Hexacosanol reduces plasma and hepatic cholesterol by activation of AMP-activated protein kinase and suppression of sterol regulatory element-binding protein-2 in HepG2 and C57BL/6J mice

Abstract

Policosanols have hypocholesterolemic activity; however, the molecular mechanism of the policosanol effects is currently poorly characterized. We hypothesized that hexacosanol, a policosanol compound derived from barley sprout, may decrease cellular and plasma cholesterol levels; we thus investigated the hypocholesterolemic activity and mechanism of hexacosanol on both hepatocytes and high-fat-induced obese C57BL/6J mice. The reduction of total cholesterol, free cholesterol, and cholesteryl ester concentrations was confirmed in hexacosanol-stimulated hepatocytes (-38%, -33%, and -53%, respectively). Plasma, hepatic cholesterol concentrations, and hepatic steatosis were significantly reduced in high-fat-fed mice orally administered with hexacosanol (0.7 mg/kg body weight a day) for 8 weeks compared with those of vehicle-fed control mice (-15% and -40%, respectively). Hexacosanol in fact bound to the allosteric regulation site of AMP-activated protein kinase (AMPK)-β subunit and thus activated AMPK that inhibited the activity of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase by inhibitory phosphorylation. In addition, activation of AMPK by hexacosanol induced hepatic autophagy activity, which could further reduce hepatic lipid accumulation. Alternatively, hexacosanol suppressed the nuclear translocation and activation of sterol regulatory element-binding protein-2 (SREBP-2), a key transcription factor in cholesterol biosynthesis. These results collectively suggest that hexacosanol is a major hypocholesterolemic compound in barley sprouts with regulation of AMPK activation and SREBP-2 suppression. These suppress 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase at both mRNA expression and protein activity levels. In conclusion, hexacosanol activates AMPK and hepatic autophagy and inhibits SREBP2, resulting in hypocholesterolemic activities and improvement of hepatic steatosis.

Keywords: AMPK; HMG-CoA reductase; Hexacosanol; Hypocholesterolemia; SREBP-2.