Cellular events leading to chondrocyte death after cartilage impact injury

Targeting regulated chondrocyte death in osteoarthritis therapy

In vivo articular cartilage degeneration is an essential hallmark of osteoarthritis (OA), involving chondrocyte senescence, extracellular matrix degradation, chondrocyte death, cartilage loss, and bone erosion. Among them, chondrocyte death is one of the major factors leading to cartilage degeneration. Many studies have reported that various cell death modes, including apoptosis, ferroptosis, and autophagy, play a key role in OA chondrocyte death. Currently, there is insufficient understanding of OA pathogenesis, and there remains a lack of treatment methods to prevent OA and inhibit its progression. Studies suggest that OA prevention and treatment are mainly directed to arrest premature or excessive chondrocyte death. In this review, we a) discuss the forms of death of chondrocytes and the associations between them, b) summarize the critical factors in chondrocyte death, c) discuss the vital role of chondrocyte death in OA, d) and, explore new approaches for targeting the regulation of chondrocyte death in OA treatment.

Verbenalin attenuates hepatic damage and mitochondrial dysfunction in alcohol-associated steatohepatitis by regulating MDMX/PPARα-mediated ferroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Verbenalin is a major compound in Verbena officinalis L. Verbena officinalis L was first recorded in the 'Supplementary Records of Famous Physicians.' Verbenalin (VE) is its active constituent and has been found to have many biological effects, including anti-obesity, anti-inflammatory, and antioxidant activities, removing jaundice, and treating malaria. It could treat lump accumulation, dysmenorrhea, throat obstruction, edema, jaundice, and malaria. Palmitic acid (PA), oleic acid (OA), ethanol, and acetaminophen liver injuries have been proven to benefit from verbenalin.

AIM OF THE STUDY

To study the effects of verbenalin on the prevention of alcoholic steatohepatitis (ASH) through the regulation of oxidative stress and mitochondrial dysfunction by regulating MDMX (Murine double minute X)/PPARα (Peroxisome proliferator-activated receptor alpha)-mediated ferroptosis.

MATERIAL AND METHODS

C57BL/6 mice treated with alcohol followed by the Gao-Binge protocol were administered verbenalin by gavage simultaneously. The mitochondrial mass and morphology were visualized using TEM. AML-12 cells were stimulated with ethanol to mimic ASH in vitro. Western blotting, co-immunoprecipitation, and kit determination were simultaneously performed. The target protein of verbenalin was identified by molecular docking, and cellular thermal shift assay (CETSA) further confirmed its interactions.

RESULTS

Verbenalin alleviates oxidative stress and ferroptosis in alcohol-associated steatohepatitis. To elucidate the molecular mechanism by which verbenalin inhibits abnormal mitochondrial dysfunction, molecular docking was performed, and MDMX was identified as the target protein of verbenalin. CETSA assays revealed a specific interaction between MDMX and verbenalin. Co-immunoprecipitation demonstrated that PPARα played a critical role in promoting the ability of MDMX to affect ferroptosis. Verbenalin regulates MDMX/PPARα-mediated ferroptosis in AML-12 cells.

CONCLUSION

Verbenalin regulates ferroptosis and highlights the therapeutic potential of verbenalin and ferroptosis inhibition in reducing alcoholic steatohepatitis.

A prospective randomized double-blind clinical trial to assess the effects of leukocyte-reduced platelet-rich plasma on pro-inflammatory, degradative, and anabolic biomarkers after closed pilon fractures

Posttraumatic osteoarthritis (PTOA) significantly affects patients with pilon fractures even after adequate anatomical reduction, and treatment strategies targeting the biologic mediators of PTOA are needed. This study was designed to determine the effects of intra-articular injection of platelet-rich plasma (PRP) on synovial fluid (SF) biomarkers for patients undergoing open reduction and internal fixation (ORIF) of pilon fractures. Patients undergoing staged management of pilon fractures were enrolled in a prospective, double-blinded, randomized, and placebo-controlled clinical trial to determine the effects of a single intra-articular injection of leukocyte-reduced PRP on SF biomarkers. Arthrocentesis of the injured and uninjured ankles was performed at the time of external skeletal fixation (ESF) and ORIF. Patients were randomized to receive either autogenous leukocyte-reduced PRP or saline (control) via intra-articular injection into the injured ankle at the time of ESF. SF biomarker concentrations were compared-uninjured, injured pretreatment, and saline-injected or PRP-injected. Eleven patients (PRP, n = 5; saline, n = 6) completed the study. Twenty-one uninjured, and 11 injured pretreatment, five PRP-treated, and six saline-treated SF samples were analyzed. PRP-treated SF contained significantly higher levels of PDGF-AA (p = 0.046) and significantly lower levels of MMP-3 (p = 0.042), MMP-9 (p = 0.009), IL-1β (p = 0.049), IL-6 (p < 0.01), IL-8 (p = 0.048), and PGE2 (p < 0.04). This study provided mechanistic data to suggest that a single intraarticular injection of leukocyte-reduced PRP is associated with anti-inflammatory, anti-degradative, and anabolic responses compared with saline control. These findings provide the impetus for investigating long-term clinical outcomes after PRP injection as an orthobiologic adjunct to ORIF for mitigating the incidence and severity of PTOA after pilon fractures.

