Chronic exposure to low dose bacterial lipopolysaccharide inhibits leptin signaling in vagal afferent neurons

Microbiota-induced inflammation mediates the impacts of a Western diet on hippocampal-dependent memory

Obesity is associated with impaired hippocampal-dependent memory, but the mechanisms driving this pathology are not fully understood. Western diets (WD) contribute to obesity, and previous reviews have described a role for WD in impaired hippocampal-dependent memory. However, there is need for a more detailed description of the pathways by which WD may impair memory. The short vs long-term effect of specific dietary components on brain structure and functions as well as the precise mechanism and molecular pathways involved are still not fully understood. This review focuses on the mechanisms and effects of gut microbiota-driven neuroinflammation. WD leads to changes and imbalance in bacterial taxa abundances that are deleterious to the host health (gut dysbiosis) and studies in rodent models show these changes are sufficient to impair hippocampal-dependent memory. Here, we discuss a variety of proposed mechanisms linking microbiota composition to hippocampal function, with a focus on neuroinflammation. Gut microbiota impacts gastrointestinal barrier function, leading to increased circulating proinflammatory bacterial products, increased blood-brain barrier permeability, and neuroinflammation.

Vagal Sensory Gut-Brain Pathways That Control Eating-Satiety and Beyond

The vagus nerve is the body's primary sensory conduit from gut to brain, traditionally viewed as a passive relay for satiety signals. However, emerging evidence reveals a far more complex system-one that actively encodes diverse aspects of meal-related information, from mechanical stretch to nutrient content, metabolic state, and even microbial metabolites. This review challenges the view of vagal afferent neurons (VANs) as simple meal-termination sensors and highlights their specialized subpopulations, diverse sensory modalities, and downstream brain circuits, which shape feeding behavior, metabolism, and cognition. We integrate recent advances from single-cell transcriptomics, neural circuit mapping, and functional imaging to examine how VANs contribute to gut-brain communication beyond satiety, including their roles in food reward and memory formation. By synthesizing the latest research and highlighting emerging directions for the field, this review provides a comprehensive update on vagal sensory pathways and their role as integrators of meal information.

From Gut to Brain: The Impact of Short-Chain Fatty Acids on Brain Cancer

The primary source of short-chain fatty acids (SCFAs), now recognized as critical mediators of host health, particularly in the context of neurobiology and cancer development, is the gut microbiota's fermentation of dietary fibers. Recent research highlights the complex influence of SCFAs, such as acetate, propionate, and butyrate, on brain cancer progression. These SCFAs impact immune modulation and the tumor microenvironment, particularly in brain tumors like glioma. They play a critical role in regulating cellular processes, including apoptosis, cell differentiation, and inflammation. Moreover, studies have linked SCFAs to maintaining the integrity of the blood-brain barrier (BBB), suggesting a protective role in preventing tumor infiltration and enhancing anti-tumor immunity. As our understanding of the gut-brain axis deepens, it becomes increasingly important to investigate SCFAs' therapeutic potential in brain cancer management. Looking into how SCFAs affect brain tumor cells and the environment around them could lead to new ways to prevent and treat these diseases, which could lead to better outcomes for people who are dealing with these challenging cancers.

Role of Increasing Body Mass Index in Gut Barrier Dysfunction, Systemic Inflammation, and Metabolic Dysregulation in Obesity

AIMS

This study explores the link between body mass index (BMI), intestinal permeability, and associated changes in anthropometric and impedance parameters, lipid profiles, inflammatory markers, fecal metabolites, and gut microbiota taxa composition in participants having excessive body mass.

METHODS

A cohort of 58 obese individuals with comparable diet, age, and height was divided into three groups based on a priori clustering analyses that fit with BMI class ranges: Group I (25-29.9), Group II (30-39.9), and Group III (>40). Anthropometric and clinical parameters were assessed, including plasma C-reactive protein and cytokine profiles as inflammation markers. Intestinal permeability was measured using a multisaccharide assay, with fecal/serum zonulin and serum claudin-5 and claudin-15 levels. Fecal microbiota composition and metabolomic profiles were analyzed using a phylogenetic microarray and GC-MS techniques.

RESULTS

The statistical analyses of the clinical parameters were based on the full sample set, whereas a subset composed of 37 randomized patients was inspected for the GC/MS metabolite profiling of fecal specimens. An increase in potentially pro-inflammatory bacterial genera (e.g., Slackia, Dorea, Granulicatella) and a reduction in beneficial genera (e.g., Adlercreutzia, Clostridia UCG-014, Roseburia) were measured. The gas chromatography/mass spectrometry analysis of urine samples evidenced a statistically significant increase in m-cymen-8-ol, 1,3,5-Undecatriene, (E, Z) and a decreased concentration of p-cresol, carvone, p-cresol, and nonane.

CONCLUSIONS

Together, these data demonstrated how an increased BMI led to significant changes in inflammatory markers, intestinal barrier metabolites, glucose metabolism, endocrine indicators, and fecal metabolomic profiles that can indicate a different metabolite production from gut microbiota. Our findings suggest that targeting intestinal permeability may offer a therapeutic approach to prevent and manage obesity and related metabolic complications, reinforcing the link between gut barrier function and obesity.

High-fat and high-carbohydrate diets worsen the mouse brain susceptibility to damage produced by enterohemorrhagic Escherichia coli Shiga toxin 2

Background

Nutrition quality could be one of the reasons why, in the face of a Shiga toxin-producing enterohemorrhagic Escherichia coli outbreak, some patients experience more profound deleterious effects than others, including unfortunate deaths. Thus, the aim of this study was to determine whether high-fat and/or high-carbohydrate diets could negatively modulate the deleterious action of Shiga toxin 2 on ventral anterior and ventral lateral thalamic nuclei and the internal capsule, the neurological centers responsible for motor activity.

Methods

Mice were fed a regular, high-fat, high-carbohydrate diet or a combination of both previous to the intravenous administration of Shiga toxin 2 or vehicle. Four days after intravenous administration, mice were subjected to behavioral tests and then sacrificed for histological and immunofluorescence assays to determine alterations in the neurovascular unit at the cellular and functional levels. Statistical analysis was performed using one-way analysis of variance followed by Bonferroni post hoc test. The criterion for significance was p = 0.0001 for all experiments.

Results

The high-fat and the high-carbohydrate diets significantly heightened the deleterious effect of Stx2, while the combination of both diets yielded the worst results, including endothelial glycocalyx and oligodendrocyte alterations, astrocyte and microglial reactivity, neurodegeneration, and motor and sensitivity impairment.

Conclusions

In view of the results presented here, poor nutrition could negatively influence patients affected by Stx2 at a neurological level. Systemic effects, however, cannot be ruled out.

Manipulation of feeding patterns in high fat diet fed rats improves microbiota composition dynamics, inflammation and gut-brain signaling

Chronic consumption of high fat (HF) diets has been shown to increase meal size and meal frequency in rodents, resulting in overeating. Reducing meal frequency and establishing periods of fasting, independently of caloric intake, may improve obesity-associated metabolic disorders. Additionally, diet-driven changes in microbiota composition have been shown to play a critical role in the development and maintenance of metabolic disorders. In this study, we used a pair-feeding paradigm to reduce meal frequency and snacking episodes while maintaining overall intake and body weight in HF fed rats. We hypothesized that manipulation of feeding patterns would improve microbiota composition and metabolic outcomes. Male Wistar rats were placed in three groups consuming either a HF, low fat diet (LF, matched for sugar), or pair-fed HF diet for 7 weeks (n = 11-12/group). Pair-fed animals received the same amount of food consumed by the HF fed group once daily before dark onset (HF-PF). Rats underwent oral glucose tolerance and gut peptide cholecystokinin sensitivity tests. Bacterial DNA was extracted from the feces collected during both dark and light cycles and sequenced via Illumina MiSeq sequencing of the 16S V4 region. Our pair-feeding paradigm reduced meal numbers, especially small meals in the inactive phase, without changing total caloric intake. This shift in feeding patterns reduced relative abundances of obesity-associated bacteria and maintained circadian fluctuations in microbial abundances. These changes were associated with improved gastrointestinal (GI) function, reduced inflammation, and improved glucose tolerance and gut to brain signaling. We concluded from these data that targeting snacking may help improve metabolic outcomes, independently of energy content of the diet and hyperphagia.

