Tear fluid content of electrochemically active components including water soluble antioxidants

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Abstract
PURPOSE. To describe the content of water-soluble antioxidants in tear fluid. METHODS. We collected tear fluid from healthy subjects, either into borosilicate glass tubing or by absorption onto Schirmer strips. High pressure liquid chromatography with electrochemical detection provided data on several components in a single assay. The system was sufficiently sensitive to provide reliable values for components present in tear fluid collected at normal (basal) or stimulated rates of secretion. RESULTS. Tear fluid at basal secretion was found to contain four compounds often considered to function in biology as antioxidants. Ascorbic acid (AA) is found at 665 µM, tyrosine at 45 µM and glutathione (GSH) at 107 µM. Cysteine (48 µM) and uric acid (328 µM) are reported for the first time; the latter is somewhat controversial as a physiologically active antioxidant. One peak on the chromatogram was consistently present but has not been identified. During stimulation of flow by brief inhalation of ammonium hydroxide fumes, the concentration of each compound was lower. CONCLUSION. This work demonstrates the presence of electro-chemically active components that might function as antioxidants at the anterior surface of the cornea against potential damage from radiation, oxygen toxicity, abrasion and environmental chemicals.