Interaction of EGF family growth factors and neurotransmitters in regulating lacrimal gland secretion

New-onset keratitis associated with epidermal growth factor receptor-based targeted therapies in Han Chinese patients with lung cancer: A multi-center cohort study

PURPOSE

To determine the risk and incidence of keratitis following treatment with epidermal growth factor receptor inhibitors (EGFRi) and subtypes of EGFRi-associated keratitis.

METHODS

This multi-center cohort study included EGFRi-treated patients and non-users with lung cancer between 2010 and 2023. EGFRi included first-generation agent gefitinib and erlotinib, second-generation agent afatinib, and third-generation agent osimertinib. The primary outcome was new-onset keratitis. Cox proportional hazard models with multivariable adjustment were applied to determine the effect of EGFRi on keratitis over time. Subgroup analyses were conducted, stratified by agents of EGFRi. Sub-outcome analyses were performed to identify the subtypes of EGFRi-associated keratitis.

RESULTS

A total of 1549 EGFRi-treated patients and 6146 non-users were included. 38 (2.5%) EGFRi-treated patients developed keratitis. The incidence of keratitis in EGFRi-treated patients was significantly higher than that in controls (incidence rate, IR, per 1000 person-years = 14.7 vs 4.49, p < 0.0001). EGFRi-treated patients presented with an increased risk for keratitis (adjusted hazard ratio, aHR = 3.14, 95% CI = 1.85-5.35, p < 0.001). Erlotinib (aHR = 2.64, 95% CI = 1.35-5.15, p = 0.004), afatinib (aHR = 4.42, 95% CI = 2.17-9.02, p < 0.001), and osimertinib (aHR = 4.67, 95% CI = 1.60-13.64, p = 0.005), but not gefitinib (aHR = 2.30, 95% CI = 0.96-5.55, p = 0.063), significantly contributed to the risk of keratitis. Subtypes of EGFRi-associated keratitis included corneal ulcer (IR = 2.31 vs 0.166, p < 0.0001) and keratoconjunctivitis (IR = 9.27 vs 2.91, p < 0.0001). None of the EGFRi-treated patients developed perforated corneal ulcer, interstitial and deep keratitis, or corneal neovascularization.

CONCLUSION

Treatment with EGFRi was associated with an increased risk of keratitis. Ocular toxicity of EGFRi was highest for third-generation agents, followed by second-generation agents, and then first-generation agents.

Tear α-synuclein as a biomarker for Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Parkinson's disease symptoms mostly manifest after significant and irreversible neuropathology. Hence, there is a need to identify biomarkers that can provide indications of disease before significant neuronal degeneration occurs.

OBJECTIVE

To estimate the difference in the concentration of α-synuclein protein in tears between individuals with Parkinson's disease and healthy controls.

DATA SOURCES

PubMed, Scopus, and Web of Science. The last database search was on December 20, 2023.

STUDY ELIGIBILITY CRITERIA

Primary prospective studies in humans measuring the level of α-synuclein in tears and clinical outcomes reported using mean or median.

PARTICIPANTS AND INTERVENTIONS

Individuals with Parkinson's disease and healthy controls.

STUDY APPRAISAL AND SYNTHESIS METHODS

The risk of bias was assessed using the Newcastle-Ottawa Scale. The I2 statistic was used to estimate heterogeneity. The outcome measure was the difference in tear total and oligomeric α-synuclein. Mean difference (MD) was used to assess the outcome. The certainty of evidence was rated following the Grading of Recommendations Assessment and Development and Evaluation (GRADE) system.

RESULTS

Three hundred twenty-seven Parkinson's disease and 312 healthy control subjects from five studies and 177 Parkinson's disease and 166 healthy control subjects from two studies were included in total α-synuclein levels and oligomeric α-synuclein levels analysis, respectively. Total α-synuclein level was not different between Parkinson's disease and healthy controls (MD = 0.02 ng/mL [95% confidence interval {CI}: 0.00 to 0.05 ng/mL; I2 = 90%; Z = 1.79; p=0.07; number of studies = 5; GRADE rating = very low]). Stratifying the data based on disease duration, total α-synuclein was higher in subjects with Parkinson's disease duration ≥7 years compared with healthy controls (MD = 0.04 ng/mL [95% CI: 0.03 to 0.05 ng/mL; I2 = 0%; Z = 8.24, p<0.00001; number of studies = 2; GRADE rating = low]) but not different between the two groups (MD = -0.12 ng/mL (95% CI: -0.38 to 0.15 ng/mL; I2 = 93%; Z = 0.84, p=0.40; number of studies = 3; GRADE rating = very low]). Oligomeric α-synuclein level was higher in Parkinson's disease compared with controls (MD = 6.50 ng/mL [95% CI: 2.79 to 10.20 ng/mL; I2 = 94%; Z = 3.44; p=0.0006; number of studies = 2; GRADE rating = very low]).

