Reconsidering the central role of mucins in dry eye and ocular surface diseases

Development and evaluation of hot-melt-extruded diquafosol tetrasodium formulations for ophthalmic inserts: A design of experiments approach

This study aimed to develop, optimize, and evaluate hot-melt-extruded ophthalmic inserts capable of sustained release of diquafosol tetrasodium (DQS) via a design of experiments approach. DQS, a tear stimulant for dry eye management, faces challenges of frequent administration and low bioavailability. The developed insert uses biodegradable polymers in varied proportions to achieve sustained release. Optimized through mixture design, the insert completely dissolved within 24 h and maintained a stable drug content, thickness, and surface pH over three months at room temperature. In vitro corneal permeation studies on excised rabbit corneas demonstrated increased bioavailability, suggesting a reduced dosing frequency compared with conventional eye drops. Therefore, this insert has potential to enhance treatment outcomes by improving patient compliance and providing sustained drug effects.

A Standardized Extract of Green-Cotyledon Small Black Soybean (EYESOY®) Ameliorates Dry Eye Syndrome in an Animal Model

PURPOSE

Dry eye syndrome is a common ocular disease that causes morbidity, high healthcare burden, and decreased quality of life. In this study, we evaluated the beneficial effects of a standardized extract of small black soybean (EYESOY®) in a benzalkonium chloride (BAC)-induced murine model of dry eye.

METHODS

Experimental dry eye was induced by instillation of 0.02% BAC on the right eye of the Sprague-Dawley rats. Saline solution or EYESOY were administered orally every day for 8 weeks.

RESULTS

EYESOY significantly improved tear volume in the cornea compared with that in the BAC group. Moreover, EYESOY inhibited damage to the corneal epithelial cells and lacrimal glands by suppressing the oxidative and inflammatory responses in a mouse dry eye model. It also increased the goblet cell density and mucin integrity in the conjunctiva.

CONCLUSIONS

Our results suggest that EYESOY has the potential to alleviate dry eye syndrome.

Blue light induced ferroptosis via STAT3/GPX4/SLC7A11/FTH1 in conjunctiva epithelium in vivo and in vitro

The prevalence of Light-emitting diodes (LEDs) has exposed us to an excessive amount of blue light (BL) which causes various ophthalmic diseases. Previous studies have shown that conjunctiva is vulnerable to BL. In this study, we aimed to investigate the underlying mechanism of BL-induced injury in conjunctiva. We placed C57BL/6 mice and human conjunctival epithelial cell lines (HCECs) under BL (440 nm ± 15 nm, 0.2 mW/cm2) to establish a BL injury model in vivo and in vitro. Immunohistochemistry and MDA assay were used to identify lipid peroxidation (LPO) in vivo. HE staining was applied to detect morphological damage of conjunctival epithelium. DCFH-DA, C11-BODIPY 581/591, Calcein-AM, and FeRhoNox™-1 probes were performed to identify ferroptosis levels in vitro. Real-time qPCR and Western blotting techniques were employed to uncover signaling pathways of blue light-induced ferroptosis. Our findings demonstrated that BL affected tear film instability and induced conjunctival epithelium injury in vivo. Ferrostatin-1 significantly alleviated blue light-induced ferroptosis in vivo and in vitro. BL downregulates the levels of solute carrier family 7 member 11 (SLC7A11), Ferritin heavy chain (FTH1), and glutathione peroxidase (GPX4) by inhibiting the activation and translocation of the Signal transducer and activator of transcription 3 (STAT3) from inducing Fe2+ burst, ROS and LPO accumulation, ultimately resulting in ferroptosis. This study will offer new insight into BL-induced conjunctival injury and LED-induced dry eye.

Combination of PEGylation and Cationization on Phospholipid-Coated Cyclosporine Nanosuspensions for Enhanced Ocular Drug Delivery

Strong precorneal clearance mechanisms including reflex blink, constant tear drainage, and rapid mucus turnover constitute great challenges for eye drops for effective drug delivery to the ocular epithelium. In this study, cyclosporine A (CsA) for the treatment of dry eye disease (DED) was selected as the model drug. Two strategies, PEGylation for mucus penetration and cationization for potent cellular uptake, were combined to construct a novel CsA nanosuspension (NS@lipid-PEG/CKC) by coating nanoscale drug particles with a mixture of lipids, DSPE-PEG2000, and a cationic surfactant, cetalkonium chloride (CKC). NS@lipid-PEG/CKC with the mean size ∼173 nm and positive zeta potential ∼+40 mV showed promoted mucus penetration, good cytocompatibility, more cellular uptake, and prolonged precorneal retention without obvious ocular irritation. More importantly, NS@lipid-PEG/CKC recovered tear production and goblet cell density more efficiently than the commercial cationic nanoemulsion on a dry eye disease rat model. All results indicated that a combination of PEGylation and cationization might provide a promising strategy to coordinate mucus penetration and cellular uptake for enhanced drug delivery to the ocular epithelium for nanomedicine-based eye drops.

Keratan sulfate, an electrosensory neurosentient bioresponsive cell instructive glycosaminoglycan

The roles of keratan sulfate (KS) as a proton detection glycosaminoglycan in neurosensory processes in the central and peripheral nervous systems is reviewed. The functional properties of the KS-proteoglycans aggrecan, phosphacan, podocalyxcin as components of perineuronal nets in neurosensory processes in neuronal plasticity, cognitive learning and memory are also discussed. KS-glycoconjugate neurosensory gels used in electrolocation in elasmobranch fish species and KS substituted mucin like conjugates in some tissue contexts in mammals need to be considered in sensory signalling. Parallels are drawn between KS's roles in elasmobranch fish neurosensory processes and its roles in mammalian electro mechanical transduction of acoustic liquid displacement signals in the cochlea by the tectorial membrane and stereocilia of sensory inner and outer hair cells into neural signals for sound interpretation. The sophisticated structural and functional proteins which maintain the unique high precision physical properties of stereocilia in the detection, transmittance and interpretation of acoustic signals in the hearing process are important. The maintenance of the material properties of stereocilia are essential in sound transmission processes. Specific, emerging roles for low sulfation KS in sensory bioregulation are contrasted with the properties of high charge density KS isoforms. Some speculations are made on how the molecular and electrical properties of KS may be of potential application in futuristic nanoelectronic, memristor technology in advanced ultrafast computing devices with low energy requirements in nanomachines, nanobots or molecular switches which could be potentially useful in artificial synapse development. Application of KS in such innovative areas in bioregulation are eagerly awaited.

How gut microbiota may impact ocular surface homeostasis and related disorders

Changes in the bacterial flora in the gut, also described as gut microbiota, are readily acknowledged to be associated with several systemic diseases, especially those with an inflammatory, neuronal, psychological or hormonal factor involved in the pathogenesis and/or the perception of the disease. Maintaining ocular surface homeostasis is also based on all these four factors, and there is accumulating evidence in the literature on the relationship between gut microbiota and ocular surface diseases. The mechanisms involved are mostly interconnected due to the interaction of central and peripheral neuronal networks, inflammatory effectors and the hormonal system. A better understanding of the influence of the gut microbiota on the maintenance of ocular surface homeostasis, and on the onset or persistence of ocular surface disorders could bring new insights and help elucidate the epidemiology and pathology of ocular surface dynamics in health and disease. Revealing the exact nature of these associations could be of paramount importance for developing a holistic approach using highly promising new therapeutic strategies targeting ocular surface diseases.

New advances in medical management of dry eye: optimizing treatment strategies for enhanced relief

PURPOSE

Dry eye disease (DED) is a prevalent ocular surface disease that is conventionally characterized by tear film hyperosmolarity and instability. This review presents a summarized classification of DED, followed by a comprehensive discussion of the most recent topical and systemic medications and clinical recommendations for selecting the most appropriate option for each patient.

METHODS

An extensive literature search was conducted on electronic databases, such as PubMed, Scopus, and Web of Science, using keywords including "dry eye syndrome," "ocular surface disease," "medical management," "artificial tears," "topical immunomodulators," and "meibomian gland dysfunction."

RESULTS

The underlying reasons for DED can range from insufficient aqueous tear production to increased tear evaporation. Recent literature has provided a more in-depth understanding of the pathophysiology of DED by examining the tear film's lipid, aqueous, and mucin layers. However, despite these advancements, medical management of patients with symptomatic DED has not fully reflected this modernized knowledge of its pathophysiology.

CONCLUSION

To develop a rationalized strategy for treating DED, it is crucial to have updated knowledge of therapeutic options, their mechanisms of actions, and indications based on the DED type and underlying causes.

