Abstract
Purpose: :
Ginkgo biloba extract has been advocated as a neuroprotective agent for several years in normal tension glaucoma especially when IOP-lowering strategies are ineffective. However, the mechanism by which it exerts its action is not well established, although several pathways have been implicated, including regulation of apoptosis-related genes Bcl-2 and Bax, modulation of inflammation (iNOS, Cox-2 and tumor necrosis factor-alpha), and reduction of oxidative stress via beta-amyloid (Aβ) and mitochondrial pathways. The aim this study was to use immunohistochemistry to examine several of these potential targets related to retinal ganglion cells in ocular hypertensive (OHT) rat eyes.
Methods: :
The IOP was elevated in DA animals using our established chronic OHT rat model. Animals were sacrificed at 1, 3 and 12 weeks after IOP elevation. Sequential 5µm thick paraffin-embedded retinal sections from OHT and age matched controls (n=3 per time point) were immunostained with different antibodies against amongst others APP, Aβ, TNF-α and its receptors, iNOS, Cox 2 and cytochrome c. Sections were graded for staining by three independent and masked observers using a well established method.
Results: :
Of all the potential targets studied, we showed the most striking changes in the pattern of cytochrome c and Aβ activity. Cytochrome C showed an increase in expression over time with peak expression at 3 weeks after OHT surgery. This coincides with the development of peak RGC apoptosis in this model, as we have previously described. APP accumulation was maximum at 1 week of IOP elevation and significantly decreased thereafter in OHT eyes compared with the control (p<0.01), whilst Aβ deposition peaked at 12 weeks of IOP elevation in all OHT eyes compared to control (p<0.01).
Conclusions: :
Up-regulation of cytochrome c activityand Aβeta accumulation in the OHT model implicates these pathways in glaucoma pathogenesis. More work is needed to establish the effects of Ginkgo Biloba on these potential targets.
Keywords: neuroprotection • ganglion cells • apoptosis/cell death