Nitric oxide inhibits the synthesis of type-II collagen without altering Col2A1 mRNA abundance: prolyl hydroxylase as a possible target

The Nrf2-HO-1 system and inflammaging

Nrf2 is a master transcriptional regulator of a number of genes involved in the adaptive response to oxidative stress. Among the genes upregulated by Nrf2, heme oxygenase-1 (HO-1) has received significant attention, given that the products of HO-1-induced heme catabolism have well established antioxidant and anti-inflammatory properties. This is evidenced in numerous models of inflammatory and autoimmune disease whereby induction of HO-1 expression or administration of tolerable amounts of HO-1 reaction products can ameliorate disease symptoms. Unsurprisingly, Nrf2 and HO-1 are now considered viable drug targets for a number of conditions. In recent years, the term 'inflammaging' has been used to describe the low-grade chronic inflammation observed in aging/aged cells. Increased oxidative stress is also a key factor associated with aging and there is convincing evidence that Nrf2, not only declines with age, but that Nrf2 and HO-1 can reduce cellular senescence and the senescence-associated secretory phenotype (SASP) which is now considered an underlying driver of age-related inflammatory disease. In this review, we describe the role of oxidative stress in 'inflammaging' and highlight the potential anti-aging properties of the Nrf2-HO-1 system. We also highlight established and newly emerging Nrf2 activators and their therapeutic application in age-related disease.

Substance P promotes transforming growth factor-β-induced collagen synthesis in human corneal fibroblasts

Corneal fibroblasts maintain homeostasis of the corneal stroma by mediating the synthesis and degradation of extracellular collagen, and these actions are promoted by transforming growth factor-β (TGF-β) and interleukin-1β (IL-1β), respectively. The cornea is densely innervated with sensory nerve fibers that are not only responsible for sensation but also required for physiological processes such as tear secretion and wound healing. Loss or dysfunction of corneal nerves thus impairs corneal epithelial wound healing and can lead to neurotrophic keratopathy. The sensory neurotransmitter substance P (SP) promotes corneal epithelial wound healing by enhancing the stimulatory effects of growth factors and fibronectin. We have now investigated the role of SP in collagen metabolism mediated by human corneal fibroblasts in culture. Although SP alone had no effect on collagen synthesis or degradation by these cells, it promoted the stimulatory effect of TGF-β on collagen type I synthesis without affecting that of IL-1β on the expression of matrix metalloproteinase-1. This effect of SP on TGF-β-induced collagen synthesis was accompanied by activation of p38 mitogen-activated protein kinase (MAPK) signaling and was attenuated by pharmacological inhibition of p38 or of the neurokinin-1 receptor. Our results thus implicate SP as a modulator of TGF-β-induced collagen type I synthesis by human corneal fibroblasts, and they suggest that loss of this function may contribute to the development of neurotrophic keratopathy.NEW & NOTEWORTHY This study investigates the role of substance P (SP) in collagen metabolism mediated by human corneal fibroblasts in culture. We found that, although SP alone had no effect on collagen synthesis or degradation by corneal fibroblasts, it promoted the stimulatory effect of transforming growth factor-β on collagen type I synthesis without affecting that of interleukin-1β on the expression of matrix metalloproteinase-1.

Control analysis of collagen synthesis by glycine, proline and lysine in bovine chondrocytes in vitro - Its relevance for medicine and nutrition

Collagen synthesis is severely diminished in osteoarthritis; thus, enhancing it may help the regeneration of cartilage. Collagen synthesis is submitted to a large procollagen cycle where the greater part of the newly synthesized protein is degraded inside the cell producing a huge waste of material and energy. We have applied the Metabolic Control Analysis approach to study the control of collagen synthesis flux by means of the response coefficients of the flux with respect to glycine, proline and lysine. Our results show that the main cause of the procollagen cycle is a protein misfolding mainly due to glycine scarcity, as well as a moderate deficiency of proline and lysine for collagen synthesis. Thus, increasing these amino acids in the diet (especially glycine) may well be a strategy for helping cartilage regeneration by enhancing collagen synthesis and reducing its huge waste in the procollagen cycle; this possibly contributes to the treatment and prevention of osteoarthritis.

Understanding the Potential Role and Delivery Approaches of Nitric Oxide in Chronic Wound Healing Management

Nitric oxide (NO) is a promising pharmaceutical component that has vasodilator, anti-bacterial, and wound healing activities. Chronic ulcers are non-healing disorders that are generally associated with distortion of lower limbs. Among the severe consequence derivatives of these diseases are the problems of chronic wound progression. NO, which is categorized as the smallest gaseous neurotransmitter, has beneficial effects in different phases of chronic inflammation. The defensive mechanism of NO is found useful in several severe conditions, such as gestational healing, gastrointestinal healing, and diabetic healing. The current review presents an updated collection of literature about the role of NO in chronic ulcers due to the prevalence of diabetes, DPN, and diabetic foot ulcers, and because of the lack of available effective treatments to directly address the pathology contributing to these conditions, novel treatments are being sought. This review also collects information about deficiency of NO synthase in diabetic patients, leading to a lack of vascularization of the peripheral nerves, which causes diabetic neuropathy, and this could be treated with vasodilators such as nitric oxide. Apart from the pharmacological mechanism of NO, the article also reviewed and analyzed to elucidate the potential of transdermal delivery of NO for the treatment of chronic ulcers.

An Update on the Role of Leptin in the Immuno-Metabolism of Cartilage

Since its discovery in 1994, leptin has been considered as an adipokine with pleiotropic effects. In this review, we summarize the actual information about the impact of this hormone on cartilage metabolism and pathology. Leptin signalling depends on the interaction with leptin receptor LEPR, being the long isoform of the receptor (LEPRb) the one with more efficient intracellular signalling. Chondrocytes express the long isoform of the leptin receptor and in these cells, leptin signalling, alone or in combination with other molecules, induces the expression of pro-inflammatory molecules and cartilage degenerative enzymes. Leptin has been shown to increase the proliferation and activation of immune cells, increasing the severity of immune degenerative cartilage diseases. Leptin expression in serum and synovial fluid are related to degenerative diseases such as osteoarthritis (OA), rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Inhibition of leptin signalling showed to have protective effects in these diseases showing the key role of leptin in cartilage degeneration.

Molecular Mechanisms That Link Oxidative Stress, Inflammation, and Fibrosis in the Liver

Activated hepatic stellate cells (HSCs) and myofibroblasts are the main producers of extracellular matrix (ECM) proteins that form the fibrotic tissue that leads to hepatic fibrosis. Reactive oxygen species (ROS) can directly activate HSCs or induce inflammation or programmed cell death, especially pyroptosis, in hepatocytes, which in turn activates HSCs and fibroblasts to produce ECM proteins. Therefore, antioxidants and the nuclear factor E2-related factor-2 signaling pathway play critical roles in modulating the profibrogenic response. The master proinflammatory factors nuclear factor-κB (NF-κB) and the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome may coordinate to produce and activate profibrogenic molecules such as interleukins 1β and 18, which effectively activate HSCs, to produce large amounts of fibrotic proteins. Furthermore, the NLRP3 inflammasome activates pro-caspase 1, which is upregulated by NF-κB, to produce caspase 1, which induces pyroptosis via gasdermin and the activation of HSCs. ROS play central roles in the activation of the NF-κB and NLRP3 signaling pathways via IκB (an inhibitor of NF-κB) and thioredoxin-interacting protein, respectively, thereby linking the molecular mechanisms of oxidative stress, inflammation and fibrosis. Elucidating these molecular pathways may pave the way for the development of therapeutic tools to interfere with specific targets.

Astilbin influences the progression of osteoarthritis in rats by down-regulation of PGE-2 expression via the NF-κB pathway

Background

Osteoarthritis (OA) is the most common joint disease, affecting most middle-aged and elderly people. Astilin (AST) is the main active ingredient isolated from the traditional Chinese medicine Astilbe chinensis and has anti-inflammatory and anti-arthritis effects. The purpose of this study was to investigate the effect and mechanism of AST on OA in rats mediated by papain.

Methods

In this study, in vivo experiments were conducted to investigate the protective effect and potential mechanism of Astilbin (AST) when it inhibited the development of osteoarthritis (OA).

Results

A rat model of OA is constructed. Through HE staining, it is found that AST can protect the articular surface and reduce damage. The results of immunohistochemical staining also prove that AST can inhibit the expression of prostaglandin E2 (PGE2) and has an excellent inhibitory effect on inflammatory factors. It is found that AST can significantly inhibit the protein expression of interleukin 1 beta (IL-1β), TNF-α, and NF-κB. Polymerase Chain Reaction (PCR) assay shows that the mRNA of IL-1β, TNF-α, and NF-κB is down-regulated, which also proves that the protective mechanism of AST is related to the NF-κB pathway.

