The etiology of osteoarthritis (OA) is multifactorial, with no effective disease-modifying-drugs. L-theanine has been reported to inhibit inflammatory responses in some diseases and this study aimed to investigate the effect of L-theanine on Interleukin-1(IL-1)β-stimulated chondrocytes, and in an injury-induced OA rat model. Primary chondrocytes were stimulated by IL-1β (10 ng/mL) for 24 h and then co-cultured with L-theanine for 24 h. The effects of L-theanine on IL-1β-stimulated expression of pro-inflammatory cytokines and hydrolytic enzyme were analyzed using Western blotting, quantitative polymerase chain reaction (q-PCR) and enzyme-linked immunosorbent assay (ELISA) kits. An immunofluorescence assay was used to detect nuclear factor kappa B (NF-κB) phosphorylation. OA was induced by anterior cruciate ligament transection (ACLT) surgery in rats and celecoxib was used as a positive control. OA severity was measured using the Osteoarthritis Research Society International (OARSI) grading system to describe histological changes. The results showed that L-theanine decreased the expression of pro-inflammatory mediators, including cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE-2), inducible nitric oxide synthase (iNOS), and nitric oxide (NO), both in vivo and in vitro. L-theanine treatment inhibited IL-1β-induced upregulation of matrix metalloproteinases (MMP)-3 and MMP-13, as well as inhibited NF-κB p65 activation. In vivo animal model showed that L-theanine administration (200 mg/kg) significantly alleviated OA lesions and decreased OARSI score. Our data indicated that L-theanine decreased inflammatory cytokines and protected extracellular matrix degradation through inhibition of the NF-κB pathway, and L-theanine may be considered a promising therapeutic strategy in OA prevention.

The specific adenosine A3 receptor (A3AR) agonist (CF101) has potential for inflammation and pain in various disease, such as arthritis, cancer and neuropathic pain, while the role of A3AR in post‐traumatic OA and the underlying mechanism is largely unknown. CF101 was orally administrated in OA rats induced by anterior cruciate ligament transection (ACLT) surgery, and the rat primary chondrocytes were stimulated by hydrogen peroxide (H2O2, 300 μM). Histologic grading system was performed for detecting cartilage degeneration and immunohistochemistry for determining pyroptosis. The moleculars associated with cartilage homeostasis and inflammatory cytokines were analysed; moreover, the activation of NLRP3 inflammasome was determined. CF101 treatment significantly attenuated OA cartilage damage, OA‐related pain and cartilage pyroptosis. Chondrocytes stimulated by H2O2 evoked ROS release, thereby promoting the activation of NLRP3 inflammasome and facilitating the cleavage of GSDMD, which ultimately resulted in the mass release of pro‐inflammatory cytokines including IL‐1β and IL‐18, and production of matrix hydrolase. The pre‐treatment with CF101 powerfully inhibited the above process both in vivo and in vitro. Our findings demonstrated that activation of A3AR attenuates OA progression and relieves pain perception through suppression of cartilage degradation and inhibition of ROS/NLRP3/GSDMD signalling, indicating pyroptosis is a potential candidate for OA treatment.

No abstract

Baicalein has been shown to have chondroprotective potential in vitro. However, its effect on disease modification in osteoarthritis (OA) is largely unknown. The present study is aimed at determining whether baicalein could slow the progression of OA and inhibit OA-related inflammation in a rat model of destabilization of the medial meniscus (DMM) and the underlying mechanisms. The rats subjected to DMM surgery were treated with baicalein (0.8, 1.6, and 3.2 μg/L, 50 μL, once a week) by intra-articular injection for 6 weeks. Dexamethasone (0.4 mg/mL, 50 μL, once a week) was used as a positive control. Histologic grading of cartilage degeneration was performed using the Osteoarthritis Research Society International (OARSI) recommended grading system (on a scale of 0-6). The expression levels of molecules associated with cartilage homeostasis and inflammatory cytokines were analyzed; moreover, the NLRP3 inflammasome activation and cartilage oxidative stress-associated molecules were determined. Baicalein treatment reduced the OARSI score and slowed OA disease progression in a dose-dependent manner within a certain range. Compared with DMM rats, intra-articular injection of baicalein led to (1) reduced levels of inflammatory mediates such as IL-1β and TNF-α, (2) reduced immunochemical staining of MMP-13 and ADAMTS-5, (3) suppressed immunochemical staining loss of type II collagen, (4) reduced expression of cartilage degradation markers including CTX-II and COMP in urine, and (5) inhibited NLRP3 inflammasome activation rather than regulated expression of SOD, GSH, and MDA. In contrast to the administration of baicalein, dexamethasone injection showed similar effects to slow OA progression, while dexamethasone inhibited NLRP3 inflammasome partly through decreasing levels of SOD, GSH, and MDA. This study indicated that baicalein may have the potential for OA prevention and exerts anti-inflammatory effects partly via suppressing NLRP3 inflammasome activation without affecting oxidative stress-associated molecules, and inhibition of cartilage catabolism enzymes in an OA rat model.

With the gradual deepening of understanding of systemic health and quality of life, the factors affecting osteoarthritis (OA) are not limited to mechanical injury, metabolic abnormality, age and obesity, etc., but circadian rhythm, which plays a non-negligible role in human daily life. The purpose of this study was to explore the molecular mechanism of chronic circadian rhythm disturbance (CRD) inducing cartilage OA-like degeneration. Rats with the anterior cruciate ligament excision transection (ACLT) were used to establish the early-stage OA model (6-week). The light/dark (LD) cycle shifted 12 h per week for 22 weeks in order to establish a chronic CRD model. BMAL1 knockdown (KD) and Wnt/β-catenin pathway inhibition were performed in chondrocytes. The contents of proinflammatory factors and OA biomarkers in serum and chondrocyte secretions were detected by ELISA. Pathological and immunohistochemical staining of articular cartilage indicated the deterioration of cartilage. WB and qPCR were used to evaluate the relationship between matrix degradation and the activation of Wnt/β-catenin signaling pathway in chondrocytes. We found that chronic CRD could cause OA-like pathological changes in knee cartilage of rats, accelerating cartilage matrix degradation and synovial inflammation. The expression of MMP-3, MMP-13, ADAMTS-4, and β-catenin increased significantly; BMAL1, Aggrecan, and COL2A1 decreased significantly in either LD-shifted cartilage or BMAL1-KD chondrocytes. The expression of β-catenin and p-GSK-3β elevated, while p-β-catenin and GSK-3β diminished. The inhibitor XAV-939 was able to mitigated the increased inflammation produced by transfected siBMAL1. Our study demonstrates that chronic CRD disrupts the balance of matrix synthesis and catabolic metabolism in cartilage and chondrocytes, and it is related to the activation of the canonical Wnt/β-catenin signaling pathway.