Dry eye and delayed tear clearance: "a call to arms."

Dry eye disease in astronauts: a narrative review

Long-duration spaceflight can have adverse effects on human health. One of the most common ocular conditions experienced by astronauts is dry eye disease (DED). Symptoms of DED include feelings of eye irritation, eye strain, foreign body sensation and blurred vision. Over 30% of International Space Station expedition crew members reported irritation and foreign body sensation. We reviewed the current literature on the prevalence and mechanisms of DED in astronauts and its potential implications for long-duration spaceflight, including the influence of environmental factors, such as microgravity and fluid shift on tear film physiology in space. DED has negative effects on astronaut performance, which is why there is a need for further research into the pathophysiology and countermeasures. As an in-flight countermeasure, neurostimulation seems to be among the most promising options.

The Ins and Outs of Clusterin: Its Role in Cancer, Eye Diseases and Wound Healing

Clusterin (CLU) is a glycoprotein originally discovered in 1983 in ram testis fluid. Rapidly observed in other tissues, it was initially given various names based on its function in different tissues. In 1992, it was finally named CLU by consensus. Nearly omnipresent in human tissues, CLU is strongly expressed at fluid-tissue interfaces, including in the eye and in particular the cornea. Recent research has identified different forms of CLU, with the most prominent being a 75-80 kDa heterodimeric protein that is secreted. Another truncated version of CLU (55 kDa) is localized to the nucleus and exerts pro-apoptotic activities. CLU has been reported to be involved in various physiological processes such as sperm maturation, lipid transportation, complement inhibition and chaperone activity. CLU was also reported to exert important functions in tissue remodeling, cell-cell adhesion, cell-substratum interaction, cytoprotection, apoptotic cell death, cell proliferation and migration. Hence, this protein is sparking interest in tissue wound healing. Moreover, CLU gene expression is finely regulated by cytokines, growth factors and stress-inducing agents, leading to abnormally elevated levels of CLU in many states of cellular disturbance, including cancer and neurodegenerative conditions. In the eye, CLU expression has been reported as being severely increased in several pathologies, such as age-related macular degeneration and Fuch's corneal dystrophy, while it is depleted in others, such as pathologic keratinization. Nevertheless, the precise role of CLU in the development of ocular pathologies has yet to be deciphered. The question of whether CLU expression is influenced by these disorders or contributes to them remains open. In this article, we review the actual knowledge about CLU at both the protein and gene expression level in wound healing, and explore the possibility that CLU is a key factor in cancer and eye diseases. Understanding the expression and regulation of CLU could lead to the development of novel therapeutics for promoting wound healing.

Therapeutic Effects of Acer palmatum Thumb. Leaf Extract (KIOM-2015E) on Benzalkonium Chloride-Induced Dry Eye in a Mouse Model

We determined the effects of two extracts from Acer palmatum Thumb. leaves (hot water extract KIOM-2015EW and 25% ethanol extract KIOM-2015EE) in a benzalkonium chloride (BAC)-induced dry eye mouse model. Dry eye was induced by 0.2% BAC for 2 weeks, followed by treatment three times (eye drop) or once (oral administration) daily with KIOM-2015E for 2 weeks. Treatment with both KIOM-2015EE and KIOM-2015EW resulted in a marked increase in tear volume production for the 4 days of treatment. The Lissamine Green staining score, TUNEL-positive cells, and inflammatory index were significantly decreased after 2 weeks. Topical KIOM-2015EE administration exhibited a greater improvement in decreasing the ocular surface staining scores, inflammation, dead cells, and increasing tear production in a dose-dependent manner compared with the other groups. Furthermore, KIOM-2015E significantly reduced the phosphorylation of NF-κB, which was activated in the BAC-treated cornea. Topical administration was much more effective than oral administration for KIOM-2015E and KIOM-2015EE was more effective than KIOM-2015EW. Application of KIOM-2015E resulted in clinical improvement, inhibited the inflammatory response, and alleviated signs of dry eye. These results indicate that KIOM-2015E has potential as a therapeutic agent for the clinical treatment of dry eye.

Tear protein analysis in patients with primary acquired nasolacrimal duct obstruction treated with lacrimal passage intubation

PURPOSE

The pathophysiology of nasolacrimal duct obstruction (NLDO) may involve quantitative as well as qualitative changes in tears. We measured tear protein concentrations in patients with primary acquired NLDO and compared them with the tear proteins in healthy individuals and patients with dry eye disease.

STUDY DESIGN

Case-control study.

