Genotoxicity and the stability of N-nitrosomorpholine activity following UVA irradiation

This study investigated N-nitrosomorpholine (NMOR) genotoxicity following UVA irradiation without metabolic activation. Following UVA irradiation, the photo treated NMOR (irradiated NMOR) was directly mutagenic, without UVA or metabolic activation, in the Ames test. The activity was relatively stable, and approximately 79% of the activity remained after 10 days of storage at 37 °C, 4 °C, or -20 °C. Micronuclei (MN) formation was observed in HaCaT cells after treatment with irradiated NMOR without metabolic activation. The action spectrum of MN formation in response to NMOR irradiation followed the NMOR absorption curve. In vivo, MN formation was observed in the peripheral blood reticulocytes of mice injected with irradiated NMOR under the inhibition of cytochrome P450-mediated metabolism of NMOR. Volatile NMOR may attach to environmental materials and be irradiated with environmental UVA light. Photoactivated NMOR-attached air pollutants could float in the air and fall onto the human body, leading to genotoxicity induced by the irradiated NMOR.

Chemo-preventive effects and antitumorigenic mechanisms of beer and nonalcoholic beer toward 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) - induced lung tumorigenesis in A/J mice

We investigated the chemopreventive effects of beer, nonalcoholic beers (NABs), and beer-components (glycine betaine (GB)) on NNK-induced lung tumorigenesis in A/J mice, and the possible mechanisms underlying the antitumorigenic effects of beer, NABs, and beer-components. Beer, NABs, and GB reduced NNK-induced lung tumorigenesis. We investigated the antimutagenicity of beer, NABs and beer-components (GB and pseudouridine (PU)) toward the mutagenicity of 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Beer, NABs, and beer components were antimutagenic toward MNNG and NNK in the Ames test using S. typhimurium TA1535. In contrast, MNNG and NNK mutagenicity detected in S. typhimurium YG7108, a strain lacking O⁶-methylguanine DNA methyltransferases (ogt_ST and ada_ST) did not decrease in the presence of beer, NABs, or beer components, suggesting that they may mediate its antimutagenic effect by enhancing DNA damage repair. Phosphorylation of Akt and STAT3, with or without epidermal growth factor stimulation, in lung epithelial-like A549 cells were significantly decreased following beer, NABs, GB and PU. They targeted both the initiation and growth/progression steps of carcinogenesis, specifically via antimutagenesis, stimulation of alkyl DNA-adduct repair, and suppression of Akt- and STAT3- mediated growth signaling. GB and PU may contribute, in part, to the biological effects of beer and NABs via the suppression of Akt and STAT3 phosphorylation.

Chemopreventive effects and anti-tumorigenic mechanisms of Actinidia arguta, known as sarunashi in Japan toward 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)- induced lung tumorigenesis in a/J mouse

BACKGROUND

Previously, we reported the inhibitory effect of Actinidia arguta juice, known as sarunashi juice (sar-j) in Japan, on mutagenesis, inflammation, and mouse skin tumorigenesis. The components of A. arguta responsible for the anti-mutagenic effects were identified to be water-soluble, heat-labile phenolic compounds. We proposed isoquercetin (isoQ) as a candidate anticarcinogenic component. In this study, we sought to investigate the chemopreventive effects of A. arguta juice and isoQ on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in A/J mice, and identify the possible mechanisms underlying the anti-tumorigenic effects of A. arguta.

RESULTS

The number of tumor nodules per mouse lung in the group injected with NNK and administered A. arguta juice orally was significantly lower than that in the group injected with NNK only. Oral administration of isoQ also reduced the number of nodules in the mouse lungs. As expected, the mutagenicity of NNK and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) detected using S. typhimurium TA1535 decreased in the presence of sar-j. However, NNK and MNNG mutagenicity detected using S. typhimurium YG7108, a strain lacking the O⁶-methylguanine DNA methyltransferases (ogt_ST and ada_ST) did not decrease in the presence of sar-j suggesting that sar-j may mediate its antimutagenic effect by enhancing the DNA damage repair by ogt_ST and ada_ST. Phosphorylation of Akt, with or without epidermal growth factor stimulation, in A549 cells was significantly decreased following sar-j and isoQ treatment, indicating that components in sar-j including isoQ suppressed the PI3K/AKT signaling pathways.

CONCLUSIONS

Sar-j and isoQ reduced NNK-induced lung tumorigenesis. Sar-j targets both the initiation and growth/progression steps during carcinogenesis, specifically via anti-mutagenesis, stimulation of alkyl DNA adduct repair, and suppression of Akt-mediated growth signaling. IsoQ might contribute in part to the biological effects of sar-j via suppression of Akt phosphorylation, but it may not be the main active ingredient.

Antimutagenic, anti-inflammatory, and antioxidative activities of the juice of Vitis ficifolia var. Ganebu, a woody vine in the grape family, known as Ryukyu-ganebu in Japan

Background

Mutation, inflammation, and oxidative damage including lipid-peroxidation are factors involved in the development of cancer. We investigated the antimutagenic, in vivo and in vitro anti-inflammatory, and antioxidative effects of the juice of Vitis ficifolia var. ganebu (known as Ryukyu-ganebu in Japan) harvested in Kuchinoshima island (hereafter, the juice is referred to as ganebu-K) in comparison with the juice of Vitis coignetiae (crimson glory vine, known as yamabudo in Japan; hereafter, the juice is referred to as yamabudo) which we found antimutagenic and anti-inflammatory effects.

Results

Ganebu-K inhibited the mutagenic activity of several carcinogens, MeIQx, IQ, Trp-P-2(NHOH), and MNNG, model compounds of tumor initiation. Using S. typhimurium YG7108, a strain lacking O⁶-methylguanine DNA methyltransferases, ganebu-K showed no significant inhibition of the mutagenicity of MNNG. Thus, DNA repair of O⁶-methylguanine produced by MNNG might be an antimutagenic target of the components in ganebu-K. Topical application of ganebu-K to the dorsal sides of mice resulted in potent suppression of acute edema induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Ganebu-K, but not yamabudo, exhibited significant inhibition of the induction of prostaglandin E₂ (PGE2) induced by TPA. Components contained in ganebu-K, but not in yamabudo, might be responsible for the inhibition of the induction of PGE2. Ganebu-K inhibited in vivo lipid peroxidation and decreased the level of glutamic oxaloacetic transaminase induced by CCL₄ treatment.

Conclusions

These results suggest that the active components in ganebu-K juice are not the same as those in yamabudo, and the components in ganebu-K are attractive candidates as chemopreventive agents.

