No abstract

Formaldehyde (FA) was tested for its genotoxicity in human blood cultures. We treated blood samples at the start of the culture to follow FA-induced DNA damage (DNA-protein crosslinks, DPX), its repair and its genetic consequences in form of sister chromatid exchanges (SCE) and micronuclei (MN). Our results clearly indicate that DPX (determined by the comet assay) are induced at FA concentrations of > or =25 microM. DPX induced by FA concentrations up to 100 microM are completely removed before lymphocytes start to replicate. SCE are induced at concentrations >100 microM parallel to the induction of cytotoxicity (measured as reduction of the replication index). MN were not induced by FA concentrations up to 250 microM (the highest analyzable concentration) added at the start of the blood cultures in the cytokinesis-block micronucleus (CBMN) test. FA-induced cytotoxicity (measured as reduction of the nuclear division index) possibly prevented division of damaged cells. MN were only significantly induced in human blood when proliferating cells were exposed to FA during the last cell cycle before preparation. Several human biomonitoring studies reported increased frequencies of SCE and MN in lymphocytes of subjects exposed to FA. Our results characterize the genotoxic potential of FA in cultured lymphocytes and lead to the conclusion that cytogenetic effects of FA are very unlikely to occur in blood cultures of FA-exposed subjects.

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The alkaline comet assay was used to further characterize the induction of DNA-protein crosslinks (DPX) by formaldehyde (FA) and their removal in the human lung cell line A549 and in primary human nasal epithelial cells (HNEC). DPX were indirectly measured as the reduction of gamma ray-induced DNA migration. FA induced DPX in A549 cells in a concentration-related manner in the range of 100-300 microM. This result is in agreement with previous studies using different mammalian cell lines. The main new findings of the present study are: (i) Determination of cytotoxicity in relation to genotoxicity strongly depend on the method used. Cytotoxicity measured as the reduction in cell counts 48 hr after addition of FA to the cultures occurred parallel to the induction of DPX while colony forming ability was already reduced at 10 times lower FA concentrations; (ii) DPX induced by a 1-hr FA treatment were completely removed within 8 hr cultivation in fresh medium while in the presence of FA in the medium DPX levels remained unchanged for 24 hr; (iii) Induction and removal of DPX did not fundamentally differ between exponentially growing and confluent A549 cultures; (iv) Slowly proliferating HNEC showed the same sensitivity towards FA-induced DPX as A549 cells (i.e. the same FA concentrations induced DPX under the same experimental conditions) and removed DPX with a similar efficiency. In summary, these results contribute to a better understanding of the genotoxic activity of FA in vitro and indicate that the tested cultured primary and permanent human cells do not differ fundamentally with regard to the processing of FA-induced primary genotoxic effects.

Formaldehyde (FA) is known to be genotoxic and mutagenic in proliferating mammalian cells in vitro. The present study was performed to further characterize its genotoxic potential in the V79 Chinese hamster cell line. The induction of DNA strand breaks and DNA-protein cross-links (DPXs) was measured by the comet assay in relationship to the induction of sister chromatid exchanges (SCEs) and micronuclei (MN). Induction of DNA strand breaks was found neither with the standard protocol of the alkaline comet assay nor with modifications using extended electrophoresis times or proteinase K. The concentration-effect relationship for the genotoxic effects was characterized by fitting different curves to the data. A two-phase regression model fitted best in comparison with a linear or a quadratic model and indicated practical thresholds for the induction of SCE and MN. For the induction of DPX as measured by the comet assay, neither a linear concentration-response relationship nor any of the tested models fitted well to the data. Three repeated treatments with genotoxic concentrations of FA with a 3-h interval led to enhanced levels of DPX and MN while the same treatments with a 24-h interval did not enhance FA genotoxicity but suggested adaptive protection against the DNA-damaging action of FA.