Cell death in cartilage

Comparison of marker gene expression in chondrocytes from patients receiving autologous chondrocyte transplantation versus osteoarthritis patients

Currently, autologous chondrocyte transplantation (ACT) is used to treat traumatic cartilage damage or osteochondrosis dissecans, but not degenerative arthritis. Since substantial refinements in the isolation, expansion and transplantation of chondrocytes have been made in recent years, the treatment of early stage osteoarthritic lesions using ACT might now be feasible. In this study, we determined the gene expression patterns of osteoarthritic (OA) chondrocytes ex vivo after primary culture and subculture and compared these with healthy chondrocytes ex vivo and with articular chondrocytes expanded for treatment of patients by ACT. Gene expression profiles were determined using quantitative RT-PCR for type I, II and X collagen, aggrecan, IL-1β and activin-like kinase-1. Furthermore, we tested the capability of osteoarthritic chondrocytes to generate hyaline-like cartilage by implanting chondrocyte-seeded collagen scaffolds into immunodeficient (SCID) mice. OA chondrocytes ex vivo showed highly elevated levels of IL-1β mRNA, but type I and II collagen levels were comparable to those of healthy chondrocytes. After primary culture, IL-1β levels decreased to baseline levels, while the type II and type I collagen mRNA levels matched those found in chondrocytes used for ACT. OA chondrocytes generated type II collagen and proteoglycan-rich cartilage transplants in SCID mice. We conclude that after expansion under suitable conditions, the cartilage of OA patients contains cells that are not significantly different from those from healthy donors prepared for ACT. OA chondrocytes are also capable of producing a cartilage-like tissue in the in vivo SCID mouse model. Thus, such chondrocytes seem to fulfil the prerequisites for use in ACT treatment.

Major biological obstacles for persistent cell-based regeneration of articular cartilage

Hyaline articular cartilage, the load-bearing tissue of the joint, has very limited repair and regeneration capacities. The lack of efficient treatment modalities for large chondral defects has motivated attempts to engineer cartilage constructs in vitro by combining cells, scaffold materials and environmental factors, including growth factors, signaling molecules, and physical influences. Despite promising experimental approaches, however, none of the current cartilage repair strategies has generated long lasting hyaline cartilage replacement tissue that meets the functional demands placed upon this tissue in vivo. The reasons for this are diverse and can ultimately result in matrix degradation, differentiation or integration insufficiencies, or loss of the transplanted cells and tissues. This article aims to systematically review the different causes that lead to these impairments, including the lack of appropriate differentiation factors, hypertrophy, senescence, apoptosis, necrosis, inflammation, and mechanical stress. The current conceptual basis of the major biological obstacles for persistent cell-based regeneration of articular cartilage is discussed, as well as future trends to overcome these limitations.

Effects of delayed stabilization on fracture healing

Previous studies have revealed that delayed internal fixation can stimulate fracture callus formation and decrease the rate of nonunion. However, the effect of delayed stabilization on stem cell differentiation is unknown. To address this, we created fractures in mouse tibiae and applied external fixation immediately, at 24, 48, 72, or 96 h after injury. Fracture healing was analyzed at 10 days by histological methods for callus, bone, and cartilage formation, and the mechanical properties of the calluses were assessed at 14 days postinjury by tension testing. The results demonstrate that delaying stabilization for 24-96 h does not significantly affect the volume of the callus tissue (TV) and the new bone (BV) that formed by 10 days, or the mechanical properties of the calluses at 14 days, compared to immediate stabilization. However, delaying stabilization for 24-96 h induces 10-40x more cartilage in the fracture calluses compared with fractures stabilized immediately. These findings suggest that delaying stabilization during the early phase of fracture healing may not significantly stimulate bone repair, but may alter the mode of bone repair by directing formation of more cartilage. Fractures that are not rigidly stabilized form a significantly larger amount of callus tissue and cartilage by 10 days postinjury than fractures stabilized at 24-96 h, indicating that mechanical instability influences chondrocytes beyond the first 96 h of fracture healing.

Morphology, mechanisms and pathology of musculoskeletal ageing

In general terms, the recognized alterations in circulating humoral factors (hormones, cytokines, growth factors) that occur in ageing, coupled with innate cellular senescence exaggerated by the slow turnover of many connective tissue cell populations and the age-associated alterations in matrix molecule cross-linking, predispose the elderly to altered connective tissue biology. These changes can be profound, leading to poor mobility, altered ability to withstand cold, weakness and an increased risk of falls, fractures and age-associated 'degenerative' diseases, such as osteoarthritis and osteoporosis. As understanding of the causes of altered connective tissue function with age increases, it is becoming clearer that many of the predisposing factors (growth hormone, cytokines, load/life style) are potential targets for improving quality of life in the elderly.

