Concentrations Of Mutagens Research Articles

Long-Term Monitoring of the Ecological Situation in Industrial Sites of Moscow with a Drosophila melanogaster Test Strain

For 12 years, recombination rate was assessed in Drosophila melanogastermales exposed on a thermoelectric power station (TPS) of Moscow. In 1994, experiments were also carried out on another Moscow TPS for comparison. The recombination frequency in exposed males was two- or threefold higher than in the control sample. Recombination frequencies observed in different years did not significantly differ from each other. Likewise, no significant difference was observed for the results obtained on two TPSs. A dramatic increase in recombination frequency in flies exposed on TPS was considered as an adequate response to high concentrations of effective mutagens discharged by TPS.

Alleviation of mutagenic effects of polycyclic aromatic agents (quinacrine mustard, ICR-191 and ICR-170) by caffeine and pentoxifylline

Previous studies performed by others indicated that apart from its other biological effects, caffeine (CAF) may have a role in protection of organisms against cancer. However, biological mechanism of this phenomenon remained unknown. Recent studies suggested that caffeine can form stacking (π–π) complexes with polycyclic aromatic chemicals. Therefore, one might speculate that effective concentrations of polycyclic aromatic mutagens could be reduced in the presence of caffeine. Here we demonstrate that caffeine and another xanthine, pentoxifylline (PTX), effectively alleviate mutagenic action of polycyclic aromatic agents (exemplified by quinacrine mustard (QM), 2-methoxy-6-chloro-9-(3-(2-chloroethyl)aminopropylamino)acridine·2HCl (ICR-191) and 1,3,7-propanediamine-N-(2-chloroethyl)-N′-(6-chloro-2-methoxy-9-acridinyl)-N-ethyl·2HCl (ICR-170)), but not of aliphatic mutagens (exemplified by mechlorethamine), in the recently developed mutagenicity test based on bacterium Vibrio harveyi. Biophysical studies indicated that caffeine and pentoxifylline can form stacking complexes with the aromatic agents mentioned above. Molecular modeling also confirmed a possibility of stacking interactions between examined molecules.

Mutant spectra analysis at hisG46 in Salmonella typhimurium strain YG1029 induced by mammalian S9- and plant-activated aromatic amines.

Mutant spectra analysis was conducted with spontaneous hisG46 revertants of Salmonella typhimurium strain YG1029 and revertants induced by the plant- and mammalian S9-activation of benzidine and 4-aminobiphenyl (4-ABP). Under preincubation conditions, YG1029 cells were exposed to benizidine or 4-ABP with mammalian S9 activation or to a high molecular weight fraction that contained the plant-activated products. The induced revertants were isolated at mutagen concentrations that caused an increased mutant frequency of approximately 4- to 10-fold above background. Genomic DNA from each revertant was isolated and the hisG region was amplified using polymerase chain reaction (PCR). Using a series of specific probes and a modified version of the ECL3's-oligolabelling and detection system, each of the six possible base-pair substitution mutations at hisG46 that leads to a reversion event was determined. Of the YG1029 spontaneous revertants, transition mutations were 31.8% and transversion mutations were 68.2%. The YG1029 spontaneous mutant spectrum differed significantly from the spontaneous spectrum of TA1535 but did not significantly differ from the spontaneous TA100 mutant spectrum. The differences of the spontaneous mutant spectra among these highly related strains illustrate that the introduction of the plasmid pKM101 into S. typhimurium increased the frequency of transversions (CCC-->ACC; CCC-->CAC) and reduced site 2 (CCC-->CTC) transitions. With plant-activated benzidine, 21.1% of recovered revertants resulted from transitions and 78.9% from transversions while S9 activated-benzidine induced revertants were recovered as 14.2% from transition and 85.8% from transversion mutations. Plant-activated 4-ABP recovered 20.0% transitions and 80.0% transversions. S9-activated 4-ABP-induced 21.4% transitions and 78.6% transversions. Chi-square analysis of mutant spectra indicated that the DNA lesions that resulted in reversion at the hisG46 allele induced by plant-activated benzidine or 4-ABP were different from those generated after mammalian S9 activation of these promutagens. The plant-activated benzidine and 4-ABP induced statistically identical mutant spectra. Also, the mammalian-activated benzidine and 4-ABP induced statistically similar mutant spectra. These data show that the plant-activated and mammalian-activated aromatic amine products inflicted different types or distributions of DNA lesions that were reflected in the resulting induced mutant spectra.

