Uptake mechanism of valproic acid in human placental choriocarcinoma cell line (BeWo)

Effects of co-administration of lamotrigine on valproate transfer across the placenta and its brain entry in developing Genetic Absence Epilepsy Rats from Strasbourg (GAERS)

During development, embryos and foetuses may be exposed to maternally ingested antiseizure medications (ASM), valproate and lamotrigine, essential in some patients to control their epilepsy symptoms. Often, the two drugs are co-administered to reduce required doses of valproate, a known potential teratogen. This study used Genetic Absence Epilepsy Rat from Strasbourg to evaluate transfer of valproate and lamotrigine across late gestation placenta and their entry into cerebrospinal fluid (CSF) and brain of developing rats, in mono- and combination therapies. Animals at embryonic day (E) 19, postnatal day (P) 0, 4 and 21, and adults were administered valproate (30 mg/kg) or lamotrigine (6 mg/kg) with their respective [3H]-tracers, either alone or in combination. In chronic experiments, females consumed valproate-containing diet from 2 weeks prior to mating until offspring were used at E19 and P0. Drugs were injected 30 min before blood, CSF and brain samples were collected from terminally anaesthetised animals. Radioactivity in samples was measured. In acute monotherapy brain entry of valproate was higher in foetal than postnatal animals, correlating with its plasma protein binding. Brain entry of lamotrigine was not age-dependent. Combination therapy enhanced entry of lamotrigine into the adult brain but had no effects on brain and CSF entry of valproate. Following chronic valproate exposure, placental transfer of valproate decreased in combination therapy; however, foetal brain entry increased. Results suggest that during pregnancy, the use of combination therapy of valproate and lamotrigine may mitigate overall foetal exposure to valproate but potential risks to foetal brain development are less clear.

Monocarboxylate transporter functions and neuroprotective effects of valproic acid in experimental models of amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a devasting neurodegenerative disorder for which no successful therapeutics are available. Valproic acid (VPA), a monocarboxylate derivative, is a known antiepileptic drug and a histone deacetylase inhibitor.

Methods

To investigate whether monocarboxylate transporter 1 (MCT1) and sodium-coupled MCT1 (SMCT1) are altered in ALS cell and mouse models, a cellular uptake study, quantitative real time polymerase chain reaction and western blot parameters were used. Similarly, whether VPA provides a neuroprotective effect in the wild-type (WT; hSOD1WT) and ALS mutant-type (MT; hSOD1G93A) NSC-34 motor neuron-like cell lines was determined through the cell viability assay.

Results

[³H]VPA uptake was dependent on time, pH, sodium and concentration, and the uptake rate was significantly lower in the MT cell line than the WT cell line. Interestingly, two VPA transport systems were expressed, and the VPA uptake was modulated by SMCT substrates/inhibitors in both cell lines. Furthermore, MCT1 and SMCT1 expression was significantly lower in motor neurons of ALS (G93A) model mice than in those of WT mice. Notably, VPA ameliorated glutamate- and hydrogen peroxide-induced neurotoxicity in both the WT and MT ALS cell lines.

Conclusions

Together, the current findings demonstrate that VPA exhibits a neuroprotective effect regardless of the dysfunction of an MCT in ALS, which could help develop useful therapeutic strategies for ALS.

Valproic acid stimulates in vitro migration of the placenta-derived mesenchymal stem/stromal cell line CMSC29

Background

The placenta is an abundant source of mesenchymal stem/stromal cells (MSC), but our understanding of their functional properties remains limited. We previously created a placental-derived chorionic MSC (CMSC) cell line to overcome the difficulties associated with conducting extensive ex vivo optimization and experimental work on primary cells. The aim of this study was to characterize the migratory behavior of the CMSC29 cell line in vitro.

Methods

Stimulators of MSC migration, including two cytokines, stromal cell-derived factor-1α (SDF-1α) and hepatocyte growth factor (HGF), and a pharmacological agent, valproic acid (VPA), were tested for their ability to stimulate CMSC29 cell migration. Assessment of cell migration was performed using the xCELLigence Real-Time Cell Analyzer (RTCA).