LIMITATIONS

High heterogeneity between studies. Potential sources of heterogeneity could not be explored due to the limited number of studies.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

Tear α-synuclein has the potential to be a noninvasive biomarker for Parkinson's disease. Studies are, however, needed to increase certainty in the biomarker and establish how the protein's changes in tears correlate with Parkinson's disease progression and severity.

Regulation of Axon Guidance by Slit2 and Netrin-1 Signaling in the Lacrimal Gland of Aqp5 Knockout Mice

Purpose

Dry eye disease (DED) is multifactorial and associated with nerve abnormalities. We explored an Aquaporin 5 (AQP5)-deficiency-induced JunB activation mechanism, which causes abnormal lacrimal gland (LG) nerve distribution through Slit2 upregulation and Netrin-1 repression.

Methods

Aqp5 knockout (Aqp5-/-) and wild-type (Aqp5+/+) mice were studied. LGs were permeabilized and stained with neuronal class III β-tubulin, tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP). Whole-mount images were acquired through tissue clearing and 3D fluorescence imaging. Mouse primary trigeminal ganglion (TG) neurons were treated with LG extracts and Netrin-1/Slit2 neutralizing antibody. Transcription factor (TF) prediction and chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR) experiments verified the JunB binding and regulatory effect on Netrin-1 and Slit2.

Results

Three-dimensional tissue and section immunofluorescence showed reduced LG nerves in Aqp5-/- mice, with sympathetic and sensory nerves significantly decreased. Netrin-1 was reduced and Slit2 increased in Aqp5-/- mice LGs. Aqp5+/+ mice LG tissue extracts (TEs) promoted Aqp5-/- TG neurons axon growth, but Netrin-1 neutralizing antibody (NAb) could inhibit that promotion. Aqp5-/- mice LG TEs inhibited Aqp5+/+ TG axon growth, but Slit2 NAb alleviated that inhibition. Furthermore, JunB, a Netrin-1 and Slit2 TF, could bind them and regulate their expression. SR11302, meanwhile, reversed the Netrin-1 and Slit2 shifts caused by AQP5 deficiency.

Conclusions

AQP5 deficiency causes LG nerve abnormalities. Persistent JunB activation, the common denominator for Netrin-1 suppression and Slit2 induction, was found in Aqp5-/- mice LG epithelial cells. This affected sensory and sympathetic nerve fibers' distribution in LGs. Our findings provide insights into preventing, reversing, and treating DED.

Development of high-throughput lacrimal gland organoid platforms for drug discovery in dry eye disease

Dysfunction and damage of the lacrimal gland (LG) results in ocular discomfort and dry eye disease (DED). Current therapies for DED do not fully replenish the necessary lubrication to rescue optimal vision. New drug discovery for DED has been limited perhaps because in vitro models cannot mimic the biology of the native LG. The existing platforms for LG organoid culture are scarce and still not ready for consistency and scale up production towards drug screening. The magnetic three-dimensional (3D) bioprinting (M3DB) is a novel system for 3D in vitro biofabrication of cellularized tissues using magnetic nanoparticles to bring cells together. M3DB provides a scalable platform for consistent handling of spheroid-like cell cultures facilitating consistent biofabrication of organoids. Previously, we successfully generated innervated secretory epithelial organoids from human dental pulp stem cells with M3DB and found that this platform is feasible for epithelial organoid bioprinting. Research targeting LG organogenesis, drug discovery for DED has extensively used mouse models. However, certain inter-species differences between mouse and human must be considered. Porcine LG appear to have more similarities to human LG than the mouse counterparts. We have conducted preliminary studies with the M3DB for fabricating LG organoids from primary cells isolated from murine and porcine LG, and found that this platform provides robust LG organoids for future potential high-throughput analysis and drug discovery. The LG organoid holds promise to be a functional model of tearing, a platform for drug screening, and may offer clinical applications for DED.

Glaucoma: Management and Future Perspectives for Nanotechnology-Based Treatment Modalities

Glaucoma, being asymptomatic for relatively late stage, is recognized as a worldwide cause of irreversible vision loss. The eye is an impervious organ that exhibits natural anatomical and physiological barriers which renders the design of an efficient ocular delivery system a formidable task and challenge scientists to find alternative formulation approaches. In the field of glaucoma treatment, smart delivery systems for targeting have aroused interest in the topical ocular delivery field owing to its potentiality to oppress many treatment challenges associated with many of glaucoma types. The current momentum of nano-pharmaceuticals, in the development of advanced drug delivery systems, hold promises for much improved therapies for glaucoma to reduce its impact on vision loss. In this review, a brief about glaucoma; its etiology, predisposing factors and different treatment modalities has been reviewed. The diverse ocular drug delivery systems currently available or under investigations have been presented. Additionally, future foreseeing of new drug delivery systems that may represent potential means for more efficient glaucoma management are overviewed. Finally, a gab-analysis for the required investigation to pave the road for commercialization of ocular novel-delivery systems based on the nano-technology are discussed.

