Interferon-γ exacerbates dry eye-induced apoptosis in conjunctiva through dual apoptotic pathways

Multifaceted mitochondrial as a novel therapeutic target in dry eye: insights and interventions

Dry eye, recognized as the most prevalent ocular surface disorder, has risen to prominence as a significant public health issue, adversely impacting the quality of life for individuals across the globe. Despite decades of extensive research into the chronic inflammation that characterizes dry eye, the intricate mechanisms fueling this persistent inflammatory state remain incompletely understood. Among the various cellular components under investigation, mitochondria-essential for cellular energy production and homeostasis-have attracted increasing attention for their role in dry eye pathogenesis. This involvement points to mechanisms such as oxidative stress, apoptosis, and sustained inflammation, which are central to the progression of the disease. This review aims to provide a thorough exploration of mitochondrial dysfunction in dry eye, shedding light on the critical roles played by mitochondrial oxidative stress, apoptosis, and mitochondrial DNA damage. It delves into the mechanisms through which diverse pathogenic factors may trigger mitochondrial dysfunction, thereby contributing to the onset and exacerbation of dry eye. Furthermore, it lays the groundwork for an overview of current therapeutic strategies that specifically target mitochondrial dysfunction, underscoring their potential in managing this complex condition. By spotlighting this burgeoning area of research, our review seeks to catalyze the development of innovative drug discovery and therapeutic approaches. The ultimate goal is to unlock promising avenues for the future management of dry eye, potentially revolutionizing treatment paradigms and improving patient outcomes. Through this comprehensive examination, we endeavor to enrich the scientific community's understanding of dry eye and inspire novel interventions that address the underlying mitochondrial dysfunctions contributing to this widespread disorder.

Safety and Efficacy of Topical Vitamin D in the Management of Dry Eye Disease Associated With Meibomian Gland Dysfunction: A Placebo-Controlled Double-Blind Randomized Controlled Trial

PURPOSE

The aim of this study was to investigate the safety and efficacy of topical vitamin D in the management of dry eye disease associated with meibomian gland dysfunction (MGD).

METHODS

In this randomized controlled trial, patients with symptomatic MGD were divided into 2 groups to receive topical vitamin D drops or placebo in their randomized eyes. The exclusion criteria consisted of patients with vitamin D deficiency, previous ocular surgery, and patients with ocular diseases affecting the tear film. Patients and researchers were masked to the study groups. The outcomes included the score of Dry Eye Questionnaire (DEQ) 5 and Ocular Surface Disease Index (OSDI), corneal and conjunctival staining score, tear breakup time (TBUT), Schirmer, and MG expressibility score evaluated at baseline and weeks 4 and 8.

RESULTS

Twenty-eight eyes of 28 patients were recruited in each group. In addition to the improvement of subjective parameters in both groups, there was a statistically significantly greater improvement in the vitamin D group compared with control for average scores of OSDI (13.38 ± 7.32 vs. 27.94 ± 7.49) and DEQ5 (9.67 ± 1.86 vs. 14.14 ± 2.45) at week 8 (Ps <0.001). In addition, a significant improvement in TBUT and Schirmer test was observed in both groups in weeks 4 and 8 ( P value <0.05). There was a significant difference between the treatment and control groups after 8 weeks for OSDI, DEQ5, Schirmer, TBUT, corneal fluorescein staining, and MG expressibility score ( P value <0.05).

CONCLUSIONS

The preliminary results of this randomized controlled trial suggested that use of topical vitamin D drops with a lipid vehicle could be safe and might significantly improve the symptoms and signs of dry eye associated with MGD.

Uveitis and Dry Eye Disease in Children: A Cross-Sectional Comparative Study

PURPOSE

This study aims to evaluate the ocular surface characteristics in children diagnosed with uveitis and explore the association between uveitis and dry eye disease (DED).

METHODS

We included 84 children, 42 with uveitis and 42 healthy children. We performed the OSDI questionnaire and several ocular surface tests, including osmolarity, NITBUT, Schirmer test, and vital staining. We used Fisher's exact test and Mann-Whitney to compare variables and a binomial logistic regression to determine the factors associated with DED.

RESULTS

The difference in the prevalence of DED between uveitis (54.8%) and healthy (31%) groups was statistically significant (p < 0.05). Most patients with uveitis had mixed DED, and none of the healthy subjects had a severe form of the disease. There were no statistically significant differences in most of the tear film tests. However, all parameters tended to worsen in the uveitis group, and lipid layer thickness was thinner (p < 0.036). The uveitis group exhibited significantly more symptoms (p < 0.05). In the multivariate logistic regression, uveitis was associated with an odds ratio (OR) of 3.0 (95% CI: 1.07-8.42, p < 0.05) for DED.

CONCLUSIONS

Our findings demonstrate a significantly higher prevalence of DED in children with uveitis compared to their healthy counterparts. Furthermore, our analysis indicates that the risk of DED in pediatric patients with uveitis is threefold higher than in healthy children. Therefore, it is crucial for clinicians to vigilantly monitor the development of DED in pediatric patients with uveitis and consider the implementation of preventive treatments.

Berberine ameliorate inflammation and apoptosis via modulating PI3K/AKT/NFκB and MAPK pathway on dry eye

BACKGROUND

Dry eye disease (DED) is a multifactorial disease in ocular surface, and inflammation plays an etiological role. Berberine (BBR) has shown efficacy in treating inflammatory diseases. Yet, there was no adequate information related to the therapeutic effects of BBR for DED.

PURPOSE

To detect the effects and explore the potential mechanisms of BBR on DED.

STUDY DESIGN

In vitro, in vivo study and network pharmacology analysis were involved.

METHOD

The human corneal epithelium cells viability was evaluated with different concentrations of BBR. Dry eye murine model was established by exposing to the desiccating stress, and Ciclosporin (CSA), BBR eye drops or vehicle were topical administration for 7 days. The phenol red cotton tests, Oregon-green-dextran staining and Periodic acid-Schiff staining were performed and evaluated the dry eye after treatment. Inflammation and apoptosis levels of ocular surface were quantified. The potential targets related to berberine and dry eye were collected from databases. The Protein-Protein interaction network analysis and GO & KEGG enrichment analysis were realized by STRING database, Metascape platform and Cytoscape software to find core targets and signaling pathways. The SchrÖdinger software was used to molecular docking and PyMOL software to visualization. Finally, the levels of PI3K/AKT/NFκB and MAPK pathways were detected.

RESULT

The data revealed BBR could rescue impaired HCE under hyperosmotic conditions. In addition, BBR eye drops could ameliorate dry eye. And BBR eye drops suppressed the inflammatory factors and CD4+T cells infiltration in conjunctiva. Besides, BBR eye drops protected ocular surface by avoiding the severe apoptosis and decreasing the level of MMP-3 and MMP-9. 148 common targets intersection between BBR and dry eye were found via network pharmacology analysis. Core proteins and core pathways were identified through PPI and GO&KEGG enrichment analysis. Molecular docking displayed excellent binding between BBR and those core targets. Finally, in vivo study verified that BBR eye drops had a therapeutic effect in dry eye by inhibiting PI3K/AKT/NFκB and MAPK pathways.

CONCLUSION

The research provided convincing evidence that BBR could be a candidate drug for dry eye.

The Molecular Mechanisms Responsible for Tear Hyperosmolarity-Induced Pathological Changes in the Eyes of Dry Eye Disease Patients

Dry eye disease (DED) is a multifactorial disorder of the lacrimal system and ocular surface, characterized by a deficiency in the quality and/or quantity of the tear fluid. The multifactorial nature of DED encompasses a number of interconnected underlying pathologies, including loss of homeostasis, instability and hyperosmolarity of the tears, and the induction and propagation of detrimental inflammatory responses in the eyes, which finally results in the development of neurosensory dysfunction and visual disruption. Dryness, grittiness, scratchiness, discomfort, inflammation, burning, watering, ocular fatigue, pain, and decreased functional visual acuity are common symptoms of DED. Eye dysfunction drastically attenuates patients' quality of life. Accordingly, a better understanding of the pathogenic processes that regulate the development and progression of DED is crucially important for the establishment of new and more effective DED-related treatment approaches, which would significantly improve the quality of life of DED patients. Since the process of osmoregulation, which guards the ocular surface epithelia and maintains normal vision, is affected when the osmolarity of the tears is greater than that of the epithelial cells, tear hyperosmolarity (THO) is considered an initial, important step in the development, progression, and aggravation of DED. In order to delineate the role of THO in the pathogenesis of DED, in this review article, we summarize current knowledge related to the molecular mechanisms responsible for the development of THO-induced pathological changes in the eyes of DED patients, and we briefly discuss the therapeutic potential of hypo-osmotic eye drops in DED treatment.

