Dose of Phenobarbital and Age of Treatment at Early Life are Two Key Factors for the Persistent Induction of Cytochrome P450 Enzymes in Adult Mouse Liver

The interaction of genes and environment on percent of juniper in the diet of goats divergently selected for high or low juniper consumption

Diet selection and preference by grazing animals are determined by genetic and environmental factors that interact and affect their efficacy for managing vegetation as targeted grazers and developing animals adapted to local grazing environments. The effect of the rearing environments on the consumption of juniper (Juniperus spp.) by goats that for 15 years were divergently selected for high (J+) or low (J-) percent juniper in their diet was investigated. To test the effect of rearing environment, at the end of the breeding season, pregnant does from both selection lines were grazed on either juniper-infested (JIR) or juniper-free (JFR) rangelands until their kids were weaned at about 75 days of age. Fecal samples were analyzed with fecal near-IR spectroscopy to determine the percent juniper in the diet. Fecal samples were collected from does on JIR when their offspring were 30 days of age and at weaning. Then, does that raised kids in both rearing environments grazed a common JIR pasture for a 28-day adaptation period before collecting fecal samples. After weaning, kids from both rearing environments grazed JIR for 22 days before collecting fecal samples. The J+ does always consumed more (P < 0.001) juniper than J- does, demonstrating different maternal role models for kids reared in the JIR environment. There was no effect of rearing environment (P = 0.488) or rearing environment × selection line interaction (P = 0.096) when J- and J+ does grazed a common JIR pasture. The percentage of juniper in J- kid diets (7%) was the same regardless of the rearing environment. However, the rearing environment did affect the percentage of juniper in the diet of J+ kids, resulting in a gene-environment interaction (P = 0.022). The percentage of juniper in the diet of J+ kids reared in JFR (16%) and JIR (24%) were about two and three times higher than J- kids, respectively, indicating that genetics and the rearing environment contributed about equally to the increase in the percentage of juniper in the J+ kid diets. Regardless of the rearing environment, the J+ kids had a higher percentage of juniper in their diets than J- kids (P < 0.001). Compared to males, female kids had a higher percentage of juniper in their diets (12 vs 17%, respectively; P = 0.002). The ability to select animals with specific dietary preferences holds promise for targeted grazing strategies to restore degraded rangelands, with potential applications in conservation and ecosystem management.

Early life phenobarbital exposure dysregulates the hippocampal transcriptome

Introduction: Phenobarbital (PB) and levetiracetam (LEV) are the first-line therapies for neonates with diagnosed seizures, however, a growing body of evidence shows that these drugs given during critical developmental windows trigger lasting molecular changes in the brain. While the targets and mechanism of action of these drugs are well understood-what is not known is how these drugs alter the transcriptomic landscape, and therefore molecular profile/gene expression during these critical windows of neurodevelopment. PB is associated with a range of neurotoxic effects in developing animals, from cell death to altered synaptic development to lasting behavioral impairment. LEV does not produce these effects. Methods: Here we evaluated the effects of PB and Lev on the hippocampal transcriptome by RNA sequencing. Neonatal rat pups were given a single dose of PB, Lev or vehicle and sacrificed 72 h later-at time at which drug is expected to be cleared. Results: We found PB induces broad changes in the transcriptomic profile (124 differentially expressed transcripts), as compared to relatively small changes in LEV-treated animals (15 transcripts). PB exposure decreased GABAergic and oligodendrocyte markers pvalb and opalin, and increased the marker of activated microglia, cd68 and the astrocyte- associated gene vegfa. These data are consistent with the existing literature showing developmental neurotoxicity associated with PB, but not LEV. Discussion: The widespread change in gene expression after PB, which affected transcripts reflective of multiple cell types, may provide a link between acute drug administration and lasting drug toxicity.

