Effect of human serum albumin on transplacental transfer of glyburide

Dispersive micro solid phase extraction of glibenclamide from plasma, urine, and wastewater using a magnetic molecularly imprinted polymer followed by its determination by a high-performance liquid chromatography-photodiode array detector

The present study describes the development of a simple and selective analytical method for dispersive micro solid phase extraction and determination of glibenclamide (GLB) using magnetic molecularly imprinted polymer (MMIP) as a sorbent. MMIP was fabricated by the non-covalent method on the surface of silicated Fe3O4 and had a high affinity for glibenclamide; dual monomers, itaconic acid and allylamine, were used for this. Polymerization was achieved by the precipitation method in the presence of glibenclamide as the template and ethylene glycol dimethacrylate as the cross-linker. The morphology and structural properties of the MMIP were characterized by different analytical methods. To achieve maximum extraction efficiency, influencing parameters were optimized. The linearity range was 1-2000 and 12-2000 μg L-1 by high-performance liquid chromatography-photodiode array detector (HPLC-PDA) and UV-vis spectroscopy, respectively. The detection and quantification limits with UV-vis and HPLC-PDA analyses were 4 and 12 μg L-1 and 0.3 and 1 μg L-1, respectively. Under optimized conditions, recovery of glibenclamide spiked in plasma, human urine, and wastewater was between 89.4 and 102.9% at the concentration levels of 25, 250, and 500 μg L-1; relative standard deviations were below 3.7% by HPLC-PDA. The developed method has a favorable pre-concentration factor of 140.0. Equilibrium data and sorption isotherms fitted well with the Langmuir model. A maximum sorption capacity of 24.260 mg g-1 was acquired based on the Langmuir model. The synthesized sorbent with high selectivity was used to separate GLB from complex biological systems and wastewater before measurement with UV-vis or HPLC-PDA.

Biophysical insight into the anti-fibrillation potential of Glyburide for its possible implication in therapeutic intervention of amyloid associated diseases

Protein aggregation is an underlying cause of many neurodegenerative diseases. Also, the overlapping pathological disturbances between neurodegenerative diseases and type-2 diabetes mellitus have urged the scientific community to explore potential of already available anti-diabetic medications in impeding amyloid formation too. Recent study brief out promising potential of an anti-diabetic drug Glyburide(GLY) as an inhibitor of amyloid fibrillation utilizing several biophysical techniques, computational methods and imaging tools. The mechanism of interaction was elucidated and the structural alterations in human serum albumin(HSA) as well as the microenvironment changes of its fluorophores(tryptophan, tyrosine) upon interacting with GLY were studied by spectroscopic techniques like Circular dichroism and synchronous fluorescence. Binding studies detailing about the GLY-HSA complex distance and the energy transfer efficiency was obtained by Fluorescence resonance energy transfer. For aggregation inhibition studies, the existence and size of aggregates formed in HSA and their inhibition by GLY was determined by Turbidity assay, Dynamic light scattering and Rayleigh light scattering along with dye binding assays. The ThT kinetics measurements analysis suggested that GLY deaccelerates fibrillation by decrement of apparent rate(K_app) constant. The inhibitory effect of GLY might be attributed to native structure stabilization of HSA by obstruction into β-sheet conversion as confirmed by CD spectroscopy results. Amyloid inhibition and suppression of amyloid-induced hemolysis by GLY was further delineated by TEM and SEM analysis respectively. All these findings for the first time report the new facet of the anti-amyloidogenic potential of GLY, making it a promising candidate to treat neurodegenerative diseases too in the near future.

