Glycan structures of ocular surface mucins in man, rabbit and dog display species differences

A common polymorphism in the Intelectin-1 gene influences mucus plugging in severe asthma

By incompletely understood mechanisms, type 2 (T2) inflammation present in the airways of severe asthmatics drives the formation of pathologic mucus which leads to airway mucus plugging. Here we investigate the molecular role and clinical significance of intelectin-1 (ITLN-1) in the development of pathologic airway mucus in asthma. Through analyses of human airway epithelial cells we find that ITLN1 gene expression is highly induced by interleukin-13 (IL-13) in a subset of metaplastic MUC5AC+ mucus secretory cells, and that ITLN-1 protein is a secreted component of IL-13-induced mucus. Additionally, we find ITLN-1 protein binds the C-terminus of the MUC5AC mucin and that its deletion in airway epithelial cells partially reverses IL-13-induced mucostasis. Through analysis of nasal airway epithelial brushings, we find that ITLN1 is highly expressed in T2-high asthmatics, when compared to T2-low children. Furthermore, we demonstrate that both ITLN-1 gene expression and protein levels are significantly reduced by a common genetic variant that is associated with protection from the formation of mucus plugs in T2-high asthma. This work identifies an important biomarker and targetable pathways for the treatment of mucus obstruction in asthma.

Review of clinical outcomes of a cationic emulsion tear substitute in patients with dry eye disease

First-line options for the treatment of dry eye disease (DED) rely on artificial tears (ATs), among which cationic emulsion (CE)-based ATs have been developed in order to mimic the healthy tear film for an improved restoration of the ocular surface homeostasis. In this review, we describe the outcomes reported in several studies, assessing the mode of action, ocular tolerance and clinical performance of a CE-based AT. Pilot studies have revealed that CE-based ATs can increase the volume and stability of the tear film while limiting its evaporation rate. Larger studies have demonstrated that CE-based ATs play a significant role in the improvement of both objective and subjective DED parameters, including superior efficacy on DED symptoms compared to several other available AT formulation types. Concomitantly, CE-based ATs have been shown to help patients to prevent or recover from corneal defects associated with refractive surgery. These positive outcomes on ocular surface epithelia are likely due to the combination of unique rheological behaviour and intrinsic anti-inflammatory properties. Based on all clinical findings, CE-based ATs represent a valuable treatment option for patients with various etiologies of DED including evaporative forms and would deserve evaluation of benefits in other surgical intervention types triggering DED.

Use of a Cationic Emulsion of Latanoprost to Treat Glaucoma Patients with Ocular Surface Disease: A Preclinical Review

Prostaglandin analogue topical medications are one of the most effective therapeutic approaches for the chronic management of glaucoma and ocular hypertension, through the reduction of elevated intra ocular pressure (IOP). While many of the first generations of anti-glaucoma eye drops were preserved with benzalkonium chloride, their repeated use may induce chronic ocular surface toxicity that leads to ocular surface disease (OSD) signs and symptoms. As a result, soft-preservatives and preservative-free formulations have been developed with the goal to avoid the long-term iatrogenic toxicity of the preservative agents. In addition, it has been suggested that OSD and its associated inflammation may negatively impact the efficacy of the IOP-lowering medications, including treatment adherence and compliance. Hence, it may be particularly interesting that glaucoma medications can concomitantly protect and "heal" the ocular surface and its environment while lowering elevated IOP, for the greater benefit of glaucoma patients. The objective of the present review is to briefly present the preclinical data of the cationic oil-in-water emulsion of latanoprost (latanoprost-CE) to shed some light on its mechanisms of action. It overall supports the following hypothesis: the restoration of a healthy ocular surface environment and treatment of the OSD signs and symptoms will allow for an improved elevated IOP reduction and glaucoma management. This would be achieved with a once daily dosing regimen to preserve glaucoma patients' vision, ocular surface, and quality-of-life and wellness.

Review of Preclinical Outcomes of a Topical Cationic Emulsion of Cyclosporine A for the Treatment of Ocular Surface Diseases

BACKGROUND

Cyclosporine A (CsA) has been used as a topical treatment for various ocular surface diseases including dry eye disease (DED). Several CsA formulations are available as solutions or emulsions.

PURPOSE

This review describes the development and the preclinical testing of a cationic oil-in-water emulsion of CsA (CE-CsA) in terms of pharmacodynamics, pharmacokinetics, and ocular tolerance. Due to the cationic charge, CE electrostatically interacts with the negatively-charged ocular surface, improving its residence time. Compared to other CsA formulations, CE-CsA and CE itself were found to reduce the signs and symptoms of DED, by restoring tear film stability and properties, and inhibiting the expression and secretion of pro-inflammatory factors. No delay in wound healing nor ocular toxicity were observed using CE formulations.

CONCLUSION

these findings indicate that the type of vehicle can significantly affect the performance of eye drops and play an ancillary role in DED treatment. CE appears as a promising strategy to deliver drugs to the ocular surface while maintaining its homeostasis.

Characterization of human tear proteome reveals differentially abundance proteins in thyroid-associated ophthalmopathy

Background

Thyroid-associated ophthalmopathy (TAO) is a common orbital inflammatory disease, but the abnormal expression of proteins in tears of TAO patients has not been systematically studied. The purpose of this study is to compare and analyze the total tear protein profile of TAO patients and to provide protein cues for TAO pathogenesis.

Methods

Tear samples were isolated from 30 TAO patients with obvious ocular surface damage and 30 healthy control subjects. Tear samples from 30 individuals were mixed and divided into three sample pools. Easy nano-scale LC-MS/MS based on labeling-free quantitative technology was utilized to profile tear proteome.

Results

Here, electrospray ionization mass spectra and SDS-PAGE results confirmed the good parallelisms among samples. A total of 313 proteins were obtained from six tear pools, among them, 103 differential abundance proteins (DAPs) were identified, including 99 up-regulated DAPs (including APOA1, HV103, IGH, and Transferrin variant) and four down-regulated DAPs (including FABA, VCC1, NUCB2, and E-cadherin) in the TAO group compared with the control group. GO analysis showed that up-regulated DAPs were mainly enriched in lipid metabolism and platelet molecular function, and down-regulated DAPs were involved in binding, cell junction, and cellular process. KEGG results indicated that DAPs were involved in 117 kinds of signal transduction pathways, among which the immune-related pathway of complement and coagulation cascades had the greatest relevance.

Conclusion

In conclusion, label-free LC-MS/MS is an effective strategy for profiling tear proteins component. Our study provides proteins and pathways altered in TAO and provides protein cues for further study on the precise mechanism of TAO pathogenesis.

