Modulation of Inflammatory Arthritis in Mice by Gut Microbiota Through Mucosal Inflammation and Autoantibody Generation

Butyrate: a bridge between intestinal flora and rheumatoid arthritis

In patients with rheumatoid arthritis (RA), intestinal flora imbalance and butyrate metabolism disorders precede clinical arthritis and are associated with the pathogenesis of RA. This imbalance can alter the immunology and intestinal permeability of the intestinal mucosa, leading to damage to the intestinal barrier. In this context, bacteria and their metabolites can enter the bloodstream and reach the distant target tissues of the host, resulting in local inflammation and aggravating arthritis. Additionally, arthritis is also exacerbated by bone destruction and immune tolerance due to disturbed differentiation of osteoclasts and adaptive immune cells. Of note, butyrate is a metabolite of intestinal flora, which not only locally inhibits intestinal immunity and targets zonulin and tight junction proteins to alleviate intestinal barrier-mediated arthritis but also inhibits osteoclasts and autoantibodies and balances the immune responses of T and B lymphocytes throughout the body to repress bone erosion and inflammation. Therefore, butyrate is a key intermediate linking intestinal flora to the host. As a result, restoring the butyrate-producing capacity of intestinal flora and using exogenous butyrate are potential therapeutic strategies for RA in the future.

Distinct mucosal endotypes as initiators and drivers of rheumatoid arthritis

Rheumatoid arthritis (RA) is a potentially devastating autoimmune disease. The great majority of patients with RA are seropositive for anti-citrullinated protein antibodies (ACPAs), rheumatoid factors, or other autoantibodies. The onset of clinically apparent inflammatory arthritis meeting classification criteria (clinical RA) is preceded by ACPA seropositivity for an average of 3-5 years, a period that is designated as 'at-risk' of RA for ACPA-positive individuals who do not display signs of arthritis, or 'pre-RA' for individuals who are known to have progressed to developing clinical RA. Prior studies of individuals at-risk of RA have associated pulmonary mucosal inflammation with local production of ACPAs and rheumatoid factors, leading to development of the 'mucosal origins hypothesis'. Recent work now suggests the presence of multiple distinct mucosal site-specific mechanisms that drive RA evolution. Indicatively, subsets of individuals at-risk of RA and patients with RA harbour a faecal bacterial strain that has exhibited arthritogenic activity in animal models and that favours T helper 17 (TH17) cell responses in patients. Periodontal inflammation and oral microbiota have also been suggested to promote the development of arthritis through breaches in the mucosal barrier. Herein, we argue that mucosal sites and their associated microbial strains can contribute to RA evolution via distinct pathogenic mechanisms, which can be considered causal mucosal endotypes. Future therapies instituted for prevention in the at-risk period, or, perhaps, during clinical RA as therapeutics for active arthritis, will possibly have to address these individual mechanisms as part of precision medicine approaches.

Exploring the pathogenesis of RA through the gut-articular axis-dysbiosis a potential factor

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a complex etiology. It has been suggested that the pathogenesis of RA begins in the mucosa and then transitions to the joints when many factors interact, including microbial dysbiosis, inflammatory responses, and immune abnormalities at the mucosal site. Data from RA animals and patients suggest there are changes in the mucosal microflora before the onset of RA, and that dysbiosis of the mucosal ecology continues to play a role in the development of arthritis. Microbial dysbiosis of the mucosa reduces the normal barrier function of the intestinal tract, promotes inflammatory reactions in the mucosal areas of the intestines, and then activates the intestinal immune cells abnormally to produce a large number of auto-reactive antibodies that exacerbate arthritis. Current findings do not clarify whether dysbiosis is only a potential trigger for the development of RA. If it is possible to intervene in such microbial changes before the onset of RA, could the clinical symptoms of arthritis be prevented or reduced? Finding new ways to regulate gut flora composition to maintain gut barrier function is an ongoing challenge for the prevention and treatment of RA.

3,3-Dimethyl-1-Butanol and its Metabolite 3,3-Dimethylbutyrate Ameliorate Collagen-induced Arthritis Independent of Choline Trimethylamine Lyase Activity

Conflicting data exist in rheumatoid arthritis and the collagen-induced arthritis (CIA) murine model of autoimmune arthritis regarding the role of bacterial carnitine and choline metabolism into the inflammatory product trimethylamine (TMA), which is oxidized in the liver to trimethylamine-N-oxide (TMAO). Using two published inhibitors of bacterial TMA lyase, 3,3-dimethyl-1-butanol (DMB) and fluoromethylcholine (FMC), we tested if TMA/TMAO were relevant to inflammation in the development of CIA. Surprisingly, DMB-treated mice demonstrated > 50% reduction in arthritis severity compared to FMC and vehicle-treated mice, but amelioration of disease was independent of TMA/TMAO production. Given the apparent contradiction that DMB did not inhibit TMA, we then investigated the mechanism of protection by DMB. After verifying that DMB acted independently of the intestinal microbiome, we traced the metabolism of DMB within the host and identified a novel host-derived metabolite of DMB, 3,3-dimethyl-1-butyric acid (DMBut). In vivo studies of mice treated with DMB or DMBut demonstrated efficacy of both molecules in significantly reducing disease and proinflammatory cytokines in CIA, while in vitro studies suggest these molecules may act by modulating secretion of proinflammatory cytokines from macrophages. Altogether, our study suggests that DMB and/or its metabolites are protective in CIA through direct immunomodulatory effects rather than inhibition of bacterial TMA lyases.

Helicobacter pylori upregulates PAD4 expression via stabilising HIF-1α to exacerbate rheumatoid arthritis

OBJECTIVE

Helicobacter pylori infection has been reported to aggravate rheumatoid arthritis (RA), but the relevant mechanism remains unclear. This study aimed to investigate the underlying pathogenic mechanism of H. pylori infection in the progression of RA.

METHODS

The Disease Activity Score (DAS-28) and serum anticitrullinated protein antibody (ACPA) levels were compared between H. pylori-negative and H. pylori-positive patients with RA. MH7A cells were stimulated with polyclonal ACPA purified from the peripheral blood of patients with RA. The citrullination levels were assessed by western blot in GES-1 cells and sera. ChIP, luciferase reporter assays, mass spectrometry and ELISA were applied to explore the molecular mechanism of H. pylori infection in RA progression.

RESULTS

The DAS-28 and ACPA levels of patients with RA in the H. pylori-positive group were significantly higher than those in the H. pylori-negative group. Polyclonal ACPA derived from H. pylori-positive patients promoted cell proliferation and induced secretion of IL-6 and IL-8. For the first time, we found that H. pylori infection induces cellular protein citrullination by upregulating protein arginine deiminase type 4 (PAD4). Furthermore, we confirmed a direct functional binding of hypoxia-inducible factor 1α on the PADI4 gene promoter. We demonstrated that PAD4 interacts with and citrullinates keratin 1 (K1), and serum and synovial fluid levels of anti-Cit-K1 antibody were markedly increased in H. pylori-infected patients with RA.

CONCLUSION

Our findings reveal a novel mechanism by which H. pylori infection contributes to RA progression. Therapeutic interventions targeting H. pylori may be a viable strategy for the management of RA.

Gut microbiota as a sensor of autoimmune response and treatment for rheumatoid arthritis

Rheumatoid arthritis (RA) is considered a multifactorial condition where interaction between the genetic and environmental factors lead to immune dysregulation causing autoreactivity. While among the various genetic factors, HLA-DR4 and DQ8, have been reported to be the strongest risk factors, the role of various environmental factors has been unclear. Though events initiating autoreactivity remain unknown, a mucosal origin of RA has gained attention based on the recent observations with the gut dysbiosis in patients. However, causality of gut dysbiosis has been difficult to prove in humans. Mouse models, especially mice expressing RA-susceptible and -resistant HLA class II genes have helped unravel the complex interactions between genetic factors and gut microbiome. This review describes the interactions between HLA genes and gut dysbiosis in sex-biased preclinical autoreactivity and discusses the potential use of endogenous commensals as indicators of treatment efficacy as well as therapeutic tool to suppress pro-inflammatory response in rheumatoid arthritis.

