A Crosslinked HA-Based Hydrogel Ameliorates Dry Eye Symptoms in Dogs

Biomedical applications of functional hydrogels: Innovative developments, relevant clinical trials and advanced products

Functional hydrogels are used for numerous biomedical applications such as tissue engineering, wound dressings, lubricants, contact lenses and advanced drug delivery systems. Most of them are based on synthetic or natural polymers forming a three-dimensional network that contains aqueous media. Among synthetic polymers, poly(meth)acrylates, polyethyleneglycols, poly(vinylalcohols), poly(vinylpyrrolidones), PLGA and poly(urethanes) are of high relevance, whereas natural polymers are mainly polysaccharides such as hyaluronic acid, alginate or chitosan and proteins such as albumin, collagen or elastin. In contrast to most synthetic polymers, natural polymers are biodegradable. Both synthetic and natural polymers are often chemically modified in order to improve or induce favorable properties and functions like high mechanical strength, stiffness, elasticity, high porosity, adhesive properties, in situ gelling properties, high water binding capacity or drug release controlling properties. Within this review we provide an overview about the broad spectrum of biomedical applications of functional hydrogels, summarize innovative approaches, discuss the concept of relevant functional hydrogels that are in clinical trials and highlight advanced products as examples for successful developments.

Current Advances in Regenerative Strategies for Dry Eye Diseases: A Comprehensive Review

Dry eye disease (DED) is an emerging health issue affecting millions of individuals annually. Ocular surface disorders, such as DED, are characterized by inflammation triggered by various factors. This condition can lead to tear deficiencies, resulting in the desiccation of the ocular surface, corneal ulceration/perforation, increased susceptibility to infections, and a higher risk of severe visual impairment and blindness. Currently, the clinical management of DED primarily relies on supportive and palliative measures, including the frequent and lifelong use of different lubricating agents. While some advancements like punctal plugs, non-steroidal anti-inflammatory drugs, and salivary gland autografts have been attempted, they have shown limited effectiveness. Recently, there have been promising developments in the treatment of DED, including biomaterials such as nano-systems, hydrogels, and contact lenses for drug delivery, cell-based therapies, biological approaches, and tissue-based regenerative therapy. This article specifically explores the different strategies reported so far for treating DED. The aim is to discuss their potential as long-term cures for DED while also considering the factors that limit their feasibility and effectiveness. These advancements offer hope for more effective and sustainable treatment options in the future.

Evaluation of a preservative-free, cross-linked sodium hyaluronate-based solution, Lacri +®, in dogs with dry eye: a pilot trial

BACKGROUND

The purpose of this pilot trial was to evaluate the efficacy and benefits of a preservative-free cross-linked sodium hyaluronate solution (Lacri +®, MP Labo, France) in 19 privately-owned dogs with dry eye. The animals were administered 2 drops of the tested product in each affected eye, twice a day (BID) for 30 days. Improvement in the global ocular clinical score (sum of the individual scores for conjunctivitis, ocular discharge, eye irritation, and corneal opacity/pigmentation/vascularization, each rated from 0 to 3) was defined as the primary outcome. Besides an improvement in each individual ocular score, tear film quality (Tear Break Up Time, TBUT), dogs' and owners' quality of life (QoL), as well as an increase in tear production (Schirmer Tear Test-1, STT1), were considered secondary outcomes. These criteria were assessed on D0, D0 + 15 days, and D0 + 30 days. Finally, a qualitative evaluation of clinical improvement was requested from the owners on D0 + 2, + 15 & + 30 days and from the investigators during the follow-up.

RESULTS

The global clinical ocular score as well as the individual conjunctival and irritation scores improved significantly (p < 0.0001) during the pilot trial. The average reduction of the global score reached 30% on D0 + 15 days and 55% on D0 + 30 days compared to D0. Ocular discharge was significantly lower (p = 0.0002) on D0 + 30 days compared to baseline; however corneal opacity did not show any significant changes from D0 to the end of the follow-up period. The quantitative tear production was increased at D + 30 (p < 0.0001), with a significant improvement as soon as 2 weeks in, with around 30% and 60% of dogs presenting an STT1 value above 10 on D0 + 15 days and on D0 + 30 days, respectively. The QoL score was significantly improved compared to D0 at all time points (p < 0.0001). After 2 days of treatment, 39% of the owners rated the efficacy as "good". The efficacy of the tested product was considered "Good" or "Very Good" by the investigators in 78% and 93% of the cases, on D0 + 15 days and D0 + 30 days, respectively. The tolerance of this preservative-free formulation was good, with only rare and transient minor local reactions, realated to administration rather than the product itself.

