Inhibitory effects of phenolics, teas and saliva on the formation of mutagenic nitrosation products of salted fish

The objectives of this study were to simulate in vitro some of the conditions that may prevail in man during the ingestion of a meal and to quantitate the inhibitory effect of phenolics and phenolic-containing beverages on the formation of mutagenic nitrosation products. The test system consisted of nitrosating (pH 2, 1 h, 37 degrees C) an aqueous fraction of a salt-preserved Chinese fish (Pak Wik) with or without the inhibitors to be tested and estimating the frequency of his+ revertants per survivor of Salmonella typhimurium (strain TA1535). The phenolics and teas were added to the nitrosation mixture. Catechin, chlorogenic acid, gallic acid, pyrogallol and tannic acid suppressed the formation of mutagenic nitrosation products. The inhibitory efficiency was comparable to that of ascorbic acid. A Japanese, a Chinese and a Ceylonese tea also prevented the formation of mutagenic nitrosated fish products at doses which are usually consumed by man. Moreover, saliva exerted an inhibitory effect. The inhibitory effect was not additive when the phenolics or saliva were added concurrently to the nitrosation mixture. The possibility that phenolics are involved in the apparent chemopreventive effect of fruits and vegetables is discussed.

Application of the micronucleus test to exfoliated cells of high cancer risk groups: tobacco chewers

Powdered tobacco (Khaini tobacco) with the addition of lime is commonly used by the residents of Bihar, India. The tobacco/lime mixture is usually placed on the inner side of the lower lip within the gingivolabial groove. About 42% of the users keep it at the front, the rest move the tobacco towards the left or right side within the oral cavity. Carcinomas (so-called "Khaini cancers") develop mainly at the site where the tobacco is in close contact with the mucosa. Scrapings of the mucosa were taken at sites where the tobacco is kept, then smears were prepared, stained with the Feulgen reaction and fast green, and screened for micronuclei which indicate the occurrence of chromosome aberrations in the dividing cell population of the basal layer. An elevated frequency of cells with micronuclei was found in the oral mucosa of all 27 examined Khaini tobacco users (Munda and Santal tribes) compared to that of non-chewers of similar ethnic background and dietary habits. The induction of micronucleated mucosa cells seems to be due to genotoxic agents released from the tobacco/lime mixture. In vitro, an aqueous extract of the Khaini tobacco elicits chromosome aberrations and micronuclei in cultured human fibroblasts and Chinese hamster ovary (CHO) cells. No chromosome-damaging effect was observed following the application of lime or calcium hydroxide (Ca(OH)2). The micronucleus test on exfoliated cells can provide evidence of carcinogen exposure in the tissue from which cancers will develop. This approach combines all the advantages of in vitro short-term tests for genotoxic and carcinogenic agents with those of using an intact organism with all its defence mechanisms.

Elevated frequency of micronucleated cells in the buccal mucosa of individuals at high risk for oral cancer: betel quid chewers

The micronucleus test was applied to buccal mucosa cells of 2 population groups at high risk for oral cancer: Khasis of the northeastern hill region of India, who eat raw betel nuts together with betel leaves and lime, and residents of the state of Orissa (India), who chew betel quids consisting mainly of perfumed tobacco, dried betel nut, betel leaf, lime and several spices. Micronuclei were scored on Feulgen/fast green-stained smear preparations of exfoliated cells obtained by scraping the surface of the buccal mucosa. All 17 raw betel nut eaters and all 20 chewers of betel quids had significantly elevated frequencies of micronucleated mucosa cells over nonchewing controls of comparable ethnic background and dietary habits. The frequencies of micronucleated exfoliated cells were higher at the site within the oral cavity where the quid was kept compared to those at the opposite buccal wall. The micronuclei frequency was lower among individuals chewing a raw betel nut, betel leaf and lime mixture compared to those using tobacco,-betel nut-, lime- and betel leaf-containing quids. Micronuclei frequencies in exfoliated human cells seem to represent a useful 'internal dosimeter' for estimating exposure to genotoxic, and by implication, carcinogenic agents in the tissue from which cancers will develop.

