Indole-3-carboxaldehyde protects mouse from Shigella infection

Abstract:

[Objective]To investigate the alleviating effect of indole-3-carboxaldehyde (I3A) on the colitis caused by Shigella infection and decipher the underlying mechanism.[Methods]We conducted the in vitro experiment to measure the minimum inhibitory concentration (MIC) and activity of I3A against Shigella by micro broth dilution method.Further,we used a microplate reader to measure the absorbance (A₆₀₀) of the bacterial suspensions with different concentrations of I3A at 600 nm and counted the number of Shigella via the plate colony counting method.In the in vivo experiment,we randomly assigned 18 mice into a control (NC) group,a SF301 group,and a SF301+I3A group.The SF301+I3A group was administrated with 200µL I3A by gavage for 8 consecutive days,and the NC group and SF301 group with 200µL sterile water.The colitis model of Shigella infection was established on the 4th day in the SF301 group and SF301+I3A group.Body weight and disease activity index (DAI) were used to evaluate the conditions of mice.After the above experiments,we euthanized all the mice,collected the middle colon for histopathological detection to observe the inflammation,determined the expression levels of interleukin-6(IL-6) and tumor necrosis factor-α(TNF-α) in the lower colon,and measured the bacterial load in feces and cecum.The safety of I3A application in vivo was monitored in mice for 14 days.[Results] In vitro experiment:the MIC of I3A was 128µg/mL.The bacterial counts and A₆₀₀in the groups treated with different concentrations of I3A were different from those in the control group (P<0.05).In vivo experiment:compared with the SF301 group,the SF301+I3A group showed the body weight and DAI close to those in the NC group and significantly relieved colonic damage.No obvious inflammation was observed in SF301+I3A group,and the bacterial load and the expression levels of inflammatory cytokines were different between SF301+I3A group and SF301 group (P<0.05).I3A had no significant effect on the body weight of mice (P>0.05).[Conclusion] We demonstrate that I3A has a protective effect on the colitis caused by Shigella infection.Specifically,I3A alleviates the colitis by inhibiting Shigella load and reducing colonic damage and inflammation levels.Moreover,I3A shows no toxicity in vivo.