Gut Hormone GIP Induces Inflammation and Insulin Resistance in the Hypothalamus

Exploring the functional, protective, and transcriptomic effects of GIP on cytokine-exposed human pancreatic islets and EndoC-βH5 cells

Immune-mediated beta-cell destruction and lack of alpha-cell responsiveness to hypoglycaemia are hallmarks of type 1 diabetes pathology. The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) may hold therapeutic potential for type 1 diabetes due to its insulinotropic and glucagonotropic effects, as well as its cytoprotective effects shown in rodent beta cells. To further increase our understanding of GIP's effects on human beta cells, we here examined the functional, protective, and transcriptomic effects of GIP in human EndoC-βH5 beta cells and isolated human islets in the presence or absence of proinflammatory cytokines (interferon (IFN)-γ ± interleukin (IL)-1β) as a mimic of type 1 diabetes. GIP dose-dependently augmented glucose-stimulated insulin secretion from EndoC-βH5 cells and increased insulin and glucagon secretion from human islets at high and low glucose concentrations, respectively. The insulinotropic effect of GIP in EndoC-βH5 cells was abrogated by KN-93, an inhibitor of calcium/calmodulin-dependent protein kinase 2 (CaMK2). GIP did not prevent cytokine-induced apoptosis in EndoC-βH5 cells or human islets, and GIP did not protect against cytokine-induced functional impairment in EndoC-βH5 cells. GIP treatment of human islets for 24 h had no effects on the transcriptome and did not modulate cytokine-induced transcriptional changes. However, GIP augmented IL-1β + IFNγ-induced secretion of interleukin (IL)-10 and c-c motif chemokine ligand (CCL)-2 from human islets while decreasing the secretion of c-x-c motif chemokine ligand (CXCL)-8. In EndoC-βH5 cells, GIP reduced IFN-γ-induced secretion of tumor necrosis factor (TNF)-α, IL-2, IL-6, and IL-10 but increased the secretion of CXCL8, CCL2, CCL4, and CCL11. In conclusion, our results suggest that the insulinotropic effect of GIP is CaMK2-dependent. Furthermore, our findings indicate that GIP neither exerts cytoprotective effects against cytokines nor modulate the transcriptome of human islets. GIP may, however, exert selective modulatory effects on secreted inflammatory factors from cytokine-exposed beta cells and islets.

Rethinking Depression-Beyond Neurotransmitters: An Integrated Psychoneuroendocrineimmunology Framework for Depression's Pathophysiology and Tailored Treatment

It is known that the effectiveness of drug treatment for depression, ammine deficit based, is largely unsatisfactory. In this review, we examine the proposal of a precision therapy has emerged and has received a strong push by the identification of the role of inflammation in depression. However, precision psychiatry risks being caught in the reductionist trap of searching for the molecular switch that resets the whole system and switches off the disease. This is an illusion since the human being is complex and depression is a systemic and variable disorder. In this study, we show the inadequacy of the reductionist paradigm, and, at the same time, illustrate the superiority of the systemic paradigm centered on psychoneuroendocrineimmunology (PNEI). According to the PNEI paradigm, depression is a disease of the whole human being, caused by different sources working together: psychological, biological, and behavioral. This means knowing the biological and psychological history of the subject, identifying relational and biological crisis factors, and building personalized treatments targeting those factors with the tools of medicine and psychology, which are not reducible to the combination of drugs and psychotherapy. Our proposal presents a paradigm shift that is both theoretical and practical, which enables clinicians to assess patients experiencing depression in a unified way and treat them in an integrated manner.

