Isolation and preliminary microheterogeneity studies of lecithin-cholesterol acyltransferase in plasma from individual patients infected with Schistosomiasis mansoni

Abstract

Lecithin-cholesterol acyltransferase (LCAT) is secreted by the liver into plasma where measurement of its catalytic activity is considered a sensitive serum test of hepatocyte synthetic capacity. The enzyme, a 68 kDa glycoprotein with a normal plasma concentration of ∼6 mg/l, contains four N-linked oligosaccharide chains which are reported to influence its activity. Because hepatic disease may result in serum glycoproteins with abnormal glycosylation patterns, we have developed a two-step procedure of immunoaffinity chromatography and high-performance liquid chomatography to isolate LCAT from plasma (1 ml) of individual subjects for subsequent characterization studies. Although patients infected with hepatosplenic schistosomiasis mansoni had half the normal plasma LCAT activity, the purified enzyme had a molecular mass indistinguishable from that of healthy subjects, as judged by SDS-PAGE and silver staining. However, in preliminary studies of microheterogeneity, isoelectric focusing revealed several acidic isoforms (pI 4.27–4.85) in patients which were reduced or absent in normal individuals. Whether such abnormal glycosylation of LCAT affects its catalytic activity and is a consistent feature of hepatosplenic schistosomiasis remains to be established.