Elevated Levels of Human α -Defensin in Tears of Patients with Allergic Conjunctival Disease Complicated by Corneal Lesions: Detection by SELDI ProteinChip System and Quantification

Sources of Variance in Human Tear Proteomic Samples: Statistical Evaluation, Quality Control, Normalization, and Biological Insight

Human tear fluid contains numerous compounds, which are present in highly variable amounts owing to the dynamic and multipurpose functions of tears. A better understanding of the level and sources of variance is essential for determining the functions of the different tear components and the limitations of tear samples as a potential biomarker source. In this study, a quantitative proteomic method was used to analyze variations in the tear protein profiles of healthy volunteers. High day-to-day and inter-eye personal variances were observed in the tear volumes, protein content, and composition of the tear samples. Several normalization and outlier exclusion approaches were evaluated to decrease variances. Despite the intrapersonal variances, statistically significant differences and cluster analysis revealed that proteome profile and immunoglobulin composition of tear fluid present personal characteristics. Using correlation analysis, we could identify several correlating protein clusters, mainly related to the source of the proteins. Our study is the first attempt to achieve more insight into the biochemical background of human tears by statistical evaluation of the experimentally observed dynamic behavior of the tear proteome. As a pilot study for determination of personal protein profiles of the tear fluids of individual patients, it contributes to the application of this noninvasively collectible body fluid in personal medicine.

Emerging Applications of Electrochemical Impedance Spectroscopy in Tear Film Analysis

Human tear film, with a flow rate of 1-3 µL/min, is a rich bodily fluid that transmits a variety of metabolites and hormones containing proteins, lipids and electrolytes that provide clues about ocular and systemic diseases. Analysis of disease biomarkers such as proteins, mRNA, enzymes and cytokines in the tear film, collected by noninvasive methods, can provide significant results for sustaining a predictive, preventive and personalized medicine regarding various diseases such as glaucoma, diabetic retinopathy, keratoconus, dry eye, cancer, Alzheimer's disease, Parkinson's disease and COVID-19. Electrochemical impedance spectroscopy (EIS) offers a powerful technique for analyzing these biomarkers. EIS detects electrical equivalent circuit parameters related to biorecognition of receptor-analyte interactions on the electrode surface. This method is advantageous as it performs a label-free detection and allows the detection of non-electroactive compounds that cannot be detected by direct electron transfer, such as hormones and some proteins. Here, we review the opportunities regarding the integration of EIS into tear fluid sampling approaches.

Host Defense Peptides at the Ocular Surface: Roles in Health and Major Diseases, and Therapeutic Potentials

Sight is arguably the most important sense in human. Being constantly exposed to the environmental stress, irritants and pathogens, the ocular surface – a specialized functional and anatomical unit composed of tear film, conjunctival and corneal epithelium, lacrimal glands, meibomian glands, and nasolacrimal drainage apparatus – serves as a crucial front-line defense of the eye. Host defense peptides (HDPs), also known as antimicrobial peptides, are evolutionarily conserved molecular components of innate immunity that are found in all classes of life. Since the first discovery of lysozyme in 1922, a wide range of HDPs have been identified at the ocular surface. In addition to their antimicrobial activity, HDPs are increasingly recognized for their wide array of biological functions, including anti-biofilm, immunomodulation, wound healing, and anti-cancer properties. In this review, we provide an updated review on: (1) spectrum and expression of HDPs at the ocular surface; (2) participation of HDPs in ocular surface diseases/conditions such as infectious keratitis, conjunctivitis, dry eye disease, keratoconus, allergic eye disease, rosacea keratitis, and post-ocular surgery; (3) HDPs that are currently in the development pipeline for treatment of ocular diseases and infections; and (4) future potential of HDP-based clinical pharmacotherapy for ocular diseases.

A Review of Emerging Tear Proteomics Research on the Ocular Surface in Ocular Allergy

Ocular allergy is an immunoglobulin E-mediated Type I hypersensitivity reaction localised to the ocular surface and surrounding tissues. Primary signs and symptoms of ocular allergy include itching, redness, irritation and inflammation. Eye-rubbing caused by itching has been shown to alter ocular surface protein concentrations in conditions linked to ocular allergy such as keratoconus. In keratoconus, the cornea begins to thin and sag over time, leading to progressive vision loss and blindness in severe conditions. Due to the high incidence of ocular allergy sufferers rubbing their eyes in response to symptoms of itching, the protein landscape of the ocular surface may be significantly altered. Differential protein expression caused by long-term inflammation and eye-rubbing may lead to subsequent changes in ocular surface structure and function over time. This review aims to summarise and explore the findings of current ocular allergy proteome research conducted using techniques such as gel electrophoresis, mass spectrometry and lab-on-a-chip proteomics. Proteins of interest for this review include differentially expressed immunoglobulins, mucins, functional proteins, enzymes and proteins with previously uncharacterised roles in ocular allergy. Additionally, potential applications of this research are addressed in terms of diagnostics, drug development and future research prospects.

