Pleiotropic activities of succinate: The interplay between gut microbiota and cardiovascular diseases

The mitochondria-gut microbiota crosstalk - A novel frontier in cardiovascular diseases

Cardiovascular diseases (CVDs), including hypertension, atherosclerosis, and cardiomyopathy among others, remain the leading cause of global morbidity and mortality. Despite advances in treatment, the complex pathophysiology of CVDs necessitates innovative approaches to improve patient outcomes. Recent research has uncovered a dynamic interplay between mitochondria and gut microbiota, fundamentally altering our understanding of cardiovascular health. However, while existing studies have primarily focused on individual components of this axis, this review examines the bidirectional communication between these biological systems and their collective impact on cardiovascular health. Mitochondria, serving as cellular powerhouses, are crucial for maintaining cardiovascular homeostasis through oxidative phosphorylation (OXPHOS), calcium regulation, and redox balance. Simultaneously, the gut microbiota influences cardiovascular function through metabolite production, barrier integrity maintenance, and immune system modulation. The mitochondria-gut microbiota axis operates through various molecular mechanisms, including microbial metabolites such as trimethylamine N-oxide (TMAO), short-chain fatty acids (SCFA), and secondary bile acids, which directly influence mitochondrial function. Conversely, mitochondrial stress signals and damage-associated molecular patterns (DAMPs) affect gut microbial communities and barrier function. Key signalling pathways, including AMP-activated protein kinase (AMPK), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and the silent information regulator 1-peroxisome proliferator-activated receptor gamma coactivator 1-alpha (SIRT1-PGC-1α) axis, integrate these interactions, highlighting their role in CVD pathogenesis. Understanding these interactions has revealed promising therapeutic targets, suggesting new therapies aimed at both mitochondrial function and gut microbiota composition. Thus, this review provides a comprehensive framework for leveraging the mitochondria-gut microbiota axis in providing newer therapeutics for CVDs by targeting the AMPK/SIRT-1/PGC-1α/NF-κB signalling.

The Role of G Protein-Coupled Receptors in the Regulation of Orthopaedic Diseases by Gut Microbiota

Exercise and diet modulate the gut microbiota, which is involved in the regulation of orthopaedic diseases and synthesises a wide range of metabolites that modulate cellular function and play an important role in bone development, remodelling and disease. G protein-coupled receptors (GPCRs), the largest family of transmembrane receptors in the human body, interact with gut microbial metabolites to regulate relevant pathological processes. This paper provides a review of different dietary and exercise effects on the pathogenic gut microbiota and their metabolites associated with GPCRs in orthopaedic diseases. RESULTS: Generally, metabolites produced by gut microbiota contribute to the maintenance of bone health by activating the corresponding GPCRs, which are involved in bone metabolism, regulation of immune response, and maintenance of gut flora homeostasis. Exercise and diet can influence gut microbiota, and an imbalance in gut microbiota homeostasis can trigger a series of adverse immune and metabolic responses by affecting GPCR function, ultimately leading to the onset and progression of various orthopaedic diseases. Understanding these relationships is crucial for elucidating the pathogenesis of orthopaedic diseases and developing personalised probiotic-based therapeutic strategies. In the future, we should further explore how to prevent and treat orthopaedic diseases through GPCR-based modulation of gut microbes and their interactions. The development of substances that precisely modulate gut microbes through different exercises and diets will provide more effective interventions to improve bone health in patients.

