Dysbiosis of the gut microbiome is a risk factor for osteoarthritis in older female adults: a case control study

Integrative review of the gut microbiome’s role in pain management for orthopaedic conditions

The gut microbiome, a complex ecosystem of microorganisms, has a significant role in modulating pain, particularly within orthopaedic conditions. Its impact on immune and neurological functions is underscored by the gut-brain axis, which influences inflammation, pain perception, and systemic immune responses. This integrative review examines current research on how gut dysbiosis is associated with various pain pathways, notably nociceptive and neuroinflammatory mechanisms linked to central sensitization. We highlight advancements in meta-omics technologies, such as metagenomics and metaproteomics, which deepen our understanding of microbiome-host interactions and their implications in pain. Recent studies emphasize that gut-derived short-chain fatty acids and microbial metabolites play roles in modulating neuroinflammation and nociception, contributing to pain management. Probiotics, prebiotics, synbiotics, and faecal microbiome transplants are explored as potential therapeutic strategies to alleviate pain through gut microbiome modulation, offering an adjunct or alternative to opioids. However, variability in individual microbiomes poses challenges to standardizing these treatments, necessitating further rigorous clinical trials. A multidisciplinary approach combining microbiology, immunology, neurology, and orthopaedics is essential to develop innovative, personalized pain management strategies rooted in gut health, with potential to transform orthopaedic pain care.

Gut Microbiota: A Modulator and Therapeutic Target for Chronic Pain

Chronic pain is a prevalent condition, impacting nearly one-fifth of the global population. Despite the availability of various clinical treatments, each comes with inherent limitations, and few offer a complete cure, resulting in a significant social and economic burden. Therefore, it is important to determine the pathogenesis and causes of chronic pain. Numerous studies have shown a close link between the intestinal microflora and chronic pain. The gut microbiota can exert their effects on chronic pain through both central and peripheral mechanisms and is able to communicate with the brain through its own components or metabolites. They also can regulate chronic pain by affecting pro- and anti-inflammatory cells. This review is aimed at reviewing the connection between gut flora and different types of chronic pain, including visceral pain, neuropathic pain, inflammatory pain, musculoskeletal pain, migraine, and chronic cancer pain; exploring the central and peripheral mechanisms of the influence of gut flora on chronic pain; and attempting to provide novel treatment options for chronic pain, that is, the gut microbiota can be regulated by probiotics, fecal microbial transplantation, and natural products to treat chronic pain. By examining the intricate relationship between gut flora and chronic pain, the review sought to pave the way for new treatment strategies that target the gut microbiota, offering hope for more effective pain management.

Osteoarthritis treatment via the GLP-1-mediated gut-joint axis targets intestinal FXR signaling

Whether a gut-joint axis exists to regulate osteoarthritis is unknown. In two independent cohorts, we identified altered microbial bile acid metabolism with reduced glycoursodeoxycholic acid (GUDCA) in osteoarthritis. Suppressing farnesoid X receptor (FXR)-the receptor of GUDCA-alleviated osteoarthritis through intestine-secreted glucagon-like peptide 1 (GLP-1) in mice. GLP-1 receptor blockade attenuated these effects, whereas GLP-1 receptor activation mitigated osteoarthritis. Osteoarthritis patients exhibited a lower relative abundance of Clostridium bolteae, which promoted the formation of ursodeoxycholic acid (UDCA), a precursor of GUDCA. Treatment with C. bolteae and Food and Drug Administration-approved UDCA alleviated osteoarthritis through the gut FXR-joint GLP-1 axis in mice. UDCA use was associated with lower risk of osteoarthritis-related joint replacement in humans. These findings suggest that orchestrating the gut microbiota-GUDCA-intestinal FXR-GLP-1-joint pathway offers a potential strategy for osteoarthritis treatment.

The Interaction Between Microbiota and Stem Cells on Progression of Osteoarthritis and Engineered Stem Cell for Enhancing Osteoarthritis Treatment

Osteoarthritis (OA) is characterized by the degeneration of articular cartilage caused by several factors of which novel most trends include microbiota. Specific microbiota and the role in the development of OA is less clear. The microbiota is presumed to influence OA occurrence and progression mainly via immune modulation. In recent years, bone marrow mesenchymal stem cells (MSCs) have shown great potential for the treatment of OA, however, the therapeutic efficiency has been seriously affected by the harsh microenvironment in the joint cavity. At present, many strategies have been used to enhance the function of MSCs, among them, engineering are a promising method. Therefore, this review mainly focuses on the latest research on how the microbiota affects the development of OA, stem cell repair, and the use of engineered MSCs in the treatment of OA. In addition, engineered MSCs can enhance the therapeutic potential of exosomes as a novel strategy for treating OA. Our review provides a comprehensive perspective on the role of microbiota in OA and the influence of MSCs therapy and engineered MSCs on the treatment of OA.

Inflammaging contributes to osteoarthritis development and human microbiota variations and vice versa: A systematic review

OBJECTIVE

To report evidence on microbiota and its relationship with inflammaging, the innate immune system and osteoarthritis (OA) in human patients.

DESIGN

A systematic review was performed in accordance with PRISMA and following the PICO model. Web of Science, Scopus, Cochrane Library for clinical trials and PubMed were searched. The analysis was focused on human OA patients, and the outcome was mainly microbiota identification, improvement or deterioration of OA pain, stiffness or inflammation.

RESULTS

After screening, 24 studies fulfilled the inclusion criteria. There is not a standardised procedure yet, as microbiota analysis in OA is relatively new. The 16S rRNA gene is the most used in bacterial phylogeny and taxonomy studies as it is highly conserved. Selected articles hypothesise about the correlation between the altered composition of the gut microbiota and OA severity, which seems to affect the immune composition by disrupting gut permeability and releasing pro-inflammatory factors. Five preliminary clinical trials used pro-prebiotics to treat OA patients, and although their results are not conclusive and the methodology needs to be improved, it might indicate a favourable approach for further studies in the prevention of OA.

CONCLUSIONS

Several hypotheses have been made on the associations between microbiota changes and inflammation. They mainly advocate that those changes in the gastrointestinal tract affect gut permeability, which alters the immune system, leading to OA progression. Research advances, along with the continual growth and improvement of technology, mark this 'microbiota-inflammaging-OA' axis as a promising line of investigation.

Gut Microbiota and Osteoarthritis: From Pathogenesis to Novel Therapeutic Opportunities

Osteoarthritis (OA) is the most common chronic degenerative joint disease, characterized by cartilage damage, synovial inflammation, subchondral bone sclerosis, marginal bone loss, and osteophyte development. Clinical manifestations include inflammatory joint pain, swelling, osteophytes, and limitation of motion. The pathogenesis of osteoarthritis has not yet been fully uncovered. With ongoing research, however, it has been gradually determined that OA is not caused solely by mechanical injury or aging, but rather involves chronic low-grade inflammation, metabolic imbalances, dysfunctional adaptive immunity, and alterations in central pain processing centers. The main risk factors for OA include obesity, age, gender, genetics, and sports injuries. In recent years, extensive research on gut microbiota has revealed that gut dysbiosis is associated with some common risk factors for OA, and that it may intervene in its pathogenesis through both direct and indirect mechanisms. Therefore, gut flora imbalance as a pathogenic factor in OA has become a hotspot topic of research, with potential therapeutic connotations. In this paper, we review the role of the gut microbiota in the pathogenesis of OA, describe its relationship with common OA risk factors, and address candidate gut microbiota markers for OA diagnosis. In addition, with focus on OA therapies, we discuss the effects of direct and indirect interventions targeting the gut microbiota, as well as the impact of gut bacteria on the efficacy of OA drugs.

