Dietary Derived Propionate Regulates Pathogenic Fibroblast Function and Ameliorates Experimental Arthritis and Inflammatory Tissue Priming

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.

Inflammatory tissue priming: novel insights and therapeutic opportunities for inflammatory rheumatic diseases

Due to optimised treatment strategies and the availability of new therapies during the last decades, formerly devastating chronic inflammatory diseases such as rheumatoid arthritis or systemic sclerosis (SSc) have become less menacing. However, in many patients, even state-of-the-art treatment cannot induce remission. Moreover, the risk for flares strongly increases once anti-inflammatory therapy is tapered or withdrawn, suggesting that underlying pathological processes remain active even in the absence of overt inflammation. It has become evident that tissues have the ability to remember past encounters with pathogens, wounds and other irritants, and to react more strongly and/or persistently to the next occurrence. This priming of the tissue bears a paramount role in defence from microbes, but on the other hand drives inflammatory pathologies (the Dr Jekyll and Mr Hyde aspect of tissue adaptation). Emerging evidence suggests that long-lived tissue-resident cells, such as fibroblasts, macrophages, long-lived plasma cells and tissue-resident memory T cells, determine inflammatory tissue priming in an interplay with infiltrating immune cells of lymphoid and myeloid origin, and with systemically acting factors such as cytokines, extracellular vesicles and antibodies. Here, we review the current state of science on inflammatory tissue priming, focusing on tissue-resident and tissue-occupying cells in arthritis and SSc, and reflect on the most promising treatment options targeting the maladapted tissue response during these diseases.

The differential crosstalk of the skin-gut microbiome axis as a new emerging actor in systemic sclerosis

OBJECTIVES

We characterized the microbiota in SSc, focusing on the skin-oral-gut axis and the serum and faecal free fatty acid (FFA) profile.

METHODS

Twenty-five SSc patients with ACA or anti-Scl70 autoantibodies were enrolled. The microbiota of faecal, saliva and superficial epidermal samples was assessed through next-generation sequencing analysis. GC-MS was used to quantify faecal and serum FFAs. Gastrointestinal symptoms were investigated with the University of California Los Angeles Scleroderma Clinical Trial Consortium Gastrointestinal Tract Instrument (UCLA GIT-2.0) questionnaire.

RESULTS

The ACA+ and anti-Scl70+ groups displayed different cutaneous and faecal microbiota profiles. The classes of cutaneous Sphingobacteriia and Alphaproteobacteria, the faecal phylum Lentisphaerae, the levels of the classes Lentisphaeria and Opitutae, and the genus NA-Acidaminococcaceae were significantly higher in faecal samples from the ACA+ patients than in samples from the anti-Scl70+ patients. The cutaneous Sphingobacteria and the faecal Lentisphaerae were significantly correlated (rho = 0.42; P = 0.03). A significant increase in faecal propionic acid was observed in ACA+ patients. Moreover, all levels of faecal medium-chain FFAs and hexanoic acids were significantly higher in the ACA+ group than in the anti-Scl70+ group (P < 0.05 and P < 0.001, respectively). In the ACA+ group, the analysis of the serum FFA levels showed an increasing trend in valeric acid.

CONCLUSION

Different microbiota signatures and FFA profiles were found for the two groups of patients. Despite being in different body districts, the cutaneous Sphingobacteria and faecal Lentisphaerae appear interdependent.

Small Intestinal Permeability and Metabolomic Profiles in Feces and Plasma Associate With Clinical Response in Patients With Active Psoriatic Arthritis Participating in a Fecal Microbiota Transplantation Trial: Exploratory Findings From the FLORA Trial

OBJECTIVE

We investigated intestinal permeability and fecal, plasma, and urine metabolomic profiles in methotrexate-treated active psoriatic arthritis (PsA) and how this related to clinical response following one sham or fecal microbiota transplantation (FMT).

