Inflammation in osteoarthritis: changing views

Genetic causality and site-specific relationship between sarcopenia and osteoarthritis: a bidirectional Mendelian randomization study

Background: Previous studies demonstrated a controversial relationship between sarcopenia (SP) and osteoarthritis (OA) and their genetic causality is unclear. Thus, we conducted a Mendelian randomization (MR) analysis to evaluate the possible causal association between sarcopenia-related traits (appendicular lean mass (ALM), grip strength, usual walking pace) and OA. Method: We used pooled genetic data from the UK Biobank for ALM(n = 450,243), left-hand grip strength (n = 461,026), right-hand grip strength (n = 461,089) and usual walking pace (n = 459,915). Moreover, summary statistics for OA were obtained from the latest study conducted by the Genetics of Osteoarthritis Consortium, including all OA (n = 826,690), hand OA (n = 303,7782), hip OA (n = 353,388) and knee OA (n = 396,054). The primary method for estimating causal effects was the inverse-variance weighted (IVW) method, with the utilizing of false discovery rate adjusted p values (P FDR). Additional MR methods such as MR-Egger regression, MR pleiotropy residual sum and outlier (MR-PRESSO), weighted median were employed as supplementary analyses. Results: We discovered ALM (odds ratio (OR) = 1.103, 95% confidence interval (CI) = 1.052-1.156, P FDR = 2.87E-04), hand grip strength (left, IVW OR = 0.823, 95% CI = 0.712 to 0.952, P FDR = 0.020; right, OR = 0.826, 95% CI = 0.718 to 0.950, P FDR = 0.020), and usual walking pace (OR = 0.339, 95% CI = 0.204 to 0.564, P FDR = 2.38E-04) were causally associated with OA risk. In the reverse MR analysis, we identified a causal effect of OA on ALM (β = -0.258, 95% CI = -0.369 to 0.146, P FDR = 0.6.07E-06), grip strength (left, β = -0.064, 95% CI = -0.104 to 0.024, P FDR = 0.002; right, β = -0.055, 95% CI = -0.095 to 0.014, P FDR = 0.008), and usual walking pace (β = -0.104, 95% CI = -0.147 to 0.061, P FDR = 1.61E-05). Conclusion: This present study suggests an obvious causality of SP on OA, with condition exhibiting site-specific effects, while evidence was also provided for the causal effect of OA on SP.

A Translational Model for Repeated Episodes of Joint Inflammation: Welfare, Clinical and Synovial Fluid Biomarker Assessment

This study investigates repeated low-dose lipopolysaccharide (LPS) injections in equine joints as a model for recurrent joint inflammation and its impact on animal welfare. Joint inflammation was induced in eight horses by injecting 0.25 ng of LPS three times at two-week intervals. Welfare scores and clinical parameters were recorded at baseline and over 168 h post-injection. Serial synoviocentesis was performed for the analysis of a panel of synovial fluid biomarkers of inflammation and cartilage turnover. Clinical parameters and a final synoviocentesis were also performed eight weeks after the last sampling point to assess the recovery of normal joint homeostasis. Statistical methods were used to compare the magnitude of response to each of the 3 LPS inductions and to compare the baseline and final measurements. Each LPS injection produced consistent clinical and biomarker responses, with minimal changes in welfare scores. General matrix metalloproteinase (MMP) activity and joint circumference showed greater response to the second LPS induction, but response to the third was comparable to the first. Gylcosaminoglycans (GAG) levels showed a significantly decreased response with each induction, while collagen-cleavage neoepitope of type II collagen (C2C) and carboxypropetide of type II collagen epitope (CPII) showed quicker responses to the second and third inductions. All parameters were comparable to baseline values at the final timepoint. In conclusion, a consistent, reliable intra-articular inflammatory response can be achieved with repeated injections of 0.25 ng LPS, with minimal impact on animal welfare, suggesting potential as a refined translational model of recurrent joint inflammation.

