The lack of effect of glucosamine sulphate on aggrecan mRNA expression and 35S-sulphate incorporation in bovine primary chondrocytes

Transdermal co-delivery of glucosamine sulfate and diacerein for the induction of chondroprotection in experimental osteoarthritis

The aim of this work was to develop a transdermal delivery system consisting of a glucosamine sulfate-laden xanthan hydrogel containing a nanoemulsion-loaded diacerein. The system was intended to prevent cartilage degradation typical of osteoarthritis. The nanoemulsion, made of soybean oil as the oil phase; soybean lecithin, Tween 80, and poloxamer 407 as surfactants; and propylene glycol as cosurfactant, was formed within the hydrogel. The hydrodynamic diameter of the nanoemulsion globules was 81.95 ± 0.256 nm with 0.285 ± 0.036 of PDI value and the zeta potential value of the formulation was 39.33 ± 0.812 mV. CryoSEM and TEM studies revealed the uniform morphology of the vehicle. A rheological study exposed the nanoemulsion-loaded hydrogel as a thixotropic system. Satisfactory storage stability under ICH conditions was established by the zeta potential and rheological studies. Furthermore, skin biocompatibility of the hydrogel was ascertained on the basis of skin irritation study. Additionally, the diffusion of the drugs across rat skin followed a controlled non-Fickian anomalous steady mechanism. Following in vivo administration in experimental osteoarthritis, the transdermal hydrogel showed a reduction in tumor necrosis factor-alpha, C-reactive protein, high mobility group box protein, and monocyte chemoattractant protein-1. Finally, histopathological analysis of the animals showed satisfactory chondroprotection in the in vivo study. In conclusion, the developed transdermal systems showed a potential against the progression of experimental osteoarthritis.

High glycine concentration increases collagen synthesis by articular chondrocytes in vitro: acute glycine deficiency could be an important cause of osteoarthritis

Collagen synthesis is severely diminished in osteoarthritis; thus, enhancing it may help the regeneration of cartilage. This requires large amounts of glycine, proline and lysine. Previous works of our group have shown that glycine is an essential amino acid, which must be present in the diet in large amounts to satisfy the demands for collagen synthesis. Other authors have shown that proline is conditionally essential. In this work we studied the effect of these amino acids on type II collagen synthesis. Bovine articular chondrocytes were cultured under a wide range of different concentrations of glycine, proline and lysine. Chondrocytes were characterized by type II collagen immunocytochemistry of confluence monolayer cultures. Cell growth and viability were assayed by trypan blue dye exclusion method. Type II collagen was measured in the monolayer, every 48 h for 15 days by ELISA. Increase in concentrations of proline and lysine in the culture medium enhances the synthesis of type II collagen at low concentrations, but these effects decay before 1.0 mM. Increase of glycine as of 1.0 mM exceeds these effects and this increase continues more persistently by 60–75%. Since the large effects produced by proline and lysine are within the physiological range, while the effect of glycine corresponds to a much higher range, these results demonstrated a severe glycine deficiency for collagen synthesis. Thus, increasing glycine in the diet may well be a strategy for helping cartilage regeneration by enhancing collagen synthesis, which could contribute to the treatment and prevention of osteoarthritis.

