Expression of xenobiotic-metabolizing cytochrome P450 forms in human full-term placenta

Bupropion metabolism by human placenta

Smoking during pregnancy is the largest modifiable risk factor for pregnancy-related morbidity and mortality. The success of bupropion for smoking cessation warrants its investigation for the treatment of pregnant patients. Nevertheless, the use of bupropion for the treatment of pregnant smokers requires additional data on its bio-disposition during pregnancy. Therefore, the aim of this investigation was to determine the metabolism of bupropion in placentas obtained from nonsmoking and smoking women, identify metabolites formed and the enzymes catalyzing their formation, as well as the kinetics of the reaction. Data obtained revealed that human placentas metabolized bupropion to hydroxybupropion, erythro- and threohydrobupropion. The rates for formation of erythro- and threohydrobupropion exceeded that for hydroxybupropion by several folds, were dependent on the concentration of bupropion and exhibited saturation kinetics with an apparent K(m) value of 40microM. Human placental 11beta-hydroxysteroid dehydrogenases were identified as the major carbonyl-reducing enzymes responsible for the reduction of bupropion to threo- and erythrohydrobupropion in microsomal fractions. On the other hand, CYP2B6 was responsible for the formation of OH-bupropion. These data suggest that both placental microsomal carbonyl-reducing and oxidizing enzymes are involved in the metabolism of bupropion.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

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.

Placental biomarkers of phthalate effects on mRNA transcription: application in epidemiologic research

BACKGROUND

CYP19 and PPARgamma are two genes expressed in the placental trophoblast that are important to placental function and are disrupted by phthalate exposure in other cell types. Measurement of the mRNA of these two genes in human placental tissue by quantitative real-time polymerase chain reaction (qPCR) offers a source of potential biomarkers for use in epidemiologic research. We report on methodologic challenges to be considered in study design.

METHODS

We anonymously collected 10 full-term placentas and, for each, sampled placental villi at 12 sites in the chorionic plate representing the inner (closer to the cord insertion site) and outer regions. Each sample was analyzed for the expression of two candidate genes, aromatase (CYP19) and peroxisome proliferator activated receptor protein gamma (PPARgamma) and three potential internal controls: cyclophilin (CYC), 18S rRNA (18S), and total RNA. Between and within placenta variability was estimated using variance component analysis. Associations of expression levels with sampling characteristics were estimated using mixed effects models.

RESULTS

We identified large within-placenta variability in both transcripts (>90% of total variance) that was minimized to <20% of total variance by using 18S as an internal control and by modelling the means by inner and outer regions. 18S rRNA was the most appropriate internal control based on within and between placenta variability estimates and low correlations of 18S mRNA with target gene mRNA. Gene expression did not differ significantly by delivery method. We observed decreases in the expression of both transcripts over the 25 minute period after delivery (CYP19 p-value for trend = 0.009 and PPARgamma (p-value for trend = 0.002). Using histologic methods, we confirmed that our samples were comprised predominantly of villous tissue of the fetal placenta with minimal contamination of maternally derived cell types.

CONCLUSION

qPCR-derived biomarkers of placental CYP19 and PPARgamma gene expression show high within-placental variability. Sampling scheme, selection of an appropriate internal control and the timing of sample collection relative to delivery can be optimized to minimize within-placenta and other sources of underlying, non-etiologic variability.

Regulation of human vitamin D(3) 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells

In this study, we examined whether 1alpha,25-dihydroxyvitamin D(3) (calcitriol), phenobarbital, and the antiretroviral drug efavirenz, drugs used by patient groups with high incidence of low bone mineral density, could affect the 25-hydroxylase activity or expression of human 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells. Fibroblasts express the 25-hydroxylating enzymes CYP2R1 and CYP27A1. LNCaP cells were found to express two potential vitamin D 25-hydroxylases-CYP2R1 and CYP2J2. The presence in different cells of nuclear receptors vitamin D receptor (VDR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR) was also determined. Phenobarbital suppressed the expression of CYP2R1 in fibroblasts and CYP2J2 in LNCaP cells. Efavirenz suppressed the expression of CYP2R1 in fibroblasts but not in LNCaP cells. CYP2J2 was slightly suppressed by efavirenz, whereas CYP27A1 was not affected by any of the two drugs. Calcitriol suppressed the expression of CYP2R1 in both fibroblasts and LNCaP cells but had no clear effect on the expression of either CYP2J2 or CYP27A1. The vitamin D(3) 25-hydroxylase activity in fibroblasts was suppressed by both calcitriol and efavirenz. In LNCaP cells, consumption of substrate (1alpha-hydroxyvitamin D(3)) was used as indicator of metabolism because no 1alpha,25-dihydroxyvitamin D(3) product could be determined. The amount of 1alpha-hydroxyvitamin D(3) remaining in cells treated with calcitriol was significantly increased. Taken together, 25-hydroxylation of vitamin D(3) was suppressed by calcitriol and drugs. The present study provides new information indicating that 25-hydroxylation of vitamin D(3) may be regulated. In addition, the current results may offer a possible explanation for the impaired bone health after treatment with certain drugs.

Novel biomarkers of prenatal methamphetamine exposure in human meconium

Meconium analysis can detect fetal exposure to drugs taken by the mother during pregnancy. Methamphetamine (MAMP) and amphetamine (AMP) have previously been observed in meconium of MAMP-exposed neonates; the presence of other metabolites has not been investigated. Detection of such analytes may lead to more sensitive identification and thus improved medical treatment of affected infants. Forty-three MAMP-positive meconium specimens were analyzed for newly identified MAMP biomarkers, p-hydroxymethamphetamine, p-hydroxyamphetamine, and norephedrine. Due to MAMP adulteration in illicit ecstasy and to simultaneously monitor 3,4-methylenedioxymethamphetamine and MAMP prenatal exposure, 3,4-methylenedioxymethamphetamine, its metabolites, and related sympathomimetic amines were assayed. MAMP, AMP, and unconjugated p-hydroxymethamphetamine were the most prevalent and abundant analytes present in meconium; however, unconjugated p-hydroxyamphetamine and norephedrine also were identified. It is possible that one of these additional analytes could be important for predicting toxicity or maternal or neonatal outcome measures in fetuses exposed to MAMP at specific gestational ages or with different metabolic capabilities. Although these new biomarkers were present in lower concentrations than MAMP and AMP in the meconium of previously confirmed specimens, additional research will determine if inclusion of these analytes can increase identification of MAMP-exposed neonates. Novel methamphetamine biomarker concentrations were characterized in meconium of infants exposed in utero to MAMP.

Excretion of biliary compounds during intrauterine life

In adults, the hepatobiliary system, together with the kidney, constitute the main routes for the elimination of several endogenous and xenobiotic compounds into bile and urine, respectively. However, during intrauterine life the biliary route of excretion for cholephilic compounds, such as bile acids and biliary pigments, is very poor. Although very early in pregnancy the fetal liver produces bile acids, bilirubin and biliverdin, these compounds cannot be efficiently eliminated by the fetal hepatobiliary system, owing to the immaturity of the excretory machinery in the fetal liver. Therefore, the potentially harmful accumulation of cholephilic compounds in the fetus is prevented by their elimination across the placenta. Owing to the presence of detoxifying enzymes and specific transport systems at different locations of the placental barrier, such as the endothelial cells of chorionic vessels and trophoblast cells, this organ plays an important role in the hepatobiliary-like function during intrauterine life. The relevance of this excretory function in normal fetal physiology is evident in situations where high concentrations of biliary compounds are accumulated in the mother. This may result in oxidative stress and apoptosis, mainly in the placenta and fetal liver, which might affect normal fetal development and challenge the fate of the pregnancy. The present article reviews current knowledge of the mechanisms underlying the hepatobiliary function of the fetal-placental unit and the repercussions of several pathological conditions on this tandem.