Conclusions

In general, this study proves that AST can be a potential therapy for degenerative joint diseases, including OA.

Chronic aerobic exercise associated to low-dose L-NAME improves contractility without changing calcium handling in rat cardiomyocytes

Nitric oxide (NO) inhibition by high-dose NG-nitro-L-arginine methyl ester (L-NAME) is associated with several detrimental effects on the cardiovascular system. However, low-dose L-NAME increases NO synthesis, which in turn induces physiological cardiovascular benefits, probably by activating a protective negative feedback mechanism. Aerobic exercise, likewise, improves several cardiovascular functions in healthy hearts, but its effects are not known when chronically associated with low-dose L-NAME. Thus, we tested whether the association between low-dose L-NAME administration and chronic aerobic exercise promotes beneficial effects to the cardiovascular system, evaluating the cardiac remodeling process. Male Wistar rats were randomly assigned to control (C), L-NAME (L), chronic aerobic exercise (Ex), and chronic aerobic exercise associated to L-NAME (ExL). Aerobic training was performed with progressive intensity for 12 weeks; L-NAME (1.5 mg·kg^-1·day^-1) was administered by orogastric gavage. Low-dose L-NAME alone did not change systolic blood pressure (SBP), but ExL significantly increased SBP at week 8 with normalization after 12 weeks. Furthermore, ExL promoted the elevation of left ventricle (LV) end-diastolic pressure without the presence of cardiac hypertrophy and fibrosis. Time to 50% shortening and relaxation were reduced in ExL, suggesting a cardiomyocyte contractile improvement. In addition, the time to 50% Ca²⁺ peak was increased without alterations in Ca²⁺ amplitude and time to 50% Ca²⁺ decay. In conclusion, the association of chronic aerobic exercise and low-dose L-NAME prevented cardiac pathological remodeling and induced cardiomyocyte contractile function improvement; however, it did not alter myocyte affinity and sensitivity to intracellular Ca²⁺ handling.

Platelet-Rich Plasma Released From Polyethylene Glycol Hydrogels Exerts Beneficial Effects on Human Chondrocytes

Osteoarthritis (OA) is a debilitating joint disease resulting from chronic joint inflammation and erosion of articular cartilage. A promising biological treatment for OA is intra-articular administration of platelet-rich plasma (PRP). However, immediate bolus release of growth factors limits beneficial therapeutic effects of PRP, thus necessitating the demand for sustained release platforms. In this study, we evaluated the therapeutic value of PRP released from a polyethylene glycol (PEG) hydrogel on articular chondrocytes/cartilage explants derived from OA patients. Lyophilized PRP (PRGF) was encapsulated in PEG hydrogels at 10% w/v and hydrogel swelling, storage modulus and degradation and PRGF release kinetics were determined. PRGF releasate from the hydrogels was collected on day 1, 4, and 11. Encapsulation of PRGF at 10% w/v in PEG hydrogels had minimal effect on hydrogel properties. PRGF was released with an initial burst followed by sustained release until complete hydrogel degradation. Effect of PRGF releasates and bolus PRGF (1% w/v PRGF) on patient-derived cartilage explants or chondrocytes was assessed by chondrocyte proliferation (pico-green assay), gene expression for COL1A1, COL2A1, MMP13, COX2, and NFKB1 (real-time polymerase chain reaction), and measurement of nitric oxide concentration (Griess' assay). Compared to bolus PRGF, PRGF releasates enhanced chondrocyte proliferation, suppressed the expression of genes like MMP13, NFKB1, COL1A1, and COL2A1 and reduced levels of nitric oxide. Taken together, these results indicate that release of PRGF from PEG hydrogels may improve the therapeutic efficacy of PRP and merits further investigation in an animal model of OA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2401-2410, 2019.

Simvastatin prevents articular chondrocyte dedifferentiation induced by nitric oxide by inhibiting the expression of matrix metalloproteinases 1 and 13

IMPACT STATEMENT

Dedifferentiation of chondrocytes is the main character of cartilage degradation. Therefore the understanding of chondrocytes dedifferentiation is essential for arthritis therapy. However, the molecular mechanism of cartilage destroy is mostly unknown. In this work we show that simvastatin (SVT) inhibits dedifferentiation by nitric oxide by blocking the expression of matrix metalloproteinases 1 and 13. These effects of SVT on dedifferentiation suggest that SVT may be used as a drug for the cure of arthritis.

Platelet-Rich Plasma and Cartilage Repair

PURPOSE OF REVIEW

To assess the utilization and efficacy of platelet-rich plasma (PRP), for the treatment of articular cartilage injury, most commonly characterized by progressive pain and loss of joint function in the setting of osteoarthritis (OA).

RECENT FINDINGS

PRP modulates the inflammatory and catabolic environment through a locally applied concentrate of platelets, leukocytes, and growth factors. Clinically, PRP has been shown to be possibly a viable treatment adjuvant for a variety of inflammatory and degenerative conditions. Recent efforts have focused on optimizing delivery methods that enable platelets to slowly degranulate their biological constituents, which may promote healing and improve OA symptoms for a longer duration. There are various factors that affect the progression of OA within joints, including inhibition of inflammatory cytokines and altering the level of enzymatic expression. PRP therapy aims to mediate inflammatory and catabolic factors in a degenerative environment through the secretion of anti-inflammatory factors and chemotaxic effects. There are a growing number of studies that have demonstrated the clinical benefit of PRP for non-operative management of OA. Additional randomized controlled trials with long-term follow-up are needed in order to validate PRP's therapeutic efficacy in this setting. Additionally, continued basic research along with well-designed pre-clinical studies and reporting standards are necessary in order to clarify the effectiveness of PRP for cartilage repair and regeneration for future clinical applications.

High glycine concentration increases collagen synthesis by articular chondrocytes in vitro: acute glycine deficiency could be an important cause of osteoarthritis

Collagen synthesis is severely diminished in osteoarthritis; thus, enhancing it may help the regeneration of cartilage. This requires large amounts of glycine, proline and lysine. Previous works of our group have shown that glycine is an essential amino acid, which must be present in the diet in large amounts to satisfy the demands for collagen synthesis. Other authors have shown that proline is conditionally essential. In this work we studied the effect of these amino acids on type II collagen synthesis. Bovine articular chondrocytes were cultured under a wide range of different concentrations of glycine, proline and lysine. Chondrocytes were characterized by type II collagen immunocytochemistry of confluence monolayer cultures. Cell growth and viability were assayed by trypan blue dye exclusion method. Type II collagen was measured in the monolayer, every 48 h for 15 days by ELISA. Increase in concentrations of proline and lysine in the culture medium enhances the synthesis of type II collagen at low concentrations, but these effects decay before 1.0 mM. Increase of glycine as of 1.0 mM exceeds these effects and this increase continues more persistently by 60–75%. Since the large effects produced by proline and lysine are within the physiological range, while the effect of glycine corresponds to a much higher range, these results demonstrated a severe glycine deficiency for collagen synthesis. Thus, increasing glycine in the diet may well be a strategy for helping cartilage regeneration by enhancing collagen synthesis, which could contribute to the treatment and prevention of osteoarthritis.

Compromised autophagy precedes meniscus degeneration and cartilage damage in mice

OBJECTIVE

Autophagy is a cellular homeostasis mechanism that facilitates normal cell function and survival. Objectives of this study were to determine associations between autophagic responses with meniscus injury, joint aging, and osteoarthritis (OA), and to establish the temporal relationship with structural changes in menisci and cartilage.

METHODS

Constitutive activation of autophagy during aging was measured in GFP-LC3 transgenic reporter mice between 6 and 30 months. Meniscus injury was created by surgically destabilizing the medial meniscus (DMM) to induce posttraumatic OA in C57BL/6J mice. Levels of autophagy proteins and activation were analyzed by confocal microscopy and immunohistochemistry. Associated histopathological changes, such as cellularity, matrix staining, and structural damage, were graded in the meniscus and compared to changes in articular cartilage.

RESULTS

In C57BL/6J mice, basal autophagy was lower in the meniscus than in articular cartilage. With increasing age, expression of the autophagy proteins ATG5 and LC3 was significantly reduced by 24 months. Age-related changes included abnormal Safranin-O staining and reduced cellularity, which preceded structural damage in the meniscus and articular cartilage. In mice with DMM, autophagy was induced in the meniscus while it was suppressed in cartilage. Articular cartilage exhibited the most profound changes in autophagy and structure that preceded meniscus degeneration. Systemic administration of rapamycin to mice with DMM induced autophagy activation in cartilage and reduced degenerative changes in both meniscus and cartilage.

