Inhibition of benzo[a]pyrene-induced mutagenesis by (-)-epigallocatechin gallate in the lung of rpsL transgenic mice.
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Epigallocatechin gallate (EGCG) is a major water-soluble component of green tea. The antimutagenic activity of EGCG against benzo[a]pyrene (B[a]P)-induced mutations was assessed by using transgenic mice carrying the rpsL gene as a monitor of mutations. Seven-week-old male mice were given drinking water containing EGCG for 3 weeks. On day 7, mice were treated with a single i.p. injection of B[a]P (500 mg/kg body wt). Two weeks after the injection, the mutations in the rpsL gene were analyzed. B[a]P treatment resulted in an approximately 4-fold increase of mutation frequency at the rpsL gene in the lung. An approximately 60% reduction in the B[a]P-induced mutations in the lung was observed when mice were given EGCG at concentrations >0.005%. B[a]P-induced mutations mainly occurred at G:C basepairs in the several specific nucleotide sequences of the rpsL gene. These were AGG, CGG, CGT, TGG, TGC and GGT: all of them contained a guanine residue. Mutations seen similarly in the human Ki-ras codon 12 or p53 codons 157, 248, and 273 of lung tumor were also found in the rpsL gene, and the mutations were suppressed by the EGCG treatment. In conclusion, the antimutagenic effects of EGCG for B[a]P-induced mutagenesis in vivo suggest that drinking green tea may reduce the tumor-initiating potency of B[a]P in the lung. (+info)
Antimutagenicity of sweetpotato (Ipomoea batatas) roots.
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Antimutagenicity of the water extracts prepared from the storage roots of four varieties of sweetpotato with different flesh colors was investigated using Salmonella typhimurium TA 98. The extract from the whole roots of the purple-colored Ayamurasaki variety effectively decreased the reverse mutation induced not only by Trp-P-1, Trp-P-2, IQ, B[a]P, and 4-NQO but also by dimethyl sulfoxide extracts of grilled beef. Comparison of the inhibitory activity of the extracts from the normal Ayamurasaki and its anthocyanin-deficient mutant one suggested that the anthocyanin pigment in the flesh decreases the mutagenic activity of the mutagens as heterocyclic amines. Two anthocyanin pigments purified from purple-colored sweet-potato, 3-(6,6'-caffeylferulylsophoroside)-5-glucoside of cyanidin (YGM-3) and peonidin (YGM-6) effectively inhibited the reverse mutation induced by heterocyclic amines, Trp-P-1, Trp-P-2, and IQ in the presence of rat liver microsomal activation systems. (+info)
Modulation of genotoxic and related effects by carotenoids and vitamin A in experimental models: mechanistic issues.
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The mechanisms involved in the modulation of genotoxic and related effects by carotenoids and vitamin A were inferred from a critical review of an ad hoc constructed database. Almost 500 results were generated in experimental models evaluating the activity of 32 structurally, metabolically and functionally related nutrients, including beta-carotene and 26 other carotenoids, retinol, retinal, all-trans-retinoic acid and retinyl esters. As many as 67 experimental test systems, either in vitro or in vivo, used a variety of cellular targets and/or end-points suggestive of distinctive mechanisms of action. The bulk of available data support the view that carotenoids and vitamin A do not induce genotoxic effects per se. Even in the absence of any genotoxic agent, these nutrients appeared, on the contrary, to display some mechanisms which play protective roles in tumor promotion and progression, such as inhibition of N-myc gene expression resulting in antiproliferative effects, up-regulation of cell-to-cell communication, an increase in connexin 43 gene expression, a decrease in the 'spontaneous' cell transformation frequency and induction of differentiation in vitro. A large number of studies investigated the modulation by carotenoids and vitamin A of genotoxic and related effects produced by 69 genotoxicants, including biological agents, physical agents, chemical compounds and complex mixtures. In spite of some discrepant data, the general trend was that both carotenoids and vitamin A are poorly effective in acting as nucleophiles, nor do they appear to substantially interfere with the induction or repair of DNA damage produced by direct-acting agents. In contrast vitamin A and carotenoids, irrespective of their provitamin A role, in most studies inhibited those genotoxicants which require metabolic activation to electrophilic derivatives in either bacterial or mammalian cells. Coupled with biochemical data, the distinctive patterns observed with genotoxic agents belonging to different chemical classes suggest a complex modulation of both phase I and phase II enzymes involved in the metabolism of xenobiotics. Furthermore, carotenoids and vitamin A shared other protective mechanisms, such as scavenging of genotoxic oxygen species, modulation of signal transduction pathways, inhibition of cell transformation induced by physical and chemical agents, and facilitation of intercellular communication inhibited by genotoxic compounds. Therefore, carotenoids and vitamin A appear to work via multiple mechanisms, which would support a potential protective role in cancer initiation and in the pathogenesis of other mutation-related diseases. These conclusions are consistent with the recognized cancer-preventive activity of these nutrients in certain animal models and with the evidence provided by observational epidemiological studies, which suggested cancer-protective effects at many sites as related to their dietary intake or plasma levels. However, all these lines of evidence and mechanistically based premises contrast with the unexpected outcome of recent clinical intervention trials, which raised the concern that supplemental use of beta-carotene and vitamin A may increase the risk of lung cancer amongst high risk individuals such as tobacco smokers and asbestos-exposed workers. (+info)
Cobaltous chloride-induced mutagenesis in the supF tRNA gene of Escherichia coli.