The role of GIPR in food intake control

Glucose-dependent insulinotropic polypeptide (GIP) is one of two incretin hormones playing key roles in the control of food intake, nutrient assimilation, insulin secretion and whole-body metabolism. Recent pharmacological advances and clinical trials show that unimolecular co-agonists that target the receptors for the incretins - GIP and glucagon-like peptide 1 (GLP-1) - offer more effective treatment strategies for obesity and type 2 diabetes mellitus (T2D) compared with GLP-1 receptor (GLP1R) agonists alone, suggesting previously underappreciated roles of GIP in regulating food intake and body weight. The mechanisms by which GIP regulates energy balance remain controversial as both agonism and antagonism of the GIP receptor (GIPR) produce weight loss and improve metabolic outcomes in preclinical models. Recent studies have shown that GIPR signalling in the central nervous system (CNS), especially in regions of the brain that regulate energy balance, is essential for its action on appetite regulation. This finding has sparked interest in understanding the mechanisms by which GIP engages brain circuits to reduce food intake and body weight. In this review, we present key knowledge around the actions of GIP on food intake regulation and the potential mechanisms by which GIPR and GIPR/GLP1R agonists may regulate energy balance.

Impact of Dietary Fiber on Inflammation in Humans

Cohort studies consistently show that a high intake of cereal fiber and whole-grain products is associated with a decreased risk of type 2 diabetes (T2DM), cancer, and cardiovascular diseases. Similar findings are also reported for infectious and chronic inflammatory disorders. All these disorders are at least partially caused by inflammaging, a chronic state of inflammation associated with aging and Metabolic Syndrome. Surprisingly, insoluble (cereal) fiber intake consistently shows stronger protective associations with most long-term health outcomes than soluble fiber. Most humans consume soluble fiber mainly from sweet fruits, which usually come with high levels of sugar, counteracting the potentially beneficial effects of fiber. In both observational and interventional studies, high-fiber diets show a beneficial impact on inflammation, which can be attributed to a variety of nutrients apart from dietary fiber. These confounders need to be considered when evaluating the effects of fiber as part of complex dietary patterns. When assessing specific types of fiber, inulin and resistant starch clearly elicit anti-inflammatory short-term effects, while results for pectins, beta-glucans, or psyllium turn out to be less convincing. For insoluble fiber, promising but sparse data have been published so far. Hypotheses on putative mechanisms of anti-inflammatory fiber effects include a direct impact on immune cells (e.g., for pectin), fermentation to pleiotropic short-chain fatty acids (for fermentable fiber only), modulation of the gut microbiome towards higher levels of diversity, changes in bile acid metabolism, a differential release of gut hormones (such as the glucose-dependent insulinotropic peptide (GIP)), and an improvement of insulin resistance via the mTOR/S6K1 signaling cascade. Moreover, the contribution of phytate-mediated antioxidative and immune-modulatory means of action needs to be considered. In this review, we summarize the present knowledge on the impact of fiber-rich diets and dietary fiber on the human inflammatory system. However, given the huge heterogeneity of study designs, cohorts, interventions, and outcomes, definite conclusions on which fiber to recommend to whom cannot yet be drawn.

Genetic Variant Analyses Identify Novel Candidate Autism Risk Genes from a Highly Consanguineous Cohort of 104 Families from Oman

Deficits in social communication, restricted interests, and repetitive behaviours are hallmarks of autism spectrum disorder (ASD). Despite high genetic heritability, the majority of clinically diagnosed ASD cases have unknown genetic origins. We performed genome sequencing on mothers, fathers, and affected individuals from 104 families with ASD in Oman, a Middle Eastern country underrepresented in international genetic studies. This approach identified 48 novel candidate genes significantly associated with ASD in Oman. In particular, 35 of these genes have been previously implicated in neurodevelopmental disorders (NDDs) in other populations, underscoring the conserved genetic basis of ASD across ethnicities. Genetic variants within these candidate genes that would impact the encoded protein included 1 insertion, 4 frameshift, 6 splicing, 12 nonsense, and 67 missense changes. Notably, 61% of the SNVs were homozygous, suggesting a prominent recessive genetic architecture for ASD in this unique population. The scarcity of genetic studies on ASD in the Arabian Peninsula has impeded the understanding of the unique genetic landscape of ASD in this region. These findings help bridge this knowledge gap and provide valuable insights into the complex genetic basis of ASD in Oman.

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.

