| Paeoniflorin (PF) is a characteristic monoterpene glucoside purified from the root of Paeonia lactiflora, and it was thought to be the main effective compounds in the extracts of Paeonia lactiflora. Therefore, the pharmacological study of this compound is greatly highlightedned. Many studies indicated that PF exhibits several pharmacological actions including anti-inflammatory and anti-allergic effects, cognitive enhancement, antihyperglycemic effects, analgesic effect, anti-hypotension effect, etc. However, little study has been carried out to investigate the effect of PF on thrombosis and endothelium protection and their related mechanism. In this study, We evaluated the anti-thrombosis effect in vivo. Furthermore, the related mechanism was investigated through cultured vascular endothelial cells, including the metabolism of arachidonic acid, secretion factors, cell metabolism activity and cell adhesion, etc.The anti-thrombotic effect of PT was evaluated in photochemical reaction microvessel thrombosis model of rats in vivo, and results indicated PF could significantly prolong mean thromobosis time and the effect was concentration-related, when HUVECs were treated with PF , t-PA activity in the culture medium was increased significantly. Furthermore, PF decrease prostacyclin production in culture medium of HUVECs and thromboxane A2 production in platelet. However, no significant effect was observed on PAI activity and vWF production. These results showed that PF can inhibit the metabolism of arachidonic acid.In order to demonstrate the protective effect of endothelial cells damage induced by photochemical reaction and H2O2, the LDH and metabolism activity of cultured endothelial cells was detected. The results indicated that PF have dose-dependent protective effects against these stimi. Besides, the necrosis percent, which was induced by H2O2 and was detected by flow cytometry, was decreased greatly after cells was pretreated by different concentration of PF. The effect was related to the inhibition of intracellular calcium increase, which was detected by laser confocal scan microscope. Moreover, PF can inhibit the increase of NO production and intracellularcalcium induced by bradykinin, and the effects were concentration related. The results showed that the protective effects of PF are partly related to the inhibition of calcium overload.PF could inhibit the ahesion between endothelial cells and HL-60 in static adhesion model. And the expression of ICAM-1 and E-SELECTIN on the membrane of endothelial cells induced by LPS were significantly inhibited by different concentration of PF. Based on the model detecting the adhesion between platelets and leukocytes in whole blood used by flow cytometry, the inhibitory effects of PF were demonstrated after the whole blood was stimulated by ADP.Based on above results, it is reasonable to draw conclusion as below. (1) PF can inhibit the metabolism of arachidonic acid, because both of TXAa and PG^ are the metabolism products of arachidonic acid. It is indicated that cyclo-oxygenase enzyme should be the acting site of PF, and TXA2 synthesisase could be another acting site (2) PF exhibited its anit-oxidation and anti-oxygen free radical effect against the damage of endothelial cells induced by photochemical reaction and HjC^. The effect was related to the inhibition of calcium overlaod, and PF could be a free radical scaverger which can clean superoxide and hydroxy radica directly. (3) PF can inhibit the adhesion between leukocytes and endothelial cells and the adhesion between leukocytes and platelets. It should be a passway through which PF exert its anti-thrombosis effect and anti-inflammation effect. Although the related mechanism remains unclear, it is hypothesized that the inhibition of LBT4 synthesis and intracellular calcium increase may be involved.
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