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

Trapping of a cross-link formed by a major purine adduct of a metabolite of the carcinogen N-nitrosomorpholine by inorganic and biological reductants

3-Hydroperoxy-N-nitrosomorpholine in buffered aqueous media in the presence of calf thymus DNA was treated with a phosphine reductant to generate the transient α-hydroxynitrosamine and subsequent diazonium ion that alkylated the DNA, as previously reported. Subsequent addition of hydride donors, for 30 min, followed by acid hydrolysis of the mixture allowed detection and quantification of 6-(2-{2-[(9H-purin-6-yl)amino]ethoxy}ethoxy)-9H-purin-2-amine, the reduced cross-link formed from deposition, via the diazonium ion, of a 3-oxapentanal fragment on O(6)-Gua, and condensation with N(6)-Ade, presumably in the vicinity. Decreasing the temperature of the reaction mixtures and decreasing the pH modestly increased the yields of the trapped cross-link. Among three borohydride reductants, NaNCBH3 is superior, being ∼4 times more effective on a molar basis, as opposed to a hydride equivalent basis, than NaBH4 or Na(AcO)3BH. For trapping with NaNCBH3, it is deduced that the reaction likely occurs with the iminium ion that is in protonic equilibrium with its conjugate base imine. In an experiment in which the hydroperoxide was decomposed and NaNCBH3 was introduced after various periods of time, the amount of cross-link was observed to increase, nearly linearly, by ∼4-fold over 1 week. These data indicate that there are a minimum of two populations of cross-links, one that forms rapidly, in minutes, and another that grows in with time, over days. Reduced nicotinamide cofactors and ascorbate are observed to effect reduction (over 3 days) of the cross-links, confirming the possibility that otherwise reversible cross-links might be immortalized under biological conditions.

Genotoxic effects of N-nitrosoketamine and ketamine as assessed by in vitro micronucleus test in Chinese hamster lung fibroblast cell line

OBJECTIVES

Ketamine hydrochloride (KT) is a secondary amine that has been safely used as an injectable anesthetic and analgesic to avoid the production of nitroso compounds in the stomach. However, ketamine in the tablet form has recently become an abused, recreational drug. The aim of this study was to investigate the genotoxic effects of N-nitrosoketamine (NKT) and KT on the basis of an in vitro micronucleus (MN) test using a Chinese hamster lung fibroblast cell line (CHL/IU).

METHODS

NKT was synthesized from KT in our laboratory. In the MN tests, CHL/IU cells were continuously treated with either NKT or KT for 24, 48, or 72 hours without the S9 mix. The cells were also treated with NKT or KT with or without the S9 mix for 6 hours, followed by a recovery period of 18, 42, or 66 hours (short-term treatment). The results were considered to be statistically significant when the p-values of both Fisher's exact test and the trend test were less than 0.05.

RESULTS

After the short-term treatment with either NKT or KT with and without the S9 mix, the frequency of micronuclei significantly increased. However, the frequency of micronuclei did not significantly increase after the continuous treatment with either NKT or KT. Both NKT and KT were determined to be genotoxic in the short-term treatment with or without the S9 mix, but they were determined to be nongenotoxic in continuous treatment.

CONCLUSION

Our findings suggest that NKT has a stronger genotoxic effect than KT.

Subchronic urinary bladder toxicity evaluation of N-Nitrosodiphenylamine in Fischer 344 rats

