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G R Mohn

Publications and source records attributed to G R Mohn.

At least 37 records · Page 2Linked to original sources
PubMed1991

Role of genotoxicity assays in the regulation of chemicals in The Netherlands: considerations and experiences.

This paper discusses genotoxicity testing and data interpretation as applied in The Netherlands in the context of the regulation of chemicals. Guidelines were first formulated in 1981 and their use evolved in practice, on the basis of increasing experience at the national and international levels. The distinction between in vitro assays to detect intrinsic genotoxic properties and in vivo assays as a subsequent phase to show the realization of this potential in an intact organism has always been a cornerstone of the Dutch approach. Several critical aspects of the use of short-term genotoxicity tests in sequential schemes are discussed, such as their predictivity for carcinogenicity, the limited database concerning the performance of short-term in vivo assays, the relevance of devising separate strategies to test for possible carcinogenicity and germ cell mutagenicity, and the use of short-term tests to discriminate between genotoxic and non-genotoxic carcinogens. Examples are given of how short-term tests contributed to the toxicological evaluation of chemicals in The Netherlands.

Animals↗
PubMed1990

Preventive action of thioethers towards in vitro DNA binding and mutagenesis in E. coli K12 by alkylating agents.

Thioethers are effective scavengers of electrophilic metabolites derived from the hepatocarcinogen N-hydroxy-2-acetylaminofluorene (van den Goorbergh et al., 1987). In this study 2 of these thioethers, 4-(methylthio)benzoic acid (MTB) and its methylester, methyl 4-(methylthio)benzoate (MMTB), have been tested for their ability to prevent in vitro DNA binding and mutation induction in E. coli K12 by the direct alkylating agents ethylnitrosourea (ENU), methylnitrosourea (MNU), ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS). In addition to MTB and MMTB, the thioether L-methionine (Met), and the thiols glutathione (GSH) and L-cysteine (Cys) were included for reasons of comparison. MTB was able to (partially) prevent DNA binding and mutation induction by ENU. However, this thioether was ineffective with EMS. DNA binding and mutagenesis by EMS were (partially) prevented by GSH and Cys, while these thiols could not prevent DNA binding and mutation induction by ENU. MMTB was unable to prevent mutation induction by these ethylating agents. With the methylating agents, similar effects of MTB were observed: MTB effectively prevented mutation induction by MNU while it was much less effective towards MMS. GSH and Cys were comparably effective as antimutagenic agents towards both methylating agents. Met was unable to prevent either DNA binding or mutation induction by these agents. Taken together, the results show that aromatic thioethers are able to trap genotoxic electrophiles derived from the nitrosoureas ENU and MNU, and may therefore act as potential anticarcinogens towards these agents, which are only poorly detoxified by GSH.

Alkylating Agents↗
PubMed1989

Mutational specificities of environmental carcinogens in the lacl gene of Escherichia coli. II: A host-mediated approach to N-nitroso-N,N-dimethylamine and endogenous mutagenesis in vivo.

An intrasanguineous host-mediated assay was used to determine the mutational specificity of the hepatocarinogen N-nitroso-N,N-dimethylamine metabolized in vivo. A total of 114 forward mutations in the lacl gene of Escherichia coli reisolated from the livers of treated Swiss albino mice were characterized at the DNA sequence level. Consistent with the methylating ability of this compound and the demonstrated mutagenic specificity of O6-methylguanine, the predominant mutation was the G:C----A:T transition. These were recovered, on average, seven times more frequently at guanines flanked (5') by a purine residue than at those preceded by a pyrimidine residue--a specificity similar to that reported for many direct-acting SN1 alkylating agents. This nitrosamine appears to be distinguished from related N-nitroso methylating compounds by the induction of additional mutational events. Here, the exceptions consisted of four A:T----G:C transitions, four A:T site transversions, and a single G:C----T:A transversion. In addition, the DNA sequence alterations of 34 I- mutants of E. coli reisolated from otherwise untreated mice were identified. The predominant mutation was the G:C----A:T transition, which accounted for almost half of all background mutations. The sites at which these mutations were recovered appear to indicate that some of these mutations may have arisen as a result of an accelerated rate of cytosine deamination. These data suggest that many of the additional "spontaneous" mutations observed under in vivo conditions resulted from genotoxic events occurring during the host-defense (immune) reaction.

Animals↗
PubMed1989

Host-mediated bacterial mutagenesis and enterohepatic circulation of benzidine-derived mutagenic metabolites in rodents.

