”E-cigarettes are about as safe as you can get. We know about the health risks of nicotine from studies in Sweden into the use of snus, a smokeless tobacco. Nicotine is not what kills you when you smoke tobacco. E-cigarettes are probably about as safe as drinking coffee. All they contain is water vapour, nicotine and propylene glycol [which is used to help vaporise the liquid nicotine].” Professor Robert West 2013
“Nicotine itself is not a particularly hazardous drug,” says Professor John Britton, who leads the tobacco advisory group for the Royal College of Physicians. ”It’s something on a par with the effects you get from caffeine.” Professor John Britton Chair Tobacco Advisory Group Royal College of Physicians (2013)
“Nicotine itself is probably safer than caffeine ….The case for regulating e-cigarettes as a pharmaceutical product is on a par with regulating coffee.” Professor Peter Hajek (2013)
In 2006, before the popularization of e-cigarettes, I spent a seven month sabbatical at the World Health Organization’s International Agency for Research in Cancer at Lyon in France. A senior colleague there had previously worked for a major pharmaceutical company at the forefront of nicotine replacement therapy (NRT). She and I had many discussions about the safety of NRT and its efficacy in helping people quit (which in real world usage, outside of professionally supported contexts – which very few smokers are interested in attending – is pretty poor).
It is well known that many smokers find NRT unsatisfactory in that it does not supply them with sufficient nicotine to overcome their cravings. I asked her why it was that the companies did not produce higher nicotine delivery products with more “grunt” which would stand a better chance of substituting for cigarettes. A cynical part of me wondered if the never-publicly-discussed business model for NRT within the pharmaceutical industry was that the dosage which might actually succeed in helping many smokers quit would not be as profitable as the dosage levels that saw high failure rates, but which saw many smokers having repeated NRT attempts with current and newer formulations.
During one of these discussions, she told me that pharmaceutical companies were acutely aware that nicotine was not a benign drug, and that they were highly sensitive to the risks involved in trying to get higher delivery NRT approved for use, and had collectively decided not to go down that path. The Food and Drug Administration would have almost certainly rejected such applications, she said. She handed me a pile of papers to read about what was already known about the non-benign nature of nicotine.
Below are a selection of such papers published since my time at IARC. Unfortunately, some are pay-walled, so only the abstracts are available to non-subscribers. Many though, have full text lnks.
After you read these, ask yourself: does this sound like a benign drug that should not be regulated (as was NRT) and made as freely available as coffee? Or should it be strictly regulated so that we don’t repeat the massive mistake that was made with treating cigarettes as a somehow above regulation of their ingredients and highly engineered chemistry.
Vaping advocates are frantically opposed to serious government regulation of e-cigarettes. The information below suggests such an attitude is utterly reckless.
Scott JG, Matuschka L, Niemelä S et al. Evidence of a causal relationship between smoking tobacco and schizophrenia spectrum disorders. Front. Psychiatry, 20 November 2018 |
Abstract: There has been emerging evidence of an association between tobacco smoking and schizophrenia spectrum disorders (SSD). Two meta-analyses have reported that people who smoke tobacco have an ~2-fold increased risk of incident schizophrenia or psychosis, even after adjusting for confounding factors. This study aimed to critically appraise the research which has examined the association between tobacco smoking and SSD against the Bradford Hill criteria for causality, to determine the strength of the evidence for a causal relationship. Eight longitudinal studies (seven cohort studies and one case control study) were identified which examined tobacco smoking as an exposure and psychosis as an outcome. All seven cohort studies were assessed as being of high quality using the Newcastle-Ottawa Scale. Six of the eight studies found a statistically significant positive association between tobacco smoking and onset of SSD. These studies reported a consistent association with a moderate to large effect size and a dose response relationship. The studies adjusted for multiple potential confounders including age, sex, socioeconomic status, shared genetic risk, prodromal symptoms, and comorbid cannabis and other substance use. The studies did not adjust for exposure to childhood trauma or prenatal tobacco. There was substantial though inconclusive evidence supporting a causal relationship between tobacco smoking and increased risk of SSD. If a causal relationship does exist, nicotine is most likely responsible for this association. This raises serious public health concerns about the increasing use of e-cigarettes and other products, particularly by adolescents whose nicotine use may increase their risk of SSD. Research is urgently needed to examine the association between e-cigarette use and incident psychosis, particularly in adolescents and young adults.
Gurillo P, Jauhar S, Murray RM, MacCabe JH. Does tobacco use cause psychosis? Systematic review and meta-analysis. Lancet Psychiatry 2015;2: 718–25.