Chemopreventive effects and anti-tumorigenic mechanisms of 2,6-dimethoxy-1,4-benzoquinone, a constituent of Vitis coignetiae Pulliat (crimson glory vine, known as yamabudo in Japan), toward 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in A/J mice

Previously, we isolated and identified anti-mutagenic and anti-inflammatory components from Vitis coignetiae (crimson glory vine, known as yamabudo in Japan) as 2,6-dimethoxy-1,4-benzoquinone (DBQ), fertaric acid and caftaric acid. We also reported that the oral intake of a partially purified fraction from yamabudo juice (yamabudo-fr) or DBQ affords significant protection against two-stage skin carcinogenesis in mice. In this study, we found that oral intake of yamabudo-fr or DBQ affords significant protection against a tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced mouse model of lung tumorigenesis. Furthermore, we investigated the anti-tumorigenic mechanisms of yamabudo juice and DBQ. NNK is known to be a DNA-methylating and alkylating agent; thus, we investigated the anti-tumorigenic mechanisms of yamabudo juice and DBQ in relation to DNA methylation. Pretreatment with yamabudo-fr or DBQ dose-dependently decreased formation of O⁶-methylguanine and N⁷-methylguanine in DNA of the A549 human lung epithelial-like cell line treated with a methylating agent, 1-methyl-3-nitro-1-nitrosoguanidine. Yamabudo juice and DBQ inhibited the mutagenicity of NNK in the Ames test using Salmonella typhimurium TA1535 but not S. typhimurium YG7108, an alkylguanine DNA alkyltransferase-deficient strain (same as TA1535 but Δada_st::Km^r, Δogt_st::Cm^r). Yamabudo juice and DBQ might accelerate the repair of DNA damage caused by NNK and reduce DNA damage to cells. We also investigated the effects of yamabudo juice and DBQ on signaling pathways in A549 cells. With or without epidermal growth factor stimulation, phosphorylation of Erk1/2, Akt and Stat3 in A549 cells was significantly decreased in the presence of yamabudo juice or DBQ, indicating that yamabudo juice and DBQ suppressed PI3K/AKT, MAPK/ERK and JAK/STAT3 signaling pathways. These results suggest that both initiation and growth/progression steps in carcinogenesis, especially anti-oxidant effects, stimulation of repair of alkyl DNA adducts and suppressed growth signaling pathways are potential anti-tumorigenic targets of yamabudo juice and DBQ in NNK-induced lung tumorigenesis.

Protective effect of Actinidia arguta in MPTP-induced Parkinson's disease model mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra. Oxidative stress-induced neuronal death has been identified as one of the major causes of nigrostriatal degeneration in PD. The fruit of Actinidia arguta (A. arguta), known as sarunashi in Japan, has been reported to show beneficial health effects such as antioxidant, anti-inflammatory, anti-mutagenic, and anticholinergic effects. In this study, we investigated the neuroprotective effects of A. arguta in 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine (MPTP)-induced PD model mice. A. arguta juice was administered to 7-week-old C57BL/6J mice continuously for 10 days before the first MPTP injection. The degeneration of dopaminergic neurons in the substantia nigra was induced by MPTP (30 mg/kg, i. p.) once daily for five consecutive days. We found that the administration of A. arguta ameliorated MPTP-induced motor impairment and suppressed the MPTP-induced reductions of tyrosine hydroxylase-positive neurons and tyrosine hydroxylase protein expression in the substantia nigra. Our findings suggest that taking A. arguta could provide neuroprotection that delays or prevents the neurodegenerative process of PD.

Mismatch repair systems might facilitate the chromosomal recombination induced by N-nitrosodimethylamine, but not by N-nitrosodiethylamine, in Drosophila

Mismatch repair (MMR) systems play important roles in maintaining the high fidelity of genomic DNA. It is well documented that a lack of MMR increases the mutation rate, including base exchanges and small insertion/deletion loops; however, it is unknown whether MMR deficiency affects the frequency of chromosomal recombination in somatic cells. To investigate the effects of MMR on chromosomal recombination, we used the Drosophila wing-spot test, which efficiently detects chromosomal recombination. We prepared MMR (MutS)-deficient flies (spel1(-/-)) using a fly line generated in this study. The spontaneous mutation rate as measured by the wing-spot test was slightly higher in MutS-deficient flies than in wild-type (spel1(+/-)) flies. Previously, we showed that N-nitrosodimethylamine (NDMA)-induced chromosomal recombination more frequently than N-nitrosodiethylamine (NDEA) in Drosophila. When the wing-spot test was performed using MMR-deficient flies, unexpectedly, the rate of NDMA-induced mutation was significantly lower in spel1(-/-) flies than in spel1(+/-) flies. In contrast, the rate of mutation induced by NDEA was higher in spel1(-/-) flies than in spel1(+/-) flies. These results suggest that in Drosophila, the MutS homologue protein recognises methylated DNA lesions more efficiently than ethylated ones, and that MMR might facilitate mutational chromosomal recombination due to DNA double-strand breaks via the futile cycle induced by MutS recognition of methylated lesions.

Increase of somatic cell mutations in oxidative damage-sensitive drosophila

Background

Oxidative damage is an important genotoxic source for almost all organisms. To efficiently detect mutations induced by oxidative damage, we previously developed a urate-null Drosophila strain. Using this Drosophila strain, we showed the mutagenic activity of environmental cigarette smoke (ECS) and the herbicide paraquat, which are known to produce reactive oxygen species (ROS). In the present study, we examined the mutagenic activities of carcinogenic mutagens that are considered to cause mutations by adduct formation, alkylation, or crosslinking of cellular DNA in the oxidative damage-sensitive Drosophila to evaluate how the oxidative damage induced by these mutagens is involved in causing mutations. In addition, we evaluated whether these oxidative damage-sensitive flies may be useful for mutation assays.

Methods

We performed the wing-spot test in oxidative damage-sensitive Drosophila (urate-null strains) to examine the mutagenicity of 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx), mitomycin C (MMC), 4-nitroquinoline N-oxide (4NQO), N-nitrosodimethyl-amine (NDMA), and N-nitrosodiethylamine (NDEA). We also observed the mutagenicity of X-ray irradiation as a control in which mutations should be mainly caused by oxidative damage.

Results

As expected, the mutagenic activity of X-ray irradiation was higher in the urate-null Drosophila than in the wild-type Drosophila. The mutagenic activities of the tested compounds were also higher in the urate-null Drosophila than in the wild-type Drosophila. In experiments using another urate-null strain, the mutagenicity of N-nitrosodialkylamines was also higher in the urate-null flies than in the wild-type ones.

Conclusions

The tested compounds in this study were more mutagenic in urate-null Drosophila than in wild-type Drosophila. It was supposed that ROS were generated and that the ROS might be involved in mutagenesis. The present results support the notion that in addition to causing DNA lesions via adduct formation, alkylation, or DNA crosslinking, these mutagens also cause mutations via ROS-induced DNA damage. As such, urate-null Drosophila appear to be useful for detecting the mutagenic activity of various mutagens, especially those that produce reactive oxygen. If the mutation rate increases on a mutation assay using urate-null Drosophila, it might suggest that the mutagen generates ROS, and that the produced ROS is involved in causing mutations.

