Substrate-bonded hyaluronic acid exhibits a size-dependent stimulation of chondrogenic differentiation of stage 24 limb mesenchymal cells in culture

Role of proteoglycans and glycosaminoglycans in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an inherited fatal X-linked myogenic disorder with a prevalence of 1 in 3500 male live births. It affects voluntary muscles, and heart and breathing muscles. DMD is characterized by continuous degeneration and regeneration cycles resulting in extensive fibrosis and a progressive reduction in muscle mass. Since the identification of a reduction in dystrophin protein as the cause of this disorder, numerous innovative and experimental therapies, focusing on increasing the levels of dystrophin, have been proposed, but the clinical improvement has been unsatisfactory. Dystrophin forms the dystrophin-associated glycoprotein complex and its proteins have been studied as a promising novel therapeutic target to treat DMD. Among these proteins, cell surface glycosaminoglycans (GAGs) are found almost ubiquitously on the surface and in the extracellular matrix (ECM) of mammalian cells. These macromolecules interact with numerous ligands, including ECM constituents, adhesion molecules and growth factors that play a crucial role in muscle development and maintenance. In this article, we have reviewed in vitro, in vivo and clinical studies focused on the functional role of GAGs in the pathophysiology of DMD with the final aim of summarizing the state of the art of GAG dysregulation within the ECM in DMD and discussing future therapeutic perspectives.

Cholangiocytes: Cell transplantation

BACKGROUND

Due to significant limitations to the access to orthotropic liver transplantation, cell therapies for liver diseases have gained large interest worldwide.

SCOPE OF REVIEW

To revise current literature dealing with cell therapy for liver diseases. We discussed the advantages and pitfalls of the different cell sources tested so far in clinical trials and the rationale underlying the potential benefits of transplantation of human biliary tree stem cells (hBTSCs).

MAJOR CONCLUSIONS

Transplantation of adult hepatocytes showed transient benefits but requires immune-suppression that is a major pitfall in patients with advanced liver diseases. Mesenchymal stem cells and hematopoietic stem cells transplanted into patients with liver diseases are not able to replace resident hepatocytes but rather they target autoimmune or inflammatory processes into the liver. Stem cells isolated from fetal or adult liver have been recently proposed as alternative cell sources for advanced liver cirrhosis and metabolic liver disease. We demonstrated the presence of multipotent cells expressing a variety of endodermal stem cell markers in (peri)-biliary glands of bile ducts in fetal or adult human tissues, and in crypts of gallbladder epithelium. In the first cirrhotic patients treated in our center with biliary tree stem cell therapy, we registered no adverse event but significant benefits.

GENERAL SIGNIFICANCE

The biliary tree stem cell could represent the ideal cell source for the cell therapy of liver diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Hyaluronan coating improves liver engraftment of transplanted human biliary tree stem/progenitor cells

BACKGROUND

Cell therapy of liver diseases with human biliary tree stem cells (hBTSCs) is biased by low engraftment efficiency. Coating the hBTSCs with hyaluronans (HAs), the primary constituents of all stem cell niches, could facilitate cell survival, proliferation, and, specifically, liver engraftment given that HAs are cleared selectively by the liver.

METHODS

We developed a fast and easy method to coat hBTSCs with HA and assessed the effects of HA-coating on cell properties in vitro and in vivo.

RESULTS

The HA coating markedly improved the viability, colony formation, and population doubling of hBTSCs in primary cultures, and resulted in a higher expression of integrins that mediate cell attachment to matrix components. When HA-coated hBTSCs were transplanted via the spleen into the liver of immunocompromised mice, the engraftment efficiency increased to 11% with respect to 3% of uncoated cells. Notably, HA-coated hBTSC transplantation in mice resulted in a 10-fold increase of human albumin gene expression in the liver and in a 2-fold increase of human albumin serum levels with respect to uncoated cells. Studies in distant organs showed minimal ectopic cell distribution without differences between HA-coated and uncoated hBTSCs and, specifically, cell seeding in the kidney was excluded.

CONCLUSIONS

A ready and economical procedure of HA cell coating greatly enhanced the liver engraftment of transplanted hBTSCs and improved their differentiation toward mature hepatocytes. HA coating could improve outcomes of stem cell therapies of liver diseases and could be immediately translated into the clinic given that GMP-grade HAs are already available for clinical use.

A novel aragonite-based scaffold for osteochondral regeneration: early experience on human implants and technical developments

INTRODUCTION

Chondral and osteochondral lesions represent a debilitating disease. Untreated lesions remain a risk factor for more extensive joint damage. The objective of this clinical study is to evaluate safety and early results of an aragonite-based scaffold used for osteochondral unit repair, by analysing both clinical outcome and MRI results, as well as the benefits of the procedure optimization through novel tapered shaped implants.

METHODS

A crystalline aragonite bi-phasic scaffold was implanted in patients affected by focal chondral-osteochondral knee lesions of the condyle and trochlea. Twenty-one patients (17 men, 4 women with a mean age of 31.0 ± 8.6 years) without severe OA received tapered shaped implants for the treatment of 2.5 ±1.7 cm² sized defects. The control group consisted of 76 patients selected according to the same criteria from a database of patients who previously underwent implantation of cylindrical-shaped implants. The clinical outcome of all patients was evaluated with the IKDC subjective score, the Lysholm score, and all 5 KOOS subscales administered preoperatively and at 6 and 12 months after surgery, while MRI evaluation was performed at the 12 month follow-up.

RESULTS

A statistically significant improvement in all clinical scores was documented both in the tapered implants and the cylindrical group. No difference could be detected in the comparison between the improvement obtained with the two implant types, neither in the clinical nor in imaging evaluations. A difference could be detected instead in terms of revision rate, which was lower in the tapered implant group with no implant removal - 0% vs 8/76-10.5% failures in the cylindrical implants.

CONCLUSIONS

This study highlighted both safety and potential of a novel aragonite-based scaffold for the treatment of chondral and osteochondral lesions in humans. A tapered shape relative to the cylindrical shaped implant design, improved the scaffold's safety profile. Tapered scaffolds maintain the clinical improvement observed in cylindrical implants while reducing the postoperative risk of revision surgery. This aragonite-based implant was associated with a significant clinical improvement at the 12 month follow-up. Moreover, MRI findings revealed graft integration with good bone and cartilage formation.

Surgical treatment of the neglected achilles tendon rupture with Hyalonect

BACKGROUND

The purpose of this study was to report the management and outcomes of ten patients with chronic Achilles tendon rupture treated with a turndown gastrocnemius-soleus fascial flap wrapped with a surgical mesh (Hyalonect).

METHODS

Ten men with neglected Achilles tendon rupture were treated with a centrally based turndown gastrocnemius fascial flap wrapped with Hyalonect. Hyalonect is a knitted mesh composed of HYAFF, a benzyl ester of hyaluronic acid. The Achilles tendon ruptures were diagnosed more than 1 month after injury. The mean patient age was 41 years. All of the patients had weakness of active plantarflexion. The mean preoperative American Orthopaedic Foot and Ankle Society score was 64.8.

RESULTS

The functional outcome was excellent. The mean American Orthopaedic Foot and Ankle Society score was 97.8 at the latest follow-up. There were significant differences between the preoperative and postoperative scores. Ankle range of motion was similar in both ankles. Neither rerupture nor major complication, particularly of wound healing, was observed.

CONCLUSIONS

For patients with chronic Achilles tendon rupture with a rupture gap of at least 5 cm, surgical repair using a single turndown fascial flap covered with Hyalonect achieved excellent outcomes.

Perspectives On: Local and Sustained Delivery of Angiogenic Growth Factors

This review emphasizes the role of angiogenesis in tissue engineering, introduces various angiogenic growth factors, and highlights current status of delivery systems for angiogenic growth factors using natural and synthetic biomaterials. A short overview of angiogenic growth factors is presented, followed by the introduction of emerging strategies for designing smart delivery carriers.

