Centrally administered GLP-1 analogue improves intestinal barrier function through the brain orexin and the vagal pathway in rats

A Cascade of Microbiota-Leaky Gut-Inflammation- Is it a Key Player in Metabolic Disorders?

PURPOSE OF REVIEW

This review addresses critical gaps in knowledge and provides a literature overview of the molecular pathways connecting gut microbiota dysbiosis to increased intestinal permeability (commonly referred to as "leaky gut") and its contribution to metabolic disorders. Restoring a healthy gut microbiota holds significant potential for enhancing intestinal barrier function and metabolic health. These interventions offer promising therapeutic avenues for addressing leaky gut and its associated pathologies in metabolic syndrome.

RECENT FINDINGS

In metabolic disorders such as obesity and type 2 diabetes (T2D), beneficial microbes such as those producing short-chain fatty acids (SCFAs) and other key metabolites like taurine, spermidine, glutamine, and indole derivatives are reduced. Concurrently, microbes that degrade toxic metabolites such as ethanolamine also decline, while proinflammatory, lipopolysaccharide (LPS)-enriched microbes increase. These microbial shifts place a higher burden on intestinal epithelial cells, which are in closest proximity to the gut lumen, inducing detrimental changes that compromise the structural and functional integrity of the intestinal barrier. Such changes include exacerbation of tight junction protein (TJP)s dysfunction, particularly through mechanisms such as destabilization of zona occludens (Zo)-1 mRNA or post-translational modifications. Emerging therapeutic strategies including ketogenic and Mediterranean diets, as well as probiotics, prebiotics, synbiotics, and postbiotics have demonstrated efficacy in restoring beneficial microbial populations, enhancing TJP expression and function, supporting gut barrier integrity, reducing leaky gut and inflammation, and ultimately improving metabolic disorders. This review summarizes the mechanisms by which gut microbiota contribute to the development of leaky gut and inflammation associated with metabolic syndrome. It also explores strategies for restoring gut microbiota balance and functionality by promoting beneficial microbes, increasing the production of beneficial metabolites, clearing toxic metabolites, and reducing the proportion of proinflammatory microbes. These approaches can alleviate the burden on intestinal epithelial cells, reduce leaky gut and inflammation, and improve metabolic health.

Brain AMPK signaling improves intestinal barrier function through brain orexin and the vagal pathway in rats

Leaky gut, an increased intestinal permeability, has been described in many diseases. We have recently demonstrated that neuropeptides such as orexin in the brain improved leaky gut, suggesting that the brain is involved in maintaining intestinal barrier function. It has been suggested that AMPK in the hypothalamus play a role in food intake. Because the hypothalamus is involved in the regulation of not only feeding behavior but also gut function, the present study was performed to clarify a hypothesis that AMPK in the brain regulate gut barrier function. Colonic permeability was determined by quantifying the absorbed Evans blue within the colonic tissue in rats. Intracisternal AICAR, an AMPK activator, could reduce LPS-induced colonic hyperpermeability while peripherally administered AICAR failed to change it. The improvement of colonic hyperpermeability by intracisternal AICAR was blocked by intracisternal but not subcutaneous compound C, AMPK inhibitor, atropine or vagotomy. The improvement of colonic hyperpermeability by intracisternal AICAR was blocked by intracisternal orexin receptor antagonist but not oxytocin or GLP-1 receptor antagonist. Intracisternal compound C prevented brain oxytocin or GLP-1 but not orexin-induced improvement of colonic hyperpermeability. These results suggest that activation of brain AMPK is capable of reducing colonic hyperpermeability through brain orexin signaling and the vagus nerve. In addition, endogenous AMPK in the brain may mediate the oxytocin or GLP-induced improvement of colonic hyperpermeability. We would suggest that improvement of leaky gut by activation of brain AMPK may play a role in leaky gut-related diseases.

Splenectomy prevents brain orexin, ghrelin, or oxytocin but not GLP-1-induced improvement of intestinal barrier function in rats

BACKGROUND

Accumulating evidence has suggested that neuropeptides such as orexin, ghrelin, or oxytocin act centrally in the brain to regulate intestinal barrier function through the vagus nerve. It has been reported that the vagal cholinergic anti-inflammatory pathway was blocked by splenectomy. In the present study, we therefore examined the effect of splenectomy on neuropeptides-induced improvement of increased intestinal permeability.

METHODS

Colonic permeability was determined in vivo by quantifying the absorbed Evans blue in colonic tissue for 15 min spectrophotometrically in rats.

