Inhibition of cartilage degradation and changes in physical properties induced by IL-1beta and retinoic acid using matrix metalloproteinase inhibitors

Candidate pathways for retina to scleral signaling in refractive eye growth

The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to reaching the retinal photoreceptors, which indicates a mismatch in its shape and optical power. This mismatch commonly results from excessive axial elongation. Important drivers of the myopia epidemic include environmental factors, genetic factors, and their interactions, e.g., genetic factors influencing the effects of environmental factors. One factor often hypothesized to be a driver of the myopia epidemic is environmental light, which has changed drastically and rapidly on a global scale. In support of this, it is well established that eye size is regulated by a homeostatic process that incorporates visual cues (emmetropization). This process allows the eye to detect and minimize refractive errors quite accurately and locally over time by modulating the rate of elongation of the eye via remodeling its outermost coat, the sclera. Critically, emmetropization is not dependent on post-retinal processing. Thus, visual cues appear to influence axial elongation through a retina-to-sclera, or retinoscleral, signaling cascade, capable of transmitting information from the innermost layer of the eye to the outermost layer. Despite significant global research interest, the specifics of retinoscleral signaling pathways remain elusive. While a few pharmacological treatments have proven to be effective in slowing axial elongation (most notably topical atropine), the mechanisms behind these treatments are still not fully understood. Additionally, several retinal neuromodulators, neurotransmitters, and other small molecules have been found to influence axial length and/or refractive error or be influenced by myopigenic cues, yet little progress has been made explaining how the signal that originates in the retina crosses the highly vascular choroid to affect the sclera. Here, we compile and synthesize the evidence surrounding three of the major candidate pathways receiving significant research attention - dopamine, retinoic acid, and adenosine. All three candidates have both correlational and causal evidence backing their involvement in axial elongation and have been implicated by multiple independent research groups across diverse species. Two hypothesized mechanisms are presented for how a retina-originating signal crosses the choroid - via 1) all-trans retinoic acid or 2) choroidal blood flow influencing scleral oxygenation. Evidence of crosstalk between the pathways is discussed in the context of these two mechanisms.

Oroxylin A attenuates IL-1β-induced inflammatory reaction via inhibiting the activation of the ERK and PI3K/AKT signaling pathways in osteoarthritis chondrocytes

Osteoarthritis (OA) is characterized by degradation of the articular cartilage, synovium inflammation, subchondral bone sclerosis and osteophyte formation. OA is the most common degenerative joint disorder among the elderly population. In particular, currently available therapeutic strategies, such as non-steroidal anti-inflammatory drugs (NSAIDs) may cause severe side-effects. Therefore, novel candidate targets for OA therapy are urgently needed. Oroxylin A (OrA) is a natural mono-flavonoid that can be extracted from Scutellariae radix. The present study aimed to investigate the potential effects of OrA on interleukin (IL)-1β-induced chondrocytes inflammatory reactions. The current study performed quantitative PCR, western blotting and cell immunofluorescence to evaluate the effect of Oroxylin A in chondrocyte inflammation. The results demonstrated that OrA significantly attenuated the upregulation of inducible nitric oxide synthase and cyclooxygenase 2 by IL-1β at both protein and mRNA levels. IL-1β-stimulated upregulation of matrix metalloproteinase (MMP)-3 and MMP-13 expression, in addition to disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5 expression, were all inhibited by OrA. Treatment with OrA significantly reversed the degradation of type II collagen and aggrecan by IL-1β. Mechanistically, OrA suppressed the IL-1β induced activation of ERK1/2 and PI3K/AKT signaling pathways. In conclusion, these findings suggest that OrA can serve as a potential therapeutic agent for the treatment of OA.

Plumbagin Prevents IL-1β-Induced Inflammatory Response in Human Osteoarthritis Chondrocytes and Prevents the Progression of Osteoarthritis in Mice

Inflammation and inflammatory cytokines have been reported to play vital roles in the development of osteoarthritis (OA). Plumbagin, a quinonoid compound extracted from the roots of medicinal herbs of the Plumbago genus, has been reported to have anti-inflammatory effects. However, the anti-inflammatory effects of plumbagin on OA have not been reported. This study aimed to assess the effects of plumbagin on human OA chondrocytes and in a mouse model of OA induced by destabilization of the medial meniscus (DMM). In vitro, human OA chondrocytes were pretreated with plumbagin (2, 5, 10 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. Production of NO, PGE2, MMP-1, MMP-3, and MMP-13 was evaluated by the Griess reagent and ELISAs. The messenger RNA (mRNA) expression of COX-2, iNOS, MMP-1, MMP-3, MMP-13, aggrecan, and collagen-II was measured by real-time PCR. The protein expression of COX-2, iNOS, p65, p-p65, IκBα, and p-IκBα was detected by Western blot. The protein expression of collagen-II was evaluated by immunofluorescence. In vivo, the severity of OA was determined by histological analysis. We found that plumbagin significantly inhibited the IL-1β-induced production of NO and PGE2; expression of COX-2, iNOS, MMP-1, MMP-3, and MMP-13; and degradation of aggrecan and collagen-II. Furthermore, plumbagin dramatically suppressed IL-1β-stimulated NF-κB activation. In vivo, treatment of plumbagin not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in mice OA models. Taken together, these results suggest that plumbagin may be a potential agent in the treatment of OA.

Effects of Inflammation on Multiscale Biomechanical Properties of Cartilaginous Cells and Tissues

Cells within cartilaginous tissues are mechanosensitive and thus require mechanical loading for regulation of tissue homeostasis and metabolism. Mechanical loading plays critical roles in cell differentiation, proliferation, biosynthesis, and homeostasis. Inflammation is an important event occurring during multiple processes, such as aging, injury, and disease. Inflammation has significant effects on biological processes as well as mechanical function of cells and tissues. These effects are highly dependent on cell/tissue type, timing, and magnitude. In this review, we summarize key findings pertaining to effects of inflammation on multiscale mechanical properties at subcellular, cellular, and tissue level in cartilaginous tissues, including alterations in mechanotransduction and mechanosensitivity. The emphasis is on articular cartilage and the intervertebral disc, which are impacted by inflammatory insults during degenerative conditions such as osteoarthritis, joint pain, and back pain. To recapitulate the pro-inflammatory cascades that occur in vivo, different inflammatory stimuli have been used for in vitro and in situ studies, including tumor necrosis factor (TNF), various interleukins (IL), and lipopolysaccharide (LPS). Therefore, this review will focus on the effects of these stimuli because they are the best studied pro-inflammatory cytokines in cartilaginous tissues. Understanding the current state of the field of inflammation and cell/tissue biomechanics may potentially identify future directions for novel and translational therapeutics with multiscale biomechanical considerations.

Effects of platycodin D on IL-1β-induced inflammatory response in human osteoarthritis chondrocytes

Platycodin D (PYD), a major saponin derived and isolated from the roots of Platycodon grandiflorum, has been reported to have anti-inflammatory and anti-tumor effects. The present study aimed to investigate the effects of PYD on IL-1β-stimulated human osteoarthritis chondrocytes. Chondrocytes were treated with PYD 1h before IL-1β treatment. The levels of MMP1, MMP13, IL-8, RANTES, PGE2, and NO were measured in this study. The expression of LXRα, NF-κB, and IκBα were detected by western blot analysis. The results showed that PYD significantly inhibited IL-1β-induced MMP1, MMP13, IL-8, RANTES, PGE2, and NO production. PYD also suppressed IL-1β-induced NF-κB activation. Furthermore, the expression of LXRα was up-regulated by PYD in a dose-dependent manner. In addition, LXRα siRNA inhibited the effects of PYD on MMP1, MMP13, PGE2, and NO production in human osteoarthritis chondrocytes. In conclusion, these results suggested that PYD attenuated IL-1β-induced inflammatory response in osteoarthritis chondrocyte by activating LXRα.

Bovine meniscal tissue exhibits age- and interleukin-1 dose-dependent degradation patterns and composition-function relationships

Despite increasing evidence that meniscal degeneration is an early event in the development of knee osteoarthritis, relatively little is known regarding the sequence or functional implications of cytokine-induced meniscal degradation or how degradation varies with age. This study examined dose-dependent patterns of interleukin-1 (IL-1)-induced matrix degradation in explants from the radially middle regions of juvenile and adult bovine menisci. Tissue explants were cultured for 10 days in the presence of 0, 1.25, 5, or 20 ng/ml recombinant human IL-1α. Juvenile explants exhibited immediate and extensive sulfated glycosaminoglycan (sGAG) loss and subsequent collagen release beginning after 4-6 days, with relatively little IL-1 dose-dependence. Adult explants exhibited a more graded response to IL-1, with dose-dependent sGAG release and a lower fraction of sGAG released (but greater absolute release) than juvenile explants. In contrast to juvenile explants, adult explants exhibited minimal collagen release over the 10-day culture. Compressive and shear moduli reflected the changes in explant composition, with substantial decreases for both ages but a greater relative decrease in juvenile tissue. Dynamic moduli exhibited stronger dependence on explant sGAG content for juvenile tissue, likely reflecting concomitant changes to both proteoglycan and collagen tissue components. The patterns of tissue degradation suggest that, like in articular cartilage, meniscal proteoglycans may partially protect collagen from cell-mediated degeneration. A more detailed view of functional changes in meniscal tissue mechanics with degeneration will help to establish the relevance of in vitro culture models and will advance understanding of how meniscal degeneration contributes to overall joint changes in early stage osteoarthritis. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:801-811, 2016.

