Metabolism of Low-Density Lipoprotein from Patients with Diabetic Hypertriglyceridemia by Cultured Human Skin Fibroblasts

To test whether triglyceride-enriched low-density lipoprotein (LDL) obtained from subjects with diabetic hypertriglyceridemia is metabolized normally by cells, LDL was separated from seven healthy control subjects (fasting plasma glucose [FPG] 91 ± 10 mg/dl [mean ± SD], triglyceride [TG] 110 ± 47 mg/dl), six diabetic normolipidemic patients (FPG 218 ± 65 mg/dl; TG 139 ± 75 mg/dl), six diabetic hypertriglyceridemic patients (FPG 214 ± 71 mg/dl; TG 1915 ± 1680 mg/dl), and five nondiabetic hypertriglyceridemic patients (FPG 92 ± 8 mg/dl; TG 2013 ± 1889 mg/dl). Binding of 125l-labeled LDL from hypertriglyceridemic subjects with and without diabetes to cultured skin fibroblasts was significantly decreased to 74 ± 19% and 78 ± 14% of that seen with LDL from normolipidemic nondiabetic subjects and diabetic normolipidemic controls (100 ± 0%, 101 ± 25%; P < 0.005). Unlabeled LDL from hypertriglyceridemic subjects with and without diabetes failed to suppress LDL receptor activity and sterol synthesis from 14C-acetate as efficiently as unlabeled LDL from healthy subjects. The ability of LDL from hypertriglyceridemic subjects, whether diabetic or not, to suppress LDL binding was inversely related to the ratio of triglyceride to protein in LDL (r = 0.71, P < 0.01) and showed a positive correlation with the LDL cholesterol/protein ratio (0.69, P < 0.01). Thus, LDL from patients with hypertriglyceridemia, with or without coexistent diabetes, shows impaired binding to LDL receptors and less ability to downregulate LDL receptor activity and sterol synthesis than does LDL from normolipidemic diabetic and nondiabetic subjects. These findings suggest that factors associated with hypertriglyceridemia rather than with diabetes result in altered metabolism of LDL in these disorders.