Potential role of gut-related factors in the pathology of cartilage in osteoarthritis

Osteoarthritis (OA) is a common progressive degenerative disease. Gut microbiota (GM) and their metabolites have been closely associated with the onset, progression, and pathology of OA. GM and their metabolites may influence the cartilage directly, or indirectly by affecting the gut, the immune system, and the endocrine system. They function through classical pathways in cartilage metabolism and novel pathways that have recently been discovered. Some of them have been used as targets for the prevention and treatment of OA. The current study sought to describe the major pathological signaling pathways in OA chondrocytes and the potential role of gut-related factors in these pathways.

Ketogenic Diet-Associated Worsening of Osteoarthritis Histologic Secerity, Increased Pain Sensitivity and Gut Microbiome Dysbiosis in Mice

OBJECTIVES

Dietary interventions are a potentially powerful treatment option for knee osteoarthritis (OA). The objective of this study was to evaluate a well-formulated ketogenic diet (KD) in the context of knee OA histology and pain using the destabilization of the medial meniscus (DMM) mouse model and correlate with gut microbiome and systemic cytokine levels.

METHODS

Adult male mice underwent unilateral DMM or sham surgery and were then fed eight weeks of KD or chow. At baseline and every two weeks, mechanical allodynia of the operated and contralateral knees was assessed via analgesiometry. Knee joints were collected for histology, gut microbiome analysis was performed on cecal material via 16S sequencing, and serum cytokines were analyzed via Bio-Plex assay.

RESULTS

KD mice had worse histopathologic OA after DMM (mean ± SEM Osteoarthritis Research Society International score: KD-DMM: 4.0 ± 0.5 vs chow-DMM: 2.7 ± 0.08; P = 0.02). KD mice had increased mechanical allodynia postsurgery (P = 0.005 in mixed-effects model). The gut microbiome changed substantially with KD: 59 clades were altered by KD in DMM and 39 by KD in sham (36 were shared, 25 overlapped with previous murine OA studies). Several clades were correlated on an individual-mouse level with both histology and allodynia (eg, Lactobacillus histology P = 0.004, allodynia P = 1 × 10-4). Serum analysis showed four cytokines increased with KD (interleukin [IL]-1β, IL-2, IL-3, and IL-13).

CONCLUSION

KD started immediately after OA induction via DMM is associated with worsened histologic outcomes. KD also worsens mechanical allodynia after either DMM or sham surgery. KD induces significant gut microbiome dysbiosis in clades previously associated with murine OA.

Correlation of fecal microbiome dysregulation to synovial transcriptome in an equine model of obesity associated osteoarthritis

Background

Osteoarthritis (OA) is increasingly thought to be a multifactorial disease in which sustained gut inflammation serves as a continued source of inflammatory mediators driving degenerative processes at distant sites such as joints. The objective of this study was to use the equine model of naturally occurring obesity associated OA to compare the fecal microbiome in OA and health and correlate those findings to differential gene expression synovial fluid (SF) cells, circulating leukocytes and cytokine levels (plasma, SF) towards improved understanding of the interplay between microbiome and immune transcriptome in OA pathophysiology.

Methods

Feces, peripheral blood mononuclear cells (PBMCs), and SF cells were isolated from healthy skeletally mature horses (n=12; 6 males, 6 females) and those with OA (n=6, 2 females, 4 males). Horses were determined to have OA via lameness evaluation, response to intra-articular (IA) diagnostic analgesia, and radiographic and arthroscopic evidence. Horses were excluded who had received medications or joint injections within 2 months. Cytokine analyses of plasma and SF were performed via multiplex immunoassay. Fecal bacterial microbial 16s DNA sequencing was performed and correlated to bulk RNA sequencing of SF cells and PBMC performed using an Illumina based platform.

Results

Horses with OA had higher body condition scores (P=0.009). Cytokines were elevated in plasma [interleukin (IL)-2, IL-6, IL-18, interferon gamma (IFN-γ), interferon gamma inducible protein 10 (CXCL10 or IP-10), granulocyte colony-stimulating factor (G-CSF)] and SF (IL-1β, IL-6, IL-17A, IL-18, IP-10, G-CSF) in OA. Microbial principal coordinate analysis (PCoA) using Bray-Curtis dissimilarity for β-diversity demonstrated distinct grouping of samples from OA versus healthy horses (P=0.003). Faith alpha diversity was reduced in OA (P=0.02). Analysis of microbiome composition showed differential relative abundance of taxa on multiple levels in OA. Specific phyla (Firmicutes, Verrucomicrobia, Tenericutes, Fibrobacteres), correlated to transcriptomic differences related to cell structure, extracellular matrix, collagen, laminin, migration, and motility, or immune response to inflammation in OA.

Conclusions

These findings provide compelling evidence for a link between obesity, gut microbiome dysbiosis and differential gene expression in distant joint sites associated with development of OA in a relevant large animal model, establishing a connection here that provides a platform from which development of therapeutic interventions targeting the gut microbiome can build.

Gut microbiome and orthopaedic health: Bridging the divide between digestion and bone integrity

The gut microbiome, a complex ecosystem of microorganisms in the digestive tract, has emerged as a critical factor in human health, influencing metabolic, immune, and neurological functions. This review explores the connection between the gut microbiome and orthopedic health, examining how gut microbes impact bone density, joint integrity, and skeletal health. It highlights mechanisms linking gut dysbiosis to inflammation in conditions such as rheumatoid arthritis and osteoarthritis, suggesting microbiome modulation as a potential therapeutic strategy. Key findings include the microbiome's role in bone metabolism through hormone regulation and production of short-chain fatty acids, crucial for mineral absorption. The review also considers the effects of diet, probiotics, and fecal microbiota transplantation on gut microbiome composition and their implications for orthopedic health. While promising, challenges in translating microbiome research into clinical practice persist, necessitating further exploration and ethical consideration of microbiome-based therapies. This interdisciplinary research aims to link digestive health with musculoskeletal integrity, offering new insights into the prevention and management of bone and joint diseases.