Undenatured type II collagen protects against collagen-induced arthritis by restoring gut-joint homeostasis and immunity

Oral administration of harmless antigens can induce suppression of reactive immune responses, a process that capitalises on the ability of the gastrointestinal tract to tolerate exposure to food and commensal microbiome without triggering inflammatory responses. Repeating exposure to type II collagen induces oral tolerance and inhibits induction of arthritis, a chronic inflammatory joint condition. Although some mechanisms underlying oral tolerance are described, how dysregulation of gut immune networks impacts on inflammation of distant tissues like the joints is unclear. We used undenatured type II collagen in a prophylactic regime -7.33 mg/kg three times/week- to describe the mechanisms associated with protective oral immune-therapy (OIT) in gut and joint during experimental Collagen-Induced Arthritis (CIA). OIT reduced disease incidence to 50%, with reduced expression of IL-17 and IL-22 in the joints of asymptomatic mice. Moreover, whilst the gut tissue of arthritic mice shows substantial damage and activation of tissue-specific immune networks, oral administration of undenatured type II collagen protects against gut pathology in all mice, symptomatic and asymptomatic, rewiring IL-17/IL-22 networks. Furthermore, gut fucosylation and microbiome composition were also modulated. These results corroborate the relevance of the gut-joint axis in arthritis, showing novel regulatory mechanisms linked to therapeutic OIT in joint disease.

Exploring the significance of microbiota metabolites in rheumatoid arthritis: uncovering their contribution from disease development to biomarker potential

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.

High fat diet increases the severity of collagen-induced arthritis in mice by altering the gut microbial community

OBJECTIVES

Research has demonstrated that obesity may be associated with rheumatoid arthritis (RA). In addition, gut microbiota and its metabolites contribute to the occurrence and development of RA and obesity. However, the mechanism by which obesity affects RA remains unclear. In this study, we aimed to investigate whether gut microbiota and their metabolites alter the effects of high fat diet (HFD) on the severity of collagen-induced arthritis (CIA) in mice.

METHODS

Briefly, mice were divided into normal group (N), CIA model group (C), HFD group (T), and HFD CIA group (CT). Hematoxylin and Eosin staining(HE) and Safranin O-fast green staining were conducted, and levels of blood lipid and inflammatory cytokines were measured. 16S rDNA sequencing technique and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics were performed to explore changes in the microbiota structure to further reveal the pathomechanism of HFD on CIA.

RESULTS

HFD aggravated the severity of CIA in mice. The CT group had the highest proportion of microbial abundance of Blautia, Oscillibacter, Ruminiclostridium-9, and Lachnospiraceae UCG 006 at the genus level, but had a lower proportion of Alistipes. Additionally, the fecal metabolic phenotype of the combined CT group shows significant changes, with differential metabolites enriched in 9 metabolic pathways, including primary bile acid biosynthesis, arginine biosynthesis, sphingolipid metabolism, purine metabolism, linoleic acid metabolism, oxytocin signaling pathway, aminoacyl-tRNA biosynthesis, the pentose phosphate pathway, and sphingolipid signaling pathway. Correlation analysis revealed that some of the altered gut microbiota genera were strongly correlated with changes in fecal metabolites, total cholesterol (TC), triglyceride (TG), and inflammatory cytokine levels.

CONCLUSIONS

This study shows that HFD may aggravate inflammatory reaction in CIA mice by altering the gut microbiota and metabolic pathways.

The parasitic worm product ES-62 protects against collagen-induced arthritis by resetting the gut-bone marrow axis in a microbiome-dependent manner

The parasitic worm-derived immunomodulator, ES-62 rescues defective levels of IL-10-producing regulatory B cells (Bregs) and suppresses chronic Th1/Th17-driven inflammation to protect against joint destruction in the mouse collagen-induced arthritis (CIA) model of rheumatoid arthritis. Such autoimmune arthritis is also associated with dysbiosis of the gut microbiota and disruption of intestinal barrier integrity. We recently further exploited the CIA model to show that ES-62's prevention of joint destruction is associated with protection of intestinal barrier integrity and normalization of the gut microbiota, thereby suppressing the gut pathology that precedes the onset of autoimmunity and joint damage in CIA-mice. As the status of the gut microbiota impacts on immune responses by influencing haematopoiesis, we have therefore investigated whether ES-62 harnesses the homeostatic mechanisms regulating this gut-bone marrow (BM) axis to resolve the chronic inflammation promoting autoimmunity and joint destruction in CIA. Reflecting this, ES-62 was found to counteract the BM myeloid/lymphoid bias typically associated with chronic inflammation and infection. This was achieved primarily by ES-62 acting to maintain the levels of lymphoid lineages (B220+ and CD3+ cells) observed in naïve, healthy mice but lost from the BM of CIA-mice. Moreover, ES-62's ability to prevent bone-destroying osteoclastogenesis was found to be associated with its suppression of CIA-induced upregulation of osteoclast progenitors (OCPs) in the BM. Critically, and supporting ES-62's targeting of the gut-BM axis, this rewiring of inflammatory haematopoiesis was lost in mice with a depleted microbiome. Underlining the importance of ES-62's actions in restoring steady-state haematopoiesis, the BM levels of B and T lymphoid cells were shown to be inversely correlated, whilst the levels of OCPs positively correlated, with the severity of joint damage in CIA-mice.

Peptoniphilus gorbachii alleviates collagen-induced arthritis in mice by improving intestinal homeostasis and immune regulation

Introduction

The intricate connection between gut microbiota and rheumatoid arthritis (RA) pathogenesis has gained prominence, although the specific microbial species contributing to RA development remain largely unknown. Recent studies have sought to comprehensively explore alterations in the human microbiome, focusing on identifying disease-related microbial species through blood analysis. Consequently, this study aimed to identify RA-associated microbial species using a serum microbial array system and to investigate the efficacy and underlying mechanisms of potential microbial species for RA treatment.

Methods

Serum immunoglobulin M levels against 384 intestinal microbial species were assessed using a microbial microarray in patients with RA and healthy individuals. We investigated the therapeutic potential of the identified microbial candidate regarding arthritis development, immune responses, gut barrier function, and gut microbiome using a collagen-induced arthritis (CIA) mouse model.

Results

Our findings revealed significant alterations in antibody levels against 36 microbial species in patients with RA compared to healthy individuals. Notably, the antibody levels against Peptoniphilus gorbachii (PG) were decreased in patients with RA and exhibited an inverse correlation with RA disease activity. In vitro experiments demonstrated that PG produced acetate and butyrate, while exhibiting anti-inflammatory properties. In CIA mice, PG administration suppressed arthritis symptoms, reduced the accumulation of inflammatory monocytes in the mesenteric lymph nodes, and downregulated gene expression of pro-inflammatory cytokines in the ileum. Additionally, PG supplementation restored intestinal barrier integrity and partially resolved gut microbial dysbiosis in CIA mice. The fecal microbiota in PG-treated mice corresponded to improved intestinal barrier integrity and reduced inflammatory responses.

Conclusion

This study highlights the potential of serum-based detection of anti-microbial antibodies to identify microbial targets at the species level for RA treatment. Moreover, our findings suggest that PG, identified through the microbial microarray analysis, holds therapeutic potential for RA by restoring intestinal barrier integrity and suppressing the immunologic response associated with RA.

Microbial Imbalance and Intestinal Permeability in the Pathogenesis of Rheumatoid Arthritis: A Mechanism Review with a Focus on Bacterial Translocation, Citrullination, and Probiotic Intervention

This review aims to investigate the role of intestinal permeability (IP) in rheumatoid arthritis (RA), following the hypotheses that leakage of intestinal microbes can influence increased citrullination of peptides leading to anti-citrullinated protein antibody (ACPA) production and inflammation in RA; and that leaked microbes can migrate to the peripheral joints, leading to immune responses and synovitis in peripheral joints. This review explored the evidence for the link between microbial dysbiosis and increased IP in the inflammatory state in RA, as well as the role of increased citrullination and bacterial translocation in the link between microbiota and immune responses in RA. Furthermore, this research aims to evaluate the potential effect of probiotics on RA symptoms and pathogenesis via proposed mechanisms, including the support of microbial balance and suppression of inflammatory factors in RA. A systematic literature search was conducted in three tranches (review, mechanism, intervention). 71 peer-reviewed papers met the inclusions criteria and are summarized in a narrative analysis. Primary studies were critically appraised, synthesized and their relevance to clinical practice evaluated. Evidence found in this mechanism review consistently supported intestinal dysbiosis and increased IP in arthritis. An altered intestinal microbiome was demonstrated in RA with specific microbes such as Collinsella and Eggerthella correlating with increased IP, mucosal inflammation, and immune responses. Hypercitrullination and ACPA production correlated with arthritic symptoms and intestinal microbes were shown to influence hypercitrullination. Some in vitro and animal studies demonstrated a link between leakage of microbes and bacterial translocation, but further research is needed to elucidate the link between IP and citrullination. Probiotic intervention studies evidenced reductions in inflammatory markers IL-6 and TNFα, associated with proliferation of synovial tissue and pain perception in RA joint inflammation. Despite some conflict in the literature, probiotics may present a promising nutritional intervention in the suppression of both, disease activity and inflammatory markers.Key teaching pointsThere is evidence for a dysbiotic profile of the RA gut with specific RA-associated microbes.Increased intestinal permeability and leakage of PAD enzyme facilitates citrullination of peptides.Hypercitrullination and ACPA production correlate to arthritic signs.Microbial leakage and translocation plays a role in the pathogenesis of RA.Probiotics (e.g. L. Casei 01) may reduce inflammation and ameliorate RA symptoms.

