The effect of bacterial lipopolysaccharides on the biosynthesis and release of proteoglycans from calf articular cartilage cultures

An enzyme-sensitive PEG hydrogel based on aggrecan catabolism for cartilage tissue engineering

A new cartilage-specific degradable hydrogel based on photoclickable thiol-ene poly(ethylene glycol) (PEG) hydrogels is presented. The hydrogel crosslinks are composed of the peptide, CRDTEGE-ARGSVIDRC, derived from the aggrecanase-cleavable site in aggrecan. This new hydrogel is evaluated for use in cartilage tissue engineering by encapsulating bovine chondrocytes from different cell sources (skeletally immature (juvenile) and mature (adult) donors and adult cells stimulated with proinflammatory lipopolysaccharide (LPS)) and culturing for 12 weeks. Regardless of cell source, a twofold decrease in compressive modulus is observed by 12 weeks, but without significant hydrogel swelling indicating limited bulk degradation. For juvenile cells, a connected matrix rich in aggrecan and collagen II, but minimal collagens I and X is observed. For adult cells, less matrix, but similar quality, is deposited. Aggrecanase activity is elevated, although without accelerating bulk hydrogel degradation. LPS further decreases matrix production, but does not affect aggrecanase activity. In contrast, matrix deposition in the nondegradable hydrogels consists of aggrecan and collagens I, II, and X, indicative of hypertrophic cartilage. Lastly, no inflammatory response in chondrocytes is observed by the aggrecanase-sensitive hydrogels. Overall, it is demonstrated that this new aggrecanase-sensitive hydrogel, which is degradable by chondrocytes and promotes a hyaline-like engineered cartilage, is promising for cartilage regeneration.

Effects of low dose X-ray irradiation on porcine articular cartilage explants

Ionizing radiation therapy is a crucial treatment for cancer, but can damage surrounding normal tissues. Damage to articular cartilage leading to arthropathy can occur at irradiated sites. It is unclear whether this response is due to damaging surrounding skeletal structures or direct effects on cartilage. In this study, we showed that irradiation with 2 Gy of X-rays causes a significant reduction in the stiffness of porcine explants 1 week post-irradiation. By using both microindentation and indentation-type atomic force microscopy, ionizing radiation reduces stiffness in both the superficial zone, and throughout the entire thickness of the tissue. Young's modulus values were 75% and 60% lower in 2 Gy irradiated samples when compared with controls using microindentation and nanoindentation, respectively. Glycosaminoglycans (GAGs) released into the culture media of irradiated samples was nearly 100% greater at 24 h after exposure. While collagen content in the tissue is similar between groups, GAG content is 55% lower in irradiated explants compared with controls 7 days after exposure. Therefore, the irradiated explants are unable to recover from the initial loss of GAGs by 1 week. This acute loss of GAGs is a likely contributor to the reduction in modulus seen after exposure to ionizing radiation.

Chondrocyte culture and assay

Chondrocytes constitute the sole cell type found within cartilage, and control the formation and composition of cartilage. Cellular, biochemical and pharmacological studies of arthritis and other cartilage disorders have increasingly focused on chondrocyte function. Three methods are presented in this unit for culturing chondrocytes, and two assays are described that characterize proteoglycan synthesis, a key measure of chondrocyte function.Chondrocytes constitute the sole cell type found within cartilage, and control the formation and composition of cartilage.

Physiological performance of a detergent decellularized heart valve implanted for 15 months in Vietnamese pigs: surgical procedure, follow-up, and explant inspection

This study features the longest experimental follow-up for decellularized heart valves implanted in an animal model. Porcine aortic heart valves were decellularized according to a disclosed standardized method in which TRITON X-100 and sodium cholate (TRICOL) are used in succession, followed by a further treatment with the endonuclease Benzonase to completely remove the nucleic acid remnants. Experimental animals (n = 17), represented by Vietnamese pigs (VPs), received a decellularized aortic allograft as a substitute for the replacement of their right ventricular outflow tract. The surgical implantation of the TRICOL-treated aortic valve conduit was successful in 11 VPs, while perioperative or postoperative complications occurred in the remaining six animals. In the sham-operated group (n = 4), the native pulmonary root was excised and immediately reimplanted orthotopically in the same animal. Echocardiography demonstrated a satisfactory hemodynamic performance of the TRICOL-treated valves during follow-up as well as the absence of relevant leaflet alterations concerning thickness and motility or valve insufficiency. At explantation, macroscopic inspection of tissue-engineered heart valve conduits did not evidence calcifications and showed a decreased wall thickness, comparable to that of the reimplanted native pulmonary roots. Noteworthy, extended functional performance, recovery of DNA content, and active extracellular matrix precursor incorporation are apparently compatible with the properties of a living self-supporting substitute.

Peptides of type II collagen can induce the cleavage of type II collagen and aggrecan in articular cartilage

The objective of this study was to determine whether a fragment(s) of type II collagen can induce cartilage degradation. Fragments generated by cyanogen bromide (CB) cleavage of purified bovine type II collagen were separated by HPLC. These fragments together with selected overlapping synthetic peptides were first analysed for their capacity to induce cleavage of type II collagen by collagenases in chondrocyte and explant cultures of healthy adult bovine articular cartilage. Collagen cleavage was measured by immunoassay and degradation of proteoglycan (mainly aggrecan) was determined by analysis of cleavage products of core protein by Western blotting. Gene expression of matrix metalloproteinases MMP-13 and MMP-1 was measured using Real-time PCR. Induction of denaturation of type II collagen in situ in cartilage matrix with exposure of the CB domain was identified with a polyclonal and monoclonal antibodies that only react with this domain in denatured but not native type II collagen. As well as the mixture of CB fragments and peptide CB12, a single synthetic peptide CB12-II (residues 195-218), but not synthetic peptide CB12-IV (residues 231-254), potently and consistently induced in explant cultures at 10 microM and 25 microM, in a time, cell and dose dependent manner, collagenase-induced cleavage of type II collagen accompanied by upregulation of MMP-13 expression but not MMP-1. In isolated chondrocyte cultures CB12-II induced very limited upregulation of MMP-13 as well as MMP-1 expression. Although this was accompanied by concomitant induction of cleavage of type II collagen by collagenases, this was not associated by aggrecan cleavage. Peptide CB12-IV, which had no effect on collagen cleavage, clearly induced aggrecanase specific cleavage of the core protein of this proteoglycan. Thus these events involving matrix molecule cleavage can importantly occur independently of each other, contrary to popular belief. Denaturation of type II collagen with exposure of the CB12-II domain was also shown to be much increased in osteoarthritic human cartilage compared to non-arthritic cartilage. These observations reveal that peptides of type II collagen, to which there is increased exposure in osteoarthritic cartilage, can when present in sufficient concentration induce cleavage of type II collagen (CB12-II) and aggrecan (CB12-IV) accompanied by increased expression of collagenases. Such increased concentrations of denatured collagen are present in adult and osteoarthritic cartilages and the exposure of chondrocytes to the sequences they encode, either in soluble or more likely insoluble form, may therefore play a role in the excessive resorption of matrix molecules that is seen in arthritis and development.

