Abnormal distribution of VLDL subfractions in Type 1 (insulin-dependent) diabetic patients: could plasma lipase activities play a role?

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Abstract
Very low density lipoproteins (VLDL) have an abnormal lipid composition in Type 1 (insulin-dependent) diabetic patients. Since VLDL represent a heterogeneous lipoprotein class, this might be due either to a shift in the distribution or to an abnormal composition of VLDL subclasses or both. In order to investigate these possibilities and to evaluate possible pathogenetic mechanisms, lipid composition (non-esterified and esterified cholesterol, triglycerides, phospholipids) of four VLDL subfractions of decreasing size (A: Svedberg flotation unit [Sf]>400, B: Sf, 175–400, C: Sf 100–175, D: Sf 20–100), isolated by density gradient preparative ultracentrifugation, and plasma post-heparin lipolytic activity (lipoprotein lipase and hepatic lipase) were evaluated in 13 male normolipidaemic insulin-dependent diabetic patients in good glycaemic control (HbA1c 6.9±0.5%) (mean±SEM) and 9 male control subjects matched for age, body mass index and plasma lipid values. Compared to control subjects, diabetic patients showed a reduced total lipid concentration of VLDL of intermediate size (B and C) reaching statistical significance only for VLDL C (0.16±0.02 vs 0.24±0.03 mmol/l; p p p p p r=−0.72; p <0.01) in diabetic patients and this relationship was independent of changes in intermediate VLDL (VLDL C). In conclusion the data suggest that Type 1 diabetic patients, although normolipidaemic and in good blood glucose control, show a shift in the distribution of VLDL subclasses toward VLDL of a smaller size which also have an abnormal composition. The different distribution of VLDL subfractions seems to be related to a reduced hepatic lipase activity.