Glibenclamide transfer across the perfused human placenta is determined by albumin binding not transporter activity

The placenta mediates the transfer of maternal nutrients into the fetal circulation while removing fetal waste products, drugs and environmental toxins that may otherwise be detrimental to fetal development. This study investigated the role of drug transporters and protein binding in the transfer of the antidiabetic drug glibenclamide across the human placental syncytiotrophoblast using placental perfusion experiments and computational modeling. In the absence of albumin, placental glibenclamide uptake from the fetal circulation was not affected by competitive inhibition with bromosulphothalein (BSP), indicating that OATP2B1 does not mediate placental glibenclamide uptake from the fetus. In the presence of maternal and fetal albumin, BSP increased placental glibenclamide uptake from the fetal circulation by displacing glibenclamide from BSA, increasing the free fraction of glibenclamide driving diffusive transport. The P-gp and BCRP inhibitor GF120918 did not affect placental glibenclamide uptake from the maternal circulation and as such this study did not find any evidence for the apical efflux transporters in placental glibenclamide transfer. Computational modeling confirmed that albumin binding and not transporter activity, is the dominant factor in the transfer of glibenclamide across the human placenta. The effect of BSP binding to albumin on promoting the diffusive transfer of glibenclamide highlights the importance of drug-protein binding interactions and their interpretation using computational modeling.

Placental perfusion and mathematical modelling

The isolated perfused placental cotyledon technique has led to numerous advances in placental biology. Combining placental perfusion with mathematical modelling provides an additional level of insight into placental function. Mathematical modelling of perfusion data provides a quantitative framework to test the understanding of the underlying biology and to explore how different processes work together within the placenta as part of an integrated system. The perfusion technique provides a high degree of control over the experimental conditions as well as regular measurements of functional parameters such as pressure, solute concentrations and pH over time. This level of control is ideal for modelling as it allows placental function to be studied across a wide range of different conditions which permits robust testing of mathematical models. By placing quantitative values on different processes (e.g. transport, metabolism, blood flow), their relative contribution to the system can be estimated and those most likely to become rate-limiting identified. Using a combined placental perfusion and modelling approach, placental metabolism was shown to be a more important determinant of amino acid and fatty acid transfer. In contrast, metabolism was a less important determinant of placental cortisol transfer than initially thought. Identifying the rate-limiting factors in the system allows future work to be focused on the factors that are most likely to underlie placental dysfunction. A combined experimental and modelling approach using placental perfusions promotes an integrated view of placental physiology that can more effectively identify the processes leading to placental pathologies.

Pregnant women, prescription, and fetal risk

Since the historical scandal of thalidomide in the 1960s, practitioners and future mothers are fearful of drugs during pregnancy. In-uterine exposure to drugs can induce major malformation of the fetus or even intrauterine fetal death. Prescribing drugs to a pregnant woman requires particular attention, and it is necessary to consider both the maternal needs and the proven and potential fetal risks. In this chapter, we review the mechanisms for medication transfer from mother to fetus, fetal risk according to pregnancy timeline, and the main dangerous drugs during pregnancy. We also focus on three prescription debates, which are relevant for neurodevelopmental disorder, because they each point to a paradigmatic situation-diethylstilbestrol, which shows transgenerational adversary effects; valproate, which impacts neurodevelopment as a whole; and antidepressants for which the adverse impact on neurodevelopment is still controversial given the impact of depression itself. Finally, we consider the implications for practice and toxicologic research to promote risk prevention.

Oral Agents for the Treatment of Gestational Diabetes

PURPOSE OF REVIEW

To review the current evidence of the safety and efficacy of the use of oral agents for treatment of gestational diabetes (GDM).

RECENT FINDINGS

The use of metformin and glyburide in pregnancy for treatment of GDM has dramatically increased since the early 2000s. Meta-analyses suggest that glyburide may increase the risk for large for gestational (LGA) infants and neonatal hypoglycemia. Conversely, metformin may potentially decrease rates of pregnancy-induced hypertension, LGA, neonatal hypoglycemia, and maternal weight gain. However, recent long-term offspring studies indicate a potential detrimental effect of metformin on fat mass that suggests an effect of such medication on fetal programming. While there have been several novel oral anti-diabetes medications brought to market in the past decade, there is minimal data to guide use and in particular data regarding long-term safety for the exposed offspring of treated women. Most professional societies recommend insulin as first-line treatment of gestational diabetes after failure of lifestyle modification. Both metformin and glyburide cross the placenta and long-term safety data is limited. However, patient satisfaction is substantially higher with use of oral agents, and the current literatures suggest that metformin may reduce several common short-term adverse outcomes related to GDM.

