Mutagenic activity of urban air samples and its modulation by chili extracts

My career development with Ames test: A personal recollection

I first became acquainted with the Ames test at the very beginning of my career in 1978, when my task at the National Institute of Health Sciences (Tokyo) was to screen for mutagenicity of food additives used in Japan, using the Ames test. I also used this test to research the metabolic activation mechanisms of chemical carcinogens, in particular, the analgesic drug, phenacetin. This chemical was not mutagenic in Salmonella typhimurium TA100 with standard 9000 × g supernatant of liver homogenates (S9) from rat but was mutagenic with hamster S9. It was revealed that hamster S9 had much higher deacetylation activities than rat S9, which accounts for the species difference. Then, my work was focused on molecular biology. We cloned the genes encoding nitroreductase and acetyltransferase in Salmonella typhimurium TA1538. Plasmids carrying these genes made strain TA98 more sensitive to mutagenic nitroarenes and aromatic amines. Because of their high sensitivity, the resulting strains such as YG1021 and YG1024 are widely used to monitor mutagenic nitroarenes and aromatic amines in complex mixtures. Later, we disrupted the genes encoding DNA polymerases in TA1538 and classified chemical mutagens into four classes depending on their use of different DNA polymerases. I was also involved in the generation of gpt delta transgenic rodent gene mutation assays, which examine the results of the Ames test in vivo. I have unintentionally developed my career under the influence of Dr. Ames and I would like to acknowledge his remarkable achievements in the field of environmental mutagenesis and carcinogenesis.

Mutagenic and antimutagenic effects of Heterotheca inuloides

The antioxidant and hepatoprotective effects of Heterotheca inuloides have been reported before, nevertheless its use as a possible chemopreventive agent has not been documented. The aim of this study was to evaluate the mutagenic and antimutagenic activities of H. inuloides extracts using the Ames test. Both, the methanolic and acetonic extracts, were mutagenic in the TA98 but not in TA100 or TA102 strains. On the other hand, the methanolic extract reduced the mutagenicity of norfloxacin, benzo[a]pyrene and 2-aminoanthracene. Quercetin, one of the main components in the methanolic extract, also presented a mutagenic/antimutagenic dual effect and is an inhibitor of Cytochrome P450 (CYP) 1A. The antigenotoxic properties of H. inuloides could be due to the antioxidant properties previously reported and to its CYP inhibitory effect mediated by quercetin. Further studies with in vivo systems will afford information about H. inuloides beneficial and detrimental properties.

Interdisciplinary review for correlation between the plant origin capsaicinoids, non-steroidal antiinflammatory drugs, gastrointestinal mucosal damage and prevention in animals and human beings

BACKGROUND

The plant origin capsaicinoids (capsaicin, dihydrocapsaicin, norcapsaicin, dihydrocapsaicin, homocapsaicin, homodihydrocapsaicin) are well known and used as nutritional additive agents in the every day nutritional practice from the last 9,500 years; however, we had have a very little scientifically based knowledge on their chemistry, physiology and pharmacology in animal observations, and in humans up to the mid-twentieth century. Our knowledge about their chemistry, physiology, pharmacology entered to be scientifically based evidence from the year 1980, dominantly in animal observations. The human observations with capsaicin (capsaicinoids), in terms of good clinical practice, have been started only in the last 10-year period (from 1997) in randomized, prospective, multiclinical studies. The name of "capsaicin" used only in the physiological and pharmacological research both in animal experiments and in human observation. The "capsaicin" (as a "chemically" used natural compound) modifies the so-called capsaicin-sensitive afferent nerves depending on their applied doses.

AIMS

The specific action of capsaicin (capsaicinoids) on sensory afferent nerves modifying gastrointestinal (GI) function (under very specific conditions) offers a possibility for the production of an orally applicable drug or for other drug combinations, which can be used in the human medical therapy. The production of new drug is based on the critical interdisciplinary review of the results obtained with capsaicinoids.

MATERIALS AND METHODS

This paper gives an interdisciplinary and critical overview on the chemical, physiological, pharmacological and toxicological actions of the natural origin capsaicinoids (from the point of drug production) under conditions of acute, subacute and chronic administration in animal experiments and human observations, toxicology, pharmacokinetics). This interdisciplinary review covers the following main chapters: (1) physiological and pharmacological research tool by capsaicin in the animals and human beings, (2) capsaicin research in animals (including the acute, subacute toxicology and chronic toxicology metabolism, genotoxicology), (3) capsaicin observation with capsaicin in human beings.

