N-retinylidene-N-retinylethanolamine (A2E) (A2E)

N-retinylidene-N-retinylethanolamine (A2E) is a toxic bis-retinoid byproduct of the visual cycle that accumulates in the retinal pigment epithelium (RPE) as a primary component of lipofuscin (PubMed, 2021; NIH, 2003). It is formed through the non-enzymatic dimerization of all-trans-retinal with phosphatidylethanolamine during the process of visual phototransduction (PubMed Central, 2021). The accumulation of A2E is highly pathogenic, as its amphiphilic and photoreactive properties lead to oxidative stress, lysosomal membrane damage, and complement activation, ultimately resulting in RPE cell death (PubMed, 2021; PMC, 2022). This destruction of the RPE layer subsequently causes the degeneration of overlying photoreceptor cells, leading to irreversible vision loss. A2E accumulation is a hallmark of Stargardt disease, caused by mutations in the ABCA4 transporter, and is a significant driver in the progression of dry age-related macular degeneration (AMD) (AAO, 2017; BioWorld, 2007). Therapeutic strategies targeting A2E focus on preventing its formation by slowing the visual cycle (e.g., RPE65 inhibition), reducing systemic retinol transport (e.g., RBP4 antagonism), or utilizing deuterated vitamin A to inhibit the chemical dimerization process (Encyclopedia MDPI, 2022).

Other names

A2EVitamin A dimerBis-retinoidLipofuscin componentRetinal-derived pyridiniumN-retinylidene-N-retinylethanolamine

Slowing of the visual cycle via RPE65 inhibition, reduction of systemic retinol transport via RBP4 antagonism, and inhibition of the dimerization rate via vitamin A deuteration (C20-D3-vitamin A) to prevent the accumulation of toxic bis-retinoid byproducts.