Is leptin resistance the cause or the consequence of diet-induced obesity?

Safflower yellow and its main component hydroxysafflor yellow A alleviate hyperleptinemia in diet-induced obesity mice through a dual inhibition of the GIP-GIPR signaling axis

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone secreted by K cells in the small intestine and is considered an obesity-promoting factor. In this study, we systematically investigated the anti-obesity effects of intragastric safflower yellow (SY)/hydroxysafflor yellow A (HSYA) and the underlying mechanism for the first time. Our results showed that intragastric SY/HSYA, rather than an intraperitoneal injection, notably decreased serum GIP levels and GIP staining in the small intestine in diet-induced obese (DIO) mice. Moreover, intragastric SY/HSYA was also first found to significantly suppress GIP receptor (GIPR) signaling in both the hypothalamus and subcutaneous White adipose tissue. Our study is the first to show that intragastric SY/HSYA obviously reduced food intake and body weight gain in leptin sensitivity experiments and decreased serum leptin levels in DIO mice. Further experiments demonstrated that SY treatment also significantly reduced leptin levels, whereas the inhibitory effect of SY on leptin levels was reversed by activating GIPR in 3 T3-L1 adipocytes. In addition, intragastric SY/HSYA had already significantly reduced serum GIP levels and GIPR expression before the serum leptin levels were notably changed in high-fat-diet-fed mice. These findings suggested that intragastric SY/HSYA may alleviate diet-induced obesity in mice by ameliorating hyperleptinemia via dual inhibition of the GIP-GIPR axis.

Sensitivity of the Neuroendocrine Stress Axis in Metabolic Diseases

Metabolic diseases are prevalent in modern society and have reached pandemic proportions. Metabolic diseases have systemic effects on the body and can lead to changes in the neuroendocrine stress axis, the critical regulator of the body's stress response. These changes may be attributed to rising insulin levels and the release of adipokines and inflammatory cytokines by adipose tissue, which affect hormone production by the neuroendocrine stress axis. Chronic stress due to inflammation may exacerbate these effects. The increased sensitivity of the neuroendocrine stress axis may be responsible for the development of metabolic syndrome, providing a possible explanation for the high prevalence of severe comorbidities such as heart disease and stroke associated with metabolic disease. In this review, we address current knowledge of the neuroendocrine stress axis in response to metabolic disease and discuss its role in developing metabolic syndrome.

Elderly rats fed with a high-fat high-sucrose diet developed sex-dependent metabolic syndrome regardless of long-term metformin and liraglutide treatment

Aim/Introduction

The study aimed to determine the effectiveness of early antidiabetic therapy in reversing metabolic changes caused by high-fat and high-sucrose diet (HFHSD) in both sexes.

Methods

Elderly Sprague-Dawley rats, 45 weeks old, were randomized into four groups: a control group fed on the standard diet (STD), one group fed the HFHSD, and two groups fed the HFHSD along with long-term treatment of either metformin (HFHSD+M) or liraglutide (HFHSD+L). Antidiabetic treatment started 5 weeks after the introduction of the diet and lasted 13 weeks until the animals were 64 weeks old.

Results

Unexpectedly, HFHSD-fed animals did not gain weight but underwent significant metabolic changes. Both antidiabetic treatments produced sex-specific effects, but neither prevented the onset of prediabetes nor diabetes.

Conclusion

Liraglutide vested benefits to liver and skeletal muscle tissue in males but induced signs of insulin resistance in females.

Lipidized PrRP Analog Exhibits Strong Anti-Obesity and Antidiabetic Properties in Old WKY Rats with Obesity and Glucose Intolerance

