"Mens sana in corpore sano": exercise and hypothalamic ER stress

Longan extract suppresses food intake through regulation of POMC/AgRP neuronal activities and endoplasmic reticulum stress in hypothalamus of db/db mice

Type 2 diabetes mellitus (T2DM) is one of the biggest public health issues worldwide and closely related to development of other chronic diseases such as cardiovascular diseases, cancer and neurodegenerative diseases. Considerable percentage of T2DM patients undergo have suffered from binge eating disorder which exacerbates insulin resistance and metabolic challenges. Longan (Dimocarpus longan L.) and its constituents are reported for their various health benefits. However, it is still unknown whether longan fruit supplementation can ameliorate glucose homeostasis and binge eating disorder found in T2DM. The current study aimed to investigate whether longan fruit extract (LE) supplementation can improve diabetic hyperglycemia through modulation of feeding center located in hypothalamus of db/db T2DM mice. As a result, LE supplementation ameliorated fasting blood glucose levels and reduced excessive epididymal fat accumulation. In addition, LE administration improved glucose tolerance and insulin sensitivity in db/db mice. Especially, LE supplemented mice showed less food consumption which was in line with increase of pro-opiomelanocortin (POMC) neuronal activities and decrease of agouti-related peptide (AgRP) neuronal activities. Furthermore, LE supplementation reduced hypothalamic endoplasmic reticulum (ER) stress which was stimulated in db/db mice. As ER stress is a crucial factor involving in appetite control and glucose homeostasis, the effect of LE supplementation on circulating glucose levels and feeding behavior might be mediated by suppression of hypothalamic ER stress. Collectively, these findings suggest that LE could be a potential nutraceutical for improvement of T2DM as well as patients with satiety issues.

Fit mothers for a healthy future: Breaking the intergenerational cycle of non-alcoholic fatty liver disease with maternal exercise

SPECIAL ISSUE: 'FOIEGRAS-Bioenergetic Remodelling in the Pathophysiology and Treatment of Non-Alcoholic Fatty Liver Disease'.

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) emerges as significant health burden worldwide. Lifestyle changes, unhealthy dietary habits and physical inactivity, can trigger NAFLD development. Persisting on these habits during pregnancy affects in utero environment and prompts a specific metabolic response in foetus resulting in offspring metabolic maladjustments potentially critical for developing NAFLD later in life. The increasing prevalence of NAFLD, particularly in children, has shifted the research focus towards preventive and therapeutic strategies. Yet, designing effective approaches that can break the NAFLD intergenerational cycle becomes even more complicated. Regular physical exercise (PE) is a powerful non-pharmacological strategy known to counteract deleterious metabolic outcomes. In this narrative review, we aimed to briefly describe NAFLD pathogenesis focusing on maternal nutritional challenge and foetal programming, and to provide potential mechanisms behind the putative intergenerational effect of PE against metabolic diseases, including liver diseases.

METHODS

Following detailed electronic database search, recent existing evidence about NAFLD development, intergenerational programming and gestational exercise effects was critically analysed and discussed.

RESULTS

PE during pregnancy could have a great potential to counteract intergenerational transmission of metabolic burden. The interplay between different PE roles-metabolic, endocrine and epigenetic-could offer a more stable in utero environment to the foetus, thus rescuing offspring vulnerability to metabolic disturbances.

CONCLUSIONS

The better understanding of maternal PE beneficial consequences on offspring metabolism could reinforce the importance of PE during pregnancy as an indispensable strategy in improving offspring health.

Ovarian insufficiency impairs glucose-stimulated insulin secretion through activation of hypothalamic de novo ceramide synthesis

Oestrogens regulate body weight through their action on hypothalamus to modulate food intake and energy expenditure. Hypothalamic de novo ceramide synthesis plays a central role on obesity induced by oestrogen deficiency. Depletion in oestrogens is also known to be associated with glucose intolerance, which favours type 2 diabetes (T2D). However, the implication of hypothalamic ceramide in the regulation of glucose homeostasis by oestrogen is unknown. Here, we studied glucose homeostasis and insulin secretion in ovariectomized (OVX) female rats. OVX induces body weight gain associated with a hypothalamic inflammation and impaired glucose homeostasis. Genetic blockade of ceramide synthesis in the ventromedial nucleus of the hypothalamus (VMH) reverses hypothalamic inflammation and partly restored glucose tolerance induced by OVX. Furthermore, glucose-stimulated insulin secretion (GSIS) is increased in OVX rats due to a raise of insulin secretion second phase, a characteristic of early stage of T2D. In contrast, GSIS from isolated islets of OVX rats is totally blunted. Inhibition of ceramide synthesis in the VMH restores GSIS from isolated OVX islets and represses the second phase of insulin secretion. Stimulation of oestrogen receptor α (ERα) by oestradiol (E2) down-regulates ceramide synthesis in hypothalamic neuronal GT1-7 cells but no in microglial SIM-A9 cells. In contrast, genetic inactivation of ERα in VMH upregulates ceramide synthesis. These results indicate that hypothalamic neuronal de novo ceramide synthesis triggers the OVX-dependent impairment of glucose homeostasis which is partly mediated by a dysregulation of GSIS.

