Clinical pharmacology of oral cotinine

Cotinine: Pharmacologically Active Metabolite of Nicotine and Neural Mechanisms for Its Actions

Tobacco use disorder continues to be a leading public health issue and cause of premature death in the United States. Nicotine is considered as the major tobacco alkaloid causing addiction through its actions on nicotinic acetylcholine receptors (nAChRs). Current pharmacotherapies targeting nicotine's effects produce only modest effectiveness in promoting cessation, highlighting the critical need for a better understanding of mechanisms of nicotine addiction to inform future treatments. There is growing interest in identifying potential contributions of non-nicotine components to tobacco reinforcement. Cotinine is a minor alkaloid, but the major metabolite of nicotine that can act as a weak agonist of nAChRs. Accumulating evidence indicates that cotinine produces diverse effects and may contribute to effects of nicotine. In this review, we summarize findings implicating cotinine as a neuroactive metabolite of nicotine and discuss available evidence regarding potential mechanisms underlying its effects. Preclinical findings reveal that cotinine crosses the blood brain barrier and interacts with both nAChRs and non-nAChRs in the nervous system, and produces neuropharmacological and behavioral effects. Clinical studies suggest that cotinine is psychoactive in humans. However, reviewing evidence regarding mechanisms underlying effects of cotinine provides a mixed picture with a lack of consensus. Therefore, more research is warranted in order to provide better insight into the actions of cotinine and its contribution to tobacco addiction.

Effect of race and glucuronidation rates on the relationship between nicotine metabolite ratio and nicotine clearance

OBJECTIVES

To investigate if the nicotine metabolite ratio (NMR, the ratio of nicotine metabolites 3'-hydroxycotinine/cotinine) is a reliable phenotypic biomarker for nicotine clearance across races, and as a function of differences in the rate of nicotine, cotinine and 3'-hydroxycotinine glucuronidation and UGT genotypes.

METHODS

Participants [Caucasians (Whites), African Americans (Blacks) and Asian-Americans (Asians)] received an oral solution of deuterium-labeled nicotine and its metabolite cotinine. Plasma and saliva concentrations of nicotine and cotinine were used to determine oral clearances. Rates of glucuronidation were assessed from urine glucuronide/parent ratios, and UGT2B10 and UGT2B17 genotypes from DNA.

RESULTS

Among the 227 participants, 96 (42%) were White, 67 (30%) Asian and 64 (28%) Black. Compared to the other two races, Whites had higher nicotine and cotinine total oral clearance, Blacks had lower nicotine and cotinine glucuronidation rates and Asians had lower 3'-hydroxycotinine glucuronidation rates. A strong positive correlation (correlations coefficients 0.77-0.84; P < 0.001) between NMR and nicotine oral clearance was found for all three races, and NMR remained a strong predictor for the nicotine oral clearance while adjusting for race, sex and age. Neither the metabolite glucuronidation ratios nor the UGT genotypes had significant effects on the ability of NMR to predict nicotine oral clearance.

CONCLUSION

NMR appears to be a reliable phenotypic biomarker for nicotine clearance across races, glucuronidation phenotypes and genotypes. Racial differences in the relationships between NMR, smoking behaviors and addiction are unlikely to be related to an inadequate estimation of nicotine clearance on the basis of NMR.

Cotinine: A Therapy for Memory Extinction in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a mental disorder that may develop after exposure to exceptionally threatening or unescapable horrifying events. Actual therapies fail to alleviate the emotional suffering and cognitive impairment associated with this disorder, mostly because they are ineffective in treating the failure to extinguish trauma memories in a great percentage of those affected. In this review, current behavioral, cellular, and molecular evidence supporting the use of cotinine for treating PTSD are reviewed. The role of the positive modulation by cotinine of the nicotinic acetylcholine receptors (nAChRs) and their downstream effectors, the protection of astroglia, and the inhibition of microglia in the PTSD brain are also discussed.