Microbiota-dependent indole production stimulates the development of collagen-induced arthritis in mice

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model, we identified alterations in tryptophan metabolism, and specifically indole, that correlated with disease. We demonstrated that both bacteria and dietary tryptophan were required for disease and that indole supplementation was sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colonic lymphocytes to indole increased the expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a unique therapeutic pathway for RA and SpA.

Comprehensive multi-omics analysis reveals the core role of glycerophospholipid metabolism in rheumatoid arthritis development

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic autoimmune disease with complex causes and recurrent attacks that can easily develop into chronic arthritis and eventually lead to joint deformity. Our study aims to elucidate potential mechanism among control, new-onset RA (NORA) and chronic RA (CRA) with multi-omics analysis.

METHODS

A total of 113 RA patients and 75 controls were included in our study. Plasma and stool samples were obtained for 16S rRNA sequencing, internally transcribed spacer (ITS) sequencing and metabolomics analysis. And PBMCs were obtained for RNA sequencing. We used three models, logistic regression, least absolute shrinkage and selection operator (LASSO), and random forest, respectively, to distinguish NORA from CRA, and finally we validated model performance using an external cohort of 26 subjects.

RESULTS

Our results demonstrated intestinal flora disturbance in RA development, with significantly increased abundance of Escherichia-Shigella and Proteobacteria in NORA. We also found that the diversity was significantly reduced in CRA compared to NORA through fungi analysis. Moreover, we identified 29 differential metabolites between NORA and CRA. Pathway enrichment analysis revealed significant dysregulation of glycerophospholipid metabolism and phenylalanine metabolism pathways in RA patients. Next, we identified 40 differentially expressed genes between NORA and CRA, which acetylcholinesterase (ACHE) was the core gene and significantly enriched in glycerophospholipid metabolism pathway. Correlation analysis showed a strong negatively correlation between glycerophosphocholine and inflammatory characteristics. Additionally, we applied three approaches to develop disease classifier models that were based on plasma metabolites and gut microbiota, which effectively distinguished between new-onset and chronic RA patients in both discovery cohort and external validation cohort.

CONCLUSIONS

These findings revealed that glycerophospholipid metabolism plays a crucial role in the development and progression of RA, providing new ideas for early clinical diagnosis and optimizing treatment strategies.

Fecal microbiota transplantation: Emerging applications in autoimmune diseases

Both genetic susceptibility and environmental factors are important contributors to autoimmune disease pathogenesis. As an environmental factor, the gut microbiome plays a crucial role in the development and progression of autoimmune diseases. Thus, strategies targeting gut microbiome alterations can potentially be used to treat autoimmune disease. Microbiota-based interventions, such as prebiotics, probiotics, dietary interventions, and fecal microbiota transplantation (FMT), have attracted growing interest as novel treatment approaches. FMT is an effective method for treating recurrent Clostridioides difficile infections; moreover, it is emerging as a promising treatment for patients with inflammatory bowel disease and other autoimmune diseases. Although the mechanisms underpinning the interaction between the gut microbiome and host are not fully understood in patients with autoimmune disease, FMT has been shown to restore altered gut microbiota composition, rebuild the intestinal microecosystem, and mediate innate and adaptive immune responses to achieve a therapeutic effect. In this review, we provide an overview of FMT and discuss how FMT can be used as a novel treatment approach for autoimmune diseases. Furthermore, we discuss recent challenges and offer future research directions.

The gut ecosystem and immune tolerance

The gastrointestinal tract is home to the largest microbial population in the human body. The gut microbiota plays significant roles in the development of the gut immune system and has a substantial impact on the maintenance of immune tolerance beginning in early life. These microbes interact with the immune system in a dynamic and interdependent manner. They generate immune signals by presenting a vast repertoire of antigenic determinants and microbial metabolites that influence the development, maturation and maintenance of immunological function and homeostasis. At the same time, both the innate and adaptive immune systems are involved in modulating a stable microbial ecosystem between the commensal and pathogenic microorganisms. Hence, the gut microbial population and the host immune system work together to maintain immune homeostasis synergistically. In susceptible hosts, disruption of such a harmonious state can greatly affect human health and lead to various auto-inflammatory and autoimmune disorders. In this review, we discuss our current understanding of the interactions between the gut microbiota and immunity with an emphasis on: a) important players of gut innate and adaptive immunity; b) the contribution of gut microbial metabolites; and c) the effect of disruption of innate and adaptive immunity as well as alteration of gut microbiome on the molecular mechanisms driving autoimmunity in various autoimmune diseases.

Gut microbiota in pre-clinical rheumatoid arthritis: From pathogenesis to preventing progression

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by progressive polyarthritis that leads to cartilage and bone damage. Pre-clinical RA is a prolonged state before clinical arthritis and RA develop, in which autoantibodies (antibodies against citrullinated proteins, rheumatoid factors) can be present due to the breakdown of immunologic self-tolerance. As early treatment initiation before the onset of polyarthritis may achieve sustained remission, optimize clinical outcomes, and even prevent RA progression, the pre-clinical RA stage is showing the prospect to be the window of opportunity for RA treatment. Growing evidence has shown the role of the gut microbiota in inducing systemic inflammation and polyarthritis via multiple mechanisms, which may involve molecular mimicry, impaired intestinal barrier function, gut microbiota-derived metabolites mediated immune regulation, modulation of the gut microbiota's effect on immune cells, intestinal epithelial cells autophagy, and the interaction between the microbiome and human leukocyte antigen alleles as well as microRNAs. Since gut microbiota alterations in pre-clinical RA have been reported, potential therapies for modifying the gut microbiota in pre-clinical RA, including natural products, antibiotic therapy, fecal microbiota transplantation, probiotics, microRNAs therapy, vitamin D supplementation, autophagy inducer-based treatment, prebiotics, and diet, holds great promise for the successful treatment and even prevention of RA via altering ongoing inflammation. In this review, we summarized current studies that include pathogenesis of gut microbiota in RA progression and promising therapeutic strategies to provide novel ideas for the management of pre-clinical RA and possibly preventing arthritis progression.

Microbiota-dependent indole production is required for the development of collagen-induced arthritis

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model we identify alterations in tryptophan metabolism, and specifically indole, that correlate with disease. We demonstrate that both bacteria and dietary tryptophan are required for disease, and indole supplementation is sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colon lymphocytes to indole increased expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a novel therapeutic pathway for RA and SpA.

Sterile triggers drive joint inflammation in TNF- and IL-1β-dependent mouse arthritis models

Arthritis is the most common extra-intestinal complication in inflammatory bowel disease (IBD). Conversely, arthritis patients are at risk for developing IBD and often display subclinical gut inflammation. These observations suggest a shared disease etiology, commonly termed "the gut-joint-axis." The clinical association between gut and joint inflammation is further supported by the success of common therapeutic strategies and microbiota dysbiosis in both conditions. Most data, however, support a correlative relationship between gut and joint inflammation, while causative evidence is lacking. Using two independent transgenic mouse arthritis models, either TNF- or IL-1β dependent, we demonstrate that arthritis develops independently of the microbiota and intestinal inflammation, since both lines develop full-blown articular inflammation under germ-free conditions. In contrast, TNF-driven gut inflammation is fully rescued in germ-free conditions, indicating that the microbiota is driving TNF-induced gut inflammation. Together, our study demonstrates that although common inflammatory pathways may drive both gut and joint inflammation, the molecular triggers initiating such pathways are distinct in these tissues.

Alteration of Gut Microbiota in Individuals at High-Risk for Rheumatoid Arthritis Associated With Disturbed Metabolome and the Initiation of Arthritis Through the Triggering of Mucosal Immunity Imbalance

OBJECTIVE

In this study, we aimed to decipher the gut microbiome (GM) and serum metabolic characteristic of individuals at high risk for rheumatoid arthritis (RA) and to investigate the causative effect of GM on the mucosal immune system and its involvement in the pathogenesis of arthritis.