The inhibitory effect of whole and deproteinized saliva on mutagenicity and clastogenicity resulting from a model nitrosation reaction

The objective of this study was to simulate in vitro at least some of the conditions that prevail in man during ingestion of nitrate and nitrosable compounds. Human saliva has been chosen because most chemicals ingested through food will interact with saliva. The nitrosation of methylurea was used as a model because the nitrosation products can be readily detected by their mutagenic (his+ revertants of S. typhimurium) and clastogenic (chromosome aberrations in CHO cells) properties. The results show that human saliva inhibits the formation of mutagenic and clastogenic nitrosation products when present during nitrosation. A 50% inhibition of mutagenicity results from the addition of a saliva sample diluted at 5% of the original concentration. In the test system used a similar inhibitory effect was obtained by 2.5 mM ascorbic acid or 2.0 mM chlorogenic acid. The main inhibitory agents seem to reside in a deproteinized fraction which was filtered through an ultrafilter UM2 (greater than 1000 MW). At strong acid levels (below pH 2) the saliva loses its inhibitory effect on the nitrosation of methylurea. The contribution of saliva to the inhibition of endogenous nitrosation within the oral cavity or stomach is discussed.

Inhibition of mutagenicity of a model nitrosation reaction by naturally occurring phenolics, coffee and tea

Several plant phenolics, one instant coffee, one instant decaffeinated coffee, one roasted coffee, one Japanese tea, one black Indian tea, and one Chinese tea were examined for their inhibitory properties on mutagenicity resulting from the nitrosation of methylurea. Mutagenicity was estimated as the number of his+ revertants per survivor of Salmonella typhimurium TA1535 which was exposed in suspension to the nitrosation mixtures and the modulating agents for 20 min. Tannic acid, gallic acid and chlorogenic acid suppressed the mutagenicity of the model nitrosation system at concentrations similar to or even lower than ascorbic acid. The three tested coffees and three tested teas exerted an inhibitory effect on the mutagenicity of the test system at doses at which they are consumed.

Induction of mitotic gene conversion by browning reaction products and its modulation by naturally occurring agents

Mitotic gene conversion in the D7 strain of Saccharomyces cerevisiae was significantly enhanced by exposure to non-enzymatic browning reaction products. These products were formed during the heating of sugar (caramelization reaction) or sugar-amino acid mixtures (Maillard reaction) at temperatures normally used during the cooking of food. Several modulating factors of this convertogenic activity were identified. These factors included two main groups: (1) trace metals which are widely distributed in the environment; and (2) several cellular enzymatic systems. The convertogenic activities of a heated glucose-lysine mixture and a commercial caramel powder were completely suppresses when yeast were concurrently exposed to these products and to either FeIII or CuII. Equimolar concentrations of MnII or sodium selenite had no effect on the convertogenic activity of the products of either model system. Horse-radish peroxidase, beef liver catalase and rat liver S9 preparations each decreased the frequency of gene conversion induced by the caramel powder and the heated glucose-lysine products. This modulating activity of the enzymes was lost if they were heat-inactivated. These studies indicate the presence of a variety of protective mechanisms which can modify genotoxic components in complex food mixtures.

Chromosome-damaging activity of saliva of betel nut and tobacco chewers

Saliva of volunteers chewing betel quid, cured betel nut (Areca catechu), betel leaves (Piper betle), a mixture of quid ingredients (dried betel nut flakes, catechu, cardamon, lime, copra and menthol) and Indian tobacco was collected and examined for its genotoxic activity. Chromosome aberrations (chromatid breaks and chromatid exchanges) in Chinese hamster ovary (CHO) cells were used to estimate the genotoxic effect. No detectable levels of clastogenic activity were observed in the saliva of non-chewing individuals. After 5 min of chewing betel quid, betel nut, betel leaves, quid ingredients and Indian tobacco, the saliva samples showed relatively potent clastogenic activities. The addition of transition metals Mn2+ and Cu2+ to the saliva samples of betel nut and Indian tobacco chewers enhanced their clastogenic activities, whereas Fe3+ increased the clastogenicity of the betel nut saliva but decreased the genotoxic effect of the saliva of Indian tobacco chewers. After removal of the betel quid or its components from the mouth, the clastogenic activity disappeared within 5 min. The western-type chewing tobacco did not produce a genotoxic activity in the saliva of chewers. A possible association between the genotoxicity in the saliva of betel quid chewers and the development of oral, pharyngeal and esophageal carcinomas is discussed.