Implication of nitro group reduction in the mutagenic and chromosome damaging activities of 22 new 5-nitroisoquinolines by the Salmonella mutagenicity test and the cytokinesis-blocked micronucleus assay

The mutagenic (MUT) and chromosome-damaging (CHR) activities of 22 potential antimalarial drugs (5-nitroisoquinoline derivatives) were evaluated by the Salmonella test and the cytokinesis-blocked micronucleus assay (CBMN). The Salmonella mutagenicity test was performed with and without metabolic activation (S9 mix) in S. typhimurium strains TA100 and YG1042 (an overproducing nitroreductase and O-acetyltransferase TA100 strain). The CBMN was carried out on human lymphocytes without metabolic activation. Four concentrations were tested: 1, 10, 100 and 1000 ng/ml. MUT was expressed as minimal mutagenic concentrations (MMC, μ m) and CHR was expressed as minimal chromosome-damaging concentrations (MCDC, n m) to compare both activities. All the 5-nitroisoquinoline compounds were mutagenic in TA100. MMC ranged from 0.1 to 52.9 μ m in TA100. A statistically significant decrease in MMC was observed in YG1042 (8×10 −3 to 3.5 μ m), implicating reduction of the nitro group. Modulation of MUT by S9 mix was not significant in TA100 and YG1042. CHR was detected in 13 products for at least one concentration. Among the chromosome-damaging compounds, the MCDC ranged from 2.9×10 −3 to 3.6 n m. No relationship was found between MUT and CHR, suggesting two distinct pathways of DNA damage.

Comparison of the Ames test and a newly developed assay for detection of mutagenic pollution of marine environments

A new assay for detection of mutagenic pollution of marine environments, based on the use of a series of genetically modified Vibrio harveyi strains, was developed recently. Here, we compared this assay with a commonly used Ames test, employing mutants of Salmonella enterica serovar Typhimurium. We found that survival of S. enterica serovar Typhimurium in artificial marine water and in different samples of marine water is dramatically reduced relative to that of V. harveyi strains. This indicates that V. harveyi strains are significantly more useful in testing samples of marine water. Moreover, sensitivity of both assays was compared. We found that using the V. harveyi assay it is possible to detect significantly (from a few to several times) lower concentrations of typical chemical mutagens than employing the Ames test. Although the higher sensitivity of the V. harveyi test relative to the Ames assay may be of minor importance when testing mutagenicity of certain chemicals in their pure form under laboratory conditions, this feature is very important in testing samples of marine water. Therefore, we assume that the V. harveyi assay may be an adequate test for detection of mutagenic pollution of marine environments.

Dietary nitrate generates potentially mutagenic concentrations of nitric oxide at the gastroesophageal junction

Twenty-five percent of absorbed dietary nitrate is re-secreted in saliva, and 30% of this is reduced to nitrite by buccal bacteria. When saliva is swallowed, the acidic gastric juice reduces the nitrite to nitric oxide. The aim of this study was to examine the anatomic distribution of nitric oxide generation within the lumen of the upper gastrointestinal tract under basal conditions and after ingesting nitrate equivalent to that in salad portion. Using custom-made sensors, the dissolved luminal nitric oxide concentration and pH were measured at 1-cm increments for 2 minutes throughout the length of the stomach and distal esophagus in 15 Helicobacter pylori-negative healthy volunteers with and without ingestion of 2 mmol potassium nitrate. Serum nitrate and saliva nitrite concentrations were also monitored. The nitrate ingestion increased mean (range) serum nitrate from 30 micromol/L (18-49) to 95 micromol/L (32-152), mean salivary nitrite from 36 micromol/L (19-153) to 252 micromol/L (32-600), and mean peak luminal nitric oxide concentration from 4.7 micromol/L (1.4-7.8) to 23.2 micromol/L (2.1-50) (P < 0.05 for each). After nitrate, the peak nitric oxide concentration occurred in 11 of the 15 (73%) subjects within 1 cm distal to the gastroesophageal pH step-up point. The mean nitric oxide concentration over the 1-cm segment immediately distal to the gastroesophageal pH step-up after nitrate was 7.5 micromol/L (range, 0.5-30.7) and was significantly higher than at all other sites. Nitric oxide concentrations greater than 50 micromol/L were observed at the precise location where neutral esophageal pH fell to acidic gastric pH. Luminal generation of nitric oxide from dietary nitrate via salivary nitrite is maximal at the gastroesophageal junction and cardia. The high concentrations of nitric oxide generated may contribute to the high incidence of mutagenesis and neoplasia at this site.