Chronic psychosocial stressors and salivary biomarkers in emerging adults

We investigated whole saliva as a source of biomarkers to distinguish individuals who have, and who have not, been chronically exposed to severe and threatening life difficulties. We evaluated RNA and DNA metrics, expression of 37 candidate genes, and cortisol release in response to the Trier Social Stress Test, as well as clinical characteristics, from 48 individuals stratified on chronic exposure to psychosocial stressors within the last year as measured by the Life Events and Difficulties Schedule. Candidate genes were selected based on their differential gene expression ratio in circulating monocytes from a published genome-wide analysis of adults experiencing different levels of exposure to a chronic stressor. In univariate analyses, we observed significantly decreased RNA integrity (RIN) score (P = 0.04), and reduced expression of glucocorticoid receptor-regulated genes (Ps < 0.05) in whole saliva RNA from individuals exposed to chronic stressors, as compared to those with no exposure. In those exposed, we observed significantly decreased BMI (P < 0.001), increased ever-smoking and increased lifetime alcohol abuse or dependence (P ≤ 0.03), and a reduction of cortisol release. In post hoc multivariate analyses including clinical and biospecimen-derived variables, we consistently observed significantly decreased expression of IL8 (Ps<0.05) in individuals exposed, with no significant association to RIN score. Alcohol use disorders, tobacco use, a reduced acute stress response and decreased salivary IL8 gene expression characterize emerging adults chronically exposed to severe and threatening psychosocial stressors.

Assessment of nicotine dependence among adolescent and young adult smokers: a comparison of measures

INTRODUCTION

Tobacco use often starts in adolescence, yet assessment of dependence among adolescent smokers remains a challenge, particularly given the potential discord between self-reports of smoking behavior and actual use. We could find no prior study, among adolescents, that directly compares the association between objective biomarkers of tobacco exposure (e.g., cotinine) and multiple measures of dependence. This study examined the concurrent validity of two common dependence measures: the Fagerström Test for Nicotine Dependence (FTND) and the Hooked on Nicotine Checklist (HONC). We further examined the FTND by removing the one item on cigarettes smoked per day.

METHODS

Based within a parent clinical trial for adolescent smoking cessation, eligible participants were 12-21years old, smoking >/=5cigarettes per day on average, and with urine cotinine >100ng/ml at baseline. Results are based on participants who completed each measure and who provided a urine cotinine sample at baseline (N=73).

RESULTS

Results showed that the FTND was associated with cotinine (p<0.001; R(2)=0.25), and that this relationship held true for the revised FTND as well (p<0.001; R(2)=0.18). However, the HONC was only marginally associated with cotinine (p=0.06; R(2)=0.09).

DISCUSSION

Our results suggest that the FTND may be better associated with actual smoking behavior in adolescents as compared to the HONC. Pending replication, our data provide caution with regard to assessment of nicotine dependence at least among established adolescent smokers who have more entrenched smoking behavior.

Urine nicotine metabolite concentrations in relation to plasma cotinine during low-level nicotine exposure

INTRODUCTION

Plasma or saliva cotinine concentrations are used widely as biomarkers of secondhand smoke (SHS) exposure and have been associated with the risk of SHS-related disease. Concentrations of cotinine and other nicotine metabolites are considerably higher in urine than in plasma or saliva, making chemical analysis easier. In addition, urine is often more convenient to collect in some SHS exposure studies. The optimal use of nicotine metabolites in urine, singly or in combination, with or without correction for urine creatinine concentration, to estimate plasma cotinine concentration with low-level nicotine exposure has not been determined.

METHODS

We dosed 36 nonsmokers with 100, 200, or 400 microg deuterium-labeled nicotine (simulating exposure to SHS) by mouth daily for 5 days and then measured plasma and urine cotinine and metabolites at various intervals over 24 hr.

RESULTS

A plasma cotinine concentration of 1 ng/ml corresponds on average to a daily intake of 100 microg nicotine. Cotinine concentrations in urine averaged four to five times those in plasma. Correction of urine cotinine for creatinine concentration improved the correlation between urine and plasma cotinine. Measuring multiple cotinine metabolites in urine did not improve the correlation with plasma cotinine, compared with the use of urine cotinine alone.

DISCUSSION

Measurement of urine cotinine corrected for creatinine concentration appears to be the best predictor of plasma cotinine.

Genome-wide linkage of cotinine pharmacokinetics suggests candidate regions on chromosomes 9 and 11

Characterizing cotinine pharmacokinetics is a useful way to study nicotine metabolism because the same liver enzyme is primarily responsible for the metabolism of both, and the clearances of nicotine and cotinine are highly correlated. We conducted a whole-genome linkage analysis to search for candidate regions influencing quantitative variation in cotinine pharmacokinetics in a large-scale pharmacokinetic study with 61 families containing 224 healthy adult participants. The strongest linkage signal was identified at 135 cM of chromosome 9 with LOD = 2.81 and P = 0.0002; two other suggestive linkage peaks appear at 31.4 and 73.5 cM of chromosome 11 with LOD = 1.96 (P = 0.0013) and 1.94 (P = 0.0014). The confidence level of the linkage between the three genome regions and cotinine pharmacokinetics is statistically significant with a genome-wide empirical probability of P = 0.029.

