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A research team led by scientists at the University of Nebraska-Lincoln (UNL) has provided the first direct evidence that an algae-infecting virus can invade and potentially replicate within some mammalian cells. Known as Acanthocystis turfacea chlorella virus 1, or ATCV-1, the pathogen is among a class of chloroviruses long believed to take up residence only in green algae. That thinking changed with a 2014 study from Johns Hopkins University and UNL that found gene sequences resembling those of ATCV-1 in throat swabs of human participants.
The new study (“Response of mammalian macrophages to challenge with the Chlorovirus ATCV-1), published in the Journal of Virology, introduced ATCV-1 to macrophage cells that serve critical functions in the immune responses of mice, humans, and other mammals. By tagging the virus with fluorescent dye and assembling three-dimensional images of mouse cells, the authors determined that ATCV-1 successfully infiltrated them.
The authors also measured a threefold increase in ATCV-1 within 24 hours of introducing the virus. The relatively modest spike nevertheless suggests that ATCV-1 can replicate within the macrophage cells, according to co-author David Dunigan, Ph.D.
Though a few studies have documented viruses jumping from one biological kingdom to another, chloroviruses were previously thought to have a limited “host range” that stopped well short of the animal kingdom, said Dr. Dunigan.
“A few years ago, no one I know would have made a prediction like this,” noted Dr. Dunigan, research professor of plant pathology and member of the Nebraska Center for Virology. “You probably would’ve been laughed out of the room. But we are now in the middle of something that is so very interesting.”
The macrophage cells underwent multiple changes characteristic of those breached by a virus, he continued. These changes eventually included a form of programmed death that virologists consider an innate “scorched earth” defense against the spread of viruses, which require living cells to survive and replicate.
Before dying, the cells exhibited multiple signs of stress that tentatively support links to mild cognitive impairments first reported in the 2014 paper. The new study measured a post-viral rise in interleukin 6, which previous research has linked with diminished spatial learning and certain neurological diseases. The authors also reported an increase in nitric oxide, an important signaling molecule that has been associated with memory impairments when produced in excess.
The 2014 investigation, which was initially designed to test the cognitive functioning of human participants, found that those with the ATCV-1 DNA performed slightly worse on measures of visual processing and visual motor speed. Mice inoculated with the virus showed similar deficits in memory and attention while navigating mazes. The 2014 paper further suggested that ATCV-1 altered the expression of more than 1,000 genes in the rodent hippocampus, an area of the brain tied to memory and spatial navigation.
The new study’s authors are continuing their collaboration with Johns Hopkins in the hope of ultimately confirming whether and how the virus contributes to any cognitive deficits suggested by the initial studies.
“It is still unclear whether the factors induced by the cell-based virus challenge could also be induced in the whole animal, and whether the induced factors cause cognitive impairments in the animal or the human,” said co-author Tom Petro, Ph.D., professor of microbiology and immunology at the University of Nebraska Medical Center.
Dr. Dunigan said he and his colleagues are also searching for other cellular responses to ATCV-1 while investigating how these responses might drive systemic changes in mice.
Tumor Associated Macrophages: The Double-Edged Sword Resolved?
Writer/Curator: Stephen J. Williams, Ph.D.
UPDATED 10/04/2021 TAMs Enhance Tumor Hypoxia and Aerobic Glycolysis
Cell-based immunity is vital for our defense against pathologic insult but recent evidence has shown the role of cell-based immunity, especially macrophages to play an important role in both the development and hindrance of tumor growth, including role in ovarian, hematologic cancers, melanoma, and breast cancer. In the past half century, new immunological concepts of cancer initiation and progression have emerged, including the importance of the harnessing the immune system as a potential anti-cancer strategy. However, as our knowledge of the immune system and tumor biology has grown, the field has realized an immunological conundrum: how can an immune system act to both prevent tumor growth and promote the tumor’s growth?
As discussed in the lower section of this post, authors of a paper in the journal Science show how different populations of tumor-associated macrophages (TAMs) may exert both positive and negative effects on tumor cells, producing a sort of ying-yang war between the tumor and the immune system.
The Immune System: Brief Overview and Role in Cancer
Figure. Cell lineage of the immune system. A description of the different cell types can be found here.
Histologic evaluation of multiple tumor types, especially solid tumors, reveal the infiltration of diverse immunological cell types, including myeloid and lymphoid cell lineages, such as macrophages and NK, T cell and B cells respectively.
The immunological conundrum
Figure. Potential inflammatory signaling pathways in breast cancer stem cells.
Breast cancer stem cells may be regulated by chemokine- and/or cytokine-mediated inflammatory signaling in an autocrine or paracrine manner. (from University of Tokyo at http://www.ims.u-tokyo.ac.jp/system-seimei/en/research2_e.htm)
Role of Tumor Associated Macrophages
There are conflicting reports as to the functional consequence of these infiltrating tumor-associated macrophages (TAMs). TAMs have been shown to secrete mediators such as interleukins and cytokines in a paracrine manner such as CCL2, IL10 and TGFβ. In certain instances these cytokines and mediators actually promote the growth of the surrounding tumors.
Figure. TAMs can be divided into subpopulations with distinctive functions and secretogogues.
For Further Reference
Tumor-associated macrophages and the profile of inflammatory cytokines in oral squamous cell carcinoma. http://www.ncbi.nlm.nih.gov/pubmed/23089461 anti-inflamm IL10 and TGFB
Figure 2: TAM functions in tumor progression. Tumor cells and stromal cells, which produce a series of chemokines and growth factors, induce monocytes to differentiate into macrophages. In the tumor, most macrophages are M2-like, and they express some cytokines, chemokines, and proteases, which promote tumor angiogenesis, metastasis, and immunosuppression. From Macrophages in Tumor Microenvironments and the Progression of Tumors
Macrophages integrate metabolic and environmental signals to promote tumor growth. Area within dotted rectangle indicates proposed mechanisms of action. ARG, arginase; HIF, hypoxia-inducible factor; MCT, monocarboxylate transporter; NADH, nicotine adenine dinucleotide, reduced; PKM2, M2 isoform of pyruvate kinase; VEGF, vascular endothelial growth factor from Tumor cells hijack macrophages via lactic acid adapted from Colegio OR, Chu N-Q, Szabo AL, Chu T, Rhebergen AM, Jairam V et al. Functional polarization of tumour-associated macrophages by tumour-derived lactic acid. Nature (e-pub ahead of print 13 July 2014; doi:10.1038/nature13490). | Article |
A recent Science paper from Cornel has investigated the origin, function, and characterization of TAMs on breast cancer growth. In summary, their efforts and research suggest different populations of TAMs with varied tumorigenic effects, a finding which may help explain the immunologic conundrum with respect to solid tumors.
The authors characterized the infiltrating immune cell types in a MMTV-PyMt model of breast cancer.
The MMTV-PyMt mouse breast cancer model:
is a transgenic model where mammary gland expression of the polyoma middle T antigen (PyMT) is driven by the Mouse Mammary Tumor Virus promoter (MMTV).
For a review of mouse models of breast cancer please see
1. Macrophages constitute the predominate myeloid cell population in MMTV-PyMT mammary tumors
Tumor infiltrating immune cells included
Myeloid cells comprised 50% of CD45+ infiltrating leukocytes.
The CD45 antigen, also known as Protein tyrosine phosphatase, receptor type, C (PTPRC) is an enzyme that, in humans, is encoded by the PTPRCgene, and acts as a regulator of B and T-lymphocytes.
Authors noted three types of cells classified as Type I, II, and III based on
2. TAMS differentiate from CCR2+ inflammatory monocytes
To determine whether Ly6C+CCR2+ inflammatory monocytes contributed to TAMs and MTMs, authors crossed PyMT mice to Ccr2−/− mice and found MTMs (mammary tumor macrophages) were significantly reduced in Ccr2−/− PyMT mice, implying that MTMs are constitutively repopulated by inflammatory monocytes
To determine whether inflammatory monocytes were required for TAM maintenance, we generated CCR2DTR PyMT mice expressing diphtheria toxin receptor (DTR) under control of the Ccr2 locus DT treatment resulted in 96% depletion of tumor-associated monocytes compared to 80% depletion in Ccr2−/− mice
To investigate whether monocytes could differentiate into TAMs in vivo, we transferred CCR2+ bone marrow cells isolated from CCR2GFP reporter mice into congenically marked CCR2DTR PyMT mice depleted of endogenous monocytes, we observed transferred cells in developing tumors demonstrate that tumor growth induces the differentiation of CCR2+ monocytes into TAMs.
3. TAMs are phenotypically distinct from AAMs (M2 or alternatively activated macrophages)
Gene-expression profiling revealed the integrin CD11b (Itgam) was expressed at lower levels in TAMs than in MTMs while several other integrins and the integrin receptor Vcam1 were up-regulated in TAMs
AM population did not express AAM markers such as Ym1, Fizz1, and Mrc1; instead, MTMs more closely resembled AAMs. The authors detected Vcam1 up-regulation on TAMs as a late differentiation event
4. RBPJ-dependent TAMs modulate the adaptive immune response
In DCs, canonical Notch signaling mediated by the key transcriptional regulator RBPJ controls lineage commitment and terminal differentiation. To explore whether Notch signaling played a role in TAM differentiation, authors used CD11ccre mice that efficiently deleted floxed DNA sequences to a greater extent in TAMs than MTMs, but not in monocytes or neutrophils (fig. S14). CD11ccreRbpjfl/fl PyMT mice exhibited a selective loss of MHCIIhiCD11blo TAMs ( 4A). However, a MHCIIhiCD11bhi population still remained
Transcriptional profiling comparing this population to WT TAMs confirmed a loss of the Notch-dependent program in RBPJ-deficient cells revealing that in the absence of RBPJ, inflammatory monocytes are unable to terminally differentiate into TAMs.
UPDATED 10/04/2021 TAMs Enhance Tumor Hypoxia and Aerobic Glycolysis
Tumor-Associated Macrophages Enhance Tumor Hypoxia and Aerobic Glycolysis
From:
Tumor-Associated Macrophages Enhance Tumor Hypoxia and Aerobic Glycolysis
HoibinJeong, SehuiKim, Beom-JuHong, Chan-JuLee, Young-EunKim, SeoyeonBok, Jung-MinOh, Seung-HeeGwak, Min YoungYoo, Min SunLee, Seock-JinChung, JoanDefrêne, PhilippeTessier, MartinPelletier, HyeongrinJeon, Tae-YoungRoh, BumjuKim, Ki HeanKim, Ji HyeonJu, SungjeeKim, Yoon-JinLee, Dong-WanKim, Il HanKim, Hak JaeKim, Jong-WanPark, Yun-SangLee, Jae SungLee, Gi JeongCheon, Irving L.Weissman, Doo HyunChung, Yoon KyungJeon and G-OneAhn
Tumor hypoxia and aerobic glycolysis are well-known resistance factors for anticancer therapies. Here, we demonstrate that tumor-associated macrophages (TAM) enhance tumor hypoxia and aerobic glycolysis in mice subcutaneous tumors and in patients with non–small cell lung cancer (NSCLC). We found a strong correlation between CD68 TAM immunostaining and PET 18fluoro-deoxyglucose (FDG) uptake in 98 matched tumors of patients with NSCLC. We also observed a significant correlation between CD68 and glycolytic gene signatures in 513 patients with NSCLC from The Cancer Genome Atlas database. TAM secreted TNFα to promote tumor cell glycolysis, whereas increased AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator 1-alpha in TAM facilitated tumor hypoxia. Depletion of TAM by clodronate was sufficient to abrogate aerobic glycolysis and tumor hypoxia, thereby improving tumor response to anticancer therapies. TAM depletion led to a significant increase in programmed death-ligand 1 (PD-L1) expression in aerobic cancer cells as well as T-cell infiltration in tumors, resulting in antitumor efficacy by PD-L1 antibodies, which were otherwise completely ineffective. These data suggest that TAM can significantly alter tumor metabolism, further complicating tumor response to anticancer therapies, including immunotherapy.
Significance: These findings show that tumor-associated macrophages can significantly modulate tumor metabolism, hindering the efficacy of anticancer therapies, including anti-PD-L1 immunotherapy.
Introduction
Tumor hypoxia and glycolysis have long been recognized as major resistance factors contributing to failures of chemo- and radiotherapy (1, 2). Traditionally, tumor hypoxia is known to occur by two mechanisms: chronic or acute hypoxia (2). Chronic hypoxia occurs as a result of rapid proliferation of cancer cells and hence being constantly forced away from blood vessels beyond the oxygen diffusion distance of approximately 150 μm (2). Acute hypoxia on the other hand occurs by a temporary cessation of the blood flow due to highly disorganized tumor vasculature (2). Regardless of the mechanism, tumor hypoxia has been extensively documented for their contribution to resistance to all anticancer therapies including chemotherapy (2), surgery (3), radiotherapy (2), and recently immunotherapy (4).
Aerobic glycolysis, also known as Warburg effect, is a phenomenon whereby many types of tumors exhibit a preference of glucose over the oxygen for their energy substrate (5), and this has allowed us to track solid tumors in patients with PET using 18fluoro-deoxyglucose (FDG) radioactive tracer (6). Although several mechanisms for Warburg effect have been suggested including mitochondrial defects, adaptation to hypoxia [hence activation of hypoxia-inducible factor (HIF)], and oncogenic signals such as MYC and RAS (7), the exact mechanism is still controversial. Tumor glycolysis has also been reported to influence the therapy outcome (8). Preclinical studies have suggested that glycolysis can increase DNA repair enzyme expressions including Rad51 and Ku70, which can facilitate radiation-induced DNA double-strand break repair (9). Lactate, a major byproduct of glycolysis, has recently been shown to be utilized as a fuel source for oxidative phosphorylation in nearby cancer cells (10), which can promote the tumor recurrence following anticancer therapies.
Tumor-associated macrophages (TAM) are bone marrow–derived immune cells recruited to tumors and have been extensively reported for their protumoral role (11). Recruited to tumors by various tumor-secreting factors including stromal cell–derived factor-1 (SDF1; ref. 12), VEGF (13), semaphorin 3A (14), and colony-stimulating growth factor-1 (CSF1; ref. 15), TAMs have been shown to produce various growth factors and proteases necessary for tumor survival (11) or immunosuppressive cytokines inhibiting antitumor immune responses (16). Macrophages in general are known to be polarized to either classically activated M1 macrophages or alternatively activated M2 phenotype depending on the cytokine milieu in which they are exposed (17). Bacterial-derived products such as lipopolysaccharide have been shown to polarize macrophages toward M1 phenotype (17), while parasite-associated signals such as IL4 and IL13 can lead to M2-polarized macrophages with increased tissue repair abilities (17). It has been suggested that TAMs are M2-like, although various subpopulations of TAM have been also identified including TIE2-positive macrophages (18), programmed cell death protein-1 (PD-1)–expressing TAM (19), and C-C chemokine receptor type-2 (CCR2)–expressing TAM (20).
In this study, we demonstrate clinically and preclinically that TAMs are a novel contributor to tumor hypoxia and aerobic glycolysis by competing oxygen and glucose with cancer cells. We further observed that TAM can significantly interfere with T-cell infiltration thereby masking programmed death-ligand 1 (PD-L1) expression in the tumors. We believe that our results have an important clinical implication such that patients with high infiltration of TAM in their tumors may poorly respond to all anticancer therapies, including the latest immunotherapy.
