Undenatured type II collagen and its role in improving osteoarthritis

Therapeutic targets in aging-related osteoarthritis: A focus on the extracellular matrix homeostasis

Osteoarthritis (OA) represents a globally prevalent degenerative bone diseases and is the primary contributors to pain and disability among middle-aged and elderly people, thereby imposing significant social and economic burdens. When articular cartilage is in the aging environment, epigenetic modifications, DNA damage and mitochondrial dysfunction lead to cell senescence. Chondrocyte senescence has been identified as a pivotal event in this metabolic dysregulation of the extracellular matrix (ECM). It can affect the composition and structure of ECM, and the mechanical and biological signals transmitted by ECM to senescent chondrocytes affect their physiology and pathology. Over the past few decades, the role of ECM in aging-related OA has received increasing attention. In this review, we summarize the changes of cartilage's major ECM (type II collagen and aggrecan) and the interaction between aging and ECM in OA, and explore therapeutic strategies targeting cartilagae ECM, such as noncoding RNAs, small-molecule drugs, and mesenchymal stem cell (MSC)-derived extracellular vesicles for OA. The aim of this study was to elucidate the potential benefits of ECM-based therapies as novel strategies for the management of OA diseases.

Quercetin-primed MSC exosomes synergistically attenuate osteoarthritis progression

BACKGROUND

Osteoarthritis (OA), a degenerative joint disease characterized by cartilage degradation and inflammation, lacks effective disease-modifying therapies. Quercetin, a bioactive flavonoid derived from Traditional Chinese Medicine, exhibits anti-inflammatory and chondroprotective properties but is limited by poor bioavailability. Mesenchymal stem cell-derived exosomes (MSC-Exos) offer a promising strategy for targeted drug delivery and cartilage regeneration.

METHODS

Bone marrow-derived MSC exosomes (Que-Exo) were isolated after preconditioning with quercetin (1µM, 24 h). Their effects were evaluated in IL-1β-stimulated chondrocytes via RT-qPCR, Western blot, transcriptomics, and proteomics. An ACLT-induced OA mouse model received intra-articular injections of Que-Exo, with cartilage integrity assessed by Safranin O staining and OARSI scoring.

RESULTS

Que-Exo significantly reduced IL-1β-induced pro-inflammatory markers (MMP9 and COX-2) and restored cartilage repair genes (SOX9 and Collagen II) compared to untreated exosomes. Multi-omics analyses revealed activation of PI3K-AKT signaling and glutathione metabolism pathways. In vivo, Que-Exo mitigated cartilage degradation and preserved proteoglycan content.

CONCLUSIONS

Quercetin-preconditioned MSC exosomes synergistically enhance chondroprotection and anti-inflammatory effects, offering a novel therapeutic strategy for OA by combining herbal bioactive compounds with exosome-mediated delivery.

Injectable biomimetic hydrogel based on modified chitosan and silk fibroin with decellularized cartilage extracellular matrix for cartilage repair and regeneration

Cartilage defect repair remains a challenge for clinicians due to the limited self-healing capabilities of cartilage. Microenvironment-specific biomimetic hydrogels have shown great potential in cartilage regeneration because of their excellent biological properties. In this study, a hydrogel system consisting of p-hydroxybenzene propanoic acid-modified chitosan (PC), silk fibroin (SF) and decellularized cartilage extracellular matrix (DCM) was prepared. Under the catalysis of horseradish peroxidase (HRP), the phenol hydroxyl groups on PC and SF were crosslinked to form a hydrogel. DCM incorporation into the hydrogel facilitated an emulation of the natural cartilage extracellular matrix. The synthesized injectable hydrogels could fill irregular defects and formed network structures that promoted cell adhesion and proliferation. In vitro experiments demonstrated that the hydrogels had biocompatibility and promoted chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). The DCM-derived hydrogel exhibited low immunogenicity in vivo, and in the treatment of both rabbit trochlear groove cartilage defects and goat femoral condyle cartilage defects, the hydrogel accelerated the cartilage regeneration. In summary, our developed composite hydrogel system in the study offers a potential strategy for the effective repair of cartilage defects.

