Nondegradative Sulfation of Polysaccharides. Synthesis and Structure Characterization of Biologically Active Heparan Sulfate Mimetics

Biomaterials and tissue engineering approaches using glycosaminoglycans for tissue repair: Lessons learned from the native extracellular matrix

Glycosaminoglycans (GAGs) are an important component of the extracellular matrix as they influence cell behavior and have been sought for tissue regeneration, biomaterials, and drug delivery applications. GAGs are known to interact with growth factors and other bioactive molecules and impact tissue mechanics. This review provides an overview of native GAGs, their structure, and properties, specifically their interaction with proteins, their effect on cell behavior, and their mechanical role in the ECM. GAGs' function in the extracellular environment is still being understood however, promising studies have led to the development of medical devices and therapies. Native GAGs, including hyaluronic acid, chondroitin sulfate, and heparin, have been widely explored in tissue engineering and biomaterial approaches for tissue repair or replacement. This review focuses on orthopaedic and wound healing applications. The use of GAGs in these applications have had significant advances leading to clinical use. Promising studies using GAG mimetics and future directions are also discussed. STATEMENT OF SIGNIFICANCE: Glycosaminoglycans (GAGs) are an important component of the native extracellular matrix and have shown promise in medical devices and therapies. This review emphasizes the structure and properties of native GAGs, their role in the ECM providing biochemical and mechanical cues that influence cell behavior, and their use in tissue regeneration and biomaterial approaches for orthopaedic and wound healing applications.

Synthetic Heparan Sulfate Mimetic Polymer Enhances Corneal Nerve Regeneration and Wound Healing after Experimental Laser Ablation Injury in Mice

(1) Background: Abnormal corneal wound healing compromises visual acuity and can lead to neuropathic pain. Conventional treatments usually fail to restore the injured corneal tissue. In this study, we evaluated the effectiveness of a synthetic heparan sulfate mimetic polymer (HSmP) in a mouse model of corneal wound healing. (2) Methods: A surgical laser ablation affecting the central cornea and subbasal nerve plexus of mice was used as a model of the wound-healing assay. Topical treatment with HSmP was contrasted to its vehicle and a negative control (BSS). Corneal repair was studied using immunofluorescence to cell proliferation (Ki67), apoptosis (TUNEL assay), myofibroblast transformation (αSMA), assembly of epithelial cells (E-cadherin) and nerve regeneration (β-tubulin III). (3) Results: At the end of the treatment, normal epithelial cytoarchitecture and corneal thickness were achieved in HSmP-treated animals. HSmP treatment reduced myofibroblast occurrence compared to eyes irrigated with vehicle (p < 0.01) or BSS (p < 0.001). The HSmP group showed 50% more intraepithelial nerves than the BSS or vehicle groups. Only HSmP-treated corneas improved the visual quality to near transparent. (4) Conclusions: These results suggest that HSmP facilitates the regeneration of the corneal epithelium and innervation, as well as restoring transparency and reducing myofibroblast scarring after laser experimental injury.

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.

Learning from BMPs and their biophysical extracellular matrix microenvironment for biomaterial design

It is nowadays well-accepted that the extracellular matrix (ECM) is not a simple reservoir for growth factors but is an organization center of their biological activity. In this review, we focus on the ability of the ECM to regulate the biological activity of BMPs. In particular, we survey the role of the ECM components, notably the glycosaminoglycans and fibrillary ECM proteins, which can be promoters or repressors of the biological activities mediated by the BMPs. We examine how a process called mechano-transduction induced by the ECM can affect BMP signaling, including BMP internalization by the cells. We also focus on the spatio-temporal regulation of the BMPs, including their release from the ECM, which enables to modulate their spatial localization as well as their local concentration. We highlight how biomaterials can recapitulate some aspects of the BMPs/ECM interactions and help to answer fundamental questions to reveal previously unknown molecular mechanisms. Finally, the design of new biomaterials inspired by the ECM to better present BMPs is discussed, and their use for a more efficient bone regeneration in vivo is also highlighted.

