Application of nicotine enantiomers, derivatives and analogues in therapy of neurodegenerative disorders

Nicotine Formulation Influences the Autonomic and Arrhythmogenic Effects of Electronic Cigarettes

INTRODUCTION

Evidence is mounting that electronic cigarette (e-cig) use induces cardiac sympathetic dominance and electrical dysfunction conducive to arrhythmias and dependent upon nicotine. A variety of nicotine types and concentrations are available in e-cigs, but their relative cardiovascular effects remain unclear. Here we examine how different nicotine forms (racemic, free base, and salt) and concentrations influence e-cig-evoked cardiac dysfunction and arrhythmogenesis and provide a mechanism for nicotine-salt-induced autonomic imbalance.

METHODS

ECG-telemetered C57BL/6J mice were exposed to filtered air (FA) or e-cig aerosols from propylene glycol and vegetable glycerin solvents either without nicotine (vehicle) or with increasing nicotine concentrations (1%, 2.5%, and 5%) for three 9-minute puff sessions per concentration. Spontaneous ventricular premature beat (VPB) incidence rates, heart rate, and heart rate variability (HRV) were compared between treatments. Subsequently, to test the role of β1-adrenergic activation in e-cig-induced cardiac effects, mice were pretreated with atenolol and exposed to either FA or 2.5% nicotine salt.

RESULTS

During puffing and washout phases, ≥2.5% racemic nicotine reduced heart rate and increased HRV relative to FA and vehicle controls, indicating parasympathetic dominance. Relative to both controls, 5% nicotine salt elevated heart rate and decreased HRV during washout, suggesting sympathetic dominance, and also increased VPB frequency. Atenolol abolished e-cig-induced elevations in heart rate and declines in HRV during washout, indicating e-cig-evoked sympathetic dominance is mediated by β1-adrenergic stimulation.

CONCLUSIONS

Our findings suggest that inhalation of e-cig aerosols from nicotine-salt-containing e-liquids could increase the cardiovascular risks of vaping by inducing sympathetic dominance and cardiac arrhythmias.

IMPLICATIONS

Exposure to e-cig aerosols containing commercially relevant concentrations of nicotine salts may increase nicotine delivery and impair cardiac function by eliciting β1-adrenoceptor-mediated sympathoexcitation and provoking ventricular arrhythmias. If confirmed in humans, our work suggests that regulatory targeting of nicotine salts through minimum pH standards or limits on acid additives in e-liquids may mitigate the public health risks of vaping.

Transition Metal Catalyzed Hiyama Cross-Coupling: Recent Methodology Developments and Synthetic Applications

Hiyama cross-coupling is a versatile reaction in synthetic organic chemistry for the construction of carbon-carbon bonds. It involves the coupling of organosilicons with organic halides using transition metal catalysts in good yields and high enantioselectivities. In recent years, hectic progress has been made by researchers toward the synthesis of diversified natural products and pharmaceutical drugs using the Hiyama coupling reaction. This review emphasizes the recent synthetic developments and applications of Hiyama cross-coupling.

Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral amines are key structural motifs present in a wide variety of natural products, drugs, and other biologically active compounds. During the past decade, significant advances have been made with respect to the enantioselective synthesis of chiral amines, many of them based on catalytic asymmetric hydrogenation (AH). The present review covers the use of AH in the synthesis of chiral amines bearing a stereogenic center either in the α, β, or γ position with respect to the nitrogen atom, reported from 2010 to 2020. Therefore, we provide an overview of the recent advances in the AH of imines, enamides, enamines, allyl amines, and N-heteroaromatic compounds.

Synthetic Methods for the Preparation of Conformationally Restricted Analogues of Nicotine

In the context of naturally occurring nitrogen heterocycles, nicotine is a chiral alkaloid present in tobacco plants, which can target and stimulate nicotinic acetylcholine receptors (nAChRs), a class of ligand-gated ion channels commonly located throughout the human brain. Due to its well-known toxicity for humans, there is considerable interest in the development of synthetic analogues; in particular, conformationally restricted analogues of nicotine have emerged as promising drug molecules for selective nAChR-targeting ligands. In the present mini-review, we will describe the synthesis of the conformationally restricted analogues of nicotine involving one or more catalytic processes. In particular, we will follow a systematic approach as a function of the heteroarene structure, considering: (a) 2,3-annulated tricyclic derivatives; (b) 3,4-annulated tricyclic derivatives; (c) tetracyclic derivatives; and (d) other polycyclic derivatives. For each of them we will also consider, when carried out, biological studies on their activity for specific nAChR subunits.

