The expression and functional role of nicotinic acetylcholine receptors in rat adipocytes

Activation of a non-neuronal cholinergic system in visceral white adipose tissue of obese mice and humans

BACKGROUND AND OBJECTIVES

Since white adipose tissue (WAT) lacks parasympathetic cholinergic innervation, the source of the acetylcholine (ACh) acting on white adipocyte cholinergic receptors is unknown. This study was designed to identify ACh-producing cells in mouse and human visceral WAT and to determine whether a non-neuronal cholinergic system becomes activated in obese inflamed WAT.

METHODS

Mouse epididymal WAT (eWAT) and human omental fat were studied in normal and obese subjects. The expression of the key molecules involved in cholinergic signaling was evaluated by qRT-PCR and western blotting whereas their tissue distribution and cellular localization were investigated by immunohistochemistry, confocal microscopy and in situ hybridization. ACh levels were measured by liquid chromatography/tandem mass spectrometry. The cellular effects of ACh were assessed in cultured human multipotent adipose-derived stem cell (hMADS) adipocytes.

RESULTS

In mouse eWAT, diet-induced obesity modulated the expression of key cholinergic molecular components and, especially, raised the expression of choline acetyltransferase (ChAT), the ACh-synthesizing enzyme, which was chiefly detected in interstitial macrophages, in macrophages forming crown-like structures (CLSs), and in multinucleated giant cells (MGCs). The stromal vascular fraction of obese mouse eWAT contained significantly higher ACh and choline levels than that of control mice. ChAT was undetectable in omental fat from healthy subjects, whereas it was expressed in a number of interstitial macrophages, CLSs, and MGCs from some obese individuals. In hMADS adipocytes stressed with tumor necrosis factor α, ACh, alone or combined with rivastigmine, significantly blunted monocyte chemoattractant protein 1 and interleukin 6 expression, it partially but significantly, restored adiponectin and GLUT4 expression, and promoted glucose uptake.

CONCLUSIONS

In mouse and human visceral WAT, obesity induces activation of a macrophage-dependent non-neuronal cholinergic system that is capable of exerting anti-inflammatory and insulin-sensitizing effects on white adipocytes.

The nervous system and adipose tissues: a tale of dialogues

White, beige, and brown adipose tissues play a crucial role in maintaining energy homeostasis. Due to the heterogeneous and diffuse nature of fat pads, this balance requires a fine and coordinated control of many actors and therefore permanent dialogues between these tissues and the central nervous system. For about two decades, many studies have been devoted to describe the neuro-anatomical and functional complexity involved to ensure this dialogue. Thus, if it is now clearly demonstrated that there is an efferent sympathetic innervation of different fat depots controlling plasticity as well as metabolic functions of the fat pad, the crucial role of sensory innervation capable of detecting local signals informing the central nervous system of the metabolic state of the relevant pads is much more recent. The purpose of this review is to provide the current state of knowledge on this subject.

Adipokines: Deciphering the cardiovascular signature of adipose tissue

Obesity and hypertension are intimately linked due to the various ways that the important cell types such as vascular smooth muscle cells (VSMC), endothelial cells (EC), immune cells, and adipocytes, communicate with one another to contribute to these two pathologies. Adipose tissue is a very dynamic organ comprised primarily of adipocytes, which are well known for their role in energy storage. More recently adipose tissue has been recognized as the largest endocrine organ because of its ability to produce a vast number of signaling molecules called adipokines. These signaling molecules stimulate specific types of cells or tissues with many adipokines acting as indicators of adipocyte healthy function, such as adiponectin, omentin, and FGF21, which show anti-inflammatory or cardioprotective effects, acting as regulators of healthy physiological function. Others, like visfatin, chemerin, resistin, and leptin are often altered during pathophysiological circumstances like obesity and lipodystrophy, demonstrating negative cardiovascular outcomes when produced in excess. This review aims to explore the role of adipocytes and their derived products as well as the impacts of these adipokines on blood pressure regulation and cardiovascular homeostasis.

Chronic Inflammation and Cancer: The Role of Endothelial Dysfunction and Vascular Inflammation

Long-lasting subclinical inflammation is associated with a wide range of human diseases, particularly at a middle and older age. Recent reports showed that there is a direct causal link between inflammation and cancer development, as several cancers were found to be associated with chronic inflammatory conditions. In patients with cancer, healthy endothelial cells regulate vascular homeostasis, and it is believed that they can limit tumor growth, invasiveness, and metastasis. Conversely, dysfunctional endothelial cells that have been exposed to the inflammatory tumor microenvironment can support cancer progression and metastasis. Dysfunctional endothelial cells can exert these effects via diverse mechanisms, including dysregulated adhesion, permeability, and activation of NF-κB and STAT3 signaling. In this review, we highlight the role of vascular inflammation in predisposition to cancer within the context of two common disease risk factors: obesity and smoking. In addition, we discuss the molecular triggers, pathophysiological mechanisms, and the biological consequences of vascular inflammation during cancer development and metastasis. Finally, we summarize the current therapies and pharmacological agents that target vascular inflammation and endothelial dysfunction.

Nicotinic acetylcholine receptors in chemotherapeutic drugs resistance: An emerging targeting candidate

There is no definitive cure for cancer, and most of the current chemotherapy drugs have limited effects due to the development of drug resistance and toxicity at high doses. Therefore, there is an ongoing need for identifying the causes of chemotherapeutic resistance, and it will be possible to develop innovative treatment approaches based on these novel targeting candidates. Cigarette smoking is known to be one of the main causes of resistance to chemotherapeutic agents. Nicotine as a component of cigarette smoke is an exogenous activator of nicotinic acetylcholine receptors (nAChRs). It can inhibit apoptosis, increase cell proliferation and cell survival, reducing the cytotoxic effects of chemotherapy drugs and cause a reduced therapeutic response. Recent studies have demonstrated that nAChRs and their downstream signaling pathways have considerable implications in different cancer's initiation, progression, and chemoresistance. In some previous studies, nAChRs have been targeted to obtain better efficacies for chemotherapeutics. Besides, nAChRs-based therapies have been used in combination with chemotherapy drugs to reduce the side effects. This strategy requires lower doses of chemotherapy drugs compared to the conditions that must be used alone. Here, we discussed the experimental and clinical studies that show the nAChRs involvement in response to chemotherapy agents. Also, controversies relating to the effects of nAChR on chemotherapy-induced apoptosis are in our focus in this review article. Delineating the complex influences of nAChRs would be of great interest in establishing new effective chemotherapy regimens.

Nicotine: Regulatory roles and mechanisms in atherosclerosis progression

Smoking is an independent risk factor for atherosclerosis. The smoke produced by tobacco burning contains more than 7000 chemicals, among which nicotine is closely related to the occurrence and development of atherosclerosis. Nicotine, a selective cholinergic agonist, accelerates the formation of atherosclerosis by stimulating nicotinic acetylcholine receptors (nAChRs) located in neuronal and non-neuronal tissues. This review introduces the pathogenesis of atherosclerosis and the mechanisms involving nicotine and its receptors. Herein, we focus on the various roles of nicotine in atherosclerosis, such as upregulation of growth factors, inflammation, and the dysfunction of endothelial cells, vascular smooth muscle cells (VSMC) as well as macrophages. In addition, nicotine can stimulate the generation of reactive oxygen species, cause abnormal lipid metabolism, and activate immune cells leading to the onset and progression of atherosclerosis. Exosomes, are currently a research hotspot, due to their important connections with macrophages and the VSMC, and may represent a novel application into future preventive treatment to promote the prevention of smoking-related atherosclerosis. In this review, we will elaborate on the regulatory mechanism of nicotine on atherosclerosis, as well as the effects of interference with nicotine receptors and the use of exosomes to prevent atherosclerosis development.

