Effect of nitric oxide on mitochondrial activity of human synovial cells

Cancer Resistance Is Mediated by the Upregulation of Several Anti-Apoptotic Gene Products via the Inducible Nitric Oxide Synthase/Nitric Oxide Pathway: Therapeutic Implications

Significance: Several therapeutic strategies for cancer treatments have been developed with time, and significant milestones have been achieved recently. However, with these novel therapies, not all cancer types respond and in the responding cancer types only a subset is affected. The failure to respond is principally the result that these cancers develop several mechanisms of resistance. Thus, a focus of current research investigations is to unravel the various mechanisms that regulate resistance and identify suitable targets for new therapeutics. Recent Advances: Hence, many human cancer types have been reported to overexpress the inducible nitric oxide synthase (iNOS) and it has been suggested that iNOS/nitric oxide (NO) plays a pivotal role in the regulation of resistance. We have postulated that iNOS overexpression or NO regulates the overexpression of pivotal anti-apoptotic gene products such as B-cell lymphoma 2 (Bcl-2), B-cell lymphoma extra large (Bcl-xL), myeloid cell leukemia-1 (Mcl-1), and survivin. In this report, we describe the various mechanisms, transcriptional, post-transcriptional, and post-translational, by which iNOS/NO regulates the expression of the above anti-apoptotic gene products. Critical Issues: The iNOS/NO-mediated regulation of the four gene products is not the same with both specific and overlapping pathways. Our findings are, in large part, validated by bioinformatic analyses demonstrating, in several cancers, several direct correlations between the expression of iNOS and each of the four examined anti-apoptotic gene products. Future Directions: We have proposed that targeting iNOS may be highly efficient since it will result in the underexpression of multiple anti-apoptotic proteins and shifting the balance toward the proapoptotic gene products and reversal of resistance. Antioxid. Redox Signal. 39, 853-889.

Upregulated Mitochondrial Dynamics Is Responsible for the Procatabolic Changes of Chondrocyte Induced by α2-Adrenergic Signal Activation

OBJECTIVE

Activation of sympathetic tone is important for cartilage degradation in osteoarthritis (OA). Recent studies reported that sympathetic signals can affect the mitochondrial function of target cells. It is unknown whether this effect exits in chondrocytes and affects chondrocyte catabolism. The contribution of mitochondrial dynamics in the activation of α2-adrenergic signal-mediated chondrocyte catabolism was investigated in this study.

DESIGN

Primary chondrocytes were stimulated with norepinephrine (NE) alone, or pretreated with an α2-adrenergic receptor (Adra2) antagonist (yohimbine) and followed by stimulation with NE. Changes in chondrocyte metabolism and their mitochondrial dynamics were investigated.

RESULTS

We demonstrated that NE stimulation induced increased gene and protein expressions of matrix metalloproteinase-3 and decreased level of aggrecan by chondrocytes. This was accompanied by upregulated mitochondriogenesis and the number of mitochondria, when compared with the vehicle-treated controls. Mitochondrial fusion and fission, and mitophagy also increased significantly in response to NE stimulation. Inhibition of Adra2 attenuated chondrocyte catabolism and mitochondrial dynamics induced by NE.

CONCLUSIONS

The present findings indicate that upregulation of mitochondrial dynamics through mitochondriogenesis, fusion, fission, and mitophagy is responsible for activation of α2-adrenergic signal-mediated chondrocyte catabolism. The hypothesis that "α2-adrenergic signal activation promotes cartilage degeneration in temporomandibular joint osteoarthritis (TMJ-OA) by upregulating mitochondrial dynamics in chondrocytes" is validated. This represents a new regulatory mechanism in the chondrocytes of TMJ-OA that inhibits abnormal activation of mitochondrial fusion and fission is a potential regulator for improving mitochondrial function and inhibiting chondrocyte injury and contrives a potentially innovative therapeutic direction for the prevention of TMJ-OA.

Alisol A 24-acetate ameliorates osteoarthritis progression by inhibiting reactive oxygen species and inflammatory response through the AMPK/mTOR pathway

INTRODUCTION

Osteoarthritis is a degenerative knee joint disease featured with articular cartilage degeneration and inflammation. Alisol A 24-acetate (ALA-24A) is an active triterpene that has antioxidant and anti-inflammatory pharmacological properties. However, its effect and molecular mechanism on osteoarthritis progression have not been reported.

METHODS

IL-1β-induced chondrocyte injury model and monosodium iodoacetate (MIA)-induced rat osteoarthritis model were used. The protective effects of ALA-24A on osteoarthritis were evaluated by determining cell viability, extracellular matrix (ECM) degradation, inflammatory response and oxidative stress using CCK-8 assay, Western blot, ELISA, and DCFH-DA fluorescent probe. The severity and matrix degradation of articular cartilage were assessed by histopathological and immunohistochemical examination.

RESULTS

We found that ALA-24A attenuated IL-1β-induced cell viability inhibition Moreover, ALA-24A suppressed expression levels of ECM degradation-related genes ADAMTS5 and MMP13, and promoted expression levels of ECM synthesis-related genes Aggrecan and Collagen II. In addition, ALA-24A treatment decreased reactive oxygen species (ROS) production and increased antioxidant enzymes (SOD, CAT, and GSH-px) activities, while increased MDA levels. The inflammatory levels of NO, PGE2, TNF-α, and IL-6 were also reduced following treatment with ALA-24A. Our data also revealed that ALA-24A treatment triggered p-AMPK upregulation and p-mTOR downregulation. In rat osteoarthritis model, ALA-24A treatment significantly alleviated the severity and matrix degradation of articular cartilage comparted with model group.

CONCLUSIONS

Our findings suggested a protective role of ALA-24A against osteoarthritis by inhibiting ROS and inflammatory response. Furthermore, ALA-24A might be a promising therapeutic option for osteoarthritis treatment.

A nitric oxide responsive AIE probe for detecting the progression of osteoarthritis

Nitric oxide (NO) is reported to be elevated in osteoarthritis (OA) both in vitro and in vivo and may be adopted to develop fluorescent probes for detecting the progression of OA. Here we report a nitric oxide responsive aggregation induced emission (AIE) probe TPE-2NHCOCH₂CH₂-(PEG)₂₄-NH-Diacerein, which is derived from tetraphenylethene (TPE) modified with the hydrophilic group long poly(ethylene glycol) chain and an anti-inflammatory drug diacerein. o-Phenylenediamine within its structure can react with NO to form benzotriazole and emit fluorescence. The results show that the NO-responsive AIE probe can smartly monitor the progression of OA with the change of fluorescence intensity in vitro and in vivo. This study may provide a new development direction for early OA monitoring in clinics.