Mutation spectrum resulting in M13mp2 phage DNA exposed to N-nitrosoproline with UVA irradiation

N-nitrosoproline (NPRO) is endogenously formed from proline and nitrite. In an effort to delineate the mechanism of NPRO-induced photomutagenicity, we investigated the mutagenic spectrum of NPRO on M13mp2 DNA with UVA irradiation. Following exposure to NPRO and UVA, the mutation frequency increased significantly in an NPRO and UVA dose-dependent manner. The sequence data derived from seventy of the mutants indicated that mutagenesis resulted mainly from an increase in single-base substitutions, the most frequent being GC to CG transversions. Non-clustering of the GC to CG mutations suggests that NPRO+UVA damage to DNA is random. These transversions may be caused by guanine adducts in DNA or in part by oxidatively modified guanine in DNA exposed to NPRO and UVA.

Inhibitory effect of Actinidia arguta on mutagenesis, inflammation and two-stage mouse skin tumorigenesis

Background

Actinidia arguta, known as sarunashi in Japan, is a vine tree native to east-Asia, including Japan, that produces small fruit rich in anthocyanins, catechins, vitamin C, chlorophyll, beta-carotene and other polyphenols.

Results

Our study revealed the inhibitory effect of the juice of A. arguta (arguta-juice) toward the mutagenicity of food-derived carcinogens and polycyclic aromatic hydrocarbons using the Ames test, and antioxidant activity of arguta-juice as determined using a free radical scavenging assay. The formation of DNA adducts in liver of mice fed 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) decreased significantly following administration of arguta-juice. The preventive effect of arguta-juice on the induction of inflammation of mouse ear by 12-O-tetradecanoylphorbol-13-acetate (TPA) was revealed. The anti-carcinogenic effect of a topically applied partially purified fraction of A. arguta was revealed on skin tumorigenesis in mice induced by treatment with 7,12-dimethylbenz(a)anthracene and TPA. In an effort to reveal the mechanisms for antimutagenicity of arguta-juice, effects on the enzymes that metabolize xenobiotics were examined. Combined effects comprising i) inhibition of the metabolic activation of mutagens with phase I enzymes, but ii) no prevention on the activity of phase II detoxification enzyme, UGT, were observed. We also investigated the characterization and partial purification of the antimutagenic components in A. arguta, which suggested that the components in A. arguta responsible for the antimutagenicity were water-soluble, heat-labile phenolic compounds.

Conclusions

These results suggested that components in A. arguta are attractive candidates for potential use as chemopreventive agents.

Somatic-cell mutation induced by short exposures to cigarette smoke in urate-null, oxidative stress-sensitive Drosophila

We previously reported that a urate-null strain of Drosophila is hypersensitive to cigarette smoke (CS), and we suggested that CS induces oxidative stress in Drosophila because uric acid is a potent antioxidant. Although the carcinogenic risk of CS exposure is widely recognized; documentation of in vivo genotoxic activity of environmental CS, especially gaseous-phase CS, remains inconclusive. To date, somatic-cell mutations in Drosophila resulting from exposure to CS have not been detected via the somatic mutation and recombination test (wing spot test) with wild-type flies, a widely used Drosophila assay for the detection of somatic-cell mutation; moreover, genotoxicity has not been documented via a DNA repair test that involves DNA repair-deficient Drosophila. In this study, we used a new Drosophila strain (y v ma-l; mwh) to examine the mutagenicity induced by gaseous-phase CS; these flies are urate-null due to a mutation in ma-l, and they are heterozygous for multiple wing hair (mwh), a mutation that functions as a marker for somatic-cell mutation. In an assay with this newly developed strain, a superoxide anion-producing weed-killer, paraquat, exhibited significant mutagenicity; in contrast, paraquat was hardly mutagenic with a wild-type strain. Drosophila larvae were exposed to CS for 2, 4 or 6h, and then kept at 25°C on instant medium until adulthood. After eclosion, mutant spots, which consisted of mutant hairs on wings, were scored. The number of mutant spots increased significantly in an exposure time-dependent manner in the urate-null females (ma-l (-/-)), but not in the urate-positive females (ma-l (+/-)). In this study, we showed that short-term exposure to CS was mutagenic in this in vivo system. In addition, we obtained suggestive data regarding reactive oxygen species production in larva after CS exposure using the fluorescence probe H2DCFDA. These results suggest that oxidative damage, which might be countered by uric acid, was partly responsible for induction of somatic cell mutations in Drosophila larvae exposed to CS.

RXR partial agonist produced by side chain repositioning of alkoxy RXR full agonist retains antitype 2 diabetes activity without the adverse effects

We previously reported RXR partial agonist CBt-PMN (1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-1H-benzotriazole-5-carboxylic acid: 5, EC50 = 143 nM, Emax = 75%), which showed a potent glucose-lowering effect without causing serious adverse effects. However, it remains important to elucidate the structural requirements for RXR efficacy and the glucose-lowering effect because RXR-permissive heterodimers such as PPAR/RXR or LXR/RXR are reported to be activated differently depending upon the chemical structure of RXR agonists. In this work, we show that an RXR partial agonist, NEt-4IB (6-[ethyl-(4-isobutoxy-3-isopropylphenyl)amino]pyridine-3-carboxylic acid: 8b, EC50 = 169 nM, Emax = 55%), can be obtained simply by repositioning the side chains (interchanging the isobutoxy and isopropoxy groups) at the hydrophobic moiety of the RXR full agonist NEt-3IB (6-[ethyl-(3-isobutoxy-4-isopropylphenyl)amino]pyridine-3-carboxylic acid: 7b, EC50 = 19 nM). NEt-4IB (8b) showed antitype 2 diabetes activity without the above side effects upon repeated oral administration to mice at 10 mg/kg/day, similarly to 5.

Chemopreventive effects of the juice of Vitis coignetiae Pulliat on two-stage mouse skin carcinogenesis

Our study revealed the inhibitory effect of Vitis coignetiae Pulliat, known as Yamabudo in Japan, at the stages of multi-step carcinogenesis. The juice of Vitis coignetiae (Y-grape juice) was antimutagenic toward dimethylbenzo[a]anthracene (DMBA), aflatoxin B1, and benzo[a]pyrene in the Ames test. The Y-grape juice was also antigenotoxic in the micronucleus test using HepG2 cells toward DMBA and aflatoxin B1. Topical and oral administration of the Y-grape juice to mice inhibited the induction of inflammation of 12-O-tetradecanoylphorbol-13-acetate (TPA). Topical and oral administration of the Y-grape juice significantly decreased the incidence and mean number of tumors in mice skin with the 2-stage tumorigenesis protocol. To elucidate the mechanisms underlying the antiinflammatory and antitumor promotion activity of the Y-grape juice, the effect of Y-grape juice on cyclooxygenase-2 (COX-2) activity in mouse ear treated with TPA was studied. Both topical and oral application of the Y-grape juice inhibited the TPA-induced increase in COX-2 activity. Caftaric acid, isolated and identified from the Y-grape juice, was antimutagenic toward DMBA and prevented TPA-induced inflammation in mice, suggesting caftaric acid participates in chemopreventive effect/activities of Y-grape juice.