Genetic insights into the roles of fatty acids and gut microbiota in osteoarthritis: A Mendelian randomization study

Traditional observational studies have shown that fatty acids and gut microbiota are crucial in osteoarthritis (OA) progression, but their findings are often conflicting due to biases, confounding factors, and measurement errors. We conducted a two-sample Mendelian randomization analysis using genome-wide association study data on fatty acids from 136,016 individuals, the gut microbiota from 7738 individuals, and osteoarthritis from 314,870 individuals. Elevated levels of total (odds ratio [OR]: 0.92; 95% CI 0.84-1.00; P = .039), saturated fatty acids (OR: 0.91; 95% CI 0.84-0.99; P = .034), and linoleic acid (OR: 0.92; 95% CI 0.85-1.00; P = .040) were associated with reduced OA risk. In terms of gut microbiota, Bifidobacterium adolescentis (OR: 0.89; 95% CI 0.80-1.00; P = .048) and Escherichia (OR: 0.90; 95% CI 0.81-1.00; P = .042) demonstrated protective roles against OA. Conversely, Oscillibacter (OR: 1.16; 95% CI 1.00-1.34; P = .043), Bilophila (OR: 1.28; 95% CI 1.07-1.54; P = .007), Erysipelotrichaceae (OR: 1.08; 95% CI 1.00-1.16; P = .044), and Bilophila within the Desulfovibrionaceae family (OR: 1.19; 95% CI 1.04-1.36; P = .012) were associated with an increased risk of OA. The findings indicate that modulating dietary factors and gut microbiota can independently reduce the risk and progression of OA, potentially improving the quality of life and health management in aging populations.

Sexually dimorphic metabolic effects of a high fat diet on knee osteoarthritis in mice

BACKGROUND

Women have a higher risk of developing osteoarthritis (OA) than men, including with obesity. To better understand this disparity, we investigated sex differences in metabolic and inflammatory factors associated with OA using a diet-induced mouse model of obesity. We hypothesized that 20 weeks of high-fat diet (HFD) would induce sexually dimorphic changes in both systemic and local risk factors of knee OA.

METHODS

Male and female C57BL/6J mice were fed Chow or HFD from 6 to 26 weeks of age (n = 12 per diet and sex). We performed broad metabolic phenotyping, 16 S gut microbiome analysis, targeted gene expression analysis of synovium-infrapatellar fat tissue, targeted gene expression and proteomic analysis of articular cartilage, chondrocyte metabolic profiling, and OA histopathology. Two-way ANOVA statistics were utilized to determine the contribution of sex and diet and their interaction on outcomes.

RESULTS

Mice fed HFD weighed 1.76-fold (p < 0.0001) and 1.60-fold (p < 0.0001) more than male and female Chow cohorts, respectively, with both sexes reaching similar body fat levels (male: 43.9 ± 2.2%; female: 44.1 ± 3.8%). HFD caused greater cartilage pathology (p < 0.024) and synovial hyperplasia (p < 0.038) versus Chow in both sexes. Cartilage pathology was greater in male versus female mice (p = 0.048), and only male mice developed osteophytes with HFD (p = 0.044). Both sexes exhibited metabolic inflexibility on HFD, but only male mice developed glucose intolerance (p < 0.0001), fatty liver (p < 0.0001), and elevated serum amylase (p < 0.0001) with HFD versus Chow. HFD treatment caused sex-dependent differences in gut microbiota beta diversity (p = 0.01) and alteration in specific microbiome clades, such as a HFD-dependent reduction in abundance of Bifidobacterium only in male mice. In knee synovium and infrapatellar fat tissue, HFD upregulated the expression of pro-inflammatory and pro-fibrotic genes predominantly in female mice. In cartilage, lipid metabolism proteins were more abundant with HFD in male mice, whereas proteins involved in glycolysis/gluconeogenesis and biosynthesis of amino acids were greater in cartilage of female mice. Sex-dependent metabolic differences were observed in cartilage from young, healthy mice prior to pubertal maturation, but not in primary juvenile chondrocytes studied in vitro.

CONCLUSIONS

HFD induced numerous sex differences in metabolic and inflammatory outcomes, especially in joint tissues, suggesting that sex-specific cellular processes are involved during development of early-stage OA with obesity.

The epithelial barrier theory and its associated diseases

The prevalence of many chronic noncommunicable diseases has been steadily rising over the past six decades. During this time, over 350,000 new chemical substances have been introduced to the lives of humans. In recent years, the epithelial barrier theory came to light explaining the growing prevalence and exacerbations of these diseases worldwide. It attributes their onset to a functionally impaired epithelial barrier triggered by the toxicity of the exposed substances, associated with microbial dysbiosis, immune system activation, and inflammation. Diseases encompassed by the epithelial barrier theory share common features such as an increased prevalence after the 1960s or 2000s that cannot (solely) be accounted for by the emergence of improved diagnostic methods. Other common traits include epithelial barrier defects, microbial dysbiosis with loss of commensals and colonization of opportunistic pathogens, and circulating inflammatory cells and cytokines. In addition, practically unrelated diseases that fulfill these criteria have started to emerge as multimorbidities during the last decades. Here, we provide a comprehensive overview of diseases encompassed by the epithelial barrier theory and discuss evidence and similarities for their epidemiology, genetic susceptibility, epithelial barrier dysfunction, microbial dysbiosis, and tissue inflammation.

Exploring the Interconnection between Metabolic Dysfunction and Gut Microbiome Dysbiosis in Osteoarthritis: A Narrative Review

Osteoarthritis (OA) is a prevalent joint disorder and the most common form of arthritis, affecting approximately 500 million people worldwide, or about 7% of the global population. Its pathogenesis involves a complex interplay between metabolic dysfunction and gut microbiome (GM) alterations. This review explores the relationship between metabolic disorders-such as obesity, diabetes, and dyslipidemia-and OA, highlighting their shared risk factors, including aging, sedentary lifestyle, and dietary habits. We further explore the role of GM dysbiosis in OA, elucidating how systemic inflammation, oxidative stress, and immune dysregulation driven by metabolic dysfunction and altered microbial metabolites contribute to OA progression. Additionally, the concept of "leaky gut syndrome" is discussed, illustrating how compromised gut barrier function exacerbates systemic and local joint inflammation. Therapeutic strategies targeting metabolic dysfunction and GM composition, including lifestyle interventions, pharmacological and non-pharmacological factors, and microbiota-targeted therapies, are reviewed for their potential to mitigate OA progression. Future research directions emphasize the importance of identifying novel biomarkers for OA risk and treatment response, adopting personalized treatment approaches, and integrating multiomics data to enhance our understanding of the metabolic-GM-OA connection and advance precision medicine in OA management.

Mapping knowledge landscapes and research frontiers of gastrointestinal microbiota and bone metabolism: a text-mining study

INTRODUCTION

Extensive research efforts have been dedicated to elucidating the intricate pathways by which gastrointestinal microbiota and their metabolites exert influence on the processes of bone formation. Nonetheless, a notable gap exists in the literature concerning a bibliometric analysis of research trends at the nexus of gastrointestinal microbiota and bone metabolism.

METHODS

To address this scholarly void, the present study employs a suite of bibliometric tools including online platforms, CiteSpace and VOSviewer to scrutinize the pertinent literature in the realm of gastrointestinal microbiota and bone metabolism.

