Limosilactobacillus reuteri ATCC 6475 metabolites upregulate the serotonin transporter in the intestinal epithelium

Hormetic Nutrition and Redox Regulation in Gut-Brain Axis Disorders

The antioxidant and anti-inflammatory effects of hormetic nutrition for enhancing stress resilience and overall human health have received much attention. Recently, the gut-brain axis has attracted prominent interest for preventing and therapeutically impacting neuropathologies and gastrointestinal diseases. Polyphenols and polyphenol-combined nanoparticles in synergy with probiotics have shown to improve gut bioavailability and blood-brain barrier (BBB) permeability, thus inhibiting the oxidative stress, metabolic dysfunction and inflammation linked to gut dysbiosis and ultimately the onset and progression of central nervous system (CNS) disorders. In accordance with hormesis, polyphenols display biphasic dose-response effects by activating at a low dose the Nrf2 pathway resulting in the upregulation of antioxidant vitagenes, as in the case of heme oxygenase-1 upregulated by hidrox® or curcumin and sirtuin-1 activated by resveratrol to inhibit reactive oxygen species (ROS) overproduction, microbiota dysfunction and neurotoxic damage. Importantly, modulation of the composition and function of the gut microbiota through polyphenols and/or probiotics enhances the abundance of beneficial bacteria and can prevent and treat Alzheimer's disease and other neurological disorders. Interestingly, dysregulation of the Nrf2 pathway in the gut and the brain can exacerbate selective susceptibility under neuroinflammatory conditions to CNS disorders due to the high vulnerability of vagal sensory neurons to oxidative stress. Herein, we aimed to discuss hormetic nutrients, including polyphenols and/or probiotics, targeting the Nrf2 pathway and vitagenes for the development of promising neuroprotective and therapeutic strategies to suppress oxidative stress, inflammation and microbiota deregulation, and consequently improve cognitive performance and brain health. In this review, we also explore interactions of the gut-brain axis based on sophisticated and cutting-edge technologies for novel anti-neuroinflammatory approaches and personalized nutritional therapies.

A mediation analysis of the role of total free fatty acids on pertinence of gut microbiota composition and cognitive function in late life depression

BACKGROUND

Extensive evidence demonstrates correlations among gut microbiota, lipid metabolism and cognitive function. However, there is still a lack of researches in the field of late-life depression (LLD). This research targeted at investigating the relationship among gut microbiota, lipid metabolism indexes, such as total free fatty acids (FFAs), and cognitive functions in LLD.

METHODS

Twenty-nine LLD patients from the Cognitive Outcome Cohort Study of Depression in Elderly were included. Cognitive functions were estimated through the Chinese version of Montreal Cognitive Assessment (MoCA). Blood samples were collected to evaluate serum lipid metabolism parameters. Fecal samples were evaluated for gut microbiota determination via 16S rRNA sequencing. Spearman correlation, linear regression and mediation analysis were utilized to explore relationship among gut microbiota, lipid metabolism and cognitive function in LLD patients.

RESULTS

Spearman correlation analysis revealed significant correlations among Akkermansia abundance, total Free Fatty Acids (FFAs) and MoCA scores (P < 0.05). Multiple regression indicated Akkermansia and total FFAs significantly predicted MoCA scores (P < 0.05). Mediation analysis demonstrated that the correlation between decreased Akkermansia relative abundance and cognitive decline in LLD patients was partially mediated by total FFAs (Bootstrap 95%CI: 0.023-0.557), accounting for 43.0% of the relative effect.

CONCLUSION

These findings suggested a significant relationship between cognitive functions in LLD and Akkermansia, as well as total FFAs. Total FFAs partially mediated the relationship between Akkermansia and cognitive functions. These results contributed to understanding the gut microbial-host lipid metabolism axis in the cognitive function of LLD.

Exploring the serotonin-probiotics-gut health axis: A review of current evidence and potential mechanisms

Modulatory effects of serotonin (5-Hydroxytryptamine [5-HT]) have been seen in hepatic, neurological/psychiatric, and gastrointestinal (GI) disorders. Probiotics are live microorganisms that confer health benefits to their host. Recent research has suggested that probiotics can promote serotonin signaling, a crucial pathway in the regulation of mood, cognition, and other physiological processes. Reviewing the literature, we find that peripheral serotonin increases nutrient uptake and storage, regulates the composition of the gut microbiota, and is involved in mediating neuronal disorders. This review explores the mechanisms underlying the probiotic-mediated increase in serotonin signaling, highlighting the role of gut microbiota in the regulation of serotonin production and the modulation of neurotransmitter receptors. Additionally, this review discusses the potential clinical implications of probiotics as a therapeutic strategy for disorders associated with altered serotonin signaling, such as GI and neurological disorders. Overall, this review demonstrates the potential of probiotics as a promising avenue for the treatment of serotonin-related disorders and signaling of serotonin.

