Pharmacodynamic effects of cotinine in abstinent cigarette smokers

The involvement of dopamine and D2 receptor-mediated transmission in effects of cotinine in male rats

Previous studies indicated that cotinine, the major metabolite of nicotine, supported intravenous self-administration and exhibited relapse-like drug-seeking behaviors in rats. Subsequent studies started to reveal an important role of the mesolimbic dopamine system in cotinine's effects. Passive administration of cotinine elevated extracellular dopamine levels in the nucleus accumbens (NAC) and the D1 receptor antagonist SCH23390 attenuated cotinine self-administration. The objective of the current study was to further investigate the role of mesolimbic dopamine system in mediating cotinine's effects in male rats. Conventional microdialysis was conducted to examine NAC dopamine changes during active self-administration. Quantitative microdialysis and Western blot were used to determine cotinine-induced neuroadaptations within the NAC. Behavioral pharmacology was performed to investigate potential involvement of D2-like receptors in cotinine self-administration and relapse-like behaviors. NAC extracellular dopamine levels increased during active self-administration of cotinine and nicotine with less robust increase during cotinine self-administration. Repeated subcutaneous injections of cotinine reduced basal extracellular dopamine concentrations without altering dopamine reuptake in the NAC. Chronic self-administration of cotinine led to reduced protein expression of D2 receptors within the core but not shell subregion of the NAC, but did not change either D1 receptors or tyrosine hydroxylase in either subregion. On the other hand, chronic nicotine self-administration had no significant effect on any of these proteins. Systemic administration of eticlopride, a D2-like receptor antagonist attenuated both cotinine self-administration and cue-induced reinstatement of cotinine seeking. These results further support the hypothesis that the mesolimbic dopamine transmission plays a critical role in mediating reinforcing effects of cotinine.

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

Animal survival depends on cognitive abilities such as learning and memory to adapt to environmental changes. Memory functions require an enhanced activity and connectivity of a particular arrangement of engram neurons, supported by the concerted action of neurons, glia, and vascular cells. The deterioration of the cholinergic system is a common occurrence in neurological conditions exacerbated by aging such as traumatic brain injury (TBI), posttraumatic stress disorder (PTSD), Alzheimer's disease (AD), and Parkinson's disease (PD). Cotinine is a cholinergic modulator with neuroprotective, antidepressant, anti-inflammatory, antioxidant, and memory-enhancing effects. Current evidence suggests Cotinine's beneficial effects on cognition results from the positive modulation of the α7-nicotinic acetylcholine receptors (nAChRs) and the inhibition of the toll-like receptors (TLRs). The α7nAChR affects brain functions by modulating the function of neurons, glia, endothelial, immune, and dendritic cells and regulates inhibitory and excitatory neurotransmission throughout the GABA interneurons. In addition, Cotinine acting on the α7 nAChRs and TLR reduces neuroinflammation by inhibiting the release of pro-inflammatory cytokines by the immune cells. Also, α7nAChRs stimulate signaling pathways supporting structural, biochemical, electrochemical, and cellular changes in the Central nervous system during the cognitive processes, including Neurogenesis. Here, the mechanisms of memory formation as well as potential mechanisms of action of Cotinine on memory preservation in aging and neurological diseases are discussed.

Relapse to cotinine seeking in rats: differential effects of sex

Relapse is a defining feature of smoking and a significant challenge in cessation management. Elucidation of novel factors underlying relapse may inform future treatments. Cotinine, the major metabolite of nicotine, has been shown to support intravenous self-administration in rats, implicating it as one potential factor contributing to nicotine reinforcement. However, it remains unknown whether cotinine would induce relapse-like behaviors. The current study investigated relapse to cotinine seeking in two relapse models, the reinstatement of drug seeking and incubation of drug craving models. In the reinstatement model, rats were trained to self-administer cotinine, underwent extinction of cotinine-associated responses, and were tested for cue-, drug-, or stress-induced reinstatement. Conditioned cues associated with cotinine self-administration, cotinine (1-2 mg/kg), or the pharmacological stressor yohimbine (1.25-2.5 mg/kg) induced reinstatement of cotinine seeking. Female rats displayed more pronounced cue-induced, but not drug- or stress-induced reinstatement than male rats. In the incubation of the craving model, rats were trained to self-administer cotinine and underwent forced withdrawal in home cages. Rats were tested for cue-induced cotinine-seeking on both withdrawal day 1 and withdrawal day 18. Rats exhibited greater cue-induced cotinine-seeking on withdrawal day 18 compared to withdrawal day 1, with no difference between male and female rats. These findings indicate that cotinine induces sex-specific relapse to drug seeking in rats, suggesting that cotinine may contribute to relapse.