Differential gene expression in human conducting airway surface epithelia and submucosal glands

Human conducting airways contain two anatomically distinct epithelial cell compartments: surface epithelium and submucosal glands (SMG). Surface epithelial cells interface directly with the environment and function in pathogen detection, fluid and electrolyte transport, and mucus elevation. SMG secrete antimicrobial molecules and most of the airway surface fluid. Despite the unique functional roles of surface epithelia and SMG, little is known about the differences in gene expression and cellular metabolism that orchestrate the specialized functions of these epithelial compartments. To approach this problem, we performed large-scale transcript profiling using epithelial cell samples obtained by laser capture microdissection (LCM) of human bronchus specimens. We found that SMG expressed high levels of many transcripts encoding known or putative innate immune factors, including lactoferrin, zinc alpha-2 glycoprotein, and proline-rich protein 4. By contrast, surface epithelial cells expressed high levels of genes involved in basic nutrient catabolism, xenobiotic clearance, and ciliated structure assembly. Selected confirmation of differentially expressed genes in surface and SMG epithelia demonstrated the predictive power of this approach in identifying genes with localized tissue expression. To characterize metabolic differences between surface epithelial cells and SMG, immunostaining for a mitochondrial marker (isocitrate dehydrogenase) was performed. Because greater staining was observed in the surface compartment, we predict that these cells use significantly more energy than SMG cells. This study illustrates the power of LCM in defining the roles of specific anatomic features in airway biology and may be useful in examining how disease states alter transcriptional programs in the conducting airways.

Examination of Glucocorticoid Receptor α-Mediated Transcriptional Regulation of P-glycoprotein, CYP3A4, and CYP2C9 Genes in Placental Trophoblast Cell Lines

The placental trophoblast at different stages of pregnancy contains some drug transporters and xenobiotic-metabolising enzymes, as well as ligand-activated nuclear receptors, which control their inducible transcriptional regulation. Glucocorticoid receptor alpha (GRalpha) is expressed in both placental syncytiotrophoblast and cytotrophoblast. GRalpha was shown to control inducible expression of several enzymes of the cytochrome P-450 family (CYP) and the drug transporter P-glycoprotein in the liver. However, GRalpha-mediated transcriptional regulation of drug transporters and CYPs has not been studied in the placental trophoblast. In this study, we examined the expression and activity of GRalpha in the transcriptional regulation of P-glycoprotein, CYP3A4, and CYP2C9 in placental trophoblast cell lines. Employing RT-PCR, Western blotting, and luciferase gene reporter assay, we detected the expression and activity of GRalpha in JEG3 and BeWo cell lines. However, we observed that only MDR1 mRNA was up-regulated after treatment of placental cells with dexamethasone. Accordingly, only the promoter of the MDR1 gene was activated by dexamethasone in gene reporter assays in placental cells and the activation was abolished by RU486, an antagonist of GRalpha. CYP3A4 and CYP2C9 promoters were activated in placental cells only after co-transfection with hepatocyte nuclear factor 4alpha (HNF4alpha), which indicates the hepatocyte-specific character of GRalpha-mediated regulation of the genes. On the other hand, coexpression of HNF4alpha had no effect on the activation of the MDR1 gene promoter, suggesting HNF4alpha-independent regulation via GRalpha. We conclude that GRalpha may be involved in the transcriptional regulation of P-glycoprotein in the placental trophoblast. We also indicate that the CYP3A4 and CYP2C9 genes are not inducible through GRalpha in placental cell lines, due to the lack of HNF4alpha expression and possibly some additional hepatocyte-specific transcriptional factors.

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.

Environmental tobacco smoke and sudden infant death syndrome: a review

Environmental tobacco smoke (ETS), containing the developmental neurotoxicant, nicotine, is a prevalent component of indoor air pollution. Despite a strong association with active maternal smoking and sudden infant death syndrome (SIDS), information on the risk of SIDS due to prenatal and postnatal ETS exposure is relatively inconsistent. This literature review begins with a discussion and critique of existing epidemiologic data pertaining to ETS and SIDS. It then explores the biologic plausibility of this association, with comparison of the known association between active maternal smoking and SIDS, by examining metabolic and placental transfer issues associated with nicotine, and the biologic responses and mechanisms that may follow exposure to nicotine. Evidence indicates that prenatal and postnatal exposures to nicotine do occur from ETS exposure, but that the level of exposure is often substantially less than levels induced by active maternal smoking. Nicotine also has the capacity to concentrate in the fetus, regardless of exposure source. Experimental animal studies show that various doses of nicotine are capable of affecting a neonate's response to hypoxic conditions, a process thought to be related to SIDS outcomes. Mechanisms contributing to deficient hypoxia response include the ability of nicotine to act as a cholinergic stimulant through nicotinic acetylcholine receptor (nAChR) binding. The need for future research to investigate nicotine exposure and effects from non-maternal tobacco smoke sources in mid to late gestation is emphasized, along with a need to discourage smoking around both pregnant women and infants.

Species differences between mouse, rat, dog, monkey and human CYP-mediated drug metabolism, inhibition and induction

Animal models are commonly used in the preclinical development of new drugs to predict the metabolic behaviour of new compounds in humans. It is, however, important to realise that humans differ from animals with regards to isoform composition, expression and catalytic activities of drug-metabolising enzymes. In this review the authors describe similarities and differences in this respect among the different species, including man. This may be helpful for drug researchers to choose the most relevant animal species in which the metabolism of a compound can be studied for extrapolating the results to humans. The authors focus on CYPs, which are the main enzymes involved in numerous oxidative reactions and often play a critical role in the metabolism and pharmacokinetics of xenobiotics. In addition, induction and inhibition of CYPs are compared among species. The authors conclude that CYP2E1 shows no large differences between species, and extrapolation between species appears to hold quite well. In contrast, the species-specific isoforms of CYP1A, -2C, -2D and -3A show appreciable interspecies differences in terms of catalytic activity and some caution should be applied when extrapolating metabolism data from animal models to humans.

Metabolic and genetic factors contributing to alcohol induced effects and fetal alcohol syndrome

Alcohol-related damages on newborns and infants include a wide variety of complications from facial anomalies to neurodevelopmental delay, known as fetal alcohol syndrome (FAS). However, only less than 10% of women drinking alcohol during pregnancy have children with FAS. Understanding the risk factors increasing the probability for newborn exposed in utero to alcohol to develop FAS is therefore a key issue. The involvement of genetics as a one risk factor in FAS has been suggested by animal models and by molecular epidemiological studies on different populations, bearing allelic variants for those enzymes, such as ADH e CYP2E1, involved in ethanol metabolism. Indeed, one of the major factors determining the peak blood alcohol exposure to the fetus is the metabolic activity of the mother, in addition to placental and fetal metabolism, explaining, at least partially, the risk of FAS. The different rates of ethanol metabolism may be the result of genetic polymorphisms, the most relevant of which have been described in the paper.

