RNA-sequencing quantification of hepatic ontogeny and tissue distribution of mRNAs of phase II enzymes in mice

Lactational transfer of sulforaphane-N-acetylcysteine in vivo and in human breast milk

Sulforaphane (SFN) is a bioactive phytonutrient found in cruciferous vegetables. There is a lack of detailed information on the lactational transfer of SFN and SFN metabolites, and potential pharmacological effects on breastfeeding infants. We carried out two maternal supplementation studies in a mouse model, wherein lactating dams received either vehicle, 300 or 600 ppm SFN from postnatal day (PND) 1 to 5, or in a second experiment, vehicle or 600 ppm SFN from PND 1 to 14. The parent compound was only detectable in milk and plasma from dams receiving 600 ppm SFN for five days. The predominant metabolite SFN-N-acetylcysteine (SFN-NAC) was readily detected in milk from dams receiving 300 and 600 ppm SFN for five days or 600 ppm for 14 days. Maternal SFN-NAC plasma levels were elevated in both 600 ppm groups. Maternal hepatic and pulmonary expression of NRF2-related genes, Nqo1, Gsta2, Gstm1, and Gstp1, were significantly increased, generally following a dose-response; however, offspring induction varied. PND5 neonates in the 600-ppm group exhibited significantly elevated expression of Nqo1, Gsta2, and Gstp1 in liver, and Gstm1 and Gstp1 in lung. Findings support maternal dietary supplementation with SFN induces NRF2-related gene expression in neonates via lactational transfer of SFN-NAC. However, NQO1 enzyme activity was not significantly elevated, highlighting the need to optimize dosing strategy. Additionally, in a pilot investigation of lactating women consuming a typical diet, without any purified SFN supplementation, 7 out of 8 breast milk samples showed SFN-NAC above the limit of quantification (LOQ). Notably, the one sample below the LOQ was collected from the only participant who reported no consumption of cruciferous vegetables in the past 24 h. The parent compound was not detected in any of the human breast milk samples. Overall, these data indicate lactational transfer of SFN-NAC at dietary relevant levels. Future studies are needed to evaluate pharmacokinetics and pharmacodynamics of lactational transfer for potential preventive or therapeutic effects in breastfeeding children.

Microsomal glutathione transferase 1 in cancer and the regulation of ferroptosis

Microsomal glutathione transferase 1 (MGST1) is a member of the MAPEG family (membrane associated proteins in eicosanoid and glutathione metabolism), defined according to enzymatic activities, sequence motifs, and structural properties. MGST1 is a homotrimer which can bind three molecules of glutathione (GSH), with one modified to a thiolate anion displaying one-third-of-sites-reactivity. MGST1 has both glutathione transferase and peroxidase activities. Each is based on stabilizing the GSH thiolate in the same active site. MGST1 is abundant in the liver and displays a broad subcellular distribution with high levels in endoplasmic reticulum and mitochondrial membranes, consistent with a physiological role in protection from reactive electrophilic intermediates and oxidative stress. In this review paper, we particularly focus on recent advances made in understanding MGST1 activation, induction, broad subcellular distribution, and the role of MGST1 in apoptosis, ferroptosis, cancer progression, and therapeutic responses.

Epigenetic Mechanisms Contribute to Intraindividual Variations of Drug Metabolism Mediated by Cytochrome P450 Enzymes

Significant interindividual and intraindividual variations on cytochrome P450 (CYP)-mediated drug metabolism exist in the general population globally. Genetic polymorphisms are one of the major contribution factors for interindividual variations, but epigenetic mechanisms mainly contribute to intraindividual variations, including DNA methylation, histone modifications, microRNAs, and long non-coding RNAs. The current review provides analysis of advanced knowledge in the last decade on contributions of epigenetic mechanisms to intraindividual variations on CYP-mediated drug metabolism in several situations, including (1) ontogeny, the developmental changes of CYP expression in individuals from neonates to adults; (2) increased activities of CYP enzymes induced by drug treatment; (3) increased activities of CYP enzymes in adult ages induced by drug treatment at neonate ages; and (4) decreased activities of CYP enzymes in individuals with drug-induced liver injury (DILI). Furthermore, current challenges, knowledge gaps, and future perspective of the epigenetic mechanisms in development of CYP pharmacoepigenetics are discussed. In conclusion, epigenetic mechanisms have been proven to contribute to intraindividual variations of drug metabolism mediated by CYP enzymes in age development, drug induction, and DILI conditions. The knowledge has helped understanding how intraindividual variation are generated. Future studies are needed to develop CYP-based pharmacoepigenetics to guide clinical applications for precision medicine with improved therapeutic efficacy and reduced risk of adverse drug reactions and toxicity. SIGNIFICANCE STATEMENT: Understanding epigenetic mechanisms in contribution to intraindividual variations of CYP-mediated drug metabolism may help to develop CYP-based pharmacoepigenetics for precision medicine to improve therapeutic efficacy and reduce adverse drug reactions and toxicity for drugs metabolized by CYP enzymes.

Sulfotransferases (SULTs), enzymatic and genetic variation in Carnivora: Limited sulfation capacity in pinnipeds

Wild carnivorans are one of the most important species due to their high positions in the food chain. They are also highly affected by numerous environmental contaminants through bioaccumulation and biomagnification. Xenobiotic metabolism is a significant chemical defense system from xenobiotics because it degrades the activity of a wide range of chemicals, generally into less active forms, resulting in their deactivation. Sulfotransferases (SULTs) are one of the most important xenobiotic metabolic enzymes, which catalyze the sulfonation of a variety of endogenous and exogenous chemicals, such as hormones, neurotransmitters, and a wide range of xenobiotic compounds. Although SULTs are of such high importance, little research has focused on these enzymes in wild carnivorans. In this study, we clarified the genetic properties of SULTs in a wide range of mammals, focusing on carnivorans, using in silico genetic analyses. We found genetic deficiencies of SULT1E1 and SULT1D1 isoforms in all pinnipeds analyzed and nonsense mutations in SULT1Cs in several carnivorans including pinnipeds. We further investigated the enzymatic activity of SULT1E1 in vitro using liver cytosols from pinnipeds. Using a SULT1E1 probe substrate, we found highly limited estradiol sulfonation in pinnipeds, whereas other mammals had relatively high sulfation. These results suggest that pinnipeds have severely or completely absent SULT1E1 activity, which importantly catalyzes the metabolism of estrogens, drugs, and environmental toxins. This further implies a high susceptibility to a wide range of xenobiotics in these carnivorans, which are constantly exposed to environmental chemicals throughout their lifetime.

