Inhibition of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline-mediated DNA-adduct formation by chlorophyllin in Drosophila

Enhancement of phase II enzyme activity by purpurin resulting in the suppression of MeIQx-DNA-adduct formation in mice

We previously demonstrated using a bacterial system that the antigenotoxic activity of the anthraquinone compounds purpurin and alizarin was due to the suppression of microsomal enzyme activity involved in the activation of mutagens. In the present study we determined the effect of purpurin and alizarin on (i) MeIQx-DNA-adduct formation in mouse tissues and (ii) the activity of phases I and II enzymes in liver fractions, the liver being the target tissue of MeIQx. The amount of MeIQx-DNA adduct formed was determined using 32P-postlabeling methods. Methoxyresorufin-O-demethylase (MROD) and ethoxyresorufin-O-deethylase (EROD) enzyme activities, which reflect CYP 1A activity, were measured as markers for phase I enzymes, and UDP-glucuronyltransferase (UGT) and glutathione S-transferase (GST) activities were determined as markers for phase II enzymes. Mice fed with a diet containing 0.5% purpurin for 3 days prior to MeIQx administration had 70% fewer MeIQx-DNA adducts in the lung and kidney, and fewer DNA adducts (insignificant, statistically) in the liver compared with mice fed a diet lacking purpurin. MROD and EROD activities in the liver of these mice increased six- and eight-fold, respectively, and were higher than those determined for the control mice within 1 day following commencement of purpurin treatment. These elevated activities were maintained during treatment and declined immediately following removal of purpurin from the diet. GST and UGT activities gradually increased 2.5- and 3-fold, respectively, following purpurin treatment, and were maintained at significantly high levels even after purpurin administration ceased. Alizarin did not significantly affect DNA-adduct formation and enzyme activity, except in the case of UGT. Taken together, our results show that purpurin reduced MeIQx-DNA-adduct formation by maintaining elevated phase II enzyme activities, thereby facilitating accelerated excretion of MeIQx.

Novel antimutagenic factors derived from the edible mushroom Agrocybe cylindracea

Studies have shown that certain foods contain compounds with antigenotoxic activities. Here, we ask if dried powders and/or extracts from three edible mushrooms, Agrocybe cylindracea, Lentinula edodes and Pleurotus ostreatus, have a mitigating effect on genotoxicity. We used two in vivo assays: the Drosophila DNA repair test and the Drosophila wing spot test (also known as SMART) which measures somatic mutation and recombination. Eight carcinogens were tested with the mushroom powders: 2-AAF, aflatoxin B1, DMBA, IQ, MeIQx, MNU NDMA, and 4NQO. We found that A. cylindracea and P. ostreatus powders can suppress DNA damage induced by each of the mutagens we tested. In contrast, L. edodes has an inhibitory effect on DNA damage induced by only a sub-set of mutagens, namely aflatoxin B1, NDMA, MNU and 4NQO. In addition, A. cylindracea extracts were able to suppress somatic cell mutation induced by aflatoxin B1, MMC, MNU, NDMA, NMOR and 4NQO. These results suggest that Agrocybe genus mushrooms contain factors with antigenotoxic activity, including anti-recombinogenic activity. Furthermore, the antigenotoxic activity of A. cylindracea powder can be extracted in water but not in ethyl acetate or methanol, and is sensitive to heat treatment. The data suggest that there is a novel antigenotoxic factor(s) in A. cylindracea, possibly in the form of a peptide or protein.

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.

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.

No Effects of Chlorophyllin on IQ (2-Amino-3-methylimidazo[4,5-f]-quinoline)-genotoxicity and -DNA Adduct Formation in Drosophila

