Hepatic ABCG5/G8 overexpression substantially increases biliary cholesterol secretion but does not impact in vivo macrophage-to-feces RCT

• Biliary cholesterol secretion is important for reverse cholesterol transport (RCT).
• Hepatic ABCG5/G8 contributes most of the mass cholesterol secreted into bile.
• Hepatic ABCG8 expression was modulated from knockout to high level overexpression.
• Despite major ABCG8-dependent changes in biliary cholesterol, RCT was unaltered.
• Increasing liver ABCG5/G8 for enhancing RCT is unlikely to be a successful strategy.

Background and aimsBiliary cholesterol secretion is important for reverse cholesterol transport (RCT). ABCG5/G8 contribute most cholesterol mass secretion into bile. We investigated the impact of hepatic ABCG5/G8 on cholesterol metabolism and RCT.MethodsBiliary and fecal sterol excretion (FSE) as well as RCT were determined using wild-type controls, Abcg8 knockout mice, Abcg8 knockouts with adenovirus-mediated hepatocyte-specific Abcg8 reinstitution and hepatic Abcg5/g8 overexpression in wild-types.ResultsIn Abcg8 knockouts, biliary cholesterol secretion was decreased by 75% (p < 0.001), while mass FSE and RCT were unchanged. Hepatic reinstitution of Abcg8 increased biliary cholesterol secretion 5-fold (p < 0.001) without changing FSE or overall RCT. Overexpression of both ABCG5/G8 elevated biliary cholesterol secretion 5-fold and doubled FSE (p < 0.001) without affecting overall RCT.ConclusionsABCG5/G8 mediate mass biliary cholesterol secretion but not from a RCT-relevant pool. Intervention strategies aiming at increasing hepatic Abcg5/g8 expression for enhancing RCT are not likely to be successful.