Duplication, Loss, and Evolutionary Features of Specific UDP-Glucuronosyltransferase Genes in Carnivora (Mammalia, Laurasiatheria)

UDP-glucuronosyltransferases (UGTs) are one of the most important enzymes for xenobiotic metabolism or detoxification. Through duplication and loss of genes, mammals evolved the species-specific variety of UGT isoforms. Among mammals, Carnivora is one of the orders that includes various carnivorous species, yet there is huge variation of food habitat. Recently, lower activity of UGT1A and 2B were shown in Felidae and pinnipeds, suggesting evolutional loss of these isoforms. However, comprehensive analysis for genetic or evolutional features are still missing. This study was conducted to reveal evolutional history of UGTs in Carnivoran species. We found specific gene expansion of UGT1As in Canidae, brown bear and black bear. We also found similar genetic duplication in UGT2Bs in Canidae, and some Mustelidae and Ursidae. In addition, we discovered contraction or complete loss of UGT1A7–12 in phocids, some otariids, felids, and some Mustelids. These studies indicate that even closely related species have completely different evolution of UGTs and further imply the difficulty of extrapolation of the pharmacokinetics and toxicokinetic result of experimental animals into wildlife carnivorans.

Dynamic 3D genome reorganization during development and metabolic stress of the porcine liver

Liver development is a complex process that is regulated by a series of signaling pathways. Three-dimensional (3D) chromatin architecture plays an important role in transcriptional regulation; nonetheless, its dynamics and role in the rapid transition of core liver functions during development and obesity-induced metabolic stress remain largely unexplored. To investigate the dynamic chromatin architecture during liver development and under metabolic stress, we generated high-resolution maps of chromatin architecture for porcine livers across six major developmental stages (from embryonic day 38 to the adult stage) and under a high-fat diet-induced obesity. The characteristically loose chromatin architecture supports a highly plastic genome organization during early liver development, which fundamentally contributes to the rapid functional transitions in the liver after birth. We reveal the multi-scale reorganization of chromatin architecture and its influence on transcriptional regulation of critical signaling processes during liver development, and show its close association with transition in hepatic functions (i.e., from hematopoiesis in the fetus to metabolism and immunity after birth). The limited changes in chromatin structure help explain the observed metabolic adaptation to excessive energy intake in pigs. These results provide a global overview of chromatin architecture dynamics associated with the transition of physiological liver functions between prenatal development and postnatal maturation, and a foundational resource that allows for future in-depth functional characterization.

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

Impact of obese levels on the hepatic expression of nuclear receptors and drug-metabolizing enzymes in adult and offspring mice

The prevalence of obesity-associated conditions raises new challenges in clinical medication. Although altered expression of drug-metabolizing enzymes (DMEs) has been shown in obesity, the impacts of obese levels (overweight, obesity, and severe obesity) on the expression of DMEs have not been elucidated. Especially, limited information is available on whether parental obese levels affect ontogenic expression of DMEs in children. Here, a high-fat diet (HFD) and three feeding durations were used to mimic different obese levels in C57BL/6 mice. The hepatic expression of five nuclear receptors (NRs) and nine DMEs was examined. In general, a trend of induced expression of NRs and DMEs (except for Cyp2c29 and 3a11) was observed in HFD groups compared to low-fat diet (LFD) groups. Differential effects of HFD on the hepatic expression of DMEs were found in adult mice at different obese levels. Family-based dietary style of an HFD altered the ontogenic expression of DMEs in the offspring older than 15 days. Furthermore, obese levels of parental mice affected the hepatic expression of DMEs in offspring. Overall, the results indicate that obese levels affected expression of the DMEs in adult individuals and that of their children. Drug dosage might need to be optimized based on the obese levels.

Ontogenic mRNA expression of RNA modification writers, erasers, and readers in mouse liver

RNA modifications are recently emerged epigenetic modifications. These diverse RNA modifications have been shown to regulate multiple biological processes, including development. RNA modifications are dynamically controlled by the “writers, erasers, and readers”, where RNA modifying proteins are able to add, remove, and recognize specific chemical modification groups on RNAs. However, little is known about the ontogenic expression of these RNA modifying proteins in various organs, such as liver. In the present study, the hepatic mRNA expression of selected RNA modifying proteins involve in m⁶A, m¹A, m⁵C, hm⁵C, m⁷G, and Ψ modifications was analyzed using the RNA-seq technique. Liver samples were collected from male C57BL/6 mice at several ages from prenatal through neonatal, infant, child to young adult. Results showed that most of the RNA modifying proteins were highly expressed in prenatal mouse liver with a dramatic drop at birth. After birth, most of the RNA modifying proteins showed a downregulation trend during liver maturation. Moreover, the RNA modifying proteins that belong to the same enzyme family were expressed at different abundances at the same ages in mouse liver. In conclusion, this study unveils that the mRNA expression of RNA modifying proteins follows specific ontogenic expression patterns in mice liver during maturation. These data indicated that the changes in expression of RNA modifying proteins might have a potential role to regulate gene expression in liver through alteration of RNA modification status.

Population pharmacokinetic analysis of intravenous busulfan: GSTA1 genotype is not a predictive factor of initial dose in Chinese adult patients undergoing hematopoietic stem cell transplantation

PURPOSE

This study aimed to develop a population pharmacokinetic (PPK) model to investigate the impact of GSTA1, GSTP1, and GSTM1 genotypes on busulfan pharmacokinetic (PK) variability in Chinese adult patients.

METHODS

Forty-three and 19 adult patients who underwent hematopoietic stem cell transplantation (HSCT) were enrolled for modeling group and validation group, respectively. All patients received twice-daily intravenous busulfan as part of conditioning regimen before HSCT. The PPK model was developed by nonlinear mixed-effect modeling. Covariates investigated were age, sex, actual body weight, body surface area, diagnoses, hepatic function markers, GST genotypes and conditioning regimen.

RESULTS

A total of 488 busulfan concentrations from 43 patients were obtained for the PPK model. The PK of intravenous busulfan was described by one-compartment model with first-order elimination with estimated clearance (CL) of 14.2 L/h and volume of distribution of 64.1 L. Inclusion of GSTA1 genotype as a covariate accounted for 1.1% of the inter-individual variability of busulfan CL (from 17.8% in the basic model to 16.7% in the final model). The accuracy and applicability of the final model were externally validated in the independent group. The difference of busulfan PK between Chinese patients and Caucasian patients existed because of the rarity of haplotype *B in Chinese population.

