Water-Soluble Products of Photooxidative Destruction of the Bisretinoid A2E Cause Proteins Modification in the Dark

Abstract

Aging of the retina is accompanied by a sharp increase in the content of lipofuscin granules and bisretinoid A2E in the cells of the retinal pigment epithelium (RPE) of the human eye. It is known that A2E can have a toxic effect on RPE cells. However, the specific mechanisms of the toxic effect of A2E are poorly understood. We investigated the effect of the products of photooxidative destruction of A2E on the modification of bovine serum albumin (BSA) and hemoglobin from bovine erythrocytes. A2E was irradiated with a blue light-emitting diode (LED) source (450 nm) or full visible light (400–700 nm) of a halogen lamp, and the resulting water-soluble products of photooxidative destruction were investigated for the content of carbonyl compounds by mass spectrometry and reaction with thiobarbituric acid. It has been shown that water-soluble products formed during A2E photooxidation and containing carbonyl compounds cause modification of serum albumin and hemoglobin, measured by an increase in fluorescence intensity at 440–455 nm. The antiglycation agent aminoguanidine inhibited the process of modification of proteins. It is assumed that water-soluble carbonyl products formed as a result of A2E photodestruction led to the formation of modified proteins, activation of the inflammation process, and, as a consequence, to the progression of various senile eye pathologies.

Lipofuscin-Mediated Photic Stress Induces a Dark Toxic Effect on ARPE-19 Cells

“…Thus, the greatest cytotoxicity in relation to RPE cells was shown by lipofuscin-fed RPE samples maintained in the dark after irradiation. These results support our assumption [ 38 , 41 ] that BisRets-OX with hydrophilic and amphiphilic features can have cytotoxic effects on RPE cells. The results of our experiments correlate with the other literature data [ 47 , 49 , 50 ].…”

“…In earlier in vitro experiments [ 38 ], we demonstrated that BisRets-OX, which are formed when LGs are irradiated with visible light, have both hydrophilic and amphiphilic properties, allowing their diffusion through the LG membrane into the RPE cell cytoplasm. It was established that these products contain cytotoxic carbonyls, which can modify cellular proteins and lipids [ 41 ].…”

“…Our findings that BisRets-OX are TBA-active and have the potential to release LGs [ 38 ] allowed us to assume that they can damage RPE cellular organelles and macromolecules in the dark [ 41 ].…”

“…Our in vitro experiments [ 38 , 41 ] have shown that BisRets-OX consist of aldehydes and ketones which are accumulated in the free state within LGs. It has also been demonstrated that these substances have hydrophilic and amphiphilic properties capable of diffusing from LGs into the cytoplasmic part of the RPE cell.…”

“…Since carbonyl products are long-lived, they can tightly bind with long-lived proteins such as collagen [ 39 ] or hemoglobin [ 40 ], resulting in the formation of advanced glycation end products that can activate inflammatory processes. The results of our in vitro experiments [ 41 ] have shown that water-soluble carbonyl products formed by A2E photodestruction lead to the formation of modified proteins, which also indicates that BisRets-OX can damage RPE cells.…”