Fisetin, morin and myricetin attenuate CD36 expression and oxLDL uptake in U937-derived macrophages

Dietary flavonoid intake has been reported to be inversely associated with the incidence of coronary artery disease. To clarify the possible role of flavonoids in the prevention of atherosclerosis, we investigated the effects of some of these compounds, including fisetin, morin and myricetin, on the susceptibility of low-density lipoprotein (LDL) to oxidative modification and on oxLDL uptake in macrophages. The results demonstrated that fisetin had stronger inhibitory activity than the other two on inhibiting Cu2+-mediated LDL oxidation measured by thiobarbituric acid-reactive substances assay (TBARS), conjugated diene formation and electrophoretic mobility. The class B scavenger receptor, CD36, to which oxLDL binds, is present in atherosclerotic lesions. Treatment of U937-derived macrophages with myricetin (20 µM) significantly inhibited CD36 cell surface protein and mRNA expression (p < 0.01). Fisetin, morin and myricetin (20 µM) also reduced the feed-forward induction of CD36 mRNA and surface protein expression by PPARγ. The inhibition of CD36 by flavonols was mediated by interference with PPARγ activation thus counteracting the deleterious autoamplification loop of CD36 expression stimulated by PPARγ ligand. All three flavonols (10 and 20 µM) markedly decreased the uptake of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanide perchlorate (DiI)-labeled oxLDL uptake in U937-derived macrophages dose-dependently. Current evidences indicate that fisetin, morin and myricetin not only prevent LDL from oxidation but also block oxLDL uptake by macrophages at least in part through reducing CD36 gene expression on macrophages. In conclusion, flavonols may play a role in ameliorating atherosclerosis.