2.5.1 Vitamin A
Synonyms Retinol, All-trans-retinol; Oleovitamin A; Biosterol; Lard factor; Vitamin A alcohol; Acon; Afaxin; Agiolan; Atav; Avibon; Avitol; Axerol; Epiteliol; Testanol; Vaflol; Vogan;
It mostly occurs in animals (not in plants) such as: milk fat, fish liver oil. However, the naturally occurring carotenoids are duly converted into Vitamin A by the liver. It is mainly extracted from fish liver oils where it invariably occurs in the esterified form.
However, total synthesis of Vitamin A has been accomplished from β-ionone and a propargyl halide.
It gets easily absorbed from the normal intestinal tract to the extent of 80-90% and is subsequently stored in body tissues, mostly in the liver. It has been observed that approximately one third of the Vitamin A consumed is usually stored in the body.
The most abundntly found dietary sources of Vitamin A are namely: fish- liver oils (e.g., codliver oil); dairy products (e.g., butter, cream, whole milk powder, cheese)., animal organs (e.g., liver, kidney, heart).
Biochemcially, carotene and provitamin A substances i.e., allied β-carotenoids undergo cessation by the presence of β-carotene oxygenase in the mucosal cells of the intestine to give rise to retinal; and a substantial portion of which is readily gets reduced by NADH to retinol.
Uses
1. It is particularly useful in the proper maintenance of vision, growth and tissue differentiation.
2. The vitamin is employed mainly as a prophylactic when there exists an insufficient normal dietary intake
3. It helps in the synthesis of specific glycoproteins.
Vitamin A Derivatives There are two important derivatives of vitamin A which find there usage in therapeutic domain, namely:
(a) 13-cis Retinoic Acid (Synonym Isotretinoin; Isotrex; Accutane; Roaccutane).
Uses
1. It is used in acute recalcitrant cystic acne.
2. It is invariably employed in keratinization disorders of the skin, that are mostly preneoplastic.
(b) All–trans Retinoic Acid (Synonyms Tretinoin; Vitamin A acid)
Uses
1. It is generally used for the treatment of acne vulgaris by virtue of the fact that it enhances epidermal cell mitosis and epidermal cell turnover.
2. It is used in several formulations like cream, solution and gel meant for tropical applications.
