Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent evidence indicates that factors involved in the activation of the coagulation system eliciting an intracoronary thrombus may contribute importantly to arrhythmogenesis during acute myocardial ischemia. In the present study, the influence of the thrombin receptor activating peptide, SFLLRNPNDKYEPF (SFLL), on intracellular Na+ ([Na+]i) and tissue lysophosphatidylcholine (LPC) content during ischemia was investigated in an isolated, blood-perfused rabbit papillary muscle preparation. During normoxic perfusion, [Na+]i, determined by an intracellular Na(+)-selective electrode, was 11.6 +/- 0.2 mM (n = 14) in the presence of a physiological concentration of LPC (125 microM) bound to albumin (control group). The addition of SFLL (100 microM, n = 12) to the LPC-containing perfusate had no significant additional effects on [Na+]i, twitch tension, action potential duration, or tissue LPC content. During zero flow ischemia, [Na+]i in the control group rose to 15.5 +/- 1.4 mM (P < 0.05) at 6 min, whereas [Na+]i in the group treated with SFLL increased rapidly from the preischemic value of 11.7 +/- 0.3 to 23.5 +/- 1.9 mM (P < 0.01 compared with that in the control group) over the same time period. This rapid rise in [Na+]i was associated with a greater accumulation of tissue LPC, an arrhythmogenic lipid metabolite, and the development of early ventricular arrhythmias. These results indicate that an increase in [Na+]i induced by activation of the thrombin receptor, likely mediated through its effect on the accumulation of LPC within ischemic myocardium, may be responsible for arrhythmogenesis during myocardial ischemia secondary to activation of the coagulation system.
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PMID:Activation of thrombin receptor increases intracellular Na+ during myocardial ischemia. 773 78

Lysophosphatidylcholine (LPC) increases extracellularly during ischemia in vivo in both animals and man as judged by measurements from venous effluents, but more recent studies have shown little or no increase in buffer-perfused, isolated heart preparations. The appearance of LPC in blood and lymph in animals and in venous effluents in man in response to ischemia suggests a vascular site for the production of LPC. The present study was performed to assess whether thrombin could stimulate phospholipase A2 in endothelial cells and whether this would evoke an increase in and release of LPC. Endothelial cells were disassociated from canine aortas by incubating with 0.1% collagenase for 20 min. Cells were plated and allowed to grow to confluence. Measurement of LPC was performed using Bligh and Dyer extraction of lipids, high performance liquid chromatography separation, and quantification of LPC using a recently developed radiometric assay employing [3H]acetic anhydride. Incubation of endothelial cells with thrombin (0.05 unit/ml) resulted in a 2.5-fold increase in LPC to 2.3 +/- 0.1 nmol/mg of protein at 2 min (p < 0.01) and returned to control levels within 20 min. The increase in LPC induced by thrombin exhibited a concentration-dependent response with an ED50 = 0.04 unit/ml. A concentration-dependent increase in LPC was also elicited by stimulation with the peptide portion of the thrombin receptor's tethered ligand SFLLRNPNDKYEPF with an ED50 = 8 microM. The LPC produced was rapidly and completely released into the surrounding media. Hirudin completely blocked the thrombin-induced increase in LPC. Dansylarginine N-(3-ethyl-1,5-pentanediyl)amide (0.1 microM), which rapidly inactivates thrombin's proteolytic activity in situ without impairing binding, or phenyl-prolyl-arginyl-chloromethyl ketone (PPACK, 5 nM), which inactivates thrombin due to chemical alteration of the proteolytic site, each prevented the increase in LPC in response to thrombin. Stimulation of protein kinase C with phorbol 12-myristate-13-acetate (PMA, 1 microM) enhanced the response to thrombin. In contrast, staurosporine (100 nM), H7 (15 microM), or chronic treatment with PMA for 20 h to down-regulate protein kinase C completely prevented the increase in LPC in response to thrombin. Thus, thrombin stimulation of endothelial cells in vivo during ischemia may be a primary mechanism contributing to the marked increase in LPC extracellularly during ischemia.
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PMID:Thrombin-induced release of lysophosphatidylcholine from endothelial cells. 839 49

