Interleukin-10 protects nitric oxide-dependent relaxation during diabetes: role of superoxide

Interleukin (IL)-10, an anti-inflammatory cytokine, preserves endothelial function during acute inflammation. We tested the hypotheses that IL-10 plays a protective role in blood vessels during diabetes by suppressing impairment of endothelium-dependent relaxation and that protection by IL-10 is mediated by effects on superoxide (O(2-)). Streptozotocin (150 mg/kg i.p.) or citrate buffer was injected into IL-10-deficient (IL-10(-/-)) mice and wild-type controls (IL-10(+/+)). In IL-10(+/+) and IL-10(-/-) mice, blood glucose levels were approximately 120 mg/dl after citrate administration and approximately 400 mg/dl after streptozotocin administration. Vasorelaxation was examined in arteries in vitro 12-16 weeks later. Maximum relaxation to acetylcholine (30 micromol/l) was 88 +/- 3% (means +/- SE) in nondiabetic mice and 84 +/- 3% in diabetic IL-10(+ /+) mice (P > 0.05). Thus, at this time point, diabetes did not impair endothelium-dependent relaxation in vessels in wild-type mice. In contrast, maximum relaxation in vessels from diabetic IL-10(-/-) mice was significantly decreased (74 +/- 5%) compared with nondiabetic IL-10(-/-) mice (93 +/- 2%, P < 0.05). Superoxide dismutase with polyethylene glycol (PEG-SOD) restored impaired responses to acetylcholine to levels seen in controls. Responses to acetylcholine also were improved by allopurinol (an inhibitor of xanthine oxidase) in vessels from diabetic IL-10(- /-) mice. Thus, diabetes produces greater impairment of relaxation to acetylcholine in IL-10(-/-) mice than in IL-10(+/ +) mice. These findings provide direct evidence that IL-10 impedes mechanisms of endothelial dysfunction during diabetes. Restoration of vasorelaxation with PEG-SOD or allopurinol suggests that the mechanism(s) by which IL-10 preserves endothelium-dependent vasorelaxation involves O(2-), perhaps by reducing production of O(2-) by xanthine oxidase.