Change in prostaglandin expression levels and synthesizing activities in dry eye disease

Tear biomarkers

An extensive exploration of lacrimal fluid molecular biomarkers in understanding and diagnosing a spectrum of ocular and systemic diseases is presented. The chapter provides an overview of lacrimal fluid composition, elucidating the roles of proteins, lipids, metabolites, and nucleic acids within the tear film. Pooled versus single-tear analysis is discussed to underline the benefits and challenges associated with both approaches, offering insights into optimal strategies for tear sample analysis. Subsequently, an in-depth analysis of tear collection methods is presented, with a focus on Schirmer's test strips and microcapillary tubes methods. Alternative tear collection techniques are also explored, shedding light on their applicability and advantages. Variability factors, including age, sex, and diurnal fluctuations, are examined in the context of their impact on tear biomarker analysis. The main body of the chapter is dedicated to discussing specific biomarkers associated with ocular discomfort and a wide array of ocular diseases. From dry eye disease and thyroid-associated ophthalmopathy to keratoconus, age-related macular degeneration, diabetic retinopathy, and glaucoma, the intricate relationship between molecular biomarkers and these conditions is thoroughly dissected. Expanding beyond ocular pathologies, the chapter explores the applicability of tear biomarkers in diagnosing systemic diseases such as multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, and cancer. This broader perspective underscores the potential of lacrimal fluid analysis in offering non-invasive diagnostic tools for conditions with far-reaching implications.

Prostaglandin E2 promotes Th17 differentiation induces corneal epithelial cell apoptosis and participates in the progression of dry eye

This study is mainly based on T helper type 17 (Th17) cells analysis of the mechanism of prostaglandin E2 (PGE2) promoting the progression of dry eye (DE). Scopolamine and dry environment were used to induce mice DE model. Celecoxib was used to inhibit PGE2. Corneal epithelial cells and CD4+ T cells were used to construct a co-culture system. The osmotic pressure was increased by adding NaCl to simulate DE in vitro. AH6809 and E7046 were used to pre-culture to inhibit EP2/4 in T cells to verify the effect of exogenous PGE2 on Th17 cell differentiation and corneal epithelial cell apoptosis. The function of Th17 cells was analyzed by detecting RORγt and interleukin-17 (IL-17). PGE2 was instilled on the ocular surface to induce DE symptoms of mice. AH6809 and E7046 were used to inhibit EP2/4. The corneal epithelial cell apoptosis was observed by TUNEL. The proportion of Th17 cells in corneal tissue and draining lymph nodes (DLNs) was detected by flow cytometry. In DE mice, the concentration of PGE2 and IL-17 increased in tears, and the proportion of Th17 increased, while inhibition of PGE2 alleviated the symptoms of DE and inhibited Th17 differentiation. Hypertonic environment induces corneal epithelial cells to secrete PGE2. PGE2 promoted the expression of EP2/4 and the differentiation of Th17 cells in vitro. The hypertonic environment promoted PGE2 level and the apoptosis of corneal epithelial cells in the co-culture system. PGE2 alone did not cause corneal epithelial cell apoptosis, while PGE2 promoted apoptosis by promoting Th17. Blocking EP2/4 reduced the induction of Th17 differentiation by PGE2 and the promoted corneal epithelial cell apoptosis. Animal experiments showed that exogenous PGE2 induced DE symptoms. Blocking EP2/4 not only inhibited the proportion of Th17, but also alleviated the apoptosis of corneal epithelial cells caused by PGE2. PGE2 induces aggravation of inflammation by promoting the level of Th17 in the ocular surface, and causes corneal epithelial cell apoptosis, thereby participating in the progression of DE.

Gene expression changes in conjunctival cells associated with contact lens wear and discomfort

PURPOSE

This study aimed to analyze the differences in the expression of pain-related genes in conjunctival epithelial cells among symptomatic contact lens (CL) wearers (SCLWs), asymptomatic CL wearers (ACLWs), and non-CL wearers (non-CLWs).

METHODS

For this study, 60 participants (20 non-CLWs, 40 CLWs) were enrolled. The CLW group comprised 20 ACLWs and 20 SCLWs according to the Contact Lens Dry Eye Questionnaire short form©. Conjunctival cells were collected using impression cytology, and RNA was isolated and used to determine the expression levels of 85 human genes involved in neuropathic and inflammatory pain. The effects of CL wear and discomfort were evaluated using mixed-effects ANOVA with partially nested fixed-effects model. Gene set enrichment analysis was performed to assign biological meaning to sets of differentially expressed genes.

RESULTS

Six genes (CD200, EDN1, GRIN1, PTGS1, P2RX7, and TNF) were significantly upregulated in CLWs compared to non-CLWs. Eleven genes (ADORA1, BDKRB1, CACNA1B, DBH, GRIN1, GRM1, HTR1A, PDYN, PTGS1, P2RX3, and TNF) were downregulated in SCLWs compared to ACLWs. These genes were mainly related to pain, synaptic transmission and signaling, ion transport, calcium transport and concentration, and cell-cell signaling.

CONCLUSIONS

CL wear modified the expression of pain- and inflammation-related genes in conjunctival epithelial cells. These changes may be in part, along with other mechanisms, responsible for CL discomfort in SCLWs.

Altered Prostaglandin E Receptor Subtype 3 Expression in Lacrimal Glands of Patients with Chronic Stevens-Johnson Syndrome

PURPOSE

To compare the prostaglandin E2 receptor subtype 3 (EP3) distribution in the lacrimal glands of normals, non-specific dacryoadenitis, and chronic Stevens-Johnson syndrome (SJS) patients.

METHODS

Biopsies from lacrimal glands of four chronic SJS patients with severe dry eye disease, four dacryoadenitis patients, and five fresh body donors were assessed for EP3 expression using immunohistochemistry.

RESULTS

In normal main and accessory lacrimal glands, EP3 is expressed strongly in nuclei and cytoplasm of majority (>75%) of acini with no ductular expression. In dacryoadenitis, EP3 expression was similar to normal glands. However, lacrimal glands from SJS patients (5-20/HPF mononuclear cells) showed a weak and reduced (<10% acini) EP3 expression within acinar cells. The reduction in intensity was more in glands with higher mononuclear cell infiltration (>10/HPF).

CONCLUSION

There is downregulation of EP3 expression in the lacrimal glands of SJS patients, whereas EP3 expression is preserved in non-specific lacrimal gland inflammations.

The role of sphingolipids in meibomian gland dysfunction and ocular surface inflammation

Inflammation occurs in response to tissue injury and invasion of microorganisms and is carried out by the innate and adaptive immune systems, which are regulated by numerous chemokines, cytokines, and lipid mediators. There are four major families of bioactive lipid mediators that play an integral role in inflammation - eicosanoids, sphingolipids (SPL), specialized pro-resolving mediators (SPM), and endocannabinoids. SPL have been historically recognized as important structural components of cellular membranes; their roles as bioactive lipids and inflammatory mediators are recent additions. Major SPL metabolites, including sphingomyelin, ceramide, ceramide 1-phosphate (C1P), sphingosine, sphingosine 1-phosphate (S1P), and their respective enzymes have been studied extensively, primarily in cell-culture and animal models, for their roles in cellular signaling and regulating inflammation and apoptosis. Less focus has been given to the involvement of SPL in eye diseases. As such, the aim of this review was to examine relationships between the SPL family and ocular surface diseases, focusing on their role in disease pathophysiology and discussing the potential of therapeutics that disrupt SPL pathways.

Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction

Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease throughout the world. Studies have shown that several molecules in meibum, including but not limited to interleukins, amino acids, cadherins, eicosanoids, carbohydrates, and proteins, are altered in meibomian gland dysfunction compared with healthy normal controls. Some of these molecules such as antileukoproteinase, phospholipase A2, and lactoperoxidase also show differences in concentrations in tears between meibomian gland dysfunction and dry eye disease, further boosting hopes as candidate biomarkers. MGD is a complex condition, making it difficult to distinguish patients using single biomarkers. Therefore, multiple biomarkers forming a multiplex panel may be required. This review aims to describe molecules comprising lipids, proteins, and carbohydrates with the potential of serving various capacities as monitoring, predictive, diagnostic, and risk biomarkers for meibomian gland dysfunction.

Metabolomics and lipidomics approaches in human tears: A systematic review

The human tear film is at the interface between the ocular surface and the external environment. Although investigation has been hindered by its small volume, improvements in preanalytical and analytical methods have allowed the omics approach to represent an innovative biomarker search strategy. There is still a significant lack of standardization, representing a barrier for performing between-studies comparisons and transferring experimental findings into clinical use and trials. We summarize the preanalytical and analytical procedures, describe the biomarkers that can be found using the metabo-lipidomics approach, and provide our expert opinion for omics investigations in human tears. For this systematic review of 38 studies, we searched PubMed by combining Boolean operators with the following keywords: tear, metabolomic, lipidomic, -omics. The human tear metabo-lipidome has been well-characterized in normal individuals using high-resolution liquid chromatography coupled with mass spectrometry. Lipid and metabolite profiles were influenced by ocular (e.g. dry eye disorders; Meibomian gland dysfunction; contact lens wear; glaucoma; keratoconus; pterygium) and systemic conditions (e.g. multiple sclerosis). Investigating the tear metabo-lipidome could improve our understanding of the pathogenesis of both ocular and systemic diseases, but also provide diagnostic as well as prognostic biomarkers.

Prostaglandin E2 and F2α Alter Expression of Select Cholesteryl Esters and Triacylglycerols Produced by Human Meibomian Gland Epithelial Cells

PURPOSE

PGF2α analogs are commonly used to treat glaucoma and are associated with higher rates of meibomian gland dysfunction (MGD). The purpose of this study was to evaluate the physiological effects of PGF2α and PGE2 on immortalized human meibomian gland epithelial cells (HMGECs).

METHODS

HMGECs were immunostained for the 4 PGE2 receptors (EP1, EP2, EP3, and EP4) and 1 PGF2α receptor (FP) and imaged. Rosiglitazone-differentiated HMGECs were exposed to PGF2α and PGE2 (10-9 to 10-6 M) for 3 hours. Cell viability was assessed by an adenosine triphosphate-based luminescent assay, and lipid extracts were analyzed for cholesteryl esters (CEs), wax esters (WEs), and triacylglycerols (TAGs) by ESI-MSMSALL in positive ion mode by a Triple TOF 5600 Mass Spectrometer using SCIEX LipidView 1.3.

RESULTS

HMGECs expressed 3 PGE2 receptors (EP1, EP2, and EP4) and the 1 PGF2α receptor (FP). Neither PGE2 nor PGF2α showed signs of cytotoxicity at any of the concentrations tested. WEs were not detected from any of the samples, but both CEs and TAGs exhibited a diverse and dynamic profile. PGE2 suppressed select CEs (CE 22:1, CE 26:0, CE 28:1, and CE 30:1). PGF2α dose dependently increased several CEs (CE 20:2, CE 20:1, CE 22:1, and CE 24:0) yet decreased others. Both prostaglandins led to nonspecific TAG remodeling.

CONCLUSIONS

PGE2 and PGF2α showed minimal effect on HMGEC viability. PGF2α influences lipid expression greater than PGE2 and may do so by interfering with meibocyte differentiation. This work may provide insight into the mechanism of MGD development in patients with glaucoma treated with PGF2α analogs.

Gallic acid and myricetin-rich Labisia pumila extract mitigated multiple diabetic eye disorders in rats

Diabetes affected about a quarter of a billion people globally, and one out of four diabetics has eye or vision problems. This study investigated whether gallic acid and myricetin-rich Labisia pumila extract (LP) consumption would help prevent diabetic eye disorders and some probable biochemistry involved relating to inflammation, vascular leakage, and oxidative tension. Male rats were divided into four groups (n = 6), namely healthy control, diabetic non-treated control, and hyperglycemic rats treated with 150 or 300 mg/kg LP. Intraperitoneal injection of 60 mg/kg streptozotocin was used to induce diabetes. Rats were fed in the morning and evening. Diabetic retinopathy was graded in rats using a dilated retinal digital ophthalmoscopy. Rats were sacrificed at 12 weeks and the retina, optic nerve, cornea, lens, sclera, ciliary bodies, iris, and conjunctiva were examined histologically. The diabetic rats consuming LP for 10 weeks showed dose-dependent, histopathologically-reduced eye abnormalities (keratopathy, cataract, sclera, conjunctiva, ciliary bodies, iris, limbus, corneal edema, epithelial barrier inefficiency, shallow punctate keratitis, lower basal layer cell density, retinopathy, glaucoma, and corneal changes). The LP significantly suppressed inflammation [increased serum tumor necrosis factor-α (TNF-α), prostaglandin-E2 (PGE2)], vascular leakage [claudin-1], abnormal vascularization [vascular endothelial growth factor (VEGF)], oxidative tension [malondialdehyde/reduced glutathione ratio], and hyperglycemia [fasting blood glucose] of the diabetic rats. The LP consumption was significantly protective against diabetic eye disorders and optic nerve dysfunction which were related to inflammation, vascular leakage, abnormal vascularization, and oxidative tension, which most likely influenced eye hemorrhage and collagen cross-linkage. PRACTICAL APPLICATIONS: The study shows that gallic acid and myricetin-rich Labisia pumila (LP) leaf consumption may be used as a complementary therapy for managing diabetes (fasting blood glucose) and preventing diabetic eye disorders (keratopathy, cataract, sclera, conjunctiva, ciliary bodies, iris, limbus, corneal edema, epithelial barrier inefficiency, shallow punctate keratitis, lower basal layer cell density, retinopathy, glaucoma, and corneal abnormalities). The LP consumptions reduced the serum biomarkers for inflammation (serum tumor necrosis factor-α TNF-α; prostaglandin-E2), vascular leakage/abnormalities (claudin-1 and vascular endothelial growth factor VEGF), and oxidative tension (malondialdehyde/reduced glutathione MDA/GSH ratio). The LP was eye-protective probably by normalizing fasting blood glucose, reducing inflammation, oxidative tension, vascular leakage, and irregular vascularization.

