Copper deficiency increases hepatic parenchymal cell's maximal binding capacity and impairs Kupffer cell's internalization of apolipoprotein E-free high density lipoprotein in rats

Abstract

The binding and internalization of apolipoprotein (apo) E-free high density lipoprotein (HDL) by hepatic parenchymal and Kupffer cells were examined with cells and HDL derived from rats fed copper (Cu)-deficient (II nmol/g) and -adequate (126 nmol/g) diets. After 8 weeks of dietary treatment, plasma apo E-free HDL was isolated by a combination of ultracentrifugation, gel filtration, and heparin-Sepharose affinity chromatography. Liver parenchymal and Kupffer cells were obtained by collagenase perfusion and purified by centrifugal elutriation. Freshly isolated cells were incubated with 125I-apo E-free HDL, either from the same treatment group or in a crossover design, to establish if treatment differences were associated with cells, HDL, or both. Binding studies performed at 0° C with increasing apo E-free HDL concentrations demonstrated increases in specific binding and maximum binding capacity (B max) in parenchymal cells from Cu-deficient rats. In addition, cell association studies at 37° C indicated that the amount of apo E-free HDL bound to the cell surface (trypsin releasable) was greater, but the amount internalized (trypsin resistant) was not altered in parenchymal cells from Cu-deficient rats. In contrast, the amount of apo E-free HDL internalized was reduced and that bound to the cell surface was unaltered in Kupffer cells from Cu-deficient rats. Thus Cu deficiency may exert different effects on HDL metabolism in hepatic parenchymal and Kupffer cells. Furthermore, the crossover design demonstrated for the first time that the source of cells from Cu-deficient rats, not HDL, was responsible for the enhanced B max and altered internalization. The results of the present study also support the contention that the hypercholesterolemia associated with the copper-deficient rat model is not the result of decreased HDL uptake by the liver.