Naphthoquinone cataract in mice: mitochondrial change and protection by superoxide dismutase.

An injection of 1,2-naphthoquinone (NQ) into the anterior chamber of mouse eye produces anterior cortical cataract. It was previously shown by histology that mitochondria in lens epithelial cells are the target of ocular drug toxicity. In this work we investigated NQ-induced cataract by closely examining morphological changes of mitochondria and other cellular organelles in the lens epithelium. Mitochondria exhibited marked swelling in 2 hrs after NQ injection but restored the normal condensed configuration at 4.5 hrs. The nuclear chromatin showed condensation at 2 hrs and returned to the normal appearance at 4.5 hrs. This was unexpected because the lens at 4.5 hrs was cataractous due to vacuole formation in fiber cell layers. The result indicates that, although lens epithelial mitochondria are the target of NQ toxicity, cataract begins to develop before mitochondria and other subcellular organelles become totally dysfunctional. At 1 week after NQ injection, most mitochondria disintegrated and the fragmented chromatin appeared to leak out through the ruptured nuclear membrane. SOD injected with NQ significantly delayed the onset of cataract and protected lens epithelial cells. A second SOD injection further delayed cataract development.