Prolactin-releasing peptide (PrRP) is an anorexigenic neuropeptide that has potential for the treatment of obesity and its complications. Recently, we designed a palmitoylated PrRP31 analog (palm¹¹-PrRP31) that is more stable than the natural peptide and able to act centrally after peripheral administration. This analog acted as an anti-obesity and glucose-lowering agent, attenuating lipogenesis in rats and mice with high-fat (HF) diet-induced obesity. In Wistar Kyoto (WKY) rats fed a HF diet for 52 weeks, we explored glucose intolerance, but also prediabetes, liver steatosis and insulin resistance-related changes, as well as neuroinflammation in the brain. A potential beneficial effect of 6 weeks of treatment with palm¹¹-PrRP31 and liraglutide as comparator was investigated. Liver lipid profiles, as well as urinary and plasma metabolomic profiles, were measured by lipidomics and metabolomics, respectively. Old obese WKY rats showed robust glucose intolerance that was attenuated by palm¹¹-PrRP31, but not by liraglutide treatment. On the contrary, liraglutide had a beneficial effect on insulin resistance parameters. Despite obesity and prediabetes, WKY rats did not develop steatosis owing to HF diet feeding, even though liver lipogenesis was enhanced. Plasma triglycerides and cholesterol were not increased by HFD feeding, which points to unincreased lipid transport from the liver. The liver lipid profile was significantly altered by a HF diet that remained unaffected by palm¹¹-PrRP31 or liraglutide treatment. The HF-diet-fed WKY rats revealed astrogliosis in the brain cortex and hippocampus, which was attenuated by treatment. In conclusion, this study suggested multiple beneficial anti-obesity-related effects of palm¹¹-PrRP31 and liraglutide in both the periphery and brain.

Actin related protein 2/3 complex subunit 1 up-regulation in the hypothalamus prevents high-fat diet induced obesity

Obesity is a major health crisis in the modern society. Studies have shown that the consumption of a high-fat diet (HFD) induces hypothalamic inflammation and leptin resistance, which consequently favours body mass gain. Actin related protein 2/3 complex subunit 1 (ARPC1B), an actin-binding protein, is highly expressed in immune cells. Recent studies have shown that ARPC1B has a certain anti-inflammatory effect. While ARPC1B expression is decreased in the hypothalamus of mice fed a HFD, the role of ARPC1B in HFD-induced obesity remains unclear. Thus, we investigated whether ARPC1B up-regulation in the hypothalamic arcuate nucleus (ARC) could inhibit the development of obesity. Herein, ARPC1B overexpression lentiviral particles were stereotaxically injected into the ARC of male C57BL/6J mice (7 weeks old) fed with HFD. Overexpression of ARPC1B in the hypothalamic ARC attenuated HFD-induced ARC inflammation, reduced body-weight gain and feed efficiency. Furthermore, up-regulation of ARC ARPC1B improved the glucose tolerance and reduced subcutaneous/epididymal fat mass accumulation, which decreased the serum total cholesterol, serum triglyceride and leptin levels. In addition, upon ARPC1B overexpression in the hypothalamic ARC, intraperitoneal injection of leptin increased the phosphorylation level of signal transducer and activator of transcription 3 (STAT3), an important transcription factor for leptin's action, in the ARC of obese mice. Accordingly, we suggest that up-regulation of ARPC1B in the hypothalamic ARC may improve the HFD-induced hypothalamic inflammation and leptin resistance. Our findings demonstrate that ARPC1B is a promising target for the treatment of diet-induced obesity.

Assessing causality between different risk factors and pulmonary embolism: A Mendelian randomization study

Objectives

Mendelian randomization (MR) was used to estimate the causal relationship between body mass index (BMI), ever smoked, heart failure, alcohol intake frequency, inflammatory bowel disease (IBD), and pulmonary embolism (PE). This study aimed to investigate whether there is a causal relationship between BMI, the presence of smoking, heart failure, frequency of alcohol intake, IBD, and PE.

Methods

Pooled data on PE from a published GWAS meta-analysis involving approximately 461,164 participants of European ancestry were selected. A publicly available pooled dataset of BMI (461,460), ever smokers (461,066), heart failure (977,323), IBD (75,000), and frequency of alcohol intake (462,346) was used from another independent GWAS. MR was performed using established analysis methods, including Wald ratios, inverse variance weighted (IVW), weighted median (WM), and MR-Egger. Also, the final expansion was validated with multivariate MR.

