SKIN CARE
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Figure 1: The three steps of the discovery of vitamin E
on the three chiral carbons cannot be mastered, and a racemate of the eight possible forms is obtained stoichiometrically that corresponds to an equimolar mixture (Figure 3). The only way to obtain 98% pure RRR-
α-tocopherol is by natural extraction, a complex process involving more than 75 steps. Regarding the special stereochemistry of RRR-α-tocopherol, Azzi et al stated that only α-tocopherol should be called vitamin E.6 In the future, it could be relevant to specify the mode of extraction of vitamin E on the labelling: synt Vitamin E for chemical synthesis and nat Vitamin E for extraction from plants could be a labelling.
RRR-α-tocopherol: the most physiological vitamin E isomer Regardless of the composition of vitamin E intake obtained from the diet, α-tocopherol is selectively enriched in human tissues. α-tocopherol is the only one that is efficiently
taken up by the human body.7 This selectivity forα-tocopherol is largely
conferred by two hepatic activities, an α-tocopherol transfer protein (α-TTP) and a catabolizing cytochrome P450 system that preferentially degrades the other dietary forms of vitamin E.8 As a result, the α-tocopherol form, which is the most physiological and has the highest binding affinity for the α-TTP has to be privileged in nutrient and drug. Moreover, the stereochemical conformation should be also specified as respectively, RRR, RRS, RSS have decreasing binding affinities to α-TTP.8
RRR-α-tocopherol present in a large amount in the skin It has been demonstrated that RRR-α-tocopherol is the predominant vitamin E isomer in human skin and exhibits a characteristic gradient with lower levels towards the outer stratum corneum layer. The highest α-tocopherol levels were found in the
lower stratum corneum, whereas the lowest levels were present in the upper layer. In addition, δ-tocopherol is present in human
stratum corneum, epidermis, dermis with a molar ratio of ten α-tocopherol for one δ-tocopherol (Figure 4).9
The physiologic delivery route for
vitamin E to skin is the sebaceous gland irrigated by the dermal vessels and capillaries. In view of the adverse effects of squalene
peroxides on skin and squalene levels in human sebum may reflect a physiological strategy to maintain low levels of squalene oxidation products in skin surface lipids and their penetration into subjacent skin layers secretion.10 However, stratum corneum which maintains
the barrier function of the skin is highly susceptible to vitamin E depletion induced by UVA, UVB and ozone that could reach to up to 90% of the endogenous vitamin E skin storage.11,12
The crucial role of RRR-α-tocopherol to fight against oxy-ageing 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 protects the membrane lipids PUFAs (polyunsaturated fatty acids) from peroxidation and preserves the biological functions of the cell membranes. Lipid peroxidation is a chain reaction caused
Figure 2: The eight isomers of the Vitamin E family
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by oxygen derivatives, in particular hydroxyl radicals (•OH) or peroxyls (ROO•-); it has multiple consequences, inducing a decrease in the fluidity of plasma membranes or membranar damages leading to apoptosis of the cell. The integrity of the cellular membrane and its mechanical properties such as fluidity can influence cellular response to processes like adhesion, transport, differentiation, proliferation
May 2025 PERSONAL CARE
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