Trimethylamine- N-oxide (TMAO) in the pathogenesis of rheumatoid arthritis and cardiovascular complications

Rheumatoid arthritis (RA) is a multifaceted autoimmune disorder characterized by chronic inflammation and joint destruction. Recent research has elucidated the intricate interplay between gut microbiota and RA pathogenesis, underscoring the role of microbiota-derived metabolites as pivotal contributors to disease development and progression. The human gut microbiota, comprising a vast array of microorganisms and their metabolic byproducts, plays a crucial role in maintaining immune homeostasis. Dysbiosis of this microbial community has been linked to numerous autoimmune disorders, including RA. Microbiota-derived metabolites, such as short-chain fatty acids (SCFAs), tryptophan derivatives, Trimethylamine-N-oxide (TMAO), bile acids, peptidoglycan, and lipopolysaccharide (LPS), exhibit immunomodulatory properties that can either exacerbate or ameliorate inflammation in RA. Mechanistically, these metabolites influence immune cell differentiation, cytokine production, and gut barrier integrity, collectively shaping the autoimmune milieu. This review highlights recent advances in understanding the intricate crosstalk between microbiota metabolites and RA pathogenesis and also discusses the potential of specific metabolites to trigger or suppress autoimmunity, shedding light on their molecular interactions with immune cells and signaling pathways. Additionally, this review explores the translational aspects of microbiota metabolites as diagnostic and prognostic tools in RA. Furthermore, the challenges and prospects of translating these findings into clinical practice are critically examined.

Author SummaryRheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by chronic inflammation in joint tissues leading to destruction of cartilage and bone. Despite some therapeutic advances, the etiology of RA pathogenesis is not yet clear, and effective treatment of RA remains a significant, unmet medical need. Hypoxia is a prominent feature of inflamed tissue within RA-affected joints, and earlier work has implicated limited involvement of hypoxia-inducible factor (HIF)-1 α. We explored the role of a second HIF family member, HIF-2α, in RA pathogenesis. We showed that HIF-2α is markedly increased in the tissue lining the RA-affected joints. Notably and in contrast to HIF-1α, when overexpressed in normal mouse joint tissues, HIF-2α is sufficient to cause RA-like symptoms. Conversely, an HIF-2α deficiency blocks the development of experimental arthritis in mice. We discovered further that HIF-2α regulates RA pathogenesis by modulating various RA-associated functions of joint-specific fibroblast-like cells, including proliferation, expression of cytokines, chemokines, and matrix-degrading enzymes, and bone-remodeling potential. HIF-2α also increases the ability of these cells to promote interleukin-6–dependent differentiation of TH17 cells, a known effector of RA pathogenesis. We thus show that HIF-1α and HIF-2α have distinct roles and act via different mechanisms in RA pathogenesis.

Thrombin is a key factor in the stimulation of fibrin deposition, angiogenesis, proinflammatory processes, and proliferation of fibroblast-like cells. Abnormalities in these processes are primary features of rheumatoid arthritis (RA) in synovial tissues. Tissue destruction in joints causes the accumulation of large quantities of free hyaluronic acid (HA) in RA synovial fluid. The present study was conducted to investigate the effects of HA and several other glycosaminoglycans on antithrombin, a plasma inhibitor of thrombin. Various glycosaminoglycans, including HA, chondroitin sulfate, keratan sulfate, heparin, and heparan, were incubated with human antithrombin III in vitro. The residual activity of antithrombin was determined using a thrombin-specific chromogenic assay. HA concentrations ranging from 250 to 1000 μg/ml significantly blocked the ability of antithrombin to inhibit thrombin in the presence of Ca2+ or Fe3+, and chondroitin A, B and C also reduced this ability under the same conditions but to a lesser extent. Our study suggests that the high concentration of free HA in RA synovium may block antithrombin locally, thereby deregulating thrombin activity to drive the pathogenic process of RA under physiological conditions. The study also helps to explain why RA occurs and develops in joint tissue, because the inflamed RA synovium is uniquely rich in free HA along with extracellular matrix degeneration. Our findings are consistent with those of others regarding increased coagulation activity in RA synovium.

