Serum Interleukin-18 Levels are Not Increased in Type 2 Diabetic Patients

Background: To investigate the effects of interleukin 18 (IL-18) on diabetic retinopathy (DR) of type 2 diabetic patients, the contents of IL-18 were measured in serum of 206 case subjects with type 2 diabetes and 40 case subjects without diabetes as control. Methods: According to the degree of DR, the diabetic patients were further divided into three groups: non-diabetic retinopathy (NDR, n=69), non-proliferative diabetic retinopathy (NPDR, n = 52) and proliferative diabetic retinopathy (PDR, n=85). Results: Unlike previous reports, we didn’t found a significant increase in serum IL-18 level in diabetic patients (mean ± SD are 107.4±36.6 and 112.5±32.0 pg/ml for control and type 2 diabetes patients respectively, p > 0.05). Further analysis also failed to found any significant increase of serum IL-18 in patients with NDR, NPDR or PDR (113.0±32.1, 110.8±31.4 and 114.5±33.4 pg/ml respectively) when compared with control (for all values, p > 0.05). Real-time qPCR suggests that the expression of IL-18 mRNA in type 2 diabetic patients with DR was comparable to that of controls ( p >0.05). Interestingly, there was a significant positive correlation between levels of serum IL -18 and the amount of fasting blood glucose (FBG, r =0.15， p =0.03) and that Hemoglobin A1c (HbA1c) was relatively higher in diabetic patients than in control subjects ( p <0.05). These results suggest that the levels of serum IL -18 in diabetic patients are within the normal range. Even in patients with diabetic retinopathy, the levels of serum IL -18 were only slightly increased in type 2 diabetic patients and was not statistically different from control subjects. Conclusion: these data suggest that the serum IL -18 levels are not associated with the severity of type 2 diabetic patients.