The pathophysiology of osteoarthritis

FT-IR imaging of native and tissue-engineered bone and cartilage

Fourier transform infrared (FT-IR) imaging and microspectroscopy have been extensively applied to the analyses of tissues in health and disease. Spatially resolved mid-IR data has provided insights into molecular changes that occur in diseases of connective or collagen-based tissues, including, osteoporosis, osteogenesis imperfecta, osteopetrosis and pathologic calcifications. These techniques have also been used to probe chemical changes associated with load, disuse, and micro-damage in bone, and with degradation and repair in cartilage. This review summarizes the applications of FT-IR microscopy and imaging for analyses of bone and cartilage in healthy and diseased tissues, and illustrates the application of these techniques for the characterization of tissue-engineered bone and cartilage.

Changes in immunolocalisation of beta-dystroglycan and specific degradative enzymes in the osteoarthritic synovium

OBJECTIVE

To investigate the immunolocalisation of beta-dystroglycan (beta-DG) and specific matrix metalloproteinases (MMPs)-3, -9, -13 and a disintegrin like and metalloproteinase thrombospondin type 1 motif 4 (ADAMTS-4) within the joint tissues of patients with osteoarthritis (OA) and unaffected controls.

DESIGN

Cartilage, synovium and synovial fluid were obtained from the hip joints of five osteoarthritic (patients undergoing total hip replacement) and five control hip joints (patients undergoing hemiarthroplasty for femoral neck fracture). The samples were analysed for beta-DG protein using Western blot technique and by immunohistochemistry for tissue distribution of beta-DG, MMP-3, -9, -13, and ADAMTS-4.

RESULTS

beta-DG was detected in the smooth muscle of both normal and osteoarthritic synovial blood vessels. Importantly, beta-DG was detected in endothelium of blood vessels of OA synovium, but not in the control endothelium. In the endothelium of osteoarthritic synovial blood vessels, beta-DG co-localised with MMP-3 and -9. MMP-13 and ADAMTS-4 showed no endothelial staining, and only weak staining of the vascular smooth muscle was found. In contrast, we did not detect beta-DG protein in cartilage or synovial fluid.

CONCLUSIONS

beta-DG has been shown to have a role in angiogenesis, and our results demonstrate for the first time that there are clear differences in beta-DG staining between OA and control synovial blood vessels. The specific immunolocalisation of beta-DG within endothelium of inflamed OA blood vessels and its co-localisation with MMP-3 and -9, reported to have pro-angiogenic roles and believed to be involved in beta-DG cleavage, may also suggest that beta-DG plays a role in angiogenesis accompanying OA.

Evidence for a protective role for adiponectin in osteoarthritis

Obesity has been associated with an increased risk of osteoarthritis (OA). However, the mechanism by which obesity contributes to OA remains uncertain. Adiponectin, an adipocyte-derived hormone, has shown anti-diabetic and anti-atherogenic properties. In the present study, we aimed to investigate the potential role of adiponectin in OA disease. We demonstrated that adiponectin was present in OA synovial fluid (SF) and its expression level was almost 100-fold decrease compared with that in OA plasma. FPLC and ELISA studies revealed the distribution and abundance of the adiponectin complexes in plasma and SF from patients with OA. The percentage of high molecular weight (HMW) per total adiponectin in OA SF was lower than in OA plasma, while that of the hexamer form was similar and the trimer form was higher. The expression levels of adiponectin receptors AdipoR1 and AdipoR2 were examined in human OA tissues by RT-PCR. AdipoR1 was abundantly expressed in cartilage, bone and synovial tissues, whereas AdipoR2 was rarely detected. Finally, the effects of adiponectin on primary chondrocyte functions were studied by using antibody-based protein array and RT-PCR. The patterns of mRNA expression and protein production strongly indicate that adiponectin is involved in the modulation of cartilage destruction in chondrocytes by up-regulating TIMP-2 and down-regulating IL-1beta-induced MMP-13. Together these findings clearly indicate that the adiponectin may act as a protective role in the progression of OA, and this also provide new thinking on the relationship between obesity and OA.