Female Fischer 344 (F344) rats were exposed to N-nitrosodiphenylamine (NDPA) by dietary feed at concentrations of 0, 250, 1000, 2000, 3000 or 4000 ppm for 5 days, 2, 4 and 13 weeks duration. Endpoints evaluated included clinical observations, body weights, urinary bladder weights, blood NDPA, gross pathology and urinary bladder histopathology. There were no NDPA exposure-related clinical signs of toxicity. The mean body weight decreased 3% to 5% compared with the control in the 4000 ppm group during study weeks 2 through to 13. Statistically significant increases in urinary bladder weight were observed as early as after 5 days exposure and were concentration dependent at ≥ 3000 ppm. NDPA-related urinary bladder microscopic alterations consisted of mixed cell infiltrates, increased mitosis, increased necrosis of epithelial cells, diffuse and/or nodular transitional epithelial hyperplasia and squamous metaplasia of transitional epithelium. These changes affected only rats exposed to NDPA concentrations ≥ 2000 ppm. Blood NDPA concentrations were negligible in animals exposed to ≤ 1000 ppm and ranged from 0.12 to 0.19 µg ml(-1) in rats of the ≥ 2000 ppm groups at the 5 days and 2 weeks time points. A no observable adverse effect level (NOAEL) of 1000 ppm NDPA (60 mg kg(-1) day(-1) ) was selected based on the absence of urinary bladder histopathology.

Lactone metabolite common to the carcinogens dioxane, diethylene glycol, and N-nitrosomorpholine: aqueous chemistry and failure to mediate liver carcinogenesis in the F344 rat

1,4-Dioxan-2-one, 1, was synthesized, and the equilibrium constant between it and the hydrolysis product 2-(2-hydroxyethoxy) acetic acid, 2, was determined as K(O) = 70 ± 4 in acidic aqueous media, 25 °C, ionic strength 1 M (KCl), and 5% by volume acetonitrile. The carboxylic acid dissociation constant of 2 was determined under the same conditions to be pK(a) = 3.31 ± 0.02. On the basis of these two determinations, the equilibrium constant between 1 and carboxylic acid anion, 3, and the proton was calculated to be K(OA) = 0.034 ± 0.002 M. The stability of 1 was determined in the range of pH between 1 and 8.5 in buffered aqueous solutions under the conditions above by UV spectrophotometric methods and exhibited simple first order kinetics of decay. On the basis of buffer dilution plots, the values of k(o), the rate constant for solvent mediated decomposition, were determined. The plot of log k(o) against pH is consistent with a three term rate law for solvolysis with a hydrogen ion catalyzed rate constant k(H+) = 1.1 (±0.1) M(-1) min(-1), a water catalyzed rate constant, k(w) = 9.9 (±0.5) × 10(-4) min(-1), and a hydroxide ion catalyzed rate constant, k(OH) = 4.1 (±0.3) × 10(4) M(-1) min(-1). The t(1/2) for decay at pH 7.0, at 25 °C, is ∼2 h. Treatment of F344 rats with aflatoxin B(1) (AFB(1)) (positive control) elicited the expected preneoplastic foci in the livers of each rat tested, while subsequent administration of 1 (a total of 1.32 g over 12 weeks) failed to statistically increase focal number or focal volume percent. In 8 rats administered 1 (1.32 g, 12 weeks) alone, no increase above background foci was detected. This study does not support compound 1 as a common carcinogen.

EFFECT OF ZINC DITHIOCARBAMATES AND THIAZOLE-BASED ACCELERATORS ON THE VULCANIZATION OF NATURAL RUBBER

Several zinc dithiocarbamates (ZDCs) as accelerator derived from safe amine has been exclusively studied in the presence of thiazole-based accelerators to introduce safe dithiocarbamate in the vulcanization of natural rubber. Comparison has been made between conventional unsafe zinc dimethyldithiocarbamate (ZDMC) with safe novel ZDC combined with thizole-based accelerators in the light of mechanical properties. The study reveals that thiuram disulfide and 2-mercaptobenzothiazole (MBT) are always formed from the reaction either between ZDC and dibenzothiazyledisulfide (MBTS) or between ZDC and N-cyclohexyl-2-benzothiazole sulfenamide (CBS). It has been conclusively proved that MBT generated from MBTS or CBS reacts with ZDC and produces tetramethylthiuram disulfide. The observed synergistic activity has been discussed based on the cure and physical data and explained through the results based on high-performance liquid chromatography and a reaction mechanism. Synergistic activity is observed in all binary systems studied. The highest tensile strength is observed in the zinc (N-benzyl piperazino) dithiocarbamate-accelerated system at 3:6 mM ratios. In respect of tensile strength and modulus value, unsafe ZDMC can be successfully replaced by safe ZDCs in combination with thiazole group containing accelerator.

