Human fibrinogen specifically binds hyaluronic acid

"Filler-Associated Acute Stroke Syndrome": Classification, Predictive Modelling of Hyaluronidase Efficacy, and Updated Case Review on Neurological and Visual Complications

INTRODUCTION

The rising use of soft tissue fillers for aesthetic procedures has seen an increase in complications, including vascular occlusions and neurological symptoms that resemble stroke. This study synthesizes information on central nervous system (CNS) complications post-filler injections and evaluates the effectiveness of hyaluronidase (HYAL) treatment.

METHODS

A thorough search of multiple databases, including PubMed, EMBASE, Scopus, Web of Science, Google Scholar, and Cochrane, focused on publications from January 2014 to January 2024. Criteria for inclusion covered reviews and case reports that documented CNS complications related to soft tissue fillers. Advanced statistical and computational techniques, including logistic regression, machine learning, and Bayesian analysis, were utilized to dissect the factors influencing therapeutic outcomes.

RESULTS

The analysis integrated findings from 20 reviews and systematic analyses, with 379 cases reported since 2018. Hyaluronic acid (HA) was the most commonly used filler, particularly in nasal region injections. The average age of patients was 38, with a notable increase in case reports in 2020. Initial presentation data revealed that 60.9% of patients experienced no light perception, while ptosis and ophthalmoplegia were present in 54.3 and 42.7% of cases, respectively. The statistical and machine learning analyses did not establish a significant linkage between the HYAL dosage and patient recovery; however, the injection site emerged as a critical determinant.

CONCLUSION

The study concludes that HYAL treatment, while vital for managing complications, varies in effectiveness based on the injection site and the timing of administration. The non-Newtonian characteristics of HA fillers may also affect the incidence of complications. The findings advocate for tailored treatment strategies incorporating individual patient variables, emphasizing prompt and precise intervention to mitigate the adverse effects of soft tissue fillers.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Development of a bioactive tunable hyaluronic-protein bioconjugate hydrogel for tissue regenerative applications

Every year, there are approximately 500 000 peripheral nerve injury (PNI) procedures due to trauma in the US alone. Autologous and acellular nerve grafts are among current clinical repair options; however, they are limited largely by the high costs associated with donor nerve tissue harvesting and implant processing, respectively. Therefore, there is a clinical need for an off-the-shelf nerve graft that can recapitulate the native microenvironment of the nerve. In our previous work, we created a hydrogel scaffold that incorporates mechanical and biological cues that mimic the peripheral nerve microenvironment using chemically modified hyaluronic acid (HA). However, with our previous work, the degradation profile and cell adhesivity was not ideal for tissue regeneration, in particular, peripheral nerve regeneration. To improve our previous hydrogel, HA was conjugated with fibrinogen using Michael-addition to assist in cell adhesion and hydrogel degradability. The addition of the fibrinogen linker was found to contribute to faster scaffold degradation via active enzymatic breakdown, compared to HA alone. Additionally, cell count and metabolic activity was significantly higher on HA conjugated fibrinogen compared previous hydrogel formulations. This manuscript discusses the various techniques deployed to characterize our new modified HA fibrinogen chemistry physically, mechanically, and biologically. This work addresses the aforementioned concerns by incorporating controllable degradability and increased cell adhesivity while maintaining incorporation of hyaluronic acid, paving the pathway for use in a variety of applications as a multi-purpose tissue engineering platform.

Chondrogenic differentiation of mesenchymal stem cells through cartilage matrix-inspired surface coatings

The stem cell niche comprises soluble molecules and extracellular matrix components which provide chemical and mechanical cues that determine the differentiation of stem cells. Here, the effect of polyelectrolyte multilayer (PEM) composition and terminal layer fabricated with layer-by-layer technique (LBL) pairing either hyaluronan [in its native (nHA) and oxidized form (oHA)] or chondroitin sulfate (CS) with type I collagen (Col I) is investigated on chondrogenic differentiation of human umbilical mesenchymal stem cells (hUC-MSCs). Physical studies performed to investigate the establishment and structure of the surface coatings show that PEM composed of HA and Col I show a dominance of nHA or oHA with considerably lesser organization of Col I fibrils. In contrast, distinguished fibrilized Col I is found in nCS-containing PEM. Generally, Col I-terminated PEM promote the adhesion, migration, and growth of hUC-MSCs more than GAG-terminated surfaces due to the presence of fibrillar Col I but show a lower degree of differentiation towards the chondrogenic lineage. Notably, the Col I/nHA PEM not only supports adhesion and growth of hUC-MSCs but also significantly promotes cartilage-associated gene and protein expression as found by histochemical and molecular biology studies, which is not seen on the Col I/oHA PEM. This is related to ligation of HA to the cell receptor CD44 followed by activation of ERK/Sox9 and noncanonical TGF-β signaling-p38 pathways that depends on the molecular weight of HA as found by immune histochemical and western blotting. Hence, surface coatings on scaffolds and other implants by PEM composed of nHA and Col I may be useful for programming MSC towards cartilage regeneration.

Identification of Novel Disease-Relevant Genes and Pathways in the Pathogenesis of Type 1 Diabetes: A Potential Defect in Pancreatic Iron Homeostasis

Multiple pathways contribute to the pathophysiological development of type 1 diabetes (T1D); however, the exact mechanisms involved are unclear. We performed differential gene expression analysis in pancreatic islets of NOD mice versus age-matched congenic NOD.B10 controls to identify genes that may contribute to disease pathogenesis. Novel genes related to extracellular matrix development and glucagon and insulin signaling/secretion were changed in NOD mice during early inflammation. During "respective" insulitis, the expression of genes encoding multiple chemosensory olfactory receptors were upregulated, and during "destructive" insulitis, the expression of genes involved in antimicrobial defense and iron homeostasis were downregulated. Islet inflammation reduced the expression of Hamp that encodes hepcidin. Hepcidin is expressed in β-cells and serves as the key regulator of iron homeostasis. We showed that Hamp and hepcidin levels were lower, while iron levels were higher in the pancreas of 12-week-old NOD versus NOD.B10 mice, suggesting that a loss of iron homeostasis may occur in the islets during the onset of "destructive" insulitis. Interestingly, we showed that the severity of NOD disease correlates with dietary iron intake. NOD mice maintained on low-iron diets had a lower incidence of hyperglycemia, while those maintained on high-iron diets had an earlier onset and higher incidence of disease, suggesting that high iron exposure combined with a loss of pancreatic iron homeostasis may exacerbate NOD disease. This mechanism may explain the link seen between high iron exposure and the increased risk for T1D in humans.

