Biomedical subjects

A Castonguay

Publications and source records attributed to A Castonguay.

At least 37 records · Page 2Linked to original sources

PubMed1998

Biodistribution of, antimutagenic efficacies in Salmonella typhimurium of, and inhibition of P450 activities by ellagic acid and one analogue.

Ellagic acid (EA) is generated by hydrolysis of ellagitannins present in fruit berries and edible nuts and grapes. Large doses of EA prevent lung tumorigenesis induced by the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A/J mice. In this study, we document the efficacies of the EA structural analogue (3,4,7,8-tetrahydroxy-6H-benzo[b,d]pyran-6-one) (analogue 1) to inhibit specific P450 activities, pulmonary metabolism of NNK in A/J mice, and NNK-induced mutations in Salmonella typhimurium. Mouse lung microsomes metabolized benzyloxyresorufin, a marker of cytochrome P450 2B1 activity, more extensively than methoxyresorufin or ethoxyresorufin. The EA analogue was more effective than EA in inhibiting dealkylation of the three alkoxyresorufins, suggesting that it is a nonspecific inhibitor of P450s. Mouse lung microsomes hydroxylate testosterone in the 7alpha and 6beta positions, suggesting contributions of P450 2A1 and P450 3A2 isozymes, respectively. Inhibition of both pathways was more effective with the EA analogue than with EA. Mouse lung explants metabolized NNK by alpha-carbon hydroxylation (activation) and pyridine N-oxidation (deactivation). Both pathways were inhibited when 100 microM EA was added to the culture medium. The EA analogue was a better inhibitor of the activation of NNK to electrophilic species than EA. Mouse lung microsomes activate NNK to intermediates mutagenic to S. typhimurium. Inhibition of NNK mutagenicity by EA or the EA analogue was 20 or 65%, respectively. The distribution of the EA analogue in lung and liver was determined following gavage with 1.7 mmol of the EA analogue. In the lung, a maximal level of EA analogue corresponding to 105 nmol was observed 30 min after administration of the analogue. The level in liver tissues was 4-fold lower than in the lung. Results of this study demonstrate that the EA analogue is more effective than EA in inhibiting the pulmonary activation of NNK and suggest that the EA analogue could be effective in preventing lung tumorigenesis.

Animals↗

PubMed1998

Inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced mouse lung tumor formation by FGN-1 (sulindac sulfone).

The sulfone derivative of the non-steroidal anti-inflammatory drug (NSAID), sulindac, has been reported to inhibit mammary and colon tumor formation in rodent models of chemically-induced carcinogenesis. Unlike its parent compound, this metabolite lacks cyclo-oxygenase inhibitory activity. A tumor induction protocol, consisting of NNK administration in the drinking water over several weeks to model chronic human exposure, was used to test whether the sulfone (called FGN-1) could inhibit the formation of primary lung tumors in mice. A total of 150 female, AIN76A-fed, A/J mice received 9 mg of NNK each. Concentrations of FGN-1 that had been previously determined not to affect body weight gain were added to the food at levels of 0, 250, 500 and 750 mg/kg of diet (30 mice/group) starting 2 weeks before NNK administration and continuing for 22 weeks. At that time pleural surface tumors were counted. Tumor incidence decreased significantly from 96 % in the control diet and 93% in the 250 FGN-1 mg/kg diet to 63 and 67% in the 500 and 750 mg FGN-1/kg diet groups, respectively (P < 0.001 by chi-square analysis). Lung tumor multiplicity decreased from 18.1+/-3 tumors/ mouse (mean+/-SEM, control diet) to 12.3+/-3 (250), 5.3+/-1 (500) and 2.1+/-1 (750) (P < 0.0005 by post hoc ANOVA). In previous studies using this carcinogenesis protocol, the maximum tolerated dose of sulindac inhibited lung tumor multiplicity by no more than 50% with no effect on incidence. This dose-dependent reduction in tumorigenesis by a non-toxic dose of FGN-1 indicates a strong chemopreventive activity against experimental induction of lung carcinogenesis. The greater potency of the sulfone over sulindac and its lack of toxic side effects because of its inability to affect cyclo-oxygenase activity suggests that clinical testing in individuals at high risk for lung cancer should be considered.

