Specific binding and uptake of apolipoprotein E-free high density lipoproteins by cultured liver parenchymal cells of copper-deficient rats

Abstract

The influence of copper deficiency on the binding and uptake of apolipoprotein E-free high density lipoprotein (apo E-free HDL) in cultured rat hepatic parenchymal cells was examined in this study. Male weanling Sprague-Dawley rats were randomly divided into two treatments, a Cu-adequate (7.33 mg Cu/kg diet) or a Cu-deficient (1.04 mg Cu/kg diet) group. After 7 weeks, plasma apo E-free HDL were isolated by a combination of ultracentrifugation, gel filtration, and heparin-Sepharose affinity chromatography. Parenchymal cells were isolated from collagenase perfused liver of Cu-deficient and adequate rats and cultured for 16 hours at 37°C prior to incubation with iodinated apo E-free HDL from the same treatment group. Cells were incubated with 5 μg/ml 125 I-apo E-free HDL for 2, 6, or 12 hours in the presence or absence of 200 μg/ml (40-fold) excess unlabeled apo E-free HDL. Increases in specific binding at 4°C and specific cell-associated uptake at 37°C as a function of time were observed with cells and HDL from Cu-deficient rats. Cells were also incubated for 6 hours with 8 concentrations of 125I-apo E-free HDL in the presence or absence of excess unlabeled HDL. Although no significant increase in specific binding was detected at 4°C as a function of ligand concentration, the response tended to be higher at 5 to 15 μg HDL/ml for the Cu-deficient treatment. However, at 37°C the specific cell-associated uptake was increased markedly with cells and HDL from Cu-deficient rats. The observed increases in HDL binding and uptake indicate that these processes may be enhanced in Cu-deficient rats. These data are also consistent with recent in vivo results which indicate that plasma clearance and tissue uptake of HDL are increased in Cu-deficient rats.