Intravenously administered gold nanoparticles pass through the blood?retinal barrier depending on the particle size, and induce no retinal toxicity

The retina maintains homeostasis through the blood?retinal barrier (BRB). Although it is ideal to deliver the drug to the retina via systemic administration, it is still challenging due to the BRB strictly regulating permeation from blood to the retina. Herein, we demonstrated that intravenously administered gold nanoparticles could pass through the BRB and are distributed in all retinal layers without cytotoxicity. After intravenous injection of gold nanoparticles into C57BL/6 mice, 100?nm nanoparticles were not detected in the retina whereas 20?nm nanoparticles passed through the BRB and were distributed in all retinal layers. 20?nm nanoparticles in the retina were observed in neurons (75 ? 5%), endothelial cells (17 ? 6%) and peri-endothelial glial cells (8 ? 3%), where nanoparticles were bound on the membrane. In the retina, cells containing nanoparticles did not show any structural abnormality and increase of cell death compared to cells without nanoparticles. Gold nanoparticles never affected the viability of retinal endothelial cells, astrocytes and retinoblastoma cells. Furthermore, gold nanoparticles never led to any change in expression of representative biological molecules including zonula occludens-1 and glut-1 in retinal endothelial cells, neurofilaments in differentiated retinoblastoma cells and glial fibrillary acidic protein in astrocytes. Therefore, our data suggests that small gold nanoparticles (20?nm) could be an alternative for drug delivery across the BRB, which could be safely applied in vivo.