Nicotine metabolism and elimination kinetics in newborns

Nicotine metabolism and addiction among adolescent smokers

AIMS

The purpose of this study was to determine the association between the nicotine metabolic rate and smoking behavior, including addiction, in adolescent smokers.

DESIGN

Baseline data from a prospective study of adolescent smoking behaviors and nicotine metabolism.

SETTING

The setting was an out-patient university hospital in San Francisco.

PARTICIPANTS

Adolescent smokers (n = 164) aged 13-17 years old.

MEASUREMENTS

Participants completed self-report measures of smoking behavior and nicotine dependence (modified Fagerström Tolerance Questionnaire: mFTQ). The nicotine metabolite ratio (NMR), a phenotypic marker of the rate of nicotine metabolism, was calculated using the ratio of concentrations of deuterium-labeled 3'-hydroxycotinine to cotinine-d(4) .

FINDINGS

Participants reported smoking a mean of 2.86 cigarettes per day (CPD) [median = 1.78, standard deviation (SD) = 3.35] for 1.37 years (median = 1.0, SD = 1.36). Results from multivariate analyses accounting for age, race/ethnicity, gender and duration of smoking indicated that slower metabolizers smoked more CPD than faster metabolizers (the NMR was inversely related to CPD; P = 0.02). Slower metabolizers also showed greater dependence on the mFTQ (NMR was negatively associated with the mFTQ; P = 0.02).

CONCLUSIONS

In adolescence, slower clearance of nicotine may be associated with greater levels of addiction, perhaps mediated by a greater number of cigarettes smoked.

Perinatal nicotine/smoking exposure and carotid chemoreceptors during development

Tobacco smoking is still a common habit during pregnancy and is the most important preventable cause of many adverse perinatal outcomes. Prenatal smoking exposure can produce direct actions of nicotine in the fetus with the disruption of body and brain development, and actions on the maternal-fetal unit by causing repeated episodes of hypoxia and exposure to many toxic smoke products (such as carbon monoxide). Specifically, nicotine through binding to nicotinic acetylcholine receptors have ubiquitous effects and can affect carotid chemoreception development through structural, functional and neuroregulatory alterations of the neural circuits involved in the chemoafferent pathway, as well as by interfering with the postnatal resetting of the carotid bodies. Reduced carotid body chemosensitivity and tonic activity have thus been reported by the majority of the human and animal studies. This review focuses on the effects of perinatal exposure to tobacco smoke and nicotine on carotid chemoreceptor function during the developmental period. A description of the effects of smoking and nicotine on the control of breathing related to carotid body activity, and of the possible physiopathological mechanisms at the origin of these disturbances is presented.

Developmental hippocampal neuroplasticity in a model of nicotine replacement therapy during pregnancy and breastfeeding

RATIONALE

The influence of developmental nicotine exposure on the brain represents an important health topic in light of the popularity of nicotine replacement therapy (NRT) as a smoking cessation method during pregnancy.

OBJECTIVES

In this study, we used a model of NRT during pregnancy and breastfeeding to explore the consequences of chronic developmental nicotine exposure on cerebral neuroplasticity in the offspring. We focused on two dynamic lifelong phenomena in the dentate gyrus (DG) of the hippocampus that are highly sensitive to the environment: granule cell neurogenesis and long-term potentiation (LTP).

METHODS

Pregnant rats were implanted with osmotic mini-pumps delivering either nicotine or saline solutions. Plasma nicotine and metabolite levels were measured in dams and offspring. Corticosterone levels, DG neurogenesis (cell proliferation, survival and differentiation) and glutamatergic electrophysiological activity were measured in pups.

RESULTS

Juvenile (P15) and adolescent (P41) offspring exposed to nicotine throughout prenatal and postnatal development displayed no significant alteration in DG neurogenesis compared to control offspring. However, NRT-like nicotine exposure significantly increased LTP in the DG of juvenile offspring as measured in vitro from hippocampal slices, suggesting that the mechanisms underlying nicotine-induced LTP enhancement previously described in adult rats are already functional in pups.

CONCLUSIONS

These results indicate that synaptic plasticity is disrupted in offspring breastfed by dams passively exposed to nicotine in an NRT-like fashion.