Prebiotic Potential of Goji Berry (Lycium barbarum) in Improving Intestinal Integrity and Inflammatory Profiles via Modification of the Gut Microbiota in High-Fat Diet-Fed Rats

Background: Imbalances in gut microbiota and subsequent destabilization of intestinal barrier equilibrium have been related to the evolution of metabolic disorders. Goji berries (Lycium barbarum; GB) and their fermented counterpart (FGB) have been identified for their prebiotic capacity in managing intestinal barrier functions and inflammatory profiles Consequently, this research was designed to investigate the effects of supplementing GB and FGB on intestinal integrity, inflammation, and changes in the composition of gut microbiota in high-fat (HF)-fed rats. Materials and Methods: Thirty-two male Sprague-Dawley rats (6 weeks old, 8 per group) were divided into four categories based on their weight and provided with either respective diets over a 6-week period: low-fat (LF; 10% of calories from fat), HF (45% of calories from fat), and HF diets supplemented with either GB or FGB at a 2% (w/w). Results: Supplementation of GB and FGB resulted in compositional changes in the gut microbiota, denoted by a distinct abundance of Faecalibacterium prausnitzii with GB and Akkermansia muciniphila species with FGB, which have been linked to ameliorated obesity phenotypes and metabolic parameters. These alterations were correlated with enhancements in gut barrier integrity, thereby protecting against local and systemic inflammation induced by a HF diet. Supplementation with GB and FGB also mitigated lipopolysaccharide-induced inflammation through inhibition of its downstream pathway. Conclusion: These findings indicate that both GB and FGB supplementation can improve gut barrier function and inflammatory profiles in HF-fed rats via modulation of the microbial composition of the gut, supporting the potential application of GB and FGB in improving gut barrier function and managing inflammation amid metabolic challenges.

Obesity- and diet-induced plasticity in systems that control eating and energy balance

In April 2023, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), in partnership with the National Institute of Child Health and Human Development, the National Institute on Aging, and the Office of Behavioral and Social Sciences Research, hosted a 2-day online workshop to discuss neural plasticity in energy homeostasis and obesity. The goal was to provide a broad view of current knowledge while identifying research questions and challenges regarding neural systems that control food intake and energy balance. This review includes highlights from the meeting and is intended both to introduce unfamiliar audiences with concepts central to energy homeostasis, feeding, and obesity and to highlight up-and-coming research in these areas that may be of special interest to those with a background in these fields. The overarching theme of this review addresses plasticity within the central and peripheral nervous systems that regulates and influences eating, emphasizing distinctions between healthy and disease states. This is by no means a comprehensive review because this is a broad and rapidly developing area. However, we have pointed out relevant reviews and primary articles throughout, as well as gaps in current understanding and opportunities for developments in the field.

Effects of non-nutritive sweeteners on growth and intestinal health by regulating hypothalamic RNA profile and ileum microbiota in guinea pigs

BACKGROUND

Non-nutritive sweeteners (NNS) are commonly used in sweetened foods and beverages; however their role in metabolic regulation is still not clear. In this experiment, we used guinea pigs as an animal model to study the effect of NNS on body growth and intestinal health by modifying gut microbiota and hypothalamus-related proteins.

RESULTS

For a 28-day feeding experiment a total of 40 guinea pigs were randomly divided into four groups, one control (CN) group and three treatments, in which three NNS were added to the diet: rebaudioside A (RA, 330 mg kg-1), sodium saccharin (SS, 800 mg kg-1), and sucralose (TGS, 167 mg kg-1), respectively. The TGS group exhibited significantly reduced food consumption in comparison with the CN group (P < 0.05) whereas the RA group showed increased food consumption in comparison with the CN group (P < 0.05). Notably, Taste receptor type 1 subunit 2 (T1R2) expression in the hypothalamus was significantly higher in the RA group than in the CN group (P < 0.05). The mRNA expressions of appetite-stimulated genes arouti-related neuropeptide (AGRP), neuropeptide Y (NPY), and thyroid stimulating hormone (TSHB) were significantly higher than those in the CN group (P < 0.05) but mRNA expressions of appetite-suppressed genes tryptophan hydroxylase 2(THP2) were significantly lower in the TGS group (P < 0.05). Furthermore, NNS in the guinea pig diets (RA, SS, TGS) significantly increased the relative abundance of Muribaculaceae but decreased the relative abundance of Clostridia_vadin BB60 in comparison with the CN group (P < 0.05). We also found that dietary supplementation with RA also significantly altered the relative abundance of Lactobacillus.

CONCLUSION

Our finding confirmed that dietary supplementation with RA and TGS affected body growth and intestinal health by modulating hypothalamic RNA profiles and ileum microbiota, suggesting that NNS should be included in guinea-pig feeding. © 2024 Society of Chemical Industry.

Influence of Bariatric Surgery on Gut Microbiota Composition and Its Implication on Brain and Peripheral Targets

Obesity remains a significant global health challenge, with bariatric surgery remaining as one of the most effective treatments for severe obesity and its related comorbidities. This review highlights the multifaceted impact of bariatric surgery beyond mere physical restriction or nutrient malabsorption, underscoring the importance of the gut microbiome and neurohormonal signals in mediating the profound effects on weight loss and behavior modification. The various bariatric surgery procedures, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), act through distinct mechanisms to alter the gut microbiome, subsequently impacting metabolic health, energy balance, and food reward behaviors. Emerging evidence has shown that bariatric surgery induces profound changes in the composition of the gut microbiome, notably altering the Firmicutes/Bacteroidetes ratio and enhancing populations of beneficial bacteria such as Akkermansia. These microbiota shifts have far-reaching effects beyond gut health, influencing dopamine-mediated reward pathways in the brain and modulating the secretion and action of key gut hormones including ghrelin, leptin, GLP-1, PYY, and CCK. The resultant changes in dopamine signaling and hormone levels contribute to reduced hedonic eating, enhanced satiety, and improved metabolic outcomes. Further, post-bariatric surgical effects on satiation targets are in part mediated by metabolic byproducts of gut microbiota like short-chain fatty acids (SCFAs) and bile acids, which play a pivotal role in modulating metabolism and energy expenditure and reducing obesity-associated inflammation, as well as influencing food reward pathways, potentially contributing to the regulation of body weight and reduction in hedonic eating behaviors. Overall, a better understanding of these mechanisms opens the door to developing non-surgical interventions that replicate the beneficial effects of bariatric surgery on the gut microbiome, dopamine signaling, and gut hormone regulation, offering new avenues for obesity treatment.

