Sulfated Hyaluronan Alters Endothelial Cell Activation in Vitro by Controlling the Biological Activity of the Angiogenic Factors Vascular Endothelial Growth Factor-A and Tissue Inhibitor of Metalloproteinase-3

Chemical Modification of Hyaluronan and Their Biomedical Applications

Hyaluronan, the extracellular matrix glycosaminoglycan, is an important structural component of many tissues playing a critical role in a variety of biological contexts. This makes hyaluronan, which can be biotechnologically produced in large scale, an attractive starting polymer for chemical modifications. This review provides a broad overview of different synthesis strategies used for modulating the biological as well as material properties of this polysaccharide. We discuss current advances and challenges of derivatization reactions targeting the primary and secondary hydroxyl groups or carboxylic acid groups and the N-acetyl groups after deamidation. In addition, we give examples for approaches using hyaluronan as biomedical polymer matrix and consequences of chemical modifications on the interaction of hyaluronan with cells via receptor-mediated signaling. Collectively, hyaluronan derivatives play a significant role in biomedical research and applications indicating the great promise for future innovative therapies.

Collagen/hyaluronan based hydrogels releasing sulfated hyaluronan improve dermal wound healing in diabetic mice via reducing inflammatory macrophage activity

Sustained inflammation associated with dysregulated macrophage activation prevents tissue formation and healing of chronic wounds. Control of inflammation and immune cell functions thus represents a promising approach in the development of advanced therapeutic strategies. Here we describe immunomodulatory hyaluronan/collagen (HA-AC/coll)-based hydrogels containing high-sulfated hyaluronan (sHA) as immunoregulatory component for the modulation of inflammatory macrophage activities in disturbed wound healing. Solute sHA downregulates inflammatory activities of bone marrow-derived and tissue-resident macrophages in vitro. This further affects macrophage-mediated pro-inflammatory activation of skin cells as shown in skin ex-vivo cultures. In a mouse model of acute skin inflammation, intradermal injection of sHA downregulates the inflammatory processes in the skin. This is associated with the promotion of an anti-inflammatory gene signature in skin macrophages indicating a shift of their activation profile. For in vivo translation, we designed HA-AC/coll hydrogels allowing delivery of sHA into wounds over a period of at least one week. Their immunoregulatory capacity was analyzed in a translational experimental approach in skin wounds of diabetic db/db mice, an established model for disturbed wound healing. The sHA-releasing hydrogels improved defective tissue repair with reduced inflammation, augmented pro-regenerative macrophage activation, increased vascularization, and accelerated new tissue formation and wound closure.

Covalent linkage of sulfated hyaluronan to the collagen scaffold Mucograft® enhances scaffold stability and reduces proinflammatory macrophage activation in vivo

Sulfated glycosaminoglycans (sGAG) show interaction with biological mediator proteins. Although collagen-based biomaterials are widely used in clinics, their combination with high-sulfated hyaluronan (sHA3) is unexplored. This study aims to functionalize a collagen-based scaffold (Mucograft®) with sHA3 via electrostatic (sHA3/PBS) or covalent binding to collagen fibrils (sHA3+EDC/NHS). Crosslinking without sHA3 was used as a control (EDC/NHS Ctrl). The properties of the sHA3-functionalized materials were characterized. In vitro growth factor and cytokine release after culturing with liquid platelet-rich fibrin was performed by means of ELISA. The cellular reaction to the biomaterials was analyzed in a subcutaneous rat model. The study revealed that covalent linking of sHA3 to collagen allowed only a marginal release of sHA3 over 28 days in contrast to electrostatically bound sHA3. sHA3+EDC/NHS scaffolds showed reduced vascular endothelial growth factor (VEGF), transforming growth factor beta 1 (TGF-β1) and enhanced interleukin-8 (IL-8) and epithelial growth factor (EGF) release in vitro compared to the other scaffolds. Both sHA3/PBS and EDC/NHS Ctrl scaffolds showed a high proinflammatory reaction (M1: CD-68+/CCR7+) and induced multinucleated giant cell (MNGC) formation in vivo. Only sHA3+EDC/NHS scaffolds reduced the proinflammatory macrophage M1 response and did not induce MNGC formation during the 30 days. SHA3+EDC/NHS scaffolds had a stable structure in vivo and showed sufficient integration into the implantation region after 30 days, whereas EDC/NHS Ctrl scaffolds underwent marked disintegration and lost their initial structure. In summary, functionalized collagen (sHA3+EDC/NHS) modulates the inflammatory response and is a promising biomaterial as a stable scaffold for full-thickness skin regeneration in the future.