Rapid Myoglobin Aggregation through Glucosamine-Induced α-Dicarbonyl Formation

The extent of glycation and conformational changes of horse myoglobin (Mb) upon glycation with N-acetyl-glucosamine (GlcNAc), glucose (Glc) and glucosamine (GlcN) were investigated. Among tested sugars, the rate of glycation with GlcN was the most rapid as shown by MALDI and ESI mass spectrometries. Protein oxidation, as evaluated by the amount of carbonyl groups present on Mb, was found to increase exponentially in Mb-Glc conjugates over time, whereas in Mb-GlcN mixtures the carbonyl groups decreased significantly after maximum at 3 days of the reaction. The reaction between GlcN and Mb resulted in a significantly higher amount of α-dicarbonyl compounds, mostly glucosone and 3-deoxyglucosone, ranging from and 27 to 332 mg/L and from 14 to 304 mg/L, respectively. Already at 0.5 days, tertiary structural changes of Mb-GlcN conjugate were observed by altered tryptophan fluorescence. A reduction of metmyoglobin to deoxy-and oxymyoglobin forms was observed on the first day of reaction, coinciding with the greatest amount of glucosone produced. In contrast to native α-helical myoglobin, 41% of the glycated protein sequence was transformed into a β-sheet conformation, as determined by circular dichroism spectropolarimetry. Transmission electron microscopy demonstrated that Mb glycation with GlcN causes the formation of amorphous or fibrous aggregates, started already at 3 reaction days. These aggregates bind to an amyloid-specific dye thioflavin T. With the aid of α-dicarbonyl compounds and advanced products of reaction, this study suggests that the Mb glycation with GlcN induces the unfolding of an initially globular protein structure into amyloid fibrils comprised of a β-sheet structure.

Studies on the Formation of Maillard and Caramelization Products from Glucosamine Incubated at 37 °C

This experiment compared the in vitro degradation of glucosamine (GlcN), N-acetylglucosamine, and glucose in the presence of NH3 incubated at 37 °C in phosphate buffer from 0.5 to 12 days. The reactions were monitored with UV-vis absorption and fluorescence emission spectroscopies, and the main products of degradation, quinoxaline derivatives of α-dicarbonyl compounds and condensation products, were determined using UHPLC-UV and Orbitrap mass spectrometry. GlcN produced two major dicarbonyl compounds, glucosone and 3-deoxyglucosone, ranging from 709 to 3245 mg/kg GlcN and from 272 to 4535 mg/kg GlcN, respectively. 3,4-Dideoxyglucosone-3-ene, glyoxal, hydroxypyruvaldehyde, methylglyoxal, and diacetyl were also detected in lower amounts compared to glucosone and 3-deoxyglucosone. Several pyrazine condensation products resulting from the reaction between dicarbonyls and GlcN were also identified. This study determined that GlcN is a significantly unstable molecule producing a high level of degradation products at 37 °C.

Dependence of light attenuation and backscattering on collagen concentration and chondrocyte density in agarose scaffolds

Optical coherence tomography (OCT) has been applied for high resolution imaging of articular cartilage. However, the contribution of individual structural elements of cartilage on OCT signal has not been thoroughly studied. We hypothesize that both collagen and chondrocytes, essential structural components of cartilage, act as important light scatterers and that variation in their concentrations can be detected by OCT through changes in backscattering and attenuation. To evaluate this hypothesis, we established a controlled model system using agarose scaffolds embedded with variable collagen concentrations and chondrocyte densities. Using OCT, we measured the backscattering coefficient (µb) and total attenuation coefficient (µt) in these scaffolds. Along our hypothesis, light backscattering and attenuation in agarose were dependent on collagen concentration and chondrocyte density. Significant correlations were found between µt and chondrocyte density (ρ = 0.853, p < 0.001) and between µt and collagen concentration (ρ = 0.694, p < 0.001). µb correlated significantly with chondrocyte density (ρ = 0.504, p < 0.001) but not with collagen concentration (ρ = 0.103, p = 0.422) of the scaffold. Thus, quantitation of light backscattering and, especially, attenuation could be valuable when evaluating the integrity of soft tissues, such as articular cartilage with OCT.