UVA activation of N-dialkylnitrosamines releasing nitric oxide, producing strand breaks as well as oxidative damages in DNA, and inducing mutations in the Ames test

We investigated the photo-mutagenicity and photo-genotoxicity of N-dialkylnitrosamines and its mechanisms of UVA activation. With simultaneous irradiation of UVA, photo-mutagenicity of seven N-dialkylnitrosamines was observed in Ames bacteria (Salmonella typhimurium TA1535) in the absence of metabolic activation. Mutagenicity of pre-irradiated N-dialkylnitrosamines was also observed with S. typhimurium hisG46, TA100, TA102 and YG7108 in the absence of metabolic activation. UVA-mediated mutation with N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) decreased by adding either the NO or OH radical scavenger. When superhelical DNA was irradiated with N-dialkylnitrosamines, nicked circular DNA appeared. Ten N-dialkylnitrosamines examined produced strand breaks in the treated DNA in the presence of UVA. The level of single-strand breaks in phiX174 DNA mediated by N-nitrosomorpholine (NMOR) and UVA decreased by adding either a radical scavenger or superoxide dismutase. When calf thymus DNA was treated with N-dialkylnitrosamines (NDMA, NDEA, NMOR, N-nitrosopyrrolidine (NPYR) and N-nitrosopiperidine (NPIP)) and UVA, the ratio of 8-oxodG/dG in the DNA increased. Action spectra were obtained to determine if nitrosamine acts as a sensitizer of UVA. Both mutation frequency and NO formation were highest at the absorption maximum of nitrosamines, approximately 340 nm. The plots of NO formation and mutation frequency align with the absorption curve of NPYR, NMOR and NDMA. A significant linear correlation between the optical density of N-dialkynitrosamines at 340 nm and NO formation in each irradiated solution was revealed by ANOVA. We would like to propose the hypothesis that the N-nitroso moiety of N-dialkylnitrosamines absorbs UVA photons, UVA-photolysis of N-dialkylnitrosamines brings release of nitric oxide, and subsequent production of alkyl radical cations and active oxygen species follow as secondary events, which cause DNA strand breaks, oxidative and alkylative DNA damages and mutation.

A possible photosensitizer: Tobacco-specific nitrosamine, 4-(N-methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), induced mutations, DNA strand breaks and oxidative and methylative damage with UVA

We discovered the directly acting mutagenicity of the tobacco-specific nitrosamine, 4-(N-methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), with UVA light (320-400nm) in Ames bacteria and phage M13mp2 in the absence of metabolic activation. We have investigated the spectrum of mutations caused by UVA-activated NNK. The majority (57%) of induced sequence changes were comprised of GC to CG, GC to TA and GC to AT. This suggested that modification of guanine residues was responsible for these mutations. Hence, we explored the formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) and O(6)-methylguanine (O(6)meG) in the DNA. When calf thymus DNA was treated with NNK and UVA, the amount of 8-oxodG/dG and O(6)meG/G in the DNA increased up to 20-fold and 100-fold, respectively, compared with the untreated control. DNA strand breaks were observed following NNK and UVA treatment, and the strand breaks were suppressed in the presence of scavengers for oxygen and NO radical. The formation of NO was also observed in NNK solutions irradiated with UVA. We analyzed the photodynamic spectrum of mutation induction, 8-oxodG formation and NO formation using monochromatic radiation. The patterns of the action spectra were comparable to the absorption spectrum of NNK. We conclude that NNK may act as a photosensitizer in response to UVA to produce NO and other oxidative and alkylative intermediates following the formation of 8-oxodG and O(6)meG in DNA, which may lead to mutations and DNA strand breaks.

Cleavage specificity of the serine protease ofAeromonas sobria, a member of the kexin family of subtilases

Subtilisin-like proteases have been grouped into six families based on a sequence of the catalytic domain. One of the six is the kexin family, of which furin is a representative protease. All members of the kexin family, except one, are from eukaryotes. The one prokaryotic protease is a serine protease of Aeromonas sorbria (ASP). Here, we examined the substrate specificity of ASP based on the cleavage of short peptides. The results showed that ASP preferentially cleaves the peptide bond following two basic residues, one of which is Lys, but not the bond following a single basic residue. This indicates that the tertiary structure around the catalytic domain of ASP resembles, but is not identical to that of furin. Prekallikrein was cleaved into four fragments by ASP, indicating that the protein must be cleaved at specific sequences.

Inhibitory effects of beer on mutation in the Ames test and DNA adduct formation in mouse organs induced by 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

An evaluation of the antigenotoxic potential of beer components against carcinogens contained in the human diet, namely heterocyclic amines (HCAs) including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), was determined. The protective mechanism involved was also investigated. Beer samples were found to inhibit the mutagenicity of HCAs in the Ames test. Beer solution, consisting of a freeze-dried and dissolved sample, given as drink-water significantly reduced the formation of PhIP-DNA adducts in mouse colon and lung compared to control mice fed with PhIP in the absence of beer solution. Furthermore, beer solution added in the diet as a food additive mimic significantly reduced the amount of DNA adducts present in the liver and lung of mice fed with PhIP. In an effort to investigate the mechanism responsible for the observed protective effect, the effect of beer solutions on HCA metabolizing enzymes was investigated. Beer solutions inhibited the activity of CYP1A1 and CYP1A2, as determined from deethylation and demethylation assays using 7-ethoxy- and 7-methoxyresolufin, respectively. Considering the overall suppression of PhIP genotoxicity by beer, this study confirmed that beer components can interfere with the enzyme activity involved in the metabolism of HCAs and subsequently suppress the observed genotoxicity. The results of this study showed that beer components act in a protective capacity against the genotoxic effects of heterocyclic amines in vivo.

