Margaret Peng

Elimination kinetics of the tobacco-specific biomarker and lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is tobacco specific and has a longer half-life than other tobacco biomarkers studied thus far. An accurate measurement of the NNAL half-life is important for optimal use to assess exposure to tobacco smoke. We determined the half-life of NNAL in urine in eight daily smokers on a clinical research ward and in five occasional smokers in a real-life environment. Total NNAL in urine was monitored for 14 days in daily smokers after stopping smoking and for up to 60 days in occasional smokers. The average half-life for the terminal phase in the daily smoker group using a two-compartmental body model was 10.3 days (beta phase), and using a noncompartmental model, it was 9.1 days. In the occasional group, these values were 17.6 and 16.0 days, respectively. The alpha-phase half-lives were 14.3 and 27.8 hours for the two groups, respectively. The inter-subject coefficient of variation of the NNAL terminal half-life ranged from 14% to 30%, and the intra-subject coefficient of variation ranged from 3% to 18%. There was very good agreement between the plasma and urinary half-lives in two subjects with plasma analyses: 7.4 versus 7.9 days and 9.2 versus 10.7 days. Mean renal clearance of NNAL was 13 ± 2.3 mL/min. The terminal half-life of NNAL of 10 to 18 days indicates that this biomarker can be used to detect tobacco smoke exposure for 6 to 12 weeks after cessation of exposure and requires a similar time to assess the steady levels of NNAL after switching from one tobacco product to another. (Cancer Epidemiol Biomarkers Prev 2009;18(12):3421–5)

Comparison of Nicotine and Carcinogen Exposure with Water Pipe and Cigarette Smoking

Background: Smoking tobacco preparations in a water pipe (hookah) is widespread in many places of the world and is perceived by many as relatively safe. We investigated biomarkers of toxicant exposure with water pipe compared with cigarette smoking. Methods: We conducted a crossover study to assess daily nicotine and carcinogen exposure with water pipe and cigarette smoking in 13 people who were experienced in using both products. Results: When smoking an average of 3 water pipe sessions compared with smoking 11 cigarettes per day (cpd), water pipe use was associated with a significantly lower intake of nicotine, greater exposure to carbon monoxide (CO), and a different pattern of carcinogen exposure compared with cigarette smoking, with greater exposure to benzene, and high molecular weight polycyclic aromatic hydrocarbon (PAH), but less exposure to tobacco-specific nitrosamines, 1,3-butadiene, acrolein, acrylonitrile, propylene oxide, ethylene oxide, and low molecular weight PAHs. Conclusions: A different pattern of carcinogen exposure might result in a different cancer risk profile between cigarette and water pipe smoking. Of particular concern is the risk of leukemia related to high levels of benzene exposure with water pipe use. Impact: Smoking tobacco in water pipes has gained popularity in the United States and around the world. Many believe that water pipe smoking is not addictive and less harmful than cigarette smoking. We provide data on toxicant exposure that will help guide regulation and public education regarding water pipe health risk. Cancer Epidemiol Biomarkers Prev; 22(5); 765–72. ©2013 AACR.

Nicotine, Carbon Monoxide, and Carcinogen Exposure after a Single Use of a Water Pipe

Background: Smoking tobacco preparations in a water pipe (hookah) is widespread in many places of the world, including the United States, where it is especially popular among young people. Many perceive water pipe smoking to be less hazardous than cigarette smoking. We studied systemic absorption of nicotine, carbon monoxide, and carcinogens from one water pipe smoking session. Methods: Sixteen subjects smoked a water pipe on a clinical research ward. Expired carbon monoxide and carboxyhemoglobin were measured, plasma samples were analyzed for nicotine concentrations, and urine samples were analyzed for the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanol (NNAL) and polycyclic aromatic hydrocarbon (PAH) metabolite biomarker concentrations. Results: We found substantial increases in plasma nicotine concentrations, comparable to cigarette smoking, and increases in carbon monoxide levels that are much higher than those typically observed from cigarette smoking, as previously published. Urinary excretion of NNAL and PAH biomarkers increased significantly following water pipe smoking. Conclusions: Absorption of nicotine in amounts comparable to cigarette smoking indicates a potential for addiction, and absorption of significant amounts of carcinogens raise concerns of cancer risk in people who smoke tobacco products in water pipes. Impact: Our data contribute to an understanding of the health impact of water pipe use. Cancer Epidemiol Biomarkers Prev; 20(11); 2345–53. ©2011 AACR.

