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

Neurobiological mechanisms of nicotine's effects on feeding and body weight

Nicotine, a neuroactive substance in tobacco products, has been widely studied for its effects on feeding and body weight, mostly focusing on the involvement of nervous system, metabolism, hormones, and gut microbiota. To elucidate the action mechanism of nicotine on feeding and body weight, especially the underlying neurobiological mechanisms, we reviewed the studies on nicotine's effects on feeding and body weight by the regulation of various nerve systems, energy expenditure, peripheral hormones, gut microbiota, etc. The role of neuronal signaling molecules such as AMP-activated protein kinase (AMPK) and kappa opioid receptor (κOR) were specialized in the nicotine-regulating energy expenditure. The energy homeostasis-related neurons, pro-opiomelanocortin (POMC), agouti-related peptide (AgRP), prolactin-releasing hormone (Prlh), etc, were discussed about the responsibility for nicotine's effects on feeding. Nicotine's actions on hypothalamus and its related neural circuits were described in view of peripheral nervous system, reward system, adipose browning, hormone secretion, and gut-brain axis. Elucidation of neurobiological mechanism of nicotine's actions on feeding and body weight will be of immense value to the therapeutic strategies of smoking, and advance the medicine research for the therapy of obesity.

Opposing effects of nicotine on hypothalamic arcuate nucleus POMC and NPY neurons

The hypothalamic arcuate nucleus (ARC) contains two main populations of neurons essential for energy homeostasis: neuropeptide Y (NPY) neurons, which are orexigenic and stimulate food intake, and proopiomelanocortin (POMC) neurons, which have an anorexigenic effect. Located near the blood-brain barrier, ARC neurons sense blood-borne signals such as leptin, insulin, and glucose. Exogenous substances, such as nicotine, can also alter ARC neuron activity and energy balance. Nicotine, an addictive drug used worldwide, inhibits appetite, and reduces body weight, although its mechanisms in regulating ARC neurons are not well understood. Using electrophysiological techniques in brain slices, we investigated the effects of nicotine on POMC and NPY neurons at physiological glucose concentrations. We found that nicotine increased the firing rate of POMC and inhibited NPY neurons. Additionally, nicotine-enhanced glutamatergic inputs to POMC cells and GABAergic inputs to NPY neurons, mediated by α7 and α4β2 nicotinic acetylcholine receptors (nAChRs), respectively. These findings can contribute to the understanding of the anorexigenic effects of nicotine in smokers.

Exploring the potential of selenium nanoparticles and fabricated selenium nanoparticles @vitamin C nanocomposite in mitigating nicotine-induced testicular toxicity in rats

Background

The tobacco epidemic signifies a major public health threat. Nicotine (NIC), a major active constituent in tobacco, impedes male fertility and semen quality. This work is implemented to explore the potential of selenium nanoparticles (SeNPs) and the newly fabricated SeNPs @vitamin C (SeNPs@VITC) nanocomposite in mitigating testicular toxicity induced by NIC.

Materials and methods

The six groups of 48 adult Wistar rats were designed as follows: the control group injected intraperitoneally with normal saline, the SeNPs group treated orally with 2 mg/kg of SeNPs, the SeNPs@VITC nanocomposite group treated orally with 2 mg/kg of SeNPs@VITC nanocomposite, the NIC group injected intraperitoneally with 1.25 mL/kg of NIC, the NIC+ SeNPs group received SeNPs plus NIC, and the NIC+ SeNPs@VITC nanocomposite group received SeNPs@VITC nanocomposite plus NIC. Treatments were administered over a 28-day period.

Results

NIC treatment significantly caused poor sperm quality, decreased serum testosterone, increased follicle-stimulating hormone (FSH), luteinizing hormone (LH) concentrations, reduced hemoglobin levels, leukocytosis, disrupted testicular oxidant/antioxidant balance, and disorganized testicular structure. The construction of the novel SeNPs@VITC nanocomposite, compared to NIC plus SeNPs alone, demonstrated a more potent ameliorative effect on NIC-induced reproductive toxicity in adult rats. The SeNPs@VITC nanocomposite significantly increased sperm count, reduced the percentage of sperm head abnormalities, lowered both serum FSH and LH concentrations, and improved the hemoglobin response.

Conclusions

Both SeNPs and SeNPs@VITC nanocomposite alleviated the testicular toxicity induced by NIC, but the SeNPs@VITC nanocomposite exhibited superior efficacy. The SeNPs@VITC nanocomposite could be employed to advance enhanced therapeutic strategies for addressing male infertility.

Association Between the Serum Copper Levels and Environmental Tobacco Exposure on the Risk of Overweight and Obesity in Children: a Study Based on the National Health and Nutrition Examination Survey

This study was to assess the individual effects of serum copper levels and environmental tobacco exposure and their joint effects on the risk of overweight and obesity among children and adolescents of 6 to 19 year olds. We analyzed cross-sectional data from 1849 children and adolescents participating in the National Health and Nutrition Examination Survey (NHANES) collected between 2011 and 2016. Environmental tobacco exposure was determined by cotinine levels. The serum copper level was divided into < median group and ≥ median groups according to the median of 109.81 µg/dL. The outcome was overweight/obese in children and adolescents. Weighted multinomial multivariate logistic regression models were used to assess the association of serum copper and cotinine levels, with the risk of overweight/obesity, and the joint effects on the risk of overweight and obesity among children and adolescents. The subgroup analyses based on age, gender, and household smoking status were conducted. Among 1849 children and adolescents, 332 children and adolescents had overweight BMI, and 450 children and adolescents had obese BMI. Higher serum copper levels were associated with the risk of obesity in children and adolescents (odds ratio (OR) 2.96, 95% confidence interval (CI) 1.39-6.31, P = 0.006). A positive association between increasing levels of cotinine levels and the risk of overweight (OR 1.83, 95% CI 1.16-2.87, P = 0.010) and obesity (OR 2.56, 95% CI 1.03-6.40, P = 0.044) in children and adolescents was observed. A remarkable association was found between higher serum copper in combination with higher cotinine levels and the risk of overweight (OR 3.23, 95% CI 1.19-8.83, P = 0.023) and obesity (OR 8.76, 95% CI 2.14-35.87, P = 0.003) in children and adolescents. The subgroup analyses revealed positive associations between high serum copper levels in combination with high cotinine levels and overweight and obesity in children and adolescents aged ≥ 12 years, of female sex, and without smoking family members. There may exist a joint effect of serum copper levels and environmental tobacco exposure on overweight/obesity among children and adolescents. These findings offer an insight that early weight control and reduction of tobacco exposure and the detection of serum copper levels may be important in reducing the risk of obesity in children.