METHODS

Twenty-four patients diagnosed with primary acquired NLDO who underwent endoscopic lacrimal passage intubation were included in the study. Tear fluid was collected with Schirmer's test strips three times: before intubation, after intubation while the nasolacrimal tube was in place, and after extubation. At the same time, 24 age-matched normal controls and 24 patients with dry eye were selected from subjects whose tears were collected during the same study period. We measured the following components of tear fluid: total protein, lactoferrin, albumin, and interleukin 6 (IL-6) levels.

RESULTS

Total proteins and albumin levels in tears of the NLDO group were significantly lower than those of the control group (P < 0.001 and P = 0.014, respectively, Mann-Whitney U test). Total proteins, albumin, and lactoferrin levels were significantly increased after extubation of nasolacrimal tube (P < 0.001, P = 0.004, and P = 0.029, respectively, Wilcoxon matched-pairs signed-rank test). There were no statistically significant differences in total protein, albumin, lactoferrin and IL-6 levels between patients with NLDO after lacrimal passage extubation and controls.

CONCLUSIONS

Our study shows distinct differences in protein composition of tear fluid in NLDO eyes and demonstrates that these can be normalized by nasolacrimal tube placement.

Therapeutic Potential of the Molecular Chaperone and Matrix Metalloproteinase Inhibitor Clusterin for Dry Eye

Evidence is presented herein supporting the potential of the natural homeostatic glycoprotein CLU (clusterin) as a novel therapeutic for the treatment of dry eye. This idea began with the demonstration that matrix metalloproteinase MMP9 is required for damage to the ocular surface in mouse dry eye. Damage was characterized by degradation of OCLN (occludin), a known substrate of MMP9 and a key component of the paracellular barrier. Following up on this finding, a yeast two-hybrid screen was conducted using MMP9 as the bait to identify other proteins involved. CLU emerged as a strong interacting protein that inhibits the enzymatic activity of MMP9. Previously characterized as a molecular chaperone, CLU is expressed prominently by epithelia at fluid-tissue interfaces and secreted into bodily fluids, where it protects cells and tissues against damaging stress. It was demonstrated that CLU also protects the ocular surface in mouse dry eye when applied topically to replace the natural protein depleted from the dysfunctional tears. CLU is similarly depleted from tears in human dry eye. The most novel and interesting finding was that CLU binds selectively to the damaged ocular surface. In this position, CLU protects against epithelial cell death and barrier proteolysis, and dampens the autoimmune response, while the apical epithelial cell layer is renewed. When present at high enough concentration, CLU also blocks staining by vital dyes used clinically to diagnose dry eye. None of the current therapeutics have this combination of properties to "protect, seal, and heal". Future work will be directed towards human clinical trials to investigate the therapeutic promise of CLU.

Tear cytokine profiling in patients with superior limbic keratoconjunctivitis who underwent medical treatment or in conjunction with surgical management

Purpose

To determine the correlation between superior limbic keratoconjunctivitis (SLK) and selected tear cytokines and to evaluate the efficacy of these cytokines in monitoring the response of patients with SLK to either medical treatment alone or in combination with conjunctival resection.

Design

A cohort study.

Methods

Twenty-five eyes of 13 patients with SLK were assigned to either medically responsive or surgical treatment groups depending on their responses 1 month after initial medical treatment. Treatment efficacy was assessed by improvements in clinical grading and decreases in the levels of tear cytokines.

Results

Fourteen eyes were improved by medical treatment alone, whereas satisfactory outcomes were achieved for the remaining 11 eyes after surgical management. The overall grading prior to medical treatment was lower in medically responsive group compared with surgical treatment group (p=0.0139). Among the examined tear cytokines, monocyte chemoattractant protein (MCP)-1 was positively associated with the severity of clinical grading (p=0.0251). While both treatments significantly decreased the levels of MCP-1 and interleukin-6, surgical treatment also decreased the levels of interferon-γ and tumour necrosis factor-α. Notably, overall cytokine levels after surgical treatment were lower than those after medical treatment alone.

Conclusions

Since an association of tear MCP-1 level with the clinical grading and treatment response of SLK was observed in this study, tear MCP-1 may be a potential indicator of SLK disease severity. According to the degree to which the tear cytokine levels were decreased, surgical treatment appears to be an effective treatment modality for patients with SLK who are refractory to medical treatment alone.

