4-Chloro-6-methoxyindole is the precursor of a potent mutagen (4-chloro-6-methoxy-2-hydroxy-1-nitroso-ndolin-3-one oxime) that forms during nitrosation of the fava bean (Vicia faba)

Occurrence of halogenated alkaloids

Once considered to be isolation artifacts or chemical "mistakes" of nature, the number of naturally occurring organohalogen compounds has grown from a dozen in 1954 to >5000 today. Of these, at least 25% are halogenated alkaloids. This is not surprising since nitrogen-containing pyrroles, indoles, carbolines, tryptamines, tyrosines, and tyramines are excellent platforms for biohalogenation, particularly in the marine environment where both chloride and bromide are plentiful for biooxidation and subsequent incorporation into these electron-rich substrates. This review presents the occurrence of all halogenated alkaloids, with the exception of marine bromotyrosines where coverage begins where it left off in volume 61 of The Alkaloids. Whereas the biological activity of these extraordinary compounds is briefly cited for some examples, a future volume of The Alkaloids will present full coverage of this topic and will also include selected syntheses of halogenated alkaloids. Natural organohalogens of all types, especially marine and terrestrial halogenated alkaloids, comprise a rapidly expanding class of natural products, in many cases expressing powerful biological activity. This enormous proliferation has several origins: (1) a revitalization of natural product research in a search for new drugs, (2) improved compound characterization methods (multidimensional NMR, high-resolution mass spectrometry), (3) specific enzyme-based and other biological assays, (4) sophisticated collection methods (SCUBA and remote submersibles for deep ocean marine collections), (5) new separation and purification techniques (HPLC and countercurrent separation), (6) a greater appreciation of traditional folk medicine and ethobotany, and (7) marine bacteria and fungi as novel sources of natural products. Halogenated alkaloids are truly omnipresent in the environment. Indeed, one compound, Q1 (234), is ubiquitous in the marine food web and is found in the Inuit from their diet of whale blubber. Given the fact that of the 500,000 estimated marine organisms--which are the source of most halogenated alkaloids--only a small percentage have been investigated for their chemical content, it is certain that myriad new halogenated alkaloids are awaiting discovery. For example, it is estimated that nearly 4000 species of bryozoans have not been examined for their chemical content. The few species that have been studied contain some extraordinary halogenated alkaloids, such as hinckdentine A (610) and the chartellines (611-613). Of the estimated 1.5 million species of fungi, secondary metabolites have been characterized from only 5000 species. The future seems bright for the collector of halogenated alkaloids!

Induction of glandular stomach cancers in Helicobacter pylori-infected Mongolian gerbils by 1-nitrosoindole-3-acetonitrile

Helicobacter pylori (H. pylori) infection and high intake of various traditional salt-preserved foods are regarded as risk factors for human gastric cancer. We previously reported that Chinese cabbage contains indole compounds, such as indole-3-acetonitrile, a mutagen precursor. 1-Nitrosoindole-3-acetonitrile (NIAN), formed by the treatment of indole-3-acetonitrile with nitrite under acidic conditions, shows direct-acting mutagenicity. In the present study, NIAN administration by gavage to Mongolian gerbils (MGs) at the dose of 100 mg/kg two times a week resulted in three adduct spots (1.6 adducts/10(8) nucleotides in total), detected in DNA samples from the glandular stomach by (32) P-postlabeling methods. Treatment with six consecutive doses of 100 mg/kg of NIAN, two times a week for 3 weeks, induced well-and moderately-differentiated glandular stomach adenocarcinomas in the MGs at the incidence of 31% under H. pylori infection at 54-104 weeks. Such lesions were not induced in MGs given broth alone, broth + NIAN or infection with H. pylori alone. Thus, endogenous carcinogens formed from nitrosation of indole compounds could be critical risk factors for human gastric cancer development under the influence of H. pylori infection.

Transition metal complexes of a new hexadentate macroacyclic N2O4-donor Schiff base: inhibitory activity against bacteria and fungi

A new hexadentate macroacyclic N(2)O(4) - donor ligand, glyoxal bis(N-nitroso phenylglycine) (gbnp), has been designed and structurally characterized. Manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes of gbnp have been prepared and characterized by elemental analyses, molar conductance measurements, magnetic moment, spectral (IR, (1)H NMR, electronic and FAB mass) and thermal studies. The molecular dynamics of the ligand was studied by the variable temperature NMR studies, which suggest the presence of two isomeric forms. The antimicrobial activity of all the compounds was studied against Escherichia coli, Bacillus cirroflagellosus, Aspergillus niger and Candida albicans. Among the new complexes, copper(II) complex has the highest potential against all the microorganisms tested.

Interleukin-8 gene polymorphism associated with susceptibility to non-cardia gastric carcinoma with microsatellite instability

BACKGROUND AND AIM

Gastric carcinoma (GC) with microsatellite instability (MSI) exhibits clinicopathological characteristics distinct from microsatellite-stable (MSS) GC. Both MSI and MSS carcinomas are mostly associated with chronic gastritis infected by Helicobacter pylori (Hp). The relationship between Hp-induced inflammation and the mutator pathway of MSI remains unclear. Recently, cytokine polymorphisms have been reported to affect the development of non-cardia GC. The objective of this study was to elucidate the relationship between cytokine polymorphisms and MSI phenotypes.

METHODS

In a case-control study including 482 controls and 181 patients with GC, interleukin (IL)-8 -251, IL-1B-511, IL-1RN, and tumor necrosis factor-A (TNFA) -857 polymorphisms were genotyped. The presence of MSI and mutations in exons 5 to 8 of the p53 gene were examined in GC cases. All clinicopathological data were collected from individual records.

