Impaired High-density Lipoprotein Antioxidant Activity and Serum Paraoxonase-1 Activity in Type II Diabetic Patients

Introduction: High-Density Lipoprotein (HDL) plays an important role in preventing Cardiovascular Disease (CVD) and atherosclerosis. Numerous studies report the atherogenic role of oxidised-LDL (ox-LDL) in development of CVD. HDL associated enzyme, Paraoxonase-1 (PON1) inhibits LDL oxidation. Decreased HDL-cholesterol is commonly found in Type II Diabetic (T2DM) patients; which makes them susceptible to CVD. Aim: To investigate the antioxidant activity of HDL and serum PON1 in T2DM patients. Materials and Methods: In the present cross-sectional study, 20 T2DM patients and 20 non-diabetic volunteers (aged 30 to 60 years) were recruited. LDL and HDL were isolated from all participants by sequential ultracentrifugation. Total Cholesterol (TC) and Triglyceride (TG) concentrations in plasma and lipoprotein fractions were measured by enzymatic assay. The antioxidant activity of HDL against LDL oxidation was calculated as percentage inhibition, while serum PON1 activity was measured spectrophotometrically using paraoxon substrate. An independent Student's t-test was used to analyse the difference between the T2DM group and the control group. The p-value <0.05 was considered to be statistically significant. Results: T2DM patients showed significantly elevated TC, TG and LDL-C levels (p-values <0.05) and reduced HDL-C levels (p-values <0.05) in comparison to control participants. The antioxidant activity of HDL against LDL oxidation and serum PON1 activity was lowered in T2DM. Furthermore, LDL isolated from T2DM was found to be prone to oxidisation. PON1 activity was also correlated with the percentage inhibition of HDL. Conclusion: T2DM patient exhibit impaired HDL antioxidant ability, which increases the risk of developing CVD. Therefore, the assessment of HDL function should be a novel target for CVD risk assessment.