Effect of nicotine and tobacco-specific nitrosamines on the metabolism of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by rat oral tissue

The effect of N'-nitrosoanatabine (NAT) and nicotine on the metabolism of N'-nitrosonornicotine (NNN) and 4-(methyl-nitrosamino)-1-(3- pyridyl)-1-butanone (NNK) by cultured rat oral tissue was investigated. The effect of NNN on NNK metabolism and the effect of NNK on NNN metabolism was also determined. NNK inhibited NNN metabolism more than NNN inhibited NNK metabolism. NAT inhibited the metabolism of NNK but not of NNN. Nicotine, which is present at greater than 500 times the levels of NNN and NNK in smokeless tobacco, inhibited the metabolism of both nitrosamines. Inhibition of 1 microM NNN metabolism was greater than that of 1 microM NNK when the concentration of nicotine was 1, 10 or 100 microM. Nicotine at 100 microM inhibited the formation of all metabolites of NNN by 85-92%. These results suggest that NNN and nicotine may be metabolized by a common enzyme.     

Evidence for 4-(3-pyridyl)-4-oxobutylation of DNA in F344 rats treated with the tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine

DNA was isolated from tissues of K344 rats 24 h after treatmentby s.c. injection with [5-³H]4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone([5-³H]NNK) or [5-³H]N'-nitrosonor-nicotine ([5-³H]NNN) It washydrolyzed with acid or at pH 7,100°C, and the hydrolysateswere analyzed by HPLC. The major product in each case was Identifiedas 4-hydroxy-1-(3-pyridyl)-1-butanone, formed by hydrolysisof a DNA adduct. It was detected in DNA from the livers of ratstreated with [5-³H]NNK or [5-³H]NNN, and in DNA from lungs ofrats treated with [5-³H]NNK. These results demonstrate that4-(3-pyridyl)-4-oxobutylation of DNA occurs in rats treatedwith NNK or NNN, and are consistent with the hypothesis thatthese nitrosamines are metabolically activated by -hydroxylation.     

Comparative tumorigenicity and DNA methylation in F344 rats by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosodimethylamine

The tumorigenic activities and DNA methylating abilities in F344 rats of the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and the structurally related nitrosamine N-nitrosodimethylamine (NDMA) were compared. Groups of 30 male rats were given 60 s.c. injections of 0.0055 mmol/kg of either NNK or NDMA over a 20-week period (total dose, 0.33 mmol/kg). The experiment was terminated after 104 weeks. The numbers of rats with tumors were as follows for NNK and NDMA, respectively: liver, 10 and 6; lung 13 and 0; and nasal cavity, 6 and 1. NNK was significantly more tumorigenic than was NDMA toward the lung (P less than 0.01) and nasal cavity (P less than 0.05). Groups of rats were treated with a single s.c. injection of 0.39 mmol/kg or 0.055 mmol/kg of NNK or NDMA and the levels of 7-methylguanine and O6-methylguanine were measured in liver, lung, and nasal mucosa 1-48 h after treatment. In liver and lung, levels of 7-methylguanine and O6-methylguanine in DNA were 3-22 times (P less than 0.001) greater in NDMA treated rats than in NNK treated rats. Levels of methylation induced by NDMA and NNK in the nasal mucosa were similar. The results of this study demonstrate that NNK is a more potent tumorigen than NDMA in the F344 rat and suggest that DNA methylation alone does not account for its strong tumorigenicity in rat lung and nasal mucosa.     

Mutagenic and cytogenetic studies of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco specific nitrosamines (TSNA) N'-nitrosonornicotine (NNN) and 4-(Methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK) were tested for mutagenic and clastogenic effects using a battery of short-term test systems. These test systems include the Ames test, micronucleus test (MNT), induction of chromosomal aberrations and sister chromatid exchange (SCEs). NNN and NNK were tested for their potency in inducing mutations in the Ames Salmonella/microsome assay and their clastogenic action were tested by the micronucleus inducing ability in vivo using Swiss mice. Studies on the induction of chromosomal aberrations and SCE exchange were carried out using human peripheral blood lymphocyte cultures. In the Ames test and MNT, NNN was positive but in comparisons with NNK, NNK was a more potent mutagen. Present studies clearly proves the genotoxic potential of both NNN and NNK and between the two NNK is more potent.     