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.

Regulation of Gender-Dependent CYP2A Expression in Pigs: Involvement of Androgens and CAR

The expression of drug metabolizing cytochrome P4502A (CYP2A) is highly gender-dependent in minipigs with the highest activity in females. In other species, orthologs of CYP2A have been shown to be under the regulation of nuclear receptor constitutive androstane receptor, whereas little is known about regulation in pigs. To investigate the effect of sex hormones on porcine cytochrome P450 CYP2A and CYP3A expression was assessed in liver samples taken before and after castration of sexually mature minipig boars. Removal of the primary androgen source resulted in significant increases of CYP2A mRNA, protein and enzyme activity levels. Likewise, expression of CYP3A was increased, although to a lesser extent. To examine the involvement of constitutive androstane receptor in the regulation of CYP2A, primary porcine hepatocytes were exposed to modulators of murine constitutive androstane receptor and human constitutive androstane receptor activity. The CYP2A activity was significantly increased by exposure to phenobarbital, an indirect activator of constitutive androstane receptor, and the human constitutive androstane receptor-ligand CITCO. In contrast, no effect was seen following exposure to the potent murine constitutive androstane receptor-ligand TCPOBOP and the hormonal murine constitutive androstane receptor-ligands androstenol and oestrone. Thus, the results support that 1) porcine CYP2A is reversibly inhibited by androgens on a transcriptional basis in vivo; 2) the induction profile of CYP2A in vitro shares similarity with that of human constitutive androstane receptor-regulated CYPs, indicating an involvement of a porcine constitutive androstane receptor in the regulation of CYP2A.

Pregnancy-induced changes in pharmacokinetics: a mechanistic-based approach

Observational studies have documented that women take a variety of medications during pregnancy. It is well known that pregnancy can induce changes in the plasma concentrations of some drugs. The use of mechanistic-based approaches to drug interactions has significantly increased our ability to predict clinically significant drug interactions and improve clinical care. This same method can also be used to improve our understanding regarding the effect of pregnancy on pharmacokinetics of drugs. Limited studies suggest bioavailability of drugs is not altered during pregnancy. Increased plasma volume and protein binding changes can alter the apparent volume of distribution (Vd) of drugs. Through changes in Vd and clearance, pregnancy can cause increases or decreases in the terminal elimination half-life of drugs. Depending on whether a drug is excreted unchanged by the kidneys or which metabolic isoenzyme is involved in the metabolism of a drug can determine whether or not a change in dosage is needed during pregnancy. The renal excretion of unchanged drugs is increased during pregnancy. The metabolism of drugs catalysed by select cytochrome P450 (CYP) isoenzymes (i.e. CYP3A4, CYP2D6 and CYP2C9) and uridine diphosphate glucuronosyltransferase (UGT) isoenzymes (i.e. UGT1A4 and UGT2B7) are increased during pregnancy. Dosages of drugs predominantly metabolised by these isoenzymes or excreted by the kidneys unchanged may need to be increased during pregnancy in order to avoid loss of efficacy. In contrast, CYP1A2 and CYP2C19 activity is decreased during pregnancy, suggesting that dosage reductions may be needed to minimise potential toxicity of their substrates. There are limitations to the available data. This analysis is based primarily on observational studies, many including small numbers of women. For some isoenzymes, the effect of pregnancy on only one drug has been evaluated. The full-time course of pharmacokinetic changes during pregnancy is often not studied. The effect of pregnancy on transport proteins is unknown. Drugs eliminated by non-CYP or non-UGT pathways or multiple pathways will need to be evaluated individually. In conclusion, by evaluating the pharmacokinetic data of a variety of drugs during pregnancy and using a mechanistic-based approach, we can start to predict the effect of pregnancy for a large number of clinically used drugs. However, because of the limitations, more clinical, evidence-based studies are needed to fully elucidate the effects of pregnancy on the pharmacokinetics of drugs.

Tumor-selective drug activation: a GDEPT approach utilizing cytochrome P450 1A1 and AQ4N

Drug metabolizing transgene products, which activate bioreductive cytotoxins, can be used to target treatment-resistant hypoxic tumors. The prodrug AQ4N is bioreduced in hypoxic cells by cytochrome P450s (CYPs) to the cytotoxin AQ4. Previously we have shown that intra-tumoral injection of CYP3A4 and CYP2B6 transgenes with AQ4N and radiation inhibits tumor growth. Here we examine the ability of other CYPs, in particular CYP1A1, to metabolize AQ4N, and to enhance radiosensitization. Metabolism of AQ4N was assessed using microsomes prepared from baculovirus-infected cells transfected with various CYP isoforms. AQ4N metabolism was most efficient with CYP1A1 (66.7 nmol/min/pmol) and 2B6 (34.4 nmol/min/pmol). Transient transfection of human CYP1A1+/-CYP reductase (CYPRED) was investigated in hypoxic RIF-1 mouse cells in vitro using the alkaline comet assay. There was a significant increase in DNA damage following transient transfection of CYP1A1 compared to non-transfected cells; inclusion of CYPRED provided no additional effect. In vivo, a single intra-tumoral injection of a CYP1A1 construct in combination with AQ4N (100 mg/kg i.p.) and 20 Gy X-rays caused a 16-day delay in tumor regrowth compared to tumors receiving AQ4N plus radiation and empty vector (P=0.0344). The results show the efficacy of a CYP1A1-mediated GDEPT strategy for bioreduction of AQ4N.

Differential accumulation of low-chlorinated (Delor 103) and high-chlorinated (Delor 106) biphenyls in human placental tissue and opposite effects on conversion of DHEA to E2

OBJECTIVE

Polychlorinated biphenyls (PCBs) and related compounds elicit a diverse spectrum of toxic responses. Additionally, they are able to pass through the human placenta. The aim of the presented data was to compare the action of low-chlorinated (Delor 103) and (Delor 106) high-chlorinated biphenyls on placental steroidogenesis.

METHODS

Explants of human placental tissue were used to test differences in PCBs accumulation and influence on placental steroidogenesis. Delor 103 or 106, were added daily for six days at a dose of 200 pg from day 0 to day 6 of culture. The media in the control and experimental groups were changed every day, and collected and frozen for steroid analysis by RIA. Determinations of PCBs of tissue and medium were analysed by GC/MS/MS.

RESULTS

Delor 103 was found at a higher level in the tissue than Delor 106. The first day of exposure to Delor 103 had no effect on the conversion of dehydroepiandrosterone (DHEA) to estradiol (E2) while there was a 2-fold decrease in E2 secretion from days 3 to 6. Conversely, Delor 106 caused an immediate increase in E2 secretion, which was maintained at higher levels throughout the exposure period.

CONCLUSION

Differences between the accumulation of lower chlorinated and higher chlorinated biphenyls in human placental tissue and in the properties of the congeners can have multiple effects that may intensify or counteract the effects on uterine contraction by PCBs.