Randomized controlled trial on the efficacy and safety of autologous serum eye drops in dry eye syndrome

BACKGROUND

Autologous serum eye drops (ASEDs), a novel treatment derived from blood serum, have emerged as a groundbreaking solution for managing dry eye syndrome (DES). These drops have shown significant promise in relieving the distressing symptoms of DES. This study aimed to evaluate the safety and effectiveness of ASEDs compared to traditional treatments, which often prove inadequate or result in unwanted side effects, particularly in individuals with moderate-to-severe DES.

AIM

To evaluate whether ASEDs are safer and more effective than conventional artificial tears in the treatment of moderate-to-severe DES.

METHODS

This multi-centered randomized controlled trial included 240 patients with moderate-to-severe DES from three ophthalmology clinics in China. They were randomly assigned to receive either ASEDs or artificial tears for 12 wk. The primary outcome was the change in the ocular surface disease index (OSDI) score, with secondary outcomes including tear break-up time (TBUT), Schirmer I test, corneal fluorescein staining (CFS), and conjunctival impression cytology (CIC). Statistics analysis was performed using an analysis of covariance with adjustments made for baseline values.

RESULTS

Our findings revealed that both ASEDs and artificial tears significantly improved the OSDI score, TBUT, Schirmer I test, CFS, and CIC from baseline to week 12. The ASEDs group showed significantly greater improvement in all these measures than the artificial tears group (all P values < 0.05). The average difference in the OSDI score between the two cohorts was -10.3 (95% confidence interval: -13.6 to -7.0), indicating a substantial improvement in the ASEDs group. The occurrence of adverse events was comparable between cohorts, with no reports of severe adverse events.

CONCLUSION

ASEDs are more effective and safer than artificial tears for mitigating symptoms of moderate-to-severe DES. ASEDs could be an alternative/supplementary therapy for patients with DES less responsive to traditional treatments.

Protection of Barrier Function in Cultured Human Corneal Epithelial Cells by Semaphorin 4D

PURPOSE

Corneal epithelial barrier function is important to maintain corneal homeostasis and is impaired by inflammation. We aimed to investigate the localization of semaphorin 4D (Sema4D) in the cornea, and its effects on the barrier function of cultured corneal epithelial cells.

METHODS

The expressions of semaphorin4 D and its receptor in the murine cornea were examined by immunoblot, immunofluorescent staining and confocal microscopy observations. Human corneal epithelial (HCE) cells stimulated by TNF-α or IL-1β were cultured with or without Sema4D. Cell viability was examined by CCK8, cell migration was evaluated by scratch wound assay, and barrier function was assessed by transepithelial electrical resistance (TEER) and Dextran-FITC permeability assay. The expression of tight junction proteins in HCE cells was examined by immunoblot, immunofluorescent staining and qRT-PCR.

RESULTS

We demonstrated that the protein of Sema4D and its receptor, plexin-B1, was expressed in murine cornea. Sema4D induced an increase in the TEER and a decrease in the permeability of HCE cells. It also induced the expression of tight junction protein ZO-1, occludin and claudin-1 in HCE cells. Furthermore, under stimulation of TNF-α or IL-1β, Sema4D treatment could inhibit the decreased TEER and the elevated permeability of HCE cells.

CONCLUSIONS

Sema4D is located distinctly in corneal epithelial cells and promoted their barrier function by increasing the expression of tight junction proteins. Sema4D may act as a preventive for maintaining corneal epithelial barrier function during ocular inflammation.

Diagnostic Performance of the Tear Meniscus Osmolarity Measurement for Dry Eye Disease in Rheumatoid Arthritis Patients

BACKGROUND

The aim of our study was to evaluate the diagnostic capacity of the tear meniscus osmolarity measurement for dry eye disease (DED) in patients with rheumatoid arthritis (RA), using a portable osmometer based on electrical impedance and an integrated circuit technology (TearLab® (Escondido, CA, USA)).

METHODS

We included 101 RA patients, 81 patients with DED and 20 without DED (controls). We measured tear osmolarity and assessed other clinical diagnostic tests as suggested by the TFOS DEWS II composite reference standard diagnostic criteria for DED using Ocular Surface Disease Index (OSDI), Five-item Dry Eye Questionnaire (DEQ-5), fluorescein tear break-up time (F-TUBT), ocular surface staining (SICCA score), and other clinical parameters to classify DED subtypes. We analyzed the agreement between osmolarity and the TFOS DEWS II composite reference standard for DED diagnosis. We conducted receiver operating characteristic (ROC) curve analyses using the DED variable and its subtypes as dependent variables and the continuous variable for osmolarity or the inter-eye difference in osmolarity as independent variable. Sensitivity, specificity, and area under the curve for all potential cut-off points were obtained and reported from ROC curves.

RESULTS

We found that tear meniscus osmolarity had a low diagnostic capacity for DED (AUC = 0.57). Tear meniscus osmolarity measurement had a sensitivity of 35% and a specificity of 80% with a kappa level of agreement of 0.08 compared to the TFOS DEWS II composite reference standard. The low diagnostic capacity of the tear meniscus osmolarity was similar for aqueous-deficient DED and for evaporative DED, being only fair for severe DED with a 57% sensitivity and 80% specificity and a kappa level of agreement of 0.36.

CONCLUSIONS

Our findings suggest that in patients with RA, tear meniscus osmolarity measured by the TearLab® showed low sensitivity, low specificity, and limited agreement with the TFOS DEWS II composite reference standard for DED diagnosis.