METHODS

Fecal samples were collected from 38 healthy individuals and 53 high-risk RA individuals with anti-citrullinated protein antibody (ACPA) positivity (Pre-RA), 12 of 53 Pre-RA individuals developed RA within 5 years of follow-up. The differences in intestinal microbial composition between the healthy controls and Pre-RA individuals or among Pre-RA subgroups were identified by 16S ribosomal RNA sequencing. The serum metabolite profile and its correlation with GM were also explored. Moreover, antibiotic-pretreated mice that received GM from the healthy control or Pre-RA groups were then evaluated for intestinal permeability, inflammatory cytokines, and immune cell populations. Collagen-induced arthritis (CIA) was also applied to test the effect of fecal microbiota transplantation (FMT) from Pre-RA individuals on arthritis severity in mice.

RESULTS

Stool microbial diversity was lower in Pre-RA individuals than in healthy controls. The bacterial community structure and function significantly differed between healthy controls and Pre-RA individuals. Although there were differences to some extent in the bacterial abundance among the Pre-RA subgroups, no robust functional differences were observed. The metabolites in the serum of the Pre-RA group were dramatically different from those in the healthy controls group, with KEGG pathway enrichment of amino acid and lipid metabolism. Moreover, intestinal bacteria from the Pre-RA group increased intestinal permeability in FMT mice and zonula occludens-1 expression in the small intestine and Caco-2 cells. Moreover, Th17 cells in the mesenteric lymph nodes and Peyer's patches were also increased in mice receiving Pre-RA feces compared to healthy controls. The changes in intestinal permeability and Th17-cell activation prior to arthritis induction enhanced CIA severity in PreRA-FMT mice compared with HC-FMT mice.

CONCLUSION

Gut microbial dysbiosis and metabolome alterations already occur in individuals at high risk for RA. FMT from preclinical individuals triggers intestinal barrier dysfunction and changes mucosal immunity, further contributing to the development of arthritis.

Tripterygium hypoglaucum extract ameliorates adjuvant-induced arthritis in mice through the gut microbiota

Traditionally, Tripterygium hypoglaucum (Levl.) Hutch (THH) are widely used in Chinese folk to treat rheumatoid arthritis (RA). This study aimed to investigate whether the anti-RA effect of THH is related with the gut microbiota. The main components of prepared THH extract were identified by HPLC-MS. C57BL/6 mice with adjuvant-induced arthritis (AIA) were treated with THH extract by gavage for one month. THH extract significantly alleviated swollen ankle, joint cavity exudation, and articular cartilage destruction in AIA mice. The mRNA and protein levels of inflammatory mediators in muscles and plasma indicated that THH extract attenuated inflammatory responses in the joint by blocking TLR4/MyD88/MAPK signaling pathways. THH extract remarkably restored the dysbiosis of the gut microbiota in AIA mice, featuring the increases of Bifidobacterium, Akkermansia, and Lactobacillus and the decreases of Butyricimonas, Parabacteroides, and Anaeroplasma. Furthermore, the altered bacteria were closely correlated with physiological indices and drove metabolic changes of the intestinal microbiota. In addition, antibiotic-induced pseudo germ-free mice were employed to verify the role of the intestinal flora. Strikingly, THH treatment failed to ameliorate the arthritis symptoms and signaling pathways in pseudo germ-free mice, which validates the indispensable role of the intestinal flora. For the first time, we demonstrated that THH extract protects joint inflammation by manipulating the intestinal flora and regulating the TLR4/MyD88/MAPK signaling pathway. Therefore, THH extract may serve as a microbial modulator to recover RA in clincial practice.ver RA in clincial practice.

Influence of genetically predicted autoimmune diseases on NAFLD

Introduction

Non-alcoholic fatty liver disease (NAFLD), the emerging cause of end-stage liver disease, is the most common liver disease. Determining the independent risk factors of NAFLD and patients who need more monitoring is important.

Methods

Two-Sample Mendelian randomization (MR) was performed in the analysis to investigate the causal association of different autoimmune diseases with NAFLD using summary level data. Genome-wide association study (GWAS) of 5 autoimmune diseases including celiac disease (CeD), Crohn's disease (CD), multiple sclerosis (MS), rheumatoid arthritis (RA), and type 1 diabetes (T1D) were selected for Instrument variables (IVs). NAFLD was included as outcome.

Result

After adjusting for confounding factors, genetic predisposition of CeD (OR= 0.973, [0.949,0.997], IVW p-value=0.026), MS (OR= 1.048, [1.012,1.085], IVW p-value= 0.008), RA (OR= 1.036, [1.006,1.066], IVW p-value=0.019), T1D (OR= 1.039, [1.002,1.079], IVW p-value= 0.041) is causally associated with NAFLD. No causal effect was found between CD and NAFLD.

Conclusion

CeD itself may be a protective factor for NAFLD, the results of previous observational studies have been influenced by confounding factors, and the morbidity of NAFLD may be higher in patients with MS, RA, and T1D than in common populations, and monitoring the prevalence of NAFLD in these populations is considerable.

3,3-dimethyl-1-butanol and its metabolite 3,3-dimethylbutyrate ameliorate collagen-induced arthritis independent of choline trimethylamine lyase activity

Previous studies have identified significant alterations in intestinal carnitine metabolism in mice with collagen-induced arthritis (CIA), potentially linking bacterial dysbiosis with autoimmunity. Bacterial trimethylamine (TMA) lyases metabolize dietary carnitine to TMA, which is oxidized in the liver to trimethylamine-N-oxide (TMAO). TMAO is associated with inflammatory diseases, such as atherosclerosis, whose immunologic processes mirror that of rheumatoid arthritis (RA). Therefore, we investigated the possibility of ameliorating CIA by inhibiting TMA lyase activity using 3,3-dimethyl-1-butanol (DMB) or fluoromethylcholine (FMC). During CIA, mice were treated with 1% vol/vol DMB, 100mg/kg FMC, or vehicle. DMB-treated mice demonstrated significant (>50%) reduction in arthritis severity compared to FMC and vehicle-treated mice. However, in contrast to FMC, DMB treatment did not reduce cecal TMA nor circulating TMAO concentrations. Using gas chromatography, we confirmed the effect of DMB is independent of TMA lyase inhibition. Further, we identified a novel host-derived metabolite of DMB, 3,3-dimethyl-1-butyric acid (DMBut), which also significantly reduced disease and proinflammatory cytokines in CIA mice. Altogether, our study suggests that DMB the immunomodulatory activity of DMB and/or its metabolites are protective in CIA. Elucidating its target and mechanism of action may provide new directions for RA therapeutic development.

Conquering rheumatic diseases: are parasitic worms the answer?

Despite the introduction of novel treatment strategies, management of rheumatic disorders remains associated with substantial unmet clinical need. Of interest therefore, it has recently become apparent that there is a global inverse relationship between the incidence of such conditions and parasitic helminth infection, with striking examples involving rheumatoid arthritis (RA)/systemic lupus erythematosus (SLE) patients and filarial nematode worm infection in studies in India. Such findings reflect that helminths are master manipulators of the immune system, particularly in being able to modulate proinflammatory responses. The aim of this article is thus to consider findings to date on this exciting and intriguing research area to form an opinion on whether parasitic worms may be exploited to generate novel therapies for rheumatic diseases.

Gut commensal Parabacteroides distasonis alleviates inflammatory arthritis

OBJECTIVE

Gut microbiota dysbiosis is closely linked to the pathogenesis of rheumatoid arthritis (RA). We aimed to identify potential probiotic gut microbes that can ameliorate the development of RA.

DESIGN

Microbiota profiling in patients with RA and healthy individuals was investigated via 16S rDNA bacterial gene sequencing and shotgun metagenomics. Collagen-induced arthritic mice and TNF-α transgenic mice were used to evaluate the roles of the gut commensal Parabacteroides distasonis in RA. The effects of P. distasonis-derived microbial metabolites on the differentiation of CD4+ T cells and macrophage polarisation were also investigated.

RESULTS

The relative abundance of P. distasonis in new-onset patients with RA and patients with RA with history of the disease was downregulated and this decrease was negatively correlated with Disease Activity Score-28 (DAS28). Oral treatment of arthritic mice with live P. distasonis (LPD) considerably ameliorated RA pathogenesis. LPD-derived lithocholic acid (LCA), deoxycholic acid (DCA), isolithocholic acid (isoLCA) and 3-oxolithocholic acid (3-oxoLCA) had similar and synergistic effects on the treatment of RA. In addition to directly inhibiting the differentiation of Th17 cells, 3-oxoLCA and isoLCA were identified as TGR5 agonists that promoted the M2 polarisation of macrophages. A specific synthetic inhibitor of bile salt hydrolase attenuated the antiarthritic effects of LPD by reducing the production of these four bile acids. The natural product ginsenoside Rg2 exhibited its anti-RA effects by promoting the growth of P. distasonis.

