The in situ up-regulation of chondrocyte interleukin-1-converting enzyme and interleukin-18 levels in experimental osteoarthritis is mediated by nitric oxide

The impact of sericin on inflammation, oxidative stress, and lipid metabolism in female rats with experimental knee osteoarthritis

OBJECTIVE

This study investigated the effects of sericin on inflammation, oxidative stress, and lipid metabolism in female rats with experimental knee osteoarthritis (KOA), focusing on evaluating its effectiveness via the sterol regulatory protein (SREBP)-1C and SREBP-2 pathways.

METHODS

The rats were randomly assigned to three experimental groups: the C group (control), the KOA group (KOA control), and the sericin group (KOA + sericin). The KOA model was created by injecting monosodium iodoacetate (MIA) into the knee joint. Sericin was administered intra-articularly to rats on days 1, 7, 14, and 21 (0.8 g/kg/mL, 50 µL). After 21 days, the rats were sacrificed, and serum samples were analyzed using an ELISA to measure tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-10, SREBP-1c, SREBP-2, acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), cholesterol, triglyceride, and total oxidant-antioxidant status (TOS-TAS) levels.

RESULTS

The KOA group exhibited higher serum TNF-α, IL-1β, TOS, SREBP-1C, ACC, FAS, triglyceride, SREBP-2, and cholesterol levels than the C group (P < 0.05). However, the levels of these cytokines, except cholesterol, were significantly lower in the sericin group than in the KOA group. The KOA group exhibited significantly lower serum TAS and IL-10 levels than the C group (P < 0.05). In the sericin group, there was a statistically significant increase (P < 0.05).

CONCLUSION

Sericin shows promising potential for reducing inflammation, oxidative stress, and lipid metabolism in experimental models of KOA in rats. However, further clinical research is necessary to validate the potential of sericin as a therapeutic agent for treating KOA. Key Points • Sericin can reduce knee osteoarthritis (KOA) symptoms in an experimental rat model. • In particular, in the serum of an experimental KOA rat model, sericin specifically reduces the levels of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β), and increases the levels of anti-inflammatory cytokines, such as IL-10. • Sericin reduced lipid metabolism via the sterol regulatory protein (SREBP)-1C and SREBP-2 pathways and oxidative stress in the serum of the experimental KOA rat model. • The intra-articular administration of sericin has been shown to significantly reduce lipid metabolism, oxidative stress, and inflammation, as supported by biochemical analysis. These findings suggest its promising potential as an alternative treatment option for KOA.

Anti-Inflammatory Effects of Boric Acid in Treating Knee Osteoarthritis: Biochemical and Histopathological Evaluation in Rat Model

This study aimed to examine the anti-inflammatory properties of boric acid (BA) in treating knee osteoarthritis (KOA) in rats, evaluating its biochemical and histopathological therapeutic effects. A KOA rat model was induced by injecting monosodium iodoacetate into the knee joint. Random assignment was performed for the experimental groups as follows: group-1(control), group-2(KOA control), group-3 (BA:4 mg/kg, orally), group-4(BA:10 mg/kg, orally), group-5(BA:4 mg/kg, intra-articularly), and group-6(BA:10 mg/kg, intra-articularly). The rats received 100 µL of BA intra-articularly on days 1, 7, 14, and 21 or 1 mL orally once a day (5 days/week) for 4 weeks. Serum levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and activity of matrix metalloproteinase-13 (MMP-13) were measured. Histopathological and immunohistochemical analyses were performed on knee joint samples using specific antibodies for IL-1β, TNF-α, MMP-13, and nitric oxide synthase-2 (NOS-2). Group-2 exhibited higher serum IL-1β and TNF-α levels and MMP-13 activity than group-1 (P < 0.05). However, IL-1β and TNF-α levels and MMP-13 activity were lower in all treatment groups than in group-2, with statistically significant reductions observed in groups-4, 5, and 6. Histopathologically, group-2 displayed joint space narrowing, cartilage degeneration, and deep fissures. Groups-5 and 6 demonstrated significant joint space enlargement, articular cartilage tissue regeneration, and immunostaining patterns similar to those in group-1. Immunohistochemically, group-2 showed significant increases in IL-1β, TNF-α, MMP-13, and NOS-2 expression. However, all treatment groups exhibited reductions in these expression levels compared to group-2, with statistically significant decreases observed in groups-5 and 6 (P < 0.01). BA shows potential efficacy in reducing inflammation in experimental KOA model in rats. It may be a promising therapeutic agent for KOA, warranting further clinical studies for validation.

Potential therapeutic strategies for osteoarthritis via CRISPR/Cas9 mediated gene editing

Osteoarthritis (OA) is an incapacitating and one of the most common physically degenerative conditions with an assorted etiology and a highly complicated molecular mechanism that to date lacks an efficient treatment. The capacity to design biological networks and accurately modify existing genomic sites holds an apt potential for applications across medical and biotechnological sciences. One of these highly specific genomes editing technologies is the CRISPR/Cas9 mechanism, referred to as the clustered regularly interspaced short palindromic repeats, which is a defense mechanism constituted by CRISPR associated protein 9 (Cas9) directed by small non-coding RNAs (sncRNA) that bind to target DNA through Watson-Crick base pairing rules where subsequent repair of the target DNA is initiated. Up-to-date research has established the effectiveness of the CRISPR/Cas9 mechanism in targeting the genetic and epigenetic alterations in OA by suppressing or deleting gene expressions and eventually distributing distinctive anti-arthritic properties in both in vitro and in vivo osteoarthritic models. This review aims to epitomize the role of this high-throughput and multiplexed gene editing method as an analogous therapeutic strategy that could greatly facilitate the clinical development of OA-related treatments since it's reportedly an easy, minimally invasive technique, and a comparatively less painful method for osteoarthritic patients.

Anti-inflammatory Effects of Boric Acid in Treating Knee Osteoarthritis: Biochemical and Histopathological Evaluation in Rat Models.. [DOI: 10.21203/rs.3.rs-3091978/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Objective: This study aimed to examine the anti-inflammatory properties of boric acid(BA) in treatingknee osteoarthritis(KOA) in rats, evaluating its biochemical and histopathological therapeutic effects. Methods: The KOA rat model was induced by injecting monosodium iodoacetate into the knee joint. Random assignment was performed for the experimental groups as follows: group-1(control), group-2(KOA control), group-3(BA:4 mg/kg,orally), group-4(BA:10 mg/kg,orally), group-5 (BA:4 mg/kg,intra-articularly), and group-6(BA:10 mg/kg,intra-articularly). The rats received 100 µL of BA intra-articularly on days 1,7,14, and 21 or 1 mL orally once a day (5 days/week) for 4 weeks. Serum levels of interleukin-1β (IL-1β), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase-13(MMP-13) were measured. Histopathological and immunohistochemical analyses were performed on knee joint samples using specific antibodies for IL-1β, TNF-α, MMP13, and nitric oxide synthase-2(NOS-2). Results. Group-2 exhibited higher serum levels of IL-1β, TNF-α, and MMP-13 than group-1(P<0.05). However, these levels were lower in all treatment groups compared to group-2, with statistically significant reductions observed in groups-4,5, and 6. Histopathologically, group-2 displayed joint space narrowing, cartilage degeneration, and deep fissures. Groups-5 and 6 demonstrated significant joint space enlargement, articular cartilage tissue regeneration, and immunostaining patterns similar to those in group-1. Immunohistochemically, group-2 showed significant increases in IL-1β, TNF-α, MMP-13, and NOS-2 expression. However, all treatment groups exhibited reductions in these expression levelscompared to group-2, with statistically significant decreases observed in groups-5 and 6(P<0.01). Conclusions. BA shows potential efficacy in reducing inflammation in experimental KOA models in rats. It may be a promising therapeutic agent for KOA, warranting further clinical studies for validation.

