Asiatic acid attenuates hypertrophic and fibrotic differentiation of articular chondrocytes via AMPK/PI3K/AKT signaling pathway

Andrographolide suppresses fibrogenic phenotype of chondrocytes and ameliorates osteoarthritis by regulating miR-137/BMP7 axis

Background

Pathogenic degeneration of cartilage and the generation of fibrotic cartilage are crucial characteristics linked to the progression of osteoarthritis (OA). The current research aims to explore the potential function of the miR-137/BMP7 pathway in regulating the fibrogenic transition of chondrocytes associated with OA, as well as assess the therapeutic potential of andrographolide.

Methods

Samples of cartilage from the knees of patients with OA and individuals without OA were gathered to investigate the expression patterns of miR-137, BMP7, and markers associated with fibrosis. A cell model using primary chondrocytes stimulated with interleukin (IL)-1β was developed to study the involvement of the miR-137/BMP7 axis during the fibrogenic transition of these cells. Additionally, we utilized an animal model of OA in order to assess the beneficial effects of the anti-inflammatory natural compound andrographolide on the fibrogenesis induced by OA in vivo.

Results

Elevated levels of fibrogenic and inflammatory factors were linked to decreased miR-137 expression in OA samples. In IL-1β-treated chondrocytes, there was an upregulation of fibrogenic markers alongside a reduction in miR-137 levels. The overexpression of miR-137 inhibited fibrogenesis through the negative regulation of BMP7. Additionally, treatment with andrographolide was effective in attenuating the fibrogenic phenotype in chondrocytes and mitigating OA pathogenesis via modulating the miR-137/BMP7 pathway.

Conclusion

miR-137 downregulation and BMP7 overexpression might contribute to the fibrogenic features in OA-related chondrocytes. Andrographolide attenuates fibrogenic phenotype in chondrocytes and alleviates the severity of OA by modulating the miR-137/BMP7 axis.

The Effect of Platelet-Rich Plasma on Synovial Fibrosis and Cartilage Degeneration in Knee Osteoarthritis

BACKGROUND

Synovial fibrosis is a prevalent pathological feature of osteoarthritis and a primary contributor to joint pain and stiffness. Studies indicate that platelet-rich plasma (PRP) is rich in growth factors and cytokines, exhibiting anti-inflammatory, anti-apoptotic, chemotactic, and proliferative properties that can facilitate tissue repair. However, little is known about its effect on synovial fibrosis in knee osteoarthritis (KOA).

PURPOSE

To determine the effect of PRP on synovial fibrosis and cartilage degeneration in KOA.

STUDY DESIGN

Controlled laboratory study.

METHOD

Anterior cruciate ligament transection was performed to induce KOA in male Sprague-Dawley rats, and then rats were randomly assigned to 4 different groups: sham operation, KOA only, KOA treated with phosphate-buffered saline (PBS), and KOA treated with PRP. Synovial collagen fiber deposition was observed using Masson and Sirius red staining, and synovial inflammation was assessed using hematoxylin and eosin (H&E) staining. Moreover, immunohistochemistry was conducted to analyze the expression of synovial fibrosis-related factors including PLOD2, COL1A1, TIMP1, TGF-β1, and α-SMA. KOA severity and articular cartilage degradation were assessed using micro-computed tomography (micro-CT), safranin O-fast green staining, H&E staining, immunohistochemistry, and the Osteoarthritis Research Society International (OARSI) criteria. A quantitative analysis of growth factors (platelet-derived growth factor, IGF-1, epidermal growth factor, TGF-β1, fibroblast growth factor, and endothelial growth factor) in activated PRP was performed using enzyme-linked immunosorbent assay.

RESULTS

Micro-CT imaging and histological staining showed that the KOA model had been successfully established. Compared with the KOA and PBS groups, Masson staining and Sirius red staining results showed that PRP aggravated the degree of synovial fibrosis, which was consistent with the results of immunohistochemistry analysis. Immunohistochemistry analysis showed that PRP promoted the protein expression of PLOD2, COL1A1, TIMP1, TGF-β1, and α-SMA, indicating that the degree of fibrosis was aggravated. However, the PRP group showed lower OARSI and synovitis scores, as well as attenuated abnormal tibial subchondral bone remodeling, suggesting that PRP inhibited further cartilage degeneration and synovial inflammation and improved the subchondral bone microarchitecture.

CONCLUSION

PRP may aggravate KOA synovial fibrosis, but it still has an inhibitory effect on cartilage degeneration and abnormal subchondral bone remodeling.

CLINICAL RELEVANCE

Synovial fibrosis is a significant pathological feature in KOA that is closely linked to clinical symptoms like joint pain and stiffness. This study offers insights into enhancing the effectiveness of PRP therapy for patients with KOA.

Fibrocartilage hyalinization: A potential therapeutic strategy for articular fibrocartilage

Articular fibrocartilage is commonly observed on the joint surface in osteoarthritis (OA) or cartilage injury, often seen as a result of cartilage degeneration. Compared to hyaline cartilage, fibrocartilage exhibits inferior mechanical properties and biological functions, which contribute to further cartilage degeneration and the progression of OA. Despite this, research on cartilage regeneration has not sufficiently addressed the specific challenges and strategies related to fibrocartilage. Although fibrocartilage formation is an unavoidable outcome during cartilage repair, it offers several benefits in the regeneration process, such as providing a natural cell source and establishing a strong integration with surrounding tissues. Recently, a therapeutic approach focused on the in-situ modification of fibrocartilage to promote hyaline cartilage regeneration, referred to as "fibrocartilage hyalinization", has been proposed. Our recent work has demonstrated the feasibility of converting existing fibrocartilage into hyaline cartilage in vivo within the injured area. Key elements of this strategy include modifying the extracellular matrix (ECM), targeting fibrotic chondrocytes, and altering the local microenvironment. This review summarizes the current understanding of articular fibrocartilage's characteristics and mechanisms, while also discussing potential approaches and the feasibility of fibrocartilage hyalinization for cartilage regeneration.

