Tear Lipocalin and Lysozyme in Sjögren and Non-Sjogren Dry Eye

Tear biomarkers

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

Role of ocular surface neurobiology in neuronal-mediated inflammation in dry eye disease

Inflammation is the consequence of dry eye disease regardless of its etiology. Several injurious or harmless processes to the ocular surface neurons promote ocular surface neurogenic inflammation, leading to the vicious cycle of dry eye disease. These processes include the regular release of neuromediators during the conduction of ocular surface sensations, hyperosmolarity-induced ocular surface neuronal damage, neuro-regenerative activities, and neuronal-mediated dendritic cell activities. Neurogenic inflammation appears to be the main culprit, instigating the self-perpetuating inflammation observed in patients with dry eye disease.

Viscoelastic properties of the human tear film

When considering eye blinking from a tribological perspective, tear viscosity is expected to play a fundamental role. The application of rheological techniques to describe the tear film dates back to the late 1980s, but there has been a continuous need of reappraisal due to new findings in tear film biochemistry and to the development of new methods of physico-chemical characterization. This review provides an overview on tear rheological behavior by analyzing the peer-reviewed literature on this topic. Specifically, examples of in-vitro and in-vivo viscosity measurements are detailed, highlighting experimental criticalities and the need of a standard convention for rheological techniques to compare data across different studies, of analyses on tears of single individuals even within the limits of the low volume available, and of a further development of in-vivo techniques. Then, the controversial role of specific tear components on viscosity is discussed, together with the alterations associated to dry eye disease and contact lens wear. Finally, an updated focus is reported on the viscosity of artificial tears formulations.

[Dry eye and qualitative tear alteration in essential blepharospasm]

PURPOSE

We aimed to analyze the tears of patients with Benin Essential Blepharospasm (BEB) to explore possible corneo-conjunctival mechanisms for photophobia, tear deficiency and ocular pain.

METHODS

Using an observational cohort of 42 patients diagnosed with BEB, we performed Schirmer's testing, measurement of tear film pH, tear film protein electrophoresis and conjunctival impression cytology.

RESULTS

Schirmer's testing showed dry eye (8.4±9.7mm) with 71.3% eyes having a Schirmer's score<10mm. Surprisingly, the pH was basic (8.4±0.4) and was improved in patients receiving the standard treatment of quarterly botulinum toxin injections (8.32±0.36 for treated patients vs. 8.74±0.53 for untreated patients; P=0.045). Together, tear protein electrophoresis and conjunctival impression cytology showed conjunctival inflammation associated with BEB.

CONCLUSION

For the first time, this study emphasizes corneo-conjunctival mechanisms to explain the photophobia, dry eye and pain in Benign Essential Blepharospasm. While encouraging, complementary studies remain necessary to evaluate the effect of correcting tear film pH and inflammation on the quality of life of blepharospasm patients.

Ocular Surface Biomarkers

ABSTRACT

Sjögren syndrome (SS) is a chronic inflammatory autoimmune disease of the lacrimal and salivary glands. Salivary gland biopsy is still one of the most valuable and acceptable diagnostic tests for SS, which however, is an invasive test. Therefore, noninvasive diagnostic biomarkers with high specificity and sensitivity are required for the diagnosis and assessment of SS. Because ophthalmological testing constitutes to an important part for the diagnosis of SS. Tears harbor biomarkers with a high potential to be used for differential diagnosis and assessment of treatment in many systemic disorders, including SS. This review aims to summarize recent advances in the identification of tear biomarkers of SS, trying to identify reliable, sensitive, and specific biomarkers that can be used to guide treatment decisions.

Recent Advances in Smart Biomaterials for the Detection and Treatment of Autoimmune Diseases

Autoimmune diseases are a group of debilitating illnesses that are often idiopathic in nature. The steady rise in the prevalence of these conditions warrants new approaches for diagnosis and treatment. Stimuli-responsive biomaterials also known as "smart", "intelligent" or "recognitive" biomaterials are widely studied for their applications in drug delivery, biosensing and tissue engineering due to their ability to produce thermal, optical, chemical, or structural changes upon interacting with the biological environment. This critical analysis highlights studies within the last decade that harness the recognitive capabilities of these biomaterials towards the development of novel detection and treatment options for autoimmune diseases.

