The passage of granulocyte-macrophage colony-stimulating factor across the human placenta perfused in vitro

OBJECTIVE

The purpose of this study was to investigate the placental passage of granulocyte-macrophage colony-stimulating factor in a placental perfusion model ex vivo.

METHODS

In an open system, 11 placentas were perfused on both the maternal and the fetal side immediately after delivery. Granulocyte-macrophage colony-stimulating factor was added to the maternal perfusion medium in concentrations from 10-55 micrograms/mL. Maternal and fetal samples were taken, and granulocyte-macrophage colony-stimulating factor (GM-CSF) was measured by enzyme-linked immunosorbent assay.

RESULTS

Accumulation of granulocyte-macrophage colony-stimulating factor in the fetal circuit averaged 2.42% of the concentration added initially to the arterial portion of the maternal circuit.

CONCLUSION

There is only low transfer of GM-CSF across the fetal membranes. This finding is particularly remarkable in view of recently published results suggesting that administration of recombinant granulocyte growth factors to pregnant women with imminent preterm delivery helps prevent neonatal sepsis.

Transfer of erythropoietin across the placenta perfused in vitro

OBJECTIVE

The purpose of this study was to investigate the placental passage of erythropoietin in a placental perfusion model ex vivo.

METHODS

In an open system 18 placentas were perfused on both the maternal and the fetal side. Erythropoietin and a reference substance were added to either the maternal or fetal perfusion medium. In the first series of experiments, radiolabeled erythropoietin was added to the perfusion medium in four different concentrations to help determine the transfer rate of erythropoietin. Based on the results of these experiments unlabeled erythropoietin was added to the perfusate in three different concentrations. Radiolabeled erythropoietin was used in addition to erythropoietin because measuring radioactivity in a gamma counter is less expensive than measuring by immunoassay.

RESULTS

Accumulation of radioactivity in the venous portion of the fetal circuit was only 3.21% of the activity added to the maternal circuit. No evidence of transfer of erythropoietin to the contralateral compartment was noted, regardless of whether the test substance was added maternally or fetally. These results were independent of the concentration used. The reference compound antipyrine showed a mean transfer rate of 27.9%, which is in keeping with previous results.

CONCLUSION

There is no transport of erythropoietin across fetal membranes. This finding is particularly remarkable in view of results published recently indicating the placenta as a site of erythropoietin production. The lack of its transport across the human placenta is most likely due to its high molecular weight.

Placental passage of angiotensin-converting enzyme inhibitors

OBJECTIVE

Placental passage of the angiotensin-converting enzyme inhibitors temocapril and enalapril was investigated in a placental perfusion model.

STUDY DESIGN

In an open system a placental lobe was perfused on both the maternal and the fetal side with a blood-free medium containing the test substances plus a reference substance on the maternal side. Six placentas were perfused with temocapril and five with enalapril. The drugs were measured by gas chromatography-mass spectrometry.

RESULTS

Both angiotensin-converting enzyme inhibitors crossed the human placenta in the maternal-fetal direction in similar quantities. Temocapril showed the same pharmacokinetic characteristics as enalapril.

CONCLUSIONS

This was the first study to quantify the placental transfer of angiotensin-converting enzyme inhibitors. These antihypertensive agents should not be taken during pregnancy, to avoid any potential hazards to the fetus.

The transfer of interleukin-8 across the human placenta perfused in vitro

OBJECTIVE

To assess the placental transfer of interleukin (IL)-8 in vitro.

METHODS

Eighteen placentas obtained immediately after delivery were perfused with a mixture of 125I-labeled IL-8 (IL-8*) and unlabeled IL-8 in two different concentrations. Antipyrine was coinfused in all experiments as a reference compound. Fetal-to-maternal and maternal-to-fetal perfusions were performed. Radioactivity was measured in a gamma counter at the end of each perfusion experiment. In four experiments, unlabeled IL-8 was analyzed in addition to labeled IL-8 to exclude a change in the IL-8/IL-8* ratio resulting from membrane transfer.

RESULTS

Two of the 18 experiments had to be discarded because of poor transfer of antipyrine. There was only faint accumulation of radioactivity in the transplacental compartment, regardless of whether the test substance was added maternally or fetally. Because measurement of unlabeled IL-8 yielded negative results, the radioactivity is clearly attributable to free iodine 125, which is generated during IL radiolabeling or which disassociates from IL-8 in small amounts after radiolabeling.

CONCLUSION

Interleukin-8 does not appear to cross the placenta by simple diffusion, regardless of the concentration or the perfusion rate. The impermeability of the placenta to the diffusion of IL-8 might explain why there is insufficient correlation between serum and amniotic fluid cytokine concentrations of pregnant women and the presence of the amnion infection syndrome.