RESULTS AND DISCUSSION

Examination of the temporal distribution of publications spanning from 2000 to 2023 reveals a discernible upward trajectory in research output, characterized by an average annual growth rate of 19.2%. Notably, China and the United States emerge as primary contributors. Predominant among contributing institutions are Emory University, Harvard University, and the University of California. Pacifici R from Emory University contributed the most research with 15 publications. In the realm of academic journals, Nutrients emerges as the foremost publisher, followed closely by Frontiers in Microbiology and PLOS One. And PLOS One attains the highest average citations of 32.48. Analysis of highly cited papers underscores a burgeoning interest in the therapeutic potential of probiotics or probiotic blends in modulating bone metabolism by augmenting host immune responses. Notably, significant research attention has coalesced around the therapeutic interventions of probiotics, particularly Lactobacillus reuteri, in osteoporosis, as well as the role of gastrointestinal microbiota in the etiology and progression of osteoarthritis. Keyword analysis reveals prevalent terms including gut microbiota, osteoporosis, bone density, probiotics, inflammation, SCFAs, metabolism, osteoarthritis, calcium absorption, obesity, double-blind, prebiotics, mechanisms, postmenopausal women, supplementation, risk factors, oxidative stress, and immune system. Future research endeavors warrant a nuanced exploration of topics such as inflammation, obesity, SCFAs, postmenopausal osteoporosis, skeletal muscle, oxidative stress, double-blind trials, and pathogenic mechanisms. In summary, this study presents a comprehensive bibliometric analysis of global research on the interplay between gastrointestinal microbiota and bone metabolism, offering valuable insights for scholars, particularly nascent researchers, embarking on analogous investigations within this domain.

Diet influences knee osteoarthritis osteophyte formation via gut microbiota and serum metabolites

Osteophyte formation, a key indicator of osteoarthritis (OA) severity, remains poorly understood in its relation to gut microbiota and metabolites in knee osteoarthritis (KOA). We conducted 16S rDNA sequencing and untargeted metabolomics on fecal and serum samples from 20 healthy volunteers, 80 KOA patients in Guangdong, and 100 in Inner Mongolia, respectively. Through bioinformatics analysis, we identified 3 genera and 5 serum metabolites associated with KOA osteophyte formation. Blautia abundance negatively correlated with meat, cheese, and bean consumption. The 5 serum metabolites negatively correlated with dairy, beef, cheese, sugar, and salt intake, yet positively with age and oil consumption. Higher Blautia levels in the gut may contribute to KOA osteophyte formation, with serum metabolites LTB4 and PGD2 potentially serving as biomarkers. KOA patients in Inner Mongolia exhibited lower Blautia levels and reduced expression of 5 serum metabolites, possibly due to cheese consumption habits, resulting in less osteophyte formation.

Microbial Symphony: Exploring the Role of the Gut in Osteoarthritis-Related Pain. A Narrative Review

One of the most common musculoskeletal disorders, osteoarthritis (OA), causes worldwide disability, morbidity, and poor quality of life by degenerating articular cartilage, modifying subchondral bone, and inflaming synovial membranes. OA pathogenesis pathways must be understood to generate new preventative and disease-modifying therapies. In recent years, it has been acknowledged that gut microbiota (GM) can significantly contribute to the development of OA. Dysbiosis of GM can disrupt the "symphony" between the host and the GM, leading to a host immunological response that activates the "gut-joint" axis, ultimately worsening OA. This narrative review summarizes research supporting the "gut-joint axis" hypothesis, focusing on the interactions between GM and the immune system in its two main components, innate and adaptive immunity. Furthermore, the pathophysiological sequence of events that link GM imbalance to OA and OA-related pain is broken down and further investigated. We also suggest that diet and prebiotics, probiotics, nutraceuticals, exercise, and fecal microbiota transplantation could improve OA management and represent a new potential therapeutic tool in the light of the scarce panorama of disease-modifying osteoarthritis drugs (DMOADs). Future research is needed to elucidate these complex interactions, prioritizing how a particular change in GM, i.e., a rise or a drop of a specific bacterial strain, correlates with a certain OA subset to pinpoint the associated signaling pathway that leads to OA.

Gold nanoparticles exhibit anti-osteoarthritic effects via modulating interaction of the "microbiota-gut-joint" axis

Osteoarthritis (OA) is a common degenerative joint disease that can cause severe pain, motor dysfunction, and even disability. A growing body of research indicates that gut microbiota and their associated metabolites are key players in maintaining bone health and in the progression of OA. Short-chain fatty acids (SCFAs) are a series of active metabolites that widely participate in bone homeostasis. Gold nanoparticles (GNPs) with outstanding anti-bacterial and anti-inflammatory properties, have been demonstrated to ameliorate excessive bone loss during the progression of osteoporosis (OP) and rheumatoid arthritis (RA). However, the protective effects of GNPs on OA progression are not clear. Here, we observed that GNPs significantly alleviated anterior cruciate ligament transection (ACLT)-induced OA in a gut microbiota-dependent manner. 16S rDNA gene sequencing showed that GNPs changed gut microbial diversity and structure, which manifested as an increase in the abundance of Akkermansia and Lactobacillus. Additionally, GNPs increased levels of SCFAs (such as butyric acid), which could have improved bone destruction by reducing the inflammatory response. Notably, GNPs modulated the dynamic balance of M1/M2 macrophages, and increased the serum levels of anti-inflammatory cytokines such as IL-10. To sum up, our study indicated that GNPs exhibited anti-osteoarthritis effects via modulating the interaction of "microbiota-gut-joint" axis, which might provide promising therapeutic strategies for OA.

Murine cartilage microbial DNA deposition occurs rapidly following the introduction of a gut microbiome and changes with obesity, aging, and knee osteoarthritis

Cartilage microbial DNA patterns have been recently characterized in osteoarthritis (OA). The objectives of this study were to evaluate the gut origins of cartilage microbial DNA, to characterize cartilage microbial changes with age, obesity, and OA in mice, and correlate these to gut microbiome changes. We used 16S rRNA sequencing performed longitudinally on articular knee cartilage from germ-free (GF) mice following oral microbiome inoculation and cartilage and cecal samples from young and old wild-type mice with/without high-fat diet-induced obesity (HFD) and with/without OA induced by destabilization of the medial meniscus (DMM) to evaluate gut and cartilage microbiota. Microbial diversity was assessed, groups compared, and functional metagenomic profiles reconstructed. Findings were confirmed in an independent cohort by clade-specific qPCR. We found that cartilage microbial patterns developed at 48 h and later timepoints following oral microbiome inoculation of GF mice. Alpha diversity was increased in SPF mouse cartilage samples with age (P = 0.013), HFD (P = 5.6E-4), and OA (P = 0.029) but decreased in cecal samples with age (P = 0.014) and HFD (P = 1.5E-9). Numerous clades were altered with aging, HFD, and OA, including increases in Verrucomicrobia in both cartilage and cecal samples. Functional analysis suggested changes in dihydroorotase, glutamate-5-semialdehyde dehydrogenase, glutamate-5-kinase, and phosphoribosylamine-glycine ligase, in both cecum and cartilage, with aging, HFD, and OA. In conclusion, cartilage microbial DNA patterns develop rapidly after the introduction of a gut microbiome and change in concert with the gut microbiome during aging, HFD, and OA in mice. DMM-induced OA causes shifts in both cartilage and cecal microbiome patterns independent of other factors.