The involvement of mesolimbic dopamine system in cotinine self-administration in rats

Cotinine is the major metabolite of nicotine and has recently been shown to be self-administered intravenously by rats. However, mechanisms underlying cotinine self-administration remained unknown. Mesolimbic dopamine system projecting from the ventral tegmental area (VTA) to nucleus accumbens (NAC) is closely implicated in drug reinforcement, including nicotine. The objective of the current study was to determine potential involvement of mesolimbic dopamine system in cotinine self-administration. An intracranial self-administration experiment demonstrates that cotinine at 0.88 and 1.76 ng/100 nl/infusion was self-infused into the VTA by rats. Rats produced more infusions of cotinine than vehicle and responded more on active than inactive lever during acquisition, reduced responding when cotinine was replaced by vehicle, and resumed responding during re-exposure to cotinine. Microinjection of cotinine at 1.76 ng/100 nl/infusion into the VTA increased extracellular dopamine levels within the NAC. Subcutaneous injection of cotinine at 1 mg/kg also increased extracellular dopamine levels within the NAC. Administration of the D1-like receptor antagonist SCH 23390 attenuated intravenous cotinine self-administration. On the other hand, bupropion, a catecholamine uptake inhibitor, did not significantly alter intravenous cotinine self-administration. These results suggest that activation of mesolimbic dopamine system may represent one cellular mechanism underlying cotinine self-administration. This shared mechanism between cotinine and nicotine suggests that cotinine may play a role in nicotine reinforcement.

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.

Possible New Symptoms of Tobacco Withdrawal III: Reduced Positive Affect-A Review and Meta-analysis

INTRODUCTION

Most descriptions of tobacco withdrawal have not changed in >30 years despite new research. This meta-analysis tested whether abstinence leads to decreased positive affect (PA) because abstinence-induced symptom changes are a core feature of the tobacco withdrawal syndrome. In addition, we examined whether reduced PA was due to withdrawal (ie, temporary decrease in a "U-shaped" curve) or offset (ie, return to baseline) effect.

METHODS

Our main inclusion criterion was a prospective within-participant test of change in PA during abstinence conditions among people who smoke cigarettes daily who were not using a cessation medication. Our search of PubMed, PsycINFO, and personal libraries yielded a total of 32 tests with 2054 participants.

RESULTS

There was a medium effect size indicating an overall decrease in PA following abstinence from cigarettes (Cohen's d = -0.40, 95% CI = -0.30 to -0.49). There was large heterogeneity (I2 = 70.7%). Most (79%) of the 24 trials that conducted significance tests reported that reduction in PA was significant. Seven tests were adequately designed to detect a withdrawal versus offset effect. Over half (57%) displayed a U-shaped curve for abstinence-induced change in PA indicative of a withdrawal symptom rather than offset effect.

CONCLUSIONS

Abstinence from cigarettes is associated with a decrease in PA. Whether low PA should be added to withdrawal measures and diagnostic criteria requires replication of the time-course of change in PA and tests of whether abstinence-induced changes in PA and negative affect occur independently.

IMPLICATIONS

Though there was substantial heterogeneity among trials, our findings suggest that (1) abstinence from cigarettes decreases positive affect and (2) this decrease may represent a withdrawal effect (vs. an offset effect). However, it is unclear whether abstinence-induced losses in positive affect are independent from increased negative affect.

Self-Administration of Cotinine in Wistar Rats: Comparisons to Nicotine

Nicotine is the major addictive component in tobacco. Cotinine is the major metabolite of nicotine and a weak agonist for nicotinic acetylcholine receptors (nAChRs). Nicotine supports self-administration in rodents. However, it remains undetermined whether cotinine can be self-administered. This study aimed to characterize cotinine self-administration in rats, to compare effects of cotinine to those of nicotine, and to determine potential involvement of nAChRs in cotinine's effects. Adult Wistar rats were trained to self-administer cotinine or nicotine (0.0075, 0.015, 0.03, or 0.06 mg/kg per infusion) under fixed-ratio (FR) and progressive-ratio (PR) schedules. Blood nicotine and cotinine levels were determined after the last FR session. Effects of mecamylamine, a nonselective nAChR antagonist, and varenicline, a partial agonist for α4β2* nAChRs, on cotinine and nicotine self-administration were determined. Rats readily acquired cotinine self-administration, responded more on active lever, and increased motivation to self-administer cotinine when the reinforcement requirement increased. Blood cotinine levels ranged from 77 to 792 ng/ml. Nicotine induced more infusions at lower doses during FR schedules and greater breakpoints at higher doses during the PR schedule than cotinine. There was no difference in cotinine self-administration between male and female rats. Mecamylamine and varenicline attenuated nicotine but not cotinine self-administration. These results indicate that cotinine was self-administered by rats. These effects of cotinine were less robust than nicotine and exhibited no sex difference. nAChRs appeared to be differentially involved in self-administration of nicotine and cotinine. These results suggest cotinine may play a role in the development of nicotine use and misuse. SIGNIFICANCE STATEMENT: Nicotine addiction is a serious public health problem. Cotinine is the major metabolite of nicotine, but its involvement in nicotine reinforcement remains elusive. Our findings indicate that cotinine, at doses producing clinically relevant blood cotinine levels, supported intravenous self-administration in rats. Cotinine self-administration was less robust than nicotine. Mecamylamine and varenicline attenuated nicotine but not cotinine self-administration. These results suggest cotinine may play a role in the development of nicotine use and misuse.

Effects of nicotine, nornicotine and cotinine, alone or in combination, on locomotor activity and ultrasonic vocalization emission in adult rats

RATIONALE

The behavioral effects of the nicotine metabolites nornicotine and cotinine have not been investigated extensively.

OBJECTIVES

To evaluate the effects of nicotine, cotinine, and nornicotine, given alone or in combination, on locomotor activity and emission of ultrasonic vocalizations in male adult rats.

