Organotrope carcinogene Wirkungen bei 65 verschiedenen N-Nitroso-Verbindungen an BD-Ratten

Nitrosamines in rubber bands used for orthodontic purposes

Fourteen samples from eight brands of elastic-rubber bands used in orthodontics were tested for their nitrosamine content. The presence of N-nitrosodibutylamine and N-nitrosopiperidine was confirmed. The potential for nitrosamine formation from accelerating agents used for vulcanization and from other nitrosatable amines, which may be present in rubber exposed to salivary nitrite, justifies further investigations.

Nitrosamine excretion in patients with continent ileal reservoirs for urinary diversion

Adenocarcinomas are a recognized complication following ureterosigmoidostomy for which the endogenous formation of N-nitroso compounds may be a risk factor. As an alternative means of urinary diversion, the continent ileal reservoir has recently been developed. Microbiological and chemical investigations on the urine of patients with an ileal reservoir showed the presence of bacteria, nitrate, nitrite and N-nitrosamines formed endogenously in the ileal pouch. The role of nitrosamines in carcinogenesis in these patients as a late stage complication resulting from the use of a continent ileal reservoir is discussed.

Initial changes of rat leukemia induced by 1-ethyl-1-nitrosourea and 1-butyl-1-nitrosourea

The initial histological changes of leukemia were investigated in rats to which 1-ethyl-1-nitrosourea and 1-butyl-1-nitrosourea were orally administered. The appearance of orthochromatic erythroblasts in the peripheral blood was used as the index of the initial stage of leukemia. The rat leukemia progressed from solitary lesions to scattered and further diffuse lesions. These leukemias are thought to begin as one, or only a few nodular foci, mainly in the bone marrow and partly in the spleen.

N-nitrosodialkylamine dealkylation in reconstituted systems containing cytochrome P-450 purified from phenobarbital- and beta-naphthoflavone-treated rats

Five cytochrome P-450 forms were purified from livers of rats pretreated with phenobarbital (PB) or beta-naphthoflavone (BNF), and the oxidative dealkylation of N-nitrosodialkylamines by the reconstituted cytochrome P-450 systems was measured. PB-II (P450IIB1) showed very high N-nitrosomethybutylamine (NMBA) debutylase activity, high NMBA demethylase activity and high N-nitrosomethyl-benzylamine (NMBeA) debenzylase activity, suggesting that the increase following PB treatment in hepatic microsomal NMBA debutylation and NMBeA debenzylation was due to the induction of PB-II. BNF-H (P450IA2) showed very high NMBA debutylase and high NMBeA debenzylase activities, and BNF-L (P450IA1) showed NMBA debutylase and high NMBeA debenzylase activities. These results suggested that the increase by BNF pretreatment in hepatic microsomal NMBA debutylation was due mainly to the induction of BNF-H and in some part to that of BNF-L. PB-II also showed very high dealkylation activity of lipophilic N-nitrosodialkylamines with long alkyl moieties. On the other hand, BNF-H dealkylated N-nitrosodipropylamine (NDPA), N-nitrosomethylbutylamine (NMBA) and N-nitrosoethylbutylamine (NEBA) at higher rates than N-nitrosodibutylamine (NDBA). BNF-L dealkylated NEBA at higher rates than NMBeA and NDBA. These results reveal that substrate specificity of each cytochrome P-450 form in N-nitrosodialkylamine metabolism is different from each other and several forms of cytochrome P-450 support each N-nitrosamine dealkylase activity in mammalians.

Mutational specificities of N-nitrosamines in a host-mediated assay: comparison with direct-acting N-nitroso compounds in vitro and an approach to deducing the nature of ultimate mutagens in vivo

The mutational activities and specificities of several N-nitrosamines in Salmonella recovered from mouse liver in the host-mediated assay (HMA) were compared with the specificities of related direct-acting N-nitroso compounds in vitro. The specificities of the direct-acting methyl, ethyl, propyl, and 2-hydroxypropyl compounds were all different and presumably are attributable to the DNA adducts resulting from the corresponding alkyldiazonium or carbonium ions. Introduction of a 2-hydroxyl group greatly influenced the mutational specificity. The 2-oxopropyl compound showed the same specificity as the methyl compound. This result is consistent with one of the known breakdown pathways of the oxopropyl diazonium ion (or related reactive species), which leads to a methyl diazonium ion. The N-nitrosodialkylnitrosamines N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodipropylamine (NDPA), which all require metabolic activation, showed specificities in the HMA similar to those of their direct-acting counterparts. The cyclic nitrosamine N-nitrosopyrrolidine was weakly active in the HMA, although its direct-acting derivative was a potent mutagen in vitro. The results for NDMA and NDEA were consistent with most previous studies of the metabolism of these compounds in vivo. However, NDPA can yield methylating, and probably hydroxypropylating, species in addition to propyldiazonium ion. As the specificity of NDPA was similar to that of a propylating agent, NDPA appears to lead to genotoxic products in the mouse liver mainly by direct alpha-hydroxylation. The initial results described here indicate that mutational specificity in the HMA can be used to deduce metabolic pathways leading to genotoxic products when the appropriate proximate mutagens are available as standards. Furthermore, we observed a reasonable correlation between potency in the HMA and hepatocarcinogenesis.

Renal pelvic carcinoma which shows metastatic potential to distant organs, induced by N-butyl-N-(4-hydroxybutyl)nitrosamine in NON/Shi mice

Renal pelvic carcinoma was induced in mice by giving N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). Initially, differences in renal pelvic carcinogenesis by BBN were examined in three male mouse strains: NON/Shi, which demonstrate spontaneous hydronephrosis with incidences of 10-30%, and DS/Shi and B6C3F1, which do not exhibit hydronephrosis. When mice of these strains were given 0.05% BBN in the drinking water for 12 weeks followed by water without BBN for 8 weeks, renal pelvic carcinoma morphologically similar to human carcinomas developed in 8 of 23 NON/Shi mice (35%). Metastasis to the lung was found in one of them (13%). B6C3F1 and DS/Shi mice had no pelvic tumors, but the response to urinary bladder carcinogenesis in NON/Shi mice was nearly equal to that in DS/Shi and B6C3F1 mice. These results suggest that renal pelvic carcinogenesis is related to the presence of stagnant urine containing carcinogen in the renal pelvis. In a second experiment, we examined renal pelvic carcinogenesis in NON/Shi mice given BBN for 4 weeks followed by water without BBN for 32 weeks. The incidence of renal pelvic carcinoma (28%) was similar to that in the first experiment, but the incidence of metastasis was markedly elevated to 60%. These results indicate that BBN treatment can induce renal pelvic carcinoma which often metastasizes to the lung in NON/Shi mice.

