Inflammatory cytokine concentrations are acutely increased by hyperglycemia in humans: Role of oxidative stress

Abstract

Background - Circulating levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are elevated in diabetic patients. We assessed the role of glucose in the regulation of circulating levels of IL-6, TNF-α, and interleukin-18 (IL-18) in subjects with normal or impaired glucose tolerance (IGT), as well as the effect of the antioxidant glutathione. Methods and Results - Plasma glucose levels were acutely raised in 20 control and 15 IGT subjects and maintained at 15 mmol/L for 5 hours while endogenous insulin secretion was blocked with octreotide. In control subjects, plasma IL-6, TNF-α, and IL-18 levels rose (P<0.01) within 2 hours of the clamp and returned to basal values at 3 hours. In another study, the same subjects received 3 consecutive pulses of intravenous glucose (0.33 g/kg) separated by a 2-hour interval. Plasma cytokine levels obtained at 3, 4, and 5 hours were higher (P<0.05) than the corresponding values obtained during the clamp. The IGT subjects had fasting plasma IL-6 and TNF-α levels higher (P<0.05) than those of control subjects. The increase in plasma cytokine levels during the clamping lasted longer (4 hours versus 2 hours, P<0.01) in the IGT subjects than in the control subjects, and the cytokine peaks of IGT subjects after the first glucose pulse were higher (P<0.05) than those of control subjects. On another occasion, 10 control and 8 IGT subjects received the same glucose pulses as above during an infusion of glutathione; plasma cytokine levels did not show any significant change from baseline after the 3 glucose pulses. Conclusions - Hyperglycemia acutely increases circulating cytokine concentrations by an oxidative mechanism, and this effect is more pronounced in subjects with IGT. This suggests a causal role for hyperglycemia in the immune activation of diabetes.