Modification of the mutagenicity of aflatoxin B1 and N-methyl-N'-nitro-N-nitrosoguanidine by certain phenolic compounds.

Five natural and two synthetic phenolic compounds were tested for their ability to suppress mutagenicity of aflatoxin B1 (AFB1) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Salmonella typhimurium tester strain TA100. Caffeic acid and eugenol were observed to inhibit mutagenicity of both the carcinogens, while chlorogenic acid was effective in the case of AFB1 alone and ellagic acid and butylated hydroxytoluene were found to be antimutagenic only for MNNG. These differential activities of the phenolic compounds appeared to be due to their different modes of action towards direct and indirect acting carcinogens.

Effect of certain trace elements on the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine.

Tests have been carried out to detect inhibitory activity of various trace elements on mutagenesis induced by the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine in Salmonella typhimurium strain TA100. Selenium has been found to be most active in this regard while copper has displayed moderate inhibitory ability. The action of selenium is mediated through an interaction resulting in rapid deactivation of the carcinogen.

Modifying role of dietary factors on the mutagenicity of aflatoxin B1: in vitro effect of plant flavonoids.

Eighteen flavonoids have been tested for their ability to inhibit the mutagenicity of aflatoxin B1 (AFB1) towards strains TA100 and TA98 of Salmonella typhimurium provided with a rat liver activation system. These flavonoids belong to 5 different groups: flavone, isoflavone, flavanone, flavanol and flavonol, and many individual members are natural products present in edible portions of a variety of food plants. Several flavonoids exhibited significant inhibitory ability in both strains. Flavonols in general are more active in this regard, while flavanones show a strain-specific response. The flavanol group of compounds did not display any activity. Among the most effective flavonoids are kaempferol, morin, fisetin, biochanin A and the glycoside rutin, all of which exhibit a dose-dependent inhibition pattern. Kaempferol and rutin, in particular, show exceptional activity inasmuch as, on a molar basis, only a 10-fold excess dose of each can inhibit the mutagenic activity of AFB1 in strain TA98 by 50%. The action of flavonoids is possibly mediated through interaction with microsomal activating enzymes. Previous evidence from this laboratory about their inhibitory action on DNA-adduct formation and metabolic activation together with the present results suggests that certain flavonoids, notably polyhydroxylated flavonols, may have potential anticarcinogenic activity against AFB1.

Modifying role of dietary factors on the mutagenicity of aflatoxin B1: in vitro effect of sulphur-containing amino acids.

Sulphur-containing amino acids including some derivatives have been tested for their effectiveness in suppressing the mutagenic activity of aflatoxin B1 in Salmonella typhimurium strains provided with a rat liver activation system. Cysteine and N-acetylcysteine have been found to be most effective in the 2 strains tested (TA100 and TA98). Glutathione (oxidised and reduced forms) has shown partial activity, while cystine and methionine are found to be partially effective only in strain TA100. Inhibition of mutagenicity may be due to interaction of these substances with microsomal enzymes resulting in interference with the formation of ultimate mutagenic species.

Modifying role of dietary factors on the mutagenicity of aflatoxin B1: in vitro effect of trace elements.

Using Salmonella typhimurium strains TA100 and TA98 tests have been carried out to detect the inhibitory activity of various trace elements on mutagenesis induced by aflatoxin B1 (AFB1) in the presence of a rat liver microsomal activation system. Several trace elements have shown significant modulating activity in both the strains, while a few show inhibition only in a particular strain. Among the most effective elements are copper, manganese, zinc and selenium, all of which exhibit an inhibition pattern which is dose-dependent. Copper, in particular, shows exceptional activity, since the molar excess dose of this element required to inhibit AFB1 mutagenicity by 50% has been observed to be very low. The action of trace elements is possibly mediated through interaction with microsomal enzymes, thereby modulating the formation of the reactive metabolite before modification of DNA. These results suggest that certain trace elements notably copper may have potential anticarcinogenic activity against AFB1.

Modifying role of dietary factors on the mutagenicity of aflatoxin B1: in vitro effect of vitamins.

19 vitamins including some derivatives have been tested for their ability to suppress mutagenic activity of aflatoxin B1 (AFB1) towards Salmonella typhimurium strain TA100 activated with a rat-liver metabolic activation system. Several vitamins have shown an ability to inhibit the mutagenic potency of AFB1. The values of ID50, i.e. the dose required to inhibit mutagenic activity by 50% calculated from dose-response curves for each vitamin show retinoids, riboflavin, folic acid, menadione, cyanocobalamin, ascorbic acid and pyridoxine to be significantly antimutagenic. Although inhibition by vitamins is apparent over a range of AFB1 concentrations, their effect is more pronounced at lower concentrations of AFB1. When combined data are expressed in terms of specific mutagenicity, riboflavin, retinol and menadione have been found to possess exceptional inhibitory ability in as much as, on a molar basis, only 15-40-fold excess vitamins can inhibit the mutagenic potency of AFB1 by 50%. Their action is possibly mediated through interaction with microsomal activating enzymes. Previous evidence from this laboratory about their inhibitory action on DNA-adduct formation and metabolic activation together with the present results suggest that certain vitamins notably retinoids and riboflavin may have potential anticarcinogenic activity against AFB1.

