Binding free energies for nicotine analogs inhibiting cytochrome P450 2A6 by a combined use of molecular dynamics simulations and QM/MM-PBSA calculations

Molecular dynamics (MD) simulations and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations have been performed to explore the dynamic behaviors of cytochrome P450 2A6 (CYP2A6) binding with nicotine analogs (that are typical inhibitors) and to calculate their binding free energies in combination with Poisson-Boltzmann surface area (PBSA) calculations. The combined MD simulations and QM/MM-PBSA calculations reveal that the most important structural parameters affecting the CYP2A6-inhibitor binding affinity are two crucial internuclear distances, that is, the distance between the heme iron atom of CYP2A6 and the coordinating atom of the inhibitor, and the hydrogen-bonding distance between the N297 side chain of CYP2A6 and the pyridine nitrogen of the inhibitor. The combined MD simulations and QM/MM-PBSA calculations have led to dynamic CYP2A6-inhibitor binding structures that are consistent with the observed dynamic behaviors and structural features of CYP2A6-inhibitor binding, and led to the binding free energies that are in good agreement with the experimentally-derived binding free energies. The agreement between the calculated binding free energies and the experimentally-derived binding free energies suggests that the combined MD and QM/MM-PBSA approach may be used as a valuable tool to accurately predict the CYP2A6-inhibitor binding affinities in future computational design of new, potent and selective CYP2A6 inhibitors.

[Influence of stimulation and blockade of α4β2 nicotinic acetylcholine receptors on learning of female rats in basic phases of ovary cycle]

The present work was devoted to the comparative analysis of α4β2 nicotinic acetylcholine receptors (nAChRs) in learning/memory processes during ovary cycle in the adult female rats. RJR-2403 (1.0 mg/kg, i. p.), α4β2 nAChRs agonist and mecamylamine (1.0 mg/kg, i. p.), α4β2 nAChRs antagonist were injected chronically during 14 days. The processes of learning/memory were assessed in different models of learning: passive avoidance performance and Morris water maze. Chronic RJR-2403 administration to females improved the passive avoidance performance in proestrous and estrous as compared to the control animals. Also, RJR-2403 restored spatial learning of rats during proestrous phases in Morris water maze, and stimulated the dynamics of spatial learning during estrous phases. On the contrary, the chronic mecamylamine administration impaired non-spatial, and especially, spatial learning in females during key phases of ovary cycle. The results of the study suggest positive effect of α4β2 nAChRs stimulation in learning/memory processes during ovary cycle in the adult female rats.

Nicotine-like behavioral effects of the minor tobacco alkaloids nornicotine, anabasine, and anatabine in male rodents

Tobacco use is associated with lethal diseases in an estimated 440,000 persons in the United States each year (Centers for Disease Control and Prevention, 2005). Successful smoking quit-rates are estimated at 5%-8%, even though a quarter of those attempts included use of smoking-cessation aids (Messer et al., 2008; Henningfield et al., 2009). Current projections are that 16% of the U.S. population-35 million people-will still smoke in 2025, thus more effective smoking-cessation aids are urgently needed (Pollock et al., 2009). The minor tobacco alkaloids may be promising candidates, but further research is necessary (Hoffman & Evans, 2013). Accordingly, we systematically evaluated the minor tobacco alkaloids nornicotine, anabasine, and anatabine using assays of behavioral tolerability, nicotine withdrawal, nicotine discrimination, and nicotine self-administration in male rodents. At doses that were well tolerated, all 3 minor alkaloids dose-dependently engendered robust substitution for a nicotine discriminative stimulus in mice (0.32 mg/kg, IP), and anabasine attenuated nicotine withdrawal. When the ED50 dose of each alkaloid was administered in combination with nicotine, the discriminative stimulus effects of nicotine were not enhanced by any of the alkaloids, and anatabine blunted nicotine's effects. In drug self-administration studies, only nornicotine was self-administered by rats that self-administered nicotine intravenously; anabasine and anatabine had no reinforcing effects. Moreover, prior administration of each of the minor tobacco alkaloids dose-dependently decreased nicotine self-administration. Collectively these results suggest that the minor tobacco alkaloids may substitute for the subjective effects of nicotine and attenuate withdrawal and craving without the abuse liability of nicotine.