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The spectrum of mutations induced by cobalt(II) chloride (CoCl2) was examined using plasmid pUB3 DNA, which was propagated after transfection into Escherichia coli SY1032/pKY241 host cells. The vector plasmid carried an E.coli supF suppressor tRNA gene as a target for mutations. After CoCl2 treatment, 64 independent nalidixic acid-resistant, ampicillin-resistant and Lac+ (SupF-) clones were obtained and the altered sequences of the mutated supF genes were determined. Deletions and frameshifts were the predominant mutational event (61%) induced by CoCl2 and base substitutions were induced to a lesser degree (29%). Analysis of sequence alterations at all the sites of mutation revealed that: (i) 18 of 19 base substitutions and eight of 10 frameshifts occurred at G:C sites, suggesting that the formation of N7G-Co(II) adducts may be responsible for premutagenic lesions of these mutations; (ii) short sequence repeats were mostly found at the sites of deletions and frameshifts. Slippage-misalignment is also suggested to be a mechanism for the induction of mutations at these sites. (+info)
Genotoxic effects of benzyl isothiocyanate, a natural chemopreventive agent.
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Benzyl isothiocyanate (BITC) is contained in cruciferous plants which are part of the human diet. Numerous reports indicate that BITC prevents chemically induced cancer in laboratory animals and it has been postulated that BITC might also be chemoprotective in humans. On the other hand, evidence is accumulating that this compound is a potent genotoxin in mammalian cells by itself. To further elucidate the potential hazards of BITC, we investigated its genotoxic effects in different in vitro genotoxicity tests and in animal models. In in vitro experiments [differential DNA repair assay with Escherichia coli, micronucleus assay with human HepG2 cells and single cell gel electrophoresis (SCGE) assay with hepatocytes and gastrointestinal tract cells] pronounced dose-dependent genotoxic effects were found at low dose levels (+info)
Antimutagenic effects of centchroman--a contraceptive and a candidate drug for breast cancer in multiple mutational assays.
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Centchroman (CC), a non-steroidal oral contraceptive and a candidate drug for breast cancer, has been reported to exhibit partial to complete remission of lesions in 40.5% of breast cancer patients. The potent anti-oestrogenic activity, negligible side-effects and anti-breast cancer activity of CC prompted us to evaluate the antimutagenic effects of this compound in a bacterial mutagenicity assay and CHO/HPRT and AS52/GPT mutation assays in vitro and in vivo in female Swiss albino mice as measured by both sister chromatid exchange (SCE) and chromosome aberrations (CA) against three known positive mutagen compounds, dimethylbenz[a]anthracene (DMBA), cyclophosphamide (CP) and mitomycin C (MMC). Antimutagenicity assays in Salmonella strains TA97a, TA100, TA98 and TA102 were carried out against commonly used known positive mutagens, sodium azide, 4-nitro-o-phenylenediamine, cumine hydroperoxide, 2-aminofluorene and danthron. A significantly reduced number of bacterial histidine revertant colonies was observed in the plates treated with 0.1, 1, 5 and 10 microg/plate CC and a positive compound when compared with bacterial plates treated with the respective positive compound alone. Ethyl methanesulfonate (EMS), a commonly used positive mutagen for CHO/HPRT and AS52/GPT gene mutation assays, was used for antimutagenicity assay in these cells. CC exhibited protective effects against the mutagenicity of EMS in these two mammalian cell mutation assays, CHO/HPRT and AS52/GPT. In the in vivo studies, pretreatment with CC reduced DMBA-induced SCE and CA and CP- and MMC-induced CA when compared with the group treated only with the positive compounds. These results indicate that CC can reduce the mutagenic effects of known genotoxic compounds. (+info)
Simple chemicals can induce maturation and apoptosis of dendritic cells.
