NNK Metabolism Research Articles

Identification of Formaldehyde-Induced DNA-RNA Cross-Links in the A/J Mouse Lung Tumorigenesis Model.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung carcinogen present in tobacco products, and exposure to it is likely one of the factors contributing to the development of lung cancer in cigarette smokers. To exert its carcinogenic effects, NNK must be metabolically activated into highly reactive species generating a wide spectrum of DNA damage. We have identified a new class of DNA adducts, DNA-RNA cross-links found for the first time in NNK-treated mice lung DNA using our improved high-resolution accurate mass segmented full scan data-dependent neutral loss MS3 screening strategy. The levels of these DNA-RNA cross-links were found to be significantly higher in NNK-treated mice compared to the corresponding controls, which is consistent with higher levels of formaldehyde due to NNK metabolism as compared to endogenous levels. We hypothesize that this DNA-RNA cross-linking occurs through reaction with NNK-generated formaldehyde and speculate that this phenomenon has broad implications for NNK-induced carcinogenesis. The structures of these cross-links were characterized using high-resolution LC-MS2 and LC-MS3 accurate mass spectral analysis and comparison to a newly synthesized standard. Taken together, our data demonstrate a previously unknown link between DNA-RNA cross-link adducts and NNK and provide a unique opportunity to further investigate how these novel NNK-derived DNA-RNA cross-links contribute to carcinogenesis in the future.

Metabolism and DNA Adduct Formation of Tobacco-Specific N-Nitrosamines.

The tobacco-specific N-nitrosamines 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N′-nitrosonornicotine (NNN) always occur together and exclusively in tobacco products or in environments contaminated by tobacco smoke. They have been classified as “carcinogenic to humans” by the International Agency for Research on Cancer. In 1998, we published a review of the biochemistry, biology and carcinogenicity of tobacco-specific nitrosamines. Over the past 20 years, considerable progress has been made in our understanding of the mechanisms of metabolism and DNA adduct formation by these two important carcinogens, along with progress on their carcinogenicity and mutagenicity. In this review, we aim to provide an update on the carcinogenicity and mechanisms of the metabolism and DNA interactions of NNK and NNN.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced Histone Acetylation via α7nAChR-Mediated PI3K/Akt Activation and Its Impact on γ-H2AX Generation.

A typical tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known as a strong carcinogen. We previously reported that metabolized NNK induced histone H2AX phosphorylation (γ-H2AX), a DNA damage-induced histone modification. In this study, we found that NNK globally acetylated histone H3, which affected γ-H2AX generation. Human lung adenocarcinoma A549 was treated with several doses of NNK. NNK induced dose-dependent global histone H3 acetylation (Ac-H3), at 2 to 12 h after the treatment, independent of the cell cycle. The Ac-H3 pattern was not affected by CYP2A13 overexpression unlike γ-H2AX, indicating no requirement of NNK metabolism to induce Ac-H3. Immunofluorescence staining of Ac-H3 was uniform throughout the nucleus, whereas γ-H2AX was formed as foci and did not coincide with Ac-H3. Nicotinic receptor antagonist methyllycaconitine inhibited Ac-H3 and also γ-H2AX. Phosphoinositide-3-kinase (PI3K)/Akt inhibitors, LY294002, wortmannin, and GSK690693, also suppressed both Ac-H3 and γ-H2AX, whereas KU-55933, an inhibitor of ataxia telangiectasia mutated (ATM) upstream of γ-H2AX, inhibited γ-H2AX but not Ac-H3. These results suggested that binding of NNK to the nicotinic acetylcholine receptor (α7nAChR) activated the PI3K/Akt pathway, resulting in Ac-H3. The activated pathway leading to Ac-H3 enhanced γ-H2AX, suggesting that NNK-induced DNA damage is impacted by the α7nAChR-mediated signal transduction pathway.

Toxicokinetic and Genotoxicity Study of NNK in Male Sprague Dawley Rats Following Nose-Only Inhalation Exposure, Intraperitoneal Injection, and Oral Gavage.

The tobacco-specific nitrosamine NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone] is found in tobacco products and tobacco smoke. NNK is a potent genotoxin and human lung carcinogen; however, there are limited inhalation data for the toxicokinetics (TK) and genotoxicity of NNK in vivo. In the present study, a single dose of 5 × 10-5, 5 × 10-3, 0.1, or 50 mg/kg body weight (BW) of NNK, 75% propylene glycol (vehicle control), or air (sham control) was administered to male Sprague-Dawley (SD) rats (9-10 weeks age) via nose-only inhalation (INH) exposure for 1 h. For comparison, the same doses of NNK were administered to male SD rats via intraperitoneal injection (IP) and oral gavage (PO). Plasma, urine, and tissue specimens were collected at designated time points and analyzed for levels of NNK and its major metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and tissue levels of DNA adduct O6-methylguanine by LC/MS/MS. TK data analysis was performed using a non-linear regression program. For the genotoxicity subgroup, tissues were collected at 3 h post-dosing for comet assay analysis. Overall, the TK data indicated that NNK was rapidly absorbed and metabolized extensively to NNAL after NNK administration via the three routes. The IP route had the greatest systemic exposure to NNK. NNK metabolism to NNAL appeared to be more efficient via INH than IP or PO. NNK induced significant increases in DNA damage in multiple tissues via the three routes. The results of this study provide new information and understanding of the TK and genotoxicity of NNK.