Resistance of the murine cornea to bacterial colonization during experimental dry eye

The healthy cornea is remarkably resistant to infection, quickly clearing deliberately inoculated bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus. Contrasting with the adjacent conjunctiva and other body surfaces, it also lacks a resident viable bacterial microbiome. Corneal resistance to microbes depends on intrinsic defenses involving tear fluid and the corneal epithelium. Dry eye, an ocular surface disease associated with discomfort and inflammation, can alter tear fluid composition and volume, and impact epithelial integrity. We previously showed that experimentally-induced dry eye (EDE) in mice does not increase corneal susceptibility to P. aeruginosa infection. Here, we explored if EDE alters corneal resistance to bacterial colonization. EDE was established in mice using scopolamine injections and dehumidified air-flow, and verified by phenol-red thread testing after 5 and 10 days. As expected, EDE corneas showed increased fluorescein staining versus controls consistent with compromised epithelial barrier function. Confocal imaging using mT/mG knock-in mice with red-fluorescent membranes revealed no other obvious morphological differences between EDE corneas and controls for epithelium, stroma, and endothelium. EDE corneas were imaged ex vivo and compared to controls after alkyne-functionalized D-alanine labeling of metabolically-active colonizing bacteria, or by FISH using a universal 16S rRNA gene probe. Both methods revealed very few viable bacteria on EDE corneas after 5 or 10 days (median of 0, upper quartile of ≤ 1 bacteria per field of view for each group [9–12 eyes per group]) similar to control corneas. Furthermore, there was no obvious difference in abundance of conjunctival bacteria, which included previously reported filamentous forms. Thus, despite reduced tear flow and apparent compromise to corneal barrier function (fluorescein staining), EDE murine corneas continue to resist bacterial colonization and maintain the absence of a resident viable bacterial microbiome.

Patients with non-Sjögren's sicca report poorer general and oral health-related quality of life than patients with Sjögren's syndrome: a cross-sectional study

Understanding the impact of the disease on quality of life is crucial in patient management. In this cross-sectional study, general and oral health-related quality of life questionnaires, and thorough examinations of oral and ocular dryness were performed in age- and sex-matched patients with primary Sjögren’s syndrome (pSS group), non-Sjögren’s syndrome sicca (non-SS group) and healthy controls. General and oral health-related quality of life were investigated with the 36-Item Short Form Health Survey and the 14-Item Oral Health Impact Profile questionnaires, respectively. Subjective symptoms of xerostomia and ocular dryness were recorded using the Summated Xerostomia Inventory and Ocular Surface Disease Index, respectively. Clinical examinations included evaluation of clinical oral dryness scores, candida counts, unstimulated and stimulated saliva secretory rates, tear osmolarity, tear film break-up time, Schirmer I test and ocular surface staining. Both patient groups had pronounced signs and symptoms of xerostomia and ocular dryness. Even though the non-SS patients had less severe clinical signs than the pSS patients, they demonstrated much poorer general and oral health-related quality of life. In conclusion, non-SS patients require more attention in order to improve their quality of life.

Presence of Histatin-1 in Human Tears and Association with Aqueous Deficient Dry Eye Diagnosis: A Preliminary Study

The aims of this study were to determine if histatin-1 (H1) is present in normal human tears and whether tear levels of H1 varied between normal patients and those with aqueous deficient dry eye disease (ADDE). Patient samples were obtained from 11 normal patients and 11 severe ADDE patients. Relevant patient characteristics, including age, sex, and dry eye disease (DED) diagnostic parameters were collected. Multiple qualitative and quantitative methods were used to compare the concentration of H1 between patient groups. Mixed linear modeling was used to compare H1 levels between groups, and diagnostic performance was assessed using the receiver-operator-characteristic (ROC). ADDE patients had significantly lower H1 concentrations (85.9 ± 63.7 ng/ml) than the normal group (891.6 ± 196.5 ng/ml) (p < 0.001), while controlling for age and sex. ROC analysis indicated that H1 concentration is potentially a biomarker for ADDE (area under curve = 0.96). Reclassification of patients by DED parameters including, Ocular Surface Disease Index (OSDI) (≤13, >13) and Schirmer I (without anesthesia) (<10 mm, ≥10 mm) showed significant differences in H1 level (OSDI, p = 0.004) and Schirmer I ((p = 0.010). In conclusion, this is the first preliminary report of the presence of H1 in human tears. H1 concentrations are lower in ADDE patients and H1 may have diagnostic potential in evaluation ADDE patients.