Lead-induced liver fibrosis and inflammation in mice by the AMPK/MAPKs/NF-κB and STAT3/TGF-β1/Smad2/3 pathways: the role of Isochlorogenic acid a

Lead (Pb) is a nonessential heavy metal, which can cause many health problems. Isochlorogenic acid A (ICAA), a phenolic acid present in tea, fruits, vegetables, coffee, plant-based food products, and various medicinal plants, exerts multiple effects, including anti-oxidant, antiviral, anti-inflammatory and antifibrotic functions. Thus, the purpose of our study was to determine if ICAA could prevent Pb-induced hepatotoxicity in ICR mice. An evaluation was performed on oxidative stress, inflammation and fibrosis, and related signaling. The results indicate that ICAA attenuates Pb-induced abnormal liver function. ICAA reduced liver fibrosis, inflammation and oxidative stress caused by Pb. ICAA abated Pb-induced fibrosis and decreased inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-alpha (TNF-α). ICAA abrogated reductions in activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Masson staining revealed that ICAA reduced collagen fiber deposition in Pb-induced fibrotic livers. Western blot and immunohistochemistry analyses showed ICAA increased phosphorylated AMP-activated protein kinase (p-AMPK) expression. ICAA also reduced the expression of collagen I, α-smooth muscle actin (α-SMA), phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated c-jun N-terminal kinase (p-JNK), p-p38, phosphorylated signal transducer and phosphorylated activator of transcription 3 (p-STAT3), transforming growth factor β1 (TGF-β1), and p-Smad2/3 in livers of mice. Overall, ICAA ameliorates Pb-induced hepatitis and fibrosis by inhibiting the AMPK/MAPKs/NF-κB and STAT3/TGF-β1/Smad2/3 pathways.

Preventive effects of caffeine on nicotine plus high-fat diet-induced hepatic steatosis and gain weight: a possible explanation for why obese smokers with high coffee consumption tend to be leaner

Non-alcoholic fatty liver disease (NAFLD) is a prevalent liver disorder, affecting approximately 25 % of the population. Coffee-drinking obese smokers exhibit lower body weights and decreased NAFLD rates, but the reasons behind this remain unclear. Additionally, the effect of nicotine, the main component of tobacco, on the development of NAFLD is still controversial. Our study aimed to explore the possible reasons that drinking coffee could alleviate NAFLD and gain weight and identify the real role of nicotine in NAFLD of obese smokers. A NAFLD model in mice was induced by administering nicotine and a high-fat diet (HFD). We recorded changes in body weight and daily food intake, measured the weights of the liver and visceral fat, and observed liver and adipose tissue histopathology. Lipid levels, liver function, liver malondialdehyde (MDA), superoxide dismutase (SOD), serum inflammatory cytokine levels and the expression of hepatic genes involved in lipid metabolism were determined. Our results demonstrated that nicotine exacerbated the development of NAFLD and caffeine had a hepatoprotective effect on NAFLD. The administration of caffeine could ameliorate nicotine-plus-HFD-induced NAFLD by reducing lipid accumulation, regulating hepatic lipid metabolism, alleviating oxidative stress, attenuating inflammatory response and restoring hepatic functions. These results might explain why obese smokers with high coffee consumption exhibit the lower incidence rate of NAFLD and tend to be leaner. It is essential to emphasise that the detrimental impact of smoking on health is multifaceted. Smoking cessation remains the sole practical and effective strategy for averting the tobacco-related complications and reducing the risk of mortality.

Phytochemicals derived from Nicotiana tabacum L. plant contribute to pharmaceutical development

The Nicotiana tabacum L. plant, a medicinal resource, holds significant potential for benefiting human health, as evidenced by its use in Native American and ancient Chinese cultures. Modern medical and pharmaceutical studies have investigated that the abundant and distinctive function metabolites in tobacco including nicotine, solanesol, cembranoid diterpenes, essential oil, seed oil and other tobacco extracts, avoiding the toxic components of smoke, mainly have the anti-oxidation, anti-lipid production, pro-lipid oxidation, pro-insulin sensitivity, anti-inflammation, anti-apoptosis and antimicrobial activities. They showed potential pharmaceutical value mainly as supplements or substitutes for treating neurodegenerative diseases including Alzheimer's and Parkinson's disease, inflammatory diseases including colitis, arthritis, sepsis, multiple sclerosis, and myocarditis, and metabolic syndrome including Obesity and fatty liver. This review comprehensively presents the research status and the molecular mechanisms of tobacco and its metabolites basing on almost all the English and Chinese literature in recent 20 years in the field of medicine and pharmacology. This review serves as a foundation for future research on the medicinal potential of tobacco plants.

Acute nicotine intake increases feeding behavior through decreasing glucagon signaling in dependent male and female rats

Chronic use of nicotine is known to dysregulate metabolic signaling through altering circulating levels of feeding-related hormones, contributing to the onset of disorders like type 2 diabetes. However, little is known about the acute effects of nicotine on hormonal signaling. We previously identified an acute increase in food intake following acute nicotine, and we sought to determine whether this behavior was due to a change in hormone levels. We first identified that acute nicotine injection produces an increase in feeding behavior in dependent rats, but not nondependent rats. We confirmed that chronic nicotine use increases circulating levels of insulin, leptin, and ghrelin, and these correlate with rats' body weight and food intake. Acute nicotine injection in dependent animals decreased circulating GLP-1 and glucagon levels, and administration of glucagon prior to acute nicotine injection prevented the acute increase in feeding behavior. Thus, acute nicotine injection increases feeding behavior in dependent rats by decreasing glucagon signaling.

The health benefits of dietary short-chain fatty acids in metabolic diseases

Short-chain fatty acids (SCFAs) are a subset of fatty acids that play crucial roles in maintaining normal physiology and developing metabolic diseases, such as obesity, diabetes, cardiovascular disease, and liver disease. Even though dairy products and vegetable oils are the direct dietary sources of SCFAs, their quantities are highly restricted. SCFAs are produced indirectly through microbial fermentation of fibers. The biological roles of SCFAs in human health and metabolic diseases are mainly due to their receptors, GPR41 and GPR43, FFAR2 and FFAR3. Additionally, it has been demonstrated that SCFAs modulate DNMTs and HDAC activities, inhibit NF-κB-STAT signaling, and regulate G(i/o)βγ-PLC-PKC-PTEN signaling and PPARγ-UCP2-AMPK autophagic signaling, thus mitigating metabolic diseases. Recent studies have uncovered that SCFAs play crucial roles in epigenetic modifications of DNAs, RNAs, and post-translational modifications of proteins, which are critical regulators of metabolic health and diseases. At the same time, dietary recommendations for the purpose of SCFAs have been proposed. The objective of the review is to summarize the most recent research on the role of dietary SCFAs in metabolic diseases, especially the signal transduction of SCFAs in metabolic diseases and their functional efficacy in different backgrounds and models of metabolic diseases, at the same time, to provide dietary and nutritional recommendations for using SCFAs as food ingredients to prevent metabolic diseases.