Could Metformin Manage Gestational Diabetes Mellitus instead of Insulin?

Gestational diabetes mellitus (GDM) complicates a significant number of pregnancies. Blood glucose control improves perinatal outcomes. Medical nutrition therapy is the foundation in management. Aim of This Study. To evaluate efficacy of metformin in comparison to insulin for managing GDM. Methods. In prospective randomized comparative study, 150 antenatal women whose pregnancies had been complicated by GDM and did not respond to diet alone were recruited from antenatal clinics at Obstetrics Department in Zagazig University Hospitals from November 2012 to December 2014. They were divided randomly into two groups, 75 patients in each, and were subjected to either insulin or metformin medication. Outcomes were comparing the effects of both medications on maternal glycemic control, antenatal complications, and neonatal outcome. Results. No significant difference in controlling high blood sugar in GDM with the use of metformin or insulin (P = 0.95, 0.15). Maternal complications in both groups had no significant difference and fetal outcomes were as well similar except the fact that the hypoglycemia occurred more in insulin group with P value 0.01. Conclusion. Glycaemic control in GDM can be achieved by using metformin orally without increasing risk of maternal hypoglycemia with satisfying neonatal outcome.

Pharmacokinetics, efficacy and safety of glyburide for treatment of gestational diabetes mellitus

INTRODUCTION

Gestational diabetes mellitus (GDM) complicates 10% of all pregnancies and is defined as hyperglycemia first noted during pregnancy. Rates of GDM are rising and untreated GDM results in complications for both mother and fetus. GDM is often managed by diet and exercise but 30-40% of women will require pharmacological intervention. Insulin has traditionally been the treatment of choice but since 2007, glyburide, a second generation sulfonylurea has become the most prescribed medication for GDM.

AREAS COVERED

This review will cover the pharmacokinetics, efficacy, and safety of glyburide for the management of GDM.

EXPERT OPINION

Management of GDM is challenging secondary to the stringent glycemic goals that mimic the lower glucose levels in pregnancy. Glyburide is generally effective in treating hyperglycemia. However, several studies have raised safety concerns showing higher neonatal intensive care unit (NICU) admissions, higher rates of macrosomia, large for gestational age and pre-eclampsia in the mother. For this reason, insulin should be first-line therapy for GDM. In areas of limited resources where the self-monitoring needed for accurate insulin dosing is not possible, where access to refrigeration for insulin storage is not universal, or severe needle phobia then the benefits of glyburide (controlling hyperglycemia) outweighs the harm of NICU admissions and macrosomia.

Maternal-fetal disposition of glyburide in pregnant mice is dependent on gestational age

Gestational diabetes mellitus is a major complication of human pregnancy. The oral clearance (CL) of glyburide, an oral antidiabetic drug, increases 2-fold in pregnant women during late gestation versus nonpregnant controls. In this study, we examined gestational age-dependent changes in maternal-fetal pharmacokinetics (PK) of glyburide and metabolites in a pregnant mouse model. Nonpregnant and pregnant FVB mice were given glyburide by retro-orbital injection. Maternal plasma was collected over 240 minutes on gestation days (gd) 0, 7.5, 10, 15, and 19; fetuses were collected on gd 15 and 19. Glyburide and metabolites were quantified using high-performance liquid chromatography-mass spectrometry, and PK analyses were performed using a pooled data bootstrap approach. Maternal CL of glyburide increased approximately 2-fold on gd 10, 15, and 19 compared with nonpregnant controls. Intrinsic CL of glyburide in maternal liver microsomes also increased as gestation progressed. Maternal metabolite/glyburide area under the curve ratios were generally unchanged or slightly decreased throughout gestation. Total fetal exposure to glyburide was <5% of maternal plasma exposure, and was doubled on gd 19 versus gd 15. Fetal metabolite concentrations were below the limit of assay detection. This is the first evidence of gestational age-dependent changes in glyburide PK. Increased maternal glyburide clearance during gestation is attributable to increased hepatic metabolism. Metabolite elimination may also increase during pregnancy. In the mouse model, fetal exposure to glyburide is gestational age-dependent and low compared with maternal plasma exposure. These results indicate that maternal glyburide therapeutic strategies may require adjustments in a gestational age-dependent manner if these same changes occur in humans.