Age-related decrease in the activity of collagenase in the femoral head in patients with hip osteoarthritis

The aim of the study was to evaluate the relation between the activity of collagenase in the subchondral bone of the femoral head and the age of patients with hip osteoarthritis. Thirty-two patients were enrolled into the study. The mean age was 66 (range from 37 to 80 years). Bone samples of the femoral head were harvested during total hip replacement. The activity of collagenase was measured through spectrofluorimetry. We found statistically a significant correlation between collagenase activity in the bone and age. The mean activity of collagenase in younger patients (37-68 years) was 64.17 IU/microg. In older patients (69-80 years), the mean collagenase activity was 52.26 IU/microg. In patients with hip osteoarthritis the activity of collagenase in the subchondral bone of the femoral head tended to decrease with an increase in age.

Matrix metalloproteinase 2 and tissue inhibitors of metalloproteinases regulate human aortic smooth muscle cell migration during in vitro aging

As a direct correlation between aging and the risk of onset of vascular disease has been universally accepted, we prepared an in vitro aging model consisting in sequential passages of human aortic smooth muscle cells (AoSMC) in order to evaluate the cell behavior changes during aging. Because matrix metalloproteinases (MMP) are actively involved in matrix remodeling and disease outcome, in our model we found active MMP-2 only in the conditioned medium of young AoSMCs, whereas aged cells showed only the inactive zymogen form of MMP-2 (pro-MMP-2). We ascribed the pro-MMP-2 activation in young cells to an increase in membrane type 1 matrix metalloproteinase (MT1-MMP) content. Furthermore, we found that transcripts coding for tissue inhibitor of metalloproteinases (TIMPs) were up-regulated in aged cells, and this increase of TIMPs could also prevent pro-MMP-2 activation in aged cells. Moreover, we demonstrated that young AoSMCs possess higher migratory capabilities than aged cells. The young AoSMC migration can be inhibited by adding TIMP-1 and TIMP-2 to the cells reproducing aged AoSMC migratory behavior. Finally, the role of MMP-2 and TIMP-2 in AoSMC migration was confirmed silencing MMP-2 and TIMP-2 in young and aged AoSMCs, respectively; therefore, in this study we showed that these enzymes play a pivotal role in the regulation of the AoSMC migration during in vitro aging.

Synthesis and SAR of α-sulfonylcarboxylic acids as potent matrix metalloproteinase inhibitors

A series of novel carboxylic acid-based alpha-sulfone MMP inhibitors have been synthesized and the in vitro enzyme SAR is discussed. A potential binding mode in the active site of the MMP-9 homology model was highlighted. These compounds are potent MMP-9 inhibitors and are selective over MMP-1.

Activity-dependent release of precursor nerve growth factor, conversion to mature nerve growth factor, and its degradation by a protease cascade

In this report, we provide direct demonstration that the neurotrophin nerve growth factor (NGF) is released in the extracellular space in an activity-dependent manner in its precursor form (proNGF) and that it is in this compartment that its maturation and degradation takes place because of the coordinated release and the action of proenzymes and enzyme regulators. This converting protease cascade and its endogenous regulators (including tissue plasminogen activator, plasminogen, neuroserpin, precursor matrix metalloproteinase 9, and tissue inhibitor metalloproteinase 1) are colocalized in neurons of the cerebral cortex and released upon neuronal stimulation. We also provide evidence that this mechanism operates in in vivo conditions, as the CNS application of inhibitors of converting and degrading enzymes lead to dramatic alterations in the tissue levels of either precursor NGF or mature NGF. Pathological alterations of this cascade in the CNS might cause or contribute to a lack of proper neuronal trophic support in conditions such as cerebral ischemia, seizure and Alzheimer's disease or, conversely, to excessive local production of neurotrophins as reported in inflammatory arthritis pain.

Regulation of matrix metalloproteinase expression by dynamic tensile strain in rat fibrochondrocytes

OBJECTIVE

We sought to determine the molecular basis for the anticatabolic effects of mechanical signals on fibrocartilage cells by studying the expression of a variety of matrix metalloproteinases (MMPs). Furthermore, we examined whether the effects of biomechanical strain on MMP gene expression are sustained.

