fphar-09-01027 September 10, 2018 Time: 17:35 # 1 REVIEW published: 12 September 2018 doi: 10.3389/fphar.2018.01027 Physiology and Pathophysiology of Steroid Biosynthesis, Transport and Metabolism in the Human Placenta Waranya Chatuphonprasert1,2, Kanokwan Jarukamjorn3 and Isabella Ellinger1* 1 Pathophysiology of the Placenta, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria, 2 Faculty of Medicine, Mahasarakham University, Maha Sarakham, Thailand, 3 Research Group for Pharmaceutical Activities of Natural Products Using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen, Thailand The steroid hormones progestagens, estrogens, androgens, and glucocorticoids as well as their precursor cholesterol are required for successful establishment and maintenance of pregnancy and proper development of the fetus. The human placenta forms at the interface of maternal and fetal circulation. It participates in biosynthesis and metabolism of steroids as well as their regulated exchange between maternal and fetal compartment. This review outlines the mechanisms of human placental handling of steroid compounds. Cholesterol is transported from mother to offspring involving Edited by: lipoprotein receptors such as low-density lipoprotein receptor (LDLR) and scavenger Tea Lanisnik Rizner, University of Ljubljana, Slovenia receptor class B type I (SRB1) as well as ATP-binding cassette (ABC)-transporters, Reviewed by: ABCA1 and ABCG1. Additionally, cholesterol is also a precursor for placental Gary Grosser, progesterone and estrogen synthesis. Hormone synthesis is predominantly performed Justus-Liebig-Universität Giessen, by members of the cytochrome P-450 (CYP) enzyme family including CYP11A1 or Germany Christian Wadsack, CYP19A1 and hydroxysteroid dehydrogenases (HSDs) such as 3b-HSD and 17b-HSD. Medizinische Universität Graz, Austria Placental estrogen synthesis requires delivery of sulfate-conjugated precursor molecules Andrzej T. Slominski, The University of Alabama from fetal and maternal serum. Placental uptake of these precursors is mediated by at Birmingham, United States members of the solute carrier (SLC) family including sodium-dependent organic anion *Correspondence: transporter (SOAT), organic anion transporter 4 (OAT4), and organic anion transporting Isabella Ellinger polypeptide 2B1 (OATP2B1). Maternal–fetal glucocorticoid transport has to be tightly [email protected] regulated in order to ensure healthy fetal growth and development. For that purpose, the Specialty section: placenta expresses the enzymes 11b-HSD 1 and 2 as well as the transporter ABCB1. This article was submitted to This article also summarizes the impact of diverse compounds and diseases on the Experimental Pharmacology and Drug Discovery, expression level and activity of the involved transporters, receptors, and metabolizing a section of the journal enzymes and concludes that the regulatory mechanisms changing the physiological to a Frontiers in Pharmacology pathophysiological state are barely explored. The structure and the cellular composition Received: 11 April 2018 Accepted: 24 August 2018 of the human placental barrier are introduced. While steroid production, metabolism Published: 12 September 2018 and transport in the placental syncytiotrophoblast have been explored for decades, few Citation: information is available for the role of placental-fetal endothelial cells in these processes. Chatuphonprasert W, Jarukamjorn K With regard to placental structure and function, significant differences exist between and Ellinger I (2018) Physiology and Pathophysiology of Steroid species. To further decipher physiologic pathways and their pathologic alterations in Biosynthesis, Transport placental steroid handling, proper model systems are mandatory. and Metabolism in the Human Placenta. Front. Pharmacol. 9:1027. Keywords: cholesterol, progestagens, estrogens, glucocorticoids, gestational diabetes mellitus, preeclampsia, doi: 10.3389/fphar.2018.01027 intrauterine growth retardation, oxysterols Frontiers in Pharmacology| www.frontiersin.org 1 September 2018| Volume 9| Article 1027 fphar-09-01027 September 10, 2018 Time: 17:35 # 2 Chatuphonprasert et al. Steroids and the Human Placenta INTRODUCTION “placental barrier,” which prevents direct contact of maternal and fetal blood. Biosynthesis, metabolism, and transport of steroids The placenta is a multifunctional organ enabling optimal fetal occur in the chorionic villi (Benirschke et al., 2012). growth. Structure and function can adapt to diverse external Chorionic villi are composed of several cell types (Jones stressors. In case of failure of adaptation or inadequate placental and Fox, 1991; Benirschke et al., 2012). The