Abstract: Background: Although the association between psychotic illness and cigarette smoking is well known, the reasons are unclear why people with psychosis are more likely to smoke than are the general population. We aimed to test several hypotheses. First, that daily tobacco use is associated with an increased risk of psychotic illness in both case-control and prospective studies. Second, that smoking is associated with an earlier age at onset of psychotic illness. Finally, that an earlier age at initiation of smoking is associated with an increased risk of psychosis. We also aimed to derive an estimate of the prevalence of smoking in patients presenting with their first episode of psychosis.
Methods:We searched Embase, Medline, and PsycINFO and selected observational studies in which rates of smoking were reported in people with psychotic disorders, compared with controls. We calculated the weighted mean difference for age at onset of psychosis and age at initiation of smoking. For categorical outcomes, we calculated odds ratios from cross-sectional studies and risk ratios from prospective studies.
Findings: Of 3717 citations retrieved, 61 studies comprising 72 samples met inclusion criteria. The overall sample included 14 555 tobacco users and 273 162 non-users. The prevalence of smoking in patients presenting with their first episode of psychosis was 0∙57 (95% CI 0∙52–0∙62; p<0∙0001). In case-control studies, the overall odds ratio for the first episode of psychosis in smokers versus non-smokers was 3.22 (95% CI 1.63–6.33), with some evidence of publication bias (Egger’s test p=0.018, Begg’s test p=0.007). For prospective studies, we calculated an overall relative risk of new psychotic disorders in daily smokers versus non-smokers of 2.18 (95% CI 1.23–3.85). Daily smokers developed psychotic illness at an earlier age than did non-smokers (weighted mean difference –1.04 years, 95% CI –1∙82 to –0.26). Those with psychosis started smoking at a non-significantly earlier age than did healthy controls (–0.44 years, 95% CI –1∙21 to 0∙34).
Interpretation Daily tobacco use is associated with increased risk of psychosis and an earlier age at onset of psychotic illness. The possibility of a causal link between tobacco use and psychosis merits further examination. [Note: the discussion section of this paper includes a detailed consideration of the possible role of nicotine in the development of psychosis].
Niemelä S, Sourander A, Surcel H-M et al Prenatal nicotine exposure and risk of schizophrenia among offspring in a national birth cohort. Am J Psychiatry. 2016 Aug 1;173(8):799-806.
Objective: Cigarette smoking during pregnancy is a major public health problem leading to adverse health outcomes and neurodevelopmental abnormalities among offspring. Its prevalence in the United States and Europe is 12%–25%. This study examined the relationship between prenatal nicotine exposure (cotinine level) in archived maternal sera and schizophrenia in offspring from a national birth cohort.
Method: The authors conducted a population-based nested case-control study of all live births in Finland from 1983 to 1998. Cases of schizophrenia in offspring (N=977) were identified from a national registry and matched 1:1 to controls on date of birth, sex, and residence. Maternal serum cotinine levels were prospectively measured, using quantitative immunoassay, from early- to mid-gestation serum specimens archived in a national biobank.
Results: A higher maternal cotinine level, measured as a continuous variable, was associated with an increased odds of schizophrenia (odds ratio=3.41, 95% confidence interval, 1.86–6.24). Categorically defined heavy maternal nicotine exposure was related to a 38% increased odds of schizophrenia. These findings were not accounted for by maternal age, maternal or parental psychiatric disorders, socioeconomic status, and other covariates. There was no clear evidence that weight for gestational age mediated the associations.
Conclusions: To the authors’ knowledge, this is the first study of the relationship between a maternal smoking biomarker and schizophrenia. It provides the most definitive evidence to date that smoking during pregnancy is associated with schizophrenia. If replicated, these findings suggest that preventing smoking during pregnancy may decrease the incidence of schizophrenia.