Efficacy of bilateral OC-01 (varenicline solution) nasal spray in alleviating signs and symptoms of dry eye disease: A systematic review

PURPOSE

To comprehensively review the efficacy and safety of OC-01 varenicline nasal spray versus vehicle nasal spray (VNS) in the treatment in dry eye disease (DED).

METHODS

A systematic review that included full-length randomized controlled studies (RCTs), as well as post hoc analyses of RCTs reporting new findings on OC-01 VNS treatment in three databases, PubMed, Scopus and Web of Science, was performed according to the PRISMA statement. The search period included studies published between December 2021 and September 2023. The Cochrane risk of bias tool was used to analyze the quality of the studies selected.

RESULTS

A total of 8 studies were included in this systematic review. OC-01 VNS treatment achieved higher improvement than vehicle in all reported variables. The mean differences between both groups were in favor of OC-01 VNS treatment and were as follow: eye dryness score base on a visual analogue scale (EDS-VAS) of -7.5 ± 2.2 points [-11.6 to -5.6], Schirmer test (ST) with anesthesia of 6.6 ± 2.3 mm [4.9 to 11.8] and total corneal fluorescein staining (tCFS) of -1.2 ± 0.01 points [-1.2 to -1.1]. Similar improvements were reported with OC-01 VNS 0.03 mg and 0.06 mg. Adverse events (AEs) were 15.5 ± 19.4 % [-13 to 80.5] higher in the OC-01 VNS group with an overall adherence > 93 %.

CONCLUSIONS

OC-01 VNS improves dry eye symptoms and signs with a satisfactory tolerability. Therefore, OC-01 VNS seems to be a safe and effective treatment that could be recommended in patients with DED. This new treatment could be particularly useful in those patients who have difficulties with the administration of traditional topical therapies.

Recent progress of nanomedicine in managing dry eye disease

Background

Dry eye disease (DED) is a commonly reported ocular complaint that has garnered significant attention in recent research. The global occurrence of DED ranges from 5% to 50%, impacting a substantial proportion of individuals worldwide with increasing frequency. Although topical administration remains the mainstream drug delivery method for ocular diseases, it suffers from drawbacks such as low bioavailability, rapid drug metabolism, and frequent administration requirements. Fortunately, the advancements in nanomedicine offer effective solutions to address the aforementioned issues and provide significant assistance in the treatment of DED.

Main text

DED is considered a multifactorial disease of the ocular surface and tear film, in which the integrity of tear film function and structure plays a crucial role in maintaining the homeostasis of the ocular surface. The conventional treatment for DED involves the utilization of artificial tear products, cyclosporin, corticosteroids, mucin secretagogues, and nonsteroidal anti-inflammatory drugs. Furthermore, nanomedicine is presently a significant field of study, with numerous clinical trials underway for various nanotherapeutics including nanoemulsions, nanosuspensions, liposomes, and micelles. Notably, some of these innovative nanoformulations have already received FDA approval as novel remedies for DED, and the advancement of nanomedicine is poised to offer enhanced prospects to solve the shortcomings of existing treatments for DED partially.

Conclusions

This article provides an overview of the latest advancements in nanomedicine for DED treatment, while the field of DED treatment is expected to witness a remarkable breakthrough shortly with the development of nanomedicine, bringing promising prospects for patients worldwide suffering conditions.

Evaluation of Dry Eye Severity and Ocular Surface Inflammation in Patients with Pemphigus and Pemphigoid

PURPOSE

To evaluate ocular surface involvement, tear cytokine levels, and histopathological changes in pemphigus and pemphigoid patients.

METHODS

A total of 22 patients (15 pemphigus and 7 pemphigoids) and 21 non-diseased controls were enrolled in our study. All participants underwent ocular surface evaluation, which included ocular surface disease index test, slit lamp observation, dry eye-related examination, tear multicytokine analysis, and conjunctival impression cytology.

RESULTS

Pemphigus and pemphigoid patients presented much more severe conjunctivochalasis, corneal epithelial defects, corneal opacity, symblepharon   and dry eye. Severe ocular surface squamous metaplasia and a significant increase of tear macrophage inflammatory protein-1beta, tumor necrosis factor-alpha, interleukin (IL)-1β, IL -6, and IL-8 occurred in pemphigus and pemphigoid patients.

CONCLUSIONS

Our results revealed that ocular surface inflammation and dry eye persist in most pemphigus and pemphigoid patients, and do not occur in parallel with the systemic course. Regular ophthalmological examinations and local anti-inflammatory should be provided for pemphigus and pemphigoid patients.

DZ2002 alleviates corneal angiogenesis and inflammation in rodent models of dry eye disease via regulating STAT3-PI3K-Akt-NF-κB pathway

Dry eye disease (DED) is a prevalent ocular disorder with a multifactorial etiology. The pre-angiogenic and pre-inflammatory milieu of the ocular surface plays a critical role in its pathogenesis. DZ2002 is a reversible type III S-adenosyl-L-homocysteine hydrolase (SAHH) inhibitor, which has shown excellent anti-inflammatory and immunosuppressive activities in vivo and in vitro. In this study, we evaluated the therapeutic potential of DZ2002 in rodent models of DED. SCOP-induced dry eye models were established in female rats and mice, while BAC-induced dry eye model was established in female rats. DZ2002 was administered as eye drops (0.25%, 1%) four times daily (20 μL per eye) for 7 or 14 consecutive days. We showed that topical application of DZ2002 concentration-dependently reduced corneal neovascularization and corneal opacity, as well as alleviated conjunctival irritation in both DED models. Furthermore, we observed that DZ2002 treatment decreased the expression of genes associated with angiogenesis and the levels of inflammation in the cornea and conjunctiva. Moreover, DZ2002 treatment in the BAC-induced DED model abolished the activation of the STAT3-PI3K-Akt-NF-κB pathways in corneal tissues. We also found that DZ2002 significantly inhibited the proliferation, migration, and tube formation of human umbilical endothelial cells (HUVECs) while downregulating the activation of the STAT3-PI3K-Akt-NF-κB pathway. These results suggest that DZ2002 exerts a therapeutic effect on corneal angiogenesis in DED, potentially by preventing the upregulation of the STAT3-PI3K-Akt-NF-κB pathways. Collectively, DZ2002 is a promising candidate for ophthalmic therapy, particularly in treating DED.

Engineered assemblies from isomeric pentapeptides augment dry eye treatment

Changing positions of amino acid residues in the peptide sequence alters the peptide' s assembly behaviors, affording various nanostructures. However, it remains elusive that how subtle changes in the peptide sequence influence the in vivo bioactivity of peptide-based nanocarriers, further impacting the efficacy of the encapsulated drugs. We report here a class of isomeric pentapeptide amphiphiles that associate into filaments with different dimensions, which were further used as carriers of Diquafosol tetrasodium (DQS), for the treatment of dry eye disease. Our results suggest that subtle changes in peptide sequences resulted in dramatically different molecular packings and distinct morphologies, which were verified by molecular dynamics simulations. In vivo results show that the drug retention time could be prolonged by the peptidic nanostructures on the ocular surface but were highly morphological-dependent. The longer retention time promised better therapeutic efficacy. In terms of facile synthesis and good biocompatibility, we believe that these peptides could be used for eye disease treatments or other related areas.

Comparison of Transcriptomic Analysis of the Conjunctiva in Glaucoma-Treated Eyes with Dry Eyes and Healthy Controls

Ocular surface disease (OSD) associated with topical glaucoma drugs is a common issue impacting treatment adherence. We aimed to identify conjunctival transcriptomic changes in glaucoma and dry eye patients, comparing them to healthy controls. Bulbar conjunctival specimens were collected via impression cytology from 33 patients treated for glaucoma, 9 patients with dry eye, and 14 healthy controls. RNA extraction and bulk RNA sequencing were performed, followed by bioinformatics analysis to detect gene dysregulation. Ingenuity pathways analysis (IPA) identified pathways and biological processes associated with these transcriptomic changes. Sequencing analysis revealed 200 modified genes in glaucoma patients compared to healthy individuals, 233 differentially expressed genes in dry eye patients versus controls, and 650 genes in treated versus dry eye samples. In glaucoma patients, 79% of altered pathways were related to host defense, while dry eye patients showed a 39% involvement of host response, 15% in cellular proliferation and integrity, and 16% of mitochondrial dysfunction. These findings were validated through qRT-PCR. Glaucoma patients showed an intensified conjunctival immune response as a potential cause of OSD, whereas in dry eye patients, in addition to the immune response, other mechanisms such as mitochondrial dysfunction or reduced cellular proliferation were observed.