Lithium chloride prevents interleukin-1β induced cartilage degradation and loss of mechanical properties

Osteoarthritis is a chronic degenerative disease that affects the articular cartilage. Recent studies have demonstrated that lithium chloride exhibits significant efficacy as a chondroprotective agent, blocking cartilage degradation in response to inflammatory cytokines. However, conflicting literature suggests lithium may affect the physicochemical properties of articular cartilage and thus long-term exposure may negatively affect the mechanical functionality of this tissue. This study aims to investigate the effect of lithium chloride on the biomechanical properties of healthy and interleukin-1β treated cartilage in vitro and examines the consequences of long-term exposure to lithium on cartilage health in vivo. Bovine cartilage explants were treated with lithium chloride for 12 days. Chondrocyte viability, matrix catabolism and the biomechanical properties of bovine cartilage explants were not significantly altered following treatment. Consistent with these findings, long term-exposure (9 months) to dietary lithium did not induce osteoarthritis in rats, as determined by histological staining. Moreover, lithium chloride did not induce the expression of catabolic enzymes in human articular chondrocytes. In an inflammatory model of cartilage destruction, lithium chloride blocked interleukin-1β signaling in the form of nitric oxide and prostaglandin E2 release and prevented matrix catabolism such that the loss of mechanical integrity observed with interleukin-1β alone was inhibited. This study provides further support for lithium chloride as a novel compound for the treatment of osteoarthritis.

Is collagen fiber damage the cause of early softening in articular cartilage?

OBJECTIVE

Because collagen damage and cartilage softening have not yet been determined simultaneously in one study for the very early onset of osteoarthritis (OA), it remains questionable whether they are associated. The aim of the present study is therefore to evaluate whether indeed, initial collagen damage can be found when tissue softening occurs as a result of excessive mechanical loading.

METHODS

To investigate this aim, a series of specific indentation loading protocols were designed to induce and monitor cartilage softening in osteochondral explants of bovine carpometacarpal joints. The experiment contained one control group (n = 6) in which no damage was induced and four experimental groups in which samples received either a constant load of 3 (n = 5), 6 (n = 5) or 15 N (n = 6), or an increasing load (n = 7) from 2 to 13 N in 11 steps. Moreover, to determine mechanically induced collagen damage, Col2-3/4M (cumulative collagen damage) and Col2-3/4C(short) (only enzymatic damage) staining were compared.

RESULTS

The normalized peak and equilibrium reaction forces decreased in the groups that received increasing and 15 N peak loading. However, Col2-3/4M staining was negative in all samples, while enzymatic damage (Col2-3/4C(short)) appeared similar in experiments and in unloaded control groups.

CONCLUSION

It was shown that a loading magnitude threshold exists above which softening occurs in cartilage. However, in samples that did show softening, we were unable to detect collagen damage. Thus, our results demonstrate that cartilage softening most likely precedes collagen damage.

Streaming potential-based arthroscopic device is sensitive to cartilage changes immediately post-impact in an equine cartilage injury model

Models of post-traumatic osteoarthritis where early degenerative changes can be monitored are valuable for assessing potential therapeutic strategies. Current methods for evaluating cartilage mechanical properties may not capture the low-grade cartilage changes expected at these earlier time points following injury. In this study, an explant model of cartilage injury was used to determine whether streaming potential measurements by manual indentation could detect cartilage changes immediately following mechanical impact and to compare their sensitivity to biomechanical tests. Impacts were delivered ex vivo, at one of three stress levels, to specific positions on isolated adult equine trochlea. Cartilage properties were assessed by streaming potential measurements, made pre- and post-impact using a commercially available arthroscopic device, and by stress relaxation tests in unconfined compression geometry of isolated cartilage disks, providing the streaming potential integral (SPI), fibril modulus (Ef), matrix modulus (Em), and permeability (k). Histological sections were stained with Safranin-O and adjacent unstained sections examined in polarized light microscopy. Impacts were low, 17.3 ± 2.7 MPa (n = 15), medium, 27.8 ± 8.5 MPa (n = 13), or high, 48.7 ± 12.1 MPa (n = 16), and delivered using a custom-built spring-loaded device with a rise time of approximately 1 ms. SPI was significantly reduced after medium (p = 0.006) and high (p<0.001) impacts. Ef, representing collagen network stiffness, was significantly reduced in high impact samples only (p < 0.001 lateral trochlea, p = 0.042 medial trochlea), where permeability also increased (p = 0.003 lateral trochlea, p = 0.007 medial trochlea). Significant (p < 0.05, n = 68) moderate to strong correlations between SPI and Ef (r = 0.857), Em (r = 0.493), log(k) (r = -0.484), and cartilage thickness (r = -0.804) were detected. Effect sizes were higher for SPI than Ef, Em, and k, indicating greater sensitivity of electromechanical measurements to impact injury compared to purely biomechanical parameters. Histological changes due to impact were limited to the presence of superficial zone damage which increased with impact stress. Non-destructive streaming potential measurements were more sensitive to impact-related articular cartilage changes than biomechanical assessment of isolated samples using stress relaxation tests in unconfined compression geometry. Correlations between electromechanical and biomechanical methods further support the relationship between non-destructive electromechanical measurements and intrinsic cartilage properties.

Effects of Refrigeration and Freezing on the Electromechanical and Biomechanical Properties of Articular Cartilage

In vitro electromechanical and biomechanical testing of articular cartilage provide critical information about the structure and function of this tissue. Difficulties obtaining fresh tissue and lengthy experimental testing procedures often necessitate a storage protocol, which may adversely affect the functional properties of cartilage. The effects of storage at either 4°C for periods of 6 days and 12 days, or during a single freeze-thaw cycle at −20°C were examined in young bovine cartilage. Non-destructive electromechanical measurements and unconfined compression testing on 3 mm diameter disks were used to assess cartilage properties, including the streaming potential integral (SPI), fibril modulus (Ef), matrix modulus (Em), and permeability (k). Cartilage disks were also examined histologically. Compared with controls, significant decreases in SPI (to 32.3±5.5% of control values, p<0.001), Ef (to 3.1±41.3% of control values, p=0.046), Em (to 6.4±8.5% of control values, p<0.0001), and an increase in k (to 2676.7±2562.0% of control values, p=0.004) were observed at day 12 of refrigeration at 4°C, but no significant changes were detected at day 6. A trend toward detecting a decrease in SPI (to 94.2±6.2% of control values, p=0.083) was identified following a single freeze-thaw cycle, but no detectable changes were observed for any biomechanical parameters. All numbers are mean±95% confidence interval. These results indicate that fresh cartilage can be stored in a humid chamber at 4°C for a maximum of 6 days with no detrimental effects to cartilage electromechanical and biomechanical properties, while one freeze-thaw cycle produces minimal deterioration of biomechanical and electromechanical properties. A comparison to literature suggested that particular attention should be paid to the manner in which specimens are thawed after freezing, specifically by minimizing thawing time at higher temperatures.

Aggrecanolysis and in vitro matrix degradation in the immature bovine meniscus: mechanisms and functional implications

Introduction

Little is known about endogenous or cytokine-stimulated aggrecan catabolism in the meniscal fibrocartilage of the knee. The objectives of this study were to characterize the structure, distribution, and processing of aggrecan in menisci from immature bovines, and to identify mechanisms of extracellular matrix degradation that lead to changes in the mechanical properties of meniscal fibrocartilage.

Methods

Aggrecanase activity in the native immature bovine meniscus was examined by immunolocalization of the aggrecan NITEGE neoepitope. To investigate mechanisms of cytokine-induced aggrecan catabolism in this tissue, explants were treated with interleukin-1α (IL-1) in the absence or presence of selective or broad spectrum metalloproteinase inhibitors. The sulfated glycosaminoglycan (sGAG) and collagen contents of explants and culture media were quantified by biochemical methods, and aggrecan catabolism was examined by Western analysis of aggrecan fragments. The mechanical properties of explants were determined by dynamic compression and shear tests.

Results

The aggrecanase-generated NITEGE neoepitope was preferentially localized in the middle and outer regions of freshly isolated immature bovine menisci, where sGAG density was lowest and blood vessels were present. In vitro treatment of explants with IL-1 triggered the accumulation of NITEGE in the inner and middle regions. Middle region explants stimulated with IL-1 exhibited substantial decreases in sGAG content, collagen content, and mechanical properties. A broad spectrum metalloproteinase inhibitor significantly reduced sGAG loss, abrogated collagen degradation, and preserved tissue mechanical properties. In contrast, an inhibitor selective for ADAMTS-4 and ADAMTS-5 was least effective at blocking IL-1-induced matrix catabolism and loss of mechanical properties.