Local and systemic carcinogenic effects of alkylating carcinogens in rats treated by intravesicular administration

Several nitrosamines and an azoxyalkane have been administered intravesically to groups of 12 female F344 rats, twice a week for 20 or 30 weeks. Many of the nitrosamines were as efficacious in giving rise to the same tumors of internal organs as when similar doses were administered orally, showing that absorption from the bladder was as rapid as from other sites. The tumors produced included lung and kidney tumors by nitrosodimethylamine, colon and Zymbal gland tumors by azoxymethane, liver tumors by methylnitrosoethylamine (but not by nitrosodimethylamine), liver and esophagus tumors by nitrosodiethylamine, liver and lung tumors by methylnitrosamino-3-pyridylbutanone, liver tumors by nitrosomorpholine, and tumors of the esophagus by methylnitroso-n-butylamine, 2,6-dimethyl-nitrosomorpholine and methylnitrosamino-N,N-dimethylethylamine. Bladder tumors were induced by intravesicular administration of only low doses of nitrosobis-(2-oxopropyl)amine and to a lesser extent by methylnitroso-n-hexylamine and nitroso-(2-hydroxypropyl)(2-oxopropyl)amine, which all induced tumors systemically in addition. The bladder mucosa seemed to lack enzymes necessary to activate most nitrosamines to locally acting proximate carcinogens, but was quite transparent to the passage of carcinogenic nitrosamines present in the urine into the body to induce tumors in distant organs.

Oncogenicity study of trifluralin in B6C3F1 mice

B6C3F1 mice were maintained for 24 months on diets containing 0, 563, 2250 or 4500 ppm trifluralin. These dietary concentrations corresponded to daily doses of approximately 70, 285 or 570 mg/kg body weight, respectively. The control group contained 120 mice/sex and treated groups consisted of 80 mice/sex. There were no treatment-related effects on the survival, appearance or behaviour of the mice. Survival at test termination was at least 67% in each group. Compared with controls, mean body weight was significantly reduced in a dose-related manner in mice of both sexes given the 2250 and 4500 ppm diets. At 21 months, the reduction in body weight was greater than or equal to 15 and greater than or equal to 30%, respectively. At study termination, dose-related decreases in erythrocytic and leucocytic values were also observed at dietary levels of 2250 and 4500 ppm. In clinical chemistry evaluations, blood urea nitrogen levels and alkaline phosphatase activity in mice of both sexes were significantly increased at trifluralin levels of 2250 and 4500 ppm. Blood urea nitrogen also showed a marginal increase in females given the low dose of trifluralin. Alanine aminotransferase activity was significantly increased in males at all treatment levels. Although there were a number of absolute and relative organ weight changes in all three treatment groups that were significantly different from the control values, the reduced relative kidney weights in males and the increased relative liver weights in both sexes at dietary levels of 2250 and 4500 ppm were the only changes that could be correlated with altered clinical chemistry values.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative metabolism and urinary excretion of N-mononitrosopiperazine and N,N'-dinitrosopiperazine in the rat

The metabolism of N-mononitrosopiperazine (NPz) and N,N'-dinitrosopiperazine (DNPz) was investigated in Sprague-Dawley rats. When an oral dose of 50 micrograms/rat NPz was administered, 10.5% of the dose was recovered unchanged in urine together with N-nitroso-3-hydroxypyrrolidine (NHPYR, 1.3% of administered NPz dose) and N-nitrosodiethanolamine (NDELA, 0.3%). For DNPz, 7.7% of the administered dose together with NPz (0.04%), NHPYR (2.9%), NDELA (6.7%) and N-nitroso(2-hydroxyethyl)glycine (NHEG, 20.2%) was recovered in urine after 24 h. These results show extensive metabolism of both NPz and DNPz and suggest that both NPz and NHPYR could be analysed in urine as markers for the endogenous nitrosation of piperazine in patients receiving antihelminthic treatment with piperazine.

Urinary excretion of S-benzylmercapturic acid as an indicator of N-nitroso-N-methylbenzylamine exposure

The excretion of S-benzylmercapturic acid (SBzMA) in the urine of rats treated with N-nitroso-N-methylbenzylamine (NMBzA) was determined by gas chromatography-mass spectrometry (GC-MS). The identity of SBzMA in the urine was confirmed by full scan GC-MS. The amount of urinary SBzMA varied with the dose of NMBzA (up to 5 mg/kg) and with rat strain. For the three strains investigated, most of a 2.5 mg/kg dose of SBzMA was excreted within 24 h. Comparison of the levels of this SBzMA excreted by rats treated with equivalent doses of either NMBzA or benzaldehyde indicates that urinary SBzMA is derived mainly from benzylating species resulting from the hydroxylation of the methyl group of NMBzA.

Cancer morbidity in nitrate fertilizer workers

A cohort of 2,131 male nitrate fertilizer workers was evaluated for cancer morbidity from 1963 to 1986. No significant increase in total cancer, stomach cancer (5 actual vs 6.7 expected cases), or lung cancer (13 vs 13 expected) was found. On the other hand, 26 actual cases of prostate cancer were observed vs 16 expected cases (standardized morbidity ratio, SMR = 161; 95%, confidence interval, CI = 107-239). This risk increase however, was, not enhanced by applying at least a 10-year latency period. In a cohort of 1,148 male fertilizer workers who had never been exposed to nitrate, there was an increased incidence of lung cancer (SMR = 151,95% CI = 103-220) but not of stomach cancer or prostate cancer. There was no association between airborne nitrate exposure dose and total cancer, stomach cancer, lung cancer or prostate cancer, respectively.

