Oxidative stress induced inflammation initiates functional decline of tear production

A cerium oxide loaded glycol chitosan nano-system for the treatment of dry eye disease

Dry eye (DE) disease is an uprising health epidemic that directly affects the surface of the eye. We developed a water soluble cerium oxide loaded glycol chitosan nanoparticle as a new type of eye drop, namely GCCNP (glycol chitosan cerium oxide nanoparticles). GCCNP is capable of scavenging cellular reactive oxygen species (ROS) for the treatment of DE disease. The antioxidative effects of GCCNP were assessed in mice primary corneal and conjunctival cells in vitro and in a DE murine model in vivo. GCCNP's effect on the DE models was assessed via histological evaluations, migration assays, cell viability assays, cellular uptake analyses, intracellular ROS scavenging assays, wound healing assays, mitochondrial membrane potential readings, corneal fluorescein staining, tear volume concentrations, tear film break up time analyses, and lastly, analytical/spectroscopic analyses of GCCNP eye drop formulations. Spectroscopic analysis showed that cerium oxide was entrapped into the glycol chitosan (GC). The solubility of cerium in GC (GCCNP) increased to 709.854±24.3μg/ml compared to its original solubility in cerium oxide, which was measured as 0.020±0.002μg/ml. GCCNP had no cytotoxic effect and showed improvements on dry eye disease models by stabilizing the tear film, scavenging ROS, up-regulating SOD, promoting and maintaining corneal and conjunctival cell growth and integrity. We provided convincing evidence that GCCNP is an effective treatment for DE and may represent a potential new class of drug for DE disease.

Hydrogen-producing milk to prevent reduction in tear stability in persons using visual display terminals

PURPOSE

To examine the effect of hydrogen (H₂)-producing milk, which induces H₂ production by intestinal microbiota, on the prevention of dry eye disease.

METHODS

A randomized, double-blind, placebo-controlled, parallel-group comparative study was conducted in humans. Of 118 candidates aged 20-60 years who were using visual display terminals daily, 54 subjects (mean age, 42.4 years) with mild-to-moderate dry eye symptoms, who were not dry eye patients based on the 2006 Japanese Diagnostic Criteria for Dry Eye, were included in the study. Subjects were assigned to the H₂-producing milk group or the placebo group. They were instructed to ingest the assigned test beverage once per day for three consecutive weeks. Breath H₂ concentration, fluorescein tear film breakup time (fTBUT), Schirmer's test, 8-OHdG concentration in tears, reported ocular symptoms using the dry eye-related QOL score questionnaire, and the visual analogue scale were assessed at weeks 0 and 3.

RESULTS

Change in fTBUT in the H₂-producing milk group was significantly greater than that in the placebo group. A significant decline in fTBUT was observed in the placebo group (p = 0.04), but not the H₂-producing group (p = 0.26). This phenomenon was strongly observed in females. We found a positive correlation between the change in fTBUT and net H₂ production, and a negative correlation between the change in 8-OHdG concentration and net H₂ production in young females.

CONCLUSIONS

H₂-producing milk appeared to retard the decline in tear stability and may prevent short fTBUT-type dry eye by decreasing oxidative stress in the lacrimal functional unit.

Tear Lactoferrin and Lysozyme as Clinically Relevant Biomarkers of Mucosal Immune Competence

Tears have attracted interest as a minimally-invasive biological fluid from which to assess biomarkers. Lactoferrin (Lf) and lysozyme (Lys) are abundant in the tear fluid and have antimicrobial properties. Since the eye is a portal for infection transmission, assessment of immune status at the ocular surface may be clinically relevant. Therefore, the aim of this series of studies was to investigate the tear fluid antimicrobial proteins (AMPs) Lf and Lys as biomarkers of mucosal immune status. To be considered biomarkers of interest, we would expect tear AMPs to respond to stressors known to perturb immunity but be robust to confounding variables, and to be lower in participants with heightened risk or incidence of illness. We investigated the relationship between tear AMPs and upper respiratory tract infection (URTI; study 1) as well as the response of tear AMPs to prolonged treadmill exercise (study 2) and dehydration (study 3). Study 1 was a prospective cohort study conducted during the common cold season whereas studies 2 and 3 used repeated-measures crossover designs. In study 1, tear Lys concentration (C) as well as tear AMP secretion rates (SRs) were lower in individuals who reported pathogen-confirmed URTI (n = 9) throughout the observation period than in healthy, pathogen-free controls (n = 17; Lys-C, P = 0.002, d = 0.85; Lys-SR, P < 0.001, d = 1.00; Lf-SR, P = 0.018, d = 0.66). Tear AMP secretion rates were also lower in contact lens wearers. In study 2, tear AMP SRs were 42-49% lower at 30 min-1 h post-exercise vs. pre-exercise (P < 0.001, d = 0.80-0.93). Finally, in study 3, tear AMPs were not influenced by dehydration, although tear AMP concentrations (but not secretion rates) displayed diurnal variation. We conclude that Lf and Lys have potential as biomarkers of mucosal immune competence; in particular, whether these markers are lower in infection-prone individuals warrants further investigation.

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.

The role of autophagy in the pathogenesis of exposure keratitis

Incomplete tear film spreading and eyelid closure can cause defective renewal of the ocular surface and air exposure-induced epithelial keratopathy (EK). In this study, we characterized the role of autophagy in mediating the ocular surface changes leading to EK. Human corneal epithelial cells (HCECs) and C57BL/6 mice were employed as EK models, respectively. Transmission electron microscopy (TEM) evaluated changes in HCECs after air exposure. Each of these models was treated with either an autophagy inhibitor [chloroquine (CQ) or 3-methyladenine (3-MA)] or activator [Rapamycin (Rapa)]. Immunohistochemistry assessed autophagy-related proteins, LC3 and p62 expression levels. Western blotting confirmed the expression levels of the autophagy-related proteins [Beclin1 and mammalian target of rapamycin (mTOR)], the endoplasmic reticulum (ER) stress-related proteins (PERK, eIF2α and CHOP) and the PI3K/Akt/mTOR signalling pathway-related proteins. Real-time quantitative PCR (qRT-PCR) determined IL-1β, IL-6 and MMP9 gene expression levels. The TUNEL assay detected apoptotic cells. TEM identified autophagic vacuoles in both EK models. Increased LC3 puncta formation and decreased p62 immunofluorescent staining and Western blotting confirmed autophagy induction. CQ treatment increased TUNEL positive staining in HCECs, while Rapa had an opposite effect. Similarly, CQ injection enhanced air exposure-induced apoptosis and inflammation in the mouse corneal epithelium, which was inhibited by Rapa treatment. Furthermore, the phosphorylation status of PERK and eIF2α and CHOP expression increased in both EK models indicating that ER stress-induced autophagy promoted cell survival. Taken together, air exposure-induced autophagy is indispensable for the maintenance of corneal epithelial physiology and cell survival.

[Oxidative stress correction in the treatment of severe keratoconjunctivitis sicca in patients with Sjorgen's syndrome]

PURPOSE

To evaluate the antioxidative effect of artificial tears in the treatment of keratoconjunctivitis sicca (KCS).

MATERIAL AND METHODS

The study included 43 patients (60 eyes) with severe KCS: 38 women (50 eyes) and 5 men (10 eyes) aged from 27 to 76 years (in average 52 years). Patients were randomly divided into 2 groups; all patients used therapeutic silicone hydrogel soft contact lens (SCL) and instillations of 0.05% Cyclosporin A (CyA) 2 times a day. Patients of the first group (22 people, 30 eyes) used 0.15% hyaluronic acid. In the second group, patients (21 people, 30 eyes) used a tear substitute with similar surface-active component, but with antioxidant properties. The results of the treatment were evaluated using basic and additional research methods at 1, 3, 6 and 12 months.