CONCLUSIONS

P. distasonis and ginsenoside Rg2 might represent probiotic and prebiotic agents in the treatment of RA.

The interplay between Epstein-Barr virus DNA and gut microbiota in the development of arthritis in a mouse model

Epstein-Barr virus (EBV) DNA may influence the development of autoimmune diseases by increasing the production of proinflammatory cytokines. Such cytokines have been associated with inducing the dysbiosis of colonic microbiota, which, in turn, is a risk factor for autoimmune diseases such as rheumatoid arthritis (RA). Therefore, we investigated the role that EBV DNA may play in modulating the intestinal microbiota and consequent exacerbation of arthritis in a mouse model. Mice were treated with collagen (arthritis-inducing agent), EBV DNA and collagen, EBV DNA, or water. Fecal samples were collected from arthritic and control mice, and 16S rRNA sequencing was performed to determine the effect of EBV DNA on the composition of colonic microbiota. EBV DNA causes a change in the alpha diversity of the microbiota resulting in an increased Chao1 microbial richness and decreased Shannon diversity index in the RA mouse model. In addition, the abundance of particular genera/genus clusters was significantly altered among the various groups, with the EBV DNA-exacerbated arthritic group having the highest number of altered genera/genus cluster abundances. This group also had the highest number of cells co-expressing IL-17A, FOXP3, and IFNγ in the colons. Antimicrobial-cleared mice transplanted with fecal samples from EBV DNA-exacerbated arthritic mice showed a higher incidence and enhanced severity of RA compared to those transplanted with fecal samples from water or collagen-treated mice. IMPORTANCE Epstein-Barr virus (EBV) DNA alters the composition and diversity of the gut microbiota in a rheumatoid arthritis (RA) mouse model. These induced changes are associated with enhanced severity of symptoms. This better understanding of the various factors involved in the development of RA will possibly help in creating individualized treatments for RA patients including target mediators triggered by viral DNA. Given that a large swathe of the population harbors EBV, a significant proportion of subjects with arthritis may benefit from possible approaches that target EBV or mediators triggered by this virus.

Causal relationship between gut microbiota and type 2 diabetes: a two-sample Mendelian randomization study

Background

Studies showed that development of gut microbial dysbiosis has a close association with type 2 diabetes (T2D). It is not yet clear if there is a causal relationship between gut microbiota and T2D.

Methods

The data collected from the published genome-wide association studies (GWASs) on gut microbiota and T2D were analyzed. Two-sample Mendelian randomization (MR) analyses were performed to identify causal relationship between bacterial taxa and T2D. Significant bacterial taxa were further analyzed. To confirm the findings' robustness, we performed sensitivity, heterogeneity, and pleiotropy analyses. A reverse MR analysis was also performed to check for potential reverse causation.

Results

By combining the findings of all the MR steps, we identified six causal bacterial taxa, namely, Lachnoclostridium, Oscillospira, Roseburia, Ruminococcaceae UCG003, Ruminococcaceae UCG010 and Streptococcus. The risk of T2D might be positively associated with a high relative abundance of Lachnoclostridium, Roseburia and Streptococcus but negatively associated with Oscillospira, Ruminococcaceae UCG003 and Ruminococcaceae UCG010. The results of MR analyses revealed that there were causal relationships between the six different genera and T2D. And the reverse MR analysis did not reveal any evidence of a reverse causality.

Conclusion

This study implied that Lachnoclostridium, Roseburia and Streptococcus might have anti-protective effect on T2D, whereas Oscillospira, Ruminococcaceae UCG003 and Ruminococcaceae UCG010 genera might have protective effect on T2D. Our study revealed that there was a causal relationship between specific gut microbiota genera and T2D.

Limosilactobacillus reuteri in immunomodulation: molecular mechanisms and potential applications

Frequent use of hormones and drugs may be associated with side-effects. Recent studies have shown that probiotics have effects on the prevention and treatment of immune-related diseases. Limosilactobacillus reuteri (L. reuteri) had regulatory effects on intestinal microbiota, host epithelial cells, immune cells, cytokines, antibodies (Ab), toll-like receptors (TLRs), tryptophan (Try) metabolism, antioxidant enzymes, and expression of related genes, and exhibits antibacterial and anti-inflammatory effects, leading to alleviation of disease symptoms. Although the specific composition of the cell-free supernatant (CFS) of L. reuteri has not been clarified, its efficacy in animal models has drawn increased attention to its potential use. This review summarizes the effects of L. reuteri on intestinal flora and immune regulation, and discusses the feasibility of its application in atopic dermatitis (AD), asthma, necrotizing enterocolitis (NEC), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS), and provides insights for the prevention and treatment of immune-related diseases.

Triggers and regulation: the gut microbiome in rheumatoid arthritis

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.

The Integral Role of Diets Including Natural Products to Manage Rheumatoid Arthritis: A Narrative Review

Genetic and environmental factors including lifestyle are thought to play a key role in the pathophysiology of rheumatoid arthritis (RA). There is evidence that diet can enhance the inflammatory response in genetically predisposed individuals. On the other hand, certain types of diets can alleviate RA symptoms due to their anti-inflammatory and antioxidant activities. Also, natural compounds with potential effectiveness in RA management belong to different chemical classes such as flavonoids, polyphenols, carotenoids, and alkaloids with their antioxidant characteristics as well as probiotics. The nutritional approaches to prevent or extenuate the disease progress were examined in this narrative review which was conducted using the PubMed, ScienceDirect and Google Scholar databases and conforms to the Scale for the Assessment of Narrative Review Articles (SANRA) guidelines. Mediterranean and vegan diets equally have been shown to exhibit positive effects on RA as the consumption of dietary fiber, antioxidants and anti-inflammatory compounds from fruits, vegetables, grains, nuts, and seeds are high. Whereas Mediterranean diet additionally includes beneficial nutrients of animal origin such as omega-3 polyunsaturated fatty acids from fish and seafood, patients on vegan diet need to be monitored closely for intake of all critical nutrients. Certain calorie restrictions and intermittent fasting diets have been shown to benefit RA patients although there is an obvious need for further studies to establish solid evidence-based recommendations and guidelines. The research data available strongly suggest that dietary approaches with anti-inflammatory properties may help delay the onset of RA and/or improve symptoms and thus nutrition should be routinely addressed to facilitate management of the disease.

Analysis of PD-L1 Expression in Breast Cancer: A Systematic Review and Meta-Analysis in Asian Population

OBJECTIVE

This study aimed to investigate the level of PD-L1 protein expression in patients with BCs who were of Asian descent.

METHODS

Three databases were conducted on this article up to August 10th, 2022. The reference lists of the publications were examined for further studies, and in cases of duplicates, a study with a larger sample size was added. In survival analysis, the hazard ratio (HR) was applied to the circumstances characterized by the frequency of occurrences, and for the clinicopathological characteristic, the best-adjusted odds ratio (OR) with a 95% confidence interval (CI) was employed. The Newcastle-Ottawa Scale (NOS) was utilized to evaluate selection criteria, comparison, and exposure to establish the quality of the technique in the under-consideration studies. The Z test determined the association analysis of OS, DFS, and clinicopathological characteristics with PD-L1 expression.

RESULT

All eight trials for OS and six for DFS were considered, with 4.111 and 3.071 participants, respectively. Overexpression of PD-L1 was linked to a reduced OS compared to individuals with undetectable expression (HR= 1.58, 95% CI 1.04-2.40; P=0.03). We analyzed clinicopathological features, and it elevated in individuals with histological grade III (OR=2.39, 95% CI 1.26-4.54; P=0.008) and positive node (OR=0.68, 95% CI 0.48-0.97; P<0.05).

CONCLUSION

Overexpression of PD-L1 was associated with a shorter OS in BCs patients. High PDL1 was higher in persons with nodal positivity and histological grade III.

Toddalia asiatica extract attenuates adjuvant-induced arthritis by modulating colon Th17/Treg balance and colony homeostasis

ETHNOPHARMACOLOGICAL RELEVANCE

Given the adverse effects of the current principal treatments, there is still a great need for effective cures for rheumatoid arthritis (RA), an immune-mediated disease. Toddalia asiatica (L.) Lam is a traditional medicinal herb that can be used for RA treatment because of its anti-inflammatory and analgesic properties.

