Interactions between endothelial secretogogues

Phytochemical Analysis of Anti-atherogenic Constituents of Xue-Fu-Zhu-Yu-Tang Using HPLC-DAD-ESI-MS

Xue-Fu-Zhu-Yu-Tang is a famous traditional Chinese medicine (TCM) formula for treating cardiovascular disease and related ailments in China for centuries. To profile the phytochemical constituents of the formula, an HPLC-DAD-ESI-MS analytical method has been developed to separate and determinate the medium- or non-polar fraction of the decoction, which has been demonstrated potency to lower the serum total triglyceride concentration, strongly decrease the TXA(2)/PGI(2) ratio and attenuate production of proinflammatory cytokines in high cholesterol-fed rats. By comparing their retention time, UV and MS data with those obtained from the authentic compounds, ferulic acid (1), naringin (2), neohesperindin (3), naringenin (8), marmin (13), senkyunolide A (14), dehydrosafynol (16), safynol (17) and Z-ligustlide (18) are unequivocally determined. Moreover, additional thirteen compounds are tentatively identified as senkyunolide I (4), senkyunolide H (5), poncirin (7), benzoylpaeoniflorin (10), (Z)-6,7-epoxyligustilide (11), senkyunolide G (12), 2-methoxy-safynol (15), cnidilide (19), tangeritin (20), saikosaponin b(2) (21), 29-O-acetylsaikosaponin b(2) (22), saikosaponin b(1) (23) and auraptene (24), according to the comparison of their UV and MS data with the published data. The present study provides an approach to rapidly characterize bioactive constituents in TCM formulae.

eNOS 894T allele and coronary blood flow at rest and during adenosine-induced hyperemia

The 894T allele of a G894T polymorphism in the endothelial nitric oxide synthase (eNOS) gene is associated with decreased eNOS activity, cleavage of the protein, and endothelial dysfunction. The present study evaluated the association with coronary blood flow (CBF) at rest and during adenosine (ADO)-induced hyperemia. CBF was determined by Doppler flow wire and angiography in 97 left anterior descending arteries of individuals without coronary artery disease. At rest, average peak velocity (APV) was lower and coronary vascular resistance (CVR) was higher in homozygous carriers of the 894T allele than in heterozygotes and individuals without the 894T allele. CBF tended to be lower in eNOS 894T allele carriers. During ADO-induced hyperemia (18 microg ic), APV, CVR, and CBF were not statistically different between the genotypes. The reduced APV at rest in conjunction with an increased CVR indicates a vasomotor dysfunction related to an increased microvascular resting tone in eNOS 894T allele carriers.

Stroke: antithrombin versus antiplatelet therapy

The success of thrombolytic therapy for acute stroke has demonstrated that neurologic outcome can be improved with timely treatment. However, the severely restricted use of thrombolytics has reinforced the need to develop alternative and complementary therapies. Antithrombin and antiplatelet agents represent promising therapeutic approaches for stroke management. Antiplatelet therapy has modestly improved outcome in both acute stroke (aspirin) and in secondary stroke prevention (aspirin with or without dipyridamole; adenosine receptor antagonists), although bleeding and other adverse events associated with antithrombin therapy have largely negated their potential benefit. These findings have prompted innovative solutions to the pharmacokinetic and pharmacodynamic challenges that are crucial to advancing these strategies for acute, primary and secondary stroke therapy. Currently, inhibitors of the platelet surface glycoprotein IIb/IIIa (GP IIb/IIIa, fibrinogen) receptor are being examined in clinical trials while antithrombin therapies focus on thrombin antagonists and inhibitors as well as inhibitors of Factor Xa. Further advances in stroke treatment will include combination therapies. Additionally, the successful design of future drug therapies will result from a more complete understanding of the activity of these agents not only on platelet function and the coagulation cascade, but also for their effects on the endothelium and within the brain parenchyma. The sum of these activities will allow for the maintenance of cerebral blood flow, blood-brain barrier integrity and neuronal function.

Antiplatelet therapy in acute cerebral ischemia

BACKGROUND

Improved recognition of stroke signs and symptoms has paralleled the development of pharmacological strategies that may be examined to reduce stroke mortality and morbidity. Presently, tissue plasminogen activator is the only therapy that significantly improves outcome in acute stroke, with no agent demonstrating a significant reduction in mortality.

SUMMARY OF REVIEW

Antiplatelet agents are a heterogenous class of drugs that have been successfully used for more than 2 decades in secondary stroke prevention. These agents include aspirin, with or without dipyridamole, and more recently, the adenosine antagonists ticlopidine and clopidogrel. However, studies of the use of antiplatelet agents within 48 hours of the ictus have examined only aspirin. Only 1 study, the Multicentre Acute Stroke Trial-Italy (MAST-I), entered patients within 6 hours of the ictus. These data suggest that an improvement in mortality may be related to the speed of administration. No significant adverse events were noted with early antiplatelet monotherapy. However, MAST-I did note a significant increase in early mortality in patients receiving aspirin plus streptokinase, a finding not adequately explained by an increase in the intracranial hemorrhage rate.

