Emerging drugs for the treatment of dry eye disease

Design and delivery effect of prolonged-retention dexamethasone and tacrolimus microcrystals eye drops

The improvement of drug solubility is essential for enhancing drug absorption of eye drops, particularly for poorly soluble drugs. In this study, drug crystallization techniques were utilized to synthesize dexamethasone microcrystals (DES MCs) and tacrolimus microcrystals (TAM MCs). To further enhance the retention of the MCs, DES MCs@(PEI/HA)3 and TAM MCs@(PEI/HA)3 were prepared by the alternate deposition of polyethyleneimine (PEI) and hyaluronic acid (HA) on the surface of the MCs through electrostatic adsorption. The sustained release effect of TAM MCs@(PEI/HA)3, resulting from enhanced solubility through micro-crystallization, was confirmed via solubility measurements and in vitro release studies. Similarly, DES MCs@(PEI/HA)3 exhibited comparable sustained release properties. Subsequently, the hydrophobicity, safety, and efficacy of DES MCs@(PEI/HA)3 and TAM MCs@(PEI/HA)3 were investigated through the in vitro and in vivo experiments. Notably, TAM MCs@(PEI/HA)3 demonstrated superior efficacy over commercially available TALYMUS®, enabling a once-daily dosing regimen. In conclusion, microcrystal preparation exhibited a more significant impact on the delivery of tacrolimus compared to dexamethasone. The TAM MCs@(PEI/HA)3 microcrystals suspension eye drops prepared using the layer-by-layer self-assembly technique, offer a promising strategy for enhancing the solubility of poorly soluble drugs and ocular drug delivery.

Diquafosol sodium reduces neuronal activity in trigeminal subnucleus caudalis in a rat model of chronic dry eye disease

Patients with persistent and severe dry eye disease (DED) have corneal hypersensitivity, resulting in ocular pain, and diquafosol sodium, a potent P2Y₂ receptor agonist, is commonly used to improve the resultant tear film stability. This study determined the effects of diquafosol instillation on the suppression of trigeminal subnucleus caudalis (Vc) neuronal activity and ocular pain by enhancing tear film stability in the model for chronic DED. The effects of diquafosol on the ocular surface were assessed by the topical application for 28 days, starting from the 14th day since unilateral exorbital gland removal (chronic DED). Loss of tear volume secretion in chronic DED rats was significantly reversed by diquafosol instillation after 28 days, compared with saline treatment. The number of eyeblinks and pERK-IR neurons in the superficial laminae of Vc following hypertonic saline administration to the ocular surface was lower in diquafosol-treated chronic DED rats than in saline-treated rats. The neuronal activity evoked by hypertonic saline and mechanical stimulation along with the spontaneous neuronal activity in the superficial laminae of the Vc were suppressed in diquafosol-treated chronic DED rats. These findings suggest that ocular surface instillation of diquafosol for 28 days attenuates the neuronal hyperactivity in the Vc and the ocular pain that often occurs in chronic DED.

TRPV1 and TRPM8 Channels and Nocifensive Behavior in a Rat Model for Dry Eye

Purpose

Persistent ocular surface pain occurs in moderate to severe dry eye disease (DE); however, the mechanisms that underlie this symptom remain uncertain. The aim of this study was to determine if the transient receptor potential vanilloid ion channels play a role in hypertonic saline (HS)-evoked corneal reflexes in a model for aqueous tear deficient DE.

Methods

Eye wipe behavior and orbicularis oculi muscle activity (OOemg) were measured after ocular instillation of HS, capsaicin, or menthol 14 days after exorbital gland removal. Total RNA and protein were measured from anterior eye segment and trigeminal ganglia of sham and DE rats.

Results

Eye wipe behavior was enhanced in DE rats after HS and capsaicin instillation, but not after menthol when compared to sham rats. DE rats displayed greater OOemg activity after HS and capsaicin, but not after menthol, compared to sham rats. HS-evoked OOemg activity was reduced by selective TRPV1 antagonists and by coapplication of capsaicin plus QX-314, a charged lidocaine derivative. Menthol did not affect OOemg activity; however, selective antagonism of TRPM8 reduced HS-evoked OOemg activity. TRPV1 protein levels were increased in anterior eye segment and trigeminal ganglion samples from DE rats, whereas TRPM8 levels were not affected.