Collagen and chondrocyte concentrations control ultrasound scattering in agarose scaffolds

Ultrasound imaging has been proposed for diagnostics of osteoarthritis and cartilage injuries in vivo. However, the specific contribution of chondrocytes and collagen to ultrasound scattering in articular cartilage has not been systematically studied. We investigated the role of these tissue structures by measuring ultrasound scattering in agarose scaffolds with varying collagen and chondrocyte concentrations. Ultrasound catheters with center frequencies of 9 MHz (7.1-11.0 MHz, -6 dB) and 40 MHz (30.1-45.3 MHz, -6 dB) were applied using an intravascular ultrasound device. Ultrasound backscattering quantified in a region of interest starting right below sample surface differed significantly (p < 0.05) with the concentrations of collagen and chondrocytes. An ultrasound frequency of 40 MHz, as compared with 9 MHz, was more sensitive to variations in collagen and chondrocyte concentrations. The present findings may improve diagnostic interpretation of arthroscopic ultrasound imaging and provide information necessary for development of models describing ultrasound propagation within cartilage.

The effect of glucosamine sulfate on the proliferative potential and glycosaminoglycan synthesis of nucleus pulposus intervertebral disc cells

STUDY DESIGN

On the basis of the similarities in the structure of cartilage and intervertebral disc and on the property of glucosamine of being the building block for the construction of proteoglycan aggregates, we investigated the compound's role in the proliferation of nucleus pulposus cells under iso- and hyperosmotic conditions, the putative activation of signaling cascades, and the induction of glycosaminoglycan production.

OBJECTIVE

We examined the mode of action of glucosamine in nucleus pulposus cells.

SUMMARY OF BACKGROUND DATA

Glucosamine that naturally occurs in cartilage tissues has been widely used for treating osteoarthritis, but its role in nucleus pulposus cells is largely unknown.

METHODS

The effect of glucosamine sulfate on the viability and proliferation of nucleus pulposus cells was assessed by the microculture tetrazolium test (MTT) assay, direct cell counting, and tritiated thymidine incorporation. Changes in the expression and phosphorylation profile of selected proteins were estimated by Western analysis. Glycosaminoglycan production was measured using the Blyscan assay.

RESULTS

We showed that glucosamine sulfate up to 1 mM did not influence the viability, proliferation rate, or novel DNA synthesis of nucleus pulposus cells in the presence or absence of elevated osmolality but induced the transient phosphorylation of p38 mitogen-activated protein kinase. The highest concentration used (10 mM) negatively affected cellular proliferation and resulted in deactivation of extracellular signal-regulated kinases and c-Jun N-terminal kinases. Interestingly, these effects resulted from an additional hyperosmotic stress provoked by glucosamine alone. Finally, we found that a long-term incubation with glucosamine leads to an increase in the glycosaminoglycan content of nucleus pulposus cells.

CONCLUSION

Glucosamine sulfate was not found to reverse the high osmolality-mediated delay of proliferation in nucleus pulposus cells needed for the maintenance of the tissue's homeostasis. In addition, glycosaminoglycan synthesis stimulated by glucosamine provides a possible promising clinical role for treating disc degenerative disorders.

BIOLOGICAL EFFECTS OF OLIGOSACCHARIDE CHONDROITIN SULFATE C ON HUMAN ARTICULAR CHONDROCYTES

Chondroitin sulfate C (CSC) is an important extracellular matrix (ECM) component of native cartilage tissue. Since ECM is considered to play an important role in guiding proper cellular functions, such as proliferation, differentiation, migration, synthesis or degradation of ECM, in specific tissues, we would like to elucidate the effects of CSC on chondrocytes are cultured on type-II collagen (COL II) scaffolds in this study. In particular, we want to investigate if the oligosaccharides of CSC (O-CSC) have much stronger effects on the chondrocytes. In this in vitro study, human articular chondrocytes were cultured on porous scaffolds made of COL II, cross-linked by genipin. Media containing different molecular weights of CSC were used to cultivate the cells. The results were examined mainly from the gene expression profiles of the cultured cells. The expression levels of several genes were examined by real-time PCR. These included genes of COL II, aggrecan, SRY-related high mobility group-box gene 9 (SOX9) and cartilage oligo matrix protein (COMP), alkaine phosphtase (ALP), a disintegrin and metalloproteinases with thrombospondin motifs 4 (ADAMTS-4), a disintegrin and metalloproteinases with thrombospondin motifs 5 (ADAMTS-5), matrix metalloproteinases 3 (MMP-3) and tissue inhibitors of metalloproteinases 3 (TIMP-3). The results suggested that O-CSC is more potent in upregulating genes that promote chondrogenesis and downregulating genes that degrade cartilage ECM. The results suggest low-molecular-weight glycosaminoglycans may have therapeutic values in osteoarthritis treatment and may lead to further understanding of the basic mechanism of the interactions between the chondrocytes and their ECM.

