Chemical mutagenesis testing in Drosophila. IV. Results of 45 coded compounds tested for the National Toxicology Program

Mutagenicity of the agriculture pesticide chlorothalonil assessed by somatic mutation and recombination test in Drosophila melanogaster

Chlorothalonil (CTL) is a pesticide widely used in Brazil, yet its mutagenic potential is not fully determined. Thus, we assessed the mutagenicity of CTL and its bioactivation metabolites using the somatic mutation and recombination test (SMART) in Drosophila melanogaster, by exposing individuals, with basal and high bioactivation capacities (standard and high bioactivation cross offspring, respectively), from third instar larval to early adult fly stages, to CTL-contaminated substrate (0.25, 1, 10 or 20 μM). This substrate served as food and as physical medium. Increased frequency of large single spots in standard cross flies' wings exposed to 0.25 μM indicates that, if CTL is genotoxic, it may affect Drosophila at early life stages. Since the total spot frequency did not change, CTL cannot be considered mutagenic in SMART. The same long-term exposure design was performed to test whether CTL induces oxidative imbalance in flies with basal (wild-type, WT) or high bioactivation (ORR strain) levels. CTL did not alter reactive oxygen species and antioxidant capacity against peroxyl radicals levels in adult flies. However, lipid peroxidation (LPO) levels were increased in WT male flies exposed to 1 μM CTL. SMART and LPO alterations were observed only in flies with basal bioactivation levels, pointing to direct CTL toxicity to DNA and lipids. Survival, emergence and locomotor behavior were not affected, indicating no bias due to lethality, developmental and behavioral impairment. We suggest that, if related to CTL exposure, DNA and lipid damages may be residual damage of earlier life stages of D. melanogaster.

In vivo effects of 1,4-dioxane on genotoxic parameters and behavioral alterations in Drosophila melanogaster

1,4-Dioxane (DXN) is used as solvent in different consumer products including cosmetics, paints, surfactants, and waxes. In addition, DXN is released as an unwanted contaminating by-product as a result of some reactions including ethoxylation of alcohols, which occurs with in personal care products. Consequently, DXN pollution was detected in drinking water and is considered as an environmental problem. At present, the genotoxicity effects attributed to DXN are controversial. The present study using an in vivo model organism Drosophila melanogaster aimed to determine the toxic/genotoxic, mutagenic/recombinogenic, oxidative damage as evidenced by ROS production, phenotypic alterations as well as behavioral and developmental alterations that are closely related to neuronal functions. Data demonstrated that nontoxic DXN concentration (0.1, 0.25, 0.5, or 1%) induced mutagenic (1%) and recombinogenic (0.1, 0.25, or 0.5%) effects in wing spot test and genotoxicity in hemocytes using comet assay. The nontoxic concentrations of DXN (0.1, 0.25, 0.5, or 1%) significantly increased oxidative stress, climbing behavior, thermal sensivity and abnormal phenotypic alterations. Our findings show that in contrast to in vitro exposure, DXN using an in vivo model Drosophila melanogaster this compound exerts toxic and genotoxic effects. Data suggest that additional studies using other in vivo models are thus warranted.

Toxicology and carcinogenesis studies of di(2-ethylhexyl) phthalate administered in feed to Sprague Dawley (Hsd:Sprague Dawley SD) rats

Di(2-ethylhexyl) phthalate (DEHP) is a member of the phthalate ester chemical class that occurs commonly in the environment and to which humans are widely exposed. Lifetime exposure to DEHP is likely to occur, including during the in utero and early postnatal windows of development. To date, no carcinogenicity assessments of DEHP have used a lifetime exposure paradigm that includes the perinatal period (gestation and lactation). The National Toxicology Program (NTP) tested the hypothesis that exposure during the perinatal period would alter the DEHP carcinogenic response quantitatively (more neoplasms) or qualitatively (different neoplasm types). Two chronic carcinogenicity assessments of DEHP were conducted in which Sprague Dawley (Hsd:Sprague Dawley SD) rats were exposed to dosed feed containing 0, 300, 1,000, 3,000, or 10,000 ppm DEHP for 2 years using different exposure paradigms. In Study 1, groups of 45 F0 time-mated females were provided dosed feed beginning on gestation day (GD) 6 through lactation. On postnatal day (PND) 21, groups of 50 F1 rats per sex continued on the study and were provided dosed feed containing the same DEHP concentration as their respective dam for 2 years. In Study 2, groups of 50 rats per sex, aged 6 to 7 weeks at study start, were provided dosed feed containing DEHP for 2 years. (Abstract Abridged).

Cancer Hazard Identification Integrating Human Variability: The Case of Coumarin

Coumarin is a naturally occurring sweet-smelling benzopyrone that may be extracted from plants or synthesized for commercial uses. Its uses include as a flavoring agent, fragrance enhancer, and odor-masking additive. We reviewed and evaluated the scientific evidence on the carcinogenicity of coumarin, integrating information from carcinogenicity studies in animals with mechanistic and other relevant data, including data from toxicogenomic, genotoxicity, and metabolism studies, and studies of human variability of a key enzyme, CYP2A6. Increases in tumors were observed in multiple studies in rats and mice in multiple tissues. Our functional pathway analysis identified several common cancer-related biological processes/pathways affected by coumarin in rat liver following in vivo exposure and in human primary hepatocytes exposed in vitro. When coumarin 7-hydroxylation by CYP2A6 is compromised, this can lead to a shift in metabolism to the 3,4-epoxidation pathway and increased generation of electrophilic metabolites. Mechanistic data align with 3 key characteristics of carcinogens, namely formation of electrophilic metabolites, genotoxicity, and induction of oxidative stress. Considerations of metabolism, human variability in CYP2A6 activity, and coumarin hepatotoxicity in susceptible individuals provide additional support for carcinogenicity concern. Our analysis illustrates the importance of integrating information on human variability in the cancer hazard identification process.

In vivo genotoxicity of 1,4-dioxane evaluated by liver and bone marrow micronucleus tests and Pig-a assay in rats

1,4-Dioxane, used widely as a solvent in the manufacture of chemicals and as a laboratory reagent, induced liver adenomas and carcinomas in mice and rats, and nasal tumors in rats in several long-term studies. 1,4-Dioxane has been reported to be non-genotoxic in vitro, and there is no clear conclusion concerning its in vivo genotoxicity in rodents. In the present study, we investigated the ability of 1,4-dioxane to induce micronuclei in the liver and bone marrow of rats. For the liver micronucleus test, we performed the juvenile animal method and two methods using partial hepatectomy (PH), dosing before PH or dosing after PH. We also evaluated the in vivo mutagenicity of 1,4-dioxane by Pig-a gene mutation assay using rat peripheral blood. As a result, all methods of liver micronucleus test showed an increase in the frequency of micronucleated hepatocytes by 1,4-dioxane. The dosing before PH, a suitable method for detecting structural chromosome aberration inducers, showed the clearest response for micronucleated hepatocytes induction among the three methods. This finding is consistent with a previous report that 1,4-dioxane induces mainly chromosome breakage in the liver. Negative results were obtained in the bone marrow micronucleus test and Pig-a gene mutation assay in our study. These results suggested that 1,4-dioxane is clastogenic in the liver but not genotoxic in the bone marrow of rats.

