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Two brothers with MEPAN Syndrome: A Rare Genetic Disorder
Reporter: Amandeep Kaur
In the early 40s, a married couple named Danny and Nikki, had normal pregnancy and delivered their first child in October 2011. The couple was elated after the birth of Carson because they were uncertain about even conceiving a baby. Soon after birth, the parents started facing difficulty in feeding the newborn and had some wakeful nights, which they used to called “witching hours”. For initial six months, they were clueless that something was not correct with their infant. Shortly, they found issues in moving ability, sitting, and crawling with Carson. Their next half year went in visiting several behavioral specialists and pediatricians with no conclusion other than a suggestion that there is nothing to panic as children grow at different rates.
Later in early 2013, Caron was detected with cerebral palsy in a local regional center. The diagnosis was based on his disability to talk and delay in motor development. At the same time, Carson had his first MRI which showed no negative results. The parents convinced themselves that their child condition would be solved by therapies and thus started physical and occupational therapies. After two years, the couple gave birth to another boy child named Chase in 2013. Initially, there was nothing wrong with Chase as well. But after nine months, Chase was found to possess the same symptoms of delaying in motor development as his elder brother. It was expected that Chase may also be suffering from cerebral palsy. For around one year both boys went through enormous diagnostic tests starting from karyotyping, metabolic screen tests to diagnostic tests for Fragile X syndrome, lysosomal storage disorders, Friedreich ataxia and spinocerebellar ataxia. Gene panel tests for mitochondrial DNA and Oxidative phosphorylation (OXPHOS) deficiencies were also performed. No conclusion was drawn because each diagnostic test showed the negative results.
Over the years, the condition of boys was deteriorating as their movements became stiffer and ataxic, they were not able to crawl anymore. By the end of 2015, the boys had an MRI which showed some symmetric anomalies in their basal ganglia indicating a metabolic condition. The symptoms of Carson and Chase was not even explained by whole exome sequencing due to the absence of any positive result. The grievous journey of visits to neurologist, diagnostic tests and inconclusive results led the parents to rethink about anything happened erroneous due to them such as due to their lifestyle, insufficient intake of vitamins during pregnancy or exposure to toxic agents which left their sons in that situation.
During the diagnostic odyssey, Danny spent many restless and sleepless nights in searching PubMed for any recent cases with symptoms similar to his sons and eventually came across the NIH’s Undiagnosed Diseases Network (UDN), which gave a light of hope to the demoralized family. As soon as Danny discovered about the NIH’s Diseases Network, he gathered all the medical documents of both his sons and submitted the application. The submitted application in late 2015 got accepted a year later in December 2016 and they got their first appointment in early 2017 at the UDN site at Stanford. At Stanford, the boys had gone through whole-genome sequencing and some series of examinations which came back with inconclusive results. Finally, in February 2018, the family received some conclusive results which explained that the two boys suffer from MEPAN syndrome with pathogenic mutations in MECR gene.
MEPAN means Mitochondrial Enoyl CoA reductase Protein-Associated Neurodegeneration
MEPAN syndrome is a rare genetic neurological disorder
MEPAN syndrome is associated with symptoms of ataxia, optic atrophy and dystonia
The wild-type MECR gene encodes a mitochondrial protein which is involved in metabolic processes
The prevalence rate of MEPAN syndrome is 1 in 1 million
Currently, there are 17 patients of MEPAN syndrome worldwide
The symptoms of Carson and Chase of an early onset of motor development with no appropriate biomarkers and T-2 hyperintensity in the basal ganglia were matching with the seven known MEPAN patient at that time. The agonizing journey of five years concluded with diagnosis of rare genetic disorder.
Despite the advances in genetic testing and their low-cost, there are many families which still suffer and left undiagnostic for long years. To shorten the diagnostic journey of undiagnosed patients, the whole-exome and whole-genome sequencing can be used as a primary tool. There is need of more research to find appropriate treatments of genetic disorders and therapies to reduce the suffering of the patients and families. It is necessary to fill the gap between the researchers and clinicians to stimulate the development in diagnosis, treatment and drug development for rare genetic disorders.
The family started a foundation named “MEPAN Foundation” (https://www.mepan. org) to reach out to the world to educate people about the mutation in MECR gene. By creating awareness among the communities, clinicians, and researchers worldwide, the patients having rare genetic disorder can come closer and share their information to improve their condition and quality of life.
Alnylam Announces First-Ever FDA Approval of an RNAi Therapeutic, ONPATTRO™ (patisiran) for the Treatment of the Polyneuropathy of Hereditary Transthyretin-Mediated Amyloidosis in Adults
Dysregulation of ncRNAs in association with Neurodegenerative Disorders
Curator: Amandeep Kaur
Research over the years has added evidences to the hypothesis of “RNA world” which explains the evolution of DNA and protein from a simple RNA molecule. Our understanding of RNA biology has dramatically changed over the last 50 years and rendered the scientists with the conclusion that apart from coding for protein synthesis, RNA also plays an important role in regulation of gene expression.
The universe of non-coding RNAs (ncRNAs) is transcending the margins of preconception and altered the traditional thought that the coding RNAs or messenger RNAs (mRNAs) are more prevalent in our cells. Research on the potential use of ncRNAs in therapeutic relevance increased greatly after the discovery of RNA interference (RNAi) and provided important insights into our further understanding of etiology of complex disorders.
Latest research on neurodegenerative disorders has shown the perturbed expression of ncRNAs which provides the functional association between neurodegeneration and ncRNAs dysfunction. Due to the diversity of functions and abundance of ncRNAs, they are classified into Housekeeping RNAs and Regulatory ncRNAs.
The best known classes of ncRNAs are the microRNAs (miRNAs) which are extensively studied and are of research focus. miRNAs are present in both intronic and exonic regions of matured RNA (mRNA) and are crucial for development of CNS. The reduction of Dicer-1, a miRNA biogenesis-related protein affects neural development and the elimination of Dicer in specifically dopaminergic neurons causes progressive degeneration of these neuronal cells in striatum of mice.