High glucose-induced increasing reactive nitrogen species accumulation triggered mitochondrial dysfunction, inflammation, and apoptosis in keratinocytes

Growing evidence indicates that skin injuries are a common complication of diabetes. However, the cellular and molecular mechanisms of high glucose (HG) environment trigger nitrosative stress-mediated inflammation and apoptosis in keratinocytes remains unknown. Here we investigated whether reactive nitrogen species (RNS) induced by HG environment restrain antioxidant activity, and mitochondrial dysfunction leading to inflammation, and apoptosis via stress signaling pathways in keratinocytes. Our results established that the HG environment enhanced the production of nitric oxide (NO) and peroxynitrite anion (ONOO-) by inducible NO synthase (iNOS) in keratinocytes. Overproduction of RNS in HG environment suppress the antioxidants activity leading to mitochondrial dysfunction, characterized by loss of mitochondrial membrane potential (ΔΨm), increase in mitochondrial mass, decrease in mitochondrial transcription factor A(TFAM), increase in mitochondrial DNA (mtDNA) displacement loop (D-loop) and decrease in glycolytic flux concentration, which was attenuated by pharmacological inhibitors of NO/ONOO-, Nω-Nitro-l-argininemethyl ester hydrochloride (NAME)/hydralazine hydrochloride (Hyd.HCl). Excess production of RNS in HG environment restrained 8-oxoguanine DNA glycosylase-1 (OGG1) expression and increased 8-hydroxydeoxyguanosine (8-OHdG) accumulations in DNA were regulated by NO or ONOO-. Further, HG-induced RNA production caused an increase in the production of inflammatory mediators accompanied by activation of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3 signaling cascade, lipid peroxidation (LPO), and protein carbonylation (PC) reactions followed by breakdown the cell-cell communication and apoptosis. Pre-treatment of cell with NAME/Hyd.HCl, diminished the expression of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3, inflammatory mediators, and attenuated apoptosis in keratinocytes. Together, our results indicated that excess production of RNS in HG environment triggered inflammation and apoptosis, mediated by activation of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3 signaling cascades in keratinocytes.

Mitochondrial Dysfunction and Oxidative Stress in Rheumatoid Arthritis

Control of excessive mitochondrial oxidative stress could provide new targets for both preventive and therapeutic interventions in the treatment of chronic inflammation or any pathology that develops under an inflammatory scenario, such as rheumatoid arthritis (RA). Increasing evidence has demonstrated the role of mitochondrial alterations in autoimmune diseases mainly due to the interplay between metabolism and innate immunity, but also in the modulation of inflammatory response of resident cells, such as synoviocytes. Thus, mitochondrial dysfunction derived from several danger signals could activate tricarboxylic acid (TCA) disruption, thereby favoring a vicious cycle of oxidative/mitochondrial stress. Mitochondrial dysfunction can act through modulating innate immunity via redox-sensitive inflammatory pathways or direct activation of the inflammasome. Besides, mitochondria also have a central role in regulating cell death, which is deeply altered in RA. Additionally, multiple evidence suggests that pathological processes in RA can be shaped by epigenetic mechanisms and that in turn, mitochondria are involved in epigenetic regulation. Finally, we will discuss about the involvement of some dietary components in the onset and progression of RA.

Impact of High-Altitude Hypoxia on Bone Defect Repair: A Review of Molecular Mechanisms and Therapeutic Implications

Reaching areas at altitudes over 2,500–3,000 m above sea level has become increasingly common due to commerce, military deployment, tourism, and entertainment. The high-altitude environment exerts systemic effects on humans that represent a series of compensatory reactions and affects the activity of bone cells. Cellular structures closely related to oxygen-sensing produce corresponding functional changes, resulting in decreased tissue vascularization, declined repair ability of bone defects, and longer healing time. This review focuses on the impact of high-altitude hypoxia on bone defect repair and discusses the possible mechanisms related to ion channels, reactive oxygen species production, mitochondrial function, autophagy, and epigenetics. Based on the key pathogenic mechanisms, potential therapeutic strategies have also been suggested. This review contributes novel insights into the mechanisms of abnormal bone defect repair in hypoxic environments, along with therapeutic applications. We aim to provide a foundation for future targeted, personalized, and precise bone regeneration therapies according to the adaptation of patients to high altitudes.

Evaluation of Antioxidant Activity and Histopathological Changes Occurred by the Oral Ingestion of CuO Nanoparticles in Monosodium Urate Crystal-Induced Hyperuricemic BALB/c Mice

Nanotechnology is an intensive branch of science due to the unique features of nano range particles (1-100 nm). Their nano size results in a high surface area of absorption when orally administered. Monosodium urate crystal excessive deposition causes a commonly known inflammatory disease called gout into the synovial joints. Previously it has been observed that copper oxide nanoparticles (CuONPs) had a significant effect in reducing the serum uric acid levels in BALB/c mice as well as reducing the inflammation in the ankles of mice. This study was made to investigate the antioxidant and histopathological changes in hyperuricemic BALB/c mice upon the oral administration of copper oxide nanoparticles. Different concentrations of copper oxide nanoparticles 5, 10, and 20 ppm were given orally to gouty mice. To investigate the antioxidant activity of CuONPs, various antioxidant protocols were applied. It was noted that the nanoparticle-treated group of 20 ppm showed no significant changes in superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), thiobarbituric acid reactive substances (TBARS), and ROS values while the protein estimation values of the negative control group exhibited a significant increase (0.001). When compared to negative control, no significant effect was shown on the interpretation of histopathological changes of muscles, kidney, and liver tissues.

Role of Mitochondria in Physiology of Chondrocytes and Diseases of Osteoarthritis and Rheumatoid Arthritis

PURPOSE OF REVIEW

Mitochondria are recognized to be one of the most important organelles in chondrocytes for their role in triphosphate (ATP) generation through aerobic phosphorylation. Mitochondria also participate in many intracellular processes involving modulating reactive oxygen species (ROS), responding to instantaneous hypoxia stress, regulating cytoplasmic transport of calcium ion, and directing mitophagy to maintain the homeostasis of individual chondrocytes.

DESIGNS

To summarize the specific role of mitochondria in chondrocytes, we screened related papers in PubMed database and the search strategy is ((mitochondria) AND (chondrocyte)) AND (English [Language]). The articles published in the past 5 years were included and 130 papers were studied.

RESULTS

In recent years, the integrity of mitochondrial structure has been regarded as a prerequisite for normal chondrocyte survival and defect in mitochondrial function has been found in cartilage-related diseases, such as osteoarthritis (OA) and rheumatoid arthritis (RA). However, the understanding of mitochondria in cartilage is still largely limited. The mechanism on how the changes in mitochondrial structure and function directly lead to the occurrence and development of cartilage-related diseases remains to be elusive.

CONCLUSION

This review aims to summarize the role of mitochondria in chondrocytes under the physiological and pathological changes from ATP generation, calcium homeostasis, redox regulation, mitophagy modulation, mitochondria biogenesis to immune response activation. The enhanced understanding of molecular mechanisms in mitochondria might offer some new cues for cartilage remodeling and pathological intervention.

