Proteoglycan synthesis in suspension cultures of Swarm rat chondrosarcoma chondrocytes and inhibition by exogenous hyaluronate

Facilitating In Vivo Articular Cartilage Repair by Tissue-Engineered Cartilage Grafts Produced From Auricular Chondrocytes

BACKGROUND

Insufficient cell numbers still present a challenge for articular cartilage repair. Converting heterotopic auricular chondrocytes by extracellular matrix may be the solution.

HYPOTHESIS

Specific extracellular matrix may convert the phenotype of auricular chondrocytes toward articular cartilage for repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

For in vitro study, rabbit auricular chondrocytes were cultured in monolayer for several passages until reaching status of dedifferentiation. Later, they were transferred to chondrogenic type II collagen (Col II)-coated plates for further cell conversion. Articular chondrogenic profiles, such as glycosaminoglycan deposition, articular chondrogenic gene, and protein expression, were evaluated after 14-day cultivation. Furthermore, 3-dimensional constructs were fabricated using Col II hydrogel-associated auricular chondrocytes, and their histological and biomechanical properties were analyzed. For in vivo study, focal osteochondral defects were created in the rabbit knee joints, and auricular Col II constructs were implanted for repair.

RESULTS

The auricular chondrocytes converted by a 2-step protocol expressed specific profiles of chondrogenic molecules associated with articular chondrocytes. The histological and biomechanical features of converted auricular chondrocytes became similar to those of articular chondrocytes when cultivated with Col II 3-dimensional scaffolds. In an in vivo animal model of osteochondral defects, the treated group (auricular Col II) showed better cartilage repair than did the control groups (sham, auricular cells, and Col II). Histological analyses revealed that cartilage repair was achieved in the treated groups with abundant type II collagen and glycosaminoglycans syntheses rather than elastin expression.

CONCLUSION

The study confirmed the feasibility of applying heterotopic chondrocytes for cartilage repair via extracellular matrix-induced cell conversion.

CLINICAL RELEVANCE

This study proposes a feasible methodology to convert heterotopic auricular chondrocytes for articular cartilage repair, which may serve as potential alternative sources for cartilage repair.

Differential effect of ECM molecules on re-expression of cartilaginous markers in near quiescent human chondrocytes

The limited source of healthy primary chondrocytes restricts the clinical application of tissue engineering for cartilage repair. Therefore, method to maintain or restore the chondrocyte phenotype during in vitro expansion is essential. The objective of this study is to establish the beneficial effect of ECM molecules on restoring the re-expression of cartilaginous markers in primary human chondrocytes after extensive monolayer expansion. During the course of chondrocyte serial expansion, COL2A1, SOX9, and AGN mRNA expression levels, and GAG accumulation level were reduced significantly in serially passaged cells. Exogenous type II collagen dose-dependently elevated GAG level and induced the re-expression of cartilaginous marker mRNAs in P7 chondrocytes. Chondroitin sulfate did not show significant effect on P7 chondrocytes, while hyaluronic acid inhibited the expression of SOX9 and AGN mRNAs. Upon treatment with type II collagen, FAK, ERK1/2, and JNK were activated via phosphorylation in P7 chondrocytes within 15 min. Furthermore, GFOGER integrin blocking peptide, MEK inhibitor and JNK inhibitor, not p38 inhibitor, significantly reduced the type II collagen-induced GAG deposition level. Finally, in the presence of TGF-β1 and IGF-I, P7 chondrocytes cultured in 3D type II collagen matrix exhibited better cartilaginous features than those cells cultured in the type I collagen matrix. In conclusion, type II collagen alone can effectively restore cartilaginous features of expanded P7 human chondrocytes. It is probably mediated via the activation of FAK-ERK1/2 and FAK-JNK signaling pathways. The potential application of type II collagen in expanding a scarcity of healthy chondrocytes in vitro for further tissue engineering is implicated.