RESULTS

High and low frequency of MSI (MSI-H and MSI-L) and MSS were detected in 16 (8.8%), 14 (7.7%) and 151 (83.4%) GC cases, respectively. We found that IL-8 -251 T/T genotype was significantly associated with increased risk of MSI-H GC compared to MSI-L/MSS GC and controls. We found no association between other cytokine polymorphisms and MSI-H GC. The percentage of smokers and the frequency of p53 mutations were significantly lower in MSI-H than MSI-L/MSS GC. We found significant associations of MSI-H with synchronous or metachronous multiple occurrence, antral location and intestinal type.

CONCLUSIONS

Our study shows that MSI-H GC is associated with IL-8-251 T/T (low expression genotype) and is inversely correlated with cigarette smoking.

Comparative genomic hybridization analysis of N-methyl-N'-nitrosoguanidine-induced rat gastrointestinal tumors discloses a cytogenetic fingerprint

Exposure to N-nitroso compounds is thought to play a key role in the development of gastric cancer in humans. The alkylating agent N-methyl-N'-nitrosoguanidine (MNNG) is carcinogenic in a number of animal models and its preferential target tissue is the gastrointestinal (GI) tract. The genetic synteny among rats and humans makes the rat a useful model for induced tumorigenesis. However, because of the limited availability of genetic information, cytogenetic and molecular studies are rarely performed in the rat. We report an investigation of eight MNNG-induced rat gastric tumors by comparative genomic hybridization (CGH). The tumors were from forestomach (induced by a single dose of MNNG) and from pylorus (induced by chronic exposure). CGH identified a genetic fingerprint of chromosomal imbalances common to the two types of the tumors. Frequent gains were observed at 9q11-q12, 15q22-25, and Xq11-q12. Forestomach carcinomas were also characterized by gains in 7q11-q12, 20q13, and Yq12. Homology studies between the rat and human genomes indicate the presence of genes within these regions with potential relevance to tumorigenesis in the GI tract. Our findings provide new insights into the location of genes involved in MNNG-induced gastric cancer initiation and/or progression in the rat.

Nutrition and dietary carcinogens

Three major factors for human carcinogenesis are (i) cigarette smoking, (ii) infection and inflammation and (iii) nutrition and dietary factors. Nutrition and dietary factors include two categories, namely genotoxic agents and constituents including tumor promotion-associated phenomena. This article first describes the genotoxic agents as microcomponents. These are mutagens/carcinogens in cooked food, fungal products, plant and mushroom substance, and nitrite-related materials, polycyclic aromatic hydrocarbons and oxidative agents. Emphasis has been given to heterocyclic amines (HCAs) to which humans are continuously exposed in an ordinary lifestyle. HCAs in food are mainly produced from creatin(in)e, sugar and from amino acids in meat (upon heating). They are imidazoquinoline and imidazoquinoxaline derivatives and phenylimidazopyridine. HCAs are pluripotent in producing cancers in various organs including breast, colon and prostate. Discussion is also given to plant flavonoids which are mutagenic but not carcinogenic. As a macrocomponent, overintake of total calories, fat and sodium chloride is discussed from the viewpoint of the increase of genetic alterations in tissues and of tumor promotion-associated issues. Studies of nutrition and dietary condition will eventually lead us to cancer prevention, namely delay of onset of cancer to the late phase of human life, which is called 'natural-end cancer' (Tenju-gann).

Characterization of azo coupling adducts of benzenediazonium ions with aromatic amino acids in peptides and proteins

A synthetic peptide, VLSPADKTNWGHEYRMF(cmC)QIG, was reacted with 4-chlorobenzenediazonium hexafluorophosphate as a model for reactions of aromatic diazonium ions with proteins. At a ratio of diazonium ion to peptide of 0.8:1, three products could be seen by reversed-phase HPLC. Electrospray mass spectrometric analysis of the isolated products revealed that two of the products had the same mass of 2648 Da, being 138 Da higher than the parent peptide and corresponding to the addition of a 4-chlorobenzenediazo group. The third isolated product had a mass of 2787 Da which corresponded to the addition of two 4-chlorobenzenediazo groups (276 Da). Digestion of the monoadducted intact peptides with trypsin or endoproteinase Glu-C and HPLC separation of adduct oligopeptides followed by sequencing with electrospray ionization tandem mass spectrometry showed unambiguously that histidine and tyrosine residues were the major sites of modification. Incubation of human serum albumin with 4-chlorobenzenediazonium hexafluorophosphate at molar ratios of 1:1, 1:2, and 1:10 resulted in adduct formation as detected by shifts in the HPLC retention time of the protein and also by an increase in mass as determined by electrospray mass spectrometry.