1. Administration of benzidine (100 mg/kg, i.p.) to bile duct-cannulated rats led to a sustained excretion of metabolites in bile which, following glucuronide hydrolysis, were mutagenic to Salmonella typhimurium strain TA98. 2. When the biliary metabolites were re-infused into the duodena of a further group of rats, enterohepatic circulation of mutagens was indicated by extensive re-excretion of biliary mutagens in the recipients. 3. Furthermore, in mouse host-mediated mutagenicity assays, both i.p. injection of benzidine (100 mg/kg) and intracaecal administration of rat biliary metabolites of benzidine produced a mutagenic response in Salmonella typhimurium strain TA98 cells isolated from the liver. 4. The results indicate that enterohepatic circulation adds to the biological persistence of reactive metabolites of benzidine and may contribute to the carcinogenicity of this aromatic amine.

Animals↗
PubMed1989

Relationship between DNA-adduct formation, DNA repair, mutation frequency and mutation spectra.

DNA-adduct formation by a series of ethylating agents was determined and correlated with induction of gene mutations. This approach gave information concerning the DNA-adduct(s) likely to be responsible for the observed mutations. A methodology has been developed which is used for the DNA sequence analysis of point mutations in the HPRT gene of mammalian cells. This method can be used to obtain mutation spectra and to determine whether the base-pair changes do occur at those sites where DNA-adducts are likely to occur. Measurements of DNA repair in specific DNA sequences show that actively transcribed genes are repaired faster than the genome overall. This stresses the importance of studying removal DNA-adducts in the gene that is used for the analysis of mutation induction.

Animals↗
PubMed1988

Biochemical characterization of glutathione-deficient mutants of Escherichia coli K12 and Salmonella strains TA1535 and TA100.

Glutathione-deficient mutants of Escherichia coli K12/343/408 and Salmonella typhimurium TA1535 and TA100 were characterized biochemically by measuring the rate of formation of (14C)gamma-glutamylcysteine and (14C)glutathione in cell-free extracts of the strains. gamma-Glutamylcysteine synthetase activity was found to be absent in the NGR-2 mutant of E. coli and in the Salmonella mutants TA1535/NG-19, TA100/NG-57 and TA100/NG-11, while only low activities were found in the NGR-9 and NG-54 mutant of E. coli and Salmonella respectively. These results correspond with the decreased levels of glutathione found in these strains. Extracts of the parent strains have normal glutathione levels and show high gamma-glutamylcysteine synthetase activities. It is concluded that the present GSH-deficient strains of E. coli and Salmonella are gshA mutants, analogous to those previously described in E. coli. In addition, the present results show that the fluorometric method used for the determination of glutathione, employing o-phthalaldehyde as a reagent, is not specific for glutathione (at pH 8.0), but also sensitively reacts with gamma-glutamylcysteine.

Escherichia coli↗
PubMed1987

1,2-Dibromo compounds. Their mutagenicity in Salmonella strains differing in glutathione content and their alkylating potential.

The mutagenic activities of several structurally related dibromo compounds were compared in Salmonella strains sensitive to base substitution mutagenesis (TA1535 and/or TA100) and in the glutathione (GSH)-deficient derivative TA100/NG-57, using a preincubation procedure. The compounds tested were 1,2-dibromoethane (DBE), 1,2-dibromopropane (DBP), 1,2-dibromo-1-phenylethane (DBPE) and model compounds for the half-mustards resulting from their conjugation with GSH, i.e. the N-acetyl-S-2-bromoalkyl-L-cysteine methyl esters SBE, SBP, and SBPE, respectively. The alkylating potential of all compounds was assayed with the 4-(p-nitrobenzyl)pyridine (NBP) alkylation test. Five of the compounds showed a good correlation between relative mutagenic activity in TA100 and electrophilic reactivity in the NBP-test, the order of decreasing potency being SBE greater than SBP greater than DBPE greater than DBP. SBPE displayed the highest reactivity in the NBP-test, but was devoid of mutagenic activity. The mutagenic activity of DBE was substantially decreased in the GSH-deficient strain TA100/NG-57 and could be restored by pretreating the cells with GSH. None of the other chemicals showed different mutagenic activities in TA100 and TA100/NG-57. From the results it can be concluded that 2-bromothioethers possess higher alkylating activities than the 1,2-dibromo compounds. Methyl substitution has a deactivating effect on the mutagenic activity. The results with the phenyl-substituted analogue, DBPE, show that a higher alkylating activity does not always lead to a higher mutagenic activity.