Cholinergic Receptor Modulation as a Target for Preventing Dementia in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative condition characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) in the midbrain resulting in progressive impairment in cognitive and motor abilities. The physiological and molecular mechanisms triggering dopaminergic neuronal loss are not entirely defined. PD occurrence is associated with various genetic and environmental factors causing inflammation and mitochondrial dysfunction in the brain, leading to oxidative stress, proteinopathy, and reduced viability of dopaminergic neurons. Oxidative stress affects the conformation and function of ions, proteins, and lipids, provoking mitochondrial DNA (mtDNA) mutation and dysfunction. The disruption of protein homeostasis induces the aggregation of alpha-synuclein (α-SYN) and parkin and a deficit in proteasome degradation. Also, oxidative stress affects dopamine release by activating ATP-sensitive potassium channels. The cholinergic system is essential in modulating the striatal cells regulating cognitive and motor functions. Several muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChRs) are expressed in the striatum. The nAChRs signaling reduces neuroinflammation and facilitates neuronal survival, neurotransmitter release, and synaptic plasticity. Since there is a deficit in the nAChRs in PD, inhibiting nAChRs loss in the striatum may help prevent dopaminergic neurons loss in the striatum and its pathological consequences. The nAChRs can also stimulate other brain cells supporting cognitive and motor functions. This review discusses the cholinergic system as a therapeutic target of cotinine to prevent cognitive symptoms and transition to dementia in PD.

Determination of (R)-(+)- and (S)-(-)-Nicotine Chirality in Puff Bar E-Liquids by 1H NMR Spectroscopy, Polarimetry, and Gas Chromatography-Mass Spectrometry

Tobacco products generally contain tobacco-derived nicotine (TDN; having ∼99+% (S)-(-)-nicotine). Recent United States regulation has led some producers to transition to synthetic ("tobacco-free") nicotine. For example, Puff Bar is now marketed with tobacco-free nicotine (TFN; presumed to be racemic). To evaluate the claim that these new products contain TFN, we evaluated the presence of the two nicotine optical isomers by 1H NMR spectroscopy, polarimetry, and gas chromatography-mass spectrometry. Older Puff Bars were found to contain (S)-(-)-nicotine, and newer "TFN" Puff Bars were found to contain both (R)-(+) and (S)-(-) isomers-indicating TFN, albeit with slightly more of the (S)-(-)-nicotine form.

Anxiolytic, Promnesic, Anti-Acetylcholinesterase and Antioxidant Effects of Cotinine and 6-Hydroxy-L-Nicotine in Scopolamine-Induced Zebrafish (Danio rerio) Model of Alzheimer's Disease

Cotinine (COT) and 6-hydroxy-L-nicotine (6HLN) are two nicotinic derivatives that possess cognitive-improving abilities and antioxidant properties in different rodent models of Alzheimer's disease (AD), eluding the side-effects of nicotine (NIC), the parent molecule. In the current study, we evaluated the impact of COT and 6HLN on memory deterioration, anxiety, and oxidative stress in the scopolamine (SCOP)-induced zebrafish model of AD. For this, COT and 6HLN were acutely administered by immersion to zebrafish that were treated with SCOP before testing. The memory performances were assessed in Y-maze and object discrimination (NOR) tasks, while the anxiety-like behavior was evaluated in the novel tank diving test (NTT). The acetylcholinesterase (AChE) activity and oxidative stress were measured from brain samples. The RT-qPCR analysis was used to evaluate the npy, egr1, bdnf, and nrf2a gene expression. Our data indicated that both COT and 6HLN attenuated the SCOP-induced anxiety-like behavior and memory impairment and reduced the oxidative stress and AChE activity in the brain of zebrafish. Finally, RT-qPCR analysis indicated that COT and 6HLN increased the npy, egr1, bdnf, and nrf2a gene expression. Therefore, COT and 6HLN could be used as tools for improving AD conditions.