Hyaluronan and hyaluronan-binding proteins in cartilaginous tissues

Recent developments in the biology of hyaluronan in cartilage are reviewed. The homology between the hyaluronan-binding sites of cartilage proteoglycan and link protein is discussed. Previous reports indicate that an increased concentration of extracellular hyaluronan inhibits 35S-proteoglycan synthesis by several types of chondrocyte. We report data showing that this response varies in its reproducibility and sensitivity to low concentrations of hyaluronan in rat chondrosarcoma chondrocytes and pig laryngeal chondrocytes in suspension culture. Two newly recognized hyaluronan-binding proteins have been isolated from extracts of Swarm rat chondrosarcoma. The major protein has a molecular mass of 102 kDa and the less prominent protein a molecular mass of 91 kDa. The latter may be derived from the former. Neither protein cross-reacts with antisera against cartilage proteoglycan HABR (hyaluronan-binding region), link protein, hyaluronectin or type II collagen.

Effects of hyaluronan on proteoglycan content of osteoarthritic chondrocytes in vitro

PURPOSE

To investigate the effect of hyaluronic acid (HA) on proteoglycan (PG) concentration in alginate cultures of human osteoarthritic chondrocytes and to analyze whether HA exhibit anti-degradative effects in the presence of the cytokine IL-1beta.

METHODS

Cartilage samples from ten patients with osteoarthritis of the knee were harvested and chondrocytes were cultivated in alginate beads. Four groups were cultured: control group with and without IL-1beta (500 pg/ml) and HA group (100 microg/ml) with and without IL-1beta (500 pg/ml). PG concentration was estimated by a dimethylmethylene blue assay. To assess cell proliferation, we measured DNA content fluorometrically.

RESULTS

The proliferation rate (DNA) was unchanged in all culture groups. In the control-group PG/DNA (ng/ng) concentration was 27.1 +/- 7.2. Supplementation of the medium with HA decreased PG concentration to 25.3 +/- 6.9 (p < 0.05). After administration of IL-1beta PG/DNA concentration dropped to 23.1 +/- 6.0 (p < 0.01). By contrast HA treatment of IL-1beta stimulated chondrocytes did not further decrease PG concentration (23.9 +/- 6.1). In fact the negative effect of isolated HA application was inverted if HA was given with IL-1beta (p < 0.05).

CONCLUSIONS

In osteoarthritic chondrocytes cultured phenotypically stable, HA could exhibit protective effects only in the presence of the degradative cytokine IL-1beta. Thus, the reported anti-inflammatory effects of HA to cartilage matrix seem to be more indirect by blocking degradative effects of cytokines to the matrix.

Inducible nitric oxide expression in equine articular chondrocytes: effects of antiinflammatory compounds

OBJECTIVE

To determine the effects of recombinant equine IL-1beta and a number of antiinflammatory compounds on the expression and activity of inducible nitric oxide synthase (iNOS) in cultured equine chondrocytes.

DESIGN

RT-PCR methods were used to amplify a portion of the equine iNOS message to prepare an RNA probe. Northern blot analysis was used to quantify the expression of iNOS in first passage cultures of equine articular chondrocytes propagated in the presence or absence of recombinant equine interleukin-1beta (reIL-1beta), dexamethasone (DEX), polysulfated glycosaminoglycan (PSGAG), hyaluronan (HA), and phenylbutazone (PBZ), each at concentrations of 10 and 100 microg/ml. Nitrite concentrations in conditioned media of similarly treated cells were used to quantify iNOS activity.

RESULTS

Recombinant equine IL-1beta increased the expression of iNOS in a dose-dependent manner. This result was paralleled by an increased concentration of nitrite in the culture media of reIL-1beta-treated cells. DEX and PSGAG significantly reduced iNOS gene expression and media supernatant nitrite concentrations in cytokine-stimulated cultures. HA and PBZ had no consistent effect on the expression of iNOS and did not significantly influence nitrite content of conditioned media.

