Inflammatory Effect And Mechanism Of Polystyrene Microplastics On Colon Of Rats

Objective:To investigate the effects of polystyrene microplastics（PS-MPs）exposure on colonic inflammation in rats,and to explore the mechanism of PS-MPs action on colonic inflammation in rats,so as to provide scientific basis for clarifying the toxic effect and mechanism of PS-MPs and preventing and treating health hazards caused by PS-MPs.Methods:Forty-eight six-week-old SPF male Wistar rats were randomly divided into 4groups:control group,0.5mg/kg/d PS-MPs group,5mg/kg/d PS-MPs group and50mg/kg/d PS-MPs group,with 12 rats in each group.Poisoning was administered by gavage once a day for 90 days.The infected group was given the corresponding concentration of 0.5μm polystyrene microplastics,and the control group was given the corresponding volume of distilled water.The rats were anesthetized 24h after the last exposure.Blood samples were collected from the heart,serum was separated,and colon tissue was collected.The levels of inflammatory factors IL-1β,IL-6 and TNF-αin serum and colon tissue of rats were determined by ELISA.Histopathological changes of colon were observed by HE staining.Real-time RCR and Western Blot were used to detect the m RNA and protein expression levels of TLR4/NF-κB/COX-2 signaling pathway genes TLR4,My D88,IKKβ,COX-2 and PGE₂ in rat colon tissue.IBM SPSS 24.0 software was used for statistical analysis,and the normal distribution measurement data was represented by（?）±s.One-way ANOVA was used to compare the differences between groups,and LSD test was used for pairwise comparison between groups.The correlation between TLR4/NF-κB/COX-2 signaling pathway proteins and inflammatory factors was analyzed by Pearson correlation analysis.The test level wasα=0.05.Results:1.The goblet cells were reduced,the muscularis were disordered,and the crypt structure was destroyed and discontinuous.A large number of inflammatory cells were observed in the colonic mucosa and submucosa of rats in 5mg/kg/d and 50mg/kg/d groups.2.The level of IL-1βin serum of infected groups was significantly higher than that of control group（P<0.05）.Serum TNF-αlevel in 5mg/kg/d and 50mg/kg/d groups was significantly higher than that in control group（P<0.05）,and IL-6 level was significantly higher than that in control group and 0.5mg/kg/d groups（P<0.05）.3.The level of TNF-αin colon of infected groups was significantly higher than that of control group（P<0.05）.The level of colon IL-1βin 5mg/kg/d and 50mg/kg/d groups was significantly higher than that in control group and 0.5mg/kg/d group（P<0.05）.The level of colon IL-6 in 50mg/kg/d group was significantly higher than that in control group（P<0.05）.4.The expression level of IKKβm RNA in the colon tissue of rats exposed to PS-MPs was significantly increased with the increase of PS-MPs dose（P<0.05）.The m RNA expression levels of TLR4 and My D88 in 50mg/kg/d group were significantly higher than those in other groups（P<0.05）,and the m RNA expression level of COX-2in 50mg/kg/d group was significantly lower than that in other groups（P<0.05）.PTGER2 m RNA expression in colon of rats in 5mg/kg/d and 50mg/kg/d groups was significantly lower than that in control group（P<0.05）.5.The expression level of TLR4 protein in colon of rats exposed to 50mg/kg/d group was significantly higher than that of control group and 0.5mg/kg/d group（P<0.05）,the expression level of My D88 protein was significantly higher than that of other groups（P<0.05）,and the expression level of IKKβprotein was significantly higher than that of control group（P<0.05）.COX-2 protein expression level was significantly lower than that of control group（P<0.05）.The expression level of PGE₂protein in colon of rats in 5mg/kg/d and 50mg/kg/d groups was significantly lower than that in control group（P<0.05）.6.The expression levels of TLR4 and My D88 were positively correlated with the expression levels of IL-1β,IL-6 and TNF-αin colon of rats（P<0.05）.IKKβprotein expression was positively correlated with IL-1βlevel（P<0.05）.The expression of COX-2 protein was negatively correlated with IL-1βand TNF-α（P<0.05）.PGE₂ protein level was negatively correlated with the expression levels of IL-1β,TNF-αand IL-6（P<0.05）.Conclusion:1.PS-MPs exposure can cause histopathological changes in the colon of rats.2.PS-MPs can increase the levels of inflammatory factors IL-1β,IL-6 and TNF-αin serum and colon of rats.3.PS-MPs can affect the m RNA and protein expression of TLR4/NF-κB/COX-2signaling pathway in colon of rats,and cause colon inflammation in rats.