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Naltrexone, an opioid antagonist primarily metabolized by aldo-keto reductase 1C4 (AKR1C4), treats pediatric conditions involving compulsiveness (e.g., autism spectrum, Prader-Willi, eating disorders, non-suicidal self-injury). Pharmacokinetic variability is apparent in adults, yet no data are available for children. This study aimed to examine the impact of age and genetic variation on naltrexone biotransformation. Human liver cytosol (HLC) samples (n = 158) isolated from children and adult organ donors were incubated with therapeutically relevant concentrations of naltrexone (0.1, 1 µM). Naltrexone biotransformation was determined by ultraperformance mass spectrometry quantification of the primary metabolite, 6-beta-naltrexol (6βN), and 6βN formation rates (pmol/mg protein/min) were calculated. HLCs from organ donors, age range 0–79 y (mean 16.0 ± 18.2 y), 37% (n = 60) female, 20% (n = 33) heterozygous and 1.2% (n = 2) homozygous for co-occurring AKR1C4 variants (S145C/L311V) showed >200-fold range in 6βN formation (0.37–76.5 pmol/mg protein/min). Source of donor samples was found to be a substantial contributor to variability. Model estimates for a trimmed data set of source-adjusted pediatric samples (aged 0–18 y) suggested that AKR1C4 genetic variation, age, and sex explained 36% of the variability in 6βN formation. Although activity increased steadily from birth and peaked in middle childhood (2–5 years), genetic variation (S145C/L311V) demonstrated a greater effect on activity than did age. Naltrexone biotransformation is highly variable in pediatric and adult livers and can be partly accounted for by individual factors feasible to obtain (e.g., genetic variability, age, sex). These data may inform a precision therapeutics approach (e.g., exposure optimization) to further study Naltrexone responsiveness in children and adults. SIGNIFICANCE STATEMENT: Biotransformation of the commonly used opioid antagonist naltrexone is highly variable and may contribute to reduced therapeutic response. Age, sex, and genetic variation in the drug-metabolizing enzyme, AKR1C4, are potential factors contributing to this variability. In pediatric samples, genetic variation (S145C/L311V) demonstrates a greater impact on activity than age. Additionally, the source of donor samples was identified as an important contributor and must be accounted for to confidently elucidate the biological variables most impactful to drug biotransformation.

Microsomal protein per gram of liver (MPPGL) is an important scaling factor for bottom-up physiology-based pharmacokinetic modeling and simulation, but data in pediatrics are limited. Therefore, MPPGL was determined in 160 liver samples from pediatric (n = 129) and adult (n = 31) donors obtained from four sources: the University of Maryland Brain and Tissue Bank (UMBTB), tissue retrieval services at the University of Minnesota and University of Pittsburgh, and Sekisui-Xenotech. Tissues were homogenized and subjected to differential centrifugation to prepare microsomes, and cytochrome c reductase activities in tissue homogenates and microsomes were used to estimate cytochrome P450 reductase (POR) activity as a marker of microsomal recovery; microsomal POR content was also assessed by quantitative proteomics. MPPGL values varied 5- to 10-fold within various age groups/developmental stages, and tissue source was identified as a contributing factor. Using a “trimmed” dataset comprised of samples ranging from 3 to 18 years of age common to the four sources, POR protein abundance and activity in microsomes and POR activity in homogenates was lower in UMBTB samples (autopsy) compared with other sources (perfused/flash-frozen). Regression analyses revealed that the UMBTB samples were driving an apparent age effect as no effect of age on log-transformed MPPGL values was observed when the UMBTB samples were excluded. We conclude that a mean±SD MPPGL value of 30.4±1.7 mg/g is representative between one month postnatal age and early adulthood. Potential source effects should be considered for studies involving tissue samples from multiple sources with different procurement and processing procedures. SIGNIFICANCE STATEMENT: Microsomal protein per gram of liver (MPPGL) is an important scaling factor for bottom up PBPK modeling and simulation, but data in pediatrics are limited. Although MPPGL varies 5- to 10-fold at a given developmental stage, a value of 30.4 ± 1.7 mg/g (mean ± SD) is representative between one month postnatal age and early adulthood. However, when tissue samples are obtained from multiple sources, different procurement and processing procedures may influence the results and should be taken into consideration.