OA susceptibility in mice is partially mediated by the gut microbiome, is transferrable via microbiome transplantation and is associated with immunophenotype changes

OBJECTIVES

The Murphy Roths Large (MRL)/MpJ 'superhealer' mouse strain is protected from post-traumatic osteoarthritis (OA), although no studies have evaluated the microbiome in the context of this protection. This study characterised microbiome differences between MRL and wild-type mice, evaluated microbiome transplantation and OA and investigated microbiome-associated immunophenotypes.

METHODS

Cecal material from mixed sex C57BL6/J (B6) or female MRL/MpJ (MRL) was transplanted into B6 and MRL mice, then OA was induced by disruption of the medial meniscus surgery (DMM). In other experiments, transplantation was performed after DMM and transplantation was performed into germ-free mice. Transplanted mice were bred through F2. OARSI, synovitis and osteophyte scores were determined blindly 8 weeks after DMM. 16S microbiome sequencing was performed and metagenomic function was imputed. Immunophenotypes were determined using mass cytometry.

RESULTS

MRL-into-B6 transplant prior to DMM showed reduced OA histopathology (OARSI score 70% lower transplant vs B6 control), synovitis (60% reduction) and osteophyte scores (30% reduction) 8 weeks after DMM. When performed 48 hours after DMM, MRL-into-B6 transplant improved OA outcomes but not when performed 1-2 weeks after DMM. Protection was seen in F1 (60% reduction) and F2 progeny (30% reduction). Several cecal microbiome clades were correlated with either better (eg, Lactobacillus, R=-0.32, p=0.02) or worse (eg, Rikenellaceae, R=0.43, p=0.001) OA outcomes. Baseline immunophenotypes associated with MRL-into-B6 transplants and MRL included reduced double-negative T cells and increased CD25+CD4+ T cells.

CONCLUSION

The gut microbiome is responsible in part for OA protection in MRL mice and is transferrable by microbiome transplantation. Transplantation induces resting systemic immunophenotyping changes that correlate with OA protection.

Bioactives and their roles in bone metabolism of osteoarthritis: evidence and mechanisms on gut-bone axis

Bioactives significantly modify and maintain human health. Available data suggest that Bioactives might play a beneficial role in chronic inflammatory diseases. Although promised, defining their mechanisms and opting to weigh their benefits and limitations is imperative. Detailed mechanisms by which critical Bioactives, including probiotics and prebiotics such as dietary lipids (DHA, EPA, alpha LA), vitamin D, polysaccharides (fructooligosaccharide), polyphenols (curcumin, resveratrol, and capsaicin) potentially modulate inflammation and bone metabolism is limited. Certain dietary bioactive significantly impact the gut microbiota, immune system, and pain response via the gut-immune-bone axis. This narrative review highlights a recent update on mechanistic evidence that bioactive is demonstrated demonstrated to reduce osteoarthritis pathophysiology.

The Complex Interplay between the Gut Microbiome and Osteoarthritis: A Systematic Review on Potential Correlations and Therapeutic Approaches

The objective of this review is to systematically analyze the potential correlation between gut microbiota and osteoarthritis (OA) as well as to evaluate the feasibility of microbiota-targeted therapies for treating OA. Studies conducted from October 2013 to October 2023 were identified via a search on electronic databases such as PubMed, Web of Science, and Scopus, following established PRISMA statement standards. Two reviewers independently screened, assessed, and extracted relevant data, and then they graded the studies using the ROBINS I tool for non-randomized interventions studies and SYRCLE's risk-of-bias tool for animal studies. A search through 370 studies yielded 38 studies (24 preclinical and 14 clinical) that were included. In vivo research has predominantly concentrated on modifying the gut microbiota microenvironment, using dietary supplements, probiotics, and prebiotics to modify the OA status. Lactobacilli are the most thoroughly examined with Lactobacillus acidophilus found to effectively reduce cartilage damage, inflammatory factors, and pain. Additionally, Lactobacillus M5 inhibits the development of OA by preventing high-fat diet (HFD)-induced obesity and protecting cartilage from damage. Although there are limited clinical studies, certain compositions of intestinal microbiota may be associated with onset and progression of OA, while others are linked to pain reduction in OA patients. Based on preclinical studies, there is evidence to suggest that the gut microbiota could play a significant role in the development and progression of OA. However, due to the scarcity of clinical studies, the exact mechanism linking the gut microbiota and OA remains unclear. Further research is necessary to evaluate specific gut microbiota compositions, potential pathogens, and their corresponding signaling pathways that contribute to the onset and progression of OA. This will help to validate the potential of targeting gut microbiota for treating OA patients.

Association between gut microbiome-related metabolites and symptomatic hand osteoarthritis in two independent cohorts

BACKGROUND

Since gut microbiome dysbiosis can cause inflammatory disorders by affecting host metabolism, we postulate that the gut microbiome and related metabolites could play a role in hand osteoarthritis. We characterised gut microbiome-related metabolites in people with symptomatic hand osteoarthritis (SHOA) in two independent cohorts.

METHODS

Using data collected from a large-sample community-based observational study (discovery cohort), we assessed the relations of the microbial function and plasma key metabolites related to altered microbial function with SHOA. Finally, we verified the relations of plasma metabolites to SHOA in an independent observational study (validation cohort).

FINDINGS

In the discovery cohort (n = 1359), compared to those without SHOA, participants with SHOA had significantly altered microbial functions related to tryptophan metabolism (Q = 0.025). Therefore we measured the plasma tryptophan metabolites and found that participants with SHOA had higher levels of 5-hydroxyindoleacetic acid (odds ratio [OR] = 1.25, 95% confidence interval [CI]: 1.09-1.42) and 5-hydroxytryptophol (OR = 1.13, 95% CI: 1.04-1.23), but lower levels of indole-3-lactic acid (ILA) (OR = 0.85, 95% CI: 0.72-1.00), skatole (OR = 0.93, 95% CI: 0.88-0.99) and 3-hydroxyanthranilic acid (OR = 0.90, 95% CI: 0.85-0.96). Findings from the validation cohort (n = 142) verified that lower levels of ILA were related to SHOA (OR = 0.70, 95% CI: 0.53-0.92).

INTERPRETATION

Alterations of the microbial function of tryptophan biosynthesis and tryptophan metabolites, especially lower levels of ILA, are associated with SHOA. These findings suggest the role of the microbiome and tryptophan metabolites in developing of SHOA and may contribute to future translational opportunities.

FUNDING

National Key Research and Development Plan and National Natural Science Foundation of China.