Microfluidic tank assisted nicotine sensing property of field effect transistor composed of an atomically thin MoS2 channel

We investigated the sensor behavior of a field effect transistor, the channel of which is made of atomically thin MoS2 layers, focusing on the interaction of the MoS2 channel with the solution containing target molecules. For this purpose, we made a newly designed device in which the mask covered the electrodes of the source and the drain in order to make the solution contact only with the channel. In addition, a micro-fluid tank was fabricated above the channel as a solution reservoir. We examined the FET properties of this device for the sensing of the nicotine molecule for the development of a detection system for this molecule in the human body under in vivo conditions. We detected the sensor behavior both for the drop-cast process and for the condition where the channel contacts with the solution. The drain-current vs. gate-voltage variation of the MoS2-FET with the attachment of the nicotine molecule was clearly observed for both cases. For the latter case, the threshold voltage shifted in the negative gate-voltage direction with the increase of the concentration of the nicotine in the solution. This can be explained by the electron transfer from the molecule to the MoS2 channel, which was further confirmed by analyzing the X-ray photoemission spectroscopy and Raman spectroscopy together with the DFT calculation. The sensor can detect the variation of the nicotine concentration in the IPA solution by detecting the Vth change of the MoS2-FET.

Structural and functional computational analysis of nicotine analogs as potential neuroprotective compounds in Parkinson disease

As the mechanism of interaction between nicotinic receptors with nicotine analogs is not yet fully understood, information at molecular level obtained from computational calculations is needed. In this sense, this work is a computational study of eight nicotine analogs, all with pyrrolidine ring modifications over a nicotine-based backbone optimized with B3LYP-D3/aug-cc-pVDZ. A molecular characterization was performed focusing on geometrical parameters such as pseudo-rotation angles, atomic charges, HOMO and LUMO orbitals, reactivity indexes and intermolecular interactions. Three analogs, A2 (3-(1,3-dimethyl-4,5-dihydro-1h-pirazole-5-yl) pyridine), A3 (3-(3-methyl-4,5-dihydro-1H-pyrazol-5-yl)-pyridine) and A8 (5-methyl-3-(pyridine-3-yl)-4,5-dihydroisoxazole), were filtered suggesting putative neuroprotective activity taking into account different reactivity values, such as their lowest hardness: 2.37 eV (A8), 2.43 eV (A2) and 2.56 eV (A3), compared to the highest hardness value found: 2.71 eV for A5 (3-((2S,4R)-4-(fluoromethyl)-1-methylpyrrolidine-2-il) pyridine), similar to the value of nicotine (2.70 eV). Additionally, molecular docking of all 8 nicotine analogs with the α 7 nicotinic acetylcholine receptor (α 7 nAChR) was performed. High values of interaction between the receptor and the three nicotine analogs were obtained: A3 (-7.1 kcal/mol), A2 (-6.9 kcal/mol) and A8 (-6.8 kcal/mol); whereas the affinity energy of nicotine was -6.4 kcal/mol. Leu116 and Trp145 are key residues in the binding site of α 7 nAChR interacting with nicotine analogs. Therefore, based upon these results, possible application of these nicotine analogs as neuroprotective compounds and potential implication at the design of novel Parkinson's treatments is evidenced.

Strategies for the Treatment of Parkinson's Disease: Beyond Dopamine

Parkinson’s disease (PD) is the second-leading cause of dementia and is characterized by a progressive loss of dopaminergic neurons in the substantia nigra alongside the presence of intraneuronal α-synuclein-positive inclusions. Therapies to date have been directed to the restoration of the dopaminergic system, and the prevention of dopaminergic neuronal cell death in the midbrain. This review discusses the physiological mechanisms involved in PD as well as new and prospective therapies for the disease. The current data suggest that prevention or early treatment of PD may be the most effective therapeutic strategy. New advances in the understanding of the underlying mechanisms of PD predict the development of more personalized and integral therapies in the years to come. Thus, the development of more reliable biomarkers at asymptomatic stages of the disease, and the use of genetic profiling of patients will surely permit a more effective treatment of PD.