Results

In the IVW model, genetically elevated BMI was causally associated with PE [OR = 1.002, 95% CI (1.001, 1004), P = 0.039]. Cochran's Q test was used to detect heterogeneity in the MR-Egger analysis (P = 0.576). Therefore, the effect of gene-level heterogeneity was not considered. In the MR analysis of other risk factors, we observed genes for ever smoking [IVW OR = 1.004, 95% CI (0.997, 1.012)], heart failure [IVW OR = 0.999, 95% CI (0.996, 1.001)], IBD [IVW OR = 1.000, 95% CI (0.999, 1.001)], and frequency of alcohol intake [IVW OR = 1.002, 95% CI (1.000, 1.004)] were not causally associated with PE. Analysis using multivariate MR expansion showed no causal effect of BMI on PE considering the effect of height as well as weight (P = 0.926).

Conclusion

In European populations, a causal relationship exists between BMI and PE: increased BMI leads to PE. In contrast, ever smoking, heart failure, frequency of alcohol intake, and IBD are not directly associated with PE. There was no causal effect of BMI with PE in multivariate Mendelian randomized analysis.

Pharmacological targeting of glutamatergic neurons within the brainstem for weight reduction

Food intake and body weight are tightly regulated by neurons within specific brain regions, including the brainstem, where acute activation of dorsal raphe nucleus (DRN) glutamatergic neurons expressing the glutamate transporter Vglut3 (DRN^Vglut3) drive a robust suppression of food intake and enhance locomotion. Activating Vglut3 neurons in DRN suppresses food intake and increases locomotion, suggesting that modulating the activity of these neurons might alter body weight. Here, we show that DRN^Vglut3 neurons project to the lateral hypothalamus (LHA), a canonical feeding center that also reduces food intake. Moreover, chronic DRN^Vglut3 activation reduces weight in both leptin-deficient (ob/ob) and leptin-resistant diet-induced obese (DIO) male mice. Molecular profiling revealed that the orexin 1 receptor (Hcrtr1) is highly enriched in DRN Vglut3 neurons, with limited expression elsewhere in the brain. Finally, an orally bioavailable, highly selective Hcrtr1 antagonist (CVN45502) significantly reduces feeding and body weight in DIO. Hcrtr1 is also co-expressed with Vglut3 in the human DRN, suggesting that there might be a similar effect in human. These results identify a potential therapy for obesity by targeting DRN^Vglut3 neurons while also establishing a general strategy for developing drugs for central nervous system disorders.

Cannabis sativa as a Treatment for Obesity: From Anti-Inflammatory Indirect Support to a Promising Metabolic Re-Establishment Target

Introduction: Obesity is defined as an excess of accumulation of fat that can be harmful to health. Storage of excess fat in the adipose tissue triggers an inflammatory process, which makes obesity a low-grade chronic inflammatory disease. Obesity is considered a complex and multifactorial disease; hence, no intervention strategy appears to be an ideal treatment for all individuals. Therefore, new therapeutic alternatives are often studied for the treatment of this disease. Currently, herbal medicines are gaining ground in the treatment of obesity and its comorbidities. In this context, much attention is being paid to Cannabis sativa derivatives, and their therapeutic functions are being widely studied, including in treating obesity. Objective: Highlight the pharmacological properties of Δ9-tetrahydrocannabivarin (THCV), Δ9-tetrahydrocannabidinol (THC), and cannabidiol (CBD), the predominant isolated components of Cannabis sativa, as well as its therapeutic potential in the treatment of obesity. Methods: This is a narrative review that shows the existing scientific evidence on the clinical application of Cannabis sativa as a possible treatment for obesity. Data collection was performed in the PubMed electronic database. The following word combinations were used: Cannabis and obesity, Cannabis sativa and obesity, THCV and obesity, THC and obesity, CBD and obesity, and Cannabis sativa and inflammation. Results: Evidence shows that Cannabis sativa derivatives have therapeutic potential due to their anti-inflammatory properties. In addition, people who use cannabis have a lower body mass index than those who do not, making the plant an option to reduce and reverse inflammation and comorbidities in obesity. Conclusion: It is concluded that phytocannabinoids derived from Cannabis sativa have therapeutic potential due to its anti-inflammatory, antioxidant, and neuroprotective properties, making the plant a study option to reduce and reverse inflammation and comorbidities associated with obesity.