Inflammatory Process on Knee Osteoarthritis in Cyclists

Osteoarthritis is a disorder affecting the joints and is characterized by cellular stress and degradation of the extracellular matrix cartilage. It begins with the presence of micro- and macro-lesions that fail to repair properly, which can be initiated by multiple factors: genetic, developmental, metabolic, and traumatic. In the case of the knee, osteoarthritis affects the tissues of the diarthrodial joint, manifested by morphological, biochemical, and biomechanical modifications of the cells and the extracellular matrix. All this leads to remodeling, fissuring, ulceration, and loss of articular cartilage, as well as sclerosis of the subchondral bone with the production of osteophytes and subchondral cysts. The symptomatology appears at different time points and is accompanied by pain, deformation, disability, and varying degrees of local inflammation. Repetitive concentric movements, such as while cycling, can produce the microtrauma that leads to osteoarthritis. Aggravation of the gradual lesion in the cartilage matrix can evolve to an irreversible injury. The objective of the present review is to explain the evolution of knee osteoarthritis in cyclists, to show the scarce research performed in this particular field and extract recommendations to propose future therapeutic strategies.

PPAR-γ Activation Alleviates Osteoarthritis through Both the Nrf2/NLRP3 and PGC-1α/Δψm Pathways by Inhibiting Pyroptosis

Osteoarthritis (OA) is a common degenerative joint disease with a gradually increasing morbidity in the aging and obese population. Emerging evidence has implicated pyroptosis in the etiology of OA and it may be recognized as a therapeutic target in OA. We have previously reported regarding another disease that peroxisome proliferator-activated receptor gamma (PPAR-γ) activation exerts an anti-inflammatory effect by suppressing the nucleotide-binding and oligomerization domain-like receptor containing protein (NLRP) 3 inflammasome. However, the relationship between PPAR-γ and NLRP3-mediated pyroptosis in OA cartilage and its underlying mechanisms is fully unclear. In this study, we found that the level of NLRP3-mediated pyroptosis in severe lateral femoral condyle cartilage wear in the knee of an OA patient was significantly higher than that in the mild lateral femoral condyle cartilage wear areas. Moreover, in lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-induced primary chondrocytes and knee OA rat models, we demonstrated that activation of PPAR-γ by pioglitazone (Piog) attenuated LPS/ATP-induced chondrocyte pyroptosis and arthritis. These effects were partially counteracted by either blocking the nuclear factor erythroid-2-related factor (Nrf2)/NLRP3 or PGC1-α/Δψm signaling pathway. Simultaneous depression of these two signaling pathways can completely abrogate the protective effects of Piog on OA and chondrocytes. Taken together, Piog protects OA cartilage against pyroptosis-induced damage by simultaneously activating both the Nrf2/NLRP3 and PGC-1α/Δψm pathways, which enhances antioxidative and anti-inflammatory responses as well as mitochondrial biogenesis. Therefore, Piog may be a promising agent for human OA cartilage damage in future clinical treatments.

Connection between Osteoarthritis and Nitric Oxide: From Pathophysiology to Therapeutic Target

Osteoarthritis (OA), a disabling joint inflammatory disease, is characterized by the progressive destruction of cartilage, subchondral bone remodeling, and chronic synovitis. Due to the prolongation of the human lifespan, OA has become a serious public health problem that deserves wide attention. The development of OA is related to numerous factors. Among the factors, nitric oxide (NO) plays a key role in mediating this process. NO is a small gaseous molecule that is widely distributed in the human body, and its synthesis is dependent on NO synthase (NOS). NO plays an important role in various physiological processes such as the regulation of blood volume and nerve conduction. Notably, NO acts as a double-edged sword in inflammatory diseases. Recent studies have shown that NO and its redox derivatives might be closely related to both normal and pathophysiological joint conditions. They can play vital roles as normal bone cell-conditioning agents for osteoclasts, osteoblasts, and chondrocytes. Moreover, they can also induce cartilage catabolism and cell apoptosis. Based on different conditions, the NO/NOS system can act as an anti-inflammatory or pro-inflammatory agent for OA. This review summarizes the studies related to the effects of NO on all normal and OA joints as well as the possible new treatment strategies targeting the NO/NOS system.

Regulatory network-based model to simulate the biochemical regulation of chondrocytes in healthy and osteoarthritic environments

In osteoarthritis (OA), chondrocyte metabolism dysregulation increases relative catabolic activity, which leads to cartilage degradation. To enable the semiquantitative interpretation of the intricate mechanisms of OA progression, we propose a network-based model at the chondrocyte level that incorporates the complex ways in which inflammatory factors affect structural protein and protease expression and nociceptive signals. Understanding such interactions will leverage the identification of new potential therapeutic targets that could improve current pharmacological treatments. Our computational model arises from a combination of knowledge-based and data-driven approaches that includes in-depth analyses of evidence reported in the specialized literature and targeted network enrichment. We achieved a mechanistic network of molecular interactions that represent both biosynthetic, inflammatory and degradative chondrocyte activity. The network is calibrated against experimental data through a genetic algorithm, and 81% of the responses tested have a normalized root squared error lower than 0.15. The model captures chondrocyte-reported behaviors with 95% accuracy, and it correctly predicts the main outcomes of OA treatment based on blood-derived biologics. The proposed methodology allows us to model an optimal regulatory network that controls chondrocyte metabolism based on measurable soluble molecules. Further research should target the incorporation of mechanical signals.

miR-107 affects cartilage matrix degradation in the pathogenesis of knee osteoarthritis by regulating caspase-1

Background

Knee osteoarthritis (KOA) seriously affects the quality of life of KOA patients. This study aimed to investigate whether miR-107 could regulate KOA through pyroptosis to affect collagen protein secreted by chondrocytes through IL-1β.

Methods

The proliferation of chondrocytes was detected by CCK-8 assay. RT-qPCR analysis was used to identify miR-107 expression and transfection effects. The expression of Col II, IL-1β, IL-18, and MMP13 in supernatant of chondrocytes or chondrocytes was detected by ELISA assay and western blot analysis. The pyroptosis of chondrocytes was analyzed by TUNEL assay and the expression of pyroptosis-related proteins was analyzed by western blot. Luciferase reporter assay confirmed the relation of miR-107 to caspase-1.

Results

The proliferation of chondrocytes was decreased after LPS induction and further decreased by treatment of ATP. Single LPS treatment for chondrocytes downregulated the Col II expression while upregulated the expression of IL-1β, IL-18, and MMP-13, which was further changed by ATP treatment. miR-107 expression was decreased in chondrocytes induced by LPS and further decreased in chondrocytes induced by LPS and ATP. In addition, miR-107 overexpression increased the proliferation and decreased the pyroptosis of chondrocytes induced by LPS and ATP. miR-107 overexpression upregulated the Col II expression while down-regulated the expression of IL-1β, IL-18, and MMP-13 in supernatant of chondrocytes or chondrocytes induced by LPS and ATP. miR-107 overexpression down-regulated the expression of caspase-1, c-caspase-1, GSDMD-N, and TLR4 in chondrocytes induced by LPS and ATP. Furthermore, miR-107 directly targeted caspase-1.

Conclusions

miR-107 can protect against KOA by downregulating caspase-1 to decrease pyroptosis, thereby promoting collagen protein secreted by chondrocytes by down-regulating IL-1β.

Hyaluronic acid injection reduces inflammatory and apoptotic markers through modulation of AKT by repressing the oxidative status of neutrophils from osteoarthritic synovial fluid

Hyaluronic acid (HA) injection into the osteoarthritis (OA) knee is one of the most popular treatment methods. The study aimed to determine whether HA exhibits antioxidant and antiapoptotic functions in the treatment of OA. Sixty-two outpatient patients with a diagnosis of knee OA were recruited. All patients received (HA) injections twice at a 2-week interval. Synovial fluid through sono-guided aspiration was collected for neutrophils isolation. Oxidative stress, apoptotic markers and related pathways in neutrophils were investigated. Among the oxidative stress markers, 4-hydroxynonenal (4-HNE) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) significantly decreased after HA injection, while superoxide dismutase (SOD) and catalase did not change, which indicated that HA injection had an antioxidant effect that was not through activation of antioxidant enzymes. In addition, we found that HA injection decreased p-AKT levels and decreased p-p53 and p-p38 but not p-GSK-3β. Moreover, we confirmed that HA injection reduced proapoptotic markers through a mitochondria-dependent pathway and proinflammatory events. In vitro investigations also confirmed that HA reduced TNF-α-caused apoptosis in chondrocytes, however, this phenomenon was vanished by AKT inhibitor. Taken together, HA injection into human OA knees resulted antioxidant and antiapoptotic functions, as well as reduced inflammation, through modulation of the AKT pathway.