Guo, Z-Z1,Cao Q-A, Li Z-Z et al. SP600125 Attenuates Nicotine-Related aortic aneurysm formation by inhibiting matrix metalloproteinase production and CC chemokine-mediated macrophage migration. Mediators of Inflammation 2016 (full text)
Abstract Nicotine, a major chemical component of cigarettes, plays a pivotal role in the development of abdominal aortic aneurysm (AAA). c-Jun N-terminal kinase (JNK) has been demonstrated to participate in elastase-induced AAA. This study aimed to elucidate whether the JNK inhibitor SP600125 can attenuate nicotine plus angiotensin II- (AngII-) induced AAA formation and to assess the underlying molecular mechanisms. SP600125 significantly attenuated nicotine plus AngII-induced AAA formation. The expression of matrix metalloproteinase- (MMP-) 2, MMP-9, monocyte chemoattractant protein- (MCP-) 1, and regulated-onactivation, normal T-cells expressed and secreted (RANTES) was significantly upregulated in aortic aneurysm lesions but inhibited by SP600125. In vitro, nicotine induced the expression of MCP-1 and RANTESin bothRAW264.7 (mouse macrophage) and MOVAS (mouse vascular smooth muscle) cells in a dose-dependent manner; expression was upregulated by 0.5 ng/mL nicotine but strongly downregulated by 500 ng/mL nicotine. SP600125 attenuated the upregulation of MCP-1 and RANTES expression and subsequent macrophage migration. In conclusion, SP600125 attenuates nicotine plus AngII-induced AAA formation likely by inhibiting MMP- 2, MMP-9, MCP-1, and RANTES. The expression of chemokines in MOVAS cells induced by nicotine has an effect on RAW264.7 migration, which is likely to contribute to the development of nicotine-related AAA.
Dang N, Meng X, Song H. Nicotinic acetylcholine receptors and cancer (Review). Biomedical Reports 2016;4:515-518 (full text)
Abstract: Nicotine, the primary addictive constituent of cigarettes, is believed to contribute to cancer promotion and progression through the activation of nicotinic acetylcholine receptors (nAChRs), which are membrane ligand‑gated cation channels. nAChRs activation can be triggered by the neurotransmitter Ach, or certain other biological compounds, such as nicotine. In recent years, genome‑wide association studies have indicated that allelic variation in the α5‑α3‑β4 nAChR cluster on chromosome 15q24‑15q25.1 is associated with lung cancer risk. The role of nAChRs in other types of cancer has also been reported. The present review highlights the role of nAChRs in types of human cancer.
England LJ, Bunnell RE, Pechacek TF, Tong VT, McAfee TA. Nicotine and the developing human: a neglected element in the electronic cigarette debate American Journal of Preventive Medicine 2015 Aug;49(2):286-93. [full text]
Abstract: The elimination of cigarettes and other combusted tobacco products in the U.S. would prevent tens of millions of tobacco-related deaths. It has been suggested that the introduction of less harmful nicotine delivery devices, such as electronic cigarettes or other electronic nicotine delivery systems, will accelerate progress toward ending combustible cigarette use. However, careful consideration of the potential adverse health effects from nicotine itself is often absent from public health debates. Human and animal data support that nicotine exposure during periods of developmental vulnerability (fetal through adolescent stages) has multiple adverse health consequences, including impaired fetal brain and lung development, and altered development of cerebral cortex and hippocampus in adolescents. Measures to protect the health of pregnant women and children are needed and could include (1) strong prohibitions on marketing that increase youth uptake; (2) youth access laws similar to those in effect for other tobacco products; (3) appropriate health warnings for vulnerable populations; (4) packaging to prevent accidental poisonings; (5) protection of non-users from exposure to secondhand electronic cigarette aerosol; (6) pricing that helps minimize youth initiation and use; (7) regulations to reduce product addiction potential and appeal for youth; and (8) the age of legal sale.
Mishra M, Chaturvedi P, Datta S et al. Harmful effects of nicotine. Indian J Med Paediatr Oncol. 2015 Jan-Mar;36(1):24-31. (full text)
With the advent of nicotine replacement therapy, the consumption of the nicotine is on the rise. Nicotine is considered to be a safer alternative of tobacco. The IARC monograph has not included nicotine as a carcinogen. However there are various studies which show otherwise. We undertook this review to specifically evaluate the effects of nicotine on the various organ systems. A computer aided search of the Medline and PubMed database was done using a combination of the keywords. All the animal and human studies investigating only the role of nicotine were included. Nicotine poses several health hazards. There is an increased risk of cardiovascular, respiratory, gastrointestinal disorders. There is decreased immune response and it also poses ill impacts on the reproductive health. It affects the cell proliferation, oxidative stress, apoptosis, DNA mutation by various mechanisms which leads to cancer. It also affects the tumor proliferation and metastasis and causes resistance to chemo and radio therapeutic agents. The use of nicotine needs regulation. The sale of nicotine should be under supervision of trained medical personnel.
