Retinylester

Retinyl esters are esters of retinol (vitamin A) with fatty acids. They are the principal storage form of vitamin A in animals and the major circulating form after absorption of dietary fats. The most common retinyl ester is retinyl palmitate; others include retinyl oleate and retinyl stearate.

Dietary retinyl esters are found in animal-derived foods such as liver, dairy products, eggs, and certain fish, and are used in fortified foods and supplements. Retinyl esters are also used in cosmetics, notably retinyl palmitate, as a vitamin A–related ingredient. In the body, vitamin A activity can come from retinyl esters or from free retinol released during digestion and transport.

Digestion and metabolism begin in the intestine, where dietary retinyl esters are hydrolyzed by pancreatic enzymes to retinol and fatty acids. Retinol is absorbed by enterocytes, then re-esterified to retinyl esters by enzymes such as lecithin retinol acyltransferase (LRAT) and acyl-CoA retinol acyltransferases (ARAT) and packed into chylomicrons for lymphatic transport to the liver and other tissues. In the liver, most retinyl esters are stored in hepatic stellate cells. When needed, retinyl esters are hydrolyzed by retinyl ester hydrolases to release retinol, which binds to retinol-binding protein (RBP) for transport in the bloodstream and delivery to target tissues.

Functionally, vitamin A supports vision (via retinal), immune function, and epithelial cell differentiation; retinoic acid derived from retinol acts as a regulator of gene expression. Retinyl esters thus serve as the storage and transport form that maintains vitamin A homeostasis. Excess intake of retinyl esters can contribute to toxicity.