Simvastatin abolishes nitric oxide- and reactive oxygen species-induced cyclooxygenase-2 expression by blocking the nuclear factor κB pathway in rabbit articular chondrocytes

Nitric oxide (NO) and reactive oxygen species (ROS) have been shown to be linked with numerous diseases, including osteoarthritis (OA). Our study aimed to examine the effect of simvastatin on NO- or ROS-induced cyclooxygenase-2 (COX-2) expression in OA. Simvastatin has attracted considerable attention since the discovery of its pharmacological effects on different pathogenic processes, including inflammation. Here, we report that simvastatin treatment blocked sodium nitroprusside (SNP)- and interleukin 1 beta (IL-1β)-induced COX-2 production. In addition, simvastatin attenuated SNP-induced NO production and IL-1β-induced ROS generation. Treatment with simvastatin prevented SNP- and IL-1β-induced nuclear factor kappa B (NF-κB) activity. Inhibiting NO production and ROS generation using N-acetylcysteine (NAC) and NG-monomethyl- l-arginine ( l-NMMA), respectively, accelerated the influence of simvastatin on NF-κB activity. In addition, NAC blocked SNP and simvastatin-mediated COX-2 production and NF-κB activity but did not alter IL-1β and simvastatin-mediated COX-2 expression. l-NMMA treatment also abolished IL-1β-mediated COX-2 expression and NF-κB activation, whereas SNP and simvastatin-mediated COX-2 expression were not altered compared with the levels in the SNP and simvastatin-treated cells. Our findings suggested that simvastatin blocks COX-2 expression by inhibiting SNP-induced NO production and IL-1β-induced ROS generation by blocking the NF-κB pathway.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

The Pathobiology of the Meniscus: A Comparison Between the Human and Dog

Serious knee pain and related disability have an annual prevalence of approximately 25% on those over the age of 55 years. As curative treatments for the common knee problems are not available to date, knee pathologies typically progress and often lead to osteoarthritis (OA). While the roles that the meniscus plays in knee biomechanics are well characterized, biological mechanisms underlying meniscus pathophysiology and roles in knee pain and OA progression are not fully clear. Experimental treatments for knee disorders that are successful in animal models often produce unsatisfactory results in humans due to species differences or the inability to fully replicate disease progression in experimental animals. The use of animals with spontaneous knee pathologies, such as dogs, can significantly help addressing this issue. As microscopic and macroscopic anatomy of the canine and human menisci are similar, spontaneous meniscal pathologies in canine patients are thought to be highly relevant for translational medicine. However, it is not clear whether the biomolecular mechanisms of pain, degradation of extracellular matrix, and inflammatory responses are species dependent. The aims of this review are (1) to provide an overview of the anatomy, physiology, and pathology of the human and canine meniscus, (2) to compare the known signaling pathways involved in spontaneous meniscus pathology between both species, and (3) to assess the relevance of dogs with spontaneous meniscal pathology as a translational model. Understanding these mechanisms in human and canine meniscus can help to advance diagnostic and therapeutic strategies for painful knee disorders and improve clinical decision making.

Inducible nitric oxide synthase as a target for osteoarthritis treatment

INTRODUCTION

Inducible nitric oxide synthase (iNOS) is the enzyme responsible for the production of nitric oxide (NO), a major proinflammatory and destructive mediator in osteoarthritis (OA). Areas covered: This is a comprehensive review of the recent literature on the involvement of iNOS in osteoarthritis and its potential to be used as a target for OA treatment. Evidence from in vitro, in vivo and human studies was systematically collected using medical search engines. Preclinical studies have focused on the effect of direct and indirect iNOS inhibitors in both animal and human tissues. Apart from direct inhibitors, common pharmacological agents, herbal and dietary medicines as well as hyperbaric oxygen, low level laser and low intensity pulsed ultrasound have been shown to exhibit a chondroprotective effect by inhibiting the expression of iNOS. Expert opinion: Data support the further investigation of iNOS inhibitors for the treatment of OA in human studies and clinical trials. Indirect iNOS inhibitors such as interleukin 1 inhibitors also need to be studied in greater detail. Finally, human studies need to be conducted on the herbal and dietary medicines and on the non-invasive, non-pharmacological treatments.

Pentosan polysulfate inhibits IL-1β-induced iNOS, c-Jun and HIF-1α upregulation in canine articular chondrocytes

Osteoarthritic (OA) chondrocytes are shown to express inducible nitric oxide synthase (iNOS) which produces high concentrations of nitric oxide (NO), particularly when stimulated with proinflammatory cytokines. NO is involved in OA cartilage degradation. On the other hand, c-Jun N-terminal Kinase (JNK) pathway mediates the activation and transcription of c-Jun, which is required for interleukin-1 (IL-1)-induction of matrix metalloproteinases-13 (MMP-13) in OA pathogenesis. Therefore, the selective inhibition of iNOS and c-Jun is a promising target for treatment and prevention of OA. The purpose of the study was to investigate the inhibitory effects of pentosan polysulfate (PPS) on IL-1β-induced iNOS, c-Jun and HIF-α isoforms upregulation in canine articular chondrocytes (CACs). Primary (P0) chondrocytes were isolated and cultured from femoral head cartilages of three (3) dogs. First passage (P1) chondrocytes were preincubated with 0, 1, 5, 15 and 40 μg/mL of PPS for 4 hr before treatment with 10 ng/mL rhIL-1β for a further 8 hr. In addition, we evaluated the effects of single and multiple cytokine with or without LPS on iNOS protein induction. PPS significantly inhibited (P < 0.05) IL-1β-induced iNOS, c-Jun and HIF-1α mRNA upregulation in a dose-dependent pattern. iNOS mRNA was significantly inhibited at 15 and 40 μg/mL whereas c-Jun and HIF-1α were significantly downregulated at 5, 15 and 40 μg/mL of PPS compared to chondrocytes treated with only rhIL-1β. Intriguingly, CACs were recalcitrant to single IL-1β, TNF-α or LPS-induction of iNOS protein including to a combination of IL-1β+TNF-α, IL-1β+LPS except to TNF-α+LPS and IL-1β+TNF-α+LPS suggestive of a protective mechanism from iNOS detrimental effects on perpetuating OA. IL-1β+TNF-α+LPS-induced iNOS protein expression was significantly abrogated by PPS. We demonstrate for the first time that PPS is a novel inhibitor of IL-1β-induced iNOS, c-Jun, and HIF-1α mRNA upregulation and iNOS protein induction which may be beneficial for prevention and treatment OA.

Administration of 17β-Estradiol Improves Motoneuron Survival and Down-regulates Inflammasome Activation in Male SOD1(G93A) ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease manifested by the progressive loss of upper and lower motoneurons. The pathomechanism of ALS is complex and not yet fully understood. Neuroinflammation is believed to significantly contribute to disease progression. Inflammasome activation was recently shown in the spinal cord of human sporadic ALS patients and in the SOD1(G93A) mouse model for ALS. In the present study, we investigated the neuroprotective and anti-inflammatory effects of 17β-estradiol (E2) treatment in pre-symptomatic and symptomatic male SOD1(G93A) mice. Symptomatic mice with E2 substitution exhibited improved motor performance correlating with an increased survival of motoneurons in the lumbar spinal cord. Expression of NLRP3 inflammasome proteins and levels of activated caspase 1 and mature interleukin 1 beta were significantly reduced in SOD1(G93A) mice supplemented with E2.