Tobacco use and neurogenesis: A theoretical review of pathophysiological mechanism affecting the outcome of peripheral nerve regeneration

Peripheral nerve injury often requires medical intervention. Unfortunately, many patients never have a full recovery, despite a multi-disciplinary approach, including operative intervention and physical and/or occupational therapy. Outcomes are multifactorial, but are largely affected by the original injury severity, and patient comorbidities. A lcoholism, diabetes mellitus and ageing may detrimentally affect the outcomes of nerve injury; however little is known about tobacco's potential impact on nerve regeneration. Tobacco has known immunomodulatory effects, which suggests that it might affect peripheral nerve regeneration and functional recovery following injury. This review characterizes the effects of tobacco use on the complex cellular and chemokine interactions in peripheral nerve regeneration.

Effects of Exposure to Tobacco Cigarette, Electronic Cigarette and Heated Tobacco Product on Adipocyte Survival and Differentiation In Vitro

Cigarette smoking (CS) causes significant morbidity worldwide, attributed to the numerous toxicants generated by tobacco combustion. Electronic cigarettes (ECIG) and heated tobacco products (HTP) are considered alternative smoking/vaping products that deliver nicotine through an inhaled aerosol and emit fewer harmful constituents than CS. However, their long-term impacts on human health are not well established. Nicotine exposure has been linked to lipolysis and body weight loss, while smoking has been associated with insulin resistance and hyperinsulinemia. Enhanced function of beige (thermogenic) adipocytes has been proposed as a means to reduce obesity and metabolic disorders. In this study, we compared the effect of extract-enriched media via exposure of culture medium to CS, HTP aerosol, and ECIG aerosol on the viability and the differentiation of 3T3-L1 pre-adipocytes to beige adipocytes. Only CS extract caused a decrease in cell viability in a dose- and time-dependent manner. Furthermore, relative lipid accumulation and expression levels of the adipocyte markers Pgc-1α, Ppar-γ and Resistin were significantly decreased in cells exposed to CS extract. Our results demonstrate that CS extract, in contrast to HTP and ECIG extracts, significantly impairs differentiation of pre-adipocytes to beige adipocytes and may therefore impact significantly adipose tissue metabolic function.

The association between maternal nicotine exposure and adipose angiogenesis in female rat offspring: A mechanism of adipose tissue function changes

Maternal smoking during pregnancy and lactation is associated with increased fat mass in the offspring, but the mechanism by which this occurs is not fully understood. Our study focused on the relationships among maternal nicotine exposure, adipose angiogenesis and adipose tissue function in female offspring. Pregnant rats were randomly assigned to nicotine or control groups. Microvascular density, lipid metabolism and α7nAChR-Egr1-FGF2 signaling pathway genes/proteins were tested in 4-, 12- and 26-week female offspring. In vitro, nicotine concentration- and time-response experiments were conducted in 3T3-L1. Lipid metabolism and α7nAChR-Egr1-FGF2 signaling pathway genes/proteins were tested. The conditioned media of differentiated 3T3-L1 treated with nicotine were used to observe tube formation in human umbilical vein endothelial cells (HUVECs). Nicotine-exposed females presented higher adipose microvascular density. The gene expression of α7nAChR, Egr1 and FGF2 was significantly increased in gonadal white adipose tissue (gWAT) and inguinal subcutaneous WAT (igSWAT) of nicotine-exposed females at 4 weeks of age. The protein expression of α7nAChR, Egr1 and FGF2 was increased in gWAT and igSWAT of nicotine-exposed females at 4 weeks of age, and increased in gWAT at 26 weeks. In vitro, nicotine increased the expression of lipid metabolism and α7nAChR-Egr1-FGF2 signaling pathway genes/proteins in a concentration- and time-dependent manner. In the tube formation experiment, adipocytes affected by nicotine promoted HUVEC angiogenesis. Therefore, maternal nicotine exposure promoted the early angiogenesis of adipose tissue via the α7nAChR-Egr1-FGF2 signaling pathway, and this angiogenesis mechanism was associated with increased adipogenesis in adipose tissue of female offspring.

E-cigarettes and Western Diet: Important Metabolic Risk Factors for Hepatic Diseases

The use of electronic nicotine delivery systems (ENDS), also known as e-cigarettes, with a variety of e-liquids/e-juices, is increasing at an alarming rate among adolescents who do not realize the potential harmful health effects. This study examines the harmful effects of ENDS on the liver. Apolipoprotein E null (ApoE-/-) mice on a western diet (WD) were exposed to saline or ENDS with 2.4% nicotine aerosol for 12 weeks using our mouse ENDS exposure model system, which delivers nicotine to mice and leads to equivalent serum cotinine levels found in human cigarette users. ApoE-/- mice on a WD exposed to ENDS exhibited a marked increase in hepatic lipid accumulation compared with ApoE-/- on a similar diet exposed to saline aerosol. The detrimental effects of ENDS on hepatic steatosis were associated with significantly greater oxidative stress, increased hepatic triglyceride levels, and increased hepatocyte apoptosis, independent of adenosine monophosphate-activated protein kinase signaling. In addition, hepatic RNA sequencing analysis revealed that 433 genes were differentially expressed in ENDS-exposed mice on WD compared with saline-exposed mice. Functional analysis indicates that genes associated with lipid metabolism, cholesterol biosynthesis, and circadian rhythm were most significantly altered in the liver in response to ENDS. Conclusion: These results demonstrate profound adverse effects of ENDS on the liver. This is important information for regulatory agencies as they regulate ENDS.

Transcutaneous Vagus Nerve Stimulation Regulates the Cholinergic Anti-inflammatory Pathway to Counteract 1, 2-Dimethylhydrazine Induced Colon Carcinogenesis in Albino wistar Rats

The present work was undertaken to study the effects of transcutaneous auricular vagus nerve stimulation (taVNS) on 1, 2-dimethyhydrazine (DMH) induced colon cancer and role of the cholinergic anti-inflammatory pathways (CAP) in the same. Groups of rats were randomly divided into ten groups (n = 8). DMH administration was very well apparent for autonomic dysfunction as observed through distorted hemodynamic (electrocardiogram and heart rate variability), increased aberrant crypt foci and flat neoplastic lesions (methylene blue staining, scanning electron microscopy and Hematoxylin and eosin staining). DMH administration was also recorded for per-oxidative damage. taVNS application restored the autonomic function, cellular morphology and curtailed the oxidative damage. DMH application conspicuously inhibited the mitochondrial apoptosis which was restored back after taVNS application, when scrutinized through immunoblotting and quantitative real time polymerase chain reaction studies. taVNS application up-regulated the CAP as perceived through increased expression for α7 nicotinic acetylcholine receptor(α7nAchR) and decreased expression for nuclear factor kappa-ligand-chain-enhancer of activated B cells (NFκBp65), tissue necrosis factor-α and high mobility group box-1 at protein and mRNA levels. All in all, taVNS up-surged the CAP to counteract DMH induced colon carcinogenesis. Among all the stimulation parameters used, taVNS 3 (pulse width-1 ms, frequency-6 Hz, voltage-6 v, duration-240 min) was observed to be the most effective. Since only chemotherapy and surgery are available options for management of CRC, which are troublesome and painful, there is currently no non-invasive method available for management of CRC. Results of the current study affirmed the effectiveness of taVNS against DMH induced colon cancer. The present study established taVNS as a novel and non-invasive approach toward the management of CRC.

