Oxidative mutagens specific for A-T base pairs induce forward mutations to L-arabinose resistance in Salmonella typhimurium

Safety Assessment of Hydrogen Peroxide as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of Hydrogen Peroxide for use in cosmetics. This ingredient is reported to function in cosmetics as an antimicrobial agent, cosmetic biocide, oral health care agent, and oxidizing agent. The Panel reviewed the data relevant to the safety of this ingredient and concluded that Hydrogen Peroxide is safe in cosmetics in the present practices of use and concentration described in this safety assessment.

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.

Subacute oral and dermal toxicity of tert-butyl hydroperoxide in Fischer F344/N rats and B6C3F1 mice

Tert-butyl hydroperoxide (TBHP) is a catalyst frequently used in oxidation and sulfonation reactions in the plastics industry. Since the toxicological evaluation of TBHP remains unknown, the National Toxicology Program (NTP) designed studies to characterize and compare TBHP toxicity by the dermal and oral (gavage) routes in male and female Fischer 344 rats and B6C3F1 mice in 14-day exposures. Rats and mice were administered TBHP at 22, 44, 88, 176 or 352 mg/kg in 0.5% aqueous methylcellulose for the gavage studies. In the dermal studies, mice were administered the same doses as above, while rats were administered four doses (22, 44, 88, 176 mg/kg) in 50% aqueous acetone. Results from the gavage studies revealed treatment-related decreases in survival in male rats and body weights in both male and female rats in the 352 mg/kg group. Clinical signs included post-treatment lethargy, thinness, abnormal breathing, ruffled fur, and/or ataxia which occurred sporadically. The male mice showed a statistically significant decrease in body weight in the 44, 88, 176, and 352 mg/kg groups. The major target organs of toxicity were the forestomach in male and female rats and mice, and the esophagus in male and female rats and in male mice. In addition, there was an increase in the absolute and relative liver weight in female mice with hepatocellular hypertrophy in the top-dose group only. Results from spin trapping experiments revealed the presence of electron paramagnetic resonance signals from radical adducts in the blood and organic extracts of the liver and kidneys of rats treated by gavage with 176 mg/kg TBHP, suggesting the involvement of free- radical generation. The no observed adverse effect level (NOAEL) was considered to be 22 mg/kg in rats and male mice, and 44 mg/kg in female mice. In the dermal studies, there was no effect on survival, body weight, or organ weights in either rats or mice. TBHP administration at the site of application resulted in dermal irritation, hyperkeratosis, hyperplasia, and/or inflammation of the epidermis and inflammation of the dermis at 176 mg/kg and above in male and female rats. Dermal irritation at the site of application was noted in all the mice exposed to 352 mg/kg TBHP. Histopathological lesions in the epidermis and dermis were seen in the 88-352 mg/kg males and in the 176-352 mg/kg females. The NOAEL was found to be 88 mg/kg for male rats and female mice, and 44 mg/kg for female rats and male mice. In conclusion, these studies demonstrate that TBHP is metabolized to free radicals and is a contact irritant affecting skin by the dermal route of exposure, and forestomach and esophagus by oral administration. There was no evidence of systemic absorption by the dermal route of exposure based on lack of pathological findings (Supported by National Institute of Environmental Health Sciences Contract No. N01-ES-65406).

Is there life after Buckley's Formocresol? Part I -- a narrative review of alternative interventions and materials

OBJECTIVES

(1) To present a narrative review of the currently available alternative interventions and materials to formocresol pulpotomy for the management of extensive caries in the primary molar, and (2) to produce a clinical protocol for pulp therapy techniques in the extensively carious primary molar.

INTRODUCTION

The International Agency for Research on Cancer has recently classified formaldehyde as carcinogenic to human beings. Since Buckley's Formocresol contains 19% formaldehyde in its full strength and, therefore, 1% in a 20% dilution, a safer alternative should be identified.

METHODS

A narrative review of the published literature for primary molar pulp therapy techniques was undertaken following an extensive and appropriate literature search. A specialist group of paediatric dentists was formed to arrive at a consensus and establish an evidence-based protocol for the management of extensively carious primary molar teeth. Part I of this paper explores the currently available alternative interventions and materials to formocresol in the form of a narrative review. The second part of the paper will present the formation of a specialist group to arrive at a consensus and establish an evidence-based protocol for the management of the extensively carious primary molar.

