N-nitroso compounds and man: sources of exposure, endogenous formation and occurrence in body fluids.
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Body Fluids↗
Biomedical subjects
S S Hecht
Publications and source records attributed to S S Hecht.
N-nitroso compounds and man: sources of exposure, endogenous formation and occurrence in body fluids.
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Carcinogens↗
Tobacco and cancer: approaches using carcinogen biomarkers and chemoprevention.
Tobacco products are the leading cause of avoidable cancer death in the U.S., accounting for approximately 30% of all cancer deaths. While avoidance of tobacco and smoking cessation are clearly the best way to decrease tobacco-related cancer, these approaches have not been uniformly successful. Approximately 25% of the U.S. population over 18 years of age smokes cigarettes, while 6% use smokeless tobacco products; these figures have not changed markedly in recent years. Our approach toward the tobacco and cancer problem is based on an understanding of the carcinogens in tobacco smoke. These carcinogens form the link between nicotine addiction and cancer. In this paper, two strategies for cancer prevention--the development of carcinogen-derived biomarkers and chemopreventive agents--are discussed. Carcinogen-derived biomarkers can provide specific information on individual metabolic activation and detoxification of tobacco carcinogens. This information can be used to assess individual risk for cancer development upon exposure to tobacco products. Chemopreventive agents can be targeted against the important carcinogens in tobacco smoke. Isothiocyanates, strong inhibitors of lung cancer development by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, are discussed as an example of this approach.
Adult↗
Tobacco addiction: implications for treatment and cancer prevention.
The American Society of Clinical Oncology and the National Cancer Institute convened a symposium in June 1996 on tobacco addiction. Additional support for the symposium was provided by the American Medical Women's Association and the American Society of Preventive Oncology. The goals of this conference were to describe the burden and public health consequences of tobacco addiction, to describe the state of science for the treatment of nicotine dependence, and to explore new strategies to increase quit rates and to prevent the uptake of tobacco use. This article summarizes and integrates the meeting presentations on tobacco addiction and includes the topics of smoking prevalence; psychobiologic aspects of nicotine dependence; and implications for disease, treatment, and prevention. Comments on regulatory approaches and national strategies for reducing dependence are also summarized in presentations by Dr. David Kessler, former Food and Drug Administration Commissioner, and Dr. C. Everett Koop, former U.S. Surgeon General.
Depression↗
Aspartame consumption in relation to childhood brain tumor risk: results from a case-control study.
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Aspartame↗
Inositol hexaphosphate inhibits cell transformation and activator protein 1 activation by targeting phosphatidylinositol-3' kinase.
Inositol hexaphosphate (InsP6) is the most abundant inositol phosphate found in plants. In mammalian cells, the concentrations of InsP6 are between 10 and 100 microM. Previous work has indicated that InsP6 is an effective cancer chemopreventive and chemotherapeutic agent. However, the molecular mechanisms involved in the inhibition of carcinogenesis by InsP6 remain unclear. In this study, we investigated the influence of InsP6 on tumor promoter-induced cell transformation and signal transduction pathways leading to activator protein 1 activation, which is considered to play a crucial role in tumor promotion. InsP6 markedly blocks epidermal growth factor-induced phosphatidylinositol-3 (PI-3) kinase activity in a dose-dependent manner in JB6 cells and directly in vitro. Blocking PI-3 kinase activity by InsP6 profoundly impairs epidermal growth factor- or phorbol ester-induced JB6 cell transformation and extracellular signal-regulated protein kinases activation, as well as activator protein 1 activation. These results provide the first evidence that the molecular mechanism of InsP6 antitumor promotion effect targets and blocks PI-3 kinase activation and demonstrate that PI-3 kinase can serve as a molecular target for the development of cancer chemopreventive agents.
Animals↗
Evidence for an important role of DNA pyridyloxobutylation in rat lung carcinogenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: effects of dose and phenethyl isothiocyanate.