CONCLUSION

(1) The capsaicin used in the physiological and pharmacological observations (in animals and human beings) chemically represents different chemical compounds, which can be obtained from the plants (paprika, chilli, etc.), (2) capsaicinoids are able to modify the capsaicin-sensitive afferent nerves, which have principle roles in the defence of different organs (including the gastrointestinal tract [against the different chemicals, heat, strech, chemical millieu-induced damage], (3) the application of capsaicin (capsaicinoids) can be repeated for the beneficial effects on the gastrointestinal tract as those in animal experiments. After this interdisciplinary and critical review, this paper demonstrates the well-planned research pathways of the discoveries of capsaicinoids from plant chemistry, via physiology, pharmacology and toxicology in animal experiments and human observations.

Evaluation of nitroreductase and acetyltransferase participation in N-nitrosodiethylamine genotoxicity

N-Nitroso compounds, such as N-nitrosodiethylamine (NDEA), are a versatile group of chemical carcinogens, being suspected to be involved in gastrointestinal tumors in humans. The intestinal microflora can modify a wide range of environmental chemicals either directly or in the course of enterohepatic circulation. Nitroreductases from bacteria seem to have a wide spectrum of substrates, as observed by the reduction of several nitroaromatic compounds, but their capacity to metabolize N-nitroso compounds has not been described. To elucidate the participation of nitroreductase or acetyltransferase enzymes in the mutagenic activity of NDEA, the bacterial (reverse) mutation test was carried out with the strains YG1021 (nitroreductase overexpression), YG1024 (acetyltransferase overexpression), TA98NR (nitroreductase deficient), and TA98DNP6 (acetyltrasferase deficient), and YG1041, which overexpresses both enzymes. The presence of high levels of acetyltransferase may generate toxic compounds that must be eliminated by cellular processes or can lead to cell death, and consequently decrease the mutagenic effect, as can be observed by the comparison of strain TA98DNP6 with the strains TA98 and YG1024. The slope curves for TA98 strain were 0.66 rev/microM (R(2) = 0.51) and 52.8 rev/microM (R(2) = 0.88), in the absence and presence of S9 mix, respectively. For YG1024 strain, the slope curve, in the presence of S9 mix was 6897 rev/microM (R(2) = 0.78). Our data suggest that N-nitroso compounds need to be initially metabolized by enzymes such as cytochromes P450 to induce mutagenicity. Nitroreductase stimulates toxicity, while acetyltransferase stimulates mutagenicity, and nitroreductase can neutralize the mechanism of mutagenicity generating innoccuos compounds, probably by acting on the product generated after NDEA activation.

The genotoxicity of ambient outdoor air, a review: Salmonella mutagenicity

Mutagens in urban air pollution come from anthropogenic sources (especially combustion sources) and are products of airborne chemical reactions. Bacterial mutation tests have been used for large, multi-site, and/or time series studies, for bioassay-directed fractionation studies, for identifying the presence of specific classes of mutagens, and for doing site- or source-comparisons for relative levels of airborne mutagens. Early research recognized that although carcinogenic PAHs were present in air samples they could not account for the majority of the mutagenic activity detected. The mutagenicity of airborne particulate organics is due to at least 500 identified compounds from varying chemical classes. Bioassay-directed fractionation studies for identifying toxicants are difficult to compare because they do not identify all of the mutagens present, and both the analytical and bioassay protocols vary from study to study. However, these studies show that the majority of mutagenicity is usually associated with moderately polar/highly polar classes of compounds that tend to contain nitroaromatic compounds, aromatic amines, and aromatic ketones. Smog chamber studies have shown that mutagenic aliphatic and aromatic nitrogen-containing compounds are produced in the atmosphere when organic compounds (even non-mutagenic compounds) are exposed to nitrogen oxides and sunlight. Reactions that occur in the atmosphere, therefore, can have a profound effect on the genotoxic burden of ambient air. This review illustrates that the mutagenesis protocol and tester strains should be selected based on the design and purpose of the study and that the correlation with animal cancer bioassay results depends upon chemical class. Future emphasis needs to be placed on volatile and semi-volatile genotoxicants, and on multi-national studies that identify, quantify, and apportion mutagenicity. Initial efforts at replacing the Salmonella assay for ambient air studies with some emerging technology should be initiated.