Can the rat be used as a valid model of human esophageal adenocarcinoma?

Animal models of Barrett's metaplasia and esophageal adenocarcinoma are important to further characterize the disease and test potential therapies. This paper reviews the development of the surgical model of esophageal adenocarcinoma in the rat and considers whether this model provides a biologically accurate representation of Barrett's esophagus and esophageal adenocarcinoma in humans.

N-methyl N-nitrosourea induced functional and structural alterations in mice brain-role of curcumin

Curcumin is being widely used both as an herbal drug and a food additive in Asian countries. However, its prophylactic potential in containing certain brain disorders is yet to be fully explored. The present study was conceived with an idea that curcumin may prove to be effective in ameliorating N-methyl N-nitrosourea (MNU)-induced adverse effects in cerebrum and cerebellum of mice. Male laca mice received either intravenous MNU treatment at a dose of 10 mg/kg body weight in sterile double distilled water, curcumin alone 60 mg/kg body weight in drinking water via oral gavage, or combined MNU and curcumin treatment on alternate days for a total duration of 2 months. MNU treatment resulted in significant alteration in neurobehavior, reactive oxygen species, lipid profile and histoarchitecture which showed appreciable signs of improvements upon curcumin supplementation. Therefore, the study concludes that prophylactic treatment with curcumin shall prove to be effective in containing MNU-induced neurotoxicity.

Evolution of research on the DNA adduct chemistry of N-nitrosopyrrolidine and related aldehydes

This perspective reviews our work on the identification of DNA adducts of N-nitrosopyrrolidine and some related aldehydes. The research began as a focused project to investigate mechanisms of cyclic nitrosamine carcinogenesis but expanded into other areas, as aldehyde metabolites of NPYR were shown to have their own diverse DNA adduct chemistry. A total of 69 structurally distinct DNA adducts were identified, and some of these, found in human tissues, have provided intriguing leads for investigating carcinogenesis mechanisms in humans due to exposure to both endogenous and exogenous agents.

Nasopharyngeal carcinoma risk by histologic type in central China: impact of smoking, alcohol and family history

The role of cigarette smoking, alcohol use, family history of cancer and the interaction of cigarettes and family history in the etiology of Nasopharyngeal carcinoma (NPC) in general and within each histologic type are unclear. We conducted a case-control study among 1,044 Han Chinese patients with NPC and 1,095 Han Chinese cancer-free control subjects. Logistic regression was used to analyze the association between histologic type of NPC and cigarette smoking, alcohol drinking and family history. The results indicated that NPC was significantly associated with cigarette smoking [adjusted odds ratio (OR) = 2.97, 95% confidence interval (CI), 2.38-3.70], and the association exhibited a dose-response relationship for intensity, duration, and cumulative consumption of cigarettes (p(trend) < 0.0001 for intensity, duration and cumulative consumption of cigarettes). Positive family history of cancer led to a significant 12-fold elevated risk of NPC (adjusted OR = 12.95, 95% CI, 7.12-23.54) and acted jointly with cigarettes in contributing to NPC risk (adjusted OR = 56.68, 95% CI, 17.25-186.19). The association of NPC risk with cigarettes was stronger for nonkeratinizing carcinoma than for keratinizing squamous cell carcinoma (KSCC), whereas family history was more closely associated with KSCC. NPC risk was not associated with alcohol consumption. Our study demonstrated that cigarette smoking and family history of cancer could serve independently and jointly as risk factors for etiology of NPC and might affect the risk of histology-specific NPC differently. This knowledge may help facilitate comprehension of NPC etiology in general as well as within each histologic type, and thereby improve prevention efforts.