Patient burden of Sjögren's: a comprehensive literature review revealing the range and heterogeneity of measures used in assessments of severity

CONTEXT

The severity of Sjögren's syndrome has been evaluated using a wide variety of clinical measures and patient-reported outcomes (PROs). This may contribute to the lack of clarity concerning the burden of Sjögren's from the patient perspective.

OBJECTIVE

To perform a comprehensive peer-reviewed literature analysis of the patient aspects of Sjögren's, focusing on PROs, to investigate the complexity underlying the evaluation of the syndrome and to elucidate the discordance between the different measures.

METHODS

We searched Embase for articles published between January 2005 and September 2015. Research articles, clinical and diagnostic reviews, and validation studies with a focus on patient aspects of Sjögren's were selected as the primary information source.

RESULTS

157 articles met the eligibility criteria. A wide variety of assessment measures used to evaluate glandular, extraglandular and functional domains were observed. Many different, non-validated Visual Analogue Scales, with a wide range of anchor words, were used in the quantification of Sjögren's disease burden, impeding comparisons between studies. Relatively few clinical trials of drug therapies used validated scales: European League Against Rheumatism Sjögren's Syndrome Patient Reported Index was used most often for symptom assessment and 36 Item Short Form Survey for quality of life (QoL).

CONCLUSION

A wide range and diversity of measures are used to evaluate the patient burden of Sjögren's; most are not validated for use in this disease. PRO endpoints, validated specifically in Sjögren's, that demonstrate improvement are needed. These measures should focus on QoL aspects important to patients and will most likely involve gauging change in function rather than patient-reported symptoms.

TFOS DEWS II Tear Film Report

The members of the Tear Film Subcommittee reviewed the role of the tear film in dry eye disease (DED). The Subcommittee reviewed biophysical and biochemical aspects of tears and how these change in DED. Clinically, DED is characterized by loss of tear volume, more rapid breakup of the tear film and increased evaporation of tears from the ocular surface. The tear film is composed of many substances including lipids, proteins, mucins and electrolytes. All of these contribute to the integrity of the tear film but exactly how they interact is still an area of active research. Tear film osmolarity increases in DED. Changes to other components such as proteins and mucins can be used as biomarkers for DED. The Subcommittee recommended areas for future research to advance our understanding of the tear film and how this changes with DED. The final report was written after review by all Subcommittee members and the entire TFOS DEWS II membership.

The role of dinucleoside polyphosphates on the ocular surface and other eye structures

Dinucleoside polyphosphates comprises a group of dinucleotides formed by two nucleosides linked by a variable number of phosphates, abbreviated NpnN (where n represents the number of phosphates). These compounds are naturally occurring substances present in tears, aqueous humour and in the retina. As the consequence of their presence, these dinucleotides contribute to many ocular physiological processes. On the ocular surface, dinucleoside polyphosphates can stimulate tear secretion, mucin release from goblet cells and they help epithelial wound healing by accelerating cell migration rate. These dinucleotides can also stimulate the presence of proteins known to protect the ocular surface against microorganisms, such as lysozyme and lactoferrin. One of the latest discoveries is the ability of some dinucleotides to facilitate the paracellular way on the cornea, therefore allowing the delivery of compounds, such as antiglaucomatous ones, more easily within the eye. The compound Ap₄A has been described being abnormally elevated in patient's tears suffering of dry eye, Sjogren syndrome, congenital aniridia, or after refractive surgery, suggesting this molecule as biomarker for dry eye condition. At the intraocular level, some diadenosine polyphosphates are abnormally elevated in glaucoma patients, and this can be related to the stimulation of a P2Y₂ receptor that increases the chloride efflux and water movement in the ciliary epithelium. In the retina, the dinucleotide dCp₄U, has been proven to be useful to help in the recovery of retinal detachments. Altogether, dinucleoside polyphosphates are a group of compounds which present relevant physiological actions but which also can perform promising therapeutic benefits.