Gastric carcinogenesis: 2-chloro-4-methylthiobutanoic acid, a novel mutagen in salted, pickled Sanma hiraki fish, or similarly treated methionine

The customary salting and pickling of fish in high risk gastric cancer regions were modeled to explore the relevant causative chemicals. The fish Sanma hiraki was treated with sodium chloride and sodium nitrite at pH 3. Previously, it had been found that an extract of the treated fish was mutagenic in Salmonella typhimurium TA 1535 without S9 and also that it induced glandular stomach cancer upon gavage to rats. We now demonstrate that the mutagenicity was enhanced by preincubation of the raw meat for several days before salt-nitrite treatment. HPLC techniques showed that three mutagens were present in the fish extract. One of the mutagens was found to be stable over the pH range of 1.0-9.0. This mutagen was purified by silica gel solid phase extraction, followed by a series of reverse phase HPLC steps, and was characterized by low and high resolution MS, NMR, and FT-IR. While N-nitroso compounds were generally believed to be associated with gastric carcinogenesis, it was unexpectedly found that the mutagen has the novel structure 2-chloro-4-methylthiobutanoic acid (CMBA). Based on the structure, it seemed likely that methionine might be the precursor, and this was, indeed, proven. Both salt and nitrite are essential factors for forming this mutagen. The yield of CMBA was linear for chloride concentrations from 0 to 800 mM NaCl. Of 20 amino acids reacted with nitrite and chloride at pH 3, only methionine generated a mutagen for S. typhimurium TA 1535. Tryptophan gave a product mutagenic in S. typhimurium TA 100 and TA 98, but not TA 1535, and in the case of tyrosine, the mutagen was active only for TA 100. These results suggest an important role for salt in gastric carcinogenesis and provide new approaches for exploring the formation of mutagens/carcinogens for specific target organs.

Nutrition and stomach cancer

Epidemiologic evidence on the relation between nutrition and stomach cancer is reviewed. Stomach cancer shows a distinct international variation and dramatic worldwide decline. These descriptive features suggest that dietary factors are important in determining the risk of stomach cancer. The authors assessed relevant data regarding specific dietary hypotheses in the etiology of stomach cancer. A negative association with fresh vegetables and fruits is highly consistent in numerous case-control studies in different populations. Both epidemiologic and experimental data suggest that vitamins C and carotenoids lower risk of stomach cancer. Evidence is sparse and inconsistent as to protective effects of vitamin E and selenium. Epidemiologic studies have not lent, and will not provide, supportive evidence for an etiologic role of nitrate intake. High salt intake has been associated with an increased risk in many case-control studies and limited cohort studies. Taken together with animal data, it is considered that high salt intake is a risk factor for stomach cancer. Both epidemiologic and experimental data are inconclusive as to whether high-starch diets confer an increased risk. Cohort studies using quantitative dietary assessment and biologic measurement of micronutrients are needed for further understanding of etiologic roles of dietary factors in the causation of stomach cancer.

The preclinical toxicological evaluation of sumatriptan

1 Sumatriptan is a potent and selective 5-HT1 receptor agonist marketed for the treatment of migraine by both oral and subcutaneous routes. An extensive toxicological programme employing high doses of sumatriptan was carried out in a range of animal species. The studies evaluated both the local and systemic tolerance to single and repeated dosing, effects on all stages of reproduction, as well as the genotoxic and oncogenic potential of sumatriptan. 2 The administration of relatively high single and repeated doses of sumatriptan was well tolerated by both rodents and dogs by the oral, subcutaneous and intravenous routes. Behavioural effects, suggestive of involvement of the central nervous system, were the most obvious result of such doses and were generally more pronounced in dogs than rodents. The reason for this may be related to the higher plasma concentrations of the drug achievable in dogs. Additional observations restricted to dogs, were transient, and included tachycardia, facial oedema and breaks in the continuity of secretion films on the corneal surface. A tendency for an increase in weight gain was seen for rats, while a slight decrease was usually seen for dogs. The only pathological changes related to treatment with high concentrations of sumatriptan consisted of local reactions at the site of subcutaneous administration. 3 Sumatriptan is an indole; the structures of this chemical class show varying propensities for nitrosation. However, appropriate testing with sumatriptan failed to identify any mutagenic nitroso compounds. 4 Sumatriptan was neither genotoxic nor oncogenic. 5 Reproductive studies demonstrated that sumatriptan was not teratogenic and had no effect on peri- and postnatal development. Some embryotoxicity was observed, but only at maternally toxic doses. A slight decrease in the success of insemination was also noted at high oral doses in rats. 6 Results of the toxicological programme performed in support of migraine therapy with sumatriptan provide good assurance of safety for subcutaneous and oral use.

Genotoxicity of nitrosated red wine and of the nitrosatable phenolic compounds present in wine: tyramine, quercetin and malvidine-3-glucoside

Phenolic compounds and biogenic amines are known to be present in some foodstuffs which become directly genotoxic after nitrosation in vitro. Red wine has previously been shown to be genotoxic and this activity has been attributed mainly to flavonoids. Besides flavonoids, red wine contains a multiplicity of compounds, including biogenic amines. Using the Ames assay and the SOS chromotest, this study has shown that red wine and some of the nitrosatable molecules present in wine become directly genotoxic on nitrosation in vitro: these include the phenolic molecules tyramine, quercetin and malvidine-3-glucoside, whereas phenylethylamine and histamine were negative on nitrosation. Interestingly, quercetin had been predicted to be negative after nitrosation, using the CASE methodology. The concentrations of these three positive nitrosatable compounds in wine were determined by HPLC. Comparison of these concentrations and their respective levels of genotoxicity suggests that the genotoxicity after nitrosation is probably attributable to other molecules. It is also possible that synergistic effects may occur between various nitrosatable compounds in wine.

