Unbalanced M1/M2 Phenotype of Peripheral Blood Monocytes in Obese Diabetic Patients: Effect of pioglitazone

The monocyte-macrophage system exists in at least two distinct phenotypes of differentiation: proinflammatory (M1) and anti-inflammatory (M2) (1,2). Macrophages, when infiltrated into obese adipose tissue, exhibit a phenotypic switch from M2 to M1 polarization, thereby contributing to obesity-induced adipose tissue inflammation and insulin resistance (1). Expression of both M1 and M2 markers is detected in circulating peripheral blood mononuclear cells as well as in atherosclerotic plaques (3). However, there have been no detailed studies on the M1/M2 phenotype of monocytes and their association with cardiovascular risks in obese subjects with type 2 diabetes. On the other hand, we demonstrated that pioglitazone, a thiazolidinedione class of insulin sensitizer, exerts an antiatherogenic effect independent of its antidiabetic effect (4). Here, we investigated the M1/M2 phenotype of peripheral blood monocytes and pulse wave velocity (PWV), an established index of arterial stiffness, and also the effect of pioglitazone in obese diabetic patients.

A total of 161 subjects (95 men and 66 women, mean age 50.4 years), including 45 normal-weight control subjects, 62 obese nondiabetic patients, and 54 obese diabetic patients with or without pioglitazone treatment for 3 months (30 mg daily), were recruited in our clinic. Peripheral blood monocytes were prepared using magnetic-assisted cell sorting and flow cytometry with anti-CD14. Expression of M1/M2 markers was analyzed by real-time quantitative PCR method and flow cytometry. The number and percentage of CD14⁺ cells among peripheral blood monocytes from obese diabetic patients were significantly increased relative to those of control subjects (P < 0.05). The CD14⁺ cells from obese nondiabetic patients showed significantly higher expression of M1 markers, tumor necrosis factor-α, and interleukin (IL)-6 and lower expression of an M2 marker, IL-10, relative to control subjects (P < 0.01). This is consistent with a report that peripheral blood mononuclear cells in obesity are in an inflammatory state (5). In addition, expression of IL-10 and CD163 in CD14⁺ cells from obese diabetic patients was significantly decreased relative to that of obese nondiabetic patients (P < 0.01). Multivariate regression analysis showed that expression of tumor necrosis factor-α is independently associated with age and BMI and that expression of IL-6 is independently associated with BMI and LDL cholesterol (P < 0.01); expression of IL-10 was negatively and independently associated with diastolic blood pressure, A1C, and triglycerides, and expression of CD163 was negatively and independently associated with insulin concentration, A1C, and PWV (P < 0.05). Moreover, only age and CD163 were independently correlated with PWV (P < 0.05). Interestingly, 3-month treatment with pioglitazone significantly increased IL-10 and CD163 and decreased IL-6 (P < 0.05) in parallel with the improvement of fasting plasma glucose, A1C, insulin concentration, homeostasis model assessment-insulin resistance index, and PWV in obese diabetic patients. Further studies are required to elucidate more detailed characterization of monocyte subsets in obese diabetic patients and the resulting pathophysiological implication in cardiovascular diseases.

This study provides evidence that an unbalanced M1/M2 phenotype of peripheral blood monocytes is associated with metabolic disorder and arterial stiffness in obese type 2 diabetic patients. We also demonstrate that peroxisome proliferator–activated receptor-γ activation improves the unbalanced M1/M2 phenotype of monocytes in obese diabetic patients, which may contribute to its antiatherogenic effect.