Formation of hemoglobin adducts upon treatment of F344 rats with the tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine

[5-3H]4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNK), [C3H3]NNK, and [5-3H]N'-nitrosonornicotine ([5-3H]NNN) were administered to F344 rats by i.p. injection. Levels of tritium present per milligram globin, 24 h after treatment were 720 fmol (0.1% of dose) for [5-3H]NNK, 640 fmol for [C3H3]NNK, and 370 fmol for [5-3H]NNN. Tritium was detectable in globin 7-8 weeks after treatment with [5-3H]NNK or [5-3H]NNN. Approximately 10-15% of the bound tritium in the globin of rats treated with [5-3H]NNK was released upon incubation of the globin with dilute NaOH or HCl. The released material was identified as 4-hydroxy-1-(3-pyridyl)-1-butanone; it was detectable in globin for 6 weeks (t1/2 = 9.1 days) after administration of [5-3H]NNK. 4-Hydroxy-1-(3-pyridyl)-1-butanone was also formed upon NaOH treatment of globin isolated from rats injected with [5-3H]NNN or [5-3H]4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone. The formation of 4-hydroxy-1-(3-pyridyl)-1-butanone under these conditions is consistent with a mechanism by which 4-(3-pyridyl)-4-oxobutyldiazohydroxide is produced upon metabolic alpha-hydroxylation of NNK or NNN and binds to globin of hemoglobin, yielding an adduct which is readily hydrolyzed by acid or base. Support for this mechanism was obtained by in vitro experiments. Levels of 4-hydroxy-1-(3-pyridyl)-1-butanone released upon base treatment of globin were 50 times greater after incubation of rat hemoglobin with [5-3H]4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone than with either [5-3H]NNK or [5-3H]4-hydroxy-1-(3-pyridyl)-1-butanone. The results of this study suggest methods that might be applicable for assessing the molecular dosimetry of NNK and NNN in individuals exposed to tobacco and tobacco smoke.     

Pharmacokinetics of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in laboratory animals

The pharmacokinetics of N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the Syrian golden hamster, the CD-1 mouse, and the baboon were compared to the pharmacokinetics in the Fischer rat. The formation and biological half-life of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), the major metabolite of NNK, was also studied in these animal species. The biological half-life of NNN in these 4 animal species ranged from 0.24 h to 3.06 h, that of NNK from 0.21 h to 0.43 h and NNAL from 0.48 h to 2.9 h. The pharmacokinetic data obtained in the baboon suggest that treatment with NNN and NNK causes an enzyme induction which accelerates the rate of elimination of these compounds.     

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.      

Effect of phenethyl isothiocyanate on the metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by cultured rat lung tissue

The effect of phenethyl isothiocyanate (PEITC), a dietary inhibitor of carcinogenesis, on the metabolism of the tobacco specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by cultured rat peripheral lung tissues was investigated. Initially, the metabolism of NNK by the tissues was studied by incubating the lung explants in medium containing 1 and 10 microM [5-3H]NNK for 3, 6, 12, and 24 h. NNK metabolites were analyzed and quantified by HPLC and expressed as nmol/mg DNA. NNK was metabolized by three pathways; alpha-carbon hydroxylation, pyridine N-oxidation and carbonyl reduction. The principal metabolic pathway involved the conversion of NNK to the pyridine N-oxidized metabolites: 4-(methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanone (NNK-N-oxide) and 4-(methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanol (NNAL-N-oxide). When combined, NNK-N-oxide and NNAL-N-oxide constituted approximately 70% of the total metabolites in the medium at 24 h. To determine the effects of PEITC on the metabolism of NNK, lung explants were either treated with both 10 microM [5-3H]NNK and PEITC (10, 50, and 100 microM) for 24 h, or they were pre-treated with these same concentrations of PEITC for 16 h and then co-treated with both PEITC and 10 microM [5-3H]NNK for 24 h. In both treatment series, PEITC inhibited the alpha-carbon hydroxylation and pyridine N-oxidation of NNK and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is produced from NNK by carbonyl reduction. In general, the inhibition of NNK metabolism was greater when the explants were pre-treated with PEITC. These results suggest that PEITC is an effective inhibitor of the conversion of NNK to metabolites that elicit DNA damage. Our results are in agreement with previously published data in which PEITC was shown to inhibit NNK metabolism and tumorigenesis in the rat lung.     

