Effects of sodium selenite and caffeine on mutagenesis induced by N-methyl-N-nitrosourea, N-methyl-N'-nitro-N-nitrosoguanidine and aflatoxin B1 in S. typhimurium

Caffeine as a photoprotective agent for diminishing phototoxicity

Skin whitening with Chinese herbal medicine has been used in ancient Asia. However, phototoxicity of the active ingredient limits the application. The modified comet assay was used in the current study to detect DNA crosslinking induced by phototoxicity. Result showed that caffeine at 5 µmol/L was able to reduce 5-methoxypsoralen-induced phototoxicity with ultraviolet C (UVC) exposure.

The antimutagenicity of 2-substituted selenazolidine-4-(R)-carboxylic acids

Selenium can have cancer chemopreventive activity, although the mechanism of action has not been well defined. Selenazolidine-4-(R)-carboxylic acids (SCAs) were devised as prodrugs of L-selenocysteine, to provide selenium in a form and at a concentration commensurate with cancer chemopreventive activity. In the present study, a series of selenazolidines has been evaluated in the Salmonella typhimurium TA98 tester strain and all were found to possess antimutagenic activity. There was little difference between the seven selenazolidines in their effectiveness against either benzo[a]pyrene (B[a]P) or 3,6-bis(dimethylamino)acridine (acridine orange), agents which differ in their requirement for mammalian enzyme bioactivation for mutagenicity. Antimutagenic activity against acridine orange was dependent on selenazolidine concentration, and EC50 values were in the 5-10 microM range. At 25 microM, the concentration tested in common for the two mutagens, the selenazolidines were more effective antimutagens against acridine orange than against B[a]P, with reductions in mutant frequency ranging from 54 to 71% for B[a]P and 79 to 93% for acridine orange. Efficacy against B[a]P was not enhanced when the concentration was increased to 50 microM. The similarity in efficacy among the selenazolidines against B[a]P mutagenicity, contrasted with inter-compound differences in their ability to inhibit S9 CYP1A activity. The CYP1A Ki values ranged from a low of 63 microM (2-[2'-hydroxyphenyl]SCA) to a high of 1.1mM (2-cyclohexylSCA), but all were above the concentration required to inhibit mutagenicity by 50%. Thus, all the SCAs possess antimutagenic activity against both B[a]P and acridine orange, the efficacy varies little between the individual selenazolidines, and for B[a]P, the efficacy is not proportional to the inhibitory effect on the mutagen bioactivating enzyme.

Assessment of the relationship between the antimutagenic action of riboflavin and glutathione and the levels of antioxidant enzymes

In this study the role of antioxidant enzymes on the antimutagenic actions of riboflavin and reduced glutathione against mutagenic potentials of 4-nitroquinoline 1-oxide and mitomycin C have been investigated. For this purpose the activities of catalase and superoxide dismutase enzymes have been determined in Salmonella typhimurium TA102 and TA100 strains preincubated with different combinations of 4-nitroquinoline 1-oxide, mitomycin C, riboflavin and reduced glutathione for thirty minutes. Also in part of the same samples, the mutagenicity has been determined for each combination of chemicals by using Salmonella preincubation test. The correlation between the levels of antioxidant enzymes and mutagenicity and antimutagenicity has been investigated.While riboflavin displayed a weakly antimutagenic effect on 4-nitroquinoline 1-oxide mutagenicity in TA102 and TA100 (0.25, 0.35 inhibition respectively), it did not have any effect on the strong mutagenicity of mitomycin C in both strains. Reduced glutathione, a well known antioxidant, had no antimutagenic effect against the mutagenicity of both compounds in TA102 and TA100 strains. The antioxidant enzymes, catalase and superoxide dismutase, seemed to have no direct effect on the antimutagenic action of riboflavin and mutagenic action of 4-nitroquinoline 1-oxide and mitomycin C because no change in the activities of catalase and superoxide dismutase was detected in relation to antimutagenicity of riboflavin and mutagenicity of 4-nitroquinoline 1-oxide and mitomycin C in both strains. It should be noted that many antimutagens have more than one mechanism of action and their effect depends on the mutagens being tested.