CONCLUSIONS

Although the GSTA1 genotype-based PPK model of intravenous busulfan was successfully developed and externally validated, the GSTA1 genotype was not considered to be clinically relevant to busulfan CL. We did not suggest the guidance of GSTA1 genotype on initial busulfan dose in Chinese adult patients.

Epigenetic Memory Is Involved in the Persistent Alterations of Drug-Processing Genes in Adult Mice due to PCN-Activated PXR during Early Life

Pregnane X receptor (PXR), which can be activated by xenobiotic chemicals (including pediatric drugs), plays a key role in the regulation of drug-processing genes (DPGs). The induction of DPGs due to PXR activation may reduce therapeutic efficacy or cause toxicity. This work aims to demonstrate the impact of pregnenolone 16α-carbonitrile (PCN)-mediated PXR activation during early life on DPGs expression and drug sensitivity in adulthood, as well as the underlying mechanism. In this study, mice were sacrificed at postnatal day 60 to detect the hepatic expression of selected DPGs and histone modifications in the Cyp3a11 promoter. We found that all doses of PCN treatment (50-200 mg/kg/day) at postnatal days 5-8 resulted in persistently increased CYP2B10 expression, whereas only high doses of PCN treatment (150 and 200 mg/kg/day) persistently induced the expression of CYP3A11, 1A2, and UGTA1A1. We also demonstrated that PCN treatment before postnatal day 15 had a long-term impact on the expression of CYP3A11, 2B10, ABCC4, and PAPSS2. Additionally, elevated expression of CYP3A11, SULT2A1, UGT1A1, and PAPSS2 was observed in PCN-treated groups at days 25-28. Attenuated inducibility of CYP3A11 by PCN was seen in the primary hepatocytes derived from PCN-pretreated mice. Moreover, enhanced H3K4me3 level and reduced H3K27me3 level in the PXR response elements (PXREs) of the Cyp3a11 promoter may contribute to the persistent up-regulation of CYP3A11 by neonatal PCN treatment. Overall, our study suggests that PXR activation during early life could persistently alter the hepatic expression of DPGs and epigenetic memory may be an underlying mechanism in mice.

RNA-Seq provides new insights on the relative mRNA abundance of antioxidant components during mouse liver development

Mammals have developed a variety of antioxidant systems to protect them from the oxygen environment and toxic stimuli. Little is known about the mRNA abundance of antioxidant components during postnatal development of the liver. Therefore, the purpose of this study was to compare the mRNA abundance of antioxidant components during liver development. Livers from male C57BL/6J mice were collected at 12 ages from prenatal to adulthood. The transcriptome was determined by RNA-Seq with transcript abundance estimated by Cufflinks. RNA-Seq provided a complete, more accurate, and unbiased quantification of the transcriptome. Among 33 known antioxidant components examined, three ontogeny patterns of liver antioxidant components were observed: (1) Prenatal-enriched, in which the mRNAs decreased from fetal livers to adulthood, such as metallothionein and heme oxygenase-1; (2) adolescent-rich and relatively stable expression, such as peroxiredoxins; and (3) adult-rich, in which the mRNA increased with age, such as catalase and superoxide dismutase. Alternative splicing of several antioxidant genes, such as Keap1, Glrx2, Gpx3, and Txnrd1, were also detected by RNA-Seq. In summary, RNA-Seq revealed the relative abundance of hepatic antioxidant enzymes, which are important in protecting against the deleterious effects of oxidative stress.

Age-associated changes in GSH S-transferase gene/proteins in livers of rats

OBJECTIVES

Glutathione S-transferases (GSTs) are phase-II metabolic enzymes playing important roles in drug metabolism, anti-oxidative stress and anti-aging. Age is a key factor influencing GSTs expression. Thus, age-related changes of 10 GSTs were examined.

METHODS

Livers from male Sprague-Dawley rats at fetus (-2 d), neonates (1, 7, 14 and 21 d), puberty (28 and 35 d), adulthood (60 and 180 d), and aging (540 and 800 d), were collected and subjected to qPCR analysis. Liver proteins from 14, 28, 60, 180, 540 and 800 d were also extracted for selected protein analysis by Western-blot.

RESULTS

The expression of GSTA1 and GSTP1 increased over the life span and the expression of GSTA4, GSTO1 and GSTZ1 gradually increased until adulthood, and slightly decreased at 800 days. The expression of GSTM1, GSTM3, GSTT1, GSTT2 and GSTK1 gradually increased until adulthood, but significantly decreased during aging of 540 and 800 days. There is a small peak at 7-14 d for GSTA1, GSTP1 and GSTZ1. The protein expression of GSTA1, GSTM1 and GSTP1 followed the trend of mRNA changes.

DISCUSSION

This study characterized three expression patterns of 10 GSTs during development and aging in rat liver, adding to our understanding of anti-aging role of GSTs.

Involvement of UDP-Glucuronosyltransferases and Sulfotransferases in the Excretion and Tissue Distribution of Resveratrol in Mice

Resveratrol is a naturally occurring polyphenolic compound with various pharmacological activities. It is unknown whether the expression of metabolizing enzymes correlates with resveratrol levels in organs and tissues. Therefore, we investigated the metabolism and tissue distribution of resveratrol in mice and assessed its association with the expression of UDP-glucuronosyltransferase (Ugt) and sulfotransferase (Sult) genes. Plasma, urine, feces, and various organs were analyzed using high-performance liquid chromatography at up to 8 h after intragastric resveratrol administration. The metabolism of resveratrol was pronounced, leading to the formation of resveratrol glucuronides and sulfates. Concentrations of resveratrol and its metabolites were high in the gastrointestinal organs, urine, and feces, but low in the liver and kidneys. In lung, heart, thymus, and brain tissues, parent resveratrol levels exceeded the sulfate and glucuronide concentrations. The formation of resveratrol conjugates correlated with the expression of certain Ugt and Sult genes. Reverse transcription quantitative PCR (RT-qPCR) analysis revealed high mRNA expression of Ugt1a1 and Ugt1a6a in the liver, duodenum, jejunum, ileum, and colon, leading to high concentrations of resveratrol-3-O-glucuronide in these organs. Strong correlations of resveratrol-3-O-sulfate and resveratrol-3-O-4'-O-disulfate formation with Sult1a1 mRNA expression were also observed, particularly in the liver and colon. In summary, our data revealed organ-specific expression of Sults and Ugts in mice that strongly affects resveratrol concentrations; this may also be predictive in humans following oral uptake of dietary resveratrol.