Carcinogenic N-nitrosamines in the diet: occurrence, formation, mechanisms and carcinogenic potential

Nitrosamines form a large group of genotoxic chemical carcinogens which occur in the human diet and other environmental media, and can be formed endogenously in the human body. N-Nitroso compounds can induce cancer in experimental animals. Some representative compounds of this class induce cancer in at least 40 different animal species including higher primates. Tumours induced in experimental animals resemble their human counterparts with respect to both morphological and biochemical properties. Extensive experimental, and some epidemiological data suggest that humans are susceptible to carcinogenesis by N-nitroso compounds and that the presence of these compounds in some foods may be regarded as an aetiological risk factor for certain human cancers including cancers of the oesophagus, stomach and nasopharynx.

DNA methylation in the digestive tract of F344 rats during chronic exposure to N-methyl-N-nitrosourea

The formation of O6-methyldeoxyguanosine (O6-MedGuo) was determined by an immuno-slot-blot assay in DNA of various tissues of F344 rats exposed to N-methyl-N-nitrosourea (MNU) in the drinking water at 400 ppm for 2 weeks. Although the pyloric region of the glandular stomach is a target organ under these experimental conditions, the extent of DNA methylation was highest in the forestomach (185 mumol O6-MedGuo/mol guanine). Fundus (91 mumol/mol guanine) and pylorus (105 mumol/mol guanine) of the glandular stomach, oesophagus (124 mumol/mol guanine) and duodenum (109 mumol/mol guanine) showed lower levels of O6-MedGuo but differed little between each other. Thus, no correlation was observed between target organ specificity and the extent of DNA methylation. This is in contrast to the gastric carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), which preferentially alkylates DNA of the pylorus, the main site of induction of gastric carcinomas by this chemical. In contrast to MNU, the non-enzymic decomposition of MNNG is accelerated by thiol compounds (reduced glutathione, L-cysteine), which are present at much higher concentrations in the glandular stomach than in the forestomach and oesophagus. During chronic exposure to MNNG (80 ppm), mucosal cells immunoreactive to O6-MedGuo are limited to the luminal surface [Kobori et al. (1988) Carcinogenesis 9:2271-2274]. Although MNU (400 ppm) produced similar levels of O6-MedGuo in the pylorus, no cells containing methylpurines were detectable by immunohistochemistry, suggesting a more uniform methylation of mucosal cells by MNU than by MNNG. After a single oral dose of MNU (90 mg/kg) cells containing methyl-purines were unequivocally identified using antibodies to O6-MedGuo and the imidazole-ring-opened product of 7-methyldeoxyguanosine. In the gastric fundus, their distribution was similar to those methylated by exposure to MNNG, whereas the pyloric region contained immunoreactive cells also in the deeper mucosal layers. After a 2-week MNU treatment, the rate of cell proliferation, as determined by bromodeoxyuridine immunoreactivity, was only slightly enhanced in the oesophagus and in the fundus, but markedly in the forestomach and the pyloric region of the glandular stomach. It is concluded that the overall extent of DNA methylation, the distribution of alkylated cells within the mucosa and the proliferative response all contribute to the organ-specific carcinogenicity of MNU.

Preferential methylation of the Ha-ras proto-oncogene by methylnitrosourea in rat mammary glands

Activation of the Ha-ras proto-oncogene, but not the Ki-ras or N-ras genes, has been found in mammary gland carcinomas induced in female rats by a single dose of methylnitrosourea (MNU). Here we show that a 10-kb restriction fragment containing the Ha-ras gene was extensively methylated by MNU in DNA isolated from mammary glands of female rats 4 h after carcinogen treatment. Fragments of similar size containing either the Ki-ras or N-ras genes were methylated less extensively. The extent of methylation of the three ras genes by MNU correlated with their transcriptional activity. These results suggest that the extent of interaction of a carcinogen with an oncogene, which depends on its transcriptional activity, may be a factor in determining whether the gene is mutated during the initiation of carcinogenesis.

Oncogene expression of FANFT- or BBN-induced rat urothelial cells

Proto-oncogene expression by cultured urothelial cells prepared from the bladders of male F344 rats that had been treated with N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) or N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were examined. Although all of the cultured cells showed varying degrees of anchorage-independent growth, only 9 of them were transplantable into nude mice. A Northern blot technique was employed for the detection of proto-oncogene transcripts. The c-Ha-ras transcripts were detected in all the cultured urothelial cells prepared from the carcinogen-treated rats and in normal urothelial cells. However, the transcript levels were several-fold higher in the former than in normal cells. Increased expression of p21, as determined by immunohistochemical techniques, was also observed in all the original bladder tissues from which the cultures were derived. c-myc transcripts were detected in the cells from carcinogen-treated rats but not in the normal cells. The presence of myc product in hyperplastic urothelial lesions and carcinomas of original bladder tissues was confirmed by immunohistochemical methods. Transcripts of mos, erb B, Ki-ras, abl and src were not detected. Since increased expression of c-myc and c-Ha-ras were present in both transplantable and non-transplantable cell lines, and the expression of p21 occurs in preneoplastic cells, this suggests that elevated expression of these 2 genes may be an early genetic event during bladder carcinogenesis in the rat and further alteration of these 2 genes or mutation of additional genes may be required for the completion of malignant transformation.