Effects of caffeine on glandular stomach carcinogenesis induced in rats by N-methyl-N'-nitro-N-nitrosoguanidine and sodium chloride

The modifying effects of caffeine ingestion on glandular stomach carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and sodium chloride (NaCl) were investigated in male Wistar rats. Animals were given a MNNG solution (100 ppm) as their drinking water and simultaneously fed a diet supplemented with 5% NaCl for 8 wk. They then received 0.25% caffeine solution (groups 1 and 3) or tap water (groups 2 and 4) as the drinking water, and were fed the NaCl diet (groups 1 and 2) or basal diet (groups 3 and 4) for the following 32 wk. Both caffeine and NaCl treatments exerted growth retardation effects, the suppression being stronger with caffeine than NaCl, and animals in group 1 (NaCl plus caffeine) showing the lowest body weight. The incidence of adenocarcinomas in the pylorus was significantly decreased in group 1 compared with the group 2 (NaCl) value (P < 0.05). The incidence of atypical hyperplasias in the fundus was also lower in group 1 than in group 2, although in both cases significantly higher (P < 0.05 and P < 0.01) than in group 4 (no treatment). These results were in good agreement with short-term assay findings whereby lipid peroxidation in the glandular stomach mucosa induced by 4% NaCl ingestion was inhibited by caffeine treatment. In group 3 (caffeine), caffeine intake by itself did not modulate glandular stomach tumour development. The results thus suggest that caffeine inhibits the gastric tumour promotion activity of NaCl in rats.

Comparative mutagenicity of chemicals selected for test in the International Program on Chemical Safety's collaborative study on plant systems for the detection of environmental mutagens

A review has been made for the four compounds (maleic hydrazide, methyl nitrosourea, sodium azide, azidoglycerol) tested in the International Program on Chemical Safety's collaborative study on plant systems. Maleic hydrazide (MH) is a weak cytotoxic/mutagenic chemical in mammalian tissues and is classified as a class 4 chemical. In contrast, with few exceptions such as Arabidopsis, MH is a potent mutagen/clastogen in plant systems. The difference in its response between plant and animal tissue is likely due to differences in the way MH is metabolized. MH appears to be noncarcinogenic and has been given a negative NCI/NTP carcinogen rating. Methyl nitrosourea (MNU) is a toxic, mutagenic, radiomimetic, carcinogenic, and teratogenic chemical. It has been shown to be a mutagen in bacteria, fungi, Drosophila, higher plants, and animal cells both in vitro and in vivo. MNU is a clastogen in both animal and human cell cultures, plant root tips and cell cultures inducing both chromosome and chromatid aberrations as well as sister-chromatid exchanges. Carcinogenicity has been confirmed in numerous studies and involves the nervous system, intestine, kidney, stomach, bladder and uterus, in the rat, mouse, and hamster. MNU produces stage-specific teratogenic effects and also interferes with embryonic development. The experimental evidence that strongly indicates the mutagenic effects of MNU underlines the possible hazard of this compound to human beings. The experimental evidence for the stringent handling of this compound is clear. Sodium azide (NaN3) is cytotoxic in several animal and plant systems and functions by inhibiting protein synthesis and replicative DNA synthesis at low dosages. It is mutagenic in bacteria, higher plants and human cells and has been used as a positive control in some systems. In general, tests for clastogenicity have been negative or weakly positive. No evidence of carcinogenicity has been reported in a 2-year study seeking carcinogenic activity in male and female rats. Its advantages in comparison to other efficient mutagens are claimed to be a high production of gene mutations accompanied by a low frequency of chromosomal rearrangements and safer handling because of its nonclastogenic and noncarcinogenic action on humans. Azidoglycerol (AG) is a very potent mutagen in bacteria, yeast and higher plants including Arabidopsis and Tradescantia; however, it only slightly enhances the frequencies of recessive lethals in Drosophila. AG is at best a weak clastogen and is without effect in inducing chromosomal aberrations and SCEs in human peripheral lymphocytes in vitro. In microbial and plant systems, AG is considerably more potent than sodium azide in the maximal frequencies of mutation induced. In particular, in Saccharomyces cerevisae, AG is 3000-fold more mutagenic than sodium azide. Its carcinogenic and teratogenic properties are unknown.

