to the regulation of renal tubular calcium and phosphate reabsorption. The modulatory effects of vitamin D on the RAS might result in a lower risk of development and progression of CV morbidity and mortality.

Evidence for stimulating effects of PTH on adrenal aldosterone secretion Aldosterone synthesis is mainly initiated by angiotensin 2 and potassium via activating the Ca2+-messenger system in zona glomerulosa (ZG) cells to stimulate the steroidogenic cascade within the mitochondria. The Ca2+-messenger system further participates in the initiation of steroidogenesis by facilitating the cholesterol transfer into the mitochondria. Findings from experimental, mechanistic, observational and interventional studies suggest that PTH contributes to the regulation of aldosterone secretion in the ZG of the adrenal glands.

The interaction between aldosterone and Klotho and its relationship to vascular osteoinduction

The interaction between aldosterone and Klotho and its relationship to vascular osteoinduction

The interaction between aldosterone and Klotho and its relationship to vascular osteoinduction

Estradiol determines the effects of PTH on ERa-dependent transcription in MC3T3-E1 cells

Monika H.E. Christensen, IS Fenne, MH Flågeng, B Almås, et al.
Biochemical and Biophysical Research Communications 450 (2014) 360–365
http://dx.doi.org/10.1016/j.bbrc.2014.05.109

Bone remodeling is a continuous process regulated by several hormones such as estrogens and parathyroid hormone (PTH). Here we investigated the influence of PTH on estrogen receptor alpha (ERa)-dependent transcriptional activity in MC3T3-E1 osteoblasts. Cells that were transfected with an ER-responsive reporter plasmid and treated with PTH showed increased luciferase activity. However, in the presence of 17b-estradiol, we observed that PTH inhibited ERa-mediated transcription. cAMP mimicked the effects by PTH, and the findings were confirmed in COS-1 cells transfected with expression vector encoding the catalytic subunit of cAMP-dependent protein kinase (PKA). Furthermore, PTH exhibited specific effects on the mRNA expression of the decoy receptor osteoprotegerin (OPG) and the receptor activator of NF kappa-B ligand (RANKL) in MC3T3-E1 osteoblasts. In the absence of 17b-estradiol, PTH and cAMP enhanced the OPG/RANKL ratio, whereas, OPG/RANKL was suppressed when estradiol was present. In conclusion, our results indicate that the presence of estradiol determines whether PTH and cAMP stimulates or inhibits ERa-dependent activity and the OPG/RANKL mRNA expression in an osteoblastic cell line.

Ginsenoside-Rb2 displays anti-osteoporosis effects through reducing oxidative damage and bone-resorbing cytokines during osteogenesis

Qiang Huang, Bo Gao, Qiang Jie, Bo-Yuan Wei, et al.
Bone 66 (2014) 306–314
http://dx.doi.org/10.1016/j.bone.2014.06.010

Reactive oxygen species (ROS) are a significant pathogenic factor of osteoporosis. Ginsenoside-Rb2 (Rb2), a 20(S)-protopanaxadiol glycoside extracted from ginseng, is a potent antioxidant that generates interest regarding the bone metabolism area. We tested the potential anti-osteoporosis effects of Rb2 and its underlying mechanism in this study. We produced an oxidative damage model induced by hydrogen peroxide (H2O2) in osteoblastic MC3T3-E1 cells to test the essential anti-osteoporosis effects of Rb2 in vitro. The results indicated that treatment of 0.1 to 10 μMRb2 promoted the proliferation of MC3T3-E1 cells, improved alkaline phosphatase (ALP) expression, elevated calcium mineralization and mRNA expressions of Alp, Col1a1, osteocalcin (Ocn) and osteopontin (Opn) against oxidative damage induced by H2O2. Importantly, Rb2 reduced the expression levels of receptor activator of nuclear factor kappa-B ligand (RANKL) and IL-6 and inhibited the H2O2-induced production of ROS. The in vivo study indicated that the Rb2 administered for 12 weeks partially decreased blood malondialdehyde (MDA) activity and elevated the activity of reduced glutathione (GSH) in ovariectomized (OVX)mice. Moreover, Rb2 improved the micro-architecture of trabecular bones and increased bone mineral density (BMD) of the 4th lumbar vertebrae (L4) and the distal femur. Altogether, these results demonstrated that the potential anti-osteoporosis effects of Rb2 were linked to a reduction of oxidative damage and bone-resorbing cytokines, which suggests that Rb2 might be effective in preventing and alleviating osteoporosis.

