Exogenous metabolic activation system

Fort DJ, Rayburn JR, DeYoung DJ, et al. 1991. Assessing the efficacy of an Aroclor 1254-induced exogenous metabolic activation system for FETAX. Drug Chem Toxicol 14 143-160. 

Cultured cells have a limited ability metabolically to activate some potential clastogens. This can be overcome by adding an exogenous metabolic activation system such as S9 mix to the cells (Ames et al., 1975 Natarajan et al., 1976 Maron and Ames, 1983 Madle and Obe, 1980). 

Genotoxic Effects. No studies were located regarding the genotoxicity of 1,2-diphenylhydrazine in humans by any route of exposure. A limited number of assays have been conducted using bacteria, mammalian cell and whole animal systems. As indicated in Table 2-2, 1,2-diphenylhydrazine was mutagenic in Salmonella typhimurium, out not in Escherichia coli, and produced chromosome aberrations and sister chromatid exchanges in Chinese hamster cells. An exogenous metabolic activation system was necessary for expression of the aforementioned effects. In in vivo studies... 

Bande JA et al (1999) Phase III interlaboratory study of FETAX, Part 3 FETAX validation using 12 compoimds with and without an exogenous metabolic activation system. J Appl Toxicol 19 447 72... 

DNA single-strand breaks were not induced by di(2-ethylhexyl) phthalate in primary cultures of rat or Syrian hamster hepatocytes or in Chinese hamster ovary (CHO) cells. Unscheduled DNA s5uithesis was not induced in rat or mouse primary hepatocytes exposed to di(2-ethylhexyl) phthalate. Only one of six studies reported induction of gene mutations at the Tk locus in mouse l5unphoma L5178Y cells exposed to di(2-ethylhexyl) phthalate in the absence of an exogenous metabolic activation system. Ouabain-resistant mutants were not induced in mouse lymphoma or BALB/c-3T3 cells. 

Chromosomal aberrations were not induced by di(2-ethylhexyl) phthalate in any of eight studies in various types of cultured cells in the absence of metabolic activation. Only three of these studies for chromosomal aberrations included an exogenous metabolic activation system. Of these, one, using Syrian hamster embryo cells, found an increase in aberration frequency. Weak effects were detected for the induction of aneuploidy and mitotic division aberrations in Chinese hamster lung cells. 

RLV/Fischer rat assay without the addition of an exogenous metabolic activation system. In a single study, mouse JB6 epidermal cells were transformed by di(2-ethyl-hexyl) phthalate without activation and in one of two studies a weak response was reported in the CSHIOT A cell transformation assay with di(2-ethylhexyl) phthalate in either the absence or presence of exogenous metabolic activation. BALB/c-3T3 cells were not transformed by di(2-ethylhexyl) phthalate with or without metabolic activation. Di(2-ethylhexyl) phthalate inhibited gap-junctional intercellular communication in Chinese hamster V79 cells in six of seven studies, but not in one study of liver cells of cynomolgus monkeys in vivo. Di(2-ethylhexyl) phthalate treatment of Syrian hamster embryo cells in a two-stage exposure with 12-O-tetradecanoylphorbol 13-acetate resulted in superinduction of ornithine decarboxylase, an early event in morphological transformation no effect was seen after a one-stage treatment with di(2-ethylhexyl) phthalate alone. 

A-Nitrosodiethanolamine was mutagenic to Salmonella typhimurium in most assays in the presence of exogenous metabolic activation systems and in some assays in the absence of such systems. 

Workers exposed to dimethyl sulfate have developed chromosomal aberrations in their circulating lymphocytes. Dimethy l sulfate has been subjected to a broad range of in-vitro tests for genotoxic activity, in which positive results were consistently found without the need for exogenous metabolic activation systems. It has also consistently produced positive responses in the small number of in-vivo tests to which it has been subjected. It forms a variety of alkylated bases with DNA in vitro and the same alkylated bases are formed in vivo. 

Phenol induced mutations at the hprt locus of Chinese hamster V79 cells in the presence of an exogenous metabolic system from the livers of phenobarbital-induced mice and tk locus mutations in mouse lymphoma L5178Y cells in the presence or the absence of an exogenous metabolic activation system. Micronuclei were induced by phenol in Chinese hamster ovary cells in one study and sister chromatid exchanges in mammalian cells were increased in several studies, including three with human lymphocytes. 

