Project description:BackgroundPatients with pelvic malignancies often receive radiosensitising chemotherapy with radiotherapy to improve survival; however, this is at the expense of increased normal tissue toxicity, particularly in elderly patients. Here, we explore if an alternative, low-cost, and non-toxic approach can achieve radiosensitisation in mice transplanted with human bladder cancer cells. Other investigators have shown slower growth of transplanted tumours in mice fed high-fibre diets. We hypothesised that mice fed a high-fibre diet would have improved tumour control following ionising radiation (IR) and that this would be mediated through the gut microbiota.ResultsWe investigated the effects of four different diets (low-fibre, soluble high-fibre, insoluble high-fibre, and mixed soluble/insoluble high-fibre diets) on tumour growth in immunodeficient mice implanted with human bladder cancer flank xenografts and treated with ionising radiation, simultaneously investigating the composition of their gut microbiomes by 16S rRNA sequencing. A significantly higher relative abundance of Bacteroides acidifaciens was seen in the gut (faecal) microbiome of the soluble high-fibre group, and the soluble high-fibre diet resulted in delayed tumour growth after irradiation compared to the other groups. Within the soluble high-fibre group, responders to irradiation had significantly higher abundance of B. acidifaciens than non-responders. When all mice fed with different diets were pooled, an association was found between the survival time of mice and relative abundance of B. acidifaciens. The gut microbiome in responders was predicted to be enriched for carbohydrate metabolism pathways, and in vitro experiments on the transplanted human bladder cancer cell line suggested a role for microbial-generated short-chain fatty acids and/or other metabolites in the enhanced radiosensitivity of the tumour cells.ConclusionsSoluble high-fibre diets sensitised tumour xenografts to irradiation, and this phenotype was associated with modification of the microbiome and positively correlated with B. acidifaciens abundance. Our findings might be exploitable for improving radiotherapy response in human patients.
Project description:A molecular method, termed hierarchical oligonucleotide primer extension (HOPE), was used to determine the relative abundances of predominant Bacteroides spp. present in fecal microbiota and wastewaters. For this analysis, genomic DNA in feces of healthy human adults, bovines, and swine and in wastewaters was extracted and total bacterial 16S rRNA genes were PCR amplified and used as the DNA templates for HOPE. Nineteen oligonucleotide primers were designed to detect 14 Bacteroides spp. at different hierarchical levels (domain, order, cluster, and species) and were arranged into and used in six multiplex HOPE reaction mixtures. Results showed that species like B. vulgatus, B. thetaiotaomicron, B. caccae, B. uniformis, B. fragilis, B. eggerthii, and B. massiliensis could be individually detected in human feces at abundances corresponding to as little as 0.1% of PCR-amplified 16S rRNA genes. Minor species like B. pyogenes, B. salyersiae, and B. nordii were detected only collectively using a primer that targeted the B. fragilis subgroup (corresponding to approximately 0.2% of PCR-amplified 16S rRNA genes). Furthermore, Bac303-related targets (i.e., most Bacteroidales) were observed to account for 28 to 44% of PCR-amplified 16S rRNA genes from human fecal microbiota, and their abundances were higher than those detected in the bovine and swine fecal microbiota and in wastewaters by factors of five and two, respectively. These results were comparable to those obtained by quantitative PCR and to those reported previously from studies using whole-cell fluorescence hybridization and 16S rRNA clone library methods, supporting the conclusion that HOPE can be a sensitive, specific, and rapid method to determine the relative abundances of Bacteroides spp. predominant in fecal samples.
Project description:Immunoglobulin A (IgA) is essential for defense of the intestinal mucosa against harmful pathogens. Previous studies have shown that Bacteroidetes, the major phylum of gut microbiota together with Firmicutes, impact IgA production. However, the relative abundances of species of Bacteroidetes responsible for IgA production were not well understood. In the present study, we identified some specific Bacteroidetes species that were associated with gut IgA induction by hsp60-based profiling of species distribution among Bacteroidetes The levels of IgA and the expression of the gene encoding activation-induced cytidine deaminase (AID) in the large intestine lamina propria, which is crucial for class switch recombination from IgM to IgA, were increased in soluble high-fiber diet (sHFD)-fed mice. We found that Bacteroides acidifaciens was the most abundant Bacteroidetes species in both sHFD- and normal diet-fed mice. In addition, the gut IgA levels were associated with the relative abundance of Bacteroides fragilis group species such as Bacteroides faecis, Bacteroides caccae, and Bacteroides acidifaciens Conversely, the ratio of B. acidifaciens to other Bacteroidetes species was reduced in insoluble high-fiber diet fed- and no-fiber diet-fed mice. To investigate whether B. acidifaciens increases IgA production, we generated B. acidifaciens monoassociated mice and found increased gut IgA production and AID expression. Collectively, soluble dietary fiber increases the ratio of gut Bacteroides fragilis group, such as B. acidifaciens, and IgA production. This might improve gut immune function, thereby protecting against bowel pathogens and reducing the incidence of inflammatory bowel diseases.IMPORTANCE Immunoglobulin A (IgA) is essential for defense of the intestinal mucosa against harmful pathogens. Gut microbiota impact IgA production, but the specific species responsible for IgA production remain largely elusive. Previous studies have shown that IgA and Bacteroidetes, the major phyla of gut microbiota, were increased in soluble high-fiber diet-fed mice. We show here that the levels of IgA in the gut and the expression of activation-induced cytidine deaminase (AID) in the large intestine lamina propria, which is crucial for class switch recombination from IgM to IgA, were correlated with the abundance of Bacteroides fragilis group species such as Bacteroides faecis, Bacteroides caccae, and Bacteroides acidifaciens B. acidifaciens monoassociated mice increased gut IgA production and AID expression. Soluble dietary fiber may improve gut immune function, thereby protecting against bowel pathogens and reducing inflammatory bowel diseases.