Inflammatory cytokines in Paget’s disease of bone

GRW de Castro, Z Buss, JS Da Rosa, TS Fröde
International Immunopharmacology 18 (2014) 277–281
http://dx.doi.org/10.1016/j.intimp.2013.12.003

This study was undertaken to evaluate the expression of inflammatory cytokines in patients with Paget’s disease of bone (PDB). Serum levels of tumoral necrosis factor-α, interleukin 1β, interleukin-6 and interleukin-17
were measured in 51 patients with PDB and in 24 controls with primary osteoarthritis. Compared to controls, patients with Paget’s disease of bone presented higher levels of interleukin 6 and reduced interleukin 17, but levels of tumoral necrosis factor α and interleukin 1 β did not differ significantly. We found no significant differences when patients were compared according to disease activity or current treatment. There were no correlations between cytokine levels and bone-specific alkaline phosphatase or extension of Paget’s disease of bone on bone scintigraphs. In conclusion, patients with PDB present significant differences on levels of certain cytokines in comparison to primary osteoarthritis patients, but these alterations did not appear to have a clear correlation with parameters of disease activity or severity.

Development and validation of a novel cell-based assay for potency determination of human parathyroid hormone (PTH)
Axel Hohenstein, Meike Hebell, Heidi Zikry, Maria El Ghazaly, et al.
Journal of Pharmaceutical and Biomedical Analysis 98 (2014) 345–350
http://dx.doi.org/10.1016/j.jpba.2014.06.004

Disorders of bone metabolism
Orthopaedics I: General Principles

Nicola Peel
Surgery 33:1

Bone remodeling is critical to bone health. Alterations in the normal processes and regulation of remodeling may impact on bone mass and bone strength. Changes may be generalized or focal and underlie many of the common disorders of bone metabolism. This article focuses on the changes in bone remodeling which underlie both the development and treatment of osteoporosis. Osteomalacia, as an example of a mineralization disorder and Paget’s disease as an example of a focal disorder of bone remodeling, are also briefly reviewed.

There are many causes of increased bone turnover with the most common being the loss of estrogen at menopause. Increased bone turnover is initiated by increased activation frequency of osteoclasts. The consequent increase in remodeling space leads to bone loss which is, at least in part, reversible. Increased bone turnover is also associated with an increased risk of trabecular perforation with the increased number of remodeling sites acting as stress risers within the trabecular architecture. Bone loss within the trabecular compartment occurs preferentially from the horizontal, non-weight bearing plates resulting in disproportionate loss of bone strength for the reduction in bone mass.
Alterations in bone turnover also have potential to affect bone.

strength by changing the degree of mineralization. Primary mineral apposition occurs early after production of bone matrix by osteoblasts. After completion of the cycle, secondary mineral apposition occurs over many months. Increased bone turnover leads to reduced mineralization as the time between remodeling cycles reduces. Conversely, decreased bone turnover rates reduce the average time between remodeling at any site and hence lead to a greater degree of mineralization. Biomechanical principles indicate that the yield strength (stiffness) of highly mineralized bone increases but that it will withstand less deformation before fracture and therefore becomes brittle. A reduced degree of mineralization results in greater pliability but a reduction in bone strength.
Alterations in bone remodeling underpin changes in bone mass and bone strength. The impact of these changes is manifest in the development and clinical presentation of osteoporosis.

