Defective metabolism of hypertriglyceridemic low density lipoprotein in cultured human skin fibroblasts. Normalization with bezafibrate therapy.

Abstract

The metabolism of hypertriglyceridemic low density lipoprotein (HTG-LDL) was investigated in upregulated cultured human skin fibroblasts. Low density lipoprotein (LDL) was isolated by zonal centrifugation from the plasma of seven HTG subjects, before and 2 wk after the initiation of bezafibrate (BZ) therapy. HTG-LDL is a cholesterol-poor, triglyceride-rich lipoprotein of smaller diameter than BZ-LDL or normal LDL (N-LDL). Binding, cell association, and proteolytic degradation of HTG-LDL were compared with that of BZ-LDL and N-LDL and were found to be significantly lower by a paired t test analysis (P < 0.001). After 6 h preincubation with unlabeled HTG-LDL, the incorporation of [14Clacetate to sterols was significantly higher than with BZ-LDL or N-LDL (577±43.7; 330±41.5; 262±47, mean±SE, picomoles sterols per milligram cell protein per 2 h, respectively; P < 0.001 by paired t test).To determine the effectiveness of HTG-LDL and BZ-LDL on the down-regulation of LDL receptor activity, up-regulated cells were incubated for 48 h with HTG-LDL and BZ-LDL. LDL receptor activity was significantly higher after preincubation with HTG-LDL compared with BZ-LDL, and the rates of sterol synthesis were similarly increased. These results demonstrate that HTG-LDL does not down-regulate the LDL receptor activity as efficiently as BZ-LDL and that its cholesterol content is not enough to adequately suppress cellular sterol synthesis.Significant correlation between LDL composition and cholesterol synthesis by cultured cells was found with all LDL preparations over a wide range of cholesteryl ester to protein ratio (0.8-2.2). This correlation indicates that the compositional and structural abnormalities of HTG-LDL, and especially the low cholesterol content of the lipoprotein, alter LDL metabolism and cellular cholesterol formation.

Plasma triglycerides determine low density lipoprotein composition, physical properties, and cell-specific binding in cultured cells.

“…Our data (Table III) confirm the previous reports ofreduced uptake of LDL derived from hypertriglyceridemic subjects in fibroblast culture (8,44). In contrast, with HepG2 cells there was enhanced uptake of native and in vitro hypertriglyceridemic LDL (Figs.…”

Lipolysis exposes unreactive endogenous apolipoprotein E-3 in human and rat plasma very low density lipoprotein.

“…Human skin fibroblasts were prepared from skin biopsies obtained from the medial part of the forearm of normal adult male donors (21 (12) except that the cells were grown in 35-mm dishes as above.…”

“…Binding, cell association, and proteolytic degradation of 123I-labeled lipoproteins were determined as previously described (21). On the day ofexperiment, the fresh medium was removed and the cells were incubated at 37°C with LPDS medium containing lipolyzed or control 1251I-VLDL-I, -II, or -III (apo B-100 equivalent to 10 gg protein/ml).…”

Pharmacological effects of lipid-lowering drugs on circulating adipokines

“…Fibrates lower triglycerides by limiting substrate availability for triglyceride synthesis in the liver [23,24] , promoting the action of lipoprotein lipase [25,26] , enhancing LDL receptor/ligand interaction [27] , promoting cholesterol excretion via bile [28] and stimulating reverse cholesterol transport [29] . The ultimate result is a reduction in triglyceride and LDL-C levels, but the data on HDL-C are varied.…”