Antimutagenic effects of casein and its digestion products

The antimutagenic potential of casein was investigated using several mutagens, including some food-related mutagens, and the Salmonella/microsome and Escherichia coli DNA-repair tests. The effect depended on the type of mutagen and the incubation time of casein with the mutagens. Casein was very effective against benzo[a]pyrene, N-methylnitrosourea and nitrosated 4-chloroindole, and was less effective towards sodium azide and N-nitroquinoline-1-oxide (NQO). Preincubation increased the antimutagenic potential of casein towards NQO. Heating of casein (up to 20 min at 130 degrees C) did not alter its antimutagenic capacity. The effect of pepsin hydrolysis under simulated gastric conditions on the antimutagenic capacity of casein was tested with sodium azide and NQO in the Salmonella/microsome test. The peptides formed were separated by ultrafiltration or by isoelectric precipitation of casein, and were characterized by HPLC size-exclusion and Kjeldahl analysis. The antimutagenic potential of casein increased with pepsin hydrolysis; this increase was due to the peptides formed and might be explained by a better accessibility of casein peptides for interaction with mutagens. The antimutagenic potential of pepsin-hydrolysed casein towards sodium azide was observed over the whole dose-response curve.

Diet modification and gastric cancer prevention

The relative strengths of the etiologic factors identified for gastric cancer are discussed. On the basis of available scientific data, it is recommended that dietary prevention of gastric cancer be based on attempts to reduce the ingestion of foods with a high content of salt and to increase the intake of fresh fruits and vegetables. Other identified etiologic factors offer promise and are being investigated but do not yet justify recommendation to the general public.

Proteins and amino acids as scavengers of nitrite: inhibitory effect on the formation of nitrosodimethylamine and diazoquinone

Protein and its components in high concentrations similar to those found in the digestive tract effectively scavenged nitrite and thus inhibited the formation of mutagens from nitrite. Various amino acids at 100 mM, bovine serum albumin (BSA) and trypsinized casein at 100 mg/ml effectively decreased the nitrite level of 50 mM-nitrite solution at pH 3 and 37 degrees C. Most, but not all, amino acids can convert nitrite into nitrogen gas; Pro can be converted into non-mutagenic nitrosoproline, CySH to S-nitrosocysteine, Trp to weakly mutagenic nitrosotryptophan and Tyr to non-mutagenic diazotyrosine. BSA was cross-linked, probably owing to the reaction of Tyr and Lys residues. Most amino acids inhibited more than 50% of nitrosodimethylamine formation in the reaction between 200 mM-dimethylamine and 50 mM-nitrite at pH 3 and 37 degrees C; BSA inhibited 50% of nitrosodimethylamine formation, and trypsinized casein, 100%. Most amino acids inhibited more than 50% of p-diazoquinone formation in the reaction between 25 mM-phenol and 100 mM-nitrite at pH 3 and 37 degrees C; BSA inhibited 80%, and trypsinized casein, 95% of such formation. Trypsinized casein effectively inhibited the development of the mutagenic effects attributable to the formation of diazobamethan from bamethan and nitrite.

Review of the occurrence and formation of non-volatile N-nitroso compounds in foods

A review of the literature published prior to July 1991 covers the occurrence and formation of non-volatile N-nitrosamines occurring in foods and beverages. The presence of identified volatile and non-volatile N-nitrosamines accounts for less than 10% of the total apparent N-nitrosamine concentration. N-Nitrosoproline and N-nitrosothiazolidine-4-carboxylic acid are the most commonly identified non-volatile N-nitrosamines in the diet. Non-volatile N-nitrosamines account for 12 of the 21 currently identified N-nitroso compounds in foods and beverages.

Mutagenic activities of tryptophan metabolites before and after nitrite treatment

The mutagenic activities of 16 kinds of tryptophan metabolites, before and after nitrite treatment, were examined in the Ames test. None of the compounds showed mutagenic activity before nitrite treatment. After nitrite treatment under acidic conditions, 11 compounds showed mutagenic activity towards Salmonella typhimurium TA100 strain in the absence of a metabolic activation system. Tryptophan induced 1000 revertant colonies/mumol, while 5-hydroxyindole, 5-hydroxytryptamine and 3-hydroxykynurenine, all containing a hydroxy group in the molecule, induced 11,000, 5200 and 2700 revertant colonies/mumol, respectively. These results indicate that the introduction by nitrite treatment of a hydroxy group into the indole or benzene ring of tryptophan-related compounds increases their mutagenic activity.

In-vitro testing and the carcinogenic potential of several nitrosated indole compounds

4-chloro-methoxyindole is a naturally occurring compound in Vicia faba which can easily react with nitrite to form a N-nitroso compound. In this in vitro study, the potential genotoxic effects of nitrosated 4-chloro-6-methoxyindole and its structural analogue 4-chloroindole were evaluated for the first time by using both Salmonella and Chinese hamster V79 cells. Additionally, the inhibition of gap junctional intercellular communication in V79 cells by these compounds was determined; this is a validated parameter for tumor-promoting activity. Most assays were also performed with nitrosated indole-3-acetonitrile, a naturally occurring compound in brassicas. Both nitrosated chloroindoles were highly mutagenic to Salmonella typhimurium TA100 without the need of exogenous metabolic activation and were potent inducers of Sister Chromatid Exchanges. Nitrosated indole-3-acetonitrile generated the same effects, although at much higher concentrations. Equivocal results were obtained for the nitrosated chloroindoles in a forward mutation assay using the hypoxanthine guaninephosphoribosyltransferase locus. All nitrosated indole compounds significantly inhibited gap junctional intercellular communication. These results indicate that nitrosated chloroindoles and nitrosated indole-3-acetonitrile should be considered as mutagens and agents with potential tumor-promoting capacity.