A technique for shotgun proteomic analysis of the precorneal tear film in dogs with naturally occurring primary glaucoma

OBJECTIVE

To introduce a protocol for the characterization of protein patterns in tears of dogs with primary angle closure glaucoma (PACG) and primary open-angle glaucoma (POAG).

ANIMALS

Nineteen dogs (25 eyes).

METHODS

Tear samples were collected using a Schirmer tear strip, from dogs with PACG (PACG-affected eyes, n = 8; unaffected eyes predisposed to PACG, n = 7), POAG (n = 4), and healthy controls (n = 6). Protein precipitation and trypsin digestion were performed for analyses via liquid chromatography-tandem mass spectrometry. Proteins were identified using the SwissProt protein sequence database. Relative protein expression in 17 eyes (15 dogs) was evaluated using Proteome Discoverer 2.0. Pathway analyses were performed to investigate molecular mechanisms associated with primary glaucoma.

RESULTS

Unique peptides were identified in 505 proteins, with Major allergen Can f 1 and albumin identified with high confidence. Proteins unique to tears from diseased eyes (PACG: n = 7; POAG: n = 14) were identified. Nucleoside diphosphate was unique to tears in PACG eyes naïve to therapy, while retinal binding protein and NSFL1 cofactor p47 were unique to medicated PACG eyes. Relative expression of 34 proteins differed between disease states. Pathway analyses identified that the 'inflammatory response' was among the top disease/disorders in dogs with primary glaucoma (PACG and POAG) but not in healthy controls.

CONCLUSION

Tear samples suitable for mass spectrometry were readily obtained from pet dogs without needing specialized equipment. Further studies to validate the findings and explore potential candidate biomarkers for early disease detection and potential therapeutic targets are indicated.

Microbiological Evaluation of Bandage Soft Contact Lenses Used in Management of Persistent Corneal Epithelial Defects

PURPOSE

To investigate the rate and agents of contamination in bandage soft contact lenses fitted for management of persistent corneal epithelial defects.

METHODS

This prospective comparative case series enrolled 57 consecutive eyes fitted with bandage contact lenses for treatment of persistent corneal epithelial defects. The lenses were collected at the time of epithelial closure or when it was necessary to exchange contact lenses and were immediately placed in sterile tubes containing an enriched thioglycolate liquid medium. When contamination of the contact lens was detected, the microorganism was cultured in different media and identified based on various tests. All isolates were tested for susceptibility to various antibiotics. Univariate analyses were used to evaluate the influence of different variables (duration of contact lens use, use of topical corticosteroids, presence of blepharitis, contact lens deposits, and presence of sutures) on bandage contact lens contamination.

RESULTS

Seventeen of the contact lenses (29.8%) were contaminated. The most commonly isolated pathogen was Staphylococcus epidermidis (n = 10), followed by Enterobacter cloacae (n = 3), Staphylococcus aureus (n = 1), Streptococcus viridans (n = 1), and Alcaligenes spp. (n = 1). One contact lens yielded a mixed infection with E. cloacae and Candida spp. Infectious keratitis was not observed in any eyes. Correlations between contact lens contamination and patient- and lens-related variables were not statistically significant.

CONCLUSIONS

Most bandage contact lenses (70.2%) used for treatment of persistent corneal epithelial defects did not show bacterial growth. Staphylococcus epidermidis was the most common microorganism isolated from the contaminated contact lenses.

Elevated Tear Human Neutrophil Peptides 1-3, Human Beta Defensin-2 Levels and Conjunctival Cathelicidin LL-37 Gene Expression in Ocular Rosacea

Purpose: To investigate the role of innate immunity in ocular rosacea. Methods: Thirty-two patients with ocular rosacea patients (group-1) and 28 healthy volunteers (group-2) who served as controls were enrolled in the study. Tear function parameters were assessed, conjunctival impression cytology was performed and tear samples were collected. Human-neutrophil-peptides (HNP) 1-3 and human-beta-defensin-2 (hBD-2) levels were measured in tears by using ELISA tests. Cathelicidin leucin-leucin-37 (LL-37), hBD-2, human-beta-defensin-9 (hBD-9) gene expression levels were measured in the conjunctival impression cytology samples using real-time polymerase chain reaction. Results: Tear HNP1-3 (p = 0.024), hBD-2 (p < 0.001), conjunctival LL-37 gene expression rate (p = 0.014) and ocular surface disease index scores (p = 0.001) were higher and the tear break-up time was lower (p = 0.003) in group-1. No other differences were found between the groups. Conclusion: The results of this study suggest the role of abnormal innate immunity in the pathophysiology of ocular rosacea by revealing elevated antimicrobial peptide levels.