Alkylating Agents↗
PubMed1987

Mutagenicity of halogenated and other substituted dinitrobenzenes in Salmonella typhimurium TA100 and derivatives deficient in glutathione (TA100/GSH-) and nitroreductase (TA100NR).

In a previous study, it was shown that 1-chloro-2,4-dinitrobenzene (CDNB) was less mutagenic in a glutathione (GSH)-deficient derivative of Salmonella typhimurium TA100 (TA100/GSH-) than in TA100 itself, suggesting that the mutagenicity of the compound is dependent on GSH, possibly mediated by the action of a bacterial nitroreductase(s) on the CDNB-GSH conjugate. In the present study a series of mutagenicity tests were performed to determine how CDNB could be activated after reaction with GSH. In liquid preincubation assays, strains TA100, TA100/GSH- and TA100NR, a nitroreductase-deficient derivative of TA100, were treated with CDNB and its fluoro and bromo analogues (FDNB and BDNB), further with its GSH conjugate (S-GSH-DNB) and possible metabolic products, such as S-cysteine-dinitrobenzene (S-Cys-DNB) and S-methyl-dinitrobenzene (S-methyl-DNB), and with 2 more analogues, O-methyl-dinitrobenzene (O-methyl-DNB) and dinitrobenzene (DNB). CDNB, FDNB and BDNB were found to be mutagenic in TA100 and TA100NR, while TA100/GSH- was much less sensitive to the mutagenic action of these halogenated dinitrobenzenes. DNB, O-methyl-DNB, S-methyl-DNB and S-Cys-DNB induced equal numbers of His+ revertants in TA100 and TA100/GSH-, but were not mutagenic in TA100NR. S-GSH-DNB showed no mutagenic activity in any of the 3 strains under the present experimental conditions. These results suggest that the halogenated aromatics may react with bacterial DNA and produce pre-mutagenic alterations according to 2 mechanisms: direct attack on the DNA through nucleophilic substitution (SN2) of the halogen atoms; activation through GSH conjugation and subsequent nitroreduction of the conjugate or its metabolic products to more reactive intermediates.

Bacterial Proteins↗
PubMed1986

The effect of mixed-function oxidase and amine oxidase inhibitors on the activation of dialkylnitrosamines and 1,2-dimethylhydrazine to bacterial mutagens in mice.

The effect of the mixed-function oxidase inhibitor phenylimidazole (PI) and the amine oxidase inhibitors iproniazid (IPRO) and aminoacetonitrile (AAN) on the mutagenic activity of various carcinogens was determined in intrasanguineous host-mediated assays, using mice as hosts and E. coli 343/113 as an indicator of mutagenic activity. The carcinogenic compounds dimethyl-, diethyl-, methylethyl-, and diethanolnitrosamine (DMNA, DENA, MENA, and DELNA respectively) and 1,2-dimethylhydrazine (SDMH) were administered i.p. to mice pretreated or not with one of the inhibitors. After 4 h exposure to each of the carcinogens, E. coli cells recovered from the liver of non-pretreated mice showed considerable induction of VALr mutations; after pretreatment of the hosts with the three inhibitors, significant reduction of the amounts of induced mutants in vivo was observed. Particularly, PI proved a very efficient inhibitor of DENA, MENA, DELNA, and SDMH mutagenicity (93%-97% reduction), suggesting that these carcinogens are mainly activated by cytochrome P-450-dependent enzymes. However, since PI might also inhibit the NAD-mediated activation of DELNA by alcohol dehydrogenase (ADH), the present experiments do not rule out an additional role of ADH in the in vivo mutagenic activation of DELNA. AAN and IPRO were less and much less effective, respectively, in reducing the mutagenic activity of all compounds. Surprisingly, PI showed less inhibition of the mutagenic activity of DMNA (60% reduction), as compared to the other carcinogens; this indicates that metabolic routes other than the cytochrome P-450-dependent enzyme system may be important for the activation of DMNA.

1,2-Dimethylhydrazine↗
PubMed1986

Use of the DNA-repair host-mediated assay for determining the organ distribution of genotoxic factors in mice treated orally with nitro-aromatic compounds.