Final Report on the Safety Assessment of Glutaral

The dialdehyde Glutaral (also commonly called glutaraldehyde) is used in a wide variety of cosmetics as a preservative. In vitro dermal penetration studies of Glutaral indicate low penetration through animal skin and even less through human skin. The oral LD50 of Glutaral for rats ranged from 66 mg/kg up to 733 mg/kg. A 28-day dermal toxicity study of Glutaral produced skin irritation and slight effects on weight and blood chemistry with concentrations as low as 50 mg/kg/day. Animal skin irritation was dose-dependant, with a no-effect concentration of 1%. Ocular exposure to Glutaral caused severe irritation in rabbits at concentrations 1%, with a no-effect level of 0.1%. Glutaral was not embryotoxic, fetotoxic, or teratogenic at concentrations that did not cause severe maternal toxicity. The no observable adverse effects level for reproduction toxicity was > 1,000 ppm. Bacterial mutagenesis tests produced mixed results, as would be expected for a preservative. In most mammalian system mutagenesis tests, Glutaral was not genotoxic. In a 2-year drinking water study in rats, there was an increase in large granular lymphocytic leukemia (LGLL), but only in females administered 50–1,000 ppm Glutaral. The response was not dose dependent. Clinical studies report some evidence of dermal irritation and sensitization, but no photosensitization. Occupational data and animal studies indicate that inhalation of Glutaral can cause respiratory irritation, in addition to skin effects. Evaluation of the increased incidence of LGLL in the 2-year drinking water study indicated that the incidence was within the historical control levels for this spontaneously occurring neoplasm. These data, however, were not considered sufficient to base a finding of safety of Glutaral in products intended for prolonged use. It was concluded that a 2-year dermal carcinogenicity study following National Toxicology Program (NTP) procedures was needed to complete the safety assessment of Glutaral for use in leave-on products. For rinse-off products, it was concluded that the ocular and dermal irritancy of Glutaral could be substantially avoided if the concentration did not exceed 0.5% and exposure was only brief and discontinuous. Because it can cause respiratory irritation, it was concluded that Glutaral should not be used in aerosolized cosmetic products.

Subchronic hepatotoxicity evaluation of hydrazobenzene in Fischer 344 rats

Male F344 rats were exposed to hydrazobenzene (HZB) by dietary feed at concentrations of 0, 5, 20, 80, 200, or 300 ppm for 5 days, 2 weeks, 4 weeks, or 13 weeks duration. End points evaluated included clinical observations, body weights, liver weights, serum chemistry, blood HZB, gross pathology, and liver histopathology. There were no HZB exposure-related clinical signs of toxicity. During study weeks 8 through 13, body weight means in rats of the 300 ppm group were 6% lower compared to control rat means. Serum alkaline phosphatase concentrations were decreased in rats of the 300 ppm group at all time points. Relative (to body weight) liver weight increases were observed in rats of the 200 and 300 ppm groups following 5 days (300 ppm only), 2 weeks, 4 weeks, and 13 weeks of exposure. Following 13 weeks of exposure, microscopic findings in the liver were observed only in rats of the 200 and 300 ppm groups and consisted of hypertrophy, macrovesiculation, eosinophilic granular cytoplasm, and bile duct duplication. Blood HZB concentrations ranged from 0.002 to 0.006 µg/mL in rats of the 200 or 300 ppm groups. A no observed effect level of 80 ppm (4.80 mg/kg per d) was selected based on the observation of microscopic hepatocyte alterations at ≥200 ppm HZB.

Metabolism, genotoxicity, and carcinogenicity of comfrey

Comfrey has been consumed by humans as a vegetable and a tea and used as an herbal medicine for more than 2000 years. Comfrey, however, produces hepatotoxicity in livestock and humans and carcinogenicity in experimental animals. Comfrey contains as many as 14 pyrrolizidine alkaloids (PA), including 7-acetylintermedine, 7-acetyllycopsamine, echimidine, intermedine, lasiocarpine, lycopsamine, myoscorpine, symlandine, symphytine, and symviridine. The mechanisms underlying comfrey-induced genotoxicity and carcinogenicity are still not fully understood. The available evidence suggests that the active metabolites of PA in comfrey interact with DNA in liver endothelial cells and hepatocytes, resulting in DNA damage, mutation induction, and cancer development. Genotoxicities attributed to comfrey and riddelliine (a representative genotoxic PA and a proven rodent mutagen and carcinogen) are discussed in this review. Both of these compounds induced similar profiles of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts and similar mutation spectra. Further, the two agents share common mechanisms of drug metabolism and carcinogenesis. Overall, comfrey is mutagenic in liver, and PA contained in comfrey appear to be responsible for comfrey-induced toxicity and tumor induction.

Genotoxic Activities of Aniline and its Metabolites and Their Relationship to the Carcinogenicity of Aniline in the Spleen of Rats

Aniline (in the form of its hydrochloride) has been shown to induce a rather rare spectrum of tumors in the spleen of Fischer 344 rats. The dose levels necessary for this carcinogenic activity were in a range where also massive effects on the blood and non-neoplastic splenotoxicity as a consequence of methemoglobinemia were to be observed. This review aimed at clarifying if aniline itself or one of its metabolites has a genotoxic potential which would explain the occurrence of the spleen tumors in rats as a result of a primary genetic activity. The database for aniline and its metabolites is extremely heterogeneous. With validated assays it ranges from a few limited Ames tests (o- and m-hydroxyacetanilide, phenylhydroxylamine, nitrosobenzene) to a broad range of studies covering all genetic endpoints partly with several studies of the same or different test systems (aniline, p-aminophenol, p-hydroxyacetanilide). This makes a direct comparison rather difficult. In addition, a varying number of results with as yet not validated systems are available for aniline and its metabolites. Most results, especially those with validated and well performed/documented studies, did not indicate a potential of aniline to induce gene mutations. In five different mouse lymphoma tests, where colony sizing was performed only in one test, aniline was positive. If this indicates a peculiar feature of a point mutagenic potential or does represent a part of the clastogenic activity for which there is evidence in vitro as well as in vivo remains to be investigated. There is little evidence for a DNA damaging potential of aniline. The clastogenic activity in vivo is confined to dose levels, which are close to lethality essentially due to hematotoxic effects. The quantitatively most important metabolites for experimental animals as well as for humans (p-aminophenol, p-hydroxyacetanilide) seem to have a potential for inducing chromosomal damage in vitro and, at relatively high dose levels, also in vivo. This could be the explanation for the clastogenic effects that have been observed after high doses/concentrations with aniline. They do not induce gene mutations and there is little evidence for a DNA damaging potential. None of these metabolites revealed a splenotoxic potential comparable to that of aniline in studies with repeated or long-term administration to rats. The genotoxicity database on those metabolites with a demonstrated and marked splenotoxic potential, i.e. phenylhydroxylamine, nitrosobenzene, is unfortunately very limited and does not allow to exclude with certainty primary genotoxic events in the development of spleen tumors. But quite a number of considerations by analogy from other investigations support the conclusion that the effects in the spleen do not develop on a primary genotoxic basis. The weight of evidences suggests that the carcinogenic effects in the spleen of rats are the endstage of a chronic high-dose damage of the blood leading to a massive overload of the spleen with iron, which causes chronic oxidative stress. This conclusion, based essentially on pathomorphological observations, and analogy considerations thereof by previous authors, is herewith reconfirmed under consideration of the more recently reported studies on the genotoxicity of aniline and its metabolites, on biochemical measurements indicating oxidative stress, and on the metabolism of aniline. It is concluded that there is no relationship between the damage to the chromosomes at high, toxic doses of aniline and its major metabolites p-aminophenol/p-hydroxyacetanilide and the aniline-induced spleen tumors in the rat.

Framework analysis for the carcinogenic mode of action of nitrobenzene

Nitrobenzene (CASRN: 98-95-3) has been shown to induce cancers in many tissues including kidney, liver, and thyroid, following chronic inhalation in animals. However, with a few exceptions, genotoxicity assays using nitrobenzene have given negative results. Some DNA binding/adduct studies have brought forth questionable results and, considering the available weight of evidence, it does not appear that nitrobenzene causes cancer via a genotoxic mode of action. Nitrobenzene produces a number of free radicals during its reductive metabolism, in the gut as well as at the cellular level, and generates superoxide anion as a by-product during oxidative melabolism. The reactive species generated during nitrobenzene metabolism are considered candidates for carcinogenicity. Furthermore, several lines of evidence suggest that nitrobenzene exerts its carcinogenicity through a non-DNA reactive (epigenetic) fashion, such as a strong temporal relationship between non-, pre-, and neoplastic lesions leading to carcinogenesis. In this report, we first describe the absorption, distribution, metabolism, and excretion of nitrobenzene followed by a summary of the available genotoxicity studies and the only available cancer bioassay. We subsequently refer to the mode of action framework of the U.S. Environmental Protection Agency's 2005 Guidelines for Carcinogen Risk Assessment as a basis for presenting possible modes of action for nitrobenzene-induced cancers of the liver, thyroid, and kidney, as supported by the available experimental data. The rationale(s) regarding human relevance of each mode of action is also presented. Finally, we hypothesize that the carcinogenic mode of action for nitrobenzene is multifactorial in nature and reflective of free radicals, inflammation, and/or altered methylation.