Enhancing auricular reconstruction: A biomimetic scaffold with 3D-printed multiscale porous structure utilizing chondrogenic activity ink

Auricular defects are highly prevalent and have a significant impact on the physical and mental well-being of patients. However, due to the intricate anatomy of the auricle, achieving personalized and precise reconstruction poses a major challenge. Currently, tissue engineering auricle scaffolds based on rigid materials are an effective therapeutic approach for auricle reconstruction. Nevertheless, these auricular scaffolds often fail to meet biomechanical requirements and lack biological activity, resulting in suboptimal treatment outcomes. In this study, polyvinyl alcohol and gelatin were used as printing inks, and nano-silica was employed as a filler to optimize the printability of the inks. Through layer-by-layer 3D printing, auricle scaffolds were fabricated that closely mimic human auricular biomechanical properties and possess a multi-scale pore structure. Subsequent in vitro experiments confirmed the biocompatibility of the scaffolds. Furthermore, a rabbit auricular cartilage defect model was established to evaluate the therapeutic efficacy of this bionic scaffold featuring a multi-scale pore structure for auricle defects. The findings demonstrated that the developed auricle scaffold not only exhibited excellent biomechanical strength and favorable biocompatibility but also provided an advantageous environment for chondrocyte growth due to its multi-scale pore structure, thereby significantly promoting chondrocyte proliferation. Overall, the 3D printed tissue engineering bionic scaffold with a multi-scale pore structure developed in this study is anticipated to significantly enhance the therapeutic efficacy for auricle defects and offer a novel therapeutic strategy for such defects.

Sustained therapeutic effects of self-assembled hyaluronic acid nanoparticles loaded with α-Ketoglutarate in various osteoarthritis stages

Osteoarthritis (OA) is a prevalent degenerative disease characterized by irreversible destruction of articular cartilage, for which no current drugs are known to modify its progression. While intra-articular (IA) injections of hyaluronic acid (HA) offer temporary relief, their effectiveness and long-term benefits are debated. Alpha-ketoglutarate (αKG) has potential chondroprotective properties, but its use is limited by a short half-life and poor cartilage-targeting efficiency. Here, we developed self-assembled HA-αKG nanoparticles (NPs) to combine the benefits of both HA and αKG, showing stability, bioavailability, and sustained pH-responsive release in the knee joint. In both early and advanced OA stages in mice, HA, αKG, and HA-αKG NPs could relieve pain, enhance mobility, and reduce cartilage damage, with HA-αKG NPs demonstrating the best efficacy. Mechanistically, αKG not only promotes cartilage matrix synthesis but also inhibits degradation by activating the PERK-ATF4 signaling pathway to reduce endoplasmic reticulum stress (ERS) in chondrocytes. This study highlights the therapeutic potential of HA-αKG NPs for treating various OA stages, with efficient and sustained effects, suggesting rapid clinical adoption and high acceptability among clinicians and patients.

Recent applications of stimulus-responsive smart hydrogels for osteoarthritis therapy

Osteoarthritis is one of the most common degenerative joint diseases, which seriously affects the life of middle-aged and elderly people. Traditional treatments such as surgical treatment and systemic medication, often do not achieve the expected or optimal results, which leads to severe trauma and a variety of side effects. Therefore, there is an urgent need to develop novel therapeutic options to overcome these problems. Hydrogels are widely used in biomedical tissue repairing as a platform for loading drugs, proteins and stem cells. In recent years, smart-responsive hydrogels have achieved excellent results as novel drug delivery systems in the treatment of osteoarthritis. This review focuses on the recent advances of endogenous stimuli (including enzymes, pH, reactive oxygen species and temperature, etc.) responsive hydrogels and exogenous stimuli (including light, shear, ultrasound and magnetism, etc.) responsive hydrogels in osteoarthritis treatment. Finally, the current limitations of application and future prospects of smart responsive hydrogels are summarized.