Strong correlations between TAM infiltration and glycolysis in patients with NSCLC. A, Representative PET/CT images for FDG uptake (top) and immunostaining of CD68 (bottom) from paired tumors of patients with NSCLC. Top, yellow circles, location of tumors. Bottom, red arrowheads, CD68-positive TAM. Scale bar, 100 μm. B, Correlation between glycolysis and CD68-positive TAM in 98 patients with NSCLC paired results as in A. Glycolysis was analyzed as FDG maximal standardized uptake value (FDG SUVmax; left) or 40% total lesion glycolysis (TLG; right). C, FDG SUVmax values for CD68low (n = 49) or CD68Hi (n = 49) NSCLC tumors. D, Subgroup analyses of FDG uptake in adenocarcinomas (n = 48; left) or squamous cell carcinomas (n = 50; right) of NSCLC. *, P < 0.05; ***, P < 0.001 in C and D as determined by the Student t test. Data are the mean ± SEM. E, TCGA analysis between CD68 and SLC2A1 (left) or HK2 (right) in 513 patients with adenocarcinoma NSCLC. P values are indicated in each plot.
TAMs make tumors more glycolytic. A, Left, PET/MRI images for FDG uptake in LLC tumors in mice before (D0, top) and after (D2, bottom) Veh or Clod treatment. Yellow circles, tumors. Right, T2-weighted MR images of LLC tumors treated with Veh or Clod pre (top)- or post (bottom)- contrast. Red arrowheads in Veh tumor, ferumoxytol-labeled TAM. B, FDG uptake SUVmax in A. **, P < 0.01, determined by two-way ANOVA. C, FACS plot indicating HoechstbrightKeratin+ (red boxes) population of cells sorted as aerobic cancer cells. D, Fold changes in gene expression in FACS-sorted aerobic cancer cells from LLC tumors treated with Clod or Veh. E, Glucose uptake (left) and lactate production (right) from the sorted aerobic cancer cells as in C. Data in D and E are the mean ± SEM from at least triplicate samples. *, P < 0.05; ***, P < 0.001 by the Student t test. F, Western blot of FACS-sorted aerobic cancer cells in C for GLUT1. β-Actin was used as the loading control. G, Oxygen consumption kinetics in FACS-sorted aerobic cancer cells as described in C. H, LLC tumor growth in mice treated with Veh, Clod, Veh + metformin (Veh + Met), or Clod + metformin (Clod + Met). *, P < 0.05; **, P < 0.01; ***, P < 0.001, determined by two-way ANOVA. I, LLC tumor growth in mice treated with Veh, Clod, Veh + 2-DG, or Clod + 2-DG. Data in H and I are the mean ± SEM, with number of animals indicated in the graphs.
Macrophages secrete TNFα to facilitate glycolysis in cancer cells. A, Gene expression changes in LLC cocultured with (LLC+BMDM) or without (LLC) BMDM. Data are the mean ± SEM from at least triplicate determinations. B, Glucose uptake (left) and lactate production (right) in LLC cocultured with or without BMDM. Data are the mean ± SEM for triplicate samples per group. **, P < 0.01 by Student t test. C, Glucose uptake in LLC cultured alone, cocultured with BMDM, or cocultured with BMDM with glucose added back to the LLC compartment of the coculture system. Data are the mean ± SEM for n = 4 replicates per group. *, P < 0.05; **, P < 0.01 by one-way ANOVA. D, Antibody cytokine arrays in the supernatant obtained from BMDM culture with (BMDM+LLC) or without (BMDM) LLC. Red boxes indicate those cytokines whose expressions were increased in BMDM cocultured with LLC compared with BMDM alone. Blue box, CXCL1, a cytokine produced by LLC cancer cells themselves (Supplementary Fig. S2D). E, Luminex cytokine assays for TNFα in the supernatant from culture media, LLC alone, BMDM alone, or BMDM cocultured with LLC. Data are the mean ± SEM for n = 3 replicates per group. ***, P < 0.001 by one-way ANOVA. F, Glucose uptake in LLC alone (none), LLC cocultured with BMDM (+BMDM), or LLC treated with TNFα (+TNFα) or with IFNγ (+IFNγ). Data are the mean ± SEM from n = 3 samples per group. **, P < 0.01; ***, P < 0.001 by one-way ANOVA. G, Western blot for LLC cells treated with increasing concentrations of recombinant TNFα protein for GLUT1, HK2, or PGC-1α. β-Actin was used as the loading control. H, TNFα concentrations in the supernatant from LLC cultured with (+BMDM) or without (alone) BMDM, or in BMDM cultured with (+LLC) or without (alone) LLC, measured by ELISA. BD, below the detection limit. **, P < 0.01 by Student t test. I, Immunostaining of TNFα (red) and CD68 (green) in LLC tumors grown in mice. Nuclei are shown in blue with DAPI counterstaining. The inset shows magnified regions where indicated with the asterisk (*). White arrowheads, CD68-positive TAM-expressing TNFα. Scale bar, 100 μm. J, TNFα concentrations measured by ELISA in the supernatant from CD11b and F4/80 double-positive TAM sorted by FACS. Data are the mean ± SEM from triplicate determinations. ***, P < 0.001, determined by one-way ANOVA. K, TCGA analysis of clinical correlations between CD68 and TNF (left) or between TNF and HK2 (right) in 513 patients with adenocarcinoma NSCLC. P values are indicated in each plot.
TAMs directly contribute to tumor hypoxia. A, Immunostaining of LLC tumors grown in mice for TAM by using S100A8 (red) and hypoxia by using pimonidazole (PIMO; green) antibodies. Nuclei are shown in blue with DAPI counterstaining. B, FACS analysis demonstrating that CD11b and F4/80 double-positive TAMs are pimonidazole-positive. C, Gene expression in CD11b and F4/80 double-positive TAM isolated from LLC tumors compared with those in cultured BMDM. Data are the mean ± SEM from triplicate determinations. D, Two-photon microscopy images of the dorsal window chamber whereby 5 × HRE-GFP–expressing LLC tumors had been implanted. Images were taken at 24 hours after a single intratumoral injection of PBS (+PBS) or PBS containing FACS-sorted TAM (+TAM). Scale bars in A and D, 100 μm. E, Representative FACS plots demonstrating HoechstbrightKeratin+ as aerobic tumor cells (red boxes) and HoechstdimKeratin+ as hypoxic tumor cells in LLC tumors grown in mice treated with Veh or Clod. F, Quantification of aerobic or hypoxic tumor cells in E. Data are the mean ± SEM for n = 6 mice per group. *, P < 0.05 by Student t test. G, TCGA analysis between CD68 and HIF1A in 513 patients with adenocarcinoma NSCLC. P value is indicated in the graph. H, Growth of LLC tumor treated with Veh or Clod immediately prior to a single dose of 20 Gy ionizing irradiation. *, P < 0.05 by two-way ANOVA.
Other posts on this site on Immunology and Cancer include
“A research team from Stanford University’s School of Medicine is now one step closer to uncovering a cancer treatment that could be applicable across the board in killing every kind of cancer tumor” (1). It appeared that their antibody-drug against the CD47 protein, enabled the shrinking of all tumor cells. After completing their animal studies the researchers now move into a human phase clinical trials. CD47 has been previously studied and evaluated for its role in multiple cells, some of this data however, is somewhat controversy. So where do we stand?
CD47
CD47 (originally named integrin-associated protein (IAP)) is a cell surface protein of the immunoglobulin (Ig) superfamily, which is heavily glycosylated and expressed by virtually all cells in the body and overexpressed in many types of cancer including breast, ovarian, colon, prostate and others (3). CD47 was first recognized as a 50 kDa protein associated and copurified with the Alpha-v-Beta-3 integrin in placenta and neutrophil granulocytes and later shown to have the capacity to regulate integrin function and the responsiveness of leukocytes to RGD-containing extracellular matrix proteins. CD47 has also been shown to be identical to the OA-3/OVTL3 antigen highly expressed on most ovarian carcinomas (4,5).
CD47 consists of an extracellular IgV domain, a five times transmembrane-spanning domain, and a short alternatively spliced cytoplasmic tail. In both humans and mice, the cytoplasmic tail can be found as four different splice isoforms ranging from 4 to 36 amino acids, showing different tissue expression patterns (3).
CD47 interactions (3, 6):
Thrombospondin-1 (TSP-1) – a secreted glycoprotein that plays a role in vascular development and angiogenesis. Binding of TSP-1 to CD47 influences several fundamental cellular functions including cell migration and adhesion, cell proliferation or apoptosis, and plays a role in the regulation of angiogenesis and inflammation.
Signal-regulatory protein-alpha (SIRPα) – an inhibitory transmembrane receptor present on myeloid cells. The CD47/SIRPα interaction leads to bidirectional signaling, resulting in different cell-to-cell responses including inhibition of phagocytosis, stimulation of cell-cell fusion, and T-cell activation.
Integrins – several membrane integrins, most commonly integrin avb3. These interactions result in CD47/integrin complexes that effect a range of cell functions including adhesion, spreading and migration
These interactions with multiple proteins and cells types create several important functions, which include:
Cell proliferation – cell proliferation is heavily dependent on cell type as both activation and loss of CD47 can result in enhanced proliferation. For example, activation of CD47 with TSP-1 in wild-type cells inhibits proliferation and reduces expression of stem cell transcription factors. In cancer cells however, activation of CD47 with TSP-1 increases proliferation of human U87 and U373 astrocytoma. it is likely that CD47 promotes proliferation via the PI3K/Akt pathway in cancerous cells but not normal cells (7). Loss of CD47 allows sustained proliferation of primary murine endothelial cells and enables these cells to spontaneously reprogram to form multipotent embryoid body-like clusters (8).
Apoptosis – Ligation of CD47 by anti-CD47mAbs was found to induce apoptosis in a number of different cell types (3). For example: Of the two SIRP-family members known to bind the CD47 IgV domain (SIRPα and SIRPγ), SIRPα as a soluble Fc-fusion protein does not induce CD47-dependent apoptosis, hile SIRPα or SIRPγ bound onto the surface of beads induces apoptosis through CD47 in Jurkat T cells and the myelomonocytic cell line U937.
Migration – CD47 role on cell migration was first demonstrated in neutrophils, these effects were shown to be dependent on avb3 integrins, which interact with and are activated by CD47 at the plasma membrane. In cancer, Blocking CD47 function has been shown to inhibit migration and metastasis in a variety of tumor models. Blockade of CD47 by neutralizing antibodies reduced migration and chemotaxis in response to collagen IV in melanoma, prostate cancer and ovarian cancer-derived cells (9).
Angiogenesis – The mechanism of the anti-angiogenic activity of CD47 is not fully understood, but introduction of CD47 antibodies and TSP-1 have been shown to inhibit nitric oxide (NO)-stimulated responses in both endothelial and vascular smooth muscle cells (10). More so, CD47 signaling influences the SDF-1 chemokine pathway, which plays a role in angiogenesis (11). (12)
Inflammatory response – Interactions between endothelial cell CD47 and leukocyte SIRPγ regulate T cell transendothelial migration (TEM) at sites of inflammation. CD47 also functions as a marker of self on murine red blood cells which allows RBC to avoid phagocytosis. Tumor cells can also evade macrophage phagocytosis through the expression of CD47 (2, 13).
It appears that CD47 ligation induce different responses, depending on cell type and partner for ligation.
Therapeutic and clinical aspect of CD47 in human cancer:
CD47 is overexpressed in many types of human cancers and its known function as a “don’t eat me” signal, suggests the potential for targeting the CD47-SIRPα pathway as a common therapy for human malignancies (2,13). Upregulation of CD47 expression in human cancers also appears to influence tumor growth and dissemination. First, increased expression of CD47 in several hematologic malignancies was found to be associated with a worse clinical prognosis, and in ALL to predict refractoriness to standard chemotherapies (13, 14-16). Second, CD47 was demonstrated to regulate tumor metastasis and dissemination in both MM and NHL (13, 17).
Efforts have been made to develop therapies inhibiting the CD47-SIRPα pathway, principally through blocking monoclonal antibodies directed against CD47, but also possibly with a recombinant SIRPα protein that can also bind and block CD47.
Chao MP et al. 2012 Combination strategies targeting CD47 in cancer
While monotherapies targeting CD47 were efficacious in several pre-clinical tumor models, combination strategies involving inhibition of the CD47-SIRPα pathway offer even greater therapeutic potential. Specifically, antibodies targeting CD47-SIRPα can be included in combination therapies with other therapeutic antibodies, macrophage-enhancing agents, chemo-radiation therapy, or as an adjuvant therapy to inhibit metastasis (13).
For example, anti-SIRPα antibody was found to potentiate antibody-dependent cellular cytotoxicity (ADCC) mediated by the anti-Her2/Neu antibody trastuzumab against breast cancer cells (18). CD47–SIRPα interactions and SIRPα signaling negatively regulate trastuzumab-mediated ADCC in vitro and antibody-dependent elimination of tumor cells in vivo
More so, chemo-radiation therapy-mediated upregulation of cell surface calreticulin may potentially augment the activity of anti-CD47 antibody. However, this approach may also lead to increased toxicity as cell surface calreticulin is expressed on non-cancerous cells undergoing apoptosis, a principle effect of chemo-radiation therapy (19).
Highlights:
Phagocytic cells, macrophages, regulate tumor growth through phagocytic clearance
CD47 binds SIRPα on phagocytes which delivers an inhibitory signal for phagocytosis
A blocking anti-CD47 antibody enabled phagocytic clearance of many human cancers
Phagocytosis depends on a balance of anti-(CD47) and pro-(calreticulin) signals
Anti-CD47 antibody synergized with an FcR-engaging antibody, such as rituximab
Summary
Evasion of immune recognition is a major mechanism by which cancers establish and propagate disease. Recent data has demonstrated that the innate immune system plays a key role in modulating tumor phagocytosis through the CD47-SIRPα pathway. Careful development of reagents that can block the CD47/SIRPα interaction may indeed be useful to treat many forms of cancer without having too much of a negative side effect in terms of inducing clearance of host cells. Therapeutic approaches inhibiting this pathway have demonstrated significant efficacy, leading to the reduction and elimination of multiple tumor types.
Dr. Weissman says: “We are now hopeful that the first human clinical trials of anti-CD47 antibody will take place at Stanford in mid-2014, if all goes well. Clinical trials may also be done in the United Kingdom”. These clinical trials must be designed so that the data they generate will produce a valid scientific result!!!
