MEASUREMENT OF PREBETA-1 HDL IN HUMAN PLASMA BY AN ULTRAFILTRATION-ISOTOPE DILUTION TECHNIQUE

Prebeta-1 HDL is a 67-kDa species of plasma high-density lipoproteins (HDL) that contains two copies of apolipoprotein A-I. It functions in a metabolic cycle of cholesterol retrieval and may be formed during li polysis in plasma. We have found that centrifugal ultrafiltration usin g a membrane with a permeability limit of 100 kDa discriminates catego rically between the 67-kDa species and larger HDL particle species. Th us, the ultrafiltrate samples the pool of prebeta-1 HDL in plasma. We have developed a technique using the dispersal of purified prebeta-1 H DL, labeled covalent-ly with tritium, in plasma samples, to label the prebeta-1 HDL pool. Subsequent determination of the specific activity of prebeta-1 HDL in the ultrafiltrate provides a means of calculating the content of prebeta-1 HDL in plasma by the isotope dilution princip le. We employ a modification of an enzyme-linked immunosorbent assay t echnique for apolipoprotein A-I that allows the equal detection of tha t protein in prebeta-1 HDL and in other HDL particle species for deter mination of the fraction of total apolipoprotein A-I that is present i n the prebeta-1 HDL particle species. The mean level of prebeta-1 HDL- associated apolipoprotein A-I in plasma samples from 86 normolipidemic adults was 74 +/- 43 mu g/ml (+/-SD), representing all average of 6.6 % of the total apolipoprotein A-I in plasma. (C) 1997 Academic Press.