Radiation protection of DNA and membrane in vitro by extract of Hemidesmus indicus.

Radioprotective effect of H. indicus root extract on lipid peroxidation in rat liver microsomes and plasmid DNA was examined. Hemidesmus indicus (HI) root extract was found to protect microsomal membranes as evident from reduction in lipid peroxidation values. The extract could also protect DNA from radiation induced strand breaks.

Modifying role of vitamins on the mutagenic action of N-methyl-N'-nitro-N-nitrosoguanidine.

Several vitamin compounds have been tested for their ability to suppress the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine, a direct acting mutagen/carcinogen, in Salmonella typhimurium strain TA100. Menadione, alpha-tocopherol, retinal and retinol have displayed high inhibitory activity. The antimutagenic activity of menadione, in particular, has been found to be remarkable in as much as less than equimolar amount can reduce the mutagenic potency of the carcinogen by 50%. In vitro data suggest that its action is mediated by accelerating the deactivation of the N-nitroso carcinogen, possibly involving the formation of a quinone radical.

Modulating effect of plant flavonoids on the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine.

Tests have been carried out with several plant flavonoids to detect their ability to suppress mutagenesis in Salmonella typhimurium strain TA100 NR induced by the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine. Among the most effective flavonoids are the isoflavone, biochanin A, the flavanone glycoside, naringin, and its aglycone, naringenin, and several flavonols, e.g. morin, fisetin, kaempferol, gossypetin and quercetin, including a flavonol glycoside, rutin. In particular, naringin possesses exceptional antimutagenic activity, in as much as, less than half the equimolar amount can reduce the mutagenic potency of this carcinogen by 50%. These flavonoids appear to act either by preventing passage of the carcinogen into bacterial cells or by altering some cellular processes.

Cytotoxicity of ethyl methanesulfonate in mice spermatogonia.

Enumeration of different types of spermatogonia, following a single i.p. administration of different doses of ethyl methanesulfonate in mice, showed a survival of A1-A4 and in spermatogonia is markedly reduced due to cell killing while the remaining types of spermatogonia were affected marginally. The cell killing effect was dose-dependent, and replenishment of these cells was observed by the end of one cycle of the seminiferous epithelium comprising of 8.5 days.

Effects on the spermatogonia of mice following treatment with sodium bisulfite.

The effect of sodium bisulfite on differentiating spermatogonia has been investigated. Adult mice were given either a single intraperitoneal injection (500, 600, 700, 800, 900 and 1000 mg/kg body weight) or repeated intraperitoneal injections (200 and 400 mg/kg body weight) of sodium bisulfite. In the latter case, the doses were administered 20, 30 and 40 times during 28, 42 and 56 days respectively. Different types of spermatogonia were enumerated from paraffin sections of tests stained with periodic acid--Schiff and Ehrlich's hematoxylin. No mortality was observed up to 700 mg/kg dose within 24 hours. At 1000 mg/kg dose 80% of the mice died within 24 hours post treatment. Cytotoxicity data showed that sodium bisulfite, at any of the dosage level tested after acute or repeated administration did not alter the population of various types of spermatogonia.

Cytoplasmic changes during thioacetamide induced hepatocarcinogenesis in rats.

Cytoplasmic changes were investigated in livers of rats at various intervals up to 50 weeks during primary induction of hepatoma by thioacetamide feeding.Microsomal Glucose-6-phosphatase and ATPase activities were shown to decrease progressively with increased period of thioacetamide feeding the fall in activities being more pronounced during the first 15 weeks.Hormonal induction of tryptophan pyrrolase and tyrosine transaminase activities was shown to undergo a significant decrease of 65% and 55% respectively at the end of 50 weeks feeding.The substrate induced tryptophan pyrrolase activity was decreased to 50% during the 50 weeks period whereas the substrate induced tyrosine transaminase activity gradually increased to 200%. The latter is attributable to differences in the optimal induction dose of tyrosine in normal and carcinogen fed rats.The m-RNA template lifetime for tryptophan pyrrolase was shown to be exceeding 24 hours in normal rats as against that of 13 hours in rats fed with carcinogen for 30 weeks. On the other hand the m-RNA template lifetime for tyrosine transaminase was 3 hours in control rats while it was 7 hours in the carcinogen fed rats.The observed changes were shown to occur long before the onset of malignant transformation.The alterations in terms of decreased Glucose-6-phosphatase and substrate induced tryptophan pyrrolase activities were shown to be reversible when the carcinogen was withdrawn from the diet after 30 weeks of feeding.The significance of these observations is discussed in relation to damage to endoplasmic reticulum during hepatocarcinogenesis.

Protection of DNA and microsomal membranes in vitro by Glycyrrhiza glabra L. against gamma irradiation.

The radioprotective effect of the root extract of Glycyrrhiza glabra L on lipid peroxidation in rat liver microsomes and plasmid pBR322 DNA was investigated. The extract was found to protect microsomal membranes, as evident from reduction in lipid peroxidation, and could also protect plasmid DNA from radiation-induced strand breaks.