Tomato juice protects the lungs of the offspring of female rats exposed to nicotine during gestation and lactation

Maternal nicotine exposure during gestation and lactation adversely affects lung development in the offspring. It has been suggested that the "program" that control long-term maintenance of the structural integrity of the lung may be compromised. The aim of the study was to study the long-term effect of maternal nicotine exposure on the structural integrity of the lungs of the offspring, and secondly to determine whether supplementing the mother's diet with tomato juice, as a rich source of antioxidants such as lycopene, will prevent the effects of nicotine on the lungs of the offspring. Wistar rats were used in the study. After mating the rats were randomly divided into three groups. One group received nicotine (1 mg/kg body weight/day); a second group received tomato juice; and a third group received nicotine and tomato juice. The controls receive saline. Morphological and morphometric techniques were used to evaluate changes in the lung structure of the offspring at postnatal days 21, 42, 63, and 84. Neither nicotine nor tomato juice had any effect on the growth of the offspring. Although maternal nicotine exposure during gestation and lactation had no effect on the lung parenchyma of the offspring up to weaning, deterioration, and other structural changes started to appear around postnatal day 42, that is, 3 weeks after weaning and thus the onset of nicotine withdrawal. Microscopic emphysema was apparent at postnatal day 42, the increase in male and female lung volume from postnatal day 63 and thickening of the alveolar walls at postnatal day 84. All these nicotine-induced structural changes were prevented by supplementing the mother's diet with tomato juice.

Nicotine induced CpG methylation of Pax6 binding motif in StAR promoter reduces the gene expression and cortisol production

Steroidogenic acute regulatory protein (StAR) mediates the rate-limiting step in the synthesis of steroid hormones, essential to fetal development. We have reported that the StAR expression in fetal adrenal is inhibited in a rat model of nicotine-induced intrauterine growth retardation (IUGR). Here using primary human fetal adrenal cortex (pHFAC) cells and a human fetal adrenal cell line NCI-H295A, we show that nicotine inhibits StAR expression and cortisol production in a dose- and time-dependent manner, and prolongs the inhibitory effect on cells proliferating over 5 passages after termination of nicotine treatment. Methylation detection within the StAR promoter region uncovers a single site CpG methylation at nt -377 that is sensitive to nicotine treatment. Nicotine-induced alterations in frequency of this point methylation correlates well with the levels of StAR expression, suggesting an important role of the single site in regulating StAR expression. Further studies using bioinformatics analysis and siRNA approach reveal that the single CpG site is part of the Pax6 binding motif (CGCCTGA) in the StAR promoter. The luciferase activity assays validate that Pax6 increases StAR gene expression by binding to the glucagon G3-like motif (CGCCTGA) and methylation of this site blocks Pax6 binding and thus suppresses StAR expression. These data identify a nicotine-sensitive CpG site at the Pax6 binding motif in the StAR promoter that may play a central role in regulating StAR expression. The results suggest an epigenetic mechanism that may explain how nicotine contributes to onset of adult diseases or disorders such as metabolic syndrome via fetal programming.

Prenatal tobacco exposure influences cerebral oxygenation in preterm infants

AIM

Our aim was to determine the influence of prenatal tobacco exposure on regional cerebral tissue oxygen saturation (r(c)SO(2)) and fractional tissue oxygen extraction (FTOE) in preterm infants. We hypothesized that as a result of vasoconstriction caused by prenatal tobacco exposure r(c)SO(2) would be lower and FTOE would be higher during the first days after birth in infants exposed to tobacco during pregnancy.

METHODS

Sixty preterms were included in this prospective, observational cohort study (median gestational age 29.9 weeks, range 26.0-31.8, median birth weight 1248 g, range 615-2250). Fourteen infants had been exposed to tobacco during pregnancy. All mothers smoked more than five cigarettes a day till delivery. We measured r(c)SO(2) and transcutaneous arterial oxygen saturation (tcSaO(2)) in all infants on days 1-5, 8, and 15. FTOE was calculated: FTOE=(tcSaO(2)-r(c)SO(2))/tcSaO(2).

RESULTS

In preterm infants exposed to tobacco during pregnancy, r(c)SO(2) was lower during days 1, 2, and 8 after birth, median 73% versus 81%, 73% versus 80% and 71% versus 78% respectively. FTOE was higher during days 1 and 8 after birth, median 0.24 versus 0.15 and 0.26 versus 0.19 respectively. On the second day, FTOE tended to be higher, 0.18 versus 0.14.

CONCLUSIONS

During the first two days and day 8 after birth cerebral oxygen saturation is lower and oxygen extraction higher in preterm infants following prenatal tobacco exposure. Our data suggest that prenatal tobacco exposure may have an effect on cerebral oxygenation of the infant.

