Metformin Attenuates Monosodium-Iodoacetate-Induced Osteoarthritis via Regulation of Pain Mediators and the Autophagy-Lysosomal Pathway

Zwitterion-Lubricated Hydrogel Microspheres Encapsulated with Metformin Ameliorate Age-Associated Osteoarthritis

Chondrocyte senescence and reduced lubrication play pivotal roles in the pathogenesis of age-related osteoarthritis (OA). In the present study, highly lubricated and drug-loaded hydrogel microspheres are designed and fabricated through the radical polymerization of sulfobetaine (SB)-modified hyaluronic acid methacrylate using microfluidic technology. The copolymer contains a large number of SB and carboxyl groups that can provide a high degree of lubrication through hydration and form electrostatic loading interactions with metformin (Met@SBHA), producing a high drug load for anti-chondrocyte senescence. Mechanical, tribological, and drug release analyses demonstrated enhanced lubricative properties and prolonged drug dissemination of the Met@SBHA microspheres. RNA sequencing (RNA-seq) analysis, network pharmacology, and in vitro assays revealed the extraordinary capacity of Met@SBHA to combat chondrocyte senescence. Additionally, inducible nitric oxide synthase (iNOS) has been identified as a promising protein modulated by Met in senescent chondrocytes, thereby exerting a significant influence on the iNOS/ONOO-/P53 pathway. Notably, the intra-articular administration of Met@SBHA in aged mice ameliorated cartilage senescence and OA pathogenesis. Based on the findings of this study, Met@SBHA emerges as an innovative and promising strategy in tackling age-related OA serving the dual function of enhancing joint lubrication and mitigating cartilage senescence.

Metformin as adjuvant therapy in obese knee osteoarthritis patients

AIMS

This study aimed at investigating the efficacy of metformin as adjuvant therapy for obese knee osteoarthritis (OA) patients, considering its anti-inflammatory and cartilage-protective effects.

PATIENTS AND METHODS

In this randomized, double-blind, placebo-controlled study, 50 obese knee OA patients were assigned randomly to two groups, the metformin group (n = 25) which was treated with metformin 500 mg orally BID plus celecoxib 200 mg orally once daily, and the placebo group (n = 25) which was treated with placebo tablets BID plus celecoxib 200 mg orally once daily for 12 weeks. Cartilage Oligomeric Matrix Protein (COMP), C-terminal cross-linked telopeptide of type I collagen (CTX-1), and Interleukin 1-beta (IL-1β) serum levels were measured, while Western Ontario and McMaster Universities Arthritis Index (WOMAC) score assessed knee pain, stiffness, and physical function at baseline and after 12 weeks.

RESULTS

Following a 12-week treatment, the metformin group exhibited significantly reduced levels of COMP, CTX-1, and IL-1β in the serum compared to the placebo group (p = 0.0081, p = 0.0106, and p = 0.0223, respectively). Furthermore, metformin group produced significant improvements in WOMAC total scale (p < 0.0001), specifically in knee pain, stiffness, and physical function compared to placebo group (p < 0.0001, p < 0.0001, and p < 0.0001, respectively).

CONCLUSION

Metformin as an adjuvant therapy in obese knee OA patients may have beneficial effects on cartilage degradation and inflammation, as evidenced by the significant decreases in serum COMP, CTX-1, and IL-1β levels. Additionally, metformin may improve clinical outcomes, as shown by the significant improvements in WOMAC scores.

CLINICALTRIALS

GOV ID

NCT05638893/Registered December 6, 2022 - Retrospectively.

Targeting lysosomal quality control as a therapeutic strategy against aging and diseases

Previously, lysosomes were primarily referred to as the digestive organelles and recycling centers within cells. Recent discoveries have expanded the lysosomal functional scope and revealed their critical roles in nutrient sensing, epigenetic regulation, plasma membrane repair, lipid transport, ion homeostasis, and cellular stress response. Lysosomal dysfunction is also found to be associated with aging and several diseases. Therefore, function of macroautophagy, a lysosome-dependent intracellular degradation system, has been identified as one of the updated twelve hallmarks of aging. In this review, we begin by introducing the concept of lysosomal quality control (LQC), which is a cellular machinery that maintains the number, morphology, and function of lysosomes through different processes such as lysosomal biogenesis, reformation, fission, fusion, turnover, lysophagy, exocytosis, and membrane permeabilization and repair. Next, we summarize the results from studies reporting the association between LQC dysregulation and aging/various disorders. Subsequently, we explore the emerging therapeutic strategies that target distinct aspects of LQC for treating diseases and combatting aging. Lastly, we underscore the existing knowledge gap and propose potential avenues for future research.

The dysregulated autophagy in osteoarthritis: Revisiting molecular profile

The risk factors of osteoarthritis (OA) are different and obesity, lifestyle, inflammation, cell death mechanisms and diabetes mellitus are among them. The changes in the biological mechanisms are considered as main regulators of OA pathogenesis. The dysregulation of autophagy is observed in different human diseases. During the pathogenesis of OA, the autophagy levels (induction or inhibition) change. The supportive and pro-survival function of autophagy can retard the progression of OA. The protective autophagy prevents the cartilage degeneration. Moreover, autophagy demonstrates interactions with cell death mechanisms and through inhibition of apoptosis and necroptosis, it improves OA. The non-coding RNA molecules can regulate autophagy and through direct and indirect control of autophagy, they dually delay/increase OA pathogenesis. The mitochondrial integrity can be regulated by autophagy to alleviate OA. Furthermore, therapeutic compounds, especially phytochemicals, stimulate protective autophagy in chondrocytes to prevent cell death. The protective autophagy has ability of reducing inflammation and oxidative damage, as two key players in the pathogenesis of OA.

