Carcinogen In Laboratory Animals Research Articles

PI-3K and Akt are mediators of AP-1 induction by 5-MCDE in mouse epidermal Cl41 cells.

5-Methylchrysene has been found to be a complete carcinogen in laboratory animals. However, the tumor promotion effects of (±)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) remain unclear. In the present work, we found that 5-MCDE induced marked activator protein-1 (AP-1) activation in Cl41 cells. 5-MCDE also induced a marked activation of phosphatidylinositol 3-kinase (PI-3K). Inhibition of PI-3K impaired 5-MCDE–induced AP-1 transactivation, suggesting that PI-3K is an upstream kinase involved in AP-1 activation by 5-MCDE. Furthermore, we found that Akt is a PI-3K downstream mediator for 5-MCDE–induced AP-1 transactivation, whereas another PI-3K downstream kinase, p70S6K, was not involved in AP-1 activation by 5-MCDE. Moreover, inhibition of Akt activation blocked 5-MCDE–induced activation of extracellular signal–regulated protein kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs), whereas it did not affect p38K activation. Consistently, overexpression of a dominant-negative mutant of ERK2 or JNK1 blocked the AP-1 activation by 5-MCDE. These results demonstrate that 5-MCDE is able to induce AP-1 activation, and the AP-1 induction is specifically through a PI-3K/Akt–dependent and p70S6K-independent pathway.

Role of cytochrome P4501B1 in benzo[a]pyrene bioactivation to DNA-binding metabolites in mouse vascular smooth muscle cells: evidence from 32P-postlabeling for formation of 3-hydroxybenzo[a]pyrene and benzo[a]pyrene-3,6-quinone as major proximate genotoxic intermediates.

Benzo[a]pyrene (BP), a polycylic aromatic hydrocarbon (PAH), is a potent atherogen and carcinogen in laboratory animals. Since genotoxic mechanisms may contribute to the development of atherosclerosis by PAHs, we have tested the hypotheses that: 1) BP induces DNA adducts in mouse aortic smooth muscle cells (SMCs); 2) 3-hydroxybenzo[a]pyrene (3-OH-BP) and benzo[a]pyrene-3,6-quinone (BPQ) are proximate genotoxic metabolites; and 3) cytochrome P4501B1 (CYP1B1) mediates the activation of BP and its metabolites to ultimate genotoxic intermediates. Cultured mouse aortic SMCs were treated with BP, 3-OH-BP, or BPQ for 24 h, and DNA adduct formation was analyzed by (32)P-postlabeling. In some experiments, cells were pretreated with the CYP1B1 inhibitor 1-ethynylpyrene (EP) prior to exposure to BP or its metabolites. BP, 3-OH-BP, and BPQ induced formation of several DNA adducts that were not observed in dimethylsulfoxide-treated cells. Re- and cochromatography experiments indicated that 3-OH-BP and BPQ were proximate genotoxic metabolites of BP. DNA adduct formation was strongly inhibited by EP, a specific inhibitor of CYP1B1. BP treatment of SMCs resulted in induction of aryl hydrocarbon hydroxylase (AHH) activity and CYP1B1, but not CYP1A1, apoprotein. EP also blocked AHH induction by BP. In conclusion, the results of this study support the hypothesis that in SMCs, which are target sites for the development of atherosclerosis, the major bioactivation pathway of BP entails CYP1B1-mediated formation of the 3-OH-BP and BPQ, which are proximate genotoxic metabolites that may in turn get transformed to ultimate DNA-binding metabolites, which may contribute to atherogenesis by PAHs.

Carcinogenic activity of the flame retardant, 2,2-bis(bromomethyl)-1,3-propanediol in rodents, and comparison with the carcinogenicity of other NTP brominated chemicals.