Orientin alleviates chondrocyte senescence and osteoarthritis by inhibiting PI3K/AKT pathway

AIMS

Osteoarthritis (OA) is a common degenerative disease that leads to pain, disability, and reduced quality of life. Orientin exhibits considerable anti-inflammatory and antioxidative properties, but its role in chondrocyte senescence and OA progress has not yet been fully characterized. The aim of this study was to evaluate the protective effects of orientin on OA.

METHODS

The role of orientin in extracellular matrix (ECM) degradation, mitochondrial homeostasis, and chondrocyte senescence was investigated in vitro. Meanwhile, we used molecular docking, small molecular inhibitors, and RNA interference to screen and validate candidate proteins regulated by orientin. In an anterior cruciate ligament transection (ACLT) rat model, radiograph, micro-CT, and various histological examinations were applied to evaluate the therapeutic effects of orientin on OA.

RESULTS

We found that orientin inhibited ECM degradation and senescence-associated secretory phenotype (SASP) factor expression in interleukin (IL)-1β-treated chondrocytes. Additionally, orientin reduced the level of reactive oxygen species (ROS) and improved mitochondrial homeostasis. Furthermore, orientin suppressed IL-1β-induced activation of the nuclear factor kappa B (NF-κB) signalling pathway. We also found that orientin bound to phosphoinositide 3-kinase (PI3K) and inhibited NF-κB cascades via the PI3K/AKT pathway. In vivo, we demonstrated that orientin improved cartilage wear and reduced synovial inflammation and osteophyte in an ACLT rat model.

CONCLUSION

Orientin improves mitochondrial homeostasis, inhibits chondrocyte senescence, and alleviates OA progress via the PI3K/AKT/NF-κB axis, which suggests that orientin is a potential effective therapeutic agent for OA.

Therapeutic efficacy of intra-articular injection of human adipose-derived mesenchymal stem cells in a sheep model of knee osteoarthritis

BACKGROUND

Mesenchymal stem cells have great potential for repairing articular cartilage and treating knee osteoarthritis (KOA). Nonetheless, little is known about the efficacy of human adipose-derived mesenchymal stem cells (haMSCs) for KOA in large animal models.

METHODS

This study evaluated the therapeutic efficacy of haMSCs in knee articular cartilage repair in a sheep model of KOA. haMSCs were isolated, cultured, and characterized. KOA was surgically induced by anterior cruciate ligament transection and medial meniscectomy, followed by intra-articular injection of saline (negative control group) or haMSCs (haMSC group) into the right knee joint at 6 and 9 weeks after surgery. Sheep were sacrificed 21 weeks after surgery, and samples (whole knee joints, femoral condyles, and tibias) were collected, processed, and analyzed. Changes in knee articular cartilage were assessed by magnetic resonance imaging, micro-computed tomography, macroscopic analysis, histology, and immunohistochemistry.

RESULTS

KOA caused the degeneration of the medial femoral condyle in the sheep model of KOA. Conversely, haMSCs repaired chondral defects and increased the thickness of knee articular cartilage.

CONCLUSIONS

These data suggest that the intra-articular injection of haMSCs can effectively repair articular cartilage defects in the knee.

Targeting Chondrocyte Hypertrophy as Strategies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common joint disease characterized by pain and functional impairment, which severely impacts the quality of life of middle-aged and elderly individuals. During normal bone development, chondrocyte hypertrophy is a natural physiological process. However, in the progression of OA, chondrocyte hypertrophy becomes one of its key pathological features. Although there is no definitive evidence to date confirming that chondrocyte hypertrophy is the direct cause of OA, substantial experimental data indicate that it plays an important role in the disease's pathogenesis. In this review, we first explore the mechanisms underlying chondrocyte hypertrophy in OA and offer new insights. We then propose strategies for inhibiting chondrocyte hypertrophy from the perspectives of targeting signaling pathways and tissue engineering, ultimately envisioning the future prospects of OA treatment.

The effect of Miya on skeletal muscle changes by regulating gut microbiota in rats with osteoarthritis through AMPK pathway

BACKGROUND

The study aimed to explore whether Miya (MY), a kind of Clostridium butyricum, regulated osteoarthritis (OA) progression through adenosine 5'-monophosphate-activated protein kinase (AMPK) pathway.

METHODS

The OA rats were orally given MY daily for 4 weeks and were intramuscularly injected with AMPK inhibitor once a week for 4 weeks. Hematoxylin eosin (HE) staining was used to observe the histological morphology of the knee joint. The levels of succinate dehydrogenase (SDH) and muscle glycogen (MG) in the tibia muscle of rats were detected by the corresponding kits, as well as the expression of related genes/proteins were assessed by real-time quantitative PCR (RT-qPCR) and western blot.

RESULTS

HE staining suggested that MY suppressed the symptoms of OA, which was abolished by AMPK inhibitor. Furthermore, the SDH and MG contents in the OA + MY + AMPK inhibitor group were lower than in the OA + MY group. At last, the levels of AMPK, PI3K, AKT1, Ldh, Myod, Chrna1, and Chrnd were notably decreased after AMPK inhibitor treatment, while the levels of Lcad and Mcad were up-regulated by AMPK inhibitor. Furthermore, their protein expression levels detected by western blot were consistent with those from RT-qPCR.

CONCLUSION

MY may partially regulate skeletal muscle changes and prevente OA development through the AMPK pathway.