Comparison of cellular response in bovine intervertebral disc cells and articular chondrocytes: effects .of lipopolysaccharide on proteoglycan metabolism

Lipopolysaccharide (LPS) induces matrix degradation and markedly stimulates the production of several cytokines, i.e., interleukin-1beta, -6, and -10, by disc cells and chondrocytes. We performed a series of experiments to compare cellular responses of cells from the bovine intervertebral disc (nucleus pulposus and annulus fibrosus) and from bovine articular cartilage to LPS. Alginate beads containing cells isolated from bovine intervertebral discs and articular cartilage were cultured with or without LPS in the presence of 10% fetal bovine serum. The DNA content and the rate of proteoglycan synthesis and degradation were determined. In articular chondrocytes, LPS strongly suppressed cell proliferation and proteoglycan synthesis in a dose-dependent manner and stimulated proteoglycan degradation. Compared with articular chondrocytes, nucleus pulposus cells responded in a similar, although less pronounced manner. However, treatment of annulus fibrosus cells with LPS showed no significant effects on proteoglycan synthesis or degradation. A slight, but statistically significant, inhibition of cell proliferation was observed at high concentrations of LPS in annulus fibrosus cells. Thus, LPS suppressed proteoglycan synthesis and stimulated proteoglycan degradation by articular chondrocytes and nucleus pulposus cells. The effects of LPS on annulus fibrosus cells were minor compared with those on the other two cell types. The dissimilar effects of LPS on the various cell types suggest metabolic differences between these cells and may further indicate a divergence in pathways of LPS signaling and a differential sensitivity to exogenous stimuli such as LPS.

Effect of selected wound antiseptics on adult articular cartilage (bovine sesamoid bone) in the presence of Escherichia coli and Staphylococcus aureus

After removing an inoculum of 10(8)-10(9) cfu of Escherichia coli (E. coli) or Staphylococcus aureus (S. aureus) effectively within 2 h from bovine sesamoid bones (bsb) using the iodophore Betaisodona [0.5 and 1.0% (v/v) PVP-I], the biguanide polihexanide (PHMB) [0.005 and 0.01% (v/v)], and the bispyridinamine Octenidine (Oct) [0.005 and 0.01% (v/v)] the metabolic effect on proteoglycans (PG) in bsb was investigated by subsequent culture of bsb for 7 d and biosynthetically labeling with (35)S-sulfate for a period of 24 h. The treatment with the iodophore stimulates the incorporation of (35)S-sulfate into PG, whereas that of Oct was toxic. The PHMB treatment was both tolerated and effective only when it was used at low concentrations (0.005%). The antiseptic treatment did not result in an increase of catabolism of PG. This in vitro study clearly demonstrates that irrigation of cartilage with an antiseptic should be limited to an effective concentration and treatment time compatible with antiseptic function. Iodophores have no negative feedback on cartilage metabolism, moreover, they stimulate chondrocytes in vitro. Cationic antiseptics are not suited as irrigating solutions.

Involvement of CD44 in induction of matrix metalloproteinases by a COOH-terminal heparin-binding fragment of fibronectin in human articular cartilage in culture

OBJECTIVE

To investigate the mechanism of induction of matrix metalloproteinases (MMPs) by a 40-kd COOH-terminal heparin-binding fibronectin fragment (HBFN-f) containing III12-14 and IIICS domains in human articular cartilage in culture.

METHODS

Human articular cartilage was removed from macroscopically normal femoral heads and cultured with HBFN-f. MMP secretion into conditioned media was analyzed by immunoblotting (MMPs 1 and 13) and by gelatin zymography (MMPs 2 and 9). Type II collagen cleavage by collagenase was monitored in culture by immunoassay. Involvement of specific peptide-binding domains in HBFN-f and the involvement of CD44 were assessed with synthetic peptides and an anti-CD44 antibody. Immunofluorescence histochemistry was performed using fluorescein isothiocyanate-conjugated anti-CD44 antibody.

RESULTS

HBFN-f stimulated production of MMPs 1, 2, 9, and 13 in association with type II collagen cleavage by collagenase in human articular cartilage. Peptide V (WQPPRARI) of HBFN-f, which can bind cell surface heparan sulfate proteoglycan (HSPG), blocked MMP induction by HBFN-f, while the scrambled peptide V (RPQIPWAR) had no effect. Peptide CS-1 of 25 amino acids in IIICS of HBFN-f caused no significant effect. Treatment of cartilage with anti-CD44 antibody or HSPG resulted in significant inhibition of HBFN-f-stimulated MMP production. Preincubation with peptide V blocked binding of the anti-CD44 antibody to chondrocytes in cartilage.

CONCLUSION

Interaction of the peptide V sequence in HBFN-f with glycosaminoglycans, such as those in CD44, plays an important role in HBFN-f-stimulated MMP production in articular cartilage. Because CD44 is up-regulated in osteoarthritic and rheumatoid arthritic cartilage, the role of the interaction between CD44 and HBFN-f in these pathologies should be of relevance and should be studied further.

Preferential incorporation of glucosamine into the galactosamine moieties of chondroitin sulfates in articular cartilage explants

OBJECTIVE

To determine the metabolic fate of glucosamine (GlcN) in intact articular cartilage tissue.

METHODS

Intact articular cartilage explants were cultured for up to 13 days in Dulbecco's modified Eagle's medium supplemented with 1) 1-13C-labeled GlcN, 2) 1-13C-labeled glucose (Glc), or 3) no labeling. Every 3-4 days, samples were removed and frozen in liquid nitrogen for carbon-13 magnetic resonance spectroscopic (MRS) analysis. The metabolic products of the labeled precursors were determined from the MRS data based on resonance positions and comparison with known standards and published values.

RESULTS

GlcN was taken up by the chondrocytes and incorporated selectively into the hexosamine, but not the hexuronic acid, components of the glycosaminoglycan chains of articular cartilage proteoglycan. The data also demonstrated that GlcN is the substrate of choice for the galactosamine moieties of the chondroitin sulfates, incorporating at levels 300% higher than with an equivalent amount of labeled Glc.

CONCLUSION

The results indicate that GlcN facilitates the production of proteoglycan components that are synthesized through the hexosamine biochemical pathway.

Effects of anti-inflammatory drugs on lipopolysaccharide-challenged and -unchallenged equine synovial explants

OBJECTIVE

To evaluate the effects of anti-inflammatory drugs on lipopolysaccharide (LPS)-challenged and -unchallenged equine synovial membrane in terms of production of prostaglandin E2 (PGE2) and hyaluronan, viability, and histomorphologic characteristics.

SAMPLE POPULATION

Synovial membranes were collected from the carpal, tarsocrural, and femoropatellar joints of 6 adult horses.

PROCEDURE

Synovial membranes from each horse were minced and pooled and explants were treated with one of the following: no drug (control), drug, LPS alone, or LPS and drug. Treatment drugs were phenylbutazone (PBZ), flunixin meglumine (FNX), ketoprofen (KET), carprofen (CRP), meloxicam (MEL), low-concentration methylprednisolone (METH), high-concentration METH, dimethyl sulfoxide (DMSO), or an experimental COX-2 inhibitor (dissolved in DMSO). Following 48 hours of culture, medium was assayed for PGE2 and hyaluronan concentration. Synovial explants were assessed for viability and histomorphologic characteristics.

RESULTS

For the LPS-challenged explants, PBZ, FNX, KTP CRF MEL, and low-concentration METH suppressed PGE2 production, compared with LPS challenge alone. Only MEL suppressed PGE2 production from LPS-challenged explants, compared with unchallenged explants. Synovial explants maintained > 90% viability and there was no significant difference in viability or hyaluronan production among explants. Histomorphologic scores were significantly decreased for explants treated with low-concentration METH or DMSO.