Gut flora-derived succinate exacerbates Allergic Airway Inflammation by promoting protein succinylation

Allergic airway inflammation (AAI) is a prevalent respiratory disorder that affects a vast number of individuals globally. There exists a complex interplay among inflammation, immune responses, and metabolic processes, which is of paramount importance in the pathogenesis of AAI. Metabolic dysregulation and protein translational modification (PTM) are well-recognized hallmarks of diseases, playing pivotal roles in the onset and progression of numerous ailments. However, the role of gut microbiota metabolites in the development of AAI, as well as their influence on PTM modifications within this disease context, have not been thoroughly explored and investigated thus far. In AAI patients, succinate was identified as a key metabolite, positively correlated with certain immune parameters and IgE levels, and having good diagnostic value. In AAI mice, gut bacteria were the main source of high succinate levels. Mendelian randomization showed succinate as a risk factor for asthma. Exogenous succinate worsened AAI in mice, increasing airway resistance and inflammatory factor levels. Protein succinylation in AAI mice lungs differed significantly from normal mice, with up-regulated proteins in metabolic pathways. FMT alleviated AAI symptoms by reducing succinate and protein succinylation levels. In vitro, succinate promoted protein succinylation in BEAS-2B cells, and SOD2 was identified as a key succinylated protein, with the K68 site crucial for its modification and enzyme activity regulation. Gut flora-derived succinate exacerbates AAI in mice by increasing lung protein succinylation, and FMT can reverse this. These findings offer new insights into AAI mechanisms and potential therapeutic targets.

Sex Differences in Atrial Fibrillation: Evidence from Circulating Metabolites

Background: Significant sex differences exist in atrial fibrillation (AF). Better understanding of its underlying mechanism would help AF management. This study aimed to investigate the contribution of circulating metabolites to sex differences in AF and the association between them. Methods: A total of 108 patients with AF were enrolled. Untargeted metabolomics were performed in plasma samples of male and female patients. Correlation analysis with clinical characteristics and Mendelian randomization were used to identify sex-specific metabolites associated with AF, which was further validated in additional patients. Transcriptomics data of the left atrium were used to investigate the molecular alteration of the left atrium responding to identified sex-specific circulating metabolites. The effect of selected sex-specific metabolites on cardiomyocytes was further investigated. Results: A total of 60 annotated metabolites were found with different levels between male and female patients. Among these sex-specific metabolites, three metabolites, 7-Methylguanosine, succinic acid, and N-Undecylbenzenesulfonic acid, were positively related to the left atrial remodeling. Additionally, succinic acid was significantly associated with increased risk of AF (OR = 1.26; 95% CI: 1.13 to 1.40; p < 0.001). And, SUCLA2, the gene of succinic acid metabolism, was significantly increased in the left atrium of male patients (fold change = 1.53; p = 0.008). Treatment with succinic acid led to cardiomyocyte hypertrophy and mitochondrial dysfunction. Conclusions: This study highlights sex differences in circulating metabolites in patients with AF and identifies the associations between sex-specific metabolites and AF. succinic acid, which is much higher in male patients, contributes to the process of AF.

Metabolomics in Atrial Fibrillation: Unlocking Novel Biomarkers and Pathways for Diagnosis, Prognosis, and Personalized Treatment

BACKGROUND/OBJECTIVES

Atrial fibrillation (AF) is the most frequent arrhythmia in the adult population associated with a high rate of severe consequences leading to significant morbidity and mortality worldwide. Therefore, its prompt recognition is of high clinical importance. AF detection often remains challenging due to unspecific symptoms and a lack of reliable biomarkers for its prediction. Herein, novel bioanalytical methodologies, such as metabolomics, offer new opportunities for a better understanding of the underlying pathological mechanisms of cardiovascular diseases, including AF. The metabolome, considered a complete set of small molecules present in the organism, directly reflects the current phenotype of the studied system and is highly sensitive to any changes, including arrhythmia's onset. A growing body of evidence suggests that metabolite profiling has prognostic value in AF prediction, highlighting its potential role not only in early diagnosis but also in guiding therapeutic interventions. By identifying specific metabolites as a disease biomarker or recognising particular metabolomic pathways involved in the AF pathomechanisms, metabolomics could be of great clinical value for further clinical decision-making, risk stratification, and an individual personalised approach. The presented narrative review aims to summarise the current state of knowledge on metabolomics in AF with a special emphasis on its implications for clinical practice and personalised medicine.

