3-oxo-C12:2-HSL, quorum sensing molecule from human intestinal microbiota, inhibits pro-inflammatory pathways in immune cells via bitter taste receptors

Gut bacterial quorum sensing molecules and their association with inflammatory bowel disease: Advances and future perspectives

Inflammatory Bowel Disease (IBD) is an enduring inflammatory disease of the gastrointestinal tract (GIT). The complexity of IBD, its profound impact on patient's quality of life, and its burden on healthcare systems necessitate continuing studies to elucidate its etiology, refine care strategies, improve treatment outcomes, and identify potential targets for novel therapeutic interventions. The discovery of a connection between IBD and gut bacterial quorum sensing (QS) molecules has opened exciting opportunities for research into IBD pathophysiology. QS molecules are small chemical messengers synthesized and released by bacteria based on population density. These chemicals are sensed not only by the microbial species but also by host cells and are essential in gut homeostasis. QS molecules are now known to interact with inflammatory pathways, therefore rendering them potential therapeutic targets for IBD management. Given these intriguing developments, the most recent research findings in this area are herein reviewed. First, the global burden of IBD and the disruptions of the gut microbiota and intestinal barrier associated with the disease are assessed. Next, the general QS mechanism and signaling molecules in the gut are discussed. Then, the roles of QS molecules and their connection with IBD are elucidated. Lastly, the review proposes potential QS-based therapeutic targets for IBD, offering insights into the future research trajectory in this field.

Momordica charantia Bioactive Components: Hypoglycemic and Hypolipidemic Benefits Through Gut Health Modulation

Momordica charantia (MC), a member of the Cucurbitaceae family, is well known for its pharmacological activities that exhibit hypoglycemic and hypolipidemic properties. These properties are largely because of its abundant bioactive compounds and phytochemicals. Over the years, numerous studies have confirmed the regulatory effects of MC extract on glycolipid metabolism. However, there is a lack of comprehensive reviews on newly discovered MC-related components, such as insulin receptor-binding protein-19, adMc1, and MC protein-30 and triterpenoids 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al, and the role of MC in gut microbiota and bitter taste receptors. This review offers an up-to-date overview of the recently reported chemical compositions of MC, including polysaccharides, saponins, polyphenolics, peptides, and their beneficial effects. It also provides the latest updates on the role of MC in the regulation of gut microbiota and bitter taste receptor signaling pathways. As a result, this review will serve as a theoretical basis for potential applications in the creation or modification of MC-based nutrient supplements.

Quorum sensing modulates bacterial virulence and colonization dynamics of the gastrointestinal pathogen Citrobacter rodentium

Quorum Sensing (QS) is a form of cell-to-cell communication that enables bacteria to modify behavior according to their population density. While QS has been proposed as a potential intervention against pathogen infection, QS-mediated communication within the mammalian digestive tract remains understudied. Using an LC-MS/MS approach, we discovered that Citrobacter rodentium, a natural murine pathogen used to model human infection by pathogenic Escherichia coli, utilizes the CroIR system to produce three QS-molecules. We then profiled their accumulation both in vitro and across different gastrointestinal sites over the course of infection. Importantly, we found that in the absence of QS capabilities the virulence of C. rodentium is enhanced. This highlights the role of QS as an effective mechanism to regulate virulence according to the pathogen's spatio-temporal context to optimize colonization and transmission success. These results also demonstrate that inhibiting QS may not always be an effective strategy for the control of virulence.

Anti-Quorum Sensing Activity of Probiotics: The Mechanism and Role in Food and Gut Health

Background: Quorum sensing (QS) is a cell-to-cell communication mechanism that occurs between inter- and intra-bacterial species and is regulated by signaling molecules called autoinducers (AIs). It has been suggested that probiotics can exert a QS inhibitory effect through their metabolites. Purpose: To provide an overview of (1) the anti-QS activity of probiotics and its mechanism against foodborne pathogenic and spoilage bacteria; (2) the potential role of the QS of probiotics in gut health; and (3) the impact of microencapsulation on QS. Results: Lactobacillus species have been extensively studied for their anti-QS activity and have been found to effectively disrupt QS in vitro. However, their effectiveness in a food matrix is yet to be determined as they interfere with the AI receptor or its synthesis. QS plays an important role in both the biofilm formation of probiotics and pathogenic bacteria. Moreover, in vitro and animal studies have shown that QS molecules can modulate cytokine responses and gut dysbiosis and maintain intestinal barrier function. In this scenario, microencapsulation was found to enhance AI activity. However, its impact on the anti-QS activity of probiotics and its underlying mechanism remains unclear. Conclusions: Probiotics are potential candidates to block QS activity in foodborne pathogenic and food spoilage bacteria. Microencapsulation increases QS efficacy. However, more research is still needed for the identification of the QS inhibitory metabolites from probiotics and for the elucidation of the anti-QS mechanism of probiotics (microcapsules and free cells) in food and the human gut.

