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T. N. Raju, R. Vangipurapu, U. Pulakurthy; Elevated Expression of Indoleamine 2, 3-Dioxygenase (IDO) and Accumulation of Kynurenic Acid in the Pathogenesis of STZ-Induced Diabetic Cataract in Wistar Rats. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2285.
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Indoleamine 2, 3-dioxygenase (IDO) is an interferon (IFN)-γ-inducible, enzyme that catalyses the initial and rate-limiting step in the degradation of the essential amino acid tryptophan via. the kynurenine pathway. Fluctuations in the levels of kynurenines have been implicated in the pathogenesis of cataract. The aim of the present study was to determine the expression and activity of IDO, and the levels of tryptophan (TRP) and kynurenic acid (KYNA) in the streptozotocin (STZ)-induced diabetic cataract in Wistar rats.
Male Wistar-NIN rats were divided into two groups: (a) non-diabetic control (G-I), and (b) diabetic (G-II) and maintained for 8 weeks on AIN-93 diet. Diabetes was induced by a intraperitoneal injection of STZ (34 mg/kg body weight). A slit lamp biomicroscope was used to monitor the progression of cataract induced by hyperglycemia. The rats were sacrificed at the end of 8 weeks, and the levels of key enzymes in several biochemical pathways (kynurenines, polyol, oxidative stress, and redox systems) that play a critical role in the pathogenesis of cataract were determined.
Mature cataract was observed 8 weeks after the injection of STZ in G-II rats. The levels of mRNA and enzyme activity of IDO, as well as the content of tryptophan (TRP) and kynurenic acid (KYNA) were elevated in these rats. In addition, levels of polyol enzymes and oxidative stress markers were significantly increased along with alterations in antioxidant reserves.
Our observations indicate a correlation between the levels of tryptophan (TRP), kynurenic acid (KYNA) and polyol enzymes with the formation and progression of diabetic cataract in Wistar rats.
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