Altered hyaluronic acid content in tear fluid of patients with adenoviral conjunctivitis

The adenoviral conjunctivitis is one of the biggest causes of conjunctival infection in the world. Conjunctivitis causes relatively nonspecific symptoms, as hyperaemia and chemosis. Even after biomicroscopy, complex laboratory tests, such as viral culture, are necessary to identify the pathogen or its etiology. To contribute to the better understanding of the pathobiology of the adenoviral conjunctivitis, the tear fluids of patients with unilateral acute adenovirus conjunctivitis (UAAC), normal donors (control) and patients with allergic conjunctivitis were analyzed. Tear samples were collected with Schirmer strips from control, allergic conjunctivitis and UAAC patients, diagnosed by clinical signs. UAAC tears were tested positive in viral cultures. After the elution, HA was quantified using an ELISA-like fluorometric assay and the protein profile was determined by SDS-PAGE. A profound increase in the HA tear content in UAAC patients was found when compared to control and ALC. This HA increase in UAAC tears remarkably was not observed in tears from contralateral eyes without clinical signs, nor in allergic conjunctivitis. In addition a distinct profile of UAAC tear proteins was observed in patients with UAAC. The quantification of HA in the tear fluid is a rapid, sensitive and specific test. This molecule might be a biomarker candidate for acute conjunctivitis.

Unraveling the molecular repertoire of tears as a source of biomarkers: beyond ocular diseases

Proteomics and metabolomics investigations of body fluids present several challenges for biomarker discovery of several diseases. The search for biomarkers is actually conducted in different body fluids, even if the ideal biomarker can be found in an easily accessible biological fluid, because, if validated, the biomarker could be sought in the healthy population. In this regard, tears could be considered an optimum material obtained by noninvasive procedures. In the past years, the scientific community has become more interested in the study of tears for the research of new biomarkers not only for ocular diseases. In this review, we provide a discussion on the current state of biomarkers research in tears and their relevance for clinical practice, and report the main results of clinical proteomics studies on systemic and eye diseases. We summarize the main methods for tear samples analyses and report recent advances in "omics" platforms for tears investigations. Moreover, we want to take stock of the emerging field of metabolomics and lipidomics as a new and integrated approach to study protein-metabolites interplay for biomarkers research, where tears represent a still unexplored and attractive field.

Practical issues concerning tear protein assays in dry eye

Dry eye is a common clinical condition diagnosed by cumulative evidence of symptoms and signs. Many new treatments in dry eye are either expensive, invasive, have potential for side effects, or are not easily accessible. In severe dry eye, the ideal modality of treatment to begin with is often not clear as specific molecular disturbances are not evident from just examination of clinical manifestations. Assessing the effects of ongoing treatment is not straight forward since there is lack of agreement between clinical signs and symptoms. There is a need to have more objective methods of selecting treatment for dry eye and monitoring the effect of treatment. Recently, there are many new technologies applied to the discovery of tear biomarkers, for e.g., mass spectrometry based proteomics techniques and multiplex assays such as the bead-based sandwich indirect immunofluorescent assays. Tear proteins assays have even been made available as point-of-care devices. This review focuses on the evidence for the involvements of tear proteins in dry eye, possible changes in tear concentrations with therapy and the strength of evidence regarding dry eye pathology. Much remains to be done in terms of developing office-based assays and ascertaining their reliability, but current evidence suggests that tear proteins have a role in the clinical practice of dry eye.

Adaptation of impression cytology to enable conjunctival surface cell transcriptome analysis

PURPOSE

This study investigates the extent of the human transcriptome that can be quantified from conjunctival impression cytology extracts. The aim is to determine if sufficient RNA can be isolated from a patient's conjunctival surface to identify differences in gene expression between dry eye and normal patients of (a) an array of 96 inflammatory biomarkers and associated receptors, and (b) if this comparison can be expanded to the entire transcriptome.