The Impact of One-week Dietary Supplementation with Kava on Biomarkers of Tobacco Use and Nitrosamine-based Carcinogenesis Risk among Active Smokers.

Tobacco smoking is the primary risk factor for lung cancer, driven by the addictive nature of nicotine and the indisputable carcinogenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) as well as other compounds. The integration of lung cancer chemoprevention with smoking cessation is one potential approach to reduce this risk and mitigate lung cancer mortality. Experimental data from our group suggest that kava, commonly consumed in the South Pacific Islands as a beverage to promote relaxation, may reduce lung cancer risk by enhancing NNK detoxification and reducing NNK-derived DNA damage. Building upon these observations, we conducted a pilot clinical trial to evaluate the effects of a 7-day course of kava on NNK metabolism in active smokers. The primary objective was to compare urinary total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL plus its glucuronides, major metabolites of NNK) before and after kava administration as an indicator of NNK detoxification. Secondary objectives included determining kava's safety, its effects on DNA damage, tobacco use, and cortisol (a biomarker of stress). Kava increased urinary excretion of total NNAL and reduced urinary 3-methyladenine in participants, suggestive of its ability to reduce the carcinogenicity of NNK. Kava also reduced urinary total nicotine equivalents, indicative of its potential to facilitate tobacco cessation. Plasma cortisol and urinary total cortisol equivalents were reduced upon kava use, which may contribute to reductions in tobacco use. These results demonstrate the potential of kava intake to reduce lung cancer risk among smokers.

ECL Array and LC-MS Studies of Nitrosamine-Metabolite-Mediated DNA Oxidation

Metabolites of nitrosamines in cigarette smoke and E-cigarette (E-cig) vapor cause DNA damage that has been projected to lead to cancers in “genotoxic” pathways. DNA oxidation can also be mediated by reactive oxygen species (ROS) generated from redox cycling reactions involving nitrosamine metabolites, metal ions (Cu2+) and NADPH. DNA adducts of tobacco nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosonornicotine (NNN) are well known tobacco-related biomarkers, but only a few reports implicate NNK and NNN in DNA oxidation. We used electrochemiluminescent (ECL) arrays and LC-MS to explore pathways of DNA oxidation driven by metabolites of NNK and NNN facilitated by Cu2+ and NADPH which are present in significant amounts in lung tissue. We used a 3-D printed microfluidic array that first makes reactive metabolites of test compounds using metabolic enzymes (mostly cyt P450s) and DNA in thin films. The assay measurement step detects DNA oxidation selectively by ECL using a new ECL dye, [Os(tpy-benz-COOH)2]2+ that is highly sensitive for primary DNA oxidation product 8-oxodG, which serves as a co-reactant in the ECL generation. Array results reveal that NNK and NNN oxidize DNA at relatively high rates. DNA/metabolic enzyme films on magnetic beads were utilized with nitrosamines, Cu2+, and NADPH for measurement of 8-oxodG in oxidized DNA by LC-MS/MS and specific ROS involved were identified by ROS-specific assays, that showed that nitrosamines metabolism in the presence of Cu2+ and NADPH produces hydroxyl radical (•OH), singlet oxygen (1O2), and hydrogen peroxide (H2O2). Possible reactive metabolites of NNK and NNN involved in ROS generation were identified by LC-MS/MS. Results provide insight into mechanistic pathways of cyt P450-mediated metabolism of NNK and NNN in ROS production and oxidation of DNA.

Metabolism of NNK in Japanese Americans

Metabolism of NNK in Japanese Americans

Betel quid containing safrole enhances metabolic activation of tobacco specific 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Cigarette smoking (CS) and betel quid (BQ) chewing are two known risk factors that have synergistic potential for the enhancing the development of oral squamous cell carcinoma (OSCC) in Taiwan. Most mutagens and carcinogens are metabolically activated by cytochrome P450 (CYP450) to exert their mutagenicity or carcinogenicity. Previous studies have shown that metabolic activation of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), by CYP2A6 activity determines NNK-induced carcinogenesis. In addition, safrole affects cytochrome P450 activity in rodents. However, the effect of BQ safrole on the metabolism of tobacco-specific NNK and its carcinogenicity remains elusive. This study demonstrates that safrole (1 mg/kg/d) induced CYP2A6 activity, reduced urinary 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) levels, and increased NNK-induced DNA damage, including N7-methylguanine, 8-OH-deoxyguanosine and DNA strand breaks in a Syrian golden hamster model. Furthermore, altered NNK metabolism and increased NNK-induced DNA damage were also observed in healthy subjects with CS and BQ chewing histories compared to healthy subjects with CS histories. In conclusion, BQ containing safrole induced tobacco-specific NNK metabolic activation, resulting in higher NNK-induced genotoxicity. This study provides valuable insight into the synergistic mechanisms of CS- and BQ-induced OSCC.