Nicotine and its metabolites in amniotic fluid at birth--assessment of prenatal tobacco smoke exposure

Amniotic fluid was collected from 78 pregnant women at birth additionally with their urine prior to delivery as well as neonatal urine and meconium. The smoking markers, nicotine and its metabolites cotinine and trans-3'-hydroxycotinine (OH-cotinine), were determined using high-performance liquid chromatography (HPLC). The self-reported smoking status during pregnancy determined by means of a questionnaire was verified by measurement of maternal urine. In all smokers, nicotine metabolites were detected in amniotic fluid and in 80% of them nicotine as well. However, the sum of the nicotine metabolites (Sum(met)) was significantly lower (p < .001) in amniotic fluid (704 +/- 464 nmol/L) than in meconium (921 +/- 588 nmol/L), neonatal urine (1139 +/- 813 nmol/L) and maternal urine (4496 +/- 3535 nmol/L). Concentrations of nicotine metabolites in amniotic fluid correlated well (p < .001) with that in the other specimen types. After environmental tobacco smoke (ETS) exposure, no nicotine or nicotine metabolites were detectable in amniotic fluid but only in maternal and neonatal urine. Analysis of amniotic fluid at birth lends itself to verifying smoking habits during pregnancy and clearly discriminating from ETS exposure, but it is not a suitable approach to differentiating between ETS exposure and non-exposure.

Enzyme-linked immunosorbent assay of nicotine metabolites

INTRODUCTION

The level of cotinine in biological specimens, such as serum, urine, and saliva, measured by gas or liquid chromatography is the most validated and reliable indicator of exposure to tobacco smoke. However, chromatographic methods are not always suitable for all types of situations.

METHODS

We validated a commercially available enzyme-linked immunosorbent assay (ELISA) that uses a polyclonal antibody to cotinine as a practical alternative to chromatographic methods.

RESULTS

The cotinine antibody cross-reacts to 3-hydroxycotinine (3HC) and its glucuronide, thus generating a value for immunoreactive (IR) cotinine, which is a complex comprising cotinine, 3HC, and 3HC-glucuronide. The levels of IR cotinine in the urine of kindergarten children closely correlated with those of cotinine measured by gas chromatography-mass spectrometry (GC-MS) and reflected the smoking behavior of their parents more precisely than cotinine levels determined by GC-MS.

DISCUSSION

Our findings showed that the cotinine-based ELISA can be a practical biomarker of exposure to tobacco smoke.

Methods for quantification of exposure to cigarette smoking and environmental tobacco smoke: focus on developmental toxicology

Active and passive smoking have been associated with an array of adverse effects on health. The development of valid and accurate scales of measurement for exposures associated with health risks constitutes an active area of research. Tobacco smoke exposure still lacks an ideal method of measurement. A valid estimation of the risks associated with tobacco exposure depends on accurate measurement. However, some groups of people are more reluctant than others to disclose their smoking status and exposure to tobacco. This is particularly true for pregnant women and parents of young children, whose smoking is often regarded as socially unacceptable. For others, recall of tobacco exposure may also prove difficult. Because relying on self-report and the various biases it introduces may lead to inaccurate measures of nicotine exposure, more objective solutions have been suggested. Biomarkers constitute the most commonly used objective method of ascertaining nicotine exposure. Of those available, cotinine has gained supremacy as the biomarker of choice. Traditionally, cotinine has been measured in blood, saliva, and urine. Cotinine collection and analysis from these sources has posed some difficulties, which have motivated the search for a more consistent and reliable source of this biomarker. Hair analysis is a novel, noninvasive technique used to detect the presence of drugs and metabolites in the hair shaft. Because cotinine accumulates in hair during hair growth, it is a unique measure of long-term, cumulative exposure to tobacco smoke. Although hair analysis of cotinine holds great promise, a detailed evaluation of its potential as a biomarker of nicotine exposure, is needed. No studies have been published that address this issue. Because the levels of cotinine in the body are dependent on nicotine metabolism, which in turn is affected by factors such as age and pregnancy, the characterization of hair cotinine should be population specific. This review aims at defining the sensitivity, specificity, and clinical utilization of different methods used to estimate exposure to cigarette smoking and environmental tobacco smoke.

Nicotine chemistry, metabolism, kinetics and biomarkers

Nicotine underlies tobacco addiction, influences tobacco use patterns, and is used as a pharmacological aid to smoking cessation. The absorption, distribution and disposition characteristics of nicotine from tobacco and medicinal products are reviewed. Nicotine is metabolized primarily by the liver enzymes CYP2A6, UDPglucuronosyltransferase (UGT), and flavin-containing monooxygenase (FMO). In addition to genetic factors, nicotine metabolism is influenced by diet and meals, age, sex, use of estrogen-containing hormone preparations, pregnancy and kidney disease, other medications, and smoking itself. Substantial racial/ethnic differences are observed in nicotine metabolism, which are likely influenced by both genetic and environmental factors. The most widely used biomarker of nicotine intake is cotinine, which may be measured in blood, urine, saliva, hair, or nails. The current optimal plasma cotinine cut-point to distinguish smokers from non-smokers in the general US population is 3 ng ml(-1). This cut-point is much lower than that established 20 years ago, reflecting less secondhand smoke exposure due to clear air policies and more light or occasional smoking.