CONCLUSIONS

The use of antiplatelet therapy in acute stroke, clinical or experimental, has only recently received attention. It is likely that the use of antiplatelet agents for acute stroke therapy will be less restrictive than that currently seen for thrombolytics. Future studies should include an examination of those agents that have previously demonstrated efficacy in secondary stroke prevention, most notably, aspirin. The recognition that all platelet stimuli share a final common pathway that is dependent on the surface glycoprotein IIb/IIIa (fibrinogen) receptor has resulted in the development of various agents which block this receptor and are currently the focus for clinical trials. The role of nitric oxide in stroke therapy will depend on minimizing the hypotensive side effects of this agent. Stroke models are needed to provide preliminary data on the efficacy of antiplatelet therapy, especially as relates to the interaction of antiplatelet agents with thrombolytics.

Effect of camonagrel, a selective thromboxane synthase inhibitor, on retinal vascularization in experimental diabetes

Platelet hyperactivity accompanied by an increased synthesis of thromboxane and/or a decreased prostacyclin production are important factors in ischemic diabetic retinopathy. We studied the effect of camonagrel and dazoxiben, two thromboxane synthase inhibitors, on retinal vascularization in a model of streptozotocin-induced diabetes in rats. Ten nondiabetic rats, 10 diabetic animals treated with saline (i.e., not treated), and 60 diabetic animals treated with dazoxiben or camonagrel (10, 50 or 100 mg kg(-1) day(-1) p.o.) were studied. All treatments lasted for 90 days. Dazoxiben and camonagrel produced a dose-dependent reduction in platelet aggregation and thromboxane synthesis. Dazoxiben increased prostacylin synthesis by 78% at 100 mg kg(-1) day(-1), and camonagrel by 154%. Dazoxiben increased retinal vascularity by 74%, and by 183% after camonagrel treatment. Prostacyclin synthesis showed a direct linear correlation with the degree of retinal vascularization (r2=0.6733, P < 0.00001). We conclude that an increased prostacyclin synthesis may have a greater influence than the inhibition of thromboxane synthesis in preventing ischemic diabetic retinopathy in experimental diabetes. Camonagrel may be an alternative treatment in the prevention of these lesions.

Nitric oxide reverses aspirin antagonism of t-PA thrombolysis in a rabbit model of thromboembolic stroke

Randomized trials of thrombolytic therapy in stroke have reported an improvement in neurologic outcome; however, the addition of aspirin has resulted in a significant increase in mortality and antagonism of clot lysis in clinical and animal studies, respectively. This finding is in contradistinction to the known synergy in mortality reduction for aspirin and thrombolytics in myocardial infarction. It is hypothesized that aspirin antagonism of clot lysis is related to inhibition of nitric oxide (NO) and may be reversed by providing a source of NO. Twenty rabbits were treated with aspirin (20 mg/kg, i.v.) prior to internal carotid clot embolization. One-half hour following embolization, rabbits were randomized to receive vehicle (n = 5), the NO precursor L-arginine (300 mg/kg, i.v. bolus at 0.5 and 2.5 h postembolus; n = 5), or a nitric oxide donor (nitroprusside, 1 mg/kg/h, i.a., or nitroglycerin, 10 microg/kg/min, i.v., n = 5 each agent). Tissue plasminogen activator (t-PA) (6.3 mg/kg) was administered from 1 to 3 h after embolization. Lysis of the tin-tagged clot was followed with serial X rays and gross examination. No rabbit in the control group experienced complete clot lysis. However, 2 of 5 rabbits in the L-arginine group and 6 of 10 rabbits in the nitric oxide donor (nitroprusside and nitroglycerin) groups noted complete clot lysis (P < 0.05, Fisher exact test). Thus, administration of an NO donor (nitroglycerin or nitroprusside) and, to a lesser extent L-arginine, reversed aspirin's antagonism of t-PA thrombolysis. This study may help explain the discrepant results seen with aspirin and thrombolytics.

Thrombolytic action of ticlopidine: possible mechanisms

Ticlopidine (Ticlide), an anti-platelet drug with a broad scope of clinical applications, is claimed to be an antagonist of adenosine diphosphate on platelet receptors. In vitro this antagonism cannot be demonstrated. Ex vivo it is detectable many hours after oral administration of the drug, perhaps subsequently to its biotransformation to an unknown metabolite. Here, we report for the first time that in patients with peripheral arterial disease and in cats with extracorporal circulation ticlopidine evokes instantaneous thrombolytic or fibrinolytic effects which are not associated with inhibition of platelet aggregation. Shortening of euglobulin clot lysis time and increase in plasma levels of tissue plasminogen activator were observed 1-2 h after oral ingestion of ticlopidine at a single dose of 500 mg. In cats ticlopidine produced instantaneous anti-thrombotic and thrombolytic effects at doses of 0.3-1 mg/kg and 10-15 mg/kg i.v., respectively. Thrombolysis by ticlopidine (10 mg/kg i.v.) was comparable to that by prostacyclin at a dose of 0.3 microgram/kg i.v. Ticlopidine at a concentration of 100 microM increased endothelial thromboresistance in vitro. The drug did not inhibit the activity of cyclooxygenase-1 or 12-lipoxygenase while it inhibited lipid autooxidation (IC50 = 18 microM) in rat liver microsomes. Our data point to a possibility that the therapeutic efficacy of ticlopidine might be associated not only with its delayed anti-platelet effects but also with its immediate thrombolytic action which is likely to be mediated by endothelial prostacyclin and tissue plasminogen activator rather than by platelet mechanisms.