Cytochrome P450 Enzyme Contributions to the N‐oxide Detoxification Pathway of Tobacco‐Specific Nitrosamines; a Possible Role in Tobacco‐Related Cancer Risk

Tobacco‐specific nitrosamines (TSNAs) including 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) are among the most potent carcinogens found in tobacco products. The major mode of metabolism of NNK is by reduction to form 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL), which, like other TSNAs including N′‐nitrosonornicotine (NNN), N′‐nitrosoanabasine (NAB), and N′‐nitrosoanabatine (NAT), is detoxified primarily by UDP‐glucuronosyltransferases (UGTs) to their glucuronide products, but also by N‐oxidation of the common pyridine ring. TSNA‐N‐oxides were identified previously in the urine of rodents exposed to TSNAs, and NNAL‐N‐oxide was found in the urine of smokers. The enzymes responsible for this conversion have not yet been determined. To identify enzymes that catalyze TSNA‐N‐oxide formation, we used specific inhibitors (furafylline, tranylcypromine, clopidrogrel, montelukast, sulfaphenazole, quinidine, chlomethiazole, and ketoconazole) of the major hepatic cytochrome P450 (CYP) enzymes including CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 in oxidation reactions using pooled human liver microsomes. Inhibition of NNK‐N‐oxide and NNAL‐N‐oxide formation was observed when using inhibitors of CYPs 2A6, 2C8, 2C19, 2E1 and 3A4; no detectable levels of NNN‐, NAT‐ or NAB‐N‐oxide formation were observed in human liver microsomes. To confirm results from these inhibition studies, NNK‐N‐oxide and NNAL‐N‐oxide formation were examined using microsomal fractions from CYP over‐expressing HEK293 cell lines. CYPs 2A13, 2C8 and 2E1 exhibited the highest oxidation activity against NNK, with Vmax/KM values of 675, 610 and 559 nL•min−1•mg−1, respectively, and against NNAL, with Vmax/KM values of 105, 67 and 86 nL•min−1•mg−1, respectively. These data suggest that several cytochrome P450 enzymes play an important role in the in situ detoxification of NNK and NNAL and that inter‐individual variability in the activity of these enzymes could potentially be important in TSNA‐induced cancer risk assessment.Support or Funding InformationThis work is supported by grants from NIH, National Institutes of Environmental Health Sciences (grant R01‐ES025460; to P. Lazarus), the Fulbright‐Garcia Robles Program (to Y. Perez‐Paramo), and the Health Sciences and Services Authority of Spokane, Washington (grant WSU002292 to College of Pharmacy and Pharmaceutical Sciences, Washington State University)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Role of Placental Carbonyl Reducing Enzymes in Biotransformation of Bupropion and 4-methylnitrosamino-1-(3-pyridyl)-1-butanone.

Bupropion (BUP) has a potential to be an effective pharmacotherapy for smoking cessation during pregnancy. Smoking during pregnancy stimulates placental carbonyl reductases that catalyze the biotransformation of BUP. 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen of cigarette smoke. Carbonyl reduction of NNK into 4- methylnitrosamino-1-(3-pyridyl)-1-butanol (NNAL) constitutes a major step in NNK detoxification. Thus, placentas of pregnant smokers on BUP therapy can become a site of drug-drug interaction. Therefore, we investigated the effect of continuous exposure to BUP and cigarette smoke on the activity of placental carbonyl reductases in the formation of NNAL from NNK. The reductive metabolism of NNK was determined using microsomal and cytosolic subcellular fractions of placentas obtained from non-smoking women treated with BUP for depression, and women not exposed to BUP: non-smokers (control) and smokers. The effect of BUP and its metabolites on the reductive metabolism of NNK was investigated using subcellular fractions of control placentas. The formation of NNAL from NNK by placental cytosolic fractions of heavy smokers (≥20 cigarettes per day) was lower than that of control (12.1±3.5 nmol.mgP-1 vs 16.5±6.0 nmol.mgP-1, P<0.05). While being exposed to BUP, the activity of placental carbonyl reductases remained unaffected, the formation of NNAL in the placental cytosolic fraction decreased only in the presence of high concentrations of BUP metabolites. Smoking during pregnancy decreases the detoxifying capacity of soluble carbonyl reductases towards NNK. Given the experimental conditions, exposure to BUP and its metabolites should not impede the reductive metabolism of NNK by placenta in vivo.

