Hypoxia and inflammation in human retinal cells

Purpose Retina is extremely sensitive to low oxygen tension as its metabolic rate is the highest one among tissues. In diabetic macular edema, there always occur both hypoxia and inflammation. It is not, however, clear if VEGF release in hypoxia takes place without inflammation in retinal cells. We set out to study the issue using both human ARPE cells and human primary RPE cell culture. Methods Human ARPE‐19 cells were routinely cultured in humified CO2 atmosphere as reported previously. The cells were exposed for 24 h to hypoxia and a part of a cell culture was followed up to 48 h. Inflammatory responses were induced with a pre‐treatment by bacterial lipopolysaccharide (LPS). In parallel, human primary RPE cells were used to verify results. IL‐6, IL‐8, IL‐1β, IL‐18 and VEGF were measured with specific ELISA kits. Statistical analyses were performed with the GraphPadPrism software. Results Significantly increased IL‐6 and IL‐8 levels were found after hypoxia exposure in ARPE cells and the trend was seen in the primary RPE cell culture as well; LPS‐treatment did not change the expression profile of these interleukins. Hypoxia and LPS pre‐treatment did not affect the release of IL‐1β and IL‐18. The hypoxia exposure increased significantly the release of VEGF as anticipated but the LPS pre‐treatment had no effects on the release. Conclusions Hypoxia induced inflammation both in human ARPE cells and in human primary RPE cell culture as shown with IL‐6 and IL‐8. LPS pretreatment increased this response. Hypoxia stimulated directly the VEGF secretion independent of the inflammatory pathway.