Nicotine enhances alcoholic fatty liver in mice: Role of CYP2A5

Tobacco and alcohol are often co-abused. Nicotine can enhance alcoholic fatty liver, and CYP2A6 (CYP2A5 in mice), a major metabolism enzyme for nicotine, can be induced by alcohol. CYP2A5 knockout (cyp2a5^-/-) mice and their littermates (cyp2a5^+/+) were used to test whether CYP2A5 has an effect on nicotine-enhanced alcoholic fatty liver. The results showed that alcoholic fatty liver was enhanced by nicotine in cyp2a5^+/+ mice but not in the cyp2a5^-/- mice. Combination of ethanol and nicotine increased serum triglyceride in cyp2a5^+/+ mice but not in the cyp2a5^-/- mice. Cotinine, a major metabolite of nicotine, also enhanced alcoholic fatty liver, which was also observed in cyp2a5^+/+ mice but not in the cyp2a5^-/- mice. Nitrotyrosine and malondialdehyde (MDA), markers of oxidative/nitrosative stress, were induced by alcohol and were further increased by nicotine and cotinine in cyp2a5^+/+ mice but not in the cyp2a5^-/- mice. Reactive oxygen species (ROS) production during microsomal metabolism of nicotine and cotinine was increased in microsomes from cyp2a5^+/+ mice but not in microsomes from cyp2a5^-/- mice. These results suggest that nicotine enhances alcoholic fatty liver in a CYP2A5-dependent manner, which is related to ROS produced during the process of CYP2A5-dependent nicotine metabolism.

Analysis of changes on adiponectin levels and abdominal obesity after smoking cessation

Purpose

The blood levels of Adiponectin, anti-inflammatory and anti-arteriosclerotic adipocytokine, decrease due to smoking and obesity. Cigarette smokers are generally known to gain weight after smoking cessation (SC). Nevertheless, precise changes in serum adiponectin levels after SC and specific effects of abdominal obesity on those changes remain unknown. The objective of this study was to elucidate the changes in serum adiponectin levels after SC and the effects of abdominal obesity on those changes.

Methods

In 86 patients (56 males and 30 females) who had successfully quit smoking, serum adiponectin levels were measured using an enzyme-linked immunosorbent assay at baseline and 1 year after beginning SC.

Results

Body mass index and waist circumference (WC) were significantly increased 1 year after beginning SC. Adiponectin levels, however, did not change after SC. Using the median ΔWC (+2.8%) as the cutoff point, patients were then divided into two groups. The percent change in adiponectin levels from baseline to 1 year was significantly greater in the ΔWC < median group (−1.1%) than in the ΔWC ≥ median group (+8.1%) (p = 0.011).

Conclusions

Despite weight gain and increased abdominal obesity, serum adiponectin levels did not decrease after SC. Therefore, the beneficial effect of SC may eliminate the adverse effects of subsequent weight gain. Conversely, patients with less abdominal obesity had increased adiponectin levels 1 year after SC. Therefore, in such patients, the beneficial effect of SC on adiponectin levels is apparent.

Ameliorative effect of nicotine exposure on insulin resistance is accompanied by decreased cardiac glycogen synthase kinase-3 and plasminogen activator inhibitor-1 during oral oestrogen-progestin therapy

CONTEXT

Cigarette smoking is considered to be a major risk factor for the development of diabetes and cardiovascular disease. Oestrogen-progestin combined oral contraceptive (COC) use has been associated with adverse cardiometabolic events.

OBJECTIVE

We hypothesized that nicotine would ameliorate insulin resistance (IR) that is accompanied by decreased cardiac glycogen synthase kinase-3 (GSK-3) and plasminogen activator inhibitor-1 (PAI-1).

METHODS

Female Wistar rats received (po) low-(0.1 mg/kg) or high-nicotine (1.0 mg/kg) with or without COC containing 5.0 µg levonorgestrel plus 1.0 µg ethinylestradiol daily for 8 weeks.

RESULTS

Data showed that COC treatment or nicotine exposure led to IR, glucose deregulation, atherogenic dyslipidemia, increased corticosterone, aldosterone, cardiac and circulating GSK-3 values and PAI-1. However, these effects with the exception of corticosterone and aldosterone were ameliorated in COC + nicotine-exposed rats.

CONCLUSION

Amelioration of IR induced by COC treatment is accompanied by decreased circulating PAI-1, cardiac PAI-1 and GSK-3 instead of circulating aldosterone and corticosterone.

Cigarette Smoking and Adipose Tissue: The Emerging Role in Progression of Atherosclerosis

Smoking is an established risk factor for atherosclerosis through several underlying pathways. Moreover, in the development of atherosclerotic plaque formation, obesity, defined as excess fat mass accumulation, also plays a vital role in dyslipidemia and insulin resistance. Substantial evidence shows that cigarette smoking induces multiple pathological effects in adipose tissue, such as differentiation of adipocytes, lipolysis, and secretion properties in adipose tissue. Therefore, there is an emerging speculation in which adipose tissue abnormality induced by smoking or nicotine is likely to accelerate the progression of atherosclerosis. Herein, this review aims to investigate the possible interplay between smoking and adipose tissue dysfunction in the development of atherosclerosis.

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

Cholinergic activation suppresses palmitate-induced macrophage activation and improves acylation stimulating protein resistance in co-cultured adipocytes

Acylation-stimulating protein (ASP), produced through activation of the alternative complement immune system, modulates lipid metabolism. Using a trans-well co-culture cell model, the mitigating role of α7-nicotinic acetylcholine receptor (α7nAChR)-mediated cholinergic pathway on ASP resistance was evaluated. ASP signaling in adipocytes via its receptor C5L2 and signaling intermediates Gαq, Gβ, phosphorylated protein kinase C-α, and protein kinase C-ζ were markedly suppressed in the presence of TNFα or medium from palmitate-treated RAW264.7 macrophages, indicating ASP resistance. There was no direct effect of α7nAChR activation in 3T3-L1 cell culture. However, α7nAChR activation almost completely reversed the ASP resistance in adipocytes co-cultured with palmitate-treated RAW264.7 macrophages. Further, α7nAChR activation could suppress the production of pro-inflammatory molecules TNFα and interleukin-6 produced from palmitate-treated co-cultured macrophages. These results suggest that macrophages play a significant role in the pathogenesis of ASP resistance and α7nAChR activation secondarily improves adipose ASP resistance through suppression of inflammation in macrophages. Impact statement 1. Adipocyte-macrophage interaction in acylation-stimulating protein (ASP) resistance 2. Lipotoxicity induced inflammatory response in ASP resistance 3. A vicious circle between lipotoxicity and inflammatory response in ASP resistance 4. Cholinergic modulation of inflammatory response in adipocyte and macrophage.