The comet assay with MCL-5 cells as an indicator of genotoxic treatment with chemicals and cigarette smoke condensates.

The metabolically competent human lymphoblastoid cell line MCL-5 was treated with a panel of mutagens to assess the induction of DNA damage. Treatment effects were observed by monitoring cell proliferation and by single-cell gel electrophoresis (SCGE). The direct-acting mutagens benzo[a]pyrene-7,8-diol 9,10-epoxide (BPDE) and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), as well as pro-mutagens requiring metabolic activation, i.e. benzo[a]pyrene (BaP), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 4-N-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and cigarette-smoke condensate (CSC), were assayed by SCGE. Assay schemes were adapted for the MCL-5 cell line and for low levels of strand break induction, by inclusion of the DNA synthesis inhibitors cytosine arabinoside and hydyroxyurea, and by extending the electrophoresis time. For all mutagens tested, dose-dependent increases of median and average tail moment values among 50 nucleoids per slide were observed. The determining factors for selecting the treatment doses for mutation-induction experiments were the solubility of BaP and PhIP in the exposure medium, and the cytotoxicity exhibited by BPDE, MNNG and CSC. Induction of DNA strand breaks was obtained at mutagen concentrations permitting sufficient cell proliferation, except in the case of MNNG.

Effect of genotypic differences in interleukin-1 beta on gastric acid secretion in Japanese patients infected with helicobacter pylori

Although several studies have demonstrated a close relation between Helicobacter pylori infection and various upper gastrointestinal disorders, including gastric cancer (1–3), the specific pathophysiological explanations for this association are not known. H. pylori infection causes histological gastritis and affects gastric acid secretion (4 – 6). In patients with severe gastritis of the corpus, acid secretion is decreased markedly and the pH of gastric juice is increased (4 – 6). This decrease in acid secretion delays the elimination of bacterial toxins and products of inflammation, such as reactive oxygen radicals and nitrogen oxide (7), thereby increasing the concentration of these well-known mutagens in the stomach. Decreased acid secretion may also result in increased production of carcinogenic N-nitroso compounds because of superinfection by other bacteria or a reduction in vitamin C levels in gastric juice (8,9). An increased rate of cell turnover in inflamed mucosa further increases the opportunity for DNA damage. Moreover, decreased gastric acid secretion permits the reflux of duodenal juice, including bile, into the stomach, which can induce intestinal metaplasia, a precancerous change (10). Therefore, H. pylori–induced gastritis and subsequent acid hyposecretion may be associated with an increased risk of gastric cancer. Several inflammatory cytokines are upregulated in gastric mucosa infected with H. pylori. One of these cytokines, interleukin-1beta (IL-1 ), is important in initiating and amplifying the inflammatory responses to H. pylori infection (11). IL-1 is also a potent inhibitor of gastric acid secretion (12–14), as we have previously observed in patients infected with H. pylori (15). Increased IL-1 gene expression and severe corpus gastritis are related to increased pH of the gastric juice. In an animal model, we have recently reported that acid secretion is decreased by H. pylori infection, which is accompanied by an increase in the expression of IL-1 messenger ribonucleic acid (mRNA) in gastric mucosa as has been observed in humans. Furthermore, the decreased acid secretion in this animal model was restored to normal levels by administration of an antagonist of the IL-1 receptor (16). Therefore, IL-1 may cause the acid hyposecretion that is observed in patients with H. pylori infection and severe gastritis. Polymorphisms in the promoter region of the IL-1 gene have been associated with differences in the production of IL-1 by leukocytes in vitro (17,18). In white patients, polymorphisms in or near the interleukin gene have been associated with enhanced IL-1 production and an increased risk of gastric cancer (7). However, one of the polymorphisms (IL-1RN*2) is rare in Japan (19). Moreover, the polymorphisms in the promoter region of IL-1 (at positions 511 and 31) are closely linked and thus may not convey independent information (7,19). We studied whether gastric pH differed among the different IL-1 ( 511) genotypes in Japanese patients infected with H. pylori.