AIM OF THE STUDY

To investigate the possible effects of Toddalia asiatica extract (TAE) on intestinal immunity and the intestinal bacterial flora in a rat model of RA.

MATERIALS AND METHODS

The anti-arthritis effect of TAE was evaluated in arthritis rats induced by complete Freund's adjuvant-induced arthritis (AIA). Arthritis index (AI) scores, systemic inflammation scores, histopathologic changes in the colon and ankle were detected by hematoxylin and eosin staining. Western blot analysis was performed to assess the protein expression of IL-17A, RORC, IL-1β, IL-6, FOXP3, IL-10 in the colon. RT-PCR was performed to assess the expression of the colon's mRNA. Finally, changes to the gut microbiome by sequencing 16S rDNA. Microbial function prediction was performed using PICRUSt with the KEGG databases and correlation analysis was carried out by computing Spearman's rank correlations.

RESULTS

demonstrated that TAE administration at a dose of 3 g/kg dramatically decreased AI scores, systemic inflammation scores, and histopathologic lesions of the ankle and colon in AIA rats. TAE was found to significantly reduce the expression levels of Th17-related proteins and mRNAs (IL-17A, RORC, IL-1β and IL-6) in the colon, while increasing the expression levels of Treg-related proteins and mRNA (IL-10 and FOXP3), which helped restore the balance of Th17/Treg immune cells in the colon. Meanwhile, TAE was also found to be capable of remodeling the gut microbiota in AIA rats. Depleting RA-associated genera and thereby increasing α-diversity enriched the gut microbiota's diversity and shifted the community composition dramatically, leading to the increase of Firmicutes_unclassified, Ruminococcaceae_unclassified, Muribaculum, Subdoligranulum, Lachnospira, Marvinbryantia, and the reduction of RA-related bacteria Ligilactobacillus, Streptococcus and Eubacterium-eligens-group. Furthermore, PICRUSt analysis revealed that metabolic pathways were associated with TAE treatment, with metabolic pathways dominating. Among them, metabolic pathways were predominant. Correlation studies showed that a total of 9 microorganisms, including Ligilactobacillus, Eubacterium-eligens-group and Subdoligranulum, were significantly associated with Th17/Treg expression.

CONCLUSIONS

This study demonstrates that TAE is a low-toxicity poly alkaline drug that can rapidly and effectively improve joint symptoms in RA rats and increases beneficial intestinal bacteria and decreases harmful ones, which is associated with modulating Th17/Treg interactions in intestinal T cells and reversing microbial disorders.

Fusobacterium nucleatum aggravates rheumatoid arthritis through FadA-containing outer membrane vesicles

Rheumatoid arthritis (RA) is an autoimmune disorder that has been associated with the gut microbiota. However, whether and how the gut microbiota plays a pathogenic role in RA remains unexplored. Here, we observed that Fusobacterium nucleatum is enriched in RA patients and positively associated with RA severity. F. nucleatum similarly aggravates arthritis in a mouse model of collagen-induced arthritis (CIA). F. nucleatum outer membrane vesicles (OMVs) containing the virulence determinant FadA translocate into the joints, triggering local inflammatory responses. Specifically, FadA acts on synovial macrophages, resulting in the activation of the Rab5a GTPase involved in vesicle trafficking and inflammatory pathways and YB-1, a key regulator of inflammatory mediators. OMVs containing FadA and heightened Rab5a-YB-1 expression were observed in RA patients compared with controls. These findings suggest a causal role of F. nucleatum in aggravating RA and provide promising therapeutic targets for clinically ameliorating RA.

The role of the microbiome in rheumatoid arthritis: a review

The close bidirectional relationship between the microbiome and the immune system is well supported, and a role of gut dysbiosis has been implied in many systemic autoimmune diseases. This review aims to provide a critical summary and appraisal of 6 murine studies and 16 clinical studies. The findings of the literature review suggest that gut dysbiosis precedes arthritis and that local intestinal inflammation leads to systemic inflammation in genetically predisposed individuals. However, the exact mechanism by which microorganisms provoke immune responses at distal sites remains to be elucidated. Although a characteristic RA microbiome was not identified, there were some common findings among studies: overabundance of Prevotella copri in early RA patients, and proliferation of the genus Collinsela and some Lactobacillus species. Three mechanisms by which microbiota might contribute to RA pathogenesis were proposed: inflammatory responses (P. copri and Lactobacillus), molecular mimicry (P. copri) and loss of intestinal barrier integrity (Collinsella). Larger longitudinal studies are required in order to shed light on the mechanisms involved and unravel the therapeutic potential of the microbiome, and clinical trials are needed to evaluate the safety and efficacy of the implied therapeutic interventions.

Gut dysbiosis in autoimmune diseases: Association with mortality

To better understand the impact of gut dysbiosis on four autoimmune diseases [Sjögren’s syndrome (SS), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS)], this review investigated the altered gut bacteria in each disease and the shared ones among the four diseases. The enriched gut bacteria shared by three of the four autoimmune diseases were Streptococcus, Prevotella, and Eggerthella, which are associated with autoantibody production or activation of Th17 cells in immune-related diseases. On the other hand, Faecalibacterium comprises depleted gut bacteria shared by patients with SLE, MS, and SS, which is associated with various anti-inflammatory activities. The indexes of gut dysbiosis, defined as the number of altered gut bacterial taxa divided by the number of studies in SLE, MS, RA, and SS, were 1.7, 1.8, 0.7, and 1.3, respectively. Interestingly, these values presented a positive correlation trend with the standardized mortality rates —2.66, 2.89, 1.54, and 1.41, respectively. In addition, shared altered gut bacteria among the autoimmune diseases may correlate with the prevalence of polyautoimmunity in patients with SLE, SS, RA, and MS, that is, 41 percent, 32.6 percent, 14 percent, and 1–16.6 percent, respectively. Overall, this review suggests that gut dysbiosis in autoimmune diseases may be closely related to the failure of the gut immune system to maintain homeostasis.

Levofloxacin induces differential effects in the transcriptome between the gut, peripheral and axial joints in the Spondyloarthritis DBA/1 mice: Improvement of intestinal dysbiosis and the overall inflammatory process

To analyze the effect of levofloxacin-induced intestinal microbiota modifications on intestinal, joint, and systemic inflammation in the DBA/1 mice with spontaneous arthritis. The study included two groups of mice, one of which received levofloxacin. The composition and structure of the microbiota were determined in the mice's stool using 16S rRNA sequencing; the differential taxa and metabolic pathway between mice treated with levofloxacin and control mice were also defied. The effect of levofloxacin was evaluated in the intestines, hind paws, and spines of mice through DNA microarray transcriptome and histopathological analyses; systemic inflammation was measured by flow cytometry. Levofloxacin decreased the pro-inflammatory bacteria, including Prevotellaceae, Odoribacter, and Blautia, and increased the anti-inflammatory Muribaculaceae in mice's stool. Histological analysis confirmed the intestinal inflammation in control mice, while in levofloxacin-treated mice, inflammation was reduced; in the hind paws and spines, levofloxacin also decreased the inflammation. Microarray showed the downregulation of genes and signaling pathways relevant in spondyloarthritis, including several cytokines and chemokines. Levofloxacin-treated mice showed differential transcriptomic profiles between peripheral and axial joints and intestines. Levofloxacin decreased the expression of TNF-α, IL-23a, and JAK3 in the three tissues, but IL-17 behaved differently in the intestine and the joints. Serum TNF-α was also reduced in levofloxacin-treated mice. Our results suggest that the microbiota modification aimed at reducing pro-inflammatory and increasing anti-inflammatory bacteria could potentially be a coadjuvant in treating inflammatory arthropathies.