Sarcopenia and Sarcopenic Obesity and Osteoarthritis: A Discussion among Muscles, Fat, Bones, and Aging

Aging is a physical procedure for people and nature. Our aging world is expanding because of the life span extension. Aging has a crucial relationship with our body composition (muscles, bones, and adipose tissue), which is characterized by an increase in fat mass and a gradual decrease in muscle mass and strength and bone density. These alterations affect physical performance and impact quality of life enhancing the risk for non-communicable diseases, immobilization, and disability. As far we know, osteoarthritis of lower limbs, sarcopenic obesity, and muscle mass and/or strength loss are treated separately. However, bones, muscles, adipose tissue, and aging appear to have an interconnection through a dialogue as they talk to each other. Health disorders are coming into the surface when this relationship is disrupted. The aim of our study is to search deeper into this interconnection, so that when adipose tissue increases, we have to take a look into the condition of muscle mass, bone, and connective tissue and vice versa, through the assessment of physical performance. Consequently, the triad muscle-bone-adipose tissue disorders by aging should be treated as a single entity.

A short review on key role of plants and their extracts in boosting up immune response to combat COVID-19

In the wake of the recent global pandemic of COVID-19, there has been an increasing concern among the general public to improve their immune system. The causative agent of COVID-19 is SARS CoV-2, similar to its relative viruses SARS Cov-1 and MERS. Up till now, no vaccine has been developed against this disease and the only way one can stay safe is via prevention and developing one's immune system. Plants have been used since ancient times in herbal medicines and many chemicals and extracts in them are found to boost the immune system. Therefore, a consciously maintained diet consisting of plant-based immunity boosters is the need of the hour. Plants are known to provide many chemicals, natural therapeutics and vitamins which naturally enhance our immune system. Recently, vaccination research is also being carried out in transgenic plants. In this review, we have focused on highlighting some of the main players within the Kingdom Plantae which, when taken up in regular diet, can significantly boost our immune system capacity and thus provide the best possible measure to combat this pandemic.

A Roadmap of In Vitro Models in Osteoarthritis: A Focus on Their Biological Relevance in Regenerative Medicine

Osteoarthritis (OA) is a multifaceted musculoskeletal disorder, with a high prevalence worldwide. Articular cartilage and synovial membrane are among the main biological targets in the OA microenvironment. Gaining more knowledge on the accuracy of preclinical in vitro OA models could open innovative avenues in regenerative medicine to bridge major gaps, especially in translation from animals to humans. Our methodological approach entailed searches on Scopus, the Web of Science Core Collection, and EMBASE databases to select the most relevant preclinical in vitro models for studying OA. Predicting the biological response of regenerative strategies requires developing relevant preclinical models able to mimic the OA milieu influencing tissue responses and organ complexity. In this light, standard 2D culture models lack critical properties beyond cell biology, while animal models suffer from several limitations due to species differences. In the literature, most of the in vitro models only recapitulate a tissue compartment, by providing fragmented results. Biotechnological advances may enable scientists to generate new in vitro models that combine easy manipulation and organ complexity. Here, we review the state-of-the-art of preclinical in vitro models in OA and outline how the different preclinical systems (inflammatory/biomechanical/microfluidic models) may be valid tools in regenerative medicine, describing their pros and cons. We then discuss the prospects of specific and combinatorial models to predict biological responses following regenerative approaches focusing on mesenchymal stromal cells (MSCs)-based therapies to reduce animal testing.

Discovery of bone morphogenetic protein 7-derived peptide sequences that attenuate the human osteoarthritic chondrocyte phenotype

Treatment of osteoarthritis (OA) is mainly symptomatic by alleviating pain to postpone total joint replacement. Bone morphogenetic protein 7 (BMP7) is a candidate morphogen for experimental OA treatment that favorably alters the chondrocyte and cartilage phenotype. Intra-articular delivery and sustained release of a recombinant growth factor for treating OA are challenging, whereas the use of peptide technology potentially circumvents many of these challenges. In this study, we screened a high-resolution BMP7 peptide library and discovered several overlapping peptide sequences from two regions in BMP7 with nanomolar bioactivity that attenuated the pathological OA chondrocyte phenotype. A single exposure of OA chondrocytes to peptides p[63-82] and p[113-132] ameliorated the OA chondrocyte phenotype for up to 8 days, and peptides were bioactive on chondrocytes in OA synovial fluid. Peptides p[63-82] and p[113-132] required NKX3-2 for their bioactivity on chondrocytes and provoke changes in SMAD signaling activity. The bioactivity of p[63-82] depended on specific evolutionary conserved sequence elements common to BMP family members. Intra-articular injection of a rat medial meniscal tear (MMT) model with peptide p[63-82] attenuated cartilage degeneration. Together, this study identified two regions in BMP7 from which bioactive peptides are able to attenuate the OA chondrocyte phenotype. These BMP7-derived peptides provide potential novel disease-modifying treatment options for OA.