An updated evaluation of the carcinogenic potential of 1,4-dioxane

This paper presents a critical review of the information pertaining to the potential carcinogenicity of 1,4-dioxane. The primary target organs for cancer via the oral route are the liver and the nasal cavity, however, the relevance of nasal cavity tumors to human exposures has been questioned. Liver tumors were accompanied by degenerative changes and appear only to occur at high doses where clearance mechanisms are saturated and liver toxicity is significant. Genetic toxicity data suggests that 1,4-dioxane is a very weak genotoxin. An increase in hepatocyte cell proliferation was reported and 1,4-dioxane was shown to act as a tumor promoter in rat liver and mouse skin carcinogenicity assays. Two reports are available from the literature regarding physiologically based pharmacokinetic (PBPK) modeling approaches to assess the risk of liver cancer for 1,4-dioxane. A comparison of cancer risk estimates from linear and nonlinear models in the presence or absence of PBPK modeling suggests that USEPAs current cancer slope factor significantly overestimates the potential cancer risk from 1,4-dioxane. This critical review of the scientific literature indicates that a formal reevaluation of the carcinogenic potency of 1,4-dioxane is warranted.

Pyrrolizidine Alkaloids—Genotoxicity, Metabolism Enzymes, Metabolic Activation, and Mechanisms

Pyrrolizidine alkaloid-containing plants are widely distributed in the world and are probably the most common poisonous plants affecting livestock, wildlife, and humans. Because of their abundance and potent toxicities, the mechanisms by which pyrrolizidine alkaloids induce genotoxicities, particularly carcinogenicity, were extensively studied for several decades but not exclusively elucidated until recently. To date, the pyrrolizidine alkaloid-induced genotoxicities were revealed to be elicited by the hepatic metabolism of these naturally occurring toxins. In this review, we present updated information on the metabolism, metabolizing enzymes, and the mechanisms by which pyrrolizidine alkaloids exert genotoxicity and tumorigenicity.

The rodent carcinogens 1,4-dioxane and thiourea induce meiotic non-disjunction in Drosophila melanogaster females

The ability of the rodent carcinogens 1,4-dioxane (DX) and thiourea (TU) to induce meiotic non-disjunction (ND) was assessed in 3- and 6-day-old Drosophila melanogaster females. The chemicals were administered orally and three 24 h and one 48 h broods were obtained after mating, to sample oocytes treated in increasingly earlier stages of development. The broods represent mainly mature oocytes (brood I), nearly mature oocytes (brood II), early oocytes (brood III) and very early oocytes (brood IV). The toxicity of DX increased with dose (1% (not toxic), 1.5, 2, 3, 3.5%) as well as a reduction in fecundity which was moderate. Induction of ND in mature oocytes was positive with 2, 3 and 3.5% concentrations and was not related to dose. In immature oocytes it was also positive though already at the lowest concentration tested (1%), suggesting a sensitivity higher than that of mature oocytes. TU at 0.10-10%, did not affect viability, but since fecundity was seriously impaired at high doses, ND was not assessed beyond the 1.5% concentration. TU also induced ND in mature and in immature oocytes; neither a threshold nor a dose effect was detected. The response of mature oocytes was lower than that of immature oocytes. TU induced increases of ND in the earliest cells tested in a more consistent fashion than DX. The data clearly show that both chemicals induced ND in mature oocytes and in the three subsets in which immature oocytes were fractionated. Though toxicity may play a significant unspecific role in the induction of chromosome malsegregation by DX and TU, the induction of ND at low doses, moderately toxic to the oocytes, suggests that the interaction with specific targets contributed to the results obtained.

Genetic toxicology studies with glutaraldehyde

Glutaraldehyde (GA; CAS no. 111-30-8) has a wide spectrum of industrial, scientific and biomedical applications, with a potential for human exposure particularly in its biocidal applications. The likelihood for genotoxic effects was investigated in vitro and in vivo. A Salmonella typhimurium reverse mutation assay showed no evidence for mutagenic activity with strains TA98, TA1535, TA1537 and TA1538, with or without metabolic activation. However, there was a weak mutagenic response (1.9-2.3-fold at the highest non-toxic concentration) with TA100 in the presence of metabolic activation. In a Chinese hamster ovary (CHO) forward gene mutation assay (HGPRT locus) there were no consistent, statistically significant, reproducible or dosage-related increases in the frequency of 6-thioguanine resistant cells. There were no reproducible or dosage-related increases in sister chromatid exchanges in an in vitro test in CHO cells. An in vitro cytogenetics study in CHO cells showed no evidence for an increase in chromosomal aberrations on treatment with GA, either in the presence or absence of metabolic activation. In vivo, a mouse peripheral blood micronucleus test showed no increase in micronucleated polychromatophils at sampling times of 30, 48 and 72 h after acute gavage dosing with GA at 40, 80 and 125 mg kg(-1) (corresponding to 25, 50 and 85% of the LD(50)). The absence of an in vivo clastogenic potential was confirmed by no increase in chromosomal aberrations in a rat bone marrow cytogenetics study with sampling at 12, 24 and 48 h after acute gavage dosing with GA (12.5, 30 or 60 mg kg(-1) with males, and 7.5, 20 or 40 mg kg(-1) with females). Thus, in this series of tests, GA produced genotoxic effects in vitro only in a bacterial reverse mutation assay with no evidence for in vivo genotoxicity.

Toxicological, medical and industrial hygiene aspects of glutaraldehyde with particular reference to its biocidal use in cold sterilization procedures

Aqueous solutions of > or =5% glutaraldehyde (GA) are of moderate acute peroral toxicity and those of < or =2% are of slight toxicity. By single sustained skin contact, aqueous GA solutions of > or =45% are of moderate acute percutaneous toxicity, those of 25% are of slight toxicity and those of </=15% do not present an acute percutaneous hazard. Vapor generated at ambient temperature may cause sensory irritant effects to the eye and respiratory tract, but not acute respiratory tract injury. The 50% decrease in respiratory rate (rd(50)) is 13.86 ppm. A 0.1% solution of GA is not irritating to the eye; the threshold for conjunctival irritation is 0.2% and for corneal injury it is 1.0%. Eye injury is moderate at 2% and severe at > or =5%. Primary skin irritation depends on the duration and contact site, occlusion and solvent. By sustained contact, the threshold for skin irritation is 1%, above which erythema and edema are dose related. With 45% and higher, skin corrosion may occur. There is a low incidence of skin sensitizing reactions, with an eliciting threshold of 0.5% aqueous GA. However, GA is neither phototoxic nor photosensitizing. Subchronic repeated exposure studies by the peroral route show only renal physiological compensatory effects, secondary to reduced water consumption. Repeated skin contact shows only minor skin irritant effects without systemic toxicity. By subchronic vapor exposure, effects are limited to the nasal mucosa at 1.0 ppm, with a no-effect concentration generally at 0.1 ppm. There is no evidence for systemic target organ or tissue toxicity by subchronic repeated exposure by any route. A chronic drinking water study showed an apparent increase, in females only, of large granular cell lymphocytic leukemia but this was not dosage related. This is most likely the result of a modifying effect on the factor(s) responsible for the expression of this commonly occurring rat neoplasm. A chronic (2-year) inhalation toxicity/oncogenicity study showed inflammatory changes in the anterior nasal cavity but no neoplasms or systemic toxicity. In vitro genotoxicity studies--bacterial mutagenicity, forward gene mutation (HGPRT and TK loci), sister chromatid exchange, chromosome aberration, UDS and DNA repair tests--have given variable results, ranging from no effect through to weak positive. In vivo genotoxicity studies--micronucleus, chromosome aberration, dominant lethal and Drosophila tests--generally have shown no activity but one mouse intraperitoneal study showed bone marrow cell chromosome aberrations. Developmental toxicity studies show GA not to be teratogenic, and a two-generation study showed no adverse reproductive effects. Percutaneous pharmacokinetic studies showed low skin penetration, with lowest values measured in vitro in rats and human skin. Overexposure of humans produces typical sensory irritant effects on the eye, skin and respiratory tract. Some reports have described an asthmatic-like reaction by overexposure to GA vapor. In most cases this resembles reactive airways dysfunction syndrome, and the role of immune mechanisms is uncertain. Local mucosal effects may occur if medical instruments or endoscopes are not adequately decontaminated. Protection of individuals from the potential adverse effects of GA exposure requires that there be adequate protection of the skin, eyes and respiratory tract. The airborne concentration of GA vapor should be kept below the recommended safe exposure level (e.g. the threshold limit value) by the use of engineering controls. Those who work with GA should, through a training program, be aware of the properties of GA, its potential adverse effects, how to handle the material safely and how to deal with accidental situations involving GA. If effects develop in exposed workers, the reasons should be determined immediately and corrective methods initiated. (c) 2001 John Wiley & Sons, Ltd.

