Suppressive Effects of Insulin on Tumor Necrosis Factor-Dependent Early Osteoarthritic Changes Associated With Obesity and Type 2 Diabetes Mellitus

Exploration of the association between estimated glucose disposal rate and osteoarthritis in middle-aged and older adults: An analysis of NHANES data from 2011 to 2018

Background

It is unclear how the estimated glucose disposal rate (eGDR) index relates to osteoarthritis (OA). The goal of this research is to explore the possible link between the eGDR index and the likelihood of OA development.

Methods

The study encompassed 9,051 individuals from the National Health and Nutrition Examination Survey (2011-2018). Participants were divided into quartiles according to their eGDR, calculated with the equation: eGDR (mg/kg/min) = 21.158 - (0.09 × waist circumference) - (3.407 × hypertension) - (0.551 × glycosylated hemoglobin). We assessed the independent correlation between the eGDR metric and the incidence of OA through weighted multivariate regression, stratified analysis, and threshold effect evaluation.

Results

The study encompassed 9,051 participants, who had an average eGDR of 7.09. Participants with OA had lower eGDR levels compared to those without OA (6.27 ± 0.09 vs 7.31 ± 0.06, P < 0.001). The odds ratios (ORs) for OA associated with the eGDR index in the logistic regression models were 0.87 (95% confidence interval [CI]: 0.84, 0.89) in the unadjusted model I and 0.87 (95% CI: 0.84, 0.91) in model II (adjusted for all covariates). Higher eGDR index was associated with a reduced risk of OA when compared to the lowest quartile (Q1). A restricted cubic spline analysis indicated a linear negative relationship between eGDR and OA risk.

Conclusion

An increased eGDR index is inversely related to the risk of OA. The eGDR may serve as a valuable biomarker for the detection of OA and offers a new perspective for the assessment and management of the condition.

Identification and validation of up-regulated TNFAIP6 in osteoarthritis with type 2 diabetes mellitus

Lines of evidence have indicated that type 2 diabetes mellitus (T2DM) is an independent risk factor for osteoarthritis (OA) progression. However, the study focused on the relationship between T2DM and OA at the transcriptional level remains empty. We downloaded OA- and T2DM-related bulk RNA-sequencing and single-cell RNA sequencing data from the Gene Expression Omnibus (GEO) dataset. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to screen out hub genes between OA and T2DM, and functional enrichment was done. Single-cell sequencing analysis was further used to screen key genes on OA and T2DM datasets. Rat chondrocytes and human articular cartilage were used to validate biomarkers among OA and T2DM. Sixty-eight hub genes were obtained, which were mainly enriched in the inflammatory response. We found that the hub gene TNFAIP6 is not only closely related to OA and T2DM but also a marker of prehypertrophic chondrocytes, which are closely related to the progression of OA. TNFAIP6 was found to be significantly elevated in CD14 + monocytes in T2DM patients, and this group of cells can promote inflammation. Validation on rat chondrocytes and human cartilage showed that TNFAIP6 was highly expressed in OA and further increased in the presence of T2DM or high glucose. Our study identified several characteristic modules and hub genes in the pathogenesis of T2DM-induced OA, which may facilitate further investigation of its molecular mechanisms. Up-regulated TNFAIP6 may contribute to OA in patients with T2DM by the recruitment of pro-inflammatory CD14 + monocytes in the OA synovium, which provides a potential target for the diagnosis and treatment of T2DM-associated 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.

Interplay of Glucose Metabolism and Hippo Pathway in Chondrocytes: Pathophysiology and Therapeutic Targets

In this review, we explore the intricate relationship between glucose metabolism and mechanotransduction pathways, with a specific focus on the role of the Hippo signaling pathway in chondrocyte pathophysiology. Glucose metabolism is a vital element in maintaining proper chondrocyte function, but it has also been implicated in the pathogenesis of osteoarthritis (OA) via the induction of pro-inflammatory signaling pathways and the establishment of an intracellular environment conducive to OA. Alternatively, mechanotransduction pathways such as the Hippo pathway possess the capacity to respond to mechanical stimuli and have an integral role in maintaining chondrocyte homeostasis. However, these mechanotransduction pathways can be dysregulated and potentially contribute to the progression of OA. We discussed how alterations in glucose levels may modulate the Hippo pathway components via a variety of mechanisms. Characterizing the interaction between glucose metabolism and the Hippo pathway highlights the necessity of balancing both metabolic and mechanical signaling to maintain chondrocyte health and optimal functionality. Furthermore, this review demonstrates the scarcity of the literature on the relationship between glucose metabolism and mechanotransduction and provides a summary of current research dedicated to this specific area of study. Ultimately, increased research into this topic may elucidate novel mechanisms and relationships integrating mechanotransduction and glucose metabolism. Through this review we hope to inspire future research into this topic to develop innovative treatments for addressing the clinical challenges of OA.

Obesity, Metabolic Syndrome, and Osteoarthritis Require Integrative Understanding and Management

Osteoarthritis (OA) is a progressive chronic disease affecting the articular joints, leading to pain and disability. Unlike traditional views that primarily link OA to aging, recent understanding portrays it as a multifactorial degenerative disease of the entire joint. Emerging research highlights metabolic and immune dysregulation in OA pathogenesis, emphasizing the roles of obesity, dyslipidemia, and insulin resistance in altering joint homeostasis. Recent studies have increasingly focused on the complex role of white adipose tissue (WAT) in OA. WAT not only serves metabolic functions but also plays a critical role in systemic inflammation through the release of various adipokines. These adipokines, including leptin and adiponectin, have been implicated in exacerbating cartilage erosion and promoting inflammatory pathways within joint tissues. The overlapping global crises of obesity and metabolic syndrome have significantly impacted joint health. Obesity, now understood to contribute to mechanical joint overload and metabolic dysregulation, heightens the risk of developing OA, particularly in the knee. Metabolic syndrome compounds these risks by inducing chronic inflammation and altering macrophage activity within the joints. The multifaceted effects of obesity and metabolic syndrome extend beyond simple joint loading. These conditions disrupt normal joint function by modifying tissue composition, promoting inflammatory macrophage polarization, and impairing chondrocyte metabolism. These changes contribute to OA progression, highlighting the need for targeted therapeutic strategies that address both the mechanical and biochemical aspects of the disease. Recent advances in understanding the molecular pathways involved in OA suggest potential therapeutic targets. Interventions that modulate macrophage polarization, improve chondrocyte function, or normalize adipokine levels could serve as preventative or disease-modifying therapies. Exploring the role of diet, exercise, and pharmacological interventions in modulating these pathways offers promising avenues for reducing the burden of OA. Furthermore, such methods could prove cost-effective, avoiding the increase in access to healthcare.

Impact of diabetes mellitus on osteoarthritis: a scoping review on biomarkers

Osteoarthritis (OA) commonly affects the knee and hip joints and accounts for 19.3% of disability-adjusted life years and years lived with disability worldwide (Refs , ). Early management is important in order to avoid disability uphold quality of life (Ref. ). However, a lack of awareness of subclinical and early symptomatic stages of OA often hampers early management (Ref. ). Moreover, late diagnosis of OA among those with severe disease, at a stage when OA management becomes more complicated is common (Refs , , , ). Established risk factors for the development and progression of OA include increasing age, female, history of trauma and obesity (Ref. ). Recent studies have also drawn a link between OA and metabolic syndrome, which is characterized by insulin resistance, dyslipidaemia and hypertension (Refs , ).

Triglyceride-glucose index in the prediction of new-onset arthritis in the general population aged over 45: the first longitudinal evidence from CHARLS

OBJECTIVE

Insulin resistance (IR) imposes a significant burden on inflammatory diseases, and the triglyceride-glucose (TyG) index, which is an easily accessible indicator for detecting IR, holds great application potential in predicting the risk of arthritis. The aim of this study is to analyze the association between the TyG index and the risk of new-onset arthritis in the common population aged over 45 using a prospective cohort study design.