Multi-tissue epigenetic analysis of the osteoarthritis susceptibility locus mapping to the plectin gene PLEC

OBJECTIVE

In cartilage, the osteoarthritis (OA) associated single nucleotide polymorphism (SNP) rs11780978 correlates with differential expression of PLEC, and with differential methylation of PLEC CpG dinucleotides, forming eQTLs and mQTLs respectively. This implies that methylation links chondrocyte genotype and phenotype, thus driving the functional effect of this genetic risk signal. PLEC encodes plectin, a cytoskeletal protein that enables tissues to respond to mechanical forces. We sought to assess whether these PLEC functional effects were cartilage specific.

METHOD

Cartilage, fat pad, synovium and peripheral blood were collected from patients undergoing arthroplasty. PLEC CpGs were analysed for mQTLs and allelic expression imbalance (AEI) was performed to test for eQTLs. Plectin was knocked down in a mesenchymal stem cell (MSC) line using CRISPR/Cas9 and cells phenotyped by RNA-sequencing.

RESULTS

mQTLs were discovered in fat pad, synovium and blood. Their effects were however stronger in the joint tissues and of comparable effect between these tissues. We observed AEI in synovium in the same direction as for cartilage and correlations between methylation and PLEC expression. Knocking-down plectin impacted on pathways reported to have a role in OA, including Wnt signalling, glycosaminoglycan biosynthesis and immune regulation.

CONCLUSIONS

Synovium is also a target of the rs11780978 OA association functionally operating on PLEC. In fat pad, mQTLs were identified but these did not correlate with PLEC expression, suggesting the functional effect is not joint-wide. Our study highlights interplay between genetic risk, DNA methylation and gene expression in OA, and reveals clear differences between tissues from the same diseased joint.

Generating evidence and understanding the treatment of osteoarthritis in Brazil: a study through Delphi methodology

OBJECTIVES

This study aimed to provide evidence for understanding how to treat osteoarthritis (OA) in our country. Therefore, it was necessary to match information and investigations related to the treatment of the disease from the three main types of specialists involved: physiatrists, orthopedists and rheumatologists.

METHODS

The authors acted as a scientific advisory committee. From the initial discussions, a structured questionnaire was developed for use with a group of specialists on OA using the Delphi technique. The questionnaire was sent to 21 experts appointed by the authors, and the results obtained were critically analyzed and validated.

RESULTS

The prevalence of OA was 33% in Brazil, corresponding to one-third of the individuals in the reference population, which included individuals over 25 years of age. Another significant finding was that most patients did not receive any form of treatment in the early stages of OA.

CONCLUSION

The committee pointed to the need for early intervention and that the available medicinal resources can fulfil this important role, as is the case with SYSADOA treatments. Glucosamine-based medicinal products with or without chondroitin could also fulfill this need for early treatment. The other generated evidence and included investigations were then grouped together and are the subject of this publication.

Plant-Based Diets for Cardiovascular Safety and Performance in Endurance Sports

Studies suggest that endurance athletes are at higher-than-average risk for atherosclerosis and myocardial damage. The ability of plant-based regimens to reduce risk and affect performance was reviewed. The effect of plant-based diets on cardiovascular risk factors, particularly plasma lipid concentrations, body weight, and blood pressure, and, as part of a healthful lifestyle, reversing existing atherosclerotic lesions, may provide a substantial measure of cardiovascular protection. In addition, plant-based diets may offer performance advantages. They have consistently been shown to reduce body fat, leading to a leaner body composition. Because plants are typically high in carbohydrate, they foster effective glycogen storage. By reducing blood viscosity and improving arterial flexibility and endothelial function, they may be expected to improve vascular flow and tissue oxygenation. Because many vegetables, fruits, and other plant-based foods are rich in antioxidants, they help reduce oxidative stress. Diets emphasizing plant foods have also been shown to reduce indicators of inflammation. These features of plant-based diets may present safety and performance advantages for endurance athletes. The purpose of this review was to explore the role of nutrition in providing cardioprotection, with a focus on plant-based diets previously shown to provide cardiac benefits.