Deapi-platycodin D3 attenuates osteoarthritis development via suppression of PTP1B

Dysregulated chondrocyte metabolism is an essential risk factor for osteoarthritis (OA) progression. Maintaining cartilage homeostasis represents a promising therapeutic strategy for the treatment of OA. However, no effective disease-modifying therapy is currently available to OA patients. To discover potential novel drugs for OA, we screened a small-molecule natural product drug library and identified deapi-platycodin D3 (D-PDD3), which was subsequently tested for its effect on extracellular matrix (ECM) properties and on OA progression. We found that D-PDD3 promoted the generation of ECM components in cultured chondrocytes and cartilage explants and that intra-articular injection of D-PDD3 delayed disease progression in a trauma-induced mouse model of OA. To uncover the underlying molecular mechanisms supporting these observed functions of D-PDD3, we explored the targets of D-PDD3 via screening approach integrating surface plasmon resonance with liquid chromatography-tandem mass spectrometry. The results suggested that D-PDD3 targeted tyrosine-protein phosphatase non-receptor type 1 (PTP1B), deletion of which restored chondrocyte homeostasis and markedly attenuated destabilization of the medial meniscus induced OA. Further cellular and molecular analyses showed that D-PDD3 maintained cartilage homeostasis by directly binding to PTP1B and consequently suppressing the PKM2/AMPK pathway. These findings demonstrated that D-PDD3 was a potential therapeutic drug for the treatment of OA and that PTP1B served as a protein target for the development of drugs to treat OA. This study provided significant insights into the development of therapeutics for OA treatment, which, in turn, helped to improve the quality of life of OA patients and to reduce the health and economic burden.

The involvement of signaling pathways in the pathogenesis of osteoarthritis: An update

Osteoarthritis (OA) is one of the most common disabling pathologies, characterized by joint pain and reduced function, significantly worsening the quality of life. Even if important progresses have been made in OA research, little is yet known about the precise cellular and molecular mechanisms underlying OA. Understanding dysregulated signaling networks and their crosstalk in OA may offer a strong opportunity for the development of combined targeted therapies. Hence, this review highlights the recent findings on the main pathways involved in OA development, including Wnt, Notch, Hedgehog, MAPK, AMPK, and JAK/STAT, providing insights on current targeted therapies in OA patients' management.

The translational potential of this article

The identification of key signaling pathways involved in OA development and the investigation of their signaling crosstalk could pave the way for more effective treatments and improved management of OA patients in the future.

Asiatic acid prevents glucocorticoid-induced femoral head osteonecrosis via PI3K/AKT pathway

Glucocorticoid-induced osteonecrosis of the femoral head (GIONFH) represents a predominant etiology of non-traumatic osteonecrosis, imposing substantial pain, restricting hip mobility, and diminishing overall quality of life for affected individuals. Centella asiatica (L.) Urb. (CA), an herbal remedy deeply rooted in traditional oriental medicine, has exhibited noteworthy therapeutic efficacy in addressing inflammation and facilitating wound healing. Drawing from CA's historical applications, its anti-inflammatory, anti-apoptotic, and antioxidant attributes may hold promise for managing GIONFH. Asiatic acid (AA), a primary constituent of CA, has been substantiated as a key contributor to its anti-apoptotic, antioxidant, and anti-inflammatory capabilities, showcasing a close association with orthopedic conditions. For the investigation of whether AA could alleviate GIONFH through suppressing oxidative stress, apoptosis, and to delve into its potential cellular and molecular mechanisms, the connection between AA and disease was analyzed through network pharmacology. DEX-induced apoptosis in rat osteoblasts and GIONFH in rat models, got utilized for the verification in vitro/vivo, on underlying mechanism of AA in GIONFH. Network pharmacology analysis reveals a robust correlation between AA and GIONFH in multiple target genes. AA has demonstrated the inhibition of DEX-induced osteoblast apoptosis by modulating apoptotic factors like BAX, BCL-2, Cleaved-caspase3, and cleaved-caspase9. Furthermore, it effectively diminishes the ROS overexpression and regulates oxidative stress through mitochondrial pathway. Mechanistic insights suggest that AA's therapeutic effects involve phosphatidylinositol 3-kinase/Protein kinase B (PI3K/AKT) pathway activation. Additionally, AA has exhibited its potential to ameliorate GIONFH progression in rat models. Our findings revealed that AA mitigated DEX-induced osteoblast apoptosis and oxidative stress through triggering PI3K/AKT pathway. Also, AA can effectively thwart GIONFH occurrence and development in rats.

Natural products in osteoarthritis treatment: bridging basic research to clinical applications

Osteoarthritis (OA) is the most prevalent degenerative musculoskeletal disease, severely impacting the function of patients and potentially leading to disability, especially among the elderly population. Natural products (NPs), obtained from components or metabolites of plants, animals, microorganisms etc., have gained significant attention as important conservative treatments for various diseases. Recently, NPs have been well studied in preclinical and clinical researches, showing promising potential in the treatment of OA. In this review, we summed up the main signaling pathways affected by NPs in OA treatment, including NF-κB, MAPKs, PI3K/AKT, SIRT1, and other pathways, which are related to inflammation, anabolism and catabolism, and cell death. In addition, we described the therapeutic effects of NPs in different OA animal models and the current clinical studies in OA patients. At last, we discussed the potential research directions including in-depth analysis of the mechanisms and new application strategies of NPs for the OA treatment, so as to promote the basic research and clinical transformation in the future. We hope that this review may allow us to get a better understanding about the potential bioeffects and mechanisms of NPs in OA therapy, and ultimately improve the effectiveness of NPs-based clinical conservative treatment for OA patients.