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Evaluation of genotoxicity of N-nitrosodibenzylamine in Chinese hamster V79 cells and in Salmonella

Health concerns have arisen due to the formation of N-nitrosodibenzylamine (NDBzA; CAS No. 5336-53-8) in pork processed in a new type of rubber netting. In view of the potent carcinogenicity of related nitrosamines (e.g. N-nitroso-n-dibutylamine and N-nitrosodiethylamine), NDBzA was evaluated for genotoxicity in vitro in both Chinese hamster V79 cells and in Salmonella. In V79 cells, concentrations up to 25 micrograms/ml were tested with and without activation by rat or hamster hepatocytes. Significant elevation of SCE frequency was seen only at 25 micrograms/ml in the presence of uninduced hamster hepatocytes. Mutation to 6-thioguanine resistance was observed at 25 micrograms/ml, in the absence of hepatocytes and in the presence of induced (Aroclor 1254) or uninduced hamster hepatocytes, but not with rat hepatocytes. With uninduced rat hepatocytes, a small but significant (p less than 0.05) increase in the mutation frequency was seen with 10 micrograms/ml NDBzA. In the Salmonella assay, using a pre-incubation protocol and concentrations up to 1000 micrograms/ml, NDBzA was negative in strain TA98, and in TA100 with rat S9, but was positive at the highest dose in TA100 with hamster S9, and more strongly with Aroclor 1254-induced hamster S9. When activated by uninduced rat or hamster hepatocytes, as opposed to S9, NDBzA was negative with all tester strains. Hamster hepatocytes activated more than rat in the V79 studies, and hamster S9 was more strongly activating in the Salmonella assay. These results indicate that NDBzA is weakly mutagenic to both Salmonella and V79 cells.

Persistence of N-nitrosodiethanolamine contamination in American metal-working lubricants

The potent carcinogen N-nitrosodiethanolamine (NDELA) was discovered as a contaminant of commercial metal-working lubricants over a decade ago. To determine whether or not improvements in industrial practice suggested in the meantime have eliminated this contamination from United States products, a selection of cutting fluids obtained from the current marketplace was analysed for NDELA content. All six semi-synthetic fluids examined contained NDELA at levels ranging from 0.5 to 4.3 ppm. Three of six petroleum-based lubricants and five of six synthetics also contained significant NDELA (when analysed at a detection limit of 0.03 ppm), at levels of up to 0.16 and 55 ppm, respectively. The mean concentrations were 1.5 ppm for the semi-synthetics, 0.07 ppm for the petroleum-based products, and 11.4 ppm for the synthetic metal-working fluids. While these levels are far below the values of 1-2% by weight (10,000-20,000 ppm) found in some contaminated products 13 years ago, they may nevertheless pose a continuing health risk for the machinists who work with them.

Assay of suntan lotions for the carcinogenic, non-volatile N-nitrosamine N-nitrosodiethanolamine

N-nitrosodiethanolamine (NDELA) is a carcinogenic, non-volatile nitrosamine that has been shown to pass readily through the skin of animals and humans. It has often been found as a contaminant in cosmetics. Twenty different suntan lotions, available in Israel, both liquids and creams, were analyzed for NDELA content. Most products contained undetectable or trace levels, but 3 were found to be contaminated with as much as 27 ppb of the nitrosamine. Continual use of such products, especially by small children and infants, may significantly increase their exposure to NDELA.

Single-dose toxicokinetics of N-nitrosomethylethylamine and N-nitrosomethyl (2,2,2-trideuterioethyl)amine in the rat

To investigate the origins of an organotropic shift toward increasing esophageal carcinogenicity and DNA alkylation caused by beta-trideuteration of the hepatocarcinogen, N-nitrosomethylethylamine (NMEA), the single-dose toxicokinetics of NMEA and N-nitrosomethyl(2,2,2-trideuterioethyl)amine (NMEA-d3) has been characterized in 8-week-old male Fischer 344 rats by analysis using high performance liquid chromatography of serial blood samples. An i.v. bolus dose of 0.6 mumol/kg to rats revealed biphasic first order elimination with a terminal half-life of 9.46 +/- 0.69 min for unchanged NMEA and 28.9 +/- 2.4 min for total radioactivity. Extensive conversion to polar metabolites was observed in the chromatograms. The systemic blood clearance and apparent steady-state volume of distribution for unchanged NMEA were 39.9 +/- 4.6 ml/min/kg and 496 +/- 36 ml/kg, respectively. There was negligible plasma protein binding and no detectable NMEA was excreted unchanged in the urine. Larger doses given by gavage indicated a systemic bioavailability of 25 +/- 1%. Similar doses of NMEA-d3 given to other groups of rats revealed no significant differences in any of the toxicokinetic parameters. No N-nitrosomethyl(2-hydroxyethyl)amine was found as a detectable metabolite of NMEA or NMEA-d3 in any of the blood or urine samples which were analyzed. When considered together, the data suggest that previously observed differences in organ specificity for the carcinogens, NMEA and NMEA-d3, are not due to differences in the total amounts of nitrosamine reaching particular tissues, but may have other localized causes such as differences in the enzymes responsible for metabolism which are present in each tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term persistence of DNA alkylation in hamster tissues after N-nitrosobis(2-oxopropyl)amine

The persistence of 7- and O6-alkylation of guanine in DNA of cell nuclei of male Syrian hamster pancreas, liver, kidneys, lungs [target tissues of N-nitrosobis(2-oxopropyl)amine (BOP)] and salivary glands (nontarget tissue) was studied immunocytochemically 6 h, 1, 3, 7, 14, 28, and 56 days after a single s.c. injection of 20 mg BOP/kg. Conventional antisera raised against O6-methylguanine and imidazole-ring-opened 7-methyl-guanine were used. Persistent alkyl-specific staining was observed for up to 7 days (7-alkylguanine) or 56 days (O6-alkylguanine) in inter- and intralobular duct cells and centro-acinar cells of the pancreas, periportal hepatocytes and bile duct cells of the liver, cells of the proximal convoluted tubules of the renal cortex, and bronchiolar Clara and alveolar cells in the lungs. Both adducts disappeared from centrilobular liver cells within 1 day, from pancreatic acinar cells within 3 days, and from ducts and acini of the submandibular salivary glands within 14 days after BOP treatment. A high level of persistent O6-alkylation of guanine was related with a high tumor incidence only in case of the ductal/ductular system of the pancreas, the main target tissue of BOP-induced carcinogenesis. The relatively weak carcinogenicity of BOP in other tissues with long-term persistence of O6-alkylguanine in DNA indicates that the formation and persistence of DNA alkylation are not sufficient to account for the carcinogenic organotropism of BOP. Additional factors, such as cell proliferation, appropriate promoting stimuli and the (onco)genes critically involved, may be as important as the modification of DNA.

