Special isomer of the vitamin E family

ABSTRACT

Although vitamin E was discovered 100 years ago, we have to admit that today it remains a little-known vitamin. Indeed, when the term vitamin E is mentioned, few people, including scientists, realize that it is a generic term covering a family of eight molecules that exhibit an antioxidant activity and that tocopherol is the scientific denomination. Moreover, the knowledge of the stereochemistry of the vitamin E is necessary to understand why RRR-α-tocopherol is a special vitamin E isomer, as the human body is selectively enriched in human tissues because α-tocopherol is the only one that is efficiently taken up by the human body. This selectivity for α-tocopherol is largely conferred by two hepatic activities, an α-tocopherol transport protein (α-TTP) and a catabolizing cytochrome P450 system that preferentially degrades the other dietary forms of vitamin E. This explains why there is an α -tocopherol/ γ -tocopherol molar ratio in the human dermis and epidermis of 10:1. The skin, as the body’s outermost organ, is persistently and directly exposed to a peroxidative environment (exposome) characterized by factors such as UV radiation and pollution. This exposure results in cumulative oxidative stress and oxy-ageing, particularly at the cell membrane level. Vitamin E is the physiological lipophilic antioxidant that inhibits peroxidation of the plasma membrane lipids. However, UV exposure depletes over 90% of this endogenous vitamin E in the stratum corneum when it is excreted onto the skin surface via the sebaceous duct, highlighting the need for topical application of vitamin E and especially, RRR-α-tocopherol that is the more physiologic stereoisomer only be obtained pure by extraction from plants as chemical synthesis results in a racemate of the vitamin E 8 isomers

Although vitamin E was discovered 100 years ago (Figure 1), we have to admit that today it remains a little-known vitamin or it is only known as the 'vitamin of cosmetics preservation', which is very restrictive. Vitamin E was discovered in 1922 by Evans and Bishop as a vital dietary biomolecule for mammalian reproduction and was originally named Factor X.¹