Animals↗

PubMed1998

Inhibitors of lipoxygenase: a new class of cancer chemopreventive agents.

5-Lipoxygenase is a key enzyme in the metabolism of arachidonic acid to leukotrienes. The preventive efficacy of 5-lipoxygenase inhibitors against lung tumorigenesis was determined in A/J mice given the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in drinking water from week 0 to week +7. Groups of 25 mice were fed either: acetylsalicylic acid (ASA), a cyclooxygenase inhibitor; A-79175, a 5-lipoxygenase inhibitor; MK-886, an inhibitor of the 5-lipoxygenase activating-protein; a combination of ASA and A-79175 from weeks -2 to +23. ASA, A-79175 and MK-886 reduced lung tumor multiplicity by 44, 75 and 52% respectively. Furthermore, A-79175 reduced tumor incidence by 20%. Administration of A-79175 and MK-886 decreased the mean tumor volume by 64 and 44% respectively. Lung tumor multiplicity was directly proportional to tumor volume. The combination of ASA and A-79715 was the most effective preventive intervention and reduced lung tumor multiplicity by 87% and lung tumor incidence by 24%, demonstrating that inhibition of both 5-lipoxygenase and cyclooxygenase is more effective than inhibition of either pathway alone. NNK treatment increased plasma prostaglandin E2 levels from 49 to 260 pg/ml and plasma LTB4 levels from 29 to 71 pg/ml. Incubation of 82-132 and LM2 murine lung tumor cells with MK-886 and A-79715 decreased cell proliferation in a concentration-dependent manner. Soybean lipoxygenases with or without murine lung microsomal proteins metabolized NNK by alpha-carbon hydroxylation (9.5% of the metabolites) and N-oxidation (3.9%). Activation of NNK by alpha-carbon hydroxylation was inhibited by addition of arachidonic acid and A-79715. Possible mechanisms of action of 5-lipoxygenase inhibitors include inhibition of tumor growth and lipoxygenase-mediated activation of NNK. These studies suggest that inhibitors of 5-lipoxygenase may have benefits as preventive agents of lung tumorigenesis.

Animals↗

PubMed1997

Recovery from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced immunosuppression in A/J mice by treatment with nonsteroidal anti-inflammatory drugs.

BACKGROUND: We have previously reported that nonsteroidal anti-inflammatory drugs inhibit lung tumorigenesis induced by the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mice. PURPOSE: The aims of this study were to determine if NNK suppresses humoral (i.e., antibody) and cellular immune responses in mice and if nonsteroidal anti-inflammatory drugs could attenuate these immune responses. METHODS: Female A/J mice (7-8 weeks old) were fed nonsteroidal anti-inflammatory drugs starting 2 weeks before the beginning of NNK treatment (9.1 mg per mouse in total) and continuing through the 7 weeks of NNK treatment. Eight groups (two control groups and six experimental groups) of 10 mice each were used per experiment. Animals in the two control groups received the same diet and water as animals in the six experimental groups; one control group received no nonsteroidal anti-inflammatory drugs or NNK and the other control group received only NNK. The primary humoral and cellular immune responses to the various treatments were assayed by the plaque-forming cell technique and by measurement of natural killer cell cytotoxic activity, respectively. At the end of each experiment, the animals were killed, blood was collected, plasma was prepared, and levels of the immune system modulator prostaglandin E2 were measured. RESULTS: NNK treatment inhibited the plaque-forming cell response by approximately 50%; this inhibition was attenuated by treatment with sulindac or acetylsalicylic acid (P = .0001 for both). In contrast, treatment with naproxen, which had no chemopreventive (i.e., tumor inhibitory) efficacy, further increased by 26% (P = .05) the immunosuppressive effect of NNK. The cytotoxic activity of splenic natural killer cells against YAC-1 cells was reduced by 60% (P = .002); treatment with acetylsalicylic acid (254 mg/kg of diet) reduced the NNK-induced natural killer cell cytotoxicity inhibition by 50% (P = .02), whereas the administration of the specific cyclooxygenase-2 inhibitor NS-398 (7 mg/kg of diet) resulted in an almost complete recovery (approximately 95%, P = .04) of natural killer cell activity. The prostaglandin E2 plasma concentration was approximately 100% greater in NNK-treated mice than in untreated mice. Treatment of the mice with nonsteroidal anti-inflammatory drugs attenuated this elevation (from approximately 25% to 100%), and NS-398 (7 mg/kg of diet) was the most effective (100%). CONCLUSIONS AND IMPLICATIONS: The ability of various nonsteroidal anti-inflammatory drugs to inhibit NNK-induced carcinogenesis appears to be directly related to the ability of these drugs to inhibit NNK-induced immunosuppression. Our results suggest that the chemopreventive effect of nonsteroidal anti-inflammatory drugs may be mediated through the modulation of prostaglandin E2 synthesis.