Reperfusion of globally ischemic rat hearts causes the generation of inositol(1,4,5)trisphosphate [Ins(1,4,5)P3] and the initiation of arrhythmias. These responses are mediated by alpha1-adrenergic receptors (ARs), but the subtype of receptor involved has not been identified. Under normoxic conditions, hearts from transgenic animals expressing constitutively active alpha1B-ARs in heart (alpha1B-constitutively active mutant [CAM]) showed higher [3H] inositol phosphate responses to norepinephrine (2.3-fold) than hearts from nontransgenic animals (alpha1B-WT) (1.6-fold). alpha1B-WT hearts responded to 2 minutes of reperfusion after 20 minutes of global ischemia by generation of Ins(1,4,5)P3 (5301+/-1310 to 11 413+/-1597 CPM/g tissue; mean+/-SEM; n=6; P<0.01 in [3H] labeling studies and 3.8+/-0.2 to 6.3+/-0.6 nmol/g by mass analysis, n=6; P<0.05). In contrast to findings in normoxia, hearts from alpha1B-CAM animals showed no Ins(1,4,5)P3 response in early reperfusion. In parallel studies, alpha1B-WT hearts developed ventricular tachycardia and ventricular premature beats (VPB) during 5 minutes of reperfusion after 20 minutes of ischemia. The incidence of these arrhythmias was reduced in the alpha1B-CAM hearts (95% to 62% for VPB and 47% to 12% for ventricular tachycardia; both P<0.05). The resistance of the alpha1B-CAM hearts was not due to alpha1B-AR-mediated preconditioning, as the Ins(1,4,5)P3 response to thrombin receptor activation during reperfusion was not different between the 2 groups. To investigate the possibility of reduced alpha1A-receptor activity in the alpha1B-CAM hearts, expression of the mRNA for alpha1A- and alpha1B-receptors was measured. alpha1B-WT hearts contained mRNA for both receptor subtypes, but the levels of alpha1B-receptor mRNA were 5-fold higher than alpha1A-receptor mRNA. alpha1B-CAM hearts contained very high levels of alpha1B-receptor mRNA (26-fold increase), but the expression of mRNA for the alpha1A-receptors (0.141+/-0.035 amol/ microg RNA; mean+/-SEM; n=6) was reduced by 50% relative to alpha1B-WT controls (0.276+/-0.046 amol/ microg RNA; n=6; P<0.01). The reduction in arrhythmogenic and Ins(1,4,5)P3 responses in alpha1B-CAM hearts provides evidence that these response are not mediated by alpha1B-receptors.
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PMID:Reduced reperfusion-induced Ins(1,4,5)P3 generation and arrhythmias in hearts expressing constitutively active alpha1B-adrenergic receptors. 985 40

We have considered the extracellular serine protease thrombin and its receptor as endogenous mediators of neuronal protection against brain ischemia. Exposure of gerbils to prior mild ischemic insults, here two relatively short-lasting occlusions (2 min) of both common carotid arteries applied at 1-day intervals 2 days before a severe occlusion (6 min), caused a robust ischemic tolerance of hippocampal CA1 neurons. This resistance was impaired if the specific thrombin inhibitor hirudin was injected intracerebroventricularly before each short-lasting insult. Thus, efficient native neuroprotective mechanisms exist and endogenous thrombin seems to be involved therein. In vitro experiments using organotypic slice cultures of rat hippocampus revealed that thrombin can have protective but also deleterious effects on hippocampal CA1 neurons. Low concentrations of thrombin (50 pM, 0.01 unit/ml) or of a synthetic thrombin receptor agonist (10 microM) induced significant neuroprotection against experimental ischemia. In contrast, 50 nM (10 units/ml) thrombin decreased further the reduced neuronal survival that follows the deprivation of oxygen and glucose, and 500 nM even caused neuronal cell death by itself. Degenerative thrombin actions also might be relevant in vivo, because hirudin increased the number of surviving neurons when applied before a 6-min occlusion. Among the thrombin concentrations tested, 50 pM induced intracellular Ca(2+) spikes in fura-2-loaded CA1 neurons whereas higher concentrations caused a sustained Ca(2+) elevation. Thus, distinct Ca(2+) signals may define whether or not thrombin initiates protection. Taken together, in vivo and in vitro data suggest that thrombin can determine neuronal cell death or survival after brain ischemia.
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PMID:The protease thrombin is an endogenous mediator of hippocampal neuroprotection against ischemia at low concentrations but causes degeneration at high concentrations. 1068 55