Biomarkers of ocular allergy and dry eye disease

The most common disorders of the ocular surface are dry eye disease (DED) and ocular allergy (OA). These conditions are frequently coexisting with or without a clinical overlap and can cause a severe impact on the patient's quality of life. Therefore, it can sometimes be hard to distinguish between DED and OA because similar changes and manifestations may be present. Atopic patients can also develop DED, which can aggravate their manifestations. Moreover, patients with DED can develop ocular allergies, so these two pathological entities of the ocular surface can be considered as mutual conditions that share the same background. Nowadays, by using different techniques to collect tissue from ocular surfaces, the changes in molecular homeostasis can be detected and this can lead to a precise diagnosis. The article provides an up-to-date review of the various ocular surface biomarkers that have been identified in DED, OA, or both conditions. Abbreviations: DED = dry eye disease, OA = ocular allergy, SS = Sjogren syndrome, TBUT = tear break up time, TFO = tear film osmolarity, AKC = Atopic keratoconjunctivitis, ANXA1 = Annexin 1, ANXA11 = Annexin 11, CALT = Conjunctival associated lymphoid tissue, CCL2/MIP-1 = Chemokine (C-C motif) ligand2/Monocyte chemoattractant protein 1, CCL3/MIP-1α = Chemokine (C-C motif) ligand 3/Macrophage inflammatory protein 1 alpha, CCL4/MIP-1β = Chemokine (C-C motif) ligand 4/Macrophage inflammatory protein 1 beta, CCL5/RANTES = Chemokine (C-C motif) ligand 5 /Regulated on Activation, Normal T cell Expressed and Secreted, CCR2 = Chemokine (C-C motif) receptor 2, CCR5 = Chemokine (C-C motif) receptor 5, CD3+ = Cluster of differentiation 3 positive, CD4+ = Cluster of differentiation 4 positive, CD8+ = Cluster of differentiation 8 positive, CGRP = Calcitonin-gene-related peptide, CX3CL1 C-X3 = C motif -chemokine ligand 1 /Fractalkine, CXCL8 = Chemokine (C-X-C motif) ligand 8, CXCL9 = Chemokine (C-X-C motif) ligand 9, CXCL10 = Chemokine (C-X-C motif) ligand 10, CXCL11 = Chemokine (C-X-C motif) ligand 11, CXCL12 = Chemokine (C-X-C motif) ligand 12, CXCR4 = Chemokine (C-X-C motif) receptor 4, EGF = Epidermal growth factor, HLA-DR = Human leukocyte antigen-D-related, ICAM-1 = Intercellular adhesion molecule 1, IFN-γ = Interferon-gamma, IgG = Immunoglobulin G, IgE = Immunoglobulin E, IL-1 = Interleukin-1, IL-1α = Interleukin-1 alpha, IL-1β = Interleukin-1 beta, CGRP = Calcitonin-Gene-Related Peptide, IL-3 = Interleukin-3, IL-4 = Interleukin-4, IL-6 = Interleukin-6, IL-8 = Interleukin-8, IL-10 = Interleukin-10, IL-17 = Interleukin-17, IL-17A = Interleukin-17A, LPRR3 = Lacrimal proline-rich protein 3, LPRR4 = Lacrimal proline-rich protein 4, MUC5AC = Mucin 5 subtype AC, oligomeric mucus/gel-forming, MUC16 = Mucin 16, OCT = Optical coherence tomography, OGVHD = Ocular graft versus host disease, PAX6 = Paired-box protein 6, VKC = Vernal keratoconjunctivitis, TGF-β = Transforming growth factor β, S100 = proteins Calcium activated signaling proteins, Th1 = T helper 1 cell, Th17 = T helper 17 cell, MGD = Meibomian gland dysfunction, TFOS = Tear film and ocular surface society, SS-KCS = Keratoconjunctivitis Sicca, MMP-9 = Matrix metalloproteinase 9, MMP-1 = Matrix metalloproteinase 1, ZAG = Zinc alpha glycoprotein, CBA = Cytometric bead array, MALDI TOF-MS = matrix assisted laser desorption ionization-time of flight, SELDI TOF-MS = surface-enhanced laser desorption ionization-time of flight, IVCM = in vivo confocal microscopy, AS-OCT = anterior segment optical coherence tomography, iTRAQ = Isobaric tags for relative and absolute quantitation, LC-MS = Liquid chromatography-mass spectrometry, LCN-1 = lipocalin 1, PIP = prolactin induced protein, NGF = Nerve growth factor, PRR4 = proline rich protein 4, VIP = Vasoactive intestinal peptide, ELISA = enzyme linked immunoassay, TNF-α = tumor necrosis factor alpha, PAC = perennial allergic conjunctivitis, SAC = seasonal allergic conjunctivitis, IC = impression cytology, RT-PCR = reverse transcription polymerase chain reaction, PCR = polymerase chain reaction, APCs = antigen-presenting cells, NK cells = natural killer cells, HEL = hexanoyl-lysine, 4-HNE = 4-hydroxy-2-nonenal, MDA = malondialdehyde.

Effect of Lutein on Ocular Goblet Cell, IFN-γ, and IL-17 Concentration in Dry Eye-Induced Mice Model

Introduction Dry eye disease affects a substantial number of individuals globally and significantly impacts their quality of life and productivity. Understanding the underlying mechanisms and managing dry eye disease poses substantial challenges. Recent research has highlighted the involvement of various inflammatory mediators in the pathogenesis of dry eye disease, including the cytokines interferon (IFN)-γ and interleukin (IL)-17. Activation of stress signaling pathways and residential immune cells on the ocular epithelial surface ignites epithelial changes, destabilizes tear film, amplifies inflammation and creates an endless loop. Lutein is a β-carotenoid antioxidant which has been proven to be beneficial in many ocular diseases due to its protective and anti-inflammatory effect induced by various stimulators. Lutein also acts as a direct and indirect antioxidant agent, suppressing oxidative stress and mitigating oxidative damage. The purpose of this research is to investigate the potential therapeutic effects of lutein in a mouse model of dry eye, aiming to elucidate its impact on ocular manifestation, goblet cells count, IFN-γ and IL-17 level. Methods Desiccating stress was induced in C57BL/6 mice. In a separate group, lutein was administered subcutaneously on a daily basis throughout the experimental period. Clinical manifestations of dry eye, including ocular surface changes, were documented photographically. Goblet cell concentration was assessed through Periodic Acid-Schiff (PAS) staining, and the levels of IFN-γ and IL-17 were measured using enzyme-linked immunosorbent assay (ELISA). Data obtained from these assessments were compared between the experimental groups to determine the potential effects of lutein on dry eye pathology and cytokine levels. Results Significant differences were observed in clinical observations and goblet cell concentrations among the groups; however, no statistically significant differences were found in the levels of IFN-γ and IL-17 between the groups. The untreated group exhibited significantly higher opacities and irregularities compared to the lutein-treated group, whereas the mean goblet cell count was highest in the lutein-treated group. Conclusion Lutein administration improves clinical observations and goblet cell concentrations in a mouse model of dry eye. The treated group exhibited improved ocular surface integrity, but no significant differences in the tested cytokine levels were observed. These findings suggest that lutein supplementation could be a promising therapeutic option for managing dry eye disease. Further research is needed to understand the underlying mechanisms and long-term effects of lutein in dry eye management.

NLRP3 Inflammasome as a Potential Therapeutic Target in Dry Eye Disease

Dry eye disease (DED) is a multifactorial ocular surface disorder arising from numerous interrelated underlying pathologies that trigger a self-perpetuating cycle of instability, hyperosmolarity, and ocular surface damage. Associated ocular discomfort and visual disturbance contribute negatively to quality of life. Ocular surface inflammation has been increasingly recognised as playing a key role in the pathophysiology of chronic DED. Current readily available anti-inflammatory agents successfully relieve symptoms, but often without addressing the underlying pathophysiological mechanism. The NOD-like receptor protein-3 (NLRP3) inflammasome pathway has recently been implicated as a key driver of ocular surface inflammation, as reported in pre-clinical and clinical studies of DED. This review discusses the intimate relationship between DED and inflammation, highlights the involvement of the inflammasome in the development of DED, describes existing anti-inflammatory therapies and their limitations, and evaluates the potential of the inflammasome in the context of the existing anti-inflammatory therapeutic landscape as a therapeutic target for effective treatment of the disease.

Therapeutic Potential of Peucedanum japonicum Thunb. and Its Active Components in a Delayed Corneal Wound Healing Model Following Blue Light Irradiation-Induced Oxidative Stress

Blue light is reported to be harmful to eyes by inducing reactive oxygen species (ROS). Herein, the roles of Peucedanum japonicum Thunb. leaf extract (PJE) in corneal wound healing under blue light irradiation are investigated. Blue-light-irradiated human corneal epithelial cells (HCECs) show increased intracellular ROS levels and delayed wound healing without a change in survival, and these effects are reversed by PJE treatment. In acute toxicity tests, a single oral administration of PJE (5000 mg/kg) does not induce any signs of clinical toxicity or body weight changes for 15 days post-administration. Rats with OD (oculus dexter, right eye) corneal wounds are divided into seven treatment groups: NL (nonwounded OS (oculus sinister, left eye)), NR (wounded OD), BL (wounded OD + blue light (BL)), and PJE (BL + 25, 50, 100, 200 mg/kg). Blue-light-induced delayed wound healing is dose-dependently recovered by orally administering PJE once daily starting 5 days before wound generation. The reduced tear volume in both eyes in the BL group is also restored by PJE. Forty-eight hours after wound generation, the numbers of inflammatory and apoptotic cells and the expression levels of interleukin-6 (IL-6) largely increase in the BL group, but these values return to almost normal after PJE treatment. The key components of PJE, identified by high-performance liquid chromatography (HPLC) fractionation, are CA, neochlorogenic acid (NCA), and cryptochlorogenic acid (CCA). Each CA isomer effectively reverses the delayed wound healing and excessive ROS production, and their mixture synergistically enhances these effects. The expression of messenger RNAs (mRNAs) related to ROS, such as SOD1, CAT, GPX1, GSTM1, GSTP1, HO-1, and TRXR1, is significantly upregulated by PJE, its components, and the component mixture. Therefore, PJE protects against blue-light-induced delayed corneal wound healing via its antioxidative, anti-inflammatory, and antiapoptotic effects mechanistically related to ROS production.