[Histopathological examination of joint degeneration: typing, grading and staging of osteoarthritis]

Degenerative arthropathy (osteoarthritis) is one of the most common diseases in modern western societies, in particular in the elderly. The classification and grading of changes during cartilage degeneration represent complex endeavors which are only of limited value in daily pathological practice. In general, the process of joint destruction can always be evaluated for the determining pathogenesis ("typing"), extent ("staging") and degree of the most extensive focal damage ("grading"). However, for routine use one might best restrict description and reporting to the most essential features. This is in particular true for specimens obtained from endoprosthetic surgery (hips and knees), because there is currently no specific clinical relevance for further evaluation. Only the identification of secondary types of degenerative changes, such as those due to unknown rheumatoid disease, gout or extensive osteonecrosis, is of particular interest to the clinical colleague (i.e. typing of the joint lesion).

Detection and distribution of apoptotic cell death in normal and diseased canine cranial cruciate ligaments

One of the possible initiating factors in canine cranial cruciate ligament (CCL) rupture could be an abnormal pattern of ligament cell death. This study compared apoptotic cell death in sections of ruptured CCLs and normal controls, and examined nitric oxide (NO) production in joint tissues and correlated this to apoptosis. CCLs and cartilage from the lateral femoral condyle were harvested from 10 healthy dogs and 15 dogs with CCL rupture and ligaments were further processed to detect cleaved caspase-3 and to determine supernatant NO production in explant cultures. Apoptotic activity was greater in ruptured ligaments compared to controls. NO in ligaments showed a moderate but significant positive correlation with caspase-positive cells. The results suggest that increased apoptosis has a role in CCL rupture and that apoptosis may be influenced by local NO production.

Evaluation of Pentosan Polysulfate Sodium in the Postoperative Recovery from Cranial Cruciate Injury in Dogs: A Randomized, Placebo-Controlled Clinical Trial

OBJECTIVE

To evaluate the efficacy of pentosan polysulfate (PPS) for improving the recovery period and mitigate the progression of osteoarthritis (OA) of the canine stifle after extracapsular stabilization of cranial cruciate ligament (CCL) injuries.

STUDY DESIGN

Randomized, blinded, placebo-controlled clinical trial.

ANIMALS

Dogs (n=40) with unilateral CCL instability.

METHODS

Each dog had an extracapsular stabilization of the stifle with or without partial meniscectomy. Dogs were divided into 4 groups based on preoperative radiographic assessment and whether a partial meniscectomy was performed. Dogs were randomly assigned to either (3 mg/kg) PPS or placebo treatment in each group, and then injected subcutaneously weekly for 4 weeks. Lameness, radiographic changes, biological marker concentration in blood and urine, and ground reaction forces (GRFs) were collected preoperatively, and at 6, 12, 24, and 48 weeks. Data were analyzed within and between groups using repeated measures ANOVA; P<.05 was considered significant.

RESULTS

No adverse reactions to PPS were reported. Thirty-nine dogs completed a minimum of 24-weeks follow-up and 33 dogs completed 48 weeks. All dogs clinically improved after surgery without differences in lameness score, vertical GRFs, or radiographic progression. Grouped and evaluated only by initial radiographic score, PPS-treated dogs improved significantly faster in braking GRFs than placebo-treated dogs. In dogs with partial meniscectomies, urine deoxypyridinoline, and serum carboxy-propeptide of type II collagen were significantly increased at 6 weeks in placebo-treated dogs compared with PPS-treated dogs.

CONCLUSIONS

PPS administered after stabilization of the cruciate deficient stifle may prove to be a useful adjunctive treatment option, although further studies are necessary to substantiate this claim.

Chondrocyte hypertrophy can be induced by a cryptic sequence of type II collagen and is accompanied by the induction of MMP-13 and collagenase activity: implications for development and arthritis

The objective of this study was to determine whether a peptide of type II collagen which can induce collagenase activity can also induce chondrocyte terminal differentiation (hypertrophy) in articulate cartilage. Full depth explants of normal adult bovine articular cartilage were cultured with or without a 24 mer synthetic peptide of type II collagen (residues 195-218) (CB12-II). Peptide CB12-II lacks any RGD sequence and is derived from the CB12 fragment of type II collagen. Type II collagen cleavage by collagenase was measured by ELISA in cartilage and medium. Real-time RT-PCR was used to analyze gene expression of the chondrocyte hypertrophy markers COL10A1 and MMP-13. Immunostaining for anti-Ki67, anti-PCNA, (proliferation markers), type X collagen, cleavage of type II collagen by collagenases (hypertrophy markers) and TUNEL staining (hypertrophy and apoptosis markers) were used to detect progressive maturational stages of chondrocyte hypertrophy. At high but naturally occurring concentrations (10 microM and up) the collagen peptide CB12-II induced an increase in the expression of MMP-13 (24 h) and cleavage of type II collagen by collagenase in the mid zone (day 4) and also in the superficial zone (day 6). Furthermore the peptide induced an increase in proliferation on day 1 in the mid and deep zones extending to the superficial zone by day 4. There was also upregulation of COL10A1 expression at day 4 and of type X staining in the mid zone extending to the superficial zone by day 6. Apoptotic cell death was increased by day 4 in the lower deep zone and also in the superficial zone at day 7. The increase in apoptosis in the deep zone was also seen in controls. Our results show that the induction of collagenase activity by a cryptic peptide sequence of type II collagen, is accompanied by chondrocyte hypertrophy and associated with cellular and matrix changes. This induction occurs in the mid and superficial zones of previously healthy articular cartilage. This response of the chondrocyte to a cryptic sequence of denatured type II collagen may play a role in naturally occurring hypertrophy in endochondral ossification and in the development of cartilage pathology in osteoarthritis.