Biomaterials for dry eye disease treatment: Current overview and future perspectives

Dry eye disease (DED) is an emerging health problem affecting millions of individuals every year. The current treatments for DED include lubricating eye drops and anti-inflammatory agents. These agents have to be used frequently and contain preservatives, which can damage the ocular surface. A substantially long-acting treatment with better bioavailability on the ocular surface might reduce the frequency of drug use and its side effects. This review summarizes the current state of different biomaterials-nanosystems, hydrogels, and contact lenses used as drug delivery systems in DED. The explored drugs in biomaterial formulation are cyclosporin, ocular lubricants, and topical steroids. Most of the data is from animal models where increased drug delivery and desired therapeutic effects could be obtained; however, trials involving human participants are yet to happen. There is no published study comparing the different types of biomaterials for DED use. Long-term studies evaluating their ocular toxicity and biocompatibility would enhance their transition to human use. Overall they look promising for DED treatment, but they are still in the stage of technological advancement and clinical studies.

Recent Advances in Hydrogels for the Diagnosis and Treatment of Dry Eye Disease

Dry eye disease (DED) is the most common clinical ocular surface disease. Given its multifactorial etiology, no consensus has been reached on the diagnosis criteria for dry eye disease. Topical drug administration remains the mainstay of treatment but is limited to the rapid clearance from the eye surface. To address these problems, hydrogel-based materials were designed to detect biomarkers or act as drug delivery systems by taking advantage of their good biocompatibility, excellent physical and mechanical properties, and long-term implant stability. Biosensors prepared using biocompatible hydrogels can be sensitive in diagnosing DED, and the designed hydrogels can also improve the drug bioavailability and retention time for more effective and long-term treatment. This review summarizes recent advances in the use of hydrogels for diagnosing and treating dry eye, aiming to provide a novel reference for the eventual clinical translation of hydrogels in the context of dry eye disease.

Entirely S-protected thiolated hydroxyethylcellulose: Design of a dual cross-linking approach for hydrogels

AIM

The aim of this study was the synthesis and evaluation of entirely S-protected thiolated hydroxyethylcellulose (HEC) with low and high viscosity, as well as thiolated poly-L-lysine (poly-L-Lys) used as dual-acting ionic as well as thiol-disulfide exchange mediated cross-linking hydrogel.

METHODS

Bis(mercaptosuccinic acid) was covalently attached to low and high viscous HECs via Fisher esterification, obtaining S-protected polymers. Poly-L-Lys-cysteine was synthesized via amidation of poly-L-Lys-HBr with cysteine (Cys). Thiolated polymers were examined in terms of cytotoxicity and rheological behavior of hydrogels containing these thiomers was evaluated with a cone-plate rheometer.

RESULTS

Thiomers showed less cytotoxicity compared to the corresponding unmodified polymers. Rheological studies showed that cross-linking occurred between the two polymers via thiol-disulfide exchange reactions facilitated by the complementary charges. Employing poly-L-Lys-Cys in a concentration of either 0.5 or 5% (m/v) resulted in a 34.5-fold or 17.3-fold as well as a 53.6-fold or 29.6-fold improvement in dynamic viscosity within 5 min at 37 °C on S-protected thiolated low and high viscous HEC, compared to the corresponding unmodified HECs, respectively.

CONCLUSION

By the combination of anionic S-protected thiolated polymers with a cationic thiolated polymer, dual-acting hydrogels exhibiting a time dependent increase in viscosity can be designed.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

A bioinspired synthetic soft hydrogel for the treatment of dry eye

Natural soft hydrogels are unique elastic soft materials utilized by living organisms for protecting delicate tissues. Under a theoretical framework derived from the Blob model, we chemically crosslinked high molecular weight hyaluronic acid at a concentration close to its overlap concentration (c*), and created synthetic soft hydrogels that exhibited unique rheological properties similar to a natural soft hydrogel: being dominantly elastic under low shear stress while being viscous when the stress is above a small threshold. We explored a potential application of the hyaluronic acid-based soft hydrogel as a long-acting ocular surface lubricant and evaluated its therapeutic effects for dry eye. The soft hydrogel was found to be biocompatible after topical instillation on experimental animals' and companion dogs' eyes. In a canine clinical study, twice-a-day ocular instillation of the soft hydrogel in combination with cyclosporine for 1 month improved the clinical signs in more than 65% of dog patients previously unresponsive to cyclosporine treatment.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.