Kinetics of DNA methylation by the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in F344 rats

The carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was injected intravenously (0.41 mmol/kg) into F344 rats. DNA from target organs (lung, liver) and a non-target organ (kidney) was extracted hydrolysed and analysed for methylated guanines by cation-exchange high-performance liquid chromotography-fluorimetry. Levels of O6-methylguanine, a promutagenic lesion, and 7-methylguanine were three to eight times higher in the liver than in the lung. Neither base could be detected in the kidneys. The extent of methylation of hepatic DNA by NNK was 35 times lower than observed with an equimolar dose of NDMA by Swann et al. (1983). The levels of the two methylated guanines in liver and lung DNA increased between 4 and 24 h following NNK injection. NNK is metabolized rapidly in F344 rats to 4-(methylnitrosamino)-1(3-pyridyl)-butan-1-ol (NNA1). The relatively slow methylation of hepatic DNA after injection of NNK could be due to a slow release of methylating species from the major circulating metabolite NNA1. This low but sustained level of O6-methylguanine induced by NNK could, in part, explain its carcinogenic potency.     

Dose-response study of DNA and hemoglobin adduct formation by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in F344 rats

Levels of hemoglobin adducts and DNA adducts were measured in F344 rats after 4 consecutive daily i.p. injections of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The dose range was from 3 to 10,000 micrograms/kg/day. [5(-3)H]NNK and [C3H3]NNK were used to measure pyridyloxobutylation and methylation, in both globin and DNA, respectively. In globin, the level of binding increased linearly with dose. Total binding of [5(-3)H] NNK to globin was 3.2 to 8900 fmol/mg and total binding of [C3H3]NNK was 3.5 to 20,000 fmol/mg. The extents of pyridyloxobutylation of both DNA and globin were determined by measuring the amounts of 4-hydroxy-1-(3-pyridyl)-1-butanone released from each, over the dose range 15-5000 micrograms/kg/day. The levels of 4-hydroxy-1-(3-pyridyl)-1-butanone released were 3.2-650 fmol/mg globin, 18-3400 fmol/mg liver DNA, and 58-2180 fmol/mg lung DNA. The extents of DNA methylation in both lung and liver were greater than pyridyloxobutylation. When the dose range was 3-5000 micrograms/kg/day, the levels of 7-methylguanine were 0.22-246 pmol/mumol guanine (149-167,000 fmol/mg) in liver DNA and 0.23-78 pmol/mumol guanine (160-53,000 fmol/mg) in lung DNA. In the lung, the ratio of methylation to pyridyloxobutylation decreased as the dose decreased. In contrast to globin adduct formation, DNA adduct formation did not increase linearly with dose; adduct formation was greater at lower doses than would have been predicted by extrapolation from higher doses. Thus the results of this study demonstrate that there was not a linear relationship between globin adduct formation, neither pyridyloxobutylation nor methylation, and DNA adduct formation in the liver or the lung of rats treated with NNK.     

Carcinogenicity studies on the two tobacco-specific N-nitrosamines, N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacc-specific N-nitrosamines (TSNA) have been implicatedin oral cancer. However, except for one study using rats, nostudy has shown the ability of TSNA in inducing oral tumoursin experimental animals. We have studied the carcinogenic potentialsof N'-nitrcssonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK) in mice and hamsters, wherein the nitrosamines were administeredon the tongues of the mice and the cheek pouches of the hamstersto simulate the exposure conditions of humans. It was observedthat in Swiss and BALB/c male mice, both NNN and NNK inducedtumours of lung, forestomach and liver. However, no oral tumourswere induced in mice. The effect of vitamin A depletion wastested in Swiss male mice. It was found that a low vitamin Astatus did not alter the percentage incidence of tumours inducedby both nitrosamines to a significant extent. In the studiesusing Syrian golden hamsters, long-term treatment of NNK tohamster cheek pouch induced tumours in the lung, liver, stomachand cheek pouch. Subsequently, the effed of hydrogen peroxide(H₂O₂) on NNK-induced carcinogenicity in hamsters was studied.It was observed that simultaneous administration of NNK andH₂O₂ to the animals increased the incidence of cheek pouch tumours.Another pertinent observation was that even whena small initiatordase of NNK was given followed by the application of H₂O₂, avery significant increase in the tumour incidence was observed.This observation suggeststhat H₂O₂ could act as a promoter toNNK-induced carcinogenesis. In conclusion it may be stated thatboth NNN and NNK do not show any strain or species specificity.They failed to produce tumours at the site of application inmice but in hamsters few cheek pouch turnours were seen or wereinduced when NNK was applied alone. The cheek pouch tumour incidenceincreased when H₂O₂ was given concurrently or when applied fora long period after a low initiator dose of NNK was administeredin the cheek pouch.     

