The cellular mechanisms of dry eye: from pathogenesis to treatment

Conjunctival Goblet Cell Function: Effect of Contact Lens Wear and Cytokines

This review focuses on conjunctival goblet cells and their essential function in the maintenance of eye health. The main function of goblet cells is to produce and secrete mucins that lubricate the ocular surface. An excess or a defect in those mucins leads to several alterations that makes goblet cells central players in maintaining the proper mucin balance and ensuring the correct function of ocular surface tissues. A typical pathology that occurs with mucous deficiency is dry eye disease, whereas the classical example of mucous hyperproduction is allergic conjunctivitis. In this review, we analyze how goblet cell number and function can be altered in these diseases and in contact lens (CL) wearers. We found that most published studies focused exclusively on the goblet cell number. However, recent advances have demonstrated that, along with mucin secretion, goblet cells are also able to secrete cytokines and respond to them. We describe the effect of different cytokines on goblet cell proliferation and secretion. We conclude that it is important to further explore the effect of CL wear and cytokines on conjunctival goblet cell function.

Companion animals: Translational scientist's new best friends

Knowledge and resources derived from veterinary medicine represent an underused resource that could serve as a bridge between data obtained from diseases models in laboratory animals and human clinical trials. Naturally occurring disease in companion animals that display the defining attributes of similar, if not identical, diseases in humans hold promise for providing predictive proof of concept in the evaluation of new therapeutics and devices. Here we outline comparative aspects of naturally occurring diseases in companion animals and discuss their current uses in translational medicine, benefits, and shortcomings. Last, we envision how these natural models of disease might ultimately decrease the failure rate in human clinical trials and accelerate the delivery of effective treatments to the human clinical market.

Clusterin in the eye: An old dog with new tricks at the ocular surface

The multifunctional protein clusterin (CLU) was first described in 1983 as a secreted glycoprotein present in ram rete testis fluid that enhanced aggregation ('clustering') of a variety of cells in vitro. It was also independently discovered in a number of other systems. By the early 1990s, CLU was known under many names and its expression had been demonstrated throughout the body, including in the eye. Its homeostatic activities in proteostasis, cytoprotection, and anti-inflammation have been well documented, however its roles in health and disease are still not well understood. CLU is prominent at fluid-tissue interfaces, and in 1996 it was demonstrated to be the most highly expressed transcript in the human cornea, the protein product being localized to the apical layers of the mucosal epithelia of the cornea and conjunctiva. CLU protein is also present in human tears. Using a preclinical mouse model for desiccating stress that mimics human dry eye disease, the authors recently demonstrated that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration in the tears. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to LGALS3 (galectin-3), a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. CLU depletion from the ocular surface epithelia is seen in a variety of inflammatory conditions in humans and mice that lead to squamous metaplasia and a keratinized epithelium. This suggests that CLU might have a specific role in maintaining mucosal epithelial differentiation, an idea that can now be tested using the mouse model for desiccating stress. Most excitingly, the new findings suggest that CLU could serve as a novel biotherapeutic for dry eye disease.

Quantitative assessment of central and limbal epithelium after long-term wear of soft contact lenses and in patients with dry eyes: a pilot study

PurposeAnalysis of microstructural alterations of corneal and limbal epithelial cells in healthy human corneas and in other ocular conditions.Patients and methodsUnilateral eyes of three groups of subjects include healthy volunteers (G1, n=5), contact lens wearers (G2, n=5), and patients with dry eyes (G3, n=5) were studied. Imaging of basal (BC) and intermediate (IC) epithelial cells from central cornea (CC), corneal limbus (CL) and scleral limbus (SL) was obtained by in vivo confocal microscopy (IVCM). An appropriate image analysis algorithm was used to quantify morphometric parameters including mean cell area, compactness, solidity, major and minor diameter, and maximum boundary distance.ResultsThe morphometric parameters of BC and IC demonstrated no significant differences (P>0.05) between groups. Comparison between three corneal locations (CC, CL, and SL) within the groups showed significant differences (P<0.05) with mean values of cell area, compactness, solidity, and major and minor diameter of BC that increase from CC to limbus. The BC were round and regular in the central cornea (P<0.05) compared with CL and SL.ConclusionsIVCM enables high-quality confocal images from central corneal and limbal epithelium. This quantitative study demonstrated morphological differences in the basal and intermediate epithelium between limbus and central cornea, and found no differences between contact lens wearers, dry eyes, and normal subjects.