An ocular Th1 immune response promotes corneal nerve damage independently of the development of corneal epitheliopathy

Proper sight is not possible without a smooth, transparent cornea, which is highly exposed to environmental threats. The abundant corneal nerves are interspersed with epithelial cells in the anterior corneal surface and are instrumental to corneal integrity and immunoregulation. Conversely, corneal neuropathy is commonly observed in some immune-mediated corneal disorders but not in others, and its pathogenesis is poorly understood. Here we hypothesized that the type of adaptive immune response may influence the development of corneal neuropathy. To test this, we first immunized OT-II mice with different adjuvants that favor T helper (Th)1 or Th2 responses. Both Th1-skewed mice (measured by interferon-γ production) and Th2-skewed (measured by interleukin-4 production) developed comparable ocular surface inflammation and conjunctival CD4+ T cell recruitment but no appreciable corneal epithelial changes upon repeated local antigenic challenge. Th1-skewed mice showed decreased corneal mechanical sensitivity and altered corneal nerve morphology (signs of corneal neuropathy) upon antigenic challenge. However, Th2-skewed mice also developed milder corneal neuropathy immediately after immunization and independently of ocular challenge, suggestive of adjuvant-induced neurotoxicity. All these findings were confirmed in wild-type mice. To circumvent unwanted neurotoxicity, CD4+ T cells from immunized mice were adoptively transferred to T cell-deficient mice. In this setup, only Th1-transferred mice developed corneal neuropathy upon antigenic challenge. To further delineate the contribution of each profile, CD4+ T cells were polarized in vitro to either Th1, Th2, or Th17 cells and transferred to T cell-deficient mice. Upon local antigenic challenge, all groups had commensurate conjunctival CD4+ T cell recruitment and macroscopic ocular inflammation. However, none of the groups developed corneal epithelial changes and only Th1-transferred mice showed signs of corneal neuropathy. Altogether, the data show that corneal nerves, as opposed to corneal epithelial cells, are sensitive to immune-driven damage mediated by Th1 CD4+ T cells in the absence of other pathogenic factors. These findings have potential therapeutic implications for ocular surface disorders.

Heterochronic Parabiosis Causes Dacryoadenitis in Young Lacrimal Glands

Aging is associated with inflammation and oxidative stress in the lacrimal gland (LG). We investigated if heterochronic parabiosis of mice could modulate age-related LG alterations. In both males and females, there were significant increases in total immune infiltration in isochronic aged LGs compared to that in isochronic young LGs. Male heterochronic young LGs were significantly more infiltrated compared to male isochronic young LGs. While both females and males had significant increases in inflammatory and B-cell-related transcripts in isochronic and heterochronic aged LGs compared to levels isochronic and heterochronic young LGs, females had a greater fold expression of some of these transcripts than males. Through flow cytometry, specific subsets of B cells were increased in the male heterochronic aged LGs compared to those in male isochronic aged LGs. Our results indicate that serum soluble factors from young mice were not enough to reverse inflammation and infiltrating immune cells in aged tissues and that there were specific sex-related differences in parabiosis treatment. This suggests that age-related changes in the LG microenvironment/architecture participate in perpetuating inflammation, which is not reversible by exposure to youthful systemic factors. In contrast, male young heterochronic LGs were significantly worse than their isochronic counterparts, suggesting that aged soluble factors can enhance inflammation in the young host. Therapies that aim at improving cellular health may have a stronger impact on improving inflammation and cellular inflammation in LGs than parabiosis.

Influence of Light-EmittingDiode-Derived Blue Light Overexposure on Rat Ocular Surface

We aim to investigate the effect of overexposure to blue light on the rat ocular surface and explore the potential mechanisms. 450 nm light-emitting diode (LED) derived light at 1000 lux was used to irradiate SD rats, 12 hours a day, for consecutive 28 days. Rats in the control group were exposed to 400 lux white light at the same time (in an indoor environment). Tear film breakup time (TBUT), tear volume, and corneal fluorescein staining scores were used to measure the changes to the ocular surface. Expressions of nuclear factor-κB (NF-κB), inhibitor-κB (I-κB), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured by real-time PCR, and the activation of the NF-κB pathway was detected by Western blotting, respectively. Cornea ultrastructure was examined by TEM and optical microscope on day 28. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB signaling pathway, was used to measure the inhibition of blue light injury. The above indexes were detected again when compared with the solvent-treated group. On day 28, compared with day 0, the TBUT of the blue light group was significantly shorter, and the score was significantly higher. The amount of tear secretion changed slightly with time. HE and PAS staining revealed significantly decreased corneal epithelial cell layers and increased goblet cells after 28-day irradiation of blue light. Disarranged stromal cells, vacuoles in the basal nuclei, and decreased desmosomes were also found in the blue light group. Significantly increased levels of NF-κB, IL-6, TNF-α, and the ratio of phosphorylated NF-κB p65 (pNF-κB p65) to total NF-κB p65 implied blue light-induced damage and pathway activation. In addition, PDTC significantly reduced the phosphorylation of NF-κB activated in blue light-treated corneas and alleviated the ocular surface changes caused by blue light. Finally, our results demonstrated that long-term blue light exposure in rats could cause ocular surface changes and manifest as dry eye. Inflammation and activation of the NF-κB pathway may play a role in the pathogenesis.

Modulation of ocular surface desiccation in a murine model by histatin-5 application

PURPOSE

To determine the efficacy of Histatin-5 (Hst5) peptide treatment in ameliorating dry eye disease (DED) phenotype in an in-vivo mouse model of scopolamine and desiccating stress (SDS) dry eye.

METHODS

SDS was induced in female C57BL/6 mice by subcutaneous injections of scopolamine hydrobromide and exposure to low relative humidity and forced air draft for five days. Mouse eyes were topically treated with synthetic Hst5 peptide or balanced salt solution (BSS) twice a day for four days. Control mice were not exposed to SDS induction and did not receive any treatments. Oregon green dextran (OGD) staining was used to evaluate corneal permeability. Histologically, staining with periodic acid schiff (PAS), immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), were used to quantify the number of goblet cells (GC), CD45+ immune cells and apoptotic cells respectively in formalin fixed paraffin embedded (FFPE) mouse whole eye sections.

RESULTS

Compared to treatment with BSS, Hst5 treatment significantly lowered corneal epithelial permeability, prevented conjunctival epithelial GC loss, decreased conjunctival CD45+ immune cell infiltration and reduced conjunctival epithelial cell apoptosis.

CONCLUSIONS

Hst5 peptide topical treatment significantly improves the clinical parameters observed in SDS experimental model of DED. This is the first report of the efficacy of Hst5 treatment of dry eye phenotype, and potential novel treatment for DED in the clinic. Hst5 represents a new class of efficacious therapeutic agents, demonstrating pro-epithelial and anti-inflammatory activities at the ocular surface.

Bacteria and Dry Eye: A Narrative Review

(1) Background: Dry eye is a multifactorial disease of the ocular surface, the incidence of which has been increasing sharply. The pathogenesis of dry eye, especially in terms of the bacterial flora, has drawn great attention. Additionally, the potential treatment methods need to be explored. (2) Methods: We reviewed more than 100 studies and summarized them briefly in a review. (3) Results: We summarized the bacterial communities found on the ocular surface in the general population and patients with dry eye and found a relationship between dry eye and antibiotic therapy. We identified the possible mechanisms of bacteria in the development of dry eye by discussing factors such as the destruction of the antibacterial barrier, infectious diseases, microbiome homeostasis, inflammatory factors on the ocular surface and vitamin deficiency. (4) Conclusion: We systematically reviewed the recent studies to summarize the bacterial differences between patients with dry eye and the general population and brought up several possible mechanisms and possible treatment targets.

Is dry eye disease the same in young and old patients? A narrative review of the literature

Advanced age is one of the most evident risk factors for dry eye disease (DED), with male/female sex, chronic drug consumption, and prolonged device use. This article aims to review the literature about the changes of the ocular surface associated with DED in the elderly and patients < 40 years. The pathophysiologic changes of the ocular surface responsible for eye dryness are linked with inflammation and neurosensory abnormalities and may occur with a different feature in young patients compared with elders. Peculiar treatment strategies may be needed for young and older subjects with DED.