Alterations of autophagy in knee cartilage by treatment with treadmill exercise in a rat osteoarthritis model

The aim of the present study was to investigate potential alterations in the articular cartilage in a rat model of monosodium iodoacetate (MIA)-induced osteoarthritis (OA) with or without treatment with moderate treadmill exercise. A total of 30 male Sprague-Dawley rats were randomly divided into three groups (n=10), including the control, OA and OA with treadmill exercise (OAE) groups. Rats were evaluated upon completing the treadmill exercise program (speed, 18 m/min; 30 min/day; 5 days/week for 4 weeks). Interleukin (IL)-1β and IL-4 levels in the serum and intra-articular lavage fluid (IALF) were measured by ELISA. Alterations in articular cartilage and synovium were also evaluated by histology, immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction. The results revealed that IL-1β in the serum and IALF decreased in the OAE group, whereas IL-4 increased, and histological evaluation indicated that the OAE group had a clear treatment response. However, the expression of type II collagen in the articular cartilage increased in the OAE group as compared with the OA group, whereas ADAMTS5 expression decreased. In contrast to light chain 3B (LC3B), the protein expression levels of BECLIN1 and sequestosome 1 (SQSTM1) were increased in the OA group. In addition, a significant increase was observed between OA and OAE groups in LC3B and SQSTM1 protein levels, whereas no change was observed in BECLIN1 levels between the OA and OAE groups in the superficial and deep zones. The results of western blotting demonstrated that LC3II was notably decreased in the OA group and partially increased in the OAE group. The mRNA expression levels of LC3B and SQSTM1 increased in the OA and OAE groups, with a significant difference observed between the two groups, while a concomitant decrease was detected in BECLIN1 levels. In conclusion, 30 min of treadmill exercise had an evident protective effect in the articular cartilage of rats with MIA-induced OA and may promote autophagy in the articular cartilage.

α-Lipoic Acid Potentiates the Anti-Inflammatory Activity of Avocado/Soybean Unsaponifiables in Chondrocyte Cultures

Objective Pro-inflammatory mediators such as prostaglandin E-2 (PGE₂) play major roles in the pathogenesis of osteoarthritis (OA). Although current pharmacologic treatments reduce inflammation, their prolonged use is associated with deleterious side effects prompting the search for safer and effective alternative strategies. The present study evaluated whether chondrocyte production of PGE₂ can be suppressed by the combination of avocado/soybean unsaponifiables (ASU) and α-lipoic acid (LA). Design Chondrocytes from articular cartilage of equine joints were incubated for 24 hours with: (1) control media, (2) ASU, (3) LA, or (4) ASU + LA combination. Cells were activated with lipopolysaccharide (LPS), interleukin 1β (IL-1β) or hydrogen peroxide (H₂O₂) for 24 hours and supernatants were immunoassayed for PGE₂. Nuclear factor-kappa B (NF-κB) analyses were performed by immunocytochemistry and Western blot following 1 hour of activation with IL-1β. Results LPS, IL-1β, or H₂O₂ significantly increased PGE₂ production. ASU or LA alone suppressed PGE₂ production in LPS and IL-1β activated cells. Only LA alone at 2.5 µg/mL was inhibitory in H₂O₂-activated chondrocytes. ASU + LA inhibited more than either agent alone in all activated cells. ASU + LA also inhibited the IL-1β induced nuclear translocation of NF-κB. Conclusions The present study provides evidence that chondrocyte PGE₂ production can be inhibited by the combination of ASU + LA more effectively than either ASU or LA alone. Inhibition of PGE₂ production is associated with the suppression of NF-κB translocation. The potent inhibitory effect of ASU + LA on PGE₂ production could offer a potential advantage for a combination anti-inflammatory/antioxidant approach in the management of OA.