CONCLUSIONS AND CLINICAL RELEVANCE

PBZ, FNX, KTP, CRFP MEL, and low-concentration METH suppressed PGE2 production in LPS-challenged explants. Meloxicam appeared to have more selective suppression of COX-2 activity. Histomorphologic scores suggest detrimental effects of METH, DMSO, and the experimental COX-2 inhibitor. Commonly used nonsteroidal anti-inflammatory drugs suppress induced synovial membrane PGE2 production without detrimental effects on synovial membrane viability and function.

Metabolic kinetics of proteoglycans by embryonic chick sternal cartilage in culture

Explant cultures of embryonic chick sternum have been widely studied, but the kinetics of biosynthesis of proteoglycans by this tissue in culture has not been characterized. Caudal cartilaginous portions of 16-day-old embryonic chick sterna were cultured for 8 days. Histological examination showed that the fresh cartilage contained morphologically homogenous chondrocytes, which were embedded in a uniform extracellular matrix. After culture for 8 days, the histological appearance of the explant remained unchanged but the tissue increased in size with time as indicated by a progressive increase in DNA content and in the content of glycosaminoglycan and collagen. Rates of degradation and release from the tissue of proteoglycans labeled in ovo with 35S were first order during culture, as were the unlabeled proteoglycans. Proteoglycan synthesis was high during the first 2 days of culture, and this then gradually decreased from this high level during the following 2 days. Synthesis was then maintained at a constant level for the remainder of the culture period. After culture for 2 and 7 days, the proteoglycans synthesized by the explants were identical to the preexisting proteoglycans in hydrodynamic size, glycosaminoglycan chain size, and ability to form aggregates. These findings suggest that the embryonic chick sterna maintained a stable cartilage phenotype during the extended culture periods. The initial rapid rate of matrix turnover was probably attributable to an adaptation of the tissue to ex ovo culture conditions and the subsequent maintenance of cellular activities at a lower level indicated the establishment of a steady-state rate of metabolism.

Aggrecan degradation in chondrocytes is mediated by reactive oxygen species and protected by antioxidants

Reactive oxygen species (ROS) are implicated in aging of cartilage and in the pathogenesis of osteoarthritis. However, the biological role of chondrocytes-derived ROS has not been elucidated. An in-vitro model was developed to study the role of chondrocyte-derived ROS in cartilage matrix degradation. The primary articular chondrocytes were cultured and the aggrecan matrix was radiolabeled with 35-sulfate. The labeled aggrecan matrix was washed to remove unincorporated label and chondrocytes were returned to serum free balanced salt solution. The cell-monolayer-matrix sensitivity to oxidative damage due to either hydrogen peroxide or glucose oxidase was established by monitoring the release of labeled aggrecan into the medium. Lipopolysaccharide (LPS) treatment of chondrocyte-monolayer enhanced the release of labeled aggrecan. Catalase significantly prevented the release of labeled aggrecan in LPS-chondrocyte cultures, suggesting a role for chondrocyte-derived hydrogen peroxide in aggrecan degradation. Superoxide dismutase or boiled catalase had no such inhibitory effect. The effect of several antioxidants on LPS-chondrocyte-dependent aggrecan degradation was examined. Hydroxyl radical scavengers (mannitol and thiourea) significantly decreased aggrecan degradation. A spin trapping agent N-tert-butyl-phenylnitrone (but not its inactive analog tert-butyl-phenylcarbonate) significantly decreased aggrecan degradation. Butylated hydroxytoluene also inhibited aggrecan degradation, whereas the other lipophilic antioxidant tested, propyl gallate, had a marked dose-dependent inhibitory effect. These data indicate that general antioxidants, hydroxyl radical scavengers, antioxidant vitamins, iron chelating agents, lipophilic antioxidants, and spin trapping agents can influence chondrocyte-dependent aggrecan degradation. These studies support the role of a chondrocyte-dependent oxidative mechanism in aggrecan degradation and indicate that antioxidants can prevent matrix degradation and therefore may have a preventive or therapeutic value in arthritis. The enhancement of oxidative activity in chondrocytes and its damaging effect on matrix may be an important mechanism of matrix degradation in osteoarthritis.

The role and content of endogenous insulin-like growth factor-binding proteins in bovine articular cartilage

Previous work identified insulin-like growth factor (IGF)-binding proteins (IGF-BPs) in chondrocyte culture fluids, but the relationship of these proteins to the composition of intact cartilage was not established. The aim of this work was to analyze the IGF-BP system resident in bovine articular cartilage and to examine its role in IGF-1-regulated proteoglycan (PG) metabolism. Protein extracts of freshly dissected or cultured cartilage slices were analyzed by 125I-IGF-2 ligand blotting. Fresh tissue and basal cultured samples (serum-free) from nine animals, aged fetal to adult, contained two major IGF-BPs of approximately 31,000 and 24,000-21,500 Mr, with the latter doublet being dominant. The 31,000 Mr protein was identified as IGF-BP-2 by specific immunoreactivity with two polyclonal antibodies, and the 24,000-21,500 Mr doublet was identified as IGF-BP-6 by reactivity with a specific polyclonal antibody and by marked preferential affinity for IGF-2 over IGF-1 by ligand blotting. Treatment of the cartilage cultures with 10 ng/ml transforming growth factor-beta (TGF-beta1) for 1 week led to an accumulation of IGF-BP-2, while IGF-BP-6 was unchanged (ligand blots, n = 6 animals). IGF-1 had a similar but much less pronounced effect. The IGF-BP increase following TGF-beta treatment, quantified by charcoal assay, was on average 6-fold, while total protein increased only 1.2-fold (n = 4). By contrast, IGF-1 (10 ng/ml) increased IGF-BP by <2-fold (n = 4), and retinoic acid, at 1 x 10(-8) M was not effective (n = 3). As before, 10 ng/ml TGF-beta or IGF-1 increased proteoglycan synthesis and maintained its homeostasis. IGF-1 analogs with reduced affinity for the IGF-BPs were tested. The effect of an A-chain analog (Thr49, Ser50, Ile51) on PG synthesis was comparable to that of IGF-1, even though the analog had one-half of the IGF-1 affinity for the type I IGF receptor. A B-chain analog, with one-third the receptor affinity of IGF-1, promoted an average 2-fold higher PG synthesis in the linear response range to concentration. Thus, in relation to their respective affinities for the IGF-type I receptor, both IGF analogs were more effective than native IGF-1. These results suggest that an overall effect of the endogenous IGF-BP activity in articular cartilage under the test conditions is the inhibition of IGF-1-stimulated proteoglycan synthesis.

Proteoglycan metabolism of equine articular chondrocytes cultured in alginate beads

Equine chondrocytes were cultured in vitro for 30 days in ionically gelled alginate beads. The alginate polymerises into a stable gel in the presence of divalent cations (calcium), and rapid depolymerisation in the presence of a calcium chelator releases the viable chondrocytes. The chondrocytes maintained a spherical appearance for 30 days in culture, in marked contrast to monolayer cultures, which develop a dedifferentiated fibroblastic morphology. The major proteoglycan molecule produced by the encapsulated chondrocytes was aggrecan, of similar hydrodynamic size to aggrecan molecules present in the matrix of the articular cartilage from which the cells were harvested. Link protein, keratan sulphate and chondroitin sulphate were also synthesised by the chondrocytes, as demonstrated by immunohistochemistry. The proteoglycan secreted by the chondrocytes consisted of at least two pools, one remaining adjacent to the cell and forming a dense, cell-associated matrix, and another migrating more peripherally into the intercellular compartment. Newly synthesised proteoglycans extracted from the pericellular matrix and the intercellular matrix were similar in hydrodynamic size and aggregated in the presence of exogenous hyaluronan.