METHODS

Rats were first given home cage nicotine injections to make them tolerant to the drug's locomotor depressant effects. On subsequent days, locomotor activity (LMA) and ultrasonic vocalizations were recorded in an open field, for 60 min after challenge injection, using repeated measures designs. In single-drug experiments, subjects were tested with nicotine 0.05-0.4 mg/kg, cotinine 0.03-3 mg/kg, or nornicotine 0.1-10 mg/kg. In drug-combination experiments, saline or nicotine 0.2 mg/kg challenge was preceded by cotinine (0, 0.3, 3 mg/kg) or nornicotine (0, 0.1, 0.3, 1, 3 mg/kg) injection.

RESULTS

High doses of nornicotine increased LMA and blunted the locomotor stimulant effect of nicotine. Less consistently, nicotine and high doses of nornicotine decreased the 50-kHz call rate, with no clear evidence of a nornicotine × nicotine interaction. Cotinine, given alone or before nicotine injection, altered neither LMA nor the call rate. No drug altered the relative prevalence of flat vs. trill 50-kHz call subtypes, except that the highest dose of nornicotine promoted flat calls over trills. No drug evoked 22-kHz calls.

CONCLUSION

Nornicotine can exert an acute anti-nicotine effect in vivo, as previously reported in vitro. The finding that nicotine did not detectably alter the 50-kHz call profile appears consistent with this drug's mild subjective effects in human subjects.

Time-course of extracellular nicotine and cotinine levels in rat brain following administration of nicotine: effects of route and ethanol coadministration

RATIONALE

Nicotine and ethanol are commonly coabused drugs, and nicotine-laced ethanol products are growing in popularity. However, little is known about time-course changes in extracellular nicotine and cotinine levels in rat models of ethanol and nicotine coabuse.

OBJECTIVES

The objective of the present study was to determine the time-course changes in brain levels of nicotine and cotinine following subcutaneous (SC) and intragastric (IG) nicotine administration in alcohol-preferring (P) and Wistar rats.

METHODS

In vivo microdialysis was used to collect dialysate samples from the nucleus accumbens shell (NACsh) for nicotine and cotinine determinations, following SC administration of (-)-nicotine (0.18, 0.35, and 0.70 mg/kg) in female P and Wistar rats or IG administration of (-)-nicotine (0.35 and 0.70 mg/kg) in 15 % (v/v) ethanol or water in female P rats.

RESULTS

SC nicotine produced nicotine and cotinine dialysate levels as high as 51 and 14 ng/ml, respectively. IG administration of 15 % EtOH + 0.70 mg/kg nicotine in P rats resulted in maximal nicotine and cotinine dialysate levels of 19 and 14 ng/ml, respectively, whereas administration of 0.70 mg/kg nicotine in water resulted in maximal nicotine and cotinine levels of 21 and 25 ng/ml, respectively. Nicotine and cotinine levels were detectable within the first 15 and 45 min, respectively, after IG administration.

CONCLUSIONS

Overall, the results of this study suggest that nicotine is rapidly adsorbed and produces relevant extracellular brain concentrations of nicotine and its pharmacologically active metabolite, cotinine. The persisting high brain concentrations of cotinine may contribute to nicotine addiction.

New Insights into the Mechanisms of Action of Cotinine and its Distinctive Effects from Nicotine

Tobacco consumption is far higher among a number of psychiatric and neurological diseases, supporting the notion that some component(s) of tobacco may underlie the oft-reported reduction in associated symptoms during tobacco use. Popular dogma holds that this component is nicotine. However, increasing evidence support theories that cotinine, the main metabolite of nicotine, may underlie at least some of nicotine's actions in the nervous system, apart from its adverse cardiovascular and habit forming effects. Though similarities exist, disparate and even antagonizing actions between cotinine and nicotine have been described both in terms of behavior and physiology, underscoring the need to further characterize this potentially therapeutic compound. Cotinine has been shown to be psychoactive in humans and animals, facilitating memory, cognition, executive function, and emotional responding. Furthermore, recent research shows that cotinine acts as an antidepressant and reduces cognitive-impairment associated with disease and stress-induced dysfunction. Despite these promising findings, continued focus on this potentially safe alternative to tobacco and nicotine use is lacking. Here, we review the effects of cotinine, including comparisons with nicotine, and discuss potential mechanisms of cotinine-specific actions in the central nervous system which are, to date, still being elucidated.

Perturbation of cellular immune functions in cigarette smokers and protection by palm oil vitamin E supplementation

Background

Cigarette smoke contains free radicals and an have adverse effect to the immune system. Supplementation of palm oil vitamin E (palmvitee), is known has antioxidant properties is thought to be beneficial for system immune protection against free radicals activity. The objective of the study was to determine the effect of palmvitee supplementation on immune response in smokers.

Methods

This study involved a group of smokers and nonsmokers who received 200 mg/day palmvitee and placebo for the control group. Blood samples were taken at 0, 12 and 24 weeks of supplementation. Plasma tocopherol and tocotrienol were determined by HPLC, lymphocyte proliferation by lymphocyte transformation test (LTT) and enumeration of lymphocytes T and B cells by flow cytometry. Statistical analysis was performed by Mann–Whitney U-test for non-parametric data distribution and correlation among the variables was examined by Spearman.

Results

Plasma tocopherol and tocotrienol were increased in vitamin E supplemented group as compared to placebo group. Urine cotinine levels and serum α₁-antitrypsin were significantly higher in smokers compared to nonsmokers. Lymphocyte proliferation induced by PHA showed an increasing trend with palmvitee supplementation in both smokers and nonsmokers. Natural killer cells were decreased; CD4⁺ cells and B cells were increased in smokers compared to nonsmokers but were unaffected with vitamin E supplementation except in the percentage of B cells which were increased in nonsmokers supplemented palmvitee compared to placebo. CD4⁺/CD8⁺ ratio was increased in smokers compared to nonsmokers. The high TWBC count observed in smokers correlated with the increased CD4⁺ and B cells.

