Mixed hyperlipoproteinemia: Improvement in defective triglyceride removal with diet

The plasma lipoprotein composition of six patients with mixed hyperlipoproteinemia (MH) was investigated in a study of influence of apoprotein content and lipase activities on mechanisms of plasma triglyceride (TG) production and removal. Fasting blood samples were obtained initially and at monthly intervals following institution of a low fat, low carbohydrate, Type V diet. Lipoproteins were isolated by ultracentrifugation. The apolipoprotein (apo) content of chylomicrons and very low density lipoproteins was examined by isoelectric focusing. Total, hepatic, and lipoprotein lipase (LPL) were measured by radioassay, prior to and at the end of the three month study. Mean total and LPL activities increased significantly, 44% and 65% (p<0.05), with 45% increase in hepatic lipase. Mean TG levels decreased from 2535 to 1173 mg/dl. Apo E phenotypes were: E2/2 (1), E3/3 (2), and E4/3 (3). TG levels were correlated with hepatic lipase only in apo E4/3 patients (r=0.99). Apo C-III₂:apo C-total ratio (from gel scans) was increased in these hyperlipoproteinemic patients; and the ratio of LPL activator, C-II₁, to inhibitor, C-III₂, was correlated negatively with TG level (r=-0.62) in apo E4/3 patients. Apo C-II₂:apo C-total was correlated with TG only in the apo E4/3 patients. This data supports the hypothesis that a decrease in lipase activator:inhibitor is responsible in part for decreased removal of circulating TG in patients with MH and that effective diet enhances enzymatic removal.