CONCLUSIONS

After consideration of a review of extensively searched literature, a protocol and key points document have been developed to assist clinicians in their treatment planning. Further long-term studies with the highest level of evidence (i.e. randomized controlled trials) are required to enable us to identify acceptable alternatives which can replace formocresol.

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.

Heterologous expression of xenobiotic mammalian-metabolizing enzymes in mutagenicity tester bacteria: an update and practical considerations

There is an increasing need for metabolic competent cell systems for the mechanistic studies of biotransformation of xenobiotics in toxicology in general and in genotoxicology in particular. These cell systems combine the heterologous expression of a particular mammalian biotransformation enzyme with a specific target/ end point by which a functional analysis of the expressed gene product in the (geno)toxicity of chemicals can be performed. cDNAs of an increasing number of mammalian biotransformation enzymes is being cloned. The construction of specific expression vectors permits their heterologous expression in laboratory bacteria, such as Escherichia coli strains. This development does not only allow biochemical and enzymatic studies of (pure) enzyme preparations but also facilitates the engineering of metabolically competent mutagenicity tester bacteria, thereby providing new tools for genotoxicity testing and for studying of the roles of biotransformation in chemical carcinogenesis. In this review, we describe an update as well as an evaluation of enzymes expressed in mutagenicity tester bacteria. Four types of biotransformation enzymes are now expressed in these bacteria, namely, GSTs, CYPs, NATs, and STs. The expression of these enzymes in the tester bacteria and their subsequent application in mutagenicity assays demonstrates that heterologous expression in this type of bacteria has a number implications for the functionality of the biotransformation enzymes as well as for the functioning of the tester bacteria in mutagenicity detection. We also describe here a number of practical considerations in this regard.

The selection-induced His+ reversion in Salmonella typhimurium

It was previously shown that spontaneous reversion to His+ of the allele hisG46 Salmonella typhimurium occurs under the influence of histidine starvation. No pre-existing His+ revertants arisen in rich medium were observed. We have now shown that the pre-existing His+ revertants are seen under increased cell concentration (10(10) cells/ml). At the same time, it was established that the selection-induced His+ reversion events of hisG46 begin to occur after 2-3 h of incubation on histidine starvation plates, and this process continues for about 4 days. In parallel, considerable DNA synthesis was observed for the initial hours of starvation. Chloramphenicol and novobiocin inhibited this DNA synthesis, whereas the addition of trace of histidine as well as novobiocin produced the delay of adaptive His+ reversion. It was found that adaptive reversion of hisG46 is recA-independent, although it requires some activity of RecA on the mucAB genetic background. Based on these data, we suggest that the cause of adaptive His+ reversion is the DNA replication operating under histidine starvation. Using a number of mutation models, we showed that histidine starvation did not increase the general mutation rate. It was also demonstrated that intragenic revertants and extragenic ochre suppressors of the allele hisG428 arise under the influence of histidine deprivation.

Mutagenic activity of various dentine bonding agents

The potential mutagenicity of bonding agents of the new generation was characterised by employing an in vitro gene mutation assay. Eight different components of three dentine bonding systems (Scotchbond Multi Purpose, Prisma Universal Bond 3 and C&B Metabond) were tested in the Ames test using four different Salmonella strains (TA97a, TA98, TA100 and TA102). The materials were eluted in dimethyl sulphoxide and physiological saline; aliquots of the serially diluted eluates were then used in the standard plate incorporation assay. No mutagenic effects were found with Scotchbond Multi Purpose primer and adhesive, Prisma Universal Bond 3 primer, and C&B Metabond base, powder and activator. However, the glutaraldehyde-containing Prisma Universal Bond 3 adhesive elicited a strong mutagenic effect in S. typhimurium strain TA102. Mutation rates caused by dimethyl sulphoxide eluates as well as physiological saline eluates were about five times higher than solvent control values. A mutagenic effect was also observed with C&B Metabond catalyst, especially in strain TA97a when the material was eluted in physiological saline. Both mutagenic responses were not influenced by a metabolically active microsomal fraction from rat liver. We consider the results observed in the Ames test as a first indication of possible mutagenic activity in higher organisms. Therefore, the materials are currently under further investigation using a quantitative in vitro mammalian cell mutation assay.

