Iodine labeled human and rat low-density and high-density lipoprotein degradation by human liver and parenchymal and non-parenchymal cells from rat liver

Abstract

1. 1. The abilities of homogenates of human liver, rat liver parenchymal cells, rat liver non-parenchymal cells and total rat liver to catabolize human and rat iodinated high-density lipoprotein (HDL) and low-density lipoprotein (LDL) were determined by measuring the amount of trichloroacetic acid-soluble (noniodide) radioactivity liberated upon incubation at the optimum pH of 4.2. 2. 2. A comparison of the capacities of human liver, rat liver and parenchymal and non-parenchymal cells from rat liver indicated that these different preparations are all able to degrade rat iodine-labeled LDL and HDL, with a 5–6-fold higher capacity for HDL as compared to LDL. 3. 3. Iodine-labeled human HDL can be degraded by rat liver, rat parenchymal and rat non-parenchymal cells with a 5–7-fold higher rate than human iodinelabeled LDL. Human liver homogenate was more active in the degradation of both human and rat iodine-labeled LDL and rat HDL as compared to rat liver. 4. 4. A comparison of the capacities of parenchymal and non-parenchymal cells for the degradation of iodine-labeled human and rat LDL and HDL indicates that non-parenchymal cells possess a considerable higher capacity to degrade these lipoproteins per mg of cell protein. 5. 5. The results indicate that a high proportion of the total rat liver capacity for lipoprotein degradation is localized in the non-parenchymal liver cells and this, together with the active endocytic activity, suggests an important role of these liver cells in hepatic lipoprotein catabolism.