A calorimetric evidence of the interaction and transport of environmentally carcinogenic compounds through biomembranes

The effect exerted by pyrene and nitro-pyrene (N-pyrene), two structurally similar polycyclic aromatic hydrocarbons (PAH S), possessing mutagenic and carcinogenic activity, on the thermotropic behaviour of model membranes constituted by dimyristoylphosphatidylcholine (DMPC) vesicles, was investigated by differential scanning calorimetry (DSC). Attention was directed to evaluate modifications in mutagen–lipid interaction induced by compound structure and lipophily and evidences in their membrane penetration. The two examined compounds, when dispersed in liposomes during their preparation, were found to exert a very different action on the l β to l α gel-to-liquid crystal phase transition of DMPC multilamellar vesicles (MLV). Pyrene caused a detectable effect on the transition temperature ( T m), shifting it towards lower values with a concomitant decrease of the associated enthalpy (Δ H) changes, while N-pyrene was able to modify the lipid vesicles thermotropic behaviour only for low molar fractions, without deep changes in the Δ H. Modifications induced by pyrene were a function of mutagen concentration while the different behaviour of N-pyrene can be due to different polarity induced by the presence of the nitro-group, which attribute an higher hydrophilic character. Solid pyrene and N-pyrene and MLV aqueous dispersions (0.12 molar fraction) were left in touch for long incubation times at temperature higher than the transitional temperature of DMPC to detect their spontaneous transfer through the medium. By following this procedure, no interaction was detected for both pyrene and N-pyrene with lipid vesicles, suggesting that their low hydrophilic character avoid their migration through the aqueous layer surrounding the MLV vesicles. Carrying out a kinetic measurement leaving for increasing incubation times charged MLV (0.12 molar fraction) with empty DMPC vesicles the uptake of the PAHs by the empty vesicles and their successive interaction, after several periods of incubations, was monitored. Pyrene and N-pyrene showed a different kinetic behaviour: the N-pyrene rate transfer was faster than that of pyrene but both final transfer and interaction were on the same order that detected by preparation of MLV charged with a 0.06 molar fraction of PAH, carried out in organic solvent. The obtained results suggest that the PAH S, even if unable to reach and penetrate the biological membranes migrating through an aqueous layer, when dispersed in a lipophilic medium are able to penetrate and diffuse inside a model membrane. The different effects observed could be explained in terms of compound hydrophobicity and a relation between compound structure and membrane interaction can be suggested. This allows the membrane interaction with pyrene for all the tested molar fractions, but the structure of N-pyrene seems to suggest the formation of aggregate on the membrane surface for molar fractions higher than 0.09.

Life style factors and acquired susceptibility to environmental disease

Abstract Multifactorial risk factors are responsible for many diseases. They can be broadly categorized as environmental, genetic and life style factors. Much attention has been focused on the first two categories, e.g. the identification of environmental toxicants/carcinogens and the elucidation of genetic susceptibility to disease. Life style risk factors such as aging, poor nutrition, infection and exposure to toxicants can also increase susceptibility to illnesses. These life style factors can therefore be considered to cause acquired susceptibility for increased risk for environmental disease. Among Egyptians, infection with the parasite, Schistosoma, is the primary risk factor for bladder cancer and the risk is enhanced by exposure to mutagenic chemicals. We have shown that inheritance of susceptible metabolizing genes that can increase body burden of mutagenic chemicals enhances the risk. We have also hypothesized that chronic exposure to mutagenic chemicals causes cellular abnormalities that can reduce the capacity of cells to repair DNA damage and thus increase the risk for environmental disease. We have used a challenge assay to show that cells from cigarette smokers and from populations exposed to uranium, butadiene and pesticides have abnormal DNA repair responses compared to matched controls. On the other hand, the response is normal in workers exposed to very low concentrations of butadiene and benzene, and in mothers who had children with birth defects. This suggests that exposure to high enough concentrations of certain mutagens can cause acquired susceptibility in human populations. The acquired susceptibility is expected to interact with environmental factors and with genetic susceptibility to increase risk for environmental disease.