The effects of oral glucosamine on joint health: is a change in research approach needed?

OBJECTIVE

Oral glucosamine (GlcN) has been widely studied for its potential therapeutic benefits in alleviating the pain and disability of osteoarthritis (OA). Its popularity has grown despite ongoing controversy regarding its effectiveness vs placebo in clinical trials, and lack of information regarding possible mechanisms of action. Here, we review the state of knowledge concerning the biology of GlcN as it relates to OA, and discuss a framework for future research directions.

METHODS

An editorial "narrative" review of peer-reviewed publications is organized into four topics (1) Chemistry and pharmacokinetics of GlcN salts (2) Biological effects of GlcN salts in vitro (3) Therapeutic effects of GlcN salts in animal models of OA and (4) GlcN salts in the treatment of clinical OA.

RESULTS

Data reporting potent pleiotropic activities of GlcN in in vitro cell and explant cultures are discussed in the context of the established pharmacokinetic data in humans and animals. The available clinical trial data are discussed to place the patient in the context of controlled research on disease management.

CONCLUSIONS

Future research to determine therapeutic mechanisms of GlcN salt preparations will require use of standardized and clinically relevant in vitro assay systems and in vivo animal models for testing, as well as development of new outcome measures for inflammation and pain pathways in human OA.

Differential metabolic effects of glucosamine and N-acetylglucosamine in human articular chondrocytes

OBJECTIVE

Aminosugars are commonly used to treat osteoarthritis; however, molecular mechanisms mediating their anti-arthritic activities are still poorly understood. This study analyzes facilitated transport and metabolic effects of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) in human articular chondrocytes.

METHODS

Human articular chondrocytes were isolated from knee cartilage. Facilitated transport of glucose, GlcN and GlcNAc was measured by uptake of [3H]2-deoxyglucose, [3H]GlcN and [3H]GlcNAc. Glucose transporter (GLUT) expression was analyzed by Western blotting. Production of sulfated glycosaminoglycans (SGAG) was measured using [(35)S]SO4. Hyaluronan was quantified using hyaluronan binding protein.

RESULTS

Chondrocytes actively import and metabolize GlcN but not GlcNAc and this represents a cell-type specific phenomenon. Similar to facilitated glucose transport, GlcN transport in chondrocytes is accelerated by cytokines and growth factors. GlcN non-competitively inhibits basal glucose transport, which in part depends on GlcN-mediated depletion of ATP stores. In IL-1beta-stimulated chondrocytes, GlcN inhibits membrane translocation of GLUT1 and 6, but does not affect the expression of GLUT3. In contrast to GlcN, GlcNAc accelerates facilitated glucose transport. In parallel with the opposing actions of these aminosugars on glucose transport, GlcN inhibits hyaluronan and SGAG synthesis while GlcNAc stimulates hyaluronan synthesis. GlcNAc-accelerated hyaluronan synthesis is associated with upregulation of hyaluronan synthase-2.

CONCLUSION

Differences in GlcN and GlcNAc uptake, and their subsequent effects on glucose transport, GLUT expression and SGAG and hyaluronan synthesis, indicate that these two aminosugars have distinct molecular mechanisms mediating their differential biological activities in chondrocytes.

