Functional interaction between Ghrelin and GLP-1 regulates feeding through the vagal afferent system

An insoluble cellulose nanofiber with robust expansion capacity protects against obesity

An imbalance between energy intake and energy expenditure predisposes obesity and its related metabolic diseases. Soluble dietary fiber has been shown to improve metabolic homeostasis mainly via microbiota reshaping. However, the application and metabolic effects of insoluble fiber are less understood. Herein, we employed nanotechnology to design citric acid-crosslinked carboxymethyl cellulose nanofibers (CL-CNF) with a robust capacity of expansion upon swelling. Supplementation with CL-CNF reduced food intake and delayed digestion rate in mice by occupying stomach. Besides, CL-CNF treatment mitigated diet-induced obesity and insulin resistance in mice with enhanced energy expenditure, as well as ameliorated inflammation in adipose tissue, intestine and liver and reduced hepatic steatosis, without any discernible signs of toxicity. Additionally, CL-CNF supplementation resulted in enrichment of probiotics such as Bifidobacterium and decreased in the relative abundances of deleterious microbiota expressing bile salt hydrolase, which led to increased levels of conjugated bile acids and inhibited intestinal FXR signaling to stimulate the release of GLP-1. Taken together, our findings demonstrate that CL-CNF administration protects mice from diet-induced obesity and metabolic dysfunction by reducing food intake, enhancing energy expenditure and remodeling gut microbiota, making it a potential therapeutic strategy against metabolic diseases.

Neural Circuits Underlying Reciprocal Cardiometabolic Crosstalk: 2023 Arthur C. Corcoran Memorial Lecture

The interplay of various body systems, encompassing those that govern cardiovascular and metabolic functions, has evolved alongside the development of multicellular organisms. This evolutionary process is essential for the coordination and maintenance of homeostasis and overall health by facilitating the adaptation of the organism to internal and external cues. Disruption of these complex interactions contributes to the development and progression of pathologies that involve multiple organs. Obesity-associated cardiovascular risks, such as hypertension, highlight the significant influence that metabolic processes exert on the cardiovascular system. This cardiometabolic communication is reciprocal, as indicated by substantial evidence pointing to the ability of the cardiovascular system to affect metabolic processes, with pathophysiological implications in disease conditions. In this review, I outline the bidirectional nature of the cardiometabolic interaction, with special emphasis on the impact that metabolic organs have on the cardiovascular system. I also discuss the contribution of the neural circuits and autonomic nervous system in mediating the crosstalk between cardiovascular and metabolic functions in health and disease, along with the molecular mechanisms involved.

Vagal sensory pathway for the gut-brain communication

The communication between the gut and brain is crucial for regulating various essential physiological functions, such as energy balance, fluid homeostasis, immune response, and emotion. The vagal sensory pathway plays an indispensable role in connecting the gut to the brain. Recently, our knowledge of the vagal gut-brain axis has significantly advanced through molecular genetic studies, revealing a diverse range of vagal sensory cell types with distinct peripheral innervations, response profiles, and physiological functions. Here, we review the current understanding of how vagal sensory neurons contribute to gut-brain communication. First, we highlight recent transcriptomic and genetic approaches that have characterized different vagal sensory cell types. Then, we focus on discussing how different subtypes encode numerous gut-derived signals and how their activities are translated into physiological and behavioral regulations. The emerging insights into the diverse cell types and functional properties of vagal sensory neurons have paved the way for exciting future directions, which may provide valuable insights into potential therapeutic targets for disorders involving gut-brain communication.

Ghrelin as a Biomarker of "Immunometabolic Depression" and Its Connection with Dysbiosis

Ghrelin, a gastrointestinal peptide, is an endogenous ligand of growth hormone secretagogue receptor 1a (GHSR1a), which is mainly produced by X/A-like cells in the intestinal mucosa. Beyond its initial description as a growth hormone (GH) secretagogue stimulator of appetite, ghrelin has been revealed to have a wide range of physiological effects, for example, the modulation of inflammation; the improvement of cardiac performance; the modulation of stress, anxiety, taste sensation, and reward-seeking behavior; and the regulation of glucose metabolism and thermogenesis. Ghrelin secretion is altered in depressive disorders and metabolic syndrome, which frequently co-occur, but it is still unknown how these modifications relate to the physiopathology of these disorders. This review highlights the increasing amount of research establishing the close relationship between ghrelin, nutrition, microbiota, and disorders such as depression and metabolic syndrome, and it evaluates the ghrelinergic system as a potential target for the development of effective pharmacotherapies.

