Metabolism of S-nicotine in noninduced and aroclor-induced rats

Biological determinants impact the neurovascular toxicity of nicotine and tobacco smoke: A pharmacokinetic and pharmacodynamics perspective

Accumulating evidence suggests that the detrimental effect of nicotine and tobacco smoke on the central nervous system (CNS) is caused by the neurotoxic role of nicotine on blood-brain barrier (BBB) permeability, nicotinic acetylcholine receptor expression, and the dopaminergic system. The ultimate consequence of these nicotine associated neurotoxicities can lead to cerebrovascular dysfunction, altered behavioral outcomes (hyperactivity and cognitive dysfunction) as well as future drug abuse and addiction. The severity of these detrimental effects can be associated with several biological determinants. Sex and age are two important biological determinants which can affect the pharmacokinetics and pharmacodynamics of several systemically available substances, including nicotine. With regard to sex, the availability of gonadal hormone is impacted by the pregnancy status and menstrual cycle resulting in altered metabolism rate of nicotine. Additionally, the observed lower smoking cessation rate in females compared to males is a consequence of differential effects of sex on pharmacokinetics and pharmacodynamics of nicotine. Similarly, age-dependent alterations in the pharmacokinetics and pharmacodynamics of nicotine have also been observed. One such example is related to severe vulnerability of adolescence towards addiction and long-term behavioral changes which may continue through adulthood. Considering the possible neurotoxic effects of nicotine on the central nervous system and the deterministic role of sex as well as age on these neurotoxic effects of smoking, it has become important to consider sex and age to study nicotine induced neurotoxicity and development of treatment strategies for combating possible harmful effects of nicotine. In the future, understanding the role of sex and age on the neurotoxic actions of nicotine can facilitate the individualization and optimization of treatment(s) to mitigate nicotine induced neurotoxicity as well as smoking cessation therapy. Unfortunately, however, no such comprehensive study is available which has considered both the sex- and age-dependent neurotoxicity of nicotine, as of today. Hence, the overreaching goal of this review article is to analyze and summarize the impact of sex and age on pharmacokinetics and pharmacodynamics of nicotine and possible neurotoxic consequences associated with nicotine in order to emphasize the importance of including these biological factors for such studies.

Comprehensive review of epidemiological and animal studies on the potential carcinogenic effects of nicotine per se

The effects of long-term use of nicotine per se on cancer risk, in the absence of tobacco extract or smoke, are not clearly understood. This review evaluates the strength of published scientific evidence, in both epidemiological and animal studies, for the potential carcinogenic effects of nicotine per se; that is to act as a complete carcinogen or as a modulator of carcinogenesis. For human studies, there appears to be inadequate evidence for an association between nicotine exposure and the presence of or lack of a carcinogenic effect due to the limited information available. In animal studies, limited evidence suggests an association between long-term nicotine exposure and a lack of a complete carcinogenic effect. Conclusive studies using current bioassay guidelines, however, are missing. In studies using chemical/physical carcinogens or transgenic models, there appears to be inadequate evidence for an association between nicotine exposure and the presence of or lack of a modulating (stimulating) effect on carcinogenesis. This is primarily due to the large number of conflicting studies. In contrast, a majority of studies provides sufficient evidence for an association between nicotine exposure and enhanced carcinogenesis of cancer cells inoculated in mice. This modulating effect was especially prominent in immunocompromized mice. Overall, taking the human and animal studies into consideration, there appears to be inadequate evidence to conclude that nicotine per se does or does not cause or modulate carcinogenesis in humans. This conclusion is in agreement with the recent US Surgeon General's 2014 report on the health consequences of nicotine exposure.