Attenuation of phenobarbital-induced cytochrome P450 expression in carbon tetrachloride-induced hepatitis in mice models

Certain pathological conditions, such as inflammation, are known to affect basal cytochrome P450 (CYP) expression by modulating transcriptional regulation, and the pharmacokinetics of drugs can vary among patients. However, changes in drug-induced CYP expression under pathological conditions have not been elucidated in detail. Here, we investigated the effects of hepatic inflammation and injury on phenobarbital-induced expression of CYP isoforms in mice. Phenobarbital was administered once as a CYP inducer in the carbon tetrachloride-induced hepatitis model mice. The mRNA expression levels of Cyp3a11 and Cyp2b10 in the liver and small intestine were measured using reverse transcription polymerase chain reaction. The enzymatic activity of CYP3A in liver S9 was evaluated using midazolam as the substrate. Phenobarbital increased the mRNA expression of Cyp3a11 and Cyp2b10 in the liver of healthy mice, but not in the small intestine. Increased mRNA expression of hepatic Cyp3a11 and Cyp2b10 by phenobarbital was significantly suppressed in the hepatitis model mice. Hepatitis also suppressed the increased CYP3A enzymatic activity induced by phenobarbital in liver S9, consistent with the results of Cyp3a11 mRNA expression. These results suggest that the inducibility of CYP by phenobarbital may vary in patients with hepatitis, indicating that pharmacokinetic drug-drug interactions can be altered under certain pathological conditions.

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.

Constitutive Androstane Receptor Agonist, TCPOBOP: Maternal Exposure Impairs the Growth and Development of Female Offspring in Mice

Environmental chemicals, which are known to impact offspring health, have become a public concern. Constitutive activated receptor (CAR) is activated by various environmental chemicals and participates in xenobiotic metabolism. Here, we described the effects of maternal exposure to the CAR-specific ligand 1,4-bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP, TC) on offspring health outcomes. Maternal TC exposure exhibited a stronger inhibition of body weight in 3-week-old and 8-week-old first-generation (F1) offspring female mice compared to controls. Further, maternal TC exposure obtained a strong increase in hepatic drug-metabolizing enzyme expression in 3-week-old female mice that persisted into 8-week-old adulthood. Interestingly, we observed distorted intestinal morphological features in 8-week-old F1 female mice in the TC-exposed group. Moreover, maternal TC exposure triggered a loss of intestinal barrier integrity by reducing the expression of intestinal tight junction proteins. Accordingly, maternal exposure to TC down-regulated serum triglyceride levels as well as decreased the expression of intestinal lipid uptake and transport marker genes. Mechanistically, maternal TC exposure activated the intestinal inflammatory response and disrupted the antioxidant system in the offspring female mice, thereby impeding the intestinal absorption of nutrients and seriously threatening offspring health. Altogether, these findings highlight that the effects of maternal TC exposure on offspring toxicity could not be ignored.

Prenatal Lipopolysaccharide Exposure Alters Hepatic Drug-Metabolizing Enzyme Expression in Mouse Offspring via Histone Modifications

Inflammation is a major regulator of drug-metabolizing enzymes (DMEs), therefore contributing to the interindividual variability of drug effects. However, whether prenatal inflammation affects DMEs expression in offspring remains obscure. This study investigated the effects of prenatal lipopolysaccharide (LPS) exposure on hepatic expression of inflammatory-related genes, nuclear receptors, and DMEs in offspring mice. Prenatal LPS exposure on gestational day (GD) 10 led to higher expression of NF-κB, Pxr, and Cyp2b10, while lower expression of Car, Ahr, Cyp3a11, and Ugt1a1 in postnatal day (PD) 30 offspring. However, multiple doses of LPS exposure on GD10-14 resulted in higher levels of inflammatory-related genes, Cyp1a2, and Cyp2b10, and lower levels of Pxr and Cyp3a11 in PD30 offspring liver. For PD60 offspring, decreased hepatic expression of NF-κB and IL-6, and increased expression of Pxr and Cyp3a11 were seen in single-dose LPS groups, whereas opposite results were observed in the multiple-dose LPS groups. Notably, enhanced H3K4me3 levels in the PXR response elements of the Cyp3a11 promoter were observed in the liver of PD60 offspring mice from dams treated with multiple doses of LPS during pregnancy. Overall, this study suggests that parental LPS exposure could persistently alter the hepatic expression of DMEs, and histone modifications may contribute to the long-term effects.