Tears - more to them than meets the eye: why tears are a good source of biomarkers in Parkinson's disease

Tears are a known source of biomarkers for both ocular and systemic diseases with particular advantages; specifically, the noninvasiveness of sample collection and a unique and increasingly better-defined protein composition. Here, we discuss our rationale for use of tears for discovery of biomarkers for Parkinson's disease (PD). These reasons include literature supporting changes in tear flow and composition in PD, and the interconnections between the ocular surface system and neurons affected in PD. We highlight recent data on the identification of tear biomarkers including oligomeric α-synuclein, associated with neuronal degeneration in PD, in tears of PD patients and discuss possible sources for its release into tears. Challenges and next steps for advancing such biomarkers to clinical usage are highlighted.

Achyranthis radix Extract Improves Urban Particulate Matter-Induced Dry Eye Disease

Dry eye disease (DED) is a multifactorial inflammatory disease that severely impairs patients' quality of life. Particulate matter comprises a harmful mixture of particles less than 10 μm in size, which on contact with the eye, causes inflammation in the cornea/conjunctival epithelium, threatening eye health and triggering the onset of DED. Achyranthis radix is an ingredient of traditional medicine generally used for treating osteoporosis, trauma, and thrombosis in Asian countries. However, the effect of Achyranthis radix on eye health has not been elucidated. In this study, we evaluate the protective effect of Achyranthis radix hot water extract (ARE) in a rat model of urban particulate matter (UPM)-induced DED. UPM with or without ARE were topically administered on both eyes thrice daily for 10 days. ARE induced tear secretion and improved corneal irregularity. Additionally, ARE treatment protected the corneal epithelial cells from UPM-induced apoptosis. It also restored rMuc4 expression in the cornea and increased goblet cell density in the conjunctiva. These results are suggestive of the potential of ARE as a topical therapeutic agent for treating DED.

Oligomeric α-synuclein is increased in basal tears of Parkinson's patients

Aim: Secretion of proteins into basal tears of Parkinson's disease (PD) patients may be altered by changes in nerve function. Materials & methods: Oligomeric α-Syn_Oligo and total α-Syn_Total, CCL-2, DJ-1, LF and MMP-9 were measured in basal tears from 93 PD patients and 82 age- and sex-equivalent healthy controls. Results: α-Syn_Total was decreased (p = 0.0043), whereas α-Syn_Oligo (p < 0.0001) and the ratio of α-Syn_Oligo/α-Syn_Total (p < 0.0001) were increased in basal tears from PD patients compared with healthy controls. Area under receiver-operating curves of α-Syn_Oligo and α-Syn_Oligo/α-Syn_Total contents were 0.70 (95% confidence limits: 0.621-0.774) and 0.72 (95% confidence limits: 0.642-0.792). Conclusion: PD patient basal tears may contain biomarkers that can be assayed noninvasively and inexpensively.

Goblet cells: multifaceted players in immunity at mucosal surfaces

Goblet cells (GCs) are specialized epithelial cells that line multiple mucosal surfaces and have a well-appreciated role in barrier maintenance through the secretion of mucus. Moreover, GCs secrete anti-microbial proteins, chemokines, and cytokines demonstrating functions in innate immunity beyond barrier maintenance. Recently it was appreciated that GCs can form goblet cell-associated antigen passages (GAPs) and deliver luminal substances to underlying lamina propria (LP) antigen-presenting cells (APCs) in a manner capable of inducing adaptive immune responses. GCs at other mucosal surfaces share characteristics with the GAP forming intestinal GCs, suggesting that GAP formation may not be restricted to the gut, and that GCs may perform this gatekeeper function at other mucosal surfaces. Here we review observations of how GCs contribute to immunity at mucosal surfaces through barrier maintenance, the delivery of luminal substances to APCs, interactions with APCs, and secretion of factors modulating immune responses.

Comprehensive Proteomic Profiling of Patients' Tears Identifies Potential Biomarkers for the Traumatic Vegetative State

The vegetative state is a complex condition with unclear mechanisms and limited diagnostic, prognostic, and therapeutic methods. In this study, we aimed to explore the proteomic profile of tears from patients in a traumatic vegetative state and identify potential diagnostic markers using tears-a body fluid that can be collected non-invasively. Using iTRAQ quantitative proteomic technology, in the discovery phase, tear samples collected from 16 patients in a traumatic vegetative state and 16 normal individuals were analyzed. Among 1080 identified tear proteins, 57 were upregulated and 15 were downregulated in the patients compared to the controls. Bioinformatics analysis revealed that the differentially-expressed proteins were mainly involved in the wound response and immune response signaling pathways. Furthermore, we verified the levels of 7 differentially-expressed proteins in tears from 50 traumatic vegetative state patients and 50 normal controls (including the samples used in the discovery phase) using ELISA. The results showed that this 7-protein panel had a high discrimination ability for traumatic vegetative state (area under the curve = 0.999). In summary, the altered tear proteomic profile identified in this study provides a basis for potential tear protein markers for diagnosis and prognosis of the traumatic vegetative state and also provides novel insights into the mechanisms of traumatic vegetative state.