Arcuate Nucleus-Dependent Regulation of Metabolism-Pathways to Obesity and Diabetes Mellitus

The central nervous system (CNS) receives information from afferent neurons, circulating hormones, and absorbed nutrients and integrates this information to orchestrate the actions of the neuroendocrine and autonomic nervous systems in maintaining systemic metabolic homeostasis. Particularly the arcuate nucleus of the hypothalamus (ARC) is of pivotal importance for primary sensing of adiposity signals, such as leptin and insulin, and circulating nutrients, such as glucose. Importantly, energy state-sensing neurons in the ARC not only regulate feeding but at the same time control multiple physiological functions, such as glucose homeostasis, blood pressure, and innate immune responses. These findings have defined them as master regulators, which adapt integrative physiology to the energy state of the organism. The disruption of this fine-tuned control leads to an imbalance between energy intake and expenditure as well as deregulation of peripheral metabolism. Improving our understanding of the cellular, molecular, and functional basis of this regulatory principle in the CNS could set the stage for developing novel therapeutic strategies for the treatment of obesity and metabolic syndrome. In this review, we summarize novel insights with a particular emphasis on ARC neurocircuitries regulating food intake and glucose homeostasis and sensing factors that inform the brain of the organismal energy status.

Hypothalamic mechanisms of obesity-associated disturbance of hypothalamic-pituitary-ovarian axis

Ovulatory disorders are the most common clinical feature exhibited among obese women. Initiation of ovulation physiologically requires a surge of gonadotropin-releasing hormone (GnRH) released from GnRH neurons located in the hypothalamus. These GnRH neurons receive metabolic signals from circulation and vicinal neurons to regulate GnRH release. Leptin acts indirectly on GnRH via adjacent leptin receptor (LEPR)-expressing neurons such as proopiomelanocortin (POMC), neuropeptide Y (NPY)/agouti-related peptide (AgRP), and neuronal nitric oxide (NO) synthase (nNOS) neurons to affect GnRH neuronal activities. Additionally, hypothalamic inflammation also affects ovulation independent of obesity. Therefore, this review focuses on hypothalamic mechanisms that underlie the disturbance of hypothalamic-pituitary-ovarian (HPO) axis during obesity with an attempt to promote future studies and/or novel therapeutic strategies for ovulatory disorders in obesity.

Helminth and Host Crosstalk: New Insight Into Treatment of Obesity and Its Associated Metabolic Syndromes

Obesity and its associated Metabolic Syndromes (Mets) represent a global epidemic health problem. Metabolic inflammation, lipid accumulation and insulin resistance contribute to the progression of these diseases, thereby becoming targets for drug development. Epidemiological data have showed that the rate of helminth infection negatively correlates with the incidence of obesity and Mets. Correspondingly, numerous animal experiments and a few of clinic trials in human demonstrate that helminth infection or its derived molecules can mitigate obesity and Mets via induction of macrophage M2 polarization, inhibition of adipogenesis, promotion of fat browning, and improvement of glucose tolerance, insulin resistance and metabolic inflammation. Interestingly, sporadic studies also uncover that several helminth infections can reshape gut microbiota of hosts, which is intimately implicated in the pathogenesis of obesity and Mets. Overall, these findings indicate that the crosstalk between helminth and hosts may be a novel direction for obesity and Mets therapy. The present article reviews the molecular mechanism of how helminth masters immunity and metabolism in obesity.

TNF-α Antagonizes the Effect of Leptin on Insulin Secretion through FOXO1-Dependent Transcriptional Suppression of LepRb in INS-1 Cells