Ternary complex of soluble undenatured type II collagen-hydrophobic phytochemical-chondroitin sulfate facilitates high stability and targeted intestinal release properties to active substance

Researchers have reported that soluble undenatured type II collagen (SC II) and hydrophobic phytochemicals (HPs) can ameliorate osteoarthritis (OA) through several mechanisms. However, the solubility of HPs, the stability of SC II, and the bio-accessibility of both need to be greatly improved before they can be successfully used for this purpose. In this study, two common HPs, curcumin (CUR, a hydrophobic polyphenol) and astaxanthin (AST, a carotenoid), were first loaded into SC II, which was then complexed with chondroitin sulfate (CS) to form ternary complexes: SC II-HP-CS. The results showed that SC II had the highest loading capacity for CUR (19.00 ± 0.76 μg/mg) and AST (21.15 ± 1.67 μg/mg) at pH 2.0. The CUR and AST bound to the SC II through non-covalent interactions (mainly hydrophobic interaction) and they both existed in an amorphous form within the complexes. In addition, the binding affinity and hydrophobic interaction between SC II and CUR was higher than those of AST. The thermal stability of the SC II-CUR-CS (Td = 118.0 ± 2.1 °C) and SC II-AST-CS (Td = 118.8 ± 3.5 °C) complexes were significantly higher than that of the SC II-CUR (Td = 104.27 ± 0.28 °C) and SC II-AST (Td = 103.8 ± 1.6 °C) complexes. SC II-HP complexes dissolved in gastric fluids, resulting in serious degradation of the SC II, while SC II-HP-CS complexes existed in an insoluble form to protect the triple helix structure of SC II (24-46 % retained). The CUR release (94.2 ± 5.8 %) and the free radical scavenging activity (84.6 ± 5.3 %) of SC II-CUR-CS was relatively high after 6 h of intestinal digestion, while AST in SC II-AST and SC II-AST-CS had low solubility and antioxidant activity. Therefore, the ternary complex of SC II-HP-CS was more advantageous as multifunctional delivery systems for the encapsulation, protection, and controlled release of hydrophobic polyphenols, which may provide guidance for the synergistic use of hydrophobic polyphenols and SC II to improve OA.

Recent advances in osteoarthritis research: A review of treatment strategies, mechanistic insights, and acupuncture

Osteoarthritis (OA) is a chronic joint condition affecting millions worldwide, characterized by the gradual degeneration of joint cartilage, leading to pain, stiffness, and functional impairment. Although the pathogenesis of OA is not fully understood, the roles of inflammation, metabolic dysregulation, and biomechanical stress are increasingly recognized. Current treatments, including pharmacotherapy, physical therapy, and surgical interventions, aim to alleviate symptoms and improve quality of life, yet they face limitations and challenges. In recent years, researchers have explored a variety of new treatment strategies, such as molecular targeted therapy, biologic treatments, regenerative medicine, and lifestyle modifications, aiming to directly address the root causes and complex mechanisms of OA. This review aims to summarize the latest research advancements to provide fresh perspectives for clinical treatment and lay the foundation for future research and development of treatment strategies for OA.

Protective role of Yougui Yin in experimental knee osteoarthritis: From the perspective of macrophage polarization

