Induction of lung and exocrine pancreas tumors in F344 rats by tobacco-specific and Areca-derived N-nitrosamines

The tobacco-specific N-nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), as well as the Areca-derived N-nitrosoguvacoline (NG) were assayed for carcinogenicity in male F344 rats by lifetime administration in the drinking water. Groups of 30 to 80 rats were treated with 0.5 ppm, 1.0 ppm, or 5.0 ppm of NNK; 5.0 ppm of NNAL, 20 ppm of NG, a mixture of 20 ppm of NG and 1 ppm of NNK, and water only in the control group. The approximate total doses of the nitrosamines (mmol/kg of body weight) in these groups were: NNK, 0.073, 0.17, and 0.68; NNAL, 0.69; NG, 4.1; NG and NNK, 4.1 and 0.17. As in previous assays in which NNK was tested by s.c. injection, the lung was its principle target organ. Lung tumor incidences in the 0.5-, 1.0-, and 5.0-ppm groups were nine of 80, 20 of 80, and 27 of 30 compared to six of 80 in the control rats. This trend was significant, P less than 0.005. Significant incidences of nasal cavity and liver tumors were observed only in the rats treated with 5.0 ppm of NNK. In contrast to the results of the s.c. bioassays of NNK, tumors of the exocrine pancreas were observed in five of 80 and nine of 80 rats treated with 0.5 and 1.0 ppm. This trend was significant, P less than 0.025. This is the first example of pancreatic tumor induction by a constituent of tobacco smoke. It is also the first finding of duct-like carcinomas in the rat pancreas, including one tumor containing epidermoid, keratin-generating tissue. NNAL, the major metabolite of NNK, induced lung tumors in 26 of 30 rats and pancreatic tumors in eight of 30 rats. It appears to be the proximate pancreatic carcinogen of NNK. NG induced pancreatic tumors in four of 30 rats, P less than 0.05. This finding requires confirmation. The mixture of NG and NNK induced lung tumors in eleven of 30 rats. There were no apparent synergistic interactions of NG and NNK. The observation of benign and malignant tumors of the lung and pancreas of rats treated with the tobacco-specific nitrosamines NNK and NNAL is discussed in respect to the causal association between cigarette smoking and cancer of the lung and pancreas.

N-nitroso-N-2-fluorenylacetamide: a new direct-acting mutagen and teratogen

Reaction of N-2-fluorenylacetamide (2-FAA, CAS No. 53-96-3) with nitrous fume (N2O3) in glacial acetic acid at 0 degree C yields N-nitroso-N-2-fluorenylacetamide (N-NO-2-FAA), 3-nitro-N-2-fluorenylacetamide, N-nitroso-3-nitro-N-2-fluorenylacetamide and other compounds. N-NO-2-FAA is the major product (80%) and fairly stable at low temperature (-20 degrees C), but extremely labile at ambient temperature. The chemical structure of N-NO-2-FAA is characterized by spectrometric analysis of its naphthol coupling derivatives. This new compound is highly mutagenic to Salmonella typhimurium TA97, TA98, TA100 and TA1538 and requires no microsomal metabolic activation. The mutagenicity of N-NO-2-FAA in TA98 is higher than that of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, CAS No. 70-25-7) and N-acetoxy-N-2-fluorenylacetamide (N-AcO-2-FAA). The teratogenic potential of N-NO-2-FAA was studied with white Leghorn chick embryos given a single dose of 1-100 micrograms/egg on day 6 of incubation. A high incidence of flaccid paralysis of the legs and a low incidence of feather, claw and bill malformations were found in the treated group; no such malformed embryos were found in the control group. The teratogenicity of N-NO-2-FAA was found to be weaker than that of MNNG, but comparable to that of N-methyl-N-nitrosourea (CAS No. 684-93-5). N-NO-2-FAA is a strong electrophile and reacts readily with histidine, lysine, cysteine, glutathione, tryptophan, adenosine, cytidine at neutral pH. In contrast to N-AcO-2-FAA, N-NO-2-FAA does not react significantly with guanosine and thymidine. It seems that N-NO-2-FAA is a strong direct-acting mutagen and probably a new prototype of synthetic carcinogen.

