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Vitamin A (retinol)

The term vitamin A includes a number of chemically similar compounds with different effect in the human and animal organism. These include as essential groups the alcohol of the vitamin, retinol, the transport form of the vitamin in blood, the aldehyde, the biologically active metabolite in the visual process, retinal ester, the storage form of the vitamin in the liver and in mucous membranes and reproductive glands, and retinoic acid with various derivatives which play a part in particular in the differentiation processes of the skin. Vitamin A (retinol) and most derivatives thereof having vitamin A activity are water-insoluble, being hydrophobic, lipid-soluble compounds. For example, retinoic acid is not water-soluble. Retinol is an endogenous compound which occurs naturally in the human body and is essential for normal epithelial cell differentiation. Natural and synthetic vitamin A derivatives have been used extensively in the treatment of a variety of skin disorders and have been used as skin repair or renewal agents. The most stable and more bioavailable form of Vitamin A is the trans isomer. The cis isomeric forms, i.e., 13-cis retinol, 9-cis retinol, and 9, 13-di-cis retinol materials are less stable. Cis isomers are formed during production and they oxidize more readily than the trans isomers. Retinoid useful for skin caring includes retinol (vitamin A alcohol), retinal (vitamin A aldehyde) and retinyl acetate, retinyl propionate, retinyl linoleate and retinyl palmitate as retinyl esters. In addition to their important role in the transmission of pleitrophic effects on morphogenesis, differentiation and hemostasis during the embryonic and postnatal phase of life, vitamin A acid shows a great potential as pharmacological active substance. Vitamin A is commercially prepared by extraction from fish liver oils or by chemical synthesis from the reaction of beta ionone and a propargyl halide. Retinol acetate is converted to retinol palmitate through a transesterification reaction with methyl palmitate. Both retinol acetate and retinol palmitate are commonly used for supplementation.

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