Knee osteoarthritis (KOA) refers to a prevalent musculoskeletal disorder, frequently complicated by substantial pain and physical disability. Yougui Yin (YGY) is a classic Chinese herbal mixture which has demonstrated potential in treating KOA. Considering that, its cryptic mechanism warrants to be deciphered, which is the subject of our present research. In vivo, H&E staining, Alcian blue staining and Masson staining assessed the histomorphology. Commercial kits and ELISA evaluated oxidative stress markers. ELISA also assayed serum inflammatory cytokines. TUNEL staining appraised apoptosis. Western blotting examined cartilage matrix degradation, apoptotic and NLRP3 inflammasome proteins. Immunofluorescence assay estimated macrophage polarization. In vitro, ELISA assayed oxidative stress markers and inflammatory cytokines. Immunofluorescence and flow cytometry assay estimated macrophage polarization. MTT and flow cytometry assays severally measured cell viability and apoptosis. DCFH-DA probe detected ROS formation. RT-qPCR and Western blotting examined chondrocyte markers, apoptotic and pyroptotic genes. YGY significantly eased the histomorphological damage, apoptosis and pyroptosis in the cartilage tissues of KOA mice. Besides, YGY exerted anti-oxidant and anti-inflammatory activities and drove M1-to-M2 polarization of macrophages both in vitro and in vivo. Further, the co-culture of macrophages treated by LPS and serum containing YGY improved the viability, eliminated the apoptosis, pyroptosis, inflammation, oxidative stress and cartilage degradation in TNF-α-exposed chondrocytes co-cultured with LPS-intervened macrophages. Overall, YGY might mediate macrophage polarization to impede the advancement of KOA.

Application of collagen in bone regeneration

At present, there is a significant population of individuals experiencing bone deficiencies caused by injuries, ailments affecting the bones, congenital abnormalities, and cancer. The management of substantial bone defects a significant global orthopedic challenge due to the intricacies involved in promoting and restoring the growth of fresh osseous tissue. Autografts are widely regarded as the "gold standard" for repairing bone defects because of their superior tissue acceptance and ability to control osteogenesis. However, patients undergoing autografts may encounter various challenges, including but not limited to hernia, bleeding, nerve impairment, tissue death. Therefore, researchers in regenerative medicine are striving to find alternatives. Collagen is the most abundant protein in the human body, and its triple helix structure gives it unique characteristics that contribute to its strength and functionality in various tissues. Collagen is commonly processed into various forms such as scaffolds, sponges, membranes, hydrogels, and composite materials, due to its unique compatibility with the human body, affinity for water, minimal potential for immune reactions, adaptability, and ability to transport nutrients or drugs. As an alternative material in the field of bone regeneration, collagen is becoming increasingly important. The objective of this review is to provide a comprehensive analysis of the primary types and sources of collagen, their processes of synthesis and degradation, as well as the advancements made in bone regeneration research and its potential applications. A comprehensive investigation into the role of collagen in bone regeneration is undertaken, providing valuable points of reference for a more profound comprehension of collagen applications in this field. The concluding section provides a comprehensive overview of the prospective avenues for collagen research, underscoring their promising future and highlighting their significant potential in the field of bone regeneration. The Translational Potential of this Article. The comprehensive exploration into the diverse functions and translational potential of collagen in bone regeneration, as demonstrated in this review, these findings underscore their promising potential as a treatment option with significant clinical implications, thus paving the way for innovative and efficacious therapeutic strategies in this domain.

RIP1 inhibition reduces chondrocyte apoptosis through downregulating nuclear factor-kappa B signaling in a mouse osteoarthritis model

BACKGROUND

Excessive chondrocyte death is a critical player in the process of osteoarthritis (OA). The present study was aimed to study the role of receptor-interacting serine/threonine kinase (RIP) 1-mediated signaling for programmed cell death in OA.

METHODS

In the present study, RIP1 protein expression was evaluated in mouse OA cartilage and cultured primary murine chondrocytes exposed to tumor necrosis factor-alpha (TNF-α). Protein expression involved in necroptosis and apoptosis and chondrocyte-derived extracellular matrix were examined. Inhibition of RIP1 was conducted using the RNAi technique and pharmacological inhibition. Western blot, immunohistochemistry, and immunofluorescence examination were applied.

