[The role of oxygen free radical in experimental keratitis].

OBJECTIVE

To test a possible role of active oxygen species in corneal inflammation.

METHODS

A keratitis model was induced by an intrastromal injection of lipopolysaccharide (LPS) in one eye of New Zealand albino rabbits. During the inflammation process, the activity of corneal superoxide dismutase (SOD), an enzymatic scavenger of the superoxide free radical, was measured by chemoluminescent test, the level of corneal malonaldehyde (MDA), the final product of lipid peroxidation, was determined by thiobarbituric acid test, and the clinical and histopathological changes in cornea were observed. All the results of inflammatory cornea were compared with that of saline injected cornea.

RESULTS

It was found that: (1) Significant decrease in SOD activity (P < 0.001) and increase in MDA level (P = 0.001) were observed in inflammatory cornea when compared with the controls. In the period of corneal inflammation, the increase in MDA level occurred after the decrease in SOD activity. (2) The severity of corneal inflammation was negatively correlated with the corneal SOD activity (r = -0.954, P < 0.001) and positively with corneal MDA level (r = 0.734, P < 0.001). Also a statistically significant negative correlation existed between SOD activity and MDA level in the inflammatory cornea (r = -0.623, P < 0.01).

CONCLUSION

These findings suggest that active oxygen species play a role in LPS-induced keratitis and cause corneal injury by lipid peroxidation reactions on the polyunsaturated fatty acid of biological membranes.