Reconstitution of degenerated ovine lumbar discs by STRO-3-positive allogeneic mesenchymal precursor cells combined with pentosan polysulfate

OBJECTIVE Disc degeneration and associated low-back pain are major causes of suffering and disability. The authors examined the potential of mesenchymal precursor cells (MPCs), when formulated with pentosan polysulfate (PPS), to ameliorate disc degeneration in an ovine model. METHODS Twenty-four sheep had annular incisions made at L2-3, L3-4, and L4-5 to induce degeneration. Twelve weeks after injury, the nucleus pulposus of a degenerated disc in each animal was injected with ProFreeze and PPS formulated with either a low dose (0.1 million MPCs) or a high dose (0.5 million MPCs) of cells. The 2 adjacent injured discs in each spine were either injected with PPS and ProFreeze (PPS control) or not injected (nil-injected control). The adjacent noninjured L1-2 and L5-6 discs served as noninjured control discs. Disc height indices (DHIs) were obtained at baseline, before injection, and at planned death. After necropsy, 24 weeks after injection, the spines were subjected to MRI and morphological, histological, and biochemical analyses. RESULTS Twelve weeks after the annular injury, all the injured discs exhibited a significant reduction in mean DHI (low-dose group 17.19%; high-dose group 18.01% [p < 0.01]). Twenty-four weeks after injections, the discs injected with the low-dose MPC+PPS formulation recovered disc height, and their mean DHI was significantly greater than the DHI of PPS- and nil-injected discs (p < 0.001). Although the mean Pfirrmann MRI disc degeneration score for the low-dose MPC+PPS-injected discs was lower than that for the nil- and PPS-injected discs, the differences were not significant. The disc morphology scores for the nil- and PPS-injected discs were significantly higher than the normal control disc scores (p < 0.005), whereas the low-dose MPC+PPS-injected disc scores were not significantly different from those of the normal controls. The mean glycosaminoglycan content of the nuclei pulposus of the low-dose MPC+PPS-injected discs was significantly higher than that of the PPS-injected controls (p < 0.05) but was not significantly different from the normal control disc glycosaminoglycan levels. Histopathology degeneration frequency scores for the low-dose MPC+PPS-injected discs were lower than those for the PPS- and Nil-injected discs. The corresponding high-dose MPC+PPS-injected discs failed to show significant improvements in any outcome measure relative to the controls. CONCLUSIONS Intradiscal injections of a formulation composed of 0.1 million MPCs combined with PPS resulted in positive effects in reducing the progression of disc degeneration in an ovine model, as assessed by improvements in DHI and morphological, biochemical, and histopathological scores.

Osteochondral regeneration with a novel aragonite-hyaluronate biphasic scaffold: up to 12-month follow-up study in a goat model

BACKGROUND

The regeneration of articular hyaline cartilage remains an elusive goal despite years of research. Recently, an aragonite-hyaluronate (Ar-HA) biphasic scaffold has been described capable of cartilage regeneration over a 6-month follow-up period. This study was conducted in order to assess the fate of the regenerated osteochondral tissue in a 12-month-long validated caprine model.

HYPOTHESIS/PURPOSE

The hypothesis was that the implantation of the Ar-HA implant leads to tissue regeneration and maturation.

STUDY DESIGN

A two-arm caprine model of a critical osteochondral defect compares the fate of acute osteochondral defects (group A) to Ar-HA implanted defects (group B).

METHODS

Critical 6 mm in diameter and 10-mm in depth osteochondral defects were created in the load-bearing medial femoral condyle of 20 mature goats and randomized into two groups. In group A (n = 6), a blood clot spontaneously filled the defect; in group B (n = 14), a single Ar-HA implant reconstructed the defect. The animals were sacrificed after either 6 or 12 months. Parameters assessed included clinical evaluation, x-rays, micro-CT, ultrasound and histology at both time points, and specimen high-field magnetic resonance imaging with T2 mapping at the 12-month time point.

RESULTS

In most group A animals, the defects were not reconstructed (1/3 at 6 months, and 0/3 at 12 months). Defects in group B were mostly reconstructed (5/7 at 6 months and 6/7 at 12 months). Group A defects were either empty or contained fibrous repair tissue; while group B filling was compatible with hyaline cartilage and normal bone.

CONCLUSION

Ar-HA scaffolds implanted in critical osteochondral defects result in hyaline cartilage formation and subchondral bone regeneration. The results improved at the 12-month time point compared to the 6-month time point, indicating a continuous maturation process without deterioration of the repair tissue.

CLINICAL RELEVANCE

Osteochondral defects are common in humans; the results of the current study suggest that an acellular Ar-HA scaffold might induce cartilage and subchondral bone regeneration.

Hyaluronan - a functional and structural sweet spot in the tissue microenvironment

Transition from homeostatic to reactive matrix remodeling is a fundamental adaptive tissue response to injury, inflammatory disease, fibrosis, and cancer. Alterations in architecture, physical properties, and matrix composition result in changes in biomechanical and biochemical cellular signaling. The dynamics of pericellular and extracellular matrices, including matrix protein, proteoglycan, and glycosaminoglycan modification are continually emerging as essential regulatory mechanisms underlying cellular and tissue function. Nevertheless, the impact of matrix organization on inflammation and immunity in particular and the consequent effects on tissue healing and disease outcome are arguably under-studied aspects of adaptive stress responses. Herein, we review how the predominant glycosaminoglycan hyaluronan (HA) contributes to the structure and function of the tissue microenvironment. Specifically, we examine the evidence of HA degradation and the generation of biologically active smaller HA fragments in pathological settings in vivo. We discuss how HA fragments versus nascent HA via alternate receptor-mediated signaling influence inflammatory cell recruitment and differentiation, resident cell activation, as well as tumor growth, survival, and metastasis. Finally, we discuss how HA fragmentation impacts restoration of normal tissue function and pathological outcomes in disease.

Osteochondral regeneration using a novel aragonite-hyaluronate bi-phasic scaffold in a goat model

PURPOSE

The objective of this study was to examine whether different mechanical modifications and/or impregnation of hyaluronic acid (HA) might enhance aragonite-based scaffold properties for the regeneration of cartilage and bone in an animal model.

METHODS

Bi-phasic osteochondral scaffolds were prepared using coralline aragonite with different modifications, including 1- to 2-mm-deep drilled channels in the cartilage phase (Group 1, n = 7) or in the bone phase (Group 2, n = 8), and compared with unmodified coral cylinders (Group 3, n = 8) as well as empty control defects (Group 4, n = 4). In each group, four of the implants were impregnated with HA to the cartilage phase. Osteochondral defects (6 mm diameter, 8 mm depth) were made in medial and lateral femoral condyles of 14 goats, and the scaffolds were implanted according to a randomization chart. After 6 months, cartilage and bone regeneration were evaluated macroscopically and histologically by an external laboratory.

RESULTS

Group 1 implants were replaced by newly formed hyaline cartilage and subchondral bone (combined histological evaluation according to the ICRS II-2010 and O'Driscoll et al. 34 ± 4 n = 7). In this group, the cartilaginous repair tissue showed a smooth contour and was well integrated into the adjacent native cartilage, with morphological evidence of hyaline cartilage as confirmed by the marked presence of proteoglycans, a marked grade of collagen type II and the absence of collagen type I. The average scores in other groups were significantly lower (Group 2 (n = 8) 28.8 ± 11, Group 3 (n = 8) 23 ± 9 and Group 4 (empty control, n = 4) 19.7 ± 15).

CONCLUSIONS

The implants with the mechanical modification and HA impregnation in the cartilage phase outperformed all other types of implant. Although native coral is an excellent material for bone repair, as a stand-alone material implant, it does not regenerate hyaline cartilage. Mechanical modification with drilled channels and impregnation of HA within the coral pores enhanced the scaffold's cartilage regenerative potential. The modified implant shows young hyaline cartilage regeneration. This implant might be useful for the treatment of both chondral and osteochondral defects in humans.

Human adipose-derived mesenchymal stem cells can survive and integrate into the adult rat eye following xenotransplantation

BACKGROUND

Novel threads of discovery provide the basis for optimism for the development of a stem-cell-based strategy for the treatment of retinal blindness. Accordingly, achievement to suitable cell source with potential-to-long-term survival and appropriate differentiation can be an effective step in this direction.