Proinflammatory cytokines play a causal role in the development of hyperinsulinemia and T2MD. FOXO1, a transcription factor which is known to enhance proinflammation, was recently shown to be involved in obesity-induced β cell dysfunction. However, molecular mechanisms for the association remained elusive. In this study, we first found that both leptin (10 nM) and TNF-α (20 ng/ml) significantly inhibited glucose-stimulated insulin secretion (GSIS) of INS-1E cells. When in combination, the GSIS function of INS-1E cells was significantly increased compared with that of the leptin alone treatment, indicating that TNF-α attenuated the inhibiting effect of leptin on GSIS of INS-1E cells. Similarly, we found that TNF-α has the same inhibitory effect on leptin in regulating insulin synthesis and secretion, and the survival and apoptosis of insulin cells. Further studies showed that TNF-α blocks leptin pathway by reducing the expression of leptin receptor (LepRb, also called OBRb) and inhibiting the activation of STAT3, a key molecule involved in the leptin signaling pathway in INS-1E cells. Besides, the downregulated expression of phosphorylated FOXO1 was found to be involved in the possible mechanism of TNF-α. Overexpression of constitutively active FOXO1 markedly aggravated the LepRb reduction by TNF-α treatment of INS-1E cells, and the endogenous FOXO1 knockdown abolished the effect of TNF-α on INS-1E cells. Furthermore, we have proved that FOXO1 could directly bind to the promoter of LepRb as a negative transcription regulator. Taken together, the results of this study reveal that TNF-α-induced LepRb downregulated in pancreatic β cells and demonstrate that transcriptional reduction of FOXO1 might be the primary mechanism underlying TNF-α promoting INS-1E leptin resistance and β cell dysfunction. Conclusions. Our current studies based on INS-1E cells in vitro indicate that the inflammatory factor TNF-α plays an important role in the development of INS-1E leptin resistance and glucose metabolism disorders, probably through FOXO1-induced transcription reduction of LepRb promoter in pancreatic β cells, and FOXO1 may be a novel target for treating β cell dysfunction in obesity-induced hyperinsulinemia and T2DM.

Was it something I ate? Understanding the bidirectional interaction of migraine and appetite neural circuits

Migraine attacks can involve changes of appetite: while fasting or skipping meals are often reported triggers in susceptible individuals, hunger or food craving are reported in the premonitory phase. Over the last decade, there has been a growing interest and recognition of the importance of studying these overlapping fields of neuroscience, which has led to novel findings. The data suggest additional studies are needed to unravel key neurobiological mechanisms underlying the bidirectional interaction between migraine and appetite. Herein, we review information about the metabolic migraine phenotype and explore migraine therapeutic targets that have a strong input on appetite neuronal circuits, including the calcitonin gene-related peptide (CGRP), the pituitary adenylate cyclase-activating polypeptide (PACAP) and the orexins. Furthermore, we focus on potential therapeutic peptide targets that are involved in regulation of feeding and play a role in migraine pathophysiology, such as neuropeptide Y, insulin, glucagon and leptin. We then examine the orexigenic - anorexigenic circuit feedback loop and explore glucose metabolism disturbances. Additionally, it is proposed a different perspective on the most reported feeding-related trigger - skipping meals - as well as a link between contrasting feeding behaviors (skipping meals vs food craving). Our review aims to increase awareness of migraine through the lens of appetite neurobiology in order to improve our understanding of the earlier phase of migraine, encourage better studies and cross-disciplinary collaborations, and provide novel migraine-specific therapeutic opportunities.

A targeted proteomics investigation of the obesity paradox in venous thromboembolism

The obesity paradox, the controversial finding that obesity promotes disease development but protects against sequelae in patients, has been observed in venous thromboembolism (VTE). The aim of this investigation was to identify a body mass-related proteomic signature in VTE patients and to evaluate whether this signature mediates the obesity paradox in VTE patients. Data from the Genotyping and Molecular Phenotyping in Venous ThromboEmbolism Project, a prospective cohort study of 693 VTE patients, were analyzed. A combined end point of recurrent VTE or all-cause death was used. Relative quantification of 444 proteins was performed using high-throughput targeted proteomics technology. Measurements were performed in samples collected during the acute VTE event and at 12-month follow-up. An 11-protein signature (CLEC4C, FABP4, FLT3LG, IL-17C, LEP, LYVE1, MASP1, ST2, THBS2, THBS4, TSLP) for body mass in VTE patients was identified. The signature did not significantly mediate the obesity paradox (change in hazard ratio [HR]: 0.04; likelihood ratio test of nested models = 7.7; P = .74), but its main constituent protein, leptin, was inversely associated with recurrent VTE or death (adjusted HR [95% confidence interval] per standard deviation increase: 0.66 [0.46-0.94]). This relationship was significantly (P = .007) modified by markers of leptin resistance (ie, high body mass index and high circulating matrix metalloproteinase-2 levels). Although the signature did not substantially explain the obesity paradox, leptin appears to be protective against disease recurrence and death in VTE patients. This protective effect was abrogated under conditions of leptin resistance and hence was unrelated to the obesity paradox.

