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

Genotoxic effects of methyl isothiocyanate

Aim of the study was to investigate the genotoxic effects of methyl isothiocyanate (MITC), a compound widely distributed in the environment as a constituent of certain vegetables, a soil fumigant and breakdown product of carbamate pesticides. MITC caused only marginal mutation induction in reversion assays with Salmonella strains TA100 and TA98 and, the maximum effect (<2-fold increase over the background rate) was seen at 100microg/ml. In differential DNA-repair assays with E. coli (strains 343/763 uvrB/recA and 343/765 uvr(+)/rec(+)), a pronounced dose-response effect (induction of repairable DNA-damage) was seen at low concentrations (>/=4microg/ml). In both bacterial assays, addition of activation mix (rat liver S-9) led to a reduction of the genotoxic effects. In micronucleus assay and in single cell gel electrophoresis assay with human hepatoma cells (HepG2), clear cut positive results were obtained at exposure concentrations of <5microg/ml. On the contrary, only marginal effects were seen in differential DNA-repair host-mediated assays where E. coli indicator cells were recovered from different inner organs of mice that had been treated orally with a high dose (90mg/kg bw) of the test compound. Further in vitro experiments showed that MITC is inactivated by body fluids (saliva, gastric juice) and that its DNA-damaging properties are attenuated by non-enzymatic protein binding. Since exposure of HepG2 cells to MITC led to formation of thiobarbituric acid reactive substances, it is likely that its DNA-damaging effects involve lipid peroxidation processes. Overall, our findings show that MITC induces only marginal effects at extremely high (almost lethal) doses in inner organs in vivo, but it causes DNA-damage at low concentrations in vitro.

Genotoxic effects of allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC)

Two isothiocyanates (ITCs) commonly found in human diet, allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC), were tested for genotoxic effects in a battery of assays: Salmonella/microsome assay with TA 98 and TA 100, differential DNA repair assay with E. coli and micronucleus (MN) induction assay with human derived Hep G2 cells. Albeit to a different degree, both ITCs induced genotoxic effects in all test systems. AITC was more genotoxic in bacterial test systems than in Hep G2 cells; in contrast, the effect of PEITC was stronger in Hep G2 cells. In in vivo assays with E. coli indicators in which mice were exposed to relatively high doses of the compounds (90 and 270 mg/kg), AITC induced moderate but significant effects; PEITC failed to induce significant effects in any of the organs. To find out the reason for the weak genotoxicity of AITC and PEITC under in vivo test conditions, we exposed E. coli indicator cells to the test substances in the absence or presence of rat liver homogenate (with and without cofactors), bovine serum albumin (BSA) and human saliva. All of them markedly attenuated the genotoxicity of AITC and PEITC, implying that the test substances are detoxified by direct non-enzymatic binding to proteins. Additional experiments carried out on the mechanistic aspects of AITC and PEITC-induced genotoxicity showed that the compounds induce the formation of thiobarbituric acid reactive substances (TBARS) in Hep G2 cells. Furthermore, in in vitro assays with E. coli, radical scavengers reduced the differential DNA damage induced by AITC and PEITC. The latter two findings give a clue that reactive oxygen species might be involved in the genotoxic effect of the ITCs. Although ITCs have been repeatedly advocated as very promising anticancer agents, the data presented here indicate that the compounds are genotoxic, and probably carcinogenic, in their own right.