Purple Corn Extract Improves Dry Eye Symptoms in Models Induced by Desiccating Stress and Extraorbital Lacrimal Gland Excision

Dry eye disease (DED) occurs when there are not enough tears, and the associated symptoms-burns, itching, and a gritty feeling in the eye-can cause great discomfort. The purpose of this study was to evaluate the therapeutic effect of purple corn extract (PCE) on DED. Pretreatment with PCE prevented desiccation-stress-induced cell damage in human retinal pigment epithelial cells and primary human corneal epithelial cells. Furthermore, PCE reduced the mRNA expression of inflammatory mediators in the induction of desiccation stress. The therapeutic effects of PCE on DED were evaluated in an animal model with induced unilateral excision of the exorbital lacrimal gland. The administration of PCE was effective at recovering tear production, corneal surface irregularity, and conjunctival goblet cell density, as well as at reducing apoptotic cell death in the outer layer of the corneal epithelium. Collectively, PCE improved dry eye symptoms, and, therefore, it could be a potential agent to ameliorate and/or treat DED.

Update on Dry Eye Disease Treatment: Evidence From Randomized Controlled Trials

ABSTRACT

Although the ultimate goal of dry eye disease (DED) management is to restore the ocular surface and tear film homeostasis and address any accompanying symptoms, addressing this is not an easy task. Despite the wide range of current treatment modalities targeting multiple aspects of DED, the available DED management literature is quite heterogeneous, rendering evaluation or comparison of treatment outcomes hard or almost impossible. There is still a shortage of well-designed, large-scale, nonsponsored, randomized, controlled trials (RCTs) evaluating long-term safety and efficacy of many targeted therapies individually or used in combination, in the treatment of identified subgroups of patients with DED. This review focuses on the treatment modalities in DED management and aims to reveal the current evidence available as deduced from the outcomes of RCTs.

Animal Models in Eye Research: Focus on Corneal Pathologies

The eye is a complex sensory organ that enables visual perception of the world. The dysfunction of any of these tissues can impair vision. Conduction studies on laboratory animals are essential to ensure the safety of therapeutic products directly applied or injected into the eye to treat ocular diseases before eventually proceeding to clinical trials. Among these tissues, the cornea has unique homeostatic and regenerative mechanisms for maintaining transparency and refraction of external light, which are essential for vision. However, being the outermost tissue of the eye and directly exposed to the external environment, the cornea is particularly susceptible to injury and diseases. This review highlights the evidence for selecting appropriate animals to better understand and treat corneal diseases, which rank as the fifth leading cause of blindness worldwide. The development of reliable and human-relevant animal models is, therefore, a valuable research tool for understanding and translating fundamental mechanistic findings, as well as for assessing therapeutic potential in humans. First, this review emphasizes the unique characteristics of animal models used in ocular research. Subsequently, it discusses current animal models associated with human corneal pathologies, their utility in understanding ocular disease mechanisms, and their role as translational models for patients.

A cocktail of small molecules maintains the stemness and differentiation potential of conjunctival epithelial cells

PURPOSE

The conjunctival epithelial cells cultured with bovine serum or feeder cells were not suitable for clinical application. Therefore, we developed a novel serum-free and feeder cell-free culture system containing only a cocktail of three chemicals (3C) to expand the conjunctival epithelial cells.

METHODS

The cell proliferative ability was evaluated by counting, crystal violet staining and Ki67 immunostaining. Co-staining of K7 and MUC5AC was performed to identify goblet cells. PAS staining was used to assess the ability of cells to synthesis and secrete glycoproteins. In vivo, eye drops containing 3C was administered to verify the role of 3C in the mouse conjunctival injury model. PAS, HE and immunofluorescence staining were performed to show conjunctival epithelial repair.

RESULTS

Compared with other small molecule groups and the serum group, the cells in 3C group showed superior morphology and proliferative ability. Meanwhile, 3C maintained the well-proliferative capacity of cells even after fifth passage. The 3C group also exhibited more K7 and MUC5AC double positive cells, and the PAS staining positive areas were present in both the cytoplasm and extracellular matrix. The cell sheets treated with 3C in air-lifted culture were obviously stratified. In vivo, more goblet cells in the conjunctival epithelium were observed in the 3C group.

CONCLUSION

Overall, our culture system can expand the conjunctival epithelial cells and retain their potential to differentiate into mature goblet cells, which provided a promising source of seed cells for conjunctival reconstruction. Furthermore, this system provides new insights for the clinical treatment of ocular surface diseases.

Roles unveiled for membrane-associated mucins at the ocular surface using a Muc4 knockout mouse model

Membrane-associated mucins (MAMs) are proposed to play critical roles at the ocular surface; however, in vivo evidence has been lacking. Here we investigate these roles by phenotyping of a Muc4 KO mouse. Histochemical analysis for expression of the beta-galactosidase transgene replacing Muc4 revealed a spiraling ribbon pattern across the corneal epithelium, consistent with centripetal cell migration from the limbus. Depletion of Muc4 compromised transcellular barrier function, as evidenced by an increase in rose bengal staining. In addition, the corneal surface was less smooth, consistent with disruption of tear film stability. While surface cells presented with well-developed microprojections, an increase in the number of cells with fewer microprojections was observed. Moreover, an increase in skin-type keratin K10 and a decrease in transcription factor Pax6 was observed, suggesting an incipient transdifferentiation. Despite this, no evidence of inflammatory dry eye disease was apparent. In addition, Muc4 had no effect on signaling by toll-like receptor Tlr4, unlike reports for MUC1 and MUC16. Results of this study provide the first in vivo evidence for the role of MAMs in transcellular barrier function, tear film stability, apical epithelial cell architecture, and epithelial mucosal differentiation at the ocular surface.

Isolation and Identification of a Novel Anti-Dry Eye Peptide from Tilapia Skin Peptides Based on In Silico, In Vitro, and In Vivo Approaches

Tilapia skin is a great source of collagen. Here, we aimed to isolate and identify the peptides responsible for combating dry eye disease (DED) in tilapia skin peptides (TSP). In vitro cell DED model was used to screen anti-DED peptides from TSP via Sephadex G-25 chromatography, LC/MS/MS, and in silico methods. The anti-DED activity of the screened peptide was further verified in the mice DED model. TSP was divided into five fractions (TSP-I, TSP-II, TSP-III, TSP-IV, and TSP-V), and TSP-II exerted an effective effect for anti-DED. A total of 131 peptides were identified using LC/MS/MS in TSP-II, and NGGPSGPR (NGG) was screened as a potential anti-DED fragment in TSP-II via in silico methods. In vitro, NGG restored cell viability and inhibited the expression level of Cyclooxygenase-2 (COX-2) protein in Human corneal epithelial cells (HCECs) induced by NaCl. In vivo, NGG increased tear production, decreased tear ferning score, prevented corneal epithelial thinning, alleviated conjunctival goblet cell loss, and inhibited the apoptosis of corneal epithelial cells in DED mice. Overall, NGG, as an anti-DED peptide, was successfully identified from TSP, and it may be devoted to functional food ingredients or medicine for DED.

Ocular Surface Allostasis-When Homeostasis Is Lost: Challenging Coping Potential, Stress Tolerance, and Resilience

The loss of ocular surface (OS) homeostasis characterizes the onset of dry eye disease. Resilience defines the ability to withstand this threat, reflecting the ability of the ocular surface to cope with and bounce back after challenging events. The coping capacity of the OS defines the ability to successfully manage cellular stress. Cellular stress, which is central to the outcome of the pathophysiology of dry eye disease, is characterized by intensity, continuity, and receptivity, which lead to the loss of homeostasis, resulting in a phase of autocatalytic dysregulation, an event that is not well-defined. To better define this event, here, we present a model providing a potential approach when homeostasis is challenged and the coping capacities have reached their limits, resulting in the stage of heterostasis, in which the dysregulated cellular stress mechanisms take over, leading to dry eye disease. The main feature of the proposed model is the concept that, prior to the initiation of the events leading to cellular stress, there is a period of intense activation of all available coping mechanisms preventing the imminent dysregulation of ocular surface homeostasis. When the remaining coping mechanisms and resilience potential have been maximally exploited and have, finally, been exceeded, there will be a transition to manifest disease with all the well-known signs and symptoms, with a shift to allostasis, reflecting the establishment of another state of balance. The intention of this review was to show that it is possibly the phase of heterostasis preceding the establishment of allostasis that offers a better chance for therapeutic intervention and optimized recovery. Once allostasis has been established, as a new steady-state of balance at a higher level of constant cell stress and inflammation, treatment may be far more difficult, and the potential for reversal is drastically decreased. Homeostasis, once lost, can possibly not be fully recovered. The processes established during heterostasis and allostasis require different approaches and treatments for their control, indicating that the current treatment options for homeostasis need to be adapted to a more-demanding situation. The loss of homeostasis necessarily implies the establishment of a new balance; here, we refer to such a state as allostasis.

