Nicotine administration decreases neuropeptide Y expression and increases leptin receptor expression in the hypothalamus of food-deprived rats

Cross talk about the role of Neuropeptide Y in CNS disorders and diseases

A peptide composed of a 36 amino acid called Neuropeptide Y (NPY) is employed in a variety of physiological processes to manage and treat conditions affecting the endocrine, circulatory, respiratory, digestive, and neurological systems. NPY naturally binds to G-protein coupled receptors, activating the Y-receptors (Y1-Y5 and y6). The findings on numerous therapeutic applications of NPY for CNS disease are presented in this review by the authors. New targets for treating diseases will be revealed by medication combinations that target NPY and its receptors. This review is mainly focused on disorders such as anxiety, Alzheimer's disease, Parkinson's disease, Huntington's disease, Machado Joseph disease, multiple sclerosis, schizophrenia, depression, migraine, alcohol use disorder, and substance use disorder. The findings from the preclinical studies and clinical studies covered in this article may help create efficient therapeutic plans to treat neurological conditions on the one hand and psychiatric disorders on the other. They may also open the door to the creation of novel NPY receptor ligands as medications to treat these conditions.

Updated Role of Neuropeptide Y in Nicotine-Induced Endothelial Dysfunction and Atherosclerosis

Cardiovascular disease is the leading cause of death worldwide. Endothelial dysfunction of the arterial vasculature plays a pivotal role in cardiovascular pathogenesis. Nicotine-induced endothelial dysfunction substantially contributes to the development of arteriosclerotic cardiovascular disease. Nicotine promotes oxidative inflammation, thrombosis, pathological angiogenesis, and vasoconstriction, and induces insulin resistance. However, the exact mechanism through which nicotine induces endothelial dysfunction remains unclear. Neuropeptide Y (NPY) is widely distributed in the central nervous system and peripheral tissues, and it participates in the pathogenesis of atherosclerosis by regulating vasoconstriction, energy metabolism, local plaque inflammatory response, activation and aggregation of platelets, and stress and anxiety-related emotion. Nicotine can increase the expression of NPY, suggesting that NPY is involved in nicotine-induced endothelial dysfunction. Herein, we present an updated review of the possible mechanisms of nicotine-induced atherosclerosis, with a focus on endothelial cell dysfunction associated with nicotine and NPY.

Nicotine' actions on energy balance: Friend or foe?

Obesity has reached pandemic proportions and is associated with severe comorbidities, such as type 2 diabetes mellitus, hepatic and cardiovascular diseases, and certain cancer types. However, the therapeutic options to treat obesity are limited. Extensive epidemiological studies have shown a strong relationship between smoking and body weight, with non-smokers weighing more than smokers at any age. Increased body weight after smoking cessation is a major factor that interferes with their attempts to quit smoking. Numerous controlled studies in both humans and rodents have reported that nicotine, the main bioactive component of tobacco, exerts a marked anorectic action. Furthermore, nicotine is also known to modulate energy expenditure, by regulating the thermogenic activity of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT), as well as glucose homeostasis. Many of these actions occur at central level, by controlling the activity of hypothalamic neuropeptide systems such as proopiomelanocortin (POMC), or energy sensors such as AMP-activated protein kinase (AMPK). However, direct impact of nicotine on metabolic tissues, such as BAT, WAT, liver and pancreas has also been described. Here, we review the actions of nicotine on energy balance. The relevance of this interaction is interesting, because considering the restricted efficiency of obesity treatments, a possible complementary approach may focus on compounds with known pharmacokinetic profile and pharmacological actions, such as nicotine or nicotinic acetylcholine receptors signaling.