Characterization of adducts formed in the reaction of 2-chloro-4-methylthiobutanoic acid with 2'-deoxyguanosine

2-chloro-4-methylthiobutanoic acid (CMBA) is a direct-acting mutagen found in salt-nitrite-treated Sanma fish or similarly treated methionine solution. In this study, CMBA was reacted with 2'-deoxyguanosine (dG) in phosphate buffer (pH 7.4) at 37 degrees C. The HPLC-UV analysis showed that two products were mainly formed during the reaction. These were isolated, purified by semipreparative HPLC, and characterized as N7-guanine adducts: N7-(3-carboxy-3-methylthiopropyl)guanine (A1) and N7-(1-carboxy-3-methylthiopropyl)guanine (A2). Furthermore, liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) analysis was employed to investigate the possible formation of minor products during the time-course of the reaction of CMBA with dG. It was found that N7-dG adducts, the precursors of A1 and A2, were formed early in the reaction and that subsequently the spontaneous depurination occurred to yield stable N7-guanine adducts A1 and A2. Stability studies in phosphate buffer (pH 7.4) at 37 degrees C showed that the amount of each N7-dG adduct decreased rapidly with a half-life of 6 h and 4 h to yield A1/A2, respectively. A regioisomer of N7-dG adducts was also observed in the LC/ESI-MS/MS analysis, but it was not characterized in detail because it was present only in trace amounts. On the basis of structural features, A1 and A2 seemed to be formed from the reaction of dG with 1-methyl-2-thietaniumcarboxylic acid, an intermediate resulting from the cyclization of CMBA. However, A2 might also have formed from the direct reaction of dG and CMBA. N7-Alkylation of the guanine residue and subsequent depurination are known to produce apurinic sites in DNA that induce point mutations and may be responsible for the observed CMBA-induced mutagenesis.

Inhibition of PhIP-induced mammary carcinogenesis in female rats by ingestion of freeze-dried beer

This study evaluated the modulating effect of non-alcoholic constituents of beer on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mammary carcinogenesis. Female Sprague-Dawley (SD) rats at 6 weeks of age were divided into four groups (n=26-30) and fed either a high fat diet or high fat diets containing 1, 2 or 4% freeze-dried beer (FD beer). One week after the start of feeding, rats received PhIP at a dose of 85 mg/kg by gavage four times weekly for 2 weeks. There were no differences in the body weights or diet intakes of rats between the control and the experimental groups. Weekly observation of palpable tumors indicated that tumor incidence and tumor multiplicity in the 2 and 4% FD beer groups were lower than in the control group throughout the experiment. Neoplastic lesions were pathologically examined at the end of the 22-weeks experiment. Tumor development was inhibited by FD beer intake in a dose-dependent manner. Tumor incidence (38.5%) and tumor multiplicity (0.8+/-0.4) for the group fed with a diet containing 4% FD were significantly reduced as compared with the control group (73.3% and 1.8+/-0.7). Supplementation with FD beer for 3 weeks together with the PhIP treatments resulted in increased liver GST activity, decreased liver CYP1A2 activity and a decrease in the number of DNA adducts in the mammary tissue, though these values were not significant. In conclusion, our results suggest that intake of FD beer may reduce the risk of carcinogenesis caused by heterocyclic amines.

Evaluation of photo-mutagenicity and photo-cytotoxicity of food coloring agents

Pigments extracted from natural products are widely used for food coloration in Japan. An investigation concerning the photo-mutagenicity and photo-carcinogenicity of frequently used colorants in Japan was performed. Colorants examined were from Laccifer lacca (lac-color), Coccus cacti (cochineal-color), Carthamus tinctorius (carthamus yellow), Gardenia augusta (gardenia yellow and gardenia blue), Monascus anka and Monascus purpureus (monascus red), the skin of Vitis vinifera and Vitis labrusca (grape-skin color), Tamarindus indica (tamarind brown) and Beta vulgaris (beet red). No significant increase in bacterial mutation was found when Salmonella typhimurium TA98, TA100 and TA102 were simultaneously treated with colorants and subjected to UVA irradiation for 30 min. When colorant solutions were subjected to UVA irradiation for 4 h, irradiated solutions containing lac-color became slightly mutagenic toward S.typhimurium TA98 without metabolic activation. A decrease in cell survival resulted when WTK-1 cells were subjected to UVA irradiation for 60 min in the presence of purpurin at 1 mg/ml. Delayed cytotoxicity was also observed following 24 h incubation in fresh medium of samples that were subjected to UVA irradiation for 60 min in the presence of colorant (carthamus yellow, grape-skin color, gardenia blue, cochineal-color, monascus red or purpurin).

Inhibitory effects of heterocyclic amine-induced DNA adduct formation in mouse liver and lungs by beer

An evaluation of the in vivo antigenotoxic potential of beer components on heterocyclic amines including 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 3-amino-1-methyl-5H-pyrido[4.3-b]indole (Trp-P-2) was determined with particular focus on the target organs of tumorigenesis, and the protective mechanisms involved were investigated. Beer-solution, consisting of a freeze-dried and dissolved sample, given as drinking water, reduced the formation of MeIQx-DNA adducts in mouse liver and lungs. Beer-solution added in the diet as a mimic of food additives also significantly reduced the amount of DNA adducts present in the liver, lung, and kidney DNA of mice fed with MeIQx compared to control mice fed with MeIQx in the absence of beer-solution. The amount of adducts present in the liver of mice with single or continuous administration of Trp-P-2 was significantly reduced when beer-solution was given as part of the diet compared to control mice given Trp-P-2 without beer-solution. Protective effects were observed both with lager- and stout-type samples. In an effort to investigate the mechanisms responsible for the observed protective effects, the effects of beer-solution on metabolizing enzymes for heterocyclic amines were examined. Beer-solutions inhibited the metabolic activation of Trp-P-2 to Trp-P-2(NHOH), as demonstrated by HPLC analysis. Considering the overall suppression of the genotoxicity of MeIQx and Trp-P-2 by beer, we have shown that beer components can inhibit the metabolic activation of heterocyclic amines and subsequently suppress the observed genotoxicity. The results of this study show that beer components are protective against the genotoxic effects of heterocyclic amines on target organs associated with tumorigenesis in vivo.

Inhibitory effects of beer on heterocyclic amine-induced mutagenesis and PhIP-induced aberrant crypt foci in rat colon

Anti-mutagenic and anti-carcinogenic effects of beer on heterocyclic amine (HCA)-induced carcinogenesis were studied in vitro and in vivo. Four commercial beers (two pilsner-type, black, and stout) showed inhibitory effects against five HCAs, 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), in the Ames assay using Salmonella typhimurium TA98 in the presence of rat S9 mix. The inhibitory effects of dark-colored beers (stout and black beer) were greater than those of pilsner-type beers. Dark-colored beers suppressed CYP1A2 activity in a dose-dependent manner, suggesting that inhibition of HCA activation is partly responsible for their strong anti-mutagenic effects. Anti-mutagenic effects were also observed when the pooled human S9 mix or activated IQ was used in the assay. The micronucleus test using Chinese hamster lung CHL/IU cells showed that the addition of freeze-dried samples of pilsner-type and stout beer to the culture medium significantly reduced the number of cells with micronuclei induced with PhIP or Trp-P-2. Single-cell gel electrophoresis assay (comet assay) revealed that oral ingestion of pilsner-type and stout beers for 1 week significantly inhibited DNA damage in the liver cells of male ICR mice exposed to MeIQx (13 mg/kg, i.p.). A decrease in the formation of DNA adducts was also observed using a 32P-postlabeling method. Male Fischer 344 rats orally received PhIP (75 mg/kg, five times a week for 2 weeks) and aberrant crypt foci (ACF) formation in the colon was analyzed after 5 weeks. The number of ACF was significantly reduced in rats fed a diet containing freeze-dried beer. These results suggest that beer inhibits the genotoxic effects of HCAs and may reduce the risk of carcinogenesis caused by food borne carcinogens.