Biological effects of oxysterols: current status

A review of relevant literature on biological activities of oxysterols (OS) and cholesterol is presented. The data clearly demonstrate manifold biological activities, often detrimental, for OS compared with little or no such activity of a deleterious nature for cholesterol itself. Cholesterol is perhaps the single most important compound in animal tissue and, as such, it is difficult to imagine it as a toxin or hazard. In contrast, OS exhibit cytotoxicity to a wide variety of cells leading to angiotoxic and atherogenic effects; alter vascular permeability to albumin; alter prostaglandin synthesis and stimulate platelet aggregation, an important process facilitating atherosclerosis and thrombosis; alter the functionality of low density lipoprotein (LDL) receptors, possibly stimulating hypercholesterolaemia; modify cholesteryl ester accumulation in various cells, inducing foam cell formation; and enrich the LDL particle in cholesteryl esters, possibly increasing its atherogenicity. Furthermore, OS are mutagenic and carcinogenic, although some have been studied as antitumour agents based on their cytotoxic properties. Moreover, numerous studies have implicated OS in membrane and enzyme alterations that are interrelated with many of the foregoing effects. The authors find that OS deserve much more attention than cholesterol itself in terms of research activity but that unfortunately the reverse is true with regard to funding.

SOS chromotest results in a broader context: empirical relationships between genotoxic potency, mutagenic potency, and carcinogenic potency

Environmental monitoring requires that large numbers of samples be processed in a relatively short period of time. While microbioassays facilitate rapid testing, the results are often difficult to interpret in the broader context of human or animal health. Determining the consequences of exposure to genotoxic substances will ultimately require in situ monitoring of exposed organisms. However, it is immediately possible to construct a broad empirical framework within which available microbioassay results can be interpreted. To do this for SOS Chromotest results, we investigated the empirical relationships between SOS genotoxic potency and mutagenic potency (as measured with the Salmonella/microsome assay), as well as between genotoxic potency and carcinogenic potency (as measured using standard, chronic animal bioassays). Strong relationships were identified between; 1) genotoxic potency and mutagenic potency for 268 direct-acting substances (r2=0.76) and 2) genotoxic potency and mutagenic potency for 126 S9-activated substances (r2=0.65). Ordinary least squares regression analyses of the SOS genotoxicity-Salmonella mutagenicity relationship revealed a significant effect of SOS genotoxicity as well as differences in mutagenic potency that can be attributed to the Salmonella strain used to measure mutagenic potency. Analyses of S9-activated substances revealed a significant interaction between the SOS genotoxic potency (SOSIP) effect and the Salmonella strain effect. Two regression models relating SOS genotoxicity and Salmonella mutagenicity were used to predict the mutagenic potency of several industrial effluent extracts previously analyzed for SOS genotoxicity by White et al. [(1996): Environ Mol Mutagen 27:116-139]. Predictions are consistent with published mutagenic potency values for similar industrial waste materials. A consistent relationship was also identified between genotoxic potency and carcinogenic potency for 51 substances. Linear regression analyses revealed an effect of SOS genotoxic potency as well as differences in carcinogenic potency that may be attributable to experimental animal and route of exposure. The correlation between genotoxicity and carcinogenicity was fairly weak (maximum r value = 0.51). Previous studies revealed similar strength of association between Ames mutagenicity and carcinogenicity. Predicted carcinogenic potencies of previously examined genotoxic, industrial effluent extracts are generally low compared to the pure substances included in the data set.

Mutagenicity of dentin bonding agents

Aside from the considerable number of reports on the physical and chemical properties of dental bonding agents, information concerning their biologic effects is sparse. Three dentin bonding agents (Prisma Universal Bond, Pertac Universal Bond, and Syntac) and the ingredients methylmethacrylate, 2-hydroxyethyl-methacrylate, and glutaraldehyde were investigated in the Salmonella typhimurium mutagenicity test system using five different bacterial strains (TA97a, TA98, TA100, TA102, and TA104). The materials as well as the ingredients were eluted in both dimethyl sulfoxide and physiologic saline, and serially diluted eluates were used in the plate incorporation test. Pertac Universal Bond and Prisma Universal Bond did not elicit any mutagenic effects in any of the bacterial strains. In contrast, Syntac adhesive showed clear mutagenicity in S. typhimurium strain TA102. Dimethyl sulfoxide eluates, as well as physiologic saline eluates of the Syntac bonding agent, caused numbers of revertants that were about 6 times higher than control values. Reversion rates with other strains were moderately enhanced. Glutaraldehyde, an ingredient of Syntac adhesives, caused mutagenicity in a manner similar to Syntac adhesive eluates. Neither 2-hydroxyethyl-methacrylate nor methylmethacrylate monomer was found to be mutagenic over a broad concentration range.

