Derivatized dextrans mimic heparin as stabilizers, potentiators, and protectors of acidic or basic FGF

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Dextran sulfate-amplified extracellular matrix deposition promotes osteogenic differentiation of mesenchymal stem cells

The development of bone-like tissues in vitro that exhibit key features similar to those in vivo is needed to produce tissue models for drug screening and the study of bone physiology and disease pathogenesis. Extracellular matrix (ECM) is a predominant component of bone in vivo; however, as ECM assembly is sub-optimal in vitro, current bone tissue engineering approaches are limited by an imbalance in ECM-to-cell ratio. We amplified the deposition of osteoblastic ECM by supplementing dextran sulfate (DxS) into osteogenically induced cultures of human mesenchymal stem cells (MSCs). DxS, previously implicated to act as a macromolecular crowder, was recently demonstrated to aggregate and co-precipitate major ECM components, including collagen type I, thereby amplifying its deposition. This effect was re-confirmed for MSC cultures undergoing osteogenic induction, where DxS supplementation augmented collagen type I deposition, accompanied by extracellular osteocalcin accumulation. The resulting differentiated osteoblasts exhibited a more mature osteogenic gene expression profile, indicated by a strong upregulation of the intermediate and late osteogenic markers ALP and OCN, respectively. The associated cellular microenvironment was also enriched in bone morphogenetic protein 2 (BMP-2). Interestingly, the resulting decellularized matrices exhibited the strongest osteo-inductive effects on re-seeded MSCs, promoted cell proliferation, osteogenic marker expression and ECM calcification. Taken together, these findings suggest that DxS-mediated enhancement of osteogenic differentiation by MSCs is mediated by the amplified ECM, which is enriched in osteo-inductive factors. We have thus established a simple and reproducible approach to generate ECM-rich bone-like tissue in vitro with sequestration of osteo-inductive factors. STATEMENT OF SIGNIFICANCE: As extracellular matrix (ECM) assembly is significantly retarded in vitro, the imbalance in ECM-to-cell ratio hampers current in vitro bone tissue engineering approaches in their ability to faithfully resemble their in vivo counterpart. We addressed this limitation by leveraging a poly-electrolyte mediated co-assembly and amplified deposition of ECM during osteogenic differentiation of human mesenchymal stem cells (MSCs). The resulting pericelluar space in culture was enriched in organic and inorganic bone ECM components, as well as osteo-inductive factors, which promoted the differentiation of MSCs towards a more mature osteoblastic phenotype. These findings thus demonstrated a simple and reproducible approach to generate ECM-rich bone-like tissue in vitro with a closer recapitulation of the in vivo tissue niche.

The Potential of FGF-2 in Craniofacial Bone Tissue Engineering: A Review

Bone is a hard-vascularized tissue, which renews itself continuously to adapt to the mechanical and metabolic demands of the body. The craniofacial area is prone to trauma and pathologies that often result in large bone damage, these leading to both aesthetic and functional complications for patients. The "gold standard" for treating these large defects is autologous bone grafting, which has some drawbacks including the requirement for a second surgical site with quantity of bone limitations, pain and other surgical complications. Indeed, tissue engineering combining a biomaterial with the appropriate cells and molecules of interest would allow a new therapeutic approach to treat large bone defects while avoiding complications associated with a second surgical site. This review first outlines the current knowledge of bone remodeling and the different signaling pathways involved seeking to improve our understanding of the roles of each to be able to stimulate or inhibit them. Secondly, it highlights the interesting characteristics of one growth factor in particular, FGF-2, and its role in bone homeostasis, before then analyzing its potential usefulness in craniofacial bone tissue engineering because of its proliferative, pro-angiogenic and pro-osteogenic effects depending on its spatial-temporal use, dose and mode of administration.

Fibroblast Growth Factor 2-A Review of Stabilisation Approaches for Clinical Applications

Basic fibroblast growth factor (FGF)-2 has been shown to regulate many cellular functions including cell proliferation, migration, and differentiation, as well as angiogenesis in a variety of tissues, including skin, blood vessel, muscle, adipose, tendon/ligament, cartilage, bone, tooth, and nerve. These multiple functions make FGF-2 an attractive component for wound healing and tissue engineering constructs; however, the stability of FGF-2 is widely accepted to be a major concern for the development of useful medicinal products. Many approaches have been reported in the literature for preserving the biological activity of FGF-2 in aqueous solutions. Most of these efforts were directed at sustaining FGF-2 activity for cell culture research, with a smaller number of studies seeking to develop sustained release formulations of FGF-2 for tissue engineering applications. The stabilisation approaches may be classified into the broad classes of ionic interaction modification with excipients, chemical modification, and physical adsorption and encapsulation with carrier materials. This review discusses the underlying causes of FGF-2 instability and provides an overview of the approaches reported in the literature for stabilising FGF-2 that may be relevant for clinical applications. Although efforts have been made to stabilise FGF-2 for both in vitro and in vivo applications with varying degrees of success, the lack of comprehensive published stability data for the final FGF-2 products represents a substantial gap in the current knowledge, which has to be addressed before viable products for wider tissue engineering applications can be developed to meet regulatory authorisation.

Evaluation of corneal epithelial wound healing after penetrating keratoplasty in patients receiving a new matrix therapy agent (regenerating agent)

OBJECTIVES

Complete epithelial wound healing is a milestone in early postoperative care after penetrating keratoplasty. The re-epithelialization rate after penetrating keratoplasty was measured in patients receiving a new matrix therapy agent (regenerating agent, Cacicol^®) that mimics heparan sulphates.

METHODS

This was a prospective, open-label, uncontrolled, single-centre observational study. A total of 33 consecutive patients (33 eyes) who underwent an 8.25-mm diameter penetrating keratoplasty were treated with regenerating agent eye drops: one drop in the operating theatre immediately after graft, then on alternate days. Patients were divided into those at low risk (13 patients) and high risk (20 patients) of delayed wound healing, and follow-up was performed by digital slit lamp with fluorescein-dye testing repeated daily at a fixed time. Dye area was measured using ImageJ freeware. The main endpoint was epithelial healing after regenerating agent therapy.

RESULTS

The mean ± standard deviation time to complete healing for all patients was 2.7 ± 1.1 (median: 3, range: 1-6) days. This was obtained on Day 1 for 15% of patients, Day 2 for 33%, Day 3 for 88%, Day 4 for 94% and Day 6 for 100%. There was no significant difference between low- and high-risk patients. The area of epithelial defect decreased by a mean ± standard deviation of 75% ± 22% between Day 1 and Day 2, corresponding to a mean ± standard deviation wound-healing rate of 11.5 ± 6.5 mm²/D. There were no systemic or local side effects related to regenerating agent.

CONCLUSION

These preliminary data suggest that regenerating agent could be a useful, non-invasive therapeutic approach in postoperative management of penetrating keratoplasty with the potential to accelerate re-epithelialization.

