Culture and differentiation of chondrocytes entrapped in alginate gels

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Apple procyanidins promote mitochondrial biogenesis and proteoglycan biosynthesis in chondrocytes

Apples are well known to have various benefits for the human body. Procyanidins are a class of polyphenols found in apples that have demonstrated effects on the circulatory system and skeletal organs. Osteoarthritis (OA) is a locomotive syndrome that is histologically characterized by cartilage degeneration associated with the impairment of proteoglycan homeostasis in chondrocytes. However, no useful therapy for cartilage degeneration has been developed to date. In the present study, we detected beneficial effects of apple polyphenols or their procyanidins on cartilage homeostasis. An in vitro assay revealed that apple polyphenols increased the activities of mitochondrial dehydrogenases associated with an increased copy number of mitochondrial DNA as well as the gene expression of peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), suggesting the promotion of PGC-1α-mediated mitochondrial biogenesis. Apple  procyanidins also enhanced proteoglycan biosynthesis with aggrecan upregulation in primary chondrocytes. Of note, oral treatment with apple procyanidins prevented articular cartilage degradation in OA model mice induced by mitochondrial dysfunction in chondrocytes. Our findings suggest that apple procyanidins are promising food components that inhibit OA progression by promoting mitochondrial biogenesis and proteoglycan homeostasis in chondrocytes.

3D dynamic culture of rabbit articular chondrocytes encapsulated in alginate gel beads using spinner flasks for cartilage tissue regeneration

Cell-based therapy using chondrocytes for cartilage repair suffers from chondrocyte dedifferentiation. In the present study, the effects of an integrated three-dimensional and dynamic culture on rabbit articular chondrocytes were investigated. Cells (passages 1 and 4) were encapsulated in alginate gel beads and cultured in spinner flasks in chondrogenic and chondrocyte growth media. Subcutaneous implantation of the cell-laden beads was performed to evaluate the ectopic chondrogenesis. It was found that cells remained viable after 35 days in the three-dimensional dynamic culture. Passage 1 cells demonstrated a proliferative growth in both media. Passage 4 cells showed a gradual reduction in DNA content in growth medium, which was attenuated in chondrogenic medium. Deposition of glycosaminoglycans (GAG) was found in all cultures. While passage 1 cells generally produced higher amounts of GAG than passage 4 cells, GAG/DNA became similar on day 35 for both cells in growth media. Interestingly, GAG/DNA in growth medium was greater than that in chondrogenic medium for both cells. Based on GAG quantification and gene expression analysis, encapsulated passage 1 cells cultured in growth medium displayed the best ectopic chondrogenesis. Taken together, the three-dimensional and dynamic culture for chondrocytes holds great potential in cartilage regeneration.

Monocarboxylate transporter 10 functions as a thyroid hormone transporter in chondrocytes

Thyroid hormone is essential for normal proliferation and differentiation of chondrocytes. Thus, untreated congenital hypothyroidism is marked by severe short stature. The monocarboxylate transporter 8 (MCT8) is a highly specific transporter for thyroid hormone. The hallmarks of Allan-Herndon-Dudley syndrome, caused by MCT8 mutations, are severe psychomotor retardation and elevated T(3) levels. However, growth is mostly normal. We therefore hypothesized that growth plate chondrocytes use transporters other than MCT8 for thyroid hormone uptake. Extensive analysis of thyroid hormone transporter mRNA expression in mouse chondrogenic ATDC5 cells revealed that monocarboxylate transporter 10 (Mct10) was most abundantly expressed among the transporters known to be highly specific for thyroid hormone, namely Mct8, Mct10, and organic anion transporter 1c1. Expression levels of Mct10 mRNA diminished with chondrocyte differentiation in these cells. Accordingly, Mct10 mRNA was expressed most abundantly in the growth plate resting zone chondrocytes in vivo. Small interfering RNA-mediated knockdown of Mct10 mRNA in ATDC5 cells decreased [(125)I]T(3) uptake up to 44% compared with negative control (P < 0.05). Moreover, silencing Mct10 mRNA expression abolished the known effects of T(3), i.e. suppression of proliferation and enhancement of differentiation, in ATDC5 cells. These results suggest that Mct10 functions as a thyroid hormone transporter in chondrocytes and can explain at least in part why Allan-Herndon-Dudley syndrome patients do not exhibit significant growth impairment.

ENCAPSULATION AND GROWTH CHARACTERISTICS OF THREE DIFFERENT CELLS IN ALGINATE GEL BEADS CONTAINING RECONSTITUTED COLLAGEN FIBERS

Alginate gel beads containing reconstituted collagen fibers were fabricated and used to culture three different cells - GH3 pituitary tumor cells, L929 fibroblasts and rat calvaria osteoblasts. These cells when entrapped within the collagen-containing alginate behaved differently from those grown in the alginate matrix. Of the three cells tested, the existence of collagen fibers is most beneficial for the viability and proliferation of GH3 cells which can grow either as suspended or attached to the matrix. For the case of osteoblasts derived from the primary culture of rat calvaria, most of the cells entrapped in alginate lost their viability after seeding. The collagen fibers in the alginate gel beads nevertheless decelerated the apotosis process. Furthermore, the entrapped osteoblasts were capable of migrating out of the collagen-containing alginate matrix when the alginate gel beads were in contact with the culture dish. The mineralization of matrix, a key phenotypic expression of osteoblatic cells, was shown by von-Kosa staining on the culturing dish after 14 days cultivation of the cells which crawled out of the gel beads. The collagen-containing alginate beads appear to be more versatile than the conventional alginate gel beads for biomedical applications.

Nasal chondrocytes and fibrin sealant for cartilage tissue engineering

Hybrid constructs associating a biodegradable matrix and autologous chondrocytes hold promise for the treatment of articular cartilage defects. In this context, our objective was to investigate the potential use of nasal chondrocytes associated with a fibrin sealant for the treatment of articular cartilage defects. The phenotype of primary nasal chondrocytes (NC) from human (HNC) and rabbit (RNC) origin were characterized by RT-PCR. The ability of constructs associating fibrin sealant and NC to form a cartilaginous tissue in vivo was investigated, firstly in a subcutaneous site in nude mice and secondly in an articular cartilage defect in rabbit. HNC express type II collagen and aggrecan, the two major hallmarks of a chondrocytic phenotype. Furthermore, when injected subcutaneously into nude mice within a fibrin sealant, these chondrocytes were able to form a cartilage-like tissue. Our data indicate that RNC also express type II collagen and aggrecan and maintained their phenotype in three-dimensional culture within a fibrin sealant. Moreover, treatment of rabbit articular cartilage defects with autologous RNC embedded in a fibrin sealant led to the formation of a hyalin-like repair tissue. The use of fibrin sealant containing hybrid autologous NC therefore appears as a promising approach for cell-based therapy of articular cartilage.