The impact of physical activity rate on subjective well-being among North-Western Italian population during COVID-19 nationwide lockdown

BACKGROUND

Several factors influence subjective well-being, and one of them is the rate of physical activity. However, the possibilities to perform physical activity are compromised by the running COVID-19 pandemic. Thus, the present study aimed to explore the relationship between self-reported physical activity levels during COVID-19 and subjective well-being. Furthermore, our secondary aim was to investigate whether personal well-being was different between men and women and between people with different self-reported physical activity levels.

METHODS

Physical activity rate and subjective well-being were assessed using specific online surveys. Well-being was investigated using the 5-item World Health Organization Well-being Index while physical activity rates using the official Italian short form of IPAQ. Participation was voluntary, and people could fill the questionnaire simply by clicking on a specific link reachable via Social Networks or by email.

RESULTS

The final sample size was 595 Italian responders. Male and female were equally distributed (50,3% male and 49,7% female). The multiple regression indicated that the model was a significant predictor of subjective well-being (R2 =,070,F (3,59) = 14,68, p< 0.0001). The univariate ANOVA detected a statistically significant difference in subjective well-being perception between gender (p<0,05; ƞ²= ,01) and among physical activity rates ((whole sample: p<0,0001, ƞ²=0,03); Males: F(2,296)=4,364, p<0,01, ƞ²=0,03; Females: F(2,293)=5,256, p<0,001, ƞ²=0,04)). Tuckey's post hoc identified a difference between Low active and moderate active males (p< 0,01) and low active and very active females (p< 0,01).

CONCLUSIONS

More vigorous activities are necessary for women to reach the goal of feeling good and satisfied with life than men. Therefore, women should be encouraged to spend more time practising physical activity at a more vigorous rate. This outcome might help practitioners set specific home training programs to be advised during periods of social life restrictions as the running COVID-19 pandemic.

The positive impact of physical activity on the reduction of anxiety scores: a pilot study

OBJECTIVES

To compare anxiety scores between physical activity practitioners and sedentary, men and women and to relate them to physical activity frequency and age.

METHODS

In this cross-sectional study, a sample of 256 regular aerobic physical activity practitioners was compared to a sample of 256 sedentary individuals (control group). Anxiety scores were quantified by Anxiety Inventory Spielberger State-Trait (STAI). The scores of the groups were compared using the Student t-test and chi-square test for parametric and non-parametric data, respectively. The correlation between scores of different variables was performed using the Pearson test.

RESULTS

There was a significant difference between the average anxiety scores (p <0.001) and the chi-square test proved there is a higher prevalence of severe anxiety (p <0.001) in the sedentary group. Age did not correlate with worse anxiety scores (p <0.05). Comparing by gender, women had a higher prevalence of intense anxiety.

CONCLUSIONS

Individuals who engage in regular physical activity have lower levels of anxiety, and both sexes are benefited with the anxiolytic potential of physical activity. Therefore, this study proved that the Roman poet Juvenal was right, and his expression "Mens sana in corpore sano," could also be interpreted in the opposite direction, i.e., a healthy body correlates with a healthy mind.

Orexins/Hypocretins: Key Regulators of Energy Homeostasis

Originally described to be involved in feeding regulation, orexins/hypocretins are now also considered as major regulatory actors of numerous biological processes, such as pain, sleep, cardiovascular function, neuroendocrine regulation, and energy expenditure. Therefore, they constitute one of the most pleiotropic families of hypothalamic neuropeptides. Although their orexigenic effect is well documented, orexins/hypocretins also exert central effects on energy expenditure, notably on the brown adipose tissue (BAT) thermogenesis. A better comprehension of the underlying mechanisms and potential interactions with other hypothalamic molecular pathways involved in the modulation of food intake and thermogenesis, such as AMP-activated protein kinase (AMPK) and endoplasmic reticulum (ER) stress, is essential to determine the exact implication and pathophysiological relevance of orexins/hypocretins on the control of energy balance. Here, we will review the actions of orexins on energy balance, with special focus on feeding and brown fat function.