Effect of trichloroethylene on DNA methylation and expression of early-intermediate protooncogenes in the liver of B6C3F1 mice

Trichloroethylene (TCE) is a multimedia environmental pollution that is carcinogenic in mouse liver. The ability of TCE to modulate DNA methylation and the expression of immediate-early protooncogenes was evaluated. Female B6C3F1 mice were administered 1000 mg/kg TCE by gavage 5 days/week and killed after 5, 12, or 33 days of exposure. Methylation of DNA as 5-methylcytosine was decreased by 5 days of treatment with TCE and remained reduced for 33 days. TCE also decreased the methylation of the promoter regions for the protooncogenes, c-jun and c-myc. The expression of the mRNA for the two protooncogenes was increased between 60 and 120 minutes after administering the last dose of TCE and returned to control level by 24 hours. The expression of the mRNA for c-fos remained undetectable after administering TCE. Hence, TCE decreased the methylation both of total DNA and the promoters for the c-jun and c-myc genes and increased the expression of their mRNA. The decreased methylation and increased expression of the two immediate-early protooncogenes might be associated with TCE-induced increase in cell proliferation and promotion of tumors.

Lack of effect of coumarin on unscheduled DNA synthesis in the in vivo rat hepatocyte DNA repair assay

The ability of coumarin to induce UDS in male Sprague-Dawley CD rat hepatocytes in vivo was assessed using the unscheduled DNA synthesis (UDS) assay. From a preliminary toxicity study the oral maximum tolerated dose (MTD) of coumarin was determined to be 320 mg/kg body weight. For the UDS studies, rats were treated with 0 (corn oil control), 32 (one-tenth the MTD), 107 (one-third the MTD) and 320 (MTD) mg/kg coumarin via oral gavage. Rats were also treated with 20mg/kg body weight dimethylnitrosamine (DMN) or 50mg/kg body weight 2-acetylaminofluorene (2-AAF) as positive controls for the 2-4 hr and 12-16 hr expression of UDS, respectively. Hepatocytes were isolated by liver perfusion either 2-4 hr or 12-16 hr after treatment and cultured in medium containing [methyl-(3)H]thymidine for 4 hr and assessed for UDS by grain counting of autoradiographs. Coumarin treatment at doses of 32-320 mg/kg body weight had no statistically significant or dose-related effect on UDS in rat hepatocytes either 2-4 hr or 12-16 hr after dosing. In contrast, both DMN 2-4 hr after dosing and 2-AAF 12-16 hr after dosing produced significant increases in UDS assessed as the net nuclear grain count. Both genotoxins also increased the percentage of hepatocyte nuclei with greater than 5 net grains. Treatment with coumarin, DMN and 2-AAF had no statistically significant effect on the proportion of rat hepatocytes undergoing replicative DNA synthesis. In summary, this study demonstrates that coumarin does not induce UDS in hepatocytes of male Sprague-Dawley CD rats after oral administration at doses up to the MTD of 320 mg/kg. The responsiveness of the animals used in this study to genotoxic agents was demonstrated by the clear induction of DNA repair after treatment with DMN and 2-AAF.

Coumarin metabolism, toxicity and carcinogenicity: relevance for human risk assessment

The metabolism, toxicity and results of tests for carcinogenicity have been reviewed with respect to the safety for humans of coumarin present in foodstuffs and from fragrance use in cosmetic products. Coumarin is a natural product which exhibits marked species differences in both metabolism and toxicity. The majority of tests for mutagenic and genotoxic potential suggest that coumarin is not a genotoxic agent. The target organs for toxicity and carcinogenicity in the rat and mouse are primarily the liver and lung. Moreover, the dose-response relationships for coumarin-induced toxicity and carcinogenicity are non-linear, with tumour formation only being observed at high doses which are associated with hepatic and pulmonary toxicity. Other species, including the Syrian hamster, are seemingly resistant to coumarin-induced toxicity. There are marked differences in coumarin metabolism between susceptible rodent species and other species including humans. It appears that the 7-hydroxylation pathway of coumarin metabolism, the major pathway in most human subjects but only a minor pathway in the rat and mouse, is a detoxification pathway. In contrast, the major route of coumarin metabolism in the rat and mouse is by a 3,4-epoxidation pathway resulting in the formation of toxic metabolites. The maximum daily human exposure to coumarin from dietary sources for a 60-kg consumer has been estimated to be 0.02 mg/kg/day. From fragrance use in cosmetic products, coumarin exposure has been estimated to be 0.04 mg/kg/day. The total daily human exposure from dietary sources together with fragrance use in cosmetic products is thus 0.06 mg/kg/day. No adverse effects of coumarin have been reported in susceptible species in response to doses which are more than 100 times the maximum human daily intake. The mechanism of coumarin-induced tumour formation in rodents is associated with metabolism-mediated, toxicity and it is concluded that exposure to coumarin from food and/or cosmetic products poses no health risk to humans.

Evaluation of the genotoxicity of aniline.HCl in Drosophila melanogaster

The induction of X-chromosome malsegregation, sex-linked recessive lethals and II-III autosomal translocations by aniline.HCl was investigated in Drosophila melanogaster. Nondisjunction was tested in 2 and 4 d old virgin females fed on aniline.HCl solutions (3, 5, 10 and 15%) using a system where exceptional females (XXY) and only 1/4 of the expected regular progeny are viable. After mating, the females were subcultured daily. Similarly treated 7-day-old wild-type males were used to run classical II-III translocation and recessive lethal tests; for the latter, the solutions were also injected intraabdominally. In all cases, five broods were obtained. A direct correlation was observed between concentration and toxicity. Furthermore, males were more sensitive than females, and the latter's sensitivity was higher at 4-day-old than at 2-day-old. This could be attributed to a decrease with age in the efficiency of a detoxifying mechanism, or to the generation of a toxic metabolite in older flies. Significant increases in nondisjunction were observed with 5, 10 and 15% solutions suggesting the existence of a threshold. No dose effect was detected within the range of the effective concentrations used. The increases were observed in the first subculture (representing mostly stage 14 oocyte, i.e., cells in metaphase I) and in the third subculture, representing cells in which the spindle has not yet formed, thereby pointing to a direct effect of the chemical on the chromosomes and not on the spindle. It is proposed that the second sensitivity peak detected might be the outcome of the transient loss of a protective configuration provided by the karyosome, due to its expansion in stages 9 and 10 of the developing oocytes. No sex-linked lethals or translocations were induced.

1,4-Dioxane is not mutagenic in five in vitro assays and mouse peripheral blood micronucleus assay, but is in mouse liver micronucleus assay

1,4-Dioxane, an animal carcinogen, was not previously genotoxic in in vitro assays. We reevaluated the compound's genotoxic potential in five in vitro genotoxicity tests in the presence and absence of S9 mix using recommended new protocols. We used the bacterial reverse mutation assay with Salmonella TA and E. coli WP2 strains, including the plate and preincubation methods, the CHO chromosomal aberration assay, including examination of polyploid induction and extended sampling time, the CHO sister-chromatid exchange assay with short and long treatment time, the mouse lymphoma tk assay (microtiter method), including longer treatment time (24 hr), and the CHO micronucleus assay with short and long treatment times. The highest concentration we used was five mg/ml or plate. We also evaluated the genotoxic effect of 1,4-dioxane in vivo by conducting peripheral blood and liver micronucleus assays in the same mice after single oral administration of up to 3,000 mg/kg. All in vitro assays and the peripheral blood micronucleus assay were negative. The mouse liver micronucleus assay, on the other hand, was positive, indicating that 1,4-dioxane might be genotoxic. It is also conceivable that the positive result in mouse liver micronucleus assay was due to a nongenotoxic mechanism, i.e., errors in genetic repair following enhancement of hepatocyte proliferation.