The Role of Neuropeptide Y (NPY) in Alcohol and Drug Abuse Disorders

Neuropeptide Y (NPY) is a neuromodulator that is widely expressed throughout the central nervous system (CNS) and which is cosecreted with classic neurotransmitters including GABA and glutamate. There is a long history of research implicating a role for NPY in modulating neurobiological responses to alcohol (ethanol) as well as other drugs of abuse. Both ethanol exposure and withdrawal from chronic ethanol have been shown to produce changes in NPY and NPY receptor protein levels and mRNA expression in the CNS. Importantly, manipulations of NPY Y1 and Y2 receptor signaling have been shown to alter ethanol consumption and self-administration in a brain region-specific manner, with Y1 receptor activation and Y2 receptor blockade in regions of the extended amygdala promoting robust reductions of ethanol intake. Similar observations have been made in studies examining neurobiological responses to nicotine, psychostimulants, and opioids. When taken together with observations of potential genetic linkage between the NPY system and the human alcohol abuse disorders, NPY represents a promising target for treating problematic alcohol and drug use, and in protecting individuals from relapse during abstinence.

Effects of drugs of abuse on the central neuropeptide Y system

Neuropeptide Y (NPY), which is widely expressed in the central nervous system is involved in several neuropathologies including addiction. Here we comprehensively and systematically review alterations on the central NPY system induced by several drugs. We report on the effects of psychostimulants [cocaine, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA) and nicotine], ethanol, and opioids on NPY protein levels and expression of different NPY receptors. Overall, expression and function of NPY and its receptors are changed under conditions of drug exposure, thus affecting several physiologic behaviors, such as feeding, stress and anxiety. Drugs of abuse differentially affect the components of the NPY system. For example methamphetamine and nicotine lead to a consistent increase in NPY mRNA and protein levels in different brain sites whereas ethanol and opioids decrease NPY mRNA and protein expression. Drug-induced alterations on the different NPY receptors show more complex regulation pattern. Manipulation of the NPY system can have opposing effects on reinforcing and addictive properties of drugs of abuse. NPY can produce pro-addictive effects (nicotine and heroin), but can also exert inhibitory effects on addictive behavior (AMPH, ethanol). Furthermore, NPY can act as a neuroprotective agent in chronically methamphetamine and MDMA-treated rodents. In conclusion, manipulation of the NPY system seems to be a potential target to counteract neural alterations, addiction-related behaviors and cognitive deficits induced by these drugs.

Aortic remodelling in chronic nicotine-administered rat

Vascular remodelling is an adaptive mechanism, which counteracts pressure changes in blood circulation. Nicotine content in cigarette increases the risk of hypertension. The exact relationship between nicotine and vascular remodelling still remain unknown. Current study was aimed to determine the effect of clinically relevant dosage of nicotine (equivalent to light smoker) on aortic reactivity, oxidative stress markers and histomorphological changes. Twelve age-matched male Sprague-Dawley rats were randomly divided into two groups, i.e.: normal saline as control or 0.6 mg/kg nicotine for 28 days (i.p., n=6 per group). On day-29, the rats were sacrificed and the thoracic aorta was dissected immediately for further studies. Mean arterial pressure (MAP) and pulse pressure (PP) of nicotine-treated vs. control were significantly increased (p<0.05). Nicotine-treated group showed significant (p<0.05) increase tunica media thickness, and decrease in lumen diameter, suggesting vascular remodelling which lead to prior hypertension state. The phenylephrine (PE)-induced contractile response in nicotine group was significantly higher than control group (ED50=1.44×10(5) M vs. 4.9×10(6) M) (p<0.05~0.001). However, nicotine-treated rat showed significantly lower endothelium-dependent relaxation response to acetylcholine (ACh) than in control group (ED50=6.17×10(7) M vs. 2.82×10(7) M) (p<0.05), indicating loss of primary vascular function. Malondialdehyde (MDA), a lipid peroxidation marker was significantly higher in nicotine group. Superoxide dismutase (SOD) enzymatic activity and glutathione (GSH) were all reduced in nicotine group (p<0.05) vs. control, suggesting nicotine induces oxidative imbalance. In short, chronic nicotine administration impaired aortic reactivity, probably via redox imbalance and vascular remodelling mechanism.

