Comparative study on corneal epithelium healing: effects of crosslinked hyaluronic acid and amniotic membrane extract eye drops in rats

To evaluate to effect of experimental dry eye on ocular surface apoptosis. Aqueous tear production and clearance were inhibited by systemic administration of scopolamine and exposure to an air draft for 12 days in 4- to 6-week-old 129SvEv/CD-1 mixed white mice. Eyes and ocular adnexa were excised, cryosectioned, and evaluated for apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay, immunohistochemical assay for caspase-3 and poly(ADP-ribose) phosphate (PARP), and examination of nuclear morphologic changes by Hoechst DNA nuclear staining and transmission electron microscopy. The number of TUNEL-positive cells in the mice with induced dry eye was significantly increased compared with control mice in the following ocular regions: central corneal (P < 0.0014), peripheral corneal (P < 0.0001), bulbar conjunctival (P < 0.0021), and tarsal conjunctival (P < 0.0046) epithelia; tarsal conjunctival stroma (P < 0.0274); and lid margin (P < 0.0219, n = 4 in all cases). There were no significant differences observed between treated and control groups in the central corneal, peripheral corneal, or bulbar conjunctival stroma; meibomian glands; skin; retina-choroid; or episcleral regions. Immunohistochemistry for caspase-3 and poly(ADP-ribose) polymerase p85 fragment revealed increased immunoreactivity in regions of increased TUNEL positivity, particularly in the corneal and conjunctival epithelial cells. Ultrastructural morphologic changes consistent with apoptosis were observed in the conjunctival epithelial cells. Experimentally induced dry eye in mice causes apoptosis of cells in ocular surface tissues including the central and peripheral corneal epithelium, bulbar and tarsal conjunctival epithelia, tarsal conjunctival stroma, and lid margin. Apoptosis may play a key role in the pathogenesis of keratoconjunctivitis sicca and may be a therapeutic target for this condition.

Knowledge and resources derived from veterinary medicine represent an underused resource that could serve as a bridge between data obtained from diseases models in laboratory animals and human clinical trials. Naturally occurring disease in companion animals that display the defining attributes of similar, if not identical, diseases in humans hold promise for providing predictive proof of concept in the evaluation of new therapeutics and devices. Here we outline comparative aspects of naturally occurring diseases in companion animals and discuss their current uses in translational medicine, benefits, and shortcomings. Last, we envision how these natural models of disease might ultimately decrease the failure rate in human clinical trials and accelerate the delivery of effective treatments to the human clinical market.

Human corneal epithelial cells respond rapidly following injury to restore the integrity of the ocular surface. What stimulates and guides cells to move into the wound to heal? One candidate is the wound-induced electric field. Using vibrating probe techniques, we provide detailed temporal and spatial mapping of endogenous electric currents at rat corneal wounds. We find Cl- and Na+ are the major components of electric currents in rat corneal wounds. Na+ is the major component of ionic transport in the resting (nonwounded) rat cornea and of the wound center leakage current, whereas Cl- is a more important component of the endogenous electrical current at the wound edges. Enhancing or decreasing Cl- flow with clinically approved pharmacological agents such as aminophylline, ascorbic acid, or furosemide increased or decreased endogenous wound electric currents, respectively. These changes in wound currents correlated directly with the rate of wound healing in vivo. Thus, pharmacologically enhancing or decreasing wound-induced electric currents increased and decreased wound healing rate, respectively. This may have wide-reaching and novel therapeutic potential in the management of wound healing and may help explain some mechanistic aspects of the effects of some clinically used agents.