Conclusions

These results suggest that TRPV1 plays a significant role in mediating enhanced nocifensive behavior in DE, while TRPM8 may play a lesser role. Strategies to target specific transducer molecules on corneal nerves may prove beneficial as adjunct therapies in managing ocular pain in moderate to severe cases of DE.

Using stem cell biology to study and treat ophthalmologic and oculoplastic diseases

With the rapid growth of the stem cell biology field, the prospect of regenerative medicine across multiple tissue types comes closer to reality. Several groundbreaking steps paved the way for applying stem cell biology to the several subfields within ophthalmology and oculoplastic surgery. These steps include the use of stem cell transplants as well as studies of various ophthalmologic pathologies at the molecular level. The necessity of stem cell transplant is readily apparent, having already been used for several studies such as artificial lacrimal gland design and eyelid reconstruction. Investigating the stem cell biology behind oncological diseases of the eye has also developed recently, such as with the identification of specific markers to label cancer stem cells in orbital adenoid cystic carcinoma. The advent of induced pluripotent stem cells led to a burst of productivity in the field of regenerative medicine, making it possible to take a patient's own cells, reprogram them, and use them to either study patient-specific pathology in vitro or use them for eventual patient specific therapeutics. Patient-specific adipose-derived stem cells (ASCs) have been used for a variety of treatments, such as wound healing and burn therapies. As the fields of stem cell biology and regenerative medicine continue to progress, its use will become a mainstay of patient-specific cell therapies in the future.

Autologous serum eye-drops and enhanced epithelial healing time after photorefractive keratectomy

BACKGROUND

The aim of the study is to test whether use of autologous serum eye-drops can provide earlier epithelial healing following the application of photorefractive keratectomy.

METHOD

Sixty patients (60 eyes) underwent photorefractive keratectomy for myopia. Thirty eyes received autologous serum drops (Study group) while 30 eyes received conventional artificial tears (Control group) after photorefractive keratectomy. An 8 mm epithelial opening was prepared with the application of 18 per cent alcohol for 20 seconds. Photorefractive keratectomy was performed using ESIRIS excimer laser (SCHWIND, Kleinostheim, Germany) with an optic zone of 6.5 mm. Total duration of epithelial healing was monitored as the main outcome measure. The comparisons were done with chi-square test and independent samples t-test. Statistical significance was considered at p < 0.05.

RESULTS

Preoperative myopic spherical refraction and ablation depths were similar in the study and control groups. The mean duration for epithelial healing was about one day shorter in the eyes receiving autologous serum compared to the eyes receiving conventional treatment (2.2 ± 0.25 days versus 3 ± 0 days, p = 0.001). All eyes achieved 6/7.5 or better uncorrected visual acuity in six months. In both groups, more than 90 per cent of eyes were within ±0.50 D of emmetropia in 12 months. No significant difference was noted for the incidence of +1 haze.

CONCLUSION

Use of autologous serum drops reduces epithelial healing duration following surface ablation for two days.

A novel TRPM8 agonist relieves dry eye discomfort

Background

Physical cooling of the eye surface relieves ocular discomfort, but translating this event to drug treatment of dry eye discomfort not been studied. Here, we synthesized a water-soluble TRPM8 receptor agonist called cryosim-3 (C3, 1-diisopropylphosphorylnonane) which selectively activates TRPM8 (linked to cooling) but not TRPV1 or TRPA1 (linked to nociception) and tested C3 in subjects with mild forms of dry eye disease.