Preparation, toxicity and mutagenicity of 1-methyl-2-nitrosoimidazole. A toxic 2-nitroimidazole reduction product

1-Methyl-2-nitrosoimidazole (INO), the 2-electron reduction product of 1-methyl-2-nitroimidazole (INO2), was prepared by electrochemical reduction of INO2 to 2-hydroxylamino-1-methyl-imidazole (INHOH), followed by back oxidation with iodine. Although stable in crystalline form, INO reacted in water, phosphate-buffered saline, and mammalian cell growth medium. Half-lives for decay were determined by UV-visible spectroscopy. INO was found to be highly toxic towards Chinese hamster ovary (CHO) cells, concentrations of 10-60 microM producing significant cytotoxicity. The rate of INO decay was found to be increased in the presence of CHO cells. INO was also toxic and mutagenic towards Salmonella typhimurium TA-100. When compared on a molar basis to the parent nitro compound INO2, and the 4- and 6-electron reduction products INHOH and 2-amino-1-methylimidazole (INH2), INO was by far (two orders of magnitude) the most toxic under aerobic conditions. These results suggest that the nitroso reduction product of 2-nitroimidazoles may be the reduced species responsible for hypoxic cell selective toxicity of 2-nitroimidazoles.

Mammalian cell toxicity and bacterial mutagenicity of nitrosoimidazoles

It is currently believed that the biological activity of such therapeutic 5-nitroimidazoles as metronidazole is mediated by a short-lived, highly toxic species that arises from nitro group reduction. We found that the 5-nitroimidazole, 1-methyl-4-phenyl-5-nitroimidazole (5-NO2), is at least 1000-fold less cytotoxic for CHO cells and mutagenic for Ames tester strain TA100 than its homologous nitroso compound, 1-methyl-4-phenyl-5-nitrosoimidazole (5-NO). Such evidence, along with previous work showing a similar relative bactericidal potency of these compounds, is consistent with the labile nitrosoimidazole being a biologically active species of the nitroimidazole, and indicates that mammalian cells are very susceptible to such an active form. The high potency of both 5-NO and 1-methyl-4-nitroso-5-phenylimidazole (4-NO), in contrast to the lack of potency of 1-methyl-4-nitro-5-phenylimidazole (4-NO2) relative to 5-NO2, is additional evidence to support the suggestion that the activity of a nitroimidazole is determined mainly by the ease with which it is reduced.

The initiator tRNA acceptance assay as a short-term test for carcinogens. 3. Results with 69 N-nitroso compounds

The activity of 69 carcinogenic and non-carcinogenic N-nitroso compounds was tested by the recently developed initiator tRNA acceptance assay for carcinogens. Of 51 carcinogens tested, 50 were active in the assay. Only N-nitrosopropylpropanolamine showed a false negativity. Eleven out of 14 tested non-carcinogenic compounds were not active in the assay, nitrosoethyl-tert-butylamine and nitrosoprolineethylester were positive. As calculated from these data, the sensitivity of the assay was 98.0%, specificity 84.6%, accuracy 95.4% and predictive value 94.4%. Comparison of relative carcinogenicities in animal bioassays with quantitative results (% stimulation of initiator tRNA charging) of the short-term test showed a good correlation for non-carcinogenic compounds and strong carcinogens. However, carcinogens of low and median potency could not be easily distinguished. A good correlation was obtained for three isomer N-nitrosomethylaminopyridines between the TD50-value and activity in the tRNA acceptance assay. The initiator tRNA acceptance assay thus seems preferable for recognizing and classifying carcinogenic and non-carcinogenic N-nitroso compounds than any other individual short-term test for carcinogenicity.

