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Stimulatory effect of repeated treatment with lipopolysaccharide on a key enzyme of the kynurenine pathway in both genders in rats

Stimulatory effect of repeated treatment with lipopolysaccharide on a key enzyme of the... Keywords Kúcové slová: Immune challenge ­ Kynurenine-3-monooxygenase - Gender imunitná aktivácia ­ kynurenín-3-monooxygenáza - pohlavie INTRODUCTION Lipopolysaccharide (LPS) is an endotoxin of the outer membrane of Gram-negative bacteria Escherichia coli. Repeated administration of LPS can be used as a model of chronic stress and also as a model for immune system activation. Among others, the administration of LPS leads to activation of the kynurenine pathway of tryptophan metabolism (Kubesova et al. 2015). The kynurenine pathway consists of two functionally distinct branches that generate several neuroactive metabolites. Under basal conditions, kynurenine metabolism favours the formation of neuroprotective kynurenic acid. Disruptions in homoeostasis can shift the balance towards an increased production of the neurotoxic quinolinic acid. Kynurenine-3monooxygenase (KMO) is a key enzyme involved in regulating the production of these two metabolites. Changes in KMO * E-mail: csano.agi@gmail.com © European Pharmaceutical Journal expression or activity may contribute to the development of neurodegenerative, neuropsychiatric and neurodevelopmental diseases (Parrott and O´Connor, 2015). The aim of the present study was to test the hypothesis that repeated treatment with LPS has an impact on plasma concentrations of KMO. To our knowledge, there is no information on gender differences in LPS-induced activation of the kynurenine pathway. Therefore, the present experiments were performed in both male and female rats. MATERIAL AND METHODS Sprague-Dawley rats were treated either with LPS in increasing doses (to prevent the development of tolerance) Eur. Pharm. J. LXIII, 2016 (1): 20-22. Stimulatory effect of repeated treatment with lipopolysaccharide on a key enzyme of the ... for 5 days (50­200 µg/kg) or vehicle, thus simulating a shortterm inflammatory state. All procedures were approved by the Animal Health and Animal Welfare Division of the State Veterinary and Food Administration of the Slovak Republic. Two hours after the last injection, the animals were quickly decapitated and blood was collected. Plasma concentrations of KMO were measured by an enzyme-linked immunosorbent assay (ELISA) kit according to the manufacturer's instructions (CSB-EL012475RA, Cusabio). The sensitivity of the assay was 3.9 pg/ml with the intra-assay and inter-assay coefficient of variation of < 8% and < 10%, respectively. The results were analysed by two-way ANOVA for factors treatment and gender. RESULTS The activation of the immune system by a repeated treatment with LPS was confirmed by a decrease in body weight gain and increased mRNA levels of proinflammatory cytokines (data not shown). The analysis by two-way ANOVA revealed a significant main effect of treatment (F(1.28) = 74.915; p < 0.001). Concentrations of KMO in plasma were significantly higher in rats repeatedly treated with LPS compared to those in vehicle-treated animals (Fig. 1). No statistically significant differences were observed for gender. Figure 1. Concentrations of KMO in plasma of rats treated with increasing doses of LPS or vehicle for 5 days. Results are expressed as means ± SEM DISCUSSION AND CONCLUSION The present findings confirmed our hypothesis and showed that repeated treatment with the endotoxin LPS increases plasma concentrations of KMO, a key enzyme of the kynurenine pathway of tryptophan metabolism. This activation was present in both genders. The observation of enhanced levels of KMO is consistent with previous studies describing the effects of acute administration of LPS. Single peripheral injection of LPS induced a robust increase in the KMO gene expression in the rat brain cortex and hippocampus (Connor et al. 2008). KMO mRNA levels were also increased in isolated microglia of mice after acute treatment with LPS (Corona et al. 2010). No studies evaluating the concentrations or gene expression of KMO under repeated LPS treatment have been reported in the available literature. Another factor that could modify the action of LPS is gender. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Facultatis Pharmaceuticae Universitatis Comenianae de Gruyter