Effects of Eye Drops Containing Hyaluronic Acid-Nimesulide Conjugates in a Benzalkonium Chloride-Induced Experimental Dry Eye Rabbit Model

Dry eye syndrome (DES) is a common ocular disease worldwide. Currently, anti-inflammatory agents and immunosuppressive drugs, such as cyclosporine A, have been widely used to treat this chronic condition. However, the multifactorial etiology of DES, poor tolerance, low bioavailability, and prolonged treatment to response time have limited their usage. In this study, nimesulide, a cyclooxygenase (COX)-2 selective inhibitor, was conjugated with hyaluronic acid (HA), and the HA-nimesulide conjugates were expected to increase the solubility and biocompatibility for alleviating the DES in the benzalkonium chloride (BAC)-induced goblet cell-loss dry eye model. The therapeutic efficacy of HA-nimesulide was assessed using fluorescein staining, goblet cell density by conjunctival impression cytology, and histology and immunohistochemistry of corneal tissues. Compared to commercial artificial tears and Restasis®, the HA-nimesulide conjugates could promote goblet cell recovery and enhance the regeneration of the corneal epithelium. Importantly, immunofluorescent staining studies demonstrated that the HA-nimesulide conjugates could decrease the number of infiltrating CD11b-positive cells after two weeks of topical application. In the anti-inflammatory test, the HA-nimesulide conjugates could inhibit the production of pro-inflammatory cytokines and prostaglandin E2 (PGE2) in the lipopolysaccharide (LPS)-stimulated Raw 264.7 cell model. In conclusion, we demonstrated that HA-nimesulide conjugates had anti-inflammatory activity, and promoted goblet cell recovery and corneal epithelium regeneration when used as topical eye drops; accordingly, the HA-nimesulide conjugates could potentially be effective for the treatment of DES.

The potential of lipid mediator networks as ocular surface therapeutics and biomarkers

In the last twenty years an impressive body of evidence in diverse inflammatory animal disease models and human tissues, has established polyunsaturated fatty acids (PUFA) derived specialized-pro-resolving mediators (SPM), as essential mediators for controlling acute inflammation, immune responses, wound healing and for resolving acute inflammation in many non-ocular tissues. SPM pathways and receptors are highly expressed in the ocular surface where they regulate wound healing, nerve regeneration, innate immunity and sex-specific regulation of auto-immune responses. Recent evidence indicates that in the eye these resident SPM networks are important for maintaining ocular surface health and immune homeostasis. Here, we will review and discuss evidence for SPMs and other PUFA-derived mediators as important endogenous regulators, biomarkers for ocular surface health and disease and their therapeutic potential.

Profile of tear lipid mediator as a biomarker of inflammation for meibomian gland dysfunction and ocular surface diseases: Standard operating procedures

Human tear is a biological fluid rich in lipids that is increasingly collected in clinical and biological research. The repertoire of small lipids or lipid mediators (often termed eicosanoids or oxylipins) found in human tear provides insight into metabolism of fatty acids and physiology of the ocular surface and Meibomian glands. Disturbances in the tear lipid mediators profile also occur during inflammation of the ocular surface that is not directly linked to lipid metabolism. The changes in the levels of pro-inflammatory and pro-resolution lipid mediators in the tear help assess the severity and stage of inflammation in ocular surface tissues. Mass spectrometry, used in the evaluation of tear lipid mediators, is an emerging tool in clinical diagnostics and personalized medicine. Here we describe the reproducibility, accuracy, and precision of quantifying lipid mediators in human tears, with a suggested method for tear collection and sample handling. The ranges of lipid mediators concentrations in tear fluid of healthy and diseased individuals with Meibomian gland dysfunction are reported, as well as the impact of age and disease on individual lipid mediators. We would like to recommend a set of guidelines, which can be further discussed in workshops. This will facilitate harmonization of future tear lipid mediators data across different instrument platforms in various laboratories. We hope that other fields requiring lipid mediators assays will also benefit from such an effort.

Inflammation in Dry Eye Syndrome: Identification and Targeting of Oxylipin-Mediated Mechanisms

Dry eye syndrome (DES) is characterized by decreased tear production and stability, leading to desiccating stress, inflammation and corneal damage. DES treatment may involve targeting the contributing inflammatory pathways mediated by polyunsaturated fatty acids and their derivatives, oxylipins. Here, using an animal model of general anesthesia-induced DES, we addressed these pathways by characterizing inflammatory changes in tear lipidome, in correlation with pathophysiological and biochemical signs of the disease. The decline in tear production was associated with the infiltration of inflammatory cells in the corneal stroma, which manifested one to three days after anesthesia, accompanied by changes in tear antioxidants and cytokines, resulting in persistent damage to the corneal epithelium. The inflammatory response manifested in the tear fluid as a short-term increase in linoleic and alpha-linolenic acid-derived oxylipins, followed by elevation in arachidonic acid and its derivatives, leukotriene B4 (5-lipoxigenase product), 12-hydroxyeicosatetraenoic acid (12-lipoxigeanse product) and prostaglandins, D2, E2 and F2α (cyclooxygenase products) that was observed for up to 7 days. Given these data, DES was treated by a novel ophthalmic formulation containing a dimethyl sulfoxide-based solution of zileuton, an inhibitor of 5-lipoxigenase and arachidonic acid release. The therapy markedly improved the corneal state in DES by attenuating cytokine- and oxylipin-mediated inflammatory responses, without affecting tear production rates. Interestingly, the high efficacy of the proposed therapy resulted from the synergetic action of its components, namely, the general healing activity of dimethyl sulfoxide, suppressing prostaglandins and the more specific effect of zileuton, downregulating leukotriene B4 (inhibition of T-cell recruitment), as well as upregulating docosahexaenoic acid (activation of resolution pathways).

Change of tear lipid mediators in a post-trabeculectomy cohort

PURPOSE

Trabeculectomy surgery could affect ocular surface disease (OSD) in several ways, through cessation of long term glaucoma eyedrops, exposure to operative mitomycin C and post-operative eyedrops including corticosteroids and aminoglycosides and reduction in eyelid hygiene measures. Previously we showed the relevance of tear lipid mediators (also referred oxylipins) in OSD. Here, we aim to evaluate changes of these lipids in a post-trabeculectomy cohort.

METHODS

Patients undergoing trabeculectomy were prospectively evaluated and had tear collected using Schirmer's strips, preoperatively and postoperatively at 0.5, 1.0 and 3.0 years. Lipid mediators were analyzed using liquid chromatography mass spectrometry.

RESULTS

The normalized concentrations of 40 lipid mediators were between 0.1 and 8.0 ng/mL, whereas docosahexaenoic acid (DHA), Arachidonic acid (AA) and eicosapentaenoic acid (EPA) ranged up to a few hundred ng/mL. The concentrations of lipid mediators, except DHA, EPA, and thromboxane (TXB₁), showed reduction after surgery. At the last visit, these lipids were significantly reduced by ¹/₃ to ½, compared to pre-operative values: 8-HETE, 15-HETE, 15-oxoETE, 11-HDoHE, 17-HDoHE, and 20-OH-LTB₄. To examine collective changes of lipids, clustering analysis revealed 10 groups of lipids consistent with known metabolic pathways.