A Comparison of the Effects of Neuronal Nitric Oxide Synthase and Inducible Nitric Oxide Synthase Inhibition on Cartilage Damage

The objective of this study was to investigate the effects of selective inducible nitric oxide synthase and neuronal nitric oxide synthase inhibitors on cartilage regeneration. The study involved 27 Wistar rats that were divided into five groups. On Day 1, both knees of 3 rats were resected and placed in a formalin solution as a control group. The remaining 24 rats were separated into 4 groups, and their right knees were surgically damaged. Depending on the groups, the rats were injected with intra-articular normal saline solution, neuronal nitric oxide synthase inhibitor 7-nitroindazole (50 mg/kg), inducible nitric oxide synthase inhibitor amino-guanidine (30 mg/kg), or nitric oxide precursor L-arginine (200 mg/kg). After 21 days, the right and left knees of the rats were resected and placed in formalin solution. The samples were histopathologically examined by a blinded evaluator and scored on 8 parameters. Although selective neuronal nitric oxide synthase inhibition exhibited significant (P = 0.044) positive effects on cartilage regeneration following cartilage damage, it was determined that inducible nitric oxide synthase inhibition had no statistically significant effect on cartilage regeneration. It was observed that the nitric oxide synthase activation triggered advanced arthrosis symptoms, such as osteophyte formation. The fact that selective neuronal nitric oxide synthase inhibitors were observed to have mitigating effects on the severity of the damage may, in the future, influence the development of new agents to be used in the treatment of cartilage disorders.

ROS/oxidative stress signaling in osteoarthritis

Osteoarthritis is the most common joint disorder with increasing prevalence due to aging of the population. Its multi-factorial etiology includes oxidative stress and the overproduction of reactive oxygen species, which regulate intracellular signaling processes, chondrocyte senescence and apoptosis, extracellular matrix synthesis and degradation along with synovial inflammation and dysfunction of the subchondral bone. As disease-modifying drugs for osteoarthritis are rare, targeting the complex oxidative stress signaling pathways would offer a valuable perspective for exploration of potential therapeutic strategies in the treatment of this devastating disease.

Soluble biglycan: a potential mediator of cartilage degradation in osteoarthritis

Background

Soluble biglycan (sBGN) and soluble decorin (sDCN), are two closely related essential components of extracellular matrix which both have been shown to possess proinflammatory properties. We studied whether sBGN or sDCN were present in synovial fluid (SF) of osteoarthritis (OA) or rheumatoid arthritis (RA) patients and studied sBGN or sDCN potential role in the degradation of OA cartilage.

Methods

SF obtained from meniscus tear, OA, and RA patients were analysed for sBGN and sDCN using enzyme-linked immunosorbent assays. OA chondrocytes and cartilage explants were stimulated for 48 h with 5 μg/ml sBGN or 1 μg/ml lipopolysaccharide. Messenger RNA (mRNA) levels of Toll-like receptors (TLRs), proteinases and cartilage matrix molecules were determined using quantitative real-time polymerase chain reaction. Protein levels of matrix metalloproteinases (MMPs) and cytokines were measured using Luminex xMap technology. Production of nitric oxide (NO), release of proteoglycans and soluble collagen were measured from conditioned culture media using biochemical assays. OA cartilage explant proteoglycans were stained for Safranin O and quantified using image analysis. TLR4 activation by sBGN and sDCN was studied in engineered HEK-293 cells with TLR4 signalling genes inserted together with a reporter gene.

Results

sBGN was found in meniscus tear SF (14 ± 2 ng/ml), OA SF (582 ± 307 ng/ml) and RA SF (1191 ± 482 ng/ml). Low levels of sDCN could also be detected in SF of meniscus tear (51 ± 4) ng/ml, OA (52 ± 3 ng/ml), and RA (49 ± 4 ng/ml). Stimulation of chondrocytes with sBGN increased significantly the mRNA and protein expression of catabolic MMPs, including MMP1, MMP9 and MMP13, and of inflammatory cytokines interleukin (IL)-6 and IL-8, whereas the expression of anabolic markers aggrecan and collagen type II was decreased. sBGN induced release of proteoglycans, collagen and NO from chondrocytes and cartilage explants. The catabolic response in explants was dependent of OA cartilage degradation stage. The mechanism of action of sBGN was mainly mediated through the TLR4-nuclear factor-κB pathway.

Conclusions

High levels of sBGN was found in advanced OA and RA SF. sBGN activates chondrocytes mainly via TLR4, which results in net loss of cartilage. Thus, sBGN can be a mediator of OA cartilage degradation and also a potential biomarker for arthritis.

Evaluation of the anti-inflammatory, anti-catabolic and pro-anabolic effects of E-caryophyllene, myrcene and limonene in a cell model of osteoarthritis

Osteoarthritis is a progressive joint disease and a major cause of disability for which no curative therapies are yet available. To identify compounds with potential anti-osteoarthritic properties, in this study, we screened one sesquiterpene, E-caryophyllene, and two monoterpenes, myrcene and limonene, hydrocarbon compounds for anti-inflammatory, anti-catabolic and pro-anabolic activities in human chondrocytes. At non-cytotoxic concentrations, myrcene and limonene inhibited IL-1β-induced nitric oxide production (IC50=37.3μg/ml and 85.3µg/ml, respectively), but E-caryophyllene was inactive. Myrcene, and limonene to a lesser extent, also decreased IL-1β-induced NF-κB, JNK and p38 activation and the expression of inflammatory (iNOS) and catabolic (MMP-1 and MMP-13) genes, while increasing the expression of anti-catabolic genes (TIMP-1 and -3 by myrcene and TIMP-1 by limonene). Limonene increased ERK1/2 activation by 30%, while myrcene decreased it by 26%, relative to IL-1β-treated cells. None of the compounds tested was able to increase the expression of cartilage matrix-specific genes (collagen II and aggrecan), but both compounds prevented the increased expression of the non-cartilage specific, collagen I, induced by IL-1β. These data show that myrcene has significant anti-inflammatory and anti-catabolic effects in human chondrocytes and, thus, its ability to halt or, at least, slow down cartilage destruction and osteoarthritis progression warrants further investigation.

Inflammasome activation in response to dead cells and their metabolites

Cell death cannot go unnoticed. It demands that the surrounding cells clear away the corpses in a manner appropriate to the type of cell death. Dying cells represent a threat to the body that should be eliminated by the host immune response. Inflammasome activation followed by IL-1alpha release and IL-1beta maturation is crucial for tackling pathological conditions, including infections, whereas inflammasome activation precedes inflammatory pyroptotic cell death. On the other hand, recent studies have shown that the inflammasome plays an important role in the pathogenesis of metabolic diseases, including obesity, diabetes, and atherosclerosis. Here, we review current knowledge of the association between cell death, excess metabolites, and inflammasome activation as it relates to chronic inflammatory diseases.

Effect of S-methylisothiourea, an inducible nitric oxide synthase inhibitor, in joint pain and pathology in surgically induced model of osteoarthritis

The aim of the present study was to evaluate in vivo modulatory effect of S-methylisothiourea (SMT), a preferential inhibitor of inducible nitric oxide synthase (iNOS) on pain and pathology in the surgical model of osteoarthritis (OA) in rats. The OA was produced by the anterior cruciate ligament transection (ACLT) and medial meniscectomy (MMx) of right knee. SMT was administered 1 day prior to the production of OA and continued up to day 42 postoperation. Mechanical hyperalgesia, thermal hyperalgesia, tail flick latency after repeated flexion and extension of OA knee and knee diameter of right knee were determined at weekly intervals. Serum levels of IL-1β, TNF-α and nitrite concentration were determined at the end of the experiment. Glycosaminoglycan (GAG) content, collagen content and histopathological evaluation of articular cartilage were also determined at the end of the experiment. SMT reduced mechanical hyperalgesia and the serum levels of IL-1β, TNF-α and nitrite. Further, SMT reduced the loss of GAG from articular cartilage. Microscopically, SMT reduced the severity of the cartilage lesion. The results indicate the effectiveness of SMT in attenuating the pain and pathology of experimental OA phase by reducing the production of nitric oxide and interleukin-1β and tumor necrosis factor-α, which are known to play a major role in the pathophysiology of OA.

