THE DETECTION AND EVALUATION OF ANEUGENIC CHEMICALS

Although aneuploidy makes a significant contribution to both somatic a nd inherited disease the mechanisms by which environmental chemicals m ay induce numerical chromosome aberrations are only poorly defined. Th e European Union Project was aimed to further our understanding of tho se chemical interactions with the components of the mitotic and meioti c cell division cycle which may lead to aneuploidy and to characterise the parameters such as cellular metabolism which may influence the ac tivity of aneugenic chemicals. C-mitosis can be induced by the highly lipophilic polychlorinated biphenyl and the completion of mitosis and cleavage can be modified by agents which deplete cellular levels of re duced glutathione. Modifications of the fidelity of chromosome segrega tion were produced by inhibiting the functioning of topoisomerase II d uring chromatid separation. In contrast, the modification of centromer e integrity resulted in chromosome breakage as opposed to disturbance of segregation. Modifiers of tubulin assembly and centriolar functioni ng in somatic cells such as acrylamide, vinblastine and diazepam repro duced their activity in rodent bone marrow and male germ cells. The an alysis of chromosome malsegregation in Aspergillus nidulans by a struc turally related series of halogenated hydrocarbons was used to develop a QSAR model which had high predictive value for the results of funga l tests for previously untested related chemicals. Metabolic studies o f potential aneugens in genetically engineered human lymphoblastoid ce lls demonstrated the detoxification of the aneugenic activity of chlor al hydrate and the activation of 2,3-dichlorobutane, 1,1,2-trichloroet hane and trichloroethylene by Phase I biotransforming enzymes. Cell tr ansformation studies in Syrian hamster dermal cultures using a panel o f 22 reference and or potential aneugens indicated that 15 of the 22 p roduced positive results following single exposures. Five of the aneug ens which were negative following single exposures produced positive r esults where cultures were continuously exposed for up to 6 weeks to l ow concentrations following a single non-transforming exposure to the mutagen dimethyl sulphate. The transformation studies indicate that a significant proportion of chemical aneugens are potential complete car cinogens and/or co-carcinogens. To optimise the enumeration of chromos omes following exposure to potential chemical aneugens whole chromosom e paints and centromere specific probes suitable for use in fluorescen ce in situ hybridisation (FISH) were developed for the rat, mouse and Chinese hamster and selected human probes evaluated for their suitabil ity for routine use. Molecular chromosome probes were used to develop protocols for enumerating chromosomes in metaphase cells and centromer es and micronuclei in interphase cells. The analysis of segregation of specific centromeres in binucleate cells following cytochalasin B tre atment was shown to be a potentially valuable system for characterisin g non-disjunction following chemical exposure. Whole chromosome paints and centromere specific probes were used to demonstrate the presence of dose-response thresholds following treatment with a reference panel of spindle inhibiting chemicals. These data indicate that the FISH te chnology is suitable for evaluating the relative hazards of low-dose e xposures to aneugenic chemicals.