RESULTS

An increase in the level of 2,3-dinor-8-isoPGF_2α between 0 and 0.5 year was associated with inferior corneal staining at 0.5 year. In 14 patients who required post-operative needling, six lipid mediators were found to be significantly higher at 1.0 year compared to non-needled patients.

CONCLUSIONS

In this 3-years study, trabeculectomy reduced the tear level of pro-inflammatory lipid mediators. Patients who required needling of the bleb to maintain surgical success may have a chronic underlying inflammatory process associated with fibrosis.

Comparative lipidomic analysis of inflammatory mediators in the aqueous humor and tear fluid of humans and rabbits

INTRODUCTION

Ocular inflammation is a key pathogenic factor in most blindness-causing visual disorders. It can manifest in the aqueous humor (AH) and tear fluid (TF) as alterations in polyunsaturated fatty acids (PUFAs) and their metabolites, oxylipins, lipid mediators, which are biosynthesized via enzymatic pathways involving lipoxygenase, cyclooxygenase or cytochrome P450 monooxygenase and specifically regulate inflammation and resolution pathways.

OBJECTIVES

This study aimed to establish the baseline patterns of PUFAs and oxylipins in AH and TF by their comprehensive lipidomic identification and profiling in humans in the absence of ocular inflammation and comparatively analyze these compounds in the eye liquids of rabbits, the species often employed in investigative ophthalmology.

METHODS

Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for qualitative and quantitative characterization of lipid compounds in the analyzed samples.

RESULTS

A total of 28 lipid compounds were identified, including phospholipid derivatives and PUFAs, as well as 22 oxylipins. Whereas the PUFAs included arachidonic, docosahexaenoic and eicosapentaenoic acids, the oxylipins were derived mainly from arachidonic, linoleic and α-linolenic acids. Remarkably, although the concentration of oxylipins in AH was lower compared to TF, these liquids showed pronounced similarity in their lipid profiles, which additionally exhibited noticeable interspecies concordance.

CONCLUSION

The revealed correlations confirm the feasibility of rabbit models for investigating pathogenesis and trialing therapies of human eye disorders. The identified metabolite patterns suggest enzymatic mechanisms of oxylipin generation in AH and TF and might be used as a reference in ocular inflammation studies.

Reduced association between dendritic cells and corneal sub-basal nerve fibers in patients with fibromyalgia syndrome

In our study, we aimed at investigating corneal langerhans cells (LC) in patients with fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) as potential contributors to corneal small fiber pathology. We enrolled women with FMS (n = 134) and SFN (n = 41) who underwent neurological examination, neurophysiology, prostaglandin analysis in tear fluid, and corneal confocal microscopy (CCM). Data were compared with those of 60 age-matched female controls. After screening for dry eye disease, corneal LC were counted and sub-classified as dendritic (dLC) and non-dendritic (ndLC) cells with or without nerve fiber association. We further analyzed corneal nerve fiber density (CNFD), length (CNFL), and branch density (CNBD). Neurological examination indicated deficits of small fiber function in patients with SFN. Nerve conduction studies were normal in all participants. Dry eye disease was more prevalent in FMS (17%) and SFN (28%) patients than in controls (5%). Tear fluid prostaglandin levels did not differ between FMS patients and controls. While corneal LC density in FMS and SFN patients was not different from controls, there were fewer dLC in association with nerve fibers in FMS and SFN patients than in controls (P < .01 each). Compared to controls, CNFL was lower in FMS and SFN patients (P < .05 each), CNFD was lower only in FMS patients (P < .05), and CNBD was lower only in SFN patients (P < .001). There was no difference in any CCM parameter between patients with and without dry eyes. Our data indicate changes in corneal innervation and LC distribution in FMS and SFN, potentially based on altered LC signaling.

Association between the levels of prostaglandin E2 in tears and severity of dry eye

AIM

To investigate the relationship between the levels of prostaglandin E2 (PGE2) in tears and dry eye disease severity based on both clinical symptoms and signs.

METHODS

Tear samples were collected from 36 non-Sjögren syndrome dry eye patients (10 males and 26 females, mean age 50.11±11.17y). All participants completed the Ocular Surface Disease Index (OSDI) questionnaire and underwent a detailed ophthalmic examination including, tear film breakup time (TBUT), ocular surface fluorescein staining, Schirmer I test, and meibomian gland assessment. The level of PGE2 in tears was measured using enzyme-linked immunosorbent assay (ELISA). The independent associations between tear PGE2 levels and other variables including demographics, OSDI scores, TBUT, Schirmer scores, ocular surface staining scores, and stage of meibomian gland dysfunction (MGD) were evaluated using linear regression analysis.

RESULTS

The mean PGE2 level in tears of dry eye patients was 537.85±234.02 pg/mL. The tear PGE2 levels significantly positively correlated with OSDI scores (R=0.608, P<0.001), however, they did not significantly associate with TBUT (R=0.153, P=0.373), Schirmer scores (R=-0.098, P=0.570), ocular surface staining scores (R=0.282, P=0.095), and stage of MGD (R=-0.107, P=0.535). Male sex was significantly negatively correlated with tear PGE2 levels.

CONCLUSION

The levels of PGE2 in tears are positively correlated with dry eye symptoms. However, no significant association was found between tear PGE2 levels and the results of other common dry eye diagnostic tests.

Detection of Lipid Mediators of Inflammation in the Human Tear Film

PURPOSE

Lipid mediators of inflammation are a group of signaling molecules produced by various cells under physiological conditions and modulate the inflammatory process during various pathologic conditions. Although eicosanoids and F2-isoprostanes are recognized lipid mediators of inflammation, there is no consensus yet on the extraction and mass spectrometry (MS) method for their analysis in individual human tear samples. Thus, the aim of this study was to develop an optimal method for extraction of lipid mediators of inflammation in the tear film and evaluate MS techniques for their analysis.

METHODS

Basal tears were collected from each eye of 19 subjects using glass microcapillaries. Lipid extraction was performed using either varying concentrations of acidified methanol, a modified Folch method, or solid-phase extraction. Initially, an untargeted analysis of the extracts was performed using SCIEX TripleTOF 5600 mass spectrometer to identify any lipid mediators of inflammation (eicosanoids) and later a targeted analysis was performed using the SCIEX 6500 Qtrap to identify and quantify prostaglandins and isoprostanes. Mass spectra and chromatograms were analyzed using Peakview, XCMS, and Multiquant software.

RESULTS

Prostaglandins and isoprostanes were observed and quantified using the Qtrap mass spectrometer under multiple reaction monitoring (MRM) mode after solid-phase extraction. Extraction with acidified methanol along with the Folch method produced cleaner spectra during MS with the Triple time of flight (TOF) mass spectrometer. Lipid mediators of inflammation were not observed in any of the tear samples using the Triple TOF mass spectrometer.

CONCLUSIONS

Solid-phase extraction may be the method of choice for extraction of prostaglandins and isoprostanes in low volumes of tears. The SCIEX Qtrap 6500 in MRM mode may be suitable to identify and quantify similar lipid mediators of inflammation.