Mutagen formation on nitrite treatment of indole compounds derived from indole-glucosinolate

The mutagenicities of 8 indole compounds (indole-3-acetonitrile, indole-3-carbinol, indole-3-acetamide, indole-3-acetic acid, 3-methylindole, indole-3-aldehyde, indole-3-carboxylic acid and indole) derived from indole glucosinolate were studied by mutation tests on Salmonella typhimurium TA98 and TA100 and Escherichia coli WP2 uvrA/pKM101 with and without S9 mix. None of the 8 indole compounds were mutagenic, but they became mutagenic on these 3 tester strains when treated with nitrite at pH 3. The nitrite-treated indole compounds were mutagenic without metabolic activation system (S9 mix), and their mutagenicities were decreased by the addition of S9 mix.

Trace analysis of nitrosated foodstuffs for nitrosamides

An analytical procedure previously developed for the trace determination of nitrosamides was applied to a screening of nitrosated foodstuffs for nitrosoureas. Different types of foodstuffs were nitrosated both under chemical conditions using a high nitrite concentration, and under simulated gastric conditions. Methylating activity corresponding to N-nitroso-N-methylurea (MNU) was detected in most samples. Under chemical conditions, the yields spanned several orders of magnitude with processed fish and meat products being at the top, and plant products at the bottom of the scale. After nitrosation under simulated gastric conditions, the range of MNU activity was significantly smaller. No correlation exists between the yields determined under chemical and simulated gastric conditions.

The epidemiology of gastric cancer

The etiology of gastric carcinoma, especially its "epidemic" or "intestinal" type is reviewed. The prevailing etiologic hypothesis, based on the selective targeting of etiologic agents in different points of the chain of causation, is described. Support for the hypothesis is updated, based on descriptive and analytical epidemiologic studies as well as on recently obtained laboratory and experimental evidence. Primary and secondary prevention measures are briefly discussed.

Several known indole compounds are not important precursors of direct mutagenic N-nitroso compounds in green cabbage

In this study we investigated the role of indole-3-acetonitrile, indole-3-carbinol, indole and tryptophan in the formation of N-nitroso compounds in green cabbage extracts. Green cabbage extracts were separated by gel permeation chromatography. Fractions were treated with nitrite, tested for mutagenicity and analysed for total N-nitroso content. Fractions in which spiked indole-3-acetonitrile, indole-3-carbinol, indole and tryptophan eluted appeared to be low in mutagenic activity and contained relatively small amounts of N-nitroso compounds. To detect indole compounds other than the ones used in the gel permeation chromatography experiments, high-performance liquid chromatography and gas chromatography-mass spectrometry analyses were performed of green cabbage extracts. Indole-3-carboxaldehyde was found to be the most commonly occurring indole compound, but it did not show direct mutagenic activity upon nitrite treatment. Indole-3-acetonitrile was the second most common compound; although it was mutagenic after nitrite treatment, its contribution to the mutagenicity of nitrite-treated green cabbage was roughly estimated to be only 2%. No other indole compounds were detected. From this study we conclude that neither the tested indole compounds nor indole-3-carboxaldehyde play a significant role in the formation of direct mutagenic N-nitroso compounds in nitrite-treated green cabbage extracts.

Isolation and characterization of some products of the BHA-nitrite reaction: examination of their mutagenicity

The reaction mixture and several products arising from the reaction of butylated hydroxyanisole (BHA) and nitrite in anaerobic aqueous acidic solution were separated and tested in the Salmonella mutagenicity test. Among the nine products separable by thin-layer chromatography, 1-hydroxyl-2-tert-butyl-4-methoxy-6-nitrobenzene (BHA-NO2), tert-butyl-substituted para-quinone (t-BuQ) and 3-tert-butyl-5-methoxy-1,2-benzoquinone (t-Bu-o-Q) are dominant. The last compound has not been previously reported in this system. Spot testing indicated at least one further compound of nitroso character and traces of tert-butylhydroquinone (t-BuHQ), which reacts with nitrite to yield t-BuQ. No evidence was found for the formation of the BHA dimer under our conditions. The substances gave no evidence of mutagenicity in the Salmonella typhimurium strains TA 98 and TA 100, either in the standard plate incorporation assay or in the procedure with preincubation with or without S9 mix. In some instances the substances were unstable in the test procedure.

Nitrosamines as potential environmental carcinogens in man

Nitrosamines are ubiquitous in our environment and diet. Many nitroso compounds are carcinogenic in animals and most probably in man. Nitrosamines are formed from the reaction of nitrite with primary, secondary, or tertiary amines in an acid medium. Nitrate should be considered as a nitrosating agent because it can be converted to nitrite by microbial action. Many aliphatic and nitrogen-containing heterocyclic compounds can be nitrosated to form carcinogenic substances. The occurrence in food and in some drugs of several nitrosamines or their nitrosatable precursors is described. Several tobacco-specific nitrosamines have been considered as possible causative agents for human cancer. Nitrosamines may be implicated in the induction of certain human gastric cancers.

Synthesis, characterization and mutagenicity of 2-nitroso-6,7-dimethoxytetrahydroisoquinoline

The compound 6,7-dimethoxytetrahydroisoquinoline (Scheme 2, (ii] reacts with nitrous acid at ambient temperature and pH approximately 3.0 to give, in high yield the expected 2-nitroso-6,7-dimethoxytetrahydroisoquinoline (Scheme 2, (iii)). An unequivocal chemical structure of this nitroso derivative was established by high resolution mass spectrometry and 1H NMR spectrometry. Unlike many N-nitroso compounds, (iii) crystallizes in a single rotational isomer which spontaneously forms, in dimethylsulfoxide (DMSO) solution, an equilibrium mixture of the two E/Z isomeric forms with a t1/2 approximately 53 h. The compound is mutagenic to Salmonella tester strains TA98, TA100, TA1538, TA1535, and TA1537 but only in the presence of induced rat liver microsomes. The highest mutagenic activity of approximately 10 net revertants/nM was obtained with TA100 at a dose of 10 micrograms/plate. The compound (ii) is a close structural analog to the tetrahydroisoquinolines formed by endogenous condensation/cyclization reactions that can occur, between acetaldehyde and dopamine or norepinephrine, when alcohol is consumed.

