Kynurenic Acid Modulates the Expression of Genes and the Activity of Cellular Antioxidant Enzymes in the Hypothalamus and Hippocampus in Sheep

Kynurenic acid (KYNA), a tryptophan metabolite, is believed to exert neuromodulatory and neuroprotective effects in the brain. This study aimed to examine KYNA’s capacity to modify gene expression and the activity of cellular antioxidant enzymes in specific structures of the sheep brain. Anestrous sheep were infused intracerebroventricularly with two KYNA doses—lower (4 × 5 μg/60 μL/30 min, KYNA20) and higher (4 × 25 μg/60 μL/30 min, KYNA100)—at 30 min intervals. The abundance of superoxide dismutase 2 (SOD2), catalase (CAT), and glutathione peroxidase 1 (GPx1) mRNA, as well as enzyme activities, were determined in the medial–basal hypothalamus (MBH), the preoptic (POA) area of the hypothalamus, and in the hippocampal CA1 field. Both doses of KYNA caused a decrease (p < 0.01) in the expression of SOD2 and CAT mRNA in all structures examined compared to the control group (except for CAT in the POA at the KYNA100 dose). Furthermore, lower levels of SOD2 mRNA (p < 0.05) and CAT mRNA (p < 0.01) were found in the MBH and POA and in the POA and CA, respectively, in sheep administered with the KYNA20 dose. Different stimulatory effects on GPx1 mRNA expression were observed for both doses (p < 0.05-p < 0.01). KYNA exerted stimulatory but dose-dependent effects on SOD2, CAT, and GPx1 activities (p < 0.05-p < 0.001) in all brain tissues examined. The results indicate that KYNA may influence the level of oxidative stress in individual brain structures in sheep by modulating the expression of genes and the activity of at least SOD2, CAT, and GPx1. The present findings also expand the general knowledge about the potential neuroprotective properties of KYNA in the central nervous system.