Genotoxic effects of benzyl isothiocyanate, a natural chemopreventive agent

Benzyl isothiocyanate (BITC) is contained in cruciferous plants which are part of the human diet. Numerous reports indicate that BITC prevents chemically induced cancer in laboratory animals and it has been postulated that BITC might also be chemoprotective in humans. On the other hand, evidence is accumulating that this compound is a potent genotoxin in mammalian cells by itself. To further elucidate the potential hazards of BITC, we investigated its genotoxic effects in different in vitro genotoxicity tests and in animal models. In in vitro experiments [differential DNA repair assay with Escherichia coli, micronucleus assay with human HepG2 cells and single cell gel electrophoresis (SCGE) assay with hepatocytes and gastrointestinal tract cells] pronounced dose-dependent genotoxic effects were found at low dose levels (</=5 microg/ml). In contrast, substantially weaker effects were obtained in in vivo experiments with laboratory rodents: in the differential DNA repair assay with E.coli cells, only moderate genotoxic effects were seen in indicator cells recovered from various organs of mice after treatment with high doses (between 90 and 270 mg/kg), while in SCGE assay with rats a change in the DNA migration pattern was seen at a dose level of 220 mg/kg body wt. These findings indicate that BITC is detoxified under in vivo test conditions. This assumption was supported by the results of in vitro experiments which showed that the genotoxic effects of BITC are markedly reduced by bovine serum albumin and human body fluids such as saliva and gastric juice. Additional experiments carried out on the mechanistic aspects of the genotoxicity of BITC showed that this compound causes formation of thiobarbituric acid-reactive substances in HepG2 cells and that its DNA damaging properties are diminished by alpha-tocopherol, vitamin C, sodium benzoate and beta-carotene, indicating the possible involvement of free radicals in the genotoxicity of BITC. The doses of BITC required to cause measurable DNA damage in laboratory rodents exceeded by far the dietary exposure levels of humans, but are similar to those which were required to inhibit chemically induced cancer in earlier animal experiments.

Genotoxic effects of three Fusarium mycotoxins, fumonisin B1, moniliformin and vomitoxin in bacteria and in primary cultures of rat hepatocytes

The genotoxic effects of three widespread Fusarium toxins, vomitoxin (VOM), moniliformin (MON) and fumonisin B1 (FB1) were investigated in bacterial tests and in micronucleus (MN) and chromosomal aberration (CA) assays with primary rat hepatocytes. All three toxins were devoid of activity in gene mutation assays with Salmonella typhimurium strains TA98 and TA100 and in SOS chromotests with E. coli strain PQ37 in the presence and absence of metabolic activation. FB1 and VOM gave negative results in differential DNA repair assays with E. coli K-12 strains (343/753, uvrB/recA and 343/765, uvr+/rec+); with MON, a marginal effect was seen in the absence of metabolic activation mix at relatively high concentrations (> or = 55 micrograms/ml). In metabolically competent rat hepatocytes stimulated to proliferate with EGF and subphysiological Ca2+ concentrations, a decrease of cell division was observed with all three toxins at concentrations > or = 10 micrograms/ml, VOM was strongly cytotoxic at 100 micrograms/ml. All three mycotoxins caused moderate increases of the MN frequencies at low concentrations (< or = 1 microgram/ml), but no clear dose-response effects were seen and at higher exposure levels the MN frequencies declined. In the CA experiments with hepatocytes, pronounced dose-dependent effects were observed with all three toxins. MON caused a 9-fold increase over the spontaneous background level after exposure of the cells to 1 microgram/ml for 3 h, with FB1 and VOM, the increases were 6- to 7-fold under identical experimental conditions. This is the first report on clastogenic effects of VOM and FB1 in mammalian cells, with MON induction of CAs in V-79 cells has been described earlier. Since all three mycotoxins caused CAs at very low concentration levels in liver cells in vitro, it is possible that such effects may also occur in humans and mammals upon consumption of Fusarium-infected cereals.

Assessment of the role of diet in cancer prevention

Population studies have demonstrated a clear relationship between the incidence of various cancers and consumption of different classes of foods, indicating that diet can have a protective effect. Diets, however, contain many hundreds of nutrient and non-nutrient compounds. Moving beyond the generalities provided by population studies requires short-term studies in which diets can be adjusted to test the effects of specific ingredients or compounds. The cost of this approach is the loss of direct outcome measures. Biomarkers related to early events in the cancer process which can show significant change within the duration of a trial, have to substitute. The choice of marker and the ability to validate its use are crucial both to the refining of dietary advice and to the search for the active principles of diet.