Inhibitory effects of (-)-epigallocatechin gallate on the mutation, DNA strand cleavage, and DNA adduct formation by heterocyclic amines

Green tea is known to be a potential chemopreventive agent against cancer. In this study, we investigated the inhibitory activities of tea extracts, and in particular the polyphenolic component (-)-epigallocatechin gallate (EGCG), against heterocyclic amine-induced genotoxicity. The tea extracts displayed inhibition of 2-hydroxyamino-6-methyldipyrido[1,2-a,3',2'-d]imidazole (Glu-P-1(NHOH))-induced mutagenicity. This inhibition can be accounted for by the presence of EGCG in the extracts. The mutagenic effect of Glu-P-1(NHOH), which induces single-strand cleavage in supercoiled circular DNA under neutral conditions, was inhibited by EGCG. Using the Drosophila repair test, a test for gross DNA damage, and DNA adduct detection by (32)P-postlabeling, we showed that EGCG prevented 2-amino-3,8-dimethylimidazo[4,5-f]quinoline-induced DNA damage and adduct formation in insect DNA. EGCG was found to accelerate the degradation of Glu-P-1(NHOH) in vitro. This observation suggested that the inhibition by EGCG is associated with an accelerated degradation of metabolically activated heterocyclic amines.

Beta-pseudouridine, a beer component, reduces radiation-induced chromosome aberrations in human lymphocytes

We previously found that drinking beer reduces chromosome aberrations in blood lymphocytes that were collect and irradiated in vitro. In this study, human whole-blood was in vitro exposed to 200kVp X-rays or 50keV/microm carbon ions in the presence or absence of beer, ethanol and beta-pseudouridine (one of the beer components). All three agents reduced the chromosome aberrations (dicentric) caused by either X-rays or carbon ions of 4Gy. The maximum protection for X-rays by ethanol, beer and beta-pseudouridine was 64, 26 and 34%, respectively, while the maximum protection for carbon-ion by ethanol, beer and beta-pseudouridine was 22, 26 and 32%, respectively. It is concluded that beta-pseudouridine, a nucleoside present in tRNA, is a potent protector against damage caused by radiation with direct and indirect actions.

Inhibition of human cytochrome P450 1B1, 1A1 and 1A2 by antigenotoxic compounds, purpurin and alizarin

Recently we have shown that anthraquinone food pigments such as purpurin and alizarin suppress the genotoxic activities of several mutagens including heterocyclic amines and polycyclic aromatic hydrocarbons in the Drosophila DNA repair test and in the Ames test. To investigate the mechanism of this inhibition, we have now examined the effects of these anthraquinone pigments on enzymes that metabolize xenobiotics. The activities of eight human recombinant cytochrome P450 (CYP) isozymes were measured in the presence of purpurin, alizarin or carminic acid. Purpurin and alizarin strongly inhibited the activities of CYP1A1, CYP1A2 and CYP1B1, and weakly suppressed those of CYP2A6 and CYP2E1 in a dose-dependent manner, but did not inhibit those of CYP2C19, CYP3A4 and CYP3A5. Carminic acid did not affect the activities of any CYPs tested. CYP1B1 was the most strongly affected CYP molecule by purpurin and alizarin among CYPs examined in this study. From kinetic analysis, it was shown that the inhibition by purpurin on CYP1B1 was both competitive and non-competitive, and that by alizarin was competitive. The values of slopes obtained from Lineweaver-Burk plots are proportional to the square of purpurin concentration. This observation suggests that two molecules of purpurin are interacting with one molecule of CYP1B1. The K(m) value of CYP1B1 was 11 microM, and the K(i) value of purpurin and alizarin against CYP1B1 was 0.7 microM(2) and 0.5 microM, respectively. We also examined the effects of these pigments on the mutagenicities of MeIQx and B[a]P in the Ames test, using Salmonella typhimurium TA1538 co-expressing each form of human CYP and NADPH-cytochrome P450 reductase (OR). The mutagenicity of MeIQx in TA1538 1A2/OR or 1B1/OR was suppressed by purpurin and alizarin but not by carminic acid. Purpurin also reduced the mutagenicity of B[a]P in TA1538 1A1/OR or 1B1/OR. These results suggest that the antigenotoxic activities of purpurin and alizarin can be explained by inhibition of CYP activities responsible for activating the mutagens.

Mutation, DNA strand cleavage and nitric oxide formation caused by N-nitrosoproline with sunlight: a possible mechanism of UVA carcinogenicity

N-Nitrosoproline (NPRO) is endogenously formed from proline and nitrite. NPRO has been reported to be nonmutagenic and noncarcinogenic. In this study, we have detected the direct mutagenicity of NPRO plus natural sunlight towards Salmonella typhimurium. Furthermore, formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a mutagenic lesion, was observed in calf thymus DNA treated with NPRO plus simulated sunlight. The treatment with NPRO and sunlight induced single strand breaks in the superhelical replicative form of phage M13mp2 DNA. Single-strand DNA breaks also occurred in the human fibroblast cells on treatment with NPRO plus UVA, as detected by the comet assay. An analysis using scavengers suggested that both reactive oxygen species and NO radical mediate the strand breaks. The formation of nitric oxide was observed in NPRO solution irradiated with UVA. We analyzed the photodynamic spectrum of mutation induction and DNA breakage using monochromatic radiation at a series of wavelengths between 300 and 400 nm. Both mutation frequencies and DNA breakage were highest at the absorption maximum of NPRO, 340 nm. The co-mutagenic and co-toxic actions of NPRO and sunlight merit attention as possible mechanisms increasing the carcinogenic risk from UVA irradiation.