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 involvement of reactive oxygen species in the direct-acting mutagenicity of wine

The Ara forward mutagenicity assay with Salmonella typhimurium detected wine as a strong mutagen in the absence of mammalian microsomal activation and/or glycosidase activities, in agreement with previous findings. The standard amount (50 microliters) of S9 fraction in the preincubation mutagenesis test abolished most of the mutagenic activity of red wine in the Ara assay. The S9 fraction exerted the same inactivating capacity on hydrogen peroxide and coffee, a complex mixture generating H2O2. Catalase was identified as the putative S9 component responsible for its inactivating capacity. This specific scavenger for H2O2 abolished around 90% of the mutagenicity of red wine. The suppressing effect of catalase was much less noticeable in white and rose wines. Phenolics are proposed to be responsible for the direct-acting mutagenicity of wine through an auto-oxidative process leading to the production of H2O2.

Characteristics of mutagenesis by glyoxal in Salmonella typhimurium: contribution of singlet oxygen

The characteristics of mutagenesis by glyoxal in Salmonella tester strains TA100 and TA104, and particularly a possible role of active oxygen species, were investigated. Glyoxal was converted into a non-mutagenic chemical with glutathione (GSH) by glyoxalase I, and the mutagenic activity was enhanced by the depletion of intracellular GSH. Glyoxal caused the reduction of nitro blue tetrazolium, which was suppressed by the addition of 2,5-diphenylfuran, superoxide dismutase (SOD) and catalase (CAT), scavengers of singlet oxygen (1O2), superoxide radical (O2-) and hydrogen peroxide (H2O2), respectively. However, only the 1O2 scavenger almost completely suppressed the mutagenic activity of glyoxal. Mutagenicity assays using strains pretreated with N,N-diethyldithiocarbamate of a SOD inhibitor and strains with low levels of SOD and CAT indicated that the mutagenesis by glyoxal was independent of intracellular levels of SOD and CAT, though glyoxal itself repressed them. Therefore, all the results suggest that 1O2 formed from glyoxal is related to its mutagenesis, but that neither O2- nor H2O2 is intracellularly predominantly related to it. The action of glyoxal against SOD and CAT, and the formation of glyoxal adducts with amino acids as their components are also discussed.

'Rec-lac test' for detecting SOS-inducing activity of environmental genotoxic substance

beta-Galactosidase activities (beta-GA) of E. coli strains carrying the fusion gene of recA and lacZ, GE94 and its DNA repair-deficient derivatives such as KY946[uvrA], KY945[recA] and KY943[lexA] treated with UV, 4NQO, MNNG and MMC were examined. The beta-GA, reflecting the SOS-inducing activity, of GE94 and KY946 treated with these compounds increased significantly with a clear dose-response relationship, and reached a maximum level within 60 min, while no response was seen in KY945 and KY943. Using KY946 and KY945 as a positive and a negative indicator, respectively, the SOS-inducing activity of oxidative mutagens, i.e., hydrogen peroxide (H2O2), formaldehyde, tert-butyl hydroperoxide, cumene hydroperoxide and streptonigrin, was investigated. Clear dose-dependent increases in beta-GA were observed in KY946 treated with all oxidative mutagens tested, but not in KY945. Significant increases in beta-GA were observed with a lower concentration of H2O2 and a shorter incubation time of 4NQO in this assay than in the umu-test. The assay, called 'Rec-lac test' by us, may be useful to detect environmental genotoxic substances.

Evaluation of mutagenicity of restorative dental materials using the Ames Salmonella/microsome test