Maternal smoking during pregnancy and newborn neurobehavior: effects at 10 to 27 days

OBJECTIVE

To examine effects of maternal smoking during pregnancy on newborn neurobehavior at 10 to 27 days.

STUDY DESIGN

Participants were 56 healthy infants (28 smoking-exposed, 28 unexposed) matched on maternal social class, age, and alcohol use. Maternal smoking during pregnancy was determined by maternal interview and maternal saliva cotinine. Postnatal smoke exposure was quantified by infant saliva cotinine. Infant neurobehavior was assessed through the NICU Network Neurobehavioral Scale.

RESULTS

Smoking-exposed infants showed greater need for handling and worse self-regulation (P < .05) and trended toward greater excitability and arousal (P < .10) relative to matched, unexposed infants (all moderate effect sizes). In contrast to prior studies of days 0 to 5, no effects of smoking-exposure on signs of stress/abstinence or muscle tone emerged. In stratified, adjusted analyses, only effects on need for handling remained significant (P < .05, large effect size).

CONCLUSIONS

Effects of maternal smoking during pregnancy at 10 to 27 days are subtle and consistent with increased need for external intervention and poorer self-regulation. Along with parenting deficits, these effects may represent early precursors for long-term adverse outcomes from maternal smoking during pregnancy. That signs of abstinence shown in prior studies of 0- to 5-day-old newborns did not emerge in older newborns provides further evidence for the possibility of a withdrawal process in exposed infants.

Nicotine acts on growth plate chondrocytes to delay skeletal growth through the alpha7 neuronal nicotinic acetylcholine receptor

BACKGROUND

Cigarette smoking adversely affects endochondral ossification during the course of skeletal growth. Among a plethora of cigarette chemicals, nicotine is one of the primary candidate compounds responsible for the cause of smoking-induced delayed skeletal growth. However, the possible mechanism of delayed skeletal growth caused by nicotine remains unclarified. In the last decade, localization of neuronal nicotinic acetylcholine receptor (nAChR), a specific receptor of nicotine, has been widely detected in non-excitable cells. Therefore, we hypothesized that nicotine affect growth plate chondrocytes directly and specifically through nAChR to delay skeletal growth.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the effect of nicotine on human growth plate chondrocytes, a major component of endochondral ossification. The chondrocytes were derived from extra human fingers. Nicotine inhibited matrix synthesis and hypertrophic differentiation in human growth plate chondrocytes in suspension culture in a concentration-dependent manner. Both human and murine growth plate chondrocytes expressed alpha7 nAChR, which constitutes functional homopentameric receptors. Methyllycaconitine (MLA), a specific antagonist of alpha7 nAChR, reversed the inhibition of matrix synthesis and functional calcium signal by nicotine in human growth plate chondrocytes in vitro. To study the effect of nicotine on growth plate in vivo, ovulation-controlled pregnant alpha7 nAChR +/- mice were given drinking water with or without nicotine during pregnancy, and skeletal growth of their fetuses was observed. Maternal nicotine exposure resulted in delayed skeletal growth of alpha7 nAChR +/+ fetuses but not in alpha7 nAChR -/- fetuses, implying that skeletal growth retardation by nicotine is specifically mediated via fetal alpha7 nAChR.

CONCLUSIONS/SIGNIFICANCE

These results suggest that nicotine, from cigarette smoking, acts directly on growth plate chondrocytes to decrease matrix synthesis, suppress hypertrophic differentiation via alpha7 nAChR, leading to delayed skeletal growth.

Effect of secondhand cigarette smoke, RSV bronchiolitis and parental asthma on urinary cysteinyl LTE4