Liproxstatin-1 alleviates cartilage degradation by inhibiting chondrocyte ferroptosis in the temporomandibular joint

BGROUND INFORMATION

Ferroptosis contributes to temporomandibular joint osteoarthritis (TMJOA) lesion development and is still poorly understood.

RESULTS

In this study, we used different TMJOA animal models to examine whether ferroptosis was related to disease onset in TMJOA induced by monosodium iodoacetate (MIA), IL-1β, occlusion disorder (OD), and unilateral anterior crossbite (UAC). Immunohistochemical staining and Western blot analysis were used to detect ferroptosis- and cartilage degradation-related protein expression. Our results revealed reduced levels of the ferroptosis-related protein GPX4 in the cartilage layer, but the levels of ACSL4 and P53 were increased in the condyle. Injection of the ferroptosis inhibitor liproxstatin-1 (Lip-1) effectively decreased ACSL4, P53 and TRF expression. In vitro, IL-1β reduced cartilage extracellular matrix expression in mandibular condylar chondrocytes (MCCs). Lip-1 maintained the morphology and function of mitochondria and ameliorated the exacerbation of lipid peroxidation and reactive oxygen species (ROS) production induced by IL-1β.

CONCLUSION

These results suggest that chondrocyte ferroptosis plays an important role in the development and progression of TMJOA.

SIGNIFICANCE

Inhibiting condylar chondrocyte ferroptosis could be a promising therapeutic strategy for TMJOA.

A Blend of Tamarindus Indica and Curcuma Longa Extracts Alleviates Monosodium Iodoacetate (MIA)-Induced Osteoarthritic Pain and Joint Inflammation in Rats

BACKGROUND AND OBJECTIVE

NXT15906F6 (TamaFlexTM) is a proprietary herbal composition containing Tamarindus indica seeds and Curcuma longa rhizome extracts. NXT15906F6 supplementation has been shown clinically effective in reducing knee joint pain and improving musculoskeletal functions in healthy and knee osteoarthritis (OA) subjects. The objective of the present study was to assess the possible molecular basis of the anti-OA efficacy of NXT15906F6 in a monosodium iodoacetate (MIA)-induced model of OA in rats.

METHODS

Healthy male Sprague Dawley rats (age: 8-9 wk body weight, B.W.: 225-308 g (n = 12) were randomly assigned to one of the six groups, (a) vehicle control, (b) MIA control, (c) Celecoxib (10 mg/kg B.W.), (d) TF-30 (30 mg/kg B.W.), (e) TF-60 (60 mg/kg B.W.), and (f) TF-100 (100 mg/kg B.W.). OA was induced by an intra-articular injection of 3 mg MIA into the right hind knee joint. The animals received either Celecoxib or TF through oral gavage over 28 days. The vehicle control animals received intra-articular sterile normal saline.

RESULTS

Post-treatment, NXT15906F6 groups showed significant (p < 0.05) dose-dependent pain relief as evidenced by improved body weight-bearing capacity on the right hind limb. NXT15906F6 treatment also significantly reduced the serum tumor necrosis factor-α (TNF-α, p < 0.05) and nitrite (p < 0.05) levels in a dose-dependent manner. mRNA expression analyses revealed the up-regulation of collagen type-II (COL2A1) and down-regulation of matrix metalloproteinases (MMP-3, MMP-9 and MMP-13) in the cartilage tissues of NXT15906F6-supplemented rats. Cyclooxygenase-2 and inducible nitric oxide synthase (iNOS) protein expressions were down-regulated. Decreased immunolocalization of NF-κβ (p65) was observed in the joint tissues of NXT15906F6-supplemented rats. Furthermore, microscopic observations revealed that NXT15906F6 preserved MIA-induced rats' joint architecture and integrity.

CONCLUSION

NXT15906F6 reduces MIA-induced joint pain, inflammation, and cartilage degradation in rats.

Metformin for knee osteoarthritis with obesity: study protocol for a randomised, double-blind, placebo-controlled trial

INTRODUCTION

Over half of the populations with knee osteoarthritis (OA) have obesity. These individuals have many other shared metabolic risk factors. Metformin is a safe, inexpensive, well-tolerated drug that has pleiotropic effects, including structural protection, anti-inflammatory and analgesic effects in OA, specifically the knee. The aim of this randomised, double-blind, placebo-controlled trial is to determine whether metformin reduces knee pain over 6 months in individuals with symptomatic knee OA who are overweight or obese.

METHODS AND ANALYSIS

One hundred and two participants with symptomatic knee OA and overweight or obesity will be recruited from the community in Melbourne, Australia, and randomly allocated in a 1:1 ratio to receive either metformin 2 g or identical placebo daily for 6 months. The primary outcome is reduction of knee pain [assessed by 100 mm Visual Analogue Scale (VAS)] at 6 months. The secondary outcomes are OMERACT-OARSI (Outcome Measures in Rheumatology-Osteoarthritis Research Society International) responder criteria [Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain, function and participant's global assessment (VAS)] at 6 months; change in knee pain, stiffness, function using WOMAC at 6 months and quality of life at 6 months. Adverse events will be recorded. The primary analysis will be by intention to treat, including all participants in their randomised groups.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the Alfred Hospital Ethics Committee (708/20) and Monash University Human Research Ethics Committee (28498). Written informed consent will be obtained from all the participants. The findings will be disseminated through peer-review publications and conference presentations.

TRIAL REGISTRATION NUMBER

ACTRN12621000710820 .