METHODS

After derivation of human adipose-derived mesenchymal stem cells (HAD-MSCs), they were stably transfected with a vector containing Turbo-green fluorescent protein (GFP) and JRed to be able to trace them after transplantation. Labeled HAD-MSCs were transplanted into the intact adult rat eye and their survival, integration, and migration during 6 months post-transplantation were assessed.

RESULTS

The transplanted cells were traceable in the rat vitreous humor (VH) up until 90 days after transplantation, with gradual reduction in numbers, their adhesion and expansion capacity after recovery. These cells were also integrated into the ocular tissues. Nonetheless, some of the implanted cells succeeded to cross the blood-retina barrier (BRB) and accumulate in the spleen with time.

CONCLUSIONS

The survival of the HAD-MSCs for a period of 90 days in VH and even longer period of up to 6 months in other eye tissues makes them a promising source to be considered in regenerative medicine of eye diseases. However, the potency of crossing the BRB by the implanted cells suggests that use of HAD-MSCs must be handled with extreme caution.

Hyaluronan synthesis and myogenesis: a requirement for hyaluronan synthesis during myogenic differentiation independent of pericellular matrix formation

Exogenous hyaluronan is known to alter muscle precursor cell proliferation, migration, and differentiation, ultimately inhibiting myogenesis in vitro. The aim of the current study was to investigate the role of endogenous hyaluronan synthesis during myogenesis. In quantitative PCR studies, the genes responsible for synthesizing hyaluronan were found to be differentially regulated during muscle growth, repair, and pathology. Although all Has genes (Has1, Has2, and Has3) were differentially regulated in these models, only Has2 gene expression consistently associated with myogenic differentiation. During myogenic differentiation in vitro, Has2 was the most highly expressed of the synthases and increased after induction of differentiation. To test whether this association between Has2 expression and myogenesis relates to a role for Has2 in myoblast differentiation and fusion, C2C12 myoblasts were depleted of Has2 by siRNA and induced to differentiate. Depletion of Has2 inhibited differentiation and caused a loss of cell-associated hyaluronan and the hyaluronan-dependent pericellular matrix. The inhibition of differentiation caused by loss of hyaluronan was confirmed with the hyaluronan synthesis inhibitor 4-methylumbelliferone. In hyaluronan synthesis-blocked cultures, restoration of the pericellular matrix could be achieved through the addition of exogenous hyaluronan and the proteoglycan versican, but this was not sufficient to restore differentiation to control levels. These data indicate that intrinsic hyaluronan synthesis is necessary for myoblasts to differentiate and form syncytial muscle cells, but the hyaluronan-dependent pericellular matrix is not sufficient to support differentiation alone; additional hyaluronan-dependent cell functions that are yet unknown may be required for myogenic differentiation.

Identification of potential biophysical and molecular signalling mechanisms underlying hyaluronic acid enhancement of cartilage formation

This study determined the effects of exogenous hyaluronic acid (HA) on the biomechanical and biochemical properties of self-assembled bovine chondrocytes, and investigated biophysical and genetic mechanisms underlying these effects. The effects of HA commencement time, concentration, application duration and molecular weight were examined using histology, biomechanics and biochemistry. Additionally, the effects of HA application on sulphated glycosaminoglycan (GAG) retention were assessed. To investigate the influence of HA on gene expression, microarray analysis was conducted. HA treatment of developing neocartilage increased compressive stiffness onefold and increased sulphated GAG content by 35 per cent. These effects were dependent on HA molecular weight, concentration and application commencement time. Additionally, applying HA increased sulphated GAG retention within self-assembled neotissue. HA administration also upregulated 503 genes, including multiple genes associated with TGF-β1 signalling. Increased sulphated GAG retention indicated that HA could enhance compressive stiffness by increasing the osmotic pressure that negatively charged GAGs create. The gene expression data demonstrate that HA treatment differentially regulates genes related to TGF-β1 signalling, revealing a potential mechanism for altering matrix composition. These results illustrate the potential use of HA to improve cartilage regeneration efforts and better understand cartilage development.

Stimulation of in vivo angiogenesis by in situ crosslinked, dual growth factor-loaded, glycosaminoglycan hydrogels

As part of a study of elicited angiogenesis, hyaluronan (HA)-based hydrogels crosslinked by polyethylene glycol diacrylate (PEGDA) were loaded with combinations of the cytokine growth factors vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1), keratinocyte growth factor (KGF) and platelet-derived growth factor (PDGF). GF release in vivo was controlled by covalent incorporation of thiol-modified heparin into thiolated HA hydrogels, which were injected into the ear pinnae of mice and allowed to crosslink in situ. GF release in vivo was controlled by covalent incorporation of thiol-modified heparin in the gels. The ears were harvested at 7 or 14 days post-implantation, and vascularization evaluated via a Neovascularization Index (NI). The study demonstrates that in situ gelling implants produced no gross inflammation, redness or swelling, and an improved tolerance compared to HA-based dry film implants. All treatments showed significantly more vascularization than either contralateral ears or ears receiving a sham surgery. The maximum response was observed after 14 days in the ears receiving 0.3% Hp, gelatin-containing gels loaded with VEGF + KGF (NI = 3.91). The study revealed injected growth factor-loaded HA-based hydrogels can successfully produce localized controllable vascularization, while minimizing tissue necrosis, polymorphonuclear leukocytes and inflammation. The ability to target and controllably release growth factors can prove a useful tool in specific diseased tissue/organ angiogenesis.

Emerging technologies and fourth generation issues in cartilage repair

The goals of successful cartilage repair include reducing pain, improving symptoms, and long-term function; preventing early osteoarthritis and subsequent total knee replacements; and rebuilding hyaline cartilage instead of fibrous tissue. Current methods such as microfracture, osteoarticular autograft transfer system, mosaicplasty, and autologous chondrocyte implantation are somewhat successful in regenerating cartilage; however, they also have significant limitations. The future of fourth generation cartilage repair focuses on gene therapy, the use of stem cells (bone marrow, adipose, or muscle derived), and tissue engineering. Emerging techniques include creating elastin-like polymers derived from native elastin sequences to serve as biocompatible scaffolds; using hydrogels to obtain a homogeneous distribution of cells within a 3-dimensional matrix; and using nonviral gene delivery via nucleofection to allow mesenchymal stem cells the ability to express osteogenic growth factors. Although many of the techniques mentioned have yet to be used in a cartilage regeneration model, we have tried to anticipate how methods used in other specialties may facilitate improved cartilage repair.

Association between cancer and "acid mucopolysaccharides": an old concept comes of age, finally

"Acid mucopolysaccharides" is an old name for the glycosaminoglycans. These carbohydrate polymers of the extracellular matrix provide tissue organization, cell-cell communication and a platform for signaling. They also support tumor cell proliferation, progression and invasion. Among the most prevalent is hyaluronan. Its support of cancer is an old concept, but only now is it recognized as an integral component of the cancerous state. Hyaluronan occurs not only in malignant cells, but also in peritumor stroma. Finally, it is now realized that the association between tumor and stroma must be investigated to fully understand the process of cancer growth and metastasis. Most recently, hyaluronan has been identified as essential to malignant stem cells, and a component of the cancer stem cell niche. While hyaluronan does not give up its secrets easily, recent progress justifies a review of its role in malignancy.

The properties and turnover of hyaluronan

Hyaluronan (HA) was discovered over 50 years ago but its metabolism and cellular interactions have only recently received detailed attention. HA is synthesized in the plasma membrane by addition of monosaccharides to the reducing terminal. In tissues, it occurs bound to plasma membranes, aggregated with other macromolecules, or as free polysaccharide. Tissue HA enters the bloodstream in significant amounts through the lymph and is rapidly absorbed via a receptor into liver endothelial cells, where degradation follows. HA levels in serum are normally 10-100 micrograms/l, but can be elevated in cirrhosis, rheumatoid arthritis and scleroderma, due either to impaired hepatic uptake or to increased production. Studies on aqueous humour, middle ear secretion, amniotic fluid, lung lavage fluid, urine, skin diseases and cancer have identified other causes of deranged HA metabolism. HA can be visualized on some cell surfaces as a coating impermeable to particulate material. Specific HA binding occurs on lymphoma cell lines, lung macrophages and SV-3T3 cells but, except in synthesis or uptake, the significance of membrane-associated HA is incompletely understood. It has been reported to activate macrophages and granulocytes, protect cells, control cell migration, and cooperate with intercellular matrix in cell detachment; it also plays a central role in growth control, cellular differentiation and tissue morphogenesis.