Several brominated chemicals have been shown to be multisite-multispecies carcinogens in laboratory animals, and in this paper we report that the flame retardant, 2,2-bis(bromomethyl)-1,3-propanediol (BMP) is also a multisite carcinogen in both sexes of Fischer 344 rats and B6C3F1 mice. BMP was administered continuously in the diet for up to 2 yr to rats at doses of 0, 2,500, 5,000, or 10,000 ppm and to mice at doses of 0, 312, 625, or 1,250 ppm. Interim groups of rats were examined at 15 mo. An additional recovery group of male rats received the chemical for 3 mo at 20,000 ppm in the feed, and then the control diet for the remainder of the study. Chemical exposure caused neoplasms of the skin, subcutaneous tissue, mammary gland, Zymbal's gland, oral cavity, esophagus, forestomach, small intestine, large intestine, mesothelium, kidney, urinary bladder, lung, thyroid gland, seminal vesicle, hematopoietic system, and pancreas in the male rat; mammary gland, oral cavity, esophagus, and thyroid gland in the female rat; lung, kidney, and Harderian gland in male mice; and subcutaneous tissue, lung, and Harderian gland in the female mouse. The recovery group of male rats presented with the same spectrum of treatment-related neoplasms as in the core study. In this recovery group, BMP (at 20,000 ppm) caused irreversible effects at numerous sites after 90 days of exposure that was not detectable by histologic examination, but without further exposure resulted in carcinogenic responses at 2 yr. BMP is mutagenic in the salmonella test, but it was not determined if the BMP-induced effects that eventually lead to development of neoplasms at multiple sites are the same in both species and in all organ systems affected.

Effect of discounting certain tumor types/sites on evaluations of carcinogenicity in laboratory animals.

It has been suggested that, for mechanistic reasons, certain tumors found in experimental animals should be discounted when evaluating carcinogenic effects. The questioned tumors are: mouse liver, rat thyroid follicular cell, bladder and kidney (male rat), forestomach (mouse and rat, gavage route), and lung (mouse and rat, inhalation of particles). We sought to determine the effects of discounting those tumors on classification of chemicals as carcinogens in animals. We looked at carcinogenicity data for chemicals studied in NCI-NTP bioassays and/or reviewed in IARC monographs and we found that deleting the questioned tumors would have significant impact on evaluations of carcinogenicity in animals. Fifty-six of 234 (24%) chemicals determined to be carcinogenic in the NCI-NTP bioassay program would no longer be considered carcinogenic: 102 (44%) would have weaker evidence of carcinogenic effects. Thirty-three of 361 (9%) chemicals determined by IARC to have "limited" or "sufficient" evidence of carcinogenicity would no longer be considered carcinogenic; 119 (33%) would have weaker evidence of carcinogenic effects. Because such a large number of chemicals currently considered carcinogenic would be affected by categorical deletion of tumors and because we are not aware of data that would justify such categorical deletions, it would be preferable to consider mechanistic justifications for discounting tumors on a case-by-case basis for each individual chemical. Deletion of tumors on a categorical basis has serious implications for regulation of toxic chemicals and for public health.

Biomonitoring of 1,3-butadiene and related compounds.

The 1990 Clean Air Act Amendments list several volatile organic chemicals as hazardous air pollutants, including ethylene oxide, butadiene, styrene, and acrylonitrile. The toxicology of many of these compounds shares several common elements such as carcinogenicity in laboratory animals, genotoxicity of the epoxide intermediates, involvement of cytochrome P450 for metabolic activation (except ethylene oxide), and involvement of at least two enzymes for detoxication of the epoxides (e.g., hydrolysis or conjugation with glutathione). These similarities facilitate research strategies for identifying and developing biomarkers of exposure. This article reviews the current knowledge about biomarkers of butadiene. Butadiene is carcinogenic in mice and rats, which raises concern for potential carcinogenicity in humans. Butadiene is metabolized to DNA-reactive metabolites, including 1,2-epoxy-3-butene and diepoxybutane. These epoxides are thought to play a critical role in butadiene carcinogenicity. Butadiene and some of its metabolites (e.g., epoxybutene) are volatile. Exhalation of unchanged butadiene and excretion of butadiene metabolites in urine represent major routes of elimination. Therefore, biomonitoring of butadiene exposure could be based on chemical analysis of butadiene in exhaled breath, blood levels of butadiene epoxides, excretion of butadiene metabolites in urine, or adducts of butadiene epoxides with DNA or blood proteins. Mutation induction in specific genes (e.g., HPRT) following butadiene exposure can be potentially used as a biomarker. Excretion of 1,2-dihydroxy-4-(N-acetylcysteinyl-S)butane or the product of epoxybutene with N-7 in guanine in urine, epoxybutene-hemoglobin adducts, and HPRT mutation have been used as biomarkers in recent studies of occupational exposure to butadiene. Data in laboratory animals suggest that diepoxybutane may be a more important genotoxic metabolite than epoxybutene. Biomonitoring methods need to be developed for diepoxybutane and other putative reactive butadiene metabolites. With butadiene and related compounds, the ultimate challenge is to identify useful biomarkers of exposure in which quantitative linkages between exposure and internal dose of the important DNA-reactive metabolites are established.