Integrated single-cell and bulk RNA sequencing analysis identified pyroptosis-related signature for diagnosis and prognosis in osteoarthritis

Osteoarthritis (OA), a degenerative disease of the joints, has one of the highest disability rates worldwide. This study investigates the role of pyroptosis-related genes in osteoarthritis and their expression in different chondrocyte subtypes at the individual cell level. Using OA-related datasets for single-cell RNA sequencing and RNA-seq, the study identified PRDEGs and DEGs and conducted Cox regression analysis to identify independent prognostic factors for OA. CASP6, NOD1, and PYCARD were found to be prognostic factors. Combined Weighted Gene Correlation Network Analysis with PPI network, a total of 15 hub genes related to pyroptosis were involved in the notch and oxidative phosphorylation pathways, which could serve as biomarkers for the diagnosis and prognosis of OA patients. The study also explored the heterogeneity of chondrocytes between OA and normal samples, identifying 19 single-cell subpopulation marker genes that were significantly different among 7 chondrocyte cell clusters. AGT, CTSD, CYBC, and THYS1 were expressed differentially among different cell subpopulations, which were associated with cartilage development and metabolism. These findings provide valuable insights into the molecular mechanisms underlying OA and could facilitate the development of new therapeutic strategies for this debilitating disease.

Albiflorin alleviation efficacy in osteoarthritis injury using in-vivo and in-vitro models

OBJECTIVES

Osteoarthritis seriously affects the daily life of people. Albiflorin (AF) has anti-inflammatory and antioxidant functions in various human diseases. This study aimed to clarify the function and mechanism of AF in osteoarthritis.

METHODS

The functions of AF on rat chondrocyte proliferation and apoptosis, inflammatory response, oxidative stress and extracellular matrix (ECM) degradation in rat chondrocytes induced by interleukin-1beta (IL-1β) were evaluated by Western blot, immunofluorescence, flow cytometry and enzyme-linked immunosorbent assay. The mechanism of AF on the IL-1β induced rat chondrocyte injury was investigated by multiple experiments in vitro. Meanwhile, the AF function in vivo was assessed using haematoxylin-eosin staining, Alcian blue, Safranin O/Fast green staining, immunohistochemical analysis and TUNEL assay.

KEY FINDINGS

Functionally, AF accelerated the rat chondrocyte proliferation and repressed cell apoptosis. Meanwhile, AF reduced the inflammatory response, oxidative stress and ECM degradation in rat chondrocytes caused by IL-1β. Mechanistically, the receptor activator of the NF-kappaB ligand (RANKL), an activator for the NF-κB signalling pathway, partially reversed the alleviating effect of AF on IL-1β-induced chondrocyte injury. Furthermore, the in-vitro results confirmed that AF exerted protective properties against osteoarthritis injury in vivo.

CONCLUSION

Albiflorin relieved osteoarthritis injury in rats by inactivating the NF-κB pathway.

Metformin Alleviates Sepsis-Associated Myocardial Injury by Enhancing AMP-Activated Protein Kinase/Mammalian Target of Rapamycin Signaling Pathway-Mediated Autophagy

ABSTRACT

Sepsis-associated myocardial injury is one of the main causes of death in intensive care units, and current clinical treatments have not been satisfactory. Therefore, finding an effective intervention is an urgent requirement. Metformin, an anti-type 2 diabetes drug, has been reported to be an autophagic activator agent that confers protection in some diseases. However, it is unclear whether it can provide defense against sepsis-associated myocardial injury. In this study, we investigated the cardioprotective effects of metformin pretreatment against lipopolysaccharide (LPS)-induced myocardial injury in C57BL/6J mice or H9c2 cells and the possible underlying mechanisms. Metformin was administered at a dose of 100 mg/kg for a week before LPS intraperitoneal injection. Twenty-four hours after LPS intervention, echocardiographic evaluation, reactive oxygen species measurement, Hoechst staining, western blotting, hematoxylin and eosin staining, and enzyme-linked immunosorbent assay were performed. Inhibitors of autophagy and AMP-activated protein kinase (AMPK) were used to further clarify the mechanisms involved. Metformin pretreatment effectively attenuated cardiac dysfunction, reduced the levels of myocardial enzymes, and alleviated cardiac hydroncus in LPS-treated mice. In addition, metformin restored the LPS-disrupted antioxidant defense and activated LPS-reduced autophagy by modulating the AMPK/mammalian target of rapamycin (AMPK/mTOR) pathway both in vivo and in vitro. The antioxidant effects of metformin on cardiomyocytes were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Treatment with compound C, an AMPK inhibitor, reversed the metformin-induced autophagy in LPS-treated H9c2 cells. In conclusion, metformin pretreatment alleviates LPS-induced myocardial injury by activating AMPK/mTOR pathway-mediated autophagy.

Metformin combined with rapamycin ameliorates podocyte injury in idiopathic membranous nephropathy through the AMPK/mTOR signaling pathway

Autophagy activation protects against podocyte injury in idiopathic membranous nephropathy (IMN). The AMPK/mTOR signaling pathway is a vital autophagy regulatory pathway. Metformin promotes autophagy, whereas rapamycin is an autophagy agonist. However, the therapeutic mechanisms of metformin and rapamycin in IMN remain unclear. Thus, we examined the mechanisms of action of metformin and rapamycin in IMN by regulating the AMPK/mTOR autophagy signaling pathway. Female Sprague-Dawley (SD) rats were treated with cationic bovine serum albumin (C-BSA) to establish an IMN model and were randomly divided into IMN model, metformin, rapamycin, and metformin + rapamycin groups. A control group was also established. Metformin and rapamycin were used as treatments. Renal histological changes, urinary protein excretion, the protein expression levels of key AMPK/mTOR signaling pathway proteins, renal tissue cell apoptosis, and autophagy-associated proteins (Beclin 1 and LC3) were examined. In addition, a C5b-9 sublysis model using the MPC-5 mouse podocyte cell line was established to verify the effect of metformin combined with rapamycin on podocytes. Metformin combined with rapamycin improved urinary protein excretion in IMN rats. Metformin combined with rapamycin attenuated the inflammatory response, renal fibrosis, and podocyte foot process fusion. In addition, it improved autophagy in podocytes as demonstrated by the enhanced expression of Beclin-1, p-AMPK/AMPK, LC3-II/I, and autophagosomes in podocytes and decreased p-mTOR/mTOR expression. In conclusion, metformin combined with rapamycin decreased proteinuria, improved renal fibrosis and podocyte autophagy via AMPK/mTOR pathway in IMN rats. The metformin and rapamycin decreased proteinuria and inproved renal fibrosis in IMN model rats.