(5Z,11Z,15R)-15-Hydroxyeicosa-5,11-dien-13-ynoic acid: A stable isomer of 15(S)-HETE that retains key vasoconstrictive and antiproliferative activity

15(S)-Hydroxyeicosa-(5Z,8Z,11Z,13E)-tetraenoic acid (15(S)-HETE) is a metabolite of arachidonic acid that elicits a number of biological effects including vasoconstriction and angiogenesis. (5Z,11Z,15R)-15-Hydroxyeicosa-5,11-dien-13-ynoic acid (HETE analog 1) is a synthetic isomer of 15(S)-HETE that is much more stable to autoxidation. Using isometric recording of isolated pulmonary arteries from male and female rabbits, HETE analog 1 and 15(S)-HETE were found to elicit concentration-dependent contractions that were slightly greater in females compared to males. The maximal response in females was greater with 15(S)-HETE. HETE analog 1 and 15(S)-HETE increased [(3)H]-thymidine incorporation in vascular smooth muscle cells cultured from male rabbit pulmonary arteries; both the maximal response and potency were greater with 15(S)-HETE. In contrast, HETE analog 1 produced a concentration-dependent inhibition in proliferation and migration of human hormone-independent prostate carcinoma PC-3 cells. The protocol for synthesis of HETE analog 1 is reported. The stability of this substance and its similar biological profile to 15(S)-HETE support future studies in eicosanoid research.

Corneal and conjunctival sensitivity in rosacea patients

Purpose

To assess corneal and conjunctival sensitivity in rosacea patients.

Methods

A total of 55 patients with rosacea and 37 control subjects participated in the study. Corneal and conjunctival sensitivity was determined by Cochet-Bonnet esthesiometer. Subjective symptoms of ocular dryness were evaluated using Ocular Surface Disease Index (OSDI). Schirmer’s I test (ST), tear breakup time (tBUT) and ocular surface staining with fluorescein were carried out to measure objective signs.

Results

The mean corneal and conjunctival sensitivity did not differ significantly between rosacea patients and controls (all p > 0.05). Schirmer’s I test and tBUT were significantly reduced (p = 0.004 for OD and p < 0.001 for OS) and grade of ocular surface staining was significantly high (p = 0.018 for OD and p = 0.038 for OS) in rosacea patients. Corneal and conjunctival sensitivity did not show significant correlation with ST, tBUT, ocular surface staining (Oxford Schema), duration of rosacea and OSDI score.

Conclusions

Corneal and conjunctival sensitivity did not change significantly in rosacea.

Burning Eye Syndrome: Do Neuropathic Pain Mechanisms Underlie Chronic Dry Eye?

OBJECTIVE

Dry eye is a multi-factorial disorder that manifests with painful ocular symptoms and visual disturbances, which can only be partly attributed to tear dysfunction. This disorder may also involve neuroplasticity in response to neuronal injury. This review will emphasize the key characteristics of dry eye pain and its pathologic mechanisms, making the argument that a subset of dry eye represents a neuropathic pain disorder of the eye, more appropriately called "burning eye syndrome."

METHODS

A literature review was conducted using a PubMed search focusing on dry eye, corneal nociception, and neuropathic pain. Articles were reviewed and those discussing clinical course, pathophysiology, and neuronal regulation of chronic ocular pain as related to dry eye were summarized.

RESULTS

We found that there is a discordance between ocular pain and dryness on the ocular surface. Although tear dysfunction may be one of the initial insults, its persistence may be associated with repeated ocular sensory nerve injury leading to an acute-to-chronic pain transition associated with neuropathologic changes (peripheral and central sensitization), neuronal dysfunction, and spontaneous ocular pain.