Periodontal reconstruction by heparan sulfate mimetic-based matrix therapy in Porphyromonas gingivalis-infected mice

BACKGROUND

Periodontitis is a set of chronic inflammatory diseases affecting the supporting structures of the teeth, during which a persistent release of lytic enzymes and inflammatory mediators causes a self-perpetuating vicious cycle of tissue destruction and repair. A matrix-based therapy using a heparan sulfate (HS) analogue called ReGeneraTing Agent (RGTA) replaces destroyed HS by binding to available heparin-binding sites of structural molecules, leading to restoration of tissue homeostasis in several inflammatory tissue injuries, including a hamster periodontitis model.

METHODS

The ability of RGTA to restore the periodontium was tested in a model of Porphyromonas gingivalis-infected Balb/cByJ mice. After 12 weeks of disease induction, mice were treated weekly with saline or RGTA (1.5 mg/kg) for 8 weeks. Data were analyzed by histomorphometry.

RESULTS

RGTA treatment restored macroscopic bone loss. This was related to (1) a significant reduction in gingival inflammation assessed by a decrease in infiltrated connective tissue, particularly in cells expressing interleukin 1ß, an inflammatory mediator selected as a marker of inflammation; (2) a normalization of bone resorption parameters, i.e. number, activation and activity of osteoclasts, and number of preosteoclasts; (3) a powerful bone formation reaction. The Sharpey's fibers of the periodontal ligament recovered their alkaline phosphatase coating. This was obtained while P. gingivalis infection was maintained throughout the treatment period.

CONCLUSIONS

RGTA treatment was able to control the chronic inflammation characteristic of periodontitis and blocked destruction of periodontal structures. It ensured tissue regeneration with recovery of the periodontium's anatomy.

Transmural Endothelialization of Vascular Prostheses is Regulated in Vitro by Fibroblast Growth Factor 2 and Heparan-Like Molecule

Endothelialization of vascular prostheses may result from transmural migration of endothelial cells. Angiogenesis is controlled by growth factors like Fibroblast Growth Factor 2 (FGF2) and regulators like heparan-like molecules. To that end, we used heparan-like molecules named RGTA for ReGeneraTing Agent. The RGTA11 used was a chemically derived dextran obtained by successive substitutions with carboxymethyl, benzylamide, and benzylamide sulfonate groups on glucose residues. This agent was further selected for its ability to bind, stabilize and protect FGF2. We defined firstly the angiogenic capability of FGF2 in combination with RGTA 11 on bovine aortic endothelial cells (BAEC) cultured on collagen I gels. Secondly, the role of FGF2 and RGTA 11 in transmural endothelialization was assessed in a three-dimensional in vitro model using a polyethylene terephtalate prosthesis included in collagen gel. BAEC seeded on the external face can migrate to the luminal face of the prosthesis. Microscopic and histological evaluations were performed at 4 and 7 days. Results showed that the addition of RGTA 11 alone did not promote angiogenesis while FGF2 alone did. However, RGTA11 combined with FGF2 produced a significant acceleration in angiogenesis compared to FGF2 alone. This combination magnifies and enhances the angiogenic processes leading to endothelialization of luminal face through transmural cellular migration. Our data demonstrates that in vitro transmural endothelialization of porous vascular prostheses by BAEC cultured on collagen I gels is upregulated by RGTA 11 combined with FGF2.

RGTA® or ReGeneraTing Agents mimic heparan sulfate in regenerative medicine: from concept to curing patients

The importance of extracellular matrix (ECM) integrity in maintaining normal tissue function is highlighted by numerous pathologies and situations of acute and chronic injury associated with dysregulation or destruction of ECM components. Heparan sulfate (HS) is a key component of the ECM, where it fulfils important functions associated with tissue homeostasis. Its degradation following tissue injury disrupts this delicate equilibrium and may impair the wound healing process. ReGeneraTing Agents (RGTA^®s) are polysaccharides specifically designed to replace degraded HS in injured tissues. The unique properties of RGTA^® (resistance to degradation, binding and protection of ECM structural and signaling proteins, like HS) permit the reconstruction of the ECM, restoring both structural and biochemical functions to this essential substrate, and facilitating the processes of tissue repair and regeneration. Here, we review 25 years of research surrounding this HS mimic, supporting the mode of action, pre-clinical studies and therapeutic efficacy of RGTA^® in the clinic, and discuss the potential of RGTA^® in new branches of regenerative medicine.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

A Heparin-Mimicking Block Copolymer Both Stabilizes and Increases the Activity of Fibroblast Growth Factor 2 (FGF2)

Fibroblast growth factor 2 (FGF2) is a protein involved in cellular functions in applications such as wound healing and tissue regeneration. Stabilization of this protein is important for its use as a therapeutic since the native protein is unstable during storage and delivery. Additionally, the ability to increase the activity of FGF2 is important for its application, particularly in chronic wound healing and the treatment of various ischemic conditions. Here we report a heparin mimicking block copolymer, poly(styrenesulfonate-co-poly(ethylene glycol) methyl ether methacrylate)-b-vinyl sulfonate) (p(SS-co-PEGMA)-b-VS, that contains a segment that enhances the stability of FGF2 and one that binds to the FGF2 receptor. The FGF2 conjugate retained activity after exposure to refrigeration (4 °C) and room temperature (23 °C) for 7 days, while unmodified FGF2 was inactive after these standard storage conditions. A cell study performed with a cell line lacking native heparan sulfate proteoglycans indicated that the conjugated block copolymer facilitated binding of FGF2 to its receptor similar to the addition of heparin to FGF2. A receptor-based enzyme-linked immunosorbant assay (ELISA) confirmed the results. The conjugate also increased the migration of endothelial cells by 80% compared to FGF2 alone. Additionally, the FGF2-p(SS-co-PEGMA)-b-VS stimulated endothelial cell sprouting 250% better than FGF2 at low concentration. These data verify that this rationally designed protein-block copolymer conjugate enhances receptor binding, cellular processes such as migration and tube-like formation, and stability, and suggest that it may be useful for applications in biomaterials, tissue regeneration, and wound healing.

RGTA®-based matrix therapy - A new branch of regenerative medicine in locomotion

Matrix therapy is an innovative, minimally invasive approach in the field of regenerative medicine, that aims to promote tissue regeneration by reconstructing the cellular microenvironment following tissue injury. This approach has significant therapeutic potential in the treatment of pathologies characterized by tissue inflammation and damage, or following injury, conditions which can be incapacitating and cost-consuming. Heparan sulfate mimics, termed ReGeneraTing Agents (RGTA^®s) have emerged as a unifying approach to treat these diverse pathologies. Today, skin and corneal healing topical products have already been used in clinics, demonstrating a proof of concept in humans. In this review, we present key evidence that RGTA^®s regenerate damaged tissue in bone, muscle, tendon and nerve, with astonishing results. In animal models of bone surgical defects and inflammatory bone loss, RGTA^® induced healing of injured bones by controlling inflammation and bone resorption, and stimulated bone formation by coordinating vascularization, recruitment and differentiation of competent cells from specific niches, restoring tissue quality to that of uninjured tissue, evoking true regeneration. In models of muscle injury, RGTA^® had marked effects on healing speed and quality, evidenced by increased muscle fiber density, maturation, vascularization and reduced fibrosis, more mature motor endplates and functional recovery. Applications merging RGTA^®-based matrix therapy and cell therapy, combining Extra-Cellular Matrix reconstruction with cells required for optimal tissue repair show significant promise. Hence restoration of the proper microenvironment is a new paradigm in regenerative medicine. Harnessing the potential of RGTA^® in this brave, new vision of regenerative therapy will therefore be the focus of future studies.