Neonatal nicotine exposure affects adult rat hepatic pathways involved in endoplasmic reticulum stress and macroautophagy in a sex-dependent manner

Nonalcoholic fatty liver disease (NAFLD) involves changes in hepatic pathways, as lipogenesis, oxidative stress, endoplasmic reticulum (ER) stress, and macroautophagy. Maternal nicotine exposure exclusively during lactation leads to fatty liver (steatosis) only in the adult male offspring, not in females. Therefore, our hypothesis is that neonatal exposure to nicotine sex-dependently affects the signaling pathways involved in hepatic homeostasis of the offspring, explaining the hepatic lipid accumulation phenotype only in males. For this, between postnatal days 2 and 16, Wistar rat dams were implanted with osmotic minipumps, which released nicotine (NIC; 6 mg/Kg/day) or vehicle. The livers of offspring were evaluated at postnatal day 180. Only the male offspring that had been exposed to nicotine neonatally showed increased protein expression of markers of unfolded protein response (UPR), highlighting the presence of ER stress, as well as disruption of the activation of the macroautophagy repair pathway. These animals also had increased expression of diacylglycerol O-acyltransferase 1 and 4-hydroxynonenal, suggesting increased triglyceride esterification and oxidative stress. These parameters were not altered in the female offspring that had been neonatally exposed to nicotine, however they exhibited increased phospho adenosine monophosphate-activated protein kinase pAMPK expression, possibly as a protective mechanism. Thus, the disturbance in the hepatic homeostasis by UPR, macroautophagy, and oxidative stress modifications seem to be the molecular mechanisms underlying the liver steatosis in the adult male offspring of the nicotine-programming model. This highlights the importance of maternal smoking cessation during breastfeeding to decrease the risk of NAFLD development, especially in males.

Central and peripheral actions of nicotine that influence blood glucose homeostasis and the development of diabetes

Cigarette smoking has long been recognized as a risk factor for type 2 diabetes (T2D), although the precise causal mechanisms underlying this relationship remain poorly understood. Recent evidence suggests that nicotine, the primary reinforcing component in tobacco, may play a pivotal role in connecting cigarette smoking and T2D. Extensive research conducted in both humans and animals has demonstrated that nicotine can elevate blood glucose levels, disrupt glucose homeostasis, and induce insulin resistance. The review aims to elucidate the genetic variants of nicotinic acetylcholine receptors associated with diabetes risk and provide a comprehensive overview of the available data on the mechanisms through which nicotine influences blood glucose homeostasis and the development of diabetes. Here we emphasize the central and peripheral actions of nicotine on the release of glucoregulatory hormones, as well as its effects on glucose tolerance and insulin sensitivity. Notably, the central actions of nicotine within the brain, which encompass both insulin-dependent and independent mechanisms, are highlighted as potential targets for intervention strategies in diabetes management.

The controversial effect of smoking and nicotine in SARS-CoV-2 infection

The effects of nicotine and cigarette smoke in many diseases, notably COVID-19 infection, are being debated more frequently. The current basic data for COVID-19 is increasing and indicating the higher risk of COVID-19 infections in smokers due to the overexpression of corresponding host receptors to viral entry. However, current multi-national epidemiological reports indicate a lower incidence of COVID-19 disease in smokers. Current data indicates that smokers are more susceptible to some diseases and more protective of some other. Interestingly, nicotine is also reported to play a dual role, being both inflammatory and anti-inflammatory. In the present study, we tried to investigate the effect of pure nicotine on various cells involved in COVID-19 infection. We followed an organ-based systematic approach to decipher the effect of nicotine in damaged organs corresponding to COVID-19 pathogenesis (12 related diseases). Considering that the effects of nicotine and cigarette smoke are different from each other, it is necessary to be careful in generalizing the effects of nicotine and cigarette to each other in the conducted researches. The generalization and the undifferentiation of nicotine from smoke is a significant bias. Moreover, different doses of nicotine stimulate different effects (dose-dependent response). In addition to further assessing the role of nicotine in COVID-19 infection and any other cases, a clever assessment of underlying diseases should also be considered to achieve a guideline for health providers and a personalized approach to treatment.

The importance of estradiol for body weight regulation in women

Obesity in women of reproductive age has a number of adverse metabolic effects, including Type II Diabetes (T2D), dyslipidemia, and cardiovascular disease. It is associated with increased menstrual irregularity, ovulatory dysfunction, development of insulin resistance and infertility. In women, estradiol is not only critical for reproductive function, but they also control food intake and energy expenditure. Food intake is known to change during the menstrual cycle in humans. This change in food intake is largely mediated by estradiol, which acts directly upon anorexigenic and orexigenic neurons, largely in the hypothalamus. Estradiol also acts indirectly with peripheral mediators such as glucagon like peptide-1 (GLP-1). Like estradiol, GLP-1 acts on receptors at the hypothalamus. This review describes the physiological and pathophysiological mechanisms governing the actions of estradiol during the menstrual cycle on food intake and energy expenditure and how estradiol acts with other weight-controlling molecules such as GLP-1. GLP-1 analogs have proven to be effective both to manage obesity and T2D in women. This review also highlights the relationship between steroid hormones and women's mental health. It explains how a decline or imbalance in estradiol levels affects insulin sensitivity in the brain. This can cause cerebral insulin resistance, which contributes to the development of conditions such as Parkinson's or Alzheimer's disease. The proper use of both estradiol and GLP-1 analogs can help to manage obesity and preserve an optimal mental health in women by reducing the mechanisms that trigger neurodegenerative disorders.

Treat more than heat-New therapeutic implications of Cimicifuga racemosa through AMPK-dependent metabolic effects

BACKGROUND

Cimicifuga racemosa extracts (CRE) have obtained a "well-established use status" in the treatment of postmenopausal (i.e., climacteric) complaints, which predominantly include vasomotor symptoms such as hot flushes and sweating, as well as nervousness, irritability, and metabolic changes. Although characteristic postmenopausal complaints are known for a very long time and the beneficial effects of CRE on climacteric symptoms are well accepted, both the pathophysiology of postmenopausal symptoms and the mechanism of action of CREs are not yet fully understood. In particular, current hypotheses suggest that changes in the α-adrenergic and serotonergic signaling pathways secondary to estrogen depletion are responsible for the development of hot flushes.

PURPOSE

Some of the symptoms associated with menopause cannot be explained by these hypotheses. Therefore, we attempted to extend our classic understanding of menopause by integrating of partly age-related metabolic impairments.

METHODS

A comprehensive literature survey was performed using the PubMed database for articles published through September 2021. The following search terms were used: (cimicifuga OR AMPK) AND (hot flush* OR hot flash* OR menopaus* OR osteoporos* OR cancer OR antioxida* OR cardiovasc*). No limits were set with respect to language, and the references cited in the articles retrieved were used to identify additional publications.

RESULTS

We found that menopause is a manifestation of the general aging process, with specific metabolic changes that aggravate menopausal symptoms, which are accelerated by estrogen depletion and associated neurotransmitter dysregulation. Cimicifuga extracts with their metabolic effects mitigate climacteric symptoms but may also modulate the aging process itself. Central to these effects are effects of CRE on the metabolic key regulator, the AMP-activated protein kinase (AMPK).

CONCLUSIONS

As an extension of this effect dimension, other off-label indications may appear attractive in the sense of repurposing of this herbal treatment.

Nicotine in Inflammatory Diseases: Anti-Inflammatory and Pro-Inflammatory Effects

As an anti-inflammatory alkaloid, nicotine plays dual roles in treating diseases. Here we reviewed the anti-inflammatory and pro-inflammatory effects of nicotine on inflammatory diseases, including inflammatory bowel disease, arthritis, multiple sclerosis, sepsis, endotoxemia, myocarditis, oral/skin/muscle inflammation, etc., mainly concerning the administration methods, different models, therapeutic concentration and duration, and relevant organs and tissues. According to the data analysis from recent studies in the past 20 years, nicotine exerts much more anti-inflammatory effects than pro-inflammatory ones, especially in ulcerative colitis, arthritis, sepsis, and endotoxemia. On the other hand, in oral inflammation, nicotine promotes and aggravates some diseases such as periodontitis and gingivitis, especially when there are harmful microorganisms in the oral cavity. We also carefully analyzed the nicotine dosage to determine its safe and effective range. Furthermore, we summarized the molecular mechanism of nicotine in these inflammatory diseases through regulating immune cells, immune factors, and the vagus and acetylcholinergic anti-inflammatory pathways. By balancing the “beneficial” and “harmful” effects of nicotine, it is meaningful to explore the effective medical value of nicotine and open up new horizons for remedying acute and chronic inflammation in humans.

