Interaction of Pseudomonas aeruginosa with human tear fluid components

Mass spectrometry analysis of human tear fluid biomarkers specific for ocular and systemic diseases in the context of 3P medicine

Over the last two decades, a large number of non-communicable/chronic disorders reached an epidemic level on a global scale such as diabetes mellitus type 2, cardio-vascular disease, several types of malignancies, neurological and eye pathologies-all exerted system's enormous socio-economic burden to primary, secondary, and tertiary healthcare. The paradigm change from reactive to predictive, preventive, and personalized medicine (3PM/PPPM) has been declared as an essential transformation of the overall healthcare approach to benefit the patient and society at large. To this end, specific biomarker panels are instrumental for a cost-effective predictive approach of individualized prevention and treatments tailored to the person. The source of biomarkers is crucial for specificity and reliability of diagnostic tests and treatment targets. Furthermore, any diagnostic approach preferentially should be noninvasive to increase availability of the biomaterial, and to decrease risks of potential complications as well as concomitant costs. These requirements are clearly fulfilled by tear fluid, which represents a precious source of biomarker panels. The well-justified principle of a "sick eye in a sick body" makes comprehensive tear fluid biomarker profiling highly relevant not only for diagnostics of eye pathologies but also for prediction, prognosis, and treatment monitoring of systemic diseases. One prominent example is the Sicca syndrome linked to a cascade of severe complications that include dry eye, neurologic, and oncologic diseases. In this review, protein profiles in tear fluid are highlighted and corresponding biomarkers are exemplified for several relevant pathologies, including dry eye disease, diabetic retinopathy, cancers, and neurological disorders. Corresponding analytical approaches such as sample pre-processing, differential proteomics, electrophoretic techniques, high-performance liquid chromatography (HPLC), enzyme-linked immuno-sorbent assay (ELISA), microarrays, and mass spectrometry (MS) methodology are detailed. Consequently, we proposed the overall strategies based on the tear fluid biomarkers application for 3P medicine practice. In the context of 3P medicine, tear fluid analytical pathways are considered to predict disease development, to target preventive measures, and to create treatment algorithms tailored to individual patient profiles.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

Pseudomonas aeruginosa Survival at Posterior Contact Lens Surfaces after Daily Wear

PURPOSE

Pseudomonas aeruginosa keratitis is a sight-threatening complication of contact lens wear, yet mechanisms by which lenses predispose to infection remain unclear. Here, we tested the hypothesis that tear fluid at the posterior contact lens surface can lose antimicrobial activity over time during lens wear.

METHODS

Daily disposable lenses were worn for 1, 2, 4, 6, or 8 hours immediately after removal from their packaging or after presoaking in sterile saline for 2 days to remove packaging solution. Unworn lenses were also tested, some coated in tears "aged" in vitro for 1 or 8 hours. Lenses were placed anterior surface down into tryptic soy agar cradles containing gentamicin (100 μg/mL) to kill bacteria already on the lens and posterior surfaces inoculated with gentamicin-resistant P. aeruginosa for 3 hours. Surviving bacteria were enumerated by viable counts of lens homogenates.

RESULTS

Posterior surfaces of lenses worn by patients for 8 hours supported more P. aeruginosa growth than lenses worn for only 1 hour, if lenses were presoaked before wear (∼ 2.4-fold, p = 0.01). This increase was offset if lenses were not presoaked to remove packaging solution (p = 0.04 at 2 and 4 hours). Irrespective of presoaking, lenses worn for 8 hours showed more growth on their posterior surface than unworn lenses coated with tear fluid that was aged for 8 hours in vitro (∼ 8.6-fold, presoaked, p = 0.003; ∼ 5.4-fold from packaging solution, p = 0.004). Indeed, in vitro incubation did not impact tear antimicrobial activity.