Stimulatory effect of repeated treatment with lipopolysaccharide on a key enzyme of the kynurenine pathway in both genders in rats

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de Gruyter
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Copyright © 2016 by the
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2453-6725
DOI
10.1515/afpuc-2016-0009
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Abstract

Keywords Kúcové slová: Immune challenge ­ Kynurenine-3-monooxygenase - Gender imunitná aktivácia ­ kynurenín-3-monooxygenáza - pohlavie INTRODUCTION Lipopolysaccharide (LPS) is an endotoxin of the outer membrane of Gram-negative bacteria Escherichia coli. Repeated administration of LPS can be used as a model of chronic stress and also as a model for immune system activation. Among others, the administration of LPS leads to activation of the kynurenine pathway of tryptophan metabolism (Kubesova et al. 2015). The kynurenine pathway consists of two functionally distinct branches that generate several neuroactive metabolites. Under basal conditions, kynurenine metabolism favours the formation of neuroprotective kynurenic acid. Disruptions in homoeostasis can shift the balance towards an increased production of the neurotoxic quinolinic acid. Kynurenine-3monooxygenase (KMO) is a key enzyme involved in regulating the production of these two metabolites. Changes in KMO * E-mail: csano.agi@gmail.com © European Pharmaceutical Journal expression or activity may contribute to the development of neurodegenerative, neuropsychiatric and neurodevelopmental diseases (Parrott and O´Connor, 2015). The aim of the present study was to test the hypothesis that repeated treatment with LPS has an impact on plasma concentrations of KMO. To our knowledge, there is no information on gender differences in LPS-induced activation of the kynurenine pathway. Therefore, the present experiments were performed in both male and female rats. MATERIAL AND METHODS Sprague-Dawley rats were treated either with LPS in increasing doses (to prevent the development of tolerance) Eur. Pharm. J. LXIII, 2016 (1): 20-22. Stimulatory effect of repeated treatment with lipopolysaccharide on a key enzyme of the ... for 5 days (50­200 µg/kg) or vehicle, thus simulating a shortterm inflammatory state. All procedures were approved by the Animal Health and Animal Welfare Division of the State Veterinary and Food Administration of the Slovak Republic. Two hours after the last injection, the animals were quickly decapitated and blood was collected. Plasma concentrations of KMO were measured by an enzyme-linked immunosorbent assay (ELISA) kit according to the manufacturer's instructions (CSB-EL012475RA, Cusabio). The sensitivity of the assay was 3.9 pg/ml with the intra-assay and inter-assay coefficient of variation of < 8% and < 10%, respectively. The results were analysed by two-way ANOVA for factors treatment and gender. RESULTS The activation of the immune system by a repeated treatment with LPS was confirmed by a decrease in body weight gain and increased mRNA levels of proinflammatory cytokines (data not shown). The analysis by two-way ANOVA revealed a significant main effect of treatment (F(1.28) = 74.915; p < 0.001). Concentrations of KMO in plasma were significantly higher in rats repeatedly treated with LPS compared to those in vehicle-treated animals (Fig. 1). No statistically significant differences were observed for gender. Figure 1. Concentrations of KMO in plasma of rats treated with increasing doses of LPS or vehicle for 5 days. Results are expressed as means ± SEM DISCUSSION AND CONCLUSION The present findings confirmed our hypothesis and showed that repeated treatment with the endotoxin LPS increases plasma concentrations of KMO, a key enzyme of the kynurenine pathway of tryptophan metabolism. This activation was present in both genders. The observation of enhanced levels of KMO is consistent with previous studies describing the effects of acute administration of LPS. Single peripheral injection of LPS induced a robust increase in the KMO gene expression in the rat brain cortex and hippocampus (Connor et al. 2008). KMO mRNA levels were also increased in isolated microglia of mice after acute treatment with LPS (Corona et al. 2010). No studies evaluating the concentrations or gene expression of KMO under repeated LPS treatment have been reported in the available literature. Another factor that could modify the action of LPS is gender.

Journal

Acta Facultatis Pharmaceuticae Universitatis Comenianaede Gruyter

Published: Sep 1, 2016

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