METHODS

This exploratory study is based on the FLORA trial cohort, in which 31 patients with moderate-to-high peripheral PsA disease activity, despite at least 3 months of methotrexate-treatment, were included in a 26-week, double-blind, 1:1 randomized, sham-controlled trial. Participants were randomly allocated to receive either one healthy donor FMT (n = 15) or sham (n = 16) via gastroscopy. The primary trial end point was the proportion of treatment failures through 26 weeks. We performed a lactulose-to-mannitol ratio (LMR) test at baseline (n = 31) and at week 26 (n = 26) to assess small intestinal permeability. Metabolomic profiles in fecal, plasma, and urine samples collected at baseline, weeks 4, 12, and 26 were measured using 1 H Nuclear Magnetic Resonance.

RESULTS

Trial failures (n = 7) had significantly higher LMR compared with responders (n = 19) at week 26 (0.027 [0.017-0.33]) vs. 0.012 [0-0.064], P = 0.013), indicating increased intestinal permeability. Multivariate analysis revealed a significant model for responders (n = 19) versus failures (n = 12) at all time points based on their fecal (P < 0.0001) and plasma (P = 0.005) metabolomic profiles, whereas urine metabolomic profiles did not differ between groups (P = 1). Fecal N-acetyl glycoprotein GlycA correlated with Health Assessment Questionnaire Disability Index (coefficient = 0.50; P = 0.03) and fecal propionate correlated with American College of Rheumatology 20 response at week 26 (coefficient = 27, P = 0.02).

CONCLUSION

Intestinal permeability and fecal and plasma metabolomic profiles of patients with PsA were associated with the primary clinical trial end point, failure versus responder.

MCT-Induced Ketosis and Fiber in Rheumatoid Arthritis (MIKARA)-Study Protocol and Primary Endpoint Results of the Double-Blind Randomized Controlled Intervention Study Indicating Effects on Disease Activity in RA Patients

Fatty acids, such as medium-chain fatty acids (MCFAs) and short-chain fatty acids (SCFAs), both important components of a normal diet, have been reported to play a role in bone-related diseases such as rheumatoid arthritis (RA). However, the role of medium-chain triglycerides (MCTs) has not been investigated in RA to date. The aim of this study was to investigate the effect of supplementation of regular diet with MCT with and without fiber on disease activity as measured with the SDAI (Simplified Disease Activity Index) in RA patients. A total of 61 RA patients on stable drug treatment were randomly assigned to a twice-daily control regimen or to a twice-daily regimen of a formulation containing medium-chain triglycerides (MCTs) 30 g/day for 8 weeks followed by a second twice-daily regimen of combining MCT (30 g/day) plus fiber (30 g/day) for an additional 8 weeks. The control group received a formulation containing long-chain triglycerides (LCTs) instead of MCTs. The preliminary results showed a significant reduction in SDAI from baseline to week 16 in the test group and a significant increase in β-hydroxybutyrate (BHB) levels, while no improvement in SDAI was observed in the control group.

Role of microbiota short-chain fatty acid chains in the pathogenesis of autoimmune diseases

There is emerging evidence that microbiota and its metabolites play an important role in helath and diseases. In this regard, gut microbiota has been found as a crucial component that influences immune responses as well as immune-related disorders such as autoimmune diseases. Gut bacterial dysbiosis has been shown to cause disease and altered microbiota metabolite synthesis, leading to immunological and metabolic dysregulation. Of note, microbiota in the gut produce short-chain fatty acids (SCFAs) such as acetate, butyrate, and propionate, and remodeling in these microbiota metabolites has been linked to the pathophysiology of a number of autoimmune disorders such as type 1 diabetes, multiple sclerosis, inflammatory bowel disease, rheumatoid arthritis, celiac disease, and systemic lupus erythematosus. In this review, we will address the most recent findings from the most noteworthy studies investigating the impact of microbiota SCFAs on various autoimmune diseases.