Human placenta: a human organ for developmental toxicology research and biomonitoring

Pregnant mothers are exposed to a wide variety of foreign chemicals. This exposure is most commonly due to maternal medication, lifestyle factors, such as smoking, drug abuse, and alcohol consumption, or occupational and environmental sources. Foreign compounds may interfere with placental functions at many levels e.g. signaling, production and release of hormones and enzymes, transport of nutrients and waste products, implantation, cellular growth and maturation, and finally, at the terminal phase of placental life, i.e. delivery. Placental responses may also be due to pharmaco-/toxicodynamic responses to foreign chemicals, e.g. hypoxia. On the other hand, placental xenobiotic-metabolizing enzymes can detoxify or activate foreign chemicals, and transporters either enhance or prevent cellular accumulation and transfer across the placenta. The understanding of what xenobiotics do to the placenta and what the placenta does to the xenobiotics should provide the basis for the use of placenta as a tool to investigate and predict some aspects of developmental toxicity. This review aims to give an update of the fate and behavior of xenobiotics in the placenta from the viewpoint of xenobiotic-metabolizing enzymes and transporters. Their response levels will be described according to gestational status and methods used. The effects of foreign chemicals on placental metabolizing enzymes will be discussed. Also, interactions in the transporter protein level will be covered. The role of the placenta in contributing to developmental effects and fetotoxicity will be examined. The toxicological effects of maternal medications, smoking, and environmental exposures (dioxins, pesticides) as well as some possibilities for biomonitoring will be highlighted.

Lipopolysaccharide treatment downregulates the expression of the pregnane X receptor, cyp3a11 and mdr1a genes in mouse placenta

The cytochrome P450 3A (CYP3A) is a member of the cytochrome P450 monooxygenase superfamily. The multidrug resistance 1 (MDR1) gene belongs to the ATP-binding cassette (ABC) family. Pregnane X receptor (PXR) is a nuclear receptor that regulates its target gene transcription in a ligand-dependent manner. Lipopolysaccharide (LPS)-induced downregulation of PXR, CYP3A and MDR1 in liver has been demonstrated in a series of studies. However, it is not clear whether LPS represses the expression of PXR, CYP3A and MDR1 in placenta. In the present study, we investigated the effects of LPS on the expression of PXR, cyp3a11 and mdr1a in mouse placenta. Pregnant ICR mice were injected intraperitoneally with different doses of LPS (0.1-0.5 mg/kg) on gestational day (gd) 17. Placental PXR, cyp3a11 and mdr1a mRNA levels were determined at 12 h after LPS treatment using RT-PCR. Results showed that LPS significantly downregulated PXR, cyp3a11 and mdr1a mRNA levels in a dose-dependent manner. LPS-induced downregulation of PXR, cyp3a11 and mdr1a mRNA in placenta was significantly attenuated after pregnant mice were pre- and post-treated with alpha-phenyl-N-t-butylnitrone (PBN), a free radical spin trapping agent. Additional experiments revealed that LPS increased lipid peroxidation and proinflammatory cytokine expressions in mouse placenta, all of which were also attenuated by PBN. Furthermore, LPS-induced downregulation of PXR, cyp3a11 and mdr1a mRNA in mouse placenta was prevented by N-acetylcysteine (NAC). NAC also inhibited LPS-initiated lipid peroxidation, GSH depletion and proinflammatory cytokine expressions in mouse placenta. These results indicated that LPS downregulates placental PXR, cyp3a11 and mdr1a mRNA expressions. Reactive oxygen species (ROS) may be involved in LPS-induced downregulation of PXR, cyp3a11 and mdr1a in mouse placenta.

Induction of fibroblast growth factor-9 and interleukin-1alpha gene expression by motorcycle exhaust particulate extracts and benzo(a)pyrene in human lung adenocarcinoma cells

Motorcycle exhaust particulates (MEP) contain carcinogenic polycyclic aromatic hydrocarbons including benzo(a)pyrene. This study has determined the ability of MEP to alter the expression of select genes from drug metabolism, cytokine, oncogene, tumor suppressor, and estrogen signaling families of human lung adenocarcinoma CL5 cells. cDNA microarray analyses and confirmation studies were performed using CL5 cells treated with 100 microg/ml MEP extract for 6 h. The results showed that MEP increased the mRNA levels of metabolic enzymes CYP1A1 and CYP1B1, proinflammatory cytokines interleukin (IL)-1alpha, IL-6, and IL-11, fibroblast growth factor (FGF)-6 and FGF-9, vascular endothelial growth factor (VEGF)-D, oncogene fra-1, and tumor suppressor p21. In contrast, MEP decreased tumor suppressor Rb mRNA in CL5 lung epithelial cells. Treatment with 10 microM benzo(a)pyrene for 6 h altered gene expression profiles, in a manner similar to those by MEP. Induction of IL-1alpha, IL-6, IL-11, and FGF-9 mRNA by MEP and benzo(a)pyrene was concentration and time dependent. Cotreatment with 2 mM N-acetylcysteine blocked the MEP- and benzo(a)pyrene-mediated induction. Treatment with MEP or benzo(a)pyrene increased IL-6 and IL-11 releases to CL5 cell medium. Incubation of human lung fibroblast WI-38 with MEP- or benzo(a)pyrene-induced CL5 conditioned medium for 4 days stimulated cell growth of the fibroblasts. Inhalation exposure of rats to 1:10 diluted motorcycle exhaust 2 h daily for 4 weeks increased CYP1A1, FGF-9, and IL-1alpha mRNA in lung. This present study shows that MEP and benzo(a)pyrene can induce metabolic enzyme, inflammatory cytokine, and growth factor gene expression in CL5 cells and stimulate lung epithelium-fibroblast interaction.

Induction of cytochrome P450 isozymes by phenobarbital in pregnant rat and fetal livers and placenta

Cytochrome P450 (CYP) isozymes are important in metabolizing xenobiotics. They are found in extrahepatic tissues such as placenta as well as liver. Previously, we reported that CYP3A1 was detected in the cytoplasm of giant cells in the trophoblastic region of placenta of rats through pregnancy. In this study, we examined the changes in the expression of CYP proteins in the pregnant rat and fetal livers and placenta after treatment with phenobarbital (PB), one of the antiepileptic drugs which is well known to induce several phase I and phase II drug metabolizing enzymes in the liver. Namely, F344 pregnant rats were treated with PB (80 mg/kg, i.p.) from 13 days of gestation (DG) to 16 DG. All animals were sacrificed on 17 DG, and Western blot analysis and immunohistochemical staining on nine CYP proteins (CYP1A1, CYP2B1, CYP2C6, CYP2C12, CYP2D1, CYP2D4, CYP2E1, CYP3A1, and CYP4A1) and histological examination were done in the dam's liver, placenta, and the fetal liver. Western blot analysis revealed that CYP3A1 protein was significantly induced, CYP2B1 protein was detected, and CYP2D1 protein was significantly decreased in the dam's liver after PB-treatment. In placenta, only CYP3A1 was detected with no difference between control and PB-treated animals. The results of immunohistochemical staining corresponded closely to those of Western blot analysis in the dam's liver and placenta. In the fetal liver, CYP3A1 and CYP2C6 proteins were significantly induced after the PB-treatment, but their immunostainability was not prominent. The present results are considered useful as a basis for further investigation of drug metabolism in pregnant animals.