Indomethacin is used commonly in preterm neonates for the prevention of intracranial hemorrhage and closure of an abnormally open cardiac vessel. Due to biomedical advances, the infants who receive this drug in the neonatal intensive care unit setting have become younger, smaller, and less mature (more preterm) at the time of treatment. To develop a pharmacokinetics (PK) model to aid future dosing, we designed a prospective cohort study to characterize indomethacin PK in a dynamically changing patient population. A population PK base model was created using NONMEM, and a covariate model was developed in a primary development cohort and subsequently was tested for accuracy in a validation cohort. Postnatal age was a significant covariate for hepatic clearance (CL

Pharmacogenetics (PGx) seeks to enable selection of the right dose of the right drug for each patient to optimize therapeutic outcomes. Most PGx focuses on pharmacokinetics (PKs), due to our relatively advanced understanding of the genes involved in PKs and the causative effects of variants in those genes. Genetic variants can also affect pharmacodynamics (PDs), but relatively few PGx-PD associations have been identified. This is partially due to a more limited understanding of the relevant genes and the consequences of genetic variation, but is also due in part to the potential confounding of PK variability in assessments of clinical outcomes that have a contribution from both PKs and PDs. For example, it is challenging to confirm the effect of mu opioid receptor (OPRM1) genetic variation on opioid response due to the contribution of CYP2D6 genotype to bioactivation of some opioid drugs (i.e., codeine and tramadol). The objectives of this mini-review are to describe several recent efforts to discover and validate PGx-PD that disentangle the influence of PK variability and propose potential approaches that could be used in future PGx-PD analyses. We use the effect of OPRM1 genetics on opioid response to illustrate how these analyses could be conducted and conclude by discussing how PGx-PD could be translated into clinical practice to improve therapeutic outcomes.

Developmental changes that occur throughout childhood have long been known to impact drug disposition. However, pharmacokinetic studies in the paediatric population have historically been limited due to ethical concerns arising from incorporating children into clinical trials. As such, much of the early work in the field of developmental pharmacology was reliant on difficult-to-interpret in vitro and in vivo animal studies. Over the last 2 decades, our understanding of the mechanistic processes underlying age-related changes in drug disposition has advanced considerably. Progress has largely been driven by technological advances in mass spectrometry-based methods for quantifying proteins implicated in drug disposition, and in silico tools that leverage these data to predict age-related changes in pharmacokinetics. This review summarizes our current understanding of the impact of childhood development on drug disposition, particularly focusing on research of the past 20 years, but also highlighting select examples of earlier foundational research. Equally important to the studies reviewed herein are the areas that we cannot currently describe due to the lack of research evidence; these gaps provide a map of drug disposition pathways for which developmental trends still need to be characterized.

Opioids are mainly used to treat both acute and chronic pain. Several opioids are metabolized to some extent by CYP2D6 (codeine, tramadol, hydrocodone, oxycodone, and methadone). Polymorphisms in CYP2D6 have been studied for an association with the clinical effect and safety of these drugs. Other genes that have been studied for their association with opioid clinical effect or adverse events include OPRM1 (mu receptor) and COMT (catechol-O-methyltransferase). This guideline updates and expands the 2014 Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 genotype and codeine therapy and includes a summation of the evidence describing the impact of CYP2D6, OPRM1, and COMT on opioid analgesia and adverse events. We provide therapeutic recommendations for the use of CYP2D6 genotype results for prescribing codeine and tramadol and describe the limited and/or weak data for CYP2D6 and hydrocodone, oxycodone, and methadone, and for OPRM1 and COMT for clinical use.

