retinal-dimer and Macular-Degeneration

Genetic association studies and investigations of the constituents of subretinal deposits (drusen) have implicated complement dysregulation as one factor predisposing individuals to increased risk of age-related macular degeneration (AMD). Here we review evidence that molecular fragments released by photooxidation of the bisretinoids of retinal pigment epithelial lipofuscin, can activate complement. Complement activation by this mechanism is dependent on the alternative pathway. The diretinal conjugates comprising RPE lipofuscin accumulate in the cells throughout the lifetime of an individual. As such, these photooxidative processes, in a setting of complement dysregulation could contribute to chronic inflammation underlying AMD pathogenesis.

Topics: C-Reactive Protein; Complement Activation; Complement Factor B; Humans; Lipofuscin; Macular Degeneration; Oxidation-Reduction; Peptides, Cyclic; Pyridinium Compounds; Retinal Pigment Epithelium; Retinaldehyde; Retinoids

Effective clearance of all-trans-retinal (atRAL) from retinal pigment epithelial (RPE) cells is important for avoiding its cytotoxicity. However, the metabolism of atRAL in RPE cells is poorly clarified. The present study was designed to analyze metabolic products of atRAL and to compare the cytotoxicity of atRAL versus its derivative all-trans-retinal dimer (atRAL-dimer) in human RPE cells. We found that all-trans-retinol (atROL) and a mixture of atRAL condensation metabolites including atRAL-dimer and A2E were generated after incubating RPE cells with atRAL for 6h, and the amount of atRAL-dimer was significantly higher than that of A2E. In the eyes of Rdh8

Topics: Alcohol Oxidoreductases; Animals; ATP-Binding Cassette Transporters; Cell Line; Cell Survival; DNA, Complementary; Epithelial Cells; Humans; Macular Degeneration; Membrane Potential, Mitochondrial; Mice; Mice, Knockout; Mitochondria; Oxidative Stress; Reactive Oxygen Species; Retinal Pigment Epithelium; Retinaldehyde

Gene and drug therapies are being developed to alleviate vision loss in patients with Stargardt's disease and age-related macular degeneration (AMD). To evaluate the therapeutic effects of these treatments, organic solvents are routinely used to extract and quantify bisretinoid lipofuscin constituents, such as N-retinylidene-N-retinyl-ethanolamine (A2E) and all-trans-retinal dimer (ATR-dimer). By high-performance liquid chromatography (HPLC), we found that A2E and ATR-dimer were both altered by tetrahydrofuran (THF) and chloroform, but were stable in dimethyl sulfoxide (DMSO) or methanol (MeOH). In addition, cyclohexane and ethanol (EtOH) did not alter ATR-dimer, whereas an alteration of A2E occurred in EtOH. On the basis of these findings, we designed processes II-IV, generated by modifications of process I, a routine method to measure bisretinoid compounds in vivo. Extra amounts of either ATR-dimer or A2E in mouse eyecups were released by processes II-IV versus process I. Efforts to clarify the effects of organic solvents on lipofuscin pigments are important because such studies can guide the handling of these fluorophores in related experiments.

Topics: Animals; Chromatography, High Pressure Liquid; Lipofuscin; Macular Degeneration; Mice; Mice, Inbred C57BL; Pigment Epithelium of Eye; Retinaldehyde; Solvents; Stargardt Disease

Aging of retinal pigment epithelial (RPE) cells of the eye is marked by accumulations of bisretinoid fluorophores; two of the compounds within this lipofuscin mixture are A2E and all-trans-retinal dimer. These pigments are implicated in pathological mechanisms involved in some vision-threatening disorders including age-related macular degeneration (AMD). Studies have shown that bisretinoids are photosensitive compounds that undergo photooxidation and photodegradation when irradiated with short wavelength visible light. Utilizing ultra performance liquid chromatography (UPLC) with electrospray ionization mass spectrometry (ESI-MS) we demonstrate that photodegradation of A2E and all-trans-retinal dimer generates the dicarbonyls glyoxal (GO) and methylglyoxal (MG), that are known to modify proteins by advanced glycation endproduct (AGE) formation. By extracellular trapping with aminoguanidine, we established that these oxo-aldehydes are released from irradiated A2E-containing RPE cells. Enzyme-linked immunosorbant assays (ELISA) revealed that the substrate underlying A2E-containing RPE was AGE-modified after irradiation. This AGE deposition was suppressed by prior treatment of the cells with aminoguanidine. AGE-modification causes structural and functional impairment of proteins. In chronic diseases such as diabetes and atherosclerosis, MG and GO modify proteins by non-enzymatic glycation and oxidation reactions. AGE-modified proteins are also components of drusen, the sub-RPE deposits that confer increased risk of AMD onset. These results indicate that photodegraded RPE bisretinoid is likely to be a previously unknown source of MG and GO in the eye.

Topics: Cells, Cultured; Chromatography, Liquid; Enzyme-Linked Immunosorbent Assay; Glycation End Products, Advanced; Glyoxal; Guanidines; Humans; Lipofuscin; Macular Degeneration; Phenylhydrazines; Pyridinium Compounds; Pyruvaldehyde; Retina; Retinal Drusen; Retinaldehyde; Retinoids; Spectrometry, Mass, Electrospray Ionization

The bis-retinoid pigments that accumulate in retinal pigment epithelial cells as lipofuscin are associated with inherited and age-related retinal disease. In addition to A2E and related cis isomers, we previously showed that condensation of two molecules of all-trans-retinal leads to the formation of a protonated Schiff base conjugate, all-trans-retinal dimer-phosphatidylethanolamine. Here we report the characterization of the related pigments, all-trans-retinal dimer-ethanolamine and unconjugated all-trans-retinal dimer, in human and mouse retinal pigment epithelium. In eyecups of Abcr(-/-) mice, a model of recessive Stargardt macular degeneration, all-trans-retinal dimer-phosphatidylethanolamine was increased relative to wild type and was more abundant than A2E. Total pigment of the all-trans-retinal dimer series (sum of all-trans-retinal dimer-phosphatidylethanolamine, all-trans-retinal dimer-ethanolamine, and all-trans-retinal dimer) increased with age in Abcr(-/-) mice and was modulated by amino acid variants in Rpe65. In in vitro assays, enzyme-mediated hydrolysis of all-trans-retinal dimer-phosphatidylethanolamine generated all-trans-retinal dimer-ethanolamine, and protonation/deprotonation of the Schiff base nitrogen of all-trans-retinal dimer-ethanolamine was pH-dependent. Unconjugated all-trans-retinal dimer was a more efficient generator of singlet oxygen than A2E, and the all-trans-retinal dimer series was more reactive with singlet oxygen than was A2E. By analyzing chromatographic properties and UV-visible spectra together with mass spectrometry, mono- and bis-oxygenated all-trans-retinal dimer photoproducts were detected in Abcr(-/-) mice. The latter findings are significant to an understanding of the adverse effects of retinal pigment epithelial cell lipofuscin.

Topics: Animals; ATP-Binding Cassette Transporters; Carrier Proteins; Chromatography, High Pressure Liquid; cis-trans-Isomerases; Eye Proteins; Humans; Lipofuscin; Macular Degeneration; Mice; Phosphatidylethanolamines; Pigment Epithelium of Eye; Pyridinium Compounds; Retinaldehyde; Retinoids; Singlet Oxygen