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.

The sulfation of biomimetic glycosaminoglycan substrates controls binding of growth factors and subsequent neural and glial cell growth

Sulfated glycosaminoglycans (GAGs) are key structural and functional extracellular matrix (ECM) molecules involved in numerous signaling pathways mainly through their interaction with growth factors. Alginate sulfate mimics sulfated GAGs and binds growth factors such as basic fibroblast growth factor (FGF-2). Here, natural biomimetic substrates were engineered by immobilizing biotinylated alginate sulfates with varying degrees of sulfation (DS, from 0 to 2.7) on gold and polystyrene substrates using biotin-streptavidin binding. The build-up of films and the effect of the DS and biotinylation method on FGF-2 binding were assessed using quartz crystal microbalance with dissipation monitoring (QCM-D) and immunohistochemistry. The role of substrate sulfation and FGF-2 loading on the growth of A172 (human glioblastoma multiforme), SH-SY5Y (human neuroblastoma), and PC-12 (rat pheochromocytoma) cell lines was evaluated in vitro using proliferation and neurite outgrowth assessment. An increase in the DS of alginates resulted in augmented FGF-2 binding as evidenced by higher frequency and dissipation shifts measured with QCM-D and confirmed with immunostaining. All sulfated alginate substrates supported the attachment and growth of neural/glial cell lines better than controls with the highest increase in cell proliferation observed for the highest DS (p < 0.05 for all the cell lines). Moreover, FGF-2 loaded substrates with the highest DS induced the most significant increase in neurite-positive PC-12 cells and average neurite length. The developed biomimetic coatings can be used to functionalize substrates for biosensing applications (e.g. gold substrates) and to induce defined cellular responses via controlled growth factor delivery for basic and applied sciences.

Muscle fibrosis in the soft palate: Delivery of cells, growth factors and anti-fibrotics

The healing of skeletal muscle injuries after major trauma or surgical reconstruction is often complicated by the development of fibrosis leading to impaired function. Research in the field of muscle regeneration is mainly focused on the restoration of muscle mass while far less attention is paid to the prevention of fibrosis. In this review, we take as an example the reconstruction of the muscles in the soft palate of cleft palate patients. After surgical closure of the soft palate, muscle function during speech is often impaired by a shortage of muscle tissue as well as the development of fibrosis. We will give a short overview of the most common approaches to generate muscle mass and then focus on strategies to prevent fibrosis. These include anti-fibrotic strategies that have been developed for muscle and other organs by the delivery of small molecules, decorin and miRNAs. Anti-fibrotic compounds should be delivered in aligned constructs in order to obtain the organized architecture of muscle tissue. The available techniques for the preparation of aligned muscle constructs will be discussed. The combination of approaches to generate muscle mass with anti-fibrotic components in an aligned muscle construct may greatly improve the functional outcome of regenerative therapies for muscle injuries.

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.

A New Matrix Therapy Agent for Faster Corneal Healing and Less Ocular Discomfort Following Epi-off Accelerated Corneal Cross-linking in Progressive Keratoconus

PURPOSE

To investigate the hypothesis that a new matrix therapy agent (ReGeneraTing Agent, [RGTA]) would speed up the corneal reepithelialization, improve stromal healing, and reduce ocular symptoms after epi-off corneal cross-linking (CXL).

METHODS

Sixty eyes of 60 patients with progressive keratoconus were enrolled in the study. Epi-off accelerated CXL was performed in all patients. Sixty eyes were randomized into two groups according to use of RGTA eye drops prior to contact lens fitting at the end. Identical medical agents were started postoperatively for the two groups. All participants were monitored on 3 consecutive days after the CXL. Ocular pain, burning, stinging, tearing, photophobia, conjunctival hyperemia, and corneal healing status were evaluated.

