Antimutagens and their modes of action

Antioxidant and antimutagenic activities of Randia echinocarpa fruit

We report for the first time the antioxidant and antimutagenic activities of fractions from Randia echinocarpa fruit, which is a Rubiaceae plant native to Sinaloa, Mexico. This fruit has been traditionally used in the prevention or treatment of cancer, among other diseases. The pulp of the fruit was sequentially extracted with solvents of different polarity (i.e. hexane, chloroform, methanol and water). A high extraction yield was obtained with methanol (72.17% d.w.). The aqueous extract showed the highest content of phenolics (2.27 mg/g as ferulic acid equivalents) and the highest antioxidant activity based on the beta-carotene bleaching method (486.15). The commercial antioxidant BHT was used as control (835.05). Antimutagenic activity of the aqueous extract (0-500 microg/tube) was evaluated using the Salmonella microsuspension assay (YG1024 strain) and 1-NP as the mutagen (50 and 100 ng/tube). The aqueous extract was neither toxic nor mutagenic and the percentage of inhibition on 1-NP mutagenicity was 32 and 53% at doses of 50 and 100 ng/tube, respectively. The results of the double incubation assay suggest that the extract inhibited the mutagenicity of 1-NP by a combination of desmutagenic and bioantimutagenic effects.

Antimutagenicity of cinnamaldehyde and vanillin in human cells: Global gene expression and possible role of DNA damage and repair

Vanillin (VAN) and cinnamaldehyde (CIN) are dietary flavorings that exhibit antimutagenic activity against mutagen-induced and spontaneous mutations in bacteria. Although these compounds were antimutagenic against chromosomal mutations in mammalian cells, they have not been studied for antimutagenesis against spontaneous gene mutations in mammalian cells. Thus, we initiated studies with VAN and CIN in human mismatch repair-deficient (hMLH1(-)) HCT116 colon cancer cells, which exhibit high spontaneous mutation rates (mutations/cell/generation) at the HPRT locus, permitting analysis of antimutagenic effects of agents against spontaneous mutation. Long-term (1-3 weeks) treatment of HCT116 cells with VAN at minimally toxic concentrations (0.5-2.5mM) reduced the spontaneous HPRT mutant fraction (MF, mutants/10(6) survivors) in a concentration-related manner by 19-73%. A similar treatment with CIN at 2.5-7.5microM yielded a 13-56% reduction of the spontaneous MF. Short-term (4-h) treatments also reduced the spontaneous MF by 64% (VAN) and 31% (CIN). To investigate the mechanisms of antimutagenesis, we evaluated the ability of VAN and CIN to induce DNA damage (comet assay) and to alter global gene expression (Affymetrix GeneChip) after 4-h treatments. Both VAN and CIN induced DNA damage in both mismatch repair-proficient (HCT116+chr3) and deficient (HCT116) cells at concentrations that were antimutagenic in HCT116 cells. There were 64 genes whose expression was changed similarly by both VAN and CIN; these included genes related to DNA damage, stress responses, oxidative damage, apoptosis, and cell growth. RT-PCR results paralleled the Affymetrix results for four selected genes (HMOX1, DDIT4, GCLM, and CLK4). Our results show for the first time that VAN and CIN are antimutagenic against spontaneous mutations in mammalian (human) cells. These and other data lead us to propose that VAN and CIN may induce DNA damage that elicits recombinational DNA repair, which reduces spontaneous mutations.

Inhibition of spontaneous mutagenesis by vanillin and cinnamaldehyde in Escherichia coli: Dependence on recombinational repair

Vanillin (VAN) and cinnamaldehyde (CIN) are dietary antimutagens that effectively inhibit both induced and spontaneous mutations. We have shown previously that VAN and CIN reduced the spontaneous mutant frequency in Salmonella TA104 (hisG428, rfa, DeltauvrB, pKM101) by approximately 50% and that both compounds significantly reduced mutations at GC sites but not at AT sites. Previous studies have suggested that VAN and CIN may reduce mutations in bacterial model systems by modulating DNA repair pathways, particularly by enhancing recombinational repair. To further explore the basis for inhibition of spontaneous mutation by VAN and CIN, we have determined the effects of these compounds on survival and mutant frequency in five Escherichia coli strains derived from the wild-type strain NR9102 with different DNA repair backgrounds. At nontoxic doses, both VAN and CIN significantly reduced mutant frequency in the wild-type strain NR9102, in the nucleotide excision repair-deficient strain NR11634 (uvrB), and in the recombination-proficient but SOS-deficient strain NR11475 (recA430). In contrast, in the recombination-deficient and SOS-deficient strain NR11317 (recA56), both VAN and CIN not only failed to inhibit the spontaneous mutant frequency but actually increased the mutant frequency. In the mismatch repair-defective strain NR9319 (mutL), only CIN was antimutagenic. Our results show that the antimutagenicity of VAN and CIN against spontaneous mutation required the RecA recombination function but was independent of the SOS and nucleotide excision repair pathways. Thus, we propose the counterintuitive notion that these antimutagens actually produce a type of DNA damage that elicits recombinational repair (but not mismatch, SOS, or nucleotide excision repair), which then repairs not only the damage induced by VAN and CIN but also other DNA damage-resulting in an antimutagenic effect on spontaneous mutation.