Machine Learning Neuroprotective Strategy Reveals a Unique Set of Parkinson Therapeutic Nicotine Analogs

AIMS

Present a novel machine learning computational strategy to predict the neuroprotection potential of nicotine analogs acting over the behavior of unpaired signaling pathways in Parkinson's disease.

BACKGROUND

Dopaminergic replacement has been used for Parkinson's Disease (PD) treatment with positive effects on motor symptomatology but low progression and prevention effects. Epidemiological studies have shown that nicotine consumption decreases PD prevalence through neuroprotective mechanisms activation associated with the overstimulation of signaling pathways (SP) such as PI3K/AKT through nicotinic acetylcholine receptors (e.g α7 nAChRs) and over-expression of anti-apoptotic genes such as Bcl-2. Nicotine analogs with similar neuroprotective activity but decreased secondary effects remain as a promissory field.

OBJECTIVE

The objective of this study is to develop an interdisciplinary computational strategy predicting the neuroprotective activity of a series of 8 novel nicotine analogs over Parkinson's disease.

METHODS

We present a computational strategy integrating structural bioinformatics, SP manual reconstruction, and deep learning to predict the potential neuroprotective activity of 8 novel nicotine analogs over the behavior of PI3K/AKT. We performed a protein-ligand analysis between nicotine analogs and α7 nAChRs receptor using geometrical conformers, physicochemical characterization of the analogs and developed manually curated neuroprotective datasets to analyze their potential activity. Additionally, we developed a predictive machine-learning model for neuroprotection in PD through the integration of Markov Chain Monte-Carlo transition matrix for the 2 SP with synthetic training datasets of the physicochemical properties and structural dataset.

RESULTS

Our model was able to predict the potential neuroprotective activity of seven new nicotine analogs based on the binomial Bcl-2 response regulated by the activation of PI3K/AKT.

CONCLUSION

Hereby, we present a robust novel strategy to assess the neuroprotective potential of biomolecules based on SP architecture. Our theoretical strategy can be further applied to the study of new treatments related to SP deregulation and may ultimately offer new opportunities for therapeutic interventions in neurodegenerative diseases.

Palladium-Catalyzed Hiyama Cross-Couplings of Arylsilanes with 3-Iodoazetidine: Synthesis of 3-Arylazetidines

The first palladium-catalyzed Hiyama cross-coupling reactions of arylsilanes with 3-iodoazetidine were described. The protocol provides a convenient access to a variety of useful 3-arylazetidines which are of great interest in pharmaceutical laboratories in moderate to good yields (30%-88%). In addition, this strategy has the advantage of easy operation and mild reaction conditions.

Determination of tobacco alkaloid enantiomers using reversed phase UPLC/MS/MS

Nʹ-Nitrosonornicotine (NNN), a carcinogenic tobacco-specific Nʹ-nitrosamine (TSNA), is on the FDA list of harmful and potentially harmful constituents (HPHCs). Nornicotine, a product of the demethylation of nicotine, is the immediate alkaloid precursor for NNN formation. Nicotine, nornicotine and NNN are optically active. The accumulation of the isomers of nicotine, nornicotine, and NNN impacts their biological activity. In this paper, we report the determination of tobacco alkaloid enantiomers (including nicotine, nornicotine, anabasine, and anatabine) in samples of different tobacco lines using a reversed phase ultra-performance liquid chromatography-tandem mass spectrometer (UPLC/MS/MS) method. Current method demonstates excellent detection capability for all alkaloid enantiomers, with correlation coefficients (r²) > 0.996 within their linear dynamic ranges. The limit of detection (LOD) and limit of quantitation (LOQ) of all analytes are less than 10 ng/mL and 30 ng/mL, respectively. In addition, their recovery and coefficient of variation (CV%) are within 100–115% and 0.2–3.7%, respectively. The method validated in this paper is simple, fast, and sensitive for the quantification of alkaloid enantiomers in tobacco leaf and has been applied to investigations of tobacco alkaloid enantiomer ratios in different tobacco lines and tobacco products.