Runx1 mediates the development of the granular convoluted tubules in the submandibular glands

The mouse granular convoluted tubules (GCTs), which are only located in the submandibular gland (SMG) are known to develop and maintain their structure in an androgen-dependent manner. We previously demonstrated that the GCTs are involuted by the epithelial deletion of core binding factor β (CBFβ), a transcription factor that physically interacts with any of the Runt-related transcription factor (RUNX) proteins (RUNX1, 2 and 3). This result clearly demonstrates that the Runx /Cbfb signaling pathway is indispensable in the development of the GCTs. However, it is not clear which of the RUNX proteins plays useful role in the development of the GCTs by activating the Runx /Cbfb signaling pathway. Past studies have revealed that the Runx /Cbfb signaling pathway plays important roles in various aspects of development and homeostatic events. Moreover, the Runx genes have different temporospatial requirements depending on the biological situation. In the present study, the GCTs of the SMG showed a remarkable phenotype of, which phenocopied the epithelial deletion of Cbfb, in epithelial-specific Runx1 conditional knock-out (cKO) mice. The results indicate that Runx1 works as a partner of Cbfb during the development of the GCTs. We also discovered that the depletion of Runx1 resulted in the reduced secretion of saliva in male mice. Consistent with this finding, one of the water channels, Aquaporin-5 (AQP5) was mislocalized in the cytoplasm of the Runx1 mutants, suggesting a novel role of Runx1 in the membrane trafficking of AQP5. In summary, the present findings demonstrated that RUNX1 is essential for the development of the GCTs. Furthermore, RUNX1 could also be involved in the membrane trafficking of the AQP5 protein of the acinar cells in the SMG in order to allow for the proper secretion of saliva.

Evaluation of commonly used tear sampling methods and their relevance in subsequent biochemical analysis

The human precorneal tear film is a special body fluid, since it is a complex mixture of proteins, lipids, small bioactive molecules, and their concentrations and relative distribution represent not only the metabolic state of the ocular surface but also the systemic and local homeostasis of the outer eye and the human body. This suggests that biochemical analysis of the precorneal tear film composition may provide a non-invasive tool for diagnosis and monitoring of disease progression or treatment efficacy in human medicine. However, collecting tears is demanding, and obtaining reproducible and unaltered samples is challenging because of the small sample volumes of tears. Several methods are available for tear collection as a preparatory step of precorneal tear film analysis, and the collection method used has to be assessed since it has a critical impact on the effectiveness of the assays and on the quality of the results. Each sampling method has advantages and disadvantages; therefore, it is not easy to choose the appropriate collecting method for tear collection. To overcome these limitations various methods have been recommended by different authors for special aspects of specific tests. The aim of our review was to evaluate tear sampling methods with regard to our ongoing biochemical analysis.

Application of lipid nanoparticles to ocular drug delivery

INTRODUCTION

Although eye drops are widely used as drug delivery systems for the anterior segment of the eye, they are also associated with poor drug bioavailability due to transient contact time and rapid washout by tearing. Moreover, effective drug delivery to the posterior segment of the eye is challenging, and alternative routes of administration (periocular and intravitreal) are generally needed, the blood-retinal barrier being the major obstacle to systemic drug delivery. Areas covered: Nanotechnology, and especially lipid nanoparticles, can improve the therapeutic efficiency, compliance and safety of ocular drugs, administered via different routes, to both the anterior and posterior segment of the eye. This review highlights the main ocular barriers to drug delivery, as well as the most common eye diseases suitable for pharmacological treatment in which lipid nanoparticles have proved efficacious as alternative delivery systems. Expert opinion: Lipid-based nanocarriers are among the most biocompatible and versatile means for ocular delivery. Mucoadhesion with consequent increase in pre-corneal retention time, and enhanced permeation due to cellular uptake by corneal epithelial cells, are the essential goals for topical lipid nanoparticle delivery. Gene delivery to the retina has shown very promising results after intravitreal administration of lipid nanoparticles as non-viral vectors.

Ocular Surface as Barrier of Innate Immunity

Sight is one of the most important senses that human beings possess. The ocular system is a complex structure equipped with mechanisms that prevent or limit damage caused by physical, chemical, infectious and environmental factors. These mechanisms include a series of anatomical, cellular and humoral factors that have been a matter of study. The cornea is not only the most powerful and important lens of the optical system, but also, it has been involved in many other physiological and pathological processes apart from its refractive nature; the morphological and histological properties of the cornea have been thoroughly studied for the last fifty years; drawing attention in its molecular characteristics of immune response. This paper will review the anatomical and physiological aspects of the cornea, conjunctiva and lacrimal apparatus, as well as the innate immunity at the ocular surface.