ER stress in obesity pathogenesis and management

Given the unprecedented global pandemic of obesity, a better understanding of the etiology of adiposity will be necessary to ensure effective management of obesity and related complications. Among the various potential factors contributing to obesity, endoplasmic reticulum (ER) stress refers to a state of excessive protein unfolding or misfolding that is commonly found in metabolic diseases including diabetes mellitus, insulin resistance (IR), and non-alcoholic fatty liver disease, although its role in obesogenesis remains controversial. ER stress is thought to drive adiposity by dampening energy expenditure, making ER stress a likely therapeutic target for the management of obesity. We summarize the role of ER stress and the ER stress response in the onset and development of obesity, and discuss the underlying mechanisms involved with a view to identifying novel therapeutic strategies for obesity prevention and management.

A mouse model of weight gain after nicotine withdrawal

Smoking cessation increases body weight. The underlying mechanisms, however, have not been fully understood. We here report an establishment of a mouse model that exhibits an augmented body weight gain after nicotine withdrawal. High fat diet-fed mice were infused with nicotine for two weeks, and then with vehicle for another two weeks using osmotic minipumps. Body weight increased immediately after nicotine cessation and was significantly higher than that of mice continued on nicotine. Mice switched to vehicle consumed more food than nicotine-continued mice during the first week of cessation, while oxygen consumption was comparable. Elevated expression of orexigenic agouti-related peptide was observed in the hypothalamic appetite center. Pair-feeding experiment revealed that the accelerated weight gain after nicotine withdrawal is explained by enhanced energy intake. As a showcase of an efficacy of pharmacologic intervention, exendin-4 was administered and showed a potent suppression of energy intake and weight gain in mice withdrawn from nicotine. Our current model provides a unique platform for the investigation of the changes of energy regulation after smoking cessation.

Critical roles of FTO-mediated mRNA m6A demethylation in regulating adipogenesis and lipid metabolism: Implications in lipid metabolic disorders

The goal this review is to clarify the effects of the fat mass and obesity-associated protein (FTO) in lipid metabolism regulation and related underlying mechanisms through the FTO-mediated demethylation of m⁶A modification. FTO catalyzes the demethylation of m⁶A to alter the processing, maturation and translation of the mRNAs of lipid-related genes. FTO overexpression in the liver promotes lipogenesis and lipid droplet (LD) enlargement and suppresses CPT-1–mediated fatty acid oxidation via the SREBP1c pathway, promoting excessive lipid storage and nonalcoholic fatty liver diseases (NAFLD). FTO enhances preadipocyte differentiation through the C/EBPβ pathway, and facilitates adipogenesis and fat deposition by altering the alternative splicing of RUNX1T1, the expression of PPARγ and ANGPTL4, and the phosphorylation of PLIN1, whereas it inhibits lipolysis by inhibiting IRX3 expression and the leptin pathway, causing the occurrence and development of obesity. Suppression of the PPARβ/δ and AMPK pathways by FTO-mediated m⁶A demethylation damages lipid utilization in skeletal muscles, leading to the occurrence of diabetic hyperlipidemia. m⁶A demethylation by FTO inhibits macrophage lipid influx by downregulating PPARγ protein expression and accelerates cholesterol efflux by phosphorylating AMPK, thereby impeding foam cell formation and atherosclerosis development. In summary, FTO-mediated m⁶A demethylation modulates the expression of lipid-related genes to regulate lipid metabolism and lipid disorder diseases.

Medium chain triglycerides improve lipid metabolism in obese rats by increasing the browning of adipose tissue through the sympathetic regulation

This study aimed to determine the mechanism of medium chain triglyceride (MCT) promoting the browning of adipose tissue. High fat diet was fed to the Sprague-Dawley rats to induce obesity,...

Nicotine Improves Survivability, Hypotension, and Impaired Adenosinergic Renal Vasodilations in Endotoxic Rats: Role of α7-nAChRs/HO-1 Pathway

The nicotinic/cholinergic antiinflammatory pathway protects against acute kidney injury and other end-organ damages induced by endotoxemia. In this study, we tested the hypothesis that functional α7-nAChRs/heme oxygenase-1 (HO-1) pathway is imperative for the nicotine counteraction of hemodynamic and renovascular dysfunction caused by acute endotoxemia in rats. Renal vasodilations were induced by cumulative bolus injections of acetylcholine (ACh, 0.01 nmol-7.29 nmol) or ethylcarboxamidoadenosine (NECA, adenosine receptor agonist, 1.6 nmol-100 nmol) in isolated phenylephrine-preconstricted perfused kidneys. The data showed that 6-h treatment with lipopolysaccharide (LPS, 5 mg/kg i.p.) decreased systolic blood pressure and renal vasodilations caused by NECA but not Ach. The endotoxic insult also increased the mortality rate and elevated serum urea and creatinine. These LPS effects were sex-unrelated, except hypotension, and enhanced mortality which were more evident in male rodents, and abrogated after co-administration of nicotine (0.5, 1 mg/kg and 2 mg/kg) in a dose-dependent fashion. The advantageous effects of nicotine on NECA vasodilations, survivability, and kidney biomarkers in endotoxic male rats disappeared upon concurrent exposure to methyllycaconitine citrate (α7-nAChR blocker) or zinc protoporphyrin (HO-1 inhibitor) and were reproduced after treatment with bilirubin, but not hemin (HO-1 inducer) or tricarbonyldichlororuthenium (II) dimer (carbon monoxide-releasing molecule). Together, current biochemical and pharmacological evidence suggests key roles for α7-nAChRs and the bilirubin byproduct of the HO-1 signaling in the nicotine counteraction of renal dysfunction and reduced adenosinergic renal vasodilator capacity in endotoxic rats.

The Role of AMPK Signaling in Brown Adipose Tissue Activation

Obesity is becoming a pandemic, and its prevalence is still increasing. Considering that obesity increases the risk of developing cardiometabolic diseases, research efforts are focusing on new ways to combat obesity. Brown adipose tissue (BAT) has emerged as a possible target to achieve this for its functional role in energy expenditure by means of increasing thermogenesis. An important metabolic sensor and regulator of whole-body energy balance is AMP-activated protein kinase (AMPK), and its role in energy metabolism is evident. This review highlights the mechanisms of BAT activation and investigates how AMPK can be used as a target for BAT activation. We review compounds and other factors that are able to activate AMPK and further discuss the therapeutic use of AMPK in BAT activation. Extensive research shows that AMPK can be activated by a number of different kinases, such as LKB1, CaMKK, but also small molecules, hormones, and metabolic stresses. AMPK is able to activate BAT by inducing adipogenesis, maintaining mitochondrial homeostasis and inducing browning in white adipose tissue. We conclude that, despite encouraging results, many uncertainties should be clarified before AMPK can be posed as a target for anti-obesity treatment via BAT activation.