Enantiomeric composition of nicotine in tobacco leaf, cigarette, smokeless tobacco, and e-liquid by normal phase high-performance liquid chromatography

Evaluating the source of nicotine in e-liquid is a problem. Tobacco-derived nicotine contains predominantly (S)-(-)-nicotine, whereas tobacco-free nicotine products may not. Thus, we developed a new normal phase high-performance liquid chromatography method to determinate the enantiomeric composition of nicotine in 10 kinds of flue-cured tobacco, 3 kinds of burley, 1 kind of cigar tobacco, 2 kinds of oriental tobacco, 5 kinds of Virginia cigarette, 5 kinds of blend cigarette, 10 kinds of e-liquid, and 4 kinds of smokeless tobacco. The amount of (R)-(+)-nicotine ranged from ~0.02% to ~0.76% of total nicotine. An e-liquid sample had the highest level of (R)-(+)-nicotine. The extraction and purification processes used to obtain commercial (S)-(-)-nicotine from the tobacco do not decrease the amount of (R)-(+)-nicotine in tobacco. So the amount of (R)-(+)-nicotine in samples in our work were the same as tobacco samples.

A comprehensive methodology for the chiral separation of 40 tobacco alkaloids and their carcinogenic E/Z-(R,S)-tobacco-specific nitrosamine metabolites

The predominant enantiomer of nicotine found in nature is (S)-nicotine and its pharmacology has been widely established. However, pharmacologic information concerning individual enantiomers of nicotine-related compounds is limited. Recently, a modified macrocyclic glycopeptide chiral selector was found to be highly stereoselective for most tobacco alkaloids and metabolites. This study examines the semi-synthetic and native known macrocyclic glycopeptides for chiral recognition, separation, and characterization of the largest group of nicotine-related compounds ever reported (tobacco alkaloids, nicotine metabolites and derivatives, and tobacco-specific nitrosamines). The enantioseparation of nicotine is accomplished in less than 20s for example. All liquid chromatography separations are mass spectrometry compatible for the tobacco alkaloids, as well as their metabolites. Ring-closed, cyclized structures were identified and separated from their ring-open, straight chain equilibrium structures. Also, E/Z-tobacco-specific nitrosamines and their enantiomers were directly separated. E/Z isomers also are known to have different physical and chemical properties and biological activities. This study provides optimal separation conditions for the analysis of nicotine-related isomers, which in the past have been reported to be ineffectively separated which can result in inaccurate results. The methodology of this study could be applied to cancer studies, and lead to more information about the role of these isomers in other diseases and as treatment for diseases.

Evaluation of nicotine in tobacco-free-nicotine commercial products

Recently, a variety of new tobacco-free-nicotine, TFN, products have been commercialized as e-liquids. Tobacco-derived nicotine contains predominantly (S)-(-)-nicotine, whereas TFN products may not. The TFN products are said to be cleaner, purer substances, devoid of toxic components that come from the tobacco extraction process. A variety of commercial tobacco and TFN products were analyzed to identify the presence and composition of each nicotine enantiomer. A rapid and effective enantiomeric separation of nicotine has been developed using a modified macrocyclic glycopeptide bonded to superficially porous particles. The enantiomeric assay can be completed in <2 min with high resolution and accuracy using high performance liquid chromatography with electrospray ionization mass spectrometry. The results of this study suggest the need for pharmacological studies of (R)-(+)-nicotine, which is present in much greater quantities in commercial TFN products compared to commercial tobacco-derived products. Such studies are required by the FDA for new enantiomeric pharmacological products. Copyright © 2016 John Wiley & Sons, Ltd.