Selenophosphate synthetase 1 deficiency exacerbates osteoarthritis by dysregulating redox homeostasis

Aging and mechanical overload are prominent risk factors for osteoarthritis (OA), which lead to an imbalance in redox homeostasis. The resulting state of oxidative stress drives the pathological transition of chondrocytes during OA development. However, the specific molecular pathways involved in disrupting chondrocyte redox homeostasis remain unclear. Here, we show that selenophosphate synthetase 1 (SEPHS1) expression is downregulated in human and mouse OA cartilage. SEPHS1 downregulation impairs the cellular capacity to synthesize a class of selenoproteins with oxidoreductase functions in chondrocytes, thereby elevating the level of reactive oxygen species (ROS) and facilitating chondrocyte senescence. Cartilage-specific Sephs1 knockout in adult mice causes aging-associated OA, and augments post-traumatic OA, which is rescued by supplementation of N-acetylcysteine (NAC). Selenium-deficient feeding and Sephs1 knockout have synergistic effects in exacerbating OA pathogenesis in mice. Therefore, we propose that SEPHS1 is an essential regulator of selenium metabolism and redox homeostasis, and its dysregulation governs the progression of OA.

Osteoarthritis is caused by the gradual accumulation of oxidative stress in cartilage. Here, the authors show that dysregulation of the selenium metabolic pathway underlies a shift in redox homeostasis in chondrocytes, leading to chronic osteoarthritic changes in joints.

Stress-activated miR-204 governs senescent phenotypes of chondrocytes to promote osteoarthritis development

A progressive loss of cartilage matrix leads to the development of osteoarthritis (OA). Matrix homeostasis is disturbed in OA cartilage as the result of reduced production of cartilage-specific matrix and increased secretion of catabolic mediators by chondrocytes. Chondrocyte senescence is a crucial cellular event contributing to such imbalance in matrix metabolism during OA development. Here, we identify miR-204 as a markedly up-regulated microRNA in OA cartilage. miR-204 is induced by transcription factors GATA4 and NF-κB in response to senescence signals. Up-regulated miR-204 simultaneously targets multiple components of the sulfated proteoglycan (PG) biosynthesis pathway, effectively shutting down PG anabolism. Ectopic expression of miR-204 in joints triggers spontaneous cartilage loss and OA development, whereas miR-204 inhibition ameliorates experimental OA, with concomitant recovery of PG synthesis and suppression of inflammatory senescence-associated secretory phenotype (SASP) factors in cartilage. Collectively, we unravel a stress-activated senescence pathway that underlies disrupted matrix homeostasis in OA cartilage.

Articular reductions - how close is close enough? A narrative review

Intra-articular fractures are a unique subset of fractures as they involve a varying extent of damage to cartilage. The impact of this articular fracture causes significant microscopic and macroscopic changes, as well as biomechanical irregularities, which can lead to further cartilage damage, and ultimately cascade down the dreaded path to arthritis. It is generally believed that an anatomic reduction of an articular fracture is the necessary goal of treatment for these injuries, however it yet to be delineated how perfect this reduction has to be. A comprehensive literature review was carried out to create a best available evidence guide to the acceptability of upper extremity and lower extremity articular fracture reductions. Ultimately, a perfect anatomic reduction is the best strategy to minimize abnormal loading and wear patterns, however this should be balanced with the realistic factors of each individual case, such as the level of difficulty, joint involved, surgical timing, and patient activity levels.

Resistance training decreases matrix metalloproteinase-2 activity in quadriceps tendon in a rat model of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative disease that induces peri-articular tissue degradation. OA induces an imbalance between synthesis and degradation of the extracellular matrix components in favor of catabolic events, promoting pathological remodeling and involving degradative enzymes, such as matrix metalloproteinases (MMPs).

OBJECTIVE

This study aimed to investigate the effects of 8-weeks resistance training (RT) on MMP-2 activity in the quadriceps tendon and patellar tendon in an OA model.

METHODS

Twenty-four Wistar rats were randomly divided into six groups: Control, Exercise, Sham, Sham with Exercise, OA, and OA with Exercise (OAE). The OA model was performed by anterior cruciate ligament transection surgery on the left knee. The 8-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals' tails. MMP-2 activity was analyzed by zymography.

RESULTS

The OAE group displayed lower pro, intermediate, and active MMP-2 activity in the quadriceps tendon compared with the OA group (p<0.05). For the patellar tendon, there was no significant difference between the OAE group compared with the other groups (p>0.05) for pro, intermediate, and active MMP-2 activity. Moreover, MMP-2 activity differed between tissues, the OA and OAE groups presented lower pro, intermediate, and active MMP-2 activity in the quadriceps tendon compared to the patellar tendon.

CONCLUSION

RT induced down-regulated MMP-2 activity in the quadriceps tendon. RT is a potential therapeutic approach to minimize the deleterious effects of extracellular matrix degeneration.