A new class of regulatory ncRNAs, tRNAs-derived fragments (tRFs) is superabundantly present in brain cells. tRFs are considered as risk factors in conditions of neural degeneration because of accumulation with aging. tRFs have heterogenous functions with regulation of gene expression at multiple layers including regulation of mRNA processing and translation, inducing the activity of silencing of target genes, controlling cell growth and differentiation processes.
The existence of long non-coding RNAs (lncRNAs) was comfirmed by the ENCODE project. Numerous studies reported that approximately 40% of lncRNAs are involved in gene expression, imprinting and pluripotency regulation in the CNS. lncRNA H19 is of paramount significance in neural viability and contribute in epilepsy condition by activating glial cells. Other lncRNAs are highly bountiful in neurons including Evf2 and MALAT1 which play important function in regulating neural differentiation and synapse formation and development of dendritic cells respectively.
Recently, a review article in Nature mentioned about the complex mechanisms of ncRNAs contributing to neurodegenerative conditions. The ncRNA-mediated mechanisms of regulation are as follows:
Epigenetic regulation: Various lncRNAs such as BDNF-AS, TUG1, MEG3, NEAT1 and TUNA are differentially expressed in brain tissue and act as epigenetic regulators.
RNAi: RNA interference includes post-transcriptional repression by small-interfering RNAs (siRNAs) and binding of miRNAs to target genes. In a wide spectrum of neurodegenerative diseases such as Alzheimer’s disease, Parkinson disease, Huntington’s disease, Amyotrophic lateral sclerosis, Fragile X syndrome, Frontotemporal dementia, and Spinocerebellar ataxia, have shown perturbed expression of miRNA.
Alternative splicing: Variation in splicing of transcripts of ncRNAs has shown adverse affects in neuropathology of degenerative diseases.
mRNA stability: The stability of mRNA may be affected by RNA-RNA duplex formation which leads to the degradation of sense mRNA or blocking the access to proteins involved in RNA turnover and modify the progression of neurodegenerative disorders.
Translational regulation: Numerous ncRNAs including BC200 directly control the translational process of transcripts of mRNAs and effect human brain of Alzheimer’s disease.
Molecular decoys: Non-coding RNAs (ncRNAs) dilute the expression of other RNAs by molecular trapping, also known as competing endogenous RNAs (ceRNAs) which hinder the normal functioning of RNAs. The ceRNAs proportion must be equivalent to the number of target miRNAs that can be sequestered by each ncRNAs in order to induce consequential de-repression of the target molecules.
The unknown functions of numerous annotated ncRNAs may explain the underlying complexity in neurodegenerative disorders. The profiling of ncRNAs of patients suffering from neurodevelopmental and neurodegenerative conditions are required to outline the changes in ncRNAs and their role in specific regions of brain and cells. Analysis of Large-scale gene expression and functional studies of ncRNAs may contribute to our understanding of these diseases and their remarkable connections. Therefore, targeting ncRNAs may provide effective therapeutic perspective for the treatment of neurodegenerative diseases.
Mechanistic link between SARS-CoV-2 infection and increased risk of stroke using 3D printed models and human endothelial cells
Reporter: Adina Hazan, PhD
Kaneko, et al. from UCLA aimed to explore why SARS-CoV-2 infection is associated with an increased rate of cerebrovascular events, including
ischemic stroke and
intracerebral hemorrhage
While some suggested mechanisms include an overall systemic inflammatory response including increasing circulating cytokines and leading to a prothrombotic state, this may be only a partial answer. A SARS-CoV-2 specific mechanism could be likely, considering that both angiotensin-converting enzyme-2 (ACE2), the receptor necessary for SARS-CoV-2 to gain entry into the cell, and SARS-CoV-2 RNA have been reportedly detected in the human brain postmortem.
One of the difficulties in studying vasculature mechanisms is that the inherent 3D shape and blood flow subject this tissue to different stressors, such as flow, that could be critically relevant during inflammation. To accurately study the effect of SARS-CoV-2 on the vasculature of the brain, the team generated 3D models of the human middle cerebral artery during intracranial artery stenosis using data from CT (computed tomography) angiography. This data was then exported with important factors included such as
shear stress during perfusion,
streamlines, and
flow velocity to be used to fabricate 3D models.
These tubes were then coated with endothelial cells isolated and sorted from normal human brain tissue resected during surgery. In doing so, this model could closely mimic the cellular response of the vasculature of the human brain.
Surprisingly, without this 3D tube, human derived brain endothelial cells displayed very little expression of ACE2 or, TMPRSS2 (transmembrane protease 2), a necessary cofactor for SARS-COV-2 viral entry.
Interestingly,
horizontal shear stress increased the expression of ACE2 and
increased the binding of spike protein to ACE2, especially within the stenotic portion of the 3D model.
By exposing the endothelial cells to liposomes expressing the SARS-CoV-2 spike protein, they also were able to explore key upregulated genes in the exposed cells, in which they found that
“binding of SARS-CoV-2 S protein triggered 83 unique genes in human brain endothelial cells”.
This included many inflammatory signals, some of which have been previously described as associated with SARS-COV-2, and others whose effects are unknown. This may provide an important foundation for exploring potential therapeutic targets in patients susceptible to cerebrovascular events.
Overall, this study shows important links between the
mechanisms of SARS-CoV-2 and the
increase in ischemic events in these patients. It also has important implications for
treatment for SARS-CoV-2, as high blood pressure and atherosclerosis may be increasing ACE2 expression in patients, providing the entry port for viral particles into brain endothelia.
