Gut Microbial Metabolites on Host Immune Responses in Health and Disease

Gut Microbiome Interventions: From Dysbiosis to Next-Generation Probiotics (NGPs) for Disease Management

The gut microbiome, sometimes referred to as the "second brain," the "lost organ," the "identification card of the individual," and the "fingerprint of the host," possesses diverse traits and functions that influence health. The impact of gut commensal bacteria on health, as opposed to environmental pathogenic factors, has generated increasing interest in recent years, culminating in a substantial body of study. Research indicates that dysbiosis of the intestinal microbiota is commonly observed in chronic inflammatory diseases, including colitis, obesity/metabolic syndrome, diabetes mellitus, liver infections, allergic conditions, cardiovascular diseases, COVID-19, cancers, and neurodegenerative disorders. The International Scientific Association for Probiotics and Prebiotics has recently refined the theory of complementary and synergistic synbiotics. In recent years, the field of microbiome research has been significantly advanced by technological developments such as massive culturomics, gnotobiotics, metabolomics, parallel DNA sequencing, and RNA sequencing. This review article examined the potential next generation probiotics (NGPs) and explored some of them, Faecalibacterium prausnitzii, Bacteroides thetaiotaomicron, Akkermansia muciniphila, Parabacteroides goldsteinii, Bacteroides fragilis, Eubacterium hallii, Roseburia intestinalis, Christensenella minuta, Prevotella copri, and Oscillospira guilliermondii. In addition to these useful probiotic strains, psychobiotics, members of the families of Lactobacilli, Streptococci, Bifidobacteria, Escherichia, and Enterococci, have extended applicability in the use for neurodevelopmental and neurodegenerative disorders. The article also reviewed current trends and limitations in NGPs to enhance our comprehensive understanding of key concepts associated with the consumption of probiotics and proposed necessary initiatives for researchers to engage in collaborative translational research as future therapeutic solutions.

Gut microbiota in epilepsy: How antibiotics induce dysbiosis and influence seizure susceptibility

Epilepsy, a widespread chronic neurological disorder, has recently come under scrutiny for its potential association with the intricate dynamics of gut microbiota. Numerous investigations into the microbiota-gut-brain axis have revealed a close relationship between gut microbiota and epilepsy, suggesting gut microbiota as a potential treatment strategy. In clinical practice, a longstanding correlation has been observed between some kinds of antibiotics and the potential to induce seizures. Consequently, we have conceived a hypothesis that antibiotics might impact seizure activity by modulating the gut microbiota and influencing the physiological processes within the microbiota-gut-brain axis. In this review, our primary objective is to present the existing evidence and theoretical foundations supporting the hypothesis that dysbiosis within the gut microbiota may play a significant role in the pathophysiology of epilepsy. Furthermore, we aim to summarize the possible mechanisms between microbiota-gut-brain axis and epilepsy, offering insights into the selection of appropriate antibiotics for long-term epilepsy management and enhancing therapeutic efficacy through modulation of the gut microbiota. Further research is necessary to fully elucidate the intricate relationship between gut microbiota ecosystem and epilepsy. Exploring these connections holds promise for advancing our understanding of epilepsy pathogenesis and improving patient treatment and care.

Cinnamaldehyde Alleviates Salmonellosis in Chicks by Regulating Gut Health

Due to the high mortality rate in chicks caused by pullorum disease (PD) and the drawbacks of antibiotic resistance, the poultry industry is increasingly interested in using natural herbal antimicrobial agents as alternatives, with cinnamaldehyde (CA) being a focus due to its multitarget and synergistic effects. This study aimed to evaluate the effects of oral administration of CA on restoring intestinal physical integrity, intestinal microbial barrier, and intestinal metabolism in a laboratory model of Salmonella pullorum (S. pullorum) infection in chicks. Thirty-six chicks were divided into six groups. The S.P and CA groups were infected with 5 × 108 CFU/mL, 0.5 mL S. pullorum, while the CON group received an equal-volume saline injection. The CA group was treated with 100 mg/kg CA, and the others received phosphate buffer saline (PBS). Samples were collected 24 h after the last treatment. Intestinal physical integrity was assessed by H&E staining, and ELISA was used to measure inflammatory factors. In situ hybridization (ISH) and RT-qPCR were used to measure the expression of tight-junction protein mRNA. The microbiota was analyzed by 16S rRNA gene sequencing of the ileal contents, and metabolite analysis was performed on the intestinal contents. After CA treatment, the expression of IL-1β and TNF-α was reduced, and IL-10 was increased (p < 0.05). H&E staining showed that the intestinal structure was partially restored after treatment. ISH results showed that the fluorescence intensity indicating gene expression status was low in the S.P group and high in the CA group, indicating reduced intestinal permeability. RT-qPCR showed that CA up-regulated the mRNA expression of tight-junction proteins (claudin-1, occludin-1, and zo-1, p < 0.05). The 16S rRNA gene sequence analysis showed that Salmonella was significantly enriched in the S.P group (LDA score > 2.0, p < 0.05), while specific genera were significantly more abundant in the treated groups. Untargeted sequencing of intestinal contents showed that key metabolites (butyrate, alanine, glutamate, cholesterol, and propionate) in the CA group were significantly changed compared with the S.P group (p < 0.05). CA treatment was the most effective method for reducing PD intestinal colonization and maintaining better intestinal homeostasis, possibly by regulating intestinal microbiota and metabolic functions.

