Wet age-related macular degeneration (AMD) is characterised by choroidal neovascular membrane (CNVM) formation. It is thought that localised hypoxia within the retina results in overexpression of growth factors such as vascular endothelial growth factor (VEGF), which induces CNVM formation. VEGF expression is enhanced by hypoxia in cultured retinal pigment epithelium (RPE) and photoreceptor cells. VEGF expression increases via several mechanisms but is largely mediated by hypoxia-inducible factor-1 (HIF-1). VEGF expression in cultured hypoxic RPE cells is inhibited by the interference of HIF-1a messenger RNA (mRNA). In laser induced CNVM HIF-1a knockout mice the disruption of HIF-1a in RPE attenuated the overexpression of VEGF. Ginko bilboa extract (GBE) is already established in improving blood flow and has been widely used in a variety of disorders including dementia and peripheral vascular disease. A study demonstrated recently that GBE inhibited cell death of cultured RPE cells under hypoxic conditions. This study investigated the effects of GBE on HIF-1a and VEGF expression in cultured human RPE cells in hypoxic conditions. RPE cells were cultured into three different groups; untreated control group, hypoxic group and hypoxic group with GBE. The groups were then analysed at different time points for expression of HIF-1a and VEGF. HIF-1a and VEGF mRNA were quantified using real-time polymerase chain reaction (PCR) and nuclei using enzyme linked immunosorbent assay (ELISA). In the hypoxia group levels of HIF-1a mRNA, VEGF mRNA, HIF-1a and VEGF levels were higher compared to the control group. In addition levels of HIF-1a mRNA and VEGF mRNA were also reduced. ELISA testing showed decreased HIF-1a and VEGF protein concentrations in this group. These results are encouraging and further studies would be needed to truly determine the beneficial effects of GBE regarding AMD. This study was an in vitro experiment using cells and therefore the clinical effect of GBE should be judged carefully. It is also unclear how much GBE consumption would have an effect and caution should be taken before encouraging increasing vitamin and mineral supplements for patients, as like medicines they too have adverse side-effects.

Effects of Ginko bilboa extract on cultured human retinal pigment epithelial cells under chemical hypoxia.
Oh JH, Oh J, Togloom A, et al.
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Khadijah Basheer

Moorfields Eye Hospital, London, UK.

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