Effect of iNOS inhibitor S-methylisothiourea in monosodium iodoacetate-induced osteoathritic pain: implication for osteoarthritis therapy

Much information is available on the role of nitric oxide (NO) in osteoarthritis (OA). However, its role has not been studied in the monosodium iodoacetate (MIA)-induced model of osteoarthritic pain. The present study was undertaken in rats to investigate the effect of iNOS inhibitor S-methylisothiourea (SMT) in MIA-induced osteoathritic pain and disease progression in rats. Osteoarthritis was produced by single intra-articular injection of the MIA in the right knee joint on day 0. Treatment groups were orally gavazed with different doses of SMT (10, 30 and 100mg/kg) and etoricoxib (10mg/kg) daily for 21 days. On days 0, 3, 7, 14 and 21, pain was measured and histopathology of right knee joint was done on day 21. SMT produced analgesia in a dose-dependent manner as shown by mechanical, heat hyperalgesia, knee vocalization, knee squeeze test, and spontaneous motor activity test. SMT reduced NO production in synovial fluid. Histopathological findings indicated that SMT reduced disease progression as evident from complete cartilage formation in rats treated with SMT at 30 mg/kg. In conclusion, the results indicate that SMT attenuates the MIA-induced pain and histopathological changes in the knee joint. The antinociceptive and antiarthritic effects of SMT were mediated by inhibiting cartilage damage and suppression of NO in synovial fluid. It is suggested that SMT has potential as a therapeutic modality in the treatment of osteoarthritis.

Oxidative stress in secondary osteoarthritis: from cartilage destruction to clinical presentation?

Due to an increasing life expectance, osteoarthritis (OA) is one of the most common chronic diseases. Although strong efforts have been made to regenerate degenerated joint cartilage, OA is a progressive and irreversible disease up to date. Among other factors the dysbalance between free radical burden and cellular scavenging mechanisms defined as oxidative stress is a relevant part of OA pathogenesis. Here, only little data are available about the mediation and interaction between different joint compartments. The article provides a review of the current literature regarding the influence of oxidative stress on cellular aging, senescence and apoptosis in different joint compartments (cartilage, synovial tissue and subchondral bone). Free radical exposure is known to promote cellular senescence and apoptosis. Radical oxygen species (ROS) involvement in inflammation, fibrosis control and pain nociception has been proven. The data from literature indicates a link between free radical burden and OA pathogenesis mediating local tissue reactions between the joint compartments. Hence, oxidative stress is likely not only to promote cartilage destruction but also to be involved in inflammative transformation, promoting the transition from clinically silent cartilage destruction to apparent OA. ROS induced by exogenous factors such as overload, trauma, local intraarticular lesion and consecutive synovial inflammation cause cartilage degradation. In the affected joint, free radicals mediate disease progression. The interrelationship between oxidative stress and OA etiology might provide a novel approach to the comprehension and therefore modification of disease progression and symptom control.

Physiology and pathophysiology of nitrosative and oxidative stress in osteoarthritic joint destruction

Osteoarthritis (OA) is one of the most common chronic diseases, with increasing importance due to increased life expectancy. On a cellular level, the pathophysiology of joint function impairment and ultimate destruction associated with OA remains poorly understood. Free radicals are highly reactive molecules involved in both normal intracellular signal transduction and degenerative cellular processes. An imbalance between the free radical burden and cellular scavenging mechanisms, defined as oxidative stress, has been identified as a relevant factor in OA pathogenesis. This literature review elucidates the involvement of nitrosative and oxidative stress in cellular ageing in joints, cell senescence, and apoptosis. Free radical exposure is known to promote cellular senescence and apoptosis, and the involvement of radical oxygen species (ROS) in inflammation, fibrosis control, and pain nociception has been proven. A relatively novel approach to OA pathophysiology considers the joint to be a dynamic system consisting of 3, continuously interacting compartments, cartilage, synovial tissue, and subchondral bone. Current knowledge concerning free radical involvement in paracrine signalling in OA is reviewed. The interrelationship between oxidative imbalances and OA pathophysiology may provide a novel approach to the comprehension, and therefore modification, of OA disease progression and symptom control.

Association between radiographic hand osteoarthritis and RANKL, OPG and inflammatory markers

OBJECTIVE

The aim of the study was to evaluate the association between prevalence and severity of radiographic hand osteoarthritis (OA) and serum levels of systemic inflammatory markers in a community-based population sample.

DESIGN

A cross-sectional observational study was conducted on a population comprised 1452 Chuvashians (763 males, aged 49.23 ± 17.43; and 689 females, aged 50.37 ± 17.47 years). OA was evaluated in 14 joints of each hand using Kellgren and Lawrence (K-L), joint space narrowing (JSN) and osteophyte (OS) scores. Serum levels of systemic inflammatory and osteoclastogenic cytokines were measured by an enzyme-linked immunosorbent assay (ELISA). Statistical analyses included descriptive statistics, correlation analysis and multiple linear regressions.

RESULTS

Monocyte chemotactic protein-1 (MCP-1) and osteoprotegerin (OPG) levels were associated with OA traits, but the statistically significant correlations were weak and/or moderate. In particular, the MCP-1 inflammation marker showed a statistically significant association with JSN (β=0.077, P=0.022) and OS (β=0.067, P=0.024) scores, but not with the number of affected joints (K-L ≥ 2). OPG was significantly correlated with the scores as to the number of affected joints (β=0.063, P=0.035) and OS (β=0.077, P=0.028). No significant associations were found between levels of other inflammatory [interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-17] and osteoclastogenic [receptor activator for nuclear factor κ B ligand (RANKL), macrophage colony-stimulating factor (M-CSF)] cytokines and OA characteristics.

CONCLUSIONS

This study strengthens the premise that OPG might be a valid biomarker of hand OA. Confirmation of these results in larger cohorts of patients will reinforce our theory that the RANKL/OPG pathway is a suitable target for developing novel agents against OA.

Leptin enhances synthesis of proinflammatory mediators in human osteoarthritic cartilage--mediator role of NO in leptin-induced PGE2, IL-6, and IL-8 production

Obesity is an important risk factor for osteoarthritis (OA) in weight-bearing joints, but also in hand joints, pointing to an obesity-related metabolic factor that influences on the pathogenesis of OA. Leptin is an adipokine regulating energy balance, and it has recently been related also to arthritis and inflammation as a proinflammatory factor. In the present paper, the effects of leptin on human OA cartilage were studied. Leptin alone or in combination with IL-1 enhanced the expression of iNOS and COX-2, and production of NO, PGE₂, IL-6, and IL-8. The results suggest that the effects of leptin are mediated through activation of transcription factor nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathway c-Jun NH₂-terminal kinase (JNK). Interestingly, inhibition of leptin-induced NO production with a selective iNOS inhibitor 1400 W inhibited also the production of IL-6, IL-8, and PGE₂, and this was reversed by exogenously added NO-donor SNAP, suggesting that the effects of leptin on IL-6, IL-8, and PGE₂ production are dependent on NO. These findings support the idea of leptin as a factor enhancing the production of proinflammatory factors in OA cartilage and as an agent contributing to the obesity-associated increased risk for osteoarthritis.

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.

Cytokines and apoptosis in supraspinatus tendinopathy

The role of inflammatory cells and their products in tendinopathy is not completely understood. Pro-inflammatory cytokines are upregulated after oxidative and other forms of stress. Based on observations that increased cytokine expression has been demonstrated in cyclically-loaded tendon cells we hypothesised that because of their role in oxidative stress and apoptosis, pro-inflammatory cytokines may be present in rodent and human models of tendinopathy. A rat supraspinatus tendinopathy model produced by running overuse was investigated at the genetic level by custom micro-arrays. Additionally, samples of torn supraspinatus tendon and matched intact subscapularis tendon were collected from patients undergoing arthroscopic shoulder surgery for rotator-cuff tears and control samples of subscapularis tendon from ten patients with normal rotator cuffs undergoing arthroscopic stabilisation of the shoulder were also obtained. These were all evaluated using semiquantitative reverse transcription polymerase chain-reaction and immunohistochemistry.

We identified significant upregulation of pro-inflammatory cytokines and apoptotic genes in the rodent model (p = 0.005). We further confirmed significantly increased levels of cytokine and apoptotic genes in human supraspinatus and subscapularis tendon harvested from patients with rotator cuff tears (p = 0.0008).