Expression of CYP4A isoforms in developing rat placental tissue and rat trophoblastic cell models

Maintaining fatty acid homeostasis during pregnancy is critical for normal fetal development. As an organ that controls nutrient supply from the mother to the fetus, the placenta plays a significant role in guiding fatty acid transfer to the developing fetus. The cytochrome P450 4A (CYP4A) subfamily of metabolizing enzymes is a group of structurally and functionally conserved proteins that are specialized in the omega/omega-1 hydroxylation of saturated and unsaturated fatty acids and their derivatives. To understand the function of the CYP4A system in the placenta and its significance in maintaining fetal fatty acid homeostasis, information about the placental expression of individual CYP4A isoforms is required. In the present study, we have elucidated the temporal and spatial patterns of expression of the four known rat CYP4A isoforms (CYP4A1, CYP4A2, CYP4A3, and CYP4A8) in the junctional and labyrinthine zones of the developing rat chorioallantoic placenta as well as two rat trophoblastic cell lines, HRP-1 and Rcho-1, using semi-quantitative RT-PCR and immunohistochemical analyses. The mRNA from the four rat CYP4A isoforms was detected in the developing rat placenta with CYP4A1 exhibiting the strongest expression (4A1 > 4A2 >> 4A3 approximately equal to 4A8). CYP4A1 was also detected by immunohistochemical staining in the developing rat placenta. We also observed CYP4A1 in both HRP-1 and Rcho-1 cells by RT-PCR, suggesting the utility of these cells as in vitro tools to study the effects of xenobiotics on placental fatty acid metabolism. Establishing the expression of CYP4A isoforms in these tissues and cell models provides a framework for further investigation of their functional and physiological significance in guiding proper fetal development.

Regulation of theCyp2a5Gene Involves an Aryl Hydrocarbon Receptor-Dependent Pathway

We have investigated the role of the aryl hydrocarbon receptor (AHR) in the regulation of the Cyp2a5 gene. The C57BL/6 and DBA/2 mouse strains with a genetically determined difference in AHR function were used to study the CYP2A5 induction by typical AHR ligands, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene. The CYP2A5 mRNA up-regulation in these mouse strains showed a difference in response, typical for AHR-regulated genes, both by TCDD in cultured primary hepatocytes and by 3-methylcholanthrene in vivo. In primary hepatocytes, TCDD caused a 3-fold elevation of the CYP2A5 protein level and a similar induction of the CYP2A5-catalyzed coumarin 7-hydroxylation activity. In reporter gene assays, the Cyp2a5 promoter region -3033 to +10 mediated a 2- to 5-fold induction of luciferase activity by TCDD treatment in primary hepatocytes and in Hepa-1 hepatoma cells with an intact AHR/AHR nuclear translocator (ARNT) complex. In Hepa-1 variant cell lines with deficiencies in the AHR/ARNT complex, the absence of ARNT abolished the induction. A putative AHR response element (XRE) was identified in the Cyp2a5 promoter at the position -2514 to -2492 and found to interact with the AHR/ARNT heterodimer. Transfection experiments combined with mutation of the XRE site indicated that the site partly mediates the TCDD induction of Cyp2a5. An additional AHR-dependent mechanism also regulates the proximal promoter of the Cyp2a5 gene. In conclusion, our studies showed that AHR ligands up-regulate Cyp2a5 transcriptionally by an AHR/ARNT-dependent mechanism and established Cyp2a5 as a novel AHR-regulated gene.

Cytochrome P450 expression and activities in human tongue cells and their modulation by green tea extract

The expression, inducibility, and activities of several cytochrome P450 (CYP) enzymes were investigated in a human tongue carcinoma cell model, CAL 27, and compared with the human liver model HepG2 cells. The modulation effects of green tea on various CYP isoforms in both cell lines were also examined. RT-PCR analysis of CAL 27 cells demonstrated constitutive expression of mRNA for CYPs 1A1, 1A2, 2C, 2E1, 2D6, and 4F3. The results were negative for CYP2A6, 2B6/7, 3A3/4, and 3A7. Both cell lines displayed identical expression and induction profiles for all of the isoforms examined in this study except 3A7 and 2B6/7, which were produced constitutively in HepG2 but not Cal-27 cells. CYP1A1 and 1A2 were both induced by treatment with beta-napthoflavone as indicated by RT-PCR and Western blotting, while CYP2C mRNA was upregulated by all-trans retinoic acid and farnesol. RT-PCR and Western blot analysis showed that the expressions of CYP1A1 and 1A2 were induced by green tea extract (GTE), which also caused an increase in mRNA for CYP2E1, CYP2D6, and CYP2C isoforms. The four tea catechins, EGC, EC, EGCG and ECG, applied to either HepG2 or Cal-27 cells at the concentration found in GTE failed to induce CYP1A1 or CYP1A2, as determined by RT-PCR. Of the isoforms that were apparently induced by GTE, only 7-ethoxycoumarin deethylase (ECOD) activity could be detected in CAL 27 or HepG2 cells. Interestingly, mRNA and protein for CYP1A1 and CYP1A2 were detected in both cell lines, and although protein and mRNA levels of CYP1A1 and CYP1A2 were increased by GTE, the observed ECOD activity in both cell lines was decreased.

Tobacco smoke-dependent changes in cytochrome P450 1A1, 1A2, and 2E1 protein expressions in fetuses, newborns, pregnant rats, and human placenta

Tobacco smoke (TS) was described as a mixture of numerous cytochrome P450 (P450) substrates, inducers, and inhibitors. These inducers and inhibitors may modify drug clearance and xenobiotic or endogenous metabolism affecting P450s expression. In the present study, the effect of gestation and TS on: (1) cytochrome P450 CYP1A1, CYP1A2, and CYP2E1 protein expressions, and (2) cytochrome P450-linked microsomal enzyme activities, were studied in fetal rat liver, rat, and human placenta and in newborn and adult rat hepatic and extrahepatic tissues. Non-pregnant and pregnant 4-month-old female Wistar rats were exposed to TS (500, 1,000, or 1,500 mg carbon monoxide per m(3) air) in a toxicological chamber for 3 weeks (6 h daily, 5 days weekly). Human placentas were sampled from non-smoking, passive smoking, or active smoking primiparas. The efficacy of exposure was assessed by measuring urine cotinine levels. The TS-dependent inductory effect on the expression of CYP1A1 and 1A2 and related monooxygenase activities, and the inhibitory/inductory effect on CYP2E1 expression in rat tissues were observed. Pregnancy was associated with decreased levels of constitutive CYP1A1 and 2E1 in hepatic and extrahepatic tissues, TS-inducible CYP1A2 expression in the liver, and CYP1A1 expression in lungs and heart, but had no inhibitory effect on TS-inducible CYP1A1 and 2E1 expression, EROD, and P450-cooperated enzyme activities in the liver, kidney, and, in the latter case, in the heart. The presence of TS-induced CYP1A1 protein was confirmed in rat and human placenta and showed in newborn liver and lungs. CYP1A2 and 2E1 proteins were detectable in fetal rat liver. It was concluded that the expression of CYP1A1, 1A2, and 2E1, which metabolize some drugs and activate carcinogens, is controlled by age-, pregnancy-, and tissue-specific regulatory mechanisms in rats. Gestational differences in the regulation of expression of CYP1A subfamily members are not excluded. CYP1A1 and 2E1, but not CYP1A2 inductory mechanisms seem to be functional in fetal liver at day 21 of pregnancy but they appeared to be uninducible under a TS exposure. In TS-exposed pregnant females and fetuses the effects of metabolic activation of CYP1A1 and 1A2 substrates might be reduced because of lower CYP expressions or poor induction, respectively.

