Hyaluronan, heterogeneity, and healing: The effects of ultrapure hyaluronan of defined molecular size on the repair of full-thickness pig skin wounds

Hyaluronic Acid: Molecular Mechanisms and Therapeutic Trajectory

Hyaluronic acid (also known as hyaluronan or hyaluronate) is naturally found in many tissues and fluids, but more abundantly in articular cartilage and synovial fluid (SF). Hyaluronic acid (HA) content varies widely in different joints and species. HA is a non-sulfated, naturally occurring non-protein glycosaminoglycan (GAG), with distinct physico-chemical properties, produced by synoviocytes, fibroblasts, and chondrocytes. HA has an important role in the biomechanics of normal SF, where it is partially responsible for lubrication and viscoelasticity of the SF. The concentration of HA and its molecular weight (MW) decline as osteoarthritis (OA) progresses with aging. For that reason, HA has been used for more than four decades in the treatment of OA in dogs, horses and humans. HA produces anti-arthritic effects via multiple mechanisms involving receptors, enzymes and other metabolic pathways. HA is also used in the treatment of ophthalmic, dermal, burns, wound repair, and other health conditions. The MW of HA appears to play a critical role in the formulation of the products used in the treatment of diseases. This review provides a mechanism-based rationale for the use of HA in some disease conditions with special reference to OA.

Re-epithelialization of adult skin wounds: Cellular mechanisms and therapeutic strategies

Cutaneous wound healing in adult mammals is a complex multi-step process involving overlapping stages of blood clot formation, inflammation, re-epithelialization, granulation tissue formation, neovascularization, and remodelling. Re-epithelialization describes the resurfacing of a wound with new epithelium. The cellular and molecular processes involved in the initiation, maintenance, and completion of epithelialization are essential for successful wound closure. A variety of modulators are involved, including growth factors, cytokines, matrix metalloproteinases, cellular receptors, and extracellular matrix components. Here, we focus on cellular mechanisms underlying keratinocyte migration and proliferation during epidermal closure. Inability to re-epithelialize is a clear indicator of chronic non-healing wounds, which fail to proceed through the normal phases of wound healing in an orderly and timely manner. This review summarizes the current knowledge regarding the management and treatment of acute and chronic wounds, with a focus on re-epithelialization, offering some insights into novel future therapies.

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

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

The use of hyaluronic acid based dressings to treat burns: A review

Deep cutaneous lesions such as burns, traumas or ulcers are all conditions characterized by a massive loss of dermis, bringing several important consequences. For the treatment of these conditions, the evolution of material science has made available new dressings based on natural and synthetic polymers. Hyaluronic acid (HA) is involved in many steps of the wound healing process, such as inflammation, granulation and re-epithelialization. In order to overcome the poor physical properties of the native polymer, such as solubility and rapid degradation, insoluble molecules starting from the natural compound were produced via esterification. Thanks to their improved structural properties, the dressings based on these hyaluronic acid derivatives represent a valuable option for the treatment of deep burns. This narrative monograph describes the development and the outcome of the use of these products in burns. The currently available clinical experience suggests that these HA medical devices represent a safe therapeutic method useful for the treatment of acute wounds.

Differential regeneration of myocardial infarction depending on the progression of disease and the composition of biomimetic hydrogel

Hydrogel has been used for regenerating myocardial infraction (MI) as a delivery vehicle for cells and growth factors. This study showed that injectable hyaluronic acid (HA)-based hydrogels alone would effectively regenerate the damaged infarcted heart tissue. We found that there are two major factors of regeneration in MI. One is molecular weight of HA and another is the progression of MI; sub-acute and chronic. Rat MI model was prepared by ligating the left anterior descending coronary artery (LAD). Four weeks after injection of hydrogel, functional analysis of the heart and histological analysis was assessed. When different molecular weight HA-based hydrogels with 50 kDa, 130 kDa, and 170 kDa were applied to the infarcted area in the sub-acute model, 50 kDa HA-based hydrogel showed the most significant regeneration of myocardium as well as functional recovery among samples. For the disease progression, 50 kDa HA-based hydrogels were injected to sub-acute and chronic MI models. The regeneration activity was significantly decreased in the chronic models reflecting that injection timing of the therapeutic agents is also major determinants in the regeneration process. These results suggest that injection time and composition of hydrogel are two major points treating MI.