RESULTS

Splenectomy increased colonic permeability. The increased permeability by splenectomy was significantly blocked by vagal activation induced by carbachol or 2-deoxy-d-glucose which was prevented by atropine, suggesting vagal activation could prevent colonic hyperpermeability in splenectomized rats. In the splenectomized rats, intracisternal injection of orexin, ghrelin, oxytocin, or butyrate failed to inhibit increased colonic permeability while intracisternal glucagon-like peptide-1 (GLP-1) analogue, liraglutide, potently blocked the increased colonic permeability in a dose-dependent manner. The liraglutide-induced improvement of increased colonic permeability was blocked by atropine in splenectomized rats. Intracisternal injection of GLP-1 receptor antagonist attenuated 2-deoxy-d-glucose-induced improvement of colonic hyperpermeability in splenectomized rats.

CONCLUSION

The present results suggested that the spleen is important in the improvement of intestinal barrier function by brain orexin, ghrelin or oxytocin, and butyrate. On the other hand, GLP-1 acts centrally in the brain to improve colonic hyperpermeability in a spleen-independent manner. All these results suggest that dual mechanisms (spleen dependent or independent) may exist for the brain-gut regulation in intestinal barrier function.

Mechanisms of Insulin Signaling as a Potential Therapeutic Method in Intestinal Diseases

Gastrointestinal diseases are becoming a growing public health problem. One of them is inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD). The incidence of IBD is increasing in developing countries and declining in developed countries, affecting people of all ages. Researchers have been exploring new treatment options including insulin signaling pathways in the inflammation of the gastrointestinal tract. It seems that a better understanding of the mechanism of IGF-1, GLP-1 and TL1A on the gut microbiota and inflammation may provide new advances in future therapeutic strategies for patients with IBD, but also other intestinal diseases. This review aims to synthesize insights into the effects of GLP, IGF and anti-TL1A on inflammation and the gut microbiota, which may enable their future use in therapy for people with intestinal diseases.

Brain histamine improves colonic hyperpermeability through the basal forebrain cholinergic neurons, adenosine A2B receptors and vagus nerve in rats

Intestinal barrier dysfunction, leaky gut, is implicated in various diseases, including irritable bowel syndrome (IBS) and neurodegenerative conditions like Alzheimer's disease. Our recent investigation revealed that basal forebrain cholinergic neurons (BFCNs), critical for cognitive function, receive signals from butyrate and orexin, playing a role in regulating intestinal barrier function through adenosine A2B signaling and the vagus. This study explores the involvement and function of brain histamine, linked to BFCNs, in the regulation of intestinal barrier function. Colonic permeability, assessed by quantifying absorbed Evans blue in rat colonic tissue, showed that histamine did not affect increased colonic permeability induced by LPS when administered subcutaneously. However, intracisternal histamine administration improved colonic hyperpermeability. Elevating endogenous histamine levels in the brain with SKF91488, a histamine N-methyltransferase inhibitor, also improved colonic hyperpermeability. This effect was abolished by intracisternal chlorpheniramine, an histamine H1 receptor antagonist, not ranitidine, an H2 receptor antagonist. The SKF91488-induced improvement in colonic hyperpermeability was blocked by vagotomy, intracisternal pirenzepine (suppressing BFCNs activity), or alloxazine (an adenosine A2B receptor antagonist). Additionally, intracisternal chlorpheniramine injection eliminated butyrate-induced improvement in colonic hyperpermeability. These findings suggest that brain histamine, acting via the histamine H1 receptor, regulates intestinal barrier function involving BFCNs, adenosine A2B signaling, and the vagus. Brain histamine appears to centrally regulate intestinal barrier function influenced by butyrate, differentiating its actions from peripheral histamine in conditions like IBS, where mast cell-derived histamine induces leaky gut. Brain histamine emerges as a potential pharmacological target for diseases associated with leaky gut, such as dementia and IBS.

Pharmacotherapy for gastric and intestinal cramping pain: ‎ current and emerging therapies

INTRODUCTION

Acute gastrointestinal cramping pain (GICP) is a debilitating condition that affects many people worldwide, significantly reducing their quality of life. As such, prompt treatment is crucial.

AREAS COVERED

This article will explore relevant literature from databases such as PubMed, Scopus, Google Scholar, Cochrane Library, and Web of Science. Additionally, we searched ClinicalTrials.gov and the WHO ICTRP database for the latest clinical trials.

EXPERT OPINION

Consensus dictates that antispasmodics such as hyoscine-N-butyl bromide and mebeverine should be the primary treatment for GICP. If these prove ineffective, patients can switch to an antispasmodic with a different mode of action or add acetaminophen/NSAIDs for more severe cases. Currently, several antispasmodics are undergoing clinical trials, including drotaverine, alverine, pinaverium, otilonium bromide, fenoverine, tiropramide, otilonium bromide, trimebutine, and peppermint oil. Well-designed head-to-head studies are necessary to evaluate current antispasmodics' safety, efficacy, pharmacokinetic, and pharmacoeconomics profiles. Recent studies have shown that fixed-dose combinations of antispasmodics + NSAIDs or two different antispasmodics can improve patient compliance and synergistically reduce GICP. Therefore, it is recommended that the global availability and accessibility of these products be enhanced.