Untangling Mucosal Drug Delivery: Engineering, Designing, and Testing Nanoparticles to Overcome the Mucus Barrier

Mucus is a complex viscoelastic gel and acts as a barrier covering much of the soft tissue in the human body. High vascularization and accessibility have motivated drug delivery to various mucosal surfaces; however, these benefits are hindered by the mucus layer. To overcome the mucus barrier, many nanomedicines have been developed, with the goal of improving the efficacy and bioavailability of drug payloads. Two major nanoparticle-based strategies have emerged to facilitate mucosal drug delivery, namely, mucoadhesion and mucopenetration. Generally, mucoadhesive nanoparticles promote interactions with mucus for immobilization and sustained drug release, whereas mucopenetrating nanoparticles diffuse through the mucus and enhance drug uptake. The choice of strategy depends on many factors pertaining to the structural and compositional characteristics of the target mucus and mucosa. While there have been promising results in preclinical studies, mucus-nanoparticle interactions remain poorly understood, thus limiting effective clinical translation. This article reviews nanomedicines designed with mucoadhesive or mucopenetrating properties for mucosal delivery, explores the influence of site-dependent physiological variation among mucosal surfaces on efficacy, transport, and bioavailability, and discusses the techniques and models used to investigate mucus-nanoparticle interactions. The effects of non-homeostatic perturbations on protein corona formation, mucus composition, and nanoparticle performance are discussed in the context of mucosal delivery. The complexity of the mucosal barrier necessitates consideration of the interplay between nanoparticle design, tissue-specific differences in mucus structure and composition, and homeostatic or disease-related changes to the mucus barrier to develop effective nanomedicines for mucosal delivery.

Human ocular mucins: The endowed guardians of sight

Mucins are an ancient group of glycoproteins that provide viscoelastic, lubricating and hydration properties to fluids bathing wet surfaced epithelia. They are involved in the protection of underlying tissues by forming a barrier with selective permeability properties. The expression, processing and spatial distribution of mucins are often determined by organ-specific requirements that in the eye involve protecting against environmental insult while allowing the passage of light. The human ocular surface epithelia have evolved to produce an extremely thin and watery tear film containing a distinct soluble mucin product secreted by goblet cells outside the visual axis. The adaptation to the ocular environment is notably evidenced by the significant contribution of transmembrane mucins to the tear film, where they can occupy up to one-quarter of its total thickness. This article reviews the tissue-specific properties of human ocular mucins, methods of isolation and detection, and current approaches to model mucin systems recapitulating the human ocular surface mucosa. This knowledge forms the fundamental basis to develop applications with a promising biological and clinical impact.

Purified mucins in drug delivery research

One of the main challenges in the field of drug delivery remains the development of strategies to efficiently transport pharmaceuticals across mucus barriers, which regulate the passage and retention of molecules and particles in all luminal spaces of the body. A thorough understanding of the molecular mechanisms, which govern such selective permeability, is key for achieving efficient translocation of drugs and drug carriers. For this purpose, model systems based on purified mucins can contribute valuable information. In this review, we summarize advances that were made in the field of drug delivery research with such mucin-based model systems: First, we give an overview of mucin purification procedures and discuss the suitability of model systems reconstituted from purified mucins to mimic native mucus. Then, we summarize techniques to study mucin binding. Finally, we highlight approaches that made use of mucins as building blocks for drug delivery platforms or employ mucins as active compounds.

The effect of ingredients commonly used in nasal and inhaled solutions on the secretion of mucus in vitro

Hypersecretion of mucus is associated with impaired mucociliary clearance that can influence the retention of active pharmaceutical ingredients in the airway but is also linked with recurrent airway disease. Therefore, the effect on mucin secretion of a range of ingredients used in solutions delivered to the nose and lung was studied. Mucin secretion from explants of ovine epithelium was quantified using an enzyme-linked lectin assay (ELLA) or sandwich ELLA depending on the compatibility of the ingredients with the assay. Benzalkonium chloride (0.015% w/w), Methocel™ E50 premium LV (1.0% w/w), propylene glycol (1.5% w/w), potassium sorbate + propylene glycol (0.3% w/w + 1.5% w/w) and polysorbate 80 (0.025% w/w), used at common working concentrations, all increased the secretion of mucin from the explants (P < 0.05). Ethylenediamine tetraacetic acid-disodium salt (EDTA) (0.015% w/w), Avicel® RC591 (1.5% w/w), fluticasone furoate (0.0004% w/w, concentration in solution) and dimethyl sulfoxide (DMSO) (0.2% w/w) did not affect mucin secretion. Compounds increasing mucin secretion could alter the rate of mucociliary clearance and the mucus could provide a barrier to drug absorption. This could predispose patients to disease and affect the activity of delivered drugs, decreasing or increasing their clinical efficacy.

Comparative analysis of 0.1% cyclosporin A cationic emulsion and 0.05% cyclosporin A emulsion in murine dry eye cases with different severities

Dry eye (DE), especially severe DE (SDE), can cause ocular surface defects and reduce the patient's quality of life. Several clinical studies have shown that 0.1% cyclosporin A cationic emulsion (CsA CE) could decrease corneal damage. However, no experimental study has reported the effect of 0.1% CsA CE on SDE. The present study aimed to compare the efficacy of 0.1% CsA CE with that of 0.05% CsA emulsion for ocular surface damage and inflammation in the cases of murine DE with different severities. Following exposure to desiccating stress and subcutaneous injection of scopolamine for 5 days, C57BL/6 female mice were divided into SDE and non-SDE (NSDE) groups based on corneal fluorescein staining scores (CFSs). Mice from both groups were topically treated with 0.05% CsA emulsion or 0.1% CsA CE for 10 days. The results demonstrated that 0.1% CsA CE-treated mice in the SDE and NSDE groups exhibited significant improvements in all the clinical and experimental parameters. Furthermore, the CFS of 0.1% CsA CE-treated mice in the SDE group was lower compared with that of the 0.05% CsA-treated mice. In addition, in the SDE group, 0.1% CsA CE-treated mice had significantly lower levels of nuclear factor-κB activation, inflammatory infiltrations and apoptosis on the ocular surface, and they also exhibited higher conjunctival goblet cell density compared with the 0.05% CsA-treated mice. In summary, these findings indicated that 0.1% CsA CE was more effective than topical 0.05% CsA emulsion at improving corneal epithelial injury and decreasing the levels of inflammatory cytokines and T cells in mice with SDE.

Highly sialylated mucin-type glycopeptide from porcine intestinal mucosa after heparin extraction: O-glycan profiling and immunological activity evaluation

Mucins are the major proteins that distributed on the intestinal mucosa layer and protect the intestine from pathogens infection. The composition of intestinal mucin O-glycans can affect the health of the gastrointestinal tract in pigs. Porcine intestinal mucosa is widely used as the main raw material of heparin extraction. The heparin extraction residues rich in mucins were usually wasted. The structure of mucin derived O-glycans in porcine intestinal mucosa are currently unknown. In this study, we isolated the mucins from the heparin extraction residues and profiled the O-glycans. After heparin extraction, mucin was digested with trypsin, and separated by strong anion exchange chromatography. The mucin derived O-glycans were release by alkaline β elimination, and analyzed by ultra high performance liquid chromatography-porous graphitized carbon-Fourier transform mass spectrometry (UPLC-PGC-FTMS/MS). Thirty five kinds of O-glycans were identified, most of which were Core 3-derived glycans. In particular, the O-glycans containing sialic acid Neu5Ac accounted for 71.93% of the total O-glycans, which were different from that of other species, including mouse intestine, fish intestine, and porcine colon. The high content sialylated mucin may explain its effect in biological processes. Furthermore, the immunological activity results indicated that the porcine intestinal mucin could promote phagocytosis and proliferation without any cytotoxic effects, which may aid in the development of immunomodulators.