The use of glyburide in the management of gestational diabetes mellitus: a meta-analysis

PURPOSE

Glyburide has been used for managing gestational diabetes mellitus (GDM) in a number of countries. It is rather inexpensive. However, its efficacy and safety remain controversial. With this meta-analysis, we evaluated glyburide in comparison with insulin.

MATERIAL/METHODS

With a systematic literature search strategy, a total of 93 randomized controlled trials (RCTs) with insulin and glyburide comparison were identified. Based on the revised Consolidated Standards of Reporting Trials (CONSORT) checklist, five of them met the inclusion criteria and were included in this meta-analysis.

RESULTS

Six hundred and seventy four subjects were included in these five RCTs. When compared with insulin, glyburide had an increased relative risk (RR) for neonatal hypoglycemia (RR: 1.98; 95% confidence interval [CI]: 1.17, 3.36). Estimation of standard mean differences (SMD) showed that both fetal birth weight and incidence of macrosomia were higher in subjects receiving glyburide than in those receiving insulin (SMD: 0.21; 95% CI: 0.06, 0.36; RR: 2.22; 95% CI: 1.07, 4.61 respectively). There were no significant differences in maternal glucose control, glycated hemoglobin, the rate of Cesarean section, large-for-gestational age, neonatal hypocalcemia, length of stay for neonatal ICU admissions, preterm birth, or congenital anomalies.

CONCLUSIONS

Our study suggested that in women with GDM, glyburide is as effective as insulin, but the risks of neonatal hypoglycemia, high fetal birth weight, and macrosomia were higher.

Placental transfer of maraviroc in an ex vivo human cotyledon perfusion model and influence of ABC transporter expression

Nowadays, antiretroviral therapy is recommended during pregnancy to prevent mother-to-child transmission of HIV. However, for many antiretroviral drugs, including maraviroc, a CCR5 antagonist, very little data exist regarding placental transfer. Besides, various factors may modulate this transfer, including efflux transporters belonging to the ATP-binding cassette (ABC) transporter superfamily. We investigated maraviroc placental transfer and the influence of ABC transporter expression on this transfer using the human cotyledon perfusion model. Term placentas were perfused ex vivo for 90 min with maraviroc (600 ng/ml) either in the maternal-to-fetal (n = 10 placentas) or fetal-to-maternal (n = 6 placentas) direction. Plasma concentrations were determined by ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Fetal transfer rates (FTR) and clearance indexes (CLI) were calculated as ratios of fetal to maternal concentrations at steady state (mean values between 30 and 90 min) and ratios of FTR of maraviroc to that of antipyrine, respectively. ABC transporter gene expression levels were determined by quantitative reverse transcription (RT)-PCR and ABCB1 protein expression by Western blotting. For the maternal-to-fetal direction, the mean FTR and CLI were 8.0% ± 3.0 and 0.26 ± 0.07, respectively, whereas the mean CLI was 0.52 ± 0.23 for the fetal-to-maternal direction. We showed a significant inverse correlation between maraviroc CLI and ABCC2, ABCC10, and ABCC11 placental gene expression levels (P < 0.05). To conclude, we report a low maraviroc placental transfer probably involving ABC efflux transporters and thus in all likelihood associated with a limited fetal exposition. Nevertheless, these results would need to be supported by in vivo data obtained from paired maternal and cord blood samples.