The Gut-Joint Axis in Osteoarthritis

Osteoarthritis (OA) is a complex and prevalent joint disease with a multifaceted pathogenesis, presenting a persistent challenge to medical researchers. However, recent investigations into the gut microbiota (GMB) have unveiled an intriguing connection with OA, giving rise to the concept of the "gut-joint axis". The human gut houses a diverse microbial ecosystem that plays pivotal roles in nutrient synthesis, metabolism, and immune modulation. Dysbiosis, or disruption of this microbial balance, can lead to inflammation through the release of proinflammatory cytokines and the production of inflammatory metabolites. This editorial delves into the evolving understanding of how the GMB may influence OA development and progression. Notably, short-chain fatty acids (SCFAs) produced by gut microorganisms have emerged as potential players in maintaining bone homeostasis and reducing inflammation. Furthermore, compromised gut integrity can lead to endotoxemia and a pro-inflammatory state, contributing to OA. Recent research has highlighted differences in GMB composition and functionality between OA patients and healthy individuals, shedding light on specific microbial taxa and functional pathways associated with OA. The gut mycobiome (fungi) and virome (viruses) in OA remain largely unexplored, presenting exciting opportunities for future investigations. The emerging understanding of the gut-joint axis offers promising avenues for innovative OA prevention and treatment strategies, though further research is needed to fully elucidate these complex interactions.

Possible relationship between the gut leaky syndrome and musculoskeletal injuries: the important role of gut microbiota as indirect modulator

This article aims to examine the evidence on the relationship between gut microbiota (GM), leaky gut syndrome and musculoskeletal injuries. Musculoskeletal injuries can significantly impair athletic performance, overall health, and quality of life. Emerging evidence suggests that the state of the gut microbiota and the functional intestinal permeability may contribute to injury recovery. Since 2007, a growing field of research has supported the idea that GM exerts an essential role maintaining intestinal homeostasis and organic and systemic health. Leaky gut syndrome is an acquired condition where the intestinal permeability is impaired, and different bacteria and/or toxins enter in the bloodstream, thereby promoting systemic endotoxemia and chronic low-grade inflammation. This systemic condition could indirectly contribute to increased local musculoskeletal inflammation and chronificate injuries and pain, thereby reducing recovery-time and limiting sport performance. Different strategies, including a healthy diet and the intake of pre/probiotics, may contribute to improving and/or restoring gut health, thereby modulating both systemically as local inflammation and pain. Here, we sought to identify critical factors and potential strategies that could positively improve gut microbiota and intestinal health, and reduce the risk of musculoskeletal injuries and its recovery-time and pain. In conclusion, recent evidences indicate that improving gut health has indirect consequences on the musculoskeletal tissue homeostasis and recovery through the direct modulation of systemic inflammation, the immune response and the nociceptive pain.

"Cross-talk" between gut microbiome dysbiosis and osteoarthritis progression: a systematic review

Objectives

The aim of this systematic review was to summarize the available literature on gut microbiome (GMB) and osteoarthritis (OA), analyze the correlation between GMB and OA, and explore potential underlying mechanisms.

Methods

A systematic search of the PubMed, Embase, Cochrane, and Web of Science with the keywords "Gut Microbiome" and "Osteoarthritis" was conducted to identify the human and animal studies exploring the association between GMB and OA. The retrieval time range was from the database inception to July 31, 2022. Studies reported the other arthritic diseases without OA, reviews, and studies focused on the microbiome in other parts of the body with OA, such as oral or skin, were excluded. The included studies were mainly reviewed for GMB composition, OA severity, inflammatory factors, and intestinal permeability.

Results

There were 31 studies published met the inclusion criteria and were analyzed, including 10 human studies and 21 animal studies. Human and animal studies have reached a consistent conclusion that GMB dysbiosis could aggravate OA. In addition, several studies have found that alterations of GMB composition can increase intestinal permeability and serum levels of inflammatory factors, while regulating GMB can alleviate the changes. Owing to the susceptibility of GMB to internal and external environments, genetics, and geography, the included studies were not consistent in GMB composition analysis.

Conclusion

There is a lack of high-quality studies evaluating the effects of GMB on OA. Available evidence indicated that GMB dysbiosis aggravated OA through activating the immune response and subsequent induction of inflammation. Future studies should focus on more prospective, cohort studies combined with multi-omics to further clarify the correlation.

Indole-3-propionic acid alleviates chondrocytes inflammation and osteoarthritis via the AhR/NF-κB axis

BACKGROUND

Osteoarthritis (OA) is a common chronic disease characterized by chronic inflammation and extracellular matrix degradation. Indole-3-propionic acid (IPA) is a tryptophan metabolite secreted by intestinal flora, which can exert anti-inflammatory effects in a variety of diseases. In this study, we further investigated the potential therapeutic role of IPA in OA and the underlying mechanism.

METHODS

IL-1β was utilized to induce chondrocyte inflammation. Then, the cytotoxicity of IPA on rat chondrocytes was assessed. Meanwhile, RT-qPCR, Griess reaction, ELISA, Western blot and immunofluorescence were performed to evaluate the expression of inflammatory factors and stromal proteins, and the NF-κB pathway in chondrocytes treated with IL-1β alone, with IPA or with aryl hydrocarbon receptor (AhR) knockdown. An OA rat model was established by anterior cruciate ligament transection, and hematoxylin-eosin staining, Safranin-O/Fast Green staining and immunochemistry were applied to estimate OA severity.

RESULTS

IPA did not affect cellular viability at concentrations up to 80 µM. IPA significantly inhibited the IL-1β-induced expression of inflammatory factors (Nitric oxide, PGE2, TNF-α, IL-6, iNOS and COX-2) and matrix-degrading enzymes (MMP-3, MMP-13 and ADAMTS-5), upregulated the expression of anabolic markers (aggrecan and collagen-II) and inactivated the NF-κB pathway. However, AhR knockdown could abolish the above protection capabilities and the suppression of the NF-κB pathway induced by IPA. Furthermore, IPA significantly reduced serum inflammatory cytokines expression, cartilage destruction and synovitis in vivo, demonstrating its protective role in OA progression.

CONCLUSION

IPA improved IL-1β-induced chondrocyte inflammation and extracellular matrix degradation through the AhR/NF-κB axis, which provides an innovative therapeutic strategy for OA.

An unexpected connection: A narrative review of the associations between Gut Microbiome and Musculoskeletal Pain

PURPOSE

Multiple diverse factors contribute to musculoskeletal pain, a major cause of physical dysfunction and health-related costs worldwide. Rapidly growing evidence demonstrates that the gut microbiome has overarching influences on human health and the body's homeostasis and resilience to internal and external perturbations. This broad role of the gut microbiome is potentially relevant and connected to musculoskeletal pain, though the literature on the topic is limited. Thus, the literature on the topic of musculoskeletal pain and gut microbiome was explored.