Effects of nitrosation on the chemical composition and epidermal carcinogenicity of the nitrogen-rich fraction of a high-boiling coal liquid

An 800-850 degrees F solvent-refined coal-II liquid was fractionated into chemical classes to obtain the aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH), nitrogen-containing polycyclic aromatic compounds (NPAC), and hydroxy-substituted PAH (hydroxy-PAH). The isolated NPAC fraction was refractionated by chemical class both before and after undergoing a nitrosation reaction. The nitrosated and non-nitrosated refractionated NPAC fractions were further subfractionated into secondary amine (pyrroles), primary amine-enriched (amino-PAH), and tertiary amine (azaarene) classes. The PAH and hydroxy-PAH composition of the NPAC fraction increased upon nitrosation, whereas the amino-PAH fraction composition decreased upon nitrosation. Nitrosation of standards indicated the amino-PAH compounds reacted to form parent PAH, chloro-substituted PAH, and methoxy-substituted PAH when analyzed by high-resolution gas chromatography (GC) and GC/mass spectrometry (MS). Some easily oxidized PAH compounds reacted to form ketones and quinones. All other standard reference compounds, chosen to be representative of the major chemical classes of compounds present in coal liquefaction materials, were unchanged by the nitrosation reaction. The amino-PAH of the nitrosated NPAC fraction reacted to form parent and some chloro-substituted PAH when analyzed by low-voltage direct-probe MS in addition to the methods given above. Epidermal carcinogenesis studies with the PAH, NPAC, nitrosated NPAC, and hydroxy-PAH fractions isolated from the 800-850 degrees F coal liquid indicated the PAH and NPAC were the most important determiners of skin carcinogenesis, with the PAH giving a higher response than the NPAC. The tumorigenicity of the NPAC was drastically reduced by nitrosation, probably due to the destruction of the amino-PAH upon nitrosation.

Formation of a mutagenic diazoquinone by interaction of phenol with nitrite

Reaction of phenol with nitrite under mildly acidic conditions produced p-nitrosophenol, p-diazoquinone and o-diazoquinone. p-Diazoquinone showed mutagenicity in Salmonella typhimurium strains TA98 and TA100 without metabolic activation; the number of his+ revertant colonies in strain TA98 was 85 with a dose of 20 nmol (after deduction of the background (control) number of about 20). Higher doses of the compound were bactericidal. While the reaction of phenol with an equivalent amount of nitrite at pH 3 produced p-nitrosophenol in high yield, reaction with excess nitrite produced a high yield of p-diazoquinone. p-Nitrosophenol was converted to p-diazoquinone by reaction with nitrite. Formation of o-diazoquinone also increased with increasing amounts of nitrite. The formation of these compounds was not greatly affected by the presence of dimethylamine. Nitrosation of dimethylamine with nitrite was stimulated by phenol because of the formation of p-nitrosophenol and its stimulatory effect. Thus, the reaction of phenol with nitrite can produce mutagenic p-diazoquinone, and can also stimulate nitrosation of secondary amines by production of p-nitrosophenol.

Intestinal cancer induced by N-nitroso compounds

Several N-nitroso compounds induce tumors of the colon, and some induce tumors in other parts of the intestinal tract as well. The nitrosamines that induce colon tumors are beta oxidized n-propyl-nitrosamines. These require metabolic activation, as do 1,2-dimethylhydrazine, azomethane, and azoxymethane, another group of colon carcinogens. Several nitrosoalkylureas induce tumors in rat colons after oral administration, although the monoalkylnitrosoureas are fairly unstable and might not be expected to reach the colon. However, monoalkylnitrosoureas are equally effective with the much more stable dialkylnitrosoureas. Although nitrosomethylurea did not induce colon tumors under these conditions, nitrosoethylurea did, together with nitrosodiethylurea and other nitrosoethylalkylureas. Nitroso-n-butyl-, n-amyl-, n-hexyl-urea, and nitrosohydroxyethylurea also induced colon tumors, but the last, like nitrosoethylurea, also induced tumors of the duodenum and ileum. In most of these experiments male rats were more susceptible to induction of intestinal tumors than female rats. An explanation for the differences between these compounds of similar structure might be found in variations in their ability to alkylate DNA in intestinal cells, or in differences in stability of the alkylated product between the compounds. The physical properties of the compounds might also modulate the process of carcinogenesis, however.

