Study of Phototoxic Properties of Retinal and Its Derivatives in a Photoreceptor Cell by the Method of Pulsed Photolysis

Abstract

It is believed that one of the causes of photodamage to the retina is the accumulation of all-trans-retinal (ATR) in the visual cells. However, the ATR is formed during photolysis inside the disk of the photoreceptor cell and transferred to the cytoplasm of the cell, where it is converted with a high yield to retinol, a nonphototoxic compound. Inside the disk, where ATR can accumulate, it can form Schiff bases, which are also not phototoxic compounds, with the amino groups of proteins and lipids. In addition, the resulting free retinal (R) isomers bind to specific retinal-binding proteins that can shield them from oxygen. Thus, the question on the concentrations in which free ATR can accumulate inside a cell is ambiguous. In this study, it is proposed to evaluate the concentration of free ATR in a cell by the yield of the excited triplet state, since neither the Schiff bases of ATR nor retinol are transformed into an excited triplet state. It is shown that 70% of ATR form Schiff bases in the equilibrium state in the native cell. This significantly reduces the likelihood that ATR is the main inducer of photodamage. Moreover, it is shown that the quantum yield of the formation reaction of an excited triplet state of R when it is bound to interfotoreceptor proteins is significantly reduced.