Animals↗

PubMed1997

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.

Animals↗

PubMed1997

Inhibition of lung tumourigenesis by sulindac: comparison of two experimental protocols.

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung carcinogen in mice and is most likely involved in the aetiology of tobacco-induced lung cancer. Two protocols using NNK and A/J mice have been developed. In the single-dose protocol, each mouse was injected once with 2 mg of NNK. In the 7-week protocol, each mouse received 9.1 mg of NNK in drinking water during 7 weeks. Mice were killed 16 weeks after NNK treatment. We observed a near-Gaussian distribution in the number of tumours per mouse in the single protocol, but not in the 7-week protocol. In the 7-week protocol, a significant number (8.6%) of mice had more than 20 tumours/mouse. In the single-dose protocol, no mouse had more than 20 tumours. Sulindac at a dose of 123 mg/kg of diet inhibits lung tumourigenesis in the 7-week protocol, but not in the single-dose protocol. We observed that the inhibition of tumourigenesis in the 7-week protocol was proportional to the logarithm of the dose of sulindac between 15 and 123 mg/kg of diet. Treatment of mice for 7 weeks inhibits the primary humoral response to sheep red blood cells by 70%. This observation is particularly significant considering that NNK is present in tobacco smoke and that tobacco smoking suppresses both the specific and non-specific humoral and cellular immunity. Single injections of 2.0, 3.5 or 5.0 mg of NNK had no effect on this response. Our results suggest that the immunosuppressive effects of NNK contribute to its high carcinogenic potency particularly in sustained or life-time exposure models. We hypothesize that sulindac promotes the recovery of immune system from the NNK-mediated suppression observed in the 7-week protocol. This study illustrates the importance of selecting the most appropriate protocol of carcinogen treatment in investigating the efficacies of cancer chemopreventive agents.

Administration, Oral↗

PubMed1997

Chemopreventive efficacies of aspirin and sulindac against lung tumorigenesis in A/J mice.