Experimental study of the mechanism of induction of conjunctival goblet cell hyperexpression using CHIR-99021 in vitro

A component of the tear film, mucin is produced by conjunctival goblet cells and is crucial to preserving the tear film's stability. Severe thermal burns, chemical burns, and severe ocular surface diseases can cause extensive damage to the conjunctiva, destroy the secretory function of goblet cells, and affect the stability of the tear film and integrity of the ocular surface. Currently, the expansion efficiency of goblet cells in vitro is low. In this study, we observed that rabbit conjunctival epithelial cells exhibited dense colony morphology after stimulation with the Wnt/β-catenin signaling pathway activator CHIR-99021 and promoted the differentiation of conjunctival goblet cells and the expression of its specific marker Muc5ac, among which the best induction effect was observed after 72 h in vitro culture with 5 μmol/L CHIR-99021. Under optimal culture conditions, CHIR-99021 increased the expression levels of the Wnt/β-catenin signaling pathway factors Frzb, β-catenin, SAM pointed domain containing ETS transcription factor, and glycogen synthase kinase-3β and the levels of the Notch signaling pathway factors Notch1 and Krüppel-like factor 4 while decreasing the expression levels of Jagged-1 and Hes1. The expression level of ABCG2, a marker of epithelial stem cells, was raised to keep rabbit conjunctival epithelial cells from self-renewing. Our study showed that CHIR-99021 stimulation successfully activated the Wnt/β-catenin signaling pathway and conjunctival goblet cell differentiation was stimulated, in which the Notch signaling pathway played a combined role. Those results provide a novel idea for the expansion of goblet cells in vitro.

The Role of Membrane-Tethered Mucins in Axial Epithelial Adhesion in Controlled Normal Stress Environments

The collective adhesive behavior of epithelial cell layers mediated by complex macromolecular fluid environments plays a vital role in many biological processes. Mucins, a family of highly glycosylated proteins, are known to lubricate cell-on-cell contacts in the shear direction. However, the role of mucins mediating axial epithelial adhesion in the direction perpendicular to the plane of the cell sheet has received less attention. This article subjects cell-on-cell layers of live ocular epithelia that express mucins on their apical surfaces to compression/decompression cycles and tensile loading using a customized instrument. In addition to providing compressive moduli of native cell-on-cell layers, it is found that the mucin layer between the epithelia acts as a soft cushion between the epithelial cell layers. Decompression experiments reveal mucin layers act as soft, nonlinear springs in the axial direction. The cell-on-cell layers withstand decompression before fracturing by a cohesive failure within the mucin layer. When mucin deficiency is induced via a protease treatment, it is found that the axial adhesion between the cell layers is increased. The findings which correlate changes in biological factors with changes in mechanical properties might be of interest to challenges in ophthalmology, vision care, and mucus research.

The role of high molecular weight hyaluronic acid in mucoadhesion on an ocular surface model

Hyaluronic acid (HA) is frequently formulated in eye drops to improve the stability of the tear film by hydration and lubrication. Mucoadhesion is related to the ocular residence time and therefore to the effectiveness of the eye drops. The ocular residence time of the HA formulation is correlated with the ability of HA to create specific strong interactions in the ocular surface with the mucus layer, mainly composed of a mixture of secreted mucins (MUC; gel forming MUC5AC and MUC2) and shed membrane-bound soluble mucins (MUC1, MUC4, and MUC16). Dry eye disease (DED) is a multifactorial pathology of the preocular tear film with possible damage to the ocular surface classified in two types: (1) aqueous-deficient dry eye and (2) evaporative dry eye, caused by a decrease in goblet cell density that reduces MUC expression and/or by meibomian gland dysfunction, that results in a drop in the lipidic fraction of the tear film. In this work, the binding affinity between HA and MUC2 has been evaluated with three complementary approaches because the secreted MUCs play a pivotal role in the viscoelastic properties of the tear film: 1. Rheological analysis, measuring the mucoadhesive index and the complex viscosity in relation to MM (Molecular Mass) and concentration; 2. Fluorescence analysis, using a fluorescent hydrophobic probe, to investigate the conformational change of MUC2 during the interaction with the HA polymer; 3. Surface plasmon resonance analysis, used to measure the affinity between MUC2 (immobilized on the surface of a sensor chip) and the HA polymers that flowed on it at the molecular level. For all these tests, the mucoadhesive performance of the natural HA linearly increases with the MM, whereas cross-linked HA and other emollient and gelling agents (formulated in artificial tears) do not show the same mucoadhesive properties (with the exception of xanthan gum). The mucoadhesive performance of high MM HA has also been confirmed in conditions that simulate the pathological condition of the tear film during DED by decreasing the MUC2 or oleic acid concentration. Physico-chemical analysis of a series of marketed artificial tears confirms the linear correlation between the MM of the HA used in the products and the mucoadhesive index measured on the ocular surface model.

Transmembrane Mucin Response in Conjunctival Epithelial Cells Exposed to Wall Shear Stresses

Human conjunctival epithelium cells (HCEC) line the inner surface of the eyelid and cover the sclera and are continuously subjected to wall shear stresses (WSS). The effects of external forces on the conjunctival epithelium are not fully known. The conjunctival epithelium contains stratified squamous cells that synthesize the membrane-spanning mucins MUC1 and MUC16, which play important roles in protecting the ocular surface. Alterations in both gel-forming and membrane-tethered mucins occur in drying ocular surface diseases. The aim of this study was to explore the mechanobiological characteristics of transmembrane mucin secretion and cellular alterations of primary HCEC exposed to airflow-induced WSS perturbations. We exposed the HCEC to a steady WSS of 0.5 dyne/cm2 for durations of 15 and 30 min. Cytoskeletal alterations and MUC1 secretions were studied using immunohistochemically fluorescent staining with specific antibodies. We investigated for the first time an in vitro model of membrane-tethered mucin secretion by HCEC in response to WSS. The exposure of HCEC to WSS increased the polymerization of F-actin, altered the cytoskeletal shape and reduced the secretion of membrane-tethered MUC1.

Improving ocular bioavailability of hydrophilic drugs through dynamic covalent complexation

The clinical benefits of diquafosol tetrasodium (DQS), a hydrophilic P2Y2 receptor agonist for dry eye, have been hindered by a demanding dosing regimen. Nevertheless, it is challenging to achieve sustained release of DQS with conventional drug delivery vehicles which are mainly designed for hydrophobic small molecule drugs. To address this, we developed an affinity hydrogel for DQS by taking advantage of borate-mediated dynamic covalent complexation between DQS and hydroxypropyl guar. The resultant formulation (3% DQS Gel) was characterized by sustained release, low corneal permeation, and extended ocular retention, which were desirable attributes for ocular surface drug delivery. Both in vitro and in vivo studies had been carried out to verify the biocompatibility of 3% DQS Gel. Using corneal fluorescein staining, the Schirmer's test, PAS staining, quantitative PCR and immunohistological analyses as outcome measures, the superior therapeutic effects of 3% DQS Gel over PBS, the hydrogel vehicle and free DQS were demonstrated in a mouse dry eye model. Our DQS delivery strategy reported herein is readily applicable to other hydrophilic small molecule drugs with cis-diol moieties, thus providing a general solution to improve clinical outcomes of numerous diseases.

