Metabolic Adaptation of Corneal Epithelium following Hypoxia

Abstract

Abstract: : Purpose: To determine if adaptation to hypoxia (e.g., following contact lens wear) alters glycolytic metabolism or oxygen consumption in corneal epithelium. Methods: Corneal oxygen consumption (Q_C), Corneal swelling (CS) following closed-eye hydrogel lens wear for 2 hours, and the change in stromal pH (ΔpH) following lens wear (equivalent to lactate production) were measured in thirty contact lens wearers and controls (non-lens wearers). Q_C was measured by phosphorescence quenching of a porphyrin dye bound to the hydrogel surface. Corneal thickness changes were measured by Orbscan pachometry. Stromal pH was measured using the fluorescence ratio (Ex 490/450) change of fluorescein during closed eye lens wear. Habitual lens wear was discontinued for 36 hours prior to testing. Lactate production was also measured in epithelial cell cultures during hypoxia in controls and cultures that were pre-adapted to hypoxia (48 hours hypoxia followed by 4 hours normoxia). Results: Q_C was the same for both groups of subjects. Corneal swelling was 17% less in the contact lens wearers (p < 0.05). The ΔpH following closed eye lens wear was 20% less (p < 0.05) in the contact lens wearing group. In cultured epithelial cells pre-adapted to hypoxia, lactate production and glucose consumption were reduced by 20% and 38%, respectively (p < 0.05), during hypoxic challenge. Conclusions: Pre-adaptation to hypoxia reduces lactic acid production during subsequent hypoxic challenge. Since Q_C is unaffected, we speculate that oxidative phosphorylation is more efficient in hypoxia-adapted corneas.

Keywords: metabolism • cornea: epithelium • contact lens