Liver-Expressed Antimicrobial Peptide 2 Is a Hepatokine That Predicts Weight Loss and Complete Remission of Type 2 Diabetes Mellitus after Vertical Sleeve Gastrectomy in Japanese Individuals

INTRODUCTION

Vertical sleeve gastrectomy (VSG) is considered one of the most effective treatments for sustained weight loss and complete remission of type 2 diabetes mellitus (CR-T2DM). Liver-expressed antimicrobial peptide 2 (LEAP2), a ghrelin receptor antagonist peptide, is a metabolic hormone regulated by VSG. However, it is unknown whether LEAP2 can be used to predict the outcomes of VSG. This study aimed to evaluate LEAP2 as a predictive factor for weight loss and CR-T2DM after VSG.

METHODS

This retrospective study included 39 Japanese participants with obesity who underwent VSG. Serum LEAP2, des-acyl ghrelin (DAG), and other metabolic and anthropometric parameters were studied before and at 12 months after VSG. Receiver operating characteristics (ROC) curve was generated to evaluate predictive score for weight loss with cut-off value of >50 percent excess weight loss. ROC curve was also generated to assess CR-T2DM.

RESULTS

Serum LEAP2 levels were significantly higher in participants with body mass index (BMI) 32-50 kg/m2 than in those with normal weight. Participants with BMI >50 kg/m2 had lower serum LEAP2 concentrations than those with BMI 32-50 kg/m2. VSG caused a significant reduction in serum DAG concentrations, but it did not affect serum LEAP2 concentrations in either male or female participants. Preoperative serum LEAP2 concentration of 2.88 pmol/mL was the optimal cutoff value for predicting weight loss after VSG, with sensitivity of 80.0% and specificity of 75.9%. Preoperative serum LEAP2 level higher than 4.67 pmol/mL predicted CR-T2DM after VSG with sensitivity of 100% and specificity of 58.8%.

CONCLUSION

Preoperative serum LEAP2 could predict weight loss and CR-T2DM as outcomes of VSG.

Variation in responses to incretin therapy: Modifiable and non-modifiable factors

Type 2 diabetes (T2D) and obesity have reached epidemic proportions. Incretin therapy is the second line of treatment for T2D, improving both blood glucose regulation and weight loss. Glucagon-like peptide-1 (GLP-1) and glucose-stimulated insulinotropic polypeptide (GIP) are the incretin hormones that provide the foundations for these drugs. While these therapies have been highly effective for some, the results are variable. Incretin therapies target the class B G protein-coupled receptors GLP-1R and GIPR, expressed mainly in the pancreas and the hypothalamus, while some therapeutical approaches include additional targeting of the related glucagon receptor (GCGR) in the liver. The proper functioning of these receptors is crucial for incretin therapy success and here we review several mechanisms at the cellular and molecular level that influence an individual's response to incretin therapy.

Administration of Alphitobius diaperinus or Tenebrio molitor before meals transiently increases food intake through enterohormone regulation in female rats

BACKGROUND

It has been previously shown that acutely administered insect Alphitobius diaperinus protein increases food intake in rats and modifies the ex vivo enterohormone secretory profile differently than beef or almond proteins. In this study, we aimed to evaluate whether these effects could be maintained for a longer period and determine the underlying mechanisms.

RESULTS

We administered two different insect species to rats for 26 days and measured food intake at different time points. Both insect species increased food intake in the first week, but the effect was later lost. Glucagon-like peptide 1 (GLP-1) and ghrelin were measured in plasma and ex vivo, and no chronic effects on their secretion or desensitization were found. Nevertheless, digested A. diaperinus acutely modified GLP-1 and ghrelin secretion ex vivo.