Physical Binding of a Tobacco-Specific Carcinogen (NNK) Metabolite to the Human TP53 Gene with Ramifications for DNA Damage and Mutations

The most prevalent and carcinogenic of the tobacco-specific nitrosamines is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNK is a potent carcinogen that causes numerous types of cancers, most commonly lung adenomas and adenocarcinomas. The diazonium ion formed through the enzymatic metabolism of NNK by cytochrome P450s, can bind chemically to DNA (DNA damage). These adducts, if not repaired, can cause mutations that lead to tumorigenesis. We do not have a complete understanding of the binding of the diazonium ion to DNA which is important for future preventative strategies of NNK-associated cancers. The focus of this research is to computationally model and understand the physical interactions between the NNK diazonium ion and exon 5 of the human TP53 gene. We used a Lamarckian genetic algorithm to minimize a physics-based free energy function that allows us to estimate the free energy differences between the NNK diazonium ion along with TP53 in an unbound state and when they are physically bound. The free energy function employs pair-wise terms that evaluate dispersion, Pauli repulsions, hydrogen bonding, electrostatics and desolvation, along with a term for the lost conformational energy when the molecules bind. We will present the most probable NNK diazonium ion-TP53 physical binding sites and discuss how DNA damage (pyridyloxobutylated adducts in particular) may be occurring when it is exposed to this tobacco-specific carcinogen.

P1.01-012 Kava Effects on the Metabolism of Tobacco-Specific Carcinogen 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone (NNK) in Humans

Kava is extracted from the roots of piper methysticum and is consumed by South Pacific Islanders as a relaxing beverage. Epidemiologic evidence points to a protective effect of kava against tobacco-induced lung cancer. NNK is a potent tobacco-specific carcinogen indisputably linked to lung cancer formation. Kava reduced NNK-induced lung adenoma formation in the A/J mouse model. Data also suggest that enhanced NNAL detoxification may be a potential mechanism by which kava exerts a chemopreventive effect. In humans, urinary NNAL is a validated biomarker of NNK uptake. We conducted a clinical trial in smokers to assess the effect of kava on NNK metabolism. The primary objective was to compare urinary total NNAL before and after kava administration. Secondary objectives included comparing the NNAL-gluc/NNAL-free ratio, determining the safety of kava, and quantifying O6-methylguanine adducts. The hypothesis was that kava administration would result in increased levels of NNAL in the urine (and increased NNAL-gluc/NNAL-free ratio), reflecting increased elimination and/or increased detoxification of NNK. Additionally, we hypothesized that kava could reduce O6-methylguanine adducts. We conducted a single-arm, open-label clinical trial in adult healthy smokers, in which subjects took a commercial kava supplement three times daily for seven days. Twenty-four hour urine collections were collected at baseline, days 4-5, and days 6-7 of the kava intervention for NNAL quantification. Blood samples were collected at baseline, day 4, and day 7 of the kava intervention for safety monitoring and for DNA adduct analysis. Subjects also completed a detailed tobacco questionnaire, food diary, smoking diary, and cigarette evaluation scale (CES) questionnaire. To date, 17 subjects (goal = 18) have completed the study. The results and statistics are being finalized. Short-term kava administration was safe with no evidence of hepatotoxicity. Subjects experienced less of the reinforcing effects of smoking after short-term kava administration as determined by the CES scores. The total CES score decreased on average by 4.47, from 45.53 to 41.06 (p=0.053, 95% CI -0.06-9.01). Notably, the smoking “satisfaction” scores decreased by 0.607 (p=0.024, 95% CI 0.09-1.12). This is the first study investigating the effect of kava on NNK metabolism in humans and is the first step to gain a more sophisticated mechanistic understanding of kava’s role in potentially modulating tobacco-related lung cancer risk. Short-term kava administration is safe in healthy adult smokers. Kava holds potential as a possible chemopreventive agent for smokers or tobacco cessation aide.

In vitro metabolism of N′-Nitrosonornicotine catalyzed by cytochrome P450 2A13 and its inhibition by nicotine, N′-Nitrosoanatabine and N′-Nitrosoanabasine