N-nitroso compounds: detection in ambient air

By use of a new, highly selective detection technique for N-nitroso compounds, which is sensitive to picogram quantities and which is based on the catalytic cleavage of the N-NO bond and the subsequent detection of the nitrosyl radical, dimethylnitrosamine has been found in concentrations of 0.02 to 0.96 part per billion in three out of five air samples from Baltimore, Maryland, and 0.014 to 0.051 part per billion in five out of six air samples from Belle, West Virginia. The sensitivity of the analytical procedures used was 1 part in 10(12). The presence of dimethylnitrosamine has been confirmed by using the new detector in conjunction with both a gas-liquid chromatograph and a high-performance liquid chromatograph. In addition, between one and three as yet unidentified N-nitroso compounds were detected in both cities. N-Nitroso compounds were not found in air samples from Philadelphia, Pennsylvania; Wilmington, Delaware; and Waltham, Massachusetts.

Mass spectrometric analysis of a cyclic 7,8-butanoguanine adduct of N-nitrosopyrrolidine: comparison to other N-nitrosopyrrolidine adducts in rat hepatic DNA

The well established rat hepatocarcinogen N-nitrosopyrrolidine (NPYR, 1) requires metabolic activation to DNA adducts to express its carcinogenic activity. Among the NPYR-DNA adducts that have been identified, the cyclic 7,8-butanoguanine adduct 2-amino-6,7,8,9-tetrahydro-9-hydroxypyrido[2,1-f]purine-4(3H)-one (6) has been quantified using moderately sensitive methods, but its levels have never been compared to those of other DNA adducts of NPYR in rat hepatic DNA. Therefore, in this study, we developed a sensitive new LC-ESI-MS/MS-SRM method for the quantitation of adduct 6 and compared its levels to those of several other NPYR-DNA adducts formed by different mechanisms. The new method was shown to be accurate and precise, with good recoveries and low fmol detection limits. Rats were treated with NPYR by gavage at doses of 46, 92, or 184 mg/kg body weight and sacrificed 16 h later. Hepatic DNA was isolated and analyzed for NPYR-DNA adducts. Adduct 6 was by far the most prevalent, with levels ranging from about 900-3000 micromol/mol Gua and responsive to dose. Levels of adducts formed from crotonaldehyde, a metabolite of NPYR, were about 0.2-0.9 micromol/mol dGuo, while those of adducts resulting from reaction with DNA of tetrahydrofuranyl-like intermediates were in the range of 0.01-4 micromol/mol deoxyribonucleoside. The results of this study demonstrate that, among typical NPYR-DNA adducts, adduct 6 is easily the most abundant in hepatic DNA. Since previous studies have shown that it can be detected in the urine of NPYR-treated rats, the results suggest that it is a potential candidate as a biomarker for assessing human exposure to and metabolic activation of NPYR.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.

Phosphorylation by c-Jun NH2-terminal kinase 1 regulates the stability of transcription factor Sp1 during mitosis

The transcription factor Sp1 is ubiquitously expressed in different cells and thereby regulates the expression of genes involved in many cellular processes. This study reveals that Sp1 was phosphorylated during the mitotic stage in three epithelial tumor cell lines and one glioma cell line. By using different kinase inhibitors, we found that during mitosis in HeLa cells, the c-Jun NH(2)-terminal kinase (JNK) 1 was activated that was then required for the phosphorylation of Sp1. In addition, blockade of the Sp1 phosphorylation via inhibition JNK1 activity in mitosis resulted in the ubiquitination and degradation of Sp1. JNK1 phosphorylated Sp1 at Thr278/739. The Sp1 mutated at Thr278/739 was unstable during mitosis, possessing less transcriptional activity for the 12(S)-lipoxygenase expression and exhibiting a decreased cell growth rate compared with wild-type Sp1 in HeLa cells. In N-methyl-N-nitrosourea-induced mammary tumors, JNK1 activation provided a potential relevance with the accumulation of Sp1. Together, our results indicate that JNK1 activation is necessary to phosphorylate Sp1 and to shield Sp1 from the ubiquitin-dependent degradation pathway during mitosis in tumor cell lines.