CONCLUSIONS

NO is considered an important mediator in the pathophysiologic processes of arthritis and an inducible NOS is expressed by equine chondrocytes. Pre-translational regulation of the iNOS gene by DEX and PSGAG appears to contribute to the cartilage-sparing properties of these compounds.

Effects of hyaluronan on engineered articular cartilage extracellular matrix gene expression in 3-dimensional collagen scaffolds

Hyaluronan (HA) is a component of cartilage matrix with known effects on chondrocytes. We tested the effects of adding HA to 3-dimensional (3-D) collagen. sponges on chondrocyte function in vitro. Bovine articular chondrocytes isolated by collagenase digestion were injected into either collagen or HA/collagen scaffolds comprising different amounts of HA (2, 5, 10, and 14% w/w). Expression of aggrecan and type II collagen genes was measured by gene-specific quantitative competitive reverse transcriptase-polymerase chain reactions, and the extracellular matrix was estimated by histomorphometrical analyses. After 7-day culture, the chondrocytes in 2% (w/w) HA sponges expressed fourfold more mRNA transcripts for type II collagen (p = 0.002) and twofold more mRNA transcripts for aggrecan (p = 0.022) than in control collagen sponges. Furthermore, there was 45% more extracellular matrix in 2% (w/w) HA sponges and 43% less matrix in the 10% (w/w) HA sponges compared with plain collagen sponges (p > 0.05). In sum, a small amount of HA in 3-D collagen scaffolds enhanced chondrogenesis, but a greater amount was inhibitory. This 3-D system represents a novel tool to identify mechanisms by which extracellular matrix molecules influence chondrocyte function. Further, these results show the potential for modifying scaffolds to improve production of engineered cartilage for in vivo applications.

Characterization of proteoglycan accumulation during formation of cartilagenous tissue in vitro

In order to study proteoglycan retention and accumulation, we optimized a chondrocyte cell culture system in which isolated bovine articular chondrocytes accumulate extracellular matrix to form a continuous layer of cartilagenous tissue. The tissue can attain a thickness of up to 110 microns by 35 days. The cells synthesize large keratan sulfate containing proteoglycans and type II collagen indicating that the chondrocytes maintain their phenotype in these culture conditions. Matrix accumulation is enhanced by increased cell density and the presence of serum and ascorbic acid. The amount of proteoglycans synthesized by the chondrocytes increases up to day 21 and then decreases to the same levels as are synthesized during the first week of culture. The percentage of newly synthesized proteoglycans retained in the matrix increases from 20% on day 6 to a maximum of 85% by day 35. The proteoglycan and collagen content in the tissue increases with time in culture. The changes in the percentage of proteoglycans retained parallels the increase in proteoglycan content. After day 35, there is no further increase in the amount of proteoglycans and collagen nor in the percentage of newly synthesized proteoglycans retained in the extracellular matrix. These studies demonstrate that the cultures are going through two phases: one of matrix accumulation and then one of maintaining the existing matrix. The period of matrix accumulation occurs between days 10-21 whereas matrix maintenance is observed after day 35. Using this culture system to study proteoglycan accumulation and maintenance during these culture periods may prove useful in identifying the mechanisms regulating these processes.

Effects of certain antiarthritic agents on the synthesis of type II collagen and glycosaminoglycans in rat chondrosarcoma cultures