Toxicity of aerosols of nicotine and pyruvic acid (separate and combined) in Sprague-Dawley rats in a 28-day OECD 412 inhalation study and assessment of systems toxicology

Toxicity of nebulized nicotine (Nic) and nicotine/pyruvic acid mixtures (Nic/Pyr) was characterized in a 28-day Organization for Economic Co-operation and Development 412 inhalation study with additional transcriptomic and lipidomic analyses. Sprague-Dawley rats were nose-only exposed, 6 h/day, 5 days/week to filtered air, saline, nicotine (50 µg/l), sodium pyruvate (NaPyr, 33.9 µg/l) or equimolar Nic/Pyr mixtures (18, 25 and 50 µg nicotine/l). Saline and NaPyr caused no health effects, but rats exposed to nicotine-containing aerosols had decreased body weight gains and concentration-dependent increases in liver weight. Blood neutrophil counts were increased and lymphocyte counts decreased in rats exposed to nicotine; activities of alkaline phosphatase and alanine aminotransferase were increased, and levels of cholesterol and glucose decreased. The only histopathologic finding in non-respiratory tract organs was increased liver vacuolation and glycogen content. Respiratory tract findings upon nicotine exposure (but also some phosphate-buffered saline aerosol effects) were observed only in the larynx and were limited to adaptive changes. Gene expression changes in the lung and liver were very weak. Nic and Nic/Pyr caused few significant changes (including Cyp1a1 gene upregulation). Changes were predominantly related to energy metabolism and fatty acid metabolism but did not indicate an obvious toxicity-related response. Nicotine exposure lowered plasma lipids, including cholesteryl ester (CE) and free cholesterol and, in the liver, phospholipids and sphingolipids. Nic, NaPyr and Nic/Pyr decreased hepatic triacylglycerol and CE. In the lung, Nic and Nic/Pyr increased CE levels. These data suggest that only minor biologic effects related to inhalation of Nic or Nic/Pyr aerosols were observed in this 28-day study.

Structural elucidation of N-oxidized clemastine metabolites by liquid chromatography/tandem mass spectrometry and the use of Cunninghamella elegans to facilitate drug metabolite identification

Cunninghamella elegans is a filamentous fungus that has been shown to biotransform drugs into the same metabolites as mammals. In this paper we describe the use of C. elegans to aid the identification of clemastine metabolites since high concentrations of the metabolites were produced and MS(n) experiments were facilitated. The combination of liquid chromatography and tandem mass spectrometry with two different ionization techniques and hydrogen/deuterium exchange were used for structural elucidation of the clemastine metabolites. Norclemastine, four isomers of hydroxylated clemastine, and two N-oxide metabolites were described for the first time in C. elegans incubations. The N-oxidations were confirmed by hydrogen/deuterium exchange and deoxygenation (-16 Da) upon atmospheric pressure chemical ionization mass spectrometry. By MS(n) fragmentation it was concluded that two of the hydroxylated metabolites were oxidized on the methylpyrridyl moiety, one on the aromatic ring with the chloro substituent, and one on the aromatic ring without the chlorine.

Effect of filtration by activated charcoal on the toxicological activity of cigarette mainstream smoke from experimental cigarettes

Activated charcoal (AC) filtration reportedly decreases the yields of smoke vapor phase constituents including some identified as human carcinogens and respiratory irritants. Non-clinical studies including chemical smoke analysis, in vitro cytotoxicity and mutagenicity (bacterial and mammalian cells), and in vivo subchronic rat inhalation studies were carried out using machine smoking at ISO conditions with lit-end research cigarettes containing AC filters. The objective was to assess whether AC filter technology would alter the established toxicity profile of mainstream smoke by increasing or decreasing any known toxicological properties, or elicit new ones. The reduced yield of vapor phase irritants from AC filter cigarettes correlated with markedly decreased in vitro cytotoxicity and in vivo morphology of the nose and lower respiratory tract. Increased yields of particulate phase constituents (e.g. polycyclic aromatic hydrocarbons) in AC filtered smoke were noted in comparison to controls in some studies. The in vitro bacterial mutagenicity of AC filtered smoke particulate preparations was occasionally increased over control levels. Laryngeal epithelial thickness was increased in some rats inhaling AC filtered smoke in comparison to controls, an effect perhaps related to higher inspiratory flow. When tested under more intense Massachusetts Department of Public Health smoking conditions, AC filter associated reductions in vapor phase constituent yields were smaller than those seen with ISO conditions, but the effect on in vitro cytotoxicity remained.