CONCLUSION

Autophagy is significantly affected in the meniscus during aging and injury and precedes structural damage. Maintenance of autophagic activity appears critical for meniscus and cartilage integrity.

Modulation of Apoptosis and Differentiation by the Treatment of Sulfasalazine in Rabbit Articular Chondrocytes

This study was conducted to examine the cellular regulatory mechanisms of sulfasalazine (SSZ) in rabbit articular chondrocytes treated with sodium nitroprusside (SNP). Cell phenotype was determined, and the MTT assay, Western blot analysis and immunofluorescence staining of type II collagen was performed in control, SNP-treated and SNP plus SSZ (50~200 μg/mL) rabbit articular chondrocytes. Cellular proliferation was decreased significantly in the SNP-treated group compared with that in the control (p < 0.01). SSZ treatment clearly increased the SNP-reduced proliferation levels in a concentration-dependent manner (p < 0.01). SNP treatment induced significant dedifferentiation and inflammation compared with control chondrocytes (p < 0.01). Type II collagen expression levels increased in a concentration-dependent manner in response to SSZ treatment but were unaltered in SNP-treated chondrocytes (p < 0.05 and < 0.01, respectively). Cylooxygenase-2 (COX-2) expression increased in a concentration-dependent manner in response to SSZ treatment but was unaltered in SNP-treated chondrocytes (p < 0.05). Immunofluorescence staining showed that SSZ treatment increased type II collagen expression compared with that in SNP-treated chondrocytes. Furthermore, phosphorylated extracellular regulated kinase (pERK) expression levels were decreased significantly in the SNP-treated group compared with those in control chondrocytes (p < 0.01). Expression levels of pERK increased in a concentration-dependent manner by SSZ but were unaltered in SNP-treated chondrocytes. pp38 kinase expression levels increased in a concentration-dependent manner by SSZ but were unaltered in control chondrocytes (p < 0.01). In summary, SSZ significantly inhibited nitric oxide-induced cell death and dedifferentiation, and regulated extracellular regulated kinases 1 and 2 and p38 kinase in rabbit articular chondrocytes.

Rebamipide Attenuates Mandibular Condylar Degeneration in a Murine Model of TMJ-OA by Mediating a Chondroprotective Effect and by Downregulating RANKL-Mediated Osteoclastogenesis

Temporomandibular joint osteoarthritis (TMJ-OA) is characterized by progressive degradation of cartilage and changes in subchondral bone. It is also one of the most serious subgroups of temporomandibular disorders. Rebamipide is a gastroprotective agent that is currently used for the treatment of gastritis and gastric ulcers. It scavenges reactive oxygen radicals and has exhibited anti-inflammatory potential. The aim of this study was to investigate the impact of rebamipide both in vivo and in vitro on the development of cartilage degeneration and osteoclast activity in an experimental murine model of TMJ-OA, and to explore its mode of action. Oral administration of rebamipide (0.6 mg/kg and 6 mg/kg) was initiated 24 h after TMJ-OA was induced, and was maintained daily for four weeks. Rebamipide treatment was found to attenuate cartilage degeneration, to reduce the number of apoptotic cells, and to decrease the expression levels of matrix metalloproteinase-13 (MMP-13) and inducible nitric oxide synthase (iNOS) in TMJ-OA cartilage in a dose-dependent manner. Rebamipide also suppressed the activation of transcription factors (e.g., NF-κB, NFATc1) and mitogen-activated protein kinases (MAPK) by receptor activator of nuclear factor kappa-B ligand (RANKL) to inhibit the differentiation of osteoclastic precursors, and disrupted the formation of actin rings in mature osteoclasts. Together, these results demonstrate the inhibitory effects of rebamipide on cartilage degradation in experimentally induced TMJ-OA. Furthermore, suppression of oxidative damage, restoration of extracellular matrix homeostasis of articular chondrocytes, and reduced subchondral bone loss as a result of blocked osteoclast activation suggest that rebamipide is a potential therapeutic strategy for TMJ-OA.

Molecular Cloning, Characterization, and Expression Analysis of a Prolyl 4-Hydroxylase from the Marine Sponge Chondrosia reniformis

Prolyl 4-hydroxylase (P4H) catalyzes the hydroxylation of proline residues in collagen. P4H has two functional subunits, α and β. Here, we report the cDNA cloning, characterization, and expression analysis of the α and β subunits of the P4H derived from the marine sponge Chondrosia reniformis. The amino acid sequence of the α subunit is 533 residues long with an M r of 59.14 kDa, while the β subunit counts 526 residues with an M r of 58.75 kDa. Phylogenetic analyses showed that αP4H and βP4H are more related to the mammalian sequences than to known invertebrate P4Hs. Western blot analysis of sponge lysate protein cross-linking revealed a band of 240 kDa corresponding to an α2β2 tetramer structure. This result suggests that P4H from marine sponges shares the same quaternary structure with vertebrate homologous enzymes. Gene expression analyses showed that αP4H transcript is higher in the choanosome than in the ectosome, while the study of factors affecting its expression in sponge fragmorphs revealed that soluble silicates had no effect on the αP4H levels, whereas ascorbic acid strongly upregulated the αP4H mRNA. Finally, treatment with two different tumor necrosis factor (TNF)-alpha inhibitors determined a significant downregulation of αP4H gene expression in fragmorphs demonstrating, for the first time in Porifera, a positive involvement of TNF in sponge matrix biosynthesis. The molecular characterization of P4H genes involved in collagen hydroxylation, including the mechanisms that regulate their expression, is a key step for future recombinant sponge collagen production and may be pivotal to understand pathological mechanisms related to extracellular matrix deposition in higher organisms.

Chondroprotective and anti-inflammatory effects of S-methylisothiourea, an inducible nitric oxide synthase inhibitor in cartilage and synovial explants model of osteoarthritis

Objectives

To study the chondroprotective and anti-inflammatory potential of inducible nitric oxide synthase (iNOS) inhibitor S-methylisothiourea (SMT) in in-vitro model.

Methods

Rabbit cartilage explants were stimulated with recombinant human interleukin 1β (rhIL-1β), and the chondroprotective and anti-inflammatory effects of SMT were investigated. Rat synovial explants were stimulated with LPS, and the anti-inflammatory effect of SMT on synovium was studied. To examine the role of SMT in synovial inflammation mediated cartilage damage, LPS stimulated synovial explants were cultured with dead cartilage with or without SMT for 72 h. The culture medium was analysed for sulfated glycosaminoglycans (GAGs) and hydroxyproline as measure of proteoglycans and collagen degradation, respectively.

Key findings

SMT significantly reduced GAGs, hydroxyproline, matrix metalloproteinase (MMP)-13, tumour necrosis factor alpha (TNF-α), prostaglindin E2 (PGE2) and nitrite release in stimulated rabbit cartilage media indicating chondroprotective and anti-inflammatory effects of SMT in osteoarthritis (OA). Stimulated synovial explants caused release of nitrite, PGE2, IL-1β and TNF-α in the medium which were significantly reduced by SMT indicating its anti-inflammatory action. SMT significantly reduced GAGs and hydroxyproline in medium and shown protective effect against synovium-mediated cartilage damage.

Conclusions

SMT inhibited cartilage degradation, synovial inflammation and synovium-mediated cartilage damage, suggesting that SMT may be an agent for pharmacological intervention in OA.

Effect of ghrelin on chronic liver injury and fibrogenesis in male rats: possible role of nitric oxide

Recent studies have revealed that ghrelin may be an antioxidant and anti-inflammatory agent in many organs, however its role in chronic liver injury (CLI) remains unclear. The role of nitric oxide (NO) in CLI is controversial as evidence suggests that NO is either a primary mediator of liver cell injury or exhibits a protective effect against injurious stimuli. Recent evidence demonstrated that the therapeutic potential for ghrelin was through eNOS activation and increase in NO production. However, its role on NO production in the liver has not been previously investigated. The aim of this study was to investigate the role of ghrelin in treatment of CLI, and whether this action is mediated through NO. Forty male rats were divided into four groups: Group I: Control; Group II: chronic liver injury (CLI); Group III: CLI+Ghrelin; and Group IV: CLI+Ghrelin+l-NAME. Liver enzymes and tumor necrosis factor alpha (TNF-α), were measured to assess hepatocellular injury. Liver tissue collagen content, malondialdehyde (MDA), gene expression of Bax, Bcl-2, and eNOS were assessed to determine the mechanism of ghrelin action. Results showed that ghrelin decreased serum liver enzymes and TNF-α levels. Ghrelin also reduced liver tissue collagen, MDA, and Bax gene expression, and increased Bcl-2 and eNOS gene expression. The effects on TNF-α, collagen, MDA, Bax, and eNOS were partially reversed in Group IV, suggesting that ghrelin's action could be through modulation of NO levels. Therefore, ghrelin's hepatoprotective effect is partially mediated by NO release.