The distribution of genotoxic factors in various organs of mice treated orally with nitro-aromatic compounds of actual or potential use as chemotherapeutic (antiprotozoal and anthelminthical) agents was investigated in the DNA-repair host-mediated assay, with mice as host animals and a pair of E. coli K12 strains differing in DNA-repair capacity as indicators of genotoxicity. The test substances were derivatives of nitroimidazole (metronidazole), nitrofuran (SQ 18 506) and nitrodiphenylamine (amoscanate). Animal-mediated assays were performed by injecting mixtures of the two E. coli strains both intravenously and orally into mice, which were subsequently treated with the test chemicals, and from which the differential survival of indicator bacteria present in liver, lungs, spleen, kidneys, stomach, small intestine, colon and the blood stream was determined on selective agar medium. The same strains and selection procedures were used for assessing the genotoxic activity of the compounds in vitro. All three compounds displayed genotoxic activity in vitro, the order of potency on the basis of exposure concentration being SQ 18 506 greater than metronidazole greater than amoscanate. In the animal-mediated assays the same ranking order of genotoxic activity was observed, but the exposure levels required to produce significant genotoxic effects in vivo were (substantially) higher than in the in vitro tests: SQ 18 506 was active at 0.1 mg/kg body weight, metronidazole at 4 mg/kg, and amoscanate at dosages higher than 10 mg/kg. In host-mediated assays the highest genotoxic activity for all three chemicals was observed in organs of the gastro-intestinal tract (usually in the stomach). All three chemicals also induced genotoxic effects in organs remote from the gastro-intestinal tract although with substantially lower activity, the order of potency being again SQ 18 506 greater than metronidazole greater than amoscanate. In the case of SQ 18 506 and metronidazole, dose-dependent genotoxic activities were observed in liver, spleen, lungs, kidneys and the blood stream, with no clear indication of a preferential target or non-target organ, while the minor genotoxic effects of amoscanate were restricted to bacteria present in the blood stream. This can be taken as an indication that the substances (or active metabolites thereof) have been transported from the intestinal tract into the blood stream and distributed evenly in organ tissues, without an indication of organ specific deactivation during the time periods (less than 180 min) presently investigated.(ABSTRACT TRUNCATED AT 400 WORDS)

5-Amino-3-((5-nitro-2-furyl)vinyl)-1,2,4-oxadiazol↗
PubMed1986

Evaluation of the DNA repair host-mediated assay. II. Presence of genotoxic factors in various organs of mice treated with chemotherapeutic agents.

The DNA repair host-mediated assay was further calibrated by testing 7 chemotherapeutic agents known to possess carcinogenic activity, namely bleomycin (BLM), cis-diamminedichloroplatinum-II (cis-Pt), cyclophosphamide (CP), diethylstilboestrol (DES), isonicotinic acid hydrazide (isoniazid, INH), natulan (NAT) and mitomycin C (MMC). Differential survival of wild-type and uvrB/recA E. coli strains served as a measure of genotoxic activity. In in vitro assays, BLM, cis-Pt and MMC exhibited high genotoxic activity. The other 4 compounds had no measurable effect on the survival of the two strains, either with or without mouse liver preparations. In the host-mediated assays BLM, cis-Pt, MMC and also NAT induced strong killing of the DNA repair-deficient bacteria recovered from liver, spleen, lungs, kidneys and the blood of treated mice compared to the wild-type strain. The results are not indicative of large organ-specific differences in genotoxically active amounts of the drugs immediately after their application to the host animals. CP, INH and DES did not show geneotix activity in these assays even at very high exposure levels. To compare the genetic endpoint measured in the DNA repair assays, i.e. induction of repairable DNA damage, with the induction of gene mutations, the ability of the 7 drugs to induce valine-resistant (VALr) mutants in E. coli was measured in host-mediated assays under identical treatment conditions. INH showed considerable mutagenic activity in E. coli cells recovered from liver and spleen, while BLM and MMC induced a 3-4-fold increase in VALr mutants above spontaneous levels. The other compounds showed no mutagenic activity under these in vivo conditions. From these results it can be concluded that the type of primary DNA lesions produced by these chemotherapeutic agents (cross-links by MMC and cis-Pt, and strand breaks by BLM and possibly by NAT; base alkylation by INH) appears to determine whether a compound will be highly positive in the DNA repair assay as in the case of BLM, cis-Pt, MMC and NAT, and less effective in inducing mutations under similar conditions, or whether the opposite will occur, as in the case of INH; DES and CP probably do not interact sufficiently with bacterial DNA to show an effect in either of the genetic endpoints; and the present DNA repair host-mediated assay may represent a sensitive, rapid and economic method for monitoring genotoxic factors in various organs of experimental animals which have been treated with cytostatic drugs.