Parkinson’s Disease (PD), characterized by both motor and non-motor system pathology, is a common neurodegenerative disorder affecting about 1% of the population over age 60. Its prevalence presents an increasing social burden as the population ages. Since its introduction in the 1960’s, dopamine (DA)-replacement therapy (e.g., L-DOPA) has remained the gold standard treatment. While improving PD patients’ quality of life, the effects of treatment fade with disease progression and prolonged usage of these medications often (>80%) results in side effects including dyskinesias and motor fluctuations. Since the selective degeneration of A9 mDA neurons (mDANs) in the substantia nigra (SN) is a key pathological feature of the disease and is directly associated with the cardinal motor symptoms, dopaminergic cell transplantation has been proposed as a therapeutic strategy.
Researchers showed that mammalian fibroblasts can be converted into embryonic stem cell (ESC)-like induced pluripotent stem cells (iPSCs) by introducing four transcription factors i.e., Oct4, Sox2, Klf4, and c-Myc. This was then accomplished with human somatic cells, reprogramming them into human iPSCs (hiPSCs), offering the possibility of generating patient-specific stem cells. There are several major barriers to implementation of hiPSC-based cell therapy for PD. First, probably due to the limited understanding of the reprogramming process, wide variability exists between the differentiation potential of individual hiPSC lines. Second, the safety of hiPSC-based cell therapy has yet to be fully established. In particular, since any hiPSCs that remain undifferentiated or bear sub-clonal tumorigenic mutations have neoplastic potential, it is critical to eliminate completely such cells from a therapeutic product.
In the present study the researchers established human induced pluripotent stem cell (hiPSC)-based autologous cell therapy. Researchers reported a platform of core techniques for the production of mDA progenitors as a safe and effective therapeutic product. First, by combining metabolism-regulating microRNAs with reprogramming factors, a method was developed to more efficiently generate clinical grade iPSCs, as evidenced by genomic integrity and unbiased pluripotent potential. Second, a “spotting”-based in vitro differentiation methodology was established to generate functional and healthy mDA cells in a scalable manner. Third, a chemical method was developed that safely eliminates undifferentiated cells from the final product. Dopaminergic cells thus produced can express high levels of characteristic mDA markers, produce and secrete dopamine, and exhibit electrophysiological features typical of mDA cells. Transplantation of these cells into rodent models of PD robustly restored motor dysfunction and reinnervated host brain, while showing no evidence of tumor formation or redistribution of the implanted cells.
Together these results supported the promise of these techniques to provide clinically applicable personalized autologous cell therapy for PD. It was recognized by researchers that this methodology is likely to be more costly in dollars and manpower than techniques using off-the-shelf methods and allogenic cell lines. Nevertheless, the cost for autologous cell therapy may be expected to decrease steadily with technological refinement and automation. Given the significant advantages inherent in a cell source free of ethical concerns and with the potential to obviate the need for immunosuppression, with its attendant costs and dangers, it was proposed that this platform is suitable for the successful implementation of human personalized autologous cell therapy for PD.
Lesson 4 Cell Signaling And Motility: G Proteins, Signal Transduction: Curations and Articles of reference as supplemental information: #TUBiol3373
Curator: Stephen J. Williams, Ph.D.
Updated 7/15/2019
Below please find the link to the Powerpoint presentation for lesson #4 for #TUBiol3373. The lesson first competes the discussion on G Protein Coupled Receptors, including how cells terminate cell signals. Included are mechanisms of receptor desensitization. Please NOTE that desensitization mechanisms like B arrestin decoupling of G proteins and receptor endocytosis occur after REPEATED and HIGH exposures to agonist. Hydrolysis of GTP of the alpha subunit of G proteins, removal of agonist, and the action of phosphodiesterase on the second messenger (cAMP or cGMP) is what results in the downslope of the effect curve, the termination of the signal after agonist-receptor interaction.
Stroke is a leading cause of death worldwide and the most common cause of long-term disability amongst adults, more particularly in patients with diabetes mellitus and arterial hypertension. Increasing evidence suggests that disordered physiological variables following acute ischaemic stroke, especially hyperglycaemia, adversely affect outcomes.
Post-stroke hyperglycaemia is common (up to 50% of patients) and may be rather prolonged, regardless of diabetes status. A substantial body of evidence has demonstrated that hyperglycaemia has a deleterious effect upon clinical and morphological stroke outcomes. Therefore, hyperglycaemia represents an attractive physiological target for acute stroke therapies.
However, whether intensive glycaemic manipulation positively influences the fate of ischaemic tissue remains unknown. One major adverse event of management of hyperglycaemia with insulin (either glucose-potassium-insulin infusions or intensive insulin therapy) is the occurrence of hypoglycaemia, which can also induce cerebral damage.
Doctors all over the world have debated whether intensive glucose management, which requires the use of IV insulin to bring blood sugar levels down to 80-130 mg/dL, or standard glucose control using insulin shots, which aims to get glucose below 180 mg/dL, lead to better outcomes after stroke.
A period of hyperglycemia is common, with elevated blood glucose in the periinfarct period consistently linked with poor outcome in patients with and without diabetes. The mechanisms that underlie this deleterious effect of dysglycemia on ischemic neuronal tissue remain to be established, although in vitro research, functional imaging, and animal work have provided clues.
While prompt correction of hyperglycemia can be achieved, trials of acute insulin administration in stroke and other critical care populations have been equivocal. Diabetes mellitus and hyperglycemia per se are associated with poor cerebrovascular health, both in terms of stroke risk and outcome thereafter.
Interventions to control blood sugar are available but evidence of cerebrovascular efficacy are lacking. In diabetes, glycemic control should be part of a global approach to vascular risk while in acute stroke, theoretical data suggest intervention to lower markedly elevated blood glucose may be of benefit, especially if thrombolysis is administered.
Both hypoglycaemia and hyperglycaemia may lead to further brain injury and clinical deterioration; that is the reason these conditions should be avoided after stroke. Yet, when correcting hyperglycaemia, great care should be taken not to switch the patient into hypoglycaemia, and subsequently aggressive insulin administration treatment should be avoided.