Grando SA. Connections of nicotine to cancer. Nature Reviews Cancer (2014) 14:419-429 [Full text]
Abstract: This Opinion article discusses emerging evidence of direct contributions of nicotine to cancer onset and growth. The list of cancers reportedly connected to nicotine is expanding and presently includes small-cell and non-small-cell lung carcinomas, as well as head and neck, gastric, pancreatic, gallbladder, liver, colon, breast, cervical, urinary bladder and kidney cancers. The mutagenic and tumour-promoting activities of nicotine may result from its ability to damage the genome, disrupt cellular metabolic processes, and facilitate growth and spreading of transformed cells. The nicotinic acetylcholine receptors (nAChRs), which are activated by nicotine, can activate several signalling pathways that can have tumorigenic effects, and these receptors might be able to be targeted for cancer therapy or prevention. There is also growing evidence that the unique genetic makeup of an individual, such as polymorphisms in genes encoding nAChR subunits, might influence the susceptibility of that individual to the pathobiological effects of nicotine. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the evaluation of regulations on nicotine product manufacturing, distribution and marketing.
Schaal C, Chellappan SP. Nicotine-mediated cell proliferation and tumor progression in smoking-related cancers. Mol Cancer Res. 2014 Jan;12(1):14-23. (full text)
Abstract: Tobacco smoke contains multiple classes of established carcinogens including benzo(a)pyrenes, polycyclic aromatic hydrocarbons, and tobacco specific nitrosamines. Most of these compounds exert their genotoxic effects by forming DNA adducts and generation of reactive oxygen species, causing mutations in vital genes like K-Ras and p53. In addition, tobacco specific nitrosamines can activate nicotinic acetylcholine receptors (nAChRs) and to a certain extent β-Adrenergic receptors (β-ARs), promoting cell proliferation. Further, it has been demonstrated that nicotine, the major addictive component of tobacco smoke, can induce cell cycle progression, angiogenesis, and metastasis of lung and pancreatic cancers. These effects occur mainly through the α7-nAChRs, with possible contribution from the β-ARs and/or epidermal growth factor receptors (EGFRs). This review article will discuss the molecular mechanisms by which nicotine and its oncogenic derivatives such as NNK (4-methylnitrosamino)-1-(3-pyridyl)-1-butanone) and NNN (N-nitrosonornicotine) induce cell cycle progression and promote tumor growth. A variety of signaling cascades are induced by nicotine through nAChRs, including the MAPK/ERK pathway, PI3K/AKT pathway and JAK/STAT signaling. In addition, studies have shown that nAChR activation induces Src kinase in a β-arrestin-1 dependent manner, leading to the inactivation of Rb protein and resulting in the expression of E2F1-regulated proliferative genes. Such nAChR-mediated signaling events enhance the proliferation of cells and render them resistant to apoptosis induced by various agents. These observations highlight the role of nAChRs in promoting the growth and metastasis of tumors and raise the possibility of targeting them for cancer therapy
Nordenvall C, Nilsson PJ, Ye W, Andersson TM, Nyrén O. Tobacco use and cancer survival: A cohort study of 40,230 Swedish male construction workers with incident cancer. Int J Cancer 2013; 132 (1):155-61. (full text)
Abstract: On theoretical grounds, nicotine has been implicated as a modifier of cancer progression. We investigated possible associations of smoking or use of Scandinavian moist snuff (snus) with survival after cancer among Swedish male construction workers. Snus use is associated with substantial exposure to nicotine but not to the combustion products in smoke. Among 336,381 workers with detailed information on tobacco use in 1971–1992, we observed 40,230 incident cancers. Complete follow-up through 2007 was accomplished through linkage to population and health registers. Hazard ratios (HRs) and 95% confidence intervals (CIs) for death from any cause, cancer-specific death and death from other causes were derived from Cox proportional hazards regression models adjusted for age at diagnosis, body mass index at study entry and period of diagnosis. Never users of any tobacco served as reference. Increased risks of cancer-specific death were observed both among exclusive smokers (HRall cancer 1.15, 95% CI: 1.10–1.21) and never-smoking snus users (1.15, 95% CI: 1.05–1.26). As regards deaths due to other causes, exclusive smokers had higher relative risks than exclusive snus users (p = 0.03). A history of tobacco use, even exclusive use of the seemingly benign snus, is associated with moderately increased cancer-specific mortality. Although nicotine might play a role, the mechanisms warrant further investigation.