METHOD

This population-based cohort study involved 4418 participants from the China Health and Retirement Longitudinal Study (from Wave 1 to Wave 4). Multivariate logistic regression models were employed to investigate the association between the TyG index and new-onset arthritis, and RCS analyses were used to investigate potential non-linear relationships. Moreover, decision trees were utilized to identify high-risk populations for incident arthritis.

RESULT

Throughout a 7-year follow-up interval, it was found that 396 participants (8.96%) developed arthritis. The last TyG index quartile group (Q4) presented the highest risk of arthritis (OR, 1.39; 95% CI, 1.01, 1.91). No dose-response relationship between the TyG index and new-onset arthritis was identified (Poverall=0.068, Pnon-linear=0.203). In the stratified analysis, we observed BMI ranging from 18.5 to 24 exhibited a heightened susceptibility to the adverse effects of the TyG index on the risk of developing arthritis (P for interaction = 0.035).

CONCLUSION

The TyG index can be used as an independent risk indicator for predicting the start of new-onset arthritis within individuals aged 45 and above within the general population. Improving glucose and lipid metabolism, along with insulin resistance, may play a big part in improving the primary prevention of arthritis.

Association between higher triglyceride glucose index and increased risk of osteoarthritis: data from NHANES 2015-2020

BACKGROUND

The relationship between the triglyceride glucose (TyG) index and osteoarthritis (OA) remains unclear. The objective of this study was to examine potential associations between an elevated TyG index and an increased risk of OA prevalence.

METHODS

3,921 participants with OA from the National Health and Nutrition Examination Survey (2015-2020) were included in this study. Participants were categorized into quartiles based on TyG index, which was determined using the formula: Ln [triglyceride (mg/dL) fasting blood glucose (mg/dL)/2]. Weighted multivariable regression, subgroup analyses, and threshold effect analyses were performed to calculate the independent association between TyG index and OA.

RESULTS

A total of 25,514 people were enrolled, with a mean TyG index of 8.48 ± 0.65. The results of multivariable logistic regression analysis after full adjustment showed a significant association between higher TyG index values and an increased risk of OA. Specifically, each incremental unit increase in the TyG index was associated with a 634% higher risk of OA [OR = 7.34; 95% CI: 2.25, 23.93; p = 0.0010]. Based on interaction tests, age, gender, BMI, and smoking status did not significantly affect the relationship between the TyG index and OA, while diabetes showed a stronger positive correlation between the TyG index and OA.

CONCLUSION

An increased risk of OA was associated with a higher TyG index. TyG could be a valuable predictor of OA and offer novel perspectives on the assessment and treatment of OA.

Targeting YAP1-regulated Glycolysis in Fibroblast-Like Synoviocytes Impairs Macrophage Infiltration to Ameliorate Diabetic Osteoarthritis Progression

The interplay between immune cells/macrophages and fibroblast-like synoviocytes (FLSs) plays a pivotal role in initiating synovitis; however, their involvement in metabolic disorders, including diabetic osteoarthritis (DOA), is largely unknown. In this study, single-cell RNA sequencing (scRNA-seq) is employed to investigate the synovial cell composition of DOA. A significant enrichment of activated macrophages within eight distinct synovial cell clusters is found in DOA synovium. Moreover, it is demonstrated that increased glycolysis in FLSs is a key driver for DOA patients' synovial macrophage infiltration and polarization. In addition, the yes-associated protein 1 (YAP1)/thioredoxin-interacting protein (TXNIP) signaling axis is demonstrated to play a crucial role in regulating glucose transporter 1 (GLUT1)-dependent glycolysis in FLSs, thereby controlling the expression of a series of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) which may subsequently fine-tune the infiltration of M1-polarized synovial macrophages in DOA patients and db/db diabetic OA mice. For treatment, M1 macrophage membrane-camouflaged Verteporfin (Vt)-loaded PLGA nanoparticles (MVPs) are developed to ameliorate DOA progression by regulating the YAP1/TXNIP signaling axis, thus suppressing the synovial glycolysis and the infiltration of M1-polarized macrophages. The results provide several novel insights into the pathogenesis of DOA and offer a promising treatment approach for DOA.

Association of non-alcoholic fatty liver disease with self-reported osteoarthritis among the US adults

BACKGROUND

The association between non-alcoholic fatty liver disease (NAFLD) and osteoarthritis (OA) has not been well elucidated. The aim of the present study was to investigate the association between NAFLD and OA in the US adults.

METHODS

A cross-sectional study was performed on participants in the 2017-2018 National Health and Nutrition Examination Survey (NHANES) cycle. NAFLD was defined by the vibration-controlled transient elastography. The diagnosis of OA was based on self-reported data. Weighted multiple logistic regression models and stratified analyses were performed to explore the relationship and verify the stability of the conclusions. Sensitivity analysis using multiple imputation for missing data and propensity score matching (PSM) were performed.

RESULTS

In total, 2622 participants [Male: 1260 (47.8%)] were included in this study with a mean age of 48.1 years old (95% CI, 46.6-49.6 years old), containing 317 (12.8%) OA patients and 1140 NAFLD patients (41.5%). A logistic regression indicated a significant association between NAFLD and OA without adjustment [odds ratio (OR) = 2.05; 95% CI, 1.52-2.78]. The association remained stable after adjustment for covariates (OR = 1.72; 95% CI, 1.26-2.34). Sensitivity analysis of missing data with multiple interpolation and PSM found similar results. A significant and consistent association of NAFLD with OA was still observed in each subgroup stratified by age and metabolic syndrome (MetS). Stratified by sex, obesity, and sensitivity c-reactive protein (hs-CRP) category, a statistically significant association was only shown in females, those without obesity, and those without hyper hs-CRP. The results illustrated that the relationship between NAFLD and OA was stable in all subgroups and had no interaction.

CONCLUSIONS

NAFLD was positively correlated with OA. Given the current pandemic of NAFLD and OA, clinicians should screen for NAFLD in arthritis patients and intervene early.

Risk of metabolic abnormalities in osteoarthritis: a new perspective to understand its pathological mechanisms

Although aging has traditionally been viewed as the most important risk factor for osteoarthritis (OA), an increasing amount of epidemiological evidence has highlighted the association between metabolic abnormalities and OA, particularly in younger individuals. Metabolic abnormalities, such as obesity and type II diabetes, are strongly linked to OA, and they affect both weight-bearing and non-weight-bearing joints, thus suggesting that the pathogenesis of OA is more complicated than the mechanical stress induced by overweight. This review aims to explore the recent advances in research on the relationship between metabolic abnormalities and OA risk, including the impact of abnormal glucose and lipid metabolism, the potential pathogenesis and targeted therapeutic strategies.

Genome-wide CRISPR activation screening in senescent cells reveals SOX5 as a driver and therapeutic target of rejuvenation

Our understanding of the molecular basis for cellular senescence remains incomplete, limiting the development of strategies to ameliorate age-related pathologies by preventing stem cell senescence. Here, we performed a genome-wide CRISPR activation (CRISPRa) screening using a human mesenchymal precursor cell (hMPC) model of the progeroid syndrome. We evaluated targets whose activation antagonizes cellular senescence, among which SOX5 outperformed as a top hit. Through decoding the epigenomic landscapes remodeled by overexpressing SOX5, we uncovered its role in resetting the transcription network for geroprotective genes, including HMGB2. Mechanistically, SOX5 binding elevated the enhancer activity of HMGB2 with increased levels of H3K27ac and H3K4me1, raising HMGB2 expression so as to promote rejuvenation. Furthermore, gene therapy with lentiviruses carrying SOX5 or HMGB2 rejuvenated cartilage and alleviated osteoarthritis in aged mice. Our study generated a comprehensive list of rejuvenators, pinpointing SOX5 as a potent driver for rejuvenation both in vitro and in vivo.