Bacterial distribution on the ocular surface of patients with primary Sjögren's syndrome

Many studies have shown that gut microbial dysbiosis is a major factor in the etiology of autoimmune diseases but none have suggested that the ocular surface (OS) microbiome is associated with Sjögren’s syndrome (SS). In this prospective study, we analyzed bacterial distribution on the OS in patients with primary SS. Among the 120 subjects included in this study, 48 patients (group A) had primary SS, whereas 72 subjects (group B) had dry eye symptoms that were unrelated to SS. We evaluated clinical dry eye parameters such as the OS disease index, ocular staining score (OSS), Schirmer’s I test, and tear break-up time (TBUT). Conjunctival swabs were used to analyze the microbial communities from the two groups. Bacterial 16S rRNA genes were sequenced using the Illumina MiSeq platform, and the data were analyzed using the QIIME 1.9.1 program. The Shannon index was significantly lower in group A than in group B microbiota (p < 0.05). An analysis of similarity using the Bray–Curtis distance method found no difference in beta-diversity between the two groups (p > 0.05). In group A, Actinobacteria at the phylum level and Corynebacteria at the genus level exhibited low abundance than group B, but the differences were not statistically significant (p > 0.05). SS apparently decreases the diversity of the OS microbial community. These observations may be related to the pathophysiology of SS and should be investigated in future studies.

Autoimmune Epithelitis and Chronic Inflammation in Sjögren's Syndrome-Related Dry Eye Disease

Autoimmune epithelitis and chronic inflammation are one of the characteristic features of the immune pathogenesis of Sjögren’s syndrome (SS)-related dry eye disease. Autoimmune epithelitis can cause the dysfunction of the excretion of tear fluid and mucin from the lacrimal glands and conjunctival epithelia and meibum from the meibomian glands. The lacrimal gland and conjunctival epithelia express major histocompatibility complex class II or human leukocyte antigen-DR and costimulatory molecules, acting as nonprofessional antigen-presenting cells for T cell and B cell activation in SS. Ocular surface epithelium dysfunction can lead to dry eye disease in SS. Considering the mechanisms underlying SS-related dry eye disease, this review highlights autoimmune epithelitis of the ocular surface, chronic inflammation, and several other molecules in the tear film, cornea, conjunctiva, lacrimal glands, and meibomian glands that represent potential targets in the treatment of SS-related dry eye disease.

Comparison of Two Experimental Mouse Dry Eye Models through Inflammatory Gene Set Enrichment Analysis Based on a Multiplexed Transcriptomic Approach

The goal of this study was to explore the specific signaling pathways related to inflammation in two experimental mouse dry eye (EDE) models. Female C57BL/6 mice housed for 10 days in a controlled desiccative environment were either treated with scopolamine (EDE-1; n = 18) or subjected to extraorbital lacrimal gland excision bilaterally (EDE-2; n = 10). Non-induced mice (n = 20) served as healthy controls. A corneal fluorescein staining (CFS) scoring was used at baseline through to day (D) 10 to evaluate epitheliopathy. At D10, corneas and conjunctivas were collected for multiplexed transcriptomic analysis with the NanoString^® mouse inflammatory CodeSet. Both EDE-1 and EDE-2 mice presented a change in corneal integrity, with a significant increase in CFS scores at D10. More gene transcripts were identified in EDE-2 compared with EDE-1 (116 vs. 96, respectively), and only a few were common to both models, 13 for the cornea and 6 for the conjunctiva. The gene functional annotation analysis revealed that the same inflammatory pathways were involved in both models. Comparative profiling of gene expression in the two EDE models leads to the identification of various targets and signaling pathways, which can be extrapolated to and confirmed in human disease.

Autoimmunity in dry eye disease - An updated review of evidence on effector and memory Th17 cells in disease pathogenicity

The classic Th1/Th2 dogma has been significantly reshaped since the subsequent introduction of several new T helper cell subsets, among which the most intensively investigated during the last decade is the Th17 lineage that demonstrates critical pathogenic roles in autoimmunity and chronic inflammation - including the highly prevalent dry eye disease. In this review, we summarize current concepts of Th17-mediated disruption of ocular surface immune homeostasis that leads to autoimmune inflammatory dry eye disease, by discussing the induction, activation, differentiation, migration, and function of effector Th17 cells in disease development, highlighting the phenotypic and functional plasticity of Th17 lineage throughout the disease initiation, perpetuation and sustention. Furthermore, we emphasize the most recent advance in Th17 memory formation and function in the chronic course of dry eye disease, a major area to be better understood for facilitating the development of effective treatments in a broader field of autoimmune diseases that usually present a chronic course with recurrent episodes of flare in the target tissues or organs.

Recent Developments About the Pathogenesis of Dry Eye Disease: Based on Immune Inflammatory Mechanisms

Dry eye disease is a common and frequently occurring ophthalmology with complex and diverse causes, and its incidence is on the upward trend. The pathogenesis of DED is still completely clear. However, the immune response based on inflammation has been recognized as the core basis of this disease. In this review, we will systematically review the previous research on the treatment of DED in immune inflammation, analyze the latest views and research hotspots, and provide reference for the prevention and treatment of DED.

Differentially Expressed Gene Pathways in the Conjunctiva of Sjögren Syndrome Keratoconjunctivitis Sicca

Sjögren syndrome (SS) is an autoimmune condition that targets the salivary and lacrimal glands, with cardinal clinical signs of dry eye (keratoconjunctivitis sicca, KCS) and dry mouth. The conjunctiva of SS patients is often infiltrated by immune cells that participate in the induction and maintenance of local inflammation. The purpose of this study was to investigate immune-related molecular pathways activated in the conjunctiva of SS patients. Female SS patients (n=7) and controls (n=19) completed a series of oral, ocular surface exams. Symptom severity scores were evaluated using validated questionnaires (OSDI and SANDE). All patients fulfilled the ACR/EULAR criteria for SS and the criteria for KCS. Fluorescein and lissamine green dye staining evaluated tear-break-up time (TBUT), corneal and conjunctival disease, respectively. Impression cytology of the temporal bulbar conjunctiva was performed to collect cells lysed and subjected to gene expression analysis using the NanoString Immunology Panel. 53/594 differentially expressed genes (DEGs) were observed between SS and healthy controls; 49 DEGs were upregulated, and 4 were downregulated (TRAF5, TGFBI, KLRAP1, and CMKLRI). The top 10 DEGs in descending order were BST2, IFITM1, LAMP3, CXCL1, IL19, CFB, LY96, MX1, IL4R, CDKN1A. Twenty pathways had a global significance score greater or equal to 2. Spearman correlations showed that 29/49 upregulated DEGs correlated with either TBUT (inverse) or OSDI or conjunctival staining score (positive correlations). Venn diagrams identified that 26/29 DEGs correlated with TBUT, 5/26 DEGs correlated with OSDI, and 16/26 correlated with conjunctival staining scores. Five upregulated DEGs (CFB, CFI, IL1R1, IL2RG, IL4R) were uniquely negatively correlated with TBUT. These data indicate that the conjunctiva of SS patients exhibits a phenotype of immune activation, although some genes could be inhibitory. Some of the DEGs and pathways overlap with previous DEGs in salivary gland biopsies, but new DEGs were identified, and some of these correlated with symptoms and signs of dry eye. Our results indicate that gene analysis of conjunctiva imprints is a powerful tool to understand the pathogenesis of SS and develop new therapeutic targets.

Impact of P2X7 Purinoceptors on Goblet Cell Function: Implications for Dry Eye

By providing ~70% of the eye’s refractive power, the preocular tear film is essential for optimal vision. However, its integrity is often jeopardized by environmental and pathologic conditions that accelerate evaporation and cause sight-impairing dry eye. A key adaptive response to evaporation-induced tear film hyperosmolarity is the reflex-triggered release of tear-stabilizing mucin from conjunctival goblet cells. Here, we review progress in elucidating the roles of ion channels in mediating this important exocytotic response. Much is now known about the modulatory impact of ATP-sensitive potassium channels, nonspecific cation channels and voltage-gated calcium channels. Recently, we discovered that during unremitting extracellular hyperosmolarity, P2X₇ receptor/channels also become activated and markedly impair goblet cell viability. However, our understanding of possible adaptive benefits of this P2X₇ activation remains limited. In the present study, we utilized high-temporal resolution membrane capacitance measurements to monitor the exocytotic activity of single goblet cells located in freshly excised rat conjunctiva. We now report that activation of P2X₇ purinoceptors boosts neural-evoked exocytosis and accelerates replenishment of mucin-filled granules after exocytotic depletion. Thus, P2X₇ activation exerts a yin-yang effect on conjunctival goblet cells: the high-gain benefit of enhancing the supply of tear-stabilizing mucin is implemented at the high-risk of endangering goblet cell survival.

