Sarah Hemauer

Role of human placental apical membrane transporters in the efflux of glyburide, rosiglitazone, and metformin

OBJECTIVE Substrates of placental efflux transporters could compete for a single transporter, which could result in an increase in the transfer of each substrate to the fetal circulation. Our aim was to determine the role of placental transporters in the biodisposition of oral hypoglycemic drugs that could be used as monotherapy or in combination therapy for gestational diabetes. STUDY DESIGN Inside-out brush border membrane vesicles from term placentas were used to determine the efflux of glyburide, rosiglitazone, and metformin by P-glycoprotein, breast cancer resistance protein, and multidrug resistance protein. RESULTS Glyburide was transported by multidrug resistance protein (43 +/- 4%); breast cancer resistance protein (25 +/- 5%); and P-glycoprotein (9 +/- 5%). Rosiglitazone was transported predominantly by P-glycoprotein (71 +/- 26%). Metformin was transported by P-glycoprotein (58 +/- 20%) and breast cancer resistance protein (25 +/- 14%). CONCLUSION Multiple placental transporters contribute to efflux of glyburide, rosiglitazone, and metformin. Administration of drug combinations could lead to their competition for efflux transporters.

Modulation of human placental P-glycoprotein expression and activity by MDR1 gene polymorphisms

The ABC transporter P-glycoprotein is a product of the MDR1 gene and its function in human placenta is to extrude xenobiotics from the tissue thus decreasing fetal exposure. The goal of this investigation was to examine the effect of three polymorphisms in the MDR1 gene on the expression and activity of placental P-gp. In 199 term placentas examined, the C1236T variant was associated with 11% lower P-gp protein expression than wild-type, while the C3435T and G2677T/A variants each were associated with a 16% reduction (p<0.05). Homozygotes for the C1236T and C3435T variant allele (TT) were associated with 42% and 47% increase in placental P-gp transport activity, respectively (p=0.04 and p=0.02) of the prototypic substrate, [(3)H]-paclitaxel. These findings indicate that the C3435T and G2677T/A SNPs in MDR1 are significantly associated with decreased placental P-gp protein expression, while the C1236T and C3245T homozygous variants are significantly associated with an increase in its efflux activity.

Opiates inhibit paclitaxel uptake by P-glycoprotein in preparations of human placental inside-out vesicles

The use of either methadone or buprenorphine for treatment of the pregnant opiate-dependent patient improves maternal and neonatal outcome. However, patient outcomes are often complicated by neonatal abstinence syndrome (NAS). The incidence and severity of NAS should depend on opiate concentration in the fetal circulation. Efflux transporters expressed in human placental brush border membranes decrease fetal exposure to medications by their extrusion to the maternal circulation. Accordingly, the concentration of either methadone or buprenorphine in the fetal circulation is, in part, dependent on the activity of the efflux transporters. The objective of this study was to characterize the activity of P-gp and its interaction with opiates in the placental apical membrane. Therefore, brush border membrane vesicles were prepared from human placenta. The vesicles were oriented approximately 75% inside-out, exhibited saturable ATP-dependent uptake of P-gp substrate [(3)H]-paclitaxel with an apparent K(t) of 66+/-38 nM and V(max) of 20+/-3 pmol mg protein (-1)min(-1). Methadone, buprenorphine, and morphine inhibited paclitaxel transport with apparent K(i) of 18, 44, and 90 microM, respectively. Our data indicate that a method has been established to determine the activity of the efflux transporter P-gp, expressed in placental brush border membranes, and the kinetics for the transfer of its prototypic substrate paclitaxel. Furthermore, the method was used to determine the effects of methadone, buprenorphine, and morphine on paclitaxel transfer by placental P-gp and revealed that they have higher affinity to the transporter than its classical inhibitor verapamil (K(i), 300 microM).

