Abstract
To investigate the possible role of the low density lipoprotein (LDL) receptor in the catabolism of LDL by the human liver, the binding of 125I-labeled LDL to membrane fractions prepared from human liver biopsies was determined. Biopsy samples taken for routine histology were obtained from seven patients with heterozygous familial hypercholesterolemia, one with non-familial hypercholesterolemia, and seven normocholesterolemic subjects. LDL was bound by the membranes from normal subjects in a saturable manner that was inhibited by 56% in the presence of excess LDL. Binding of LDL was also inhibited by modification of the lipoproteins with 1,2-cyclohexanedione. The amount of 125I-labeled LDL bound to membranes from familial hypercholesterolemic livers that could be displaced with excess LDL was significantly less than that bound by normocholesterolemic membranes. These observations suggest that LDL receptors are expressed in normal human liver and are defective in the livers of familial hypercholesterolemic patients.