Gut-Modulating Agents and Amyotrophic Lateral Sclerosis: Current Evidence and Future Perspectives

Amyotrophic Lateral Sclerosis (ALS) is a highly fatal neurodegenerative disorder characterized by the progressive wasting and paralysis of voluntary muscle. Despite extensive research, the etiology of ALS remains elusive, and effective treatment options are limited. However, recent evidence implicates gut dysbiosis and gut-brain axis (GBA) dysfunction in ALS pathogenesis. Alterations to the composition and diversity of microbial communities within the gut flora have been consistently observed in ALS patients. These changes are often correlated with disease progression and patient outcome, suggesting that GBA modulation may have therapeutic potential. Indeed, targeting the gut microbiota has been shown to be neuroprotective in several animal models, alleviating motor symptoms and mitigating disease progression. However, the translation of these findings to human patients is challenging due to the complexity of ALS pathology and the varying diversity of gut microbiota. This review comprehensively summarizes the current literature on ALS-related gut dysbiosis, focusing on the implications of GBA dysfunction. It delineates three main mechanisms by which dysbiosis contributes to ALS pathology: compromised intestinal barrier integrity, metabolic dysfunction, and immune dysregulation. It also examines preclinical evidence on the therapeutic potential of gut-microbiota-modulating agents (categorized as prebiotics, probiotics, and postbiotics) in ALS.

Gut-brain communication mediates the impact of dietary lipids on cognitive capacity

Cognitive impairment, as a prevalent symptom of nervous system disorders, poses one of the most challenging aspects in the management of brain diseases. Lipids present in the cell membranes of all neurons within the brain and dietary lipids can regulate the cognition and memory function. In recent years, the advancements in gut microbiome research have enabled the exploration of dietary lipids targeting the gut-brain axis as a strategy for regulating cognition. This present review provides an in-depth overview of how lipids modulate cognition via the gut-brain axis depending on metabolic, immune, neural and endocrine pathways. It also comprehensively analyzes the effects of diverse lipids on the gut microbiota and intestinal barrier function, thereby affecting the central nervous system and cognitive capacity. Moreover, comparative analysis of the positive and negative effects is presented between beneficial and detrimental lipids. The former encompass monounsaturated fatty acids, short-chain fatty acids, omega-3 polyunsaturated fatty acids, phospholipids, phytosterols, fungal sterols and bioactive lipid-soluble vitamins, as well as lipid-derived gut metabolites, whereas the latter (detrimental lipids) include medium- or long-chain fatty acids, excessive proportions of n-6 polyunsaturated fatty acids, industrial trans fatty acids, and zoosterols. To sum up, the focus of this review is on how gut-brain communication mediates the impact of dietary lipids on cognitive capacity, providing a novel theoretical foundation for promoting brain cognitive health and scientific lipid consumption patterns.

Inflammation of some visceral sensory systems and autonomic dysfunction in cardiovascular disease

The sensitization and hypertonicity of visceral afferents are highly relevant to the development and progression of cardiovascular and respiratory disease states. In this review, we described the evidence that the inflammatory process regulates visceral afferent sensitivity and tonicity, affecting the control of the cardiovascular and respiratory system. Some inflammatory mediators like nitric oxide, angiotensin II, endothelin-1, and arginine vasopressin may inhibit baroreceptor afferents and contribute to the baroreflex impairment observed in cardiovascular diseases. Cytokines may act directly on peripheral afferent terminals that transmit information to the central nervous system (CNS). TLR-4 receptors, which recognize lipopolysaccharide, were identified in the nodose and petrosal ganglion and have been implicated in disrupting the blood-brain barrier, which can potentiate the inflammatory process. For example, cytokines may cross the blood-brain barrier to access the CNS. Additionally, pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and some of their receptors have been identified in the nodose ganglion and carotid body. These pro-inflammatory cytokines also sensitize the dorsal root ganglion or are released in the nucleus of the solitary tract. In cardiovascular disease, pro-inflammatory mediators increase in the brain, heart, vessels, and plasma and may act locally or systemically to activate/sensitize afferent nervous terminals. Recent evidence demonstrated that the carotid body chemoreceptor cells might sense systemic pro-inflammatory molecules, supporting the novel proposal that the carotid body is part of the afferent pathway in the central anti-inflammatory reflexes. The exact mechanisms of how pro-inflammatory mediators affects visceral afferent signals and contribute to the pathophysiology of cardiovascular diseases awaits future research.

Novel therapeutic strategy for obesity through the gut microbiota-brain axis: A review article

Background: The interaction between commensal bacteria and the host is essential for health and the gut microbiota-brain axis plays a vital role in this regard. Obesity as a medical problem not only affect the health of the individuals, but also the economic and social aspects of communities. The presence of any dysbiosis in the composition of the gut microbiota disrupts in the gut microbiota-brain axis, which in turn leads to an increase in appetite and then obesity. Because common treatments for obesity have several drawbacks, the use of microbiota-based therapy in addition to treatment and prevention of obesity can have other numerous benefits for the individual. In this review, we intend to investigate the relationship between obesity and the gut microbiota-brain axis as well as novel treatment strategies based on this axis with an emphasis on gut microbiota.

The Characteristics, Mechanisms and Therapeutics: Exploring the Role of Gut Microbiota in Obesity

Presently, obesity has emerged as a significant global public health concern due to its escalating prevalence and incidence rates. The gut microbiota, being a crucial environmental factor, has emerged as a key player in the etiology of obesity. Nevertheless, the intricate and specific interactions between obesity and gut microbiota, along with the underlying mechanisms, remain incompletely understood. This review comprehensively summarizes the gut microbiota characteristics in obesity, the mechanisms by which it induces obesity, and explores targeted therapies centered on gut microbiota restoration.

Protective effect of β-glucan on Poly(I:C)-induced acute lung injury/inflammation: Therapeutic implications of viral infections in the respiratory system

AIMS

Acute lung inflammation, particularly acute respiratory distress syndrome (ARDS), is caused by a variety of pathogens including bacteria and viruses. β-Glucans have been reported to possess both anti-inflammatory and immunomodulatory properties. The current study evaluated the therapeutic effect of β-glucans on polyinosinic:polycytidylic acid (Poly(I:C)) induced lung inflammation in both hamster and mice models.

MAIN METHODS

Poly(I:C)-induced ALI/inflammation models were developed in hamsters (2.5 mg/kg) and mice (2 mg/kg) by delivering the Poly(I:C) intratracheally, and followed with and without β-glucan administration. After treatment, lung mechanics were assessed and lung tissues were isolated and analyzed for mRNA/protein expression, and histopathological examinations.

KEY FINDINGS

Poly(I:C) administration, caused a significant elevation of inflammatory marker's expression in lung tissues and showed abnormal lung mechanics in mice and hamsters. Interestingly, treatment with β-glucan significantly (p < 0.001) reversed the Poly(I:C)-induced inflammatory events and inflammatory markers expression in both mRNA (IL-6, IL-1β, TNF-α, CCL2 and CCL7) and protein levels (TNF-α, CD68, myeloperoxidase, neutrophil elastase, MUC-5Ac and iNOS). Lung functional assays revealed that β-glucan treatment significantly improved lung mechanics. Histopathological analysis showed that β-glucan treatment significantly attenuated the Poly(I:C) induced inflammatory cell infiltration, injury and goblet cell population in lung tissues. Consistent with these findings, β-glucan treatment markedly reduced the number of neutrophils and macrophages in lung tissues. Our findings further demonstrated that β-glucan could reduce inflammation by suppressing the MAPK pathway.

SIGNIFICANCE

These results suggested that β-glucan may attenuate the pathogenic effects of Poly(I:C)-induced ALI/ARDS via modulating the MAPK pathway, indicating β-glucan as a possible therapeutic agent for the treatment of viral-pulmonary inflammation/injury.

The gut-brain axis mediates bacterial driven modulation of reward signaling

OBJECTIVE

Our goal is to investigate if microbiota composition modulates reward signaling and assess the role of the vagus in mediating microbiota to brain communication.

METHODS

Male germ-free Fisher rats were colonized with gastrointestinal contents from chow (low fat (LF) ConvLF) or HF (ConvHF) fed rats.

