The Role And Mechanism Of Kynurenine Pathway Of Tryptophan Metabolism In Gas Explosion Brain Injury

BackgroundBlast-related traumatic brain injury（b TBI）refers a brain tissue damage directly or indirectly caused by shockwave after blast exposure.For moderate and severe b TBI,in addition to symptomatic treatment,there is currently no effective treatment method.Recent studies suggested that b TBI may be mediated by excessive inflammation and oxidative stress.Excessive inflammatory activation and oxidative stress lead to excessive activation of the tryptophan（Trp）catabolism kynurenine pathway（KP）,which produces neurotoxic substances such as kynurenic acid and quinolinic acid.At present,the role of KP in b TBI is still unclear,and regulating KP may be an important direction for the treatment of b TBI.ObjectivesTo observe the changes of neurons in the hippocampal CA1 area of SD rats after exposure to a certain pressure of a single explosive shock wave and the changes of Kynureninase（KYNU）and Kynurenine-3-monooxygenase（KMO）expression after blast exposure.In vitro,investigate the effects of KMO inhibitors and KYNU inhibitors on apoptosis of hippocampal neurons.In vivo,observe the behavioral changes and the morphological and quantitative changes of neurons in the hippocampal CA1 area after treatment with KMO inhibitor and KYNU inhibitor.Methods1.The rat b TBI model was established by gas explosion in a large-scale tunnel,and the rats located 160 m away from the explosion source were selected as the observation objects.Brain tissues were collected at different time points,fixed in paraffin,and sliced..2.Nissl staining was used to analyze the injury of hippocampal CA1 neurons in b TBI model,and immunohistochemistry was used to analyze the expression of KMO and KYNU.3.In vitro hippocampal organ models were established using the technique of hippocampal slices,and the apoptosis of hippocampal neurons was observed by TUNEL staining after treatment with KMO and KYNU inhibitors.4.The rat b TBI model was re-established by shock tube,and behavioral testing was performed.The model rats were intraperitoneally injected with KMO inhibitor Ro61-8048（RO）and KYNU inhibitor Benserazide hydrochloride（BH）for 7 days and then behavioral testing was performed again to observe the treatment effect.5.After the behavioral test,the rats were anesthetized and perfused to fix the brain tissue.Nissl staining was used to compare the morphological changes of the hippocampal CA1 area in each group.Results1.After gas explosion,the number of neurons decreased and the expression of KYNU and KMO increased in the CA1 area of the rat hippocampus.2.The in vitro model of b TBI was established by organotypic hippocampal slice culture,and it was found that both KMO inhibitor RO and KYNU inhibitor BH could reduce the proportion of TUNEL-positive neurons in the hippocampus.3.Compared with the control group,the behavior of b TBI rats treated with RO was significantly improved,and the number of survived neurons in hippocampal CA1 region increased;while the neurons in hippocampal CA1 region of b TBI rats treated with BH were not significantly different from those of the control group,and the behavior of b TBI rats was not significantly improved.ConclusionsKMO and KYNU increased in the hippocampus of the b TBI rats,which may mediate the damage of b TBI.Furthermore,KMO inhibitor showed a significant protective effect on b TBI.