The role of nitrate, nitrite and N-nitrosamines in carcinogenesis of colon tumours following ureterosigmoidostomy

Urinary diversion in both a rat model for ureterosigmoidostomy and in ureterosigmoidostomy patients result in an increased incidence of colon tumours. Bacterial and chemical investigations on feces-urine mixtures from both the rat model and ureterosigmoidostomy patients showed the presence of a complex nitrate-reducing bacterial flora in both rats and humans. This bacterial flora actively reduced urinary nitrate to nitrite in humans and increased the endogenous formation of N-nitroso compounds. No evidence of urinary nitrate reduction and increased nitrosamine formation in the rectosigmoid of rats was found. The results support the N-nitrosamine theory of carcinogenesis of the colon following ureterosigmoidostomy in humans, but not in rats. As the rat model induces colon carcinomas, factors other than the increased endogenous formation of N-nitroso compounds in the rectosigmoid may contribute to the initiation of colon carcinomas following ureterosigmoidostomy.

Mutational specificities of environmental carcinogens in the lacl gene of Escherichia coli. III: The cyclic nitrosamine N-nitrosopyrrolidine is a complex mutagen

The mutational specificity of the cyclic nitrosamine N-nitrosopyrrolidine (NPYR) was determined through the DNA sequence characterization of 33 lacl-d mutations of Escherichia coli. Base substitution was the predominant class of mutation induced (91%). The majority of these (64%) occurred at GC base pairs, in accordance with the predicted significance of NPYR-derived guanine adducts. In addition, this nitrosamine efficiently produced other kinds of base substitution events as 11 of the 33 mutations occurred at AT base pairs. Deletion, frameshift, and duplication events were also recovered. The complexity of the NPYR mutational spectrum appears to be consistent with the suggestion that this compound acts through both direct and indirect mutational pathways.

Activating missense mutations in Ha-ras-1 genes in a malignant subset of bladder lesions induced by N-butyl-N-(4-hydroxybutyl)nitrosamine or N-[4-(5-nitro-2-furanyl)-2-thiazolyl]formamide

Urothelial cell cultures generated from urinary bladders from a series of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)- or N-[4-(5-nitro-2-furanyl)-2-thiazolyl]formamide (FANFT)-treated Fischer 344 rats were examined for activating missense mutations in Ha-ras-1 genes. Our overall objective was to identify oncogene-activating mutations in this system and to determine what altered biological properties correlate with such genetic changes. The urinary bladders from the treated animals showed a spectrum of histopathologies, from simple hyperplasia to transitional cell carcinoma (TCC). Using restriction analysis, oligonucleotide hybridization, and DNA sequencing, we found that approximately 20% (3/14) of the bladder cell cultures had acquired oncogenic single-base substitutions in codon 61 of Ha-ras-1 genes (CAA----AAA or CGA). The donor bladder lesions for these three cultures, which also harbored the same ras-activating mutations, were all classified as stage A or B TCCs. However, four other TCCs also arising in this series were found to have normal Ha-ras genes. Whereas approximately half of the bladder cultures derived from the carcinogen-treated rats were nontumorigenic in athymic mice, the three cultures containing ras oncogenes were all highly tumorigenic (forming tumors within 5 wk of injection into athymic mice). These cultures also displayed a high degree of anchorage-independent growth and NIH 3T3-transforming activity in gene transfer assays. The nontumorigenic cultures were derived from bladder lesions that included three hyperplasias and three stage A TCCs. We conclude that ras-activating missense mutations were present in a malignant subset of bladder lesions induced by BBN or FANFT, but most of the lesions in this system appeared to involve genetic alterations elsewhere. Thus other oncogenes besides activated Ha-ras may apparently be associated with the same bladder histopathologies and transformation markers.

Implications of the carcinogenic hazard of low doses of three hepatocarcinogenic N-nitrosamines

The data of a large-scale experiment on single and combination effects of very low doses of the hepatocarcinogenic N-nitrosamines N-nitrosodiethylamine (NDEA), N-nitrosopyrrolidine (NPYR), and N-nitrosodiethanolamine (NDElA) were modeled by new statistical methods to derive implications of the carcinogenic hazard of dose ranges so low as to result in long-term toxic effects only slightly different from the background. According to this model a linear relationship was found to exist between daily exposure to low N-nitrosamine levels and time to death with liver tumor. Extrapolation of these data to zero exposure suggested the occurrence of one to ten percent of spontaneous liver tumors in animals surviving more than 1000 days. At this advanced age a further reduction of carcinogen-induced liver tumor incidence does not contribute to a longer overall survival due to competitive, probably independent, causes of death. A quasi-threshold in terms of a "no-observed-effect level" can thus be derived from the data. The observed combination effect indicates a mere additivity in liver tumor occurrence, even at very low doses which alone cause no significant carcinogenic effect during the animal's lifetime. Within the combination of NDEA, NPYR and NDElA, N-nitrosodiethylamine was found to be the most carcinogenic agent: it contributes by at least 17 orders of magnitude more to the relative risk of dying with liver tumor than the other two compounds, if the daily dose is increased by one unit (0.1 mg/kg). Likewise, NDEA shows the steepest slope when assessing the relationship between daily carcinogen doses and time to liver tumor occurrence; relative to NDElA--the least potent carcinogen on a weight basis--and NPYR a 40-fold and 9-fold quicker appearance of liver tumors has to be expected, if the daily doses are increased by an equivalent amount.

Toxicity of N-nitrosodimethylamine, N-nitrosomethylbenzylamine, and 1,2-dimethylhydrazine in isolated rat hepatocytes

N-Nitrosodimethylamine and 1,2-dimethylhydrazine were shown to injure lethally primary monolayer cultures of rat hepatocytes only after incubation periods in excess of 24 hr. The toxic action of these agents, therefore, mimics the time dependency of their hepatoxicity in vivo. The viability of hepatocytes treated with N-nitrosomethylbenzylamine was not different from controls at times up to 54 hr following treatment, a result which is also consistent with the inability of this compound to produce hepatotoxicity in vivo.