RESULTS

The protein presence of RIP1, but not RIP3, was increased in the mouse OA tissue and cultured chondrocytes exposed to TNF-α. Knockdown of RIP1 increased protein expression of collagen II and sex-determining region Y-box transcription factor 9, and reduced protein expression of matrix metallopeptidases 13 and a disintegrin and metalloproteinase with thrombospondin motifs 5. Inhibition of RIP1 reduced the phosphorylated NF-κB signals, decreased cell apoptosis, and restored extracellular matrix expression in cultured chondrocytes. Both RNAi and pharmacological inhibition of RIP1 decelerated the progress of OA in mice.

CONCLUSION

RIP1 regulates chondrocyte apoptosis through NF-κB signaling. Inhibition of RIP1 provides a novel therapeutic approach for OA therapy.

Sappanone a alleviates osteoarthritis progression by inhibiting chondrocyte ferroptosis via activating the SIRT1/Nrf2 signaling pathway

Osteoarthritis (OA) is a common degenerative joint disease that cause pain and disability in adults. Chondrocyte ferroptosis is found to be involved in OA progression. Sappanone A has been found as an anti-inflammatory and antioxidative agent in several diseases. This study aims to investigate the effects of sappanone A on OA progression and chondrocyte ferroptosis. IL-1β-induced chondrocytes and destabilization of the medial meniscus (DMM)-induced rats were respectively used as the OA model in vitro and in vivo. The effects of sappanone A on inflammation, extracellular matrix (ECM) metabolism, and ferroptosis were determined. Our results showed that in IL-1β-induced chondrocytes, sappanone A suppressed the production of NO, PGE2, TNF-α, IL-6, iNOS, and COX2. Sappanone A also inhibited the expression of MMP3, MMP13, and ADAMTS5, while increasing collagen II expression. Moreover, sappanone A alleviated cytotoxicity and decreased the levels of intracellular ROS, lipid ROS, MDA, and iron, while increasing GSH levels. Additionally, sappanone A increased the protein expression of SLC7A11 and GPX4. Administration of ferroptosis activator reversed the inhibitory effects of sappanone A on IL-1β-induced inflammation and ECM degradation. More importantly, Sappanone A activated the Nrf2 signaling by targeting SIRT1. The inhibition of sappanone A on ferroptosis was greatly eliminated due to the addition of SIRT1 inhibitor. Furthermore, intra-articular injection of sappanone A mitigated cartilage destruction and ferroptosis in DMM-induced OA rats. In conclusion, sappanone A protects against inflammation and ECM degradation in OA via decreasing chondrocyte ferroptosis by activating the SIRT1/Nrf2 signaling. These findings deepen our understanding of chondrocyte ferroptosis in OA and highlight the therapeutic potential of sappanone A for OA.

Kinetics and Retention of Polystyrenesulfonate for Proteoglycan Replacement in Cartilage

Tissue hydration provides articular cartilage with dynamic viscoelastic properties. Early stage osteoarthritis (OA) is marked by loss of proteoglycans and glycosaminoglycans (GAG), lowering fixed charge density, and impairing tissue osmotic function. The most common GAG replacement, chondroitin sulfate (CS), has failed to show effectiveness. Here, we investigated a synthetic polyelectrolyte, poly(styrenesulfonate) (PSS), both as a model compound to investigate polyelectrolyte transport in cartilage, and as a potential candidate to restore bulk fixed charge density in cartilage with GAG loss. Through bovine explants and histology, we determined zonal-based effective diffusion coefficients for three different molecular weights of PSS. Compared to CS, PSS was retained longer in GAG-depleted cartilage in static and compression-based desorption experiments. We explained enhanced solute performance of PSS by its more compact morphology and higher charge density by small-angle X-ray scattering. This study may improve design of GAG mimetic molecules for repairing osmotic function in OA cartilage.