Post-photorefractive keratectomy contact lens microbiological findings of individuals who work in a hospital environment

OBJECTIVE

To describe the microbiological findings from bandage contact lenses in patients who work in a hospital environment submitted to photorefractive keratectomy (PRK).

METHODS

This prospective comparative case series enrolled 43 eyes of 22 volunteers (28.05 ± 3.50 years). Fourteen individuals (n = 27) were health care professionals who work in health care facilities or community physician's offices. Eight individuals (n = 16) were patients who do not work in hospital environment. Photorefractive keratectomy was performed using standard technique, and a silicone hydrogel bandage contact lens was placed on the cornea and evaluated for adequate fit. Seven days after surgery, the bandage lenses were removed and imprinted in the following culture media: blood agar, chocolate agar, anaerobic-selective agar, and Sabouraud agar. When microbial growth was detected, the microorganism was identified, colony-forming units were quantified, and morphology and Gram-staining properties were analyzed. All isolates were tested for susceptibility to various antibiotics. Significance was assessed by Fisher exact test.

RESULTS

Microbial growth was detected in 16.27% of all contact lenses samples. No fungi or anaerobes were found. Microbial growth was only observed in bandage lenses removed from patients who work in hospital environments. Most microorganisms found were sensitive to all antibiotics tested.

CONCLUSION

These results suggest that working in hospital environments increase contamination of the contact lenses after PRK.

Absolute quantification of human tear lactoferrin using multiple reaction monitoring technique with stable-isotopic labeling

The mass spectrometry technique of multiple reaction monitoring (MRM) was used to quantify and compare the expression level of lactoferrin in tear films among control, prostate cancer (CaP), and benign prostate hyperplasia (BPH) groups. Tear samples from 14 men with CaP, 15 men with BPH, and 14 controls were analyzed in the study. Collected tears (2 μl) of each sample were digested with trypsin overnight at 37 °C without any pretreatment, and tear lactoferrin was quantified using a lactoferrin-specific peptide, VPSHAVVAR, both using natural/light and isotopic-labeled/heavy peptides with MRM. The average tear lactoferrin concentration was 1.01 ± 0.07 μg/μl in control samples, 0.96 ± 0.07 μg/μl in the BPH group, and 0.98 ± 0.07 μg/μl in the CaP group. Our study is the first to quantify tear proteins using a total of 43 individual (non-pooled) tear samples and showed that direct digestion of tear samples is suitable for MRM studies. The calculated average lactoferrin concentration in the control group matched that in the published range of human tear lactoferrin concentration measured by enzyme-linked immunosorbent assay (ELISA). Moreover, the lactoferrin was stably expressed across all of the samples, with no significant differences being observed among the control, BPH, and CaP groups.

Tear fluid protein biomarkers

The tear film covers and protects the ocular surface. It contains various molecules including a large variety of proteins. The protein composition of the tear fluid can change with respect to various local and systemic diseases. Prior to the advent of the proteomic era, tear protein analysis was limited to a few analytical techniques, the most common of which was immunoelectrophoresis, an approach dependent on antibody availability. Using proteomics, hundreds of tear proteins could potentially be identified and subsequently studied. Although detection of low-abundance proteins in the complex tear proteome remains a challenge, advances in sample fractionation and mass spectrometry have greatly enhanced our ability to detect these proteins. With increasing proteomic applications, tears show great potential as biomarkers in the development of clinical assays for various human diseases. In this chapter, we discuss the structure and functions of the tear film and methods for its collection. We also summarize potential tear protein biomarkers identified using proteomic techniques for both ocular and systemic diseases. Finally, modern proteomic techniques for tear biomarker research and future challenges are explored.

Advances in MALDI mass spectrometry in clinical diagnostic applications

The concept of matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) was first reported in 1985. Since then, MALDI MS technologies have been evolving, and successfully used in genome, proteome, metabolome, and clinical diagnostic research. These technologies are high-throughput and sensitive. Emerging evidence has shown that they are not only useful in qualitative and quantitative analyses of proteins, but also of other types of biomolecules, such as DNA, glycans, and metabolites. Recently, parallel fragmentation monitoring (PFM), which is a method comparable to selected reaction monitoring, has been reported. This highlights the potentials of MALDI-TOF/TOF tandem MS in quantification of metabolites. Here we critically review the applications of the major MALDI MS technologies, including MALDI-TOF MS, MALDI-TOF/TOF MS, SALDI-TOF MS, MALDI-QqQ MS, and SELDI-TOF MS, to the discovery and quantification of disease biomarkers in biological specimens, especially those in plasma/serum specimens. Using SELDI-TOF MS as an example, the presence of systemic bias in biomarker discovery studies employing MALDI-TOF MS and its possible solutions are also discussed in this chapter. The concepts of MALDI, SALDI, SELDI, and PFM are complementary to each other. Theoretically, all these technologies can be combined, leading to the next generation of the MALDI MS technologies. Real applications of MALDI MS technologies in clinical diagnostics should be forthcoming.

