Transfer of methadone across the dually perfused preterm human placental lobule.

OBJECTIVE: The objective of the study was to determine the effect of gestational age and P-glycoprotein expression on transplacental transfer of methadone. STUDY DESIGN: Dual perfusion of placental lobule was utilized. Methadone (200 ng/mL) and its [3H]-isotope were cotransfused from the maternal-to-fetal circuit with the marker compound antipyrine (20 microg/mL) and its [14C]-isotope. Concentration of the drugs in trophoblast tissue and both circuits was determined by liquid scintillation spectrometry. RESULTS: Fetal transfer rate of methadone in preterm placentas was 19 +/- 5.8%, and in term placentas it was 31 +/- 9.7% (P < .01). Clearance index of methadone in preterm placentas (0.57 +/- 0.2) was lower than in term placentas (0.95 +/- 0.3, P < .01). P-glycoprotein expression was higher in preterm than term placentas. CONCLUSION: The ex vivo transfer of methadone across preterm placentas is 30% lower than in term placentas.

Role of human placental efflux transporter P-glycoprotein in the transfer of buprenorphine, levo-alpha-acetylmethadol, and paclitaxel.

This study examines the role of placental P-glycoprotein (P-gp) in the transfer of buprenorphine (BUP) and L-alpha-acetylmethadol (LAAM) across the dually perfused human placental lobule. BUP (10 ng/mL) and LAAM (35 ng/mL) were perfused in the maternal-to-fetal direction. The following kinetic parameters were determined: fetal transfer rate (TR (f)), maternal clearance (Cl (m)), and clearance index (Cl (index)). The opiates were perfused in the presence of P-gp inhibitor GF120918 (experimental group) and in its absence (control group). The kinetic parameters for the control group were set at 100% and were as follows for LAAM in the experimental group: TR (f), 123 +/- 20%, Cl (m) 116 +/- 23%, and Cl (index) 123 +/- 22% ( P < 0.05). The corresponding parameters for BUP were not different from controls. The data indicate that LAAM, but not BUP, is extruded by the efflux transporter P-gp. Therefore, it is reasonable to assume that the activity of P-gp could be one of the factors affecting the extent of fetal exposure to LAAM during pregnancy.

Transfer of metformin across the dually perfused human placental lobule.

OBJECTIVE: The purpose of this study was to determine the transfer characteristics of metformin across placentas that were obtained from uncomplicated pregnancies and from patients with gestational diabetes mellitus. STUDY DESIGN: The technique of dual perfusion of placental lobule was used. Metformin, 5 microg/mL and its [14C]-isotope were co-transfused with the marker compound antipyrine, 20 microg/mL and its [3H]-isotope from the maternal to fetal circuit. The drug content in both circulations and placental tissue was determined by liquid scintillation spectrometry. RESULTS: The transfer of metformin across term human placentas that were obtained from uncomplicated pregnancies was rapid and was not different from that in placentas that were obtained from patients with gestational diabetes mellitus. Metformin is distributed between the maternal and fetal circuits, with reliable amounts retained by the tissue. CONCLUSION: In an ex vivo model system, metformin was transferred readily from the maternal to fetal circuit across placentas that were obtained from uncomplicated pregnancies and pregnancies with gestational diabetes mellitus.

Effects of nicotine-specific antibodies, Nic311 and Nic-IgG, on the transfer of nicotine across the human placenta.

The adverse effects of smoking during pregnancy on fetal development are, in part, due to nicotine. These effects may be due to the actions of nicotine in fetal circulation or on placental functions. In pregnant rats, vaccination with a nicotine immunogen reduces the transfer of nicotine from the maternal to fetal circulation. However, extrapolation of these results to pregnant women might not be valid due to the well-recognized differences between human and rat placentas. In the current investigation, the effects of nicotine-specific antibodies on the transfer of nicotine from the maternal to fetal circuit of the dually perfused human placental lobule were determined. Two types of nicotine-specific antibodies were investigated; nicotine-specific mouse monoclonal antibody (Nic311, K(d) for nicotine 60nM) and IgG from rabbits vaccinated with a nicotine immunogen (Nic-IgG, K(d) 1.6nM). Transfer of the antibodies from maternal to fetal circuits was negligible. Both rabbit Nic-IgG and, to a lesser extent, mouse monoclonal Nic311 significantly reduced nicotine transfer from the maternal to fetal circuit as well as the retention of the drug by placental tissue. These effects were mediated by a substantial increase in the protein binding of nicotine and a reduction in the unbound nicotine concentration. Therefore, the data cited in this report suggest that the use of nicotine-specific antibodies might reduce fetal exposure to the drug, and that antibody affinity for nicotine is a key determinant of the extent of nicotine transfer.

Bidirectional transfer of methadone across human placenta.

Methadone maintenance programs are considered the standard of care for the pregnant opiate addict. However, data on changes in methadone pharmacokinetics (PK) during pregnancy are limited and do not include its disposition by the placenta due to obvious ethical and safety considerations. Accordingly, investigations in our laboratory are focusing on human placental disposition of opiates including methadone. Recently, we reported on methadone metabolism by placental aromatase and provide here data on its bidirectional transfer across the tissue utilizing the technique of dual perfusion of placental lobule. The concentrations of the opiate transfused into the term placental tissue were those reported for its in vivo levels in the maternal serum of women under treatment with the drug. Data obtained indicated that the opiate has no adverse effects on placental viability and functional parameters and that it is retained by the tissue. Also, methadone transfer and its clearance index in the fetal to maternal direction (0.97+/-0.05) was significantly higher (P<0.05) than in the maternal to fetal (0.83+/-0.09). The observed asymmetry in methadone transfer could be explained by the unidirectional activity of the efflux transporter P glycoprotein (P-gp) that is highly expressed in variable amounts in trophoblast tissue. Therefore, placental disposition of methadone might be an important contributor to the regulation of its concentration in the fetal circulation and consequently may affect the incidence and intensity of neonatal abstinence syndrome for women treated with the drug during pregnancy.

Methadone metabolism by human placenta.

Methadone pharmacotherapy is considered the standard for treatment of the pregnant heroin/opioid addict. One of the factors affecting the transfer kinetics of opioids across human placenta and their levels in the fetal circulation is their metabolism by the tissue. The aim of this investigation is to identify the enzyme(s) responsible for the metabolism of methadone, determine the kinetics of the reaction and the metabolites formed utilizing placental tissue obtained from term healthy pregnancies. Microsomal fractions of trophoblast tissue homogenates had the highest activity in catalyzing the metabolism of methadone. The product formed was identified by HPLC-UV as 2-ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Inhibitors selective for cytochrome P450 (CYP) isozymes were used to identify the enzyme catalyzing the biotransformation of methadone. Aminoglutethimide and 4-hydroxyandrostenedione inhibited EDDP formation by 88 and 70%, respectively, suggesting that CYP19/aromatase is the enzyme catalyzing the reaction. This was confirmed by the effect of monoclonal antibodies raised against CYP19 that caused an 80% inhibition of the reaction. The apparent K(m) and V(max) values for the CYP19 catalyzed metabolism of methadone to EDDP were 424 +/- 92 microM and 420 +/- 89 pmol(mgprotein)(-1)min(-1), respectively. Kinetic analysis of a cDNA-expressed CYP19 for the metabolism of methadone to EDDP was identical to that by placental microsomes. Taken together, these data indicate that CYP19/aromatase is the major enzyme responsible for the metabolism of methadone to EDDP in term human placentas obtained from healthy pregnancies.