A brief review on in vivo models for Gouty Arthritis

Gout is more common in men than in women, by a factor of 3.1–10.1. Gout prevalence and incidence have increased in recent decades, with prevalence reaching 11–13% and incidence reaching 0.4% in people over the age of 80. Age-related renal impairment, altered drug distribution, and increased prevalence of comorbidities have significant consequences for safe and effective gout pharmacotherapy. The Discovery of Fruitful in-vivo animal models needs the effective screening of drugs or formulations used in the treatment of gout. In vivo animal models of Gouty arthritis are extensively used to investigate pathogenic mechanisms governing inflammation-driven bone and cartilage damage. Four commonly utilized models include the Potassium oxonate induced hyperuricemic model, MSU crystals induced gouty arthritis animal model, Animal Model of Acute Gouty Arthritis with Hyperuricemia, and Diet-induced hyperuricemia. These offer unique advantages for correlating different aspects of gouty arthritis with human disease. In-vivo animal models served as testing beds for novel biological therapies, including cytokine blockers and small molecule inhibitors of intracellular signaling that have revolutionized gouty arthritis treatment. This review highlights a brief overview of in vivo experimental models for assessment of hypouricemic, anti-inflammatory, as well as renal protective effects of test compounds with some evaluation parameters in detail.

The Role of Oxidative Stress in Hyperuricemia and Xanthine Oxidoreductase (XOR) Inhibitors

Uric acid is the end product of purine metabolism in humans. Hyperuricemia is a metabolic disease caused by the increased formation or reduced excretion of serum uric acid (SUA). Alterations in SUA homeostasis have been linked to a number of diseases, and hyperuricemia is the major etiologic factor of gout and has been correlated with metabolic syndrome, cardiovascular disease, diabetes, hypertension, and renal disease. Oxidative stress is usually defined as an imbalance between free radicals and antioxidants in our body and is considered to be one of the main causes of cell damage and the development of disease. Studies have demonstrated that hyperuricemia is closely related to the generation of reactive oxygen species (ROS). In the human body, xanthine oxidoreductase (XOR) catalyzes the oxidative hydroxylation of hypoxanthine to xanthine to uric acid, with the accompanying production of ROS. Therefore, XOR is considered a drug target for the treatment of hyperuricemia and gout. In this review, we discuss the mechanisms of uric acid transport and the development of hyperuricemia, emphasizing the role of oxidative stress in the occurrence and development of hyperuricemia. We also summarize recent advances and new discoveries in XOR inhibitors.

Mitochondrial DNA from osteoarthritic patients drives functional impairment of mitochondrial activity: a study on transmitochondrial cybrids

With the redefinition of osteoarthritis (OA) and the understanding that the joint behaves as an organ, OA is now considered a systemic illness with a low grade of chronic inflammation. Mitochondrial dysfunction is well documented in OA and has the capacity to alter chondrocyte and synoviocyte function. Transmitochondrial cybrids are suggested as a useful cellular model to study mitochondrial biology in vitro, as they carry different mitochondrial variants with the same nuclear background. The aim of this work was to study mitochondrial and metabolic function of cybrids with mitochondrial DNA from healthy (N) and OA donors. In this work, the authors demonstrate that cybrids from OA patients behave differently from cybrids from N donors in several mitochondrial parameters. Furthermore, OA cybrids behave similarly to OA chondrocytes. These results enhance our understanding of the role of mitochondria in the degeneration process of OA and present cybrids as a useful model to study OA pathogenesis.

Amentadione from the Alga Cystoseira usneoides as a Novel Osteoarthritis Protective Agent in an Ex Vivo Co-Culture OA Model

Osteoarthritis (OA) remains a prevalent chronic disease without effective prevention and treatment. Amentadione (YP), a meroditerpenoid purified from the alga Cystoseira usneoides, has demonstrated anti-inflammatory activity. Here, we investigated the YP anti-osteoarthritic potential, by using a novel OA preclinical drug development pipeline designed to evaluate the anti-inflammatory and anti-mineralizing activities of potential OA-protective compounds. The workflow was based on in vitro primary cell cultures followed by human cartilage explants assays and a new OA co-culture model, combining cartilage explants with synoviocytes under interleukin-1β (IL-1β) or hydroxyapatite (HAP) stimulation. A combination of gene expression analysis and measurement of inflammatory mediators showed that the proposed model mimicked early disease stages, while YP counteracted inflammatory responses by downregulation of COX-2 and IL-6, improved cartilage homeostasis by downregulation of MMP3 and the chondrocytes hypertrophic differentiation factors Col10 and Runx2. Importantly, YP downregulated NF-κB gene expression and decreased phosphorylated IkBα/total IkBα ratio in chondrocytes. These results indicate the co-culture as a relevant pre-clinical OA model, and strongly suggest YP as a cartilage protective factor by inhibiting inflammatory, mineralizing, catabolic and differentiation processes during OA development, through inhibition of NF-κB signaling pathways, with high therapeutic potential.

The Role of Glial Mitochondria in α-Synuclein Toxicity

The abnormal accumulation of alpha-synuclein (α-syn) aggregates in neurons and glial cells is widely known to be associated with many neurodegenerative diseases, including Parkinson’s disease (PD), Dementia with Lewy bodies (DLB), and Multiple system atrophy (MSA). Mitochondrial dysfunction in neurons and glia is known as a key feature of α-syn toxicity. Studies aimed at understanding α-syn-induced toxicity and its role in neurodegenerative diseases have primarily focused on neurons. However, a growing body of evidence demonstrates that glial cells such as microglia and astrocytes have been implicated in the initial pathogenesis and the progression of α-Synucleinopathy. Glial cells are important for supporting neuronal survival, synaptic functions, and local immunity. Furthermore, recent studies highlight the role of mitochondrial metabolism in the normal function of glial cells. In this work, we review the complex relationship between glial mitochondria and α-syn-mediated neurodegeneration, which may provide novel insights into the roles of glial cells in α-syn-associated neurodegenerative diseases.