Comparison of the Enhancing Effects of Dehydroepiandrosterone with the Structural Analog 16α-Fluoro-5-androsten-17-one on Aflatoxin B1 Hepatocarcinogenesis in Rainbow Trout

Dehydroepiandrosterone (DHEA) is an adrenal steroid with chemoprotective effects against a wide variety of conditions including cancer, obesity, diabetes, and cardiovascular disease. However, DHEA is also a carcinogen in laboratory animals, possibly through its function as a precursor of sex steroids or peroxisome proliferation. The structural analog 16α-fluoro-5-androsten-17-one (8354) has been reported to have enhanced chemopreventive activity without the steroid precursor and peroxisome proliferating effects of DHEA. This study compares DHEA and 8354 in rainbow trout, a species that is resistant to peroxisome proliferation but is highly susceptible to the carcinogenic and tumor enhancing effects of DHEA. Trout were exposed as fry to aflatoxin B1 (AFB1) or given a sham exposure, then were fed diets containing 444 ppm DHEA or 8354 for 6 months. Postinitiation treatment with DHEA significantly increased liver tumor incidence, multiplicity, and size compared to initiated controls. The analog 8354 slightly increased tumor incidence (p=0.06) but had no effect on multiplicity or size. Six percent of trout treated with DHEA alone developed tumors, whereas no tumors occurred in noninitiated trout fed control or 8354-containing diets. Serum levels of androstenedione were elevated by DHEA (48-fold) or 8354 (6-fold) treatment Serum β-estradiol titers were increased in DHEA-but not 8354-treated trout. Vitellogenin was induced significantly by either DHEA (434-fold) or 8354 (21-fold). Peroxisomal β-oxidation was not increased by either compound and catalase activity was decreased in DHEA-treated animals. Both steroids were potent inhibitors in vitro of trout liver glucose-6-phosphate dehydrogenase with IC50s of 24 and 0.5 μM for DHEA and 8354, respectively.

Can laboratory animal carcinogenicity studies predict cancer in exposed children?

A key to the prevention of childhood cancer is the control of carcinogens to which children are exposed. The first step in this process is to identify those chemicals that are likely to cause cancer in children. The best way to identify carcinogens, today, is the use of the rodent lifetime cancer test--the bioassay. The test has vocal critics, but is adequately reliable if properly used. Perhaps the major criticism concerns the use of the maximum tolerated dose as the highest dose tested. Critics claim that this dose causes cellular killing. The resultant cellular proliferation "fixes" preexisting mutations that can lead to cancer. This occurs but in a small fraction of the tests, and the high dose is necessary to achieve statistical sensitivity. All human carcinogens have been shown, when properly studied, to be carcinogenic in rodents. Many human carcinogens were first shown to cause cancer in rodent tests. Regulators rarely ban chemicals that have been demonstrated to be carcinogenic. Further, most chemicals in use today have not been properly tested. The potential errors in the rodent cancer test seem small when compared to the errors in the economic projections of the effects of restricting chemicals. Although not perfect, the rodent cancer test, when used properly, can help protect our children, and us, from cancer.

Can Laboratory Animal Carcinogenicity Studies Predict Cancer in Exposed Children?

Can Laboratory Animal Carcinogenicity Studies Predict Cancer in Exposed Children?

