The influence of postprandial hypertriacylglycerolemic state of type 2 diabetes with varied insulin resistance on alterations of apoproteins in triacylglycerol-rich lipoproteins study using mass spectrometry

Abstract

It is known that insulin resistance plays role in diabetic dyslipidemia especially hypertriacylglycerolemia (HTAG). However, in good metabolic controlled type2 diabetes mellitus who have normal fasting triacylglycerol level, the HTAG can observed only in postprandial state. In this research, the influence of insulin resistance on lipoprotein profiling and apoprotein of triacylglycerol-rich lipoprotein especially very low-density liprotein (VLDL) were studied. Eleven type2 diabetic subjects with moderated metabolic control (HbA1c <8%), were classified as lower insulin resistance, LIR (HOMA-IR<2.5), n=5 and higher insulin resistance, HIR (HOMA-IR 2.5-5.0), n=6 comparable to 10 nondiabetic controls. After at least 12 hours of fasting, subjects consumed a fat-rich meal. Before and the 4 hours after the meal, blood samples were taken for determination of glucose, insulin, lipids and lipoproteins in Experiment I. The increasing of postprandial triacylglycerol was found in chylomicron VLDL and HDL fractions especially in HIR group. For Experiment II, VLDL was isolated using sequential ultracentrifugation, delipidated and separated with 2D-PAGE and identified using ESI-IT, LC-MS/MS and MALDI-TOF MS. In total 26 protein spots representing 14 proteins including novel protein, transthyretin (TTR) with their isoforms were identified in VLDL. The comparisons of 14 proteins were analyzed in 6 pooled VLDL between fasting state and postprandial state within the same group as well as among different groups. The significant alterations compared between fasting and postprandial state of VLDL proteins (p<0.05) in all groups were observed among apoC-II, apoC-III, apoE, apoA-I, except for TTR which was found only in HIR one. In fasting state, the significant changes of apoA-I, apoA-IV, and apoC-II were observed in LIR and HIR, whereas of apoC-III, apoE and TTR were observed in HIR in comparison to controls. In addition, significant modifications were found in apoA-I, apoC-II, apoC-III, apoE, and TTR of postprandial state compared to controls. These findings illustrate that insulin resistance is not only associated with increased VLDL triacylglycerol levels but also with alterations in VLDL protein composition which possibly affect the lipoprotein metabolism in diabetic patients.