Search

The eyelid meibomian gland secretions form the outer layer of the tear film. That layer functions as a lubricant during a blink, and as a barrier against intrusion of foreign bodies. The lipid film is also exposed to proteins present in the aqueous phase that may adsorb there, and thus form an integral part of the surface of the tear film, or possibly, cause disruption to the outermost layer. Therefore, the adsorption of tear proteins to the meibomian lipid layer was object of the present investigation. A model tear was set up coating a pendant drop of saline with a film of meibomian lipids and measuring variations of the interfacial pressure after the injection of tear proteins into the aqueous subphase at their physiological concentration. All tear proteins adsorbed at the interface causing the initial surface pressure to increase. For each protein, a limiting surface pressure at which a given protein was no longer able to insert into the lipid layer was found. Among the proteins tested, lipocalin was the most surface active one and inserted into the lipid layer in the whole range of surface pressure exerted by the meibomian lipid mixture. Lactoferrin, lysozyme and IgA also interacted with the lipids whereas albumin interacted more weakly. The timescale of the protein insertion into the lipid layer was of the order of 10(2) s. It was hypothesized that protein adsorption at the interface could be associated with structural changes. Indeed, the enzymatic activity of lysozyme was maintained in the presence of an outermost meibomian lipid layer that prevented its denaturation while exposure at the air/aqueous interface induced significant lysozime degradation. meibomian lipid composition is therefore functional to maintain tear proteins activity.

Cyclooxygenases (COXs) are the key enzymes in the production of prostaglandins (PGs) and exist in two isoforms. Isoform 1 (COX-1) is constitutively expressed in most tissues, whereas cyclooxygenase-2 (COX-2) is rapidly induced by a variety of different stimuli. In this study, we have quantitatively analyzed mRNA expression of COX-1 and COX-2 and protein distribution during corneal reparative processes after wound. Total RNA was isolated from cornea samples of New Zealand rabbits that had been subjected to corneal wound by mechanical brush scraping. Quantification of RT-PCR results was made by using a DNA mimic approach. The localization and expression of the enzymes was studied by immunocytochemistry and Western blotting. In normal corneas COX-1 is expressed throughout the cornea in the whole tissue, while COX-2 is strongly expressed in stromal keratocytes. Following injury, COX-2 levels drastically increase and, at least in the epithelium, COX-2 becomes the predominant isoform of cyclooxygenases at an early stage of healing. Moreover, in the epithelium COX-2 is expressed predominantly by those cells close to the wound. These cells become migratory and move toward the injured area. In contrast, COX-1 levels remain unaffected in all corneal tissues. The system returns to the pre-injury state in about 24h. Thus, the expression of COX-2 in the corneal epithelium during wound repair is tightly regulated both temporally and spatially.

The objective of this paper is to assess the gelatinase production by some ocular pathogenic bacterial strains, and evaluate the ability of (-)epigallocatechin-3-gallate (EGCg) to inhibit this gelatinase activity and thus limit bacterial invasion. The effect of EGCg on bacterial gelatinase activity was tested by classic zymography methods, while its effect on bacterial invasion was evaluated through the ability of growing bacteria to liquefy and thus penetrate a semisolid gelatine substrate. It was found that EGCg inhibits bacterial gelatinases with an IC(50) of about 0.2 mM, and limits invasion of gelatinase-positive bacteria at concentrations above 2 mM. These results show for the first time that EGCg, as well as having direct antibacterial activity, can also inhibit bacterial gelatinases, thus limiting their invasion on gelatine. Possible use of EGCg is thus suggested as an adjuvant in antibacterial chemotherapy.