Porcine platelet lysates exert the efficacy of chondroregeneration and SMAD2-mediated anti-chondrofibrosis on knee osteoarthritis

BACKGROUND

The lack of self-repairability in cartilage and the formation of fibrocartilage pose significant challenges in treating knee osteoarthritis, and there is still no ideal solution. Autologous platelet lysates have been clinically applied to treat kOA and exert satisfactory cartilage-repair efficacy, but the preparation of human PL brings damage to patients and is hardly standardized.

METHODS

In this study, porcine PL was developed to replace hPL, and its chondroregenerative and anti-chondrofibrosis effects were explored. Enzyme-Linked Immunosorbent Assay was applied to qualify the PL products. In vivo, partial-thickness cartilage defects were created on rats as a kOA model, and the von Frey test, histopathological observation, immunohistochemical analysis, and western blot analysis were conducted. In vitro, CCK-8 assay, real-time PCR analysis, immunofluorescence test, and WB analysis were conducted for the mechanism study of pPL.

RESULTS

The in vivo data showed that pPL significantly repaired the cartilage defect by improving matrix synthesis and also ameliorated the pain response in the kOA model of rats. In addition, pPL exerted an anti-fibrosis effect on cartilage by suppressing the expressions of COL1, COL3, α-SMA, VIMENTIN, SMAD2, p-SMAD2, and CTGF in cartilage. The in vitro data verified these effects and indicated that the SMAD2 pathway mediated the anti-fibrosis mechanism of pPL. Moreover, the comparable effects between pPL and rat PL indicate that there is no immune rejection from pPL.

CONCLUSIONS

This study firstly demonstrated the anti-kOA effects of pPL on both cartilage-repair and anti-chondrofibrosis. It developed pPL as a promising alternative to autologous PL for clinical applications.

One-step stromal vascular fraction therapy in osteoarthritis with tropoelastin-enhanced autologous stromal vascular fraction gel

Background: Osteoarthritis (OA) is a debilitating degenerative joint disease, leading to significant pain and disability. Despite advancements, current regenerative therapies, such as mesenchymal stem cells (MSCs), face challenges in clinical efficacy and ethical considerations. This study aimed to evaluate the therapeutic potential of stromal vascular fraction gel (SVF-gel) in comparison to available treatments like hyaluronic acid (HA) and adipose-derived stem cells (ADSCs) and to assess the enhancement of this potential by incorporating tropoelastin (TE). Methods: We conducted a comparative laboratory study, establishing an indirect co-culture system using a Transwell assay to test the effects of HA, ADSCs, SVF-gel, and TE-SVF-gel on osteoarthritic articular chondrocytes (OACs). Chondrogenic and hypertrophic markers were assessed after a 72-hour co-culture. SVF-gel was harvested from rat subcutaneous abdominal adipose tissue, with its mechanical properties characterized. Cell viability was specifically analyzed for SVF-gel and TE-SVF-gel. The in vivo therapeutic effectiveness was further investigated in a rat model of OA, examining MSCs tracking, effects on cartilage matrix synthesis, osteophyte formation, and muscle weight changes. Results: Cell viability assays revealed that TE-SVF-gel maintained higher cell survival rates than SVF-gel. In comparison to the control, HA, and ADSCs groups, SVF-gel and TE-SVF-gel significantly upregulated the expression of chondrogenic markers COL 2, SOX-9, and ACAN and downregulated the hypertrophic marker COL 10 in OACs. The TE-SVF-gel showed further improved expression of chondrogenic markers and a greater decrease in COL 10 expression compared to SVF-gel alone. Notably, the TE-SVF-gel treated group in the in vivo OA model exhibited the most MSCs on the synovial surface, superior cartilage matrix synthesis, increased COL 2 expression, and better muscle weight recovery, despite the presence of fewer stem cells than other treatments. Discussion: The findings suggest that SVF-gel, particularly when combined with TE, provides a more effective regenerative treatment for OA by enhancing the therapeutic potential of MSCs. This combination could represent an innovative strategy that overcomes limitations of current therapies, offering a new avenue for patient treatment. Further research is warranted to explore the long-term benefits and potential clinical applications of this combined approach.

Correlation analysis of differentially expressed long non-coding RNA HOTAIR with PTEN/PI3K/AKT pathway and inflammation in patients with osteoarthritis and the effect of baicalin intervention

OBJECTIVE

This study aims to investigate the correlation of long non-coding RNA HOX transcript antisense RNA (lncRNA HOTAIR) with the PTEN/PI3K/AKT pathway and clinical-related indicators in osteoarthritis (OA) and determine the effect of baicalin intervention.

METHODS

The levels of clinical lipid metabolism indexes and immune-inflammatory indexes in OA patients and normal controls was detected. OA chondrocytes (OA-CHs) were induced with peripheral blood mononuclear cells (PBMCs), followed by baicalin treatment (50 ug/mL). RT-qPCR was performed to measure lncRNA HOTAIR expression. The levels of inflammatory cytokines and adiponectin were detected using ELISA kits. CCK-8 assay was used to assess the viability of CHs. The related protein expression was measured using Western blot analysis.

RESULTS

LncRNA HOTAIR might act as a biomarker of OA in vivo. LncRNA HOTAIR was positively correlated with TC, hs-CRP, IgA, TNF-α, and VAS score. Overexpression of lncRNA HOTAIR in vitro inhibited cell proliferation, reduced IL-10 and PTEN expression, but augmented TNF-α, p-PI3K, and p-AKT proteins in OA-CHs stimulated by OA-PBMCs. The changes of above indexes were also observed in OA-CHs stimulated by OA-PBMCs treated with si-lncRNA HOTAIR or baicalin, implying the synergistic effects of baicalin and lncRNA HOTAIR silencing on OA.