New Trends in Drug Delivery Systems for Veterinary Applications

BACKGROUND

The veterinary pharmaceutical industry has shown significant growth in recent decades. Several factors contribute to this increase as the demand for the improvement of the quality of life of both domestic and wild animals, together with the need to improve the quality, productivity, and safety of foodstuffs of animal origin.

METHODS

The goal of this work was to identify the most suitable medicines for animals that focus on drug delivery routes as those for humans, although they may have different devices, such as collars and ear tags.

RESULTS

Recent advances in drug delivery systems for veterinary use are discussed, both from academic research and the global market. The administration routes commonly used for veterinary medicines are also explored, while special attention is given to the latest technological trends to improve the drug performance, reducing the number of doses, animal stress, and side effects.

CONCLUSION

Drug delivery system in veterinary decreased the number of doses, side effects, and animal stress that are a small fraction of the benefits of veterinary drug delivery systems and represent a significant increase in profit for the industry; also, it demands investments in research regarding the quality, safety, and efficacy of the drug and the drug delivery systems.

Development of a novel hyaluronic acid membrane for the treatment of ocular surface diseases

Ocular surface diseases (OSD) can cause serious visual deterioration and discomfort. Commercial artificial tear solution containing hyaluronic acid (HA) show excellent biocompatibility and unique viscoelastic characteristics. Here, we developed a novel HA membrane (HAM) by chemical crosslinking using 1,4-butanediol diglycidyl ether for the effective treatment of OSDs. The main purpose of HAMs is to provide sustained release of HA to modulate the wound healing response in OSDs. The safety and efficacy of HAMs were investigated using primary cultured human corneal epithelial cells and various OSD rabbit models. In the dry state, the HAM is firm, transparent, and easy to manipulate. When hydrated, it swells rapidly with high water retention and over 90% transmission of visible light. Human corneal epithelial cells and rabbit eyes showed no toxic response to HAM. Addition of HAMs to the culture medium enhanced human corneal epithelial cell viability and expression of cell proliferation markers. Investigation of HAM wound healing efficacy using mechanical or chemical corneal trauma and conjunctival surgery in rabbits revealed that application of HAMs to the ocular surface enhanced healing of corneal epithelium and reduced corneal limbal vascularization, opacity and conjunctival fibrosis. The therapeutic potential of HAMs in various OSDs was successfully demonstrated.

Efficacy of 0.1% crosslinked hyaluronic acid, coenzyme Q10 and vitamin E in the management of dry eye disease in menopause patients receiving antidepressants

PURPOSE

The purpose of this study is to test non-inferiority of a lower dose of crosslinked hyaluronic acid (CLHA) to a higher dose of carmellose eye drop in menopause patients receiving antidepressant treatments.

METHODS

This prospective, double-blind, single-center study enrolled sixty female patients. Mean age was 63.25 ± 9.13 years. We examined patients with Schirmer I, breakup time (TBUT) and the ocular surface disease index (OSDI) at the first visit. Tear A eyedrops were formulated with crosslinked hyaluronic acid, coenzyme Q10 and vitamin E. Control tear B was formulated with carmellose sodium. Posology was two and five times, respectively.

RESULTS

After 2 months of treatment, the tear A obtained 14.12 ± 7.47 score points for OSDI (t = 11.74, p < 0.01), and tear B obtained 19.46 ± 10.03 score points (t = 7.59, p < 0.01). The tear A obtained 13.77 ± 7.78 score points for Schirmer test (t = 0.88, p > 0.05), and tear B obtained 14.20 ± 8.62 score points (t = 2.92, p < 0.01). The tear A obtained 8.30 ± 2.08 s for TBUT (t = 15.50, p < 0.01), and tear B obtained 7.23 ± 2.40 s (t = 8.79, p < 0.01).

