Metabolism of benzo[a]pyrene by cultured rat and human buccal mucosa cells

Abstract

Primary cultures of epithelial and fibroblast cells derived from human oral mucosa were studied for the ability to activate a tobacco smoke carcinogen, benzo[a]pyrene (BP). The cells were exposed to benzo[a]pyrene for 18 h. The cell-free medium was extracted with ethylacetate/acetone, and high-pressure liquid chromatography analysis of this fraction revealed that BP tetrols and diols were the major metabolites formed by both epithelial and fibroblast cells. However, the epithelial cells had a much higher rate of biotransformation of BP as measured by binding to cellular DNA. The mean binding level to human buccal mucosal DNA was among the highest observed in stratified human epithelia. The major BP-DNA adduct was formed by the reaction of the 'bay-region' BP diolepoxide with the exocyclic 2-amino group in guanine. In contrast to human cells, BP phenols and BP 9,10-diol were the major metabolites produced by primary epithelial and fibroblast cells derived from rat buccal mucosa. The DNA binding levels of BP in the two rat cell types were identical, and the binding level was several-fold lower than in the human epithelial cells. When an established rat tongue epithelial cell line (RTE 2) was treated with polycyclic aromatic hydrocarbons--BP and 7,12-dimethylbenz[a]-anthracene--a slight toxic effect was observed. Our results indicate that primary cultures of oral mucosa are able to metabolize BP into its ultimate carcinogenic form at a rate similar to or higher than other potential target tissues for BP-induced carcinogenesis.

In vitrosystems toxicology approach to investigate the effects of repeated cigarette smoke exposure on human buccal and gingival organotypic epithelial tissue cultures

“…Other studies have also reported that buccal epithelial cells in vitro exhibit active metabolism of tobacco smoke constituents, such as nicotine-derived nitrosamine ketone [i.e. 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone] and benzo[a]pyrene (Autrup et al, 1985; Liu et al, 1993). …”

Assessment of cytogenic damage in the form of micronuclei in oral epithelial cells in patients using smokeless and smoked form of tobacco and non-tobacco users and its relevance for oral cancer

“…Oral mucosal cells are the first barrier for inhalation or ingestion route and are capable of metabolizing proximate carcinogens to reactive products. [3][4][5][6] Approximately, 90% of human cancers originate from oral epithelial cells. [7] They represent a preferred target site for early genotoxic events induced by carcinogenic agents entering the body through inhalation and ingestion.…”

Transcript profiling of enzymes involved in detoxification of xenobiotics and reactive oxygen in human normal and simian virus 40 T antigen‐immortalized oral keratinocytes

“…3,4 Detoxification enzymes play variable roles in oral cancer development as implied from several studies. Expression of mRNA for various CYPs 5,6 and metabolism of the polycyclic aromatic hydrocarbon benzo(a)pyrene to DNA binding intermediates 7 in cultured human NOK indicate existence of oxidative metabolism. Moreover, both normal and transformed keratinocyte lines significantly oxidize specific CYP substrates, e.g., ethoxyresorufin and the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, known to undergo metabolism by several CYPs.…”