Carcinogenicity of 1-(4-amino-2-methylpyrimidine-5-yl)-methyl-3-(2-chloroethyl)-3- nitrosoureahydrochloride and three related N-nitroso derivatives following repeated intravenous administration to male Wistar rats

Long-term toxic evaluation of 1-(4-amino-2-methylpyrimidine-5-yl)-methyl-3- (2-chloroethyl)-3-nitrosoureahydrochloride (ACNU), 1-(2-chloroethyl)-1-nitroso-3-(methylene-2-pyridylium)-urea- hydrochloride (CNMPU), 1-(2-chloroethyl)-1-nitroso-3-(4-thiomorpholino)-urea (CNTMU) and 4-[N-(2-chloroethyl)-N-nitrosocarbamoyl]-morpholine (CNCM) which were administered each at five dosages, adapted to the clinical situation, revealed significantly increased tumor risks for the first three agents in the lung and the adrenal gland. Additionally, CNTMU and ACNU induced a significant rise in the tumor load of the neurogenic tissue; the latter compound, being in clinical use, was associated with a significantly increased number of mammary tumors as well. CNCM, however, did not exhibit significantly elevated carcinogenic activity, although the overall tumor load was up to 2.4-fold increased compared to controls. The results indicate no advantage of the newly developed ACNU with respect to its inherent carcinogenic risk as compared to clinically established 2-chloroethyl-N-nitroso derivatives.

Mutagenicity and carcinogenicity studies of homemade "rust-proof cutting fluid"

A homemade rust-proof cutting fluid (RPCF) used in China was tested for carcinogenicity by an in vivo chronic experiment and for mutagenicity by the Ames Salmonella microsomal assay. Undiluted and threefold water-diluted fluid were given as drinking water to groups of young adult Wistar rats for 2 years. The treatment induced 11/40 malignant tumors with 9/40 acinar adenocarcinomas of the pancreas in the high-dose group. Simultaneous administration of ascorbic acid dissolved in the undiluted fluid at 2 g acid per 1 g sodium nitrite resulted in 1/40 pancreatic carcinoma. The results of the Ames test showed that the technical RPCF was mutagenic to TA100 with or without metabolic activation. It was concluded that the homemade RPCF, which is comprised of sodium nitrite, triethanolamine, and polyethylene glycol, may form direct-acting mutagen(s) upon storage and form, in vivo, e.g., nitrosamines that caused acinar pancreatic carcinoma in Wistar rats. Simultaneous administration of ascorbic acid is suggested for the protection of workers exposed to the rust-proof cutting fluid.

Structure-activity relations in carcinogenesis by N-nitroso compounds

For a large number of N-nitroso compounds a comparison of their carcinogenic effects in rats and Syrian golden hamsters has been made. Nitrosamines, which require metabolic activation, and nitrosoalkylamides, which do not, produce quite different tumor responses. There are also large differences in the types of tumor induced in rats and in hamsters. In all the studies doses of the various compounds, equimolar to the extent that was possible, are administered orally. Continuous doses (in drinking water or food) often produce a response different from that after administration of the same compound in pulsed doses (by gavage), even though the same total dose is delivered. Continuous doses of nitrosamines are usually more effective than pulsed doses, but with the nitrosoalkylureas, the reverse is more generally the case. Rat and hamster liver is a common target of many nitrosamines, but rarely of nitrosamides. The most common site of tumor induction in rats by N-nitroso compounds is the esophagus, but the hamster esophagus never responds. The pancreas duct of the hamster is a common target of nitrosamines containing a beta-oxygenated propyl group, but pancreas duct tumors are never seen in rats. Nitrosomethyl-n-alkylamines (with an even numbered carbon chain) induce bladder tumors in rats and hamsters. Many nitrosoalkylureas induce tumors of the nervous system in rats, as well as a great variety of other tumors. In hamsters, nitrosoalkylureas give rise only to tumors of the forestomach and spleen, but no tumors of the nervous system. The similar carcinogenic actions of certain groups of N-nitroso compounds can be related to their generation, directly or by metabolism, of similar simple moieties having certain organs as their target.