Antigenotoxic, antimutagenic and ROS scavenging activities of a Rhoeo discolor ethanolic crude extract

Rhoeo discolor is a legendary plant used for treatment of superficial mycoses in Mexican traditional medicine. Despite its extended use, it is not known whether it has side-effects. An ethanolic crude extract from Rhoeo discolor was prepared, its mutagenic capacity was investigated by the Ames test, and its genotoxic activity in primary liver cell cultures using the unscheduled DNA synthesis assay. This extract was not mutagenic when tested with Salmonella typhimurium strains TA97, TA98 and TA100, and it did not elicit unscheduled DNA synthesis in hepatocyte cultures. In addition, we explored the antimutagenic and antigenotoxic activities of the extract and its ROS scavenger behaviour. Our results show that Rhoeo extract is antimutagenic for S. typhimurium strain TA102 pretreated with ROS-generating mutagen norfloxacin in the Ames test, and protects liver cell cultures against diethylnitrosamine induction of unscheduled DNA synthesis even at 1.9 ng per dish, which was the lowest dose tested. A free radical scavenging test was used in order to explore the antioxidant capacity of Rhoeo extract, as compared with three commercial well-known antioxidants quercetin, ascorbic acid and tocopherol. Rhoeo extract showed less radical scavenging effect than quercetin, but similar to that of alpha-tocopherol and more than ascorbic acid. It is important to note that this extract was neither mutagenic in S. typhimurium nor genotoxic in liver cell culture, even at concentrations as high as four- and 166-fold of those needed for maximal antimutagenic or chemoprotective activities, respectively.

Antimutagenic properties of bell and black peppers

The wing Somatic Mutation And Recombination Test (SMART) in Drosophila melanogaster was used to study the modulating action of bell pepper (Capsicum annuum) and black pepper (Piper nigrum) in combination with the alkylating agent methyl methanesulfonate (MMS) and the promutagen agent ethyl carbamate (EC). Larvae trans-heterozygous for the third chromosome recessive markers multiple wing hairs (mwh) and flare-3 [flr(3)] were fed genotoxins alone or in combination with each of the two spices. Genetic changes induced in somatic cells of the wing's imaginal discs lead to the formation of mutant clones on the wing blade. Our results showed that bell pepper was effective in reducing the mutational events induced by EC and MMS and black pepper was only effective against EC. Pretreatment of 2-day-old larvae with the spices for 24 h followed by a treatment with EC and MMS was only effective in reducing mutations induced by EC. Suppression of metabolic activation or interaction with the active groups of mutagens could be mechanisms by which the spices exert their antimutagenic action.

Antimutagenesis of beta-carotene to mutations induced by quinolone on Salmonella typhimurium

BACKGROUND

Quinolone-induced mutagenesis in the Salmonella typhimurium hisG48 strains suggests that these antibiotics are oxygen free radical generators. The use of beta-carotene as antioxidant was evaluated as an alternative to reduce oxidative cell damage in patients who need therapy with nalidixic acid, norfloxacin, or pipemidic acid. The studied beta-carotene (30%), used by pharmaceutical laboratories as dietary complements, was not toxic or mutagenic for the S. typhimurium TA102 strain at a dose equivalent to 1,500 I.U. At the studied concentrations, the evaluated antimutagen did not modify the minimum inhibitory concentration of nalidixic acid, norfloxacin, or pipemidic acid against uropathogenic Escherichia coli strains.

METHODS

The mutagenic effect of nalidixic acid and norfloxacin against hisG48 strains was inhibited with 1500 I.U. of beta-carotene. The antimutagenic effect of beta-carotene against mutations induced by pipemidic acid was observed even with 150 I.U. of beta-carotene. The antimutagenic effect against mutations induced on S. typhimurium TA102 or TA104 strains was observed only when the aroclor 1254 rat-induced liver S9 mixture was used.

RESULTS

This mutagenic effect was detected only when the strains were exposed to quinolones and the beta-carotene simultaneously with the S9 mixture, suggesting that quinolones induce oxygen free radicals that may be scavenged by beta-carotene.

CONCLUSIONS

The antimutagenic effect of this vitamin A precursor is probably due to the active molecule of vitamin A, a desmutagen with the ability of radical capture. A diet rich in beta-carotene or vitamin A could be a good alternative to reduce genotoxic risk to patients being treated with quinolone.