Previously we demonstrated that chlorophyllin suppressed the genotoxicities of many carcinogens. However, the genotoxicity of IQ (2-amino-3-methylimidazo[4,5-f]quinoline), a carcinogenic heterocyclic amine, was not suppressed in Drosophila. On the contrary, it has been reported that chrolophyllin suppressed the genotoxicity of IQ in rodents, rainbow trout and Salmonella. We demonstrated that the chlorophyllin-induced suppression of MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline)-genotoxicity was associated with a decrease in MeIQx-DNA adduct formation in Drosophila larval DNA. MeIQx represents another type of heterocyclic amine and is similar to IQ in structure. In this study we utilized (32)P-postlabeling to examine whether chlorophyllin reduced IQ-DNA adduct formation in Drosophila DNA in the same way as MeIQx. The results revealed that the formation of IQ-DNA adducts was unaffected by treatment with chlorophyllin. This was consistent with the absence of any inhibitory effect on genotoxicity as observed in the Drosophila repair test. These results suggest that IQ-behavior in Drosophila is not affected by chlorophyllin, indicating that the process of IQ-DNA adduct formation followed by expression of genotoxicity in Drosophila may be different from that in other organisms.

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.

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.

Inhibition of DNA adduct formation and mutagenic action of 3-amino-1-methyl-5h-pyrido[4,3-b]indole by chlorophyllin-chitosan in rpsL transgenic mice

We have studied the inhibitory effect of chlorophyllin-chitosan (Chl-Chi) complex, an insoluble form of chlorophyllin, on the DNA adduct formation and mutagenesis by a heterocyclic food mutagen-carcinogen, 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), in mice carrying the E. coli rpsL gene as a mutagenesis reporter. Upon administration of a diet containing 0.002% or 0.01% Trp-P-2, DNA adducts were formed in various tissues in a dose-dependent manner, with the maximum level observed in the liver. Addition of 3% Chl-Chi to the diet reduced the Trp-P-2 adduct by up to 90%. The rpsL mutant frequencies increased significantly in both the liver and spleen upon administration of a 0.01% Trp-P-2 diet. Addition of Chl-Chi to the diet decreased these induced mutant frequencies to the background level. No harmful effect of Chl-Chi was detected during these experiments. The results show that Chl-Chi may be a candidate chemopreventive agent against the genotoxic action of Trp-P-2, and possibly also other aromatic carcinogens in the diet.

Search for compounds that inhibit the genotoxic and carcinogenic effects of heterocyclic aromatic amines

Over the last 30 years approximately 160 reports have been published on dietary compounds that protect from the mutagenic and carcinogenic effects of heterocyclic aromatic amines (HAAs). In the first section of this review, the current state of knowledge is briefly summarized. Based on the evaluation of the available data, various protective mechanisms are described, and the use of different methodologies for the detection of protective effects is critically discussed. In most antimutagenicity studies (>70%) bacterial indicators (predominantly Salmonella strain TA98) were used, and about 600 individual compounds and complex mixtures have been identified that attenuate the effects of HAAs. The most frequently used in vivo method to detect protective effects are adduct measurements; anticarcinogenic dietary factors were identified by aberrant crypt foci assays and liver foci tests with rats. The mechanisms of protection include inactivation of HAAs and their metabolites by direct binding, inhibition of enzymes involved in the metabolic activation of the amines, induction of detoxifying enzymes, and interaction with DNA repair processes. The detection spectrum of conventional in vitro mutagenicity assays with metabolically incompetent indicator cells is limited. These procedures reflect only simple mechanisms such as direct binding of the HAAs to pyrroles and fibers. It has been shown that these compounds are also effective in rodents. More complex mechanisms, namely, interactions with metabolic activation reactions are not adequately represented in in vitro assays with exogenous enzyme homogenates, and false-negative as well as false-positive results may be obtained. More appropriate approaches for the detection of protective effects are recently developed test systems with metabolically competent cells such as the human Hep G2 line or primary hepatocytes. SCGE tests and DNA adduct measurements with laboratory rodents enable the detection of antigenotoxic effects in different organs, including those that are targets for tumor induction by the amines. Medium term assays based on aberrant crypt foci in colon and liver foci tests have been used to prove that certain compounds that prevented DNA damage by HAAs also reduced their carcinogenic effects. These experiments are costly and time consuming and, due to the weak induction capacity of the amines, only pronounced anticarcinogenic effects can be detected. Over the years, a large bulk of data on HAA protective compounds has accumulated, but only for a few (e.g., fibers, pyrroles, constituents of teas, and lactic acid bacteria) is there sufficient evidence to support the assumption that they are protective in humans as well.

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.