The effect of the flavonols quercetin and 3', 4' dihydroxyflavonol on platelet function in vitro and in vivo
Creators: name: Mosawy, Sapha
Publisher: name: RMIT University
Year: 2024

description: It is well established that platelets play an essential role in the development of cardiovascular disease and formation of vascular thrombosis particularly in diabetic patients. Studies have shown that consumption of dietary flavonols is associated with cardiovascular benefits. Flavonols are polyphenolic compounds with well documented antioxidant activity. The antiplatelet potential of the naturally occurring flavonol quercetin has been reported, but the antiplatelet mechanism is not fully elucidated. In addition to that, no studies have evaluated the antiplatelet potential of the structurally related synthetic flavonol 3’, 4’dihydroxyflavonol.<br><br>The primary aims of the studies undertaken for this thesis were to investigate the antiplatelet potential of Que and for the first time DiOHF, and to elucidate the antiplatelet mechanism<i> in vitro</i>. Furthermore, the effect of Que or DiOHF treatment on platelet function and thrombus formation in a model of <i>in vivo</i> platelet mediated arterial thrombosis in healthy and type-1 diabetic animal models were also investigated.<br><br>Accordingly, the specific aims of the first study described in Chapter three were to; determine the effects of Que or DiOHF on human platelet aggregation, dense and alpha granule exocytosis<i> in vitro</i>. Both Que and DiOHF showed a concentration dependent inhibition of platelet aggregation, and also inhibited agonist induced dense granule exocytosis. In contrast, while Que significantly inhibited alpha granule exocytosis, DiOHF did not produce significant inhibition.<br><br>The aim of the study undertaken in Chapter four was to investigate the effect of a single 6 mg/kg intravenous bolus, or daily intraperitoneal doses of 6 mg/kg of Que or DiOHF over 7 consecutive days, on thrombus formation in a well characterized mouse model of platelet mediated thrombosis, and murine platelet function<i> ex vivo</i>. Blood flow was reduced to zero for vehicle treated mice at 30 min following arterial injury for both treatments, while Que or DiOHF treated mice maintained significant blood flow for both treatment regimens. Improvement in blood flow corresponded to significant inhibition of platelet aggregation and dense granule exocytosis for both treatment regimens.<br><br>The aim of the study described in Chapter five was to investigate the effect of daily 6 mg/kg intraperitoneal doses of Que or DiOHF over 7 consecutive days on thrombus formation in a mouse model of type-1 diabetes, and murine platelet function <i>ex vivo</i>. Vehicle treated diabetic mice had 50% blood flow at 5 min, while diabetic mice treated with 6 mg/kg of Que or DiOHF significantly maintained blood flow at 30 min. Platelets derived from diabetic mice were hyper-aggregable when compared to the vehicle treated control mice. Platelet hyper-aggregability in diabetic mice was significantly reduced following treatment with Que or DiOHF. Furthermore, treatment with 6 mg/kg of Que or DiOHF significantly inhibited dense granule exocytosis as measured by quinacrine release in diabetic and control mice. In contrast, treatment with 6 mg/kg of Que or DiOHF did not produce inhibitory effect on alpha granule exocytosis in diabetic and control mice.<br><br>In conclusion, this thesis provides the first evidence of inhibition of platelet activation, aggregation and granule secretion by DiOHF. Furthermore, it demonstrates that Que and DiOHF have different potencies for inhibiting dense and alpha granules. This thesis also provides evidence of inhibition of platelet-mediated arterial thrombosis<i> in vivo</i> using different treatment regimens of these flavonols in both healthy and diabetic animal models mediated at least in part by inhibition of platelet function, and this effect persists for at least 24 hours after the last intraperitoneal dose. These data open the way for a potential clinical role for flavonols as anti-platelet therapy.