Biochemical and biomechanical alterations in equine articular cartilage following an experimentally-induced synovitis

The effects of inflammation on the biochemical and biomechanical properties of articular cartilage at two sites (dorsal and palmar) from the radial facet of the equine third carpal bone were examined in response to a synovitis induced with Escherichia coli lipopolysaccharide (LPS). Four groups were studied. In group 1 synovitis was induced at time zero and evaluated at week 6. Group 2 was the sham-treated control for group 1. In group 3 synovitis was induced at time zero and evaluated at week 2. Group 4 was the sham-treated control for group 3. There was a significant increase (P < 0.05) in newly synthesized proteoglycan PG from both sites in group 3 as compared to the sham-treated groups and group 1. No significant difference in the endogenous PG concentration between groups or sites was detected. Sepharose CL-2B revealed two peaks of newly synthesized PG in all groups; an early peak (Kav 0.11-0.13) and a late peak (Kav 0.48-0.64). Newly synthesized PG profiles from sham-treated groups and group 3 were similar, but the group 3 PG profile exhibited a more pronounced early peak. Conversely, the PG profile from group 1 demonstrated a more prominent late peak. Electrophoresis and Western blot analysis of the pooled late PG peak fractions from the sham-treated and group 1 showed a single toluidine blue stained band from both sites which reacted with monoclonal antibody (MAb) 1C6. By contrast, the late peak from the palmar site in group 3 showed an additional faster moving component on composite gels which did not react with MAb 1C6. There was a significant decrease in Poisson's ratio and a significant increase in cartilage thickness in groups 1 and 3 which had received synovitis. The increase in cartilage thickness of groups 1 and 3 was also significantly affected by site (dorsal > palmar). There was no significant difference in aggregate modulus or permeability constant among groups. Primary joint inflammation induced by LPS alters the biochemical and biomechanical properties of the articular cartilage as a function of time and site. An increase in chondrocyte PG synthesis in the early period following synovitis may be a reparative response to the inflammatory insult. Continued alterations in the qualitative PG composition in the later period following synovitis may represent a shift in chondrocyte metabolism to repopulate the existing cartilage matrix.

Pulsed electromagnetic fields influence hyaline cartilage extracellular matrix composition without affecting molecular structure

Pulsed electromagnetic fields (PEMF) influence the extracellular matrix metabolism of a diverse range of skeletal tissues. This study focuses upon the effect of PEMF on the composition and molecular structure of cartilage proteoglycans. Sixteen-day-old embryonic chick sterna were explanted to culture and exposed to a PEMF for 3 h/day for 48 h. PEMF treatment did not affect the DNA content of explants but stimulated elevation of glycosaminoglycan content in the explant and conserved the tissue's histological integrity. The glycosaminoglycans in sterna exposed to PEMF were indistinguishable from those in controls in their composition of chondroitin sulfate resulting from chondroitinase ABC digestion. Specific examination with [35S]-sulfate labels showed that PEMF treatment significantly suppressed both the degradation of pre-existing glycosaminoglycans biosynthetically labeled in ovo and the synthesis of new [35S]-sulfated glycosaminoglycans. The average size and aggregating ability of pre-existing and newly synthesized [35S]-sulfated proteoglycans extracted with 4 M guanidinium chloride from PEMF-treated cartilage explants were identical to controls. The chain length and degree of sulfation of [35S]-sulfated glycosaminoglycans also were identical in control and PEMF-treated cultures. PEMF treatment also reduced the amount of both unlabeled glycosaminoglycans and labeled pre-existing and newly synthesized [35S]-sulfated glycosaminoglycans recovered from the nutrient media. [35S]-Sulfated proteoglycans released to the media of both control and PEMF-treated cultures were mostly degradation products although their glycosaminoglycan chain size was unchanged. These results demonstrate that exposure of embryonic chick cartilage explants to PEMF for 3 h/day maintains a balanced proteoglycan composition by down-regulating its turnover without affecting either molecular structure or function.

Proteoglycan metabolism of equine articular cartilage and its modulation by insulin-like growth factors

The effect of human recombinant insulin-like growth factor 1 (rhIGF-1) on proteoglycan (PG) metabolism of full thickness equine articular cartilage explants was investigated. PG synthesis was stimulated at all ages, but higher concentrations of rhIGF-1 were required for maximal stimulation of adult cartilage. There were no changes in the hydrodynamic size, electrophoretic heterogeneity or composition of proteoglycans isolated from rhIGF-1-stimulated cartilage. rhIGF-1 reduced the rate of turnover of both newly synthesized and endogenous proteoglycans in all ages of cartilage investigated. The structure of proteoglycan fragments retained within the matrix and those released into the culture medium was unaffected by IGF-1 stimulation, suggesting that this peptide is a key regulator of the proteoglycan composition of equine articular cartilage extracellular matrix.

Experimentally-induced synovitis as a model for acute synovitis in the horse

The use of extremely small dosages of intra-articular E. coli lipopolysaccharide (LPS) endotoxin can create a model of synovitis that mimics acute synovitis in horses. Dosages of 5000 ng, 25 ng, 0.5 ng, 0.25 ng, 0.17 ng and 0.125 ng per joint were injected into various joints of a total of 6 horses. The dose response of LPS on clinical signs and synovial fluid parameters was evaluated at baseline and 12, 24, 36 and 48 h after LPS injection. Peripheral venous blood analysis was performed at baseline and at 0, 4, and 12 h after LPS injection. Dosages greater than 0.5 ng/joint resulted in clinical signs of endotoxaemia including fever, depression, inappetence and non-weightbearing lameness. Although the total peripheral venous leucocyte count was not decreased at any dosage, the 5000 ng/joint dosage of LPS altered venous leucocyte differential resulting in an increase in the number of segmented and band neutrophils with a concomitant decrease in lymphocytes. Synovial fluid total nucleated cell count (TNC) and total protein (TP) was linearly responsive to increases in intra-articular LPS dosages up to the 0.5 ng/joint dose. At dosages of LPS > 0.5 ng, synovial fluid mean +/- s.e.m. TNC and TP were 122.0 +/- 27 x 10(9) cells/l and 59.3 +/- 1.7 milligrams respectively, at 12 h after injection. This may represent the maximal response of the joint to increased concentrations of LPS endotoxin over 0.5 ng/joint.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation of the proteoglycan metabolism of mature equine articular cartilage and its regulation by interleukin-1

The effect of human recombinant interleukin-1 beta (rhIL-1 beta) on proteoglycan metabolism was investigated in cultures of full thickness explants of articular cartilage from horses 3-21 years of age. Proteoglycan synthesis was inhibited at all ages but no alteration in the hydrodynamic size or electrophoretic heterogeneity was observed in proteoglycan isolated from rhIL-1 beta stimulated cartilage. The sulphation pattern of the newly synthesised proteoglycan molecules was, however, significantly affected by the presence of the peptide regulatory factor. Interleukin-1 had no effect on the rate of turnover of newly synthesised or endogenous proteoglycans in mature equine articular cartilage and did not influence the structure of proteoglycan fragments released into the culture medium. These observations suggest that IL-1, released into synovial fluid during inflammation, may modify the proteoglycan composition of normal equine cartilage not by stimulating catabolic enzymes capable of degrading the resident proteoglycans but by promoting the deposition of a reduced number of newly synthesised proteoglycan molecules of abnormal composition.