Pharmacotherapy in pregnancy; effect of ABC and SLC transporters on drug transport across the placenta and fetal drug exposure

Pharmacotherapy during pregnancy is often inevitable for medical treatment of the mother, the fetus or both. The knowledge of drug transport across placenta is, therefore, an important topic to bear in mind when deciding treatment in pregnant women. Several drug transporters of the ABC and SLC families have been discovered in the placenta, such as P-glycoprotein, breast cancer resistance protein, or organic anion/cation transporters. It is thus evident that the passage of drugs across the placenta can no longer be predicted simply on the basis of their physical-chemical properties. Functional expression of placental drug transporters in the trophoblast and the possibility of drug-drug interactions must be considered to optimize pharmacotherapy during pregnancy. In this review we summarize current knowledge on the expression and function of ABC and SLC transporters in the trophoblast. Furthermore, we put this data into context with medical conditions that require maternal and/or fetal treatment during pregnancy, such as gestational diabetes, HIV infection, fetal arrhythmias and epilepsy. Proper understanding of the role of placental transporters should be of great interest not only to clinicians but also to pharmaceutical industry for future drug design and development to control the degree of fetal exposure.

Fate of the teratogenic and carcinogenic ochratoxin A in human perfused placenta

Ochratoxin A (OTA) is one of the most frequent mycotoxins detected in human blood worldwide. Apart from its well known nephrotoxicity, OTA-induced teratogenicity and carcinogenicity proven in animals are potential effects also in humans. Pregnant women have been exposed to this food contaminant via dietary exposure in a continuous and widespread manner. Although the transplacental transfer of OTA has been demonstrated in laboratory animals and the presence of OTA in human fetal samples has been reported, little is known about the role of human placenta in OTA toxicokinetics. In this study, human perfused placenta was used to reveal the actual placental toxicokinetics of OTA using concentrations found in serum of pregnant women. Moreover, the effect of protein concentration and biological significance of placental transporters on the OTA transfer in human placenta were also determined. Our study is the first to pursue the transfer of OTA through perfused human placenta. The transfer of OTA through term human placenta was barely detectable in all perfusions. Inhibitors of neither ABCG2 nor ABCC2 increased the transport of OTA to fetal circulation in placental perfusion, and thus these transporters apparently do not have biological significance in inhibiting transplacental transfer of OTA. Human albumin has inhibited OTA transfer through a tight monolayer of BeWo b30 cells. Finding from this study clearly contradict the existing epidemiological studies reporting higher OTA levels in fetal than in maternal circulation in vivo.

Antibiotic Treatment of Dogs and Cats during Pregnancy

The use of pharmacological agents in pregnant females poses a major clinical challenge due to the marked physiological changes that may modify the pharmacokinetics of drugs and to the potential effects on the fetus. The purpose of this paper is to review briefly our knowledge on the use of antibacterial drugs during pregnancy and to provide information for the judicious selection of an antimicrobial treatment for use in pregnant bitches and queens. The risk to the fetus is a result of the ability of a drug to reach the fetal circulation and to produce toxic effects. The placenta functions as a barrier that protects the fetus due to the presence of transporters and metabolising enzymes; however, during pregnancy, the presence and activity of both enzymes and transporters may change. Antimicrobial agents that have been shown to be safe for use during pregnancy include betalactams, macrolides, and lincosamides. Pharmacotherapy during pregnancy in all species may affect adversely the developing fetus; therefore, it should be avoided when possible.

Transplacental transfer and metabolism of bupropion

OBJECTIVE

In order to evaluate the potential use of bupropion as smoking cessation therapy during pregnancy, the aim of this investigation was to determine transplacental transfer and metabolism of bupropion and its distribution among placental tissue and maternal and fetal circuits of the dually perfused placental lobule.

METHODS

Placentas obtained from healthy term pregnancies were perfused with bupropion at two concentrations 150 ng/ml and 450 ng/ml, along with the marker compound antipyrine 20 microg/ml. Radioactive isotopes of the two drugs were co-transfused to enhance their detection limits. Concentrations of bupropion and its metabolite were determined by liquid chromatography and liquid scintillation spectrometry.

RESULTS

The fetal/maternal concentration ratio of bupropion was 1.07 +/- 0.22. Following 4 h of its perfusion, 48 +/- 6% of bupropion was retained by placental tissue, 32 +/- 5% remained in the maternal circuit, and 20 +/- 6% was transferred to the fetal circuit. A metabolite of bupropion, threohydrobupropion, was identified.

