Metformin reduces circulating malondialdehyde-modified low-density lipoprotein in type 2 diabetes mellitus

Purpose: Type 2 diabetes is known to be associated with increasing cardiovascular mortality. Malondialdehyde-modified LDL (MDA-LDL) is an oxidized LDL and is increased in patients with diabetes or hypertriglyceridemia. Elevated MDA-LDL has been reported to be a risk factor of atherosclerosis or cardiovascular disease. Sitagliptin is a dipeptidyl peptidase-4 inhibitor and a new class of hypoglycemic agents. In this study, the effects of increasing the dose of metformin and add-on sitagliptin on MDA-LDL were examined in type 2 diabetes patients. Methods: Seventy patients with type 2 diabetes, inadequately controlled despite on-going treatment with metformin 500 mg/day, were enrolled in this randomized controlled trial. The patients received additional metformin (500 mg/day) or sitagliptin (50 mg/day) for 6 months, and changes in metabolic parameters including MDA-LDL were evaluated. Results: After 6 months of treatment, add-on sitagliptin (n=35) improved fasting blood glucose (FBG) and hemoglobin A1c (HbA1c) to significantly greater extent than increasing the dose of metformin (n=35). There were no differences in total cholesterol and low-density lipoprotein cholesterol levels between two groups. MDA-LDL levels (mean±S.E.) decreased significantly with increasing the dose of metformin (from 94.40±6.35 to 77.83±4.74 U/L, P < 0.005), but remained unchanged with add-on sitagliptin treatment (from 89.94±5.59 to 98.46±6.78 U/L, p > 0.05). Multiple linear regression analysis identified increasing the dose of metformin treatment as the only independent factor associated with decreased MDA-LDL (β coefficient 0.367, P < 0.0119), and no significant correlation between change in MDA-LDL and fasting blood glucose or HbA1c. Conclusion: These results suggest that increasing the dose of metformin improves serum MDA-LDL levels in type 2 diabetes mellitus.