Evaluation of mucositis induced by irinotecan after microbial colonization in germ-free mice

Mucositis is one of the most debilitating side effects of chemotherapy and some previous studies suggest a role for indigenous microbiota in the course of this pathology. Therefore, the aim of our study was to evaluate the differences in phenotype between germ-free (GF) and conventional (CV) mice, and the role of beta-glucuronidase-producing bacteria in the development of irinotecan treatment in a murine model. After mucositis induction, CV mice showed a significant increase in all inflammatory parameters when compared to GF mice. CV animals also showed more lesions of the intestinal epithelium, coherent with their higher intestinal permeability. The conventionalization of GF animals reversed their phenotype to that found in CV mice. In addition, gnotobiotic mice monoassociated with an Escherichia coli strain producing beta-glucuronidase showed an increased permeability when compared to gnotobiotic mice monoassociated with an E. coli strain deleted for the gene encoding beta-glucuronidase, but these did not show any differences in the influx of neutrophils, eosinophils or histological characteristics. Our data confirmed that components of the gut microbiota are involved in the signs of mucositis. Nevertheless, other mechanisms than this enzyme are involved in the irinotecan treatment, since the monoassociation was not able to restore the entire phenotype observed in the CV animals with irinotecan treatment in our murine model.