Bavara JH, Tae H, Settlage RE, Garner HR. Characterizing the Genetic Basis for Nicotine Induced Cancer Development: A Transcriptome Sequencing Study. PLoS One 2013; Jun 18 [Full text]
Abstract: Nicotine is a known risk factor for cancer development and has been shown to alter gene expression in cells and tissue upon exposure. We used Illumina® Next Generation Sequencing (NGS) technology to gain unbiased biological insight into the transcriptome of normal epithelial cells (MCF-10A) to nicotine exposure. We generated expression data from 54,699 transcripts using triplicates of control and nicotine stressed cells. As a result, we identified 138 differentially expressed transcripts, including 39 uncharacterized genes. Additionally, 173 transcripts that are primarily associated with DNA replication, recombination, and repair showed evidence for alternative splicing. We discovered the greatest nicotine stress response by HPCAL4 (up-regulated by 4.71 fold) and NPAS3 (down-regulated by -2.73 fold); both are genes that have not been previously implicated in nicotine exposure but are linked to cancer. We also discovered significant down-regulation (-2.3 fold) and alternative splicing of NEAT1 (lncRNA) that may have an important, yet undiscovered regulatory role. Gene ontology analysis revealed nicotine exposure influenced genes involved in cellular and metabolic processes. This study reveals previously unknown consequences of nicotine stress on the transcriptome of normal breast epithelial cells and provides insight into the underlying biological influence of nicotine on normal cells, marking the foundation for future studies.
Cardinal A, Nastrucci C, Cesario A, Russo P. Nicotine: specific role in angiogenesis, proliferation and apoptosis. Critical Reviews in Toxicology, 2012; 42(1): 68–89
Abstract: Nowadays, tobacco smoking is the cause of ~5-6 million deaths per year, counting 31% and 6% of all cancer deaths (affecting 18 different organs) in middle-aged men and women, respectively. Nicotine is the addictive component of tobacco acting on neuronal nicotinic receptors (nAChR). Functional nAChR, are also present on endothelial, haematological and epithelial cells. Although nicotine itself is regularly not referred to as a carcinogen, there is an ongoing debate whether nicotine functions as a ‘tumour promoter’. Nicotine, with its specific binding to nAChR, deregulates essential biological processes like regulation of cell proliferation, apoptosis, migration, invasion, angiogenesis, inflammation and cell-mediated immunity in a wide variety of cells including foetal (regulation of development), embryonic and adult stem cells, adult tissues as well as cancer cells. Nicotine seems involved in fundamental aspects of the biology of malignant diseases, as well as of neurodegeneration. Investigating the biological effects of nicotine may provide new tools for therapeutic interventions and for the understanding of neurodegenerative diseases and tumour biology.
Momi N, Kaur S, Ponnusamy MP, Kumar S, Wittel UA, Batra SK. Interplay between smoking-induced genotoxicity and altered signaling in pancreatic carcinogenesis. Carcinogenesis. 2012 Sep;33(9):1617-28. [full text]
Abstract: Despite continuous research efforts directed at early diagnosis and treatment of pancreatic cancer (PC), the status of patients affected by this deadly malignancy remains dismal. Its notoriety with regard to lack of early diagnosis and resistance to the current chemotherapeutics is due to accumulating signaling abnormalities. Hoarding experimental and epidemiological evidences have established a direct correlation between cigarette smoking and PC risk. The cancer initiating/promoting nature of cigarette smoke can be attributed to its various constituents including nicotine, which is the major psychoactive component, and several other toxic constituents, such as nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and polycyclic aromatic hydrocarbons. These predominant smoke-constituents initiate a series of oncogenic events facilitating epigenetic alterations, self-sufficiency in growth signals, evasion of apoptosis, sustained angiogenesis, and metastasis. A better understanding of the molecular mechanisms underpinning these events is crucial for the prevention and therapeutic intervention against PC. This review presents various interconnected signal transduction cascades, the smoking-mediated genotoxicity, and genetic polymorphisms influencing the susceptibility for smoking-mediated PC development by modulating pivotal biological aspects such as cell defense/tumor suppression, inflammation, DNA repair, as well as tobacco-carcinogen metabolization. Additionally, it provides a large perspective toward tumor biology and the therapeutic approaches against PC by targeting one or several steps of smoking-mediated signaling cascades.
Petros WP, Younis IR, Ford JN, Weed SA. Effects of tobacco smoking and nicotine on cancer treatment. Pharmacotherapy. 2012 Oct;32(10):920-31
Abstract: A substantial number of the world’s population continues to smoke tobacco, even in the setting of a cancer diagnosis. Studies have shown that patients with cancer who have a history of smoking have a worse prognosis than nonsmokers. Modulation of several physiologic processes involved in drug disposition has been associated with long-term exposure to tobacco smoke. The most common of these processes can be categorized into the effects of smoking on cytochrome P450-mediated metabolism, glucuronidation, and protein binding. Perturbation in the pharmacokinetics of anticancer drugs could result in clinically significant consequences, as these drugs are among the most toxic, but potentially beneficial, pharmaceuticals prescribed. Unfortunately, the effect of tobacco smoking on drug disposition has been explored for only a few marketed anticancer drugs; thus, little prescribing information is available to guide clinicians on the vast majority of these agents. The carcinogenic properties of several compounds found in tobacco smoke have been well studied; however, relatively little attention has been given to the effects of nicotine itself on cancer growth. Data that identify nicotine’s effect on cancer cell apoptosis, tumor angiogenesis, invasion, and metastasis are emerging. The implications of these data are still unclear but may lead to important questions regarding approaches to smoking cessation in patients with cancer.