Alterations of Cytochrome P450-Mediated Drug Metabolism during Liver Repair and Regeneration after Acetaminophen-Induced Liver Injury in Mice

Acetaminophen (APAP)-induced liver injury (AILI) is the leading cause of acute liver failure in the United States, but its impact on metabolism, therapeutic efficacy, and adverse drug reactions (ADRs) of co- and/or subsequent administered drugs are not fully investigated. The current work explored this field with a focus on the AILI-mediated alterations of cytochrome P450-mediated drug metabolism. Various levels of liver injury were induced in mice by treatment with APAP at 0, 200, 400, and 600 mg/kg. Severity of liver damage was determined at 24, 48, 72, and 96 hours by plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), microRNA miR122, and tissue staining. The expression and activities of CYP3A11, 1A2, 2B10, 2C29, and 2E1 were measured. Sedation efficacy and ADRs of midazolam, a CYP3A substrate, were monitored after APAP treatment. ALT, AST, and miR122 increased at 24 hours after APAP treatment with all APAP doses, whereas only groups treated with 200 and 400 mg/kg recovered back to normal levels at 72 and 96 hours. The expression and activity of the cytochromes P450 significantly decreased at 24 hours with all APAP doses but only recovered back to normal at 72 and 96 hours with 200 and 400, but not 600, mg/kg of APAP. The alterations of cytochrome P450 activities resulted in altered sedation efficacy and ADRs of midazolam, which were corrected by dose justification of midazolam. Overall, this work illustrated a low cytochrome P450 expression window after AILI, which can decrease drug metabolism and negatively impact drug efficacy and ADRs. SIGNIFICANCE STATEMENT: The data generated in the mouse model demonstrated that expression and activities of cytochrome P450 enzymes and correlated drug efficacy and ADRs are altered during the time course of liver repair and regeneration after liver is injured by treatment with APAP. Dose justifications based on predicted changes of cytochrome P450 activities can achieve desired therapeutic efficacy and avoid ADRs. The generated data provide fundamental knowledge for translational research to drug treatment for patients during liver recovery and regeneration who have experienced AILI.

Effects of Overexpression of Fibroblast Growth Factor 15/19 on Hepatic Drug Metabolizing Enzymes

Fibroblast growth factors 15 (FGF15) and 19 (FGF19) are endocrine growth factors that play an important role in maintaining bile acid homeostasis. FGF15/19-based therapies are currently being tested in clinical trials for the treatment of nonalcoholic steatohepatitis and cholestatic liver diseases. To determine the physiologic impact of long-term elevations of FGF15/19, a transgenic mouse model with overexpression of Fgf15 (Fgf15 Tg) was used in the current study. The RNA sequencing (RNA-seq) analysis revealed elevations of the expression of several genes encoding phase I drug metabolizing enzymes (DMEs), including Cyp2b10 and Cyp3a11, in Fgf15 Tg mice. We found that the induction of several Cyp2b isoforms resulted in increased function of CYP2B in microsomal metabolism and pharmacokinetics studies. Because the CYP2B family is known to be induced by constitutive androstane receptor (CAR), to determine the role of CAR in the observed inductions, we crossed Fgf15 Tg mice with CAR knockout mice and found that CAR played a minor role in the observed alterations in DME expression. Interestingly, we found that the overexpression of Fgf15 in male mice resulted in a phenotypical switch from the male hepatic expression pattern of DMEs to that of female mice. Differences in secretion of growth hormone (GH) between male and female mice are known to drive sexually dimorphic, STAT5b-dependent expression patterns of hepatic genes. We found that male Fgf15 Tg mice presented with many features similar to GH deficiency, including lowered body length and weight, Igf-1 and Igfals expression, and STAT5 signaling. SIGNIFICANCE STATEMENT: The overexpression of Fgf15 in mice causes an alteration in DMEs at the mRNA, protein, and functional levels, which is not entirely due to CAR activation but associated with lower GH signaling.