Paget’s disease

Paget’s disease

Paget’s disease: (a) increased uptake on nuclear medicine scanning in the right hemipelvis, sacrum and left femur and (b) left femur showing radiological changes of Paget’s including a fissure fracture in the proximal lateral cortex

Paget’s disease is an example of a localised disorder of bone turnover. Its aetiology remains unclear. Paget’s disease is not uncommon but is often asymptomatic and diagnosed coincidentally. It is estimated to affect approximately 2% of adults over the age of 55 in the UK but the prevalence varies markedly between populations. It is increasingly prevalent with increasing age and affects men more frequently than women. In 80% of cases more than one bone is involved, characteristically in an asymmetric distribution.
Pagetic bone is characterized by the presence of giant multinucleated osteoclasts resulting in dramatic increases in bone resorption in the affected bones. These regions undergo a lytic phase followed by a compensatory increase in bone formation. Rapid bone formation results in an accumulation of woven bone, which is mechanically abnormal resulting in loss of bone strength.
The typical clinical manifestation is of bone pain, which may be associated with bone expansion and deformity. Complications of Paget’s disease include the development of secondary osteoarthritis, fissure fractures and very rarely, osteosarcomatous change (<1% of cases).

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Reported by: Dr. V.S. Karra, Ph.D.

The European equivalent of the US Food and Drug Administration (FDA) yesterday recommended withdrawing calcitonin nasal spray — indicated for treating osteoporosis in the European Union — because of an increased risk for cancer.
The European Medicines Agency (EMA) also said that the long-term use of calcitonin-containing medicines delivered by injection or infusion increases the risk for cancer. Calcitonin in any formulation should not be used to treat osteoporosis at all, the agency said.

In the United States, 2 nasal-spray versions of calcitonin are FDA-approved for treating postmenopausal osteoporosis in women: Fortical (Upsher-Smith Laboratories) and Miacalcin (Novartis). Neither of the labels for the 2 drugs contains restrictions on how they should be used or a warning about the risk for cancer.

Calcitonin, also called calcitonin-salmon, is a synthetic copy of a polypeptide hormone secreted by the ultimobranchial gland of salmon.

The EMA said it based its recommendations on a review of the benefits and risks of calcitonin-containing medicines. Conducted by the agency’s Committee for Medicinal Products for Human Use (CHMP), the review encompassed available data from the companies that market these drugs, postmarketing safety data, randomized controlled studies, 2 studies of unlicensed oral calcitonin drugs, and experimental cancer studies, among other sources.

CHMP found that “a higher proportion of patients treated with calcitonin for long periods of time develop cancer of various types, compared with patients taking placebo.” The increase in cancer rates ranged from 0.7% for oral formulations to 2.4% for the nasal formulation. CHMP concluded that the benefits of calcitonin for osteoporosis did not exceed the risks. The nasal spray’s only indication is for osteoporosis, thus justifying the drug’s removal from the market.

As a solution for injection or infusion, calcitonin should be administered for no more than 4 weeks to prevent acute bone loss resulting from sudden immobilization, and normally for no more than 3 months to treat Paget’s disease, the EMA said. The agency did not specify a time frame for the short-term use of calcitonin for treating hypercalcemia caused by cancer.

For further details go to their website

Source

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Curator: Ritu Saxena, Ph.D.

Reporters: Ritu Saxena, Ph.D. and Dr. Venkat S. Karra, Ph.D.

Merck & Co. declared yesterday, July 12 2012, that it is ending a last-stage clinical trial of the osteoporosis drug Odanacatib based on the results demonstrating the effectively in reducing the post-menopausal fracture risk.

Safety and effectiveness of the drug were being evaluated in the trial enrolling more than 16,000 post-menopausal women and there was clear evidence that the drug was working. Hence, an independent committee decided to end the trial before completion. It was expected to continue until hip fractures had been reported in 237 patients. Merck said the interim analysis was conducted when around 70 percent of the targeted number of hip fractures had been reported. Merck said that it expects to target regulatory approval in the U.S., European Union and Japan in the first half of next year.

Odanacatib is designed to block cathepsin K, the major enzyme in osteoclasts that is responsible for breakdown of existing bone tissue. Osteoclasts, bone “eroding” cells along with bone forming cells, osteoblasts, are involved in bone turnover. In post menopausal osteoporosis, there is a decrease in bone turnover. Blocking the activity of osteoclasts would shift the equilibrium towards bone formation by relative increase in osteoblasts.