Cysteinyl leukotrienes promote airway inflammation, bronchoconstriction and mucus hypersecretion. Cigarette smoking and respiratory syncytial virus (RSV) bronchiolitis are known to increase urinary cysteinyl leukotriene E4 (uLTE4), the end product of the cysteinyl leukotriene biosynthetic pathway. We tested the following hypotheses: (1) Secondhand smoke (SHS) exposure increases uLTE4 in well infants and in those hospitalized for RSV bronchiolitis; (2) Length of hospital stay for those with RSV bronchiolitis correlates with uLTE4; and (3) Infants with parent(s) with asthma will have higher uLTE4. Parental asthma for infants hospitalized with RSV bronchiolitis (n = 79) and Well babies (n = 31) was determined by questionnaire. Urine was analyzed for LTE4, cotinine, and creatinine. SHS exposure was determined by cotinine to creatinine ratio. Chi square, or t-tests were used to determine significant differences between two groups. A three-way analysis of variance compared the effects of SHS exposure and parental asthma on uLTE4 in Well versus RSV babies. Independent variables predicting length of hospital stay were determined by stepwise multiple regression. High SHS exposure and RSV significantly increased uLTE4. The SHS induced increase in uLTE4 was seen in infants with no parental asthma but not in those with parental asthma. Length of hospital stay positively correlated with uLTE4. We concluded that SHS exposure may increase the severity of bronchiolitis in RSV-infected infants by enhancing production of cysLTs in infants with no parental asthma.

Assessment of prenatal tobacco smoke exposure by determining nicotine and its metabolites in meconium

Meconium samples collected from 115 neonates were analysed for nicotine, cotinine and trans -3-hydroxycotinine (OH-cotinine) by means of high-performance liquid chromatography (HPLC) to identify prenatal smoke exposure. The self-reported maternal smoking status during pregnancy was determined by means of a questionnaire and verified by measurements in urine prior to childbirth. The total sum of nicotine and its metabolites (Sum(tot)) of the first passed meconium samples was 1560 +/- 1024 pmol/g in newborns of smoking mothers. Smoking of less than five cigarettes was clearly detected. Sum(tot) remained constant in all meconium samples passed by a neonate in succession. However, the proportion of nicotine decreased with the time of passage after birth and the OH-cotinine proportion increased, whereas cotinine hardly changed. Nicotine or its metabolites were not detectable in meconium (detection limit < 20 pmol/g), when the mothers were only exposed to environmental tobacco smoke (ETS) using the HPLC method. The hypothesis that the content of nicotine metabolites in meconium reflects long-term smoke exposure could not be confirmed in newborns whose mothers had quit smoking during the latter half of pregnancy. Determining Sum(tot) enables the intensity of continuous smoking during pregnancy to be estimated in all meconium samples passed by a newborn.

Correlating atmospheric and biological markers in studies of secondhand tobacco smoke exposure and dose in children and adults

OBJECTIVE

We sought to directly compare secondhand smoke (SHS) atmospheric markers to each other and to SHS dosimetric biomarkers, permitting intercomparison of clinical and atmospheric studies.

METHODS

We used atmospheric and pharmacokinetic (PK) models for the quantitative estimation of SHS exposure and dose for infants, children, and adults, based on building smoker density and air exchange rate, and from exposure duration, default PK parameters, and respiration rates.

RESULTS

We estimate the SHS serum cotinine doses for the typical and most-exposed individuals in the U.S. population; predictions compare well to measurements on a national probability sample. Using default respiration rates, we estimate serum cotinine dose from SHS nicotine exposure for 40 adults exposed to SHS in an environmental chamber; predictions agreed with observations. We correlate urine cotinine and hair nicotine levels for 127 infants exposed to parental smoking, and estimate corresponding atmospheric nicotine exposure via PK modeling.

CONCLUSIONS

Our "Rosetta Stone" Equations allow the SHS atmospheric markers, respirable particles, nicotine, and carbon monoxide, to be related to the SHS biomarkers, cotinine in blood, urine, and saliva and nicotine in hair, permitting intercomparison of clinical and atmospheric studies of SHS for the first time.

Validation and application of a method for the determination of nicotine and five major metabolites in smokers' urine by solid-phase extraction and liquid chromatography-tandem mass spectrometry

An SPE-LC-MS/MS method was developed, validated and applied to the determination of nicotine and five major metabolites in human urine: cotinine, trans-3'-hydroxycotinine, nicotine-N-glucuronide, cotinine-N-glucuronide and trans-3'-hydroxycotinine-O-glucuronide. A 500 microL urine sample was pH-adjusted with phosphate buffer (1.5 mL) containing nicotine-methyl-d3, cotinine-methyl-d3 and trans-3'-hydroxycotinine-methyl-d3 internal standards. For the unconjugated metabolites, an aliquot (800 microL) of the buffered solution was applied to a 30 mg Oasis HLB-SPE column, rinsed with 2% NH4OH/H2O (3.0 mL) and H2O (3.0 mL) and eluted with methanol (500 microL). The eluate was analyzed isocratically (100% methanol) by LC-MS/MS on a diol column (50 x 2.1 mm). For the total metabolites, a beta-glucuronidase/buffer preparation (100 microL) was added to the remaining buffered solution and incubated at 37 degrees C (20 h). An aliquot (800 microL) of the enzymatically treated buffered solution was extracted and analyzed in the same manner. The conjugated metabolites were determined indirectly by subtraction. The quantitation range of the method (ng/mL) was 14-10,320 for nicotine, 15-9800 for cotinine and 32-19,220 for trans-3'-hydroxycotinine. The validated method was used to observe diurnal variations from a smoker's spot urine samples, elimination half-lives from a smoker's 24 h urine samples and metabolite distribution profiles in the spot and 24 h urine samples.

