| Summary: | 碩士 === 嘉南藥理科技大學 === 生物科技系暨研究所 === 95 === Atherosclerosis is a complex and chronic inflammatory disease. It is one of the primary causes of thrombosis, stroke and myocardial infraction. Oxidation of low density lipoprotein is a critical early stage in the pathogenesis of atherosclerosis. The earliest atherosclerotic lesion is the “fatty streak”, the intimal collections of lipid-laden macrophages and smooth muscle cells.
CD36, a class B scavenger receptor, is a macrophage recptor which binds native and oxidized low density lipoprotein (ox-LDL), and plays a critical role in atherosclerotic foam cell formation. On the other hand, the effect of ox-LDL on CD36 is due, in part, to its ability to activate the transcription factor, PPAR??n(peroxisome proliferator activated receptor-??. PPAR??nligands, such as 15dPGJ2 (15-deoxy??2,14-prostaglandin J2) also increase CD36 expression. Thus, inhibition of LDL oxidation and CD36 expression is one of the major issues in the prevention of initiation and progression of atherosclerosis
Flavonols are phenolic substances isolated from a wide range of plants. In this study, the anti-atherogenic mechanism of five flavonols, namely fisetin, kaempferol, morin, myricetin and quercetin, was investigated. In vitro experiments demonstrated that the five flavonols effectively inhibited MDA formation and LDL surface net charge change as well as notably delayed conjugated dienes synthesis during copper-induced LDL oxidation. Among them, quercetin and fisetin exhibited stronger antioxidant activity than the other flavonols.
Cell culture experiment was first employed in U937 cells to investigate the effects of flavonol treatment on PMA-stimulated cell differentiation. Flow cytometry analyses revealed that kaempherol (20 ?嵱) decreased the ratio of differentiated cells as compared with control (p<0.01); on the other hand, quercetin not only increased the ratio but also induce cell surface CD36 protein expression in non-differentiated cells. Fisetin (20 ?嵱) induced cell surface CD36 protein expression in both non-differentiated and differentiated cells (p<0.01).
In the next section, U937 monocytes were differentiated into macrophages before treated with flavols (20 ?嵱). It was found that cell surface CD36 protein expression was significantly inhibited by fisetin and myricetin (20 ?嵱) (p<0.05 and p<0.01, respectively) in U937-derived macrophages. RT-Q-PCR showed myricetin (20 ?嵱) significantly inhibited CD36 mRNA expression (p<0.01). Furthermore, when PPAR? was further activated by 15dPGJ2, fisetin, morin and myricetin markedly inhibited CD36 protein expression (p<0.05, p<0.05 and p<0.01, respectively). RT-Q-PCR showed that all five flavonols significantly inhibited 15dPGJ2-induced CD36 mRNA expression.
To further investigate whether flavonols directly inhibited PPAR? activation in U937-derived macrophages, the PPRE binding activity of nuclear extract was analyzed. It was found that only kaempherol and quercetin (20 ?嵱) significantly inhibited PPAR? activation (p<0.05 and 0.01). Finally, the ultimate effect of flavonols on form cell formation was investigated in U937-derived macrophages. All five flavonols (20 ?嵱) markedly decreased the uptake of DiI-oxLDL regardless of effect on CD36 expression.
In conlusion, consumption of food rich in flavonols may prevent atherosclerosis through their antioxidant and inhibitory activity on foam cell formation.
|
|---|
