リポ蛋白代謝における脂肪酸の意義

Abstract

To elucidate the role of polyunsaturated fatty acid (PUFA) in the metabolism of lipoprotein, the effect of different fat supplemented diets on the uptake of lipoproteins by hepatocytes and the influence of the fatty acid composition of lipoprotein phospholipids (PL) on the plasma PL transfer activity were investigated.Rats were divided into two groups which received a diet supplemented with either butter or margarine (linoleic acid; 63%). Lipoproteins (HDL from rat serum and LDL from human serum) were prepared by ultracentrifugation and labeled with 125I. Hepatocytes were isolated from rats, and incubated with labeled HDL or LDL in the absence and presence of unlabeled lipoproteins.There were no differences in the binding, uptake and degradation by hepatocytes between butterfed rat HDL and margarine-fed rat HDL. And there were no differences in the binding, uptake and degradation of HDL and LDL between butterfed rat hepatocyte and margarine-fed rat hepatocyte, too.Lipoproteins (HDL, LDL and VLDL) and lipoprotein deficient serum (LDS) were isolated from human serum. Small PL vesicles were prepared from different synthetic 14C-labeled phosphatidyl-cholines (PC) (C 16:0, 16:0, C 16:0, 18:1, C 16:0, 18:2) by sonication. HDL was incubated with 14C-labeled PL vesicles in the absence and presence of LDS at 37°C. HDL was selectively precipitated by addition of anti-Apo A-I rabbit γ-globulin. PL transfer activity was determined by measuring of radioactivity in the supernatant that was not precipitated. PL transfer activities from HDL to LDL and from HDL to VLDL were assayed by incubating labeled HDL with LDL and with VLDL, respectively.The PL transfer activities from PL vesicles to HDL, from HDL to LDL and from HDL to VLDL were enhanced as the degree of unsaturation of acyl chains in the PL of donors (PL vesicles and HDL) were increased.These results suggest that the increased proportion of PUFA in the lipoproteins facilitates the lipid transfer among lipoproteins, but the change in the PUFA composition has no significant effect on the uptake of lipoproteins by hepatocyte.