DNA and hemoglobin alkylation by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and its major metabolite 4-(methylnitros-amino)-1-(3-pyridyl)-1-butanol in F344 rats

Alkylation of DNA and hemoglobin was compared in male F344 ratsgiven a single s.c. injection of the tobacco-specific nitrosamine4-(methyInitrosamino)-1-(3-pyridyl)-1-butanone (NNK), or itsmajor metabolite formed by carbonyl reduction, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol(NNAL).In hepatic DNA, levels of 7-methylguanine and O⁶-methyl-guanineformed from NNK 1-48 h after treatment were similar to thoseformed from NNAL. In nasal mucosa and lung DNA, levels of 7-methylguanineand O⁶Amethylguanine were somewhat higher after treatment withNNK than with NNAL. Acid hydrolysis of hepatric DNA, isolatedfrom rats treated with either [5-³H]NNK or [5-³H]NNAL, gave180 ± 48 or 120 ± 23 µuno/mol guanine, respectively,of 4-hydroxy-1-(3-pyridyl)-1-butanone. Basic hydrolysis of globinisolated from rats treated with either [5-³H]NNK of 5-³H]NNALgave 4.1 ± 0.7 or 2.0 ± 0.1 pmol/mg, respectivelyof 4-hydroxy-1-(3-pyridyl)-1-butanone. These results indicatethat NNAL is not a detoxification product of NNK, since treatmentof rats with NNAL results in modifications of DNA which arequalitativerly and quantitatively similar to those observedupon treatment with NNK. Alkylation of DNA and globin by NNALmay result mainly from its metabolic reconversion to NNK.     

Biliary excretion of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in the rat

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK) is a potent pancreas carcinogen in rats. The biliary excretionof NNK was therefore studied in anesthetized female Sprague— Dawley rats following i.p. administration of 0.7 µmol/kg[carbonyl-¹⁴C]NNK. The concentration of radioactivity peakedwithin 30 min and decreased thereafter exponentially. Cumulativeexcretion of radioactivity reached a plateau at 6–9% ofthe total dose. HPLC analysis revealed the presence of 4-hydroxy-4-(3-pyridyl)butyricacid (hydroxy acid), 4-oxo-4-(3-pyridyl)-butyric acid (ketoacid), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butyl ß-D-glucopyranosiduronicacid (NNAL Glu), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol(NNAL) and NNK. NNAL Glu was the major metabolite contributing34 ± 4% of total radioactivity in bile at 30 min and58 ± 4% at 5 h. The percentage of acidic metabolitesremained constant at     

Metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by hamster respiratory tissues cultured with ellagic acid

Previous studies have shown that the nicotine-derived N-nitrosamine-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces tracheal papillomas and lung carcinomas in Syrian golden hamsters. In this study, we showed that hamster tracheal and lung explants metabolize NNK by alpha-carbon hydroxylation, pyridine N-oxidation and carbonyl reduction. alpha-Methylene hydroxylation and methyl hydroxylation yield methylating and pyridyloxobutylating intermediates, respectively. Levels of binding of the pyridyloxobutyl moiety to explant proteins was 200 times lower than the total amount of metabolites formed by alpha-carbon hydroxylation and released in the culture medium. Viable and heat-treated lung explants were cultured with [CH3-3H]NNK or [5-3H]NNK. In viable explants, the rate of binding of the methyl group was 2-fold higher than the rate of binding of the pyridyloxobutyl moiety of NNK. Heat treatment reduced 54-fold the binding of [CH3-3H] NNK but only 5-fold the binding [5-3H]NNK. Tracheal explants were cultured with [5-3H]NNK (5.6 microM) and ellagic acid (EA, 10 microM), a naturally-occurring plant phenol. EA did not inhibit any of the three metabolic pathways nor the binding of the pyridyloxobutyl moiety to explant proteins. Lung explants were cultured with NNK (3.7 microM) and with or without EA (100 microM). EA inhibits alpha-carbon hydroxylation by 19% and the overall metabolism of NNK by 6%. Formation of 7-methylguanine and O6-methylguanine was observed in lung explants and the levels of both adducts were reduced by EA (100 microM). These results suggest that high concentrations of EA modulate the metabolism of NNK and that NNK does not necessarily require enzymatic activation to bind to protein.     