Hyaluronic Acid: Known for Almost a Century, but Still in Vogue

Hyaluronic acid (HA) has a special position among glycosaminoglycans. As a major component of the extracellular matrix (ECM). This simple, unbranched polysaccharide is involved in the regulation of various biological cell processes, whether under physiological conditions or in cases of cell damage. This review summarizes the history of this molecule’s study, its distinctive metabolic pathway in the body, its unique properties, and current information regarding its interaction partners. Our main goal, however, is to intensively investigate whether this relatively simple polymer may find applications in protecting against ionizing radiation (IR) or for therapy in cases of radiation-induced damage. After exposure to IR, acute and belated damage develops in each tissue depending upon the dose received and the cellular composition of a given organ. A common feature of all organ damage is a distinct change in composition and structure of the ECM. In particular, the important role of HA was shown in lung tissue and the variability of this flexible molecule in the complex mechanism of radiation-induced lung injuries. Moreover, HA is also involved in intermediating cell behavior during morphogenesis and in tissue repair during inflammation, injury, and would healing. The possibility of using the HA polymer to affect or treat radiation tissue damage may point to the missing gaps in the responsible mechanisms in the onset of this disease. Therefore, in this article, we will also focus on obtaining answers from current knowledge and the results of studies as to whether hyaluronic acid can also find application in radiation science.

Increased Plasma Hyaluronan Levels are Associated With Acute Traumatic Coagulopathy

INTRODUCTION

Acute traumatic coagulopathy (ATC) is an endogenous impairment in hemostasis that often contributes to early mortality after trauma. Endothelial glycocalyx damage is associated with trauma-induced coagulation abnormalities; however, the specific relationship between hyaluronan (HA), a key glycocalyx constituent, and ATC has not been evaluated.

METHODS

We performed a secondary analysis of prospectively collected data from a recent study in which trauma patients (>18 years) admitted to our Level I trauma center with an ABC Score≥2 were enrolled. Partial thromboplastin time (PTT), international normalized ratio (INR), and thromboelastography (TEG) parameters were recorded at arrival. Injury characteristics and clinical outcomes were obtained. Plasma HA levels were measured in healthy controls (HC) and in trauma subjects at arrival (t = 0 h) and 12, 24, and 48 h. ATC was defined as admission INR>1.2 or PTT≥36.5 s. Comparisons of HA levels were assessed, and Spearman's correlations were performed between 0 h and 24 h HA levels, coagulation measures and clinical outcomes. P values < 0.05 were considered significant.

RESULTS

Forty-eight trauma patients and 22 controls were enrolled for study. Sixteen trauma subjects were coagulopathic at admission. HA levels in subjects with ATC were higher than non-coagulopathic subjects at all time points and elevated above HC levels at 24 and 48 h. At arrival, HA levels correlated with TEG R-time, PTT, and INR. HA levels at 24 h correlated with increased transfusion requirements and intensive care unit and hospital lengths of stay.

CONCLUSION

Shed HA is associated with early coagulation abnormalities in trauma patients, which may contribute to worse outcomes. These findings highlight the need for additional studies to evaluate the mechanistic role of HA in ATC.

The CNS/PNS Extracellular Matrix Provides Instructive Guidance Cues to Neural Cells and Neuroregulatory Proteins in Neural Development and Repair

Background. The extracellular matrix of the PNS/CNS is unusual in that it is dominated by glycosaminoglycans, especially hyaluronan, whose space filling and hydrating properties make essential contributions to the functional properties of this tissue. Hyaluronan has a relatively simple structure but its space-filling properties ensure micro-compartments are maintained in the brain ultrastructure, ensuring ionic niches and gradients are maintained for optimal cellular function. Hyaluronan has cell-instructive, anti-inflammatory properties and forms macro-molecular aggregates with the lectican CS-proteoglycans, forming dense protective perineuronal net structures that provide neural and synaptic plasticity and support cognitive learning. Aims. To highlight the central nervous system/peripheral nervous system (CNS/PNS) and its diverse extracellular and cell-associated proteoglycans that have cell-instructive properties regulating neural repair processes and functional recovery through interactions with cell adhesive molecules, receptors and neuroregulatory proteins. Despite a general lack of stabilising fibrillar collagenous and elastic structures in the CNS/PNS, a sophisticated dynamic extracellular matrix is nevertheless important in tissue form and function. Conclusions. This review provides examples of the sophistication of the CNS/PNS extracellular matrix, showing how it maintains homeostasis and regulates neural repair and regeneration.

Modulation of Fibrinolytic System Components in Mesothelial Cells by Hyaluronan

← Objective

Hyaluronan (HA) is an important extracellular matrix component and is involved in fluid homeostasis, tissue repair, and response to infections. Previous studies have shown that supplementation of dialysis fluid with high molecular weight HA may have a positive impact on peritoneal solute and fluid transport characteristics. In the present study, we investigated the impact of HA on the synthesis of tissue-type plasminogen activator (t-PA) and its inhibitor, plasminogen activator inhibitor type 1 (PAI-1) in cultured human peritoneal mesothelial cells (MC).

← Methods

Cultured human peritoneal MC isolated from omental tissue were used for the experiments. Concentrations of t-PA and PAI-1 antigens were measured in conditioned media of confluent MC using ELISA. Northern blot analysis was performed to investigate mRNA expression of t-PA, PAI-1, and low-density lipoprotein receptor-related protein.

← Results

Hyaluronan in a concentration as suggested for supplementation of dialysis fluid (10 mg/dL) did not have a significant impact on the synthesis of t-PA or PAI-1 in human MC. However, incubation of MC with higher concentrations of HA (30 – 1000 mg/dL) resulted in a concentration- and time- (8 – 48 hours) dependent decrease in t-PA antigen release and mRNA expression. In contrast, PAI-1 antigen secretion was distinctly but not significantly increased in the presence of HA.

← Conclusion

The expression of t-PA and PAI-1 in MC was not affected by low concentrations of HA. Therefore, it is reasonable to assume that supplementation of dialysis fluid with HA (10 mg/dL) will not decrease mesothelial fibrinolytic activity. Only high concentrations (> 50 mg/dL) may disturb the balance between intraperitoneal generation and degradation of fibrin by decreasing t-PA synthesis.

