Continuous Low-Level Blue Light Irradiation Induces Phospholipid Oxidation and Angiogenic Cytokine Expression in the Retina

Abstract

Purpose:: We previously showed that oxidized phospholipids increase in human retina with age and in AMD. In this study, we induced oxidized phospholipids in mice retina with blue light irradiation and determined if induced oxidized phospholipids in mice retina with age. We also examined whether monocyte chemotactic protein (MCP)-1 increases in light irradiated mice retina and if the oxidized phospholipids induce the expression of MCP-1 in human retinal pigment epithelium cell culture.

Methods:: We compared 2 and 12-month-old C57/BL6 mice, which were exposed to blue light emitting diode (LED) light continuously for 7 days in a specially designed cage (2mW/cm², peak wavelength: 480 nm). We performed immunohistochemistry with DLH3, an anti-oxidized phospholipid antibody, and an anti-MCP-1 antibody, competitive enzyme-linked immunosorbent assay (competitive ELISA) to evaluate the quantity of the oxidized phospholipids, and ELISA to estimate the quantity of MCP-1. An in vitro experiment, ARPE-19 cells were cultured with oxidized products of phospholipids, 10 and 50 µmol 5- and 9-CHOPC, for 6 hours and the supernatants were assessed for MCP-1 by ELISA.

Results:: The immunoreactivity for oxidized phospholipids in the 12-month-old light irradiated mice was greater than in the 2-month-old mice. A significant (p<0.001) amount of oxidized phospholipids was induced using blue LED light and increased with age(p<0.001). Positive staining for MCP-1 was observed in the RPE and choroid of the 12-month-old light irradiated mice. A significant (p<0.001) amount of MCP-1 was induced using blue LED light and increased with age (p<0.001). Oxidized phospholipids induced MCP-1 production by RPE in a dose dependent manner.

Conclusions:: These results indicate that oxidized phospholipids induced by low-level blue light irradiation in the retina increase with age and oxidized phospholipids may stimulate expression of MCP-1 in the RPE. Our findings suggest that aging may make the retina subjected to oxidative stress and these data demonstrate a proinflammatory role for oxidized phospholipids in mediation of the RPE cells to produce monocyte chemotactic activity in AMD.

Keywords: age-related macular degeneration • oxidation/oxidative or free radical damage • aging