Induction by Phenobarbital of Phase I and II Xenobiotic-Metabolizing Enzymes in Bovine Liver: An Overall Catalytic and Immunochemical Characterization

In cattle, phenobarbital (PB) upregulates target drug-metabolizing enzyme (DME) mRNA levels. However, few data about PB's post-transcriptional effects are actually available. This work provides the first, and an almost complete, characterization of PB-dependent changes in DME catalytic activities in bovine liver using common probe substrates and confirmatory immunoblotting investigations. As expected, PB increased the total cytochrome P450 (CYP) content and the extent of metyrapone binding; moreover, an augmentation of protein amounts and related enzyme activities was observed for known PB targets such as CYP2B, 2C, and 3A, but also CYP2E1. However, contradictory results were obtained for CYP1A, while a decreased catalytic activity was observed for flavin-containing monooxygenases 1 and 3. The barbiturate had no effect on the chosen hydrolytic and conjugative DMEs. For the first time, we also measured the 26S proteasome activity, and the increase observed in PB-treated cattle would suggest this post-translational event might contribute to cattle DME regulation. Overall, this study increased the knowledge of cattle hepatic drug metabolism, and further confirmed the presence of species differences in DME expression and activity between cattle, humans, and rodents. This reinforced the need for an extensive characterization and understanding of comparative molecular mechanisms involved in expression, regulation, and function of DMEs.

Impact of neonatal activation of nuclear receptor CAR (Nr1i3) on Cyp2 gene expression in adult mouse liver

Perinatal exposure to environmental chemicals is proposed to reprogram development and alter disease susceptibility later in life. Supporting this, neonatal activation of the nuclear receptor CAR (Nr1i3) by TCPOBOP induces persistent expression of mouse hepatic Cyp2 genes into adulthood, attributed to long-term epigenetic memory of the early life exposure [Hepatology (2012) 56:1499-1509]. Here, we confirm that the same high-dose (15x ED50) neonatal TCPOBOP exposure used in that work induces prolonged (12 weeks) increases in hepatic Cyp2 expression; however, we show that the persistence of expression can be fully explained by the persistence of residual TCPOBOP in liver tissue. When the long-term presence of TCPOBOP in tissue was eliminated by decreasing the neonatal TCPOBOP dose 22-fold (0.67x ED50), strong neonatal increases in hepatic Cyp2 expression were still obtained but did not persist into adulthood. Furthermore, the neonatal ED50-range TCPOBOP exposure did not sensitize mice to a subsequent, low-dose TCPOBOP treatment. In contrast, neonatal treatment with phenobarbital, a short half-life (t1/2=8 h) agonist of CAR and of PXR (Nr1i2), induced high-level neonatal activation of Cyp2 genes and also altered their responsiveness to low-dose phenobarbital exposure at adulthood by either increasing (Cyp2b10) or decreasing (Cyp2c55) expression. Thus, neonatal xenobiotic exposure can reprogram hepatic Cyp2 genes and alter their responsiveness to exposures later in life. These findings highlight the need to carefully consider xenobiotic dose, half-life and persistence in tissue when evaluating the long-term effects of early life environmental chemical exposures.

Epigenetics and microRNAs in UGT1As

UDP-glucuronosyltransferases (UGTs) are the main phase II drug-metabolizing enzymes mediating the most extensive glucuronidation-binding reaction in the human body. The UGT1A family is involved in more than half of glucuronidation reactions. However, significant differences exist in the distribution of UGT1As in vivo and the expression of UGT1As among individuals, and these differences are related to the occurrence of disease and differences in metabolism. In addition to genetic polymorphisms, there is now interest in the contribution of epigenetics and noncoding RNAs (especially miRNAs) to this differential change. Epigenetics regulates UGT1As pretranscriptionally through DNA methylation and histone modification, and miRNAs are considered the key mechanism of posttranscriptional regulation of UGT1As. Both epigenetic inheritance and miRNAs are involved in the differences in sex expression and in vivo distribution of UGT1As. Moreover, epigenetic changes early in life have been shown to affect gene expression throughout life. Here, we review and summarize the current regulatory role of epigenetics in the UGT1A family and discuss the relationship among epigenetics and UGT1A-related diseases and treatment, with references for future research.