Sex differences in nicotine action

Accumulating evidence suggests that the antecedents, consequences, and mechanisms of drug abuse and dependence are not identical in males and females and that gender may be an important variable in treatment and prevention. Although there has been a decline in smoking prevalence in developed countries, females are less successful in quitting. Tobacco use is accepted to be a form of addiction, which manifests sex differences. There is also evidence for sex differences in the central effects of nicotine in laboratory animals. Although social factors impact smoking substantially in humans, findings from nonhuman subjects in controlled experiments provide support that sex differences in nicotine/tobacco addiction have a biological basis. Differences in the pharmacokinetic properties of nicotine or the effect of gonadal hormones may underlie some but not all sex differences observed. Laboratory-based information is very important in developing treatment strategies. Literature findings suggest that including sex as a factor in nicotine/tobacco-related studies will improve our success rates in individually tailored smoking cessation programs.

Reduced toxicological activity of cigarette smoke by the addition of ammonia magnesium phosphate to the paper of an electrically heated cigarette: subchronic inhalation toxicology

Cigarette smoke is a complex chemical mixture that causes a variety of diseases, such as lung cancer. With the electrically heated cigarette smoking system (EHCSS), temperatures are applied to the tobacco below those found in conventional cigarettes, resulting in less combustion, reduced yields of some smoke constituents, and decreased activity in some standard toxicological tests. The first generation of electrically heated cigarettes (EHC) also resulted in increased formaldehyde yields; therefore, a second generation of EHC was developed with ammonium magnesium phosphate (AMP) in the cigarette paper in part to address this increase. The toxicological activity of mainstream smoke from these two generations of EHC and of a conventional reference cigarette was investigated in two studies in rats: a standard 90-day inhalation toxicity study and a 35-day inhalation study focusing on lung inflammation. Many of the typical smoke exposure-related changes were found to be less pronounced after exposure to smoke from the second-generation EHC with AMP than to smoke from the first-generation EHC or the conventional reference cigarette, when compared on a particulate matter or nicotine basis. Differences between the EHC without AMP and the conventional reference cigarette were not as prominent. Overall, AMP incorporated in the EHC cigarette paper reduced the inhalation toxicity of the EHCSS more than expected based on the observed reduction in aldehyde yields.

Chronic nose-only inhalation study in rats, comparing room-aged sidestream cigarette smoke and diesel engine exhaust

Nose-only exposure of male and female Wistar rats to a surrogate for environmental tobacco smoke, termed room-aged sidestream smoke (RASS), to diesel engine exhaust (DEE), or to filtered, fresh air (sham) was performed 6 hours/day, 7 days/week for 2 years, followed by a 6-month post-exposure period. The particulate concentrations were 3 and 10 mg/m3. Markers of inflammation in bronchoalveolar lavage showed that DEE (but not RASS) produced a dose-related and persistent inflammatory response. Lung weights were increased markedly in the DEE (but not RASS) groups and did not decrease during the 6-month post-exposure period. Bulky lung DNA adducts increased in the RASS groups, but not in the DEE groups. Cell proliferation in the lungs was unaffected by either experimental treatment. Histopathological responses in the RASS groups were minimal and almost completely reversible; lung tumors were similar in number to those seen in the sham-exposed groups. Rats exposed to DEE showed a panoply of dose-related histopathological responses: largely irreversible and in some cases progressive. Malignant and multiple tumors were seen only in the DEE groups; after 30 months, the tumor incidence (predominantly bronchiolo-alveolar adenomas) was 2% in the sham-exposed groups, 5%in the high RASS groups, and 46% in the high DEE groups (sexes combined). Our results suggest that in rats exposed to DEE, but not to RASS, the following series of events occurs: particle deposition in lungs --> lung "overload" --> pulmonary inflammation --> tumorigenesis, without a significant modifying role of cell proliferation or DNA adduct formation.

