Soy protein reduces hepatic lipotoxicity in hyperinsulinemic obese Zucker fa/fa rats

Hepatic steatosis is commonly present during the development of insulin resistance, and it is a clear sign of lipotoxicity attributable in part to an accelerated lipogenesis. There is evidence that a soy protein diet prevents the overexpression of hepatic sterol-regulatory element binding protein-1 (SREBP-1), decreasing lipid accumulation. Therefore, the aim of the present work was to study whether a soy protein diet may prevent the development of fatty liver through the regulation of transcription factors involved in lipid metabolism in hyperinsulinemic and hyperleptinemic Zucker obese fa/fa rats. Serum and hepatic cholesterol and triglyceride levels, as well as VLDL-triglyceride and LDL-cholesterol, were significantly lower in rats fed soy protein than in rats fed a casein diet for 160 days. The reduction in hepatic cholesterol was associated with a low expression of liver X receptor-alpha and its target genes, 7-alpha hydroxylase and ABCA1. Soy protein also decreased the expression of SREBP-1 and several of its target genes, FAS, stearoyl-CoA desaturase-1, and delta5 and delta6 desaturases, decreasing lipogenesis even in the presence of hyperinsulinemia. Reduction in SREBP-1 was not associated with the presence of soy isoflavones. Finally, soy protein reduced SREBP-1 expression in adipocytes, preventing hypertrophy, which also helps prevent the development of hepatic lipotoxicity.