Osteochondral defect repair with autologous bone marrow-derived mesenchymal stem cells in an injectable, in situ, cross-linked synthetic extracellular matrix

A co-cross-linked synthetic extracellular matrix (sECM) composed of chemically modified hyaluronic acid and gelatin was used as a cell delivery vehicle for osteochondral defect repair in a rabbit model. A full-thickness defect was created in the patellar groove of the femoral articular cartilage in each of 2 rabbit joints, and 4 experimental groups were assigned (12 rabbits/group): untreated control, autologous mesenchymal stem cells (MSCs) only, sECM only, and MSCs + sECM. The sECM hydrogels were allowed to cross-link in the defect in situ. Rabbits were sacrificed at 4, 8, and 12 weeks post-surgery, and cartilage repair was evaluated and scored. In the controls, defects were filled with fibrous tissue. In the MSC-only group, hyaline-like cartilage filled the peripheral area of the defect, but the center was filled with fibrous tissue. In the sECM-only group, hyaline cartilage with zonal architecture filled the defect at 12 weeks, but an interface between repaired and adjacent host cartilage was evident. In the MSCs + sECM group, defects were completely filled with elastic, firm, translucent cartilage at 12 weeks and showed superior integration of the repair tissue with the normal cartilage. The sECM delivers and retains MSCs, and the injectable cell-seeded sECM could be delivered arthroscopically in the clinic.

Hyalograft C: hyaluronan-based scaffolds in tissue-engineered cartilage

Articular cartilage injuries have poor reparative capability and, if left untreated, may progress to osteo-arthritis. Unsatisfactory results with conventional treatment methods have prompted the development of innovative solutions including the use of cell transplantations, with or without a supporting scaffold. Tissue engineering combines cells, scaffolds and bio-active factors, which represents one of the most promising approaches for the restoration of damaged tissues. Available today, hyaluronan, also known as hyaluronic acid, is a natural glycosaminoglycan present in all soft tissues of higher organisms and in particularly high concentrations in the extracellular matrix of articular cartilage and in the mesenchyme during embryonic development in which it plays a number of biological functions, not only as a structural component but as an informational molecule as well. Moreover, hyaluronan can be manufactured in a variety of physical forms including hydrogels, sponges, fibres and fabrics allowing to develop a variety of hyaluronan-based scaffolds. This review will present both theoretical and experimental evidences that led to the development of Hyalograft C, an exploitation of hyaluronic acid technology and a tissue engineering approach for the resolution of articular cartilage defects.

Synthesis and evaluation of injectable, in situ crosslinkable synthetic extracellular matrices for tissue engineering

Simple and effective biocompatible materials that mimic the natural extracellular matrix (ECM) were developed for a variety of uses in regenerative medicine. These synthetic ECMs (sECMs) were designed to recapitulate the minimal composition required to obtain functional ECMs. The sECM components are crosslinkable in situ, and may be seeded with cells prior to injection in vivo, without compromising either the cells or the recipient tissues. Several sECM compositions were evaluated to establish which formulation would be most beneficial for cell growth and tissue remodeling. Three natural ECM macromonomeric building blocks were employed: hyaluronan (HA), chondroitin sulfate (CS), and gelatin (Gtn). The carboxyl-rich glycosaminoglycans and Gtn were each chemically modified to give the corresponding thiolated dithiopropionylhydrazide (DTPH) derivatives (CS-DTPH, HA-DTPH, and Gtn-DTPH). Different compositions of CS-Gtn and HA-Gtn hydrogels were fabricated by crosslinking the thiolated biomacromonomers with polyethylene glycol diacrylate. Each sECM had high water content (>96%), biologically suitable mechanical properties, and a useful gelation time ( approximately 2-6 min). The bioerosion rates for the sECMs were determined, and a given composition could be selected to meet the requirements of a given clinical application. Both the HA-Gtn and CS-Gtn sECM hydrogels supported cell growth and proliferation with cultured murine fibroblasts in vitro. Moreover, subcutaneous injection of a suspension of murine fibroblasts in each of the two sECM hydrogels into nude mice in vivo resulted in the formation of viable and uniform soft tissue in vivo.

In Vivo Chondrogenesis of Mesenchymal Stem Cells in a Photopolymerized Hydrogel

BACKGROUND

Surgical options for cartilage reconstruction can be significantly improved through advances in cartilage tissue engineering, whereby functional tissue replacements are created by growing cells on polymer scaffolds. The objective of this study was to use a photopolymerizable hydrogel to implant bone marrow-derived mesenchymal stem cells subcutaneously in a minimally invasive manner and promote cartilage tissue formation by the cells in vivo.

METHODS

Athymic nude mice were injected subcutaneously with polymer solutions of poly(ethylene) oxide diacrylate containing mesenchymal stem cells and placed under a UVA lamp to transdermally photopolymerize (solidify) the injected liquid. Experimental groups included polymer solutions with hyaluronic acid (HA), transforming growth factor (TGF)-beta3, or both. After 3 weeks of implantation, cartilage formation was evaluated by gene expression analysis and histologic techniques.

RESULTS

Hyaluronic acid increased the viscosity of the polymer solutions, which helped maintain the injections at the desired site during photopolymerization. Mesenchymal stem cells in hydrogels containing both HA and TGF-beta3 produced the highest quality cartilage, based on expression of the cartilage-specific genes and production of proteoglycan and collagen II. When used independently, TGF-beta3 and HA alone induced cartilage-specific gene expression and collagen type II production; however, TGF-beta3 was essential for proteoglycan production. HA enhanced proteoglycan production when combined with TGF-beta3 and reduced expression and production of collagen I.

CONCLUSIONS

This study is the first to demonstrate the minimally invasive implantation and subsequent chondrogenic differentiation of mesenchymal stem cells in the subcutaneous environment. This lays the foundation for further optimization of a novel and practical technology for cartilage reconstruction.

Stimulation of in vivo angiogenesis using dual growth factor-loaded crosslinked glycosaminoglycan hydrogels

Crosslinked, chemically modified hyaluronan (HA) hydrogels pre-loaded with two cytokine growth factors, vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), were employed to elicit new microvessel growth in vivo, in both the presence and absence of heparin (Hp) in the gels. HA hydrogel film samples were surgically implanted in the ear pinnae of mice, and the ears were harvested at 7 or 14 days post-implantation. Analysis of neovascularization showed that each of the treatment groups receiving an implant, except for HA/Hp at day 14, demonstrated significantly more microvessel density than control ears undergoing surgery but receiving no implant (p<0.015). Treatment groups receiving either Ang-1 alone, or aqueous co-delivery of both Ang-1 and VEGF, were statistically unchanged with time. In contrast, film delivery of both growth factors produced continuing increases in vascularization from day 7 to day 14 in the absence of Hp, but decreases in its presence. However, presentation of both VEGF and Ang-1 in crosslinked HA gels containing Hp generated intact microvessel beds with well-defined borders. The HA hydrogels containing Ang-1+VEGF produced the greatest angiogenic response of any treatment group tested at day 14 (NI=7.44 in the absence of Hp and 4.67 in its presence, where NI is a neovascularization index). Even in the presence of Hp, this had 29% greater vessel density than the next largest treatment group receiving HA/Hp+VEGF (NI=3.61, p=0.04). New therapeutic approaches for numerous pathologies could be notably enhanced by the localized, sustained angiogenic response produced by release of both VEGF and Ang-1 from crosslinked HA films.