Mutation rate: a simple concept has become complex

The factors that cause new mutations or affect the rate at which they occur have important implications for many areas of genetics. But recent work on phenomena such as premeiotic mutations, which yield a cluster of identical new mutants at the some time, led us to realize that researchers are using the term "mutation rate" in different, and sometimes contradictory, ways. One premeiotic genetic change may ultimately yield several new mutant offspring, but should this be considered one new mutation or many? The way the data are handled in analyses can have a significant effect on the results. How, then, does one handle clusters in the estimation of mutation rates? We explore this question and propose that geneticists begin to distinguish clearly between three different phenomena that to this point have been given the same name: the initial prerepair "genetic damage rate," the postrepair "mutational event rate," and the observed "mutation rate" as it is expressed in the proportion of new mutant offspring. We believe that all new mutant offspring should be counted when estimating mutation rate, irrespective of when in the developmental cycle it is believed that the initial mutational event occurred.

Genetic toxicities of human teratogens

Birth defects cause a myriad of societal problems and place tremendous anguish on the affected individual and his or her family. Current estimates categorize about 3% of all newborn infants as having some form of birth defect or congenital anomaly. As more precise means of detecting subtle anomalies become available this estimate, no doubt, will increase. Even though birth defects have been observed in newborns throughout history, our knowledge about the causes and mechanisms through which these defects are manifested is limited. For example, it has been estimated that around 20% of all birth defects are due to gene mutations, 5-10% to chromosomal abnormalities, and another 5-10% to exposure to a known teratogenic agent or maternal factor [D.A. Beckman, R.L. Brent, Mechanisms of teratogenesis. Ann. Rev. Pharmacol. Toxicol. 24 (1984) 483-500; K. Nelson, L.B. Holmes Malformations due to presumed spontaneous mutations in newborn infants, N. Engl. J. Med. 320 (1989) 19-23.]. Together, these percentages account for only 30-40%, leaving the etiology of more than half of all human birth defects unexplained. It has been speculated that environmental factors account for no more than one-tenth of all congenital anomalies [D.A. Beckman, R.L. Brent, Mechanisms of teratogenesis, Ann. Rev. Pharmacol. Toxicol. 24 (1984) 483-500]. Furthermore, since there is no evidence in humans that the exposure of an individual to any mutagen measurably increases the risk of congenital anomalies in his or her offspring' [J.F. Crow, C. Denniston, Mutation in human populations, Adv. Human Genet. 14 (1985) 59-121; J.M. Friedman, J.E. Polifka, Teratogenic Effects of Drugs: A Resource for Clinicians (TERIS). The John Hopkins University Press, Baltimore, 1994], the mutagenic activity of environmental agents and drugs as a factor in teratogenesis has been given very little attention. Epigenetic activity has also been given only limited consideration as a mechanism for teratogenesis. As new molecular methods are developed for assessing processes associated with teratogenesis, especially those with a genetic or an epigenetic basis, additional environmental factors may be identified. These are especially important because they are potentially preventable. This paper examines the relationships between chemicals identified as human teratogens (agents that cause birth defects) and their mutagenic activity as evaluated in one or more of the established short-term bioassays currently used to measure such damage. Those agents lacking mutagenic activity but with published evidence that they may otherwise alter the expressions or regulate interactions of the genetic material, i.e. exhibit epigenetic activity, have likewise been identified. The information used in making these comparisons comes from the published literature as well as from unpublished data of the U.S. National Toxicology Program (NTP).

Oxidative liver DNA damage in rats treated with pesticide mixtures

Oxidative damage was quantified in the liver of rats by measuring the levels of 8-OH-2-deoxyguanosine (8-OH-2DG) relative to 2-deoxyguanosine in DNA after treating rats for 10 days at a total dose of 1 mg/kg/day with a mixture of the 15 pesticides most commonly found in Italian foods (comprised of dithiocarbamate, benomyl, procymidone, methidathion, chlorpyrifos-ethyl, parathion-methyl, chlorpropham, parathion, vinclozolin, chlorfenvinphos, pirimiphos ethyl, thiabendazole, fenarimol, diphenylamine and chlorothalonil). We fractionated this pesticide mixture into subgroups in order to determine which molecules, if any, induced DNA oxidative damage. The administration of diphenylamine (0.09-1.4 mg/kg/day) and chlorothalonil (0.13-1 mg/kg/day) induced a dose-dependent increase in 8-OH-2DG levels in liver DNA. The other 13 pesticides of the mixture on the contrary, did not produce oxidative liver DNA damage. These results indicate that the toxicity of low doses of pesticide mixtures present in food might be further reduced by eliminating diphenylamine and chlorothalonil.

Toxicology of mono-, di-, and triethanolamine

The chemistry, biochemistry, toxicity, and industrial use of monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are reviewed. The dual function groups, amino and hydroxyl, make them useful in cutting fluids and as intermediates in the production of surfactants, soaps, salts, corrosion control inhibitors, and in pharmaceutical and miscellaneous applications. In 1995, the annual U.S. production capacity for ethanolamines was 447,727 metric tons. The principal route of exposure is through skin, with some exposure occurring by inhalation of vapor and aerosols. MEA, DEA, and TEA in water penetrate rat skin at the rate of 2.9 x 10(-3), 4.36 x 10(-3) and 18 x 10(-3) cm/hr, respectively. MEA, DEA, and TEA are water-soluble ammonia derivatives, with pHs of 9-11 in water and pHa values of 9.3, 8.8, and 7.7, respectively. They are irritating to the skin, eyes, and respiratory tract, with MEA being the worst irritant, followed by DEA and TEA. The acute oral LD50s are 2.74 g/kg for MEA, 1.82 g/kg for DEA, and 2.34 g/kg for TEA (of bw), with most deaths occurring within 4 d of administration. MEA is present in nature as a nitrogenous base in phospholipids. These lipids, composed of glycerol, two fatty acid esters, phosphoric acid, and MEA, are the building blocks of biomembranes in animals. MEA is methylated to form choline, another important nitrogenous base in phospholipids and an essential vitamin. The rat dietary choline requirement is 10 mg kg-1 d-1; 30-d oral administration of MEA (160-2670 mg kg-1 d-1) to rats produced "altered" liver and kidney weights in animals ingesting 640 mg kg-1 d-1 or greater. Death occurred at dosages of 1280 mg kg-1 d-1. No treatment-related effects were noted in dogs administered as much as 22 mg kg-1 d-1 for 2 yr. DEA is not metabolized or readily eliminated from the liver or kidneys. At high tissue concentrations, DEA substitutes for MEA in phospholipids and is methylated to form phospholipids composed of N-methyl and N, N-dimethyl DEA. Dietary intake of DEA by rats for 13 wk at levels greater than 90 mg kg-1 d-1 resulted in degenerative changes in renal tubular epithelial cells and fatty degeneration of the liver. Similar effects were noted in drinking water studies. The findings are believed to be due to alterations in the structure and function of biomembranes brought about by the incorporation of DEA and methylated DEA in headgroups. TEA is not metabolized in the liver or incorporated into phospholipids. TEA, however, is readily eliminated in urine. Repeated oral administration to rats (7 d/wk, 24 wk) at dose levels up to and including 1600 mg kg-1 d-1 produced histopathological changes restricted to kidney and liver. Lesions in the liver consisted of cloudy swelling and occasional fatty changes, while cloudy swelling of the convoluted tubules and loop of Henle were observed in kidneys. Chronic administration (2 yr) of TEA in drinking water (0, 1%, or 2% w/v; 525 and 1100 mg kg-1 d-1 in males and 910 and 1970 mg kg-1 d-1 in females) depressed body and kidney weights in F-344 rats. Histopathological findings consisted of an "acceleration of so-called chronic nephropathy" commonly found in the kidneys of aging F-344 rats. In B6C3F1 mice, chronic administration of TEA in drinking water (0, 1%, or 2%) produced no significant change in terminal body weights between treated and control animals or gross pathological changes. TEA was not considered to be carcinogenic. Systemic effects in rats chronically administered TEA dermally (0, 32, 64, or 125 mg kg-1 d-1 in males; 0, 63, 125, or 250 mg kg-1 d-1 in females) 5 d/wk for 2 yr were primarily limited to hyperplasia of renal tubular epithelium and small microscopic adenomas. In a companion mouse dermal study, the most significant change was associated with nonneoplastic changes in livers of male mice consistent with chronic bacterial hepatitis.

