Transfer and Metabolism of Cortisol by the Isolated Perfused Human Placenta

Abstract

Context: Fetal overexposure to glucocorticoids in utero is associated with fetal growth restriction and is postulated to be a key mechanism linking suboptimal fetal growth with cardiovascular disease in later life.

Objective: To develop a model to predict maternal-fetal glucocorticoid transfer. We hypothesized placental 11-β-hydroxysteroid dehydrogenase-type 2 (11β-HSD2) would be the major rate-limiting step in maternal cortisol transfer to the fetus.

Design: We used a deuterated cortisol tracer in the ex vivo placental perfusion model, in combination with computational modeling, to investigate the role of interconversion of cortisol and its inactive metabolite cortisone on transfer of cortisol from mother to fetus.

Participants: Term placentas were collected from five women with uncomplicated pregnancies, at elective caesarean delivery.

Intervention: Maternal artery of the isolated perfused placenta was perfused with D4-cortisol.

Main outcome measures: D4-cortisol, D3-cortisone, and D3-cortisol were measured in maternal and fetal venous outflows.

Results: D4-cortisol, D3-cortisone, and D3-cortisol were detected and increased in maternal and fetal veins as the concentration of D4-cortisol perfusion increased. D3-cortisone synthesis was inhibited when 11-β-hydroxysteroid dehydrogenase (11β-HSD) activity was inhibited. At the highest inlet concentration, only 3.0% of the maternal cortisol was transferred to the fetal circulation, whereas 26.5% was metabolized and 70.5% exited via the maternal vein. Inhibiting 11β-HSD activity increased the transfer to the fetus to 7.3% of the maternal input, whereas 92.7% exited via the maternal vein.

Conclusions: Our findings challenge the concept that maternal cortisol diffuses freely across the placenta and confirm that 11β-HSD2 acts as a major "barrier" to cortisol transfer to the fetus.

Figure 1.

Model schematic and metabolism of deuterium-labeled glucocorticoids. (a) Model schematic showing the three compartments (maternal, syncytiotrophoblast, and fetal) distinguished in the model. It is assumed that transfer between compartments is by simple diffusion, whereas metabolic conversion between cortisol and cortisone takes place in the syncytiotrophoblast (equations 1 to 6, see “Methods” section). The input concentration of D4-cortisol in the maternal compartment varies over time according to the experimental protocol, whereas the input concentration in the fetal compartment is zero at all times. The output concentrations of the maternal and fetal compartments from the model can be compared with the experimental data. D4-Cortisol is inactivated by 11β-HSD2 to D3-cortisone, with the loss of the deuterium on C11. (b) 11β-HSD1 regenerates D3-cortisol from D3-cortisone, with the addition of an unlabeled hydrogen.

Figure 2.

Model fit of experimental data. The maternal circulation was perfused from 0 to 30 minutes with EBB alone, maternal circulation was 0 to 30 minutes EBB alone, 30 to 60 minutes EBB + 20 nM D4-cortisol, 60 to 90 minutes EBB + 200 nM D4-cortisol, 90 to 120 minutes EBB + 80 0nM D4-cortisol, 120 to 150 minutes EBB + 800 nM D4-cortisol + 0.001 M carbenoxolone, and 150 to 170 minutes EBB alone. The appearance of D4-cortisol in the fetal circulation is consistent with free transplacental passage of D4-cortisol. Inactivation of D4-cortisol by 11β-HSD2 is indicated by the appearance of D3-cortisone in the maternal or fetal circulations, and cortisol regeneration from D3-cortisone is indicated by the appearance of D3-cortisol. Model fit of the experimental data for D4-cortisol in the (a) maternal and (b) fetal compartments, with a single set of parameters. Results show an excellent correspondence between model (straight line) and experiments (plotted data and error bars) (R² = 0.99). (c, d) Model prediction of D3-cortisone in comparison with the scaled experimental data. Note the experimental units for D3-cortisone could not be directly related to concentration and have been scaled here to allow comparison of the relative changes predicted by the model. The same conversion factor was applied to both maternal and fetal D3-cortisone based on the average ratio between experimental units and computed concentrations at the highest input level (time points t = 110, 115, and 120 minutes). (e, f) Experimental data for D3-cortisol. Values were comparatively low and were not modeled as they do not contribute significantly to the overall mass balance. All experimental results are the average of five placentas, expressed as mean and standard error of the mean (n = 5). Abbreviations: CBX, carbenoxolone; D4F, D4-cortisol.

Figure 3.

Sensitivity analysis for D4-cortisol transfer to the fetus as a function of variations in the model parameters. The model parameters were varied with respect to the values for the reference fit. The reported changes in placental transfer predicted by the model were based on the steady-state results at the highest maternal input concentration. Abbreviations: k_BM, BM permeability constant; K_m, Michaelis-Menton constant; k_MVM, MVM permeability constant; Q_f, fetal flow rate, L/min; Q_m, maternal flow rate, L/min; V_f, fetal compartment volume; V_m, maternal compartment volume; V^max, maximum rate of reaction; V_s, syncytiotrophoblast compartment volume.