Manganese dioxide nanoparticles protect cartilage from inflammation-induced oxidative stress

Oxidative stress has been implicated in the pathogenesis of osteoarthritis and has become an important therapeutic target. Investigations of various antioxidant supplements, reactive oxidative species (ROS) pathway mediators, and free radical scavengers for treating osteoarthritis have demonstrated common disadvantages including poor bioavailability and stability, as well as rapid joint clearance or release profiles from delivery vehicles. Moreover, these therapies do not target cartilage, which irreversibly degenerates in the presence of oxidative stress. The goal of this study was to engineer a nanoparticle system capable of sustained retention in the joint space, localization to cartilage, and mitigation of oxidative stress. Towards this goal, ROS scavenging manganese dioxide nanoparticles with physicochemical properties (less than 20 nm and cationic) that facilitate their uptake into cartilage were developed and characterized. These particles penetrated through the depth of cartilage explants and were found both in the extracellular matrix as well as intracellularly within the resident chondrocytes. Furthermore, the particles demonstrated chondroprotection of cytokine-challenged cartilage explants by reducing the loss of glycosaminoglycans and release of nitric oxide. Quantitative PCR analysis revealed that the particles mitigated impacts of oxidative stress related genes in cytokine-challenged chondrocytes. When injected intra-articularly into rats, the particles persisted in the joint space over one week, with 75% of the initial signal remaining in the joint. Biodistribution and histological analysis revealed accumulation of particles at the chondral surfaces and colocalization of the particles with the lacunae of chondrocytes. The results suggest that the manganese dioxide nanoparticles could be a promising approach for the chondroprotection of osteoarthritic cartilage.

Changes in proinflammatory cytokines, neuropeptides, and microglia in an animal model of monosodium iodoacetate-induced hip osteoarthritis

The aim of this study was to investigate the local production of proinflammatory cytokines, pain-related sensory innervation of dorsal-root ganglia (DRG), and spinal changes in a rat model of induced hip osteoarthritis (OA). Seventy-five Sprague-Dawley rats were used, including 25 controls and 50 injected into the right hip joints (sham group, injected with 25 µl of sterile saline: N = 25; and monosodium iodoacetate (MIA) group, injected with 25 µl of sterile saline with 2 mg of MIA: N = 25). We measured the local production of TNF-α, immunoreactive (-ir) neurons for calcitonin gene-related peptide (CGRP), and growth associated protein-43 (GAP-43) in DRG, and immunoreactive neurons for ionized-calcium-binding adaptor molecule-1 (Iba-1) in the dorsal horn of spinal cord, on post-induction days 7, 14, 28, 42, and 56 (N = 5 rats/group/time point). For post-induction days 7-42, the MIA group presented significantly elevated concentrations of TNF-α than the other groups (p < 0.01), and a higher expression of CGRP-ir in FG-labeled DRG neurons than the sham group (p < 0.01). MIA rats also presented significantly more FG-labeled GAP-43-ir DRG neurons than the sham group on post-induction days 28, 42, and 56 (p < 0.05), and a significantly higher number of Iba-1-ir microglia in the ipsilateral dorsal horn than the other groups, on post-induction days 28, 42, and 56. The results suggest that in rat models, pain-related pathologies due to MIA-induced hip OA, originate from inflammation caused by cytokines, which leads to progressive, chronic neuronal damage that may cause neuropathic pain. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2978-2986, 2018.

Articular Incongruity in the Lower Extremity: How Much Is Too Much?

Intraarticular fractures carry a significant risk for posttraumatic osteoarthritis, and this risk varies across different joint surfaces of the lower extremity. These differences are likely due to the anatomic and biomechanical specifics of each joint surface. High-quality human studies are lacking to delineate the threshold articular incongruity that significantly increases risk for posttraumatic osteoarthritis and diminished clinical outcomes for many joint surfaces. Even with anatomic reduction of the articular surface, close attention must be paid to mechanical axis and joint stability to optimize outcomes.

Mitoprotective therapy preserves chondrocyte viability and prevents cartilage degeneration in an ex vivo model of posttraumatic osteoarthritis

No disease-modifying osteoarthritis (OA) drugs are available to prevent posttraumatic osteoarthritis (PTOA). Mitochondria (MT) mediate the pathogenesis of many degenerative diseases, and recent evidence indicates that MT dysfunction is a peracute (within minutes to hours) response of cartilage to mechanical injury. The goal of this study was to investigate cardiolipin-targeted mitoprotection as a new strategy to prevent chondrocyte death and cartilage degeneration after injury. Cartilage was harvested from bovine knee joints and subjected to a single, rapid impact injury (24.0 ±1.4 MPa, 53.8 ± 5.3 GPa/s). Explants were then treated with a mitoprotective peptide, SS-31 (1µM), immediately post-impact, or at 1, 6, or 12 h after injury, and then cultured for up to 7 days. Chondrocyte viability and apoptosis were quantified in situ using confocal microscopy. Cell membrane damage (lactate dehydrogenase activity) and cartilage matrix degradation (glycosaminoglycan loss) were quantified in cartilage-conditioned media. SS-31 treatment at all time points after impact resulted in chondrocyte viability similar to that of un-injured controls. This effect was sustained for up to a week in culture. Further, SS-31 prevented impact-induced chondrocyte apoptosis, cell membrane damage, and cartilage matrix degeneration.

CLINICAL SIGNIFICANCE

This study is the first investigation of cardiolipin-targeted mitoprotective therapy in cartilage. These results suggest that even when treatment is delayed by up to 12 h after injury, mitoprotection may be a useful strategy in the prevention of PTOA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-10, 2018.