CONCLUSIONS

Bupropion was transferred from the maternal to fetal circuit and was biotransformed by placental tissue enzymes to its metabolite threohydrobupropion. Bupropion and its metabolite did not affect placental tissue viability or functional parameters. These data suggest that bupropion has the potential of being used for smoking cessation during pregnancy and should be further investigated for its safety and efficacy.

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.

Identification of the major human hepatic and placental enzymes responsible for the biotransformation of glyburide

One of the factors affecting the pharmacokinetics (PK) of a drug during pregnancy is the activity of hepatic and placental metabolizing enzymes. Recently, we reported on the biotransformation of glyburide by human hepatic and placental microsomes to six metabolites that are structurally identical between the two tissues. Two of the metabolites, 4-trans-(M1) and 3-cis-hydroxycyclohexyl glyburide (M2b), were previously identified in plasma and urine of patients treated with glyburide and are pharmacologically active. The aim of this investigation was to identify the major human hepatic and placental CYP450 isozymes responsible for the formation of each metabolite of glyburide. This was achieved by the use of chemical inhibitors selective for individual CYP isozymes and antibodies raised against them. The identification was confirmed by the kinetic constants for the biotransformation of glyburide by cDNA-expressed enzymes. The data revealed that the major hepatic isozymes responsible for the formation of each metabolite are as follows: CYP3A4 (ethylene-hydroxylated glyburide (M5), 3-trans-(M3) and 2-trans-(M4) cyclohexyl glyburide); CYP2C9 (M1, M2a (4-cis-) and M2b); CYP2C8 (M1 and M2b); and CYP2C19 (M2a). Human placental microsomal CYP19/aromatase was the major isozyme responsible for the biotransformation of glyburide to predominantly M5. The formation of significant amounts of M5 by CYP19 in the placenta could render this metabolite more accessible to the fetal circulation. The multiplicity of enzymes biotransforming glyburide and the metabolites formed underscores the potential for its drug interactions in vivo.

BCRP/ABCG2 in the placenta: expression, function and regulation

Knowledge concerning transport of maternally administered drugs across the placental barrier is essential for determining potential toxicity of drugs to the fetus and the value of drug therapy during pregnancy. An important determinant for fetal drug exposure is the expression of efflux transporters in the placenta. Among human tissues, the ATP-binding cassette efflux transporter BCRP (gene symbol ABCG2) is most abundantly expressed in the apical membrane of placental syncytiotrophoblasts. Although the precise physiological role of BCRP in the placenta is still unclear, existing data strongly suggest that BCRP plays an important role in protecting the fetus against the potential toxicity of drugs, xenobiotics, and metabolites by expelling them across the placental barrier. In this review, we summarize the current knowledge with respect to the expression, function, and polymorphisms of BCRP, as well as transcriptional and posttranscriptional regulation of the transporter in the placenta. Finally, clinical significance of BCRP in the placenta for drug therapy in pregnant women is discussed.

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.

The human placenta – An alternative for studying foetal exposure

Pregnant women are daily exposed to a wide selection of foreign substances. Sources are as different as lifestyle factors (smoking, daily care products, alcohol consumption, etc.), maternal medication or occupational/environmental exposures. The placenta provides the link between mother and foetus, and though its main task is to act as a barrier and transport nutrients and oxygen to the foetus, many foreign compounds are transported across the placenta to some degree and may therefore influence the unborn child. Foetal exposures to environmental and medicinal products may have impact on the growth of the foetus (e.g. cigarette smoke) and development of the foetal organs (e.g. methylmercury and thalidomide). The scope of this review is to give insight to the placental anatomy, development and function. Furthermore, the compounds physical properties and the transfer mechanism across the placental barrier are evaluated. In order to determine the actual foetal risk from exposure to a chemical many studies regarding the topic are necessary, including means of transportation, toxicological targets and effects. For this purpose several in vivo and in vitro models including the placental perfusion system are models of choice.