RESULTS

By day 2, 25 eyes (83.3%) with RGTA revealed complete healing compared to 4 eyes (13.3%) that revealed complete healing in the control group (P < .001). All eyes had complete corneal epithelial defect closure by day 3 in both groups. Ocular pain scores were lower in the RGTA group on days 0, 1, and 2 (all P < .05). Burning scores were lower on days 1 and 2; stinging scores on days 2 and 3; tearing scores on days 2 and 3; and photophobia on days 1 and 2 (P < .05) in the RGTA group compared to the control group.

CONCLUSIONS

RGTA ophthalmic solution facilitates corneal healing by reconstructing the extracellular matrix in the wound area, leading to an earlier relief of symptoms for patients. [J Refract Surg. 2017;33(3):163-170.].

Circulating endothelial progenitors in vascular repair

Endothelial Colony Forming Cells (ECFCs) are obtained in culture from Circulating Endothelial Progenitor Cells. They display all characteristics of endothelial cells and they display stem cells features. Cord blood-derived ECFCs (CB-ECFCs) have a high clonogenic and proliferative potentials, and exhibit vascular repair capabilities useful for the treatment of ischemic diseases. However, the link between immaturity and functional properties of CB-ECFCs is still poorly defined. We showed that these cells have a high clonogenic potential and are capable to be efficiently reprogrammed into induced pluripotent stem cells. Moreover, we analyzed the expression of a broad panel of genes involved in embryonic stem cell properties. We define a novel stem cell transcriptional signature for CB-ECFCs fora better characterization and stratification according to their stem cell profile. We then improved the yield of CB-ECFC production for obtaining cells more functional in fewer passages. We used Glycosaminoglycans (GAG), components from the extracellular matrix which potentiate heparin binding growth factor activities. GAG mimetics were designed, having the capacity to increase the yield of ECFC during the isolation process, to increase the number of colonies, improve adhesion, proliferation, migration and self-renewal. GAG mimetics have thus great interest for vascular regeneration in combination with ECFC. Our results show that CB-ECFC are immature cells harboring specific functions such as formation of colonies, proliferation and formation of vascular structures in vitro and in vivo.

The Effect of a Synthetic Heparan Sulfate on the Healing of Colonic Anastomoses

Background

The mimetic compound OTR4120 may replace endogenous-degraded heparan sulfates that normally maintain the bioactivity of growth factors that are important for tissue repair. Herein, we investigated the effect of OTR4120 on the healing of normal colonic anastomoses.

Methods

We evaluated the following two treatment groups of male Sprague Dawley rats (220–256 g): control-treated colonic anastomoses (n = 25) and OTR4120-treated colonic anastomoses (n = 25). We resected 10 mm of the left colon and then applied either saline alone (control) or OTR4120 (100 μg/mL) in saline to the colonic ends before an end-to-end single-layer anastomosis was constructed and again on the anastomosis before the abdomen and skin were closed.

Results

On postoperative day 3, the anastomotic breaking strengths were 1.47 ± 0.32 N (mean ± SD) in the control group and 1.52 ± 0.27 N in the OTR4120-treated animals (P = 0.622). We also found that the hydroxyproline concentration (indicator of collagen) in the anastomotic wounds did not differ (P = 0.571) between the two groups.

Conclusions

Our data demonstrate that a single local application of OTR4120 intraoperatively did not increase the biomechanical strength of colonic anastomoses at the critical postoperative day 3 when the anastomoses are the weakest.

Heparan sulfate proteoglycans as key regulators of the mesenchymal niche of hematopoietic stem cells

The complex microenvironment that surrounds hematopoietic stem cells (HSCs) in the bone marrow niche involves different coordinated signaling pathways. The stem cells establish permanent interactions with distinct cell types such as mesenchymal stromal cells, osteoblasts, osteoclasts or endothelial cells and with secreted regulators such as growth factors, cytokines, chemokines and their receptors. These interactions are mediated through adhesion to extracellular matrix compounds also. All these signaling pathways are important for stem cell fates such as self-renewal, proliferation or differentiation, homing and mobilization, as well as for remodeling of the niche. Among these complex molecular cues, this review focuses on heparan sulfate (HS) structures and functions and on the role of enzymes involved in their biosynthesis and turnover. HS associated to core protein, constitute the superfamily of heparan sulfate proteoglycans (HSPGs) present on the cell surface and in the extracellular matrix of all tissues. The key regulatory effects of major medullar HSPGs are described, focusing on their roles in the interactions between hematopoietic stem cells and their endosteal niche, and on their ability to interact with Heparin Binding Proteins (HBPs). Finally, according to the relevance of HS moieties effects on this complex medullar niche, we describe recent data that identify HS mimetics or sulfated HS signatures as new glycanic tools and targets, respectively, for hematopoietic and mesenchymal stem cell based therapeutic applications.