Inhibition of Aberrant α(1,2)-Fucosylation at Ocular Surface Ameliorates Dry Eye Disease

Fucosylation is involved in a wide range of biological processes from cellular adhesion to immune regulation. Although the upregulation of fucosylated glycans was reported in diseased corneas, its implication in ocular surface disorders remains largely unknown. In this study, we analyzed the expression of a fucosylated glycan on the ocular surface in two mouse models of dry eye disease (DED), the NOD.B10.H2^b mouse model and the environmental desiccating stress model. We furthermore investigated the effects of aberrant fucosylation inhibition on the ocular surface and DED. Results demonstrated that the level of type 2 H antigen, an α(1,2)-fucosylated glycan, was highly increased in the cornea and conjunctiva both in NOD.B10.H2^b mice and in BALB/c mice subjected to desiccating stress. Inhibition of α(1,2)-fucosylation by 2-deoxy-D-galactose (2-D-gal) reduced corneal epithelial defects and increased tear production in both DED models. Moreover, 2-D-gal treatment suppressed the levels of inflammatory cytokines in the ocular surface and the percentages of IFN-γ⁺CD4⁺ cells in draining lymph nodes, whereas it did not affect the number of conjunctival goblet cells, the MUC5AC level or the meibomian gland area. Together, the findings indicate that aberrant fucosylation underlies the pathogenesis of DED and may be a novel target for DED therapy.

Membrane-associated mucins of the human ocular surface in health and disease

Mucins are a family of high molecular weight, heavily-glycosylated proteins produced by wet epithelial tissues, including the ocular surface epithelia. Densely-packed O-linked glycan chains added post-translationally confer the biophysical properties of hydration, lubrication, anti-adhesion and repulsion. Membrane-associated mucins (MAMs) are the distinguishing components of the mucosal glycocalyx. At the ocular surface, MAMs maintain wetness, lubricate the blink, stabilize the tear film, and create a physical barrier to the outside world. In addition, it is increasingly appreciated that MAMs function as cell surface receptors that transduce information from the outside to the inside of the cell. Recently, our team published a comprehensive review/perspectives article for molecular scientists on ocular surface MAMs, including previously unpublished data and analyses on two new genes MUC21 and MUC22, as well as new MAM functions and biological roles, comparing human and mouse (PMID: 31493487). The current article is a refocus for the audience of The Ocular Surface. First, we update the gene and protein information in a more concise form, and include a new section on glycosylation. Next, we discuss biological roles, with some new sections and further updating from our previous review. Finally, we provide a new chapter on MAM involvement in ocular surface disease. We end this with discussion of an emerging mechanism responsible for damage to the epithelia and their mucosal glycocalyces: the unfolded protein response (UPR). The UPR offers a novel target for therapeutic intervention.

Characterization of the rabbit conjunctiva: Effects of sulfur mustard

Sulfur mustard (SM; bis (2-chloroethyl) sulfide) is a potent vesicant which causes irritation of the conjunctiva and damage to the cornea. In the present studies, we characterized the ocular effects of SM in New Zealand white rabbits. Within one day of exposure to SM, edema and hazing of the cornea were observed, followed by neovascularization which persisted for at least 28 days. This was associated with upper and lower eyelid edema and conjunctival inflammation. The conjunctiva is composed of a proliferating epithelium largely consisting of stratified columnar epithelial cells overlying a well-defined dermis. Superficial layers of the conjunctival epithelium were found to express keratin 1, a marker of differentiating squamous epithelium, while in cells overlying the basement membrane expressed keratin 17, a marker of stratified squamous epithelium. SM exposure upregulated keratin 17 expression. Mucin 5 ac producing goblet cells were interspersed within the conjunctiva. These cells generated both acidic and neutral mucins. Increased numbers of goblet cells producing neutral mucins were evident after SM exposure; upregulation of expression of membrane-associated mucin 1 and mucin 4 in the superficial layers of the conjunctival epithelium were also noted. These data demonstrate that ocular exposure of rabbits to SM causes significant damage not only to the cornea, but to the eyelid and conjunctiva, suggesting multiple targets within the eye that should be assessed when evaluating the efficacy of potential countermeasures.

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

Preclinical animal studies provide valuable opportunities to better understand human diseases and contribute to major advances in medicine. This review provides a comprehensive overview of ocular parameters in humans and selected animals, with a focus on the ocular surface, detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition. We describe major pitfalls that tremendously limit the translational potential of traditional laboratory animals (i.e., rabbits, mice, and rats) in ophthalmic research, and highlight the benefits of integrating companion dogs with clinical analogues to human diseases into preclinical pharmacology studies. This One Health approach can help accelerate and improve the framework in which ophthalmic research is translated to the human clinic. Studies can be conducted in canine subjects with naturally occurring or noninvasively induced ocular surface disorders (e.g., dry eye disease, conjunctivitis), reviewed herein, and tear fluid can be easily retrieved from canine eyes for various bioanalytical purposes. In this review, we discuss common tear collection methods, including capillary tubes and Schirmer tear strips, and provide guidelines for tear sampling and extraction to improve the reliability of analyte quantification (drugs, proteins, others).

Cationic nanoemulsions with prolonged retention time as promising carriers for ophthalmic delivery of tacrolimus

Tacrolimus, also known as FK506, is a first-line drug for the topical treatment of immune-mediated inflammatory anterior ocular diseases (IIAODs). However, due to its limited water solubility, hydrophobic nature and relatively high molecular weight, topical application of FK506 features poor bioavailability. Numbers of formulations have been attempted to enhance the erratic bioavailability of FK506 through various techniques. But until now, none of them could satisfy the clinical needs completely. Here, a novel formulation of FK506, FK506-loaded cationic nanoemulsions (FK506 CNE), was developed to prolong the precorneal residence time of FK506, thereby enhancing the bioavailability of FK506 for IIAODs therapy. FK506 CNE was prepared by high-pressure homogenization, and its composition was screened and optimized by single-factor experiments. The FK506 CNE showed spherical morphology with a mean diameter of 178.8 ± 2.7 nm and a zeta potential of +25.6 ± 0.6 mV. Results from in vivo gamma scintigraphy studies proved that the precorneal residence time of FK506 CNE was significantly increased, compared with FK506-loaded neutral nanoemulsions (FK506 NE) and saline. The data of aqueous humor pharmacokinetic study in rabbits showed that the relative bioavailability of FK506 CNE was 1.68-fold and 1.77-fold of FK506 NE and the marketed FK506 eye drops (Talymus®), respectively. Finally, hematoxylin and eosin staining images and in vitro cytotoxicity data confirmed the safety of the FK506 CNE. Taking all these into consideration, we propose that FK506 CNE is a promising topical ophthalmic nanoformulation for the management of IIAODs.