Fundamentals of osteoarthritis: Inflammatory mediators in osteoarthritis

OBJECTIVES

As more has become known of the pathophysiology of osteoarthritis (OA), evidence that inflammation plays a critical role in its development and progression has accumulated. Here, we aim to review current knowledge of the complex inflammatory network in the OA joint.

DESIGN

This narrative review is presented in three main sections: local inflammation, systemic inflammation, and therapeutic implications. We focused on inflammatory mediators and their link to OA structural changes in the joint.

RESULTS

OA is characterized by chronic and low-grade inflammation mediated mostly by the innate immune system, which results in cartilage degradation, bone remodeling and synovial changes. Synovitis is regarded as an OA characteristic and associated with increased severity of symptoms and joint dysfunction. However, the articular cartilage and the subchondral bone also produce several pro-inflammatory mediators thus establishing a complex interplay between the different tissues of the joint. In addition, systemic low-grade inflammation induced by aging, obesity and metabolic syndrome can contribute to OA development and progression. The main inflammatory mediators associated with OA include cytokines, chemokines, growth factors, adipokines, and neuropeptides.

CONCLUSIONS

Future research is needed to deeper understand the molecular pathways mediating the inflammation in OA to provide new therapeutics that target these pathways, or to repurpose existing drugs.

The microbiota-metabolic syndrome axis as a promoter of metabolic osteoarthritis

The relation between obesity and osteoarthritis (OA) development has been traditionally explained as consequence of the excessive joint effort derived of overweight. However, in the last two decades a metabolic OA has been suggested through diverse molecular mechanism implying metabolic syndrome, although more investigation must be conducted to elucidate it. Metabolic syndrome is responsible of the release of diverse inflammatory cytokines, specially the increased adipokine in obesity, causing a chronic low-grade inflammatory status that alters the joint homeostasis. In this scenario, the microbiota dysbiosis contribute by worsening the low-grade chronic inflammation or causing metabolic disorders mediated by endotoxemia generated by an increased lipopolysaccharides intake. This results in joint inflammation and cartilage degradation, which contributes to the development of OA. Also, the insulin resistance provoked by type 2 Diabetes contributes to the OA development. When intake patterns are considered, some coincidences can be pointed between the food patterns associated to the metabolic syndrome and the food patterns associated to OA development. Therefore, these coincidences support the idea of a molecular mechanism of the OA development caused by the molecular mechanism generated under the metabolic syndrome status. This review points the relation between metabolic syndrome and OA, showing the connected molecular mechanisms between both pathologies as well as the shared dietary patterns that promote or prevent both pathologies.

The association between triglyceride glucose index and arthritis: a population-based study

OBJECTIVES

Insulin resistance is a well-established contributor to inflammation; however, the specific association between the triglyceride glucose (TyG) index, a biomarker reflecting insulin resistance, and arthritis remains unexplored. As a result, the main aim of this study was to examine the correlation between the TyG index and arthritis.

METHODS

This observational study used data from the National Health and Nutrition Examination Survey (NHANES), which was conducted between 2007 and 2018. To investigate the relationship between the TyG index and arthritis, various statistical analyses were employed, including weighted multivariable logistic regression analysis, subgroup analysis, curve fit analysis, and threshold effect analysis.

RESULTS

In total, 14,817 patients were enrolled in the trial, with 4,191 individuals (28.29%) diagnosed with arthritis. An increased risk of arthritis was found to be significantly correlated with higher TyG index values (odds ratio OR = 1.15, 95% confidence interval CI: 1.07-1.23), according to the results of multivariable logistic regression analysis after full adjustment. Subgroup analysis and interaction tests further indicated that the TyG index exhibited an additive effect when combined with other established risk factors, including age (OR = 1.29; 95% CI: 1.17-1.41), body mass index (BMI) (OR = 1.43; 95% CI: 1.24-1.69), and diabetes (OR = 1.20; 95% CI: 1.11-1.31). Additionally, curve fit analysis and threshold effect analysis demonstrated a nonlinear relationship with a breakpoint identified at 8.08 µmol/L.

CONCLUSION

The TyG index was positively correlated with arthritis in adults under 60 years of age in the United States who had normal weight and no diabetes. Further large-scale prospective studies are warranted for a comprehensive analysis of the role of the TyG index in arthritis.

Obesity-Related Knee Osteoarthritis-Current Concepts

The knee is the joint most frequently involved in osteoarthritis and represents a significant contributor to patient morbidity and impaired functional status. Major risk factors include genetics, age, sex, mechanical load and obesity/metabolic syndrome. Recent studies highlighted the role of obesity and metabolic syndrome in the pathogenesis of knee osteoarthritis not simply through increased mechanical loading but the systemic effects of obesity-induced inflammation. The current concept of knee osteoarthritis is that of a 'whole joint disease', which highlights the involvement not only of articular cartilage but also the synovium, subchondral bone, ligaments and muscles. Obesity and metabolic syndrome are associated with higher levels of pro-inflammatory cytokines, increased production of adipokines with both protective and destructive effects on articular cartilage, an up-regulation of proteolytic enzymes such as matrix metalloproteinases and aggrecanases and an increase in free fatty acids and reactive oxygen species induced by dyslipidemia. These findings underscore that the adequate management of knee osteoarthritis needs to include an optimization of body weight and a beneficial mobility regimen. The possible introduction of pharmacological therapy targeting specific molecules involved in the pathogenesis of obesity-related osteoarthritis will likely also be considered in future therapeutic strategies, including personalized treatment approaches.

Study of hydrogen sulfide biosynthesis in synovial tissue from diabetes-associated osteoarthritis and its influence on macrophage phenotype and abundance

Type 2 diabetes (DB) is an independent risk factor for osteoarthritis (OA). However, the mechanisms underlying the connection between both diseases remain unclear. Synovial macrophages from OA patients with DB present a marked pro-inflammatory phenotype. Since hydrogen sulphide (H₂S) has been previously described to be involved in macrophage polarization, in this study we examined H₂S biosynthesis in synovial tissue from OA patients with DB, observing a reduction of H₂S-synthetizing enzymes in this subset of individuals. To elucidate these findings, we detected that differentiated TPH-1 cells to macrophages exposed to high levels of glucose presented a lower expression of H₂S-synthetizing enzymes and an increased inflammatory response to LPS, showing upregulated expression of markers associated with M1 phenotype (i.e., CD11c, CD86, iNOS, and IL-6) and reduced levels of those related to M2 fate (CD206 and CD163). The co-treatment of the cells with a slow-releasing H₂S donor, GYY-4137, attenuated the expression of M1 markers, but failed to modulate the levels of M2 indicators. GYY-4137 also reduced HIF-1α expression and upregulated the protein levels of HO-1, suggesting their involvement in the anti-inflammatory effects of H₂S induction. In addition, we observed that intraarticular administration of H₂S donor attenuated synovial abundance of CD68⁺ cells, mainly macrophages, in an in vivo model of OA. Taken together, the findings of this study seem to reinforce the key role of H₂S in the M1-like polarization of synovial macrophages associated to OA and specifically its metabolic phenotype, opening new therapeutic perspectives in the management of this pathology.

Beyond mechanical loading: The metabolic contribution of obesity in osteoarthritis unveils novel therapeutic targets

Osteoarthritis (OA) is a prevalent progressive disease that frequently coexists with obesity. For several decades, OA was thought to be the result of ageing and mechanical stress on cartilage. Researchers' perspective has been greatly transformed when cumulative findings emphasized the role of adipose tissue in the diseases. Nowadays, the metabolic effect of obesity on cartilage tissue has become an integral part of obesity research; hoping to discover a disease-modifying drug for OA. Recently, several adipokines have been reported to be associated with OA. Particularly, metrnl (meteorin-like) and retinol-binding protein 4 (RBP4) have been recognized as emerging adipokines that can mediate OA pathogenesis. Accordingly, in this review, we will summarize the latest findings concerned with the metabolic contribution of obesity in OA pathogenesis, with particular emphasis on dyslipidemia, insulin resistance and adipokines. Additionally, we will discuss the most recent adipokines that have been reported to play a role in this context. Careful consideration of these molecular mechanisms interrelated with obesity and OA will undoubtedly unveil new avenues for OA treatment.