Enhanced Growth of Cultured Fibroblasts by a Synthetic Polyanionic Polymer

A synthetic polyanionic polymer, poly(maleic acid-alt-7,12-dioxaspiro[5,6]dodec-9-ene), exhibits mitogen-like behavior for cultured fibro-blasts. Cultures of L929 and STO fibroblasts in the presence of this polymer resulted in enhanced growth by both fibroblast cell lines. After three days, at optimum polymer concentrations, the cell numbers increased 3.7-fold for the STO cells and 1.9-fold for the L929 cells compared to the cells cultured in the same environment without the polymer. The polymer promoted this growth without any other external growth factors. This result suggests that the polymer has a direct effect on the growth of both of these fibroblast cells.

Blood compatibility of heparin-inspired, lactose containing, polyureas depends on the chemistry of the polymer backbone

Sulfated glycopolymers were synthesized from diisocyanates and lactose containing diamines. Blood compatibility assays indicated highly sulfated glycopolymers with methylene bis(4-cyclohexyl isocyanate) backbones result in prolonged clotting times.

Mussel-inspired coatings on Ag nanoparticle-conjugated carbon nanotubes: bactericidal activity and mammal cell toxicity

Silver nanoparticle (AgNP)-based nanohybrids have been proposed as efficient antimicrobial agents because of their robust bactericidal activity.

Recent advances on plasmin inhibitors for the treatment of fibrinolysis-related disorders

Growing evidence suggests that plasmin is involved in a number of physiological processes in addition to its key role in fibrin cleavage. Plasmin inhibition is critical in preventing adverse consequences arising from plasmin overactivity, e.g., blood loss that may follow cardiac surgery. Aprotinin was widely used as an antifibrinolytic drug before its discontinuation in 2008. Tranexamic acid and ε-aminocaproic acid, two small molecule plasmin inhibitors, are currently used in the clinic. Several molecules have been designed utilizing covalent, but reversible, chemistry relying on reactive cyclohexanones, nitrile warheads, and reactive aldehyde peptidomimetics. Other major classes of plasmin inhibitors include the cyclic peptidomimetics and polypeptides of the Kunitz and Kazal-type. Allosteric inhibitors of plasmin have also been designed including small molecule lysine analogs that bind to plasmin's kringle domain(s) and sulfated glycosaminoglycan mimetics that bind to plasmin's catalytic domain. Plasmin inhibitors have also been explored for resolving other disease states including cell metastasis, cell proliferation, angiogenesis, and embryo implantation. This review highlights functional and structural aspects of plasmin inhibitors with the goal of advancing their design.

RGTA-based matrix therapy in severe experimental corneal lesions: safety and efficacy studies

Corneal alteration potentially leading to ulceration remains a major health concern in ocular surface diseases. A treatment that would improve both the quality and speed of healing and control the inflammation would be of great interest. Regenerating agents (RGTAs) have been shown to stimulate wound healing and modulate undesired fibrosis in various in vivo systems. We investigated the effects of RGTA-OTR4120(®) in a rabbit corneal model in order to assess its potential use in ocular surface diseases. First, we assessed its safety for 7 and 28 days using the Draize test criteria in healthy rabbit eyes; then, we investigated the effect of a single dose (50μl, 5μg) in an alkali-burned cornea model. Daily follow-up of clinical signs of healing was scored, and histology was performed at D7. RGTA was well tolerated; no signs of ocular irritation were observed. In the corneal alkali-burn model, non-RGTA-treated eyes showed inflammatory clinical signs, and histology confirmed a loss of superficial corneal layers with epithelial disorganization, neovascularization and infiltration of inflammatory cells. When compared to NaCl control, RGTA treatment appeared effective in reducing clinical signs of inflammation, enhancing re-epithelialization, and improving histological patterns: edema, fibrosis, neovascularization and inflammation. Three to four layers of epithelial cells were already organized, stroma was virtually unvascularized and keratocytes well implanted in parallel collagen fibers with an overall reorganization similar to normal cornea. RGTA appears to be a promising agent for controlling ocular surface inflammation and promoting corneal healing and was well tolerated. This study offers preclinical information and supports the findings of other (compassionate or pilot) studies conducted in patients with various ocular surface diseases.

Effect of a dextran derivative associated with TGF-β1 or FGF-2 on dermal fibroblast behaviour in dermal equivalents

Dextran derivatives that mimic the action of heparin have been shown to protect heparin-binding growth factors, such as Transforming Growth Factor-beta1 (TGF-beta1) and Fibroblast Growth Factor-2 (FGF-2). The aim of this study was to investigate the effect of LS21 DMCBSu, a dextran derivative which contains methylcarboxylate, benzylamide and sulfate groups, both by itself and when combined with TGF-beta1 and FGF-2, on the behaviour of fibroblasts. Two systems were assessed: a monolayer culture and three-dimensional collagenous matrices (dermal equivalent). Polymeric biomaterial LS21 DMCBSu and LS21 DMCBSu associated with either TGF-beta1 or FGF-2, were added to the monolayer culture on day 3. After 7 days of culture the number of cells was determined. Two treatments were carried out on the dermal equivalents: 9 days of treatment from day 0 to day 9 of culture and 9 days of treatment from day 21 to day 30 of culture for the premature and the mature dermal equivalents respectively. In the monolayer culture, the bioactive polymer produced a slight increase in fibroblast growth (10% with 10 microg/ml of LS21 DMCBSu) and promoted the stimulating effect of the growth factors on cell growth. In the premature dermal equivalents growth was stimulated by 20% when 10 microg/ml LS21 DMCBSu was added. The dextran derivative mixed with TGF-beta1 slightly inhibited the growth effect of the growth factor in the dermal equivalents. The functionalized dextran with FGF-2 enhanced the stimulating effect of the growth factor in the premature dermal equivalent. A significant increase in cell growth was observed with the fibroblasts treated with the FGF-2 LS21 DMCBSu mixture and FGF-2 (51% and 40%, respectively). However, none of the described treatments affected the cell growth in the mature dermal equivalent. Furthermore, the dextran derivative had no effect on dermal contraction under these experimental conditions (3D culture).