Diadenosine tetraphosphate contributes to carbachol-induced tear secretion

The purpose of this study is to investigate if the cholinergic stimulation by carbachol on tear secretion is a direct process or if it is also mediated by purinergic mechanisms. Experiments were performed in New Zealand male rabbits. The amount of tear secretion was measured with Schirmer's test and then analyzed by a HPLC protocol in order to study the nucleotide levels. Animal eyes were instilled with carbachol (a cholinergic agonist), pirenzepine, gallamine and 4-DAMP (muscarinic antagonists), PPADS, suramin and reactive blue 2 (purinergic antagonists), and a P2Y2 receptor small interfering RNA (siRNA). Tear secretion increased with the instillation of carbachol, approximately 84 % over control values 20 min after the instillation and so did Ap4A and ATP release. When we applied carbachol in the presence of muscarinic antagonists, tear volume only increased to 4 % with atropine, 12 % in the case of pirenzepine, 3 % with gallamine, and 8 % with 4-DAMP. In the presence of carbachol and purinergic antagonists, tear secretion was increased to 12 % (all values compared to basal tear secretion). By analyzing tear secretion induced with carbachol in presence of a P2Y2 receptor siRNA, we found that tear secretion was diminished to 60 %. The inhibition of tear secretion in the presence of carbachol and purinergic antagonists or P2Y2 siRNA occurred with no apparent change in the tear amount of Ap4A. These experiments demonstrated the participation of Ap4A in lacrimal secretion process.

Dry eye disease and microbial keratitis: is there a connection?

Dry eye is a common ocular surface disease of multifactorial etiology characterized by elevated tear osmolality and inflammation leading to a disrupted ocular surface. The latter is a risk factor for ocular surface infection, yet overt infection is not commonly seen clinically in the typical dry eye patient. This suggests that important innate mechanisms operate to protect the dry eye from invading pathogens. This article reviews the current literature on epidemiology of ocular surface infection in dry eye patients and laboratory-based studies on innate immune mechanisms operating at the ocular surface and their alterations in human dry eye and animal models. The review highlights current understanding of innate immunity in dry eye and identifies gaps in our knowledge to help direct future studies to further unravel the complexities of dry eye disease and its sequelae.

High expression of macrophage migration inhibitory factor in the murine lacrimal gland

PURPOSE

To report the expression of macrophage migration inhibitory factor (MIF) in murine lacrimal glands.

METHODS

Six lacrimal glands from 3 female 8-week-old CBA/J mice were analyzed using a gene microarray method (Oligo GEArray mouse inflammatory cytokines and receptors, Catalog No. OMM-011, SuperArray Bioscience) and immunofluorescent staining for MIF. Nine lacrimal glands from 8-week-old CBA/J mice, 9 lacrimal glands from 8-week-old C57BL/6 mice, and 7 lacrimal glands from 8-week-old BALB/c mice were analyzed using real-time reverse transcription-polymerase chain reaction. Five spleens, 5 livers, and 5 serum samples from 5 female 8-week-old CBA/J mice were analyzed using enzyme-linked immunosorbent assay.

RESULTS

Microarray analysis revealed that MIF is highly expressed in the murine lacrimal gland. Lacrimal acinar cells stain strongly with anti-MIF antibodies. Real-time reverse transcription-polymerase chain reaction revealed that the MIF mRNA expression level is lower in lacrimal glands of CBA/J mice compared with C57BL/6 and BALB/c mice when normalized against the expression of beta-actin mRNA. Enzyme-linked immunosorbent assay revealed that MIF level was higher in lacrimal glands and spleens compared with livers and sera.

CONCLUSION

The murine lacrimal gland expresses high levels of macrophage MIF without any evidence of lacrimal gland inflammation.

Long-term topical cyclosporine treatment improves tear production and reduces keratoconjunctivitis in rabbits with induced autoimmune dacryoadenitis

PURPOSE

To use a rabbit model of induced autoimmune dacryoadenitis to evaluate the efficacy of topical ophthalmic cyclosporine A (CsA).

METHODS

Autoimmune dacryoadenitis was induced by injecting autologous peripheral blood lymphocytes, which had been activated in a mixed cell reaction with acinar cells isolated from one inferior lacrimal gland (LG), back into the donor animal's remaining inferior LG. Schirmer's test, tear breakup time, and rose Bengal staining were assessed. Animals with established disease were treated topically with either CsA or Endura twice daily for 5 months.

RESULTS

Without treatment tear production and tear stability were abnormal for 6 months, and clear signs of ocular surface defects were evident. Severe immune cell infiltration was observed in the LG. Long-term CsA treatment increased tear production only slightly, but the severity of LG histopathology decreased noticeably. CD4(+) T-cell infiltration of the LG was decreased and infiltration by MHC class II-expressing cells was also decreased. For the Endura-treated group tear production did not improve, rose Bengal scores remained high, and histopathology showed infiltration comparable to the untreated group, but by the end of the study the tear breakup time did improve.

