LAUSR

BACKGROUND & AIMS Alterations in the intestinal microbiota affect development of colorectal cancer (CRC) and drug metabolism. We studied whether the intestinal microbiota affects the ability of aspirin to reduce colon tumor development in mice. METHODS We performed studies with APCmin/+ mice and mice given azoxymethane and dextran sulfate sodium (DSS) to induce colorectal carcinogenesis. Some mice were given antibiotics, to deplete intestinal microbes, with or without aspirin throughout the entire experiment. Germ-free mice were studied in validation experiments. Colon tissues were collected and analyzed by histopathology, quantitative reverse-transcription PCR and immunoblots. Blood samples and gut luminal contents were analyzed by liquid chromatography/mass spectrometry and an arylesterase activity assay. Fecal samples were analyzed by 16S rRNA gene and shotgun metagenome sequencing. RESULTS Administration of aspirin to mice reduced colorectal tumor number and load in APCmin/+ mice, and mice given azoxymethane and DSS, that had been given antibiotics (depleted gut microbiota) but not in mice with intact microbiota. Germ-free mice given aspirin developed fewer colorectal tumors than conventionalized germ-free mice given aspirin. Plasma levels of aspirin were higher in mice given antibiotics than in mice with intact gut microbiota. Analyses of luminal contents revealed that aerobic gut microbes, including Lysinibacillus sphaericus, degrade aspirin. Germ-free mice fed L sphaericus had lower plasma levels of aspirin than germ-free mice that were not fed this bacterium. There was an inverse correlation between aspirin dose and colorectal tumor development in conventional mice, but this correlation was lost with increased abundance of L sphaericus. Fecal samples from mice fed aspirin were enriched in Bifidobacterium and Lactobacillus genera, which are considered beneficial, and had reductions in Alistipes finegoldii and Bacteroides fragili, which are considered pathogenic. CONCLUSIONS Aspirin reduces development of colorectal tumors in APCmin/+ mice and mice given azoxymethane and DSS, depending on the presence of intestinal microbes. L sphaericus in the gut degrades aspirin and reduced its chemopreventive effects in mice. Fecal samples from mice fed aspirin were enriched in beneficial bacteria, with reductions in pathogenic bacteria.