CONCLUSION

Lower total daily dose of crosslinked hyaluronic acid eyedrops obtained similar efficacy results in terms of tear stability and subjective dry eye sensation than higher carmellose total daily dose. A lower total daily dose of crosslinked eyedrops was sufficient to achieve better dry eye disease management compared to carmellose.

Electrolyte composition of tears in normal dogs and its comparison to serum and plasma

PURPOSE

The dog is an important animal model for tear dysfunction diseases, however to-date the electrolyte composition of the dog's tears is unknown. The aim of this study was to analyze the electrolyte content of canine tears and compare it to serum and plasma.

METHODS

Tear samples were collected from 18 eyes of 9 dogs. Blood for serum was collected in tubes with no anticoagulants; plasma was obtained by using two different anticoagulants: Citrate-Phosphate-Dextrose (CPD) and heparin. The electrolytes were measured in all samples, analyzed, and compared.

RESULTS

Most of the electrolyte values in tears were statistically different (P < 0.05) from electrolyte values in serum and plasma. Potassium and chloride values were significantly higher in tears compared to serum and plasma, while calcium and phosphate values were significantly lower. Sodium values in tears were higher than in serum and heparinized-plasma, but lower than CPD-plasma. Bicarbonate values were lower in tears compared to serum and heparinized plasma, but was not statistically different than CPD-plasma. While magnesium values were lower in tears compared to serum and heparinized-plasma, the difference was not statistically different.

CONCLUSIONS

Herein, we report for the first time the electrolyte composition of the canine tears and its comparison to serum and plasma.

Novel Cross-Linked Ocular Bandage Gel Improves Reepithelialization After Photorefractive Keratectomy: A Randomized, Masked Prospective Study

Purpose: To compare, in a masked manner, a novel cross-linked hyaluronic acid ocular bandage gel (OBG) versus standard-of-care bandage contact lens (BCL) plus artificial tears with respect to safety and effectiveness in healing epithelial defects created for photorefractive keratectomy (PRK). Methods: This was a randomized, reading center-masked, exploratory study. Forty-five patients (myopic without significant anisometropia) scheduled for bilateral PRK (9-mm epithelial defect) were randomized post-PRK to treatment with OBG 8 times daily for 3 days, followed by 4 times daily for 11 days (Group 1); OBG 4 times daily for 14 days (Group 2); or BCL and artificial tears (Control). A masked reading center used image analysis of digital slit lamp photos of the fluorescein-stained cornea to evaluate defect size during the 14-day postoperative follow-up period. Effectiveness endpoints were (1) time to complete closure of the corneal defect and (2) proportion of patients with complete healing on day 3 postoperatively, whose defect remained closed. Safety assessments included findings for adverse events and vision, Standard Patient Evaluation of Eye Dryness (SPEED^™) Questionnaire, slit lamp, intraocular pressure, and fundus examinations. Results: The proportion of patients with complete healing at 3 days was 73.3%, 86.7%, and 66.7% of patients in Groups 1, 2, and Control, respectively. On day 2, the mean wound size was 6%-26% smaller in Groups 1 and 2 compared with Control. No safety concern arose. SPEED scores were not significantly different across groups. Conclusion: OBG offers a well-tolerated and effective therapy for quickly reepithelializing the cornea following trauma, disease, or surgery.

Efficacy of adjunctive therapy using Vizoovet in improving clinical signs of keratoconjunctivitis sicca in dogs: A pilot study

OBJECTIVE

To assess the clinical safety and efficacy of adjunctive therapy using Vizoovet to ameliorate clinical signs of keratoconjunctivitis sicca (KCS) in dogs.

ANIMALS STUDIED

Twenty client-owned dogs.

PROCEDURES

Canine patients diagnosed with KCS were enrolled in this prospective study. Patients were randomly selected to receive either Vizoovet or GenTeal drops twice daily in addition to twice daily tacrolimus 0.03% solution. Data were collected from only one eye of each patient and included STT-1, IOP, TFBUT, and results of objective clinical scoring performed by pet owners. Statistical significance was set at P ≤ .05.

