Abstract
The effects of onion peel extract (OPE) in collagen (5 μg/mL)-stimulated washed rat platelet aggregation were investigated. OPE inhibited platelet aggregation via inhibition of aggregation-inducing molecules, intracellular Ca2+ and thromboxane A2 (TXA2) by blocking cyclooxygenase-1 (COX-1) and TXA2 synthase (TXAS) activities in a dose-dependent manner. In addition, OPE elevated the formation of cyclic adenosine monophosphate (cAMP), aggregation-inhibiting molecule, but not cyclic guanosine monophosphate (cGMP). High performance liquid chromatography (HPLC) analysis of OPE revealed that OPE contains quercetin, one of the major flavonoids, which has anti-platelet effect. In conclusion, we suggest that OPE is an effective inhibitor of collagen-stimulated platelet aggregation in vitro. Therefore, it can be a promising and safe strategy for anti-cardiovascular diseases.
Highlights
When normal blood vessels are damaged, platelets are activated by stimuli which are present in the walls of blood vessels, and induce aggregation (Nieswandt and Watson 2003)
We investigated that onion peel extract (OPE) has inhibitory effects on platelet-mediated thrombotic disorders via down-regulation of thromboxane A2 (TXA2) through reducing the [Ca2+]i, COX-1 and TXA2 synthase (TXAS) activities, as well as up-regulation of cyclic adenosine monophosphate (cAMP) levels in collagen-stimulated rat platelet aggregation without any toxicity in vitro
The half-maximal inhibitory concentration (IC50) of quercetin in collagen (5 μg/mL)-induced platelet aggregation was 6 μg/mL (32.0 ± 4.0%, n = 3, data not shown). These results show that anti-platelet effects of OPE is linked with quercetin as a main component, other two peaks were not unconfirmed (Figure 1)
Summary
When normal blood vessels are damaged, platelets are activated by stimuli which are present in the walls of blood vessels, and induce aggregation (Nieswandt and Watson 2003). In vitro and in vivo, onion has been concerned with anti-thrombotic effects by inhibiting platelet aggregation and activation (Kawakishi and Morimitsu 1988; Ali et al 1999; Moon et al 2000; Briggs et al 2001). While those studies have investigated the effects of anti-platelet aggregation of onion bulb extract, the signaling for anti-platelet effects of the outer skin extract of onion have been barely analyzed. We investigated that OPE has inhibitory effects on platelet-mediated thrombotic disorders via down-regulation of TXA2 through reducing the [Ca2+]i, COX-1 and TXAS activities, as well as up-regulation of cAMP levels in collagen-stimulated rat platelet aggregation without any toxicity in vitro
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