Phosphosulindac is efficacious in an improved concanavalin A-based rabbit model of chronic dry eye disease

Dry eye disease (DED) currently has no satisfactory treatment partly because of the lack of informative animal models. We evaluated the anti-inflammatory phosphosulindac (PS) for the treatment of DED using a new rabbit model of DED based on the concanavalin A (Con A) acute DED model: we injected all lacrimal glands with Con A weekly under ultrasound guidance, which prolonged DED to >3 weeks, and thoroughly assessed efficacy with tear break-up time (TBUT), tear osmolarity, Schirmer test, and tear lactoferrin levels. Rabbits with DED (n = 8-10 eyes per group) were treated topically with PS or vehicle 3×/day for 21days. PS restored TBUT, tear osmolarity, and lactoferrin levels (P < 0.0001-0.04) to normal but did not significantly improve the results of the Schirmer test. PS showed no side effects and was much more efficacious than cyclosporine or lifitegrast. In the cornea, PS suppressed the activation of nuclear factor kappa-B, the levels of transforming growth factor beta, interleukin-1 beta, interleukin-6, and interleukin-8, and the levels of matrix metalloproteinase (MMP)-1 and MMP-9, and MMP activity. Levels of prostaglandin E₂ (PGE₂) in tears and cornea were preserved in PS-treated rabbits. Ketorolac and diclofenac, two ophthalmic NSAIDs causing corneal melt, nearly completely suppressed PGE₂ levels but had no effect on MMPs. The effects of PS on PGE₂ and MMPs likely account for its apparent ocular safety. Our results establish an animal model for acute and chronic DED suitable for drug efficacy studies and indicate that PS merits evaluation for DED.

Tear eicosanoids in healthy people and ocular surface disease

Meibomian gland (MG) dysfunction is the leading cause of evaporative dry eye and it leads to inflammation of the ocular surface. Eicosanoids may be involved in inflammation of dry eye. This study aimed to profile tear eicosanoid levels in healthy individuals and those with MG dysfunction, and to examine if these levels are associated with clinical factors and expressibility of MG. Forty participants with MG dysfunction and 30 healthy controls were recruited in this study. Clinical signs of MG dysfunction were assessed, and tear lactoferrin concentration was evaluated. Tear eicosanoids were extracted from Schirmer's strips and analyzed using mass spectrometry. We were able to quantify 38 tear eicosanoids and levels were increased in older individuals. In participants with MG dysfunction, higher 5-HETE, LTB₄, 18-HEPE, 12-HEPE and 14-HDoHE were associated with poorer MG expressibility. The eicosanoids PGF_2α, 18-HEPE, 20-HDoHE and 17-HDoHE were elevated with increased corneal staining; higher 5-HETE, LTB₄ were associated with lower tear lactoferrin levels. The receiver-operating-characteristics analysis shows higher levels of 5-HETE, LTB₄ and 18-HEPE were able to predict poor expressibility of MGs. In conclusion, tear eicosanoid levels are age-dependent and specific eicosanoids may be indicators of clinical obstruction of MG or the severity of ocular surface damage.

Dry eye disease and oxidative stress

Dry eye, an age-related condition, is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear film instability. Environmental factors are also often implicated in dry eye including exposure to pollutants, ultraviolet (UV) radiation and ozone as well as the chronic use of preserved eyedrops such as in the treatment of glaucoma. These factors increase oxidative stress and ocular surface inflammation. Here, we reviewed the cellular, animal and clinical studies that point to the role of oxidative stress in dry eye disease. The biomarkers used to indicate oxidative damage in ocular surface tissues include 8-hydroxy-2 deoxyguanosine (8-OHdG), 4-hydroxynonenal (HNE) and malondialdehyde (MDD). Antioxidative defences in the ocular surface occur in the form of tear proteins such as lactoferrin and S100A proteins, and enzymes such as superoxide dismutase (SOD), peroxidase, catalase and mitochondrial oxidative enzymes. An imbalance between the level of reactive oxygen species (ROS) and the action of protective enzymes will lead to oxidative damage, and possibly inflammation. A small number of interventional studies suggest that oxidative stress may be directly targeted in topical therapy of dry eye treatment. For example, in vitro studies suggest that L-carnitine and pterostilbene, a blueberry component may reduce oxidative stress, and in animal studies, alpha-lipoic acid (ALP) and selenoprotein P may be helpful. Examples of treatments used in clinical trials include vitamin B12 eyedrops and iodide iontophoresis. With recent emphasis on ageing medicine and preventive holistic health, as well as the role of environmental science, research on oxidative stress in the ocular surface is likely to have increasing impact in the coming years.

Neuropathic symptoms of the ocular surface: dryness, pain, and itch

PURPOSE OF REVIEW

This review aims to describe the recent findings on epidemiology, pathophysiology, and management of neuropathic symptoms of the ocular surface, with a focus on potential similarities between sensations of dry eye, pain and itch.

RECENT FINDINGS

A narrative review of the literature was undertaken. Key references from research in dry eye, neuropathic symptoms of the ocular surface, ocular pain and itch, as well as general references on itch and pain neurobiology were included. Recent findings suggest aspects of dry eye, chronic ocular pain and itch symptomatology are driven by neuropathic pain mechanisms involving peripheral and central sensitization processes.

SUMMARY

Ocular dryness, pain, and itch are prevalent complaints with several of shared features. Multiple lines of evidence suggest that peripheral and central neuronal sensitization processes are involved in generating and maintaining ocular sensory symptoms. Research is warranted on the epidemiology of ocular sensations, molecular mechanisms involved in nociception and pruriception in the eye, electrophysiological alterations in animal models of eye conditions, and therapeutic modalities that can alleviate unpleasant ocular sensations.

Neuropathic pain and dry eye

Dry eye is a common, multifactorial disease currently diagnosed by a combination of symptoms and signs. Its epidemiology and clinical presentation have many similarities with neuropathic pain outside the eye. This review highlights the similarities between dry eye and neuropathic pain, focusing on clinical features, somatosensory function, and underlying pathophysiology. Implications of these similarities on the diagnosis and treatment of dry eye are discussed.

Analysis of Cytokine Levels in Tears and Clinical Correlations After Intense Pulsed Light Treating Meibomian Gland Dysfunction

PURPOSE

To investigate the change from baseline of inflammatory markers in tears of dry eye disease (DED) subjects owing to meibomian gland dysfunction (MGD) after intense pulsed light (IPL) treatment and meibomian gland expression (MGE) compared to sham treatment, and the correlations with ocular surface parameters.

DESIGN

Randomized, double-masked, controlled study.

METHODS

Those randomized into the active treatment arm received 3 consecutive treatments (14∼16 J/cm²) approximately 4 weeks apart in the periocular region. Control eyes received 3 treatments in the same intervals of 0 J/cm². Tear samples in all eyes were collected and analyzed at baseline, week 12, and/or week 4 for interleukin (IL)-17A, IL-6, and prostaglandin E2 (PGE2). The correlations between cytokines and ocular surface parameters were analyzed before and after IPL treatment.