The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), selectively induces lung tumors in F344 rats. NNK is metabolically activated to intermediates that methylate and pyridyloxobutylate DNA. To explore the importance of pyridyloxobutyl DNA adducts in NNK-induced rat lung tumorigenesis, the first study in this report examined levels of these adducts in whole lung and pulmonary cells of F344 rats treated with different doses of NNK (0.3, 1.0, 10.0, and 50 mg/kg; 3 x weekly for 2 weeks). Pyridyloxobutyl DNA adducts were highest in Clara cells compared to alveolar Type II cells, alveolar macrophages, and small cells, suggesting that enzymes involved in the formation of the pyridyloxobutylating species are concentrated in Clara cells. When we compared lung tumor incidence at the different doses of NNK (S. A. Belinsky et al., Cancer Res., 50: 3772-3780, 1990) versus pyridyloxobutyl DNA adducts in Type II cells, we observed a significant correlation. Because NNK-induced lung tumors arise from the Type II cells, this suggests an important role for pyridyloxobutyl DNA adducts. In the second study presented in this report, we examined the effect of dietary phenethyl isothiocyanate (PEITC), an inhibitor of lung tumor induction in F344 rats by NNK, on O6-methyldeoxyguanosine (O6-mG) and pyridyloxobutyl DNA adducts in whole lung and lung cells of F344 rats treated with NNK. F344 rats were fed control or PEITC-containing diets (3 micromol/g diet) before and throughout NNK treatment (1.76 mg/kg, three times weekly for 4, 8, 12, 16, or 20 weeks). PEITC inhibited formation of pyridyloxobutyl DNA adducts in whole lung and all lung cells except macrophages. There was also inhibition of O6-mG, but it varied with cell type and length of NNK treatment. Overall, PEITC treatment decreased pyridyloxobutyl DNA adducts by 57% in Clara cells, 51% in Type II cells, 40% in small cells, and 44% in whole lung. PEITC treatment decreased O6-mG levels by 52% in Clara cells, 19% in Type II cells and small cells, and 36% in whole lung. These results support the hypothesis that PEITC inhibition of NNK-induced lung tumors is a result of decreased metabolic activation and DNA binding of NNK. The 50% reduction of pyridyloxobutyl DNA adducts in Type II cells agreed well with the 50% reduction of NNK-induced lung tumors by PEITC. Because NNK-induced tumors arise from Type II cells, these results suggest an important role for pyridyloxobutyl DNA adducts in NNK-induced rat lung tumorigenesis.
Animals↗
A cyclic N7,C-8 guanine adduct of N-nitrosopyrrolidine (NPYR): formation in nucleic acids and excretion in the urine of NPYR-treated rats.
N-Nitrosopyrrolidine (NPYR) is a well-established hepatocarcinogen that is present in the diet and tobacco smoke and may form endogenously in humans. Biomarkers to assess NPYR exposure and metabolic activation in humans are needed. The cyclic N7,C-8 guanine adduct 2-amino-6,7,8,9-tetrahydro-9-hydroxypyrido[2,1-f]purin-4(3H)-one (8), which is formed in tissues of rats treated with NPYR, is one potential candidate for such a biomarker. In this study, we evaluated the formation of this and other NPYR adducts in reactions of alpha-acetoxyNPYR with dGuo, Guo, DNA, and RNA and determined the extent of urinary excretion of adduct 8 in rats treated with NPYR. alpha-AcetoxyNPYR, a stable precursor to the major product of NPYR metabolic activation, was allowed to react with dGuo, Guo, DNA, or RNA at 37 degrees C, pH 7. The most striking observation was that the cyclic N7,C-8 guanine adduct 8 was formed 9 times more extensively in the reaction with Guo than with dGuo. It was also formed 2.5 times more extensively in RNA than in DNA. In rats treated with NPYR, levels of the cyclic N7,C-8 guanine adduct 8 were 2 times as high in RNA than in DNA. Rats treated with [14C]adduct 8 excreted 51% of this adduct unchanged in urine. Rats treated with [3,4-3H]NPYR excreted 0.00004% of the dose as adduct 8. The major differences in product formation in reactions of alpha-acetoxyNPYR with dGuo versus Guo are unusual for alkylating agents; potential mechanisms are discussed. The higher levels of adduct 8 in RNA than in DNA suggest that RNA may be superior as a source of adduct 8 as a biomarker.
Animals↗
Pyridyloxobutyl adduct O6-[4-oxo-4-(3-pyridyl)butyl]guanine is present in 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone-treated DNA and is a substrate for O6-alkylguanine-DNA alkyltransferase.
The lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is activated to reactive metabolites that methylate or pyridyloxobutylate DNA. Previous studies demonstrated that pyridyloxobutylated DNA interferes with the repair of O6-methylguanine (O6-mG) by O6-alkylguanine-DNA alkyltransferase (AGT). The AGT reactivity of pyridyloxobutylated DNA was attributed to (pyridyloxobutyl)guanine adducts. One potential AGT substrate adduct, 2'-deoxy-O6-[4-oxo-4-(3-pyridyl)butyl]guanosine (O6-pobdG), was prepared. This adduct was stable at pH 7.0 for greater than 13 days and to neutral thermal hydrolysis conditions (pH 7.0, 100 degrees C, 30 min). Under mild acid hydrolysis conditions (0.1 N HCl, 80 degrees C), O6-pobdG was depurinated to yield O6-[4-oxo-4-(3-pyridyl)butyl]guanine (O6-pobG). O6-pobdG was hydrolyzed to 4-hydroxy-1-(3-pyridyl)-1-butanone and guanine under strong acid hydrolysis conditions (0.8 N HCl, 80 degrees C). O6-pobG was detected in 0.1 N HCl hydrolysates of DNA alkylated with the model pyridyloxobutylating agent 4-(acetoxymethylnitrosamino)-1-(3-[5-3H]pyridyl)-1-butanone ([5-3H]NNKOAc). When [5-3H]NNKOAc-treated DNA was incubated with either rat liver or recombinant human AGT, O6-pobG was removed, presumably a result of transfer of the pyridyloxobutyl group from the O6-position of guanine to AGT's active site.
Animals↗
Characterization of amino acid and glutathione adducts of cis-2-butene-1,4-dial, a reactive metabolite of furan.
Metabolic activation of the hepatocarcinogen furan yields metabolites that react covalently with proteins. cis-2-Butene-1,4-dial is a microsomal metabolite of furan. This reactive aldehyde is thought to be the toxic metabolite that is responsible for the carcinogenic activity of furan. In order to characterize the chemistry by which this unsaturated dialdehyde could alkylate proteins, the products formed upon reaction of cis-2-butene-1,4-dial with model nucleophiles in pH 7.4 buffer were investigated. N(alpha)-Acetyl-L-lysine (AcLys) reacts with cis-2-butene-1,4-dial to form N-substituted pyrrolin-2-one adducts. N-Acetyl-L-cysteine (AcCys) reacts rapidly with cis-2-butene-1,4-dial to form multiple uncharacterized products. The inclusion of AcLys in this reaction mixture yielded an N-substituted 3-(S-acetylcysteinyl)pyrrole adduct which links the two amino acid residues. Related compounds were isolated when cis-2-butene-1,4-dial and glutathione (GSH) were combined. In this case, cis-2-butene-1,4-dial cross-linked two molecules of GSH resulting in either cyclic or acyclic adducts depending on the relative GSH concentration. Incubation of furan with rat liver microsomes in the presence of [glycine-2-3H]GSH led to the formation of radioactive peaks that coeluted with synthetic standards for the bisgluthathione conjugates. These studies demonstrate that the reactive cis-2-butene-1,4-dial formed during the microsomal oxidation of furan reacts rapidly and completely with amino acid residues to form pyrrole and pyrrolin-2-one derivatives. Therefore, this metabolite is a likely candidate for the activated furan derivative that binds to proteins. The ease with which cis-2-butene-1,4-dial cross-links amino acids suggests that pyrrole-thiol cross-links may be involved in the toxicity observed following furan exposure.
Aldehydes↗
Evidence for endogenous formation of tobacco-specific nitrosamines in rats treated with tobacco alkaloids and sodium nitrite.
Carcinogenic tobacco-specific nitrosamines are present in tobacco products and are believed to play a significant role in human cancers associated with tobacco use. Additional amounts of tobacco-specific nitrosamines could be formed endogenously. We tested this hypothesis by treating rats with nicotine and sodium nitrite and analyzing their urine. Initially, we treated groups of rats with (S)-nicotine (60 micromol/kg) and NaNO2 (180 micromol/kg), (S)-nicotine alone, NaNO2 alone or 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 12 nmol/kg) by gavage twice daily for 4 days. We collected urine and analyzed for two metabolites of NNK; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide. We did not detect these metabolites in the urine of rats treated with nicotine alone or nicotine plus NaNO2, indicating that endogenous conversion of nicotine to NNK did not occur. However, the urine did contain N'-nitrosonornicotine (NNN), N'-nitrosoanabasine (NAB) and N'-nitrosoanatabine (NAT). Analysis of the (S)-nicotine used in this experiment demonstrated that it contained trace amounts of nornicotine, anabasine and anatabine. In a second experiment, we used an identical protocol to compare the endogenous nitrosation of this (S)-nicotine with that of synthetic (R,S)-nicotine, which did not contain detectable amounts of nornicotine, anabasine or anatabine. NNN (0.53 x 10(-3)% of nicotine dose), NAB (0.68%) and NAT (2.1%) were detected in the urine of the rats treated with the (S)-nicotine and NaNO2. NNN (0.47 x 10(-3)% of dose), but not NAB or NAT, was present in the urine of the rats treated with synthetic (R,S)-nicotine and NaNO2. NNN probably formed via nitrosation of metabolically formed nornicotine. These results demonstrate for the first time that endogenous formation of tobacco-specific nitrosamines occurs in rats treated with tobacco alkaloids and NaNO2. The potential significance of the results with respect to nitrosamine formation in people who use tobacco products or nicotine replacement therapy is discussed.