CONCLUSIONS

The rabbit model of autoimmune dacryoadenitis had signs of chronic dry eye disease 6 months after induction of disease. Tear production improved slightly with CsA treatment and CD4(+) T-cell infiltration decreased significantly in the LG. This suggests that some Sjögren's patients may benefit from long-term CsA treatment.

Vasomotor (perennial chronic) conjunctivitis

PURPOSE OF REVIEW

To increase the awareness of nonimmunoglobulin E-mediated conjunctival disorders similar to those recognized to affect other organs that are targets in immunoglobulin E-mediated disorders. Such conditions may include 'vasomotor' instability, that is vasomotor conjunctivitis, which leads to a more common perennial chronic conjunctivitis. These conditions are not commonly included in the differential diagnosis of allergic conjunctivitis.

RECENT FINDINGS

Although there have not been specific recent findings regarding the eye, it appears that evidence for such disorders in the rhinitis literature suggests that they can be involved in more than 25% of chronic conjunctivitis cases. The extrapolation of such conditions to the conjunctival surface clearly reflects these syndromes which have clearly been underappreciated and underdiagnosed.

SUMMARY

A significant amount of work remains to be performed to understand perennial chronic conjunctivitis (vasomotor conjunctivitis or nonallergic noninfectious conjunctivitis) as well as other forms of chronic conjunctivitis that can mimic or exist in a comorbid state with ocular allergy. These disorders need to be better defined, categorized and classified to determine the best treatment modalities. Management guidelines and parameters of chronic noninfectious conjunctivitis need to be set on a national and international basis that will advance clinically applicable research results, pharmaceutical development and relief for patients.

Haze after photorefractive keratectomy caused by iatrogenic lagophthalmos

A 22-year-old man had shortening of the levator muscle for a congenital blepharoptosis in the right eye in 2000. In September 2004, he was successfully treated by bilateral photorefractive keratectomy (PRK) for myopia and was asymptomatic with an uncorrected visual acuity of 20/20. In October 2005, right eye visual acuity decreased because of an inferiorly localized haze caused by nocturnal lagophthalmos. Fluorometholone eyedrops and lubrication induced full visual recovery after 2 months, but corresponding topographical abnormalities were only partially improved. Corneal exposure can induce haze after PRK, even in the long term. The efficacy of topical steroids indicates a role for inflammatory mediators in this condition. Eyelid position and dynamics must be evaluated before PRK to rule out lagophthalmos.

Hyperosmolar Saline Is a Proinflammatory Stress on the Mouse Ocular Surface

PURPOSE

To investigate whether hyperosmolar stress stimulates production of inflammatory mediators and activates the mitogen-activated protein kinase (MAPK) signaling pathways, c-jun n-terminal kinases (JNKs), extracellular-regulated kinases (ERKs), and p38 on the mouse ocular surface.

METHODS

129SvEv/CD-1 mixed mice were treated with a balanced salt solution (BSS) (305 mOsM) or a hyperosmotic saline solution (HOSS) (500 mOsM). Untreated age-matched mice were used as controls. The concentrations of interleukin 1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) were measured by enzyme-linked immunosorbent assay. Gelatinase activity was determined by in situ zymography. Corneal and conjunctival epithelia were lysed for Western blot with MAPK antibodies or used for semiquantitative reverse transcription and polymerase chain reaction and gene array.

RESULTS

Compared with age-matched controls and mice treated with BSS, the concentration of IL-1beta in tear fluid washings and the concentrations of IL-1beta and TNF-alpha and gelatinolytic activity in the corneal and conjunctival epithelia were significantly increased in mice treated with HOSS for 2 days. The expressions of IL-1beta, TNF-alpha, and matrix metalloproteinase 9 (MMP-9) messenger RNA by the corneal and conjunctival epithelia were also notably stimulated in mice treated with HOSS. The levels of phosphorylated JNK1/2, ERK1/2, and p38 MAPKs in the corneal and conjunctival epithelia were slightly increased in mice treated with BSS, but markedly increased in mice treated with HOSS.

CONCLUSIONS

These results show that the hyperosmolarity stimulates expression and production of IL-1beta, TNF-alpha, and MMP-9 and activates JNK, ERK, and p38 MAPK signaling pathways on the mouse ocular surface. These findings suggest that hyperosmolar stress, as it may occur in dry eye, promotes ocular surface inflammation.