RESULTS

All of the inflammatory markers declined in value compared to baselines. IL-17A and IL-6 showed statistically significant decreases compared to sham treatment at each measured time point. PGE2 showed statistically significant decreases compared to sham at week 12. Results showed that the expressions of IL-17A and IL-6 correlated well with ocular surface parameters of the lower eyelid before IPL. The changed values of IL-6 and PGE2 in tears correlated with the changed values of partial ocular surface parameters after IPL treatment in study eyes, respectively.

CONCLUSIONS

The study results suggest that IPL can significantly reduce inflammatory markers in tears of patients suffering with DED owing to MGD after IPL treatment. These findings indicate that IL-17A and IL-6 play roles in the pathogenesis of DED owing to MGD, and the reduction of the inflammatory factors is consistent with the improvement of partial clinical symptoms and signs.

Lacrimal gland-derived IL-22 regulates IL-17-mediated ocular mucosal inflammation

Inflammatory damage of mucosal surface of the eye is a hallmark of dry eye disease (DED) and, in severe cases, can lead to significant discomfort, visual impairment, and blindness. DED is a multifactorial autoimmune disorder with a largely unknown pathogenesis. Using a cross-sectional patient study and a well-characterized murine model of DED, herein we investigated the immunoregulatory function of interleukin-22 (IL-22) in the pathogenesis of DED. We found that IL-22 levels were elevated in lacrimal fluids of DED patients and inversely correlated with severity of disease. Acinar cells of the lacrimal glands (LGs), not inflammatory immune cells, are the primary source of IL-22, which suppresses inflammation in ocular surface epithelial cells upon desiccating stress. Moreover, loss of function analyses using IL-22 knockout mice demonstrated that IL-22 is essential for suppression of ocular surface infiltration of Th17 cells and inhibition of DED induction. Our novel findings elucidate immunoregulatory function of LG-derived IL-22 in inhibiting IL-17-mediated ocular surface epitheliopathy in DED thus making IL-22 a new relevant therapeutic target.

The Relationship Between Ocular Itch, Ocular Pain, and Dry Eye Symptoms (An American Ophthalmological Society Thesis)

PURPOSE

To evaluate associations between sensations of ocular itch and dry eye (DE) symptoms, including ocular pain, and DE signs.

METHODS

A cross-sectional study of 324 patients seen in the Miami Veterans Affairs eye clinic was performed. The evaluation consisted of questionnaires regarding ocular itch, DE symptoms, descriptors of neuropathic-like ocular pain (NOP), and evoked pain sensitivity testing on the forehead and forearm, followed by a comprehensive ocular surface examination including corneal mechanical sensitivity testing. Analyses were performed to examine for differences between those with and without subjective complaints of ocular itch.

RESULTS

The mean age was 62 years with 92% being male. Symptoms of DE and NOP were more frequent in patients with moderate-severe ocular itch compared to those with no or mild ocular itch symptoms. With the exception of ocular surface inflammation (abnormal matrix metalloproteinase 9 testing) which was less common in those with moderate-severe ocular itch symptoms, DE signs were not related to ocular itch. Individuals with moderate-severe ocular itch also demonstrated greater sensitivity to evoked pain on the forearm and had higher non-ocular pain, depression, and post-traumatic stress disorders scores, compared to those with no or mild itch symptoms.

CONCLUSIONS

Subjects with moderate-severe ocular itch symptoms have more severe symptoms of DE, NOP, non-ocular pain and demonstrate abnormal somatosensory testing in the form of increased sensitivity to evoked pain at a site remote from the eye, consistent with generalized hypersensitivity.

ω-3 Tear Film Lipids Correlate With Clinical Measures of Dry Eye

PURPOSE

ω-3 and ω-6 polyunsaturated fatty acids modulate inflammatory processes throughout the body through distinct classes of lipid mediators that possess both proinflammatory and proresolving properties. The purpose of this cross-sectional study was to explore the relationship between lipid profiles in human tears and dry eye (DE) symptoms and signs.

METHODS

Forty-one patients with normal eyelid and corneal anatomy were prospectively recruited from a Veterans Administration Hospital over 18 months. Symptoms and signs of DE were assessed, and tear samples was analyzed by mass spectrometry-based lipidomics. Statistical analyses comparing the relationship between tear film lipids and DE included Pearson/Spearman correlations and t-tests.

RESULTS

Arachidonic acid (AA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) were present in more than 90% of tear film samples. The ratio of ω-6 (AA) to ω-3 (DHA+EPA) fatty acids was correlated with multiple measures of tear film dysfunction (tear breakup time, Schirmer 2 scores, and corneal staining; all P < 0.05). Arachidonic acid-derived prostaglandin E2 was detected in the majority of samples and correlated with low tear osmolarity, meibomian gland plugging, and corneal staining.

CONCLUSIONS

Both ω-3 and ω-6 lipid circuits are activated in the human tear film. The ratio of ω-6:ω-3 tear lipids is elevated in DE patients in proportion to the degree of tear film dysfunction and corneal staining. Metabolic deficiency of ω-3 tear film lipids may be a driver of chronic ocular surface inflammation in DE.

Langerhans cells prevent subbasal nerve damage and upregulate neurotrophic factors in dry eye disease

The functional role of Langerhans cells (LCs) in ocular surface inflammation and nerve damage in dry eye (DE) disease has yet to be determined. This study was performed to investigate this relationship through both clinical study on DE patients and in vivo mouse models with induced DE disease. In a cross-sectional case-control study (54 eyes of DE patients; 34 eyes of control patients), average cell density, area, and process length of LCs were measured using confocal microscopy. Data were analyzed to determine whether changes in LCs are correlated with subbasal nerve plexus (SNP) parameters (nerve density, beading, and tortuosity). In DE patients, SNP density marginally decreased and nerve beading and tortuosity were significantly increased compared to the control group. The total number of LCs significantly increased in DE patients, and some LCs with elongated processes were found to be attached to nerve fibers. Interestingly, nerve loss and deformation were correlated with inactivation of LCs. In an in vivo experiment to elucidate the role of LCs in ocular surface inflammation and corneal nerve loss, we used a genetically modified mouse model (CD207-DTR) that reduced the population of CD207 (Langerin) expressing cells by injection of diphtheria toxin. In CD207-depleted mice with DE disease (CD207-dDTR+DE), corneal nerves in the central region were significantly decreased, an effect that was not observed in wild-type (WT)+DE mice. In CD207-dDTR+DE mice, infiltration of CD4+, CD19+, CD45+, and CD11b+ cells into the ocular surface was increased, as confirmed by flow cytometry. Increased IL-17 and IFN-γ mRNA levels, and decreased expression of neurotrophic factors and neurotransmitters, were also found in the CD207-dDTR+DE mice. These data support a functional role for LCs in negatively regulating ocular surface inflammation and exhibiting a neuroprotective function in DE disease.