Mutagenic activity in gastric juice and urine of subjects with chronic atrophic gastritis, gastric epithelial dysplasia and gastric cancer

Gastric juice and urine samples from consecutive patients who underwent endoscopy for upper GI tract complaints were examined for the presence of mutagens. Patients endoscopically and histologically diagnosed as having either chronic atrophic gastritis (CAG) or gastric cancer (GC) had higher than normal levels of mutagens in their gastric juice and urine. The gastric juice pH of these patients was also elevated and, in the case of the CAG patients, contained detectable levels of nitrites. No correlation was however found between gastric mutagen levels and urinary mutagen excretion in the individuals examined.

The stability of the nitrosated products of indole, indole-3-acetonitrile, indole-3-carbinol and 4-chloroindole

The nitrosation rates of indole-3-acetonitrile, indole-3-carbinol, indole and 4-chloroindole and the stability of their nitrosated products were investigated. Each of the nitrosated indole compounds was directly mutagenic to Salmonella typhimurium TA100 in the following order of potency: 4-chloroindole much greater than indole-3-carbinol greater than or equal to indole greater than indole-3-acetonitrile. Total N-nitroso determinations, carried out according to a modified method of Walters et al. (Analyst, Lond. 1978, 103, 1127), and Ames test results revealed that each of the indole compounds immediately formed mutagenic N-nitroso products upon nitrite treatment under acidic conditions. However, the nitrosation rates of indole and 4-chloroindole were higher than those of indole-3-acetonitrile and indole-3-carbinol. For indole-3-carbinol, indole-3-acetonitrile and indole, no change in the amount of nitrosated products was observed at increasing incubation times from about 15 up to 60 min. For 4-chloroindole the amount of nitrosated products decreased with increasing incubation times. In all cases the responses in the Ames test paralleled the amounts of nitrosated products. The stabilities of the nitrosated products of the indole compounds were investigated at pH 2 and 8. Both mutagenicity data and measurements by high-performance liquid chromatography using a photohydrolysis detector indicated that the nitrosation products of indole-3-acetonitrile, indole-3-carbinol and indole were more stable at pH 8 than at pH 2. Conversely, nitrosated 4-chloroindole was stable at pH 2 but not at pH 8. The pH 8 chromatograms showed a large nitrite peak. From this we hypothesized that the presence of free nitrite might be responsible for the stability of nitrosated indole-3-acetonitrile, indole-3-carbinol and indole at pH 8. Experiments confirmed the existence of an equilibrium between the nitrosated indole compound and the free indole compound plus nitrite.

In vivo and in vitro genotoxic evaluation of indorenate

5-Methoxytryptamine, beta-methylcarboxylate hydrochloride (indorenate) is a new antihypertensive serotonin derivative. We evaluated its genotoxic activity using the mouse bone marrow and cytogenetic test and the human lymphocyte culture cytogenetic assay. As endpoints we measured chromosomal aberrations, sister-chromatid exchanges and cellular proliferation kinetics. Our results agree in both systems showing that indorenate is a non-genotoxic agent in these assays.

Formation of direct-acting genotoxic substances in nitrosated smoked fish and meat products: identification of simple phenolic precursors and phenyldiazonium ions as reactive products

Epidemiological studies have associated the consumption of smoked fish and meat products with an increased risk of stomach cancer. Therefore, the reaction of such smoked foods with nitrite under acidic conditions was investigated and was shown to produce potent direct-acting genotoxic substances as detected by the SOS Chromotest. Similar genotoxic activity was observed in nitrosated samples of wood-smoke condensates. Simple phenolic compounds such as phenol, 3-methoxycatechol, catechol and vanillin were identified as the precursors of the genotoxic substances. These phenolic compounds also exhibited direct-acting genotoxicity after nitrosation. The major genotoxic substances formed after nitrosation of phenol were isolated and identified as 4- and 2-hydroxyphenyldiazonium ions. Nitrosation of various wood-smoke condensates was found to generate the same type of diazonium compounds, which in part account for the genotoxicity of nitrosated smoked foods.

Inhibitors of endogenous nitrosation. Mechanisms and implications in human cancer prevention

Although the proof that N-nitroso compounds (NOC), a versatile class of carcinogens in animals, are also carcinogenic in man is lacking, humans are exposed through ingestion or inhalation to preformed NOC in the environment and through the endogenous nitrosation of amino precursors in the body. Activated macrophages can synthesize nitrate, nitrite and nitrosating agents that can form NOC. A number of bacterial strains isolated from human infections can produce NOC enzymatically from precursors at neutral pH. As a consequence endogenous nitrosation may occur at various sites of the body such as the oral cavity, stomach, urinary bladder, lungs, and at other sites of infection or inflammation. Since the demonstration by Mirvish et al. (1972) showing that ascorbate can reduce tumor formation in animals following feeding of nitrite plus amine, numerous substances to which humans are exposed have been identified and shown to inhibit formation of NOC in vitro, in animal models and in humans. Such inhibitors of nitrosation include vitamins C and E, phenolic compounds, and complex mixtures such as fruit and vegetable juices or other plant extracts. Nitrosation inhibitors normally destroy the nitrosating agents and thus act as competitors for the amino compound that serves as substrate for the nitrosating species. Independently, epidemiological studies have already established that fresh fruits and vegetables that are sources of vitamin C, other vitamins and polyphenols have a protective effect against cancers at various sites and in particular gastric cancer. Although the evidence that endogenously formed NOC are involved in human cancers is far from conclusive, it is suggestive and justifies preventive measures for reducing exposure to NOC. This article briefly reviews (i) the chemistry of NOC formation and inhibition, (ii) the studies in experimental animals which showed that inhibition of endogenous NOC synthesis leads to a reduction of toxic, mutagenic and carcinogenic effects, (iii) recent studies in humans where the degree of inhibition of endogenous NOC synthesis was directly quantified and lastly (iv) the contribution of nitrosation inhibitors to human cancer prevention.

