Formaldehyde-induced sister chromatid exchanges in vitro and the influence of the exogenous metabolizing systems S9 mix and primary rat hepatocytes.

Formaldehyde-induced sister chromatid exchanges (SCE) in vitro and the influence of the exogenous metabolizing systems, S9 mix and primary rat hepatocytes, were studied. The SCE-frequency in V79 cells was dose dependent. A three- to four-fold increase at non-toxic doses was observed. However, in the presence of an exogenous metabolizing system, the number of formaldehyde-induced SCE decreased. S9 mix as well as hepatocytes reduced the SCE frequency to nearly that of the control range. It could be demonstrated that the reduction was not due to an unspecific binding of formaldehyde to macromolecules of the added S9 mix. The decrease in genotoxic effects, due to rapid metabolisation of formaldehyde in vitro and in vivo, explains the differences between results obtained in the in vitro experiments--performed without metabolizing systems--and in vivo results.