Catassi A, Servent S, Paleari L, Cesario A, Russo P. Multiple roles of nicotine on cell proliferation and inhibition of apoptosis: implications on lung carcinogenesis. Mutat Res. 2008 Sep-Oct;659(3):221-31.
Abstract: The genotoxic effects of tobacco carcinogens have long been recognized, the contribution of tobacco components to cancerogenesis by cell surface receptor signaling is relatively unexplored. Nicotine, the principal tobacco alkaloid, acts through nicotinic acetylcholine receptor (nAChR). nAChR are functionally present on human lung airway epithelial cells, on lung carcinoma [SCLC and NSCLC] and on mesothelioma and build a part of an autocrine-proliferative network that facilitates the growth of neoplastic cells. Different nAChR subunit gene expression patterns are expressed between NSCLC from smokers and non-smokers. Although there is no evidence that nicotine itself could induce cancer, different studies established that nicotine promotes in vivo the growth of cancer cells and the proliferation of endothelial cells suggesting that nicotine might contribute to the progression of tumors already initiated. These observations led to the hypothesis that nicotine might be playing a direct role in the promotion and progression of human lung cancers. Here, we briefly overview the role and the effects of nicotine on pulmonary cell growth and physiology and its feasible implications in lung carcinogenesis.
Slotkin TA. If nicotine is a developmental neurotoxicant in animal studies, dare we recommend nicotine replacement therapy in pregnant women and adolescents? Neurotoxicol Teratol. 2008 Jan-Feb;30(1):1-19.
Abstract: Tobacco use in pregnancy is a leading cause of perinatal morbidity and contributes in major ways to attention deficit hyperactivity disorder, conduct disorders and learning disabilities that emerge in childhood and adolescence. Over the past two decades, animal models of prenatal nicotine exposure have demonstrated that nicotine is a neurobehavioral teratogen that disrupts brain development by preempting the natural, neurotrophic roles of acetylcholine. Through its actions on nicotinic cholinergic receptors, nicotine elicits abnormalities of neural cell proliferation and differentiation, promotes apoptosis and produces deficits in the number of neural cells and in synaptic function. The effects eventually compromise multiple neurotransmitter systems because of the widespread regulatory role of cholinergic neurotransmission. Importantly, the long-term alterations include effects on reward systems that reinforce the subsequent susceptibility to nicotine addiction in later life. These considerations strongly question the appropriateness of nicotine replacement therapy (NRT) for smoking cessation in pregnant women, especially as the pharmacokinetics of the transdermal patch may actually enhance fetal nicotine exposure. Further, because brain maturation continues into adolescence, the period when smoking typically commences, adolescence is also a vulnerable period in which nicotine can change the trajectory of neurodevelopment. There are also serious questions as to whether NRT is actually effective as an aid to smoking cessation in pregnant women and adolescents. This review considers the ramifications of the basic science findings of nicotine’s effects on brain development for NRT in these populations.
Egleton RD, Brown KC, Dasgupta P. Nicotinic acetylcholine receptors in cancer: multiple roles in proliferation and inhibition of apoptosis. Trends Pharmacol Sci. 2008 Mar;29(3):151-8.
Abstract: Nicotinic acetylcholine receptors (nAChRs) constitute a heterogeneous family of ion channels that mediate fast synaptic transmission in neurons. They have also been found on non-neuronal cells such as bronchial epithelium and keratinocytes, underscoring the idea that they have functions well beyond neurotransmission. Components of cigarette smoke, including nicotine and NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone], are agonists of nAChRs. Given the association of tobacco use with several diseases, the non-neuronal nAChR signaling pathway has considerable implications for cancer and cardiovascular disease. Recent studies have shown that alpha7 is the main nAChR subunit that mediates the proliferative effects of nicotine in cancer cells. As a result, alpha7 nAChR might be a valuable molecular target for therapy of cancers such as lung cancer and mesothelioma. Future studies involving the design of nAChR antagonists with improved selectivity might identify novel strategies for the treatment of tobacco-related cancers. Here we review the cellular roles of non-neuronal nAChRs, including regulation of cell proliferation, angiogenesis, apoptosis, migration, invasion and secretion.