METHODS

Fibrochondrocytes from temporomandibular joint (TMJ) discs were exposed to dynamic tensile strain for various time intervals in the presence of interleukin (IL)-1beta. The regulation of the messenger RNA (mRNA) expression and synthesis of MMPs and tissue inhibitors of MMPs (TIMPs) were examined by end-point and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) as well as Western blot analysis.

RESULTS

Fibrochondrocytes expressed mRNA for MMP-2, -3, -7, -8, -9, -11, -13, -14, -16, -17, and -19 as well as TIMP-1, -2, and -3, IL-1beta induced a significant (P<0.05) upregulation of mRNA for MMP-3, -7, -8, -9, -13, -16, -17, and -19. The IL-1beta-stimulated upregulation of these MMPs was significantly (P<0.05) abrogated by dynamic tensile strain. However, MMP-2, -11, -14, and TIMPs were not affected by either IL-1beta or tensile strain. Biomechanical strain also inhibited the IL-1beta-stimulated protein synthesis of MMP-3, -7, -8, -9, -13, -16, and -17. Application of mechanical strain for various time intervals during a 24-h incubation with IL-1beta showed that the suppressive effects of mechanical signals are sustained.

CONCLUSIONS

The data provide evidence that biomechanical signals can downregulate the catabolic activity of fibrocartilage cells in an inflammatory environment by inhibiting the expression of a variety of MMPs. Furthermore, the matrix-protective effects of biomechanical signals are sustained even in an inflammatory environment.

Dynamic biophysical strain modulates proinflammatory gene induction in meniscal fibrochondrocytes

Fibrochondrocytes of meniscus adapt to changes in their biomechanical environment by mechanisms that are yet to be elucidated. In this study, the mechanoresponsiveness of fibrochondrocytes under normal and inflammatory conditions was investigated. Fibrochondrocytes from rat meniscus were exposed to dynamic tensile forces (DTF) at various magnitudes and frequencies. The mechanoresponsiveness was assessed by examining the expression of inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-alpha), and matrix metalloproteinase-13 mRNA expression. The mRNA and protein analyses revealed that DTF at magnitudes of 5% to 20% did not induce proinflammatory gene expression. IL-1beta induced a rapid increase in the iNOS mRNA. DTF strongly repressed IL-1beta-dependent iNOS induction in a magnitude-dependent manner. Exposure to 15% DTF resulted in >90% suppression of IL-1beta-induced mRNA within 4 h and this suppression was sustained for the ensuing 20 h. The mechanosensitivity of fibrochondrocytes was also frequency dependent and maximal suppression of iNOS mRNA expression was observed at rapid frequencies of DTF compared with lower frequencies. Like iNOS, DTF also inhibited IL-1beta-induced expression of proinflammatory mediators involved in joint inflammation. The examination of temporal effects of DTF revealed that 4- or 8-h exposure of DTF was sufficient for its sustained anti-inflammatory effects during the next 20 or 16 h, respectively. Our findings indicate that mechanical signals act as potent anti-inflammatory signals, where their magnitude and frequency are critical determinants of their actions. Furthermore, mechanical signals continue attenuating proinflammatory gene transcription for prolonged periods of time after their removal.

An introductory review of cell mechanobiology

Mechanical loads induce changes in the structure, composition, and function of living tissues. Cells in tissues are responsible for these changes, which cause physiological or pathological alterations in the extracellular matrix (ECM). This article provides an introductory review of the mechanobiology of load-sensitive cells in vivo, which include fibroblasts, chondrocytes, osteoblasts, endothelial cells, and smooth muscle cells. Many studies have shown that mechanical loads affect diverse cellular functions, such as cell proliferation, ECM gene and protein expression, and the production of soluble factors. Major cellular components involved in the mechanotransduction mechanisms include the cytoskeleton, integrins, G proteins, receptor tyrosine kinases, mitogen-activated protein kinases, and stretch-activated ion channels. Future research in the area of cell mechanobiology will require novel experimental and theoretical methodologies to determine the type and magnitude of the forces experienced at the cellular and sub-cellular levels and to identify the force sensors/receptors that initiate the cascade of cellular and molecular events.