Evaluation of biomimetic hyaluronic-based hydrogels with enhanced endogenous cell recruitment and cartilage matrix formation

Biomaterials play a pivotal role in cell-free cartilage repair approaches, where cells must migrate through the scaffold, fill the defect, and then proliferate and differentiate facilitating tissue remodeling. Here we used multiple assays to test the influence of chemokines and growth factors on cell migration and cartilage repair in two different hyaluronan (HA)-based hydrogels. We first investigated bone marrow Mesenchymal Stromal Cells (BMSC) migration in vitro, in response to different concentrations of platelet-derived growth factor-BB (PDGF-BB), chemokine ligand 5 (CCL5/RANTES) and stromal cell-derived factor 1 (SDF-1), using a 3D spheroid-based assay. PDGF-BB was selected as most favourable chemotactic agent, and MSC migration was assessed in the context of physical impediment to cell recruitment by testing Fibrin-HA and HA-Tyramine hydrogels of different cross-linking densities. Supplementation of PDGF-BB stimulated progressive migration of MSC through the gels over time. We then investigated in situ cell migration into the hydrogels with and without PDGF-BB, using a cartilage-bone explant model implanted subcutaneously in athymic mice. In vivo studies show that when placed into an osteochondral defect, both hydrogels supported endogenous cell infiltration and provided an amenable microenvironment for cartilage production. These processes were best supported in Fibrin-HA hydrogel in the absence of PDGF-BB. This study used an advanced preclinical testing platform to select an appropriate microenvironment provided by implanted hydrogels, demonstrating that HA-based hydrogels can promote the initial and critical step of endogenous cell recruitment and circumvent some of the clinical challenges in cartilage tissue repair. STATEMENT OF SIGNIFICANCE: The challenge of articular cartilage repair arises from its complex structure and architecture, which confers the unique mechanical behavior of the extracellular matrix. The aim of our research is to identify biomaterials for implants that can support migration of endogenous stem and progenitor cell populations from cartilage and bone tissue, in order to permanently replace damaged cartilage with the original hyaline structure. Here, we present an in vitro 3D spheroid-based migration assay and an osteochondral defect model, which provide the opportunity to assess biomaterials and biomolecules, and to get stronger experimental evidence of the not well-characterized dynamic process of endogenous cells colonization in an osteochondral defect. Furthermore, the delicate step of early cell migration into biomaterials towards functional tissue engineering is reproduced. These tests can be used for pre-clinical testing of newly developed material designs in the field of scaffold engineering.

A placebo-controlled study comparing the efficacy of intra-articular injections of hyaluronic acid and a novel hyaluronic acid-platelet-rich plasma conjugate in a canine model of osteoarthritis

Background

The objective of this study was to assess the efficacy of intra-articular injections of hyaluronic acid (HA) and a novel, on-site conjugate of HA with autologous fibrinogen in platelet-rich plasma (HA-PRP) in a canine model of osteoarthritis (OA)

Methods

Twelve beagle dogs underwent a unilateral resection of the cranial cruciate ligament (CrCL) of the stifle joint. Clinical and radiographic signs of OA were confirmed in all dogs 8 weeks following CrCL resection and prior to treatment. The dogs were randomized into three groups: saline (n = 4), HA (n = 4), and HA-PRP (n = 4). Each dog received intra-articular injections of the respective substance into the affected joint at pre-determined time points. The dogs were assessed for adverse effects for 3 days after each injection and for lameness, pain, range of motion, kinetics, and radiographic OA severity prior to treatment and 3 months after injection. OA severity as determined by radiographic examination was not significantly different among the groups at any time point. The dogs were then humanely euthanatized and the stifle joint assessed by gross and histological examinations.

Results

Dogs treated with four weekly injections of HA or two biweekly injections of HA-PRP were significantly (p < 0.05) better than dogs treated with four weekly injections of saline at 2-, 4-, and 12-week time points based on a comfortable range of motion (CROM) and clinical lameness score. Gait analysis measuring symmetry and weight distribution on pressure sensor walkway showed significantly (p < 0.05) improved limb function for dogs treated with HA and HA-PRP compared with dogs treated with saline yet with better clinical outcome for the HA-PRP-treated group at 12 and 20 weeks follow-up. Gross and histological analysis of synovium and articular cartilage demonstrated significant (p < 0.05) improvement by both treatments groups compared to controls. There was however significantly (p < 0.05) less damage to the cartilage in the HA-PRP group compared to the HA-treated group.

Conclusions

These data suggest that while injection of HA and HA-PRP may be sufficient for short-term amelioration of the symptoms associated with OA, treatment with HA-PRP conjugates may be superior, providing significantly better long-term cartilage preservation.

Biofabrication of phenotypic pulmonary fibrosis assays

Biofabrication techniques have enabled the formation of complex models of many biological tissues. We present a framework to contextualize biofabrication techniques within a disease modeling application. Fibrosis is a progressive disease interfering with tissue structure and function, which stems from an aberrant wound healing response. Epithelial injury and clot formation lead to fibroblast invasion and activation, followed by contraction and remodeling of the extracellular matrix. These stages have healthy wound healing variants in addition to the pathogenic analogs that are seen in fibrosis. This review evaluates biofabrication of a variety of phenotypic cell-based fibrosis assays. By recapitulating different contributors to fibrosis, these assays are able to evaluate biochemical pathways and therapeutic candidates for specific stages of fibrosis pathogenesis. Biofabrication of these culture models may enable phenotypic screening for improved understanding of fibrosis biology as well as improved screening of anti-fibrotic therapeutics.

Characterisation and the effects of bilirubin binding to human fibrinogen

Fibrinogen, a protein involved in blood coagulation, is very susceptible to oxidation. Oxidation alters its function and usually makes it more thrombogenic. Bilirubin, an end-product of the haem degradation in vertebrates, is known for its antioxidant properties. The present paper describes interaction between fibrinogen and bilirubin, and the influence of bilirubin on the formation of fibrin and protection against oxidation. The binding constant of 4.5 × 10⁴ M^-1 was determined for the fibrinogen/bilirubin complex at 37 °C. There is no change in secondary and tertiary structure of fibrinogen or its thermal stability upon bilirubin binding. The binding site of fibrinogen is not stereospecific for bilirubin and is able to accommodate both bilirubin conformers. A change in absorption maximum of bilirubin occurs upon its interaction with fibrinogen, suggesting an alteration in the conformation of bilirubin to the more cyclic one. Bilirubin exerts antioxidant effect on fibrinogen, preventing its carbonylation and aggregation. The presence of bilirubin induces the formation of fibrin with thicker fibres, as assessed by the coagulation assay. Fibrinogen and bilirubin interact at physiological concentrations, bilirubin may act as an antioxidant for fibrinogen and may modulate an important event in haemostasis, which altogether suggests possible physiological relevance of this interaction.