Early identification and prompt management of hyperglycaemia, especially in acute ischaemic stroke, is recommended. Although the appropriate level of blood glucose during acute stroke is still debated, a reasonable approach is to keep the patient in a mildly hyperglycaemic state, rather than risking hypoglycaemia, using continuous glucose monitoring.
The primary results from the Stroke Hyperglycemia Insulin Network Effort (SHINE) study, a large, multisite clinical study showed that intensive glucose management did not improve functional outcomes at 90 days after stroke compared to standard glucose therapy. In addition, intense glucose therapy increased the risk of very low blood glucose (hypoglycemia) and required a higher level of care such as increased supervision from nursing staff, compared to standard treatment.
Today’s lesson 3 explains how extracellular signals are transduced (transmitted) into the cell through receptors to produce an agonist-driven event (effect). This lesson focused on signal transduction from agonist through G proteins (GTPases), and eventually to the effectors of the signal transduction process. Agonists such as small molecules like neurotransmitters, hormones, nitric oxide were discussed however later lectures will discuss more in detail the large growth factor signalings which occur through receptor tyrosine kinases and the Ras family of G proteins as well as mechanosignaling through Rho and Rac family of G proteins.
Transducers: The Heterotrimeric G Proteins (GTPases)
An excellent review of heterotrimeric G Proteins found in the brain is given by
Cyclic AMP is an important second messenger. It forms, as shown, when the membrane enzyme adenylyl cyclase is activated (as indicated, by the alpha subunit of a G protein).
The cyclic AMP then goes on the activate specific proteins. Some ion channels, for example, are gated by cyclic AMP. But an especially important protein activated by cyclic AMP is protein kinase A, which goes on the phosphorylate certain cellular proteins. The scheme below shows how cyclic AMP activates protein kinase A.
Updated 7/15/2019
Additional New Studies on Regulation of the Beta 2 Adrenergic Receptor
We had discussed regulation of the G protein coupled beta 2 adrenergic receptor by the B-AR receptor kinase (BARK)/B arrestin system which uncouples and desensitizes the receptor from its G protein system. In an article by Xiangyu Liu in Science in 2019, the authors describe another type of allosteric modulation (this time a POSITIVE allosteric modulation) in the intracellular loop 2. See below:
Mechanism of β2AR regulation by an intracellular positive allosteric modulator
Xiangyu Liu1,*, Ali Masoudi2,*, Alem W. Kahsai2,*, Li-Yin Huang2, Biswaranjan Pani2, Dean P. Staus2, Paul J. Shim2, Kunio Hirata3,4, Rishabh K. Simhal2, Allison M. Schwalb2, Paula K. Rambarat2, Seungkirl Ahn2, Robert J. Lefkowitz2,5,6,†, Brian Kobilka1
Positive reinforcement in a GPCR
Many drug discovery efforts focus on G protein–coupled receptors (GPCRs), a class of receptors that regulate many physiological processes. An exemplar is the β2-adrenergic receptor (β2AR), which is targeted by both blockers and agonists to treat cardiovascular and respiratory diseases. Most GPCR drugs target the primary (orthosteric) ligand binding site, but binding at allosteric sites can modulate activation. Because such allosteric sites are less conserved, they could possibly be targeted more specifically. Liu et al. report the crystal structure of β2AR bound to both an orthosteric agonist and a positive allosteric modulator that increases receptor activity. The structure suggests why the modulator compound is selective for β2AR over the closely related β1AR. Furthermore, the structure reveals that the modulator acts by enhancing orthosteric agonist binding and stabilizing the active conformation of the receptor.
Abstract
Drugs targeting the orthosteric, primary binding site of G protein–coupled receptors are the most common therapeutics. Allosteric binding sites, elsewhere on the receptors, are less well-defined, and so less exploited clinically. We report the crystal structure of the prototypic β2-adrenergic receptor in complex with an orthosteric agonist and compound-6FA, a positive allosteric modulator of this receptor. It binds on the receptor’s inner surface in a pocket created by intracellular loop 2 and transmembrane segments 3 and 4, stabilizing the loop in an α-helical conformation required to engage the G protein. Structural comparison explains the selectivity of the compound for β2– over the β1-adrenergic receptor. Diversity in location, mechanism, and selectivity of allosteric ligands provides potential to expand the range of receptor drugs.
Recent structures of GPCRs bound to allosteric modulators have revealed that receptor surfaces are decorated with diverse cavities and crevices that may serve as allosteric modulatory sites (1). This substantiates the notion that GPCRs are structurally plastic and can be modulated by a variety of allosteric ligands through distinct mechanisms (2-7). Most of these structures have been solved with negative allosteric modulators (NAMs), which stabilize receptors in their inactive states (1). To date, only a single structure of an active GPCR bound to a small-molecule positive allosteric modulator (PAM) has been reported, namely, the M2 muscarinic acetylcholine receptor with LY2119620 (8). Thus, mechanisms of PAMs and their potential binding sites remain largely unexplored.