RESULTS

Following colonization, ConvHF rats consumed significantly more food than ConvLF animals. ConvHF rats displayed lower feeding-induced extracellular DOPAC levels (a metabolite of dopamine) in the Nucleus Accumbens (NAc) as well as reduced motivation for HF foods compared to ConvLF rats. Dopamine receptor 2 (DDR2) expression levels in the NAc were also significantly lower in ConvHF animals. Similar deficits were observed in conventionally raised HF fed rats, showing that diet-driven alteration in reward can be initiated via microbiota. Selective gut to brain deafferentation restored DOPAC levels, DRD2 expression, and motivational drive in ConvHF rats.

CONCLUSIONS

We concluded from these data that a HF-type microbiota is sufficient to alter appetitive feeding behavior and that bacteria to reward communication is mediated by the vagus nerve.

The Impact of Microbiota on the Gut-Brain Axis: Examining the Complex Interplay and Implications

The association and interaction between the central nervous system (CNS) and enteric nervous system (ENS) is well established. Essentially ENS is the second brain, as we call it. We tried to understand the structure and function, to throw light on the functional aspect of neurons, and address various disease manifestations. We summarized how various neurological disorders influence the gut via the enteric nervous system and/or bring anatomical or physiological changes in the enteric nervous system or the gut and vice versa. It is known that stress has an effect on Gastrointestinal (GI) motility and causes mucosal erosions. In our literature review, we found that stress can also affect sensory perception in the central nervous system. Interestingly, we found that mutations in the neurohormone, serotonin (5-HT), would result in dysfunctional organ development and further affect mood and behavior. We focused on the developmental aspects of neurons and cognition and their relation to nutritional absorption via the gastrointestinal tract, the development of neurodegenerative disorders in relation to the alteration in gut microbiota, and contrariwise associations between CNS disorders and ENS. This paper further summarizes the synergetic relation between gastrointestinal and neuropsychological manifestations and emphasizes the need to include behavioral therapies in management plans.

Dietary Fat Modulation of Gut Microbiota and Impact on Regulatory Pathways Controlling Food Intake

Obesity is a multifactorial disease that continues to increase in prevalence worldwide. Emerging evidence has shown that the development of obesity may be influenced by taxonomic shifts in gut microbiota in response to the consumption of dietary fats. Further, these alterations in gut microbiota have been shown to promote important changes in satiation signals including gut hormones (leptin, ghrelin, GLP-1, peptide YY and CCK) and orexigenic and anorexigenic neuropeptides (AgRP, NPY, POMC, CART) that influence hyperphagia and therefore obesity. In this review, we highlight mechanisms by which gut microbiota can influence these satiation signals both locally in the gastrointestinal tract and via microbiota-gut-brain communication. Then, we describe the effects of dietary interventions and associated changes in gut microbiota on satiety signals through microbiota-dependent mechanisms. Lastly, we present microbiota optimizing therapies including prebiotics, probiotics, synbiotics and weight loss surgery that can help restore beneficial gut microbiota by enhancing satiety signals to reduce hyperphagia and subsequent obesity. Overall, a better understanding of the mechanisms by which dietary fats induce taxonomical shifts in gut microbiota and their impact on satiation signaling pathways will help develop more targeted therapeutic interventions in delaying the onset of obesity and in furthering its treatment.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

Current Treatments and New, Tentative Therapies for Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative pathology, the origin of which is associated with the death of neuronal cells involved in the production of dopamine. The prevalence of PD has increased exponentially. The aim of this review was to describe the novel treatments for PD that are currently under investigation and study and the possible therapeutic targets. The pathophysiology of this disease is based on the formation of alpha-synuclein folds that generate Lewy bodies, which are cytotoxic and reduce dopamine levels. Most pharmacological treatments for PD target alpha-synuclein to reduce the symptoms. These include treatments aimed at reducing the accumulation of alpha-synuclein (epigallocatechin), reducing its clearance via immunotherapy, inhibiting LRRK2, and upregulating cerebrosidase (ambroxol). Parkinson’s disease continues to be a pathology of unknown origin that generates a significant social cost for the patients who suffer from it. Although there is still no definitive cure for this disease at present, there are numerous treatments available aimed at reducing the symptomatology of PD in addition to other therapeutic alternatives that are still under investigation. However, the therapeutic approach to this pathology should include a combination of pharmacological and non-pharmacological strategies to maximise outcomes and improve symptomatological control in these patients. It is therefore necessary to delve deeper into the pathophysiology of the disease in order to improve these treatments and therefore the quality of life of the patients.

Leptin Increases: Physiological Roles in the Control of Sympathetic Nerve Activity, Energy Balance, and the Hypothalamic-Pituitary-Thyroid Axis

It is well established that decreases in plasma leptin levels, as with fasting, signal starvation and elicit appropriate physiological responses, such as increasing the drive to eat and decreasing energy expenditure. These responses are mediated largely by suppression of the actions of leptin in the hypothalamus, most notably on arcuate nucleus (ArcN) orexigenic neuropeptide Y neurons and anorexic pro-opiomelanocortin neurons. However, the question addressed in this review is whether the effects of increased leptin levels are also significant on the long-term control of energy balance, despite conventional wisdom to the contrary. We focus on leptin's actions (in both lean and obese individuals) to decrease food intake, increase sympathetic nerve activity, and support the hypothalamic-pituitary-thyroid axis, with particular attention to sex differences. We also elaborate on obesity-induced inflammation and its role in the altered actions of leptin during obesity.

Vagus Nerve and Underlying Impact on the Gut Microbiota-Brain Axis in Behavior and Neurodegenerative Diseases

The gut microbiota is the most abundant and diverse microbiota in the human body and the vagus nerve is the most widely distributed and complex nerve in the body, both of them are essential in maintaining homeostasis. The most important phenomenon is how they coordinate to regulate functions, which has attracted the great attention of scientists. The academic literature on the correlation with a host of intestinal diseases and even systemic diseases has revealed the bidirectional communication between the gut microbiota and the brain, which can be carried out via multiple patterns. In the review, firstly, we have a general overview of the gut microbiota and the gut microbiota-brain axis. Secondly, according to the distribution characteristics of the vagus nerve, we analyzed and summarized its function in the intestinal tract. At the same time, we have summarized the underlying mechanism of some behavior changes such as depressive and anxiety-like behaviors and related neurodegenerative diseases caused by the vagus nerve and intestinal microecological environment disorders, and then we also analyzed inconsistency of the experimental evidence in order to propose novel strategies for the clinical practice.

Factors Affecting the Circulating Levels of Oxyntomodulin in Health and After Acute Pancreatitis

OBJECTIVES

To investigate the factors associated with the circulating levels of oxyntomodulin in healthy individuals and individuals after an episode of acute pancreatitis (AP).

METHODS

Blood samples were collected from all participants after an overnight fast and analyzed for 28 biomarkers. Participants also underwent comprehensive body composition analysis on a 3-T magnetic resonance imaging scanner. Regression analyses were done to investigate the associations between oxyntomodulin and the studied factors.

RESULTS

The study included 105 individuals who had a primary diagnosis of AP and 58 healthy individuals. Peptide YY (B coefficient, 0.094; 95% confidence interval [95% CI], 0.164-0.123), pancreatic polypeptide (0.048; 95% CI, 0.030-0.066), and leptin (0.394; 95% CI, 0.128-0.661) had significant associations with oxyntomodulin in healthy individuals. Peptide YY was the most prominent factor associated with oxyntomodulin, explaining 60% of its variance in health. Cholecystokinin (0.014; 95% CI, 0.010-0.018), amylin (-0.107; 95% CI, -0.192 to -0.021), and glycated hemoglobin (-0.761; 95% CI, -1.249 to -0.273) had significant associations with oxyntomodulin in individuals after AP. Cholecystokinin was the most prominent factor associated with oxyntomodulin, explaining 44% of its variance after AP.