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs. In this study, we demonstrated the efficacy of aspirin to inhibit lung tumorigenesis in A/J mice. Lung tumors (9.9 tumors/mouse) were induced by the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), administered in drinking water between week 0 and week +7. Groups of mice were fed sulindac (123 mg/kg diet), acetylsalicylic acid (ASA; 294 mg/kg), non-buffered Aspirin (294 mg/kg) or buffered Aspirin (294 mg/kg) in AIN-76A diet from week -2 to the end of the bioassay (week +23). These doses are comparable to the maximal doses recommended for humans. ASA and non-buffered Aspirin were the most effective inhibitors and reduced lung multiplicities by 60 and 62%, respectively. Sulindac inhibited lung tumor multiplicity by 52%. Inhibition by buffered Aspirin was not statistically significant. We evaluated the efficacies of NSAIDs to inhibit NNK activation by h1A2 v2 cells expressing human P-450 1A2. Salicylates, at doses of 500 microM and 1 mM, had no effect on NNK activation. Sulindac and its sulfide and sulfone metabolites (1 mM) inhibited NNK metabolism by 90, 92 and 65%, respectively. We observed a 76% inhibition with SKF 525A, a P-450 inhibitor. Taken together, these results indicate that salicylates and sulindac could be equally effective as chemopreventive agents, but they could differ in their mode of action.

Adenoma↗

PubMed1996

Modulation of the mutagenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by phenolic compounds.

NNK is a potent environmental carcinogen generated during tobacco processing and smoking. The carcinogenic response to tobacco smoking is modulated by nutritional factors. In this study, liver microsomes from phenobarbital and beta-naphthoflavone-treated or control hamsters were used to assay the mutagenicity (Salmonella typhimurium TA1535) of NNK. Western analysis of these microsomal preparations revealed an increased expression of protein recognized by polyclonal antibodies specific for P-450 1A2 in beta-naphthoflavone-induced microsomes and P-450 2B1/2B2 in phenobarbital-induced microsomes. Both inducers significantly increased the mutagenicity of NNK. Metabolism of NNK by the three microsomal preparations was compared. Metabolites formed by methyl-hydroxylation of NNK by microsomes from control animals were significantly greater than those formed by alpha-methylene hydroxylation. Phenobarbital treatment had the greatest effect on alpha-methylene hydroxylation while beta-naphthoflavone had the greatest effect on methyl hydroxylation. The antimutagenic action of the polyphenolic compounds ellagic acid, esculetin and propyl gallate correlated with an inhibition of the metabolism of NNK. There were, however, differences in the effects of these compounds on specific pathways of NNK metabolism depending upon the microsomal enzyme induction treatment. This suggests that phenolic compounds have selective affinity for specific P-450 isozymes activating NNK.

Animals↗

PubMed1996

Chemical carcinogenesis, mutagenesis, and teratogenesis.

An international symposium entitled Chemical Carcinogenesis, Mutagenesis and Teratogenesis: a Tribute to James and Elizabeth Miller was held in Toronto, Ont., July 19, 1994. This symposium theme was discussed in the presence of James Miller, 79 years young, who with his wife, Elizabeth Miller (1920-1987), are considered to be the pioneers of this medical and environmental toxicology research field. It is generally believed that the susceptibility of an individual to chemical carcinogenesis or teratogenesis varies considerably depending upon their genetic makeup, diet, lifestyle, and their environmental exposure. One goal of the research discussed at this symposium was an examination of the role of the enzymes involved in the metabolic activation and detoxification of carcinogens and teratogens. The interindividual variabilities in the levels and activity of these enzymes could contribute to the susceptibility of the individual to chemical carcinogens or teratogens. At the symposium evidence was presented indicating that theta-class glutathione (GSH) S-transferase levels activate dihalomethanes and could therefore initiate the carcinogenic response to butadiene and 1,2-dibromo-3-chloropropane. The dramatic genetic polymorphism of this class of GSH S-transferase could thereby contribute to the individual's susceptibility to these carcinogens. Similarly, the GSH S-transferase and GSH levels in the embryo and yolk sac that are determined during organogenesis could also be important factors in determining the susceptibility of the embryo to teratogens. The levels of cytochrome P450 1A2, aromatic amine N-acetyltransferases, and sulfotransferases could also determine the susceptibility of the individual to carcinogenic arylamines. Accordingly, an Ames tester strain was described that was genetically engineered so as to express both aromatic amine N-acetyltransferase and human cytochrome P450 1A2. This should prove useful for predicting which arylamines are likely to be carcinogenic to humans. Nonsteroidal anti-inflammatory drugs may also prove useful in inhibiting the cytochrome P450s that activate the nitrosamines found in tobacco smoke suspected to cause lung cancer. Finally, the sulfotransferase isoforms involved in the metabolic activation of carcinogenic arylamines were identified.