Cartilage destruction is a characteristic feature of osteoarthritis. Treatment with certain nonsteroidal anti-inflammatory drugs could exacerbate cartilage destruction by impairing the synthesis of cartilage matrix proteins, type II collagen and proteoglycan. In order to monitor the changes occurring in cartilage collagen synthesis, we developed a type II collagen specific ELISA. The effects of antiarthritic agents on type II collagen and glycosaminoglycan synthesis were examined in rat chondrosarcoma cultures. Drugs were added to the monolayer cultures and 4 days later the total type II collagen, as determined by the type II collagen ELISA, and glycosaminoglycan content, as measured by dimethyl-methylene blue dye binding assay, was measured. All drugs except tiaprofenic acid decreased type II collagen synthesis by at least 40% at 100 micrograms/ml. Tiaprofenic acid at 1 microgram/ml increased type II collagen content by 54% of the controls. Glycosaminoglycan synthesis was decreased by acetylsalicylic acid, diclofenac and tiaprofenac acid, at 50 micrograms/ml or above. Indomethacin, naproxen and dexamethasone had no effect. Interestingly, tenidap stimulated the glycosaminoglycan synthesis by 32% at 100 micrograms/ml. We show that the combination of chondrosarcoma cultures, type II collagen specific ELISA and dimethylmethylene blue dye binding assay serves as a useful model for screening the effects of agents capable of modulating type II collagen and glycosaminoglycan synthesis.

UDP-sugar metabolism in Swarm rat chondrosarcoma chondrocytes

UDP-sugars and adenine nucleotides were extracted from freshly isolated chondrocytes and primary cell cultures and analysed by anion-exchange h.p.l.c. The pool sizes of UDP-N-acetylglucosamine, UDP-N-acetylgalactosamine, UDP-glucose-galactose, UDP-glucuronate and UDP-xylose were 2.9, 1.2, 2.5, 0.6 and 0.03 nmol/10(6) freshly isolated chondrocytes. When chondrocytes were maintained in Dulbecco's modified Eagle medium supplemented with 15% foetal-bovine serum, synthesis of [35S]proteoglycan and [3H]protein decreased over the first 48 h in culture, as did the pools of UDP-glucuronate and ATP. In contrast, the size of the UDP-N-acetylhexosamine pools underwent little change during culture. [35S]Proteoglycan and [3H]protein syntheses were stimulated in cultures supplemented with serum or insulin compared with those maintained in medium alone, in agreement with previous results. However, the UDP-sugar pool sizes were the same in both supplemented and non-supplemented cultures. In cultures maintained in the presence of [1-3H]glucose, the UDP-sugars were labelled to a constant 3H specific radioactivity which was very similar to that of the labelling medium. UDP-N-acetylhexosamines were labelled to constant 3H specific radioactivity with [6-3H]glucosamine as a precursor, but only about 1 in 375 of these UDP-sugars was derived from the amino sugar in the presence of glucose. The half-life (t1/2) for UDP-hexoses, UDP-glucuronate and UDP-N-acetylhexosamines was about 12, 12 and 50 min respectively.

Hyaluronan receptor-directed assembly of chondrocyte pericellular matrix

Initial assembly of extracellular matrix occurs within a zone immediately adjacent to the chondrocyte cell surface termed the cell-associated or pericellular matrix. Assembly within the pericellular matrix compartment requires specific cell-matrix interactions to occur, that are mediated via membrane receptors. The focus of this study is to elucidate the mechanisms of assembly and retention of the cartilage pericellular matrix proteoglycan aggregates important for matrix organization. Assembly of newly synthesized chondrocyte pericellular matrices was inhibited by the addition to hyaluronan hexasaccharides, competitive inhibitors of the binding of hyaluronan to its cell surface receptor. Fully assembled chondrocyte pericellular matrices were displaced using hyaluronan hexasaccharides as well. When exogenous hyaluronan was added to matrix-free chondrocytes in combination with aggrecan, a pericellular matrix equivalent in size to an endogenous matrix formed within 30 min of incubation. Addition of hyaluronan and aggrecan to glutaraldehyde-fixed chondrocytes resulted in matrix assembly comparable to live chondrocytes. These matrices could be inhibited from assembling by the addition of excess hyaluronan hexasaccharides or displaced once assembled by subsequent incubation with hyaluronan hexasaccharides. The results indicate that the aggrecanrich chondrocyte pericellular matrix is not only on a scaffolding of hyaluronan, but actually anchored to the cell surface via the interaction between hyaluronan and hyaluronan receptors.