Galectin-1 in cartilage: expression, influence on chondrocyte growth and interaction with ECM components

Galectin-1 is a 14 kDa beta-galactoside binding protein, capable of forming lattice-like structures with glycans of cellular glycoconjugates and inducing intracellular signaling. The expression of Galectin-1 in porcine cartilage is described in this work for the first time. Immunocytochemical methods revealed distinct distribution patterns for both articular and growth plate cartilage. In articular cartilage, the highest reactivity for Galectin-1 was found in all chondrocytes at the superficial zone and in most of those at the lower layer of the middle zone. In the growth plate, marked reactivity was seen in chondrocytes at the proliferative zone and reached a maximum level for the column-forming cells at the hypertrophic zone. In addition, different Galectin-1 distribution patterns were observed at the subcellular level. With regards to the metabolic effects of Galectin-1, the results in vitro seem to indicate an inhibitory effect of Galectin-1 on articular chondrocyte anabolism (i.e. inhibition of cell proliferation and anabolic gene expression) and a stimulation of catabolic processes (i.e. induction of matrix degradation and hypertrophy marker expression). These data represent a starting point for the understanding the molecular mechanisms underlining ECM-Galectin-1 interaction and the subsequent signaling-cell transduction processes involving cartilage formation and maturation.

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Implantation of Cultured Preadipocyte Using Chitosan/Alginate Sponge

Alginate was a proven biocompatible biomatrice for cells but it was known not to provide a proper microenvironment needed for the proliferation of cells because of its anionic property, which caused its low affinity for cells. Water-soluble chitosan was well known as wound healing material and it also had cationic property which helped cell-to-matrix adhesion. The purpose of this study is to assess the ability of a chitosan/alginate mixed sponge as a scaffold for preadipocytes to serve as a biological implant for soft tissue augmentation. Chitosan/alginate and calcium alginate sponges were made by lyophilizing of alginate with water-soluble chitosan mixture and with calcium chloride mixture, respectively, and those were observed by SEM. Preadipocytes seeded in those sponges were cultured for 2 weeks. In vivo study was designed that chitosan/alginate sponges with and without preadipocytes were implanted subcutaneously into nude mouse. Chitosan/alginate and calcium alginate sponges which had highly porosity and 50-200㎛ pore size. In the chitosan/alginate sponge, the levels of DNA amount were significantly higher than those in calcium alginate sponge (P<0.05). In both groups, they increased progressively with time. On the in vivo study, it was observed that adipose tissue layer in the margin of chitosan/alginate sponge on the 2 weeks after implantation of nude mouse. On the 8 weeks after implantation, thick layer of adipose tissue and neovascularization were observed in the chitosan/alginate sponge. Consequently, chitosan/alginate sponge provided proper microenvironment to human preadipocyte, increased the cell proliferation and maintained the pore that offered neovascularization, so turned out to be effective form of fat transplantation for soft tissue augmentation and reconstruction.

A Developmental Study of Artificial Skin Using the Alginate Dermal Substrate

Alginate, which is isolate from brown seaweed, a bioabsorbable long chain polysaccharides of guluronic acid and mannuronic acid. The authors produced alginate, fibroblastgrowth- factor mixed alginate and alginate-collagen complex as a disc form. For study of wound healing, full thickness skin defects were made on the dorsal area of the animal model. And then alginate, fibroblast-growth-factor mixed alginate, alginate-collagen complex, vaseline gauze as control were applied on the wound and evaluated grossly and histopathologically. For biocompatibility test, alginate and alginate-collagen complex discs were implanted on back of New Zealand white rabbits. And we measured size of wound healing, size of wound epithelization, size of wound contracture at 5, 10, 15, 20, and 25 days. Four weeks after implantation, implanted animals were examined immunologically against alginate and collagen. Alginate and FGF-mixed alginate, alginate-collagen complex group showed statistically higher percentage of wound contraction and wound healed than control group(p<0.05) Alginate-collagen complex group and FGF-mixed alginate group showed statistically higher percentage of wound healed than alginate group. In conclusion, high-purified alginate from seaweeds by our purification method, has the ability of wound healing and addition of FGF or collagen increase the ability of alginate, it shows the possibility of alginate as dermal substrate.

Chondrocyte-alginate bioconstructs: An nuclear magnetic resonance relaxation study

Proton nuclear magnetic resonance (NMR) relaxometry can give informations about hydrogel scaffold properties. As these properties can be modified with culture time and conditions according to scaffold biodegradability and new tissue biosynthesis, the aim of this research was to test the efficiency of this noninvasive NMR technique in the follow-up of 3D cultures for tissue engineering. The distributions of proton relaxation times T1 and T2 have been measured on cylindrical gel samples of different types of alginate, in the presence or absence of hyaluronate, in gels or bioconstructs with encapsulated chondrocytes cultured for 30 days in normal or reduced weight conditions. It was found that T2 increases with the mannuronate/guluronate ratio in alginate samples and with the presence of hyaluronate. The distributions of both T1 and T2 result wider for bioconstructs cultured in normal gravity than for those cultured in reduced weight conditions. Neither cell growing nor collagen production but only GAG neosynthesis have been demonstrated in our experimental conditions. In conclusion, T2 is sensitive to the gel properties (possibly to the rigidity of macromolecular components). The homogeneity of bioconstructs can be monitored by the distribution of T1 and T2. We propose that nonspatially resolved NMR relaxometry can efficiently be used in monitoring tissue development in a biodegradable scaffold for tissue engineering.

Markedly different effects of hyaluronic acid and chondroitin sulfate-A on the differentiation of human articular chondrocytes in micromass and 3-D honeycomb rotation cultures

A source of morphologically and functionally available human cartilagenous tissue for implantation is required in the field of tissue engineering. To achieve this goal, we evaluated the effects of hyaluronic acid (HA-810 and 1680 kDa), and chondroitin sulfate (CS-A 16 and C-34 kDa) on human articular chondrocytes (HC) in micromass and rotation culture conditions. Cell proliferation was increased by CS-A 16 kDa under micromass and rotation cultures, while cell differentiation was increased under rotation but not micromass conditions. Proliferation and differentiation due to CS-C 34 kDa were very similar to the control under both culture conditions. With HA, cell proliferation was increased depending on the molecular weight under micromass and rotation conditions. In contrast, chondrocyte differentiation was enhanced under rotation conditions, but decreased under micromass conditions depending on the molecular weight of HA. In both culture conditions, aggrecan gene was continuously expressed. However, the collagen type II gene was more weakly expressed in rotation than the micromass culture conditions. Thus, the chemical structures of polysaccharides, and the culture condition, rotation or micromass, caused differences in chondrogenesis.

Effects of a biodegradable polymer synthesized with inorganic tin on the chondrogenesis of human articular chondrocytes

Recent study has shown that biodegradable polymers are attractive candidates for chondrocyte fixation and further transplantation in cartilage tissue engineering. Poly (glycolic acid) (PGA), a polymer of glycolic acid, is widely used in orthopedic applications as a biodegradable polymer. Organotin, lead, antimony, and zinc are catalysts commonly used in synthesizing PGA. Here, we investigated the biocompatibility of PGA, synthesized with and without inorganic tin as a catalyst in chondrogenesis of human articular chondrocytes in a micromass culture system. Significant enhancement of chondrocyte proliferation and expression of the collagen type II protein gene were observed in cultures treated with PGA synthesized with a tin catalyst. However, aggrecan gene expression was very similar to the control culture. Amount of collagen type II protein was also increased in the same group of cultured chondrocytes. In contrast, PGA without a catalyst caused overall inhibition of chondrogenesis. Despite several positive findings, extensive investigations are essential for the feasibility of this PGA(Sn) in future clinical practice.