MATERIALS AND METHODS

CIC was used to collect conjunctival surface cells from 53 qualifying normal and dry eye patients. Based on prior optimization of all assay steps, RNA was isolated from the samples using a Qiagen RNeasy Plus Mini Kit and qRT-PCR was used to determine gene expression of 96 genes using TaqMan Low Density Array cards. Samples from six normal and six dry eye patients were then assayed on an Illumina Human HT-12 BeadChip.

RESULTS

Optimization steps yielded an RNA processing procedure that improved yield from an initial 12 genes through 96, then to the entire human transcriptome. For the HT-12 BeadChip, more than 30 genes differed by a factor of >1.5 between the dry eye and normal groups and seven genes were down-regulated by a factor of >2.0 in the dry eye group: HLA-DRB5, PSCA, FOS, lysozyme, TSC22D1, CAPN13 and CXCL6.

CONCLUSIONS

Conjunctival impression cytology can be used to collect sufficient RNA from conjunctival surface cells that, when processed optimally, allows successful transcriptome-wide expression analysis. While the current transcriptome analysis used a limited patient group, larger studies of patients with various types and severities of dry eye should reveal significant gene expression trends that can then be targeted to improve dry eye treatment options.

Surfactant protein D contributes to ocular defense against Pseudomonas aeruginosa in a murine model of dry eye disease

Dry eye disease can cause ocular surface inflammation that disrupts the corneal epithelial barrier. While dry eye patients are known to have an increased risk of corneal infection, it is not known whether there is a direct causal relationship between these two conditions. Here, we tested the hypothesis that experimentally-induced dry eye (EDE) increases susceptibility to corneal infection using a mouse model. In doing so, we also examined the role of surfactant protein D (SP-D), which we have previously shown is involved in corneal defense against infection. Scopolamine injections and fan-driven air were used to cause EDE in C57BL/6 or Black Swiss mice (wild-type and SP-D gene-knockout). Controls received PBS injections and were housed normally. After 5 or 10 days, otherwise uninjured corneas were inoculated with 10(9) cfu of Pseudomonas aeruginosa strain PAO1. Anesthesia was maintained for 3 h post-inoculation. Viable bacteria were quantified in ocular surface washes and corneal homogenates 6 h post-inoculation. SP-D was measured by Western immunoblot, and corneal pathology assessed from 6 h to 4 days. EDE mice showed reduced tear volumes after 5 and 10 days (each by ∼75%, p<0.001) and showed fluorescein staining (i.e. epithelial disruption). Surprisingly, there was no significant difference in corneal pathology between EDE mice and controls (∼10-14% incidence). Before bacterial inoculation, EDE mice showed elevated SP-D in ocular washes. After inoculation, fewer bacteria were recovered from ocular washes of EDE mice (<2% of controls, p = 0.0004). Furthermore, SP-D knockout mice showed a significant increase in P. aeruginosa corneal colonization under EDE conditions. Taken together, these data suggest that SP-D contributes to corneal defense against P. aeruginosa colonization and infection in EDE despite the loss of barrier function to fluorescein.

Comparison of low-abundance biomarker levels in capillary-collected nonstimulated tears and washout tears of aqueous-deficient and normal patients

PURPOSE

Low tear volume limits the use of nonstimulated (NS) microcapillary tear collection in aqueous-deficient (AD) patients. Adding a small amount of "washout" fluid to the eye prior to tear collection is a potentially viable alternative method for abundant proteins, but is relatively untested for low-abundance biomarkers. This study determined the feasibility of the washout (WO) method as an NS alternative for low-abundance biomarkers. NS and WO biomarker profiles were compared between AD patients and non-AD controls to determine if the two methods identify the same intergroup differences.

METHODS

Matching NS and WO tears were collected from 48 patients by micropipette, the WO sample after instillation of 10 μL saline. Tear cytokine levels were measured by 27-Plex Bio-Rad assay. Bland-Altman analyses for each biomarker determined the agreement between tear sample types. Patients were grouped as AD or non-AD based on Schirmer score to determine if NS profile between-group differences were preserved in WO tears.