CONCLUSIONS

Conclusively, lncRNA HOTAIR was highly expressed in OA-CHs, which facilitated OA inflammatory responses by orchestrating inflammatory cytokines and the PTEN/PI3K/AKT pathway. Baicalin exerted therapeutic effects by inhibiting the expression of lncRNA HOTAIR, decreasing the protein levels of p-PI3K and p-AKT, and increasing the protein levels of PTEN, APN, and ADIPOR1.

Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Articular cartilage shows limited self-healing ability owing to its low cellularity and avascularity. Untreated cartilage defects display an increased propensity to degenerate, leading to osteoarthritis (OA). During OA progression, articular chondrocytes are subjected to significant alterations in gene expression and phenotype, including a shift towards a hypertrophic-like state (with the expression of collagen type X, matrix metalloproteinases-13, and alkaline phosphatase) analogous to what eventuates during endochondral ossification. Present OA management strategies focus, however, exclusively on cartilage inflammation and degradation. A better understanding of the hypertrophic chondrocyte phenotype in OA might give new insights into its pathogenesis, suggesting potential disease-modifying therapeutic approaches. Recent developments in the field of cellular/molecular biology and tissue engineering proceeded in the direction of contrasting the onset of this hypertrophic phenotype, but knowledge gaps in the cause-effect of these processes are still present. In this review we will highlight the possible advantages and drawbacks of using this approach as a therapeutic strategy while focusing on the experimental models necessary for a better understanding of the phenomenon. Specifically, we will discuss in brief the cellular signaling pathways associated with the onset of a hypertrophic phenotype in chondrocytes during the progression of OA and will analyze in depth the advantages and disadvantages of various models that have been used to mimic it. Afterwards, we will present the strategies developed and proposed to impede chondrocyte hypertrophy and cartilage matrix mineralization/calcification. Finally, we will examine the future perspectives of OA therapeutic strategies.

Gingko biloba-inspired lactone prevents osteoarthritis by activating the AMPK-SIRT1 signaling pathway

BACKGROUND

Uncoupled extracellular matrix (ECM) causes cartilage degeneration and osteoarthritis (OA) by suppressing the synthesis and activating the degradation of ECM components. Gingko biloba is a natural Chinese herb with a variety of biological functions; however, the extent to which it can protect against OA and the mechanisms involved are unknown.

METHODS

In our study, using bioinformatics tools, we were able to identify an important lactone, bilobalide (BB), from Gingko biloba. In vitro experiments were performed to evaluate the potential therapeutic effects of BB on ECM homeostasis. In vivo experiments were conducted to assess the protection of systemic administration of BB on cartilage degeneration. Molecular mechanisms underlying BB-regulated anti-arthritic role were further explored.

RESULTS

In interleukin-1β-incubated human chondrocytes, in vitro treatment with BB increased the expression of cartilage anabolic proteins, while inhibiting the activities of ECM degrading enzymes. In a mice model, systemic administration of BB, in vivo, prevented post-traumatic cartilage erosion and attenuated the formation of abnormal osteophytes in the subchondral bone. Mechanistically, the activation of the adenosine 5'-monophosphate-activated protein kinase (AMPK)-sirtuin 1 (SIRT1) signaling pathway was involved in the anti-arthritic effects of BB. In vitro, blocking BB's chondroprotection with the AMPK-specific inhibitor Compound C abrogated it.

CONCLUSIONS

These results demonstrated that BB extracted from Gingko biloba regulates ECM balance to prevent OA by activating the AMPK-SIRT1 signaling pathway. This study proposed the monomer BB, a traditional Chinese medicine, as a de novo therapeutic insight for OA. Schematic representation of the experimental design. Based on the bioinformatic analysis, bilobalide (BB), a natural herb Gingko biloba-derived ingredient, was identified as a candidate for treating osteoarthritis. In vitro, BB treatment not only facilitates cartilage extracellular matrix synthesis but also inhibits proteolytic enzyme activities. In vivo intraperitoneal injection of BB improves cartilage degeneration and subchondral bone sclerosis. BB, in particular, had anti-arthritic effects by activating the AMPK-SIRT1 signaling pathway.

Chicoric acid attenuates tumor necrosis factor-α-induced inflammation and apoptosis via the Nrf2/HO-1, PI3K/AKT and NF-κB signaling pathways in C28/I2 cells and ameliorates the progression of osteoarthritis in a rat model

Osteoarthritis (OA) is the most common arthritis, and is characterized by inflammation and cartilage degradation. Chicoric acid (CA), a bioactive caffeic acid derivative isolated from the root of Taraxacum mongolicumHand. - Mazz., has been reported to have anti-inflammatory effects. However, the therapeutic effects of CA on chondrocyte inflammation remain unknown. Our study aimed to explore the effect of CA on OA both in vivo and in vitro. In vitro, CA treatment significantly suppressed the overproduction of nitric oxide (NO), prostaglandin E2 (PGE2), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and IL-12 in tumor necrosis factor alpha (TNF-α)-induced human C28/I2 chondrocytes. Moreover, CA attenuated TNF-α induced degradation of the extracellular matrix (ECM) by upregulating the expression of collagen Ⅱ and aggrecan, and downregulating ADAMTS-5 and matrix metalloproteinases (MMPs). Additionally, CA treatment inhibited apoptosis in C28/I2 cells by upregulating of Bcl-2 levels, downregulating Bax and ROS levels, and activating the Nrf2/HO-1 pathway. Mechanistically, CA exerted an anti-inflammatory effect by inhibiting the PI3K/AKT and NF-κB signaling pathways, enhancing Nrf-2/HO-1 to limit the activation of NF-κB. In vivo experiments also proved the therapeutic effects of CA on OA in rats. These findings indicate that CA may become a new drug for the treatment of OA.