Antimutagenic activity of browning reaction products

The Salmonella typhimurium assay was used to determine the antimutagenic effect of products of 2 non-enzymatic browning reactions obtained by heating a lysine-fructose mixture at 121 degrees C for 1 h and by carmelizing D-sucrose at 180 degrees C for 1.5 h. The antimutagenic effect was tested by exposing strain TA1535 in suspension to N-methyl-N' -nitro-N-Nitrosoguanidine (MNNG) in the presence of the browning reaction products. In the case of aflatoxin B1, strain TA98 was used and the browning reaction products were added to the precarcinogen and an S9 mixture. The mutagenic activity of both carcinogens was significantly suppressed by the browning reaction products.

The action of transition metals on the genotoxicity of simple phenols, phenolic acids and cinnamic acids

Simple phenols (catechol, 4-methyl catechol, resorcinol, phloroglucinol and pyrogallol), phenolic acids (p-hydroxybenzoic acid, protocatechuic acid, vanillic acid, gallic acid, syringic acid and salicylic acid), a phenylacetic acid (3,4-dihydroxyphenylacetic acid) and eugenol were assayed for clastogenic activity in Chinese hamster ovary (CHO) cells with and without the addition of a n S9 mixture, Cu2+ (10-4M) and Mn2+ (10-4M). All dihydroxylated and trihydroxylated phenolics induced chromatid breaks and exchanges. The introduction of a methyl group seems to reduce the clastogenic capacity. The addition of an S9 mixture or the transition metals Cu2+ and Mn2+ enhanced the chromosome-damaging activity in some phenolics and suppressed it in others.

Potentiation of genotoxicity by concurrent application of compounds found in betel quid: arecoline, eugenol, quercetin, chlorogenic acid and Mn2+

5 components of the betel quid were examined for their clastogenic activities individually and in various combinations. They included the alkaloid, arecoline, from the betel nut (Areca catechu L.), eugenol, from the betel vine (Piper belle L.), chlorogenic acid, from tobacco leaves (Nicotiana tabacum), quercetin, from fennel seeds (Foeniculus vulgare Mill.) and the ubiquitous transition metal Mn2+. The clastogenic effects of the concurrent applications of arecoline plus eugenol, arecoline plus quercetin and arecoline plus chlorogenic acid were greater than the sum of the action of each individual component. Similarly, the combinations of arecoline, chlorogenic acid and Mn2+ induced frequencies of chromosome aberrations which exceeded the sum of the clastogenic activities of individually applied compounds or the sum of the clastogenic activities of 2 jointly applied compounds (arecoline plus Mn2+, or chlorogenic acid plus Mn2+). The clastogenic activity was estimated as the frequency of metaphase plates with at least 1 chromatid break or chromatid exchange, or the average number of chromatid breaks and exchanges per Chinese hamster ovary (CHO) cell. A potentiating (enhancing) action was also evident when 2 clastogens were used at doses which would not lead to a detectable increase in the frequency of chromosome aberrations when applied individually. It may be useful to distinguish between a "genotoxic range", which would be applicable to individually assayed compounds, and a "cogenotoxic range", which may include concentrations at which a chemical exerts a potentiating effect when combined with other genotoxic or non-genotoxic compounds.

A comparative genotoxicity study of chlorogenic acid (3-0-caffeoylquinic acid)

Chlorogenic acid, a compound which occurs naturally in many food items, was assayed for genotoxic activity in 3 different test systems: reverse mutations in the preincubation test with Salmonella typhimurium, gene conversion with Saccharomyces cerevisiae strain D7, and chromosome aberrations in Chinese hamster ovary (CHO) cells. Chlorogenic acid was directly convertogenic and clastogenic, but lacked a mutagenic capacity in the Salmonella bioassay. The transition metal Mn2+ enhanced the clastogenic and convertogenic activity of chlorogenic acid. In the presence of Mn2+ (10(-4)M), chlorogenic acid increased the frequency of his+ revertants in TA98 and TA100 strains of S. typhimurium. Caffeic acid and, to a lesser degree, quinic acid, which are components of chlorogenic acid, also showed genotoxic activity. The results show the importance of using several assays in combination with transition metals when testing for genotoxicity.