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.

In vitro and in vivo evaluation of cord blood hematopoietic stem and progenitor cells amplified with glycosaminoglycan mimetic

BACKGROUND

Expansion protocols aim at both increasing the number of umbilical cord blood (UCB) hematopoietic stem cells and progenitor cells (HSPCs) and reducing the period of neutropenia in UCB HSPC graft. Because glycosaminoglycans (GAGs) are known to be important components of the hematopoietic niche and to modulate growth factor effects, we explored the use of GAG mimetic OTR4131 to potentiate HSPC's in vitro expansion and in vivo engraftment.

METHODS

UCB CD34+ cells were expanded with serum-free medium, SCF, TPO, FLT3-lig and G-CSF during 12 days in the absence or the presence of increasing OTR4131 concentrations (0-100 μg/mL). Proliferation ratio, cell viability and phenotype, functional assays, migration capacity and NOD-scid/γc(-/-) mice engraftment were assessed after expansion.

RESULTS

At Day 12, ratios of cell expansion were not significantly increased by OTR4131 treatment. Better total nucleated cell viability was observed with the use of 1 μg/mL GAG mimetic compared to control (89.6 % ± 3.7 % and 79.9 % ± 3.3 %, respectively). Phenotype analysis showed a decrease of monocyte lineage in the presence of OTR4131 and HSPC migration capacity was diminished when GAG mimetic was used at 10 μg/mL (10.9 % ± 4.1 % vs. 52.9 % ± 17.9 % for control). HSPC clonogenic capacities were similar whatever the culture conditions. Finally, in vivo experiments revealed that mice successfully engrafted in all conditions, even if some differences were observed during the first month. Three months after graft, bone marrow chimerism and blood subpopulations were similar in both groups.

CONCLUSIONS

UCB HSPCs ex-vivo expansion in the presence of OTR4131 is a safe approach that did not modify cell function and engraftment capacities. In our experimental conditions, the use of a GAG mimetic did not, however, allow increasing cell expansion or optimizing their in vivo engraftment.

A Direct Sulfation Process of a Marine Polysaccharide in Ionic Liquid

GY785 is an exopolysaccharide produced by a mesophilic bacterial strain Alteromonas infernus discovered in the deep-sea hydrothermal vents. GY785 highly sulfated derivative (GY785 DRS) was previously demonstrated to be a promising molecule driving the efficient mesenchymal stem cell chondrogenesis for cartilage repair. This glycosaminoglycan- (GAG-) like compound was modified in a classical solvent (N,N′-dimethylformamide). However, the use of classical solvents limits the polysaccharide solubility and causes the backbone degradation. In the present study, a one-step efficient sulfation process devoid of side effects (e.g., polysaccharide depolymerization and/or degradation) was developed to produce GAG-like derivatives. The sulfation of GY785 derivative (GY785 DR) was carried out using ionic liquid as a reaction medium. The successful sulfation of this anionic and highly branched heteropolysaccharide performed in ionic liquid would facilitate the production of new molecules of high specificity for biological targets such as tissue engineering or regenerative medicine.

