Aim: Visual loss in age-related macular degeneration usually develops secondary to choroidal neovascularisation. Vascular endothelial growth factor (VEGF) is a critical regulator of retinal angiogenesis and vascular permeability, especially in hypoxic conditions. We hypothesise that hypothermia may reduce the retinal pigment epithelium (RPE) metabolism and, consequently, the levels of VEGF secretion by cultured RPE cells under hypoxic conditions. The effects of hypothermia were compared with the metabolic inhibiting effects of thiopental and nicotinamide.
Methods: ARPE-19 cells were grown in culture for up to 5 days under normoxic (20% O(2)) and hypoxic (1% O(2)) conditions at temperatures ranging from 27°C to 40°C. For experiments with pharmacological agents, thiopental and nicotinamide were added to the media. VEGF levels in the media were measured by ELISA and cell metabolic activity was measured by a fluorescent cell metabolic assay.
Results: We found that hypothermia reduced ARPE-19 cell metabolism in a temperature-dependent fashion. Hypothermia also reduced ARPE-19 cell VEGF secretion in a temperature-dependent fashion. ARPE-19 cell VEGF secretion was reduced by 38% at 34°C compared with cells grown at 37°C. Conversely, ARPE-19 cell VEGF secretion was increased by 32% at 40°C compared with cells grown at 37°C. Hypoxia increased ARPE-19 cell VEGF secretion by 84% at 37°C. However, hypothermia decreased the hypoxia-induced increase of ARPE-19 cell VEGF secretion by 30%. The effect of hypothermia on ARPE-19 cell VEGF secretion was reversible after 4 days. In contrast to hypothermia, thiopental and nicotinamide were able to reduce RPE cell metabolism but not VEGF secretion.
Conclusion: Hypothermia decreases both VEGF secretion and cellular metabolism in ARPE-19 cells. Hypothermia also mitigates the hypoxia-induced increase in ARPE-19 cell VEGF secretion. These effects of hypothermia are potentially unique and cannot be obtained by other pharmacological agents that slow cellular metabolism.