A Pyrrhic Victory: The PMN Response to Ocular Bacterial Infections

Some tissues of the eye are susceptible to damage due to their exposure to the outside environment and inability to regenerate. Immune privilege, although beneficial to the eye in terms of homeostasis and protection, can be harmful when breached or when an aberrant response occurs in the face of challenge. In this review, we highlight the role of the PMN (polymorphonuclear leukocyte) in different bacterial ocular infections that invade the immune privileged eye at the anterior and posterior segments: keratitis, conjunctivitis, uveitis, and endophthalmitis. Interestingly, the PMN response from the host seems to be necessary for pathogen clearance in ocular disease, but the inflammatory response can also be detrimental to vision retention. This "Pyrrhic Victory" scenario is explored in each type of ocular infection, with details on PMN recruitment and response at the site of ocular infection. In addition, we emphasize the differences in PMN responses between each ocular disease and its most common corresponding bacterial pathogen. The in vitro and animal models used to identify PMN responses, such as recruitment, phagocytosis, degranulation, and NETosis, are also outlined in each ocular infection. This detailed study of the ocular acute immune response to infection could provide novel therapeutic strategies for blinding diseases, provide more general information on ocular PMN responses, and reveal areas of bacterial ocular infection research that lack PMN response studies.

Profiling and Structural Characterization of High Neu5Gc or Sulfate-containing O-glycans from Hyla Rabbit Intestinal Mucin

Intestinal mucins constitute the major component of the mucus covering the epithelium of the gastrointestinal tract, thereby forming a barrier against microbial colonization. Rabbits are bred in large numbers worldwide, with little known about intestinal O-glycosylation despite this insight being crucial to the understanding of host-pathogen interactions. In the present study, a major mucin-type glycopeptide (RIF6) of hyla rabbit intestine was isolated and the O-glycans were extensively characterized based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with bioinformatics approaches. Thirty-three O-glycans were identified, and most of them were sulfated or sialylated glycans. It was worth noting that Neu5Gc-containing structures within sialylated O-glycans accounted for 91%, which were extremely different from that of other species including humans, mice, chickens, etc. Sulfated glycans accounted for 58%, unique disufated and sulfated-sialylated glycans were also detected in rabbit intestinal mucin. These structural characterization reflected species diversity and may provide deeper insights into explaining the adaptability of hyla rabbit to the environment.

Glycosylation pathways of human corneal and conjunctival epithelial cell mucins

Mucin glycoproteins on the ocular surface are rich in O-glycans and have important roles in the protection from physical, chemical and microbial impact. In this work, we have cultured human corneal and conjunctival epithelial cells to examine the glycosyltransferase activities that synthesize the O-glycans of mucins. The results indicate that ocular surface epithelial cells have active enzymes that synthesize O-glycans with sialylated core 1, Galβ1-3GalNAcα, and core 2, GlcNAcβ1-6(Galβ1-3)GalNAcα structures which corresponds to previous structural studies. Eye cells also have enzymes that synthesize complex N-glycans that are found on mucins. Results from treatment of eye cells with TNFα suggest that epithelial O-glycosylation changes in a dynamic fashion during inflammatory stimuli of the eye surface.

Evaluation of lacrimal production, osmolarity, crystallization, proteomic profile, and biochemistry of capuchin monkeys' tear film

BACKGROUND

To evaluate the composition and characteristics of capuchin monkey (CM) tear film.

METHODS

Eleven CM (Sapajus sp.) was evaluated. Strip meniscometry test (SMT), osmolarity, and tear ferning test (TFT) (by Rolando and Masmali scales) were assessed. Tear protein profile (SDS-PAGE), and total protein, albumin, urea, glucose, and cholesterol levels in tear film and blood serum were screened.

RESULTS

Median ± semi-interquatil range for SMT and osmolarity values were 8.0 ± 1.625 and 303.0 ± 9.875, respectively. TFT for Rolando was 2.0 ± 0.5, and Masmali was 2.0 ± 0.0. Monkeys's tear obtained type II and III for Rolando, and 1 and 2 for Masmali. Tear components showed protein bands among 23-217 kDa, and presence of albumin, urea, glucose, and cholesterol.

CONCLUSIONS

The results of SMT, osmolarity, TFT, SDS-PAGE, and tear biochemistry may serve as a reference baseline for CM, and the data may serve as a basis for future experimental model evaluations.

Beyond Bacteria: Bacteriophage-Eukaryotic Host Interactions Reveal Emerging Paradigms of Health and Disease

For decades, a wealth of information has been acquired to define how host associated microbial communities contribute to health and disease. Within the human microbiota this has largely focused on bacteria, yet there is a myriad of viruses that occupy various tissue sites, the most abundant being bacteriophages that infect bacteria. Animal hosts are colonized with niche specific microbial communities where bacteria are continuously co-evolving with phages. Bacterial growth, metabolic activity, pathogenicity, antibiotic resistance, interspecies competition and evolution can all be influenced by phage infection and the beneficial nature of such interactions suggests that to an extent phages are tolerated by their hosts. With the understanding that phage-specific host–microbe interactions likely contribute to bacterial interactions with their mammalian hosts, phages and their communities may also impact aspects of mammalian health and disease that have gone unrecognized. Here, we review recent progress in understanding how bacteria acquire and tolerate phage in both pure culture and within complex communities. We apply these findings to discuss how intra-body phages interact with bacteria to influence their eukaryotic hosts through potential contributions to microbial homeostasis, mucosal immunity, immune tolerance and autoimmunity.

Glycosylation pathways at the ocular surface

Glycosylation is a major form of enzymatic modification of organic molecules responsible for multiple biological processes in an organism. The biosynthesis of glycans is controlled by a series of glycosyltransferases, glycosidases and glycan-modifying enzymes that collectively assemble and process monosaccharide moieties into a diverse array of structures. Many studies have provided insight into various pathways of glycosylation at the ocular surface, such as those related to the biosynthesis of mucin-type O-glycans and N-glycans on proteins, but many others still remain largely unknown. This review provides an overview of the different classes of glycans described at the ocular surface focusing on their biosynthetic pathways and biological relevance. A precise understanding of these pathways under physiological and pathological conditions could help identify biomarkers and novel targets for therapeutic intervention.

Tear ferning test in healthy dogs

PURPOSE

To evaluate and compare three tear sampling methods using two grading scales for administering the tear ferning test (TFT) to healthy dogs.

METHODS

In total, 90 dogs (180 eyes) were subjected to tear sampling using millimetered strips, reused after the Schirmer tear test (STT) (Schirmer group, SG). Then, the dogs were subdivided into three groups according to sampling approach: micropipette (MPG), microcapillary (MCG), and Schirmer sample 2 (S2G). The collected tears were dried on a clean microscope glass slide at room temperature and humidity. The ferning patterns were observed under a polarized light microscope and classified according to the Rolando and Masmali grading scales.

