UMLS:C0038454 - FACTA Search

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Query: UMLS:C0038454 (stroke)
147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of circulating platelets by exposed vessel wall collagen is a primary step in the pathogenesis of heart attack and stroke, and drugs to block platelet activation have successfully reduced cardiovascular morbidity and mortality. In humans and mice, collagen activation of platelets is mediated by glycoprotein VI (GPVI), a receptor that is homologous to immune receptors but bears little sequence similarity to known matrix protein adhesion receptors. Here we present the crystal structure of the collagen-binding domain of human GPVI and characterize its interaction with a collagen-related peptide. Like related immune receptors, GPVI contains 2 immunoglobulin-like domains arranged in a perpendicular orientation. Significantly, GPVI forms a back-to-back dimer in the crystal, an arrangement that could explain data previously obtained from cell-surface GPVI inhibition studies. Docking algorithms identify 2 parallel grooves on the GPVI dimer surface as collagen-binding sites, and the orientation and spacing of these grooves precisely match the dimensions of an intact collagen fiber. These findings provide a structural basis for the ability of an immune-type receptor to generate signaling responses to collagen and for the development of GPVI inhibitors as new therapies for human cardiovascular disease.
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PMID:Structural basis for platelet collagen responses by the immune-type receptor glycoprotein VI. 1686 47

At sites of vascular injury, platelets come into contact with the subendothelial extracellular matrix which triggers their activation and the formation of a hemostatic plug. This process is crucial for normal hemostasis, but may also lead to pathological thrombus formation causing diseases such as myocardial infarction or stroke. The initial capture of flowing platelets is mediated by the interaction of the glycoprotein (GP) Ib-V-IX complex with von Willebrand factor (vWF) immobilized on exposed collagens. This interaction allows the binding of the collagen receptor GPVI to its ligand and to initiate cellular activation, a process that is reinforced by locally produced thrombin and soluble mediators released from platelets. These events lead to the shift of beta1 and beta3 integrins on the platelet surface from a low to a high affinity state, thereby enabling them to bind their ligands and to mediate firm adhesion, spreading, coagulant activity, and aggregation. This review summarizes the most important structural and functional properties of these adhesion receptors and briefly discusses their potential as targets for antithrombotic therapy.
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PMID:Cell adhesion mechanisms in platelets. 1817 60

Several recent findings point to an important role for redox regulation of platelet responses to collagen involving the receptor, glycoprotein (GP)VI. First, the antioxidant dietary compound, quercetin, was shown to inhibit GPVI-dependent platelet activation and signaling responses to collagen. Second, collagen increased platelet production of the oxygen radical, superoxide anion (O2-), mediated by the multi-subunit enzyme nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidase. In that case, O2- was implicated in regulating not initial aggregation, but collagen-induced thrombus stabilization involving release of ADP. Third, our laboratory showed that an unpaired thiol in the GPVI cytoplasmic tail undergoes rapid oxidation to form GPVI homodimers following ligand binding, preceding GPVI signaling and ectodomain metalloproteolysis, and indicating formation of an oxidative submembranous environment in activated platelets. This review examines receptor/redox regulation in other cells, and relevance to the pathophysiological function of GPVI and other platelet receptors initiating thrombus formation in haemostasis or thrombotic diseases such as heart attack and stroke.
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PMID:Platelet receptor redox regulation. 1823 33

The role of platelets in hemostasis is to produce a plug to arrest bleeding. During thrombocytopenia, spontaneous bleeding is seen in some patients but not in others; the reason for this is unknown. Here, we subjected thrombocytopenic mice to models of dermatitis, stroke, and lung inflammation. The mice showed massive hemorrhage that was limited to the area of inflammation and was not observed in uninflamed thrombocytopenic mice. Endotoxin-induced lung inflammation during thrombocytopenia triggered substantial intra-alveolar hemorrhage leading to profound anemia and respiratory distress. By imaging the cutaneous Arthus reaction through a skin window, we observed in real time the loss of vascular integrity and the kinetics of skin hemorrhage in thrombocytopenic mice. Bleeding-observed mostly from venules-occurred as early as 20 minutes after challenge, pointing to a continuous need for platelets to maintain vascular integrity in inflamed microcirculation. Inflammatory hemorrhage was not seen in genetically engineered mice lacking major platelet adhesion receptors or their activators (alphaIIbbeta3, glycoprotein Ibalpha [GPIbalpha], GPVI, and calcium and diacylglycerol-regulated guanine nucleotide exchange factor I [CalDAG-GEFI]), thus indicating that firm platelet adhesion was not necessary for their supporting role. While platelets were previously shown to promote endothelial activation and recruitment of inflammatory cells, they also appear indispensable to maintain vascular integrity in inflamed tissue. Based on our observations, we propose that inflammation may cause life-threatening hemorrhage during thrombocytopenia.
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PMID:Inflammation induces hemorrhage in thrombocytopenia. 1846 3