Sphingosine 1-phosphate counteracts the effects of interleukin-1β in human chondrocytes

OBJECTIVE

The lipid mediator sphingosine 1-phosphate (S1P) is found in the synovial fluid of osteoarthritis (OA) patients. S1P protects bovine cartilage by counteracting the effects of interleukin-1β (IL-1β). This study was undertaken to examine the interaction of S1P and IL-1β in human OA chondrocytes.

METHODS

Human cartilage was obtained from patients undergoing total knee joint replacement. Chondrocytes were cultured in monolayer and treated with IL-1β and S1P. Expression of S1P receptor subtypes and genes involved in cartilage degradation was evaluated using real-time polymerase chain reaction, immunohistochemistry, and Western blotting. S1P signaling was evaluated using inhibitors of S1P receptors and small interfering RNA (siRNA) knockdown of the S1P2 receptor. Phosphorylation of MAP kinases and NF-κB in response to IL-1β and S1P was detected by Western blotting.

RESULTS

S1P2 was identified as the most prevalent S1P receptor subtype in human OA cartilage and chondrocytes in vitro. S1P reduced expression of inducible nitric oxide synthase (iNOS) in IL-1β-treated chondrocytes. Reduction of ADAMTS-4 and matrix metalloproteinase 13 expression by S1P correlated with S1P2 expression. Pharmacologic inhibition of the S1P2 receptor, but not the S1P1 and S1P3 receptors, abrogated the inhibition of iNOS expression. Similar results were observed using siRNA knockdown. S1P signaling inhibited IL-1β-induced phosphorylation of p38 MAPK.

CONCLUSION

In human chondrocytes, S1P reduces the induction of catabolic genes in the presence of IL-1β. Activation of the S1P2 receptor counteracts the detrimental phosphorylation of p38 MAPK by IL-1β.

Local NO synthase inhibition produces histological and functional recovery in Achilles tendon of rats after tenotomy: tendon repair and local NOS inhibition

Repair of injured tendon is a very slow process and involves the release of many molecules, including nitric oxide. We investigate the influence of local nitrergic inhibition in histological and functional recovery of injured Achilles tendon. A standard murine model of tendon injury by rupture was used. The animals were divided into three experimental groups: control, injury + vehicle (normal saline) and injury + Nω-nitro-L-arginine methyl ester (L-NAME). The products were injected into the paratendinous region every 2 days and body weight gain and Achilles functional index (AFI) were evaluated on days 0, 7, 14 and 21 after tendon injury. On day 21 post-injury, the animals were killed to evaluate nitric oxide production and tissue organization. We observed that tendon surgical division led to increased tissue nitrite levels, which were reduced in L-NAME-treated rats. The AFI revealed functional recovery of L-NAME-treated animals on day 21 post-injury, which was not observed in the saline-treated group. Microscopic analysis of hematoxylin-eosin staining and collagen autofluorescence showed that L-NAME-treated rats had more aligned areas of collagen fibers and that the diameter of newly organized collagen in this group was also greater than that in the vehicle-treated one. We demonstrate that local treatment with L-NAME significantly improves the functional parameters and accelerates histomorphological recovery.

Hemoglobin: a nitric-oxide dioxygenase

Members of the hemoglobin superfamily efficiently catalyze nitric-oxide dioxygenation, and when paired with native electron donors, function as NO dioxygenases (NODs). Indeed, the NOD function has emerged as a more common and ancient function than the well-known role in O2 transport-storage. Novel hemoglobins possessing a NOD function continue to be discovered in diverse life forms. Unique hemoglobin structures evolved, in part, for catalysis with different electron donors. The mechanism of NOD catalysis by representative single domain hemoglobins and multidomain flavohemoglobin occurs through a multistep mechanism involving O2 migration to the heme pocket, O2 binding-reduction, NO migration, radical-radical coupling, O-atom rearrangement, nitrate release, and heme iron re-reduction. Unraveling the physiological functions of multiple NODs with varying expression in organisms and the complexity of NO as both a poison and signaling molecule remain grand challenges for the NO field. NOD knockout organisms and cells expressing recombinant NODs are helping to advance our understanding of NO actions in microbial infection, plant senescence, cancer, mitochondrial function, iron metabolism, and tissue O2 homeostasis. NOD inhibitors are being pursued for therapeutic applications as antibiotics and antitumor agents. Transgenic NOD-expressing plants, fish, algae, and microbes are being developed for agriculture, aquaculture, and industry.

The immunosuppressant FTY720 (fingolimod) enhances glycosaminoglycan depletion in articular cartilage

Background

FTY720 (Fingolimod) is a novel immunosuppressive drug investigated in clinical trials for organ transplantation and multiple sclerosis. It acts as a functional sphingosine-1-phosphate (S1P) receptor antagonist, thereby inhibiting the egress of lymphocytes from secondary lymphoid organs. As S1P is able to prevent IL-1beta induced cartilage degradation, we examined the direct impact of FTY720 on cytokine induced cartilage destruction.

Methods

Bovine chondrocytes were treated with the bioactive phosphorylated form of FTY720 (FTY720-P) in combination with IL-1beta or TNF-alpha. Expression of MMP-1,-3.-13, iNOS and ADAMTS-4,-5 and COX-2 was evaluated using quantitative real-time PCR and western blot. Glycosaminoglycan depletion from cartilage explants was determined using a 1,9-dimethylene blue assay and safranin O staining.

Results

FTY720-P significantly reduced IL-1beta and TNF-alpha induced expression of iNOS. In contrast FTY720-P increased MMP-3 and ADAMTS-5 mRNA expression. Furthermore depletion of glycosaminoglycan from cartilage explants by IL-1beta and TNF-alpha was significantly enhanced by FTY720-P in an MMP-3 dependent manner.

Conclusions

Our results suggest that FTY720 may enhance cartilage degradation in pro-inflammatory environment.

Cytoglobin: biochemical, functional and clinical perspective of the newest member of the globin family

Since the discovery of cytoglobin (Cygb) a decade ago, growing amounts of data have been gathered to characterise Cygb biochemistry, functioning and implication in human pathologies. Its molecular roles remain under investigation, but nitric oxide dioxygenase and lipid peroxidase activities have been demonstrated. Cygb expression increases in response to various stress conditions including hypoxia, oxidative stress and fibrotic stimulation. When exogenously overexpressed, Cygb revealed cytoprotection against these factors. Cygb was shown to be upregulated in fibrosis and neurodegenerative disorders and downregulated in multiple cancer types. CYGB was also found within the minimal region of a hereditary tylosis with oesophageal cancer syndrome, and its expression was reduced in tylotic samples. Recently, Cygb has been shown to inhibit cancer cell growth in vitro, thus confirming its suggested tumour suppressor role. This article aims to review the biochemical and functional aspects of Cygb, its involvement in various pathological conditions and potential clinical utility.

Platelet-rich plasma releasate inhibits inflammatory processes in osteoarthritic chondrocytes

BACKGROUND

Platelet-rich plasma (PRP) has recently been postulated as a treatment for osteoarthritis (OA). Although anabolic effects of PRP on chondrocytes are well documented, no reports are known addressing effects on cartilage degeneration. Since OA is characterized by a catabolic and inflammatory joint environment, the authors investigated whether PRP was able to counteract the effects of such an environment on human osteoarthritic chondrocytes.

HYPOTHESIS

Platelet-rich plasma inhibits inflammatory effects of interleukin-1 (IL-1) beta on human osteoarthritic chondrocytes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human osteoarthritic chondrocytes were cultured in the presence of IL-1 beta to mimic an osteoarthritic environment. Medium was supplemented with 0%, 1%, or 10% PRP releasate (PRPr, the active releasate of PRP). After 48 hours, gene expression of collagen type II alpha 1 (COL2A1), aggrecan (ACAN), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)4, ADAMTS5, matrix metalloproteinase (MMP)13, and prostaglandin-endoperoxide synthase (PTGS)2 was analyzed. Additionally, glycosaminoglycan (GAG) content, nitric oxide (NO) production, and nuclear factor kappa B (NFκB) activation were studied.

RESULTS

Platelet-rich plasma releasate diminished IL-1 beta-induced inhibition of COL2A1 and ACAN gene expression. The PRPr also reduced IL-1 beta-induced increase of ADAMTS4 and PTGS2 gene expression. ADAMTS5 gene expression and GAG content were not influenced by IL-1 beta or additional PRPr. Matrix metalloproteinase 13 gene expression and NO production were upregulated by IL-1 beta but not affected by added PRPr. Finally, PRPr reduced IL-1 beta-induced NFκB activation to control levels containing no IL-1 beta.