Enrichment of Pisum sativum gene resources through combined use of physical and chemical mutagens

The potential of induced mutations is of importance in genetic improvement of crops. In the experiments different physical and chemical mutagens were used (g-rays, fast neutrons, ethyl methanesulfonate (EMS), ethylene imine (EI), diethyl sulfate (DES), and nitroso methyl urethane (NMU)) applied in single or combined treatments. Frequency of main mutations was considerably higher after combined treatment compared to single treatment. Combined treatment with 150 Gy and 0.01% NMU caused a hyper-additive mutation effect (4.76%), double the theoretically expected one. The chemical mutagen concentrations had considerable influence on the effect of the combined treatment. The mutation spectrum also differed in various kinds of treatments. Significant changes in the mutagen efficiency occurred with the increase of EMS concentrations in combined treatment with g-rays. The highest efficiency coefficient (3.65) was obtained in the variant with 40 Gy g-rays and 0.2% EMS, which correlates with the highest mutation fre...

Genetically modified Vibrio harveyi strains as potential bioindicators of mutagenic pollution of marine environments.

For biodetection of mutagenic pollution of marine environments, an organism naturally occurring in these habitats should be used. We found that marine bacterium Vibrio harveyi may be an appropriate bioindicator of mutagenic pollution. For positive selection of mutants, we developed a simple method for isolation of V. harveyi mutants resistant to neomycin. We constructed genetically modified V. harveyi strains that produce significantly more neomycin-resistant mutants upon treatment with low concentrations of mutagens than the wild-type counterpart. The sensitivity of the mutagenicity test with the V. harveyi strains is at least comparable to (if not higher than) that of the commonly used Ames test, which uses Salmonella enterica serovar Typhimurium strains. Therefore, we consider that the V. harveyi strains described in this report could be used as potential bioindicators of mutagenic pollution of marine environments.

Water Treatment Practice and the Formation of Genotoxic Chlorohydroxyfuranones

It is generally known that chlorine disinfection of drinking water that is derived from surface water leads to the formation of mutagenic compounds. A very significant portion (in some cases over 60%) of the mutagenicity has been attributed to the presence of various chlorohydroxyfuranones (CHFs). Besides producing mutagenicity in bacterial assays, the CHFs have been reported to alter the genetic properties of animal and human cells. Recently, one of the compounds, namely 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), was shown to be a potent multiorgan carcinogen in rats. These findings have led to concern about the health effects associated with the mutagens in drinking water. This paper is a short review of the work aiming at the identification of hydroxyfuranones and related compounds in disinfected drinking water. In addition, results are presented that show how change in water treatment practice is reflected in the mutagenicity of the drinking water and in the concentration of the main mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX).

Mutagenicity of C 24H 14 PAH in human cells expressing CYP1A1

Relatively little is known about the mutagenicity of C 24H 14 PAH, a diverse group of five- and six-ring PAH, some of which are present at trace levels in the environment. To better understand the mutagenicity of this class of compounds, 11 C 24H 14 PAH, including benzo[ a]perylene, benzo[ b]perylene, dibenzo[ a, e]fluoranthene, dibenzo[ a, f]fluoranthene, dibenzo[ j, l]fluoranthene, dibenzo[ a, h]pyrene, dibenzo[ a, i]pyrene, dibenzo[ e, l]pyrene, naphtho[1,2- b]fluoranthene, naphtho[2,3- a]pyrene, and naphtho[2,3- e]pyrene, were tested in a mutagenicity assay based on human h1A1v2 cells. h1A1v2 cells are a line of human B-lymphoblastoid cells that have been engineered to express cytochrome P4501A1 (CYP1A1), an enzyme capable of metabolizing promutagenic PAH. Mutagenicity was measured at the thymidine kinase ( tk) locus following a 72-h exposure period. Our results show that nine of the compounds were mutagenic. Benzo[ a]perylene, dibenzo[ a, e]fluoranthene, dibenzo[ a, i]pyrene, and naphtho[2,3- a]pyrene were the most potent mutagens, having minimum mutagenic concentrations (MMC) (i.e., the dose at which the induced response was twice that of the negative controls) in the 1–5 ng/ml range. Benzo[ b]perylene, dibenzo[ a, h]pyrene, dibenzo[ a, f]fluoranthene, and naphtho[2,3- e]pyrene were somewhat less potent mutagens, having MMC in the 10–30 ng/ml range. Dibenzo[ e, l]pyrene, which had an MMC of 280 ng/ml, was the least potent mutagen. Dibenzo[ j, l]fluoranthene and naphtho[1,2- b]fluoranthene were not mutagenic at the doses tested (1–3000 ng/ml). The most mutagenic compounds were also quite toxic. At the highest doses tested, benzo[ a]perylene, dibenzo[ a, e]fluoranthene, dibenzo[ a, i]pyrene, dibenzo[ a, h]pyrene, and dibenzo[ a, f]fluoranthene induced >60% killing, and naphtho[2,3- a]pyrene and naphtho[2,3- e]pyrene induced >50% killing. Benzo[ b]perylene, dibenzo[ e, l]pyrene, dibenzo[ j, l]fluoranthene, and naphtho[1,2- b]fluoranthene induced <50% killing at the highest doses tested. Comparing these results to a previous study in which nine other C 24H 14 PAH were tested for mutagenicity in this same assay, it was found that dibenzo[ a]pyrene isomers were generally more mutagenic than the other groups of C 24H 14 PAH tested. These observations are discussed with emphasis given to identifying C 24H 14 PAH that may be important environmental mutagens.