κ-Opioid Signaling in the Lateral Hypothalamic Area Modulates Nicotine-Induced Negative Energy Balance

Several studies have reported that nicotine, the main bioactive component of tobacco, exerts a marked negative energy balance. Apart from its anorectic action, nicotine also modulates energy expenditure, by regulating brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. These effects are mainly controlled at the central level by modulation of hypothalamic neuropeptide systems and energy sensors, such as AMP-activated protein kinase (AMPK). In this study, we aimed to investigate the kappa opioid receptor (κOR)/dynorphin signaling in the modulation of nicotine’s effects on energy balance. We found that body weight loss after nicotine treatment is associated with a down-regulation of the κOR endogenous ligand dynorphin precursor and with a marked reduction in κOR signaling and the p70 S6 kinase/ribosomal protein S6 (S6K/rpS6) pathway in the lateral hypothalamic area (LHA). The inhibition of these pathways by nicotine was completely blunted in κOR deficient mice, after central pharmacological blockade of κOR, and in rodents where κOR was genetically knocked down specifically in the LHA. Moreover, κOR-mediated nicotine effects on body weight do not depend on orexin. These data unravel a new central regulatory pathway modulating nicotine’s effects on energy balance.

Reprint of: Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Nicotine Causes Nephrotoxicity through the Induction of NLRP6 Inflammasome and Alpha7 Nicotinic Acetylcholine Receptor

Current cigarette smoking is associated with chronic kidney disease (CKD) or death from end-stage renal disease (ESRD). Mainstream cigarette smoke includes over 4000 compounds. Among the compounds present in tobacco smoke, nicotine is one of a large number of biologically stable and active compounds present in tobacco. However, the mechanisms by which nicotine exacerbates kidney disease progression have not been identified. It is known that the inflammasomes constitute an important innate immune pathway and contribute to the pathophysiology of diverse kidney diseases. The relationship between inflammasomes and nicotine-induced kidney damage still remains unclear. In the present study, we studied the mechanisms of nicotine-induced nephrotoxicity. We found that nicotine decreased cell viability and induced reactive oxygen species (ROS) generation in human kidney cells. Furthermore, nicotine significantly increased the expression of the alpha7 nicotinic acetylcholine receptor (α7nAChR). Nicotine activated the NLRP6 inflammasome and induced endoplasmic reticulum (ER) stress. Nicotine caused mild apoptosis and necrosis but triggered significant autophagy in human kidney cells. In addition, nicotine induced the NLRP6 inflammasome and autophagy via α7nAChR. In an animal model, the histological analysis in kidney showed evident changes and injury. The results indicated that α7nAChR, IRE1α, LC3 and NLRP6 expression in kidney sections was markedly increased in the nicotine groups. These findings suggest that nicotine causes kidney damage by modulating α7nAChR, NLRP6 inflammasome, ER stress and autophagy.

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.

Recent Updates on Obesity Treatments: Available Drugs and Future Directions

In the last thirty years, obesity has reached epidemic proportions and is now regarded as a major health issue in contemporary society trending to serious economic and social burdens. The latest projections of the World Health Organization are alarming. By 2030, nearly 60% of the worldwide population could be either obese or overweight, highlighting the needs to find innovative treatments. Currently, bariatric surgery is the most effective way to efficiently lower body mass. Although great improvements in terms of recovery and patient care were made in these surgical procedures, bariatric surgery remains an option for extreme forms of obesity and seems unable to tackle obesity pandemic expansion. Throughout the last century, numerous pharmacological strategies targeting either peripheral or central components of the energy balance regulatory system were designed to reduce body mass, some of them reaching sufficient levels of efficiency and safety. Nevertheless, obesity drug therapy remains quite limited on its effectiveness to actually overcome the obesogenic environment. Thus, innovative unimolecular polypharmacology strategies, able to simultaneously target multiple actors involved in the obesity initiation and expansion, were developed during the last ten years opening a new promising avenue in the pharmacological management of obesity. In this review, we first describe the clinical features of obesity-associated conditions and then focus on the outcomes of currently approved drug therapies for obesity as well as new ones expecting to reach the clinic in the near future.

Opportunities and challenges in the therapeutic activation of human energy expenditure and thermogenesis to manage obesity

The current obesity pandemic results from a physiological imbalance in which energy intake chronically exceeds energy expenditure (EE), and prevention and treatment strategies remain generally ineffective. Approaches designed to increase EE have been informed by decades of experiments in rodent models designed to stimulate adaptive thermogenesis, a long-term increase in metabolism, primarily induced by chronic cold exposure. At the cellular level, thermogenesis is achieved through increased rates of futile cycling, which are observed in several systems, most notably the regulated uncoupling of oxidative phosphorylation from ATP generation by uncoupling protein 1, a tissue-specific protein present in mitochondria of brown adipose tissue (BAT). Physiological activation of BAT and other organ thermogenesis occurs through β-adrenergic receptors (AR), and considerable effort over the past 5 decades has been directed toward developing AR agonists capable of safely achieving a net negative energy balance while avoiding unwanted cardiovascular side effects. Recent discoveries of other BAT futile cycles based on creatine and succinate have provided additional targets. Complicating the current and developing pharmacological-, cold-, and exercise-based methods to increase EE is the emerging evidence for strong physiological drives toward restoring lost weight over the long term. Future studies will need to address technical challenges such as how to accurately measure individual tissue thermogenesis in humans; how to safely activate BAT and other organ thermogenesis; and how to sustain a negative energy balance over many years of treatment.

HYPOTHesizing about central comBAT against obesity

The hypothalamus is a brain region in charge of many vital functions. Among them, BAT thermogenesis represents an essential physiological function to maintain body temperature. In the metabolic context, it has now been established that energy expenditure attributed to BAT function can contribute to the energy balance in a substantial extent. Thus, therapeutic interest in this regard has increased in the last years and some studies have shown that BAT function in humans can make a real contribution to improve diabetes and obesity-associated diseases. Nevertheless, how the hypothalamus controls BAT activity is still not fully understood. Despite the fact that much has been known about the mechanisms that regulate BAT activity in recent years, and that the central regulation of thermogenesis offers a very promising target, many questions remain still unsolved. Among them, the possible human application of knowledge obtained from rodent studies, and drug administration strategies able to specifically target the hypothalamus. Here, we review the current knowledge of homeostatic regulation of BAT, including the molecular insights of brown adipocytes, its central control, and its implication in the development of obesity.