Metformin use and associated risk of total joint replacement in patients with type 2 diabetes: a population-based matched cohort study

BACKGROUND

It is uncertain whether metformin use is associated with reduced risk of joint replacement in patients with type 2 diabetes mellitus. We aimed to establish whether metformin use was associated with a reduced risk of total knee replacement (TKR) or total hip replacement (THR) among these patients.

METHODS

We selected patients with type 2 diabetes mellitus that was diagnosed between 2000 and 2012 from the Taiwan National Health Insurance Research Database. We used prescription time-distribution matching and propensity-score matching to balance potential confounders between metformin users and nonusers. We assessed the risks of TKR or THR using Cox proportional hazards regression.

RESULTS

We included 20 347 participants who were not treated with metformin and 20 347 who were treated with metformin, for a total of 40 694 participants (mean age 63 yr, standard deviation 11 yr; 49.8% were women) after prescription time-distribution matching. Compared with participants who did not use metformin, those who used metformin had lower risks of TKR or THR (adjusted hazard ratio [HR] 0.70, 95% confidence interval [CI] 0.60-0.81 for TKR or THR; adjusted HR 0.71, 95% CI 0.61-0.84 for TKR; adjusted HR 0.61, 95% CI 0.41-0.92 for THR) after adjustment for covariates. Propensity-score matching analyses (10 163 participants not treated with metformin v. 10 163 treated with metformin) and sensitivity analyses using inverse probability of treatment weighting and competing risk regression showed similar results.

INTERPRETATION

Metformin use in patients with type 2 diabetes mellitus was associated with a significantly reduced risk of total joint replacement. Randomized controlled clinical trials in patients with osteoarthritis are warranted to determine whether metformin is effective in decreasing the need for joint replacement.

Obesity, Inflammation, and Immune System in Osteoarthritis

Obesity remains the most important risk factor for the incidence and progression of osteoarthritis (OA). The leading cause of OA was believed to be overloading the joints due to excess weight which in turn leads to the destruction of articular cartilage. However, recent studies have proved otherwise, various other factors like adipose deposition, insulin resistance, and especially the improper coordination of innate and adaptive immune responses may lead to the initiation and progression of obesity-associated OA. It is becoming increasingly evident that multiple inflammatory cells are recruited into the synovial joint that serves an important role in pathological changes in the synovial joint. Polarization of macrophages and macrophage-produced mediators are extensively studied and linked to the inflammatory and destructive responses in the OA synovium and cartilage. However, the role of other major innate immune cells such as neutrophils, eosinophils, and dendritic cells in the pathogenesis of OA has not been fully evaluated. Although cells of the adaptive immune system contribute to the pathogenesis of obesity-induced OA is still under exploration, a quantity of literature indicates OA synovium has an enriched population of T cells and B cells compared with healthy control. The interplay between a variety of immune cells and other cells that reside in the articular joints may constitute a vicious cycle, leading to pathological changes of the articular joint in obese individuals. This review addresses obesity and the role of all the immune cells that are involved in OA and summarised animal studies and human trials and knowledge gaps between the studies have been highlighted. The review also touches base on the interventions currently in clinical trials, different stages of the testing, and their shortcomings are also discussed to understand the future direction which could help in understanding the multifactorial aspects of OA where inflammation has a significant function.

Synovial inflammation in osteoarthritis progression

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. Synovial inflammation is present in the OA joint and has been associated with radiographic and pain progression. Several OA risk factors, including ageing, obesity, trauma and mechanical loading, play a role in OA pathogenesis, likely by modifying synovial biology. In addition, other factors, such as mitochondrial dysfunction, damage-associated molecular patterns, cytokines, metabolites and crystals in the synovium, activate synovial cells and mediate synovial inflammation. An understanding of the activated pathways that are involved in OA-related synovial inflammation could form the basis for the stratification of patients and the development of novel therapeutics. This Review focuses on the biology of the OA synovium, how the cells residing in or recruited to the synovium interact with each other, how they become activated, how they contribute to OA progression and their interplay with other joint structures.

Interactions between diabetes mellitus and osteoarthritis; from animal studies to clinical data

Diabetes mellitus (DM) and osteoarthritis (OA) are commonly known metabolic diseases that affect a large segment of the world population. These two conditions share several risk factors such as obesity and aging; however, there is still no consensus regarding the direct role of DM on OA development and progression. Interestingly, both animal and human studies have yielded conflicting results, with some showing a significant role for DM in promoting OA, while others found no significant interactions between these conditions. In this review, we will discuss preclinical and clinical data that assessed the interaction between DM and OA. We will also discuss possible mechanisms associated with the effect of high glucose on the articular cartilage and chondrocytes. An emerging theme dominates the breath of published work in this area: most of the studies discussed in this review do not take into consideration the role of other factors such as the type of diabetes, age, biological sex, type of animal model, body mass index, and the use of pain medications when analyzing and interpreting data. Therefore, future studies should be more rigorous when designing experiments looking at DM and its effects on OA and should carefully account for these confounding factors, so that better approaches can be developed for monitoring and treating patients at risk of OA and DM. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Fundamentals of OA. An initiative of Osteoarthritis and Cartilage. Obesity and metabolic factors in OA

OBJECTIVE

Obesity was once considered a risk factor for knee osteoarthritis (OA) primarily for biomechanical reasons. Here we provide an additional perspective by discussing how obesity also increases OA risk by altering metabolism and inflammation.

DESIGN

This narrative review is presented in four sections: 1) metabolic syndrome and OA, 2) metabolic biomarkers of OA, 3) evidence for dysregulated chondrocyte metabolism in OA, and 4) metabolic inflammation: joint tissue mediators and mechanisms.

RESULTS

Metabolic syndrome and its components are strongly associated with OA. However, evidence for a causal relationship is context dependent, varying by joint, gender, diagnostic criteria, and demographics, with additional environmental and genetic interactions yet to be fully defined. Importantly, some aspects of the etiology of obesity-induced OA appear to be distinct between men and women, especially regarding the role of adipose tissue. Metabolomic analyses of serum and synovial fluid have identified potential diagnostic biomarkers of knee OA and prognostic biomarkers of disease progression. Connecting these biomarkers to cellular pathophysiology will require future in vivo studies of joint tissue metabolism. Such studies will help reveal when a metabolic process or a metabolite itself is a causal factor in disease progression. Current evidence points towards impaired chondrocyte metabolic homeostasis and metabolic-immune dysregulation as likely factors connecting obesity to the increased risk of OA.

CONCLUSIONS

A deeper understanding of how obesity alters metabolic and inflammatory pathways in synovial joint tissues is expected to provide new therapeutic targets and an improved definition of "metabolic" and "obesity" OA phenotypes.

Association Between Gut Microbiota and Osteoarthritis: A Review of Evidence for Potential Mechanisms and Therapeutics

Osteoarthritis (OA) is a multifactorial joint disease characterized by degeneration of articular cartilage, which leads to joints pain, disability and reduced quality of life in patients with OA. Interpreting the potential mechanisms underlying OA pathogenesis is crucial to the development of new disease modifying treatments. Although multiple factors contribute to the initiation and progression of OA, gut microbiota has gradually been regarded as an important pathogenic factor in the development of OA. Gut microbiota can be regarded as a multifunctional “organ”, closely related to a series of immune, metabolic and neurological functions. This review summarized research evidences supporting the correlation between gut microbiota and OA, and interpreted the potential mechanisms underlying the correlation from four aspects: immune system, metabolism, gut-brain axis and gut microbiota modulation. Future research should focus on whether there are specific gut microbiota composition or even specific pathogens and the corresponding signaling pathways that contribute to the initiation and progression of OA, and validate the potential of targeting gut microbiota for the treatment of patients with OA.