Inhibitory effects of thiols on a mutagenic contaminant from the synthesis of N-nitrosothiazolidine

The effect of S9 and various thiols were studied for potential modifying effects on a mutagenic trace artifact ('NTHZ') formed during the synthesis of N-nitrosothiazolidine (NTHZ) from cysteamine, formaldehyde and nitrite. Induced and uninduced S9 prepared from Syrian hamster livers reduced mutagenic activity in Salmonella TA100. Incorporation of boiled S9 into the preincubation medium produced similar effects, indicating a non-enzymatic mechanism for the detoxification reaction. Thiols alone also lowered revertant yields, and inhibitory efficacy was, in general, related to the pKa of the compound. At equimolar concentrations mutagenic activity was reduced in the following order (pKa values in parentheses): Thioglycolate (10.7) greater than mercaptoethanol (9.6) greater than reduced glutathione (8.8) greater than cysteine (8.35) greater than cystine (8.2). N-Acetylcysteine (9.52) and cysteamine (8.35), however, did not fit this pattern. The results of this study suggest that normal hepatic mechanisms may minimize 'NTHZ' genotoxicity thereby reducing potential health risks associated with its exposure.

Characterization of a CHO variant in respect to alkylating agent-induced biological effects and DNA repair

From the Chinese hamster ovary line CHO-9 a resistant variant, Cl 3, was isolated after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Cl 3 cells were much more resistant to the cytotoxic effects of MNNG (D10 of 1.8 microgram/ml MNNG as compared to 0.23 microgram/ml for parental line) and other methylating N-nitroso compounds, but they had the same sensitivity to various other alkylating agents. MNNG was equally effective in sensitive parent line and resistant variant in inducing sister-chromatid exchanges (SCEs) and mutations to 6-thioguanine resistance. The increased resistance of Cl 3 was not due to reduced cellular uptake of MNNG, to a more efficient repair of methylated purine bases, or to differences in MNNG-induced inhibition of DNA synthesis. It is concluded that the resistant variant has some unknown tolerance mechanism which alters the cytotoxic, but not the SCE- and mutation-inducing effects of methylating N-nitroso compounds.

Dose-response curves for liver DNA fragmentation induced in rats by sixteen N-nitroso compounds as measured by viscometric and alkaline elution analyses

A new viscometric technique, capable of detecting DNA strand breaks and alkali-labile sites by monitoring time-dependent changes of DNA-reduced viscosity, has been used to analyze dose-response curves for the induction of DNA damage in liver of rats treated with single p.o. doses of sixteen N-nitroso compounds. Statistically significant changes of DNA viscometric parameters, which are considered indicative of DNA fragmentation, were produced by N-nitrosodimethylamine (0.022 mg/kg), N-nitrosomethylethylamine (0.025 mg/kg), N-nitrosodiethylamine (0.067 mg/kg), N-nitrosodiethanolamine (1.03 mg/kg), N-nitrosodi-n-propylamine (0.31 mg/kg), N-nitrosodi-n-butylamine (0.083 mg/kg), N-nitroso-N-methylurea (0.56 mg/kg), N-nitroso-N-ethylurea (0.37 mg/kg), N-nitroso-N-butylurea (0.16 mg/kg), streptozotocin (20 mg/kg), N-nitrosomorpholine (0.4 mg/kg), N-nitrosopiperidine (2.22 mg/kg), N-nitrosopyrrolidine (5.0 mg/kg), 1-nitroso-2-imidazolidinone (0.31 mg/kg), and N-methyl-N'-nitro-N-nitrosoguanidine (5.57 mg/kg). The contemporary measurement of liver DNA fragmentation by the alkaline elution technique revealed that in our experimental conditions higher doses are needed to produce a statistically significant increase of DNA elution rate. This suggests that the viscometric method is capable of detecting smaller levels of N-nitroso compound-induced DNA fragmentation, but it does not exclude that the sensitivity of alkaline elution can be improved by appropriate modifications of the experimental procedure. With both techniques DNA damage was undetectable in liver of rats treated with 540 mg/kg of the non-hepatocarcinogen N-nitrosodiphenylamine. With the exception of N-nitrosodiethanolamine, that exhibited a plateau effect, all the other N-nitroso compounds examined displayed a linear dose-response curve over the entire wide range of doses tested. Consequently, a nonlinearity of the relationship between dose and tumor response cannot be attributed to a nonlinearity of the pharmacokinetic processes involved in the formation of DNA damage.