Genotoxic effects of crude juices from Brassica vegetables and juices and extracts from phytopharmaceutical preparations and spices of cruciferous plants origin in bacterial and mammalian cells

Crude juices of eight Brassica vegetables as well as juices and extracts of spices and phytopharmaceutical preparations from cruciferous vegetables were tested for induction of point mutations in Salmonella TA98 and TA100, repairable DNA damage in E.coli K-12 cells and clastogenic effects in mammalian cells. In bacterial assays, all juices caused genotoxic effects in the absence of metabolic activation, the ranking order being: Brussels sprouts > white cabbage > cauliflower > green cabbage > kohlrabi > broccoli > turnip > black radish. In experiments with mammalian cells, six juices induced structural chromosome aberrations. Brussels sprouts, white and green cabbage caused the strongest effects (800 microliters of juice induced a 5-fold increase over the background). In sister chromatid exchange assays, positive results were measured as well, but the effects were less pronounced. With all juices the genotoxic effects seen in mammalian cells were paralleled by a pronounced decrease in cell viability. Column fractionation experiments showed that 70-80% of the total genotoxic activity of the juices is found in the fraction which contains isothiocyanates and other breakdown products of glucosinolates, whereas phenolics and flavonoids contributed to a lesser extent to the overall effects. On the basis of these findings, and considering the negative results obtained with non-cruciferous vegetables (tomato, carrot and green pepper), it seems likely that the genotoxic effects of the juices are due to specific constituents of cruciferous plants such as glucosinolates and/or their breakdown products, in particular, isothiocyanates, which we found previously to be potent genotoxins in bacterial and mammalian cells. Finally, spices (mustards and horse radish paste) and phytopharmaceutical preparations were tested in bacterial assays. Mustards and horse radish caused very weak effects while most of the pharmaceutical preparations gave negative results, except cabbage tablets, which caused a strong and dose dependent induction of his revertants in Salmonella TA100. The present findings clearly indicate that cruciferous vegetables contain DNA damaging constituents. These observations are in contrast to earlier findings, which emphasized the antimutagenic effects of vegetable juices and also raise the question whether greatly increased consumption of Brassica vegetables or their concentrated constituents as a means for cancer prevention is indeed recommendable.

Effects of phenethyl isothiocyanate on metabolism and on genotoxicity of dimethylnitrosamine and 2-amino-1-methyl-6-phenylimidazo[4, 5-beta]pyridine (PhIP)

Phenethyl isothiocyanate (PEITC), a constituent of cruciferous vegetables, inhibited the genotoxic effects of N-nitrosodimethylamine (DMN) and of 2-amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine (PhIP) in differential DNA repair assays with E. coli K-12 strains in vitro and in animal mediated assays with mice. In Salmonella typhimurium, the mutagenic activities of DMN and PhIP measured after activation with S-9 homogenates from several organs of PEITC-treated mice were substantially lower than those obtained with homogenates of untreated animals as well. PEITC also reduced the formation of micronuclei by DMN in metabolically competent Hep-G-2 cells of human origin but was ineffective in combination with PhIP. Biochemical investigations showed that the prevention of genotoxic effects of DMN by PEITC results form an inhibition of its alpha-hydroxylation. The effect of oral administration of PEITC on the formation of DNA adducts of PhIP was examined in the colon and liver of mice. No inhibition of adduct formation was observed in these experiments. Biochemical experiments showed that PEITC reduces not only the metabolic activation of PhIP via 2-hydroxyamino PhIP but also inhibits a detoxification pathway (formation of 4-hydroxy PhIP). The present results can be taken as an indication that the anticarcinogenic activities of isothiocyanates towards nitrosamines are paralleled by antimutagenic effects, and that probably no such protective effects occur in combination with heterocyclic amines. Furthermore, our findings show that the effects of chemopreventive agents demonstrated in bacteria in vitro cannot always be extrapolated to reactions occurring in intact mammalian cells.