Human anulus fibrosis and nucleus pulposus cells of the intervertebral disc: effect of degeneration and culture system on cell phenotype

STUDY DESIGN

Human intervertebral disc cells were harvested from patients with adolescent idiopathic scoliosis (AIS) and from donors with degenerative disc disease. Anulus fibrosis (AF) was separated from nucleus pulposus (NP), and cells were cultured separately in two different cell culture models.

OBJECTIVES

To investigate changes in gene expression of human disc cells during in vitro expansion and to determine whether cells from adolescent idiopathic scoliosis donors show different gene expression profiles compared with cells from patients operated for degenerative disc disease.

SUMMARY OF BACKGROUND DATA

During in vitro expansion, cells undergo a dedifferentiation process, which is characterized by a switch in gene expression. Markers for the differentiation and dedifferentiation status of human disc cells are not yet known. Moreover, it is not known whether changes in the gene expression pattern occur during the degeneration process.

METHODS

Cells from AF and NP tissues were expanded in monolayer and alginate cultures under controlled and defined conditions. Cells were then harvested, and analysis of phenotype was performed using quantitative real-time polymerase chain reaction (PCR). The mRNA expression of Type I, II, and X collagen, aggrecan, and interleukin-1beta in scoliosis and degenerative human intervertebral disc cells was analyzed.

RESULTS

The gene expression of Type II and X collagen and of aggrecan significantly decreased for both cell types during monolayer expansion. Reexpression of all genes was observed when cells were cultured in alginate. Additionally, NP cells from degenerative tissues displayed significant lower levels of Type II collagen compared with NP cells from scoliosis donors.

CONCLUSIONS

These results provide a better understanding of how the phenotype of human healthy and degenerative disc cells is influenced by in vitro expansion. This may be useful for future tissue engineering purposes.

In Vitro Cartilage Regeneration From Proliferated Adult Elastic Chondrocytes

The purpose of this study was to investigate cellular feasibility in the proliferation and differentiation status of adult chondrocytes for cartilage regeneration in comparison to fetal chondrocytes. Primary cells were isolated from adult (n = 6) and fetal (n = 6) sheep ear cartilages and expanded in 10% fetal bovine serum (FBS) containing Ham's F12 medium, in which adult and fetal cell proliferation rates were compared using a WST-1 assay kit. Approximately 4 million cells were seeded onto each 1 x 1 x 0.2-cm (200 microL) nonwoven fabric scaffold made from polyglycolic acid. Cell/polymer constructs were cultured in serum-free DMEM/F12 medium supplemented with 5 ng/mL TGF-beta2 and 5 ng/mL des(1-3)IGF-I (adult chondrocytes, group A) or in 10% FBS containing Ham's F12 medium (adult chondrocytes, group B, and fetal chondrocytes, group C) as controls in a rotating bioreactor for 6 weeks. The proliferation assay showed that fetal cells had a significantly better growth potential than did adult cells. Histology and extracellular matrix analyses revealed that groups A and C qualitatively displayed better matrix deposition than did group B. In conclusion, although adult sheep elastic chondrocytes had less growth potential than did fetal cells, the serum-free medium supplemented with growth factors significantly enhanced the production of cartilage matrix secreted from proliferated adult sheep elastic chondrocytes.

The aggregation of pig articular chondrocyte and synthesis of extracellular matrix by a lactose-modified chitosan

A reductive amination reaction (N-alkylation) obtained exploiting the aldheyde group of lactose and the amino group of the glucosamine residues of chitosan (d.a. 89%) afforded a highly soluble engineered polysaccharide (chitlac) for a potential application in the repair of the articular cartilage. Chitosan derivatives with 9% and 64% of side chain groups introduced have been prepared and characterized by means of potentiometric titration, (1)H-NMR and intrinsic viscosity. Both polymers, with respect to the unmodified chitosan, induce cell aggregation when in contact with a primary culture of pig chondrocytes, leading to the formation of nodules of considerable dimensions (up to 0.5-1 mm in diameter). The nodules obtained from chondrocytes treated with chitlac with the higher degree of substitution have been studied by means of optical and electron microscopy (SEM, TEM) and the production of glycosaminoglycans (GAGs) and collagen has been measured by means of colorimetric assays. The chondro-specificity of GAG and collagen was determined by RT-PCR. The results show that the lactose-modified chitosan is non-toxic and stimulates the production of aggrecan and type II collagen.

Neocartilage from human mesenchymal stem cells in alginate: Implied timing of transplantation

Previous reports have demonstrated the suitability of alginate microencapsulation for chondrogenesis of human mesenchymal stem cells (MSCs) in vitro. This study examined the MSCs-alginate constructs that were transplanted beneath the dorsal skin of nude mice for 8 weeks after a variety of in vitro culture periods. The in vitro culture had great effects on gross morphology and histological characteristics of transplants. The integrity of alginate of transplants increased as the in vitro culture period increased. Transplants were characterized by an opaque and yellowish color, fair burnish, a firm to elastic texture, but without any evidence of calcification spots. Histological findings agreed with the clinical determination of hyaline cartilage, characterized by isolated cells with basophilic ground substance positive in Safranin-O staining and collagen type II immunohistochemistry. Transplants with exposure to TGF-beta1 for more than 2 weeks before transplantation, lost burnish, were flexible in texture, and had an increased formation of calcification spots. Accordingly, 1-week exposure to TGF-beta1 in vitro before transplantation is appropriate for neocartilage formation of human MSCs in alginate. These findings suggested that regeneration using cell therapy or tissue engineering should assist in ascertaining the optimal timing of transplantation.

The in vitro effects of dehydroepiandrosterone on human osteoarthritic chondrocytes

OBJECTIVE

To investigate the in vitro effects of dehydroepiandrosterone (DHEA) on human osteoarthritic chondrocytes.

DESIGN

Chondrocytes isolated from human osteoarthritic knee cartilage were three-dimensionally cultured in alginate beads, except for cell proliferation experiment. Cells were treated with DHEA in the presence or absence of IL-1beta. The effects on chondrocytes were analyzed using a 3-(4,5-dimethylthiazol-2yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay (for chondrocyte proliferation), a dimethylmethylene blue (DMB) assay (for glycosaminoglycan (GAG) synthesis), and an indole assay (for DNA amount). Gene expressions of type I and II collagen, metalloproteinase-1 and -3 (MMP-1 and -3), and tissue inhibitor of metalloproteinase-1 (TIMP-1) as well as the IL-1beta-induced gene expressions of MMP-1 and -3 were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The protein synthesis of MMP-1 and -3 and TIMP-1 was determined by Western blotting.