Geonotoxicity study of illegal drug MDMA and its nitroso derivative N-MDMA by micronucleus and chromosomal aberration tests using Chinese hamsger lung fibroblast cell line

OBJECTIVES

An increase in incidence of the illegal use of tablets containing 3,4-methylenedioxymethamphetamine hydrochloride (MDMA) has recently become a widespread social problem. MDMA ingested orally reacts with nitrite in the stomach and is synthesized intoN-nitroso-3,4-methylenedioxymethamphetamine (N-MDMA). The aim of this study is to investigate the genotoxic effects of MDMA and N-MDMA on the basis of the results of an in vitro micronucleus (MN) test and an in vitro chromosomal aberration (CA) test using a Chinese hamster lung fibroblast cell line (CHL/IU).

METHODS

Tablets containing MDMA obtained from the Regional Bureau of the Ministry of Health, Labor and Welfare were purified, and N-MDMA was synthesized from MDMA in our laboratory. To evaluate the effects of MDMA and N-MDMA, the MN test established by our laboratory and the CA test in accordance with the guidelines for toxicity studies of drugs recommended by the Ministry of Health, Labor and Welfare were performed.

RESULTS

In the MN test, no increased frequency of MNs was not found for MDMA. On the other hand, an apparently increased frequency of MNs was observed for N-MDMA. In the CA test, no CA was found for MDMA, but CA was observed for N-MDMA apparently.

CONCLUSION

N-MDMA genotoxicity was observed in the MN and CA tests. However, no MDMA genotoxicity was observed.

Examination of the mutagenicity of RDX and its N-nitroso metabolites using the Salmonella reverse mutation assay

The mutagenicity of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its N-nitroso derivatives hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) were evaluated using the Salmonella tryphimurium reverse mutation assay (Ames assay) with strains TA97a, TA98, TA100, and TA102. Using a preincubation procedure and high S9 activation (9%), RDX was observed to induce weak mutagenesis to strain TA97a with a mutagenicity index (MI) of 1.5-2.0 at a dose range of 32.7-1090microg/plate. MNX induced moderate mutagenesis to strain TA97a with an MI of 1.6-2.8 at a dose range of 21.7-878microg/plate. TNX also induced moderate mutagenesis in strain TA97a with an MI of 2.0-3.5 to TA97a at a dose range of 22.7-1120microg/plate. TNX also caused weak mutagenesis to strain TA100 with S9 activation at the dose of 1200microg/plate. MNX and TNX induced weak to moderate mutagenesis to strain TA102. Strain TA97a was found to be the most sensitive strain among these four strains. No cytotoxicity of RDX, MNX, and TNX was observed at the concentrations used in this study. Doses were verified by HPLC.

Genotoxic and carcinogenic risk to humans of drug-nitrite interaction products

The large majority of N-nitroso compounds (NOC) have been found to produce genotoxic effects and to cause tumor development in laboratory animals; four NOC have been classified by the International Agency for Research on Cancer (IARC) as probably and another 15 as possibly carcinogenic to humans. A considerable fraction of drugs are theoretically nitrosatable due to the presence of amine, amide or other groups which by reacting with nitrite in the gastric environment, or even in other sites, can give rise to the formation of NOC, and in some cases other reactive species. This review provides a synthesis of information on the chemistry of NOC formation, the carcinogenic activity of NOC in animals and humans and the inhibitors of nitrosation reactions. It contains information on the drugs which have been tested for the formation of NOC by reaction with nitrite and the genotoxic-carcinogenic effects of their nitrosation products. In an extensive search we have found that 182 drugs, representing a wide variety of chemical structures and therapeutic activities, were examined in various experimental conditions for their ability to react with nitrite, and 173 (95%) of them were found to form NOC or other reactive species. Moreover, 136 drugs were examined in short-term genotoxicity tests and/or in long-term carcinogenesis assays, either in combination with nitrite or using their nitrosation product, in order to establish whether they produce genotoxic and carcinogenic effects; 112 (82.4%) of them have been found to give at least one positive response. The problem of endogenous drug nitrosation is largely unrecognized. Only a small fraction of theoretically nitrosatable drugs have been examined for the possible formation of genotoxic-carcinogenic NOC, guidelines for genotoxicity testing of pharmaceuticals do not indicate the need of performing the appropriate tests, and patients are not informed that the drug-nitrite interaction and the consequent risk can be reduced to a large extent by consuming the nitrosatable drug with ascorbic acid.

