Evaluation of mutagenic effects of formaldehyde in vitro: Detection of crosslinks and mutations in mouse lymphoma cells

Abstract

Formaldehyde (FA) is known to be a genotoxic substance. FA induces DNA-protein crosslinks (DPC) as the primary DNA lesion. However, the significance of DPC for FA-induced mutations and the mechanism(s) of mutation formation are at present poorly understood. Our previous results indicated that FA-induced DPC seem to be related to cytotoxicity and clastogenicity but do not lead to gene mutations in mammalian cells. We now demonstrate that FA efficiently induces mutations in the mouse lymphoma assay (MLA). Treatment of L5178Y cells with FA for 2 h caused a clear and concentration-related mutagenic effect in the MLA. As this mutagenic effect was mainly due to a strong increase in small colony mutants, we suggest that FA mainly causes mutations by induction of chromosomal aberrations. Molecular characterization of spontaneous and FA-induced mutants by loss of heterozygosity analysis showed an extensive loss of functional tk sequences, supporting a clastogenic mechanism of mutation formation. Whole chromosome fluorescence in situ hybridization was used to further elucidate the mechanism(s) of chromosome mutations. Our results indicate that small-scale chromosomal rearrangements (e.g. deletions or recombinations) are mainly involved in FA-induced mutagenesis in the MLA.