Conclusions

Aggrecanase-mediated aggrecanolysis, typical of degenerative articular cartilage, may play a physiologic role in the development of the immature bovine meniscus. IL-1-induced release of sGAG and loss of mechanical properties can be ascribed primarily to the activity of MMPs or aggrecanases other than ADAMTS-4 and ADAMTS-5. These results may have implications for the clinical management of osteoarthritis.

Composition-function relationships during IL-1-induced cartilage degradation and recovery

OBJECTIVE

To examine the relationships between biochemical composition and mechanical properties of articular cartilage explants during interleukin-1 (IL-1)-induced degradation and post-exposure recovery.

DESIGN

Bovine articular cartilage explants were cultured for up to 32 days with or without 20 ng/mL IL-1. The dynamic shear modulus |G*(dyn)| and equilibrium and dynamic unconfined compression moduli (E(equil) and |E*(dyn)|) were measured at intervals throughout the culture period. In a subsequent recovery study, explants were cultured for 4 days with or without 20ng/mL IL-1 and for an additional 16 days in control media. The dynamic moduli |E*(dyn)| and |G*(dyn)| were measured at intervals during degeneration and recovery. Conditioned media and explant digests were assayed for sulfated glycosaminoglycans (sGAG) and collagen content.

RESULTS

Continuous IL-1 stimulation triggered progressive decreases in E(equil), |E*(dyn)|, and |G*(dyn)| concomitant with the sequential release of sGAG and collagen from the explants. Brief IL-1 exposure resulted in a short release of sGAG but not collagen, followed by a gradual and incomplete repopulation of sGAG. The temporary sGAG depletion was associated with decreases in both |E*(dyn)| and |G*(dyn)| which also recovered after removal of IL-1. During IL-1-induced degradation and post-exposure recovery, explant mechanical properties correlated well with tissue sGAG concentration.

CONCLUSIONS

As previously shown for developing cartilages and engineered cartilage constructs, cytokine-induced changes in sGAG concentration (i.e., fixed charge density) are coincident with changes in compressive and shear properties of articular cartilage. Further, recovery of cartilage mechanical properties can be achieved by relief from proinflammatory stimuli and subsequent restoration of tissue sGAG concentration.

Mechanical injury and cytokines cause loss of cartilage integrity and upregulate proteins associated with catabolism, immunity, inflammation, and repair

The objectives of this study were to perform a quantitative comparison of proteins released from cartilage explants in response to treatment with IL-1beta, TNF-alpha, or mechanical compression injury in vitro and to interpret this release in the context of anabolic-catabolic shifts known to occur in cartilage in response to these insults in vitro and their implications in vivo. Bovine calf cartilage explants from 6-12 animals were subjected to injurious compression, TNF-alpha (100 ng/ml), IL-1beta (10 ng/ml), or no treatment and cultured for 5 days in equal volumes of medium. The pooled medium from each of these four conditions was labeled with one of four iTRAQ labels and subjected to nano-2D-LC/MS/MS on a quadrupole time-of-flight instrument. Data were analysed by ProQuant for peptide identification and quantitation. k-means clustering and biological pathways analysis were used to identify proteins that may correlate with known cartilage phenotypic responses to such treatments. IL-1beta and TNF-alpha treatment caused a decrease in the synthesis of collagen subunits (p < 0.05) as well as increased release of aggrecan G2 and G3 domains to the medium (p < 0.05). MMP-1, MMP-3, MMP-9, and MMP-13 were significantly increased by all treatments compared with untreated samples (p < 0.10). Increased release of proteins involved in innate immunity and immune cell recruitment were noted following IL-1beta and TNF-alpha treatment, whereas increased release of intracellular proteins was seen most dramatically with mechanical compression injury. Proteins involved in insulin-like growth factor and TGF-beta superfamily pathway modulation showed changes in pro-anabolic pathways that may represent early repair signals. At the systems level, two principal components were sufficient to describe 97% of the covariance in the data. A strong correlation was noted between the proteins released in response to IL-1beta and TNF-alpha; in contrast, mechanical injury resulted in both similarities and unique differences in the groups of proteins released compared with cytokine treatment.

Fibroblast growth factor 2 inhibits induction of aggrecanase activity in human articular cartilage

OBJECTIVE

Articular chondrocytes are surrounded by an extracellular pool of fibroblast growth factor 2 (FGF-2). We undertook this study to investigate the possible role of FGF-2 in aggrecan catabolism by aggrecanase in human articular cartilage.

METHODS

Aggrecan catabolism was induced by interleukin-1alpha (IL-1alpha) in normal human articular cartilage and assessed by measuring the release of glycosaminoglycan (GAG) and aggrecanase-dependent fragments by Western blotting with antibodies against neoepitopes. ADAMTS-4 and ADAMTS-5 messenger RNA (mRNA) expression was measured by quantitative real-time reverse transcriptase-polymerase chain reaction. Production of matrix metalloproteinases (MMPs) 1, 3, and 13 and tissue inhibitors of metalloproteinases (TIMPs) 1 and 3 was measured by Western blotting. IL-6 and IL-8 were measured by enzyme-linked immunosorbent assay. Proteoglycan synthesis was monitored by 35S-sulfate incorporation.

RESULTS

IL-1alpha caused cleavage of aggrecan in cultured human articular cartilage explants, with release of GAG and aggrecan fragments containing ARGS and AGEG neoepitopes. This was inhibited by FGF-2 (1-100 ng/ml). Tumor necrosis factor alpha and retinoic acid also stimulated release of neoepitope, and this was also suppressed by FGF-2. IL-1alpha induced ADAMTS-4 and ADAMTS-5 mRNA in primary human chondrocytes, and this was inhibited by FGF-2. IL-1alpha-induced aggrecan breakdown was inhibited by TIMP-1 or by the N-terminal portion of TIMP-3, although FGF-2 did not affect production of the inhibitors TIMP-1 and TIMP-3 when IL-1alpha was present. FGF-2 did not prevent IL-1alpha suppression of proteoglycan synthesis and did not negate its ability to stimulate the production of IL-6, IL-8, and MMPs 1, 3, and 13.

CONCLUSION

Our findings suggest that FGF-2 may play a chondroprotective role in human articular cartilage by controlling the expression and activity of the aggrecanases ADAMTS-4 and ADAMTS-5.

Experimental repair of tracheal defect using a bioabsorbable copolymer

BACKGROUND

We investigated epithelialization and newly formed cartilage in an artificial trachea constructed using a bioabsorbable copolymer.

MATERIALS AND METHODS

Fifteen male Japanese white rabbits (2.5-2.8 kg) were divided into three groups. A full-thickness anterior defect (4 mm x 10 mm) was created in the trachea. The defect was implanted with one of the following bioabsorbable copolymers: caprolactone-lactide copolymer sponge sheet reinforced with poly(glycolic acid) fiber mesh (Cop) (n = 6, group A), Cop-incorporating gelatin hydrogel (n = 4, group B), and Cop-incorporating gelatin hydrogel with 100 microg of basic fibroblast growth factor (n = 5, group C). Each trachea was reinforced with an external nondegradable polymer stent. Three rabbits in each group were sacrificed at 1, 3, and 6 mo postoperatively and the trachea was evaluated histologically; other animals were sacrificed up to 12 mo postoperatively.

RESULTS

In groups A, B, and C there were two, one, and one postoperative deaths, respectively. In group A, epithelialization was recognized from 1 mo to 12 mo postoperatively, but no new cartilage was formed during the 12 mo following implantation. In group B, epithelialization was recognized 3 and 6 mo postoperatively, and new cartilage was detected at 6 mo after the operation. In group C, newly formed cartilage and epithelialization were observed 3, 6, and even 12 mo postoperatively. Furthermore, neovascularization was observed in groups B and C.

CONCLUSIONS

A bioabsorbable copolymer incorporating gelatin hydrogel induces tracheal epithelialization and formation of cartilage and vessels in tracheal defects, and could be available for clinical use in children.

Mechanism of proteoglycan aggregate degradation in cartilage stimulated with oncostatin M

OBJECTIVE

To investigate the potential synergistic and differential effects of cytokine combinations on proteoglycan aggregate catabolism in cartilage.

METHODS

Bovine articular cartilage explants were maintained in organ culture and subjected to stimulation with cytokine combinations including interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, IL-17, tumor necrosis factor-alpha (TNFalpha) and oncostatin M (OSM). Aggrecan, link protein and hyaluronan (HA) release and degradation were analyzed, and the effect of the hyaluronidase inhibitor apigenin was investigated.

RESULTS

For all cytokine mixtures studied cleavage of aggrecan only by aggrecanase action was apparent. However, OSM acting synergistically with IL-1 or TNFalpha produced a rapid release of all proteoglycan aggregate components due to both aggrecan and HA degradation. This was abolished by the hyaluronidase inhibitor, apigenin. In addition, in the presence of OSM a low molecular weight aggrecan G3 product was observed, suggesting altered aggrecanase cleavage activity is induced by this cytokine.