Role of CD4+ T Helper Cells in the Development of BAC-Induced Dry Eye Syndrome in Mice

Purpose

To evaluate the role of CD4⁺ T helper cells in benzalkonium chloride (BAC)-induced ocular surface disorder in C57BL/6 mice.

Methods

Topical 0.075% BAC was applied twice daily in C57BL/6 mice for 7 consecutive days; PBS-treated and untreated mice served as controls. Adoptive transfer of CD4⁺ T cells isolated from the BAC-treated mice or PBS-treated mice into nude mice was conducted to identify the roles of CD4⁺ T cells, with untreated nude mice as controls. Oregon green dextran staining, PAS staining, and the phenol red cotton test were carried out in these two models. The gene and protein levels of T-bet, IFN-γ, RORγt, and IL-17 were detected by quantitative RT-PCR and ELISA, respectively. The activation and subsets of CD4⁺ T cells were identified by double immunofluorescent staining and flow cytometry.

Results

An increase in CD4⁺CD69⁺, CD4⁺IFN-γ⁺, and CD4⁺IL-17⁺ cells was induced by BAC in C57BL/6 mice. IFN-γ, IL-17, Th1, Th17, and the transcription factors T-bet and RORγt were increased in BAC-treated mice compared with control mice. In addition, ocular surface damage, including corneal barrier dysfunction, goblet cell loss, and decreased tear production, was induced by BAC. Interestingly, adoptive transfer of CD4⁺ T cells isolated from BAC-treated mice into nude mice resulted in ocular surface manifestations similar to those of direct topical BAC treatment of C57BL/6 mice, including increased CD4⁺ T cells, IFN-γ, IL-17, and ocular surface disorders.

Conclusions

Topical application of BAC induced a dry-eye-like ocular surface disorder partly through the CD4⁺ T cell-mediated inflammatory response.

Aged Mice Devoid of the M3 Muscarinic Acetylcholine Receptor Develop Mild Dry Eye Disease

The parasympathetic nervous system is critically involved in the regulation of tear secretion by activating muscarinic acetylcholine receptors. Hence, various animal models targeting parasympathetic signaling have been developed to induce dry eye disease (DED). However, the muscarinic receptor subtype (M₁–M₅) mediating tear secretion remains to be determined. This study was conducted to test the hypothesis that the M₃ receptor subtype regulates tear secretion and to evaluate the ocular surface phenotype of mice with targeted disruption of the M₃ receptor (M3R^−/−). The experimental techniques included quantification of tear production, fluorescein staining of the ocular surface, environmental scanning electron microscopy, assessment of proliferating cells in the corneal epithelium and of goblet cells in the conjunctiva, quantification of mRNA for inflammatory cytokines and prooxidant redox enzymes and quantification of reactive oxygen species. Tear volume was reduced in M3R^−/− mice compared to age-matched controls at the age of 3 months and 15 months, respectively. This was associated with mild corneal epitheliopathy in the 15-month-old but not in the 3-month-old M3R^−/− mice. M3R^−/− mice at the age of 15 months also displayed changes in corneal epithelial cell texture, reduced conjunctival goblet cell density, oxidative stress and elevated mRNA expression levels for inflammatory cytokines and prooxidant redox enzymes. The findings suggest that the M₃ receptor plays a pivotal role in tear production and its absence leads to ocular surface changes typical for DED at advanced age.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

Ophthalmologic Manifestations of Primary Sjögren's Syndrome

Sjögren’s syndrome (SS) is a chronic, progressive, inflammatory, autoimmune disease, characterized by the lymphocyte infiltration of exocrine glands, especially the lacrimal and salivary, with their consequent destruction. The onset of primary SS (pSS) may remain misunderstood for several years. It usually presents with different types of severity, e.g., dry eye and dry mouth symptoms, due to early involvement of the lacrimal and salivary glands, which may be associated with parotid enlargement and dry eye; keratoconjunctivitis sicca (KCS) is its most common ocular manifestation. It is still doubtful if the extent ocular surface manifestations are secondary to lacrimal or meibomian gland involvement or to the targeting of corneal and conjunctival autoantigens. SS is the most representative cause of aqueous deficient dry eye, and the primary role of the inflammatory process was evidenced. Recent scientific progress in understanding the numerous factors involved in the pathogenesis of pSS was registered, but the exact mechanisms involved still need to be clarified. The unquestionable role of both the innate and adaptive immune system, participating actively in the induction and evolution of the disease, was recognized. The ocular surface inflammation is a central mechanism in pSS leading to the decrease of lacrimal secretion and keratoconjunctival alterations. However, there are controversies about whether the ocular surface involvement is a direct autoimmune target or secondary to the inflammatory process in the lacrimal gland. In this review, we aimed to present actual knowledge relative to the pathogenesis of the pSS, considering the role of innate immunity, adaptive immunity, and genetics.

Allergy and Dry Eye Disease

Ocular allergy (OA) and dry eye disease (DED) are the most common ocular surface disorders with a potential severe impact on the patient's quality of life. OA and DED may coexist and have a significant clinical overlap. Therefore, clinical features commonly believed to be distinctive of OA or DED may be sometimes insufficient for a differential diagnosis. Alterations of the tear film, epithelial barrier, and corneal innervation are described in OA and can pave the way to DED. Conversely, DED may facilitate or worsen allergic reactions in predisposed (atopic) patients. For these reasons, OA and DED should be considered as reciprocal predisposing conditions that share ocular surface inflammation as a common background.

Evidence of Polyphenols Efficacy against Dry Eye Disease

Dry eye disease is a multifactorial pathology compromising the quality of life of patients, resulting in significant damage of the ocular surface and discomfort. The current therapeutical strategies are not able to definitively resolve the underlying causes and stop the symptoms. Polyphenols are promising natural molecules that are receiving increasing attention for their activity/effects in counteracting the main pathologic mechanisms of dry eye disease and reducing its symptoms. In the present review, a deep literature search focusing on the main polyphenols tested against dry eye disease was conducted, analyzing related in vitro, in vivo, and clinical studies to provide a comprehensive and current review on the state of the art. Polyphenols present multiple effects against dry eye diseases-related ocular surface injury. In particular, the observed beneficial effects of polyphenols on corneal cells are the reduction of the pathological processes of inflammation, oxidative stress, and apoptosis and modulation of the tear film. Due to numerous studies reporting that polyphenols are effective and safe for treating the pathological mechanisms of this ocular surface disease, we believe that future studies should confirm and extend the evidence of polyphenols efficacy in clinical practice against dry eye disease and help to develop new ophthalmic drug(s).

Defining Dry Eye from a Clinical Perspective

Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.

A Review of the Mechanism of Action of Cyclosporine A: The Role of Cyclosporine A in Dry Eye Disease and Recent Formulation Developments

Dry eye disease (DED) is a multifactorial disease of the ocular surface and tear film that has gained awareness as a public health problem. Characteristics of DED include tear film instability, hyperosmolarity, and ocular surface inflammation, which can occur independently or may be a sequela of numerous ocular diseases, ocular surgery or contact lens wear. Much has been learned about the impact of the disease to help affected individuals who report symptoms of poor vision, pain, and tearing. Recently, new research highlights the importance of the role of ocular surface inflammation and damage in DED-leading to a vicious cycle of inflammation as well as loss of tear film homeostasis. DED immunopathophysiology is characterized by four stages: initiation, amplification, recruitment, and re-initiation. Cyclosporine is proven to be a valuable ophthalmic therapeutic for DED through its immunomodulatory actions and regulation of the adaptive immune response. Cyclosporine mechanism of action is well described in the published literature and the myriad of benefits in all four stages lend a broad-based immunomodulatory function particularly suitable for addressing DED. Furthermore, cyclosporine has unique goblet cell density improvement capabilities as well as anti-apoptotic properties. Topical formulations of cyclosporine are centered around addressing the highly lipophilic nature of the molecule. The poor aqueous solubility of cyclosporine traditionally presented technical challenges in drug delivery to the ocular surface. Newer formulations such as cationic emulsions and nanomicellar aqueous solutions address formulation, tissue concentration, and drug delivery challenges.