Tissue-Specific Metabolic Reprogramming in Innate Lymphoid Cells and Its Impact on Disease

Recent advances have highlighted the crucial role of metabolic reprogramming in shaping the functions of innate lymphoid cells (ILCs), which are vital for tissue immunity and homeostasis. As tissue-resident cells, ILCs dynamically respond to local environmental cues, with tissue-derived metabolites such as short-chain fatty acids and amino acids directly modulating their effector functions. The metabolic states of ILC subsets-ILC1, ILC2, and ILC3-are closely linked to their ability to produce cytokines, sustain survival, and drive proliferation. This review provides a comprehensive analysis of how key metabolic pathways, including glycolysis, oxidative phosphorylation, and fatty acid oxidation, influence ILC activation and function. Furthermore, we explore the complex interactions between these metabolic pathways and tissue-specific metabolites, which can shape ILC-mediated immune responses in health and disease. Understanding these interactions reveals new insights into the pathogenesis of conditions such as asthma, inflammatory bowel disease, and cancer. A deeper understanding of these mechanisms may not only advance our knowledge of disease pathogenesis but also lead to the development of novel therapeutic strategies targeting metabolic pathways in ILCs to treat tissue-specific immune disorders.

Control of T-cell immunity by fatty acid metabolism

Fatty acids play critical roles in maintaining the cellular functions of T cells and regulating T-cell immunity. This review synthesizes current research on the influence of fatty acids on T-cell subsets, including CD8+ T cells, TH1, TH17, Treg (regulatory T cells), and TFH (T follicular helper) cells. Fatty acids impact T cells by modulating signaling pathways, inducing metabolic changes, altering cellular structures, and regulating gene expression epigenetically. These processes affect T-cell activation, differentiation, and function, with implications for diseases such as autoimmune disease and cancer. Based on these insights, fatty acid pathways can potentially be modulated by novel therapeutics, paving the way for novel treatment approaches for immune-mediated disorders and cancer immunotherapy.

IL-33 Induces a Switch in Intestinal Metabolites Revealing the Tryptophan Pathway as a Target for Inducing Allograft Survival

BACKGROUND

IL-33, a pleiotropic cytokine, has been associated with a plethora of immune-related processes, both inflammatory and anti-inflammatory. T regulatory (Treg) cells, the main leukocyte population involved in immune tolerance, can be induced by the administration of IL-33, the local microbiota, and its metabolites. Here, we demonstrate that IL-33 drastically induces the production of intestinal metabolites involved on tryptophan (Trp) metabolism.

METHODS

naïve mice were treated with IL-33 for 4 days and leukocyte populations were analyzed by flow cytometry, and feces were processed for microbiota and intestinal metabolites studies. Using a murine skin transplantation model, the effect of Kynurenic acid (KA) on allograft survival was tested.

RESULTS

Under homeostatic conditions, animals treated with IL-33 showed an increment in Treg cell frequencies. Intestinal bacterial abundance analysis indicates that IL-33 provokes dysbiosis, demonstrated by a reduction in Enterobacteria and an increment in Lactobacillus genera. Furthermore, metabolomics analysis showed a dramatic IL-33 effect on the abundance of intestinal metabolites related to amino acid synthesis pathways, highlighting molecules linked to Trp metabolism, such as kynurenic acid (KA), 5-Hydroxyindoleacetic acid (5-HIAA), and 6-Hydroxynicotinic acid (6-HNA), which was supported by an enhanced expression of Ido and Kat mRNA in MLN cells, which are two enzymes involved on KA synthesis. Interestingly, animals receiving KA in drinking water and subjected to skin transplantation showed allograft acceptance, which is associated with an increment in Treg cell frequencies.