Estradiol Regulates Energy Balance by Ameliorating Hypothalamic Ceramide-Induced ER Stress

Compelling evidence has shown that, besides its putative effect on the regulation of the gonadal axis, estradiol (E2) exerts a dichotomic effect on the hypothalamus to regulate food intake and energy expenditure. The anorectic effect of E2 is mainly mediated by its action on the arcuate nucleus (ARC), whereas its effects on brown adipose tissue (BAT) thermogenesis occur in the ventromedial nucleus (VMH). Here, we demonstrate that central E2 decreases hypothalamic ceramide levels and endoplasmic reticulum (ER) stress. Pharmacological or genetic blockade of ceramide synthesis and amelioration of ER stress selectively occurring in the VMH recapitulate the effect of E2, leading to increased BAT thermogenesis, weight loss, and metabolic improvement. These findings demonstrate that E2 regulation of ceramide-induced hypothalamic lipotoxicity and ER stress is an important determinant of energy balance, suggesting that dysregulation of this mechanism may underlie some changes in energy homeostasis seen in females.

Hypothalamic AMPK and energy balance

AMP-activated protein kinase (AMPK) is the main cellular energy sensor. Activated following a depletion of cellular energy stores, AMPK will restore the energy homoeostasis by increasing energy production and limiting energy waste. At a central level, the AMPK pathway will integrate peripheral signals (mostly hormones and metabolites) through neuronal networks. Hypothalamic AMPK is directly implicated in feeding behaviour, brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT). It also participates in other metabolic functions: glucose and muscle metabolisms, as well as hepatic function. Numerous anti-obesity and/or antidiabetic agents, such as nicotine, metformin and liraglutide, are known to induce their effects through a modulation of AMPK pathway, either at central or at peripheral levels. Moreover, the weight-gaining side effects of antipsychotic drugs, such as olanzapine, are also mediated by hypothalamic AMPK. Therefore, considering hypothalamic AMPK as a therapeutic target in metabolic diseases appears as an interesting strategy due to its implication in feeding and energy expenditure, the two sides of the energy balance equation.

Genetic Targeting of GRP78 in the VMH Improves Obesity Independently of Food Intake

Recent data have demonstrated that the hypothalamic GRP78/BiP (glucose regulated protein 78 kDa/binding immunoglobulin protein) modulates brown adipose tissue (BAT) thermogenesis by acting downstream on AMP-activated protein kinase (AMPK). Herein, we aimed to investigate whether genetic over-expression of GRP78 in the ventromedial nucleus of the hypothalamus (VMH: a key site regulating thermogenesis) could ameliorate very high fat diet (vHFD)-induced obesity. Our data showed that stereotaxic treatment with adenoviruses harboring GRP78 in the VMH reduced hypothalamic endoplasmic reticulum ER stress and reversed vHFD-induced obesity. Herein, we also demonstrated that this body weight decrease was more likely associated with an increased BAT thermogenesis and browning of white adipose tissue (WAT) than to anorexia. Overall, these results indicate that the modulation of GRP78 in the VMH may be a target against obesity.

Hypothalamic GRP78, a new target against obesity?

The chaperone GRP78 (glucose related protein 78), also called BiP (binding immunoglobulin protein) is a key regulator of endoplasmic reticulum (ER) stress. We recently described that over-expression of GRP78 specifically in the ventromedial nucleus of the hypothalamus (VMH) releases hypothalamic ER stress in rodent obese models leading to weight loss, reduced hepatic steatosis and improved insulin and leptin sensitivity. The action of GRP78 is mediated by a feeding-independent mechanism involving increased sympathetic tone, augmented brown adipose tissue (BAT) thermogenesis and induction browning of white adipose tissue (WAT).

