Quantitation of apolipoprotein A-I of human plasma high density lipoprotein

High density lipoproteins (HDL) may be controlled via their major apolipoprotein, A-I. To study this apolipoprotein, a simple, precise, and accurate immunodiffusion assay for A-I was developed and applied in a sample of Bell Telephone Company employees. A-I showed a slight increase with age in men ( r = 0.11, n = 263) and women ( r = 0.15, n = 257). A-I correlated closely with HDL cholesterol ( r = 0.72). It was weakly related to total triglyceride in women ( r = 0.24) but was inversely related in men ( r = −0.17). Women on estrogen had the highest A-I levels (149 mg/dl ± 26, x ± S.D., n = 29, p < 0.05), followed by women on combination oral contraceptives (141 ± 26, n = 80) whereas women on no medication had lower levels (129 ± 25, n = 99, p < 0.01) but men had the lowest levels (120 ± 20, p < 0.01). In a separate group of 14 women given estrogen for 2 wk (1 μg/kg/day), A-I increased by 24%. Thus A-I is increased by exogenous and, most likely, endogenous estrogen. Among hyperlipidemic referral subjects, those with hypercholesterolemia ( n = 43) and hypertriglyceridemic women ( n = 33) had normal A-I levels. Among hypertriglyceridemic men both A-I and HDL cholesterol values were decreased (115 ± 20, p < 0.01 and 37 ± 3, p < 0.01, respectively, n = 68) but were significantly lower among a group of myocardial infarction survivors (107 ± 16, p < 0.01, and 27 ± 6, p < 0.01, respectively, n = 24). High density lipoprotein levels and the content of cholesterol in HDL associated with A-I appear to be decreased in coronary heart disease.