Potential antitumour mitosenes: relationship between in vitro DNA interstrand cross-link formation and DNA damage in Escherichia coli K-12 strains

This investigation was aimed at determining the possible relationship between DNA interstrand cross-linking and the cytotoxic activity of potential antitumour mitosene compounds. Mitosenes, possessing two good leaving groups at C-1 and C-10, were found to be able to cross-link calf thymus DNA under hypoxic conditions following sodium dithionite (Na2S2O4) reduction at pH 7.0 and pH 5.5. DNA interstrand cross-linking was pH dependent for most of the mitosenes used, with a higher amount of cross-links formed at pH 5.5 compared to pH 7.0. Without reduction or under aerobic conditions no cross-link formation was detected. The importance of DNA damage for the toxic effect of these mitosenes was assayed by comparing the survival in a DNA repair deficient and a DNA repair proficient E. coli K-12 strain. A correlation between the number of cross-links formed in calf thymus DNA in vitro and the IC50 values in the DNA repair deficient E. coli strain was found. The effect of hypoxia on toxicity of mitosenes was studied in Chinese hamster V79 cells. In these cells, mitosenes appeared to be very active. Under severe hypoxic conditions toxicity of these mitosenes increased, most likely due to the increased lifetime of the activated mitosene species as compared to aerobic conditions. The results suggest that DNA cross-linking following reductive activation is important for the eventual activity of mitosenes in a bacterial system. Increased activity of mitosenes under hypoxic conditions in the V79 cells indicates that these mitosenes may be more active in hypoxic parts of tumours.

Induction of genotoxic effects by chlorohydroxyfuranones, byproducts of water disinfection, in E. coli K-12 cells recovered from various organs of mice

The genotoxic effects of three chlorohydroxyfuranones (CHFs), 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), 3-chloro-4-(chloromethyl)-5-hydroxy-2[5H]furanone (CMCF) and 3,4,-dichloro-5-hydroxy-2[5H]furanone (MCA), which are formed as byproducts of water disinfection with chlorine, were investigated in bacterial differential DNA repair assays in vitro and in animal-mediated assays in vivo. As indicators of DNA damage, E. coli K-12 strains were used that differ in their repair capacity (uvrB/recA vs. uvr+/rec+). Liquid incubation of the compounds without metabolic activation caused a pronounced reduction of the viability of the repair-deficient strain relative to the repair-proficient wild-type strain. The order of potency of genotoxic activity in vitro (dose range 0.004-10 micrograms/ml) was MX > CMCF > MCA. Addition of mouse S-9 mix or bovine serum albumin to the incubation mixtures resulted in an almost complete loss of the activity of all three test compounds. In the animal-mediated assays, mixtures of the indicator bacteria were injected intravenously into mice which were subsequently treated with the test compounds (200 mg/kg b.w.). Two hours later, the cells were recovered from various organs and the relative survival frequencies determined. Under these conditions, all three compounds caused pronounced genotoxic effects, MX and CMCF being stronger genotoxins than MCA. The strongest effects were consistently found in the gastrointestinal tract, but statistically significant DNA damage was also observed in indicator cells recovered from lungs, liver, spleen and kidneys. In a further experiment, the effects of lower doses of MX (4.3, 13 and 40 mg/kg) were investigated. In these experiments dose-dependent effects were measured in all organs. CMCF and MA caused only marginal effects at 40 mg/kg except in the stomach where approximately a 50% reduction of relative survival frequency was observed with CMCF. The results of these animal-mediated assays indicate that (i) all three CHFs cause genotoxic effects in the living animal, and (ii) the potencies of the three compounds observed under in vivo conditions are not commensurate with their extremely high activities measured in vitro. One possible explanation for the weaker responses observed in the animal-mediated assays might be that CHFs are inactivated by non-specific protein binding.

Evaluation of the DNA-repair host-mediated assay. III. Relationship between metabolic activation of dimethylnitrosamine and organ-specific differential lethality induced in E. coli indicator strains