Changes in Joint Contact Mechanics in a Large Quadrupedal Animal Model After Partial Meniscectomy and a Focal Cartilage Injury

Acute mechanical damage and the resulting joint contact abnormalities are central to the initiation and progression of post-traumatic osteoarthritis (PTOA). Study of PTOA is typically performed in vivo with replicate animals using artificially induced injury features. The goal of this work was to measure changes in a joint contact stress in the knee of a large quadruped after creation of a clinically realistic overload injury and a focal cartilage defect. Whole-joint overload was achieved by excising a 5-mm wedge of the anterior medial meniscus. Focal cartilage defects were created using a custom pneumatic impact gun specifically developed and mechanically characterized for this work. To evaluate the effect of these injuries on joint contact mechanics, Tekscan (Tekscan, Inc., South Boston, MA) measurements were obtained pre-operatively, postmeniscectomy, and postimpact (1.2-J) in a nonrandomized group of axially loaded cadaveric sheep knees. Postmeniscectomy, peak contact stress in the medial compartment is increased by 71% (p = 0.03) and contact area is decreased by 35% (p = 0.001); the center of pressure (CoP) shifted toward the cruciate ligaments in both the medial (p = 0.004) and lateral (p = 0.03) compartments. The creation of a cartilage defect did not significantly change any aspect of contact mechanics measured in the meniscectomized knee. This work characterizes the mechanical environment present in a quadrupedal animal knee joint after two methods to reproducibly induce joint injury features that lead to PTOA.

The NAD-Dependent Deacetylase Sirtuin-1 Regulates the Expression of Osteogenic Transcriptional Activator Runt-Related Transcription Factor 2 (Runx2) and Production of Matrix Metalloproteinase (MMP)-13 in Chondrocytes in Osteoarthritis

Aging is one of the major pathologic factors associated with osteoarthritis (OA). Recently, numerous reports have demonstrated the impact of sirtuin-1 (Sirt1), which is the NAD-dependent deacetylase, on human aging. It has been demonstrated that Sirt1 induces osteogenic and chondrogenic differentiation of mesenchymal stem cells. However, the role of Sirt1 in the OA chondrocytes still remains unknown. We postulated that Sirt1 regulates a hypertrophic chondrocyte lineage and degeneration of articular cartilage through the activation of osteogenic transcriptional activator Runx2 and matrix metalloproteinase (MMP)-13 in OA chondrocytes. To verify whether sirtuin-1 (Sirt1) regulates chondrocyte activity in OA, we studied expressions of Sirt1, Runx2 and production of MMP-13, and their associations in human OA chondrocytes. The expression of Sirt1 was ubiquitously observed in osteoarthritic chondrocytes; in contrast, Runx2 expressed in the osteophyte region in patients with OA and OA model mice. OA relating catabolic factor IL-1βincreased the expression of Runx2 in OA chondrocytes. OA chondrocytes, which were pretreated with Sirt1 inhibitor, inhibited the IL-1β-induced expression of Runx2 compared to the control. Since the Runx2 is a promotor of MMP-13 expression, Sirt1 inactivation may inhibit the Runx2 expression and the resultant down-regulation of MMP-13 production in chondrocytes. Our findings suggest thatSirt1 may regulate the expression of Runx2, which is the osteogenic transcription factor, and the production of MMP-13 from chondrocytes in OA. Since Sirt1 activity is known to be affected by several stresses, including inflammation and oxidative stress, as well as aging, SIRT may be involved in the development of OA.

Chondropenia: current concept review

The term "chondropenia" indicates the early stage of degenerative cartilage disease, and it has been identified by carefully monitoring early-stage osteoarthritis (OA). Not only is it the loss of articular cartilage volume, but it is also a rearrangement of biomechanical, ultrastructural, biochemical and molecular properties typical of healthy cartilage tissue. Diagnosing OA at an early stage or an advanced stage is valuable in terms of clinical and therapeutic outcome. In fact degenerative phenomena are supported by a complex biochemical cascade which unbalances the extracellular matrix homeostasis, closely regulated by chondrocytes. In the first stage an intense inflammatory reaction is triggered: pro-catabolic cytokines such as IL-1β and TNF-α triggering matrix metalloproteases and aggrecanase (ADAMT-4 and 5), responsible for the early loss of ultrastructural components, such as type II collagen and aggrecan. In addition nitric oxide and reactive oxygen species modulate the physiopathology of the condral matrix inducing apoptosis of chondrocytes through a mitochondria-dependent pathway. In addition, "Lonely Death": chondrocytes, are confined within a dense, avascular extracellular matrix capsule, and can trigger a genetically induced apoptosis and necrosis. The degenerative process starts from a central point and then spreads in a centrifugal manner in depth and in adjacent areas, eventually covering the whole joint; chondropenia represents a journey from the first clinically detectable time-point until it can be characterized as frank osteoarthritis. Currently, there are no instruments sensitive enough which allow a timely diagnosis of chondropenia. Innovative magnetic resonance imaging techniques, such as T2 mapping, can be effective and a sensitive diagnostic instrument for quantifying cartilage volume and proteoglycan content. However, avant-garde biophysical techniques, such as mechanical indenters, ultrasound and biochemical markers (uCTX-II), are rational and scientific tools applicable to the clinical and therapeutic management of early degenerative cartilage disease. The objective of this review on chondropenia is to present a state of the art and innovative concepts.

A high-throughput model of post-traumatic osteoarthritis using engineered cartilage tissue analogs

OBJECTIVE

A number of in vitro models of post-traumatic osteoarthritis (PTOA) have been developed to study the effect of mechanical overload on the processes that regulate cartilage degeneration. While such frameworks are critical for the identification therapeutic targets, existing technologies are limited in their throughput capacity. Here, we validate a test platform for high-throughput mechanical injury incorporating engineered cartilage.

METHOD

We utilized a high-throughput mechanical testing platform to apply injurious compression to engineered cartilage and determined their strain and strain rate dependent responses to injury. Next, we validated this response by applying the same injury conditions to cartilage explants. Finally, we conducted a pilot screen of putative PTOA therapeutic compounds.