Downregulation of aquaporin 9 decreases catabolic factor expression through nuclear factor‑κB signaling in chondrocytes

Aquaporins (AQPs) are small integral membrane proteins that are essential for water transport across membranes. AQP9, one of the 13 mammalian AQPs (including AQP0 to 12), has been reported to be highly expressed in hydrarthrosis and synovitis patients. Given that several studies have identified signal transduction as an additional function of AQPs, it is hypothesized that AQP9 may modulate inflammatory signal transduction in chondrocytes. Therefore, the present study used a model of interleukin (IL)‑1β‑induced inflammation to determine the mechanisms associated with AQP9 functions in chondrocytes. Osteoarthritis (OA) and normal cartilage samples were subjected to immunohistological analysis. In addition, matrix metalloproteinase (MMP)3, MMP13 and a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS‑5) mRNA and protein analysis was conducted in normal human articular chondrocytes from the knee (NHAC‑Kn) stimulated with IL‑1β by reverse transcription‑polymerase chain reaction (RT‑qPCR) and western blotting, respectively. AQP9 knockdown was also performed by transfection of AQP9‑specific small interfering RNA using Lipofectamine. AQP1, 3, 7, 9 and 11 mRNA expression levels were detected in OA human chondrocytes and in IL‑1β‑treated normal human chondrocytes. The levels of AQP9, MMP‑3, MMP‑13 and ADAMTS‑5 mRNA were increased by treatment with 10 ng/ml IL‑1β in a time‑dependent manner, while knockdown of AQP9 expression significantly decreased the mRNA levels of the MMP3, MMP13 and ADAMTS‑5 genes, as well as the phosphorylation of IκB kinase (IKK). Treatment with a specific IKK inhibitor also significantly decreased the expression levels of MMP‑3, MMP‑13 and ADAMTS‑5 in response to IL‑1β stimulation. Furthermore, immunohistochemical analysis demonstrated that AQP9 and inflammatory markers were highly expressed in OA cartilage. In addition, the downregulation of AQP9 in cultured chondrocytes decreased the catabolic gene expression in response to IL‑1β stimulation through nuclear factor‑κB signaling. Therefore, AQP9 may be a promising target for the treatment of OA.

Initial In Vitro Development of a Potassium-Based Intra-Articular Injection for Osteoarthritis

The long-term goal of this work is to develop a potassium (K⁺)-based intra-articular (IA) injection for osteoarthritis treatment. Within this context, the objectives of this study were to (1) demonstrate that hyperosmolar K⁺ solutions can suppress proinflammatory macrophage activation and (2) evaluate the therapeutic potential of a hyperosmolar K⁺ solution relative to a clinically utilized drug-based (methylprednisolone acetate [MPA]-a corticosteroid) or cell-based (human mesenchymal stem cell [hMSC]) IA injectable. A 3D in vitro model with poly(ethylene glycol) diacrylate hydrogels encapsulated with proinflammatory interferon-gamma (IFN)-stimulated macrophages (M(IFN)s) was utilized. Long-term changes in cell phenotype in response to short-term stimulation (i.e., mimicking an IA injection) were assessed following treatment with 80 mM K⁺ gluconate, hMSCs, or MPA. Addition of 80 mM K⁺ gluconate to culture media significantly reduced iNOS and TNF protein levels in M(IFN)s. Furthermore, short-term stimulation with K⁺ gluconate elicited a significant increase in the anti/proinflammatory cytokine profile in M(IFN)s, a response that is not noticed with either clinically utilized MPA or an hMSC injectable. Hyperosmolar K⁺ solutions are capable of attenuating proinflammatory macrophage activation. Moreover, when evaluated in an in vitro setting mimicking an IA injection, K⁺ performed significantly better than hMSCs or the corticosteroid MPA. Cumulatively, these results support further development and application of a K⁺-based IA injection toward osteoarthritis research.

Varus knee osteoarthritis: Elevated synovial CD15 counts correlate with inferior biomechanical properties of lateral-compartment cartilage

The study analyzed the influence of synovitis on the histological and biomechanical properties of lateral-compartment cartilage. In a prospective cohort study, 84 patients (100 knees) with varus deformity of the knee were included. Osteochondral samples from the distal lateral femur underwent biomechanical and histologic analysis. Synovial tissue was sampled for histological (chronic synovitis score) and immunohistochemical evaluation of the degree of synovitis. CD15 (neutrophils), Ki-67 (dividing cells), and CD68 (macrophages) were tested in all synovial samples. While the histological synovitis score did not correlate with the degree of cartilage degeneration (histological OARSI grades), both CD15 (r_s  = 0.297, p = 0.006) and Ki-67 (r_s  = 0.249, p = 0.023) correlated with histological OARSI grades. There was a weak negative correlation of CD15 with biomechanical properties of cartilage of the distal lateral femur (aggregate modulus (Ha): r_s  = -0.125; p = 0.257; dynamic modulus (DM): r_s  = -0.216; p = 0.048). No correlations were observed for Ki-67 and CD68. In addition, biomechanical properties were inferior in knees with a CD15 of >8/high power field compared to knees with a CD15 of ≤8/high power field (Ha: p = 0.031, d = 0.46; DM: p = 0.005, d = 0.68). The study demonstrates an association of increased inflammatory activity with advanced cartilage degeneration. Lateral-compartment cartilage in knees with elevated synovial CD15 counts has a reduced ability to withstand compressive loads. CD15 might serve as an indicator for inferior biomechanical cartilage properties. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:841-846, 2018.