CONCLUSIONS

Under cytokine stimulation, aggrecan release from cartilage may take place via proteolysis of the aggrecan core protein or via depolymerization of HA, with the latter mechanism being induced by OSM. OSM is associated with joint inflammation and its participation may account for the more rapid loss of aggrecan from articular cartilage in the inflammatory arthritides, compared to osteoarthritis.

Analysis of cartilage matrix fixed charge density and three-dimensional morphology via contrast-enhanced microcomputed tomography

Small animal models of osteoarthritis are often used for evaluating the efficacy of pharmacologic treatments and cartilage repair strategies, but noninvasive techniques capable of monitoring matrix-level changes are limited by the joint size and the low radiopacity of soft tissues. Here we present a technique for the noninvasive imaging of cartilage at micrometer-level resolution based on detecting the equilibrium partitioning of an ionic contrast agent via microcomputed tomography. The approach exploits electrochemical interactions between the molecular charges present in the cartilage matrix and an ionic contrast agent, resulting in a nonuniform equilibrium partitioning of the ionic contrast agent reflecting the proteoglycan distribution. In an in vitro model of cartilage degeneration we observed changes in x-ray attenuation magnitude and distribution consistent with biochemical and histological analyses of sulfated glycosaminoglycans, and x-ray attenuation was found to be a strong predictor of sulfated glycosaminoglycan density. Equilibration with the contrast agent also permits direct in situ visualization and quantification of cartilage surface morphology. Equilibrium partitioning of an ionic contrast agent via microcomputed tomography thus provides a powerful approach to quantitatively assess 3D cartilage composition and morphology for studies of cartilage degradation and repair.

A review on the mechanical quality of articular cartilage - implications for the diagnosis of osteoarthritis

The functional behaviour of articular cartilage in diarthrodial joints is determined by its morphological and biomechanical properties. Whereas morphological changes are mainly detectable in the progressed stages of osteoarthritis, biomechanical properties seem to be more sensitive to early degenerative variations since they are determined by the biochemical composition and structural arrangement of the extracellular matrix. The objective of this paper is to review studies focussing on variations in the mechanical compressive properties during the early pre-osteoarthritic stage. The aim is to quantify the requirements to detect the early cartilage degeneration in pre-osteoarthritis based on the mechanical parameters and to create an updated basis for a better understanding of inherent relationships between characteristic parameters in articular cartilage. Correlations between mechanical and biochemical parameters as well as magnetic resonance, ultrasonic, histological and structural parameters were observed. In early osteoarthritis, static moduli decrease below 80% of healthy controls and dynamic moduli below 30% of controls. To identify osteoarthritic changes of articular cartilage based on static or dynamic mechanical parameters in an early stage of the disease progression the accuracy of a mechanical testing method has to be adequate to detect changes of 10% in cartilage stiffness.

Role of aggrecanase 1 in Lyme arthritis

OBJECTIVE

Arthritis is one of the hallmarks of late-stage Lyme disease. Previous studies have shown that infection with Borrelia burgdorferi, the causative agent of Lyme disease, results in degradation of proteoglycans and collagen in cartilage. B burgdorferi do not appear to produce any exported proteases capable of digesting proteoglycans and collagen, but instead, induce and activate host proteases, such as matrix metalloproteinases (MMPs), which results in cartilage degradation. The role of aggrecanases in Lyme arthritis has not yet been determined. We therefore sought to delineate the contribution of aggrecanases to joint destruction in Lyme arthritis.

METHODS

We examined the expression patterns of aggrecanases 1 and 2 (ADAMTS 4 and 5, respectively) in B burgdorferi-infected primary human chondrocyte cell cultures, in synovial fluid samples from patients with active Lyme arthritis, and in the joints of mice by real-time quantitative reverse transcription-polymerase chain reaction and immunoblotting techniques. Bovine cartilage explants were used to determine the role of aggrecanases in B burgdorferi-induced cartilage degradation.

RESULTS

ADAMTS-4, but not ADAMTS-5, was induced in human chondrocytes infected with B burgdorferi. The active forms of ADAMTS-4 were increased in synovial fluid samples from patients with active Lyme arthritis and were elevated in the joints of mice infected with B burgdorferi. Using cartilage explant models of Lyme arthritis, it appeared that the cleavage of aggrecan was predominantly mediated by "aggrecanases" rather than MMPs.

CONCLUSION

The induction of ADAMTS-4 by B burgdorferi results in the cleavage of aggrecan, which may be an important first step that leads to permanent degradation of cartilage.

Interleukin-1alpha induction of tensile weakening associated with collagen degradation in bovine articular cartilage

OBJECTIVE

To determine whether interleukin-1alpha (IL-1alpha) induces tensile weakening of articular cartilage that is concomitant with the loss of glycosaminoglycans (GAGs) or the subsequent degradation of the collagen network.

METHODS

Explants of young adult bovine cartilage obtained from the superficial (including the articular surface), middle, and deep layers were cultured with or without IL-1alpha for 1 week or 3 weeks. Then, portions of the explants were analyzed for their tensile properties (ramp modulus, strength, and failure strain); other portions of explants and spent culture medium were analyzed for the amount of GAG and the amount of cleaved, denatured, and total collagen.

RESULTS

The effect of IL-1alpha treatment on cartilage tensile properties and content was dependent on the duration of culture and the depth of the explant from the articular surface. The tensile strength and failure strain of IL-1alpha-treated samples from the superficial and middle layers were lower after 3 weeks of culture, but not after 1 week of culture. However, by 1 week of culture, IL-1alpha had already induced release of the majority of tissue GAGs into the medium, without detectable loss or degradation of collagen. In contrast, after 3 weeks of culture, IL-1alpha induced significant collagen degradation, as indicated by the amount of total, cleaved, or denatured collagen in the medium or in explants from the superficial and middle layers.

CONCLUSION

IL-1alpha-induced degradation of cartilage results in tensile weakening that occurs subsequent to the depletion of GAG and concomitant with the degradation of the collagen network.

Selective and non-selective metalloproteinase inhibitors reduce IL-1-induced cartilage degradation and loss of mechanical properties

Articular cartilage undergoes matrix degradation and loss of mechanical properties when stimulated with proinflammatory cytokines such as interleukin-1 (IL-1). Aggrecanases and matrix metalloproteinases (MMPs) are thought to be principal downstream effectors of cytokine-induced matrix catabolism, and aggrecanase- or MMP-selective inhibitors reduce or block matrix destruction in several model systems. The objective of this study was to use metalloproteinase inhibitors to perturb IL-1-induced matrix catabolism in bovine cartilage explants and examine their effects on changes in tissue compression and shear properties. Explanted tissue was stimulated with IL-1 for up to 24 days in the absence or presence of inhibitors that were aggrecanase-selective, MMP-selective, or non-selective. Analysis of conditioned media and explant digests revealed that aggrecanase-mediated aggrecanolysis was delayed to varying extents with all inhibitor treatments, but that aggrecan release persisted. Collagen degradation was abrogated by MMP- and non-selective inhibitors and reduced by the aggrecanase inhibitor. The inhibitors delayed but did not reduce loss of the equilibrium compression modulus, whereas the losses of dynamic compression and shear moduli were delayed and reduced. The data suggest that non-metalloproteinase mechanisms participate in IL-1-induced matrix degradation and loss of tissue material properties.

Tensorial electrokinetics in articular cartilage

Electrokinetic phenomena contribute to biomechanical functions of articular cartilage and underlie promising methods for early detection of osteoarthritic lesions. Although some transport properties, such as hydraulic permeability, are known to become anisotropic with compression, the direction-dependence of cartilage electrokinetic properties remains unknown. Electroosmosis experiments were therefore performed on adult bovine articular cartilage samples, whereby fluid flows were driven by electric currents in directions parallel and perpendicular to the articular surface of statically compressed explants. Magnitudes of electrokinetic coefficients decreased slightly with compression (from approximately -7.5 microL/As in the range of 0-20% compression to -6.0 microL/As in the 35-50% range) consistent with predictions of microstructure-based models of cartilage material properties. However, no significant dependence on direction of the electrokinetic coupling coefficient was detected, even for conditions where the hydraulic permeability tensor is known to be anisotropic. This contrast may also be interpreted using microstructure-based models, and provides insights into structure-function relationships in cartilage extracellular matrix and physical mediators of cell responses to tissue compression. Findings support the use of relatively simple isotropic modeling approaches for electrokinetic phenomena in cartilage and related materials, and indicate that measurement of electrokinetic properties may provide particularly robust means for clinical evaluation of cartilage matrix integrity.