Presence of nitrosable mutagen precursors in cooked meat and fish

Broiled chicken, pork, mutton, beef and sun-dried sardine were found to yield direct-acting mutagenicity after nitrite treatment. When 50% methanol extracts of cooked foods were treated with 50 mM nitrite at pH 3 for 1 h at 37 degrees C, they induced 3800-17,900 revertants of Salmonella typhimurium TA100 and 15,000-43,600 revertants of TA98 per g. In contrast, raw meat and uncooked sun-dried sardine showed little or no mutagenicity after nitrite treatment. Treatment of broiled chicken with 0.5-3 mM nitrite, which is a physiologically feasible concentration in the human stomach under some conditions, induced direct-acting mutagenicity. When broiled chicken was treated with 1 mM nitrite at pH 3 for 1 h at 37 degrees C, its mutagenicities on TA100 and TA98 without S9 mix were 7100 and 5400 revertants/g, respectively.

Formation of mutagenic N-nitroso compounds in vegetable extracts upon nitrite treatment: a comparison with the glucosinolate content

More than 30 vegetables were screened for their potential to form biologically active N-nitroso compounds upon treatment with nitrite under acidic conditions. The total N-nitroso content was determined in the nitrite-treated and untreated extracts of the vegetables according to a modified method of Walters et al. (Analyst, Lond. 1978, 103, 1127). All treated extracts contained N-nitroso compounds at levels ranging from 23 to 789 nmol/25 mg dry matter. In the same samples the mutagenic activity was determined using the Salmonella typhimurium assay. About half of the vegetables were found to be mutagenic upon nitrite treatment. (Nitrite-treated extracts were considered to be mutagenic if the number of induced revertants was at least twice as high as that induced by the corresponding untreated extract). The content of different glucosinolates in the dry matter of the vegetables was also determined. Glucosinolates could be detected only in cruciferous vegetables, at levels ranging from 1.8 to 26.0 mumol/g dry matter. Although the nitrite-treated extracts of brassica species contained more N-nitroso compounds and induced more revertants than did other vegetables, there was no significant correlation between these parameters. However, the amounts of N-nitroso compounds formed upon nitrite treatment (expressed per fresh weight) did correlate significantly (P less than 0.01) with the amounts of glucosinolates (r = 0.95). When the glucosinolates were divided into aryl/alkyl- and indolyl-glucosinolates, the significant correlation was maintained for both subgroups (r = 0.93 and 0.95, respectively). From this it can be concluded that glucosinolates are probably involved in the formation of N-nitroso compounds in certain nitrite-treated vegetables.

Alkylating activity in food products--especially sauerkraut and sour fermented dairy products--after incubation with nitrite under quasi-gastric conditions

N-Nitroso compounds may well rank high among the genotoxic carcinogens present in our environment. Small amounts of such compounds may be formed in the human stomach after consumption of high-nitrate vegetables. Volatile nitrosamines can be conveniently determined but reliable methods of analysis for non-volatile N-nitroso compounds are still lacking. In this study we have used the 4-(4-nitrobenzyl)pyridine test to look for the formation of alkylating compounds such as N-nitroso-N-methylurea in a wide range of food products after incubation with nitrite under simulated gastric conditions. Our results indicate that many food products do not form alkylating compounds in appreciable amounts, even though the nitrite concentration used was five to ten times that found in saliva after a high-nitrate meal. Comparatively strong alkylating activity, however, was detected after incubation of samples of sauerkraut, certain dairy products (yoghurt, biogarde, quark, buttermilk and milk), wine and smoked mackerel. Samples of sauerkraut incubated with simulated gastric fluid, but without (added) nitrite, also displayed appreciable alkylating activity. The formation of alkylating substances in non-fat yoghurt was markedly inhibited by addition of ascorbic acid. The identity of the alkylating agents remains unknown. The isolation procedure was optimized for N-nitroso-N-methylurea, but will certainly result in the isolation of other compounds, such as C-nitroso-, C-nitro- or perhaps even C-nitroso-C'-nitro-compounds as well. Biogenic amines, glucosinolates, indole derivatives or other compounds may be involved as precursors. If alkylating agents are formed in vivo after ingestion of high-nitrate vegetables or drinking water, this is likely to occur only when the food products mentioned above are ingested simultaneously with or shortly after the nitrate load and not appreciably (except perhaps in the case of sauerkraut) when they are ingested alone, without a nitrate source. The health implications of these findings cannot yet be established. Many alkylating agents, however, have strong carcinogenic properties and continued investigation of food products (and their interaction products with nitrite) is indicated.

