The lipoproteins and lipid transport in abetalipoproteinemia.

Abstract

The lipoproteins in the plasma of 6 patietns with abetalipoproteinemia have been studied. Antisera were employed to characterize the lipoproteins of D<1. 21. The relative amino acid content and amino-terminal amino acid composition of the high and low density lipoprotein proteins were also determined. In plasma lipoproteins concentrated greater than 8-fold, no trace of material having the antigenic properties of beta-lipoprotein was detected in any of the 6 patients. Examination was extended to lipoprotein concentrates raised up to 8-fold higher than the plasma concentration. Alpha-lipoproteins were the only lipoproteins present. Five to 25% of these floated at D<1. 63, and more than 1/2 were isolated between D <1. 063 and 1.1. The protein portions of all these lipoproteins were immunochemically identical and had amino acid patterns indistinguishable from those in normal alpha-lipoproteins. The abnormal shift in density were considered likely due to excessive lipid loading of normal alpha-lipoproteins. The abnormally low plasma glycerides of these patients were unchanged, and no pre-beta (very low density) lipoproteins were produced by diets that regularly induce hyperglyceridemia in normal subjects and patients with alpha-lipoprotein deficiency. These findings are offered as further support to the concept that abetalipoproteinemia is due to an inability to synthesize or release the specific apoprotein of plasma beta-lipoproteins. The beta protein probably has a function in transport of both exogenous and endogenous glyceride from cells that cannot be adequately assumed by alpha-lipoprotein.