Zeilder R, Albermann K, Lang S. Nicotine and apoptosis. Apoptosis. 2007 Nov;12(11):1927-43.
Abstract: Cigarette smoking is associated with a plethora of different diseases. Nicotine is the addictive component of cigarette but also acts onto cells of the non-neuronal system, including immune effector cells. Although nicotine itself is usually not referred to as a carcinogen, there is ongoing debate whether nicotine functions as a ‘tumor enhancer.‘ By binding to nicotinic acetylcholine receptors, nicotine deregulates essential biological processes like angiogenesis, apoptosis, and cell-mediated immunity. Apoptosis plays critical roles in a wide variety of physiologic processes during fetal development and in adult tissue and is also a fundamental aspect of the biology of malignant diseases. This review provides an overlook how nicotine influences apoptotic processes and is thus directly involved in the etiology of pathological conditions like cancer and obstructive diseases.
Wickström R. Effects of nicotine during pregnancy: human and experimental evidence. Curr Neuropharmacol. 2007 Sep;5(3):213-22. [full text]
Abstract: Prenatal exposure to tobacco smoke is a major risk factor for the newborn, increasing morbidity and even mortality in the neonatal period but also beyond. As nicotine addiction is the factor preventing many women from smoking cessation during pregnancy, nicotine replacement therapy (NRT) has been suggested as a better alternative for the fetus. However, the safety of NRT has not been well documented, and animal studies have in fact pointed to nicotine per se as being responsible for a multitude of these detrimental effects. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and exposure during development interferes with normal neurotransmitter function, thus evoking neurodevelopmental abnormalities by disrupting the timing of neurotrophic actions. As exposure to pure nicotine is quite uncommon in pregnant women, very little human data exist aside from the vast literature on prenatal exposure to tobacco smoke. The current review discusses recent findings in humans on effects on the newborn of prenatal exposure to pure nicotine and non-smoke tobacco. It also reviews the neuropharmacological properties of nicotine during gestation and findings in animal experiments that offer explanations on a cellular level for the pathogenesis of such prenatal drug exposure. It is concluded that as findings indicate that functional nAChRs are present very early in neuronal development, and that activation at this stage leads to apoptosis and mitotic abnormalities, a total abstinence from all forms of nicotine should be advised to pregnant women for the entirety of gestation.
Grozio A, Catassi A, Cavalieri Z et al Nicotine, lung and cancer. Anticancer Agents Med Chem. 2007 Jul;7(4):461-6.
Abstract: The respiratory epithelium expresses the cholinergic system including nicotinic receptors (nAChRs). It was reported that normal human bronchial epithelial cells (BEC), which are the precursor for squamous cell carcinomas, and small airway epithelial cells (SAEC), which are the precursor for adenocarcinomas, have slightly different repertoires of nAChRs. Studies show that nAChRs expressed on lung carcinoma or mesothelioma form a part of an autocrine-proliferative network facilitating the growth of neoplastic cells; others demonstrated that nicotine can promote the growth of colon, gastric, and lung cancers. Nicotine and structurally related carcinogens like NNK [4-(methylnitrosoamino)- 1-(3-pyridyl)-1-butanone] and NNN (N’-nitrosonornicotine) could induce the proliferation of a variety of small cell lung carcinoma cell lines and endothelial cells and nicotine in non-neuronal tissues -including lung- induces the secretion of growth factors (bFGF, TGF-alpha, VEGF and PDGF), up regulation of the calpain family proteins, COX-2 and VEGFR-2, causing the eventual activation of Raf/MAPK kinase/ERK (Raf/MEK/ERK) pathway contributing to the growth and progression of tumors exposed to nicotine through tobacco smoke or cigarette substitutes. It has been demonstrated that nicotine promotes the growth of solid tumors in vivo, suggesting that might induce the progression of tumors already initiated. While tobacco carcinogens can initiate and promote tumorigenesis, the exposure to nicotine could confer a proliferative advantage to early tumors but there is no evidence that nicotine itself provokes cancer. This is supported by the findings that nicotine can prevent apoptosis induced by various agents – such as chemotherapeutic in NSCLC, conferring a survival advantage as well.