Metabolism and Disposition Kinetics of Nicotine

Nicotine is of importance as the addictive chemical in tobacco, pharmacotherapy for smoking cessation, a potential medication for several diseases, and a useful probe drug for phenotyping cytochrome P450 2A6 (CYP2A6). We review current knowledge about the metabolism and disposition kinetics of nicotine, some other naturally occurring tobacco alkaloids, and nicotine analogs that are under development as potential therapeutic agents. The focus is on studies in humans, but animal data are mentioned when relevant to the interpretation of human data. The pathways of nicotine metabolism are described in detail. Absorption, distribution, metabolism, and excretion of nicotine and related compounds are reviewed. Enzymes involved in nicotine metabolism including cytochrome P450 enzymes, aldehyde oxidase, flavin-containing monooxygenase 3, amine N-methyltransferase, and UDP-glucuronosyltransferases are represented, as well as factors affecting metabolism, such as genetic variations in metabolic enzymes, effects of diet, age, gender, pregnancy, liver and kidney diseases, and racial and ethnic differences. Also effects of smoking and various inhibitors and inducers, including oral contraceptives, on nicotine metabolism are discussed. Due to the significance of the CYP2A6 enzyme in nicotine clearance, special emphasis is given to the effects and population distributions of CYP2A6 alleles and the regulation of CYP2A6 enzyme.

Genetically decreased CYP2A6 and the risk of tobacco dependence: a prospective study of novice smokers

OBJECTIVE

Case control studies in adults suggest that defective alleles in the gene that codes for the hepatic cytochrome P450 2A6 (CYP2A6) protect against nicotine dependence (ND) and higher levels of cigarette consumption. These two hypotheses were tested in young adolescents.

DESIGN

Self reports of tobacco use and ND symptoms were collected every 3-4 months in a prospective study of 1293 grade 7 students from a convenience sample of 10 schools.

SUBJECTS

281 smokers with genetic data were analysed; those who were not already tobacco dependent and who had inhaled (n = 228) were followed 29.9 months on average, until they became dependent or were censored.

MAIN OUTCOME MEASURES

The association between metabolic activity, represented by CYP2A6 genotype, and conversion to dependence was analysed using Cox's proportional hazards model.

RESULTS

During follow up 67 subjects (29.4%) became dependent. Relative to CYP2A6*1/*1, having 1-2 copies of the inactive CYP2A6*2 or *4 variant was a strong risk factor for developing dependence (hazard ratio 2.8, 95% confidence 1.3 to 6.3). Subjects with 1-2 partially inactive CYP2A6*9 or *12 variants were not at increased risk. Mean past-week cigarette consumption at the end of follow up (controlling for age, sex, and number of months since first inhalation) among dependent subjects was 29.1 among normal inactivators, compared to 17.2, and 12.7 among slower (1-2 copies of *9 or *12), and slowest (1-2 copies of *2 or *4) inactivators, respectively (p = 0.09).

CONCLUSION

Adolescents with 1-2 copies of CYP2A6*2 or *4 are at substantially increased risk of becoming dependent but smoke less once dependent. Genetic risk for ND may need to be considered in the conceptualisation of tobacco control programmes for adolescents.

Cotinine and N-(2-hydroxyethyl)valine as markers of passive exposure to tobacco smoke in children

Large segments of populations, including children, are exposed to environmental tobacco smoke (ETS), a risk factor for lung cancer and heart, circulatory and respiratory diseases. Recently, ETS was classified as a class A carcinogen by USEPA, as carcinogenic to humans by IARC (group 1) and by the National Toxicology Program of the US National Institutes of Health. Cotinine, a product of the metabolism of nicotine, is measurable in urine and, correlates strictly and directly to ETS exposure, therefore representing a well-known internal dose marker. Another marker of active tobacco smoking is the N-(2-hydroxyethyl) valine (HOEtVal) which results from the reaction between ethylene oxide (EtO) and the N-terminal valine of hemoglobin. The aim of this study was the evaluations of ETS markers, namely urinary cotinine and HOEtVal measured in blood in 100 children with ages ranging between 3 and 13 years. Experimental findings show that cotinine, as a specific internal dose marker, and HOEtVal, as a nonspecific biological effective dose marker, both depend on the passive exposure to ETS as well as on the active habit of smoking.