Conclusions

Smoking caused alterations in certain immune parameters and palmvitee supplementation tended to cause an increase in lymphocytes transformation test but had no effect on CD3⁺, CD4⁺, CD8⁺, NK cells and B cells except B cells percentage in nonsmokers.

Nicotine metabolism in pregnant and nonpregnant rabbits

Smoking during pregnancy remains a major public health concern and is associated with numerous adverse effects. Recently the clearance of nicotine and cotinine was shown to be substantially increased in pregnant women compared with nonpregnant controls. The present study investigated the usefulness of the rabbit for studying the molecular basis for the observed changes in nicotine and cotinine disposition during pregnancy. Nicotine was largely metabolized to cotinine in rabbit liver microsomes (approximately 50% of total metabolism); significant amounts of nicotine-N'-oxide and nornicotine also were detected. The conversion of nicotine to cotinine also was detected in rabbit placental and fetal liver microsomes, albeit at only a fraction of the rate found in adult rabbit liver microsomes. The major products of cotinine metabolism in rabbit liver microsomes were 5'-hydroxycotinine, cotinine-N'-oxide, and norcotinine. Differences between human and rabbit liver were most apparent for cotinine. The major human metabolite, 3'-hydroxycotinine, was formed at only low levels in rabbit liver microsomes. Pregnancy had no effect on the metabolism of nicotine or on the expression of CYP2A6 immunoreactive proteins in rabbit liver microsomes. These studies provide a complete quantitative assessment of nicotine metabolism in rabbit liver microsomes and suggest that the rabbit may not be an appropriate animal model to study the effects of pregnancy on nicotine and cotinine metabolism. However, a molecular understanding of these effects is essential for prediction of the pharmacological and toxicological consequences of smoking during pregnancy.

Development of an anti-cotinine vaccine to potentiate nicotine-based smoking cessation strategies

Nicotine replacement therapies (NRT) have limited success in smoking cessation. The efficacy of nicotine may be compromised by its main metabolite, cotinine. An anti-cotinine vaccine to remove this antagonism could enhance the efficacy of NRT. We show that cotinine is a weak nicotinic agonist and decreases responses to nicotine, consistent with antagonism through receptor desensitisation. trans-4-Thiol cotinine was coupled to tetanus toxoid, and rats immunised repeatedly. Vaccination raised antibodies specific for cotinine that do not recognise other metabolites or nicotine. Increased serum cotinine concentrations following nicotine administration indicate sequestration of cotinine by antibodies, encouraging further evaluation of this vaccine in behavioural models of nicotine addiction and relapse.

Withdrawal from chronic nicotine in adolescent and adult rats

The purpose of the present experiment is to assess potential differences in nicotine withdrawal in both adolescent and adult rats. Nicotine dependence was induced via osmotic minipump in adolescent rats (releasing 22.2 mg/kg/day on Postnatal Day 28) and adults (release rate of 18.4 mg/kg/day on Postnatal Day 60); differential initial release rates were used across age to compensate for the more rapid weight gain of adolescents. On Day 7 of nicotine exposure, withdrawal was induced via the administration of a nicotinic antagonist, mecamylamine (1.0 mg/kg i.p.), and withdrawal-induced anxiogenesis assessed on the elevated plus maze. On Days 1 and 4 after pump removal, animals were examined for startle responses and prepulse inhibition in an acoustic startle chamber. Adult animals exhibited a nicotine withdrawal-induced increase in anxiety, while adolescents did not. One day following the removal of minipumps, only nicotine dependent adolescent animals exhibited a disruption in prepulse inhibition. Nicotine withdrawal failed to produce an alteration in acoustic startle response in either group. Together these data suggest that ontogenic differences in nicotine withdrawal are dependent on the withdrawal measure examined, with adolescents being less sensitive than adults to anxiety-like symptoms, while being more sensitive to withdrawal-induced cognitive disruption.

Characterization and comparison of nicotine and cotinine metabolism in vitro and in vivo in DBA/2 and C57BL/6 mice

DBA/2 and C57BL/6 are two commonly used mouse strains that differ in response to nicotine. Previous studies have shown that the nicotine-metabolizing enzyme CYP2A5 differs in coumarin metabolism between these two strains, suggesting differences in nicotine metabolism. Nicotine was metabolized to cotinine in vitro by two enzymatic sites. The high-affinity sites exhibited similar parameters (Km, 10.7 +/- 4.8 versus 11.4 +/- 3.6 microM; Vmax, 0.58 +/- 0.18 versus 0.50 +/- 0.07 nmol/min/mg for DBA/2 and C57BL/6, respectively). In vivo, the elimination half-lives of nicotine (1 mg/kg, s.c.) were also similar between DBA/2 and C57BL/6 mice (8.6 +/- 0.4 versus 9.2 +/- 1.6 min, respectively); however, cotinine levels were much higher in DBA/2 mice. The production and identity of the putative cotinine metabolite 3'-hydroxycotinine in mice was confirmed by liquid chromatography/mass spectrometry/mass spectrometry. The in vivo half-life of cotinine (1 mg/kg, s.c.) was significantly longer in the DBA/2 mice compared with the C57BL/6 mice (50.2 +/- 4.7 versus 37.5 +/- 9.6 min, respectively, p < 0.05). The in vitro metabolism of cotinine to 3'-hydroxycotinine was also less efficient in DBA/2 than C57BL/6 mice (Km, 51.0 +/- 15.6 versus 9.5 +/- 2.1 microM, p < 0.05; Vmax, 0.10 +/- 0.01 versus 0.04 +/- 0.01 nmol/min/mg, p < 0.05, respectively). Inhibitory antibody studies demonstrated that the metabolism of both nicotine and cotinine was mediated by CYP2A5. Genetic differences in Cyp2a5 potentially contributed to similar nicotine but different cotinine metabolism, which may confound the interpretation of nicotine pharmacological studies and studies using cotinine as a biomarker.