RESULTS

In all, 20 dogs (20 eyes) were enrolled in this prospective randomized study. Females (n = 12; 60%) outnumbered males (n = 8; 40%) and all dogs were spayed/neutered. Mean age of all dogs was 10.6 ± 3.79 years. In both treatment groups, the improvement in STT-1 values over the course of the study was significant (P = .002). When comparing the STT-1 improvements between groups, no significance was found (P = .78). In both groups, the improvement in TFBUT was significant (P = .0018). When comparing the TFBUT improvements between groups, no significance was found (P = .14). Squinting, rubbing, ocular discharge, and medication administration scores all significantly improved throughout the course of the study; however, they did not differ significantly between groups. Throughout the study, no adverse side effects were noted clinically or by the pet owner in either group.

CONCLUSIONS AND CLINICAL RELEVANCE

Adjunctive treatment with Vizoovet was as safe and effective as GenTeal drops at improving clinical signs of dry eye in dogs.

Physicochemical Properties of Hyaluronic Acid-Based Lubricant Eye Drops

PURPOSE

To assess the physicochemical properties of hyaluronic acid (HA)-based artificial tears.

METHODS

The average molecular weight (MW) and polydispersion index (PDI) of HA in 18 commercially available artificial tears were determined by light scattering/high-performance liquid chromatography. Osmolality, pH, viscosity, and sodium concentration were determined using an osmometer, pH meter, rheometer, and inductively coupled plasma mass spectrometer, respectively.

RESULTS

The MW of HA varied considerably between formulations. The PDI was >2.0 in two formulations (2.28 and 4.94), suggesting the presence of a copolymer and/or HA size variability. Three formulations exhibited viscosity exceeding the blur threshold at different shear rates. Viscosity at low shear rates was generally highest in formulations containing high-MW HA. Correlations were found between observed viscosity and a predictive/calculated value, except for four copolymer-containing formulations, and osmolality (range, 154-335 mOsm/kg) and sodium concentration (range, 22-183 mM), with two exceptions. Compared with organic osmolytes, adding sodium decreased viscosity, particularly at lower shear rates.

CONCLUSIONS

In the context of the literature, our findings suggest that for most patients with dry eye disease, the ideal HA-based artificial tear should include high-MW HA with a low PDI and exhibit enhanced viscosity at low shear rate (without exceeding the blur threshold). The inclusion of synergistic copolymers and a low sodium concentration may increase viscosity, but whether any of these physicochemical properties or correlations can predict clinical efficacy will require further investigation.

TRANSLATIONAL RELEVANCE

Understanding the properties of HA-based artificial tears will support the development of unique formulations that target specific ocular surface conditions.

Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature

Thiolated polymers designated "thiomers" are obtained by covalent attachment of thiol functionalities on the polymeric backbone of polymers. In 1998 these polymers were first described as mucoadhesive and in situ gelling compounds forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins and crosslinking through inter- and intrachain disulfide bond formation. In the following, it was shown that thiomers are able to form disulfides with keratins and membrane-associated proteins exhibiting also cysteine-rich substructures. Furthermore, permeation enhancing, enzyme inhibiting and efflux pump inhibiting properties were demonstrated. Because of these capabilities thiomers are promising tools for drug delivery guaranteeing a strongly prolonged residence time as well as sustained release on mucosal membranes. Apart from that, thiomers are used as drugs per se. In particular, for treatment of dry eye syndrome various thiolated polymers are in development and a first product has already reached the market. Within this review an overview about the thiomer-technology and its potential for different applications is provided discussing especially the outcome of studies in non-rodent animal models and that of numerous clinical trials. Moreover, an overview on product developments is given.

Physicochemical Properties of Hyaluronic Acid-Based Lubricant Eye Drops

PURPOSE

To assess the physicochemical properties of hyaluronic acid (HA)-based artificial tears.

METHODS

The average molecular weight (MW) and polydispersion index (PDI) of HA in 18 commercially available artificial tears were determined by light scattering/high-performance liquid chromatography. Osmolality, pH, viscosity, and sodium concentration were determined using an osmometer, pH meter, rheometer, and inductively coupled plasma mass spectrometer, respectively.

RESULTS

The MW of HA varied considerably between formulations. The PDI was >2.0 in two formulations (2.28 and 4.94), suggesting the presence of a copolymer and/or HA size variability. Three formulations exhibited viscosity exceeding the blur threshold at different shear rates. Viscosity at low shear rates was generally highest in formulations containing high-MW HA. Correlations were found between observed viscosity and a predictive/calculated value, except for four copolymer-containing formulations, and osmolality (range, 154-335 mOsm/kg) and sodium concentration (range, 22-183 mM), with two exceptions. Compared with organic osmolytes, adding sodium decreased viscosity, particularly at lower shear rates.