CONCLUSIONS

Our study reveals a new property for IL-33 as a modulator of the intestinal microbiota and metabolites, especially those involved with Trp metabolism. In addition, we demonstrate that KA favors Tregs in vivo, positively affecting skin transplantation survival.

From gut to bone: deciphering the impact of gut microbiota on osteoporosis pathogenesis and management

Osteoporosis (OP) is characterized by decreased bone mineral density (BMD) and increased fracture risk, poses a significant global health burden. Recent research has shed light on the bidirectional relationship between gut microbiota (GM) and bone health, presenting a novel avenue for understanding OP pathogenesis and developing targeted therapeutic interventions. This review provides a comprehensive overview of the GM-bone axis, exploring the impact of GM on OP development and management. We elucidate established risk factors and pathogenesis of OP, delve into the diversity and functional changes of GM in OP. Furthermore, we examine experimental evidence and clinical observations linking alterations in GM composition or function with variations in BMD and fracture risk. Mechanistic insights into microbial mediators of bone health, such as microbial metabolites and products, are discussed. Therapeutic implications, including GM-targeted interventions and dietary strategies, are also explored. Finally, we identify future research directions and challenges in translating these findings into clinical practice.

Gut Bacteria Provide Genetic and Molecular Reporter Systems to Identify Specific Diseases

With genetic information gained from next-generation sequencing (NGS) and genome-wide association studies (GWAS), it is now possible to select for genes that encode reporter molecules that may be used to detect abnormalities such as alcohol-related liver disease (ARLD), cancer, cognitive impairment, multiple sclerosis (MS), diabesity, and ischemic stroke (IS). This, however, requires a thorough understanding of the gut-brain axis (GBA), the effect diets have on the selection of gut microbiota, conditions that influence the expression of microbial genes, and human physiology. Bacterial metabolites such as short-chain fatty acids (SCFAs) play a major role in gut homeostasis, maintain intestinal epithelial cells (IECs), and regulate the immune system, neurological, and endocrine functions. Changes in butyrate levels may serve as an early warning of colon cancer. Other cancer-reporting molecules are colibactin, a genotoxin produced by polyketide synthetase-positive Escherichia coli strains, and spermine oxidase (SMO). Increased butyrate levels are also associated with inflammation and impaired cognition. Dysbiosis may lead to increased production of oxidized low-density lipoproteins (OX-LDLs), known to restrict blood vessels and cause hypertension. Sudden changes in SCFA levels may also serve as a warning of IS. Early signs of ARLD may be detected by an increase in regenerating islet-derived 3 gamma (REG3G), which is associated with changes in the secretion of mucin-2 (Muc2). Pro-inflammatory molecules such as cytokines, interferons, and TNF may serve as early reporters of MS. Other examples of microbial enzymes and metabolites that may be used as reporters in the early detection of life-threatening diseases are reviewed.

Spermidine improves the antioxidant capacity and morphology of intestinal tissues and regulates intestinal microorganisms in Sichuan white geese

Introduction

Intestinal health is very important to the health of livestock and poultry, and is even a major determining factor in the performance of livestock and poultry production. Spermidine is a type of polyamine that is commonly found in a variety of foods, and can resist oxidative stress, promote cell proliferation and regulate intestinal flora.

Methods

In this study, we explored the effects of spermidine on intestinal health under physiological states or oxidative stress conditions by irrigation with spermidine and intraperitoneal injection of 3-Nitropropionic acid (3-NPA) in Sichuan white goose.

Results and discussion

Our results showed that spermidine could increase the ratio of intestinal villus to crypt and improve intestinal morphology. In addition, spermidine can also reduce malondialdehyde (MDA) accumulation caused by 3-NPA by increasing superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) enzyme activity, thus alleviating intestinal damage. Furthermore, spermidine can regulate intestinal digestive enzyme activities and affect intestinal digestion and absorption ability. Spermidine can also promote an increase in intestinal microbial diversity and abundance and alleviate the change of microflora structure caused by 3-NPA. In conclusion, spermidine promotes the production of beneficial intestinal metabolites such as Wikstromol, Alpha-bisabolol and AS 1-5, thus improving the level of intestinal health. Taken together, these results indicate that spermidine can improve intestinal health by improving intestinal morphology, increasing antioxidant capacity and regulating intestinal flora structure.

