Biological Activities of Purple Rice Extract on Inhibition of Lipid Accumulation and Anti-Insulin Resistance in Fat Cells

Abstract

Rice (Oryza sativa L. indica) contains a variety of ingredients that provide benefits in prevention of many chronic diseases, including diabetes mellitus. Dysfunction of adipocytes triggers inflammation which impairs intracellular signaling of insulin leading to the insulin resistance and diabetes. Thus, this study was aimed to determine the effect of purple rice compared to brown rice on adipogenesis and the inflammation-induced insulin resistance in murine adipocyte (3T3-L1) cell line. Whole grain of three species of purple rice, Doisaket (DSK), Nan (NAN), Phayao (PYO) and unpolished white rice (RD6) were extracted using methanol and dichloromethane. The extracts were evaluated in 3T3-L1 cell line for cytotoxicity, adipocyte differentiation, fat deposition, and the suppression of insulin resistance induced by tumor necrosis factor  (TNF-α). Viability and proliferation of 3T3-L1 adipocyte was determined using WST-1 assay. Treatments with 5 - 200 μg/mL of rice extracts had no significant inhibitory effects on the cell viability, but slightly induced the cell proliferation. Dichloromethane extract of purple rice at the highest concentration (200 μg/mL) inhibited the preadipocyte differentiation, and prevented the lipid accumulation as detected by Oil-red O staining. Both extracts of RD6 showed the highest activities in anti-obesity of adipocyte. All rice extracts significantly improved the insulin-stimulated glucose uptake in a dose dependent manner. The methanol rice extracts were more effective than the dichloromethane rice extracts as they increased higher amount of glucose uptake into the insulin-resistant 3T3-L1 cells. Among the methanol rice extracts, NAN and RD6 were found to have the highest ability to enhance the glucose uptake. Moreover, all rice extracts, especially methanol extract of NAN could effectively reverse the TNF--induced lipolysis due to the less amounts of free glycerol release upon treatment with the rice extracts. Finally, this study clearly showed the anti-obesity and anti-insulin resistant effects of purple rice though less than that of brown rice in 3T3-L1 adipocyte.