Effects of hyaluronic acid on the release of proteoglycan from the cell matrix in rabbit chondrocyte cultures in the presence and absence of cytokines

OBJECTIVE

To investigate the effects of hyaluronic acid (HA) on the release of proteoglycan by cultured rabbit chondrocytes.

METHODS

Articular cartilage chondrocytes were isolated from the knee joints of New Zealand white rabbits. Proteoglycan synthesis after incubation with HA was determined by measuring 35S-sulfate incorporation. Cells incubated with HA were labeled with 3H-glucosamine and applied to a Sepharose CL-2B column. After incubation of confluent cells with 35S-sulfate and then with HA in various concentrations in the presence or absence of cytokines, proteoglycan release from the cell matrix layer was measured.

RESULTS

HA (M(r) 3 x 10(5) to 19 x 10(5)), at 10 micrograms/ml to 1 mg/ml, had little effect on the incorporation of 35S-sulfate or 3H-glucosamine into cartilage matrix proteoglycans, or on the hydrodynamic size of proteoglycan monomers, in rabbit chondrocyte cultures. However, at 10-1,000 micrograms/ml, HA suppressed the release of 35S-proteoglycans from the cell matrix layer into the medium in the presence and absence of interleukin-1, tumor necrosis factor alpha, or basic fibroblast growth factor.

CONCLUSION

These results suggest that HA is a potent inhibitor of the displacement of matrix proteoglycan into culture medium.

Purification and characterization of a hyaluronan-binding protein from rat chondrosarcoma

Swarm rat chondrosarcoma contains a hyaluronan-binding protein of molecular mass 102 kDa (HABP102). The protein is present in 4 M-guanidinium chloride extracts of the chondrosarcoma and can be incorporated into reconstituted proteoglycan aggregates, but it is not present in native proteoglycan aggregates or in 0.5 M-guanidinium chloride extracts. HABP102 is unlikely to be an integral membrane protein, as it does not require detergent for extraction, is not enriched in hydrophobic amino acids and does not bind avidly to octyl-Sepharose. The protein stains poorly with Coomassie Blue and is only visible on PAGE gels after staining with silver. Disulphide bonds are essential for the binding of HABP102 to hyaluronan, and bivalent cations are not required for this interaction. HABP102 can be purified from dissociative chondrosarcoma extracts by sequential density-gradient centrifugation, hyaluronan-Sepharose affinity chromatography and hydrophobic-interaction chromatography. The amino acid composition is similar to that of domains 1-4 of the chondrosarcoma proteoglycan core protein, but peptide analysis after digestion with Staphylococcus aureus V8 proteinase and chymotrypsin and different immunoreactivity suggest that HABP102 is not closely related to proteoglycan hyaluronan-binding region. HABP102 is a glycoprotein containing N-acetylgalactosamine, N-acetylglucosamine, mannose and galactose.

Large cartilage proteoglycan (PG-LA) influences the biosynthesis of macromolecules by isolated chondrocytes

Bovine articular and tracheal chondrocytes were cultured at high density in multilayers. Intact or fragmented large aggregating proteoglycans (PG-LA) from cartilage were added to the cultures and the biosynthetic response studied by the incorporation of [3H]-leucine and [35S]-sulfate for proteins and proteoglycans respectively. Incorporated radiolabel and patterns of synthesized macromolecules were compared with control cultures without additives and cultures containing either of the synthetic polymers dextran or dextran sulfate. All proteoglycans and derivatives containing globular protein structures had a stimulatory effect on the biosynthesis of both proteins and proteoglycans as did the highly polyanionic polymer dextran sulfate. Distribution of the radiolabeled material between the cell- and medium pools were however different in the various cultures. A radiolabeled protein, migrating as a triplet band at a position of approximately 140 kDa after reduction, was detected by SDS-PAGE and fluorography. The protein was present in all cell extracts and in the media of cultures stimulated with proteoglycans and proteoglycan fragments, except chondroitin sulfate side chains. The protein was shown to be collagenous in nature by collagenase digestion and identified as procollagen II by immunoprecipitation.