Effective Technical Protocol for Producing a Mono-Iodoacetate-Induced Temporomandibular Joint Osteoarthritis in a Rat Model

An animal model of osteoarthritis (OA) induced by monosodium iodoacetate (MIA) can be effectively adjusted based on the concentration of MIA to control the onset, progression, and severity of OA as required. The rat temporomandibular joint osteoarthritis (TMJOA) model using MIA is a useful tool for studying the effectiveness of disease-modifying OA drugs in TMJOA research. However, the intricate and complex anatomy of the rat TMJ often poses challenges in achieving consistent TMJOA induction during experiments. In the previous article, a reference point was established by drawing parallel lines based on the line connecting the external ear and the zygomatic arch. However, this is not suitable for the anatomical characteristics of the rat. We used the zygomatic arch as a reference, which is a technical protocol that considers it. In our protocol, we designated a point ∼1 mm away from the point where the zygomatic arch bends toward the ear as the injection site. To ensure precise injection of MIA and increase the likelihood of inducing OA, it is recommended to insert the needle at a 45° angle so that the needle tip contacts the joint projection. To confirm TMJOA induction, we identified changes in the condyle using in vivo microcomputed tomography (CT) in a rat model of MIA-induced OA and measured the degree of pain-related inflammation using head withdrawal threshold (HWT) measurements. Micro-CT scanning revealed typical OA-like lesions, including degenerative changes and subchondral bone remodeling induced by MIA in the TMJ. Pain, a major clinical feature of OA, showed an appropriate response corresponding to the structural changes shown in micro-CT scanning. In addition, the MIA concentration suitable for long-term observation of lesions was determined through ex vivo micro-CT imaging and HWT measurements. The 8 mg concentration exhibited a significant difference compared with others, confirming the sustained presence of lesions, particularly through changes in subchondral bone over an extended period. Consequently, we have successfully established a reliable rat TMJOA induction model and identified the MIA concentration suitable for long-term observation of subchondral bone research, which will greatly contribute to the study of TMJOA-an incurable disease lacking specific treatment options. The Clinical Trial Registration number is 2021-12-208.

What is new in pharmacological treatment for osteoarthritis?

Osteoarthritis (OA) is a degenerative joint disease in which structural changes of hyaline articular cartilage, subchondral bone, ligaments, capsule, synovium, muscles, and periarticular changes are involved. The knee is the most commonly affected joint, followed by the hand, hip, spine, and feet. Different pathological mechanisms are at play in each of these various involvement sites. Although systemic inflammation is more prominent in hand OA, knee and hip OA have been associated with excessive joint load and injury. As OA has varied phenotypes and the primarily affected tissues differ, treatment options must be tailored accordingly. In recent years, ongoing efforts have been made to develop disease-modifying options that halt or slow disease progression. Many are still in clinical trials, and as insights into the pathogenesis of OA evolve, novel therapeutic strategies will be developed. In this chapter, we provide an overview of the novel and emerging strategies in the management of OA.

Metformin attenuates symptoms of osteoarthritis: role of genetic diversity of Bcl2 and CXCL16 in OA

OBJECTIVE

This study aimed to evaluate the effectiveness of metformin versus placebo in overweight patients with knee osteoarthritis (OA). In addition, to assess the effects of inflammatory mediators and apoptotic proteins in the pathogenesis of OA, the genetic polymorphisms of two genes, one related to apoptosis (rs2279115 of Bcl-2) and the other related to inflammation (rs2277680 of CXCL-16), were investigated.

METHODS

In this double-blind placebo-controlled clinical trial, patients were randomly divided to two groups, one group receiving metformin (n = 44) and the other one receiving an identical inert placebo (n = 44) for 4 consecutive months (starting dose 0.5 g/day for the first week, increase to 1 g/day for the second week, and further increase to 1.5 g/day for the remaining period). Another group of healthy individuals (n = 92) with no history and diagnosis of OA were included in this study in order to evaluate the role of genetics in OA. The outcome of treatment regimen was evaluated using the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire. The frequency of variants of rs2277680 (A181V) and rs2279115 (938C>A) were determined in extracted DNAs using PCR-RFLP method.

RESULTS

Our results indicated an increase in scores of pain (P ≤ 0.0001), activity of daily living (ADL) (P ≤ 0.0001), sport and recreation (Sport/Rec) (P ≤ 0.0001), and quality of life (QOL) (P = 0.003) and total scores of the KOOS questionnaire in the metformin group compared to the placebo group. Susceptibility to OA was associated with age, gender, family history, CC genotype of 938C>A (Pa = 0.001; OR = 5.2; 95% CI = 2.0-13.7), and GG+GA genotypes of A181V (Pa = 0.04; OR = 2.1; 95% CI = 1.1-10.5). The C allele of 938C>A (Pa = 0.04; OR = 2.2; 95% CI = 1.1-9.8) and G allele of A181V (Pa = 0.02; OR = 2.2; 95% CI = 1.1-4.8) were also associated with OA.

CONCLUSION

Our findings support the possible beneficial effects of metformin on improving pain, ADL, Sport/Rec, and QOL in OA patients. Our findings support the association between the CC genotype of Bcl-2 and GG+GA genotypes of CXCL-16 and OA.

