N-retinylidene-N-retinylethanolamine (A2E)

N-retinylidene-N-retinylethanolamine (A2E) is a major bis-retinoid component of lipofuscin that accumulates in the retinal pigment epithelium (RPE) as a byproduct of the visual cycle (Sparrow et al., 2000, J Biol Chem). It is formed by the non-enzymatic condensation of two molecules of all-trans-retinal with phosphatidylethanolamine (Radu et al., 2003, PNAS). While A2E is a natural consequence of light detection, its excessive accumulation is pathogenic, exerting detergent-like effects on lysosomal membranes and inducing phototoxicity upon exposure to blue light (Sparrow et al., 2012, Prog Retin Eye Res). These processes lead to RPE cell death and subsequent loss of photoreceptors, which are the primary pathological features of Stargardt disease and dry age-related macular degeneration (AMD) (Boyer et al., 2012, Clin Ophthalmol). Because A2E is a metabolic byproduct rather than a protein, therapeutic strategies focus on preventing its formation by modulating the visual cycle. This includes inhibiting the enzyme RPE65 (e.g., Emixustat), reducing the delivery of retinol to the eye via RBP4 antagonism (e.g., Tinlarebant, Fenretinide), or using deuterated vitamin A (ALK-001) to slow the chemical dimerization rate (Kubota et al., 2014, Retina; Charbel Issa et al., 2015, Expert Opin Pharmacother).

Other names

A2EN-retinylidene-N-retinyl-ethanolaminePyridinium bis-retinoidLipofuscin fluorophoreA2-E

Reduction of A2E accumulation through visual cycle modulation, including RPE65 inhibition, RBP4 antagonism, and deuterated vitamin A substitution (Kubota et al., 2014; Charbel Issa et al., 2015).