Nicotine affects protein complex rearrangement in Caenorhabditis elegans cells

Nicotine may affect cell function by rearranging protein complexes. We aimed to determine nicotine-induced alterations of protein complexes in Caenorhabditis elegans (C. elegans) cells, thereby revealing links between nicotine exposure and protein complex modulation. We compared the proteomic alterations induced by low and high nicotine concentrations (0.01 mM and 1 mM) with the control (no nicotine) in vivo by using mass spectrometry (MS)-based techniques, specifically the cetyltrimethylammonium bromide (CTAB) discontinuous gel electrophoresis coupled with liquid chromatography (LC)-MS/MS and spectral counting. As a result, we identified dozens of C. elegans proteins that are present exclusively or in higher abundance in either nicotine-treated or untreated worms. Based on these results, we report a possible network that captures the key protein components of nicotine-induced protein complexes and speculate how the different protein modules relate to their distinct physiological roles. Using functional annotation of detected proteins, we hypothesize that the identified complexes can modulate the energy metabolism and level of oxidative stress. These proteins can also be involved in modulation of gene expression and may be crucial in Alzheimer's disease. The findings reported in our study reveal putative intracellular interactions of many proteins with the cytoskeleton and may contribute to the understanding of the mechanisms of nicotinic acetylcholine receptor (nAChR) signaling and trafficking in cells.

Nicotine versus 6-hydroxy-l-nicotine against chlorisondamine induced memory impairment and oxidative stress in the rat hippocampus

6-Hydroxy-l-nicotine (6HLN), a nicotine derivative from nicotine degradation by Arthrobacter nicotinovorans pAO1 strain was found to improve behavioral deficits and to reverse oxidative stress in the rat hippocampus. Rats were given CHL (10mg/kg, i.p.) were used as an Alzheimer's disease-like model. The nicotine (0.3mg/kg) and 6HLN (0.3mg/kg) were administered alone or in combination in the CHL-treated rats. Memory-related behaviors were evaluated using Y-maze and radial arm-maze tests. The antioxidant enzymes activity and the levels of the biomarkers of oxidative stress were measured in the hippocampus. Statistical analyses were performed using two-way ANOVA and Tukey's post hoc test. F values for which p<0.05 were regarded as statistically significant. CHL-caused memory deficits and oxidative stress enhancing were observed. Both nicotine and 6HLN administration attenuated the cognitive deficits and recovered the antioxidant capacity in the rat hippocampus of the CHL rat model. Our results suggest that 6HLN versus nicotine confers anti-amnesic properties in the CHL-induced a rat model of memory impairment via reversing cholinergic function and decreasing brain oxidative stress, suggesting the use of this compound as an alternative agent in AD treatment.

Nicotine alkaloids as antioxidant and potential protective agents against in vitro oxidative haemolysis

The capacity of eleven nicotine alkaloids to reduce oxidative stress was investigated. In order to provide a structure-activity relationships analysis, new nicotine derivatives with a substituent introduced into the pyrrolidine ring were synthesized and investigated together with nicotine and its known analogs. All newly synthesized compounds were characterized by (1)H, (13)C NMR and EI-MS technique. The antioxidant properties of nicotine, its known analogs and newly produced derivatives, were evaluated by various antioxidant assays such 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH(•)) scavenging, ferrous ions (Fe(2+)) chelating activity and total reducing ability determination by Fe(3+) → Fe(2+) transformation assay. The protective effects of all compounds tested against 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) and tert-butyl hydroperoxide (t-BuOOH)-induced oxidative haemolysis and morphological injury of human erythrocytes, were estimated in vitro. The results showed that nicotine alkaloids exhibited various antiradical efficacy and antioxidant activity in a structure- and a dose-dependent manner. In addition, the capacity of nicotine alkaloids to protect erythrocytes from AAPH- and t-BuOOH-induced oxidative haemolysis, was dependent on its incubation time with cells. Our findings showed that chemical and biological investigations conducted simultaneously can provide comprehensive knowledge concerning the antioxidant potential of nicotine alkaloids. This knowledge can be helpful in better understanding the properties of nicotine alkaloids under oxidative stress conditions.

