Independent anti-inflammatory effect of insulin in newly diagnosed type 2 diabetes

Although insulin has been reported to have an anti-inflammatory effect, whether this effect is independent of its property to reduce blood glucose with insulin treatment in type 2 diabetes has not been investigated in detail. The purpose of this study was to evaluate the independent anti-inflammatory effect of insulin in patients with newly diagnosed type 2 diabetes.

An 8-week, randomized, parallel-group study that enrolled 90 patients with newly diagnosed type 2 diabetes, who were randomly assigned to receive either insulin or metformin, was carried out. The doses of insulin and metformin were titrated according to fasting plasma glucose (FPG) and postprandial plasma glucose (PPG) during the 4 weeks; the target of FPG was 126 mg/dL and that of PPG was 160 mg/dL. The blood glucose levels were kept stabilized till the end of the study. The serum concentrations of high-sensitive C-reactive protein (hsCRP) and interleukin (IL)-6 were measured before starting the study and 4 and 8 weeks after initiation of insulin or metformin therapy.

After 4 weeks of dose titration, the levels of FPG were reduced in the two groups compared to baseline (p < 0.001), but there was no significant difference between the two groups (p > 0.05). During the next 4 weeks' treatment, the levels of FPG were stable, but the serum concentration of hsCRP and IL-6 was markedly reduced in the insulin-treated group compared with that in the metformin-treated group (p < 0.001).

Our data suggest that insulin has an anti-inflammatory effect that is independent of the reduction it causes in blood glucose.