The development of posttraumatic arthritis after articular fracture

Posttraumatic arthritis (PTA) is one of the most frequent causes of disability after trauma involving weight-bearing joints and is estimated to be responsible for approximately 10% of the 21 million Americans who have osteoarthritis. Despite a number of similarities in the pathology and end-stage disease of PTA with primary osteoarthritis, the mechanisms involved in the onset and progression of joint degeneration after articular fracture are poorly understood. The largest area of study regarding articular fractures and the development of arthritic changes has focused on the role of adequate surgical reduction of the articular surfaces. However, it is now apparent that a number of complex and interacting biomechanical, biochemical, and, possibly, genetic factors contribute to the development of osteoarthritic changes in the joint after joint trauma, ranging from the cell and molecular level to the joint and systemic level. In this paper, we discuss the potential roles of the initial impact and fracture as well as the subsequent alterations in joint loading, biomechanical and metabolic properties of the cartilage, local and systemic inflammatory cytokines, and viability of chondrocytes in the progression of PTA. An improved understanding of the mechanisms involved in the development of PTA will hopefully lead to the improvement of surgical and nonsurgical therapies for this disease.

Posttraumatic osteoarthritis: a first estimate of incidence, prevalence, and burden of disease

Although posttraumatic osteoarthritis (OA) is a common and important entity in orthopedic practice, no data presently exist regarding its prevalence or its relative burden of disease. A population-based estimate was formulated, based on one large institution's experience in terms of its fraction of patients with OA presenting to lower-extremity adult reconstructive clinics with OA of posttraumatic origin. The relative proportion of these patients undergoing total joint replacement provided a basis for extrapolating institutional experience with posttraumatic OA to a populationwide estimate because the numbers of lower-extremity total joint arthroplasty procedures performed were reliably tabulated both within the institution and populationwide. By this methodology, approximately 12% of the overall prevalence of symptomatic OA is attributable to posttraumatic OA of the hip, knee, or ankle. This corresponds to approximately 5.6 million individuals in the United States being affected by posttraumatic OA sufficiently severe to have caused them to present for care by an orthopedic lower-extremity adult reconstructive surgeon. Further, based on the relative prevalence of OA versus rheumatoid arthritis, and their relative impacts as assessed by the SF-36 (Short-Form 36) lower-extremity physical composite scores, about 85.5% of the societal costs of arthritis are attributable to OA. The corresponding aggregate financial burden specifically of posttraumatic OA is Dollars 3.06 billion annually, or approximately 0.15% of the total U.S. health care direct cost outlay.

Gross, histologic, and gene expression characteristics of osteoarthritic articular cartilage of the metacarpal condyle of horses

OBJECTIVE

To identify patterns and correlations of gross, histologic, and gene expression characteristics of articular cartilage from horses with osteoarthritis.

ANIMALS

10 clinically normal horses and 11 horses with osteoarthritis of the metacarpal condyles.

PROCEDURES

Metacarpophalangeal joints were opened and digitally photographed, and gross lesions were scored and quantified. Representative cartilage specimens were stained for histologic scoring. Total RNA from dorsal and palmar articular surfaces was processed on an equine gene expression microarray.

RESULTS

Histologic scores were greater in both regions of osteoarthritic joints, compared with corresponding regions in control joints. Cartilage from the palmar aspect of diseased joints had the highest histologic scores of osteoarthritic sites or of either region in control joints. A different set of genes for dorsal and palmar osteoarthritis was identified for high and low gene expression. Articular cartilage from the dorsal region had surface fraying and greater expression of genes coding for collagen matrix components and proteins with anti-apoptotic function, compared with control specimens. Articular cartilage from the palmar region had greater fraying, deep fissures, and less expression of genes coding for glycosaminoglycan matrix formation and proteins with anti-apoptotic function, compared with cartilage from disease-free joints and the dorsal aspect of affected joints.

CONCLUSIONS AND CLINICAL RELEVANCE

Metacarpal condyles of horses with naturally occurring osteoarthritis had an identifiable and regional gene expression signature with typical morphologic features.

Chondrolysis after continuous intra-articular bupivacaine infusion: an experimental model investigating chondrotoxicity in the rabbit shoulder

PURPOSE

Postoperative pain pumps are increasingly used to deliver a continuous infusion of local anesthetic into the surgical wound or the joint. Recently, there have been concerns that the use of such devices may be associated with chondrotoxicity and even cases of chondrolysis in the shoulder. An experimental model is presented that investigates potential chondrotoxic effects of a continuous intra-articular infusion of bupivacaine in the rabbit shoulder.