In ischemic stroke, treatment options are limited. Therapeutic thrombolysis is restricted to the first few hours after stroke, and the utility of current platelet aggregation inhibitors, including GPIIb/IIIa receptor antagonists, and anticoagulants is counterbalanced by the risk of intracerebral bleeding complications. Numerous attempts to establish neuroprotection in ischemic stroke have been unfruitful. Thus, there is strong demand for novel treatment strategies. Major advances have been made in understanding the molecular functions of platelet receptors such as glycoprotein Ib (GPIb) and GPVI and their downstream signaling pathways that allow interference with their function. Inhibition of these receptors in the mouse stroke model of transient middle cerebral artery occlusion prevented infarctions without increasing the risk of intracerebral bleeding. Similarly, it is now clear that the intrinsic coagulation factor XII (FXII) and FXI play a functional role in thrombus formation and stabilization during stroke: their deficiency or blockade protects from cerebral ischemia without overtly affecting hemostasis. Based on the accumulating evidence that thrombus formation and hemostasis are not inevitably linked, new concepts for prevention and treatment of ischemic stroke may eventually emerge without the hazard of severe bleeding complications. This review discusses recent advances related to antithrombotic strategies in experimental stroke research.
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PMID:Molecular mechanisms of thrombus formation in ischemic stroke: novel insights and targets for treatment. 1867 80

Platelets are essential for wound healing and inflammatory processes, but can also play a deleterious role by causing heart attack and stroke. Normal platelet activation is dependent on tetraspanins, a superfamily of glycoproteins that function as 'organisers' of cell membranes by recruiting other receptors and signalling proteins into tetraspanin-enriched microdomains. However, our understanding of how tetraspanin microdomains regulate platelets is hindered by the fact that only four of the 33 mammalian tetraspanins have been identified in platelets. This is because of a lack of antibodies to most tetraspanins and difficulties in measuring mRNA, due to low levels in this anucleate cell. To identify potentially platelet-expressed tetraspanins, mRNA was measured in their nucleated progenitor cell, the megakaryocyte, using serial analysis of gene expression and DNA microarrays. Amongst 19 tetraspanins identified in megakaryocytes, Tspan9, a previously uncharacterized tetraspanin, was relatively specific to these cells. Through generating the first Tspan9 antibodies, Tspan9 expression was found to be tightly regulated in platelets. The relative levels of CD9, CD151, Tspan9 and CD63 were 100, 14, 6 and 2 respectively. Since CD9 was expressed at 49000 cell surface copies per platelet, this suggested a copy number of 2800 Tspan9 molecules. Finally, Tspan9 was shown to be a component of tetraspanin microdomains that included the collagen receptor GPVI (glycoprotein VI) and integrin alpha6beta1, but not the von Willebrand receptor GPIbalpha or the integrins alphaIIbbeta3 or alpha2beta1. These findings suggest a role for Tspan9 in regulating platelet function in concert with other platelet tetraspanins and their associated proteins.
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PMID:Identification of Tspan9 as a novel platelet tetraspanin and the collagen receptor GPVI as a component of tetraspanin microdomains. 1879 91