Glucosamine sulphate does not increase extracellular matrix production at low oxygen tension

Low oxygen tension may change the dependence of chondrocytes on exogenous carbohydrate sources. In this study, we have investigated whether glucosamine sulphate (GS) stimulates proteoglycan synthesis, the mRNA expression of aggrecan and of type II collagen, and UDP-sugar levels in bovine primary chondrocytes under a low oxygen (O(2)) atmosphere. Chondrocytes from bovine femoral condyles were cultivated with or without GS or sulphate at various concentrations in low- (5.5 mM) or high-glucose (25 mM) DMEM under either a 5% or 20% O(2) atmosphere for 2 or 8 days after isolation. The mRNA expression of aggrecan and type II collagen and the synthesis of glycosaminoglycan (GAG) were determined by quantitative real-time reverse transcription with polymerase chain reaction and a [(35)S]-sulphate incorporation assay, respectively. Aggrecan promoter activity was analysed by a dual-luciferase reporter gene assay. Intracellular UDP-N-acetylhexosamines (UDP-HexN), UDP-glucuronic acid and UDP-hexoses were analysed by reversed-phase high-performance liquid chromatography electrospray ionization mass spectrometry. A low (5%) O(2) atmosphere significantly increased GAG synthesis, mRNA expression of aggrecan and of type II collagen and aggrecan promoter activity in bovine primary chondrocytes. A high (1 mM) concentration of GS was required to increase the level of UDP-HexN. However, GS did not increase GAG synthesis, aggrecan promoter activity or mRNA expression of aggrecan and of type II collagen. Interestingly, a 5% O(2) atmosphere increased the level of UDP-HexN in 8-day cultures without GS treatment. Thus, exogenous GS does not change chondrocyte metabolism, whereas a 5% O(2) atmosphere stimulates extracellular matrix production in bovine primary chondrocytes. The balance of UDP-sugars is changed under a 5% O(2) atmosphere for longer culture periods.

Dietary glucosamine under question

Annual sales of glucosamine as a neutraceutical for affecting cartilage in treatment of osteoarthritis are close to a billion dollars, but recent clinical studies have currently raised severe criticism regarding its functional value. Additional doubts can be raised by the knowledge of the well-defined cellular steps in glucosamine formation and production of glycosaminoglycans such as chondroitin. Glucosamine is produced in an activated state from glucose by essentially all cells for incorporation into glycosaminoglycans and glycoproteins, and there have been no reports of any deficiencies in its production under any conditions. Nevertheless, many investigations of glucosamine, using cells or tissues, have claimed effects on cartilage and chondroitin sulfate. The significance of these studies is questionable since they have invariably been with concentrations that were 10- to 1000-fold higher than has been found in human serum or plasma after glucosamine ingestion. Experiments with cells or tissues using glucosamine in the low concentrations found after ingestion need to be examined before any conclusions are drawn concerning its direct action on cartilage and its potential for modifying osteoarthritis.

Effects of methylprednisolone acetate and glucosamine on proteoglycan production by equine chondrocytes in vitro

OBJECTIVE

To evaluate the effects of methylprednisolone acetate (MPA) on proteoglycan production by equine chondrocytes and to investigate whether glucosamine hydrochloride modulates these effects at clinically relevant concentrations.

SAMPLE POPULATION

Articular cartilage with normal gross appearance from metacarpophalangeal and metatarsophalangeal joints of 8 horses (1 to 10 years of age).

PROCEDURES

In vitro chondrocyte pellets were pretreated with glucosamine (0, 1, 10, and 100 microg/mL) for 48 hours and exposed to MPA (0, 0.05, and 0.5 mg/mL) for 24 hours. Pellets and media were assayed for proteoglycan production (Alcian blue precipitation) and proteoglycan content (dimethylmethylene blue assay), and pellets were assayed for DNA content.