N′-Nitrosonornicotine (NNN) is considered to be one of the most carcinogenic compounds of the four conventionally measured tobacco-specific N-nitrosamines (TSNAs). In order to evaluate the significance of metabolic activation for the carcinogenic potential of NNN, its catalysis by different phase I enzymes and its interaction with nicotine and nicotine-derived TSNAs need to be investigated. Using an in vitro model system, NNN was found to interact with various cytochrome P450 enzymes, predominantly CYP2A13. Mass-spectrometric analysis confirmed the presence of various predicted NNN metabolites, including 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and 4-hydroxy-4-(3-pyridyl)-butyric acid (hydroxy acid) but little amount of 4-oxo-4-(3-pyridyl) butanal (OPB), which was somewhat different from in vitro NNK metabolism. Addition of nicotine, N′-Nitrosoanatabine (NAT), N′-Nitrosoanabasine (NAB) resulted in a competitive inhibition for NNN metabolism. The inhibition constant Ki value was calculated as 0.98 μM (nicotine), 1.37 μM (NAT), 0.71 μM (NAB) for HPB formation, 1.35 μM (nicotine), 1.35 μM (NAT), 1.01 μM (NAB) for hydroxy acid formation and 8.40 μM (nicotine), 3.40 μM (NAT), 3.04 μM (NAB) for OPB formation, respectively. These results implied that CYP2A13 is the most efficient enzyme to metabolize NNN in vitro and structurally similar tobacco constitutes including nicotine, NAT and NAB influence the metabolic activation of NNN, which may further interfere in its carcinogenicity.

Clinical Trial of 2-Phenethyl Isothiocyanate as an Inhibitor of Metabolic Activation of a Tobacco-Specific Lung Carcinogen in Cigarette Smokers.

2-Phenethyl isothiocyanate (PEITC), a natural product found as a conjugate in watercress and other cruciferous vegetables, is an inhibitor of the metabolic activation and lung carcinogenicity of the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in F344 rats and A/J mice. We carried out a clinical trial to determine whether PEITC also inhibits the metabolic activation of NNK in smokers. Cigarette smokers were recruited and asked to smoke cigarettes containing deuterium-labeled [pyridine-D4]NNK for an acclimation period of at least 1 week. Then subjects were randomly assigned to one of two arms: PEITC followed by placebo, or placebo followed by PEITC. During the 1-week treatment period, each subject took PEITC (10 mg in 1 mL of olive oil, 4 times per day). There was a 1-week washout period between the PEITC and placebo periods. The NNK metabolic activation ratio [pyridine-D4]hydroxy acid/total [pyridine-D4]NNAL was measured in urine samples to test the hypothesis that PEITC treatment modified NNK metabolism. Eighty-two smokers completed the study and were included in the analysis. Overall, the NNK metabolic activation ratio was reduced by 7.7% with PEITC treatment (P = 0.023). The results of this trial, while modest in effect size, provide a basis for further investigation of PEITC as an inhibitor of lung carcinogenesis by NNK in smokers. Cancer Prev Res; 9(5); 396-405. ©2016 AACR.

The inhibition of cytochrome P450 2A13-catalyzed NNK metabolism by NAT, NAB and nicotine.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is considered to be the most carcinogenic of the four tobacco-specific nitrosamines (TSNAs) and it needs to be metabolically activated to exert its carcinogenic effect on humans. For the simultaneous intake of NNK and other compounds with similar molecular structures in the context of tobacco smoke, whether (R,S)-N-nitrosoanatabine (NAT), (R,S)-N-nitrosoanabasine (NAB) and nicotine contribute to the inhibitory potency of the cytochrome P450 (CYP) enzyme-catalyzed NNK metabolism or not needs to be investigated. In the in vitro study, 4-oxo-4-(3-pyridyl) butanal (OPB), 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and 4-oxo-4-(3-pyridyl) butanoic acid (OPBA) were established as the products of the CYP2A13-catalyzed NNK metabolism and the kinetic parameters were calculated from the Michaelis-Menten equation. Addition of NAT, NAB or nicotine resulted in a competitive inhibition for the NNK metabolism catalyzed by CYP2A13. The inhibition constant Ki values were calculated to be 0.21 μM (NAT), 0.23 μM (NAB) and 8.51 μM (nicotine) for OPB formation; 0.71 μM (NAT), 0.87 μM (NAB) and 25.01 μM (nicotine) for HPB formation and 0.36 μM (NAT), 0.50 μM (NAB) and 6.57 μM (nicotine) for OPBA formation, respectively. In addition, the study of the transformation of the three metabolites revealed OPB was not only an end product but also an intermediate product of the CYP2A13-catalyzed NNK metabolism. These results suggest that structurally similar tobacco constituents with weak or no carcinogenicity influence the metabolic activation of NNK, which interferes with its carcinogenicity to some extent.

Exposure and Metabolic Activation Biomarkers of Carcinogenic Tobacco-Specific Nitrosamines.