RESULTS

The treatment of chondrocytes with DHEA did not affect chondrocyte proliferation or GAG synthesis up to 100 micro M of concentration. The gene expression of type II collagen increased in a dose-dependent manner, while that of type I decreased. DHEA suppressed the expression of MMP-1 significantly at concentrations exceeding 50 micro M. The gene expression of MMP-3 was also suppressed, but this was without statistical significance. The expression of TIMP-1 was significantly increased by DHEA at concentrations exceeding 10 micro M. The effects of DHEA on the gene expressions of MMP-1 and -3 were more prominent in the presence of IL-1beta, in which DHEA suppressed not only MMP-1, but also MMP-3 at the lower concentrations, 10 and 50 micro M, respectively. Western blotting results were in agreement with RT-PCR, which indicates that DHEA acts at the gene transcription level.

CONCLUSIONS

Our study demonstrates that DHEA has no toxic effect on chondrocytes up to 100 micro M of concentration and has an ability to modulate the imbalance between MMPs and TIMP-1 during OA at the transcription level, which suggest that it has a protective role against articular cartilage loss.

Chondrogenesis of human mesenchymal stem cells encapsulated in alginate beads

Mesenchymal stem cells (MSCs) have the capacity for self-renewal and can form bone, fat, and cartilage. Alginate forms a viscous solution when dissolved in 0.9% saline and gels on contact with divalent cations. The viability and phenotype maintenance of chondrocytes in alginate beads have been well documented. However, little is known about the effect of microencapsulation in alginate on chondrogenesis of MSCs. In this study, human MSCs encapsulated in alginate beads were cultured in serum-free medium with the addition of transforming growth factor (TGF)beta1 (10 ng/mL), dexamethasone (10(-7) M), and ascorbate 2-phosphate (50 microg/mL). The MSCs in alginate assumed a rounded morphology with lacunae around them after 1 week in culture. Cell aggregates were observed at 2 weeks or longer in culture. Histological findings agreed with the clinical determination of hyaline cartilage, characterized by isolated cells with ground substance positive in Safranin-O staining and immunohistochemistry for collagen type II at the periphery of cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the expression of COL2A1 and COL10A1, marker of chondrocytes and hypertrophy chondrocytes, respectively. These results indicate MSCs in alginate can form cartilage and the MSCs-alginate system represents a relevant model for the study of the molecular mechanisms involved in the chondrogenesis and endochondral ossification.

Chondrogenic differentiation of human mesenchymal stem cells within an alginate layer culture system

Human mesenchymal stem cells (hMSCs) derived from bone marrow have the capacity to differentiate along a number of connective tissue pathways and are an attractive source of chondrocyte precursor cells. When these cells are cultured in a three-dimensional format in the presence of transforming growth factor-beta, they undergo characteristic morphological changes concurrent with deposition of cartilaginous extracellular matrix (ECM). In this study, factors influencing hMSC chondrogenesis were investigated using an alginate layer culture system. Application of this system resulted in a more homogeneous and rapid synthesis of cartilaginous ECM than did micromass cultures and presented a more functional format than did alginate bead cultures. Differentiation was found to be dependent on initial cell seeding density and was interrelated to cellular proliferation. Maximal glycosaminoglycan (GAG) synthesis defined an optimal hMSC seeding density for chondrogenesis at 25 x 10(6) cells/ml. Inclusion of hyaluronan in the alginate layer at the initiation of cultures enhanced chondrogenic differentiation in a dose-dependent manner, with maximal effect seen at 100 microg/ml. Hyaluronan increased GAG synthesis at early time points, with greater effect seen at lower cell densities, signifying cell-cell contact involvement. This culture system offers additional opportunities for elucidating conditions influencing chondrogenesis and for modeling cartilage homeostasis or osteoarthritic changes.

Proliferation of canine intervertebral disk chondrocytes in three-dimensional alginate microsphere culture

Proliferation of chondrocytes from nucleus pulposus (NP) and anulus fibrosus (AF) was confirmed in three-dimensional culture using alginate microspheres. Cells isolated from NP and AF were incorporated in microspheres and cultured for 14 days. Round mononuclear cells of 20-25 microm in diameter proliferated and formed aggregates. At day 14, alcian blue positive matrix surrounded the proliferating cells. The cells had cytoplasmic vacuoles stained positively by toluidine blue. On electron microscopy, the cells contained proteoglycan vacuoles and lipid droplets in the cytoplasm and synthesized collagen fibrils and electron dense granules surrounding the cell. These features of the cells were characteristic for chondrocytes. This culture system should be useful to further investigate metabolic activities of intervertebral disk chondrocytes.

Enhancement of chondrogenic differentiation of human articular chondrocytes by biodegradable polymers

Biodegradable polymers are attractive candidates for chondrocyte embedding and transplantation in cartilage tissue engineering. In an attempt to determine the effects of a variety of biodegradable materials on cartilage proliferation and extracellular matrix production, poly-L-lactic acid (PLLA) with a molecular weight of 5,000, polyglycolic acid (PGA) with a molecular weight of 3,000, and copolymer of poly(L-lactic acid-glycolic acid) 50:50 (PLGA) with a molecular weight of 5,000, were dissolved in DMSO and added into the medium for 4 weeks in in vitro high-density micromass culture of multiplied human articular chondrocytes (HAC). PLLA with a molecular weight of 270,000 (PLAO3) was used as thin film. Cell proliferation and differentiation in these biomaterials were compared with tissue culture polystyrene (TCPS) as a control. Alamar blue and alcian blue staining were carried out to determine the chondrocyte proliferation and differentiation, respectively. Samples exposed to these biomaterials promoted cell proliferation in the range of 86-105% of the control proliferation, and a slight but significant increase in cell proliferation was noted only in the culture exposed to PLGA. The sample exposed to PGA elicited a significant 3.7-fold higher (p < 0.01) cell differentiation than controls and was significantly higher than that of the samples exposed to PLLA, PLAO3, and PLGA. After 4 weeks of culture, the cell differentiation from most to least was in the following order PGA > PLAO3 > PLGA = PLLA > Cont. = DMSO. Chondrocyte differentiation of the samples exposed to various biomaterials were significantly higher compared with controls. Thus, serially passage chondrocytes are competent for cell growth and quantifiable matrix production, and biodegradable polymers, especially PGA, hold promise as suitable substrates for scaffolding materials for human cartilage tissue engineering.

Poly(L-lactide)acid/alginate composite membranes for guided tissue regeneration

The barrier membranes for guided tissue regeneration (GTR) to treat bone defects have to satisfy the criteria of biocompatibility, cell-occlusiveness, space-making, tissue integration and clinical manageability. In this study a system constituted of a poly(L-lactide) acid (PLLA) asymmetric membrane combined with an alginate film was prepared. The PLLA membrane functions to both support the alginate film and separate the soft tissue; the alginate film is intended to act as potential vehicle for the growth factors to promote osteogenesis. The structural, morphological, and mechanical properties of the bilamellar membrane and its stability in culture medium were evaluated. Moreover, the feasibility of using the alginate membranes as controlled-release delivery vehicles of TGF-beta was monitored. Finally, the bacterial adhesion and permeability of Streptococcus mutans, selected for the high adhesive affinity, were monitored. The results showed that the surfaces of the alginate side, to be used in contact with the bone defect, were rougher than PLLA ones. When in contact with complete culture medium, the PLLA-alginate membrane retained its mechanical and structural properties for more than 100 days. Then, the degradation processes occurred but the membrane continued to be stable and manageable for 6 months. Growth factors such as TGF-beta can be incorporated into alginate membranes functioning as drug delivery vehicle, and retain the biological activity when tested in an in vitro model system. The obtained membrane acted as a barrier to the passage of S. mutans bacteria and showed to promote a lower bacterial adhesion with respect to commercial GTR membranes.