Glycosaminoglycan mimetic improves enrichment and cell functions of human endothelial progenitor cell colonies

Human circulating endothelial progenitor cells isolated from peripheral blood generate in culture cells with features of endothelial cells named late-outgrowth endothelial colony-forming cells (ECFC). In adult blood, ECFC display a constant quantitative and qualitative decline during life span. Even after expansion, it is difficult to reach the cell dose required for cell therapy of vascular diseases, thus limiting the clinical use of these cells. Glycosaminoglycans (GAG) are components from the extracellular matrix (ECM) that are able to interact and potentiate heparin binding growth factor (HBGF) activities. According to these relevant biological properties of GAG, we designed a GAG mimetic having the capacity to increase the yield of ECFC production from blood and to improve functionality of their endothelial outgrowth. We demonstrate that the addition of [OTR(4131)] mimetic during the isolation process of ECFC from Cord Blood induces a 3 fold increase in the number of colonies. Moreover, addition of [OTR(4131)] to cell culture media improves adhesion, proliferation, migration and self-renewal of ECFC. We provide evidence showing that GAG mimetics may have great interest for cell therapy applied to vascular regeneration therapy and represent an alternative to exogenous growth factor treatments to optimize potential therapeutic properties of ECFC.

Glycosaminoglycan mimetic associated to human mesenchymal stem cell-based scaffolds inhibit ectopic bone formation, but induce angiogenesis in vivo

Tissue engineering approaches to stimulate bone formation currently combine bioactive scaffolds with osteocompetent human mesenchymal stem cells (hMSC). Moreover, osteogenic and angiogenic factors are required to promote differentiation and survival of hMSC through improved vascularization through the damaged extracellular matrix (ECM). Glycosaminoglycans (GAGs) are ECM compounds acting as modulators of heparin-binding protein activities during bone development and regenerative processes. GAG mimetics have been proposed as ECM stabilizers and were previously described for their positive effects on bone formation and angiogenesis after local treatment. Here, we developed a strategy associating the GAG mimetic [OTR4120] with bone substitutes to optimize stem cell-based therapeutic products. We showed that [OTR4120] was able to potentiate proliferation, migration, and osteogenic differentiation of hMSC in vitro. Its link to tricalcium phosphate/hydroxyapatite scaffolds improved their colonization by hMSC. Surprisingly, when these combinations were tested in an ectopic model of bone formation in immunodeficient mice, the GAG mimetics inhibit bone formation induced by hMSC and promoted an osteoclastic activity. Moreover, the inflammatory response was modulated, and the peri-implant vascularization stimulated. All together, these findings further support the ability of GAG mimetics to organize the local ECM to coordinate the host response toward the implanted biomaterial, and to inhibit the abnormal bone formation process on a subcutaneous ectopic site.

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.

Glycosaminoglycans in biomedicine

Glycosaminoglycans (GAGs) compose one of four classes of mammalian biopolymers, and are arguably the most complex. The research areas of glycobiology, glycopolymers, and the use of GAGs within tissue engineering and regenerative medicine have grown exponentially during the past decade. Researchers are closing in on high throughput methods for GAG synthesis and sequencing, but our understanding of glycan sequence and the information contained in this sequence lags behind. Screening methods to identify key GAG-biopolymer interactions are providing insights into important targets for nanomedicine, regenerative medicine, and pharmaceutics. Importantly, GAGs are most often found in the form of glycolipids and proteoglycans. Several studies have shown that the clustering of GAGs, as is often the case in proteoglycans, increases the affinity between GAGs and other biopolymers. In addition, GAG clustering can create regions of high anionic charge, which leads to high osmotic pressure. Recent advances have led to proteoglycan mimics that exhibit many of the functions of proteoglycans including protection of the extracellular matrix from proteolytic activity, regulation of collagen fibril assembly on the nanoscale, alteration of matrix stiffness, and inhibition of platelet adhesion, among others. Collectively, these advances are stimulating possibilities for targeting of drugs, nanoparticles, and imaging agents, opening new avenues for mimicking nanoscale molecular interactions that allow for directed assembly of bulk materials, and providing avenues for the synthesis of proteoglycan mimics that enhance opportunities in regenerative medicine.