An improved phosphorus assay for oils without carcinogenic hydrazine sulfate

AbstractAn improved spectrophotometric method for phosphorus determination in oils is proposed. The proposed new method has made significant improvements in safety, sensitivity, and efficiency in comparison with the current American Oil Chemists’ Society (AOCS) Official Method (Ca 12–55, corrected 1992). The AOCS method employs hydrazine sulfate as the reducing agent to generate molybdenum blue. Hydrazine sulfate is a known carcinogen in laboratory animals and a suspected human carcinogen. The chemical also irritates skin and mucous membranes. In the improved method ascorbic acid is used as the reducing agent. Ascorbic acid is equally effective as hydrazine sulfate for the color reaction. The improved method is approximately 75 times more sensitive than the AOCS method. The sensitivity is improved by measuring absorbance at the absorption peak, 825 nm, and reducing the final volume of reaction mixture for color reaction. The AOCS method determines phosphorus by measuring absorbance at 650 nm, which is about 40% of that at the absorption peak. The efficiency of this improved method is also significantly increased by reducing sample size and the volumes of sample preparation. Therefore, the improved method is more cost‐effective than the AOCS method because less chemical reagents and smaller glassware are used, and the hazardous chemical waste disposal cost is eliminated. The improved method also avoids concentrated HCl and 50% KOH for sample preparation.

Cancer risk of heterocyclic amines in cooked foods: an analysis and implications for research

Heterocyclic amines (HAs) are formed as pyrolysis products during the cooking of meats/fish. These substances are potent mutagens in the Ames/Salmonella assay and are also carcinogens in laboratory animals. In order to assess the magnitude of the cancer risk posed by their presence in the US diet, we estimated the average intakes of HAs, based on analyses of the concentrations of HAs in cooked foods and data from a dietary survey of the US population and quantified the cancer potencies of the individual compounds using dose-response data from animal bioassays. Measured concentrations of HAs in cooked foods were taken from a major review of the open literature. Only those concentrations that were associated with normal cooking conditions were chosen for use in estimating dietary intakes. The average consumption of HA-bearing foods was determined by analyzing statistically the intakes of 3563 individuals who provided 3 day dietary records in a USDA sponsored random survey of the US population during 1989. Dietary intakes of the five principal HAs in descending order were 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) > 2-amino-9H-pyrido[2,3-b]indole (A alpha C) > 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) > 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) > 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). The carcinogenic potencies, in contrast, were almost the reverse order: IQ > DiMeIQx > MeIQx > PhIP > A alpha C. An upper-bound estimate of the incremental cancer risk is 1.1 x 10(-4), using cancer potencies based on a body surface area basis. Nearly half (46%) of the incremental risk was due to ingestion of PhIP. Consumption of meat and fish products contributed the most (approximately 80%) to total risk.

Effects of nonsteroidal antiinflammatory drugs on oxidative pathways in A/J mice

The tobacco-specific N-nitrosamine, NNK, is a potent carcinogen in laboratory animals. The authors have shown previously that NNK-induced lung tumorigenesis in A/J mice can be reduced significantly by certain nonsteroidal antiinflammatory drugs (NSAIDs), such as sulindac, ibuprofen, or piroxicam treatments. In this study, the authors investigated whether NSAIDs could reduce NNK-induced oxidative DNA damage and/or inhibit endogenous lipid peroxidation, or prostaglandin E 2 (PGE 2) synthesis in A/J mice. In the first experiment, A/J mice were gavaged with NNK (112 μmol/kg b. w.) three times a week while being maintained on a diet to which either ibuprofen (263 mg/kg diet), naproxen (230 mg/kg), sulindac (123 mg/kg), piroxicam (25 mg/kg), indomethacin (5 mg/kg), or no NSAIDs had been added. Levels of 8-OH-dG in the DNA of lung and liver were measured by high-performance liquid chromatography with electron capture detector. Treatment with NSAIDs had no significant effects on the endogenous or NNK-induced formation of 8-OH-dG in the lung of the mice. In a second experiment, after treatment of A/J mice with NSAIDs for 2 weeks, lipid peroxidation was assayed by determining thiobarbituric acid-reactive substances (TBA-RS) in lung tissues, and prostaglandin E 2 levels were measured in plasma by an enzyme immunoassay. Treatments with some NSAIDs lowered the levels of lipid peroxidation and plasma levels of PGF 2 below basal levels. Taken together, these results suggest that the inhibition of NNK-induced lung tumorigenesis by NSAIDs is more likely related to an inhibition of prostaglandin synthesis than to a direct inhibition of lipid peroxidation or oxidative DNA damage induced by NNK.