Biotransformation↗

PubMed1995

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 E2 (PGE2) synthesis in A/J mice. In the first experiment, A/J mice were gavaged with NNK (112 mumol/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 E2 levels were measured in plasma by an enzyme immunoassay. Treatments with some NSAIDs lowered the levels of lipid peroxidation and plasma levels of PGE2 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.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed1995

Expression of xenobiotic-metabolizing enzymes in cultured rat tracheal epithelial cells.

Rat tracheal epithelial (RTE) cells were cultured on membrane support with and without retinoic acid (RA). In early (6-day-old) cultures, the epithelium is a monolayer or bilayer of undifferentiated cells and secretes little mucuslike product either in the absence or presence of RA. In late (12- to 15-day-old) cultures, the epithelium differentiates as a mucociliary epithelium in the presence of RA and as a squamous epithelium in the absence of RA. The purpose of our study was to determine whether a number of xenobiotic enzymes are expressed in these cultures and whether their expression depends on the state of differentiation. Enzyme expression was characterized by electrophoresis and immunoblotting as a function of time in culture and phenotypic differentiation. Cytochrome P450 1A1 was not expressed in freshly harvested RTE cells. This isoenzyme was induced in rats by gavage with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or by exposure of early RTE cell cultures to TCDD, provided RA was also added to the cultures. Cytochrome P450 2B1 was observed in freshly isolated RTE cells, but not in early or late RTE cultures. In contrast, expression of NADPH-cytochrome P450 reductase was decreased in early cultures, but was increased in well-differentiated cultures. Flavin-containing monooxygenase was detected in lung tissue, but not in freshly harvested or cultured RTE cells. Glutathione S-transferase (GST) mu and pi were expressed in freshly harvested RTE cells. GST pi was expressed in early and late cultures, whereas GST mu was expressed in late cultures, but could not be found in early cultured RTE cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Ki-ras mutations in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-initiated and butylated hydroxytoluene-promoted lung tumors in A/J mice.

The promotional effects of butylated hydroxytoluene (BHT) on lung tumorigenesis induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was evaluated in a two-stage model of lung tumorigenesis in the A/J mouse. Mice were treated in two separate experiments with 1.54 mmol/kg (9.1 mg/mouse) NNK, which induced an average of 8.4 and 9.1 tumors/mouse in the experiments. Animals fed a diet that contained 1 g/kg BHT after administration of the carcinogen in these two experiments demonstrated an increase of the tumor multiplicity by 63% and 43%. Multiplicity of forestomach tumors was not effected by BHT in the diet. No differences in lung tumor morphology were seen as a result of the promoting effect of BHT. Mutations in the Ki-ras oncogene from lung tumors induced by NNK (19 tumors) or by NNK plus a diet containing BHT (34 tumors) were characterized by polymerase chain reaction, single-strand conformational polymorphism, and direct sequencing. All 19 NNK-induced tumors not promoted with BHT contained activated Ki-ras genes with GC-->AT transitions at the second base of codon 12. Only 11 of 34 NNK-induced and BHT-promoted tumors (32%) had this characteristic Ki-ras alteration. These data suggest that the NNK-initiated mouse lung tumorigenesis pathway, which involves the specific mutation of the Ki-ras oncogene, is altered to a predominantly non-ras mechanism when these tumors are promoted by BHT in the diet.

Adenoma↗

PubMed1994

Transplacental carcinogenicity of low doses of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone administered subcutaneously or intratracheally to hamsters.