Image-guided evaluation and monitoring of treatment response in patients with dry eye disease

BACKGROUND

Dry eye disease (DED) is one of the most common ocular disorders worldwide. The pathophysiological mechanisms involved in the development of DED are not well-understood, and thus treating DED has been a significant challenge for ophthalmologists. Most of the currently available diagnostic tests demonstrate low correlation to patient symptoms and have low reproducibility.

METHODS

Recently, sophisticated in vivo imaging modalities have become available for patient care, namely, in vivo confocal microscopy (IVCM) and optical coherence tomography (OCT). These emerging modalities are powerful and non-invasive, allowing real-time visualization of cellular and anatomical structures of the cornea and ocular surface. Here we discuss how, by providing both qualitative and quantitative assessment, these techniques can be used to demonstrate early subclinical disease, grade layer-by-layer severity, and allow monitoring of disease severity by cellular alterations. Imaging-guided stratification of patients may also be possible in conjunction with clinical examination methods.

CONCLUSIONS

Visualization of subclinical changes and stratification of patients in vivo allows objective image-guided evaluation of tailored treatment response based on cellular morphological alterations specific to each patient. This image-guided approach to DED may ultimately improve patient outcomes and make it possible to study the efficacy of novel therapies in clinical trials.

The anatomical and functional relationship between allergic conjunctivitis and allergic rhinitis

There are numerous anatomic connections between the allergic conjunctivitis and allergic rhinitis. The most obvious reason is the physical connection via the nasolacrimal apparatus. However, a closer look at innervation, circulatory, lymphatic, and neurogenic systems reveals much more than a physical connection. The eye is richly innervated by parasympathetic nerves that enter the eyes after traveling in conjunction with the parasympathetic input to the nasal cavity. Parasympathetic innervation governing the tear film and nasal secretion can intersect at the pterygopalatine ganglion. Neurogenic inflammation affects both the eye and the nose as evidenced by the presence of the same neurogenic factors. Venous flow is in the SOV area connecting the eye and the nose, once thought to be without valves. In the past, this thinking is the basis for concern about the danger triangle of the face. Recent literature has shown otherwise. Although valves are present, there are still pathways where bidirectional flow exists and a venous connection is made. The most likely area for venous communication is the pterygoid plexus and cavernous sinus. The venous flow and connections also offers a pathway for allergic shiners. Understanding the mutual connections between the nasal mucosa and the ocular surface can also affect treatment strategies.

Tear film mucins: front line defenders of the ocular surface; comparison with airway and gastrointestinal tract mucins

The ocular surface including the cornea and conjunctiva and its overlying tear film are the first tissues of the eye to interact with the external environment. The tear film is complex containing multiple layers secreted by different glands and tissues. Each layer contains specific molecules and proteins that not only maintain the health of the cells on the ocular surface by providing nourishment and removal of waste products but also protect these cells from environment. A major protective mechanism that the corneal and conjunctival cells have developed is secretion of the innermost layer of the tear film, the mucous layer. Both the cornea and conjunctiva express membrane spanning mucins, whereas the conjunctiva also produces soluble mucins. The mucins present in the tear film serve to maintain the hydration of the ocular surface and to provide lubrication and anti-adhesive properties between the cells of the ocular surface and conjunctiva during the blink. A third function is to contribute to the epithelial barrier to prevent pathogens from binding to the ocular surface. This review will focus on the different types of mucins produced by the corneal and conjunctival epithelia. Also included in this review will be a presentation of the structure of mucins, regulation of mucin production, role of mucins in ocular surface diseases, and the differences in mucin production by the ocular surface, airways and gastrointestinal tract.

Identification of orexins and cognate receptors in the lacrimal gland of sheep

The aim of the present work was to study, by means of immunohistochemical and RT-PCR techniques, the presence and distribution of immunopositivity for orexin A and B (OXA and OXB) and orexin type 1 and 2 receptors (OX(1)R and OX(2)R) in the lacrimal gland of sheep as well as the gene expressions for prepro-orexin (PPOX) and cognate receptors. In serial sections, positive staining for OXA and OXB were localized in the same nervous fibers within the connective tissue septa. Positive staining for OX(1)R was evidenced in the wall of small arteries while that for OX(2)R was observed in the secretory portion of the acinar gland cells with a characteristic localization in the apical cytoplasm. RT-PCR analysis showed the presence of transcripts for PPOX, OX(1)R and OX(2)R in the sheep lacrimal gland; the gene expression of OX(1)R was two-fold greater (p<0.01) than that of OX(2)R. Taken together the present findings raise intriguing questions on the potential role of the orexinergic system in the regulation of lacrimal gland functions that require further investigations.