RESULTS

Corneal epithelialization was achieved after 1 month of conservative treatment in all patients who wore SCLs and were treated with instillations of 0.05% CyA and artificial tears. Then the lenses were removed and the patients were switched to instillations of CyA and artificial tears. Comparative analysis of the results showed that higher functional indicators were achieved in the second group, where patients used Artelac Rebalance drops with antioxidant properties.

CONCLUSION

Improvement of clinical and functional parameters in the treatment of severe forms of KCS was achieved by direct action on both links of pathogenesis with minimal amounts of the drugs and the frequency of their use. Subsequent supportive therapy contributed to stabilization of the results and further increase of the functional parameters.

Manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin, a superoxide dismutase mimetic, reduces disease severity in in vitro and in vivo models for dry-eye disease

PURPOSE

To determine the efficacy of the superoxide dismutase mimetic, manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin (Mn-TM-2-PyP), in vitro in human corneal epithelial (HCE-T) cells and in vivo in a preclinical mouse model for dry-eye disease (DED).

METHODS

In vitro, HCE-T cultures were exposed either to tert-butylhydroperoxide (tBHP) to generate oxidative stress or to hyperosmolar conditions modeling cellular stress during DED. Cells were pre-treated with Mn-TM-2-PyP or vehicle. Mn-TM-2-PyP permeability across stratified HCE-T cells was assayed. In vivo, Mn-TM-2-PyP (0.1% w/v in saline) was delivered topically as eye drops in a desiccating stress/scopolamine model for DED. Preclinical efficacy was compared to untreated, vehicle- and ophthalmic cyclosporine emulsion-treated mice.

RESULTS

Mn-TM-2-PyP protected HCE-T cells in a dose-dependent manner against tBHP-induced oxidative stress as determined by calculating the IC₅₀ for tBHP in the resazurin, MTT and lactate dehydrogenase release cell viability assays. Mn-TM-2-PyP did not protect HCE-T cells from hyperosmolar insult. Its permeability coefficient across a barrier of HCE-T cells was 1.1 ± 0.05 × 10^-6 cm/s and the mass balance was 62 ± 0.6%. In vivo, topical dosing with Mn-TM-2-PyP resulted in a statistically significant reduction of corneal fluorescein staining, similar to ophthalmic cyclosporine emulsion. Furthermore, Mn-TM-2-PyP significantly reduced leukocyte infiltration into lacrimal glands and prevented degeneration of parenchymal tissue. No protective effect against loss of conjunctival goblet cells was observed. Notably, Mn-TM-2-PyP did not produce ocular toxicity when administered topically.

DISCUSSION

Our data suggest that Mn-TM-2-PyP, a prototypic synthetic metalloporphyrin compound with potent catalytic antioxidant activity, can improve signs of DED in vivo by reducing oxidative stress in corneal epithelial cells.

Ocular Manifestations of Rheumatoid Arthritis: Implications of Recent Clinical Trials

While rheumatoid arthritis (RA) typically presents with synovitis of the small and medium joints of the hands, ocular manifestations of the disease are generally overlooked and largely underdiagnosed. These complications usually present in longstanding RA population and occasionally represents the first manifestation of the disease and generally affect the anterior chamber of the eye, leading to keratoconjunctivitis sicca, episcleritis, scleritis, peripheral ulcerative keratitis and anterior uveitis. In this review, we present the current understanding of the pathophysiologic mechanisms for ocular disease in RA, including the role of oxidative stress, cytokine imbalance, chronic inflammation, vascular permeability, immune complex deposition and the role of T-cells as well as the contribution of tear hyperosmolarity among other factors. We also discuss the clinical presentation and diagnosis of each of the ocular disease entities highlighting the latest strategies in the management of this serious disorders that could potentially lead to blindness and the implications of recently completed and ongoing clinical trials in the field. While RA disease control is the cornerstone in the management of RA-associated ocular manifestations, early recognition of ocular pathology with prompt referral to ophthalmology is of paramount importance in order to prevent blindness and improve the quality of life in this patient population.

The Role of SKQ1 (Visomitin) in Inflammation and Wound Healing of the Ocular Surface

Introduction

SkQ1 (Visomitin) is a novel mitochondrial-targeted antioxidant that holds promise in the treatment of inflammation associated with ocular surface diseases such as dry eye disease (DED) and corneal wounds. However, the specific role of SkQ1 in ocular surface epithelial tissue has yet to be explicated. The goal of this study is to identify roles of SkQ1 in conjunctival inflammation and corneal wound healing.

Methods

To determine the role of SkQ1 in inflammation, human conjunctival epithelial (HCjE) cell cultures were sensitized with pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) followed by treatments with SkQ1. The production of inflammatory biomarker prostaglandin E2 (PGE2) and cell viability were quantitatively evaluated. To determine the role of SkQ1 in wound healing, human corneal limbus epithelial (HCLE) cell cultures were streaked to create wounds. The wound closure times, ability to support single HCLE cell proliferation and changes of cell migration in the presence of SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK), were further compared.

Results

The HCjE and HCLE cultures showed no apparent cytotoxicity to SkQ1 in concentrations up to 250 nM (HCjE) or 2500 nM (HCLE). The HCLE cultures showed no toxicity to SkQ1 at all the SkQ1 concentrations tested. SkQ1 significantly suppressed PGE2 production of HCjE at concentrations < 300 nM (24 h) and 50 nM (48 h), apparently being SkQ1 dose and treatment time dependent. The wound closure rates were increased by 4% in 4 h and by 9% after 8–12 h in the presence of 50 nM SkQ1. Furthermore, as little as 25 nM of SkQ1 significantly stimulated HCLE single-cell proliferation. Lastly, the SkQ1-stimulated wound healing was completely abolished by SB203580.

Conclusion

Results of the current study demonstrate that SkQ1 exhibits an anti-inflammatory role and can be safely applied to ocular surface epithelium up to a concentration of 300 nM (181 ng/ml) for 24 h. SkQ1 also significantly enhances corneal epithelial wound healing, likely through enhancement of cell proliferation and migration. The data provide solid support for SkQ1 as a promising new therapeutic strategy for treatment of conjunctival inflammation as well as corneal wounds.

Funding

This study was sponsored by Mitotech SA Pharmaceuticals.

Electronic supplementary material

The online version of this article (10.1007/s40123-018-0158-2) contains supplementary material, which is available to authorized users.

[Prevention and treatment of degenerative changes in ocular surface epithelium in patients with dry eye syndrome]

In current understanding of the pathogenesis of xerotic changes of the ocular surface in patients with dry eye syndrome (DES), great importance is given to hyperosmolarity of the tear film, inflammatory process and oxidative stress. By now, no convincing data has been obtained on whether the oxidative stress is primary in relation to the inflammatory process in the ocular surface tissues, or if it is a complication. Furthermore, in the complex treatment of patients with DES, antioxidant therapy has so far received little attention. This problem can be solved with the 'artificial tears' preparation containing cyanocobalamin (vitamin B12), which antioxidant, anti-inflammatory and clinical effectiveness has been convincingly proved in a number of experimental and clinical studies of recent years. Improving the methods of vital diagnostics of xerosis of the ocular surface also enables detection of subclinical changes in epithelium of the cornea and conjunctiva, thus allowing timely prescription of metabolic therapy. One of the promising directions of such treatment is the use of 5% dexpanthenol, which stimulates the processes of reparative regeneration and possesses an anti-inflammatory effect.

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.

Experimental and Clinical Applications of Chamaecyparis obtusa Extracts in Dry Eye Disease

Purpose

To investigate the effects of Chamaecyparis obtusa (CO) on human corneal epithelial (HCE) cells, a murine experimental dry eye (EDE) model, and the efficacy of antioxidant eye mask in dry eye disease (DED) patients.

Methods

0.001%, 0.01%, and 0.1% CO extracts were used to treat HCE cells, cell viability, and production of antioxidative enzymes, and reactive oxygen species (ROS) were assessed. Afterwards, CO extracts or balanced salt solution (BSS) was applied in EDE. Clinical and experimental parameters were measured at 7 days after treatment. In addition, DED patients were randomly assigned to wear either an eye mask containing CO extracts or a placebo. Clinical parameters were evaluated.

