Levobetaxolol-induced up-regulation of retinal bFGF and CNTF mRNAs and preservation of retinal function against a photic-induced retinopathy

Betaxolol (racemic), a β-adrenoceptor antagonist that is used to lower intraocular pressure in the treatment of glaucoma, has been shown to protect inner retina cells from various insults. To determine if such protection could be afforded to retinal photoreceptors and retinal pigment epithelial cells (RPE), levobetaxolol (S-betaxolol) was evaluated in a photic-induced retinopathy model. Rats were dosed (IP) with vehicle or levobetaxolol (10 and 20 mg kg^-1) 48, 24 and 0 hr prior to exposure for 6 hr to fluorescent blue light. The electroretinogram (ERG) and retinal morphology were assessed after a 3 week recovery period. Evaluation of the ERG demonstrated significant protection of retinal function in levobetaxolol (20 mg kg^-1)-dosed rats compared to vehicle-dosed rats. Similarly, the RPE and outer nuclear layer were significantly thicker in levobetaxolol (20 mg kg^-1)-dosed rats compared to vehicle-dosed rats. To elucidate potential mechanism(s) of the neuroprotective activity of levobetaxolol, bFGF and CNTF mRNA levels in normal rat retinas were evaluated 12 hr after a single i.p. injection. Northern blot analysis of levobetaxolol treated retinas demonstrated a 10-fold up-regulation of bFGF and a two-fold up-regulation of CNTF mRNA levels, trophic factors that have been shown to inhibit retinal degeneration in a number of species. These studies suggest that levobetaxolol can be used as a novel neuroprotective agent to ameliorate retinopathy.