Metabolism of cholesterol and low- and high-density lipoproteins in primary biliary cirrhosis: cholesterol absorption and synthesis related to lipoprotein levels and their kinetics

Abstract

Cholesterol absorption, elimination, and synthesis, and low-density lipoprotein (LDL) and high density lipoprotein (HDL) kinetics were studied in patients with mild to severe primary biliary cirrhosis (PBC) (n = 16) to show how this cholestatic disease modified cholesterol and lipoprotein metabolism as compared with healthy controls (n = 50). Serum total and lipoprotein cholesterol and triglyceride levels were similar in the two groups, but in PBC, especially in severe forms, very low density lipoprotein (VLDL) was rich in apoprotein (apo) B and cholesterol and low in triglycerides, whereas LDL was rich in triglycerides and low in esterified cholesterol, and HDL was enriched by surface lipids, phospholipids, and free cholesterol. In severe PBC, the fractional catabolic rate (FCR) for LDL apo B was reduced. The transport rate (TR) for LDL apo B was unaffected and it tended to correlate with the LDL apo B and LDL cholesterol levels in PBC, whereas in the controls the LDL apo B concentration was regulated by both the FCR and TR, and LDL cholesterol was regulated only by FCR. FCR for apo A-I in HDL was unaltered in PBC, but TR for apo A-I was reduced in the severe cases. Cholesterol absorption efficiency was significantly reduced in PBC (14.5 ± 3.0% in severe PBC and 34.0 ± 2.5% in mild PBC vs. 47.4 ± 1.4% in the controls, respectively). Bile acid synthesis and cholesterol transport were significantly diminished in PBC, but, even in a case with severe PBC and low basal absorption efficiency and synthesis of cholesterol, lowering of LDL cholesterol by combined inhibition of hydroxymethyl-glutaryl-coenzyme A reductase and cholesterol absorption, removal of LDL apo B could still be upregulated. The significant interrelations between the LDL apo B level, cholesterol absorption efficiency and synthesis, and LDL apo B kinetics, observed in the controls, were lacking in PBC, suggesting that cholestasis and hepatic parenchymal cell dysfunction modified the relationship between cholesterol and lipoprotein metabolism so that treatment of hypercholesterolemia and bile acid-related itching might not be constantly successful.