Phenotypic stability of bovine articular chondrocytes after long-term culture in alginate beads

Articular chondrocytes embedded in alginate gel produce de novo a matrix rich in collagens and proteoglycans. A major advantage of this culture system is that the cells can be recovered by chelating the calcium, which otherwise maintains the alginate in its gel state. Chondrocytes thus released are surrounded by tightly bound cell-associated matrix, which seems to correspond to the pericellular and territorial matrices identified in cartilage by electron microscopy. The cells and their associated matrix can be easily separated by mild centrifugation from more soluble matrix components derived principally from the ‘interterritorial’ matrix. This new cell culture system thus makes it possible to study the assembly and turnover of molecules present in two distinct matrix pools. Importantly, a significant proportion of the aggrecan molecules in each of these two pools can be extracted using a non-denaturing solvent, thereby making possible studies of the metabolism and turnover of native proteoglycan aggregates. We show in this report that chondrocytes isolated from the full depth of adult bovine articular cartilage and maintained for 8 months in alginate gel are still metabolically active and continue to synthesize cartilage-specific type II collagen and aggrecan. The cells did not synthesize large amounts of type I collagen or of the small nonaggregating proteoglycans as usually occurs when chondrocytes lose their phenotypic stability. After this extended period of time in culture, the cells were present as two populations exhibiting differences in size, shape and amount of extracellular matrix surrounding them. The first population was found only near the surface of the bead: these cells were flattened and surrounded by a matrix sparse in proteoglycans and collagen fibrils. The second population was found throughout the remaining depth of the bead: the cells were more round and almost always surrounded by a basket-like meshwork consisting of densely packed fibrils running tangential to the surface.

Platelet-derived growth factor stimulates hyaluronate but not proteoglycan synthesis by human gingival fibroblasts in vitro

The effect of PDGF-BB on human gingival fibroblasts was monitored in an in vitro system. PDGF was found to be mitogenic for these cells, although it required the presence of low concentrations of fetal calf serum to be active. Proteoglycan and hyaluronate synthesis was analyzed by labeling newly synthesized macromolecules with [35S]-sulfate or [3H]-glucosamine, respectively. Identification of specific glycosaminoglycans was achieved by selective enzymatic or chemical degradations. It was found that cells cultured in the presence of PDGF showed no discernible differences in proteoglycan synthesis relative to the control cultures. There were no alterations in amounts of proteoglycans synthesized, types of sulfated glycosaminoglycans synthesized, or relative hydrodynamic sizes of the proteoglycans. In contrast to the proteoglycans, hyaluronate synthesis was significantly increased in the presence of PDGF. The increase in [3H]-glucosamine incorporation into newly synthesized hyaluronate correlated with an increase in the activity of the enzyme hyaluronate synthetase but could not be accounted for entirely by changes in the specific activity of sugar nucleotide precursors, which did alter slightly under differing culture conditions. It is concluded from these results that PDGF stimulates gingival fibroblasts to proliferate and is associated with a differential effect of proteoglycan and hyaluronate synthesis. These observations may correlate with the observed early events associated with wound healing and repair.

Kinetics of proteoglycan turnover in bovine articular cartilage explants

The turnover of proteoglycans was studied in explant cultures of mature bovine articular cartilage. The aim of the study was to compare the in vitro turnover rates of newly synthesized proteoglycans and endogenous proteoglycans. Cartilage was maintained in the presence of various serum concentrations in order to determine the conditions of steady-state proteoglycan metabolism. The steady state was achieved in medium containing 20% fetal calf serum. The proteoglycan synthesis rate and the half-life of labeled proteoglycans in steady-state cultures were used to calculate the size of the metabolic pool of newly synthesized proteoglycans in steady state. This metabolic pool was shown to be equal to the total amount of proteoglycans in the matrix. It is concluded that all of the proteoglycans in the matrix have the same half-life in vitro. Taking another approach, aggrecan was isolated from the cartilage and the medium of steady-state cultures prelabeled with [35S]sulfate. The specific activity of the glycosaminoglycans from cartilage aggrecan were compared with that of glycosaminoglycans from medium aggrecan. These proved to be the same throughout the culture period. This shows that newly synthesized aggrecan and endogenous aggrecan have the same turnover rate in vitro. The significance of explant culture systems for the study of proteoglycan turnover is discussed.

Synthesis and turnover of proteoglycans by human and bovine adult articular chondrocytes cultured in alginate beads

Human and bovine adult articular chondrocytes cultured in alginate beads or agarose gel retain their spherical shape and typical chondrocytic appearance for at least 5 weeks. Aggrecan is always the major population of proteoglycans (PGs) synthesized; its size varies depending upon the age of the cartilage from which the cells are derived but it is not influenced by the culture system used. Studies of human chondrocytes cultured in alginate showed that the majority of the newly-synthesized aggrecan molecules are rapidly incorporated into aggregates which can be extracted from the gel in their native form. About one-third of the aggregates formed during a 4-hour period of incubation in the presence of [35S]-sulfate are packed at high concentration in the cell-associated matrix; the remainder is present in areas of the gel further removed from the cells. Aggrecan appears to be turned over more slowly by human than by bovine cells in both culture systems; in both species, the rate of turnover is slower in alginate than in agarose. Decorin is also synthesized in small amounts but it is rapidly lost from the agarose or alginate gel.

The interaction between retinoic acid and the transforming growth factors-beta in calf articular cartilage organ cultures

In calf articular cartilage organ cultures, retinoic acid depressed proteoglycan anabolism to levels approximately 10% of control values and increased their catabolism approximately 14-fold at concentrations of 1 x 10(-8) and 1 x 10(-6) M, respectively, leading to a severe depletion of this component from the extracellular matrix (95% loss in 3 weeks). These effects were powerfully antagonized by maximal levels of transforming growth factors-beta (TGF-beta s) 1, 2, and 3, leading to preservation of matrix components. At a concentration of 1 x 10(-8) M retinoic acid, the TGF-beta s restored anabolism to control levels and lowered catabolic rates greater than 3-fold. While the TGF-beta s increased protein synthesis 2- to 3-fold over controls, retinoic acid alone did not change protein synthesis, as determined by incorporation of [3H]serine. Nevertheless, retinoic acid effectively antagonized the stimulation of protein synthesis by TGF-beta and restored control levels of synthesis at 1 x 10(-7) M. Analysis of proteins, labeled using [3H]serine and [35S]sulfate as precursors, by SDS-PAGE revealed that large molecular weight proteins (greater than 100 kDa) were not detectable in retinoic-acid-treated cultures, but treatment with the TGF-beta s restored these components in coincubation cultures, again supporting the antagonistic role of the polypeptide effectors on retinoid action. Treatment of the cultures with retinoic acid elevated levels of TGF-beta 2 synthesis, but not TGF-beta 1. While the role of the newly synthesized TGF-beta 2 in the set of events elicited by retinoic acid in articular cartilage is unclear, the results establish an intrinsic metabolic link between the isoprenoid and TGF-beta in articular cartilage. We propose that the retinoids and TGF-beta s are integral parts of a regulatory network that controls homeostasis, resorption, or growth, depending on their relative contributions.