The role of H19, a long non-coding RNA, in mouse liver postnatal maturation

H19 RNA is highly expressed at early postnatal ages and precipitously decreases at a specific time corresponding with increases in expression of genes important for mature liver function, such as drug metabolizing enzymes. H19’s role in the regulation of liver maturation is currently unknown. Using an H19 knockout mouse model to determine the role of H19 in liver development, we quantified gene expression for insulin growth factor signaling, Wnt signaling, key cytochrome P450 (P450) enzymes known to change as the liver develops, and fetal and adult plasma protein produced in liver. In mice lacking H19 expression, liver weights were significantly increased immediately after birth and significant increases were found in the number of actively proliferating cells. Increases in cell proliferation may be due to increases in β-catenin protein affecting Wnt signaling, increases in insulin-like growth factor 2 (IGF2) expression, and/or increases in insulin-like growth factor 1 receptor (IGF1R) expression at the protein level. Loss of targeted inhibition of IGF1R by microRNA 675 (miR-675) may be the cause of IGF1R increases, as miR-675 expression is also abrogated with loss of H19 expression in our model. P450 expression patterns were largely unchanged. No change in the production of plasma proteins was found, indicating H19 may not be important for liver maturation despite its role in controlling cell proliferation during liver growth. H19 may be important for normal liver development, and understanding how the liver matures will assist in predicting drug efficacy and toxicity in pediatric populations.

Role of Farnesoid X Receptor in the Determination of Liver Transcriptome during Postnatal Maturation in Mice

The liver is a vital organ with critical functions in metabolism of various biologically useful materials, synthesis of several vital proteins, detoxification of toxic substances, and immune defense. Most liver functions are not mature at birth and many changes happen during postnatal liver development, which lead to differential vulnerabilities of the liver at different developmental stages. However, the details of what changes occur in liver after birth, at what developmental stages they occur, and molecular mechanisms in the regulation of the developmental process are not clearly known. The nuclear receptor Farnesoid X receptor (FXR) is an important transcriptional regulator in liver. Here, we used RNA-Sequencing to analyze the transcriptome of mouse liver from perinatal to adult ages in both C57BL/6 and Fxr-/- mice. We have defined a clear timeline of functional transition from prenatal through neonatal and adolescent to adult in C57BL/6 mice. Without FXR, activation of neonatal-specific pathways was prolonged and maturation of multiple metabolic pathways was delayed. The loss of FXR also led to increased expression of 27 other transcription regulators. Our data support a conclusion that developmental transcriptome revealed significant functional transition during postnatal liver development and FXR plays an important role in control of postnatal liver maturation.

A framework and case studies for evaluation of enzyme ontogeny in children's health risk evaluation

Knowledge of the ontogeny of Phase I and Phase II metabolizing enzymes may be used to inform children's vulnerability based upon likely differences in internal dose from xenobiotic exposure. This might provide a qualitative assessment of toxicokinetic (TK) variability and uncertainty pertinent to early lifestages and help scope a more quantitative physiologically based toxicokinetic (PBTK) assessment. Although much is known regarding the ontogeny of metabolizing systems, this is not commonly utilized in scoping and problem formulation stage of human health risk evaluation. A framework is proposed for introducing this information into problem formulation which combines data on enzyme ontogeny and chemical-specific TK to explore potential child/adult differences in internal dose and whether such metabolic differences may be important factors in risk evaluation. The framework is illustrated with five case study chemicals, including some which are data rich and provide proof of concept, while others are data poor. Case studies for toluene and chlorpyrifos indicate potentially important child/adult TK differences while scoping for acetaminophen suggests enzyme ontogeny is unlikely to increase early-life risks. Scoping for trichloroethylene and aromatic amines indicates numerous ways that enzyme ontogeny may affect internal dose which necessitates further evaluation. PBTK modeling is a critical and feasible next step to further evaluate child-adult differences in internal dose for a number of these chemicals.

Nicotinamide N-Methyltransferase in Health and Cancer

Over the past decade, the roles of nicotinamide N-methyltransferase and its product 1-methyl nicotinamide have emerged from playing merely minor roles in phase 2 xenobiotic metabolism as actors in some of the most important scenes of human life. In this review, the structures of the gene, messenger RNA, and protein are discussed, together with the role of the enzyme in many of the common cancers that afflict people today.

RNA Sequencing Reveals Age and Species Differences of Constitutive Androstane Receptor-Targeted Drug-Processing Genes in the Liver

The constitutive androstane receptor (CAR/Nr1i3) is an important xenobiotic-sensing nuclear receptor that is highly expressed in the liver and is well known to have species differences. During development, age-specific activation of CAR may lead to modified pharmacokinetics and toxicokinetics of drugs and environmental chemicals, leading to higher risks for adverse drug reactions in newborns and children. The goal of this study was to systematically investigate the age- and species-specific regulation of various drug-processing genes (DPGs) after neonatal or adult CAR activation in the livers of wild-type, CAR-null, and humanized CAR transgenic mice. At either 5 or 60 days of age, the three genotypes of mice were administered a species-appropriate CAR ligand or vehicle once daily for 4 days (i.p.). The majority of DPGs were differentially regulated by age and/or CAR activation. Thirty-six DPGs were commonly upregulated by CAR activation regardless of age or species of CAR. Although the cumulative mRNAs of uptake transporters were not readily altered by CAR, the cumulative phase I and phase II enzymes as well as efflux transporters were all increased after CAR activation in both species. In general, mouse CAR activation produced comparable or even greater fold increases of many DPGs in newborns than in adults; conversely, humanized CAR activation produced weaker induction in newborns than in adults. Western blotting and enzyme activity assays confirmed the age and species specificities of selected CAR-targeted DPGs. In conclusion, this study systematically compared the effect of age and species of CAR proteins on the regulation of DPGs in the liver and demonstrated that the regulation of xenobiotic biotransformation by CAR is profoundly modified by age and species.