New nanocarried phenobarbital formulation: Maintains better control of pentylenetetrazole-Induced seizures

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For the first time, phenobarbital was intercalated in the layered double hydroxide.

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This study evaluated the slow release efficacy of intercalated phenobarbital.

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The time of the anticonvulsant effect was verified by electroencephalographic records.

This study aims to evaluate the efficacy of slow release phenobarbital in the control of convulsions triggered by pentylenetetrazole (PTZ), verifying the time of permanence in the anticonvulsant effect through behavior and electroencephalographic records. A total of 162 male Wistar rats weighing between 100 and 120 g were divided into two groups, one for behavior analysis (n = 90) and biochemistry, and another for the acquisition of electrocorticographic record (n = 72). Hepatic enzymes were measured by obtaining a blood sample from the animals studied by means of a biochemical analysis. The procedures for electrode implant and electrocorticographic recordings were performed. The intercalation of phenobarbital in layered double hydroxide (LDH) nanocarrier allowed us to evaluate a new slow release pharmaceutical formulation based on methodologies that have proven longer residence time and lower side effects. This study demonstrates that phenobarbital can be a new perspective pharmaceutical formulation.

Acetaminophen-Induced Liver Injury Alters Expression and Activities of Cytochrome P450 Enzymes in an Age-Dependent Manner in Mouse Liver

Drug-induced liver injury (DILI) is a global medical problem. The risk of DILI is often related to expression and activities of drug-metabolizing enzymes, especially cytochrome P450s (P450s). However, changes on expression and activities of P450s after DILI have not been determined. The aim of this study is to fill this knowledge gap. Acetaminophen (APAP) was used as a model drug to induce DILI in C57BL/6J mice at different ages of days 10 (infant), 22 (child), and 60 (adult). DILI was assessed by levels of alanine aminotransferase and aspartate aminotransferase in plasma with a confirmation by H&E staining on liver tissue sections. The expression of selected P450s at mRNA and protein levels was measured by real-time polymerase chain reaction and liquid chromatography-tandem mass spectrometry, respectively. The activities of these P450s were determined by the formation of metabolites from probe drugs for each P450 using ultraperformance liquid chromatography-quadrupole time of flight mass spectrometry. DILI was induced at mild to severe levels in a dose-dependent manner in 200, 300, and 400 mg/kg APAP-treated groups at child and adult ages, but not at the infant age. Significantly decreased expression at mRNA and protein levels as well as enzymatic activities of CYP2E1, 3A11, 1A2, and 2C29 were found at child and adult ages. Adult male mice were more susceptible to APAP-induced liver injury than female mice with more decreased expression of P450s. These results suggest that altered levels of P450s in livers severely injured by drugs may affect the therapeutic efficacy of drugs, which are metabolized by P450s, more particularly for males. SIGNIFICANCE STATEMENT: The current study in an animal model demonstrates that acetaminophen-induced liver injury results in decreased expression and enzyme activities of several examined drug-metabolizing cytochrome P450s (P450s). The extent of such decreases is correlated to the degree of liver injury severity. The generated data may be translated to human health for patients who have drug-induced liver injury with decreased capability to metabolize drugs by certain P450s.

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.

Multiomics analysis profile acute liver injury module clusters to compare the therapeutic efficacy of bifendate and muaddil sapra

The pathogenesis of acute liver injury has been plagued by biologists and physicians. We know little about its therapeutic mechanism. Therefore, this study explored the mechanism of bifendate and muaddil sapra in the treatment of acute liver injury. Firstly, co-expression and cluster analysis of disease-related genes were carried out, and the Go function and KEGG pathway of modules and related genes were identified. Secondly, pivot analysis of modules can identify key regulators. On the other hand, based on the acute liver injury induced by CCl4, we use the combined analysis of proteomics and transcriptome to find therapeutic targets and related mechanisms of drugs. A total of 21 dysfunction modules were obtained, which were significantly involved in immune system, hepatitis and other related functions and pathways. Transcriptome analysis showed 117 targets for bifendate treatment, while 119 for muaddil sapra. Through exploring the mechanism, we found that the two drugs could modulate the module genes. Moreover, bifendate regulate the dysfunction module through ncRNA (SNORD43 and RNU11). Muaddil sapra can mediate dysfunction modules not only by regulating ncRNA (PRIM2 and PIP5K1B), but also by regulating TF (STAT1 and IRF8), thus having a wider therapeutic potential. On the other hand, proteome analysis showed that bifendate mainly regulated Rac2, Fermt3 and Plg, while muaddil sapra mainly regulated Sqle and Stat1. In addition, muaddil sapra regulates less metabolic related proteins to make them more effective. Overall, this study not only provides basic theory for further study of the complex pathogenesis of acute liver injury, but also provides valuable reference for clinical use of bifendate and muaddil sapra in the treatment of acute liver injury.