The Contributive Role of IGFBP-3 and Mitochondria in Synoviocyte-Induced Osteoarthritis through Hypoxia/Reoxygenation Injury: A Pathogenesis-Focused Literature Review

Osteoarthritis (OA), one of the most common joint disorders, is characterized by chronic progressive cartilage degradation, osteophyte formation, and synovial inflammation. OA lesions are not only located in articular cartilage but also in the entire synovial joint. Nevertheless, most of the early studies done mostly focused on the important role of chondrocyte apoptosis and cartilage degeneration in the pathogenesis and progress of OA. The increased expression of hypoxia-inducible factors (HIF-1α and HIF-2α) is known to be the cellular and biochemical signal that mediates the response of chondrocytes to hypoxia. The role of the synovium in OA pathogenesis had been poorly evaluated. Being sensitive to hypoxia/reoxygeneration (H/R) injury, fibroblast-like synoviocytes (FLS) play an essential role in cartilage degradation during the course of this pathology. Insulin-like growth factor binding protein 3 (IGFBP-3) acts as the main carrier of insulin-like growth factor I (IGF-I) in the circulation and remains the most abundant among the six IGFBPs. Synovial fluids of OA patients have markedly increased levels of IGFBP-3. We aim to discuss the interconnected behavior of IGFBP-3 and synoviocytes during the course of osteoarthritis pathogenesis, especially under the influence of hypoxia-inducible factors. In this review, we present information related to the essential role that is played by IGFBP-3 and mitochondria in synoviocyte-induced osteoarthritis through H/R injury. Little research has been done in this area. However, strong evidences show that the level of IGFBP-3 in synovial fluid significantly increased in OA, inhibiting the binding of IGF-1 to IGFR 1 (IGF receptor-1) and therefore the inhibition of cell proliferation. To the best of our knowledge, this is the first paper providing a comprehensive explanatory contribution of IGFBP-3 and mitochondria in synovial cell-induced osteoarthritis through hypoxia/reoxygenation mechanism.

Potential role of mitochondria in synoviocytes

Synoviocytes are located in the synovium lining layer, which is composed of macrophage-like synoviocytes (MLS) and fibroblast-like synoviocytes (FLS) with different characteristics. Mitochondria, which exist in most cells, are two membrane-covered organelles. In addition to providing the necessary ATP for synoviocytes, mitochondria are involved in the regulation of redox homeostasis and the integration of synoviocytes death signals. In recent years, mitochondrial dysfunction has been found in rheumatoid arthritis (RA) and osteoarthritis (OA). Interestingly, recent studies have started uncovering that mitochondria that were previously reported to play a role in chondrocytes or immune cells, but not known to have pronounced roles in synoviocytes, can actually play crucial roles in the regulation of the pathological properties of the synoviocytes. The purpose of this review is to summarize our current understanding of the key role of mitochondria in synoviocytes, including mitochondrial dysfunction in synoviocytes can induce and aggravate inflammatory responses and changes in mitochondrial structure and function with the involvement of multiple cytokines, signal pathway, and hypoxic state of synovial tissue alter the response of synoviocytes to apoptotic stimulation. Also, mitochondrial abnormalities in synoviocytes promote the synoviocytes invasion and proliferation.

Hypoxia/reoxygenation activates the JNK pathway and accelerates synovial senescence

Hypoxia/reoxygenation (H/R) may play an important role via senescence in the mechanism of osteoarthritis (OA) development. The synovial membrane is highly sensitive to H/R due to its oxygen consumption feature. Excessive mechanical loads and oxidative stress caused by H/R induce a senescence-associated secretory phenotype (SASP), which is related to the development of OA. The aim of the present study was to investigate the differences of SASP manifestation in synovial tissue masses between tissues from healthy controls and patients with OA. The present study used tumor necrosis factor-α (TNF-α) to pre-treat synovial tissue and fibroblast-like synoviocytes (FLS) to observe the effect of inflammatory cytokines on the synovial membrane before H/R. It was determined that H/R increased interleukin (IL)-1β and IL-6 expression levels in TNF-α-induced cell culture supernatants, increased the proportion of SA-β-gal staining, and increased the expression levels of high mobility group box 1, caspase-8, p16, p21, matrix metalloproteinase (MMP)-3 and MMP-13 in the synovium. Furthermore, H/R opened the mitochondrial permeability transition pore, caused the loss of mitochondrial membrane potential (ΔΨm) and increased the release of reactive oxygen species (ROS). Moreover, H/R caused the expansion of the mitochondrial matrix and rupture of the mitochondrial extracorporeal membrane, with a decrease in the number of cristae. In addition, H/R induced activation of the JNK signaling pathway in FLS to induce cell senescence. Thus, the present results indicated that H/R may cause inflammation and escalate synovial inflammation induced by TNF-α, which may lead to the pathogenesis of OA by increasing changes in synovial SASP and activating the JNK signaling pathway. Therefore, further studies expanding on the understanding of the pathogenesis of H/R etiology in OA are required.

Adenosine A2A receptor (A2AR) stimulation enhances mitochondrial metabolism and mitigates reactive oxygen species-mediated mitochondrial injury

In OA chondrocytes, there is diminished mitochondrial production of ATP and diminished extracellular adenosine resulting in diminished adenosine A2A receptor (A2AR) stimulation and altered chondrocyte homeostasis which contributes to the pathogenesis of OA. We tested the hypothesis that A2AR stimulation maintains or enhances mitochondrial function in chondrocytes. The effect of A2AR signaling on mitochondrial health and function was determined in primary murine chondrocytes, a human chondrocytic cell line (T/C-28a2), primary human chondrocytes, and a murine model of OA by transmission electron microscopy analysis, mitochondrial stress testing, confocal live imaging for mitochondrial inner membrane polarity, and immunohistochemistry. In primary murine chondrocytes from A2AR^-/- null mice, which develop spontaneous OA by 16 weeks, there is mitochondrial swelling, dysfunction, and reduced mitochondrial content with increased reactive oxygen species (ROS) burden and diminished mitophagy, as compared to chondrocytes from WT animals. IL-1-stimulated T/C-28a2 cells treated with an A2AR agonist had reduced ROS burden with increased mitochondrial dynamic stability and function, findings which were recapitulated in primary human chondrocytes. In an obesity-induced OA mouse model, there was a marked increase in mitochondrial oxidized material which was markedly improved after intraarticular injections of liposomal A2AR agonist. These results are consistent with the hypothesis that A2AR ligation is mitoprotective in OA.

The evaluation of oxidative stress in osteoarthritis

Osteoarthritis (OA) is a whole joint disease driven by abnormal biomechanics and attendant cell-derived and tissue-derived factors. The disease is multifactorial and polygenic, and its progression is significantly related to oxidative stress and reactive oxygen species (ROS). Augmented ROS generation can cause the damage of structural biomolecules of the joint and, by acting as intracellular signaling component, ROS are associated with various inflammatory responses. By activating several signaling pathways, ROS have a vital importance in the patho-physiology of OA. This review is focused on the mechanism of ROS which regulate intracellular signaling processes, chondrocyte senescence and apoptosis, extracellular matrix synthesis and degradation, along with synovial inflammation and dysfunction of the subcondral bone, targeting the complex oxidative stress signaling pathways.