Results

The viability of HCE cells and antioxidative enzyme expression significantly improved after treatment with 0.1% CO extracts. Mice treated with 0.1% CO extracts showed significant improvement in clinical parameters. During the trial, the clinical parameters significantly improved in the treatment group at 4 weeks after application.

Conclusions

0.1% CO extracts could promote the expression of antioxidative proteins and ROS production. In addition, an eye mask containing CO extracts could improve DED clinical parameters. These suggest that CO extracts may be useful as an adjunctive option for the DED treatment.

Effects of Lycium barbarum (goji berry) on dry eye disease in rats

Lycium barbarum (goji berry) has long been used as a food and traditional herbal medicine. This study aimed to investigate the beneficial effect of the goji berry on dry eye disease in rats. Male Sprague-Dawley rats with induced dry eye disease were randomly assigned to four groups: Vehicle (control), low-dose goji berry extract [GBE; 250 mg/kg/body weight (bw)], median-dose GBE (350 mg/kg/bw), and high-dose GBE (500 mg/kg/bw). Three methods, Schirmer's test, tear break-up time (BUT) measurement and keratoconjunctival fluorescein staining, were used to evaluate the effect of GBE on symptoms of dry eye disease experienced by the rats. The results of the present study revealed that both the Schirmer's test score and tear BUT significantly increased following 1 week of GBE administration. Furthermore, the severity of the keratoconjunctival staining decreased significantly. In addition, the results suggested that administration of GBE may ameliorate dry eye disease symptoms in a dose-dependent manner. There were no mortalities and no apparent abnormal histopathology changes in the liver or kidney tissues of rats administered GBE for 21 consecutive days. Polysaccharides and betaine present in GBE may have important effects in alleviating dry eye disease induced by oxidative stress and inflammation. In conclusion, the goji berry is a safe, functional food with beneficial effects in alleviating dry eye disease.

Ambient fine particulate matters induce cell death and inflammatory response by influencing mitochondria function in human corneal epithelial cells

Ambient fine particulate matter (AFP) is a main risk factor for the cornea as ultraviolet light. However, the mechanism of corneal damage following exposure to AFP has been poorly understood. In this study, we first confirmed that AFP can penetrate the cornea of mice, considering that two-dimensional cell culture systems are limited in reflecting the situation in vivo. Then, we investigated the toxic mechanism using human corneal epithelial (HCET) cells. At 24h after exposure, AFP located within the autophagosome-like vacuoles, and cell proliferation was clearly inhibited in all the tested concentration. Production of ROS and NO and secretion of pro-inflammatory cytokines were elevated in a dose-dependent manner. Additionally, conversion of LC3B from I-type to II-type and activation of caspase cascade which show autophagic- and apoptotic cell death, respectively, were observed in cells exposed to AFP. Furthermore, AFP decreased mitochondrial volume, inhibited ATP production, and altered the expression of metabolism-related genes. Taken together, we suggest that AFP induces cell death and inflammatory response by influencing mitochondrial function in HCET cells. In addition, we recommend that stringent air quality regulations are needed for eye health.

The Pathophysiology of Dry Eye Disease: What We Know and Future Directions for Research

Clinical and laboratory studies performed over the past few decades have discovered that dry eye is a chronic inflammatory disease that can be initiated by numerous extrinsic or intrinsic factors that promote an unstable and hyperosmolar tear film. These changes in tear composition, in some cases combined with systemic factors, lead to an inflammatory cycle that causes ocular surface epithelial disease and neural stimulation. Acute desiccation activates stress signaling pathways in the ocular surface epithelium and resident immune cells. This triggers production of innate inflammatory mediators that stimulate the production of matrix metalloprotease, inflammatory cell recruitment, and dendritic cell maturation. These mediators, combined with exposure of autoantigens, can lead to an adaptive T cell-mediated response. Cornea barrier disruption develops by protease-mediated lysis of epithelial tight junctions, leading to accelerated cell death; desquamation; an irregular, poorly lubricated cornea surface; and exposure and sensitization of epithelial nociceptors. Conjunctival goblet cell dysfunction and death are promoted by the T helper 1 cytokine interferon gamma. These epithelial changes further destabilize the tear film, amplify inflammation, and create a vicious cycle. Cyclosporine and lifitegrast, the 2 US Food and Drug Administration-approved therapies, inhibit T-cell activation and cytokine production. Although these therapies represent a major advance in dry eye therapy, they are not effective in improving discomfort and corneal epithelial disease in all patients. Preclinical studies have identified other potential therapeutic targets, biomarkers, and strategies to bolster endogenous immunoregulatory pathways. These discoveries will, it is hoped, lead to further advances in diagnostic classification and treatment.

ROS-induced Oxidative Injury involved in Pathogenesis of Fungal Keratitis via p38 MAPK Activation

This study was to explore the mechanism by which reactive oxygen species (ROS)-induced oxidative stress involved in the pathogenesis of fungal keratitis using an in vivo experimental keratitis mouse model and an in vitro culture model of human corneal epithelial cells (HCECs). Compared to normal control mice and HCECs, ROS production was markedly increased in fungal corneas and HCECs exposed to Candida albicans, accompanied by p38 mitogen-activated protein kinases (MAPK) activation. Increased products of oxidative markers, malondialdehyde (MDA), 4–hydroxynonenal (HNE), mitochondria DNA 8-OHdG and aconitase-2 were observed in fungal infected corneas and HCECs. Fungal infection also increased the mRNA expression and protein production of heme oxygenase-1 (HMOX1) and cyclooxygenase-2 (COX2), with suppressed levels of antioxidant enzymes, superoxide dismutase-1 (SOD1), glutathione peroxidase-1 (GPx1) and peroxiredoxin-4 (PRDX4). Interestingly, the levels of ROS, oxidative markers and oxygenases were significantly reduced by co-cultured p38 inhibitor SB203580. Furthermore, SB203580 restored the levels of antioxidant enzymes suppressed by fungus. Our findings demonstrated for the first time that ROS-induced oxidative injury is involved in pathogenesis of fungal keratitis via p38 MAPK pathway, suggesting the novel therapeutic targets for the potential treatment of fungal keratitis.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

Edaravone protects against hyperosmolarity-induced oxidative stress and apoptosis in primary human corneal epithelial cells

An increase in the osmolarity of tears induced by excessive evaporation of the aqueous tear phase is a major pathological mechanism behind dry eye. Exposure of epithelial cells on the surface of the human eye to hyperosmolarity leads to oxidative stress, mitochondrial dysfunction, and apoptosis. Edaravone, a hydroxyl radical scavenging agent, is clinically used to reduce neuronal damage following ischemic stroke. In this study, we found that treatment with hyperosmotic media at 400 and 450 mOsM increased the levels of ROS and mitochondrial oxidative damage, which were ameliorated by edaravone treatment in a dose-dependent manner. We also found that edaravone could improve mitochondrial function in HCEpiCs by increasing the levels of ATP and mitochondrial membrane potential. MTT and LDH assays indicated that edaravone could attenuate hyperosmolarity-induced cell death. It was found that edaravone prevented apoptosis by decreasing the level of cleaved caspase-3, and attenuating the release of cytochrome C. Mechanistically, we found that edaravone augmented the expression of Nrf2 and its target genes, such as HO-1, GPx-1, and GCLC.