RESULTS

Bland-Altman plots showed good biomarker level agreement between NS and WO tears for most cytokines. Five biomarkers, among those most often cited as differing in AD dry eye, differed significantly between non-AD and AD groups in both tear types. Additional biomarker differences were seen in NS tears only.

CONCLUSIONS

The WO tear collection method is a viable alternative to NS tears for many low-abundance biomarkers and is able to replicate major NS tear differences between dry eye groups. More subtle intergroup differences are lost in WO samples because of reduced statistical power.

A novel fluorescent lipid probe for dry eye: retrieval by tear lipocalin in humans

PURPOSE

A fluorescent probe was used to identify mucin-depleted areas on the ocular surface and to test the hypothesis that tear lipocalin retrieves lipids from the eyes of normal and dry eye subjects.

METHODS

Fluorescein-labeled octadecyl ester, FODE, was characterized by mass spectrometry and absorbance spectrophotometry. The use of FODE to define mucin defects was studied with impression membranes under conditions that selectively deplete mucin. The kinetics of FODE removal from the ocular surface were analyzed by sampling tears from control and dry eye patients at various times. The tear protein-FODE complexes were isolated by gel filtration and ion exchange chromatographies, monitored with absorption and fluorescent spectroscopies, and analyzed by gel electrophoresis. Immunoprecipitation verified FODE complexed to tear lipocalin in tears.

RESULTS

FODE exhibits an isosbestic point at 473 nm, pKa of 7.5, and red shift relative to fluorescein. The low solubility of FODE in buffer is enhanced with 1% Tween 80 and ethanol. FODE adheres to the ocular surface of dry eye patients. FODE produces visible staining at the contact sites of membranes, which correlates with removal of mucin. Despite the fact that tear lipocalin is reduced in dry eye patients, FODE removal follows similar rapid exponential decay functions for all subjects. FODE is bound to tear lipocalin in tears.

CONCLUSIONS

Tear lipocalin retrieves lipid rapidly from the human ocular surface in mild to moderate dry eye disease and controls. With improvements in solubility, FODE may have potential as a fluorescent probe to identify mucin-depleted areas.

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.

Evaluation of dry eye

Dry eye is a common yet complex condition. Intrinsic and extrinsic factors can cause dysfunction of the lids, lacrimal glands, meibomian glands, ocular surface cells, or neural network. These problems would ultimately be expressed at the tear film-ocular surface interface. The manifestations of these problems are experienced as symptoms such as grittiness, discomfort, burning sensation, hyperemia, and secondary epiphora in some cases. Accurate investigation of dry eye is crucial to correct management of the condition. Techniques can be classed according to their investigation of tear production, tear stability, and surface damage (including histological tests). The application, validity, reliability, compatibility, protocols, and indications for these are important. The use of a diagnostic algorithm may lead to more accurate diagnosis and management. The lack of correlation between signs and symptoms seems to favor tear film osmolarity, an objective biomarker, as the best current clue to correct diagnosis.

Tear lipocalin: structure and function

Lipocalins are a family of diverse low molecular weight proteins that act extracellularly. They use multiple recognition properties that include 1) ligand binding to small hydrophobic molecules, 2) macromolecular complexation with other soluble macromolecules, and 3) binding to specific cell surface receptors to deliver cargo. Tear lipocalin (TLC) is a major protein in tears and has a large ligand-binding cavity that allows the lipocalin to bind an extensive and diverse set of lipophilic molecules. TLC can also bind to macromolecules, including the tear proteins lactoferin and lysozyme. The receptor to which TLC binds is termed tear lipocalin-interacting membrane receptor (LIMR). LIMR appears to work by endocytosis. TLC has a variety of suggested functions in tears, including regulation of tear viscosity, binding and release of lipids, endonuclease inactivation of viral DNA, binding of microbial siderophores (iron chelators used to deliver essential iron to bacteria), serving as a biomarker for dry eye, and possessing anti-inflammatory activity. Additional research is warranted to determine the actual functions of TLC in tears and the presence of its receptor on the ocular surface.