Metabolism of myosmine in Wistar rats

The alkaloid myosmine is present not only in tobacco products but also in various foods. Myosmine is easily nitrosated, yielding 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and the esophageal tobacco carcinogen N'-nitrosonornicotine. Due to its widespread occurrence, investigations on the metabolism and activation of myosmine are needed for risk assessment. Therefore, the metabolism of myosmine has been studied in Wistar rats treated with single oral doses of [pyridine-5-3H]myosmine at 0.001, 0.005, 0.5, and 50 micromol/kg body weight. Oral administration was achieved by feeding a labeled apple bite. Radioactivity was completely recovered in urine and feces within 48 h. At the two lower doses, 0.001 and 0.005 micromol/kg, a higher percentage of the radioactivity was excreted in urine (86.2 +/- 4.9% and 88.9 +/- 1.7%) as compared with the higher doses, 0.5 and 50 micromol/kg, where only 77.8 +/- 7.3% and 75.4 +/- 6.6% of the dose was found in urine. Within 24 h, urinary excretion of radioactivity was nearly complete with less than 4% of the total urinary output appearing between 24 and 48 h. The two major metabolites accounting for >70% of total radioactivity in urine were identified as 3-pyridylacetic acid (20-26%) and 4-oxo-4-(3-pyridyl)butyric acid (keto acid, 50-63%) using UV-diode array detection and gas chromatography-mass spectrometry measurements. 3-Pyridylmethanol (3-5%), 3'-hydroxymyosmine (2%) and HPB (1-3%) were detected as minor metabolites. 3'-Hydroxymyosmine is exclusively formed from myosmine and therefore might be used as a urinary biomarker for myosmine exposure in the future.

The whole truth and nothing but the truth? The research that Philip Morris did not want you to see

The tobacco industry maintained, for many years, that it was unaware of research about the toxic effects of smoking. By the 1970s, however, the industry decided that it needed this information but they were unwilling to seek it in a way that was open to public scrutiny. By means of material from internal industry documents it can be revealed that one company, Philip Morris, acquired a research facility, INBIFO, in Germany and created a complex mechanism seeking to ensure that the work done in the facility could not be linked to Philip Morris. In particular it involved the appointment of a Swedish professor as a 'co-ordinator', who would synthesise reports for onward transmission to the USA. Various arrangements were made to conceal this process, not only from the wider public, but also from many within Philip Morris, although it was known to some senior executives. INBIFO appears to have published only a small amount of its research and what was published appears to differ considerably from what was not. In particular, the unpublished reports provided evidence of the greater toxicity of sidestream than mainstream smoke, a finding of particular relevance given the industry's continuing denial of the harmful effects of passive smoking. By contrast, much of its published work comprises papers that convey a message that could be considered useful to the industry, in particular casting doubt on methods used to assess the effects of passive smoking.

Sex differences in the contribution of nicotine and nonpharmacological stimuli to nicotine self-administration in rats

RATIONALE

Sex differences have been reported for the impact of nicotine and nonpharmacological cues on smoking. While nonpharmacological environmental stimuli have also been shown to influence nicotine self-administration in rats, there have been no attempts to examine the impact of sex differences in the contributions of nicotine and nondrug stimuli to this behavior.

OBJECTIVES

This experiment investigated sex differences in operant responding for nicotine in rats when drug infusions were delivered either in the absence of, or in combination with, a nonpharmacological stimulus.

METHODS

Initially, male and female rats acquired self-administration for nicotine alone across a range of doses (0.03, 0.06, and 0.15 mg kg(-1) inf(-1), freebase). After stable acquisition, nicotine infusions were combined with a weakly reinforcing, compound visual stimulus.

RESULTS

While there was no overall effect of dose on active lever responding for nicotine in the absence of the visual stimulus, female rats responded more on the reinforced lever than males at 0.06 and 0.15 mg kg(-1) inf(-1) on an FR5 schedule. However, they also showed increased responding on the nonreinforced lever compared to males at the same doses. Combining nicotine infusions with the visual stimulus doubled responding compared to nicotine alone at 0.03 and 0.06, but not at 0.15 mg kg(-1) inf(-1): this effect was significantly greater for female rats.