Fig 1. Structure of the active state T4L-B2AR in complex with the orthosteric agonist BI-167107, nanobody 689, and compound 6FA. (A) The chemical structure of compound-6FA (Cmpd-6FA). (B) Isoproterenol (ISO) competition binding with 125I-cyanopindolol (CYP) to the β2AR reconstituted in nanodisks in the presence of vehicle (0.32% dimethylsulfoxide; DMSO), Cmpd-6, or Cmpd-6FA at 32 μM. Values were normalized to percentages of the maximal 125I-CYP binding level obtained from a one-site competition binding–log IC50 (median inhibitory concentration) curve fit. Binding curves were generated by GraphPad Prism. Points on curves represent mean ± SEM obtained from five independent experiments performed in duplicate. (C) Analysis of Cmpd-6FA interaction with the BI-167107–bound β2AR by ITC. Representative thermogram (inset) and binding isotherm, of three independent experiments, with the best titration curve fit are shown. Summary of thermodynamic parameters obtained by ITC: binding affinity (KD = 1.2 ± 0.1 μM), stoichiometry (N = 0.9 ± 0.1 sites), enthalpy (ΔH = 5.0 ± 1.2 kcal mol−1), and entropy (ΔS =13 ± 2.0 cal mol−1 deg−1). (D) Side view of T4L-β2AR bound to the orthosteric agonist BI-167107, nanobody 6B9 (Nb6B9), and Cmpd-6FA. The gray box indicates the membrane layer as defined by the OPM database. (E) Close-up view of Cmpd-6FA binding site. Covering Cmpd-6FA is 2Fo– Fc electron density contoured at 1.0 σ (green mesh).From Science 28 Jun 2019:
Vol. 364, Issue 6447, pp. 1283-1287
Fig 3. Fig. 3Mechanism of allosteric activation of the β2AR by Cmpd-6FA.
(A) Superposition of the inactive β2AR bound to the antagonist carazolol (PDB code: 2RH1) and the active β2AR bound to the agonist BI-167107, Cmpd-6FA, and Nb6B9. Close-up view of the Cmpd-6FA binding site is shown. The residues of the inactive (yellow) and active (blue) β2AR are depicted, and the hydrogen bond formed between Asp1303.49and Tyr141ICL2 in the active state is indicated by a black dashed line. (B) Topography of Cmpd-6FA binding surface on the active β2AR (left, blue) and the corresponding surface of the inactive β2AR (right, yellow) with Cmpd-6FA (orange sticks) docked on top. Molecular surfaces are of only those residues involved in interaction with Cmpd-6FA. Steric clash between Cmpd-6FA and the surface of inactive β2AR is represented by a purple asterisk. (C) Overlay of the β2AR bound to BI-167107, Nb6B9, and Cmpd-6FA with the β2AR–Gscomplex (PDB code: 3SN6). The inset shows the position of Phe139ICL2 relative to the α subunit of Gs. (D) Superposition of the active β2AR bound to the agonist BI-167107, Nb6B9, and Cmpd-6FA (blue) with the inactive β2AR bound to carazolol (yellow) (PDB code: 2RH1) as viewed from the cytoplasm. For clarity, Nb6B9 and the orthosteric ligands are omitted. The arrows indicate shifts in the intracellular ends of the TM helices 3, 5, and 6 upon activation and their relative distances.
Allosteric sites may not face the same evolutionary pressure as do orthosteric sites, and thus are more divergent across subtypes within a receptor family (24–26). Therefore, allosteric sites may provide a greater source of specificity for targeting GPCRs.
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Additional information on Nitric Oxide as a Cellular Signal
Nitric oxide is actually a free radical and can react with other free radicals, resulting in a very short half life (only a few seconds) and so in the body is produced locally to its site of action (i.e. in endothelial cells surrounding the vascular smooth muscle, in nerve cells). In the late 1970s, Dr. Robert Furchgott observed that acetylcholine released a substance that produced vascular relaxation, but only when the endothelium was intact. This observation opened this field of research and eventually led to his receiving a Nobel prize. Initially, Furchgott called this substance endothelium-derived relaxing factor (EDRF), but by the mid-1980s he and others identified this substance as being NO.
Nitric oxide is implicated in many pathologic processes as well. Nitric oxide post translational modifications have been attributed to nitric oxide’s role in pathology however, although the general mechanism by which nitric oxide exerts its physiological effects is by stimulation of soluble guanylate cyclase to produce cGMP, these post translational modifications can act as a cellular signal as well. For more information of NO pathologic effects and how NO induced post translational modifications can act as a cellular signal see the following:
UPDATED on 12/26/2020 – CABG: a Superior Revascularization Modality to PCI in Patients with poor LVF, Multivessel disease and Diabetes, Similar Risk of Stroke between 31 days and 5 years, post intervention
Reporter: Aviva Lev-Ari, PhD, RN
UPDATED on 12/26/2020
Five-Year Outcomes after PCI or CABG for Left Main Coronary Disease
Long-term outcomes after percutaneous coronary intervention (PCI) with contemporary drug-eluting stents, as compared with coronary-artery bypass grafting (CABG), in patients with left main coronary artery disease are not clearly established.
METHODS
We randomly assigned 1905 patients with left main coronary artery disease of low or intermediate anatomical complexity (according to assessment at the participating centers) to undergo either PCI with fluoropolymer-based cobalt–chromium everolimus-eluting stents (PCI group, 948 patients) or CABG (CABG group, 957 patients). The primary outcome was a composite of death, stroke, or myocardial infarction.
RESULTS
At 5 years, a primary outcome event had occurred in 22.0% of the patients in the PCI group and in 19.2% of the patients in the CABG group (difference, 2.8 percentage points; 95% confidence interval [CI], −0.9 to 6.5; P=0.13). Death from any cause occurred more frequently in the PCI group than in the CABG group (in 13.0% vs. 9.9%; difference, 3.1 percentage points; 95% CI, 0.2 to 6.1). In the PCI and CABG groups, the incidences of definite cardiovascular death (5.0% and 4.5%, respectively; difference, 0.5 percentage points; 95% CI, −1.4 to 2.5) and myocardial infarction (10.6% and 9.1%; difference, 1.4 percentage points; 95% CI, −1.3 to 4.2) were not significantly different. All cerebrovascular events were less frequent after PCI than after CABG (3.3% vs. 5.2%; difference, −1.9 percentage points; 95% CI, −3.8 to 0), although the incidence of stroke was not significantly different between the two groups (2.9% and 3.7%; difference, −0.8 percentage points; 95% CI, −2.4 to 0.9). Ischemia-driven revascularization was more frequent after PCI than after CABG (16.9% vs. 10.0%; difference, 6.9 percentage points; 95% CI, 3.7 to 10.0).