Dry Eye Disease Associated with Meibomian Gland Dysfunction: Focus on Tear Film Characteristics and the Therapeutic Landscape

Meibomian gland dysfunction (MGD) is highly prevalent and is the leading cause of evaporative dry eye disease (DED). MGD is characterized by a reduction in meibum secretion and/or a change in meibum composition that results in the disruption of the tear film lipid layer and an increase in the tear film evaporation rate. Excessive evaporation causes tear film instability, desiccation, tear hyperosmolarity, inflammation, and apoptosis of ocular surface cells, resulting in a continuous cycle of DED. The primary treatment goal for DED associated with MGD is to restore the tear film lipid layer and decrease evaporation, thereby reducing ocular signs and symptoms. The management of MGD includes home care options (eyelid hygiene, warming eye masks, ocular lubricants) and office-based treatments (manual expression, microblepharoexfoliation, thermal pulsation, intense pulsed light, intraductal probing). Topical ophthalmic prescription medications attempt to alter various factors that may contribute to DED (e.g., inflammation, bacterial growth, inadequate tear production). In this review, clinical evidence regarding available treatments and emerging therapies from randomized studies in patients with DED associated with MGD is summarized. Although some treatment modalities have been evaluated specifically for DED patients with MGD, large-scale randomized controlled trials are needed to confirm efficacy and safety in this patient population. Currently, there are no approved prescription pharmacologic treatments specifically indicated for DED associated with MGD, and those medications approved for the treatment of DED do not target the key driver of the disease (i.e., excessive evaporation). NOV03 (perfluorohexyloctane; under review with the US Food and Drug Administration) is the most advanced emerging therapy for DED associated with MGD and has demonstrated statistically significant improvements in both signs and symptoms in randomized controlled trials. Development of novel pharmacotherapies will improve therapeutic options and allow for a more individualized approach for patients with DED associated with MGD.

Biopolymers in Mucoadhesive Eye Drops for Treatment of Dry Eye and Allergic Conditions: Application and Perspectives

Dry eye syndrome and allergic conjunctivitis are the most common inflammatory disorders of the eye surface. Although eye drops are the most usual prescribed dosage form, they are characterized by low ocular availability due to numerous barrier mechanisms of the eye. The use of biopolymers in liquid ophthalmic preparations has numerous advantages, such as increasing the viscosity of the tear film, exhibiting bioadhesive properties, and resisting the drainage system, leading to prolonged retention of the preparation at the site of application, and improvement of the therapeutic effect. Some mucoadhesive polymers are multifunctional excipients, so they act by different mechanisms on increasing the permeability of the cornea. Additionally, many hydrophilic biopolymers can also represent the active substances in artificial tear preparations, due to their lubrication and moisturizing effect. With the modification of conventional ophthalmic preparations, there is a need for development of new methods for their characterization. Numerous methods for the assessment of mucoadhesiveness have been suggested by the literature. This review gives an overview related to the development of mucoadhesive liquid ophthalmic formulations for the treatment of dry eye and allergic conditions.

Inhibition of microRNA-328 Increases Ocular Mucin Expression and Conjunctival Goblet Cells

We previously reported anti-miR-328 therapy for dry eye disease (DED). Since decreased mucin secretion is a risk factor for DED, we aimed to explore whether anti-miR-328 affects mucin expression and goblet cells. MiR-328 was increased in goblet cells when they were under desiccating stress or treated with benzalkonium chloride (BAC), both of which are risk factors for DED. Based on bioinformatics tool results, miR-328 was predicted to directly target the transcription factor CREB1 that has been known to promote the expression of mucin5AC. The inhibitory effect of miR-328 on CREB1 was confirmed by the transfection assay. A miR-328 binding site on the CREB1 gene was confirmed by the luciferase assay. Furthermore, anti-miR-328 increased CREB1 and mucin5AC in cultured goblet cells according to qPCR, Western blot, and IF staining experiments. Anti-miR-328 increased mucin5AC secretion from the cultured goblet cells based on an ELISA assay for the cultured medium. Finally, impression cytology data revealed anti-miR-328 increased conjunctival goblet cells in the DED rabbits induced by BAC. In conclusion, anti-miR-328 increases CREB1 expression leading to an increase in mucin5AC production and secretion. Furthermore, anti-miR-328 also increases conjunctival goblet cells. These results warrant the further development of anti-miR-328 therapy for DED.

Expression of GPR-68 in Human Corneal and Conjunctival Epithelium. Possible indicator and mediator of attrition associated inflammation at the ocular surface

INTRODUCTION

Attrition and osmotic stress have been identified as major forces in the pathophysiology of dry eye. Impaired tolerance to mechano-transduction in the presence of insufficient lubrication has been associated with disturbances of ocular surface homeostasis and encouragement of inflammatory reactions, challenging the usual regulatory coping mechanisms. In spite of the probable link between enhanced attrition and secondary inflammation, the key mediators driving the vicious cycle of severe dry eye disease have not yet been identified. The goal of this study was therefore to investigate human corneal and conjunctival epithelium for the presence of the G protein-coupled receptor GPR-68. This protein had most recently been shown to be not only chemically activated but also mechanically, possibly through attrition.

METHODS

De-identified sections of human cornea and conjunctiva were stained for the presence of G protein-coupled receptor 68 with specific antibodies using immunohistochemical methods. Results Specific staining for G-protein-coupled receptor 68 (GPR68) was observed in all samples of the cornea throughout the epithelial layers of the corneal epithelium, most prominently in the area of the wing cells and the basement membrane. Even in the conjunctiva, specific staining for GPR-68 was found.

DISCUSSION

The detection of G protein-coupled receptor GPR-68 in human corneal and conjunctival epithelium raises the question of its function and purpose. The mechanical activation of GPR68 in situations with enhanced friction and attrition could modify various cellular functions and possibly jeopardize normal inflammatory homeostasis at the ocular surface. Accordingly, decreased lubrication in dry eye disease could result in activation of GPR-68. This could lead to secondary inflammation, initially in the epithelium and surrounding stroma. Continuous mechanical stress could result in chronic inflammation, also reaching deeper structures of the cornea, possibly making GPR-68 an important actor in the vicious cycle of dry eye disease.

CONCLUSION

G protein-coupled receptor GPR-68, sensitive to flow and mechanic stimulation, is present in the human corneal epithelium and conjunctiva. Decreased lubrication and increased attrition, accompanied by sensations typical for dry eye, might lead to local inflammation. It is possible that subtle signs of conjunctival, and later corneal, surface damage in the context of these sensations could be a better indicator of the need for and success of therapy than the clinical signs of dry eye disease alone, at least in the early stages of the disease. Inhibition of G protein-coupled receptor GPR-68 could represent a new strategy in the treatment of dry eye disease.

Generic benzalkonium chloride-preserved travoprost eye drops are not identical to the branded polyquarternium-1-preserved travoprost eye drop: Effect on cultured human conjunctival goblet cells and their physicochemical properties

PURPOSE

To investigate the effect of polyquaternium-1 (PQ)-preserved and benzalkonium chloride (BAK)-preserved travoprost eye drops on viability of primary human conjunctival goblet cell (GC) cultures and on secretion of mucin and cytokines. Furthermore, to evaluate the physicochemical properties of the branded travoprost eye drop Travatan® and available generics.

METHODS

The effect of travoprost eye drops was evaluated on GC cultures. Cell viability was assessed through lactate dehydrogenase (LDH) and tetrazolium dye (MTT) colorimetric assays. Mucin secretion was evaluated by immunohistochemical staining. Secretion of interleukin (IL)-6 and IL-8 was measured using BD Cytometric Bead Arrays. pH, viscosity, droplet mass, osmolality and surface tension were measured for all included eye drops.

RESULTS

In the LDH assay, BAK travoprost caused significant GC loss after 2 hrs of incubation compared to the control. PQ travoprost caused no GC loss at any time point. Both PQ- and BAK travoprost caused secretion of mucin to the cytoplasma. No difference in IL-6 and IL-8 secretion was identified compared to controls. The pH values for the generics were lower (pH 6.0) than the pH value for Travatan (pH 6.7; p < 0.0001). The viscosity was lowest for Travatan, while the mean droplet mass was higher for Travatan (35 mg) than the generics (28-30 mg; p ≤ 0.0318). The osmolality and surface tension did not differ between the eye drops investigated.

CONCLUSION

BAK travoprost caused GC loss, indicating that PQ preservation may be preferable in treatment of glaucoma. Furthermore, physicochemical properties of branded and generic travoprost eye drops can not be assumed to be identical.