Histomorphological and proliferative characterization of developing periosteal neochondrocytes in vitro

Periosteal chondrogenesis is relevant to cartilage repair and fracture healing. Cell proliferation is a limiting factor of cartilage production. We used an in vitro organ culture model to test the hypothesis that proliferative activity correlates with cell morphology. One hundred and four periosteal explants from 26 two-month old New Zealand rabbits were cultured for up to 42 days. They were analyzed histomorphologically, and immunohistochemically with proliferative cell nuclear antigen (PCNA). The periosteal neocartilage displayed a consistent zonal pattern of chondrocyte cell shapes. The flat cell zone from day 7 to 21, consisted of uniform-sized small spindle-shaped cells. The round cell zone, which appeared on day 14, consisted of variable-sized round cells averaging 510 +/- 250 microm2 in area. They were subdivided into small round (<510 microm2) and large round cells (>510 microm2). The proliferative index was highest in the small round cell group (32 +/- 6%), intermediate in the flat cell group (27 +/- 6%), and lowest in the large round cell group (20 +/- 7%) (P < 0.001). Furthermore, the proliferative indices in the round cell group were inversely proportional to cell size. Therefore, (1) there is a sequential progression of cell morphology during periosteal chondrogenesis, (2) cell differentiation is arrested prior to terminal differentiation for some cells and not for others, and (3) proliferative activity is strongly related to cell morphology. This organ culture model provides us with opportunities to study the regulation of terminal chondrocyte differentiation and the control of cell proliferation. This will contribute to our understanding of cartilage repair, fracture healing and growth plate physiology.

Localization of chondrocyte precursors in periosteum

OBJECTIVE

Periosteal chondrogenesis is relevant to cartilage repair and fracture healing. Periosteum contains two distinct layers: a thick, outer fibrous layer and a thin, inner cambium layer which is adjacent to the bone. Specific chondrocyte precursors are known to exist in periosteum but have not yet been identified. In this study, the location of the chondrocyte precursors in periosteum was determined.

METHOD

One hundred and twenty periosteal explants from 30 2-month-old NZ rabbits were cultured for up to 42 days. Histomorphological changes and spatio-temporal localization of Col. II mRNA and protein were analysed.

RESULTS

On day 7, chondrocyte differentiation appeared in the most juxtaosseous region in the cambium layer. Col. II mRNA and protein were also evident in the same region. By day 14, chondrocyte differentiation progressed further into the juxtaosseous cambium layer, as did Col. II mRNA and protein. With growth of the neocartilage, the cambium layer gradually diminished to the extent that by 21-28 days it was no longer evident. Cartilage growth was significant and followed an appositional pattern, growing away from the fibrous layer. The fibrous layer remained essentially unchanged from 0-42 days, without evidence of hypertrophy or atrophy. Col. II mRNA expression was never seen in the fibrous layer.

CONCLUSION

From these data, three conclusions can be drawn concerning chondrogenesis from periosteum: (1) the chondrocyte precursors are located in the cambium layer of periosteum; (2) chondrogenesis commences in the juxtaosseous area in the cambium layer and progresses from the juxtaosseous region to the juxtafibrous region of the cambium layer; (3) neocartilage growth is appositional, which displaces the fibrous layer away from the cartilage already formed, as new cartilage is formed between these two layers. These findings suggest that the least differentiated (stem or reserve) cells are located in the cambium layer furthest from the bone.

CLINICAL RELEVANCE

These findings show that the chondrocyte precursors are located in the cambium layer of periosteum. Preservation of this layer is essential for chondrogenesis. As neocartilage growth is appositional, away from the fibrous layer, it can be expected that the new cartilage deposited in and adjacent to a periosteal graft would be expected to be located on the side of the cambium layer, rather than on the side of the fibrous layer of the graft.

Chondrocyte extracellular matrix synthesis and turnover are influenced by static compression in a new alginate disk culture system

The goal of this study was to examine the effects of mechanical compression on chondrocyte biosynthesis of extracellular matrix (ECM) components during culture in a new alginate disk culture system. Specifically, we have examined chondrocyte biosynthesis rates, and the structure of aggrecan core protein species present in the cell-associated matrix (CM), in the further removed matrix (FRM) and in the surrounding culture medium. In this alginate disk culture system, chondrocytes can be subjected to mechanical deformations similar to those experienced in vivo. Our results show that over an 8-week culture period, chondrocytes synthesize a functional ECM and can respond to mechanical forces similarly to chondrocytes maintained in native cartilage. In the alginate disk system, static compression was shown to decrease and dynamic compression to increase synthesis of aggrecan of bovine chondrocytes. Western blot analysis of the core proteins of aggrecan molecules identified a number of different species that were present in different relative amounts in the CM, FRM, and medium. Over 21 days of culture, the predominant form of aggrecan found in the ECM was a full-length link-stabilized species. In addition, our data show that the application of 40 h of static compression caused an increase in the proportion of newly synthesized aggrecan molecules released into the medium. However, this was not accompanied by a significant change in the size and composition of aggrecan and aggrecan fragments in the different compartments, suggesting that mechanical compression did not alter the catabolic pathways. Together, these data show that chondrocyte function is maintained in an alginate disk culture system and that this culture system is a useful model to examine chondrocyte ECM assembly and some aspects of catabolism normally found in vivo.

Bovine articular chondrocyte function in vitro depends upon oxygen tension

Articular cartilage is a physiologically hypoxic tissue with a proposed gradient of oxygen tension ranging from about 10% oxygen at the cartilage surface to less than 1% in the deepest layers. The position of the chondrocyte within this gradient may modulate the cell's behavior and phenotype. Moreover, the oxygen gradient is likely to be disturbed during joint diseases in which the pO(2)of the synovial fluid declines which may cause changes in chondrocyte behavior and gene expression. Thus, there is a need to understand the chondrocyte's response to different oxygen tensions. We compared the behavior of bovine articular chondrocytes cultured in alginate beads for 7 days in medium maintained at <0.1, 5, 10 or 20% oxygen. The chondrocytes' survival, differentiation, cell division, viability and matrix production were assessed at each oxygen tension and rRNA and mRNA abundance was measured. Chondrocytes were able to survive under all oxygen tensions for at least 7 days but cells cultured under anoxic conditions were metabolically less active than cells maintained in higher oxygen tensions; this was associated with a decrease in matrix production. In <0.1% oxygen there was a marked decrease in rRNA and mRNA abundance in the cells. There were no differences in cell division or differentiation between any oxygen tensions. These findings indicate that articular chondrocytes can be cultured successfully in the pO(2)range in which they are thought to exist in vivo (5-10% pO(2)) and are fully active under these conditions. Under anoxic conditions (<0.1% pO(2)) function is severely compromised.