A comparison of basal and eye-flush tears for the analysis of cat tear proteins

PURPOSE

To identify a rapid and effective tear collection method providing sufficient tear volume and total protein content (TPC) for analysis of individual proteins in cats.

METHODS

Domestic adult short-haired cats (12-37 months; 2.7-6.6 kg) were used in the study. Basal tears without stimulation and eye-flush tears after instillation of saline (10 μl) were collected using microcapillary tubes from animal eyes either unwounded control or wounded with 9-mm central epithelial debridement giving four groups with n = 3. Tear comparisons were based on total time and rate for tear collection, TPC using micro bicinchoninic acid (BCA), tear immunoglobulin A (IgA), total matrix-metalloproteinase (MMP)-9 concentration using sandwich enzyme-linked immunosorbent assay (ELISA) and MMP-9 activity.

RESULTS

Eye-flush tears were collected significantly faster than basal tears in wounded eyes with higher rates for tear collection in unwounded control and wounded eyes. TPC was significantly lower in eye-flush tears compared to basal tears. The relative proportion of tear IgA normalized to TPC (% IgA of TPC) was not significantly different between basal and eye-flush tears. In unwounded control eyes, MMP-9 was slightly higher in eye-flush than in basal tears; activity of MMP-9 in both tear types was similar. In wounded eyes, eye-flush tears showed highest MMP-9 levels and activity on Day 1, which subsequently decreased to Day 7. MMP-9 activity in basal tears from wounded eyes did not display changes in expression.

CONCLUSIONS

Eye-flush tears can be collected rapidly providing sufficient tear volume and TPC. This study also indicates that eye-flush tears may be more suitable than basal tears for the analysis of MMPs following corneal wounding.

Validation of the flush method as an alternative to basal or reflex tear collection

PURPOSE

To validate the more easily applicable "flush" tear collection technique as a viable alternative to basal and reflex tear collection.

MATERIALS AND METHODS

Total protein content (TPC) and immunoglobulin A (IgA) concentrations were determined in the basal, reflex, and flush tears of 16 healthy non-contact lens wearers. The overall protein profile was established using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MS).

RESULTS

Collection-rates were 4.6 ± 6.7 μl/min, 13.9 ± 11.1 μl/min, and 25.7 ± 12.4 μl/min for the basal, reflex, and flush tears, respectively. TPC was 7.14 ± 2.22 mg/mL, 6.01 ± 2.11 mg/mL, and 3.79 ± 1.51 mg/ mL for basal, reflex, and flush tears, respectively, with flush tears being significantly less concentrated than basal (p = 0.001) and reflex (p = 0.008). IgA concentration was 1.04 ± 0.29 mg/ mL, 0.64 ± 0.26 mg/mL, and 0.65 ± 0.23 mg/mL for basal, reflex, and flush tears, respectively, with basal tears being significantly more concentrated (p < 0.001). As a percentage of TPC, IgA represented 19.8 ± 14.9%, 11.4 ± 3.9%, and 19.8 ± 8.7% for basal, reflex, and flush, respectively. The flush was not significantly different to basal (p = 1.00) but significantly greater than reflex (p = 0.02). SDS-PAGE showed the same tear profiles for basal and flush tears. MS identified the most abundant proteins in all tear types.

CONCLUSIONS

The flush method allows much faster collection than basal secretion sampling but returns essentially the same spectrum of proteins in similar proportions. This behavior is confirmation that the flush technique has utility as a more convenient alternative to basal tear sampling in studies involving composition analysis.