RESULTS

Methylprednisolone decreased production of proteoglycan by equine chondrocytes at both concentrations studied. Glucosamine protected proteoglycan production at all 3 concentrations studied.

CONCLUSIONS AND CLINICAL RELEVANCE

Methylprednisolone, under noninflammatory conditions present in this study, decreased production of proteoglycan by equine chondrocytes. Glucosamine had a protective effect against inhibition of proteoglycan production at all 3 concentrations studied. This suggested that glucosamine may be useful as an adjunct treatment when an intra-articular injection of a corticosteroid is indicated and that it may be efficacious at concentrations relevant to clinical use.

Effects of intra-articular administration of glucosamine and a peptidyl-glucosamine derivative in a rabbit model of experimental osteoarthritis: a pilot study

The aim of this pilot study was to analyze the effects of glucosamine (GlcN) and its N-acetyl-phenylalanine derivative (NAPA) in Vitamin A model of osteoarthritis (OA) in rabbits. GlcN or NAPA or saline solution was intra-articularly administered in rabbit OA knees. Histological analysis revealed that treatment with GlcN or NAPA was associated with more homogeneous chondrocyte cellularity, absence of fissures and fragmentation and more intense staining of the matrix with Alcian Blue compared to the articular surfaces of the knees treated with saline solution. Comparative in vitro study performed on rabbit primary chondrocytes revealed that GlcN and NAPA were also able to counteract the IL-1beta-upregulation of genes coding for metalloproteases and inflammatory cytokines. Our preliminary in vivo and in vitro studies suggest that GlcN and NAPA could play a disease-modifying protective role in OA by an anti-catabolic effect and an anti-inflammatory activity on chondrocytes.

Effects of glucosamine sulfate on intracellular UDP-hexosamine and UDP-glucuronic acid levels in bovine primary chondrocytes

OBJECTIVE

To analyze the effects of exogenously added glucose (Glc), glucosamine (GlcN) and glucosamine sulfate (GS) on the intracellular UDP-hexoses (UDP-Hex), UDP-N-acetylhexosamines (UDP-HexN) and UDP-glucuronic acid (UDP-GlcA) levels in bovine primary chondrocytes.

METHODS

Chondrocytes were incubated with different concentrations of Glc, GlcN and GS either in high- or low-glucose DMEM for up to 120min to analyze the intracellular levels of UDP-Hex, UDP-GlcA and UDP-HexN by a reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry analysis. Glycosaminoglycan (GAG) synthesis rate and aggrecan mRNA expression levels were quantified using (35)S-sulfate incorporation assay and quantitative real-time RT-PCR, respectively. The cells were cultivated for 2 days or 8 days before UDP-sugar analysis.

RESULTS

Levels of UDP-HexN and UDP-GlcA were unchanged at 10microM concentration of GS in low-glucose DMEM, while addition of 1mM GlcN or GS in low-glucose DMEM for 10min increased UDP-HexN level. The highest intracellular level of UDP-HexN was reached at 30min after addition of 1mM GS to the cells. The intracellular contents of UDP-HexN and UDP-GlcA related to UDP-Hex were higher after prolonged cultivation of chondrocytes for 8 days compared with 2-day-old cultures. Aggrecan mRNA expression and GAG synthesis remained at control level after the cells were treated with 10, 100microM or 1mM of GS for 24h.

CONCLUSION

Physiologically relevant level of GS could not increase the intracellular UDP-HexN and UDP-GlcA levels in bovine primary chondrocyte, while longer-time culture itself appeared to increase the intracellular UDP-HexN and UDP-GlcA levels.

The effects of glucosamine hydrochloride on subchondral bone changes in an animal model of osteoarthritis

OBJECTIVE

To quantify periarticular subchondral bone changes in a rabbit model of experimental osteoarthritis (OA), and to determine the effects of continuous administration of a clinically relevant dose of glucosamine HCl on subchondral bone changes in this model.

