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

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.The aim of the present study was to determine the expression of IDO and levels of tryptophan metabolites in serum samples of DR patients.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.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.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.