RESULTS

Although all three methods were feasible, the STT was easier to perform in clinical settings. Type I and Grade 1 were the most commonly observed (64.17% and 61.7%, respectively) regardless of collection method. There was no significant difference between the STT median values and the TFT classifications.

CONCLUSIONS

The TFT is appropriate for dogs and can be performed using the three suggested sampling methods, with a higher frequency of Type I and Grade 1. Thus, it is possible to use both grading scales in the classification of tear ferning in dogs.

Relevance of Lipid-Based Products in the Management of Dry Eye Disease

Components of the ocular surface synergistically contribute to maintaining and protecting a smooth refractive layer to facilitate the optimal transmission of light. At the air-water interface, the tear film lipid layer (TFLL), a mixture of lipids and proteins, plays a key role in tear surface tension and is important for the physiological hydration of the ocular surface and for ocular homeostasis. Alterations in tear fluid rheology, differences in lipid composition, or downregulation of specific tear proteins are found in most types of ocular surface disease, including dry eye disease (DED). Artificial tears have long been a first line of treatment in DED and aim to replace or supplement tears. More recently, lipid-containing eye drops have been developed to more closely mimic the combination of aqueous and lipid layers of the TFLL. Over the last 2 decades, our understanding of the nature and importance of lipids in the tear film in health and disease has increased substantially. The aim of this article is to provide a brief overview of our current understanding of tear film properties and review the effectiveness of lipid-based products in the treatment of DED. Liposome lid sprays, emulsion eye drops, and other lipid-containing formulations are discussed.

A randomized study of the efficacy and safety of 0.1% cyclosporine A cationic emulsion in treatment of moderate to severe dry eye

PURPOSE

The SICCANOVE study aimed to compare the efficacy and safety of 0.1% cyclosporine A cationic emulsion (CsA CE) versus vehicle in patients with moderate to severe dry eye disease (DED).

METHODS

In this multicenter, double-masked, parallel-group, controlled study, patients were randomized (1:1) to receive CsA CE (Ikervis®) or vehicle for 6 months. The co-primary efficacy endpoints at month 6 were mean change from baseline in corneal fluorescein staining (CFS; modified Oxford scale) and in global ocular discomfort (visual analogue scale [VAS]).

RESULTS

The mean change in CFS from baseline to month 6 (CsA CE: n = 241; vehicle: n = 248) was significantly greater with CsA CE than with vehicle (-1.05 ± 0.98 and -0.82 ± 0.94, respectively; p = 0.009). Ocular discomfort improved similarly in both groups; however, the percentage of patients with ≥25% improvement in VAS was significantly higher with CsA CE (50.2%) than with vehicle (41.9%; p = 0.048). In a post hoc analysis of patients with severe ocular surface damage (CFS score 4) at baseline (CsA CE: n = 43; vehicle: n = 42), the percentage of patients with improvements of ≥2 grades in CFS score and ≥30% in Ocular Surface Disease Index score was significantly greater with CsA CE (p = 0.003). Treatment compliance and ocular tolerability were satisfactory and as expected for CsA use.

CONCLUSION

Cyclosporine A CE was well-tolerated and effectively improved signs and symptoms in patients with moderate to severe DED over 6 months, especially in patients with severe disease, who are at risk of irreversible corneal damage.

Targeted delivery of hyaluronic acid to the ocular surface by a polymer-peptide conjugate system for dry eye disease

Hyaluronic acid (HA) solutions effectively lubricate the ocular surface and are used for the relief of dry eye related symptoms. However, HA undergoes rapid clearance due to limited adhesion, which necessitates frequent instillation. Conversely, highly viscous artificial tear formulations with HA blur vision and interfere with blinking. Here, we developed an HA-eye drop formulation that selectively binds and retains HA for extended periods of time on the ocular surface. We synthesized a heterobifunctional polymer-peptide system with one end binding HA while the other end binding either sialic acid-containing glycosylated transmembrane molecules on the ocular surface epithelium, or type I collagen molecule within the tissue matrix. HA solution was mixed with the polymer-peptide system and tested on both ex vivo and in vivo models to determine its ability to prolong HA retention. Furthermore, rabbit ocular surface tissues treated with binding peptides and HA solutions demonstrated superior lubrication with reduced kinetic friction coefficients compared to tissues treated with conventional HA solution. The results suggest that binding peptide-based solution can keep the ocular surface enriched with HA for prolonged times as well as keep it lubricated. Therefore, this system can be further developed into a more effective treatment for dry eye patients than a standard HA eye drop.

STATEMENT OF SIGNIFICANCE

Eye drop formulations containing HA are widely used to lubricate the ocular surface and relieve dry eye related symptoms, however its low residence time remains a challenge. We designed a polymer-peptide system for the targeted delivery of HA to the ocular surface using sialic acid or type I collagen as anchors for HA immobilization. The addition of the polymer-peptide system to HA eye drop exhibited a reduced friction coefficient, and it can keep the ocular surface enriched with HA for prolonged time. This system can be further developed into a more effective treatment for dry eye than a standard HA eye drop.

Eukaryotic protein glycosylation: a primer for histochemists and cell biologists

Proteins undergo co- and posttranslational modifications, and their glycosylation is the most frequent and structurally variegated type. Histochemically, the detection of glycan presence has first been performed by stains. The availability of carbohydrate-specific tools (lectins, monoclonal antibodies) has revolutionized glycophenotyping, allowing monitoring of distinct structures. The different types of protein glycosylation in Eukaryotes are described. Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given. In particular, mucins and their glycosylation patterns are considered as instructive proof-of-principle case. The tissue and cellular location of glycoprotein biosynthesis and metabolism is reviewed, with attention to new findings in goblet cells. Finally, protein glycosylation in disease is documented, with selected examples, where aberrant glycan expression impacts on normal function to let disease pathology become manifest. The histological applications adopted in these studies are emphasized throughout the text.

Ex vivo rabbit and human corneas as models for bacterial and fungal keratitis

PURPOSE

In the study of microbial keratitis, in vivo animal models often require a large number of animals, and in vitro monolayer cell culture does not maintain the three-dimensional structure of the tissues or cell-to-cell communication of in vivo models. Here, we propose reproducible ex vivo models of single- and dual-infection keratitis as an alternative to in vivo and in vitro models.

METHODS

Excised rabbit and human corneoscleral rims maintained in organ culture were infected using 10⁸ cells of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans or Fusarium solani. The infection was introduced by wounding with a scalpel and exposing corneas to the microbial suspension or by intrastromal injection. Post-inoculation, corneas were maintained for 24 and 48 h at 37 °C. After incubation, corneas were either homogenised to determine colony-forming units (CFU)/cornea or processed for histological examination using routine staining methods. Single- and mixed-species infections were compared.