Involvement of hypothalamic neuropeptide Y in pentazocine induced suppression of food intake in rats

The potent orexigenic peptide neuropeptide Y (NPY) has been considered as a possible endogenous ligand for a subpopulation of sigma receptors (SigR). However, their mutual interaction with reference to feeding behavior remains poorly understood. In the present study, we explored the possible interaction between sigma1 receptors (Sig1R) agonist, pentazocine, and NPY on food intake in satiated rats. While pentazocine dose-dependently reduced the food intake, NPY significantly increased it at 2, 4 and 6h post injection time points. In combination studies, pretreatment with NPY (0.1 nmol/rat, intra-PVN) normalized the inhibitory effect of pentazocine (60 μg/rat, intra-PVN) on food intake. Similarly, pre-treatment with pentazocine (30 μg/rat, intra-PVN) significantly antagonized the orexigenic effect of NPY (0.5 and 1.0 nmol/rat, intra-PVN). Moreover, pentazocine treatment decreased NPY immunoreactivity in arcuate (ARC), paraventricular (PVN), dorsomedial (DMH) and ventromedial (VMH) nuclei of hypothalamus. However, no change was observed in lateral hypothalamus (LH). Study implicates the reduced NPY immunoreactivity for the anorectic effect observed following pentazocine injections. Therefore, the concomitant activation of the NPYergic system along with the Sig1R agonist treatment may serve a useful purpose in the management of the unwanted side effects related to energy homeostasis.

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.

Nicotine induces negative energy balance through hypothalamic AMP-activated protein kinase

Smokers around the world commonly report increased body weight after smoking cessation as a major factor that interferes with their attempts to quit. Numerous controlled studies in both humans and rodents have reported that nicotine exerts a marked anorectic action. The effects of nicotine on energy homeostasis have been mostly pinpointed in the central nervous system, but the molecular mechanisms controlling its action are still not fully understood. The aim of this study was to investigate the effect of nicotine on hypothalamic AMP-activated protein kinase (AMPK) and its effect on energy balance. Here we demonstrate that nicotine-induced weight loss is associated with inactivation of hypothalamic AMPK, decreased orexigenic signaling in the hypothalamus, increased energy expenditure as a result of increased locomotor activity, increased thermogenesis in brown adipose tissue (BAT), and alterations in fuel substrate utilization. Conversely, nicotine withdrawal or genetic activation of hypothalamic AMPK in the ventromedial nucleus of the hypothalamus reversed nicotine-induced negative energy balance. Overall these data demonstrate that the effects of nicotine on energy balance involve specific modulation of the hypothalamic AMPK-BAT axis. These targets may be relevant for the development of new therapies for human obesity.

Anti-inflammatory effects of nicotine in obesity and ulcerative colitis

Cigarette smoke is a major risk factor for a number of diseases including lung cancer and respiratory infections. Paradoxically, it also contains nicotine, an anti-inflammatory alkaloid. There is increasing evidence that smokers have a lower incidence of some inflammatory diseases, including ulcerative colitis, and the protective effect involves the activation of a cholinergic anti-inflammatory pathway that requires the α7 nicotinic acetylcholine receptor (α7nAChR) on immune cells. Obesity is characterized by chronic low-grade inflammation, which contributes to insulin resistance. Nicotine significantly improves glucose homeostasis and insulin sensitivity in genetically obese and diet-induced obese mice, which is associated with suppressed adipose tissue inflammation. Inflammation that results in disruption of the epithelial barrier is a hallmark of inflammatory bowel disease, and nicotine is protective in ulcerative colitis. This article summarizes current evidence for the anti-inflammatory effects of nicotine in obesity and ulcerative colitis. Selective agonists for the α7nAChR could represent a promising pharmacological strategy for the treatment of inflammation in obesity and ulcerative colitis. Nevertheless, we should keep in mind that the anti-inflammatory effects of nicotine could be mediated via the expression of several nAChRs on a particular target cell.