CONCLUSIONS

Factors affecting the circulating levels of oxyntomodulin are different in health and after AP. These insights will enable the determination of populations that benefit from oxyntomodulin therapeutics in the future.

Evidence for Constitutive Microbiota-Dependent Short-Term Control of Food Intake in Mice: Is There a Link with Inflammation, Oxidative Stress, Endotoxemia, and GLP-1?

Aims: Although prebiotics, probiotics, and fecal transplantation can alter the sensation of hunger and/or feeding behavior, the role of the constitutive gut microbiota in the short-term regulation of food intake during normal physiology is still unclear. Results: An antibiotic-induced microbiota depletion study was designed to compare feeding behavior in conventional and microbiota-depleted mice. Tissues were sampled to characterize the time profile of microbiota-derived signals in mice during consumption of either standard or high-fat food for 1 h. Pharmacological and genetic tools were used to evaluate the contribution of postprandial endotoxemia and inflammatory responses in the short-term regulation of food intake. We observed constitutive microbial and macronutrient-dependent control of food intake at the time scale of a meal; that is, within 1 h of food introduction. Specifically, microbiota depletion increased food intake, and the microbiota-derived anorectic effect became significant during the consumption of high-fat but not standard food. This anorectic effect correlated with a specific postprandial microbial metabolic signature, and did not require postprandial endotoxemia or an NOD-, LRR-, and Pyrin domain-containing protein 3-inflammasome-mediated inflammatory response. Innovation and Conclusion: These findings show that the gut microbiota controls host appetite at the time scale of a meal under normal physiology. Interestingly, a microbiota-derived anorectic effect develops specifically with a high-fat meal, indicating that gut microbiota activity is involved in the satietogenic properties of foods. Antioxid. Redox Signal. 37, 349-369.

Differential effects of lipopolysaccharide on cognition, corticosterone and cytokines in socially-housed vs isolated male rats

Social isolation is an established risk factor for mental illness and impaired immune function. Evidence suggests that neuroinflammatory processes contribute to mental illness, possibly via cytokine-induced modulation of neural activity. We examined the effects of lipopolysaccharide (LPS) administration and social home cage environment on cognitive performance in the 5-Choice Serial Reaction Time Task (5CSRTT), and their effects on corticosterone and cytokines in serum and brain tissue. Male Long-Evans rats were reared in pairs or in isolation before training on the 5CSRTT. The effects of saline and LPS (150 µg/kg i.p.) administration on sickness behaviour and task performance were then assessed. LPS-induced sickness behaviour was augmented in socially-isolated rats, translating to increased omissions and slower response times in the 5CSRTT. Both social isolation and LPS administration reduced impulsive responding, while discriminative accuracy remained unaffected. With the exception of reduced impulsivity in isolated rats, these effects were not observed following a second administration of LPS, revealing behavioural tolerance to repeated LPS injections. In a separate cohort of animals, social isolation potentiated the ability of LPS to increase serum corticosterone and IL-6, which corresponded to increased IL-6 in the orbitofrontal and medial prefrontal cortices and the nucleus accumbens. Basal IL-4 levels in the nucleus accumbens were reduced in socially-isolated rats. These findings are consistent with the adaptive response of reduced motivational drive following immune challenge, and identify social isolation as an exacerbating factor. Enhanced IL-6 signalling may play a role in mediating the potentiated behavioural response to LPS administration in isolated animals.

The Role of Gut Microbiota in the Skeletal Muscle Development and Fat Deposition in Pigs

Pork quality is a factor increasingly considered in consumer preferences for pork. The formation mechanisms determining meat quality are complicated, including endogenous and exogenous factors. Despite a lot of research on meat quality, unexpected variation in meat quality is still a major problem in the meat industry. Currently, gut microbiota and their metabolites have attracted increased attention in the animal breeding industry, and recent research demonstrated their significance in muscle fiber development and fat deposition. The purpose of this paper is to summarize the research on the effects of gut microbiota on pig muscle and fat deposition. The factors affecting gut microbiota composition will also be discussed, including host genetics, dietary composition, antibiotics, prebiotics, and probiotics. We provide an overall understanding of the relationship between gut microbiota and meat quality in pigs, and how manipulation of gut microbiota may contribute to increasing pork quality for human consumption.

Lessons to Learn from the Gut Microbiota: A Focus on Amyotrophic Lateral Sclerosis

The gut microbiota is able to modulate the development and homeostasis of the central nervous system (CNS) through the immune, circulatory, and neuronal systems. In turn, the CNS influences the gut microbiota through stress responses and at the level of the endocrine system. This bidirectional communication forms the “gut microbiota–brain axis” and has been postulated to play a role in the etiopathology of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Numerous studies in animal models of ALS and in patients have highlighted the close communication between the immune system and the gut microbiota and, therefore, it is possible that alterations in the gut microbiota may have a direct impact on neuronal function and survival in ALS patients. Consequently, if the gut dysbiosis does indeed play a role in ALS-related neurodegeneration, nutritional immunomodulatory interventions based on probiotics, prebiotics, and/or postbiotics could emerge as innovative therapeutic strategies. This review aimed to shed light on the impact of the gut microbiota in ALS disease and on the use of potential nutritional interventions based on different types of biotics to ameliorate ALS symptoms.

Role of the gut-brain axis in energy and glucose metabolism

The gastrointestinal tract plays a role in the development and treatment of metabolic diseases. During a meal, the gut provides crucial information to the brain regarding incoming nutrients to allow proper maintenance of energy and glucose homeostasis. This gut-brain communication is regulated by various peptides or hormones that are secreted from the gut in response to nutrients; these signaling molecules can enter the circulation and act directly on the brain, or they can act indirectly via paracrine action on local vagal and spinal afferent neurons that innervate the gut. In addition, the enteric nervous system can act as a relay from the gut to the brain. The current review will outline the different gut-brain signaling mechanisms that contribute to metabolic homeostasis, highlighting the recent advances in understanding these complex hormonal and neural pathways. Furthermore, the impact of the gut microbiota on various components of the gut-brain axis that regulates energy and glucose homeostasis will be discussed. A better understanding of the gut-brain axis and its complex relationship with the gut microbiome is crucial for the development of successful pharmacological therapies to combat obesity and diabetes.

The Mechanism Underlying the Influence of Indole-3-Propionic Acid: A Relevance to Metabolic Disorders

The increasing prevalence of metabolic syndrome has become a serious public health problem. Certain bacteria-derived metabolites play a key role in maintaining human health by regulating the host metabolism. Recent evidence shows that indole-3-propionic acid content can be used to predict the occurrence and development of metabolic diseases. Supplementing indole-3-propionic acid can effectively improve metabolic disorders and is considered a promising metabolite. Therefore, this article systematically reviews the latest research on indole-3-propionic acid and elaborates its source of metabolism and its association with metabolic diseases. Indole-3-propionic acid can improve blood glucose and increase insulin sensitivity, inhibit liver lipid synthesis and inflammatory factors, correct intestinal microbial disorders, maintain the intestinal barrier, and suppress the intestinal immune response. The study of the mechanism of the metabolic benefits of indole-3-propionic acid is expected to be a potential compound for treating metabolic syndrome.