Effects of androsterone on the protective action of various antiepileptic drugs against maximal electroshock-induced seizures in mice

This study evaluated the effect of androsterone (AND), a metabolite of testosterone, on the ability of selected classical and novel antiepileptic drugs to prevent seizures caused by maximal electroshock (MES), which may serve as an experimental model of human generalized tonic-clonic seizures in mice. Single intraperitoneal (i.p.) administration of AND (80 mg kg^-1) significantly raised the threshold for convulsions in the MES seizure threshold test. Lower doses of AND (5, 10, 20, and 40 mg kg^-1) failed to change the threshold. AND at a subthreshold dose of 40 mg kg^-1 significantly enhanced the protective activity of carbamazepine, gabapentin, and phenobarbital against MES-induced seizures decreasing their median effective doses (ED₅₀) values ± SEM from 8.59 ± 0.76 to 6.05 ± 0.81 mg kg^-1 (p = 0.0308) for carbamazepine, from 419.9 ± 120.6 to 111.5 ± 41.1 mg kg^-1 (p = 0.0405) for gabapentin, and from 20.86 ± 1.64 to 10.0 ± 1.21 mg kg^-1 (p = 0.0007) for phenobarbital. There were no significant changes in total brain concentrations of carbamazepine, gabapentin, and phenobarbital following AND administration. This suggests that the enhancing effects of AND on the protective activity of these antiepileptic drugs are not related to pharmacokinetic factors. A lower dose of AND (20 mg kg^-1) had no effect on the protective activity of carbamazepine, gabapentin, and phenobarbital. AND administered at a dose of 40 mg kg^-1 failed to change the anticonvulsant activity of lamotrigine, oxcarbazepine, phenytoin, topiramate, and valproate in the MES test. In the chimney test, AND given at a dose enhancing the protective activity of carbamazepine, gabapentin, and phenobarbital (which alone was without effect on motor performance of mice) did not affect impairment of motor coordination produced by the antiepileptics. Our findings recommend further preclinical and clinical research on AND in respect of its use as adjuvant therapy in the management of epilepsy in men with deficiency of androgens.

Health-Relevant Phenotypes in the Offspring of Mice Given CAR Activators Prior to Pregnancy

Hepatic induction in response to drugs and environmental chemicals affects drug therapies and energy metabolism. We investigated whether the induction is transmitted to the offspring. We injected 3-day- and 6-week-old F0 female mice with TCPOBOP, an activator of the nuclear receptor constitutive androstane receptor (CAR, NR1I3), and mated them 1-6 weeks afterward. We detected in the offspring long-lasting alterations of CAR-mediated drug disposition, energy metabolism, and lipid profile. The transmission to the first filial generation (F1) was mediated by TCPOBOP transfer from the F0 adipose tissue via milk, as revealed by embryo transfer, crossfostering experiments, and liquid chromatography-mass spectrometry analyses. The important environmental pollutant PCB153 activated CAR in the F1 generation in a manner similar to TCPOBOP. Our findings indicate that chemicals accumulating and persisting in adipose tissue may exert liver-mediated, health-relevant effects on F1 offspring simply via physical transmission in milk. Such effects may occur even if treatment has been terminated far ahead of conception. This should be considered in assessing developmental toxicity and in the long-term follow-up of offspring of mothers exposed to both approved and investigational drugs, and to chemicals with known or suspected accumulation in adipose tissue.