[Management of herpes zoster neurotrophic ulcer using a new matrix therapy agent (RGTA): A case report]

Neurotrophic keratopathy is a potential consequence of herpes simplex virus (HSV) or varicella zoster virus (VZV) infection. The treatment is based on artificial tears and the withdrawal of preserved eye drops or other types of epitheliotoxic topical medicines. Autologous serum or amniotic membrane transplantation may also be used in severe cases, but their cost and safety are still under debate. We report a case of a patient with a history of herpes zoster ophthalmicus, who developed a persistent epithelial ulcer after cataract surgery, with no improvement despite 3 weeks of artificial tears (eight drops per day). A new ophthalmologic solution based on a regenerating agent (RGTA, Cacicol20(®)) was then used, with a dosage of two eye drops per week for 6 weeks. Improvement was observed 1 week later, and complete healing was obtained in less than 3 weeks, with no side effects. This heparin mimetic, which may stimulate extracellular matrix healing, may be a possible alternative therapy to autologous serum or amniotic membrane transplantation in severe neurotrophic ulcer. However, randomized studies are necessary to validate this observation.

FGF-1 induces ATP release from spinal astrocytes in culture and opens pannexin and connexin hemichannels

Spinal astrocytes are coupled by connexin (Cx) gap junctions and express pannexin 1 (Px1) and purinergic receptors. Fibroblast growth factor 1 (FGF-1), which is released in spinal cord injury, activated spinal astrocytes in culture, induced secretion of ATP, and permeabilized them to relatively large fluorescent tracers [ethidium (Etd) and lucifer yellow (LY)] through "hemichannels" (HCs). HCs can be formed by connexins or pannexins; they can open to extracellular space or can form gap junction (GJ) channels, one HC from each cell. (Pannexins may not form gap junctions in mammalian tissues, but they do in invertebrates). HC types were differentiated pharmacologically and by Px1 knockdown with siRNA and by use of astrocytes from Cx43 knockout mice. Permeabilization was reduced by apyrase (APY), an ATPase, and by P2X(7) receptor antagonists, implicating secretion of ATP and autocrine and/or paracrine action. Increased permeability of cells exposed to FGF-1 or ATP for 2 h was mediated largely by Px1 HCs activated by P2X(7) receptors. After a 7-h treatment, the permeability was mediated by both Cx43 and Px1 HCs. FGF-1 also caused reduction in gap junctional communication. Botulinum neurotoxin A, a blocker of vesicular release, reduced permeabilization when given 30 min before FGF-1 application, but not when given 1 h after FGF-1. We infer that ATP is initially released from vesicles and then it mediates continued release by action on P2X(7) receptors and opening of HCs. These changes in HCs and gap junction channels may promote inflammation and deprive neurons of astrocyte-mediated protection in spinal cord trauma and neurodegenerative disease.

Heparin mimicking polymer promotes myogenic differentiation of muscle progenitor cells

Heparin and heparan sulfate mediated basic fibroblast growth factor (bFGF) signaling plays an important role in skeletal muscle homeostasis by maintaining a balance between proliferation and differentiation of muscle progenitor cells. In this study we investigate the role of a synthetic mimic of heparin, poly(sodium-4-styrenesulfonate) (PSS), on myogenic differentiation of C2C12 cells. Exogenous supplementation of PSS increased the differentiation of C2C12 cells in a dose-dependent manner, while the formation of multinucleated myotubes exhibited a nonmonotonic dependence with the concentration of PSS. Our results further suggest that one possible mechanism by which PSS promotes myogenic differentiation is by downregulating the mitogen activated extracellular regulated signaling kinase (MAPK/ERK) pathway. The binding ability of PSS to bFGF was found to be comparable to heparin through molecular docking calculations and by native PAGE. Such synthetic heparin mimics could offer a cost-effective alternative to heparin and also reduce the risk associated with batch-to-batch variation and contamination of heparin.

Extracellular matrix-derived products modulate endothelial and progenitor cell migration and proliferation in vitro and stimulate regenerative healing in vivo

Most adult mammals heal without restorative replacement of lost tissue and instead form scar tissue at an injury site. One exception is the adult MRL/MpJ mouse that can regenerate ear and cardiac tissue after wounding with little evidence of scar tissue formation. Following production of a MRL mouse ear hole, 2mm in diameter, a structure rapidly forms at the injury site that resembles the amphibian blastema at a limb amputation site during limb regeneration. We have isolated MRL blastemal cells (MRL-B) from this structure and adapted them to culture. We demonstrate by RT-PCR that even after continuous culturing of these cells they maintain expression of several progenitor cell markers, including DLK (Pref-1), and Msx-1. We have isolated the underlying extracellular matrix (ECM) produced by these MRL-B cells using a new non-proteolytic method and studied the biological activities of this cell-free ECM. Multiplex microELISA analysis of MRL-B cell-free ECM vs. cells revealed selective enrichment of growth factors such as bFGF, HGF and KGF in the matrix compartment. The cell-free ECM, degraded by mild enzyme treatment, was active in promoting migration and proliferation of progenitor cells in vitro and accelerating wound closure in a mouse full thickness cutaneous wound assay in vivo. In vivo, a single application of MRL-B cell matrix-derived products to full thickness cutaneous wounds in non-regenerative mice, B6, induced re-growth of pigmented hair, dermis and epidermis at the wound site whereas scar tissue replaced these tissues at wound sites in mice treated with vehicle alone. These studies suggest that matrix-derived products can stimulate regenerative healing and avert scar tissue formation in adult mammals.

Benzylaminated dextran-modified hydrogels: a long-term bioactive TGF-beta1 carrier

Highly porous dextran-based hydrogels [in which various amounts (up to 16.6%, w/w) of a benzylaminated dextran (DMCB) exhibiting high affinity for TGFbeta1 was immobilized] were developed to achieve long-term retention of bioactive TGFbeta1 in situ. Unmodified hydrogels rapidly desorbed 80-90% compared with only 40-60% of the preloaded TGFbeta1 from the DMCB-modified hydrogels during a period of 21 days in PBS in vitro. TGFbeta1 release experiments (performed with high ionic strength solutions) indicated that formation of the complex between TGFbeta1 and functionalized hydrogels was governed by different interactions, depending on the degree of conjugation with DMCB: ionic interactions in the case of weakly conjugated matrices and nonionic interactions in highly conjugated matrices. Using cells containing a TGFbeta-sensitive luciferase reporter gene, weakly DMCB-modified hydrogels sequestered bioactive TGFbeta1 in situ, giving much higher, long-term signaling performance than highly functionalized hydrogels. Because these biocompatible functionalized hydrogels can provide long-term bioactive TGFbeta1, they could be used as scaffolds for cells to stimulate and regulate human tissue repair processes.

