Hyaluronic Acid and Wound Healing

Background. We developed an experimental model of ethanol-induced dermatotoxicity and hepatocytoxicity using normal human keratinocytes and normal human hepatocytes that preserve inducible cytochrome p450 activities. The original work was described in several articles. The objective of this study was to determine whether hyaluronic acid attenuates skin necrosis, and to further clarify its uses in wound repair in humans, animal models and in vitro studies. Methods. We performed a systematic review of the literature using the terms " hyaluronic acid " and " wound healing ". PubMed was searched for studies published during the period 2010-2014. Results. Hyaluronic acid is used in tissue regeneration alone or in combination with herbal or Western medicine. Scaffolds made up of hyaluronic acid were used to embed basic fibroblast growth factor. Conclusion. Hyaluronic acid extracts are safe and efficacious products to be used in skin repair.


INTRODUCTION
Hyaluronic acid (HA) is a polysaccharide that belongs to the glycosaminoglycan family and consists of a basic unit of two sugars, glucuronic acid and N-acetyl-glucosamine. HA usually exists as a high molecular mass in the synovial fluid that surrounds joints, cartilage, and tissues of the eye and skin.Previously, our group was able to reduce alcohol-induced fibrogenesis in vitro in human normal hepatocytes (1) and to induce in vitro healing of human epithelial cells (2) using a preparation of HA obtained from human umbilical cord excision.The present work reviews in depth some of the mechanisms of tissue damage and repair in which HA plays an important role.

TISSUE REGENERATION
Recent studies using HA for tissue regeneration are discussed in Table 1.HA has recently been used in several in vitro studies (2)(3)(4)(5).Our group has used HA jellies at concentrations of 2%, 4% and 8% that were formulated at the Placentary Histotherapy Center in Cuba from residual umbilical cords of human placentas obtained according to the National Recollection Program.We showed that HA 2% and 4% has a protective dose-dependent effect on skin cells exposed to ethanol.HA protected against ethanol-induced cytotoxicity by a mechanism that involves the prevention of apoptosis, and this is mediated by decreased inflammation.Cells exposed to the same amount of ethanol in the presence of HA 8% were not protected against toxicity.We believe this to be the result of an inability of this highly viscous gel to penetrate into the cells (2).In a separate study, Wu et al. (5) show that high molecular weight (HMW)-HA (1525 kDa) has superior cytoprotective effects compared to low molecular weight (LMW)-HA (127 kDa).HMW-HA 0.3% facilitates cell migration and wound healing (5).HMW-HA also promotes wound healing and cell survival in a rat heart ischemiareperfusion model, while LMW-HA has no protective effects (4).Another recent in vitro study showed that amniotic fluid is associated with reepithelialisation, mediated by the presence of HA (3)._______________________________________________ HA was further used in animal models (6-13).HA was used for its wound healing potential in two full-thickness surgical wound models.HA facilitated re-epithelialization, led to the formation of soft tissue with good elasticity, and increased microvascular density (6, 7).HA also showed promising results for connective tissue repair in terms of tendon and cartilage repair in two rabbit models (8, 9).Bone repair is further shown in rat and rabbit models (10, 11).Zanchetta et al. (11) found that histological and overall appearance of the healing bone were superior in untreated hole made in the left side of the parietal bone compared to HA-treated hole made in the right side.Better results obtained in the control site could be partly explained by the transport of the treatment components in blood, thereby spreading them evenly and suggesting systemic activity (11).
The use of chitosan-hyaluronan/silk fibroin cardiac patches led to cardiac repair in a rat model of myocardial infarction.Blood vessel-like structures were widely distributed in myocardial infarction regions of the left ventricle in the treatment group, yet were absent under the control condition.This further led to higher secretion of paracrine factors in myocardial infarction regions of the left ventricle in the treatment group compared to control (12).In another rat model, artificial tears containing HA and high potassium ion concentration promoted corneal epithelial wound healing in a mechanical scraping model but not in an alkali burn model (13).
HA was used in humans in several studies (14-21).The skin re-epithelialization potential of Avena rhealba extract® and HA was shown in a small sample of volunteers in which skin lesions were produced with erbium-YAG laser (14).Different gel formulations of HA were used in burn patients (15, 16), and for the treatment of persistent ulcers (17-19).Four cases of upper limb deep wounds treated with HA, bacterial fermented sodium hyaluronate salt (0.2% w/w), and bacterial collagenase obtained from non-pathogenic Vibrio alginolyticus are described in a case series.Aside from wound healing, this treatment led to satisfactory aesthetic results, and optimal recovery of the affected limb functionality (22).
In humans, platelet rich plasma and HA were used to treat postoperative wound dehiscence and tendon exposure after surgery in patients with Morton's neuroma, an entrapment neuropathy of the plantar digital nerve (21).Elsewhere, the application of HA-containing gels in early wound healing after scaling and root planting was tested in individuals with chronic periodontitis.HA led to significantly higher reduction in probing depth, as well as the number of pockets with probing depth ≥5 mm, compared to scaling and root planting alone (20).

SCAFFOLD FOR WOUND HEALING
Table 2 describes studies in which HA was used as a component of scaffolds for wound healing.A number of animal studies using wound models assessed the usefulness of HA-based scaffolds (23-30).These scaffolds, made up of various biological components, promote dermis regeneration and wound healing.In one case, dermal/epidermal cell fractions entrapped directly within the hydrogel accelerated wound healing.Elsewhere, the scaffold was used to embed basic fibroblast growth factor (23-26).
An injectable hydrogel provided an adhesion barrier in a rat model following midline abdominal incision, and facilitated wound healing ( 27).An HA-based spongy sheet embedded with epidermal growth factor aided wound healing in a rat model with excised portion of the peritoneum (28).Bone formation was achieved in two calvaria defect models using HA-based scaffolding.In one study, these scaffolds were loaded with growth and differentiation factor 5, which aided new bone formation with increased bone mineral density (29, 30).In a retrospective study, an HA sheet was used as scaffold with or without autologous cultured dermal fibroblasts after the removal of basal cell carcinoma on the face (31).The use of autologous skin grafting on an HA scaffold in patients undergoing surgical scar removal facilitates better integration of the graft into the surrounding tissues, with dermis regeneration (32).

CONCLUSION
HA is commonly used as a therapeutic in a wide range of applications, including osteoarthritis, ophthalmic surgery, cosmetic application and tissue engineering.It may be injected intradermally or it may be used topically.HA extracts are safe and efficacious products to be used in skin repair.

ACKNOWLEDGMENTS
In Vitro Drug Safety and Biotechnology, Toronto, Canada supported the work.All authors have read the journal's policy on conflicts of interest and have none to declare.Also, all authors have read the journal's policy on authorship and there are no conflicts of interest.

Table 2 .
Scaffold for Wound Healing Studies