CONCLUSION

Our results suggest that increases in food intake could be explained by a local ghrelin reduction acting in the small intestine. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mesolimbic exendin-4 attenuates reward salience evoked by neuropeptide Y and ghrelin

In the present study, we investigated the effects of the glucagon-like peptide-1 (GLP-1) agonist exendin-4 (Ex-4) on the stimulatory action of neuropeptide Y (NPY) and ghrelin. These effects were examined in relation to operant responding for palatable food or voluntary ethanol intake in a two-bottle limited access paradigm. Male Sprague Dawley rats, each with ventral tegmental area (VTA) unilateral guide cannulae, were used. Ex-4 was paired with either NPY, ghrelin, or combined NPY and ghrelin treatment. Our results indicated that while NPY and ghrelin reliably stimulated operant responding for sucrose pellets and increased ethanol intake, Ex-4 suppressed intake and, most importantly, significantly reduced the effects of NPY and ghrelin. Overall, this work provides compelling evidence that VTA GLP-1, NPY, and ghrelin systems interact within the brain to modulate reward salience.

Ghrelin deficiency sex-dependently affects food intake, locomotor activity, and adipose and hepatic gene expression in a binge-eating mouse model

Binge-eating disorder is the most prevalent eating disorder diagnosed, affecting three times more women than men. Ghrelin stimulates appetite and reward signaling, and loss of its receptor reduces binge-eating behavior in male mice. Here, we examined the influence of ghrelin itself on binge-eating behavior in both male and female mice. Five-wk-old wild-type (WT) and ghrelin-deficient (Ghrl^-/-) mice were housed individually in indirect calorimetry cages for 9 wks. Binge-like eating was induced by giving mice ad libitum chow, but time-restricted access to a Western-style diet (WD; 2 h access, 3 days/wk) in the light phase (BE); control groups received ad libitum chow (CO), or ad libitum access to both diets (CW). All groups of BE mice showed binge-eating behavior, eating up to 60% of their 24-h intake during the WD access period. Subsequent dark phase chow intake was decreased in Ghrl^-/- mice and remained decreased in Ghrl^-/- females on nonbinge days. Also, nonbinge day locomotor activity was lower in Ghrl^-/- than in WT BE females. Upon euthanasia, Ghrl^-/- BE mice weighed less and had a lower lean body mass percentage than WT BE mice. In BE and CW groups, ghrelin and sex altered the expression of genes involved in lipid processing, thermogenesis, and aging in white adipose tissue and livers. We conclude that, although ghrelin deficiency does not hamper the development of binge-like eating, it sex-dependently alters food intake timing, locomotor activity, and metabolism. These results add to the growing body of evidence that ghrelin signaling is sexually dimorphic.NEW & NOTEWORTHY Ghrelin, a peptide hormone secreted from the gut, is involved in hunger and reward signaling, which are altered in binge-eating disorder. Although sex differences have been described in both binge-eating and ghrelin signaling, this interaction has not been fully elucidated. Here, we show that ghrelin deficiency affects the behavior and metabolism of mice in a binge-like eating paradigm, and that the sex of the mice impacts the magnitude and direction of these effects.

Altered Plasma Proteins in Myogenous Temporomandibular Disorders

The aims of this study were (1) to compare the levels and interactions of several plasma proteins in patients with myogenous temporomandibular disorders (TMDM) compared to healthy and pain-free controls, (2) to compare the levels and interactions in two TMDM subgroups, myalgia (MYA) and myofascial pain (MFP), and (3) to explore associations between the proteins and clinical data. Thirty-nine patients with TMDM (MFP, n = 25, MYA, n = 14), diagnosed according to the diagnostic criteria for TMD (DC/TMD), aged 38 years, and sex-matched pain-free controls completed an extended DC/TMD Axis II questionnaire and the plasma concentration of 87 biomarkers were analyzed. Nine proteins separated TMDM from controls (p = 0.0174) and 12 proteins separated MYA from MFP (p = 0.019). Pain duration, characteristic pain intensity, pain catastrophizing, perceived stress, and insomnia severity were significantly associated with protein markers (p < 0.001 to p < 0.022). In conclusion, several plasma proteins were upregulated in TMDM and either upregulated or downregulated in MYA compared to MFP. Some proteins in TMDM were associated with pain variables, sleep disturbance, and emotional function. These results show that systemic differences in protein expression exist in patients with TMDM and that altered levels of specific plasma proteins are associated with different clinical variables.

