Metformin restores the correlation between serum-oxidized LDL and leptin levels in type 2 diabetic patients

Introduction: Leptin has lipid peroxidation properties in healthy individuals. Here we aimed to study the correlation between serum-oxidized low-density lipoprotein (ox-LDL) and leptin levels in patients with type 2 diabetes. We also studied the effect of metformin therapy on the correlation between serum ox-LDL and leptin levels in patients with newly diagnosed diabetes. Methods: We performed a cross-sectional study on two groups of patients with type 2 diabetes stratified according to (1) patients with newly diagnosed diabetes and (2) patients with long-standing diabetes plus healthy controls. Patients with newly diagnosed diabetes were followed for 3 months after the initiation of metformin therapy. Results: Patients with type 2 diabetes had a higher serum ox-LDL, ox-LDL/LDL ratio, waist circumference, fasting blood sugars (FBSs), hemoglobin A1C (HbA1C), triglyceride, homeostatic model assessment of insulin resistance (HOMA-IR) and a lower serum leptin levels than controls. Serum ox-LDL, ox-LDL/LDL ratio (0.08 (0.08-0.12) vs. 0.06 (0.05-0.08), P < 0.001) and HOMA-IR (3.26 +/- 0.23 vs. 2.93 +/- 0.32; P < 0.01) were decreased when serum leptin levels (15.9 +/- 1.6 vs. 21.4 +/- 2.5, P < 0.01) were increased after 3 months of metformin therapy. This remained significant after multiple adjustments for age, body mass index, FBS, HbA1c, and HOMA-IR. Leptin was significantly correlated with ox-LDL/LDL ratio in controls (r = 0.78, P < 0.01), and in patients with newly diagnosed diabetes (r = 0.4, P < 0.05), after metformin therapy. There were not any correlation between leptin and ox-LDL/LDL ratio in patients with long-standing diabetes and patients with newly diagnosed diabetes before treatment. Discussion: Metformin restores the positive correlation between serum ox-LDL and leptin levels in patients with type 2 diabetes.