Mechanism for lipid abnormalities of erythrocyte membranes in biliary obstruction: Lecithin content and its fatty acyl composition

Abstract

The lipid compositions of erythrocyte membranes, plasma and bile of 16 patients with biliary obstruction were analysed to obtain information regarding the origin of excess lecithin which is usually found in the erythrocyte membranes in obstructive jaundice. Phospholipids and free cholesterol were found to be increased proportionally to the degree of biliary obstruction with an elevation in the free cholesterol/phospholipid ratio in the red cell membranes. The increase in phospholipid content is primarily due to lecithin. There was a highly significant alteration in the fatty acid composition of lecithin of erythrocyte membranes, plasma and bile from patients with severe jaundice. Red cell membrane lecithin amounted to more than 40% of the total phospholipid in these patients. Interestingly, the fatty acid composition of lecithin showed a similar pattern in erythrocyte membranes, plasma and bile. In addition, the fatty acyi chain composition of lecithin in lipoprotein-X was very similar to that of the red cell membrane. Freeze-fracture electron microscopy showed an alteration in membrane morphology and a reduced number of membrane-associated particles in the fractured faces. From these findings, we suggest that the lecithin of lipoprotein-X is derived from abnormal bile lecithin, which is incorporated into erythrocyte membranes by fusion with lipoprotein-X. On the other hand, the fatty acid composition of bile lecithin from patients with mild jaundice, whose erythrocyte membrane lecithin amounted to less than 31% of total phospholipid, was not different from that of normal individuals. However, in sharp contrast to the bile content, the fatty acid composition of erythrocyte membranes and plasma in these same patients showed a similar but small change compared to that of patients with severe biliary obstruction. The red cells of patients with mild jaundice were almost normal, biconcave disc-shaped, as observed by scanning electron microscopy and no abnormalities in the distribution or number of membrane particles were detected by freezefracturing. We propose that the abnormal lecithin content of erythrocyte membranes in patientd with mild jaundice can be explained by the gradual exchange of lecithin between red blood cells and plasma lipoprotein.