A Hibiscus Abelmoschus seed extract as a protective active ingredient to favour FGF-2 activity in skin

In the skin, heparin, heparan sulphate and heparan sulphate proteoglycans control the storage and release of growth factors and protect them from early degradation. We developed a cosmetic active ingredient containing Hibiscus Abelmoschus seed extract (trade name Linefactor) that can maintain the FGF-2 content in the skin by mimicking the protective effect of heparan sulphate proteoglycans. By preventing the natural degradation of FGF-2, Hibiscus Abelmoschus seed extract maintains the bioavailability of this growth factor for its target cells, i.e. skin fibroblasts. Our in vitro evaluations showed that this ingredient exhibited heparan sulphate-like properties and dose-dependently protected FGF-2 from thermal degradation. We could also show that, in turn, the protected FGF-2 could stimulate the synthesis of sulphated GAGs, the natural protective molecules for FGF-2, thus providing a double protection. Finally, the in vitro results were confirmed in vivo thanks to a clinical study in which skin biomechanical properties and reduction in wrinkles were assessed.

Inhibitors of slit protein interactions with the heparan sulphate proteoglycan glypican-1: potential agents for the treatment of spinal cord injury

1. The heparan sulphate proteoglycan glypican-1 is a major high-affinity ligand of the Slit proteins. 2. Messenger RNA for both Slit-2 and glypican-1 is strongly upregulated and coexpressed in the reactive astrocytes of injured adult brain, suggesting a possible function of Slit proteins and glypican-1 in the adult central nervous system as significant components of the inhibitory environment that prevents axonal regeneration after injury. 3. Based on the hypothesis that adverse effects on axonal regeneration may be due to a glypican-Slit complex or the retention of glypican-binding C-terminal proteolytic processing fragments of Slit at the injury site, we used ELISA to examine a number of small molecules and low molecular weight heparin analogues for their ability to inhibit glypican-Slit interactions. 4. Our studies have led to the identification of several potent inhibitors with a favourable therapeutic profile that can now be tested in a spinal cord injury model. Among the most promising of these are a low molecular weight heparin produced by periodate oxidation and having no significant anticoagulant activity, the chemically sulphonated yeast-derived phosphomannan PI-88 and a number of randomly derivatized water-soluble sulphated dextrans.

Differential effect triggered by a heparan mimetic of the RGTA family preventing oral mucositis without tumor protection

PURPOSE

Oral mucositis is a common side effect induced by radio/chemotherapy in patients with head and neck cancer. Although it dramatically impairs patient quality of life, no efficient and safe therapeutic solution is available today. Therefore, we investigated the protective efficacy of a new heparan mimetic biopolymer, RGTA-OTR4131, used alone or in combination with amifostine, for oral mucositis and simultaneously evaluated its effect on tumor growth in vitro and in vivo.

METHODS AND MATERIALS

A single dose of 16.5 Gy was selectively delivered to the snout of mice, and the effects of OTR4131 or amifostine-OTR4131 were analyzed by macroscopic scoring and histology. The effect of OTR4131 administration on tumor growth was then investigated in vitro and in xenograft models using two cell lines (HEP-2 and HT-29).

RESULTS

Amifostine and OTR4131 significantly decreased the severity and duration of lip mucosal reactions. However, amifostine has to be administered before irradiation, whereas the most impressive protection was obtained when OTR4131 was injected 24 h after irradiation. In addition, OTR4131 was well tolerated, and the combination of amifostine and OTR4131 further enhanced mucosal protection. At the tumor level, OTR4131 did not modify HEP-2 cell line clonogenic survival in vitro or protect xenografted tumor cells from radiotherapy. Of interest, high doses of OTR4131 significantly decreased clonogenic survival of HT-29 cells.

CONCLUSIONS

RGTAs-OTR4131 is a well-tolerated, natural agent that effectively reduces radio-induced mucositis without affecting tumor sensitivity to irradiation. This suggests a possible transfer into the clinic for patients' benefit.

Enhancement of the biological activity of BMP-2 by synthetic dextran derivatives

In the present study, we explored the binding capacity of synthetic heparin-like dextran derivatives to recombinant human bone morphogenetic protein 2 (BMP-2), a heparin-binding osteoinductive growth factor. Affinity electrophoresis analysis provided evidence that carboxymethylated dextran polymers grafted with high amounts of benzylamide groups (named DMCB) interact with BMP-2. The capability of such polysaccharides to potentiate the growth factor biological activity was then investigated. In vitro, DMCB dose-dependently promoted osteoblast differentiation induced by BMP-2 in C2C12 myoblasts more efficiently than heparin. A screening study provided evidence that the potentiating effects of the dextran derivatives on the BMP-2-induced alkaline phosphatase activity improved with their benzylamide groups content and, therefore, with their affinity for the growth factor. The biological activity of BMP-2 was monitored in the culture medium after 6 days using C2C12 cells (containing a BMP sensitive luciferase reporter gene). Like heparin, DMCB sustained the biological activity of the growth factor; this result suggests that the formation of the BMP-2/DMCB complex may protect the protein from being inactivated. In rats in vivo, DMCB also stimulated ectopic calcification mediated by BMP-2. These data indicate that dextran-based polysaccharides prolong the half-life of the growth factor and promote its biological activity.

Significant reduction in neural adhesions after administration of the regenerating agent OTR4120, a synthetic glycosaminoglycan mimetic, after peripheral nerve injury in rats

OBJECT

Extradural and intraneural scar formation after peripheral nerve injury frequently causes tethering and compression of the nerve as well as inhibition of axonal regeneration. Regenerating agents (RGTAs) mimic stabilizing and protective properties of sulphated glycosaminoglycan toward heparin-binding growth factors. The aim of this study was to assess the effect of an RGTA known as OTR4120 on extraneural fibrosis and axonal regeneration after crush injury in a rat sciatic nerve model.

METHODS

Thirty-two female Wistar rats underwent a standardized crush injury of the sciatic nerve. The animals were randomly allocated to RGTA treatment or sham treatment in a blinded design. To score neural adhesions, the force required to break the adhesions between the nerve and its surrounding tissue was measured 6 weeks after nerve crush injury. To assess axonal regeneration, magnetoneurographic measurements were performed after 5 weeks. Static footprint analysis was performed preoperatively and at Days 1, 7, 14, 17, 21, 24, 28, 35, and 42 postoperatively.

RESULTS

The magnetoneurographic data show no significant difference in conduction capacity between the RGTA and the control group. In addition, results of the static footprint analysis demonstrate no improved or accelerated recovery pattern. However, the mean pullout force of the RGTA group (67 +/- 9 g [mean +/- standard error of the mean]) was significantly (p < 0.001) lower than that of the control group (207 +/- 14 g [mean +/- standard error of the mean]).

CONCLUSIONS

The RGTAs strongly reduce nerve adherence to surrounding tissue after nerve crush injury.

