Fluorometholone modulates gene expression of ocular surface mucins

A topical fluorometholone nanoformulation fabricated under aqueous condition for the treatment of dry eye

Fluorometholone (FMT) is a frequently prescribed drug for the alleviation of dry eye. However, due to low aqueous solubility, it has been routinely used as an ophthalmic suspension, which is characterized by low bioavailability, inconvenience of administration, and difficulty in delivering accurate dose. Furthermore, the opaque appearance of the ophthalmic suspension is not desirable for optical purpose. In the present study, a transparent FMT nanoformulation (FMT-CD NPs) was fabricated by the cyclodextrin (CD) nanoparticle technology without organic solvents. It was demonstrated that FMT was encapsulated in an amorphous form, which was associated with increased release rate and enhanced corneal penetration efficiency. The biocompatibility of FMT-CD NPs was confirmed by the Live/Dead assay, CCK-8 assay and the wound healing assay. Most importantly, FMT-CD NPs alleviated dry eye signs more efficiently than the commercial eye drop, with one-fifth the dosage of FMT in the latter. Collectively, our study provides a promising FMT formulation for improved management of dry eye while reducing drug related side effects.

Current Advances in Mechanisms and Treatment of Dry Eye Disease: Toward Anti-inflammatory and Immunomodulatory Therapy and Traditional Chinese Medicine

Dry eye is currently one of the most common ocular surface disease. It can lead to ocular discomfort and even cause visual impairment, which greatly affects the work and quality of life of patients. With the increasing incidence of dry eye disease (DED) in recent years, the disease is receiving more and more attention, and has become one of the hot research fields in ophthalmology research. Recently, with the in-depth research on the etiology, pathogenesis and treatment of DED, it has been shown that defects in immune regulation is one of the main pathological mechanisms of DED. Since the non-specific and specific immune response of the ocular surface are jointly regulated, a variety of immune cells and inflammatory factors are involved in the development of DED. The conventional treatment of DED is the application of artificial tears for lubricating the ocular surface. However, for moderate-to-severe DED, treatment with anti-inflammatory drugs is necessary. In this review, the immunomodulatory mechanisms of DED and the latest research progress of its related treatments including Chinese medicine will be discussed.

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.

Effect of High Glucose on Ocular Surface Epithelial Cell Barrier and Tight Junction Proteins

Purpose

Patients with diabetes mellitus are reported to have ocular surface defects, impaired ocular surface barrier function, and a higher incidence of corneal and conjunctival infections. Tight junctions are critical for ocular surface barrier function. The present study was designed to investigate the effect of high glucose exposure on human corneal and conjunctival epithelial cell barrier function and tight junction proteins.

Methods

Human corneal and conjunctival epithelial cells were exposed to 15 mM and 30 mM glucose for 24 and 72 hours. The barrier function was measured using transepithelial electrical resistance (TEER). The cell migration was quantified using scratch assay. The cells were harvested for protein extraction and mRNA isolation. Gene and protein expression of claudins, zonula occludens (ZOs), and occludin was quantified using real-time PCR and Western blot.

Results

Glucose caused a significant decrease in TEER after 72 hours of exposure in both corneal and conjunctival epithelial cells. Glucose did not cause any notable change in migration of either corneal or conjunctival epithelial cells. Glucose exposure did not cause any notable change in protein expression of claudin-1, ZO-1, ZO-2, ZO-3, or occludin. On the other hand, 15 mM glucose caused an increase in gene expression of claudin-1, claudin-3, ZO-2, ZO-3, and occludin, a likely response to osmotic stress since 15 mM mannitol also caused consistently similar increase in gene expression of these proteins.

Conclusions

High glucose exposure causes impairment of corneal and conjunctival epithelial cell barrier function, but this detrimental effect is not caused by a decrease in expression of tight junction proteins: claudin-1, ZO-1, ZO-2, ZO-3, and occludin.