Oxidative stress is associated with diabetes mellitus: a role of vascular NADPH oxidase as a source of superoxide has been demonstrated. We determined whether in type 2 diabetes mononuclear cells, NADPH oxidase and the inducible hemeoxygenase (HO-1) gene expressions are activated. In monocytes from 25 outpatients with type 2 diabetes, p22(phox) gene expression was higher (0.71 +/- 0.09 p22(phox)/beta-actin gene expression ratio) than that observed in 19 controls (0.56 +/- 0.09, P < 0.001). Similarly, HO-1 gene expression was significantly higher in diabetic patients (0.77 +/- 0.12 HO-1/beta-actin gene expression ratio) than in controls (0.41 +/- 0.14, P < 0.001). The p22(phox) and HO-1 gene expressions were also determined during (plasma glucose 363 +/- 40 mg/dl) and after (125 +/- 11 mg/dl) metabolic decompensation in 10 type 2 diabetic patients. The correction of the metabolic milieu was associated with a 19% +/- 3% (P < 0.01) and 30% +/- 3% (P < 0.01) decrease in the p22(phox) and HO-1 gene expressions, respectively. In a multivariate analysis, age was independently associated to p22(phox) gene expression in circulating monocytes in type 2 diabetics [13% (adjusted R(2)), P < 0.05]. Decompensated type 2 diabetes is associated with increased p22(phox) and HO-1 gene expressions in circulating monocytes; the metabolic normalization reduces but does not normalize this activation. These findings suggest that these cells, which play a crucial role in the earliest events of atherosclerotic lesion, are subjected to an increased oxidative stress.