2. Willingham SB, Volkmer JP, Gentles AJ, Sahoo D, Dalerba P, Mitra SS, Wang J, Contreras-Trujillo H, Martin R, Cohen JD, Lovelace P, Scheeren FA, Chao MP, Weiskopf K, Tang C, Volkmer AK, Naik TJ, Storm TA, Mosley AR, Edris B, Schmid SM, Sun CK, Chua MS, Murillo O, Rajendran P, Cha AC, Chin RK, Kim D, Adorno M, Raveh T, Tseng D, Jaiswal S, Enger PØ, Steinberg GK, Li G, So SK, Majeti R, Harsh GR, van de Rijn M, Teng NN, Sunwoo JB, Alizadeh AA, Clarke MF, Weissman IL. The CD47-signal regulatory protein alpha (SIRPa) interaction is a therapeutic target for human solid tumors. Proc Natl Acad Sci U S A. 2012 Apr 24;109(17):6662-6667. http://www.pnas.org/content/early/2012/03/20/1121623109
3. Oldenborg PL. CD47: A Cell Surface Glycoprotein Which Regulates Multiple Functions of Hematopoietic Cells in Health and Disease. ISRN Hematology Volume 2013 (2013), Article ID 614619, 19 pages. http://www.hindawi.com/isrn/hematology/2013/614619/
4. G. Campbell, P. S. Freemont, W. Foulkes, and J. Trowsdale, “An ovarian tumor marker with homology to vaccinia virus contains an IgV- like region and multiple transmembrane domains,”Cancer Research, vol. 52, no. 19, pp. 5416–5420, 1992. http://cancerres.aacrjournals.org/content/52/19/5416.long
5. L. G. Poels, D. Peters, Y. van Megen et al., “Monoclonal antibody against human ovarian tumor-associated antigens,” Journal of the National Cancer Institute, vol. 76, no. 5, pp. 781–791, 1986. http://www.ncbi.nlm.nih.gov/pubmed/3517452
7. Sick E, Boukhari A, Deramaudt T, Rondé P, Bucher B, André P, Gies JP, Takeda K (February 2011). “Activation of CD47 receptors causes proliferation of human astrocytoma but not normal astrocytes via an Akt-dependent pathway”. Glia59 (2): 308–319. http://www.ncbi.nlm.nih.gov/pubmed/21125662
9. Shahan TA, Fawzi A, Bellon G, Monboisse JC, Kefalides NA. “Regulation of tumor cell chemotaxis by type IV collagen is mediated by a Ca(2+)-dependent mechanism requiring CD47 and the integrin alpha(V)beta(3)”. J. Biol. Chem 2000.275 (7): 4796–4802. http://www.jbc.org/content/275/7/4796
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Other related articles on this Open Access Online Scientific Journal include the following:
This is the first of a three part series on the evolution of vascular biology and the studies of the effects of biomaterials in vascular reconstruction and on drug delivery, which has embraced a collaboration of cardiologists at Harvard Medical School , Affiliated Hospitals, and MIT, requiring cardiovascular scientists at the PhD and MD level, physicists, and computational biologists working in concert, and an exploration of the depth of the contributions by a distinguished physician, scientist, and thinker.
The first part – Vascular Biology and Disease – will cover the advances in the research on
vascular biology,
signaling pathways,
drug diffusion across the endothelium and
the interactions with the underlying muscularis (media),
with additional considerations for type 2 diabetes mellitus.
The second part – Stents and Drug Delivery – will cover the
purposes,
properties and
evolution of stent technology with
the acquired knowledge of the pharmacodynamics of drug interactions and drug distribution.
The third part – Problems and Promise of Biomaterials Technology – will cover the shortcomings of the cardiovascular devices, and opportunities for improvement
Early work on endothelial injury and drug release principles
The insertion of a catheter for the administration of heparin is not an innocuous procedure. Heparin is infused to block coagulation, lowering the risk of a dangerous
clot formation and
dissemination.
It was shown experimentally that the continuous infusion of heparin
suppresses smooth muscle proliferation after endothelial injury. It may lead to
hemorrhage as a primary effect.
The anticoagulant property of heparin was removed by chemical modification without loss of the anti-proliferative effect.
In this study, MIT researches placed ethylene-vinyl acetate copolymer matrices containing standard and modified heparin adjacent to rat carotid arteries at the time of balloon deendothelialization.
Matrix delivery of both heparin compounds effectively diminished this proliferation in comparison to controls without producing systemic anticoagulation or side effects.
This mode of therapy appeared more effective than administering the agents by either
intravenous pumps or
heparin/polymer matrices placed in a subcutaneous site distant from the injured carotid artery
This indicated that the site of placement at the site of injury is a factor in the microenvironment, and is a preference for avoiding restenosis after angioplasty and other interventions.
This raised the question of why the proliferation of vascular muscle occurs in the first place. Edelman, Nugent and Karnovsky (1) showed that the proliferation required first the denudation of vascular surface endothelium. This exposed the underlayer to the effect of basic fibroblast growth factor, which stimulates mitogenesis of the exposed cell, explained by the endothelium as a barrier from circulating bFGF.
To answer this question, they compared the effect of
125I-labelled bFGF intravenously given with perivascular controlled bFGF release.
Polymeric controlled release devices delivered bFGF to the extravascular spacewithout transendothelial transport. Deposition within the blood vessel wall was rapidly distributed circumferentially and was substantially greater than that observed following intravenous injection.
The amount of bFGF deposited in arteries adjacent to the release devices was 40 times that deposited in similar arteries in animals who received a single intravenous bolus of bFGF.
The presence of intimal hyperplasia increased deposition of perivascularly released bFGF 2.4-fold but decreased the deposition of intravenously injected bFGF by 67%.
bFGF was 5- to 30-fold more abundant in solid organs after intravenous injection than it was following perivascular release, and
bFGF deposition was greatest in the kidney, liver, and spleen and was substantially lower in the heart and lung.
This result indicated that vascular deposition of bFGF is independent of endothelium, and
bFGF delivery is effectively perivascular. (2)
Drug activity studies have to be done in well controlled and representative conditions. Edelsman’s Lab researchers studied the
dose response of injured arteries to exogenous heparin in vivo by providing steady and predictable arterial levels of drug.
Controlled-release devices were fabricated to direct heparin uniformly and at a steady rate to the adventitial surface of balloon-injured rat carotid arteries.
Researchers predicted the distribution of heparin throughout the arterial wall using computational simulations and correlated these concentrations with the biologic response of the tissues.
Researchers determined from this process that an in vivo arterial concentration of 0.3 mg/ml of heparin is required to maximallyinhibit intimal hyperplasia after injury.
This estimation of the required tissue concentration of a drug is
independent of the route of administration and
applies to all forms of drug release.
In this way the Team was able to
evaluate the potential of widely disparate forms of drug release and, to finally
create some rigorous criteria by which to guide the development of particular delivery strategies for local diseases. (3)
(2) Perivascular and intravenous administration of basic fibroblast growth factor: Vascular and solid organ deposition. ER Edelman, MA Nugent, and MJ Karnovsky. PNAS Feb 1993; 90: 1513-1517.
(3) Tissue concentration of heparin, not administered dose, correlates with the biological response of injured arteries in vivo. MA Lovich and ER Edelman. PNAS Sep 1999; 96: 11111–11116.
Perlecan is a heparin-sulfate proteoglycan that might be critical for regulation of vascular repair by inhibiting the binding and mitogenic activity of basic fibroblast growth factor-2 (bFGF-2) in vascular smooth muscle cells .
The Team generated
Clones of endothelial cells expressing an antisense vector targeting domain III of perlecan. The transfected cells produced significantly less perlecan than parent cells, and they had reduced bFGF in vascular smooth muscle cells.
Endothelial cells were seeded onto three-dimensional polymeric matrices and implanted adjacent to porcine carotid arteries subjected to deep injury.
The parent endothelial cells prevented thrombosis, but perlecan deficient cells were ineffective.
The ability of endothelial cells to inhibit intimal hyperplasia, however, was only in part suppressed by perlecan. The differential regulation by perlecan of these aspects of vascular repair may clarify why control of clinical clot formation does not lead to full control of intimal hyperplasia.
The use of genetically modified tissue engineered cells provides a new approach for dissecting the role of specific factors within the blood vessel wall.(1) Successful implementation of local arterial drug delivery requires transmural distribution of drug. The physicochemical properties of the applied compound govern its transport and tissue binding.
Hydrophilic compounds are cleared rapidly.
Hydrophobic drugs bind to fixed tissue elements, potentially prolonging tissue residence and biological effect.
Local vascular drug delivery provides
elevated concentrations of drug in the target tissue while
minimizing systemic side effects.
To better characterize local pharmacokinetics the Team examined the arterial transport of locally applied dextran and dextran derivatives in vivo.
Using a two-compartment pharmacokinetic model to correct
The measured transmural flux of these compounds for systemic
Redistribution and elimination as delivered from a photo-polymerizable hydrogel.
The diffusivities and the transendothelial permeabilities were strongly dependent on molecular weight and charge
For neutral dextrans, the diffusive resistance increased with molecular weightapproximately 4.1-fold between the molecular weights of 10 and 282 kDa.
Endothelial resistance increased 28-fold over the same molecular weight range.
The effective medial diffusive resistance was unaffected by cationic charge as such molecules moved identically to neutral compounds, but increased approximately 40% when dextrans were negatively charged.
Transendothelial resistance was 20-fold lower for the cationic dextrans, and 11-fold higher for the anionic dextrans, when both were compared to neutral counterparts.
These results suggest that, while
low molecular weight drugs will rapidly traverse the arterial wall with the endothelium posing a minimal barrier,
the reverse is true for high molecular weight agents.
The deposition and distribution of locally released vascular therapeutic compounds might be predicted based upon chemical properties, such as molecular weight and charge. (2)
Paclitaxel is hydrophobic and has therapeutic potential against proliferative vascular disease. The favorable preclinical data with this compound may, in part, result from preferential tissue binding. The complexity of Paclitaxel pharmacokinetics required in-depth investigation if this drug is to reach its full clinical potential in proliferative vascular diseases.
Equilibrium distribution of Paclitaxel reveals partitioning above and beyond perfusate concentration and a spatial gradient of drug across the arterial wall.
The effective diffusivity (Deff) was estimated from the Paclitaxel distribution data to
facilitate comparison of transport of Paclitaxel through arterial parenchyma with that of other vasoactive agents and to
characterize the disparity between endovascular and perivascular application of drug.
This transport parameter described the motion of drug in tissues given an applied concentration gradient and includes, in addition to diffusion,
the impact of steric hindrance within the arterial interstitium;
nonspecific binding to arterial elements; and, in the preparation used here,
convective effects from the applied transmural pressure gradient.
At all times, the effective diffusivity for endovascular delivery exceeded that of perivascular delivery. The arterial transport of Paclitaxel was quantified through application ex vivo and measurement of the subsequent transmural distribution.
Arterial Paclitaxel deposition at equilibrium varied across the arterial wall.
Permeation into the wall increased with time, from 15 minutes to 4 hours, and
varied with the origin of delivery.
In contrast to hydrophilic compounds, the concentration in tissue exceeded the applied concentration and the rate of transport was markedly slower. Furthermore, endovascular and perivascular Paclitaxel application led to differences in deposition across the blood vessel wall.
This leads to a conclusion that Paclitaxel interacts with arterial tissue elements as it moves under the forces of
diffusion and
convection and
can establish substantial partitioning and spatial gradients across the tissue. (3)
Endovascular drug-eluting stents have changed the practice of cardiovascular vascularization, and yet it is unclear how they so dramatically reduce restenosis
We don’t know how to distinguish between the different formulations available. Researchers are now questioning whether individual properties of different drugs beyond lipid avidity effect arterial transport and distribution.
In bovine internal carotid segments, tissue-loading profiles for
Hydrophobic Paclitaxel and Rapamycin are indistinguishable, reaching load steady state after 2 days.
Hydrophilic dextran reaches equilibrium in hours.
Paclitaxel and Rapamycin bind to the artery at 30–40 times bulk concentration, and bind to specific tissue elements.
Transmural drug distribution profiles are markedly different for the two compounds.
Rapamycin binds specifically to FKBP12 binding protein and it distributes evenly through the artery,
Paclitaxel binds specifically to microtubules, and remains primarily in the subintimal space.
The binding of Rapamycin and Paclitaxel to specific intracellular proteins plays an essential role in
determining arterial transport and distribution and in
distinguishing one compound from another.
These results offer further insight into the
mechanism of local drug delivery and the
specific use of existing drug-eluting stent formulations. (4)
The Role of Amyloid beta (A) in Creation of Vascular Toxic Plaque
Amyloid beta (A) is a peptide family produced and deposited in neurons and endothelial cells (EC). It is found at subnanomolar concentrations in the plasma of healthy individuals. Simple conformational changes produce a form of A-beta , A-beta 42, which creates toxic plaque in the brains of Alzheimer’s patients.
Oxidative stress induced blood brain barrier degeneration has been proposed as a key factor for A-beta 42 toxicity.
This cannot account for lack of injury from the same peptide in healthy tissues. Researchers hypothesized that cell state mediates A-beta’s effect. They examined the viability in the presence of A-beta secreted from transfected Chinese hamster ovary cells (CHO) of
aortic Endothelial Cells (EC),
vascular smooth muscle cells (SMC) and
epithelial cells (EPI) in different states
A-beta was more toxic to all cell types when they were subconfluent. Subconfluent EC sprouted and SMC and EPI were inhibited by A-beta. Confluent EC were virtually resistant to A-beta and suppressed A-beta production by A-beta +CHO.
Products of subconfluent EC overcame this resistant state, stimulating the production and toxicity of A-beta 42. Confluent EC overgrew >35% beyond their quiescent state in the presence of A-beta conditioned in media from subconfluent EC.
These findings imply that A-beta 42 may well be even more cytotoxic to cells in injured or growth states and potentially explain the variable and potent effects of this protein.
One may now need to consider tissue and cell state in addition to local concentration of and exposure duration to A-beta.
The specific interactions of A-beta and EC in a state-dependent fashion may help understand further the common and divergent forms of vascular and cerebral toxicity of A-beta and the spectrum of AD. (5)
(1) Perlecan is required to inhibit thrombosis after deep vascular injury and contributes to endothelial cell-mediated inhibition of intimal hyperplasia. MA Nugent, HM Nugent, RV Iozzoi, K Sanchack, and ER Edelman. PNAS Jun 2000; 97(12): 6722-6727
(2) Correlation of transarterial transport of various dextrans with their physicochemical properties. O Elmalak, MA Lovich, E Edelman. Biomaterials 2000; 21: 2263-2272
(3) Arterial Paclitaxel Distribution and Deposition. CJ Creel, MA Lovich, ER Edelman. Circ Res. 2000;86:879-884
Autoimmunity may drive vascular disease through anti-endothelial cell (EC) antibodies. This raises a question about whether an increased morbidity of cardiovascular diseases in concert with systemic illnesses may involve these antibodies.
Matrix-embedded ECs act as powerful regulators of vascular repair accompanied by significant reduction in expected systemic and local inflammation.
The Lab researchers compared the immune response against free and matrix-embedded ECs in naive mice and mice with heightened EC immune reactivity. Mice were presensitized to EC with repeated subcutaneous injections of saline-suspended porcine EC (PAE) (5*10^5 cells).
On day 42, both naive mice (controls) and mice with heightened EC immune reactivity received 5*10^5 matrix-embedded or free PAEs. Circulating PAE-specific antibodies and effector T-cells were analyzed 90 days after implantation for –
PAE-specific antibody-titers,
frequency of CD4+-effector cells, and
xenoreactive splenocytes
These were 2- to 4-fold lower (P<0.0001) when naıve mice were injected with matrix-embedded instead of saline-suspended PAEs.
Though basal levels of circulating antibodies were significantly elevated after serial PAE injections (2210+341 mean fluorescence intensity, day 42) and almost doubled again 90 days after injection of a fourth set of free PAEs, antibody levels declined by half in recipients of matrix-embedded PAEs at day 42 (P<0.0001), as did levels of CD4+-effector cells and xenoreactive splenocytes.
A significant immune response to implantation of free PAE is elicited in naıve mice, that is even more pronounced in mice with pre-developed anti-endothelial immunity.