Polyglycolic acid-induced inflammation: role of hydrolysis and resulting complement activation

Tissue and organ replacement have quickly outpaced available supply. Tissue bioengineering holds the promise for additional tissue availability. Various scaffolds are currently used, whereas polyglycolic acid (PGA), which is currently used in absorbable sutures and orthopedic pins, provides an excellent support for tissue development. Unfortunately, PGA can induce a local inflammatory response following implantation. Therefore, we investigated the molecular mechanism of inflammation in vitro and in vivo. Degraded PGA induced an acute peritonitis, characterized by neutrophil (PMN) infiltration following intraperitoneal injection in mice. Similar observations were observed using the metabolite of PGA, glycolide. Dissolved PGA or glycolide, but not native PGA, activated the classical complement pathway in human sera, as determined by classical complement pathway hemolytic assays, C3a and C5a production, and C3 and immunoglobulin deposition. To investigate whether these in vitro observations translated to in vivo findings, we used genetically engineered mice. Intraperitoneal administration of glycolide or dissolved PGA in mice deficient in C1q, factor D, C1q and factor D, or C2 and factor B demonstrated significantly reduced PMN infiltration compared to congenic controls (WT). Mice deficient in C6 also demonstrated acute peritonitis. However, treatment of WT or C6 deficient mice with a monoclonal antibody against C5 prevented the inflammatory response. These data suggest that the hydrolysis of PGA to glycolide activates the classical complement pathway. Furthermore, complement is amplified via the alternative pathway and inflammation is induced by C5a generation. Inhibition of C5a may provide a potential therapeutic approach to limit the inflammation associated with PGA-derived materials following implantation.

Extracellular matrix changes in knee joint cartilage following bone-active drug treatment

Certain drugs or treatments that are known to affect bone quality or integrity might have side effects on the extracellular matrix of articular cartilage. We investigated the effects of vitamin D and calcium deficiency, estrogen deficiency, and hypercortisolism alone or in combination with bisphosphonates or sodium fluoride in an animal model, viz., the Göttingen miniature pig (n=29). The articular cartilage from knee joints was analyzed for its content of glycosaminoglycans (GAGs, as macromolecules responsible for the elasticity of articular cartilage) by a spectrometric method with dimethylene blue chloride. In cryo- or paraffin sections, alkaline phosphatase (AP, as an enzyme indicating mineralization or reorganization of articular cartilage matrix) was localized by enzyme histochemistry, and positive cells were counted, whereas differently sulfated GAGs were stained histochemically. A significant decrease in GAG content was measured in ovariectomized and long-term glucocorticoid-treated animals compared with untreated animals. In the glucocorticoid/sodium fluoride group, GAGs were significantly diminished, and significantly fewer AP-positive chondrocytes were counted compared with the control. GAG content was slightly higher, and significantly more AP-positive chondrocytes were counted in short-term glucocorticoid-treated animals then in the control group. GAGs, as part of proteoglycans, are responsible for the water-storage capacity that gives articular cartilage its unique property of elasticity. Thus, ovariectomy and long-term glucocorticoid therapy, especially when combined with sodium fluoride, have detrimental effects on this tissue.

Quantification of cartilage biomechanical and biochemical properties via T1rho magnetic resonance imaging

The aim of this study is to develop T1rho as an MR marker of the compositional and functional condition of cartilage. Specifically, we investigate the correlation of changes in cartilage biomechanical and biochemical properties with T1rho relaxation rate in a cytokine-induced model of degeneration. Bovine cartilage explants were cultured with 30 ng/mL of interleukin-1beta to mimic the cartilage degradation of early osteoarthritis. The average rate of T1rho relaxation was calculated from T(1rho) maps acquired on a 4.7 T research scanner. Stress-relaxation biomechanical tests were conducted with a confined compression apparatus to measure uniaxial aggregate modulus (HA) and hydraulic permeability (k0) using linear biphasic theory. Proteoglycan, collagen, and water content were measured via biochemical assays. Average T(1rho) relaxation rate was strongly correlated with proteoglycan content (R2 = 0.926), HA (R2 = 0.828), and log10 k0 (R2 = 0.862). Results of this study demonstrate that T1rho MRI can detect changes in proteoglycan content and biomechanical properties of cartilage in a physiologically relevant model of cartilage degeneration. The T1rho technique can potentially be used to noninvasively and quantitatively assess the biochemical and biomechanical characteristics of articular cartilage in humans during the progression of osteoarthritis.

The role of computational models in the search for the mechanical behavior and damage mechanisms of articular cartilage

Articular cartilage plays a vital role in the function of diarthrodial joints. Due to osteoarthritis degeneration of articular cartilage occurs. The initial event that triggers the pathological process of cartilage degeneration is still unknown. Cartilage damage due to osteoarthritis is believed to be mechanically induced. Hence, to investigate the initiation of osteoarthritis the stresses and strains in the cartilage must be determined. So far the most common method to accomplish that is finite element analysis. This paper provides an overview of computational descriptions developed for this purpose, and what they can be used for. Articular cartilage composition and structure are discussed in relation with degenerative changes, and how these affect mechanical properties.

Role for interleukin 1alpha in the inhibition of chondrogenesis in autologous implants using polyglycolic acid-polylactic acid scaffolds

Significant challenges remain in generating tissue-engineered cartilage in immunocompetent animals. Scaffold materials such as polyglycolic acid lead to significant inflammatory reactions, inhibiting homogeneous matrix synthesis. This study examined the generation of tissue-engineered cartilage, using a polyglycolic acid-polylactic acid copolymer (Ethisorb; Ethicon, Norderstedt, Germany) in an autologous immunocompetent pig model. The goals of this study were to determine the role of interleukin 1alpha (IL-1alpha) in this system and to assess the effect of serum treatment on tissue generation. Porcine auricular chondrocytes were seeded onto Ethisorb disks cultured for 1 week in medium supplemented with either fetal bovine serum or serum-free insulin-transferrin-selenium supplement. Specimens were implanted autogenously in pigs with unseeded scaffolds as controls. After 1, 4, or 8 weeks, six specimens from each group were explanted and analyzed histologically (hematoxylin and eosin, safranin O, trichrome, and Verhoeff's staining) and biochemically (glycosaminoglycan content). The presence and distribution of IL-1alpha were assessed by immunohistochemistry. Histology revealed acute inflammation surrounding degrading scaffold. Cartilage formation was observed as early as 1 week after implantation and continued to increase with time; however, homogeneous matrix synthesis was not present in any of the specimens. Strong IL-1alpha expression was detected in chondrocytes at the implant periphery and in cells in the vicinity of degrading polymer. Histologically there was no significant difference between the experimental groups with respect to the amount of matrix synthesis or inflammatory infiltration. The glycosaminoglycan content was significantly higher in the serum-free group. These results suggest that inflammatory reactions against scaffold materials and serum components lead to the production of cytokines such as IL-1alpha that may inhibit cartilage tissue formation in autologous transplant models.

Analysis of ADAMTS4 and MT4-MMP indicates that both are involved in aggrecanolysis in interleukin-1-treated bovine cartilage

OBJECTIVE

To investigate the mechanism of aggrecanolysis in interleukin-1 (IL-1)-treated cartilage tissue by examining the time course of aggrecan cleavages and the tissue and medium content of membrane type 4-matrix metalloproteinases (MT4-MMP) and a disintegrin and metalloproteinase with thrombospondin type I motifs (ADAMTS)4.

METHODS

Articular cartilage explants were harvested from newborn bovine femoropatellar groove. The effects of IL-1 treatment with or without aggrecanase blockade were investigated by Western analysis of aggrecan fragment generation, ADAMTS4 species (p68 and p53), and MT4-MMP, as well as by realtime PCR (polymerase chain reaction) for ADAMTS4 and 5. Aggrecanase was blocked with mannosamine (ManN), an inhibitor of glycosylphosphatidylinositol anchor synthesis, and esculetin (EST), an inhibitor of MMP-1, MMP-3, and MMP-13 gene expression.

RESULTS

IL-1 treatment caused a major increase in MT4-MMP abundance in the tissue and medium. ADAMTS4 (p68) was abundant in fresh cartilage and this was retained in the tissue in untreated cartilage. IL-1 treatment for 6 days caused a marked loss of p68 from the cartilage and the appearance of p53 in the medium. Addition of either 1.35 mM ManN or 31-500 microM EST blocked IL-1-mediated aggrecanolysis and this was accompanied by nearly complete inhibition of the MT4-MMP increase, the p68 loss and the formation of p53. IL-1 treatment increased mRNA abundance for ADAMTS4 ( approximately 3-fold) and ADAMTS5 ( approximately 10-fold) but this was not accompanied by a marked change in enzyme protein abundance.

CONCLUSION

These studies support a central role for MT4-MMP in IL-1-induced cartilage aggrecanolysis and are consistent with the identification of p68 as the aggrecanase that cleaves within the CS2 domain, and of p53 as the aggrecanase that generates G1-NITEGE. Since the induction by IL-1 was not accompanied by marked changes in total ADAMTS4 protein, but rather in partial conversion of p68 to p53 and release of both from the tissue, we conclude that aggrecanolysis in this model system results from MT4-MMP-mediated processing of a resident pool of ADAMTS4 and release of the p68 and p53 from their normal association with the cell surface.

Effects of tissue inhibitor of metalloproteinases on canine chondrocytes cultured in vitro with tumor necrosis factor-

OBJECTIVE

To elucidate tissue inhibitor of metalloproteinase (TIMP)-mediated effects on chondrocytes.

SAMPLE POPULATION

Articular cartilage from humeral heads of 6 dogs.