METHODS

We divided 30 rabbits into 3 groups that received continuous infusions of either saline solution, bupivacaine, or bupivacaine with epinephrine into the glenohumeral joint over a period of 48 hours. Animals were killed after 1 week, and osteochondral and synovial samples from the glenohumeral joint underwent analyses with confocal microscopy for live/dead cell assay, metabolic sulfate uptake assessment, and conventional histologic analysis.

RESULTS

Infusion of bupivacaine with epinephrine and without epinephrine decreased sulfate uptake by 56% (P = .009) and 50% (P = .02), respectively, when compared with saline solution; cell viability decreased by 20% (P = .08) and 32% (P = .02), respectively. Histologic analysis yielded significantly worse scores for bupivacaine infusion with epinephrine (P = .004) and without epinephrine (P = .02). The results for bupivacaine with or without epinephrine were not significantly different.

CONCLUSIONS

Continuous intra-articular infusion of bupivacaine with and without epinephrine led to significant histopathologic and metabolic changes in articular cartilage.

CLINICAL RELEVANCE

Bupivacaine showed profound chondrotoxic effects in an experimental model that closely followed the current clinical application of postoperative pain pumps. The results caution against the use of such devices in applications for smaller joints with minimal clearance or dilution as a result of hematoma, where continuous exposure of cartilage to bupivacaine is expected.

Caspase inhibitors reduce severity of cartilage lesions in experimental osteoarthritis

OBJECTIVE

To examine the therapeutic efficacy of caspase inhibitors in experimental osteoarthritis (OA).

METHODS

Experimental OA was induced in rabbits by anterior cruciate ligament transection (ACLT). Rabbits were treated with intraarticular (i.a.) injections of caspase inhibitors 3 times per week starting 1 week postoperatively. Animals were killed 9 weeks after ACLT, for macroscopic, histologic, and immunohistochemical assessment of the knee joints.

RESULTS

I.a. administration of the pan-caspase inhibitor Z-VAD-FMK significantly reduced cartilage degradation, as assessed by macroscopic and microscopic criteria. Untreated knees showed large numbers of chondrocytes with active caspase 3 and the p85 fragment of poly(ADP-ribose) polymerase (PARP p85) that is generated during apoptosis. The frequency of cells positive for PARP p85 and active caspase 3 was reduced in Z-VAD-FMK-treated knees. Inhibitors specific for caspase 3 or caspase 8 showed no significant efficacy. Caspase 1 inhibitor and the combination of caspase 3 and caspase 8 inhibitors reduced OA pathology.

CONCLUSION

These results provide direct support for a role of cell death in OA pathogenesis. Caspase inhibitors reduced the severity of cartilage lesions in experimental OA, suggesting that they may have disease-modifying activity in human OA.

Chondrocyte cell death mediated by reactive oxygen species-dependent activation of PKC-betaI

Signals generated by the extracellular matrix (ECM) promote cell survival. We have shown that chondrocytes detached from their native ECM and plated without serum at low density on poly-l-lysine undergo significant cell death that is associated with the production of reactive oxygen species (ROS). No cell death or ROS production was observed when cells were plated on fibronectin under the same conditions. Cell death on poly-l-lysine could be completely inhibited with the addition of either antioxidants or inhibitors of specific protein kinase C (PKC) isoforms including PKC-betaI. PKC-betaI was noted to translocate from the cytosol to the particulate membrane after plating on poly-l-lysine, and this translocation was inhibited by the addition of an antioxidant. Time-course analyses implicated endogenous ROS production as a secondary messenger leading to PKC-betaI activation and subsequent chondrocyte cell death. Cell survival on poly-l-lysine was significantly improved in the presence of oligomycin or DIDS, suggesting that ROS production occurred via complex V of the electron transport chain of the mitochondria and that ROS were released to the cytosol via voltage-dependent anion channels. Together, these results represent a novel mechanism by which ROS can initiate cell death through the activation of PKC-betaI.

CD95-induced osteoarthritic chondrocyte apoptosis and necrosis: dependency on p38 mitogen-activated protein kinase

One of the hallmarks of osteoarthritic cartilage is the loss of chondrocyte cellularity due to cell death. However, considerable controversy has recently arisen surrounding the extent of apoptotic cell death involved in development of osteoarthritis (OA). To shed light on this issue, we characterized cell death in primary OA chondrocytes mediated by the CD95 (Fas) pathway. Treatment of chondrocytes with anti-CD95 not only increased the rate of cell death but also increased the production of CD95 ligand by chondrocytes. This reveals a novel autocrine regulatory loop whereby activated chondrocytes may amplify CD95 signals by inducing synthesis of CD95 ligand. Multiple morphologic detection analyses indicated that apoptosis accounted for only a portion of chondrocyte death, whereas the other chondrocytes died by necrosis. Both chondrocyte apoptosis and necrosis depended on the activity of p38 mitogen-activated protein kinase (MAPK) within chondrocytes. Treatment of chondrocytes with the p38 MAPK inhibitor SB203580 abolished anti-CD95 induced cell death by inhibiting the activities of activating transcription factor-2 and caspase-3. In addition, inhibition of p38 MAPK activity in chondrocytes stimulated chondrocyte proliferation, as indicated by 5-bromo-2-deoxyuridine (BrdU) index. Thus, p38 MAPK is a potential therapeutic target, inhibition of which may maintain the cellularity of articular chondrocytes by inhibiting cell death and its amplification signal and by increasing cell proliferation.