Posology, efficacy, and safety of epidermal growth factor eye drops in 305 patients: logistic regression and group-wise odds of published data

The aim of this article is to investigate clinical research on indications, posology, efficacy, and safety of epidermal growth factor (EGF) eye drops in the treatment of some human corneal disorders. Methods used include systematic search and selection of series of cases and clinical trials in Medline database up to January 2012, kappa index (K) to validate retrieval information, cumulative Mantel-Haenszel-stratified meta-analysis, 2×2 contingency table of randomized EGF-vehicle-controlled treated groups, and statistical program SPSSv12. Our results indicate that EGF eye drops appear to be a very effective treatment of acute heterogeneous corneal diseases, without significant adverse effects, with a 86.8% clinical efficacy reported by authors, a 98% (P<0.05) probabilistic expected efficacy, and 51.3 (17.4-148.7 confidence interval 95%; P<0.05) odds ratio EGF/vehicle. However, clinical trials are scarce, with low sample sizes and serious inconsistencies in EGF posology. EGF eye drops (50-1,000 ng, 2-3 times/day) could be a useful treatment for promoting postoperative refractive surgery, reversing cases of keratopathy secondary to systematic EGF receptor inhibitors, diabetic keratopathy, and other corneal and conjunctival disorders.

Muscarinic receptor agonists and antagonists: effects on ocular function

Muscarinic agonists act mainly via muscarinic M₃ cholinoceptors to cause contraction of the iris sphincter, ciliary muscle and trabecular meshwork as well as increase outflow facility of aqueous humour. In the iris dilator, the effect of muscarinic agonists is species dependent but is predominantly relaxation via muscarinic M₃ receptors. In the conjunctiva, muscarinic agonists stimulate goblet cell secretion which contributes to the protective tear film. Muscarinic M₂ and M₃ receptors appear mainly involved. In the lens muscarinic agonists act via muscarinic M₁ receptors to produce depolarization and increase [Ca(2+)](i). All five subtypes of muscarinic receptor are present in the retina. In the developing retina, acetylcholine appears to limit purinergic stimulation of retinal development and decrease cell proliferation. In the adult retina acetylcholine and other muscarinic agonists may have complex effects, for example, enhancing light-evoked neuronal firing in transient ON retinal ganglion cells and inhibiting firing in OFF retinal ganglion cells. In the lacrimal gland, muscarinic agonists activate M₃ receptors on secretory globular acinar cells to stimulate tear secretion and also cause contraction of myoepithelial cells. In Sjögren's syndrome, antibodies to the muscarinic M₃ receptor disrupt normal gland function leading to xerophthalmia although the mechanism of action of the antibody is still not clear. Atropine and pirenzepine are useful in limiting the development of myopia in children probably by an action on muscarinic receptors in the sclera, although many other muscarinic receptor antagonists are not effective.

Distinct activation of epidermal growth factor receptor by UTP contributes to epithelial cell wound repair

The release of nucleotides after injury activates purinergic receptors, leading to phosphorylation of site-specific residues on epidermal growth factor receptor (EGFR). To elucidate the differences between the injury-induced response and that induced by exogenous EGF, we examined recruitment of docking proteins, internalization of EGFR, and migration after injury. Injury induced by scratch wounds or stimulation by addition of UTP caused a brief internalization of EGFR, which paralleled the lesser association with growth factor receptor-bound protein 2 (Grb2) and phosphorylation of EGFR. The internalization caused by EGF was sustained and detected for longer than 60 minutes and correlated with phosphorylation of the receptor. The EGF caused recruitment of Grb2, phospholipase C-γ-1 (PLCγ1), Shc, and Src to EGFR. Glutathione S-transferase pull downs were performed, and glutathione S-transferase-PLCγ1 showed binding of Grb2 when stimulated with EGF but not with UTP or injury. Furthermore, UTP did not induce PLCγ1 phosphorylation, and the phosphorylation induced by EGF was attenuated by costimulation with UTP. The response to heparin-binding EGF was equivalent to that of EGF. Site-directed mutagenesis showed that phosphorylation of Y1068 and Y1086 of EGFR is required for repair. Together, our results show that injury and activation of purinergic receptors and direct activation of EGFR via EGF induce distinct downstream pathways.

Identification of the Raf-1 signaling pathway used by cAMP to inhibit p42/p44 MAPK in rat lacrimal gland acini: role in potentiation of protein secretion

PURPOSE

The lacrimal gland is primarily responsible for the aqueous portion of the tear film. Simultaneous addition of cholinergic agonists or growth factors with cAMP-dependent agonists potentiates secretion. Recent investigations revealed that cAMP decreases p44/p42 mitogen-activated protein kinase (MAPK) activity stimulated by cholinergic agonists and growth factors that could account for this potentiation. In this study the authors identify the signal transduction pathway used by cAMP to inhibit MAPK activity.

METHODS

Rat lacrimal gland acini were incubated with H89, an inhibitor of protein kinase A, before the addition of dibutyryl cAMP (dbcAMP, 10(-3) M) for 30 minutes. Basal MAPK and CREB activity and MAPK activity after stimulation with the cholinergic agonist carbachol (Cch) or epidermal growth factor (EGF) for 5 minutes was determined. The effect of dbcAMP on EGF receptor activity and basal and stimulated Ras, Raf-1, mitogen-activated protein kinase kinase (MEK), and MAPK activity was determined. The effect of a Rap-1 inhibitor, GGTI-298, on MAPK activity after the addition of dbcAMP was also determined.