Brain Ceramide Metabolism in the Control of Energy Balance

The regulation of energy balance by the central nervous system (CNS) is a key actor of energy homeostasis in mammals, and deregulations of the fine mechanisms of nutrient sensing in the brain could lead to several metabolic diseases such as obesity and type 2 diabetes (T2D). Indeed, while neuronal activity primarily relies on glucose (lactate, pyruvate), the brain expresses at high level enzymes responsible for the transport, utilization and storage of lipids. It has been demonstrated that discrete neuronal networks in the hypothalamus have the ability to detect variation of circulating long chain fatty acids (FA) to regulate food intake and peripheral glucose metabolism. During a chronic lipid excess situation, this physiological lipid sensing is impaired contributing to type 2 diabetes in predisposed subjects. Recently, different studies suggested that ceramides levels could be involved in the regulation of energy balance in both hypothalamic and extra-hypothalamic areas. Moreover, under lipotoxic conditions, these ceramides could play a role in the dysregulation of glucose homeostasis. In this review we aimed at describing the potential role of ceramides metabolism in the brain in the physiological and pathophysiological control of energy balance.

The cellular and molecular bases of leptin and ghrelin resistance in obesity

Obesity, a major risk factor for the development of diabetes mellitus, cardiovascular diseases and certain types of cancer, arises from a chronic positive energy balance that is often due to unlimited access to food and an increasingly sedentary lifestyle on the background of a genetic and epigenetic vulnerability. Our understanding of the humoral and neuronal systems that mediate the control of energy homeostasis has improved dramatically in the past few decades. However, our ability to develop effective strategies to slow the current epidemic of obesity has been hampered, largely owing to the limited knowledge of the mechanisms underlying resistance to the action of metabolic hormones such as leptin and ghrelin. The development of resistance to leptin and ghrelin, hormones that are crucial for the neuroendocrine control of energy homeostasis, is a hallmark of obesity. Intensive research over the past several years has yielded tremendous progress in our understanding of the cellular pathways that disrupt the action of leptin and ghrelin. In this Review, we discuss the molecular mechanisms underpinning resistance to leptin and ghrelin and how they can be exploited as targets for pharmacological management of obesity.

EJE PRIZE 2017: Hypothalamic AMPK: a golden target against obesity?

AMP-activated protein kinase (AMPK) is a cellular gauge that is activated under conditions, such as low energy, increasing energy production and reducing energy waste. Centrally, the AMPK pathway is a canonical route regulating energy homeostasis, by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. Current evidence links hypothalamic AMPK with feeding, brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT), as well as muscle metabolism, hepatic function and glucose homeostasis. The relevance of these data is interesting from a therapeutic point of view as several agents with potential anti-obesity and/or antidiabetic effects, some currently in clinical use, such as nicotine, metformin and liraglutide are known to act through AMPK, either peripherally or centrally. Furthermore, the orexigenic and weight-gaining effects of the worldwide use of antipsychotic drugs (APDs), such as olanzapine, are also mediated by hypothalamic AMPK. Overall, this evidence makes hypothalamic AMPK signaling an interesting target for the drug development, with its potential for controlling both sides of the energy balance equation, namely feeding and energy expenditure through defined metabolic pathways.

Hypothalamus and thermogenesis: Heating the BAT, browning the WAT

Brown adipose tissue (BAT) has been also considered as the main thermogenic organ responsible of maintenance body temperature through heat production. However, a new type of thermogenic fat has been characterized during the last years, the beige or brite fat, that is developed from white adipose tissue (WAT) in response to different stimuli by a process known as browning. The activities of brown and beige adipocytes ameliorate metabolic disease, including obesity in mice and correlate with leanness in humans. Many genes and pathways that regulate brown and beige adipocyte biology have now been identified, providing a variety of promising therapeutic targets for metabolic disease. The hypothalamus is the main central place orchestrating the outflow signals that drive the sympathetic nerve activity to BAT and WAT, controlling heat production and energy homeostasis. Recent data have revealed new hypothalamic molecular mechanisms, such as hypothalamic AMP-activated protein kinase (AMPK), that control both thermogenesis and browning. This review provides an overview of the factors influencing BAT and WAT thermogenesis, with special focus on the integration of peripheral information on hypothalamic circuits controlling thermoregulation.