Sodium acetate protects against nicotine-induced excess hepatic lipid in male rats by suppressing xanthine oxidase activity

Fatty liver is the hepatic consequence of chronic insulin resistance (IR) and related syndromes. It is mostly accompanied by inflammatory and oxidative molecules. Increased activity of xanthine oxidase (XO) exerts both inflammatory and oxidative effects and has been implicated in metabolic derangements including non-alcoholic fatty liver disease. Short chain fatty acids (SCFAs) elicit beneficial metabolic alterations in IR and related syndromes. In the present study, we evaluated the preventive effects of a SCFA, acetate, on nicotine-induced dysmetabolism and fatty liver. Twenty-four male Wistar rats (n = 6/group): vehicle-treatment (p.o.), nicotine-treated (1.0 mg/kg; p.o.), sodium acetate-treated (200 mg/kg; p.o.) and nicotine + sodium acetate-treated groups. The treatments lasted for 8 weeks. IR was estimated by oral glucose tolerance test and homeostatic model assessment of IR. Plasma and hepatic free fatty acid, triglyceride (TG), glutathione peroxidase, adenosine deaminase (ADA), XO and uric acid (UA) were measured. Nicotine exposure resulted in reduced body weight, liver weight, visceral adiposity, glycogen content and glycogen synthase activity. Conversely, exposure to nicotine increased fasting plasma glucose, lactate, IR, plasma and hepatic TG, free fatty acid, TG/HDL-cholesterol ratio, lipid peroxidation, liver function enzymes, plasma and hepatic UA, XO and ADA activities. However, plasma and hepatic glucose-6-phosphate dehydrogenase-dependent antioxidant defense was not affected by nicotine. Concomitant treatment with acetate ameliorated nicotine-induced effects. Taken together, these results indicate that nicotine exposure leads to excess deposition of lipid in the liver by enhancing XO activity. The results also imply that acetate confers hepatoprotection and is accompanied by decreased XO activity.

Low-dose nicotine promotes autophagy of cardiomyocytes by upregulating HO-1 expression

Nicotine as a major component of addiction in cigarettes has been reported to play protective roles in some pathological processes. It is reported that activation of the nicotinic acetylcholine receptor also has a cardioprotective effect. Thus, in our study, we investigated the effect and mechanism of nicotine on the autophagy of cardiomyocytes, and whether nicotine protects cardiomyocytes against palmitic acid (PA) injury. The results indicated that low-dose nicotine promoted neonatal mouse cardiac myocytes (NMCMs) autophagy and accelerated autophagic flux while inhibiting NMCMs apoptosis, but high-dose nicotine inhibited autophagy and promoted apoptosis. Moreover, low-dose nicotine upregulated heme oxygenase-1 (HO-1) expression and knocking down HO-1 abolished the effects of nicotine on the autophagy and apoptosis of NMCMs. Methyllycaconitine citrate (α7-nAChR blocker, MLA) inhibited HO-1 expression and the effects of nicotine on autophagy and apoptosis of NMCMs. Furthermore, low-dose nicotine improved the inhibited autophagy and increased apoptosis induced by palmitic acid (PA) in NMCMs and these effects were reversed by knocking down HO-1. In conclusion, our data suggested that low-dose nicotine promoted autophagy and inhibited apoptosis of cardiomyocytes by upregulating HO-1.

Central nicotine induces browning through hypothalamic κ opioid receptor

Increased body weight is a major factor that interferes with smoking cessation. Nicotine, the main bioactive compound in tobacco, has been demonstrated to have an impact on energy balance, since it affects both feeding and energy expenditure at the central level. Among the central actions of nicotine on body weight, much attention has been focused on its effect on brown adipose tissue (BAT) thermogenesis, though its effect on browning of white adipose tissue (WAT) is unclear. Here, we show that nicotine induces the browning of WAT through a central mechanism and that this effect is dependent on the κ opioid receptor (KOR), specifically in the lateral hypothalamic area (LHA). Consistent with these findings, smokers show higher levels of uncoupling protein 1 (UCP1) expression in WAT, which correlates with smoking status. These data demonstrate that central nicotine-induced modulation of WAT browning may be a target against human obesity.

Nicotine reduces food intake and increases energy expenditure in brown adipose tissue. Here the authors show that nicotine also induces white adipose tissue browning via central kappa opioid receptor action.

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.

Inhibition of endoplasmic reticulum stress in high-fat-diet-induced obese C57BL/6 mice: Efficacy of a novel extract from mulberry (Morus alba) leaves fermented with Cordyceps militaris

A few clues about correlation between endoplasmic reticulum (ER) stress and mulberry (Morus alba) leaves were investigated in only the experimental autoimmune myocarditis and streptozotocin-induced diabetes. To investigate whether a novel extract of mulberry leaves fermented with Cordyceps militaris (EMfC) could suppress ER in fatty liver, alterations in the key parameters for ER stress response were measured in high fat diet (HFD)-induced obese C57L/6 mice treated with EMfC for 12 weeks. The area of adipocytes in the liver section were significantly decreased in the HFD+EMfC treated group as compared to the HFD+Vehicle treated group, while their level was higher in HFD+Vehicle treated group than No treated group. The level of the eukaryotic initiation factor 2 alpha (eIF2α) and inositol-requiring enzyme 1 beta (IRE1α) phosphorylation and CCAAT-enhancer-binding protein homologous protein (CHOP) expression were remarkably enhanced in the HFD+Vehicle treated group. However, their levels were restored in the HFD+EMfC treated group, although some differences were detected in the decrease rate. Similar recovery was observed on the ER stress-induced apoptosis. The level of Caspase-3, Bcl-2 and Bax were decreased in the HFD+EMfC and HFD+orlistat (OT) treated group compared to the HFD+Vehicle treated group. The results of the present study therefore provide first evidence that EMfC with the anti-obesity effects can be suppressed ER stress and ER stress-induced apoptosis in the hepatic steatosis of HFD-induced obesity model.

The partial inhibition of hypothalamic IRX3 exacerbates obesity

Background

The Iroquois homeobox 3 (Irx3) gene has been identified as a functional long-range target of obesity-associated variants within the fat mass and obesity-associated protein (FTO) gene. It is highly expressed in the hypothalamus, and both whole-body knockout and hypothalamic restricted abrogation of its expression results in a lean phenotype, which is mostly explained by the resulting increased energy expenditure in the brown adipose tissue. Because of its potential implication in the pathogenesis of obesity, we evaluated the hypothalamic cell distribution of Irx3 and the outcomes of inhibiting its expression in a rodent model of diet-induced obesity.

Methods

Bioinformatics tools were used to evaluate the correlations between hypothalamic Irx3 and neurotransmitters, markers of thermogenesis and obesity related phenotypes. Droplet-sequencing analysis in >20,000 hypothalamic cells was used to explore the types of hypothalamic cells expressing Irx3. Lentivirus was used to inhibit hypothalamic Irx3 and the resulting phenotype was studied.

Findings

IRX3 is expressed predominantly in POMC neurons. Its expression is inhibited during prolonged fasting, as well as when mice are fed a high-fat diet. The partial inhibition of hypothalamic Irx3 using a lentivirus resulted in increased diet-induced body mass gain and adiposity due to increased caloric intake and reduced energy expenditure.

Interpretation

Contrary to the results obtained when lean mice are submitted to complete inhibition of Irx3, partial inhibition of hypothalamic Irx3 in obese mice causes an exacerbation of the obese phenotype. These data suggest that at least some of the Irx3 functions in the hypothalamus are regulated according to a hormetic pattern, and modulation of its expression can be a novel approach to modifying the body's energy-handling regulation.

Fund

Sao Paulo Research Foundation grants 2013/07607-8 (LAV) and 2017/02983-2 (JDJ); NIH grants R01DK083567 (YBK).

