Human hepatic low-density lipoprotein receptors: associations of receptor activities in vitro with plasma lipid and apolipoprotein concentrations in vivo

Abstract The relationships of plasma lipid and apolipoprotein (apo) concentrations to hepatic low-density lipoprotein (LDL) receptor activity were examined in 21 subjects (16 females, 5 males), who were undergoing laparotomy for non-neoplastic disease (cholecystectomy in 16). None had familial hypercholesterolemia, or renal, endocrine or hepatic disease. Ages were 37–77 years (mean, 58 years), plasma cholesterol concentrations 4.09–6.72 mmol/l (5.38) and plasma triacylglycerol concentrations 0.75–2.35 mmol/l (1.36). Receptor activity was quantified in vitro as the total saturable binding and EDTA-suppressible binding (representing apoB,E receptors) of 125 I-labelled human LDL (15μg protein/ml) by liver homogenate at 37° C. There were no significant differences between men and women in 125 I-labeled LDL binding. In the pooled data, EDTA-suppressible binding averaged 50 ng 125 I-LDL protein/mg cell protein (S.D., 15). Total saturable binding averaged 2-fold greater (mean, 101 ng/mg; S.D., 32). Plasma cholesterol, LDL cholesterol and apoB concentrations were negative functions of both EDTA-suppressible binding and total saturable binding, but the correlations with EDTA-suppressible binding were stronger (cholesterol: r =−0.59, P r = −0.48, P r = −0.61, P