Additive coclastogenicity of sodium selenite and caffeine in CHO cells treated with N-methyl-N'-nitro-N-nitrosoguanidine

The clastogenic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster ovary (CHO) cells and its modulation by Na2SeO3 and caffeine were studied by metaphase analysis of chromosome aberrations (CA) as well as by measuring the formation and repair of single-strand (ss) DNA breaks employing hydroxylapatite chromatography. Treatment of CHO cells with MNNG (1.25 or 2.5 x 10-5M) for 3 h caused CA in 11 and 19% of metaphases scored, respectively. Pretreatment of cells with Na2SeO3 (1-5 micrograms/mL) or caffeine (0.2-2.0 mg/mL) for 2 h resulted in a 2-3.5-fold increase of CA frequency. Addition of both modulators during the mutagen exposure tended to cause a slight inhibition of clastogenic activity of MNNG (1.25 x 10(-5) M) or had no effect on CA number when MNNG was used at a concentration of 2.5 x 10(-5) M). Posttreatment of CHO cells with Na2SeO3 for 20 h after MNNG was ineffective in influencing the number of metaphases with CA, whereas, at these conditions, caffeine enhanced up to 6-7-fold the clastogenic activity of MNNG. Addition of both modulators during the whole experiment, 2 h pretreatment included, resulted in a further significant increase of CA frequency up to the total pulverization of chromosomes in all metaphases scored. The coclastogenic effect of caffeine was greater in this case. The enhancement of chromosome-damaging activity of MNNG by selenite and caffeine was better expressed when this carcinogen was applied at the higher concentration used. An additive coclastogenic effect was observed in CHO cells treated simultaneously with Na2SeO3 and caffeine plus MNNG.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential genotoxic, mutagenic and antimutagenic effects of coffee: a review

Coffee and caffeine are mutagenic to bacteria and fungi, and in high concentrations they are also mutagenic to mammalian cells in culture. However, the mutagenic effects of coffee disappear when bacteria or mammalian cells are cultured in the presence of liver extracts which contain detoxifying enzymes. In vivo, coffee and caffeine are devoid of mutagenic effects. Coffee and caffeine are able to interact with many other mutagens and their effects are synergistic with X-rays, ultraviolet light and some chemical agents. Caffeine seems to potentiate rather than to induce chromosomal aberrations and also to transform sublethal damage of mutagenic agents into lethal damage. Conversely, coffee and caffeine are also able to inhibit the mutagenic effects of numerous chemicals. These antimutagenic effects depend on the time of administration of coffee as compared to the acting time of the mutagenic agent. In that case, caffeine seems to be able to restore the normal cycle of mitosis and phosphorylation in irradiated cells. Finally, the potential genotoxic and mutagenic effects of the most important constituents of coffee are reviewed. Mutagenicity of caffeine is mainly attributed to chemically reactive components such as aliphatic dicarbonyls. The latter compounds, formed during the roasting process, are mutagenic to bacteria but less to mammalian cells. Hydrogen peroxide is not very active but seems to considerably enhance mutagenic properties of methylglyoxal. Phenolic compounds are not mutagenic but rather anticarcinogenic. Benzopyrene and mutagens formed during pyrolysis are not mutagenic whereas roasting of coffee beans at high temperature generates mutagenic heterocyclic amines. In conclusion, the mutagenic potential of coffee and caffeine has been demonstrated in lower organisms, but usually at doses several orders of magnitude greater than the estimated lethal dose for caffeine in humans. Therefore, the chances of coffee and caffeine consumption in moderate to normal amounts to induce mutagenic effects in humans are almost nonexistent.