No difference in 4‐nitroquinoline induced tumorigenesis between germ‐free and colonized mice

Abstract

Variations in oral bacterial communities have been linked to oral cancer suggesting that the oral microbiome is an etiological factor that can influence oral cancer development. The 4‐nitroquinoline 1‐oxide (4‐NQO)‐induced murine oral and esophageal cancer model is frequently used to assess the effects of preventive and/or therapeutic agents. We used this model to assess the impact of the microbiome on tumorigenesis using axenic (germ‐free) and conventionally housed mice. Increased toxicity was observed in germ‐free mice, however, no difference in tumor incidence, multiplicity, and size was observed. Transcriptional profiling of liver tissue from germ‐free and conventionally housed mice identified 254 differentially expressed genes including ten cytochrome p450 enzymes, the largest family of phase‐1 drug metabolizing enzymes in the liver. Gene ontology revealed that differentially expressed genes were enriched for liver steatosis, inflammation, and oxidative stress in livers of germ‐free mice. Our observations emphasize the importance of the microbiome in mediating chemical toxicity at least in part by altering host gene expression. Studies on the role of the microbiome in chemical‐induced cancer using germ‐free animal models should consider the potential difference in dose due to the microbiome‐mediated changes in host metabolizing capacity, which might influence the ability to draw conclusions especially for tumor induction models that are dose dependent.

IL-1β transgenic mouse model of inflammation driven esophageal and oral squamous cell carcinoma

“…Interestingly, in our study, IL-1 β mice raised under both SPF and GF conditions showed similar grades/incidence of esophageal squamous dysplasia and ESCC development. Similarly, in a different study, 4-nitroquinoline treated GF and SPF mice showed comparable oral and esophageal tumorigenesis 23 .…”

“…Elevated tissue iNOS and NO lead to oxidative stress-related DNA double-strand breaks and genomic instability during esophageal squamous cell carcinogenesis in human patients and mouse models 11 , 16 – 19 . Animal models to study esophageal and oral squamous cell carcinomas (SCCs) are mostly based on chronic exposure to carcinogens such as 4-nitroquinoline-1-oxide (4NQO) or a combination of genetically engineered mice and chemical carcinogenesis models as well as orthotopic tumor xenograft models 5 , 20 – 23 . However, genetically engineered mouse models with spontaneous esophageal and/oral SCC development in an inflammatory setting are relatively sparse in the literature 24 , 25 .…”

Microbiome dysbiosis inhibits carcinogen-induced murine oral tumorigenesis

“…Bacterial toxins and metabolites can prevent tumor growth and activate the immune system, leading to reduced tumor development 38 . In oral cancer, using germ-free animal models to evaluate the role of the microbiome in 4-NQO-induced oral cancer, that it did not differ in tumor incidence, diversity, and size, the authors also suggested that the dose of the carcinogen may affect the ability to draw conclusions 15 . Stashenko et al recently reported that directly transplanting the oral microbiome of donor mice (whether normal mice or oral cancer patients) into germ-free mice can promote 4-NQO-induced oral tumors 16 .…”

“…Antibiotic-induced microbiome depletion has been used frequently to study the role of the gut microbiome in pathological conditions 13 , 14 . In oral cancer, previous studies have used germ-free mouse models to assess the role of the microbiome in carcinogen-induced oral cancer, but with conflicting results 15 , 16 . Therefore, the effects of antibiotic-induced oral microbiome dysbiosis or depletion on oral carcinogenesis remain to be investigated.…”