Our previous studies have shown that prior intracerebral infusion of a low dose of thrombin (thrombin preconditioning; TPC) reduces the brain edema that follows a subsequent intracerebral infusion of a high dose of thrombin or an intracerebral hemorrhage. In vitro studies have also demonstrated that low concentrations of thrombin protect neurons and astrocytes from hypoglycemia and oxidative stress-induced damage. This study, therefore, examines the hypothesis that TPC would offer protection from ischemic brain damage in vivo. This was a blinded design study. The rat brain was preconditioned with 1 U thrombin by direct infusion into the left caudate nucleus. Seven days after thrombin pretreatment, permanent middle cerebral artery occlusion (MCAO) was induced. Twenty-four hours post-ischemia, neurological deficit was evaluated and infarction volume, brain water and ion contents were measured. Compared to saline-treated rats, thrombin pretreatment significantly attenuated brain infarction in cortex (90+/-33 vs. 273+/-22 mm(3); P<0.05) and basal ganglia (56+/-17 vs. 119+/-12 mm(3); P<0.05) that followed 24 h of permanent MCAO. TPC also reduced the brain edema in cortex and basal ganglia by 50 and 53% (P<0.05). Neurological deficit was improved in thrombin pretreatment group (P<0.05). These effects of TPC were, in part, prevented by co-injection of hirudin, a thrombin inhibitor, indicating that the protection was indeed thrombin mediated. Cerebral TPC significantly reduces ischemic brain damage, perhaps by activation of the thrombin receptor. This finding provides a new mechanism by which to study ischemic tolerance.
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PMID:The effects of thrombin preconditioning on focal cerebral ischemia in rats. 1083 11

Microglia, brain resident macrophages, become activated in brains injured due to trauma, ischemia, or neurodegenerative diseases. In this study, we found that thrombin treatment of microglia induced NO release/inducible nitric-oxide synthase expression, a prominent marker of activation. The effect of thrombin on NO release increased dose-dependently within the range of 5-20 units/ml. In immunoblot analyses, inducible nitric-oxide synthase expression was detected within 9 h after thrombin treatment. This effect of thrombin was significantly reduced by protein kinase C inhibitors, such as Go6976, bisindolylmaleimide, and Ro31-8220. Within 15 min, thrombin activated three subtypes of mitogen-activated protein kinases: extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase/stress-activated protein kinase. Inhibition of the extracellular signal-regulated kinase pathway and p38 reduced the NO release of thrombin-treated microglia. Thrombin also activated nuclear factor kappaB (NF-kappaB) within 5 min, and N-acetyl cysteine, an inhibitor of NF-kappaB, reduced NO release. However, thrombin receptor agonist peptide (an agonist of protease activated receptor-1 (PAR-1)), could not mimic the effect of thrombin, and cathepsin G, a PAR-1 inhibitor, did not reduce the effect of thrombin. These results suggest that thrombin can activate microglia via protein kinase C, mitogen-activated protein kinases, and NF-kappaB but that this occurs independently of PAR-1.
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PMID:Thrombin induces NO release from cultured rat microglia via protein kinase C, mitogen-activated protein kinase, and NF-kappa B. 1089 7

Platelet activation is involved in the pathogenesis of cerebrovascular ischemia, but the major agonist involved has yet to be identified. To investigate the role of thrombin in platelet activation in patients with acute ischemic stroke, and while thrombin is the most likely candidate for activation of the thrombin receptor PAR-1 in vivo, we assessed its cleavage and internalization using the antibodies SPAN12, binding to uncleaved PAR-1, and WEDE15, recognizing cleaved and uncleaved, but not internalized PAR-1. In contrast to healthy age-matched controls, platelets from stroke patients exhibited significant cleavage and internalization of PAR-1 (P<0.001) and failed to respond to thrombin in vitro. Enhanced surface expression of CD62P, CD63, TSP-1 and less mepacrine uptake showed platelet degranulation during stroke. Platelets from patients with acute cerebral ischemia are exhausted and desensitized to thrombin through cleavage of PAR-1, indicating that high concentrations of thrombin occur with acute cerebrovascular ischemic events in vivo.
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PMID:Platelets in patients with acute ischemic stroke are exhausted and refractory to thrombin, due to cleavage of the seven-transmembrane thrombin receptor (PAR-1). 1496 Nov 62

Platelet-leukocyte conjugates are increased in patients with coronary artery disease but the relationship between conjugate formation and myocardial ischemic outcome is unknown. We prospectively evaluated the relationship between conjugate formation and the development of recurrent myocardial ischemia in patients with acute coronary syndromes (ACS). Platelet-leukocyte conjugate formation (induced by thrombin receptor activating peptide (TRAP)) and platelet aggregation (induced by ADP and arachidonic acid) were assessed in 30 patients with unstable angina or non-ST elevation myocardial infarction. All patients were treated with beta-blockers, aspirin, heparin, and GPIIb-IIIa antagonists and were followed for in-hospital recurrent myocardial ischemia. Troponin I and C-reactive protein (CRP) were also measured. Seven patients (23%) experienced recurrent ischemia. Platelet-neutrophil conjugates were greater in ischemic patients (59 +/- 9 and 36 +/- 4%, P = 0.007, for + ischemia and -ischemia, respectively). Platelet aggregation did not differ between ischemic and nonischemic patients, and there was no significant relationship between aspirin resistance and ischemic outcome. Troponin I was greater in patients who developed recurrent ischemia (3.04 +/- 1.73 vs. 0.70 +/- 0.21 ng/ml, P = 0.03, for +ischemia and -ischemia, respectively) but CRP was not. TRAP-induced platelet-neutrophil conjugate formation was an independent predictor of ischemic outcome (OR 1.07, 95% CI 1.00-1.15, for each 1% increase in conjugate formation). Receiver operator characteristic analysis showed platelet-neutrophil conjugates to have good ability to discriminate between ischemic and nonischemic patients (AUC of 0.84, P < 0.05). TRAP induced platelet-neutrophil conjugate formation is related to in vivo ischemic risk in ACS patients.
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PMID:Prospective evaluation of the relationship between platelet-leukocyte conjugate formation and recurrent myocardial ischemia in patients with acute coronary syndromes. 1498 71