These findings suggest that pro-inflammatory cytokines may play a role in tendinopathy and may provide a target for preventing tendinopathies.

Nitric oxide in inflammation and pain associated with osteoarthritis

Osteoarthritis (OA) is a degenerative disease involving chondrocytes, cartilage and other joint tissues, and has a number of underlying causes, including both biochemical and mechanical factors. Although proinflammatory factors including nitric oxide (NO) are associated with OA, there is recent evidence suggesting that NO and its redox derivatives may also play protective roles in the joint. However, the mechanisms that underlie the development and progression of OA are not completely understood. Experiments have demonstrated that NO plays a catabolic role in the development of OA and mediates the inflammatory response, is involved in the degradation of matrix metalloproteinases, inhibits the synthesis of both collagen and proteoglycans, and helps to mediate apoptosis. However, there is also evidence that in cultured chondrocytes the addition of exogenous NO may inhibit proinflammatory activation by preventing the nuclear localization of the transcription factor nuclear factor-κB, whereas the presence of peroxynitrite – a redox derivative of NO – appears to enhance the inflammatory response by sustaining the nuclear localization of nuclear factor-κB. In addition, under some conditions exogenous NO can stimulate collagen synthesis in cultured rat fibroblasts and human tendon cells. The protective roles of NO in multiple cell types, along with the opposing activities in cultured chondrocytes, suggest that NO may play additional protective roles in chondrocyte function. NO and its derivatives have a similarly complicated involvement in nociception and pain, which may contribute to the functional disability of OA. Further research may help to elucidate a potential role for NO-donating agents in the management of OA.

Cartilage in normal and osteoarthritis conditions

The preservation of articular cartilage depends on keeping the cartilage architecture intact. Cartilage strength and function depend on both the properties of the tissue and on their structural parameters. The main structural macromolecules are collagen and proteoglycans (aggrecan). During life, cartilage matrix turnover is mediated by a multitude of complex autocrine and paracrine anabolic and catabolic factors. These act on the chondrocytes and can lead to repair, remodeling or catabolic processes like those that occur in osteoarthritis. Osteoarthritis is characterized by degradation and loss of articular cartilage, subchondral bone remodeling, and, at the clinical stage of the disease, inflammation of the synovial membrane. The alterations in osteoarthritic cartilage are numerous and involve morphologic and metabolic changes in chondrocytes, as well as biochemical and structural alterations in the extracellular matrix macromolecules.

Osteoarthritis and nitric oxide

Osteoarthritis (OA) is caused by both biochemical and mechanical factors. While the mechanisms that underlie the disease are not completely understood, investigators have characterized a number of catabolic and protective factors that have a role in the disease process. Nitric oxide (NO) and its redox derivatives appear to have a number of different functions in both normal and pathophysiological joint conditions. Until recently, NO was considered a catabolic factor that was responsible for perpetuating the OA disease process by mediating the expression of proinflammatory cytokines, inhibiting the synthesis of collagen and proteoglycans and inducing apoptosis. However, recent studies suggest that NO and its redox derivatives may also have protective effects on cartilage. This review will summarize the literature on the effects of NO on cartilage and chondrocytes as well as discuss some evidence that suggests potential protective effects of NO and/or its derivatives on other cell types. More research is needed to elucidate the role of NO and its derivatives on both normal and osteoarthritis cartilage.

Nitric oxide enhances aggrecan degradation by aggrecanase in response to TNF-alpha but not IL-1beta treatment at a post-transcriptional level in bovine cartilage explants

OBJECTIVE

The objective of this study was to determine the role of nitric oxide (NO) in tumor necrosis factor alpha (TNF-alpha)-induced matrix damage, compared to interleukin 1 beta (IL-1beta), in bovine cartilage explant cultures.

METHODS

Cartilage explants were subjected to treatment with TNF-alpha (100ng/ml), IL-1beta (10 ng/ml) and to the nitric oxide synthase inhibitor, N-methyl-arginine (L-NMA; 1.25 mM) for 26, 50 or 120 h (5 days). The collected medium was analyzed for sulfated glycosaminoglycan (sGAG), nitrate and nitrite, matrix metalloproteinase (MMP) activity by zymography, and aggrecan degradation by immunoblotting of aggrecan-G1 and aggrecan-G1-NITEGE fragments. RNA was extracted from the 26 and 50 h treated explants for real time quantitative PCR analyses.

RESULTS

TNF-alpha and IL-1beta treatment caused a 3-5 fold increase in sGAG release with an increase in aggrecanase-specific aggrecan breakdown and an increase in nitrate and nitrite production. L-NMA treatment inhibited almost 50% of the sGAG release caused by TNF-alpha treatment, with concomitant decrease in the aggrecanase-specific-NITEGE neo-epitope of aggrecan released into the medium. No L-NMA effect was identified with IL-1beta. TNF-alpha and IL-1beta both increased a disintegrin and matrix metalloproteinase with thrombospondin motif (ADAMTS)4 and ADAMTS5 transcription with no effect by L-NMA, suggesting that NO regulates aggrecanase activity at a post-transcriptional level in response to TNF-alpha. TNF-alpha and IL-1beta both caused an increase in protease transcription (MMP-3, MMP-13, ADAMTS4 and ADAMTS5) and in pro-inflammatory enzymes, inducible nitric oxide synthase and cyclooxygenase (COX)-2, as well as a decrease in matrix protein transcription, including collagen II, aggrecan, fibromodulin and link protein (IL-1beta only), and an increase in MMP-3 and MMP-9 secretion. L-NMA had no effect on gene transcription or MMP secretion.

CONCLUSION

NO regulates aggrecanase activity at a post-transcriptional level in response to TNF-alpha treatment while having no effect on IL-1beta treated cartilage explants.

Calcium signaling leads to mitochondrial depolarization in impact-induced chondrocyte death in equine articular cartilage explants

OBJECTIVE

Chondrocyte apoptosis is an important factor in the progression of osteoarthritis. This study aimed to elucidate the mechanisms involved upstream of caspase 9 activation and, in particular, calcium signaling and mitochondrial depolarization.

METHODS

Articular cartilage explants obtained from healthy horses were subjected to a single impact load (500-gm weight dropped from a height of 50 mm) and cultured in vitro for up to 48 hours. Chondrocyte death was quantified by the TUNEL method. Release of proteoglycans was determined by the dimethylmethylene blue assay. Weight change was measured, and mitochondrial depolarization was determined using JC-1 staining. To assess the role of calcium signaling in impact-induced chondrocyte death, explants were preincubated in culture medium containing various concentrations of calcium. Inhibitors were used to assess the role of individual signaling components in impact-induced chondrocyte death.

RESULTS

Calcium quenching, inhibitors of calpains, calcium/calmodulin-regulated kinase II (CaMKII), and mitochondrial depolarization reduced impact-induced chondrocyte death after 48 hours in culture. Transient mitochondrial depolarization was observed 3-6 hours following a single impact load. Mitochondrial depolarization was prevented by calcium quenching, inhibitors of calpain, CaMKII, permeability transition pore formation, ryanodine receptor, and the mitochondrial uniport transporter. Cathepsin B did not appear to be involved in impact-induced chondrocyte death. The calpain inhibitor prevented proteoglycan loss, but the percentage weight gain and proteoglycan loss were unaffected by all treatments used.

CONCLUSION

Following a single impact load, calcium is released from the endoplasmic reticulum via the ryanodine receptor and is taken up by the mitochondria via the uniport transporter, causing mitochondrial depolarization and caspase 9 activation. In addition, calpains and CaMKII play important roles in causing mitochondrial depolarization.