CONCLUSION

Platelet-rich plasma releasate diminished multiple inflammatory IL-1 beta-mediated effects on human osteoarthritic chondrocytes, including inhibition of NFκB activation.

CLINICAL RELEVANCE

Platelet-rich plasma releasate counteracts effects of an inflammatory environment on genes regulating matrix degradation and formation in human chondrocytes. Platelet-rich plasma releasate decreases NFκB activation, a major pathway involved in the pathogenesis of OA. These results encourage further study of PRP as a treatment for OA.

Modulation of fibrosis in systemic sclerosis by nitric oxide and antioxidants

Systemic sclerosis (scleroderma: SSc) is a multisystem, connective tissue disease of unknown aetiology characterized by vascular dysfunction, autoimmunity, and enhanced fibroblast activity resulting in fibrosis of the skin, heart, and lungs, and ultimately internal organ failure, and death. One of the most important and early modulators of disease activity is thought to be oxidative stress. Evidence suggests that the free radical nitric oxide (NO), a key mediator of oxidative stress, can profoundly influence the early microvasculopathy, and possibly the ensuing fibrogenic response. Animal models and human studies have also identified dietary antioxidants, such as epigallocatechin-3-gallate (EGCG), to function as a protective system against oxidative stress and fibrosis. Hence, targeting EGCG may prove a possible candidate for therapeutic treatment aimed at reducing both oxidant stress and the fibrotic effects associated with SSc.

Celecoxib: considerations regarding its potential disease-modifying properties in osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive loss of articular cartilage, subchondral bone sclerosis, osteophyte formation, and synovial inflammation, causing substantial physical disability, impaired quality of life, and significant health care utilization. Traditionally, non-steroidal anti-inflammatory drugs (NSAIDs), including selective cyclooxygenase (COX)-2 inhibitors, have been used to treat pain and inflammation in OA. Besides its anti-inflammatory properties, evidence is accumulating that celecoxib, one of the selective COX-2 inhibitors, has additional disease-modifying effects. Celecoxib was shown to affect all structures involved in OA pathogenesis: cartilage, bone, and synovium. As well as COX-2 inhibition, evidence indicates that celecoxib also modulates COX-2-independent signal transduction pathways. These findings raise the question of whether celecoxib, and potentially other coxibs, is more than just an anti-inflammatory and analgesic drug. Can celecoxib be considered a disease-modifying osteoarthritic drug? In this review, these direct effects of celecoxib on cartilage, bone, and synoviocytes in OA treatment are discussed.

Gene expression profile of the synovium and cartilage in a chronic arthritis rat model

BACKGROUND

Primary osteoarthritis (OA) is a polygenic disease. To investigate the gene expression profile of cartilage and synovium from osteoarthritis and healthy rats using cDNA microarray is beneficial to recognize the pathogenesis of osteoarthritis and provide evidence for gene therapy of osteoarthritis.

OBJECTIVE

The present study aimed to investigate the gene expression profile of the cartilage and synovium of chronic arthritis and healthy rats through cDNA microarray assay, and identify the differentially expressed genes. This study may be helpful for understanding the role of differentially expressed genes in osteoarthritis and the gene polymorphism of osteoarthritis.

METHODS

A total of 24 male Wistar rats were randomly divided into control group and osteoarthritis group (n = 12 per group). The synovial and cartilage were obtained and total RNA was extracted. cDNA microarray assay was performed to identify the differentially expressed genes, and cluster analysis was conducted.

RESULTS AND CONCLUSION

A total of 82 differentially expressed genes were identified, among which 27 were up-regulated and 55 down-regulated. Gene microarray assay is effective to identify differentially expressed genes and may find out novel osteoarthritis associated genes. Multiple genes are involved in the pathogenesis of osteoarthritis. The differentially expressed genes provide important information for further studies on the pathogenesis of osteoarthritis and gene therapy of osteoarthritis.

Nitric-oxide dioxygenase function of human cytoglobin with cellular reductants and in rat hepatocytes

Cytoglobin (Cygb) was investigated for its capacity to function as a NO dioxygenase (NOD) in vitro and in hepatocytes. Ascorbate and cytochrome b(5) were found to support a high NOD activity. Cygb-NOD activity shows respective K(m) values for ascorbate, cytochrome b(5), NO, and O(2) of 0.25 mm, 0.3 microm, 40 nm, and approximately 20 microm and achieves a k(cat) of 0.5 s(-1). Ascorbate and cytochrome b(5) reduce the oxidized Cygb-NOD intermediate with apparent second order rate constants of 1000 m(-1) s(-1) and 3 x 10(6) m(-1) s(-1), respectively. In rat hepatocytes engineered to express human Cygb, Cygb-NOD activity shows a similar k(cat) of 1.2 s(-1), a K(m)(NO) of 40 nm, and a k(cat)/K(m)(NO) (k'(NOD)) value of 3 x 10(7) m(-1) s(-1), demonstrating the efficiency of catalysis. NO inhibits the activity at [NO]/[O(2)] ratios >1:500 and limits catalytic turnover. The activity is competitively inhibited by CO, is slowly inactivated by cyanide, and is distinct from the microsomal NOD activity. Cygb-NOD provides protection to the NO-sensitive aconitase. The results define the NOD function of Cygb and demonstrate roles for ascorbate and cytochrome b(5) as reductants.

Hyaluronic acid inhibits nitric oxide-induced apoptosis and dedifferentiation of articular chondrocytes in vitro

OBJECTIVE

Nitric oxide is an important mediator in Osteoarthritis (OA), and causes apoptosis and dedifferentiation in articular chondrocytes. Protein kinase Calpha is involved in modulating apoptosis and dedifferentiation of articular chondrocytes induced by nitric oxide. Hyaluronic acid is widely used in the treatment of osteoarthritis and exerts significant chondroprotective effects. The exact mechanisms of its chondroprotective action are not yet fully elucidated. The present study was performed to investigate the effects and mechanisms of hyaluronic acid in NO-induced apoptosis and dedifferentiation of chondrocytes.

METHODS

The ratio of apoptotic cell and cell viability was surveyed by TUNEL, MTT assay and flow cytometry. The expression of aggrecan, type II collagen, and PKCalpha were determined by real-time PCR and Western blot. The expression changes of caspase-3 and bcl-2 was detected by Western blot. The mitochondrial membrane potential (DeltaPsim) was evaluated by Rhodamine-123 fluorescence.

RESULTS

HA reduces the TUNEL positive cell, nuclei fragment and the impairment of DeltaPsim. NO-induced chondrocyte dedifferentiation was blocked by HA, which restores expression of aggrecan and type II collagen of chondrocytes and cell viability. HA can block inhibition of PKC-alpha by NO.

CONCLUSION

Our results show that HA blocks NO-induced apoptosis and dedifferentiation of articular chondrocytes by modulation of DeltaPsim and PKCalpha.

SHP-1, a novel peptide isolated from seahorse inhibits collagen release through the suppression of collagenases 1 and 3, nitric oxide products regulated by NF-kappaB/p38 kinase

Considerable efforts have been taken to identify natural peptides as potential bioactive substances. In this study, novel peptide (SHP-1) derived from seahorse (Hippocampus, Syngnathidae) hydrolysate was explored for its inhibitory effects on collagen release in arthritis with the investigation of its underlying mechanism of action. The efficacy of SHP-1 was determined on cartilage protective effects such as inhibition of collagen and GAG release. SHP-1 was able to suppress not only the expression of collagenases 1 and 3, but also the production of NO via down-regulation of iNOS. However, it presented an irrelevant effect on the level of GAG release in chondrocytic and osteoblastic cells. Inhibition of collagen release by SHP-1 is associated with restraining the phosphorylation of NF-kappaB and p38 kinase cascade. Therefore, it could be suggested that SHP-1 has a potential to be used in arthritis treatment.

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.

Effect of monosaccharides composing glycosaminoglycans on type 2 collagen accumulation in a three-dimensional culture of chondrocytes

The effect of the addition of monosaccharides composing glycosaminoglycans (GAGs) on the accumulation of type 2 collagen (COL(II)) in a three-dimensional (3D) culture of porcine chondrocyte cells was investigated for possible application to cartilage regenerative medicine. Primary chondrocytes from porcine cartilage were cultivated in three-dimension employing atelo collagen gel for 3 weeks with the addition of several saccharides. The addition of d-glucuronic acid (d-GlcA), N-acetyl-d-galactosamine (d-GalNAc), chondroitin sulfate C (CSC), d-galactose, N-acetyl-d-glucosamine, and l-iduronic acid increased markedly not aggrecan but COL(II) accumulation although the addition of d-fructose and d-mannose not composing GAGs did not show such an effect. The addition of d-GlcA and d-GalNAc had no synergistic effect. The addition of CSC, d-GlcA, and d-GalNAc also increased COL(II) mRNA expression while aggrecan mRNA expression was not increased by these compounds. In conclusion, the addition of monosaccharides composing GAGs might be valuable for increasing COL(II) accumulation in the 3D culture of chondrocytes.

