Free insulin growth factor-I and vascular endothelial growth factor in the vitreous fluid of patients with proliferative diabetic retinopathy

Abstract

PURPOSE: To investigate the relationship between insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in the vitreous fluid of diabetic patients with proliferative diabetic retinopathy (PDR). DESIGN: Observational case-control study. METHODS: In a prospective study, 37 consecutive diabetic patients with PDR (14 type I and 23 type II diabetes mellitus) in whom a vitrectomy was performed were compared with 21 nondiabetic patients with other conditions requiring vitrectomy (control group). Free IGF-I and VEGF were measured by ELISA. RESULTS: Vitreal levels of both free IGF-1 and VEGF were higher in diabetic patients with PDR than in control subjects ( P < .01, and P < .0001, respectively). After adjusting for total intravitreous protein concentration, VEGF (ng/mg of proteins) remained significantly higher in diabetic patients with PDR than in the control group ( P < .0001), whereas free IGF-I (ng/mg of proteins) was lower in diabetic patients than in control subjects ( P < .0001). The vitreous concentrations of VEGF were higher in patients with active PDR than in patients with quiescent PDR ( P < .005), whereas vitreous free IGF-I was not related to PDR activity. Finally, we did not observe a correlation between the vitreal levels of free IGF-I and VEGF. CONCLUSIONS: We conclude that free IGF-I and VEGF are both increased, but not related, within the vitreous fluid of diabetic patients with PDR. In addition, our results support the current concept that VEGF is directly involved in the pathogenesis of PDR, whereas the precise role of free IGF-I remains to be established.