Transforming growth factor-beta in calf articular cartilage organ cultures: synthesis and distribution

Transforming growth factor beta 1 (TGF-beta 1) has been shown to play a prominent role in controlling proteoglycan synthesis and breakdown as measured following addition to organ cultures of calf articular cartilage (Morales, T. I., and Roberts, A. B., J. Biol. Chem., 263, 12,828-12,831, 1988). In this study, we compare two closely related TGF-beta isoforms, TGF-beta 1 and TGF-beta 2, both by assessing the effects of exogenous peptide as well as by analyzing the biosynthesis and total amount of these two isoforms in cartilage explants. Added exogenously, TGF-beta 1 and TGF-beta 2 induce a comparable increase in proteoglycan synthesis over basal controls with saturation at approximately 5 ng/ml. Synthesis of TGF-beta by basal calf cartilage cultures is demonstrated by (i) immunolocalization of intracellular TGF-beta, (ii) Northern blot analysis of steady-state mRNA levels, and (iii) immunoprecipitation of metabolically labeled TGF-beta from tissue extracts and conditioned culture medium. The net amount of extractable TGF-beta 1 and TGF-beta 2 in the basal cartilage cultures was assessed by a functional assay involving inhibition of proliferation of CCL-64 mink lung epithelial cells and by sandwich enzyme-linked immunosorbent assay. The predominant isoform was TGF-beta 1 (60-85%) and the total TGF-beta 1 + TGF-beta 2 was in excess of the amount required for maximal activation of proteoglycan synthesis. The level of both isoforms was maintained relatively constant between Days 2 and 7 of culture despite a sharp (approximately two to fourfold) drop in proteoglycan synthesis. This suggests that cartilage contains a large pool of TGF-beta which is not readily accessible to the chondrocyte. We propose that much of the polypeptide is sequestered in the matrix awaiting release upon demand.

Effects of compression on the loss of newly synthesized proteoglycans and proteins from cartilage explants

The effects of mechanical compression of calf cartilage explants on the catabolism and loss into the medium of proteoglycans and proteins radiolabeled with [35S]sulfate and [3H]proline were examined. A single 2- or 12-h compression of 3-mm diameter cartilage disks from a thickness of 1.25 to 0.50 mm, or slow cyclic compression (2 h on/2 h off) from 1.25 mm to 1.00, 0.75, or 0.50 mm for 24 h led to transient alterations and/or sustained increases in loss of radiolabeled macromolecules. The effects of imposing or removing loads were consistent with several compression-induced physical mediators including fluid flow, diffusion, and matrix disruption. Cyclic compression induced convective fluid flow and enhanced the loss of 35S- and 3H-labeled macromolecules from tissue into medium. In contrast, prolonged static compression induced matrix consolidation and appeared to hinder the diffusional transport and loss of 35S- and 3H-labeled macromolecules. Since high amplitude cyclic compression led to a sustained increase in the rate of loss of 3H- and 35S-labeled macromolecules that was accompanied by an increase in the rate of loss of [3H]hydroxyproline residues and an increase in tissue hydration, such compression may have caused disruption of the collagen meshwork. The 35S-labeled proteoglycans lost during such cyclic compression were of smaller average size than those from controls, but contained a similarly low proportion (approximately 15%) that could form aggregates with excess hyaluronate and link protein. The size distribution and aggregability of the remaining tissue proteoglycans and 35S-labeled proteoglycans were not markedly affected. The loss of tissue proteoglycan paralleled the loss of 35S-labeled macromolecules. This study provides a framework for elucidating the biophysical mechanisms involved in the redistribution, catabolism, and loss of macromolecules during cartilage compression.

Effect of insulin on the altered production of proteoglycans in rib cartilage of experimentally diabetic rats

Costal cartilage from experimentally diabetic rats, labeled in vivo or in vitro with [35S]sulfate, was shown to incorporate less label into proteoglycans than cartilage from nondiabetic rats. Analyses of guanidine HCl cartilage extracts by gel chromatography on Sepharose CL-2B showed two major peaks at Kav approximately 0.4 and 0.8 (peaks I and II, respectively). Cartilage extracts from the diabetic rats contained predominantly peak II proteoglycans, while 60 and 55%, respectively, of the total 35S-labeled proteoglycans extracted from control cartilage labeled in vivo and in vitro with [35S]sulfate were present in peak I. After insulin treatment of the diabetic rats, the relative amount of peak I 35S-labeled proteoglycans synthesized in vivo was increased to 70%. The overall in vivo incorporation of [35S]sulfate into proteoglycans was also stimulated in diabetic rats treated with insulin to levels above those found for control rats. Thus, diabetes-induced changes in the biosynthesis of rat costal cartilage proteoglycans may be alleviated by normalization of the diabetic state by insulin treatment. However, addition of insulin (10(-5)-10(-9) M) to the culture medium did not affect the amount of 35S-labeled proteoglycans synthesized in vitro or the relative amounts of peak I proteoglycans produced by control or diabetic cartilage, suggesting that insulin does not have a direct effect on proteoglycan production. Moreover, no decrease in the amount of 35S-labeled proteoglycans produced was found when glucose at high concentrations was present in the culture medium. However, the presence of rat serum resulted in an increase in the amount of 35S-labeled proteoglycans produced by both control and diabetic cartilage, demonstrating that the cartilage explants were metabolically responsive to stimulatory factors.

Age-related differences in the metabolism of proteoglycans in bovine articular cartilage explants maintained in the presence of insulin-like growth factor I

Articular cartilage explants from bovine calf and steer were cultured for up to 19 days in medium with or without 20% fetal bovine serum (FBS) or insulin-like growth factor I (IGF-I). Lower concentrations of IGF-I were required for maximal stimulation of PG synthesis in calf than in steer. In calf, but not in steer, IGF-I was as effective as 20% FBS in stimulating PG synthesis. The stimulation by IGF-I or FBS was not accompanied at either age by alterations in the composition of the aggregating PGs nor by changes in the proportions of CS-rich and CS-poor PG subpopulations. In calf, IGF-I and FBS did not markedly alter the rate of turnover of either the 35S-PGs synthesized in vitro or the unlabeled PGs. In steer, explants cultured in the absence of IGF-I or FBS exhibited very fast rates of turnover and depletion of matrix PG with time; IGF-I and FBS were both effective in reducing the turnover rate of 35S-PGs and unlabeled PGs and in preventing PG depletion.

Effect of the microbial constituents, LPS and BCG, on the glycosaminoglycans of chondrocyte cultures

Earlier we reported that articular chondrocytes in monolayer culture produce pericellular proteoglycans both with short and long half lives, T-1 and T-2 (Kittlick et al. 1991 b). Now monolayer cultures have been investigated to assess the influence on the metabolism of pericellular proteoglycans or glycosaminoglycans by lipopolysaccharide of E. coli and S. typhimurium as well as by Bacillus Calmette-Guérin.

Effect of temperature on the metabolism of proteoglycans in explants of bovine articular cartilage

The turnover of proteoglycans in bovine articular cartilage was determined in explant cultures, maintained at 32 degrees C or 37 degrees C. Both the rate of proteoglycan synthesis and the release of newly synthesized proteoglycans were decreased in cultures incubated at 32 degrees C compared to 37 degrees C. At both temperatures the newly synthesized proteoglycans were similar in hydrodynamic size and chain length of the glycosaminoglycans. However, the ratio of 6-sulfated disaccharides over 4-sulfated disaccharides of the newly synthesized glycosaminoglycans, differed less from the endogenous ratio at 32 degrees C than at 37 degrees C. At both temperatures, the incorporated 35S-sulfate is released from explants in two pools. Twenty-three percent of the 35S-radiolabel was released into the culture medium during an initial short phase (t1/2 = 1.1 day at 32 degrees C, 1.3 day at 37 degrees C), 77% had a much longer half-life. The lowered temperature markedly decreased the release of 35S-sulfate with a slow turnover (t1/2 = 60 days at 32 degrees C, 38 days at 37 degrees C).