In the present study the sensitivity of differential lethality as an endpoint for monitoring the presence of organ-specific genotoxic factors within the DNA-repair host-mediated assay (HMA) was determined. The induction of differential lethality in chemically exposed animals was assessed by measuring the recovery ratio Q, i.e., the relative survival of a repair-deficient E. coli K-12 derivative in comparison with its repair-proficient counterpart. Using untreated animals the interindividual fluctuation of the recovery ratio Q was first quantified and then used to determine the level below which it could be considered indicative of chemically induced differential lethality. This Q value was found to be 0.65 or lower. Using this criterion, a significant decrease of the Q value was observed in mice exposed to DMNA at a dose level as low as 15-30 mumole/kg, i.p. Inter-organ transport (liver----extrahepatic organs) of indicator bacteria was studied in reconstruction experiments using the direct-acting methylating agent MNU. These studies showed that inter-organ transport of indicator bacteria did not interfere with MNU-induced differential lethality. Time-related experiments were used to study the effects of inter-organ transport of genotoxic DMNA metabolites. In these studies significant, time-related differences were found in the induction of differential lethality in various organs of mice treated with DMNA. At a dose level of 200 mumole/kg (i.p.) genotoxic factors appeared within 25 min after administration in the liver. In the lungs and kidneys such factors appeared at a substantially slower rate, e.g., 20-120 min after DMNA administration. In persistence experiments differential lethality reached a maximum 30 min after DMNA treatment. No residual effects were detected 60 min after the injection of the carcinogen. These experiments showed that DMNA-derived genotoxic factors diffused from the liver into the bloodstream. The diffusion of these reactive species followed by their transport via the bloodstream to the lungs accounted for maximally 50% of differential lethality observed in bacteria recovered from the latter organ. In contrast, no indications were found for the transport of genotoxic DMNA metabolites from the liver via the bloodstream to the spleen and the kidneys. These results show that organ-specific effects observed in the DNA-repair HMA procedure after DMNA exposure can be primarily attributed to in situ metabolism, rather than diffusion of genotoxic metabolites from the liver to extrahepatic organs.

Use of differential DNA-repair host mediated assays to investigate the biotransformation of xenobiotics in Drosophila melanogaster. I. Genotoxic effects of nitrosamines

A rapid differential DNA-repair assay procedure was developed to investigate the biotransformation of xenobiotics in Drosophila melanogaster in vivo. Indicator of genotoxic activity was a pair of streptomycin-dependent Escherichia coli strains differing vastly in DNA repair capacity (uvr+/rec+ vs. uvrB/recA). Prior to the experiments with test compounds, mixtures of the two strains were injected into the abdomina of untreated animal hosts (male Berlin-K flies) and the time-dependent recovery kinetics determined. Subsequently, different aliphatic and aromatic nitrosamines were tested. Solutions of the compounds were injected simultaneously with the indicator cells. Three hours later, the flies were killed, homogenized and the induction of (repairable) DNA damage determined by comparison of the survival rates of the two strains in single animals. Eight carcinogenic compounds (nitrosodiethylamine, NDEA; nitrosodimethylamine, NDMA; nitrosodi-npropylamine, NDPA; nitrosodiethanolamine, NDELA; nitrosomethylaniline, NMA; 4-methyl-nitrosopiperidine, MNPIP; nitrosopyrrolidine, NPYR; nitrosomorpholine, NMOR) and one whose tumorigenic activities are still controversially discussed (nitrosodiphenylamine, NDPhA) induced dose-dependent differential killing effects in the present system. One agent which has not been found carcinogenic in rodents (2.6-dimethyl-nitrosopiperidiine. NDMPIP) gave negative results. The ranking order of genotoxic activities of the nitrosamines found in Drosophila in vivo is in good agreement with those of carcinogenic potencies established on the basis of experiments with rats. The most pronounced exceptions are the rather weak response towards NMA and the stronger DNA damaging activity of NMPIP compared to NDMA. Phenobarbital (5-ethyl-5-phenyl-2,4,6-trioxohepatahydropyramidine) (PB) feeding of the flies resulted in an increase of the DNA damaging potencies of all nitrosamines tested. Substantial enhancement of the induction of DNA damage was however, restricted to NDEA, NPYR and NMOR, whereas with nitrosodiphenylamine (NDPhA), NDELA and NDMA only a moderate (less than 25%) increase of differential killing effects was found. In the case of the two latter compounds, these results might be due to the fact that enzymes other than the MFO are involved in their activation. Attempts to localize the formation and/or distribution of metabolites in the bodies of fruitflies by separation of the tagmata of chemically treated animals and determination of genotoxic effects in the different segments indicate that the most pronounced effects occur in the abdomina whereas in heads and thoraxes comparatively lower activities are detectable.