Osteoarthritis: an overview of the disease and its treatment strategies

Osteoarthritis (OA) is currently defined by the American College of Rheumatology as a "heterogeneous group of conditions that leads to joint symptoms and signs which are associated with defective integrity of articular cartilage, in addition to related changes in the underlying bone at the joint margins." Its prevalence after the age of 65 years is about 60% in men and 70% in women. The etiology of OA is multifactorial, with inflammatory, metabolic, and mechanical causes. A number of environmental risk factors, such as obesity, occupation, and trauma, may initiate various pathological pathways. OA indicates the degeneration of articular cartilage together with changes in subchondral bone and mild intraarticular inflammation. The principal treatment objectives are to control pain adequately, improve function, and reduce disability. Acetaminophen is frequently used for symptomatic OA with mild to moderate pain. Nonsteroidal antiinflammatory drugs (NSAIDs) are more effective in the case of moderate-severe pain, but they have an increased risk of serious upper gastrointestinal adverse events. The newer cyclooxygenase COX-2 specific inhibitors (Coxibs) are as efficacious as traditional NSAIDs and have a better gastrointestinal safety profile. Other compounds (eg, chondroitin sulfate, diacerein, glucosamine sulfate) have a symptomatic effect that is slower and less than that of NSAIDs. The structure-modifying effects of drugs are currently being evaluated, and both glucosamine sulfate and diacerein have been shown in some trials to have a beneficial structural effect. Nonpharmacological interventions are frequently and widely used in the management of OA patients, but there is little evidence that they are effective: the best studied and most successful nonpharmacological interventions are patient education, self-management, and exercise. There is some evidence for the pain-relieving efficacy of thermotherapy and transcutaneous electrical nerve stimulation (TENS) but not of electrotherapy, acupuncture, homeopathy, or manual therapy. The value of interventions aimed at improving function and maximizing independence (occupational therapy, walking aids, workplace adaptation) is also unclear. The disease course and patient's requirements often change over time, thus requiring a periodic review and readjustment of therapy rather than the rigid continuation of a single treatment.

New biochemical insights into the pathogenesis of osteoarthritis and the role of laboratory investigations in clinical assessment

Osteoarthritis (OA) is among the most frequent diseases in the population and a common cause of pain and disability in adults. The principal disease hallmarks for assessment of OA are still clinical observation and radiographic aspects. However, the efficacy of therapeutic interventions is complicated by the time required to observe radiographic signs, useful for both diagnosis and assessment. Thus, laboratory markers have received growing attention in recent years, in an attempt to improve diagnosis, assessment of disease activity and severity, and evaluation of therapeutic effects. Many biomarkers have been proposed, in particular those reflecting cartilage and bone turnover and synovitis. Among these, COMP, antigenic keratan sulphate, hyaluronan, YKL-40, type III collagen N-propeptide, and urinary glucosyl-galactosyl pyridinoline appear to be the most promising. However, serum or urinary determinations of these molecules are difficult to interpret adequately due to their complex metabolism. New ultrasensitive methods for C-reactive protein have improved the usefulness of this marker, especially in the assessment of disease activity. Routine examination of synovial fluid is still essential for diagnosis and includes leukocyte count and crystal detection; specialized testing includes the evaluation of the levels of markers of local inflammation such as metalloproteinases and cytokines, which appear to be crucial to the pathogenesis of OA.

Biological basis for the use of botanicals in osteoarthritis and rheumatoid arthritis: a review

Osteoarthritis (OA) of the knee and hip is a debilitating disease affecting more women than men and the risk of developing OA increases precipitously with aging. Rheumatoid arthritis (RA), the most common form of inflammatory joint diseases, is a disease of unknown etiology and affects approximately 1% of the population worldwide, and unlike OA, generally involves many joints because of the systemic nature of the disease. Non-steroidal anti-inflammatory drugs (NSAIDs) are the first drugs of choice for the symptomatic treatment of both OA and RA. Because of the risks associated with the use of NSAIDs and other limitations, the use of alternative therapies, such as acupuncture and medicinal herbs, is on the rise and according to reports approximately 60-90% of dissatisfied arthritis patients are likely to seek the option of complementary and alternative medicine (CAM). This paper reviews the efficacy of some of the common herbs that have a history of human use and their anti-inflammatory or antiarthritic properties have been evaluated in animal models of inflammatory arthritis, in studies employing well defined and widely accepted in vitro models that use human chondrocytes/cartilage explants or in clinical trials. Available data suggests that the extracts of most of these herbs or compounds derived from them may provide a safe and effective adjunctive therapeutic approach for the treatment of OA and RA. This, in turn, argues for trials to establish efficacy and optimum dosage of these compounds for treating human inflammatory and degenerative joint diseases.