Results

There was no significant increase in CMSC29 cell migration towards serum free medium with increasing concentration gradients of SDF-1α or HGF. In contrast, treating CMSC29 cells with VPA alone significantly increased their migration towards serum free medium.

Conclusions

Immortalized CMSC29 cells retain important properties of primary CMSC, but their migratory properties are altered. CMSC29 cells do not migrate in response to factors that reportedly stimulate primary MSC/CMSC migration. However, CMSC29 increase their migration in response to VPA treatment alone. Further studies are needed to determine the mechanism by which VPA acts alone to stimulate CMSC29 migration. Still, this study provides evidence that VPA pre-treatment may improve the benefits of cell-based therapies that employ certain MSC sub-types.

The role of various transporters in the placental uptake of ofloxacin in an in vitro model of human villous trophoblasts

Introduction

Six years after the US Food and Drug Administration approval of the broad-spectrum antibiotic ofloxacin (OFLX), the chiral switching of this racemic mixture resulted in a drug composed of the L-optical isomer levofloxacin (LVFX). Since both fluoroquinolones (FQs) were introduced to the pharmaceutical market, they have been widely prescribed by physicians, with careful administration during pregnancy and breastfeeding. Therefore, the role of the influx and efflux placental transporters in the concentrations of these drugs that permeate through human placental barrier model was investigated in this study.

Methods

The contribution of major carriers on the transplacental flux of OFLX and LVFX uptake into choriocarcinoma BeWo cells was evaluated in the presence vs absence of well-known inhibitors.

Results

Our results reveal that neither the influx transporters such as organic cation transporters, organic anion transporters, and monocarboxylate transporters nor the efflux transporters such as P-glycoprotein or breast cancer resistance protein significantly affected the transport of OFLX. In contrast, multiple transporters revealed pronounced involvement in the transfer of the levorotatory enantiomer in and out of the in vitro placental barrier. These data suggest a non-carrier-mediated mechanism of transport of the racemic mixture, while LVFX is subjected to major influx and efflux passage through the placental brush border membranes.

Conclusion

This study provides underlying insights to elucidate the governing factors that influence the flux of these FQs through organ barriers, in view of the controversial safety profile of these drugs in pregnant population.

Transport mechanism of ursodeoxycholic acid in human placental BeWo cells

Ursodeoxycholic acid (UDCA) is a first-line drug to treat intrahepatic cholestasis of pregnancy (ICP). However, its effects on the fetus are not clearly known. To better guide its clinical use, we aimed to study the mechanism underlying the placental transport of UDCA. The uptake and efflux of UDCA across placental apical membranes were studied using BeWo cells; effects of different exposure durations, UDCA concentrations, temperatures, and inhibitors of transporters were studied. A transwell assay was performed, and UDCA concentration in both fetal and maternal sides was measured using LC-MS/MS. Higher unidirectional transport of UDCA was observed in the basolateral-to-apical direction than in the apical-to-basolateral direction. Ko143 and verapamil, which are typical inhibitors of efflux transporters, significantly increased UDCA transport from different directions. UDCA uptake from the apical membrane of BeWo cells was time-dependent, but sodium-independent. It was inhibited by inhibitors of energy metabolism and of organic anion transporters, indicating an active transport mechanism. UDCA uptake from the apical membranes of BeWo cells could be mediated by organic anion-transporting polypeptides, whereas its efflux could be mediated by breast cancer resistance protein and multidrug resistant protein 3. The results of the present study may provide a basis for UDCA use in pregnancy.