Matrix-embedding protects xenogeneic ECs against immune reaction in naive mice and in mice with heightened immune reactivity.
Matrix-embedded EC might offer a promising approach for treatment of advanced cardiovascular disease. (1)
Researchers examined the molecular mechanisms through which
mechanical force and hypertension modulate
endothelial cell regulation of vascular homeostasis.
Exposure to mechanical strain increased the paracrine inhibition of vascular smooth muscle cells (VSMCs) by endothelial cells.
Mechanical strain stimulated the production by endothelial cells of perlecan and heparan-sulfate glycosaminoglycans. By inhibiting the expression of perlecan with an antisense vector researchers demonstrated that perlecan was essential to the strain-mediated effects on endothelial cell growth control.
Mechanical regulation of perlecan expression in endothelial cells was
governed by a mechano-transduction pathway
requiring transforming growth factor (TGF-β) signaling and
intracellular signaling through the ERK pathway.
Immunohistochemical staining of the aortae of spontaneously hypertensive rats demonstrated strong correlations between
endothelial TGF-β,
phosphorylated signaling intermediates, and
arterial thickening.
Studies on ex vivo arteries exposed to varying levels of pressure demonstrated that
ERK and TGF-beta signaling were required for pressure-induced upregulation of endothelial HSPG.
The Team’s findings suggest a novel feedback control mechanism in which
net arterial remodeling to hemodynamic forces is controlled by a dynamic interplay between growth stimulatory signals from vSMCs and
growth inhibitory signals from endothelial cells. (2)
Heparan-sulfate proteoglycans (HSPGs) are potent regulators of vascular remodeling and repair. The major enzyme capable of degrading HSPGs is heparanase, which led us to examine the role of heparanase in controlling
arterial structure,
mechanics, and
remodeling.
In vitro studies suggested heparanase expression in endothelial cells serves as a negative regulator of endothelial inhibition of vascular smooth muscle cell (vSMC) proliferation.
ECs inhibit vSMC proliferation through the interplay between
growth stimulatory signals from vSMCs and
growth inhibitory signals from ECs.
This would be expected if ECs had HSPGs that are degraded by heparanase. Arterial structure and remodeling to injury is modified by heparanase expression. Transgenic mice overexpressing heparanase had
increased arterial thickness,
cellular density, and
mechanical compliance.
Endovascular stenting studies in Zucker rats demonstrated increased heparanase expression in the neointima of obese, hyperlipidemic rats in comparison to lean rats.
The extent of heparanase expression within the neointima strongly correlated with the neointimal thickness following injury. To test the effects of heparanase overexpression on arterial repair, researchers developed a novel murine model of stent injury using small diameter self-expanding stents.
Using this model, researchers found that increased
neointimal formation and
macrophage recruitment occurs in transgenic mice overexpressing heparanase.
Taken together, these results support a role for heparanase in the regulation of arterial structure, mechanics, and repair. (3)
The first host–donor reaction in transplantation occurs at the blood–tissue interface. When the primary component of the implant (donor) is the endothelial cells, it incites an immunologic reaction. Injections of free endothelial cell implants elicit a profound major histocompatibility complex (MHC) II dominated immune response.
Endothelial cells embedded within three-dimensional matrices behave like quiescent endothelial cells.
Perivascular implants of such embedded ECs cells are the most potent inhibitor of intimal hyperplasia and thrombosis following controlled vascular injury, but without any immune reactivity.
Allo- and even exenogenic endothelial cells evoke no significant humoral or cellular immune response in immune-competent hosts when embedded within matrices. Moreover, endothelial implants are immune-modulatory, reducing the extent of the memory response to previous free cell implants.
Attenuated immunogenicity results in muted activation of adaptive and innate immune cells. These findings point toward a pivotal role of matrix–cell-interconnectivity for
the cellular immune phenotype and might therefore assist in the design of
extracellular matrix components for successful tissue engineering. (4)
Because changes in subendothelial matrix composition are associated with alterations of the endothelial immune phenotype, researchers sought to understand if
cytokine-induced NF-κB activity and
downstream effects depend on substrate adherence of endothelial cells (EC).
The team compared the upstream
phosphorylation cascade,
activation of NF-ĸβ, and
expression/secretion
of downstream effects of EC grown on tissue culture polystyrene plates (TCPS) with EC embedded within collagen-based matrices (MEEC).
Adhesion of natural killer (NK) cells was quantified in vitro and in vivo.
NF-κβ subunit p65 nuclear levels were significantly lower and
p50 significantly higher in cytokine-stimulated MEEC than in EC-TCPS.
Despite similar surface expression of TNF-α receptors, MEEC had significantly decreased secretion and expression of IL-6, IL-8, MCP-1, VCAM-1, and ICAM-1.
Attenuated fractalkine expression and secretion in MEEC (two to threefold lower than in EC-TCPS; p < 0.0002) correlated with 3.7-fold lower NK cell adhesion to EC (6,335 ± 420 vs. 1,735 ± 135 cpm; p < 0.0002).
Furthermore, NK cell infiltration into sites of EC implantation in vivo was significantly reduced when EC were embedded within matrix.
Matrix embedding enables control of EC substratum interaction.
This in turn regulates chemokine and surface molecule expression and secretion, in particular – of those compounds within NF-κβ pathways,
chemoattraction of NK cells,
local inflammation, and
tissue repair. (5)
Monocyte recruitment and interaction with the endothelium is imperative to vascular recovery.
Tie2 plays a key role in endothelial health and vascular remodeling. Researchers studied monocyte-mediated Tie2/angiopoietin signaling following interaction of primary monocytes with endothelial cells and its role in endothelial cell survival.
The direct interaction of primary monocytes with subconfluent endothelial cells
resulted in transient secretion of angiopoietin-1 from monocytes and
the activation of endothelial Tie2. This effect was abolished by preactivation of monocytes with tumor necrosis factor-α (TNFα).
Although primary monocytes contained high levels of
Seeding of monocytes on serum-starved endothelial cells reduced caspase-3 activity by 46+5.1%, and 52+5.8% after TNFα treatment, and it decreased single-stranded DNA levels by 41+4.2% and 40+ 3.5%, respectively.
This protective effect of monocytes on endothelial cells was reversed by Tie2 silencing with specific short interfering RNA.
The antiapoptotic effect of monocytes was further supported by the
activation of cell survival signaling pathways involving phosphatidylinositol 3-kinase,
STAT3, and
AKT.
Monocytes and endothelial cells form a unique Tie2/angiopoietin-1 signaling system that affects endothelial cell survival and may play critical a role in vascular remodeling and homeostasis. (6)
(5) NF-kB Activity in Endothelial Cells Is Modulated by Cell Substratum Inter-actions and Influences Chemokine-Mediated Adhesion of Natural Killer Cells. S Hess, H Methe, Jong-Oh Kim, ER Edelman. Cell Transplantation 2009; 18: 261–273
Rabbits fed on a hypercholesterolemic diet underwent bilateral iliac artery balloon denudation and stent deployment.
Liposomal alendronate (3 or 6 mg/kg) was given concurrently with stenting.
Monocyte counts were reduced by 90% 24 to 48 hours aftera single injection of liposomal alendronate, returning to basal levels at 6 days.
This treatment significantly reduced
intimal area at 28 days, from 3.88+0.93 to 2.08+0.58 and 2.16 +0.62 mm2.
Lumen area was increased from 2.87+0.44 to 3.57+0.65 and 3.45+0.58 mm2, and
arterial stenosis was reduced from 58 11% to 37 8% and 38 7% in controls, in rabbits treated with 3 mg/kg, and with 6 mg/kg, respectively (mean+SD, n=8 rabbits/group, P< 0.01 for all 3 parameters).
No drug-related adverse effects were observed. Reduction in neointimal formation was associated with
reduced arterial macrophage infiltration and proliferation at 6 days and with an
equal reduction in intimal macrophage and smooth muscle cell content at 28 days after injury.
Conversely, drug regimens ineffective in reducing monocyte levels did not inhibit neointimal formation. Researchers have shown that a
single liposomal bisphosphonates injection concurrent with injury reduces in-stent neointimal formation and
arterial stenosis in hypercholesterolemic rabbits, accompanied by systemic transient depletion of monocytes and macrophages. (1)
Diabetes and insulin resistance are associated with increased disease risk and poor outcomes from cardiovascular interventions.
Even drug-eluting stents exhibit reduced efficacy in patients with diabetes. Researchers reported the first study of vascular response to stent injury in insulin-resistant and diabetic animal models.
Endovascular stents were expanded in the aortae of
obese insulin-resistant and
type 2 diabetic Zucker rats,
in streptozotocin-induced type 1 diabetic Sprague-Dawley rats, and
in matched controls.
Insulin-resistant rats developed thicker neointima (0.46+0.08 versus 0.37+0.06 mm2, P 0.05), with decreased lumen area (2.95+0.26 versus 3.29+0.15 mm2, P 0.03) 14 days after stenting compared with controls, but without increased vascular inflammation (tissue macrophages).
Insulin-resistant and diabetic rat vessels did exhibit markedly altered signaling pathway activation 1 and 2 weeks after stenting, with up to a 98% increase in p-ERK (anti-phospho ERK) and a 54% reduction in p-Akt (anti-phospho Akt) stained cells. Western blotting confirmed a profound effect of insulin resistance and diabetes on Akt and ERK signaling in stented segments. p-ERK/p-Akt ratio in stented segments uniquely correlated with neointimal response (R2 = 0.888, P< 0.04) , but not in lean controls.
Transfemoral aortic stenting in rats provides insight into vascular responses in insulin resistance and diabetes.
Shifts in ERK and Akt signaling related to insulin resistance may reflect altered tissue repair in diabetes accompanied by a
shift in metabolic : proliferative balance.
These findings may help explain the increased vascular morbidity in diabetes and suggest specific therapies for patients with insulin resistance and diabetes. (2)
Researchers investigated the role of Valsartan (V) alone or in combination with Simvastatin (S) on coronary atherosclerosis and vascular remodeling, and tested the hypothesis that V or V/S attenuate the pro-inflammatory effect of low endothelial shear stress (ESS).
Twenty-four diabetic, hyperlipidemic swine were allocated into Early (n = 12) and Late (n=12) groups. Diabetic swine in each group were treated with Placebo (n=4), V (n = 4) and V/S (n = 4) and followed for 8 weeks in the Early group and 30 weeks in the Late group.
Blood pressure, serum cholesterol and glucose were similar across the treatment subgroups. ESS was calculated in plaque-free subsegments of interest (n = 109) in the Late group at week 23. Coronary arteries of this group were harvested at week 30, and the subsegments of interest were identified, and analyzed histopathologically.
Intravascular geometrically correct 3-dimensional reconstruction of the coronary arteries of 12 swine was performed 23 weeks after initiation of diabetes mellitus and a hyperlipidemic diet. Local endothelial shear stress was calculated
in plaque-free subsegments of interest (n=142) with computational fluid dynamics, and
the coronary arteries (n=31) were harvested and the same subsegments were identified at 30 weeks.
V alone or with S
reduced the severity of inflammation in high-risk plaques. Both regimens attenuated the severity of enzymatic degradation of the arterial wall, reducing the severity of expansive remodeling.
attenuated the pro-inflammatory effect of low ESS. V alone or with S
exerts a beneficial effect of reducing and stabilizing high-risk plaque characteristics independent of a blood pressure- and lipid-lowering effect. (3)
This study tested the hypothesis that low endothelial shear stress augments the
expression of matrix-degrading proteases, promoting the
formation of thin-capped atheromata.
Researchers assessed the messenger RNA and protein expression, and elastolytic activity of selected elastases and their endogenous inhibitors.
Subsegments with low endothelial shear stress at week 23 showed
reduced endothelial coverage,
enhanced lipid accumulation, and
intense infiltration of activated inflammatory cells at week 30.
These lesions showed increased expression of messenger RNAs encoding
matrix metalloproteinase-2, -9, and -12, and cathepsins K and S
relative to their endogenous inhibitors and
increased elastolytic activity.
Expression of these enzymes correlated positively with the severity of internal elastic lamina fragmentation.
Thin-capped atheromata in regions with
lower preceding endothelial shear stress had
reduced endothelial coverage,
intense lipid and inflammatory cell accumulation,
enhanced messenger RNA expression and
elastolytic activity of MMPs and cathepsins with
severe internal elastic lamina fragmentation.
Low endothelial shear stress induces endothelial discontinuity and
accumulation of activated inflammatory cells, thereby
augmenting the expression and activity of elastases in the intima and
shifting the balance with their inhibitors toward matrix breakdown.
Team’s results provide new insight into the mechanisms of regional formation of plaques with thin fibrous caps. (4)
Elevated CRP levels predict increased incidence of cardiovascular events and poor outcomes following interventions. There is the suggestion that CRP is also a mediator of vascular injury.
Transgenic mice carrying the human CRP gene (CRPtg) are predisposed to arterial thrombosis post-injury.
Researchers examined whether CRP similarly modulates the proliferative and hyperplastic phases of vascular repair in CRPtg when thrombosis is controlled with daily aspirin and heparin at the time of trans-femoral arterial wire-injury.
Complete thrombotic arterial occlusion at 28 days was comparable for wild-type and CRPtg mice (14 and 19%, respectively). Neointimal area at 28d was 2.5 fold lower in CRPtg (4190±3134 m2, n = 12) compared to wild-types (10,157±8890 m2, n = 11, p < 0.05).
Likewise, neointimal/media area ratio was 1.10±0.87 in wild-types and 0.45±0.24 in CRPtg (p < 0.05).
Seven days post-injury, cellular proliferation and apoptotic cell number in the intima were both less pronounced in CRPtg than wild-type.
No differences were seen in leukocyte infiltration or endothelial coverage. CRPtg mice had significantly reduced p38 MAPK signaling pathway activation following injury.
The pro-thrombotic phenotype of CRPtg mice was suppressed by aspirin/heparin, revealing CRP’s influence on neointimal growth after trans-femoral arterial wire-injury.
Signaling pathway activation,
cellular proliferation, and
neointimal formation
were all reduced in CRPtg following vascular injury. Increasingly the Team was aware of CRP multipotent effects. Once considered only a risk factor, and recently a harmful agent, CRP is a far more complex regulator of vascular biology. (5)
(1) Liposomal Alendronate Inhibits Systemic Innate Immunity and Reduces In-Stent Neointimal Hyperplasia in Rabbits. HD Danenberg, G Golomb, A Groothuis, J Gao…, ER Edelman. Circulation. 2003;108:2798-2804
(2) Vascular Neointimal Formation and Signaling Pathway Activation in Response to Stent Injury in Insulin-Resistant and Diabetic Animals. M Jonas, ER Edelman, A Groothuis, AB Baker, P Seifert, C Rogers. Circ. Res. 2005;97;725-733. http://dx.doi.org/10.1161/01.RES.0000183730.52908.C6 http://circres.ahajournals.org/cgi/content/full/97/7/725
(3) Attenuation of inflammation and expansive remodeling by Valsartan alone or in combination with Simvastatin in high-risk coronary atherosclerotic plaques. YS Chatzizisis, M Jonas, R Beigel, AU Coskun… ER Edelman, CL Feldman, PH Stone. Atherosclerosis 203 (2009) 387–394
(5) Neointimal formation is reduced after arterial injury in human crp transgenic mice HD Danenberg, E Grad, RV Swaminathan, Z Chenc,…ER Edelman Atherosclerosis 201 (2008) 85–91
A Rattle Bag of Science and the Art of Translation
Elazer R. Edelman is the Thomas D. and Virginia W. Cabot Professor of Health Sciences and Technology at MIT, Professor of Medicine at Harvard Medical School, a coronary care unit cardiologist at the Brigham and Women’s Hospital, and Director of the Harvard-MIT Biomedical Engineering Center. E-mail: ere@mit.edu
Garret A. FitzGerald is the McNeil Professor in Translational Medicine and Therapeutics, Chair of the Department of Pharmacology, and Director of the Institute for Translational Medicine & Therapeutics, University of Pennsylvania. E-mail: garret@upenn.edu
In 2011, the American Association for the Advancement of Science (AAAS) founded Science Translational Medicine (STM) to disseminate interdisciplinary science integrating basic and clinical research that defines and fosters new therapeutics, devices, and diagnostics.