Earlier studies have performed 2-3 year long clinical trials showing its effectiveness in treating post-menopausal osteoporosis with a progressive increase in the bone mineral density, increase in bone formation markers expression in molecular studies and that it was generally well tolerated.. The oral drug, taken weekly, is considered more convenient than an older class of osteoporosis drugs known as bisphosphonates. Bisphosphonates, target osteoclasts and have shown to increase the risk of a severe bone disease, osteonecrosis of the jaw. Other safety concerns have also lead to the decline in the use of bisphosphonates.

Sales of Merck’s bisphosphonate drug Fosamax reached $3 billion in 2007, but that revenue has plunged since emergence of generic competition in early 2008. Wall Street analysts, on average, have forecast annual sales of odanacatib at $402 million by 2016, according to Thomson Pharma.

Source: http://www.dddmag.com/news/2012/07/merck-ends-odanacatib-study-early?et_cid=2744025&et_rid=45527476&linkid=http%3a%2f%2fwww.dddmag.com%2fnews%2f2012%2f07%2fmerck-ends-odanacatib-study-early

http://www.huffingtonpost.com/2012/07/12/odanacatib-osteoporosis-drug-fracture-bone_n_1666631.html

http://www.ncbi.nlm.nih.gov/pubmed/20740685

http://www.ncbi.nlm.nih.gov/pubmed/19874198

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Curator and Reporter: Ritu Saxena, Ph.D.

Recently, an article published in the journal Bone described that the low magnitude vibrations might be helpful in mitigating osteopenia in spontaneous granulosa cell ovarian cancer.

Osteopenia is defined as the bone mineral density (BMD) that is lower than normal peak BMD but not low enough to be classified as the diseased condition called osteoporosis. Bone mineral density is a measurement of the level of minerals in the bones, that shows how dense and strong they are. Having osteopenia means there is a greater risk that, as time passes, you may develop BMD that is very low compared to normal, known as osteoporosis

Cancer progression is often paralleled by a decline in bone mass, raising risk of fracture. Loss in bone mass can be therapeutically treated by using bone anabolic agents that increase the process of bone formation compared to bone resorption thus leading to an overall increase in bone mass. However, use of anabolic agents for preventing cancer associated bone loss presents a lot of concern as they may exacerbate cancer tissue expansion.

Bone is a mechanosensitive organ. Osteoblastogenesis, or the process of differentiation of precursor cells to bone forming cells (osteoblasts) is encouraged by low intensity vibration (LIV) via a mechanical signal. Rubin et al explored the possibility of slow cancer-associated bone loss, but this goal must be achieved without fostering disease progression. The hypothesis was tested in the murine model.

Seventy female F1-SWRxSWXJ-9 mice, a strain prone to developing granulosa cell tumors, were divided into three groups – baseline control (BC: n=10), age-matched control (AC: n=30), and LIV (n=30), which received mechanical signals (90Hz @ 0.3g) for 15m/day, 5day/w over the course of 1year. Survival curves observed in the three groups indicated that longevity was unperturbed by LIV. Rubin et al stated that “1year, bone volume of proximal tibiae in LIV mice was 25% greater than AC while bone volume of L5 vertebrae was 16% higher in LIV over AC (p<0.02). Primary lesions and peripheral metastases were apparent in both LIV and AC; however, overall tumor incidence was approximately 30% less in LIV (p=0.27) and, when disease was evident, involved fewer organ systems (p=0.09).”

These experiments indicate that LIV helps protect bone mass in mice inherently susceptible to cancer without compromising life expectancy, perhaps through mechanical control of stem cell fate. Further, these data reflect the numerous system-level benefits of exercise in general, and mechanical signals in particular, in the preservation of bone density and the suppression of cancer progression.

Source: Journal article- http://www.thebonejournal.com/article/S8756-3282(12)00867-8/abstract, http://www.webmd.com/osteoporosis/tc/osteopenia-overview

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Reporter: Ritu Saxena, Ph.D.

Singapore, May 14, 2012 (ACN Newswire via COMTEX) — Scientists at A*STAR’s Institute of Medical Biology (IMB), in collaboration with doctors and scientists in Jordan, Turkey, Switzerland and USA, have identified the genetic cause of a birth defect known as Hamamy syndrome[1]. Their groundbreaking findings were published on May 13th in the prestigious journal Nature Genetics. The work lends new insights into common ailments such as heart disease, osteoporosis, blood disorders and possibly sterility.