A high-throughput protocol for measuring solution pH of bacterial cultures using UV-Vis absorption spectrophotometry

We present a protocol for measuring the pH of cell-free bacterial-conditioned media based on changes in the ultraviolet-visible (UV-Vis) absorbance spectrum using the pH indicator dye litmus. This protocol includes detailed procedures for performing bacterial culturing, examining bacterial growth, collecting cell-free supernatant, litmus dye addition, and pH-based calibration curve preparations. This assay has been designed for flexible formatting that can accommodate both high-volume and low-volume sample sets.

Limosilactobacillus mucosae and Lactobacillus amylovorus Protect Against Experimental Colitis via Upregulation of Colonic 5-Hydroxytryptamine Receptor 4 and Transforming Growth Factor-β2

BACKGROUND

Limosilactobacillusmucosae (LM) exerts anti-inflammatory and health-promoting effects. However, its role in the modulation of gut serotonin or 5-hydroxytryptamine (5-HT) metabolism and 5-HT receptors (HTRs) in inflammation requires further investigation.

OBJECTIVES

We compared LM with Lactobacillus amylovorus (LA) for the regulation of 5-HT, HTRs, inflammatory mediators, and their correlations in the colon of mice with experimental colitis.

METHODS

Male C57BL/6 mice were randomly assigned to 6 groups: control (Con), LM, LA, dextran sodium sulfate (DSS), and DSS with pre-administration of LM (+LM) or LA (+LA). After 7 d of DSS treatment, mice were killed to analyze the expression of inflammatory mediators, HTRs, and concentrations of 5-HT and microbial metabolites in the colon.

RESULTS

LM was more effective than LA in alleviating DSS-induced colonic inflammation. Compared with mice in the DSS group, mice receiving DSS + LM or DSS + LA treatment had lower (P < 0.05) colonic mRNA expression of proinflammatory cytokines. DSS + LM treatment had lower mRNA expression of Il1b, Tnfa, and Ccl3, an abundance of p-STAT3, and greater expression of Tgfb2 and Htr4 in the colon (P < 0.05). The expression of inflammatory mediators (including Tgfb-1) was positively correlated (P < 0.05) with 5-HT and Htr2a and negatively correlated (P < 0.05) with Htr4. However, the expression of Tgfb-2 showed reversed correlations with the 5-HT and HTRs described above. Patterns for these correlations were different for LM and LA. Mice receiving the DSS + LM treatment had greater (P < 0.05) concentrations of acetate and valerate and lower (P < 0.05) concentrations of indole-3-acetic acid in the cecal and colonic contents.

CONCLUSIONS

LM showed greater efficacy than LA in alleviating DSS-induced colonic inflammation. The coordinated regulation of transforming growth factor-β subtypes and serotonin receptors in the colon may be one of the most important mechanisms underlying the probiotic effects of lactobacilli in gut inflammation.

Gut Microbiota-Derived Short-Chain Fatty Acids: Novel Regulators of Intestinal Serotonin Transporter

Serotonin (5-HT) is a key neurotransmitter synthesized both in the gut and the central nervous system. It exerts its signaling through specific receptors (5-HTR), which regulate numerous behaviors and functions such as mood, cognitive function, platelet aggregation, gastrointestinal motility, and inflammation. Serotonin activity is determined mainly by the extracellular availability of 5-HT, which is controlled by the serotonin transporter (SERT). Recent studies indicate that, by activation of innate immunity receptors, gut microbiota can modulate serotonergic signaling by SERT modulation. As part of its function, gut microbiota metabolize nutrients from diet to produce different by-products, including short-chain fatty acids (SCFAs): propionate, acetate, and butyrate. However, it is not known whether these SCFAs regulate the serotonergic system. The objective of this study was to analyze the effect of SCFAs on the gastrointestinal serotonergic system using the Caco-2/TC7 cell line that expresses SERT and several receptors constitutively. Cells were treated with different SCFAs concentrations, and SERT function and expression were evaluated. In addition, the expression of 5-HT receptors 1A, 2A, 2B, 3A, 4, and 7 was also studied. Our results show that the microbiota-derived SCFAs regulate intestinal serotonergic system, both individually and in combination, modulating the function and expression of SERT and the 5-HT1A, 5-HT2B, and 5-HT7 receptors expression. Our data highlight the role of gut microbiota in the modulation of intestinal homeostasis and suggest microbiome modulation as a potential therapeutic treatment for intestinal pathologies and neuropsychiatric disorders involving serotonin.