Liver-expressed antimicrobial peptide 2 functions independently of growth hormone secretagogue receptor in calorie-restricted mice

Ghrelin is a gastric-derived peptide that stimulates feeding, blood glucose elevation, body temperature reduction, and growth hormone (GH) secretion. Liver-expressed antimicrobial peptide 2 (LEAP2) is an endogenous antagonist of the ghrelin receptor, also called growth hormone secretagogue receptor (GHSR). We studied the effects of LEAP2 administration on feeding, body weight, glycemia, body temperature, and inflammation-related genes in the liver in C57BL/6 J mice and Ghsr-knockout (Ghsr-KO) mice. We found that a single administration of LEAP2 did not abolish fasting-induced food intake in 24-h fasted C57BL/6 J mice or Ghsr-KO mice. Moreover, continuous LEAP2 administration to mice fed ad libitum for 6 days did not affect feeding, body temperature, plasma ghrelin, or blood glucose. By contrast, continuous LEAP2 administration to calorie-restricted C57BL/6 J mice and Ghsr-KO mice induced body weight loss, hypoglycemia, body temperature reduction, and upregulation of Il-6 and Il-1β mRNAs in the liver. Our findings suggest that LEAP2 functions independently of GHSR, implying that LEAP2 affects physiology beyond the ghrelin-GHSR system.

The controversial role of the vagus nerve in mediating ghrelin´s actions: gut feelings and beyond

Ghrelin is a stomach-derived peptide hormone that acts via the growth hormone secretagogue receptor (GHSR) and displays a plethora of neuroendocrine, metabolic, autonomic and behavioral actions. It has been proposed that some actions of ghrelin are exerted via the vagus nerve, which provides a bidirectional communication between the central nervous system and peripheral systems. The vagus nerve comprises sensory fibers, which originate from neurons of the nodose and jugular ganglia, and motor fibers, which originate from neurons of the medulla. Many anatomical studies have mapped GHSR expression in vagal sensory or motor neurons. Also, numerous functional studies investigated the role of the vagus nerve mediating specific actions of ghrelin. Here, we critically review the topic and discuss the available evidence supporting, or not, a role for the vagus nerve mediating some specific actions of ghrelin. We conclude that studies using rats have provided the most congruent evidence indicating that the vagus nerve mediates some actions of ghrelin on the digestive and cardiovascular systems, whereas studies in mice resulted in conflicting observations. Even considering exclusively studies performed in rats, the putative role of the vagus nerve in mediating the orexigenic and growth hormone (GH) secretagogue properties of ghrelin remains debated. In humans, studies are still insufficient to draw definitive conclusions regarding the role of the vagus nerve mediating most of the actions of ghrelin. Thus, the extent to which the vagus nerve mediates ghrelin actions, particularly in humans, is still uncertain and likely one of the most intriguing unsolved aspects of the field.

Hypoglycemia and Dysautonomia After Bariatric Surgery: a Systematic Review and Perspective

INTRODUCTION

With the increasing performance of bariatric surgery, rare complications are becoming prevalent. We review the diagnosis and treatment of dysautonomia after bariatric surgery and the limited treatment options available. We summarize the suggested mechanisms and explain why a complete understanding of the etiology has yet to be determined.

METHODS

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic review was performed.

RESULTS

Of 448 studies identified in the literature search, 4 studies were reviewed, describing 87 patients diagnosed with dysautonomia. We present a patient who developed severe dysautonomia following conversion of sleeve gastrectomy to gastric bypass.

CONCLUSION

Treatment needs to focus on optimizing nutrition, avoiding hypoglycemia, and optimizing volume status.