[Effect of alpha4beta2 nicotinic acetylcholine receptor agonists and antagonists on learning in female rats during different phases of ovary cycle]

The present work was devoted to the comparative analysis of alpha4beta2 nicotinic acetylcholine receptors (nAChRs) in learning/ memory processes during ovary cycle assessed in adult female rats. RJR-2403 (1.0 mg/kg, i.p.), alpha4beta2 nAChRs agonist and mecamylamine (1.0 mg/kg, i.p.), alpha4beta2 nAChRs antagonist were injected chronically during 14 days. The processes of learning/memory were assessed in different models of learning: passive avoidance performance and Morris water maze. Chronic RJR-2403 administration to female rats improved the passive avoidance performance in proestrous and estrous as compared to the control animals. Also, RJR-2403 restored spatial learning during proestrous phases in Morris water maze, and stimulated the dynamics of spatial learning during estrous phases. On the contrary, chronic mecamylamine administration impaired non-spatial, and especially, spatial learning in females during key phases of ovary cycle. The results of the study suggest positive effect of alpha4beta2 nAChRs stimulation in learning/ memory processes during ovary cycle in the adult female rats.

(R)-nicotine biosynthesis, metabolism and translocation in tobacco as determined by nicotine demethylase mutants

Nicotine is a chiral compound and consequently exists as two enantiomers. Since (R)-nicotine consists of less than 0.5% of total nicotine pool in tobacco, few investigations relating to (R)-nicotine have been reported. However, previous studies of nicotine demethylases suggested there was substantial amount of (R)-nicotine at synthesis in the tobacco plant. In this study, the accumulation and translocation of (R)-nicotine in tobacco was analyzed. The accumulation of nicotine and its demethylation product the nornicotine enantiomers, were investigated in different tobacco plant parts and at different growth and post-harvest stages. Scion/rootstock grafts were used to separate the contributions of roots (source) from leaves (sink) to the final accumulation of nicotine and nornicotine in leaf tissue. The results indicate that 4% of nicotine is in the (R) form at synthesis in the root. After the majority of (R)-nicotine is selectively demethylated by CYP82E4, CYP82E5v2 and CYP82E10 in the root, nicotine and nornicotine are translocated to leaf, where more nicotine becomes demethylated. Depending on the CYP82E4 activity in senescing leaf, constant low (R)-nicotine remains in the tobacco leaf and variable nornicotine composition is produced. These results confirmed the enantioselectivity of three nicotine demethylases in planta, could be used to predict the changes of nicotine and nornicotine composition, and may facilitate demethylase discovery in the future.

[Design, synthesis and evaluation of bis-nicotine derivatives as inhibitors of cholinesterases and beta-amyloid aggregation]

A novel series of bis-nicotine derivatives (3a-3i) were designed, synthesized and evaluated as bivalent anti-Alzheimer's disease agents. The pharmacological results indicated that compounds 3e-3i inhibited both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in the micromolar range (IC50, 2.28-117.86 micromol x L(-1) for AChE and 1.67-125 micromol x L(-1) for BChE), which was at the same potency as rivastigmine. A Lineweaver-Burk plot and molecular modeling study showed that these derivatives targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Besides, these compounds could significantly inhibit the self-induced Abeta aggregation with inhibition activity (11.85%-62.14%) at the concentration of 20 micromol x L(-1).

ZY-1, a novel nicotinic analog, promotes proliferation and migration of adult hippocampal neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) of the subgranular zone have been implicated in cognitive processes, which represent a potentially important source of regenerative medicine for the treatment of neurodegenerative diseases such as Alzheimer's disease (AD). In our previous studies, ZY-1, a novel nicotinic analog, improved cognitive function in transgenic mice model of AD. However, the effect of ZY-1 on the NSPCs remains unclear. Here, we show that ZY-1 significantly increased proliferation and migration of NSPCs, but failed to affect NSPCs differentiation in vitro. Furthermore, during the proliferative period, ZY-1 enhanced intracellular reactive oxygen species (ROS) levels. Meanwhile, ZY-1 also inhibited the levels of Aβ42-induced ROS. Our data indicate that ZY-1 regulates adult hippocampal neurogenesis in vitro, at least partly due to modulating intracellular ROS levels. These results, taken together with those of our previous studies, suggest that ZY-1 might have a potential therapeutic effect for the treatment of AD.