Membrane-associated hyaluronate-binding activity of chondrosarcoma chondrocytes

The association of hyaluronate with the surface of chondrocytes was examined by several approaches using primary cultures of chondrocytes derived from the Swarm rat chondrosarcoma. In culture, chondrosarcoma chondrocytes produced large pericellular coats, which can be visualized by particle exclusion, and which can be removed by Streptomyces hyaluronidase. Exposure of chondrocytes, which had been metabolically labelled with 3H-acetate, to exogenous hyaluronate or to Streptomyces hyaluronidase resulted in the release of 36-38% of the endogenous, labelled chondroitin sulfate from the cell layer into the incubation solution. These results imply that at least 37% of the cell layer chondroitin sulfate proteoglycan is retained there by an interaction with hyaluronate. Thus membranes were prepared from cultured chondrocytes and examined for sites which bind 3H-hyaluronate. Binding was observed and found to be saturable, specific for hyaluronate, of high affinity (Kd = approximately 10(-10) M), and destroyed by treating the membranes with trypsin. The 3H-hyaluronate-binding activity was inhibited competitively by hyaluronate decasaccharides but not by hexasaccharides or octasaccharides, indicating that the binding sites recognize a sequence of hyaluronate composed of five disaccharide repeats. The binding activity was partially purified from a detergent extract of chondrocyte membranes by ion exchange chromatography on DEAE-cellulose, followed by affinity chromatography on wheat germ agglutinin-agarose. Analysis of the partially purified binding activity by SDS-PAGE revealed five protein bands of 48,000-66,000 daltons in silver-stained gels. SDS-PAGE followed by Western blotting and exposure to monoclonal antibodies which recognize epitopes present in link protein and in the hyaluronate-binding region of cartilage proteoglycan revealed no immunoreactive protein bands in the partially purified material. We conclude that one mechanism by which hyaluronate associates with the chondrocyte surface may be via interaction with a membrane-bound hyaluronate-binding protein which is distinct from link protein and proteoglycan.

Does chondroitin sulfate have a role to play in the morphogenesis of the chick primary corneal stroma?

This paper makes three points about how the chick corneal epithelium lays down the primary stroma, an orthogonally arranged array of well-spaced, 20-nm-diameter collagen fibrils. (1) Isolated corneal epithelia will, when cultured, lay down de novo stromas whose fibril-diameter distribution, fibril spacing, and proteoglycan profile are similar to those laid down in vivo. They differ from embryonic stromas in two ways: first, much of the chondroitin sulfate is released to the medium and, second, there is a relatively small amount of orthogonal organization. Epithelia seem only to lay down such stromas if they are separated from their original stromas with dispase, which leaves an intact basal lamina, and spread out, basal lamina downward, on a Nuclepore filter (poresize, 0.1 micron). (2) Chondroitin sulfate (CS), the predominant proteoglycan (greater than 85%), seems to play no significant role in collagen fibrillogenesis in vitro. Stromas laid down in its absence were indistinguishable from controls as assayed by fibril diameter, organization, and spacing and the amount of collagen synthesized. For these experiments, epithelia were cultured in the presence of hyaluronidase, which degrades CS, and p-nitrophenyl beta-D-xyloside, which inhibits the formation of links between the core protein and glycosaminoglycan side chains in the PG; the absence of intact CS was confirmed by gel filtration. We suggest that, in vivo, CS may facilitate the interfibrillar movement that takes place as the cornea grows. We have also found that keratinase, which degrades the very small amount of keratan sulfate present in the primary stroma, has no effect on stromal deposition. (3) There are substantial amounts of unidentified matrix components in primary stromas laid down both in vivo and in vitro. This conclusion was drawn from SEM observations on both types of stroma after they had been freeze-dried, a process which does not condense hydrated macromolecules. Even after being treated with hyaluronidase to remove the CS, substantial amounts of interfibrillar matrix were still present. Until these components are identified and their interactions with collagen are understood, the mechanisms responsible for stromal morphogenesis are unlikely to be understood.