Gabapentin Attenuates Ocular Inflammation: In vitro and In vivo Studies

To investigate the effects of gabapentin, a structural analog of γ-amino butyric acid (GABA), on the inflammatory response of lipopolysaccharide (LPS)-stimulated rabbit corneal cells (SIRC) and on endotoxin-induced uveitis (EIU) in rabbits. We investigated the LPS-induced expression of several inflammatory mediators, such as TNF-α, IL-1β, cPLA₂, COX-2, and PGE₂ in the SIRC cells with or without gabapentin treatment. Gabapentin treatment significantly (p < 0.05) attenuated cytokines production, cPLA₂ activation, COX-2 expression, and PGE₂ levels in SIRC. EIU was induced by an intraocular injection of 0.1 μg of LPS in albino rabbit eye. After 7 and 24 h from LPS injection clinical signs of ocular inflammation were examined by slit lamp with or without topical treatment of 0.5% gabapentin. Tears, aqueous, cornea, conjunctiva, and iris-ciliary body were collected and inflammatory biomarkers assessed. Topical treatment with gabapentin significantly (p < 0.05) reduced clinical signs and biomarkers of inflammation compared with the LPS group both at 7 and 24 h. In conclusion, the results generated in the present study suggest that ophthalmic formulation based on gabapentin may be useful in the treatment of inflammatory conditions associated to ocular pain such as uveitis, and that clinical studies to evaluate this possibility may be warranted.

Identification and Profiling of Specialized Pro-Resolving Mediators in Human Tears by Lipid Mediator Metabolomics

Specialized pro-resolving mediators (SPM), e.g. Resolvin D1, Protectin D1, Lipoxin A₄, and Resolvin E1 have each shown to be active in ocular models reducing inflammation. In general, SPMs have specific agonist functions that stimulate resolution of infection and inflammation in animal disease models. The presence and quantity of SPM in human emotional tears is of interest. Here, utilizing a targeted LC-MS-MS metabololipidomics based approach we document the identification of pro-inflammatory (Prostaglandins and Leukotriene B₄) and pro-resolving lipid mediators (D-series Resolvins, Protectin D1, and Lipoxin A₄) in human emotional tears from 12 healthy individuals. SPMs from the Maresin family (Maresin 1 and Maresin 2) were not present in these samples. Principal Component Analysis (PCA) revealed gender differences in the production of specific mediators within these tear samples as the SPMs were essentially absent in these female donors. These results indicate that specific SPM signatures are present in human emotional tears at concentrations known to be bioactive. Moreover, they will help to further appreciate the mechanisms of production and action of SPMs in the eye, as well as their physiologic roles in human ocular disease resolution.

Lipid-Based Therapy for Ocular Surface Inflammation and Disease

Ocular surface diseases such as dry eye, allergic keratoconjunctivitis, and infection are very prevalent conditions and involve ocular surface stress and inflammation. Recently, various lipid-based therapies have been advocated for the modulation of ocular surface inflammation. Here we review the latest developments and challenges of these strategies. These include administration of essential fatty acids, cyclooxygenase (COX) inhibitors and resolvin analogs. Lipids form part of the tear film and are crucial for tear film stability; loss of tear film stability can aggravate ocular surface inflammation. Strategies to replenish tear film lipids - namely, eyelid warming and eye drops containing natural or synthetic lipids - are evaluated. Recent advances in the use of lipids as ocular drug delivery vehicles, antioxidants, and diagnostic markers are discussed.

Effects of androgen on ultrastructure of corneal epithelium and function of the tear film in BALB/c mice

PURPOSE

The aim of this study was to investigate the effects of androgen on the ultrastructure of corneal epithelium and function of the tear film in a mouse model.

METHODS

Healthy adult male BALB/c mice were randomly apportioned to normal control, sham-operated, or orchiectomy groups. In the orchiectomy group, 4 subgroups with treatment [blank group, dihydrotestosterone (DHT) eye drop group, DHT injection group, and dimethyl sulfoxide (DMSO) eye drop group] were further established at 3 weeks after orchiectomy. Tear production, tear break-up time, and corneal fluorescein staining were evaluated in all groups at multiple time points. Serum androgen concentrations were measured by competitive radioimmunoassay, and ultrastructure of corneal epithelial cells was examined by transmission electron microscopy.

RESULTS

Before orchiectomy, the mean serum concentration of androgen was 43.4 ng/μL, which decreased to approximately 0 ng/μL at 1 week after orchiectomy. Significantly less tear production, shorter tear break-up time, higher corneal fluorescein staining score, shorter and flattened corneal epithelial microvilli, and looser intercellular desmosomes were observed in mice after orchiectomy. DHT supplements increased serum androgen levels, and some of the tear film functions and morphological features of microvilli and desmosomes were gradually close to those at baseline in the DHT injection group.

CONCLUSIONS

Persistent corneal staining, decreased tear production, short break-up time, and unhealthy corneal ultrastructure were observed in mice that received orchiectomy for at least 8 weeks. A mouse that received orchiectomy could be used as a dry eye model. Exogenous DHT supplement improved corneal epithelial ultrastructure and tear film function in this model.

Global Metabonomic and Proteomic Analysis of Human Conjunctival Epithelial Cells (IOBA-NHC) in Response to Hyperosmotic Stress

"Dry eye" is a multifactorial inflammatory disease affecting the ocular surface. Tear hyperosmolarity in dry eye contributes to inflammation and cell damage. Recent research efforts on dry eye have been directed toward biomarker discovery for diagnosis, response to treatment, and disease mechanisms. This study employed a spontaneously immortalized normal human conjunctival cell line, IOBA-NHC, as a model to investigate hyperosmotic stress-induced changes of metabolites and proteins. Global and targeted metabonomic analyses as well as proteomic analysis were performed on IOBA-NHC cells incubated in serum-free media at 280 (control), 380, and 480 mOsm for 24 h. Twenty-one metabolites and seventy-six iTRAQ-identified proteins showed significant changes under at least one hyperosmotic stress treatment as compared with controls. SWATH-based proteomic analysis further confirmed the involvement of inflammatory pathways such as prostaglandin 2 synthesis in IOBA-NHC cells under hyperosmotic stress. This study is the first to identify glycerophosphocholine synthesis and O-linked β-N-acetylglucosamine glycosylation as key activated pathways in ocular surface cells under hyperosmotic stress. These findings extend the current knowledge in metabolite markers of dry eye and provide potential therapeutic targets for its treatment.

Efficacy of bromfenac sodium ophthalmic solution for treatment of dry eye disease

PURPOSE

To evaluate the efficacy of bromfenac sodium ophthalmic solution (BF) in patients with dry eye disease (DED) inadequately controlled by monotherapy with artificial tears (ATs).

DESIGN

An investigator-oriented trial with a single-arm, nonrandomized, open-label design.

METHODS

Twenty-six patients, who showed no symptomatic improvement of DED after 1 month of AT treatment, were enrolled. Bromfenac sodium ophthalmic solution was administered adjunctively with AT for 1 month. The BF treatment was then discontinued, and AT treatment alone was continued for 3 months. The signs and symptoms were evaluated at the beginning of BF treatment (Pre), at the end of the combined BF and AT treatment (BF1M), and at 1 and 3 months after discontinuation of BF treatment (Po1M and Po3M, respectively).