Recent Advances Regarding the Molecular Mechanisms of Triterpenic Acids: A Review (Part I)

Triterpenic acids are phytocompounds with a widespread range of biological activities that have been the subject of numerous in vitro and in vivo studies. However, their underlying mechanisms of action in various pathologies are not completely elucidated. The current review aims to summarize the most recent literature, published in the last five years, regarding the mechanism of action of three triterpenic acids (asiatic acid, oleanolic acid, and ursolic acid), corelated with different biological activities such as anticancer, anti-inflammatory, antidiabetic, cardioprotective, neuroprotective, hepatoprotective, and antimicrobial. All three discussed compounds share several mechanisms of action, such as the targeted modulation of the PI3K/AKT, Nrf2, NF-kB, EMT, and JAK/STAT3 signaling pathways, while other mechanisms that proved to only be specific for a part of the triterpenic acids discussed, such as the modulation of Notch, Hippo, and MALAT1/miR-206/PTGS1 signaling pathway, were highlighted as well. This paper stands as the first part in our literature study on the topic, which will be followed by a second part focusing on other triterpenic acids of therapeutic value.

Cross-Communication Between Knee Osteoarthritis and Fibrosis: Molecular Pathways and Key Molecules

Knee fibrosis is characterized by the presence of excessive connective tissue due to dysregulated fibroblast activation following local or systemic tissue damage. Knee fibrosis constitutes a major clinical problem in orthopaedics due to the severe limitation in the knee range of motion that leads to compromised function and patient disability. Knee osteoarthritis is an extremely common orthopedic condition that is associated with patient disability and major costs to the health-care systems worldwide. Although knee fibrosis and osteoarthritis (OA) have traditionally been perceived as two separate pathologic entities, recent research has shown common ground between the pathophysiologic processes that lead to the development of these two conditions. The purpose of this review was to identify the pathophysiologic pathways as well as key molecules that are implicated in the development of both knee OA and knee fibrosis in order to understand the relationship between the two diagnoses and potentially identify novel therapeutic targets.

Asiatic Acid Attenuates Osteoporotic Bone Loss in Ovariectomized Mice Through Inhibiting NF-kappaB/MAPK/ Protein Kinase B Signaling Pathway

Osteoporosis is a condition associated with osteolytic bone disease that is primarily characterized by inordinate osteoclast activation. Protein kinase B (Akt) pathways activated by receptor activator of nuclear factor kappa-B ligand (RANKL) are essential for osteoclastogenesis. Asiatic acid (AA) is a natural pentacyclic triterpenoid compound extracted from a traditional Chinese herb that exhibits a wide range of biological activities. AA has been found to alleviate the hypertrophic and fibrotic phenotype of chondrocytes via the Akt signaling pathway. In this study, we investigated whether AA alleviated bone loss by inhibiting the Akt signaling pathway during osteoclastogenesis and its effect on osteoblasts. The effect of AA cytotoxicity on mouse bone marrow-derived macrophages/monocytes (BMMs) was evaluated in vitro using a Cell Counting Kit-8 assay. The effects of AA on osteoclast differentiation and function were detected using tartrate-resistant acid phosphatase (TRAP) staining and a pit formation assay. A Western blot and qRT-PCR were conducted to evaluate the expression of osteoclast-specific genes and protein signaling molecules. In addition, alkaline phosphatase and alizarin red staining were performed to assess osteoblast differentiation and mineralization. The bone protective effect of AA was investigated in vivo using ovariectomized mice. we found that AA could dose-dependently inhibit RANKL-induced osteoclastogenesis. Moreover, the pit formation assay revealed that osteoclast function was suppressed by treatment with AA. Moreover, the expression of osteoclast-specific genes was found to be substantially decreased during osteoclastogenesis. Analysis of the molecular mechanisms showed that AA could inhibit NF-kappaB/MAPK/Akt signaling pathway, as well as the downstream factors of NFATc1 in the osteoclast signaling pathway activated by RANKL. However, AA did not significantly promote osteoblast differentiation and mineralization. The in vivo experiments suggested that AA could alleviate ovariectomy-induced bone loss in ovariectomized mice. Our results demonstrate that AA can inhibit osteoclastogenesis and prevent ovariectomy-induced bone loss by inhibiting the NF-kappaB/MAPK/Akt signaling pathway. The discovery of the new molecular mechanism that AA inhibits osteoclastogenesis provides essential evidence to support the use of AA as a potential drug for the treatment of osteoclast-related diseases.

Tropoelastin improves adhesion and migration of intra-articular injected infrapatellar fat pad MSCs and reduces osteoarthritis progression

Intra-articular injection of mesenchymal stem cells (MSCs) is a promising strategy for osteoarthritis (OA) treatment. However, more and more studies reveal that the injected MSCs have poor adhesion, migration, and survival in the joint cavity. A recent study shows that tropoelastin (TE) regulates adhesion, proliferation and phenotypic maintenance of MSCs as a soluble additive, indicating that TE could promote MSCs-homing in regenerative medicine. In this study, we used TE as injection medium, and compared it with classic media in MSCs intra-articular injection such as normal saline (NS), hyaluronic acid (HA), and platelet-rich plasma (PRP). We found that TE could effectively improve adhesion, migration, chondrogenic differentiation of infrapatellar fat pad MSCs (IPFP-MSCs) and enhance matrix synthesis of osteoarthritic chondrocytes (OACs) in indirect-coculture system. Moreover, TE could significantly enhance IPFP-MSCs adhesion via activation of integrin β1, ERK1/2 and vinculin (VCL) in vitro. In addition, intra-articular injection of TE-IPFP MSCs suspension resulted in a short-term increase in survival rate of IPFP-MSCs and better histology scores of rat joint tissues. Inhibition of integrin β1 or ERK1/2 attenuated the protective effect of TE-IPFP MSCs suspension in vivo. In conclusion, TE promotes performance of IPFP-MSCs and protects knee cartilage from damage in OA through enhancement of cell adhesion and activation of integrin β1/ERK/VCL pathway. Our findings may provide new insights in MSCs intra-articular injection for OA treatment.