RESULTS

Engineered cartilage response to injury was strain dependent, with a 2-fold increase in glycosaminoglycan (GAG) loss at 75% compared to 50% strain. Extensive cell death was observed adjacent to fissures, with membrane rupture corroborated by marked increases in lactate dehydrogenase (LDH) release. Testing of established PTOA therapeutics showed that pan-caspase inhibitor [Z-VAD-FMK (ZVF)] was effective at reducing cell death, while the amphiphilic polymer [Poloxamer 188 (P188)] and the free-radical scavenger [N-Acetyl-L-cysteine (NAC)] reduced GAG loss as compared to injury alone.

CONCLUSIONS

The injury response in this engineered cartilage model replicated key features of the response of cartilage explants, validating this system for application of physiologically relevant injurious compression. This study establishes a novel tool for the discovery of mechanisms governing cartilage injury, as well as a screening platform for the identification of new molecules for the treatment of PTOA.

Articular cartilage changes in maturing athletes: new targets for joint rejuvenation

Context:

Articular cartilage has a unique functional architecture capable of providing a lifetime of pain-free joint motion. This tissue, however, undergoes substantial age-related physiologic, mechanical, biochemical, and functional changes that reduce its ability to overcome the effects of mechanical stress and injury. Many factors affect joint function in the maturing athlete—from chondrocyte survival and metabolism to structural composition and genetic/epigenetic factors governing cartilage and synovium. An evaluation of age-related changes for joint homeostasis and risk for osteoarthritis is important to the development of new strategies to rejuvenate aging joints.

Objective:

This review summarizes the current literature on the biochemical, cellular, and physiologic changes occurring in aging articular cartilage.

Data Sources:

PubMed (1969-2013) and published books in sports health, cartilage biology, and aging.

Study Selection:

Keywords included aging, athlete, articular cartilage, epigenetics, and functional performance with age.

Study Design:

Systematic review.

Level of Evidence:

Level 3.

Data Extraction:

To be included, research questions addressed the effect of age-related changes on performance, articular cartilage biology, molecular mechanism, and morphology.

Results:

The mature athlete faces challenges in maintaining cartilage health and joint function due to age-related changes to articular cartilage biology, morphology, and physiology. These changes include chondrocyte loss and a decline in metabolic response, alterations to matrix and synovial tissue composition, and dysregulation of reparative responses.

Conclusion:

Although physical decline has been regarded as a normal part of aging, many individuals maintain overall fitness and enjoy targeted improvement to their athletic capacity throughout life. Healthy articular cartilage and joints are needed to maintain athletic performance and general activities. Genetic and potentially reversible epigenetic factors influence cartilage physiology and its response to mechanical and injurious stimuli. Improved understandings of the physical and molecular changes to articular cartilage with aging are important to develop successful strategies for joint rejuvenation.

Pathogenesis and prevention of posttraumatic osteoarthritis after intra-articular fracture

Posttraumatic osteoarthritis (PTOA) occurs after traumatic injury to the joint. It is most common following injuries that disrupt the articular surface or lead to joint instability. The reported risk of PTOA following significant joint trauma is as high as 75%; articular fractures can increase the risk more than 20-fold. Despite recent advances in surgical management, the incidence of PTOA following intra-articular fractures has remained relatively unchanged over the last few decades. Pathogenesis of PTOA after intra-articular fracture is likely multifactorial and may be associated with acute cartilage injury as well as chronic joint overload secondary to instability, incongruity, and malalignment. Additional studies are needed to better elucidate how these factors contribute to the development of PTOA and to develop advanced treatment algorithms that consist of both acute biologic interventions targeted to decrease inflammation and cellular death in response to injury and improved surgical methods to restore stability, congruity, and alignment.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation and progression of osteoarthritis. However, our understanding of which mechanical parameters are most important, and what their impact is on the disease, is limited by the challenge of measuring the most important mechanical quantities in living subjects. Consequently, comprehensive statements cannot be made about how mechanics should be modified to prevent, slow or arrest osteoarthritis. Our current understanding is based largely on studies of deviations from normal mechanics caused by malalignment, injury, and deformity. Some treatments for osteoarthritis focus on correcting mechanics, but there appears to be scope for more mechanically based interventions.

Mechanical injury of bovine cartilage explants induces depth-dependent, transient changes in MAP kinase activity associated with apoptosis

OBJECTIVE

To characterize mitogen activated protein (MAP) kinase activity and chondrocyte apoptosis in an in vitro model of cartilage mechanical injury as a function of tissue depth and time post-injury.

DESIGN

Mechanically injured osteochondral explants were assessed for cell viability, MAP kinase and caspase-3 activity over 15 days using immunofluorescence microscopy and Western blot. Zonal distributions of cell viability and apoptosis were quantified in the presence of specific mitogen activated protein kinase inhibitors.

RESULTS

Viability rapidly decreased post-injury, most significantly in the superficial zone, with some involvement of the middle and deep zones, which correlated with increased caspase-3 activity. Transient and significant increases in extracellular-regulated protein kinase (ERK) activity were observed in middle and deep zones at 1 and 6 days post-injury, while c-Jun-amino terminal protein kinase activity increased in the deep zone at 1 and 6 days compared to uninjured controls. Changes in p38 activity were particularly pronounced, with significant increases in all three zones 30 min post-injury, but only in the middle and deep zones after 1 and 6 days. Inhibition of ERK and p38 increased chondrocyte viability which correlated with decreased apoptosis.