A new antioxidant made from a pterostilbene functionalized graphene nanocomposite as an efficient treatment for dry eye disease

Dry eye disease is a common condition that affects the eyes. It is caused by problems with the tear film and the tear dynamics. Dry eye can be caused by an increase in the amount of reactive oxygen species (ROS) in the corneal epithelium. The treatment for dry eye typically focuses on relieving the uncomfortable symptoms by using eye drops such as artificial tears, antibiotics, and by using anti-inflammatory/immunosuppressive agents such as cyclosporine, and lifitegrast. However, the recovery of patients with dry eye can take several years particularly if the symptoms are severe. This is because the present treatment approaches for dry eye are not based on its cause, e.g., the oxidative stress arising from the rapid increase in ROS. This work describes a new type of antioxidant made from pterostilbene (PS) and carboxyl-chitosan modified graphene (CG). The use of a hydrophilic two-dimensional CG nanosheet to improve the properties of PS is reported. Superior enhanced properties including better cellular permeability, long sustained release period (over 30 h), and antioxidant properties, were realized by using PS-CG. A hyperosmotic (HS) damaged human corneal epithelial cell (HCEC) model was used for antioxidant tests. This model has an intracellular ROS level 4 times more than that of a control group. The ROS content was declined efficiently to the same amount as normal cells in the PS-CG treated HS group. There was a significant decline in the content of lactate dehydrogenase (LDH) and the apoptosis rate of HCEC in the PS-CG treated HS group when compared to that seen in the HS model. Real-time polymerase chain reaction (PCR) and western blots (WB) were used to understand the antioxidant mechanism of PS-CG. The results showed that the antioxidant was working by activating the Keap1-Nrf2-ARE signalling pathway. In vivo testing testing using a dry eye mouse model suggested that the PS-CG acted as an efficient antioxidant. More tear production and healthier corneal and conjunctival epithelial cells were achieved when PC-CG was applied to this model. The use of PS-CG could be a new strategy for treating dry eye and other ocular diseases caused by ROS.

Moxifloxacin-Based Extended Depth-of-Field Fluorescence Microscopy for Real-Time Conjunctival Goblet Cell Examination

Conjunctival goblet cells (CGCs) are mucin-secreting cells in the eye and play essential roles for ocular surface homeostasis. Since various ocular surface pathologies are related to CGC dysfunction, CGC examination is important for the evaluation of ocular surface conditions. Recently we introduced moxifloxacin-based fluorescence microscopy (MBFM) for non-invasive CGC imaging. However, the imaging speed was up to 1 frame per second (fps) and needed to be improved for clinical applications. In this study, we developed a high-speed moxifloxacin-based, extended depth-of-field (EDOF) microscopy system that operates at a maximum imaging speed of 15 fps. The system used a deformable mirror for the high-speed axial sweeping of focal plane during single-frame acquisitions. The acquired images contained both in-focus and out-of-focus information, and deconvolution was used to filter the in-focus information. The system had a DOF of 800 [Formula: see text], field-of-view of 1.2 mm ×1.2 mm, and resolution of [Formula: see text]. Its performance was demonstrated by real-time, breathing-motion-insensitive CGC imaging of mouse and rabbit models, in vivo. High-speed EDOF microscopy has potentials for non-invasive, real-time CGC examinations of human subjects.

Corneal Refractive Surgery Considerations in Patients on Dupilumab

Dupilumab is a biologic approved by the United States Food and Drug Administration (US FDA) for the treatment of atopic dermatitis. While it is an effective medication for eczema, ocular side effects are common in patients receiving dupilumab therapy. Greater consideration is needed when evaluating these individuals for corneal refractive surgery. Dupilumab patients may suffer from atopy, a condition that also merits consideration in those desiring refractive surgery. Additional testing and careful consideration are needed, as these patients have an increased risk of dry eye syndrome, keratoconus, cataracts, diffuse lamellar keratitis, viral keratitis, and perioperative infection. This commentary discusses the current understanding of dupilumab ocular side effects and investigates factors to consider when evaluating these patients for corneal refractive surgery.

Early Dry Eye Disease Onset in a NOD.H-2h4 Mouse Model of Sjögren's Syndrome

Purpose

To develop a mouse model of human dry eye disease (DED) for investigation of sex differences in autoimmune-associated dry eye pathology.

Methods

Ocular surface disease was assessed by quantifying corneal epithelial damage with lissamine green stain in the NOD.H-2^h4,IFNγ^−/−,CD28^−/− (NOD.H-2^h4 DKO) mouse model of Sjögren's syndrome (SS). Lacrimal gland function was assessed by tear volume quantification with phenol red thread and lacrimal gland inflammation (i.e., dacryoadenitis) was assessed by quantification of immune cell foci, flow cytometric analysis of immune cell composition, and expression of proinflammatory markers.

Results

The NOD.H-2^h4 DKO mouse model of SS exhibits greater age-dependent increases in corneal damage than in NOD.H-2^h4 parental mice and demonstrates an earlier disease onset in females compared to males. The severity of ocular surface disease correlates with loss of goblet cell density, increased conjunctivitis, and dacryoadenitis that is more pronounced in NOD.H-2^h4 DKO than NOD.H-2^h4 mice. B cells dominate lacrimal infiltrates in 16-week-old NOD.H-2^h4 and NOD.H-2^h4 DKO mice, but T helper cells and macrophages are also present. Lacrimal gland expression of proinflammatory genes, including the P2X7 and P2Y₂ purinergic receptors, is greater in NOD.H-2^h4 DKO than NOD.H-2^h4 mice and correlates with dacryoadenitis.

Conclusions

Our results demonstrate for the first time that autoimmune dry eye disease occurs in both sexes of NOD.H-2^h4 DKO and NOD.H-2^h4 mice, with earlier onset in female NOD.H-2^h4 DKO mice when compared to males of the same strain. This study demonstrates that both NOD.H-2^h4 and NOD.H-2^h4 DKO mice are novel models that closely resemble SS-related and sex-dependent DED.

Mussel-Inspired Microgel Encapsulated NLRP3 Inhibitor as a Synergistic Strategy Against Dry Eye

The inflammatory response mediated by oxidative stress is the main pathogenesis of dry eye, but clinical observations have shown that scavenging oxygen-free radicals alone has limited therapeutic effect. Moreover, the unique anatomy and physiology of the ocular surface result in low bioavailability of drugs, and higher concentration is required to achieve the desired efficacy, which, however, may bring systemic side effects. These problems pose a challenge, but the revelation of the ROS-NLRP3-IL-1β signaling axis opens up new possibilities. In this investigation, an NLRP3 inhibitor was successfully encapsulated in polydopamine-based microgels and used for dry eye treatment. It was demonstrated that the well-designed microgels exhibited good biocompatibility, prolonged drug retention time on the ocular surface, and effective inhibition of corneal epithelial damage and cell apoptosis. In addition, due to the synergistic effect, the NLRP3 inhibitor–loaded microgels could exert enhanced oxygen radical scavenging and inflammation-inhibiting effects at a lower dose than monotherapy. These findings suggest that polydopamine-based microgels have advantages as ocular surface drug delivery platforms and have promising applications in oxidative damage–related inflammatory diseases in synergy with anti-inflammatory drugs.

A Mucin-Deficient Ocular Surface Mimetic Platform for Interrogating Drug Effects on Biolubrication, Antiadhesion Properties, and Barrier Functionality

Dry eye disease (DED) affects more than 100 million people worldwide, causing significant patient discomfort and imposing a multi-billion-dollar burden on global health care systems. In DED patients, the natural biolubrication process that facilitates pain-free blinking goes awry due to an imbalance of lipids, aqueous medium, and mucins in the tear film, resulting in ocular surface damage. Identifying strategies to reduce adhesion and shear stresses between the ocular surface and the conjunctival cells lining the inside of the eyelid during blink cycles is a promising approach to improve the signs and symptoms of DED. However, current preclinical models for screening ocular lubricants rely on scarce, heterogeneous tissue samples or model substrates that do not capture the complex biochemical and biophysical cues present at the ocular surface. To recapitulate the hierarchical architecture and phenotype of the ocular interface for preclinical drug screening, we developed an in vitro mucin-deficient DED model platform that mimics the complexity of the ocular interface and investigated its utility in biolubrication, antiadhesion, and barrier protection studies using recombinant human lubricin, a promising investigational therapy for DED. The biomimetic platform recapitulated the pathological changes in biolubrication, adhesion, and barrier functionality often observed in mucin-deficient DED patients and demonstrated that recombinant human lubricin can reverse the damage induced by mucin loss in a dose- and conformation-dependent manner. Taken together, these results highlight the potential of the platform─and recombinant human lubricin─in advancing the standard of care for mucin-deficient DED patients.

Ocular Surface Ion-Channels Are Closely Related to Dry Eye: Key Research Focus on Innovative Drugs for Dry Eye

Abundant ion-channels, including various perceptual receptors, chloride channels, purinergic receptor channels, and water channels that exist on the ocular surface, play an important role in the pathogenesis of dry eye. Channel-targeting activators or inhibitor compounds, which have shown positive effects in in vivo and in vitro experiments, have become the focus of the dry eye drug research and development, and individual compounds have been applied in clinical experimental treatment. This review summarized various types of ion-channels on the ocular surface related to dry eye, their basic functions, and spatial distribution, and discussed basic and clinical research results of various channel receptor regulatory compounds. Therefore, further elucidating the relationship between ion-channels and dry eye will warrant research of dry eye targeted drug therapy.

