Isolation and one-step preparation of A2E and iso-A2E, fluorophores from human retinal pigment epithelium

Age-related macular degeneration, a major cause of blindness for which no s atisfactory treatments exist, leads to a gradual decrease in central high a cuity vision. The accumulation of fluorescent materials, called lipofuscin, in retinal pigment epithelial cells of the aging retina is most pronounced in the macula, One of the fluorophores of retinal pigment epithelial lipof uscin has been characterized as A2E, a pyridinium bis-retinoid, which is de rived from two molecules of vitamin A aldehyde and one molecule of ethanola mine. An investigation aimed at optimizing the in vitro synthesis of A2E ha s resulted in the one-step biomimetic preparation of this pigment in 49% yi eld, readily producing more than 50 mg in one step. These results have allo wed for the optimization of HPLC conditions so that nanogram quantities of A2E can be detected from extracts of tissue samples. By using 5% of the ext ract from individual aged human eyes, this protocol has led to the quantifi cation of A2E and the characterization of iso-A2E, a new A2E double bond is omer; all-trans-retinol and 13-cis-retinol also have been identified in the se HPLC chromatograms, Exposure of either A2E or iso-A2E to light gives ris e to 4:1 A2E:iso-A2E equilibrium mixtures, similar to the composition of th ese two pigments in eye extracts. A2E and iso-A2E may exhibit surfactant pr operties arising from their unique wedge-shaped structures.