PROCEDURE

Chondrocytes from harvested specimens were cultured in 3-dimensional (3-D) agarose at 10(6) cells/mL. We prepared 3-D constructs exposed to only tumor necrosis factor (TNF)-alpha (50 ng/mL). Recombinant human TIMP-1 (255nM), -2 (285nM), or -3 (250nM) was added to liquid media bathing 3-D constructs cultured with TNF-alpha. Chondrocytes cultured without TIMP or TNF-alpha served as control samples. Samples of liquid media were collected on days 6, 9, 15, and 21 of culture for evaluation of glycosaminoglycan (GAG) and nitric oxide concentrations. The 3-D constructs were collected on days 9, 15, and 21 for evaluation of GAG, hydroxyproline (HP), and DNA contents.

RESULTS

GAG content in control samples increased significantly during the study, whereas GAG content in 3-D constructs cultured with TNF-alpha or TNF-alpha plus TIMP did not increase. On day 9, GAG release from 3-D constructs cultured with TNF-alpha was significantly higher than that in other constructs. The HP content in control samples increased during the study and was significantly higher than that in all other constructs on day 21. Concentrations of nitric oxide were significantly lower in control samples on day 6, compared with concentrations for all other constructs.

CONCLUSIONS AND CLINICAL RELEVANCE

Addition of TIMPs did not counteract suppression of GAG and HP accumulation in 3-D constructs exposed to TNF-alpha. Apparently, adverse effects on chondrocytes exposed to TNF-alpha cannot be prevented by addition of TIMP alone.

Release of hyaluronan and hyaladherins (aggrecan G1 domain and link proteins) from articular cartilage exposed to ADAMTS-4 (aggrecanase 1) or ADAMTS-5 (aggrecanase 2)

OBJECTIVE

To determine whether aggrecanase (ADAMTS) activities in articular cartilage can directly lead to the release of hyaluronan (HA) and hyaladherins (aggrecan G1 domain and link proteins), as may occur ex vivo during stimulation of cartilage explants with interleukin-1 (IL-1) or retinoic acid or in vivo in synovial joints during aging and joint pathology.

METHODS

Bovine articular cartilage discs (live or freeze-killed) were cultured in the presence of IL-1 or were incubated in digestion buffer containing recombinant human ADAMTS-4 (rHuADAMTS-4; aggrecanase 1) or rHuADAMTS-5 (aggrecanase 2). Culture media, digestion supernatants, and tissue extracts were assayed for sulfated glycosaminoglycan (sGAG) content and analyzed by Western blotting to detect aggrecanase-generated G1 domain (using neoepitope monoclonal antibody AGG-C1/anti-NITEGE(373)) and link proteins (using monoclonal antibody 8-A-4), as well as by quantitative enzyme-linked immunosorbent assays to detect aggrecanase-generated G1 domain (G1-NITEGE(373)) and HA.

RESULTS

IL-1 treatment of live cartilage explants induced a time-dependent release of sGAG, aggrecanase-generated G1 domain (G1-NITEGE(373)), and HA into the culture media. Exposure of live or freeze-killed articular cartilage discs to rHuADAMTS-4 or rHuADAMTS-5 resulted in a dose- and time-dependent release of sGAG and hyaluronan from the tissue, accompanied by a concomitant release of functionally intact hyaladherins (aggrecan G1-NITEGE(373) and link proteins).

CONCLUSION

Coincident with aggrecanolysis, aggrecanase activities in articular cartilage may actuate the release of HA and associated hyaladherins, thereby further compromising the integrity of the cartilage matrix during degenerative joint diseases such as osteoarthritis.

ADAMTS4 (aggrecanase-1) activation on the cell surface involves C-terminal cleavage by glycosylphosphatidyl inositol-anchored membrane type 4-matrix metalloproteinase and binding of the activated proteinase to chondroitin sulfate and heparan sulfate on syndecan-1

C-terminal truncation of ADAMTS-4 from the p68 form to the p53 form is required for activation of its capacity to cleave the Glu(373)-Ala(374) interglobular domain bond of aggrecan. In transfected human chondrosarcoma cells, this process is not autoproteolytic because the same products form with an inactive mutant of ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin-like motif 4) and truncation is completely blocked by tissue inhibitor of metalloproteinase-1. Instead, activation can be mediated by glycosylphosphatidyl inositol-anchored membrane type 4-matrix metalloproteinase (MT4-MMP, MMP-17) because co-transfection with the active form of MT4-MMP markedly enhanced activation, whereas an inactive mutant of MT4-MMP was ineffective. Treatment of co-transfected cells with phosphatidylinositol-specific phospholipase C liberated the complex of MT4-MMP and p68 ADAMTS4 from the cell membrane, but the p53 ADAMTS4 remained associated. Specific glycosaminoglycan lyase digestions, followed by product analyses using fluorescence-assisted carbohydrate electrophoresis and immunoprecipitation experiments, showed that the p53 form is associated with syndecan-1 through both chondroitin sulfate and heparan sulfate. We conclude that ADAMTS-4 activation in this cell system involves the coordinated activity of both glycosylphosphatidyl inositol-anchored MT4-MMP and the proteoglycan form of syndecan-1 on the cell surface.

Structure-Function Relationships in Enzymatically Modified Articular Cartilage

The present study is aimed at revealing structure-function relationships of bovine patellar articular cartilage. Collagenase, chondroitinase ABC and elastase were used for controlled and selective enzymatic modifications of cartilage structure, composition and functional properties. The effects of the enzymatic degradations were quantitatively evaluated using quantitative polarized light microscopy, digital densitometry of safranin O-stained sections as well as with biochemical and biomechanical techniques. The parameters related to tissue composition and structure were correlated with the indentation stiffness of cartilage. In general, tissue alterations after enzymatic digestions were restricted to the superficial cartilage. All enzymatic degradations induced superficial proteoglycan (PG) depletion. Collagenase also induced detectable superficial collagen damage, though without causing cartilage fibrillation or tissue swelling. Quantitative microscopic techniques were more sensitive than biochemical methods in detecting these changes. The Young's modulus of cartilage decreased after enzymatic treatments indicating significant softening of the tissue. The PG concentration of the superficial zone proved to be the major determinant of the Young's modulus (r(2) = 0.767, n = 72, p < 0.001). Results of the present study indicate that specific enzymatic degradations of the tissue PGs and collagen can provide reproducible experimental models to clarify the structure-function relationships of cartilage. Effects of these models mimic the changes observed in early osteoarthrosis. Biomechanical testing and quantitative microscopic techniques proved to be powerful tools for detecting the superficial structural and compositional changes while the biochemical measurements on the whole uncalcified cartilage were less sensitive.

TIMP-3 inhibits aggrecanase-mediated glycosaminoglycan release from cartilage explants stimulated by catabolic factors

Aggrecanases are considered to play a key role in the destruction of articular cartilage during the progression of arthritis. Here we report that the N-terminal inhibitory domain of tissue inhibitor of metalloproteinases 3 (N-TIMP-3), but not TIMP-1 or TIMP-2, inhibits glycosaminoglycan release from bovine nasal and porcine articular cartilage explants stimulated with interleukin-1alpha or retinoic acid in a dose-dependent manner. This inhibition is due to the blocking of aggrecanase activity induced by the catabolic factors. Little apoptosis of primary porcine chondrocytes is observed at an effective concentration of N-TIMP-3. These results suggest that TIMP-3 may be a candidate agent for use against cartilage degradation.

Biochemical characterisation of navicular hyaline cartilage, navicular fibrocartilage and the deep digital flexor tendon in horses with navicular disease

The study hypothesis was that navicular disease is a process analogous to degenerative joint disease, which leads to changes in navicular fibrocartilage and in deep digital flexor tendon (DDFT) matrix composition and that the process extends to the adjacent distal interphalangeal joint. The objectives were to compare the biochemical composition of the navicular articular and palmar cartilages from 18 horses with navicular disease with 49 horses with no history of front limb lameness, and to compare navicular fibrocartilage with medial meniscus of the stifle and collateral cartilage of the hoof. Cartilage oligomeric matrix protein (COMP), deoxyribonucleic acid (DNA), total glycosaminoglycan (GAG), metalloproteinases MMP-2 and MMP-9 and water content in tissues were measured. Hyaline cartilage had the highest content of COMP and COMP content in hyaline cartilage and tendon was higher in lame horses than in sound horses (p<0.05). The concentration of MMP-2 amount in hyaline cartilage was higher in lame horses than in sound horses. The MMP-2 amounts were significantly higher in tendons compared to other tissue types. Overall, 79% of the lame horses with lesions had MMP-9 in their tendons and the amount was higher than in sound horses (p<0.05). In horses with navicular disease there were matrix changes in navicular hyaline and fibrocartilage as well as the DDFT with potential implications for the pathogenesis and management of the condition.