Effects of cigarette smoking and carbon monoxide on chlorzoxazone and caffeine metabolism

Our objectives were to examine the effects of cigarette smoking on the disposition kinetics of chlorzoxazone and caffeine as probes of cytochrome P450 (CYP) 2E1, CYP1A2, xanthine oxidase, and N‐acetyltransferase‐2 activity and to test the hypothesis that carbon monoxide inhibits drug metabolism via these pathways.

Exposure to Nicotine and Selected Toxicants in Cigarette Smokers Who Switched to Electronic Cigarettes: A Longitudinal Within-Subjects Observational Study

Introduction: Electronic cigarettes (e-cigarettes) are purported to deliver nicotine aerosol without any toxic combustion products present in tobacco smoke. In this longitudinal within-subjects observational study, we evaluated the effects of e-cigarettes on nicotine delivery and exposure to selected carcinogens and toxicants. Methods: We measured seven nicotine metabolites and 17 tobacco smoke exposure biomarkers in the urine samples of 20 smokers collected before and after switching to pen-style M201 e-cigarettes for 2 weeks. Biomarkers were metabolites of 13 major carcinogens and toxicants in cigarette smoke: one tobacco-specific nitrosamine (NNK), eight volatile organic compounds (1,3-butadiene, crotonaldehyde, acrolein, benzene, acrylamide, acrylonitrile, ethylene oxide, and propylene oxide), and four polycyclic aromatic hydrocarbons (naphthalene, fluorene, phenanthrene, and pyrene). Changes in urine biomarkers concentration were tested using repeated measures analysis of variance. Results: In total, 45% of participants reported complete abstinence from cigarette smoking at 2 weeks, while 55% reported continued smoking. Levels of total nicotine and some polycyclic aromatic hydrocarbon metabolites did not change after switching from tobacco to e-cigarettes. All other biomarkers significantly decreased after 1 week of using e-cigarettes (p < .05). After 1 week, the greatest percentage reductions in biomarkers levels were observed for metabolites of 1,3-butadiene, benzene, and acrylonitrile. Total NNAL, a metabolite of NNK, declined by 57% and 64% after 1 and 2 weeks, respectively, while 3-hydroxyfluorene levels declined by 46% at week 1, and 34% at week 2. Conclusions: After switching from tobacco to e-cigarettes, nicotine exposure remains unchanged, while exposure to selected carcinogens and toxicants is substantially reduced. Implications: To our knowledge, this is the first study that demonstrates that substituting tobacco cigarettes with an e-cigarette may reduce user exposure to numerous toxicants and carcinogens otherwise present in tobacco cigarettes. Data on reduced exposure to harmful constituents that are present in tobacco cigarettes and e-cigarettes can aid in evaluating e-cigarettes as a potential harm reduction device.

Nicotine and Carcinogen Exposure after Water Pipe Smoking in Hookah Bars

Background: Water pipe tobacco smoking is spreading globally and is increasingly becoming popular in the United States, particularly among young people. Although many perceive water pipe smoking to be relatively safe, clinical experimental studies indicate significant exposures to tobacco smoke carcinogens following water pipe use. We investigated biomarkers of nicotine intake and carcinogen exposure from water pipe smoking in the naturalistic setting of hookah bars. Methods: Fifty-five experienced water pipe users were studied before and after smoking water pipe in their customary way in a hookah bar. Urine samples were analyzed for nicotine, cotinine, the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and mercapturic acid metabolites of volatile organic compounds (VOC). Results: We found an average 73-fold increase in nicotine, 4-fold increase in cotinine, 2-fold increase in NNAL, and 14% to 91% increase in VOC mercapturic acid metabolites immediately following water pipe smoking. We saw moderate to high correlations between changes in tobacco-specific biomarkers (nicotine, cotinine, and NNAL) and several mercapturic acid metabolites of VOCs. Conclusion: Water pipe smoking in a hookah bar is associated with significant nicotine intake and carcinogen exposure. Impact: Given the significant intake of nicotine and carcinogens, chronic water pipe use could place users at increased risk of cancer and other chronic diseases. Cancer Epidemiol Biomarkers Prev; 23(6); 1055–66. ©2014 AACR.