METHODS

This narrative review explores the vast array of reported metabolites associated with inflammation and immune-metabolic response, which are known contributors to musculoskeletal pain. Moreover, it covers known modifiable (e.g., diet, lifestyle choices, exposure to prescription drugs, pollutants, and chemicals) and non-modifiable factors (e.g., gut architecture, genetics, age, birth history, and early feeding patterns) that are known to contribute to changes to the gut microbiome. Particular attention is devoted to modifiable factors, as the ultimate goal of researching this topic is to implement gut microbiome health interventions into clinical practice.

RESULTS

Overall, numerous associations exist in the literature that could converge on the gut microbiome's pivotal role in musculoskeletal health. Particularly, a variety of metabolites that are either directly produced or indirectly modulated by the gut microbiome have been highlighted.

CONCLUSION

The review highlights noticeable connections between the gut and musculoskeletal health, thus warranting future research to focus on the gut microbiome's role in musculoskeletal conditions.

Analysis of gut microbiome composition, function, and phenotype in patients with osteoarthritis

Gut microbiome (GMB) disturbance can induce chronic low-grade inflammation, which is closely related to the occurrence and development of osteoarthritis (OA). However, the relationship between GMB and OA remains unclear. In this study, we collected stool samples from OA patients and healthy people, and performed Alpha diversity, Beta diversity, MetaStat, and LEfSe analysis by 16S rRNA sequencing to find out the species with significant difference between the two groups. Random forest analysis was performed to find out biomarkers that could distinguish between OA patients and healthy people. PICRUSt and Bugbase analysis were used to compare the difference in functions and phenotypes. Multivariate linear regression analysis (MaAsLin) was used to adjust for gender, age, and body mass index (BMI). The results showed that there was a significant difference in the overall composition of GMB between the two groups (p = 0.005). After adjusting for gender, age, and BMI, we found that p_Bacteroidota (Q = 0.039), c_Bacteroidia (Q = 0.039), and o_Bacteroidales (Q = 0.040) were enriched in the OA group, while s_Prevotella_copri (Q = 0.001) was enriched in the healthy control group. Prevotella could distinguish between OA patients and healthy people with a better diagnostic power (AUC = 77.5%, p < 0.001, 95% CI: 66.9-88.1%). The functions of DNA transcription, amino acid metabolism (including histidine, lysine, and isoleucine), ATP metabolism, and phospholipid metabolism significantly decreased, while glucose metabolism, protein acetylation, and aspartate kinase activity significantly increased in the OA group. In terms of phenotypes, we found that the relative abundance of aerobic (p = 0.003) and Gram-negative (p < 0.001) was higher in the OA group, while contains mobile elements (p = 0.001) and Gram-positive (p < 0.001) were higher in the healthy control group. Our study preliminarily demonstrated that there were differences in the composition, function, and phenotype of GMB in stool samples between OA patients and healthy people, which provided a novel perspective on further study in OA.

Roles of Gut Microbiome in Bone Homeostasis and Its Relationship with Bone-Related Diseases

The extended microbial genome-the gut microbiome (GM)-plays a significant role in host health and disease. It is able to influence a number of physiological functions. During dysbiosis, GM is associated with the development of various chronic diseases with impaired bone quality. In general, GM is important for bone homeostasis and can affect it via several mechanisms. This review describes the roles of GM in bone homeostasis through influencing the immune and endocrine functions, short-chain fatty acids production, calcium absorption and the gut-brain axis. The relationship between GM composition and several bone-related diseases, specifically osteoporosis, osteoarthritis, rheumatoid arthritis, diabetes mellitus, obesity and bone cancer, is also highlighted and summarized. GM manipulation may become a future adjuvant therapy in the prevention of many chronic diseases. Therefore, the beneficial effects of probiotic therapy to improve the health status of individuals with aforementioned diseases are provided, but further studies are needed to clearly confirm its effectiveness. Recent evidence suggests that GM is responsible for direct and indirect effects on drug efficacy. Accordingly, various GM alterations and interactions related to the treatment of bone-related diseases are mentioned as well.

The effects and significance of gut microbiota and its metabolites on the regulation of osteoarthritis: Close coordination of gut-bone axis

Osteoarthritis (OA) is a common chronic degenerative disease of articular cartilage in middle-aged and older individuals, which can result in the joint pain and dysfunction, and even cause the joint deformity or disability. With the enhancing process of global aging, OA has gradually become a major public health problem worldwide. Explaining pathogenesis of OA is critical for the development of new preventive and therapeutic interventions. In recent years, gut microbiota (GM) has been generally regarded as a “multifunctional organ,” which is closely relevant with a variety of immune, metabolic and inflammatory functions. Meanwhile, more and more human and animal researches have indicated the existence of gut-bone axis and suggested that GM and its metabolites are closely involved in the pathogenic process of OA, which might become a potential and promising intervention target. Based on the close coordination of gut-bone axis, this review aims to summarize and discuss the mechanisms of GM and its metabolites influencing OA from the aspects of the intestinal mucosal barrier modulation, intestinal metabolites modulation, immune modulation and strategies for the prevention or treatment of OA based on perspectives of GM and its metabolites, thus providing a profound knowledge and recognition of it.

A systematic review of microbiome composition in osteoarthritis subjects

OBJECTIVE

Osteoarthritis (OA) started to be associated to shifted microbiota composition recently. This systematic review aims to elucidate if there is a common microbiota composition linked with OA between different studies.

METHODS

We screened PubMed, Scopus, Web of Science and Cochrane databases up to July 26^th 2021 to identify original studies in which microbiome was assessed from OA individuals, both in human and laboratory animals' studies. Bacteria associated with OA were summarized to find common patterns between the studies.

RESULTS

We identified 37 original studies where the microbiota composition was assessed in OA subjects. We identified some bacteria (Clostridium, Streptococcus, Bacteroides and Firmicutes) that were reported to be upregulated in OA subjects, whereas Lactobacillus and Bifidobacterium longum were associated with improved OA outcomes. The heterogeneity of sampling and analysis methods, different taxonomical levels reported and the lack of healthy controls in several studies made it difficult to compare the studies and reach conclusions about a potential causal link.

CONCLUSIONS

The current study demonstrated that some bacteria were identified as regulators of OA. Future works following standardized methodologies with more proper controls are needed to elucidate our understanding of the role of the microbiota in OA pathogenesis and progress towards new treatments.

The Microbiome in Osteoarthritis: a Narrative Review of Recent Human and Animal Model Literature

PURPOSE OF THE REVIEW

The microbiome has recently emerged as a powerful contributor to health and illness in chronic, systemic disorders. Furthermore, new microbiome niches beyond traditional gut locations are frequently being described. Over the past 5 years, numerous pivotal studies have demonstrated associations between changes in various microbiome niches and the development of osteoarthritis (OA). Herein, we review the most impactful recent literature, including microbiome associations with disease and the potential therapeutic value of microbiome manipulation.