Investigations on the use of EDTA-permeabilized E. coli cells in liquid suspension and animal-mediated genotoxicity assays

The potential use of EDTA-permeabilized E. coli cells for the investigation of genotoxic effects of compounds with a large molecular configuration in vitro and in animal-mediated differential DNA-repair assays was studied. The indicator for the induction of (repairable) DNA damage was a pair of E. coli K-12 strains (343/765 and 343/753) differing vastly in DNA-repair capacity (uvr+/rec+ vs. uvrB/recA). Investigations on the influence of EDTA treatment on the viability of these strains show that during short-term exposure (3 min), the EDTA level should not exceed 0.5 mmole/l in the pretreatment mix, since at higher concentrations a marginal titer reduction of the repair-deficient strain occurs, thus indicating a weak genotoxic activity of this chelating agent. Comparisons of the results gained in vitro with permeabilized and untreated cells demonstrate that EDTA exposure leads to a substantial enhancement of the sensitivity of the indicator bacteria towards DNA damage induced by B(a)P and N-Ac-2AAF which is essential for the detection of genotoxic activities of these polycyclic aromatic compounds. Experiments to elucidate the possibility of employing EDTA-treated cells in vivo show that following intravenous and oral administration the recovery rates of permeabilized indicator strains from various mouse organs are substantially lower than those found under identical conditions (exposure time 150 min) with untreated strains. Nevertheless enough viable cells can be recovered from liver, spleen, kidneys, lungs and stomach to allow the investigation of organ-specific genotoxicity. It is furthermore noteworthy that exposure of permeabilized indicator cells in control animals (for 150 min) resulted in a marginal reduction of the relative survival of the repair-deficient strain in all organs investigated, whereas with non-treated strains such effects are only detectable after extended exposure periods. The observation of a slightly elevated genotoxic background under in vivo conditions does not prevent the assessment of the organ distribution of genotoxic effects induced by mutagens and/or carcinogens: in the case of B(a)P, intraperitoneal administration to mice in the dose range of 10-50 mg/kg body weight resulted in a pronounced dose-dependent inactivation of the uvrB/recA cells in the liver. Also in the lungs differential killing effects occurred at the highest dose tested, whereas no genotoxic activities were detectable in stomach, kidneys and spleen of the host animals.

DNA alkylation and formation of DNA interstrand cross-links by potential antitumour 2,5-bis(1-aziridinyl)-1,4-benzoquinones

A series of 3,6-substituted 2,5-bis(1-aziridinyl)-1,4-benzoquinone derivatives was shown to alkylate calf thymus DNA and to form DNA interstrand cross-links. Alkylation and cross-link formation were enhanced after electrochemical reduction of the compounds and increased with lower pH in the pH range from 4.5 to 8.0. Reduction especially shifts the pH at which cross-linking and alkylation occurs to higher values, which are more physiologically relevant. This shift is probably caused by the increase in pKa value of the aziridine ring after reduction of the quinone moiety. The inactivation of single-stranded bacteriophage M13mp19 DNA to form phages in an E. coli host, by the 3,6-unsubstituted parent compound 2,5-bis(1-aziridinyl)-1,4-benzoquinone (TW13) was dependent upon reduction and pH in a similar way as was alkylation. The compound in our series with the least bulky, 3,6-substituents, TW13, caused a high amount of cross-link formation. Compounds with methyl-substituted aziridine rings showed low cross-linking ability. Our results support the concept that the protonated reduced compound is the reactive species that alkylates DNA, and that steric factors play an important role in the reactivity towards DNA. A correlation is observed between the ability to induce DNA interstrand cross-links and inactivation of M13mp19 bacteriophage DNA. Cross-link formation was also demonstrated in E. coli K12 cells, where the compounds are reduced endogenously by bacterial reductases.

