Relevance of Microbiome to Cigarette Smoking and Oral Cancer

Methods: Oral wash samples were collected from 9 patients with OSCC, 1 patient with leukoplakia, and 10 non-cancer controls (including 5 smokers and 5 non-smokers). A 16S rRNA gene survey was performed by 454 pyrosequencing of the V3-5 region. Also, a mock community, composed of 5 bacterial species found in the oral microbiome, was tested for its ability to metabolize cigarette carcinogens. Results: Samples of the oral microbiome were classified into two types, based on taxonomic similarity between samples. The type I microbiome was dominated by Gram-positive bacteria and associated with non-cancer controls (9/10), while the type II microbiome was more abundant in Gram-negative bacteria and primarily found in patients with OSCC/leukoplakia (6/10). Furthermore, OSCC/leukoplakia was associated with an apparent decrease in the relative abundance of streptococcus (22.3%) compared with non-smoking (39.4%) and smoking controls (40.1%). There was a step-wise increase in the relative abundance of Veilonella along the non-smoking controls (2.3%)-smoking controls (6.8%)-OSCC/leukoplakia (9.9%) sequence. Metabolomic analysis demonstrated that the mock bacterial community including Streptococcus mitis and veilonella dispar hydroxylated N-Nitrosodiethylamine and degraded p-Chloroaniline, both being carcinogens found in cigarette smoke.

Conclusions: Cigarette smoking and oral squamous cell carcinoma are associated with an alteration of the oral microbiome. The oral microbiome has the potential to modulate oral cancer risk by activating or degrading some cigarette carcinogens. Metabolomic analysis is a feasible approach to demonstrate biological/functional relevance of the oral microbiome in the development of OSCC.

Support: supported in part by grants UH2CA140233 from the NIH Human Microbiome Project and R01AI063477 from NIAID.