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.

Expression of CYP4F12 in Gastrointestinal and Urogenital Epithelia*

Cytochrome P450 4F12 (CYP4F12) was originally cloned from human liver and small intestine. CYP4F12 can oxidize arachidonic acid, two stable prostaglandin H2 analogues, and an antihistamine, ebastine, but the tissue distribution and catalytic properties of CYP4F12 have not been fully investigated. An antipeptide polyclonal antibody was raised against the C-terminal of CYP4F12 (PLNVGLQ), evaluated by Western blot analysis and used for immunohistological analysis of 50 human tissues. Western blot analysis of recombinant CYP4F12, expressed in yeast, and microsomal proteins from adult and foetal liver, kidney, placenta at term, seminal vesicles, the prostate gland and purified prostasomes showed that the polyclonal antibody detected a protein of the expected size, approximately 60 kDa. CYP4F12 mRNA could be detected in seminal vesicles and prostate gland by reverse transcription-PCR. Prominent CYP4F12 immunoreactivity occurred, inter alia, in the epithelial cells of the gastrointestinal tract (stomach, small intestine, and colon), collecting tubules, transitional epithelium, ovarian follicles, the endothelium of microvessels of placental villi (first trimester), and epidermis. We screened recombinant CYP4F12 for catalytic activity. Arachidonic acid (20:4n-6) was hydroxylated at C18 and laurate at C11, but significant amounts of metabolites of 18:2n-6, 20:3n-9, 20:5n-3, 22:5n-6, and some prostaglandins could not be detected. We conclude that CYP4F12 is widely distributed in gastrointestinal and urogenital epithelia and exhibits a narrow substrate specificity.

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.

Aromatase is the major enzyme metabolizing buprenorphine in human placenta

Buprenorphine (BUP) is a partial opiate agonist used for treatment of the adult and the pregnant addicted to this class of narcotics. The kinetic parameters for transplacental transfer and the metabolism of BUP during its perfusion in a placental lobule were the subject of an earlier report from our laboratory. The aim of this investigation is to identify and characterize the enzyme catalyzing the metabolism of BUP in term human placenta. Norbuprenorphine (norBUP) is the only metabolite formed as determined by high performance liquid chromatography and mass spectrometry. The activity of the enzyme responsible for BUP metabolism is highest in the microsomal fraction and lowest in the cytosolic, with the mitochondrial in between. Compounds with selective affinity to the enzyme aromatase (CYP 19), namely 4-hydroxyandrostenedione and aminoglutethimide, caused >70% inhibition of norBUP formation. Monoclonal antibodies raised against CYP 19 were the most potent inhibitors of BUP dealkylation. A comparison between the data obtained from the saturation isotherm for BUP dealkylation by placental microsomes and a commercially available system of cDNA-expressed CYP 19 indicated similar kinetic parameters, with apparent Km values of 12 +/- 4.0 and 14 +/- 8.0 microM, respectively. Therefore, aromatase is the major enzyme catalyzing the biotransformation of BUP to norBUP in term human placentas obtained from healthy pregnancies. The minor involvement of other cytochrome P450 isoforms or enzyme(s) in the metabolism of BUP in placental tissue cannot be ruled out.

Tissue distribution of mRNA expression of human cytochrome P450 isoforms assessed by high-sensitivity real-time reverse transcription PCR

Pairs of forward and reverse primers and TaqMan probes specific to each human cytochrome P450 isoform were prepared. Analysis of the mRNA level of each CYP isoform in total RNA from pooled specimens of various human organs was performed by real-time reverse transcription PCR using an ABI PRISM 7700 sequence detector system. The expression of CYP3A4 mRNA was similar to that of CYP3A7 mRNA in the fetal liver, and CYP3A4 mRNA levels in the fetal liver were about 0.1 times lower than in the adult liver. CYP2E1 showed the highest level of mRNA expression in the liver. The mRNA expression of 30 CYP isoforms (CYP1A1, 1A2, 1B1, 2A6, 2A7, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2J2, 3A4, 3A5, 3A7, 4A11, 4F2, 4F3, 5A1, 7B1, 8A1, 8B1, 17, 26A1, 27, 27B1, 39A1, 46, and 51) in the liver was successfully detected by this method. CYP2F1, 4B1, 4F8, 11s (11A, 11B1, and 11B2), 19, and 24 mRNA levels were the highest in the lung, lung, prostate, adrenal gland, placenta, and kidney, respectively; however, the mRNA expression of these eight CYP isoforms in the liver was not detected by this method. The mRNA levels of the CYP isoforms determined in various human tissues were in good agreement with previously reported data. The method described here has the advantages of high specificity and excellent quantification over a wide range of mRNA concentrations, making it suitable for the evaluation of a large number of samples in the assessment of the expression profile of drug-metabolizing enzymes.

The aryl hydrocarbon receptor and its xenobiotic ligands: a fundamental trigger for cardiovascular diseases

This review reconsiders a major cause of cardiovascular diseases, tobacco smoking, as the activation of the Aryl hydrocarbon Receptor (AhR), also known as the dioxin receptor, by aryl hydrocarbons from the tar fraction of tobacco in various organs of the cardiovascular domain. This concept sheds new light on well-known albeit controversial epidemiological concepts such as the Mediterranean diet and the French paradox. We also review the discovery that resveratrol, a natural AhR antagonist, may be of interest in the prevention and treatment of cardiovascular diseases.

Thalidomide-induced suppression of embryo fibroblast proliferation requires CYP1A1-mediated activation

An enzyme involved in the metabolic activation of thalidomide has been investigated using embryo fibroblast proliferation as a marker. Thalidomide (30 microM) induced-suppression of embryo fibroblast proliferation was detected in the presence of liver microsomes from rabbit but not from mouse. The addition of a selective inhibitor of CYP1A, alpha-naphthoflavone (4 microM), or furafylline (4 microM), to the incubation mixture abolished the thalidomide-induced suppression. Furthermore, addition of anti-rat CYP1A1 antibody also resulted in inhibition of suppression. The thalidomide-induced suppression was also observed with the microsomal system from human HepG2 cells pretreated with 3-methylcholanthrene (10 microM) but not from those pretreated with the vehicle. Both CYP1A1 and CYP1A2 proteins were detected in the rabbit liver microsomes by immunoblot analyses, but only CYP1A2 protein was detected in the mouse liver microsomes. In addition, CYP1A1 protein was detected in microsomes from HepG2 cells pretreated with 3-methylcholanthrene but not with the vehicle. These results strongly suggest the involvement of CYP1A1 in the thalidomide-induced suppression of embryo fibroblast proliferation.