Comparison of Trehalose/Hyaluronic Acid (HA) vs. 0.001% Hydrocortisone/HA Eyedrops on Signs and Inflammatory Markers in a Desiccating Model of Dry Eye Disease (DED)

Background: Dry eye disease (DED) is a multifactorial disease where ocular surface inflammation and damage play key etiological roles. Purpose: To compare a combination of 3% trehalose (T) and 0.15% hyaluronic acid (HA) (Thealoz duo^®, T/HA) with a tear substitute containing 0.001% hydrocortisone (I) and 0.2% HA (Idroflog^®, I/HA), with respect to changes on signs and inflammatory markers in a mouse DED model. Methods: Thirty 12-week-old C57BL/6 mice were exposed in a controlled-environment chamber as a desiccating stress model of DED for 35 days. At day 14 (T1), administration of 5 µL T or I in the right eye (RE) or NaCl 0.9% in the left eye (LE) started, twice a day. Animals were sacrificed after 7 (T2), 14 (T3), 21 (T4, endpoint) days from the beginning of treatment. Corneal fluorescein staining ratio (Image J), histological and histochemical assessment of ocular surface tissues (goblet cell GC density and characterization —PAS, Alcian blue pH 2.5, pH 1.0, and MUC4 expression—in the superior and inferior conjunctiva), and levels of inflammatory markers HLA-DR, IL-1β and TNF-α in cornea and conjunctiva were measured. Results: No animal fully recovered from DED signs at the endpoint. Difference between arms was observed at T3 and T4, with T treated eyes showing a higher corneal damage reduction, PAS-positive GC recovery, lower inflammatory marker expression as compared to the I treated ones. Conclusions: Data suggest that 21 days of treatment with T/HA improved signs, GC recovery and inflammatory markers in a DED mouse model, to a greater extent as compared to I/HA. Data suggest that 21 days of treatment with T/HA improved signs, GC recovery and inflammatory markers in a DED mouse model, to a greater extent as compared to I/HA.

Transmembrane Mucin 1 Blocks Fluorescein Ingress to Corneal Epithelium

Purpose

To determine the role of transmembrane mucins in blocking fluorescein ingress to the corneal epithelium and its deficiency in contributing to corneal fluorescein punctate staining.

Methods

A dry eye model was established by extirpating lacrimal and Harderian glands in rabbits to correlate the expression of mucins with fluorescein-stained areas on the corneal button using immunofluorescence. Expression of transmembrane mucins was promoted in human corneal epithelial cells (HCECs) by culturing with the mucin-promoting medium (MPM) or diquafosol treatment. Conversely, the expression of mucins was downregulated by knockdown with short hairpin RNA. The role of mucin1 extracellular domain in fluorescein ingress was further verified by overexpression of N-terminally truncated mucin1 in HCECs.

Results

In the rabbit dry eye model, the expression level of mucin1 was significantly decreased in superficial corneal epithelial cells where fluorescein punctate staining was observed. Upregulation of mucin1 and mucin16 in HCECs promoted by MPM or by diquafosol treatment impeded intracellular fluorescein ingress. Downregulation of mucin1 and mucin16 enhanced fluorescence ingress in HCECs after fluorescein staining. Overexpression of truncated mucin1 did not alter the fluorescein intensity of fluorescein-stained HCECs, supporting the notion that the ability of mucin1 to block fluorescein ingress was primarily mediated by its extracellular domain. Minimal inherent expression of mucin16 in the rabbit cornea limited the validation of its role in blocking fluorescein ingress in vivo.

Conclusion

Transmembrane mucin1 blocks fluorescein ingress in the corneal epithelium, explaining how fluorescein staining is positive when the level of transmembrane mucins is disturbed in dry eyes.

Oxidative and antioxidative stress markers in dry eye disease: A systematic review and meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis on the levels of oxidative stress markers and antioxidants in dry eye disease (DED) compared with healthy subject.

METHOD

The PubMed, Cochrane Library, Embase, Science Direct and Google Scholar databases were searched on 10 January 2021 for studies reporting oxidative and antioxidative stress markers in DED and healthy controls. Main meta-analysis was stratified by type of biomarkers, type of samples (tears, conjunctival cells or biopsies), Sjögren's syndrome (SS) (patients with or without SS) and by geographical zones (Asia or Europe).

RESULTS

We included nine articles, for a total of 333 patients (628 eye samples) with DED and 165 healthy controls (451 eye samples). There is an overall increase in oxidative stress markers in DED compared with healthy controls (standard mean deviation = 2.39, 95% confidence interval 1.85-2.94), with a significant increase in lipid peroxide (1.90, 0.69-3.11), myeloperoxidase (2.17, 1.06-3.28), nitric oxide synthase 3 (2.52, 0.95-4.08), xanthine oxidase/oxidoreductase (2.41, 1.40-5.43), 4-hydroxy-2-nonenal (4HNE) (4.75, 1.67-7.84), malondialdehyde (3.00, 2.55-3.45) and reactive oxygen species (1.31, 0.94-1.68). Oxidative stress markers were higher in tears, conjunctival cells and conjunctival biopsies of DED than controls. Even if small number of studies were included for antioxidants, catalase seemed to be decreased in DED compared with healthy controls (-2.17, -3.00 to -1.34), with an increase of antioxidants in tears of DED patients without SS (1.13, 0.76-1.49).

CONCLUSION

Oxidative stress markers, and probably antioxidants, were dysregulated in DED, establishing a local oxidative environment in tears, conjunctival cells and tissues.

Impact of benzalkonium chloride-preserved and preservative-free latanoprost eye drops on cultured human conjunctival goblet cells upon acute exposure and differences in physicochemical properties of the eye drops

Objective

To investigate the short-term impact on human conjunctival goblet cell (GC) survival and mucin release of acute exposure to benzalkonium chloride (BAK) preserved and preservative-free (PF) 0.005% (w/v) latanoprost (LT) eye drops, and to compare the eye drops’ physicochemical properties.

Methods and analysis

Primary GC cultures were established from human conjunctival donor tissue. The impact of eye drops on GC survival was assessed using a lactate dehydrogenase assay. Mucin release was evaluated through mucin-specific immunostaining. pH value, osmolality, drop mass and surface tension for all LT eye drops were measured.

Results

After application with PF-LT for 30 min (min), the GC survival was maintained compared with control (p=0.9941), while all BAK-LT eye drops reduced survival with approximately 30% (p<0.02). Following application with PF-LT for 30 min, mucin was found around the GC nucleus, as seen in the vehicle control, indicating no secretion. In contrast, BAK-LT caused diffuse staining of mucin, similar to the secretagogue histamine, indicating stimulation of secretion. The pH value of the BAK-LT and PF-LT eye drops were 6.0–6.9 and 6.8, respectively. The osmolality was 258–288 mOsm/kg for the BAK-LT eye drops and 276 for PF-LT eye drops. The mean drop mass was 26–31 mg for the BAK-LT eye drops and 30 mg for PF-LT. The surface tension was lower for all BAK-LT eye drops (31.1–32.1 mN/m) compared with PF-LT (42 mN/m).

Conclusion

PF-LT compared with various branded and generic LT preparations containing BAK are less cytotoxic when applied to cultured GCs.

Secreted Ly-6/uPAR-related protein-1 (SLURP1) is a pro-differentiation factor that stalls G1-S transition during corneal epithelial cell cycle progression

PURPOSE

Previously we demonstrated that the secreted Ly-6/uPAR related protein-1 (SLURP1), abundantly expressed in the corneal epithelium (CE) and secreted into the tear fluid, serves as an anti-inflammatory and anti-angiogenic molecule. Here we describe the Slurp1-null (Slurp1X-/-) mouse corneal phenotype for the first time.

METHODS

We compared the 10-week-old wild type (WT) and Slurp1X-/- mouse corneal (i) histology by hematoxylin-eosin and periodic acid-Schiff's reagent staining, (ii) cell proliferation by immunostaining for Ki67, (iii) cell adhesion molecules by immunostaining for desmosomal and tight junction proteins, (iv) barrier function by fluorescein staining and (v) wound-healing by epithelial debridement. Effect of SLURP1 on cell cycle was quantified in human corneal limbal epithelial (HCLE) cells engineered to express SLURP1 (HCLE-SLURP1).