RESULTS

We observed a significant increase in CFU after 48 h compared to 24 h with S. aureus and P. aeruginosa. However, no such increase was observed in corneas infected with C. albicans or F. solani. The injection method yielded an approximately two- to 100-fold increase (p < 0.05) in the majority of organisms from infected corneas. Histology of the scalpel-wounded and injection models indicated extensive infiltration of P. aeruginosa throughout the entire cornea, with less infiltration observed for S. aureus, C. albicans and F. solani. The models also supported dual infections.

CONCLUSIONS

Both scalpel wounding and injection methods are suitable for inducing infection of ex vivo rabbit and human cornea models. These simple and reproducible models will be useful as an alternative to in vitro and in vivo models for investigating the detection and treatment of microbial keratitis, particularly when this might be due to two infective organisms.

Cationic lipid emulsions as potential bioadhesive carriers for ophthalmic delivery of palmatine

Palmatine (PM) is a potent anti-infective agent used to treat eye diseases. However, PM is less effective for ocular application due to short residence time within the eyes. This study aimed to develop a cationic lipid emulsions (CLEs) for ophthalmic delivery of PM and evaluate its suitability in infection treatment. PM-loaded CLEs (PM-CLEs) were prepared through emulsifying/high-pressure homogenisation and characterised by particle size, ζ potential and morphology. The resulting PM-CLEs possessed a particle size of 192 nm and ζ potential of 45 mV around. In vitro release illustrated that PM was released less from CLEs. Corneal bioadhesion test showed that PM-CLEs exhibited an enhanced ocular residence time. Improved anti-infective activity was achieved in the model of fungus-induced keratitis. Furthermore, PM-CLEs demonstrated predominant cellular uptake and internalisation in the corneal epithelial cells. These results provide proof of concept that CLEs are promising bioadhesive carriers for ophthalmic delivery of PM.

Signaling Pathways of Purinergic Receptors and Their Interactions with Cholinergic and Adrenergic Pathways in the Lacrimal Gland

PURPOSE

Purinergic receptors play a key role in the function of the lacrimal gland (LG) as P1 purinergic receptors A₁, A_2A, and A_2B, P2X_1-7 receptors, and many of the P2Y receptors are expressed.

METHODS

This review examines the current knowledge of purinergic receptors in the LG as well as the signaling pathways activated by these receptors.

RESULTS

These receptors are expressed on the acinar, ductal, and myoepithelial cells. Considerable crosstalk exists between the pathways activated by P2X₇ receptors with those activated by M₃ muscarinic or α_1D adrenergic receptors. The mechanism of the crosstalk between P2X₇ and M₃ muscarinic receptors differs from that of the crosstalk between P2X₇ and α_1D adrenergic receptors.

CONCLUSIONS

Understanding purinergic receptors and how they modulate protein secretion could play a key role in normal and pathological responses of the LG.

Development of cationic nanocrystals for ocular delivery

A cationic nanocrystal formulation containing dexamethasone acetate nanocrystals (0.05%) and polymyxin B (0.10%) for ophthalmic application was produced using a self-developed small scale method for wet bead milling. The formulation developed offers the advantage of increased saturation solubility of the drug (due to the nano-size of the crystals) and increased residence time in the eye (due to small size and increased mucoadhesion by the cationic charge) resulting ultimately in potential increased bioavailability. Characterization of the nanosuspensions by photon correlation spectroscopy (PCS) and transmission electron microscopy showed that the production method was successful in achieving dexamethasone crystals in the range of about 200-250nm. The physical stabilization of the nanocrystals and generation of the positive charge were realized by using cetylpyridinium chloride (CPC) and benzalkonium chloride (BAC) at the concentration of 0.01%. In contrast to other cationic excipients, they are regulatorily accepted due to their use as preservatives. The drug polymyxin B also contributed to the positive charge. Positive zeta potentials in the range +20 to +30mV were achieved. Isotonicity was adjusted using NaCl and non-ionic excipients (glycerol, sorbitol, dextrose). Physical and chemical stabilities were monitored for a period of 6months at room temperature, 5°C and 40°C. Particle size of the bulk population assessed by PCS remained practically unchanged over 6months of storage for the various formulations without isotonicity agents, and for the CPC-containing formulations with non-ionic isotonicity excipients. The chemical content also proved stable after 6months for all 3 temperatures evaluated. In vitro investigation of mucoadhesion was tested using mucin solutions at different concentrations, and the generated negative zeta potential was used as a measure of the interaction. The zeta potential reversed to about -15mV, indicating distinct interaction. The results show the potential of increased mucoadhesion of such cationic nanocrystals compared to standard eye drop formulations. The positively charged nanocrystal formulation also showed no in vitro cytotoxicity as assessed on fibroblast cell culture. In summary, 3 formulation candidates were identified being a promising alternative for ocular delivery with increased performance compared to what is presently available.

FleA Expression in Aspergillus fumigatus Is Recognized by Fucosylated Structures on Mucins and Macrophages to Prevent Lung Infection

The immune mechanisms that recognize inhaled Aspergillus fumigatus conidia to promote their elimination from the lungs are incompletely understood. FleA is a lectin expressed by Aspergillus fumigatus that has twelve binding sites for fucosylated structures that are abundant in the glycan coats of multiple plant and animal proteins. The role of FleA is unknown: it could bind fucose in decomposed plant matter to allow Aspergillus fumigatus to thrive in soil, or it may be a virulence factor that binds fucose in lung glycoproteins to cause Aspergillus fumigatus pneumonia. Our studies show that FleA protein and Aspergillus fumigatus conidia bind avidly to purified lung mucin glycoproteins in a fucose-dependent manner. In addition, FleA binds strongly to macrophage cell surface proteins, and macrophages bind and phagocytose fleA-deficient (∆fleA) conidia much less efficiently than wild type (WT) conidia. Furthermore, a potent fucopyranoside glycomimetic inhibitor of FleA inhibits binding and phagocytosis of WT conidia by macrophages, confirming the specific role of fucose binding in macrophage recognition of WT conidia. Finally, mice infected with ΔfleA conidia had more severe pneumonia and invasive aspergillosis than mice infected with WT conidia. These findings demonstrate that FleA is not a virulence factor for Aspergillus fumigatus. Instead, host recognition of FleA is a critical step in mechanisms of mucin binding, mucociliary clearance, and macrophage killing that prevent Aspergillus fumigatus pneumonia.