TREATMENT OF ARTERIAL HYPERTENSION - Blood pressure (BP) should be regularly measured in all patients with CKD (Strength of Recommendation C). - BP control and proteinuria reduction delay progression of CKD (Strength of Recommendation A) and reduce cardiovascular risk (Strength of Recommendation C). Thus, control of both factors should be the treatment objective. - The BP target in patients with CKD should be < 130/80 mmHg, and 125/75 mmHg if proteinuria is > 1 g/24 hours (Strength of Recommendation A). - Lifestyle changes should be made: low-sodium diet (less than 100 mEq/day of sodium or 2.4 g/day of salt); weight reduction if patient is overweight (body mass index 20-25 kg/m2); regular aerobic physical exercise and moderate alcohol intake for BP control and prevention of cardiovascular risk (Strength of Recommendation A). - The choice of the antihypertensive drug in patients with CKD depends on the etiology of CKD, cardiovascular risk, or presence of clinical or subclinical cardiovascular disease (Strength of Recommendation A). - Two or more antihypertensive drugs are usually required to control blood pressure in patients with CKD (Strength of Recommendation B), and will frequently include a diuretic, which in stages 4-5 should be a loop diuretic (Strength of Recommendation B). - Renin-angiotensin-aldosterone system (RAAS) inhibitors are first choice drugs in patients with diabetic nephropathy, patients with non-diabetic nephropathy with a protein/creatinine ratio higher than 200 mg/g, and patients with heart failure (Strength of Recommendation A). The combination of ACEIs and ARBs is indicated for reducing proteinuria that remains high despite treatment with a RAAS inhibitor, provided potassium levels do not exceed 5.5 mEq/L (Strength of Recommendation B). - When RAAS blockers are started or their dose is changed in patients with advanced CKD, kidney function and serum potassium levels should be monitored at least after 1-2 weeks. DIAGNOSIS AND TREATMENT OF DYSLIPIDEMIA - A complete evaluation of the lipid profile including total cholesterol, LDL-C, HDL-C, and triglycerides should be performed in any patient with CKD at baseline and at least annually (Strength of Recommendation B). - In patients with stage 4-5 CKD and LDL-C >or= 100 mg/dL, treatment to decrease levels to < 100 mg/dL should be considered because of their high CV risk. This reduction is recommended in secondary prevention and in primary prevention in diabetic patients. Lipid-lowering treatment is recommended in all other patients, although no evidence showing its benefits is available yet (Strength of Recommendation C). - In patients with stage 4-5 CKD and triglyceride levels >or= 500 mg/dL which are not corrected by treating the underlying cases, treatment with triglyceride-lowering drugs may be considered to reduce the risk of pancreatitis. However, treatment with fibrates should be used with caution, and these drugs should not be associated to statins due to the risk of rhabdomyolysis (Strength of Recommendation C). There is little experience on the efficacy and safety of omega-3 fatty acids for the treatment of hypertriglyceridemia in patients with grade 4-5 CRF, but they may be considered a possibly safer alternative to fibrates (Strength of Recommendation C). SMOKING - Smoking is a cardiovascular risk factor and a risk factor for progression of kidney disease in patients with CRF (Strength of Recommendation B). - Use of active measures to achieve smoking cessation is recommended in patients with CRF (Strength of Recommendation C). HOMOCYSTEINE - Hyperhomocysteinemia has been postulated as a cardiovascular risk factor in the general population and in kidney patients, but the available evidence is not consistent. - There is no evidence that vitamin therapy decreases cardiovascular risk in patients with CRF, and recommendation of routine vitamin measurement and start of vitamin therapy to reduce cardiovascular risk in these patients is therefore questionable (Strength of Recommendation B). LEFT VENTRICULAR HYPERTROPHY - Left ventricular hypertrophy (LVH) is a cardiovascular risk factor in patients with CRF (Strength of Recommendation B). - It is advisable to perform an echocardiogram at baseline and every 12-24 months and to consider treatments allowing for LVH regression (Strength of Recommendation C). The approach to LVH should be early and multifactorial because its reversibility is limited once established (Strength of Recommendation C). - RAAS blockade with ACEIs or ARBs partially reverts LVH in patients with CRF (Strength of Recommendation B). ANTI-PLATELET AGGREGATION - Because of the high cardiovascular risk in patients with CKD, anti-platelet aggregant therapy, especially low-dose aspirin, would be indicated in patients with type 2 diabetes as primary prevention, and in all patients with CKD as secondary prevention. There is however no evidence of the benefits of anti-platelet aggregant therapy in primary prevention in patients with CKD, particularly in stages 4-5; indication for treatment in this situation should therefore be individualised because of its greater risk of bleeding. - Adequate good blood pressure control should previously be achieved to minimise the risk of haemorrhagic stroke (Strength of Recommendation C).
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PMID:[Arterial hypertension and dyslipidemia in patients with chronic kidney disease (CKD). Anti-platelet aggregation. Goal oriented treatment]. 1901 37