CONCLUSIONS

In the context of the literature, our findings suggest that for most patients with dry eye disease, the ideal HA-based artificial tear should include high-MW HA with a low PDI and exhibit enhanced viscosity at low shear rate (without exceeding the blur threshold). The inclusion of synergistic copolymers and a low sodium concentration may increase viscosity, but whether any of these physicochemical properties or correlations can predict clinical efficacy will require further investigation.

TRANSLATIONAL RELEVANCE

Understanding the properties of HA-based artificial tears will support the development of unique formulations that target specific ocular surface conditions.

Cross-Linked Hyaluronic Acid as Tear Film Substitute

Purpose: The aim of this review is to clarify the role of cross-linked Hyaluronic acid (HA) molecule as a tear supplement and to define its possible applications in dry eye disease. Methods: Current Literature about HA and its cross-linked derivatives has been examined. Results: HA is superior in increasing the viscosity and stability of the tear film compared with other tear supplements such as polyvinyl alcohol, hydroxypropyl methylcellulose, carboximethyl cellulose and polyethylene glycol. Moreover, HA can be modified in different ways to improve its properties such as molecular weight, viscosity, and hydrophobicity to adapt the new artificial molecule to different aims. Conclusions: The current pharmacological trend is to improve the properties of HA by cross-linking parts of the molecule to achieve better bioavailability and resistence to degradation. In dry eye disease, cross-linked HA as tear supplement seems to provide better ocular comfort than linear HA and is therefore subjected to growing interest and diffusion.

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.

Effect of 0.15% sodium hialuronate and 0.5% carboxymethylcellulose on tear film breakup time in healthy dogs and in dogs with keratoconjunctivitis sicca

ABSTRACT This study aimed to evaluate the effect of the 0.15% sodium hyaluronate (SH) and of 0.5% carboxymethylcellulose (CMC) on tear film breakup time (TFBUT) in 10 healthy dogs and in 32 eyes of dogs with keratoconjunctivis sicca (KCS). In addition, the goblet cell density (GCD) of this population was quantified. TFBUT was assessed at baseline and at different time points following the instillation of SH and CMC. KCS was graded as mild, moderate, and severe. GCD were quantified from conjunctival biopsies. The number of GCD differed significantly between patients with mild and moderate KCS (P<0.01). TFBUT of healthy dogs increased only for 1 minute after treatment with SH (P<0.01). Regarding baseline and treatments, SH significantly increased TFBUT for up to 30 minutes on the ocular surface, in comparison to CMC, in all categories of KCS (P<0.01). TFBUT and GCD correlated positively when the healthy and diseased eyes were grouped (r=0.41, P=0.006). It can be concluded that in dogs with KCS, SH lasts longer periods on the ocular surface than CMC, but such agents does not increase TFBUT in healthy dogs. Additionally, tear film stability tends to reduce in a linear fashion from the mild to severe form of KCS.

Thiolated Hyaluronic Acid as Versatile Mucoadhesive Polymer: From the Chemistry Behind to Product Developments-What Are the Capabilities?

Within the last decade, intensive research work has been conducted on thiolated hyaluronic acids (HA-SH). By attaching sulfhydryl ligands onto naturally occurring hyaluronic acid various types of HA-SH can be designed. Due the ability of disulfide bond formation within the polymer itself as well as with biological materials, certain properties such as mucoadhesive, gelling, enzyme inhibitory, permeation enhancing and release controlling properties are improved. Besides the application in the field of drug delivery, HA-SH has been investigated as auxiliary material for wound healing. Within this review, the characteristics of novel drug delivery systems based on HA-SH are summarized and the versatility of this polymer for further applications is described by introducing numerous relevant studies in this field.

