Influence of beta-myrcene on sister-chromatid exchanges induced by mutagens in V79 and HTC cells.

The influence of beta-myrcene (MC) on sister-chromatid exchanges (SCE) in V79 cells induced by 4 S9 mix-activated indirect mutagens was studied. The mutagens used were cyclophosphamide (CP), benzo[a]pyrene (BP), aflatoxin B1 (AFB) and 9,10-dimethyl-1,2-benz[a]anthracene (DMBA). MC effectively inhibited SCEs induced by CP and AFB in a dose-dependent manner, but it had no effect on SCE induction by BP and DMBA. MC also reduced CP-induced SCE frequencies in a hepatic tumor cell line (HTC). These cells are metabolically competent and activate CP into its biologically active metabolites. Our results support the suggestion that MC modulates the genotoxicity of indirect-acting mutagens by inhibiting certain forms of the cytochrome P-450 enzymes required for activation of premutagens like CP and AFB.

Inhibition of clastogenic effects of cesium chloride in mice in vivo by chlorophyllin.

The antagonistic effect of chlorophyllin was tested in reducing the clastogenic action of cesium chloride (CsCl) in vivo on mice bone marrow cells. CsCl induced chromosomal aberration in frequencies directly proportional to the dose administered. Chlorophyllin, when given alone, was not clastogenic even at a concentration of 1.5 mg/kg body wt. of the animal. Simultaneous administration of chlorophyllin and CsCl reduced chromosomal aberrations significantly at 24 h. Exposure to the same dose of chlorophyllin 2 h before exposure to CsCl also decreased clastogenic effects but to a lesser extent. These findings are of importance in view of the uptake of radioactive Cs by green plants after nuclear fallout.

Chemopreventive properties of chlorophyllin: inhibition of aflatoxin B1 (AFB1)-DNA binding in vivo and anti-mutagenic activity against AFB1 and two heterocyclic amines in the Salmonella mutagenicity assay.

Chlorophyllin (CHL), a sodium/copper derivative of chlorophyll, has been used to treat a number of human conditions with no toxic effects being reported. Recent studies have described the anti-mutagenic activity of CHL in several short-term genotoxicity assays; however, this compound has not been reported to inhibit carcinogen--DNA binding in vivo, and it has yet to be evaluated as an anti-carcinogen in any species. The chemopreventive properties of CHL were studied in trout using inhibition of aflatoxin B1 (AFB1)--DNA binding as an end-point. Chlorophyllin and AFB1 were coadministered in the diet, and carcinogen--DNA binding levels were determined in liver after 1, 3, 5 and 7 days. Linear increases in AFB1--DNA binding occurred with time of treatment at each CHL dose level (0, 500, 1000 and 2000 p.p.m.). Each increase in CHL dose produced a concomitant decrease in AFB1--DNA binding, resulting in a series of curves of decreasing slope. At the highest CHL dose level of 2000 p.p.m., AFB1--DNA binding was inhibited by 70%. These results suggest that CHL should be a potent inhibitor of AFB1-induced hepatocarcinogenesis in this model. In the Salmonella assay, CHL exhibited potent anti-mutagenic activity against AFB1 and two heterocyclic amines when incubated in the presence of trout liver activation systems. CHL also inhibited the mutagenic activity of AFB1-8,9-epoxide in the absence of a metabolic activation system. Dietary CHL substantially inhibited liver AFB1-DNA binding in vivo, even when AFB1 was given by i.p. injection to avoid direct AFB1--CHL interaction in the diet or gut. Collectively, these studies support a CHL inhibitory mechanism involving complex formation with the carcinogen in the gut coupled with electrophile scavenging or further complexing in the target organ.

Inhibition by diacylmethane derivatives of mutagenicity in Salmonella typhimurium and tRNA-binding of chemical carcinogens.