Comprehensive Characterization of Mouse UDP-Glucuronosyltransferase (Ugt) Belonging to the Ugt2b Subfamily: Identification of Ugt2b36 as the Predominant Isoform Involved in Morphine Glucuronidation

UDP-Glucuronosyltransferases (UGTs) are classified into three subfamilies in mice: Ugt1a, 2b, and 2a. In the Ugt1a subfamily, Ugt1a1 and 1a6 appear to correspond to human UGT1A1 and 1A6 The mouse is an important animal for its use in investigations, but the substrate specificities of Ugt isoforms belonging to the 2b subfamily in mice remain largely unknown. To address this issue, we characterized the substrate specificity of all isoforms of the Ugt2b subfamily expressed in the mouse liver. The cDNAs of Ugt1a1, Ugt2a3, and all the Ugt2b isoforms expressed in the liver were reverse-transcribed from the total RNA of male FVB-mouse livers and then amplified. A baculovirus-Sf9 cell system for expressing each Ugt was established. Of all the Ugts examined, Ugt2b34, 2b36, and 2b37 exhibited the ability to glucuronidate morphine with Ugt2b36, the most active in this regard. Ugt1a1, but also Ugt2b34, 2b36, and 2b37 to a lesser extent, preferentially catalyzed the glucuronidation of 17β-estradiol on the 3-hydroxyl group (E3G). With these isoforms, E3G formation by Ugt1a1 was efficient; however, Ugt2b5 exhibited a preference for the 17β-hydroxyl group (E17G). Ugt2b1 and Ugt2a3 formed comparable levels of E3G and E17G. Ugt2b1 and 2b5 were the only isoforms involved in chloramphenicol glucuronidation. As Ugt2b36 is highly expressed in the liver, it is most likely that Ugt2b36 is a major morphine Ugt in mouse liver. Regarding E3G formation, Ugt1a1, like the human homolog, seems to play an important role in the liver.

Hepatic expression of transcription factors affecting developmental regulation of UGT1A1 in the Han Chinese population

PURPOSE

Complete or partial inactivity of UGT1A1, the unique enzyme responsible for bilirubin glucuronidation, is commonly associated with hyperbilirubinemia. We investigated the dynamic expression of UGT1A1, and that of the transcription factors (TFs) involved in its developmental regulation, during human hepatic growth in Han Chinese individuals.

METHODS

Eighty-eight prenatal, pediatric, and adult liver samples were obtained from Han Chinese individuals. Quantitative real-time polymerase chain reaction was used to evaluate mRNA expression of UGT1A1 and TFs including PXR, CAR, HNF1A, HNF4A, PPARA, etc. UGT1A1 protein levels and metabolic activity were determined by western blotting and high-performance liquid chromatography. Direct sequencing was employed to genotype UGT1A1*6 (211G˃A) and UGT1A1*28 (TA6˃TA7) polymorphisms.

RESULTS

UGT1A1 expression was minimal in prenatal samples, but significantly elevated during pediatric and adult stages. mRNA and protein levels and metabolic activity were prominently increased (120-, 20-, and 10-fold, respectively) in pediatric and adult livers compared to prenatal samples. Furthermore, expression did not differ appreciably between pediatric and adult periods. Dynamic expression of TFs, including PXR, CAR, HNF1A, HNF4A, and PPARA, was consistent with UGT1A1 levels at each developmental stage. A pronounced correlation between expression of these TFs and that of UGT1A1 (P < 0.001) was observed. Moreover, UGT1A1*6 and UGT1A1*28 polymorphisms reduced levels of UGT1A1 by up to 40-60 %.

CONCLUSIONS

Hepatic expression of transcription factors is associated with developmental regulation of UGT1A1 in the Han Chinese population. Moreover, UGT1A1 polymorphisms are associated with reduced expression of UGT1A1 mRNA and protein, as well as enzyme activity.

Effect of nine diets on mRNAs of phase-II conjugation enzymes in livers of mice

1. Phase-II enzymes are important in metabolizing many xenobiotics including prescription drugs and chemical carcinogens. Whereas it is known that diet can alter the expression of phase-II conjugation enzymes, the previous studies are limited in using only two or three diets and examining only a few enzymes. 2. Adult male C57BL6 mice were fed one of nine diets for 3 weeks. Of the 87 genes encoding major hepatic phase-II enzymes, approximately one-half (43) were altered by at least one diet. Diet restriction altered the hepatic expression of the most genes encoding phase-II enzymes (27), followed by lab chow (15), atherogenic diet (13), high-fat diet (10), western diet (7), high-fructose diet (5), and essential fatty acid-deficient diet (3), whereas the low n-3 fatty acid diet had no effect on the hepatic expression of these phase-II enzymes. 3. This comprehensive study provides detailed information on which conjugation enzymes are changed by these diets, and these data can be used to further investigate the mechanism for these changes in messenger RNAs, and whether these changes result in alterations in enzyme activity and drug action.

Comparison of mercury sulfides with mercury chloride and methylmercury on hepatic P450, phase-2 and transporter gene expression in mice

Zuotai (mainly β-HgS) and Zhusha (also called as cinnabar, mainly α-HgS) are used in traditional medicines in combination with herbs or even drugs in the treatment of various disorders, while mercury chloride (HgCl2) and methylmercury (MeHg) do not have known medical values but are highly toxic. This study aimed to compare the effects of mercury sulfides with HgCl2 and MeHg on hepatic drug processing gene expression. Mice were orally administrated with Zuotai (β-HgS, 30mg/kg), α-HgS (HgS, 30mg/kg), HgCl2 (33.6mg/kg), or MeHg (3.1mg/kg) for 7days, and the expression of genes related to phase-1 drug metabolism (P450), phase-2 conjugation, and phase-3 (transporters) genes were examined. The mercurials at the dose and duration used in the study did not have significant effects on the expression of cytochrome P450 1-4 family genes and the corresponding nuclear receptors, except for a slight increase in PPARα and Cyp4a10 by HgCl2. The expressions of UDP-glucuronosyltransferase and sulfotransferase were increased by HgCl2 and MeHg, but not by Zuotai and HgS. HgCl2 decreased the expression of organic anion transporter (Oatp1a1), but increased Oatp1a4. Both HgCl2 and MeHg increased the expression of multidrug resistance-associated protein genes (Mrp1, Mrp2, Mrp3, and Mrp4). Zuotai and HgS had little effects on these transporter genes. In conclusion, Zuotai and HgS are different from HgCl2 and MeHg in hepatic drug processing gene expression; suggesting that chemical forms of mercury not only affect their disposition and toxicity, but also affect their effects on the expression of hepatic drug processing genes.