Tissue engineering of autologous cartilage for craniofacial reconstruction by injection molding

Each year, more than one million patients undergo some type of procedure involving cartilage reconstruction. Polymer hydrogels such as alginate have been demonstrated to be effective carriers of chondrocytes for subcutaneous cartilage formation. The goal of this study was to develop a simple method to create complex structures with good three-dimensional tolerance in order to form cartilage in specific shapes in an autologous animal model. Six alginate implants that had been seeded with autologous chondrocytes through an injection molding process were implanted subcutaneously in sheep, harvested after 6 months, and analyzed histologically, biochemically, and biomechanically, in comparison with original auricular cartilage. Molds of craniofacial implants were prepared with Silastic E RTV (Dow Corning, Midland, Mich.). Chondrocytes were harvested from sheep auricular cartilage and suspended in 2% alginate at a concentration of 50 x 10(6) cells/ml. The mixture of cells and gel was injected into the Silastic molds and removed after 20 minutes. Chondrocyte-alginate constructs were implanted subcutaneously in the necks of the sheep from which the cells had originally been harvested, and the constructs were removed after 30 weeks. Analyses of the implanted constructs indicated cartilage formation with three-dimensional shape retention. The proteoglycan and collagen contents of the constructs increased with time to approximately 80 percent of the values for native tissue. The equilibrium modulus and the hydraulic permeability were 74 and 105 percent of those of native sheep auricular cartilage, respectively.

The effects of TIMP-1 and -2 on canine chondrocytes cultured in three-dimensional agarose culture system

OBJECTIVE

To investigate the effects of tissue inhibitor of metalloproteinase (TIMP)-1 and -2 on chondrocytes cultured with or without interleukin (IL)-1 beta.

DESIGN

Canine articular chondrocytes were cultured in three-dimensional (3-D) agarose constructs. Cells were distributed into each of the two groups, those without IL-1 beta and those with IL-1 beta added to the liquid media. Each group was subdivided into three groups, based on the presence of TIMP-1 or -2. IL-1 beta and TIMPs were added to liquid media bathing the 3-D constructs beginning on day 3. The liquid media and the 3-D constructs were collected on days 9, 15, and 24, and analyzed histologically, biochemically, and immunohistochemically.

RESULTS

Addition of TIMP-1 or -2 resulted in decreases in matrix metalloproteinase (MMP)-3 concentrations of 37 and 41%, and MMP-1 immunoreactivity of 32 and 36%, respectively, compared with the IL-1 beta group, on day 9. Chondrocytes in groups without IL-1 beta maintained viability and produced abundant extracellular matrix (ECM). Chondrocytes in IL-1 beta groups appeared less viable and produced less ECM compared with those without IL-1 beta. Glycosaminoglycan (GAG) concentrations in 3-D constructs (GAG/weight) were significantly (P<0.001) higher in groups without IL-1 beta than in those with IL-1 beta, on days 15 and 24.

CONCLUSIONS

The addition of TIMP was not detrimental to chondrocytes, as used in this study. Despite evidence of decreased MMP levels, TIMPs did not prevent IL-1 beta-associated changes in cellular or ECM characteristics. Further study is necessary before clinically relevant conclusions can be drawn regarding the use of TIMPs in the treatment of osteoarthritis.

A role for the interleukin-1 receptor in the pathway linking static mechanical compression to decreased proteoglycan synthesis in surface articular cartilage

Loading of articular cartilage during weight bearing is essential for the maintenance of cartilage function. Although certain cyclic loading protocols stimulate extracellular matrix synthesis, constant or static compression decreases proteoglycan and collagen synthesis in cartilage explants. The goal of this study was to determine whether the compression-induced decrease in proteoglycan synthesis involves an interleukin-1 (IL-1) signaling pathway. Cartilage explants were compressed 50% in the presence of IL-1 receptor antagonist (IL-1ra), and the incorporation of [35S]sulfate into macromolecules was measured. IL-1ra increased sulfate incorporation in compressed cartilage but not in cartilage maintained at the in situ thickness (0% compression). IL-1alpha and IL-1beta mRNAs were detected in cartilage compressed 50% for at least 3h, while nitric oxide synthase II mRNA was only detected in cartilage compressed 50% for 6h. The data support a role for the IL-1 receptor in the pathway linking static compression to reduced proteoglycan synthesis.

Microenvironment regulation of extracellular signal-regulated kinase activity in chondrocytes: effects of culture configuration, interleukin-1, and compressive stress

OBJECTIVE

To compare extracellular signal-regulated kinase (ERK) activity in response to interleukin-1 (IL-1) in chondrocytes under various culture configurations designed for the study of cartilage biology and repair, and also in response to dynamic load for chondrocytes in cartilage.

METHODS

Isolated bovine articular chondrocytes were maintained in serum-supplemented medium under 4 culture configurations: high-density monolayer, attached to a cut surface of cartilage, within tissue-engineered constructs, or within intact cartilage explants. Samples were subjected to a change of medium with or without IL-1. Cartilage explants were also subjected to dynamic compression.

RESULTS

In chondrocyte monolayers, both basal and IL-1-stimulated ERK activities were similarly elevated at 0.5 hours after medium change, diminishing by 74% after 16 hours. In contrast, chondrocytes in other culture configurations exhibited lower basal levels of ERK activity and a moderate activation of ERK in response to IL-1 that was sustained over the 16-hour treatment time. The dynamic component of loading of cartilage explants led to a 5-fold activation of ERK, compared with free-swelling controls, that was indistinguishable from the effects of IL-1.

CONCLUSION

ERK signaling in response to IL-1 in chondrocyte monolayers exhibited a pattern that was distinct from that in other culture systems, suggesting that the extracellular matrix plays an important regulatory role in modulating the response to extracellular stimuli. Since IL-1 and dynamic loading have distinct effects on chondrocyte biosynthesis, signaling pathways other than ERK participate in the chondrocyte responses to these stimuli.

Detection and analysis of cartilage degeneration by spatially resolved streaming potentials

Cartilage molecular changes in osteoarthritis are most commonly related to the degradation and loss of proteoglycan and collagen fibrils of the extracellular matrix, which directly influence tissue stiffness and compression-generated streaming potentials. In this study, we evaluated the potential of a new technique, spatially resolved mapping of streaming potentials, to non-destructively indicate cartilage health or degeneration. Matched pairs of bovine cartilage/bone explant disks were cultured for 11 days in a serum free medium with and without interleukin-lalpha (IL-1alpha). The electromechanical properties (static stiffness, dynamic stiffness and streaming potentials) of cartilage disks were measured during unconfined compression using a mechanical tester coupled with a linear array of eight 50 microm diameter platinum-iridium microelectrodes. After 11 days of culture, the proteoglycan content of IL-1alpha treated disks was significantly reduced and the denatured and cleaved collagen content was increased compared to control disks. These biochemical alterations were concomitant with the reductions in the amplitudes of the static stiffness, the dynamic stiffness and the streaming potential profile as well as changes in the shape of the streaming potential profile. We found that spatial mapping of streaming potentials presents several advantages for the development of a clinical instrument to evaluate the degeneration of articular cartilage.

Age-related changes in the composition and mechanical properties of human nasal cartilage

Nasal cartilage is widely used in reconstructive surgery for the replacement of soft tissue defects and nasal reconstruction procedures. The ability to shape harvested tissue and the performance in the transplant site are related to the mechanical properties of nasal cartilage. Several studies have documented changes in composition and mechanical properties of other cartilages with age, but little is known about these processes in nasal cartilage. In this study, 45 human nasal septum specimens were gathered from patients 15-60 years of age after reconstructive surgery. Samples were cut to 6 mm in diameter and tested in confined compression to determine equilibrium modulus and hydraulic permeability and analyzed for glycosaminoglycan and hydroxyproline content. Equilibrium modulus decreased significantly with increasing donor age (P<0.01) while hydraulic permeability increased significantly (P<0.02). Glycosaminoglycan (GAG) content decreased significantly with age (P<0.05), while hydroxyproline content showed a slight, but not significant, increase with age (P>0.2). These trends are qualitatively similar to those observed in articular cartilage, suggesting the existence of a systemic process of cartilage degradation that is independent of mechanical loading. Further, the relationships between biochemical composition and mechanical properties were age-dependent, with cartilage from patients less than 30 years of age showing greater dependence of equilibrium modulus and hydraulic permeability on GAG and hydroxyproline content. This suggests that changes in matrix organization may accompany changes in tissue composition.

Autologous tissue-engineered trachea with sheep nasal chondrocytes

OBJECTIVE

This study was designed to evaluate the ability of autologous tissue-engineered trachea shaped in a helix to form the structural component of a functional tracheal replacement.

METHODS

Nasal septum were harvested from six 2-month-old sheep. Chondrocytes and fibroblasts were isolated from tissue and cultured in media for 2 weeks. Both types of cells were seeded onto separate nonwoven meshes of polyglycolic acid. The chondrocyte-seeded mesh was wound around a 20-mm-diameter x 50-mm-long helical template and then covered with the fibroblast-seeded mesh. In 2 separate studies the implants were placed either in a subcutaneous pocket in the nude rat (rat tissue-engineered trachea) or in the neck of a sheep (sheep tissue-engineered trachea). Rat tissue-engineered tracheas were harvested after 8 weeks and analyzed by means of histology and biochemistry. Sheep tissue-engineered tracheas were harvested from the neck at 8 weeks and anastomosed into a 5-cm defect in the sheep trachea.

