Functional and proteomic alterations of plasma high density lipoproteins in type 1 diabetes mellitus

Abstract

Objective: Higher HDL-cholesterol (HDL-C) is linked to lower cardiovascular risk but individuals with type 1 diabetes mellitus (T1DM) with normal or high HDL-C have higher cardiovascular events compared to age matched non-diabetic controls (ND). We determined whether altered HDL functions despite having normal HDL-C concentration may explain increased cardiovascular risk in T1DM individuals. We also determined whether irreversible posttranslational modifications (PTMs) of HDL bound proteins occur in T1DM individuals with altered HDL functions.

Methods: T1DM with poor glycemic control (T1D-PC, HbA1c≥8.5%, n=15) and T1DM with good glycemic control (T1D-GC, HbA1c≤6.6%, n=15) were compared with equal numbers of NDs, ND-PC and ND-GC respectively, matched for age, sex and body mass index (BMI). We measured cholesterol efflux capacity (CEC) of HDL in the serum using J774 macrophages, antioxidant function of HDL as the ability to reverse the oxidative damage of LDL and PON1 activity using commercially available kit. For proteomic analysis, HDL was isolated by density gradient ultracentrifugation and was analyzed by mass spectrometry and shotgun proteomics method.

Results: Plasma HDL-C concentrations in both T1DM groups were similar to their ND. However, CEC (%) of T1D-PC (16.9±0.8) and T1D-GC (17.1±1) were lower than their respective ND (17.9±1, p=0.01 and 18.2±1.4, p=0.02). HDL antioxidative function also was lower (p<0.05). The abundance of oxidative PTMs of apolipoproteins involved in CEC and antioxidative functions of HDL were higher in T1D-PC (ApoA4, p=0.041) and T1D-GC (ApoA4, p=0.025 and ApoE, p=0.041) in comparison with ND. Both T1D-PC and T1D-GC groups had higher abundance of amadori modification of ApoD (p=0.002 and p=0.041 respectively) and deamidation modification of ApoA4 was higher in T1D-PC (p=0.025).

Conclusions: Compromised functions of HDL particles in T1DM individuals, irrespective of glycemic control, could be explained by higher abundance of irreversible PTMs of HDL proteins. These results lend mechanistic support to the hypothesis that HDL quality rather than quantity determines HDL function in T1DM and suggest that measurements of concentrations of HbA1c and HDL-C are not sufficient as biomarkers of effective treatment to lower cardiovascular risk in T1DM individuals.

Keywords: Functions; High density lipoproteins; Posttranslational modifications; Proteomics; Type 1 diabetes mellitus.