To evaluate the bidirectional causal relationship between gut microbiota and Rheumatoid arthritis using Mendelian randomization (MR). Using gut microbiota data from the IEU OpenGWAS database (n = 5959, Finnish cohort) and rheumatoid arthritis genetic data from the Finnish database (6236 cases and 1,47,221 controls), forward and reverse MR analyses were conducted with gut microbiota and rheumatoid arthritis as exposure factors and outcomes, respectively. The significance threshold for forward MR was set at 1 × 10−5, and the significance threshold for reverse MR analysis was set at 5 × 10−8. The analysis primarily used inverse-variance-weighted (IVW) methods, supplemented by MR-Egger regression, weighted median methods, simple mode methods, and weighted mode methods. Sensitivity analyses were conducted to ensure the reliability of the results. The forward MR analysis indicated that increased abundances of Bacilli (CAG-345 sp000433315; PIVW = .040), Eubacterium_F sp000434115 (PIVW = .031), Fimbriimonadia (PIVW = .022), Christensenellales (GCA-900199385 sp900320755; PIVW = .006), Muribaculaceae (PIVW = .046), Lachnospira rogosae (PIVW = .023), Leuconostoc (PIVW = .025), Provencibacterium massiliense (PIVW = .021), Provencibacterium (PIVW = .039), and Rubneribacter sp002159915 (PIVW = .016) elevated the risk of rheumatoid arthritis, while higher abundances of Actinobacteriota (PIVW = .028), Bifidobacterium breve (PIVW = .007), Bifidobacterium kashiwanohense (PIVW = .009), Oscillospirales (CAG-448; PIVW = .029), and Syntrophomonadia (PIVW = .015) were protective against rheumatoid arthritis. The reverse MR analysis showed that rheumatoid arthritis was associated with increased abundances of 15 types of gut microbiota, including Blautia_A sp900066145 (PIVW = .025), Lachnospiraceae (PIVW = .041), Lactococcus lactis (PIVW = .026), Terrisporobacter (PIVW = .013), and Veillonella (PIVW = .046), and decreased abundances of 17 types of gut microbiota, including Alistipes shahii (PIVW = .032), Alistipes (PIVW = .010), Barnesiellaceae (PIVW = .008), Desulfovibrionaceae (PIVW = .029), and Parabacteroides (PIVW = .027). Cross-analysis did not reveal significant shared gut microbiota between forward and inverse MR analysis. Bidirectional sensitivity analysis validated the reliability of the study results. This study highlights the potential significance of specific gut microbiota in the pathogenesis of rheumatoid arthritis, providing new insights for the development of prevention, diagnosis, and therapeutic strategies for rheumatoid arthritis.

Dysbiosis of the gut microbiota plays a key role in the pathogenesis of rheumatoid arthritis (RA). However, it is still unclear whether the classic prescription Er Miao San (EMS) can exert therapeutic effects on RA by regulating the gut microbiota. In this study, we investigated whether EMS alleviates collagen-induced arthritis (CIA) by modulating the gut microbiota and its metabolites. We demonstrated that EMS significantly reduced arthritis severity, paw swelling, and systemic inflammation in CIA mice. In addition, 16S rRNA sequencing analysis revealed that EMS restored gut microbiota homeostasis, as evidenced by an increased abundance of Bacteroidetes, and a decreased Bacteroidetes/Firmicutes ratio. Crucially, antibiotic depletion of the gut microbiota abolished the protective effects of EMS, whereas fecal microbiota transplantation (FMT) from EMS-treated donors replicated its anti-arthritic efficacy, confirming the indispensable role of the microbiota. Measurement of short-chain fatty acids (SCFAs) further revealed a significant increase in the microbial metabolite butyrate following EMS treatment. Subsequent supplementation with sodium butyrate mimicked the therapeutic effects of EMS, ameliorating joint inflammation and cartilage damage. Mechanistically, butyrate enhanced the expression of intestinal tight junction proteins (ZO-1 and occludin), thereby restoring intestinal barrier integrity. Collectively, our results demonstrate that EMS exerts its anti-arthritic effects by modulating the gut microbiota-butyrate-intestinal barrier axis, highlighting the critical value of microbial metabolites in RA treatment. This study provides novel insights into the mechanism of EMS and suggests the therapeutic potential of butyrate for RA.