Effects of diacylmethanes on the mutagenicity of 2-naphthohydroxamic acid, methylnitrosourea, benzo[a]pyrene and aflatoxin B1 in S. typhimurium and the tRNA binding by benzo[a]pyrene and aflatoxin B1 were investigated. Acetylacetone, benzoylacetone and dibenzoylmethane inhibited the mutagenicity of 2-naphthohydroxamic acid, and dibenzoylmethane and 1,3-indandione inhibited that of methylnitrosourea, benzo[a]pyrene and aflatoxin B1. The binding to tRNA of benzo[a]pyrene and aflatoxin B1 was inhibited by benzoylacetone and dibenzoylmethane, and dibenzoylmethane, 1,3-indandione and 1,1,1-trifluoroacetylacetone, respectively. The inhibition of methylnitrosourea mutagenicity was observed when the bacteria were exposed concomitantly to the inhibitors and the mutagen, but not when they were exposed to the inhibitors 1 h after exposure to the mutagen. These results demonstrate that active methylene compounds can inhibit mutagenicity and nucleic acid-binding of chemical carcinogens presumably by trapping carcinogenic electrophiles, and they are potential anti-carcinogenic agents during the initiation stage.

Effects of sulfhydryl modulation on ethyl acrylate-induced forestomach toxicity.

Acute administration of a single dose of ethyl acrylate (EA) to F344 rats by gavage caused time- and dose-dependent forestomach edema. Evidence from our laboratory and others suggested that EA is hydrolyzed to acrylic acid (AA) and ethanol both in vivo and in vitro. The major metabolites detected in teh urine of rats treated with EA were derivatives of the glutathione conjugates of EA and AA. The current work was undertaken to investigate the effects of sulfhydryl-depleting agents (diethylmaleate and fasting) and sulfhydryl-containing agents (cysteine and cysteamine) on EA-induced forestomach edema. Results presented in this report revealed that pretreatment of rats with sulfhydryl-containing chemicals such as cysteine or cysteamine has potentiated EA-induced forestomach edema. In contrast, depletion of indigenous sulfhydryls by fasting of rats or pretreatment with diethylmaleate (DEM) protected against EA-induced forestomach edema. Furthermore, repetitive daily administration of EA by gavage induced mucosal forestomach hyperplasia. Co-administration of cysteamine and EA resulted in a significant enhancement of the severity of EA-induced forestomach mucosal hyperplasia. In conclusion, current data suggest that modulation of indigenous sulfhydryls play a role in EA-induced forestomach toxicity; however, the exact mechanism underlying this role remains to be characterized.

[Changes in the mutagenic effect of a medium containing aflatoxin B1 as a result of the yeast activity]. / Izmenenie mutagennoi aktivnosti sredy, soderzhashchei aflatoksin B1, v rezul'tate zhiznedeiatel'nosti drozhzhei.

Changes in the mutagenic activity of the nutrient medium containing aflatoxin Br as a result of living activity of the yeast Rhodotorula mucilaginosa I B has been studied. Reduction of mutagenic activity of the medium when tested on the strains Salmonella typhimurium TA98 (6.3 times fold), TA100 (2.2 times fold), AG262 (2 times fold) has been revealed. The data obtained leads to the conclusion that the technology, based on the use of the indicated strain of the yeast for the treatment of food and feed stuffs contaminated by aflatoxin B1, can be used.

Studies on the effect of ascorbic acid and selenium on the genotoxicity of nitrofurans: nitrofurazone and furazolidone.

The genotoxic properties of nitrofurazone and furazolidone were studied using the Ames test and SOS-chromotest. Both compounds were found to act as strong mutagens on the TA97 and TA102 strains of S. typhimurium and to induce the SOS-repair system in the PQ37 strain of E. coli. A good concordance was found between the mutagenic activity and the ability to induce the SOS system. Ascorbic acid and sodium selenite only very slightly lowered the genotoxic effect of the 2 nitrofurans studied both in the Ames test and in the SOS-chromotest.

Catechin inhibition of mutagenesis and alteration of DNA binding of 2-acetyl-aminofluorene in rat hepatocytes.

Bioflavonoids are naturally occurring plant products that have demonstrated inhibitory effects on chemically induced carcinogenesis or mutagenesis. The chemoprotective effects are either direct scavenging of reactive molecules or indirect effects, such as enzyme activity alteration. Exposure of cultures of isolated rat hepatocytes to catechin (0.01-1.0 mM), a plant phenolic flavonoid, and subsequent addition of 2-acetylaminofluorene (AAF) resulted in an enhanced binding of AAF metabolites to hepatocellular DNA. Incubations of hepatocytes with catechin and S. typhimurium demonstrated no mutagenicity of catechin. At 1.0 and 5.0 mM concentrations of catechin with AAF and 30-min incubation with hepatocytes prior to plating there was inhibition of AAF-induced mutagenicity. However, at 0.5 mM of catechin there was a significant enhancement in mutagenicity. The increase in DNA binding of AAF in the cultures of hepatocytes is due to the alteration of metabolism by exposure to catechin. Catechin increases both N-hydroxylation and deacetylation pathways in the hepatocytes producing increases in N-hydroxy-AAF and aminofluorene. Both of these metabolites are important in AAF intermediates binding with DNA. The short-term incubation of catechin, AAF, hepatocytes, and S. typhimurium in the mutagenesis assay is not sufficient for induction of metabolic pathways. However, previously reported inhibition of detoxification pathways and/or scavenging of the proximate carcinogen can occur to alter mutagenesis in a dose-dependent manner.

