retinaldehyde

Retinaldehyde, also known as retinal, is the aldehyde form of vitamin A with the chemical formula C20H28O. It functions as an intermediate in both vision and vitamin A metabolism and is one of the early steps in forming active retinoids used by cells.

In vertebrate vision, retinaldehyde is intimately involved in the vertebrate visual cycle. The chromophore 11-cis-retinal binds to the protein opsin to form rhodopsin in photoreceptor cells. Upon absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, triggering a signal transduction cascade that underlies vision. All-trans-retinal is then reduced to all-trans-retinol and transported to the retinal pigment epithelium, where it is recycled back to 11-cis-retinal to regenerate the visual pigment.

Biosynthesis and metabolism of retinaldehyde begin with provitamin A carotenoids, such as beta-carotene, which can be cleaved to retinal. In mammals, retinol is converted to retinaldehyde by retinol dehydrogenases, and retinaldehyde can be further oxidized to retinoic acid by aldehyde dehydrogenases to activate gene regulation pathways. Retinaldehyde thus lies at a crossroads between storage forms of vitamin A and the active retinoid signaling molecules.

In cosmetics and dermatology, retinaldehyde is used as a retinoid ingredient in some skincare products. It is considered to have greater potency than retinol in promoting cell turnover and collagen remodeling, while often being milder on the skin than retinaldehyde-derived retinoic acid. As with other retinoids, use can increase photosensitivity and irritation, so sunscreen and gradual introduction are advised, especially during pregnancy.