CONCLUSIONS

This study shows that postlens tear fluid can lose antimicrobial activity over time during contact lens wear, supporting the idea that efficient tear exchange under a lens is critical for homeostasis. Additional studies are needed to determine applicability to other lens types, wearing modalities, and relevance to contact lens-related infections.

Antimicrobial compounds in tears

The tear film coats the cornea and conjunctiva and serves several important functions. It provides lubrication, prevents drying of the ocular surface epithelia, helps provide a smooth surface for refracting light, supplies oxygen and is an important component of the innate defense system of the eye providing protection against a range of potential pathogens. This review describes both classic antimicrobial compounds found in tears such as lysozyme and some more recently identified such as members of the cationic antimicrobial peptide family and surfactant protein-D as well as potential new candidate molecules that may contribute to antimicrobial protection. As is readily evident from the literature review herein, tears, like all mucosal fluids, contain a plethora of molecules with known antimicrobial effects. That all of these are active in vivo is debatable as many are present in low concentrations, may be influenced by other tear components such as the ionic environment, and antimicrobial action may be only one of several activities ascribed to the molecule. However, there are many studies showing synergistic/additive interactions between several of the tear antimicrobials and it is highly likely that cooperativity between molecules is the primary way tears are able to afford significant antimicrobial protection to the ocular surface in vivo. In addition to effects on pathogen growth and survival some tear components prevent epithelial cell invasion and promote the epithelial expression of innate defense molecules. Given the protective role of tears a number of scenarios can be envisaged that may affect the amount and/or activity of tear antimicrobials and hence compromise tear immunity. Two such situations, dry eye disease and contact lens wear, are discussed here.

Preservation of human tear protein structure and function by a novel contact lens multipurpose solution containing protein-stabilizing agents

OBJECTIVES

Tear film proteins have antimicrobial and other functions that may be lost after denaturation during contact lens wear. A new multipurpose solution has recently become available (Biotrue, Bausch + Lomb Inc., Rochester, NY), which contains protein-stabilizing agents including hyaluronic acid, poloxamine, and sulfobetaine 10, the latter used previously as a laboratory tool to renature proteins. We examine whether this new multipurpose solution formulation can prevent the denaturation of human lactoferrin and lysozyme at physiologic levels in response to a powerful denaturing challenge.

METHODS

Human lactoferrin and lysozyme were treated with sodium dodecyl sulfate (SDS) either with or without an investigational version of the new multipurpose solution (without its two disinfectant agents) (investigational multipurpose solution [iMPS]). The structure was assessed by native-polyacrylamide gel electrophoresis (PAGE), differential scanning calorimetry (DSC), and fluorometry; additionally, antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus was measured.

RESULTS

The iMPS prevented an SDS-induced shift in the native-PAGE banding position of lactoferrin. The SDS treatment substantially altered the lactoferrin DSC and fluorescence spectra, indicating that the protein had denatured. This change did not occur in the presence of iMPS. Lactoferrin and lysozyme showed antibacterial and bacteriolytic activity, which was abolished after SDS treatment; this loss of activity did not occur for proteins treated with iMPS.

CONCLUSIONS

These data clearly show that the iMPS prevents the denaturation of physiologic levels of human lactoferrin and lysozyme by the strongly denaturing surfactant SDS and that stabilized proteins retain their function. We conclude that this solution has the capacity to stabilize the structure and function of tear proteins.