Association of Polymorphisms in the Promoter Region of NOS2A Gene with Primary Knee Osteoarthritis in the Greek Population

Introduction

A new emerging role of nitric oxide (NO) in the aetiology of osteoarthritis (OA) has been reported. Inducible NO synthase (iNOS), produced by chondrocytes, is the major source of NO in the osteoarthritic cartilage. The aim of this study is to evaluate the potential association between the -1173C/T (rs9282799), -1026 C/A (rs 2779249) and -954G/C (rs1800482) single nucleotide polymorphisms (SNPs) in the promoter of the iNOS gene (NOS2A) and the incidence of knee OA in Greek population.

Methods

Ninety-six patients with primary knee OA were included in the study along with 44 controls. Genotypes were identified using polymerase chain reaction (PCR) and DNA sequencing techniques. Allelic and genotypic frequencies were compared between patients and controls.

Results

None of the -1173C/T, -1026 C/A and -954G/C SNPs were detected in the studied population, either in patients or controls. However, another SNP was identified at the site -1056 at the promoter region, where the initial G allele was substituted by the T allele. Interestingly, the TT genotype was completely absent in controls, but was detected in six patients with a 6.2% observed frequency. The difference between patients and controls was not statistically significant (p-value = 0.18). In male OA patients, the observed frequency of the TT genotype was higher (28.6%) in comparison to the 0% of the male controls (p-value = 0.1). The frequency of the G allele was 0.82 in controls and 0.78 in OA patients (p-value = 0.53).

Conclusions

The present study demonstrates that the 954G/C, -1026C/A, -1056G/T and -1173C/T SNPs of the NOS2A gene are not a risk factor for primary knee OA in Greek population. Moreover, -954G/C, -1026C/A and -1173C/T are rare, if not completely absent, in the Greek population. Additional research is mandatory in order to investigate the association of these SNPs with OA in different ethnic populations.

Mesenchymal stem cell repression of Th17 cells is triggered by mitochondrial transfer

Background

Mesenchymal stem cells (MSCs) are multipotent cells with broad immunosuppressive capacities. Recently, it has been reported that MSCs can transfer mitochondria to various cell types, including fibroblast, cancer, and endothelial cells. It has been suggested that mitochondrial transfer is associated with a physiological response to cues released by damaged cells to restore and regenerate damaged tissue. However, the role of mitochondrial transfer to immune competent cells has been poorly investigated.

Methods and results

Here, we analyzed the capacity of MSCs from the bone marrow (BM) of healthy donors (BM-MSCs) to transfer mitochondria to primary CD4⁺CCR6⁺CD45RO⁺ T helper 17 (Th17) cells by confocal microscopy and fluorescent-activated cell sorting (FACS). We then evaluated the Th17 cell inflammatory phenotype and bioenergetics at 4 h and 24 h of co-culture with BM-MSCs. We found that Th17 cells can take up mitochondria from BM-MSCs already after 4 h of co-culture. Moreover, IL-17 production by Th17 cells co-cultured with BM-MSCs was significantly impaired in a contact-dependent manner. This inhibition was associated with oxygen consumption increase by Th17 cells and interconversion into T regulatory cells. Finally, by co-culturing human synovial MSCs (sMSCs) from patients with rheumatoid arthritis (RA) with Th17 cells, we found that compared with healthy BM-MSCs, mitochondrial transfer to Th17 cells was impaired in RA-sMSCs. Moreover, artificial mitochondrial transfer also significantly reduced IL-17 production by Th17 cells.

Conclusions

The present study brings some insights into a novel mechanism of T cell function regulation through mitochondrial transfer from stromal stem cells. The reduced mitochondrial transfer by RA-sMSCs might contribute to the persistence of chronic inflammation in RA synovitis.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1307-9) contains supplementary material, which is available to authorized users.

Hyaluronic Acid: Molecular Mechanisms and Therapeutic Trajectory

Hyaluronic acid (also known as hyaluronan or hyaluronate) is naturally found in many tissues and fluids, but more abundantly in articular cartilage and synovial fluid (SF). Hyaluronic acid (HA) content varies widely in different joints and species. HA is a non-sulfated, naturally occurring non-protein glycosaminoglycan (GAG), with distinct physico-chemical properties, produced by synoviocytes, fibroblasts, and chondrocytes. HA has an important role in the biomechanics of normal SF, where it is partially responsible for lubrication and viscoelasticity of the SF. The concentration of HA and its molecular weight (MW) decline as osteoarthritis (OA) progresses with aging. For that reason, HA has been used for more than four decades in the treatment of OA in dogs, horses and humans. HA produces anti-arthritic effects via multiple mechanisms involving receptors, enzymes and other metabolic pathways. HA is also used in the treatment of ophthalmic, dermal, burns, wound repair, and other health conditions. The MW of HA appears to play a critical role in the formulation of the products used in the treatment of diseases. This review provides a mechanism-based rationale for the use of HA in some disease conditions with special reference to OA.

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.

HIF-1α:CRAT:miR-144-3p axis dysregulation promotes osteoarthritis chondrocyte apoptosis and VLCFA accumulation

The functional role(s) of peroxisomes in osteoarthritis remains unclear. We demonstrated that peroxisomal dysfunction in osteoarthritis is responsible for very-long-chain fatty acid (VLCFA) accumulation. Through gene-profiling analyses, we identified CRAT as the gene responsible for this event. CRAT expression was suppressed in osteoarthritis chondrocytes, and its knockdown yielded pathological osteoarthritic characteristics, including VLCFA accumulation, apoptosis, autophagic inhibition, and mitochondrial dysfunction. Subsequent miRNA profiling revealed that peroxisomal dysfunction upregulates miR-144-3p, which overlapped with the osteoarthritis pathological characteristics observed upon CRAT knockdown. Moreover, knocking down HIF-1α in normal chondrocytes suppressed CRAT expression while stimulating miR-144-3p. Our data indicate that deregulation of a HIF-1a:CRAT:miR-144-3p axis impairs peroxisomal function during the pathogenesis of osteoarthritis.

The mitochondrial inhibitor oligomycin induces an inflammatory response in the rat knee joint

Background

Recent findings support a connection between mitochondrial dysfunction and activation of inflammatory pathways in articular cells. This study investigates in vivo in an acute model whether intra-articular administration of oligomycin, an inhibitor of mitochondrial function, induces an oxidative and inflammatory response in rat knee joints.

Methods

Oligomycin was injected into the rat left knee joint on days 0, 2, and 5 before joint tissues were obtained on day 6. The right knee joint served as control. Results were evaluated by macroscopy and histopathology and by measuring cellular and mitochondrial reactive oxygen species (ROS), 4-hydroxy-2-nonenal (4-HNE, a marker of lipid peroxidation), nuclear factor erythroid 2-related factor 2 (Nrf2), and CD68 (macrophages) and chemokine levels. The marker of mitochondrial mass COX-IV was also evaluated.