"Coffee Ring Effect" in Ophthalmology: "Anionic Dye Deposition" Hypothesis Explaining Normal Lid Margin Staining

The process of formation of Marx line is studied in this article. Various theories have been proposed previously, in order to explain the mechanisms which lead to the development of Marx line. These theories are based on the characteristics of stained area and do not pay attention to the behavior of dye solution itself on the surface. The aim of this study is to investigate the latter behavior and introduce a new theory based on it, in order to explain the process of the Marx line formation.This study also introduces "Coffee Ring Effect" and its possible applications in explaining some ophthalmological phenomena.The effect of dye solution's behavior on the beneath surface is adopted in order to propose a novel theory. This new hypothesis is called "Anionic Dye Deposition" which was based on "Coffee Ring Effect" phenomenon. For evaluation of this theory, Evaporation pattern of Rose Bengal and fluorescein were analyzed on different surfaces. Furthermore, the effect of tear meniscus alteration on lid margin staining is studied.During the evaporation process of dye solutions, it was observed that almost all of the solute was deposited at the edge of the drop on hydrophilic surfaces. Furthermore, in the study of lid margin staining, it is observed that tear meniscus alteration during gaze affects staining pattern. This observation invalidates former hypotheses which only focus on stained surface characteristics.According to the observations in this study, it is proposed that Marx line staining occurs as a result of "anionic dye deposition" due to evaporation.

Molecular dynamics of sialic acid analogues complex with cholera toxin and DFT optimization of ethylene glycol-mediated zinc nanocluster conjugation

Cholera is an infectious disease caused by cholera toxin (CT) protein of bacterium Vibrio cholerae. A sequence of sialic acid (N-acetylneuraminic acid, NeuNAc or Neu5Ac) analogues modified in its C-5 position is modelled using molecular modelling techniques and docked against the CT followed by molecular dynamics simulations. Docking results suggest better binding affinity of NeuNAc analogue towards the binding site of CT. The NeuNAc analogues interact with the active site residues GLU:11, TYR:12, HIS:13, GLY:33, LYS:34, GLU:51, GLN:56, HIE:57, ILE:58, GLN:61, TRP:88, ASN:90 and LYS:91 through intermolecular hydrogen bonding. Analogues N-glycolyl-NeuNAc, N-Pentanoyl-NeuNAc and N-Propanoyl-NeuNAc show the least XPGscore (docking score) of -9.90, -9.16, and -8.91, respectively, and glide energy of -45.99, -42.14 and -41.66 kcal/mol, respectively. Stable nature of CT-N-glycolyl-NeuNAc, CT-N-Pentanoyl-NeuNAc and CT-N-Propanoyl-NeuNAc complexes was verified through molecular dynamics simulations, each for 40 ns using the software Desmond. All the nine NeuNAc analogues show better score for drug-like properties, so could be considered as suitable candidates for drug development for cholera infection. To improve the enhanced binding mode of NeuNAc analogues towards CT, the nine NeuNAc analogues are conjugated with Zn nanoclusters through ethylene glycol (EG) as carriers. The NeuNAc analogues conjugated with EG-Zn nanoclusters show better binding energy towards CT than the unconjugated nine NeuNAc analogues. The electronic structural optimization of EG-Zn nanoclusters was carried out for optimizing their performance as better delivery vehicles for NeuNAc analogues through density functional theory calculations. These sialic acid analogues may be considered as novel leads for the design of drug against cholera and the EG-Zn nanocluster may be a suitable carrier for sialic acid analogues.

Pattern recognition receptors in microbial keratitis

Microbial keratitis is a significant cause of global visual impairment and blindness. Corneal infection can be caused by a wide variety of pathogens, each of which exhibits a range of mechanisms by which the immune system is activated. The complexity of the immune response to corneal infection is only now beginning to be elucidated. Crucial to the cornea's defences are the pattern-recognition receptors: Toll-like and Nod-like receptors and the subsequent activation of inflammatory pathways. These inflammatory pathways include the inflammasome and can lead to significant tissue destruction and corneal damage, with the potential for resultant blindness. Understanding the immune mechanisms behind this tissue destruction may enable improved identification of therapeutic targets to aid development of more specific therapies for reducing corneal damage in infectious keratitis. This review summarises current knowledge of pattern-recognition receptors and their downstream pathways in response to the major keratitis-causing organisms and alludes to potential therapeutic approaches that could alleviate corneal blindness.

An evaluation of Retaine™ ophthalmic emulsion in the management of tear film stability and ocular surface staining in patients diagnosed with dry eye

A single-center, open-label study consisting of two visits over the course of approximately 2 weeks was conducted to evaluate the efficacy of Retaine™ ophthalmic emulsion in improving the signs and symptoms of dry eye. Forty-two subjects were enrolled and received 1–2 drops twice daily of Retaine™ beginning at the first visit (day 1) and ending at the second visit. Subjects were instructed to complete a symptomatology diary twice daily prior to drop instillation through the morning of the second visit. Ocular sign and symptom assessments, visual acuity procedures, and comfort assessments were conducted during both visits. A statistically significant reduction was observed in mean breakup area on the second visit between the predose time and the postdose time (P=0.026). On the second visit, subjects had significantly less corneal fluorescein staining in the superior (P=0.002), central (P=0.017), corneal sum (P=0.011), and all ocular regions combined (P=0.038) than on the first visit. On the second visit, statistically significant reductions in dryness (P<0.001), grittiness (P=0.0217), ocular discomfort (P=0.0017), and all symptoms (P<0.001) were also seen as measured by the Ora Calibra™ Ocular Discomfort and 4-Symptom Questionnaire (0–5 scale). Subjects reported a statistically significant improvement in their abilities to work with a computer at night (P=0.044). Mean drop comfort scores ranged from 1.29–1.81 on the Ora Calibra™ 0–10 Drop Comfort Scale, on which 0 is very comfortable and 10 is very uncomfortable. Retaine™ demonstrates promising results as a novel artificial tear option for individuals suffering from dry eye. The unique mechanism of action of Retaine™ provides enhanced comfort and improves the quality of life of dry eye subjects while reducing the ocular signs of dry eye.

Unencapsulated Streptococcus pneumoniae from conjunctivitis encode variant traits and belong to a distinct phylogenetic cluster

Streptococcus pneumoniae, an inhabitant of the upper respiratory mucosa, causes respiratory and invasive infections as well as conjunctivitis. Strains that lack the capsule, a main virulence factor and the target of current vaccines, are often isolated from conjunctivitis cases. Here we perform a comparative genomic analysis of 271 strains of conjunctivitis-causing S. pneumoniae from 72 postal codes in the United States. We find that the vast majority of conjunctivitis strains are members of a distinct cluster of closely related unencapsulated strains. These strains possess divergent forms of pneumococcal virulence factors (such as CbpA and neuraminidases) that are not shared with other unencapsulated nasopharyngeal S. pneumoniae. They also possess putative adhesins that have not been described in encapsulated pneumococci. These findings suggest that the unencapsulated strains capable of causing conjunctivitis utilize a pathogenesis strategy substantially different from that described for S. pneumoniae at other infection sites.

Benefits of cetalkonium chloride cationic oil-in-water nanoemulsions for topical ophthalmic drug delivery

Objectives

Topical ocular administration is the most convenient route of administration of drugs for the treatment of eye diseases. However, the bioavailability of drugs following eye instillations of eye drops is very low. Over the past 20 years, extensive efforts have been put into research to improve drug bioavailability without compromising treatment compliance and patients' quality of life.