Consequences of Phenytoin Exposure on Hepatic Cytochrome P450 Expression during Postnatal Liver Maturation in Mice

The induction of cytochrome P450 (P450) enzymes in response to drug treatment is a significant contributing factor to drug-drug interactions, which may reduce therapeutic efficacy and/or cause toxicity. Since most studies on P450 induction are performed in adults, enzyme induction at neonatal, infant, and adolescent ages is not well understood. Previous work defined the postnatal ontogeny of drug-metabolizing P450s in human and mouse livers; however, there are limited data on the ontogeny of the induction potential of each enzyme in response to drug treatment. Induction of P450s at the neonatal age may also cause permanent alterations in P450 expression in adults. The goal of this study was to investigate the short- and long-term effects of phenytoin treatment on mRNA and protein expressions and enzyme activities of CYP2B10, 2C29, 3A11, and 3A16 at different ages during postnatal liver maturation in mice. Induction of mRNA immediately following phenytoin treatment appeared to depend on basal expression of the enzyme at a specific age. While neonatal mice showed the greatest fold changes in CYP2B10, 2C29, and 3A11 mRNA expression following treatment, the levels of induced protein expression and enzymatic activity were much lower than that of induced levels in adults. The expression of fetal CYP3A16 was repressed by phenytoin treatment. Neonatal treatment with phenytoin did not permanently induce enzyme expression in adulthood. Taken together, our data suggest that inducibility of drug-metabolizing P450s is much lower in neonatal mice than it is in adults and neonatal induction by phenytoin is not permanent.

Liver lobe and strain differences in the activity of murine cytochrome P450 enzymes

The cytochrome P450 (CYP) enzyme superfamily is the most important enzyme system for phase I biotransformation. For toxico- and pharmacokinetic studies, use of liver-based microsomes, including those of mice, is state-of-the-art to study CYP-dependent metabolism. However, reproducibility and interpretation of these data is still very variable, partly because current testing guidelines do not cover details on organ sampling and potential liver lobe differences. Hence, we analyzed CYP activity, CYP protein content, mRNA expression of CYP1A, CYP2C, CYP2D and CYP3A isozymes, and cytochrome P450 reductase (CPR) activity of the four different liver lobes and processus papillaris of male C57BL/6J mice in comparison to whole liver. Additionally, we used whole liver of Balb/cJ and 129S1/SvImJ for strain comparison. Our data show significant differences in CYP activity, being most prominent in lobus sinister lateralis and lobus medialis, and lowest in processus papillaris. These differences were not caused by varying Cyp gene expression or CYP protein level, but partly correspond with lobe specific CPR activities. We also observed significant strain differences in CYP mRNA expression and activities with overall high activities in 129S1/SvImJ mice and low activities in Balb/cJ mice compared to C57BL/6J mice. In addition, strain specific differences in CYP2C and CYP2D activity seem to be reflected in strain dependent differences in CPR activity. In summary, our results indicate that in mice CYP activity and gene expression are strain dependent and may vary highly between liver lobes. To ensure reproducibility and comparability of different probes and studies, this should be taken into account when liver samples are collected for the analysis of CYP-dependent metabolism.

Phenobarbital Treatment at a Neonatal Age Results in Decreased Efficacy of Omeprazole in Adult Mice

Drug-drug interactions (DDIs) occur when the action of one drug interferes with or alters the activity of another drug taken concomitantly. This can lead to decreased drug efficacy or increased toxicity. Because of DDIs, physicians in the clinical practice attempt to avoid potential interactions when multiple drugs are coadministrated; however, there is still a large knowledge gap in understanding how drugs taken in the past can contribute to DDIs in the future. The goal of this study was to investigate the consequence of neonatal drug exposure on efficacy of other drugs administered up through adult life. We selected a mouse model to test phenobarbital exposure at a neonatal age and its impact on efficacy of omeprazole in adult life. The results of our experiment show an observed decrease in omeprazole's ability to raise gastric pH in adult mice that received single or multiple doses of phenobarbital at a neonatal age. This effect may be associated with the permanent induction of cytochrome P450 enzymes in adult liver after neonatal phenobarbital treatment. Our data indicates that DDIs may result from drugs administered in the past in an animal model and should prompt re-evaluation of how DDIs are viewed and how to avoid long-term DDIs in clinical practice.