Distribution of sialic acids on mucins and gels: a defense mechanism

Moist mucosal epithelial interfaces that are exposed to external environments are dominated by sugar epitopes, some of which (e.g., sialic acids) are involved in host defense. In this study, we determined the abundance and distribution of two sialic acids to assess differences in their availability to an exogenous probe in isolated mucins and mucous gels. We used atomic force microscopy to obtain force maps of human preocular mucous and purified ocular mucins by probing and locating the interactions between tip-tethered lectins Maackia amurensis and Sambucus nigra and their respective receptors, α-2,3 and α-2,6 N-acetylneuraminic (sialic) acids. The rupture force distributions were not affected by neighboring sugar-bearing molecules. Energy contours for both lectin-sugar bonds were fitted to a two-barrier model, suggesting a conformational change before dissociation. In contrast to data from purified mucin molecules, the preocular gels presented numerous large clusters (19,000 ± 4000 nm(2)) of α-2,6 sialic acids, but very few small clusters (2000 ± 500 nm(2)) of α-2,3 epitopes. This indicates that mucins, which are rich in α-2,3 sialic acids, are only partially exposed at the surface of the mucous gel. Microorganisms that recognize α-2,3 sialic acids will encounter only isolated ligands, and the adhesion of other microorganisms will be enhanced by large islands of neighboring α-2,6 sialic acids. We have unveiled an additional level of mucosal surface heterogeneity, specifically in the distribution of pro- and antiadhesive sialic acids that protect underlying epithelia from viruses and bacteria.

Factors impacting corneal epithelial barrier function against Pseudomonas aeruginosa traversal

PURPOSE

Mechanisms determining epithelial resistance versus susceptibility to microbial traversal in vivo remain poorly understood. Here, a novel murine model was used to explore factors influencing the corneal epithelial barrier to Pseudomonas aeruginosa penetration.

METHODS

Murine corneas were blotted with tissue paper before inoculation with green fluorescent protein-expressing P. aeruginosa. The impact of blotting on epithelial integrity was evaluated by susceptibility to fluorescein staining and histology. Using fluorescence imaging, blotted corneas were compared to nonblotted corneas for susceptibility to bacterial binding and epithelial penetration after 5 hours or were monitored for disease development. In some experiments, inoculation was performed ex vivo to exclude tear fluid or corneas were pretreated with EGTA to disrupt Ca(2+)-dependent factors. The role of surfactant protein D (SP-D), which inhibits P. aeruginosa cell invasion in vitro, was examined using knockout mice.

RESULTS

Blotting enabled fluorescein penetration through the epithelium into the underlying stroma without obvious disruption to corneal morphology. Although blotting enabled bacterial binding to the otherwise adhesion-resistant epithelial surface, adherent bacteria did not penetrate the surface or initiate pathology. In contrast, bacteria penetrated blotted corneas after EGTA treatment and in SP-D knockouts. Visible disease occurred and progressed only in aged, blotted, and EGTA-treated, SP-D knockout mice.

CONCLUSIONS

Neither fluorescein staining nor bacterial adhesion necessarily predict or enable corneal susceptibility to bacterial penetration or disease. Corneal epithelial defenses limiting traversal by adherent bacteria include EGTA-sensitive factors and SP-D. Understanding mechanisms modulating epithelial traversal by microbes could improve our understanding of susceptibility to infection and may indicate new strategies for preventing disease.

Assessment of Streptococcus pneumoniae capsule in conjunctivitis and keratitis in vivo neuraminidase activity increases in nonencapsulated pneumococci following conjunctival infection

PURPOSE

The pneumococcal capsule is required for pathogenesis in systemic infections, yet reports show most conjunctivitis outbreaks are caused by nonencapsulated pneumococci, while keratitis infections are caused by encapsulated strains. This study aims to determine the effect of capsule in pneumococcal keratitis and conjunctivitis in rabbit models of infection.

METHODS

A capsule-deficient isogenic mutant was created using homologous transformation. Parent and mutant strains were injected within the upper bulbar conjunctiva (conjunctivitis) or into the corneal stroma (keratitis) of New Zealand white rabbits. Clinical examinations were performed 24 and 48 hr post-infection at which time corneas or conjunctivae were removed, homogenized, and plated to determine the recovered bacterial load. Whole eyes were removed for histological examination. The neuraminidase activity was determined following in vitro and in vivo growth.