Connection of Nicotine to Diet-Induced Obesity and Non-Alcoholic Fatty Liver Disease: Cellular and Mechanistic Insights

Non-alcoholic fatty liver disease (NAFLD) poses a serious health hazard affecting 20-40% of adults in the general population in the USA and over 70% of the obese and extremely obese people. In addition to obesity, nicotine is recognized as a risk factor for NAFLD, and it has been reported that nicotine can exaggerate obesity-induced hepatic steatosis. The development of NAFLD has serious clinical complications because of its potential progression from simple hepatic steatosis to non-alcoholic steatohepatitis (NASH), liver cirrhosis, and hepatocellular carcinoma. Multiple mechanisms can be involved in nicotine plus high-fat diet-induced (HFD) hepatic steatosis. Emerging evidence now suggests that nicotine exacerbates hepatic steatosis triggered by HFD, through increased oxidative stress and hepatocellular apoptosis, decreased phosphorylation (inactivation) of adenosine-5-monophosphate-activated protein kinase and, in turn, up-regulation of sterol response-element binding protein 1-c, fatty acid synthase, and activation of acetyl-coenzyme A-carboxylase, leading to increased hepatic lipogenesis. There is also growing evidence that chronic endoplasmic reticulum stress through regulation of several pathways leading to oxidative stress, inflammation, perturbed hepatic lipid homeostasis, apoptosis, and autophagy can induce hepatic steatosis and its progression to NASH. Evidence also suggests a central role of the gut microbiota in obesity and its related disorders, including NAFLD. This review explores the contribution of nicotine and obesity to the development of NAFLD and its molecular underpinning.

Cellular protein and mRNA expression of β1 nicotinic acetylcholine receptor (nAChR) subunit in brain, skeletal muscle and placenta

The β1 nicotinic acetylcholine receptor (nAChR) subunit is a muscle type subunit of this family and as such, is found predominantly in muscle. Recent reports document its expression in other tissues and cell lines including adrenal glands, carcinomas, lung and brain. However, the majority of studies were of tissue lysates, thus the cellular distribution was not determined. This study aimed to determine the cellular distribution of the β1 nAChR subunit in the brain, at both the mRNA and protein levels, using non-radioactive in situ hybridization (ISH) and immunohistochemistry (IHC), respectively, and to compare it to two muscle tissue types, skeletal and placenta. Tissue was formalin fixed and paraffin embedded (all tissue types) and frozen (placenta) from humans. Additional control tissue from the piglet and mouse brain were also studied, as was mRNA for the α3 nAChR and N-methyl-d-aspartate receptor 1 (NR1) subunit. We found no β1 nAChR subunit mRNA expression in the human and piglet brain despite strong protein expression. Some signal was seen in the mouse brain but considered inconclusive given the probes designed were not of 100% homology to the mouse. In the skeletal muscle and placenta tissues, β1 nAChR subunit mRNA expression was prominent and mirrored protein expression. No α3 nAChR or NR1 mRNA was seen in the skeletal muscle, as expected, although both subunit mRNAs were present in the placenta. This study concludes that further experiments are required to conclusively state that the β1 nAChR subunit is expressed in the human, piglet and mouse brain.

Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation.

The influence of chronic nicotine treatment on proteins expressed in the mouse hippocampus and cortex

Chronic treatment with nicotine, the primary psychoactive substance in tobacco smoke, affects central nervous system functions, such as synaptic plasticity. Here, to clarify the effects of chronic nicotine treatment on the higher brain functions, proteomic analysis of the hippocampus and cortex of mice treated for 6 months with nicotine was performed using two-dimensional gel electrophoresis (2-DE) followed by mass spectrometry. There was significant change in the expression of 16 proteins and one phosphoprotein in the hippocampus (increased tubulin β-5, atp5b, MDH1, cytochrome b-c1 complex subunit 1, Hsc70, dynamin, profilin-2, 4-aminobutyrate aminotransferase, mitochondrial isoform 1 precursor, calpain small subunit 1, and vacuolar adenosine triphosphatase subunit B and decreased γ-actin, α-tubulin isotype M-α-2, putative β-actin, tubulin β-2A, NDUFA10, and G6PD) and 24 proteins and two phosphoproteins in the cortex (increased spectrin α chain, non-erythrocytic 1 isoform 1, tubulin β-5, γ-actin, creatine kinase B-type, LDH-B, secernin-1, UCH-L1, 14-3-3 γ, type II peroxiredoxin 1, PEBP-1, and unnamed protein product and decreased tubulin α-1C, α-internexin, γ-enolase, PDHE1-B, DPYL2, vacuolar adenosine triphosphatase subunit A, vacuolar adenosine triphosphatase subunit B, TCTP, NADH dehydrogenase Fe-S protein 1, protein disulfide-isomerase A3, hnRNP H2, γ-actin, atp5b, and unnamed protein product). Additionally, Western blotting validated the changes in dynamin, Hsc70, MDH1, NDUFA10, α-internexin, tubulin β-5 chain, and secernin-1. Thus, these findings indicate that chronic nicotine treatment changes the expression of proteins and phosphoproteins in the hippocampus and cortex. We propose that effect of smoking on higher brain functions could be mediated by alterations in expression levels of these proteins.

Smoking Cessation Carries a Short-Term Rising Risk for Newly Diagnosed Diabetes Mellitus Independently of Weight Gain: A 6-Year Retrospective Cohort Study

Background. The effects of smoking on human metabolism are complex. Although smoking increases risk for diabetes mellitus, smoking cessation was also reported to be associated with weight gain and incident diabetes mellitus. We therefore conducted this study to clarify the association between smoking status and newly diagnosed diabetes mellitus. Methods. An analysis was done using the data of a mass health examination performed annually in an industrial park from 2007 to 2013. The association between smoking status and newly diagnosed diabetes mellitus was analyzed with adjustment for weight gain and other potential confounders. Results. Compared with never-smokers, not only current smokers but also ex-smokers in their first two years of abstinence had higher odds ratios (ORs) for newly diagnosed diabetes mellitus (never-smokers 3.6%, OR as 1; current smokers 5.5%, OR = 1.499, 95% CI = 1.147-1.960, and p = 0.003; ex-smokers in their first year of abstinence 7.5%, OR = 1.829, 95% CI = 0.906-3.694, and p = 0.092; and ex-smokers in their second year of abstinence 9.0%, OR = 2.020, 95% CI = 1.031-3.955, and p = 0.040). Conclusion. Smoking cessation generally decreased risk for newly diagnosed diabetes mellitus. However, increased odds were seen within the first 2 years of abstinence independently of weight gain.

Cross-talk between α7 nAChR-mediated cholinergic pathway and acylation stimulating protein signaling in 3T3-L1 adipocytes: role of NFκB and STAT3

Inflammation is a key feature in adipose tissue, especially in association with obesity comorbidies. The novel adipokine acylation stimulating protein (ASP) is one factor implicated in the inflammatory response. The disruption of the α7 nicotine acetylcholine receptor (α7nAChR), an important component of the endogenous non-neural cholinergic defense system, may exacerbate sustained inflammatory phenotype. We examined cholinergic regulation of ASP-initiated inflammatory response in 3T3-L1 adipocytes. Our results show that preincubation of 3T3-L1 cells with α7nAChR agonist GTS-21 significantly reduces ASP-mediated chemokine MCP-1 secretion, which is regulated though nuclear factor κB (NFκB) and signal transducer and activator of transcription 3 (STAT3). Treatment of 3T3-L1 cells with GTS-21 significantly reduced NFκB activation by DNA binding and STAT3 activation by disturbing post-translational modification.