Semi-supervised meta-learning elucidates understudied molecular interactions

Many biological problems are understudied due to experimental limitations and human biases. Although deep learning is promising in accelerating scientific discovery, its power compromises when applied to problems with scarcely labeled data and data distribution shifts. We develop a deep learning framework-Meta Model Agnostic Pseudo Label Learning (MMAPLE)-to address these challenges by effectively exploring out-of-distribution (OOD) unlabeled data when conventional transfer learning fails. The uniqueness of MMAPLE is to integrate the concept of meta-learning, transfer learning and semi-supervised learning into a unified framework. The power of MMAPLE is demonstrated in three applications in an OOD setting where chemicals or proteins in unseen data are dramatically different from those in training data: predicting drug-target interactions, hidden human metabolite-enzyme interactions, and understudied interspecies microbiome metabolite-human receptor interactions. MMAPLE achieves 11% to 242% improvement in the prediction-recall on multiple OOD benchmarks over various base models. Using MMAPLE, we reveal novel interspecies metabolite-protein interactions that are validated by activity assays and fill in missing links in microbiome-human interactions. MMAPLE is a general framework to explore previously unrecognized biological domains beyond the reach of present experimental and computational techniques.

Glucose-dependent insulinotropic polypeptide (GIP) alleviates ferroptosis in aging-induced brain damage through the Epac/Rap1 signaling pathway

Glucose-dependent insulinotropic polypeptide (GIP), a 42-aminoacid hormone, exerts multifaceted effects in physiology, most notably in metabolism, obesity, and inflammation. Its significance extends to neuroprotection, promoting neuronal proliferation, maintaining physiological homeostasis, and inhibiting cell death, all of which play a crucial role in the context of neurodegenerative diseases. Through intricate signaling pathways involving its cognate receptor (GIPR), a member of the G protein-coupled receptors, GIP maintains cellular homeostasis and regulates a defense system against ferroptosis, an essential process in aging. Our study, utilizing GIP-overexpressing mice and in vitro cell model, elucidates the pivotal role of GIP in preserving neuronal integrity and combating age-related damage, primarily through the Epac/Rap1 pathway. These findings shed light on the potential of GIP as a therapeutic target for the pathogenesis of ferroptosis in neurodegenerative diseases and aging. [BMB Reports 2024; 57(9): 417-423].

Obesogens: a unifying theory for the global rise in obesity

Despite varied treatment, mitigation, and prevention efforts, the global prevalence and severity of obesity continue to worsen. Here we propose a combined model of obesity, a unifying paradigm that links four general models: the energy balance model (EBM), based on calories as the driver of weight gain; the carbohydrate-insulin model (CIM), based on insulin as a driver of energy storage; the oxidation-reduction model (REDOX), based on reactive oxygen species (ROS) as a driver of altered metabolic signaling; and the obesogens model (OBS), which proposes that environmental chemicals interfere with hormonal signaling leading to adiposity. We propose a combined OBS/REDOX model in which environmental chemicals (in air, food, food packaging, and household products) generate false autocrine and endocrine metabolic signals, including ROS, that subvert standard regulatory energy mechanisms, increase basal and stimulated insulin secretion, disrupt energy efficiency, and influence appetite and energy expenditure leading to weight gain. This combined model incorporates the data supporting the EBM and CIM models, thus creating one integrated model that covers significant aspects of all the mechanisms potentially contributing to the obesity pandemic. Importantly, the OBS/REDOX model provides a rationale and approach for future preventative efforts based on environmental chemical exposure reduction.

Mendelian randomization analyses suggest a causal role for circulating GIP and IL-1RA levels in homeostatic model assessment-derived measures of β-cell function and insulin sensitivity in Africans without type 2 diabetes

BACKGROUND

In vitro and in vivo studies have shown that certain cytokines and hormones may play a role in the development and progression of type 2 diabetes (T2D). However, studies on their role in T2D in humans are scarce. We evaluated associations between 11 circulating cytokines and hormones with T2D among a population of sub-Saharan Africans and tested for causal relationships using Mendelian randomization (MR) analyses.