The model of litter size reduction induces long-term disruption of the gut-brain axis: An explanation for the hyperphagia of Wistar rats of both sexes

The gut microbiota affects the host's metabolic phenotype, impacting health and disease. The gut-brain axis unites the intestine with the centers of hunger and satiety, affecting the eating behavior. Deregulation of this axis can lead to obesity onset. Litter size reduction is a well-studied model for infant obesity because it causes overnutrition and programs for obesity. We hypothesize that animals raised in small litters (SL) have altered circuitry between the intestine and brain, causing hyperphagia. We investigated vagus nerve activity, the expression of c-Fos, brain-derived neurotrophic factor (BDNF), gastrointestinal (GI) hormone receptors, and content of bacterial phyla and short-chain fatty acids (SCFAs) in the feces of adult male and female Wistar rats overfed during lactation. On the 3rd day after birth, litter size was reduced to 3 pups/litter (SL males or SL females) until weaning. Controls had normal litter size (10 pups/litter: 5 males and 5 females). The rats were killed at 5 months of age. The male and female offspring were analyzed separately. The SL group of both sexes showed higher food consumption and body adiposity than the respective controls. SL animals presented dysbiosis (increased Firmicutes, decreased Bacteroidetes) and had increased vagus nerve activity. Only the SL males had decreased hypothalamic GLP-1 receptor expression, while only the SL females had lower acetate and propionate in the feces and higher CCK receptor expression in the hypothalamus. Thus, overfeeding during lactation differentially changes the gut-brain axis, contributing to hyperphagia of the offspring of both sexes.

The Gut-Brain Axis and Its Relation to Parkinson's Disease: A Review

Parkinson's disease is a chronic neurodegenerative disease characterized by the accumulation of misfolded alpha-synuclein protein (Lewy bodies) in dopaminergic neurons of the substantia nigra and other related circuitry, which contribute to the development of both motor (bradykinesia, tremors, stiffness, abnormal gait) and non-motor symptoms (gastrointestinal issues, urinogenital complications, olfaction dysfunction, cognitive impairment). Despite tremendous progress in the field, the exact pathways and mechanisms responsible for the initiation and progression of this disease remain unclear. However, recent research suggests a potential relationship between the commensal gut bacteria and the brain capable of influencing neurodevelopment, brain function and health. This bidirectional communication is often referred to as the microbiome-gut-brain axis. Accumulating evidence suggests that the onset of non-motor symptoms, such as gastrointestinal manifestations, often precede the onset of motor symptoms and disease diagnosis, lending support to the potential role that the microbiome-gut-brain axis might play in the underlying pathological mechanisms of Parkinson's disease. This review will provide an overview of and critically discuss the current knowledge of the relationship between the gut microbiota and Parkinson's disease. We will discuss the role of α-synuclein in non-motor disease pathology, proposed pathways constituting the connection between the gut microbiome and the brain, existing evidence related to pre- and probiotic interventions. Finally, we will highlight the potential opportunity for the development of novel preventative measures and therapeutic options that could target the microbiome-gut-brain axis in the context of Parkinson's disease.

Leveraging the Microbiome for Obesity: Moving From Form to Function

Treatment of obesity, an ongoing global epidemic, is challenging, as weight-loss efforts require a multidisciplinary approach addressing both behavioral and biologic needs that are not completely understood. Recent studies of the gut microbiome may provide better insight into the condition, and ultimately serve to advance more effective therapies. Research in this field has shifted from analyzing microbiome compositional differences to investigating functional changes that affect disease pathophysiology and outcome. Bacteria-derived metabolites are a way to bridge compositional changes to functional consequences. Through the production of metabolites, such as short chain fatty acids, tryptophan derivatives and bile acids, and interactions with peripheral and central signaling pathways, the gut microbiome may alter the body's metabolic and behavioral responses to food. Here, we summarize these mechanisms driven by gut-derived metabolites, through which the microbiome is thought to contribute to obesity, as well as review recent investigations of interventions related to these metabolites. Limitations of existing research, primarily due to paucity of causal studies in humans, are also discussed in this review.

Aging in Male Wistar Rats Associates With Changes in Intestinal Microbiota, Gut Structure, and Cholecystokinin-Mediated Gut-Brain Axis Function

Aging in mammals is characterized by failure of the homeostatic mechanisms that regulate energy balance. Several mechanisms have been proposed such as the presence of a low-grade chronic inflammation in different tissues, as well as leptin and insulin resistance, but the primary alteration is not fully elucidated. The gut microbiota has recently emerged as a key player in a variety of metabolic and neurological disorders. A main concept in this context is the gut-brain axis that refers to alterations in the gut that mediate effects in the central nervous system, including those related with the control of energy balance. Using 16S rRNA analysis, we demonstrate that aged male Wistar rats have increased presence of mucin-degrading and lipopolysaccharide (LPS)-producing bacteria. In addition, old animals exhibit a lower number of neutral mucin secreting goblet cells, and a decrease of tight junctions and adherens junctions marker proteins, zonula occludens protein-1 (ZO-1) and β-catenin, respectively. These data are compatible with a thinner mucus layer and a weaker gut barrier in older animals that likely facilitate LPS leakage. Our data also show that cholecystokinin (CCK) satiating effect is impaired in aged rats, one of the expected effects of increased LPS leakage. In contrast, no overt signs of gut or systemic inflammation are observed. Changes in microbiota in old male Wistar rats present features of situations of increased adiposity, but different from those of obese animals. These could partly explain the increased adiposity and fat deposition in liver and heart as observed here.

Microbiota's Role in Diet-Driven Alterations in Food Intake: Satiety, Energy Balance, and Reward

The gut microbiota plays a key role in modulating host physiology and behavior, particularly feeding behavior and energy homeostasis. There is accumulating evidence demonstrating a role for gut microbiota in the etiology of obesity. In human and rodent studies, obesity and high-energy feeding are most consistently found to be associated with decreased bacterial diversity, changes in main phyla relative abundances and increased presence of pro-inflammatory products. Diet-associated alterations in microbiome composition are linked with weight gain, adiposity, and changes in ingestive behavior. There are multiple pathways through which the microbiome influences food intake. This review discusses these pathways, including peripheral mechanisms such as the regulation of gut satiety peptide release and alterations in leptin and cholecystokinin signaling along the vagus nerve, as well as central mechanisms, such as the modulation of hypothalamic neuroinflammation and alterations in reward signaling. Most research currently focuses on determining the role of the microbiome in the development of obesity and using microbiome manipulation to prevent diet-induced increase in food intake. More studies are necessary to determine whether microbiome manipulation after prolonged energy-dense diet exposure and obesity can reduce intake and promote meaningful weight loss.

Acute Diallyl Disulfide Administration Prevents and Reveres Lipopolysaccharide-Induced Depression-Like Behaviors in Mice via Regulating Neuroinflammation and Oxido-Nitrosative Stress

Neuroinflammation and oxidative stress play critical roles in pathogenesis of depression. Diallyl disulfide (DADS), an active compound in garlic oil, has been shown to exhibit obvious anti-inflammatory and anti-oxidative activities. Preliminary evidence indicates that depression is associated with high levels of pro-inflammatory cytokines and oxidative markers, suggesting that inhibition of neuroinflammatory response and oxidative stress may be beneficial for depression interruption. Here, we investigated the antidepressant effect of DADS as well as it mechanisms in a depression-like model induced by lipopolysaccharide (LPS). Similarly to imipramine (10 mg/kg), a clinical antidepressant, DADS (40 or 80 mg/kg), which was administered 1 h before LPS treatment (pre-LPS) or 1.5 h and 23.5 h after LPS treatment (post-LPS), prevented and reversed LPS (100 μg/kg)-induced increase in immobility time in the tail suspension test (TST) and forced swim test (FST) in mice. Mechanistic studies revealed that DADS pre-treatment or post-treatment at the dose of 40 and 80 mg/kg prevented and reversed (i) LPS-induced increases in interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and nitric oxide (NO) levels in the hippocampus and prefrontal cortex, (ii) LPS-induced increases in contents of malondialdehyde (MDA), a parameter reflecting high levels of oxidative stress, and (iii) LPS-induced decreases in contents of GSH, a marker reflecting weakened anti-oxidative ability, in the hippocampus and prefrontal cortex in mice. These results indicate that DADS is comparable to imipramine in effectively ameliorating LPS-induced depression-like behaviors in mice, providing a potential value for DADS in prevention and/or therapy of depression.