Temporospatial expression of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in mouse antigen-induced arthritis

Several lines of evidence speak for an important role of matrix metalloproteinases (MMPs) in the development of progressive joint destruction. To better understand the role of MMPs and their tissue inhibitors (TIMPs) in this process, we have used the antigen-induced arthritis model to study the temporospatial expression of several MMPs and TIMPs during the progression of arthritis. Arthritis was induced by a single intra-articular injection of methylated bovine serum albumin (mBSA) into one or both knee joints of adult mice previously immunised against mBSA. Samples were collected at 3, 7, 21 and 42 days after induction of arthritis for histology and RNA extraction, and analysed by Northern hybridisation, histochemistry and immunohistochemistry for production of several MMPs and TIMPs -1, -2 and -3. A systematic analysis of MMP and TIMP mRNA levels in mouse knee joints demonstrated a general upregulation of both MMPs and TIMPs during progression of arthritis. Upregulation of MMP-9, -13 and -14 coincided with the advancement of cartilage degeneration, but the expression patterns of MMP-9 and -13 also followed the course of synovial inflammation. TIMPs were steadily upregulated throughout the examination period. Immunohistochemical localisation of MMPs and TIMPs suggested the synovium to be the major source of MMP and TIMP production in arthritis, although articular cartilage chondrocytes also showed an increased production of both MMPs and TIMPs.

Increased pentosidine, an advanced glycation end product, in serum and synovial fluid from patients with knee osteoarthritis and its relation with cartilage oligomeric matrix protein

BACKGROUND

Pentosidine, an advanced glycation end product, increasingly accumulates in articular cartilage with age, and contributes to the pathogenesis of osteoarthritis (OA). Increased pentosidine concentrations are associated with inflammatory disorders-for example, rheumatoid arthritis.

OBJECTIVE

To compare pentosidine serum concentrations in patients with knee OA and in healthy volunteers and to determine a relationship between pentosidine and cartilage oligomeric matrix protein (COMP)-a marker of articular cartilage destruction.

METHODS

Paired serum and synovial fluid samples were obtained by arthrocentesis from 38 patients with knee OA and from 38 healthy volunteers. Pentosidine concentration was measured by reverse phase high performance liquid chromatography with fluorescent detection and COMP was determined by sandwich ELISA.

RESULTS

Significantly increased serum pentosidine (p<0.01) and COMP (p<0.05) levels were detected in the patients with OA compared with the control group. Serum pentosidine correlated significantly with synovial fluid pentosidine (p<0.001). Pentosidine in synovial fluid (p<0.05) and in serum (p<0.05) correlated significantly with synovial fluid COMP. Pentosidine and COMP concentrations did not correlate significantly with the radiological stage of the disease.

CONCLUSION

Increased pentosidine serum concentration in patients with OA and its correlation with the cartilage destruction marker COMP in synovial fluid suggests that pentosidine may be important in OA pathology and is a new potential OA marker.

Wnt Influence on Chondrocyte Differentiation and Cartilage Function

The Wnt signaling network regulates chondrocyte differentiation, proliferation, and maturation during embryonic limb development. In this review, we summarize studies of Wnt signaling during the chondrocyte life cycle in avian and mammalian systems, both before and after birth. Recent reports that implicate abnormal Wnt signaling as a contributing factor to pathogenic joint conditions are also discussed. In addition, we show new data that suggests Wnt signaling is active in adult cartilage. Overall, it appears that the Wnt network has dual roles in cartilage, as has been described in other tissues: it is an important regulator of chondrocyte development, but deregulated signaling is detrimental to mature tissues and may lead to disease.

