Anti-Thrombotic Effects of Artesunate through Regulation of cAMP and PI3K/MAPK Pathway on Human Platelets.

Normal activation of platelets and their aggregation are crucial for proper hemostasis. It appears that excessive or abnormal aggregation of platelets may bring about cardiovascular diseases such as stroke, atherosclerosis, and thrombosis. For this reason, finding a substance that can regulate platelet aggregation or suppress aggregation will aid in the prevention and treatment of cardiovascular diseases. Artesunate is a compound extracted from the plant roots of Artemisia or Scopolia, and its effects have shown to be promising in areas of anticancer and Alzheimer's disease. However, the role and mechanisms by which artesunate affects the aggregation of platelets and the formation of a thrombus are currently not understood. This study examines the ways artesunate affects the aggregation of platelets and the formation of a thrombus on platelets induced by U46619. As a result, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) production were increased significantly by artesunate relative to the doses, as well as phosphorylated vasodilator-stimulated phosphoprotein (VASP) and inositol 1,4,5-trisphosphate receptor (IP3R), substrates to cAMP-dependent kinase and cGMP-dependent kinase, in a significant manner. The Ca2+, normally mobilized from the dense tubular system, was inhibited due to IP3R phosphorylation from artesunate, and phosphorylated VASP aided in inhibiting platelet activity via αIIb/ß3 platelet membrane inactivation and inhibiting fibrinogen binding. In addition, MAPK and PI3K/Akt phosphorylation was inhibited via artesunate in a significant manner, causing the production of TXA2 and intracellular granular secretion (serotonin and ATP release) to be reduced. Therefore, we suggest that artesunate has value as a substance that inhibits platelet aggregation and thrombus formation through an antiplatelet mechanism.

Effect of phospholipase C blockade on cerebral vasospasm.

BACKGROUND: Delayed cerebral ischemia due to cerebral vasospasm remains a major cause of morbidity and mortality following subarachnoid hemorrhage. Oxyhemoglobin (OxyHb) and vasoconstrictor prostanoids have been suggested as putative spasmogens. We have previously reported a synergistic vasoconstrictive action between thromboxane A(2) (TXA(2)) and OxyHb. In the present study we examine the effect of neomycin, a phospholipase C inhibitor, on the cerebral vasoconstriction induced by TXA(2) and OxyHb. METHODS: Using an in vitro tissue bath method, we assess the effect of neomycin in a concentration-dependent manner, on isolated porcine basilar arteries constricted by U-46619 (TXA(2) analogue) and OxyHb. RESULTS: The functional synergism between TXA(2) and OxyHb, leading to significant cerebral vasoconstriction, is attenuated in a dose-dependent manner by neomycin. CONCLUSION: Blockade of phospholipase C may provide an alternative strategy in the treatment of subarachnoid-hemorrhage-induced cerebral vasospasm.

Action of prostanoids on the emetic reflex of Suncus murinus (the house musk shrew).

Several prostanoids were investigated for a potential to induce emesis in Suncus murinus. The TP receptor agonist 11alpha,9alpha-epoxymethano-15S-hydroxyprosta-5Z,13E-dienoic acid (U46619) induced emesis at doses as low as 3 microg/kg, i.p. but the DP receptor agonist 5-(6-Carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl) hydantoin (BW245C) was approximately 1000 times less potent. The emetic action of U46619 (300 microg/kg, i.p.) was antagonized significantly by the TP receptor antagonist, vapiprost (P<0.05). EP (prostaglandin E(2), 17-phenyl-omega-trinor prostaglandin E(2), misoprostol and sulprostone), FP (prostaglandin F(2alpha) and fluprostenol) and IP (iloprost and cicaprost) receptor agonists failed to induce consistent emesis at doses up to 300-1000 microg/kg, i.p. Fluprostenol reduced nicotine (5 mg/kg, s.c.)-but not copper sulphate (120 mg/kg, intragastric)-induced emesis; the other inconsistently emetic prostanoids were inactive to modify drug-induced emesis. The results indicate an involvement of TP and possibly DP and FP receptors in the emetic reflex of S. murinus.