Endogenous reactive oxygen species cause astrocyte defects and neuronal dysfunctions in the hippocampus: a new model for aging brain

The etiology of astrocyte dysfunction is not well understood even though neuronal defects have been extensively studied in a variety of neuronal degenerative diseases. Astrocyte defects could be triggered by the oxidative stress that occurs during physiological aging. Here, we provide evidence that intracellular or mitochondrial reactive oxygen species (ROS) at physiological levels can cause hippocampal (neuronal) dysfunctions. Specifically, we demonstrate that astrocyte defects occur in the hippocampal area of middle‐aged Tet‐mev‐1 mice with the SDHC^V69E mutation. These mice are characterized by chronic oxidative stress. Even though both young adult and middle‐aged Tet‐mev‐1 mice overproduced MitoSOX Red‐detectable mitochondrial ROS compared to age‐matched wild‐type C57BL/6J mice, only young adult Tet‐mev‐1 mice upregulated manganese and copper/zinc superoxide dismutase (Mn‐ and Cu/Zn‐SODs) activities to eliminate the MitoSOX Red‐detectable mitochondrial ROS. In contrast, middle‐aged Tet‐mev‐1 mice accumulated both MitoSOX Red‐detectable mitochondrial ROS and CM‐H₂DCFDA‐detectable intracellular ROS. These ROS levels appeared to be in the physiological range as shown by normal thiol and glutathione disulfide/glutathione concentrations in both young adult and middle‐aged Tet‐mev‐1 mice relative to age‐matched wild‐type C57BL/6J mice. Furthermore, only middle‐aged Tet‐mev‐1 mice showed JNK/SAPK activation and Ca²⁺ overload, particularly in astrocytes. This led to decreasing levels of glial fibrillary acidic protein and S100β in the hippocampal area. Significantly, there were no pathological features such as apoptosis, amyloidosis, and lactic acidosis in neurons and astrocytes. Our findings suggest that the age‐dependent physiologically relevant chronic oxidative stress caused astrocyte defects in mice with impaired mitochondrial electron transport chain functionality.

Influence of Light Emitting Diode-Derived Blue Light Overexposure on Mouse Ocular Surface

Purpose

To investigate the influence of overexposure to light emitting diode (LED)-derived light with various wavelengths on mouse ocular surface.

Methods

LEDs with various wavelengths were used to irradiate C57BL/6 mice at an energy dose of 50 J/cm², twice a day, for 10 consecutive days. The red, green, and blue groups represented wavelengths of 630 nm, 525 nm, and 410 nm, respectively. The untouched group (UT) was not exposed to LED light and served as the untreated control. Tear volume, tear film break-up time (TBUT), and corneal fluorescein staining scores were measured on days 1, 3, 5, 7, and 10. Levels of interferon (IFN)-γ, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α were measured in the cornea and conjunctiva using a multiplex immunobead assay at day 10. Levels of malondialdehyde (MDA) were measured with an enzyme-linked immunosorbent assay. Flow cytometry, 2’7’-dichlorofluorescein diacetate (DCF-DA) assay, histologic analysis, immunohistochemistry with 4-hydroxynonenal, and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) staining were also performed.

Results

TBUT of the blue group showed significant decreases at days 7 and 10, compared with the UT and red groups. Corneal fluorescein staining scores significantly increased in the blue group when compared with UT, red, and green groups at days 5, 7, and 10. A significant increase in the corneal levels of IL-1β and IL-6 was observed in the blue group, compared with the other groups. The blue group showed significantly increased reactive oxygen species production in the DCF-DA assay and increased inflammatory T cells in the flow cytometry. A significantly increased TUNEL positive cells was identified in the blue group.

Conclusions

Overexposure to blue light with short wavelengths can induce oxidative damage and apoptosis to the cornea, which may manifest as increased ocular surface inflammation and resultant dry eye.

Therapeutic Efficacy of Topically Applied Antioxidant Medicinal Plant Extracts in a Mouse Model of Experimental Dry Eye

Purpose. To investigate the therapeutic effects of topical administration of antioxidant medicinal plant extracts in a mouse model of experimental dry eye (EDE). Methods. Eye drops containing balanced salt solution (BSS) or 0.001%, 0.01%, and 0.1% extracts were applied for the treatment of EDE. Tear volume, tear film break-up time (BUT), and corneal fluorescein staining scores were measured 10 days after desiccating stress. In addition, we evaluated the levels of interleukin- (IL-) 1β, tumor necrosis factor- (TNF-) α, IL-6, interferon- (IFN-) γ, and IFN-γ associated chemokines, percentage of CD4+C-X-C chemokine receptor type 3 positive (CXCR3+) T cells, goblet cell density, number of 4-hydroxy-2-nonenal (4-HNE) positive cells, and extracellular reactive oxygen species (ROS) production. Results. Compared to the EDE and BSS control groups, the mice treated with topical application of the 0.1% extract showed significant improvements in all clinical parameters, IL-1β, IL-6, TNF-α, and IFN-γ levels, percentage of CD4+CXCR3+ T cells, goblet cell density, number of 4-HNE-positive cells, and extracellular ROS production (P < 0.05). Conclusions. Topical application of 0.1% medicinal plant extracts improved clinical signs, decreased inflammation, and ameliorated oxidative stress marker and ROS production on the ocular surface of the EDE model mice.

A glimpse at the aging eye

Extensive investigations have demonstrated that organismal aging is associated with tissue dysfunction in many organs. The eye is no exception to this rule. Under healthy conditions, the eye is designed like an advanced camera with the central role of translating light from the external world into a coherent neural signal that can be transmitted to the brain for processing into a precise visual image. This complex process requires precisely maintained machinery. At the front of the eye, the transparency of both the cornea and the lens are crucial to allow passage of photons to the light-sensitive portion of the eye. Similarly, the highly organized structure of the retina located at the back of the eye is indispensable to allow for effective signal transduction and efficient signal transmission. Aging affects ocular structures in various ways, and these sequelae have been well defined as distinct clinical entities. In many instances, aging leads to ocular tissue dysfunction and disease. Nonetheless, despite clear evidence that age-associated visual impairment has significant psychosocial consequences, current treatment paradigms for many of these conditions are inadequate. In addition, strategies to decelerate or reverse age-associated deterioration in ocular function are still in their infancy. This review focuses on the cellular and molecular pathophysiology of the aging eye. Ultimately, we hope that a refined understanding of the aging eye can guide targeted therapies against cellular aging and disease.

Serum 25-Hydroxyvitamin D Levels and Dry Eye Syndrome: Differential Effects of Vitamin D on Ocular Diseases

Purpose

To investigate associations between serum 25-hydroxyvitamin D levels and dry eye syndrome (DES), and to evaluate the differential effect of vitamin D on ocular diseases including age-related macular disease (AMD), diabetic retinopathy (DR), cataract, and DES.

Methods

A total of 16,396 participants aged >19 years were randomly selected from the Korean National Health and Nutrition Examination Survey. All participants participated in standardized interviews, blood 25-hydroxyvitamin D level evaluations, and comprehensive ophthalmic examinations. DES was defined by a history of clinical diagnosis of dry eyes by a physician. The association between vitamin D and DES was compared to the associations between vitamin D and AMD, DR, cataract, and DES from our previous studies.

Results

The odds of DES non-significantly decreased as the quintiles of serum 25-hydroxyvitamin D levels increased (quintile 5 versus 1, OR = 0.85, 95%CI: 0.55–1.30, P for trend = 0.076) after adjusting for potential confounders including age, sex, hypertension, diabetes, smoking status, and sunlight exposure times. The relative odds of DES (OR = 0.70, 95% CI: 0.30–1.64) and cataract (OR = 0.76, 95% CI: 0.59–0.99) were relatively high, while those of DR (OR = 0.37, 95% CI: 0.18–0.76) and late AMD (OR = 0.32, 95% CI: 0.12–0.81) were lower in men.

Conclusions

The present study does not support an association between serum 25-hydroxyvitamin D levels and DES. The preventive effect of serum 25-hydroxyvitamin D may be more effective for DR and late AMD than it is for cataract and DES.

