Protective Effects Of Aryl Hydrocarbon Receptor Activation On Intestinal Barrier Damage In A Mouse Model Of Total Parenteral Nutrition

Background and purpose:Maintaining proper nutrition in patients can promote wound healing,improve immune function,avoid complications due to malnutrition,shorten the length of hospital stay,and significantly improve the quality of life.The most optimal and physiological form of nutrition is through the gastrointestinal tract;however,many patients are unable to utilize the intestinal tract to obtain nutrition due to mechanical,functional,or postoperative defects.For these patients who lack nutrition in the intestine,total parenteral nutrition(TPN)is an alternative nutritional therapy that provides nutrition and calories through the vein.TPN has been widely used in clinical treatment for nearly half a century.However,long-term TPN treatment can bring various complications such as intestinal injury,parenteral nutrition-related liver,lung and kidney damage,intestinal microbial disorders,metabolic disorders and infections.There is no effective method to deal with these complications in clinical practice,and research and exploration of various complications caused by TPN relying on animal experiments are of great clinical significance in the field of nutrition therapy.Existing studies on the intestine-hepatic axis,intestine-brain axis,and intestine-lung axis all suggest that intestinal barrier damage plays an important role in mediating TPN-related distant organ damage.Aryl hydrocarbon receptor(Ah R)is a nuclear transcription factor activated by specific ligands,which is widely present in the cytoplasm of cells and enters the nucleus after binding to ligands to regulate downstream gene expression.It also plays an important role in regulating intestinal barrier function and maintaining the homeostasis of the intestinal microenvironment.Ligand-activated Ah R induces CYP1A1 expression through a series of downstream cascade reactions,which is the classical Ah R activation signaling pathway.Evidence suggests that metabolic disturbances during TPN lead to a decrease in endogenous ligands of intestinal Ah R,which may reduce Ah R activity and thus promote the development of intestinal injury.To investigate the potential mechanisms of TPN-related intestinal injury,in the first part,we first constructed a mouse TPN model by external jugular vein placement infusion,took intestinal tissues from TPN mice for transcriptome sequencing analysis,and took cecum contents from TPN mice for ITS(Internal Transcribed Spacer)fungal sequencing analysis.Based on the key gene CYP1A1,which was found to be significantly down-regulated in expression after TPN by transcriptome sequencing,and previous studies,we hypothesized that intestinal Ah R activation was suppressed during TPN.Therefore,in the second part,we investigated the protective effect of aromatic hydrocarbon receptor(Ah R)activation on intestinal barrier damage in TPN mice by exogenously administering 6-Formylindolo[3,2-B]carbazole(6-For Mylindolo[3,2-b]carbazole,FICZ)to activate Ah R.Methods:Part I: 1.A TPN mouse model was constructed by external jugular vein placement and fasting infusion of parenteral nutrition solution;2.Ileal tissues of mice were taken for transcriptome sequencing analysis;3.Cecum contents of mice were taken for fungal ITS sequencing analysis.Part II: 18 mice were randomly divided into three groups: control group,TPN group,and TPN+FICZ group after infusion via external jugular vein placement.7 days later,we compared the weight changes of mice before and after modeling,and used HE staining,histological scoring,RT-PCR,ELISA,Western blot and other techniques to observe the length of small intestine and morphological changes of intestinal tissues,and to detect Ah R in The intestinal expression and activity,intestinal tissue-related inflammatory factor levels,tight junction protein expression and intestinal mucosal barrier damage and function were examined.Results:Part I: 1.Mice survived stably for 7 days after tube placement,and a mouse TPN model was successfully established;2.Transcriptome sequencing of the ileum of TPN mice identified a total of 891 differentially expressed genes,including 446 up-regulated genes and 445 downregulated genes.CYP1A1 gene expression levels were significantly reduced in TPN mice and were closely related to the significantly enriched functions and pathways;3.The dominant fungi at the genus level included Candida,Penicillium,Aspergillus,and Talaromyces.Part II: Compared with the control group,the mice in the TPN group had significantly decreased body weight and significantly shortened small intestine length(P< 0.05),and pathology showed that the mucosal damage of small intestine and Chiu score were elevated in the mice in the TPN group;the levels of serum intestinal barrier function indexes FITC-D,i FABP and intestinal tissue inflammatory factors TNF-α and IL-1β were high and significantly elevated(P< 0.05),and the levels of intestinal Ah R activation index CYP1A1,intestinal barrier tight junction protein ZO-1,Occludin and intestinal tissue anti-inflammatory factor IL-10 levels were significantly lower(P< 0.05).Compared with the TPN group,mice with FICZ intervention showed significantly lower body weight loss and small intestine shortening(P< 0.05),improved small intestine mucosal damage and lower Chiu score(P< 0.05);serum FITC-D,i FABP and intestinal tissue TNF-α and IL-1β levels were significantly lower(P< 0.05),and intestinal tissue CYP1A1,ZO-1,Occludin and IL-10 levels were significantly increased(P< 0.05).Conclusion:In this study,we constructed a TPN mouse model by external jugular vein placement and activated intestinal Ah R in TPN mice using FICZ,and the results suggest that Ah R activation may alleviate TPN-induced intestinal barrier damage in mice by alleviating intestinal mucosal inflammation and participating in regulating tight junction protein expression.It provides a new potential approach for the clinical prevention and treatment of TPN-related complications.In addition,this study analyzed the effect of TPN on intestinal fungi in mice by ITS sequencing for the first time,which may provide a theoretical basis for the subsequent prevention and treatment about TPN-related intestinal microbial disorders and metabolic disorders.