Upregulation of apoptotic and matrix-related gene expression during fresh osteochondral allograft storage

We identified changes in proapoptotic and extracellular matrix-related gene expression with prolonged storage of fresh osteochondral allografts using gene array analysis to better understand the process of graft degradation during storage. Six human distal femurs were obtained according to standard organ harvesting protocol and stored in serum-free allograft media. Each was examined at baseline (within 72 hours postmortem), 21 days (average time of implantation), and 35 days (maximum time to implantation) for proapoptotic and extracellular matrix-related gene expression using two 100-gene microarrays, cell viability using confocal microscopy, and proteoglycan synthesis via SO4 incorporation. We found numerous genes showing upregulation associated with increased storage time, including CD30, CD30 ligand, Fas, Fas ligand, tumor necrosis factor-alpha, and several caspases. Cell viability and proteoglycan synthesis also were significantly decreased with increased storage. Loss of chondrocytes via apoptosis is likely a key determinant of osteochondral allograft viability during storage, whereas extracellular matrix degeneration may occur at a later stage. These findings provide targets for future media modulation. Improved graft viability and the potential for lengthened storage periods through improved storage conditions may improve clinical outcomes and availability of fresh osteochondral allografts.

Gene transfer with HSP 70 in rat chondrocytes confers cytoprotection in vitro and during experimental osteoarthritis

Osteoarthritis is characterized by a gradual degradation of extracellular matrix, resulting from an excess of chondrocyte cell death, mainly due to an increase in apoptotis. Recent studies have revealed the essential role of HSP70 in protecting cells from stressful stimuli. Therefore, overexpressing HSP70 in chondrocytes could represent a good strategy to prevent extracellular matrix destruction. To this end, we have developed a vector carrying HSP70/GFP, and transduced chondrocytes were thus more resistant to cell death induced by mono-iodoacetate (MIA). To overcome the barrier-effect of matrix, we investigated the efficacy of plasmid delivery by electroporation (EP) in rat patellar cartilage. Two days after EP, 50% of patellar chondrocytes were HSP/GFP+. After 3 months, long-term expression of transgene was only depicted in the deep layer (20-30% positive cells). HSP70 overexpression inhibited the natural endochondral ossification in the deep layer, thus leading to a lesser decrease in chondrocyte distribution. Moreover, overexpression of HSP70, after a preventive EP transfer in rat patella, was sufficient to decrease the severity of osteoarthritis-induced lesions, as demonstrated histologically and biochemically. In conclusion, intracellular overexpression of HSP70, through EP delivery, could protect chondrocytes from cellular injuries and thus might be a novel chondroprotective modality in rat OA.

Osteoarthritis cartilage histopathology: grading and staging

OBJECTIVE

Current osteoarthritis (OA) histopathology assessment methods have difficulties in their utility for early disease, as well as their reproducibility and validity. Our objective was to devise a more useful method to assess OA histopathology that would have wide application for clinical and experimental OA assessment and would become recognized as the standard method.

DESIGN

An OARSI Working Group deliberated on principles, standards and features for an OA cartilage pathology assessment system. Using current knowledge of the pathophysiology of OA morphologic features, a proposed system was presented at OARSI 2000. Subsequently, this was widely circulated for comments amongst experts in OA pathology.

RESULTS

An OA cartilage pathology assessment system based on six grades, which reflect depth of the lesion and four stages reflecting extent of OA over the joint surface was developed.

CONCLUSIONS

The OARSI cartilage OA histopathology grading system appears consistent and simple to apply. Further studies are required to confirm the system's utility.

Transforming growth factor-beta2 suppresses collagen cleavage in cultured human osteoarthritic cartilage, reduces expression of genes associated with chondrocyte hypertrophy and degradation, and increases prostaglandin E(2) production