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Covalent linking of high-sulfated hyaluronan (sHA3) to collagen allows a sustained release of sHA3.

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Covalent linking of sHA3 to collagen modulates the release of growth factor and cytokines in vitro.

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Covalent linking of sHA3 to collagen suppresses the induction of multinucleated giant cells in vivo.

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Covalent linking of sHA3 to collagen reduces the proinflammatory macrophage M1 response in vivo.

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Functionalized collagen with sHA3 is promising for full-thickness skin regeneration.

Update on the Role of the Endothelial Glycocalyx in Angiogenesis and Vascular Inflammation

The endothelial glycocalyx is a negatively charged, carbohydrate-rich structure that arises from the luminal surface of the vascular endothelium and is comprised of proteoglycans, glycoproteins, and glycolipids. The glycocalyx, which sits at the interface between the endothelium and the blood, is involved in a wide array of physiological and pathophysiological processes, including as a mechanotransducer and as a regulator of inflammation. Most recently, components of the glycocalyx have been shown to play a key role in controlling angiogenesis. In this review, we briefly summarize the structure and function of the endothelial glycocalyx. We focus on its role and functions in vascular inflammation and angiogenesis and discuss the important unanswered questions in this field.

Insights into structure, affinity, specificity, and function of GAG-protein interactions through the chemoenzymatic preparation of defined sulfated oligohyaluronans

High amounts of glycosaminoglycans (GAG) such as hyaluronan (HA) occur in connective tissues. There is nowadays increasing evidence that a "sulfation code" exists which mediates numerous GAG functions. High molecular weight and inhomogeneity of GAG, however, aggravated detailed studies. Thus, synthetic oligosaccharides were urgently required. We will review here chemoenzymatic and analytic strategies to provide defined sulfated and anomerically modified GAG oligosaccharides of the HA type. Representative studies of protein/GAG interactions by (bio)chemical and biophysical methods are reported yielding novel insights into GAG-protein binding. Finally, the biological conclusions and in vivo applications of defined sulfated GAG oligosaccharides will be discussed.

Structural insights into the modulation of PDGF/PDGFR-β complexation by hyaluronan derivatives

Angiogenesis is an important physiological process playing a crucial role in wound healing and cancer progression. Vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) are key players in angiogenesis. Based on previous findings regarding the modulation of VEGF activity by glycosaminoglycans (GAG), here we explore the interaction of hyaluronan (HA)-based GAG with PDGF and its receptor PDGFR-β by applying molecular modeling and dynamics simulations in combination with surface plasmon resonance (SPR). Computational analysis on the interaction of oligo-hyaluronan derivatives with different sulfation pattern and functionalization shows that these GAG interact with PDGF in relevant regions for receptor recognition, and that high sulfation as well as modification with the TAMRA group convey stronger binding. On the other hand, the studied oligo-hyaluronan derivatives are predicted to scarcely recognize PDGFR-β. SPR results are in line with the computational predictions regarding the binding pattern of HA tetrasaccharide (HA4) derivatives to PDGF and PDGFR-β. Furthermore, our experimental results also show that the complexation of PDGF to PDGFR-β can be modulated by HA4 derivatives. The results found open the path for considering HA4 derivatives as potential candidates to be exploited for modulation of the PDGF/PDGFR-β signaling system in angiogenesis and related disease conditions.

Scavenging of Dickkopf-1 by macromer-based biomaterials covalently decorated with sulfated hyaluronan displays pro-osteogenic effects