RGTA OTR4120, a heparan sulfate mimetic, is a possible long-term active agent to heal burned skin

Burn-related skin fibrosis leads to loss of tissue function and hypertrophic scar formation with damaging consequences for the patient. There is therefore a great need for an efficient agent to treat burned skin. We report that ReGeneraTing Agent (RGTA) reduces burn-induced skin alteration. The tissue-regenerating effect of RGTA OTR4120 was evaluated after 1-6 days and after 10 months in a rat skin burn model. This effect was also examined in vitro using fibroblasts isolated from control and 6-day-old burned skins. We measured production of dermal collagen I, III, and V and activities of metalloproteinases 2 and 9 (MMP-2 and MMP-9). Ratio of collagen III over collagen I production increased 6 days after the burn, because of a decrease in collagen I production. After 10 months, ratio of collagen III over collagen I in burn sites was still increased compared with control skin, because of an increase in collagen III production. Both abnormalities were corrected by OTR4120. OTR4120 increased pro- and active MMP-2 and MMP-9, compared with healthy and burned controls and therefore accelerated remodeling. Similar data were obtained with cultured fibroblasts from healthy and burned skins. OTR4120 enhanced healing in short- and long-term after burns, reducing the formation of fibrotic tissue, and then represents a potential agent to improve burned skin healing.

Polysaccharide microarrays for polysaccharide-platelet-derived-growth-factor interaction studies

Polysaccharide microarrays have great potential for the high-throughput analysis of polysaccharide-protein interactions. Here we demonstrate that a polysaccharide microarray prepared by printing a library of dextran polymers derivatized by methylcarboxylate, benzylamide, and sulfate groups (DMCBSu compounds) on to glass slides permitted the rapid identification of a set of compounds able to interact with the platelet-derived growth factor BB (PDGF-BB) isoform, a growth factor involved in wound healing. Microarray interaction results were compared to the capacity of DMCBSu compounds to potentiate the in vitro PDGF-BB-induced proliferation of human dermal fibroblasts.

Dextran derivatives modulate collagen matrix organization in dermal equivalent

Dextran derivatives can protect heparin binding growth factor implied in wound healing, such as transforming growth factor-beta1 (TGF-beta1) and fibroblast growth factor-2 (FGF-2). The first aim of this study was to investigate the effect of these compounds on human dermal fibroblasts in culture with or without TGF-beta1. Several dextran derivatives obtained by substitution of methylcarboxylate (MC), benzylamide (B) and sulphate (Su) groups were used to determine the effects of each compound on fibroblast growth in vitro. The data indicate that sulphate groups are essential to act on the fibroblast proliferation. The dextran derivative LS21 DMCBSu has been chosen to investigate its effect on dermal wound healing process. Fibroblasts cultured in collagenous matrices named dermal equivalent were treated with the bioactive polymer alone or associated to TGF-beta1 or FGF-2. Cross-sections of dermal equivalent observed by histology or immunohistochemistry, demonstrated that the bioactive polymer accelerates the collagen matrices organization and stimulates the human type-III collagen expression. This bioactive polymer induces apoptosis of myofibroblast, property which may be beneficial in treatment of hypertrophic scar. Culture media analyzed by zymography and Western blot showed that this polymer significantly increases the secretion of zymogen and active form of matrix metalloproteinase-2 (MMP-2), involved in granulation tissue formation. These data suggest that this bioactive polymer has properties which may be beneficial in the treatment of wound healing.

Heparin‐like synthetic polymers, named RGTAs, mimic biological effects of heparinin vitro

A family of biopolymers engineered to protect and stabilize heparin binding growth factors (HBGFs) show remarkable properties as wound healing agents in several in vivo tissue repair models to the extend that damaged tissues would recover almost its initial aspect and properties. These polymers where named RGTA for regenerating agents and proposed to act in vivo by enhancing the bioavailability of HBGFs at the site of the injury. To provide support for this hypothesis, we studied interaction of RGTA with FGF-2, taken as the paradigm of HBGFs, and its high- and low-affinity receptors as well as its ability to inhibit heparanase activity. We show that RGTA is comparable to heparin as it favors FGF-2 binding to FGFR-1 and FGF-2 dimerization and potentiates FGF-2-induced mitogenic activity. Furthermore, we show that RGTA inhibits the release of FGF-2 from its extracellular matrix storage sites by heparanase. Our data provide new evidence to support that RGTA may act in vivo both by enhancing HBGF activity and preserving HBGF availability by protecting the matrix low affinity heparan sulfates from rapid heparanase degradation.

Les agents de régénération (ou RGTAs) : une nouvelle approche thérapeutique

RGTAs, or ReGeneraTing Agents constitute a new class of medicinal substance that enhance both speed and quality of tissue healing and leading in some case to a real tissue regenerating process. RGTAs consist of chemically engineered polymers adapted to interact with and protect against proteolytic degradation of cellular signaling proteins known as growth factors, cytokines, interleukins, colony stimulating factors, chemokines, neurotrophic factors etc. Indeed almost all these proteins of cellular communication are naturally stored in the extra cellular matrix interacting specifically with the heparan sulfates or HS. After tissue injury of any cause, cells die liberating glycanases and proteases inducing first HS degradation then liberation of the cytokines which in turn are susceptible to degradation as they are no longer protected. By replacing the natural HS, RGTAs will protect cytokines from proteolyses as they are liberated from the matrix compartment matter in the wound. This spatio-temporal selective protection of cytokines results in a preservation of the natural endogenous signaling of a tissue and is reflected by spectacular tissue regeneration or by a very greatly improved tissue repair. These observations indicate that mammals have an unexpected ability to regenerate and that RGTA helps to reveal this capacity. The aim of OTR3 is to develop RGTA into a drug to treat specific tissue lesions.

Periodontitis destructions are restored by synthetic glycosaminoglycan mimetic

Periodontitis are bacterium-driven inflammatory diseases that destroy tooth-supporting tissues whose complete restoration is not currently possible. RGTA, a new class of agents, have this capacity in an animal model. Periodontitis was induced in hamsters and, starting 8 weeks later, injected RG1503, a glycosaminoglycan synthesized from a 40 kDa dextran behaving like a heparan sulfate mimetic (1.5 mg kg(-1) w(-1)) or saline for 8 weeks. The three periodontium compartments were evaluated by immunohistochemistry and morphometry. The gingival extracellular matrix disorganized by inflammation was restoring under treatment. The collagen network was repaired and resumed its previous organization. Fibrillin-1 expression was restored so that the elastic network rebuilt at a distance from the pocket and began to reconstruct near the pocket. Apoptotic cell numbers were decreased in the pocket epithelium, and more so in the infiltrated connective tissue. The continuity and the thickness of the basement membrane were restored and testified normalization of epithelium connective tissue interaction. The amount of alveolar bone increased around the first molar, and the interradicular bone was rebuilt. The root cementum was thickened and the number of proliferating cells in the periodontal ligament was increased close to the cementum. RG1503 treatment induces potent anabolic reactions in the extracellular matrices of the different tissues of the periodontium and recruitment of progenitors. In particular, the cell proliferation close to the root surface suggests the reformation of a functional attachment apparatus. These results demonstrate that RG1503 reverses the degenerative changes induced by inflammation and favors the conditions of a regenerative process. Thus, RGTA, a known matrix component mimetic and protector, may be considered as a new therapeutic tool to regenerate the tissues destroyed by periodontitis.