Alkaloids↗
Effects of long term dietary phenethyl isothiocyanate on the microsomal metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in F344 rats.
Phenethyl isothiocyanate (PEITC), a cruciferous vegetable component, inhibits lung tumor induction by the tobacco specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). To gain insight into the mechanism of PEITC lung tumor inhibition, we examined, in male F344 rats, the effects of dietary PEITC (3 micromol/g NIH-07 diet) in combination with NNK treatment (1.76 mg/kg, s.c., three times a week) for 4, 12 and 20 weeks on liver and lung microsomal metabolism of NNK and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of NNK and also a lung carcinogen. This was compared with rats fed NIH-07 diet, without PEITC, and treated with NNK alone or saline. The protocol was identical to that employed for inhibition of lung tumorigenesis by PEITC. We observed decreased rates of alpha-hydroxylation of NNK and NNAL in lung microsomes of 4-, 12- and 20-week PEITC + NNK treated rats compared with those treated with NNK or saline. NNK treatment alone also decreased lung alpha-methylene hydroxylation of NNK. Long-term NNK + PEITC administration did not significantly affect liver oxidative metabolism of NNK or NNAL, and did not affect the rate of glucuronidation of NNAL in liver microsomes when compared with rats treated with NNK or saline. Thus, PEITC selectively inhibited lung metabolic activation of NNK and NNAL. These results support the hypothesis that PEITC inhibits NNK-induced lung tumors by inhibiting metabolic activation of NNK in the lung. This study also demonstrated that PEITC inhibits lung alpha-hydroxylation of NNAL; this may play a role in PEITC inhibition of lung tumorigenesis by NNK.
Animals↗
Absolute configuration of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol formed metabolically from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is an important metabolite of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Using the chiral derivatizing agent, (R)-(+)-alpha-methylbenzyl isocyanate [(R)-(+)-MBIC], previous work has shown that the enantiomeric ratio of metabolically formed NNAL and its glucuronide derivative may be species dependent. However, the absolute configuration of such NNAL has not been previously reported. Synthetically prepared racemic NNAL was converted to diastereomeric esters by reaction with (R)-(+)- and (S)-(-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetic acid (MTPA) chloride (Mosher's reagent) and the products were characterized by 1H-NMR. Based on chemical shift data, the absolute configuration of NNAL in each diastereomeric ester was assigned. Hydrolysis of (R)-NNAL-(R)-MTPA gave (R)-NNAL. This was converted to the corresponding carbamate by reaction with (R)-(+)-alpha-MBIC and the absolute configurations of the diastereomeric carbamates formed by reaction of (R)- and (S)-NNAL with (R)-(+)-MBIC were thereby assigned. Conversion of metabolically produced NNAL to the same carbamates allowed us to assign the NNAL formed from NNK by rat liver microsomes as (R)-NNAL. The major and minor NNAL-glucuronide diastereomers found in the urine of patas monkeys and humans exposed to NNK were similarly assigned; they were formed from (R)-NNAL and (S)-NNAL, respectively.
Animals↗
Approaches to chemoprevention of lung cancer based on carcinogens in tobacco smoke.