Multifunctional magnetic-responsive hydrogels to engineer tendon-to-bone interface

Photocrosslinkable magnetic hydrogels are attracting great interest for tissue engineering strategies due to their versatility and multifunctionality, including their remote controllability ex vivo, thus enabling engineering complex tissue interfaces. This study reports the development of a photocrosslinkable magnetic responsive hydrogel made of methacrylated chondroitin sulfate (MA-CS) enriched with platelet lysate (PL) with tunable features, envisioning their application in tendon-to-bone interface. MA-CS coated iron-based magnetic nanoparticles were incorporated to provide magnetic responsiveness to the hydrogel. Osteogenically differentiated adipose-derived stem cells and/or tendon-derived cells were encapsulated within the hydrogel, proliferating and expressing bone- and tendon-related markers. External magnetic field (EMF) application modulated the swelling, degradation and release of PL-derived growth factors, and impacted both cell morphology and the expression and synthesis of tendon- and bone-like matrix with a more evident effect in co-cultures. Overall, the developed magnetic responsive hydrogel represents a potential cell carrier system for interfacial tissue engineering with EMF-controlled properties.

Fabrication and characteristics of dual functionalized vascular stent by spatio-temporal coating

Stent implantation with balloon angioplasty is a widely used treatment for coronary artery diseases. Stents have been developed from bare metal stent (BMS) to advanced forms such as drug-eluting stent (DES). However, modern DES still causes thrombosis and/or in-stent restenosis as long-term outcomes. For effective prevention of these problems, we fabricated a dual functionalized stent using spatio-temporal coating, which has two different surfaces, as a novel type of DES. Hyaluronic acid conjugated with dopamine (HA-DA) was applied to a bare cobalt-chromium (CC) stent prior to abluminal coating of sirolimus (SRL)-in-polymer such as poly(d,l-lactide). The SRL-in-polymer (P+S) coated on the abluminal surface of the HA-DA modified stent showed highly stable coating layer and prevented the crack formation after ballooning. In the blood- and cyto-compatibility tests, HA-DA coating displayed suppressive effects on adhesion and activation of platelets and maintained the cell viability and proliferation of human coronary artery endothelial cells even under the existence of SRL. In in vivo study using porcine restenosis model, the neointimal area and inflammation score of the dual functionalized stent with HA-DA and P+S were significantly reduced than those of BMS. It is expected that this novel type of DES can be effectively applied to utilize diverse anti-proliferative drugs and bioactive polymers.

STATEMENT OF SIGNIFICANCE

Stents have been developed from bare metal stent to advanced forms such as drug-eluting stents (DESs). However, even DESs can still cause in-stent restenosis as long-term outcomes. This paper demonstrated a novel DES using spatio-temporal coating by dopamine-mediated hyaluronic acid coating (HA-DA) before asymmetric coating of sirolimus-in-poly(d,l-lactide) (P+S). It showed stable coating surface and prevented crack formation after ballooning. HA-DA coating also had an inhibitive effect on adhesion of platelets and maintained cell viability of endothelial cells even under the existence of sirolimus. Additionally, in vivo neointima area and inflammation score of HA-DA/P+S stent significantly decreased than those of BMS. We expected that this novel type of DES can be effectively applied to introduce diverse anti-proliferative drugs and bioactive molecules.

Carbohydrate-binding activities of coagulation factors fibrinogen and fibrin

The coagulation factors fibrinogen and fibrin play important roles in the final stage of the blood coagulation cascade. It has not been revealed whether fibrinogen has lectin activity or not. Here we demonstrate that fibrinogen and fibrin have carbohydrate-specific binding activities that inhibit fibrin clot formation. A solid-phase binding study using sugar-biotinyl polymer probes revealed that fibrinogen has the highest affinity to mannose (Man) in both the presence and absence of 5 mM Ca(2+). Fibrin, which is proteolytically produced from fibrinogen by thrombin, binds to the same sugar residues as fibrinogen in the presence of 5 mM Ca(2+), while it markedly binds to N-acetylneuraminic acid in the absence of Ca(2+). Thrombin-induced fibrin polymerization was monitored by turbidity at 350 nm. In the presence of Ca(2+), Man and sugars having N-acetyl groups were found to inhibit the increase in turbidity, but only Man inhibited it in the absence of Ca(2+). Scanning electron microscopy observation of fibrin clots formed in the presence of various sugars showed that fibrin fibers formed in the presence of Man and N-acetyl group sugars were thinner and more branched. In contrast, thrombin has neither carbohydrate-binding activity nor is affected by sugars. These results suggest that carbohydrates and glycoconjugates may regulate fibrin clot formation in vivo.

A two-component pre-seeded dermal-epidermal scaffold

We have developed a bilayered dermal-epidermal scaffold for application in the treatment of full-thickness skin defects. The dermal component gels in situ and adapts to the lesion shape, delivering human dermal fibroblasts in a matrix of fibrin and cross-linked hyaluronic acid modified with a cell adhesion-promoting peptide. Fibroblasts were able to form a tridimensional matrix due to material features such as tailored mechanical properties, presence of protease-degradable elements and cell-binding ligands. The epidermal component is a robust membrane containing cross-linked hyaluronic acid and poly-l-lysine, on which keratinocytes were able to attach and to form a monolayer. Amine-aldehyde bonding at the interface between the two components allows the formation of a tightly bound composite scaffold. Both parts of the scaffold were designed to provide cell-type-specific cues to allow for cell proliferation and form a construct that mimics the skin environment.

Platelet hyaluronidase-2: an enzyme that translocates to the surface upon activation to function in extracellular matrix degradation

Following injury, platelets rapidly interact with the exposed extracellular matrix (ECM) of the vessel wall and the surrounding tissues. Hyaluronan (HA) is a major glycosaminoglycan component of the ECM and plays a significant role in regulating inflammation. We have recently reported that human platelets degrade HA from the surfaces of activated endothelial cells into fragments capable of inducing immune responses by monocytes. We also showed that human platelets contain the enzyme hyaluronidase-2 (HYAL2), one of two major hyaluronidases that digest HA in somatic tissues. The deposition of HA increases in inflamed tissues in several inflammatory diseases, including inflammatory bowel disease (IBD). We therefore wanted to define the mechanism by which platelets degrade HA in the inflamed tissues. In this study, we show that human platelets degrade the proinflammatory matrix HA through the activity of HYAL2 and that platelet activation causes the immediate translocation of HYAL2 from a distinct population of α-granules to platelet surfaces where it exerts its catalytic activity. Finally, we show that patients with IBD have lower platelet HYAL2 levels and activity than healthy controls.