Hamamy syndrome is a rare genetic disorder which is marked by abnormal facial features and defects in the heart, bone, blood and reproductive cells. Its exact cause was unknown until now. The international team, led by scientists at IMB, have pinpointed the genetic mistake to be a mutation in a single gene called IRX5.

This is the first time that a mutation in IRX5 (and the family of IRX genes) has ever been discovered in man. IRX5 is part of a family of transcription factors that is highly conserved in all animals, meaning that this gene is present not only in humans but also in mice, fish, frogs, flies and even worms. Using a frog model, the scientists demonstrated that Irx5 orchestrates cell movements in the developing foetus which underlie head and gonad formation.

Carine Bonnard, a final-year PhD student at IMB and the first author of the paper, said, “Because Hamamy syndrome causes a wide range of symptoms, not just in newborn babies but also in the adult, this implies that IRX5 is critical for development in the womb as well as for the function of many organs in our adult body. For example, patients with this disease cannot evacuate tears from their eyes, and they will also go on to experience repetitive bone fractures (Annex A) or progressive myopia as they age. This discovery of the causative gene is a significant finding that will catalyze research efforts into the role of the Irx gene family and greatly increase our understanding of human health, such as bone homeostasis, or gamete formation for instance.”

“We believe that this discovery could open up new therapeutic solutions to common diseases like osteoporosis, heart disease, anaemia which affect millions of people worldwide,” said Dr Bruno Reversade, Senior Principle Investigator at IMB. “The findings also provide a framework for understanding fascinating evolutionary questions, such as why humans of different ethnicities have distinct facial features and how these are embedded in our genome. IRX genes have been repeatedly co-opted during evolution, and small variation in their activity could underlie fine alterations in the way we look, or perhaps even drastic ones such as the traits seen in an elephant, whale, turtle or frog body pattern.”

Only a handful of people in the world have been identified with Hamamy Syndrome making it a very rare genetic disorder. Rare genetic diseases, usually caused by mutations in a single gene, provide a unique opportunity to better understand more common disease processes. These “natural” experiments are similar to carefully controlled knockout animal experiments in which the function of single genes are analyzed and often give major insights into general health issues.[2]

Prof Birgitte Lane, Executive Director of IMB, said, “Understanding how various pathways in the human body function is the foundation for developing new therapeutic targets. This is an important piece of research that I believe will be of great interest to many scientists and clinicians around the world because of the clinical and genetic insights it brings to a large range of diseases.”

Notes for editor:

The research findings described in this news release can be found on Nature Genetics’s website under the title “Mutations in IRX5 impair craniofacial development and germ cell migration via SDF1” by Carine Bonnard[1], Anna C Strobl[2], Mohammad Shboul1, Hane Lee[3], Barry Merriman[3], Stanley F Nelson[3], Osama H Ababneh[4], Elif Uz[5],[6], Tulay Guran[7], Hulya Kayserili[8], Hanan Hamamy[9],[10] & Bruno Reversade[1],[11].

[1] Institute of Medical Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore

[2] Division of Systems Biology, Medical Research Council National Institute for Medical Research, London, UK

[3] Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California, USA

[4] Department of Opthalmology, Faculty of Medicine, University of Jordan, Amman, Jordan

[5] Department of Biology, Faculty of Arts and Sciences, Duzce University, Duzce, Turkey

[6] Gene Mapping Laboratory, Department of Medical Genetics, Hacettepe University Medical Faculty, Ankara, Turkey

[7] Pediatric Endocrinology and Diabetes, Marmara University Hospital, Istanbul, Turkey

[8] Medical Genetics Department, Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey

[9] Department of Genetic Medicine and Development, Geneva University Hospital, Geneva, Switzerland

[11] Department of Pediatrics, National University of Singapore, Singapore

Correspondence should be addressed to B.R. (Bruno@reversade.com)

The article can be accessed fromhttp://www.nature.com/ng/journal/vaop/ncurrent/full/ng.2259.html .

