CELL-PROLIFERATION AND FORMALDEHYDE-INDUCED RESPIRATORY CARCINOGENESIS

Formaldehyde is a nasal carcinogen in the rat but the cancer risk this chemical poses for humans remains to be determined. Formaldehyde indu ces nonlinear, concentration-dependent increases in nasal epithelial c ell proliferation and DNA-protein cross-link formation following short -term exposure. Presented in this review are results from a mechanisti cally based formaldehyde inhalation study in which an important endpoi nt was the measurement of cell proliferation indices in target sites f or nasal tumor induction. Male Fischer 344 rats were exposed to 0, 0.7 , 2, 6, 10, or 15 ppm formaldehyde for up to 2 years (6 hr/day, 5 day/ week). Statistically significant increases in cell proliferation were confined to the 10 and 15 ppm groups, which remained elevated througho ut the study. The concentration-dependent increases in cell proliferat ion correlated strongly with the tumor response curve, supporting the proposal that sustained increases in cell proliferation are an importa nt component of formaldehyde carcinogenesis. The nonlinearity observed in formaldehyde-induced rodent nasal cancer is consistent with a high -concentration effect of regenerative cell proliferation of the target organ coupled with the genotoxic effects of formaldehyde. Cell kineti c data from these studies provide important information that may be ut ilized in the assessment of risk for humans exposed to formaldehyde.