Nicotine excites hypothalamic arcuate anorexigenic proopiomelanocortin neurons and orexigenic neuropeptide Y neurons: similarities and differences

Two of the biggest health problems facing us today are addiction to nicotine and the increased prevalence of obesity. Interestingly, nicotine attenuates obesity, but the underlying mechanism is not clear. Here we address the hypothesis that if weight-reducing actions of nicotine are mediated by anorexigenic proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus, nicotine should excite these cells. Nicotine at concentrations similar to those found in smokers, 100-1,000 nM, excited POMC cells by mechanisms based on increased spike frequency, depolarization of membrane potential, and opening of ion channels. This was mediated by activation of both α7 and α4β2 nicotinic receptors; by itself, this nicotine-mediated excitation could explain weight loss caused by nicotine. However, in control experiments nicotine also excited the orexigenic arcuate nucleus neuropeptide Y (NPY) cells. Nicotine exerted similar actions on POMC and NPY cells, with a slightly greater depolarizing action on POMC cells. Immunocytochemistry revealed cholinergic axons terminating on both cell types. Nicotine actions were direct in both cell types, with nicotine depolarizing the membrane potentials and reducing input resistance. We found no differences in the relative desensitization to nicotine between POMC and NPY neurons. Nicotine inhibited excitatory synaptic activity recorded in NPY, but not POMC, cells. Nicotine also excited hypocretin/orexin neurons that enhance cognitive arousal, but the responses were smaller than in NPY or POMC cells. Together, these results indicate that nicotine has a number of similar actions, but also a few different actions, on POMC and NPY neurons that could contribute to the weight loss associated with smoking.

Detrimental metabolic effects of combining long-term cigarette smoke exposure and high-fat diet in mice

Obesity and cigarette smoking are both important risk factors for insulin resistance, cardiovascular disease, and cancer. Smoking reduces appetite, which makes many people reluctant to quit. Few studies have documented the metabolic impact of combined smoke exposure (se) and high-fat-diet (HFD). Neuropeptide Y (NPY) is a powerful hypothalamic feeding stimulator that promotes obesity. We investigated how chronic se affects caloric intake, adiposity, plasma hormones, inflammatory mediators, and hypothalamic NPY peptide in animals fed a palatable HFD. Balb/c mice (5 wk old, male) were exposed to smoke (2 cigarettes, twice/day, 6 days/wk, for 7 wk) with or without HFD. Sham-exposed mice were handled similarly without se. Plasma leptin, hypothalamic NPY, and adipose triglyceride lipase (ATGL) mRNA were measured. HFD induced a 2.3-fold increase in caloric intake, increased adiposity, and glucose in both sham and se cohorts. Smoke exposure decreased caloric intake by 23%, with reduced body weight in both dietary groups. Fat mass and glucose were reduced only by se in the chow-fed animals. ATGL mRNA was reduced by HFD in se animals. Total hypothalamic NPY was reduced by HFD, but only in sham-exposed animals; se increased arcuate NPY. We conclude that although se ameliorated hyperphagia and reversed the weight gain associated with HFD, it failed to reverse fat accumulation and hyperglycemia. The reduced ATGL mRNA expression induced by combined HFD and se may contribute to fat retention. Our data support a powerful health message that smoking in the presence of an unhealthy Western diet increases metabolic disorders and fat accumulation.

Nicotine regulates mRNA expression of feeding peptides in the arcuate nucleus in neonatal rat pups

Maternal smoking results in low birth weight. Using a neonatal gastric intubation model corresponding to the third trimester in humans, nicotine, the major psychoactive ingredient in tobacco, causes growth retardation in rat pups. Here, we wanted to determine the underlying mechanisms of nicotine's anorexic effects. In adults, body weight and energy expenditure are regulated by the adiposity hormone leptin and the orexigenic peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP) and anorexic peptides proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) expressed in the hypothalamic arcuate (Arc) nucleus. Activation of nicotinic acetylcholine receptors (nAChRs) could regulate leptin release and/or peptide expression in the Arc. Neonatal rat pups were treated twice daily with nicotine (0.25, 1.5, and 3 mg/kg) from postnatal day 1 to 8 (P1-8). This resulted in an upregulation of heteromeric nAChR binding sites in the ventromedial nucleus of the hypothalamus and Arc. Nicotine at all three doses significantly reduced body weight gain and increased mRNA expression of NPY, AgRP, and POMC effects, which were blocked by dihydro-beta-erythroidine (DHbetaE), an alpha4beta2* nAChR antagonist, but CART expression was unaffected. In contrast, serum leptin levels were significantly increased only by 3 and 1.5 mg/kg, and the increase was only partially blocked by DHbetaE. These data suggest that in neonates chronic nicotine regulates body weight gain independent from serum leptin levels by a central mechanism involving alpha4beta2* heteromeric nAChRs and stimulated increased expression of the anorexic peptide POMC. Whereas, increased NPY and AgRP expression could be a secondary response to reduction in weight gain.