Comparison of DNA alkali-labile sites induced by 4-(methylnitrosamino)-1(3-pyridyl)-1-butanone and 4-oxo-4-(3-pyridyl)butanal in rat hepatocytes

4-Oxo-4-(3-pyridyl)butanal (OPB) is an aldehyde formed during the activation of the tobacco-specific N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Using the DNA alkaline elution technique, the properties of DNA alkali-labile sites induced in the isolated rat hepatocytes by NNK and OPB were compared. The DNA single-strand break (SSB) frequencies in vitro, as measured by the elution rate (ER), ranged from 0.015 to 0.479 and were proportional (r2 = 0.991) to the dose (0-2 mM) of OPB. These concentrations, however, were slightly cytotoxic. For example, the LC50 after 4 h of exposure was 2.8 mM. This suggests that OPB-induced DNA SSB result from additive effects of OPB-DNA interaction and the indirect DNA damage associated with OPB cytotoxicity. NNK induced a significant and dose-dependent increase of DNA fragmentation at concentrations ranging from 0.5 to 5.0 mM with ER values ranging from 0.012 to 0.274 (r2 = 0.951). Genotoxicity as measured by the DNA-damaging potency coefficient (DDP) was 810, 345, 131 and 75 for N-methyl-N-nitrosourea (MNU), N-nitrosodimethylamine (NDMA), OPB and NNK respectively. Both MNU- and NNK-induced DNA lesions showed increased lability with increased pH (from 12.1 to 12.5) of the eluting buffer (r2 = 0.979 and 0.967 respectively). In contrast, the number of OPB-induced labile sites were not affected by increases in the pH. These results indicate that OPB is not the metabolite contributing the majority of alkali-labile sites generated by NNK. The filter elution procedure was used to study the in vitro rejoining of SSB in DNA induced by NNK. The extent of DNA SSB rejoining after 18 h of culture of hepatocytes in NNK-free medium were dependent on the concentration of NNK (0.5, 2.0 and 5.0 mM) and ranged from 50 to 90%. Rats were injected s.c. with NNK (0.39 mmol/kg). SSB frequency in liver DNA increased rapidly and reached a maximum 12 h after injection. DNA SSB frequency declined during the next 2 weeks with biphasic kinetics. The fast phase (75% rejoining of DNA SSB between 12 h and 2 days) was followed by a slow one (25% of DNA SSB maintained during the next 5 days but not present after 2 weeks). The results of this study better define the role of OPB-induced DNA damage. The persistence of DNA SSB in the liver of NNK-treated rats reflects the inability of this tissue to repair all DNA lesions.     

Mutagenesis induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosonornicotine in lacZ upper aerodigestive tissue and liver and inhibition by green tea

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and nitrosonornicotine (NNN) were administered to lacZ mice (MutaMouse) at equal concentrations in drinking water (2 weeks at 0.1 followed by 2 weeks at 0.2 mg/ml) over a 4 week period, for a total estimated dose of 615 mg/kg) and mutagenesis in a number of organs was measured. For mutagenesis induced by NNK the potency order was: liver > lung> pooled oral tissues kidney > esophagus > tongue. The mutant fraction varied from approximately 6 to 40 mutants per 10(-5) plaque forming units This corresponds to approximately 2-13 times the background levels. A somewhat different pattern was observed with NNN, where the order was liver > esophagus oral tissue approximately tongue > lung > kidney. The potency of NNK was about twice that of NNN in liver and lung, but somewhat less in aerodigestive tract tissue. When compared with results previously obtained for a similar administered dose of benzo[a]pyrene, NNK was approximately 10-100% as mutagenic in the corresponding organs. Reported target organs for carcinogenesis by NNN and NNK in rodents were targets for mutagenesis, but mutagenesis was also observed at other sites, suggesting that these sites are initiated. The effect of green tea consumption on mutagenesis by NNK was also investigated. Green tea reduced mutagenesis by approximately 15-50% in liver, lung, pooled oral tissue and esophagus.     