Heme oxygenase-1 induction by (S)-enantiomer of YS-51 (YS-51S), a synthetic isoquinoline alkaloid, inhibits nitric oxide production and nuclear factor-kappaB translocation in ROS 17/2.8 cells activated with inflammatory stimulants

Activation of the inducible nitric oxide synthase (iNOS) pathway contributes to inflammation-induced osteoporosis by suppressing bone formation and causing osteoblast apoptosis. We investigated the mechanism of action by which YS-51S, a synthetic isoquinoline alkaloid, inhibits iNOS expression and nitric oxide (NO) production in ROS 17/28 osteoblast cells activated with the mixture of TNF-alpha, IFN-gamma and LPS (MIX). YS-51S, concentration- and time-dependently, increased heme oxygenase (HO-1) expression. Treatment with YS-51S 1 h prior to MIX significantly reduced MIX-induced NO production and iNOS expression with the IC50 to NO production of 47+/-3.3 microM. Electrophoretic mobility shift assay (EMSA) and western blot analysis showed that YS-51S inhibited MIX-mediated activation and translocation of NF-kappaB to nucleus by suppressing the degradation of its inhibitory protein IkappaBalpha in cytoplasm. YS-51S also reduced NF-kappaB-luciferase activity. In addition, an HO-1 inhibitor ZnPPIX, antagonized the inhibitory effect of YS-51S on iNOS expression and DNA strand break induced by MIX, indicating prevention of NO production by YS-51S is associated with HO-1 activity. Moreover, YS-51S inhibited the oxidation of cytochrome c(2+) by peroxynitrite (PN). Our results indicated that YS-51S may be beneficial in NO-mediated inflammatory conditions such as rheumatoid arthritis by alleviating iNOS expression and NO-mediated cell death of osteoblast with 1) inducing HO-1 expression, 2) interfering the activation of NF-kappaB and 3) quenching of PN.

Prostanoid pattern and iNOS expression during chondrogenic differentiation of human mesenchymal stem cells

Availability of human chondrocytes is a major limiting factor regarding drug discovery projects and tissue replacement therapies. As an alternative human mesenchymal stem cells (hMSCs) from bone marrow are taken into consideration as they can differentiate along the chondrogenic lineage. However, it remains to be shown whether they could form a valid model for primary chondrocytes with regards to inflammatory mediator production, like nitric oxide (NO) and prostanoids. We therefore investigated the production of NO and prostanoids in hMSCs over the course of chondrogenic differentiation and in response to IL-1beta using primary OA chondrocytes as reference. Chondrogenic differentiation was monitored over 28 days using collagen I, collagen II, and collagen X expression levels. Expression levels of inducible nitric oxide synthase (iNOS), levels of NO, and prostanoids were assessed using PCR, Griess assay, and GC/MS/MS, respectively. The hMSCs collagen expression profile during course of differentiation was consistent with a chondrocytic phenotype. Contrary to undifferentiated cells, differentiated hMSCs expressed iNOS and produced NO following stimulation with IL-1beta. Moreover, this induction of iNOS expression was corticosteroid insensitive. The spectrum of prostanoid production in differentiated hMSCs showed similarities to that of OA chondrocytes, with PGE2 as predominant product. We provide the first detailed characterization of NO and prostanoid production in hMSCs in the course of chondrogenic differentiation. Our results suggest that differentiated hMSCs form a valid model for chondrocytes concerning inflammatory mediator production. Furthermore, we propose that IL-1beta stimulation, leading to corticosteroid-insensitive NO synthesis, can be used as a sensitive marker of chondrogenesis.

Pathophysiological roles for IL-18 in inflammatory arthritis

IL-18 is a unique cytokine with prominently wide spectrum biological actions. Among these, its IFN-gamma/TNF-alpha-inducing activity primarily contributes to the development of various inflammatory diseases including inflammatory arthritis. IL-18 levels correlate with the disease activity of rheumatoid arthritis (RA) and osteoarthritis (OA). IL-18 is spontaneously released from RA synovial cells and OA chondrocytes and seems to participate in the development of the inflammatory and destructive alterations of joints via induction of TNF-alpha, a potent effector molecule. TNF-alpha, in turn, increases IL-18 expression in RA synovial cells. Recent clinical trials have revealed the efficacy of TNF-alpha in RA with a reduction in circulatory IL-18 levels. These may implicate the positive circuit between IL-18 and TNF-alpha for development of RA. As IL-18-deficient mice evade collagen-induced arthritis in a mouse RA model, therapeutics targeting IL-18 may be beneficial against RA/OA. Here, the authors review the possible roles of IL-18 in inflammatory arthritis.

Implication of interleukin 18 in production of matrix metalloproteinases in articular chondrocytes in arthritis: direct effect on chondrocytes may not be pivotal

OBJECTIVE

To clarify the effect of interleukin (IL) 18 on cartilage degeneration by studying the profile of IL18 receptor (IL18R) on chondrocytes and the direct effect of IL18 on production of matrix metalloproteinases (MMPs), aggrecanases, and tissue inhibitors of metalloproteinases (TIMPs) in articular chondrocytes.

METHODS

Monolayer cultured human articular chondrocytes were isolated from non-arthritic subjects and patients with rheumatoid arthritis or osteoarthritis. Gene expression of IL18, IL18Ralpha, IL18Rbeta, MMPs, and aggrecanases was detected by RT-PCR. Protein levels of IL18Ralpha were analysed by flow cytometry. Protein levels of IL18, MMPs, and TIMPs were measured by ELISA. Aggrecanase-2 mRNA expression was quantitatively analysed by real time RT-PCR. Protein levels of signalling molecules were assayed by western blotting.

RESULTS

IL18 mRNA was constitutively expressed in chondrocytes, and was enhanced by IL1beta stimulation. Flow cytometric analysis showed that IL1beta, tumour necrosis factor alpha, and IL18 up regulated IL18Ralpha expression levels. The level of IL18Rbeta mRNA was much lower than that of IL18Ralpha, and was slightly up regulated by IL1beta. In chondrocytes responding to IL18, IL18 (1-100 ng/ml) slightly increased the production of MMP-1, MMP-3, and MMP-13, which was blocked by NF-kappaB inhibitor and p38 mitogen activated protein kinase inhibitor. IL18 up regulated mRNA expression of aggrecanase-2, but not aggrecanase-1. IL18 also slightly stimulated TIMP-1 production?through extracellular signal regulated kinase activation.

CONCLUSION

IL18 induces production of MMPs from chondrocytes in inflammatory arthritis. Although the direct effect of IL18 on chondrocytes may not be pivotal for the induction of cartilage degeneration, IL18 seems to play some part in the degradation of articular cartilage in arthritis.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

Agastache rugosa leaf extract inhibits the iNOS expression in ROS 17/2.8 cells activated with TNF-α and IL-1β

It has been suggested that nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) may act as a mediator of cytokine-induced effects on bone turn-over. NO is also recognized as an important factor in bone remodeling, i.e., participating in osteoblast apoptosis in an arthritic joint. The components of Agastache rugosa are known to have many pharmacological activities. In the present study, we investigated the effects of Agastache rugosa leaf extract (ELAR) on NO production and the iNOS expression in ROS 17/2.8 cells activated by a mixture of inflammatory cytokines including TNF-alpha and IL-1beta. A preincubation with ELAR significantly and concentration-dependently reduced the expression of iNOS protein in ROS 17/2.8 cells activated with the cytokine mixture. Consequently, the NO production was also significantly reduced by ELAR with an IC50 of 0.75 mg/mL. The inhibitory mechanism of iNOS induction by ELAR prevented the activation and translocation of NF-kappaB (p65) to the nucleus from the cytosol fraction. Furthermore, ELAR concentration-dependently reduced the cellular toxicity induced by sodium nitroprusside, an NO-donor. These results suggest that ELAR may be beneficial in NO-mediated inflammatory conditions such as osteoporosis.

Inhibition of p38 pathway suppresses human islet production of pro-inflammatory cytokines and improves islet graft function

Nonspecific inflammation is associated with primary graft nonfunction (PNF). Inflammatory islet damage is mediated at least partially by pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) produced by resident islet macrophages. The p38 pathway is known to be involved in cytokine production in the cells of the monocyte-macrophage lineage. Therefore, inhibition of the p38 pathway may prevent pro-inflammatory cytokine production by resident islet macrophages and possibly reduce the incidence of PNF. Our present study has demonstrated that inhibition of the p38 pathway by a chemical p38 inhibitor, SB203580, suppresses IL-1beta and TNF-alpha production in human islets exposed to lipopolysaccharide (LPS) and/or inflammatory cytokines. Although IL-1beta is predominantly produced by resident macrophages, ductal cells and islet vascular endothelial cells were found to be another cellular source of IL-1beta in isolated human islets. SB203580 also inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in the treated islets. Furthermore, human islets treated with SB203580 for 1 h prior to transplantation showed significantly improved graft function. These results suggest that inhibition of the p38 pathway may become a new therapeutic strategy to improve graft survival in clinical islet transplantation.