Transformation of hamster pancreatic duct cells by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), in vitro.

The tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen in laboratory animals. In the present study, in vitro transformation of spontaneously immortal hamster pancreatic duct cells following exposure to 20 mM NNK for 1,3,5 and 7 days is described. NNK imparted a dose-dependent and time-dependent toxicity to pancreatic duct cells in vitro. After NNK treatment, duct cells were grown either in complete duct medium (CDM) or in the absence of bovine pituitary extract, epidermal growth factor and Nu-serum (incomplete duct medium, IDM). Addition of NNK to the culture for 1 and 3 days did not affect the growth of the cells, whereas exposure of the cells for 5 and 7 days was inhibitory. One and 3 day NNK-treated cells were able to grow in the absence of growth factors and serum immediately after the treatment without any inhibition of growth. Untreated cells grew as a monolayer consisting of tightly packed polygonal cells with single nuclei. NNK treated cells also grew as a monolayer with numerous mitotic figures and multi-nucleated large cells. The doubling time between the untreated (16 h) and NNK-treated cells (14 h) was not significantly different prior to injection into the nude mice. NNK treated cells grown in IDM displayed anchorage independency in soft-agar. The tumorigenicity of the untreated and NNK treated cells (5 x 10(6)) was determined in nude mice. One and 3 day NNK-treated cells grown in CDM produced well-differentiated, mucinous tumors with a lower frequency (2/4 sites) and longer duration, but produced tumors at a higher frequency (4/4 sites) and shorter duration when grown in IDM. Five and 7 day NNK-treated cells grown in CDM did not produce any tumors; however, they produced tumors when grown in CDM followed by IDM (5/8 and 6/8 sites) with a shorter duration in nude mice. Analysis of DNA for k-ras mutation at codons 12, 13 and 61 showed G-A transition at codon 12 of the k-ras oncogene in tumor cells of 1 and 3 day NNK treatment. No mutation was detected in tumor cells from 5 and 7 day treatment.

The effect of pyridine on the in vitro and in vivo metabolism of ethyl carbamate (urethane) by rat and mouse

Ethyl carbamate (EC, urethane) is a known carcinogen in laboratory animals. A genotoxic mechanism has been proposed which involves the bioactivation of EC to a reactive epoxide by the ethanol-inducible CYP2E1. The purpose of this study was to determine if pyridine (200 mg/kg i.p.), an inducer of CYP2E1, would increase the in vitro metabolism of EC and the in vivo binding of EC to cellular macromolecules. Treatment of rats or mice with pyridine increased hepatic microsomal metabolism of [14C-carbonyl]EC to CO2, but had little effect on pulmonary microsomal metabolism. The increase in hepatic metabolism was inhibited by the CYP2E1 inhibitor diethyldithiocarbamate, but not by the esterase inhibitor paraoxon, clearly indicating a role for this isozyme in hepatic metabolism of EC. In vivo, pyridine (200 mg/kg i.p.) administered 18 h prior to dosing with EC decreased the binding of [14C-ethyl]EC to cellular macromolecules. These data indicate that pyridine administration to rats and mice induces CYP2E1 metabolism of EC in vitro, but inhibits EC metabolism in vivo, perhaps by acting as an alternate substrate for CYP2E1.

Chemicals and cancer in humans: first evidence in experimental animals.

Certain human diseases have been traced to exposure to environmental and occupational chemicals. In many instances the first evidence of potential adverse effects came from experimental studies and were subsequently discovered in humans. Associations of human cancers, as a diverse group of diseases, and chemicals have been made since the middle 1700s. Since then, nearly 100 chemicals, mixtures of chemicals, or exposure circumstances are now recognized as being or strongly implicated as being carcinogenic to humans. Of the less than 1000 agents evaluated adequately for carcinogenicity in laboratory animals, a varying spectrum of data from studies on humans are available for only about 20-25%. So far, more than 60 agents are linked unequivocally as causing cancer in humans, and another 50 or so are strongly suspected of being carcinogenic to humans. Not all of these have been or can be evaluated in animals because some are industrial processes or "occupations," some are environmental and cultural risk factors, and some are mixtures of agents. For those that can be studied experimentally, the qualitative concordance between humans and animals approaches unity, and in every case there is at least one common organ site of cancer in both species. The evidence of carcinogenicity in experimental animals preceded that observed in humans for nearly 30 agents and is the subject of this paper.