Oral anti-hyperglycemic agents for the management of gestational diabetes mellitus

The purpose of this review is to provide a brief overview for understanding the management guidelines of gestational diabetes. The rationale for the use of oral antidiabetic drugs is provided based on validation by appropriately conducted research trials. Concerns over teratogenicity due to possible placental transfer, neonatal and maternal outcome, and basic pharmacologic benefits are addressed.

The fate and effects of xenobiotics in human placenta

During past decades, knowledge on placental drug metabolism and mechanisms of placental transfer has increased significantly. Most pharmaceutical drugs administered during pregnancy cross the placenta to some extent. The important properties determining the placental transfer by passive diffusion are molecular weight, pK(a), lipid solubility and protein binding. In addition to passive diffusion, compounds may cross the placenta via active transfer, facilitated diffusion, phagocytosis and pinocytosis. This review gives an update of efflux transporter proteins and xenobiotic-metabolizing enzymes that modify the fate and effects of drugs in the placenta.

Kinetics of glyburide metabolism by hepatic and placental microsomes of human and baboon

Glyburide (glibenclamide) is under investigation for treatment of gestational diabetes. Two metabolites of glyburide have been previously identified in patients, namely, 4-trans-(M1) and 3-cis-(M2) hydroxycyclohexyl glyburide. Recently, the metabolism of glyburide by microsomes of liver and placenta from humans and baboons revealed the formation of four additional metabolites: 4-cis-(M2a), 3-trans-(M3), and 2-trans-(M4) hydroxycyclohexyl glyburide, and ethyl-hydroxy glyburide (M5). The aim of this investigation was to determine the kinetics for the metabolism of glyburide by cytochrome P450 (CYP) isozymes of human and baboon placental and hepatic microsomes. The metabolism of glyburide by microsomes from the four organs revealed saturation kinetics and apparent K(m) values between 4 and 12 microM. However, the rates for formation of the metabolites varied between organs and species. M1 was the major metabolite (36% of total), formed by human hepatic microsomes with V(max) of 80+/-13 pmol mg protein(-1)min(-1), and together with M2, accounted for only 51% of the total. M5 was the major metabolite (87%) formed by human placental microsomes with V(max) of 11 pmol mg protein(-1)min(-1). In baboon liver, M5 had the highest rate of formation (V(max) 135+/-32 pmol mg protein(-1)min(-1), 39% of total), and in its placenta, was M4 (V(max) 0.7+/-0.1 pmol mg protein(-1)min(-1), 65%). The activity of human and baboon hepatic microsomes in metabolizing glyburide was similar, but the activity of human and baboon placental microsomes was 7% and 0.3% of their respective hepatic microsomes. The data obtained suggest that more than 1 CYP isozyme is responsible for catalyzing the hydroxylation of glyburide.

Identification of glyburide metabolites formed by hepatic and placental microsomes of humans and baboons

Glyburide (glibenclamide) is a second-generation sulfonylurea used for treatment of type-2 and gestational diabetes mellitus. To date, two glyburide metabolites have been identified in maternal urine: namely, 4-trans-hydroxycyclohexyl glyburide and 3-cis-hydroxycyclohexyl glyburide. The use of glyburide to treat gestational diabetes prompted us to investigate its metabolism by the placenta. The metabolism of glyburide by microsomal preparations from human and baboon placenta was compared with metabolism by their livers. The metabolites formed by the microsomes of the four tissues were identified by high-performance liquid chromatography-mass spectrometry using retention times, ion current (extracted at m/z 510), and selected-ion monitoring. The data obtained revealed the formation of six distinct hydroxylated derivatives of glyburide by each of the four microsomal preparations. However, the amounts of the six metabolites formed by the placentas were a fraction of that formed by the livers. Moreover, the relative quantities of each metabolite formed differed between species as well as between the two tissues. Also, the structure of the unidentified metabolites was determined by comparison with synthesized standards. These metabolites were identified as the 4-cis-hydroxycyclohexyl glyburide, 3-trans-hydroxycyclohexyl glyburide, and 2-trans-hydroxycyclohexyl glyburide. Therefore, one glyburide metabolite remains to be identified, but the data we obtained allowed us to suggest its structure.