Linking serotonin homeostasis to gut function: Nutrition, gut microbiota and beyond

Serotonin (5-HT) produced by enterochromaffin (EC) cells in the digestive tract is crucial for maintaining gut function and homeostasis. Nutritional and non-nutritional stimuli in the gut lumen can modulate the ability of EC cells to produce 5-HT in a temporal- and spatial-specific manner that toning gut physiology and immune response. Of particular interest, the interactions between dietary factors and the gut microbiota exert distinct impacts on gut 5-HT homeostasis and signaling in metabolism and the gut immune response. However, the underlying mechanisms need to be unraveled. This review aims to summarize and discuss the importance of gut 5-HT homeostasis and its regulation in maintaining gut metabolism and immune function in health and disease with special emphasis on different types of nutrients, dietary supplements, processing, and gut microbiota. Cutting-edge discoveries in this area will provide the basis for the development of new nutritional and pharmaceutical strategies for the prevention and treatment of serotonin homeostasis-related gut and systematic disorders and diseases.

Lactobacillus acidophilus regulates abnormal serotonin availability in experimental ulcerative colitis

OBJECTIVES

Probiotics are known to play a beneficial role in curing irritable bowel syndrome such as ulcerative colitis. Commensal Lactobacillus species are thought to play a protective role against ulcerative colitis, as they restore homeostasis in intestinal disorders. Abnormal serotonin availability has been described in ulcerative colitis, but the underlying mechanism is still unclear. The aim of this study was to determine the anti-inflammatory role of Lactobacillus acidophilus (L. acidophilus) and its effect on serotonin expression.

METHODS

Ulcerative colitis was created with the intrarectal administration of acetic acid. A total of 40 adult male rats were divided into five groups of eight rats as control, sham, experimental colitis, treatment (Colitis + L. acidophilus) and protective group (L. acidophilus + colitis). To evaluate the effects of L. acidophilus on serotonin expression in ulcerative colitis, this bacterial strain was administered orally to the rats with acetic acid-induced colitis. After oral administration of L. acidophilus for 14 days, serotonin content was biochemically measured and serotonin expression was evaluated immunohistochemically.

RESULTS

The expression of serotonin and its protein content was significantly increased in colitis compared to the control and sham groups. Abnormal serotonin availability in the rats with acetic acid-induced colitis was significantly reduced by the L. acidophilus.

CONCLUSIONS

In our study, it was observed that the amount of serotonin in the intestinal tissue increased excessively with ulcerative colitis. In addition, L.acidophilus has been found to reduce the abnormally increased amount of serotonin in the colon tissue, as well as reduce the inflammation in the intestinal tissue that occurs with ulcerative colitis. With our findings, it is predicted that probiotic application can be used as a treatment option in ulcerative colitis.

Toward manipulating serotonin signaling via the microbiota-gut-brain axis

It is now well established in humans that there is a bidirectional pathway of communication between the central and enteric nervous systems in which members of the microbiome participate. This microbiota-gut-brain axis (MGBA) is crucial for normal development and physiology, and its dysregulation has been implicated in a range of neurological and intestinal disorders. Investigations into the mechanistic underpinnings of the MGBA have identified serotonin as a molecule of particular interest. In this review, we highlight recent advances toward understanding the role of endogenous serotonin in microbial communities, how microbial communities bidirectionally interact with host serotonin, and potential future engineering opportunities to leverage these novel mechanisms for biomedical applications.

Direct and indirect mechanisms by which the gut microbiota influence host serotonin systems

Mounting evidence highlights the pivotal role of enteric microbes as a dynamic interface with the host. Indeed, the gut microbiota, located in the lumen of the gastrointestinal (GI) tract, influence many essential physiological processes that are evident in both healthy and pathological states. A key signaling molecule throughout the body is serotonin (5-hydroxytryptamine; 5-HT), which acts in the GI tract to regulate numerous gut functions including intestinal motility and secretion. The gut microbiota can modulate host 5-HT systems both directly and indirectly. Direct actions of gut microbes, evidenced by studies using germ-free animals or antibiotic administration, alter the expression of key 5-HT-related genes to promote 5-HT biosynthesis. Indirectly, the gut microbiota produce numerous microbial metabolites, whose actions can influence host serotonergic systems in a variety of ways. This review summarizes the current knowledge regarding mechanisms by which gut bacteria act to regulate host 5-HT and 5-HT-mediated gut functions, as well as implications for 5-HT in the microbiota-gut-brain axis.