UV-Induced Apoptosis in Lens: Prevention by Caffeine

Abstract

Purpose: UV irradiation is a well-known etiological factor in the genesis of human cataracts. Irradiation with such wavelengths is known to initiate formation of reactive oxygen species implicated in the onset and progression of cataracts. As a corollary to our previous reports showing that caffeine can protect against UV-induced physiological damage to the lens, apparent by the effect against the decrease in the levels of adenosine triphosphate (ATP) and glutathione (GSH) as well as the associated inhibition of the active transport activity, further experiments were undertaken to find out whether caffeine would also be effective in inhibiting the eventual UV-triggered apoptotic cell death. Method: Freshly isolated mice lenses were incubated exposed to UV in the absence and presence of caffeine (2.5 mM) for a period of 5 hours. The blank controls were run in the dark. The medium of incubation was Tyrode. Subsequently, they were fixed in 10% buffered formalin and processed for sectioning and staining. Nuclear localization was done by staining with diamidino-2-phenylindole (DAPI). Apoptosis was histochemically detected with terminal deoxynucleotidyl transferase–catalyzed labeling of the 3′-OH termini in the DNA breaks using fluorescein-labeled dUTP as substrate, that is, the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) reaction. Results: As expected, incubation of the lenses under UV led to extensive apoptosis of the epithelium. The majority of the epithelial cells became TUNEL positive. Such transformation was thwarted if incubation was conducted in the medium fortified with caffeine. Another notable cellular abnormality, also apparent by DAPI staining, was the partial denudation and loss of epithelial cells from the anterior surface of the lens. A significant number of apoptotic cells also appeared to have migrated to the posterior capsule. Caffeine prevented these effects. Conclusion: The results demonstrate that caffeine has a significant inhibitory effect against the onset of apoptotic cell death of the lens epithelium induced by UV irradiation. The caffeine effect is apparently exerted by its property of scavenging reactive oxygen species produced photochemically. We therefore hypothesize that the compound could be useful in attenuating the cataractogenic effect of UV.