Absence of metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by flavin-containing monooxygenase (FMO)

The N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung carcinogen present in tobacco and tobacco smoke. Carbonyl reduction, alpha-carbon hydroxylation (activation) and N- oxidation of the pyridyl ring (detoxification) are the three main pathways of metabolism of NNK. In this study, metabolism of NNK was studied with lung and liver microsomes from F344 rats, Syrian golden hamsters and pigs and cloned flavin-containing monooxygenases (FMOs) from human and rabbit liver. Thermal inactivation at 45 degrees C for 2 min reduced FMO S-oxygenating activity but did not affect N-oxidation of NNK, leading to the conclusion that FMOs are not implicated in the detoxification of NNK. Detoxification of NNK was not increased by n- octylamine or by incubation at pH 8.4, supporting the conclusion that FMOs are not involved in the metabolism of NNK. SKF-525A (1 mM) significantly reduced N-oxidation and alpha-carbon hydroxylation, suggesting that these two pathways were catalyzed by cytochromes P450. Metabolism of NNK was lower with lung microsomes than with liver microsomes. Inhibition of metabolism of NNK by SKF-525A was also observed with rat lung microsomes, leading to the conclusion that cytochromes P450 are involved in pulmonary metabolism of NNK. Cloned FMOs did not metabolize NNK. In conclusion, cytochromes P450 rather than FMOs are involved in N-oxidation of NNK. The high capacity of hamster liver microsomes to activate NNK does not correlate with the resistance of this tissue to NNK-induced hepatocarcinogenesis.      

Inhibition of the metabolism and genotoxicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in rat hepatocytes by (+)-catechin

(+)-Catechin is a plant flavonoid which decreases the mutagenicity of several mutagens and carcinogens. In this study, we have investigated how (+)-catechin could inhibit the metabolism and DNA damage induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific carcinogen. Addition of 5 to 1000 microM (+)-catechin to rat hepatocytes cultured with 4.5 mM NNK caused a concentration-dependent reduction of alpha-carbon hydroxylation which is the activation pathway of NNK. Under the same conditions, (+)-catechin had a less significant effect on pyridine N-oxidation, which is a deactivation pathway. Reduction of the carbonyl group of NNK was not inhibited by (+)-catechin. We had previously shown that NNK induced single-strand breaks (SSBs) in primary culture of hepatocytes. In this study, we observed that 1.0 mM (+)-catechin inhibited the DNA SSBs induced by 1 mM NNK by 31%. With 1 mM N-nitrosodimethylamine, the inhibition of DNA SSBs was 30%. We concluded that (+)-catechin selectively inhibits the enzymes involved in the activation of NNK. Rats were gavaged with (+)-catechin (1.5 mmol/kg), injected s.c. 1 h later with NNK (0.39 mmol/kg) and killed 4 h after NNK treatment. (+)-Catechin significantly reduced DNA SSBs induced by NNK. Rats were injected s.c. with 0.39 mmol/kg NNK. (+)-Catechin reduced the methylation of liver DNA at the O6-guanine and N-7 guanine sites by 28 and 34% respectively. These results demonstrate that (+)-catechin inhibits the formation of DNA-damaging intermediates by selectively impairing the enzymatic activation of NNK. They suggest that (+)-catechin could be an effective preventive agent against NNK hepatocarcinogenicity.     

Tumorigenic activity of the tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL) and N'-nitrosonornicotine (NNN) on topical application to Sencar mice

The tumor-initiating activities of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL) and N'-nitrosonornicotine (NNN) were evaluated on the skin of female SENCAR mice. A total initiator dose of 28 mumol/mouse of each nitrosamine was applied in 10 subdoses administered every second day. Promotion commenced 10 days after the last initiator dose and consisted of twice weekly application of 2.0 micrograms of tetradecanoylphorbol acetate for 20 weeks. NNK induced a 79% incidence of skin tumors with an average of 1.6 tumors/mouse and a 59% incidence of lung adenomas. In contrast, iso-NNAL and NNN were not active as tumor initiators in either the skin or lung of mice. The tumorigenic activity of NNK on SENCAR mouse skin was evaluated at several doses. At a total initiator dose of 28 and 5.6 mumol/mouse, NNK exhibited significant activity (P less than 0.005) inducing a 59% and 24% incidence of skin tumors, respectively. In this dose response bioassay, NNK at a total initiator dose of 28 mumol induced a 63% incidence (P less than 0.005) of lung adenomas. The numbers of lung adenomas induced at the lower doses employed were not significant. NNK, at a total initiation dose of 1.4 mumol, did not exhibit significant tumorigenic activity (P greater than 0.05). Analysis of DNA from the skin of mice treated with NNK using HPLC with fluorescence detection failed to detect O6- and N-methylguanine (O6-MG and N7-MG) adducts. These data indicate that NNK can exert a contact carcinogenic effect and suggest that mechanisms other than DNA methylation may be involved in its activation to a tumorigenic agent in mouse skin.