[Co-administration of RJR-2403 with low dose of 17beta-estradiol on spatial learning in ovariectomized rats]

The aim of this work was to study the influence of stimulation or blockade Nalpha7-cholinoreceptors on dynamics of spatial learning in water Morris maze and on behavior in the "open field" test in adult ovariectomized (OVX) females given with a low dose of 17beta-estradiol. Agonist of Nalpha7-cholinoreceptors - RJR-2403 (1.0 mg/kg, i.p.) or antagonist of Nalpha7-cholinoreceptors - mecamylamine (1.0 mg/kg, i.p.) treated chronically (14 days) alone and in a combination with low dose of 17beta-estradiol (0.5 micro/rat, s.c.) to OVX rats. Co-administration of RJR-2403 with low dose of 17beta-estradiol completely restored impaired spatial learning in water Morris maze in OVX females. Moreover, OVX rats treated with RJR-2403 and low dose of 17beta-estradiol demonstrated increased exploratory and grooming behavior in the "open field" test. Both mecamylamine alone and in combination with low dose of 17beta-estradiol failed to influence on spatial learning and failed to modify behavior in the "open field" test in OVX rats. The results of the present study suggest a positive effect of RJR-2403 in combination with low dose of 17beta-estradiol on spatial learning at estrogen deficiency.

[Influence of agonist and antagonist Nalpha7-cholinoreceptors on active avoidance learning and gonadal hormones levels in ovariectomized female rats]

The aim of this work was to study the influence of co-administration of agonist and antagonist of Nalpha7-cholinoreceptors with low dose of 17beta-estradiol on dynamics of acquisition and retention in active avoidance test, on the behavior in the "open field" test, as well as tropic and gonadal hormones levels in ovariectomiczed female rats. Antagonist of Nalpha7-cholinoreceptors - RJR-2403 (1.0 mg/kg, i. p.) and antagonist of Nalpha7-cholinoreceptors - mecamylamine (1.0 mg/kg, i. p.) were administered chronically (14 days) isolated or in combination with low dose of 17beta-estradiol (0.5 m/rat, s. c.) to ovariectomized rats. It was revealed that RJR-2403 in combination with low dose of 17beta -estradiol completely restored impairments in mechanisms of dynamics of active avoidance performance and increased exploratory and grooming behavior in the "open field" test in ovariectomized rats. Moreover, RJR-2403 treatment decreased follitropine and lutropine levels and increased estradiol level in the blood serum in ovariectomized rats. Administration ofmecamylamine alone or in combination with low dose of 17beta-estradiol in ovariectomiczed rats failed to influence on dynamics of passive avoidance learning and failed to modify behavior in the "open field" test. The results of the present study suggest positive effect of Nalpha7-cholinoreceptors stimulation on background of low dose for 17beta-estradiol on active avoidance learning and tropic and gonadal hormones levels at estrogen deficiency.

Feasibility of identifying the tobacco-related global metabolome in blood by UPLC-QTOF-MS

Metabolomics is likely an ideal tool to assess tobacco smoke exposure and the impact of cigarette smoke on human exposure and health. To assess reproducibility and feasibility of this by UPLC-QTOF-MS, three experiments were designed for the assessment of smokers' blood. Experiment I was an analysis of 8 smokers with 8 replicates. Experiment II was an analysis of 62 pooled quality control (QC) samples from 7 nonsmokers' plasma placed as every tenth sample among a study of 613 samples from 160 smokers. Finally, to examine the feasibility of metabolomic study in assessing smoke exposure, Experiment III consisted of 9 smokers and 10 nonsmokers' serum to evaluate differences in their global metabolome. There was minimal measurement and sample preparation variation in all experiments, although some caution is needed when analyzing specific parts of the chromatogram. When assessing QC samples in the large scale study, QC clustering indicated high stability, reproducibility, and consistency. Finally, in addition to the identification of nicotine metabolites as expected, there was a characteristic profile distinguishing smokers from nonsmokers. Metabolites selected from putative identifications were verified by MS/MS, showing the potential to identify metabolic phenotypes and new metabolites relating to cigarette smoke exposure and toxicity.