SF1-Specific AMPKα1 Deletion Protects Against Diet-Induced Obesity

AMPK is a cellular gauge that is activated under conditions of low energy, increasing energy production and reducing energy waste. Current evidence links hypothalamic AMPK with the central regulation of energy balance. However, it is unclear whether targeting hypothalamic AMPK has beneficial effects in obesity. Here, we show that genetic inhibition of AMPK in the ventromedial nucleus of the hypothalamus (VMH) protects against high-fat diet (HFD)-induced obesity by increasing brown adipose tissue (BAT) thermogenesis and subsequently energy expenditure. Notably, this effect depends upon the AMPKα1 isoform in steroidogenic factor 1 (SF1) neurons of the VMH, since mice bearing selective ablation of AMPKα1 in SF1 neurons display resistance to diet-induced obesity, increased BAT thermogenesis, browning of white adipose tissue, and improved glucose and lipid homeostasis. Overall, our findings point to hypothalamic AMPK in specific neuronal populations as a potential druggable target for the treatment of obesity and associated metabolic disorders.

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 endoplasmic reticulum stress as a key mediator of obesity-induced leptin resistance

Obesity is an epidemic disease that is increasing worldwide and is a major risk factor for many metabolic diseases. However, effective agents for the prevention or treatment of obesity remain limited. Therefore, it is urgent to clarify the pathophysiological mechanisms underlying the development and progression of obesity and exploit potential agents to cure and prevent this disease. According to a recent study series, obesity is associated with the development of endoplasmic reticulum stress and the activation of its stress responses (unfolded protein response) in metabolically active tissues, which contribute to the development of obesity-related insulin and leptin resistance, inflammation and energy imbalance. Hypothalamic endoplasmic reticulum stress is the central mechanism underlying the development of obesity-associated leptin resistance and disruption of energy homeostasis; thus, targeting endoplasmic reticulum stress offers a promising therapeutic strategy for improving leptin sensitivity, increasing energy expenditure and ultimately combating obesity. In this review, we highlight the relationship between and mechanism underlying hypothalamic endoplasmic reticulum stress and obesity-associated leptin resistance and energy imbalance and provide new insight regarding strategies for the treatment of obesity.

Central regulation of energy metabolism by estrogens

BACKGROUND

Estrogenic actions in the brain prevent obesity. Better understanding of the underlying mechanisms may facilitate development of new obesity therapies.

SCOPE OF REVIEW

This review focuses on the critical brain regions that mediate effects of estrogens on food intake and/or energy expenditure, the molecular signals that are involved, and the functional interactions between brain estrogens and other signals modulating metabolism. Body weight regulation by estrogens in male brains will also be discussed.

MAJOR CONCLUSIONS

17β-estradiol acts in the brain to regulate energy homeostasis in both sexes. It can inhibit feeding and stimulate brown adipose tissue thermogenesis. A better understanding of the central actions of 17β-estradiol on energy balance would provide new insight for the development of therapies against obesity in both sexes.

Self-administered nicotine increases fat metabolism and suppresses weight gain in male rats

RATIONALE

The ability of nicotine to suppress body weight is cited as a factor impacting smoking initiation and the failure to quit. Self-administered nicotine in male rats suppresses weight independent of food intake, suggesting that nicotine increases energy expenditure.

OBJECTIVE

The current experiment evaluated the impact of self-administered nicotine on metabolism in rats using indirect calorimetry and body composition analysis.

METHODS

Adult male rats with ad libitum access to powdered standard rodent chow self-administered intravenous infusions of nicotine (60 μg/kg/infusion or saline control) in daily 1-h sessions in the last hour of the light cycle. Indirect calorimetry measured respiratory exchange ratio (RER), energy expenditure, motor activity, and food and water consumption for 22.5 h between select self-administration sessions.

RESULTS

Self-administered nicotine suppressed weight gain and reduced the percent of body fat without altering the percent of lean mass, as measured by Echo MRI. Nicotine reduced RER, indicating increased fat utilization; this effect was observed prior to weight suppression. Moreover, nicotine intake did not affect motor activity or energy expenditure. Daily food intake was not altered by nicotine self-administration; however, a trend in suppression of meal size, a transient suppression of water intake, and an increase in meal frequency was observed.

CONCLUSION

These data provide evidence that self-administered nicotine suppresses body weight via increased fat metabolism, independent of significant changes in feeding, activity, or energy expenditure.

Feeding of tobacco blend or nicotine induced weight loss associated with decreased adipocyte size and increased physical activity in male mice

Although epidemiological data and results from rodent studies support an inverse relationship between nicotine consumption and body weight, the molecular mechanisms are poorly understood. CD-1 mice were fed a basal diet or a basal diet containing low or high dose smokeless tobacco blend or high dose nicotine tartrate for 14 weeks. High dose tobacco blend and nicotine tartrate diets vs. basal diet reduced mouse body weight (16.3% and 19.7%, respectively), epididymal (67.6% and 72.5%, respectively) and brown adipose weight (42% and 38%, respectively), epididymal adipocyte size (46.4% and 41.4%, respectively), and brown adipose tissue lipid droplet abundance, with no elevation of adipose tissue inflammation. High dose tobacco blend and nicotine diets also increased mouse physical activity and decreased respiratory exchange ratio, suggesting that high dose nicotine intake induces adipose tissue triglyceride lipolysis to provide fatty acids as an energy source. Both low and high dose tobacco blend and nicotine diet feeding vs. basal diet increased plasma insulin levels (2.9, 3.6 and 4.3-fold, respectively) and improved blood glucose disposal without affecting insulin sensitivity. Feeding of the high dose tobacco blend or nicotine feeding in mice induces body weight loss likely by increasing physical activity and stimulating adipose tissue triglyceride lipolysis.

Nicotinic acetylcholine receptor α7 subunit improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide; yet, the pathogenesis of the disorder is not completely understood. The nicotinic acetylcholine receptor α7 subunit (α7nAChR) plays an indispensable role in the vagus nerve-regulated cholinergic anti-inflammatory pathway.

METHODS

In the present study, we investigated the key role of α7nAChR in NAFLD development. Male wild-type (WT) and α7nAChR knockout (α7nAChR^-/-) mice were fed a normal chow or a high-fat diet (HFD) for 16weeks to induce NAFLD.

RESULTS

We found that both the mRNA and protein levels of α7nAChR in the liver tissue of NAFLD mice were significantly higher than those in mice fed normal chow. There were no differences in food intake, body weight, hepatic cholesterol and triglyceride contents, and insulin sensitivity between WT and α7nAChR^-/- mice under normal condition. When the WT and α7nAChR^-/- mice were challenged with HFD, the body weight of α7nAChR^-/- mice became higher than that of WT mice. The oxygen consumption and energy expenditure in HFD-fed α7nAChR^-/- mice were significantly lower than that in HFD-fed WT mice. The HFD-fed α7nAChR^-/- mice also showed more aggravated hepatic lipid accumulation, steatosis and oxidative stress than HFD-fed WT mice. Macrophage infiltration; mRNA levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β; and liver fibrosis were significantly accelerated in HFD-fed α7nAChR^-/- mice compared to that in HFD-fed WT mice. In addition, the bolus insulin injection-activated insulin signaling pathway, which was reflected by the phosphorylation of insulin receptor at Tyr1162/Tyr1163 site (p-IR^{Tyr1162/Tyr1163}), insulin receptor substrate-1 at Tyr612 site (p-IRS-1^Tyr612) and Akt at Ser473 (p-Akt^Ser473), was significantly compromised in liver tissues of HFD-fed α7nAChR^-/- mice relative to HFD-fed WT mice. Finally, pharmacologically activation of α7nAChR in HFD-fed mice, with a selective agonist PNU-282987, remarkably ameliorated the hepatic steatosis, inflammatory cell infiltration and fibrosis.