ObjectivesImmune and stromal cell communication is central in the pathogenesis of rheumatoid arthritis (RA) and psoriatic arthritis (PsA), however, the nature of these interactions in the synovial pathology of the...

Comment on: ‘Metagenome-wide association study of gut microbiome revealed novel aetiology of rheumatoid arthritis in the Japanese population’ by Kishikawa et al

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation, progressive cartilage and bone destruction, and resulting functional disability. Its pathogenesis is multifactorial, involving both genetic predisposition and environmental influences. In recent years, the interaction between the oral microbiota and RA has emerged as a prominent research focus. Dysbiosis of the oral microbiome, defined as an imbalance in microbial composition relative to a healthy state, accompanies disease onset and may further act as a trigger of systemic autoimmune responses. Specific virulence factors, including the peptidylarginine deiminase from Porphyromonas gingivalis and leukotoxin A from Aggregatibacter actinomycetemcomitans, promote excessive protein citrullination and anti-citrullinated protein antibody generation, thereby contributing to the loss of immune tolerance, particularly in genetically susceptible individuals. Moreover, the bidirectional relationship between RA and periodontitis highlights shared inflammatory pathways that contribute to both periodontal and joint tissue destruction. Potential mechanisms include bacteremia induced by routine oral activities, systemic dissemination of bacterial products, and colonization of oral microbiota in the gastrointestinal tract. Current evidence suggests that periodontal therapy may reduce systemic inflammatory markers and occasionally improve RA activity, although results remain inconsistent. In this review, we explored the potential mechanisms underlying the imbalance of the oral microbiota and its contribution to the onset and progression of RA, focusing on microbially induced citrullination, host genetic susceptibility, and common inflammatory pathways, while also discussing the impact of comprehensive periodontal management and lifestyle interventions on RA outcomes. Overall, these insights underscore the role of the oral microbiome in RA pathogenesis and suggest that addressing microbial dysbiosis through integrated therapeutic strategies may complement conventional care.

BackgroundDisorders of acquired and adaptive immunity play an important role in the rheumatoid arthritis (RA) pathogenesis. Important changes can nevertheless be detected at the metabolic level in the immune cells...

ObjectiveSubstantial progress has been made in understanding the involvement of malondialdehyde-acetaldehyde (MAA) adducts in rheumatoid arthritis (RA) pathogenesis. This systematic review synthesizes current evidence on the role of MAA-modified macromolecules and anti-MAA antibodies in the development, manifestation, and progression of RA.MethodsMEDLINE, EMBASE, the Cochrane Library, Scopus, and SciFinder were searched through May 6, 2025. Studies were screened based on predefined inclusion/exclusion criteria. Study characteristics were extracted, and quality assessments were performed.ResultsMAA-modified proteins and MAA-specific autoreactive B cells are elevated in synovial and lung tissues of RA patients. Anti-MAA antibodies are enriched in RA-derived synovial fluids compared to serum. Serum levels of anti-MAA IgG and IgA are increased prior to RA onset, and though not RA-specific, were higher in RA patients than those with other conditions. Anti-MAA antibodies do not cross-react with other autoantibodies, such as anti-citrullinated protein autoantibodies, and can be detected in sera from seronegative RA patients. Elevated anti-MAA antibody levels correlate with progression of joint, lung, and cardiovascular complications, as well as biologic treatment responses. Human and animal studies have begun to elucidate mechanisms by which MAA and anti-MAA antibody might contribute to inflammatory and fibrotic changes in RA.ConclusionsThis review provides a comprehensive overview of MAA and its involvement in RA pathogenesis. MAA adducts contribute to loss of immune tolerance and promote both inflammation and fibrosis in RA. Given associations of anti-MAA antibodies with RA disease activity and complications, MAA-related pathways hold promise as both biomarkers and treatment targets in RA.Systematic Review Registrationhttps://www.crd.york.ac.uk/PROSPERO/, identifier CRD4202454490.