Toward Development of a Diabetic Synovium Culture Model

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation and inflammation of synovium, the specialized connective tissue that envelops the diarthrodial joint. Type 2 diabetes mellitus (DM) is often found in OA patients, with nearly double the incidence of arthritis reported in patients with diabetes (52%) than those without it (27%). The correlation between OA and DM has been attributed to similar risk factors, namely increasing age and joint loading due to obesity. However, a potential causative link is not well understood due to comorbidities involved with treating diabetic patients, such as high infection rates and poor healing response caused by hyperglycemia and insulin resistance. The purpose of this study was to investigate the effect of hyperglycemic and insulin culture conditions on synovium properties. It was hypothesized that modeling hyperglycemia-induced insulin resistance in synovium would provide novel insights of OA pathogenesis in DM patients. To simulate DM in the synovial joint, healthy synovium was preconditioned in either euglycemic (EG) or hyperglycemic (HG) glucose concentrations with insulin in order to induce the biological response of the diseased phenotype. Synovium biochemical composition was evaluated to determine ECM remodeling under hyperglycemic culture conditions. Concurrent changes in AKT phosphorylation, a signaling pathway implicated in insulin resistance, were measured along with gene expression data for insulin receptors, glucose transporters, and specific glycolysis markers involved in glucose regulation. Since fluid shear stress arising during joint articulation is a relevant upstream stimulus for fibroblast-like synoviocytes (FLS), the predominant cell type in synovium, FLS mechanotransduction was evaluated via intracellular calcium ([Ca²⁺]_i). Incidence and length of primary cilia, a critical effector of cell mechanosensing, were measured as potential mechanisms to support differences in [Ca²⁺]_i responses. Hyperglycemic culture conditions decreased collagen and GAG content compared to EG groups, while insulin recovered ECM constituents. FLS mechanosensitivity was significantly greater in EG and insulin conditions compared to HG and non-insulin treated groups. Hyperglycemic treatment led to decreased incidence and length of primary cilia and decreased AKT phosphorylation, providing possible links to the mechanosensing response and suggesting a potential correlation between glycemic culture conditions, diabetic insulin resistance, and OA development.

Osteoarthritis: Mechanistic Insights, Senescence, and Novel Therapeutic Opportunities

Osteoarthritis (OA) is the most common joint disease. In the last years, the research community has focused on understanding the molecular mechanisms that led to the pathogenesis of the disease, trying to identify different molecular and clinical phenotypes along with the discovery of new therapeutic opportunities. Different types of cell-to-cell communication mechanisms have been proposed to contribute to OA progression, including mechanisms mediated by connexin43 (Cx43) channels or by small extracellular vesicles. Furthermore, changes in the chondrocyte phenotype such as cellular senescence have been proposed as new contributors of the OA progression, changing the paradigm of the disease. The use of different drugs able to restore chondrocyte phenotype, to reduce cellular senescence and senescence-associated secretory phenotype components, and to modulate ion channel activity or Cx43 appears to be promising therapeutic strategies for the different types of OA. In this review, we aim to summarize the current knowledge in OA phenotypes related with aging and tissue damage and the new therapeutic opportunities currently available.

Metabolic Syndrome Predisposes to Osteoarthritis: Lessons from Model System

OBJECTIVE

The present study aims to assess for temporal changes in tibial subchondral bone and cartilage in WNIN/Gr-Ob rats (portraying obesity, insulin resistance, dyslipidemia, impaired glucose tolerance, hypertension) in comparison with Wistar controls (WNIN) using anthropometry, micro-computed tomography (micro-CT), scanning electron microscopy (SEM), histopathology, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence.

DESIGN

Body weight, abdominal circumference, body mass index (BMI), lean/fat mass, serum tumor necrosis factor (TNF)-α levels were measured (ELISA), followed by ultrastructural analysis of tibial subchondral bone (micro-CT) and cartilage architecture (histopathology and SEM) in WNIN/Gr-Ob and WNIN rats with age (3, 6 and 9 months). Additionally, primary cultures of articular chondrocytes isolated from 6-month-old WNIN/Gr-Ob and WNIN rats were assessed for matrix metalloproteinase (MMP)-13 and Collagen type II (COL2A1) by immunofluorescence.

RESULTS

WNIN/Gr-Ob rats exhibited frank obesity with increased BMI, lean and fat mass vis-à-vis significantly higher levels of serum TNF-α (6>9>3 months) as compared with the controls. With an increase in BMI, WNIN/Gr-Ob rats presented with tibial cartilage fibrillation, erosion, osteophyte formation (6 months) and subchondral bone cyst (9 months) confirmed by histology and SEM. An increase in subchondral trabecular bone volume (sclerosis with decreased plate porosity) was observed in all ages in WNIN/Gr-Ob rats compared to their Control. Gaining insights, primary cultures of articular chondrocytes complemented with altered cellular expressions of COL2A1 and MMP-13 from WNIN/Gr-Ob rats, indicating osteoarthritis (OA) progression.

CONCLUSION

Multiple metabolic perturbations featured in WNIN/Gr-Ob rats were effective to induce spontaneous OA-like degenerative changes affecting knee joints akin to human OA.

Cholesterol metabolism related genes in osteoarthritis

Cholesterol homeostasis plays a significant role in skeletal development and the dysregulation of cholesterol-related mechanism has been shown to be involved in the development of cartilage diseases including osteoarthritis (OA). Epidemiological studies have shown an association between elevated serum cholesterol levels and OA. Furthermore, abnormal lipid accumulation in chondrocytes as a result of abnormal regulation of cholesterol homeostasis has been demonstrated to be involved in the development of OA. Although, many in vivo and in vitro studies support the connection between cholesterol and cartilage degradation, the mechanisms underlying the complex interactions between lipid metabolism, especially HDL cholesterol metabolism, and OA remain unclear. The current review aims to address this problem and focuses on key molecular players of the HDL metabolism pathway and their role in ΟΑ pathogenesis. Understanding the complexity of biological processes implicated in OA pathogenesis, such as cholesterol metabolism, may lead to new targets for drug therapy of OA patients.

CXCL2 Impairs Functions of Bone Marrow Mesenchymal Stem Cells and Can Serve as a Serum Marker in High-Fat Diet-Fed Rats

In modern society excessive consumption of a high-fat diet (HFD) is a significant risk factor for many diseases such as diabetes, osteoarthritis and certain cancers. Resolving cellular and molecular mechanisms underlying HFD-associated disorders is of great importance to human health. Mesenchymal stem cells (MSCs) are key players in tissue homeostasis and adversely affected by prolonged HFD feeding. Low-grade systemic inflammation induced by HFD is characterized by increased levels of pro-inflammatory cytokines and alters homeostasis in many organs. However, whether, which and how HFD associated inflammatory cytokines impair MSCs remain unclear. Here we demonstrated that HFD induced serum cytokines disturbances, especially a continuous elevation of serum CXCL2 level in rats. Coincidentally, the differentially expressed genes (DEGs) of bone marrow MSCs (BMSCs) which functions were impaired in HFD rats were enriched in cytokine signaling. Further mechanism analysis revealed that CXCL2 treatment in vitro suppresses the adipogenic potential of BMSCs via Rac1 activation, and promoted BMSC migration and senescence by inducing over-production of ELMO1 and reactive oxygen species (ROS) respectively. Moreover, we found that although glycolipid metabolism indicators can be corrected, the CXCL2 elevation and BMSC dysfunctions cannot be fully rescued by diet correction and anti-inflammatory aspirin treatment, indicating the long-lasting deleterious effects of HFD on serum CXCL2 levels and BMSC functions. Altogether, our findings identify CXCL2 as an important regulator in BMSCs functions and may serve as a serum marker to indicate the BMSC dysfunctions induced by HFD. In addition, our findings underscore the intricate link among high-fat intake, chronic inflammation and BMSC dysfunction which may facilitate development of protective strategies for HFD associated diseases.