Unless otherwise indicated, studies were carried out with an 80/20 mixture of 2,4/2,6-toluene diisocyanates. In one of two studies, toluene diisocyanate induced mutations in Salmonella typhimurium strains TAIOO, TAI 538, and TA98 in the presence of an exogenous metabolic activation system only. It induced sex-linked recessive lethal mutations in Drosophila in a single study. 

Toluene diisocyanate did not induce unscheduled DNA synthesis in rat primary hepatocytes. 2,4-Toluene diisocyanate induced mutations in mouse lymphoma L5178Y cells at the tk locus in the presence of exogenous metabolic activation and increased the frequency of sister chromatid exchanges but not chromosomal aberrations in Chinese hamster ovary cells. 2,6-Toluene diisocyanate induced gene mutations in L5178Y cells in the presence of an exogenous metabolic activation system and induced sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary cell cultures. 

Resorcinol did not induce gene mutations in Salmonella typhimurium or in Escherichia coli strains in either the presence or absence of an exogenous metabolic activation system. 

Tetrachloroethane induced gene mutations in the mouse lymphoma tH -assay only in the presence of an exogenous metabolic activation system. It did not increase the frequency of chromosomal aberrations in Chinese hamster lung fibroblasts or ovary cells but did induce sister chromatid exchanges in Chinese hamster ovary cells and aneuploidy in Chinese hamster lung fibroblasts in the absence of exogenous activation. 1,1,1,2-Tetrachloroethane did not induce cell transformation in BALB/C-3T3 cells. 

Chlorodifluoromethane is mutagenic to Salmonella typhimurium but it did not induce either mutation or gene conversion in Saccharomyces cerevisiae. Chlorodifluoromethane did not induce mutations at the hprt locus or imscheduled DNA synthesis in mammalian cell lines in the presence or absence of an exogenous metabolic activation system. In vivo, it did not induce chromosomal aberrations in bone-marrow cells or dominant lethal effects (lARC, 1987b). These conclusions are supported by a more recent review (WHO, 1991). 

Diethy Ihydrazine is weakly mutagenic to Salmonella typhimurium TAIOO and particularly TAI 02. but only in the absence of an exogenous metabolic activation system. The activity in strain TA 102 rapidly disappears with time of incubation, so that after 7 h it is halved and after 11 h, there is no activity. 

Pentachloroethane is not mutagenic to Salmonella typhimurium. In the presence of an exogenous metabolic activation system, there was weak induction of mutation and gene conversion in yeast. In Chinese hamster ovary CHO cells, there was induction of sister chromatid exchanges, but not of chromosomal aberrations. In Chinese hamster lung CHL cells, chromosomal aberrations and aneuploidy were induced. Mutations were induced at the tk locus of mouse lymphoma L5178Y cells. 

Fort, D.J., E.L. Stover, J.A. Bantle, J.R. Rayburn, M.A. Hull, R.A. Finch, D.T. Burton, S.D. Turley, D.A. Dawson, G. Linder, D. Buchwalter, M. Kumsher-King, and A.M. Gaudet-Hull. 1998. Phase III interlaboratory study of FETAX, Part 2 Interlaboratory validation of an exogenous metabolic activation system for frog embryo teratogenesis assay-Xenopus (FETAX). Drug Chem. Toxicol. 21(1) 1-14. 

Fox, D.J. et al. 1998. Phase III interlaboratory study of FETAX, Part 2. Interlaboratory validation of exogenous metabolic activation system for frog embryo teratoge-nesis assay—Xenopus (FETAX). Drug Chem. Toxicol. 21 1-14. 

Table 4 shows that A -nitrosodiphenylamine gave negative results in both short-term tests. Of the six carcinogens, all but A -nitrosodiethylamine (DEN) were positive in the standard test. However, as discussed later, DEN gave positive results after the addition of exogenous metabolic activation systems. Results with the bacterial mutagenesis test concurred completely with the reported carcinogenicity of the compounds. 

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