Cartilage proteoglycan aggregate and fibronectin can modulate the expression of type X collagen by embryonic chick chondrocytes cultured in collagen gels

Chick embryo sternal chondrocytes from the caudal and cephalic regions were cultured within type I collagen gels and type I collagen/proteoglycan aggregate composite gels in normal serum. Caudal region chondrocytes were also cultured within type I collagen gels in the presence of fibronectin-depleted serum. There was a marked stimulation of type X collagen synthesis by the caudal region chondrocytes after 9 days in the presence of fibronectin-depleted serum and after 14 days in the presence of proteoglycan aggregate. These results provide evidence for the ability of chondrocytes from a zone of permanent cartilage to synthesise type X collagen and for the involvement of extracellular matrix components in the control of type X collagen gene expression.

Hyaluronic acid in human articular cartilage. Age-related changes in content and size

Total tissue content and molecular mass of hyaluronic acid was determined in papain digests of human articular cartilage using a sensitive radiosorbent assay [Laurent & Tengblad (1980) Anal. Biochem. 109, 386-394]. 1) Hyaluronic acid content increased from 0.5 microgram/mg wet wt. to 2.5 micrograms/mg wet wt. between the ages of 2.5 years and 86 years. 2) Hyaluronic acid chain size decreased from Mr 2.0 x 10(6) to 3.0 x 10(5) over the same age range. 3) There was no age-related change in the size of newly-synthesized hyaluronic acid, which was of very high molecular mass, in both immature and mature cartilage. The results are consistent with an age-related decrease in proteoglycan aggregate size and suggest that modification of the hyaluronic acid chain may take place in the extracellular matrix.

Insulin stimulates secretion of a collagenase inhibitor by Swarm rat chondrosarcoma chondrocytes

Swarm rat chondrosarcoma chondrocytes produce an inhibitor of collagenase similar to that found in bovine articular chondrocytes and extracts of bovine scapular cartilage. These cells synthesize normal levels of cartilage type proteoglycans when cultured in serum free medium with insulin. Collagen synthesis is also increased when insulin is added to chondrosarcoma chondrocytes. We have demonstrated that insulin stimulates collagenase inhibitor production by these chondrocytes. Enhancement of inhibitory activity occurs over the range of 10 to 1000 ng/ml. A 3.2 fold stimulation was observed at a concentration of 1 microgram/ml. There was a lag period of 24 to 48 hours before the insulin effect became evident. Latent or active collagenase was not detectable under these conditions. These results suggest that the hormone insulin controls the levels of collagen in this tumor by stimulating synthesis of collagen and inhibitors of collagenase.

Tunicamycin partially delays release of newly synthesized hyaluronate from Swarm rat chondrosarcoma chondrocytes

Tunicamycin (5-100 micrograms/ml) inhibits total [3H]hyaluronate synthesis in cultures of Swarm rat chondrosarcoma chondrocytes by approx. 15%. In agreement with previous results (Lohmander, L.S., Fellini, S.K., Kimura, J.H., Stevens, R.L. and Hascall, V.C. (1983) J. Biol. Chem. 258, 12280-12286) the relative decrease in [3H]hyaluronate radioactivity in the culture medium was greater than in the cell layer. Treated cultures show a concentration-related decrease in the proportion of medium 35S-labelled proteoglycans forming 'natural aggregates'. Pulse-chase experiments in cultures pretreated with tunicamycin (100 micrograms/ml, 13 h) showed that 30-40% of the total [3H]hyaluronate synthesized is released more slowly from these chondrocytes than from control culture chondrocytes. Release of some hyaluronate molecules may be delayed by 6 h or more. After a 24 h chase period almost all the [3H]hyaluronate is released from the cells. The proportion of 35S-labelled proteoglycans present as aggregates in the 24 h chase medium (57%) remained depressed compared to controls (81%), although the monomers could form aggregates if exogenous hyaluronate was added. Hyaluronate synthesized in the presence of tunicamycin has the same hydrodynamic size as control culture hyaluronate, as assessed by its sedimentation profile in CsSO4 gradients and its chromatographic profile on a dissociative Sephacryl S-1000 column.