Heparin mimetics

Explorations of the therapeutic potential of heparin mimetics, anionic compounds that are analogues of glycosaminoglycans (GAGs), have gone hand-in-hand with the emergence of understanding as to the role of GAGs in many essential biological processes. A myriad of structurally different heparin mimetics have been prepared and examined in many diverse applications. They range in complexity from heterogeneous polysaccharides that have been chemically sulphated to well-defined compounds, designed in part to mimic the natural ligand, but with binding specificity and potency increased by conjugation to non-carbohydrate pharmacophores. The maturity of the field is illustrated by the seven heparin mimetics that have achieved marketing approval and there are several more in late-stage clinical development. An overview of the structural determinants of heparin mimetics is presented together with an indication of their activities. The challenges in developing heparin mimetics as drugs, specificity and potential toxicity issues, are highlighted. Finally, the development path of three structurally very different mimetics, PI-88(®), GMI-1070 and RGTAs, each of which is in clinical trials, is described.

[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.

Xylan and Xylan Derivatives – Basis of Functional Polymers for the Future

This review highlights xylan and xylan derivatives. It depicts the occurrence and structural diversity of the biopolymer, followed by a presentation of different ways of isolation from biomass. The determination of characteristics, i.e., molecular weight, interaction with other polysaccharides, thermal behaviour, and the biological activity of xylan are reviewed. The application potential arising from the structural features of the unmodified xylan is pointed out. Special attention is concentrated on the possibilities of the modification of functional properties by chemical functionalization of the biopolymers in order to design advanced materials. Within this review recent results in the field are accompanied with selected results of our own work.

Receptor-targeted iron oxide nanoparticles for molecular MR imaging of inflamed atherosclerotic plaques

In a number of literature reports iron oxide nanoparticles have been investigated for use in imaging atherosclerotic plaques and found to accumulate in plaques via uptake by macrophages, which are critical in the process of atheroma initiation, propagation, and rupture. However, the uptake of these agents is non-specific; thus the labeling efficiency for plaques in vivo is not ideal. We have developed targeted agents to improve the efficiency for labeling macrophage-laden plaques. These probes are based on iron oxide nanoparticles coated with dextran sulfate, a ligand of macrophage scavenger receptor type A (SR-A). We have sulfated dextran-coated iron oxide nanoparticles (DIO) with sulfur trioxide, thereby targeting our nanoparticle imaging agents to SR-A. The sulfated DIO (SDIO) remained mono-dispersed and had an average hydrodynamic diameter of 62 nm, an r(1) relaxivity of 18.1 mM(-1) s(-1), and an r(2) relaxivity of 95.8 mM(-1) s(-1) (37 °C, 1.4 T). Cell studies confirmed that these nanoparticles were nontoxic and specifically targeted to macrophages. In vivo MRI after intravenous injection of the contrast agent into an atherosclerotic mouse injury model showed substantial signal loss on the injured carotid at 4 and 24 h post-injection of SDIO. No discernable signal decrease was seen at the control carotid and only mild signal loss was observed for the injured carotid post-injection of non-sulfated DIO, indicating preferential uptake of the SDIO particles at the site of atherosclerotic plaque. These results indicate that SDIO can facilitate MRI detection and diagnosis of vulnerable plaques in atherosclerosis.

Heparan sulfate glycosaminoglycan mimetic improves pressure ulcer healing in a rat model of cutaneous ischemia-reperfusion injury

Pressure ulcers are a major clinical problem, with a large burden on healthcare resources. This study evaluated the effects of the heparan sulfate glycosaminoglycan mimetic, OTR4120, on pressure ulceration and healing. Ischemia-reperfusion (I-R) was evoked to induce pressure ulcers by external clamping and then removal of a pair of magnet disks on rat dorsal skin for a single ischemic period of 16 hours. Immediately after magnet removal, rats received an intramuscular injection of OTR4120 weekly for up to 1 month. During the ischemic period, normal skin perfusion was reduced by at least 60% and at least 20-45% reperfused into the ischemic region after compression release. This model caused sustained skin incomplete necrosis for up to 14 days and led to grade 2-3 ulcers. OTR4120 treatment decreased the area of skin incomplete necrosis and degree of ulceration. OTR4120 treatment also reduced inflammation and increased angiogenesis. In OTR4120-treated ulcers, the contents of vascular endothelial growth factor, platelet-derived growth factor, and transforming growth factor beta-1 were increased. Moreover, OTR4120 treatment promoted early expression of alpha-smooth muscle actin and increased collagen biosynthesis. Long-term restoration of wounded tissue biomechanical strength was significantly enhanced after OTR4120 treatment. Taken together, we conclude that OTR4120 treatment reduces pressure ulcer formation and potentiates the internal healing bioavailability.