Relationship between Oxidative Stress, Circadian Rhythms, and AMD

This work reviews concepts regarding oxidative stress and the mechanisms by which endogenous and exogenous factors produce reactive oxygen species (ROS). It also surveys the relationships between oxidative stress, circadian rhythms, and retinal damage in humans, particularly those related to light and photodamage. In the first section, the production of ROS by different cell organelles and biomolecules and the antioxidant mechanisms that antagonize this damage are reviewed. The second section includes a brief review of circadian clocks and their relationship with the cellular redox state. In the third part of this work, the relationship between retinal damage and ROS is described. The last part of this work focuses on retinal degenerative pathology, age-related macular degeneration, and the relationships between this pathology, ROS, and light. Finally, the possible interactions between the retinal pigment epithelium (RPE), circadian rhythms, and this pathology are discussed.

Protective Effects of L-Carnitine Against Oxidative Injury by Hyperosmolarity in Human Corneal Epithelial Cells

PURPOSE

L-carnitine suppresses inflammatory responses in human corneal epithelial cells (HCECs) exposed to hyperosmotic stress. In this study, we determined if L-carnitine induces this protective effect through suppression of reactive oxygen species (ROS)-induced oxidative damage in HCECs.

METHODS

Primary HCECs were established from donor limbal explants. A hyperosmolarity dry-eye model was used in which HCECs are cultured in 450 mOsM medium with or without L-carnitine for up to 48 hours. Production of reactive oxygen species (ROS), oxidative damage markers, oxygenases and antioxidative enzymes were analyzed by 2',7'-dichlorofluorescein diacetate (DCFDA) kit, semiquantitative PCR, immunofluorescence, and/or Western blotting.

RESULTS

Reactive oxygen species production increased in HCECs upon substitution of the isotonic medium with the hypertonic medium. L-carnitine supplementation partially suppressed this response. Hyperosmolarity increased cytotoxic membrane lipid peroxidation levels; namely, malondialdehyde (MDA) and hydroxynonenal (HNE), as well as mitochondria DNA release along with an increase in 8-OHdG and aconitase-2. Interestingly, these oxidative markers were significantly decreased by coculture with L-carnitine. Hyperosmotic stress also increased the mRNA expression and/or protein production of heme oxygenase-1 (HMOX1) and cyclooxygenase-2 (COX2), but inhibited the levels of antioxidant enzymes, superoxide dismutase-1 (SOD1), glutathione peroxidase-1 (GPX1), and peroxiredoxin-4 (PRDX4). However, L-carnitine partially reversed this altered imbalance between oxygenases and antioxidant enzymes induced by hyperosmolarity.

CONCLUSIONS

Our findings demonstrate for the first time that L-carnitine protects HCECs from oxidative stress by lessening the declines in antioxidant enzymes and suppressing ROS production. Such suppression reduces membrane lipid oxidative damage markers and mitochondrial DNA damage.

Ocular Surface and Tear Film Changes in Older Women Working with Computers

The aim of this work is to investigate changes in the ocular surface (OS) and tear film (TF) by means of questionnaire-based subjective symptoms, TF break-up time, Schirmer test, and TF analysis in women working with computers and to analyze the effects of the oral supplementation with antioxidants/omega 3 fatty acids (A/ω3) in the OS outcomes. Women aged 40–65 years (n = 148) were recruited at the Administrative Offices of Valencia (Spain) and distributed into two age groups, 40–52 years (AGE1; n = 87) and 53–65 years (AGE2; n = 61), and then subdivided according to being (or not) computer users (CUG; NCUG) during the workday. Homogeneous subgroups were randomly assigned (or not) to the daily intake of three pills of A/ω3 for three months. At baseline and at the end of follow-up, personalized interviews and ocular examination were done. Reflex tear samples were collected from the inferior meniscus and processed for a multiplexed particle-based flow cytometry assay to measure proinflammatory molecules. Statistics were performed using the SPSS 15.0 program. The OS pathology was clinically evident in the AGE1-CUG (33%) versus the AGE2-CUG (64%) of women. Significantly higher interleukins-1β and -6 tear levels were found in the AGE1 versus the AGE2 women employees (P = 0.006 and P = 0.001, resp.), as well as in the CUG versus the NCUG (P = 0.001 and P = 0.000, resp.). Supplementation with A/ω3 positively influenced the OS pathology as manifested by the amelioration of the clinical signs/symptoms related to computer uses. Strategies involving a safe environment and oral micronutrient supplements may be managed within eye-care standards in older women.

Effects of L-carnitine, erythritol and betaine on pro-inflammatory markers in primary human corneal epithelial cells exposed to hyperosmotic stress

PURPOSE

To explore the effects of osmoprotectants on pro-inflammatory mediator production in primary human corneal epithelial cells (HCECs) exposed to hyperosmotic stress.

METHODS

HCECs cultured in iso-osmolar medium (312 mOsM) were switched to hyperosmotic media with or without prior incubation with 2-20 mM of l-carnitine, erythritol or betaine for different time periods. The mRNA expression and protein production of pro-inflammatory markers in HCECs were evaluated by RT-qPCR and ELISA.

RESULTS

Hyperosmolar media significantly stimulated the mRNA and protein expression of pro-inflammatory cytokines, TNF-α, IL-1β and IL-6, and chemokines, IL-8, CCL2 and CCL20 in HCECs in an osmolarity dependent manner. The stimulated expression of these pro-inflammatory mediators was significantly but differentially suppressed by l-carnitine, erythritol or betaine. l-Carnitine displayed the greatest inhibitory effects and down-regulated 54-77% of the stimulated mRNA levels of TNF-α (down from 12.3-5.7 fold), IL-1β (2.2-0.9 fold), IL-6 (7.3-2.9 fold), IL-8 (4.6-2.0 fold), CCL2 (15.3-3.5 fold) and CCL20 (4.1-1.5 fold) in HCECs exposed to 450 mOsM. The stimulated protein production of TNF-α, IL-1β, IL-6 and IL-8 was also significantly suppressed by l-carnitine, erythritol and betaine. l-carnitine suppressed 49-79% of the stimulated protein levels of TNF-α (down from 81.3 to 17.4 pg/ml), IL-1β (56.9-29.2 pg/ml), IL-6 (12.8-4.6 ng/ml) and IL-8 (21.2-10.9 ng/ml) by HCECs exposed to 450 mOsM. Interestingly, hyperosmolarity stimulated increase in mRNA and protein levels of TNF-α, IL-1β and IL-6 were significantly suppressed by a transient receptor potential vanilloid channel type 1 (TRPV1) activation inhibitor capsazepine.

CONCLUSIONS

l-carnitine, erythritol and betaine function as osmoprotectants to suppress inflammatory responses via TRPV1 pathway in HCECs exposed to hyperosmotic stress. Osmoprotectants may have efficacy in reducing innate inflammation in dry eye disease.

The core mechanism of dry eye disease is inflammation

PURPOSE

The purpose of this article is to review the evidence for the hypothesis that the core mechanism of dry eye disease (DED) is inflammation, including evidence from recent basic, clinical, and translational research involving human patients, animal models, and cell cultures.

METHODS

Using the key words "dry eye + inflammation," the authors conducted a comprehensive search of the PubMed and Web of Science databases for scientific articles published in English between January 1, 1900 and August 30, 2013 on the role of inflammation in DED in cell cultures, animal models, and humans. The resulting articles were then categorized and reviewed.

RESULTS

The literature search revealed a total of 458 publications, almost all published after 1992. The percentages of original studies and review articles are 77.29% (354) and 22.71% (104), respectively. Among the original studies, the number of reports on human DED is 200 (43.7%), on animal models is 115 (25.1%), and cell cultures is 39 (8.5%). A yearly distributing plot revealed that 76% were published from 2003 to 2011, 53% from 2008 to 2012, and 11% during the first 9 months of 2013. This distribution signifies a rapidly growing awareness of the importance of inflammation in DED pathogenesis.

CONCLUSIONS

Inflammation plays a key role in the pathogenesis of DED as evidenced by research using tissue culture, animal models, and subjects with DED. Developing biomarkers for inflammation of the ocular surface will provide improved understanding of the mechanisms leading to DED, classification of the severity of DED, and objective metrics for outcome measures of treatment. The chronicity of the disease suggests that dysregulation of immune mechanisms leads to a cycle of continued inflammation, accompanied by alterations in both innate and adaptive immune responses. Given the underlying mechanism for DED, developing effective and safe anti-inflammatory treatments is likely to be beneficial for patients with DED.