Compounds of five commercially available dental material kits were examined for mutagenic potential by use of the Ames Salmonella/microsome test. Dimethyl sulfoxide (DMSO) was used as the solvent for all materials, except MONO-LOK2 Primer and Right-On Activator, which were dissolved in 95% ethanol. The Tenure, Fuji, and Gluma materials were initially screened at 2 mg (solids) or 2 microL (liquids) per plate, without S9 (Aroclor 1254-induced rat liver microsomes), and dose-response studies were conducted for those materials showing potential mutagenicity. The components of three dental kits, MONO-LOK2, Right-On, and Gluma, were further examined, both with and without S9 activation, at doses of 0.2, 4, 20, 100, 500, and 2500 micrograms (nL for liquid components) per plate. The data showed no mutagenic potential for the components of Fuji Glass Ionomer (Type III), Tenure Dentin Bonding System, and MONO-LOK2 kits, or Right-On Paste. However, Gluma 3, a component of the Gluma/Lumifor Bonding System, exhibited mutagenic activity in a dose-response manner. The mutagenicity of Gluma 3 was demonstrated in repeated experiments. Gluma 4 and the resin of the Gluma dental kit, as well as Right-On Activator, caused a slight increase in the number of revertants, and judgment regarding their mutagenicity could not be made conclusively. The results of this study indicate that some commercial dental materials may not have been adequately tested for mutagenicity, and that a reliable test program for evaluation of mutagenicity of dental materials is needed so that their safe use in dental practice can be ensured.

Influence of S9 mix on the expression of mutants in the L-arabinose resistance test of Salmonella typhimurium

S9 mix produces an effect similar to that of D-glucose in the L-arabinose resistance test of Salmonella typhimurium, releasing the growth inhibition exerted by L-arabinose. Two elements are responsible for this effect: the glucose-6-phosphate present in the cofactors of the S9 mix and the S9 fraction itself. UV light was used as a mutagen to compare the efficiency of S9 mix and D-glucose in allowing phenotypic expression of mutants in selective plates with L-arabinose; 0.5 ml of S9 mix per plate showed and efficacy similar to that of 0.5 mg of D-glucose per plate. To verify that the S9 mix is equivalent to D-glucose traces in selective plates with respect to the number of induced mutants in compounds requiring metabolic activation, we utilized 2 direct-acting nitrofurans. Our conclusion is that activation of agents could be erroneously attributed to the S9 mix, when plates with 0.5 mg of D-glucose are compared to plates with 0.5 ml of S9 mix plus 0.5 mg of D-glucose. Our results suggest that D-glucose traces be omitted in experiments requiring the presence of the S9 mixture.

Genotoxicity of chromium compounds. A review

This article reviews approximately 700 results reported in the literature with 32 chromium compounds assayed in 130 short-term tests, using different targets and/or genetic end-points. The large majority of the results obtained with Cr(VI) compounds were positive, as a function of Cr(VI) solubility and bioavailability to target cells. On the other hand, Cr(III) compounds, although even more reactive than Cr(VI) with purified nucleic acids, did not induce genotoxic effects in the majority of studies using intact cells. Coupled with the findings of metabolic studies, the large data-base generated in short-term test systems provides useful information for predicting and interpreting the peculiar patterns of Cr(VI) carcinogenicity.

Induction of sfiA SOS function by peroxides using three different E. coli strains

Five peroxides and two related compounds were tested for genotoxicity by the SOS Chromotest using 3 different E. coli strains (PQ37, PM21, GC4798). All tested hydroperoxides (hydrogen peroxide, tert-butylhydroperoxide, cumene hydroperoxide) were clearly positive in all strains. From a comparison of results obtained from the different strains it can be concluded that neither DNA lesions leading to the induction of excision repair nor covalent binding of radicals to DNA is responsible for the induction of sfiA-SOS function by hydroperoxides. Among the remaining compounds tested, only dibenzoylperoxide gave a clearly positive result in strain PQ37 whereas di-tert-butylperoxide and azobisisobutyronitrile showed only borderline activity. When using strains PM21 and GC4798, none of the latter compounds was positive. Paraquat was inactive in all strains.

Simple method for precise determination of chemical lethality in the L-arabinose resistance test of Salmonella typhimurium

A simple method is described for the determination of the lethal effects of chemicals assayed with the L-arabinose resistance test of Salmonella typhimurium. The method uses a mixed culture of 2 isogenic bacterial strains which are distinguished on the basis of their different nutritional requirements: sensitivity or resistance to L-arabinose, auxotrophy or prototrophy to histidine and leucine. BA13 (the mutation indicator strain) is the strain for routine screening of mutagens and allows the selection of forward mutation from L-arabinose sensitivity to L-arabinose resistance. BAL13 (the survival indicator strain) is a derivative of BA13. Both bacterial strains are found to be equally sensitive to the lethal effects of mutagens. The method described permits the measurement of cell survival at the same high cell concentration as used in the measurement of the mutant yield and in the same type of minimal medium with L-arabinose and glycerol, except for the histidine supplement in the mutant plates or the leucine in the survival plates.