Regulation of intracellular glutathione in rat embryos and visceral yolk sacs and its effect on 2-nitrosofluorene-induced malformations in the whole embryo culture system

The dysmorphogenic effects of 2-nitrosofluorene (NF) in vitro were modulated in Day 10 rat embryos by agents which regulate intracellular glutathione (GSH) levels. The incidence of abnormal axial rotation caused by NF alone increased in a dose-dependent manner at NF concentrations in excess of 25 microM. No effects were observed at 15 microM NF and doses of 100 microM resulted in a 100% incidence of mortality. L-Buthionine-S,R-sulfoximine (BSO), an inhibitor of GSH synthesis, produced malformations (50%) in embryos exposed to 15 microM NF but produced no additional effects on embryos at higher NF concentrations. BSO treatment alone resulted in a greater than 50% decrease in GSH content in visceral yolk sacs and had a lesser but likewise significant effect (15% decrease) on the GSH content of embryos. Protein content was inversely affected as embryonic levels were increased by 20% and yolk sac levels were unchanged. When BSO was added in combination with NF at the onset of the culture period, embryonic GSH decreased in a dose-dependent manner, suggesting a relatively low rate of embryonic GSH turnover that could be increased by addition of an exogenous substrate capable of forming adducts with and removing GSH from the cells. 2-Oxothiazolidine-4-carboxylate (OTC), a compound which is enzymatically modified to provide an additional source of intracellular cysteine and increase GSH synthesis, produced no significant changes in embryonic or yolk sac GSH when added alone to the culture medium. When OTC (5 mM) was added in combination with NF, however, NF-elicited malformations were eliminated. This was also the case at 100 microM NF in which OTC not only prevented malformations but completely protected embryos against the loss in viability. The GSH and protein levels were indistinguishable from controls when OTC and NF were added simultaneously except for the 41 microM NF dose at which a highly significant increase in both embryonic and yolk sac protein was observed. This study clearly demonstrates the potential importance of GSH in the modulation of chemical dysmorphogenesis and provides an important new tool for the study of mechanisms of developmental toxicity.

Computer automated structure evaluation of the carcinogenicity of N-nitrosothiazolidine and N-nitrosothiazolidine 4-carboxylic acid

N-Nitrosothiazolidine 4-carboxylic acid (NTCA), a sulphur-containing nitrosamine present in human urine, was predicted to be non-carcinogenic by CASE, the newly developed Computer Automated Structure Evaluating system. On the other hand, N-nitrosothiazolidine (NTHZ), a nitrosamine present in food products, was predicted to be carcinogenic. The putative non-carcinogenic NTCA may be metabolized to NTHZ, a predicted carcinogen.

Carcinogenicity and mutagenicity of N-nitroso compounds

The carcinogenic activities in rats and hamsters and the mutagenic activity in Salmonella of a number of N-nitroso compounds belonging to various classes have been compared. While most directly acting N-nitroso compounds and those requiring metabolic activation are mutagenic with appropriate activation and seem to alkylate DNA in vivo, there are exceptions. Some of these are mutagens that are not carcinogenic; others are carcinogens that are nonmutagenic. Even among the mutagenic carcinogens, there is no quantitative relationship between mutagenic and carcinogenic activities. This implies to directly acting compounds and to those requiring metabolic activation. The lack of congruence between the two activities among the nitrosamines is due to the complexity of the metabolic activating processes leading to formation of proximate carcinogens. The deficiencies in the mutagenesis assay appear to arise from a lack of the necessary enzymes in the liver microsomal fractions used for activation. Nitrosamines bearing oxygen on the beta carbon of an alkyl chain are not oxidized by rat microsomal enzymes and hence are not converted to bacterial mutagens by rat liver microsomes. Bacterial mutagenicity is not a guide to carcinogenic activity of N-nitroso compounds or to the mechanisms by which these compounds induce cancer.