Novel aspects of cholinergic regulation of colonic ion transport

Nicotinic receptors are not only expressed by excitable tissues, but have been identified in various epithelia. One aim of this study was to investigate the expression of nicotinic receptors and their involvement in the regulation of ion transport across colonic epithelium. Ussing chamber experiments with putative nicotinic agonists and antagonists were performed at rat colon combined with reverse transcription polymerase chain reaction (RT-PCR) detection of nicotinic receptor subunits within the epithelium. Dimethylphenylpiperazinium (DMPP) and nicotine induced a tetrodotoxin-resistant anion secretion leading to an increase in short-circuit current (I sc) across colonic mucosa. The response was suppressed by the nicotinic receptor antagonist hexamethonium. RT-PCR experiments revealed the expression of α2, α4, α5, α6, α7, α10, and β4 nicotinic receptor subunits in colonic epithelium. Choline, the product of acetylcholine hydrolysis, is known for its affinity to several nicotinic receptor subtypes. As a strong acetylcholinesterase activity was found in colonic epithelium, the effect of choline on I sc was examined. Choline induced a concentration-dependent, tetrodotoxin-resistant chloride secretion which was, however, resistant against hexamethonium, but was inhibited by atropine. Experiments with inhibitors of muscarinic M1 and M3 receptors revealed that choline-evoked secretion was mainly due to a stimulation of epithelial M3 receptors. Although choline proved to be only a partial agonist, it concentration-dependently desensitized the response to acetylcholine, suggesting that it might act as a modulator of cholinergically induced anion secretion. Thus the cholinergic regulation of colonic ion transport - up to now solely explained by cholinergic submucosal neurons stimulating epithelial muscarinic receptors - is more complex than previously assumed.

Chronic nicotine treatment enhances vascular smooth muscle relaxation in rats

AIM

To investigate the effect of chronic nicotine treatment on vascular function and to identify the underlying mechanisms.

METHODS

Adult rats were treated with nicotine (3 mg·kg(-1)·d(-1), sc) for 6 weeks. After the rats were sacrificed, aortic rings were prepared for detecting vascular reactivity, and thoracic aorta and periaortic fat samples were collected for histological and molecular biology studies.

RESULTS

Chronic nicotine treatment significantly reduced periaortic fat, and specifically enhanced smooth muscle relaxation without altering the aortic adventitial fat and endothelium function. Pretreatment with the soluble guanylyl cyclase inhibitor ODQ (3 μmol/L) or PKG inhibitor Rp-8-Br-PET-cGMP (30 μmol/L) abolished the nicotine-induced enhancement of smooth muscle relaxation, whereas the cGMP analogue 8-Br-cGMP could mimic the nicotine-induced enhancement of smooth muscle relaxation. However, the chronic nicotine treatment did not alter PKG protein expression and activity in aortic media.

CONCLUSION

Chronic nicotine treatment enhances vascular smooth muscle relaxation of rats via activation of PKG pathway.

Axonal regeneration in early stages of sciatic nerve crush injury is enhanced by α7nAChR in rats

This study investigated the role of alpha 7 nicotinic acetylcholine receptor (α7nAChR) in axonal regeneration after crush injury to the rat sciatic nerve. The time course of α7nAChR expression following injury was assessed by immunohistochemistry and western blotting, and local inflammation, as indicated by the expression of tumor necrosis factor (TNF)-α, was detected by enzyme-linked immunosorbent assay. Axonal regeneration was evaluated by the pinch-test, morphometric analysis, and by measuring growth-associated protein 43 expressions. Local α7nAChR expression increased on day 1, peaked on day 3, and remained elevated on day 5 following nerve injuries. Prominent α7nAChR immunoreactivity was observed in Schwann cells, endothelial cells of the capillaries, and a small number of inflammatory cells. Application of the selective α7nAChR agonist PNU-282987 decreased TNF-α level and enhanced axonal regeneration, but this effect was blocked by concomitant treatment with methyllycaconitine, a α7nAChR antagonist. The results indicate that the local expression of α7nAChR is increased during the early stages of sciatic nerve injury, and application of a α7nAChR agonist promotes axonal regeneration by suppression of TNF-α-mediated inflammation. The α7nAChR can act as a neuroprotective agent and α7nAChR activation may be a useful therapeutic strategy to treat peripheral nerve injury.

Concomitant alpha7 and beta2 nicotinic AChR subunit deficiency leads to impaired energy homeostasis and increased physical activity in mice

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated cation channels well characterized in neuronal signal transmission. Moreover, recent studies have revealed nAChR expression in nonneuronal cell types throughout the body, including tissues involved in metabolism. In the present study, we screen gene expression of nAChR subunits in pancreatic islets and adipose tissues. Mice pancreatic islets present predominant expression of α7 and β2 nAChR subunits but at a lower level than in central structures. Characterization of glucose and energy homeostasis in α7β2nAChR(-/-) mice revealed no major defect in insulin secretion and sensitivity but decreased glycemia apparently unrelated to gluconeogenesis or glycogenolysis. α7β2nAChR(-/-) mice presented an increase in lean and bone body mass and a decrease in fat storage with normal body weight. These observations were associated with elevated spontaneous physical activity in α7β2nAChR(-/-) mice, mainly due to elevation in fine vertical (rearing) activity while their horizontal (ambulatory) activity remained unchanged. In contrast to α7nAChR(-/-) mice presenting glucose intolerance and insulin resistance associated to excessive inflammation of adipose tissue, the present metabolic phenotyping of α7β2nAChR(-/-) mice revealed a metabolic improvement possibly linked to the increase in spontaneous physical activity related to central β2nAChR deficiency.

The time-dependent expression of α7nAChR during skeletal muscle wound healing in rats

The study on time-dependent expression of α7 nicotine acetylcholine receptor (α7nAChR) was performed by immunohistochemistry, Western blotting, and real-time PCR during skeletal muscle wound healing in rats. Furthermore, co-localization of α7nAChR with macrophage or myofibroblast marker was detected by double immunofluorescence. A total of 50 Sprague-Dawley male rats were divided into control and contusion groups (3 h, 6 h, 12 h, 1 day, 3 days, 5 days, 7 days, 10 days, and 14 days post-injury). In the uninjured controls, α7nAChR positive staining was observed in the sarcolemma and sarcoplasm of normal myofibers. In wounded specimens, a small number of polymorphonuclear cells, a number of macrophages and myofibroblasts showed positive reaction for α7nAChR in contused zones. Morphometrically, the average ratios of α7nAChR-positive cells were over 50 % from 3 to 10 days after contusion, and exceeded 60 % at 5 and 7 days post-injury. Besides, the positive ratios of α7nAChR were <50 % at the other posttraumatic intervals. By Western blotting analysis, the average ratio of α7nAChR protein expression maximized at 7 days after injury, which was >2.13. Similarly, the relative quantity of α7nAChR mRNA expression peaked at 7 days post-wounding as compared with control by real-time PCR detection, showing a relative quantity of >2.65. In conclusion, the expression of α7nAChR is upregulated and temporally distributed in macrophages and myofibroblasts during skeletal muscle wound healing, which might be closely involved in inflammatory response and fibrotic repair after injury. Moreover, α7nAChR is promising as a useful marker for wound age determination of skeletal muscle.