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.

Diminished mitochondrial DNA integrity and repair capacity in OA chondrocytes

OBJECTIVES

Osteoarthritis (OA) is characterized by the failure of chondrocytes to respond to injury and perform the cartilage remodeling process. Human articular chondrocytes actively produce reactive oxygen and nitrogen species (ROS and RNS) capable of causing cellular dysfunction and death. A growing body of evidence indicates that mitochondrial dysfunction and mitochondrial DNA (mtDNA) damage play a causal role in disorders linked to excessive generation of oxygen free radicals. The aim of this study was to determine whether mtDNA damage was present in OA chondrocytes, and whether mtDNA repair capacity is compromised in OA chondrocytes following oxidative stress, leading to chondrocyte death.

METHODS

Human articular cartilage was isolated from knee joints of cadavers available through the Anatomical Gifts Program at the University of South Alabama (normal donors) or OA patients undergoing total knee replacement surgeries (OA patients). Total DNA was isolated from either chondrocytes released following collagenase digestion, or from first passage chondrocytes grown in culture and exposed to ROS or RNS. mtDNA integrity and repair capacity were analyzed by quantitative Southern blot analysis, using a mtDNA-specific radioactive probe. Cell viability was determined by the trypan blue exclusion method.

RESULTS

mtDNA damage was found in chondrocytes from OA patients compared to normal donors. It was accompanied with reduced mtDNA repair capacity, cell viability, and increased apoptosis in OA chondrocytes following exposure to ROS and RNS.

CONCLUSIONS

These results indicate that mtDNA damage and poor mtDNA repair capacity for removing damage caused by oxidative stress may contribute to the pathogenesis of OA.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Histone deacetylase inhibitors suppress interleukin-1beta-induced nitric oxide and prostaglandin E2 production in human chondrocytes

OBJECTIVE

Overproduction of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) plays an important role in the pathogenesis of osteoarthritis (OA). In the present study, we determined the effect of trichostatin A (TSA) and butyric acid (BA), two histone deacetylase (HDAC) inhibitors, on NO and PGE(2) synthesis, inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 expression, and nuclear factor (NF)-kappaB DNA-binding activity, in interleukin-1beta (IL-1)-stimulated human OA chondrocytes, and on IL-1-induced proteoglycan degradation in cartilage explants.

METHODS

Chondrocytes were stimulated with IL-1 in the absence or presence of increasing concentrations of TSA or BA. The production of NO and PGE(2) was evaluated using Griess reagent and an enzyme immunoassay, respectively. The expression of iNOS and COX-2 proteins and mRNAs was evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), respectively. Proteoglycan degradation was measured with dimethymethylene blue assay. Electrophoretic mobility shift assay (EMSA) was utilized to analyze the DNA-binding activity of NF-kappaB.

RESULTS

HDAC inhibition with TSA or BA resulted in a dose-dependent inhibition of IL-1-induced NO and PGE(2) production. IL-17- and tumor necrosis factor-alpha (TNF-alpha)-induced NO and PGE(2) production was also inhibited by TSA and BA. This inhibition correlated with the suppression of iNOS and COX-2 protein and mRNA expression. TSA and BA also prevented IL-1-induced proteoglycan release from cartilage explants. Finally, we demonstrate that the DNA-binding activity of NF-kappaB, was induced by IL-1, but was not affected by treatment with HDAC inhibitors.

CONCLUSIONS

These data indicate that HDAC inhibitors suppressed IL-1-induced NO and PGE(2) synthesis, iNOS and COX-2 expression, as well as proteoglycan degradation. The suppressive effect of HDAC inhibitors is not due to impaired DNA-binding activity of NF-kappaB. These findings also suggest that HDAC inhibitors may be of potential therapeutic value in the treatment of OA.

IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains

OBJECTIVE

Partial meniscectomy is known to cause osteoarthritis (OA) of the underlying cartilage as well as alter the load on the remaining meniscus. Removal of 30-60% of the medial meniscus increases compressive strains from a maximum of approximately 10% to almost 20%. The goal of this study is to determine if meniscal cells produce catabolic molecules in response to the altered loading that results from a partial meniscectomy.

METHOD

Relative changes in gene expression of interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and subsequent changes in the concentration of nitric oxide (NO) released by meniscal tissue in response to compression were measured. Porcine meniscal explants were dynamically compressed for 2 h at 1 Hz to simulate physiological stimulation at either 10% strain or 0.05 MPa stress. Additional explants were pathologically stimulated to either 0% strain, 20% strain or, 0.1 MPa stress.

RESULTS

iNOS and IL-1 gene expression and NO release into the surrounding media were increased at 20% compressive strain compared to other conditions. Pathological unloading (0% compressive strain) of meniscal explants did not significantly change expression of IL-1 or iNOS genes, but did result in an increased amount of NO released compared to physiological strain of 10%.

CONCLUSION

These data suggest that meniscectomies which reduce the surface area of the meniscus by 30-60% will increase the catabolic activity of the meniscus which may contribute to the progression of OA.

Cilostazol protects rat chondrocytes against nitric oxide-induced apoptosis in vitro and prevents cartilage destruction in a rat model of osteoarthritis

OBJECTIVE

To examine whether cilostazol, a selective phosphodiesterase type III inhibitor, protects rat articular chondrocytes against nitric oxide (NO)-induced apoptosis and prevents cartilage destruction in mono-iodoacetate-induced osteoarthritis (OA) in a rat model in which inducible nitric oxide synthase (iNOS) is expressed.

METHODS

The NO donor sodium nitroprusside was administered to rat articular chondrocytes that had been pretreated with cilostazol. Induction of apoptosis was evaluated by DNA electrophoresis and pulsed-field gel electrophoresis. The expression level and the subcellular location of apoptosis-associated factors were examined by Western blot analysis and confocal microscopy, respectively. Protein kinase CK2 (PKCK2) activity was also assayed. To examine whether orally administered cilostazol prevents cartilage destruction in vivo, cartilage samples obtained from rats with experimentally induced OA were subjected to hematoxylin and eosin, Safranin O, and TUNEL staining and immunohistochemical analysis of iNOS expression.

RESULTS

Cilostazol prevented NO-induced reduction in viability, in a dose-dependent manner. It also prevented the up-regulation of phosphorylated p53 and p38, the down-regulation of heme oxygenase 1, the subcellular translocation of apoptosis-inducing factor and cytochrome c, and the activation of caspases 3, 7, and 8 induced by NO treatment, indicating that cilostazol prevented NO-induced cell death by blocking apoptosis. In addition, cilostazol prevented NO-induced translocation of cleaved Bid onto mitochondria, and caused phosphorylated Bid to accumulate in the nucleus and cytosol. Cilostazol prevented the down-regulation of PKCK2 and the reduction in PKCK2 activity induced by NO, indicating that its apoptosis-preventing activity was mediated via PKCK2. It also prevented chondrocyte apoptosis and cartilage destruction in a rat model of experimentally induced OA.

CONCLUSION

Our findings indicate that cilostazol prevents NO-induced apoptosis of chondrocytes via PKCK2 in vitro and prevents cartilage destruction in a rat model of OA.

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.

Spingosine-1-phosphate stimulates proliferation and counteracts interleukin-1 induced nitric oxide formation in articular chondrocytes

OBJECTIVE

Sphingosine-1-phosphate (S1P) is a messenger molecule, with important functions in inflammation and wound healing. The present study was performed to elucidate a possible role of S1P signaling in articular chondrocytes.

METHODS

Human and bovine primary chondrocytes were cultured in monolayer. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to detect S1P receptor mRNA. Proliferation of S1P stimulated chondrocytes was measured by 3H-thymidine uptake. Supernatants of cultured bovine chondrocytes stimulated with S1P alone or in combination with interleukin-1beta (IL-1beta) were tested for nitric oxide (NO) formation and expression of inducible nitric oxide synthase (iNOS). Matrixmetalloprotease-13 (MMP-13) and aggrecanase-1 (ADAMTS-4) were evaluated using real-time PCR. Glycosaminoglycan (GAG) loss from bovine cartilage explants was evaluated using the dimethylene blue method.

