Involvement of ascorbic acid in iron-induced apoptosis in the retina

Abstract

Aim: To investigate the correlation of ascorbic acid distribution in the retina to the occurrence of iron- induced apoptosis in the retina.

Materials and methods: Apop-Tag, an in situ apoptosis detection kit, was used to visualize the distribution of apoptosis after intraocular iron implantation in rat and rabbit eyes. Ascorbic acid distribution was visualized by the Chinoy method.

Results: On day 10, after intraocular implantation of iron, most of the outer nuclear layer was destroyed by apoptosis. However, no apoptotic nucleus was observed in the ganglion layer and inner nuclear layer of the rats’ eyes. On the contrary, apoptosis was observed in all layers in rabbits’ retinas on day 3. Ascorbic acid distribution in eye tissues was visualized by the silver granules produced from the reduction of silver nitrate by ascorbic acid. In normal rats’ retinas silver granules were observed only in the outer nuclear layer, while silver granules were distributed evenly in all layers of the rabbits’ retinas. The distribution of ascorbic acid in the retina coincided with the occurrence of iron-induced apoptosis.

Conclusion: Iron toxicity is due to free radical formation during auto-oxidation of ferrous to ferric ions. The high amount of ascorbic acid in the outer nuclear layer of the rats’ retinas regenerate ferric ion to ferrous ion allowing for continuous production of free radicals in the outer nuclear layer. This conclusion was supported by the distribution of apoptosis in all layers of the rabbits’ retinas where ascorbic acid is evenly distributed in all layers of the rabbits’ eyes.