STB, an epithelial development, fetal survival or fetal growth and development are multinucleated syncytium, covers the surface of the chorionic endangered and developmental programming of adult diseases villi. The microvillous apical membrane of the STB contacts may occur (Barker and Thornburg, 2013; Burton et al., 2016; maternal blood, while the basal plasma membrane of the STB Arabin and Baschat, 2017). Moreover, the placenta contributes is directed toward the stromal core of the villi. Apical and basal to maternal diseases such as preeclampsia, which predispose the plasma membranes of the STB are often regarded as the most mother to lifelong illness (Bokslag et al., 2016). important membrane barriers in the materno-fetal transport Essential placental functions are biosynthesis, metabolism, processes. Nutrients, hormones, or fetal waste products traverse and transport of cholesterol, sex hormones and glucocorticoids. the STB by different transport mechanisms (Desforges and Sibley, This article summarizes placental handling of these steroids 2010; Brett et al., 2014). Mononuclear CTB are located below under physiologic conditions and gives an overview on changes the STB. They proliferate and fuse into the STB, thus supporting observed due to maternal diseases and exogenous influences. growth and regeneration of this layer. Early in pregnancy, Whenever possible, data obtained in human placenta or human CTBs form a continuous layer beneath the STB (Figure 1B). in vitro systems are referenced. We also draw attention to open With progressing pregnancy, CTBs transform from a cuboidal research questions. into a flat phenotype. The CTB layer becomes incomplete, but maintains a functional network due to multiple interconnecting cell processes (Jones et al., 2008; Figure 1C). THE HUMAN PLACENTAL BARRIER AND The stromal core of the chorionic villi contains fetal blood PLACENTAL MODEL SYSTEMS vessels delineated by pFECs (Burton et al., 2009), macrophages (Reyes et al., 2017) and additional stromal cells (Sati et al., 2007), The hemochorial human placenta results from a deep invasion which are all embedded in a non-cellular matrix. pFECs are non- of embryonic cells during implantation. The mature human fenestrated endothelial cells. Early placental pFECs are probably placenta is a disk delimited by chorionic and basal plate more permeable than term pFECs. Recent years of research have (Figure 1A), which enclose the intervillous space filled with demonstrated the importance of pFEC function for the fetal maternal blood. The basal plate contacts the uterine wall. From development (Wadsack et al., 2012). Heterogeneity of pFECs the chorionic plate, both umbilical cord and the branched in the macro-circulation (umbilical cord) and microcirculation chorionic villi originate. The cells of the chorionic villi form the (chorionic villi) was shown in situ (Lang et al., 1993) and in vitro (Lang et al., 2003). Moreover, venous and arterial pFECs, Abbreviations: 7-DHC, 7-dehydrocholesterol; ABC, ATP-binding cassette; which differ in their phenotypic, genotypic, and functional ACAT, Acyl-coenzyme A:cholesterol acyltransferase; ACTH, adrenocorticotropic hormone; A-dione, androstenedione; Apo, Apolipoprotein; ART, assisted characteristics, have been described (Lang et al., 2008). The term reproductive technologies; BCRP, breast cancer resistance protein; CEH, placenta has a high degree of vascularity (Zhang et al., 2002). cholesteryl ester hydrolase; CRH, corticotropin-releasing hormone; CTB, The capillaries closely approximate the villous covering, thereby cytotrophoblasts; CYP, cytochrome P450; DHCR7, 7-dehydrocholesterol forming “vasculosyncytial membranes” that are important for reductase; DHEA, dehydroepiandrosterone; DHEA-S, dehydroepiandrosterone sulfate; E1, estrone; E2, estradiol; E3, estriol; ER, endoplasmic reticulum; materno-fetal exchange processes (Burton et al., 2009). Thus, GDM, gestational diabetes mellitus; GR, glucocorticoid receptor; hCG, the term maternal–fetal interface or placental barrier consists human chorionic gonadotropin; HDL, high-density lipoprotein; HMG-CoA, of a thin cytoplasmic layer of STB apposed to a capillary 3-hydroxy-3-methylglutaryl-coenzyme A; HMGR, HMG-CoA reductase; HPA axis, hypothalamic–pituitary–adrenal axis; HPEC, (isolated) human placental (Figure 1C). Between the STB and pFEC the extracellular epithelial cells; HSD, hydroxysteroid dehydrogenase; HSP, heat shock protein; matrix is reduced to their fused basal laminae. STB and pFEC HUVEC, human umbilical vein endothelial cells; INSIG, insulin induced actively regulate uptake, metabolism, and transfer/exchange of gene; IUGR, intrauterine growth retardation; LDL,