Methods

A set of 1-dialkylphosphoryalkanes were tested for activation of TRPM8, TRPV1 and TRPA1 receptors in transfected cells. The bioactivity profiles were compared by perioral, topical, and intravenous delivery to anesthetized rats. The selected lead candidate C3 or vehicle (water) was applied with a cotton gauze pad to upper eyelids of patients with dry eye disease (n = 30). Cooling sensation, tear film break-up time (TBUT), basal tear secretion, and corneal staining were evaluated. C3 was then applied four times daily for 2 weeks to patients using a pre-loaded single unit applicator containing 2 mg/mL of C3 in water (n = 20) or water only. TBUT, basal tear secretion, and corneal staining, and three questionnaires surveys of ocular discomfort (VAS scale, OSDI, and CVS symptoms) were analyzed before and at 1 and 2 weeks thereafter.

Results

C3 was a selective and potent TRPM8 agonist without TRPV1 or TRPA1 activity. In test animals, the absence of shaking behavior after C3 perioral administration made it the first choice for further study. C3 increased tear secretion in an animal model of dry eye disease and did not irritate when wiped on eyes of volunteers. C3 singly applied (2 mg/ml) produced significant cooling in <5 min, an effecting lasting 46 min with an increase in tear secretion for 60 min. C3 applied for 2 weeks also significantly increased basal tear secretion with questionnaire surveys of ocular discomfort indices clearly showing improvement of symptoms at 1 and 2 weeks. No complaints of irritation or pain were reported by any subject.

Conclusions

C3 is a promising candidate for study of TRPM8 function on the eye surface and for relief of dry eye discomfort.

Trial registration

ISRCTN24802609 and ISRCTN13359367. Registered 23 March 2015 and 2 September 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s12886-017-0495-2) contains supplementary material, which is available to authorized users.

Applications of stem cell biology to oculoplastic surgery

PURPOSE OF REVIEW

The review examines the utility of stem cell biology in ophthalmology and oculoplastic surgery.

RECENT FINDINGS

The applicability of stem cell biology varies across a range of different subfields within ophthalmology and oculoplastic surgery. Resident stem cells have been identified in the lacrimal gland, corneal limbus, orbital fat, and muscles of the eye, and can potentially be applied for in-vitro cell and organ cultures with the intent of disease modeling and transplants. The discovery of adipocyte-derived stem cells offered a potentially powerful tool for a variety of oculoplastic applications, such as wound healing, skin rejuvenation, and burn therapeutics. Several groups are currently identifying new uses for stem cells in oculoplastic surgery.

SUMMARY

The need for stem cell treatment spans a wide array of subfields within ophthalmology, ranging from reconstruction of the eyelid to the generation of artificial lacrimal glands and oncological therapeutics. The advent of induced pluripotent stem cells opened the realm of regenerative medicine, making the modeling of patient-specific diseases a possibility. The identification and characterization of endogenous stem cell populations in the eye makes it possible to obtain specific tissues through induced pluripotent stem cells differentiation, permitting their use in transplants for oculoplastic surgery.

Bioengineered Lacrimal Gland Organ Regeneration in Vivo

The lacrimal gland plays an important role in maintaining a homeostatic environment for healthy ocular surfaces via tear secretion. Dry eye disease, which is caused by lacrimal gland dysfunction, is one of the most prevalent eye disorders and causes ocular discomfort, significant visual disturbances, and a reduced quality of life. Current therapies for dry eye disease, including artificial tear eye drops, are transient and palliative. The lacrimal gland, which consists of acini, ducts, and myoepithelial cells, develops from its organ germ via reciprocal epithelial-mesenchymal interactions during embryogenesis. Lacrimal tissue stem cells have been identified for use in regenerative therapeutic approaches aimed at restoring lacrimal gland functions. Fully functional organ replacement, such as for tooth and hair follicles, has also been developed via a novel three-dimensional stem cell manipulation, designated the Organ Germ Method, as a next-generation regenerative medicine. Recently, we successfully developed fully functional bioengineered lacrimal gland replacements after transplanting a bioengineered organ germ using this method. This study represented a significant advance in potential lacrimal gland organ replacement as a novel regenerative therapy for dry eye disease. In this review, we will summarize recent progress in lacrimal regeneration research and the development of bioengineered lacrimal gland organ replacement therapy.