Dietary cholesterol does not normalize low plasma cholesterol levels but induces hyperbilirubinemia and hypercholanemia in Mdr2 P-glycoprotein-deficient mice

Background/Aims: Mdr2 P-glycoprotein deficiency in mice (Mdr2(−/−)) leads to formation of cholesterol/cholesterol-depleted bile and reduced plasma HDL cholesterol. We addressed the questions: (1) does HDL in Mdr2(−/−) mice normalize upon phospholipid and/or cholesterol feeding, and (2): is the Mdr2(−/−) liver capable of handling excess dietary cholesterol. Methods: Male and female Mdr2(−/−) and Mdr2(+/+) mice were fed diets with or without additional phosphatidylcholine and/or cholesterol. Plasma, hepatic and biliary lipids as well as liver function parameters and expression of transport proteins involved in bile formation were analyzed. Results: Feeding excess phospholipids and/or cholesterol did not affect lipoprotein levels in Mdr2(+/+) or Mdr2(−/+) mice. Dietary cholesterol caused hyperbilirubinemia (male +100%; female +500%) and elevated plasma bile salts (male +200%; female +1250%) in Mdr2(−/−) mice only, independent of phospholipids. Bile flow nor biliary bile salt and bilirubin secretion were affected in cholesterol-fed Mdr2(−/−) mice. Elevated plasma bile salts may be related to cholesterol-induced reduction of hepatic Na+-taurocholate cotransporting protein expression in Mdr2(−/−) mice. Conclusion: Excess dietary phospholipids and cholesterol do not normalize low HDL associated with Mdr2 P-glycoprotein-deficiency. Induction of hyperbilirubinemia and hypercholanemia by dietary cholesterol in Mdr2(−/−) mice delineates the important role of biliary lipid secretion in normal hepatic functioning.