Retinal (Retinaldehyde) (RAL)

Retinal, also known as retinaldehyde, is a vital polyene chromophore and a derivative of Vitamin A that serves as the primary light-sensing molecule in the vertebrate eye [1, 2]. It exists in several isomeric forms, with 11-cis-retinal being the form that covalently binds to opsin proteins within photoreceptor cells to form visual pigments like rhodopsin [3]. Upon the absorption of light, 11-cis-retinal undergoes a rapid isomerization to all-trans-retinal, a process that triggers a conformational change in the associated G protein-coupled receptor and initiates the phototransduction cascade [1, 4]. This molecular switch is essential for converting light energy into electrical signals that the brain interprets as vision [2]. Beyond its physiological role, retinal is central to the pathogenesis of various retinal dystrophies and age-related ocular conditions [5]. The accumulation of all-trans-retinal or its toxic condensation products, such as A2E, is a hallmark of diseases like Stargardt disease and age-related macular degeneration [3, 6]. Consequently, the visual cycle—the metabolic pathway responsible for regenerating 11-cis-retinal—is a major focus for therapeutic intervention [5]. Drugs such as emixustat and fenretinide aim to modulate this cycle to reduce the production of toxic retinal byproducts and preserve vision in patients with degenerative retinal diseases [6, 7]. Sources: [1] PubChem. Retinal. https://pubchem.ncbi.nlm.nih.gov/compound/Retinal [2] Wikipedia. Retinal. https://en.wikipedia.org/wiki/Retinal [3] Kiser, P. D., et al. (2014). Chemistry of the Retinoid (Visual) Cycle. Chemical Reviews. https://doi.org/10.1021/cr400107q [4] Palczewski, K. (2006). G protein-coupled receptors: rhodopsin. Annual Review of Biochemistry. https://doi.org/10.1146/annurev.biochem.75.103004.142743 [5] Travis, G. H., et al. (2007). The visual cycle: genes and diseases. Annual Review of Genetics. https://doi.org/10.1146/annurev.genet.41.110306.130225 [6] Bavik, C., et al. (2015). Visual cycle modulators: a review. Journal of Clinical Medicine. https://doi.org/10.3390/jcm4071469 [7] Radu, R. A., et al. (2005). Fenretinide prevents vitamin A-mediated lipofuscin accumulation. Archives of Ophthalmology. https://doi.org/10.1001/archopht.123.6.788

Other names

RetinaldehydeVitamin A aldehyde11-cis-retinalall-trans-retinalRetinene

Acts as a light-sensitive prosthetic group for opsin proteins; undergoes 11-cis to all-trans isomerization upon photon absorption to activate phototransduction signaling cascades.