METHODS

We used logistic regression analysis adjusted for age, sex, body mass index, and recruitment country to regress levels of 11 cytokines and hormones (adipsin, leptin, visfatin, PAI-1, GIP, GLP-1, ghrelin, resistin, IL-6, IL-10, IL-1RA) on T2D among Ghanaians, Nigerians, and Kenyans from the Africa America Diabetes Mellitus study including 2276 individuals with T2D and 2790 non-T2D individuals. Similar linear regression models were fitted with homeostatic modelling assessments of insulin sensitivity (HOMA-S) and β-cell function (HOMA-B) as dependent variables among non-T2D individuals (n = 2790). We used 35 genetic variants previously associated with at least one of these 11 cytokines and hormones among non-T2D individuals as instrumental variables in univariable and multivariable MR analyses. Statistical significance was set at 0.0045 (0.05/11 cytokines and hormones).

RESULTS

Circulating GIP and IL-1RA levels were associated with T2D. Nine of the 11 cytokines and hormones (exceptions GLP-1 and IL-6) were associated with HOMA-S, HOMA-B, or both among non-T2D individuals. Two-stage least squares MR analysis provided evidence for a causal effect of GIP and IL-RA on HOMA-S and HOMA-B in multivariable analyses (GIP ~ HOMA-S β =  - 0.67, P-value = 1.88 × 10-6 and HOMA-B β = 0.59, P-value = 1.88 × 10-5; IL-1RA ~ HOMA-S β =  - 0.51, P-value = 8.49 × 10-5 and HOMA-B β = 0.48, P-value = 5.71 × 10-4). IL-RA was partly mediated via BMI (30-34%), but GIP was not. Inverse variance weighted MR analysis provided evidence for a causal effect of adipsin on T2D (multivariable OR = 1.83, P-value = 9.79 × 10-6), though these associations were not consistent in all sensitivity analyses.

CONCLUSIONS

The findings of this comprehensive MR analysis indicate that circulating GIP and IL-1RA levels are causal for reduced insulin sensitivity and increased β-cell function. GIP's effect being independent of BMI suggests that circulating levels of GIP could be a promising early biomarker for T2D risk. Our MR analyses do not provide conclusive evidence for a causal role of other circulating cytokines in T2D among sub-Saharan Africans.

Relevance and consequence of chronic inflammation for obesity development

BACKGROUND

Increasing prevalence of morbid obesity accompanied by comorbidities like type 2 diabetes mellitus (T2DM) led to a demand for improving therapeutic strategies and pharmacological intervention options. Apart from genetics, inflammation processes have been hypothesized to be of importance for the development of obesity and related aspects like insulin resistance.

MAIN TEXT

Within this review, we provide an overview of the intricate interplay between chronic inflammation of the adipose tissue and the hypothalamus and the development of obesity. Further understanding of this relationship might improve the understanding of the underlying mechanism and may be of relevance for the establishment of new treatment strategies.

Obesity pharmacotherapy: incretin action in the central nervous system

The prevalence of obesity is rising, creating an urgent need for efficacious therapies. Recent clinical trials show that tirzepatide, a dual agonist of receptors for the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), yields more weight loss than selective GLP-1 receptor (GLP-1R) agonists. Incretin receptors in the central nervous system (CNS) may contribute to these effects. Yet exactly how each receptor regulates body weight from within the CNS is not clearly understood. It remains especially unclear how GIP receptor (GIPR) signalling contributes to the effects of tirzepatide because both stimulation and inhibition of CNS GIPRs yield weight loss in preclinical models. We summarise current knowledge on CNS incretin receptor pharmacology to provide insight into the potential mechanisms of action of dual GIPR/GLP-1R agonists, with tirzepatide as the exemplar. In addition, we discuss recent developments in incretin-based dual- and tri-agonism for inducing weight loss in obese individuals.