RECENT FINDINGS

The gut microbiome of human OA patients is enriched in specific bacterial clades, most notably Streptococcus, which correlates with OA pain, Firmicutes, and others. Most studies have focused on knee OA, although one publication demonstrated positive associations with 3 gut microbiome clades in hand OA. OA can be easily distinguished from RA by evaluating differences in oral microbiome composition. Most studies have also demonstrated a reduction in richness of the gut microbiome (alpha diversity) associated with OA. Several studies have identified bacterial signatures within human knee and hip cartilage, synovial fluid, and synovial tissue and have described changes in these patterns occurring with the development of OA. In animal models of OA, high-fat diet-induced obesity has been the most well-studied OA risk factor associated with changes in the microbiome, with numerous bacterial clades changed within the gut microbiome and associated with OA. Also in animal models, various oral supplementations, including dietary fiber, probiotics including Lactobacillus species, and cecal microbiome transplantation have all shown improvements in OA histopathology or cartilage healing. Microbiome changes are strongly associated with the OA disease process and with individual OA risk factors related to both the gut microbiome and the microbial DNA patterns in the joint. Microbiome-directed interventions have the potential to prevent or reduce the progression of OA. Future studies should investigate the mechanistic underpinnings of these microbiome associations and further define the therapeutic potential of microbiome augmentation.

Evaluating the Relationship Between Acute Pain Perception and Gut Microbiota Among Female University Students in Japan: A Prospective Cohort Study

The gut microbiota (GM) plays an important role in gut-brain communication, and the ‘gut-brain axis’ has attracted much attention as a factor influencing human host health. We previously reported that pain perception may be associated with GM composition in males. The aim of this study was to investigate the relationship between GM composition and pain perception among 42 healthy female university students in Japan. Pain perception was evaluated by pressure pain threshold (PPT), current perception threshold (CPT), temporal summation of pain (TSP), conditioned pain modulation (CPM), and a questionnaire on psychological state. CPT was stimulated at 5, 250, and 2,000 Hz, which reflected the thresholds of the C, Aδ, and Aβ fibers, respectively. Also, GM composition was estimated using 16S rRNA analysis. The lower alpha diversity was associated with, the lower PPT (rs = 0.330, P < 0.05) and CPT of 2000 Hz (re = 0.339, P < 0.05). Furthermore, alpha diversity was identified as an explanatory variable for PPT (β = 0.424, P < 0.01) and TSP (β = -0.317, P < 0.05), alpha diversity and state anxiety for CPT of 2000 Hz (β = 0.321, P < 0.05), and state anxiety for CPT of 250 Hz (β = 0.320, P < 0.05). However, there was no relationship between the rate of major phylum and pain perception.

Gut Microbiota Ecosystem Governance of Host Inflammation, Mitochondrial Respiration and Skeletal Homeostasis

Osteoporosis and osteoarthritis account for the leading causes of musculoskeletal dysfunction in older adults. Senescent chondrocyte overburden, inflammation, oxidative stress, subcellular organelle dysfunction, and genomic instability are prominent features of these age-mediated skeletal diseases. Age-related intestinal disorders and gut dysbiosis contribute to host tissue inflammation and oxidative stress by affecting host immune responses and cell metabolism. Dysregulation of gut microflora correlates with development of osteoarthritis and osteoporosis in humans and rodents. Intestinal microorganisms produce metabolites, including short-chain fatty acids, bile acids, trimethylamine N-oxide, and liposaccharides, affecting mitochondrial function, metabolism, biogenesis, autophagy, and redox reactions in chondrocytes and bone cells to regulate joint and bone tissue homeostasis. Modulating the abundance of Lactobacillus and Bifidobacterium, or the ratio of Firmicutes and Bacteroidetes, in the gut microenvironment by probiotics or fecal microbiota transplantation is advantageous to suppress age-induced chronic inflammation and oxidative damage in musculoskeletal tissue. Supplementation with gut microbiota-derived metabolites potentially slows down development of osteoarthritis and osteoporosis. This review provides latest molecular and cellular insights into the biological significance of gut microorganisms and primary and secondary metabolites important to cartilage and bone integrity. It further highlights treatment options with probiotics or metabolites for modulating the progression of these two common skeletal disorders.

Evidence for causal effects of sleep disturbances on risk for osteoarthritis: a univariable and multivariable Mendelian randomization study

OBJECTIVE

To disentangle whether sleep disturbances have a causal effect on the risk of osteoarthritis (OA) using genetically based approaches.

METHOD

We performed univariable and multivariable Mendelian randomization (MR) analyses using publicly released genome-wide association studies summary statistics to estimate the causal associations of sleep disturbances with OA risk. The inverse-variance weighted (IVW) method was utilized as primary MR analysis, whereas complementary methods including weighted median, weighted mode, MR-Egger regression, and MR pleiotropy residual sum and outlier (MR-PRESSO) were applied to detect and correct for the presence of pleiotropy.

RESULTS

There were 228 independent instrumental variables (IVs) for insomnia and 78, 27 and 8 IVs for sleep duration, short sleep duration and long sleep duration, respectively. Univariable MR analysis suggested that genetically determined insomnia or short sleep duration exerted a causal effect on overall OA in an unfavorable manner (Insomnia: OR = 1.22, 95%CI = 1.15-1.30, P = 8.05 × 10^-10; Short sleep duration: OR = 1.04, 95%CI = 1.02-1.07, P = 2.20 × 10^-3). More compelling, increasing genetic liability to insomnia or short sleep duration was also associated with OA risk, after accounting for effects of insomnia or short sleep duration on body mass index, type 2 diabetes and depression individually, and in a combined model considering all three confounders.

CONCLUSIONS

Findings suggested consisted evidence for an adverse effect of increased insomnia or short sleep duration on OA risk. Strategies to mitigate sleep disturbances may be one of the cornerstones protects against OA.

The relation between the gut microbiome and osteoarthritis: A systematic review of literature

Background

Along with mechanical and genetic factors, emerging evidence suggests that the presence of low-grade inflammation has a role in the pathogenesis of osteoarthritis (OA) and seems to be related to the microbiome composition of the gut.

Purpose

To provide evidence whether there is clinical or preclinical evidence of gut-joint axis in the pathogenesis and symptoms of OA.

Methods

An extensive review of the current literature was performed using three different databases. Human, as well as animal studies, were included. The risk of bias was identified using ROBINS and SYRCLE tools, while the quality of evidence was assessed using GRADE and CAMADARES criteria.

Results

A total of nineteen articles were included. Multiple animal studies demonstrated that both obesity, and high-fat and high-sugar diets resulted in a gut dysbiosis status characterized by increased Firmicutes/Bacteroidetes (F/B) phyla ratio and increased permeability. These changes were associated with increased lipopolysaccharide serum levels, which consequently resulted in synovitis and OA severity. The administration of pre-and probiotics partially reversed this bacterial composition. In addition, in human studies, a decreased amount of gut Bacteroidetes, subsequent increased F/B ratio, have also been observed in OA patients.

Conclusions

Our review confirms preliminary yet sound evidence supporting a gut-joint axis in OA in primarily preclinical models, by showing an association between diet, gut dysbiosis and OA radiological severity and self-reported symptoms. Clinical studies are needed to confirm these findings, and to investigate whether interventions targeting the composition of the microbiome will have a beneficial clinical effect.