Chemoprotective properties of some pungent ingredients present in red pepper and ginger

There has been a substantial body of data, supporting that dietary factors have a profound impact on prevention as well as etiology of human cancer. Capsaicin has been tested by many investigators for its effects on experimental carcinogenesis and mutagenesis. Data in the literature indicate that capsaicin has dual effects on carcinogenic and mutagenic processes. At present, there is no solid evidence that hot red and chili peppers or their principal pungent ingredient capsaicin are carcinogenic in humans although results of early investigations with experimental animals exhibit the moderate tumorigenicity of this compound. In contrast, recent studies reveal substantial antigenotoxic and anticarcinogenic effects of capsaicin, suggesting this compound as another important dietary phytochemical with a potential chemopreventive activity. Some pungent constituents present in ginger and other zingiberaceous plants have potent antioxidant and anti-inflammatory effects, and some of them exhibit anti-tumor promotional activity in experimental carcinogenesis.

Targeted disruption of the gene encoding the classical nitroreductase enzyme in Salmonella typhimurium Ames test strains TA1535 and TA1538

The gene encoding the 'classical nitroreductase' (CNR) of Salmonella typhimurium was disrupted. In this manner, cnr null mutant derivatives of strains TA1535 and TA1538 were constructed, and named YG7131 and YG7127, respectively. In both strain backgrounds, cnr gene disruption reduced nitrofurazone-reductase activity. This reduction almost completely eliminated the nitroreductase activity of strain TA1538. In contrast, the nitroreductase activity of strain TA1535 was much higher than that in TA1538. In this background, cnr gene disruption resulted in a reduction in nitroreductase activity by a similar absolute amount as in TA1538, but representing only about one-quarter of the original activity of TA1535. The results suggest that S. typhimurium has originally at least two distinct nitroreductases, one of which is already deficient in strain TA1538; the CNR is present in both TA1535 and TA1538. Also, these two strains (including their derivatives, TA98 and TA100) are not isogenic with regard to nitroreductase activity. After the introduction of plasmid pKM101, the sensitivities of the strains YG7132 and YG7128, the cnr-null mutants of TA98 and TA100, respectively, against several nitro compounds were compared with those of the conventional cnr-deficient strains TA98NR and TA100NR and the wild-type strains TA98 and TA100. The mutagenicities of 2-nitrofluorene and 1-nitropyrene in YG7132 or TA98NR were ten-fold lower than those of the compounds in TA98. Similarly, the mutagenicity of 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide in strain YG7128 or TA100NR was substantially lower than that of the compound in TA100. However, the mutagenicity of 2-nitronaphthalene in YG7128 was between those observed with TA100 and TA100NR, suggesting that a nitroreductase in S. typhimurium other than CNR is involved in the metabolic activation of this compound. The cnr gene of S. typhimurium positively hybridized with DNA at 13 min on the E. coli chromosome where the nfsB and nfnB genes of E. coli are mapped. These results suggest that the cnr gene of S. typhimurium is a counterpart of the nfsB and nfnB genes of E. coli, and that the newly constructed cnr-deletion strains are useful to assess the role of nitroreductases in the metabolic activation of mutagenic nitro compounds.

Inhibition of the mutagenicity of 2-nitrofluorene, 3-nitrofluoranthene and 1-nitropyrene by vitamins, porphyrins and related compounds, and vegetable and fruit juices and solvent extracts

When 21 vitamins including related compounds haemin, chlorophyllin, chlorophyll, biliverdin and bilirubin, as well as juices from five fruits and 25 vegetables and solvent extracts from the residues of fruits and vegetables were tested for their antimutagenic potencies with respect to mutagenicity induced by 2-nitrofluorene (2-NF), 3-nitrofluoranthene (3-NFA) and 1-nitropyrene(1-NP) in Salmonella typhimurium TA98 the following results were obtained. The tetracyclic nitroarenes 3-NFA and 1-NP were in general more effectively antagonized by potent antimutagenic compounds than the tricyclic 2-NF. beta-Carotene, retinol, retinal, retinoic acid, retinol palmitate, riboflavin 5'-phosphate, alpha-tocopherol, vitamins B12, C, K1 and K3 as well as biliverdin, bilirubin, chlorophyll, chlorophyllin and haemin exerted antimutagenicity against the nitroarenes cited previously. All other vitamins were inactive. While part of the juices were inactive, juices from cauliflower, carrots, chives, radishes and spinach exerted weak antimutagenic activities. However, weak to moderate co-mutagenic effects were seen with grapes, kiwi, pineapple, eggplant, celeriac, chicory greens, fennel leaves and radishes and strong effects with peppers which were not caused by the presence of growth-promoting factors. Most solvent fractions were inactive but fractions containing chlorophyll exerted antimutagenicity.