Efficacy of choline and DHA supplements or enriched environment exposure during early adult obesity in mitigating its adverse impact through aging in rats

INTRODUCTION

The aim of this study was to assess the efficacy of choline and DHA or exposure to environmental enrichment in obese adult and aging rats on alterations in body mass index, serum lipid profile and arterial wall changes, despite stopping high fat diet consumption and interventions during adulthood.

METHODS

21 day old male Sprague Dawley rats were assigned as Experiment-1 & 2 - PND rats were divided into 4 groups with interventions for 7 months (n = 8/group). NC- Normal control fed normal chow diet; OB- Obese group, fed high fat diet; OB + CHO + DHA- fed high fat diet and oral supplementation of choline, DHA. OB + EE- fed high fat diet along with exposure to enriched environment .Experiment-2 had similar groups and interventions as experiment 1 but for next 5 months were fed normal chow diet without any interventions. Body mass index was assessed and blood was analyzed for serum lipid profile. Common Carotid Artery (CCA) was processed for Haematoxylin and eosin, Verhoff Vangeison stains. Images of tissue sections were analyzed and quantified using image J and tissue quant software.

RESULTS

In experiment.1, mean body mass index (p < 0.001), serum lipid profile (p < 0.01), thickness of tunica intima (p < 0.05), tunica media (p < 0.01) and percentage of collagen fibers (p < 0.01) of CCA were significantly increased in OB compared to NC. These were significantly attenuated in OB + CHO + DHA and OB + EE compared to OB. In experiment.2, mean body mass index (p < 0.01), serum lipid profile (p < 0.05) and thickness of tunica media of CCA (p < 0.01) were significantly increased in OB compared to NC. In OB + CHO + DHA and OB + EE, significant attenuation was observed in mean body mass index and mean thickness of tunica media compared to same in OB.

CONCLUSION

Adult obesity has negative impact on body mass index, serum lipid profile and arterial wall structure that persists through aging. Supplementation of choline and DHA or exposure to enriched environment during obesity attenuates these negative impacts through aging.

Review: Obesity and COVID-19: A Detrimental Intersection

Obesity has been recognized as an independent risk factor for critical illness and major severity in subjects with coronavirus disease 2019 (COVID-19). The role of fat distribution, particularly visceral fat (often linked to metabolic abnormalities), is still unclear. The adipose tissue represents a direct source of cytokines responsible for the pathological modifications occurring within adipose tissue in obese subjects. Adipokines are a crucial connection between metabolism and immune system: their dysregulation in obesity contributes to chronic low-grade systemic inflammation and metabolic comorbidities. Therefore the increased amount of visceral fat can lead to a proinflammatory phenotypic shift. This review analyzes the interrelation between obesity and COVID-19 severity, as well as the cellular key players and molecular mechanisms implicated in adipose inflammation, investigating if adipose tissue can constitute a reservoir for viral spread, and contribute to immune activation and cytokines storm. Targeting the underlying molecular mechanisms might have therapeutic potential in the management of obesity-related complications in COVID-19 patients.

Adipokines, Myokines, and Cardiokines: The Role of Nutritional Interventions

It is now established that adipose tissue, skeletal muscle, and heart are endocrine organs and secrete in normal and in pathological conditions several molecules, called, respectively, adipokines, myokines, and cardiokines. These secretory proteins constitute a closed network that plays a crucial role in obesity and above all in cardiac diseases associated with obesity. In particular, the interaction between adipokines, myokines, and cardiokines is mainly involved in inflammatory and oxidative damage characterized obesity condition. Identifying new therapeutic agents or treatment having a positive action on the expression of these molecules could have a key positive effect on the management of obesity and its cardiac complications. Results from recent studies indicate that several nutritional interventions, including nutraceutical supplements, could represent new therapeutic agents on the adipo-myo-cardiokines network. This review focuses the biological action on the main adipokines, myokines and cardiokines involved in obesity and cardiovascular diseases and describe the principal nutraceutical approaches able to regulate leptin, adiponectin, apelin, irisin, natriuretic peptides, and follistatin-like 1 expression.