Effects of D-limonene on hepatic microsomal monooxygenase activity and paracetamol-induced glutathione depletion in mouse.

1. D-Limonene, a monoterpenoid constituent of citrus fruit oil, blocks tumour induction by chemical carcinogens in laboratory animals, apparently by preventing bioactivation of procarcinogens and by enhancing conjugation of proximal carcinogenic metabolites. 2. Inhibitory effects of D-limonene were measured in vitro using cytochrome P450 isoform-specific substrates. D-Limonene inhibited p-nitrophenol hydroxylase (pNP) activity in vitro in liver microsomes from acetone-, phenobarbital (PB)- and beta-naphthoflavone (BNF)-treated mouse, and 7-ethoxyresorufin O-deethylase (EROD) activity in microsomes from PB- and BNF-treated mouse. p-Nitrophenol and ethoxyresorufin are substrates for cytochromes P2E1 and P1A1, respectively. No inhibition of benzphetamine (BNZP) or aminopyrine (AP) demethylases by D-limonene was observed. 3. EROD, BNZP and AP activities in liver microsomes were increased 18 h after i.p. administration of D-limonene to acetone-induced mouse, while pNP activity was unchanged. The immunodetectable protein level of cytochrome P2B1 in non-acetone treated mouse was increased 18 h after D-limonene, with no differences in P2E1 or P1A1. 4. Acute D-limonene did not protect against paracetamol (acetaminophen)-induced depletion of liver reduced glutathione (GSH). A prolonged paracetamol challenge (0.6% diet for 10 days) elevated liver cytosolic GSH-S-transferase activity (GST) two-fold and decreased liver GSH to 46% of control values. Dietary D-limonene (1.0% diet for 10 days) maintained liver GSH concentrations at 92% of control values in the paracetamol-challenged mouse without altering GST activity. D-Limonene also increased liver GSH concentration (23%) in mouse fed 1.0% D-limonene alone.

Quantification of 4,4′-diaminodiphenylmethane by gas chromatography negative ion chemical lonization mass spectrometry

4,4′-Diaminodiphenylmethane (DDM) is an aromatic amine commonly used as a chemical intermediate in the production of isocyanates, polyurethanes, polymers, and elastomers. This compound is a carcinogen in laboratory animals, but no definitive data are available regarding its carcinogenicity in humans. On account of its diffusion and toxicity, specific analytical methods are required for monitoring human exposure to this compound. Methods for its quantification in biological fluids using gas chromatography-mass spectrometry (GC-MS) have been developed, using electron impact (EI) and negative ion chemical ionization (NICI). Here we described a GC-NICI-MS analytical procedure for DDM in acqueous matrices. A tetradeuterated analogue of DDM (DDM- d 4 ) was prepared in our laboratories with a simple proton-exchange reaction using deuterohydrochloric acid in deuterated methanol. This compound was used as internal standard. The samples were added with this internal standard, extracted with a solid phase column, and derivatized with a fluorinated anhydride. The final step was the GC-MS analysis of the resulting amide using the selected ion recording (SIR) mode. The use of NICI-MS as a GC detector gave high sensitivity, on account of the high response of the fluorinated species present in this type of ionization. Also, the EI ionization provided useful results and represents an alternative method. Furthermore, the accuracy of the method was guaranteed by the use of the deuterated internal Standard.

Tobacco-specific nitrosamines--metabolism and biological monitoring of exposure to tobacco products.

Tobacco-specific nitrosamines are derived from nicotine and related tobacco alkaloids and can be detected in tobacco products as well as in mainstream and sidestream smoke. Two of them, N-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, are strong carcinogens in laboratory animals. Because of its organospecificity for the lung, the latter is considered to be a causative factor in tobacco-related human lung cancer. Upon metabolic activation both nitrosamines give rise to a common reactive intermediate binding to macromolecules such as DNA and haemoglobin and hydrolysing to 4-hydroxy-1-(3-pyridyl)-1-butanone. Because of easy access to large quantities of haemoglobin from blood samples, it is most suitable for biomonitoring human exposure to tobacco-specific nitrosamines. A highly sensitive analytical method for determination of femtogram amounts of 4-hydroxy-1-(3-pyridyl)-1-butanone provides an approach to assess individual exposure to active and passive smoking.