Nornicotine nitrosation in saliva and its relation to endogenous synthesis of N'-nitrosonornicotine in humans

INTRODUCTION

We recently reported that certain amounts of the carcinogen N'-nitrosonornicotine (NNN) can be formed endogenously from nicotine and/or nornicotine in some users of oral nicotine replacement therapy products. Although the acidic environment of the stomach creates the most favorable conditions for nitrosation, this reaction could also occur in the oral cavity in the presence of bacteria that catalyze nitrosation at neutral pH.

METHODS

To test the hypothesis that endogenous formation of NNN could occur in the oral cavity, we investigated nitrosation of nicotine and nornicotine in human saliva. To specifically identify NNN as derived from precursors added to saliva, we incubated saliva samples with [pyridine-D(4)]nicotine and [pyridine-D(4)]nornicotine, with and without the addition of nitrite, and subsequently analyzed [pyridine-D(4)]NNN by liquid chromatography-tandem mass spectrometry.

RESULTS

Consistent with kinetic studies on nicotine and nornicotine nitrosation, incubation of saliva with [pyridine-D(4)]nornicotine alone produced detectable amounts of [pyridine-D(4)]NNN, whereas only traces of [pyridine-D(4)]NNN were found in samples incubated with [pyridine-D(4)]nicotine and sodium nitrite. Incubation of saliva samples from 10 nonsmoking volunteers with [pyridine-D(4)]nornicotine resulted in the formation of [pyridine-D(4)]NNN in 8 samples, with yields ranging from 0.003% to 0.051% of the added alkaloid.

CONCLUSION

Our results demonstrate that NNN can be formed from nornicotine in human saliva without deliberate addition of any other substance. Therefore, nornicotine, as present in tobacco or in nicotine replacement products, is a carcinogen precursor.

Alteration of the alkaloid profile in genetically modified tobacco reveals a role of methylenetetrahydrofolate reductase in nicotine N-demethylation

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme of the tetrahydrofolate (THF)-mediated one-carbon (C1) metabolic network. This enzyme catalyzes the reduction of 5,10-methylene-THF to 5-methyl-THF. The latter donates its methyl group to homocysteine, forming methionine, which is then used for the synthesis of S-adenosyl-methionine, a universal methyl donor for numerous methylation reactions, to produce primary and secondary metabolites. Here, we demonstrate that manipulating tobacco (Nicotiana tabacum) MTHFR gene (NtMTHFR1) expression dramatically alters the alkaloid profile in transgenic tobacco plants by negatively regulating the expression of a secondary metabolic pathway nicotine N-demethylase gene, CYP82E4. Quantitative real-time polymerase chain reaction and alkaloid analyses revealed that reducing NtMTHFR expression by RNA interference dramatically induced CYP82E4 expression, resulting in higher nicotine-to-nornicotine conversion rates. Conversely, overexpressing NtMTHFR1 suppressed CYP82E4 expression, leading to lower nicotine-to-nornicotine conversion rates. However, the reduced expression of NtMTHFR did not affect the methionine and S-adenosyl-methionine levels in the knockdown lines. Our finding reveals a new regulatory role of NtMTHFR1 in nicotine N-demethylation and suggests that the negative regulation of CYP82E4 expression may serve to recruit methyl groups from nicotine into the C1 pool under C1-deficient conditions.