Gut-joint axis: Gut dysbiosis can contribute to the onset of rheumatoid arthritis via multiple pathways

Rheumatoid Arthritis (RA) is an autoimmune disease characterized by loss of immune tolerance and chronic inflammation. It is pathogenesis complex and includes interaction between genetic and environmental factors. Current evidence supports the hypothesis that gut dysbiosis may play the role of environmental triggers of arthritis in animals and humans. Progress in the understanding of the gut microbiome and RA. has been remarkable in the last decade. In vitro and in vivo experiments revealed that gut dysbiosis could shape the immune system and cause persistent immune inflammatory responses. Furthermore, gut dysbiosis could induce alterations in intestinal permeability, which have been found to predate arthritis onset. In contrast, metabolites derived from the intestinal microbiota have an immunomodulatory and anti-inflammatory effect. However, the precise underlying mechanisms by which gut dysbiosis induces the development of arthritis remain elusive. This review aimed to highlight the mechanisms by which gut dysbiosis could contribute to the pathogenesis of RA. The overall data showed that gut dysbiosis could contribute to RA pathogenesis by multiple pathways, including alterations in gut barrier function, molecular mimicry, gut dysbiosis influences the activation and the differentiation of innate and acquired immune cells, cross-talk between gut microbiota-derived metabolites and immune cells, and alterations in the microenvironment. The relative weight of each of these mechanisms in RA pathogenesis remains uncertain. Recent studies showed a substantial role for gut microbiota-derived metabolites pathway, especially butyrate, in the RA pathogenesis.

Complement: The Road Less Traveled

The complement field has recently experienced a strong resurgence of interest because of the unexpected discovery of new complement functions extending complement's role beyond immunity and pathogen clearance, a growing list of diseases in which complement plays a role, and the proliferation of complement therapeutics. Importantly, although the majority of complement components in the circulation are generated by the liver and activated extracellularly, complement activation unexpectedly also occurs intracellularly across a broad range of cells. Such cell-autonomous complement activation can engage intracellular complement receptors, which then drive noncanonical cell-specific effector functions. Thus, much remains to be discovered about complement biology. In this brief review, we focus on novel noncanonical activities of complement in its "classic areas of operation" (kidney and brain biology, infection, and autoimmunity), with an outlook on the next generation of complement-targeted therapeutics.

Relationship between gut microbiota and rheumatoid arthritis: A bibliometric analysis

Introduction

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease. Recently, growing evidence demonstrates that gut microbiota (GM) plays an important role in RA. But so far, no bibliometric studies pertaining to GM in RA have ever been published. This study attempts to depict the knowledge framework in this field from a holistic and systematic perspective based on the bibliometric analysis.

Methods

Literature related to the involvement of GM in RA was searched and picked from the Web of Science Core Collection (WOSCC) database. The annual output, cooperation, hotspots, research status and development trend of this field were analyzed by bibliometric software (VOSviewer and Bibliometricx).

Results

255 original research articles and 204 reviews were included in the analysis. The articles in this field that can be retrieved in WOSCC were first published in 2004 and increased year by year since then. 2013 is a growth explosion point. China and the United States are the countries with the most contributions, and Harvard University is the affiliation with the most output. Frontiers in Immunology (total citations = 603) is the journal with the most publications and the fastest growth rate. eLife is the journal with the most citations (total citations = 1248). Scher, Jose U. and Taneja, Veena are the most productive and cited authors. The research in this field is mainly distributed in the evidence, mechanism and practical application of GM participating in RA through the analysis of keywords and documents. There is sufficient evidence to prove the close relationship between GM and RA, which lays the foundation for this field. This extended two colorful and tender branches of mechanism research and application exploration, which have made some achievements but still have broad exploration space. Recently, the keywords "metabolites", "metabolomics", "acid", "b cells", "balance", "treg cells", "probiotic supplementation" appeared most frequently, which tells us that research on the mechanism of GM participating in RA and exploration of its application are the hotspots in recent years.

Discussion

Taken together, these results provide a data-based and objective introduction to the GM participating in RA, giving readers a valuable reference to help guide future research.

Consequences of collagen induced inflammatory arthritis on circadian regulation of the gut microbiome

The gut microbiota is important for host health and immune system function. Moreover autoimmune diseases, such as rheumatoid arthritis, are associated with significant gut microbiota dysbiosis, although the causes and consequences of this are not fully understood. It has become clear that the composition and metabolic outputs of the microbiome exhibit robust 24 h oscillations, a result of daily variation in timing of food intake as well as rhythmic circadian clock function in the gut. Here, we report that experimental inflammatory arthritis leads to a re-organization of circadian rhythmicity in both the gut and associated microbiome. Mice with collagen induced arthritis exhibited extensive changes in rhythmic gene expression in the colon, and reduced barrier integrity. Re-modeling of the host gut circadian transcriptome was accompanied by significant alteration of the microbiota, including widespread loss of rhythmicity in symbiont species of Lactobacillus, and alteration in circulating microbial derived factors, such as tryptophan metabolites, which are associated with maintenance of barrier function and immune cell populations within the gut. These findings highlight that altered circadian rhythmicity during inflammatory disease contributes to dysregulation of gut integrity and microbiome function.

Gut immune cell trafficking: inter-organ communication and immune-mediated inflammation

Immune cell trafficking is a complex and tightly regulated process that is indispensable for the body's fight against pathogens. However, it is also increasingly acknowledged that dysregulation of cell trafficking contributes to the pathogenesis of immune-mediated inflammatory diseases (IMIDs) in gastroenterology and hepatology, such as inflammatory bowel disease and primary sclerosing cholangitis. Moreover, altered cell trafficking has also been implicated as a crucial step in the immunopathogenesis of other IMIDs, such as rheumatoid arthritis and multiple sclerosis. Over the past few years, a central role of the gut in mediating these disorders has progressively emerged, and the partly microbiota-driven imprinting of particular cell trafficking phenotypes in the intestine seems to be crucially involved. Therefore, this Review highlights achievements in understanding immune cell trafficking to, within and from the intestine and delineates its consequences for immune-mediated pathology along the gut-liver, gut-joint and gut-brain axes. We also discuss implications for current and future therapeutic approaches that specifically interfere with homing, retention, egress and recirculation of immune cells.

The pathogenesis of rheumatoid arthritis

Significant recent progress in understanding rheumatoid arthritis (RA) pathogenesis has led to improved treatment and quality of life. The introduction of targeted-biologic and -synthetic disease modifying anti-rheumatic drugs (DMARDs) has also transformed clinical outcomes. Despite this, RA remains a life-long disease without a cure. Unmet needs include partial response and non-response to treatment in many patients, failure to achieve immune homeostasis or drug free remission, and inability to repair damaged tissues. RA is now recognized as the end of a multi-year prodromal phase in which systemic immune dysregulation, likely beginning in mucosal surfaces, is followed by a symptomatic clinical phase. Inflammation and immune reactivity are primarily localized to the synovium leading to pain and articular damage, but is also associated with a broader series of comorbidities. Here, we review recently described immunologic mechanisms that drive breach of tolerance, chronic synovitis, and remission.

A high-fiber diet synergizes with Prevotella copri and exacerbates rheumatoid arthritis

Both preclinical and established rheumatoid arthritis (RA) patients display alterations in the gut microbiome. Prevotella spp. are preferentially enriched in a subset of RA patients. Here, we isolated a Prevotella strain, P. copri RA, from the feces of RA patients and showed that colonization of P. copri RA exacerbated arthritis in a collagen-induced arthritis (CIA) model. With the presence of P. copri RA colonization, a high-fiber diet exacerbated arthritis via microbial alterations and intestinal inflammation. Colonization of P. copri together with a high-fiber diet enabled the digestion of complex fiber, which led to the overproduction of organic acids, including fumarate, succinate and short-chain fatty acids. Succinate promoted proinflammatory responses in macrophages, and supplementation with succinate exacerbated arthritis in the CIA model. Our findings highlight the importance of dysbiosis when evaluating the effects of dietary interventions on RA pathogenesis and provide new insight into dietary interventions or microbiome modifications to improve RA management.

Clonal IgA and IgG autoantibodies from individuals at risk for rheumatoid arthritis identify an arthritogenic strain of Subdoligranulum

The mucosal origins hypothesis of rheumatoid arthritis (RA) proposes a central role for mucosal immune responses in the initiation or perpetuation of the systemic autoimmunity that occurs with disease. However, the connection between the mucosa and systemic autoimmunity in RA remains unclear. Using dual immunoglobulin A (IgA) and IgG family plasmablast-derived monoclonal autoantibodies obtained from peripheral blood of individuals at risk for RA, we identified cross-reactivity between RA-relevant autoantigens and bacterial taxa in the closely related families Lachnospiraceae and Ruminococcaceae. After generating bacterial isolates within the Lachnospiraceae/Ruminococcaceae genus Subdoligranulum from the feces of an individual, we confirmed monoclonal antibody binding and CD4⁺ T cell activation in individuals with RA compared to control individuals. In addition, when Subdoligranulum isolate 7 but not isolate 1 colonized germ-free mice, it stimulated T_H17 cell expansion, serum RA-relevant IgG autoantibodies, and joint swelling reminiscent of early RA, with histopathology characterized by antibody deposition and complement activation. Systemic immune responses were likely due to mucosal invasion along with the generation of colon-isolated lymphoid follicles driving increased fecal and serum IgA by isolate 7, because B and CD4⁺ T cell depletion not only halted intestinal immune responses but also eliminated detectable clinical disease. In aggregate, these findings demonstrate a mechanism of RA pathogenesis through which a specific intestinal strain of bacteria can drive systemic autoantibody generation and joint-centered antibody deposition and immune activation.