Pleiotropic Effects of Metformin in Osteoarthritis

The involvement of the knee joint is the most common localization of the pathological process in osteoarthritis (OA), which is associated with obesity in over 50% of the patients and is mediated by mechanical, inflammatory, and metabolic mechanisms. Obesity and the associated conditions (hyperglycemia, dyslipidemia, and hypertension) have been found to be risk factors for the development of knee OA, which has led to the emerging concept of the existence of a distinct phenotype, i.e., metabolic knee OA. Combined assessment of markers derived from dysfunctional adipose tissue, markers of bone and cartilage metabolism, as well as high-sensitivity inflammatory markers and imaging, might reveal prognostic signs for metabolic knee OA. Interestingly, it has been suggested that drugs used for the treatment of other components of the metabolic syndrome may also affect the clinical course and retard the progression of metabolic-associated knee OA. In this regard, significant amounts of new data are accumulating about the role of metformin-a drug, commonly used in clinical practice with suggested multiple pleiotropic effects. The aim of the current review is to analyze the current views about the potential pleiotropic effects of metformin in OA. Upon the analysis of the different effects of metformin, major mechanisms that might be involved in OA are the influence of inflammation, oxidative stress, autophagy, adipokine levels, and microbiome modulation. There is an increasing amount of evidence from in vitro studies, animal models, and clinical trials that metformin can slow OA progression by modulating inflammatory and metabolic factors that are summarized in the current up-to-date review. Considering the contemporary concept about the existence of metabolic type knee OA, in which the accompanying obesity and systemic low-grade inflammation are suggested to influence disease course, metformin could be considered as a useful and safe component of the personalized therapeutic approach in knee OA patients with accompanying type II diabetes or obesity.

Osteoarthritis: pathogenic signaling pathways and therapeutic targets

Osteoarthritis (OA) is a chronic degenerative joint disorder that leads to disability and affects more than 500 million population worldwide. OA was believed to be caused by the wearing and tearing of articular cartilage, but it is now more commonly referred to as a chronic whole-joint disorder that is initiated with biochemical and cellular alterations in the synovial joint tissues, which leads to the histological and structural changes of the joint and ends up with the whole tissue dysfunction. Currently, there is no cure for OA, partly due to a lack of comprehensive understanding of the pathological mechanism of the initiation and progression of the disease. Therefore, a better understanding of pathological signaling pathways and key molecules involved in OA pathogenesis is crucial for therapeutic target design and drug development. In this review, we first summarize the epidemiology of OA, including its prevalence, incidence and burdens, and OA risk factors. We then focus on the roles and regulation of the pathological signaling pathways, such as Wnt/β-catenin, NF-κB, focal adhesion, HIFs, TGFβ/ΒΜP and FGF signaling pathways, and key regulators AMPK, mTOR, and RUNX2 in the onset and development of OA. In addition, the roles of factors associated with OA, including MMPs, ADAMTS/ADAMs, and PRG4, are discussed in detail. Finally, we provide updates on the current clinical therapies and clinical trials of biological treatments and drugs for OA. Research advances in basic knowledge of articular cartilage biology and OA pathogenesis will have a significant impact and translational value in developing OA therapeutic strategies.

Autophagy in the pathogenesis and therapeutic potential of post-traumatic osteoarthritis

Autophagy, as a fundamental mechanism for cellular homeostasis, is generally involved in the occurrence and progression of various diseases. Osteoarthritis (OA) is the most common musculoskeletal disease that often leads to pain, disability and economic loss in patients. Post-traumatic OA (PTOA) is a subtype of OA, accounting for >12% of the overall burden of OA. PTOA is often caused by joint injuries including anterior cruciate ligament rupture, meniscus tear and intra-articular fracture. Although a variety of methods have been developed to treat acute joint injury, the current measures have limited success in effectively reducing the incidence and delaying the progression of PTOA. Therefore, the pathogenesis and intervention strategy of PTOA need further study. In the past decade, the roles and mechanisms of autophagy in PTOA have aroused great interest in the field. It was revealed that autophagy could maintain the homeostasis of chondrocytes, reduce joint inflammatory level, prevent chondrocyte death and matrix degradation, which accordingly improved joint symptoms and delayed the progression of PTOA. Moreover, many strategies that target PTOA have been revealed to promote autophagy. In this review,  we summarize the roles and mechanisms of autophagy in PTOA and the current strategies for PTOA treatment that depend on autophagy regulation, which may be beneficial for PTOA patients in the future.

Metformin attenuates high-fat diet induced metabolic syndrome related osteoarthritis through inhibition of prostaglandins

High-fat diet induces bone marrow inflammation and osteoarthritis phenotype in knee joint, but the underlying mechanisms is unknown. Here, we report that high-fat diet induces aberrant bone formation and cartilage degeneration in knee joint. Mechanistically, a high-fat diet increases the number of macrophages and the secretion of prostaglandins in subchondral bone, promoting bone formation. Metformin treatment is able to decrease the number of macrophages and also the level of prostaglandins induced by high-fat diet in subchondral bone. Importantly, metformin rescues aberrant bone formation and cartilage lesions by decreasing the number of osteoprogenitors and type-H vessels, which also results in relief of osteoarthritis pain response. Thus, we demonstrate prostaglandins secreted by macrophages may be a key reason for high-fat diet induced aberrant bone formation and metformin is a promising therapy for high-fat diet induced osteoarthritis.

Senescence in osteoarthritis: from mechanism to potential treatment

Osteoarthritis (OA) is an age-related cartilage degenerative disease, and chondrocyte senescence has been extensively studied in recent years. Increased numbers of senescent chondrocytes are found in OA cartilage. Selective clearance of senescent chondrocytes in a post-traumatic osteoarthritis (PTOA) mouse model ameliorated OA development, while intraarticular injection of senescent cells induced mouse OA. However, the means and extent to which senescence affects OA remain unclear. Here, we review the latent mechanism of senescence in OA and propose potential therapeutic methods to target OA-related senescence, with an emphasis on immunotherapies. Natural killer (NK) cells participate in the elimination of senescent cells in multiple organs. A relatively comprehensive discussion is presented in that section. Risk factors for OA are ageing, obesity, metabolic disorders and mechanical overload. Determining the relationship between known risk factors and senescence will help elucidate OA pathogenesis and identify optimal treatments.