Dickkopf-1 (DKK1), a Wnt inhibitor secreted by bone marrow stromal cells (MSC), is known to play an important role in long-term non-union bone fracture defects and glucocorticoid induced osteoporosis. Mitigating its effects in early bone defects could improve osteogenesis and bone defect healing. Here, we applied a biomaterial strategy to deplete a defect environment from DKK1 by scavenging the protein via a macromer-based biomaterial covalently decorated with sulfated hyaluronan (sHA3). The material consisted of cross-copolymerized three-armed macromers with a small anchor molecule. Using the glycidyl anchor, polyetheramine (ED900) could be grafted to the material to which sHA3 was efficiently coupled in a separate step. For thorough investigation of material modification, flat material surfaces were generated by fabricating them on glass discs. The binding capability of sHA3 for DKK1 was demonstrated in this study by surface plasmon resonance measurements. Furthermore, the surfaces demonstrated the ability to scavenge and inactivate pathologic amounts of DKK1 from complex media. In a combinatory approach with Wnt3a, we were able to demonstrate that DKK1 is the preferred binding partner of our sHA3-functionalized surfaces. We validated our findings in a complex in vitro setting of differentiating SaOS-2 cells and primary hMSC. Here, endogenous DKK-1 was scavenged resulting in increased osteogenic differentiation indicating that this is a consistent biological effect irrespective of the model system used. Our study provides insights in the mechanisms and efficiency of sHA3 surface functionalization for DKK1 scavenging, which may be used in a clinical context in the future.

Increased pore size of scaffolds improves coating efficiency with sulfated hyaluronan and mineralization capacity of osteoblasts

Background

Delayed bone regeneration of fractures in osteoporosis patients or of critical-size bone defects after tumor resection are a major medical and socio-economic challenge. Therefore, the development of more effective and osteoinductive biomaterials is crucial.

Methods

We examined the osteogenic potential of macroporous scaffolds with varying pore sizes after biofunctionalization with a collagen/high-sulfated hyaluronan (sHA3) coating in vitro. The three-dimensional scaffolds were made up from a biodegradable three-armed lactic acid-based macromer (TriLA) by cross-polymerization. Templating with solid lipid particles that melt during fabrication generates a continuous pore network. Human mesenchymal stem cells (hMSC) cultivated on the functionalized scaffolds in vitro were investigated for cell viability, production of alkaline phosphatase (ALP) and bone matrix formation. Statistical analysis was performed using student’s t-test or two-way ANOVA.

Results

We succeeded in generating scaffolds that feature a significantly higher average pore size and a broader distribution of individual pore sizes (HiPo) by modifying composition and relative amount of lipid particles, macromer concentration and temperature for cross-polymerization during scaffold fabrication. Overall porosity was retained, while the scaffolds showed a 25% decrease in compressive modulus compared to the initial TriLA scaffolds with a lower pore size (LoPo). These HiPo scaffolds were more readily coated as shown by higher amounts of immobilized collagen (+ 44%) and sHA3 (+ 25%) compared to LoPo scaffolds. In vitro, culture of hMSCs on collagen and/or sHA3-coated HiPo scaffolds demonstrated unaltered cell viability. Furthermore, the production of ALP, an early marker of osteogenesis (+ 3-fold), and formation of new bone matrix (+ 2.5-fold) was enhanced by the functionalization with sHA3 of both scaffold types. Nevertheless, effects were more pronounced on HiPo scaffolds about 112%.

Conclusion

In summary, we showed that the improvement of scaffold pore sizes enhanced the coating efficiency with collagen and sHA3, which had a significant positive effect on bone formation markers, underlining the promise of using this material approach for in vivo studies.

Dual Action of Sulfated Hyaluronan on Angiogenic Processes in Relation to Vascular Endothelial Growth Factor-A

Pathological healing characterized by abnormal angiogenesis presents a serious burden to patients’ quality of life requiring innovative treatment strategies. Glycosaminoglycans (GAG) are important regulators of angiogenic processes. This experimental and computational study revealed how sulfated GAG derivatives (sGAG) influence the interplay of vascular endothelial growth factor (VEGF)₁₆₅ and its heparin-binding domain (HBD) with the signaling receptor VEGFR-2 up to atomic detail. There was profound evidence for a HBD-GAG-HBD stacking configuration. Here, the sGAG act as a “molecular glue” leading to recognition modes in which sGAG interact with two VEGF₁₆₅-HBDs. A 3D angiogenesis model demonstrated the dual regulatory role of high-sulfated derivatives on the biological activity of endothelial cells. While GAG alone promote sprouting, they downregulate VEGF₁₆₅-mediated signaling and, thereby, elicit VEGF₁₆₅-independent and -dependent effects. These findings provide novel insights into the modulatory potential of sGAG derivatives on angiogenic processes and point towards their prospective application in treating abnormal angiogenesis.