Differential expression of proteoglycan epitopes by ovine intervertebral disc cells

The alginate bead culture system has been utilised by several groups to examine the in vitro proteoglycan (PG) metabolism of chondrocytes and intervertebral disc cells, but the nature of the PGs produced has not been examined in detail. This is largely due to the difficulty of separating the anionically charged sodium alginate support matrix from PGs which are similarly charged. In the present study ovine annulus fibrosus, transitional zone and nucleus pulposus cells were dissociated enzymatically from their respective matrices by sequential digestion with pronase/clostridial collagenase and DNAase and then cultured in alginate beads for 10 d. The beads were solubilised and subjected to DEAE Sepharose CL6B anion exchange chromatography to separate the sodium alginate bead support matrix material quantitatively from the disc cell PGs. The alginate free bead PGs were then subjected to composite agarose polyacrylamide gel electrophoresis to resolve PG populations and the PGs were transferred to nitrocellulose membranes by semidry electroblotting. The PGs were identified by probing the blots with a panel of antibodies to defined PG core protein and glycosaminoglycan side chain epitopes. Alginate beads of disc cells were also embedded in paraffin wax and 4 microm sections cut to immunolocalise decorin, biglycan, versican, and the 7-D-4 PG epitope within the beads. Decorin and biglycan had similar distributions in the beads, being localised on the cell surface whereas versican and the 7-D-4 PG epitope were immunolocalised interterritoriarly. This study is the first to demonstrate that ovine disc cells synthesise versican in alginate bead culture. Furthermore the immunoblotting studies also showed that a proportion of the 7-D-4 PG epitope was colocalised with versican.

Effects of chondroitin sulfate and interleukin-1beta on human chondrocyte cultures exposed to pressurization: a biochemical and morphological study

Objective This study investigated the in vitro effects of chondroitin sulfate (CS) on human articular chondrocytes cultivated in the presence or in the absence of interleukin-1beta (IL-1beta) during 10 days of culture with and without pressurization cycles. Design The effects of CS (10 and 100 microg/ml) with and without IL-1beta were assessed in the culture medium of cells exposed to pressurization cycles in the form of synusoidal waves (minimum pressure 1 Mpa, maximum pressure 5 Mpa) and a frequency of 0.25 Hz for 3 h by immunoenzymatic method on microplates for the quantitative measurement of human proteoglycans (PG). On the 4th and 10th day of culture the cells were used for morphological analysis by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Results The presence of IL-1beta determines a significant decrease in PG concentration measured in the culture medium. When the cells are cultured in the presence of IL-1beta and CS, a statistically significant restoration of PG levels is observed. Under pressurization conditions, we observed that PG concentration in the medium of cells presents a significant increase at baseline conditions, in the presence of IL-1beta+CS10 and IL-1beta+CS100, but not with IL-1beta alone. The results concerning metabolic evaluation are confirmed by the morphologic findings obtained by TEM and SEM. Conclusions These in vitro studies confirm the protective role of CS, which counteracts the IL-1beta induced effects and they confirm the importance of pressure on chondrocyte metabolism and morphology.

Articular cartilage repair in rabbits by using suspensions of allogenic chondrocytes in alginate

The feasibility of allogenic implants of chondrocytes in alginate gels was tested for the reconstruction in vivo of artificially full-thickness-damaged articular rabbit cartilage. The suspensions of chondrocytes in alginate were gelled by the addition of calcium chloride solution directly into the defects giving in situ a construct perfectly inserted and adherent to the subchondral bone and to the walls of intact cartilage. The tissue repair was controlled at 1, 2, 4 and 6 months after the implant by NMR microscopy, synchrotron radiation induced X-ray emission to map the sulfur of glycosaminoglycans and by histochemistry. Practically a complete repair of the defect was observed 4-6 months from the implant of the chondrocytes with the recovery of a normal tissue structure. Controls in which Ca-alginate alone was implanted developed only a fibrous cartilage.

Retention of hyaluronic acid in alginate beads: aspects for in vitro cartilage engineering

Alginate has been used successfully for three-dimensional chondrocyte cultures and may be important for cartilage transplant formation. However, alginate is not a natural component of the cartilage matrix. The aim of this study was (a) to supplement alginate with the extracellular matrix component hyaluronic acid; and (b) to analyze the hyaluronic acid retention in different alginate gels. Hyaluronan is assumed to improve proteoglycan retention and may be important for in vitro matrix formation, tissue turgor, and biomechanical quality. Alginate and hyaluronan were mixed with chondrocytes and polymerized as were alginate, hyaluronan, and fibrinogen. [3H]hyaluronan was used to quantitate the leakage of hyaluronan from the gel beads. After 28 days in culture, 1.2% alginate beads supplemented with 0.26% hyaluronan contained only 9% of the initial amount of hyaluronan whereas 2.4% alginate beads still contained about 55% of the initial 0.22% hyaluronan. Release of hyaluronan from the beads was significantly lower if the beads additionally contained fibrin. Alginate beads supplemented with hyaluronan or fibrin showed increased chondrocyte proliferation compared to controls. Supplemented hyaluronan greatly diffuses out of alginate gels of lower densities. It must be assumed also that most of the hyaluronan newly synthesized by chondrocytes in these cells diffuses into the surrounding culture medium. The in vitro development of a sufficiently hygroscopic cartilage ground substance therefore may be very limited. Sufficient hyaluronic acid retention can be achieved in alginate gels with concentrations above 1.2% or by addition of fibrin.

Re-expression of differentiated proteoglycan phenotype by dedifferentiated human chondrocytes during culture in alginate beads

The proteoglycans (PGs) synthesised by normal human articular chondrocytes and a chondrocyte cell line cultured in monolayer and alginate beads were compared. Chondrocytes became dedifferentiated after serial subcultures in monolayer, exhibited a fibroblastic morphology and synthesised a large proportion of lower molecular weight, dermatan sulphate containing PGs. When transferred into alginate beads, the cells quickly regained their spherical shape and actively incorporated [3H]thymidine and [35S]sulphate during 70 days of culture. This resulted in a continuous increase in their DNA content and a rapid deposition of PGs for the first 25 days of culture, which then remained stable. Immediately after dedifferentiated chondrocytes were encapsulated into alginate beads, they began to synthesise a population of PGs with normal monomer size and an increased ability to form aggregates. The monomer size of newly synthesised PGs remained unchanged during extended periods of culture, but their ability to form aggregates and the ratios of chondroitin-6-sulphate to chondroitin-4-sulphate in their glycosaminoglycan chains gradually increased for the first 25 days before reaching normal values. Parallel experiments with HCS-2/8 cells, derived from a human chondrosarcoma, showed that they followed a similar pattern of development in alginate culture. The ability of their newly synthesised PGs to form aggregates increased with time and their sulphation pattern also gradually became normal. These results showed that culture in alginate promoted redifferentiation of dedifferentiated articular chondrocytes and assisted differentiation of HCS-2/8 chondrocytes. However, complete redifferentiation took a period of several weeks, after which synthesis of normal aggregating PGs was maintained.