About the Institute of Medical Biology (IMB)

IMB is one of the Biomedical Sciences Institutes of the Agency for Science, Technology and Research (A*STAR). It was formed in 2007, the 7th and youngest of the BMRC Research Institutes, with a mission to study mechanisms of human disease in order to discover new and effective therapeutic strategies for improved quality of life. From 2011, IMB also hosts the inter-research institute Skin Biology Cluster platform.

IMB has 20 research teams of international excellence in stem cells, genetic diseases, cancer and skin and epithelial biology, and works closely with clinical collaborators to target the challenging interface between basic science and clinical medicine. Its growing portfolio of strategic research topics is targeted at translational research on the mechanisms of human diseases, with a cell-to-tissue emphasis that can help identify new therapeutic strategies for disease amelioration, cure and eradication. For more information about IMB, please visit www.imb.a-star.edu.sg .

About the Reversade Laboratory

Dr. Reversade, a human geneticist and embryologist holds a Senior Principal Investigator position at IMB and an adjunct faculty position at the Department of Paediatrics in the National University of Singapore. He is a Fellow of the Branco Weiss Foundation based at ETH in Switzerland and also the first recipient of an A*STAR Investigatorship, a programme which provides competitive and prestigious fellowships to support the next generation of international scientific leaders, offering funding and access to state-of-the-art scientific equipment and facilities at A*STAR. For more information about Dr. Reversade’s laboratory, please visit www.reversade.com .

About A*STAR

The Agency for Science, Technology and Research (A*STAR) is the lead agency for fostering world-class scientific research and talent for a vibrant knowledge-based and innovation-driven Singapore. A*STAR oversees 14 biomedical sciences and physical sciences and engineering research institutes, and six consortia & centres, located in Biopolis and Fusionopolis as well as their immediate vicinity. A*STAR supports Singapore’s key economic clusters by providing intellectual, human and industrial capital to its partners in industry. It also supports extramural research in the universities, and with other local and international partners. For more information about A*STAR, please visit www.a-star.edu.sg .

Source: http://www.marketwatch.com/story/scientists-make-groundbreaking-discovery-of-mutation-causing-genetic-disorder-in-humans-2012-05-14?pagenumber=1

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Curator: Ritu Saxena, Ph.D.

News Brief:

Bone-protecting protein discovered

ABC Science, April 19, 2012.

A protein produced by bone cells could help in the development of better treatments for osteoporosis. Professor Hiroshi Takayanagi, of Tokyo Medical and Dental University, and colleagues, report their findings today in the journal Nature.

“I hope our discovery will lead to better treatment developments for osteoporosis, arthritis, or bone fractures,” says Takayanagi. The strength of our bones is controlled by hormones and by the balance between bone formation and breakdown (resorption).

If too much bone is broken down and not enough is made, bone density falls and the chance of fractures increases. Takayanagi and colleagues have found that bone forming cells, or osteoblasts, produce a protein called semaphorin 3A (Sema3A), which has previously been known to regulate nerve and immune cells. They found not only does Sema3A decrease bone breakdown but, unlike current osteoporosis medications that do the same, it also boosts bone formation at the same time.

Mouse studies

When they began their study, Takayanagi and colleagues already knew another protein produced by osteoblasts, called osteoprotegerin, decreases bone breakdown. But, the team suspected there would be other proteins that did the same.

The team checked the activity of proteins produced by osteoblasts from mice genetically engineered to have no osteoprotegerin, and found they were still inhibiting bone breakdown. They isolated the molecule responsible for this inhibition and using mass spectrometry identified it as Sema3A. The researchers then tested mice genetically engineered to have no functional Sema3A and found an increase in bone breakdown and a decrease in bone density.

Surprisingly, however, they also found that bone formation was also lower in these Sema3A knockout mice. In their final experiment they injected Sema3A into diseased mice and found it prevented further bone loss in osteoporosis and accelerated bone regeneration in the case of fractures.

“Many molecules regulate either resorption or formation but this is the first molecule that regulates both at the same time,” says Takayanagi.

http://www.abc.net.au/science/articles/2012/04/19/3480418.htm

‘Exciting discovery’

Dr Gethin Thomas of the Muscoskeletal Genetics Group at The University of Queensland Diamantina Institute welcomes the research. He says more 2 million Australians are currently affected by osteoporosis and half of women over the age of 50 are expected to suffer at least one osteoporotic fracture.