Chlorella vulgaris Modulates Gut Microbiota and Induces Regulatory T Cells to Alleviate Colitis in Mice

Chlorella vulgaris (C. vulgaris) is unicellular green algae consumed worldwide as a functional food. The immune stimulatory function of C. vulgaris is known; however, no study has elucidated its immune regulatory potential and associated microbiome modulation. In the current study, we aimed to validate the immune regulatory role of C. vulgaris mediated through two mechanisms. Initially, we assessed its ability to promote the expansion of the regulatory T cell (Treg) population. Subsequently, we investigated its impact on gut microbiota composition and associated metabolites. The supplementation of C. vulgaris altered the gut microbiota composition, accompanied by increased short-chain fatty acid (SCFAs) production in mice at homeostasis. We later used C. vulgaris in the treatment of a DSS-induced colitis model. C. vulgaris intervention alleviated the pathological symptom of colitis in mice, with a corresponding increase in Treg levels. As C. vulgaris is a safe and widely used food supplement, it can be a feasible strategy to instigate cross-talk between the host immune system and the intestinal flora for the effective management of inflammatory bowel disease (IBD).

The Gut-Brain Axis as a Therapeutic Target in Multiple Sclerosis

The CNS is very susceptible to oxidative stress; the gut microbiota plays an important role as a trigger of oxidative damage that promotes mitochondrial dysfunction, neuroinflammation, and neurodegeneration. In the current review, we discuss recent findings on oxidative-stress-related inflammation mediated by the gut-brain axis in multiple sclerosis (MS). Growing evidence suggests targeting gut microbiota can be a promising strategy for MS management. Intricate interaction between multiple factors leads to increased intra- and inter-individual heterogeneity, frequently painting a different picture in vivo from that obtained under controlled conditions. Following an evidence-based approach, all proposed interventions should be validated in clinical trials with cohorts large enough to reach significance. Our review summarizes existing clinical trials focused on identifying suitable interventions, the suitable combinations, and appropriate timings to target microbiota-related oxidative stress. Most studies assessed relapsing-remitting MS (RRMS); only a few studies with very limited cohorts were carried out in other MS stages (e.g., secondary progressive MS-SPMS). Future trials must consider an extended time frame, perhaps starting with the perinatal period and lasting until the young adult period, aiming to capture as many complex intersystem interactions as possible.

Exploring probiotic effector molecules and their mode of action in gut-immune interactions

Probiotics, live microorganisms that confer health benefits when consumed in adequate amounts, have gained significant attention for their potential therapeutic applications. The beneficial effects of probiotics are believed to stem from their ability to enhance intestinal barrier function, inhibit pathogens, increase beneficial gut microbes, and modulate immune responses. However, clinical studies investigating the effectiveness of probiotics have yielded conflicting results, potentially due to the wide variety of probiotic species and strains used, the challenges in controlling the desired number of live microorganisms, and the complex interactions between bioactive substances within probiotics. Bacterial cell wall components, known as effector molecules, play a crucial role in mediating the interaction between probiotics and host receptors, leading to the activation of signaling pathways that contribute to the health-promoting effects. Previous reviews have extensively covered different probiotic effector molecules, highlighting their impact on immune homeostasis. Understanding how each probiotic component modulates immune activity at the molecular level may enable the prediction of immunological outcomes in future clinical studies. In this review, we present a comprehensive overview of the structural and immunological features of probiotic effector molecules, focusing primarily on Lactobacillus and Bifidobacterium. We also discuss current gaps and limitations in the field and propose directions for future research to enhance our understanding of probiotic-mediated immunomodulation.

Gut microbiome plays a vital role in post-stroke injury repair by mediating neuroinflammation

Cerebral stroke is a common neurological disease and often causes severe neurological deficits. With high morbidity, mortality, and disability rates, stroke threatens patients' life quality and brings a heavy economic burden on society. Ischemic cerebral lesions incur pathological changes as well as spontaneous nerve repair following stroke. Strategies such as drug therapy, physical therapy, and surgical treatment, can ameliorate blood and oxygen supply in the brain, hamper the inflammatory responses and maintain the structural and functional integrity of the brain. The gut microbiome, referred to as the "second genome" of the human body, participates in the regulation of multiple physiological functions including metabolism, digestion, inflammation, and immunity. The gut microbiome is not only inextricably associated with dangerous factors pertaining to stroke, including high blood pressure, diabetes, obesity, and atherosclerosis, but also influences stroke occurrence and prognosis. AMPK functions as a hub of metabolic control and is responsible for the regulation of metabolic events under physiological and pathological conditions. The AMPK mediators have been found to exert dual roles in regulating gut microbiota and neuroinflammation/neuronal apoptosis in stroke. In this study, we reviewed the role of the gut microbiome in cerebral stroke and the underlying mechanism of the AMPK signaling pathway in stroke. AMPK mediators in nerve repair and the regulation of intestinal microbial balance were also summarized.