Growth arrest and apoptosis induced by quercetin is not linked to adipogenic conversion of human preadipocytes

Quercetin is involved in several biological activities including inhibition of cell growth and induction of apoptosis in cancer cells. However, it is unclear and unknown whether quercetin influences cell maturation. We examined the effect of quercetin on the growth and differentiation of human preadipocyte cells AML-I. Induced growth arrest of AML-I by quercetin was accompanied by the appearance of characteristics of apoptosis under the adipogenic stimulation by annexin V-fluorescein isothiocyanate staining method. A decrease of nuclear factor-kappaB and the antiapoptotic protein Mcl-1 and an increase of the proapoptotic protein Bad were observed in time-dependent fashion in the quercetin-treated cells compared with the vehicle-treated cells by Western blot analysis. Structure-related flavonoids, including rutin (quercetin-3-O-rutinoside) and quercitrin (quercetin-3-O-rhamnoside), did not have any cytotoxic effect on AML-I. Interestingly, exposure of AML-I to quercetin for 6 days increased the amount of cytoplasmic lipid droplets as well as the expression of fatty acid synthase and peroxisome proliferator-activated receptor gamma proteins. These results suggested that apoptosis induced by quercetin was not linked to adipogenic conversion of preadipocytes.