Obesity and COVID-19: A Fatal Alliance

Most people infected with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS CoV2) are mildly symptomatic while few progress to critical illness and succumb to the infection. The disease severity is seen to be associated with increasing age and underlying comorbid conditions. Obesity, responsible for various metabolic disorders, appears to be a risk factor in determining the severity of infection despite any age group. Though this association is clinically relevant, the mechanisms underlying are not fully elucidated. SARS CoV2 enters host cell via Angiotensin Converting Enzyme 2 receptor, expression of which is upregulated in visceral fat tissue in obese people, underscoring the fact that adipose tissue is a potential reservoir for virus. Adipose tissue is also a source of many proinflammatory mediators and adipokines. High baseline C-Reactive Protein, interleukin 6, hyperleptinemia with Leptin resistance and hypoadiponectinemia associated with obesity explains the preexisting inflammatory state in obese individuals which predisposes them to worse outcomes and fatality.

Orexin A-induced inhibition of leptin expression and secretion in adipocytes reducing plasma leptin levels and hypothalamic leptin resistance

Orexin A (OXA) is a neuropeptide associated with plasma insulin and leptin levels involved in body weight and appetite regulation. However, little is known about the effect of OXA on leptin secretion in adipocytes and its physiological roles. Leptin secretion and expression were analysed in 3T3-L1 adipocytes. Plasma leptin, adiponectin and insulin levels were measured by ELISA assay. Phosphorylated signal transducer and activator of transcription 3 (pSTAT3) levels in the hypothalamus were evaluated by western blotting. OXA dose-dependently suppressed leptin secretion from 3T3-L1 adipocytes by inhibiting its gene expression while facilitating adiponectin secretion. The leptin inhibition by OXA was mediated via orexin receptors (OXR1 and OXR2). In addition to the pathway via extracellular signal-regulated kinases, OXA triggered adenylyl cyclase-induced cAMP elevation, which results in protein kinase A-mediated activation of cAMP response element-binding proteins (CREB). Accordingly, CREB inhibition restored the OXA-induced downregulation of leptin gene expression and secretion. Exogenous OXA for 4 weeks decreased fasting plasma leptin levels and increased hypothalamic pSTAT3 levels in high-fat diet-fed mice, regardless of increase in body weight and food intake. These results suggest that high dose of OXA directly inhibits leptin mRNA expression and thus secretion in adipocytes, which may be a peripheral mechanism of OXA for its role in appetite drive during fasting. It may be also critical for lowering basal plasma leptin levels and thus maintaining postprandial hypothalamic leptin sensitivity.

Palmitic acid is an intracellular signaling molecule involved in disease development

Emerging evidence shows that palmitic acid (PA), a common fatty acid in the human diet, serves as a signaling molecule regulating the progression and development of many diseases at the molecular level. In this review, we focus on its regulatory roles in the development of five pathological conditions, namely, metabolic syndrome, cardiovascular diseases, cancer, neurodegenerative diseases, and inflammation. We summarize the clinical and epidemiological studies; and also the mechanistic studies which have identified the molecular targets for PA in these pathological conditions. Activation or inactivation of these molecular targets by PA controls disease development. Therefore, identifying the specific targets and signaling pathways that are regulated by PA can give us a better understanding of how these diseases develop for the design of effective targeted therapeutics.