The presence of inducible cytochrome P450 types 1A1 and 1A2 in the BeWo cell line

The activity and inducibility of cytochrome P450 systems (CYP1A1:1A2) of the human placenta were assessed in a representative human trophoblast-like cell line, BeWo. The activity of CYP1A1 and CYP1A2 in microsome preparations from human liver, placenta, primary cultures of human cytotrophoblast, and BeWo cells was measured by O -dealkylation of 7-ethoxyresorufin (EROD) and 7-methoxyresorufin O -demethylation (MROD), respectively. Results indicated high EROD and MROD activity associated with human liver microsomes, sometimes comparable activities in human placenta microsomes prepared from smokers, and relatively low activities in human placenta microsomes from nonsmokers and in the primary cultures of cytotrophoblasts isolated from nonsmokers. Microsomes from BeWo cell monolayers exhibited the lowest EROD and MROD activities relative to all other microsome preparations. However, compared to primary cultures of normal trophoblasts, the EROD activity of the BeWo cells was far more sensitive to typical inducers, 3-methylcholanthrene, 1,2-benzanthracene, and beta-naphthoflavone. EROD activity in BeWo cells was induced approximately 200-fold by 3-methylcholanthrene. Both EROD and MROD activity in BeWo cells was readily induced by 1,2-benzanthracene, 100-fold and 60-fold, respectively. After induction with 1,2-benzanthracene, the CYP1A1 selective inhibitor, alpha-naphthoflavone, and the CYP1A2 selective inhibitor, furafylline, effectively inhibited enzyme activities with IC(50)s of 2.4 microM and 12.8 microM, respectively, in microsomes from both trophoblasts culture systems. These results show that major cytochrome P450 forms present in human placenta are present and inducible in BeWo cells, a potential model for investigation of drug metabolism mechanisms in the human trophoblast.

The pattern of xenobiotic-metabolizing enzymes in the human pancreas

Our previous study on phase II detoxifying enzymes, showing a significant reduction of glutathione S-transferase-pi in chronic pancreatitis compared to the normal pancreas, indicated that xenobiotic-metabolizing enzymes are involved in the pathogenesis of pancreatic diseases. This study presents an overall look at the distribution of the phase I xenobiotic-metabolizing enzymes, which are responsible for the metabolism of many common environmental toxins and carcinogens, in the normal pancreas. Twenty-four normal pancreases from 7 donors and 17 early autopsy cases, as well as cultured human islet cells, were analyzed by immunohistochemistry, Western blot analysis, and/or reverse-transcription polymerase chain reaction (RT-PCR) for the expression of nine cytochrome P-450 mono-oxygenases (CYP) and the NADPH cytochrome P-450 oxidoreductase. Remarkable differences in the cellular distribution of these enzymes were found between the individuals and between different pancreatic cells within the same individual. Nondiabetics expressed more of the enzymes than diabetics, females more than males, younger more than older individuals, and organ donors (all young individuals) more than autopsy specimens. CYP 2B6 was expressed in all 7 donor pancreas, compared to 8 of 17 autopsy cases. Most of the enzymes were localized in islet cells and either were distributed in all islet cells or were restricted to, or expressed in a higher concentration in, glucagon and/or pancreatic polypeptide cells. Furthermore, a different cellular localization of the enzymes was found in some individuals (e.g., cytoplasmic vs. Golgi pattern of staining and a frequent nuclear localization of CYP 2E1 in females). Except for anti-CYP 1A2 and 3A4, RT-PCR and Western blot analyses validated the specificity of the antibodies. Our results show that islet cells play a major role in the detoxification process of the pancreas. The expression of individual enzymes and their distribution in acinar, ductal, and islet cells may determine individual susceptibility to pancreatic diseases.

Assessing pregnancy risks of azole antifungals using a high throughput aromatase inhibition assay

Human aromatase (CYP19) converts C19 androgens to aromatic C18 estrogenic steroids. Its activity is critical for early and mid pregnancy maintenance and in regulating parturition in late pregnancy. Past studies have utilized placental microsome tritiated water release assay to assess drug-hormone interactions with estrogen synthesis. We compared data from human placental assays with BD Gentest's high throughput recombinant CYP19 enzyme assay using the fluorometric substrate dibenzylfluorescein. We tested a panel of azole antifungal agents that are commonly administered to women of childbearing potential, for their potential to inhibit aromatase. Potency varied by several orders of magnitude. Plasma and tissue levels of some azole drugs following oral or topical administration are at or above these IC50 values. These include the oral agents fluconazole and ketoconazole, and the topical agents econazole, bifonazole, clotrimazole, miconazole, and sulconazole.

CONCLUSIONS

1. Recombinant enzyme assay data are comparable to the human placental assay data in both SAR rank order and potency. 2. Plasma and tissue levels of some azole drugs following oral or topical administration are at or above these IC50 values. Therefore, some azole drugs may disrupt estrogen production in pregnancy, affecting pregnancy outcome. 3. Recombinant CYP19 assay using the fluorometric substrate dibenzylfluorescein, demonstrates rapid screening potential for chemicals that may affect pregnancy outcome as a result of CYP19 inhibition.

4-Hydroxylation of debrisoquine by human CYP1A1 and its inhibition by quinidine and quinine

A panel of 15 recombinant cytochromes P450 expressed in human B-lymphoblastoid cells was used to study debrisoquine 4-hydroxylation. Both CYP2D6 and CYP1A1 carried out the reaction. The apparent K(m) (micromolar) and V(max) (picomoles per minute per picomole of P450) for CYP2D6 were 12.1 and 18.2 and for CYP1A1 were 23.1 and 15.2, respectively. CYP1A1 debrisoquine 4-hydroxylase was inhibited by the CYP1A1 inhibitor alpha-naphthoflavone and the CYP1A1 substrate 7-ethoxyresorufin. Additionally and surprisingly, this reaction was also inhibited by quinidine and quinine, with respective IC(50) values of 1.38 +/- 0.10 and 3.31 +/- 0.14 microM, compared with those for CYP2D6 debrisoquine 4-hydroxylase of 0.018 +/- 0.05 and 3.75 +/- 2.07 microM, respectively. Anti-CYP1A1 monoclonal antibody (mAb) 1-7-1 abolished CYP1A1 debrisoquine hydroxylase and anti-CYP2D6 mAb 50-1-3 eradicated CYP2D6 debrisoquine 4-hydroxylase. Three further CYP2D6-specific reactions were tested: dextromethorphan O-demethylation, bufuralol 1'-hydroxylation, and sparteine dehydrogenation. The CYP2D6 specificity, judged by the CYP2D6/CYP1A1 activity ratios was 18.5, 7.0, 6.0, and 1.6 for dextromethorphan, bufuralol, sparteine, and debrisoquine, respectively. Thus, debrisoquine is not a specific CYP2D6 substrate and quinidine is not a specific CYP2D6 inhibitor. These findings have significant implications for the conduct of in vitro drug metabolism inhibition studies and underscore the fallacy of "specific chemical inhibitors" of a supergene family of enzymes that have overlapping substrate specificities. The use of highly specific mAbs in such studies is mandated. It is unclear as yet whether these findings have implications for the relationship between CYP2D6 genotype and in vivo debrisoquine 4-hydroxylase activity.