Controlled release of fibroblast growth factor-2 from an injectable 6-O-desulfated heparin hydrogel and subsequent effect onin vivo vascularization

We prepared a 6-O-desulfated (DS-) heparin (Hep) hydrogel as an excellent carrier for the controlled release of Hep-binding growth factors, such as fibroblast growth factor (FGF)-2. This material, which is partially derived from photoreactive groups, such as cinnamate, is easily crosslinked upon ultraviolet light (UV)-irradiation, resulting in a water-insoluble, viscous, and injectable hydrogel. In the present study, we examined the capacity of 6-O-DS-Hep hydrogel to immobilize FGF-2, as well as the controlled release of FGF-2 molecules from this hydrogel in vitro and in vivo. Only 10% of FGF-2 was gradually released from the FGF-2-containing 6-O-DS-Hep hydrogel (photocrosslinked 6-O-DS-Hep (4%; w/w) hydrogel containing 50 microg/mL FGF-2) into PBS (phosphate-buffered saline) within first 7 days. The 6-O-DS-Hep hydrogel in vitro maintained the original form through 1 weeks incubation in PBS, but it was gradually fragmented and could not maintain the original form by 2-3 week-washing. When the FGF-2-containing 6-O-DS-Hep hydrogel was subcutaneously injected into the back of rats, significant neovascularization and fibrous tissue formation were induced near the injected site from day 3 after the injection. And, the hydrogel had been biodegraded and completely disappeared from the injected sites in vivo within about 15-20 days after the injection. These findings indicate a controlled release of biologically active FGF-2 molecules together with fragmentation and biodegradation of 6-O-DS-Hep hydrogel and the subsequent induction of neovascularization in vivo.

A synthetic glycosaminoglycan mimetic binds vascular endothelial growth factor and modulates angiogenesis

In a previous study, we showed that in situ injection of glycosaminoglycan mimetics called RGTAs (ReGeneraTing Agents) enhanced neovascularization after skeletal muscular ischemia (Desgranges, P., Barbaud, C., Caruelle, J. P., Barritault, D., and Gautron, J. (1999) FASEB J. 13, 761-766). In the present study, we showed that the RGTA OTR4120 modulated angiogenesis in the chicken embryo chorioallantoic membrane assay, in a dose-dependent manner. We therefore investigated the effect of OTR4120 on one of the most specific angiogenesis-regulating heparin-binding growth factors, vascular endothelial growth factor 165 (VEGF165). OTR4120 showed high affinity binding to VEGF165 (Kd = 2.2 nm), as compared with heparin (Kd = 15 nm), and potentiated the affinity of VEGF165 for VEGF receptor-1 and -2 and for neuropilin-1. In vitro, OTR4120 potentiated VEGF165-induced proliferation and migration of human umbilical vein endothelial cells. In the in vivo Matrigel plug angiogenesis assay, OTR4120 in a concentration as low as 3 ng/ml caused a 6-fold increase in VEGF165-induced angiogenesis. Immunohistochemical staining showed a larger number of well differentiated VEGFR-2-expressing-cells in Matrigel sections of OTR4120-treated plug than in control sections. These findings indicate that OTR4120 enhances the VEGF165-induced angiogenesis and therefore may hold promise for treating disorders characterized by deficient angiogenesis.

Retention of transforming growth factor beta1 using functionalized dextran-based hydrogels

Functionalized dextrans (FD) are anionic water-soluble polymers bearing carboxylate, benzylamide and sulfate groups, which exhibit binding capacity to transforming growth factor-beta1 (TGF-beta1). In this paper, we have investigated the ability of dextran-based hydrogels containing FD, to bind and release recombinant human TGF-beta1. Hydrogels were prepared by chemical crosslink native dextran and FD with sodium trimetaphosphate in 1m NaOH at 50 degrees C. A wide range of hydrogels were prepared as particles ranging of 1-1.6mm of diameter and characterized with various amounts of FD and with different crosslinker feeding ratios (CFR). Dried particles were soaked with recombinant human transforming growth factor-beta1 (rhTGF-beta1) to determine their capacity to deliver the growth factor. Results indicated that the in vitro kinetics releases of rhTGF-beta1 were related to FD and CFR. Retention capacity of rhTGF-beta1 increases with an increase of negative charges of the matrices brought by both phosphate linkages and FD as demonstrated by an additional release of growth factor in high ionic strength solution. Highly crosslinked hydrogels that contained the highest amount of FD (18% (w/w)) retained up to 88% of rhTGF-beta1. Bioactivity of released growth factor was confirmed in a cell assay. These functionalized hydrogels may have important uses for the stabilization and the protection of rhTGF-beta1 as entrapment systems and could be applied to other proteins of clinical interest.

Effect of an oversulfated exopolysaccharide on angiogenesis induced by fibroblast growth factor-2 or vascular endothelial growth factor in vitro

The aim of this study was to determine the angiogenic properties of an oversulfated exopolysaccharide (OS-EPS) derived from a polysaccharide secreted by the mesophilic bacterium Alteromonas infernus. We compared the effect of this OS-EPS with that of a non-oversulfated exopolysaccharide (EPS) on human umbilical vein endothelial cell (HUVEC) proliferation, migration and differentiation induced by basic fibroblast growth factor (FGF-2) or vascular endothelial growth factor (VEGF). OS-EPS enhanced HUVEC proliferation by 58% when used alone, and by respectively 30% and 70% in the presence of FGF-2 and VEGF. OS-EPS also increased the density of tubular structures on Matrigel in the presence of FGF-2 or VEGF. Vascular tube formation was related to alpha(6) integrin subunit expression, which was enhanced by 50% in the presence of the growth factors. Indeed, a monoclonal anti-alpha(6) blocking antibody abolished this vascular tube formation. EPS had no effect in any of the experimental conditions, underlying the importance of sulfation in the angiogenic effects of exopolysaccharide. By potentiating the angiogenic activity of FGF-2 and/or VEGF, OS-EPS, which possesses low anticoagulant activity and thus a low hemorrhagic risk, could potentially be used to accelerate vascular wound healing or to promote the growth of collateral blood vessels in ischemic tissues.