CONCLUSIONS

Spatiotemporal patterns of MAP kinase signalling in cartilage after mechanical injury strongly correlate with changes in cell viability and chondrocyte apoptosis. Importantly, these signals may be pro-survival or pro-apoptotic depending on zonal location and time post-injury. These data yield mechanistic insights which may improve the diagnosis and treatment of cartilage injuries.

Effects of aging on articular cartilage homeostasis

This review is focused on aging-related changes in cells and extracellular matrix of the articular cartilage. Major extracellular matrix changes are a reduced thickness of cartilage, proteolysis, advanced glycation and calcification. The cellular changes include reduced cell density, cellular senescence with abnormal secretory profiles, and impaired cellular defense mechanisms and anabolic responses. The extracellular and cellular changes compound each other, leading to biomechanical dysfunction and tissue destruction. The consequences of aging-related changes for joint homeostasis and risk for osteoarthritis are discussed. This article is part of a Special Issue entitled "Osteoarthritis".

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

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

Synthesis of a novel photopolymerized nanocomposite hydrogel for treatment of acute mechanical damage to cartilage

Intra-articular fractures initiate a cascade of pathobiological and pathomechanical events that culminate in post-traumatic osteoarthritis (PTOA). Hallmark features of PTOA include destruction of the cartilage matrix in combination with loss of chondrocytes and acute mechanical damage (AMD). Currently, treatment of intra-articular fractures essentially focuses completely on restoration of the macroanatomy of the joint. However, current treatment ignores AMD sustained by cartilage at the time of injury. We are exploring aggressive biomaterial-based interventions designed to treat the primary pathological components of AMD. This study describes the development of a novel injectable co-polymer solution that forms a gel at physiological temperatures that can be photocrosslinked, and can form a nanocomposite gel in situ through mineralization. The injectable co-polymer solution will allow the material to fill cracks in the cartilage after trauma. The mechanical properties of the nanocomposite are similar to those of native cartilage, as measured by compressive and shear testing. It thereby has the potential to mechanically stabilize and restore local structural integrity to acutely injured cartilage. Additionally, in situ mineralization ensures good adhesion between the biomaterial and cartilage at the interface, as measured through tensile and shear testing. Thus we have successfully developed a new injectable co-polymer which forms a nanocomposite in situ with mechanical properties similar to those of native cartilage, and which can bond well to native cartilage. This material has the potential to stabilize injured cartilage and prevent PTOA.

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

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

Mechanical impact induces cartilage degradation via mitogen activated protein kinases

OBJECTIVE

To determine the activation of Mitogen activated protein (MAP) kinases in and around cartilage subjected to mechanical damage and to determine the effects of their inhibitors on impaction-induced chondrocyte death and cartilage degeneration.

DESIGN

The phosphorylation of MAP kinases was examined with confocal microscopy and immunoblotting. The effects of MAP kinase inhibitors on impaction-induced chondrocyte death and proteoglycan (PG) loss were determined with fluorescent microscopy and 1, 9-Dimethyl-Methylene Blue (DMMB) assay. The expression of catabolic genes at mRNA levels was examined with quantitative real-time PCR.

RESULTS

Early p38 activation was detected at 20 min and 1h post-impaction. At 24h, enhanced phosphorylation of p38 and extracellular signal-regulated protein kinase (ERK)1/2 was visualized in chondrocytes from in and around impact sites. The phosphorylation of p38 was increased by 3.0-fold in impact sites and 3.3-fold in adjacent cartilage. The phosphorylation of ERK-1 was increased by 5.8-fold in impact zone and 5.4-fold in adjacent cartilage; the phosphorylation of ERK-2 increased by 4.0-fold in impacted zone and 3.6-fold in adjacent cartilage. Furthermore, the blocking of p38 pathway did not inhibit impaction-induced ERK activation. The inhibition of p38 or ERK pathway significantly reduced injury-related chondrocyte death and PG losses. Quantitative Real-time PCR analysis revealed that blunt impaction significantly up-regulated matrix metalloproteinase (MMP)-13, Tumor necrosis factor (TNF)-α, and ADAMTS-5 expression.

CONCLUSION

These findings implicate p38 and ERK mitogen activated protein kinases (MAPKs) in the post-injury spread of cartilage degeneration and suggest that the risk of post-traumatic osteoarthritis (PTOA) following joint trauma could be decreased by blocking their activities, which might be involved in up-regulating expressions of MMP-13, ADAMTS-5, and TNF-α.

Optical coherence tomography detection of subclinical traumatic cartilage injury

OBJECTIVES

Posttraumatic arthritis is a major cause of disability. Current clinical imaging modalities are unable to reliably evaluate articular cartilage damage before surface breakdown, when potentially reversible changes are occurring. Optical coherence tomography (OCT) is a nondestructive imaging technology that can detect degenerative changes in articular cartilage with an intact surface. This study tests the hypothesis that OCT detects acute articular cartilage injury after impact at energy levels resulting in chondrocyte death and microstructural changes, but insufficient to produce macroscopic surface damage.

METHODS

Bovine osteochondral cores underwent OCT imaging and were divided into a control with no impact or were subjected to low (0.175 J) or moderate (0.35 J) energy impact. Cores were reimaged with OCT after impact and the OCT signal intensity quantified. A ratio of the superficial to deep layer intensities was calculated and compared before and after impact. Chondrocyte viability was determined 1 day after impact followed by histology and polarized microscopy.