Inhaled nitric oxide potentiates actions of adenosine but not of sodium nitroprusside in experimental pulmonary hypertension.

Inhaled nitric oxide (NO), a selective pulmonary vasodilator, increases intracellular cyclic guanosine monophosphate. In contrast, adenosine, another selective pulmonary vasodilator, increases intracellular cyclic adenosine monophosphate. There has been only limited study on effects of inhaled NO combined with other pulmonary vasodilators. The current study examined the hypothesis that inhaled NO would potentiate in vivo pulmonary vasodilator effects of adenosine, but not those of sodium nitroprusside (SNP). Like inhaled NO, SNP acts via cyclic guanosine monophosphate. Rabbits were anesthetized and mechanically ventilated. The NO synthesis inhibitor NG-nitro-L-arginine methyl ester was administered. U46619, a thromboxane A2 mimetic, was infused to produce pulmonary hypertension. Rabbits then received either SNP at doses of 0.5, 1, 2, 4, 8, 16, and 32 microg/kg/min or adenosine at doses of 12.5, 25, 50, 100, 150, and 300 microg/kg/min. Hemodynamic measurements were obtained with or without inhaled NO (40 ppm) at each dose of SNP or adenosine. During U46619-induced pulmonary hypertension, inhaled NO decreased pulmonary artery pressure and pulmonary vascular resistance. Adenosine and SNP produced dose-related decreases in pulmonary artery pressure and pulmonary vascular resistance and increases in cardiac output. Inhaled NO decreased pulmonary artery pressure and pulmonary vascular resistance at all doses of adenosine, but had no significant pulmonary vasodilator effects at doses of SNP >0.5 microg/kg/min. We conclude that inhaled NO does not produce additional pulmonary vasodilation over that achieved at higher doses of SNP, but does produce additional vasodilation when combined with a vasodilator having different mechanisms of action. Since both inhaled NO and adenosine produce selective pulmonary vasodilation, such combination therapy may be effective in patients with pulmonary hypertension.

Selective pulmonary vasodilation induced by aerosolized zaprinast.

BACKGROUND: Zaprinast, an inhibitor of guanosine-3',5'-cyclic monophosphate (cGMP)-selective phosphodiesterase, augments smooth muscle relaxation induced by endothelium-dependent vasodilators (including inhaled nitric oxide [NO]). The present study was designed to examine the effects of inhaled nebulized zaprinast, alone, and combined with inhaled NO. METHODS: Eight awake lambs with U46619-induced pulmonary hypertension sequentially breathed two concentrations of NO (5 and 20 ppm), followed by inhalation of aerosols generated from solutions containing four concentrations of zaprinast (10, 20, 30, and 50 mg/ml). The delivered doses of nebulized zaprinast at each concentration (mean +/- SD) were 0.23 +/- 0.06, 0.49 +/- 0.14, 0.71 +/- 0.24, and 1.20 +/- 0.98 mg x kg(-1) x min(-1), respectively. Each lamb also breathed NO (5 and 20 ppm) and zaprinast (0.23 +/- 0.06 mg x kg[-1] x min[-1]) in combination after a 2-h recovery period. RESULTS: Inhaled NO selectively dilated the pulmonary vasculature. Inhaled zaprinast selectively dilated the pulmonary circulation and potentiated and prolonged the pulmonary vasodilating effects of inhaled NO. The net transpulmonary release of cGMP was increased by inhalation of NO, zaprinast, or both. The duration of the vasodilation induced by zaprinast inhalation was greater than that induced by NO inhalation. CONCLUSIONS: Aerosolization of a cGMP-selective phosphodiesterase inhibitor alone or combined with NO may be a useful noninvasive therapeutic method to treat acute or chronic pulmonary hypertension.