Our previous studies have demonstrated that doses of 300-50 mg/kg 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) injected subcutaneously into pregnant hamsters cause a 44% incidence of respiratory-tract tumors in the offspring. In this study, we have extended the assay of the carcinogenic potency of NNK to doses ranging from 50 mg to 0.05 mg/kg body weight and to a second route of administration, intratracheal instillation, which is more relevant to inhalation of tobacco smoke by pregnant women. Among the offspring whose mothers had been injected subcutaneously with NNK (20-1 mg/kg), the total tumor incidence (57.2%-16.7%) decreased with decreasing dose levels. After intratracheal instillation of 50-0.05 mg/kg NNK the overall incidence varied from 28.6% to 50% but no dose response was observed. The main target organs were the adrenal glands (Phaechromocytomas) and nasal cavities (adenocarcinomas of the olfactory region). A low incidence of ductular adenomas of the pancreas was observed with low doses of NNK instilled intratracheally. These results demonstrate that NNK, at doses that are comparable to the cumulative exposure during a 9-month period in women, is a potent transplacental carcinogen in hamsters.

Animals↗

PubMed1994

DNA single-strand breaks and toxicity induced by 4-(methyl-nitrosamino)-1-(3- pyridyl)-1-butanone or N-nitrosodimethylamine in hamster and rat liver.

Syrian golden hamsters and F344 rats display contrasting susceptibilities to hepatocarcinogenesis induced by the tobacco-specific nitrosamine 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosodimethylamine (NDMA). In this study, the time courses of DNA single-strand breaks (SSB) and toxicity induced by NNK and NDMA in hamster and rat liver were compared. DNA SSB reached a maximum 12 h after carcinogen treatment, partially correlating with previous reports on time courses of DNA methylation. The persistence of DNA SSB up to 2-3 weeks after NNK or NDMA treatment reflects a deficient repair of some DNA lesions. No significant species differences in the kinetics of DNA SSB induction and repair were observed following NNK or NDMA (0.39 mmol/kg) treatment. However, NNK induced slightly more DNA SSB than NDMA in both species. This could reflect the formation of intermediates with more DNA-damaging capacity or inhibiting DNA processes. A significant hepatotoxic effect of NNK, evaluated by plasma markers of liver injury, was observed in rats and hamsters 12-24 h post-treatment. In contrast, NDMA induced earlier (< 12 h) enzyme elevations. Maximum hepatotoxic effects were observed 24 h (NNK-treated hamsters and rats, NDMA-treated rats) or 2 weeks (NDMA-treated hamsters) after carcinogen administration. Three weeks after treatment, hepatotoxicity of NNK and NDMA was still detected in hamsters, but not in rats. These results suggest that the toxic effects of NNK and NDMA initiate a regenerative process that occurs faster in rat than in hamster liver. Since hepatocarcinogenesis occurs in NNK- but not in NDMA-treated rats, promutagenic lesions generated from NNK might be fixed preferentially during cell proliferation.

Alanine Transaminase↗

PubMed1993

Effects of age and ethanol on DNA single-strand breaks and toxicity induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone or n-nitrosodimethylamine in hamster and rat liver.

The effects of age and ethanol exposure on liver DNA single-strand breaks (SSB) and liver cell injury induced in hamsters and rats by a single equimolar dose (0.39 mmol/kg) of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) or N-nitrosodimethylamine (NDMA) were investigated. NNK induced more DNA SSB (by 10-50%) than NDMA in the liver of adult hamsters and rats, but similar differences were not observed in newborn animals. Nitrosamine-induced hepatic DNA damages was compared in newborn and adult animals. While newborn hamsters were less sensitive to NNK-induced DNA damage than adult hamsters, newborn rats were more sensitive to NDMA-induced DNA damage than adult rats. In utero ethanol exposure did not alter significantly the induction of hepatic DNA SSB by NNK or NDMA compared to newborn hamsters and rats. Interestingly, species differences in the extents of NNK-induced hepatic DNA SSB and toxicity were observed in ethanol-consuming adult hamsters and rats. Ethanol treatment of hamsters caused a significant reduction (by 35%) of the frequency of hepatic DNA SSB and a 3.5-fold enhancement of hepatotoxicity induced by NNK.