Review of the genotoxic properties of chlorpromazine and related phenothiazines

Chlorpromazine and related phenothiazine drugs have been used in human and veterinary medications for more than 40 years, predominantly as psychotropic agents. Genotoxicity reports are in many cases of relatively antiquated test design. Overall there appears to be no genotoxic activity associated with these drugs when tested under standard conditions. Limited evidence for the potential to form mutagenic nitrosation products and some indication for the ability to modulate the genotoxic action of various mutagens have been presented in the literature. UV irradiation of chlorpromazine and other chlorinated derivatives produces reactive free radicals which possess DNA damaging properties. Induction of gene mutation and chromosomal aberrations have been observed in appropriately designed photomutagenesis experiments. Enhancement but also reduction of UV induced skin tumour formation by chlorpromazine have been found. The decisive factor for the discrepant actions has not been recognized. It is clearly advisable to avoid extensive UV exposure during therapy with these drugs.

Mutagenicity of anticancer drugs in mammalian germ cells

The evidence for mammalian germ cell mutagenicity induced by anticancer drugs is summarized. Primary attention is paid to the three major mouse germ cell mutagenicity tests- the dominant lethal, heritable translocation, and morphological specific locus tests- from which most germ cell mutagenicity data historically have been obtained. Of the 21 anticancer drugs reviewed, 16 have been tested in one or more of these three tests; with all 16 tested in the most common germ cell test, the male dominant lethal test, and 9 of the 16 also tested in the female dominant lethal test. The patterns of germ cell stage specificity for most of the anticancer drugs are similar, and generally resemble the patterns seen with other types of chemicals; however, some of the patterns are unique. For example, 2 of the 8 chemicals shown to induce dominant lethal mutations in female oocytes, do not induce dominant lethal mutations in male germ cells (adriamycin and platinol). Ten of the 16 chemicals tested in the dominant lethal test were positive in post-meiotic stages (spermatids through mature sperm), and seven also induced reciprocal translocations and/or specific locus mutations in post-meiotic stages. This propensity to induce mutations in post-meiotic stages has been observed with most mutagens. However, 5 of the anticancer drugs also induced dominant lethal mutations in spermatocytes (meiotic prophase cells) and one of them, 6-mercaptopurine, uniquely induced dominant lethal mutations exclusively in preleptotene spermatocytes. Finally, three of the anticancer drugs (melphalan, mitomycin C, procarbazine) are members of a very select group of chemicals shown to induce specific locus mutations in spermatogonial stem cells of mice. The implications for human risk are discussed.

Hepatocarcinogenic potential of di(2-ethylhexyl)phthalate in rodents and its implications on human risk

The plasticizer di(2-ethylhexyl) phthalate (DEHP), to which humans are extensively exposed, was found to be hepatocarcinogenic in rats and mice. DEHP is potentially set free from objects made of synthetic materials (e.g., those used in medicine). Chronically, the greatest amounts are transferred to persons undergoing hemodialysis (up to 3.1 mg/kg b.w. per day) who would thus be considered the individuals most endangered by tumorigenesis. Although toxicokinetics seem to play a certain unclear role in the course of DEHP-related toxicity, toxicodynamic factors appear more decisive. DEHP is a representative of "peroxisome proliferators" (PP), a distinct group of substances that, in rodents, do not only induce peroxisomes but also specific enzymes in other organelles, organ growth, and DNA synthesis. The cluster of the characteristic effects of PP is generally, although perhaps not quite appropriately summarized as "peroxisome proliferation," and is strongest in the liver. The lowest observed effect level (LOEL) and the no observed effect level (NOEL) of peroxisome proliferation in the rat, as determined by the induction of specific enzymes (peroxisomal beta-oxidation, carnitine-acetyl-transferase, cytochrome P-452), DNA synthesis, and hepatomegaly, may be assumed as 50 and 25 mg/kg b.w. per day, respectively. DEHP and other carcinogenic PP are neither genotoxic nor tumor initiators, but they appear to be tumor promoters, also implicating a threshold level for the carcinogenic effect. Although a causal relationship between a particular effect of peroxisome proliferation and hepatocarcinogenesis is as yet unknown, peroxisome proliferation as a whole phenomenon appears to be associated with the potential of tumor induction, as shown by comparison of the relative strength of individual PP and by comparison of species and organ specificities. Likewise, LOEL and NOEL of rodent carcinogenesis, that is, 300 and 50 to 100 mg/kg b.w. per day, respectively, are above but not too far from the corresponding values for the investigated parameters of peroxisome proliferation. Thus, with respect to dose alone, worst-case exposure in hemodialysis patients is at least 16-fold below the LOEL of any characterized PP-specific effect of DEHP and approximately 100-fold below that of DEHP-related tumorigenesis. Also, primates are less responsive to PP than rats with respect to the investigated biochemical and morphological parameters. If this lower primate responsiveness is extrapolated to estimate carcinogenicity in humans, we might thus arrive at an even larger safety margin than when based on exposure alone. Doses of PP hypolipidemics that had clearly induced several indicators of peroxisome proliferation in rats did not cause any clear-cut enhancements in the peroxisomes of patients, even though most of these hypolipidemics were considerably stronger PP than DEHP. Thus, an actual threat to humans by DEHP seems rather unlikely. Accordingly, hepatocarcinogenesis was neither enhanced in workers exposed to DEHP nor in patients treated with hypolipidemics.

Mechanistically-based human hazard assessment of peroxisome proliferator-induced hepatocarcinogenesis

In this review we have evaluated the relationship between peroxisome proliferation and hepatocarcinogenesis. To do so, we identified all chemicals known to produce peroxisome proliferation and selected those for which there are data (on peroxisome proliferation and hepatocarcinogenesis) which meet certain criteria chosen to facilitate comparison of these phenomena. The summarised data and definition of the methodology used has been collected in appendices. These comparisons enabled us to evaluate the relationship between these phenomena using reliable data. As there is a good correlation between them, we further explored the mechanisms of action that have been proposed (direct genotoxic activity, production of hydrogen peroxide, cell proliferation and receptor activation). The relationship between these events in other species, including humans, was also reviewed and finally an overview of the assessment of human hazard is presented in section IX. Some of the first chemicals which were shown to produce peroxisome proliferation were also hepatocarcinogens whose carcinogenicity could not be readily explained by genotoxic activity. This raised the suggestion that the unusual phenomenon of peroxisome proliferation was intricately linked to the carcinogenic activity of these agents. Three questions have exercised the attention of regulatory, industrial and academic toxicology since then; are chemicals which elicit peroxisome proliferation in the liver actually a coherent class of chemical carcinogens?; does the early biological phenomenon of peroxisome proliferation have real predictive value for and mechanistic association with rodent carcinogenesis?; and what hazard/risk do these agents pose to humans that may be exposed to them? Whether peroxisome proliferators are indeed a discrete class of rodent carcinogens would appear to be the single, most important question. If so, then the assumptions and procedures relevant to human hazard and risk assessment should be applied to the class and should be essentially generic; if not, each chemical should be considered independently. Our critical analysis of the published data for over 70 agents which have been shown to possess intrinsic ability to induce peroxisome proliferation in the livers of rodents has led to the conclusion that there exists a strong correlation between peroxisome proliferation as n early effect in the liver and hepatocarcinogenicity in chronic exposure studies. An almost perfect correlation was observed between the induction of peroxisomes in the rodent liver and the eventual appearance of tumours following chronic exposure The few exceptions to this were largely explainable (section II).(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative mutagenicity of chemicals selected for test in the International Program on Chemical Safety's collaborative study on plant systems for the detection of environmental mutagens