Comparative evaluation of inflammatory parameters and substitute insulin resistance indices in elderly women with and without type 2 diabetes mellitus

PURPOSE

To analyze the influence of inflammatory parameters and substitute insulin resistance indices on the risk of type 2 diabetes mellitus (DM) development in elderly women, as well as to compare anthropometric measures and metabolic parameters according to the presence of type 2 DM and HbA1c levels.

PATIENTS AND METHODS

One hundred and twenty elderly women (67.9 ± 6.0 years) were submitted to anthropometric analysis, determination of inflammatory and metabolic parameters. They also underwent indices of lipid accumulation product (LAP), high density triglyceride/lipoprotein ratio (TG/HDL), triglyceride glucose index (TyG), as well as TyG by body mass index (BMI) ratio (TyG-BMI) assessment.

RESULTS

Body mass index, tumor necrosis factor alpha, interleukin-2, blood glucose, TG, LAP, TG/HDL, TyG and TyG-BMI were significantly higher in elderly women with DM compared to non-diabetic women. LAP ≥ 55.4 (OR = 2.29; P = .027); TyG ≥ 8.8 (OR = 3.52; P < .001) and TyG-BMI ≥ 264.8 (OR = 3.54; P = .001) were identified as risk factors for DM.

CONCLUSION

High pro-inflammatory parameters, low levels of anti-inflammatory markers and higher levels of substitute insulin resistance indices are risk predictors for DM development in elderly women in primary health care.

Insulin Signaling in Arthritis

Inflammatory arthritis is burdened by an increased risk of metabolic disorders. Cytokines and other mediators in inflammatory diseases lead to insulin resistance, diabetes and hyperlipidemia. Accumulating evidence in the field of immunometabolism suggests that the cause-effect relationship between arthritis and metabolic abnormalities might be bidirectional. Indeed, the immune response can be modulated by various factors such as environmental agents, bacterial products and hormones. Insulin is produced by pancreatic cells and regulates glucose, fat metabolism and cell growth. The action of insulin is mediated through the insulin receptor (IR), localized on the cellular membrane of hepatocytes, myocytes and adipocytes but also on the surface of T cells, macrophages, and dendritic cells. In murine models, the absence of IR in T-cells coincided with reduced cytokine production, proliferation, and migration. In macrophages, defective insulin signaling resulted in enhanced glycolysis affecting the responses to pathogens. In this review, we focalize on the bidirectional cause-effect relationship between impaired insulin signaling and arthritis analyzing how insulin signaling may be involved in the aberrant immune response implicated in arthritis and how inflammatory mediators affect insulin signaling. Finally, the effect of glucose-lowering agents on arthritis was summarized.

Reduced Muscle Strength Is Associated With Insulin Resistance in Type 2 Diabetes Patients With Osteoarthritis

CONTEXT

Type 2 diabetes is associated with a greater risk for musculoskeletal disorders, yet its impact on joint function remains unclear.

OBJECTIVE

We hypothesized that patients with type 2 diabetes and osteoarthritis would exhibit musculoskeletal impairment, which would associate with insulin resistance and distinct microRNA profiles.

METHODS

Participants of the German Diabetes Study with type 2 diabetes (T2D, n = 39) or normal glucose tolerance (CON, n = 27), both with (+OA) or without osteoarthritis (-OA) underwent intravenous glucose tolerance and hyperinsulinemic-euglycemic clamp tests. Musculoskeletal function was assessed by isometric knee extension strength (KES), grip strength, range of motion (ROM), and balance skills, while neural function was measured by nerve conductance velocity (NCV). Arthritis-related symptoms were quantified using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire, serum arthritis-related microRNA using quantitative polymerase chain reaction.

RESULTS

Insulin sensitivity was lower in T2D+OA vs T2D-OA (4.4 ± 2.0 vs 5.7 ± 3.0 mg* kg-1*min-1) and in CON+OA vs CON-OA (8.1 ± 2.0 vs 12.0 ± 2.6 mg*kg-1,*min-1, both P < .05). In T2D+OA, KES and ROM were 60% and 22% lower than in CON+OA, respectively (both P < .05). Insulin sensitivity correlated positively with KES (r = 0.41, P < .05) among T2D, and negatively with symptom severity in CON and T2D (r = -0.60 and r = -0.46, respectively, P < .05). CON+OA and T2D+OA had inferior balance skills than CON-OA, whereas NCV was comparable in T2D+OA and T2D-OA. Expression of arthritis-related microRNAs was upregulated in T2D compared to CON, but downregulated in CON+OA compared to CON-OA (P < .05), and did not differ between T2D+OA and T2D-OA.

CONCLUSION

Musculoskeletal impairment and osteoarthritis-related symptoms are associated with insulin resistance. Type 2 diabetes can mask changes in arthritis-related microRNA profiles.

AMD3465 (hexahydrobromide) rescues the MG63 osteoblasts against the apoptosis induced by high glucose

Diabetic osteoporosis (DOP) is a serious complication of diabetes, which brings a heavy burden to patients' families and society. The SDF-1/CXCR4 signal pathway may be a target to prevent articular cartilage degeneration. In this study, we studied the effects of high glucose (20 mmol/L) and CXCR4 antagonist AMD3465 (10 μmol/L) on the apoptosis and gene expression of osteoblast-like cells MG63 to determine a new treatment for DOP. CCK8 and clone formation assays confirmed that AMD3465 resisted the decrease of proliferation caused by high glucose. According to the results of scratch and transwell analysis, AMD3465 could remedy the decrease of cell migration and invasion induced by high glucose. The results of flow cytometry analysis and double staining with Hoechst and PI showed AMD3465 corrected the apoptosis induced by high glucose. In addition, high glucose regulated the expression of cell cycle- and apoptosis-related proteins, while AMD3465 blocked the regulation of high glucose. Furthermore, high glucose enhanced the expression levels of SDF-1 and CXCR4 in MG63 cells, as well as the release of MMP1, 3, 9 and 13. AMD3465 inhibited the release of MMPs. The results showed that AMD3465 resisted the apoptosis of MG63 cells induced by high glucose, provided a new strategy for the therapy of DOP.

-308G/A polymorphism of tumor necrosis factor alpha (TNF-α) gene and metabolic syndrome susceptibility: a meta-analysis

Many studies tried to assess the relationship between -308G/A polymorphism of tumor necrosis factor alpha (TNF-α) gene and risk of metabolic syndrome (MS), but their results were contradictory. This meta-analysis aimed to precisely evaluate this association. A systematic literature search was performed in Pubmed database and WanFang Med Online, STATA software 14.0 was used for the meta-analysis. Eleven independent studies containing 3277 cases and 3312 controls were included in our meta-analysis. In overall analysis, significant association was found between -308G/A polymorphism of TNF-α and MS in both allele model (OR 1.47, 95% CI 1.09–1.98, P 0.013) and dominant model (OR 1.77, 95% CI 1.21–2.58, P 0.003). In the subgroup analysis, the A allele was associated with increased risk of MS in Asia group (allele model: OR 1.82 95% CI 1.31–2.53, P < 0.001; dominant model: OR 2.30, 95% CI 1.64–3.21 P < 0.001; homozygous model: OR 2.29, 95% CI 1.31–4.01, P 0.004), and decreased risk of MS in Europe group (dominant model: OR 0.83, 95% CI 0.70–0.99, P < 0.001; recessive model: OR 0.51, 95% CI 0.28–0.92, P 0.025; homozygous model: OR 0.49 95% CI 0.27–0.89, P 0.02). The A allele also appeared to linked to increased risk of MS in CDS group and IDF groups. No significant association was observed in NCEPATPIII group. Our results suggested that -308G/A of TNF-α gene was a risk factor for MS, but it may played different roles in different ethnics, further studies with larger sample size and more other ethnics should be performed to confirm our conclusions.