Key findings

One of the most efficient ways to improve drug bioavailability is to increase the precorneal residence time of the eye drop formulations. As a result, new eye drops, with bioadhesive properties, have been developed based on the cationic oil-in-water (o/w) nanoemulsion technology. These low viscosity eye drop nanoemulsions have improved precorneal residence time through the electrostatic interactions between the positively charged oil nanodroplets and the negatively charged ocular surface epithelium.

Summary

This review is the first to present the benefits of this new strategy used to improve ocular drug bioavailability. The roles of the cationic agent in the stabilization of a safe cationic o/w nanoemulsion have been discussed, as well as the unexpected benefits of the cationic o/w nanoemulsion for the protection and restoration of a healthy tear film and corneal epithelium.

Glycans - the third revolution in evolution

The development and maintenance of a complex organism composed of trillions of cells is an extremely complex task. At the molecular level every process requires a specific molecular structures to perform it, thus it is difficult to imagine how less than tenfold increase in the number of genes between simple bacteria and higher eukaryotes enabled this quantum leap in complexity. In this perspective article we present the hypothesis that the invention of glycans was the third revolution in evolution (the appearance of nucleic acids and proteins being the first two), which enabled the creation of novel molecular entities that do not require a direct genetic template. Contrary to proteins and nucleic acids, which are made from a direct DNA template, glycans are product of a complex biosynthetic pathway affected by hundreds of genetic and environmental factors. Therefore glycans enable adaptive response to environmental changes and, unlike other epiproteomic modifications, which act as off/on switches, glycosylation significantly contributes to protein structure and enables novel functions. The importance of glycosylation is evident from the fact that nearly all proteins invented after the appearance of multicellular life are composed of both polypeptide and glycan parts.

Distribution of cyclosporine A in ocular tissues after topical administration of cyclosporine A cationic emulsions to pigmented rabbits

PURPOSE

The aim of this study was to compare the ocular and systemic distribution of cyclosporine A (CsA) in rabbits after the instillation of preservative-free CsA cationic and anionic emulsions.

METHODS

For the single-dose pharmacokinetic (PK) study, rabbits were instilled with 50 μL of the test material. For the multiple-dose PK study, rabbits were instilled twice daily with Restasis or once daily with NOVA22007 for 10 days. At each time point, the cornea, conjunctiva, and whole blood were harvested for CsA quantification. Ocular and systemic distribution were determined after 4 times daily instillations with 50 μL of 3H-CsA cationic and anionic emulsions for 7 days. Restasis was used as a reference in all studies.

RESULTS

Single-dose PK data demonstrated that NOVA22007 0.1% and 0.05% delivered higher CsA concentrations to the cornea than Restasis [concentration maximum (C max): 2692, 1372, and 748 ng/g, respectively] and have a better exposition (area under the curve). Conjunctival Cmax values were 1914, 696, and 849 ng/g and area under the curve values were 3984, 2796, and 2515 ng/g · h, for either dose of the cationic emulsions and Restasis, respectively. The multiple-dose PK and the 3H-CsA distribution data demonstrated that the systemic distribution after repeated instillations was low and comparable for all emulsions.

CONCLUSIONS

These data demonstrate that the CsA cationic emulsions were more effective than Restasis at delivering CsA to target tissues, thus confirming the potential advantage of cationic emulsions over anionic emulsions as vehicle for ocular drug delivery for the treatment of ocular surface diseases.

Effect of hydration on structural and thermodynamic properties of pig gastric and bovine submaxillary gland mucins

One of the essential functions of mucous gel is protection of tissues against dehydration. The effect of hydration on the structural and thermodynamic properties of pig gastric mucin (PGM) and bovine submaxillary gland mucin (BSM) have been studied using atomic force microscopy (AFM), sorption, and differential scanning calorimetry (DSC). The analysis of sorption isotherms shows the higher water sorption capacity of PGM compared to BSM at RH levels lower than about 78%. The value of the hydration enthalpy at zero water content at 25 °C for both biopolymers is about -20 kJ/mol. Glass transitions of BSM and PGM occur at RH levels between 60 and 70% for both mucins. AFM indicates the presence of a dumbbell structure as well as a fiber-like structure in PGM samples. The experimental volume of the dry dumbbell molecule obtained by AFM is 3140 ± 340 nm(3). Using DSC data, the amount of nonfreezing water was calculated to be about 0.51 g/g of PGM. The phase diagram of PGM demonstrates two regions of different Tg: dependent and independent of hydration levels. In particular, at mucin concentrations from 0 to 67 wt %, the glass transition occurs at a constant temperature of about -15 °C. At higher concentrations of mucin, Tg is increasing with increasing mucin concentrations.

Site-specific characterisation of densely O-glycosylated mucin-type peptides using electron transfer dissociation ESI-MS/MS

Site-specific characterisation of mucin-type O-linked glycosylation is an analytical challenge due to glycan heterogeneity, lack of glycosylation site consensus sequence and high density of occupied glycosylation sites. Here, we report the use of electron transfer dissociation (ETD) for the site-specific characterisation of densely glycosylated mucin-type O-linked glycopeptides using ESI-IT-MS/MS. Synthetic glycopeptides from the human mucin-1 (MUC-1) tandem repeat region containing a range of O-linked, tumour-associated carbohydrate antigens, namely Tn, T and sialyl T, with different glycosylation site occupancies and an increasing number of tandem repeats were studied. In addition, a glycopeptide from the anti-freeze glycoprotein of Antarctic and Arctic notothenoids, bearing four O-linked, per-acetylated T antigens was characterised. ETD MS/MS of infused or capillary LC-separated glycopeptides provided broad peptide sequence coverage (c/z·-type fragment ions) with intact glycans still attached to the Ser/Thr residues. Thus, the glycosylation sites were unambiguously determined, while simultaneously obtaining information about the attached glycan mass and peptide identity. Highly sialylated O-glycopeptides showed less efficient peptide fragmentation, but some sequence and glycosylation site information was still obtained. This study demonstrates the capabilities of ETD MS/MS for site-specific characterisation of mucin-type glycopeptides containing high-density O-linked glycan clusters, using accessible and relative low-resolution/low-mass accuracy IT MS instrumentation.

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.

Analysing mucin degradation

Turnover of mucins in supramucosal gels is essential for the removal of surface contaminants, and the maintenance of normal mucosal barrier function. In addition to the well-known processes promoting the physical turnover of mucus gels, extracellular mucin degradation also requires the coordinated action of a range of enzyme activities including glycosidases and proteases. These are collectively termed "mucinase". Derangements of mucinase activity lead to downstream barrier defects and mucosal disease. This chapter is focussed on methods that can be used to assess the degradation of whole mucins and isolated mucin glycans. A range of approaches is described using labelled or unlabelled substrates utilised in assays based on 96-well plates, size exclusion chromatography, and NP-HPLC. These are suitable for defining the extent and progress of mucin degradation in different mucosal systems, and identifying abnormalities and critical control points.