Valproic acid transport in the choriocarcinoma placenta cell line JEG-3 proceeds independently of the proton-dependent transporters MCT1 and MCT4

Medication therapy is the first line of treatment in the management of epilepsy. Fetal exposure to valproic acid (VPA), an antiepileptic drug, poses an elevated risk of teratogenicity in early pregnancy. Some studies have reported that monocarboxylate transporters (MCTs) may be involved in the placental transport of VPA. However, it has not been determined which MCTs contribute to VPA transport into the placenta. Therefore, the aim of this study was to determine how MCTs contribute to VPA transport into the placenta using the human placenta choriocarcinoma cell line JEG-3. VPA uptake was investigated using JEG-3 cells and radiolabeled VPA. MCT expression in JEG-3 cells was detected using RT-PCR and western blotting. Knockdown of MCTs was carried out using siRNAs. VPA uptake into JEG-3 cells was pH- and concentration-dependent, and described by using the Michaelis-Menten equation (K_m = 0.95 ± 0.17 mM; V_max = 19.3 ± 1.21 nmol/mg protein/15 s). MCT1 and MCT4 expression was found in JEG-3 cells, and typical MCT inhibitors significantly inhibited VPA uptake into JEG-3 cells. However, knockdown of MCT1 and MCT4 did not alter VPA uptake. In conclusion, VPA transport is mediated by a proton-dependent transporter in JEG-3 cells, but not by MCT1 and MCT4.

Sexually dimorphic effects of prenatal exposure to lipopolysaccharide, and prenatal and postnatal exposure to propionic acid, on acoustic startle response and prepulse inhibition in adolescent rats: relevance to autism spectrum disorders

Potential environmental risk factors for autism spectrum disorders (ASD) include viral/bacterial infection and an altered microbiome composition. The present study investigated whether administration of immune and gastrointestinal factors during gestation and early life altered startle response and prepulse inhibition in adolescent offspring using lipopolysaccharide (LPS), a bacterial mimetic, and propionic acid (PPA), a short chain fatty acid and metabolic product of antibiotic resistant enteric bacteria. Pregnant Long-Evans rats were injected once a day with PPA (500 mg/kg SC) on G12-16, LPS (50 μg/kg SC) on G15 and G16, or vehicle control on G12-16 or G15-16. Male and female offspring were injected with PPA (500 mg/kg SC) or vehicle twice a day, every second day from postnatal days 10-18. Acoustic startle and prepulse inhibition was measured on postnatal days 45, 47, 49, and 51. Prenatal and postnatal treatments altered startle behavior in a sex-specific manner. Prenatal LPS treatment produced hyper-sensitivity to acoustic startle in males, but not females and did not alter prepulse inhibition. Subtle alterations in startle responses that disappeared with repeated trials occurred with prenatal PPA and postnatal PPA treatment in both male and female offspring. Prenatal PPA treatment decreased prepulse inhibition in females, but not males. Lastly, females receiving a double hit of PPA, prenatal and postnatal, showed sensitization to acoustic startle, providing evidence for the double hit hypothesis. The current study supports the hypotheses that immune activation and metabolic products of enteric bacteria may alter development and behavior in ways that resemble sensory abnormalities observed in ASD.

Pre- and neonatal exposure to lipopolysaccharide or the enteric metabolite, propionic acid, alters development and behavior in adolescent rats in a sexually dimorphic manner

Alterations in the composition of the gut microbiome and/or immune system function may have a role in the development of autism spectrum disorders (ASD). The current study examined the effects of prenatal and early life administration of lipopolysaccharide (LPS), a bacterial mimetic, and the short chain fatty acid, propionic acid (PPA), a metabolic fermentation product of enteric bacteria, on developmental milestones, locomotor activity, and anxiety-like behavior in adolescent male and female offspring. Pregnant Long-Evans rats were subcutaneously injected once a day with PPA (500 mg/kg) on gestation days G12–16, LPS (50 µg/kg) on G15–16, or vehicle control on G12–16 or G15–16. Male and female offspring were injected with PPA (500 mg/kg) or vehicle twice a day, every second day from postnatal days (P) 10–18. Physical milestones and reflexes were monitored in early life with prenatal PPA and LPS inducing delays in eye opening. Locomotor activity and anxiety were assessed in adolescence (P40–42) in the elevated plus maze (EPM) and open-field. Prenatal and postnatal treatments altered behavior in a sex-specific manner. Prenatal PPA decreased time spent in the centre of the open-field in males and females while prenatal and postnatal PPA increased anxiety behavior on the EPM in female rats. Prenatal LPS did not significantly influence those behaviors. Evidence for the double hit hypothesis was seen as females receiving a double hit of PPA (prenatal and postnatal) displayed increased repetitive behavior in the open-field. These results provide evidence for the hypothesis that by-products of enteric bacteria metabolism such as PPA may contribute to ASD, altering development and behavior in adolescent rats similar to that observed in ASD and other neurodevelopmental disorders.