Metformin as a potential disease-modifying drug in osteoarthritis: a systematic review of pre-clinical and human studies

OBJECTIVE

Osteoarthritis causes significant pain and disability with no approved disease-modifying drugs. We systematically reviewed the evidence from both pre-clinical and human studies for the potential disease-modifying effect of metformin in osteoarthritis.

METHODS

Ovid Medline, Embase and CINAHL were searched between inception and June 2021 using MeSH terms and key words to identify studies examining the association between metformin use and outcome measures related to osteoarthritis. Two reviewers performed the risk of bias assessment and 3 reviewers extracted data independently. Qualitative evidence synthesis was performed. This systematic review is registered on PROSPERO (CRD42021261052 and CRD42021261060).

RESULTS

Fifteen (10 pre-clinical and 5 human) studies were included. Most studies (10 pre-clinical and 3 human) assessed the effect of metformin using knee osteoarthritis models. In pre-clinical studies, metformin was assessed for the effect on structural outcomes (n = 10); immunomodulation (n = 5); pain (n = 4); and molecular pathways of its effect in osteoarthritis (n = 7). For human studies, metformin was evaluated for the effect on structural progression (n = 3); pain (n = 1); and immunomodulation (n = 1). Overall, pre-clinical studies consistently showed metformin having a chondroprotective, immunomodulatory and analgesic effect in osteoarthritis, predominantly mediated by adenosine monophosphate-activated protein kinase activation. Evidence from human studies, although limited, was consistent with findings in pre-clinical studies.

CONCLUSION

We found consistent evidence across pre-clinical and human studies to support a favourable effect of metformin on chondroprotection, immunomodulation and pain reduction in knee osteoarthritis. Further high-quality clinical trials are needed to confirm these findings as metformin could be a novel therapeutic drug for the treatment of osteoarthritis.

Lactobacillus (LA-1) and butyrate inhibit osteoarthritis by controlling autophagy and inflammatory cell death of chondrocytes

Osteoarthritis (OA) reduces the quality of life as a result of the pain caused by continuous joint destruction. Inactivated Lactobacillus (LA-1) ameliorated osteoarthritis and protected cartilage by modulating inflammation. In this study, we evaluated the mechanism by which live LA-1 ameliorated OA. To investigate the effect of live LA-1 on OA progression, we administered LA-1 into monosodium iodoacetate (MIA)-induced OA animals. The pain threshold, cartilage damage, and inflammation of the joint synovial membrane were improved by live LA-1. Furthermore, the analysis of intestinal tissues and feces in the disease model has been shown to affect the systems of the intestinal system and improve the microbiome environment. Interestingly, inflammation of the intestinal tissue was reduced, and the intestinal microbiome was altered by live LA-1. Live LA-1 administration led to an increase in the level of Faecalibacterium which is a short-chain fatty acid (SCFA) butyrate-producing bacteria. The daily supply of butyrate, a bacterial SCFA, showed a tendency to decrease necroptosis, a type of abnormal cell death, by inducing autophagy and reversing impaired autophagy by the inflammatory environment. These results suggest that OA is modulated by changes in the gut microbiome, suggesting that activation of autophagy can reduce aberrant cell death. In summary, live LA-1 or butyrate ameliorates OA progression by modulating the gut environment and autophagic flux. Our findings suggest the regulation of the gut microenvironment as a therapeutic target for OA.

Metformin Prevents or Delays the Development and Progression of Osteoarthritis: New Insight and Mechanism of Action

For over 60 years, metformin has been widely prescribed by physicians to treat type 2 diabetes. Along with more in-depth research on metformin and its molecular mechanism in recent decades, metformin has also been proposed as an effective drug to prevent or delay musculoskeletal disorders, including osteoarthritis (OA). The occurrence and development of OA are deemed to be associated with the impaired mitochondrial functions of articular chondrocytes. Metformin can activate the pathways and expressions of both AMPK and SIRT1 so as to protect the mitochondrial function of chondrocytes, thereby promoting osteoblast production. Moreover, the clinical significance of the metformin combination therapy in preventing OA has also been demonstrated. This review aimed to comprehensively summarize the current research progress on metformin as a proposed drug for OA prevention or treatment.

The effects of metformin in the treatment of osteoarthritis: Current perspectives

Osteoarthritis is a chronic and irreversible disease of the locomotor system which is closely associated with advancing age. Pain and limited mobility frequently affect the quality of life in middle-aged and older adults. With a global population of more than 350 million, osteoarthritis is becoming a health threat alongside cancer and cardiovascular disease. It is challenging to find effective treatments to promote cartilage repair and slow down disease progression. Metformin is the first-line drug for patients with type 2 diabetes, and current perspectives suggest that it cannot only lower glucose but also has anti-inflammatory and anti-aging properties. Experimental studies applying metformin for the treatment of osteoarthritis have received much attention in recent years. In our review, we first presented the history of metformin and the current status of osteoarthritis, followed by a brief review of the mechanism that metformin acts, involving AMPK-dependent and non-dependent pathways. Moreover, we concluded that metformin may be beneficial in the treatment of osteoarthritis by inhibiting inflammation, modulating autophagy, antagonizing oxidative stress, and reducing pain levels. Finally, we analyzed the relevant evidence from animal and human studies. The potential of metformin for the treatment of osteoarthritis deserves to be further explored.

