Figure 4.

Phytosterols regulate hepatic cholesterol metabolism. Cholesterol in the remnants of chylomicron enters the liver through the action of LDLR and LRP1, which is effectively inhibited by PS. The specific mechanism of phytosterol regulation of HMGCR, a key rate-limiting enzyme for cholesterol synthesis, is unclear. Cholesterol is converted to BAs in the liver by CYP7A1, and LXRα is an upstream regulatory gene of CYP7A1. PS can promote LXRα expression, but the regulatory role for CYP7A1 is controversial. VLDL produced by the liver can be converted to LDL-C in the blood vessels, and PS can decrease hepatic VLDL production to reduce circulating LDL-C levels. PS can also be secreted into the bile via ABCG5/8.