Assessment of the risk of formation of carcinogenic N-nitroso compounds from dietary precursors in the stomach

A literature review has shown that the daily intakes of various N-nitroso-precursor classes in a typical European diet span five orders of magnitude. Amides in the form of protein, and guanidines in the form of creatine and creatinine, are the nitrosatable groups found most abundantly in the diet, approaching levels of 100 g/day and 1 g/day, respectively. Approximately 100 mg of primary amines and amino acids are consumed daily, whereas aryl amines, secondary amines and ureas appear to lie in the 1-10 mg range. The ease of nitrosation of each precursor was estimated, the reactivities being found to span seven orders of magnitude, with ureas at the top and amines at the bottom of the scale. From this information and an assessment of the carcinogenicity of the resulting N-nitroso derivatives, the potential health risk due to gastric in vivo nitrosation was calculated. The combined effects of these risk variables were analysed using a simple mathematical model: Risk = [daily intake of precursor] X [gastric concentration of nitrite]n X [nitrosatability rate constant] X [carcinogenicity of derivative]. The risk estimates for the various dietary components spanned nine orders of magnitude. Dietary ureas and aromatic amines combined with a high nitrite burden could pose as great a risk as the intake of preformed dimethylnitrosamine in the diet. In contrast, the risk posed by the in vivo nitrosation of primary and secondary amines is probably negligibly small. The risk contribution by amides (including protein), guanidines and primary amino acids is intermediate between these two extremes. Thus three priorities for future work are a comprehensive study of the sources and levels of arylamines and ureas in the diet, determination of the carcinogenic potencies of key nitrosated products to replace the necessarily vague categories used so far, and the development of short-term in situ tests for studying the alkylating power of genotoxicity of N-nitroso compounds too unstable for inclusion in long-term studies.

[Carcinogenic and promoting effects of Roussin red methyl ester (RRME) on the forestomach epithelium of mice and esophageal epithelium of rats, and its inhibition by retinamide and vitamin C]

Carcinogenic and promoting effects of RRME as isolated from the pickled vegetables in Linxian County, a high incidence area of esophageal cancer, were studied in mice and rats. RRME alone did not cause tumor in the forestomach of mice and esophagus of rats. When the mice were intubated with a single dose of nitroso-sarcosine-ethylester (NSEE), the incidence of the forestomach carcinoma was only 9.5%. However, when the mice were given gastric doses of RRME after one single dose of NSEE, the incidence was increased to 41.0%. In rats, the tumor incidence was 5.3% in nitroso-methylbenzylamine (NMBzA) group, while in NMBzA kRME group, it was 20.7%. In rats intubated with NSEE for 7 times, no carcinoma appeared in esophageal epithelium; while followed by gastric doses of RRME, the incidence of esophagus carcinoma increased up to 63.2%. The experimental results show that RRME has distinct promoting effect on the process of cocarcinogenesis initiated by NSEE and NMBzA in the forestomach of mice and esophagus of rats, but without carcinogenic effect itself. Retinamide (RI) and massive dose of vitamin C showed an obviously inhibitory effect on promoting action of RRME in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity and DNA damage induced by 1-nitropyrene and its derivatives in Chinese hamster lung fibroblasts

