Genistein and metformin regulate glycerol kinase and the enzymes of glycerol 3-phosphate shuttle in a differential manner in myocytes, hepatocytes and adipocytes

Abstract

Glycerol kinase (GK) and glycerol 3-phosphate dehydrogenase (GPDH) are critical in glucose homeostasis. The role of genistein and metformin on these enzymes and glucose production was investigated in C2C12, HepG2, and 3 T3-L1 cells. Enzyme kinetics, Real-Time PCR and western blots were performed to determine enzyme activities and expressions of mRNAs and proteins. Glucose production and uptake were also measured in these cells. siRNAs were used to assess their impact on the enzymes and glucose production. Ki values for the compounds were determined using purified GK and GPDH. Genistein decreased GK activity by ~45 %, while metformin reduced cGPDH and mGPDH activities by ~32 % and ~ 43 %, respectively. Insignificant changes in expressions (mRNAs and proteins) of the enzymes were observed. The compounds showed dose-dependent alterations in glucose production and uptake in these cells. Genistein non-competitively inhibited GK activity (Ki 19.12 μM), while metformin non-competitively inhibited cGPDH (Ki 75.52 μM) and mGPDH (Ki 54.70 μM) activities. siRNAs transfection showed ~50 % and ~ 35 % decrease in activities of GK and mGPDH and a decrease in glucose production (0.38-fold and 0.42-fold) in 3 T3-L1 cells. Considering the differential effects of the compounds, this study may provide insights into the potential therapeutic strategies for type II diabetes mellitus.