Lipoprotein receptors in copper-deficient rats: Apolipoprotein E-free high density lipoprotein binding to liver membranes

Twenty-four male weanling Sprague-Dawley rats were randomly and equally divided into two dietary treatments, copper-deficient and adequate (0.7 mg and 8.0 mg Cu/kg diet, respectively). Deionized water and diet were provided ad libitum. After 8 weeks, rats were exsanguinated, membranes prepared from livers, and plasma high density lipoproteins (HDL) isolated by ultracentrifugation and agarose column chromatography. Heparin-sepharose affinity chromatography was used to isolate subfractions of HDL devoid of apolipoprotein E (apo E-free HDL). The apo-E-free HDL derived from rats of each dietary treatment were iodinated and bound to liver membranes prepared from rats of both treatment groups. Total binding data, specific binding data, and computer derived estimates of maximum equilibrium binding (B_max) indicate less binding was observed when lipoproteins and membranes from copper-deficient animals were used in the binding assay compared to controls. In addition, a 2 × 2 factorial analysis of binding parameters derived from all experiments demonstrated a significant lipoprotein effect, indicating the reduction in binding may be associated with apo E-free HDL obtained from copper-deficient rats. The present findings suggest a reduction in binding of apo E-free HDL to their binding sites may contribute to the hypercholesterolemia and hyperlipoproteinemia observed in copper deficiency.