Effects of Genistein on hepatic insulin signaling

Hepatic steatosis in the context of nonalcoholic fatty liver disease (NAFLD) is associated with insulin resistance. In our study we investigated the effects of genistein on insulin-responsive downstream targets in an in-vitro model of hepatic steatosis. Primary human hepatocytes and HuH-7 cells were treated with oleic and palmitic acid (2: 1 ratio, final concentration 0.5 mM) for 24h to induce an intracellular fat overaccumulation. Oilred O and SRB staining evaluated the in-vitro model of hepatic steatosis. Cells were treated with different concentrations of genistein (7.5 up to 90µM) with increased time (1 up to 36h) of incubation. Different experimental settings with insulin, glucose, estradiol, ICI182780, LY294002 and PD98059 were used to demonstrate pathways and to detect possible targets of genistein. Phosphorylation of IRS-2, Akt and ERK1/2 was detected by western blot. The mRNA expression of insulin receptor, GLUT-2, SREBP-1c, ChREBP and FOXO1 was measured by realtime-PCR.Primary human hepatocytes as well as HuH-7 cells treated with free fatty acids revealed a decreased phosphorylation of Akt and increased levels of SREBP-1c as an evidence of impaired insulin signaling. In addition 90µM genistein applied for 24 hours decreased insulin-induced phosphorylation of Akt but increased phosphorylation of ERK1/2. Furthermore, genistein decreased glucose output of hepatocytes via GLUT-2 transporter at high glucose concentration.Genistein impairs hepatic insulin signaling by inhibiting insulin-induced phosphorylation of Akt in a time and dose-dependent manner. Elevated activation of ERK1/2 is a possible mechanism whereby genistein lowers the lipid content in hepatic steatosis. It is likely that genistein modifies the carbohydrate metabolism via decreased gluconeogenesis and increased glucagon storage. Further studies are needed to elucidate the molecular mechanisms whereby genistein affects hepatic insulin resistance.

flavonoids - genistein - hepatic steatosis - insulin resistance - nonalcoholic fatty liver disease - phytoestrogens