We studied the effect of prophylactic aspirin (ASA) ingestion on platelet function in 463 patients with stroke, transient ischemic attack (TIA) or acute coronary disease (ACD), using the Platelet Function Analyzer-100 (PFA-100). We correlated ASA responsiveness with haplotypes of seven candidate genes, selected for their documented role in platelet function, namely, the genes for integrins alpha2beta1and alphaIIbbeta3 (ITGA2, ITGA2B, and ITGB3), platelet glycoproteins Ibalpha and VI (GPIBA and GP6), the purinergic receptor P2Y1 (P2RY1), and prostaglandin H synthase 1 (PTGS1 = COX1). Non-responsiveness to ASA was defined as the failure of prior ASA ingestion to prolong the PFA-100 closure time (CT) when blood was perfused through cartridges coated with collagen plus epinephrine (CEPI-CT). ASA non-responsiveness was observed in 114 of 463 patients (24.6 %), but was not associated with haplotypes of any of the seven candidate genes. There was also no association between any haplotypes and the CT when blood was perfused through cartridges coated with collagen plus ADP (CADP-CT). The ASA non-responsive cohort had significantly increased whole blood platelet counts (p = 0.03) and plasma von Willebrand Factor antigen levels (p < 0.001), which likely contributes to resistance to the inhibitory effects of ASA in the PFA-100.
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PMID:Lack of association between aspirin responsiveness and seven candidate gene haplotypes in patients with symptomatic vascular disease. 1913 98

Coronary artery disease, stroke, and peripheral vascular disease are known as "atherothrombotic" manifestations of atherosclerosis. These devastating conditions remain the major contributor of mortality and disability in a modern Western world, with estimated direct and indirect cost for 403.1 billion dollars in the United States alone. The application of current evidence-based therapy including the administration of low-dose aspirin and standard of care with clopidogrel proved to exhibit absolute mortality reduction in the randomized clinical trials International Study for Infarct Survival and Clopidogrel and Metoprolol in Myocardial Infarction Trial among patients after acute vascular events. However, these established antiplatelet medications have certain shortcomings including lack of efficacy in some patients, significant response variability, and potential "resistance." Therefore, intelligent development of novel oral antiplatelet agents is difficult to underestimate. In this review, we will focus on the developmental efforts with regard to the experimental agents such as adenosine diphosphate receptor blockers (prasugrel, ticagrelor, and cangrelor) and platelet glycoprotein VI adhesion antagonist [ProCorde GmbH 15 (PR-15)].
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PMID:Novel antiplatelet agents in development: prasugrel, ticagrelor, and cangrelor and beyond. 1926 62

In the past 5 years, metalloproteinase-mediated ectodomain shedding of platelet receptors has emerged as a new mechanism for modulating platelet function. By regulating surface expression of the platelet-specific receptors, glycoprotein (GP)VI that binds collagen, and GPIbalpha (the major ligand-binding subunit of the GPIb-IX-V complex) that binds von Willebrand factor (VWF) and other procoagulant and proinflammatory ligands, shedding not only irreversibly downregulates GPVI/GPIbalpha function, but generates proteolytic fragments that might be unique biomarkers or modulators in plasma. This is potentially significant because GPVI and GPIbalpha are involved in initiating thrombotic diseases such as heart attack and stroke, as well as autoimmune diseases where anti-platelet antibodies result in thrombocytopenia. Altered expression levels of GPIbalpha/GPVI are associated with both thrombotic propensity and platelet aging, suggesting an additional role in platelet clearance. Although emerging data are elucidating molecular mechanisms underlying GPIbalpha/GPVI shedding, evidence for the functional consequences of shedding in vivo, either clinically or in animal models, is far more limited. Here we consider recent published evidence for GPVI or GPIbalpha shedding in humans, nonhuman primates and mice, and whether conservation of sheddase cleavage sites across species points to a functional role for metalloproteolytic shedding in vivo.
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PMID:Proteolysis of platelet receptors in humans and other species. 2048 12

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