Clonal IgA and IgG autoantibodies from individuals at risk for rheumatoid arthritis identify an arthritogenic strain of Subdoligranulum

The mucosal origins hypothesis of rheumatoid arthritis (RA) proposes a central role for mucosal immune responses in the initiation or perpetuation of the systemic autoimmunity that occurs with disease. However, the connection between the mucosa and systemic autoimmunity in RA remains unclear. Using dual immunoglobulin A (IgA) and IgG family plasmablast-derived monoclonal autoantibodies obtained from peripheral blood of individuals at risk for RA, we identified cross-reactivity between RA-relevant autoantigens and bacterial taxa in the closely related families Lachnospiraceae and Ruminococcaceae. After generating bacterial isolates within the Lachnospiraceae/Ruminococcaceae genus Subdoligranulum from the feces of an individual, we confirmed monoclonal antibody binding and CD4⁺ T cell activation in individuals with RA compared to control individuals. In addition, when Subdoligranulum isolate 7 but not isolate 1 colonized germ-free mice, it stimulated T_H17 cell expansion, serum RA-relevant IgG autoantibodies, and joint swelling reminiscent of early RA, with histopathology characterized by antibody deposition and complement activation. Systemic immune responses were likely due to mucosal invasion along with the generation of colon-isolated lymphoid follicles driving increased fecal and serum IgA by isolate 7, because B and CD4⁺ T cell depletion not only halted intestinal immune responses but also eliminated detectable clinical disease. In aggregate, these findings demonstrate a mechanism of RA pathogenesis through which a specific intestinal strain of bacteria can drive systemic autoantibody generation and joint-centered antibody deposition and immune activation.

Intestinal phages interact with bacteria and are involved in human diseases

EMBL-EBI The European Bioinformatics Institute; E. coli Escherichia coli; E. faecalis Enterobacter faecalis; B. fragilis Bacteroides fragilis; B. vulgatus Bacteroides vulgatus; SaPIs Staphylococcus aureus pathogenicity islands; ARGs Antibiotic resistance genes; STEC Shiga toxigenic E. coli; Stx Shiga toxin; BLAST Basic Local Alignment Search Tool; TSST-1 Toxic shock toxin 1; RBPs Receptor-binding proteins; LPS lipopolysaccharide; OMVs Outer membrane vesicles; PT Phosphorothioate; BREX Bacteriophage exclusion; OCR Overcome classical restriction; Pgl Phage growth limitation; DISARM Defense island system associated with restrictionmodification; R-M system Restriction-modification system; BREX system Bacteriophage exclusion system; CRISPR Clustered regularly interspaced short palindromic repeats; Cas CRISPR-associated; PAMs Prospacer adjacent motifs; crRNA CRISPR RNA; SIE; OMPs; Superinfection exclusion; Outer membrane proteins; Abi Abortive infection; TA Toxin-antitoxin; TLR Toll-like receptor; APCs Antigen-presenting cells; DSS Dextran sulfate sodium; IELs Intraepithelial lymphocytes; FMT Fecal microbiota transfer; IFN-γ Interferon-gamma; IBD Inflammatory bowel disease; AgNPs Silver nanoparticles; MDSC Myeloid-derived suppressor cell; CRC Colorectal cancer; VLPs Virus-like particles; TMP Tape measure protein; PSMB4 Proteasome subunit beta type-4; ALD Alcohol-related liver disease; GVHD Graft-versus-host disease; ROS Reactive oxygen species; RA Rheumatoid arthritis; CCP Cyclic citrullinated protein; AMGs Accessory metabolic genes; T1DM Type 1 diabetes mellitus; T2DM Type 2 diabetes mellitus; SCFAs Short-chain fatty acids; GLP-1 Glucagon-like peptide-1; A. baumannii Acinetobacter baumannii; CpG Deoxycytidylinate-phosphodeoxyguanosine; PEG Polyethylene glycol; MetS Metabolic syndrome; OprM Outer membrane porin M.

Microbiota-assisted therapy for systemic inflammatory arthritis: advances and mechanistic insights

Research on the influence of gut microbiota on systemic inflammatory arthritis has exploded in the past decade. Gut microbiota changes may be a crucial regulatory component in systemic inflammatory arthritis. As a result of advancements in the field, microbiota-assisted therapy has evolved, but this discipline is still in its infancy. Consequently, we review the limitations of current systemic inflammatory arthritis treatment, analyze the connection between the microbiota and arthritis, and summarize the research progress of microbiota regulating systemic inflammatory arthritis and the further development aspects of microbiota-assisted therapy. Finally, the partial mechanisms of microbiota-assisted therapy of systemic inflammatory arthritis are being discussed. In general, this review summarizes the current progress, challenges, and prospects of microbiota-assisted therapy for systemic inflammatory arthritis and points out the direction for the development of microbiota-assisted therapy in the future.

Evaluating the Similarity of Different Collagen-Induced Arthritis Models to the Pre-Clinical Phase of RA in Female Rats

Since the development of RA is a multistep process, it is critical to take action to prevent RA in the pre-clinical phase. Animal models are currently one of the important methods to study RA, but there are very few animal models for studying the pre-clinical phase of RA (Pre-RA). This study aimed to evaluate the similarity of different collagen-induced arthritis models to Pre-RA in rats. Three types of collagen-induced arthritis (CIA) were as follows: (i) standard collagen-induced group (Std-CIA), injected with 200 μg type II collagen at day 0 and 100 μg type II collagen at day 7; (ii) single collagen-induced group (Mono-CIA), injected with 200 μg type II collagen at day 0; (iii) half-dose collagen-induced group (Half-CIA), injected with 100 μg type II collagen at day 0 and 50 μg type II collagen at day 7. Arthritis score, hind paw swelling, serum antibodies, and inflammatory cytokines were measured every 7 days. Gut microbiota analyses were performed on days 0, 11, 21, 28, and 35. Pain threshold measurement, digital radiography, and joint pathology were also assessed. Both Std-CIA and Mono-CIA could successfully cause RA symptoms, including joint swelling and bone erosion, Half-CIA induced only mild swelling in rats. Serum autoantibodies (anti-CCP and anti-CoII) showed no difference among the three types of CIA models, and so did the pain threshold at day 42. In addition, the pathological changes of joint tissues in the Mono-CIA group were the slightest among the collagen-immunized groups. Gut microbiota analysis demonstrated that Half-CIA could impose similar effects on upregulating genus Prevotella as Std-CIA, but Mono-CIA was weaker than them in rats. According to the characteristics of pre-RA, the Half-CIA model is the best suitable animal model for pre-RA among three types of CIA models in rats and can be a valuable model for pre-RA research.

Antibiotic-induced gut dysbiosis and autoimmune disease: A systematic review of preclinical studies

Antibiotic-induced gut dysbiosis is believed to be associated with the onset and development of autoimmune diseases. To evaluate microbiota's variations triggered by antibiotic therapy and its outcomes on autoimmune diseases, preclinical studies regarding these subjects were included in this review. The studies were selected on PubMed, Scopus and Web of Science from 2011 to 2021 by three researchers that extracted study data and risk of bias, which were verified by a further 3 independent researchers. The team assessed the strength of evidence across studies. Of the eligible studies, 17 showed an improvement of the studied disease after antibiotic therapy and 10 had a negative effect on the course of the condition. The ameliorating factors of the studied diseases were mostly seen when using an antibiotic cocktail. Male animals had a good outcome after therapy and, for all genders, the increase in IL-10 and Treg cells was often shown to ameliorate disease after the antibiotic intervention. Firmicutes, Proteobacteria and Bacteroidetes appeared altered after the antibiotic intervention, leading to amelioration or worsening of the condition depending on the autoimmune disease. We identified that the number of autoimmune conditions approached leads to specific conclusions regarding the interventions, making it difficult to achieve an overall conclusion. Overall, even though pre-clinical studies must be translated to the human model, the studied aspects of gender, age, lineage and disease model substantially impact the outcomes that make for many intricacies that were not-established in the study of antibiotic-induced gut dysbiosis and autoimmunity.