Conceived and nourished under the creative vision of Elias Zerhouni and Katrina Kelner, the journal has attracted widespread attention. Now, as we assume the mantle of co-chief scientific advisors, we look back on the journal’s early accomplishments, restate our mission, and make clear the kinds of manuscripts we seek and accept for publication.
STM’s mission, as articulated by Elias and Katrina, was to
“promote human health by providing a forum for communication and cross-fertilization among basic, translational, and clinical research practitioners and trainees from all relevant established and emerging disciplines.”
This statement remains relevant and accurate today. With this mission on our masthead, STM now receives ~25 manuscripts (full-length research articles) per week and publishes ~10% of them. Roughly half of the submissions are deemed inappropriate for the journal and are returned without review within 8 to 10 days of receipt.
Of those papers that undergo full peer review,
decisions to reject are made within 48 days and
the mean time to acceptance (including the revision period) is 125 days.
There is now an average wait of only 24 days between acceptance and publication.
Defining TRANSLATIONAL Medicine
In accord with the journal’s broad readership, the ideal manuscript meets five criteria: It (i) reports a discovery of translational relevance with high-impact potential; (ii) has a conceptual focus with interdisciplinary appeal; (iii) elucidates a biological mechanism; (iv) is innovative and novel; and (v) is presented in clear, broadly accessible language. STM seeks to publish research that describes
how innovative concepts drive the creative biomedical science
that ultimately improves the quality of people’s lives—
This is the broadest of our journal’s criteria but is the one that sets us apart as well. Translational relevance does not require demonstration of benefit in humans but does require the evident potential to advance clinical medicine, thus impacting the direction of our culture and the welfare of our communities. Conceptual focus and mechanistic emphasis discriminate our papers from those that contain observational descriptions of technical findings for which value is restricted to a specific discipline.
However, innovation and novelty may apply to a fundamental scientific discovery or to the nature of its application and relevance to the translational process. Criteria enable the journal to consider versatile technological advances that apply new and creative thinking but may not necessarily offer fresh insights into biological mechanisms. Finally, while the subsequent additional efforts of the STM editorial staff are not to be discounted, the clarity of writing and coherence of argument presented within a submitted manuscript are likely to facilitate its progress through the challenge of peer review.
On Causes – Hippocrates, Aristotle, Robert Koch, and the Dread Pirate Roberts
The idea of risk factors for vascular disease has evolved
from a dichotomous to continuous hazard analysis and
from the consideration of a few factors to
mechanistic investigation of many interrelated risks.
However, confusion still abounds regarding issues of association and causation. Originally, the simple presence of
tobacco abuse, hypertension, and/or hypercholesterolemia were tallied, and
the cumulative score was predictive of subsequent coronary artery disease.
Since then, dose responses have been defined for these and other factors and it has been suggested that almost 300 factors place patients at risk; these factors include elevations in plasma homocysteine. Recent studies shed interesting light on the mechanism of this potentially causal relationship, which was first noted in 1969.
Aside from putative effects on vessel wall dynamics, there is now direct evidence that homocysteine is atherogenic. Twenty-fold increases in plasma homocysteine achieved by dietary manipulation of apoE–/– mice increased aortic root lesion size 2-fold and produced a prolonged chronic inflammatory mural response accompanied by elevations in vascular cell adhesion molecule-1 (VCAM) and tumor necrosis factor-a (TNF-a).
In long term followup, homocysteine levels elevated by
dietary supplementation with methionine or homocysteine
promoted lesion size and plaque fibrosis in these
atherosclerosis-prone mice early in life, but without influencing ultimate plaque burden as the animals aged.
A number of mechanisms were proposed by which homocysteine achieved this effect, including
promotion of inflammation,
regulation of lipoprotein metabolism, and
modification of critical biochemical pathways and
metabolites including nitric oxide (NO).
See p 2569 In the present issue of Circulation,
Stühlinger et al 7 advance these mechanistic insights one critical step further by defining homocysteine’s effects at an enzymatic level.
The group led by Lentz published an association between levels of the
endogenous inhibitor of Nirtic Oxide synthase,
asymmetric dimethyl arginine (ADMA), and
homocysteine in cultured endothelial cells and in the serum of cynomolgus monkeys.
Such an association is interesting because the L-arginine–NO synthase pathway seems to be a critical component in the full range of endothelial cell biology and vascular dysfunction.
Stühlinger et al 7 now show that increased cultured endothelial cell elaboration of ADMA by homocysteine and its precursor L-methionine is associated with a dose-dependent impairment of the activity of endothelial dimethylarginine dimethylaminohydrolase (DDAH), the enzyme that degrades ADMA. Homocysteine directly inhibited DDAH activity in a cell-free system by targeting a critical sulfhydryl group on this enzyme.
Thus, one could envision that the balance of cardiovascular health and disease could well be determined by the ability of an intact Nirtic Oxide synthase system to overcome environmental, dietary, and even genetic factors.
In patients with altered enzymatic defense systems,
elevated homocysteine,
oxidized lipoproteins,
inflammation, and other
vasotoxins
may dominate even the most potent defense mechanisms. These studies raise a number of issues. Do we need to add to our list of established cardiovascular risk factors to accommodate new findings and associations? Is there a final common pathway for all risk factors or perhaps even a unified factor theory into which all potential risks can be grouped? And, as always, should we consider Nirtic Oxide at the core of this universality? Finally, should we change our focus altogether and speak not of risk factors but of
genetic predisposition,
extent of biochemical aberration, and
degree of physical damage?
Some would view these remarkable success stories and the repeated association of hyperhomocyst(e)inemia with coronary, cerebral, and peripheral vascular disease and simply advocate for increased folic acid intake for all.
Indeed, this intervention of negligible cost and
insignificant side effect is already partially in place;
many foods are fortified with folate to prevent congenital neural tube defects.
This reader considers the seminal work by Vernon Young and Yves Ingenbleek on the relationship between
S8 and regions distant from lava flows in Asia and Indian subcontinents,
where they have determined hyperhomocysteinemia and the consequence associated with:
veganism (not voluntary)
impaired methyl donor reactions and transsulfuration pathways (not corrected by B12, folate)
loss of lean body mass due to the constant relationship of S:N (insufficient from plant sources)
What happens, when we fail to continue to pursue causality,
the linkage of biological significance or scientific plausibility with
epidemiologically or statistically significant association?
In medicine, risk becomes the likelihood that people without a disease will acquire the disease through contact with factors thought to increase disease risk.
All of these risk factors are then, by nature, imprecise and nonspecific. They are stochastic measures of what will happen to normal people who fall into particular measures of these parameters.
The daring may be willing to accept these risks, citing friend and foe who live well beyond or for far lesser times than anticipated by risk alone. Such concerns may well become moot if we can simultaneously identify patients at risk
by linking phenotype with genotype,
gene expression with protein elaboration, and
environmental exposures with the biochemical consequences and
direct anatomic aberrations they induce.
This kind of characterization may well replace a family history of arterial disease as a rough estimate of
genotype,
serum cholesterol as an indirect measure of the health of lipoprotein metabolism,
serum glucose as a crude determinant of the ravages of diabetes mellitus,
blood pressure measurement as a marker of long-standing endogenous exposure to altered flow, and
tobacco abuse as a maker of long-standing exposure to exogenous toxins.
Rather than identifying patients on the basis of their serum cholesterol, we will have a direct measure of their
LDL receptor number,
internalization rate,
macrophage content in the blood vessel wall,
metalloproteinase activity, etc.
insulin receptor metabolism,
oxidative state, and
glycated burden.
Serum glucose will similarly give way to these tests
Evaluating a new way to open clogged arteries: Computational model offers insight into mechanisms of drug-coated balloons.
A new study from MIT analyzes the potential usefulness of a new treatment that combines the benefits of angioplasty balloons and drug-releasing stents, but may pose fewer risks. With this new approach, a balloon is inflated in the artery for only a brief period, during which it releases a drug that prevents cells from accumulating and clogging the arteries over time.
While approved for limited use in Europe, these drug-coated balloons are still in development in the United States and have not received FDA approval. The MIT study, which models the behavior of the balloons, should help scientists optimize their performance and aid regulators in evaluating their effectiveness and safety.
“Until now, people who evaluate such technology could not distinguish hype from promise,” says Elazer Edelman, the Thomas D. and Virginia W. Cabot Professor of Health Sciences and Technology and senior author of the paper describing the study, which appeared online recently in the journal Circulation.
Lead author of the paper is Vijaya Kolachalama, a former MIT postdoc who is now a principal member of the technical staff at the Charles Stark Draper Laboratory.
Edelman’s lab is investigating a possible alternative to the current treatments: drug-coated balloons. “We’re trying to understand how and when this therapy could work and identify the conditions in which it may not,” Kolachalama says. “It has its merits; it has some disadvantages.”
Modeling drug release
The drug-coated balloons are delivered by a catheter and inflated at the narrowed artery for about 30 seconds, sometimes longer. During that time, the balloon coating, containing a drug such as Zotarolimus, is released from the balloon. The properties of the coating allow the drug to be absorbed in the body’s tissues. Once the drug is released, the balloon is removed.
In their new study, Kolachalama, Edelman and colleagues set out to rigorously characterize the properties of the drug-coated balloons. After performing experiments in tissue grown in the lab and in pigs, they developed a computer model that explains the dynamics of drug release and distribution. They found that factors such as the size of the balloon, the duration of delivery time, and the composition of the drug coating all influence how long the drug stays at the injury site and how effectively it clears the arteries.
One significant finding is that when the drug is released, some of it sticks to the lining of the blood vessels. Over time, that drug is slowly released back into the tissue, which explains why the drug’s effects last much longer than the initial 30-second release period.
“This is the first time we can explain the reasons why drug-coated balloons can work,” Kolachalama says. “The study also offers areas where people can consider thinking about optimizing drug transfer and delivery.”
MIT’s Edelman’s Lab conducted the pioneering work in Vascular biology, animal models of drug eluting stents and was at the forefront of Empirical Molecular Cardiology in its studies in vascular physiology, biology and biomaterials for medical devices.
Hypertriglyceridemia concurrent Hyperlipidemia: Vertical Density Gradient Ultracentrifugation a Better Test to Prevent Undertreatment of High-Risk Cardiac Patients
Fight against Atherosclerotic Cardiovascular Disease: A Biologics not a Small Molecule – Recombinant Human lecithin-cholesterol acyltransferase (rhLCAT) attracted AstraZeneca to acquire AlphaCore
High-Density Lipoprotein (HDL): An Independent Predictor of Endothelial Function & Atherosclerosis, A Modulator, An Agonist, A Biomarker for Cardiovascular Risk
Peroxisome proliferator-activated receptor (PPAR-gamma) Receptors Activation: PPARγ transrepression for Angiogenesis in Cardiovascular Disease and PPARγ transactivation for Treatment of Diabetes
Clinical Trials Results for Endothelin System: Pathophysiological role in Chronic Heart Failure, Acute Coronary Syndromes and MI – Marker of Disease Severity or Genetic Determination?
Inhibition of ET-1, ETA and ETA-ETB, Induction of NO production, stimulation of eNOS and Treatment Regime with PPAR-gamma agonists (TZD): cEPCs Endogenous Augmentation for Cardiovascular Risk Reduction – A Bibliography
Positioning a Therapeutic Concept for Endogenous Augmentation of cEPCs — Therapeutic Indications for Macrovascular Disease: Coronary, Cerebrovascular and Peripheral
Cardiovascular Outcomes: Function of circulating Endothelial Progenitor Cells (cEPCs): Exploring Pharmaco-therapy targeted at Endogenous Augmentation of cEPCs
Vascular Medicine and Biology: CLASSIFICATION OF FAST ACTING THERAPY FOR PATIENTS AT HIGH RISK FOR MACROVASCULAR EVENTS Macrovascular Disease – Therapeutic Potential of cEPCs
Cardiac Surgery Theatre in China vs. in the US: Cardiac Repair Procedures, Medical Devices in Use, Technology in Hospitals, Surgeons’ Training and Cardiac Disease Severity”
Dilated Cardiomyopathy: Decisions on implantable cardioverter-defibrillators (ICDs) using left ventricular ejection fraction (LVEF) and Midwall Fibrosis: Decisions on Replacement using late gadolinium enhancement cardiovascular MR (LGE-CMR)
Competition in the Ecosystem of Medical Devices in Cardiac and Vascular Repair: Heart Valves, Stents, Catheterization Tools and Kits for Open Heart and Minimally Invasive Surgery (MIS)
Global Supplier Strategy for Market Penetration & Partnership Options (Niche Suppliers vs. National Leaders) in the Massachusetts Cardiology & Vascular Surgery Tools and Devices Market for Cardiac Operating Rooms and Angioplasty Suites
Visceral Myopathy in Statins (Photo credit: Snipergirl)
Medical science has advanced significantly since 1507, when Leonardo da Vinci drew this diagram of the internal organs and vascular systems of a woman. (Photo credit: Wikipedia)
English: Lee Hood, MD, PhD, President and Co-found of the Institute for Systems Biology (Photo credit: Wikipedia)
AIDS was first reported in 1981 followed by the identification of HIV as the cause of the disease in 1983 and is now a global pandemic that has become the leading infectious killer of adults worldwide. By 2006, more than 65 million people had been infected with the HIV virus worldwide and 25 million had died of AIDS (Merson MH. The HIV-AIDS pandemic at 25 – the global response. (1, 2). This has caused tremendous social and economic damage worldwide, with developing countries, particularly Sub-Saharan Africa, heavily affected.
A cure for HIV/AIDS has been elusive in almost 30 years of research. Early treatments focused on antiretroviral drugs that were effective only to a certain degree. The first drug, zidovudine, was approved by the US FDA in 1987, leading to the approval of a total of 25 drugs to date, many of which are also available in fixed-dose combinations and generic formulations for use in resource-limited settings (to date, only zidovudine and didanosine are available as true generics in the USA).
However, it was the advent of a class of drugs known as protease inhibitors and the introduction of triple-drug therapy in the mid-1990s that revolutionized HIV/AIDS treatment (3,4). This launched the era of highly active antiretroviral therapy (HAART), where a combination of three or more different classes of drugs are administered simultaneously.
Challenges of HIV/AIDS treatment
HIV resides in latent cellular and anatomical reservoirs where current drugs are unable to completely eradicate the virus.