Inhibition of monocarboxylate transporter-mediated absorption of valproic acid by Gegen-Qinlian-Tang

Valproic acid (VPA), an anti-epileptic drug with a narrow therapeutic index, is a substrate of the monocarboxylate transporter (MCT). In this study, we investigated the effect of Gegen-Qinlian-Tang (GQT), a Chinese Medicine prescription containing Puerariae Radix (PR), Scutellariae Radix (SR), Coptidis Rhizoma (CR) and Glycyrrhizae Radix (GR), on the pharmacokinetics of VPA, as a probe drug of MCT, in rats and the underlying mechanism. Sprague-Dawley rats were orally administered VPA with and without GQT in crossover design. The serum concentrations of VPA were determined by a fluorescence polarization immunoassay. The results showed that coadministration with 2.0 and 4.0 g/kg of GQT remarkably decreased the Cmax of VPA by 72% and 74% and reduced the AUC 0-t by 63% and 53%, respectively. The mechanism study using Caco-2 cells revealed that the uptake function of MCT was inhibited by GQT and each component herb. In conclusion, the MCT-mediated absorption of VPA was significantly decreased by GQT and its component herbs.

In vitro simulation of placental transport: part I. Biological model of the placental barrier

INTRODUCTION

The placental barrier (PB) is the thin biological membrane made of endothelial cells (EC), trophoblast cells (TC) and basal membrane that separates between maternal and fetal blood circulations within the placenta and facilitates feto-maternal transport characteristics, which are not completely understood.

METHODS

An in vitro biological model of the PB model was co-cultured of human TC (HTR8) and human umbilical vein EC (HUVEC) on both sides of a denuded amniotic membrane (AM) using custom designed wells.

RESULTS

Confocal and transmission electron microscopy (TEM) imaging confirmed the morphology expressions of human EC and TC. Further support on the integrity of the new PB model was obtained from the existence of tight junctions and permeability experiments with fluorescence markers of small and large molecules. The monolayer of EC demonstrated the limiting layer for the transport resistance across this complex barrier.

DISCUSSION AND CONCLUSION

This new in vitro viable model mimics the architecture of the human PB and can be used in in vitro simulations of transplacental transport studies.

A Chinese herb formula decreases the monocarboxylate transporter-mediated absorption of valproic acid in rats

Huang-Qin-Tang (HQT), a Chinese medicine prescription containing Scutellariae Radix (SR), Paeoniae Radix (PR), Glycyrrhizae Radix (GR) and JuJubae Fructus (JF), was used for the treatments of cold with symptoms of abdominalgia and diarrhea. Valproic acid (VPA) is an antiepileptic drug with narrow therapeutic window. This study investigated the effect of coadministration of HQT on the pharmacokinetics of VPA, a probe drug for monocarboxylate transporter (MCT). Rats were administered VPA alone (200.0 mg/kg) and coadministered HQT (8.0 g/kg) at 0.5h before VPA and 1.5h after VPA in crossover designs. In addition, the chronic effect of HQT was also evaluated by coadministration of the 7th dose at 0.5h before VPA. The serum concentration of VPA was determined by a fluorescence polarization immunoassay. The results showed that coadministration of HQT at 0.5h before VPA significantly decreased the AUC(0-t) and Cmax by 62% and 77%, respectively, whereas coadministration of HQT at 1.5h after VPA exerted no significant influence. When the 7th dose of HQT was given at 0.5h before VPA, the AUC(0-t) and Cmax of VPA were markedly decreased by 65% and 82%, respectively. Mechanism study revealed that the MCT-mediated uptake of fluorescein was inhibited by HQT and each component herbs. In conclusion, the MCT-mediated absorption of VPA was significantly decreased by concomitant administration of HQT.

