COPPER DEFICIENCY INCREASES HEPATIC PARENCHYMAL-CELLS MAXIMAL BINDING-CAPACITY AND IMPAIRS KUPFFER CELLS INTERNALIZATION OF APOLIPOPROTEIN E-FREE HIGH-DENSITY-LIPOPROTEIN IN RATS

The binding and internalization of apolipoprotein (apo) E-free high de nsity lipoprotein (HDL) by hepatic parenchymal and Kupffer cells were examined with cells and HDL derived from rats fed copper (Cu)-deficien t (11 nmol/g) and -adequate (126 nmol/g) diets. After 8 weeks of dieta ry treatment, plasma apo E-free HDL was isolated by a combination of u ltracentrifugation, gel filtration, and heparin-Sepharose affinity chr omatography. Liver parenchymal and Kupffer cells were obtained by coll agenase perfusion and purified by centrifugal elutriation. Freshly iso lated cells were incubated with I-125-apo E-free HDL, either from the same treatment group or in a crossover design, to establish if treatme nt differences were associated with cells, HDL, or both. Binding studi es performed at 0-degrees-C with increasing apo E-free HDL concentrati ons demonstrated increases in specific binding and maximum binding cap acity (B(max)) in parenchymal cells from Cu-deficient rats. In additio n, cell association studies at 37-degrees-C indicated that the amount of apo E-free HDL bound to the cell surface (trypsin releasable) was g reater, but the amount internalized (trypsin resistant) was not altere d 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 C u deficiency may exert different effects on HDL metabolism in hepatic parenchymal and Kupffer cells. Furthermore, the crossover design demon strated for the first time that the source of cells from Cu-deficient rats, not HDL, was responsible for the enhanced B(max) and altered int ernalization. The results of the present study also support the conten tion that the hypercholesterolemia associated with the copper-deficien t rat model is not the result of decreased HDL uptake by the liver.