Hypothalamic kappa opioid receptor mediates both diet-induced and melanin concentrating hormone-induced liver damage through inflammation and endoplasmic reticulum stress

The opioid system is widely known to modulate the brain reward system and thus affect the behavior of humans and other animals, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors overexpressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. Endoplasmic reticulum (ER) stress was inhibited by pharmacological (tauroursodeoxycholic acid) and genetic (overexpression of the chaperone glucose-regulated protein 78 kDa) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and western blot. We show that in the LHA κOR directly controls hepatic lipid metabolism through the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor 1 (MCH-R1) in the LHA, and genetic disruption of κOR reduced melanin concentrating hormone-induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline-deficient, diet-induced and choline-deficient, high-fat diet-induced ER stress, inflammation, steatohepatitis, and fibrosis, whereas overexpression of κOR in this area promoted liver steatosis. Overexpression of glucose-regulated protein 78 kDa in the liver abolished hypothalamic κOR-induced steatosis by reducing hepatic ER stress.

CONCLUSIONS

This study reveals a novel hypothalamic-parasympathetic circuit modulating hepatic function through inflammation and ER stress independent of changes in food intake or body weight; these findings might have implications for the clinical use of opioid receptor antagonists. (Hepatology 2016;64:1086-1104).

Relationship among stress, depression, cardiovascular and metabolic changes and physical exercise

Abstract Introduction: Stress is considered one of the most significant health problems in modern society. It can be characterized as any changes in the homeostasis of an individual that require an adaptive response. An imbalance in the secretion of the primary stress mediators may be responsible for the onset and development of several diseases. Thus, chronic stress has been recognized as a risk factor for depression as well as cardiovascular and metabolic diseases. Given the pathophysiological mechanisms associated with chronic stress and related cardiovascular and metabolic changes, it is necessary to implement measures to prevent, control and/or avoid their development. Physical exercise is a non-pharmacological resource that is widely used for this purpose. Its beneficial effects include the improvement of the emotional state as well as lipid and glycemic control. Objective: The aim of this review is to discuss the relationship between stress, depression, cardiovascular and metabolic changes, and highlight the importance of physical exercise in the prevention and treatment of resulting disorders. Materials and Methods: We searched MEDLINE and SCIELO from 2000 through 2012, using the terms chronic stress, mood disorders, depression, cardiovascular and metabolic changes, and exercise. Results: Most of the studies found in our literature search have shown that exercise can attenuate and/or reverse the deleterious effects of chronic stress. Conclusion: Regular physical exercise is useful for maintaining health, especially with respect to improving mood and mental stress.

Hypothalamic-autonomic control of energy homeostasis

Regulation of energy homeostasis is tightly controlled by the central nervous system (CNS). Several key areas such as the hypothalamus and brainstem receive and integrate signals conveying energy status from the periphery, such as leptin, thyroid hormones, and insulin, ultimately leading to modulation of food intake, energy expenditure (EE), and peripheral metabolism. The autonomic nervous system (ANS) plays a key role in the response to such signals, innervating peripheral metabolic tissues, including brown and white adipose tissue (BAT and WAT), liver, pancreas, and skeletal muscle. The ANS consists of two parts, the sympathetic and parasympathetic nervous systems (SNS and PSNS). The SNS regulates BAT thermogenesis and EE, controlled by central areas such as the preoptic area (POA) and the ventromedial, dorsomedial, and arcuate hypothalamic nuclei (VMH, DMH, and ARC). The SNS also regulates lipid metabolism in WAT, controlled by the lateral hypothalamic area (LHA), VMH, and ARC. Control of hepatic glucose production and pancreatic insulin secretion also involves the LHA, VMH, and ARC as well as the dorsal vagal complex (DVC), via splanchnic sympathetic and the vagal parasympathetic nerves. Muscle glucose uptake is also controlled by the SNS via hypothalamic nuclei such as the VMH. There is recent evidence of novel pathways connecting the CNS and ANS. These include the hypothalamic AMP-activated protein kinase-SNS-BAT axis which has been demonstrated to be a key modulator of thermogenesis. In this review, we summarize current knowledge of the role of the ANS in the modulation of energy balance.

Estrogens and the control of energy homeostasis: a brain perspective

Despite their prominent roles in the control of reproduction, estrogens pervade many other bodily functions. Key metabolic pathways display marked sexual differences, and estrogens are potent modulators of energy balance, as evidenced in extreme conditions of estrogen deficiency characterized by hyperphagia and decreased energy expenditure, and leading to obesity. Compelling evidence has recently demonstrated that, in addition to their peripheral effects, the actions of estrogens on energy homeostasis are exerted at central levels, to regulate almost every key aspect of metabolic homeostasis, from feeding to energy expenditure, to glucose and lipid metabolism. We review herein the state-of-the-art of the role of estrogens in the regulation of energy balance, with a focus on their central effects and modes of action.

