Transport of Docosahexaenoic Acid via the Human Placenta: A Theoretical Study

The high demand of the fetus for Docosahexaenoic acid, DHA, is satisfied by a concert of several mechanisms that take place in the placental terminal villi. Scarcity of laboratory data makes the detailed description of these mechanisms elusive. Here, the DHA transport across the placenta is modeled as a boundary value problem that accounts for diffusion, reactions with fatty acids binding proteins, FABPs, and metabolic consumption within the Syncytiotrophoblast, ST. For any given DHA fluxes at the bordering membranes, analytical and numerical solutions yield the DHA concentration profile within the ST. We find that in order to comply with adequate DHA delivery to the fetus and with physiological DHA concentrations in the maternal and fetal circulations, it is essential to have a significant rise of DHA concentration at the microvillus membrane, MVM and a rapid dissociation of the DHA from the FABP. The model establishes the relations between the concentrations of the FABPs in the ST, their equilibrium dissociation constant from the DHA, and the placental DHA metabolic degradation rate, hitherto unknown. We conclude that the bound (to the protein) DHA molecule is degraded at a rate of 0.3-0.45 s^-1.