CONCLUSION

Dry eye is becoming a major health concern due to its increasing incidence, significant morbidity, and economic burden. Recent evidence suggests that a subset of dry eye may be better represented as a chronic neuropathic pain disorder due to its features of dysesthesia, spontaneous pain, allodynia, and hyperalgesia. Future therapies targeted at the underlying neuroplasticity may yield improved efficacy for patients with this subset of dry eye, which we term "burning eye syndrome."

Ocular surface mucins and local inflammation--studies in genetically modified mouse lines

Mucins locate to the apical surfaces of all wet-surfaced epithelia including ocular surface. The functions of the mucins include anti-adhesive, lubrication, water retention, allergens and pathogen barrier function. Ocular surface pathologies, i.e. dry eye syndrome or allergic conjunctivitis, are reportedly associated with alteration of expression pattern of mucin components. Recent investigations indicated anti-bacterial adhesion or anti-inflammatory effects of members of mucins in non-ocular tissues, i.e., gastrointestinal tracts or airway tissues, by using genetically modified mouse lines that lacks an expression of a mucin member. However, examination of ocular phenotypes of each of mucin gene-ablated mouse lines has not yet fully performed. Muc16-dficient mouse is associated with spontaneous subclinical inflammation in conjunctiva. The article reviews the roles of mucin members in modulation of local inflammation in mucous membrane tissues and phenotype of mouse lines with the loss of a mucin gene. Analysis of ocular surface of mucin-gene related mutant mouse lines are to be further performed.

Clusterin Seals the Ocular Surface Barrier in Mouse Dry Eye

Dry eye is a common disorder caused by inadequate hydration of the ocular surface that results in disruption of barrier function. The homeostatic protein clusterin (CLU) is prominent at fluid-tissue interfaces throughout the body. CLU levels are reduced at the ocular surface in human inflammatory disorders that manifest as severe dry eye, as well as in a preclinical mouse model for desiccating stress that mimics dry eye. Using this mouse model, we show here that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to the galectin LGALS3, a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. These findings define a fundamentally new mechanism for ocular surface protection and suggest CLU as a biotherapeutic for dry eye.

Associations between signs and symptoms of dry eye disease: a systematic review

PURPOSE

The accurate diagnosis and classification of dry eye disease (DED) is challenging owing to wide variations in symptoms and lack of a single reliable clinical assessment. In addition, changes and severity of clinical signs often do not correspond to patient-reported symptoms. To better understand the inconsistencies observed between signs and symptoms, we conducted a systematic literature review to evaluate published studies reporting associations between patient-reported symptoms and clinical signs of DED.

METHODS

PubMed and Embase were searched for English-language articles on the association between clinical signs and symptoms of DED up to February 2014 (no lower limit was set).

RESULTS

Thirty-four articles were identified that assessed associations between signs and symptoms, among which 33 unique studies were reported. These included 175 individual sign-symptom association analyses. Statistical significance was reported for associations between sign and symptom measures in 21 of 33 (64%) studies, but for only 42 of 175 (24%) individual analyses. Of 175 individual analyses, 148 reported correlation coefficients, of which the majority (129/148; 87%) were between -0.4 and 0.4, indicating low-to-moderate correlation. Of all individual analyses that demonstrated a statistically significant association, one-half (56%) of reported correlation coefficients were in this range. No clear trends were observed in relation to the strength of associations relative to study size, statistical methods, or study region, although results from three studies did suggest that disease severity may be a factor.

CONCLUSION

Associations between DED signs and symptoms are low and inconsistent, which may have implications for monitoring the response to treatment, both in the clinic and in clinical trials. Further studies to increase understanding of the etiopathogenesis of DED and to identify the most reliable and relevant measures of disease are needed to enhance clinical assessment of DED and the measurement of response to therapeutic interventions.

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.

Safety and pharmacokinetics of escalating doses of human recombinant nerve growth factor eye drops in a double-masked, randomized clinical trial

BACKGROUND AND OBJECTIVES

Nerve growth factor (NGF) is a neurotrophin with therapeutic possibilities that extend from the nervous system to the eye. We tested the safety, maximal tolerated dose, pharmacokinetics, and antigenicity of a novel human recombinant NGF (rhNGF) eye-drop formulation in a phase I study.