Induction of CYP1A1 and CYP1A2 expressions by prototypic and atypical inducers in the human lung

The inducibility of cytochrome P4501A1 gene (CYP1A1) expression was examined in human lung samples from 27 subjects, using an explant culture system and semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. CYP1A1 transcripts were present in all of the lung specimens and were induced by the prototypic inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo[a]pyrene (B[a]P), and by the atypical inducers pyridine, nicotine, and omeprazole. 2-Hydroxypyridine was a better inducer than pyridine, implicating metabolites in CYP1A1 induction by the parent compound. The prototypical inducers were the most effective inducers in many samples but were ineffective in some samples in which the atypical compounds were effective inducers. Cytochrome P4501A2 (CYP1A2) transcripts were also detected in most of the lung specimens and were inducible in some specimens. The results show the suitability of the explant culture system for examining the inducibility of human pulmonary CYP1A1 and CYP1A2, indicate the heterogeneity in individual sensitivity to the induction, and underscore the need to include atypical inducers in studies of CYP1A inducibility in humans.

UDP-glucuronosyltransferase activity, expression and cellular localization in human placenta at term

The activity, expression and localization of the UDP-glucuronosyltransferases (UGTs) were investigated in human placenta at term. UGT activity (measured with the substrate 4-methylumbelliferone (4-MU)) was observed in all 25 placentas sampled and maximum velocity (V(max)) ranged 13-fold from 5.1+/-0.9 to 66.9+/-17.5 nmol/min/mg protein (mean+/-SD). Substrate affinity (K(m)) ranged 5-fold from 246+/-24 to 1124+/-422 microM. Using reverse transcriptase-polymerase chain reaction (RT-PCR), expression of the isoforms UGT2B4, 2B7, 2B10, 2B11 and 2B15 was observed in all (12/12) placentas sampled and expression of UGT2B17 was noted in 8/12 placentas. Northern analysis of the UGT2B7 isoform in 12 placentas revealed a 10-fold difference in expression with RT-PCR variability and the 13-fold variation observed in UGT activity. The presence of UGT2B4 and 2B7 proteins (52 and 56kDa, respectively) was demonstrated by Western blotting. The sites of placental UGT2B transcription (in situ hybridization) and protein expression (immunohistochemistry) were located in the syncytium of the placental trophoblasts bordering the placental villi. UGT1A proteins could not be observed with immunohistochemistry or Western blotting and expression could not be observed with RT-PCR. Our discovery of UGT expression and activity at the site of maternal-fetal exchange is consistent with a role for UGTs in detoxification of exogenous and endogenous ligands and the maintenance of placental function through clearance and regulation of steroid hormones.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Transplacental transfer and metabolism of buprenorphine

Information on the direct and indirect effects of buprenorphine (BUP) on the fetus is essential for determining its potential for treatment of the pregnant opiate addict. The goal of this investigation is to determine the transplacental transfer of BUP to the fetal circulation, its metabolism, and effects on the tissue. The technique of dual perfusion of placental lobule is used. The range of BUP concentrations investigated included its peak plasma levels (10 ng/ml) in patients under treatment. A biphasic decline in concentration of the drug in the maternal circulation was observed, initially rapid then slow. During the initial (60 min), the tissue sequestered most of BUP resulting in a low (<10%) transplacental transfer of the drug to the fetal circulation. The concentration ratios of the drug in tissue/maternal and tissue/fetal were 13 +/- 6.5 and 27.4 +/- 0.4. The drug sequestered did not have any adverse effects on placental tissue viability and functional parameters. Less than 5% of the perfused BUP was metabolized to norbuprenorphine during the 4 h of perfusion and the metabolite was distributed between the tissue, maternal, and fetal circulations. Taken together, these data suggest that the therapeutic levels of BUP in the maternal circulation may have no indirect effects (via the placenta) on the fetus. The observed low transplacental transfer of BUP to the fetal circuit may explain the moderate/absence of neonatal withdrawal in the limited number of reports on mothers treated with the drug during pregnancy.

The expression of cytochrome P450 enzymes in human breast tumours and normal breast tissue

Environmental chemicals are one of the risk factors in breast cancer genesis. Cytochrome P450 (CYP) enzymes play a major role in the activation of these chemicals. Using highly specific and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. the expression profile of all major xenobiotic metabolizing CYP forms was screened in breast tumour and surrounding tumour free (control) breast tissue in a series of 20 sample pairs obtained from females with infiltrating ductal carcinoma. The levels of CYPIAI mRNA were very low in both tumour and normal tissue. CYP1B1, CYP2B6, CYP2C, CYP2D6, CYP2E1, CYP4B1, and CYP11A1 expressions were positive in both tumours and control tissue. CYP2A6, CYP2A7, CYP2A13, CYP2F1, CYP3A4, CYP3A5. and CYP3A7 mRNAs were expressed neither in tumours nor in control tissue. These results show that several CYPs. responsible for the activation of a quite large number of procarcinogens and genotoxic estrogen metabolites. are expressed in breast tissue with a lack of qualitative differences in CYP expression at mRNA level between breast tumours and surrounding normal breast.

Novel transcriptional regulation of the human CYP3A7 gene by Sp1 and Sp3 through nuclear factor kappa B-like element

Human CYP3A7 and CYP3A4 are expressed in fetal and adult livers, respectively, although the 5'-flanking regions of the two genes show 90% homology. The purpose of this study was to clarify the mechanism(s) responsible for the transcriptional regulation of the CYP3A7 gene in human hepatoma HepG2 cells that showed fetal phenotypes. Transfection studies using a series of the CYP3A7 or CYP3A4 promoter-luciferase chimeric genes identified a nuclear factor kappaB (NF-kappaB)-like element between nucleotides -2326 and -2297 that conferred the transcriptional activation of the CYP3A7 gene. A 1-base pair mismatch within the corresponding region of the CYP3A4 gene was sufficient for a differential enhancer activity. A gel shift assay using nuclear extracts from HepG2 cells showed that Sp1 and Sp3 bound to the NF-kappaB-like element of the CYP3A7 but not CYP3A4 gene. Specific activation of the CYP3A7 promoter by Sp1 and Sp3 was confirmed by a co-transfection of the p3A7NF-kappaB or p3A4NF-kappaB reporter gene with Sp1 or Sp3 expression plasmid into Drosophila cells, which lacked endogenous Sp family. Additionally, introduction of mutations into binding sites for hepatocyte nuclear factor 3beta, upstream stimulatory factor 1, and a basic transcription element in the proximal promoter attenuated luciferase activity to 20% of the level seen with the intact CYP3A7 promoter. Thus, we conclude that the expression of the CYP3A7 gene in HepG2 cells is cooperatively regulated by Sp1, Sp3, hepatocyte nuclear factor 3beta, and upstream stimulatory factor 1.

Expression of cytochrome P450 (CYP) isozymes in rat placenta through pregnancy

The placenta plays a vital role in maintenance of pregnancy and is able to metabolize many foreign chemical compounds by cytochrome P450 (CYP) system. It is very important to clarify the expression of CYPs in the rat placenta, because rats are frequently and widely used in the embryo- and feto-toxicity studies on foreign chemical compounds. In this study, we investigated the changes in the expression and localization of CYPs protein in the placenta of F344 rats at 9, 11, 13, 16 and 19 days of gestation by Western blot analysis and immunohistochemical staining. Among nine isozymes examined (CYP1A1, 2B1, 2C6, 2C12, 2D1, 2D4, 2E1, 3A1 and 4A1), only CYP3A1 was clearly detected by Western blot analysis at all days of gestation examined. Immunohistochemically, the cytoplasm of giant cells in the trophoblastic region was positively stained by anti-CYP3A1 antibodies. These results suggest that CYP3A1 may be a major component of CYP system in the rat placenta.