RESPONSE: Re: Relationship Between p53 Mutations and Inducible Nitric Oxide Synthase Expression in Human Colorectal Cancer.

Inducible Ca-independent nitric oxide synthase (NOS), also referred to as NOS2, which is expressed in a variety of human cancers (1–4), can generate mutagenic concentrations of nitric oxide (NO) in mice (5). NOS2 is the most active isoform among the three known nitric oxide synthases (6), which also include the neuronal (NOS1) and endothelial (NOS3) isoforms. Only NOS2 is capable of producing sustained NO concentrations in the micromolar range (7). We investigated the hypothesis that NO generated by NOS2 is capable of inducing mutations in the p53 (also known as TP53) gene and contributes to human colon carcinogenesis. We analyzed 118 sporadic colon tumors for NOS2 expression and p53 gene mutations. Colon tumors and surrounding normal tissues were collected from the Cooperative Human Tissue Network and the Department of Pathology, University of Baltimore, with the approval of local boards governing research on human subjects, as described previously (3). The expression of NOS2 was increased in various tumors (Fig. 1, A and B) throughout the right, left, and sigmoid colon. Adenomas showed the highest average NOS2 activity. The NOS2 activity declined with advancing tumor stage and was seen at the lowest level in metastatic tumors (Fig. 1, A). NOS2 activity correlated with NOS2 protein expression. Immunohistochemical analysis localized NOS2 protein mainly in tumor-infiltrating mononuclear cells and less frequently in en-

Cancer Risk Estimation of Genotoxic Chemicals Based on Target Dose and a Multiplicative Model

A mechanistic model and associated procedures are proposed for cancer risk assessment of genotoxic chemicals. As previously shown for ionizing radiation, a linear multiplicative model was found to be compatible with published experimental data for ethylene oxide, acrylamide, and butadiene. The validity of this model was anticipated in view of the multiplicative interaction of mutation with inherited and acquired growth‐promoting conditions. Concurrent analysis led to rejection of an additive model (i.e. the model commonly applied for cancer risk assessment). A reanalysis of data for radiogenic cancer in mouse, dog and man shows that the relative risk coefficient is approximately the same (0.4 to 0.5 percent per rad) for tumours induced in the three species.Doses in vivo, defined as the time‐integrated concentrations of ultimate mutagens, expressed in millimol X kg‐1 x h (mMh) are, like radiation doses given in Gy or rad, proportional to frequencies of potentially mutagenic events. The radiation dose equivalents of chemical doses are, calculated by multiplying chemical doses (in mMh) with the relative genotoxic potencies (in rad X mMh‐1) determined in vitro. In this way the relative cancer incidence increments in rats and mice exposed to ethylene oxide were shown to be about 0.4 percent per rad‐equivalent, in agreement with the data for radiogenic cancer.Our analyses suggest that values of the relative risk coefficients for genotoxic chemicals are independent of species and that relative cancer risks determined in animal tests apply also to humans. If reliable animal test data are not available, cancer risks may be estimated by the relative potency. In both cases exposure dose/target dose relationships, the latter via macromolecule adducts, should be determined.