RESULTS

Sheep receiving tissue-engineered trachea grafts survived for 2 to 7 days after implantation. Gross morphology and tissue morphology were similar to that of native tracheas. Hematoxylin-and-eosin staining of rat tissue-engineered tracheas and sheep tissue-engineered tracheas revealed the presence of mature cartilage surrounded by connective tissue. Safranin-O staining showed that rat tissue-engineered tracheas and sheep tissue-engineered tracheas had similar morphologies to native tracheal cartilage. Collagen, proteoglycan, and cell contents were similar to those seen in native tracheal tissue in rat tissue-engineered tracheas. Collagen and cell contents of sheep tissue-engineered tracheas were elevated compared with that of normal tracheas, whereas proteoglycan content was less than that found in normal tracheas.

CONCLUSIONS

This study demonstrated the feasibility of recreating the cartilage and fibrous portion of the trachea with autologous tissue harvested from single procedure. This approach might provide a benefit to individuals needing tracheal resection.

The mechanism of aggrecan release from cartilage differs with tissue origin and the agent used to stimulate catabolism

The mechanisms of aggrecan degradation in adult human articular, adult bovine nasal and fetal bovine epiphyseal cartilage in response to either interleukin-1beta (IL-1beta) or retinoic acid were compared using an explant culture system. Bovine nasal cartilage cultured with either IL-1beta or retinoic acid exhibited significant release of glycosaminoglycan (GAG). For both factors, aggrecan proteolysis occurred predominantly at the 'aggrecanase' site, with no evidence for the action of matrix metalloproteinases, and resulted in the appearance of the corresponding G1 fragment in tissue extracts and in culture media. In human cartilage, little effect of IL-1beta was seen, but abundant release of GAG occurred in the presence of retinoic acid, with evidence of aggrecanase action. Treatment of fetal epiphyseal cartilage with retinoic acid resulted in significant GAG release, whereas treatment with IL-1beta did not. In the retinoic acid-treated tissue, however, no evidence for the cleavage of aggrecan in the interglobular region was apparent. Thus, in the fetal system, agents in addition to aggrecanase and matrix metalloproteinases appear to be active. Taken together, these data demonstrate that the pathways utilized for aggrecan catabolism may vary between different cartilages for a given stimulatory agent, and that, for a given tissue, different factors may elicit aggrecan release via different pathways.

Control of extracellular matrix homeostasis of normal cartilage by a TGFbeta autocrine pathway. Validation of flow cytometry as a tool to study chondrocyte metabolism in vitro

OBJECTIVE

To validate flow cytometry as an experimental technique for the study of the homeostasis of the extracellular matrix (ECM) of human articular cartilage.

METHODS

Given the established insights in the relation between the transforming growth factor (TGF)-beta type II Receptor (TGF-betaRII)/TGF-beta auto/paracrine pathway, the intracellular levels of matrix metalloproteinases (MMPs) and their natural inhibitors (TIMPs), and the accumulation of ECM molecules in the ECM of articular cartilage, this metabolic pathway was used as a reference model to fulfill the objective. Chondrocytes were liberated from visually intact femoral condyle cartilage and cultured in gelled agarose to maintain their differentiated phenotype. After 2 weeks of culture, the chondrocytes were isolated from the agarose and flow cytometry was used to analyse the expression of TGF-betaRII on the plasmamembrane, the expression of TGFbeta1, MMP-1, MMP-3, TIMP-1 and TIMP-3 inside the cells, as well as the amounts of aggrecan, type II collagen and hyaluronan in the cell-associated matrix (CAM). The expression of the different substances was analysed with flow cytometry and reported as mean fluorescence intensity (MFI), which is due to the binding of FITC-labeled antibodies to their specific antigens. In addition, the effects of exogenous TGFbeta1 on the expression of these proteins was investigated on chondrocytes cultured in serum-free media. Enzyme Linked Immunosorbent Assay (ELISA) was performed to evaluate the MMP-1, MMP-3, TIMP-1 and MMP-1/TIMP-1 complex in the culture medium collected after the last 3 days of the culture period. The correlations between the data were analysed with the Spearman's test.

RESULTS

Exogenous TGF-beta1 increased the accumulation of aggrecan and hyaluronan in the CAM of chondrocytes and down-regulated the intracellular levels of MMP-1 and -3. TIMP-1 and -3 were increased after exposure to TGF-beta1. Baseline expression of TGF-betaRII on the plasmamembrane of normal human articular chondrocytes significantly correlated with the intracellular levels of TGFbeta1, TIMP-1 and TIMP-3. TGFbeta1 was correlated with TIMP-1, TIMP-3 and MMP-1. Aggrecan in the CAM was inversely correlated with the ratio of MMP-1 to TIMPs. In addition, there were correlations between TIMP-1 and TIMP-3, aggrecan and hyaluronan. ELISA also revealed the correlation between MMP-1 and TIMP-1 secreted by the chondrocytes into the nutrient medium. MMP-1/TIMP-1 complex was hardly found in the medium.

CONCLUSIONS

Some aspects of ECM metabolism of normal cartilage were evaluated by flow cytometry. Chondrocytes from normal human cartilage, when cultured in gelled agarose, showed correlations between the expression of TGF-betaRII/TGF-beta1 and the intracellular levels of TIMPs, indicating that TGF-beta autocrine pathway may contribute to homeostasis of the ECM in the normal cartilage. The relations between MMPs, TIMPs and the ECM molecules support that a physiological balance between MMPs and TIMPs results in a well-controlled matrix turnover in normal cartilage.

Cartilage tissue remodeling in response to mechanical forces

Recent studies suggest that there are multiple regulatory pathways by which chondrocytes in articular cartilage sense and respond to mechanical stimuli, including upstream signaling pathways and mechanisms that may lead to direct changes at the level of transcription, translation, post-translational modifications, and cell-mediated extracellular assembly and degradation of the tissue matrix. This review focuses on the effects of mechanical loading on cartilage and the resulting chondrocyte-mediated biosynthesis, remodeling, degradation, and repair of this tissue. The effects of compression and tissue shear deformation are compared, and approaches to the study of mechanical regulation of gene expression are described. Of particular interest regarding dense connective tissues, recent experiments have shown that mechanotransduction is critically important in vivo in the cell-mediated feedback between physical stimuli, the molecular structure of newly synthesized matrix molecules, and the resulting macroscopic biomechanical properties of the tissue.

In vitro models for investigation of the effects of acute mechanical injury on cartilage

Traumatic injury to a joint is known to increase the risk for the development of secondary osteoarthritis, but it is unclear how this process occurs. The existence of such a discrete event that can lead to an increased risk of osteoarthritis has spurred interest in developing in vitro models of traumatic joint injury. The current authors review some of the recent insights gained from these model systems into the pathogenesis of osteoarthritis, including the evidence for an initial, irreversible insult to chondrocytes during mechanical injury, the occurrence of apoptotic chondrocyte death, and attempts to identify the effects of trauma on chondrocyte metabolic response. Results also are presented from the authors' ongoing studies of the degradative pathways initiated by traumatic mechanical loads, the mechanism by which chondrocytes are affected during compression, and possible contributions of the joint capsule to posttraumatic cartilage degradation.

Use of an antineoepitope antibody for identification of type-II collagen degradation in equine articular cartilage

OBJECTIVE

To develop an antibody that specifically recognizes collagenase-cleaved type-II collagen in equine articular cartilage.

SAMPLE POPULATION

Cartilage specimens from horses euthanatized for problems unrelated to the musculoskeletal system.

PROCEDURE

A peptide was synthesized representing the carboxy- (C-) terminus (neoepitope) of the equine type-II collagen fragment created by mammalian collagenases. This peptide was used to produce a polyclonal antibody, characterized by western analysis for reactivity to native and collagenase-cleaved equine collagens. The antibody was evaluated as an antineoepitope antibody by ELISA, using peptides +/- an amino acid at the C-terminus of the immunizing peptide. Collagen cleavage was assayed from equine articular cartilage cultured with interleukin-1 (IL-1), +/- a synthetic MMP inhibitor, BAY 12-9566. Cartilage specimens from osteoarthritic and nonarthritic joints were compared for antibody staining.

RESULTS

An antibody, 234CEQ, recognized only collagenase-generated 3/4-length fragments of equine type-II collagen. This was a true antineoepitope antibody, as altering the C-terminus of the immunizing peptide significantly decreased competition for binding in an inhibition ELISA. The IL-1-induced release of type-II collagen fragments from articular cartilage was prevented with the MMP inhibitor. Cartilage from an osteoarthritic joint of a horse had increased staining with the 234CEQ antibody, compared with normal articular cartilage.

CONCLUSIONS AND CLINICAL RELEVANCE

We generated an antineoepitope antibody recognizing collagenase-cleaved type-II collagen of horses. This antibody detects increases in type-II collagen cleavage in diseased equine articular cartilage. The 234CEQ antibody has the potential to aid in the early diagnosis of arthritis and to monitor treatment responses.