Age Factors↗

PubMed1993

Transplacental induction of pancreas tumors in hamsters by ethanol and the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

Epidemiological studies suggest that smoking during pregnancy and passive exposure of children to cigarette smoke may increase the cancer risk in children and young adults. We have previously shown that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is an active transplacental carcinogen in Syrian golden hamsters when administered by s.c. injections to pregnant females. The majority of tumors in the offspring developed in the respiratory tract. Since in smoking women the respiratory tract is the portal of entry of tobacco-related carcinogens, including NNK, we have investigated the transplacental effects of NNK given by intratracheal instillation to pregnant hamsters. The modulating effect of ethanol on the transplacental carcinogenicity of NNK in this system was also investigated because smoking and consumption of alcoholic beverages are observed in pregnant women. Our data show that exposure to NNK via the maternal respiratory tract causes a similar tumor incidence in the offspring as the s.c. route of administration. Ethanol greatly enhanced the carcinogenic response to NNK, and up to 60% of the offspring exposed in utero to ethanol and NNK developed tumors of the exocrine pancreas.

Animals↗

PubMed1993

Pulmonary carcinogenesis and its prevention by dietary polyphenolic compounds.

The aims of this study were to define the cumulative exposure of Canadian smokers to NNK and to characterize the efficacy of ellagic acid to inhibit lung tumorigenesis induced by NNK. The sales-weighted average of NNK deliveries from Canadian cigarettes was 73.2 ng/cigarette. NNK deliveries were highly correlated to declared tar values and were linear with puff volumes between 20 and 50 ml. Ellagic acid inhibited lung tumorigenesis induced by NNK in A/J mice. This inhibition was related to the logarithm of the dose of ellagic acid added to the diet. The biodistribution of ellagic acid was studied in mice gavaged with ellagic acid. Pulmonary levels of ellagic acid were directly proportional to the dose of ellagic acid between 0.2 and 2.0 mmol/kg b.w.

Adenoma↗

PubMed1993

Metabolism and macromolecular interaction of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in cultured explants and epithelial cells of human buccal mucosa.

Metabolism and macromolecular interaction of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were studied in human buccal mucosa in vitro. Microautoradiographic analysis of [5-3H]NNK-exposed explant cultures demonstrated a uniform distribution of bound radioactivity in the mucosal epithelium, without significant binding in the underlying connective tissue. The metabolism of [5-3H]NNK at concentrations of both 6 and 100 microM resulted in seven identified metabolites in both explant and epithelial cell cultures. Formation of 4-(methylnitrosamino)-1-(3-pyridyl)butan-1-ol by carbonyl reduction of NNK accounted for almost 95% of the total metabolism, whereas the proportions of other metabolites obtained by alpha-carbon hydroxylation and pyridine N-oxidation reactions varied from undetectable levels to approximately 2% in both experimental systems. A positive correlation between concentration and the metabolic route associated with the formation of DNA methylating intermediates (alpha-hydroxylation at the N-methylene carbon) was found, i.e. when the concentration of NNK was raised from 6 to 100 microM, keto-acid formation which in part reflects DNA methylation was increased preferentially over ketoalcohol production, an index of DNA pyridyloxobutylation. Both the total rate of NNK metabolism and the amount of protein adducts were higher in cells from primary cultures up to the third passage than in explants cultured for 1 day. Between 10(-9) to 10(-4) M, neither NNK nor its precursor alkaloid nicotine affected the colony forming efficiency of normal and tumorous buccal epithelial cells, although at 10(-3) M each agent inhibited this function. Taken together, the results demonstrate the capability of human buccal mucosal epithelium to metabolize NNK by three major pathways, including those involved in the formation of adducts with cellular macromolecules.

Autoradiography↗