Suppressive effect of aspirin on chromosome aberration induced by mitomycin C in mice

Chromosome aberrations induced by mitomycin C (MMC) were suppressed by aspirin in a mouse micronucleus test with peripheral blood and bone marrow cells. Aspirin at doses of 0.5, 5, and 50 mg/kg was injected intraperitoneally or per administered orally 0.5, 6, or 24 h after administration of MMC and then peripheral blood and/or bone marrow cells were sampled 48 h after administration of MMC. The suppressive effect of aspirin was more pronounced in the aspirin-treated groups 24 h than 0.5 and 6 h after administration of MMC. In the aspirin-treated group at 24 h, the frequency of polychromatic erythrocytes with micronuclei was decreased by about 60-80% after intraperitoneal injection and by about 40-70% after oral administration. It is suggested that aspirin may directly act on MMC metabolites, but not on MMC itself.

Antimutagenic effect of resveratrol against Trp-P-1

The methanol extract of Yucca schidigera (YE) showed a suppressive effect on umu gene expression of the SOS response induced by 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) in Salmonella typhimurium TA1535/pSK1002. The suppressive effect of YE was also observed for 2-aminoanthracene and activated Trp-P-1, without a significant effect on bacterial growth. The extract exhibited a weak suppressive effect on SOS-induction by N-methyl-N'-nitro-N-nitrosoguanidine, but not by furylfuramide or 4-nitroquinoline-1-oxide. The antimutagenic activity of YE against Trp-P-1 was demonstrated by Ames assay using Salmonella typhimurium TA98. Isolation and purification of the active component of YE was carried out using SiO2 column chromatography, and 275 mg of antimutagenic compound was isolated from 2.5 kg of dried chips of yucca roots and branches. The compound was identified as 3,4',5-trihydroxystilbene (THS). The SOS suppression and antimutagenicity of THS against Trp-P-1 was determined by umu test and Ames test.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 1. The clastogen-suppressing effects of Tochu tea in CHO cells and mice

The suppressing effect of crude extracts of Tochu tea, an aqueous extract of Eucommia ulmoides leaves and a popular beverage in Japan, on the induction of chromosome aberrations in CHO cells and mice was studied. When CHO cells were treated with Tochu tea crude extract after MMC treatment, the frequency of chromosome aberrations was reduced. Out of 17 Tochu tea components, 5 irridoids (geniposidic acid, geniposide, asperulosidic acid, deacetyl asperulosidic acid, and asperuloside) and 3 phenols (pyrogallol, protocatechuic acid, and p-trans-coumaric acid) were found to have anticlastogenic activity. Since the anticlastogenic irridoids had an alpha-unsaturated carbonyl group, this structure was considered to play an important role in the anticlastogenicity. The anticlastogenic effect of Tochu tea extracts was examined in mice using a micronucleus assay. When mice received 1.0 ml 4% Tochu tea extract by oral gavage 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. This decrease was not due to a delay in the maturation of micronucleated reticulocytes.

Effects of Antimutagens on the Teratogenicity of N-Methyl-N'-Nitro-N-Nitrosoguanidine in Mice

We examined whether vanillin (VA) and CoCl₂ ∙6H₂ O(CoCl₂ ), antimutagens, which have mutation suppressing effect, i.e., promotion of cellular repair function in vitro, can modify the teratogenicity in mice caused by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a direct-acting monofunctional alkylating agent. ICR mice were treated with MNNG alone (single IP dose of 40 or 60 mg/kg) or in combination with the antimutagen on day 11 of gestation. Embryotoxicity and teratogenicity were examined at term. The incidence of MNNG-induced syndactyly in the fore- and hindlimbs was significantly decreased by VA (50 mg/kg, IP) or CoCl₂ (10 mg/kg, IV) and a tendency to decrease in the incidence of oligodactyly was noted as well. On the other hand, the incidence of MNNG-induced brachydactyly was increased by VA or CoCl₂ . Though the mechanism of the modifying effects of both VA and CoCl₂ on MNNG-induced malformations could not be delineated in the present study, the results indicate that the antimutagens which stimulate DNA recombination repair in vitro modify the manifestation of malformations caused by teratogens that attack the fetal DNA in the initial teratogenic mechanism.