Depletion of aquaporin 1 decreased ADAMTS‑4 expression in human chondrocytes

Inflammation serves an important role in the progression of osteoarthritis (OA), and IL-1β may act as a catabolic factor on cartilage, reducing the synthesis of primary cartilage components type II collagen and aggrecan. Aquaporin 1 (AQP1) is a 28-kDa water channel formed of six transmembrane domains on the cell membrane. AQP1 is highly expressed in the anus, gallbladder and liver, and is moderately expressed in the hippocampus, ependymal cells of the central nervous system and articular cartilage. It was hypothesized that AQP1 may be highly expressed in OA cartilage and that it may increase the expression of catabolic factors during inflammatory OA progression. Therefore, the present study evaluated AQP1 functions in human OA articular chondrocytes. Primary chondrocytes were isolated from human hip and knee cartilage tissues, cultured and transfected with AQP1-specific small interfering RNA with or without subsequent IL-1β treatment. In vitro explant culture from hip cartilages were also prepared. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to assess the expression of AQP genes in human articular cartilage, AQP1 immunohistochemistry of the cartilages and explant culture, as well as RT-quantitative PCR, western blotting and immunocytochemistry/immunofluorescence of OA chondrocytes to evaluate the expression of AQP1, and catabolic and anabolic factors. RT-PCR results demonstrated that AQP0, 1, 3, 7, 9, and 11 were expressed in OA chondrocytes. Immunohistochemistry revealed that AQP1 was highly expressed in the superficial to middle zones of OA articular cartilages. Additionally, AQP1 mRNA was significantly higher in OA cartilage and IL-1β treatment significantly increased AQP1 expression in hip explant cartilage. Furthermore, AQP1 downregulation decreased a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS)-4 expression in OA chondrocytes, though it did not affect other associated genes. Immunofluorescence showed that AQP1 and ADAMTS-4 were co-localized. These findings indicated that AQP1 depletion may decrease ADAMTS-4 expression in human OA chondrocytes. Therefore, regulating AQP1 expression may be a strategy to suppress catabolic factors during OA progression.

Mechanisms of Osteoarthritic Pain. Studies in Humans and Experimental Models

Pain due to osteoarthritis (OA) is one of the most frequent causes of chronic pain. However, the mechanisms of OA pain are poorly understood. This review addresses the mechanisms which are thought to be involved in OA pain, derived from studies on pain mechanisms in humans and in experimental models of OA. Three areas will be considered, namely local processes in the joint associated with OA pain, neuronal mechanisms involved in OA pain, and general factors which influence OA pain. Except the cartilage all structures of the joints are innervated by nociceptors. Although the hallmark of OA is the degradation of the cartilage, OA joints show multiple structural alterations of cartilage, bone and synovial tissue. In particular synovitis and bone marrow lesions have been proposed to determine OA pain whereas the contribution of the other pathologies to pain generation has been studied less. Concerning the peripheral neuronal mechanisms of OA pain, peripheral nociceptive sensitization was shown, and neuropathic mechanisms may be involved at some stages. Structural changes of joint innervation such as local loss and/or sprouting of nerve fibers were shown. In addition, central sensitization, reduction of descending inhibition, descending excitation and cortical atrophies were observed in OA. The combination of different neuronal mechanisms may define the particular pain phenotype in an OA patient. Among mediators involved in OA pain, nerve growth factor (NGF) is in the focus because antibodies against NGF significantly reduce OA pain. Several studies show that neutralization of interleukin-1β and TNF may reduce OA pain. Many patients with OA exhibit comorbidities such as obesity, low grade systemic inflammation and diabetes mellitus. These comorbidities can significantly influence the course of OA, and pain research just began to study the significance of such factors in pain generation. In addition, psychologic and socioeconomic factors may aggravate OA pain, and in some cases genetic factors influencing OA pain were found. Considering the local factors in the joint, the neuronal processes and the comorbidities, a better definition of OA pain phenotypes may become possible. Studies are under way in order to improve OA and OA pain monitoring.