Effects of carotenoids on aflatoxin B1-induced mutagenesis in S. typhimurium TA 100 and TA 98.

The effects of beta-carotene, canthaxanthin, and extracts of tomato paste (containing lycopene) and orange juice (containing cryptoxanthin) on aflatoxin B1 (AFB1)-induced mutagenesis in S. typhimurium TA 100 and TA 98 were investigated. Inhibition of mutagenesis was studied during and following completion of AFB1 metabolism (i.e., after the addition of menadione), thereby permitting separate examination of the metabolic activation and phenotypic expression phases. Each experimental carotenoid, except lycopene, inhibited AFB1-induced mutagenesis in both tester strains. Cryptoxanthin was the most potent inhibitor, being at least an order of magnitude more potent than the other carotenoids. Inhibition by beta-carotene and canthaxanthin was more prominent during the activation phase, whereas cryptoxanthin was more effective during the subsequent phenotypic expression phase. These inhibitory effects were not dependent on conversion to retinol.

Specificity of antimutagens against chemical mutagens in microbial systems.

Procedures have been developed which enable the study of antimutagenic specificity of certain antimutagenic chemicals against chemical mutagens/carcinogens. Modifications of the Ames Salmonella assay, the Bacillis subtilis rec assay of Kada and co-workers, and the Luria-Delbrück fluctuation test, along with procedures we have developed utilizing E. coli K12 strain ND160 developed by Dworkin, all are employed in these studies. Using these procedures, a number of naturally-occurring compounds and/or their derivatives have been shown to produce antimutagenic specificity either against changes at different specific genetic loci or against activity of specific chemical mutagens such as nitrofurazone, ethyl methanesulfonate, or caffeine. Compounds that demonstrate this activity include cinnamaldehyde, chlorophyllin, an extract of Glycyrrhiza glabra, spermine, and mixtures of guanosine and cytidine. The data demonstrate that some antimutagens act specifically against spontaneous mutations, while others inhibit the development of chemically-induced mutations at specific loci. These results have potential application to the prevention of chemical toxicological damage.

Antimutagenicity profiles for some model compounds.

The concept of activity profile listings and plots, already applied successfully to the display of mutagenicity data, has been modified for application to antimutagenicity data. The activity profiles are bar graphs that have been organized in two general ways: for antimutagens that have been tested in combination with a given mutagen and for mutagens that have been tested in combination with a given antimutagen. Doses from both the mutagen and the antimutagen are displayed and plotted together with results on enhancement or inhibition of mutagenic activity. The short-term tests that have been used extensively to identify mutagens and potential carcinogens are increasingly being used to identify antimutagens and potential anticarcinogens. Three model mutagens, N-methyl-N'-nitro-N-nitrosoguanidine, aflatoxin B1 and benzo[a]pyrene, and 4 model antimutagens, butylated hydroxyanisole, butylated hydroxytoluene, glutathione and disulfiram, were selected from the data surveyed in the published literature. It is not clear at the present time whether the inhibition of carcinogen-induced mutation is a good indicator of anticarcinogenic properties, and further research is needed. Nevertheless, the activity profiles are useful for the assessment of the available antimutagenesis data by providing rapid visualization of considerable dose information and experimental results.

Roles of dietary fat and fibre in the disposition and metabolism of carcinogens associated with foods.

The abilities of dietary fibre (wheat bran) or fat (olive oil) to modify the genotoxicity of radiolabelled MeIQ were evaluated in mice using in vivo and in vitro bacterial mutation assays. Bran reduced genotoxicity by restricting uptake of MeIQ from the gut lumen. In contrast, feeding mice a high fat diet led to increased hepatic conversion of MeIQ to an active genotoxin.