Chemopreventive activity of chlorophyllin against mouse skin carcinogenesis by benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide

Chlorophyllin (CHL), the sodium and copper salt of chlorophyll, was tested for its chemopreventive activity against tumorigenesis induced by benzo[a]pyrene (B[a]P) and its ultimate electrophilic and carcinogenic metabolite, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide(BPDE). Administration of CHL (15 mg/kg body wt) by gavage to female ICR mice 30 min prior to a topical application of B[a]P or BPDE resulted in significant reduction in both incidence and multiplicity of skin tumors initiated by these carcinogens. CHL was rapidly distributed in the skin and other tissues of mice after oral administration. Taken together, these results suggest that CHL is a potential chemopreventive agent.

Natural antimutagenic agents

Following a brief review of recent discoveries in the field of natural antimutagenic and tumor chemopreventive agents, contemporary findings in the author's laboratories employing the direct acting mutagen, ethyl methanesulfonate, in modified Ames tests and eukaryotic murine FM3A mammary tumor cells modified to be subject to thymidine-less death are described to illustrate the underlying principles. The EMS studies are illustrated with the isolation of the novel antimutagen, plicatin B, from the medicinal plants, Psoralea juncaea and P. plicata. The FM3A studies are carried out with extracts of Styrax asiatica, a plant previously studied extensively with the EMS system. The FM3A findings closely parallel the earlier work with EMS showing that the responsible agents, cinnamic acid, cinnamoyl ricinoleate and cinnamoyl cinnamate are effective both in prokaryotic and eukaryotic tests and that the new FM3A assay system has useful properties for screening and assay of novel antimutagenic agents.

Chemoprotective properties of chlorophyllin against vinyl carbamate, p-nitrophenyl vinyl ether and their electrophilic epoxides

Chlorophyllin (CHL), a water-soluble sodium and copper derivative of chlorophyll, has been shown to be a strong antimutagen in several test systems, but its mechanism of antimutagenic action is largely unknown. In the present study, we have found the protective properties of CHL against vinyl carbamate, p-nitrophenyl vinyl ether and their electrophilic epoxides. CHL exhibited dose-related inhibition of his+ reversion in Salmonella typhimurium TA 1535 induced by these mutagens. Formation of DNA adducts from vinyl carbamate epoxide (VCO) and 2'-(4-nitrophenoxy)oxirane (NPO) was also markedly attenuated in the presence of CHL. Oral administration of CHL prior to the topical application of each of the above carcinogens resulted in significant reduction in both incidence and multiplicity of skin tumors in mice. The effective protection by CHL against VCO and NPO suggest that its formation of inactive complexes with these carcinogens is mediated by mechanisms other than pi-pi interactions.

Capsaicin, a double-edged sword: toxicity, metabolism, and chemopreventive potential

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is a primary pungent and irritating principle present in chilies and red peppers which are widely used as spices. Because of its selective effects on the functions of a defined subpopulation of sensory neurons, capsaicin is currently used as a versatile tool for the study of pain mechanisms and also for pharmacotherapy to treat several pain disorders. Considering the frequent consumption of capsaicin as a food additive and its current medicinal use, correct assessment of hazardous effects of this compound is important. Mutagenic and carcinogenic activities of capsaicin and chili extracts have been studied, but results are conflicting. Mammalian metabolism of capsaicin has been also reported. Capsaicin appears to interact with xenobiotic metabolizing enzymes, particularly microsomal cytochrome P450-dependent monooxygenases which are involved in activation as well as detoxification of various chemical carcinogens and mutagens. Recent studies have shown that hepatic cytochrome P450 2E1 catalyzes the conversion of capsaicin to reactive species such as the phenoxy radical intermediate capable of covalently binding to the active site of the enzyme as well as tissue macromolecules. While covalent modification of protein and nucleic acids leads to toxicity including necrosis, mutagenesis, and carcinogenesis, suicidal inhibition of microsomal cytochrome P450 may prohibit further activation of capsaicin and also of other toxic xenobiotics. Results from recent studies indicate that capsaicin possesses the chemoprotective activity against some chemical carcinogens and mutagens.