Catabolic effects of muramyl dipeptide on rabbit chondrocytes

Muramyl dipeptide, an essential structure for the diverse biologic activities of bacterial cell wall peptidoglycan, inhibited the synthesis of glycosaminoglycan/proteoglycan in cultured rabbit costal chondrocytes in a dose-dependent manner. Muramyl dipeptide, as well as lipopolysaccharide and interleukin-1 alpha, also enhanced the release of 35S-sulfate-prelabeled glycosaminoglycan/proteoglycan from the cell layer, which seems to reflect, at least partially, the increasing degradation of glycosaminoglycan/proteoglycan. Five synthetic analogs of muramyl dipeptide known to be adjuvant active or adjuvant inactive were tested for their potential to inhibit synthesis of glycosaminoglycan/proteoglycan and to enhance the release of glycosaminoglycan/proteoglycan in chondrocytes. The structural dependence of these synthetic analogs on chondrocytes was found to parallel that of immunoadjuvant activity. These results suggest that muramyl dipeptide is a potent mediator of catabolism in chondrocytes.

Stimulation of human chondrocyte prostaglandin E2 production by recombinant human interleukin-1 and tumour necrosis factor

In this study we have examined the effects of recombinant cytokine preparations on the production of prostaglandin E2 (PGE2) by human articular chondrocytes in both chondrocyte monolayer and cartilage organ cultures. The cytokines chosen for this study included only those reported to be present in rheumatoid synovial fluids and which therefore could conceivably play a role in chondrocyte activation in inflammatory arthritis. Of the cytokines tested, interleukin-1 (IL-1; alpha and beta forms) consistently induced the highest levels of PGE2 production followed, to a lesser extent, by tumour necrosis factor (TNF; alpha and beta forms). The IL-1s were effective at concentrations 2-3 orders of magnitude less than the TNFs, with each cytokine demonstrating a dose-dependent increase in PGE2 synthesis for the two culture procedures. The increased PGE2 production by the chondrocytes exhibited a lag phase of 4-8 h following the addition of the IL-1 or TNF and was inhibited by actinomycin D and cycloheximide, indicating a requirement for de novo RNA and protein synthesis, respectively. Our results suggest that IL-1 may be the key cytokine involved in modulating chondrocyte PGE2 production in inflammatory arthritis; they further extend the list of human chondrocyte responses which are affected by both IL-1 and TNF.

Recombinant human interleukin-1 alpha and recombinant human interleukin-1 beta stimulate cartilage matrix degradation and inhibit glycosaminoglycan synthesis

Recombinant human interleukin-1 alpha (rhIL-1 alpha) and recombinant human interleukin 1 beta (rhIL-1 beta) stimulated the time- and concentration-dependent release of glycosaminoglycan (GAG) from bovine nasal cartilage explants. Maximum GAG release occurred during six to eight days of cartilage exposure to either species of rhIL-1; and rhIL-1 alpha was consistently more potent than rhIL-1 beta. In addition to inducing cartilage matrix resorption, rhIL-1 alpha and rhIL-1 beta also inhibited the incorporation of [35SO4]sulfate into cartilage, which is a reflection of the suppression of GAG synthesis. IL-1 had no capacity to stimulate GAG relase from or inhibit GAG synthesis by dead cartilage. Cycloheximide, an inhibitor of protein synthesis, and 1, 10-phenanthroline, a metalloproteinase inhibitor, suppressed rhIL-1-stimulated cartilage matrix resorption. Polyclonal antisera to rhIL-1 alpha and rhIL-1 beta specifically neutralized the respective cytokines.

Effects of interleukin-1 and lipopolysaccharides on protein and carbohydrate metabolism in bovine articular cartilage organ cultures

The long term (18 day) metabolic response of bovine articular cartilage to treatment with either E. Coli lipopolysaccharide (LPS) or interleukin 1 was studied. For LPS treatment, incorporation of [35S]sulfate into the large proteoglycan population was inhibited 80% while that into the small interstitial proteoglycans was only inhibited 40%. Incorporation of [3H]serine into the large proteoglycan population was inhibited approximately 72% while incorporation into other protein was inhibited only 16%. Furthermore, the rate of catabolism of [3H]serine labeled proteoglycans was increased 2-fold by LPS treatment while the rate of 3H-labeled general protein catabolism was not affected. Incorporation of [3H]glucosamine into hyaluronate was increased; however a correction for changes in the specific activity of the intracellular [3H]glucosamine precursor pool in LPS-treated cultures indicated that the net amount of hyaluronate synthesized was not altered by LPS treatment. The 3H/35S ratios in isolated chondroitin sulfate disaccharides labeled with [35S]sulfate and [3H]glucosamine precursors were significantly changed during long term LPS treatment, suggesting that general carbohydrate pathways are altered. The 3H/35S changes were larger in the disaccharides isolated from the small proteoglycans indicating that different precursor pools, probably in different cell populations, preferentially synthesize this proteoglycan population. Interleukin-1 affected the same chondrocytic pathways as LPS as shown by a) the extent of inhibition of proteoglycan synthesis, b) the selective inhibition of synthesis of the large proteoglycan species, c) acceleration of proteoglycan catabolism, d) net depletion of proteoglycans from the tissue, e) increases in guanidine HCl extractable [3H]hyaluronate, f) increases in levels of prostaglandin E2 synthesis, g) changes in 3H/35S ratios in glycosaminoglycan chains and, h) minimal effects on general protein synthesis.

Induction of articular cartilage degradation by recombinant interleukin 1 alpha and 1 beta

The purpose of this study was to compare the effects of human recombinant interleukin 1, alpha and beta, on articular cartilage. The effects of rIL-1 alpha and rIL-1 beta on proteoglycan degradation and synthesis following treatment of bovine articular cartilage in serum-free organ culture were quantified. Purified human IL-1 and both rIL-1 alpha and rIL-1 beta induced a two-fold or greater increase in glycosaminoglycan (GAG) release from cultured articular cartilage. Levels or rIL-1 alpha as low as 15 pM induced increased proteoglycan degradation whereas identical levels of rIL-1 beta did not. Killing of the cartilage cells abolished induced GAG release by all forms of IL-1. Analysis of proteoglycan size following IL-1 treatment showed limited degradation of material released into the culture medium or remaining within cartilage. Both forms of recombinant IL-1 inhibited GAG synthesis when continually present in the culture medium. Actinomycin D and cycloheximide inhibited IL-1 dependent cartilage destruction whereas indomethacin did not.