Xylan-based nanoparticles: prodrugs for ibuprofen release

Esterification of xylan with ibuprofen via activiation of the carboxylic acid with N,N'-carbonyldiimidazole (CDI) yields products of high drug loadings. Subsequent sulfation of xylan ibuprofen esters using the gentle agent SO(3)/DMF was successfully carried out in order to modify hydrophobicity of the xylan esters. The structure of the novel xylan esters was evaluated by means of NMR spectroscopy. The resulting xylan derivatives self assemble into spherical nanoparticles with mean diameters ranging from 162 to 472 nm. Preliminary stability measurements indicate that hydrolytic stability decreases with increase in degree of substitution of sulfate groups. Thus, a new concept toward improved drug delivery from polysaccharide-based nanoparticles can be established here.

Glycosaminoglycan mimetics trigger IP3-dependent intracellular calcium release in myoblasts

Glycosaminoglycans (GAG) are sulfated polysaccharides that play an important role in regulating cell functions. GAG mimetics called RGTAs (for ReGeneraTing Agents) have been shown to stimulate tissue repair. In particular they accelerate myogenesis, in part via their heparin-mimetic property towards growth factors. RGTAs also increase activity of calcium-dependent intracellular protease suggesting an effect on calcium cellular homeostasis. This effect was presently investigated on myoblasts in vitro using one member of the RGTA family molecule named OTR4120. We have shown that OTR4120 or heparin induced transient increases of intracellular calcium concentration ([Ca(2+)]i) in pre-fusing myoblasts from both mouse SolD7 cell line and rat skeletal muscle satellite cells grown in primary culture by mobilising sarcoplasmic reticulum store. This [Ca(2+)]i was not mediated by ryanodine receptors but instead resulted from stimulation of the Inositol-3 phosphate-phospholipase C activation pathway. OTR4120-induced calcium transient was not mediated through an ATP, nor a tyrosine kinase, nor an acetylcholine receptor but principally through serotonin 5-HT2A receptor. This original finding shows that the GAG mimetic can induce calcium signal through serotonin receptors and the IP3 pathway may be relevant to its ability to favour myoblast differentiation. It supports a novel and unexpected function of GAGs in the regulation of calcium homeostasis.

Matrix therapy in regenerative medicine, a new approach to chronic wound healing

Nonhealing wounds remain a major health problem whose treatment is challenging and costly. Treatments based on cells or growth factors are still not very effective. We developed an entirely novel strategy consisting in treatment of the wound-tissue matrix with biopolymers engineered to mimic heparan sulfates called OTR4120. This compound was dextran polymer with sulfated and carboxymethyl groupments. After binding to matrix proteins, the heparan-sulfate-mimicking polymer protects the microenvironment, maintaining the normal production of signals and growth factors needed for healing to occur. Here, we show that a specific biopolymer accelerates ulcer closure and improves re-epithelialization and dermal-matrix-component remodeling. OTR4120 treatment was associated with faster maturation of epidermal structures, most notably regarding the number of epithelial-cell layers, and with an appearance that more closely resembled normal skin. Treatment had also a main effect on collagen I and III expression. Necrotic skin ulcers induced in mice with doxorubicin recovered normal collagen levels and organization, with no evidence of fibrosis. Thus, appropriate polymer-based matrix therapy is a valid and simple alternative to regenerative medicine.