ACAT2 and human hepatic cholesterol metabolism: identification of important gender-related differences in normolipidemic, non-obese Chinese patients.

ACAT2 is a major cholesterol esterification enzyme specifically expressed in hepatocytes and may control the amount of hepatic free (unesterified) cholesterol available for secretion into bile or into HDL. This study aims to further elucidate physiologic roles of ACAT2 in human hepatic cholesterol metabolism. Liver biopsies from 40 normolipidemic, non-obese gallstone patients including some gallstone-free patients (female/male, 18/22) were collected and analyzed for microsomal ACAT2 activity, protein and mRNA expression. Plasma HDL-cholesterol (HDL-C) was significantly higher in females than in males, while triglycerides were significantly lower. ACAT2 activity in females was significantly lower than observed in males, regardless of the presence of gallstone disease. Moreover, the activity of ACAT2 correlated negatively with plasma levels of HDL-C (r=-0.57, P<0.05) and with Apo AI (r=-0.49, P<0.05). This is the first description of a gender-related difference in hepatic ACAT2 activity in normolipidemic non-obese Chinese patients suggesting a possible role for ACAT2 in the regulation of cholesterol metabolism in humans. The negative correlation between ACAT2 activity and HDL-C or Apo AI may reflect this regulation. Since ACAT2 activity generally has been found to be pro-atherogenic in animal models, the observed sex-related difference may contribute to female protection from complications of coronary heart disease (CHD).