Vitreous levels of IGF-I, IGF binding protein 1, and IGF binding protein 3 in proliferative diabetic retinopathy: a case-control study.

OBJECTIVE: To evaluate vitreous levels of IGF-I and its binding proteins IGFBP-1 and IGFBP-3 in patients with proliferative diabetic retinopathy (PDR). Because intravitreal proteins are elevated in patients with PDR due to the disruption of the blood-retinal barrier, we have corrected vitreal IGF-I and IGFBPs by total vitreal proteins to avoid this confounding factor. RESEARCH DESIGN AND METHODS: We compared 21 diabetic patients with proliferative retinopathy (group A) and 13 nondiabetic patients (group B) in whom a vitrectomy was performed. Both groups were matched by age, serum IGF-I, IGFBP-1, and IGFBP-3 levels. Serum and vitreous levels of IGF-I, IGFBP-1, and IGFBP-3 were measured by immunological methods. Vitreal proteins were assessed by turbidimetric method.
RESULTS: Vitreal levels of IGF-I were elevated in group A (median 1.35 ng/ml [range 0.3-8.7]) in comparison with group B (median 0.25 ng/ml [range 0-1.38]), P<0.001. After adjusting by vitreal proteins [ratio IGF-I (ng/ml)/protein (mg/ml)], the differences remain significant (P<0.005). Vitreal levels of IGFBP-1 and IGFBP-3 were also elevated in diabetic patients (IGFBP-1: group A, median 1.6 ng/ml [range 0.6-20.7]; group B, median 0.4 ng/ml [range 0.3-1.9], P<0.001. IGFBP-3: group A, median 102.6 ng/ml [range 53.9-350.8]; group B, median 29.0 ng/ml [range 3.2-87.8], P<0.001). However, when the ratio IGFBP/protein was considered, the differences were not significant.
CONCLUSIONS: Intraocular synthesis contributes to elevated vitreous concentrations of IGF-I found in PDR. By contrast, unspecific increase of intravitreal proteins is the main factor explaining the elevated vitreous levels of IGFBP-1 and IGFBP-3 found in diabetic patients.