Purpose: Obesity is a risk factor for colorectal cancer (CRC), and the intestinal microbiome is considered to contribute to CRC and obesity. Nonetheless, the role of the intestinal microbiome in obesity-related CRC is unclear. This study aimed to clarify the relationship between obesity-related CRC and the intestinal microbiome using a mouse model. Methods: We compared an obese and insulin-resistant type 2 diabetes mouse model [KKAy] to wild-type mice (WT) [C57BL/6 J]. Azoxymethane was intraperitoneally injected to develop a mouse model CRC. At 26 weeks, we compared the number of tumors and the intestinal microbiome. We also compared them across two models, namely, antibiotic cocktail and co-housing. Results: In all models, KKAy mice had a significantly greater number of tumors than WT mice. Analysis showed that the distribution of the intestinal microbiome changed in both models; however, no difference in tumor development was observed. Tumor expression was suppressed only in the antibiotic cocktail model of WT, whereas KKAy mice bore tumors (C57Bl/6 J: KKAy, 0/9:8/8; p < 0.001). KKAy mice remained predominantly tumor-bearing in all treatments. Conclusion: Based on the results, the intestinal microbiome may not be associated with tumorigenesis in obesity-related CRC. It may be necessary to think of other facts linked to obesity-related CRC.
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