Chemoprevention may be one way to prevent lung cancer in smokers who are motivated to quit but cannot stop. The approach to chemoprevention of lung cancer described in this article is based on an understanding of the lung carcinogens present in tobacco smoke. The available data indicate that the compounds in cigarette smoke most likely involved in the induction of lung cancer in humans are the complex of polynuclear aromatic hydrocarbons typified by benzo[a]pyrene (B[a]P) and the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). A large number of compounds are now available that inhibit lung tumorigenesis by B[a]P or NNK in rodents. Inhibition of NNK-induced lung carcinogenesis by phenethyl isothiocyanate (PEITC) and inhibition of B[a]P-induced lung carcinogenesis by benzyl isothiocyanate (BITC) are discussed as examples. Studies with PEITC in rodents clearly demonstrate that it inhibits NNK-induced lung tumorigenesis by inhibiting the metabolic activation of NNK. Similar changes appear to occur in humans according to data generated in smokers who ate watercress, a source of PEITC. It is likely that mixtures of chemopreventive agents with activity against carcinogens in tobacco smoke, such as NNK and B[a]P, will be useful in chemoprevention of lung cancer in smokers. Furthermore, there is a need to develop suppressing agents for lung cancer that might be applicable in both smokers and ex-smokers.
Animals↗
Approaches to cancer prevention based on an understanding of N-nitrosamine carcinogenesis.
Understanding carcinogenesis is critical for development of rational approaches to cancer prevention. This paper uses N-nitrosamine carcinogenesis as an example. N-Nitrosamines are a large group of potent carcinogens. Approximately 300 different N-nitrosamines are carcinogenic. At least 30 animal species are responsive to their effects. There is little doubt that humans exposed to sufficient amounts of N-nitrosamines would also be susceptible to their carcinogenic effects. Human exposure to preformed N-nitrosamines occurs through the diet, in certain occupational settings, and through the use of tobacco products, cosmetics, pharmaceutical products, and agricultural chemicals. Diminishing human exposure to these carcinogens is one approach to prevention of cancer, and this has been accomplished in many instances, although exposure to N-nitrosamines in tobacco products is still unacceptably high. Human exposure to N-nitrosamines also occurs by nitrosation of amines in the body, via their acid or bacterial catalyzed reaction with nitrite, or by reaction with products of nitric oxide generated during inflammation or infection. A second approach toward prevention of N-nitrosamine carcinogenesis is inhibition of this endogenous N-nitrosamine formation. Substantial reductions have been achieved with ascorbic acid and other nitrite scavengers. N-Nitrosamines undergo a simple cytochrome P450-mediated metabolic activation step, which is critical for their carcinogenicity. The third approach involves the use of chemopreventive agents that block this step, or other steps in the carcinogenic process. A large number of potent chemopreventive agents against nitrosamine carcinogenesis have been identified. Chemoprevention of lung cancer induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is discussed as an example of this approach.
Animals↗
Comparative metabolism of the tobacco-related carcinogens benzo[a]pyrene, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, and N'- nitrosonornicotine in human hepatic microsomes.
We compared the metabolism in human hepatic microsomes of three tobacco smoke carcinogens believed to be involved in the induction of cancer in humans: benzo[a]pyrene (BaP),4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N'-nitrosonomicotine (NNN). The metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of NNK, was also investigated. Although the metabolism of some of these compounds by human enzymes or tissue preparations has been previously examined in some studies, they have never been compared in the same human hepatic samples. Moreover, there have been no previous reports of NNAL metabolism by human tissues or enzymes. The tritium-labeled carcinogens (3 microM) were incubated with 10 different human hepatic microsomal preparations and cofactors for 10-20 min, and the products were analyzed by radioflow HPLC. NNN was the best substrate for oxidative metabolism, with the 5'-hydroxylation pathway being the predominant one observed (mean +/- SD = 31 +/- 17 pmol/min/mg protein). alpha-Hydroxylation of NNK by the methylene and methyl hydroxylation metabolic activation pathways was the next fastest reaction, with rates of 3.1 +/- 1.9 and 3.3 +/- 1.1 pmol/min/mg protein, respectively. Metabolism of BaP resulted in the formation of dihydrodiols and phenols; trans-7,8-dihydro-7,8-dihydroxy-BaP, its major proximate carcinogen, was formed at a rate of 1.1 +/- 0.61 pmol/min/mg protein. alpha-Hydroxylation of NNAL proceeded at a rate of 0.53 +/- 0.26 pmol/min/mg protein. The results of this study demonstrate that human hepatic microsomes metabolize all of these tobacco carcinogens resulting in a substantial stream of electrophilic intermediates capable of binding to DNA. The relative rates of oxidative metabolism to electrophiles or their precursors were NNN > NNK > BaP > NNAL. Correlation studies indicated involvement of cytochrome P4502A6 in the 5'-hydroxylation of NNN and cytochrome P4503A4 in the alpha-methylene hydroxylation and pyridine-N-oxidation of NNK and NNAL. The results of this study provide the first data on the comparative metabolism of these important carcinogens in human hepatic microsomes.