Articular cartilage degeneration in osteoarthritis (OA) involves type II collagen degradation and chondrocyte differentiation (hypertrophy). Because these changes resemble growth plate remodeling, we hypothesized that collagen degradation may be inhibitable by growth factors known to suppress growth plate hypertrophy, namely transforming growth factor (TGF)-beta2, fibroblast growth factor (FGF)-2, and insulin. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with TGF-beta2, FGF-2, and insulin in combination (growth factors) or individually. In cultured explants from five OA patients, collagenase-mediated type II collagen cleavage was significantly down-regulated by combined growth factors as measured by enzyme-linked immunosorbent assay. Individually, FGF-2 and insulin failed to inhibit collagen cleavage in some OA explants whereas TGF-beta2 reduced collagen cleavage in these 5 explants and in 19 additional explants. Moreover, TGF-beta2 effectively suppressed cleavage at low concentrations. Together or individually these growth factors did not inhibit glycosaminoglycan (primarily aggrecan) degradation while TGF-beta2 occasionally did. Semiquantitative reverse transcriptase-polymerase chain reaction of articular cartilage from six OA patients revealed that TGF-beta2 suppressed expression of matrix metalloproteinase-13 and matrix metalloproteinase-9, early (PTHrP) and late (COL10A1) differentiation-related genes, and proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha). In contrast, TGF-beta2 up-regulated PGES-1 expression and prostaglandin E(2) release. These observations show that TGF-beta2 can suppress collagen resorption and chondrocyte differentiation in OA cartilage and that this may be mediated by prostaglandin E(2). Therefore TGF-beta2 could provide therapeutic control of type II collagen degeneration in OA.

Cell and matrix morpho-functional analysis in chondrocyte micromasses

Micromass cultures represent a convenient means of studying chondrocyte physiology in the context of a tridimensional culture model. In this study, we present the first ultrastructural analysis of the distribution and organization of the extracellular components in micromasses in comparison with their cartilaginous counterparts. Primary chondrocytes obtained from osteoarthritis patients were pelleted in micromasses. Transmission electron microscopy and immunofluorescence were used to evaluate the distribution of major extracellular matrix proteins, i.e., aggrecan, chondroitin-4-sulfate, chondroitin-6-sulfate, and collagen I and II. Both approaches revealed a number of morphological features shared by micromass and cartilage chondrocytes. In particular, in micromasses, chondrocytes are in close contact with an organized extracellular matrix that adequately mimics that of cartilage. Cells were observed to establish specialized junctions for cell-extracellular matrix crosstalk. Noteworthy, cells seem endowed in a chondroitin sulfate-rich microenvironment, and thus possibly ensuring the immobilization of chemokines, a family of molecules emerging in osteoarthritis pathogenesis, in a haptotactic-like gradient to the chondrocytes, which facilitates the binding to their receptors. To determine the suitability of this model to investigate osteoarthritis pathogenesis, a potential apoptotic stimulus (endothelial IL-8) was used, and ultrastructural analysis assessed apoptosis induction. Micromass cultures were proved to be an experimental technique providing a large number of properly differentiated chondrocytes, and thus allowing reliable biochemical and morphological studies. They represent, therefore, a novel approach to osteoarthritis investigation that promises more thorough understanding of chondrocyte physiology in osteoarthritis.

Skeletal developmental effects of selective and nonselective cyclooxygenase-2 inhibitors administered through organogenesis and fetogenesis in Wistar CRL:(WI)WUBR rats

Cyclooxygenase (COX) inhibitors are the most commonly ingested drugs. The aim of the study was to evaluate the prenatal skeletal effect of selective (DFU) and nonselective (tolmetin, ibuprofen, piroxicam) COX-2 inhibitors. All the tested compounds were administered intragastrically to pregnant Wistar rats from 7 to 21 gestation day. The initial dose was set at 8.5mg/kg/dose for tolmetin and ibuprofen, 0.3 and 0.2mg/kg/dose for piroxicam and DFU. The middle dose was increased 10-times. The highest dose, except for ibuprofen, was elevated 100-times. The highest dose for ibuprofen was set at 200mg/kg/dose. Tolmetin and ibuprofen were administered three times a day. Piroxicam and DFU were dosed once daily. After routine teratological examinations, extremities of randomly selected 21-day-old fetuses were taken for histological, immunohistochemical and molecular studies. The proximal femoral epiphyses were separated and their ultrastructure evaluated. The expression of genes coding cytokines (IL-1alpha, IL-1beta, IL-6, TNF-alpha, TNF-beta) and proteins (COX-1, COX-2, cathepsin K, collagen types I, II and X; osteocalcin, osteopontin) was evaluated in femoral epiphyses by RNase Protection Assay and/or immunohistochemically. The articulate development was checked histologically and found undisturbed in any of the experimental groups. The epiphysis of the 21-day-old fetuses, presented physiological expression of COX-1 and COX-2, as well as cathepsin K, collagen types I, II and X; osteopontin, osteocalcin and TNF-alpha. Increased developmental skeletal variation was noted in groups exposed to the highest dose of nonselective drugs. Unlike the increased number of skeletal variations observed in fetuses exposed to highest doses of nonselective compounds, both groups of COX inhibitors did not disturb joint formation and morphology of femoral epiphyses when administered even in high maternal toxic doses.

