Metabolism of Oxidized High Density Lipoprotein-2(ox-HDL(2)) in Rat Hepatic Sinusoidal Cells.

Incubation of rat hepatic sinusoidal cells with FITC-HDL(2), FITC-ox-HDL(2) and [(3)H]CE-HDL(2)(rHDL(2)), ox-rHDL(2) showed that binding of FITC-HDL(2) to the cells was competitive to ox-HDL(2), but not to HDL(2). The cell-endocytic fluorescence strength (FS) of FITC-HDL(2) and radioactivity of ox-rHDL(2) were 45.5% of that of FITC-HDL(2) and 61.4% of that of rHDL(2), respectively. Endocytic FS and radioactivity were mainly in TCA-precipitable and supernatant part, respectively. The cell-released FS and radioactivity were 67.7% and 10.9% of the cell-endocytic FS and the radioactivity, respectively, and both of them were mainly TCA-precipitable. These results suggest that: (1) There is probably an ox-HDL receptor on the surface of rat hepatic sinusoidal cells, which is different from HDL receptor. (2) The metabolic behaviour of ox-rHDL(2) in the cells is similar to HDL(2). Both of them do not take a lysosomal pathway. Apoproteins and CE components dissociate from endocytic lipoprotein in the cells. After the cells have taken up most of CE, the residual CE recombines with apolipoprotein to form a lipoprotein and is released from the cells by retroendocytosis. (3) Oxidative modification of HDL(2) weakens its ability to cholesterol reverse transport.

Cooperation of HDL Receptor and Hepatic Lipase in the Selective Uptake of HDL(2)-CE by Rat Hepatic Sinusoidal Cells.

The recombined (3)H-CE-HDL(2)(rHDL(2)) keeps the biological activities of the native HDL(2). After rat hepatic sinusoidal cells were incubated with rHDL(2) at 37 degrees for 3 h (normal group), the cell-endocytic cpm was 995-/+147(mean-/+s, n=2). After the cells were further incubated for 2 h, the cell-release TCA-precipitable cpm and the TCA-supernatant cpm were 78-/+32 and 12-/+9 respectively. These values were 339-/+62, 19-/+11 and 9-/+5 respectively in the acetylimidazole-modified group, and 542-/+78, 34-/+14 and 9-/+8 respectively in the heparin-pretreated group. Our results suggested that: (1) Rat hepatic sinusoidal cells internalize HDL(2) and take up HDL(2)-CE by its HDL receptor, and HDL(3) was secreted out of the cells by retroendocytosis. (2) Hepatic lipase (HL) induces directly the selective uptake of HDL(2)-CE by the cells. (3) There is cooperation between the HDL receptor and HL in the selective uptake of HDL(2)-CE by the cells.