Vitamin E and transfer proteins.

Abstract

Recently, the intracellular transport as well as cellular uptake and excretion of alpha-tocopherol, the major representative of vitamin E, have been elucidated. Alpha-tocopherol transfer protein has been identified as the major intracellular transport protein for vitamin E, mediating alpha-tocopherol secretion into the plasma via a non-Golgi-dependent pathway, while other binding proteins seem to play a less important role. New information has accumulated concerning the role of this protein in the transport and supply of vitamin E to tissues such as the central nervous system and the feto-maternal unit. The scavenger receptor class B type I receptor, a membrane-bound protein, is capable of transferring vitamin E into the cell, while the ATP-binding cassette transporter A1 can excrete vitamin E out of the cell. Advances in the area of vitamin E metabolism have shown that alpha-CEHC (2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman) and gamma-CEHC (2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman) are formed by a cytochrome p450-mediated process, important for alpha and gamma-tocopherol excretion. Insights into the regulation of vitamin E transport and metabolism on the cellular level have made enormous advances, showing the complex interplay of influx, trafficking, efflux and metabolism of this crucial antioxidant.