Chromosomal aberrations in mouse lymphocytes exposed in vivo and in vitro to aliphatic epoxides

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Chromosomal aberrations in mouse lymphocytes exposed in vitro and in vivo to benzidine and 5 related aromatic amines

Mouse lymphocytes were exposed in vitro for 2 h or in vivo for 24 h to benzidine and related aromatic amines to test for chromosome aberrations (CA) and mitotic indices. Uninduced mouse S9 was used to activate the amines for the in vitro tests to be consistent with the in vivo tests. Contrary to a previous report, no difference could be established in the genotoxicity of benzidine following activation with uninduced S9 compared to induced S9. There were concentration related increases in CA for benzidine and all the amines in vitro except for 4,4'-diaminostilbene which exhibited the greatest cellular toxicity towards cultured lymphocytes. Benzidine and its derivatives showed significant increases in CA in vivo compared to its negative control. The CA values for 4-aminostilbene were significantly higher than the other amines in both in vivo and in vitro studies. These genotoxicity results for 4-aminostilbene are consistent with our previous report of the pronounced CA effects in murine bone-marrow cells but would not be predicted from Salmonella mutagenicity tests.