Phoenixin-14 alters transcriptome and steroid profiles in female green-spotted puffer (Dichotomyctere nigroviridis)

Phoenixin (PNX) is a highly conserved, novel hormone with diverse functions, including hypothalamic control of reproduction, appetite modulation, and regulation of energy metabolism and inflammation. While some functions appear conserved across vertebrates, additional research is required to fully characterize these complex pleiotropic effects. For instance, very little is known about transcriptome level changes associated with PNX exposure, including responses in the hypothalamic-pituitary-gonadal (HPG) axis, which is critical in vertebrate reproduction. In addition, the PNX system may be especially complex in fish, where an additional receptor is likely present in some species. The purpose of this study was to assess hypothalamic and ovarian transcriptomes after PNX-14 administration in female vitellogenic green-spotted puffer (Dichotomyctere nigroviridis). Steroid-related changes were also assessed in the liver and blood plasma. Hypothalamic responses included pro-inflammatory signals such as interleukin 1β, possibly related to gut-brain axis functions, as well as suppression of cell proliferation. Ovarian responses were more widely downregulated across all identified pathways, which may reflect progression to a less transcriptionally active state in oocytes. Both organs shared regulation in transforming growth factor-β and extracellular matrix remodeling (periostin) pathways. Reproductive processes were in general downregulated, but both inhibiting (bone morphogenetic protein 15 and follistatin) and promoting (17-hydroxyprogesterone) factors for oocyte maturation were identified. Select genes involved in reproduction (vitellogenins, estrogen receptors) in the liver were unresponsive to PNX-14 and higher doses may be needed to induce reproductive effects in D. nigroviridis. These results reinforce the complexity of PNX actions in diverse tissues and highlight important roles for this hormone in regulating the immune response, energy metabolism, and cell growth.

Glucose-Dependent Insulinotropic Polypeptide-A Postprandial Hormone with Unharnessed Metabolic Potential

Glucose-dependent insulinotropic polypeptide (GIP) is released from the upper small intestine in response to food intake and contributes to the postprandial control of nutrient disposition, including of sugars and fats. Long neglected as a potential therapeutic target, the GIPR axis has received increasing interest recently, with the emerging data demonstrating the metabolically favorable outcomes of adding GIPR agonism to GLP-1 receptor agonists in people with type 2 diabetes and obesity. This review examines the physiology of the GIP axis, from the mechanisms underlying GIP secretion from the intestine to its action on target tissues and therapeutic development. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

An orally active plant Rubisco-derived peptide increases neuronal leptin responsiveness

Nutrient excess, such as the intake of a high-fat diet, reduces hypothalamic responses to exogenously administered leptin and induces dietary obesity; however, orally active components that attenuate neural leptin dysregulation have yet to be identified. We herein demonstrated that YHIEPV, derived from the pepsin-pancreatin digestion of the green leaf protein Rubisco, increased the leptin-induced phosphorylation of STAT3 in ex vivo hypothalamic slice cultures. We also showed that YHIEPV mitigated palmitic acid-induced decreases in leptin responsiveness. Furthermore, orally administered YHIEPV promoted leptin-induced reductions in body weight and food intake in obese mice. In addition, dietary-induced body weight gain was significantly less in mice orally or centrally administered YHIEPV daily than in saline-control mice. Cellular leptin sensitivity and the levels of proinflammatory-related factors, such as IL1β and Socs-3, in the hypothalamus of obese mice were also restored by YHIEPV. YHIEPV blocked cellular leptin resistance induced by forskolin, which activates Epac-Rap1 signaling, and reduced the level of the GTP-bound active form of Rap1 in the brains of obese mice. Collectively, the present results demonstrated that the orally active peptide YHIEPV derived from a major green leaf protein increased neural leptin responsiveness and reduced body weight gain in mice with dietary obesity.

