Evaluation of indoleamine 2,3-dioxygenase expression and kynurenine pathway metabolites levels in serum samples of diabetic retinopathy patients

Context: Diabetic retinopathy (DR) is the leading cause of acquired blindness. The involvement of indoleamine 2, 3-dioxygenase (IDO) and kynurenines, the products of tryptophan degradation in various pathological conditions was well documented. Objective: The aim of the present study was to determine the expression of IDO and levels of tryptophan metabolites in serum samples of DR patients. Materials and methods: Tryptophan and its metabolites, i.e. kynurenine, kynurenic acid and 3-hydroxy kynurenine were measured by HPLC in serum of normal subjects as well as non-proliferative (NPDR) and proliferative DR (PDR) patients. The expression of IDO was measured using semi-quantitative reverse transcriptase polymerase chain reaction. Results: Elevated expression of IDO and levels of kynurenine, kynurenic acid and 3-hydroxykynurenine were observed in NPDR and a higher expression was observed in PDR. No significant change was noticed in levels of tryptophan. Conclusion: An elevation in the concentrations of tryptophan metabolites and IDO expression was evident in diabetic retinopathy patients. The results indicate probable association of IDO and tryptophan metabolites with DR.