RESULTS

Macroscopic changes to the articular surface were not observed after low and moderate impact. The OCT signal intensity ratio demonstrated a 27% increase (P = 0.006) after low impact and a 38% increase (P = 0.001) after moderate impact. Cell death increased by 150% (P < 0.001) and 200% (P < 0.001) after low and moderate energy impacts, respectively. When compared with unimpacted controls, both Mankin histology and David-Vaudey polarized microscopy scores increased (P = 0.036 and P = 0.002, respectively) after moderate energy impact.

CONCLUSIONS

This study shows that OCT detects acute cartilage changes after impact injury at levels insufficient to cause visible damage to the articular surface but sufficient to cause chondrocyte death and microscopic matrix damage. This finding supports the use of OCT to detect microstructural subsurface cartilage damage that is poorly visualized with conventional imaging.

Joint aging and chondrocyte cell death

Articular cartilage extracellular matrix and cell function change with age and are considered to be the most important factors in the development and progression of osteoarthritis. The multifaceted nature of joint disease indicates that the contribution of cell death can be an important factor at early and late stages of osteoarthritis. Therefore, the pharmacologic inhibition of cell death is likely to be clinically valuable at any stage of the disease. In this article, we will discuss the close association between diverse changes in cartilage aging, how altered conditions influence chondrocyte death, and the implications of preventing cell loss to retard osteoarthritis progression and preserve tissue homeostasis.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation, progression, and successful treatment of osteoarthritis. However, we don't yet know enough about which specific mechanical parameters are most important and what their impact is on the disease process to make comprehensive statements about how mechanics should be modified to prevent, slow, or arrest the disease process. The objectives of this review are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe current evidence for the role of mechanics in osteoarthritis initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

Chondrocyte apoptosis: implications for osteochondral allograft transplantation

Osteochondral allograft transplantation is a useful technique to manage larger articular cartilage injuries. One factor that may compromise the effectiveness of this procedure is chondrocyte cell death that occurs during the storage, preparation, and implantation of the osteochondral grafts. Loss of viable chondrocytes may negatively affect osteochondral edge integration and long-term function. A better understanding of the mechanisms responsible for chondrocyte loss could lead to interventions designed to decrease cell death and improve results. Recent studies indicate that apoptosis, or programmed cell death, is responsible for much of the chondrocyte death associated with osteochondral allograft transplantation. Theoretically, some of these cells can be rescued by blocking important apoptotic mediators. We review the role of apoptosis in cartilage degeneration, focusing on apoptosis associated with osteochondral transplantation. We also review the pathways thought to be responsible for regulating chondrocyte apoptosis, as well as experiments testing inhibitors of the apoptotic pathway. These data suggest that key contributors to the apoptotic process can be manipulated to enhance chondrocyte survival. This knowledge may lead to better surgical outcomes for osteochondral transplantation.

The acutely ACL injured knee assessed by MRI: are large volume traumatic bone marrow lesions a sign of severe compression injury?

OBJECTIVES

To map by magnetic resonance imaging (MRI) and quantitative MRI (qMRI) concomitant fractures and meniscal injuries, and location and volume of traumatic bone marrow lesions (BMLs) in the acutely anterior cruciate ligament (ACL) injured knee. To relate BML location and volume to cortical depression fractures, meniscal injuries and patient characteristics.

METHODS

One hundred and twenty-one subjects (26% women, mean age 26 years) with an ACL rupture to a previously un-injured knee were studied using a 1.5T MR imager within 3 weeks from trauma. Meniscal injuries and fractures were classified by type, size and location. BML location and volume were quantified using a multi-spectral image data set analyzed by computer software, edited by an expert radiologist.

RESULTS

Fractures were found in 73 (60%) knees. In 67 (92%) of these knees at least one cortical depression fracture was found. Uni-compartmental meniscal tears were found in 44 (36%) subjects and bi-compartmental in 24 (20%). One hundred and nineteen (98%) knees had at least one BML, all but four (97%) located in the lateral compartment. Knees with a cortical depression fracture had larger BML volumes (P<0.001) than knees without a cortical depression fracture, but no associations were found between meniscal tears and BML volume or fractures. Older age at injury was associated with smaller BML volumes (P<0.01).

CONCLUSION

A majority of the ACL injured knees had a cortical depression fracture, which was associated with larger BML volumes. This indicates strong compressive forces to the articular surface and cartilage at the time of injury, which may constitute an additional risk factor for later knee osteoarthritis development.

Cell death in osteoarthritis

To date, most studies examining cell death during the development of osteoarthritis (OA) have focused on death of chondrocytes and have primarily examined advanced stages of the disease. Very good evidence suggests that chondrocyte death does occur at some point in the pathogenesis of OA and that it can be due to apoptosis, necrosis, or some combination of the two. Chondrocyte death can be induced by mechanical injury, loss of extracellular matrix, loss of growth factors, or excessive levels of reactive oxygen species. Although therapy specifically targeting cell death in human OA has not been reported, preclinical studies in animal models have provided early evidence that inhibition of caspases might slow OA-like changes in articular cartilage. Because of potential unwanted side effects from agents systemically inhibiting cell death, treatments specifically targeting cell death in OA will likely need to be delivered locally and in a manner that prevents systemic absorption. Inhibition of cell death in OA likely will not be a sole therapeutic target but rather a desired effect of interventions designed to reverse the catabolic-anabolic imbalance occurring in OA joint tissues.