Pathomechanisms of cartilage destruction by mechanical injury

Mechanical injury is considered to be a major inductor of articular cartilage destruction and therefore a risk factor for the development of secondary osteoarthritis. Mechanical injury induces damage to the tissue matrix directly or mediated by chondrocytes via expression of matrix-degrading enzymes and reduction of biosynthetic activity. As a consequence the mechanical properties of cartilage change. Some of the pathomechanisms of mechanical injury have already been uncovered by the use of a broad range of in vitro-models. They demonstrate that mechanical injury induces tissue swelling and decrease in both the compressive and shear stiffness of articular cartilage, probably due to disruption of the collagen network. Injurious compression induces chondrocyte death by necrosis and apoptosis and the remaining cells decrease their biosynthetic activity. The tissue content of proteoglycans also decreases with time in injured cartilage, and the tissue loses its ability to respond to physiological levels of mechanical stimulation with an increase in biosynthesis. Immature cartilage seems to be more vulnerable to injurious compression than more mature tissue. The expression of several matrix-degrading enzymes like ADAM-TS5 and matrix-metalloproteinases (MMP-1, MMP-2, MMP-3, MMP-9, MMP-13) is increased after injury and may in part be regulated by an autocrine vascular endothelial growth factor (VEGF)-dependent signalling pathway. Apoptosis seems to be mediated by caspase activity and reactive oxygen species. For that reason activation of antioxidative defense mechanisms as well as the inhibition of angiogenetic factors and MMPs might be key regulators in the mechanically induced destruction of cartilage and might be suggested as potential therapeutic interventions. This review summarizes some of the most important data from in vitro injury studies dealing with the pathomechanisms of cartilage destruction.

Effects of pulsed electromagnetic fields on articular hyaline cartilage: review of experimental and clinical studies

Osteoarthritis (OA) is the most common disorder of the musculoskeletal system and is a consequence of mechanical and biological events that destabilize tissue homeostasis in articular joints. Controlling chondrocyte death and apoptosis, function, response to anabolic and catabolic stimuli, matrix synthesis or degradation and inflammation is the most important target of potential chondroprotective treatment, aimed to retard or stabilize the progression of OA. Although many drugs or substances have been recently introduced for the treatment of OA, the majority of them relieve pain and increase function, but do not modify the complex pathological processes that occur in these tissues. Pulsed electromagnetic fields (PEMFs) have a number of well-documented physiological effects on cells and tissues including the upregulation of gene expression of members of the transforming growth factor beta super family, the increase in glycosaminoglycan levels, and an anti-inflammatory action. Therefore, there is a strong rationale supporting the in vivo use of biophysical stimulation with PEMFs for the treatment of OA. In the present paper some recent experimental in vitro and in vivo data on the effect of PEMFs on articular cartilage were reviewed. These data strongly support the clinical use of PEMFs in OA patients.

Down regulation of degenerative cartilage molecules in chondrocytes grown on a hyaluronan-based scaffold

Hyaluronic-acid-based biomaterials used for cartilage repair allow the expression of specific extracellular matrix molecules by human chondrocytes grown onto them. We investigated whether these biomaterials could also create an environment in which the cells downregulate the expression of some catabolic factors. Chondrocytes were isolated from human articular cartilage obtained from the knees of patients with a history of trauma. First, the cells were expanded in monolayers and then they were seeded on a hyaluronic-acid derivative scaffold. Constructs and surnatants were collected and analysed at 1, 3, 7, 14 and 21 days after seeding. Immunohistochemical analysis for CD44 and caspase was carried out on paraffin-embedded sections. The Tunel method was used to identify chondrocyte apoptosis status. Secretion of MMP-1 and MMP-13 in the surnatants of the cells grown onto the biomaterial was measured by enzyme-linked immunosorbent assay. Nitric oxide (NO) production was evaluated by estimating the stable NO metabolite nitrite by the Griess method. A real-time RT-PCR analysis was performed on the constructs to evaluate the expression of type I and II collagens, aggrecan, Sox-9, MMP-1 and MMP-13 mRNAs at the different experimental times evaluated. Decreased levels of metalloproteinases and nitric oxide were observed in the surnatants of chondrocytes grown onto the hyaluronan-based scaffold. This was also confirmed by real-time PCR analysis which showed that the cells expressed the specific differentiated phenotype downregulating the expression of some catabolic molecules. Cells apoptosis decreased during the culture period, which further supported the biochemical data. The ability of the hyaluronan scaffold to reduce the expression and production of molecules involved in cartilage degenerative diseases indicates its use to treat early lesions of osteoarthritic patients.

Oxygen and reactive oxygen species in cartilage degradation: friends or foes?

OBJECTIVES

This review is focused on the influence of oxygen and derived reactive species on chondrocytes aging, metabolic function and chondrogenic phenotype.

METHODS

A systematic computer-aided search of the Medline database.

RESULTS

Articular cartilage is an avascular tissue, and consequently oxygen supply is reduced. Although the basal metabolic functions of the cells are well adapted to hypoxia, the chondrocyte phenotype seems to be oxygen sensitive. In vitro, hypoxia promotes the expression of the chondrogenic phenotype and cartilage-specific matrix formation, indicating that oxygen tension is probably a key parameter in chondrocyte culture, and particularly in the context of tissue engineering and stem cells transplantation. Besides the influence of oxygen itself, reactive oxygen species (ROS) play a crucial role in the regulation of a number of basic chondrocyte activities such as cell activation, proliferation and matrix remodeling. However, when ROS production exceeds the antioxidant capacities of the cell, an "oxidative stress" occurs leading to structural and functional cartilage damages like cell death and matrix degradation.