Lung cancer is the leading cause of cancer death in the world, and cigarette smoking is its main cause. Oral cavity cancer is another debilitating and often fatal cancer closely linked to tobacco product use. While great strides have been made in decreasing tobacco use in the United States and some other countries, there are still an estimated 1 billion men and 250 million women in the world who are cigarette smokers and there are hundreds of millions of smokeless tobacco users, all at risk for cancer. Worldwide, lung cancer kills about three people per minute. This Account focuses on metabolites and biomarkers of two powerful tobacco-specific nitrosamine carcinogens, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN), considered to be among the main causes of lung cancer and oral cavity cancer in people who use tobacco products. Three properties of NNK and NNN are critical for successful biomarker studies: they are present in all tobacco products, they are tobacco-specific and are not found in any other product, and they are strong carcinogens. NNK and NNN are converted in humans to urinary metabolites that can be quantified by mass spectrometry as biomarkers of exposure to these carcinogens. They are also metabolized to diazonium ions and related electrophiles that react with DNA to form addition products that can be detected and quantified by mass spectrometry. These urinary metabolites and DNA addition products can serve as biomarkers of exposure and metabolic activation, respectively. The biomarkers of exposure, in particular the urinary NNK metabolites 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides, have been extensively applied to document tobacco-specific lung carcinogen uptake in smokers and nonsmokers exposed to secondhand tobacco smoke. Highly sensitive mass spectrometric methods have been developed for quantitative analysis of these NNK metabolites as well as metabolites of NNN in human urine, blood, and toenails. Urinary and serum NNAL have been related to lung cancer risk, and urinary NNN has been related to esophageal cancer risk in prospective epidemiology studies. These results are consistent with carcinogenicity studies of NNK, NNAL, and NNN in rats, which show that NNK and NNAL induce mainly lung tumors, while NNN causes tumors of the esophagus and oral cavity. Biomarkers of metabolic activation of NNK and NNN applied in human studies include the metabolism of deuterium labeled substrates to distinguish NNK and NNN metabolism from that of nicotine and the determination of DNA and hemoglobin adducts in tissues, blood, and oral cells from people exposed to tobacco products. As these methods are continually improved in parallel with the ever increasing sensitivity and selectivity of mass spectrometers, development of a comprehensive biomarker panel for identifying tobacco users at high risk for cancer appears to be a realistic goal. Targeting high risk individuals for smoking cessation and cancer surveillance can potentially decrease the risk of developing fatal cancers.

The role of carbonyl reductases in biotransformation of bupropion and 4-methylnitrozamino-1-(3-pyridyl)-1-butanone by human placenta

s / Drug and Alcohol Dependence 156 (2015) e102–e182 e161 The role of carbonyl reductases in biotransformation of bupropion and 4-methylnitrozamino-1-(3-pyridyl)-1-butanone by human placenta Tatiana Nanovskaya1, Valentina M. Fokina1,2, X. Wang1, Cheryl Oncken3, Mahmoud S. Ahmed1, Gary Hankins1 1 OBG the reaction is catalyzed primarily by 11 hydroxisteroid dehydrogenase (11 -HSD) and aldoketoreductases. Maternal cigarette smoking has been associated with prenatal exposure to NNK, which is the most abundant and potent carcinogen of cigarette smoke. One of the metabolic pathways of NNK is carbonyl reduction to 4-methylnitrosamino-1-(3-pyridyl)1-butanol (NNAL) that initiates NNK detoxification. The goal of the current investigation is to determine placental metabolism of NNK and to identify placental enzymes responsible for its reduction. Methods: Term placentas were collected from women who smoked during pregnancy and from non-smokers. NNK metabolism was determined in vitro using placental microsomal and cytosolic subcellular fractions; the formation of NNAL was quantified by HPLC-UV. Results: The apparent Km and Vmax values for the reaction in placental subcellular fractions were determined. The formation of NNAL in placentas of heavy smokers was lower than in placentas of non-smokers: 12.1±3.5 vs. 17±6.3nmolmgP−1 for cytosolic fraction (p methamphetamine>4-MePPP>4-MEC. Conclusions: The current findings demonstrated that three second-generation synthetic cathinones functioned as reinforcers in rats, providing some justification for permanent scheduling of these drugs by regulatory agencies. Future research in our laboratory will assess the reinforcing effectiveness of these three compounds with a behavioral economics approach. Financial support: This research was supported by the UMMC Drug Abuse Development Fund and R01 DA12970 to BB. http://dx.doi.org/10.1016/j.drugalcdep.2015.07.439 Serotonin 5-HT2C receptors in the ventral subiculum regulate cocaine-evoked hyperactivity in rats Harshini Neelakantan1, Sonja J. Stutz1, Marcy J. Bubar1, Robert M. Sears3, Ralph J. DiLeone3, Kathryn A. Cunningham1,2 1 Center for Addiction Research, University of Texas Medical Branch, Galveston, TX, United States 2 Department of Pharmacy, University of Texas Medical Branch, Galveston, TX, United States 3 Department of Psychiatry, Yale University, New Haven, CT, United States Aims: The ventral subiculum (vSUB) interconnects with limbiccorticostriatal circuit which regulates the behavioral effects of cocaine. Serotonin neurons innervate the vSUB, however, little is known about its role or the 5-HT receptors that are functionally relevant in this region. We investigated the vSUB localization of the 5-HT2C receptor (5-HT2CR) and its role in the control of cocaineevoked hyperactivity. Methods: The expression of the 5-HT2CR and co-localization with GAD 67 (marker for GABA) in the vSUB were evaluated using immunohistochemical analyses in rats (n=3).We employed virally mediated genetic knockdown strategy to test the hypothesis that knockdown of the 5-HT2CR in the vSUB of rats (n=5) will modulate cocaine-evoked hyperactivity. Motor activity was assessed after saline or cocaine (10–20mg/kg) in modified open-field chambers and analyzed using repeated measures two-way ANOVA. Results:Dense immunoreactivity (IR) for 5-HT2CRwasobserved throughout the vSUB. Only a small proportion of 5-HT2CR-IR was co-localized with GAD 67-IR that was restricted to the distal end

