PREBETA-1 HDL IN PLASMA OF NORMOLIPIDEMIC INDIVIDUALS - INFLUENCES OFPLASMA-LIPOPROTEINS, AGE, AND GENDER

Prebeta-1 HDL is a molecular species of plasma HDL of approximately 67 kDa mass that contains apolipoprotein A-I, phospholipids, and unester ified cholesterol. It participates in a cyclic process involved in the retrieval of cholesterol from peripheral tissues. In this cycle, unes terified cholesterol from cells is incorporated into prebeta-1 HDL, pr oviding a substrate for esterification. Prebeta-1 HDL then becomes inc orporated into larger HDL species of alpha mobility as esterification proceeds and is regenerated during the transfer of cholesteryl esters from alpha HDL particles to acceptor lipoproteins. Thus the steady sta te level of prebeta-1 HDL in plasma reflects the relative efficiencies of the major metabolic processes involved in its generation and remov al. We have used an isotope dilution technique to measure prebeta-1 HD L levels in the plasmas of 136 normolipidemic individuals (46 M, 90 F) . The mean absolute concentration of prebeta-1 HDL as apolipoprotein A -I was 68 +/- 40 mu g/ml for women, and 84 +/- 40 m/ml for men. Prebet a-1 HDL represented 5.5 +/- 3.3% of total apolipoprotein A-I in women, and 7.2 +/- 4.0% in men. The distributions of both absolute and perce nt prebeta-1 HDL are highly asymmetric, with skew toward higher values . However, the skew appears not to be attributable to either plasma ch olesterol or triglyceride levels which are also skewed in population s amples. The percent prebeta-1 HDL was negatively correlated with HDL c holesterol levels (P < 0.0001), whereas absolute levels of prebeta-1 H DL were positively correlated with apolipoprotein A-I and negatively c orrelated with HDL cholesterol (P, for both, < 0.0001). Multiple linea r regression analysis revealed effects of age and gender, but no assoc iation with lipoprotein fractions other than HDL. Lower levels of preb eta-1 HDL were associated with female gender in all models.