Gastric cancer in San Marinese and their first degree relatives in San Marino and the United States. Gastroscopic biopsy as an epidemiological tool

The Republic of San Marino, a small, 23-square mile, independent country near the Adriatic Coast within Italy, has been noted to have a high incidence of gastric cancer in its 22,000 population (9% of all deaths from 1969-1983 with 33% of all cancer deaths attributed to gastric cancer). Gastroscopic biopsy studies on 284 first degree relatives of San Marinese gastric cancer patients in the Republic of San Marino and in Detroit, where 2,000-2,500 San Marinese reside, have allowed detection of six gastric malignancies. Intestinal metaplasia of gastric mucosa was found in 16 (52%) of 31 Detroit first degree relatives and 51 (36%) of 143 San Marino first degree relatives. Gastroscopy provides an important tool not only for the early detection of gastric cancer in populations of high risk (such as that of San Marino), but also for providing clues to the genetic and environmental factors in gastric neoplasia.

Inhibitory effect of cheese and some food constituents on mutagenicity generated in Vicia faba after treatment with nitrite

The inhibitory potential of various food constituents on the mutagenicity generated in fava beans after treatment with nitrite has been investigated. Cheese was able to inhibit this direct-acting mutagenicity. The antimutagenic factor was not extractable from cheese; solvents of different polarity were used for the extraction. Casein, pectin, gelatin, Vicia faba protein and, to a lesser extent, whey protein and starch could also inhibit mutagenicity. A decrease in mutagenicity was always accompanied by a decrease in total N-nitroso content, as measured analytically. The mutagenic principles appeared to bind more strongly onto cheese than onto V. faba. The implications of this finding are discussed.

Mutagenicities of indole and 30 derivatives after nitrite treatment

Indole and 7-derivatives, L- and D-tryptophan and 9 derivatives, and beta-carboline (norharman) and 11 derivatives were tested for mutagenicity to Salmonella typhimurium TA100 and TA98 after nitrite treatment. 1-Methylindole, which is present in cigarette smoke condensate (Grob and Voellmin, 1970; Hoffmann and Rathkamp, 1970), was the most mutagenic to TA100 without S9 mix after nitrite treatment, inducing 615,000 revertants/mg. 2-Methylindole, 1-methyl-DL-tryptophan, harmaline and (-)-(1S,3S)-1,2-dimethyl-1,2,3,4-tetrahydro-beta-carboline-3- carboxylic acid also showed strong mutagenicity after nitrite treatment, inducing 129,000, 184,000, 103,000 and 197,000 revertants/mg, respectively. These mutagenic potencies were comparable with those of benzo[alpha]pyrene, 3-methylcholanthrene and 2-amino-9H-pyrido[2,3-b]indole (A alpha C) (Sugimura, 1982). Of 31 compounds tested, 22 were mutagenic after nitrite treatment. Since various indole compounds are ubiquitous in our environment, especially in plants, the presence of their mutagenicities after nitrite treatment warrants further studies, including those on their in vivo carcinogenicities.

Food and cancer: cause and effect?

The occurrence of cancer involves the effects of two types of agents: those that alter the genetic material to give rise to neoplasms and others that modulate tumor development through epigenetic effects. In the etiology of some of the major cancers in the North American population--cancers of the upper alimentary tract, stomach, large bowel, pancreas, breast, and prostate--food can contribute elements of both types. Thus, dietary modification has the potential both to prevent the occurrence of cancers at these sites and to control recurrences in treated patients.

Mutagenicity of soy sauce treated with a physiologically feasible concentration of nitrite

Soy sauce treated with nitrite was found to be more mutagenic to Escherichia coli WP2 uvrA/pKM101 than Salmonella typhimurium TA100 without S9 mix. The mutagenicity of soy sauce treated with nitrite was affected by the concentration of soy sauce in the nitrosation mixture, and a concentration of 5% resulted in the highest specific activity (revertants/ml soy sauce equivalent). By incubating soy sauce at a concentration of 5% in a solution of 1 mM nitrite at pH 3 for 1 h at 37 degrees C, the equivalent of 1 ml of soy sauce induced 2790 revertants of E. coli WP2 uvrA/pKM101 without S9 mix.

Studies on environmental chemical carcinogenesis in Japan

The historical background of studies in Japan on chemical carcinogenesis from environmental sources is described from personal experience.

Role of fat, fiber, nitrate, and food additives in carcinogenesis: a critical evaluation and recommendations

This review presents a critical, select evaluation of the amount and type of fat or fiber in nutritional carcinogenesis, with the emphasis being on cancer development in the mammary gland and large bowel. The role of nitrate and nitrosation is described in relation to risk for cancers of the head and neck (especially the esophagus) and cancers of the stomach and the liver. Systematic tests of increasing complexity to delineate possible carcinogenic risk in food additives and contaminants are described. Specific recommendations stemming from these evaluations are made as to dietary recommendations designed to reduce cancer risk.

Appearance of direct-acting mutagenicity of various foodstuffs produced in Japan and Southeast Asia on nitrite treatment

After nitrite treatment, various kinds of pickled vegetables and sun-dried fishes produced in Japan showed direct-acting mutagenicity on Salmonella typhimurium TA100, inducing 1900-18000 revertants/g. Kimchis, sun-dried fishes, sun-dried squid, soy sauces, fish sauces, bean pastes and shrimp paste produced in Korea, the Philippines and Thailand also showed direct-acting mutagenicity after nitrite treatment. All soy sauces and fish sauces tested contained as much tyramine as 17-1020 micrograms/ml, but very low or undetectable amounts of (-)-(1S,3S)- and (-)-(1R,3S)-1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acids.