Gene expression, synthesis and degradation of hyaluronan during differentiation of 3T3-L1 adipocytes

The high molecular weight glycosaminoglycan hyaluronan (HA) is an essential component of the extracellular matrix (ECM), however, the link between HA regulation and development of the adipocyte ECM, which is essential for differentiation, remains undefined. Hyaluronan synthase gene expression, HA synthetic rate and molecular weight during differentiation of 3T3-L1 pre-adipocytes were compared to undifferentiated 3T3-L1 pre-adipocytes and non-adipogenic NIH/3T3 fibroblasts. In the 3T3-L1 pre-adipocytes, the predominant genes associated with HA metabolism were found to be HA synthase-2 (Has-2) and hyaluronidase-2 (Hyal-2) demonstrating a co-regulation of expression which was stimulated by adipogenic induction consequently resulting in increased synthesis of high molecular weight HA (>10 MDa) and its simultaneous degradation. Accumulation of HA correlated positively with cell number, although synthetic rate was inversely related suggesting a regulatory feedback mechanism. Within 24h post-induction, pre-adipocytes responded with a higher HA synthetic rate and later, accumulated cytoplasmic lipid. In contrast, undifferentiated pre-adipocytes had a reduced HA synthetic rate during clonal expansion and did not accumulate lipid. HA was continuously and rapidly metabolised throughout 3T3-L1 adipogenesis, where terminal differentiation coincided with the increased generation of low molecular weight, angiogenic HA fragments, a likely prerequisite for concurrent neovascularisation of adipose tissue. This study has highlighted a relationship between HA metabolism and adipocyte differentiation, suggesting that the balance between the formation and regulation of the adipocyte extracellular matrix is finely coordinated in a growth phase-specific dependent manner.

Hyaluronan fragments: an information-rich system

Hyaluronan is a straight chain, glycosaminoglycan polymer of the extracellular matrix composed of repeating units of the disaccharide [-D-glucuronic acid-beta1,3-N-acetyl-D-glucosamine-beta1,4-]n. Hyaluronan is synthesized in mammals by at least three synthases with products of varying chain lengths. It has an extraordinary high rate of turnover with polymers being funneled through three catabolic pathways. At the cellular level, it is degraded progressively by a series of enzymatic reactions that generate polymers of decreasing sizes. Despite their exceedingly simple primary structure, hyaluronan fragments have extraordinarily wide-ranging and often opposing biological functions. There are large hyaluronan polymers that are space-filling, anti-angiogenic, immunosuppressive, and that impede differentiation, possibly by suppressing cell-cell interactions, or ligand access to cell surface receptors. Hyaluronan chains, which can reach 2 x 10(4) kDa in size, are involved in ovulation, embryogenesis, protection of epithelial layer integrity, wound repair, and regeneration. Smaller polysaccharide fragments are inflammatory, immuno-stimulatory and angiogenic. They can also compete with larger hyaluronan polymers for receptors. Low-molecular-size polymers appear to function as endogenous "danger signals", while even smaller fragments can ameliorate these effects. Tetrasaccharides, for example, are anti-apoptotic and inducers of heat shock proteins. Various fragments trigger different signal transduction pathways. Particular hyaluronan polysaccharides are also generated by malignant cells in order to co-opt normal cellular functions. How the small hyaluronan fragments are generated is unknown, nor is it established whether the enzymes of hyaluronan synthesis and degradation are involved in maintaining proper polymer sizes and concentration. The vast range of activities of hyaluronan polymers is reviewed here, in order to determine if patterns can be detected that would provide insight into their production and regulation.

Three-year clinical outcome after chondrocyte transplantation using a hyaluronan matrix for cartilage repair

Repair of articular cartilage represents a significant clinical problem and although various new techniques - including the use of autologous chondrocytes - have been developed within the last century the clinical efficacy of these procedures is still discussed controversially. Although autologous chondrocyte transplantation (ACT) has been widely used with success, it has several inherent limitations, including its invasive nature and problems related to the use of the periosteal flap. To overcome these problems autologous chondrocytes transplantation combined with the use of biodegradable scaffolds has received wide attention. Among these, a hyaluronan-based scaffold has been found useful for inducing hyaline cartilage regeneration. In the present study, we have investigated the mid-term efficacy and safety of Hyalograft C grafts in a group of 36 patients undergoing surgery for chronic cartilage lesions of the knee. Clinical Outcome was assessed prospectively before and at 12, 24, and 36 months after surgery. No major adverse events have been reported during the 3-year follow-up. Significant improvements of the evaluated scores were observed (P < 0.02) at 1 year and a continued increase of clinical performance was evident at 2 and 3 years follow-up. Patients under 30 years of age with single lesions showed statistically significant improvements at all follow-up visits compared to those over 30 with multiple defects (P < 0.01). Hyalograft C compares favorably with classic ACT and is particularly indicated in younger patients with single lesions. The graft can be implanted through a miniarthrotomy and needs no additional fixation with sutures except optional fibrin gluing at the defect borders. These results suggest that Hyalograft C is a valid alternative to ACT.

Increase in hyaluronic acid production by Streptococcus equi subsp. zooepidemicus strain deficient in beta-glucuronidase in laboratory conditions

Streptococcus equi subsp. zooepidemicus is known to produce a hyaluronic acid capsule to resist the host immune defense. As the structure of the polysaccharide is identical to the one produced by humans, the bacteria S. equi subsp. zooepidemicus is used in biotechnological production of hyaluronic acid. In our laboratory we prepared mutated strains that are beta-glucuronidase deficient. Comparing the wild-type strain, which is positive in beta-glucuronidase activity, with the mutated strains named clone1 and clone2 in laboratory conditions, we observed that beta-glucuronidase influences the production of hyaluronic acid considerably and the molecular weight of hyaluronan slightly. The production of hyaluronic acid by the mutated strains is higher by approximately 20% and the molecular weight is larger by about 2%. The significant increase in the production of hyaluronic acid and the slight increase in the molecular weight are probably caused by an absence of free beta-glucuronic acid, due to its removal from the non-reducing termini of the polysaccharide by beta-glucuronidase. The presence of free beta-glucuronic acid would likely induce the expression of the beta-glucuronic-acid-utilizing operon, which in turn would reflect into a misuse of energy in the glucose-rich media.

Review: mesenchymal stem cells: cell-based reconstructive therapy in orthopedics

Adult stem cells provide replacement and repair descendants for normal turnover or injured tissues. These cells have been isolated and expanded in culture, and their use for therapeutic strategies requires technologies not yet perfected. In the 1970s, the embryonic chick limb bud mesenchymal cell culture system provided data on the differentiation of cartilage, bone, and muscle. In the 1980s, we used this limb bud cell system as an assay for the purification of inductive factors in bone. In the 1990s, we used the expertise gained with embryonic mesenchymal progenitor cells in culture to develop the technology for isolating, expanding, and preserving the stem cell capacity of adult bone marrow-derived mesenchymal stem cells (MSCs). The 1990s brought us into the new field of tissue engineering, where we used MSCs with site-specific delivery vehicles to repair cartilage, bone, tendon, marrow stroma, muscle, and other connective tissues. In the beginning of the 21st century, we have made substantial advances: the most important is the development of a cell-coating technology, called painting, that allows us to introduce informational proteins to the outer surface of cells. These paints can serve as targeting addresses to specifically dock MSCs or other reparative cells to unique tissue addresses. The scientific and clinical challenge remains: to perfect cell-based tissue-engineering protocols to utilize the body's own rejuvenation capabilities by managing surgical implantations of scaffolds, bioactive factors, and reparative cells to regenerate damaged or diseased skeletal tissues.

