Transport of Vitamin E Across The Perfused Placenta Studies Using Deuterolabeled Tocopherols

Abstract

LEARNING OUTCOME: To examine vitamin E transport across the placenta using perfused, human placentas.Vitamin E sufficiency has been an on-going concern in premature and term infants. Transfer of vitamin E across the human placenta has only been examined in evaluating cord blood following parturition and in animal models using a single cotyledon. With the modification of an animal organ perfusion chamber, intact human placentas (obtained after birth) were used to examine the transport of synthetic and naturally occurring α-tocopherols. Deutero-labeled vitamin E (150 mg) was administered to one female volunteer in the form of a 1:1 mixture of d3-RRR- (natural) and d6-all-rac-α-tocopheryl (synthetic) acetates for a two week period followed by withdrawing a unit of whole blood. Plasma was expressed for separation into lipoprotein components (chylomicrons, VLDL, LDL, HDL) containing the labeled vitamin E compounds. Following cannulation of the fetal artery and vein, placentas were perfused for two hours from both the maternal and fetal sides of the placenta. Labeled lipoproteins were administered separately (n=8) to the maternal reservoir in a Krebs-Ringer solution containing antipyrine and inulin. Examining the eluant from the fetal side by gas chromatography / mass spectrometry, it was determined that d3-RRR-α-tocopherol was the preferred compound for transport from the maternal to the fetal side. HDL and LDL fractions transported greater amounts of vitamin E than did chylomicrons or VLDL fractions. Although more placental perfusion studies need to be preformed to detail the mechanism of transplacental transport of vitamin E, the RRR stereoisomer is preferentially transported and is the isomer of choice by the placenta. This finding is important because synthetic vitamin E is the predominant source used in prenatal vitamin preparations.