Immunohistochemical investigations in experimentally induced tumors of the nervous system

35 tumors of brain, spinal cord and cranial and peripheral nerves were induced with ENU (ethyl-nitrosourea) in the offspring of treated BD-IX pregnant rats. 36 tumors--35 of the nervous system, one nephroblastoma--were observed in 14 rats. With these results, the number of experimental nervous system tumors of the own collection induced in BD-IX rats and classified next to the rules of human neurooncology, amounts to 2,216. All 35 tumors of the nervous system were treated by a panel of immunohistochemical reactions comprising antibodies against cytoskeleton intermediary filaments such as GFAP (glial fibrillary acid protein), neurofilament proteins, vimentin and cytokeratins and some nervous system antigens such as NSE (neuron specific enolase), MBP (myelin basic protein) and S-100 protein. In central tumors, considered to be malignant gliomas, focal reactivity against vimentin and GFAP was found. Expression of other tested markers was weak or absent. In neurinoma of trigeminal and peripheral nerves, reactivity to S-100 antigen was lacking, whilst there was strong reaction to the vimentin antigen.

Use of differential DNA-repair host mediated assays to investigate the biotransformation of xenobiotics in Drosophila melanogaster. I. Genotoxic effects of nitrosamines

A rapid differential DNA-repair assay procedure was developed to investigate the biotransformation of xenobiotics in Drosophila melanogaster in vivo. Indicator of genotoxic activity was a pair of streptomycin-dependent Escherichia coli strains differing vastly in DNA repair capacity (uvr+/rec+ vs. uvrB/recA). Prior to the experiments with test compounds, mixtures of the two strains were injected into the abdomina of untreated animal hosts (male Berlin-K flies) and the time-dependent recovery kinetics determined. Subsequently, different aliphatic and aromatic nitrosamines were tested. Solutions of the compounds were injected simultaneously with the indicator cells. Three hours later, the flies were killed, homogenized and the induction of (repairable) DNA damage determined by comparison of the survival rates of the two strains in single animals. Eight carcinogenic compounds (nitrosodiethylamine, NDEA; nitrosodimethylamine, NDMA; nitrosodi-npropylamine, NDPA; nitrosodiethanolamine, NDELA; nitrosomethylaniline, NMA; 4-methyl-nitrosopiperidine, MNPIP; nitrosopyrrolidine, NPYR; nitrosomorpholine, NMOR) and one whose tumorigenic activities are still controversially discussed (nitrosodiphenylamine, NDPhA) induced dose-dependent differential killing effects in the present system. One agent which has not been found carcinogenic in rodents (2.6-dimethyl-nitrosopiperidiine. NDMPIP) gave negative results. The ranking order of genotoxic activities of the nitrosamines found in Drosophila in vivo is in good agreement with those of carcinogenic potencies established on the basis of experiments with rats. The most pronounced exceptions are the rather weak response towards NMA and the stronger DNA damaging activity of NMPIP compared to NDMA. Phenobarbital (5-ethyl-5-phenyl-2,4,6-trioxohepatahydropyramidine) (PB) feeding of the flies resulted in an increase of the DNA damaging potencies of all nitrosamines tested. Substantial enhancement of the induction of DNA damage was however, restricted to NDEA, NPYR and NMOR, whereas with nitrosodiphenylamine (NDPhA), NDELA and NDMA only a moderate (less than 25%) increase of differential killing effects was found. In the case of the two latter compounds, these results might be due to the fact that enzymes other than the MFO are involved in their activation. Attempts to localize the formation and/or distribution of metabolites in the bodies of fruitflies by separation of the tagmata of chemically treated animals and determination of genotoxic effects in the different segments indicate that the most pronounced effects occur in the abdomina whereas in heads and thoraxes comparatively lower activities are detectable.

Tobacco-specific nitrosamines in Canadian cigarettes

Twenty-five brands of Canadian commercial cigarettes were analyzed for tobacco-specific nitrosamines (TSNA) in tobacco and in mainstream smoke as well as for nitrate in tobacco. Preformed N'-nitrosonor-nicotine (NNN) in the tobacco ranged from 265 ng to 979 ng/cigarette, preformed 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) ranged from 465 ng to 878 ng/cigarette. The mainstream smoke concentration for NNN was between 5 ng and 39 ng/cigarette and for NNK between 5 ng and 97 Ng/cigarette. The nitrate levels were between 0.3 mg and 3.4 mg/cigarette. The NNK levels in tobacco and in mainstream smoke were higher than the NNN levels, which is typical for Virginia-type cigarettes. Based upon the average mainstream smoke concentration of the three most popular Canadian cigarette brands, an average TSNA delivery for 20 cigarettes of 0.7 micrograms NNN and 1.7 micrograms NNK can be calculated, which is less than the average for West German cigarettes. The results of this investigation demonstrate that there seems to be a good correlation between the TSNA and tar deliveries in mainstream smoke. However, no correlation between the level of preformed TSNA in tobacco and the tar delivery in mainstream smoke could be observed. It is demonstrated that the good correlation between the tar and TSNA deliveries in mainstream smoke can only be attributed to the unusual good correlation between the tar delivery and the ventilation ratio. For the cigarettes investigated, which seemed to be Virginia-type cigarettes, with few exceptions, the ventilation ratio had a much higher influence on the mainstream smoke concentration than the level of preformed TSNA in tobacco.