Conversations in the Gut: The Role of Quorum Sensing in Normobiosis

An imbalance in gut microbiota, termed dysbiosis, has been shown to affect host health. Several factors, including dietary changes, have been reported to cause dysbiosis with its associated pathologies that include inflammatory bowel disease, cancer, obesity, depression, and autism. We recently demonstrated the inhibitory effects of artificial sweeteners on bacterial quorum sensing (QS) and proposed that QS inhibition may be one mechanism behind such dysbiosis. QS is a complex network of cell-cell communication that is mediated by small diffusible molecules known as autoinducers (AIs). Using AIs, bacteria interact with one another and coordinate their gene expression based on their population density for the benefit of the whole community or one group over another. Bacteria that cannot synthesize their own AIs secretly "listen" to the signals produced by other bacteria, a phenomenon known as "eavesdropping". AIs impact gut microbiota equilibrium by mediating intra- and interspecies interactions as well as interkingdom communication. In this review, we discuss the role of QS in normobiosis (the normal balance of bacteria in the gut) and how interference in QS causes gut microbial imbalance. First, we present a review of QS discovery and then highlight the various QS signaling molecules used by bacteria in the gut. We also explore strategies that promote gut bacterial activity via QS activation and provide prospects for the future.

Cellular mechanisms and molecular pathways linking bitter taste receptor signalling to cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction in heart diseases

Heart diseases and related complications constitute a leading cause of death and socioeconomic threat worldwide. Despite intense efforts and research on the pathogenetic mechanisms of these diseases, the underlying cellular and molecular mechanisms are yet to be completely understood. Several lines of evidence indicate a critical role of inflammatory and oxidative stress responses in the development and progression of heart diseases. Nevertheless, the molecular machinery that drives cardiac inflammation and oxidative stress is not completely known. Recent data suggest an important role of cardiac bitter taste receptors (TAS2Rs) in the pathogenetic mechanism of heart diseases. Independent groups of researchers have demonstrated a central role of TAS2Rs in mediating inflammatory, oxidative stress responses, autophagy, impulse generation/propagation and contractile activities in the heart, suggesting that dysfunctional TAS2R signalling may predispose to cardiac inflammatory and oxidative stress disorders, characterised by contractile dysfunction and arrhythmia. Moreover, cardiac TAS2Rs act as gateway surveillance units that monitor and detect toxigenic or pathogenic molecules, including microbial components, and initiate responses that ultimately culminate in protection of the host against the aggression. Unfortunately, however, the molecular mechanisms that link TAS2R sensing of the cardiac milieu to inflammatory and oxidative stress responses are not clearly known. Therefore, we sought to review the possible role of TAS2R signalling in the pathophysiology of cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction in heart diseases. Potential therapeutic significance of targeting TAS2R or its downstream signalling molecules in cardiac inflammation, oxidative stress, arrhythmia and contractile dysfunction is also discussed.

Impact of IBD-Associated Dysbiosis on Bacterial Quorum Sensing Mediated by Acyl-Homoserine Lactone in Human Gut Microbiota

Intestinal dysbiosis is a key feature in the pathogenesis of inflammatory bowel disease (IBD). Acyl-homoserine lactones (AHL) are bacterial quorum-sensing metabolites that may play a role in the changes in host cells-gut microbiota interaction observed during IBD. The objective of our study was to investigate the presence and expression of AHL synthases and receptor genes in the human gut ecosystem during IBD. We used an in silico approach, applied to the Inflammatory Bowel Disease Multi'omics Database comprising bacterial metagenomic and metatranscriptomic data from stools of patients with Crohn's disease (CD) (n = 50), ulcerative colitis (UC) (n = 27) and non-IBD controls (n = 26). No known putative AHL synthase gene was identified; however, several putative luxR receptors were observed. Regarding the expression of these receptor genes, the luxR gene from Bacteroides dorei was under-expressed in IBD patients (p = 0.02) compared to non-IBD patients, especially in CD patients (p = 0.02). In the dysbiosis situation, one luxR receptor gene from Bacteroides fragilis appeared to be over-expressed (p = 0.04) compared to that of non-dysbiotic patients. Targeting LuxR receptors of bacterial quorum sensing might represent a new approach to modulate the gut microbiota in IBD.