The relationship between the circulating IGF system and the presence of retinopathy in Type 1 diabetic patients

Background Patients with proliferative diabetic retinopathy (PDR) have increased vitreous levels of insulin‐like growth factor (IGF)‐I, IGF‐II and IGF binding proteins (IGFBPs). This accumulation is probably caused by increased leakiness of the blood–retina barrier and influx of circulating IGFs and IGFBPs. To date, interest has focused on the role of circulating total IGF‐I in the development of PDR, and there are only sparse data on circulating levels of free IGF‐I and IGFBPs. Methods We compared fasting serum samples from matched groups of Type 1 diabetic patients with no retinopathy (n = 29), non‐PDR (n = 13) and PDR (n = 16). We also included matched controls (n = 26). Serum was analysed for free and total IGF‐I and ‐II, free plus dissociable IGF‐I, IGFBP‐1, ‐2 and ‐3, IGFBP‐1‐bound IGF‐I as well as IGFBP‐3 proteolysis. Results When compared with controls, diabetic patients (n = 58) showed reduced (P