Possible involvement of nitric oxide in the progression of diabetic retinopathy

Abnormal nitric oxide (NO) synthesis has been implicated in the pathogenesis of diabetes mellitus. The aim of our study was to elucidate the relationship between the stages of diabetic retinopathy (DR) and the NO levels in aqueous humor and plasma. Using the chemiluminescence assay, we measured the concentrations of NO in aqueous humor and plasma samples obtained during intraocular surgery from 45 diabetic patients and 19 non-diabetic cataract patients. The patients with diabetes were classified into 4 groups: proliferative DR (PDR) with active neovascularization (active PDR; 9 cases), PDR with quiescent neovascularization (regressed PDR; 6 cases), background DR (BDR; 16 cases) and no DR (14 cases). We found that the aqueous NO levels (mean ± SE) of the active PDR group (83.2 ± 13.9 μM) were significantly higher than those of the BDR group (45.8 ± 6.0 μM, p = 0.049) and the diabetics without DR (33.3 ± 5.2 μM, p = 0.011), and, although not statistically significantly, they were also higher than those of the regressed PDR group (52.1 ± 10.3 μM, p = 0.224). However, no significant differences were observed between any of the diabetic subgroups in the plasma NO levels (p = 0.345). We therefore concluded that NO present in the ocular tissues may play important roles in the progression of DR.