Dual growth factor-induced angiogenesis in vivo using hyaluronan hydrogel implants

Crosslinked hyaluronan (HA) hydrogels preloaded with two cytokine growth factors, vascular endothelial growth factor (VEGF) and keratinocyte growth factor (KGF), were employed to elicit new microvessel growth in vivo. As a major glycosaminoglycan (GAG) component of extracellular matrix (ECM), HA is an excellent biopolymeric building block for new biomimetic, biocompatible therapeutic materials. HA hydrogel film samples were surgically implanted in the ear pinnae of mice, and the ears were harvested at 7 or 14 days post-implantation. Histologic analysis showed that each of the groups receiving an implant demonstrated significantly more microvessel density than control ears undergoing surgery but receiving no implant (p<0.001). Treatment groups receiving either co-delivery of both KGF and VEGF, an HA hydrogel lacking a growth factor or HA hydrogels containing a single cytokine were statistically unchanged with time, whereas treatment with KGF alone produced continuing increases in vascularization from day 7 to day 14. Strikingly, presentation of both VEGF and KGF in crosslinked HA generated intact microvessel beds with well-defined borders. In addition, an additive response to co-delivery of both cytokines in the HA hydrogel was observed. The HA hydrogels containing KGF+VEGF produced the greatest angiogenic response of any treatment group tested (NI=5.4 at day 14, where NI is a neovascularization index). This was 33% greater vessel density than in the next largest treatment group, that received HA+KGF (NI=4.0, p<0.002). New therapeutic approaches for numerous pathologies could be notably enhanced by the localized, sustained angiogenic response produced by release of both VEGF and KGF from crosslinked HA films.

Hyaluronic acid and autologous synovial fluid induce chondrogenic differentiation of equine mesenchymal stem cells: a preliminary study

Mesenchymal stem cells (MSC) have the potential to differentiate into distinct mesenchymal tissues including cartilage, which suggest these cells as an attractive cell source for cartilage tissue engineering approaches. Our objective was to study the effects of TGF-beta1, hyaluronic acid and synovial fluid on chondrogenic differentiation of equine MSC. For that, bone marrow was aspirated from the tibia of one 18-month-old horse (Haflinger) and MSC were isolated using percoll-density centrifugation. To promote chondrogenesis, MSC were centrifuged to form a micromass and were cultured in a medium containing 10 ng/ml TGF-beta1 or 0.1mg/ml hyaluronic acid (Hylartil, Ostenil) or either 5%, 10% or 50% autologous synovial fluid as the chondrogenesis inducing factor. Differentiation along the chondrogenic lineage was documented by type II collagen and proteoglycan expression. MSC induced by TGF-beta1 alone showed the highest proteoglycan expression. Combining TGF-beta1 with hyaluronic acid could not increase the proteoglycan expression. Cultures stimulated by autologous synovial fluid (independent of concentration) and hyaluronic acid demonstrated a pronounced, but lower proteoglycan expression than cultures stimulated by TGF-beta1. The expression of cartilage-specific type II collagen was high and about the same in all stimulated cultures. In summary, hyaluronic acid and autologous synovial fluid induces chondrogenesis of equine mesenchymal stem cells, which encourage tissue engineering applications of MSC in chondral defects, as the natural environment in the joint is favorable for chondrogenic differentiation.

Repair of osteochondral defects with hyaluronan- and polyester-based scaffolds

OBJECTIVE

The natural repair of osteochondral defects can be enhanced with biocompatible, biodegradable materials that support the repair process. It is our hypothesis that hyaluronan-based scaffolds are superior to synthetic scaffolds because they provide biological cues. We tested this thesis by comparing two hyaluronan-based scaffolds [auto cross-linked polysaccharide polymer (ACP) and HYAFF-11] to polyester-based scaffolds [poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA)] with similar pore size, porosity and degradation times.

DESIGN

Fifty-four rabbits received bilateral osteochondral defects. One defect received a hyaluronan-based scaffold and the contralateral defect received the corresponding polyester-based scaffold. Rabbits were euthanized 4, 12 and 20 weeks after surgery and the condyles dissected and processed for histology.

RESULTS

Only ACP-treated defects presented bone at the base of the defect at 4 weeks. At 12 weeks, only defects treated with rapidly dissolving implants (ACP and PLGA) presented bone reconstitution consistently, while bone was present in only one third of those treated with slowly dissolving scaffolds (HYAFF-11 and PLLA). After 20 weeks, the articular surface of PLGA-treated defects presented fibrillation more frequently than in ACP-treated defects. The surface of defects treated with slowly dissolving scaffolds presented more cracks and fissures.

CONCLUSIONS

The degradation rate of the scaffolds is critical for the repair process. Slowly dissolving scaffolds sustain thicker cartilage at the surface but, it frequently presents cracks and discontinuities. These scaffolds also delay bone formation at the base of the defects. Hyaluronan-based scaffolds appear to allow faster cell infiltration leading to faster tissue formation. The degradation of ACP leads to rapid bone formation while the slow degradation of HYAFF-11 prolongs the presence of cartilage and delays endochondral bone formation.

Stimulation of in vivo angiogenesis by cytokine-loaded hyaluronic acid hydrogel implants

Crosslinked hyaluronic acid (HA) hydrogels were evaluated for their ability to elicit new microvessel growth in vivo when preloaded with one of two cytokines, vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF). HA film samples were surgically implanted in the ear pinnas of mice, and the ears retrieved 7 or 14 days post implantation. Histologic analysis showed that all groups receiving an implant demonstrated significantly more microvessel density than control ears undergoing surgery but receiving no implant (p < 0.01). Moreover, aqueous administration of either growth factor produced substantially more vessel growth than an HA implant with no cytokine. However, the most striking result obtained was a dramatic synergistic interaction between HA and VEGF. Presentation of VEGF in crosslinked HA generated vessel density of NI = 6.7 at day 14, where NI is a neovascularization index defined below, more than twice the effect of the sum of HA alone (NI = 1.8) plus VEGF alone (NI=1.3). This was twice the vessel density generated by co-addition of HA and bFGF (NI=3.4, p<0.001). New therapeutic approaches for numerous pathologies could be notably enhanced by the localized, synergistic angiogenic response produced by release of VEGF from crosslinked HA films.

Parathyroid Hormone Rapidly Stimulates Hyaluronan Synthesis by Periosteal Osteoblasts in the Tibial Diaphysis of the Growing Rat

Short term treatment (3-24 h) with parathyroid hormone (PTH) stimulated the synthesis and accumulation of hyaluronan (HyA) in explant cultures of tibial diaphyses from young rats. PTH increased the overall HyA content of periosteum 5-fold, with the basal cambium layer exhibiting the greatest enhancement ( approximately 8-fold). PTH increased the HyA content of cortical bone by 2-fold while not affecting the HyA content of bone marrow. PTH treatment greatly enhanced HyA staining throughout all layers of the periosteum, although its most dramatic effect occurred in the basal cambium layer. Here, unlike in the control tissue sections, nearly all cambium-lining osteoblasts stained intensely positive for HyA. PTH treatment enhanced the HyA staining of osteocytes in cortical bone tissue sections to the extent that the lacunocanalicular system became visualized. Three significant findings were revealed in this study. First, mature periosteal osteoblasts, under natural conditions, do not contain much HyA in their surrounding extracellular matrix but dramatically enhance their matrix HyA content when treated with PTH. Second, pre-osteocytes and osteocytes contain more HyA in their natural matrix than mature lining osteoblasts, and they appear to have functional PTH receptors because they responded to PTH treatment with an enhancement of HyA content. Finally, it was observed that the lining cells along the endosteal surface of the diaphysis did not stain strongly positive for HyA either naturally or when exposed to PTH treatment. This indicates that periosteal and endosteal osteoblastic cell populations exhibit metabolic differences in their extracellular matrix responses to PTH.

Phenotypic plasticity of human articular chondrocytes

BACKGROUND

Progenitor cells in mesenchymal tissues are important in the maintenance of tissue homeostasis and regeneration capacity. Articular cartilage is a tissue with a very low capacity for repair. One explanation could be the lack of chondrogenic progenitor cells within the adult tissue. As a test of chondrogenic differentiation potential, we examined the ability of isolated chondrocytes to take on several phenotypic identities within the mesenchymal lineage by applying culture techniques and markers used in the study of the phenotypic plasticity of marrow-derived mesenchymal stem cells (MSCs).

METHODS

Culture-expanded human articular chondrocytes were analyzed for chondrogenic, adipogenic, and osteogenic capacity in defined in vitro culture systems. The osteochondrogenic potential of cells loaded into porous calcium-phosphate ceramic cubes implanted into mice was also determined.

