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

Pathophysiology/Complications O R I G I N A L A R T I C L E Vitreous Levels of IGF-I, IGF Binding Protein 1, and IGF Binding Protein 3 in Proliferative Diabetic Retinopathy A case-control study ROSA BURGOS, PHD CARLOS MATEO, PHD ANA CANTÓN, PHD CRISTINA HERNÁNDEZ, MD JORGE MESA, MD RAFAEL SIMÓ, MD 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. Diabetes Care 23:80–83, 2000 GF-I is a polypeptide structurally homologous to insulin that regulates the proliferation and differentiation of several cell types (1,2). In vivo, IGF-I acts in a paracrine/autocrine manner to mediate many of the physiological actions of growth hormone, and its activity in extracellular fluids is regulated by insulin-like growth factor binding proteins (IGFBPs) that prolong I IGF-I half-life in the circulation and serve as a reservoir of IGFs. Moreover, IGFBPs have been shown to modulate IGF action on target cells (3,4). Several clinical studies have suggested the role of growth hormone/IGF-I in the development of diabetic re t i n o p a t h y. Growth hormone–deficient dwarfs with diabetes and diabetic patients with hemo- From the Diabetes Research Unit (R.B., A.C., C.H., J.M., R.S.) and the Ophthalmology Department (C.M.), Hospital General Universitari Vall d’Hebron, Barcelona, Spain. Address correspondence and reprint requests to Dr. R. Simó, Diabetes Research Unit, Endocrinology Division, Hospital General Vall d’Hebron, Pg. Vall d’Hebron 119-129, 08035 Barcelona, Spain. Abbreviations: CV, coefficient of variation; IGFBP, insulin-like growth factor binding protein; PDR, proliferative diabetic retinopathy. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. 80 chromatosis and infiltrative disease of the pituitary gland have little evidence of retinopathy (5,6). Conversely, proliferative diabetic retinopathy could improve after hypophysectomy (7–10). IGF-I has been involved in the impairment of diabetic retinopathy observed in puberty and pregnancy, two physiological conditions associated with serum IGF-I increasing (11–13). Furthermore, IGF-I has been implicated in the worsening of preexisting diabetic retinopathy observed after impro v e d glycemic control by intensive insulin therapy (14–16). Interestingly, a transient elevation of serum IGF-I levels has been observed at the time of retinal vessel formation in a prospective 2-year follow-up study (17). Nevertheless, regional IGF-I concentrations in the retina may be more important than systemic levels. Vitreous fluid obtained from diabetic patients with proliferative diabetic retinopathy (PDR) submitted to a vitrectomy is a unique material to explore indirectly the synthesis of growth factors in the retina, and elevated vitreal levels of both IGF-I and IGFBPs have been reported (17–27). These proteins could be enhanced in vitreous fluid as a consequence of the increased synthesis by the retina. By contrast, the increase of vitreous levels of IGF-I and IGFBPs could be due to the disruption of the blood-retinal barrier, reflecting the leakage of proteins that occurs in diabetic microangiopathy. In fact, we have observed that intravitreal protein levels are elevated threefold in diabetic patients with PDR in comparison with control subjects (28). Therefore, the results of previous studies that have found higher intravitreous IGF-I and IGFBP concentrations could be due to this unspecific increase of proteins. In the present study, vitreal levels of IGF-I, IGFBP-1, and IGFBP-3 were determined in diabetic patients with PDR and compared with a nondiabetic control group matched by serum IGF-I, IGFBP-1, and IGFBP-3. Furthermore, the results were adjusted by total vitreal proteins. This design permits one to analyze more accurately the results obtained in diabetic patients. DIABETES CARE, VOLUME 23, NUMBER 1, JANUARY 2000 Burgos and Associates Table 1—Age and serum levels of IGF-I, IGFBP-1, and IGFBP-3 in diabetic patients with PDR (group A) and control subjects (group B) n Age (years) Serum IGF-I (ng/ml) Serum IGFBP-1 (ng/ml) Serum IGFBP-3 (ng/ml) Group A Group B P 21 62.2 ± 14.8 136.7 (66.2–302.3) 3.6 (0.7–17.2) 3,212 (1,530–4,840) 13 63.6 ± 13.5 123.3 (43–212) 2.3 (0.6–12.5) 3,141 (764–5,126) — 0.72 0.88 0.18 0.80 Data are means ± SD or medians (range). Statistical analysis was performed with the Mann-Whitney U test. RESEARCH DESIGN AND METHODS Subjects We included in the study 21 diabetic patients (6 type 1 and 15 type 2) with proliferative diabetic retinopathy in whom a classic threeport pars plana vitrectomy was performed (group A), and 13 nondiabetic patients (group B) with other conditions requiring vitrectomy (epiretinal or subretinal membrane). In all cases, a recent vitreous hemorrhage was excluded (less than 2 months). Both groups were matched by sex, age, and levels of serum IGF-I, IGFBP-1, and IGFBP-3 (Table 1). Undiluted vitreous samples were obtained at the onset of vitrectomy by aspiration into a syringe attached to the vitreous cutter, transferred to a sterile tub, placed immediately on ice, and centrifuged at 16,000g for 5 min at 4°C. The samples were frozen at 80°C until assayed. A venous blood sample was collected simultaneously with the vitrectomy, then centrifuged at 3,000g for 15 mi (...truncated)