Changes of multiple biotransformation phase I and phase II enzyme activities in human fetal adrenals during fetal development

Neonatal cytochrome P450 CYP3A7: A comprehensive review of its role in development, disease, and xenobiotic metabolism

The human cytochrome P450 CYP3A7, once thought to be an enzyme exclusive to fetal livers, has more recently been identified in neonates and developing infants as old as 24 months post-gestational age. CYP3A7 has been demonstrated to metabolize two endogenous compounds that are known to be important in the growth and development of the fetus and neonate, namely dehydroepiandrosterone sulfate (DHEA-S) and all-trans retinoic acid (atRA). In addition, it is also known to metabolize a variety of drugs and xenobiotics, albeit generally to a lesser extent relative to CYP3A4/5. CYP3A7 is an important component in the development and protection of the fetal liver and additionally plays a role in certain disease states, such as cancer and adrenal hyperplasia. Ultimately, a full understanding of the expression, regulation, and metabolic properties of CYP3A7 is needed to provide neonates with appropriate individualized pharmacotherapy. This article summarizes the current state of knowledge of CYP3A7, including its discovery, distribution, alleles, RNA splicing, expression and regulation, metabolic properties, substrates, and inhibitors.

Prenatal caffeine ingestion induces long-term alterations in scavenger receptor class B type I expression and glucocorticoid synthesis in adult male offspring rat adrenals

Caffeine is contained within many drinks and food that are consumed daily. Prenatal caffeine ingestion (PCI) is a risk factor for intrauterine growth retardation (IUGR). We previously observed that PCI inhibits scavenger receptor class B type I (SR-BI)-mediated cholesterol uptake in fetal adrenals, subsequently decreasing glucocorticoid synthesis and inducing IUGR. In the present study, we aimed to investigate the long-term effects of PCI on adrenal glucocorticoid synthesis in adult male offspring rats. After establishing the PCI-induced IUGR, adult male offspring was injected intraperitoneally with 5 mg/kg·d lipopolysaccharide (LPS) for 2 days to induce acute stress. We observed persistent inhibition of SR-BI expression in PCI adrenals before and after stress. Compared with the controls, the PCI offspring had higher corticosterone concentrations after stress. The serum cholesterol concentration was stable without intergroup differences before and after stress. The cholesterol concentration in PCI adrenals showed a higher decrease rate than that of the control after stress. In summary, PCI induced long-term alterations in SR-BI expression and glucocorticoid synthesis in adult male offspring rat adrenals. Cholesterol has to be over-consumed in PCI adrenals against acute stress. This study provides an experimental basis to explain the susceptibility of IUGR offspring to metabolic diseases in adults.

Expression of CYP3A4 and CYP3A7 in Human Foetal Tissues and its Correlation with Nuclear Receptors

Previous reports have suggested that the nuclear receptors vitamin D receptor (VDR), peroxisome proliferator-activated receptor α (PPARα), pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are involved in the regulation of the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 expression in adults. The aim of this study was to investigate the gene expression of CYP3A4 and the foetal CYP3A7 in human foetal tissues and their relation to gene expression and genetic variations in the nuclear receptors VDR, PPARα, PXR and CAR. We determined the relative expression of CYP3A4 and CYP3A7 and these nuclear receptors in foetal livers, intestines and adrenals, using quantitative PCR. In addition, the expression of these enzymes was also analysed in adult liver. There was a high interindividual variability in CYP3A4 and CYP3A7, 49 times and 326 times, respectively. Both CYP3A4 and CYP3A7 had the highest expression in the liver. There were significant correlations (p < 0.001) between the nuclear receptors studied and the expression of CYP3A4 and CYP3A7 in foetal liver, as well as the expression of CYP3A4 in foetal intestine. Polymorphisms in the VDR gene, rs1544410 and rs1523130 (TaqI), in the PXR gene, rs1523130, and in the PPARα gene, rs4253728, were not correlated with CYP3A4 or CYP3A7 expression. However, C-homozygous individuals of the TaqI VDR polymorphism had 60% lower VDR gene expression (p < 0.05), than individuals carrying one or two T alleles. In conclusion, differences in the expression of nuclear receptors might determine the variability in CYP3A4 and CYP3A7 expression observed in foetal liver.