Antibody-catalyzed oxidative degradation of nicotine using riboflavin

Tobacco abuse remains a major cause of death worldwide despite ample evidence linking nicotine to various disease states. Consequently, immunopharmacotherapeutic approaches for the treatment of nicotine abuse have received increasing attention. Although a number of nicotine-binding antibodies have been disclosed, no antibody catalysts exist which efficiently degrade nicotine into pharmacologically inactive substances. Herein, we report the first catalytic antibodies which can oxidatively degrade nicotine. These biocatalysts use the micronutrient riboflavin and visible light as a source of singlet oxygen for the production of reactive oxygen species. Along with various known nicotine metabolites, antibody-catalyzed nicotine oxidations produce two novel nicotine oxidation products that were also detected in control ozonation reactions of nicotine. The reaction is efficient, with multiple turnovers of catalyst observed and total consumption of nicotine attained. These results demonstrate the potential of harnessing riboflavin as an endogenous sensitizer for antibody-catalyzed oxidations and demonstrate a new approach for the development of an active vaccine for the treatment of nicotine addiction using in vivo catalytically active antibodies.

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.

Cotinine inhibits catecholamine release evoked by cholinergic stimulation from the rat adrenal medulla

The aim of the present study was to clarify whether cotinine affects the release of catecholamines (CA) from the isolated perfused rat adrenal gland, and to establish the mechanism of its action, in comparison with the response of nicotine. Cotinine (0.3-3 mM), when perfused into an adrenal vein for 60 min, inhibited CA secretory responses evoked by ACh (5.32 mM), DMPP (a selective neuronal nicotinic agonist, 100 microM for 2 min) and McN-A-343 (a selective muscarinic M1-agonist, 100 microM for 2 min) in dose- and time-dependent manners. However, cotinine did not affect CA secretion by high K+ (56 mM). Cotinine itself also failed to affect basal CA output. Furthermore, in the presence of cotinine (1 mM), CA secretory responses evoked by Bay-K-8644 (an activator of L-type Ca2+ channels, 10 microM) and cyclopiazonic acid (an inhibitor of cytoplasmic Ca2+-ATPase, 10 microM) were relative time-dependently attenuated. However, nicotine (30 microM), given into the adrenal gland for 60 min, initially rather enhanced CA secretory responses evoked by ACh and high K+, followed by the inhibition later, while it time-dependently depressed the CA release evoked by McN-A-343 and DMPP. Taken together, these results suggest that cotinine inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does fail to affect that by the direct membrane-depolarization. It seems that this inhibitory effect of cotinine may be exerted by the cholinergic blockade, which is associated with blocking both the calcium influx into the rat adrenal medullary chromaffin cells and Ca2+ release from the cytoplasmic calcium store. It also seems that there is a big difference in the mode of action between cotinine and nicotine in the rat adrenomedullary CA secretion.

Lack of effect of 5HT3 antagonist in mediating subjective and behavioral responses to cotinine

Previous studies have shown that cotinine, a metabolite of nicotine, may antagonize some of the therapeutic effects of nicotine. The mechanisms underlying cotinine's effects are unclear, but cotinine has been observed to increase serotonin levels in the brain. Thus, it is possible that blocking serotonin effects may antagonize the actions of cotinine, thereby reducing its impact on responses to nicotine. This study determined whether granisetron, a 5HT(3) receptor antagonist, would enhance the efficacy of the nicotine patch. Subjects were randomly assigned to one of the three granisetron conditions (N=43 for 2 mg/day; N=43 for 1 mg/day; N=42 for 0 mg/day) and asked to take the assigned medication daily during 15 days of tobacco abstinence. Because we were interested in interactions between cotinine and serotonin, all groups were also treated with a 21-mg nicotine patch. Assessments of withdrawal symptoms were made for 1 week during baseline smoking and several times during the experimental period. There was a near but nonsignificant difference among groups on a measure of tobacco withdrawal and no significant differences on global measures of drug effects or physiological measures. The data do not strongly support the hypothesis that 5HT(3) agonism is the mechanism by which cotinine offsets the effects of nicotine.

An immunotherapeutic program for the treatment of nicotine addiction: hapten design and synthesis

People continue to smoke and use tobacco products despite well-established hazardous consequences. The most contributing factor is the addictive nature of nicotine. There is no highly effective treatment for the problem of nicotine dependence. Immunotherapy offers an alternative to conventional approaches. The chemistry necessary for a comprehensive immunopharmacological program is presented. Haptens for the generation of antibodies specific for naturally occurring (S)-nicotine, (S)- and (R)-nornicotine, and the metabolite (S)-cotinine were prepared with high optical purity. Preliminary data for antinicotine antibodies are reported.