Nicotine in combination with a high-fat diet causes intramyocellular mitochondrial abnormalities in male mice

Smoking is a major risk factor for diabetes, cardiovascular disease, and nonalcoholic fatty liver disease. The health risk associated with smoking can be exaggerated by obesity. We hypothesize that nicotine when combined with a high-fat diet (HFD) can also cause ectopic lipid accumulation in skeletal muscle, similar to recently observed hepatic steatosis. Adult C57BL6 male mice were fed a normal chow diet or HFD and received twice-daily ip injections of nicotine (0.75 mg/kg body weight) or saline for 10 weeks. Transmission electron microscopy of the gastrocnemius muscle revealed substantial intramyocellular lipid accumulation in close association with intramyofibrillar mitochondria along with intramyofibrillar mitochondrial swelling and vacuolization in nicotine-treated mice on an HFD compared with mice on an HFD treated with saline. These abnormalities were reversed by acipimox, an inhibitor of lipolysis. Mechanistically, the detrimental effect of nicotine plus HFD on skeletal muscle was associated with significantly increased oxidative stress, plasma free fatty acid, and muscle triglyceride levels coupled with inactivation of AMP-activated protein kinase and activation of its downstream target, acetyl-coenzyme A-carboxylase. We conclude that 1) greater oxidative stress together with inactivation of AMP-activated protein kinase mediates the effect of nicotine on skeletal muscle abnormalities in diet-induced obesity and 2) adipose tissue lipolysis is an important contributor of muscle steatosis and mitochondrial abnormalities.

Nicotine enhances ethanol-induced fat accumulation and collagen deposition but not inflammation in mouse liver

INTRODUCTION

Alcohol and tobacco are frequently co-abused. Tobacco smoke increases alcoholic steatosis in apoE(-/-) mice. Tobacco smoke contains more than 4000 chemicals, but it is unknown which compounds in tobacco smoke play a major role in increasing alcoholic steatosis.

METHODS

C57BL/J6 mice were intraperitoneally injected with nicotine at 1 mg/kg every day or saline at the same volume as a control and the mice were fed dextrose-control or ethanol Lieber-DeCarli liquid diets. Three weeks later the mice were sacrificed after overnight fasting.

RESULTS

Neither nicotine injection nor ethanol feeding alone increased serum levels of triglyceride, but the combination of nicotine and ethanol increased serum levels of triglyceride. Both nicotine injection alone and ethanol feeding alone increased hepatic collagen type I deposition, and nicotine injection and ethanol feeding combined further increased hepatic collagen type I deposition. The combination of nicotine and ethanol also activated hepatic stellate cells, a principal liver fibrogenic cell. Hepatic fat accumulation was induced by ethanol feeding, which was further enhanced by nicotine injection. Ethanol feeding caused an increase in serum ALT, but nicotine did not further increase serum ALT levels. Lipid droplets and inflammatory foci were observed in liver sections from ethanol-fed mice; nicotine treatment increased the number and size of lipid droplets, but not the number and size of inflammatory foci. Nicotine did not further increase ethanol-induced hepatic neutrophil infiltration.

CONCLUSIONS

These results suggest that nicotine enhances ethanol-induced steatosis and collagen deposition, but nicotine has no effect on ethanol-induced inflammation.

Nicotinic receptor alpha7 expression identifies a novel hematopoietic progenitor lineage

How inflammatory responses are mechanistically modulated by nicotinic acetylcholine receptors (nAChR), especially by receptors composed of alpha7 (α7) subunits, is poorly defined. This includes a precise definition of cells that express α7 and how these impact on innate inflammatory responses. To this aim we used mice generated through homologous recombination that express an Ires-Cre-recombinase bi-cistronic extension of the endogenous α7 gene that when crossed with a reporter mouse expressing Rosa26-LoxP (yellow fluorescent protein (YFP)) marks in the offspring those cells of the α7 cell lineage (α7^lin+). In the adult, on average 20–25 percent of the total CD45⁺ myeloid and lymphoid cells of the bone marrow (BM), blood, spleen, lymph nodes, and Peyers patches are α7^lin+, although variability between litter mates in this value is observed. This hematopoietic α7^lin+ subpopulation is also found in Sca1⁺cKit⁺ BM cells suggesting the α7 lineage is established early during hematopoiesis and the ratio remains stable in the individual thereafter as measured for at least 18 months. Both α7^lin+ and α7^lin– BM cells can reconstitute the immune system of naïve irradiated recipient mice and the α7^lin+:α7^lin– beginning ratio is stable in the recipient after reconstitution. Functionally the α7^lin+:α7^lin– lineages differ in response to LPS challenge. Most notable is the response to LPS as demonstrated by an enhanced production of IL-12/23(p40) by the α7^lin+ cells. These studies demonstrate that α7^lin+ identifies a novel subpopulation of bone marrow cells that include hematopoietic progenitor cells that can re-populate an animal’s inflammatory/immune system. These findings suggest that α7 exhibits a pleiotropic role in the hematopoietic system that includes both the direct modulation of pro-inflammatory cell composition and later in the adult the role of modulating pro-inflammatory responses that would impact upon an individual’s lifelong response to inflammation and infection.

Daily regulation of hormone profiles

The highly coordinated output of the hypothalamic biological clock does not only govern the daily rhythm in sleep/wake (or feeding/fasting) behaviour but also has direct control over many aspects of hormone release. In fact, a significant proportion of our current understanding of the circadian clock has its roots in the study of the intimate connections between the hypothalamic clock and multiple endocrine axes. This chapter will focus on the anatomical connections used by the mammalian biological clock to enforce its endogenous rhythmicity on the rest of the body, using a number of different hormone systems as a representative example. Experimental studies have revealed a highly specialised organisation of the connections between the mammalian circadian clock neurons and neuroendocrine as well as pre-autonomic neurons in the hypothalamus. These complex connections ensure a logical coordination between behavioural, endocrine and metabolic functions that will help the organism adjust to the time of day most efficiently. For example, activation of the orexin system by the hypothalamic biological clock at the start of the active phase not only ensures that we wake up on time but also that our glucose metabolism and cardiovascular system are prepared for this increased activity. Nevertheless, it is very likely that the circadian clock present within the endocrine glands plays a significant role as well, for instance, by altering these glands' sensitivity to specific stimuli throughout the day. In this way the net result of the activity of the hypothalamic and peripheral clocks ensures an optimal endocrine adaptation of the metabolism of the organism to its time-structured environment.