Terminal chemical functions of polyamidoamine dendrimer surfaces and its impact on bone cell growth

Besides their use for drug and gene delivery, dendrimer molecules are also favorable for the design of new surface coatings for orthopedic and dental implants due to the wide variety of functional terminal groups and their multivalent character. The purpose of this work was to observe how covalently immobilized polyamidoamine (PAMAM) dendrimer molecules with different terminal chemical groups influenced serum protein adsorption and osteoblast behavior. To this end, fifth-generation PAMAM dendrimers were immobilized on silicon surfaces with an anhydride-containing silane coupling agent which results in positively charged terminal NH₂-groups. Coatings with a net negative charge were generated by introduction of terminal CO₂H- or CH₃-groups. Surface characterization was performed by static and dynamic contact angle and zeta potential. The in vitro studies with human MG-63 osteoblastic cells focused on cell adhesion, morphology, cell cycle, apoptosis and actin formation within 24 h. This work demonstrated that cell growth was dependent on surface chemistry and correlated strongly with the surface free energy and charge of the material. The positively charged NH₂ surface induced tight cell attachment with well-organized actin stress fibers and a well spread morphology. In contrast, CO₂H- and CH₃-functional groups provoked a decrease in cell adhesion and spreading and indicated higher apoptotic potential, although both were hydrophilic. The knowledge about the cell-material dialogue is of relevance for the development of bioactive implants in regenerative medicine.

Hyaluronan/collagen hydrogels containing sulfated hyaluronan improve wound healing by sustained release of heparin-binding EGF-like growth factor

Functional biomaterials that are able to bind, stabilize and release bioactive proteins in a defined manner are required for the controlled delivery of such to the desired place of action, stimulating wound healing in health-compromised patients. Glycosaminoglycans (GAG) represent a very promising group of components since they may be functionally engineered and are well tolerated by the recipient tissues due to their relative immunological inertness. Ligands of the Epidermal Growth Factor (EGF) receptor (EGFR) activate keratinocytes and dermal fibroblasts and, thus, contribute to skin wound healing. Heparin-binding EGF-like growth factor (HB-EGF) bound to GAG in biomaterials (e.g. hydrogels) might serve as a reservoir that induces prolonged activation of the EGF receptor and to recover disturbed wound healing. Based on previous findings, the capacity of hyaluronan (HA) and its sulfated derivatives (sHA) to bind and release HB-EGF from HA/collagen-based hydrogels was investigated. Docking and molecular dynamics analysis of a molecular model of HB-EGF led to the identification of residues in the heparin-binding domain of the protein being essential for the recognition of GAG derivatives. Furthermore, molecular modeling and surface plasmon resonance (SPR) analyses demonstrated that sulfation of HA increases binding strength to HB-EGF thus providing a rationale for the development of sHA-containing hydrogels. In line with computational observations and in agreement with SPR results, gels containing sHA displayed a retarded HB-EGF release in vitro compared to pure HA/collagen gels. Hydrogels containing HA and collagen or a mixture with sHA were shown to bind and release bioactive HB-EGF over at least 72 h, which induced keratinocyte migration, EGFR-signaling and HGF expression in dermal fibroblasts. Importantly, hydrogels containing sHA strongly increased the effectivity of HB-EGF in inducing epithelial tip growth in epithelial wounds shown in a porcine skin organ culture model. These findings suggest that hydrogels containing HA and sHA can be engineered for smart and effective wound dressings. STATEMENT OF SIGNIFICANCE: Immobilization and sustained release of recombinant proteins from functional biomaterials might overcome the limited success of direct application of non-protected solute growth factors during the treatment of impaired wound healing. We developed HA/collagen-based hydrogels supplemented with acrylated sulfated HA for binding and release of HB-EGF. We analyzed the molecular basis of HB-EGF interaction with HA and its chemical derivatives by in silico modeling and surface plasmon resonance. These hydrogels bind HB-EGF reversibly. Using different in vitro assays and organ culture we demonstrate that the introduction of sulfated HA into the hydrogels significantly increases the effectivity of HB-EGF action on target cells. Therefore, sulfated HA-containing hydrogels are promising functional biomaterials for the development of mediator releasing wound dressings.

Syntheses of defined sulfated oligohyaluronans reveal structural effects, diversity and thermodynamics of GAG-protein binding

High binding affinities of GAG toward extracellular regulatory proteins are governed by recognition diversity, sulfation pattern, length, and anomeric functionalization.