Optimising tear replacement rheology in canine keratoconjunctivitis sicca

Dry eye is a substantial problem in a large number of human and canine patients. Numerous laboratory models for tear deficiency exist using genetically predisposed rodent models, animals treated with topical anti-muscarinics, or those kept in environments with increased air flow to produce the ocular surface changes seen in human patients. Canine keratoconjunctivitis sicca, seen in many thousands of dogs kept as companion animals, can provide a valuable spontaneous model for testing tear replacement medications that might better model disease in human patients, existing as it does in an outbred population that live in the same environments as their owners. Here the development of a crosslinked hyaluronic acid topical drop is described together with the results of trials on dogs with spontaneous keratoconjunctivitis sicca. Although hyaluronic acid in its native form in tear replacement drops shows a Newtonian rheology, the crosslinked product described here behaves in a non-Newtonian manner, with the same shear thinning shown by the tear film itself. The crosslinked product thus shows itself as a potentially valuable tear replacement medication for the human dry eye population as well as for dogs with the same condition.

Novel Artificial Tears Containing Cross-Linked Hyaluronic Acid: An In Vitro Re-Epithelialization Study

Dry eye syndrome is a common disease which can damage the corneal epithelium. It is treated with eye drops to stimulate tear production and hydrate the corneal surface. The most prescribed artificial tear remedies contain hyaluronic acid (HA), which enhances epithelial wound healing, improving tissue health. To the best of our knowledge, only a few recent studies have investigated cross-linked HA (HA-CL) in eye drops for human applications. This work consists in an in vitro evaluation of the re-epithelialization ability of two different preparations containing a recently synthetized HA cross-linked with urea: 0.02% (w/v) HA-CL (solution 1, S1), and 0.4% (w/v) HA-CL (solution 2, S2). The study was conducted on both 2D human corneal cells (HCEpiC) and 3D reconstructed tissues of human corneal epithelium (HCE). Viability by 3(4,5-dimethylthiazol-2)2,5-diphenyltetrazolium bromide (MTT) test, pro-inflammatory cytokine release (interleukin-8, IL-8) by ELISA, and morphology by hematoxylin and eosin (HE) staining were evaluated. In addition, to understand the molecular basis of the re-epithelialization properties, cyclin D1 levels were assessed by western blot. The results showed no cellular toxicity, a slight decrease in IL-8 release, and restoration of epithelium integrity when the wounded 3D model was treated with S1 and S2. In parallel, cyclin D1 levels increased in cells treated with both S1 and S2.

Finite Element Design Optimization of a Hyaluronic Acid-Based Hydrogel Drug Delivery Device for Improved Retention

Drug-loaded hydrogel devices are emerging as an effective means of localized and sustained drug delivery for the treatment of corneal conditions and injuries. One such device uses a novel, thiolated crosslinked carboxymethylated, hyaluronic acid-based hydrogel (CMHA-S) film to deliver drug to the ocular surface upon placement into the inferior fornix of the eye. While proven to be very safe and effective, the CMHA-S film tends to dislodge in the highly-lubricated ocular environment, thereby reducing drug delivery efficiency and drug efficacy. In this study, we used a three-dimensional computational finite element model of the eye to determine the effect of geometry and surface friction on film retention in the inferior fornix, and to evaluate multiple geometrical film designs. Retention of the film was dependent on geometry and on the friction ratio of the film to the eyelid and globe. These effects were interactive. When the ratio of friction on the lid side to the globe side of the film was low, geometry played a large role in the film's displacement. When this ratio was high, differences in displacement due to geometry were negligible. The optimal relationship of friction between the film and its eyelid-side and globe-side surfaces was found to be linear with at least 1.4 times greater friction required on the eyelid-side for immobilization. A geometry similar to a half cylinder was found to be most effective with this friction ratio in retaining the film in the inferior fornix and in contact with the globe. Other geometries will likely require other friction ratios. In summary, CMHA-S film retention can be achieved through simple modifications of geometry and manipulation of surface interaction with the eye.

Effect of Carboxymethylation on the Rheological Properties of Hyaluronan

Chemical modifications made to hyaluronan to enable covalent crosslinking to form a hydrogel or to attach other molecules may alter the physical properties as well, which have physiological importance. Here we created carboxymethyl hyaluronan (CMHA) with varied degree of modification and investigated the effect on the viscosity of CMHA solutions. Viscosity decreased initially as modification increased, with a minimum viscosity for about 30-40% modification. This was followed by an increase in viscosity around 45-50% modification. The pH of the solution had a variable effect on viscosity, depending on the degree of carboxymethyl modification and buffer. The presence of phosphates in the buffer led to decreased viscosity. We also compared large-scale production lots of CMHA to lab-scale and found that large-scale required extended reaction times to achieve the same degree of modification. Finally, thiolated CMHA was disulfide crosslinked to create hydrogels with increased viscosity and shear-thinning aspects compared to CMHA solutions.