Association between Metformin Use and Risk of Total Knee Arthroplasty and Degree of Knee Pain in Knee Osteoarthritis Patients with Diabetes and/or Obesity: A Retrospective Study

Objectives: We aimed to examine whether metformin (MET) use is associated with a reduced risk of total knee arthroplasty (TKA) and low severity of knee pain in patients with knee osteoarthritis (OA) and diabetes and/or obesity. Methods: Participants diagnosed with knee OA and diabetes and/or obesity from June 2000 to July 2019 were selected from the information system of a local hospital. Regular MET users were defined as those with recorded prescriptions of MET or self-reported regular MET use for at least 6 months. TKA information was extracted from patients’ surgical records. Knee pain was assessed using the numeric rating scale. Log-binomial regression, linear regression, and propensity score weighting (PSW) were performed for statistical analyses. Results: A total of 862 participants were included in the analyses. After excluding missing data, there were 346 MET non-users and 362 MET users. MET use was significantly associated with a reduced risk of TKA (prevalence ratio: 0.26, 95% CI: 0.15 to 0.45, p < 0.001), after adjustment for age, gender, body mass index, various analgesics, and insurance status. MET use was significantly associated with a reduced degree of knee pain after being adjusted for the above covariates (β: −0.48, 95% CI: −0.91 to −0.05, p = 0.029). There was a significantly accumulative effect of MET use on the reduced risk of TKA. Conclusion: MET can be a potential therapeutic option for OA. Further clinical trials are needed to determine if MET can reduce the risk of TKA and the severity of knee pain in metabolic-associated OA patients.

Monosodium iodoacetate-induced subchondral bone microstructure and inflammatory changes in an animal model of osteoarthritis

The monosodium iodoacetate (MIA)-induced osteoarthritis (OA) may lead to cartilage degeneration and histopathological lesions. However, the correlation between inflammatory reaction and subchondral bone remodeling in a rodent osteoarthritic model is ambiguous. In this study, intra-articular injection of MIA was performed in 36 four-week-old specific pathogen-free male Wistar rats to induce OA. After 4 weeks of intervention, changes in intrinsic structural properties of the subchondral bones were measured, and the histological evaluation, as well as biochemical analysis, was conducted. We found that intra-articular injection of MIA increased chondrocyte apoptosis and promoted cartilage matrix degradation, such as cartilage surface defects and shallow or disappearing staining. MIA also induced inflammation, improved the expression of IL-1β, TNF-α, and matrix metalloproteinase, and decreased the expression of cartilage-specific proteins with the extension of modeling time. Meanwhile, the MIA also significantly accelerated the subchondral bone remodeling, as shown by the decreased subchondral bone density, thinning of trabeculae, disordered cartilage structure, and morphology. In conclusion, we have shown that MIA-induced rodent osteoarthritic model would cause decreased subchondral bone density, sparse trabecular bone, and other manifestations of osteoporosis accompanied by an inflammatory response, which would worsen with the progression of modeling time. Our results suggest that different phases of MIA-induced OA are associated with the changes in subchondral bone microstructure and the progression of local inflammation.

Curcumin and metformin synergistically modulate peripheral and central immune mechanisms of pain

Metformin is a well-tolerated antidiabetic drug and has recently been repurposed for numerous diseases, including pain. However, a higher dose of metformin is required for effective analgesia, which can potentiate its dose-dependent gastrointestinal side effects. Curcumin is a natural polyphenol and has beneficial therapeutic effects on pain. Curcumin has been used as an analgesic adjuvant with several analgesic drugs, allowing synergistic antinociceptive effects. Nevertheless, whether curcumin can exert synergistic analgesia with metformin is still unknown. In the present study, the nature of curcumin-metformin anti-inflammatory interaction was evaluated in in vitro using lipopolysaccharide-induced RAW 264.7 macrophage and BV-2 microglia cells. In both macrophage and microglia, curcumin effectively potentiates the anti-inflammatory effects of metformin, indicating potential synergistic effects in both peripheral and central pathways of pain. The nature of the interaction between curcumin and metformin was further recapitulated using a mouse model of formalin-induced pain. Coadministration of curcumin and metformin at a 1:1 fixed ratio of their ED₅₀ doses significantly reduced the dose required to produce a 50% effect compared to the theoretically required dose in phase II of the formalin test with a combination index value of 0.24. Besides, the synergistic interaction does not appear to involve severe CNS side effects indicated by no motor alterations, no alterations in short-term and long-term locomotive behaviors, and the general well-being of mice. Our findings suggest that curcumin exerts synergistic anti-inflammation with metformin with no potential CNS adverse effects.

Can metformin relieve tibiofemoral cartilage volume loss and knee symptoms in overweight knee osteoarthritis patients? Study protocol for a randomized, double-blind, and placebo-controlled trial

Background

Osteoarthritis (OA) is the most common joint disease, and is most frequently seen in the knees. However, there is no effective therapy to relieve the progression of knee OA. Metformin is a safe, well-tolerated oral medication that is extensively used as first-line therapy for type 2 diabetes. Previous observational studies and basic researches suggested that metformin may have protective effects on knee OA, which needs to be verified by clinical trials. This study, therefore, aims to examine the effects of metformin versus placebo on knee cartilage volume loss and knee symptoms in overweight knee OA patients by a randomized controlled trial over 24 months.

Methods

This protocol describes a multicenter, randomized, double-blind, and placebo-controlled clinical trial aiming to recruit 262 overweight knee OA patients. Participants will be randomly allocated to the two arms of the study, receiving metformin hydrochloride sustained-release tablets or identical inert placebo for 24 months (start from 0.5 g/day for the first 2 weeks, and increase to 1 g/day for the second 2 weeks, and further increase to 2 g/day for the remaining period if tolerated). Primary outcomes will be changes in tibiofemoral cartilage volume and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score over 24 months. Secondary outcomes will be changes in visual analogue scale (VAS) knee pain, tibiofemoral cartilage defects, effusion-synovitis volume, and tibiofemoral bone marrow lesions maximum size over 24 months. The primary analyses will be intention-to-treat analyses of primary and secondary outcomes. Per-protocol analyses will be performed as the secondary analyses.