[Chronic administration of RJR-2403 in combination with low-dose of 17beta-estradiol corrects passive avoidance learning in ovariectomized rats]

The aim of this work was to study the effect of stimulation or blockade of Na7-cholinoreceptors with a low dose of 17beta-estradiol on the passive avoidance performance and behavior in the open-field test in adult ovariectomized (OVX) female rats. Agonist of Na7-cholinoreceptors RJR-2403 (1.0 mg/kg, i.p.) or antagonist of Na7-cholinoreceptors mecamylamine (1.0 mg/kg, i.p.) treated chronically (14 days) alone and in a combination with low dose of 17beta-estradiol (0.5 microg/rat, s.c.) to OVX rats. Co-administration of RJR-2403 with low dose of 17P-estradiol completely restored impaired passive avoidance performance in OVX females. OVX rats treated with RJR-2403 and low dose of 17beta-estradiol demonstrated increased exploratory and grooming behavior in the open-field test. Both mecamylamine alone and in combination with low dose of 17beta-estradiol failed to influence the passive avoidance learning and failed to modify behavior in the open-field test in OVX rats. The results of the present study suggest positive effect of RJR-2403 in combination with low dose of 17beta-estradiol on passive avoidance learning at estrogen deficiency.

Enantioselective demethylation of nicotine as a mechanism for variable nornicotine composition in tobacco leaf

Nicotine and its N-demethylation product nornicotine are two important alkaloids in Nicotiana tabacum L. (tobacco). Both nicotine and nornicotine have two stereoisomers that differ from each other at 2'-C position on the pyrrolidine ring. (S)-Nicotine is the predominant form in the tobacco leaf, whereas the (R)-enantiomer only accounts for ∼0.2% of the total nicotine pool. Despite considerable past efforts, a comprehensive understanding of the factors responsible for generating an elevated and variable enantiomer fraction of nornicotine (EF(nnic) of 0.04 to 0.75) from the consistently low EF observed for nicotine has been lacking. The objective of this study was to determine potential roles of enantioselective demethylation in the formation of the nornicotine EF. Recombinant CYP82E4, CYP82E5v2, and CYP82E10, three known tobacco nicotine demethylases, were expressed in yeast and assayed for their enantioselectivities in vitro. Recombinant CYP82E4, CYP82E5v2, and CYP82E10 demethylated (R)-nicotine 3-, 10-, and 10-fold faster than (S)-nicotine, respectively. The combined enantioselective properties of the three nicotine demethylases can reasonably account for the nornicotine composition observed in tobacco leaves, which was confirmed in planta. Collectively, our studies suggest that an enantioselective mechanism facilitates the maintenance of a reduced (R)-nicotine pool and, depending on the relative abundances of the three nicotine demethylase enzymes, can confer a high (R)-enantiomer percentage within the nornicotine fraction of the leaf.

Non-functionalization of two CYP82E nicotine N-demethylase genes abolishes nornicotine formation in Nicotiana langsdorffii

Nornicotine is formed from nicotine by nicotine N-demethylase, a CYP82E family monooxygenase, and accumulates to high levels in some tobacco (Nicotiana tabacum) cultivars and many wild Nicotiana species. Nicotiana langsdorffii does not form nornicotine, whereas the closely related species N. alata accumulates this alkaloid abundantly. We show here that the two nicotine N-demethylase genes in N. langsdorffii have been inactivated by different molecular mechanisms. We identified four N. alata CYP82E genes that encode functional nicotine N-demethylases. In N. langsdorffii, however, one CYP82E gene encoding a functional enzyme was not expressed at all, whereas the other was weakly expressed but contained a one-nucleotide deletion in the first exon, yielding a truncated protein. Expression analysis of interspecific F(1) hybrids between N. alata and N. langsdorffii indicated that cis-acting polymorphisms abolish expression of the otherwise functional CYP82E gene in N. langsdorffii. Segregation analysis of tobacco alkaloids and individual CYP82E alleles in F(2) progeny revealed that duplicated CYP82E genes in both species are genetically linked, and provide genetic evidence that CYP82E genes are solely responsible for nornicotine formation in these wild Nicotiana species.