CONCLUSIONS

These data highlight the prominent contribution of nonpharmacological stimuli to nicotine-reinforced behavior across a range of doses in both male and female rats. They also reveal sex differences in operant responding for nicotine under conditions where a nonpharmacological stimulus is either absent, or combined with drug delivery.

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.

Toxicological evaluation of an electrically heated cigarette. Part 4: Subchronic inhalation toxicology

The biological activity of mainstream smoke from an electrically heated cigarette (EHC) with controlled combustion and from the University of Kentucky Reference Cigarette 1R4F was determined in Sprague Dawley rats exposed nose-only for 90 days, 6 h a day, 7 days per week. For an equivalent response comparison between the two cigarette types, two doses were chosen for the EHC where the anticipated results were in the dynamic range of the 1R4F dose-response curve (four concentrations) for most end points. The number of cigarettes smoked per m(3) of diluted smoke resulted in total particulate matter concentrations of 40 and 90 microg l (-1) for the EHC and 40-170 microg l (-1) for the 1R4F. Biomonitoring indicated achievement of target doses. Mainstream smoke yields were lower for the EHC, with the exception of formaldehyde. No smoke-related mortality, remarkable in-life observations or abnormal gross pathological findings were observed. Smoke- and dose-related clinical pathology and organ weight changes included: increases in segmented neutrophils, some liver parameters and lung and adrenal weight relative to body weight; and decreases in lymphocytes, glucose concentration and spleen weight. Smoke-related histopathological findings in the respiratory tract included epithelial cell hyperplasia, squamous metaplasia, atrophy and accumulation of pigmented alveolar macrophages; they were mostly dose-dependent, more pronounced in the upper than lower respiratory tract and completely or partially reversed by 6 weeks post-inhalation. Qualitatively, the biological effects seen for the EHC and the 1R4F were comparable and similar to those observed in other mainstream smoke inhalation studies. Quantitatively, the biological activity of the EHC mainstream smoke was, on average, 65% lower than that of the 1R4F mainstream smoke on an equal cigarette basis and equivalent activity on an equal TPM basis.

Evaluation of the potential effects of ingredients added to cigarettes. Part 4: subchronic inhalation toxicity

Mainstream smoke from blended research cigarettes with (test) and without (control) the addition of ingredients to the tobacco was assayed for inhalation toxicity. In total, 333 ingredients commonly used in cigarette manufacturing were assigned to three different groups. Each group of ingredients was introduced at a low and a high level to the test cigarettes. Male and female Sprague-Dawley rats were exposed nose-only either to fresh air (sham) or diluted mainstream smoke from the test, the control, or the Reference Cigarette 1R4F at a concentration of 150 microg total particulate matter/l for 90 days, 6h/day, 7 days/week. A 42-day post-inhalation period was included to evaluate reversibility of possible findings. There were no remarkable differences in in-life observations or gross pathology between test and control groups. An increase in activity of liver enzymes, known to be due to the high smoke dose, revealed no toxicologically relevant differences between the test and control groups. No toxicological differences were seen between the test and control groups for smoke-related hematological changes, such as a decrease in total leukocyte count. The basic smoke-related histopathological effects, which were more pronounced in the upper respiratory tract than in the lower respiratory tract, were hyperplasia and squamous metaplasia of the respiratory epithelium, squamous metaplasia and atrophy of the olfactory epithelium, and accumulation of pigmented alveolar macrophages. There were no relevant qualitative or quantitative differences in findings in the respiratory tract of the rats exposed to the smoke from the control and test cigarettes. The data indicate that the addition of these 333 commonly used ingredients, added to cigarettes in three groups, did not increase the inhalation toxicity of the smoke, even at the exaggerated levels used.

Identification of phase I and phase II metabolites of ketobemidone in patient urine using liquid chromatography-electrospray tandem mass spectrometry

Ketobemidone and five of its phase I metabolites were identified in the urine of four patients post intravenous administration of Ketogan Novum. Furthermore, indications of the presence of the glucuronide conjugates of ketobemidone and norketobemidone is presented. Both hydrolyzed (beta-glucuronidase) and unhydrolyzed human urine was extracted on a mixed-mode slightly polar cation-exchange SPEC cartridge prior to analysis with LC-ESI-MS-MS. The phase I metabolites were identified by comparison of their daughter spectra with those of synthesized standards. The glucuronides were identified by their molecular mass and interpretation of the daughter spectra, as no standards were available for these compounds.

