Serum lipid transport systems: recent advances.

Abstract

AbstractLipids circulating in the plasma are transported in water soluble form as lipid‐protein complexes. Lipoproteins can be classified according to size, density, electrophoretic mobility and protein composition. The ability of low density lipoproteins and very low density lipoproteins (VLDL) to form complexes with different polyanions has been also used as a method for separation and study of serum lipoproteins. Even within classes of lipoproteins closely related otherwise, the amount of different lipids and their ratios to each other and to protein are variable. Two enzymatic systems seem to be at least partly responsible for the different lipid compositions of serum lipoproteins: lipoprotein lipase and lecithin‐cholesterol acyltransferase (LCAT). LCAT, which seems to be associated with α‐lipoproteins, is responsible for the formation of the bulk of cholesteryl‐esters in human serum. Changes in activity of this enzyme may explain the observed changes with age and disease of serum cholesteryl‐ester fatty acids (CEFA). Differences in CEFA pattern are found between newborn and adult animals, including man. The activity of serum LCAT was observed to increase with age in animals and to decrease markedly in patients with liver cirrhosis. These patients show abnormal serum CEFA patterns and abnormally low proportions of pre‐β‐ (VLDL) and α‐ (high density) lipoproteins.