Results

The macroscopic findings showed significantly greater swelling in oligomycin-injected knees than in control knees. Likewise, the histological score of synovial damage was also increased significantly. Immunohistochemical studies showed high expression of IL-8, coinciding with a marked infiltration of polymorphonuclears and CD68+ cells in the synovium. Mitochondrial mass was increased in the synovium of oligomycin-injected joints, as well as cellular and mitochondrial ROS production, and 4-HNE. Relatedly, expression of the oxidative stress-related transcription factor Nrf2 was also increased. As expected, no histological differences were observed in the cartilage; however, cytokine-induced neutrophil chemoattractant-1 mRNA and protein expression were up-regulated in this tissue.

Conclusions

Mitochondrial failure in the joint is able to reproduce the oxidative and inflammatory status observed in arthritic joints.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-017-1621-2) contains supplementary material, which is available to authorized users.

Protective effects of Fructus sophorae extract on collagen-induced arthritis in BALB/c mice

Styphnolobium japonicum (L.) is utilized in Korean medicine for the treatment of various inflammatory diseases. The aim of the present study was to explore the effects of Fructus sophorae extract (FSE) isolated from the dried ripe fruit of S. japonicum (L.) on the development of type II collagen-induced arthritis (CIA) in BALB/c mice. The CIA mice were orally administered FSE or saline daily for 2 weeks. The incidence and severity of disease and the inflammatory response in the serum and the joint tissues were assessed. Macroscopic and histological investigation indicated that FSE protected against CIA development. FSE was associated with a significant reduction in the levels of total immunoglobulin G2a and proinflammatory cytokines and mediators in the serum. In addition, FSE suppressed the gene expression levels of proinflammatory cytokines and mediators, the mediator of osteoclastic bone remodeling, the receptor activator of nuclear factor κ-B ligand and matrix metalloproteinases in the joint tissues. The present results suggest that FSE may protect against inflammation and bone damage, and would be a valuable candidate for further investigation as a novel anti-arthritic agent.

Traditional Chinese Medicine Formula "Xiaofeng granules" suppressed gouty arthritis animal models and inhibited the proteoglycan degradation on chondrocytes induced by monosodium urate

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaofeng Granules (XF) is a kind of granules prepared by the famous traditional Chinese medicine formula for its efficiency in treating gouty diseases.

AIM OF THE STUDY

We investigated the relevance between XF that made from Modified simiaowan (MSW) as the anti-gouty arthritis drugs and protective mechanisms for cartilage matrix in order to provide the evidence for new drug application.

MATERIALS AND METHODS

In the present study, we evaluated the anti-gouty arthritis activity of XF in rats and rabbits models induced by MSU together with chondrocytes focusing on the link to proteoglycan degradation in vitro studies.

RESULTS

The results demonstrated that XF significantly reduced the swelling rate and attenuated the pathological changes in joints. The XF-containing serum were used medicated serum in cellular experiments. The in vitro data were in accordance with the in vivo results, showing that the constituents in XF-containing serum had obvious inhibitory effects on the activation of pro-inflammatory mediators in chondrocytes. Moreover, XF-containing serum substantially inhibited MSU-induced expression of glycosaminoglycans(GAG) and hydroxyproline(Hyp), and up regulated proteoglycan, which might be associated with the regulation of the balance of MMP-3/TIMP-1and ADAMTS-4/TIMP-3 inchondrocytes.

CONCLUSION

In conclusion, XF that made from MSW showed obvious effects on acute gouty arthritis, which also provided an effective protection on cartilage matrix degradation.

Monosodium urate crystals induce oxidative stress in human synoviocytes

Background

Gout is the most common inflammatory arthropathy of metabolic origin and it is characterized by intense inflammation, the underlying mechanisms of which are unknown. The aim of this study was to evaluate the oxidative stress in human fibroblast-like synoviocytes (FLS) exposed to monosodium urate (MSU) crystals, which trigger an inflammatory process.

Methods

Human FLS isolated from synovial tissue explants were stimulated with MSU crystals (75 μg/mL) for 24 h. Cellular viability was evaluated by crystal violet staining, apoptosis was assessed using Annexin V, and the cellular content of reactive oxygen species (ROS) and nitrogen species (RNS) (O₂^-, H₂O₂, NO) was assessed with image-based cytometry and fluorometric methods. In order to determine protein oxidation levels, protein carbonyls were detected through oxyblot analysis, and cell ultrastructural changes were assessed by transmission electron microscopy.

Results

The viability of FLS exposed to MSU crystals decreased by 30 % (P < 0.05), while apoptosis increased by 42 % (P = 0.01). FLS stimulated with MSU crystals exhibited a 2.1-fold increase in H₂O₂ content and a 1.5-fold increase in O₂^- and NO levels. Oxyblots revealed that the spots obtained from FLS protein lysates exposed to MSU crystals exhibited protein carbonyl immunoreactivity, which reflects the presence of oxidatively modified proteins. Concomitantly, MSU crystals triggered the induction of changes in the morphostructure of FLS, such as the thickening and discontinuity of the endoplasmic reticulum, and the formation of vacuoles and misfolded glycoproteins.

Conclusions

Our results prove that MSU crystals induce the release of ROS and RNS in FLS, subsequently oxidizing proteins and altering the cellular oxidative state of the endoplasmic reticulum, which results in FLS apoptosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1012-3) contains supplementary material, which is available to authorized users.

Gla-rich protein is involved in the cross-talk between calcification and inflammation in osteoarthritis

Osteoarthritis (OA) is a whole-joint disease characterized by articular cartilage loss, tissue inflammation, abnormal bone formation and extracellular matrix (ECM) mineralization. Disease-modifying treatments are not yet available and a better understanding of osteoarthritis pathophysiology should lead to the discovery of more effective treatments. Gla-rich protein (GRP) has been proposed to act as a mineralization inhibitor and was recently shown to be associated with OA in vivo. Here, we further investigated the association of GRP with OA mineralization-inflammation processes. Using a synoviocyte and chondrocyte OA cell system, we showed that GRP expression was up-regulated following cell differentiation throughout ECM calcification, and that inflammatory stimulation with IL-1β results in an increased expression of COX2 and MMP13 and up-regulation of GRP. Importantly, while treatment of articular cells with γ-carboxylated GRP inhibited ECM calcification, treatment with either GRP or GRP-coated basic calcium phosphate (BCP) crystals resulted in the down-regulation of inflammatory cytokines and mediators of inflammation, independently of its γ-carboxylation status. Our results strengthen the calcification inhibitory function of GRP and strongly suggest GRP as a novel anti-inflammatory agent, with potential beneficial effects on the main processes responsible for osteoarthritis progression. In conclusion, GRP is a strong candidate target to develop new therapeutic approaches.

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.

