Vitamin E delivery to human skin: studies using deuterated α-tocopherol measured by APCI LC-MS

Abstract

Enrichment of skin surface lipids with deuterium-labeled α-tocopherol was compared with plasma enrichment to evaluate kinetics of the delivery of vitamin E to skin surface lipids. For 7 d, subjects consumed 75 mg each of RRR-α-[5-(C2H3)]- (d3) and all rac-α-[5,7-(C2H3)2]- (d6) tocopheryl acetates with breakfast. Blood was drawn and skin lipids were collected daily for 2 weeks, then every other day for 2 weeks. A liquid chromatography–mass spectrometry atmospheric pressure chemical ionization method for quantification of deuterium labeled (d3, d6, d9-α-tocopherols) and unlabeled (d0-) α- and γ-tocopherols was developed. Tocopherols were quantified at their m/z [M-1] using single ion recording. α-Tocopherol detection was linear from 1 to 100 pmol with a detection limit of 40 pg (93 fmol). Detection of γ-tocopherol was twice as sensitive due to greater ionization efficiency. Though d3- and d6-α-tocopherols appeared in plasma within 24 h of the first dose, d3-α-tocopherol was not detected in skin surface lipids until ∼1 week. Plasma percentage d3 peaked at day 8, while skin surface lipid percentage d3 increased on average until day 19. Apparently skin employs a mechanism to deliver α-tocopherol into skin via lipid secretions.