Cotinine-induced convergence of the cholinergic and PI3 kinase-dependent anti-inflammatory pathways in innate immune cells

Nicotine [(S)-3-(1-methyl-2-pyrrolidinyl)pyridine] is a major component of tobacco and a highly efficient acetylcholine receptor (nAChR) agonist that triggers the cholinergic anti-inflammatory pathway. We demonstrate that pre-treatment of monocytes with the stable nicotine catabolite, cotinine [(S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone], dramatically alters the nature of the inflammatory response to Gram negative bacteria by abrogating the production of cytokines that are under the transcriptional control of the NF-kappaB system (TNF-alpha, IL-1beta, IL-6, IL-12/IL-23 p40) and shifting the response towards an IL-10-dominated anti-inflammatory profile. This anti-inflammatory phenomenon is initiated specifically by engagement of the monocytic alpha7 nAChR; and is PI3K/GSK-3beta-dependent; but NF-kappaB-independent. These mechanistic insights suggest an ability to exploit convergent, endogenous anti-inflammatory pathway(s) to either up-regulate or down-regulate the production of specific cytokine groups (pro- or anti-inflammatory cytokines) depending on the clinical necessity.

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.

Measuring tobacco smoke exposure: quantifying nicotine/cotinine concentration in biological samples by colorimetry, chromatography and immunoassay methods

Procedures to assess tobacco smoke exposure are reviewed and biomarkers used for determining the smoking status of an individual are compared. Methods used to extract these biomarkers from saliva, urine, and blood and the advantages and disadvantages of the assays are discussed. Finally, the procedures used to measure the levels of cortisol, a stress hormone speculated to be linked to nicotine metabolism, are discussed.

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.

Substance misuse in patients with schizophrenia: epidemiology and management

Substance misuse in individuals with schizophrenia is very common, especially in young men, in communities where use is frequent and in people receiving inpatient treatment. Problematic use occurs at very low intake levels, so that most affected people are not physically dependent (with the exception of nicotine). People with schizophrenia and substance misuse have poorer symptomatic and functional outcomes than those with schizophrenia alone. Unless there is routine screening, substance misuse is often missed in assessments. Service systems tend to be separated, with poor inter-communication, and affected patients are often excluded from services because of their comorbidity. However, effective management of these disorders requires a fully integrated approach because of the close inter-relationship of the disorders. Use of atypical antipsychotics may be especially important in this population because of growing evidence (especially on clozapine and risperidone) that nicotine smoking, alcohol misuse and possibly some other substance misuse is reduced. Several pharmacotherapies for substance misuse can be used safely in people with schizophrenia, but the evidence base is small and guidelines for their use are necessarily derived from experience in the general population.

Genetic variation in CYP2A6-mediated nicotine metabolism alters smoking behavior

Approximately 50% of the initiation of tobacco dependence is genetically influenced, whereas maintenance of dependent smoking behavior and amount smoked have approximately 70% genetic contribution (1-5). Determining the variation in nicotine's inactivation is important because of nicotine's role in producing tobacco dependence and regulating smoking patterns (6-11). The genetically polymorphic CYP2A6 enzyme is responsible for the majority of the metabolic inactivation of nicotine to cotinine (12-14). Both in vitro and in vivo studies have demonstrated considerable interindividual variation in CYP2A6 activity (15-17). CYP2A6 is genetically polymorphic, individuals carrying inactive CYP2A6 alleles have decreased nicotine metabolism, are less likely to become smokers and if they do, they smoke fewer cigarettes per day (13,18,19). The decrease in smoking behavior was confirmed by measuring carbon monoxide (CO, a measure of smoke inhalation) levels, plasma and urine nicotine and cotinine levels, and cigarette counts (13,18,19). A duplication variant in the CYP2A6 gene locus has been identified which increases nicotine inactivation and increases smoking (19). CYP2A6 can also activate tobacco smoke procarcinogens (e.g. NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone); current studies are investigating the role of CYP2A6 in risk for lung cancer. Based on these epidemiologic data it was postulated that inhibition of CYP2A6 activity might be useful in a therapeutic context. Kinetic studies in humans indicated that selective CYP2A6 inhibitors decrease the metabolic removal of nicotine. It was also shown that inhibiting CYP2A6 in vivo (phenocopying, or mimicking the genetic defect) in smokers results in decreased smoking, making nicotine orally bioavailable, and the rerouting of procarcinogens to detoxifying pathways (20-22).