The chemical biology of nitric oxide--an outsider's reflections about its role in osteoarthritis

Excess formation of nitric oxide (NO) has been invoked in the development of osteoarthritis and blamed for triggering chondrocyte apoptosis and matrix destruction. Much of the evidence for a deleterious role of NO in disease progression has been obtained indirectly and inferred from the measurement of nitrite/nitrate and nitrotyrosine concentrations as well as iNOS expression in biopsy specimen, cartilage explants and cytokine-stimulated cells in culture. While these results clearly indicate an involvement of NO and suggest additional contributions from oxidative stress-related components they do not necessarily establish a cause/effect relationship. Many NO metabolites are not mere dosimeters of local NO production but elicit potent down-stream effects in their own right. Moreover, oxygen tension and other experimental conditions typical of many in vitro studies would seem to be at odds with the particular situation in the joint. Recent insight into the chemical biology of NO, in particular with regard to cellular redox-regulation, mitochondrial signaling and nitration reactions, attest to a much richer network of chemical transformations and interactions with biological targets than hitherto assumed. In conjunction with the emerging biology of nitrite and nitrate this information challenges the validity of the long-held view that "too much NO" is contributing to disease progression. Instead, it suggests that part of the problem is a shift from NO to superoxide-dominated chemistries triggering changes in thiol-dependent redox signaling, hypoxia-induced gene expression and mitochondrial function. This essay aims to provide a glimpse into research areas that may hold promise for future investigations into the underlying causes of osteoarthritis.

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.

The potential role of vascular endothelial growth factor (VEGF) in cartilage: how the angiogenic factor could be involved in the pathogenesis of osteoarthritis?

Although adult human cartilage is physiologically avascular tissue, angiogenesis can be observed during the process of endochondral bone development. Inflammation in articular joints can also lead to neovascularization in cartilage. In such conditions, the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF), has been shown to play a key role, controlling not only angiogenesis but also chondrocyte metabolism. Here we review recent research findings concerning the potential role of VEGF in cartilage, focusing in particular on its possible involvement in the pathogenesis of osteoarthritis.

Anti-inflammatory and chondroprotective effects of nutraceuticals from Sasha's Blend in a cartilage explant model of inflammation

New Zealand green lipped mussel (NZGLM), abalone (AB), and shark cartilage (SC) are extensively used for treatment of and/or as preventatives for arthritis, despite a relative paucity of scientific evidence for efficacy. This research integrated a simulated digestion protocol with ultrafiltration and cartilage explants to generate new information on the anti-inflammatory and chondroprotective properties of NZGLM, SC, and AB. Each nutraceutical was artificially digested using simulated gastric and intestinal fluids, and the crude digest was ultrafiltered (50 kDa). Each filtrate was applied individually to cartilage explants before the explants were stimulated with IL-1 to induce an acute inflammatory response. Media were collected daily for 48 h and analyzed for prostaglandin E(2) (PGE(2)), glycosaminoglycan (GAG), and nitric oxide (NO), and cartilage tissue was differentially stained to determine the relative proportion of live and dead cells. SC and NZGLM significantly inhibited IL-1-induced PGE(2) synthesis and IL-1-induced GAG release, and AB was an effective inhibitor of IL-1-induced NO production. The three test nutraceuticals affect at least three major pathways involved in the catabolic cycle of arthritis and may prove important treatments and/or preventatives for the pain and degradation associated with this condition. The methodology and results describe a useful model for evaluating dietary nutraceuticals in vitro.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Water-soluble C60 fullerene prevents degeneration of articular cartilage in osteoarthritis via down-regulation of chondrocyte catabolic activity and inhibition of cartilage degeneration during disease development

OBJECTIVE

Studies have shown the roles of oxidative stress in the pathogenesis of osteoarthritis (OA) and induction of chondrocyte senescence during OA progression. The aim of this study was to examine the potential of a strong free-radical scavenger, water-soluble fullerene (C60), as a protective agent against catabolic stress-induced degeneration of articular cartilage in OA, both in vitro and in vivo.

METHODS

In the presence or absence of C60 (100 microM), human chondrocytes were incubated with interleukin-1beta (10 ng/ml) or H2O2 (100 microM), and chondrocyte activity was analyzed. An animal model of OA was produced in rabbits by resection of the medial meniscus and medial collateral ligament. Rabbits were divided into 5 subgroups: sham operation or treatment with C60 at 0.1 microM, 1 microM, 10 microM, or 40 microM. The left knee joint was injected intraarticularly with water-soluble C60 (2 ml), while, as a control, the right knee joint received 50% polyethylene glycol (2 ml), once weekly for 4 weeks or 8 weeks. Knee bone and cartilage tissue were prepared for histologic analysis. In addition, in the OA rabbit model, the effect of C60 (10 microM) on degeneration of articular cartilage was compared with that of sodium hyaluronate (HA) (5 mg/ml).

RESULTS

C60 (100 microM) inhibited the catabolic stress-induced production of matrix-degrading enzymes (matrix metalloproteinases 1, 3, and 13), down-regulation of matrix production, and apoptosis and premature senescence in human chondrocytes in vitro. In rabbits with OA, treatment with water-soluble C60 significantly reduced articular cartilage degeneration, whereas control knee joints showed progression of cartilage degeneration with time. This inhibitory effect was dose dependent, and was superior to that of HA. Combined treatment with C60 and HA yielded a significant reduction in cartilage degeneration compared with either treatment alone.

CONCLUSION

The results indicate that C60 fullerene is a potential therapeutic agent for the protection of articular cartilage against progression of OA.