Suppressive effect of Sanmiao formula on experimental gouty arthritis by inhibiting cartilage matrix degradation: An in vivo and in vitro study

Sanmiao formula (SM) is a compound prescription, which has been used in traditional Chinese medicine since the Ming Dynasty for gouty and rheumatoid arthritis treatments. However, no evidence has been unfolded to show the relationship between SM and gouty arthritis (GA), particularly inhibiting cartilage matrix degradation. In the present study, we undertook a characterization of anti-GA activity of SM using an in vivo rat model induced by potassium oxonate and cold bath together with in vitro studies with chondrocytes for further molecular characterization. Potassium oxonate and cold bath rats were treated with SM at doses of 7.2g/kg per day for 5days. SM treatments significantly suppressed the swelling rate and the severe pathologic changes in the joints of the animals in gout model. Inflammatory factors count by ELISA analysis, SM exhibited inhibition on IL-1β and TNF-α. Moreover, histological analysis of the joints and SM-serum substantially interfered with the MSU-induced expression of glycosaminoglycans (GAG), up-regulated the content of proteoglycan. Importantly, SM interfered with GA-augmented expression of matrix metalloproteinases (MMPs) -3 and aggrecanases (ADAMTS)-4, which are considered to be key enzymes in cartilage matrix degradation, and simultaneously augmented GA-reduced tissue inhibitors of metalloproteinases (TIMPs) -1 and -3 expression in the joints and chondrocytes. Therefore, SM is looking forward to be a potential novel agent that could prevent cartilage matrix degradation effectively in gouty arthritis, and this provides a new target for development of new medicines.

Molecular basis of oxidative stress in gouty arthropathy

Gout is a disorder of urate metabolism in which persistent high urate levels in the extracellular fluids result in the deposition of monosodium urate (MSU) crystal in joints and periarticular tissues. In recent years, this disease represents an increasingly common health problem, so the pace of investigation in the field has accelerated tremendously. New research advances in the pathogenesis of hyperuricemia and in the understanding of how MSU crystals induce an acute gouty attack have been focused in this review on the processes of inflammation and involvement of the innate immune response; in addition, we discuss new knowledge about the role of the reactive oxygen species in establishing oxidative stress in MSU crystal-induced arthritis.

Acute cell viability and nitric oxide release in lateral menisci following closed-joint knee injury in a lapine model of post-traumatic osteoarthritis

Background

Traumatic impaction is known to cause acute cell death and macroscopic damage to cartilage and menisci in vitro. The purpose of this study was to investigate cell viability and macroscopic damage of the medial and lateral menisci using an in situ model of traumatic loading. Furthermore, the release of nitric oxide from meniscus, synovium, cartilage, and subchondral bone was also documented.

Methods

The left limbs of five rabbits were subjected to tibiofemoral impaction resulting in anterior cruciate ligament (ACL) rupture and meniscal damage. Meniscal tear morphology was assessed immediately after trauma and cell viability of the lateral and medial menisci was assessed 24 hrs post-injury. Nitric oxide (NO) released from joint tissues to the media was assayed at 12 and 24 hrs post injury.

Results

ACL and meniscal tearing resulted from the traumatic closed joint impact. A significant decrease in cell viability was observed in the lateral menisci following traumatic impaction compared to the medial menisci and control limbs. While NO release was greater in the impacted joints, this difference was not statistically significant.

Conclusion

This is the first study to investigate acute meniscal viability following an in situ traumatic loading event that results in rupture of the ACL. The change in cell viability of the lateral menisci may play a role in the advancement of joint degeneration following traumatic knee joint injury.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-297) contains supplementary material, which is available to authorized users.

Nitric oxide compounds have different effects profiles on human articular chondrocyte metabolism

Introduction

The pathogenesis of osteoarthritis (OA) is characterized by the production of high amounts of nitric oxide (NO), as a consequence of up-regulation of chondrocyte-inducible nitric oxide synthase (iNOS) induced by inflammatory cytokines. NO donors represent a powerful tool for studying the role of NO in the cartilage in vitro. There is no consensus about NO effects on articular cartilage in part because the differences between the NO donors available. The aim of this work is to compare the metabolic profile of traditional and new generation NO donors to see which one points out the osteoarthritic process in the best way.

Methods

Human healthy and OA chondrocytes were isolated from patients undergoing joint replacement surgery, and primary cultured. Cells were stimulated with NO donors (NOC-12 or SNP). NO production was evaluated by the Griess method, and apoptosis was quantified by flow cytometry. Mitochondrial function was evaluated by analysing respiratory chain enzyme complexes, citrate synthase (CS) activities by enzymatic assay, mitochondrial membrane potential (Δψm) by JC-1 using flow cytometry, and ATP levels were measured by luminescence assays. Glucose transport was measured as the uptake of 2-deoxy-[³H]glucose (2-[³H]DG). Statistical analysis was performed using the Mann-Whitney U test.

Results

NOC-12 liberates approximately ten times more NO₂^- than SNP, but the level of cell death induced was not as profound as that produced by SNP. Normal articular chondrocytes stimulated with NOC-12 had reduced activity from complexes I, III y IV, and the mitochondrial mass was increased in these cells. Deleterious effects on ΔΨm and ATP levels were more profound with SNP, and this NO donor was able to reduce 2-[³H]DG levels. Both NO donors had opposite effects on lactate release, SNP diminished the levels and NOC-12 lead to lactate accumulation. OA chondrocytes incorporate significantly more 2-[³H]DG than healthy cells.

Conclusions

These findings suggest that the new generation donors, specifically NOC-12, mimic the OA metabolic process much better than SNP. Previous results using SNP have to be considered prudently since most of the effects observed can be induced by the interactions of secondary products of NO.

Noxa in rheumatic diseases: present understanding and future impact

Impaired programmed cell death is an important contributing mechanism in the development of chronic inflammatory and autoimmune diseases. Overexpression of Bcl-2 family proteins in such diseases has led to the concept of targeted suppression of these proteins as a primary therapeutic strategy. However, limited success with this approach has prompted pharmacologists to look at the other side of the coin, with the aim of reactivating jeopardized pro-apoptotic proteins that may neutralize Bcl-2 or other anti-apoptotic molecules. In this effort, BH3-only proteins have gained recent attention as endogenous molecules for the sensitization of resistant cells to undergo apoptosis. Among the BH3-only family, Noxa stands out as exceptional for its specificity to bind Mcl-1 and Bcl-2 and blunt their biological properties. Noxa is now being tested as a promising therapeutic target in cancer biology. Nonetheless, its role and clinical application still lack validation in autoimmune diseases, including rheumatic conditions. This is partly attributed to the significant gap in our understanding of its regulatory role and how either overexpression of Noxa or delivery of BH3 mimetics could be therapeutically exploited. In this review we highlight some recent studies in RA, OA, SLE and SS suggesting that Noxa may be used as a potential therapeutic target to circumvent invasive and tissue destructive processes in these rheumatic diseases.