Introduction Rheumatoid arthritis is a chronic inflammatory disease marked by systemic symptoms and joint degeneration. Interestingly, the development and progression of rheumatoid arthritis have been linked to the microbiome, notably the gut microbiome. Dysbiosis, an alteration in the gut microbiome, has been connected to the etiology and pathogenesis of rheumatoid arthritis. For instance, dysbiosis increases intestinal permeability and promotes the movement of bacteria and their products, which in turn triggers and aggravates systemic inflammation. Areas covered The correlation between the gut microbiome and RA. Triggers of RA including dysbiosis. The therapeutic potential of the gut microbiome in RA due to its critical function in influencing the immune response. The fecal microbiota transplantation (FMT), a therapeutic strategy that involves the transfer of healthy fecal microbiota from a donor to a recipient, has produced encouraging results in the treatment of several autoimmune illnesses, including rheumatoid arthritis. Expert opinion The role of the gut microbiome in RA is critical and serves as a basis for etiology and pathogenesis, as well as having therapeutic implications. In our opinion, FMT is an excellent example of this correlation. Still, more investigations and well-designed studies are needed in order to make firm conclusions and recommendations.

It has been well established that the pathogenesis of rheumatoid arthritis (RA) comprises three distinct but interdependent phenomena: the hyperplasia of synovial tissue, chronic inflammation (both local and systemic), and alterations in the immune response, including changes in the T-cell repertoire and the production of autoantibodies [1]. The precise nature of these interactions, however, particularly the role of autoantibodies in RA pathogenesis, is not yet fully understood. Whilst the occurrence of autoantibodies has been recognised as a characteristic feature of disease, and certain autoantibodies have become valuable tools for diagnosis, their contribution to the initiation and perpetuation of disease has remained largely elusive. A recent article by Terry Smith and William Cruikshank in the Journal of Immunology provides fascinating yet unexpected insights into how autoantibodies contribute to the maintenance of inflammatory disease processes in RA [2]. The authors report that IgG antibodies from the sera of patients with RA (RA-IgG) can stimulate RA synovial fibroblasts (RASFs) through interaction with insulin-like growth factor receptor 1 (IGF-R1). This interaction of RA-IgG with IGF-R1 increases the production of IL-16 and RANTES in RASFs provoking chemoattraction of T cells. The data demonstrate, for the first time, a bridging link between B-cell activity and T-cell trafficking. In addition, they are of potential importance for the development of innovative therapeutic strategies, in which interrupting the IGF-1/IGF-1R axis could result in sustained disease modification by affecting both the growth-factor triggered activation of fibroblasts and the accumulation of T lymphocytes. The significance of this research for understanding the pathogenesis of RA (and potentially other autoimmune disorders) goes beyond these two obvious aspects for several reasons. Although there have been reports that IgG may interact with mesenchymal cells [3-5], the present data establish a new role for (B-cell derived) autoantibodies in the pathogenesis of autoimmune disease. The hypothesis that autoantibodies not only constitute an epiphenomenon but also contribute directly to the pathogenesis of synovial inflammation and joint destruction has seen a 'revival' over the last couple of years [6,7]. This is mainly due to the observation that passive transfer of serum or immunoglobulins from arthritic K/BxN mice to healthy animals can cause arthritis [8,9]. However, these effects have been attributed mainly to the activation of complement and Fc-γ receptor pathways [6], and it has been suggested that, at a cellular level, mast cells link the autoantibodies to soluble mediators as well as to other effectors in arthritis [10]. The present data shed new light on the interaction of B-cells (more precisely B-cell derived immunoglobulins) and resident fibroblast-like cells of mesenchymal