The gut microbiome-joint connection: implications in osteoarthritis

Supplemental Digital Content is available in the text

Osteoarthritis is a debilitating disease leading to joint degeneration, inflammation, pain, and disability. Despite efforts to develop a disease modifying treatment, the only accepted and available clinical approaches involve palliation. Although many factors contribute to the development of osteoarthritis, the gut microbiome has recently emerged as an important pathogenic factor in osteoarthritis initiation and progression. This review examines the literature to date regarding the link between the gut microbiome and osteoarthritis.

Adipose tissue is a critical regulator of osteoarthritis

Osteoarthritis (OA), the leading cause of pain and disability worldwide, disproportionally affects individuals with obesity. The mechanisms by which obesity leads to the onset and progression of OA are unclear due to the complex interactions among the metabolic, biomechanical, and inflammatory factors that accompany increased adiposity. We used a murine preclinical model of lipodystrophy (LD) to examine the direct contribution of adipose tissue to OA. Knee joints of LD mice were protected from spontaneous or posttraumatic OA, on either a chow or high-fat diet, despite similar body weight and the presence of systemic inflammation. These findings indicate that adipose tissue itself plays a critical role in the pathophysiology of OA. Susceptibility to posttraumatic OA was reintroduced into LD mice using implantation of a small adipose tissue depot derived from wild-type animals or mouse embryonic fibroblasts that undergo spontaneous adipogenesis, implicating paracrine signaling from fat, rather than body weight, as a mediator of joint degeneration.

Association Among Lipid Accumulation Product, Chinese Visceral Obesity Index and Diabetic Retinopathy in Patients with Type 2 Diabetes: A Cross-Sectional Study

BACKGROUND AND AIM

Obesity often coexists with diabetes, especially abdominal obesity, recognized as a risk factor for diabetic complications. Diabetic retinopathy (DR), as one of the most common microvascular complications of diabetes, may be associated with these indices. Lipid accumulation product (LAP) and Chinese visceral obesity index (CVAI) are novel visceral obesity indicators, which have been proven to be an influential factor predicting type 2 diabetes (T2DM). However, the correlation among LAP, CVAI, and DR still lacks systematic research in T2DM. The study aimed to explore the relationship among LAP, CVAI levels in different DR stages of T2DM patients and the diagnostic efficacy of LAP and CVAI for DR.

METHODS

A total of 263 participants were recruited in this cross-sectional study. We enrolled 169 patients with T2DM, divided into the non-DR group (NDR, n = 61), non-proliferative DR group (NPDR, n = 55), and proliferative DR group (PDR, n = 53). And we also enrolled 94 healthy control participants. We collected demographic, anthropometric, and biochemical data on each subject. LAP and CVAI are calculated according to different formulas for men and women.

RESULTS

Compared with the control group, LAP and CVAI were significantly higher (P < 0.05). After adjusting for confounding factors, LAP (OR: 1.029, 95CI%: 1.010-1.049, P < 0.05), WC (OR: 1.073, 95CI%: 1.009-1.141, P < 0.05) and CVAI (OR: 1.017, 95CI%: 1.000-1.033, P < 0.05) were all associated with an increased risk of DR. Furthermore, increased LAP (OR: 1.020, 95% CI: 0.100-0.290) is associated with DR severity (P < 0.001). Moreover, the LAP had the most significant area under the receiver operating characteristics (ROC) curve (AUC) (AUC = 0.728, 95% CI: 0.653-0.804).

CONCLUSION

A high LAP is associated with an increased risk of DR in T2DM patients, and the LAP index appears to be a good predictor of DR risk and severity in patients with T2DM, compared with BMI, WC, and CVAI.

L-PGDS deficiency accelerated the development of naturally occurring age-related osteoarthritis

Osteoarthritis (OA) is the most common musculoskeletal disorder among the elderly. It is characterized by progressive cartilage degradation, synovial inflammation, subchondral bone remodeling and pain. Lipocalin prostaglandin D synthase (L-PGDS) is responsible for the biosynthesis of PGD₂, which has been implicated in the regulation of inflammation and cartilage biology. This study aimed to evaluate the effect of L-PGDS deficiency on the development of naturally occurring age-related OA in mice.

OA-like structural changes were assessed by histology, immunohistochemistry, and micro–computed tomography. Pain related behaviours were assessed using the von Frey and the open-field assays.

L-PGDS deletion promoted cartilage degradation during aging, which was associated with enhanced expression of extracellular matrix degrading enzymes, matrix metalloprotease 13 (MMP-13) and a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5), and their breakdown products, C1,2C, VDIPEN and NITEG. Moreover, L-PGDS deletion enhanced subchondral bone changes, but had no effect on its angiogenesis. Additionally, L-PGDS deletion increased mechanical sensitivity and reduced spontaneous locomotor activity. Finally, we showed that the expression of L-PGDS was elevated in aged mice. Together, these findings indicate an important role for L-PGDS in naturally occurring age-related OA. They also suggest that L-PGDS may constitute a new efficient therapeutic target in OA.

Potential emerging roles of the novel adipokines adipolin/CTRP12 and meteorin-like/METRNL in obesity-osteoarthritis interplay

BACKGROUND

Several insights into obesity-osteoarthritis (OA) relationship have been recently highlighted. Adipolin and metrnl are new adipokines also secreted by chondrocytes. However, their role in OA, and obesity-OA interplay hasn't been elucidated. Therefore, this study was designed to investigate the circulating as well as synovial fluid (SF) levels of adipolin and metrnl in osteoarthritic-patients compared to non-osteoarthritic subjects, and to study their association with OA-severity, dyslipidemia and insulin resistance (IR).

METHODS

Patients with osteoarthritis and obesity (n = 30), and subjects with obesity not suffering OA (n = 25) were enrolled in the current study. Circulating and SF-levels of adipolin, metrnl, and insulin, as well as SF-levels of matrix-metalloproteinase-13 (MMP-13) were measured by ELISA. Knee-radiographs using X-ray were done to determine OA-severity, and investigate its association with adipokines' levels.

RESULTS

Serum and SF-adipolin levels showed tendency to be lower in OA-patients compared to non-OA-subjects; serum: 0.64 [0.45-0.85] and 0.73 [0.62-0.78] ng/ml, p = 0.174, and SF: 0.53 [0.34-0.69] and 0.63 [0.44-0.74] ng/ml, p = 0.353, respectively. Additionally, serum adipolin showed negative-association with SF-MMP-13. However, when stratifying OA-patients into various severity grades, serum adipolin levels did not show a significant difference between them. Regarding serum metrnl, it was significantly lower in OA-patients compared to non-OA-subjects; 19.68 [10.40-53.40] and 48.83 [20.80-86.60] pg/ml, respectively, p = 0.018. Surprisingly, SF-metrnl levels were higher in OA-patients compared to non-OA-subjects; 912 [367-1524] and 315 [125-484] pg/ml, respectively, p = 0.007. SF-metrnl showed positive-association with insulin resistance, and negative-association with SF-MMP-13. Moreover, higher serum metrnl levels were found to be slightly associated with lower likelihood of OA in subjects with obesity; OR = 0.978, CI (0.960- 0.996), p = 0.02, and its levels were also found to be relatively lower in grade-4 compared to the less severe OAgrades.

CONCLUSIONS

Metrnl, and to a lesser extent adipolin seem to be interrelated with OA. Different in-context regulatory mechanisms for metrnl production from various tissues are strongly suggested. Importantly, the findings of the current study shed lights on metrnl as a potential novel mediator and therapeutic target to consider in obesity-OA interplay.

