Abnormalities of serum apo A1 containing lipoprotein particles in patients with primary biliary cirrhosis

Abstract

Patients with primary biliary cirrhosis (PBC) do not appear to have an increased risk of cardiovascular disease despite elevations in serum cholesterol. Recent evidence has pointed to LpA1 (an apo A1 containing particle which contains apo A1 but not apo A2) in protecting against atherosclerosis. The aim of this study was to investigate apo A1 containing particles in the serum of patients with PBC. Lipids and apolipoproteins were measured in 31 patients with PBC (30 females) and 27 control subjects (26 females). Patients were divided into 3 groups: group 1 with bilirubin <18 μmol/l ( n=17); group 2 with bilirubin >18 μmol/l ( n=11); and group 3 with end stage liver disease (ESLD, n=3). As expected group 1 and 2 patients had higher total cholesterol, HDL cholesterol and phospholipids than control subjects. Apo B and apo A1 concentrations were similar to control subjects. However, LpA1 was greatly increased: 0.96 g/l (0.60–1.50), median (range) in group 1 and 1.09 g/l (0.75–1.33) in group 2 versus 0.62 g/l (0.45–0.93) for controls both P<0.005 and the percentage of total apo A1 in the LpA1 fraction was increased: 54.8% (37.9–63.4) in group 1 and 55.7% (47.8–73.7) in group 2 versus 36.8% (25.1–49.1) for controls, both P<0.005. Apo A2 concentration was reduced in group 1 0.38 g/l (0.30–0.51) and group 2 0.31 g/l (0.14–0.58) versus controls 0.43 g/l (0.36–0.57), P<0.05 and P<0.005 respectively. Patients with ESLD had reduced HDL cholesterol, apo A1, LpA1 and apo A2 compared to controls. These results suggest that PBC is associated with an altered distribution of apo A1 favouring an increased concentration of the protective LpA-I particles. Increased LpA1 concentration may be one of the factors contributing to the paradoxically low incidence of atherosclerosis in PBC patients.