Cartilage tissue engineering with novel nonwoven structured biomaterial based on hyaluronic acid benzyl ester

The aim of this study was to investigate the possibility of using the benzyl ester of hyaluronic acid (HYAFF 11), a recently developed semisynthetic resorbable material, as a scaffold for the culture of human nasoseptal chondrocytes in tissue-engineering procedures of cartilage reconstruction. Different techniques such as immunohistochemistry, scanning electron microscopy, and confocal laser scanning microscopy were used to study the behavior, morphology, and phenotype expression of the chondrocytes, which were initially expanded and then seeded on the material. The nonwoven cell carrier allowed good viability and adhesivity of the cells without any surface treatment with additional substances. Furthermore, the cultured cells expressed cartilage-specific collagen type II, indicating that they were able to redifferentiate within the scaffold of HYAFF 11 and were able to retain a chondrocyte phenotype even after a long period of in vitro conditions. Nevertheless, the expression of collagen type I, which was produced by dedifferentiated or incompletely redifferentiated chondrocytes, was noticeable. Additional data were obtained by subcutaneous implantation of samples seeded with human cells in the in vivo model of the athymic nude mouse. The results after 1 month revealed the development of tissue similar to hyaline cartilage. This study is promising for the use of this scaffold for tissue engineering of cartilage replacements.

Cartilage formation by fetal rat chondrocytes cultured in alginate beads: a proposed model for investigating tissue-biomaterial interactions

Chondrocytes from 21-day-old rat fetal nasal cartilage were cultured in alginate beads for up to 20 days. It was found that chondrocytes retained their spherical shape and typical chondrocytic appearance. During the culture time, chondrocytes underwent differentiation, as demonstrated by the alkaline phosphatase-specific activity and rate of proteoglycan synthesis. Morphological data confirmed chondrocyte differentiation with the appearance of hypertrophic chondrocytes scattered in the alginate gel and a dense extracellular matrix containing filamentous structures and matrix vesicles. In addition, Northern blot analysis performed on day 8 of culture showed that chondrocytes cultured in alginate beads expressed type II collagen mRNA. The alginate bead method also appeared to be suitable for testing biomaterials, and the ready dissolution of the alginate beads by chelating agents provided a simple means for the rapid recovery of encapsulated chondrocytes. Powdered glass-ceramic particles entrapped in the alginate gel were colonized by chondrocytes, which then proliferated and formed a tissue similar to a true calcified cartilaginous structure. These results indicate that the alginate system represents a relevant model for studies of chondrogenesis and endochondral ossification. Furthermore, the encapsulation method could prove useful for studies of tissue-biomaterial interactions in an in vitro environment which more closely mirrors the cartilage matrix than other culture methods.

Sensitivity of chondrocytes of growing cartilage to reactive oxygen species

Vascular invasion of calcified cartilage, during endochondral ossification, is initiated and sustained by invasive cells (endothelial cells and macrophages) which degrade the tissue by releasing lytic enzymes. Concurrently, reactive oxygen species (ROS) are also released by these cells and we hypothesize that ROS also contribute to the degradation of the tissue. As a preliminary approach to this problem, the antioxidant activities and the effect of ROS on hypertrophic cartilage and chondrocytes (HCs) were investigated. Compared to resting or articular chondrocytes, HCs exhibited higher catalase but lower SOD specific activities and lower PHGPx concentration, thus revealing a defence activity specific against H2O2. Moreover, dose-dependent depletion of ATP occurred after few minutes of exposure to ROS, and a long-term treatment (16 h incubation with ROS) promoted the release of LDH activity and a significant variation of the poly- to mono-unsaturated fatty acid ratio. Finally, the incubation of HCs with low ROS doses induced the release of sedimentable alkaline phosphatase activity (matrix vesicles). How the obtained results fit the in vivo occurring events is discussed.

Dedifferentiated chondrocytes cultured in alginate beads: restoration of the differentiated phenotype and of the metabolic responses to interleukin-1beta

Chondrocytes cultivated in monolayer rapidly divide and lose their morphological and biochemical characteristics, whereas they maintain their phenotype for long periods of time when they are cultivated in alginate beads. Because cartilage has a low cellularity and is difficult to obtain in large quantities, the number of available cells often becomes a limiting factor in studies of chondrocyte biology. Therefore, we explored the possibility of restoring the differentiated properties of chondrocytes by cultivating them in alginate beads after two multiplication passages in monolayer. This resulted in the reexpression of the two main markers of differentiated chondrocytes: Aggrecan and type II collagen gene expression was strongly reinduced from day 4 after alginate inclusion and paralleled protein expression. However, 2 weeks were necessary for total suppression of type I and III collagen synthesis, indicators of a modulated phenotype. Interleukin-1beta, a cytokine that is present in the synovial fluid of rheumatoid arthritis patients, induces many metabolic changes on the chondrocyte biology. Compared with cells in primary culture, the production of nitric oxide and 92-kDa gelatinase in response to interleukin-1beta was impaired in cells at passage 2 in monolayer but was fully recovered after their culture in alginate beads for 2 weeks. This suggests that the effects of interleukin-1beta on cartilage depend on the differentiation state of chondrocytes. This makes the culture in alginate beads a relevant model for the study of chondrocyte biology in the presence of interleukin-1beta and other mediators of cartilage destruction in rheumatoid arthritis and osteoarthrosis.

Culture of chondrocytes in alginate gel: variations in conditions of gelation influence the structure of the alginate gel, and the arrangement and morphology of proliferating chondrocytes

Sodium alginate, which gels in the presence of calcium ions, is commonly used for culture of anchorage-independent cells, such as chondrocytes. Normally, the gel appears microscopically homogeneous but, depending on the conditions of gelation, it may contain a varying number of small channels that extend inward from the surface. We have examined the influence of these channels on the morphology of cultured chondrocytes entrapped in alginate beads. Growth-plate or articular chondrocytes cultured in alginate normally proliferate and form rounded cell clusters but, in alginate beads containing numerous channels, many chondrocytes become aligned and form columns similar to those in the growth plate in vivo. As the pattern of cellular growth and morphology in alginate is profoundly influenced by the presence of channels in the gel, further studies were conducted to determine what specific conditions of gelation affect their formation. The channels are especially numerous when both the alginate and the gelling solutions lack sodium ions or other monovalent cations. The channels are cavities in the gel formed by particulate blocking of the rapid diffusion of calcium ions from the gelling solution into the boundary of the calcium alginate solution, and hence they extend inward from cells at the surface of the alginate gel. An understanding of the conditions under which these channels develop makes it possible either to avoid their formation or, alternatively, to enhance the number of channels in order to encourage proliferating cells to grow in radial columns, rather than in a less organized pattern characteristic of most culture systems.

Role of oxygen tension during cartilage formation by periosteum

Tissue engineering makes regeneration of cartilage possible but requires optimization of culture conditions. The effects of oxygen tension on cartilage metabolism are controversial in the literature, and we could find no information detailing the optimal oxygen concentration for growing new cartilage (neochondrogenesis). Periosteal cells and tissues can be used to grow cartilage in vivo and in vitro. In this study, using a standard periosteal organ culture model, we found that cartilage formation by periosteal explants is affected by the ambient oxygen concentrations. A total of 480 periosteal explants from 30 2-month-old New Zealand White rabbits were cultured in agarose suspension at different oxygen concentrations (1-90%) for 6 weeks. Chondrogenesis, which was analyzed by histomorphometry and quantitative collagen typing, was maximal at 12-15% oxygen. There were no significant differences in chondrogenesis in the range of 12-45%. There was inhibition of cartilage and type-II collagen formation at very high (90%) and very low (1-5%) oxygen concentrations. However, contrary to what some have thought, chondrogenesis is maximal under aerobic conditions. If this is true for systems other than periosteal implants, it would have important implications for growing cartilage in vitro.