METHODS

This prospective, randomized, double-masked, vehicle-controlled trial, sponsored by Dompé SpA (registered as NCT01744704 at ClinicalTrials.gov), enrolled 74 healthy volunteers (24 females, 50 males, age 40.2 ± 11.8 years). Subjects were randomized in three cohorts to receive (1) a single eye-drop containing 0.0175, 0.175, or 0.7 μg rhNGF; (2) a single ascending dose of rhNGF eye drops three times a day for 1 day (total daily dose 2.1, 6.3, or 18.9 μg), or vehicle; or (3) a multiple ascending dose of rhNGF eye drops three times a day for 5 days (total dose 10.5, 31.5, or 94.5 μg), or vehicle. Outcome measures included blood chemistry, urinalyses, vital signs, electrocardiograms (ECGs), serum NGF antibodies, ocular and systemic adverse events (AEs), visual acuity, tear function, intraocular pressure, fundus oculi, and ocular symptoms.

RESULTS

Administration of rhNGF eye drops did not result in a significant increase of circulating NGF levels and no antidrug antibodies were detected in serum. No serious AEs were recorded, and a few mild, transient ocular AEs related to rhNGF administration were reported only at the highest concentration.

CONCLUSIONS

rhNGF eye drops were well tolerated, with no detectable clinical evidence of systemic AEs. These results pave the way for the development of clinical trials on rhNGF in ophthalmology.

Ocular surface changes in type II diabetic patients with proliferative diabetic retinopathy

AIM

To detect and analyze the changes on ocular surface and tear function in type II diabetic patients with proliferative diabetic retinopathy (PDR), an advanced stage of diabetic retinopathy (DR), using conventional ophthalmic tests and the high-resolution laser scanning confocal microscopy.

METHODS

Fifty-eight patients with type II diabetes were selected. Based on the diagnostic criteria and stage classification of DR, the patients were divided into the non-DR (NDR) group and the PDR group. Thirty-six patients with cataract but no other ocular and systemic disease were included as non-diabetic controls. All the patients were subjected to the conventional clinical tests of corneal sensitivity, Schirmer I Test, and corneal fluorescein staining. The non-invasive tear film break-up time (NIBUT) and tear interferometry were conducted by a Tearscope Plus. The morphology of corneal epithelia and nerve fibers was examined using the high-resolution confocal microscopy.

RESULTS

The NDR group exhibited significantly declined corneal sensitivity and Schirmer I test value, as compared to the non-diabetic controls (P< 0.001). The PDR group showed significantly reduced corneal sensitivity, Schirmer I test value, and NIBUT in comparison to the non-diabetic controls (P < 0.001). Corneal fluorescein staining revealed the progressively injured corneal epithelia in the PDR patients. Moreover, significant decrease in the corneal epithelial density and morphological abnormalities in the corneal epithelia and nerve fibers were also observed in the PDR patients.

CONCLUSION

Ocular surface changes, including blunted corneal sensitivity, reduced tear secretion, tear film dysfunction, progressive loss of corneal epithelia and degeneration of nerve fibers, are common in type II diabetic patients, particularly in the diabetic patients with PDR. The corneal sensitivity, fluorescein staining scores, and the density of corneal epithelial cells and nerve fibers in the diabetic patients correlate with the duration of diabetes. Therefore, ocular surface of the patients with PDR should be examined regularly by conventional approaches and confocal microscopy to facilitate early diagnosis and treatment of keratopathy.

Nanotherapies for the treatment of ocular diseases

The topical route is the most frequent and preferred way to deliver drugs to the eye. Unfortunately, the very low ocular drug bioavailability (less than 5%) associated with this modality of administration, makes the efficient treatment of several ocular diseases a significant challenge. In the last decades, it has been shown that specific nanocarriers can interact with the ocular mucosa, thereby increasing the retention time of the associated drug onto the eye, as well as its permeability across the corneal and conjunctival epithelium. In this review, we comparatively analyze the mechanism of action and specific potential of the most studied nano-drug delivery carriers. In addition, we present the success achieved until now using a number of nanotherapies for the treatment of the most prevalent ocular pathologies, such as infections, inflammation, dry eye, glaucoma, and retinopathies.