Artificial microniches for probing mesenchymal stem cell fate in 3D

Droplet microfluidics is combined with bio-orthogonal thiol-ene click chemistry to fabricate micrometer-sized, monodisperse fibrinogen-containing hyaluronic acid hydrogel microbeads in a mild, radical-free procedure in the presence of human mesenchymal stem cells (hMSCs). The gel beads serve as microniches for the 3D culture of single hMSCs, containing hyaluronic acid and additional fibrinogen for cell surface binding, and they are porous and stable in tissue culture medium for up to 4 weeks with mechanical properties right in the range of soft solid tissues (0.9-9.2 kPa). The encapsulation procedure results in 70% viable hMSCs in the microbeads after 24 hours of culture and a very high degree of viability of the cells after long term culture of 2 weeks. hMSCs embedded in the microniches display an overall rounded morphology, consistent with those previously observed in 3D culture. Upon induction, the multipotency and differentiation potential of the hMSCs are characterized by staining of corresponding biomarkers, demonstrating a clear heterogeneity in the cell population. These hydrogel microbeads represent a versatile microstructured material platform with great potential for studying the differences of material cues and soluble factors in stem cell differentiation in a 3D tissue-like environment at the single cell level.

A fibrin/hyaluronic acid hydrogel for the delivery of mesenchymal stem cells and potential for articular cartilage repair

Background

Osteoarthritis (OA) is a degenerative joint disease affecting approximately 27 million Americans, and even more worldwide. OA is characterized by degeneration of subchondral bone and articular cartilage. In this study, a chondrogenic fibrin/hyaluronic acid (HA)-based hydrogel seeded with bone marrow-derived mesenchymal stem cells (BMSCs) was investigated as a method of regenerating these tissues for OA therapy. This chondrogenic hydrogel system can be delivered in a minimally invasive manner through a small gauge needle, forming a three-dimensional (3D) network structure in situ. However, an ongoing problem with fibrin/HA-based biomaterials is poor mechanical strength. This was addressed by modifying HA with methacrylic anhydride (MA) (HA-MA), which reinforces the fibrin gel, thereby improving mechanical properties. In this study, a range of fibrinogen (the fibrin precursor) and HA-MA concentrations were explored to determine optimal conditions for increased mechanical strength, BMSC proliferation, and chondrogenesis potential in vitro.

Results

Increased mechanical strength was achieved by HA-MA reinforcement within fibrin hydrogels, and was directly correlated with increasing HA-MA concentration. Live/dead staining and metabolic assays confirmed that the crosslinked fibrin/HA-MA hydrogels provided a suitable 3D environment for BMSC proliferation. Quantitative polymerase chain reaction (qPCR) of BMSCs incubated in the fibrin/HA-MA hydrogel confirmed decreased expression of collagen type 1 alpha 1 mRNA with an increase in Sox9 mRNA expression especially in the presence of a platelet lysate, suggesting early chondrogenesis.

Conclusion

Fibrin/HA-MA hydrogel may be a suitable delivery method for BMSCs, inducing BMSC differentiation into chondrocytes and potentially aiding in articular cartilage repair for OA therapy.

Synovium-derived mesenchymal stem cells encapsulated in a novel injectable gel can repair osteochondral defects in a rabbit model

We developed a novel injectable type I collagen/hyaluronic acid/fibrinogen (COL/HA/FG) composite gel that encapsulated synovium-derived mesenchymal stem cells (SDSCs) for the repair of damaged articular cartilage. We first analyzed the suitability of the composite gel as a three-dimensional injectable cell carrier in vitro. In an in vivo rabbit model, the COL/HA/FG composite gel displayed the potential to regenerate and repair osteochondral defects in the knee. Culture of the SDSCs encapsulated COL/HA/FG composite gel in a chondrogenic medium resulted in high viability of the SDSCs and high expressions of type II collagen, aggrecan, and sox 9 mRNA. Moreover, glycosaminoglycans and type II collagen were accumulated within the extracellular matrix. In the animal model, the SDSCs encapsulated COL/HA/FG composite gel produced a hyaline-like cartilage construct. Twenty-four weeks after transplantation, the defects had been repaired with hyaline cartilage-like tissue that was densely stained by safranin-O and immunostained by a type II collagen antibody. This data suggest that the SDSC-encapsulated COL/HA/FG composite gel can be a good therapeutic candidate/strategy for repairing of damaged articular cartilage.

A rationale for delivery of osteoinductive proteins

Highly pure, recombinant human osteoinductive proteins make it possible to consider programmable osteoneogenesis. Until recently, it was believed that a bioresorbable excipient or physiologic solution would suffice to transport osteoinductive agents from source to wound. After considering surgical requirements, particular bone wound circumstances, scarcity of collateral circulation, phenotype plasticity of mesenchymal progenitor cells, and the morphogens' pleiotrophic effects, it becomes clear that the issue of controlled, programmable osteoneogenesis is a more complicated proposition than can be addressed solely by application of osteoinductive protein. The essential characteristics of a manufactured bone graft substitute (BGS) device are dictated by demands placed on such a device by the surgeons who will employ them and the cells that will occupy them. This review outlines a design process for BGS devices that (1) begins by surveying BGS requirements gathered from the literature from 1991 to 1995, (2) briefly reviews recent in vitro studies of rhBMP-2 and OP- 1, (3) describes commonly encountered circumstances of recipient wound beds, (4) describes behaviors of mesenchymal cells involved in connective tissue repair and regeneration, and (5) concludes with a rationale for design of an osteoinductive bone graft substitute. Emerging from this process is a composite device consisting of a bioresorbable structural polymer, a filamentous velour of hyaluronan (HY), and an osteoinductive protein. The structural polymer, D,D-L,L-polylactic acid, fabricated in the architecture of cancellous bone, is capable of maintaining its structural and architectural properties after being thoroughly saturated with water. Within its interstices is located a filamentous velour of hyaluronan which, when fully hydrated, becomes a viscoelastic gel. It is anticipated that the osteoinductive protein will either be carried on the dried hyaluronic acid velour or in solution via the viscoelastic HY gel.