Cyaonoside A-loaded composite hydrogel microspheres to treat osteoarthritis by relieving chondrocyte inflammation

Cyaonoside A (CyA), derived from the natural Chinese medicine, Cyathula officinalis Kuan, which was for a long time used to treat knee injuries and relieve joint pain in traditional Chinese medicine, showed an unclear mechanism for protecting cartilage. In addition, CyA was poorly hydrosoluble and incapable of being injected directly into the joint cavity, which limited its clinical application. This study reveals that CyA resisted IL-1β-mediated chondrogenic inflammation and apoptosis. Next, transcriptome sequencing is used to explore the potential mechanisms underlying CyA regulation of MSC chondrogenic differentiation. Based on these findings, CyA-loaded composite hydrogel microspheres (HLC) were developed and they possessed satisfactory loading efficiency, a suitable degradation rate and good biocompatibility. HLC increased chondrogenic anabolic gene (Acan, COL2A, and SOX9) expression, while downregulating the expression of the catabolic marker MMP13 in vitro. In the osteoarthritis mouse model, HLC demonstrated promising therapeutic capabilities by protecting the integrity of articular cartilage. In conclusion, this study provides insights into the regulatory mechanisms of CyA for chondrocytes and proposes a composite hydrogel microsphere-based advanced therapeutic strategy for osteoarthritis.

Senolytic therapeutics: An emerging treatment modality for osteoarthritis

Osteoarthritis (OA), a chronic joint disease affecting millions of people aged over 65 years, is the main musculoskeletal cause of diminished joint mobility in the elderly. It is characterized by lingering pain and increasing deterioration of articular cartilage. Aging and accumulation of senescent cells (SCs) in the joints are frequently associated with OA. Apoptosis resistance; irreversible cell cycle arrest; increased p16INK4a expression, secretion of senescence-associated secretory phenotype factors, senescence-associated β-galactosidase levels, secretion of extracellular vesicles, and levels of reactive oxygen and reactive nitrogen species; and mitochondrial dysregulation are some common changes in cellular senescence in joint tissues. Development of OA correlates with an increase in the density of SCs in joint tissues. Senescence-associated secretory phenotype has been linked to OA and cartilage breakdown. Senolytics and therapeutic pharmaceuticals are being focused upon for OA management. SCs can be selectively eliminated or killed by senolytics to halt the pathogenesis and progression of OA. Comprehensive understanding of how aging affects joint dysfunction will benefit OA patients. Here, we discuss age-related mechanisms associated with OA pathogenesis and senolytics as an emerging modality in the management of age-related SCs and pathogenesis of OA in preclinical and clinical studies.

High gastrointestinal digestive stability endows chondroitin sulfate-soluble undenatured type II collagen complex with high activity: Improvement of osteoarthritis in rats

Previously, we prepared a chondroitin sulfate-soluble undenatured type II collagen complex (CS-SC II) with low salt content. This paper further explored the differences between CS-SC II and SC II in terms of gastrointestinal digestive characteristics and osteoarthritis (OA) improvement. In vitro and in vivo experiments showed that the gastric digestive stability of CS-SC II was high under both pH 2.0 and pH 3.0, the α1 chain and triple helix structure of type II collagen retained >60 %. However, SC II had high gastric digestive stability only under pH 3.0. Furthermore, intestinal digestion had little effect on α1 chains of CS-SC II and SC II, and distribution experiments showed that they might exert their biological activities in the intestine. CS-SC II had obvious improvement in OA rats at 1.0 mg/kg/d, that is, the joint swelling was significantly reduced and the weight-bearing ratio of the right hind limb was increased to 49 %, which was close to that of 4.0 mg/kg/d SC II. The wear of articular cartilage, Mankin and OARSI scores of rats in CS-SC II group were significantly reduced. The effects of low-dose CS-SC II on the proportion of regulatory T cells (Treg), mRNA expression of OA key biomarkers (Il6, Ccl7, MMP-3 and MMP13) and signaling pathway genes (NF-κB, AKT or AMPKα) were comparable to those of high-dose SC II. These results showed that CS-SC II might have greater potential to improve OA at a lower dose than SC II due to its high gastrointestinal digestive stability at a wide range of pH conditions.