1-Nitropyrene and its chemically synthesised derivatives were investigated for their cytotoxicity and ability to induce DNA-strand breaks in Chinese hamster lung fibroblasts. Both 1-nitrosopyrene (0.25-60 micrograms/ml) and 1-aminopyrene (0.25-25 micrograms/ml) were cytotoxic, and induced the formation of DNA lesions, which were measured as DNA single-strand breaks after sedimentation in alkaline sucrose-density gradients. Higher doses of 1-aminopyrene (25-60 micrograms/ml) inhibited the formation of DNA single-strand breaks. 1-Nitropyrene was not toxic (0.25-60 micrograms/ml) and induced low levels of detectable DNA strand breaks, whilst N-acetyl-1-aminopyrene was inactive. The post-mitochondrial supernatant fraction of Aroclor-induced rat-liver containing 4 mM NADPH (S9 mix) did not promote the activation of 1-nitropyrene. In fact DNA strand breaks induced by either 1-nitropyrene or 1-nitrosopyrene was abolished in the presence of S9 mix. The 1-nitropyrene reduced intermediate, N-hydroxy-1-aminopyrene was synthesised by the reduction of 1-nitrosopyrene with ascorbic acid. In the presence of ascorbic acid, 1-nitrosopyrene caused a 5-fold increase in the number of DNA single-strand breaks when compared to cells treated with 1-nitrosopyrene alone. The results are discussed in terms of the metabolic activation of 1-nitropyrene and 1-aminopyrene in Chinese hamster lung cells.

Mutagenicity of para-nitroso-dimethyl- and diethyl-anilines

Low concentrations of para-nitroso-dimethylaniline (NdMA) were mutagenic to Salmonella typhimurium TA100 with optimal effect at 1.5 microM in fluctuation assays, without activating enzymes. The diethyl homologue (NdEA) had little or no mutagenic effect at low concentrations, although the bacteriocidal effects of NdMA and NdEA were similar. At higher bacteriocidal concentrations (approximately LC55-LC80) both NdMA and NdEA were mutagenic. NdMA and some other C-nitroso compounds proved carcinogenic in animal bioassays, and further research is needed to assess the human hazard from exposure to C-nitroso compounds in food, medicines or industry.

Effect of cell cycle position on the survival of 9L cells treated with nitrosoureas that alkylate, cross-link, and carbamoylate

The relationship between cell cycle position and cytotoxicity was studied in 9L rat brain tumor cells treated with nitrosoureas that, depending on their structures, can alkylate or alkylate and cross-link DNA and/or carbamoylate biomolecules. Because pure populations of G1-, S-, and G2-M-phase cells could not be obtained with the centrifugal elutriation methods used, drug sensitivity of cells in each phase of the cell cycle was estimated using a mathematical model that accounts for variation in enrichment of elutriated fractions. 1,3-Bis(2-chloroethyl)-1-nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea, 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-1-nitrosourea, which alkylate and cross-link DNA and carbamoylate biomolecules, and 2-[3-(2-chloroethyl)-3-nitrosoureido]-D-glucopyranose (chlorozotocin), which alkylates and cross-links DNA but cannot carbamoylate biomolecules, killed more cells in G1 and G2-M phases than in S phase. N-Ethylnitrosourea, which alkylates and carbamoylates but does not form DNA interstrand cross-links, was more toxic to cells in S phase than in other phases. Cell kill caused by N,N'-bis(trans-4-hydroxycyclohexyl)-N-nitrosourea, a compound that carbamoylates only, increased progressively through the cell cycle from G1 to M. Nitrosoureas that cross-link DNA were more cytotoxic than nitrosoureas that do not cross-link DNA, although the latter had phase specificity. The results suggest that the increased sensitivity of G1- and G2-M-phase cells to chloroethylnitrosoureas is related to the formation of DNA interstrand cross-links.

Analysis of the genotoxic activity of four N-nitroso compounds by the Drosophila mosaic test

Mutagenic activity of 4 nitroso compounds of environmental importance - N-nitroso-morpholine, dinitrosopiperazine, N,N'-dinitroso-pyridinol-carbamate and N-methyl-N-nitroso-p-toluenesulfonamide - was tested by the Drosophila mosaic test. Larvae were fed with the nitroso-compound-containing food for 2-4 days, and when they had developed into adults, their wings were screened for mosaic spots. All 4 compounds were positive. This finding supports the conclusion that the mosaic test - besides other test procedures - may become a tool for identifying mutagens.