No abstract

Increased oxidative stress is associated with type-2 diabetes and related cardiovascular diseases, but oxidative modification of LDL has been partially characterized. Our aim was to compare the lipid and fatty acid composition as well as the redox status of LDL from diabetic patients and healthy subjects. First, to ensure that isolation of LDL by sequential ultracentrifugation did not result in lipid modifications, lipid composition and peroxide content were determined in LDL isolated either by ultracentrifugation or fast-protein liquid chromatography. Both methods resulted in similar concentrations of lipids, fatty acids, hydroxy-octadecadienoic acid (HODE) and malondialdehyde (MDA). Then, LDLs were isolated by ultracentrifugation from eight type-2 diabetic patients and eight control subjects. Compared to control LDL, diabetic LDL contained decreased cholesteryl esters and increased triglyceride concentrations. Ethanolamine plasmalogens decreased by 49%. Proportions of linoleic acid decreased in all lipid classes, while proportions of arachidonic acid increased in cholesteryl esters. Total HODE concentrations increased by 56%, 12- and 15-hydroxy-eicosatetraenoic acid by 161 and 86%, respectively, and MDA levels increased by twofold. alpha-Tocopherol concentrations, expressed relative to triglycerides, were lower in LDL from patients compared to controls, while gamma-tocopherol did not differ. Overall, LDL from type-2 diabetic patients displayed increased oxidative stress. Determination of hydroxylated fatty acids and ethanolamine plasmalogen depletion could be especially relevant in diabetes.

Postprandial lipid metabolism is largely dependent upon lipoprotein lipase (LPL), which hydrolyses triglycerides (TGs). The time course of LPL activity in the postprandial state following a single meal has never been studied, because its determination required heparin injection. Recently, we have shown that LPL activity could be accurately measured in nonheparinized VLDL using a new assay aiming to determine the LPL-dependent VLDL-TG hydrolysis. Based on the same principle, we used in this study TG-rich lipoprotein (TRL)-bound LPL-dependent TRL-TG hydrolysis (LTTH) to compare the time course of LPL activity of 10 type 2 diabetics to that of 10 controls, following the ingestion of a lipid-rich meal. The peak TG concentration, reached after 4 h, was 67% higher in diabetics than in controls ( P Ͻ 0.005). Fasting LTTHs were 91.3 ؎ 15.6 in controls versus 70.1 ؎ 4.8 nmol NEFA/ml/h in diabetics ( P Ͻ 0.001). LTTH was increased 2 h postprandially by 190% in controls and by only 89% in diabetics, resulting in a 35% lowering of the LTTH area under the curve in diabetics. Postprandial LTTH was inversely correlated with TG or remnant concentrations in controls but not in diabetics, and with insulin resistance in both groups.These data show that TRL-bound LPL activity increases in the postprandial state and is strongly reduced in type 2 diabetes, contributing to postprandial hypertriglyceridemia. Postprandial hypertriglyceridemia is a prominent feature of dyslipidemia in type 2 diabetes and is considered to be proatherogenic (1-3). Accumulation of remnants in the postprandial state is thought to constitute a cardiovascular risk factor in insulin-resistant subjects (4, 5). Postprandial plasma triglyceride (TG) concentration depends upon the balance between intestinal and hepatic production of TG-rich lipoproteins (TRLs) and plasma clearance of remnants and VLDL. However, the precise mechanisms in TG clearance are difficult to explore, because little is known concerning the time course of the changes in the postprandial activity of lipoprotein lipase (LPL), the main enzyme involved in plasma TG hydrolysis. Because the bulk of LPL is bound to the endothelium, the release of the enzyme through heparin injection must be achieved to permit the ex vivo measurement of total LPL activity (6). In addition to being cumbersome, this process causes a prolonged release of LPL stores, which precludes any relevant time course study of LPL activity. However, several reports have described the presence of LPL protein in nonheparinized plasma (7-10). The mass concentration of the preheparinic LPL appeared to be negatively related to plasma TG concentration and positively related to HDL-cholesterol (HDL-C) (11,12). In addition, preheparinic LPL concentration was found to be increased after treatment with an insulin sensitizer, troglitazone (13), and decreased in situations in which TG catabolism was defective (14,15). Previous studies have shown that this plasma circulating LPL was bound to TRLs and exhibited some lipolytic activity (...