Esculetin protects human corneal epithelial cells from oxidative stress through Nrf-2 signaling pathway

Dry eye formation often originates from oxidative damage to the ocular surface, which can be caused by external environment or internal pathologic factors. Esculetin (6, 7-dihydroxycoumarin) is a natural product found in many plants, and has been reported to have multiple pharmacological activities. The objective of our present study is to investigate if esculetin could protect the corneal epithelial cells from oxidative damages and its underlying antioxidant molecular mechanisms. Our experimental results demonstrated that pretreatment with esculetin markedly increased the cell viability while decreased the apoptosis in H₂O₂-treated human corneal epithelial (HCE) cells, by regulating Bcl-2, Bax and caspase-3 protein expressions and by altering the imbalance of activities of intracellular reactive oxygen species (ROS) and superoxide dismutase (SOD). Our data revealed that esculetin played an antioxidant role not only through its antioxidant activity, but also by highly inducing Nrf-2 translocation to the nucleus, which in turn, enhanced Nrf2 signaling regulated antioxidant genes (HO-1, NQO1, GCLM, SOD1 and SOD2) mRNA expression levels in H₂O₂-treated HCE cells. In the present study, the protective effects of esculetin on the corneal epithelium were also confirmed by a murine desiccating stress induced dry eye model in vivo. These data illustrated, for the first time, that esculetin may have the ability to protect human corneal epithelial cells from oxidative damages through its scavenging of free radical properties and through the activation of Nrf2 signaling.

Modulation of Oxidative Stress and Inflammation in the Aged Lacrimal Gland

Inflammation and oxidative stress accompany aging. This study investigated the interplay between oxidative stress and inflammation in the lacrimal gland. C57BL/6 mice were used at 2 to 3, 12, and 24 months of age. Nuclear factor erythroid derived-2-related factor 2 (Nrf2)^-/- and corresponding wild-type mice were used at 2 to 3 and 12 to 13 months of age. A separate group of 15.5 to 17 months of age C57BL/6 mice received a diet containing an Nrf2 inducer (Oltipraz) for 8 weeks. Aged C57BL/6 lacrimal glands showed significantly greater lymphocytic infiltration, higher levels of MHC II, IFN-γ, IL-1β, TNF-α, and cathepsin S (Ctss) mRNA transcripts, and greater nitrotyrosine and 4-hydroxynonenal protein. Young Nrf2^-/- mice showed an increase in IL-1β, IFN-γ, MHC II, and Ctss mRNA transcripts compared with young wild-type mice and greater age-related changes at 12 to 13 months of age. Oltipraz diet significantly decreased nitrotyrosine and 4-hydroxynonenal and decreased the expression of IL-1β and TNF-α mRNA transcripts, while decreasing the frequency of CD45⁺CD4⁺ cells in lacrimal glands and significantly increasing conjunctival goblet cell density compared with a standard diet. The findings provide novel insight into the development of chronic, low-grade inflammation and oxidative stress in age-related dry eye. New therapies targeting oxidative stress pathways will be valuable in treating age-related dry eye.

Calcineurin Inhibitor Voclosporin Preserves Corneal Barrier and Conjunctival Goblet Cells in Experimental Dry Eye

Objective: The purpose of this study was to evaluate the potential of voclosporin (VOS) in preventing goblet cell (GC) loss and modulating interferon-gamma (IFN-γ) producing CD4⁺ T cells in the mouse desiccating stress (DS) dry eye model. Methods: Mice were subjected to DS and treated topically with vehicle, VOS, or cyclosporine A as a treatment control. Corneal barrier function was evaluated after 5 and conjunctival GC density after 10 days of desiccation. CD4⁺ T cells were isolated from ocular surface draining lymph nodes of dry eye donor mice and adoptively transferred into immune deficient RAG1^-/- mice from which tears and conjunctiva were collected for the evaluation of inflammatory cytokines/chemokines and GC density. Results: Compared to the vehicle-treated group, VOS was significantly better in preserving corneal barrier function and preventing DS-induced conjunctival GC loss. CD4⁺ T cells from VOS treated dry eye donors caused less conjunctival GC loss than vehicle and suppressed expression of IFN-γ signature genes to a similar extent and transforming growth factor-beta to a greater extent than cyclosporine in adoptive transfer recipients. Conclusion: These findings suggest that VOS preserves corneal barrier function and conjunctival GCs and suppresses IFN-γ producing CD4⁺ T cells in experimental dry eye.

Long-Term Exposure to Urban Particulate Matter on the Ocular Surface and the Incidence of Deleterious Changes in the Cornea, Conjunctiva and Retina in Rats

We investigated the time-dependent deleterious ocular changes induced by urban particulate matter (UPM) in vitro and in vivo. UPM treatment decreased human corneal epithelial cell migration and survival. Fluorescein scores were consistently increased by UPM application for 16 weeks. One week of rest at 2 or 4 weeks led to a recovery trend, whereas two weeks of rest at 8 weeks induced no change. UPM treatment decreased the tear film break-up time at 2 weeks, which was thereafter maintained until 16 weeks. No changes were found after periods of rest. UPM-treated eyes exhibited greater corneal epithelium thickness than normal eyes at 2 weeks, which recovered to normal at 4 and 8 weeks and was significantly decreased at 16 weeks. Apoptotic cell number in the epithelium was increased at 2 weeks, which remained constant except at 8 weeks. IL-6 expression in the cornea of the right eye continually increased for 16 weeks, and significant recovery was only observed at 8 weeks after 2 weeks of rest. Ocular pressure was significantly increased in the right eye at 12 and 16 weeks. Topical UPM application to the eye induced deleterious changes to various closely related parts of the eye.

Dry eye induced by exposure to cigarette smoke pollution: An in vivo and in vitro study

Exposure to cigarette smoke (CS) pollution has previously associated with dry eye symptoms but without detailed experimental data and elucidation of the mechanism. We aimed to evaluate the effects of CS on the ocular surfaces of mice and the extraction of DMSO lipid-soluble cigarette smoke particles (DCSP) on cultured human corneal epithelial cells (HCECs), and explore to elucidate the probable mechanism. C57BL mice were exposed to CS challenging. In vivo clinical evaluations, including corneal fluorescein staining, tear film break-up time, and confocal microscopic observations, were performed before exposure and post-exposure. At the end of the in vivo study, changes in corneal and conjunctival histology, corneal ultrastructure, and conjunctival goblet cell intensity were examined, expression of TUNLE and Ki67 in tissue were also detected. In vitro, cell confluence and caspase3/7 were assessed in DCSP treated HCECs. Production of TNF-α, IL-1β and IL-6, activation of NF-κB and Ki67 were evaluated by means of ELISA and Western blot respectively in HCECs cultured with 0.6 μL/mL DCSP. We found that longer-term CS exposure induced dry eye symptoms in mice. Additionally, corneal and conjunctival epithelial damage occurred, the corneal ultrastructure changed, and the density of goblet cells decreased. Apoptosis and Ki67 increased in both the conjunctiva and the cornea of CS-exposed animals. Furthermore, although DCSP inhibited the proliferation of HCECs, expression of Ki67 increased and apoptosis was only induced significantly by 2.0 μL/mL DCSP. The release of IL-1β and IL-6, activation of NF-κB were prompted by DCSP. The results indicated that CS is toxic to the ocular surface of mice and HCECs. Longer-term CS exposure in mice stimulates ocular surface changes that resemble those observed with dry eye. The mechanism may relate to inflammation and activation of NF-κB. In this study, we established a novel animal model to study dry eye, with the experimental data and elucidation of mechanism facilitating further research.

Immune - Goblet cell interaction in the conjunctiva

The conjunctiva is a goblet cell rich mucosal tissue. Goblet cells are supported by tear growth factors and IL-13 produced by resident immune cells. Goblet cell secretions are essential for maintaining tear stability and ocular surface homeostasis. In addition to producing tear stabilizing mucins, they also produce cytokines and retinoic acid that condition monocyte-derived phagocytic cells in the conjunctiva. Aqueous tear deficiency from lacrimal gland disease and systemic inflammatory conditions results in goblet cell loss that amplifies dry eye severity. Reduced goblet cell density is correlated with more severe conjunctival disease, increased IFN-γ expression and antigen presenting cell maturation. Sterile Alpha Motif (SAM) pointed domain epithelial specific transcription factor (Spdef) gene deficient mice that lack goblet cells have increased infiltration of monocytes and dendritic cells with greater IL-12 expression in the conjunctiva. Similar findings were observed in the conjunctiva of aged mice. Reduced retinoic acid receptor (RXRα) signaling also increases conjunctival monocyte infiltration, IFN-γ expression and goblet cell loss. Evidence suggests that dry eye therapies that suppress IFN-γ expression preserve conjunctival goblet cell number and function and should be considered in aqueous deficiency.