RESULTS

The different assays demonstrated that culture-expanded chondrocytes have the potential to form cartilage in pellet mass cultures, to form adipose cells in dense monolayer cultures, and to form a calcium-rich matrix in an osteogenic assay. In the in vitro assays, a variability of phenotypic plasticity was demonstrated among the donors. In contrast with MSCs, chondrocytes formed cartilage only (and not bone) in the in vivo osteochondrogenic assay.

CONCLUSIONS

These results suggest that, within articular cartilage, there are chondrogenic cells that exhibit a level of phenotypic plasticity that is comparable with that of MSCs. However, there was a difference in the expression of bone in the in vivo assay.

Evaluating specific adhesion of Plasmodium falciparum-infected erythrocytes to immobilised hyaluronic acid with comparison to binding of mammalian cells

A feature of infection with Plasmodium falciparum is the ability of parasite-infected erythrocytes to adhere to vascular endothelial cells and accumulate in vital organs, associated with severe clinical disease. Hyaluronic acid was recently identified as a receptor for adhesion and has been implicated in mediating the accumulation of parasites in the placenta. Here, we report in vitro assays to measure specific adhesion of infected erythrocytes to hyaluronic acid that is distinct from binding to chondroitin sulphate A, another glycosaminoglycan implicated as a receptor in placental malaria. In this study, specific adhesion of mature stage infected erythrocytes to hyaluronic acid of high purity immobilised on plastic surfaces was abolished by pre-treating hyaluronic acid with a specific hyaluronate lyase from Streptomyces, whereas the same treatment of chondroitin sulphate A had little effect. Adhesion to hyaluronic acid could not be explained by the presence of chondroitin sulphate A or other glycosaminoglycans in the hyaluronic acid preparations. Chinese hamster ovary cells bound in a similar manner in the assays and confirmed that hyaluronic acid was appropriately immobilised for cell adhesion. In contrast to parasites, these cells did not adhere to chondroitin sulphate A. The adsorption of hyaluronic acid onto plastic surfaces was also confirmed by the use of a specific hyaluronic acid-binding protein. Fixing cells with glutaraldehyde at the completion of adhesion assays reduced the number of parasites remaining adherent to hyaluronic acid, but not to chondroitin sulphate A or CD36. These findings have important implications for understanding and evaluating interactions between P. falciparum and hyaluronic acid that may be involved in disease pathogenesis.

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects

OBJECTIVE

To review the basic scientific status of repair in articular cartilage tissue and to assess the efficiency of current clinical therapies instigated for the treatment of structural lesions generated therein as a result of trauma or during the course of various diseases, notably osteoarthritis (OA). Current scientific trends and possible directions for the future will also be discussed.

DESIGN

A systematic and critical analysis is undertaken, beginning with a description of the spontaneous repair responses in different types of lesion. Surgical interventions aimed at inducing repair without the use of active biologics will then be considered, followed by those involving active biologics and those drawing on autogenic and allogeneic tissue transplantation principles. Cell transplantation approaches, in particular novel tissue engineering concepts, will be critically presented. These will include growth-factor-based biological treatments and gene transfection protocols. A number of technical problems associated with repair interventions, such as tissue integration, tissue retention and the role of mechanical factors, will also be analysed.

RESULTS

A critical analysis of the literature reveals the existence of many novel and very promising biologically-based approaches for the induction of articular cartilage repair, the vast majority of which are still at an experimental phase of development. But prospective, double-blinded clinical trials comparing currently practiced surgical treatments have, unfortunately, not been undertaken.

CONCLUSION

The existence of many new and encouraging biological approaches to cartilage repair justifies the future investment of time and money in this research area, particularly given the extremely high socio-economic importance of such therapeutic strategies in the prevention and treatment of these common joint diseases and traumas. Clinical epidemiological and prospective trials are, moreover, urgently needed for an objective, scientific appraisal of current therapies and future novel approaches.

Treatment of osteochondral defects with autologous bone marrow in a hyaluronan-based delivery vehicle

The natural repair of osteochondral defects can be enhanced with biocompatible, biodegradable and bioactive materials that provide structural support and molecular cuing to stimulate repair. Since bone marrow contains osteochondral progenitor cells and bioactive agents, it is hypothesized that the combination of scaffold and bone marrow would be a superior composite material for osteochondral repair. This hypothesis will be tested by comparing the outcome of osteochondral defects filled with a fibronectin-coated hyaluronan-based sponge (ACP) with or without autologous bone marrow. Thirty-three 4-month-old rabbits received 3-mm diameter osteochondral defects that were then filled with ACP loaded or not with autologous bone marrow. Rabbits were sacrificed at 2, 3, 4, 12, and 24 weeks after surgery and the condyles processed for histologic and immunohistochemical evaluation. The defects were graded with a histologic scoring scale. Except for the 3-week specimens, the histologic appearance of the defects was similar in both groups. Four weeks after surgery, the defects were filled with bone with a top layer of cartilage well integrated with the adjacent cartilage. Twelve and 24 weeks after surgery, the defects again showed bone filling. The primary difference between the 4-week samples and the 12- and 24-week samples was that the layer of cartilage that appeared to be thinner than the adjacent cartilage. At each harvest time, the overall histologic scores of the specimens did not reveal statistical differences between the treatment groups. However, as revealed by the results of the 3-week sacrifices, bone marrow loading appeared to accelerate the first stages of the repair process. The fibronectin-coated hyaluronan-based scaffold appears to organize the natural response and facilitate the integration of the neo-cartilage with the adjacent tissue. The fundamental tissue engineering principles derived from this study should provide guidelines for the development of comparable clinical reconstructive therapies.

Hyaluronic acid and chondroitin sulphate A rapidly promote differentiation of immature DC with upregulation of costimulatory and antigen-presenting molecules, and enhancement of NF-kappaB and protein kinase activity

Dendritic cells (DCs) have been identified as effective antigen-presenting cells (APCs). We demonstrate that extracellular matrix (ECM), hyaluronic acid (HA) and chondroitin sulphate A (CSA), in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), can rapidly promote the differentiation of monocyte-derived immature DCs, as characterized by the remarkable upregulation of human leucocyte antigen (HLA-DR), CD40, CD54, CD80 and CD86 expression to levels higher than those in the DCs generated by culturing with GM-CSF and interleukin (IL)-4 for 7 days and aggregation of the cells within 48 h. The upregulation of expression of HLA-DR, CD40, CD54, CD80 and CD86 was dose-dependent. Further studies showed that HA and CSA were able to augment nuclear factor (NF)-kappaB activity, as determined by gel mobility shift assay and promote protein phosphorylation. Inhibition of NF-kappaB by pyrolidine dithiocarbamate and sodium salicylate, and serine-threonine and tyrosine kinase by starosporine as well as phosphatidylinositide-3-kinase (PI-3-K) by wortmannin could prevent the effects of HA and CSA on the expression of HLA-DR, CD40, CD80 and CD86 in various degrees. Thus, our data demonstrate that HA or CSA can effectively and rapidly promote the differentiation of immature DC, suggesting that HA and CSA may possess a potential capacity in regulating immune responses.

Cartilage regeneration using principles of tissue engineering

It is well known that articular cartilage in adults has a limited ability for self-repair. Numerous methods have been devised to augment its natural healing response, but these methods generally lead to filling of the defect with fibrous tissue or fibrocartilage, which lacks the mechanical characteristics of articular cartilage and fails with time. Recently, tissue engineering has emerged as a new discipline that amalgamates aspects from biology, engineering, materials science, and surgery and that has as a goal the fabrication of functional new tissues to replace damaged tissues. The emergence of tissue engineering has facilitated the generation of new concepts and the revival of old ideas all of which has allowed a fresh approach to the repair or regeneration of tissues such as cartilage. The collaborations between scientists with different backgrounds and expertise has allowed the identification of some key principles that serve as the basis for the development of therapeutic approaches that now are less empiric and more hypothesis-driven than ever before. The current authors review some of the considerations regarding the various models used to test and validate the above repair methods and to address different aspects of the cartilage repair paradigm. Also, some key principles identified from past and current research, the need for the development of new biomaterials, and considerations in scale-up of cell-biomaterial constructs are summarized.