RESULTS

H89 relieved the inhibition of cAMP on MAPK activity and inhibited CREB activity. Incubation with dbcAMP did not have any effect either on the EGF receptor or on Ras but significantly inhibited both basal and Raf-1 and MEK activity stimulated with Cch or EGF. GGTI-298 did not have any effect on cAMP-dependent decrease in MAPK activity.

CONCLUSIONS

The authors conclude that cAMP mediates the inhibition of MAPK by PKA in a Raf-1-dependent manner.

Therapeutical approach to dry eye syndrome

Introduction. Dry eye disease or dysfunctional tear syndrome is among the most frequently established diagnoses in ophthalmology. It can be defined as a disorder of the tear film resulting in changes in the ocular surface. Mechanisms in development of dry eye disease. There are many factors causing dry eye and they can be related to deficiency in any of the components of the tear film. It has been suggested that dry eye is an inflammatory disorder that affects the ocular surface and lacrimal gland. Inflammation is the most important mechanism of corneal and conjunctival cell damage, which is responsible for the symptoms and signs of ocular surface pathology. Hormonal imbalance (particularly androgens), neural dysfunction, increased levels of pro-inflammatory cytokines and loss of immune homeostasis of the lacrimal gland and ocular surface could be possible mechanisms in the pathogenesis of dry eye disease. Discussion. The aim of this paper was to review the advances in the pathogenesis and management of the dry eye disease. The appropriate dry eye treatment presupposes knowledge of all existing pharmacologic and non-pharmacologic therapeutic modalities. The mainstay of therapy is still artificial tears, with anti-inflammatory therapy and punctual occlusion therapy as second and third line therapies.

Neural regulation of lacrimal gland secretory processes: relevance in dry eye diseases

The lacrimal gland is the major contributor to the aqueous layer of the tear film which consists of water, electrolytes and proteins. The amount and composition of this layer is critical for the health, maintenance, and protection of the cells of the cornea and conjunctiva (the ocular surface). Small changes in the concentration of tear electrolytes have been correlated with dry eye syndrome. While the mechanisms of secretion of water, electrolytes and proteins from the lacrimal gland differ, all three are under tight neural control. This allows for a rapid response to meet the needs of the cells of the ocular surface in response to environmental conditions. The neural response consists of the activation of the afferent sensory nerves in the cornea and conjunctiva to stimulate efferent parasympathetic and sympathetic nerves that innervate the lacrimal gland. Neurotransmitters are released from the stimulated parasympathetic and sympathetic nerves that cause secretion of water, electrolytes, and proteins from the lacrimal gland and onto the ocular surface. This review focuses on the neural regulation of lacrimal gland secretion under normal and dry eye conditions.

Tear glucose analysis for the noninvasive detection and monitoring of diabetes mellitus

One approach to the noninvasive monitoring of blood glucose concentration is to monitor glucose concentrations in tear fluid. While several methods for sensing glucose in tear fluid have been proposed, controversy remains as to the precise concentrations of tear glucose in normal and diabetic subjects and as to whether tear fluid glucose concentrations correlate with blood glucose concentrations. This review covers the present understanding of the physiology of glucose transport in tears, the regulation of the aqueous tear fraction, and studies of tear glucose concentration over the last 80 years. The various tear collection methods employed greatly influence the measured tear glucose concentrations. Studies that involve mechanical irritation of the conjunctiva during sampling measure the highest tear glucose concentrations, while studies that avoid tear stimulation measure the lowest concentrations. Attempts to monitor tear glucose concentration in situ by using contact lens-based sensing devices are discussed, and new observations are presented of tear glucose concentration obtained by a method designed to avoid tear stimulation. These studies indicate the importance of the sampling method in determining tear glucose concentrations. On the basis of these results, we discuss the future of in vivo tear glucose sensing and outline the studies needed to resolve the remaining questions about the relationship between tear and blood glucose concentrations.

ERK/p44p42 mitogen-activated protein kinase mediates EGF-stimulated proliferation of conjunctival goblet cells in culture

PURPOSE

To determine whether activation of the ERK pathway by EGF leads to rat and human goblet cell proliferation.

METHODS

The conjunctiva was removed from male Sprague-Dawley rats. Human conjunctiva was removed during ocular surgery. The tissue was minced and goblet cells were grown. The cells were stimulated with EGF (10(-7) M) for 1 and 5 minutes and Western blot analysis was performed with an antibody against phosphorylated EGFR, to measure the activation of the EGF receptor (EGFR). The cells were incubated with EGF (10(-7) M) for 24 hours, and cell proliferation was measured by WST-8. Inhibitors were added either 20 minutes before EGF or 2 hours after. The cells were stimulated with EGF (10(-7) M) for 1 minute to 24 hours. The number of cells expressing phosphorylated ERK (pERK) in the nucleus and Ki-67 was determined by immunofluorescence.