CONCLUSIONS
In patients with left main coronary artery disease of low or intermediate anatomical complexity, there was no significant difference between PCI and CABG with respect to the rate of the composite outcome of death, stroke, or myocardial infarction at 5 years. (Funded by Abbott Vascular; EXCEL ClinicalTrials.gov number, NCT01205776. opens in new tab.)
Is the Tide Turning on the ‘Grubby’ Affair of EXCEL and the European Guidelines?
Taggart was chair of the surgical committee for the Abbott-sponsored EXCEL trial, which compared two procedures for patients who had blockages in their left main coronary artery: percutaneous coronary intervention (PCI) using coronary stents, and coronary artery bypass graft surgery (CABG). The investigators designed the trial to compare outcomes for the two treatments using a composite endpoint of death, stroke, and myocardial infarction (MI). The 3-year follow-up data had been published in NEJM without controversy — or, at least, without public controversy.
But when it came time to publish the 5-year follow-up, there was a significantly higher rate of death in the stent group, and both Taggart and the journal editors were concerned that this finding was being downplayed in the manuscript.
In their comments to the authors, the journal editors had recommended including the mortality difference (unless clearly trivial) ‘”in the concluding statement in the final paragraph.” Yet, the concluding statement of the published paper read that there “was no significant difference between PCI and CABG.”
Over a year after the BBC received the leaked data, the EXCEL investigators published an analysis of the primary outcome using the universal definition of MI data in the Journal of the American College of Cardiology.
It shows 141 events in the PCI arm compared to 102 in the CABG arm. The investigators acknowledge that the rates of procedural MI differ depending on the definition used. According to their analysis, the protocol definition was predictive of mortality after both treatments, whereas the universal definition of procedural MI was predictive of mortality only after CABG. Not everyone agrees with this interpretation, and an accompanying editorial questioned these conclusions.
As for the guidelines, the tide may be turning.
In a joint statement with EACTS on October 6, 2020, the ESC agreed to review its guidelines for left main disease in the light of emerging, longer-term outcome data from the trials of CABG vs PCI.
SYNTAX at 10 Years: Bypass vs PCI Still a Toss-Up Overall
But CABG beats stenting for important subgroups
SYNTAX was funded by Boston Scientific.
Thuijs, Stone, and Taggart disclosed no conflicts.
Baumbach reported receiving institutional research support from Abbott Vascular; and consultation and speaker fees from AstraZeneca, Sinomed, Microport, Abbott Vascular, Cardinal Health, KSH, Medtronic.
Pagano is the Secretary General of the European Association for Cardiothoracic Surgery.
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Overall, mortality curves did not diverge over time for SYNTAX participants now included in the trial’s extension study SYNTAXES: by 1o years, all-cause death reached 27.0% among those randomized to percutaneous coronary intervention (PCI) and 23.5% of the CABG arm (HR 1.17, 95% CI 0.97-1.41), according to Daniel Thuijs, MD, of Erasmus University Medical Centre in Rotterdam, the Netherlands.
However, people with three-vessel disease had particularly high mortality when assigned to PCI in lieu of CABG (27.7% vs 20.6%, HR 1.41, 95% CI 1.10-1.80), whereas peers with left main disease were no worse off after either procedure (26.1% vs 26.7%, HR 0.90, 95% CI 0.68-1.52),Thuijs told the audience during a late-breaking trial session at the European Society of Cardiology’s annual congress. The study was also published online in The Lancet.
CABG had a mortality benefit over PCI in patients with multivessel disease, particularly those with diabetes and higher coronary complexity. No benefit for CABG over PCI was seen in patients with left main disease. Longer follow-up is needed to better define mortality differences between the revascularisation strategies.
JACC Study, 7/2018
CONCLUSIONS
This individual patient-data pooled analysis demonstrates that 5-year stroke rates are significantly lower after PCI compared with CABG, driven by a reduced risk of stroke in the 30-day post-procedural period but a similar risk of stroke between 31 days and 5 years. The greater risk of stroke after CABG compared with PCI was confined to patients with multivessel disease and diabetes. Five-year mortality was markedly higher for patients experiencing a stroke within 30 days after revascularization.
European Journal of Cardiothoracic Surgery Study, 6/2018
CONCLUSIONS
Despite a longer length of hospital stay, patients with impaired LVF requiring intervention for coronary artery disease experienced a greater post-procedural survival benefit if they received CABG compared to PCI. We have demonstrated this at 30 days, 90 days, 1 year, 3 years, 5 years and 8 years following revascularization. At present, CABG remains a superior revascularization modality to PCI in patients with poor LVF.
New Studies on Clinical Outcomes from two Revascularization Strategies: CABG and PCI
J Am Coll Cardiol. 2018 Jul 24;72(4):386-398. doi: 10.1016/j.jacc.2018.04.071.
Stroke Rates Following Surgical Versus Percutaneous Coronary Revascularization.
Coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI) are used for coronary revascularization in patients with multivessel and left main coronary artery disease. Stroke is among the most feared complications of revascularization. Due to its infrequency, studies with large numbers of patients are required to detect differences in stroke rates between CABG and PCI.
OBJECTIVES:
This study sought to compare rates of stroke after CABG and PCI and the impact of procedural stroke on long-term mortality.