Harnessing endogenous cardioprotectants is a novel therapeutic strategy to combat ischemia/reperfusion (I/R) injury. Thrombin causes I/R injury, whereas exogenous adenosine prevents I/R injury. We hypothesized that blocking thrombin receptor activation with a protease-activated receptor (PAR) 4 antagonist would unmask the cardioprotective effects of endogenous adenosine. The protective role of two structurally unrelated PAR4 antagonists, trans-cinnamoyl-YPGKF-amide (tc-Y-NH(2)) and palmitoyl-SGRRYGHALR-amide (P4pal10), were evaluated in two rat models of myocardial I/R injury. P4pal10 (10 microg/kg) treatment before ischemia significantly decreased infarct size (IS) by 31, 21, and 19% when given before, during, and after ischemia in the in vivo model. tc-Y-NH(2) (5 microM) treatment before ischemia decreased IS by 51% in the in vitro model and increased recovery of ventricular function by 26%. To assess whether the cardioprotective effects of PAR4 blockade were due to endogenous adenosine, isolated hearts were treated with a nonselective adenosine receptor blocker, 8-sulfaphenyltheophylline (8-SPT), and tc-Y-NH(2) before ischemia. 8-SPT abolished the protective effects of tc-Y-NH(2) but did not affect IS when given alone. Adenosine-mediated survival pathways were then explored. The cardioprotective effects of tc-Y-NH(2) were abolished by inhibition of Akt (wortmannin), extracellular signal-regulated kinase 1/2 [PD98059 (2'-amino-3'-methoxyflavone)], nitric-oxide synthase [N(G)-monomethyl-l-arginine (l-NMA)], and K(ATP) channels (glibenclamide). PD98059, l-NMA, and glibenclamide alone had no effect on cardioprotection in vitro. Furthermore, inhibition of mitochondrial K(ATP) channels [5-hydroxydecanoic acid (5-HD)] and sarcolemmal K(ATP) channels (sodium (5-(2-(5-chloro-2-methoxybenzamido)ethyl)-2-methoxyphenylsulfonyl)(methylcarbamothioyl)amide; HMR 1098) abolished P4pal10-induced cardioprotection in vivo. Thrombin receptor blockade by PAR4 inhibition provides protection against injury from myocardial I/R by unmasking adenosine receptor signaling and supports the hypothesis of a coupling between thrombin receptors and adenosine receptors.
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PMID:Inhibiting protease-activated receptor 4 limits myocardial ischemia/reperfusion injury in rat hearts by unmasking adenosine signaling. 1805 76

The "systemic inflammatory response" is a multifaceted defensive reaction of the body to surgical trauma and cardiopulmonary bypass (CPB), characterized by systemic activation of fibrinolysis, coagulation, complement, immune cells, platelets, and oxidative pathways, all overlaid onto localized trauma to the grafted vessel or vascular beds susceptible to ischemia/reperfusion. There is going to be no single magic bullet to diminish such a broad host defense response to surgery. The best chance lies with combinatorial--or promiscuous--pharmacotherapy. Combinations of anti-fibrinolytics, anti-coagulants targeted higher up the coagulation cascade, anti-thrombin receptor therapy, improved coated circuits, anti-complement, anti-leukocyte, and antioxidant therapies may blunt sufficient arms of the systemic inflammatory response to be clinically effective. The alternative is a promiscuous drug like aprotinin, which targets plasmin in the fibrinolytic pathway, kallikrein in the coagulation pathway, thrombin receptors on platelets and endothelium, and leukocytes at the extravasation step. Because of the overriding safety concerns relating to the use of anti-fibrinolytics in cardiothoracic surgery, any future combinatorial or promiscuous pharmacotherapy involving anti-fibrinolytics will require solid underpinning with a known mechanism of action and clinical safety data powered to detect well-defined adverse events (stroke, myocardial injury, renal failure requiring dialysis), preferably in isolation and not as a composite endpoint.
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PMID:Pharmacologic strategies for combating the inflammatory response. 1829 23


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