Joint and bone disease in mucopolysaccharidoses VI and VII: identification of new therapeutic targets and biomarkers using animal models

The mucopolysaccharidoses (MPS) are inherited metabolic disorders resulting from the defective catabolism of glycosaminoglycans. In this report, we find that the stimulation of MPS connective tissue cells by the inflammatory cytokines causes enhanced secretion of several matrix-degrading metalloproteinases (MMPs). In addition, expression of tissue inhibitor of metalloproteinase-1 was elevated, consistent with the enhanced MMP activity. These findings were not restricted to one particular MPS disorder or species, and are consistent with previous observations in animal models with chemically induced arthritis. Bromodeoxyuridine incorporation studies also revealed that MPS chondrocytes proliferated up to 5-fold faster than normal chondrocytes, and released elevated levels of transforming growth factor-beta, presumably to counteract the marked chondrocyte apoptosis and matrix degradation associated with MMP expression. Despite this compensatory mechanism, studies of endochondral ossification revealed a reduction in chondro-differentiation in the growth plates. Thus, although MPS chondrocytes grew faster, most of the newly formed cells were immature and could not mineralize into bone. Our studies suggest that altered MMP expression, most likely stimulated by inflammatory cytokines and nitric oxide, is an important feature of the MPS disorders. These data also identify several proinflammatory cytokines, nitric oxide, and MMPs as novel therapeutic targets and/or biomarkers of MPS joint and bone disease. This information should aid in the evaluation of existing therapies for these disorders, such as enzyme replacement therapy and bone marrow transplantation, and may lead to the development of new therapeutic approaches.

Fourier transform infrared imaging spectroscopy analysis of collagenase-induced cartilage degradation

Collagenase treatment of cartilage serves as an in vitro model of the pathological collagen degradation that occurs in the disease osteoarthritis (OA). Fourier transform infrared imaging spectroscopic (FT-IRIS) analysis of collagenase-treated cartilage is performed to elucidate the molecular origin of the spectral changes previously found at the articular surface of human OA cartilage. Bovine cartilage explants are treated with 0.1% collagenase for 0, 15, or 30 min. In situ collagen cleavage is assessed using immunofluorescent staining with an antibody specific for broken type II collagen. The FT-IRIS analysis of the control and treated specimens mirrors the differences previously found between normal and OA cartilage using an infrared fiber optic probe (IFOP). With collagenase treatment, the amide II/1338 cm(-1) area ratio increases while the 1238 cm(-1)/1227 cm(-1) peak ratio decreases. In addition, polarized FT-IRIS demonstrates a more random orientation of the collagen fibrils that correlate spatially with the immunofluorescent-determined regions of broken type II collagen. We can therefore conclude that the spectral changes observed in the collagenase-treated cartilage, and similarly in OA cartilage, arise from changes in collagen structure. These findings support the use of mid-infrared spectral analysis, in particular the minimally invasive IFOP, as potential techniques for the diagnosis and management of degenerative joint diseases such as osteoarthritis.

Novel Biological Approaches to the Intra-Articular Treatment of Osteoarthritis

Osteoarthritis is common, incurable and difficult to treat. Because osteoarthritis is symptomatic only in a limited number of weight-bearing joints and lacks obvious extra-articular manifestations, it is well suited to local therapy administered by intra-articular injection. Several biologically based, local therapies of this type are either in clinical use or in development. Intra-articular injections of hyaluronic acid are widely used, but are highly controversial because their mode of action is unclear and clinical trials have provided contradictory results. The conclusions of meta-analyses are also discordant. An alternative therapy, based on the intra-articular injection of autologous conditioned serum, is used in Europe. This product, known as Orthokine, is generated by incubating venous blood with etched glass beads. In this way, peripheral blood leukocytes produce elevated amounts of the interleukin-1 receptor antagonist and other anti-inflammatory mediators that are recovered in the serum. Considerable symptomatic relief has been reported in clinical trials of this product. Alternatively, instead of injecting a heterogeneous, incompletely characterized mixture of native molecules into the joint, it is possible to inject recombinant growth factors and cytokine antagonists. None of these are in routine clinical use, but promising preliminary human trials have been performed with insulin-like growth factor-1 and the interleukin-1 receptor antagonist. It is possible that sustained intra-articular production of such factors could be achieved by gene transfer. Although gene therapy for osteoarthritis is not yet a clinical reality, the first human trial should begin next year.