Identification of CYP3A7 for glyburide metabolism in human fetal livers

Glyburide is commonly prescribed for the treatment of gestational diabetes mellitus; however, fetal exposure to glyburide is not well understood and may have short- and long-term consequences for the health of the child. Glyburide can cross the placenta; fetal concentrations at term are nearly comparable to maternal levels. Whether or not glyburide is metabolized in the fetus and by what mechanisms has yet to be determined. In this study, we determined the kinetic parameters for glyburide depletion by CYP3A isoenzymes; characterized glyburide metabolism by human fetal liver tissues collected during the first or early second trimester of pregnancy; and identified the major enzyme responsible for glyburide metabolism in human fetal livers. CYP3A4 had the highest metabolic capacity towards glyburide, followed by CYP3A7 and CYP3A5 (Clint,u=37.1, 13.0, and 8.7ml/min/nmol P450, respectively). M5 was the predominant metabolite generated by CYP3A7 and human fetal liver microsomes (HFLMs) with approximately 96% relative abundance. M5 was also the dominant metabolite generated by CYP3A4, CYP3A5, and adult liver microsomes; however, M1-M4 were also present, with up to 15% relative abundance. CYP3A7 protein levels in HFLMs were highly correlated with glyburide Clint, 16α-OH DHEA formation, and 4'-OH midazolam formation. Likewise, glyburide Clint was highly correlated with 16α-OH DHEA formation. Fetal demographics as well as CYP3A5 and CYP3A7 genotype did not alter CYP3A7 protein levels or glyburide Clint. These results indicate that human fetal livers metabolize glyburide predominantly to M5 and that CYP3A7 is the major enzyme responsible for glyburide metabolism in human fetal livers.

Prenatal xenobiotic exposure and intrauterine hypothalamus-pituitary-adrenal axis programming alteration

The hypothalamic-pituitary-adrenal (HPA) axis is one of the most important neuroendocrine axes and plays an important role in stress defense responses before and after birth. Prenatal exposure to xenobiotics, including environmental toxins (such as smoke, sulfur dioxide and carbon monoxide), drugs (such as synthetic glucocorticoids), and foods and beverage categories (such as ethanol and caffeine), affects fetal development indirectly by changing the maternal status or damaging the placenta. Certain xenobiotics (such as caffeine, ethanol and dexamethasone) may also affect the fetus directly by crossing the placenta into the fetus due to their lipophilic properties and lower molecular weights. All of these factors probably result in intrauterine programming alteration of the HPA axis, which showed a low basal activity but hypersensitivity to chronic stress. These alterations will, therefore, increase the susceptibility to adult neuropsychiatric (such as depression and schizophrenia) and metabolic diseases (such as hypertension, diabetes and non-alcoholic fatty liver disease). The "over-exposure of fetuses to maternal glucocorticoids" may be the main initiation factor by which the fetal HPA axis programming is altered. Meantime, xenobiotics can directly induce abnormal epigenetic modifications and expression on the important fetal genes (such as hippocampal glucocorticoid receptor, adrenal steroidogenic acute regulatory protein, et al) or damage by in situ oxidative metabolism of fetal adrenals, which may also be contributed to the programming alteration of fetal HPA axis.

Bisphenol A-associated alterations in the expression and epigenetic regulation of genes encoding xenobiotic metabolizing enzymes in human fetal liver

Alterations in xenobiotic metabolizing enzyme (XME) expression across the life course, along with genetic, nutritional, and environmental regulation, can influence how organisms respond to toxic insults. In this study, we investigated the hypothesis that in utero exposure to the endocrine active compound, bisphenol A (BPA), influences expression and epigenetic regulation of phase I and II XME genes during development. Using healthy 1st to 2nd trimester human fetal liver specimens quantified for internal BPA levels, we examined XME gene expression using PCR Array (n = 8) and RNA-sequencing (n = 12) platforms. Of the greater than 160 XME genes assayed, 2 phase I and 12 phase II genes exhibited significantly reduced expression with higher BPA levels, including isoforms from the carboxylesterase, catechol O-methyltransferase, glutathione S-transferase, sulfotransferase, and UDP-glucuronosyltransferase families. When the promoters of these candidate genes were evaluated in silico, putative binding sites for the E-twenty-six (ETS) and activator protein1 (AP1) related transcription factor families were identified and unique to 97% of all candidate transcripts. Interestingly, many ETS binding sites contain cytosine-guanine dinucleotides (CpGs) within their consensus sequences. Thus, quantitative analysis of CpG methylation of three candidate genes was conducted across n = 50 samples. Higher BPA levels were associated with increased site-specific methylation at COMT (P < 0.005) and increased average methylation at SULT2A1 (P < 0.020) promoters. While toxicological studies have traditionally focused on high-dose effects and hormonal receptor mediated regulation, our findings suggest the importance of low-dose effects and nonclassical mechanisms of endocrine disruption during development.