Binding of sulfated glycosaminoglycans (GAG) to a wide spectrum of extracellular regulatory proteins is crucial for physiological processes such as cell growth, migration, tissue homeostasis and repair. Thus, GAG derivatives exhibit great relevance in the development of innovative biomaterials for tissue regeneration therapies. We present a synthetic strategy for the preparation of libraries of defined sulfated oligohyaluronans as model GAG systematically varied in length, sulfation pattern and anomeric substitution in order to elucidate the effects of these parameters on GAG recognition by regulatory proteins. Through an experimental and computational approach using fluorescence polarization, ITC, docking and molecular dynamics simulations we investigate the binding of these functionalized GAG derivatives to ten representative regulatory proteins including IL-8, IL-10, BMP-2, sclerostin, TIMP-3, CXCL-12, TGF-β, FGF-1, FGF-2, and AT-III, and we establish structure–activity relationships for GAG recognition. Binding is mainly driven by enthalpy with only minor entropic contributions. In several cases binding is determined by GAG length, and in all cases by the position and number of sulfates. Affinities strongly depend on the anomeric modification of the GAG. Highest binding affinities are effected by anomeric functionalization with large fluorophores and by GAG dimerization. Our experimental and theoretical results suggest that the diversity of GAG binding sites and modes is responsible for the observed high affinities and other binding features. The presented new insights into GAG–protein recognition will be of relevance to guide the design of GAG derivatives with customized functions for the engineering of new biomaterials.

Expression of MMP-2 and TIMP-3 with incidence and prognosis of giant-cell tumor of the bone

The expression of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinase-3 (TIMP-3) in giant-cell tumor of bone (GCT), and the correlation of their expression with the clinicopathologic features and prognosis were investigated. A total of 70 GCT patients treated in our hospital from September, 2013 to September, 2015, were selected, and the tumor and para-carcinoma tissues were obtained by surgery. The expression levels of MMP-2 and TIMP-3 in GCT and para-carcinoma tissues were detected via semi-quantitative polymerase chain reaction (PCR) and western blot analysis, as well as immunohistochemical staining. Moreover, the clinicopathological data of the GCT patients were collected to study the correlation of MMP-2 and TIMP-3 with clinicopathological features and prognosis of GCT. The results of semi-quantitative PCR and western blot analysis revealed that the expression level of MMP-2 in tissues of the 70 GCT patients was significantly higher than that in para-carcinoma tissues, and the difference was statistically significant (P<0.01), while the expression level of TIMP-3 was obviously lower than that in para-carcinoma tissues (P<0.01). The results of immunohistochemical staining revealed that the positive expression rate of MMP-2 was 57.6% in GCT tissues and 18.9% in para-carcinoma tissues, while that of TIMP-3 was 63.2% in GCT tissues and 13.8% in para-carcinoma tissues, and the differences were statistically significant (P<0.01). The expression levels of MMP-2 and TIMP-3 were correlated with the diameter of tumor, clinical staging, lymph node metastasis and relapse of GCT (P<0.01), but were not correlated with the age and sex of GCT patients (P>0.05). There was a negative correlation between MMP-2 and TIMP-3 expression levels (r=−0.258, P<0.05). The expression levels of MMP-2 and TIMP-3 are closely related to the clinicopathological features and prognosis of patients, which can be used as one of the clinical examination indexes of GCT and also provide new insights for the clinical treatment of GCT.

Expression of tissue inhibitor of metalloproteinases-1 and B-cell lymphoma-2 in the synovial membrane in patients with knee osteoarthritis

The purpose of this study was to determine the expression and impact of tissue inhibitor of metalloproteinases-1 (TIMP-1) and B-cell lymphoma-2 (Bcl-2) in knee osteoarthritis (KOA). We collected synovial fluids from the knee joint of 70 KOA patients and 30 controls. The expression levels of TIMP-1 and Bcl-2 were significantly higher in KOA patients than those in the control group (P<0.01). We also found positive correlation between the severity of KOA and the expression level of TIMP-1 (r=0.8027, P<0.05) and and Bcl-2 (r=0.5336, P<0.05). However, we found no correlation between the expression levels of TIMP-1 and Bcl-2 in the synovial membranes of KOA patients (P>0.05). Both TIMP-1 and Bcl-2 are expressed at high levels in the synovial membrane with KOA, and are closely related to the occurrence and development of KOA. Thus, detection of TIMP-1 and Bcl-2 in KOA patients can be helpful in diagnosing the state of KOA.