Transplacental transfer and metabolism of 17-α-hydroxyprogesterone caproate

OBJECTIVE Determine transplacental transfer and metabolism of 17-alpha-hydroxyprogesterone caproate and its distribution between the tissue and the maternal and fetal circuits of the dually perfused placental lobule. STUDY DESIGN 17-alpha-Hydroxyprogesterone caproate (21 ng/mL) and its dual-labeled isotope, 17-alpha-hydroxy-[(3)H] progesterone [(14)C] caproate were added to the maternal circuit. The concentrations of the drug and its metabolite in trophoblast tissue and both circuits were determined by high performance liquid chromatography and liquid scintillation spectrometry. RESULTS 17-alpha-Hydroxyprogesterone caproate was transferred from the maternal to fetal circuit. After a 4-hour perfusion period, a metabolite of 17-alpha-hydroxyprogesterone caproate that retained both progesterone and caproate moieties was identified in the tissue and the maternal and fetal circuits. Neither 17-alpha-hydroxyprogesterone caproate nor its metabolite, at the concentrations tested, had adverse effect on determined viability and functional parameters of placental tissue. CONCLUSION 17-alpha-Hydroxyprogesterone caproate was metabolized by term placental lobule during its perfusion and both parent compound and its metabolite(s) transferred to the fetal circuit.

Effect of albumin on transplacental transfer and distribution of rosiglitazone and glyburide

Objective. The aims of this investigation were (i) to determine the rate and extent of rosiglitazone transfer across term human placenta, and (ii) to determine the effect of human serum albumin (HSA) on rosiglitazone and glyburide transfer and distribution. Methods. These aims were achieved by utilizing the technique of dual perfusion of placental lobule (DPPL). Each hypoglycemic drug was coperfused with the marker compound antipyrine (AP). In each experiment, the [3H]-isotope of the hypoglycemic drug and the [14C]-isotope of AP were added to enhance the detection limits of each drug. Human serum albumin (HSA) was added to both the maternal and fetal circuits in the experiments in which it was investigated. Results. Transplacental transfer of rosiglitazone and glyburide from the maternal to fetal circuits in media devoid of HSA was similar. However, the addition of HSA to the maternal and fetal circuits had different effects on the transfer and distribution of the two drugs, though their binding to HSA (99.8%) was almost identical. HSA increased the maternal (M) to fetal (F) transfer of rosiglitazone, as revealed by an increase in its F/M concentration ratio from 0.17 ± 0.01 (in the absence of albumin) to 0.33 ± 0.07 (p < 0.001). Moreover, the addition of albumin decreased the amount of rosiglitazone retained by placental tissue from 539 ± 148 to 60 ± 8 ng/g (p < 0.001). Conversely, the addition of HSA to the perfusion media resulted in a decrease in glyburide transfer, as revealed by the change of its F/M concentration ratio from 0.09 ± 0.02 (in the absence of albumin) to 0.03 ± 0.01 (p < 0.01). However, similar to rosiglitazone, glyburide retention by the tissue decreased from 103 ± 26 to 19 ± 6 ng/g (p < 0.001). Conclusions. These data indicate that the binding of the two drugs to albumin, though similar, is only one of the factors that could affect their placental transfer and distribution.

Role of transporter-mediated efflux in the placental biodisposition of bupropion and its metabolite, OH-bupropion.

Cigarette smoking during pregnancy is a preventable risk factor associated with maternal and fetal complications. Bupropion is an antidepressant used successfully for smoking cessation in non-pregnant patients. Our goal is to determine whether it could benefit the pregnant patient seeking smoking cessation. The aim of this investigation was to determine the role of human placenta in the disposition of bupropion and its major hepatic metabolite, OH-bupropion. The expression of efflux transporters P-gp and BCRP was determined in placental brush border membrane (n=200) and revealed a positive correlation (p<0.05). Bupropion was transported by BCRP (K(t) 3 microM, V(max) 30 pmol/mg protein/min) and P-gp (K(t) 0.5 microM, V(max) 6 pmol/mg protein min) in placental inside-out vesicles (IOVs). OH-bupropion crossed the dually-perfused human placental lobule without undergoing further metabolism, nor was it an efflux substrate of P-gp or BCRP. In conclusion, our data indicate that human placenta actively regulates the disposition of bupropion (via metabolism, active transport), but not its major hepatic metabolite, OH-bupropion.