Two dimensional electrophoretic analysis of human tears: collection method in dry eye syndrome

Tear proteomics, by 2-DE, can give a fingerprint of the protein profile, which is well suited in clinical proteomics for biomarker identification and in diagnostics. The mode of tear collection can influence the representation of the proteins in the tear and therefore it is important to use the appropriate method. In this study, capillary and Schirmer mode of tear collection was done in the healthy controls and the Schirmer method was validated in dry eye syndrome conditions. 2-D PAGE of normal and dry eye tear was performed using pH 3-10 linear IPG strips followed by 13% SDS-PAGE. The spot intensity was analyzed by the PD quest software. The two methods were compared using Bland-Altman statistical tool. The 2-D map of capillary and Schirmer tear showed 147 ± 8 spots and 145 ± 7 spots respectively. Both the collection methods were in agreement with each other and were comparable. Dry eye tear protein showed differential expression of proteins as observed in 25-35 kDa region. One of the significantly reduced protein was identified as proline-rich 4 protein. Schirmer method of tear collection is reliable in patients with dry eye, which can display the differential protein expression and help in biomarker identification.

Proteomic approaches to Sjögren's syndrome: a clue to interpret the pathophysiology and organ involvement of the disease

Sjögren's syndrome (SS) is a chronic, inflammatory, autoimmune disease characterized by lymphocytic infiltration of the exocrine glands leading to qualitatively altered and diminished or absent salivary and lachrymal secretion, and by marked B-cell hyperreactivity. Many efforts have been made to define a panel of salivary and lachrymal markers helpful to design diagnostic tests able to replace blood tests and tissue biopsies for the diagnosis of primary and secondary SS. Several proteomic-based studies have indicated that a number of proteins and peptides can be considered SS biomarkers, being 2-3-fold up- or down-regulated compared to normal subject or having an exclusive presence in the saliva or tears of SS patients. Unfortunately, several factors make it difficult to define a comprehensive salivary and lachrymal panel of markers of SS, as the lack of a comprehensive proteomic analysis of human tears and saliva of healthy subjects, the lack of uniform protocols to collect and treat these samples, and the high grade of posttranslational modification of the proteins in these fluids.

Tear lipocalin captures exogenous lipid from abnormal corneal surfaces

Purpose. The cornea is protected by apical hydrophilic transmembrane mucins and tears. In pathologic states the mucin barrier is disrupted, creating potential for meibomian lipids to adhere more strongly. Undisplaced lipids create an unwettable surface. The hypothesis that pathologic ocular surfaces alter lipid binding and the ability of tear proteins to remove lipids was tested. Methods. Corneas with pathologic surfaces were studied for lipid adhesion and removal by tears. Capture of fluorescence-labeled phospholipids by human tears was assessed by steady state fluorometry. Tear proteins were separated by gel filtration chromatography and analyzed for bound lipids. Results. Contact angle measurements revealed strong lipid adherence to corneas submerged in buffer. Lower contact angles are observed for lipids on completely de-epithelialized corneas compared with intact corneas (P = 0.04). Lipid removal from these surfaces is greater with whole tears than with tears depleted of tear lipocalin (P < 0.0005). Significantly fewer lipids are captured by tears from Bowman's layer than from epithelial-bearing surfaces (P < 0.025). The only tear component to bind the fluorescence-tagged lipid is tear lipocalin. The histology of a rare case of dry eye disease demonstrates the dominant features of contemporaneous bullous keratopathy. Lipid sequestration from this cornea by tear lipocalin was robust. Conclusions. Lipid is captured by tear lipocalin from corneas with bullous keratopathy and dry eye. Lipid removal is slightly abrogated by greater lipid adhesion to Bowman's layer. Reduced secretion of tear lipocalin documented in dry eye disease could hamper lipid removal and exacerbate ocular surface pathology.

Dry eye in 2008

PURPOSE OF REVIEW

Although researchers continue to investigate the multifarious etiologic, anatomical, physiological, and pathological factors of dry eye, successful treatment remains a challenge.

RECENT FINDINGS

Dry eye prevalence is substantial across populations and the term 'dry eye' is used to describe numerous causes and varied pathophysiologies. Advanced study of the physiological aspects of the ocular anatomy (e.g. cornea and conjunctiva, tear film, eyelids) allows improved understanding of the mechanisms involved in dry eye and the impact of different causes on these entities. Sophisticated diagnostics are being developed to efficiently identify dry eye. Management options include a variety of novel agents in the pipeline.

SUMMARY

The development of improved etiological understanding and diagnostics for dry eye, as well as emerging therapeutics, will likely allow targeted therapy in the future.