RESULTS

The dryness scores at BF1M were significantly improved compared with Pre (P < 0.001) and significantly superior to Po3M (P < 0.001). No significant changes in the Schirmer scores were observed throughout the treatment period. The tear film breakup time was significantly improved at BF1M (4.4 ± 2.3 seconds) compared with Pre (2.8 ± 1.8 seconds; P < 0.001). Superficial punctate keratopathy showed significant improvements in the total score of area and density at BF1M compared with Pre (P < 0.001). However, these parameters had significantly worsened at Po3M compared with BF1M. No adverse events were observed.

CONCLUSIONS

Bromfenac sodium ophthalmic solution has improved the dryness of the eye and signs of DED through its anti-inflammatory effects. Nonsteroidal anti-inflammatory drugs were suitable as anti-inflammatory ophthalmic solutions for patients with DED.

Neuropathic ocular pain: an important yet underevaluated feature of dry eye

Dry eye has gained recognition as a public health problem given its prevalence, morbidity, and cost implications. Dry eye can have a variety of symptoms including blurred vision, irritation, and ocular pain. Within dry eye-associated ocular pain, some patients report transient pain whereas others complain of chronic pain. In this review, we will summarize the evidence that chronicity is more likely to occur in patients with dysfunction in their ocular sensory apparatus (ie, neuropathic ocular pain). Clinical evidence of dysfunction includes the presence of spontaneous dysesthesias, allodynia, hyperalgesia, and corneal nerve morphologic and functional abnormalities. Both peripheral and central sensitizations likely play a role in generating the noted clinical characteristics. We will further discuss how evaluating for neuropathic ocular pain may affect the treatment of dry eye-associated chronic pain.

Activation of HIF-1α (hypoxia inducible factor-1α) prevents dry eye-induced acinar cell death in the lacrimal gland

The pathogenesis of immune-mediated lacrimal gland (LG) dysfunction in Sjögren's syndrome has been thoroughly studied. However, the majority of dry eye (DE) is not related to Sjögren type, and its pathophysiology remains unclear. The purpose of this study was to determine and investigate the protective mechanisms against DE stress in mice. DE induced prominent blood vessel loss without apoptosis or necrosis in the LG. Autophagic vacuoles, distressed mitochondria, and stressed endoplasmic reticulum were observed via electron microscopy. Immunoblotting confirmed the increase in autophagic markers. Glycolytic activities were enhanced with increasing levels of succinate and malate that, in turn, activated hypoxia-inducible factor (HIF)-1α. Interestingly, the areas of stable HIF-1α expression overlapped with COX-2 and MMP-9 upregulation in LGs of DE-induced mice. We generated HIF-1α conditional knockout (CKO) mice in which HIF-1α expression was lost in the LG. Surprisingly, normal LG polarities and morphologies were completely lost with DE induction, and tremendous acinar cell apoptosis was observed. Similar to Sjögren's syndrome, CD3⁺ and CD11b⁺ cells infiltrated HIF-1α CKO LGs. Our results show that DE induced the expression of HIF-1α that activated autophagy signals to prevent further acinar cell damage and to maintain normal LG function.

The role of corneal afferent neurons in regulating tears under normal and dry eye conditions

The cornea is one of several orofacial structures requiring glandular secretion for proper lubrication. Glandular secretion is regulated through a neural reflex initiated by trigeminal primary afferent neurons innervating the corneal epithelium. Corneal sensory afferents must respond to irritating and potentially damaging stimuli, as well as drying that occurs with evaporation of the tear film, and the physiological properties of corneal afferents are consistent with these requirements. Polymodal neurons are sensitive to noxious mechanical, thermal and chemical stimuli, mechanoreceptive neurons are selectively activated by mechanical stimuli, and cool cells respond to innocuous cooling. The central terminations of corneal primary afferents are located within two regions of the spinal trigeminal nucleus. The more rostral region, located at the transition between the trigeminal subnucleus caudalis and interpolaris, represents a critical relay for the regulation of the lacrimation reflex. From this region, major control of lacrimation is carried through projections to preganglionic parasympathetic neurons located in or around the superior salivatory nucleus. Dry eye syndrome may be caused by a dysfunction in the tear secreting glands themselves or in the neuronal circuit regulating these glands. Furthermore, the dry eye condition itself may modify the properties of corneal afferents and affect their ability to regulate secretion, a possibility just now being explored.

Dry eye modifies the thermal and menthol responses in rat corneal primary afferent cool cells

Dry eye syndrome is a painful condition caused by inadequate or altered tear film on the ocular surface. Primary afferent cool cells innervating the cornea regulate the ocular fluid status by increasing reflex tearing in response to evaporative cooling and hyperosmicity. It has been proposed that activation of corneal cool cells via a transient receptor potential melastatin 8 (TRPM8) channel agonist may represent a potential therapeutic intervention to treat dry eye. This study examined the effect of dry eye on the response properties of corneal cool cells and the ability of the TRPM8 agonist menthol to modify these properties. A unilateral dry eye condition was created in rats by removing the left lacrimal gland. Lacrimal gland removal reduced tears in the dry eye to 35% compared with the contralateral eye and increased the number of spontaneous blinks in the dry eye by over 300%. Extracellular single-unit recordings were performed 8-10 wk following surgery in the trigeminal ganglion of dry eye animals and age-matched controls. Responses of corneal cool cells to cooling were examined after the application of menthol (10 μM-1.0 mM) to the ocular surface. The peak frequency of discharge to cooling was higher and the cooling threshold was warmer in dry eye animals compared with controls. The dry condition also altered the neuronal sensitivity to menthol, causing desensitization to cold-evoked responses at concentrations that produced facilitation in control animals. The menthol-induced desensitization of corneal cool cells would likely result in reduced tearing, a deleterious effect in individuals with dry eye.

Short- and long-term corneal vascular effects of tafluprost eye drops

BACKGROUND

Prostaglandin analogs are first line therapy in the treatment of glaucoma, but also display side effects during ocular inflammation. In this context, the potential side effects of prostaglandin analogs on the normally avascular cornea, the main application route for eye drops, are so far not fully defined. Therefore, the aim of this study was to evaluate the vascular effects of the prostaglandin analog tafluprost on the healthy and inflamed cornea.

METHODS

For in vitro studies, blood and lymphatic endothelial cells were treated with tafluprost; cell proliferation was assessed after 48 h. For long-term in vivo studies under healthy conditions, naïve corneas of BALB/c mice were treated with tafluprost eye drops for 4 weeks. For short-term in vivo studies under inflammatory conditions, corneal inflammation was induced by suture placement; mice then received tafluprost eye drops for 1 week. Afterwards, corneas were stained with CD31 as panendothelial and LYVE-1 as lymphendothelial (and macrophage) marker.

RESULTS

In vitro, tafluprost did not alter blood or lymphatic endothelial cell proliferation. In vivo, there was no change in limbal blood or lymphatic vessel anatomy after long-term treatment with tafluprost. Short-term treatment with tafluprost under inflammatory conditions did not influence the recruitment of LYVE-1 positive macrophages into the cornea. Moreover, treatment of inflamed corneas with tafluprost did not significantly influence corneal hem- and lymphangiogenesis.

CONCLUSIONS

Tafluprost does not affect blood and lymphatic vessel growth, neither under resting nor under inflammatory conditions. These findings suggest a safe vascular profile of tafluprost eye drops at the inflammatory neovascularized cornea.