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.

Carrier-mediated uptake of Levofloxacin by BeWo cells, a human trophoblast cell line

OBJECTIVE

Placental transfer of Levofloxacin (LF), a broad spectrum fluoroquinolone antibiotic, and its inhibition was investigated in BeWo cells, a human trophoblast cell line.

METHODS

The experiments of LF uptake by BeWo cells were performed after preincubation and in the presence of the P-glycoprotein inhibitors (Cyclosporin A, Verapamil and Quercetin), the organic anion/cation transporter inhibitor (Cimetidine) and the MCT substrates (lactic acid and salicylic acid).

RESULTS

P-glycoprotein inhibitors increased the uptake of LF by BeWo cells. The increase in LF accumulation by Cyclosporin A, Verapamil and Quercetin was by 30, 90 and 80%, respectively. Cimetidine, the organic cation inhibitor, increased the transport of LF by 48%. Lactic acid and salicylic acid, the MCT substrates, initially decreased the accumulation of LF by 30% and subsequently increased the uptake of LF by 500 and 53%, respectively.

CONCLUSIONS

The uptake of LF by human trophoblast cells is mediated by multiple transporters as well as passive diffusion.

Valproate, thalidomide and ethyl alcohol alter the migration of HTR-8/SVneo cells

BACKGROUND

Valproate, thalidomide and alcohol (ethanol) exposure during the first trimester of pregnancy is known to cause several developmental disorders. All these teratogens are known to pass the placental barrier and interfere directly with the normal development of the fetus. However, these teratogens also alter the formation and function of the placenta itself which may in turn affect the proper nourishment and development of the fetus. Optimum development of the placenta requires adequate invasion of trophoblast into the maternal uterine tissues. Changes in the migratory behavior of trophoblast by maternal exposure to these teratogens during placentogenesis may therefore alter the structure and function of the placenta.

METHODS

In the present study, the effects of sodium valproate, thalidomide and alcohol on the migration of human first trimester trophoblast cell line (HTR-8/SVneo) were examined in vitro. Cells were cultured in the wells of 48-well culture plates as mono or multilayers. Circular patches of cells were removed from the center of the wells by suction, and the migration of cells into the wound was studied using microscopy. Effects of low and high concentrations of valproate, thalidomide and alcohol were examined on the healing of wounds and on the migration rate of cells by determining the wound areas at 0, 3, 6, 12, 24 and 48 h. Effects of drugs and alcohol on the proliferation and the expression levels of integrin subunits beta1 and alpha5 in cells were examined.

RESULTS

The migration rates of trophoblast differed between wounds created in mono and multilayers of cells. Exposure to teratogens altered the migration of trophoblast into mono and multilayer wounds. The effects of valproate, thalidomide and alcohol on the proliferation of cells during the rapid migratory phase were mild. Drug exposure caused significant changes in the expression levels of beta1 and alpha5 integrin subunits.

CONCLUSION

Results suggest that exposure to valproate, thalidomide or alcohol during the first trimester of pregnancy may change the ultrastructure of the placenta by altering the migration of trophoblast cells and this effect may be mediated by drug- or alcohol-induced changes in the expression levels of beta1 and alpha5 integrin subunits.