Colonoscopy aspiration lavages for mucosal metataxonomic profiling of spondylarthritis-associated gastrointestinal tract alterations

The study of the GI-tract microbiota of spondylarthritis (SpA) patients has focused on the analysis of feces samples, that picture mostly the luminal microbiota. The aim of this study was to determine the contribution of mucosal and luminal microbiome to the gut dysbiosis in SpA, using colonoscopy aspiration lavages (CAL), a recent alternative for regional studies of the GI-tract. We analyzed 59 CAL (from sigmoid colon and distal ileum), and 41 feces samples, from 32 SpA patients and 7 healthy individuals, using 16S rRNA gene-targeted metataxonomic profiling. It was found high prevalence of GI-tract manifestations among SpA patients (65.3%). Metataxonomic profiling, confirmed CAL samples from the lower GI tract (colon or ileum) presented a distinctive and undifferentiated bacteriome and separate from that found in feces' samples or in the beginning of the GI tract (oral cavity (OC)). Lower GI-tract samples and feces of SpA patients exhibited similar behavior to the microbiota of IBD group with reduced microbial richness and diversity, comparing to the healthy controls. Interestingly, it was found increase in proinflammatory taxa in SpA patients, such as Enterobacteriaceae family (mostly in the ileum), Succinivibrio spp. and Prevotella stercorea. Conversely, SpA patients presented significant decrease in the SCFA producers Coprococcus catus and Eubacterium biforme. Our data support the value of CAL samples for the regional study of GI-tract and contribute with information of potential "disruptor taxa" involved in the GI-tract associated disorders observed in SpA patients.

Protective role of colitis in inflammatory arthritis via propionate-producing Bacteroides in the gut

Objectives

To investigate whether and how inflammatory disease in the intestine influences the development of arthritis, considering that organ-to-organ communication is associated with many physiological and pathological events.

Methods

First, mice were given drinking water containing dextran sodium sulfate (DSS) and then subjected to inflammatory arthritis. We compared the phenotypic symptoms between the cohoused and separately-housed mice. Next, donor mice were divided into DSS-treated and untreated groups and then cohoused with recipient mice. Arthritis was then induced in the recipients. The fecal microbiome was analyzed by 16S rRNA amplicon sequencing. We obtained type strains of the candidate bacteria and generated propionate-deficient mutant bacteria. Short-chain fatty acids were measured in the bacterial culture supernatant, serum, feces, and cecum contents using gas chromatography-mass spectrometry. Mice fed with candidate and mutant bacteria were subjected to inflammatory arthritis.

Results

Contrary to expectations, the mice treated with DSS exhibited fewer symptoms of inflammatory arthritis. Intriguingly, the gut microbiota contributes, at least in part, to the improvement of colitis-mediated arthritis. Among the altered microorganisms, Bacteroides vulgatus and its higher taxonomic ranks were enriched in the DSS-treated mice. B. vulgatus, B. caccae, and B. thetaiotaomicron exerted anti-arthritic effects. Propionate production deficiency further prevented the protective effect of B. thetaiotaomicron on arthritis.

Conclusions

We suggest a novel relationship between the gut and joints and an important role of the gut microbiota as communicators. Moreover, the propionate-producing Bacteroides species examined in this study may be a potential candidate for developing effective treatments for inflammatory arthritis.

Proof-of-Principle Study Suggesting Potential Anti-Inflammatory Activity of Butyrate and Propionate in Periodontal Cells