A D2 to D1 shift in dopaminergic inputs to midbrain 5-HT neurons causes anorexia in mice

Midbrain dopamine (DA) and serotonin (5-HT) neurons regulate motivated behaviors, including feeding, but less is known about how these circuits may interact. In this study, we found that DA neurons in the mouse ventral tegmental area bidirectionally regulate the activity of 5-HT neurons in the dorsal raphe nucleus (DRN), with weaker stimulation causing DRD2-dependent inhibition and overeating, while stronger stimulation causing DRD1-dependent activation and anorexia. Furthermore, in the activity-based anorexia (ABA) paradigm, which is a mouse model mimicking some clinical features of human anorexia nervosa (AN), we observed a DRD2 to DRD1 shift of DA neurotransmission on 5-HTDRN neurons, which causes constant activation of these neurons and contributes to AN-like behaviors. Finally, we found that systemic administration of a DRD1 antagonist can prevent anorexia and weight loss in ABA. Our results revealed regulation of feeding behavior by stimulation strength-dependent interactions between DA and 5-HT neurons, which may contribute to the pathophysiology of AN.

Glucose-dependent insulinotropic polypeptide and tissue inflammation: Implications for atherogenic cardiovascular disease

Glucose-dependent insulinotropic polypeptide (GIP) has pleiotropic actions on pancreatic endocrine function, adipose tissue lipid metabolism, and skeletal calcium metabolism. Recent data indicate a potential new role for GIP in the pathogenesis of cardiovascular disease. This review focuses on the emerging literature that highlights GIP’s role in inflammation—an established process in the initiation and progression of atherosclerosis. In vasculature tissue, GIP may reduce concentrations of circulating inflammatory cytokines, attenuate vascular endothelial inflammation, and directly limit atherosclerotic vascular damage. Important to recognize is that evidence exists to support both pro- and anti-inflammatory effects of GIP even within the same tissue/cell type. Therefore, future study designs must account for factors such as model heterogeneity, physiological relevance of doses/exposures, potential indirect effects on inflammatory pathways, and the glucose-dependent insulinotropic polypeptide receptor (GIPR) agonist form. Elucidating the specific effects of enhanced GIP signaling in vascular inflammation and atherosclerosis is crucial given the existing widespread use of DPP4 inhibitors and the emergence of dual-incretin receptor agonists for type 2 diabetes treatment.

Divergent Effect of Central Incretin Receptors Inhibition in a Rat Model of Sporadic Alzheimer's Disease

The incretin system is an emerging new field that might provide valuable contributions to the research of both the pathophysiology and therapeutic strategies in the treatment of diabetes, obesity, and neurodegenerative disorders. This study aimed to explore the roles of central glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) on cell metabolism and energy in the brain, as well as on the levels of these incretins, insulin, and glucose via inhibition of the central incretin receptors following intracerebroventricular administration of the respective antagonists in healthy rats and a streptozotocin-induced rat model of sporadic Alzheimer's disease (sAD). Chemical ablation of the central GIP receptor (GIPR) or GLP-1 receptor (GLP-1R) in healthy and diseased animals indicated a region-dependent role of incretins in brain cell energy and metabolism and central incretin-dependent modulation of peripheral hormone secretion, markedly after GIPR inhibition, as well as a dysregulation of the GLP-1 system in experimental sAD.

Bioactive Foods Decrease Liver and Brain Alterations Induced by a High-Fat-Sucrose Diet through Restoration of Gut Microbiota and Antioxidant Enzymes

Obesity is associated with cognitive deficit and liver alterations; however, it remains unclear whether a combination of functional foods could reverse cognitive damage and to what extent it would be associated with changes in gut microbiota and liver. With this aim, male Wistar rats were fed a high-fat-5%sucrose diet (HFS) for 4 mo. And were then fed for 1 mo. with bioactive foods. At the end of this period, liver, serum, feces, intestine, and brain samples were taken. Body composition, energy expenditure, LPS, hormones, intraperitoneal glucose tolerance test, behavioral tests, and gut microbiota were evaluated. We showed that male rats fed high-fat-sucrose diet developed gut microbiota dysbiosis, increased in body fat, decreased antioxidant activity, decreased brain neuropeptide Y, increased the number of astrocytes and activated microglia, along with reduced spine density associated with deficits in working memory. Ingestion of a combination of nopal, soy protein, curcumin, and chia seed oil (bioactive foods) for three months was associated with an increase in a cluster of bacteria with anti-inflammatory capacity, a decrease in serum LPS levels and an increase in serum eicosapentaenoic acid (EPA) with neuroprotective properties. In the liver, ingestion of bioactive food significantly increased antioxidant enzymes, decreased lipogenesis, reduced inflammation mediated by the TLR4-TNFα pathway along with a decrease in body fat, glucose intolerance, and metabolic inflexibility. Finally, neuroinflammation in the brain was reduced and working memory improved. Our study demonstrates that consumption of bioactive foods was associated with reduced liver, brain, and gut microbiota alterations in obese rats.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