origin in the perpetuation of RA. They demonstrate clearly that antibodies may interact directly with fibroblast-like cells and through this interaction form part of a signalling loop that ultimately results in the maintenance of local inflammation. Consequently, the findings add to the growing body of evidence suggesting that resident stromal cells are a key element of the local immune response [11] and contribute significantly to the switch from acute to chronic inflammation in RA [12]. In this context, the observation that the effects of RA-IgG are seen with RASFs but not osteoarthritis synovial fibroblasts (OASFs) is of particular importance. Several lines of evidence suggest that, unlike normal synovial fibroblasts or OASFs, RASFs exhibit features of stable cellular activation (also known as transformation), that leads to alteration in their apoptotic response, the attachment of these cells to articular cartilage and subsequently to the degradation of the cartilage matrix [11,13]. This notion has been derived from in vitro studies as well as the SCID-mouse in vivo model of cartilage destruction. Although a number of molecular pathways have been identified that contribute to the stable activation of RASFs, the precise cause and nature of this activation, as well as its relevance and consequences, are matters of debate. The present data indicate very clearly that stable alterations in the fibroblasts themselves are indispensable for (auto)antibodies to exert their effects on IL-16 (and RANTES) mediated chemoattraction. It has to be emphasised that the experiments were done with fibroblasts that had been cultured for 3–10 passages in vitro before being exposed to the immunoglobulins. Consequently, the data suggest that the local stromal environment in the joint (and based on previous data from the group other organs as well [14]) to a large extent determines the disease specific immune response. Given the variety of signaling pathways initiated by IGF-1 in fibroblasts, it may be speculated, as the authors mention briefly, that binding of antibodies to IGF-1R exerts a number of other, potentially disease relevant effects in autoimmune diseases such as RA. Finally, the paper draws our attention back to IL-16, a cytokine that has been demonstrated at elevated levels in the sera [15,16] and synovial fluids [17] of patients with RA, but that has not been studied extensively in RA due to controversial data on its role in the pathogenesis of disease [18]. The present research on the interaction of RA-IgG and RASFs as well as other recent data, however, may change the picture. It has been reported by Huizinga and colleagues that in a cohort of patients with recent onset arthritis, patients who later developed RA showed significantly higher serum levels of IL-16 than patients with undifferentiated arthritis and that high IL-16 levels correlated positively with the degree of joint destruction over a 2-year period [16]. These data extend the aforementioned observations and link IL-16 to the disease process of RA. In this context it is of interest, that CD4 expression per se is not sufficient to mediate IL-16 effects [19]. Rather, IL-16 mediated T cell migration appears to be linked to CCR5, a receptor that is expressed predominantly in Th1 cells and is physically associated with CD4 [20]. RASFs have been identified as major producers of IL-16 in the rheumatoid joint, and it has been demonstrated that inflammatory cytokines present in the RA synovium such as TNFα and IL-1β can upregulate IL-16 in fibroblasts [21]. By demonstrating that in addition to these cytokines, growth factor signals trigger the release of IL-16 in RASFs, the present research from Smith and Cruikshank extends the panel of signals involved in the regulation of IL-16 at least under pathologic conditions. Although the study does not explain why RASFs and OASFs react differently to stimulation with RA-IgG, other data suggest that the expression of IL-16 may be regulated by different pathways in RASFs and OASFs [22]. Taken together, the data alter current concepts of how the immune system interacts with resident fibroblast-like cells and, even more intriguingly, add to the notion that alterations in the local fibroblast environment determine the specific immune response.