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As is well known in the case of Langerhans cells, dendritic cells (DCs) play a crucial role in the initiation of immunity to simple chemicals such as noted in the contact hypersensitivity. Because DCs are scattered in non-lymphoid organs as immature cells, they must be activated to initiate primary antigen-specific immune reactions. Therefore, we hypothesized that some simple chemicals must affect the function of DCs. In this paper, we first demonstrated that human monocyte-derived DCs responded to such simple chemicals as 2, 4-dinitrochlorobenzene (DNCB), 2,4,6-trinitrochlorobenzene (TNCB), 2, 4-dinitrofluorobenzene (DNFB), NiCl2, MnCl2, CoCl2, SnCl2, and CdSO4 by augmenting their expression of CD86 or human leucocyte antigen-DR (HLA-DR), down-regulating c-Fms expression or increasing their production of tumour necrosis factor-alpha (TNF-alpha). In addition, the DCs stimulated with the chemicals demonstrated increased allogeneic T-cell stimulatory function. Next, we found that, among these chemicals, only NiCl2 and CoCl2 induced apoptosis in them. Finally, we examined the effects of these chemicals on CD86 expression by three different macrophage subsets and DCs induced from the cultures of human peripheral blood monocytes in the presence of macrophage colony-stimulating factor (M-CSF), M-CSF + interleukin-4 (IL-4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and GM-CSF + IL-4, respectively. Among them, only DCs dramatically augmented their expression of CD86. These observations have revealed unique characteristics of DCs, which convert chemical stimuli to augmentation of their antigen presenting function, although their responses to different chemicals were not necessarily uniform in the phenotypic changes, cytokine production or in the induction of apoptosis. (+info)
Modification of mutagenic activities of pro-mutagens by glyco-ursodeoxycholic acid in the Ames assay.
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Mutagenicity, co-mutagenicity and anti-mutagenicity of glycoursodeoxycholic acid (GUDCA) were examined by the Ames assay using Salmonella typhimurium strain TA98 with S9. As pro-mutagens, 2-aminoanthracene (2AA), Benzo[a]pyrene (BaP), 3-amino-1-dimethyl-5H-pyrido[4, 3-b]indole (Trp-P-2), 2-amino-3-methylimidazo[4, 5-f]quinoline (IQ) and 2-amino-3, 4-dimethylimidazo[4, 5-f]quinoline (MeIQ) were used. In addition to these pro-mutagens, blue-chitin extracts of human gallbladder bile (BCE) collected from the cholecystectomized patients with cholelithiasis were used in order to investigate the role of GUDCA on mutagen(s) actually existing in human bile. It was found that GUDCA did not show mutagenicity in this test system. Concerning the modification of mutagenic activities of pro-mutagens, GUDCA showed the different directions. GUDCA acted as co-mutagen, since it enhanced the mutagenic activities of 2AA and BaP. But, acted as anti-mutagen, since it suppressed the activities of Trp-P-2, IQ and MeIQ, all of which were classified as heterocyclic amines. GUDCA also suppressed the mutagen(s) in human bile. Because of the use of blue-chitin absorbed method for testing bile mutagenicity, the chemicals involved were considered to be heterocyclic amines and other polycyclic compounds. In these we suspect the bile mutagens are heterocyclic amines. Further examination should be directed towards the investigation into the mechanism of anti-mutagenic effects of GUDCA on mutagen(s) actually existing in human bile. (+info)