The blood-retinal barrier transporters in retinal drug delivery

The blood-retinal barrier (BRB) forms tight junction of retinal capillary endothelial cells (inner BRB) and retinal pigment epithelial cells (outer BRB) to prevent the free diffusion of substances between the circulating blood and the neural retina, and maintain the retinal homeostasis. Retina is an important tissue involved in vision, of which disorders and diseases can produce a marked drop in the quality of life in patients. To improve the therapy of severe retinal diseases, such as diabetic retinopathy, it is essential to design simpler and more effective routes for drug delivery to the retina, and it has been proposed that the transporters at the BRB are useful for the retinal drug delivery. In this review, the transporter-mediated vitamin C and verapamil transports are introduced as the transport mechanisms for nutrients and drugs across the BRB.