RESULTS

WT and Slurp1X-/- corneal histology was largely comparable, other than a few loosely attached superficial cells in Slurp1X-/- corneas. Compared with the WT, Slurp1X-/- corneas displayed (i) increase in Ki67+ cells, (ii) altered expression and/or localization of tight junction proteins Tjp1 and Pard3, and desmosomal Dsp, (iii) increased superficial fragility and (iv) slower CE wound healing. HCLE-SLURP1 cells displayed (i) decrease in Ki67+ cells, (ii) increased cell number doubling time, (iii) stalling in G1-S phase transition during cell cycle, and (iv) downregulation of cyclins CCNE and CCND1/D2, cyclin-dependent kinases CDK4 and CDK6, and upregulation of CDK inhibitor p15/CDKN2B.

CONCLUSIONS

Collectively, these results elucidate that Slurp1X-/- CE cell homeostasis is altered and suggest that SLURP1 is a pro-differentiation factor that stalls G1-S transition during cell cycle progression by downregulating cyclins and upregulating p15/CDKN2B.

The glycoproteomics of hawk and caiman tears

BACKGROUND

Glycoproteins are important tear components that participate in the stability of the ocular surface. However, the glycopeptides that are present in the tears of wild animals have not yet been described. This work aimed to describe the glycoproteomic profile of roadside hawk (Rupornis magnirostris) and caiman (Caiman latirostris) tears.

METHODS

Tears collected from 10 hawks and 70 caimans using Schirmer tear test strips were used in this study. The samples were submitted to trypsin digestion and separated using a reverse-phase column coupled to a mass spectrometer associated to a nanospray ionization source. The glycoproteins were categorized as: cellular components, biological processes and molecular function, according to the UniProt Knowledgebase.

RESULTS

As shown by the liquid chromatography-mass spectrometry, all glycopeptides found were classified as N-type. Of the 51 glycoproteins that were identified in the hawk tear film, the most abundant were ovotransferrin, globulins and complement system proteins. In the caiman tear film, 29 glycoproteins were identified. The most abundant caiman glycoproteins were uncharacterized proteins, ATPases, globulins and proteasome components. Ontological characterization revealed that the glycoproteins were extracellular, and the most identified molecular function was endopeptidase activity for both species.

CONCLUSION

Glycoproteins are abundant in the tear film of the bird and reptile species studied herein, and all these molecules were shown to have N-type modifications. Location at the extracellular space and an endopeptidase inhibitor activity were the main cell component and molecular function for both species, respectively. These profiles showed differences when compared to human tears, are possibly linked to adaptive processes and can be the basis for further studies on the search of disease biomarkers.

Characterisation of Gel-Forming Mucins Produced In Vivo and In Ex Vivo Conjunctival Explant Cultures

One key element to the health of the ocular surface encompasses the presence of gel-forming mucins in the pre-ocular tear film. Conjunctival goblet cells are specialized epithelial cells that secrete mucins necessary for tear film stability and general homeostasis. Their dysfunction can be linked to a range of ocular surface inflammation disorders and chronic injuries. To obtain new perspectives and angles to tackle mucin deficiency, the need for an accurate evaluation of their presence and corresponding mucin secretion in ex vivo conjunctival cultures has become a requisite. In vitro, goblet cells show a significant decrease in the production and secretion of gel-forming mucins, accompanied by signs of dedifferentiation or transdifferentiation. Explant cultures on laminin-treated CLP-PEG hydrogels can, however, support the production of gel-forming mucins. Together, we challenge the current paradigm to evaluate the presence of cultured goblet cells solely based on their general mucin (MUC) content through imaging analyses, showing the need for additional techniques to assess the functionality of goblet cells. In addition, we broadened the gel-forming mucin profile of in vivo goblet cells with MUC5B and MUC6, while MUC2 and MUC6 is added to the profile of cultured goblet cells.

Are there Clinical Ways to Assess Inflammation in Dry Eye Disease?

In the diagnostic process of dry eye disease, the detection of inflammatory activity is critical in order to evaluate the risk of progression and immunologic shift of the disease, to predict patient response to treatment, and to design an efficient therapeutic strategy, including artificial tear replacement, punctal occlusion or anti-inflammatory therapy.Even if it is difficult to quantify, some indicators of the presence of inflammation are collectible during the examination of the ocular surface in a first-line clinical setting. This review presents and critically discusses the assessment of inflammation in dry eye disease in clinical practice.

Membrane-associated mucins of the human ocular surface in health and disease

Mucins are a family of high molecular weight, heavily-glycosylated proteins produced by wet epithelial tissues, including the ocular surface epithelia. Densely-packed O-linked glycan chains added post-translationally confer the biophysical properties of hydration, lubrication, anti-adhesion and repulsion. Membrane-associated mucins (MAMs) are the distinguishing components of the mucosal glycocalyx. At the ocular surface, MAMs maintain wetness, lubricate the blink, stabilize the tear film, and create a physical barrier to the outside world. In addition, it is increasingly appreciated that MAMs function as cell surface receptors that transduce information from the outside to the inside of the cell. Recently, our team published a comprehensive review/perspectives article for molecular scientists on ocular surface MAMs, including previously unpublished data and analyses on two new genes MUC21 and MUC22, as well as new MAM functions and biological roles, comparing human and mouse (PMID: 31493487). The current article is a refocus for the audience of The Ocular Surface. First, we update the gene and protein information in a more concise form, and include a new section on glycosylation. Next, we discuss biological roles, with some new sections and further updating from our previous review. Finally, we provide a new chapter on MAM involvement in ocular surface disease. We end this with discussion of an emerging mechanism responsible for damage to the epithelia and their mucosal glycocalyces: the unfolded protein response (UPR). The UPR offers a novel target for therapeutic intervention.

Novel Cell Culture Paradigm Prolongs Mouse Corneal Epithelial Cell Proliferative Activity in vitro and in vivo

It has been a long-standing challenge to obtain from cell cultures adequate amounts of mouse corneal epithelial cells (mCEC) to perform transplantation surgery. This limitation is attributable to the passage dependent declines in their proliferative activity. We describe here development of a novel 6C medium that contains six different modulators of different signaling pathways, which control proliferative mCEC activity. Its usage shortens the time and effort required to obtain epithelial sheets for hastening healing of an epithelial wound in an experimental animal model. This serum-free 6C medium contains:Y27632, forskolin, SB431542, DAPT, IWP-2, LDN-193189 and also DermaLife K keratinocyte calcium. Their inclusion inhibits rises in four specific markers of epithelial mesenchymal transdifferentiation:ZEB1/2, Snail, β-catenin and α-SMA. This medium is applied in a feeder-free air-lifted system to obtain sufficient populations of epithelial progenitor cells whose procurement is facilitated due to suppression of progenitor epithelial cell transdifferentiation into epithelial-mesenchymal cells. Diminution of this decline in transdifferentiation was confirmed based on the invariance of P63, K14, Pax6, and K12 gene expression levels. This cell culture technique is expected to facilitate ex vivo characterization of mechanisms underlying cell fate determination. Furthermore, its implementation will improve yields of progenitor mouse corneal epithelial cells, which increases the likelihood of using these cells as a source to generate epithelial sheets for performing transplantation surgery to treat limbal stem cell deficiency in a clinical setting. In addition, the novel insight obtainable from such studies is expected to improve the outcomes of corneal regenerative medicine.

Topical Delivery of Levocarnitine to the Cornea and Anterior Eye by Thermosensitive in-situ Gel for Dry Eye Disease

Purpose

To prepare the levocarnitine thermosensitive in situ gel (LCTG) and evaluate its effect on dry eye disease (DED).

Methods

Draize eye irritation test and other examinations were used to evaluate the eye irritation after multiple administration of LCTG. The Schirmer test, fluorescein sodium staining, HE staining and TUNEL staining were used to detect the tear secretion, corneal injury, histopathological changes of the cornea and lacrimal gland, and the apoptosis rate of cornea epithelial cells after 3 days of the administration. The conjunctival goblet cell density was detected by PAS staining, and the expression levels of matrix metalloproteinase-3 (MMP-3) and matrix metalloproteinase-9 (MMP-9) of corneal epithelial cells were detected by immunofluorescence staining after 7 days of the administration.

Results

LCTG is non-irritating to rabbit eyes and has good biocompatibility. LCTG administration for 3 days can significantly increase the amount of tear secretion in mice with DED, promote corneal epithelial integrity and central corneal epithelium thickness recovery, and improve the pathological morphology and structure of corneal and lacrimal gland tissues, and reduce the apoptosis rate of the corneal epithelial cells. After 7 days of the administration, the preparation can promote the proliferation of conjunctival goblet cells and down-regulate the cornea expression levels of MMP-3 and MMP-9 in epithelial cells.

Conclusion

The LCTG has a good curative effect on mice with DED, and the overall curative effect is better than that of levocarnitine solution.