Impact of Drug Treatment at Neonatal Ages on Variability of Drug Metabolism and Drug-drug Interactions in Adult Life

PURPOSE OF REVIEW

As the number of patients taking more than one medication concurrently continues to increase, predicting and preventing drug-drug interactions (DDIs) is now more important than ever. Administration of one drug can cause changes in the expression and activity of drug metabolizing enzymes (DMEs) and alter the efficacy or toxicity of other medications that are substrates for these enzymes, resulting in a DDI. In today's medical practice, potential DDIs are evaluated based on the current medications a patient is taking with little regard to drugs the patient has been exposed to in the past. The purpose of this review is to discuss potential impacts of drug treatment at neonatal ages on the variability of drug metabolism and DDIs in adult life.

RECENT FINDINGS

Existing evidence from the last thirty years has shown that exposure to certain xenobiotics during neonatal life has the potential to persistently alter DME expression through adult life. With recent advancements in the understanding of epigenetic regulation on gene expression, this phenomenon is resurfacing in the scientific community in hopes of defining possible mechanisms. Exposure to compounds that have the ability to bind nuclear receptors and trigger epigenetic modifications at neonatal and pediatric ages may have long-term, if not permanent, consequences on gene expression and DME activity.

SUMMARY

The information summarized in this review should challenge the way current healthcare providers assess DDI potential and may offer an explanation to the significant interindividual variability in drug metabolism that is observed among patients.

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.

Interindividual Variability in Cytochrome P450-Mediated Drug Metabolism

The cytochrome P450 (P450) enzymes are the predominant enzyme system involved in human drug metabolism. Alterations in the expression and/or activity of these enzymes result in changes in pharmacokinetics (and consequently the pharmacodynamics) of drugs that are metabolized by this set of enzymes. Apart from changes in activity as a result of drug-drug interactions (by P450 induction or inhibition), the P450 enzymes can exhibit substantial interindividual variation in basal expression and/or activity, leading to differences in the rates of drug elimination and response. This interindividual variation can result from a myriad of factors, including genetic variation in the promoter or coding regions, variation in transcriptional regulators, alterations in microRNA that affect P450 expression, and ontogenic changes due to exposure to xenobiotics during the developmental and early postnatal periods. Other than administering a probe drug or cocktail of drugs to obtain the phenotype or conducting a genetic analysis to determine genotype, methods to determine interindividual variation are limited. Phenotyping via a probe drug requires exposure to a xenobiotic, and genotyping is not always well correlated with phenotype, making both methodologies less than ideal. This article describes recent work evaluating the effect of some of these factors on interindividual variation in human P450-mediated metabolism and the potential utility of endogenous probe compounds to assess rates of drug metabolism among individuals.

Biotransformation of Cobicistat: Metabolic Pathways and Enzymes

BACKGROUND

Cobicistat (COBI) is a pharmacoenhancer for antiretroviral therapy.

OBJECTIVE

The current study was designed to profile the metabolic pathways of COBI and to determine the enzymes that contribute to COBI metabolism.

METHOD

We screened COBI metabolites in mice and human liver microsomes. We also used cDNAexpressed human cytochromes P450 (CYPs) to explore the role of human enzymes in COBI metabolism.

RESULTS

Twenty new and three known metabolites of COBI were identified in mouse urine and feces. These new metabolic pathways of COBI include glycine conjugation, N-acetyl cysteine conjugation, morpholine ring-opening, and thiazole ring-opening. Twelve of COBI metabolites were further confirmed in mouse and human liver microsomes, including nine new metabolites. Consistent with the previous report, CYP3A4 and CYP2D6 were determined as the major enzymes that contribute to COBI metabolism.

CONCLUSION

This study provided a full map of COBI metabolism. These results can be used to manage CYP-mediated drug-drug interactions and adverse drug reactions that are associated with COBI-containing regimens in human.