HIV-1 gp120 stimulates proinflammatory cytokine-mediated pain facilitation via activation of nitric oxide synthase-I (nNOS)

It has become clear that spinal cord glia (microglia and astrocytes) importantly contribute to the creation of exaggerated pain responses. One model used to study this is peri-spinal (intrathecal, i.t.) administration of gp120, an envelope protein of HIV-1 known to activate glia. Previous studies demonstrated that i.t. gp120 produces pain facilitation via the release of glial proinflammatory cytokines. The present series of studies tested whether spinal nitric oxide (NO) contributes to i.t. gp120-induced mechanical allodynia and, if so, what effect NO has on spinal proinflammatory cytokines. gp120 stimulation of acutely isolated lumbar dorsal spinal cords released NO as well as proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta (IL1), interleukin-6 (IL6)), thus identifying NO as a candidate mediator of gp120-induced behavioral effects. Behaviorally, identical effects were observed when gp120-induced mechanical allodynia was challenged by i.t. pre-treatment with either a broad-spectrum nitric oxide synthase (NOS) inhibitor (L-NAME) or 7-NINA, a selective inhibitor of NOS type-I (nNOS). Both abolished gp120-induced mechanical allodynia. While the literature pre-dominantly documents that proinflammatory cytokines stimulate the production of NO rather than the reverse, here we show that gp120-induced NO increases proinflammatory cytokine mRNA levels (RT-PCR) and both protein expression and protein release (serial ELISA). Furthermore, gp120 increases mRNA for IL1 converting enzyme and matrix metalloproteinase-9, enzymes responsible for activation and release of proinflammatory cytokines.

The role of cytokines in cartilage matrix degeneration in osteoarthritis

Chondrocytes are the single cellular component of hyaline cartilage. Under physiologic conditions, they show steady-state equilibrium between anabolic and catabolic activities that maintains the structural and functional integrity of the cartilage extracellular matrix. Implicit in the loss of cartilage matrix that is associated with osteoarthritis is that there is a disturbance in the regulation of synthetic (anabolic) and resorptive (catabolic) activities of the resident chondrocytes that results in a net loss of cartilage matrix components and deterioration in the structural and functional properties of the cartilage. Multiple mechanisms likely are involved in the disturbance of chondrocyte remodeling activities in OA. They include the development of acquired or age-related alterations in chondrocyte function, the effects of excessive mechanical loading, and the presence of dysregulated cytokine activities. Cytokines are soluble or cell-surface molecules that play an essential role in mediating cell-cell interactions. It is possible to classify the cytokines that regulate cartilage remodeling as catabolic, acting on target cells to increase products that enhance matrix degradation; as anticatabolic, tending to inhibit or antagonize the activity of the catabolic cytokines; and as anabolic, acting on chondrocytes to increase synthetic activity. This review will focus on the role of proinflammatory cytokines and their roles in mediating the increased matrix degradation that characterizes the osteoarthritic cartilage lesion.

Cytokines as therapeutic targets for osteoarthritis

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with the aging process. With the exception of anti-inflammatory corticosteroids and nonsteroidal anti-inflammatory drugs which inhibit cyclo-oxygenase-2, the enzyme responsible for prostaglandin biosynthesis in inflammation, no specific therapy based on fundamental intracellular pathways of chondrocytes and synoviocytes exists for the medical management of OA. At the molecular level, OA is characterized by an imbalance between chondrocyte anabolism and catabolism. Disruption of chondrocyte homeostasis primarily affects the cartilage extracellular matrix (ECM), which is responsible for the biomechanical properties of the tissue. Recent evidence has implicated cytokines, among which interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-17 seem most involved in the OA process of cartilage destruction. The primary role of these cytokines is to modulate the expression of matrix metalloproteinases and cartilage ECM proteins. Cartilage repair that could restore the functional integrity of the joint is also impaired because chondrocytes in OA cartilage appear unable to respond to insulin-like growth factor-1 or respond abnormally to transforming growth factor-beta. As these growth factors also modulate cytokine expression, they may prove useful in designing strategies for suppressing 'chondrocyte activation'. Although cytokines and growth factors provide a potential therapeutic target for OA, it will be necessary to elucidate the fundamental mechanisms that cytokines employ to cause chondrocyte and synoviocyte dysfunction before 'anti-cytokine' therapy can be employed in the medical management of the disease.

Signaling transduction: target in osteoarthritis

PURPOSE OF REVIEW

The pathophysiology of osteoarthritis is the result of an imbalance between anabolic and catabolic pathways. This imbalance is the result of the activation of joint cells by inflammatory mediators, matrix components, and mechanical stress. All these mediators act through specific receptors that transmit the signals to the nucleus to activate the transcription of matrix metalloproteinases and inflammatory genes. Targeting these signaling pathways in osteoarthritis is considered a novel approach to modulate this imbalance.

RECENT FINDINGS

Although many signaling pathways are necessary for physiologic cell life, it is now well established that a few are more specifically induced in an inflammatory environment. In osteoarthritis, the nuclear factor-kappaB and mitogen-activated protein kinase pathways have been shown to play a predominant role in the expression of metalloproteinases and inflammatory genes and proteins. Also involved in the activation of osteoarthritic cells are other molecules interacting with one or several signaling pathways, such as nitric oxide, peroxisome proliferator-activated receptor-gamma ligands, or C/EBP transcriptional factors. Based on this knowledge, specific inhibitors for some of these signaling pathways have been designed and include p38 mitogen-activated protein kinase or nuclear factor-kappaB inhibitors. Experimental studies evaluating cartilage degradation in arthritis models are promising, although fewer have been done specifically in osteoarthritis models.

SUMMARY

Targeting signaling pathways in osteoarthritis did not seem feasible a few years ago because of the complexity of the multiple intracellular pathways, mainly physiologic, defined by a high degree of redundancy and cross-talk. However, important advances in the knowledge of chondrocyte and synoviocyte signaling in osteoarthritis have been achieved in recent years and suggest that inhibitors of specific signaling pathways could shortly provide effective treatments for this disease.

Galectin-3 surface expression on human adult chondrocytes: a potential substrate for collagenase-3

BACKGROUND

Galectin-3 is a lectin detected in mature and early hypertrophic chondrocytes; osteoarthritic (OA) chondrocytes can re-express hypertrophic markers.

OBJECTIVE

To investigate the synthesis and subcellular localisation of galectin-3 in adult chondrocytes as well as the possibility of cleavage of galectin-3 by collagenase-1 and -3.

METHODS

Galectin-3 was assessed by immunohistochemistry and real time polymerase chain reaction (PCR) in normal and OA cartilage. Its localisation was investigated by subcellular fractionation, immunocytology, and flow cytometry. Proteolysis of galectin-3 by collagenase-1 and -3 was determined by in vitro assay.

RESULTS

Galectin-3 expression was increased 2.4-fold as measured by reverse transcriptase (RT)-PCR (p<0.05, n = 5) and threefold by immunohistochemistry (p<0.003 n = 6) in OA cartilage compared with normal cartilage. In adult chondrocytes, galectin-3 was found in the cytosol and membrane enriched fractions. Both immunocytology and flow cytometry confirmed the presence of galectin-3 at the surface of chondrocytes. A strong correlation was found between integrin-beta1 and galectin-3 expression at the surface of chondrocytes. Moreover, collagenase-3 cleaved galectin-3 with a higher activity than collagenase-1. The proteolysed sites generated were identical to those produced by gelatinases A and B.

CONCLUSION

Galectin-3 may play a part in OA, having two roles, one intracellular and not yet identified, and another at the cell surface, possibly related to the interaction of chondrocytes and the cartilage matrix.