Natural and synthetic biomaterials for controlled drug delivery

A wide variety of delivery systems have been developed and many products based on the drug delivery technology are commercially available. The development of controlled-release technologies accelerated new dosage form design by altering pharmacokinetic and pharmacodynamics profiles of given drugs, resulting in improved efficacy and safety. Various natural or synthetic polymers have been applied to make matrix, reservoir or implant forms due to the characteristics of polymers, especially ease of control for modifications of biocompatibility, biodegradation, porosity, charge, mechanical strength and hydrophobicity/hydrophilicity. Hydrogel is a hydrophilic, polymeric network capable of imbibing large amount of water and biological fluids. This review article introduces various applications of natural and synthetic polymer-based hydrogels from pharmaceutical, biomedical and bioengineering points of view.

Applications and emerging trends of hyaluronic acid in tissue engineering, as a dermal filler and in osteoarthritis treatment

Hyaluronic acid (HA) is a naturally occurring biodegradable polymer with a variety of applications in medicine, including scaffolding for tissue engineering, dermatological fillers and viscosupplementation for osteoarthritis treatment. HA is available in most connective tissues in body fluids such as synovial fluid and the vitreous humor of the eye. HA is responsible for several structural properties of tissues as a component of extracellular matrix and is involved in cellular signaling. Degradation of HA is a stepwise process that can occur via enzymatic or non-enzymatic reactions. A reduction in HA mass or molecular weight via degradation or slowing of synthesis affects physical and chemical properties such as tissue volume, viscosity and elasticity. This review addresses the distribution, turnover and tissue-specific properties of HA. This information is used as the context for considering recent products and strategies for modifying the viscoelastic properties of HA in tissue engineering, as a dermal filler and in osteoarthritis treatment.

Characterization of CD44-mediated cancer cell uptake and intracellular distribution of hyaluronan-grafted liposomes

Hyaluronan (HA) is a biocompatible and biodegradable linear polysaccharide which is of interest for tumor targeting through cell surface CD44 receptors. HA binds with high affinity to CD44 receptors, which are overexpressed in many tumors and involved in cancer metastasis. In the present study, we investigated the impact of HA molecular weight (MW), grafting density, and CD44 receptor density on endocytosis of HA-grafted liposomes (HA-liposomes) by cancer cells. Additionally, the intracellular localization of the HA-liposomes was determined. HAs of different MWs (5-8, 10-12, 175-350, and 1600 kDa) were conjugated to liposomes with varying degrees of grafting density. HA surface density was quantified using the hexadecyltrimethylammonium bromide turbidimetric method. Cellular uptake and subcellular localization of HA-liposomes were evaluated by flow cytometry and fluorescence microscopy. Mean particle sizes of HA-liposomes ranged from 120 to 180 nm and increased with increasing size of HA. HA-liposome uptake correlated with HA MW (5-8 < 10-12 < 175-350 kDa), grafting density, and CD44 receptor density and exceeded that obtained with unconjugated plain liposomes. HA-liposomes were taken up into cells via lipid raft-mediated endocytosis, which is both energy- and cholesterol-dependent. Once within cells, HA-liposomes localized primarily to endosomes and lysosomes. The results demonstrate that cellular targeting efficiency of HA-liposomes depends strongly upon HA MW, grafting density, and cell surface receptor CD44 density. The results support a role of HA-liposomes for targeted drug delivery.

Development of a wound dressing composed of hyaluronic acid and collagen sponge with epidermal growth factor

This study was designed to investigate the effect of a wound dressing composed of hyaluronic acid (HA) and collagen (Col) sponge containing epidermal growth factor (EGF) on various parameters of wound healing in vitro and in vivo. High-molecular-weight (HMW) HA solution, hydrolyzed low-molecular-weight (LMW) HA solution and heat-denatured Col solution were mixed, followed by freeze-drying to obtain a spongy sheet. Cross-linkage between Col molecules was induced by UV irradiation to the spongy sheet (Type-I dressing). In a similar manner, a spongy sheet containing EGF was prepared (Type-II dressing). The efficacy of these products was firstly evaluated in vitro. Fibroblast proliferation was assessed in culture medium in the presence or absence of a piece of each wound dressing. EGF stimulated cell proliferation after UV irradiation and dry sterilization at 110°C for 1 h. In the second experiment, fibroblasts-embedded Col gels were elevated to the air-liquid interface to create a wound surface model, on which wound dressings were placed and cultured for 1 week. Cell proliferation and the production of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were investigated. With Type-II dressings, the amounts of VEGF and HGF released from fibroblasts in the Col gel were significantly increased compared with Type-I dressing. Next, the efficacy of these products was evaluated in vivo using Sprague-Dawley (SD) rats. Wound conditions after 1 and 2 weeks of treatment with the wound dressings were evaluated based on the gross and histological appearances. Type-II dressings promoted a decrease in wound size, re-epithelialization and granulation tissue formation associated with angiogenesis. These findings indicate that the combination of HA, Col and EGF promotes wound healing by stimulating fibroblast function.