Chronic exposure to nicotine enhances insulin sensitivity through α7 nicotinic acetylcholine receptor-STAT3 pathway

This study was to investigate the effect of nicotine on insulin sensitivity and explore the underlying mechanisms. Treatment of Sprague-Dawley rats with nicotine (3 mg/kg/day) for 6 weeks reduced 43% body weight gain and 65% blood insulin level, but had no effect on blood glucose level. Both insulin tolerance test and glucose tolerance test demonstrated that nicotine treatment enhanced insulin sensitivity. Pretreatment of rats with hexamethonium (20 mg/kg/day) to antagonize peripheral nicotinic receptors except for α7 nicotinic acetylcholine receptor (α7-nAChR) had no effect on the insulin sensitizing effect of nicotine. However, the insulin sensitizing effect but not the bodyweight reducing effect of nicotine was abrogated in α7-nAChR knockout mice. Further, chronic treatment with PNU-282987 (0.53 mg/kg/day), a selective α7-nAChR agonist, significantly enhanced insulin sensitivity without apparently modifying bodyweight not only in normal mice but also in AMP-activated kinase-α2 knockout mice, an animal model of insulin resistance with no sign of inflammation. Moreover, PNU-282987 treatment enhanced phosphorylation of signal transducer and activator of transcription 3 (STAT3) in skeletal muscle, adipose tissue and liver in normal mice. PNU-282987 treatment also increased glucose uptake by 25% in C2C12 myotubes and this effect was total abrogated by STAT3 inhibitor, S3I-201. All together, these findings demonstrated that nicotine enhanced insulin sensitivity in animals with or without insulin resistance, at least in part via stimulating α7-nAChR-STAT3 pathway independent of inflammation. Our results contribute not only to the understanding of the pharmacological effects of nicotine, but also to the identifying of new therapeutic targets against insulin resistance.

The vagus nerve and the inflammatory reflex--linking immunity and metabolism

The vagus nerve has an important role in regulation of metabolic homeostasis, and efferent vagus nerve-mediated cholinergic signalling controls immune function and proinflammatory responses via the inflammatory reflex. Dysregulation of metabolism and immune function in obesity are associated with chronic inflammation, a critical step in the pathogenesis of insulin resistance and type 2 diabetes mellitus. Cholinergic mechanisms within the inflammatory reflex have, in the past 2 years, been implicated in attenuating obesity-related inflammation and metabolic complications. This knowledge has led to the exploration of novel therapeutic approaches in the treatment of obesity-related disorders.

Additive effects of nicotine and high-fat diet on hepatic steatosis in male mice

Smoking is a major risk factor for diabetes and cardiovascular disease and may contribute to nonalcoholic fatty liver disease. We hypothesize that in the presence of nicotine, high-fat diet (HFD) causes more severe hepatic steatosis in obese mice. Adult C57BL6 male mice were fed a normal chow diet or HFD and received twice daily injections of nicotine (0.75 mg/kg body weight, ip) or saline for 10 wk. Light microscopic image analysis revealed significantly higher lipid accumulation in livers from mice on HFD plus nicotine (190 ± 19 μm(2)), compared with mice on HFD alone (28 ± 1.2 μm(2)). A significant reduction in the percent volume of endoplasmic reticulum (67.8%) and glycogen (49.2%) was also noted in hepatocytes from mice on HFD plus nicotine, compared with mice on HFD alone. The additive effects of nicotine on the severity of HFD-induced hepatic steatosis was associated with significantly greater oxidative stress, increased hepatic triglyceride levels, higher incidence of hepatocellular apoptosis, inactivation (dephosphorylation) of AMP-activated protein kinase, and activation of its downstream target acetyl-coenzyme A-carboxylase. Treatment with acipimox, an inhibitor of lipolysis, significantly reduced nicotine plus HFD-induced hepatic lipid accumulation. We conclude that: 1) greater oxidative stress coupled with inactivation of AMP-activated protein kinase mediate the additive effects of nicotine and HFD on hepatic steatosis in obese mice and 2) increased lipolysis is an important contributor to hepatic steatosis. We surmise that nicotine exposure is likely to exacerbate the metabolic abnormalities induced by high-fat intake in obese patients.

Tnfα, Cox2 and AdipoQ adipokine gene expression levels are modulated in murine adipose tissues by both nicotine and nACh receptors containing the β2 subunit

Studies have provided evidences for the effects of nicotine on adipose tissues, as well as in inflammatory response. We hypothesized that nicotine affects adipokine gene expression in adipose tissues via specific neuronal nicotinic acetylcholine receptors (nAChRs). First, we described the expression of multiple nAChR subunit genes in mouse white and brown adipose tissues (WAT and BAT), and detected differential expression in WAT and BAT (α2>α5>β2 and α2>β2>β4, respectively). Additionally, when nicotine was administered to wild-type mice, it significantly affected the expression of adipokine genes, such as Tnfα, AdipoQ, Haptoglobin and Mcp1 in WAT. Next, we demonstrated that in mice deficient for the β2 nAChR subunit (β2-/- mice), the expression levels of Cox2 and Ngfβ genes in WAT, and Leptin, Cox2, AdipoQ and Haptoglobin in BAT, were significantly altered. Furthermore, interactions between mouse β2 subunit and nicotine treatment affected the expression levels of the adipokine genes Tnfα, Cox2 and AdipoQ in WAT and of AdipoQ in BAT. Finally, analysis of a cellular model of cultured adipocytes demonstrated that application of nicotine after silencing of the β2 nAChR subunit significantly elevated the expression level of Cox2 gene. Together, our data suggest a molecular link between the β2 nACh receptor subunit and the expression levels of specific adipokines, which is also affected by nicotine.

Nicotinic regulation of energy homeostasis

INTRODUCTION

The ability of nicotine, the primary psychoactive substance in tobacco smoke, to regulate appetite and body weight is one of the factors cited by smokers that prevents them from quitting and is the primary reason for smoking initiation in teenage girls. The regulation of feeding and metabolism by nicotine is complex, and recent studies have begun to identify nicotinic acetylcholine receptor (nAChR) subtypes and circuits or cell types involved in this regulation.

DISCUSSION

We will briefly describe the primary anatomical and functional features of the input, output, and central integration structures of the neuroendocrine systems that regulate energy homeostasis. Then, we will describe the nAChR subtypes expressed in these structures in mammals to identify the possible molecular targets for nicotine. Finally, we will review the effects of nicotine and its withdrawal on feeding and energy metabolism and attribute them to potential central and peripheral cellular targets.

The endocrine effects of nicotine and cigarette smoke

With a current prevalence of approximately 20%, smoking continues to impact negatively upon health. Tobacco or nicotine use influences the endocrine system, with important clinical implications. In this review we critically evaluate the literature concerning the impact of nicotine as well as tobacco use on several parameters of the endocrine system and on glucose and lipid homeostasis. Emphasis is on the effect of smoking on diabetes mellitus and obesity and the consequences of smoking cessation on these disorders. Understanding the effects of nicotine and cigarettes on the endocrine system and how these changes contribute to the pathogenesis of various endocrine diseases will allow for targeted therapies and more effective approaches for smoking cessation.

Effect of nicotine on body composition in mice

Nicotine induces weight loss in both humans and rodents consuming a regular diet; however, the effect of nicotine on body weight and fat composition in rodents consuming a high-fat diet (HFD) has not been well studied. Thus, this study examined the effect of nicotine vs saline on body weight and fat composition in mice fed with either an HFD (62% of kcal from fat) or a standard normal chow diet (NCD) for 7 weeks. Nicotine dose dependently reduced body weight gain in mice that consumed both diets, but this effect was significantly greater in mice on the HFD. Caloric intake was decreased in nicotine-treated mice. Estimates of energy intake suggested that decreased caloric intake accounted for all the reduced weight gain in mice on an NCD and 66% of the reduced weight gain on an HFD. Computed tomography analysis for fat distribution demonstrated that nicotine was effective in reducing abdominal fat in mice that consumed the HFD, with nicotine treatment leading to lower visceral fat. The effect of nicotine on weight loss in mice on an HFD was completely blocked by mecamylamine, a nonselective nicotinic acetylcholine receptor (nAChR) antagonist, but only partially blocked by the α4β2 nAChR partial agonist/antagonist, varenicline. We conclude that nicotine is effective in preventing HFD-induced weight gain and abdominal fat accumulation.