Combinatorial synthesis of nicotine analogs using an Ugi 4-CR/cyclization-reduction strategy

A practical one-pot synthesis of nicotine analogs from Ugi 4-CR/propargyl adducts is reported. This methodology allows the rapid construction of the pyrrolidine moiety present in nicotine through an intramolecular base-promoted 5-endo cycloisomerization process, followed by a reduction of the resulting mixture of 2- and 3-pyrrolines to afford nicotine analogs in good overall yields.

Nicotine-Cadmium Interaction Alters Exploratory Motor Function and Increased Anxiety in Adult Male Mice

In this study we evaluated the time dependence in cadmium-nicotine interaction and its effect on motor function, anxiety linked behavioural changes, serum electrolytes, and weight after acute and chronic treatment in adult male mice. Animals were separated randomly into four groups of n = 6 animals each. Treatment was done with nicotine, cadmium, or nicotine-cadmium for 21 days. A fourth group received normal saline for the same duration (control). Average weight was determined at 7-day interval for the acute (D1-D7) and chronic (D7-D21) treatment phases. Similarly, the behavioural tests for exploratory motor function (open field test) and anxiety were evaluated. Serum electrolytes were measured after the chronic phase. Nicotine, cadmium, and nicotine-cadmium treatments caused no significant change in body weight after the acute phase while cadmium-nicotine and cadmium caused a decline in weight after the chronic phase. This suggests the role of cadmium in the weight loss observed in tobacco smoke users. Both nicotine and cadmium raised serum Ca²⁺ concentration and had no significant effect on K⁺ ion when compared with the control. In addition, nicotine-cadmium treatment increased bioaccumulation of Cd²⁺ in the serum which corresponded to a decrease in body weight, motor function, and an increase in anxiety.

(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.

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.

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.

Enantiomeric natural products: occurrence and biogenesis

In nature, chiral natural products are usually produced in optically pure form-however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain.

Surface plasmon resonance based biosensors for exploring the influence of alkaloids on aggregation of amyloid-β peptide

The main objective of the presented study was the development of a simple analytical tool for exploring the influence of naturally occurring compounds on the aggregation of amyloid-β peptide (Aβ₄₀) in order to find potential anti-neurodegenerative drugs. The gold discs used for surface plasmon resonance (SPR) measurements were modified with thioaliphatic acid. The surface functionalized with carboxylic groups was used for covalent attaching of Aβ₄₀ probe by creation of amide bonds in the presence of EDC/NHS. The modified SPR gold discs were used for exploring the Aβ₄₀ aggregation process in the presence of selected alkaloids: arecoline hydrobromide, pseudopelletierine hydrochloride, trigonelline hydrochloride and α-lobeline hydrochloride. The obtained results were discussed with other parameters which govern the phenomenon studied such as lipophilicity/hydrophilicy and Aβ₄₀-alkaloid association constants.

Synthesis of fused-ring nicotine derivatives from (S)-nicotine

The synthesis of novel fused-ring bicyclic (4-6) and tricyclic (7-10) nicotine derivatives from natural (S)-nicotine are described. Enantiopure bicyclic dioxino, dihydrofuro, and dihydropyranol nicotine derivatives as well as tricylic benzofuro and benzopyran derivatives were synthesized from simple alkoxy or halonicotine intermediates. Attempts to synthesize furonicotines (11, 12) resulted in formation of the furonicotine dimers 42 and 49.

Smoking, nicotine and neuropsychiatric disorders

Tobacco smoking is an extremely addictive and harmful form of nicotine (NIC) consumption, but unfortunately also the most prevalent. Although disproportionately high frequencies of smoking and its health consequences among psychiatric patients are widely known, the neurobiological background of this epidemiological association is still obscure. The diverse neuroactive effects of NIC and some other major tobacco smoke constituents in the central nervous system may underlie this association. This present paper summarizes the pharmacology of NIC and its receptors (nAChR) based on a systematic review of the literature. The role of the brain's reward system(s) in NIC addiction and the results of functional and structural neuroimaging studies on smoking-related states and behaviors (i.e. dependence, craving, withdrawal) are also discussed. In addition, the epidemiological, neurobiological, and genetic aspects of smoking in several specific neuropsychiatric disorders are reviewed and the clinical relevance of smoking in these disease states addressed.