Pseudouridine, an antimutagenic substance in beer towards N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)

Previously we reported that beer is antimutagenic against several food-derived mutagens including heterocyclic amines. We describe here the isolation and identification of pseudouridine from beer as an antimutagenic substance against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). All of the 17 samples of beer tested showed inhibition of the MNNG mutagenicity in Salmonella. Extensive fractionation through chromatography of the active components from a freeze-dried beer sample gave six antimutagenic fractions. One contained pseudouridine, as characterized by the UV spectra, nuclear magnetic resonance, and co-chromatography in HPLC. Pure pseudouridine inhibited the mutagenicity of MNNG in a dose-dependent manner. The amount of pseudouridine in the beer sample, estimated at about 0.4 mg/100 ml beer, can account for 3% of the total antimutagenicity of beer. Thus, the major active components in beer remain to be identified. The role of pseudouridine in inhibiting the mutagenicity of MNNG is to be studied further. Among analogs of pseudouridine, spongouridine, but not uridine, was antimutagenic against MNNG. The bacterial mutagenicity of another methylating agent N-methyl-N-nitrosourea was also inhibited by pseudouridine. Pseudouridine is the first example among nucleosides to be shown to possess an antimutagenic property.

Preventive effects of chlorophyllin fixed on chitosan towards DNA adduct formation of 3-amino-1-methyl-5H-pyrido [4,3-b]indole in CDF1 mice

Chlorophyllin, a water-soluble derivative of chlorophyll, is known to suppress the mutagenic and carcinogenic action of compounds having polycyclic structures, e.g., heterocyclic amines and aflatoxin B1. Recently, we reported that chlorophyllin fixed on chitosan (chl-chitosan), which is insoluble in water, can efficiently and tightly trap these heterocyclic amines. We have studied whether this adsorption to chl-chitosan can result in an interference with DNA-adduct formation caused by 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), a heterocyclic amine, in CDF1 mice, in which Trp-P-2 had been shown to induce hepatocellular carcinomas. Mice were fed a diet containing Trp-P-2 with or without chl-chitosan. After 3 d of feeding, DNA-adduct formation in liver and lung was examined by 32P-postlabeling analysis. Adducts formed from Trp-P-2 were significantly decreased by the chl-chitosan addition (p<0.05, t-test). These results suggest that the uptake of Trp-P-2 into the mouse was lowered by its adsorption to chl-chitosan, either within the digestive tract or within the food itself. This trapping agent, chl-chitosan, is thus worthy of study for cancer chemoprevention.

Oxidative damage and induced mutations in m13mp2 phage DNA exposed to N-nitrosopyrrolidine with UVA radiation

N:-Nitrosopyrrolidine (NPYR) is carcinogenic in rodents and undergoes alpha-hydroxylation upon microsomal CYP450 metabolism, giving rise to mutations. Previously, we reported the direct mutagenicity of NPYR, under ultraviolet A (UVA) irradiation, towards Salmonella typhimurium and phage M13mp2. In the present study, we measured the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in a replicative form of M13mp2 DNA exposed to NPYR plus UVA. Formation of 5-hydroxy-2'-deoxycytidine in calf thymus DNA treated with NPYR plus UVA was also observed. Singlet oxygen is likely to account for the formation of 8-oxodGuo. We analyzed the spectrum of mutations in lacZalpha of M13mp2 phages produced on transfecting Escherichia coli with the replicative form of phage DNA that had been treated with NPYR plus UVA. The role of oxidative DNA damage in mutagenesis was explored using mutM-proficient and -deficient E.coli strains as the hosts. A higher level of mutation was observed with the mutM-deficient host than with the -proficient host. Base substitutions at GC pairs predominated in both mutM-proficient and -deficient hosts. With the mutM-deficient host, we observed an overall increase in the percentage of GC-->TA transversions. In addition we noted that there were fewer GC-->AT transitions than in the mutM-proficient host. With these hosts, different hot spots were observed and a new GC-->TA hot spot was produced. The formation of 8-oxodGuo in DNA, which is known to induce GC-->TA transversion, may contribute to mutagenesis by NPYR plus UVA.

Enhancing effect of saccharides on the mutagenicity of 2-chloro-4-methylthiobutanoic acid

The mutagenicity of 2-chloro-4-methylthiobutanoic acid (CMBA), a nitrite-treated Sanma fish mutagen, in Salmonella typhimurium TA100 was enhanced by addition of D-glucose during the CMBA-treatment. Several other monosaccharides also enhanced the mutagenicity of CMBA, and the order of the enhancing potency was found to be D-mannose, D-glucose>D-fructose, D-ribose, D-galactose. A disaccharide, maltose, showed only little enhancement. No enhancement was found with L-glucose. We investigated whether saccharides affect uptake of [methyl-14C]CMBA into S. typhimurium TA100. Saccharides which enhanced CMBA-induced mutagenesis increased the uptake. L-Glucose did not enhance the uptake. There was good correlation between the enhanced mutagenesis and increased radioactivity in Salmonella, suggesting that the enhancing effect of monosaccharide on the CMBA-induced mutagenesis results from the enhanced uptake of the mutagen into bacteria.

Protection against Trp-P-2 mutagenicity by purpurin: mechanism of in vitro antimutagenesis

Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a natural pigment isolated from madder root (Rubia tinctorum) which inhibits the mutagenicity of a number of heterocyclic amines in the Ames mutagenicity test. Two effects were observed in the presence of purpurin. The rate of degradation of 3-hydroxyamino-1-methyl-5H-pyrido¿4,3-bĭndole ¿Trp-P-2(NHOH) at neutral pH was increased. The major product of this purpurin-dependent degradation was identified as the parent amine 3-amino-1-methyl-5H-pyrido¿4,3-bĭndole (Trp-P-2). Secondly, the rate of Trp-P-2 N-hydroxylation, the major route of bioactivation, by PCB-treated rat hepatic microsomes was markedly decreased. Cytochrome P450-dependent O-dealkylation of methoxy-, ethoxy- and pentoxyresorufin by these microsomes was also significantly inhibited by purpurin. The nature of this inhibition was competitive. Spectrophotometric investigations suggest no direct interaction between Trp-P-2 and purpurin. Furthermore, no evidence for Trp-P-2 binding was observed with carminic acid, a structural analog of purpurin, when it was immobilized on omega-aminohexyl agarose. Therefore, in vitro the proposed mechanism by which purpurin protects against heterocyclic amine-induced mutagenesis involves competitive inhibition of cytochrome P450-dependent bioactivation and accelerated degradation of the N-hydroxylamine to the parent amine.

Porphyrins as possible preventers of heterocyclic amine carcinogenesis

Our studies have shown that hemin and chlorophyllin can directly interact with heterocyclic amines (HAs) and prevent their mutagenic actions. Hemin and chlorophyllin can trap HAs efficiently, probably by forming face-to-face complexes with them. The trapping was most clearly demonstrated by use of solid-supported porphyrins, hemin-agarose and chlorophyllin-chitosan. Furthermore, spectroscopic measurements have suggested that there are interactions in solution between the porphyrins and the HAs. A number of in vivo data have been accumulated by efforts from many laboratories for the anticarcinogenic and antigenotoxic properties of porphyrins, particularly chlorophyllin, against HAs.

