DNA damage induced by alachlor after in vitro activation by rat hepatocytes.

We investigated the ability of alachlor to cause DNA damage by measuring single-strand breaks (SSB) in DNA, after metabolic activation by freshly isolated rat hepatocytes. Incubation of different concentrations of alachlor with rat hepatocytes led to numerous metabolites. The majority, isolated and identified by GC-MS analysis, were products arising from reactions catalyzed by the P-450 monooxygenase system, arylamidase and flavin mixed-function oxidase/cytochrome P-450 monooxygenase. The results, using freshly isolated rat hepatocytes, showed that in these conditions several potentially DNA damaging metabolites were produced; this experimental condition was used to assess DNA damage induced by the mixture of alachlor and its metabolites. The alkaline elution technique showed that at 200 microM and more clearly at 400 microM there were some small fragments that eluted in the first fraction. This fragmentation was probably due to alachlor cytotoxicity. In addition to the small DNA fragments eluting in the first fraction there were other larger DNA fragments. These DNA-SSB were most evident at the alachlor concentration of 400 microM, but also at 200 microM and 100 microM, whereas at 10 microM the DNA elution rate appeared comparable to that of controls. The results suggest that some unstable and DNA-reactive metabolites might interact with DNA causing SSB and such interaction might be important in relation to the mechanism of alachlor-induced DNA damage. However, it may not be possible to clarify whether SSB are the result of direct DNA interaction of the compound or of secondary cellular processes after chemical treatment.