The effects of different frequency treadmill exercise on lipoxin A4 and articular cartilage degeneration in an experimental model of monosodium iodoacetate-induced osteoarthritis in rats

The aim was to investigate the effects of different frequencies treadmill exercise with total exercise time being constancy on articular cartilage, lipoxin A₄ (LXA₄) and the NF-κB pathway in rat model of monosodium iodoacetate-induced osteoarthritis (OA). Fifty male Sprague-Dawley rats were randomly divided into five groups (n = 10): controls (CG), knee OA model (OAG), OA + treadmill exercise once daily (OAE1), OA + treadmill exercise twice daily, rest interval between exercise>4h (OAE2) and OA + treadmill exercise three times daily, rest interval between exercise>4h (OAE3). Rats were evaluated after completing the treadmill exercise program (speed, 18 m/min; total exercise time 60 min/day; 5 days/week for 8 weeks). Interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and LXA₄ in serum and intra-articular lavage fluid were measured by ELISA. Changes in articular cartilage were evaluated by histology, immunohistochemistry, western blotting and quantitative real-time-PCR. LXA₄ in the serum and intra-articular lavage fluid increased in all OAE groups, and histological evaluation indicated that the OAE3 group had the best treatment response. The expression of COL2A1 and IκB-β in articular cartilage increased in all OAE groups vs the OAG group, whereas expression of IL-1β, TNF-α, matrix metalloproteinase (MMP)-13, and NF-κB p65 was reduced in all OAE groups compared with the OAG. Under the condition of 60 min treadmill exercise with moderate-intensity, to fulfill in three times would have better chondroprotective effects than to fulfill in two or one time on monosodium iodoacetate-induced OA in rats. And it may be worked through the anti-inflammatory activity of LXA₄ and the NF-κB pathway.

Cyclin-Dependent Kinase Inhibitor-1-Deficient Mice are Susceptible to Osteoarthritis Associated with Enhanced Inflammation

Osteoarthritis (OA) is a multifactorial disease, and recent data suggested that cell cycle-related proteins play a role in OA pathology. Cyclin-dependent kinase (CDK) inhibitor 1 (p21) regulates activation of other CDKs, and recently, we reported that p21 deficiency induced susceptibility to OA induced by destabilization of the medial meniscus (DMM) surgery through STAT3-signaling activation. However, the mechanisms associated with why p21 deficiency led to susceptibility to OA by the STAT3 pathway remain unknown. Therefore, we focused on joint inflammation to determine the mechanisms associated with p21 function during in vitro and in vivo OA progression. p21-knockout (p21^-/- ) mice were used to develop an in vivo OA model, and C57BL/6 (p21^+/+ ) mice with the same background as the p21^-/- mice were used as controls. Morphogenic changes were measured using micro-CT, IL-1β serum levels were detected by ELISA, and histological or immunohistological analyses were performed. Our results indicated that p21-deficient DMM-model mice exhibited significant subchondral bone destruction and cartilage degradation compared with wild-type mice. Immunohistochemistry results revealed p21^-/- mice susceptibility to OA changes accompanied by macrophage infiltration and enhanced MMP-3 and MMP-13 expression through IL-1β-induced NF-κB signaling. p21^-/- mice also showed subchondral bone destruction according to micro-CT analysis, and cathepsin K staining revealed increased numbers of osteoclasts. Furthermore, p21^-/- mice displayed increased serum IL-1β levels, and isolated chondrocytes from p21^-/- mice indicated elevated MMP-3 and MMP-13 expression with phosphorylation of IκB kinase complex in response to IL-1β stimulation, whereas treatment with a specific p-IκB kinase inhibitor attenuated MMP-3 and MMP-13 expression. Our results indicated that p21-deficient DMM mice were susceptible to alterations in OA phenotype, including enhanced osteoclast expression, macrophage infiltration, and MMP expression through IL-1β-induced NF-κB signaling, suggesting that p21 regulation may constitute a possible therapeutic strategy for OA treatment. © 2017 American Society for Bone and Mineral Research.