Assessment of Full-Eye Response to Osmotic Stress in Mouse Model In Vivo Using Optical Coherence Tomography

NaCl based solutions were applied as osmotic stress agents to alter the hydration state of the mouse eye. Full-eye responses to these osmotic challenges were monitored in vivo using a custom-built optical coherence tomography (OCT) with an extended imaging range of 12.38 mm. Dynamic changes in the mouse eye were quantified based on the OCT images using several parameters, including the central corneal thickness (CCT), the anterior chamber depth (ACD), the crystalline lens thickness (LT), the cornea-retina distance (CRD), the iris curvature (IC), and the lens scattering intensity (LSI). Apparent but reversible changes in the morphology of almost all the ocular components and the light transparency of the lens are exhibited. Particularly, the ocular dehydration induced by the hypertonic challenges resulted in a closing of the iridocorneal angle and an opacification of the lens. Our results indicated that the ocular hydration is an important physiological process which might be correlated with various ocular disorders, such as dry eye, cataract, and angle-closure glaucoma, and would affect the biometry and imaging of the eye. OCT uniquely enables the comprehensive study of the dynamic full-eye responses to the ocular hydration in vivo.

Ophthalmic Uses of a Thiol-Modified Hyaluronan-Based Hydrogel

Significance: Hyaluronic acid (HA, or hyaluronan) is a ubiquitous naturally occurring polysaccharide that plays a role in virtually all tissues in vertebrate organisms. HA-based hydrogels have wound-healing properties, support cell delivery, and can deliver drugs locally. Recent Advances: A few HA hydrogels can be customized for composition, physical form, and biomechanical properties. No clinically approved HA hydrogel allows for in vivo crosslinking on administration, has a tunable gelation time to meet wound-healing needs, or enables drug delivery. Recently, a thiolated carboxymethyl HA (CMHA-S) was developed to produce crosslinked hydrogels, sponges, and thin films. CMHA-S can be crosslinked with a thiol-reactive crosslinker or by oxidative disulfide bond formation to form hydrogels. By controlled crosslinking, the shape and form of this material can be manipulated. These hydrogels can be subsequently lyophilized to form sponges or air-dried to form thin films. CMHA-S films, liquids, and gels have been shown to be effective in vivo for treating various injuries and wounds in the eye in veterinary use, and are in clinical development for human use. Critical Issues: Better clinical therapies are needed to treat ophthalmic injuries. Corneal wounds can be treated using this HA-based crosslinked hydrogel. CMHA-S biomaterials can help heal ocular surface defects, can be formed into a film to deliver drugs for local ocular drug delivery, and could deliver autologous limbal stem cells to treat extreme ocular surface damage associated with limbal stem cell deficiencies. Future Directions: This CMHA-S hydrogel increases the options that could be available for improved ocular wound care, healing, and regenerative medicine.

Efficacy of a crosslinked hyaluronic acid-based hydrogel as a tear film supplement: a masked controlled study

Keratoconjunctivitis sicca (KCS), or dry eye, is a significant medical problem in both humans and dogs. Treating KCS often requires the daily application of more than one type of eye drop in order to both stimulate tear prodcution and provide a tear supplement to increase hydration and lubrication. A previous study demonstrated the potential for a crosslinked hyaluronic acid-based hydrogel (xCMHA-S) to reduce the clinical signs associated with KCS in dogs while using a reduced dosing regimen of only twice-daily administration. The present study extended those results by comparing the use of the xCMHA-S to a standard HA-containing tear supplement in a masked, randomized clinical study in dogs with a clinical diagnosis of KCS. The xCMHA-S was found to significantly improve ocular surface health (conjunctival hyperaemia, ocular irritation, and ocular discharge) to a greater degree than the alternative tear supplement (P = 0.0003). Further, owners reported the xCMHA-S treatment as being more highly effective than the alternative tear supplement (P = 0.0024). These results further demonstrate the efficacy of the xCMHA-S in reducing the clinical signs associated with KCS, thereby improving patient health and owner happiness.