METHODS:
We performed a collaborative individual patient-data pooled analysis of 11 randomized clinical trials comparing CABG with PCI using stents; ERACI II (Argentine Randomized Study: Coronary Angioplasty With Stenting Versus Coronary Bypass Surgery in Patients With Multiple Vessel Disease) (n = 450), ARTS (Arterial Revascularization Therapy Study) (n = 1,205), MASS II (Medicine, Angioplasty, or Surgery Study) (n = 408), SoS (Stent or Surgery) trial (n = 988), SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) trial (n = 1,800), PRECOMBAT (Bypass Surgery Versus Angioplasty Using Sirolimus-Eluting Stent in Patients With Left Main Coronary Artery Disease) trial (n = 600), FREEDOM (Comparison of Two Treatments for Multivessel Coronary Artery Disease in Individuals With Diabetes) trial (n = 1,900), VA CARDS (Coronary Artery Revascularization in Diabetes) (n = 198), BEST (Bypass Surgery Versus Everolimus-Eluting Stent Implantation for Multivessel Coronary Artery Disease) (n = 880), NOBLE (Percutaneous Coronary Angioplasty Versus Coronary Artery Bypass Grafting in Treatment of Unprotected Left Main Stenosis) trial (n = 1,184), and EXCEL (Evaluation of Xience Versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization) trial (n = 1,905). The 30-day and 5-year stroke rates were compared between CABG and PCI using a random effects Cox proportional hazards model, stratified by trial. The impact of stroke on 5-year mortality was explored.
RESULTS:
The analysis included 11,518 patients randomly assigned to PCI (n = 5,753) or CABG (n = 5,765) with a mean follow-up of 3.8 ± 1.4 years during which a total of 293 strokes occurred. At 30 days, the rate of stroke was 0.4% after PCI and 1.1% after CABG (hazard ratio [HR]: 0.33; 95% confidence interval [CI]: 0.20 to 0.53; p < 0.001). At 5-year follow-up, stroke remained significantly lower after PCI than after CABG (2.6% vs. 3.2%; HR: 0.77; 95% CI: 0.61 to 0.97; p = 0.027). Rates of stroke between 31 days and 5 years were comparable: 2.2% after PCI versus 2.1% after CABG (HR: 1.05; 95% CI: 0.80 to 1.38; p = 0.72). No significant interactions between treatment and baseline clinical or angiographic variables for the 5-year rate of stroke were present, except for diabetic patients (PCI: 2.6% vs. CABG: 4.9%) and nondiabetic patients (PCI: 2.6% vs. CABG: 2.4%) (p for interaction = 0.004). Patients who experienced a stroke within 30 days of the procedure had significantly higher 5-year mortality versus those without a stroke, both after PCI (45.7% vs. 11.1%, p < 0.001) and CABG (41.5% vs. 8.9%, p < 0.001).
CONCLUSIONS:
This individual patient-data pooled analysis demonstrates that 5-year stroke rates are significantly lower after PCI compared with CABG, driven by a reduced risk of stroke in the 30-day post-procedural period but a similar risk of stroke between 31 days and 5 years. The greater risk of stroke after CABG compared with PCI was confined to patients with multivessel disease and diabetes. Five-year mortality was markedly higher for patients experiencing a stroke within 30 days after revascularization.
Head SJ, Milojevic M, Daemen J, Ahn JM, Boersma E, Christiansen EH, Domanski MJ, Farkouh ME, Flather M, Fuster V, Hlatky MA, Holm NR, Hueb WA, Kamalesh M, Kim YH, Mäkikallio T, Mohr FW, Papageorgiou G, Park SJ, Rodriguez AE, Sabik JF, Stables RH, Stone GW, Serruys PW, Kappetein AP. Mortality after coronary artery bypass grafting versus percutaneous coronary intervention with stenting for coronary artery disease: a pooled analysis of individual patient data. Lancet. 2018 Feb 22 [Epub ahead of print]. doi: 10.1016/S0140-6736(18)30423-9. PMID: 29478841
Numerous randomised trials have compared coronary artery bypass grafting (CABG) with percutaneous coronary intervention (PCI) for patients with coronary artery disease. However, no studies have been powered to detect a difference in mortality between the revascularisation strategies.
Methods
We did a systematic review up to July 19, 2017, to identify randomised clinical trials comparing CABG with PCI using stents. Eligible studies included patients with multivessel or left main coronary artery disease who did not present with acute myocardial infarction, did PCI with stents (bare-metal or drug-eluting), and had more than 1 year of follow-up for all-cause mortality. In a collaborative, pooled analysis of individual patient data from the identified trials, we estimated all-cause mortality up to 5 years using Kaplan-Meier analyses and compared PCI with CABG using a random-effects Cox proportional-hazards model stratified by trial. Consistency of treatment effect was explored in subgroup analyses, with subgroups defined according to baseline clinical and anatomical characteristics.
Findings
We included 11 randomised trials involving 11 518 patients selected by heart teams who were assigned to PCI (n=5753) or to CABG (n=5765). 976 patients died over a mean follow-up of 3·8 years (SD 1·4). Mean Synergy between PCI with Taxus and Cardiac Surgery (SYNTAX) score was 26·0 (SD 9·5), with 1798 (22·1%) of 8138 patients having a SYNTAX score of 33 or higher. 5 year all-cause mortality was 11·2% after PCI and 9·2% after CABG (hazard ratio [HR] 1·20, 95% CI 1·06–1·37; p=0·0038). 5 year all-cause mortality was significantly different between the interventions in patients with multivessel disease (11·5% after PCI vs 8·9% after CABG; HR 1·28, 95% CI 1·09–1·49; p=0·0019), including in those with diabetes (15·5% vs 10·0%; 1·48, 1·19–1·84; p=0·0004), but not in those without diabetes (8·7% vs 8·0%; 1·08, 0·86–1·36; p=0·49). SYNTAX score had a significant effect on the difference between the interventions in multivessel disease. 5 year all-cause mortality was similar between the interventions in patients with left main disease (10·7% after PCI vs 10·5% after CABG; 1·07, 0·87–1·33; p=0·52), regardless of diabetes status and SYNTAX score.
Interpretation
CABG had a mortality benefit over PCI in patients with multivessel disease, particularly those with diabetes and higher coronary complexity. No benefit for CABG over PCI was seen in patients with left main disease. Longer follow-up is needed to better define mortality differences between the revascularisation strategies.
