The interaction of indocyanine green with human retinal pigment epithelium

PURPOSE. This study sought to examine the in vitro interaction of human RPE cells with indocyanine green (ICG). The interaction between ICG and the RPE may have clinical relevance in the interpretation of clinical ICG angiography. METHOD. Cultured primary human RPE cells were incubated with ICG. Infrared fluorescence microscopy was used to detect RPE cell ICG fluorescence. The proportions of cells exhibiting ICG infrared fluorescence were quantified. Separate RPE cell populations were incubated with ouabain for 24 and 72 hours, respectively, before addition of the ICG to examine its effect on the uptake of ICG. The effect of ouabain on cell viability was assessed with trypan blue exclusion. RESULTS. Normal human RPE cells incubated with ICG exhibited strong infrared fluorescence. Exposure to ouabain for 24 hours before incubation with ICG had little effect on cell viability but significantly reduced cellular ICG fluorescence. In contrast, exposure to ouabain for 72 hours reduced cell viability and increased cellular ICG fluorescence. CONCLUSIONS. Cultured human RPE cells take up ICG dye. ICG uptake by RPE cells may involve active transport, as cells incubated with ouabain for 24 hours showed no reduction in cell viability but exhibited reduced infrared fluorescence. The paradoxical increased uptake of ICG into the cells after more prolonged exposure to ouabain may be due to ICG's movement through the damaged cell membrane. Fluorescence due to ICG uptake by RPE has clinical relevance in that it contributes to the fluorescence patterns observed in ICG angiography.