RESULTS

S1P1, S1P2 and S1P3 but not S1P4 and S1P5 receptor mRNA were detected in human and bovine chondrocytes. S1P dose dependently induced proliferation in bovine and human chondrocytes. S1P significantly reduced NO formation and iNOS mRNA and protein expression, both in un-stimulated and IL-1beta stimulated bovine chondrocytes. Furthermore, S1P dose dependently inhibited IL-1beta induced expression of ADAMTS-4 and MMP-13 and diminished IL-1beta mediated GAG depletion from cartilage explants.

CONCLUSION

These results suggest that S1P provides an anti-catabolic signal in articular chondrocytes.

Involvement of protein kinase Czeta in interleukin-1beta induction of ADAMTS-4 and type 2 nitric oxide synthase via NF-kappaB signaling in primary human osteoarthritic chondrocytes

OBJECTIVE

Protein kinase Czeta (PKCzeta), an atypical PKC, has been found to be transcriptionally up-regulated in human osteoarthritic (OA) articular cartilage. This study was undertaken to examine the role of PKCzeta in interleukin-1beta (IL-1beta)-induced NF-kappaB signaling in human OA chondrocytes, and ultimately to better understand its function in the regulation of downstream mediators of cartilage matrix degradation.

METHODS

Pharmacologic inhibitors or genetic knockdown techniques were used to investigate the role of PKCzeta. Western blot analysis was used to evaluate phosphorylation of PKCzeta and NF-kappaB. Quantitative polymerase chain reaction (PCR) and activity assays were used to evaluate ADAMTS-4 expression and aggrecanase activity, respectively. Quantitative PCR, biochemical identification, and Western blot analysis were used to evaluate type 2 nitric oxide synthase (NOS2) and NO production.

RESULTS

Phosphorylation of PKCzeta and NF-kappaB was induced by IL-1beta treatment in a time-dependent manner, and was specifically inhibited by inhibitors of atypical PKCs. Inhibition of PKCzeta suppressed IL-1beta-induced up-regulation of ADAMTS-4 messenger RNA (mRNA) and aggrecanase activity. Inhibitors of atypical PKCs also inhibited IL-1beta-induced NO production and NOS2 mRNA expression, demonstrating a novel link between PKCzeta and NO production. Furthermore, small interfering RNA- or short hairpin RNA-mediated knockdown of PKCzeta mRNA resulted in significant repression of both ADAMTS-4 and NOS2 mRNA expression.

CONCLUSION

Our results show that PKCzeta is involved in the regulation of IL-1beta-induced NF-kappaB signaling in human OA chondrocytes, which in turn regulates downstream expression of ADAMTS-4 and NOS2. Therefore, inhibition of PKCzeta could potentially regulate the production of matrix-degrading enzymes as well as NO production and have a profound effect on disease progression in OA.

Key regulatory molecules of cartilage destruction in rheumatoid arthritis: an in vitro study

Background

Rheumatoid arthritis (RA) is a chronic, inflammatory and systemic autoimmune disease that leads to progressive cartilage destruction. Advances in the treatment of RA-related destruction of cartilage require profound insights into the molecular mechanisms involved in cartilage degradation. Until now, comprehensive data about the molecular RA-related dysfunction of chondrocytes have been limited. Hence, the objective of this study was to establish a standardized in vitro model to profile the key regulatory molecules of RA-related destruction of cartilage that are expressed by human chondrocytes.

Methods

Human chondrocytes were cultured three-dimensionally for 14 days in alginate beads and subsequently stimulated for 48 hours with supernatants from SV40 T-antigen immortalized human synovial fibroblasts (SF) derived from a normal donor (NDSF) and from a patient with RA (RASF), respectively. To identify RA-related factors released from SF, supernatants of RASF and NDSF were analyzed with antibody-based protein membrane arrays. Stimulated cartilage-like cultures were used for subsequent gene expression profiling with oligonucleotide microarrays. Affymetrix GeneChip Operating Software and Robust Multi-array Analysis (RMA) were used to identify differentially expressed genes. Expression of selected genes was verified by real-time RT-PCR.

Results

Antibody-based protein membrane arrays of synovial fibroblast supernatants identified RA-related soluble mediators (IL-6, CCL2, CXCL1–3, CXCL8) released from RASF. Genome-wide microarray analysis of RASF-stimulated chondrocytes disclosed a distinct expression profile related to cartilage destruction involving marker genes of inflammation (adenosine A2A receptor, cyclooxygenase-2), the NF-κB signaling pathway (toll-like receptor 2, spermine synthase, receptor-interacting serine-threonine kinase 2), cytokines/chemokines and receptors (CXCL1–3, CXCL8, CCL20, CXCR4, IL-1β, IL-6), cartilage degradation (matrix metalloproteinase (MMP)-10, MMP-12) and suppressed matrix synthesis (cartilage oligomeric matrix protein, chondroitin sulfate proteoglycan 2).

Conclusion

Differential transcriptome profiling of stimulated human chondrocytes revealed a disturbed catabolic–anabolic homeostasis of chondrocyte function and disclosed relevant pharmacological target genes of cartilage destruction. This study provides comprehensive insight into molecular regulatory processes induced in human chondrocytes during RA-related destruction of cartilage. The established model may serve as a human in vitro disease model of RA-related destruction of cartilage and may help to elucidate the molecular effects of anti-rheumatic drugs on human chondrocyte gene expression.

Synthesis and release of human cartilage matrix proteoglycans are differently regulated by nitric oxide and prostaglandin-E2

OBJECTIVES

Recent studies showed beneficial effects of COX-2 inhibition on proteoglycan turnover of both IL-1beta/tumour necrosis factor alpha (TNFalpha) damaged cartilage and of osteoarthritic cartilage. Although proteoglycan release and content were normalised, proteoglycan synthesis was only partially influenced. Prostaglandin-E2 is the main product formed by COX-2. We therefore evaluate the role of prostaglandin-E2 in relation to nitric oxide in disturbing cartilage proteoglycan turnover.

METHODS

Human healthy cartilage, alone or in the presence of IL-1beta+TNFalpha, was cultured for 7 days with or without prostaglandin-E2 or the selective COX-2 inhibitor (celecoxib 10 microM). Changes in cartilage matrix proteoglycan turnover, levels of prostaglandin-E2 and nitric oxide were determined.

RESULTS

Proteoglycan synthesis and release of the cartilage were not affected by prostaglandin-E2 alone. Addition of IL-1beta+TNFalpha to healthy cartilage resulted in inhibition of proteoglycan synthesis and increase in proteoglycan release. When prostaglandin-E2 was added, in addition to IL-1beta+TNFalpha, proteoglycan release increased further, but proteoglycan synthesis was not influenced further. Addition of a selective COX-2 inhibitor to the IL-1beta+TNFalpha treated cartilage inhibited the enhanced prostaglandin-E2 production and almost completely normalised proteoglycan release, whereas synthesis remained unaffected. Also, the enhanced NO-levels remained elevated. Prostaglandin-E2 levels correlated significantly with proteoglycan release, whereas NO levels correlated significantly with proteoglycan synthesis.

CONCLUSION

The present results suggest involvement of prostaglandin-E2 in enhanced cartilage proteoglycan release but not synthesis, although healthy cartilage has to be sensitised by IL-1beta+tumour necrosis factor alpha (TNFalpha). IL-1beta+TNFalpha induced NO seems to be involved in inhibition of proteoglycan synthesis, independent of prostaglandin-E2, and thus seems insensitive to regulation by (selective) COX-2 inhibitors.

Prolyl 4-hydroxylases, key enzymes in the synthesis of collagens and regulation of the response to hypoxia, and their roles as treatment targets

Prolyl 4-hydroxylases (P4Hs) have central roles in the synthesis of collagens and the regulation of oxygen homeostasis. The 4-hydroxyproline residues generated by the endoplasmic reticulum (ER) luminal collagen P4Hs (C-P4Hs) are essential for the stability of the collagen triple helix. Vertebrate C-P4Hs are alpha2beta2 tetramers with three isoenzymes differing in their catalytic alpha subunits. Another P4H family, the HIF-P4Hs, hydroxylates specific prolines in the alpha subunit of the hypoxia-inducible transcription factor (HIF), a master regulator of hypoxia-inducible genes, and controls its stability in an oxygen-dependent manner. The HIF-P4Hs are cytoplasmic and nuclear enzymes, likewise with three isoenzymes in vertebrates. A third vertebrate P4H type is an ER transmembrane protein that can act on HIF-alpha but not on collagens. All P4Hs require Fe2+, 2-oxoglutarate, O2, and ascorbate. C-P4Hs are regarded as attractive targets for pharmacological inhibition to control excessive collagen accumulation in fibrotic diseases and severe scarring, while HIF-P4H inhibitors are believed to have beneficial effects in the treatment of diseases such as myocardial infarction, stroke, peripheral vascular disease, diabetes, and severe anemias. Studies with P4H inhibitors in various animal models of fibrosis, anemia, and ischemia and ongoing clinical trials with HIF-P4H inhibitors support this hypothesis by demonstrating efficacy in many applications.