METHODS

Anterior cruciate ligament transection (ACLT) was performed on the left femorotibial joints of 16 rabbits to induce OA. Ten rabbits that did not undergo ACLT served as unoperated controls. Eight rabbits that underwent ACLT and 6 control rabbits were treated with 100 mg of glucosamine daily, and the others were given a placebo. The articular cartilage was evaluated macroscopically and graded at the time of necropsy, 8 weeks after ACLT. Bone mineral density (BMD) was measured using dual-energy x-ray absorptiometry on the dissected distal femur and proximal tibia. Subchondral trabecular bone turnover, architecture, and connectivity, as well as subchondral plate thickness and mineralization were studied on the undecalcified tibia sections from each animal.

RESULTS

Eight weeks after ACLT, most of the operated joints had various degrees of cartilage damage and fibrillation. Compared with the control group, the ACLT group had significantly increased subchondral bone turnover and lower BMD, bone volume, connectivity, and bone mineralization. The high bone turnover was significantly reduced in glucosamine-treated animals that underwent ACLT. In fact, there were no significant differences between the ACLT/glucosamine group and the control/glucosamine group in most of the bone parameters studied.

CONCLUSION

This study shows that subchondral bone turnover, structure, and mineralization are significantly altered in the early stages of experimental OA, and that these changes are attenuated by glucosamine treatment.

Human articular cartilage proteoglycans are not undersulfated in osteoarthritis

Chondroitin sulfate is the major constituent of cartilage. Inadequate sulfate availability results in the production of undersulfated proteoglycans. In osteoarthritis, there is a net loss of articular cartilage proteoglycans. Theoretically, it is possible that during the progress of disease undersulfated glycosaminoglycans are synthesized producing proteoglycans with poorer biological properties. In this study, we tested whether in early human osteoarthritic articular cartilage (Mankin's score of 2 and 3) or more advanced disease (Mankin's score over 3), there are proteoglycans that contain a higher relative amount of nonsulfated chondroitin disaccharide isomer in their chondroitin sulfate chains by analyzing the molar ratios of chondroitin sulfate disaccharide isoforms with fluorophore-assisted carbohydrate electrophoresis. Our results indicated that the nonsulfated disaccharide of chondroitin sulfate formed in average only 1-2% of the total chondroitin sulfate. More important, the molar ratio of nonsulfated disaccharide did not appear to be increased in the osteoarthritic articular cartilage. We conclude that undersulfation of articular cartilage proteoglycans is not present in the human osteoarthritic joint.

Enhanced chondrogenic differentiation of murine embryonic stem cells in hydrogels with glucosamine

Differentiation of embryonic stem (ES) cells generally occurs after formation of three-dimensional cell aggregates, known as embryoid bodies (EBs). We have previously reported that hydrogels provide EBs a supportive environment for in vitro chondrogenic differentiation and three dimensional tissue formation [Hwang NS, et al. The Effects of three dimensional culture and growth factors on the chondrogenic differentiation of murine ES cells. Stem Cells 2006;24:284-91]. In this study, we report chondrogenic differentiation of murine ES cells encapsulated in photopolymerizing poly(ethylene-glycol)-based (PEG) hydrogels in the presence of glucosamine (GlcN), an amino monosaccharide found in chitin, glycoproteins and glycosaminoglycans such as hyaluronic acid, chondroitin sulfate and heparin sulfate. We examined the growth and differentiation of encapsulated EBs in standard chondrogenic differentiation medium containing 0-, 2-, and 10-mm GlcN. Morphometric analysis and examination of gene and protein expression indicated that treatment of hydrogel cultures with 2-mm GlcN for 21 days significantly increased EB size, levels of aggrecan mRNA, and tissue-specific extracellular matrix accumulation. GlcN can induce multiple aspects of cell behavior and optimal GlcN concentrations can be beneficial for directing the differentiation and tissue formation of ES cells.