BackgroundAnti-citrullinated protein antibodies (ACPA) are central to rheumatoid arthritis (RA) pathogenesis and may develop at inflamed mucosa. We investigated whether asthma, a disease of airway mucosal inflammation, was associated with elevated ACPA before RA diagnosis.MethodsWe performed a nested case-control study among women in two prospective cohorts, the Nurses’ Health Study (NHS; 1976–2014) and NHSII (1989–2015). Blood was obtained on a subset (NHS: 1989–1990; NHSII: 1996–1999). Cases met 1987 ACR or 2010 ACR/EULAR RA criteria by medical record review and were classified as seropositive (ACPA+ or rheumatoid factor positivity) or seronegative by clinical laboratory testing at diagnosis. We identified RA cases with blood drawn before the date of RA diagnosis (index date), matching each to three controls by age, cohort, year, time from blood draw to index date, and menopause. Pre-RA ACPA elevation for cases was defined as >99th percentile of the control distribution on a research assay composed of autoantibodies targeting citrullinated protein epitopes or positivity on the second-generation commercial assay for cyclic citrullinated peptide. Asthma status and covariates were obtained through biennial questionnaires before blood draw. Conditional logistic regression estimated ORs and 95%CIs for RA by pre-RA ACPA and clinical serostatus, adjusted for matching factors, smoking pack-years, passive smoking, and body mass index (BMI).ResultsWe identified 284 incident RA cases and 849 matched controls; mean age at the index date was 61.2 years (SD 10.1). Blood was drawn 9.7 years (mean; SD 5.8) before the index date. We identified 96 (33.8%) RA cases with elevated pre-RA ACPA. At blood draw, 17.7% of pre-RA ACPA+ cases and 6.3% of matched controls (p = 0.0008) reported clinician-diagnosed asthma. After adjusting for matching factors, smoking pack-years, passive smoking, and BMI, asthma was significantly associated with pre-RA ACPA+ RA (OR 3.57, 95%CI 1.58,8.04). Asthma was not associated with overall RA (OR 1.45, 95%CI 0.91,2.31), but was significantly associated with seropositive RA (OR 1.79, 95%CI 1.01,3.18).ConclusionsAsthma was strongly associated with ACPA elevation in blood drawn prior to RA diagnosis, independent of smoking. Chronic mucosal airway inflammation may contribute to ACPA development and RA pathogenesis.

Integrative lncRNA–mRNA co‐expression network analysis identifies novel lncRNA E2F3‐IT1 for rheumatoid arthritis

Background:Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune sickness characterized with the aid of persistent joint infection, leading to joint damage and useful impairment. The pathogenesis of RA is thought to be encouraged with the aid of each genetic and environmental elements, with immune device dysregulation playing a valuable role in ailment progression. Increasing proof shows that oxidative pressure, which results from an imbalance between reactive oxygen species (ROS) and antioxidant defenses, contributes to the inflammatory techniques and tissue harm seen in RA. Objectives: This take a look at aimed to investigate the relationship among oxidative pressure and immune machine dysregulation inside the pathogenesis and progression of rheumatoid arthritis (RA). Methodology:This look at turned into conducted from 1st April to 30 November 2024 and protected a total of 200 participants were covered inside the examiner, along with 150 RA patients (75 male and 75 female) and 50 wholesome controls (25 male and 25 lady). The individuals’ ages ranged from 35 to 75 years. Blood samples were collected from the outpatient clinics at Tikrit Teaching Hospital among April and October 2024, and RA patients have been identified primarily based on medical criteria with the aid of the attending physicians. Oxidative strain markers, along with malondialdehyde (MDA) and glutathione (GSH), and pro-inflammatory cytokines, together with IL-1β, IL-17, and TNF-α, had been measured. Disease interest became assessed the usage of the Disease Activity Score 28 (DAS28). Results:The effects revealed that each male and female RA patients had extensively higher levels of MDA and decrease GSH tiers compared to the healthy manage institution. Moreover, seasoned-inflammatory cytokines (IL-1β, IL-17, and TNF-α) had been appreciably improved in RA sufferers, indicating a country of chronic infection. The DAS28 ratings confirmed that a majority of the RA patients had moderate to excessive disorder hobby. No good sized gender-based variations have been discovered in oxidative strain markers, cytokine stages, or sickness interest rankings. Conclusions: Our take a look at highlights the essential interaction among oxidative strain and immune dysregulation in RA. The determined correlations among oxidative markers, pro-inflammatory cytokines, and disease severity underscore the capability for focused on these pathways inside the management of RA. Future studies are warranted to in addition explore the healing ability of antioxidant-primarily based and anti-cytokine treatments in ameliorating RA-associated inflammation and joint damage. Further research is needed to explore the underlying mechanisms and capacity treatments focused on oxidative stress and immune modulation in RA.