Metabolic syndrome and subchondral bone alterations: The rise of osteoarthritis - A review

Metabolic syndrome (MS) has become one of the top major health burdens for over three decades not only due to its effects on cardiovascular health but also its implications in orthopedics. Extensive research has shown that MS is tightly linked to osteoarthritis and inflammation, a process which appears to primarily occur in the subchondral bone via the incidence of bone-marrow lesions (BMLs). Numerous studies identify obesity, dyslipidemia, insulin resistance and hypertension as the top metabolic risk factors, the so-called "deadly quartet". These factors are responsible for the disruptive physiological processes that culminate in detrimental alterations within the subchondral bone, cartilage damage and, overall, the predominant pro-inflammatory joint microenvironment. Although it has long been thought that osteoarthritis was limited to the cartilage component of the joint, other studies indicate that the disease may originate from the harmful alterations that occur primarily in the subchondral bone, especially via means of vascular pathology. Since metabolic risk factors are manageable to a certain extent, it is therefore possible to decelerate the progression of OA and mitigate its devastating effects on the subchondral bone and subsequent articular cartilage damage.

METHODS

Literature was reviewed using PubMed and Google Scholar in order to find a correlation between metabolic syndrome and osteoarthritic progression. The investigation included a combination of nomenclature such as: "metabolic syndrome", "obesity", "insulin resistance", "hypertension", "dyslipidemia", "low-grade systemic inflammation", "osteoarthritis", "subchondral bone", "cartilage" and "inflammatory biomarkers".

CONCLUSION

Based on several studies, there seems to be a significant association between The Deadly Quartet (metabolic syndrome), dysregulation of both pro- and anti-inflammatory biomarkers, and osteoarthritic progression arising from unbridled systemic inflammation.

Harmful effects of high amounts of glucose on the immune system: An updated review

Release and storage of energy can be regulated by the metabolic parameter dependent on the central nervous system. Macrophages are one of the most professional antigen-presenting cells that are formed by the accumulation of dead or damaged cells or in response to the infection, which has the main function of phagocytosis, secretion of cytokines, and presenting antigen to T cells. A proper immune response is needed for the production of effector cytokines along with comprehensive and rapid cell proliferation and growth. Activation of the immune system and immune cells is needed to increase glucose metabolism. When the immune system responds to pathogens, chemokines inform immune cells such as macrophages and T cells to travel to the infected area. Although glucose is vital for the proper function of immune cells and their proliferation, a high amount of glucose may lead to impaired function of the immune system and pathological conditions. However, a suitable amount of glucose is indispensable for the immune system, but its elevated amount leads to excessive proinflammatory cytokines production. In this study, we focused on the master regulatory role of glucose on the immune system.

Gene therapy for follistatin mitigates systemic metabolic inflammation and post-traumatic arthritis in high-fat diet-induced obesity

Obesity-associated inflammation and loss of muscle function play critical roles in the development of osteoarthritis (OA); thus, therapies that target muscle tissue may provide novel approaches to restoring metabolic and biomechanical dysfunction associated with obesity. Follistatin (FST), a protein that binds myostatin and activin, may have the potential to enhance muscle formation while inhibiting inflammation. Here, we hypothesized that adeno-associated virus 9 (AAV9) delivery of FST enhances muscle formation and mitigates metabolic inflammation and knee OA caused by a high-fat diet in mice. AAV-mediated FST delivery exhibited decreased obesity-induced inflammatory adipokines and cytokines systemically and in the joint synovial fluid. Regardless of diet, mice receiving FST gene therapy were protected from post-traumatic OA and bone remodeling induced by joint injury. Together, these findings suggest that FST gene therapy may provide a multifactorial therapeutic approach for injury-induced OA and metabolic inflammation in obesity.

Identifying effector molecules, cells, and cytokines of innate immunity in OA

Inflammatory changes are observed in affected joints of osteoarthritis (OA) patients and are thought to be involved in the pathology that develops along OA progression. This narrative review provides an overview of the various cell types that are present in the joint during OA and which alarmins, cytokines, chemokines, growth factors, and other mediators they produce. Moreover, the involvement of more systemic processes like inflammaging and its associated cellular senescence in the context of OA are discussed.

Osteoarthritis and type 2 diabetes: From pathogenetic factors to therapeutic intervention

Over the last decades, osteoarthritis (OA) and type 2 diabetes (T2D) prevalence increased due to the global ageing population and the pandemic obesity. They currently affect a substantial part of the Western world population and are characterized by enhancing the risk of disability and reduction of quality of life. OA is a multifactorial condition whose development derives from the interaction between individual and environmental factors: The best known primarily include age, female gender, genetic determinants, articular biomechanics, and obesity (OB). Given the high prevalence of OA and T2D and their association with OB and inflammation, several studies have been conducted to investigate the causative role of biological characteristics proper to T2D on the development of OA. This review aims to analyse the relationship between of OA and T2D, in order to explain the pathophysiological drivers of the degenerative process and to delineate possible targets to which appropriate treatments may be addressed in the near future.

Impact of age on host responses to diet-induced obesity: Development of joint damage and metabolic set points

BACKGROUND

Osteoarthritis is one of the leading causes of pain and disability worldwide, and a large percentage of patients with osteoarthritis are individuals who are also obese. In recent years, a series of animal models have demonstrated that obesity-inducing diets can result in synovial joint damage (both with and without the superimposition of trauma), which may be related to changes in percentage of body fat and a series of low-level systemic inflammatory mediators. Of note, there is a disparity between whether the dietary challenges commence at weaning, representing a weanling onset, or at skeletal maturity, representing an adult onset of obesity. We wished to evaluate the effect of the dietary exposure time and the age at which animals are exposed to a high-fat and high-sucrose (HFS) diet to determine whether these factors may result in disparate outcomes, as there is evidence suggesting that these factors result in differential metabolic disturbances. Based on dietary exposure time, we hypothesized that rats fed an HFS diet for 14 weeks from weaning (HFS Weanling) would demonstrate an increase in knee joint damage scores, whereas rats exposed to the HFS diet for 4 weeks, starting at 12 weeks of age (HFS Adult) and rats exposed to a standard chow diet (Chow) would not display an increase in knee joint damage scores.

METHODS

Male Sprague-Dawley rats were fed either an HFS diet for 14 weeks from weaning (HFS Weanling) or an HFS diet for 4 weeks, starting at 12 weeks of age (HFS Adult). At sacrifice, joints were scored using the modified Mankin Criteria, and serum was analyzed for a defined subset of inflammatory markers (Interleukin-6, leptin, monocyte chemoattractant protein-1, and tumor necrosis factor α).

RESULTS

When the HFS Weanling and HFS Adult groups were compared, both groups had a similar percent of body fat, although the HFS Weanling group had a significantly greater body mass than the HFS Adult group. The HFS Weanling and HFS Adult animals had a significant increase in body mass and percentage of body fat when compared to the Chow group. Although knee joint damage scores were low in all 3 groups, we found, contrary to our hypothesis, that the HFS Adult group had statistically significant greater knee joint damage scores than the Chow and HFS Weanling groups. Furthermore, we observed that the HFS Weanling group did not have significant differences in knee joint damage scores relative to the Chow group.

CONCLUSION

These findings indicate that the HFS Weanling animals were better able to cope with the dietary challenge of an HFS diet than the HFS Adult group. Interestingly, when assessing various serum proinflammatory markers, no significant differences were detected between the HFS Adult and HFS Weanling groups. Although details regarding the mechanisms underlying an increase in knee joint damage scores in the HFS Adult group remain to be elucidated, these findings indicate that dietary exposure time maybe less important than the age at which an HFS diet is introduced. Moreover, increases in serum proinflammatory mediators do not appear to be directly linked to knee joint damage scores in the HFS Weanling group animals but may be partially responsible for the observed knee joint damage in the adults over the very short time of exposure to the HFS diet.