[Functional involvement of cerebral diazepam binding inhibitor (DBI) in the establishment of drug dependence]

Mechanisms for formation of drug dependence and emergence of withdrawal syndrome are not yet fully understood despite of a huge accumulation of experimental and clinical data. Several clinical features of withdrawal syndrome are considered to be common (i.e., anxiety) among patients with drug dependence induced by different drugs of abuse. In this review, we have discussed the possibility of the functional involvement of diazepam binding inhibitor (DBI), an endogenous neuropeptide for benzodiazepine receptors with endogenously anxiogenic potential, in the development of drug dependence and emergence of its withdrawal symptom. The levels of DBI protein and its mRNA significantly increased in the brain derived from mice dependent on alcohol (ethanol), nicotine and morphine, and abrupt cessation of these drugs facilitated further increase in DBI expression. In the cases of nicotine- and morphine-dependent mice, concomitant administration of antagonists for nicotinic acetylcholine and opioid receptors, respectively, abolished the increase in DBI expression. Therefore, these alterations in DBI expression have a close relationship with formation of drug dependence and/or emergence of withdrawal syndrome and are considered to be a common biochemical process in drug dependence induced by different drugs of abuse.

Isolation and microsequencing of a novel cotinine receptor

1. Nicotine and its main derivative. cotinine, are reported to have distinct central activities in mammals. In this study, the cotinine receptor was separated by biochemical procedures including radio receptor, affinity-chromatography, SDS-PAGE, and N-terminal sequencing assays. 2. Consistently, the results showed that distinctive cotinine receptors exist in different tissues of mammals. In rat brain, the affinity chromatography and [125I]cotinine receptor essays were used to isolate a 40-kDa protein (p40) with higher affinity for cotinine than alpha-bungarotoxin and nicotine. The N-terminus amino acid sequences of the p40 and its internal tryptic peptides showed no identity to recently described protein sequences, with the exception of homology to the human p205 synovial fluid protein. 3. These results, in agreement with other behavioral studies, are the first molecular evidence for distinctive nicotine and cotinine receptors in mammals.

Cotinine and nicotine inhibit each other's calcium responses in bovine chromaffin cells

Cotinine is the major metabolite of nicotine. It has some biological activity, but its pathophysiological effects are largely unclear. We studied whether cotinine initiates calcium transients or affects those induced by nicotine. In bovine adrenal chromaffin cells labeled with the fluorescent calcium indicator Fura 2, cotinine (0. 32-3.2 mM) concentration-dependently increased the intracellular Ca(2+) concentration ([Ca(2+)](i)). The effect was abolished by omitting extracellular Ca(2+) during the stimulations. Also nicotinic receptor channel blockers hexamethonium (10 microM-1 mM) and chlorisondamine (100 microM), as well as a competitive nicotinic receptor antagonist dihydro-beta-erythroidine (10-100 microM), inhibited the response. Cotinine (0.32-3.2 mM) preincubation for 2 min inhibited both the nicotine-induced and the cotinine-induced increases in [Ca(2+)](i). Also nicotine (3.2-10 microM) inhibited the cotinine-induced increase in [Ca(2+)](i). Tetrodotoxin (1 microM) and thapsigargin (1 microM) pretreatments did not affect the responses to cotinine, while 300 nM nimodipine partially inhibited the cotinine-induced increase in [Ca(2+)](i). The results indicate that cotinine has nicotine-like effects on chromaffin cells. It may also desensitize the nicotinic cholinergic receptors, possibly by acting as a low-affinity agonist at these receptors.

Smoking withdrawal dynamics in unaided quitters

Considerable research shows that withdrawal severity is inconsistently related to smoking cessation outcomes. This may result from measurement problems or failure to scrutinize important dimensions of the withdrawal experience. Two recent studies demonstrated that withdrawal elevation and variations in the time course of withdrawal were related to relapse in smokers treated with the nicotine patch (T. M. Piasecki, M. C. Fiore, & T. B. Baker, 1998). This article reports a conceptual replication and extension of those findings in unaided quitters. Evidence for temporal heterogeneity was found across different types of withdrawal symptoms. Patterns or slopes of affect and urge reports over time predicted smoking status at follow-up, as did mean elevation in withdrawal symptoms. These results suggest that affect and urge withdrawal symptoms make independent contributions to relapse and that relapse is related to both symptom severity and trajectory.

Evidence that nicotine acetylcholine receptors are not the main targets of cotinine toxicity

The toxicity of nicotine, cotinine and their mixtures was studied in Mus musculus mice as well their effects on growth after repetitive administration to young mice. The affinity constants of the two alkaloids for the nicotinic acetylcholine receptors (nAChRs) of Torpedo and rat brain membranes were determined. The administration of these alkaloids produced distinct symptoms of intoxication. Nicotine was 100-fold more toxic than cotinine and 10-fold more rapid than cotinine at producing respiratory arrest. The affinity of nicotine for both subtypes of nAChRs was > 100-fold higher than that of cotinine. Repetitive administrations of nicotine caused weight loss, whereas that of cotinine caused weight gain (P < 0.01). The administration of the two alkaloids as mixtures to mice caused significantly (P < 0.01) higher mortality than theoretically expected. Furthermore, hexamethonium pretreatment reduced by 2-fold (P < 0.01) the toxicity of nicotine but enhanced by 1.6-fold (P < 0.01) that of cotinine and was without effects on toxicity of mixtures. We suggest that nAChRs are not the main targets of cotinine toxicity.