Crosstalk of HNF4α with extracellular and intracellular signaling pathways in the regulation of hepatic metabolism of drugs and lipids

The liver is essential for survival due to its critical role in the regulation of metabolic homeostasis. Metabolism of xenobiotics, such as environmental chemicals and drugs by the liver protects us from toxic effects of these xenobiotics, whereas metabolism of cholesterol, bile acids (BAs), lipids, and glucose provide key building blocks and nutrients to promote the growth or maintain the survival of the organism. As a well-established master regulator of liver development and function, hepatocyte nuclear factor 4 alpha (HNF4α) plays a critical role in regulating a large number of key genes essential for the metabolism of xenobiotics, metabolic wastes, and nutrients. The expression and activity of HNF4α is regulated by diverse hormonal and signaling pathways such as growth hormone, glucocorticoids, thyroid hormone, insulin, transforming growth factor-β, estrogen, and cytokines. HNF4α appears to play a central role in orchestrating the transduction of extracellular hormonal signaling and intracellular stress/nutritional signaling onto transcriptional changes in the liver. There have been a few reviews on the regulation of drug metabolism, lipid metabolism, cell proliferation, and inflammation by HNF4α. However, the knowledge on how the expression and transcriptional activity of HNF4α is modulated remains scattered. Herein I provide comprehensive review on the regulation of expression and transcriptional activity of HNF4α, and how HNF4α crosstalks with diverse extracellular and intracellular signaling pathways to regulate genes essential in liver pathophysiology.

Editor's Highlight: Neonatal Activation of the Xenobiotic-Sensors PXR and CAR Results in Acute and Persistent Down-regulation of PPARα-Signaling in Mouse Liver

Safety concerns have emerged regarding the potential long-lasting effects due to developmental exposure to xenobiotics. The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are critical xenobiotic-sensing nuclear receptors that are highly expressed in liver. The goal of this study was to test our hypothesis that neonatal exposure to PXR- or CAR-activators not only acutely but also persistently regulates the expression of drug-processing genes (DPGs). A single dose of the PXR-ligand PCN (75 mg/kg), CAR-ligand TCPOBOP (3 mg/kg), or vehicle (corn oil) was administered intraperitoneally to 3-day-old neonatal wild-type mice. Livers were collected 24 h post-dose or from adult mice at 60 days of age, and global gene expression of these mice was determined using Affymetrix Mouse Transcriptome Assay 1.0. In neonatal liver, PCN up-regulated 464 and down-regulated 449 genes, whereas TCPOBOP up-regulated 308 and down-regulated 112 genes. In adult liver, there were 15 persistently up-regulated and 22 persistently down-regulated genes following neonatal exposure to PCN, as well as 130 persistently up-regulated and 18 persistently down-regulated genes following neonatal exposure to TCPOBOP. Neonatal exposure to both PCN and TCPOBOP persistently down-regulated multiple Cyp4a members, which are prototypical-target genes of the lipid-sensor PPARα, and this correlated with decreased PPARα-binding to the Cyp4a gene loci. RT-qPCR, western blotting, and enzyme activity assays in livers of wild-type, PXR-null, and CAR-null mice confirmed that the persistent down-regulation of Cyp4a was PXR and CAR dependent. In conclusion, neonatal exposure to PXR- and CAR-activators both acutely and persistently regulates critical genes involved in xenobiotic and lipid metabolism in liver.

RNA-Seq reveals common and unique PXR- and CAR-target gene signatures in the mouse liver transcriptome

The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known xenobiotic-sensing nuclear receptors with overlapping functions. However, there lacks a quantitative characterization to distinguish between the PXR and CAR target genes and signaling pathways in the liver. The present study performed a transcriptomic comparison of the PXR- and CAR-targets using RNA-Seq in livers of adult wild-type mice that were treated with the prototypical PXR ligand PCN (200mg/kg, i.p. once daily for 4days in corn oil) or the prototypical CAR ligand TCPOBOP (3mg/kg, i.p., once daily for 4days in corn oil). At the given doses, TCPOBOP differentially regulated many more genes (2125) than PCN (212), and 147 of the same genes were differentially regulated by both chemicals. As expected, the top pathways differentially regulated by both PCN and TCPOBOP were involved in xenobiotic metabolism, and they also up-regulated genes involved in retinoid metabolism, but down-regulated genes involved in inflammation and iron homeostasis. Regarding unique pathways, PXR activation appeared to overlap with the aryl hydrocarbon receptor signaling, whereas CAR activation appeared to overlap with the farnesoid X receptor signaling, acute-phase response, and mitochondrial dysfunction. The mRNAs of differentially regulated drug-processing genes (DPGs) partitioned into three patterns, namely TCPOBOP-induced, PCN-induced, as well as TCPOBOP-suppressed gene clusters. The cumulative mRNAs of the differentially regulated DPGs, phase-I and -II enzymes, as well as efflux transporters were all up-regulated by both PCN and TCPOBOPOP, whereas the cumulative mRNAs of the uptake transporters were down-regulated only by TCPOBOP. The absolute mRNA abundance in control and receptor-activated conditions was examined in each DPG category to predict the contribution of specific DPG genes in the PXR/CAR-mediated pharmacokinetic responses. The preferable differential regulation by TCPOBOP in the entire hepatic transcriptome correlated with a marked change in the expression of many DNA and histone epigenetic modifiers. In conclusion, the present study has revealed known and novel, as well as common and unique targets of PXR and CAR in mouse liver following pharmacological activation using their prototypical ligands. Results from this study will further support the role of these receptors in regulating the homeostasis of xenobiotic and intermediary metabolism in the liver, and aid in distinguishing between PXR and CAR signaling at various physiological and pathophysiological conditions. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

RNA Sequencing Quantification of Xenobiotic-Processing Genes in Various Sections of the Intestine in Comparison to the Liver of Male Mice

Previous reports on tissue distribution of xenobiotic-processing genes (XPGs) have limitations, because many non-cytochrome P450 phase I enzymes have not been investigated, and one cannot compare the real mRNA abundance of multiple XPGs using conventional quantification methods. Therefore, this study aimed to quantify and compare the mRNA abundance of all major XPGs in the liver and intestine using RNA sequencing. The mRNA profiles of 304 XPGs, including phase I, phase II enzymes, phase II cosubstrate synthetic enzymes, xenobiotic transporters, as well as xenobiotic-related transcription factors, were systematically examined in the liver and various sections of the intestine in adult male C57BL/6J mice. By two-way hierarchical clustering, over 80% of the XPGs had tissue-divergent expression, which partitioned into liver-predominant, small intestine-predominant, and large intestine-predominant patterns. Among the genes, 54% were expressed highest in the liver, 21% in the duodenum, 4% in the jejunum, 6% in the ileum, and 15% in the large intestine. The highest-expressed XPG in the liver was Mgst1; in the duodenum, Cyp3a11; in the jejunum and ileum, Ces2e; and in the large intestine, Cyp2c55. Interestingly, XPGs in the same family usually exhibited highly different tissue distribution patterns, and many XPGs were almost exclusively expressed in one tissue and minimally expressed in others. In conclusion, the present study is among the first and the most comprehensive investigations of the real mRNA abundance and tissue-divergent expression of all major XPGs in mouse liver and intestine, which aids in understanding the tissue-specific biotransformation and toxicity of drugs and other xenobiotics.