Self-administration of second-generation synthetic cathinones in rats

s / Drug and Alcohol Dependence 156 (2015) e102–e182 e161 The role of carbonyl reductases in biotransformation of bupropion and 4-methylnitrozamino-1-(3-pyridyl)-1-butanone by human placenta Tatiana Nanovskaya1, Valentina M. Fokina1,2, X. Wang1, Cheryl Oncken3, Mahmoud S. Ahmed1, Gary Hankins1 1 OBG the reaction is catalyzed primarily by 11 hydroxisteroid dehydrogenase (11 -HSD) and aldoketoreductases. Maternal cigarette smoking has been associated with prenatal exposure to NNK, which is the most abundant and potent carcinogen of cigarette smoke. One of the metabolic pathways of NNK is carbonyl reduction to 4-methylnitrosamino-1-(3-pyridyl)1-butanol (NNAL) that initiates NNK detoxification. The goal of the current investigation is to determine placental metabolism of NNK and to identify placental enzymes responsible for its reduction. Methods: Term placentas were collected from women who smoked during pregnancy and from non-smokers. NNK metabolism was determined in vitro using placental microsomal and cytosolic subcellular fractions; the formation of NNAL was quantified by HPLC-UV. Results: The apparent Km and Vmax values for the reaction in placental subcellular fractions were determined. The formation of NNAL in placentas of heavy smokers was lower than in placentas of non-smokers: 12.1±3.5 vs. 17±6.3nmolmgP−1 for cytosolic fraction (p methamphetamine>4-MePPP>4-MEC. Conclusions: The current findings demonstrated that three second-generation synthetic cathinones functioned as reinforcers in rats, providing some justification for permanent scheduling of these drugs by regulatory agencies. Future research in our laboratory will assess the reinforcing effectiveness of these three compounds with a behavioral economics approach. Financial support: This research was supported by the UMMC Drug Abuse Development Fund and R01 DA12970 to BB. http://dx.doi.org/10.1016/j.drugalcdep.2015.07.439 Serotonin 5-HT2C receptors in the ventral subiculum regulate cocaine-evoked hyperactivity in rats Harshini Neelakantan1, Sonja J. Stutz1, Marcy J. Bubar1, Robert M. Sears3, Ralph J. DiLeone3, Kathryn A. Cunningham1,2 1 Center for Addiction Research, University of Texas Medical Branch, Galveston, TX, United States 2 Department of Pharmacy, University of Texas Medical Branch, Galveston, TX, United States 3 Department of Psychiatry, Yale University, New Haven, CT, United States Aims: The ventral subiculum (vSUB) interconnects with limbiccorticostriatal circuit which regulates the behavioral effects of cocaine. Serotonin neurons innervate the vSUB, however, little is known about its role or the 5-HT receptors that are functionally relevant in this region. We investigated the vSUB localization of the 5-HT2C receptor (5-HT2CR) and its role in the control of cocaineevoked hyperactivity. Methods: The expression of the 5-HT2CR and co-localization with GAD 67 (marker for GABA) in the vSUB were evaluated using immunohistochemical analyses in rats (n=3).We employed virally mediated genetic knockdown strategy to test the hypothesis that knockdown of the 5-HT2CR in the vSUB of rats (n=5) will modulate cocaine-evoked hyperactivity. Motor activity was assessed after saline or cocaine (10–20mg/kg) in modified open-field chambers and analyzed using repeated measures two-way ANOVA. Results:Dense immunoreactivity (IR) for 5-HT2CRwasobserved throughout the vSUB. Only a small proportion of 5-HT2CR-IR was co-localized with GAD 67-IR that was restricted to the distal end

Abstract 4595: The impact of CYP2A6 genetic polymorphisms on nicotine metabolism and lung cancer risk in two prospective cohorts of smokers