Biochemistry of hyaluronan

Hyaluronan (hyaluronic acid) is a linear polysaccharide formed from disaccharide units containing N-acetylglucosamine and glucuronic acid. It is ubiquitously distributed in the organism but is found in the highest concentrations in soft connective tissues. The molecular weight of hyaluronan is usually in the order of 10(6) to 10(7). Due to hydrogen bonding, the chain is rather stiff and the molecule behaves in solution as an extended, randomly kinked coil. Molecules of hyaluronan start to entangle already at concentrations of less than 1 g/l and form a continuous polymer network. Some of the functions of the polysaccharide have been connected with the unique physical chemical characteristics of the network such as its rheological properties, flow resistance, osmotic pressure, exclusion properties and filter effect. Hyaluronan is synthesized in the cell membrane by adding monosaccharides to the reducing end of the chain. The precursors are UDP-glucuronic acid and UDP-N-acetylglucosamine. The polysaccharide grows out from the cell surface and it can be shown that fibroblasts, for example, surround themselves with a coat of hyaluronan. The rate of biosynthesis is regulated by various factors, such as growth factors, hormones, inflammatory mediators, etc. The responsible enzyme, hyaluronan synthase, is a phosphoprotein and the regulation of the synthetic rate is apparently via phosphorylation. The hyaluronan is at least partly carried by lymph flow from the tissues. Part of the material is taken up and degraded in the lymph nodes. Another part is carried to the general circulation and taken up in the endothelial cells in the liver sinusoids. These cells have specific receptors for hyaluronan, which also recognize chondroitin sulphate. The uptake in the liver of high-molecular weight hyaluronan is very efficient and its normal half-life in serum is only in the order of 2 to 5 min. The polysaccharide is rapidly degraded in the lysosomes to low-molecular weight products, lactate and acetate. The total turnover of hyaluronan in serum is in the order of 10-100 mg/24 h. The normal concentration of hyaluronan in serum is less than 100 micrograms/l with a mean of 30-40 micrograms/l. High serum levels have been noted in liver cirrhosis (impaired uptake in the liver) and rheumatoid arthritis (increased synthesis in the tissues). Hyaluronan has been shown to interact specifically with certain proteins and cell surfaces. It binds to proteoglycans in cartilage and other tissues and fills an important structural role in the organization of the extra-cellular matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Different growth rates of swarm chondrosarcoma in Lewis and Wistar rats correlate with different thyroid hormone levels

The transplantable Swarm rat chondrosarcoma grew to twice the weight in 5 weeks in Lewis strain rats (approximately 80 g) as it did in Wistar strain rats (approximately 40 g). Wistar tumor passaged into Lewis rats adopted the accelerated growth rate of the Lewis tumor on the second passage. Conversely Lewis tumor passaged into Wistar rats grew like Wistar lineage chondrosarcoma after two passages. Lewis and Wistar tumors had a similar histological appearance. The extracellular matrix composition of the two tumors was very similar. Tumor explant cultures synthesized about the same amount of 35S-proteoglycans and the same proportion of 3H-hyaluronate: 3H-chondroitin sulfate. Serum levels of growth hormone and insulin were the same in the two strains but T3 and T4 levels were 50% higher in Lewis rats compared to Wistar rats. It is likely that accelerated tumor growth in Lewis strain rats is related to the higher thyroid hormone levels.