CONCLUSIONS

This paper is an overview of the in vitro and in vivo studies published on the influence of oxygen and derived reactive species on chondrocyte aging, metabolic function, and the chondrogenic phenotype. It shows, that oxygen and ROS play a crucial role in the control of cartilage homeostasis and that at this time, the exact role of "oxidative stress" in cartilage degradation still remains questionable.

Development of comprehensive functional genomic screens to identify novel mediators of osteoarthritis

OBJECTIVE

The aim of this study was to develop high-throughput assays for the analysis of major chondrocyte functions that are important in osteoarthritis (OA) pathogenesis and methods for high-level gene expression and analysis in primary human chondrocytes.

METHODS

In the first approach, complementary DNA (cDNA) libraries were constructed from OA cartilage RNA and full-length clones were selected. These cDNAs were transferred into a retroviral vector using Gateway Technology. Full-length clones were over-expressed in human articular chondrocytes (HAC) by retroviral-mediated gene transfer. The induction of OA-associated markers, including aggrecanase-1 (Agg-1), matrix metalloproteinase-13 (MMP-13), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), collagen IIA and collagen X was measured by quantitative real-time polymerase chain reaction (QPCR). Induction of a marker gene was verified by independent isolation of 2-3 clones per gene, re-transfection followed by QPCR as well as nucleotide sequencing. In the second approach, whole cDNA libraries were transduced into chondrocytes and screened for chondrocyte cluster formation in three-dimensional agarose cultures.

RESULTS

Using green fluorescent protein (eGFP) as a marker gene, it was shown that the retroviral method has a transduction efficiency of >90%. A total of 40 verified hits were identified in the QPCR screen. The first set of 19 hits coordinately induced iNOS, COX-2, Agg-1 and MMP-13. The most potent of these genes were the tyrosine kinases Axl and Tyro-3, receptor interacting kinase-2 (RIPK2), tumor necrosis factor receptor 1A (TNFR1A), fibroblast growth factor (FGF) and its receptor FGFR, MUS81 endonuclease and Sentrin/SUMO-specific protease 3. The second set of seven hits induced both Agg-1 and MMP-13 but none of the other markers. Five of these seven genes regulate the phosphoinositide-3-kinase pathway. The most potently induced OA marker was iNOS. This marker was induced 20-500 fold by seven genes. Collagen IIA was also induced by seven genes, the most potent being transforming growth factor beta (TGFbeta)-stimulated protein TSC22, vascular endothelial growth factor (VEGF) and splicing factor 3a. This screening assay did not identify inducers of collagen X. The second chondrocyte cluster formation screen identified 14 verified hits. Most of the genes inducing cluster formation were kinases. Additional genes had not been previously known to regulate chondrocyte cluster formation or any other chondrocyte function.

CONCLUSIONS

The methods developed in this study can be applied to screen for genes capable of inducing an OA-like phenotype in chondrocytes on a genome-wide scale and identify novel mediators of OA pathogenesis. Thus, coordinated functional genomic approaches can be used to delineate key genes and pathways activated in complex human diseases such as OA.

Aging bone and cartilage: cross-cutting issues

Aging is a major risk factor for osteoarthritis and osteoporosis. Yet, these are not necessary outcomes of aging, and the relationship between age-related changes in bone and cartilage and development of disease is not clear. There are some well-described cellular changes associated with aging in multiple tissues that appear to be fundamental to the decline in function of cartilage and bone. A better understanding of age-related changes in cells and tissues is necessary to mitigate or, hopefully, avoid loss of bone and cartilage with aging. In addition, a better understanding of the dynamics of tissue maintenance in vivo is critical to developing tissue replacement and repair therapies. The role of stem cells in this process, and why tissues are not well maintained with advancing age, are frontiers for future aging research.

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.

Under-sulfation by PAPS synthetase inhibition modulates the expression of ECM molecules during chondrogenesis

Sulfation of proteoglycans is an important post-translational modification in chondrocytes. We previously found that 3'-phosphoadenosine 5'-phosphosulfate (PAPS) synthetase-2 levels increased more than 10-fold during mesenchymal cell chondrogenesis. Given that PAPS is the sole sulfur donor, and is produced only by PAPS synthetase in all cells, increased expression of PAPS synthetase-2 should be a prerequisite for increased sulfation activity of chondrocytes. We found that sodium chlorate, a specific inhibitor of PAPS synthetase, inhibited proteoglycan sulfation during chondrogenesis. In contrast, sodium chlorate unexpectedly induced early expression of type II collagen and increased the number of cartilage nodules during chondrogenesis. Inhibition of sulfation also accelerated the down-regulation of N-cadherin and fibronectin during chondrogenesis. These findings suggest that sulfation has an important regulatory role in coordinating the timely expression of extracellular matrix molecules during chondrogenesis, and that under-sulfation may cause the breakdown of this coordination, leading to premature chondrogenesis.