Novel glycosaminoglycan mimetic (RGTA, RGD120) contributes to enhance skeletal muscle satellite cell fusion by increasing intracellular Ca2+ and calpain activity

Glycosaminoglycans (GAG) are classes of molecules that play an important role in cellular processes. The use of GAG mimetics called regenerating agent (RGTA) represents a tool to investigate the effect of GAG moiety on cellular behavior. A first member of the RGTA family (RG1192), a dextran polymers with defined amounts of sulfate, carboxymethyl, as well as hydrophobic groups (benzylamide), was shown to stimulate skeletal muscle repair after damage and myoblast differentiation. To obtain a comprehensive insight into the mechanism of action of GAG mimetics, we investigated the effect on myoblast differentiation of a novel RGTA, named RGD120, which was devoid of hydrophobic substitution and had ionic charge similar to heparin. Myoblasts isolated from adult rat skeletal muscles and grown in primary cultures were used in this study. We found that chronic treatment with RGD120 increased the growth of adult myoblasts and induced their precocious fusion into myotubes in vitro. It also partially overcame the inhibitory effect of the calpain inhibitor N-acetyl-leu-leu-norleucinal (ALLN) on these events. Western blot and zymography analyses revealed that milli calpain was slightly increased by RGD120 chronic treatment. In addition, using fluorescent probes (Indo-1 and Boc-leu-met-MAC), we demonstrated that RGD120 added to prefusing myoblast cultures accelerates myoblast fusion into myotubes, induced an increase of cytosolic free calcium concentration, and concomitantly an increase of intracellular calpain protease activity. Altogether, these results suggested that the efficiency of RGD120 in stimulating myogenesis might be in part explained through its effect on calcium mobilization as well as on the calpain amount and activity.

Kinetic study of early regenerative effects of RGTA11, a heparan sulfate mimetic, in rat craniotomy defects

We previously reported that RGTA, a synthetic heparan sulfate mimetic, induces almost complete closure of craniotomy defects one month after surgery in adult rats. RGTA-treated wounds showed features suggesting unusual cell and matrix interactions reminiscent of developmental events. As healing success or failure is determined shortly after wounding, we examined early events in RGTA-treated wounds. Collagen plasters soaked in a solution of RGTA11 (1.5 Microg per piece) or saline (control) were implanted in rat craniotomy defects. Seven control and seven treated rats were killed daily from days 1 to 7 after surgery. The lesions and adjacent tissues were sampled and processed for morphometry. A layer of type III collagen along the dura mater (DM) thickened up to day 5 in RGTA-treated wounds (p < 0.05 vs day 1), but became thinner in control wounds. Alkaline phosphatase-positive osteoprogenitor cells were detected on day 1 in this layer. Their number increased, and they migrated toward the mid-sagittal sinus and to connective tissue adjacent to the sinus, where they aggregated and differentiated into osteoblasts, forming bone nodules on day 6. These features were not seen in control wounds. Angiogenesis was significantly enhanced in RGTA-treated wounds, especially near the sinus. In vitro, bovine bone endothelial (BBE) cell proliferation was inhibited by RGTA11 in a concentration-dependent manner. In contrast, RGTA11 strongly enhanced the effect of fibroblast growth factor-2 on BBE cell proliferation. These results show that RGTA11, possibly by interacting with heparin-binding growth factors, elicits vascular reactions accompanying the recruitment of a large pool of committed osteoprogenitors from the DM. The DM and the sinus appear to be important centers of organization for craniotomy defect healing. RGTA probably creates an environment that starts a program of directing healing towards bone formation and defect closure.

Controlled sulfatation of natural anionic bacterial polysaccharides can yield agents with specific regenerating activity in vivo

The regenerating activities of chemically modified anionic bacterial polysaccharides by O-sulfonation were investigated using a in vivo model of rat injured muscle regeneration. Glucuronan (GA), a linear homopolysaccharide of -->4)-beta-D-GlcpA-(1--> residues partially acetylated at the C-3 and/or the C-2 position, and glucoglucuronan (GGA), a linear heteropolysaccharide of -->3)-beta-D-GlcpA-(1-->4)-beta-D-Glcp-(1--> residues were sulfated. SO3-DMF sulfatation complex provided polysaccharides with different sulfur contents, however, a depolymerization occurred because we did not use large excess of pyridine to obtain pure modified polysaccharides. A regenerating activity on injured extensor digitorum longus (EDL) muscles on rats was obtained with these two sulfated anionic polymers. The position of sulfate groups on glucoglucuronan (primary or secondary alcohol) seems to have no influence on the biological activity by opposition to the degree of sulfatation both for the glucuronans and the glucoglucuronans. The yield of acetate groups in the glucuronan polymer modulated the specific activity.

Regulation of the collagen phenotype expression of gamma-irradiated vascular smooth muscle cells by heparan mimetics (RGTA)

Restenosis is characterized by vascular smooth muscle cell (VSMC) proliferation and accumulation of collagen III in a hypertrophic and disorganized extracellular matrix. Restenosis is prevented by antimitotic agents or irradiation but no significant progress has been made to control collagen expression deregulation. Previously, we have shown that a new family of biopolymers named RGTA (heparan mimetics elaborated by grafting on dextran of carboxylate, sulfate, and benzylamide units) stimulate in vivo tissue repair and reduce fibrosis in various models. Using VSMC in vitro (pig aortic VSMC irradiated with a 60Co source and labeled with [3H]Proline), we now show that gamma-irradiation reduced cell survival by 50% and collagen synthesis 6-fold with a major increase in the ratio of collagen III to collagen I biosynthesis taken as a fibrotic index. RGTA added to the cells enhanced their survival up to 80% and reduced collagen III/I ratio back to values found in normal vascular tissues. These results suggest that RGTA combined with gamma-radiation could be an efficient strategy against restenosis.

Structurally different RGTAs modulate collagen-type expression by cultured aortic smooth muscle cells via different pathways involving fibroblast growth factor-2 or transforming growth factor-beta1

We have engineered polymers called ReGeneraTing Agents (RGTAs), which mimic the protecting and potentiating properties of heparan sulfates toward heparin-binding growth factors (HBGF). RGTAs have been shown to optimize cell growth and regulate collagen production in vitro. Here, we studied relationships between RGTA structure and collagen-type expression in aortic smooth muscle cells by using two RGTAs, the carboxylmethylsulfate dextran RG-1503 and the carboxylmethylsulfate dextran with added benzylamide RG-1192. RG-1192 specifically induced a fivefold decrease in collagen III synthesis. This effect was abolished by FGF-2 neutralizing antibody. RG-1192 and FGF-2 acted synergistically to decrease collagen III. RG-1192 was more effective than heparin in this process. RG-1192 increased the pericellular localization of FGF-2 and protected FGF-2 from proteolysis. Surface plasmon resonance analysis indicated a Kd of 15.7 nM for the RG-1192/FGF-2 interaction (10.6 nM for the heparin/FGF-2 interaction). The structurally different RG-1503 (without benzylamide) did not interact with FGF-2 and worked synergistically with TGF-beta1 to specifically induce a twofold increase in collagen V. RGTAs with different structures exert different modulating effects on the collagen phenotype. Selection of appropriate RGTAs, which had been shown to enhance in vivo tissue repair, may provide a mean of correcting collagen abnormalities in vascular disorders and more generally in fibrotic diseases.