Benzo(a)pyrene↗
Analysis of human urine for pyridine-N-oxide metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a tobacco-specific lung carcinogen.
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen in rodents and is believed to be a causative factor for lung cancer in smokers. NNK also may be involved in oral cancer etiology in users of smokeless tobacco products. Pyridine-N-oxidation of NNK and its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), produces NNK-N-oxide and NNAL-N-oxide, respectively, which are detoxification products of NNK metabolism and are excreted in the urine of rodents and primates. Our goal is to develop a panel of urinary biomarkers to assess the metabolic activation and detoxification of NNK in humans. In this study, we developed methodology to analyze human urine for NNK-N-oxide and NNAL-N-oxide. The key step in the method was conversion of the N-oxides to NNK and NNAL by treatment with Proteus mirabilis. The resulting samples were then analyzed essentially by methods that we have described previously. 4-(Methylnitrosamino)-4-(3-pyridyl-N-oxide)-1-butanol (iso-NNAL-N-oxide) was used as internal standard. Levels of NNAL-N-oxide in smokers' urine ranged from 0.06 to 1.4 pmol/mg creatinine, mean +/- SD 0.53 +/- 0.36 pmol/mg creatinine. Its presence was confirmed by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry. NNK-N-oxide was not detected in smokers' urine. Levels of NNAL-N-oxide in the urine of smokeless tobacco users ranged from 0.02 to 1.2 pmol/mg creatinine, mean +/- SD 0.41 +/- 0.35 pmol/mg creatinine. The amounts of NNAL-N-oxide in urine were less than 20% of those of [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc) and were approximately 50% as great as those of free NNAL. These results demonstrate that pyridine-N-oxidation is a relatively minor detoxification pathway of NNK and NNAL in humans. The method was applied to analysis of urine from 11 smokers who consumed a diet containing watercress. In an earlier study (S.S. Hecht et al., Cancer Epidemiol., Biomarkers & Prev., 4: 877-884, 1995), we showed that consumption of watercress, a source of phenethyl isothiocyanate (PEITC), caused an increase in urinary excretion of NNAL plus NNAL-Gluc. This was attributed to inhibition of alpha-hydroxylation of NNK by PEITC, as seen in rodents in which PEITC also inhibits the pulmonary carcinogenicity of NNK. However, PEITC also could have inhibited pyridine-N-oxidation of NNK and NNAL. The urine of these smokers was analyzed for NNAL-N-oxide. The results demonstrated that watercress consumption had no effect on levels of NNAL-N-oxide in urine, supporting the conclusion that PEITC does inhibit the metabolic activation of NNK in humans.
Anticarcinogenic Agents↗
Effects of indole-3-carbinol on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in smokers.
Indole-3-carbinol (I3C) is a component of the human diet, occurring as a conjugate in certain cruciferous vegetables. I3C protects against carcinogenesis in a variety of animal models by modifying carcinogen metabolism. In mice, I3C decreases lung tumor formation by the tobacco-specific nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by enhancing its hepatic clearance (M. A. Morse et al., Cancer Res., 50: 2613-2617, 1990). In this study, our goal was to determine whether I3C would have similar effects on NNK metabolism in smokers as it did in mice. Thirteen women took 400 mg of I3C on 5 consecutive days and maintained constant smoking habits during this period. Their urine was analyzed before and after the I3C treatment period for two metabolites of NNK: 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). I3C treatment resulted in decreased levels of urinary NNAL, NNAL-Gluc, and NNAL plus NNAL-Gluc, and increased NNAL-Gluc:NNAL ratio in 10 of the 13 women. The mean decreases in NNAL (-0.27 +/- 0.09 pmol/mg creatinine, -23.4%) and NNAL plus NNAL-Gluc (-0.43 +/- 0.16 pmol/mg creatinine, -10.9%) were statistically significant as was the increase in NNAL-Gluc:NNAL ratio (1.1 +/- 0.5, 39.9%). These changes in urinary metabolites of NNK were consistent with those seen in mice treated with I3C and NNK; they suggest that I3C increased hepatic metabolism of NNK in our smokers. This is the first study to examine the effects of I3C on metabolism of an exogenous carcinogen in humans.
Adult↗