The nicotinic acetylcholine receptor α7 in subcutaneous mature adipocytes: downregulation in human obesity and modulation by diet-induced weight loss

BACKGROUND

It is known that cholinergic anti-inflammatory reflex regulates inflammation in peripheral tissues. Nicotinic acetylcholine receptors (nAChRs) are mediators of this anti-inflammatory pathway and also non-neuronal cells express functional nAChrs. A role for α7-subtype acetylcholine cholinergic receptor (α7nAChR) in insulin sensitivity improvement has already been shown in rodents both in vivo and in vitro. However, no data are available on α7nAChR expression in human adipocytes.

OBJECTIVE

To investigate the expression and protein content of α7nAChR in human subcutaneous adipose tissue (SAT) and in isolated mature adipocytes.

DESIGN

A total of 39 SAT biopsy specimens obtained from obese and normal-weight subjects were used to assess α7nAChR messenger RNA levels and to stimulate α7nAChR with a specific agonist and antagonist in vitro. Additional SATs from eight non-diabetic obese subjects were also studied, before and after a 3-month lifestyle intervention.

RESULTS

α7nAChR expression was significantly lower in the SAT of obese subjects compared with that of normal-weight subjects. In mature adipocytes isolated from morbidly obese subjects (body mass index > 40 kg m(-2)), α7nAChR expression was 75% lower compared with adipocytes from normal-weight subjects. In adipocytes of obese subjects, α7nAChR was downregulated also at protein level. In eight non-diabetic obese subjects, a lifestyle intervention (3 months of diet and physical activity) induced a significant weight loss and an increase in α7nAChR SAT expression. In vitro stimulation of adipocytes with the specific α7nAChR agonist PNU282987 induced a significant anti-inflammatory effect. Furthermore, a similar downregulation of the inflammatory profile, associated with a significant increase in α7nAChR protein level, was observed after genistein stimulation.

CONCLUSIONS

These results provide evidence that α7nAChR expression levels are significantly decreased in obese subjects, and that this receptor modulates inflammatory gene expression in human adipocytes. The upregulation of α7nAChR by genistein stimulation opens new insights for the management of low-grade inflammation linked to human obesity.

Circadian disruption and SCN control of energy metabolism

In this review we first present the anatomical pathways used by the suprachiasmatic nuclei to enforce its rhythmicity onto the body, especially its energy homeostatic system. The experimental data show that by activating the orexin system at the start of the active phase, the biological clock not only ensures that we wake up on time, but also that our glucose metabolism and cardiovascular system are prepared for increased activity. The drawback of such a highly integrated system, however, becomes visible when our daily lives are not fully synchronized with the environment. Thus, in addition to increased physical activity and decreased intake of high-energy food, also a well-lighted and fully resonating biological clock may help to withstand the increasing "diabetogenic" pressure of today's 24/7 society.

Nicotinic acetylcholine receptor α7 subunit is time-dependently expressed in distinct cell types during skin wound healing in mice

Recent studies have shown that nicotinic acetylcholine receptor alpha7 subunit (nAChRα7) plays an important role in regulation of inflammation, angiogenesis and keratinocyte biology, but little is known about its expression after the skin is wounded. A preliminary study on time-dependent expression and distribution of nAChRα7 was performed by immunohistochemistry, Western blotting and RT-PCR during skin wound healing in mice. After a 1-cm-long incision was made in the skin of the central dorsum, mice were killed at intervals ranging from 6 h to 14 days post-injury. In uninjured skin controls, nAChRα7 positive staining was observed in epidermis, hair follicles, sebaceous glands, vessel endothelium and resident dermal fibroblastic cells. In wounded specimens, a small number of polymorphonuclear cells, a large number of mononuclear cells (MNCs) and fibroblastic cells (FBCs) showed positive reaction for nAChRα7 in the wound zones. Simultaneously, nAChRα7 immunoreactivity was evident in endothelial-like cells of regenerated vessels and neoepidermis. By morphometric analysis, an up-regulation of nAChRα7 expression was verified at the inflammatory phase after skin injury and reached a peak at the proliferative phase of wound healing. The expression tendency was further confirmed by Western blotting and RT-PCR assay. By immunofluorescent staining for co-localization, the nAChRα7-positive MNCs and FBCs in skin wounds were identified as macrophages, fibrocytes and myofibroblasts. A number of nAChRα7-positive myofibroblasts were also CD45 positive, indicating that they originated from differentiation of fibrocytes. The results demonstrate that nAChRα7 is time-dependently expressed in distinct cell types, which may be closely involved in inflammatory response and repair process during skin wound healing.

The crosstalks between adipokines and catecholamines

Adipocytes, which secrete a spectrum of adipokines, play an integral role in metabolism via communications with other endocrine cells. In the present work, we have studied the interplays between adipokines and catecholamines, using 3T3-L1 adipocytes and PC12 cells as the cell models and an integrative experimental platform. We demonstrate that all catecholamines inhibit vesicle trafficking and secretion of leptin and resistin through β-adrenergic receptors, while leptin and resistin enhance the vesicle trafficking and secretion of catecholamines through PKC, PKA, MAPK kinase and Ca(2+) dependent pathways. The crosstalks between adipokines and catecholamines were further corroborated by co-culturing 3T3-L1 adipocytes and PC12 cells. Our findings highlight the importance of adipo-adrenal axis in energy metabolism and the intricate interactions between metabolic hormones.

Markers of inflammation and weight change in middle-aged adults: results from the prospective MONICA/KORA S3/F3 study

We investigated associations of markers of inflammation such as albumin, fibrinogen, C-reactive protein (CRP), and white blood cell count (WBCC) with future weight gain and weight loss in middle-aged adults in order to further elucidate the relationship between subclinical inflammation and weight change. Data were derived from the third population-based MONICA (Monitoring of Trends and Determinants in Cardiovascular Diseases) Augsburg survey (S3) conducted as part of the multinational World Health Organization MONICA project in 1994-1995 and a follow-up examination, to which all eligible subjects from S3 were invited in 2004-2005 (F3). In total, 2,792 persons (1,391 men, 1,401 women) aged 25-74 years at baseline were analyzed. Subjects with elevated concentrations of inflammatory markers were more prone to gain weight during follow-up. The odds ratios (OR) for a large mean annual weight gain (i.e., on average 1.02 kg/year) was 1.73 (95% confidence interval (CI) 1.27, 2.35) in fully adjusted analyses for subjects in the highest compared to the lowest quartile of fibrinogen. The respective ORs were 1.45 (95% CI, 1.08, 1.94) and 1.37 (95% CI, 1.03, 1.82) for CRP and WBCC. Stratified analyses revealed that associations were strongest among subjects who quitted smoking during the follow-up period (new quitters). Associations of inflammatory markers with large mean annual weight loss were weaker and became nonsignificant after multivariable adjustment. In conclusion, elevated levels of inflammatory markers are independently associated with weight gain in middle-aged adults, particularly among new quitters. This suggests that inflammation plays a key role in the process of weight gain, especially after smoking cessation.