Collagen expression in chicken tibial dyschondroplasia

Collagen expression in growth plate cartilage derived from broiler chickens with tibial dyschondroplasia was studied and compared with samples from unaffected birds. Normal growth plate contains 12% collagen (dry weight) and dyschondroplastic growth plate 19% collagen compared with articular cartilage, which contains 55%. Dyschondroplastic growth plate collagens were more resistant to extraction by pepsin treatment than were those from unaffected growth plate. Normal and dyschondroplastic growth plate cartilages contain similar amounts of type I collagen (5% of the total collagen) but dyschondroplastic growth plate cartilage contains slightly less type II and type XI collagens, and significantly more type X collagen (25% as compared to 11%) than in normal growth plate. The levels of the mature collagen cross-link, hydroxylysyl-pyridinoline, are very low in normal growth plate but are six times higher in dyschondroplastic lesions. Immunolocalisation studies show that there is little change to the normal patterns of collagen organisation in dyschondroplastic growth plate. Investigation of metalloproteinase activity showed there to be a reduction in MMP-2 levels in dyschondroplastic growth plate compared to normal growth plate. In vitro studies on articular, normal growth plate and dyschondroplastic growth plate chondrocytes cultured in alginate or on plastic revealed differences between the cell types. When plated on plastic, articular chondrocytes rapidly assume a fibroblastic morphology. In contrast, normal growth plate chondrocytes retain their polygonal morphology whereas chondrocytes derived from dyschondroplastic cartilage initially exhibit both fibroblastic and polygonal phenotypes but gradually change to totally fibroblastic. These morphological changes are reflected by the collagen synthesis in vitro. Chondrocytes derived from normal articular cartilage synthesised collagen types I, II and X when cultured in alginate but type X synthesis was lost when cultured on plastic. Chondrocytes derived from normal growth plate cartilage synthesised predominantly type X collagen when cultured in either system. Chondrocytes derived from dyschondroplastic growth plate exhibited a similar phenotype to normal growth plate chondrocytes when cultured in alginate beads, but showed signs of dedifferentiation with reduced type X collagen and increased type I collagen when plated on plastic. These results suggest that the chondrocytes in dyschondroplastic growth plate cartilage are at a different stage of maturity than normal resulting in a cartilage that is failing to turn over at a normal rate.

Culture of chondrocytes in alginate and collagen carrier gels

In this in vitro study, we compared the potential of collagen and alginate gels as carriers for chondrocyte transplantation and we studied the influence of demineralized bone matrix (DBM) on chondrocytes in the gels. Chondrocytes were assessed for cell viability, phenotype (histology), proliferation rate and sulfate incorporation. Collagen gels showed a significant increase in cell numbers, but the chondrocytes dedifferentiated into fibroblast-like cells from day 6 onwards. In alginate gels, initial cell loss was found, but the cells maintained their typical chondrocyte phenotype. Although the total quantity of proteoglycans initially synthesized per cell in collagen gel was significantly higher, expressed per cell, the quantity in alginate gel eventually surpassed collagen. No effects of culturing chondrocytes in combination with DBM could be demonstrated on cell proliferation and sulfate incorporation. The collagen and alginate gels have different advantages as carriers for chondrocyte transplantation. The high proliferation rate of chondrocytes in collagen gel may be an advantage, but the preservation of the chondrocyte phenotype and the gradually increasing proteoglycan synthesis in alginate gel is a promising method for creating a hyaline cartilage implant in vitro.

Calbindin-D28K and -D9K and 1,25(OH)2 vitamin D3 receptor immunolocalization and mineralization induction in long-term primary cultures of rat epiphyseal chondrocytes

Rat epiphyseal plat chondrocytes were grown on glass slides, as nonadhering monolayer cultures for up to 6 weeks. Chondrocyte growth, differentiation and maturation, matrix formation and mineralization, and the temporospatial distribution of the vitamin D-dependent calcium-binding proteins, calbindin-D9K and -D28K, and the 1,25(OH)2D3 receptor (VDR), were all monitored. Chondrocytes became confluent in 2.5 weeks, differentiated to acquire a chondrocyte (polygonal) morphology, produced extracellular matrix, and finally formed a true monolayer mineralizing cartilaginous tissue, with all the stages of chondrocyte development within a single culture. beta-Glycerophosphate promoted initial matrix mineralization in 4 weeks and accelerated cell differentiation. High nominal calcium and ascorbic acid were needed for abundant matrix formation. VDR occurred at all differentiation stages, in the nuclei and nucleoli and in the cytoplasm. Calbindin-D28K and -D9K were not coexpressed. Calbindin-D28K was found in prechondroblasts, chondroblasts, and in newly differentiated chondrocytes. It was cytoplasmic in prechondroblasts and subsequently also in the perinuclear region and in nuclei, suggesting migration to the nuclear chromatin. Calbindin-D28K was nuclear only in newly differentiated chondrocytes in vitro and was not found in mature chondrocytes. In contrast, calbindin-D9K was present in the cytoplasm of mature and hypertrophic chondrocytes only. It was first in the cell body and eventually migrated within and to the far end of long cell processes with a decreasing cytoplasmic concentration showed by decreased immunostaining intensity, and ultimately hypertrophy of chondrocytes in culture. These in vitro patterns of calbindins-D and VDR accurately reflect their in vivo distributions. The genomic action of vitamin D, in vitro, resulted in the synthesis of nuclear VDR and calbindins-D.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation and mineralization in chick chondrocytes maintained in a high cell density culture: a model for endochondral ossification

Chondrocytes isolated from the proliferative and differentiating zones of 3-wk-old chick growth plates were cultured in the presence of 10% fetal bovine serum (FBS) and ascorbic acid for up to 21 d in a high cell density culture within Eppendorf tubes. The proliferative, differentiating, and calcification properties of the chondrocytes were examined by immunolocalization and by enzyme histochemical and biochemical methods. The cells maintained a chondrocyte phenotype throughout culture: they were round in shape and synthesized both collagen type II and proteoglycans. The expression of a hypertrophic phenotype was evident by Day 3 of culture and from this time onwards characteristics of terminal differentiation were observed. The cells were positive for both alkaline phosphatase (ALP) activity and c-myc protein and the surrounding matrix stained strongly for collagen type X. Small foci of mineralization associated with individual chondrocytes were first evident by Day 6 and more widespread areas of mineralization occupying large areas of matrix were present by Day 15. Mineralization occurred without the addition of exogenous phosphate to the medium. This culture system displays characteristics that are similar in both morphological and developmental terms to that of chick chondrocyte differentiation and calcification in vivo and therefore offers an excellent in vitro model for endochondral ossification.