The mRNA expression of inducible nitric oxide synthase in DMBA‐induced hamster buccal‐pouch carcinomas using reverse transcription‐polymerase chain reaction

BACKGROUND: Three isoforms of NO synthase (NOS) have been identified: endothelial NOS, neuronal NOS, and inducible NOS (iNOS). The enhanced expression of iNOS, at the protein level, has been reported previously in certain chemically induced oral carcinomas in hamster buccal-pouch mucosa, however, the corresponding expression of iNOS, at the mRNA level, has not yet been demonstrated. The purpose of the present study is to assess the iNOS mRNA expression level in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas using a reverse transcription-polymerase chain reaction (RT-PCR). METHODS: Thirty-three outbred, young (six-weeks old), male, Syrian golden hamsters (Mesocricetus auratus) were randomly divided into one experimental group (13 animals) and two control groups (10 animals each). The pouches of a group of 13 animals of the experimental group were bilaterally painted with a 0.5% DMBA solution three times a week for 12 weeks. Each animal of one control group was similarly treated with mineral oil only, while the other control group of 10 animals remained untreated throughout the experiment. RESULTS: Areas of dysplasia and squamous-cell carcinomas, with a 100% tumor incidence, developed for all of the DMBA-treated buccal pouches. The mineral oil-treated and untreated pouches had no obvious changes. A band of 499-bp, corresponding to iNOS mRNA, was present in all the DMBA-treated hamster buccal-pouch mucosa animals, but not in the untreated animals or the animals treated with mineral oil. Upon direct sequencing, this 499-bp band was confirmed to be part of the iNOS gene. CONCLUSIONS: This study demonstrated that increased iNOS mRNA expression could contribute to the mechanism for experimentally induced oral carcinogenesis.