“The gold standard is to find therapies that can build bone as well as stop bone degradation, as osteoporosis is frequently only diagnosed after the bones have already become very weak,” says Thomas.

“This is a very exciting discovery identifying a completely new bone regulating pathway and one that is potentially very ‘druggable’.”

Sema3A is known to play important roles in the development of heart and nervous system, but researchers are yet understand exactly how the protein acts to boost bone formation and inhibit bone resorption. “It’s possible there might be side-effects on the heart or nerve generation but they haven’t explored that at all in this paper,” says bone cell biologist, Associate Professor Natalie Sims from the St Vincent’s Institute.

“It’s important that they’ve found this new factor and what it can do. What’s not clear is how specific it might be and that’s the obviously the next step they need to explore.”

http://www.abc.net.au/science/articles/2012/04/19/3480418.htm

Research:

Takanayagi et al published the research on Sema3a molecule’s bone formation and bone resorption activity in a recent issue of the journal Nature (2012). The research was summarized as:

The bony skeleton is maintained by local factors that regulate bone-forming osteoblasts and bone-resorbing osteoclasts, in addition to hormonal activity. Osteoprotegerin protects bone by inhibiting osteoclastic bone resorption, but no factor has yet been identified as a local determinant of bone mass that regulates both osteoclasts and osteoblasts. Here we show that semaphorin 3A (Sema3A) exerts an osteoprotective effect by both suppressing osteoclastic bone resorption and increasing osteoblastic bone formation. The binding of Sema3A to neuropilin-1 (Nrp1) inhibited receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation by inhibiting the immunoreceptor tyrosine-based activation motif (ITAM) and RhoA signalling pathways. In addition, Sema3A and Nrp1 binding stimulated osteoblast and inhibited adipocyte differentiation through the canonical Wnt/β-catenin signalling pathway. The osteopenic phenotype in Sema3a−/− mice was recapitulated by mice in which the Sema3A-binding site of Nrp1 had been genetically disrupted. Intravenous Sema3A administration in mice increased bone volume and expedited bone regeneration. Thus, Sema3A is a promising new therapeutic agent in bone and joint diseases.

http://www.nature.com/nature/journal/v485/n7396/full/nature11000.html

Semaphorins have been known as one family of inhibitory axon guidance molecules. The semaphorins include secreted, transmembrane, and GPI anchored extracellular molecules that are involved in regulating axon guidance by inhibiting axons from growing toward incorrect targets. Semaphorin 3A (Sema3A) may play a particularly interesting role in limiting axon regeneration since it is expressed in meningeal fibroblasts that invade the injured spinal cord and surround the glial scar. In addition, the Sema3A co receptors, Neuropilin 1 and Plexin A1, are expressed on axons that regenerate up to the injured region, but do not cross this Sema3A containing region. Thus, Sema3A and its co receptors may have important roles in regulating axon guidance during neuronal development and after neuronal injury.

http://www.abcam.com/Semaphorin-3A-antibody-ab25999.html

Conclusion and Future perspective:

Takayanagi et al stated in the discussion of the article “Sema3A represents the long sought soluble molecule with the capacity to bring both osteoblasts and osteoclasts into a condition that favours bone mineral increase.”

Mone Zaidi and Jameel Iqbal, bone biology researchers from the Mount Sinai School of Medicine commented on the research stating “The protein Sema3A both restrains bone degradation and stimulates bone building in mice, suggesting a potential therapy for conditions such as osteoporosis”, referring to it as probable “double protection for weakened bones”.

http://www.nature.com/nature/journal/v485/n7396/full/485047a.html

Uncoupling of bone turnover (with a decrease in bone formation and an increase in bone resorption) has been observed in postmenopausal osteoporosis and microgravity-induced bone loss. Most of the available drugs are either anti-resorptive (For eg., bisphonsphonates), or anabolic (For eg., Parathyroid hormone) on bone. However, Sema3a might act as an effective therapeutic agent by targeting both bone formation and bone resorption.

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