Biochemical and morphological studies of steady state and lipopolysaccaride treated bovine articular cartilage explant cultures

Explants of bovine articular cartilage were cultured for up to 50 days in 20% fetal calf serum in the presence or absence of the endotoxin lipopolysaccharide (LPS); or in various protocols involving different treatment times with LPS followed by recovery times in the absence of LPS. Cultures were measured in terms of rates of proteoglycan synthesis (incorporation of [35S]sulfate), proteoglycan contents and collagen contents. Histological sections were prepared for both light and electron microscopy. In fetal calf serum, the rates of synthesis and contents of proteoglycans per collagen remained constant, while for LPS treated cultures both parameters decreased. For recovery groups, the rates of proteoglycan synthesis increased during the time of recovery if the LPS treatment times were relatively short (2 weeks or less) and if the tissue was obtained from younger animals; net increase in proteoglycan contents occurred infrequently if at all during recovery protocols. Histological examinations revealed that chondrocytes in cultures maintained in fetal calf serum appeared normal with large stores of glycogen. In LPS treated cultures, chondrocytes were depleted of glycogen stores and contained numerous lipid droplets. In recovery cultures, chondrocytes replenished their glycogen contents, but the lipid droplets remained. For both LPS treated and recovery groups the extracellular matrix was depleted of proteoglycans with time in culture. The results provide further evidence for the ability of this explant culture system to maintain steady state metabolic parameters for proteoglycan metabolism over long time periods and for its utility to study reagents which regulate or perturb these parameters.

Insulin-like growth factors maintain steady-state metabolism of proteoglycans in bovine articular cartilage explants

The influences of insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II) on biosynthesis and catabolism of proteoglycans (PG) in bovine articular cartilage explants were examined to define their potential use in a chemically defined medium. In both short- (10 days) and long-term (40 days) cultures, 10 to 20 ng/ml IGF-I maintained PG synthesis at the same or higher levels than in a medium containing 20% fetal calf serum (FCS). Catabolic rates were slower in IGF-I medium than in medium with only 0.1% albumin, but somewhat faster than for cultures in medium with 20% FCS. In long-term cultures 20 ng/ml IGF-I maintained a steady-state condition; the amounts of glycosaminoglycan and DNA per hydroxyproline content were constant throughout the culture period. The half-maximal dose response for IGF-I on PG synthesis (4.5 ng/ml) was distinctly different from that for the IGF-I effect on PG catabolism (1.5 ng/ml), indicating that these two components of PG metabolism can be experimentally uncoupled. IGF-II was less potent than IGF-I in the same batches of articular cartilage; 100 ng/ml IGF-II increased PG synthesis and decreased PG catabolism relative to 0.1% albumin alone, but the responses were only about 60% of those for 5 ng/ml IGF-I. These results suggest that the chondrocytes regulate PG synthesis primarily via the type I IGF receptor and that the IGF-II response is through the same receptor. Evidence is also provided indicating that the cartilage explants initially contain about 50 ng IGF-I per gram wet weight; this matrix-bound IGF-I diffuses into the medium during culture. The chondrocytes synthesize little or no IGF-I that is released into the medium under the culture conditions used.

Fluorometric assay of DNA in cartilage explants using Hoechst 33258

A simple two-step fluorometric assay of DNA in cartilage explants, utilizing the bisbenzimidazole dye Hoechst 33258, is described. Cartilage explants were prepared for assay by digestion with papain. Aliquots of the digest were mixed with dye solution, and the fluorescence emission measured. The enhancement in fluorescence of dye was specific for DNA, as demonstrated by 97% sensitivity to DNase and resistance to RNase. In addition, little or no interference was caused by non-DNA tissue components, since DNA caused an equal enhancement in fluorescence independent of the presence of papain-digested cartilage. By performing the assay on isolated chondrocytes, the cellular content of DNA was computed to be 7.7 pg per chondrocyte. The assay was stable for at least 2 h and sensitive to as little as 6 ng of DNA or equivalently less than 1000 cells. This procedure offers advantages over other established DNA assays of cartilage and may be especially useful in metabolic studies of cartilage explants.

Effect of lipopolysaccharide on proteoglycan synthesis by adult human gingival fibroblasts in vitro

The effect of lipopolysaccharide preparations from Salmonella enteritidis, Bacteroides gingivalis, and Actinobacillus actinomycetemcomitans on human gingival fibroblasts was studied. Lipopolysaccharide from all sources inhibited fibroblast proliferation in the concentration range of 0.5 to 50 micrograms/ml, with the lipopolysaccharide from A. actinomycetemcomitans having the strongest inhibitory effect. Assessment of the effect of lipopolysaccharide on gingival fibroblast metabolism indicated both total protein and proteoglycan synthesis to be inhibited with increasing concentrations of lipopolysaccharide. As for the antiproliferative effect, lipopolysaccharide from A. actinomycetemcomitans had the greatest inhibitory effect on cell synthetic activity. This inhibitory effect was determined by pulse-chase experiments to be a true depression in synthesis. Furthermore, the effect was independent of lipopolysaccharide-induced changes in cell proliferation and prostaglandin synthesis. This study confirmed the toxic effect of lipopolysaccharide on fibroblasts and, in particular, indicated that various lipopolysaccharide preparations vary in their potency to influence cell proliferation and extracellular matrix synthesis.

Protease inhibitors decrease rabbit cartilage degradation after meniscectomy

In vitro proteoglycan (PG) synthesis and release were measured on cartilage removed from rabbit knees within 1 week of meniscectomy. Three days following partial lateral meniscectomy, 72% of the femurs and 82% of the tibias had visible ulcers. Cartilage from the weight-bearing areas incorporated 2.0-2.9 times more 35S-sulfate in vitro than cartilage from the opposite, unoperated knees. 3H-thymidine incorporation was 2.5-3.4 times higher for surgical than control groups. 35S-sulfate incorporation by the surgical group was inhibited by 22% in the presence of 10(-4) M U24522, an inhibitor of rabbit chondrocyte metalloprotease (CMP). 3H-thymidine incorporation by the surgical group was inhibited by 28% by 10(-4) M U24522. In vitro PG release from cartilage removed 2 days after surgery was 1.6-3.7 times higher for the surgical than the control group. PG release by the surgical group after 22 h of incubation was reduced to the control level by three CMP inhibitors, U24278, U24279, and U24522. PG release by cartilage from the nonsurgical group was also reduced by these compounds at 22 h. These results suggest that both the anabolic and catabolic processes that are stimulated by surgery can be isolated in vitro and that CMP may be involved in the catabolic process.

Effect of thyroid hormone deficiency on proteoglycan synthesis by human skin fibroblast cultures

Proteoglycans and hyaluronic acid synthesized by human skin fibroblasts in culture were characterized, and the effect of thyroid hormone deficiency was examined. The fibroblasts in culture synthesize hyaluronic acid, dermatan sulfate (DS) proteoglycans and heparan sulfate (HS) proteoglycans. Hyaluronic acid is almost exclusively secreted into the medium. Among the proteoglycans synthesized during 24 h label, about 70% were secreted into the medium and the remaining 30% were associated with the cell layer. About 70% of proteoglycans secreted into the medium contained DS and the remaining 30% contained HS. For cell-associated proteoglycans, 60% contained HS and the remainder contained DS. The size distributions of the glycosaminoglycans from both DS and HS proteoglycans were similar, with an average Mr of approximately 30,000. Incubation of fibroblasts in thyroid hormone deficient medium increased net synthesis of hyaluronic acid (approximately 50%) and all species of proteoglycans (approximately 85%). 3H/35S ratios in the chondroitin 4-sulfate disaccharide isolated with HPLC were not altered in thyroid hormone deficient cultures, indicating that the specific activity of 3H in UDP-N-acetylhexosamine precursors did not change. The increased incorporation of 3H into hyaluronic acid and of 3H and 35S into DS and HS proteoglycans thus indicates increased net synthesis. Degradation of cell-associated proteoglycans was not influenced by thyroid hormone deficiency.