Variable nornicotine enantiomeric composition caused by nicotine demethylase CYP82E4 in tobacco leaf

Nornicotine is the demethylation product of nicotine and the precursor of tobacco-specific nitrosamine N'-nitrosonornicotine (NNN) in tobacco (Nicotiana tabacum L.). There is an inconsistent enantiomer fraction (EF) of nornicotine reported in the literature. The objective of this study was to explore possible mechanisms to account for the variable EF(nnic) in tobacco. A survey of tobacco with different demethylating capabilities confirmed that there was variable EF(nnic). Experiments of induction and inhibition of the major nicotine demethylase CYP82E4 activity in tobacco demonstrated that CYP82E4 selectively demethylated (S)-nicotine and resulted in different EF(nnic) in tobacco leaves. Results from plants with silenced demethylases by RNAi suggested that other demethylases selectively used (R)-nicotine and resulted in high EF(nnic). In summary, enantioselective demethylation likely plays an important role in contributing to a large and variable EF(nnic) observed in tobacco.

CYP2A6- and CYP2A13-catalyzed metabolism of the nicotine Δ5'(1')iminium ion

Nicotine, the major addictive agent in tobacco, is metabolized primarily by CYP2A6-catalyzed oxidation. The product of this reaction, 5'-hydroxynicotine, is in equilibrium with the nicotine Δ5'(1')iminium ion and is further metabolized to cotinine. We reported previously that both CYP2A6 and the closely related extrahepatic enzyme CYP2A13 were inactivated during nicotine metabolism; however, inactivation occurred after metabolism was complete. This led to the hypothesis that oxidation of a nicotine metabolite, possibly the nicotine Δ5'(1')iminium ion, was responsible for generating the inactivating species. In the studies presented here, we confirm that the nicotine Δ5'(1')iminium ion is an inactivator of both CYP2A6 and CYP2A13, and inactivation depends on time, concentration, and the presence of NADPH. Inactivation was not reversible and was accompanied by a parallel loss in spectrally active protein, as measured by reduced CO spectra. These data are consistent with the characterization of the nicotine Δ5'(1')iminium ion as a mechanism-based inactivator of both CYP2A13 and CYP2A6. We also confirm that both CYP2A6 and CYP2A13 catalyze the metabolism of the nicotine Δ5'(1')iminium ion to cotinine and provide evidence that both enzymes catalyze the sequential metabolism of the nicotine Δ5'(1')iminium ion. That is, a fraction of the cotinine formed may not be released from the enzyme before further oxidation to 3'-hydroxycotinine.

In silico theoretical molecular modeling for Alzheimer's disease: the nicotine-curcumin paradigm in neuroprotection and neurotherapy

The aggregation of the amyloid-β-peptide (AβP) into well-ordered fibrils has been considered as the key pathological marker of Alzheimer‘s disease. Molecular attributes related to the specific binding interactions, covalently and non-covalently, of a library of compounds targeting of conformational scaffolds were computed employing static lattice atomistic simulations and array constructions. A combinatorial approach using isobolographic analysis was stochastically modeled employing Artificial Neural Networks and a Design of Experiments approach, namely an orthogonal Face-Centered Central Composite Design for small molecules, such as curcumin and glycosylated nornicotine exhibiting concentration-dependent behavior on modulating AβP aggregation and oligomerization. This work provides a mathematical and in silico approach that constitutes a new frontier in providing neuroscientists with a template for in vitro and in vivo experimentation. In future this could potentially allow neuroscientists to adopt this in silico approach for the development of novel therapeutic interventions in the neuroprotection and neurotherapy of Alzheimer‘s disease. In addition, the neuroprotective entities identified in this study may also be valuable in this regard.

Three nicotine demethylase genes mediate nornicotine biosynthesis in Nicotiana tabacum L.: functional characterization of the CYP82E10 gene