Oxidative stress markers induced by hyperosmolarity in primary human corneal epithelial cells

Oxidative stress has been known to be involved in pathogenesis of dry eye disease. However, few studies have comprehensively investigated the relationship between hyperosmolarity and oxidative damage in human ocular surface. This study was to explore whether and how hyperosmolarity induces oxidative stress markers in primary human corneal epithelial cells (HCECs). Primary HCECs were established from donor limbal explants. The hyperosmolarity model was made in HCECs cultured in isosmolar (312 mOsM) or hyperosmotic (350, 400, 450 mOsM) media. Production of reactive oxygen species (ROS), oxidative damage markers, oxygenases and anti-oxidative enzymes were analyzed by DCFDA kit, RT-qPCR, immunofluorescent and immunohistochemical staining and Western blotting. Compared to isosmolar medium, ROS production significantly increased at time- and osmolarity-dependent manner in HCECs exposed to media with increasing osmolarities (350–450 mOsM). Hyperosmolarity significantly induced oxidative damage markers in cell membrane with increased toxic products of lipid peroxidation, 4–hydroxynonenal (4-HNE) and malondialdehyde (MDA), and in nuclear and mitochondria DNA with increased aconitase-2 and 8-OHdG. Hyperosmotic stress also increased the mRNA expression and protein production of heme oxygenase-1 (HMOX1) and cyclooxygenase-2 (COX2), but reduced the levels of antioxidant enzymes, superoxide dismutase-1 (SOD1), and glutathione peroxidase-1 (GPX1). In conclusion, our comprehensive findings demonstrate that hyperosmolarity induces oxidative stress in HCECs by stimulating ROS production and disrupting the balance of oxygenases and antioxidant enzymes, which in turn cause cell damage with increased oxidative markers in membrane lipid peroxidation and mitochondrial DNA damage.

Reactive oxygen species activated NLRP3 inflammasomes initiate inflammation in hyperosmolarity stressed human corneal epithelial cells and environment-induced dry eye patients

In studies on dry eye (DE) disease, an association has been identified between tear film hyperosmolarity and inflammation severity elicited through receptor-induced increases in proinflammatory cytokine and chemokine release. These immune reactions might be mediated by inflammasomes, macromolecular complexes mounted around the NLRP3 protein and can be activated by reactive oxygen species (ROS) over-generation. Hence in this study we determine whether: a) ROS activated NLRP3 inflammasomes mediate hyperosmotic stress-induced inflammation in human corneal epithelial cells (HCECs); b) the ROS-NLRP3-IL-1β axis activation is associated with environment-induced DE. Immortalized HCECs were exposed to 500 mOsm medium in the presence and absence of a ROS inhibitor, N-acetyl-l-cysteine (NAC). HCECs transfected with NLRP3 siRNA or a negative control (NC) siRNA. Intracellular ROS was measured by fluorometric analysis using the probe 2',7'-dichlorofluorescin diacetate (DCFH-DA). Real-time PCR evaluated NLRP3, ASC, pro-caspase-1 and pro-IL-1β mRNA levels. Western blot analysis assessed NLRP3 protein expression whereas caspase-1 activity was determined with a fluorometric assay. Bioactive IL-1β release was assessed by ELISA. ROS production, NLRP3 inflammasome and pro-IL-1β gene expression as well as IL-1β secretion were also evaluated in the conjunctival epithelial cells and tear fluid samples of environment-induced DE patients and normal subjects. NAC suppressed hyperosmolarity-induced rises in ROS levels, NLRP3 inflammasome formation and activation, caspase-1 activity and IL-1β release. On the other hand, NLRP3 siRNA knockdown inhibited hyperosmotic stress-induced NLRP3 activation, which led to ASC, pro-caspase-1 and pro-IL-1β mRNA down-regulation followed by suppression of associated caspase-1 activity and IL-1β secretion. In addition, in ocular surface samples of environment-induced DE patients, ROS generation, NLRP3, ASC, pro-caspase-1 and pro-IL-1β gene expression as well as IL-1β secretion were upregulated. Taken together, NLRP3 mediated innate immune responses triggered by rises in ROS generation induce inflammation in hyperosmotic stressed HCECs. ROS-NLRP3-IL-1β signaling pathway might play a priming role in environment-induced DE development.

Evaluation of oxidative stress levels in the conjunctival epithelium of patients with or without dry eye, and dry eye patients treated with preservative-free hyaluronic acid 0.15 % and vitamin B12 eye drops

PURPOSE

Increased levels of oxidative stress have been seen in animal models of dry eye and in the conjunctival epithelial cells of patients with Sjögren's syndrome. The aims of this study were to compare the levels of oxidative stress in patients with dry eye and patients without dry eye and to evaluate the effects of treatment with preservative-free eye drops containing hyaluronic acid 0.15 % and vitamin B12 on oxidative stress and dry eye symptoms.

METHODS

Three cohorts of patients who were to undergo planned cataract surgery were enrolled: patients with dry eye randomized to either no treatment (n = 29) or treatment (n = 32) with hyaluronic acid/vitamin B12 eye drops, and patients without dry eye (n = 42). Patients were assessed by Schirmer's type I test, fluorescein clearance test (FCT), Break Up Time (BUT), and Ocular Surface Disease Index (OSDI). Lipid peroxidation, a marker of oxidative stress, was assessed by LP-CHOLOX test.

RESULTS

Compared with patients without dry eye, patients with dry eye had significantly increased levels of oxidative stress, higher OSDI and FCT scores, and significantly lower Schirmer's test and BUT scores. Treatment with eye drops containing hyaluronic acid 0.15 % and vitamin B12 was associated with significantly reduced levels of oxidative stress and OSDI and FCT scores and significantly increased Schirmer's test and BUT scores.

CONCLUSIONS

These findings indicate that oxidative stress is associated with dry eye and that hyaluronic acid/vitamin B12 eye drops may attenuate oxidative stress and inflammation, improving dry eye symptoms. Further study in controlled clinical trials is warranted.

Osmoprotectants suppress the production and activity of matrix metalloproteinases induced by hyperosmolarity in primary human corneal epithelial cells

PURPOSE

Hyperosmolarity has been recognized as a proinflammatory stress in the pathogenesis of dry eye disease. This study investigated the suppressive effect of osmoprotectants (L-carnitine, erythritol, and betaine) on the production and activity of matrix metalloproteinases (MMPs) in primary human corneal epithelial cells (HCECs) exposed to hyperosmotic stress.

METHODS

Primary HCECs were established from fresh donor limbal tissue explants. The cultures in iso-osmolar medium (312 mOsM) were switched to hyperosmotic media with or without prior incubation with different concentrations of L-carnitine, erythritol, or betaine (2, 10, or 20 mM). The mRNA expression of the MMPs was determined with reverse transcription and quantitative real-time PCR (RT-qPCR). Protein production and activity were evaluated with immunofluorescent staining and gelatin zymography.

RESULTS

Hyperosmotic media (400, 450, or 500 mOsM) significantly stimulated mRNA expression of collagenase MMP-13, gelatinases MMP-9 and MMP-2, stromelysin MMP-3, and matrilysin MMP-7, mostly in an osmolarity-dependent fashion. The stimulated mRNA expression and protein production of these MMPs were significantly but differentially suppressed by L-carnitine, erythritol, or betaine, as evaluated with RT-qPCR and immunofluorescent staining. Interestingly, these osmoprotectants not only suppressed production but also inhibited activation of MMP-9 and MMP-2, as evaluated with gelatin zymography.

