The Roles Of Fecal Tryptophan Metabolism In The Pathogenesis Of Colorectal Cancer

Part Ⅰ Alteration of fecal tryptophan metabolism in colorectal cancer and the correlations between fecal tryptophan metabolites and gut microbiota.Background:Dysregulation of fecal metabolism and microbiota dysbiosis are involved in the pathogenesis of colorectal cancer(CRC),and metagenomic study of gut microbiota showed an abnormal tryptophan(Trp)metabolism.Trp intaken from outside can be metabolized into indoles by bacteria or absorbed into the body.90-95%of absorbed Trp is metabolized into Kynurenine(KYN)along the Kynurenine Pathway(KP).Fecal Trp,metabolized by bacteria or absorbed into the body,is involved in tumorigenesis of CRC in vitro and in vivo.However,there are few clinical studies explored the alteration of fecal Trp metabolism and the relationship between Trp metabolism and microbiome in CRC.Aim:To investigate the alterations of fecal Trp metabolism and microbiota in CRC and explore their correlations.Methods:Seventy-nine patients(33 with colon adenoma and 46 with CRC)and 38 healthy controls(HCs)were included.Demographic and clinical features of all subjects were collected.Fecal Trp,KYN,and indoles were examined by Liquid chromatography mass spectrometry.The gut microbiota was detected by 16S ribosomal RNA gene sequencing.Correlations between fecal metabolites and microbiota were analyzed in all subjects.Results:The fecal indoles/Trp ratio was significantly decreased in patients with CRC and ADA compared to HCs,and the ratio showed a decreasing trend in the"HC-ADA-CRC" sequence,while KYN and KYN/Trp ratio were significantly increased in CRC.Both the richness and diversity of fecal microbiota were altered in CRC and ADA patients,and the Firmicutes/Bacteroidetes ratio in CRC group was lower than that in HCs.In addition,the genera Asaccharobacter(Actinobacteria),the genera Parabacteroides(Bacteroidetes),and several genus of Firmicutes phylum(Clostridium XlVb,Fusicatenibacter,Anaerofilum,and Anaerostipes)decreased in CRC and exhibited a positive correlation with some indole derivatives in all subjects.Conclusion:There are alterations of fecal Trp metabolism and microbiota in subjects with CRC compared to HCs,and the dysregulation of Trp metabolism may be related to the reduced bacteria genera involved in Trp-indole metabolism.Part Ⅱ The correlations between fecal Trp metabolism and tissue KP metabolism,intestinal barrier and inflammationBackground:The decreased fecal indoles/Trp and increased KYN and KYN/Trp ratio in the first part suggested that there might be a reciprocal relationship between fecal Trp metabolism and tissue Trp metabolism,but there are few research on their correlation.Indoleamine 2,3-dioxygenase 1(IDO1)was used to evaluate KP activity.KP is involved in the pathogenesis of CRC by activating Wnt/β-catenin.In addition,basic studies have found that metabolites of fecal Trp metabolism can reduce the incidence and number of tumors in CRC models by maintaining the homeostasis of intestinal barrier and their anti-inflammatory effects.But the relationship between reduced fecal indoles/Trp and intestinal barrier damage and body inflammation in CRC patients is unclear.Aim:To evaluate the relationship between fecal Trp metabolism and tissue KP metabolism,intestinal barrier function,and body inflammation;and to preliminarily explore the possible mechanism of fecal Trp metabolism in CRC.Methods:Twenty-four cases of ADA,39 cases of CRC and 28 cases of HC subjects were included.Tissue IDO1,Wnt-5a,and β-catenin mRNA were detected to assess the KP activity.Intestinal barrier function was evaluated by detecting serum D-lactic acid and tissue ZO-1 and Occludin,and systemic inflammation was evaluated by serum IL-6 and IL-22 levels.The correlations between fecal indoles/Trp and the above parameters were analyzed.Results:Compared with the HCs,IDO1 mRNA and Wnt-5a mRNA levels in tissues were significantly increased in CRC patients.The protein and mRNA levels of ZO-1 and Occludin were significantly reduced in patients with ADA and CRC,while the level of serum IL-6 increased significantly.Serum D-lactic acid and IL-22 levels were only significantly increased in CRC group.Fecal indoles/Trp ratio was negatively correlated with tissue IDO1 mRNA and Wnt-5a mRNA levels.Fecal indoles/Trp ratio was positively correlated with the levels of ZO-1 mRNA and ZO-1 protein in tissues,and negatively correlated with serum D-lactic acid.Conclusion:Fecal Trp-indole metabolism decreased and tissue Trp-KYN metabolism increased in patients with CRC,and there was a negative correlation between the above two pathways.These alterations may correlated with the impairment of intestinal barrier,the increase of inflammatory factors and related indicators of Wnt pathway.The damage of defense ability and activation of the carcinogenic pathway may be involved in the pathogenesis of CRC.