Macrophages are major cellular reservoirs, which also contribute to the generation of elusive mutant viral genotypes by serving as the host for viral genetic recombination.
Anatomical latent reservoirs include secondary lymphoid tissue, testes, liver, kidney, lungs, the gut and the brain.
The major challenge facing current drug regimens is that they do not fully eramacrdicate the virus from these reservoirs; requiring patients take medications for life. Under current treatment, pills are taken daily, resulting in problems of patient adherence. The drugs also have side effects and in some people the virus develops resistance against certain drugs.
Current treatment in HIV/AIDS
The use of the HAART regimen, particularly in the developed world, has resulted in tremendous success in improving the expectancy and quality of lives for patients. However, some HAART regimens have serious side effects and, in all cases, HAART has to be taken for a lifetime, with daily dosing of one or more pills. Due to the need to take the medication daily for a lifetime, patients fail to adhere to the treatment schedule, leading to ineffective drug levels in the body and rebound of viral replication.Some patients also develop resistance to certain combinations of drugs, resulting in failure of the treatment. The absence of complete cure under current treatment underscores the great need for continued efforts in seeking innovative approaches for treatment of HIV/AIDS.
Drug resistance is mainly caused by the high genetic diversity of HIV-1 and the continuous mutation it undergoes. This problem is being addressed with individualized therapy, whereby resistance testing is performed to select a combination of drugs that is most effective for each patient (5). In addition, side effects due to toxicities of the drugs are also a concern. There are reports that patients taking HAART experience increased rates of heart disease, diabetes, liver disease, cancer and accelerated aging. Most experts agree that these effects could be due to the HIV infection itself or co-infection with another virus, such as co-infection with hepatitis C virus resulting in liver disease. However, the toxicities resulting from the drugs used in HAART could also contribute to these effects.
Under current treatment, complete eradication of the virus from the body has not been possible. The major cause for this is that the virus resides in ‘latent reservoirs’ within memory CD4+ T cells and cells of the macrophage–monocyte lineage. A major study recently found that, in addition to acting as latent reservoirs, macrophages significantly contribute to the generation of elusive mutant viral genotypes by serving as the host for viral genetic recombination (6). The cells that harbor latent HIV are typically concentrated in specific anatomic sites, such as secondary lymphoid tissue, testes, liver, kidney, lungs, gut and the CNS. The eradication of the virus from such reservoirs is critical to the effective long-term treatment of HIV/AIDS patients.
Therefore, there is a great need to explore new approaches for developing nontoxic, lower-dosage treatment modalities that provide more sustained dosing coverage and effectively eradicate the virus from the reservoirs, avoiding the need for lifetime treatments.
Nanotechnology for HIV/AIDS treatment
The use of nanotechnology platforms for delivery of drugs is revolutionizing medicine in many areas of disease treatment.
Nanotechnology-based platforms for systemic delivery of antiretroviral drugs could have similar advantages.
Controlled-release delivery systems can enhance their half-lives, keeping them in circulation at therapeutic concentrations for longer periods of time. This could have major implications in improving adherence to the drugs.
Nanoscale delivery systems also enhance and modulate the distribution of hydrophobic and hydrophilic drugs into and within different tissues due to their small size. This particular feature of nanoscale delivery systems appears to hold the most promise for their use in clinical treatment and prevention of HIV. Specifically, targeted delivery of antiretroviral drugs to CD4+ T cells and macrophages as well as delivery to the brain and other organ systems could ensure that drugs reach latent reservoirs
Moreover, by controlling the release profiles of the delivery systems, drugs could be released over a longer time and at higher effective doses to the specific targets. Figure 1. Various nanoscale drug delivery systems.
Optional treatments:
Antiretroviral drugs
Gene Therapy
Immune Therapy
Prevention
The use of nanotechnology systems for delivery of antiretroviral drugs has been extensively reviewed by Nowacek et al. and Amiji et al. (7,8).
In a recent study based on polymeric systems, nanosuspensions (200 nm) of the drug rilpivirine (TMC278) stabilized by polyethylene. A series of experiments by Dou et al. showed that nanosuspension of the drug indinavir can be stabilized by a surfactant system comprised of Lipoid E80 for effective delivery to various tissues. The indinavir nanosuspensions were loaded into macrophages and their uptake was investigated. Macrophages loaded with indinavir nanosuspensions were then injected intravenously into mice, resulting in a high distribution in the lungs, liver and spleen. More significantly, the intravenous administration of a single dose of the nanoparticle-loaded macrophages in a rodent mouse model of HIV brain infection resulted in significant antiviral activity in the brain and produced measureable drug levels in the blood up to 14 days post-treatment.polypropylene glycol (poloxamer 338) and PEGylated tocopheryl succinate ester (TPGS 1000) were studied in dogs and mice. A single-dose administration of the drug in nanosuspensions resulted in sustained release over 3 months in dogs and 3 weeks in mice, compared with a half-life of 38 h for free drug. These results serve as a proof-of-concept that nanoscale drug delivery may potentially lower dosing frequency and improve adherence.
Active targeting strategies have also been employed for antiretroviral drug delivery. Macrophages, which are the major HIV reservoir cells, have various receptors on their surface such as formyl peptide, mannose, galactose and Fc receptors, which could be utilized for receptor-mediated internalization. The drug stavudine was encapsulated using various liposomes (120–200 nm) conjugated with mannose and galactose, resulting in increased cellular uptake compared with free drug or plain liposomes, and generating significant level of the drug in liver, spleen and lungs. Stavudine is a water-soluble drug with a very short serum half-life (1 h). Hence, the increased cellular uptake and sustained release in the tissues afforded by targeted liposomes is a major improvement compared with free drug. The drug zidovudine, with half-life of 1 h and low solubility, was also encapsulated in a mannose-targeted liposome made from stearylamine, showing increased localization in lymph node and spleen. An important factor to consider here is that although most of the nucleoside drugs such as stavudine and zidovudine have short serum half-lives, the clinically relevant half-life is that of the intracellular triphosphate form of the drug. For example, despite zidovudine’s 1 h half-life in plasma, it is dosed twice daily based on intracellular pharmacokinetic and clinical efficacy data. Therefore, future nanotechnology-based delivery systems will have to focus in showing significant increase of the half-lives of the encapsulated drugs to achieve a less frequent dosing such as once weekly, once-monthly or even less.
Gene Therapy for HIV/AIDS
In addition to improving existing antiretroviral therapy, there are ongoing efforts to discover alternative approaches for treatment of HIV/AIDS. One promising alternative approach is gene therapy, in which a gene is inserted into a cell to interfere with viral infection or replication. Other nucleic acid-based compounds, such as DNA, siRNA, RNA decoys, ribozymes and aptamers or protein-based agents such as fusion inhibitors and zinc-finger nucleases can also be used to interfere with viral replication.
RNAi is also considered to have therapeutic potential for HIV/AIDS. Gene silencing is induced by double stranded siRNA, which targets for destruction
he mRNA of the gene of interest. For HIV/AIDS, RNAi can either target the various stages of the viral replication cycle or various cellular targets involved in viral infection such as CD4, CCR5, and/or CXCR4, the major cell surface co-receptors responsible for viral entry. HIV replicates by reverse transcription to form DNA and uses the DNA to produce copies of its mRNA for protein synthesis; siRNA therapy could be used to knock down this viral mRNA. As with other gene therapy techniques, delivery of siRNA to specific cells and tissues has been the major challenge in realizing the potential of RNAi.
New nanotechnology platforms are tackling this problem by providing nonviral alternatives for effective and safe delivery. The first nontargeted delivery of siRNA in humans via self-assembling, cyclodextrin polymer-based nanoparticles for cancer treatment have recently entered Phase I clinical trials.
Although at an early stage, nonviral delivery of siRNA for treatment of HIV infection is also gaining ground. A fusion protein, with a peptide transduction domain and a double stranded RNA-binding domain, was used to encapsulate and deliver siRNA to T cells in vivo. CD4- and CD8-specific siRNA delivery caused RNAi responses with no adverse effects such as cyto-toxicity or immune stimulation. Similarly, a protamine-antibody fusion protein-based siRNA delivery demonstrated that siRNA knockdown of the gag gene can inhibit HIV replication in primary T cells.
Single-walled nanotubes were shown to deliver CXCR4 and CD4 specific siRNA to human T cells and peripheral blood mononuclear cells. Up to 90% knockdown of CXCR4 receptors and up to 60% knockdown of CD4 expression on T cells was observed while the knockdown of CXCR4 receptors on peripheral blood mononuclear cells was as high as 60%. In a separate study, amino-terminated carbosilane dendrimers (with interior carbon-silicon bonds) were used for delivery of siRNA to HIV-infected lymphocytes.
These pioneering studies demonstrate that nonviral siRNA delivery is possible for HIV/AIDS treatment. However, more work needs to be done in optimizing the delivery systems and utilizing designs for efficient targeting and intracellular delivery. The recent developments in polymer- and liposome-based siRNA delivery systems could be optimized for targeting cells that are infected with HIV, such as T cells and macrophages. Moreover, since HIV mutates and has multiple strains with different genetic sequences, combination siRNA therapy targeting multiple genes should be pursued. For these applications, nanotechnology platforms with capability for co-delivery and targeting need to be developed specifically for HIV-susceptible cells. A macrophage and T-cell-targeted and nanotechnology-based combination gene therapy may be a promising platform for efficient HIV/AIDS treatment.
Immunotherapy for HIV/AIDS
The various treatment approaches described above focus on treating HIV/AIDS by directly targeting HIV at the level of the host cell or the virus itself. An alternative approach is immunotherapy aimed at modulating the immune response against HIV. CD8+ cytotoxic T-cell responses to acute HIV infection appear to be relatively normal, while neutralizing antibody production by B cells is delayed or even absent.
Immunotherapy is a treatment approach involving the use of immunomodulatory agents to modulate the immune response against a disease. Similar to vaccines, it is based on immunization of individuals with various immunologic formulations; however, the purpose is to treat HIV-infected patients as opposed to protect healthy individuals (preventive vaccines will be discussed in an upcoming section). The various immunotherapy approaches for HIV/AIDS could be based on delivering cytokines (such as IL-2, IL-7 and IL-15) or antigens. The development of cellular immunity, and to a large degree humoral immunity, requires antigen-presenting cells (APCs) to process and present antigens to CD4+and CD8+ T cells. Dendritic cells (DCs) are the quintessential professional APCs responsible for initiating and orchestrating the development of cellular and humoral (antibody) immunity.
Various polymeric systems have been explored for in vivo targeting of DCs and delivery of small molecules, proteins or DNAs showing potential for immunotherapy. Poly(ethylene glycol) (PEG) stabilized poly(propylene sulfide) polymer nanoparticles accumulated in DCs in lymph nodes. Following nanoparticle injection, DCs containing nanoparticles accumulated in lymph nodes, peaking at 4 days with 40–50% of DCs and other APCs having internalized nanoparticles.
In another study, nanoparticles of the copolymer poly(D,L-lacticide-co-glycolide) (PLGA) showed efficient delivery of antigens to murine bone marrow-derived DCs in vitro, suggesting their potential use in immunotherapy. More recently, a very interesting work showed that HIV p24 protein adsorbed on the surface of surfactant-free anionic poly(D,L-lactide) (PLA) nanoparticles were efficiently taken-up by mouse DCs, inducing DC maturation. he p24-nanoparticles induced enhanced cellular and mucosal immune responses in mice. Although this targeting is seen in ex vivo-generated DCs and not in vivo DCs, the efficient delivery of the antigen to DCs through the nanoparticles is an important demonstration that may eventually be applied to in vivo DC targeting.
Clinical Trial
he most clinically advanced application of nanotechnology for immunotherapy of HIV/AIDS is the DermaVir patch that has reached Phase II clinical trials (9). DermaVir is a targeted nanoparticle system based on polyethyleimine mannose (PEIm), glucose and HIV antigen coding DNA plasmid formulated into nanoparticles (~100 nm) and administered under a patch after a skin preparation. The nanoparticles are delivered to epidermal Langerhans cells that trap the nanoparticles and mature to become highly immunogenic on their way to the lymph nodes. Mature DCs containing the nanoparticles present antigens to T cells inducing cellular immunity. Preclinical studies and Phase I clinical trials showed safety and tolerability of the DermaVir patch, which led the progression to Phase II trials. This is the first nanotechnology-based immunotherapy for HIV/AIDS that has reached the clinic and encourages further work in this area.
Table 1
Summary of nanotechnology-based treatment approaches for HIV/AIDS.
Note: to open the references in the table 1, please go to ref 1 in this post to see full ref info.
Nanotechnology for HIV/AIDS prevention
The search for a safe and effective HIV/AIDS vaccine has been challenging in the almost three decades since the discovery of the disease. Recently, high-profile clinical trial failures have prompted great debate over the vaccine research, with some suggesting the need for a major focus on fundamental research, with fewer efforts on clinical trials.
The major challenges in the development of a preventive HIV/AIDS vaccine have been the extensive viral strain and sequence diversity, viral evasion of humoral and cellular immune responses, coupled with the lack of methods to elicit broadly reactive neutralizing antibodies and cytotoxic T cells. The challenge associated with delivery of any exogenous antigen (such as nanoparticles) to APCs, is that exogenous antigens require specialized ‘cross-presentation’ in order to be presented by MHC class I and activate CD8+cytotoxic T cells.
his requirement for cytosolic delivery of antigens and cross-presentation represents yet another hurdle for HIV intracellular antigen vaccine, but potentially an advantage of nanodelivery. Humoral responses (neutralizing antibodies produced by B cells) are generated to intact antigen presented on the surface for the virus, or nanoparticles, but these humoral responses typically require ‘help’ from CD4+ T cells, but rather both. Nanoparticles have potential as adjuvants and delivery systems for vaccines. Table 2 present the different approaches.
Table 2
Summary of nanotechnology developments for prevention of HIV/AIDS.
Note: to open the references in the table 2, please go to ref 1 in this post to see full ref info.
Summary
Nanotechnology can impact the treatment and prevention of HIV/AIDS with various innovative approaches. Treatment options may be improved using nanotechnology platforms for delivery of antiretroviral drugs. Controlled and sustained release of the drugs could improve patient adherence to drug regimens, increasing treatment effectiveness.
While there is exciting potential for nanomedicine in the treatment of HIV/AIDS, challenges remain to be overcome before the potential is realized. These include toxicity of nanomaterials, stability of nanoparticles in physiological conditions and their scalability for large-scale production. These are challenges general to all areas of nanomedicine and various works are underway to tackle them.
Another important consideration in investigating nanotechnology-based systems for HIV/AIDS is the economic aspect, as the hardest hit and most vulnerable populations reside in underdeveloped and economically poor countries. In the case of antiretroviral therapy, nanotherapeutics may increase the overall cost of treatment, reducing the overall value. However, if the nanotherapeutics could improve patient adherence by reducing dosing frequency as expected, and furthermore, if they can eradicate viral reservoirs leading to a sterile immunity, these advantages may effectively offset the added cost.
Ref:
1. Mamo T, Moseman EA., Kolishetti N., Salvadoe-Morales C., Shi J., Kuritzkes DR., Langer R., von-Adrian U and Farokhzad OF. Emerging nanotechnology approaches for HIV/AIDS treatment and prevention. Nanomedicine (Lond) 2010; 5(2): 269-295.