Mutation and DNA modification in Salmonella exposed to N-nitrosodimethylamine under UVA- and sunlight-irradiation

Previously, we reported that when Salmonella typhimurium and Escherichia coli were treated with N-nitrosodimethylamine (NDMA) under irradiation with ultraviolet-A (UVA), mutagenesis of the bacteria took place without externally added activation enzymes. We also observed the formation of O(6)-methylguanine (O(6)-meG), N(7)-methylguanine (N(7)-meG) and 7,8-dihydro-8-oxodeoxyguanosine (8-oxodG) in calf thymus DNA treated with NDMA plus UVA. In this study, we observed the mutagenicity of NDMA under irradiation of natural sunlight in S. typhimurium. Furthermore, we detected the formation of O(6)-meG, N(7)-meG and 8-oxodG in calf thymus DNA treated with NDMA plus simulated sunlight. Regarding the mutagenesis of S. typhimurium by NDMA plus UVA, we have now identified and quantified O(6)-meG formed in the genomic DNA of the bacteria under conditions of the mutagenesis.

Protection against the bacterial mutagenicity of heterocyclic amines by purpurin, a natural anthraquinone pigment

Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a naturally occurring anthraquinone pigment found in species of madder root. We have found that the presence of purpurin in bacterial mutagenicity assays is responsible for a marked inhibition of mutagenicity induced by food-derived heterocyclic amines. Purpurin was found to be a better inhibitor of Trp-P-2-dependent mutagenicity than either epigallocatechin gallate or chlorophyllin both of which are well-established anti-mutagenic components of diet. Inhibition of Trp-P-2(NHOH) mutagenicity by purpurin was dependent upon pH. It was a better inhibitor in neutral than acidic conditions. Purpurin was protective against the direct mutagen Trp-P-2(NHOH) in both the presence and the absence of hepatic S9 but required pre-incubation. Finally, purpurin was responsible for the inhibition of human CYP1A2 and human NADPH-cytochrome P450 reductase and a decrease in the bioactivation of Trp-P-2 by these enzymes when they were expressed in Salmonella typhimurium TA1538ARO. However, inhibition of Trp-P-2(NHOH)-dependent mutations suggests purpurin also has a direct effect on this mutagen in addition to inhibiting its formation by CYP1A2.

A simple and rapid method for analyzing the Monascus pigment-mediated degradation of mutagenic 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole by in-capillary micellar electrokinetic chromatography

A simple and rapid method is described for analyzing the Monascus pigment-mediated degradation of 3-hydroxyamino-1-methyl-5H-pyrido[4, 3-b]indole (Trp-P-2(NHOH)). We used the in-capillary micellar electrokinetic chromatography (MEKC). During the electrophoresis, the mutagen and the pigment, due to their different migration velocities, mix for a certain period of time to interact, and then they are separated and quantified. Using this technique, we were able to demonstrate that Trp-P-2(NHOH) is degraded by the pigment. The degradation was pigment-dose dependent, and because the pigment was recovered unchanged, it was deduced that the pigment acted catalytically for the degradation. The entire MEKC procedure takes 8 min.

Glycine betaine in beer as an antimutagenic substance against 2-chloro-4-methylthiobutanoic acid, the sanma-fish mutagen

Beer can inhibit the mutagenicity of the sanma-fish mutagen, 2-chloro-4-methylthiobutanoic acid (CMBA) in Salmonella typhimurium TA100 and TA1535. The antimutagenic component was isolated from beer and identified as glycine betaine, a compound known to be distributed widely in plants and animals including humans. Beer also contains components that interfere the antimutagenic action of glycine betaine. Glycine betaine seems to antagonize CMBA in a specific manner, since several other direct-acting mutagens tested were not subject to inhibition by glycine betaine. CMBA was stable in the presence of glycine betaine under neutral conditions. Since a treatment of Salmonella with glycine betaine before the bacteria was exposed to CMBA resulted in inhibition of the mutagenesis, the antimutagenic action of glycine betaine may be taking place inside the cells. These observations suggest that the mutagenic action of CMBA may be modified by the presence of both extracellular and intracellular glycine betaine.

Inhibitory effects of beer and other alcoholic beverages on mutagenesis and DNA adduct formation induced by several carcinogens

The possibility that beer and other alcoholic beverages could be antimutagenic against the heterocyclic amines (HAs), a group of carcinogens produced on cooking proteinaceous foods, has been explored. In the Salmonella mutation assays, beer showed inhibitory effects against several HAs [preactivated Trp-P-1, Trp-P-2(NHOH), and Glu-P-1(NHOH)] that are directly mutagenic in bacteria. Japanese sake, red and white wines, and brandy were also effective. However, ethyl alcohol alone did not show these effects. The formation of O(6)-methylguanine by N-methyl-N'-nitro-N-nitrosoguanidine in the DNA of Salmonella YG7108 was also inhibited by beer. Nonvolatile beer components were administered orally to CDF(1) mice together with Trp-P-2. Adducts in the liver DNA were significantly decreased by the beer, as compared to those in controls fed Trp-P-2 only. Although several phenolic compounds known to be present in beer were antimutagenic toward these mutagens, their effects were very small. It was concluded that some yet to be identified component(s) of beer is (are) responsible for this antimutagenicity.

Induced mutations in M13mp2 phage DNA exposed to N-nitrosopyrrolidine with UVA irradiation

It is known that N-nitrosopyrrolidine (NPYR), a carcinogen in rodents, is metabolically activated by microsomal cytochrome P450 to form an alpha-hydroxylated derivative, which induces mutations. The mutations have been demonstrated by use of Salmonella typhimurium and Escherichia coli. We discovered directly acting mutagenicity of NPYR plus ultraviolet light-A (UVA) in bacteria and phage. With an O(6)-alkyltransferase-deficient strain of S.typhimurium, the NPYR plus UVA treatment gave greater mutation frequencies compared to those found with the parent strain. We identified the structure of the direct-acting mutagen as N-nitroso-1-phosphonooxypyrrolidine, and analyzed the spectrum of mutations induced in the DNA of M13mp2 phage. The basepair substitutions GC to TA and GC to AT appear to occur predominantly. Several hotspots were observed. In the conditions where SOS response was induced in the host E.coli, greater varieties of mutations were observed in phage DNA compared to those without the SOS response induction. These results suggest that alkylations of DNA occur by the photoactivated NPYR. The roles of the produced damage to the mutations are discussed.

Use of activated heterocyclic amines in the screening of dietary antimutagens

Experimental methods suitable for detecting antimutagenic substances against heterocyclic amines are described. The proposed methodology will allow identification of direct interactions between the metabolically activated form of a heterocyclic amine and an antimutagenic compound.