Preliminary Study On The Protective Effect Of Taurine Against Listeria Monocytogens Infection And Its Mechanism

Objective:Taurine is a sulfur-containing amino acid widely distributed in various tissues of animals.It has various biological functions such as binding bile salt,regulating osmotic pressure,membrane stabilization and calcium regulation.In addition,the metabolic intermediate of taurine,chloramine taurine,has antioxidant,anti-inflammatory and other immunomodulatory effects.Taurine is one of the main components of the traditional Chinese medicine bezoar.It is used in a variety of Chinese patent medicines to clear heat and detoxify.Taurine is also added to many food and energy drinks.In the current epidemic of novel coronavirus,little is known about the effect of taurine supplementation on intracellular pathogen infection,so it is necessary to study this.Listeria monocytogens（Lm）is a common cytoplasmic parasite that can induce strong innate and adaptive cellular immunity in mice.It is similar to the immune response caused by viruses,and is a commonly used model for the study of intracellular infection.In this study,BALB/c mice were used to establish a Lm infection model,observe the changes of physiological indexes such as body weight and survival rate in Lm infected mice and taurine treated mice,and detect the pathological progression,inflammatory factors and immune cell activation in each group of mice,so as to observe the effect of taurine on intracellular bacterial infection and explore the preliminary mechanism of taurine anti-infection.To provide more experimental evidence for the use of taurine as nutritional supplement and antipyretic and detoxifying drug.Methods:1.Lm was cultured in TSB medium at 37℃overnight,and 1ml overnight culture was added to 100ml TSB containing 0.01g/ml,0.05g/ml and 0.1g/ml taurine,respectively.Taurine free bacterial culture was used as control.The absorbance at 600nm was detected at 1h,2h,4h,6h,8h,10h and 12h,respectively,and the bacterial growth curve was drawn.2.BALB/c mice were used to establish listeria infection model.Mice in the treatment group were injected intraperitoneically daily at the dose of 400mg/kg taurine.The changes in body weight,survival rate and the differences in the amount of bacteria carried in brain,liver and spleen of the two groups were monitored daily.HE staining was used to observe the pathological injury of liver and spleen tissue,so as to compare the disease course of the two groups of mice.3.The oxidative stress and inflammation of mice were analyzed by comparing the contents of MPO and H₂O₂and the expressions of inflammatory factors（TNF-α,IL-1β,IL-6 and IFN-γ）in different tissues between the infection group and the treatment group.4.Flow cytometry was used to detect the change of T cell content and the expression of IFN-γin it,so as to study the regulatory effect of taurine on immune cells in infection.5.The protein expressions of NF-κB（P65）,ERK pathway and NLRP3 were detected by Western Blot,and the mechanism of inhibiting Lm infection by taurine was analyzed.Results:1.Taurine below 0.01g/ml had no significant effect on the growth of Lm in vitro,while taurine above 0.05mg/ml had inhibitory effect on the growth of Lm.2.The dose of taurine with theoretical concentration lower than 0.01g/ml was selected for in vivo experiment.Mice infected with Lm were intraperitoneally injected with400mg/kg taurine,and the weight loss caused by infection was improved and the survival rate was improved.The bacterial load in liver,spleen and brain of mice in the treatment group was significantly reduced,and the pathological results showed that the damage of liver,spleen and brain in the taurine treatment group was significantly improved.3.Taurine intervention alleviated oxidative stress and inflammation in mice:the contents of MPO and H₂O₂ in liver,spleen and brain of mice in the treatment group were significantly decreased compared with those in the infection group,and the contents of various inflammatory factors（TNF-α,IL-1β,IL-6,IFN-γ）in spleen were decreased.4.Taurine reversed lymphocyte depletion caused by Lm,increased the number of activated T cells（especially CD8⁺T cells）,and played a role in killing pathogens.5.Taurine treatment increased the phosphorylated expression of ERK protein,activated the ERK pathway,and decreased the NLRP3 expression level.Conclusions:1.Taurine can significantly improve the oxidative stress and inflammation of mice tissues induced by Lm infection,which may be related to the inhibition of NLRP3 pathway.2.Taurine can reverse lymphocyte depletion caused by Lm and increase the number of activated CD8⁺T cells to resist Lm infection.3.Taurine can activate the ERK pathway and may play a role in T cell activation.