CONCLUSION

In conclusion, our results demonstrate that activation of α7nAChR improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease.

α7-Nicotinic Acetylcholine Receptor Agonist Ameliorates Nicotine Plus High-Fat Diet-Induced Hepatic Steatosis in Male Mice by Inhibiting Oxidative Stress and Stimulating AMPK Signaling

α7-Nicotinic acetylcholine receptor (α7nAChR) agonists confer protection against a wide variety of cytotoxic insults and suppress oxidative stress and apoptosis in various cell systems, including hepatocytes. We recently demonstrated that nicotine, when combined with a high-fat diet (HFD), triggers oxidative stress, activates hepatocyte apoptosis, and exacerbates HFD-induced hepatic steatosis in male mice. This study evaluates whether PNU-282987 (PNU), a specific α7nAChR agonist, is effective in preventing nicotine plus HFD-induced hepatic steatosis. Adult C57BL6 male mice were fed a normal chow diet or HFD with 60% of calories derived from fat and received twice-daily intraperitoneal injections of 0.75 mg/kg body weight (BW) of nicotine, PNU (0.26 mg/kg BW), PNU plus nicotine, or saline for 10 weeks. PNU treatment was effective in attenuating nicotine plus HFD-induced increase in hepatic triglyceride levels, hepatocyte apoptosis, and hepatic steatosis. The preventive effects of PNU on nicotine plus HFD-induced hepatic steatosis were mediated by suppression of oxidative stress and activation of adenosine 5'-monophosphate-activated protein kinase (AMPK) together with inhibition of its downstream target sterol regulatory element binding protein 1c (SREBP1c), fatty acid synthase (FAS), and acetyl-coenzyme A-carboxylase (ACC). We conclude that the α7nAChR agonist PNU protects against nicotine plus HFD-induced hepatic steatosis in obese mice. PNU appears to work at various steps of signaling pathways involving suppression of oxidative stress, activation of AMPK, and inhibition of SREBP1c, FAS, and ACC. α7nAChR agonists may be an effective therapeutic strategy for ameliorating fatty liver disease, especially in obese smokers.

An excess dietary vitamin E concentration does not influence Nrf2 signaling in the liver of rats fed either soybean oil or salmon oil

Background

Reactive oxygen species (ROS) are known to stimulate the activation of nuclear factor-erythroid 2-related factor-2 (Nrf2), the key regulator of the antioxidant and cytoprotective defense system in the body. The hypothesis underlying this study was that high dietary concentrations of vitamin E suppress Nrf2 activation, and thus could weaken the body’s antioxidative and cytoprotective capacity. As the effect of vitamin E on Nrf2 pathway might be influenced by concentrations of fatty acids susceptible to oxidation in the diet, we used also diets containing either soybean oil as a reference oil or salmon oil as a source of oil rich in n-3 polyunsatuated fatty acids.

Methods

Seventy-two rats were divided into 6 groups of rats which received diets with either 25, 250 or 2500 mg vitamin E/kg, with either soybean oil or salmon oil as dietary fat sources according to a bi-factorial experimental design. Electron spin resonance spectroscopy was used to determine ROS production in the liver. qPCR analysis and western blot were performed to examine the expression of Nrf2 target genes in the liver of rats.

Results

Rats fed the salmon oil diet with 25 mg vitamin E/kg showed a higher production of ROS in the liver than the 5 other groups of rats which did not differ in ROS production. Relative mRNA concentrations of NFE2L2 (encoding Nrf2), KEAP1 and various Nrf2 target genes, protein concentrations of glutathione peroxidase (GPX), heme oxygenase 1 (HO-1), NAD(P)H quinone dehydrogenase 1 (NQO1) and activities of the antioxidant enzymes GPX, superoxide dismutase and catalase were not influenced by the dietary vitamin E concentration. The dietary fat had also less effect on Nrf2 target genes and no effect on protein concentrations of GPX, HO-1, NQO1 and activities of antioxidant enzymes. Dietary vitamin E concentration and type of fat moreover had less effect on mRNA concentrations of genes and concentrations of proteins involved in the unfolded protein response, a pathway which is closely linked with activation of Nrf2.

Conclusion

We conclude that excess dietary concentrations of vitamin E do not suppress Nrf2 signaling, and thus do not weaken the endogenous antioxidant and cytoprotective capacity in the liver of rats.

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.

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.

Hydrogen Sulfide Inhibits Cigarette Smoke-Induced Endoplasmic Reticulum Stress and Apoptosis in Bronchial Epithelial Cells

Background: Apoptosis of lung structural cells contributes to the process of lung damage and remodeling in chronic obstructive pulmonary disease (COPD). Our previous studies demonstrated that exogenous hydrogen sulfide (H₂S) can reduce the lung tissue pathology score, anti-inflammation and anti-oxidation effects in COPD, but the effect of H₂S in regulating cigarette smoke (CS) induced bronchial epithelial cell apoptosis and the underlying mechanisms are not clear.

Objectives: To investigate the effect of H₂S on CS induced endoplasmic reticulum stress (ERS) and bronchial epithelial cell apoptosis.

Methods: Male Sprague–Dawley rats randomly divided into four groups for treatment: control, CS, NaHS + CS, and propargylglycine (PPG) + CS. The rats in the CS group were exposed to CS generated from 20 commercial unfiltered cigarettes for 4 h/day, 7 days/week for 4 months. Since the beginning of the third month, freshly prepared NaHS (14 μmol/kg) and PPG (37.5 mg/kg) were intraperitoneally administered 30 min before CS-exposure in the NaHS and PPG groups. 16HBE cells were pretreated with Taurine (10 mM), 5 mmol/L 4-phenylbutyric acid (4-PBA) or NaHS (100, 200, and 400 μM) for 30 min, and then cells were exposed to 40 μmol/L nicotine for 72 h. ERS markers (GRP94, GRP78) and ERS-mediated apoptosis markers 4-C/EBP homologous protein (CHOP), caspase-3 and caspase-12 were assessed in rat lung tissues and human bronchial epithelial cells. The apoptotic bronchial epithelial cells were detected by Hoechst staining in vitro and TUNEL staining in vivo.

Results: In CS exposed rats, peritoneal injection of NaHS significantly inhibited CS induced overexpression ERS-mediated apoptosis markers and upregulation of apoptotic rate in rat lungs, and inhibiting the endogenous H2S production by peritoneal injection of PPG exacerbated these effects. In the nicotine-exposed bronchial epithelial cells, appropriate concentration of NaHS and ERS inhibitors taurine and 4-PBA inhibited nicotine-induced upregulation of apoptotic rate and overexpression of ERS-mediated apoptosis markers.

Conclusion: H₂S inhibited lung tissue damage by attenuating CS induced ERS in rat lung and exogenous H₂S attenuated nicotine induced ERS-mediated apoptosis in bronchial epithelial cells.