Age-Specific Regulation of Drug-Processing Genes in Mouse Liver by Ligands of Xenobiotic-Sensing Transcription Factors

The xenobiotic-sensing transcription factors (xeno-sensors) AhR, CAR, and PXR upregulate the expression of many drug-processing genes (DPGs) in liver. Previous studies have unveiled profound changes in the basal expression of DPGs during development; however, knowledge on the ontogeny of the inducibility of DPGs in response to pharmacological activation of xeno-sensors is still limited. The goal of this study was to investigate the age-specific regulation of DPGs by prototypical xeno-sensor ligands: 2,3,7,8-tetrachlorodibenzodioxin (TCDD) for AhR; 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP) for CAR; and pregnane-16α-carbonitrile (PCN) for PXR during mouse liver development. The basal mRNAs of most DPGs were low during neonatal age, but gradually increased to adult levels, whereas some DPGs (Cyp1a2, Cyp2b10, Cyp3a11, Gstm2, Gstm3, Papss2, and Oatp1a4) exhibited an adolescent-predominant expression pattern. The inducibility of DPGs was age-specific: 1) during neonatal age, the highest fold increase in the mRNA expression was observed for Cyp1a2, Sult5a1, and Ugt1a9 by TCDD; Cyp3a11 and Mrp2 by TCPOBOP; as well as Gstm2 and Gstm3 by PCN; 2) during adolescent age, the highest fold increase in the mRNA expression was observed for Ugt1a6 and Mrp4 by TCDD, Cyp2b10, Ugt2b34, and Ugt2b35 by TCPOBOP, as well as Gsta1, Gsta4, Sult1e1, Ugt1a1, Mrp3, and Mrp4 by PCN; 3) in adults, the highest fold increase in the mRNA expression was observed for Aldh1a1, Aldh1a7, and Ugt2b36 by TCPOBOP, as well as Papss2 and Oatp1a4 by PCN. In conclusion, the inducibility of hepatic DPGs following the pharmacological activation of xeno-sensors is age specific.

Moderate activation of IKK2-NF-kB in unstressed adult mouse liver induces cytoprotective genes and lipogenesis without apparent signs of inflammation or fibrosis

Background

The NF-kB signaling, regulated by IKK1-p52/RelB and IKK2-p65, is activated by various stresses to protect or damage the liver, in context-specific manners. Two previous studies of liver-specific expression of constitutive active IKK2 (IKK2ca) showed that strong activation of IKK2-NF-kB in mouse livers caused inflammation, insulin resistance, and/or fibrosis. The purpose of this study was to understand how moderate activation of IKK2-NF-kB in adult mouse livers alters hepatic gene expression and pathophysiology.

Method

We generated mice with adult hepatocyte-specific activation of Ikk2 (Liv-Ikk2ca) using Alb-cre mice and Ikk2ca Rosa26 knockin mice in which a moderate expression of Ikk2ca transgene was driven by the endogenous Rosa26 promoter.

Results

Surprisingly, compared to wild-type mice, adult male Liv-Ikk2ca mice had higher hepatic mRNA expression of Ikk2 and classical NF-kB targets (e.g. Lcn2 and A20), as well as IKK1, NIK, and RelB, but no changes in markers of inflammation or fibrosis. Blood levels of IL-6 and MCP-1 remained unchanged, and histology analysis showed a lack of injury or infiltration of inflammatory cells in livers of Liv-Ikk2ca mice. Moreover, Liv-Ikk2ca mice had lower mRNA expression of prooxidative enzymes Cyp2e1 and Cyp4a14, higher expression of antioxidative enzymes Sod2, Gpx1, and Nqo1, without changes in key enzymes for fatty acid oxidation, glucose utilization, or gluconeogenesis. In parallel, Liv-Ikk2ca mice and wild-type mice had similar levels of hepatic reduced glutathione, endogenous reactive oxygen species, and lipid peroxidation. Additionally, Liv-Ikk2ca mice had higher Cyp3a11 without down-regulation of most drug processing genes. Regarding nuclear proteins of NF-kB subunits, Liv-Ikk2ca mice had moderately higher p65 and p50 but much higher RelB. Results of ChIP-qPCR showed that the binding of p50 to multiple NF-kB-target genes was markedly increased in Liv-Ikk2ca mice. Additionally, Liv-Ikk2ca mice had moderate increase in triglycerides in liver, which was associated with higher lipogenic factors Pparγ, Lxr, Fasn, Scd1, and CD36.

Conclusion

In summary, moderate activation of IKK2-NF-kB in unstressed adult mouse hepatocytes produces a cytoprotective gene expression profile and induces lipogenesis without apparent signs of inflammation or fibrosis, likely due to strong activation of the anti-inflammatory IKK1-RelB alternative NF-kB pathway as well as the Lxr.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-015-0325-z) contains supplementary material, which is available to authorized users.