Abstract Background. Cytochrome P450 2A6 (CYP2A6) is polymorphic and catalyzes the metabolism of nicotine and certain tobacco-specific carcinogens, including 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), thus may affect smoking behavior and contribute to substantial inter-individual variation in risk of smoking-related lung cancer. CYP2A6 genetic profiling coupled with biomarkers of tobacco constituents may enhance our understanding of the gene-environmental interaction on lung cancer risk and identify high-risk smokers for targeted preventive interventions. Methods. A nested case-control study including 513 incident lung cancers and an equal number of individually matched controls, all current smokers, was conducted within two population-based prospective cohorts with &amp;gt;80,000 Chinese men and women aged 45-74 years in Shanghai and Singapore. Quantified were 4 common allelic variants of CYP2A6 (*4, *7, *9 and rs1137115), urinary total nicotine, total cotinine (COT), total 3-hydroxy cotinine (3HC), and total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, a NNK metabolite). Calculated were total nicotine equivalent (TNE = the sum of total nicotine, COT and 3HC), and the 3HC:COT ratio as a measure of CYP2A6 activity. Logistic regression method was used to calculate odd ratios and 95% confidence intervals for lung cancer associated CYP2A6 genotypes and urinary biomarkers. Results. The smoking-adjusted ORs (95% CIs) of lung cancer comparing the highest to lowest quartile of total nicotine, total COT, total 3HC, TNE, and total NNAL were 2.49 (1.72-3.62), 3.03 (2.35-5.41), 3.56 (2.35-5.41), 3.35 (2.25-5.00), and 2.43 (1.65-3.57), respectively (all Ps for trend &amp;lt; 0.001). All 4 individual mutant variants of CYP2A6 were associated with reduced 3HC:COT ratio (all Ps for trend &amp;lt; 0.05). When all 4 genotypes were combined to create a CYP2A6 index with 5 groups: G1 (most efficient) to G5 (least efficient), the 3HC:COT ratio for G1 was 4 times that of G5 with a strong dose-dependent genotype-phenotype relation (P trend &amp;lt; 0.001). Smokers with CYP2A6 G5 consumed significantly fewer cigarettes and excreted lower urinary TNE (P trend &amp;lt; 0.001). Compared with CYP2A6 G1, the multivariate-adjusted ORs (95% CIs) of lung cancer for G2, G3, G4 and G5 were 0.95 (0.64-1.42), 1.04 (0.67-1.63), 0.54 (0.34-0.86) and 0.69 (0.43-1.13), respectively, (P trend = 0.005). Furthermore, there was a suggestive interaction between CYP2A6 index and total NNAL on lung cancer risk (P interaction = 0.087). Conclusion. CYP2A6 genetic polymorphisms have a strong influence on cigarette consumption, nicotine uptake and metabolism. In addition to reduced carcinogen exposure, altered metabolism of the tobacco-specific carcinogen NNK may contribute to the reduced risk of lung cancer in smokers with low functional CYP2A6 genotypes. Grants: R01 CA129534, R01 CA144034, UM1 CA182876. Citation Format: Jian-Min Yuan, Heather H. Nelson, Lesley M. Butler, Steven G. Carmella, Renwei Wang, Jennifer Adams-Haduch, Stephen S. Hecht, Woon-Puay Koh, Yu-Tang Gao, Sharon E. Murphy. The impact of CYP2A6 genetic polymorphisms on nicotine metabolism and lung cancer risk in two prospective cohorts of smokers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4595. doi:10.1158/1538-7445.AM2015-4595

The role of placental carbonyl-reducing enzymes in biotransformation of bupropion and 4-methylnitrozamino-1-(3-pyridyl)-1-butanone (NNK)

Background: Bupropion (BUP) has a potential to be an effective pharmacotherapy for smoking cessation during pregnancy. Smoking during pregnancy stimulates placental carbonyl reductases that catalyze the biotransformation of BUP. 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen of cigarette smoke. Carbonyl reduction of NNK into 4-methylnitrosamino-1-(3-pyridyl)-1-butanol (NNAL) constitutes a major step in NNK detoxification. Thus, placentas of pregnant smokers on BUP therapy can become a site of drug-drug interaction. Therefore, we investigated the effect of continuous exposure to BUP and cigarette smoke on the activity of placental carbonyl reductases in the formation of NNAL from NNK. Methods: The reductive metabolism of NNK was determined using microsomal and cytosolic subcellular fractions of placentas obtained from non-smoking women treated with BUP for depression, and women not exposed to BUP: non-smokers (control) and smokers. The effect of BUP and its metabolites on the reductive metabolism of NNK was investigated using subcellular fractions of control placentas. Results: The formation of NNAL from NNK by placental cytosolic fractions of heavy smokers (≥20 cigarettes per day) was lower than that of control (12.1±3.5 nmol.mgP-1 vs 16.5±6.0 nmol.mgP-1, P<0.05). While exposure to BUP did not affect the activity of placental carbonyl reductases, the formation of NNAL in the placental cytosolic fraction was decreased only in the presence of high concentrations of BUP metabolites. Conclusion: Smoking during pregnancy decrease the detoxifying capacity of soluble carbonyl reductases towards NNK. Given the experimental conditions, exposure to BUP and its metabolites should not impede the reductive metabolism of NNK by placenta in vivo.