Tear analysis in ocular surface diseases

The thin layer of tears covering the ocular surface are a complex body fluid containing thousands of molecules of varied form and function of several origins. In this review, we have discussed some key issues in the analysis of tears in the context of understanding and diagnosing eye disease using current technologies of proteomics and metabolomics, and for their potential for clinical application. In the last several years, advances in proteomics/metabolomics/lipidomics technologies have greatly expanded our knowledge of the chemical composition of tear fluid. The quickened pace of studies has shown that tears as a complex extra-cellular fluid of the ocular surface contains a great deal of molecular information useful for the diagnosis, prognosis, and treatment of ocular surface diseases that has the ability to addresses the emphasis on personalized medicine and biomarkers of disease. Future research directions will likely include (1) standardize tear collection, storage, extraction, and sample preparation; (2) quantitative proteomic analysis of tear proteins using multiple reaction monitoring (MRM)-based mass spectrometry; (3) population based studies of human tear proteomics/metabolomics; (4) tear proteomics/metabolomics for systemic diseases; and (5) functional studies of tear proteins.

Role of host-defence peptides in eye diseases

The eye and its associated tissues including the lacrimal system and lids have evolved several defence mechanisms to prevent microbial invasion. Included among this armory are several host-defence peptides. These multifunctional molecules are being studied not only for their endogenous antimicrobial properties but also for their potential therapeutic effects. Here the current knowledge of host-defence peptide expression in the eye will be summarised. The role of these peptides in eye disease will be discussed with the primary focus being on infectious keratitis, inflammatory conditions including dry eye and wound healing. Finally the potential of using host-defence peptides and their mimetics/derivatives for the treatment and prevention of eye diseases is addressed.

Atopic dermatitis and keratoconjunctivitis

Atopic dermatitis, a chronic disease seen by allergist-immunologists, has both dermatologic and ocular manifestations. The ocular component is often disproportionately higher than the dermatologic disease. Even if skin abnormalities seem well controlled, these patients require ophthalmic evaluation. Atopic keratoconjunctivitis in atopic dermatitis patients is characterized by acute exacerbations and requires maintenance therapy for long-term control. Future studies will continue to emphasize the use of steroid-sparing, immunomodulating agents that have the potential to provide long-lasting anti-inflammatory control with a more favorable side-effect profile.

The role of antimicrobial peptides at the ocular surface

Antimicrobial peptides (AMPs) such as defensins and cathelicidins are small peptides with broad-spectrum activity against bacteria, fungi and viruses. In addition, several AMPs modulate mammalian cell behaviours including migration, proliferation and cytokine production. This review describes findings from recent studies showing the presence of various AMPs at the human ocular surface and discusses their mechanism of antimicrobial action and potential non-microbicidal roles. Corneal and conjunctival epithelial cells produce beta-defensins and the cathelicidin LL-37, whereas neutrophils, infiltrating in response to a specific stimulus, supply additional LL-37 as well as alpha-defensins. In vitro studies suggest that LL-37 and human beta-defensin-3 are the most likely to have significant independent antimicrobial activity, while other AMPs may act synergistically to help protect the ocular surface from invading pathogens. Current evidence also supports a role for some AMPs in modulating wound healing responses. Although yet to be brought to fruition, AMPs hold significant potential as therapeutic agents for the prophylaxis and treatment of infection, promotion of wound healing and immune modulation.

Laboratory findings in tear fluid analysis

The tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The tear film covering the ocular surface presents a mechanical and antimicrobial barrier and ensures an optical refractive surface. The lipid component originates from the meibomian glands of the tarsus and forms the superficial layer of the tear film. The aqueous component contains electrolytes, water, and a large variety of proteins, peptides and glycoproteins, and is primarily secreted by the lacrimal gland. Mucins are glycoproteins expressed by epithelial tissues of mucous surfaces. They protect tissues by functioning as antioxidants, providing lubrication, and inhibiting bacterial adherence. Quantitatively and qualitatively, its composition must be maintained within the fairly narrow limits to maintain a healthy and functional visual system. Abnormalities of the tear film, affecting the constituents or the volume, can rapidly result in serious dysfunction of the eyelids and conjunctiva and ultimately affect the transparency of the cornea. Many ocular surface tests have been developed for the clinical diagnosis of dry eye syndromes. This paper provides an overview on laboratory methods for the analysis of the tear film. Understanding the components of the tear film will aid in the treatment of dry eye syndromes and the ocular surface diseases.