Discussion

If metformin is proved to slow knee cartilage volume loss and to relieve knee symptoms among overweight knee OA patients, it will have the potential to become a disease modifying drug for knee OA. Metformin is a convenient intervention with low cost, and its potential effects on slowing down the structural progression and relieving the symptoms of knee OA would effectively reduce the disease burden worldwide.

Trial registration

ClinicalTrials. gov NCT05034029. Registered on 30 Sept 2021.

Repurposed and investigational disease-modifying drugs in osteoarthritis (DMOADs)

In spite of a major public health burden with increasing prevalence, current osteoarthritis (OA) management is largely palliative with an unmet need for effective treatment. Both industry and academic researchers have invested a vast amount of time and financial expense to discover the first diseasing-modifying osteoarthritis drugs (DMOADs), with no regulatory success so far. In this narrative review, we discuss repurposed drugs as well as investigational agents which have progressed into phase II and III clinical trials based on three principal endotypes: bone-driven, synovitis-driven and cartilage-driven. Then, we will briefly describe the recent failures and lessons learned, promising findings from predefined post hoc analyses and insights gained, novel methodologies to enhance future success and steps underway to overcome regulatory hurdles.

Metformin and its therapeutic applications in autoimmune inflammatory rheumatic disease

Metformin is a first-line therapeutic agent for type 2 diabetes. Apart from its glucose-lowering effect, metformin is attracting interest regarding possible therapeutic benefits in various other conditions. As metformin regulates cell metabolism, proliferation, growth, and autophagy, it may also modulate immune cell functions. Given that metformin acts on multiple intracellular signaling pathways, including adenosine monophosphate (AMP)-activated protein kinase (AMPK) activation, and that AMPK and its downstream intracellular signaling control the activation and differentiation of T and B cells and inflammatory responses, metformin may exert immunomodulatory and anti- inflammatory effects. The efficacy of metformin has been investigated in preclinical and clinical studies on rheumatoid arthritis, osteoarthritis, systemic lupus erythematosus, Sjögren's syndrome, scleroderma, ankylosing spondylitis, and gout. In this review, we discuss the potential mechanisms through which metformin exerts its therapeutic effects in these diseases, focusing particularly on rheumatoid arthritis and osteoarthritis.

Disease-Modifying Potential of Metformin and Alendronate in an Experimental Mouse Model of Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease causing progressive damages of the cartilage and subchondral bone, synovial inflammation, and severe pain. Despite the complex pathomorphological changes that occur in OA, the approach to different forms of OA is standardized. The global results from pharmacological treatment are not satisfactory. Hence, this study aimed to explore the effects of metformin, alendronate, and their combination on OA development and progression in mice with collagenase-induced osteoarthritis (CIOA). Female ICR (CD-2) mice were randomized to five groups: control group, CIOA untreated, CIOA + metformin, CIOA + alendronate, and CIOA + metformin + alendronate. OA was induced by the intra-articular (i.a.) injection of collagenase. OA phenotype was analyzed by flow cytometry (bone marrow cell differentiation), ELISA (serum levels of the adipokines leptin and resistin), and histology (pathological changes of the knee joint). Treatment with metformin, alendronate, or their combination inhibited the expression of RANK and RANKL on osteoblasts and osteoclasts obtained by ex vivo cultivation of bone marrow cells in mineralization or osteoclastogenic media. In addition, metformin treatment was effective for the attenuation of fibroblast differentiation, but not of mesenchymal stem cells (MSCs), while alendronate had an opposite effect. The combination of metformin and alendronate had a suppressive effect on both MSCs and fibroblasts differentiation. Treatment with metformin, alendronate, and their combination decreased serum concentrations of leptin and resistin in the chronic phase of arthritis. The histopathological examination showed that compared with the untreated CIOA group (OA score 9), the groups treated with metformin (OA score 4) or alendronate (OA score 6) had lower scores for cartilage changes. Metformin combined with alendronate significantly decreased the degree of cartilage degeneration (OA score 2), suggesting that this combination might be a useful approach for the treatment of OA patients.

Hyperbaric Oxygen Therapy Attenuates Burn-Induced Denervated Muscle Atrophy

Background: Neuronal apoptosis and inflammation in the ventral horn of the spinal cord contribute to denervated muscle atrophy post-burn. Hyperbaric oxygen therapy (HBOT) exerts anti-inflammation and neuroprotection. Furthermore, hypoxia-inducible factor (HIF)-1α has been reported to promote inflammation and apoptosis. We investigated the therapeutic potential of HBOT and the role of HIF-1α post-burn. Methods: Sprague-Dawley rats were divided into three groups: a control group, an untreated burn group receiving burn and sham treatment, and a HBOT group receiving burn injury and HBOT. The burn injury was induced with 75ºC ± 5ºC at the right hindpaw. HBOT (100% oxygen at 2.5 atmosphere, 90 min/day) and sham HBOT (21% oxygen at 1 atmosphere, 90 min/day) was started on day 28 after burn injury and continued for 14 treatments (days 28-41). Incapacitance (hind limb weight bearing) testing was conducted before burn and weekly after burn. At day 42 post-burn, the gastrocnemius muscle and the spinal cord ventral horn were analyzed. Results: HBOT improved burn-induced weight bearing imbalance. At day 42 post-burn, less gastrocnemius muscle atrophy and fibrosis were noted in the HBOT group than in the untreated burn group. In the ventral horn, HBOT attenuated the neuronal apoptosis and glial activation post-burn. The increases in phosphorylated AKT/mTOR post-burn were reduced after HBOT. HBOT also inhibited HIF-1α signaling, as determined by immunofluorescence and western blot. Conclusions: HBOT reduces burn-induced neuronal apoptosis in the ventral horn, possibly through HIF-1α signaling.