Pregnancy induces resistance to the anorectic effect of hypothalamic malonyl-CoA and the thermogenic effect of hypothalamic AMPK inhibition in female rats

During gestation, hyperphagia is necessary to cope with the metabolic demands of embryonic development. There were three main aims of this study: Firstly, to investigate the effect of pregnancy on hypothalamic fatty acid metabolism, a key pathway for the regulation of energy balance; secondly, to study whether pregnancy induces resistance to the anorectic effect of fatty acid synthase (FAS) inhibition and accumulation of malonyl-coenzyme A (CoA) in the hypothalamus; and, thirdly, to study whether changes in hypothalamic AMPK signaling are associated with brown adipose tissue (BAT) thermogenesis during pregnancy. Our data suggest that in pregnant rats, the hypothalamic fatty acid pathway shows an overall state that should lead to anorexia and elevated BAT thermogenesis: decreased activities of AMP-activated protein kinase (AMPK), FAS, and carnitine palmitoyltransferase 1, coupled with increased acetyl-CoA carboxylase function with subsequent elevation of malonyl-CoA levels. This profile seems dependent of estradiol levels but not prolactin or progesterone. Despite the apparent anorexic and thermogenic signaling in the hypothalamus, pregnant rats remain hyperphagic and display reduced temperature and BAT function. Actually, pregnant rats develop resistance to the anorectic effects of central FAS inhibition, which is associated with a reduction of proopiomelanocortin (POMC) expression and its transcription factors phospho-signal transducer and activator of transcription 3, and phospho-forkhead box O1. This evidence demonstrates that pregnancy induces a state of resistance to the anorectic and thermogenic actions of hypothalamic cellular signals of energy surplus, which, in parallel to the already known refractoriness to leptin effects, likely contributes to gestational hyperphagia and adiposity.

Central ceramide-induced hypothalamic lipotoxicity and ER stress regulate energy balance

Hypothalamic endoplasmic reticulum (ER) stress is a key mechanism leading to obesity. Here, we demonstrate that ceramides induce lipotoxicity and hypothalamic ER stress, leading to sympathetic inhibition, reduced brown adipose tissue (BAT) thermogenesis, and weight gain. Genetic overexpression of the chaperone GRP78/BiP (glucose-regulated protein 78 kDa/binding immunoglobulin protein) in the ventromedial nucleus of the hypothalamus (VMH) abolishes ceramide action by reducing hypothalamic ER stress and increasing BAT thermogenesis, which leads to weight loss and improved glucose homeostasis. The pathophysiological relevance of this mechanism is demonstrated in obese Zucker rats, which show increased hypothalamic ceramide levels and ER stress. Overexpression of GRP78 in the VMH of these animals reduced body weight by increasing BAT thermogenesis as well as decreasing leptin and insulin resistance and hepatic steatosis. Overall, these data identify a triangulated signaling network involving central ceramides, hypothalamic lipotoxicity/ER stress, and BAT thermogenesis as a pathophysiological mechanism of obesity.

Nicotine improves obesity and hepatic steatosis and ER stress in diet-induced obese male rats

Nicotine, the main addictive component of tobacco, promotes body weight reduction in humans and rodents. Recent evidence has suggested that nicotine acts in the central nervous system to modulate energy balance. Specifically, nicotine modulates hypothalamic AMP-activated protein kinase to decrease feeding and to increase brown adipose tissue thermogenesis through the sympathetic nervous system, leading to weight loss. Of note, most of this evidence has been obtained in animal models fed with normal diet or low-fat diet (LFD). However, its effectiveness in obese models remains elusive. Because obesity causes resistance towards many factors involved in energy homeostasis, the aim of this study has been to compare the effect of nicotine in a diet-induced obese (DIO) model, namely rats fed a high-fat diet, with rats fed a LFD. Our data show that chronic peripheral nicotine treatment reduced body weight by decreasing food intake and increasing brown adipose tissue thermogenesis in both LFD and DIO rats. This overall negative energy balance was associated to decreased activation of hypothalamic AMP-activated protein kinase in both models. Furthermore, nicotine improved serum lipid profile, decreased insulin serum levels, as well as reduced steatosis, inflammation, and endoplasmic reticulum stress in the liver of DIO rats but not in LFD rats. Overall, this evidence suggests that nicotine diminishes body weight and improves metabolic disorders linked to DIO and might offer a clear-cut strategy to develop new therapeutic approaches against obesity and its metabolic complications.