A review has been made for the four compounds (maleic hydrazide, methyl nitrosourea, sodium azide, azidoglycerol) tested in the International Program on Chemical Safety's collaborative study on plant systems. Maleic hydrazide (MH) is a weak cytotoxic/mutagenic chemical in mammalian tissues and is classified as a class 4 chemical. In contrast, with few exceptions such as Arabidopsis, MH is a potent mutagen/clastogen in plant systems. The difference in its response between plant and animal tissue is likely due to differences in the way MH is metabolized. MH appears to be noncarcinogenic and has been given a negative NCI/NTP carcinogen rating. Methyl nitrosourea (MNU) is a toxic, mutagenic, radiomimetic, carcinogenic, and teratogenic chemical. It has been shown to be a mutagen in bacteria, fungi, Drosophila, higher plants, and animal cells both in vitro and in vivo. MNU is a clastogen in both animal and human cell cultures, plant root tips and cell cultures inducing both chromosome and chromatid aberrations as well as sister-chromatid exchanges. Carcinogenicity has been confirmed in numerous studies and involves the nervous system, intestine, kidney, stomach, bladder and uterus, in the rat, mouse, and hamster. MNU produces stage-specific teratogenic effects and also interferes with embryonic development. The experimental evidence that strongly indicates the mutagenic effects of MNU underlines the possible hazard of this compound to human beings. The experimental evidence for the stringent handling of this compound is clear. Sodium azide (NaN3) is cytotoxic in several animal and plant systems and functions by inhibiting protein synthesis and replicative DNA synthesis at low dosages. It is mutagenic in bacteria, higher plants and human cells and has been used as a positive control in some systems. In general, tests for clastogenicity have been negative or weakly positive. No evidence of carcinogenicity has been reported in a 2-year study seeking carcinogenic activity in male and female rats. Its advantages in comparison to other efficient mutagens are claimed to be a high production of gene mutations accompanied by a low frequency of chromosomal rearrangements and safer handling because of its nonclastogenic and noncarcinogenic action on humans. Azidoglycerol (AG) is a very potent mutagen in bacteria, yeast and higher plants including Arabidopsis and Tradescantia; however, it only slightly enhances the frequencies of recessive lethals in Drosophila. AG is at best a weak clastogen and is without effect in inducing chromosomal aberrations and SCEs in human peripheral lymphocytes in vitro. In microbial and plant systems, AG is considerably more potent than sodium azide in the maximal frequencies of mutation induced. In particular, in Saccharomyces cerevisae, AG is 3000-fold more mutagenic than sodium azide. Its carcinogenic and teratogenic properties are unknown.

Chemical mutagenesis testing in Drosophila. IX. Results of 50 coded compounds tested for the National Toxicology Program

Fifty chemicals were tested for mutagenic activity in post-meiotic and meiotic germ cells of male Drosophila melanogaster using the sex-linked recessive lethal (SLRL) assay. As in the previous studies in this series, feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. One gaseous chemical (1,3-butadiene) was tested only by inhalation. Those chemicals that were mutagenic in the sex-linked recessive lethal assay were further tested for the ability to induce reciprocal translocations. Eleven of the 50 chemicals tested were mutagenic in the SLRL assay. These included bis(2-chloroethyl) ether, 1,4-butanediol diglycidyl ether, 1-chloro-2-propanol, dimethyl methylphosphonate, dimethyl morpholinophosphoramidate, dimethyloldihydroxyethylene urea, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isatin-5-sulfonic acid (Na salt), isopropyl glycidyl ether, and urethane. Five of these, including 1,4-butanediol diglycidyl ether, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isopropyl glycidyl ether, and urethane, also induced reciprocal translocations.

Assessing the risk of heritable gene mutation in mammals: drosophila sex-linked recessive lethal test and tests measuring DNA damage and repair in mammalian germ cells

The former U.S. EPA OPPT tiered test scheme for heritable gene mutations included the Drosophila sex-linked recessive lethal (SLRL) test in which positive results triggered the mouse specific locus (MSL) test. However, review of available literature indicated that the evaluation of mutations in the germ cells of this insect is not a good predictor of the risk of heritable gene mutations in mammals. The database contained 29 compounds for which there were conclusive MSL test results in either spermatogonial and/or postspermatogonial cells. Results in the SLRL test were available for 27 of those compounds. Of the 24 SLRL-positive chemicals, only 13 (54%) induced heritable mutations in mice; the three SLRL-negative compounds were nonmutagenic in mouse germ cells. The overall concordance between the two tests was 59%. In contrast, results of unscheduled DNA synthesis (UDS: 18 chemicals) and alkaline elution (AE: 14 chemicals) assays in rodent testicular cells following in vivo exposure correlated well with results in the MSL test (83% and 86%, respectively). MSL test results in spermatogonia and postspermatogonia were also compared separately to the SLRL, UDS, and AE assays. The concordances for the two cell types in the SLRL relative to the MSL test were 36% and 79%, respectively, indicating that the SLRL test is extremely poor in predicting heritable gene mutations in mammalian spermatogonia. Concordances for UDS and AE assays relative to MSL test results in spermatogonia (53% and 54%, respectively) and postspermatogonia (91% and 100%, respectively) were greater. Based on these analyses, the U.S. EPA OPPT has revised its tiered test scheme using assays for interaction with gonadal DNA (e.g., UDS and AE) in place of the SLRL test.

Chemical mutagenesis testing in Drosophila. X. Results of 70 coded chemicals tested for the National Toxicology Program

Seventy chemicals were tested for the ability to induce sex-linked recessive lethal (SLRL) mutations in postmeiotic and meiotic germ cells of male Drosophila melanogaster. As in the previous studies in this series, adult feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. Two chemicals, n-butane and propylene, were gaseous and therefore tested only by inhalation. One chemical (dimethylcarbamoyl chloride) was tested only by injection. Those chemicals that were mutagenic in the SLRL assay were further tested for the ability to induce reciprocal translocations. Sixteen of the 70 chemicals tested were mutagenic in the SLRL assay: 3-chloro-2-methylpropene, 3-(chloromethyl)pyridine HCl, dimethylcarbamoyl chloride, HC blue 1,3-iodo-1,2-propanediol, malaoxon, N,N'-methylene-bis-acrylamide, 4,4'-methylenedianiline 2HCl, ziram, cis-dichlorodiaminoplatinum II, 1,2-dibromoethane, dibromomannitol, 1,2-epoxypropane, glycidol, myleran, and toluene diisocyanate. The last seven also induced reciprocal translocations. A comparison of the results from the SLRL assay with other assays for mutagens and carcinogens suggests that the SLRL assay is highly specific, but poorly sensitive, both for mutagens and potential carcinogens.

A survey of EPA/OPP and open literature data on selected pesticide chemicals tested for mutagenicity. I. Introduction and first ten chemicals

Parties interested in registering a pesticide chemical with the U.S. Environmental Protection Agency's (USEPA's) Office of Pesticide Programs (OPP) must submit toxicity information to support the registration. Mutagenicity data are a part of the required information that must be submitted. This information is available to the public via Freedom of Information requests to the OPP. However, it is felt that this information would be more effectively and widely disseminated if presented in a published medium. Beginning with this publication, sets of mutagenicity data on pesticide chemicals will be periodically published in the Genetic Activity Profile (GAP) format. In addition, mutagenicity data extracted from the currently available open literature is also presented to provide a more complete database and to allow comparisons between the OPP-submitted data and other publicly available information.

The genetic toxicology of putative nongenotoxic carcinogens

This report examines a group of putative nongenotoxic carcinogens that have been cited in the published literature. Using short-term test data from the U.S. Environmental Protection Agency/International Agency for Research on Cancer genetic activity profile (EPA/IARC GAP) database we have classified these agents on the basis of their mutagenicity emphasizing three genetic endpoints: gene mutation, chromosomal aberration and aneuploidy. On the basis of results of short-term tests for these effects, we have defined criteria for evidence of mutagenicity (and nonmutagenicity) and have applied these criteria in classifying the group of putative nongenotoxic carcinogens. The results from this evaluation based on the EPA/IARC GAP database are presented along with a summary of the short-term test data for each chemical and the relevant carcinogenicity results from the NTP, Gene-Tox and IARC databases. The data clearly demonstrate that many of the putative nongenotoxic carcinogens that have been adequately tested in short-term bioassays induce gene or chromosomal mutations or aneuploidy.

