Retinol binding protein 3 as biomarker for diabetic retinopathy

We thank Dr. Rusciano and Dr. Bagnoli for their interest in our article “Retinol binding protein 3 is increased in the retina of patients with diabetes resistant to diabetic retinopathy” (1). Our article identified the first neuroretinal selective protein to act on retinal vasculature, suggesting numerous therapeutic and diagnostic possibilities. Several reports have suggested potential circulatory biomarkers which may be associated with severity of diabetic retinopathy (DR) (2-10). However, a major limiting factor in those studies is that the expression of those factors is not limited to the retina and are generally primarily expressed in other tissues. Thus, the circulating levels of those factors do not specifically represent retinal changes. However, RBP3 is very selectively expressed in the photoreceptors of the retina, with only very minor expression in the pineal gland. With the development of a highly sensitive and selective ELISA, we can measure RBP3 in the vitreous and accessible human fluids including the serum. Future studies are needed to elucidate the utility of circulating RBP3 levels as a biomarker for the severity or potential progression of DR.