In most tobacco (Nicotiana tabacum L.) plants, nornicotine is a relatively minor alkaloid, comprising about 2-5% of the total pyridine alkaloid pool in the mature leaf. Changes in gene expression at an unstable locus, however, can give rise to plants that produce high levels of nornicotine, specifically during leaf senescence and curing. Minimizing the nornicotine content in tobacco is highly desirable, because this compound serves as the direct precursor in the synthesis of N'-nitrosonornicotine, a potent carcinogen in laboratory animals. Nornicotine is likely produced almost entirely via the N-demethylation of nicotine, in a process called nicotine conversion that is catalyzed by the enzyme nicotine N-demethylase (NND). Previous studies have identified CYP82E4 as the specific NND gene responsible for the unstable conversion phenomenon, and CYP82E5v2 as a putative minor NND gene. Here, by discovery and characterization of CYP82E10, a tobacco NND gene, is reported. PCR amplification studies showed that CYP82E10 originated from the N. sylvestris ancestral parent of modern tobacco. Using a chemical mutagenesis strategy, knockout mutations were induced and identified in all three tobacco NND genes. By generating a series of mutant NND genotypes, the relative contribution of each NND gene toward the nornicotine content of the plant was assessed. Plants possessing knockout mutations in all three genes displayed nornicotine phenotypes that were much lower (∼0.5% of total alkaloid content) than that found in conventional tobacco cultivars. The introduction of these mutations into commercial breeding lines promises to be a viable strategy for reducing the levels of one of the best characterized animal carcinogens found in tobacco products.

A cessation program for snuff-dippers with long-term, extensive exposure to Swedish moist snuff: A 1-year follow-up study

OBJECTIVE

Smokeless tobacco (Swedish moist 'snus') users are often strongly addicted to nicotine. Compared to the large number of smoking-cessation studies, there have been few evaluated clinical cessation programs in conjunction with nicotine replacement therapy (NRT). The aim of this study was to evaluate a cessation program for snus users with a weekly use of >2 cans/week for >10 years.

MATERIAL AND METHODS

A prospective, open, non-randomized intervention trial was undertaken including baseline oral examination and soft tissue biopsy, minor physical examination, brief cessation advice, NRT recommendations and five prospective follow-up visits within 12 months. Individual cessation counseling was given, together with oral examination in the dental office. Fifty snus users with a minimum consumption of 100 g/week who were actively seeking cessation treatment were recruited through advertising. Self-reported abstaining, including random-sample biochemical verification, and NRT use were evaluated at 6 weeks and 3, 6 and 12 months.

RESULTS

At the 3-, 6- and 12-month visits, 58%, 46% and 30% of subjects, respectively were tobacco-abstinent. All nicotine abstinence was randomly controlled during the study except at 12 months, where all subjects claiming abstinence were confirmed biochemically and clinically.

CONCLUSION

Smokeless tobacco cessation achieved together with suitable NRT seems a promising way to improve a persistent tobacco-free condition.

A novel pathway for nicotine degradation by Aspergillus oryzae 112822 isolated from tobacco leaves

An efficient nicotine-degrading fungus was isolated from tobacco leaves and identified as Aspergillus oryzae 112822 based on morphological characteristics and sequence analysis of 18S rDNA, 5.8S rDNA and the internal transcribed spacer (5.8S-ITS region). When the strain was cultured in a medium with tobacco leaf extract for 40 h, the maximum amount of cell growth was 3.6 g l(-1) and nicotine degradation was 2.19 g l(-1). The intermediates of nicotine degradation by resting cells were isolated by preparative TLC or semi-preparative HPLC, and identified by TLC, MS, NMR, Fourier-transform (FT)-IR and GC-MS analysis. The pathway for nicotine degradation in A. oryzae 112822 was proposed to be from nicotine to 2,3-dihydroxypyridine through the intermediates nornicotine, myosmine, N-methylnicotinamide and 2-hydroxy-N-methylnicotinamide. The ring of 2,3-dihydroxypyridine was opened between the 2- and 3-hydroxy positions to yield succinic acid. N-methylnicotinamide and 2,3-dihydroxypyridine were satisfactorily verified as metabolites of nicotine degradation. This is the first elucidation of a pathway for nicotine degradation in fungi.

Oral ulceration due to chronic use of Nicorette gum: case report

Oral ulceration is a common presentation in a dental clinic. These ulcers may be acute or chronic, based on the duration of symptoms. The etiology of oral ulceration can range from trauma to squamous cell carcinoma. It is the responsibility of the dentist to differentiate the various etiologies of oral ulceration for proper management. This case report is presented to remind dentists that the long-term use of Nicorette gum should be considered in the differential diagnosis of chronic oral ulcers.