The genotoxicity of the anti-cancer drug mitoxantrone in somatic and germ cells of Drosophila melanogaster

The novel antineoplastic drug mitoxantrone was studied for its genotoxic effects in Drosophila melanogaster. In male germ cells, the clinical preparation Novantrone, the dihydrochloride salt of mitoxantrone, did not induce sex-linked recessive lethal mutations in feeding and injection experiments with adult flies, although statistically the results were inconclusive rather than truly negative. However, the free base mitoxantrone was weakly, but significantly genotoxic in this test (0.14% lethals/mM exposure concentration); this is most probably the result of prolonged exposure. On the other hand, both forms of mitoxantrone assayed were clearly genotoxic in the somatic mutation and recombination test of the wing. This test assays the cells of the proliferating imaginal wing discs of larvae. Depending on the feeding method used, the overall clone induction frequency was in the range of about 2-6 x 10(-5) per cell and cell generation and per mM exposure dose. Correction of these frequencies according to mean clone size led to slightly higher estimates (by about 5-25% higher). Although the majority of the clone induction events are due to mitotic recombination, a significant proportion can be attributed to mutational events (gene and chromosome mutations). The genotoxicity of mitoxantrone seems to depend mainly on impaired DNA synthesis in cycling cells owing to the compound's ability to inhibit topoisomerase II by intercalation into DNA.

A critical review of the toxicology of glutaraldehyde

Glutaraldehyde, a low molecular weight aldehyde, has been investigated for toxicity in humans and animals. Examination of this dialdehyde was indicated from previous studies with other aldehydes in which carcinogenicity of formaldehyde and toxicity of acetaldehyde and malonaldehyde have been disclosed. Information gaps concerning the actions of glutaraldehyde have been identified in this review and recommendations are suggested for additional short- and long-term studies. In particular, information regarding irritation of the respiratory tract, potential neurotoxicity, and developmental effects would assist in a complete hazard evaluation of glutaraldehyde. Further study related to disposition, metabolism, and reactions of glutaraldehyde may elucidate the mechanism of action.

The genetic toxicology of acridines

Acridine and its derivatives are planar polycyclic aromatic molecules which bind tightly but reversibly to DNA by intercalation, but do not usually covalently interact with it. Acridines have a broad spectrum of biological activities, and a number of derivatives are widely used as antibacterial, antiprotozoal and anticancer drugs. Simple acridines show activity as frameshift mutagens, especially in bacteriophage and bacterial assays, by virtue of their intercalative DNA-binding ability. Acridines bearing additional fused aromatic rings (benzacridines) show little activity as frameshift mutagens, but interact covalently with DNA following metabolic activation (forming predominantly base-pair substitution mutations). Compounds where the acridine acts as a carrier to target alkylating agents to DNA (e.g. the ICR compounds) cause predominantly frameshift as well as base-pair substitution mutations in both bacterial and mammalian cells. Nitroacridines may act as simple acridines or (following nitro group reduction) as alkylating agents, depending upon the position of the nitro group. Acridine-based topoisomerase II inhibitors, although frameshift mutagens in bacteria and bacteriophage systems, are primarily chromosomal mutagens in mammalian cells. These mutagenic activities are important, since the compounds have considerable potential as clinical antitumour drugs. Although evidence suggests that simple acridines are not animal or human carcinogens, a number of the derived compounds are highly active in this capacity.

The non-genotoxicity to rodents of the potent rodent bladder carcinogens o-anisidine and p-cresidine

The two potent rodent bladder carcinogens o-anisidine and p-cresidine, and the structurally related non-carcinogen 2,4-dimethoxyaniline, have been extensively evaluated for genotoxicity to rodents and found to be inactive. Most data were generated on o-anisidine, an agent that is also only marginally genotoxic in vitro. The two carcinogens induced methaemoglobinaemia in rodents indicating that the chemicals are absorbed and metabolically oxidized. Despite their total lack of genotoxicity in vivo, the two carcinogens have the hall-marks of being genotoxic carcinogens given that most test animals of both sexes of B6C3F1 mice and F344 rats are reported to have succumbed rapidly to malignant bladder cancer. No reasons for this dramatic conflict of test data are so far apparent. The experiments described involve, in one or other combination, 2 strains of mice (including B6C3F1) and 4 strains of rat (including F344), the use of oral and i.p. routes of exposure and observations made after 1, 3 or 6 doses of test chemical. 6 tissues (including the rat bladder) were assayed using 3 genetic endpoints (unscheduled DNA synthesis, DNA single-strand breaks and micronuclei induction). Aroclor-induced rats were employed in one set of experiments with o-anisidine. In the case of one set of mouse bone-marrow micronucleus experiments the same batch of the 3 chemicals as used in the cancer bioassays, and the same strain of mouse, were used. Possible further experiments and the implications of these findings are discussed.

Inhalation exposure in Drosophila mutagenesis assays: experiments with aliphatic halogenated hydrocarbons, with emphasis on the genetic activity profile of 1,2-dichloroethane

A series of mutation experiments was carried out with Drosophila melanogaster using inhalation exposure. 1,2-Dichloroethane (DCE) and 1,2-dibromoethane (DBE) were active in the sex-linked recessive lethal assay (SLRLT), whereas dichloromethane, dibromomethane, 1,2-dichloropropane and 1,3-dichloropropane were not. Compared to DBE, DCE is a less potent mutagen in the SLRL system. For both compounds, there is no evidence of a clear-cut dose-rate effect. DCE and dichloromethane were also investigated in the somatic mutation and recombination test (SMART), with results similar to those from the SLRLT. For DCE the genetic activity profile was further analyzed by carrying out a sex-chromosome loss assay and a complementation analysis of a series of induced recessive lethal mutations. A review of the use of inhalation in mutagenicity assays with Drosophila shows that this route of exposure is an effective one. Especially with chronic exposure times, rather low exposure concentrations can be detected. With compounds of intermediate volatility inhalation is not superior to other modes of administration; nor is it likely to be sensitive enough for in situ monitoring.

Is 1,4-dioxane a genotoxic carcinogen?

Female Sprague-Dawley rats were given 0, 168, 840, 2550 or 4200 mg/kg of 1,4-dioxane 21 and 4 h before sacrifice. Hepatic DNA damage (by the alkaline elution technique), ornithine decarboxylase activity (ODC), reduced glutathione content, cytochrome P-450 content and serum alanine aminotransferase activity (ALT) were determined. Treatment with 1,4-dioxane increased hepatic DNA damage and cytochrome P-450 content at doses of 2550 and 4200 mg/kg. Large increases in the activity of hepatic ODC were observed at 840, 2550 and 4200 mg/kg of 1,4-dioxane. Thus the data suggest that 1,4-dioxane is a weak genotoxic carcinogen in addition to being a strong promoter of carcinogenesis (a non-genotoxic carcinogen).

Cancer risk assessment for dioxane based upon a physiologically-based pharmacokinetic approach

A cancer bioassay conducted in 1974 (Kociba et al.) indicated that rats given drinking water containing dioxane at a dose of 1184 mg.kg-1.d-1 produced an increased incidence of liver tumors. Applying the linearized multistage extrapolation model to these data, the administered dose estimated to present a human cancer risk of 1 in 100,000 (10(-5)) was 0.01 mg.kg-1.d-1. As in customary regulatory policy, this estimate assumed that humans were about 5.5 times more sensitive than rats on a mg/kg basis. However, this approach did not consider that the metabolism of dioxane is saturable at high doses. Based on experience with similar chemicals, it is known that the conventional risk extrapolation method may overestimate the most likely human cancer risk. In order to determine more accurately the likely human response following lifetime exposure to dioxane, a physiologically-based pharmacokinetic (PB-PK) model was developed. The objective of this study was to establish a quantitative relationship between the administered dose of dioxane and the internal dose delivered to the target organ. Using this PB-PK model, and assuming that the best dose surrogate for estimating the liver tumor response was the time-weighted average lifetime liver dioxane concentration, the cancer risk for humans exposed to low doses of dioxane was estimated. The dose surrogate in humans most likely to be associated with a tumorigenic response of 1 in 100,000 is 280 mumol/l, equivalent to an administered dose of about 59 mg.kg-1.d-1. The 95% lower confidence limit on the dose surrogate at the same response level is 1.28 mumol/l, equivalent to an administered dose of 0.8 mg.kg-1.d-1. This PB-PK analysis indicated that conventional approaches based on the administered doses in the rodent bioassay, if uncorrected for metabolic and physiological differences between rats and humans, will overestimate the human cancer risk of dioxane by as much as 80-fold.