Arthur Chesterfield-Evans said:
No doubt true Simon, but y9ou are going down the wrong rabbit hole. E-cigarettes are a new genre of product to make vaping a new behaviour and a new money spinner for the next century. If they had to prove that they were safe, they probably cannot. What is in the vapour? A random number of flavours and drugs can be added. Presumably the big vaping companies will sell a few benign ones and deny liability for the ones that are toxic and sold by someone else using their delivery device. Nicotine replacement is just the way that they get short-term legitimacy to get lots of people vaping so it cannot be banned. Arguing over nicotine’s pharmacology is great stuff, but irrelevant to the political and economic issue at hand, ‘Do we want vaping to become a normal part of life? If so, are we happy to take the risk that it is harmless without testing it properly?’ If it proves harmful with 60 years of use and takes 50 years to be proven harmful and the vaping industry denies it for another 50 years until it is banned we will have allowed another tobacco-like epidemic to be grown on the back of the current one. The industry has to prove it is safe, which they probably cannot do. It should be banned now, until they do. The Industry is once again reversing the onus of proof and has everyone chasing red herrings.
Colin Mendelsohn said:
I found no evidence in these papers to support your claim that nicotine causes significant harm.
The first three papers (Scott; Gurillo; Niemala) refer to the known association between smoking and schizophrenia. They provide no evidence that nicotine is the cause, although do speculate that it may be.
The paper by Guo found changes in mouse cells from exposure to nicotine in a laboratory. This does not indicate a risk from human use although it is probably best if rodents avoid nicotine.
The papers by Dang and Grando attempt to draw a causal link between nicotine and cancer. However, the IARC and the US Surgeon General reports both say there is no evidence that nicotine causes cancer. I agree there is some laboratory evidence nicotine may promote an existing cancer.
Regarding pregnancy (England), nicotine has been found to be harmful to fetus in animal models, but it is not clear how the data can be transferred to humans. There is certainly no evidence of harm from NRT in pregnant women, although the data is limited.
Similarly, while there is evidence of harm from nicotine to the adolescent brain in animal studies, there is no evidence in humans. There is also no epidemiological evidence of brain damage from the hundreds of millions of smokers who began in adolescence.
Simon Chapman AO said:
Thank you Colin for your detailed critical appraisals of all these papers. I appreciate the time you must have put into your reply.
I’m surprised you haven’t shared your insights in correspondence with the journals which published the three papers about new evidence highly relevant to the causal hypothesis about nicotine and psychosis. The first one by Scott et al is from an Australian group and only published a few months ago. It considered the Bradford Hill criteria for causation in its review of the evidence. Please consider enlightening us all with a thorough critique in a reply to the authors.
Two of your comments mock the relevance of animal studies for humans. I’m sure the entire fields of toxicology and drug safety testing, and the drug, chemical, food additives, agrichemicals and poisons regulatory authorities around the world which consider such safety information when considering registration and regulation of new and changed formulations will now consider abandoning this testing after your authoritative critique. Why should governments and industries all over the world waste all that money and effort testing on animals, when you have concluded that it means nothing for humans?
You wrote “There is also no epidemiological evidence of brain damage from the hundreds of millions of smokers who began in adolescence.” Perhaps you are unaware of evidence that smokers have lower IQs than never and former smokers. eg: this massive longitudinal twin study https://www.ncbi.nlm.nih.gov/pubmed/19931961 (“A strong inverse association between IQ and smoking status emerged in unmatched analyses over the entire range of IQ distribution.”)
The question remains whether low IQ predisposes to smoking or whether smoking lowers IQ. I couldn’t guess which way you would argue.
For those who don’t know, Colin Mendelsohn is a Sydney general practitioner and an inveterate ecigarette promoter. He is a director of ATHRA which has accepted financial support from two commercial vaping interests and from KAC, which is funded by the fully Philip Morris International funded Foundation for a Smoke Free World see https://www.smh.com.au/healthcare/independent-doctor-led-vaping-group-accepts-tobacco-tainted-funding-20181004-p507rq.html and https://www.smh.com.au/healthcare/secret-industry-funding-of-doctor-led-vaping-lobby-group-laid-bare-20180823-p4zzc5.html
Because of this, any future posts from you on this blog over the next three years on any aspect of tobacco control or vaping will require you to declare that support, as while I understand ATHRA has declared it will no longer accept such support, many journals and agencies requiring competing interest statements follow the Internal Committee of Medical Journal Editors requirement that authors should:
“Report all sources of revenue paid (or promised to be paid) directly to you or your institution on your behalf over the 36 months prior to submission of the work. This should include all monies from sources with relevance to the submitted work, not just monies from the entity that sponsored the research. Please note that your interactions with the work’s sponsor that are outside the submitted work should also be listed here. If there is any question, it is usually better to disclose a relationship than not to do so.”
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