A review of xenobiotic membrane transporter expression within the human placenta: Lessons gained from primary tissue and in vitro methodologies

The human placenta acts as a critical barrier within the body, protecting the fetus from the potentially harmful effects of xenobiotics encountered by the mother during pregnancy. Membrane transporter proteins play a central role in this protective function, yet their expression patterns and how this changes across gestation remains poorly understood. A range of in vitro models have been generated to try and understand human placental transport processes; however, uncertainties persist regarding the developmental stage and cellular composition that each model represents. This review summarises the current understanding of membrane transporter expression in the most widely used in vitro systems, including primary placental tissue, choriocarcinoma cell lines and trophoblast stem cells. It also highlights recent advances in culturing techniques. Key gaps in the knowledge are identified, and opportunities for refining experimental approaches to study xenobiotic uptake and transport across the placenta in vitro are discussed.