The 'antimutagenic' effect of cinnamaldehyde is due to a transient growth inhibition

Addition of cinnamaldehyde to the selective medium causes a reduction in the number of revertant colonies of S. typhimurium or E. coli when the cells have been mutagenized with 4NQO but not when they have been mutagenized with MNNG. Toxicity of the cinnamaldehyde exposure depends largely on the status of growth and/or nutrient supply of the cells. We present evidence that simple growth inhibition due to lack of nutrients mimics the effect of cinnamaldehyde in 4NQO- and MNNG-treated cells. This argues that the reduction of mutant colonies is due to a transient growth retardation caused by cinnamaldehyde exposure, which presumably allows the cells to repair 4NQO-induced damage--but not MNNG-induced damage--via a more error-free pathway.

Cytotoxicity and induction of repairable DNA damage by photoactivated 5-nitrofurfural

5-Nitrofurfural (NFA) an important photodecomposition product and metabolite of medicinal nitrofurans is phototoxic in bacterial test systems. Its major photodecomposition product 5-hydroxymethylene-2(5H)-furanone (HMF) appears to be responsible for this. Furthermore HMF and photoactivated nitrofurfural can induce repairable DNA damage in Escherichia coli bacteria. These effects may be important with respect to skin and allergic reactions and carcinogenicity appearing in nitrofuran therapy.

Studies on curcumin and curcuminoids. IX: Investigation of the photobiological activity of curcumin using bacterial indicator systems

The dye curcumin is a natural, nontoxic food constituent. On irradiation with visible light, curcumin proves to be phototoxic for Salmonella typhimurium and Escherichia coli, even at very low concentrations. The observed phototoxicity makes curcumin a potential photosensitizing drug which might find application in the phototherapy of, for example, psoriasis, cancer, and bacterial and viral diseases.

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.

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.

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)

Quantitative comparative mutagenesis in bacteria, mammalian cells, and animal-mediated assays. A convenient way of estimating genotoxic activity in vivo?

The accumulation of environmental compounds which exhibit genotoxic properties in short-term assays and the increasing lag of time for obtaining confirmation or not in long-term animal mutagenicity and carcinogenicity tests, makes it necessary to develop alternative, rapid methodologies for estimating genotoxic activity in vivo. In the experimental approach used here, it was assumed that the genotoxic activity of foreign compounds in animals, and ultimately humans, is determined among others by exposure level, organ distribution of (DNA) dose, and genotoxic potency per unit of dose, and that knowledge about these 3 parameters may allow to rapidly determine the expected degree of genotoxicity in various organs of exposed animals. In view of the high degree of qualitative correlation between mutagenic activity of chemicals in bacteria and in cultured mammalian cells, and their mutagenic and carcinogenic properties in animals, and in order to be able to distinguish whether mutagenic potency differences were due to differences in (DNA) dose rather than other physiological factors, the results of mutagenicity tests obtained in the present experiments using bacteria and mammalian cells were compared on the basis of DNA dose rather than exposure concentrations, with the following questions in mind: Is there an absolute or a relative correlation between the mutagenic potencies of various ethylating agents in bacteria (E. coli K12) and in mammalian cells (V79 Chinese hamster) after treatment in standardized experiments, and can specific DNA adducts be made responsible for mutagenicity? Is the order of mutagenic potency of various ethylating agents observed in bacteria in vitro representative of the ranking of mutagenic potency found in vivo? Since the answer to this last question was negative, a further question addressed to was whether short-term in vivo assays could be developed for a rapid determination of the presence (and persistence) of genotoxic factors in various organs of mice treated with chemicals. In quantitative comparative mutagenesis experiments using E. coli K12 and Chinese hamster cells treated under standardized conditions in vitro with 5 ethylating agents, there was no indication of an absolute correlation between the number of induced mutants per unit of dose in the bacteria and the mammalian cells. The ranking of mutagenic potency was, however, identical in bacteria and mammalian cells, namely, ENNG greater than ENU greater than or equal to DES greater than DEN congruent to EMS, the mutagenic activity of DEN being dependent on the presence of mammalian liver preparations.(ABSTRACT TRUNCATED AT 400 WORDS)