Expression and Role of Nucleotide-Binding Oligomerization Domain 2 (NOD2) in the Ocular Surface of Murine Dry Eye

Purpose

To investigate expression and role of nucleotide-binding oligomerization domain 2 (NOD2) in the ocular surface of experimental dry eye (EDE), which is a nod-like receptor member and is involved in innate immune response.

Methods

C57/BL6 female mice were divided into the groups: untreated (UT), EDE, and NOD2 knockout (KO) mice exposed to desiccating stress for 14 days. Clinical parameters and levels of inflammatory cytokine were measured at 3,5,7, and 14 days. Immunofluorescent staining for NOD2 and Western blot for RIP2 and NF-κB were performed at 14 days. Flow cytometry, PAS staining and TUNEL staining were performed.

Results

After EDE induction, NOD2 was expressed in the corneal epithelium of the EDE group. The EDE group showed a significantly increased RIP2 expression compared to the UT and NOD2-KO groups. A significantly lower expression of NF-κB and lower levels of IL-1β, IL-6, IFN-γ, and TNF-α were noted in the NOD2-KO group than in the EDE group. The NOD2-KO group had lower CD11b+ and CD4+CCR5+ T cells, TUNEL-positive cells and corneal staining score and higher density of conjunctival goblet cell density, tear volume, and tear film break-up time than the EDE group. The UT group showed significant differences in inflammatory and clinical parameters compared to the EDE and NOD2-KO groups.

Conclusions

The NOD2 receptor pathway induced inflammation and apoptosis by activation of RIP2 and NF-κB on the ocular surface of EDE, thereby reducing tear secretion. Therefore, NOD2 pathway may be involved in the pathogenesis of dry eye.

Ocular mucins in dry eye disease

Dry eye disease is a common and multifactorial disease with a high prevalence worldwide. Water loss, reduced expression of glycocalyx mucins, and loss of goblet cells secreting gel-forming mucins are hallmarks of dry eye disease. Mucins are large and complex heavily glycosylated proteins. Their organization in the tear film remains unclear, but they play a key role to protect and maintain integrity of the ocular surface. Mice have been extremely valuable mammalian models with which to study ocular physiology and disease, and to evaluate eye therapies. Genetically modified mice and spontaneously occurring mutants with eye defects have proven to be powerful tools for the pharmaceutical industry, clinicians, and basic researchers investigating dry eye disease. However, ocular mucins remain relatively under-studied and inadequately characterized. This review aims to summarize current knowledge about mucin production at the ocular surface in healthy individuals and in dry eye disease, and to compile an overview of mouse models available for the study of mucins in dry eye disease.

Age-associated antigen-presenting cell alterations promote dry-eye inducing Th1 cells

Aging is a significant risk factor for dry eye. Here we used a murine aging model to investigate the effects of aging on antigen presenting cells (APCs) and generation of pathogenic T helper (Th)-1 cells. Our results showed that APCs from aged mice accumulate at the conjunctiva, have higher levels of co-activation marker CD86 and lower aldehyde dehydrogenase activity. Using topical ovalbumin peptide as a surrogate antigen, we observed an increased number of antigen-loaded APCs in the draining cervical lymph nodes in the aged group and loss of tight junction protein occludin in the conjunctiva. Aged cervical lymph nodes APCs showed a greater generation of Th1 cells than young APCs in antigen-presentation assays in vitro. Aged lacrimal glands, and draining nodes showed an accumulation of IFN-γ producing CD4+T cells, while Th-17 cells were present only in aged draining nodes. There was also an age-related increase in CD4+CXCR3+IFN-γ+ cells in the conjunctiva, nodes, and lacrimal glands while CD4+CCR6+IL-17A+ cells increased in the draining nodes of aged mice. Adoptive transfer of aged CD4+CXCR3+ cells into young, naive immunodeficient recipients caused greater goblet cell loss than young CD4+CXCR3+ donor cells. Our results demonstrate that age-associated changes in APCs are critical for the pathogenesis of age-related dry eye.

Effects of fine particulate matter on the ocular surface: An in vitro and in vivo study

Exposure to ambient fine particulate matter (fine PM) pollution has been previously associated with ocular surface diseases. But, to the best of our knowledge, the in vivo long-term effects of fine PM on the ocular surface have not been investigated. We aimed to evaluate the effects of fine PM on cultured human corneal epithelial (HCE) cells and on the ocular surfaces of mice, with standard reference material of fine PM(SRM 2786). We applied fine PM suspension to the eyes of C57BL/6 mice for up to 6 months. In vivo examinations, including tear secretion, tear film break-up time (TBUT) and corneal fluorescein staining, were performed in the 3^rd and 6^th month. At the end of the in vivo study, the corneal histological changes and conjunctival goblet cells were examined by staining, and cytokines in tissue were also detected. In addition, HCE cells were treated with fine PM for 12 h and 24 h. Then, cell apoptosis and reactive oxygen species (ROS) formation was detected. We found that fine PM damages the mouse eye in a dose- and time-dependent manner. In mice, the tear secretion and tear film break-up time were significantly reduced, along with the development of corneal epithelial damage, apoptosis of conjunctival epithelial cells and hypoplasia of conjunctival goblet cells. In addition, IL-18, IL-22, IL-23 and MCP-1 were increased in both conjunctiva and cornea of the fine PM-treated animals. Furthermore, increased apoptosis and ROS production were observed in time- and dose-dependent manner in HCE cells after fine PM exposure for 12 h and 24 h. Our results indicate that fine PM is cytotoxic to both HCE cells and the ocular surface. Long-term topical application of fine PM suspension in mice results in ocular surface changes that are similar to those observed with dry eye.

Inflammatory Response in Dry Eye

Purpose

Dry eye is a major ocular pathology worldwide. Although dry eye is a multifactorial disease, recent studies have shown that chronic immunologic processes have a pivotal role in its pathogenesis, characterized by the infiltration of immune cells in the lacrimal glands, elevated levels of tear inflammatory cytokines, and increased density of immune cells in the cornea and conjunctiva. This review describes the recent advances in understanding the relationship between dry eye and inflammation.

Methods

This narrative review is based on searches of recent international literature using terms related to the immune response in dry eye, and includes clinical trials, animal experiments, and expert reviews.

Results

Although dry eye presents clinically as tear film instability associated with corneal/conjunctival epithelial disorders, Meibomian gland dysfunction, and decreased visual function, recent laboratory and clinical studies have indicated inflammation in the lacrimal glands, Meibomian glands, conjunctiva, cornea, and aqueous tears. Furthermore, inflammation at these locations leads to conjunctival goblet cell apoptosis, corneal epithelial barrier disruption, and corneal nerve damage. These inflammatory outcomes can be exacerbated by intrinsic and extrinsic factors, such as aging, sex steroid hormone, autoimmune diseases, contact lens use, visual display terminals, and dry environment.

Conclusions

Recent advances in dry eye research have revealed the inflammatory process and its pathogenesis, which has been proposed as an "inflammatory vicious cycle" of dry eye. Comprehensive assessment of dry eye based on inflammation will improve the selection of treatments and help break the inflammatory cycle in clinical settings.

Rebamipide ophthalmic solution modulates the ratio of T helper cell 17/regulatory T cells in dry eye disease mice

The aim of the present study was to confirm the effect of 2% rebamipide ophthalmic solution on a scopolamine‑induced dry eye (DE) mouse model, and to investigate its effect on the ratio of T helper cell 17 (Th17)/regulatory T cell (Treg) numbers. C57BL/6 mice received subcutaneous injections of scopolamine and were exposed to a low‑humidity environment in order to establish a DE model. Rebamipide eye drops (2%) administered four times daily for 2 weeks, significantly reduced the corneal staining scores and increased the tear film breakup time and tear production in the DE mice. Pathologically, the rebamipide restored the histological changes induced by DE in the cornea, conjunctiva and lacrimal gland. At a molecular level, it downregulated pro‑inflammatory and upregulated anti‑inflammatory cytokines in the conjunctiva and lacrimal gland. Furthermore, the increased Th17 and Treg levels were restored following treatment with rebamipide. In conclusion, the anti‑inflammatory and Th17/Treg balance‑preserving effects of rebamipide may contribute to the treatment of DE in mice.