Animals↗
PubMed1986

On the distribution of genotoxic factors in various organs of mice treated with cycasin.

The distribution of genotoxic factors in various organs of mice treated orally with methylazoxymethanol-beta-D-glycoside (cycasin) was investigated using the DNA-repair host mediated assay. Indicator of genotoxic activity was a pair of streptomycin dependent Escherichia coli strains differing vastly in DNA repair capacity; uvrB/recA vs. uvr+/rec+. The animal-mediated assays were performed by injecting mixtures of the two strains i.v. and orally into mice, which were subsequently treated with the test chemical and from which the differential survival of the indicator bacteria present in several organs was determined. The same strains and selection procedures were also used for assessing the DNA-damaging activity in vitro. In the animal-mediated assays in which cycasin was applied orally, significant effects were observed at doses of 100 and 500 mg/kg body weight. The organ distribution of genotoxic factors in the host animal was as follows: the highest genotoxic activity was observed in the liver, followed by intestine and stomach; a clear effect was also observed in the kidneys and, to a lower extent, in the blood stream and in the lungs at the highest dose administered (500 mg/kg body weight). Under in vitro conditions a marginal genotoxic effect was observed even in the absence of liver homogenate, indicating that the test compound is possible activated (hydrolysed) by the E. coli cells. Therefore the genotoxic activity of cycasin observed in the gastrointestinal tract was not unexpected, since the substance was applied orally, thereby exposing the indicator bacteria in these organs to high levels of unmetabolised compound, especially in the stomach. In the intestine members of the microbial flora probably contribute to the metabolic activation of the test compound. The occurrence of genotoxic factors remote from the gastrointestinal tract shows that the present compound or active metabolites thereof penetrate through the intestinal barrier. The extraordinarily high genotoxic activity observed in the liver suggests that the compound is additionally activated in this organ. In compliance with previous in vitro findings this second activation step might lead to the formation of the highly reactive aldehydic form of methylazoxymethanol (MAMAL) mediated by dehydrogenases. Comparison with carcinogenicity studies indicates a good correlation between the distribution of genotoxic effects as determined in the present studies and the localisation of tumors in various organs of rodents treated with cycasin.

Animals↗
PubMed1985

Mutagenic activity of various chemicals in Salmonella strain TA100 and glutathione-deficient derivatives. On the role of glutathione in the detoxification or activation of mutagens inside bacterial cells.

Several mutants with decreased levels of reduced glutathione (GSH) were isolated from the sensitive mutagen tester strain Salmonella typhimurium TA100 after treatment with u.v. and selection for resistance to N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) and its methyl analogue MNNG. Estimation of the GSH concentration and GSH S-transferase activity in extracts of these strains and of TA100 indicates that the GSH- derivatives contain 10-30% of the GSH level found in TA100, and that they exhibit normal GSH S-transferase activity. The mutagenic activities of 7 chemicals, namely, MNNG, ENNG, 1,2-dibromoethane (DBE), 1-chloro-2,4-dinitrobenzene (CDNB), styrene-7,8-oxide (STOX), N-ethyl-N-nitrosourea (ENU) and methyl methane sulphonate (MMS) were compared in TA100 and in one representative GSH- strain, denominated NG-57. MNNG, ENNG, DBE and CDNB are potent to extremely potent mutagens in TA100, but induce very low levels of His+ mutants in NG-57. Pretreatment of NG-57 with 1 mM GSH (partially) restores the mutant yields to the levels usually found in TA100. The mutagenic activities of STOX, ENU and MMS are similar in both strains. These results support some previous findings, namely that ENNG, MNNG and DBE, but not ENU are activated to mutagens inside the test bacteria, and also suggest that CDNB is activated by bacterial GSH. The latter finding is in contrast with the current view that CDNB is detoxified by GSH, as is also presently evidenced by a strong reduction of the compound's mutagenicity in the presence of extracts of rat liver, which contains GSH and GSH S-transferase activity. The results with STOX indicate that GSH plays in bacteria a much less important role in the detoxification of xenobiotics than in mammalian tissue, presumably due to a much lower GSH S-transferase activity in the first organism.

Biotransformation↗
PubMed1985

Quantitative comparison of genetic effects of ethylating agents on the basis of DNA adduct formation. Use of O6-ethylguanine as molecular dosimeter for extrapolation from cells in culture to the mouse.