A Bilayer Hyaluronic Acid Wound Dressing to Promote Wound Healing in Diabetic Ulcer

Several spongy wound dressings composed of various hyaluronic acid (HA) materials were developed: HA aqueous solution with cross-linking agent (epoxy compound (HAWC), without cross-linking agent (HAWOC), and combined bilayer material HAWC and HAWOC (2LHA). The microstructure, sensitivity to hyaluronidase, sensitivity to free radicals, in vitro cytotoxicity, healing potential on full-thickness defect on and diabetic ulcers were evaluated. Scanning electron micrograph views of all HA wound dressings showed an interconnected channel and high porosity structure. HAWOC was degraded rapidly in hyaluronidase and free radical solution. The in vitro cytotoxicity of HAWC was significantly (p<0.05) higher than other HA wound dressings and reduced the released amount of VEGF from human fibroblast. The HAWOC remarkably facilitated the formation of vascularized granulation tissue and provided a HA enrichment wound healing process of either a full-thickness defect or a diabetic ulcer. In contrast, the presence of un-degradable products of HAWC seemed to interfere dermal tissue restoration. Nevertheless, because of the fragile properties, rapid degradation and wound adhesion of HAWOC, the 2LHA should be developed for diabetic ulcer therapy.

Using an esterified hyaluronan fleece to promote healing in difficult-to-treat wounds

Hyaluronic acid enhances angiogenesis and promotes re-epithelialisation and scar formation. Two case studies illustrate how a dressing that creates a hyaluronan-rich environment at the wound surface achieved full healing in two patients with underlying physiological problems.

Functions of hyaluronan in wound repair

Hyaluronan is a major carbohydrate component of the extracellular matrix and can be found in skin, joints, eyes and most other organs and tissues. It has a simple, repeated disaccharide linear copolymer structure that is completely conserved throughout a large span of the evolutionary tree, indicating a fundamental biological importance. Amongst extracellular matrix molecules, it has unique hygroscopic, rheological and viscoelastic properties. Hyaluronan binds to many other extracellular matrix molecules, binds specifically to cell bodies through cell surface receptors, and has a unique mode of synthesis in which the molecule is extruded immediately into the extracellular space upon formation. Through its complex interactions with matrix components and cells, hyaluronan has multifaceted roles in biology utilizing both its physicochemical and biological properties. These biological roles range from a purely structural function in the extracellular matrix to developmental regulation through effects of cellular behavior via control of the tissue macro- and microenvironments, as well as through direct receptor mediated effects on gene expression. Hyaluronan is also thought to have important biological roles in skin wound healing, by virtue of its presence in high amounts in skin. Hyaluronan content in skin is further elevated transiently in granulation tissue during the wound healing process. In this review, the general physicochemical and biological properties of hyaluronan, and how these properties may be utilized in the various processes of wound healing: inflammation, granulation and reepithelization, are presented.

Postural vasoregulation and mediators of reperfusion injury in venous ulceration

PURPOSE

To test the hypothesis that ischemia and reperfusion injury may contribute to the cause or nonhealing of venous ulcers, the effects of postural change on the microcirculation of ulcers and on levels of known mediators of reperfusion injury in their venous effluent were studied.

METHODS

A standard protocol of stabilization (20 minutes), limb dependency (1 hour), and reelevation (2 hours) was used in 10 patients with venous leg ulcers as proven by clinical history, examination, ankle-brachial pressure index, and light reflective rheography. Superficial blood flow in and around ulcers was repeatedly examined with a new laser-Doppler scanning technique. Blood samples from the saphenous vein or a tributary adjacent to the ulcer before dependency and at 0, 10, 30, 60, and 120 minutes after reelevation were analyzed for tumor necrosis factor-alpha, interleukin (IL)-1RA, IL-1 beta, IL-6, platelet-activating factor, thromboxane B2, leukotriene B4, and P-selectin.

RESULTS

Scans showed a consistent pattern of high ulcer blood flow, which decreased on dependency (p < 0.05) and then returned to baseline levels on reelevation and (in 7 of 10) eventually exceeded initial values. Mediator assays showed that levels of platelet-activating factor, IL-1RA, and IL-6 were significantly higher in resting ulcer venous effluent than in systemic venous samples; the reverse was true for P-selectin. There was no statistically significant change in effluent concentration of any mediator as a function of posture, ulcer size, or healing.

CONCLUSIONS

Postural vasoregulation causes relative ischemia and reperfusion in venous leg ulcers. However, this is not associated with changes in release of mediators known to be related to reperfusion injury in internal organs.