Hyaluronan-based polymers in the treatment of osteochondral defects

Articular cartilage in adults has limited ability for self-repair. Some methods devised to augment the natural healing response stimulate some regeneration, but the repair is often incomplete and lacks durability. Hyaluronan-based polymers were tested for their ability to enhance the natural healing response. It is hypothesized that hyaluronan-based polymers recreate an embryonic-like milieu where host progenitor cells can regenerate the damaged articular surface and underlying bone. Osteochondral defects were made on the femoral condyles of 4-month-old rabbits and were left empty or filled with hyaluronan-based polymers. The polymers tested were ACP sponge, made of crosslinked hyaluronan, and HYAFF-11 sponge, made of benzylated hyaluronan. The rabbits were killed 4 and 12 weeks after surgery, and the condyles were processed for histology. All 12-week defects were scored with a 29-point scale, and the scores were compared with a Kruskall-Wallis analysis of variance on ranks. Untreated defects filled with bone tissue up to or beyond the tidemark, and the noncalcified surface layer varied from fibrous to hyaline-like tissue. Four weeks after surgery, defects treated with ACP exhibited bone filling to the level of the tidemark and the surface layer was composed of hyaline-like cartilage well integrated with the adjacent cartilage. At 12 weeks, the specimens had bone beyond the tidemark that was covered with a thin layer of hyaline cartilage. Four weeks after surgery, defects treated with HYAFF-11 contained a rim of chondrogenic cells at the interface of the implant and the host tissue. In general, the 12-week defects exhibited good bone fill and the surface was mainly hyaline cartilage. Treated defects received significantly higher scores than untreated defects (p < 0.05), and ACP-treated defects scored significantly higher than HYAFF-11-treated defects (p < 0.05). The introduction of these hyaluronan-based polymers into defects provides an appropriate scaffolding and favorable microenvironment for the reparative process. Further work is required to fully assess the long-term outcome of defects treated with these polymers.

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.

Hyaluronan interactions with hydroxyapatite do not alter in vitro hydroxyapatite crystal proliferation and growth

The interaction of hyaluronan (Mr range 80-120 x 10(4)) with poorly crystalline hydroxyapatite, such as is found in calcified cartilage and bone, was studied to challenge the hypothesis that free hyaluronan found in proteoglycan aggregate preparations could affect in vitro mineralization. Using a Langmuir adsorption isotherm, based on uronic acid content, hyaluronan was found to bind to hydroxyapatite with an affinity K of 0.12 ml/microgram uronate and N = 6.8 micrograms uronate/m2 hydroxyapatite binding sites. This is contrasted with K = .047 ml/microgram uronate and N = 9.0 micrograms uronate/m2 for a bovine nasal proteoglycan monomer preparation. Although the proteoglycan monomer and aggregate preparations have been reported to inhibit hydroxyapatite growth at concentrations of 1 mg/ml, using solution concentrations of 0, 0.01, 0.1 and 1 mg/ml hyaluronan there were no detectable alterations in the rate of seeded hydroxyapatite growth and proliferation. These data indicate that although in vitro hyaluronan may bind with weak affinity to hydroxyapatite, this interaction does not affect mineral growth, and the presence of hyaluronan would not contribute to the increased inhibitory potential of cartilage proteoglycan aggregate relative to monomer preparations.

Degradation of newly synthesized high molecular mass hyaluronan in the epidermal and dermal compartments of human skin in organ culture

Human whole skin was labeled for 24 h with [6-3H]-glucosamine in organ culture and epidermis, dermis and culture medium were separately analyzed for the molecular mass and content of the [3H]-labeled hyaluronan (HA). Gel filtration on Sephacryl S-1000 of HA purified by HPLC showed a large proportion of the newly synthesized HA to be of a very high molecular mass (greater than 2 X 10(6) Da) in both epidermis and dermis, whereas HA in the medium was of a smaller size. After 24 h chase, most of the high molecular mass HA, and 42-48% of total labeled HA disappeared from both tissue compartments. The size of labeled HA recovered in the chase media was further reduced but the content roughly corresponded to that lost from tissue. The amount of unlabeled HA was not significantly altered in epidermis, whereas in dermis it was reduced to about 10% of the initial values during 5-d culture. The results demonstrate that HA of both epidermis and dermis is synthesized as a very high molecular mass compound but rapidly undergoes a limited degradation into large fragments. The fragmentation of HA is suggested to enhance its diffusion from the tissues, particularly dermis.

Heterogeneity amongst fibroblasts in the production of migration stimulating factor (MSF): implications for cancer pathogenesis

Fetal skin fibroblasts migrate into 3D collagen gels to a significantly greater extent than do adult cells. This enhanced motility of fetal fibroblasts appears to result from the production of a "migration stimulating factor" (MSF) which is not made by their normal adult counterparts. Adult skin fibroblasts retain responsiveness to MSF and cells exposed to this factor achieve the elevated levels of migration characteristic of fetal cells. MSF has been purified to homogeneity, has an apparent molecular mass of 70 kD and has been further characterized in terms of a number of biochemical parameters. Studies concerned with the mechanism of action of MSF indicate that it stimulates the production of a high molecular weight class of hyaluronic acid (HA). Concurrent exposure of cells to Streptomyces hyaluronidase blocks the stimulation of adult fibroblast migration by MSF. In a related series of experiments, we have shown that TGF-beta inhibits the effects of MSF on both cell migration and HA production. Taken together, these data suggest that the stimulation of fibroblast migration by MSF is dependent upon (and may directly result from) a primary induction of HA synthesis. We have previously reported that skin fibroblasts obtained from patients with sporadic and familial breast cancer, as well as the unaffected first-degree relatives of familial breast cancer patients, commonly display a fetal-like migratory phenotype. Subsequent work has indicated that (a) these fetal-like cells also produce MSF, and (b) detectable levels of MSF are present in the serum of sporadic breast cancer patients both prior to and following surgical resection of the primary tumor mass. On the basis of these and related observations, we have put forward an hypothesis suggesting that the disruption in normal epithelial-mesenchymal interactions caused by the persistent production of MSF by fibroblasts in the adult may contribute directly to the pathogenesis of an epithelial cancer. The demonstration of aberrant fibroblasts in sporadic cancer patients (both in our own and independent studies) is not consistent with the "germ-line genetic lesion" model commonly invoked to account for the presence of such cells in patients with hereditary cancer syndromes.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of action of the migration stimulating factor produced by fetal and cancer patient fibroblasts: effect on hyaluronic and synthesis

We have previously demonstrated that confluent fetal fibroblasts migrate into three-dimensional collagen gels to a significantly greater extent than their normal adult counterparts. Recent studies have revealed that this behavioral difference results from the secretion by fetal fibroblasts of a soluble migration-stimulating factor (MSF) which acts on these cells in an autocrine fashion. Adult fibroblasts do not produce MSF but remain responsive to it. Skin fibroblasts from cancer patients resemble fetal fibroblasts (rather than normal adult cells) with respect to their migratory behavior on collagen gels and continued production of MSF. This communication is concerned with elucidating the biochemical basis of MSF activity. Data are presented indicating that a) hyaluronic acid is required for the elevated migratory activity displayed by confluent fetal and breast cancer patient skin fibroblast; b) adult fibroblasts exhibit a bell-shaped dose-response to MSF, with maximal stimulation of migration observed at a concentration of 10 ng/ml; c) the migratory activity of adult fibroblasts pre-incubated with MSF remains high in the absence of additional factor: and d) MSF affects both the quantity and size class distribution of hyaluronic acid synthesized by adult fibroblasts. We have previously speculated that the persistent fetal-like fibroblasts of breast cancer patients play a direct role in disease pathogenesis by perturbing normal epithelial-mesenchymal interactions. The observations reported here suggest that MSF-induced alterations in hyaluronic acid synthesis may contribute to the molecular basis of such perturbations.