Intra-Individual Temporal Variation of Lipid and Apolipoprotein Levels in Patients With Type II Diabetes Mellitus and Normolipidemic Individuals

Hypertriglyceridemia is frequently observed with diabetes mellitus (DM) and is associated with increased cardiovascular disease (CVD) risk. In conditions of insulin deficiency or resistance, increased levels of free fatty acids are seen by the liver, which trigger increased lipogenesis and secretion of triglyceride (TG) rich lipoprotein (TRL) particles. However, a high number of specific ApoC-III on TRL particles suppress their return to the liver leading to a continuous circulation of highly atherogenic TRL remnants. To better understand the effect of intra-individual temporal variations on the differentiation of lipid and apolipoprotein profiles in DM vs. normal individuals, a small time course study over a 4 week period was performed on 3 normolipidemic, and 3 type II DM patients. Our laboratory has developed a method to separate lipoproteins based on hydrodynamic size coupled with mass spectrometry based analysis. Whole serum and lipoprotein size fractions were analyzed for 8 apolipoproteins (ApoA-I, ApoA-II, ApoA-IV, B-100, ApoC-I, ApoC-II, ApoC-III and E) and non-polar lipids (FC, CE, TG) while monitoring other proteins (ApoD, ApoM, CETP, LCAT, PLTP, PON1 and SAA4). In whole serum over the course of 4 weeks, ApoA-IV levels of DM vs. normal subjects differed the most, 3.2 (0.7) vs. 1.8 (0.4) μM, respectively, more significantly than intra-group or intra-individual variations. On the contrary, significantly lower whole serum levels were found for FC, CE, ApoM and PON1 (Prob<0.01). HDL-ApoC-III/LDL-ApoC-III was also lower in DM vs. normal subjects, 3.0 (1.9) vs. 7.2 (4.1). By metrics of molar ratio measured in 20-35 nm LDL fractions, the most significant difference was found between DM vs. normal subjects in ApoC-III/ApoB-100 (1.8 (0.6) vs. 0.9 (0.3)), C-II/ApoB-100 (0.8 (0.4) vs. 0.4 (0.2)) and ApoE/ApoC-III (0.11 (0.09) vs. 0.24 (0.15)). These LDL composition differences indicate lower lipase activity and inhibition of LDL uptake. However, no significant differences were observed in these molar ratios as function of LDL particle size. In conclusion, due to less significant temporal deviations, apolipoprotein molar ratios are a more useful and informative measure of CVD risk in DM subjects than LDL size distribution characteristics.