Disentangling the molecular mystery of tumour-microbiota interactions: Microbial metabolites

The profound impact of the microbiota on the initiation and progression of cancer has been a focus of attention. In recent years, many studies have shown that microbial metabolites serve as key hubs that connect the microbiome and cancer progression, but the underlying molecular mechanisms have not been fully elucidated. Multiple mechanisms that influence tumour development and therapy resistance, including disrupting cellular signalling pathways, triggering oxidative stress, inducing metabolic reprogramming and reshaping tumour immune microenvironment, are reviewed. Focusing on recent advancements in this field, this review also summarises the methodological framework of studies regarding microbial metabolites. In this review, we outline the current state of research on tumour-associated microbial metabolites and describe the challenges in future scientific research and clinical applications. KEY POINTS: Metabolites derived from both gut and intratumoural microbiota play important roles in cancer initiation and progression. The dual roles of microbial metabolites pose an obstacle for clinical translations. Absolute quantification and tracing techniques of microbial metabolites are essential for addressing the gaps in studies on microbial metabolites. Integrating microbial metabolomics with multi-omics transcends current research paradigms.

Prophylactic supplementation with Bifidobacterium infantis or its metabolite inosine attenuates cardiac ischemia/reperfusion injury

Emerging evidence has demonstrated the profound impact of the gut microbiome on cardiovascular diseases through the production of diverse metabolites. Using an animal model of myocardial ischemia-reperfusion (I/R) injury, we found that the prophylactic administration of a well-known probiotic, Bifidobacterium infantis (B. infantis), exhibited cardioprotective effects in terms of preserving cardiac contractile function and preventing adverse cardiac remodeling following I/R and that these cardioprotective effects were recapitulated by its metabolite inosine. Transcriptomic analysis further revealed that inosine mitigated I/R-induced cardiac inflammation and cell death. Mechanistic investigations elucidated that inosine suppressed the production of pro-inflammatory cytokines and reduced the numbers of dendritic cells and natural killer cells, achieved through the activation of the adenosine A2A receptor (A2AR) that when inhibited abrogated the cardioprotective effects of inosine. Additionally, in vitro studies using C2C12 myoblasts revealed that inosine attenuated cell death by serving as an alternative carbon source for adenosine triphosphate (ATP) generation through the purine salvage pathway when subjected to oxygen-glucose deprivation/reoxygenation that simulated myocardial I/R injury. Likewise, inosine reversed the I/R-induced decrease in ATP levels in mouse hearts. Taken together, our findings indicate that B. infantis or its metabolite inosine exerts cardioprotective effects against I/R by suppressing cardiac inflammation and attenuating cardiac cell death, suggesting prophylactic therapeutic options for acute ischemic cardiac injury.

From heart to gut: Exploring the gut microbiome in congenital heart disease

Congenital heart disease (CHD) is a prevalent birth defect and a significant contributor to childhood mortality. The major characteristics of CHD include cardiovascular malformations and hemodynamical disorders. However, the impact of CHD extends beyond the circulatory system. Evidence has identified dysbiosis of the gut microbiome in patients with CHD. Chronic hypoxia and inflammation associated with CHD affect the gut microbiome, leading to alterations in its number, abundance, and composition. The gut microbiome, aside from providing essential nutrients, engages in direct interactions with the host immune system and indirect interactions via metabolites. The abnormal gut microbiome or its products can translocate into the bloodstream through an impaired gut barrier, leading to an inflammatory state. Metabolites of the gut microbiome, such as short-chain fatty acids and trimethylamine N-oxide, also play important roles in the development, treatment, and prognosis of CHD. This review discusses the role of the gut microbiome in immunity, gut barrier, neurodevelopment, and perioperative period in CHD. By fostering a better understanding of the cross-talk between CHD and the gut microbiome, this review aims to contribute to improve clinical management and outcomes for CHD patients.