Demystifying functional role of cocaine- and amphetamine-related transcript (CART) peptide in control of energy homeostasis: A twenty-five year expedition

Cocaine- and amphetamine-related transcript (CART) is a neuropeptide first discovered in the striatum of the rat brain. Later, the genetic sequence and function of CART peptide (CARTp) was found to be conserved among multiple mammalian species. Over the 25 years, since its discovery, CART mRNA (Cartpt) expression has been reported widely throughout the central and peripheral nervous systems underscoring its role in diverse physiological functions. Here, we review the localization and function of CARTp as it relates to energy homeostasis. We summarize the expression changes of central and peripheral Cartpt in response to metabolic states and make use of available large data sets to gain additional insights into the anatomy of the Cartpt expressing vagal neurons and their expression patterns in the gut. Furthermore, we provide an overview of the role of CARTp as an anorexigenic signal and its effect on energy expenditure and body weight control with insights from both pharmacological and transgenic animal studies. Subsequently, we discuss the role of CARTp in the pathophysiology of obesity and review important new developments towards identifying a candidate receptor for CARTp signalling. Altogether, the field of CARTp research has made rapid and substantial progress recently, and we review the case for considering CARTp as a potential therapeutic target for stemming the obesity epidemic.

Roles for the gut microbiota in regulating neuronal feeding circuits

The gut microbiota has the capacity to affect host appetite via intestinal satiety pathways, as well as complex feeding behaviors. In this Review, we highlight recent evidence that the gut microbiota can modulate food preference across model organisms. We discuss effects of the gut microbiota on the vagus nerve and brain regions including the hypothalamus, mesolimbic system, and prefrontal cortex, which play key roles in regulating feeding behavior. Crosstalk between commensal bacteria and the central and peripheral nervous systems is associated with alterations in signaling of neurotransmitters and neuropeptides such as dopamine, brain-derived neurotrophic factor (BDNF), and glucagon-like peptide-1 (GLP-1). We further consider areas for future research on mechanisms by which gut microbes may influence feeding behavior involving these neural pathways. Understanding roles for the gut microbiota in feeding regulation will be important for informing therapeutic strategies to treat metabolic and eating disorders.

The critical role of CCK in the regulation of food intake and diet-induced obesity

In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons' (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.

Roux-en-Y gastric bypass contributes to weight loss-independent improvement in hypothalamic inflammation and leptin sensitivity through gut-microglia-neuron-crosstalk

Objective

Hypothalamic inflammation and endoplasmic reticulum (ER) stress are extensively linked to leptin resistance and overnutrition-related diseases. Surgical intervention remains the most efficient long-term weight-loss strategy for morbid obesity, but mechanisms underlying sustained feeding suppression remain largely elusive. This study investigated whether Roux-en-Y gastric bypass (RYGB) interacts with obesity-associated hypothalamic inflammation to restore central leptin signaling as a mechanistic account for post-operative appetite suppression.

Methods

RYGB or sham surgery was performed in high-fat diet-induced obese Wistar rats. Sham-operated rats were fed ad libitum or by weight matching to RYGB via calorie restriction (CR) before hypothalamic leptin signaling, microglia reactivity, and the inflammatory pathways were examined to be under the control of gut microbiota-derived circulating signaling.

Results

RYGB, other than CR-induced adiposity reduction, ameliorates hypothalamic gliosis, inflammatory signaling, and ER stress, which are linked to enhanced hypothalamic leptin signaling and responsiveness. Mechanistically, we demonstrate that RYGB interferes with hypothalamic ER stress and toll-like receptor 4 (TLR4) signaling to restore the anorexigenic action of leptin, which most likely results from modulation of a circulating factor derived from the altered gut microbial environment upon RYGB surgery.

Conclusions

Our data demonstrate that RYGB interferes with hypothalamic TLR4 signaling to restore the anorexigenic action of leptin, which most likely results from modulation of a circulating factor derived from the post-surgical altered gut microbial environment.

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RYGB surgery-related weight loss independently restores hypothalamic leptin signaling and action in diet-induced obesity.

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RGYB modulates hypothalamic TLR4-mediated pro-inflammatory signaling and ER stress to restore leptin's anorexigenic action.

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Humoral factors contribute to modulated microglia-POMC neuron interaction, which appears specific to the RYGB procedure.

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Altering the gut microbiota environment by antibiotics deteriorates leptin's feeding suppressive action after RYGB.

The Role of the Gut Microbiota in the Gut-Brain Axis in Obesity: Mechanisms and Future Implications

Interaction between the gut and the brain is essential for energy homeostasis. In obesity, this homeostasis is disrupted, leading to a positive energy balance and weight gain. Obesity is a global epidemic that affects individual health and strains the socioeconomic system. Microbial dysbiosis has long been reported in obesity and obesity-related disorders. More recent literature has focused on the interaction of the gut microbiota and its metabolites on human brain and behavior. Developing strategies that target the gut microbiota could be a future approach for the treatment of obesity. Here, we review the microbiota–gut–brain axis and possible therapeutic options.

A Review on the Role of Food-Derived Bioactive Molecules and the Microbiota-Gut-Brain Axis in Satiety Regulation

Obesity is a chronic disease resulting from an imbalance between energy intake and expenditure. The growing relevance of this metabolic disease lies in its association with other comorbidities. Obesity is a multifaceted disease where intestinal hormones such as cholecystokinin (CCK), glucagon-like peptide 1 (GLP-1), and peptide YY (PYY), produced by enteroendocrine cells (EECs), have a pivotal role as signaling systems. Receptors for these hormones have been identified in the gut and different brain regions, highlighting the interconnection between gut and brain in satiation mechanisms. The intestinal microbiota (IM), directly interacting with EECs, can be modulated by the diet by providing specific nutrients that induce environmental changes in the gut ecosystem. Therefore, macronutrients may trigger the microbiota-gut-brain axis (MGBA) through mechanisms including specific nutrient-sensing receptors in EECs, inducing the secretion of specific hormones that lead to decreased appetite or increased energy expenditure. Designing drugs/functional foods based in bioactive compounds exploiting these nutrient-sensing mechanisms may offer an alternative treatment for obesity and/or associated metabolic diseases. Organ-on-a-chip technology represents a suitable approach to model multi-organ communication that can provide a robust platform for studying the potential of these compounds as modulators of the MGBA.

The metabolic impact of small intestinal nutrient sensing

The gastrointestinal tract maintains energy and glucose homeostasis, in part through nutrient-sensing and subsequent signaling to the brain and other tissues. In this review, we highlight the role of small intestinal nutrient-sensing in metabolic homeostasis, and link high-fat feeding, obesity, and diabetes with perturbations in these gut-brain signaling pathways. We identify how lipids, carbohydrates, and proteins, initiate gut peptide release from the enteroendocrine cells through small intestinal sensing pathways, and how these peptides regulate food intake, glucose tolerance, and hepatic glucose production. Lastly, we highlight how the gut microbiota impact small intestinal nutrient-sensing in normal physiology, and in disease, pharmacological and surgical settings. Emerging evidence indicates that the molecular mechanisms of small intestinal nutrient sensing in metabolic homeostasis have physiological and pathological impact as well as therapeutic potential in obesity and diabetes.

The gastrointestinal tract participates in maintaining metabolic homeostasis in part through nutrient-sensing and subsequent gut-brain signalling. Here the authors review the role of small intestinal nutrient-sensing in regulation of energy intake and systemic glucose metabolism, and link high-fat diet, obesity and diabetes with perturbations in these pathways.

