Interplay between β-carotene and lipoprotein metabolism at the maternal-fetal barrier

Vitamin A is an essential nutrient, critical for proper embryonic development in mammals. Both embryonic vitamin A-deficiency or -excess lead to congenital malformations or lethality in mammals, including humans. This is due to the defective transcriptional action of retinoic acid, the active form of vitamin A, that regulates in a spatial- and temporal-dependent manner the expression of genes essential for organogenesis. Thus, an adequate supply of vitamin A from the maternal circulation is vital for normal mammalian fetal development. Provitamin A carotenoids circulate in the maternal bloodstream and are available to the embryo. Of all the dietary carotenoids, 5-carotene is the main vitamin A precursor, contributing at least 30% of the vitamin A intake in the industrialized countries and often constituting the sole source of retinoids (vitamin A and its derivatives) in the developing world. In humans, up to 40% of the absorbed dietary 5-carotene is incorporated in its intact form in chylomicrons for distribution to other organs within the body, including the developing tissues. Here, it can serve as a source of vitamin A upon conversion into apocarotenoids by its cleavage enzymes. Given that 5carotene is carried in the bloodstream by lipoproteins, and that the placenta acquires, assembles and secretes lipoproteins, it is becoming evident that the maternal-fetal transfer of 5-carotene relies on lipoprotein metabolism. Here, we will explore the current knowledge about this important biological process, the cross-talk between carotenoid and lipid metabolism in the context of the maternal-fetal transfer of this provitamin A precursor, and the mechanisms whereby 5-carotene is metabolized by the developing tissues. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.