Prenatal programming of childhood overweight and obesity

OBJECTIVE

To review the scientific evidence for prenatal programming of childhood overweight and obesity, and discuss its implications for MCH research, practice, and policy.

METHODS

A systematic review of observational studies examining the relationship between prenatal exposures and childhood overweight and obesity was conducted using MOOSE guidelines. The review included literature posted on PubMed and MDConsult and published between January 1975 and December 2005. Prenatal exposures to maternal diabetes, malnutrition, and cigarette smoking were examined, and primary study outcome was childhood overweight or obesity as measured by body mass index (BMI) for children ages 5 to 21.

RESULTS

Four of six included studies of prenatal exposure to maternal diabetes found higher prevalence of childhood overweight or obesity among offspring of diabetic mothers, with the highest quality study reporting an odds ratio of adolescent overweight of 1.4 (95% CI 1.0-1.9). The Dutch famine study found that exposure to maternal malnutrition in early, but not late, gestation was associated with increased odds of childhood obesity (OR 1.9, 95% CI 1.5-2.4). All eight included studies of prenatal exposure to maternal smoking showed significantly increased odds of childhood overweight and obesity, with most odds ratios clustering around 1.5 to 2.0. The biological mechanisms mediating these relationships are unknown but may be partially related to programming of insulin, leptin, and glucocorticoid resistance in utero.

CONCLUSION

Our review supports prenatal programming of childhood overweight and obesity. MCH research, practice, and policy need to consider the prenatal period a window of opportunity for obesity prevention.

Cigarette Smoke Exposure Reprograms the Hypothalamic Neuropeptide Y Axis to Promote Weight Loss

RATIONALE

Despite irrefutable epidemiologic evidence, cigarette smoking remains the major preventable cause of lung disease morbidity worldwide. The appetite-suppressing effect of tobacco is a major behavioral determinant of smoking, but the underlying molecular and neuronal mechanisms are not understood. Neuropeptide Y (NPY) is an orexigenic neuropeptide, whose activity in the hypothalamic paraventricular nucleus governs appetite.

OBJECTIVES

To compare the effects of smoke exposure and equivalent food restriction on body weight, organ mass, cytokines, and brain NPY in Balb/c mice.

METHODS

A pair-feeding study design compared smoke exposure (4 wk; 1 cigarette, 3 x /d, 5 d/wk) to equivalent food restriction (pair-fed) and sham-exposed control mice.

RESULTS

Smoke exposure rapidly induced mild anorexia. After 4 wk, smoke-exposed and pair-fed groups were lighter than control mice (22.0 +/- 0.2, 23.2 +/- 0.5, 24.9 +/- 0.4 g, respectively; p < 0.05). Brown and white fat masses were only reduced by smoke exposure, relative to control mice. NPY concentration in the paraventricular nucleus was significantly and paradoxically reduced by smoke exposure, despite lower plasma leptin concentrations; this was not observed in the pair-fed group experiencing 19% food restriction. Adipose mRNA expression of uncoupling proteins, inflammatory cytokines interleukin 6 and tumor necrosis factor alpha, and adipose triglyceride lipase was decreased by smoke exposure, and even lower in pair-fed mice.

CONCLUSIONS

In contrast to food restriction, smoke exposure caused a reduction in hypothalamic NPY and fat mass, and regulated adipose cytokines. These findings may contribute to understanding weight loss in smoking-related lung disease and in the design of more effective smoking cessation strategies.