2. Merson MH. The HIV-AIDS pandemic at 25 – the global response. N Engl J Med.2006;354(23):2414–2417
3. Walensky RP, Paltiel AD, Losina E, et al. The survival benefits of AIDS treatment in the United States. J Infect Dis. 2006;194(1):11–19
4. Richman DD, Margolis DM, Delaney M, Greene WC, Hazuda D, Pomerantz RJ. The challenge of finding a cure for HIV infection. Science. 2009;323(5919):1304–1307)
5.Sax PE, Cohen CJ, Kuritzkes DR. HIV Essentials. Physicians’ Press; Royal Oak, MI, USA: 2007.
6. Lamers SL, Salemi M, Galligan DC, et al. Extensive HIV-1 intra-host recombination is common in tissues with abnormal histopathology. PLoS One. 2009;4(3):E5065.
7. Vyas TK, Shah L, Amiji MM. Nanoparticulate drug carriers for delivery of HIV/AIDS therapy to viral reservoir sites. Expert Opin Drug Deliv. 2006;3(5):613–628.
8. Amiji MM, Vyas TK, Shah LK. Role of nanotechnology in HIV/AIDS treatment: Potential to overcome the viral reservoir challenge. Discov Med. 2006;6(34):157–162
9. Lori F, Calarota SA, Lisziewicz J. Nanochemistry-based immunotherapy for HIV-1. Curr Med Chem. 2007;14(18):1911–1919
This post is in continuation to Part 1 by the same title.
In part one I covered the basics of role of redox chemistry in immune reactions, the phagosome cauldron, and how bacteria bacteria, virus and parasites trigger the complex pathway of NO production and its downstream effects. While we move further in this post, the previous post can be accessed here.
Regulation of the redox immunomodulators—NO/RNS and ROS
In addition to eradicating pathogens, NO/RNS and ROS and their chemical interactions act as effective immunomodulators that regulate many cellular metabolic pathways and tissue repair and proinflammatory pathways. Figure 3 shows these pathways.
Figure 3. Schematic overview of interactive connections between NO and ROS-mediated metabolic pathways. Credit: (Wink et al., 2011)
Regulation of iNOS enzyme activity is critical to NO production. Factors such as the availability of arginine, BH4, NADPH, and superoxide affect iNOS activity and thus NO production. In the absence of arginine and BH4 iNOS becomes a O2_/H2O2 generator (Vásquez-Vivar et al., 1999). Hence metabolic pathways that control arginine and BH4 play a role in determining the NO/superoxide balance. Arginine levels in cells depend on various factors such as type of uptake mechanisms that determine its spatial presence in various compartments and enzymatic systems. As shown in Fig3 Arginine is the sole substrate for iNOS and arginase. Arginase is another key enzyme in immunemodulation. AG is also regulated by NOS and NOX activities. NOHA, a product of NOS, inhibits AG, and O2–increases AG activity. Importantly, high AG activity is associated with elevated ROS and low NO fluxes. NO antagonises NOX2 assembly that in turn leads to reduction in O2_ production. NO also inhibits COX2 activity thus reducing ROS production. Thus, as NO levels decline, oxidative mechanisms increase. Oxidative and nitrosative stress can also decrease intracellular GSH (reduced form) levels, resulting in a reduced antioxidant capability of the cell.
Immune-associated redox pathways regulate other important metabolic cell functions that have the potential for widespread impact on cells, organs, and organisms. These pathways, such as mediated via methionine and polyamines, are critical for DNA stabilization, cell proliferation, and membrane channel activity, all of which are also involved in immune-mediated repair processes.
NO levels dictate the immune signaling pathway
NO/RNS and ROS actively control innate and adaptive immune signaling by participating in induction, maintenance, and/or termination of proinflammatory and anti-inflammatory signaling. As in pathogen eradication, the temporal and spatial concentration profiles of NO are key factors in determining immune-mediated processes.
Brune and coworkers (Messmer et al., 1994) first demonstrated that p53 expression was associated with the concentrations of NO that led to apoptosis in macrophages. Subsequent studies linked NO concentration profiles with expression of other key signaling proteins such as HIF-1α and Akt-P (Ridnour et al., 2008; Thomas et al., 2008). Various levels of NO concentrations trigger different pathways and expectedly this concentration-dependent profile varies with distance from the NO source.NO is highly diffucible and this characteristic can result in 1000 fold reduction in concentration within one cell length distance travelled from the source of production. Time course studies have also shown alteration in effects of same levels of NO over time e.g. NO-mediated ERK-P levels initially increased rapidly on exposure to NO donors and then decreased with continued NO exposure (Thomas et al., 2004), however HIF-1α levels remained high as long as NO levels were elevated. Thus some of the important factors that play critical role in NO effects are: distance from source, NO concentrations, duration of exposure, bioavailability of NO, and production/absence of other redox molecules.
Figure and legend credits: (Wink et al., 2011)
Fig 4: The effect of steady-state flux of NO on signal transduction mechanisms.
This diagram represents the level of sustained NO that is required to activate specific pathways in tumor cells. Similar effects have been seen on endothelial cells. These data were generated by treating tumor or endothelial cells with the NO donor DETANO (NOC-18) for 24 h and then measuring the appropriate outcome measures (for example, p53 activation). Various concentrations of DETANO that correspond to cellular levels of NO are: 40–60 μM DETANO = 50 nM NO; 80–120 μM DETANO = 100 nM NO; 500 μM DETANO = 400 nM NO; and 1 mM DETANO = 1 μM NO. The diagram represents the effect of diffusion of NO with distance from the point source (an activated murine macrophage producing iNOS) in vitro (Petri dish) generating 1 μM NO or more. Thus, reactants or cells located at a specific distance from the point source (i.e., iNOS, represented by star) would be exposed to a level of NO that governs a specific subset of physiological or pathophysiological reactions. The x-axis represents the different zone of NO-mediated events that is experienced at a specific distance from a source iNOS producing >1 μM. Note: Akt activation is regulated by NO at two different sites and by two different concentration levels of NO.
Species-specific NO production
The relationship of NO and immunoregulation has been established on the basis of studies on tumor cell lines or rodent macrophages, which are readily available sources of NO. However in humans the levels of protein expression for NOS enzymes and the immune induction required for such levels of expression are quite different than in rodents (Weinberg, 1998). This difference is most likely due to the human iNOS promotor rather than the activity of iNOS itself. There is a significant mismatch between the promoters of humans and rodents and that is likely to account for the notable differences in the regulation of gene induction between them. The combined data on rodent versus human NO and O2– production strongly suggest that in general, ROS production is a predominant feature of activated human macrophages, neutrophils, and monocytes, and the equivalent murine immune cells generate a combination of O2– and NO and in some cases, favor NO production. These differences may be crucial to understanding how immune responses are regulated in a species-specific manner. This is particularly useful, as pathogen challenges change constantly.
The next post in this series will cover the following topics:
The impact of NO signaling on an innate immune response—classical activation
NO and proinflammatory genes
NO and regulation of anti-inflammatory pathways
NO impact on adaptive immunity—immunosuppression and tissue-restoration response
Coronary Artery Disease – Medical Devices Solutions: From First-In-Man Stent Implantation, via Medical Ethical Dilemmas to Drug Eluting Stents August 13, 2012
Cardiovascular Disease (CVD) and the Role of agent alternatives in endothelial Nitric Oxide Synthase (eNOS) Activation and Nitric Oxide Production July 19, 2012
Curator and Research Study Originator: Aviva Lev-Ari, PhD, RN
Macrovascular Disease – Therapeutic Potential of cEPCs: Reduction Methods for CV Risk
July 2, 2012
An Investigation of the Potential of circulating Endothelial Progenitor Cells (cEPCs) as a Therapeutic Target for Pharmacological Therapy Design for Cardiovascular Risk Reduction: A New Multimarker Biomarker Discovery
Inhibition of ET-1, ETA and ETA-ETB, Induction of NO production, stimulation of eNOS and Treatment Regime with PPAR-gamma agonists (TZD): cEPCs Endogenous Augmentation for Cardiovascular Risk Reduction – A Bibliography
Nitric oxide (NO), reactive nitrogen species (RNS) and reactive oxygen species (ROS) perform dual roles as immunotoxins and immunomodulators. An incoming immune signal initiates NO and ROS production both for tackling the pathogens and modulating the downstream immune response via complex signaling pathways. The complexity of these interactions is a reflection of involvement of redox chemistry in biological setting (fig. 1)
Fig 1. Image credit: (Wink et al., 2011)
Previous studies have highlighted the role of NO in immunity. It was shown that macrophages released a substance that had antitumor and antipathogen activity and required arginine for its production (Hibbs et al., 1987, 1988). Hibbs and coworkers further strengthened the connection between immunity and NO by demonstrating that IL2 mediated immune activation increased NO levels in patients and promoted tumor eradication in mice (Hibbs et al., 1992; Yim et al., 1995).
In 1980s a number of authors showed the direct evidence that macrophages made nitrite, nitrates and nitrosamines. It was also shown that NO generated by macrophages could kill leukemia cells (Stuehr and Nathan, 1989). Collectively these studies along with others demonstrated the important role NO plays in immunity and lay the path for further research in understanding the role of redox molecules in immunity.
NO is produced by different forms of nitric oxide synthase (NOS) enzymes such as eNOS (endothelial), iNOS (inducible) and nNOS (neuronal). The constitutive forms of eNOS generally produce NO in short bursts and in calcium dependent manner. The inducible form produces NO for longer durations and is calcium independent. In immunity, iNOS plays a vital role. NO production by iNOS can occur over a wide range of concentrations from as little as nM to as much as µM. This wide range of NO concentrations provide iNOS with a unique flexibility to be functionally effective in various conditions and micro-environements and thus provide different temporal and concentration profiles of NO, that can be highly efficient in dealing with immune challenges.
Redox reactions in immune responses
NO/RNS and ROS are two categories of molecules that bring about immune regulation and ‘killing’ of pathogens. These molecules can perform independently or in combination with each other. NO reacts directly with transition metals in heme or cobalamine, with non-heme iron, or with reactive radicals (Wink and Mitchell, 1998). The last reactivity also imparts it a powerful antioxidant capability. NO can thus act directly as a powerful antioxidant and prevent injury initiated by ROS (Wink et al., 1999). On the other hand, NO does not react directly with thiols or other nucleophiles but requires activation with superoxide to generate RNS. The RNS species then cause nitrosative and oxidative stress (Wink and Mitchell, 1998).
The variety of functions achieved by NO can be understood if one looks at certain chemical concepts. NO and NO2 are lipophilic and thus can migrate through cells, thus widening potential target profiles. ONOO-, a RNS, reacts rapidly with CO2 that shortens its half life to <10 ms. The anionic form and short half life limits its mobility across membranes. When NO levels are higher than superoxide levels, the CO2-OONO–intermediate is converted to NO2 and N2O3 and changes the redox profile from an oxidative to a nitrosative microenvironment. The interaction of NO and ROS determines the bioavailability of NO and proximity of RNS generation to superoxide source, thus defining a reaction profile. The ROS also consumes NO to generate NO2 and N2O3 as well as nitrite in certain locations. The combination of these reactions in different micro-environments provides a vast repertoire of reaction profiles for NO/RNS and ROS entities.
The Phagosome ‘cauldron’
The phagosome provides an ‘isolated’ environment for the cell to carry out foreign body ‘destruction’. ROS, NO and RNS interact to bring about redox reactions. The concentration of NO in a phagosome can depend on the kind of NOS in the vicinity and its activity and other localised cellular factors. NO and is metabolites such as nitrites and nitrates along with ROS combine forces to kill pathogens in the acidic environment of the phagosome as depicted in the figure 2 below.
Fig 2. The NO chemistry of the phagosome. (image credit: (Wink et al., 2011)
This diagram depicts the different nitrogen oxide and ROS chemistry that can occur within the phagosome to fight pathogens. The presence of NOX2 in the phagosomes serves two purposes: one is to focus the nitrite accumulation through scavenging mechanisms, and the second provides peroxide as a source of ROS or FA generation. The nitrite (NO2−) formed in the acidic environment provides nitrosative stress with NO/NO2/N2O3. The combined acidic nature and the ability to form multiple RNS and ROS within the acidic environment of the phagosome provide the immune response with multiple chemical options with which it can combat bacteria.
Bacteria
There are various ways in which NO combines forces with other molecules to bring about bacterial killing. Here are few examples
E.coli: It appears to be resistant to individual action of NO/RNS and H2O2 /ROS. However, when combined together, H2O2 plus NO mediate a dramatic, three-log increase in cytotoxicity, as opposed to 50% killing by NO alone or H2O2 alone. This indicates that these bacteria are highly susceptible to their synergistic action.
Staphylococcus: The combined presence of NO and peroxide in staphylococcal infections imparts protective effect. However, when these bacteria are first exposed to peroxide and then to NO there is increased toxicity. Hence a sequential exposure to superoxide/ROS and then NO is a potent tool in eradicating staphylococcal bacteria.
Mycobacterium tuberculosis: These bacterium are sensitive to NO and RNS, but in this case, NO2 is the toxic species. A phagosome microenvironment consisting of ROS combined with acidic nitrite generates NO2/N2O3/NO, which is essential for pathogen eradication by the alveolar macrophage. Overall, NO has a dual function; it participates directly in killing an organism, and/or it disarms a pathway used by that organism to elude other immune responses.
Parasites
Many human parasites have demonstrated the initiation of the immune response via the induction of iNOS, that then leads to expulsion of the parasite. The parasites include Plasmodia(malaria), Leishmania(leishmaniasis), and Toxoplasma(toxoplasmosis). Severe cases of malaria have been related with increased production of NO. High levels of NO production are however protective in these cases as NO was shown to kill the parasites (Rockett et al., 1991; Gyan et al., 1994). Leishmania is an intracellualr parasite that resides in the mamalian macrophages. NO upregulation via iNOS induction is the primary pathway involved in containing its infestation. A critical aspect of NO metabolism is that NOHA inhibits AG activity, thereby limiting the growth of parasites and bacteria including Leishmania, Trypanosoma, Schistosoma, Helicobacter, Mycobacterium, and Salmonella, and is distinct from the effects of RNS. Toxoplasma gondii is also an intracellular parasite that elicits NO mediated response. INOS knockout mice have shown more severe inflammatory lesions in the CNS that their wild type counterparts, in response to toxoplasma exposure. This indicates the CNS preventative role of iNOS in toxoplasmosis (Silva et al., 2009).
Virus
Viral replication can be checked by increased production of NO by induction of iNOS (HIV-1, coxsackievirus, influenza A and B, rhino virus, CMV, vaccinia virus, ectromelia virus, human herpesvirus-1, and human parainfluenza virus type 3) (Xu et al., 2006). NO can reduce viral load, reduce latency and reduce viral replication. One of the main mechanisms as to how NO participates in viral eradication involves the nitrosation of critical cysteines within key proteins required for viral infection, transcription, and maturation stages. For example, viral proteases or even the host caspases that contain cysteines in their active site are involved in the maturation of the virus. The nitrosative stress environment produced by iNOS may serve to protect against some viruses by inhibiting viral infectivity, replication, and maturation.