Expression of cyclooxygenase isoforms in developing rat placenta, human term placenta, and BeWo human trophoblast model

Cyclooxygenase (COX) catalyzes the rate-limiting step in the conversion of essential fatty acids (EFAs) to bioactive molecules such as prostaglandins (PGs), which play critical roles in many aspects of female reproduction and in fetal development. There are two primary related COX isoforms, the constitutively expressed COX-1 and the inducible COX-2. Although the expression of COX-1 and COX-2 has been demonstrated in the amnion, chorion, and decidua, relatively little information exists with regard to their expression and physiological function in the placenta during gestation. In this study, we have elucidated the spatial and temporal patterns of COX-1 and COX-2 expression in the labyrinthine and junctional zones of the developing rat placenta, in the human term placenta, and in the BeWo human trophoblast model using semiquantitative RT-PCR, Western blot, and immunohistochemical analyses. The mRNA and protein expression of COX-1 and COX-2 were demonstrated in the developing rat placenta with increasing expression observed toward parturition. COX-2 exhibited greater expression than COX-1 after mid-gestation and had a corresponding shift in spatial expression from the labyrinthine to the junctional zone at term. COX-1 and -2 were also expressed in human term placenta, while BeWo cells exhibited moderate expression of COX-1 and weak expression of COX-2. The results demonstrate that COX-1 and COX-2 are expressed in the rat and human placentas. The differential expression patterns in the rat placenta, especially of COX-2, imply that there may be gestational changes in the biosynthesis of PGs and other potential bioactive EFA metabolites. Establishing the expression of the COX isoforms provides a framework for future investigations into the functional and physiological significance of COX-1 and COX-2 in the placenta, particularly with respect to influencing normal pregnancy and fetal development, and to provide insights into therapeutic utilization of COX inhibitors in pregnancy.

EXPRESSION AND FUNCTIONAL ACTIVITY OF BREAST CANCER RESISTANCE PROTEIN (BCRP, ABCG2) TRANSPORTER IN THE HUMAN CHORIOCARCINOMA CELL LINE BEWO

1. Breast cancer resistance protein (BCRP, ABCG2) is a drug efflux transporter that is believed to affect the drug disposition of several drugs and xenobiotics. In the present study, we evaluated the localization and functional expression of BCRP in the human choriocarcinoma cell line BeWo, an in vitro model of the human trophoblast, and compared it with the expression of P-glycoprotein (MDR1, ABCB1) as the most widely studied placental transporter. In addition, the expression of BCRP at the mRNA level was compared with that of MDR1 in the human term placenta. 2. Western blotting analysis revealed high endogenous expression of BCRP protein in BeWo cells. Using indirect immunofluorescence microscopy, we found that the BCRP transporter appears to be localized predominantly at the apical plasma membrane. Functional studies showed a significant effect of the BCRP inhibitors GF120918 (5 micromol/L) and Ko143 (1 micromol/L) on mitoxantrone accumulation and, thus, confirmed efflux activity of BCRP in BeWo cells. 3. Using absolute mRNA quantification with real-time reverse transcription-polymerase chain reaction, we found high expression of BCRP in BeWo cells, whereas no transcript of MDR1 (P-glycoprotein), the most extensively studied drug transporter, was detected. 4. In the human placenta, BCRP was localized predominantly in the syncytiotrophoblast layer; however, immunopositivity for the BXP-21 antibody was also observed in fetal vessels of the chorionic villi. The number of BCRP transcripts in the human term placenta was found to be more than 10-fold higher compared with the expression of MDR1. 5. In conclusion, we suggest that BeWo cells could serve as a suitable in vitro model to study trans-trophoblast transport of BCRP substrates and that placental BCRP can play an important role in preventing the accumulation of potentially toxic xenobiotics in the trophoblast cells.

The role of pH dynamics and the Na+/H+ antiporter in the etiopathogenesis and treatment of cancer. Two faces of the same coin--one single nature