Appetite regulation by plant-derived bioactive peptides for promoting health

Appetite is closely regulated not only by gut hormonal and neuronal peptides but also by exogenous peptides derived from food proteins. Food proteins are now recognized to contain many thousands of bioactive compounds that provide additional health benefits beyond their nutritional effects. Bioactive peptides are beneficial to the life and/or to regulate physiological functions. Although animal protein products have been widely applied in the food industry, exploring the possibilities of developing functional foods based on plant protein-derived peptides is considered attractive for achieving sustainable development goals. In addition, peptides from plant proteins have the potential to treat numerous diseases or risk factors and may therefore facilitate a healthy life expectancy. In this review, we discuss the identified plant-based bioactive peptides and their appetite regulating effects. Plant-based bioactive peptides may provide new opportunities to discover novel approaches that can improve and prevent diseases in a sustainable environment.

The Role of GIP Receptor in the CNS for the Pathogenesis of Obesity

Glucose-dependent insulinotropic polypeptide (GIP) (also known as gastric inhibitory polypeptide) is a hormone produced in the upper gut and secreted to the circulation in response to the ingestion of foods, especially fatty foods. Growing evidence supports the physiological and pharmacological relevance of GIP in obesity. In an obesity setting, inhibition of endogenous GIP or its receptor leads to decreased energy intake, increased energy expenditure, or both, eventually causing weight loss. Further, supraphysiological dosing of exogenous long-lasting GIP agonists alters energy balance and has a marked antiobesity effect. This remarkable yet paradoxical antiobesity effect is suggested to occur primarily via the brain. The brain is capable of regulating both energy intake and expenditure and plays a critical role in human obesity. In addition, the GIP receptor is widely distributed throughout the brain, including areas responsible for energy homeostasis. Recent studies have uncovered previously underappreciated roles of the GIP receptor in the brain in the context of obesity. This article highlights how the GIP receptor expressed by the brain impacts obesity-related pathogenesis.

Nutrition, Exercise, and Stress Management for Treatment and Prevention of Psychiatric Disorders. A Narrative Review Psychoneuroendocrineimmunology-Based

Psychoneuroendocrineimmunology (PNEI) brings together knowledge acquired since the 1930s from endocrinology, immunology, neuroscience, and psychology. With PNEI, a model of research and interpretation of health and disease is emerging, which sees the human body as a structured and interconnected unit, where the psychological and biological systems are mutually coordinated. In the PNEI view, many factors could influence mental health, with the endocrine system involved in mediating the effects of environmental stress on mental health and inflammation in the onset and course of psychiatric disorders as a result of individual and collective conditions and behaviors. Among these, nutrition is one way by which the environment impacts physiology: indeed, many pieces of research showed that several elements (e.g., probiotics, fish oil, zinc) have a positive effect on mental disorders thus being potentially augmentation agents in treatment. Still, physical activity can moderate depressive symptoms, while prolonged stress increases the risk of psychopathology. Taken together, the PNEI-based approach may inform prevention and treatment strategies, also in the field of mental health care.