RESULTS

There were no significant differences in clinical scores between the eyes infected with the parent or mutant for either infection, nor was there a difference in the amount of bacteria recovered from the cornea. In the conjunctivae, however, the mutant strain was cleared by the host faster than the parent strain. Histological examination showed slightly more infiltrating polymorphonuclear leukocytes (PMN) and macrophages in the conjunctivae infected with the parent strain. The neuraminidase activity of both strains was not significantly different when the strains were grown in vitro. However, the neuraminidase activity of the parent was significantly less than that of the mutant at 3 and 12 hr post conjunctival infection.

CONCLUSIONS

Although more outbreaks of pneumococcal conjunctivitis are tied to nonencapsulated S. pneumoniae strains, this study showed that an encapsulated strain was capable of establishing conjunctivitis in a rabbit injection model and survive attack by the host immune system longer than its nonencapsulated isogenic mutant. Nonetheless, the nonencapsulated pneumococci had an increased neuraminidase activity level in vivo when compared to the parent strain.

Pathogenesis of contact lens-associated microbial keratitis

Sight-threatening microbial keratitis associated with contact lens wear remains a serious concern for patients, eye-care practitioners, and the contact lens industry. Several decades of research and some major advances in lens and solution technology have not resulted in a decline in disease incidence. Here, we offer a perspective on the complex pathogenesis of microbial keratitis, the factors that have prevented a better understanding of this disease, and new approaches being used to tackle this important clinical problem.

Optimal neural differentiation and extension of hybrid neuroblastoma cells (NDC) for nerve-target evaluations using a multifactorial approach

In vitro models of tissues, such as the cornea, represent systems for modeling cell-to-cell interactions and tissue function. The objective of this study was to develop an optimized nerve differentiation medium to incorporate into a 3D in vitro model to study innervation and cell targeting. A hybrid neuroblastoma cell line (NDC) was examined for its ability to differentiate into neurons, produce neurites, and functionally contact target cells. Neuronal differentiation of NDCs was optimized through a combinatorial approach which involved culturing cells in the presence of various extracellular matrices and soluble factors. A serum-free medium containing nerve growth factor (NGF), dimethyl sulfoxide (DMSO), or dexamethasone resulted in the greatest proportion of NDCs demonstrating a neuronal morphology. Similarly, with supplementation of cyclic AMP (cAMP) or NGF, neurite extension was optimized. Combining these factors generated an optimized differentiation and extension medium, relative to the individual components alone. In co-culture with epithelial cells, NDC neurites generated in the optimized medium formed contacts with epithelial targets and produced substance P. Similarly, NDCs seeded into a collagen matrix produced neurites that projected through the matrix to target epithelial cells, promoted epithelial stratification, and increased the rate of epithelial wound healing. As well, differentiated NDCs could target and alter acetylcholine receptor clustering in mouse C2C12 myotubes, demonstrating synaptic plasticity. Our data supports the use of NDCs, in combination with optimized medium, for generating an innervated in vitro model.

Life at the front: dissecting bacterial-host interactions at the ocular surface

The ocular surface usually looks quiet, presenting a general impression of biological inactivity. Yet, the ability of the cornea to maintain health while continually exposed to environmental insults, and in the relative absence of immune strategies afforded by other body sites, reflects its complexity. Because it is critical for transparency and, therefore, our survival, the fine structure of the cornea has likely provided the driving force for the evolution of what appears to be a truly remarkable system. While several molecules are now known to participate, we are only beginning to obtain the knowledge to fully explain the mechanisms involved in corneal resistance to infection. Full explanation will require a better understanding of the interplay between microbes and various components of the ocular surface, and of the critical factors determining health as the usual outcome. To understand infectious disease, we need to consider how the scenario changes in conditions associated with susceptibility. What we learn in the process could yield a wealth of potential therapies for a wide variety of diseases of the eye and of other sites.