Stiffness and heterogeneity of the pulmonary endothelial glycocalyx measured by atomic force microscopy

The mechanical properties of endothelial glycocalyx were studied using atomic force microscopy with a silica bead (diameter ∼18 μm) serving as an indenter. Even at indentations of several hundred nanometers, the bead exerted very low compressive pressures on the bovine lung microvascular endothelial cell (BLMVEC) glycocalyx and allowed for an averaging of stiffness in the bead-cell contact area. The elastic modulus of BLMVEC glycocalyx was determined as a pointwise function of the indentation depth before and after enzymatic degradation of specific glycocalyx components. The modulus-indentation depth profiles showed the cells becoming progressively stiffer with increased indentation. Three different enzymes were used: heparinases III and I and hyaluronidase. The main effects of heparinase III and hyaluronidase enzymes were that the elastic modulus in the cell junction regions increased more rapidly with the indentation than in BLMVEC controls, and that the effective thickness of glycocalyx was reduced. Cytochalasin D abolished the modulus increase with the indentation. The confocal profiling of heparan sulfate and hyaluronan with atomic force microscopy indentation data demonstrated marked heterogeneity of the glycocalyx composition between cell junctions and nuclear regions.

Advantages of hyaluronic acid as a component of fibrin sheet for care of acute wound

Skin injury is followed by accumulation of a fibrin based provisional matrix which normally drives the process of wound repair. Exogenous fibrin with extra cellular matrix (ECM) components can also favor the wound healing process. In a preliminary study we found that lyophilized fibrin sheet (FS) arrest bleeding from rabbit skin wound but it remained dry during the repair period and did not accelerate the healing process better than untreated control. In the current study, hyaluronic acid (HA) was incorporated into FS and the resultant HA-FS promoted water retention and improved wound healing process. Gross-morphology, histopathology and histomorphometry were employed to compare qualitative and quantitative difference of wound healing in treated group against controls. In experimental sites (HA-FS), re-epithelialization was completed by 14 days with neo-vascularization and deposition of wavy bundles of collagen in the treated sites. Rate of healing process was different in treated and untreated wounds and most striking difference was the appearance of appendages, sebaceous gland and hair follicle at some locations in HA-FS treated sites. Therefore, HA with fibrin can create an effective wound care matrix which promotes water retention and wound healing potential.

Hyaluronan (HA) deposition precedes and promotes leukocyte recruitment in intestinal inflammation

Increased hyaluronan (HA) deposition is a common feature of inflamed tissues, including inflammatory bowel disease (IBD)-involved intestines. However, whether HA accumulation promotes or is the result of intestinal inflammation is unknown. Using the mouse dextran sulfate sodium (DSS)-induced experimental model of colitis, we investigated changes in HA deposition in the colon over time in conjunction with evolving pathological changes of tissue architecture. Profound changes in colon HA deposition occurred within 3-7 days of oral DSS administration and, more important, they preceded the inflammatory infiltrate. Interestingly, HA deposition within blood vessels of the colon is observed as early as 3 days during the course of colitis induction, well before any significant inflammatory infiltrate. HA deposition is also observed in blood vessels of inflamed human colon of IBD patients. We determined that human intestinal endothelial cells generate HA in response to proinflammatory stimuli by demonstrating a TNF-alpha-induced increase in hyaluronan synthase-3 mRNA expression and the accumulation of HA cable-like structures that are adhesive for leukocytes. Additionally, IBD mucosal endothelial cells produce higher levels of cell surface HA in response to TNF-alpha than non-IBD control cells. Therefore, HA deposition is an early event in inflamed gut tissue, preceding and likely promoting leukocyte infiltration.

Platelet-derived hyaluronidase 2 cleaves hyaluronan into fragments that trigger monocyte-mediated production of proinflammatory cytokines

Hyaluronan (HA) occurs in the body as a large, hydrating, space-filling, carbohydrate polymer in the extracellular matrix; it has both anti-angiogenic and immunosuppressive properties. Cleavage of HA results in the generation of variably sized fragments that stimulate multiple angiogenic and inflammatory responses in a size-specific manner. In this study, we report that platelets, as well as their megakaryocyte precursors, are unusual among somatic cells in that they contain only hyaluronidase 2 (HYAL2) but not HYAL1. Platelet HYAL2 is sufficient to cleave HA into fragments that are specific for inflammatory and angiogenic signaling; this process occurs in the absence of HYAL1, which is necessary in all other tissues to perform further HA degradation. Platelets can bind to HA, some of which derives from the stressed microvessel endothelial cell surface. Platelet-derived HYAL2 cleaves HA into fragments that stimulate mononuclear leukocytes in the immediate microenvironment to produce proinflammatory cytokines, including interleukin-6 and interleukin-8. Platelets, thus, are not only involved in hemostasis, the earliest step in wound healing, but are also important in the signaling of subsequent inflammatory and angiogenic steps. We hypothesize that aberrations in these sequential steps can promote chronic inflammation, as found in inflammatory bowel disease. The platelet may thus provide an interface between acute and chronic inflammation, wound healing, and their subsequent fibrotic responses.

The specific interaction between fibrin(ogen) and hyaluronan: possible consequences in haemostasis, inflammation and wound healing

We have proposed that fibrin and hyaluronan (HA) are macromolecular regulators during inflammation and wound healing. Here we extend our studies to characterize the specific interaction between fibrin(ogen) and HA. 125I-labelled HA (Mr approximately 32,000) was bound by plastic surfaces coated with human fibrinogen but not bovine serum albumin, ovalbumin, beta-lactoglobin or rabbit immunoglobulin G. 125I-labelled fibrinogen bound to a unique hexylamine derivative of HA coupled to Sepharose and was eluted specifically by HA oligosaccharides in a size-dependent manner. A dot blot assay, in which proteins are adsorbed to nitrocellulose and probed with 125I-HA, also showed specific binding to human fibrinogen. This assay was used to examine fibrinogens from other mammalian species. No specific 125I-HA binding was observed with the protein from horse, rat or cow. Significant binding was detected with human, sheep, rabbit, dog, baboon, goat and pig fibrinogens. Thrombin-induced formation of fibrin clots is also affected by HA, which decreases the lag time before clotting and increases the rate of clot formation. The rate of fibrin polymerization increased over 500% in the presence of 60 microM HA. Furthermore, the structure of the fibrin gel, as assessed by light scattering, was altered by HA or chondroitin sulphate in a concentration-dependent manner. The results support the proposed wound-healing model and indicate that an increase in circulating HA levels could adversely affect haemostasis and increase the risk of thrombosis or bleeding. The interaction between HA and fibrinogen emphasizes the importance of the liver endothelial cell HA receptor in the removal of glycosaminoglycans from the blood. Cultured cells continuously endocytosing 125I-HA for 4 h reutilized their total cellular HA receptors at least once every 50 min even in the presence of cycloheximide. This endocytotic receptor was therefore shown to be part of a recycling system.