The homeoviscous adaptation to dietary lipids (HADL) model explains controversies over saturated fat, cholesterol, and cardiovascular disease risk

SFAs play the leading role in 1 of the greatest controversies in nutrition science. Relative to PUFAs, SFAs generally increase circulating concentrations of LDL cholesterol, a risk factor for atherosclerotic cardiovascular disease (ASCVD). However, the purpose of regulatory mechanisms that control the diet-induced lipoprotein cholesterol dynamics is rarely discussed in the context of human adaptive biology. We argue that better mechanistic explanations can help resolve lingering controversies, with the potential to redefine aspects of research, clinical practice, dietary advice, public health management, and food policy. In this paper we propose a novel model, the homeoviscous adaptation to dietary lipids (HADL) model, which explains changes in lipoprotein cholesterol as adaptive homeostatic adjustments that serve to maintain cell membrane fluidity and hence optimal cell function. Due to the highly variable intake of fatty acids in humans and other omnivore species, we propose that circulating lipoproteins serve as a buffer to enable the rapid redistribution of cholesterol molecules between specific cells and tissues that is necessary with changes in dietary fatty acid supply. Hence, circulating levels of LDL cholesterol may change for nonpathological reasons. Accordingly, an SFA-induced raise in LDL cholesterol in healthy individuals could represent a normal rather than a pathologic response. These regulatory mechanisms may become disrupted secondarily to pathogenic processes in association with insulin resistance and the presence of other ASCVD risk factors, as supported by evidence showing diverging lipoprotein responses in healthy individuals as opposed to those with metabolic disorders such as insulin resistance and obesity. Corresponding with the model, we suggest alternative contributing factors to the association between elevated LDL cholesterol concentrations and ASCVD, involving dietary factors beyond SFAs, such as an increased endotoxin load from diet-gut microbiome interactions and subsequent chronic low-grade inflammation that interferes with fine-tuned signaling pathways.

Multiple organs involved in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) represents the leading cause of chronic liver disease worldwide and the anticipated health burden is huge. There are limited therapeutic approaches for NAFLD now. It’s imperative to get a better understanding of the disease pathogenesis if new treatments are to be discovered. As the hepatic manifestation of metabolic syndrome, this disease involves complex interactions between different organs and regulatory pathways. It’s increasingly clear that brain, gut and adipose tissue all contribute to NAFLD pathogenesis and development, in view of their roles in energy homeostasis. In the present review, we try to summarize currently available data regarding NAFLD pathogenesis and to lay a particular emphasis on the inter-organ crosstalk evidence.

Metabolic Responses to Butyrate Supplementation in LF- and HF-Fed Mice Are Cohort-Dependent and Associated with Changes in Composition and Function of the Gut Microbiota

The gut microbiota and associated metabolites have emerged as potential modulators of pathophysiological changes in obesity and related metabolic disorders. Butyrate, a product of bacterial fermentation, has been shown to have beneficial effects in obesity and rodent models of diet-induced obesity. Here, we aimed to determine the beneficial effects of butyrate (as glycerol ester of butyrate monobutyrin, MB) supplementation on metabolic phenotype, intestinal permeability and inflammation, feeding behavior, and the gut microbiota in low-fat (LF)- and high-fat (HF)-fed mice. Two cohorts (separated by 2 weeks) of male C57BL/6J mice (n = 24 in each cohort, 6/group/cohort; 6 weeks old) were separated into four weight-matched groups and fed either a LF (10 % fat/kcal) or HF (45% fat/kcal) with or without supplementation of MB (LF/MB or HF/MB) at 0.25% (w/v) in drinking water for 6 weeks. Metabolic phenotypes (body weight and adiposity), intestinal inflammation, feeding behavior, and fecal microbiome and metabolites were measured. Despite identical genetic and experimental conditions, we found marked differences between cohorts in the response (body weight gain, adiposity, and intestinal permeability) to HF-diet and MB. Notably, the composition of the gut microbiota was significantly different between cohorts, characterized by lower species richness and differential abundance of a large number of taxa, including subtaxa from five phyla, including increased abundance of the genera Bacteroides, Proteobacteria, and Parasutterella in cohort 2 compared to cohort 1. These differences may have contributed to the differential response in intestinal permeability to the HF diet in cohort 2. MB supplementation had no significant effect on metabolic phenotype, but there was a trend to protect from HF-induced impairments in intestinal barrier function in cohort 1 and in sensitivity to cholecystokinin (CCK) in both cohorts. These data support the concept that microbiota composition may have a crucial effect on metabolic responses of a host to dietary interventions and highlight the importance of taking steps to ensure reproducibility in rodent studies.

Non-neuronal crosstalk promotes an inflammatory response in nodose ganglia cultures after exposure to byproducts from gram positive, high-fat-diet-associated gut bacteria

Vagal afferent neurons (VAN) projecting to the lamina propria of the digestive tract are the primary source of gut-originating signals to the central nervous system (CNS). VAN cell bodies are found in the nodose ganglia (NG). Responsiveness of VAN to gut-originating signals is altered by feeding status with sensitivity to satiety signals such as cholecystokinin (CCK) increasing in the fed state. Chronic high-fat (HF) feeding results in inflammation at the level of the NG associated with a loss of VAN ability to switch phenotype from the fasted to the fed state. HF feeding also leads to compositional changes in the gut microbiota. HF diet consumption notably drives increased Firmicutes to Bacteroidetes phyla ratio and increased members of the Actinobacteria phylum. Firmicutes and Actinobacteria are largely gram positive (GP). In this study, we aimed to determine if byproducts from GP bacteria can induce an inflammatory response in cultured NG and to characterize the mechanism and cell types involved in the response. NG were collected from male Wistar rats and cultured for a total of 72 hours. At 48-68 hours after plating, cultures were treated with neuronal culture media in which Serinicoccus chungangensis had been grown and removed (SUP), lipoteichoic acid (LTA), or meso-diaminopimelic acid (meso-DAP). Some treatments included the glial inhibitors minocycline (MINO) and/or fluorocitrate (FC). The responses were evaluated using immunocytochemistry, qPCR, and electrochemiluminescence. We found that SUP induced an inflammatory response characterized by increased interleukin (IL)-6 staining and increased expression of genes for IL-6, interferon (IFN)γ, and tumor necrosis factor (TNF)α along with genes associated with cell-to-cell communication such as C-C motif chemokine ligand-2 (CCL2). Inclusion of inhibitors attenuated some responses but failed to completely normalize all indications of response, highlighting the role of immunocompetent cellular crosstalk in regulating the inflammatory response. LTA and meso-DAP produced responses that shared characteristics with SUP but were not identical. Our results support a role for HF associated GP bacterial byproducts' ability to contribute to vagal inflammation and to engage signaling from nonneuronal cells.

Estrogen and gut satiety hormones in vagus-hindbrain axis

Estrogens modulate different physiological functions, including reproduction, inflammation, bone formation, energy expenditure, and food intake. In this review, we highlight the effect of estrogens on food intake regulation and the latest literature on intracellular estrogen signaling. In addition, gut satiety hormones, such as cholecystokinin, glucagon-like peptide 1 and leptin are essential to regulate ingestive behaviors in the postprandial period. These peripheral signals are sensed by vagal afferent terminals in the gut wall and transmitted to the hindbrain axis. Here we 1. review the role of the vagus-hindbrain axis in response to gut satiety signals and 2. consider the potential synergistic effects of estrogens on gut satiety signals at the level of vagal afferent neurons and nuclei located in the hindbrain. Understanding the action of estrogens in gut-brain axis provides a potential strategy to develop estrogen-based therapies for metabolic diseases and emphasizes the importance of sex difference in the treatment of obesity.