Short-chain fatty acids (SCFAs) are potent immune modulators present in the gingival crevicular fluid. It is therefore likely that SCFAs exert a role in periodontal health and disease. To better understand how SCFAs can module inflammation, we screened acetic acid, propionic acid, and butyric acid for their potential ability to lower the inflammatory response of macrophages, gingival fibroblasts, and oral epithelial cells in vitro. To this end, RAW 264.7 and primary macrophages were exposed to LPSs from Porphyromonas gingivalis (P. gingivalis) with and without the SCFAs. Moreover, gingival fibroblasts and HSC2 oral epithelial cells were exposed to IL1β and TNFα with and without the SCFAs. We report here that butyrate was effective in reducing the lipopolysaccharide (LPS)-induced expression of IL6 and chemokine (C-X-C motif) ligand 2 (CXCL2) in the RAW 264.7 and primary macrophages. Butyrate also reduced the IL1β and TNFα-induced expression of IL8, chemokine (C-X-C motif) ligand 1 (CXCL1), and CXCL2 in gingival fibroblasts. Likewise, butyrate lowered the induced expression of CXCL1 and CXCL2, but not IL8, in HSC2 cells. Butyrate further caused a reduction of p65 nuclear translocation in RAW 264.7 macrophages, gingival fibroblasts, and HSC2 cells. Propionate and acetate partially lowered the inflammatory response in vitro but did not reach the level of significance. These findings suggest that not only macrophages, but also gingival fibroblasts and oral epithelial cells are susceptive to the anti-inflammatory activity of butyrate.

Health Benefits and Side Effects of Short-Chain Fatty Acids

The gut microbiota and their metabolites could play an important role in health and diseases of human beings. Short-chain fatty acids (SCFAs) are mainly produced by gut microbiome fermentation of dietary fiber and could also be produced by bacteria of the skin and vagina. Acetate, propionate, and butyrate are three major SCFAs, and their bioactivities have been widely studied. The SCFAs have many health benefits, such as anti-inflammatory, immunoregulatory, anti-obesity, anti-diabetes, anticancer, cardiovascular protective, hepatoprotective, and neuroprotective activities. This paper summarizes health benefits and side effects of SCFAs with a special attention paid to the mechanisms of action. This paper provides better support for people eating dietary fiber as well as ways for dietary fiber to be developed into functional food to prevent diseases.

“Osteomicrobiology”: The Nexus Between Bone and Bugs

A growing body of scientific evidence supports the notion that gut microbiota plays a key role in the regulation of various physiological and pathological processes related to human health. Recent findings have now established that gut microbiota also contributes to the regulation of bone homeostasis. Studies on animal models have unraveled various underlying mechanisms responsible for gut microbiota-mediated bone regulation. Normal gut microbiota is thus required for the maintenance of bone homeostasis. However, dysbiosis of gut microbiota communities is reported to be associated with several bone-related ailments such as osteoporosis, rheumatoid arthritis, osteoarthritis, and periodontitis. Dietary interventions in the form of probiotics, prebiotics, synbiotics, and postbiotics have been reported in restoring the dysbiotic gut microbiota composition and thus could provide various health benefits to the host including bone health. These dietary interventions prevent bone loss through several mechanisms and thus could act as potential therapies for the treatment of bone pathologies. In the present review, we summarize the current knowledge of how gut microbiota and its derived microbial compounds are associated with bone metabolism and their roles in ameliorating bone health. In addition to this, we also highlight the role of various dietary supplements like probiotics, prebiotics, synbiotics, and postbiotics as promising microbiota targeted interventions with the clinical application for leveraging treatment modalities in various inflammatory bone pathologies.

Stromal cell regulation of inflammatory responses

In the last fifteen years it has become apparent that tissue-resident mesenchymal cells such as fibroblasts, which are the structural elements of all organs, play a cardinal role in the pathology of immune-mediated inflammatory diseases. We now know that all fibroblasts originate from universal pan-organ cellular ancestors and that they are diversified into more specific subsets according to the functional needs of their home tissue-and its activation state. In arthritis, a plethora of activated joint-resident and migrating fibroblast types have been recently described that are central for pathogenesis and persistence of inflammatory joint-disease. Here we provide a current overview on the multiple inflammatory and immune-related functions of fibroblasts and how they could be curbed to induce long-lasting abatement of disease.