Effect of nitric oxide and peroxynitrite on type I collagen synthesis in normal and scleroderma dermal fibroblasts

Nitric oxide ((.-)NO) is an important physiological signaling molecule and potent vasodilator. Recently, we have shown abnormal (.-)NO metabolism in the plasma of patients with systemic sclerosis (SSc), a disease that features excessive collagen overproduction as well as vascular dysfunction. The current study investigates the effects of (.-)NO and peroxynitrite (ONOO(-)) on secretion of type I collagen by SSc dermal fibroblasts, compared with those from normal dermal fibroblasts (CON) and a dermal fibroblast cell line (AG). Dermal fibroblasts were incubated with (.-)NO donors (SNP, DETA-NONOate) with or without the antioxidant ascorbic acid, or ONOO(-) for 24-72 h. In CON and AG fibroblasts, type I collagen was dose dependently decreased by SNP or DETA-NONOate. However, (.-)NO had no effect in SSc fibroblasts. Furthermore, the inhibition of collagen synthesis by (.-)NO was reversed by ascorbic acid and was not affected by 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanyl cyclase, or 8-bromoguanosine cyclic 3',5'-monophosphate, a cGMP agonist. SNP also showed a significant up-regulation of matrix metalloproteinase-1 (MMP-1) protein and activity levels, an essential collagenase involved in collagen degradation, in the AG fibroblasts. Additionally, (.-)NO-treated fibroblasts had lower prolyl hydroxylase activity, an enzyme important in the post-translational processing of collagen, while there was no effect on total protein levels. There were no significant effects on type I collagen levels when dermal fibroblasts were treated with ONOO(-). Taken together, ()NO inhibits collagen secretion in normal dermal fibroblasts but regulation is lost in SSc fibroblasts, while ONOO(-) itself is ineffective. (.-)NO inhibition of collagen was by cGMP-independent regulatory mechanisms and in part may be due to up-regulation of MMP-1 and/or inhibition of prolyl hydroxylase. These differences may contribute to the observed pathology of SSc.

Suppression of NF-kappaB activation by curcumin leads to inhibition of expression of cyclo-oxygenase-2 and matrix metalloproteinase-9 in human articular chondrocytes: Implications for the treatment of osteoarthritis

Pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) play a key role in the pathogenesis of osteoarthritis (OA). Anti-inflammatory agents capable of suppressing the production and catabolic actions of these cytokines may have therapeutic potential in the treatment of OA and a range of other osteoarticular disorders. The purpose of this study was to examine the effects of curcumin (diferuloylmethane), a pharmacologically safe phytochemical agent with potent anti-inflammatory properties on IL-1beta and TNF-alpha signalling pathways in human articular chondrocytes maintained in vitro. The effects of curcumin were studied in cultures of human articular chondrocytes treated with IL-1beta and TNF-alpha for up to 72h. Expression of collagen type II, integrin beta1, cyclo-oxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9) was monitored by western blotting. The effects of curcumin on the expression, phosphorylation and nuclear translocation of protein components of the NF-kappaB system were studied by western blotting and immunofluorescence, respectively. Treatment of chondrocytes with curcumin suppressed IL-1beta-induced NF-kappaB activation via inhibition of IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation and p65 nuclear translocation. Curcumin inhibited the IL-1beta-induced stimulation of up-stream protein kinase B Akt. These events correlated with down-regulation of NF-kappaB targets including COX-2 and MMP-9. Similar results were obtained in chondrocytes stimulated with TNF-alpha. Curcumin also reversed the IL-1beta-induced down-regulation of collagen type II and beta1-integrin receptor expression. These results indicate that curcumin has nutritional potential as a naturally occurring anti-inflammatory agent for treating OA through suppression of NF-kappaB mediated IL-1beta/TNF-alpha catabolic signalling pathways in chondrocytes.

The catabolic pathway mediated by Toll-like receptors in human osteoarthritic chondrocytes

OBJECTIVE

To examine the catabolic pathways mediated by Toll-like receptor (TLR) ligands in human osteoarthritic (OA) chondrocytes.

METHODS

The presence of TLRs in OA and non-OA articular cartilage was analyzed by immunohistochemistry. The regulation of TLR messenger RNA (mRNA) by interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) was analyzed by reverse transcription-polymerase chain reaction. For stimulation of TLR-2 and TLR-4, chondrocytes were treated with Staphylococcus aureus peptidoglycan and lipopolysaccharides (LPS), respectively. Production of matrix metalloproteinases (MMPs) 1, 3, and 13 and prostaglandin E2 (PGE2) was evaluated by enzyme-linked immunosorbent assay. Production of nitric oxide (NO) was analyzed by the Griess reaction. Regulation of cyclooxygenase 2 protein and phosphorylation of MAPKs (p38, ERK, and JNK) were evaluated by Western blotting or solid-phase kinase assay. NF-kappaB activation was evaluated by electrophoretic mobility shift assay.

RESULTS

Expression of TLRs 2 and 4 was up-regulated in lesional areas of OA cartilage. Treatment with IL-1, TNFalpha, peptidoglycan, and LPS all significantly up-regulated TLR-2 mRNA expression in cultured chondrocytes. Production of MMPs 1, 3, and 13 and of NO and PGE2 was significantly increased after treating chondrocytes with either of the TLR ligands. Prolonged culture of cartilage explants with TLR ligands also led to a significant increase in the release of proteoglycan and type II collagen degradation product. Treatment with TLR ligands led to phosphorylation of all 3 MAPKs and activation of NF-kappaB.

CONCLUSION

We found that TLRs are increased in OA cartilage lesions. TLR-2 and TLR-4 ligands strongly induce catabolic responses in chondrocytes. Modulation of TLR-mediated signaling as a therapeutic strategy would require detailed elucidation of the signaling pathways involved.

Gout in solid organ transplantation: a challenging clinical problem

Hyperuricaemia occurs in 5-84% and gout in 1.7-28% of recipients of solid organ transplants. Gout may be severe and crippling, and may hinder the improved quality of life gained through organ transplantation. Risk factors for gout in the general population include hyperuricaemia, obesity, weight gain, hypertension and diuretic use. In transplant recipients, therapy with ciclosporin (cyclosporin) is an additional risk factor. Hyperuricaemia is recognised as an independent risk factor for cardiovascular disease; however, whether anti-hyperuricaemic therapy reduces cardiovascular events remains to be determined. Dietary advice is important in the management of gout and patients should be educated to partake in a low-calorie diet with moderate carbohydrate restriction and increased proportional intake of protein and unsaturated fat. While gout is curable, its pharmacological management in transplant recipients is complicated by the risk of adverse effects and potentially severe interactions between immunosuppressive and hypouricaemic drugs. NSAIDs, colchicine and corticosteroids may be used to treat acute gouty attacks. NSAIDs have effects on renal haemodynamics, and must be used with caution and with close monitoring of renal function. Colchicine myotoxicty is of particular concern in transplant recipients with renal impairment or when used in combination with ciclosporin. Long-term urate-lowering therapy is required to promote dissolution of uric acid crystals, thereby preventing recurrent attacks of gout. Allopurinol should be used with caution because of its interaction with azathioprine, which results in bone marrow suppression. Substitution of mycophenylate mofetil for azathioprine avoids this interaction. Uricosuric agents, such as probenecid, are ineffective in patients with renal impairment. The exception is benzbromarone, which is effective in those with a creatinine clearance >25 mL/min. Benzbromarone is indicated in allopurinol-intolerant patients with renal failure, solid organ transplant or tophaceous/polyarticular gout. Monitoring for hepatotoxicty is essential for patients taking benzbromarone. Physicians should carefully consider therapeutic options for the management of hypertension and hyperlipidaemia, which are common in transplant recipients. While loop and thiazide diuretics increase serum urate, amlodipine and losartan have the same antihypertensive effect with the additional benefit of lowering serum urate. Atorvastatin, but not simvastatin, may lower uric acid, and while fenofibrate may reduce serum urate it has been associated with a decline in renal function. Gout in solid organ transplantation is an increasing and challenging clinical problem; it impacts adversely on patients' quality of life. Recognition and, if possible, alleviation of risk factors, prompt treatment of acute attacks and early introduction of hypouricaemic therapy with careful monitoring are the keys to successful management.