Effects of nicotine on cytochrome P450 2A6 and 2E1 activities

AIMS Smoking slows the metabolism of nicotine and accelerates the metabolism of chlorzoxazone, which are probe reactions for cytochrome P450 2A6 (CYP2A6) and CYP2E1 activities, respectively. We aimed to determine the role of nicotine in these metabolic effects of cigarette smoking. METHODS The study had a single-blind, randomized, crossover two-arm design. Twelve healthy smokers were given two transdermal patches with 42-mg nicotine a day or placebo patches, each for 10 days. The subjects abstained from smoking during the study arms. Oral chlorzoxazone was given on day 7 and deuterium-labelled nicotine-d(2) and cotinine-d(4) infusion on day 8. RESULTS There was no significant influence of transdermal nicotine administration on pharmacokinetic parameters of nicotine-d(2) or on the formation of cotinine-d(2). Nicotine decreased the volume of distribution (62.6 vs. 67.7 l, 95% confidence interval of the difference -9.7, -0.6, P= 0.047) of infused cotinine-d(4). There were no significant differences in disposition kinetics of chlorzoxazone between the treatments. CONCLUSIONS CYP2A6 and CYP2E1 activities are not affected by nicotine. The tobacco smoke constituents responsible for the reduced CYP2A6 and increased CYP2E1 activities remain unknown.

Effect of nicotine on cytochrome P450 1A2 activity

Cigarette smoking accelerates the metabolism of certain drugs, particularly those primarily metabolized by cytochrome P450 1A2 (CYP1A2) and, to a lesser extent, CYP2E1 and some UDP-glucuronosyltransferases [1, 2]. The induction of CYP1A2 is mediated by binding of polycyclic aromatic hydrocarbons of the tobacco smoke to the aryl hydrocarbon receptor (AHR) with consequent transcriptional activation of the CYP1A2 gene. Furthermore, CYP1A1 and CYP1B1 enzymes are induced by tobacco smoking via AHR in various human tissues such as lung and placenta [3]. As CYP1A1 and CYP1B1 are mostly expressed in extrahepatic tissues, their induction by smoking is not known to affect the pharmacokinetics of any medication. There is evidence of the role of nicotine in the induction of CYP1A1 and CYP1A2 enzymes in vitro in rat lung [4], and in vivo in rat lung, kidney and liver [5–7], liver and placenta of pregnant rats [8] and in brains of mice and rats [9, 10], probably through mechanisms not involving AHR. Some evidence exists for the induction of CYP1A1 by nicotine in human pulmonary explant culture [11]. We recently published a study on the effects of 10 day dosing of nicotine on human CYP2A6 and CYP2E1 activities [12]. An additional aim of that study was to determine the effects of high dose nicotine on the pharmacokinetics of oral caffeine and to test the hypothesis that nicotine induces CYP1A2-mediated metabolism of caffeine to paraxanthine, a well-established probe reaction of CYP1A2 activity [13]. No previous study has studied the effects of nicotine on CYP1A2 activity in humans in vivo. The details of the experimental protocol and the subject characteristics are described in a prior report [12]. Briefly, 12 healthy smokers were given two 21 mg transdermal patches delivering a total of 42 mg nicotine day−1 or placebo patches, each for 10 days in a randomized and crossover design. Subjects were not allowed to smoke or to use any tobacco products during hospitalization. At noon on the eighth hospital day, 200 mg of oral caffeine was given. Blood samples were collected for measurement of caffeine and metabolites at 0, 30 and 60 min, and then 2, 3, 4, 6, 8, 12, 20, 32, 44 and 52 h after ingestion of caffeine. In addition, deuterium-labelled nicotine-D2 and cotinine-D4 phenotyping for CYP2A6, bupropion phenotyping for CYP2B6 and chlorzoxazone phenotyping for CYP2E1 were performed on the seventh and eighth hospital days as previously described [12]. Concentrations of caffeine, paraxanthine, theobromine and theophylline in plasma were determined using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Stable isotope-labelled analogues of paraxanthine and caffeine were used as internal standards. Following protein precipitation, samples (0.2 ml) were treated with phosphate buffer and extracted with a mixture of methylene chloride, ethyl acetate and isopropyl alcohol. The extracts were evaporated, reconstituted in the LC mobile phase, and injected into the LC-MS/MS system. The mass spectrometer was operated using atmospheric pressure chemical ionization, and selected reaction monitoring was used for quantitation. Calibration curves were constructed using the peak area ratio of analyte : internal standard and linear regression. Limits of quantitation for all analytes were 10 ng ml−1. Precision (within-run, % coefficient of variation) ranged from 1.7 to 10.3%, and accuracy (% of expected value) ranged from 88 to 118% for concentrations from 10 ng ml−1 to 5000 ng ml−1. Oral clearance of caffeine was computed as follows: CL = Dose/AUC. The oral CL of caffeine and the paraxanthine : caffeine AUC(0,52 h) ratio were used as measures of CYP1A2 activity. The pharmacokinetic parameters were compared across treatments by paired Students t-test. The effects of nicotine on the disposition kinetics of caffeine are presented in Table 1. There was no significant influence of nicotine administration on the pharmacokinetic parameters of caffeine or the formation pharmacokinetics of paraxanthine, theophylline and theobromine. Since caffeine metabolism to paraxanthine is a specific probe reaction for CYP1A2 [13], it can be concluded that CYP1A2 activity is not affected by 8 days of nicotine dosing. Although previous studies in experimental animals have provided evidence for the role of nicotine in the induction of CYP1A1 and CYP1A2 enzymes [4–10], our study disproves the hypothesis that nicotine induces CYP1A2 activity in humans in vivo. The discrepancy between human and animal data may be explained by tissue and species specific expression patterns. The human caffeine phenotyping probes the hepatic CYP1A2 activity, whereas the animal studies are mainly on extrahepatic CYP1A1 induction or based on methods not capable of differentiating between CYP1A1 and CYP1A2 enzymes. Table 1 Effect of nicotine on caffeine disposition kinetics and formation and elimination pharmacokinetics of paraxanthine, theobromine and theophylline In addition to nicotine and caffeine, bupropion and chlorzoxazone were administered during the study to phenotype CYP2B6 and CYP2E1 activities, respectively. We are not aware of any clinical studies demonstrating that bupropion inhibits CYP1A2 activity. In human liver microsomes in vitro, bupropion incubated with melatonin or phenacetin (probes for CYP1A2) shows no inhibitory effects on CYP1A2-mediated pathways [14–16]. Chlorzoxazone and caffeine have been dosed together in several metabolic cocktail approaches to phenotype CYP enzymes without any detected metabolic interactions [17–19]. Thus, there is no known interaction between the study medications affecting the phenotyping of CYP1A2. In conclusion, this study shows that human CYP1A2 activity is not affected by nicotine and provides evidence that high dose nicotine treatment has a low potential for interaction with concurrently administered CYP1A2 substrates. Nicotine has no role in the induction of CYP1A2 that is known to occur in smokers.