The many ways to cleave hyaluronan

Hyaluronan is being used increasingly as a component of artificial matrices and in bioengineering for tissue scaffolding. The length of hyaluronan polymer chains is now recognized as informational, involving a wide variety of size-specific functions. Inadvertent scission of hyaluronan can occur during the process of preparation. On the other hand, certain size-specific hyaluronan fragments may be desirable, endowing the finished bioengineered product with specific properties. In this review, the vast arrays of reactions that cause scission of hyaluronan polymers is presented, including those on an enzymatic, free radical, and chemical basis.

Hyaluronan levels during laparoscopic versus open colonic resections

BACKGROUND

Plasma hyaluronan binds to fibrinogen, affecting intravascular fibrin polymerization and fibrin clot formation. It has been hypothesized that alterations in fibrin clot formation influence the risk of thromboembolism in those undergoing surgery. The aim of this study is to quantify the intravascular components, especially plasma hyaluronan levels, in laparoscopic and conventional colorectal resections that contribute to thromboembolism formation.

METHODS

Prospective cohort analysis of consecutive patients which were participating in the prospective randomized multi-center trial Lapkon II comparing the long-term effects of laparoscopic and conventional resection for colon cancer. Plasma samples were obtained from 15 patients at the beginning and the end of laparoscopic or conventional colorectal resections. Concentrations and activities of tissue plasminogen activator(t-PA), plasminogen activator inhibitor type 1(PAI-1), t-PA/PAI complex, fibrinogen, d-dimers and hyaluronan were determined by using commercial enzyme-linked immunosorbent assay (ELISA) kits.

RESULTS

No differences in age, sex and type of resection between the laparoscopic and conventional-surgery groups were observed. Laparoscopic procedures lasted longer (p < 0.05). Concentration and activities of t-PA, PAI-1, t-PA/PAI complex, fibrinogen and d-dimers did not vary between the two groups. Plasma hyaluronan decreased from 28.6 to 17.9 IU/ml (p < 0.05) during laparoscopic compared to conventional procedures. Plasma hyaluronan levels were significantly different at the end of operation between the two groups (p < 0.05) .

CONCLUSIONS

Plasma hyaluronan levels were decreased in patients undergoing laparoscopic colorectal resections, compared to those undergoing conventional procedures. Therefore, interactions between plasma hyaluronan and fibrinogen may be lower, with a sequential decrease in fibrin polymerization, and a possibly reduced risk of deep venous thrombosis.

Improved growth factor directed vascularization into fibrin constructs through inclusion of additional extracellular molecules

Using the chick chorioallantoic membrane assay (CAM) and a novel histological technique, we investigated the ability of blood vessels to directly invade fibrin-based scaffolds. In our initial experiments utilizing vascular endothelial growth factor (VEGF(165)), we found no direct invasion. Instead, the fibrin was completely degraded and replaced with highly vascularized new tissue. Addition of fibroblast growth factor-2 (FGF-2), bone morphogenic protein-2 (BMP-2), or platelet-derived growth factor-BB (PDGF-BB) to the fibrin construct also did not result in construct vascularization. Because natural and regenerating tissues exhibit complex extracellular matrices (ECMs), we hypothesized that a more complex scaffold may improve blood vessel invasion. Addition of fibronectin, hyaluronic acid, and collagen type I within 20 mg/mL fibrin constructs resulted in no significant improvement. However, the same additive concentrations within 10 mg/mL fibrin constructs resulted in dramatic improvements, specifically with hyaluronic acid. Overall, we believe that these results indicate the importance of structural and functional cues of not only in the initial scaffold but also as the construct is degraded and remodeled. Furthermore, the CAM assay may represent a useful model for understanding ECM interactions as well as for screening and designing tissue-engineered scaffolds.

Investigating the Interactions of Hyaluronan Derivatives with Biomolecules. The Use of Diffusional NMR Techniques

[Chemical structure: see text] The interactions between a biomaterial and biomolecules present in body fluids often determine the fate of the biomaterial. This paper presents a study on hyaluronan (HA)-containing materials (in soluble or colloidal form) that focuses on their interactions with lipids and proteins and for the first time uses PFG NMR as an analytical technique for probing these events. The interactions of HA-based polymers with phospholipids (DPPC and DPPG liposomes) are shown to depend both on charge and hydrophobicity factors. Despite the difference in behavior between albumin (substantially non-adhesive) and fibrinogen (adhesive), the interactions of the polymers with proteins do not seem to be based on hydrophobic effects but on surface polar interactions.

Tissue-engineered Cartilage Using Fibrin/Hyaluronan Composite Gel and Its In Vivo Implantation

The importance of scaffold biomaterials has been emphasized for in vitro culture of tissue-engineered cartilage in a three-dimensional (3D) environment. In this study, we examined the feasibility of fibrin glue, mixed with hyaluronic acid (HA) as a composite scaffold. Fibrin glue has been a useful cell delivery matrix for cartilage tissue engineering and HA is a key component of normal articular cartilage. Our hypothesis is that compared to fibrin itself, a fibrin/HA composite can have significantly enhanced properties, due mainly to the added benefits of HA in the matrix. Pieces of cartilage were isolated from rabbit knees and the chondrocytes were harvested through enzymatic digestion. Both fibrin and fibrin/HA composite were prepared and subsequently implanted in nude mice (n = 9, each group) for 1, 2, and 4 weeks, respectively. The retrieved specimens were then analyzed and the results were compared. Cartilage-like tissue formation was detected earlier with fibrin/HA specimens. They produced significantly higher amounts of the extracellular matrix (ECM) molecules, GAG, and collagen at each time point than those in fibrin. Interestingly, the fibrin/HA composite was also competent in maintaining its initial size. Histology--Safranin O/fast green and Alcian blue--of the retrieved specimens found more intense, uniform staining in the fibrin/HA composites. Analysis of the gene expression of the ECM molecules also confirmed the benefits of the composite with added HA in the maintenance of phenotypic stability. The present study suggests that fibrin/HA composite may serve as a dependable cell delivery vehicle as well as a structural basis for tissue-engineered cartilage.