Nicotine induced CpG methylation of Pax6 binding motif in StAR promoter reduces the gene expression and cortisol production

Steroidogenic acute regulatory protein (StAR) mediates the rate-limiting step in the synthesis of steroid hormones, essential to fetal development. We have reported that the StAR expression in fetal adrenal is inhibited in a rat model of nicotine-induced intrauterine growth retardation (IUGR). Here using primary human fetal adrenal cortex (pHFAC) cells and a human fetal adrenal cell line NCI-H295A, we show that nicotine inhibits StAR expression and cortisol production in a dose- and time-dependent manner, and prolongs the inhibitory effect on cells proliferating over 5 passages after termination of nicotine treatment. Methylation detection within the StAR promoter region uncovers a single site CpG methylation at nt -377 that is sensitive to nicotine treatment. Nicotine-induced alterations in frequency of this point methylation correlates well with the levels of StAR expression, suggesting an important role of the single site in regulating StAR expression. Further studies using bioinformatics analysis and siRNA approach reveal that the single CpG site is part of the Pax6 binding motif (CGCCTGA) in the StAR promoter. The luciferase activity assays validate that Pax6 increases StAR gene expression by binding to the glucagon G3-like motif (CGCCTGA) and methylation of this site blocks Pax6 binding and thus suppresses StAR expression. These data identify a nicotine-sensitive CpG site at the Pax6 binding motif in the StAR promoter that may play a central role in regulating StAR expression. The results suggest an epigenetic mechanism that may explain how nicotine contributes to onset of adult diseases or disorders such as metabolic syndrome via fetal programming.

Steroid metabolome in fetal and maternal body fluids in human late pregnancy

Despite the extensive research during the last six decades the fundamental questions concerning the role of steroids in the initiation of human parturition and origin and function of some steroids in pregnancy were not definitely answered. Based on steroid metabolomic data found in the literature and our so far unpublished results, we attempted to bring new insights concerning the role of steroids in the sustaining and termination of human pregnancy, and predictive value of these substances for estimation of term. We also aimed to explain enigmas concerning the biosynthesis of progesterone and its bioactive catabolites considering the conjunctions between placental production of CRH, synthesis of bioactive steroids produced by fetal adrenal, localization of placental oxidoreductases and sustaining of human pregnancy. Evaluation of data available in the literature, including our recent findings as well as our new unpublished data indicates increasing progesterone synthesis and its concurrently increasing catabolism with approaching parturition, confirms declining production of pregnancy sustaining 5β-pregnane steroids providing uterine quiescence in late pregnancy, increased sulfation of further neuroinhibiting and pregnancy sustaining steroids. In contrast to the established concept considering LDL cholesterol as the primary substrate for progesterone synthesis in pregnancy, our data demonstrates the functioning of alternative mechanism for progesterone synthesis, which is based on the utilization of fetal pregnenolone sulfate for progesterone production in placenta. Close relationships were found between localization of placental oxidoreductases and consistently higher levels of sex hormones, neuroactive steroids and their metabolites in the oxidized form in the fetus and in the reduced form in the maternal compartment.

The distribution of placental oxidoreductase isoforms provides different milieus of steroids influencing pregnancy in the maternal and fetal compartment

Using information based on the steroid metabolome in maternal and fetal body fluids, we attempted to ascertain whether there is a common mechanism, which is based on the placental distribution of various isoforms of 17β-hydroxysteroid dehydrogenases and aldo-keto reductases. This system simultaneously provides a higher proportion of active progestogens in fetal circulation and a higher proportion of active estrogens and GABAergic steroids in the maternal compartment. The data obtained using gas chromatography-mass spectrometry completely support the aforementioned hypothesis. We confirmed a common trend to higher ratios of steroids with hydroxy-groups in the 3α-, 17β-, and 20α-positions to the corresponding 3-oxo-, 17-oxo-, and 20-oxo-metabolites, respectively, in the maternal blood when compared with the fetal circulation, and the same tendency was obvious in the 3α-hydroxy/3β-hydroxy steroid ratios. A decreasing trend was observed in the ratios of active estrogens and neuro-inhibitory steroids to their inactive counterparts in fetal and maternal body fluids. This was probably associated with a limited capacity of placental oxidoreductases in the converting of estrone to estradiol during the transplacental passage. Although we observed a decreasing trend in pregnancy-sustaining steroids with increasing gestational age, we recorded rising levels of estradiol and particularly of estriol, regardless of the limited capacity of placental oxidoreductases. Besides the estradiol, which is generally known as an active estrogen, estriol may be of importance for the termination of pregnancy with respect to its excessive concentrations near term which allows its binding to estrogen receptors.