Clastogenicity of furans found in food

Cultured Chinese hamster ovary (CHO) cells were exposed for 3 h to furan and 6 furan derivatives (furfural, furfuryl alcohol, 5-methyl furfural, 2-methyl furan, 2,5-dimethyl furan and 2-furyl methyl ketone). Each of the 6 furan derivatives induced a relatively high frequency of chromatid breaks and chromatid exchanges in the absence of a liver microsomal activation preparation. The response of the furans to the addition of an S9 mixture differed. The clastogenic activities of 5-methyl furfural, 2-furyl methyl ketone, furfural and furfuryl alcohol were increased, whereas that of 2-methyl furan and 2,5-dimethyl furan were significantly decreased. Furan itself showed a clastogenic activity only in the presence of an S9 mixture.

Chromosome-damaging activity of ferritin and its relation to chelation and reduction of iron

Ferritin from horse spleen was found to cause severe chromosome aberrations in cultured Chinese hamster ovary cells. Ferritin at 15 to 170 microgram/ml was clastogenic and at higher doses was cytotoxic. At comparable concentrations of protein or iron, neither apoferritin nor complexed iron was clastogenic. Sulfhydryl compounds glutathione and cysteine reduced the cytotoxic and clastogenic activities of ferritin. Physiological concentrations of glutathione may normally be sufficient to protect cells from damage. The reducing agent ascorbate had little protective effect. Chelating agents varied in their inhibitory activity: ethylenediaminetetraacetic acid (hexadentate) greater than nitrilotriacetic acid (tetradentate) greater than salicylate (bidentate). 2,2'-Bipyridyl enhance the chromosome-damaging action of ferritin while histidine did not markedly alter the frequencies of aberrations. Catalase and superoxide dismutase showed no inhibitory activity. The mechanism of DNA damage may involve reduction of Fe(III) in the ferritin core to Fe(II), followed by reoxidation of Fe(II) with possible formation of free radicals.

Clastogenic activity of dried fruits

The clastogenic activities of several commercially-dried fruits, including black and golden-seedless raisins, medium-sized California prunes, table dates, bananas, California black mission figs and breakfast apricots, were examined using Chinese hamster ovary (CHO) cells as the test organism and chromosome aberrations as the endpoint. Treatment of the CHO cells with water extracts of these dried fruits significantly increased the frequencies of metaphase plates with 1 chromosome break or exchange as well as the average number of chromosome exchanges per metaphase plate. A liver microsomal S9 mixture reduced this clastogenic activity. Dried fruits represent an example of widely consumed food products with strong genotoxic activities.

Clastogenic activity of caramel and caramelized sugars

Cultured Chinese hamster ovary (CHO) cells were exposed for 3 h to caramelized solutions of the sugars sucrose, glucose, mannose, arabinose, maltose and fructose. Each of these caramelized sugars induced a relatively high frequency of chromosome breaks and exchanges in the treated cells. The non-caramelized sugars did not increase the frequency of chromosome aberrations. A potent clastogenic effect was also observed when a commercially used caramel powder was assayed. Up to 54% of all examined metaphase plates of the treated CHO cells had at least one chromosome break or exchange. This chromosome-damaging action of commercial caramel powder was reduced in the presence of liver microsomal (S9) preparation or FeII and FeIII. The transition metals CuII and MnII neither enhanced nor reduced the clastogenic activity of the caramel powder.

