Abstract
Purpose: :
Significant numbers of UV photons are known to penetrate the intraocular structures inducing several vision impairing pathologies including retinal degeneration. One of the mechanisms by which UV irradiation induces tissue damage is known to be via an excessive generation of reactive species of oxygen (ROS). The primary aim of this study is hence to examine the effectiveness of caffeine, a xanthine alkaloid known to effectively scavenge such species, in protecting the retina against such UV-induced damage.
Methods: :
The protective effect of caffeine against UV-induced damage to the retina was examined by incubation studies with retinas isolated from freshly enucleated lamb eyes. The tissue was cut into 0.5cm2 pieces and incubated overnight in medium 199 exposed to UVR-A (365nm, Intensity: 0.6mW/cm2) at 37°C in the absence and presence of 5mM caffeine. Dark controls were also run in the absence and presence of caffeine. Following incubation, the tissues were rinsed with normal saline and analyzed for the contents of protein and glutathione (GSH). In addition, the tissues were also examined for morphological changes by light microscopy following H&E staining of the paraffin-embedded tissues.
Results: :
Incubation under UV led to a significant decrease in the content of GSH, to ~52% of the controls incubated in the dark. Caffeine prevented this decrease, the level of GSH in this group being maintained at ~88% of the dark controls. The damage at the morphological level was reflected by a decrease in the thickness of the outer nuclear, outer plexiform and the inner nuclear layers. There was an overall disruption of these layers. These disruptive changes were significantly thwarted by caffeine, the morphology appearing similar to the controls.
Conclusions: :
The results suggest that the biochemical and structural changes induced by UV irradiation are substantially prevented by caffeine. Since the induction of tissue damage by UVR is considered to be through generation of oxygen radicals, it is hypothesized that the protective effect of caffeine is exerted through its radical scavenging properties. However, the possibility that it could also act via increasing the c-AMP levels by inhibiting phosphodiesterase and through its agonistic action on adenosine receptors remains to be investigated.
Keywords: radiation damage: light/UV • antioxidants • retina