DNA-adduct formation and induction of gene mutations were determined simultaneously after treatment with the four ethylating agents, ethyl methanesulfonate (EMS), ethylnitrosourea (ENU), diethyl sulfate (DES), and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Both, in E. coli K-12 (NAL-resistance) and in V79 Chinese hamster cells in culture (HPRT-deficiency), the frequencies of mutation induction by all chemicals were the same when plotted against the amount of O6-ethylguanine formed in DNA, suggesting that this DNA adduct can be used as a common dosimeter for the comparisons of the frequencies of gene mutations induced by ethylating agents in various mutagenicity assay systems. Using ENU, such a comparison was performed between mutation induction in V79 cells in vitro and in the specific-locus assay in the mouse. The data indicate that at equal levels of O6-ethylguanine in the DNA of V79 cells and in testicular DNA from male mice treated with ENU, the frequencies of induced mutants in both assay systems were quite similar. These results support the concept that the determination of premutagenic DNA adducts in vivo can be used to monitor exposure to chemical mutagens and that genetic risk estimations may ultimately be performed on the basis of such measurements and of comparative mutagenesis in vitro and in vivo.

Alkylating Agents↗
PubMed1984

The DNA repair host-mediated assay as a rapid and sensitive in vivo procedure for the determination of genotoxic factors present in various organs of mice. Some preliminary results with mitomycin C.

The DNA repair host-mediated assay, in which repairable DNA damage is determined in E. coli cells present in various organs of mice exposed to genotoxic agents, was further developed to broaden the range of organs under study and to simplify the procedure of assessing differential bacterial cell survival. A pair of derivatives of E. coli K-12 strain 343/113 was constructed which differed vastly in DNA repair capacity (uvr+/rec+ vs uvrB/recA), as a means of assessing DNA damaging effects; furthermore, the strains differed in their ability to ferment lactose (delta Lac vs Lac+), so that the individual survival of both strains could be determined on a single agar medium (containing neutral red as pH indicator), on which the strains had different colony colour morphology (red, Lac+ vs white, Lac- colonies). Finally, the strains were made streptomycin-dependent, to prevent uncontrolled growth of the bacterial cells within the various organs and also to inhibit contamination of the survival agar medium by representatives of the normal intestinal microflora. The experimental procedure consisted of injecting mixtures of stationary cells of the two strains (ca. 3-5 X 10(8) viable cells per mouse) both intravenously and orally into mice, either pretreated or subsequently treated with test chemicals. Ninety minutes after injection of the bacteria, the liver, spleen, lungs, kidneys, stomach, intestine, colon, and ca. 50 microliter blood, were removed, suspended in buffer, homogenized, and the survival of the two strains determined on neutral red agar supplemented with streptomycin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Methodologies for the determination of various genetic effects in permeable strains of E. coli K-12 differing in DNA repair capacity. Quantification of DNA adduct formation, experiments with organ homogenates and hepatocytes, and animal-mediated assays.

Derivatives of E. coli K-12 strain 343/113 differing in DNA repair capacity, in permeability to large molecules, and in some metabolizing activities (nitroreductase, glutathione), were constructed for the quantitative determination of the induction of various genetic effects, such as forward and back mutations, lysogenic induction of prophage lambda, and repairable DNA damage. These E. coli strains can be used in assay procedures which allow variation and control over several experimental conditions, such as oxygen tension, time, pH, temperature of incubation and growth phase of the indicator cells. Methods are described for the simultaneous determination of genetic effects and of DNA-adduct formation during mutagen treatment, i.e. by using radio-labeled compounds or by means of an enzyme-linked immunosorbent assay (ELISA). Mammalian biotransformation of xenobiotics can be investigated by including various fractions of mammalian organs in the system. Examples of the relative effectiveness of the activating potential of S9, S100 and isolated hepatocytes for dialkylnitrosamines and other carcinogens are presented. Host-mediated assays, finally, are described which, in addition to gene mutations, can also be used for the determination of repairable DNA damage in bacteria present in different organs, including the liver, spleen, lungs, kidneys, pancreas, and the blood stream of chemically treated mice. It is concluded that quantitative tests in vitro for assessment of induced mutagenic spectrum and genotoxic potency, combined with the host-mediated assay as a monitor, in vivo, of genotoxic factors present in various organs of animals, may become useful in the assessment of genotoxic (and possibly tumor-initiating) properties of chemicals for which long-term in-vivo mutagenicity and/or carcinogenicity data are not yet available.

Alkylation↗