Comparative effects of dietary stigmasterol and oxidised stigmasterol on cholesterol absorption and metabolism in mice.

Dietary phytosterols exert hypocholesterolemic effects by inhibiting cholesterol absorption in the small intestine. However, oxidised phytosterols exert harmful effects. In this study, we compared the effects of dietary stigmasterol or oxidised stigmasterol (OS) on cholesterol absorption and metabolism in mice. Institute of Cancer Research (ICR) male mice were fed one of the following diets: a standard American Institute of Nutrition (AIN) diet; the standard diet plus 0·25 % cholesterol; the standard diet plus 0·25 % cholesterol and 0·25 % stigmasterol or the standard diet plus 0·25 % cholesterol and 0·25 % OS. Stigmasterol, but not OS, decreased plasma total cholesterol levels. Unlike stigmasterol, dietary OS increased the cholesterol levels in micellar solutions. Thus, OS could not exert hypocholesterolemic effects as it could not displace cholesterol in micellar solutions. In contrast, dietary OS downregulates the mRNA expression of genes involved in cholesterol synthesis and upregulates the mRNA expression of genes involved in cholesterol catabolism in mice fed cholesterol. In addition, dietary stigmasterol and OS increased the levels of faecal-neutral steroids by downregulating the mRNA expression of Niemann-Pick C1-like 1 protein (NPC1L1) in the small intestine. Dietary stigmasterol may directly regulate the mRNA expression of NPC1L1, whereas dietary OS may reduce the mRNA expression of sterol regulatory element-binding protein 2 and act as a Liver X receptor α agonist, reducing the mRNA expression of NPC1L1. Therefore, OS may affect cholesterol absorption and metabolism through a mechanism different from that of stigmasterol.