RESULTS

EGF increased the activation of EGFR in rat conjunctival goblet cells. EGF-stimulated proliferation was inhibited by the EGFR inhibitor AG1478 and the MEK inhibitor U0126 in rat and human cultured goblet cells. EGF caused the translocation of pERK to the nucleus in a biphasic manner. Inhibition of the second peak with U0126 prevented proliferation. EGF-stimulated goblet cells progressed through the cell cycle expressing pERK in the nucleus.

CONCLUSIONS

EGF stimulated human and rat conjunctival goblet cell proliferation by activating the EGFR. EGFR stimulated ERK causing its biphasic translocation to the nucleus. The second peak response is responsible for cell proliferation, but the role of the first peak is not known.

Growth Factors in the Tear Film: Role in Tissue Maintenance, Wound Healing, and Ocular Pathology

Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.

Lipid Deposition on Hydrogel Contact Lenses: How History Can Help Us Today

The tear film is a complex fluid that is precisely maintained and which is essential to the health of the ocular surface. One of the major components of the tear film is lipid, which is produced by the meibomian glands and serves many important functions on the ocular surface. It is estimated that there are more than 45 individual lipids within the tear film, which vary greatly in their structure and properties. The composition of the lipid within the tear film has an enormous influence on the stability of the tear film, with a subsequent impact on the occurrence of dry eye and the ultimate success of contact lens wear. The purpose of this review article is to describe the composition of the tear film lipids and their interaction with contact lens materials, with a particular emphasis on how the chemistry of novel silicone hydrogel materials has resulted in clinicians needing to understand the deposition of lipids onto contact lenses and how they may best manage this complication.

Molecular mechanisms of lacrimal acinar secretory vesicle exocytosis

The acinar epithelial cells of the lacrimal gland are responsible for the production, packaging and regulated exocytosis of tear proteins into ocular surface fluid. This review summarizes new findings on the mechanisms of exocytosis in these cells. Participating proteins are discussed within the context of different categories of trafficking effectors including targeting and specificity factors (rabs, SNAREs) and transport factors (microtubules, actin filaments and motor proteins). Recent information describing fundamental changes in basic exocytotic mechanisms in the NOD mouse, an animal model of Sjögren's syndrome, is presented.

Effect of inflammation on lacrimal gland function

The lacrimal gland is the main contributor to the aqueous layer of the tear film. It secretes proteins, electrolytes and water, which helps to nourish and protect the ocular surface. Lacrimal gland secretion is primarily under neural control, which is achieved through a neural reflex arc. Stimuli to the ocular surface activate afferent sensory nerves in the cornea and conjunctiva. This in turn activates efferent parasympathetic and sympathetic nerves in the lacrimal gland to stimulate secretion. Sex steroid hormones are also important regulators of lacrimal gland functions. A decrease or lack of lacrimal gland secretion is the leading cause of aqueous tear deficient dry eye syndrome (DES). It has been suggested that DES is an inflammatory disorder that affects the ocular surface and the lacrimal gland. In several pathological instances, the lacrimal gland can become a target of the immune system and show signs of inflammation. This can result from autoimmune diseases (Sjögren's syndrome), organ transplantation (graft versus host disease), or simply as a result of aging. The hallmarks of lacrimal gland inflammation are the presence of focal lymphocytic infiltrates and increased production of proinflammatory cytokines. The mechanisms leading to lacrimal gland dysfunction are still poorly understood. Apoptosis, production of autoantibodies, hormonal imbalance, alterations in signaling molecules, neural dysfunction, and increased levels of proinflammatory cytokines have been proposed as possible mediators of lacrimal gland insufficiency in disease states.

Tear urea nitrogen and creatinine levels in horse and their correlation with serum values

The objective of this paper was to determine the physiological values of urea nitrogen and creatinine in tears, and to compare the results with those obtained from serum. Thirty healthy thoroughbred horses were included in the study. Tear fluid samples were obtained using a glass capillary tube placed in lower conjunctival cul-de-sac. Blood samples were taken from the jugular vein. Tear and serum urea nitrogen and creatinine levels were quantitatively analyzed by an enzymatic colorimetric method. Urea nitrogen values were 4.22+/-1.84 mmol/l in tears and 4.44+/-1.78 mmol/l in serum, whereas creatinine values in tears were 14.14+/-7.74 micromol/l and in serum 147.63+/-12.17 micromol/l. Statistical analysis confirmed a significant correlation between serum and tear urea levels (P<0001). However, there was no significant correlation between blood and tear creatinine values. Mean value of creatinine obtained from tears was 9.6% of the mean value from serum. Urea nitrogen and creatinine levels can be measured in tears. A significant correlation was found between serum and tears urea levels. This finding may permit development of a new alternative laboratory diagnosis of uremia based on the content of urea in tears.