Analysis of the interaction between hyaluronan and hyaluronan-binding proteins by capillary affinity electrophoresis: significance of hyaluronan molecular size on binding reaction

We developed a method for the analysis of the interaction between hyaluronan (HA) oligosaccharides and hyaluronan-binding proteins (HABPs) using capillary affinity electrophoresis (CAE). The method is based on high-resolution separation of fluorescent-labeled HA molecules in the presence of hyaluronan-binding proteins at different concentrations by capillary electrophoresis (CE) with laser-induced fluorescent detection. Hyaluronan-binding protein from bovine nasal cartilage interacts strongly with HA decasaccharide or larger oligosaccharides. Effect of the molecular size of HA oligomers clearly showed that longer carbohydrate chains than decasaccharide were required for recognition by HA binding protein. Interestingly, the interaction did not cause retardation of HA oligomers as observed in many binding reactions such as the interaction between pharmaceuticals and serum albumin, but showed disappearance of the oligomer peak. Although we cannot explain the accurate mechanism on the interaction, disappearance is probably due to low equilibrium rate between free and conjugate states. The present technique will be useful to compare the relative binding affinity, and to understand the mechanism on the interaction between hyaluronan and hyaluronan-binding proteins.

Endocytic function, glycosaminoglycan specificity, and antibody sensitivity of the recombinant human 190-kDa hyaluronan receptor for endocytosis (HARE)

The human hyaluronan receptor for endocytosis (hHARE) mediates the endocytic clearance of hyaluronan (HA) and chondroitin sulfate from lymph fluid and blood. Two hHARE isoforms (190 and 315 kDa) are present in sinusoidal endothelial cells of liver, spleen, and lymph nodes (Zhou, B., McGary, C. T., Weigel, J. A., Saxena, A., and Weigel, P. H. (2003) Glycobiology 13, 339-349). Here we report the specificity and function of the 190-kDa HARE, expressed without the larger isoform, in Flp-In 293 cell lines (190hHARE cells). Like the native protein, recombinant hHARE contains approximately 25 kDa of N-linked oligosaccharides, binds HA in a ligand blot assay, cross-reacts with three anti-rat HARE monoclonal antibodies, and is inactivated by reduction. The 190hHARE cell lines mediated rapid, continuous (125)I-HA endocytosis and degradation for >1 day. About 30-50% of the total cellular receptors were on the cell surface, and their recycling time for reutilization was approximately 8.5 min. The average K(d) for the binding of HA to the 190-kDa hHARE at 4 degrees C was 7 nm with 118,000 total HA binding sites per cell. Competition studies at 37 degrees C indicated that the 190-kDa hHARE binds HA and chondroitin better than dermatan sulfate and chondroitin sulfates A, C, D, and E, but it does not bind to heparin, heparan sulfate, or keratan sulfate. Although competition was observed at 37 degrees C, none of the glycosaminoglycans tested, except HA, competed for (125)I-HA binding by 190hHARE cells at 4 degrees C. Anti-HARE monoclonal antibodies #30 and #154, which do not inhibit (125)I-HA uptake mediated by the 175-kDa rat HARE, partially blocked HA endocytosis by the 190-kDa hHARE. We conclude that the 190-kDa hHARE can function independently of other hHARE isoforms to mediate the endocytosis of multiple glycosaminoglycans. Furthermore, the rat and human small HARE isoforms have different glycosaminoglycan specificities and sensitivities to inhibition by cross-reacting antibodies.

Characterization of the recombinant rat 175-kDa hyaluronan receptor for endocytosis (HARE)

Hyaluronan (HA) and chondroitin sulfate (CS) clearance from lymph and blood in mammals is mediated by the HA receptor for endocytosis (HARE), which is present as two isoforms in rat and human (175/300 kDa and 190/315 kDa, respectively) in the sinusoidal endothelial cells of liver, spleen, and lymph nodes (Zhou, B., McGary, C. T., Weigel, J. A., Saxena, A., and Weigel, P. H. (2003) Glycobiology 13, 339-349). The small rat and human HARE proteins are not encoded directly by mRNA but are derived from larger precursors. Here we characterize the specificity and function of the 175-kDa HARE, expressed in the absence of the 300-kDa species, in stably transfected SK-Hep-1 cells. The HARE cDNA was fused with a leader sequence to allow correct orientation of the membrane protein. The recombinant rHARE contained approximately 25 kDa of N-linked oligosaccharides and, like the native protein, was able to bind HA in a ligand blot assay, even after de-N-glycosylation. SK-HARE cell lines demonstrated specific 125I-HA endocytosis, receptor recycling, and delivery of HA to lysosomes for degradation. The Kd for the binding of HA (number-average molecular mass approximately 133 kDa) to the 175-kDa HARE at 4 degrees C was 4.1 nm with 160,000 to 220,000 HA-binding sites per cell. The 175-kDa rHARE binds HA, dermatan sulfate, and chondroitin sulfates A, C, D, and E, but not chondroitin, heparin, heparan sulfate, or keratan sulfate. Surprisingly, recognition of glycosaminoglycans (GAGs) other than HA by native or recombinant HARE was temperature-dependent. Although competition was observed at 37 degrees C, none of the other GAGs competed for 125I-HA binding to SK-HARE cells at 4 degrees C. Anti-HARE monoclonal antibody-174 showed a similar temperature-dependence in its ability to block HA endocytosis. These data suggest that temperature-induced conformational changes may alter the GAG specificity of HARE. The results confirm that the 175-kDa rHARE does not require the larger HARE isoform to mediate endocytosis of multiple GAGs.

Study of Hyaluronan-Binding Proteins and Receptors Using Iodinated Hyaluronan Derivatives

This chapter detailed methodology for the purification of high molecular weight HA, as well as procedures to fragment the HA to prepare large oligosaccharides in the range of 40,000-80,000 Da. The aforementioned procedures used to prepare HA-alkylamine and HA-Bolton-Hunter adducts, as well as 125I-labeled HA, have been very reproducible, and the latter preparations are of adequate length to retain high-affinity interactions and specific binding, e.g., to human fibrinogen and HARE. For example, we were able to isolate, characterize, and clone the rat HARE using 125I-labeled HA initially with the dot blot assay to monitor solubilization and partial purification, and later with the ligand blot assay, to identify the protein after SDS-PAGE. The ligand blot assay enabled us to determine that HARE is actually present as two discrete isoreceptors of different molecular masses. These techniques should provide a means to analyze purification strategies and to characterize additional HA receptors and binding proteins involved in a variety of physiologic processes.