Rutin present in Alibertia edulis extract acts on human platelet aggregation through inhibition of cyclooxygenase/thromboxane.

Alibertia edulis leaf extract is commonly used in folk medicine, with rutin caffeic and vanillic acids being its major compounds. The Alibertia edulis leaf extract was investigated for its pharmacological effects via platelet aggregation, calcium mobilization, cyclic nucleotides levels, vasodilator-stimulated phosphoprotein Ser157 and Ser239 and protein kinase Cß2 phosphorylation, thromboxane B2, cyclooxygenases 1 and 2, docking and molecular dynamics. Alibertia edulis leaf extract significantly inhibited (100-1000 µg mL-1) platelet aggregation induced by different agonists. Arachidonic acid increased levels of calcium and thromboxane B2, phosphorylation of vasodilator-stimulated phosphoprotein Ser157 and Ser239, and protein kinase Cß, which were significantly reduced by Alibertia edulis leaf extract, rutin, and caffeic acid as well mixtures of rutin/caffeic acid. Cyclooxygenase 1 activity was inhibited for Alibertia edulis leaf extract, rutin and caffeic acid. These inhibitions were firsrtly explored by specific stabilization of rutin and caffeic acid compared to diclofenac at the catalytic site from docking score and free-energy dissociation profiles. Then, simulations detailed the rutin interactions close to the heme group and Tyr385, responsible for catalyzing the conversion of arachidonic acid to its products. Our results reveal the antiplatelet aggregation properties of Alibertia edulis leaf extract, rutin and caffeic acid providing pharmacological information about its origin from cyclooxygenase 1 inhibition and its downstream pathway.

Involvement of brain thromboxane A in hypotension induced by haemorrhage in rats.

1. In the present study, we aimed to determine the involvement of brain thromboxane A2 (TXA2) in blood pressure decreases evoked by acute and/or graded haemorrhage in rats. 2. Sprague-Dawley rats were used throughout the study. Acute haemorrhage was achieved by withdrawing a total volume of 2.1 and 2.5 mL blood/100 g bodyweight over a period of 10 min. A microdialysis study was performed in a hypothalamic area to measure extracellular TXA2 levels. Graded haemorrhage was conducted successively by withdrawing carotid arterial blood (0.55 mL/100 g bodyweight) over a 10 s period four times (S1-S4) at 5 min intervals. Furegrelate (125, 250 and 500 microg), a TXA2 synthase inhibitor, was injected intracerebroventricularly (i.c.v.) 60 min before acute or graded haemorrhage was initiated. U-46619 (0.5, 1 and 2 microg, i.c.v.), a synthetic TXA2 analogue, was administered 5 min before acute haemorrhage (2.1 mL/100 g bodyweight). 3. Acute haemorrhage produced a severe and long-lasting decrease in blood pressure and had a tendency to increase heart rate. Both haemorrhage protocols (2.1 or 2.5 mL/100 g) generated similar approximate twofold increases in extracellular hypothalamic TXA2 levels. Intracerebroventricular furegrelate (250 microg) pretreatment completely blocked the TXA2 increases induced by acute haemorrhage. Furegrelate administration (100, 250 and 500 microg, i.c.v.) attenuated the fall in arterial pressure evoked by acute haemorrhage and caused significant increases in heart rate at all doses injected. 4. Graded haemorrhage progressively lowered arterial pressure and increased plasma vasopressin and adrenaline levels in the last period. Furegrelate-injected rats were greatly resistant to the hypotensive effect of haemorrhage for all degrees of blood removed. Plasma adrenaline and vasopressin levels were significantly elevated in furegrelate-pretreated rats compared with the saline-treated group during S2-S3 and S4, respectively. U-46619 administration caused small but statistically significant decreases in arterial pressure induced by haemorrhage. 4. The results show that acute hypotensive haemorrhage increases extracellular hypothalamic TXA2 levels. The increase in brain endogenous TXA2 levels involves a decrease in blood pressure evoked by haemorrhage because the blockade of TXA2 synthesis by furegrelate pretreatment attenuated the haemorrhagic hypotension. Increases in plasma adrenaline and vasopressin levels may mediate this effect.