Hepatic progenitor cells, stem cells, and AFP expression in models of liver injury

Adult hepatocytes and liver-cell progenitors play a role in restoring liver tissue after injury. For the study of progenitor cells in liver repair, experimental models included (a) surgical removal of liver tissue by partial hepatectomy; (b) acute injury by carbontetrachloride; (c) acute injury by d-galactosamine (GalN) and N-nitrosomorpholine (NNM); and (d) chemical hepatocarcinogenesis by feeding NNM in low and high doses. Serological and immunohistological detection of alpha-fetoprotein gene expression served to follow pathways of cellular differentiation. Stem cells were not required in models of surgical removal of parenchyma and in carbon tetrachloride intoxication of adult hepatocytes. In contrast, regeneration of liver occurred through biliary epithelial cells in injuries induced by GalN and NNM. These biliary epithelial cells, collectively called oval cells, are most probably derived from the canals of Hering. Proliferating bile duct cells reached a level of differentiation with reactivation of foetal genes and significant alpha-1-fetoprotein (AFP) synthesis signalling a certain degree of retrodifferentiation with potential stemness. Due to the same embryonic origin of bile ducts and hepatocytes, biliary epithelium and its proliferating progeny (oval cells) have a defined role in liver regeneration as a transit and amplification compartment. In their early proliferation stage, oval cells were heavily engaged in DNA synthesis ([3H]thymidine labelling). Pulse-chase experiments during experimental hepatocarcinogenesis exhibited their development into hepatocytes with high risk for transformation and leading to foci of altered hepatocytes. Hepatocellular carcinomas may arise either from proliferating/differentiating oval cells or from adult hepatocytes; both cell types have stem-like properties. AFP-positive and AFP-negative carcinomas occurred in the same liver. They may represent random clonal origin. The heterogeneity of phenotypic marker (AFP) correlated with a process of retrodifferentiation.

Modification by curcumin of mutagenic activation of carcinogenic N-nitrosamines by extrahepatic cytochromes P-450 2B1 and 2E1 in rats

To elucidate the mechanism underlying suppression by curcumin of esophageal carcinogenesis induced by NMBA, we evaluated the CYP level and mutagenic activation of environmental carcinogens, by immunoblot analyses and Ames preincubation test, respectively, and bilirubin, 4-nitrophenol and testosterone UDPGT activities in F344 rats treated with curcumin and/or NMBA. No significant alterations in the hepatic levels of constitutive CYP proteins, mutagenic activation by liver S9 or hepatic UDPGT activities were produced by subcutaneous treatment with 0.5 mg/kg NMBA for 5 weeks and/or feeding of 0.05% and 0.2% curcumin for 6 weeks. In contrast, gavage of 0.2% curcumin decreased esophageal CYP2B1 and 2E1 by up to 60%, compared with vehicle control. Similarly, intragastric treatment with 270 mg/kg curcumin decreased esophageal and gastric CYP2B1 and CYP2E1, but not in lung, kidney or intestine. Conversely, large intestinal CYP2B1 was 2.8-fold higher in the treated rats than in control rats. Mutagenic activities of NOC, including NMBA, in the presence of esophagus and stomach S9 were markedly decreased in the treated rats, whereas those in the presence of large intestine S9 were 2.2-3.0-fold above control. These results show that modifying effects of curcumin on esophageal carcinogenesis can be attributed to a decrease in metabolic activation of NMBA by esophageal CYP2B1 during the initiation phase, without the contribution of metabolic activation and inactivation by liver. Further, the present findings suggest the potential of curcumin for modification of gastric and intestinal carcinogenesis initiated with NOC.