Central Neurocircuits Regulating Food Intake in Response to Gut Inputs-Preclinical Evidence

The regulation of energy balance requires the complex integration of homeostatic and hedonic pathways, but sensory inputs from the gastrointestinal (GI) tract are increasingly recognized as playing critical roles. The stomach and small intestine relay sensory information to the central nervous system (CNS) via the sensory afferent vagus nerve. This vast volume of complex sensory information is received by neurons of the nucleus of the tractus solitarius (NTS) and is integrated with responses to circulating factors as well as descending inputs from the brainstem, midbrain, and forebrain nuclei involved in autonomic regulation. The integrated signal is relayed to the adjacent dorsal motor nucleus of the vagus (DMV), which supplies the motor output response via the efferent vagus nerve to regulate and modulate gastric motility, tone, secretion, and emptying, as well as intestinal motility and transit; the precise coordination of these responses is essential for the control of meal size, meal termination, and nutrient absorption. The interconnectivity of the NTS implies that many other CNS areas are capable of modulating vagal efferent output, emphasized by the many CNS disorders associated with dysregulated GI functions including feeding. This review will summarize the role of major CNS centers to gut-related inputs in the regulation of gastric function with specific reference to the regulation of food intake.

GIP-GIPR promotes neurite outgrowth of cortical neurons in Akt dependent manner

The intrinsic capacity of axonal growth is varied among the neurons form different tissues or different developmental stages. In this study, we established an in vitro model to compare the axonal growth of neurons from embryonic 18 days, post-natal 1 day and post-natal 3 days rat. The E18 neurons showed powerful ability of neuritogenensis and axon outgrowth and the ability decreased rapidly along with development. The transcriptome profile of these neurons revealed a set of genes positively correlated with the capacity of neurite outgrowth. Glucose-dependent insulinotropic polypeptide receptor (GIPR) is identified as a gene to promote neurite outgrowth, which was approved by siRNA knock down assay in E18 neuron. Glucose-dependent insulinotropic polypeptide (GIP), a ligand of GIPR secreted from enteroendocrine K cells, is well-known for its role in nutrient sensing and intake. To verify the effect of GIP-GIPR signal on neurite outgrowth, we administrated GIP to stimulate the E18 neurons, the results showed that GIP significantly improved extension of axon. We further revealed that GIP increased Rac1/Cdc42 phosphorylation in Akt dependent manner. In summary, our study established an in vitro model to screen the genes involved in neurite outgrowth, and we provided mechanical insight on the GIP-GIPR axis to promote axonal outgrowth.

Targeting the GIPR for obesity: To agonize or antagonize? Potential mechanisms

BACKGROUND

Glucose-dependent insulinotropic peptide (GIP) is one of two incretin hormones that communicate nutrient intake with systemic metabolism. Although GIP was the first incretin hormone to be discovered, the understanding of GIP's biology was quickly outpaced by research focusing on the other incretin hormone, glucagon-like peptide 1 (GLP-1). Early work on GIP produced the theory that GIP is obesogenic, limiting interest in developing GIPR agonists to treat type 2 diabetes. A resurgence of GIP research has occurred in the last five years, reinvigorating interest in this peptide. Two independent approaches have emerged for treating obesity, one promoting GIPR agonism and the other antagonism. In this report, evidence supporting both cases is discussed and hypotheses are presented to reconcile this apparent paradox.

SCOPE OF THE REVIEW

This review presents evidence to support targeting GIPR to reduce obesity. Most of the focus is on the effect of singly targeting the GIPR using both a gain- and loss-of-function approach, with additional sections that discuss co-targeting of the GIPR and GLP-1R.

MAJOR CONCLUSIONS

There is substantial evidence to support that GIPR agonism and antagonism can positively impact body weight. The long-standing theory that GIP drives weight gain is exclusively derived from loss-of-function studies, with no evidence to support that GIPR agonisms increases adiposity or body weight. There is insufficient evidence to reconcile the paradoxical observations that both GIPR agonism and antagonism can reduce body weight; however, two independent hypotheses centered on GIPR antagonism are presented based on new data in an effort to address this question. The first discusses the compensatory relationship between incretin receptors and how antagonism of the GIPR may enhance GLP-1R activity. The second discusses how chronic GIPR agonism may produce desensitization and ultimately loss of GIPR activity that mimics antagonism. Overall, it is clear that a deeper understanding of GIP biology is required to understand how modulating this system impacts metabolic homeostasis.