Comparison of the survival between coronary artery bypass graft surgery versus percutaneous coronary intervention in patients with poor left ventricular function (ejection fraction <30%): a propensity-matched analysis.
Existing evidence comparing the outcomes of coronary artery bypass graft (CABG) surgery versus percutaneous coronary intervention (PCI) in patients with poor left ventricular function (LVF) is sparse and flawed. This is largely due to patients with poor LVF being underrepresented in major research trials and the outdated nature of some studies that do not consider drug-eluting stent PCI.
METHODS:
Following strict inclusion criteria, 717 patients who underwent revascularization by CABG or PCI between 2002 and 2015 were enrolled. All patients had poor LVF (defined by ejection fraction <30%). By employing a propensity score analysis, 134 suitable matches (67 CABG and 67 PCI) were identified. Several outcomes were evaluated, in the matched population, using data extracted from national registry databases.
RESULTS:
CABG patients required a longer length of hospital stay post-revascularization compared to PCI in the propensity-matched population, 7 days (lower-upper quartile; 6-12) and 2 days (lower-upper quartile; 1-6), respectively (Mood’s median test, P = 0.001). Stratified Cox-regression proportional-hazards analysis of the propensity-matched population found that PCI patients experienced a higher adjusted 8-year mortality rate (hazard ratio 3.291, 95% confidence interval 1.776-6.101; P < 0.001). This trend was consistent amongst urgent cases of revascularization: patients with 3 or more vessels with coronary artery disease and patients where complete revascularization was achieved. Although sub-analyses found no difference between survival distributions of on-pump versus off-pump CABG (log-rank P = 0.726), both modes of CABG were superior to PCI (stratified log-rank P = 0.002).
CONCLUSIONS:
Despite a longer length of hospital stay, patients with impaired LVF requiring intervention for coronary artery disease experienced a greater post-procedural survival benefit if they received CABG compared to PCI. We have demonstrated this at 30 days, 90 days, 1 year, 3 years, 5 years and 8 years following revascularization. At present, CABG remains a superior revascularization modality to PCI in patients with poor LVF.
Using “Cerebral Organoids” to Trace the Elemental Composition of a Developing Brain
Curator: Marzan Khan, B.Sc
A research focused on the detection of micronutrient accumulation in the developing brain has been conducted recently by a team of scientific researchers in Brazil(1). Their study was comprised of a cutting-edge technology – human cerebral organoids, which are a close equivalent of the embryonic brain, in in-vitro models to identify some of the minerals essential during brain development using synchroton radiation(1). Since the majority of studies done on this matter have relied on samples from animal models, the adult brain or post-mortem tissue, this technique has been dubbed the “closest and most complete study system to date for understanding human neural development and its pathological manifestations”(2).
Cerebral organoids are three-dimensional miniature structures derived from human pluripotent stem cells that further differentiate into structures closely resembling the developing brain(2). Concentrating on two different time points during the developmental progression, the researchers illustrated the micronutrient content during an interval of high cell division marked on day 30 as well as day 40 when the organoids were starting to become mature neurons that secrete neurotransmitters, arranging into layers and forming synapses(2).
Synchrotron radiation X-ray fluorescence (SR-XRF) spectroscopy was used to discern each type of element present(2). After an incident beam of X-ray was directed at the sample, each atom emitted a distinct photon signature(2). Phosphorus (P), Potassium (P), Sulphur (S), Calcium (Ca), Iron (Fe), and Zinc (Zn) were found to be present in the samples in significant concentrations(2). Manganese (Mn), Nickel (Ni) and Copper (Cu) were also detected, but in negligible amounts, and therefore tagged as “ultratrace” elements(2). The distribution of these minerals, their concentration as well as their occurrence in pairs were examined at each interval(2).
Phosphorus was discovered to be the most abundant element in the cerebral organoid samples(3). Between the two time points at 30 days (cell proliferation) and 45 days (neuronal maturation) there was a marked decrease in P content(2). Since phosphorus is a major component of nucleotides and phospholipids, this reduction was clarified as a shift from a stage of cell division that requires the production of DNA and phospholipids, to a migratory and differentiation phase(2). Potassium levels were maintained during both phases, substantiating its role in mitotic cell division as well as cell migration over long distances(2). Sulfur levels were reportedly high at 30 days and 45 days(2). It was hypothesized that this element was responsible for the patterning of the organoids(2). Calcium, known to control transcription factors involved in neuronal differentiation and survival were detected in the micromolar range, along with zinc and iron(2). Zinc commits the differentiation of pluripotent stem cells into neuronal cells and iron is necessary for neuronal tissue expansion(2).
The cells in an embryo start to differentiate very early on- the neural plate is formed on the 16th day of contraception, which further folds and bulges out to become the nervous system (containing the brain and spinal cord regions)(3). Nutrients obtained from the mother are the primary sources of diet and energy for a developing embryo to fully differentiate and specialize into different organs(2). Lack of proper nutrition in pregnant mothers has been linked to many neurodegenerative diseases occurring in their progeny(2). Spina bifida which is characterized by the incomplete development of the brain and spinal cord, is a classic example of maternal malnutrition(2,4). Paucity of minerals in the diet of pregnant women are known to hamper learning and memory in children(2). Even Schizophrenia, Parkinson’s and Huntington’s disease have been associated to malnourishment(2). By showing the different types of elements present in statistically significant concentrations in cerebral organoids, the results of this study underscore the necessity of a healthy nourishment available to mothers during pregnancy for optimal development of the fetal brain(2).
2.Sartore RC, Cardoso SC, Lages YVM, Paraguassu JM, Stelling MP, Madeiro da Costa RF, Guimaraes MZ, Pérez CA, Rehen SK.(2017)Trace elements during primordial plexiform network formation in human cerebral organoids. PeerJ 5:e2927https://doi.org/10.7717/peerj.292
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