Sex differences in brain and behavior: emphasis on nicotine, nitric oxide and place learning

Although males and females are unmistakably different, the recognition of sex as a key variable in science and medicine is considered a revolution in some circles. Sex differences transcend reproductive functions, are evident in the structural and functional organization of the brain, and are reflected in group differences in cognitive abilities and behavior. Males and females have different neural organizational patterns for information processing and different strategies in problem solving. Research on sex differences not only provides descriptive data, but also allows us to elucidate mechanisms that underlie our behavior. In this review, sex differences in the central actions of nicotine (an addictive substance) and nitric oxide, and performance on active avoidance and place learning tasks are discussed as examples, and biobehavioral approaches relating to these topics are presented.

Stereoselective metabolism of nicotine and tobacco-specific N-nitrosamines to 4-hydroxy-4-(3-pyridyl)butanoic acid in rats

The carcinogenic tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) are believed to play a role in cancers associated with the use of tobacco products. Urinary metabolites of NNK and NNN could be used as biomarkers for an individual's ability to metabolically activate or detoxify these nitrosamines. While several metabolites of NNK can be quantified in human urine, no assay is available to determine human urinary levels of NNK and NNN metabolites resulting from the critical alpha-hydroxylation metabolic activation pathways. The major urinary metabolites resulting from alpha-hydroxylation of NNK and NNN in rodents are 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid). The major obstacle to the use of these metabolites as biomarkers of metabolic activation is the fact that they are also metabolites of nicotine, which is present at levels 1400-13000 times greater than those of the nitrosamines in cigarette smoke. However, the chirality of hydroxy acid could be useful in overcoming this problem. If different enantiomers of hydroxy acid were formed from nicotine versus the nitrosamines, and if the overall yield of hydroxy acid from nicotine were substantially smaller than that from the nitrosamines, then hydroxy acid might be useful as a urinary biomarker of NNK and NNN alpha-hydroxylation. To these ends, F-344 rats were administered either [5-3H]NNK, [5-3H]NNN, [5-3H]keto acid, or [2'-14C]nicotine. The levels of urinary hydroxy acid were determined by HPLC analysis. Its stereochemistry was determined by conversion to its methyl ester, reaction with (S)-(-)-alpha-methylbenzyl isocyanate, and separation and quantitation of the resulting diastereomers by HPLC. Urinary hydroxy acid accounted for 12% of the NNK dose and 31% of the NNN dose, but only 1 and 0.1% of the dose of keto acid and nicotine, respectively. Furthermore, metabolism of NNK produced mainly (S)-hydroxy acid in the urine, while metabolism of keto acid and nicotine gave predominantly (R)-hydroxy acid. Both enantiomers were present in the urine of NNN-treated rats. Therefore, in the rat, it is possible to distinguish the hydroxy acid derived from nicotine from that derived from the nitrosamines. If similar pathways occur in humans, (S)-hydroxy acid could potentially be developed as a urinary biomarker of NNK and NNN alpha-hydroxylation in smokers.

Quantitation of 4-oxo-4-(3-pyridyl)butanoic acid and enantiomers of 4-hydroxy-4-(3-pyridyl)butanoic acid in human urine: A substantial pathway of nicotine metabolism

A liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (LC-APCI-MS/MS) method was developed to analyze human urine for 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and the enantiomers of 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid) to test our hypothesis that (S)-hydroxy acid could be a biomarker of metabolic activation of the tobacco-specific carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) while (R)-hydroxy acid would be formed predominantly from nicotine, as indicated by studies with rats. Urine was collected from smokers, and from the same individuals after they had stopped smoking and used a nicotine transdermal system (nicotine patch) for 3 weeks. If (S)-hydroxy acid were a biomarker of NNK and NNN metabolic activation, its levels should be higher in the urine of smokers than in nicotine patch users because tobacco smoke, but not the nicotine patch, contains NNK and NNN. Internal standard, [2,2,3,3,4-D5]hydroxy acid, was added to an aliquot of urine, which was then subjected to solid phase extraction. The eluant containing hydroxy acid was esterified with acidic methanol, followed by treatment with (S)-(-)-alpha-methylbenzyl isocyanate, producing methyl-4(S)- or methyl-4(R)-[(S)-alpha-methylbenzylcarbamoyl]-4-(3-pyridyl)buta noate [(S,S)- or (R,S)-MMPB, respectively]. After HPLC purification, the MMPB diastereomers were separated and quantified by LC-APCI-MS/MS. Mean levels of (S)- and (R)-hydroxy acid were 14.1 +/- 8.0 and 1120 +/- 600 ng/mL, respectively, in smokers during ad lib smoking (n = 18), while the corresponding levels during nicotine patch use (n = 18) were 4.1 +/- 3.3 and 363 +/- 228 ng/mL. The amounts of (S)-hydroxy acid were far higher than could be formed from NNK and NNN, and the total amount of hydroxy acid indicated that it was a substantial urinary metabolite of nicotine, in contrast to results with rats. Therefore, the study was extended to quantify keto acid. This was accomplished by NaBH4 treatment of urine, which converted keto acid to hydroxy acid quantitatively, which was in turn analyzed as described above. Levels of keto acid while subjects were smoking and using the nicotine patch were 228 +/- 129 (n = 8) and 97.5 +/- 80.6 ng/mL (n = 8), respectively. These results indicate that conversion of nicotine to keto acid and hydroxy acid is a substantial metabolic pathway in humans, accounting for an estimated 14% of the nicotine dose. Apparently, keto acid is extensively converted to hydroxy acid in humans, in contrast to the results with rats. (S)-Hydroxy acid in human urine cannot be used as a biomarker of NNK and NNN metabolic activation because it is overwhelmed by the (S)-hydroxy acid formed from nicotine, despite the fact that >98% of the urinary hydroxy acid has the (R)-configuration. These results provide new insights about nicotine metabolism in humans.

Pharmacokinetics and metabolism of N-(2-hydroxyethyl)-2,5-[14C]-pyrrolidine (HEP, Epolamine) in male healthy volunteers

N-(2-hydroxyethyl)-pyrrolidine (HEP, Epolamine) is a strong base used to salify organic acids of pharmaceutical interest in order to improve their solubility in water. Diclofenac-HEP (Flector) is the first example of an epolamine salt of a drug. In this study, [14C]-HEP was administered by oral route (300 mg, about 50 microCi/subject) to 3 volunteers with the aim to investigate its plasma profile and to calculate the relevant pharmacokinetic parameters. The experimental data correlated with a two-compartment pharmacokinetic model. Total radioactivity in urine and faeces was also measured. The radioactivity was excreted preferentially by the faecal route (about 65% of the dose administered in the 0-72 h collection interval). Urinary excretion accounted for about 30% of the dose and occurred very rapidly (about 22% of the dose was in the 0-8 h collection interval). Metabolic investigations were carried out on urine samples. TLC analysis with radioscan detector indicated a main radioactive zone, accounting for about 98% of the radioactivity in the plate. After scraping off and purification of the radioactive areas, the compound isolated (Met I) was analysed by gas chromatography-mass spectrometry with electron-impact ionization process. The structure of the metabolite was postulated to be pyrrolidine N-oxide.

N-hydroxymethylnorcotinine, a new primary in vitro metabolite of cotinine

1. N-Hydroxymethylnorcotinine; 5-(3'-pyridyl)-1-hydroxymethyl-pyrrolidone-2, was found as a new primary metabolite of cotinine in vitro. 2. N-Hydroxymethylnorcotinine was synthesized and characterized by gas chromatography-mass spectrometry, mass spectra, nuclear magnetic resonance and ultraviolet spectroscopy. 3. This new metabolite is formed by incubation of cotinine with hamster hepatic microsomes in the presence of NADPH and oxygen.