Mutagenicity and effect on gap-junctional intercellular communication of 4,4'-methylenebis(2-chloroaniline) and its oxidized metabolites

Oxidized metabolites of 4,4'-methylenebis(2-chloroaniline) (MBOCA) were tested for direct mutagenicity in a Salmonella typhimurium assay and for effects on gap-junctional communication of WB-F344 rat liver cells. The mutagenicities of the N-hydroxy, mononitroso and o-hydroxy (ring) metabolites of MBOCA were assayed without adding activating enzyme systems, using the frame-shift sensitive strain TA98 and the base pair substitution sensitive strain TA100. The mutagenicity of the hydroxylamine was demonstrated by a linear increase in the formation of mutant colonies in both strains, with a formation of two revertants/nmol by TA98 and 21 revertants/nmol by TA100. The mononitroso metabolite showed a slight positive effect on TA100, but effects were masked by its cytotoxicity towards this strain. This metabolite was neither mutagenic nor cytotoxic to TA98. The o-hydroxy and the dinitroso metabolites were negative for mutagenicity at concentrations up to 50 and 500 micrograms/plate, respectively. The effects of parent MBOCA and N-hydroxy, mononitroso and o-hydroxy metabolites on cell-cell communication were determined by a scrape loading/fluorescent dye transfer technique. Cytotoxicity was assessed by determination of colony-forming efficiency and lactate dehydrogenase release. MBOCA itself caused an inhibition of dye transfer at concentrations of 7.5, 11.3 and 15 nmol/ml, whereas measures of cytotoxicity were not seen until 15 and 30 nmol/ml for LDH release and plating efficiency, respectively. None of the oxidized metabolites were active in inhibiting dye transfer at non-cytotoxic concentrations.