Developmental Regulation of Drug-Processing Genes in Livers of Germ-Free Mice

Very little is known about the effect of gut microbiota on the ontogeny of drug-processing genes (DPGs) in liver. In this study, livers were harvested from conventional (CV) and germ-free (GF) male and female mice from 1 to 90 days of age. RNA-Seq in livers of 90-day-old male mice showed that xenobiotic metabolism was the most downregulated pathway within the mRNA transcriptome in absence of intestinal bacteria. In male livers, the mRNAs of 67 critical DPGs partitioned into 4 developmental patterns (real-time-quantitative polymerase chain reaction): Pattern-1 gradually increased to adult levels in livers of CV mice and were downregulated in livers of GF mice, as exemplified by the major drug-metabolizing enzymes cytochrome 3a (Cyp3a) family, which are prototypical pregnane X receptor (PXR)-target genes. Genes in Pattern-2 include Cyp1a2 (aryl hydrocarbon receptor-target gene), Cyp2c family, and Cyp2e1, which were all upregulated mainly at 90 days of age; as well as the peroxisome proliferator-activated receptor α (PPARα)-target genes Cyp4a family and Aldh3a2, which were upregulated not only in 90-days adult age, but also between neonatal and adolescent ages (from 1 to 30 days of age). Genes in Pattern-3 were enriched predominantly in livers of 15-day-old mice, among which the sterol-efflux transporter dimers Abcg5/Abcg8 were downregulated in GF mice. Genes in Pattern-4 were neonatal-enriched, among which the transporter Octn1 mRNA tended to be lower in GF mice at younger ages but higher in adult GF mice as compared with age-matched CV mice. Protein assays confirmed the downregulation of the PXR-target gene Cyp3a protein (Western-blot and liquid chromatography tandem mass spectroscopy), and decreased Cyp3a enzyme activities in male GF livers. Increased microsomal-Cyp4a proteins and nuclear-PPARα were also observed in male GF livers. Interestingly, in contrast to male livers, the mRNAs of Cyp2c or Cyp4a were not readily upregulated in female GF livers approaching adult age, suggesting the maturation of female-specific hormones interferes with the interactions between intestinal microbiota and DPG ontogeny. In conclusion, intestinal microbiota markedly impacts the ontogeny of many hepatic DPGs in a gender-specific manner.

Ontogenic expression of human carboxylesterase-2 and cytochrome P450 3A4 in liver and duodenum: postnatal surge and organ-dependent regulation

Human carboxylesterase-2 (CES2) and cytochrome P450 3A4 (CYP3A4) are two major drug metabolizing enzymes that play critical roles in hydrolytic and oxidative biotransformation, respectively. They share substrates but may have opposite effect on therapeutic potential such as the metabolism of the anticancer prodrug irinotecan. Both CES2 and CYP3A4 are expressed in the liver and the gastrointestinal tract. This study was conducted to determine whether CES2 and CYP3A4 are expressed under developmental regulation and whether the regulation occurs differentially between the liver and duodenum. A large number of tissues (112) were collected with majority of them from donors at 1-198 days of age. In addition, multi-sampling (liver, duodenum and jejunum) was performed in some donors. The expression was determined at mRNA and protein levels. In the liver, CES2 and CYP3A4 mRNA exhibited a postnatal surge (1 versus 2 months of age) by 2.7 and 29 fold, respectively. CYP3A4 but not CES2 mRNA in certain pediatric groups reached or even exceeded the adult level. The duodenal samples, on the other hand, showed a gene-specific expression pattern at mRNA level. CES2 mRNA increased with age but the opposite was true with CYP3A4 mRNA. The levels of CES2 and CYP3A4 protein, on the other hand, increased with age in both liver and duodenum. The multi-sampling study demonstrated significant correlation of CES2 expression between the duodenum and jejunum. However, neither duodenal nor jejunal expression correlated with hepatic expression of CES2. These findings establish that developmental regulation occurs in a gene and organ-dependent manner.

Metabolism of cisplatin in the organs of Rattus norvegicus: role of Glutathione S-transferase P1

Glutathione S-transferases (GSTs) play an important role in the biotransformation of endogenous compounds and xenobiotics as well as in the metabolic inactivation of pharmacologically active substances, including anticancer drugs. Using cisplatin as the prototype drug, we investigated if any correlation exists between GSH levels, GSTs/GSTP1 activity and the fate of cisplatin in different organs of Rattus norvegicus. GSH-cisplatin complex was prepared, purified by anion-exchange chromatography and subjected to mass spectroscopic analysis which confirmed the structure to be diglutathione-monoplatinum (diglutathionylplatinum). Purified diglutathionylplatinum was used to quantify metabolite formed in different tissue homogenates. Specific GSTP1 activity was found to be highest in kidneys, which correlated positively with the levels of metabolite formed in renal tissues. Altogether, our results showed that cisplatin metabolism in different organs of rats correlated positively with specific GSTP1 activities and this enzyme may be a critical determinant of extent of cellular uptake or retention of cisplatin in renal and liver tissues.

Establishment of metabolism and transport pathways in the rodent and human fetal liver

The ultimate fate of drugs and chemicals in the body is largely regulated by hepatic uptake, metabolism, and excretion. The liver acquires the functional ability to metabolize and transport chemicals during the perinatal period of development. Research using livers from fetal and juvenile rodents and humans has begun to reveal the timing, key enzymes and transporters, and regulatory factors that are responsible for the establishment of hepatic phase I and II metabolism as well as transport. The majority of this research has been limited to relative mRNA and protein quantification. However, the recent utilization of novel technology, such as RNA-Sequencing, and the improved availability and refinement of functional activity assays, has begun to provide more definitive information regarding the extent of hepatic drug disposition in the developing fetus. The goals of this review are to provide an overview of the early regulation of the major phase I and II enzymes and transporters in rodent and human livers and to highlight potential mechanisms that control the ontogeny of chemical metabolism and excretion pathways.

RNA-sequencing quantification of hepatic ontogeny of phase-I enzymes in mice

Phase-I drug metabolizing enzymes catalyze reactions of hydrolysis, reduction, and oxidation of drugs and play a critical role in drug metabolism. However, the functions of most phase-I enzymes are not mature at birth, which markedly affects drug metabolism in newborns. Therefore, characterization of the expression profiles of phase-I enzymes and the underlying regulatory mechanisms during liver maturation is needed for better estimation of using drugs in pediatric patients. The mouse is an animal model widely used for studying the mechanisms in the regulation of developmental expression of phase-I genes. Therefore, we applied RNA sequencing to provide a "true quantification" of the mRNA expression of phase-I genes in the mouse liver during development. Liver samples of male C57BL/6 mice at 12 different ages from prenatal to adulthood were used for defining the ontogenic mRNA profiles of phase-I families, including hydrolysis: carboxylesterase (Ces), paraoxonase (Pon), and epoxide hydrolase (Ephx); reduction: aldo-keto reductase (Akr), quinone oxidoreductase (Nqo), and dihydropyrimidine dehydrogenase (Dpyd); and oxidation: alcohol dehydrogenase (Adh), aldehyde dehydrogenase (Aldh), flavin monooxygenases (Fmo), molybdenum hydroxylase (Aox and Xdh), cytochrome P450 (P450), and cytochrome P450 oxidoreductase (Por). Two rapidly increasing stages of total phase-I gene expression after birth reflect functional transition of the liver during development. Diverse expression patterns were identified, and some large gene families contained the mRNA of genes that are enriched at different stages of development. Our study reveals the mRNA abundance of phase-I genes in the mouse liver during development and provides a valuable foundation for mechanistic studies in the future.