CONCLUSIONS

Our findings for the first time demonstrate that osmoprotectants, L-carnitine, erythritol, and betaine, suppress the gene expression, protein production, and enzymatic activity of MMPs in HCECs exposed to hyperosmotic stress. L-carnitine appears to have the broadest and strongest suppressive effect on these MMPs. These osmoprotectants may have potential effects in protecting ocular surface epithelia from MMP-mediated disorders in dry eye disease.

Mitochondrial oxidative stress in the retinal pigment epithelium leads to localized retinal degeneration

PURPOSE

Oxidative stress in the RPE is widely accepted as a contributing factor to AMD. We have previously shown that ribozyme-mediated reduction in the antioxidant enzyme manganese superoxide dismutase (MnSOD) leads to some of the features of geographic atrophy in mice. To develop a mouse model independent of viral injection, we used a conditional knockout of the Sod2 gene in the RPE to elevate mitochondrial oxidative stress in that cell layer.

METHODS

Experimental mice in which exon 3 of Sod2 was flanked by loxP sites were also transgenic for PVMD2-rtTA and tetO-PhCMV cre, so that cre recombinase was expressed only in the RPE. Pups of this genotype (Sod2(flox/flox)VMD2cre) were induced to express cre recombinase by feeding doxycycline-laced chow to nursing dams. Controls included mice of this genotype not treated with doxycycline and doxycycline-treated Sod2(flox/flox) mice lacking the cre transgene. Expression of cre in the RPE was verified by immunohistochemistry, and deletion of Sod2 exon 3 in the RPE was confirmed by PCR. Mice were followed up over a period of 9 months by spectral-domain optical coherence tomography (SD-OCT), digital fundus imaging, and full-field ERG. Following euthanasia, retinas were examined by light and electron microscopy or by immunohistochemistry. Contour length of rod outer segments and thickness of the RPE layer were measured by unbiased stereology.

RESULTS

Following doxycycline induction of cre, Sod2(flox/flox) cre mice demonstrated increased signs of oxidative stress in the RPE and accumulation of autofluorescent material by age 2 months. They showed a gradual decline in the ERG response and thinning of the outer nuclear layer (by SD-OCT), which were statistically significant by 6 months. In addition, OCT and electron microscopy revealed increased porosity of the choroid. At the same interval, hypopigmented foci appeared in fundus micrographs, and vascular abnormalities were detected by fluorescein angiography. By 9 months, the RPE layer in Sod2(flox/flox) cre mice was thicker than in nontransgenic littermates, and the rod outer segments were significantly longer over most of the retina, although localized atrophy of photoreceptors was also obvious in some eyes.

CONCLUSIONS

Conditional tissue-specific reduction in MnSOD induced oxidative stress in mouse RPE, leading to RPE dysfunction, damage to the choroid, and death of photoreceptor cells. The RPE oxidative stress did not cause drusen-like deposits, but the model recapitulated certain key aspects of the pathology of dry AMD and may be useful in testing therapies.

Antioxidant effect of 0.2% xanthan gum in ocular surface corneal epithelial cells

PURPOSE

Oxidative damage and inflammation are expected to be involved in age-related functional decline of lachrymal gland, that induces lachrymal dysfunction; this resulting in dry eye disease. Therefore, we investigated the potential antioxidant effect of 0.2% xanthan gum (XNT) in human corneal epithelial cells (HCE), in comparison with other widely used tear substitute polymers, such as 0.2% hydroxyethylcellulose (HEC), 0.2% hyaluronic acid (HA) and 0.5% carboxymethylcellulose (CMC).

METHODS

Subconfluent (80%) HCE (Human Corneal Epithelial) cultures were treated with the different polysaccharides at the above reported concentrations. The effect of every polymer was investigated with and without 0.5 mM H2O2 In detail, hydrogen peroxide was added 1 hour after the addition of polysaccharides. Twelve hours later, reactive oxygen species (ROS) production (dichlorofluorescein diacetate spectrofluorimetric test) was assessed and their values were normalized versus protein content. Morphological analysis was performed by optical microscopy.

RESULTS

No morphological differences in HCE compared to control cells (CTRL, cells treated with the buffer used for polymer solubilization) were observed in any of the tested polymers, whereas, in the presence of 0.5 mM H2O2 HCE clearly showed signs of cytotoxicity. Polymers did protect cultures from oxidative stress with XNT>HA = HEC>CMC, as evidenced by microscopic analysis. These results were confirmed from ROS measurements, which showed XNT as the only polysaccharide to restore the levels of ROS comparable to CTRL, in presence of H2O2.

CONCLUSIONS

0.2% xanthan gum was able to protect HCE by oxidative stress, bringing the ROS level down to CTRL values. Considering that in dry eye syndrome oxidative stress sustains inflammation and apoptotic cell death, the use of xanthan gum in ophthalmic preparations could be beneficial.

Reactive oxygen species activated NLRP3 inflammasomes prime environment-induced murine dry eye

Tear film hyperosmolarity along with exposure to oxidant stress are factors that can induce chronic ocular surface inflammation and pain. However, there is limited information on how increases in reactive oxygen species (ROS) generated by oxidant exposure can induce inflammation. There is emerging evidence in other tissues that innate immune responses to a variety of environmental stresses stem from ROS-induced cytosolic NLRP3 inflammasome activation. Once this occurs, pro-caspase-1 is converted into its catalytic active form, which in turn cleaves pro-IL-1β thereby generating its bioactive form. We determined the role of ROS generation in mediating increases in IL-1β secretion through caspase-1 activation caused by NLRP3 inflammasome activation in an environment-induced murine dry eye (DE) model. An intelligently controlled environmental system (ICES) induced evaporative DE in female 4-6 week old C57BL/6J mice. Increases in ROS production preceded rises in corneal and conjunctival gene expression of NLRP3 inflammasome components and IL-1β that were identified using real-time PCR. Confocal microscopy evaluated concomitant increases in NLPR3, caspase-1 and IL-1β immunostaining. Increases in caspase-1 activity were used as an indicator of inflammasome activation. Rises in ROS generation occurred after 1 week of ICES exposure, which preceded increases in gene expression of three NLRP3 inflammasome components (i.e. NLRP3, ASC and caspase-1) leading to rises in bioactive IL-1β release. Increases in caspase-1 activity occurred after 2 weeks of ICES exposure. Eyedrops containing 0.3% N-acetyl-l-cysteine (NAC) were applied to quench ROS generation by mice kept in the ICES for 2 weeks. This scavenger reduced corneal fluorescein staining and decreased ROS production. NAC also down-regulated both increases in NLRP3, ASC, caspase-1 and IL-1β mRNA levels, along with their immunostaining. It robustly attenuated rises in inflammasome mediated increases in caspase-1 catalytic activity. We show in a dessicating DE disease murine model that rises in ROS generation trigger NLRP3 inflammasome complexation and activation leading to increases in bioactive IL-1β secretion. These results prompt us to suggest that the ROS-NLRP3-IL-1β signaling pathway might play a priming role in environment-induced DE progression. Finally, our findings provide a basis for developing novel strategies that may improve the management of patients requiring treatment for environment-induced dry eye disease.

Genetically induced oxidative stress in mice causes thrombocytosis, splenomegaly and placental angiodysplasia that leads to recurrent abortion

Historical data in the 1950s suggests that 7%, 11%, 33%, and 87% of couples were infertile by ages 30, 35, 40 and 45, respectively. Up to 22.3% of infertile couples have unexplained infertility. Oxidative stress is associated with male and female infertility. However, there is insufficient evidence relating to the influence of oxidative stress on the maintenance of a viable pregnancy, including pregnancy complications and fetal development. Recently, we have established Tet-mev-1 conditional transgenic mice, which can express the doxycycline-induced mutant SDHC^V69E transgene and experience mitochondrial respiratory chain dysfunction leading to intracellular oxidative stress. In this report, we demonstrate that this kind of abnormal mitochondrial respiratory chain-induced chronic oxidative stress affects fertility, pregnancy and delivery rates as well as causes recurrent abortions, occasionally resulting in maternal death. Despite this, spermatogenesis and early embryogenesis are completely normal, indicating the mutation's effects to be rather subtle. Female Tet-mev-1 mice exhibit thrombocytosis and splenomegaly in both non-pregnant and pregnant mice as well as placental angiodysplasia with reduced Flt-1 protein leading to hypoxic conditions, which could contribute to placental inflammation and fetal abnormal angiogenesis. Collectively these data strongly suggest that chronic oxidative stress caused by mitochondrial mutations provokes spontaneous abortions and recurrent miscarriage resulting in age-related female infertility.