Mitochondrial respiratory chain dysfunction modulates metalloproteases -1, -3 and -13 in human normal chondrocytes in culture

BACKGROUND

Mitochondrion has an important role in the osteoarthritis (OA) pathology. We have previously demonstrated that the alteration of the mitochondrial respiratory chain (MRC) contributes to the inflammatory response of the chondrocyte. However its implication in the process of cartilage destruction is not well understood yet. In this study we have investigated the relationship between the MRC dysfunction and the regulation of metalloproteases (MMPs) in human normal chondrocytes in culture.

METHODS

Human normal chondrocytes were isolated from human knees obtained form autopsies of donors without previous history of rheumatic disease. Rotenone, 3-Nitropropionic acid (NPA), Antimycin A (AA), Sodium azide and Oligomycin were used to inhibit the activity of the mitochondrial complexes I, II, III, IV and V respectively. The mRNA expression of MMPs -1, -3 and -13 was studied by real time PCR. The intracellular presence of MMP proteins was evaluated by western blot. The liberation of these proteins to the extracellular media was evaluated by ELISA. The presence of proteoglycans in tissue was performed with tolouidin blue and safranin/fast green. Immunohistochemistry was used for evaluating MMPs on tissue.

RESULTS

Firstly, cells were treated with the inhibitors of the MRC for 24 hours and mRNA expression was evaluated. An up regulation of MMP-1 and -3 mRNA levels was observed after the treatment with Oligomycin 5 and 100 μg/ml (inhibitor of the complex V) for 24 hours. MMP-13 mRNA expression was reduced after the incubation with AA 20 and 60 μg/ml (inhibitor of complex III) and Oligomycin. Results were validated at protein level observing an increase in the intracellular levels of MMP-1 and -3 after Oligomycin 25 μg/ml stimulation [(15.20±8.46 and 4.59±1.83 vs. basal=1, respectively (n=4; *P<0.05)]. However, AA and Oligomycin reduced the intracellular levels of the MMP-13 protein (0.70±0.16 and 0.3±0.24, respectively vs. basal=1). In order to know whether the MRC dysfunction had an effect on the liberation of MMPs, their levels were evaluated in the supernatants. After 36 hours of stimulation, values were: MMP-1=18.06±10.35 with Oligomycin 25 μg/ml vs. basal=1, and MMP-3=8.49±4.32 with Oligomycin 5 μg/ml vs. basal=1 (n=5; *P<0.05). MMP-13 levels in the supernatants were reduced after AA 60 μg/ml treatment (0.50±0.13 vs. basal=1) and Oligomycin 25 μg/ml (0.41±0.14 vs. basal=1); (n=5; *P<0.05). The treatment of explants with Oligomycin, showed an increase in the positivity of MMP-1 and -3. Explants stimulated with AA or Oligomycin revealed a decrease in MMP-13 expression. Proteoglycan staining demonstrated a reduction of proteoglycan levels in the tissues treated with Oligomycin.

CONCLUSIONS

These results reveal that MRC dysfunction modulates the MMPs expression in human normal chondrocytes demonstrating its role in the regulation of the cartilage destruction.

Mitochondrial dysfunction and the inflammatory response

Inflammation has been linked to multiple degenerative and acute diseases as well as the aging process. Moreover, mitochondrial alterations play a central role in these processes. Mitochondria have an important role in pro-inflammatory signaling; similarly, pro-inflammatory mediators may also alter mitochondrial function. Both of these processes increase mitochondrial oxidative stress, promoting a vicious inflammatory cycle. Additionally, damage-associated molecular patterns derived from mitochondria could contribute to inflammasome formation and caspase-1 activation, while alterations in mitochondrial autophagy may cause inflammation. Strategies aimed at controlling excessive oxidative stress within mitochondria may represent both preventive and therapeutic interventions in inflammation.

Pycnogenol attenuates the inflammatory and nitrosative stress on joint inflammation induced by urate crystals

Acute gouty arthritis results from monosodium urate (MSU) crystal deposition in joint tissues. Deposited MSU crystals induce an acute inflammatory response which leads to damage of joint tissue. Pycnogenol (PYC), an extract from the bark of Pinus maritime, has documented antiinflammatory and antioxidant properties. The present study aimed to investigate whether PYC had protective effects on MSU-induced inflammatory and nitrosative stress in joint tissues both in vitro and in vivo. MSU crystals upregulated cyclooxygenase 2 (COX-2), interleukin 8 (IL-8) and inducible nitric oxide synthase (iNOS) gene expression in human articular chondrocytes, but only COX-2 and IL-8 in synovial fibroblasts. PYC inhibited the up-regulation of COX-2, and IL-8 in both articular chondrocytes and synovial fibroblasts. PYC attenuated MSU crystal induced iNOS gene expression and NO production in chondrocytes. Activation of NF-κB and SAPK/JNK, ERK1/2 and p38 MAP kinases by MSU crystals in articular chondrocytes and synovial fibroblasts in vitro was attenuated by treatment with PYC. The acute inflammatory cell infiltration and increased expression of COX-2 and iNOS in synovial tissue and articular cartilage following intra-articular injection of MSU crystals in a rat model was inhibited by coadministration of PYC. Collectively, this study demonstrates that PYC may be of value in treatment of MSU crystal-induced arthritis through its anti-inflammatory and anti-nitrosative activities.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Inflammation in osteoarthritis

PURPOSE OF REVIEW

This review focuses on the novel stress-induced and proinflammatory mechanisms underlying the pathogenesis of osteoarthritis, with particular attention to the role of synovitis and the contributions of other joint tissues to cellular events that lead to the onset and progression of the disease and irreversible cartilage damage.

RECENT FINDINGS

Studies during the past 2 years have uncovered novel pathways that, when activated, cause the normally quiescent articular chondrocytes to become activated and undergo a phenotypic shift, leading to the disruption of homeostasis and ultimately to the aberrant expression of proinflammatory and catabolic genes. Studies in animal models and retrieved human tissues indicate that proinflammatory factors may be produced by the chondrocytes themselves or by the synovium and other surrounding tissues, even in the absence of overt inflammation, and that multiple pathways converge on the upregulation of aggrecanases and collagenases, especially MMP-13. Particular attention has been paid to the contribution of synovitis in posttraumatic joint injury, such as meniscal tears, and the protective role of the pericellular matrix in mediating chondrocyte responses through receptors, such as discoidin domain receptor-2 and syndecan-4. New findings about intracellular signals, including the transcription factors NF-κB, C/EBPβ, ETS, Runx2, and hypoxia-inducible factor-2α, and their modulation by inflammatory cytokines, chemokines, adipokines, Toll-like receptor ligands, and receptor for advanced glycation end-products, as well as CpG methylation and microRNAs, are reviewed.

SUMMARY

Further work on mediators and pathways that are common across different models and occur in human osteoarthritis and that impact the osteoarthritis disease process at different stages of initiation and progression will inform us about new directions for targeted therapies.