miR-125a-5p-abundant exosomes derived from mesenchymal stem cells suppress chondrocyte degeneration via targeting E2F2 in traumatic osteoarthritis

miRNAs are broad participants in vertebrate biological processes, and they are also the major players in pathological processes. miR-125a-5p was recently found a modulator in the progression of osteoarthritis (OA). Our study was aimed to explore the role and underlying mechanisms of miR-125a-5p-abundant exosomes derived from mesenchymal stem cells (MSC) on OA progression. We separated bone marrow mesenchymal stem cells (BMSCs) as well as the exosomes from traumatic OA patients. The immunofluorescence and cartilage staining were implemented for the observation and the assessment on endocytosis of chondrocytes and exosomal miR-125a-5p efficacy to cartilage degradation. Dual luciferase reporter assay was performed to verified the relationship between miR-125a-5p and E2F2. Then, the function of exosomal miR-125a-5p were examined on chondrocyte degeneration in vitro and in vivo. Our findings indicated that E2F2 expression was elevated while the miR-125a-5p was down in traumatic OA cartilage tissue, showing a negative correlation of the former and the latter. miR-125a-5p targets E2F2 in traumatic OA cartilage tissue and leads to the down-expression of E2F2. The E2F2 expression in chondrocytes was decreased after internalization of exosomes. We additionally found that BMSCs-derived exosomes were rich in miR-125a-5p content and chondrocytes can have it internalized. miR-125a-5p is endowed with a trait of accelerating chondrocytes migration, which is going along with the up-expressions of Collagen II, aggrecan and SOX9 and the down-expression of MMP-13 in vitro. Besides that, the mice model with post-traumatic OA turned out that exosomal miR-125a-5p might beget an alleviation in chondrocyte extracellular matrix degradation. All these outcomes revealed that BMSCs-derived exosomal miR-125a-5p is a positive regulator for chondrocyte migration and inhibit cartilage degeneration We thus were reasonable to believe that transferring of exosomal miR-125a-5p is a prospective strategy for OA treatment.

Corosolic acid and its structural analogs: A systematic review of their biological activities and underlying mechanism of action

BACKGROUND

The corosolic acid (CA), also known as plant insulin, is a pentacyclic triterpenoid extracted from plants such as Lagerstroemia speciosa. It has been shown to have anti-diabetic, anti-inflammatory and anti-tumor effects. Its structural analogs ursolic acid (UA), oleanolic acid (OA), maslinic acid (MA), asiatic acid (AA) and betulinic acid (BA) display similar individual pharmacological activities to those of CA. However, there is no systematic review documenting pharmacological activities of CA and its structural analogues. This study aims to fill this gap in literature.

PURPOSE

This systematic review aims to summarize the medical applications of CA and its analogues.

METHODS

A systematic review summarizes and compares the extraction techniques, pharmacokinetic parameters, and pharmacological effects of CA and its structural analogs. Hypoglycemic effect is one of the key inclusion criteria for searching Web of Science, PubMed, Embase and Cochrane databases up to October 2020 without language restrictions. 'corosolic acid', 'ursolic acid', 'oleanolic acid', 'maslinic acid', 'asiatic acid', 'betulinic acid', 'extraction', 'pharmacokinetic', 'pharmacological' were used to extract relevant literature. The PRISMA guidelines were followed.

RESULTS

At the end of the searching process, 140 articles were selected for the systematic review. Information of CA and five of its structural analogs including UA, OA, MA, AA and BA were included in this review. CA and its structural analogs are pentacyclic triterpenes extracted from plants and they have low solubilities in water due to their rigid scaffold and hydrophobic properties. The introduction of water-soluble groups such as sugar or amino groups could increase the solubility of CA and its structural analogs. Their biological activities and underlying mechanism of action are reviewed and compared.

CONCLUSION

CA and its structural analogs UA, OA, MA, AA and BA are demonstrated to show activities in lowering blood sugar, anti-inflammation and anti-tumor. Their oral absorption and bioavailability can be improved through structural modification and formulation design. CA and its structural analogs are promising natural product-based lead compounds for further development and mechanistic studies.

Asiatic acid protects articular cartilage through promoting chondrogenesis and inhibiting inflammation and hypertrophy in osteoarthritis