Inhibition of nicotinic responses by cotinine in bovine adrenal chromaffin cells

We studied the effects of cotinine, the major metabolite of nicotine, on nicotine-induced increase in [3H]phorbol dibutyrate binding, activation of protein kinase C and [3H]noradrenaline release in primary cultured bovine adrenal chromaffin cells. Cotinine (1 mM, 15 min.) and nicotine (10 microM, 5 min.) increased the [3H]phorbol binding by 100% and 150%, respectively. Both a short-term (10 min.) and a long-term (24 hr) pretreatment with cotinine inhibited the effect of nicotine. A 24 hr pretreatment with cotinine (1 mM) also reduced the nicotine-induced increase in membrane-bound protein kinase C activity. Cotinine pretreatment (10 min.) dose-dependently inhibited the release of [3H]noradrenaline induced by nicotine and dimethylphenylpiperazinium. Cotinine pretreatment did not reduce the [3H]noradrenaline release induced by high extracellular potassium (56 mM) or veratrine (10 mg l-1). The results indicate that cotinine inhibits activation of protein kinase C and noradrenaline release induced by nicotinic agonists in primary cultures of bovine adrenal chromaffin cells. The results suggest that pre-existing cotinine could modify responses to acute exposure to nicotine in neural systems.

Rationale for cigarette smoking and for mentholation preference in cocaine- and nicotine-dependent outpatients

We asked 43 cocaine- and nicotine-dependent outpatients at a substance abuse clinic their reasons for combining cocaine and cigarette use, and for preferring either mentholated or nonmentholated cigarettes. Responses to open-ended questions asked during a semistructured interview were categorized by an analysis of expressed motives for cigarette smoking. Responses that did not fit the categorization were analyzed separately in a qualitative design. Sedating, stimulating, or addictive effects were frequently stated as reasons for the combined use of cigarettes with cocaine. Sedating or calming effects of cigarette smoking included reduction of cocaine-induced paranoia. Cocaine-substituting and cocaine-enhancing effects of cigarette smoking were categorized as stimulating effects. Addictive effects included craving for cigarette smoking on its own or triggered by cocaine use. Sensorimotor or stimulating effects were frequently stated as reasons for a preference for mentholated or nonmentholated cigarettes. Sensorimotor effects of menthol included taste, anesthetic, cooling, and decongestant properties. Some responses provided by our patient sample suggest a need for research on the effect of cigarette smoking on absorption of smoked cocaine.

Effect of nicotine and cotinine on the susceptibility to in vitro oxidation of LDL in healthy non smokers and smokers

Cigarette smoke of which the major component is nicotine plays an important role in the development of cardiovascular diseases. To study the effect of in vitro incubation of LDL with nicotine and its metabolite, cotinine on a copper-induced peroxidation, we monitored the formation of conjugated dienes, hydroperoxides and thiobarbituric acid-reactive substances production. The LDL studied were taken from six non-smokers (aged 41.5 years) and six smokers who consumed at least ten cigarettes per day (40.7 years). LDL oxidation with CuSO4 showed that cigarette smoking promotes LDL susceptibility to peroxidative modification. During the peroxidation of LDL with nicotine (O to 5 mmol/1) and CuSO4 (5 micromol/l), the formation of hydroperoxides decreased when nicotine concentrations increased and the production of TBARS increased in a concomitant manner. The results showed that the presence of nicotine destabilized the production of hydroperoxides in LDL and increased the formation of secondary oxidation products. On the other hand, cotinine had no effect on LDL oxidative susceptibility in smokers and non-smokers.

Nicotine is more efficient than cotinine at passing the blood-brain barrier in rats

1. Nicotine and its main metabolite, cotinine, were reported to have distinct behavioral activities in mammals. 2. In this study, cotinine was synthesized without detectable nicotine contamination to compare the ability of nicotine and cotinine to pass the blood-brain barrier (BBB) in rats. 3. The alkaloids were extracted from plasma and brain tissues by methanol, identified by thin-layer chromatography, and quantified by high-pressure liquid chromatography and radioimmunoassays. 4. Consistently, the three methods showed that the passage of cotinine was time, route of administration, and dose dependent and that nicotine was more efficient than cotinine to pass the BBB. 5. The results suggest that these alkaloids may have central activities that probably result from their actions at distinct molecular levels.

Tobacco addiction: implications for treatment and cancer prevention

The American Society of Clinical Oncology and the National Cancer Institute convened a symposium in June 1996 on tobacco addiction. Additional support for the symposium was provided by the American Medical Women's Association and the American Society of Preventive Oncology. The goals of this conference were to describe the burden and public health consequences of tobacco addiction, to describe the state of science for the treatment of nicotine dependence, and to explore new strategies to increase quit rates and to prevent the uptake of tobacco use. This article summarizes and integrates the meeting presentations on tobacco addiction and includes the topics of smoking prevalence; psychobiologic aspects of nicotine dependence; and implications for disease, treatment, and prevention. Comments on regulatory approaches and national strategies for reducing dependence are also summarized in presentations by Dr. David Kessler, former Food and Drug Administration Commissioner, and Dr. C. Everett Koop, former U.S. Surgeon General.