Coronary Artery Disease – Medical Devices Solutions: From First-In-Man Stent Implantation, via Medical Ethical Dilemmas to Drug Eluting Stents August 13, 2012
Cardiovascular Disease (CVD) and the Role of agent alternatives in endothelial Nitric Oxide Synthase (eNOS) Activation and Nitric Oxide Production July 19, 2012
Curator and Research Study Originator: Aviva Lev-Ari, PhD, RN
Macrovascular Disease – Therapeutic Potential of cEPCs: Reduction Methods for CV Risk
July 2, 2012
An Investigation of the Potential of circulating Endothelial Progenitor Cells (cEPCs) as a Therapeutic Target for Pharmacological Therapy Design for Cardiovascular Risk Reduction: A New Multimarker Biomarker Discovery
Inhibition of ET-1, ETA and ETA-ETB, Induction of NO production, stimulation of eNOS and Treatment Regime with PPAR-gamma agonists (TZD): cEPCs Endogenous Augmentation for Cardiovascular Risk Reduction – A Bibliography
Nitric oxide (NO) is a lipophilic, highly diffusible and short-lived molecule that acts as a physiological messenger and has been known to regulate a variety of important physiological responses including vasodilation, respiration, cell migration, immune response and apoptosis. Jordi Muntané et al
NO is synthesized by the Nitric Oxide synthase (NOS) enzyme and the enzyme is encoded in three different forms in mammals: neuronal NOS (nNOS or NOS-1), inducible NOS (iNOS or NOS-2), and endothelial NOS (eNOS or NOS-3). The three isoforms, although similar in structure and catalytic function, differ in the way their activity and synthesis in controlled inside a cell. NOS-2, for example is induced in response to inflammatory stimuli, while NOS-1 and NOS-3 are constitutively expressed.
Regulation by Nitric oxide
NO is a versatile signaling molecule and the net effect of NO on gene regulation is variable and ranges from activation to inhibition of transcription.
The intracellular localization is relevant for the activity of NOS. Infact, NOSs are subject to specific targeting to subcellular compartments (plasma membrane, Golgi, cytosol, nucleus and mitochondria) and that this trafficking is crucial for NO production and specific post-translational modifications of target proteins.
Role of Nitric oxide in Cancer
One in four cases of cancer worldwide are a result of chronic inflammation. An inflammatory response causes high levels of activated macrophages. Macrophage activation, in turn, leads to the induction of iNOS gene that results in the generation of large amount of NO. The expression of iNOS induced by inflammatory stimuli coupled with the constitutive expression of nNOS and eNOS may contribute to increased cancer risk. NO can have varied roles in the tumor environment influencing DNA repair, cell cycle, and apoptosis. It can result in antagonistic actions including DNA damage and protection from cytotoxicity, inhibiting and stimulation cell proliferation, and being both anti-apoptotic and pro-apoptotic. Genotoxicity due to high levels of NO could be through direct modification of DNA (nitrosative deamination of nucleic acid bases, transition and/or transversion of nucleic acids, alkylation and DNA strand breakage) and inhibition of DNA repair enzymes (such as alkyltransferase and DNA ligase) through direct or indirect mechanisms. The Multiple actions of NO are probably the result of its chemical (post-translational modifications) and biological heterogeneity (cellular production, consumption and responses). Post-translational modifications of proteins by nitration, nitrosation, phosphorylation, acetylation or polyADP-ribosylation could lead to an increase in the cancer risk. This process can drive carcinogenesis by altering targets and pathways that are crucial for cancer progression much faster than would otherwise occur in healthy tissue.
NO can have several effects even within the tumor microenvironment where it could originate from several cell types including cancer cells, host cells, tumor endothelial cells. Tumor-derived NO could have several functional roles. It can affect cancer progression by augmenting cancer cell proliferation and invasiveness. Infact, it has been proposed that NO promotes tumor growth by regulating blood flow and maintaining the vasodilated tumor microenvironment.NO can stimulate angiogenesis and can also promote metastasis by increasing vascular permeability and upregulating matrix metalloproteinases (MMPs). MMPs have been associated with several functions including cell proliferation, migration, adhesion, differentiation, angiogenesis and so on. Recently, it was reported that metastatic tumor-released NO might impair the immune system, which enables them to escape the immunosurveillance mechanism of cells. Molecular regulation of tumour angiogenesis by nitric oxide.
S-nitrosylation and Cancer
The most prominent and recognized NO reaction with thiols groups of cysteineresidues is called S-nitrosylation or S-nitrosation, which leads to the formation of more stable nitrosothiols. High concentrations of intracellular NO can result in high concentrations of S-nitrosylated proteins and dysregulated S-nitrosylation has been implicated in cancer. Oxidative and nitrosative stress is sensed and closely associated with transcriptional regulation of multiple target genes.
Following are a few proteins that are modified via NO and modification of these proteins, in turn, has been known to play direct or indirect roles in cancer.
NO mediated aberrant proteins in Cancer
Bcl2
Bcl-2 is an important anti-apoptotic protein. It works by inhibiting mitochondrial Cytochrome C that is released in response to apoptotic stimuli. In a variety of tumors, Bcl-2 has been shown to be upregulated, and it has additionally been implicated with cancer chemo-resistance through dysregulation of apoptosis. NO exposure causes S-nitrosylation at the two cysteine residues – Cys158 and Cys229 that prevents ubiquitin-proteasomal pathway mediated degradation of the protein. Once prevented from degradation, the protein attenuates its anti-apoptotic effects in cancer progression. The S-nitrosylation based modification of Bcl-2 has been observed to be relevant in drug treatment studies (for eg. Cisplatin). Thus, the impairment of S-nitrosylated Bcl-2 proteins might serve as an effective therapeutic target to decrease cancer-drug resistance.
p53
p53 has been well documented as a tumor suppressor protein and acts as a major player in response to DNA damage and other genomic alterations within the cell. The activation of p53 can lead to cell cycle arrest and DNA repair, however, in case of irrepairable DNA damage, p53 can lead to apoptosis. Nuclear p53 accumulation has been related to NO-mediated anti-tumoral properties. High concentration of NO has been found to cause conformational changes in p53 resulting in biological dysfunction.. In RAW264.7, a murine macrophage cell line, NO donors induce p53 accumulation and apoptosis through JNK-1/2.
HIF-1a
Hypoxia-inducible factor 1 (HIF1) is a heterodimeric transcription factor that is predominantly active under hypoxic conditions because the HIF-1a subunit is rapidly degraded in normoxic conditions by proteasomal degradation. It regulates the transciption of several genes including those involved in angiogenesis, cell cycle, cell metabolism, and apoptosis. Hypoxic conditions within the tumor can lead to overexpression of HIF-1a. Similar to hypoxia-mediated stress, nitrosative stress can stabilize HIF-1a. NO derivatives have also been shown to participate in hypoxia signaling. Resistance to radiotherapy has been traced back to NO-mediated HIF-1a in solid tumors in some cases.
PTEN
Phosphatase and tensin homolog deleted on chromosome ten (PTEN), is again a tumor suppressor protein. It is a phosphatase and has been implicated in many human cancers. PTEN is a crucial negative regulator of PI3K/Akt signaling pathway. Over-activation of PI3K/Akt mediated signaling pathway is known to play a major role in tumorigenesis and angiogenesis. S-nitrosylation of PTEN, that could be a result of NO stress, inhibits PTEN. Inhibition of PTEN phosphatase activity, in turn, leads to promotion of angiogenesis.
C-Src
C-src belongs to the Src family of protein tyrosine kinases and has been implicated in the promotion of cancer cell invasion and metastasis. It was demonstrated that S-nitrosylation of c-Src at cysteine 498 enhanced its kinase activity, thus, resulting in the enhancement of cancer cell invasion and metastasis.
Jaiswal M, et al. Nitric oxide in gastrointestinal epithelial cell carcinogenesis: linking inflammation to oncogenesis. Am J Physiol Gastrointest Liver Physiol. 2001 Sep;281(3):G626-34. http://www.ncbi.nlm.nih.gov/pubmed/11518674
Recently, two world renowned innovators, Steve Jobs-the CEO of Apple Inc. and Dr. Steinman-winner of 2011 Nobel prize in Physiology or medicine lost their life battle against Pancreatic cancer. Although both Jobs and Steinman suffered from the same disease, they were diagnosed with two fundamentally different forms of cancer of pancreas.
Steve lived with the disease for 8 years, a relatively long time for Pancreatic cancer patients to survive. The reason is attributed to the rare form of cancer of pancreas he suffered from-referred to as pancreatic neuroendocrine tumor. Steinman, on the other hand died due to a more common form of pancreatic cancer, the adenocarcenoma.
Neuroendocrine tumors arise from islands of hormone-producing cells (islets), that happen to be in that organ. Jobs learned in 2003 that he had an extremely rare form of this cancer, an islet-cell neuroendocrine tumor. In his email to Apple employees in 2004, Steven Jobs wrote “I have some personal news that I need to share with you, and I wanted you to hear it directly from me,” Jobs said in the message, which he sent from his hospital bed. “I had a very rare form of pancreatic cancer called an islet cell neuroendocrine tumor, which represents about 1 percent of the total cases of pancreatic cancer diagnosed each year, and can be cured by surgical removal if diagnosed in time (mine was). I will not require any chemotherapy or radiation treatments.”
About 2,500 cases of pancreatic islet cell tumors are seen in the United States each year, according to the University of Southern California’s Center for Pancreatic and Biliary Diseases. These tumors, which are derived from neuroendocrine cells, tend to be slow growing and are treatable even after they have metastasized, said the center’s Web site. http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/08/02/MNGMJ816F41.DTL&ao=all
The management strategy of neuroendrocrine tumors (NET) like any other disease is supposed to be curative where possible. As suggested by several researchers including Ramage et al (http://www.ncbi.nlm.nih.gov/pubmed/15686165, ), surgery is the only curative option currently available for NETs. The updated guidelines published for the NET management state the over the past few years, there have been advances in the management of neuroendocrine tumours, which have included clearer characterisation, more specific and therapeutically relevant diagnosis, and improved treatments. However, because of the uncommon nature of the disease, there remain few randomised trials in the field, hence all evidence mentioned in the research article is considered relatively weak compared with other more common cancers. For patients who are diagnosed early enough to be candidates for surgery, the aim is to keep the patient disease- and symptom-free for as long as possible. For patients suffering from advanced-stage NETs, operative therapy is rarely curative and chemotherapy could be used on metastasized NETs. http://www.ncbi.nlm.nih.gov/pubmed/22052063.
As reported in a story covered by CNN in 2008, there was a lot of speculation when he appeared rail-thin at the unveiling of the new iPhone. Jobs eventually said in January 2009 that doctors said he dropped so much weight because of “a hormone imbalance that has been ‘robbing’ me of the proteins my body needs to be healthy. Sophisticated blood tests have confirmed this diagnosis.” http://tech.fortune.cnn.com/2008/06/13/steve-jobs-life-after-the-whipple/ This statement explains how symptoms of hormonal excess in NET patients must be controlled before surgical procedure is followed. Also, recommended management of the symptoms of hormonal hypersecretion depends on the hormone secreted. For example, glucose levels in patients with insulinomas should be stabilized with diet and/or diazoxide. Gastrin hypersecretion in patients with gastrinomas may be managed with proton pump inhibitors (PPIs). http://www.neuroendocrinetumor.com/health-care-professional/net-treatment-options.jsp
Steinman, on the other hand, suffered from adenocarcenoma that arises from the pancreatic cells themselves, referred to as the “far more common form of pancreatic cancer” by Jobs. He further wrote in his memo “…(adenocarcenoma) is currently not curable and usually carries a life expectancy of around one year after diagnosis. I mention this because when one hears ‘pancreatic cancer’ (or Googles it), one immediately encounters this far more common and deadly form, which, thank God, is not what I had.”
Dr. Steinman won the 2011 Nobel Prize for Medicine or Physiology for his early-career landmark discovery about the immune system in the 1970s when he first described ‘dendritic cells’ with the help of his mentor Zanvil Cohn at Rockefeller University. Unfortunately, he died just three days before the official announcement. http://www.scientificamerican.com/article.cfm?id=steinman-nobel-laureate-explains-discovery-dendritic-cells. He had been suffering from pancreatic cancer for four years, had been undergoing treatment using a pioneering immunotherapy based on his own research. Dendritic cells from his body were deployed to mount an assault on his cancer. His early research at Rockefeller, began as an attempt to understand the primary white cells of the immune system — the large “eating” macrophages and the exquisitely specific lymphocytes, which operate in a variety of ways to spot, apprehend and destroy infectious microorganisms and tumor cells. Steinman’s subsequent research pointed to dendritic cells as important and unique accessories in the onset of several immune responses, including clinically important situations such as rejection of graft, resistance to tumors, autoimmune diseases and infections including AIDS. http://newswire.rockefeller.edu/2011/10/03/rockefeller-university-scientist-ralph-steinman-honored-today-with-nobel-prize-for-discovery-of-dendritic-cells-dies-at-68/
The standard of care in the United States for the treatment of locally advanced pancreatic cancer is a combination of low-dose chemotherapy given simultaneously with radiation treatments to the pancreas and surrounding tissues. Radiation treatments are designed to lower the risk of local growth of the cancer, thereby minimizing the symptoms that local progression causes (back or belly pain, nausea, loss of appetite, intestinal blockage, jaundice). http://www.medicinenet.com/pancreatic_cancer/page6.htm#advanced
Research Efforts on Pancreatic Cancer: The untimely passing of the geniuses reminds us how important research in the area of pancreatic cancer is which lead to finding new therapeutic targets that might stem reliable therapies. A recent example is the report published in Science Daily stating that the protein RGL2 might be a promising therapeutic target for pancreatic cancer. http://www.sciencedaily.com/releases/2010/11/101105101400.htm. The conclusion was derived via research published in November in the Journal of Biological Chemistry by a team led by Channing Der, PhD from UNC Lineberger Cancer Center. http://www.jbc.org/content/285/45/34729.long For almost three decades, scientists and physicians have known that a gene called the KRAS oncogene is mutated in virtually all pancreatic cancers, making it an important target for scientists looking for a way to stop the growth of pancreatic cancer tumors. The problem is that the KRAS gene triggers cancer cell growth in numerous ways, through multiple cell signaling pathways, and scientists have had difficulty determining which one will be the most promising to block — an important first step in designing a drug for use in patients. Dr. Der said that “We are particularly optimistic about RGL2 because we know that this protein is a critical component of KRAS signaling to another class of proteins called Ral GTPases, which are essential for the growth of almost all pancreatic tumors.”
Another groundbreaking research was published in the journal Nature talks about discovering the link between a gene and the prognosis of Pancreatic Ductal Adenocarcenoma. The team found that when a gene involved in protein degradation is switched-off through chemical tags on the DNA’s surface, pancreatic cancer cells are protected from the bodies’ natural cell death processes, become more aggressive, and can rapidly spread. Their research study proposed USP9X to be a major tumour suppressor gene with prognostic and therapeutic relevance in pancreatic cancer. http://www.sanger.ac.uk/about/press/2012/120429.htmlhttp://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature11114.pdf
Although, most of the research efforts are concentrated on the more common form of cancer, pancreatic adenocarcenoma, similar research efforts are needed for developing cure for the uncommon form, the one Steve Jobs suffered from, neuroendocrine cancer.
What we lost to the disease is more than the two geniuses, we lost the possibility of further innovation that might have changed the world in ways we could not imagine. The loss, though, sheds light on the importance of finding a cure for the disease and its different types. Hope the research community is able to interpret and find answers to the enigma of Pancreatic cancer and its diverse forms in which it strikes.
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