Breast cancer resistance protein (BCRP)-mediated glyburide transport: effect of the C421A/Q141K BCRP single-nucleotide polymorphism.

The antidiabetic agent glyburide (glibenclamide) is frequently used for the treatment of type II diabetes and is increasingly being used for the treatment of gestational diabetes. Evidence suggests that breast cancer resistance protein/ATP-binding cassette, subfamily G, member 2 (ABCG2) expressed in the placenta protects the fetus against the accumulation of glyburide. A number of studies have investigated the significance of several single-nucleotide polymorphisms (SNPs) in the ABCG2 gene. Associations between the Q141K (C421A) SNP and ABCG2 protein expression, membrane surface translocation, efflux activity, or ATPase activity have been shown. Therefore, alterations in glyburide transport across the placenta, resulting in increased fetal glyburide exposure, may be seen in individuals carrying the C421A allele. The purpose of this study is to investigate whether the Q141K SNP causes alterations in ABCG2-mediated glyburide transport. Glyburide accumulation assays were carried out with stably transfected human embryonic kidney (HEK)-293 cells expressing wild-type ABCG2 (Arg482) and polymorphic ABCG2 (Q141K). Glyburide kinetic parameters were determined for comparison of wild-type and SNP ABCG2 activity by simultaneously fitting data for ABCG2-expressing cells (saturable transport) and empty vector-expressing cells (nonsaturable transport) by nonlinear regression analysis. The apparent K(t) and V(max) values for the transfected HEK-293 cells expressing the polymorphic variant (Q141K) of ABCG2 were significantly higher than those values determined for the wild-type ABCG2-expressing cells (p < 0.05). Our results indicate that the Q141K variant of ABCG2 may have the potential to alter the placental pharmacokinetics of glyburide used in pregnancy.

Genetic polymorphisms in placental transporters: implications for fetal drug exposure to oral antidiabetic agents.

INTRODUCTION: The prevalence of diabetes among women of childbearing age is increasing. This will inevitably increase the number of pregnancies complicated by diabetes. The management of diabetes mellitus often necessitates the use of oral antidiabetic drugs including biguanides, sulfonylureas, metiglinide analogs and thiazolidinediones. However, a significant concern with the use of these agents in pregnancy is the potential for developmental toxicity. Various antidiabetic drugs have been identified as substrates for transporters present in the syncytiotrophoblast. Therefore, the extent of transfer and fetal exposure to oral antidiabetic drugs used in pregnancy may be altered by polymorphisms in genes encoding these transport proteins. AREAS COVERED: This review covers current research examining genetic polymorphisms in transporters expressed in the syncytiotrophoblast and evidence supporting the involvement of these transporters in the transport of oral antidiabetic agents. The aim is to provide insight into how the transfer of antidiabetic drugs across the placental trophoblast may be altered by polymorphisms in drug transporters. EXPERT OPINION: There is a paucity of studies examining the influence of polymorphisms on transporter activity in the placenta and how the transfer of oral antidiabetics may be altered. Further research employing in vivo models is required to allow for the prediction of the potential consequences of polymorphisms on placental transporter expression and function.

Oral hypoglycemic therapy: understanding the mechanisms of transplacental transfer.

The current trend towards an increase in the rate of Type 2 diabetes in women of childbearing age will inevitably result in an increasing number of women requiring hypoglycemic therapy throughout pregnancy. For patients with Type 2 diabetes or gestational diabetes, oral hypoglycemic agents (OHAs) represent an attractive alternative to insulin therapy. However, there exists some apprehension regarding the use of OHAs during pregnancy. Although the current accepted understanding is that most drugs administered during pregnancy can permeate the placental barrier, there is sufficient evidence to suggest that the placenta is capable of limiting fetal exposure to drugs. In particular, large sets of data on the transplacental transfer and clinical use of glyburide in pregnancy have suggested that glyburide may be a safe alternative to insulin therapy. Glyburide's limited fetal transfer has been attributed to its high protein binding, rapid clearance rate and the role of placental efflux transporters such as the breast cancer resistance protein. However, there are a number of maternal, placental and fetal factors that may alter the transplacental passage of drugs used in pregnancy. Therefore, it is essential that OHAs are further investigated to determine their safety with confidence and provide better treatment options for diabetes in pregnancy.

Insulin glargine safety in pregnancy: a transplacental transfer study.

OBJECTIVE: Insulin glargine (Lantus) is an extended-action insulin analog with greater stability and duration of action than regular human insulin. The long duration of action and decreased incidence of hypoglycemia provide potential advantages for its use in pregnancy. However, the placental pharmacokinetics of insulin glargine have not been studied. Therefore, the objective of this study was to determine whether insulin glargine crosses the human placenta using the human perfused placental lobule technique. RESEARCH DESIGN AND METHODS: Placentae were obtained with informed consent after elective cesarean section delivery of noncomplicated term pregnancies. Insulin glargine, at a therapeutic concentration of 150 pmol/l (20 microU/ml) was added to the maternal circulation. Additional experiments were carried out at insulin glargine concentrations 1,000-fold higher than therapeutic levels (150, 225, and 300 nmol/l). A subsequent perfusion for which the maternal circuit remained open and insulin glargine was continuously infused at 150 pmol/l was completed for further confirmation of findings. The appearance of insulin glargine in the fetal circulation was analyzed by a chemiluminescence immunoassay. RESULTS: Results from perfusions carried out at therapeutic concentrations (150 pmol/l) of insulin glargine showed no detectable insulin glargine in the fetal circuit. After perfusion with very high insulin glargine concentrations of 150, 225, and 300 nmol/l, the rate of transfer remained low at 0.079 +/- 0.01, 0.14, and 0.064 pmol . min(-1) . g tissue(-1), respectively. CONCLUSIONS: Insulin glargine, when used at therapeutic concentrations, is not likely to cross the placenta.