Assessment of Sources of Second-Hand Smoke Exposure in a Putatively Unexposed Population

The authors sought to determine levels of urinary cotinine and its association with collateral exposure to second-hand smoke in public health workers. Urinary cotinine was measured twice at 1-wk intervals in 28 public health workers or their spouses. Information on sources of second-hand smoke exposure and a dietary history were obtained from each participant. Geometric mean and median cotinine levels were 2.74 and 2.33 ng/mL, respectively. Only 6 instances of second-hand smoke exposure were reported from a combined 204 days of potential exposure, and these did not correspond to higher cotinine values. There was no association between consumption of foods containing nicotine and log-transformed urine cotinine levels (p = .80). The authors' analysis indicates dietary sources of nicotine are not important, even for persons with very low urinary cotinine levels. Further study is needed to determine sources of variation in urinary cotinine among largely unexposed populations.

Does passive smoke exposure trigger acute asthma attack in children?

The relationship between asthma and passive smoking has been well established. However, it is still not clear whether an acute asthma attack can be induced by acute smoke exposure. The specific aims of this study were: 1- To assess the degree of smoke exposure through urinary cotinine levels in asthmatic children during and 4 weeks after asthma attacks and, 2- To evaluate the reliability of parental questionnaires in asthmatic children by comparing the data obtained from cotinine measurements and parental reports. Thirty-two consecutive asthmatic children who were admitted to the emergency clinic were included in the study. Parents were asked to complete a questionnaire about their smoking habits and housing conditions. Urinary cotinine and creatinine levels were measured in children during and 4 weeks after the acute asthma attack. The mean age of the patients was 5.7 +/- 3.2 years. The mean attack rate was 3.5 +/- 3.8 per year. Thirty-eight percent of the patients were taking no preventive treatment. In 80 % of patients, urinary cotinine and creatinine ratios (CCR) were significantly above the non-exposed, non-smoker levels. However, CCR levels during acute asthma attacks were not higher than those measured 4 weeks after the acute attack (314.6 +/- 299.1 vs. 203.8 +/- 165.2 ng/mg respectively, p > 0.05). Although parental reports of passive smoke exposure was 71 %, CCR levels revealed that 81 % and 97 % of children were exposed to passive smoke during acute attacks and asymptomatic periods, respectively. In conclusion, although the proportion of children with acute asthma attacks who were exposed to passive smoking was high, the degree of passive smoke exposure was not higher during acute attacks. Parental questionnaires were found to be unreliable in reporting passive smoke exposure in asthmatic children during acute attacks.

Incorporating children's toxicokinetics into a risk framework

Children's responses to environmental toxicants will be affected by the way in which their systems absorb, distribute, metabolize, and excrete chemicals. These toxicokinetic factors vary during development, from in utero where maternal and placental processes play a large role, to the neonate in which emerging metabolism and clearance pathways are key determinants. Toxicokinetic differences between neonates and adults lead to the potential for internal dosimetry differences and increased or decreased risk, depending on the mechanisms for toxicity and clearance of a given chemical. This article raises a number of questions that need to be addressed when conducting a toxicokinetic analysis of in utero or childhood exposures. These questions are organized into a proposed framework for conducting the assessment that involves problem formulation (identification of early life stage toxicokinetic factors and chemical-specific factors that may raise questions/concerns for children); data analysis (development of analytic approach, construction of child/adult or child/animal dosimetry comparisons); and risk characterization (evaluation of how children's toxicokinetic analysis can be used to decrease uncertainties in the risk assessment). The proposed approach provides a range of analytical options, from qualitative to quantitative, for assessing children's dosimetry. Further, it provides background information on a variety of toxicokinetic factors that can vary as a function of developmental stage. For example, the ontology of metabolizing systems is described via reference to pediatric studies involving therapeutic drugs and evidence from in vitro enzyme studies. This type of resource information is intended to help the assessor begin to address the issues raised in this paper.