Human tear fluid protects against Pseudomonas aeruginosa keratitis in a murine experimental model

Pseudomonas aeruginosa keratitis is an acute sight-threatening infection. We previously reported that human tear fluid could protect individual human corneal epithelial cells in vitro against invasion by and cytotoxicity due to clinical and laboratory isolates of P. aeruginosa and that the protective mechanism was independent of bacteriostatic activity. In the present study, we examined the effects of human tear fluid in vivo. Tears were collected from healthy human volunteers and were studied in vivo in mice. The effects on the virulence of both invasive and cytotoxic clinical isolates of P. aeruginosa were examined. Tear fluid was found to reduce the severity of disease when corneas were challenged with cytotoxic bacteria immediately after scratch injury, and it completely protected against susceptibility to infection by a cytotoxic strain in a model in which corneas were infected during the healing process 6 h after scratching. Visible protection correlated with the inhibition of bacterial colonization 1, 4, and 48 h postinoculation. Tear fluid also significantly reduced the severity of infections caused by invasive P. aeruginosa in the 6-h-healing model. This result also coincided with significantly reduced bacterial colonization at 48 h. In vitro, human tear fluid significantly reduced the ability of invasive and cytotoxic bacteria to translocate across corneal epithelia and increased transepithelial resistance with or without bacterial inoculation. These data show that human tear fluid can protect against P. aeruginosa corneal infection in vivo and that the mechanism likely involves enhanced epithelial barrier function in addition to protection of individual epithelial cells against bacterial internalization and cytotoxicity.

MUC16 in the lacrimal apparatus

The aim of the present study was to determine the possible expression of the mucin MUC16 in the lacrimal apparatus. Expression and distribution of MUC16 in lacrimal gland, accessory lacrimal glands, and nasolacrimal ducts was monitored by RT-PCR and immunohistochemistry. MUC16 was expressed and detected in all tissues investigated. Comparable to conjunctiva and cornea it was membrane-anchored in accessory lacrimal glands whereas in lacrimal gland acinar cells and columnar cells of the nasolacrimal ducts it was stored in intracytoplasmic vesicles without membrane-association. Subepithelial serous glands of the nasolacrimal ducts revealed staining of the secretion product. Intracelluar production of MUC16 is present in lacrimal gland and epithelial cells of the nasolacrimal ducts but it is not clear whether this MUC16 is secreted. MUC16 seems to be shedded or secreted from the epithelial surface of subepithelial serous glands of the nasolacrimal ducts. Our results show that MUC16 is present in the whole lacrimal apparatus. Its distribution pattern suggests different physiological functions with regard to tear film physiology and tear outflow. Moreover, the results demonstrate the existence of so far not recognized qualitative differences in the secretion product of main lacrimal gland and accessory lacrimal glands (glands of Krause).

The Pathogenesis of Contact Lens-Related Keratitis

Bacterial infection of the cornea is a rare, but sight-threatening, complication of contact lens wear that was first reported shortly after soft lenses were introduced onto the market in the 1970s. During the past 3 decades, various attempts to solve the problem with new lens types and lens care products have failed to make a significant impact on its incidence. Eliminating contact lens-related infections will likely require a better understanding of the ocular defense system, microbial virulence strategies, how they affect one another, and the effects of contact lens wear on both. Each of these topics is complex. Although research in this area is therefore challenging and necessitates a multidisciplinary approach, what we are learning along the way has significance beyond contact lens-related infection and could ultimately lead to the development of new strategies to prevent this and a range of other sight- and life-threatening diseases.

Mucins and TFF peptides of the tear film and lacrimal apparatus

The three-dimensional organization of the tear film, which is produced and drained by the different structures of the ocular adnexa, is essential for maintainance and protection of the ocular surface. This is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins, the mucins, which are usually expressed in association with a class of peptides having a well-defined, structurally conserved trefoil domain, the mammalian trefoil factor family (TFF) peptides. In this review, the latest information regarding mucin and TFF peptide function and regulation in the human lacrimal system, the tear film and the ocular surface is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes and certain disease states such as dry eye, dacryostenosis and dacryolith formation.