Mutagenic lipid peroxides from edible oils

Weak mutagenic activity was detected in several commercially available edible palm and corn oils using liquid incubation bioassays with Salmonella typhimurium TA1537. Chromatographic fractionation of unrefined palm oil established that mutagenic activity was present in three fractions that also contained fatty acyl hydroperoxides. Similar weak mutagenic activity was also demonstrated for linoleic and linolenic acid hydroperoxides. In all cases, the mutagenicity was abolished by exogenous catalase, implying that the observed activity was moderated by hydrogen peroxide.

Hydrogen peroxide mutagenicity towards Salmonella typhimurium

In bioassays conducted under controlled, comparable conditions, weak direct mutagenicity responses were observed for hydrogen peroxide in the standard (Ames test) agar plate incorporation bioassay with Salmonella typhimurium strains TA97, TA98, TA102, and TA1537, in a 20 min preincubation test with strains TA97, TA98, TA100, TA102, TA1537, and TA1538, and in a liquid incubation modification using strain TA1537. These results conclusively demonstrate that hydrogen peroxide is a weak mutagen, especially in strains that are sensitive to oxidative damage under suitable bioassay conditions.

Study on the mutagenicity of nifurtimox and eight derivatives with the L-arabinose resistance test of Salmonella typhimurium

The mutagenicity of nifurtimox (nfx) and 8 nfx analogues has been investigated with the L-arabinose forward-mutation assay of Salmonella typhimurium. The nfx analogues tested were obtained by replacing the 3-methyl-4-yl-tetrahydro-1,4-thiazine-1,1-dioxide group of the parent compound with the following other groups: indazol-1-yl (1); pyrazol-1-yl (2); benzimidazol-1-yl (3); 1,2,4-triazol-4-yl (4); 1-methyl-3-methylthio-1,2,4-triazol-4-yl-5-thione (5); 3,5-bis(methylthio)-1,2,4-triazol-4-yl (6); 1-adamantyl (7); 4,6-diphenylpyridin-1-yl-2-one (8). The mutagenic activity of each chemical was determined by the standard plate-incorporation test, in the presence or absence of the S9 activation mixture. The 9 compounds were mutagenic and exhibited linear dose-mutagenic response relationships. They were direct-acting mutagens and showed a nearly 1000-fold range in mutagenic potency from chemical 1 to nfx. In most cases, the addition of S9 mixture to the test plates decreased the mutagenicity of compounds. This effect was particularly noticeable in the case of chemicals 1-3, 5 and 7 where a more than 70% decrease in mutagenic activity was observed in the presence of the S9 mixture. The mutagenic potency of compounds in the Ara test showed a negative linear correlation with previously reported antitrypanosomal activity. Thus, chemicals 6 and 8 with in vitro activities against Trypanosoma cruzi clearly superior to that of nfx showed 2 of the lowest mutagenic potencies in the Ara test and these were only somewhat higher than the mutagenicity of the reference drug.

Study of the causes of direct-acting mutagenicity in coffee and tea using the Ara test in Salmonella typhimurium

The mutagenic activities of 6 of the chemicals identified in coffee solutions were assayed with the Salmonella Ara test, under experimental conditions optimized for coffee mutagenicity. Caffeine was the only non-mutagenic compound. Among the other 5 chemicals, hydrogen peroxide was the strongest mutagen and chlorogenic acid the weakest; methylglyoxal, glyoxal and caffeic acid exhibited intermediate mutagenicities. The minimal mutagenic doses of these components correlated negatively with their relative concentrations in coffee. It was concluded that chlorogenic acid, caffeic acid, glyoxal and methylglyoxal cannot contribute alone to the mutagenicity of coffee in the Ara test, since their minimal mutagenic concentrations were much higher than their respective levels in the coffee samples assayed. By contrast, 40-60% of the mutagenic activity in coffee and also in tea could be attributed to their H2O2 contents. Catalase abolished more than 95% of the mutagenic activity of coffee, as detected by the Ara test. A similar sensitivity to catalase has been reported by other authors in relation to the coffee mutagenicity identified by the Salmonella His test. Nevertheless, the results presented in this paper suggest that the Ara forward and the His reverse mutation tests are sensitive to the mutagenicity of different constituents in coffee solutions. We propose that the His test, sensitive at high coffee doses, mainly recognizes the mutagenicity of methylglyoxal, whilst the Ara test, sensitive at low coffee doses, mainly detects the mutagenic activity of hydrogen peroxide. The data reported also suggest that the direct-acting mutagenicity(ies) detected by the Ara test in tea solutions is (are) based on similar, if not identical, mechanisms.

Response of the L-arabinose forward mutation assay of Salmonella typhimurium to frameshift-type mutagens

The present study was designed to evaluate the capacity of the L-arabinose resistance test of Salmonella typhimurium in the detection of frameshift-type mutagens. To this end the response of the Ara test was examined with respect to 15 chemicals which had been previously described as able to revert the Ames tester strain TA97. The mutagenicity of each compound was determined by the liquid test under experimental conditions which optimize the mutagenic response of the Ara test with the tester strain BA9. Strain TA97 was used simultaneously with BA9. The Ara forward-mutation assay efficiently detected the mutagenic activity of 14 out of the 15 chemicals assayed. PR toxin was the only compound which gave a weak dose response without doubling the spontaneous mutant level. In comparison with the Ara test, a total of 3 chemicals (HZ, PE and PR toxin) were not found to be mutagenic with strain TA97. In most cases (11/15) the mutagenic response of the Ara test was comparatively greater than that of strain TA97. Three chemicals (DEO, PRF and 9-AA) were detected with quite similar degrees of sensitivity by both mutation assays. ICR-191, which seems highly specific in reverting frameshift mutations with added cytosines in a run of cytosines, was the only chemical with a lower mutagenic activity in the Ara test than in strain TA97. The results enhance the interest of the L-arabinose forward-mutation assay as an alternative to the set of specific tester strains used by the histidine reverse-mutation assay in massive, general and primary screening for genotoxic agents.

Bleomycin-induced mutagenesis in repackaged lambda phage: base substitution hotspots at the sequence C-G-C-C

DNA isolated from lambda phage was treated with bleomycin A2 plus Fe2+. The bleomycin-damaged DNA was added to lambda packaging extracts and the resulting phage were grown in SOS-induced E. coli. Under these conditions, treatment of the DNA with 0.8 microM bleomycin reduced the viability of the repackaged phage to 3% and increased the frequency of clear-plaque mutants in the progeny by a factor of 16. Bleomycin-induced mutations which mapped to the DNA-binding domain of the cI gene were subjected to DNA-sequence analysis. The most frequent events were single-base substitutions at G:C base pairs, nearly all of which occurred at cytosines in the sequence Py-G-C. Cytosines in the third position of the sequence C-G-C-C were particularly susceptible to mutation. At A:T base pairs, mutations were less frequent and were a mixture of single-base substitutions and -1 frameshifts, occurring primarily at G-T and A-T sequences. Thus, the overall specificity of bleomycin-induced mutations matches that of bleomycin-induced DNA lesions (strand breaks and apyrimidinic sites), which are formed at G-C (particularly Py-G-C), G-T and, to a lesser extent, A-T sequences. Furthermore, the frequency of various types of substitutions was consistent with selective incorporation of A and T residues opposite apyrimidinic sites at these sequences. The highly selective nature of bleomycin-induced mutations may explain the lack of mutagenesis by this compound in a number of reversion assays.

A role of oxidative DNA sugar damage in mutagenesis by neocarzinostatin and bleomycin

The anti-tumor antibiotics neocarzinostatin and bleomycin specifically oxidize deoxyribose in DNA at the C-5' and C-4' positions, respectively. The resulting DNA lesions include strand breaks and apyrimidinic sites. Both agents are broad specificity mutagens, inducing, in various systems, base substitutions, frameshifts and deletions. Sequencing studies in bacterial systems have suggested that the base substitutions may result primarily from replicative bypass of the oxidized apyrimidinic sites.

Implication of active oxygen species in the direct-acting mutagenicity of tea

The present study shows that the L-arabinose resistance test with Salmonella typhimurium detects that freshly infused tea is highly mutagenic in the absence of mammalian microsomal activation. Both the mutagenesis protocol (preincubation test) and the additional genetic characteristics of the bacterial tester strain (excision repair deficiency, normal lipopolysaccharide barrier and the presence of plasmid pKM101) were critical factors in the optimal induction by tea of forward mutations to L-arabinose resistance. The TA104 strain--a histidine auxotroph specific to oxidative mutagens--was the most sensitive tester strain of the Ames test to the direct-acting mutagenicity of tea. In comparison with strain TA104, the sensitivity of the Ara forward mutation test was 18 times higher, one cup of tea (200 ml) inducing 3 X 10(6) AraR mutants. More than 90% of the mutagenicity of 150 microliter of a fresh tea infusion, or that of the equivalent amount (1.32 mg) of the corresponding lyophilized residue, was suppressed by 10 units of catalase. In contrast to catalase, superoxide dismutase was rather ineffective. These results indicate that hydrogen peroxide is produced in tea solutions, playing an essential role in its mutagenicity. In comparison, the role of superoxide anion seems negligible. Like catalase, the chelating agent DETAPAC showed a protective effect with respect to the mutagenicity of tea, suggesting the additional implication of hydroxyl radicals.

Coffee is highly mutagenic in the L-arabinose resistance test in Salmonella typhimurium

The present study shows that the L-arabinose resistance test in Salmonella typhimurium detects coffee as a strong mutagen in the absence of mammalian microsomal activation. The response of the Ara forward mutation assay was 8.5 times higher than that of TA104, which is the most sensitive to coffee of the tester strains of the Ames test. Both the mutagenesis protocol (preincubation test) and the additional genetic characteristics of the bacterial tester strain (excision repair deficiency, normal lipopolysaccharide barrier, and the presence of plasmid pKM101) were critical factors in the optimal induction by coffee of forward mutations to L-arabinose resistance. All ten samples of roasted coffee analyzed with the Ara assay were highly mutagenic: one cup of coffee (150 ml) was calculated to induce 3-4 X 10(6) AraR mutants. In contrast, coffee prepared from unroasted beans (green coffee) had no mutagenic activity. Regular- and sugar-roasted coffees showed similar mutagenicities, but the specific mutagenic activity of instant coffees (1559 AraR mutants/mg) was almost 2 times that of noninstant ones (834 AraR mutants/mg). The Ara assay allowed the direct testing of coffee, although it was demonstrated that lyophilization has no effect on the mutagenicity of this beverage. Like roasted coffee, roasted barley induced a large number of AraR mutants per mg (227), though its specific mutagenic activity was approximately 4 and 7 times lower than that of noninstant and instant coffees, respectively.

Mutagenic sterol hydroperoxides

Sterol hydroperoxides 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide and 3 beta-hydroxycholest-5-ene-7 alpha-hydroperoxide show weak dose-response direct mutagenicity towards Salmonella typhimurium strain TA 1537 in a liquid medium incubation bioassay. Responses were compromised by metabolism of the sterol hydroperoxides and by phase separation during the incubation period. Mutagenicity responses were increased by added superoxide dismutase but diminished by added rat liver S9 enzymes and abolished by added catalase. Catalase also abolished the stimulatory effect of superoxide dismutase. These results indicate that superoxide and peroxide be implicated in the mutagenicity responses.

Mutagenicity study on pyrazole, seven pyrazole derivatives, and two nitroimidazoles with the L-arabinose resistance test of Salmonella typhimurium

The mutagenicity of pyrazole and seven pyrazole derivatives (4-nitropyrazole, 4-bromopyrazole, 1-methyl-4-nitropyrazole, 3,5-dimethyl-4-nitropyrazole, 1-methyl-4-bromopyrazole, 4,4'-dinitro-1, 1'-methylene-dipyrazole and 4,4'-dibromo-1,1'-methylene-dipyrazole) has been investigated with the L-arabinose forward mutation assay of Salmonella typhimurium. Two nitroimidazoles (1-methyl-5-nitroimidazole and metronidazole) were included as reference drugs. The mutagenicity of each chemical was determined by both preincubation and liquid tests, in the presence or absence of S9 microsomal fraction. The mutagenic response was expressed as the absolute number of L-arabinose resistant mutants growing in selective plates, supplemented with traces of D-glucose. Strain BA13 with a wildtype lipopolysaccharide barrier was used as a comparison to the deep rough derivative BA9. No mutagenic effect was detected with pyrazole and two of its derivatives, 1-methyl-4-bromopyrazole and 4,4'-dibromo-1,1'-methylene-dipyrazole. The other five pyrazole derivatives were mutagenic to different degrees, although their mutagenic potencies were always considerably lower than those of the two nitroimidazoles. The results suggest that 4-nitropyrazoles, as well as 4,4'-dinitro-1, 1'-methylene-dipyrazoles, should be investigated further as alternatives to, or even substitutes for, the currently used nitroimidazoles.