Agreement between maternal self-reported ethanol intake and tobacco use during pregnancy and meconium assays for fatty acid ethyl esters and cotinine

Reliance on self-reported use of tobacco and intake of ethanol during pregnancy is associated with a high probability of error. Use of biological markers, or biomarkers, potentially offers a more valid method to assess exposure. Although cotinine is an established biomarker for tobacco use, there is no established biomarker for in utero ethanol exposure. Recent reports suggest that fatty acid ethyl esters (FAEE) could serve this purpose. To assess agreement between maternal self-reported tobacco use and ethanol intake during pregnancy and detection of metabolites associated with tobacco use (cotinine) and ethanol intake (FAEE), the authors studied maternal histories and meconium samples obtained in November-December 1999 from 436 consecutive mother-infant pairs at a large urban regional perinatal center in Honolulu, Hawaii. Cohen's kappa coefficient and 95% confidence intervals were calculated. Moderate agreement was found between reported tobacco use during the third trimester and detected cotinine level (kappa = 0.53, 95% confidence interval: 0.39, 0.68); however, there was no agreement between reported ethanol intake during the third trimester and detected FAEE (kappa = -0.02, 95% confidence interval: -0.04, 0.00). No mother reporting ethanol intake during the third trimester had detectable FAEE. Findings support the need for additional refinement and validation of the use of FAEE as a biomarker for maternal ethanol intake.

Nicotine metabolism, human drug metabolism polymorphisms, and smoking behaviour

Large interindividual differences occur in human nicotine disposition, and it has been proposed that genetic polymorphisms in nicotine metabolism may be a major determinant of an individual's smoking behaviour. Hepatic cytochrome P4502A6 (CYP2A6) catalyses the major route of nicotine metabolism: C-oxidation to cotinine, followed by hydroxylation to trans-3'-hydroxycotinine. Nicotine and cotinine both undergo N-oxidation and pyridine N-glucuronidation. Nicotine N-1-oxide formation is catalysed by hepatic flavin-containing monooxygenase form 3 (FMO3), but the enzyme(s) required for cotinine N-1'-oxide formation has not been identified. trans-3'-Hydroxycotinine is conjugated by O-glucuronidation. The uridine diphosphate-glucuronosyltransferase (UGT) enzyme(s) required for N- and O-glucuronidation have not been identified. CYP2A6 is highly polymorphic resulting in functional differences in nicotine C-oxidation both in vitro and in vivo; however, population studies fail to consistently and conclusively demonstrate any associations between variant CYP2A6 alleles encoding for either reduced or enhanced enzyme activity with self-reported smoking behaviour. The functional consequences of FMO3 and UGT polymorphisms on nicotine disposition have not been investigated, but are unlikely to significantly affect smoking behaviour. Therefore, current evidence does not support the hypothesis that genetic polymorphisms associated with nicotine metabolism are a major determinant of an individual's smoking behaviour and exposure to tobacco smoke.

Assessment of prenatal smoke exposure by determining nicotine and its metabolites in maternal and neonatal urine

Urine specimens were collected from 75 pregnant women before childbirth and from their newborns within 48 postnatal hours. A high-performance liquid chromatography (HPLC) method was used to determine urinary nicotine and its metabolites, cotinine and trans-3'-hydroxycotinine (OH-cotinine) to objectivise prenatal smoke exposure. Using the sum of nicotine metabolites as a marker, 34 women were classed as not exposed to smoke ( < 15 nmol/l), 18 as passive smokers (15-400 nmol/l), and 23 as active smokers ( > 400 nmol/1). The newborns of active smokers exhibited significantly (P < 0.001) higher nicotine metabolite concentrations than did those of either non-exposed women or passive smokers. A close correlation was found to exist between maternal and neonatal nicotine and cotinine concentrations (r=0.8968 and r=0.9205, respectively). For OH-cotinine, this correlation was particularly close when maternal, but not neonatal, OH - cotinine was adjusted to creatinine (r=0.9792). The neonatal/maternal urine concentration ratios for cotinine and OH-cotinine were noted to not significantly depend on the time of postpartal urine collection. Within the first two postnatal days, the extent of current prenatal smoke exposure attributable to active smoking of the mother was best reflected by the urinary concentrations of cotinine plus OH-cotinine without adjustment to creatinine.

Brain imaging and the effects of caffeine and nicotine

Caffeine and nicotine are the most common psychostimulant drugs used worldwide. Structural neuroimaging findings associated with caffeine and nicotine consumption are limited and primarily reflect the putative relationship between smoking and white matter hyperintensities (WMH), a finding that warrants further appraisal of its clinical implications. The application of newer brain imaging modalities that measure subtle haemodynamic changes or tissue-based chemistry in order to better elucidate brain functional processes, including mechanisms underlying addiction to nicotine and caffeine and the brain functional consequences, provide intriguing findings. Potential influences of caffeine and nicotine on the functional contrast, or metabolic response, to neural activation also necessitates the careful appraisal of the effects that these commonly used drugs may have on the results of functional imaging.