Contribution of CNS nicotine metabolites to the neuropharmacological effects of nicotine and tobacco smoking

Nicotine, the principal alkaloid in tobacco products, is generally accepted to be the active pharmacological agent responsible for CNS effects resulting from tobacco use. Arguments are presented in this commentary which take issue with this popular dogma, by providing evidence that nicotine metabolites may also be responsible for the CNS effects commonly attributed to nicotine. CNS effects attributed to nicotine include reinforcing effects, mood elevation, arousal, locomotor stimulant effects, and learning and memory enhancement. The reinforcing and locomotor stimulant effects of nicotine have been suggested to be the result of activation of CNS dopaminergic systems, and nicotine-induced modulation of dopaminergic neurotransmission has been studied in detail. Nicotine acts at a family of nicotinic receptor subtypes composed of multiple subunits; however, the exact composition of the subunits in native nicotinic receptors and the functional significance of the receptor subtype diversity are currently unknown. This nicotinic subtype diversity increases the complexity of the potential mechanisms of action of nicotine and its metabolites. Although peripheral metabolism of nicotine has been studied extensively, metabolism in the CNS has not been investigated to any great extent. Recently, studies from our laboratory have demonstrated that several nicotine metabolites are present in the CNS after acute nicotine administration. Moreover, nicotine metabolites are pharmacologically active in neurochemical and behavioral assays. Thus, CNS effects resulting from nicotine exposure may not be due solely to nicotine, but may result, at least in part, from the actions of nicotine metabolites.

Safety of cotinine in humans: physiologic, subjective, and cognitive effects

Preliminary data suggest that cotinine, the major metabolite of nicotine, may be behaviorally active. Studies involving the administration of cotinine at doses that produce high blood concentrations (in excess of those produced by cigarette smoking) may be of interest. This inpatient, 10-day human study examined the safety and the effects from several high doses of oral cotinine fumarate (40, 80, or 160 mg) or placebo in abstinent cigarette smokers. All subjects smoked cigarettes ad lib during the first 2 days of the study, then were required to be abstinent beginning on the third day. All subjects were given placebo on this day to wash out nicotine before the administration of cotinine. Subjects were subsequently randomly assigned in a double-blind manner to cotinine or placebo for the next 3 days to determine the safety profile of cotinine. All subjects were given placebo on the final 3 days to examine cotinine withdrawal symptoms. The results showed no significant physiologic, subjective, or performance effects across the various doses of cotinine and placebo. Furthermore, no cotinine withdrawal effects were observed. This study demonstrates that short-term administration of cotinine to humans at levels as high as 10 times that attained from cigarette smoking is safe with no observable acute or withdrawal effects from cotinine in this setting.

Cotinine concentrations in plasma of smoking pregnant women and their infants

In the Netherlands 30% of all women of reproductive age are habitual smokers. One third of these women continue to smoke during pregnancy. Tobacco smoke consists of more than 3600 different compounds. One of its chief pharmacologically active ingredients is nicotine of which 60% is metabolized to cotinine. Cotinine is the best available biochemical marker of nicotine consumption because it is specific for tobacco smoke exposure and it has a relatively long mean t1/2 of 15 hours. In the present study nicotine and cotinine concentrations were measured in 25 smoking and 25 non-smoking healthy pregnant women. In all 25 non-smoking pregnant women nicotine and cotinine levels were < 10 mg/l. Light smokers (< 10 cigarettes/day) were found to have nicotine blood concentrations < 10 mg/l and cotinine levels varying between 40 and 99 mg/l. Heavy smokers (> or = 10 cigarettes/day) had nicotine concentrations < 10 mg/l, but high cotinine levels varying from 115 to 199 mg/l. Cotinine was also determined in 25 neonates of non-smoking mothers and in 34 neonates of smoking mothers. In 9 of these 34 newborns the relationship between maternal and neonatal cotinine concentrations was investigated. Cotinine levels in neonates born to non-smokers and to women who smoked less than 10 cigarettes/day were below the detection limit of 10 mg/l. Cotinine values in neonates whose mothers smoked > or = 10 cigarettes/day were significantly higher than in those whose mothers smoked < 10 cigarettes/day, but significantly lower than in their mothers. The results of this study confirm that cotinine is more useful than nicotine in discriminating non-smokers, light and heavy smokers. Cotinine concentrations were significantly lower in the neonates than in their mothers, but there was a strong positive linear relationship between maternal and neonatal cotinine concentrations.

Deficient C-oxidation of nicotine

In most people, nicotine is extensively (70% to 80%) metabolized to cotinine by C-oxidation. In a clinical trial, a 57-year-old woman was found to have the expected plasma levels of nicotine but unusually low plasma levels of cotinine both when smoking cigarettes and while receiving transdermal nicotine. To characterize her metabolism, simultaneous infusions of deuterium-labeled nicotine (d2) and cotinine (d4) were administered, with comparison to 20 other control smokers. The clearance of nicotine was unusually low (6.5 ml/min/kg versus 17.2 ml/min/kg), and the half-life of nicotine significantly longer (348 minutes versus 138 minutes) in the index case subject compared with the control subjects. The clearance of cotinine was normal. The index case subject converted only 9% of nicotine to cotinine, compared with 72% for the control subjects. As far as we know, this is the first person with deficient C-oxidation of nicotine to be characterized. Deficient C-oxidation of nicotine is associated with a long half-life of nicotine and deficient generation of cotinine, both of which could influence the risks and addictiveness of tobacco use in affected individuals.