Toxicological principles of metal carcinogenesis with special emphasis on cadmium.

Metals are an important and emerging class of carcinogens. At least three metals, specifically nickel, chromium, and arsenic, are confirmed human carcinogens, and several more are suspected to have carcinogenic potential in man. Considering that the list of known human carcinogens of any type is very small, it becomes clear that metals make up a substantial portion of the list. Furthermore, many metals are very potent carcinogens in laboratory animals. Despite this, relatively little attention has been given to the topic of metal carcinogenesis. The reasons for this relative lack of attention are not clear but perhaps are fostered by a perception that, because metals are the simplest of molecules, their mechanism of action must also be simple. This could not be farther from the truth and, although no clear mechanisms have emerged in the area of metal carcinogenesis, it has become apparent that they are anything but simple. Metal carcinogens possess several unique characteristics including a remarkable target site specificity. Detection of the mechanism, or mechanisms, of metal carcinogenesis has, however, proven elusive, in part because of a wide diversity of metallic carcinogenic agents and the intricate nature of metal interactions in biologic systems. The following review explores this broad topic, with special emphasis on toxicological principles including dose-response relationships and potential mechanisms, using cadmium as an example.

A study of betel quid carcinogenesis IX. Comparative carcinogenicity of 3-(methylnitrosamino)propionitrile and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone upon local application to mouse skin and rat oral mucosa

The Areca-derived 3-(methylnitrosamino)propionitrile (MNPN) was tested for its tumor initiating activity on mouse skin and for its tumorigenic potential in the oral mucosa of rats. On mouse skin, like the otherwise strongly carcinogenic, tobacco-specific 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), MNPN showed only weak local tumor initiator activity. However, the application of MNPN to mouse skin led also to multiple distant tumors in the lungs of the animals. Twice daily swabbing of the oral cavity of rats with aqueous solutions of MNPN or NNK for up to 61 weeks led only to one oral tumor in each group of 30 animals. Yet, these N-nitrosamines proved again to be strong organ-specific carcinogens. Thus, MNPN induced nasal tumors in 80% of the rats and lung adenomas in 13%, liver tumors in 10% and papillomas of the esophagus in 7%. NNK induced lung adenoma and/or adenocarcinoma in 90%, nasal tumors in 43% and liver adenomas/adenocarcinomas in 30% of the rats. These results confirm previous observations that, independent of the site and mode of application, MNPN and NNK remain strong organ-specific carcinogens in laboratory animals.

Modulation of 4-(methylnitrosamino)-1-(3-pyridyl)-1 butanone demethylation and denitrosation by rat liver microsomes

The nicotine-derived N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1 butanone (NNK) is abundant in tobacco smoke and is a potent carcinogen in laboratory animals. We have characterized and compared methyl hydroxylation leading to formaldehyde formation (activation pathway) and denitrosation (putative deactivation pathway) of NNK using rat liver microsomes. Methyl hydroxylation was linear between 10 and 50 min and denitrosation was linear between 20 and 65 min. The ratio of nitrite/formaldehyde formation was smaller with 4 mM NNK (0.016) than with N-nitrosodimethylamine (NDMA) (0.037). Liver microsomes exhibited at least two apparent K m values (0.005 and 0.534 mM) for NNK methyl hydroxylation. In vitro methyl hydroxylation of NDMA and NNK were induced by pretreatment of the rat with isopropanol. Butylated hydroxytoluene pretreatment doubled the rate of microsomal denitrosation but did not affect the rate of methyl hydroxylation. (+)-Catechin is a flavonoid present in tea, wine and apple skin. We observed that 0.10 mM (+)-catechin inhibited methyl hydroxylation and denitrosation of 4 mM NNK by 40% and 62%, respectively. These results indicated that NNK could be deactivated by denitrosation. Hydroxylation of the NNK methyl group by rat liver microsomes was 34 times more extensive than denitrosation.