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SDHC mutation induces oxidative stress in the female reproductive organs.

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Early development is completely normal in Tet-mev-1 mice.

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Non-pregnant and pregnant Tet-mev-1 mice exhibit thrombocytosis and splenomegaly.

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Pregnant mice have placental angiodysplasia with decreased Flt-1/ VEGFR-1.

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Habitual abortion is frequently caused with occasional maternal death in Tet-mev-1 mice.

The cellular mechanisms of dry eye: from pathogenesis to treatment

Dry eye is a complex disease characterized by changes in the ocular surface epithelia related to reduced quality and/or quantity of tears, inflammatory reaction, and impairment of ocular surface sensitivity. It has recently been proposed that increased tear osmolarity represents a main trigger to the altered cellular mechanisms leading to epithelial damage in dry eye. However, dry eye pathogenesis is multifactorial, with cytotoxic inflammatory mediators, altered lacrimal gland secretion and nerve function, squamous metaplasia of the conjunctival epithelium and decrease of goblet cells density, all playing a role in a detrimental loop that perpetuates and worsens damage to the corneal and conjunctival epithelia. Current topical treatments for dry eye patients include the use of lubricants and anti-inflammatory drugs. However, lubricants only improve symptoms temporarily, and chronic use of topical steroids is associated to severe ocular side effects such as cataract and glaucoma. The deeper understanding of the cellular mechanisms that are altered in dry eye is opening novel perspectives for patients and physicians, who are seeking treatments capable not only of improving symptoms but also of restoring the homeostasis of the ocular surface. In this review, we will focus on novel anti-inflammatory agents and on nerve growth factor, a neurotrophin that is altered in dry eye and has been suggested as a main player in the neuroimmune cross-talk of the ocular surface as well as in the stimulation of corneal sensitivity, epithelial proliferation and differentiation, and stimulation of mucin production by goblet cells. J. Cell. Physiol. 228: 2253-2256, 2013. © 2013 Wiley Periodicals, Inc.

Effects of eye drops containing a mixture of omega-3 essential fatty acids and hyaluronic acid on the ocular surface in desiccating stress-induced murine dry eye

PURPOSE

To investigate the efficacy of the topical application of omega-3 essential fatty acids (EFAs) and hyaluronic acid (HA) mixtures in a mouse model of experimental dry eye (EDE).

METHODS

Eye drops consisting of 0.1% HA, 0.02%, or 0.2% omega-3 EFAs alone and mixture of 0.02%, or 0.2% omega-3 EFAs and 0.1% HA were applied in desiccating stress-induced murine dry eye. Corneal irregularity scores and fluorescein staining scores were measured 5 and 10 days after treatment. Levels of interleukin (IL)-1β, -17, and interferon gamma-induced protein (IP)-10 were measured in the conjunctiva at 10 days using a multiplex immunobead assay. The concentrations of hexanoyl-lys (HEL) and 4-hydroxynonenal (4-HNE) in conjunctiva tissue were measured with enzyme-linked immunosorbent assays.

RESULTS

Mice treated with the mixture containing 0.2% omega-3 EFAs showed a significant improvement in corneal irregularity scores and corneal fluorescein staining scores compared with EDE, HA, 0.02% or 0.2% omega-3 EFAs alone, and 0.02% omega-3 EFAs mixture-treated mice. A significant decrease in the levels of IL-1β, -17, and IP-10 were observed in the 0.2% EFAs mixture-treated group, compared with the other groups. In the mice treated with the mixture containing 0.2% omega-3 EFAs, the concentration of 4-HNE was also lower than the other groups. Although 0.2% omega-3 EFAs alone group also had a significant improvement in corneal irregularity scores and IL-17, IL-10, and 4 HNE levels compared with the other groups, the efficacy was lower than 0.2% omega-3 mixture group.

CONCLUSIONS

Topically applied eye drops containing a mixture of omega-3 EFAs and HA could improve corneal irregularity and corneal epithelial barrier disruption, and decrease inflammatory cytokines and oxidative stress markers on the ocular surface. Topical omega-3 EFAs and HA mixture may have a greater therapeutic effect on clinical signs and inflammation of dry eye compared with HA artificial tears.

Anti-inflammatory properties of kaempferol via its inhibition of aldosterone signaling and aldosterone-induced gene expression

Osteopontin (OPN), also called cytokine Eta-1, is a pro-inflammatory cytokine. Recent studies have shown that aldosterone increases OPN gene expression in endothelial cells. As a flavonoid compound, kaempferol has potent anti-inflammatory properties, but whether kaempferol regulates aldosterone signaling and aldosterone-induced gene expression is still unknown. Human umbilical vein endothelial cells (HUVECs) were pretreated with kaempferol (0, 1, 3, or 10 μmol/L) for 1 h prior to exposure to aldosterone (10−6 mol/L) for 24 h. Aldosterone induced generation of reactive oxygen species; OPN and cluster of differentiation 44 gene expression; phospho-p38 MAPK and NF-κB binding activity. The effect of aldosterone was abrogated by kaempferol and spironolactone (10−6 mol/L). The present results suggest that kaempferol exerts its anti-inflammatory properties via its inhibition of aldosterone signaling and aldosterone-induced gene expression in HUVECs.

Is household air pollution a risk factor for eye disease?

In developing countries, household air pollution (HAP) resulting from the inefficient burning of coal and biomass (wood, charcoal, animal dung and crop residues) for cooking and heating has been linked to a number of negative health outcomes, mostly notably respiratory diseases and cancers. While ocular irritation has been associated with HAP, there are sparse data on adverse ocular outcomes that may result from acute and chronic exposures. We consider that there is suggestive evidence, and biological plausibility, to hypothesize that HAP is associated with some of the major blinding, and painful, eye conditions seen worldwide. Further research on this environmental risk factor for eye diseases is warranted.

Prevalence of dry eye disease and its risk factors in visual display terminal users: the Osaka study

PURPOSE

To investigate tear function and prevalence of dry eye disease (DED) in visual display terminal (VDT) users.

DESIGN

Cross-sectional study.

METHODS

Six hundred and seventy-two young and middle-aged Japanese office workers who used VDT completed questionnaires and underwent dry eye testing. We estimated the prevalence of DED using logistic regression analysis to examine associations between DED and possible risk factors. The ocular surface feature, prevalence of DED, and risk factors were evaluated.

RESULTS

Of the 672 workers, 561 (83.5%, mean age: 43.3 ± 9.1 years) completed the questionnaire. The percentage of women with a composite outcome of definite DED or probable DED was 76.5%, which was higher than that among men (60.2%; odds ratio [OR] = 2.00; 95% confidence interval [CI], 1.29-3.10, P = .002). Workers over 30 years of age had a higher risk of DED (OR = 2.22; 95% CI, 1.06-4.66), as did workers using a VDT >8 hours per day (OR = 1.94; 95% CI, 1.22-3.09). Average Schirmer value was 18.7 ± 11.7 mm and tear break-up time (TBUT) was 4.0 ± 2.5 seconds (78.6% of study participants had TBUT ≤5 seconds).

CONCLUSIONS

DED is prevalent among young to middle-aged Japanese VDT users. Ophthalmic findings revealed short TBUT and corneal staining accompanied by normal Schirmer test values. Increased risk for DED was noted for women aged over 30 years and prolonged VDT use. Measures to modify the adverse impact of VDT use on the ocular surface may provide a positive impact on public health and quality of life for office workers using VDTs.