Natural small molecules have become attractive in osteoarthritis (OA) treatment. This study aims to investigate the effect of asiatic acid (AA) on OA development in vitro and in vivo. Chondrocytes were pretreated with AA at optimized concentrations and subsequently treated with interleukin-1 beta (IL-1β). Inflammatory mediator nitric oxide (NO) was measured by Griess method. The mRNA expression level of inflammatory markers nitric oxide synthase (iNOS) and cyclooxygenase 2 (Cox2), as well as chondrogenic or hypertrophic markers including SRY-box transcription factor 9 (Sox9), Aggrecan, Collagen 2a1 (Col II), and Matrix metalloproteinase-13 (Mmp13) were measured by using real-time PCR analysis. The nuclear factor-kappa B (NF-κB) signaling activity was determined by dual luciferase assay and Western blot analysis. Surgery-induced OA animal model was constructed, and AA was administrated to study its effect on OA pathogenesis. AA induced a dose-dependent inhibitory effect up to -67.4% on NO production. AA could repress iNOS and Cox2 protein expression levels (-77.2% and -73.4%, respectively) in IL-1β induced chondrocytes. AA increased the formation of cartilage extracellular matrix components including glycosaminoglycans (GAGs) and collagen type II. AA also mRNA expression of chondrogenesis marker including Aggrecan, Sox9, Col II and Fibronectin (402.87%, 151.04%, 314.15% and 187.76%, respectively) as well as hypertrophic marker Mmp13 (-67.8%). AA repressed the chondrocyte inflammation by directly inhibiting NF-κB signaling activity, which was revealed by the inhibition effect of AA on IκBα phosphorylation (-105.4%) and NF-κB/p65 translocation (-60.9%) induced by IL-1β. Furthermore, In vivo OA study indicated the protective effect of AA on OA progression by preventing articular cartilage from degeneration and destruction. AA treatment could significantly reduce OA score (16.125 vs 5.25) and repress mRNA expression level of Mmp13 and Col X (23.5, vs 2.375 and 18.125 vs 94.5). Taken together, our findings suggest that AA could effectively rescue IL-1β induced chondrocytes and protected cartilage in OA progression, which shed light on a potential novel therapeutic strategy of OA treatment.

AMPK Signaling in Energy Control, Cartilage Biology, and Osteoarthritis

The adenosine monophosphate (AMP)-activated protein kinase (AMPK) was initially identified as an enzyme acting as an "energy sensor" in maintaining energy homeostasis via serine/threonine phosphorylation when low cellular adenosine triphosphate (ATP) level was sensed. AMPK participates in catabolic and anabolic processes at the molecular and cellular levels and is involved in appetite-regulating circuit in the hypothalamus. AMPK signaling also modulates energy metabolism in organs such as adipose tissue, brain, muscle, and heart, which are highly dependent on energy consumption via adjusting the AMP/ADP:ATP ratio. In clinics, biguanides and thiazolidinediones are prescribed to patients with metabolic disorders through activating AMPK signaling and inhibiting complex I in the mitochondria, leading to a reduction in mitochondrial respiration and elevated ATP production. The role of AMPK in mediating skeletal development and related diseases remains obscure. In this review, in addition to discuss the emerging advances of AMPK studies in energy control, we will also illustrate current discoveries of AMPK in chondrocyte homeostasis, osteoarthritis (OA) development, and the signaling interaction of AMPK with other pathways, such as mTOR (mechanistic target of rapamycin), Wnt, and NF-κB (nuclear factor κB) under OA condition.

The role of metabolism in chondrocyte dysfunction and the progression of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by low-grade inflammation and high levels of clinical heterogeneity. Aberrant chondrocyte metabolism is a response to changes in the inflammatory microenvironment and may play a key role in cartilage degeneration and OA progression. Under conditions of environmental stress, chondrocytes tend to adapt their metabolism to microenvironmental changes by shifting from one metabolic pathway to another, for example from oxidative phosphorylation to glycolysis. Similar changes occur in other joint cells, including synoviocytes. Switching between these pathways is implicated in metabolic alterations that involve mitochondrial dysfunction, enhanced anaerobic glycolysis, and altered lipid and amino acid metabolism. The shift between oxidative phosphorylation and glycolysis is mainly regulated by the AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) pathways. Chondrocyte metabolic changes are likely to be a feature of different OA phenotypes. Determining the role of chondrocyte metabolism in OA has revealed key features of disease pathogenesis. Future research should place greater emphasis on immunometabolism and altered metabolic pathways as a means to understand the pathophysiology of age-related OA. This knowledge will advance the development of new drugs against therapeutic targets of metabolic significance.

Cartilage Targets of Knee Osteoarthritis Shared by Both Genders

As the leading cause of disability, osteoarthritis (OA) affects people of all ages, sexes, and races. With the increasing understanding of OA, the sex differences have attracted specific attention as the burden of OA is greater in women. There is no doubt that gender-specific OA management has great potential for precision treatment. On the other hand, from the marketing aspect, a medication targeting the OA-responsive biomarker(s) shared by both genders is more favorable for drug development. Thus, in the current study, a published transcriptome dataset of knee articular cartilage was used to compare OA and healthy samples for identifying the genes with the same significantly different expression trend in both males and females. With 128 genes upregulated and 143 genes downregulated in both OA males and females, 9 KEGG pathways have been enriched based on the current knowledge, including 'renal cell carcinoma,' 'ECM-receptor interaction,' 'HIF-1 signaling pathway,' 'MicroRNAs in cancer,' 'focal adhesion,' 'Relaxin signaling pathway,' 'breast cancer,' 'PI3K-Akt signaling pathway,' and 'human papillomavirus infection.' Here, we explore the potential impacts of these clusters in OA. We also analyze the identified 'cell plasma membrane related genes' in-depth to identify the potential chondrocyte cell surface target(s) of OA management.

The Role of Fibrosis in Osteoarthritis Progression

Osteoarthritis (OA) is a chronic degenerative joint disease where the main characteristics include cartilage degeneration and synovial membrane inflammation. These changes in the knee joint eventually dampen the function of the joint and restrict joint movement, which eventually leads to a stage where total joint replacement is the only treatment option. While much is still unknown about the pathogenesis and progression mechanism of OA, joint fibrosis can be a critical issue for better understanding this disease. Synovial fibrosis and the generation of fibrocartilage are the two main fibrosis-related characteristics that can be found in OA. However, these two processes remain mostly misunderstood. In this review, we focus on the fibrosis process in OA, especially in the cartilage and the synovium tissue, which are the main tissues involved in OA.