Enhancing and inhibiting effects of propyl gallate on carcinogen-induced mutagenesis

The food additive propyl gallate has a significant effect on the mutagenic activities of several carcinogens as measured by the Salmonella/microsome mutagenesis assay. Propyl gallate (10(-2) to 10(-4) M) inhibits the mutagenic activites of the carcinogens N-methyl-N-'nitro-N-nitrosoguanidine (MNNG) and N-acetoxy-2-acetylaminofluorene (N-acetoxy-AAF). It also reduces the mutagenic effect of aflatoxin B1, a carcinogen which requires activation with a S-9 microsomal preparation. In contrast, propyl gallate at equimolar concentrations causes an enhancement of the mutagenic activities of the carcinogens N-hydroxy-2-acetylaminofluorene (N-hydroxy-AAF) and 4-nitroquinoline 1-oxide (4NQO). The enhancement of 4NQO-induced mutagenesis occurs with a range of 4NQO concentrations. Moreover, both frameshift (TA98) and base substitution (TA100) bacteria indicator strains demonstrate an enhanced mutagenesis to 4NQO in the presence of the propyl-gallate. Propylgallate alone has no effect on the spontaneous reversion rate of S. typhimurium to histidine propotrophy.

Mutagenicity of fecal extracts from carnivorous and herbivorous animals

Extracts of the feces of 3 carnivorous animals (dog, river otter and sea gull) and 5 herbivorous animals (cow, horse, sheep, chicken and goose) induced chromosome aberrations (breaks and exchanges) in cultured CHO cells. The addition of CuII (10(-4)M) enhanced the clastogenic effect of fecal extracts of the examined animals with the exceptiion of 1 dog and 3 cow samples. Catalase reduced the chromosome-breaking and mitosis-inhibiting capacities of fecal extracts. These results indicate the presence of hydrogen peroxide-forming compounds. The possibility must be considered that animal and human excreta may be a major source of mutagens entering man's environment.

Unscheduled DNA synthesis and chromosome aberrations induced by inorganic and organic selenium compounds in the presence of glutathione

Glutathione strongly enhanced the induction of unscheduled DNA synthesis (UDS) in cultured human cells by inorganic selenium compounds: sodium selenate, sodium selenite and sodium selenide. In the presence of 10(-3) M glutathione, high levels of UDS (74-114 grains per nucleus) were observed in cells treated with (i) selenate at 10(-3) M, (ii) selenite at 10(-5)-3 X 10(-4) 7, and (iii) selenide at 10(-5)-10(-3) M. Glutathione at 10(-3) M also enhanced the clastogenic and cytotoxic effects of selenite and selenate in Chinese hamster ovary (CHO) cells. Glutathione at 10(-4) M or 10(-2) M caused less enhancement of DNA damage and toxicity in both the UDS and chromosome aberration assays. In the absence of glutathione, these inorganic selenium compounds induced low levels of UDS (up to 13 grains per nucleus) and moderate frequencies of chromosome aberrations (up to 11%). 3 organic selenium compounds (selenocystine, selenocystamine and selenomethionine) were also examined for the induction of UDS. No unscheduled DNA synthesis was detected in cells treated with selenocystamine or selenomethione, with or without added glutathione. However, selenocystine alone at 10(-4)-10(-3) M induced a low level of UDS; glutathione enhanced the DNA-damaging effect of selenocystine. The maximum amount of UDS (22 grains/nucleus) occurred in the presence of 10(-2) M glutathione. This was about one-fifth of that detected in cells treated with inorganic selenium compounds and 10-fold lower concentrations of glutathione (10(-3) M). The results suggest that recution is involved in the conversion of selenium compounds to mutagenic forms. The active mutagens may be selenols, GS-Se- from inorganic selenium and R-Se- from organic selenium compounds.

Mutagenic activity of ascorbate in mammalian cell cultures

Exposure of Chinese hamster ovary (CHO) cells to solutions of ascorbate (2--5 x 10(-4) M) resulted in the induction of somatic mutations at the hypoxanthineguanine phosphoribosyl transferase (HGPRT) locus. Mutant cells were resistant to 6-thioguanine (10 microgram/ml) and sensitive to HAT (hypoxanthine, aminopterin, thymidine) medium. Doses of ascorbate which were mutagenic were also toxic. Addition of catalase to such ascorbate concentrations prevented both mutagenesis and toxicity. This suggests that mutagenic metabolites of ascorbate may involve peroxide radicals.