Apolipoprotein E-Rich HDL Binding to Liver Plasma Membranes in Copper-Deficient Rats

Copper deficiency in rats raises plasma cholesterol concentration while reducing liver cholesterol concentration. One consequence of this cholesterol redistribution is the accumulation of a large high-density lipoprotein (HDL) particle rich in apolipoprotein E (apo E). The purpose of this study was to determine, using an in vitro binding assay, if the interaction of apo E-rich HDL with hepatic lipoprotein binding sites may be affected by copper deficiency. Male Sprague-Dawley rats were divided into two dietary treatments (copper-deficient and -adequate) and placed on a dietary regimen for 8 weeks. Subsequent to exsanguination, hepatic plasma membranes were prepared and apo E-rich HDL was isolated from rats of each treatment by ultracentrifugation, agarose column chromatography, and heparin-Sepharose affinity chromatography. Total binding and experimentally derived specific binding of ¹²⁵I-apo E-rich HDl to hepatic plasma membranes indicated greater binding when lipoproteins and membranes from copper-deficient animals were used in the assay compared to controls. Scatchard analysis of specific binding data indicated that equilibrium binding affinity (K_d) was also affected by copper deficiency. The hepatic binding sites recognizing apo E-rich HDL were not affected by EDTA or pronase, of relatively high capacity, and recognized a variety of other rat lipoproteins.