Inhalation carcinogenesis of N-nitrosomorpholine (NMOR) in rats and hamsters

N-Nitrosomorpholine (NMOR) is a potent liver carcinogen in rats when administered orally. NMOR was found in the atmosphere at working places in the rubber industry in concentrations up to several hundred micrograms/m3. It can be assumed that NMOR inhalation may play a role in human carcinogenesis. Therefore an inhalation study was carried out to evaluate the carcinogenic potency of NMOR vapors in rats and hamsters. The concentration of volatile NMOR in the inhalation chamber was continuously determined with a Thermal Energy Analyzer. The rats received 29 administrations (4th/day, 5 days/week; mean inhaled daily dose: 130 micrograms/animal; total dose: 15 mg/kg bodyweight). The hamsters inhaled a total of 38 mg/kg of NMOR (21 applications, daily dose 260 micrograms/animal). In rats 4 carcinomas and 5 neoplastic nodules of the liver, 1 neuroblastoma and 1 mucoepidermoidal carcinoma of the nose, and 1 carcinoma of the thyroid gland were induced. In treated hamsters 4 carcinomas of the liver, 2 neurogenic sarcomas of the nasal region, and 5 papillomas of the trachea were found. None of these tumors were observed in control rats and control hamsters.

Volatile nitrosamine levels and genotoxicity of food samples from high-risk areas for nasopharyngeal carcinoma before and after nitrosation

Traditional life-style, especially food habits, infection by Epstein-Barr virus (EBV) and genetic factors, have been associated with an increased risk of nasopharyngeal carcinoma (NPC). N-Nitroso compounds and other carcinogens either present in food or formed endogenously, as well as food constituents that activate EBV, have been suspected as etiological factors in NPC pathogenesis. For their characterization preserved food items, frequently consumed in NPC endemic areas in Tunisia, South China and Greenland, were sampled and screened for the presence of mutagens and volatile nitrosamines before and after nitrosation. Aqueous extracts as well as 2 organic extracts of the samples were assayed for genotoxicity in 2 Salmonella typhimurium strains and the SOS chromotest. The same extracts had previously been analyzed for volatile nitrosamines and for EBV-activating substances in Raji cells. In our study, 13 out of 16 food samples showed a weak, directly-acting genotoxicity in the SOS chromotest in at least one of the extracts, but only one sample from Greenland was found to be weakly mutagenic in Salmonella TA 98. Chemical nitrosation for 9 out of 15 samples of aqueous food extracts increased the genotoxic effect in the SOS chromotest. Levels of volatile nitrosamines were also elevated for 12 out of 15 samples; highest levels of N-nitrosodimethylamine were found in hard salted and dried fish from China (1,200 micrograms/kg) and highest N-nitrosopyrrolidine levels in a Tunisian spice (3,840 micrograms/kg). In non-nitrosated aqueous food extracts, the level of volatile nitrosamines and genotoxic activities were not correlated with the EBV-inducing activity of the same samples. After chemical nitrosation, EBV-inducing activity was decreased or showed no change and was not correlated with increases in either the genotoxicity or the nitrosamine levels. Our results suggest that EBV-activating compounds belong to a different class of substances. However, there was an association between the changes in genotoxicity and nitrosamine levels due to nitrosation.

Similar carcinogenic actions of nitrosoalkylureas of varying structure given to rats by gavage

To relate the tumorigenic effects of directly acting alkylating nitrosoalkylureas to their chemical structure, a series of these compounds was given to F344 rats by gavage at approximately equimolar doses. In some cases, more than one dose rate was used. Potency, as measured by time to death with tumors, was similar for nitrosomethylurea and nitrosoethylurea, although the tumor pattern was different between the two. Nitrosoallylurea was of similar potency, and induced a spectrum of tumors similar to nitroethylurea. Nitroso-n-butyl-, n-amyl- and n-hexyl-ureas were less potent than nitrosoethylurea, but induced a similar pattern of tumors. All of the nitrosoureas induced tumors of the forestomach, usually in high incidence, except nitroso-2-hydroxypropylurea, which caused death of the rats with thymic lymphoma within 6 months. Nitroso-3-hydroxypropylurea was much less potent than its 2-isomer, but induced no tumors of the thymus and was the only one of this group to induce tumors of the glandular stomach. Only nitrosomethylurea induced a high incidence of tumors of the nervous system, but no mammary carcinomas, which most of the other nitrosoureas induced in high incidence in females. Tumors of the lung, duodenum, colon and intestines were induced by several of the compounds, more commonly in males than in females, but a high incidence of liver tumors was found only in rats of both sexes given nitroso-2-phenylethylurea.

Thymic lymphomas induced by N-propyl-N-nitrosourea (PNU) in the BUF/Mna rat, an inbred strain with a high incidence of spontaneous thymoma

N-Propyl-N-nitrosourea (PNU) is known to be a strong leukemogen, inducing myelogenous leukemia or thymic lymphoma in some strains of rat. The thymic lymphomagenic effect of PNU has been demonstrated in F344 rats. On the other hand, the BUF/Mna rat has been established as an inbred strain that develops spontaneous thymomas after one year of age. In the present experiment, PNU was continuously administered in drinking water to male and female BUF/Mna rats starting at 5 weeks of age. Thymic lymphomas were induced in all PNU-treated rats with an average latent period as short as 14 experimental weeks. These results show the high susceptibility of the BUF/Mna rat to the lymphomagenic activity of PNU. The BUF/Mna rat is an ideal strain for studies on epithelial cell-lymphocyte interaction, not only in the development of thymic lymphomas but also in that of spontaneous thymoma. Karyotypes of twelve primary thymic lymphomas induced by PNU were analyzed for chromosomal abnormalities. Chromosomal abnormalities were often found in chromosomes 11 and 2. In some types of abnormality, dup (11q) and del(2q) were most frequently observed. In addition, trisomy of chromosome 7, on which the c-myc gene is mapped, was observed in five lymphomas, and monosomy of chromosomes 20 and X in six and five cases, respectively, though these changes were generally observed in a minor cell population in each case.