Detection of G Protein-coupled Receptor Expression in Mouse Vagal Afferent Neurons using Multiplex In Situ Hybridization

This study describes a protocol for the multiplex in situ hybridization (ISH) of the mouse jugular-nodose ganglia, with a particular emphasis on detecting the expression of G protein-coupled receptors (GPCRs). Formalin-fixed jugular-nodose ganglia were processed with the RNAscope technology to simultaneously detect the expression of two representative GPCRs (cholecystokinin and ghrelin receptors) in combination with one marker gene of either nodose (paired-like homeobox 2b, Phox2b) or jugular afferent neurons (PR domain zinc finger protein 12, Prdm12). Labeled ganglia were imaged using confocal microscopy to determine the distribution and expression patterns of the aforementioned transcripts. Briefly, Phox2b afferent neurons were found to abundantly express the cholecystokinin receptor (Cck1r) but not the ghrelin receptor (Ghsr). A small subset of Prdm12 afferent neurons was also found to express Ghsr and/or Cck1r. Potential technical caveats in the design, processing, and interpretation of multiplex ISH are discussed. The approach described in this article may help scientists in generating accurate maps of the transcriptional profiles of vagal afferent neurons.

The Gut-Brain-Microbiome Axis and Its Link to Autism: Emerging Insights and the Potential of Zebrafish Models

Research involving autism spectrum disorder (ASD) most frequently focuses on its key diagnostic criteria: restricted interests and repetitive behaviors, altered sensory perception, and communication impairments. These core criteria, however, are often accompanied by numerous comorbidities, many of which result in severe negative impacts on quality of life, including seizures, epilepsy, sleep disturbance, hypotonia, and GI distress. While ASD is a clinically heterogeneous disorder, gastrointestinal (GI) distress is among the most prevalent co-occurring symptom complex, manifesting in upward of 70% of all individuals with ASD. Consistent with this high prevalence, over a dozen family foundations that represent genetically distinct, molecularly defined forms of ASD have identified GI symptoms as an understudied area with significant negative impacts on quality of life for both individuals and their caregivers. Moreover, GI symptoms are also correlated with more pronounced irritability, social withdrawal, stereotypy, hyperactivity, and sleep disturbances, suggesting that they may exacerbate the defining behavioral symptoms of ASD. Despite these facts (and to the detriment of the community), GI distress remains largely unaddressed by ASD research and is frequently regarded as a symptomatic outcome rather than a potential contributory factor to the behavioral symptoms. Allowing for examination of both ASD's impact on the central nervous system (CNS) as well as its impact on the GI tract and the associated microbiome, the zebrafish has recently emerged as a powerful tool to study ASD. This is in no small part due to the advantages zebrafish present as a model system: their precocious development, their small transparent larval form, and their parallels with humans in genetics and physiology. While ASD research centered on the CNS has leveraged these advantages, there has been a critical lack of GI-centric ASD research in zebrafish models, making a holistic view of the gut-brain-microbiome axis incomplete. Similarly, high-throughput ASD drug screens have recently been developed but primarily focus on CNS and behavioral impacts while potential GI impacts have not been investigated. In this review, we aim to explore the great promise of the zebrafish model for elucidating the roles of the gut-brain-microbiome axis in ASD.

Evidence from two cohorts for the frailty syndrome as an emergent state of parallel dysregulation in multiple physiological systems

Frailty is a clinical syndrome often present in older adults and characterized by a heightened vulnerability to stressors. The biological antecedents and etiology of frailty are unclear despite decades of research: frailty is associated with dysregulation in a wide range of physiological systems, but no specific cause has been identified. Here, we test predictions stemming from the hypothesis that there is no specific cause: that frailty is an emergent property arising from the complex systems dynamics of the broad loss of organismal homeostasis. Specifically, we use dysregulation of six physiological systems using the Mahalanobis distance approach in two cohorts of older adults to test the breadth, diffuseness, and nonlinearity of associations between frailty and system-specific dysregulation. We find clear support for the breadth of associations between frailty and physiological dysregulation: positive associations of all systems with frailty in at least some analyses. We find partial support for diffuseness: the number of systems or total amount of dysregulation is more important than the identity of the systems dysregulated, but results only partially replicate across cohorts. We find partial support for nonlinearity: trends are exponential but not always significantly so, and power is limited for groups with very high levels of dysregulation. Overall, results are consistent with-but not definitive proof of-frailty as an emergent property of complex systems dynamics. Substantial work remains to understand how frailty relates to underlying physiological dynamics across systems.