Solid-phase genotoxicity assay for organic compounds in soil

A genotoxicity assay was developed for samples from environments in which toxic organic compounds are largely sorbed. The assay entails measurement of the rate of mutation of a strain of Pseudomonas putida to rifampicin resistance. The ratio of induced to spontaneous mutants was a function of the concentration of a test mutagen in soil. In studies of the utility of the assay in samples amended with 2-aminofluorene as a test mutagen, the ratio of induced to spontaneous mutants declined with time. The decline paralleled the disappearance of extractable 2-aminofluorene from the soil. The ratio of induced to spontaneous mutants also fell in four other soils with dissimilar properties. We suggest that this solid-phase assay is more appropriate for the estimation of genotoxicants sorbed in soil than assays involving extractants or suspensions of soil or sediment samples.

2-Amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) in human hair as biomarker for dietary exposure

Heterocyclic aromatic amines (HAAs), formed during cooking of meat, are multipotent rodent carcinogens and are suspected to cause cancer in humans. In a search for suitable biomarkers for human dietary exposure to HAAs, we have investigated the concentration of a common fried food mutagen, 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), in human hair. Fourteen volunteers participated in the study, each contributing hair from a regular haircut, and completing a questionnaire about consumption of fried/grilled meat and smoking habits. Hair samples were treated with 1 N NaOH at 100 C, and the HAAs extracted under alkaline and acidic conditions, derivatized and analysed by gas chromatography-mass spectrometry. PhIP was found in 12 out of 14 hair samples, in amounts from approx. 50 to 5000 pg g-1 hair, while two samples were below the detection limit (<50 pg g-1 hair). Grey/white hair straws from subjects with a mixture of coloured and grey/white hair had about a 50% reduction in PhIP concentration as compared with the natural hair mixture from the same person. This demonstrates that melanin, responsible for hair colour and spectrophotometrically characterized in the samples, participates in PhIP binding. Thus, when HAA binding components of the hair are taken into account, hair seems like an interesting object of further investigation as a biomarker for human exposure to dietary PhIP.

Cancer risk estimation of genotoxic chemicals based on target dose and a multiplicative model.

A mechanistic model and associated procedures are proposed for cancer risk assessment of genotoxic chemicals. As previously shown for ionizing radiation, a linear multiplicative model was found to be compatible with published experimental data for ethylene oxide, acrylamide, and butadiene. The validity of this model was anticipated in view of the multiplicative interaction of mutation with inherited and acquired growth-promoting conditions. Concurrent analysis led to rejection of an additive model (i.e. the model commonly applied for cancer risk assessment). A reanalysis of data for radiogenic cancer in mouse, dog and man shows that the relative risk coefficient is approximately the same (0.4 to 0.5 percent per rad) for tumours induced in the three species. Doses in vivo, defined as the time-integrated concentrations of ultimate mutagens, expressed in millimol x kg-1 x h (mMh) are, like radiation doses given in Gy or rad, proportional to frequencies of potentially mutagenic events. The radiation dose equivalents of chemical doses are, calculated by multiplying chemical doses (in mMh) with the relative genotoxic potencies (in rad x mMh-1) determined in vitro. In this way the relative cancer incidence increments in rats and mice exposed to ethylene oxide were shown to be about 0.4 percent per rad-equivalent, in agreement with the data for radiogenic cancer. Our analyses suggest that values of the relative risk coefficients for genotoxic chemicals are independent of species and that relative cancer risks determined in animal tests apply also to humans. If reliable animal test data are not available, cancer risks may be estimated by the relative potency. In both cases exposure dose/target dose relationships, the latter via macromolecule adducts, should be determined.

Water treatment practice and the formation of genotoxic chlorohydroxyfuranones

It is generally known that chlorine disinfection of drinking water that is derived from surface water leads to the formation of mutagenic compounds. A very significant portion (in some cases over 60%) of the mutagenicity has been attributed to the presence of various chlorohydroxyfuranones (CHFs). Besides producing mutagenicity in bacterial assays, the CHFs have been reported to alter the genetic properties of animal and human cells. Recently, one of the compounds, namely 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H )-furanone (MX), was shown to be a potent multiorgan carcinogen in rats. These findings have led to concern about the health effects associated with the mutagens in drinking water. This paper is a short review of the work aiming at the identification of hydroxyfuranones and related compounds in disinfected drinking water. In addition, results are presented that show how change in water treatment practice is reflected in the mutagenicity of the drinking water and in the concentration of the main mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX).