Interactions of histidine-containing test substances and extraction methods with the Ames mutagenicity test

Safety evaluation of Gamisoyo-san: genotoxicity, acute toxicity, and influence on drug-metabolizing enzymes

Gamisoyo-san is an herbal formula widely used to treat psychological issues, menopausal symptoms, and dysmenorrhea. However, there is insufficient information on its safety profile. This study aimed to confirm the genotoxic and acute toxic potential of Gamisoyo-san. We performed a battery of tests, which included a bacterial reverse mutation test (Ames test) using five bacterial strains, an in vitro chromosomal aberration test using Chinese hamster lung (CHL) cells, an in vivo micronucleus test in mice, and human Cytochrome P450 (CYP450) and UDP-glucuronosyltransferase (UGT) assays. In the acute toxicity study, male and female rats were orally administered Gamisoyo-san 1000, 2000, or 5000 mg/kg and observed for 14 days. The activities of human CYP450s and UGTs were evaluated using recombinant baculosomes. Gamisoyo-san showed no signs of genotoxicity in the five bacterial strains, CHL cells, or mouse bone marrow cells. The acute toxicity test showed that the median lethal dose (LD50) of Gamisoyo-san was greater than 5000 mg/kg in rats. Gamisoyo-san inhibited the activities of CYP1A2, CYP2C19, and UGT1A1. In conclusion, Gamisoyo-san may not exert severe toxicological events or genotoxic effects at doses up to 5000 mg/kg in rats.

Potential pitfalls associated with testing of enzyme preparations in the Salmonella/microsome assay

The effect of a sample of food enzyme preparations on S9 activity was evaluated in bacterial mutation assays with the Salmonella typhimurium strains TA98 and TA100 using benzo(a)pyrene, 2-aminoanthracene and 2-aminofluorene as model compounds. Under the experimental conditions applied, Aspergillus oryzae protease and porcine pancreas trypsin, applied at low non-toxic doses, proved to effectively inhibit the metabolic activation of benzo(a)pyrene by Aroclor induced rat liver 9, while the activation of 2-aminoanthracene and 2-aminofluorene was only marginally affected. The tolerance of metabolic activation of 2-aminoanthracene to the presence of proteolytic enzymes, compared to the strong inhibition elicited on the metabolic activation of benzo(a)pyrene, points to the involvement of different components of liver S9 in their biotransformation. Overall, data indicate that the use of 2-aminoanthracene as positive control in the Ames test can give a misleading indication of S9 proficiency, and thus it should be used with caution or in conjunction with other chemicals, especially in the testing of crude enzyme preparations in which proteases may be present as minor components.

In vitro and in vivo safety evaluation of Acer tegmentosum

ETHNOPHARMACOLOGICAL RELEVANCE

Acer tegmentosum, which contains salidroside and tyrosol, has been used for the treatment of hepatic disorders in eastern Asia. However, little is known about its safety.

AIM OF THE STUDY

To determine the safety of Acer tegmentosum, we evaluated its acute oral toxicity and genotoxicity profiles.

MATERIALS AND METHODS

Salidroside and tyrosol present in Acer tegmentosum were quantified using high-performance liquid chromatography. Acute oral toxicity testing of Acer tegmentosum was performed in rats. Genotoxicity of Acer tegmentosum was assessed by bacterial reverse mutation, chromosomal aberration, and bone marrow micronucleus tests. All the tests were conducted in accordance with the good laboratory practices.

RESULTS

The amounts of salidroside and tyrosol in Acer tegmentosum were found to be 85.01±1.21mg/g and 3.12±0.04mg/g, respectively. In the bacterial reverse mutation test, Acer tegmentosum increased the number of revertant Salmonella typhimurium TA98 colonies, regardless of metabolic activation by S9 mixture. In contrast, Acer tegmentosum application did not significantly increase the number of chromosomal aberrations in Chinese hamster ovary (CHO)-K1 cells and micronucleated polychromatic erythrocytes in mice. In the acute oral toxicity test, the median lethal dose (LD50) of Acer tegmentosum was found to be >2000mg/kg in rats.

CONCLUSION

Take together, Acer tegmentosum exhibits mutagenicity, which was evident from the bacterial reverse mutation test. Further studies are needed to identify the components responsible for such an effect and the underlying mechanisms.

Phase I Clinical Study of the Dietary Supplement, Agaricus blazei Murill, in Cancer Patients in Remission

Although many cancer patients use complementary and alternative medicine, including Agaricus blazei Murill (ABM), safety is not yet well understood. Cancer survivors took 1.8, 3.6, or 5.4 g ABM granulated powder (Kyowa Wellness Co., Ltd., Tokyo, Japan) per day orally for 6 months. Adverse events were defined by subjective/objective symptoms and laboratory data according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0 (NCI-CTCAE v3.0). Seventy-eight patients were assessed for safety of ABM (30/24/24 subjects at 1/2/3 packs per day, resp.). Adverse events were observed in 9 patients (12%). Most were digestive in nature such as nausea and diarrhea, and one patient developed a liver dysfunction-related food allergy, drug lymphocyte product. However, none of these adverse events occurred in a dose-dependent manner. This study shows that ABM does not cause problems in most patients within laboratory parameters at the dosages tested over 6 months. This trial supports previous evidence that the ABM product is generally safe, excluding possible allergic reaction.

Follow-up actions from positive results of in vitro genetic toxicity testing

Appropriate follow-up actions and decisions are needed when evaluating and interpreting clear positive results obtained in the in vitro assays used in the initial genotoxicity screening battery (i.e., the battery of tests generally required by regulatory authorities) to assist in overall risk-based decision making concerning the potential effects of human exposure to the agent under test. Over the past few years, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Project Committee on the Relevance and Follow-up of Positive Results in In Vitro Genetic Toxicity (IVGT) Testing developed a decision process flow chart to be applied in case of clear positive results in vitro. It provides for a variety of different possibilities and allows flexibility in choosing follow-up action(s), depending on the results obtained in the initial battery of assays and available information. The intent of the Review Subgroup was not to provide a prescriptive testing strategy, but rather to reinforce the concept of weighing the totality of the evidence. The Review Subgroup of the IVGT committee highlighted the importance of properly analyzing the existing data, and considering potential confounding factors (e.g., possible interactions with the test systems, presence of impurities, irrelevant metabolism), and chemical modes of action when analyzing and interpreting positive results in the in vitro genotoxicity assays and determining appropriate follow-up testing. The Review Subgroup also examined the characteristics, strengths, and limitations of each of the existing in vitro and in vivo genotoxicity assays to determine their usefulness in any follow-up testing.

Mutagenicity of Chinese traditional medicine Semen Armeniacae amarum by two modified Ames tests

Background

Semen armeniacae amarum (SAA) is a Chinese traditional medicine and has long been used to control acute lower respiratory tract infection and asthma, as a result of its expectorant and antiasthmatic activities. However, its mutagenicity in vitro and in vivo has not yet been reported. The Ames test for mutagenicity is used worldwide. The histidine contained in biological samples can induce histidine-deficient cells to replicate, which results in more his⁺ colonies than in negative control cells, therefore false-positive results may be obtained. So, it becomes a prerequisite to exclude the effects of any residual histidine from samples when they are assayed for their mutagenicity. Chinese traditional herbs, such as SAA, are histidine-containing biological sample, need modified Ames tests to assay their in vitro mutagenicity.

Methods

The mutagenicity of SAA was evaluated by the standard and two modified Ames tests. The first modification used the plate incorporation test same as standard Ames teat, but with new negative control systems, in which different amounts of histidine corresponding to different concentrations of SAA was incorporated. When the number of his⁺ revertants in SAA experiments was compared with that in new negative control, the effect of histidine contained in SAA could be eliminated. The second modification used a liquid suspension test similar to the standard Ames test, except with histidine-rich instead of histidine-limited medium. The aim of this change was to conceal the effect of histidine contained in SAA on the final counting of his⁺ revertants, and therefore to exclude false-positive results of SAA in the Ames test. Furthermore, the effect of SAA on chromosomal aberration in mammalian bone marrow cells was tested.

Results

The standard Ames test showed a positive result for mutagenicity of SAA. In contrast, a negative response was obtained with the modified plate incorporation and modified suspension Ames tests. Moreover, no apparent chromosomal aberrations were observed in mammalian bone marrow cells treated with SAA.

Conclusion

The standard Ames test was not suitable for evaluating the mutagenicity of SAA, because false-positive result could be resulted by the histidine content in SAA. However, the two modified Ames tests were suitable, because the experimental results proved that the effect of histidine in SAA and therefore the false-positive result were effectively excluded in these two modified Ames tests. This conclusion needs more experimental data to support in the future. Moreover, the experimental results illustrated that SAA had no mutagenicity in vitro and in vivo. This was in agreement with the clinical safety of SAA long-term used in China.

A modified suspension test for estimating the mutagenicity of samples containing free and (or) protein-bound histidine

The Ames test has not been very effective in estimating the mutagenicity of histidine-containing samples because external free and (or) protein-bound histidine in these samples would allow the histidine auxotrophs in such test samples to grow more compared with the negative controls that were used as the reference. This could give rise to a false positive.n this study, a modified suspension mutagenicity assay (MS assay) was deveopled. The tester strains were incubated in Luria-Bertani (LB) broth containing different concentrations of traditional Chineses medicines (TCMs) until the declining phase, and the test samples were assayed to be mutagenic or not by observing whether statistically significant differences were demonstrated in the relative reversion frequencies (RRFs) between the negative control groups and the test groups. Collectively, using LB broth as the test medium and comparing the RRFs in the declining phase made this assay less influenced by the presence of histidine in the test samples.The mutagenicity of some TCMs was measured with the MS assay. The results in MS assay were consistent with those in the mammalian bone marrow chromosomal aberration test, which indicated that the MS assay was appropriate to estimate the mutagenicity of samples containing free and (or) protein-bound histidine.

In vitro approaches to develop weight of evidence (WoE) and mode of action (MoA) discussions with positive in vitro genotoxicity results

A recent analysis by Kirkland et al. [Kirkland, D., Aardema, M., Henderson, L. and Müller, L. (2005) Evaluation of the ability of a battery of 3 in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens. I. Sensitivity, specificity and relative predictivity. Mutat. Res. 584, 1-256] demonstrated an extremely high false positive rate for in vitro genotoxicity tests when compared with carcinogenicity in rodents. In many industries, decisions have to be made on the safety of new substances, and health risk to humans, without rodent carcinogenicity data being available. In such cases, the usual way to determine whether a positive in vitro genotoxicity result is relevant (i.e. indicates a hazard) for humans is to develop weight of evidence (WoE) or mode of action (MoA) arguments. These are based partly on further in vitro investigations, but usually rely heavily on tests for genotoxicity in one or more in vivo assays. However, for certain product types in the European Union, the use of animals for genotoxicity testing (as well as for other endpoints) will be prohibited within the next few years. Many different examples have been described that indicate DNA damage and genotoxic responses in vitro can arise through non-relevant in vitro events that are a result of the test systems and conditions used. The majority of these non-relevant in vitro events can be grouped under a category of 'overload of normal physiology' that would not be expected to occur in exposed humans. However, obtaining evidence in support of such MoAs is not easy, particularly for those industries prohibited from carrying out in vivo testing. It will become necessary to focus on in vitro studies to provide evidence of non-DNA, threshold or in vitro-specific processes and to discuss the potential for such genotoxic effects to occur in exposed humans. Toward this end, we surveyed the published literature for in vitro approaches that may be followed to determine whether a genotoxic effect observed in vitro will occur in humans. Unfortunately, many of the approaches we found are based on only a few published examples and validated approaches with consensus recommendations often do not exist. This analysis highlights the urgent need for developing consensus approaches that do not rely on animal studies for dealing with in vitro genotoxins.

Modified bacterial mutation test procedures for evaluation of peptides and amino acid-containing material

Biological materials can release amino acids during the course of bacterial mutation testing. Low levels of released amino acids from soluble materials can cause moderate increases in the number of revertant colonies on the plate, whereas higher levels lead to overgrowth of the background lawn, making counting of revertant colonies impossible. For poorly soluble material, the released amino acids can be present at high levels in localized spots on the plate, leading to the growth of 'pseudorevertant' colonies. The 'treat and wash' modified preincubation method employed here is an adaptation of the treat and plate method (used for evaluation of antibiotics) and involves washing the bacteria free of test compound after a 90 min exposure prior to plating out on minimal plates. The MC overlay method is a modified version of the standard plate incorporation assay, in which a top overlay containing 4% high viscosity methylcellulose is used in place of agar to stabilize the test compound in solution, preventing precipitation and subsequent localized amino acid release. Both modified methods produce the expected results for negative and positive controls. Peptides [synthetic curtailed analogs of human parathyroid hormone, PTH(1-34) and Ostabolin-C] that produced false positive results or could not be evaluated owing to overgrowth of the background lawn using standard methods, showed no artifacts and no evidence of genotoxicity using the modified methods. It is concluded that the treat and wash and MC overlay methods are valid versions of the bacterial mutation test for avoiding complications associated with released amino acids.

Mutagenicity of Helicobacter pylori in the Ames test using Salmonella typhimurium TA100

Infection with Helicobacter pylori has been recognized as a risk factor for gastric cancer, although it is still unclear whether strains of this organism behave as carcinogens. We have studied 30 H. pylori clinical isolates from 15 patients with gastric cancer and 15 patients with other gastroduodenal diseases. Bacterial pellet and supernatant fluid of broth cultures were tested for mutagenicity by means of the Ames test using the pre-incubation technique. The average Ames ratio was 1.111 in the bacterial pellet and 1.312 in the supernatant of strains from the gastric-cancer group, and 0.858 and 0.950 in those from the non-gastric-cancer group, respectively. The strains from the gastric-cancer group had a significantly higher ratio than those from the non-gastric-cancer group, although all results were below the cut-off ratio of the Ames test, and were thus regarded as having no mutagenicity. The Ames ratio of the supernatant was higher than that of the bacterial pellet in both groups. The results indicate that all of the H. pylori strains tested revealed no mutagenicity, but the difference in Ames ratio between strains might reflect differences in genotoxicity between the strains.

Mutagen content and metabolic activation of promutagens by molluscs as biomarkers of marine pollution

Organisms combat pollutants by inducing biotransformation pathways, which can be used for biomonitoring. Several parameters--biomarkers--change in stressed organisms or populations at different organisation levels. Molecular or cellular biomarkers are early-warning indicators of pollution. Xenobiotics are first biotransformed by phase I enzymes and then conjugated with endogenous metabolites by phase II enzymes. Many organic xenobiotics are initially biotransformed by cytochrome P4501A1; in mammals, it is induced by pollutants via Ah receptor, although in marine invertebrates, its inducibility is much more equivocal. Metallothioneins are small Cys-rich proteins which bind transition metals; they detoxicate pollutant metals and are clearly induced in metal-exposed marine invertebrates. Some pollutants are genotoxins or can be converted into them. Determination of mutagens in bivalve molluscs following extraction with solvents and assay of mutagenicity with bacterial tests is a useful biomarker for marine pollution. While some pollutants are directly mutagenic, others are only mutagenic after they are activated to mutagenic derivatives by monooxygenases or conjugative enzymes. Many of these catalysts are induced by xenobiotics; thus, increased activation of known promutagens can be used as biomarker of environmental pollution. Bioactivation of promutagens requires the simultaneous action of different pathways, thus, reproducing more closely the in vivo situation than the specific assay of individual biotransforming enzymes. Study of molluscs with different pollution levels indicates that polluted animals have higher capacity to activate 2-aminoanthracene and contain more apolar mutagens than those from reference areas.

Optimization of the Salmonella/mammalian microsome assay for urine mutagenesis by experimental designs

Assessing urine mutagenicity with the Salmonella mutagenicity test is often limited by the volumes of the samples. Optimization of the assay was performed with factorial and Doehlert designs. Two fractional factorial designs 2(3-1) (3 factors, 4 experiments) were used to estimate the main effects of the percent S9 in the mix, the time of liquid incubation, the inoculum size and the growth conditions. A Doehlert design (3 factors, 13 experiments) was used to study the main effects and the interactions of the NADP, G6P and S9 in the mix. The positive markers were benzo[a]pyrene (BaP, 0.3 microgram/plate) and a pool of smokers' urine (SU, 1.25 ml equivalent/plate). The response was limited to the induction factor (IF, number of induced revertants/number of spontaneous revertants) with Salmonella typhimurium TA98. The optimal conditions for BaP were: a 60 min period of liquid incubation and a volume of 0.1 ml (approx. 10(8) cells/plate) of an overnight culture grown in 50 ml of Nutrient Broth No. 2 from a 250 ml flask. The S9 mix (0.1 ml, final volume) included 1.5% of S9, 1.0 mM NADP and 4.4 mM G6P. The maximal IF was 15.79. The optimal conditions for SU were: a 60 min period of liquid incubation and a volume of 0.1 ml (approx. 10(8) cells/plate) of an overnight culture grown in 7 ml of Nutrient Broth No. 2 from a 20 x 180 mm tube. The S9 mix (0.1 ml, final volume) included: 4% S9, 4.2 mM NADP and 5.2 mM G6P. The maximal IF was 10.95. These optimal conditions did not modify the spontaneous frequencies of the tester strains: TA97a, TA98, TA100 and TA102. The dose-response curves of mutagenic urine samples were found to be non-linear. This micromethod required 8-fold less urine sample and 12.5-fold less liver homogenate as compared to the standard plate incorporation assay and was from 6.2- to 11.8-fold more sensitive to evaluate urine mutagenicity. The sensitivity of this technique was found to be limited to individuals smoking more than approx. 5 cigarettes/day by the standard extraction-concentration procedure.

Synergistic/comutagenic action in the Ames test as an indication of irrelevant positive findings

A number of structurally very diverse compounds which cause weak positive effects in the Ames test by evident or suspect irrelevant mechanisms is discussed. As a unifying observation we describe synergistic effects in combination with known mutagens in the responsive strains and comutagenic effects in initially unresponsive strains. We argue that the compounds enhance the formation of spontaneous (or mutagen-induced) revertant colonies by test-specific mechanisms likely to be of no relevance to multicellular eukaryotic organisms rather than possessing intrinsic genotoxic (i.e. DNa-damaging) properties in the Ames test.

Geographical variations in mutagenicity of blue rayon extracts of Japanese human bile

The mutagenicity of human bile was investigated in the Ames test after blue rayon treatment. In the present study, 52 and 59 bile samples were collected from the high and the low risk population for gallbladder cancer (GBC), respectively. The bile mutagenicity was detected only when the blue rayon extracts of bile were assayed with Salmonella typhimurium TA98 in the presence of S9 mix. Thirty-two (61.5%) of 52 samples obtained from the high risk population were mutagenic. In our previous study (Mano et al., 1993), the mutagenicity was observed in 14 (58.3%) of 24 samples. After combining this data with the results of the present study, 46 (60.5%) of 76 samples revealed the mutagenicity. On the other hand, the mutagenicity was detected in only 7 (11.9%) of 59 samples collected from the low risk population. Therefore, we found a significant geographical difference in the bile mutagenicity.

Mutagenicity of blue rayon extracts of human bile in the Ames test

The mutagenicity of human bile was examined in the Ames Salmonella/microsome assay. Bile samples were obtained from the gallbladders resected from patients with cholelithiasis, choledocholithiasis, gallbladder cancer, extrahepatic bile duct cancer and other diseases. For extraction of mutagenic components, the bile samples were treated with blue rayon and the adsorbed materials were assayed with Salmonella typhimurium TA98 in the presence of S9 mix. Twenty-four bile samples were tested and positive mutagenic activity was found in 14 samples. A 200-microliter bile equivalent material gave 6.3 times as many revertant colonies as the solvent control. With several samples that had undergone two cycles of blue rayon extraction, clear dose-response relationships in mutagenicity were demonstrated.

Detection of mutagenic activity in textiles with Salmonella typhimurium

A hundred and ninety-six textile samples were tested in a modified version of the Salmonella/microsome assay for release of mutagenic contaminants. As heat sterilization of the samples can result in reduction of mutagenic activity, tests were performed with streptomycin resistant derivatives of Salmonella tester strains TA98 and TA100. Textile samples were preincubated in buffered saline (PBS), DMSO or ethanol. Subsequently, the fabrics were placed on streptomycin supplemented selective agar plates. In total, 18 samples (9.2%) exerted mutagenic activity. DMSO was the most effective solvent (15 positives) followed by ethanol (9 positive samples) and PBS (7 positives). Most fabrics (16) caused mutagenic effects only upon metabolic activation with liver S9 mix. Chemical analysis indicates that the positive results obtained with PBS are not due to release of histidine or formaldehyde. Three directly active samples gave negative results in strain TA98NR which is devoid of classical nitroreductase. With one exception all other textiles were negative in strain TA98/1,8-DNP6 (which lacks O-acetyltransferase). These findings indicate that nitroaromatics and amines might be responsible for the mutagenic effects of the textiles.

Renin inhibitors as an example of presumptive irrelevant positive findings in the Salmonella/mammalian microsome assay (Ames test)

An increase in the number of mutant colonies in the Ames test is generally taken as a strong indication for a genotoxic (e.g., DNA damaging) property of the test compound or its metabolites. However, a few examples are known in which mechanisms usually related to some sort of growth enhancement will lead to increases in mutant frequencies of spontaneous origin. The renin inhibitor Ro 42-5892 increased the number of mutant colonies of strain TA1538 and to a lesser degree of TA98 in the standard plate incorporation assay (Ames test). Since there is no chemical basis for a 'DNA reactivity' of this compound, experiments were performed to obtain information about possible indirect mechanisms of enhancing the number of spontaneous mutant colonies. Circumstantial evidence is presented to attribute the weak activity not to an inherent genotoxic property but rather to an as yet undefined indirect effect on the expression of spontaneous mutants. Since Ro 42-5892 contains a histidine residue it was a reasonable assumption to suspect a growth enhancing property of the test compound. However, none of the strains showed an elevation of the number of revertant colonies or an increase in the density of the background growth. In addition, structurally related non-histidine containing renin inhibitors showed absolutely no increase in the number of revertant colonies. Furthermore, no growth induction (either in liquid or under selective conditions) and no histidine cleave off by a TA1538/TA98 specific metabolism could be shown. A second line of evidence showing parallelism to growth enhancing compounds concerns the comutagenicity of histidine containing renin inhibitors. When Ro 42-5892 was tested in combination with established mutagens, a multiplicative synergism was found. This effect was observed not only in strains TA1538 and TA98 but also in the standard Salmonella tester strains where the spontaneous mutant frequency was not increased by Ro 42-5892. Analogous effects were previously shown for free histidine, isohistidine, phenobarbital and tetracycline and in part explained by molecular mechanisms.

Mutagenicity testing of protein-containing and biological samples using the Ames/Salmonella plate incorporation test and the fluctuation test

Mutagenicity testing of biological samples and proteins is complicated by the presence of histidine and histidine-related growth factors which may produce a false positive result in the Ames/Salmonella plate incorporation test. A bioassay method, utilizing an automated dispenser-photometer and Salmonella typhimurium strain TA1535 as the indicator bacteria, was used to estimate the presence of histidine-related growth factors in three enzyme solutions submitted for mutagenicity testing. One of the solutions was clearly positive in the Ames/Salmonella test and also contained the highest amount of L-histidine-HCl-equivalents. The two other solutions, with low or undetectable amounts of L-histidine-HCl-equivalents, gave equivocal and negative results, respectively, in the Ames/Salmonella test. Studies were also performed with strains TA98, TA100 and TA1535 to determine the amount of added L-histidine-HCl that would result in a 'positive' result in the Ames/Salmonella test. Because the minimum amount of L-histidine-HCl required to double the number of revertant colonies was 150 nmol/plate, and the maximum amount of L-histidine-HCl-equivalents supplied by the enzyme preparations was 40 nmol/plate at the highest tested dose, the mutagenicity test results of the enzyme solutions cannot be explained solely by histidine or related compounds. Smokers' and non-smokers' urines, concentrated with liquid extraction (CHCl3) and adsorbent (XAD-2 and XAD-2/Sep-Pak C18) techniques, were studied to reveal differences in efficiencies to extract histidine and histidine-related compounds in the urines. Amounts of 'histidine' in concentrates of urine were measured using the bioassay method and a chemical method employing derivatization with fluorescamine. The fluorescamine method also efficiently detected 3-methyl-L-histidine, a product of muscle metabolism excreted in urine, which was found to be unable to support auxotrophic growth in TA1535, leading to exaggerated estimations of the auxotrophic growth enhancing properties of urine extracts. The urine extracts, and pure L-histidine-HCl, were tested using a two-step fluctuation test to estimate auxotrophic growth factor effects in this type of test. Because of a strong dilution effect when adding the histidine-free selection medium, the fluctuation test employed in this study was not found to be particularly sensitive to growth factors. The results of this study indicate that use of a bioassay, employing the same indicator bacteria as the mutagenicity test themselves, is a reliable way to measure histidine-related growth factors in biological samples.(ABSTRACT TRUNCATED AT 400 WORDS)

The mutagenicity of edible mushrooms in a histidine-independent bacterial test system

In mutagenicity screening of 40 edible mushroom species, special attention was paid to the selection of the test system, since complex mixtures such as mushroom extracts may interfere with the genetic endpoint of the assay. This paper shows that the weak mutagenicity of some mushrooms in the Ames test, as reported by several authors, is actually an artefact due to the presence of free histidine in the mushroom extracts, which apparently increases the reversion of bacteria from histidine auxotrophy to prototrophy. To avoid amino-acid interaction, a combination of the forward mutation assay to 8-azaguanine resistance in Salmonella typhimurium TM677 and a liquid test was used. Out of 35 wild and commercially grown mushrooms tested, 13 species exhibited mutagenic activity. In the case of the five samples of dried mushrooms, weak mutagenicity could be detected for Auricularia sp. The presence of microsomal enzymes (S-9) reduced the mutagenic effects of all the mushrooms, with the exception of Agaricus abruptibulbus and Cantharellus cibarius, where metabolic activation enhanced the mutagenic activity.

Formation of heterocyclic amines during meat extract processing and cooking

Standardized biological in vitro systems and in particular those used for cancer prediction are being used to monitor the development of food products in order to ensure the absence of potential mutagens or carcinogens. Maillard reactions occurring during meat extract production was followed in order to reduce the formation of heterocyclic amines. Possibilities to reduce the content of heterocyclic amines during meat extract processing have been proposed. However, several aspects, such as interaction with food-borne mutagen or carcinogen inhibitors, keeping quality, and organoleptic properties have also been taken into consideration. Whenever possible, food contaminants must be analytically determined and compared to total intake exposure and tolerated levels of other comparable food contaminants to establish realistic "tolerated" contamination levels.

The risks of handling cytotoxic drugs. I. Methods of testing exposure

Results of various biological and physical/chemical tests of the urines or blood of health-care personnel working with cytotoxic drugs are discussed. The outcomes of these tests are conflicting and inconclusive. The physical/chemical tests seem to be an alternative method. However, until now it has not been possible to establish the threshold concentration in urine or blood beneath which no effect has to be expected. Therefore, the interpretation of the concentration of cytotoxic drugs and/or the metabolites in the urine or blood is difficult. As long as one will not be able to provide conclusive data on the health hazards when working with cytotoxic drugs, protective measures have to be taken in order to lower the risk as much as possible.

Plasmid copy number and mutant frequencies in S. typhimurium TA102

Tetracycline and chloramphenicol increase the number of mutant colonies of strain TA102, which carries the reverting gene on the plasmid pAQ1. Determination of the plasmid content by agarose gel analysis shows that the increase of the mutant colony number is paralleled closely by an increase of the number of pAQ1 plasmids per cell, indicating that the two compounds do not increase the frequency of mutants "per gene," but only enhance the number of the genes at which mutations can occur. Thus, not considering the molecular processes could result in mistakenly attributing the increase in the number of mutants per plate (respective to the number of mutants per cell) to a mutagenic activity of the antibiotics.

Study of the amniotic fluid from smokers and non-smokers in the Ames test

Amniotic fluid from smokers and non-smokers was tested by the Salmonella/mammalian microsome test. Concentrated amniotic fluid from heavy smokers at term showed an increase in the number of revertants with increasing exposure to tar. However, some of the non-smokers had a higher number of revertants than the smokers. No significant differences were found between second-trimester samples from smokers and non-smokers, but the limited volumes available at this stage of pregnancy may be a source of error.

Absence of mutagenicity in the urine of autopsy service workers exposed to formaldehyde: factors influencing mutagenicity testing of urine

Hospital autopsy service workers and a matched control group were studied using a battery of genetic monitoring tests performed on samples of blood, semen and urine. The results of the analysis of urine for mutagens are described in this report. The participants in the study were matched with the controls for sex, age and their use of alcohol, tobacco and marijuana. Information was collected on general health, usage of medications and any exposure which might affect the outcome of the study. Individuals were sampled three times at approximately two month intervals. Time weighed average exposures to formaldehyde in the work areas were estimated at 0.61 to 1.32 ppm. Additionally, studies were carried out which examined various parameters affecting the testing of human urine samples for mutagenicity. No increase in mutagenicity was seen in the autopsy workers as compared to the control group. One individual who was receiving metronidazole and one control who smoked two packs of cigarettes per day had significantly mutagenic urine. A large proportion of the exposed individuals had toxic urine while only two of the control individuals had similar toxic urine. The material responsible for the toxicity has been isolated and purified but does not appear to be related to the formaldehyde exposure. Studies on the parameters affecting mutagenicity testing of urine with Salmonella typhimurium suggest that in the plate incorporation assay, TA100, but not TA98, can be affected by exogenous histidine. Furthermore, with the conditions employed in this study, 3 to 4% of labeled histidine added to urine samples was retained by the XAD-2 and subsequently eluted in the urine concentrate. Urinary histidine levels of unconcentrated samples ranged from 112 to 2614 nmol per ml (mean 994 nmol per ml) and the amount of histidine present correlated with the corresponding increases in histidine revertants with strain TA100.

Mutagenicity studies on coffee. The influence of different factors on the mutagenic activity in the Salmonella/mammalian microsome assay

Recently, mutagenic activity on several strains of Salmonella typhimurium has been found in many heat-processed foodstuffs. The previously reported direct-acting mutagenic activity of coffee in Salmonella typhimurium TA100 (Ames assay) was confirmed in our study. In addition to TA100, a mutagenic effect of coffee was also found by using the newly developed strain TA102. The mutagenic activity was abolished by the addition of rat-liver homogenate. 10% S9 mix completely eliminated the mutagenic activity of 30 mg of coffee per plate. The addition of reduced glutathione to active S9 further decreased the mutagenic activity and also reduced the mutagenicity together with inactivated S9. The compound or compounds responsible for this inactivation are heat-labile and seem to be located in the cytosol fraction of the S9. Part of the mutagenicity of coffee was also lost spontaneously upon incubation at temperatures between 0 degrees and 50 degrees C. The loss of activity was dependent on temperature, being more pronounced at 50 degrees C compared to 0 degrees C (at 50 degrees C approximately 50% of the mutagenic activity was lost after 6 h). As anaerobic conditions prevented this loss of mutagenicity almost totally, oxidative processes are probably responsible for the inactivation. The stability of the mutagen was not influenced by incubation at low pH values (pH 1-3), with or without the addition of pepsinogen. The mutagenic properties of methylglyoxal, which to some extent could be responsible for the mutagenic activity of coffee, were compared with those of coffee. Methylglyoxal was strongly mutagenic towards Salmonella typhimurium TA100 and TA102. Its mutagenic activity was partially inactivated by the addition of 10% S9. Glyoxalase I and II together with reduced glutathione abolished the mutagenic activity of methylglyoxal but reduced the mutagenicity of coffee by only 80%. Since these enzymes occur in mammalian cells, the mutagenic compound(s) of coffee could also be degraded in vivo. This conclusion is supported by the fact that a long-term carcinogenicity study with rats was negative. These results clearly demonstrate that the effects observed in vitro do not necessarily also occur in vivo, but that in vitro experiments may contribute to the understanding of fundamental mechanisms of chemical carcinogenesis.

Genetic toxicology in the food industry

In vitro testing of food products for mutagenic activity presents particular problems, especially in connection with the administration of the test material to the assay system, the possible interference of food components with the genetic end-point used for the assay, the presence in foods of various factors that may modify mutagenic activity, the identification of appropriate negative or positive controls and the avoidance of artefactual mutagen formation during the preparation of test samples. Ideally mutagenicity testing requires in vivo studies (although these too have particular problems when applied to foods) but, at present, in vitro tests provide the only practical means of screening large numbers of food samples or modifying factors and of assessing food-processing techniques. The tests can be carried out on model systems (e.g. amino acid/sugar mixtures), on isolated and purified constituents of foods, on fractionated solvent extracts or on whole-food homogenates subjected to digestion procedures. However, to determine genotoxic risk from foodstuffs, quantitative data from mammalian in vivo tests and from human consumption and metabolism studies are also required.

Urinary excretion of frameshift mutagens in rats caused by passive smoking

Several male Wistar rats were individually placed in a chamber resembling a room provided with minimal air flow. They were exposed separately to the main- and sidestream smoke of a commercial brand of cigarettes smoked by a smoking machine. Exposure to both sidestream and mainstream smoke of at least two cigarettes resulted in significant excretions of frameshift mutagens in urine within 24 h, detected by the bacterial microtiter fluctuation test with Salmonella typhimurium TA1538. Doubling exposure to the mainstream smoke resulted in similar quantitative mutagenic activities. Doubling exposure to the sidestream smoke resulted in reduced water intake by the animals and thus toxic effects of the urine concentrates on the test bacteria.

Evaluation of the mutagenic potential of corn (Zea mays L.) grown in untreated and atrazine (AAtrex) treated soil in the field

Bacterial assays using extracts from field corn plants (harvested at one month, silage and mature stages) do not indicate that soil treatment with atrazine, at its maximum use rate, alters the endogenous mutagens present in these extracts, nor that atrazine itself is degraded to mutagenic products. Extracts of corn grown in soil treated with AAtrex were equally mutagenic with those of corn grown in untreated soil when tested in Salmonella typhimurium TA-100 by a reversion assay or in Salmonella typhimurium TM-677 in a forward mutation assay. Higher concentrations of histidine in corn grown in AAtrex treated soil may interfere with the reversion assay, but do not affect the forward mutation assay. The nature of the agent(s) responsible for the positive response was not determined. The mutagenicity may be due to natural plant constituents, an artifact of the sample preparation, or mycotoxins from some unrecognized plant infection. The experimental results in these field studies do not show that atrazine is degraded or metabolized by corn plants to mutagens in this sensitive bacterial assay.

Mutagenicity testing of two tropical plant materials with pesticidal potential in Salmonella typhimurium: Phytolacca dodecandra berries and oil from seeds of Azadirachta indica

In this study the mutagenic potential of two tropical plant materials was investigated in Salmonella typhimurium strains TA98 and TA100. The oil extract from seeds of Azadirachta indica showed no mutagenic activity in either strain with or without addition of metabolizing systems. When extracts of Phytolacca dodecandra berries were tested, only the butanol extract caused direct mutagenicity in TA98. After addition of rat liver homogenate, again only the butanol extract was positive in TA98. Addition of gut flora extract as metabolizing system generated positive effects in both the methanol extract and the butanol extract. The water extract showed only a slight positive effect, which can most probably be ascribed to the presence of histidine in the sample.