Chemical induction of brain tumors in rats by nitrosoureas: molecular biology and neuropathology

Nitrosourea-induced rat brain tumors are among the best investigated experimental systems for neuropathological, biochemical, diagnostic and therapeutic research in neurooncology. This review summarizes data concerning molecular biology, neuropathology, in vitro studies, transplantation models and antigen expression of experimental gliomas in inbred rat strains. Systemic application of nitroso-compounds, i.e., ENU and MNU, leads to the alkylation of DNA bases, which, due to a specific repair deficiency, persist in the nervous system remarkably longer than in other organs. The hypothesis is that alkylated bases cause base-mispairing and point mutations followed by uncontrolled expression of oncogenes and growth factor receptors, resulting in permanent cell proliferation. Thus, nitrosoureas are considered to be biological hazards, especially as potent endogenous and exogenous neurotoxins. Neuropathology and growth characteristics of these experimental tumors are comparable to human malignant gliomas. Similar to the human WHO grade III and IV tumors, they reveal cellular pleomorphism, elevated mitotic activity, proliferation of blood vessels, blood-brain barrier disturbances, necrosis and invasiveness. Nitrosourea-induced brain tumors have been used in investigations concerning glioma growth and regression, brain edema, glioma immunology, metabolism, regional biochemistry, and experimental therapy. The studies included conventional morphology, immunohistochemistry, -cytochemistry and -electronmicroscopy, morphometry, cell culture, hybridoma technology, tumor transplantation and regional imaging by autoradiography, bioluminescence, magnetic resonance and immunoscintigraphy.

The stimulating effect of acetic acid, alcohol and thermal burn injury on esophagus and forestomach carcinogenesis induced by N-nitrososarcosin ethyl ester in rats

Five groups of outbred white male rats were given N-nitrososarcosin ethyl ester (NSEE) i.g. for 4 or 6 months at a daily dose of 50 mg/kg of body wt. 5 days/week. Some groups of animals were given a 3% water solution of acetic acid or a 40% solution of ethanol i.g. for 8 months from the beginning of the experiment. The remaining groups of these rats received controlled local thermal burn injury of the esophageal mucosa 15 days before the beginning of the experiment. Acetic acid solution increased the multiplicity of benign and malignant tumors as well as carcinoma incidence in the esophagus. Ethanol in combination with NSEE did not influence carcinogenesis in the esophagus but increased the incidence of leukokeratosis and the multiplicity of forestomach papillomas. In rats treated with NSEE after thermal burn injury, a significant increase in the frequency and multiplicity of papillomas was found in the burn zone.

An important role for cytosol in the microsomal metabolism of N-nitrosodimethylamine to a mutagen: evidence for two different mutagenic metabolites

Microsomal-mediated mutagenesis induced by N-nitrosodimethylamine (NDMA) in Salmonella TA100 at neutral pH was only slightly affected by cytosol and was similar in its threshold type dose-response curve to mutagenesis induced by direct-acting N-nitroso-N-methyl compounds. However, mutagenesis in strain TA104 was greatly enhanced by cytosol and this mutagenesis did not exhibit a threshold. In the presence of microsomes alone NDMA was more potent in TA100 than TA104, but in the presence of microsomes plus cytosol (S-9 fraction) this order was reversed at the doses tested. A possible explanation for these results is that NDMA is metabolized by microsomes to a mutagen (presumably methyldiazonium ion; MDI) that is more potent in TA100 than in TA104, but in the presence of S-9 fraction a fraction of the NDMA is metabolized by a pathway leading to a different mutagen with a different specificity. The ratio of metabolism via these pathways appears to be dependent on pH.

A study of tobacco carcinogenesis XLIV. Bioassay in A/J mice of some N-nitrosamines

The evaluation of the tumorigenic activity in A/J mouse lung of certain tobacco N-nitrosamines, namely 3-(methylnitrosamino)propionic acid (NMPA), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-4-(3-pyridyl)-butyric acid (iso-NNAC), had the following results (total dose in micromol per mouse/lung tumors per mouse): NMPA (200/7.1 +/- 2.9); NNK (2/15.7 +/- 4.1); iso-NNAC (200/0.24 +/- 0.43); saline control (0.2 +/- 0.4). The tumorigenic activity of NMPA was not surprising since its lower homologue, N-nitrososarcosine, as well as its higher homologue, 4-(methylnitrosamino)-butyric acid, are known carcinogens. The high tumorigenic activity of NNK in strain A/J mice confirms earlier findings as to its carcinogenic potency in rats and hamsters. The lack of tumorigenic activity of iso-NNAC supports the observation that the pyridyl rest adjacent to the nitrosamino group inhibits the activity of some tobacco-specific N-nitrosamines (TSNA). Iso-NNAC is most likely formed endogenously from the nicotine metabolites cotinine and 4-(methylamino)-4-(3-pyridyl)butyric acid.

Carcinogenesis in rats by nitrosodialkylureas containing methyl and ethyl groups given by gavage and in drinking water

The carcinogenic effects in male and female F344 rats of four nitrosodialkylureas containing methyl or ethyl groups have been compared by two modes of administration, gavage in oil solution or dissolved in drinking water. Weekly doses of 20 and 40 mumol were given to each rat by either route and treatment lasted usually 30 wk, resulting in a total dose per rat of 0.6 or 1.2 mmol. Nitrosodimethylurea and nitroso-1-methyl-3-ethylurea gave rise primarily to tumors of the nervous system, whereas nitrosodiethylurea and nitroso-1-ethyl-3-methylurea gave rise to tumors of the mammary gland, lung, intestinal tract, nervous system, and testicular mesotheliomas. The effect of nitrosodimethylurea was weaker than that of the other three compounds, as measured by rate of mortality with tumors. Drinking water treatment was less effective than treatment by gavage, by the same criterion. The tumorigenic effects paralleled those of the corresponding monoalkylnitrosourea, suggesting the presence in the target organs of receptors for which ethylnitrosoureas or methylnitrosoureas, respectively, have affinity.

Formation of directly mutagenic alpha-hydroxy-N-nitrosopiperidine phosphate ester by near-ultraviolet irradiation of N-nitrosopiperidine in phosphate buffer

Previously we found that direct-acting mutagens can be formed from N-nitrosodialkylamines on exposure to near-ultraviolet light in the presence of phosphates. We have now isolated the mutagenic photoproduct formed from N-nitrosopiperidine and inorganic phosphate and identified its structure as the phosphate ester of alpha-hydroxy-N-nitrosopiperidine. This reaction represents a new, non-enzymatic activation of promutagenic N-nitrosodialkylamines.