Looked at from the genetic point-of-view cancer represents a daunting and, frankly, confusing multiplicity of diseases (at least 100) that require an equally large variety of therapeutic strategies and substances designed to treat the particular tumor. However, when analyzed phenotypically cancer is a relatively uniform disease of very conserved 'hallmark' behaviors across the entire spectrum of tissue and genetic differences [D. Hanahan, R.A. Weinberg, Hallmarks of cancer, Cell 100 (2000) 57-70]. This suggests that cancers do, indeed, share common biochemical and physiological characteristics that are independent of the varied genetic backgrounds, and that there may be a common mechanism underlying both the neoplastic transformation/progression side and the antineoplastic/therapy side of oncology. The challenge of modern oncology is to integrate all the diverse experimental data to create a physiological/metabolic/energetic paradigm that can unite our thinking in order to understand how both neoplastic progression and therapies function. This reductionist view gives the hope that, as in chemistry and physics, it will possible to identify common underlying driving forces that define a tumor and will permit, for the first time, the actual calculated manipulation of their state. That is, a rational therapeutic design. In the present review, we present evidence, obtained from a great number of studies, for a fundamental, underlying mechanism involved in the initiation and evolution of the neoplastic process. There is an ever growing body of evidence that all the important neoplastic phenotypes are driven by an alkalization of the transformed cell, a process which seems specific for transformed cells since the same alkalinization has no effect in cells that have not been transformed. Seen in that light, different fields of cancer research, from etiopathogenesis, cancer cell metabolism and neovascularization, to multiple drug resistance (MDR), selective apoptosis, modern cancer chemotherapy and the spontaneous regression of cancer (SRC) all appear to have in common a pivotal characteristic, the aberrant regulation of hydrogen ion dynamics [S. Harguindey, J.L. Pedraz, R. García Cañero, J. Pérez de Diego, E.J. Cragoe Jr., Hydrogen ion-dependent oncogenesis and parallel new avenues to cancer prevention and treatment using a H+-mediated unifying approach: pH-related and pH-unrelated mechanisms, Crit. Rev. Oncog. 6 (1) (1995) 1-33]. Cancer cells have an acid-base disturbance that is completely different than observed in normal tissues and that increases in correspondence with increasing neoplastic state: an interstitial acid microenvironment linked to an intracellular alkalosis.

Drug Transfer and Metabolism by the Human Placenta

The major function of the placenta is to transfer nutrients and oxygen from the mother to the foetus and to assist in the removal of waste products from the foetus to the mother. In addition, it plays an important role in the synthesis of hormones, peptides and steroids that are vital for a successful pregnancy. The placenta provides a link between the circulations of two distinct individuals but also acts as a barrier to protect the foetus from xenobiotics in the maternal blood. However, the impression that the placenta forms an impenetrable obstacle against most drugs is now widely regarded as false. It has been shown that that nearly all drugs that are administered during pregnancy will enter, to some degree, the circulation of the foetus via passive diffusion. In addition, some drugs are pumped across the placenta by various active transporters located on both the fetal and maternal side of the trophoblast layer. It is only in recent years that the impact of active transporters such as P-glycoprotein on the disposition of drugs has been demonstrated. Facilitated diffusion appears to be a minor transfer mechanism for some drugs, and pinocytosis and phagocytosis are considered too slow to have any significant effect on fetal drug concentrations. The extent to which drugs cross the placenta is also modulated by the actions of placental phase I and II drug-metabolising enzymes, which are present at levels that fluctuate throughout gestation. Cytochrome P450 (CYP) enzymes in particular have been well characterised in the placenta at the level of mRNA, protein, and enzyme activity. CYP1A1, 2E1, 3A4, 3A5, 3A7 and 4B1 have been detected in the term placenta. While much less is known about phase II enzymes in the placenta, some enzymes, in particular uridine diphosphate glucuronosyltransferases, have been detected and shown to have specific activity towards marker substrates, suggesting a significant role of this enzyme in placental drug detoxification. The increasing experimental data on placental drug transfer has enabled clinicians to make better informed decisions about which drugs significantly cross the placenta and develop dosage regimens that minimise fetal exposure to potentially toxic concentrations. Indeed, the foetus has now become the object of intended drug treatment. Extensive research on the placental transfer of drugs such as digoxin and zidovudine has assisted with the safe treatment of the foetus with these drugs in utero. Improved knowledge regarding transplacental drug transfer and metabolism will result in further expansion of pharmacological treatment of fetal conditions.