Intake of toxic and carcinogenic volatile organic compounds from secondhand smoke in motor vehicles.

Background: Volatile organic compounds (VOC) from tobacco smoke are associated with cancer, cardiovascular, and respiratory diseases. The objective of this study was to characterize the exposure of nonsmokers to VOCs from secondhand smoke (SHS) in vehicles using mercapturic acid metabolites. Methods: Fourteen nonsmokers were individually exposed in the backseat to one hour of SHS from a smoker seated in the drivers seat who smoked three cigarettes at 20-minute intervals in a stationary car with windows opened by 10 cm. Baseline and 0- to 8-hour postexposure mercapturic acid metabolites of nine VOCs were measured in urine. Air-to-urine VOC ratios were estimated on the basis of respirable particulate matter (PM2.5) or air nicotine concentration, and lifetime excess risk (LER) of cancer death from exposure to acrylonitrile, benzene, and 1,3-butadiene was estimated for adults. Results: The greatest increase in 0- to 8-hour postexposure concentrations of mercapturic acids from baseline was MHBMA-3 (parent, 1,3-butadiene; 2.1-fold), then CNEMA (acrylonitrile; 1.7-fold), PMA (benzene; 1.6-fold), MMA (methylating agents; 1.6-fold), and HEMA (ethylene oxide; 1.3-fold). The LER of cancer death from exposure to acrylonitrile, benzene, and 1,3-butadiene in SHS for 5 hours a week ranged from 15.5 × 10−6 to 28.1 × 10−6 for adults, using air nicotine and PM2.5 to predict air VOC exposure, respectively. Conclusion: Nonsmokers have significant intake of multiple VOCs from breathing SHS in cars, corresponding to health risks that exceed the acceptable level. Impact: Smoking in cars may be associated with increased risks of cancer, respiratory, and cardiovascular diseases among nonsmokers. Cancer Epidemiol Biomarkers Prev; 23(12); 2774–82. ©2014 AACR.