Rats that are predisposed to excessive obesity show reduced (leptin-induced) thermoregulation even in the preobese state

Both feeding behavior and thermogenesis are regulated by leptin. The sensitivity to leptin's anorexigenic effects on chow diet was previously shown to predict the development of diet-induced obesity. In this study, we determined whether the sensitivity to leptin's anorexigenic effects correlates with leptin's thermogenic response, and if this response is exerted at the level of the dorsomedial hypothalamus (DMH), a brain area that plays an important role in thermoregulation. Based on the feeding response to injected leptin on a chow diet, rats were divided into leptin-sensitive (LS) and leptin-resistant (LR) groups. The effects of leptin on core body, brown adipose tissue (BAT) and tail temperature were compared after intravenous versus intra-DMH leptin administration. After intravenous leptin injection, LS rats increased their BAT thermogenesis and reduced heat loss via the tail, resulting in a modest increase in core body temperature. The induction of these thermoregulatory mechanisms with intra-DMH leptin was smaller, but in the same direction as with intravenous leptin administration. In contrast, LR rats did not show any thermogenic response to either intravenous or intra-DMH leptin. These differences in the thermogenic response to leptin were associated with a 1°C lower BAT temperature and reduced UCP1 expression in LR rats under ad libitum feeding. The preexisting sensitivity to the anorexigenic effects of leptin, a predictor for obesity, correlates with the sensitivity to the thermoregulatory effects of leptin, which appears to be exerted, at least in part, at the level of the DMH.

Individual Differences in Behavioral Responses to Palatable Food or to Cholecystokinin Predict Subsequent Diet-Induced Obesity

OBJECTIVE

This study investigated whether individual differences in behavioral responses to palatable food and to the satiation signal cholecystokinin (CCK) in outbred chow-maintained Sprague-Dawley rats enabled prediction of individual differences in weight gained after subsequent high-fat/high-sugar diet (HFHSD) maintenance.

METHODS

Meal size, meal number, and early dark cycle intake during initial HFHSD exposure were measured, as were early dark cycle sucrose solution and chow intake, chow meal size and meal number, the intake-suppressive effects of 0.5-µg/kg CCK injection, and CCK-induced c-Fos activation in the nucleus tractus solitarius. Subsequently, rats were maintained on an HFHSD for 5 weeks, and weight gain was determined.

RESULTS

Rats that took larger and less frequent meals on the first day of HFHSD exposure, whose early dark cycle intake (HFHSD and sucrose) was larger during initial HFHSD exposure, gained more weight after HFHSD maintenance. Rats with lesser sucrose intake suppression in response to CCK gained more weight after HFHSD maintenance and displayed reduced CCK-induced c-Fos activation in the nucleus tractus solitarius.

CONCLUSIONS

Together, these data identify individual differences in behavioral responses to palatable food and to CCK as novel predictors of diet-induced obesity.

Stressing the importance of choice: Validity of a preclinical free-choice high-caloric diet paradigm to model behavioural, physiological and molecular adaptations during human diet-induced obesity and metabolic dysfunction

Humans have engineered a dietary environment that has driven the global prevalence of obesity and several other chronic metabolic diseases to pandemic levels. To prevent or treat obesity and associated comorbidities, it is crucial that we understand how our dietary environment, especially in combination with a sedentary lifestyle and/or daily-life stress, can dysregulate energy balance and promote the development of an obese state. Substantial mechanistic insight into the maladaptive adaptations underlying caloric overconsumption and excessive weight gain has been gained by analysing brains from rodents that were eating prefabricated nutritionally-complete pellets of high-fat diet (HFD). Although long-term consumption of HFDs induces chronic metabolic diseases, including obesity, they do not model several important characteristics of the modern-day human diet. For example, prefabricated HFDs ignore the (effects of) caloric consumption from a fluid source, do not appear to model the complex interplay in humans between stress and preference for palatable foods, and, importantly, lack any aspect of choice. Therefore, our laboratory uses an obesogenic free-choice high-fat high-sucrose (fc-HFHS) diet paradigm that provides rodents with the opportunity to choose from several diet components, varying in palatability, fluidity, texture, form and nutritive content. Here, we review recent advances in our understanding how the fc-HFHS diet disrupts peripheral metabolic processes and produces adaptations in brain circuitries that govern homeostatic and hedonic components of energy balance. Current insight suggests that the fc-HFHS diet has good construct and face validity to model human diet-induced chronic metabolic diseases, including obesity, because it combines the effects of food palatability and energy density with the stimulating effects of variety and choice. We also highlight how behavioural, physiological and molecular adaptations might differ from those induced by prefabricated HFDs that lack an element of choice. Finally, the advantages and disadvantages of using the fc-HFHS diet for preclinical studies are discussed.