Cytochrome P450 2D6 (CYP2D6), is responsible for the metabolism and elimination of approximately 25% of clinically used drugs, including antidepressants and antipsychotics, and its activity varies considerably on a population basis primary due to genetic variation. CYP2D6 phenotype can be assessed

This study investigated the impact of SLCO1B1 genotype on rosuvastatin systemic exposure in hypercholesterolemic children and adolescents. Participants (8-21 years) with at least one allelic variant of SLCO1B1 c.521T>C (521TC, n = 13; 521CC, n = 2) and wild type controls (521TT, n = 13) completed a single oral dose pharmacokinetic study. The variability contributed by SLCO1B1 c.521 sequence variation to rosuvastatin (RVA) systemic exposure among our pediatric cohort was comparable to previous studies in adults. RVA concentration-time curve from 0-24 hours (AUC0-24 ) was 1.4-fold and 2.2-fold higher in participants with c.521TC and c.521CC genotype compared 521TT participants, respectively. Interindividual variability of RVA exposure within SLCO1B1 genotype groups exceeded the ~ 1.5-fold to 2-fold difference in mean RVA exposure observed among SLCO1B1 genotype groups, suggesting that other factors also contribute to interindividual variability in the rosuvastatin dose-exposure relationship. A multivariate model performed confirmed SLCO1B1 c.521T>C genotype as the primary factor contributing to RVA systemic exposure in this pediatric cohort, accounting for ~ 30% of the variability RVA AUC0-24 . However, of the statins investigated to date in the pediatric population, RVA has the lowest magnitude of variability in systemic exposure.

Mitochondrial amidoxime-reducing component (mARC) enzymes are molybdenum-containing proteins that metabolize a number of endobiotics and xenobiotics. The interindividual variability and differential tissue abundance of mARC1 and mARC2 were quantified using targeted proteomics in three types of tissue fractions: 1) pediatric liver tissue homogenates, 2) total membrane fraction of the paired liver and kidney samples from pediatric and adult donors, and 3) pooled S9 fractions of the liver, intestine, kidney, lung, and heart. The absolute levels of mARC1 and mARC2 in the pediatric liver homogenate were 40.08 ± 4.26 and 24.58 ± 4.02 pmol/mg homogenate protein, respectively, and were independent of age and sex. In the total membrane fraction of the paired liver and kidney samples, the abundance of hepatic mARC1 and mARC2 was comparable, whereas mARC2 abundance in the kidney was approximately 9-fold higher in comparison with mARC1. The analysis of the third set of samples (i.e., S9 fraction) revealed that mARC1 abundance in the kidney, intestine, and lung was 5- to 13-fold lower than the liver S9 abundance, whereas mARC2 abundance was approximately 3- and 16-fold lower in the intestine and lung than the liver S9, respectively. In contrast, the kidney mARC2 abundance in the S9 fraction was approximately 2.5-fold higher as compared with the hepatic mARC2 abundance. The abundance of mARC enzymes in the heart was below the limit of quantification (∼0.6 pmol/mg protein). The mARC enzyme abundance data presented here can be used to develop physiologically based pharmacokinetic models for the prediction of in vivo pharmacokinetics of mARC substrates. SIGNIFICANCE STATEMENT: A precise targeted quantitative proteomics method was developed and applied to quantify newly discovered drug-metabolizing enzymes, mARC1 and mARC2, in pediatric and adult tissue samples. The data suggest that mARC enzymes are ubiquitously expressed in an isoform-specific manner in the human liver, kidney, intestine, and lung, and the enzyme abundance is not associated with age and sex. These data are important for developing physiologically based pharmacokinetic models for the prediction of in vivo pharmacokinetics of mARC substrates.

An accurate understanding of the changes in height and weight of children with age is critical to the development of models predicting drug concentrations in children (i.e., physiologically-based pharmacokinetic models). However, curves describing the growth of a typical population of children may not accurately characterize growth of children with various conditions, such as obesity. Therefore, to develop height and weight versus age growth curves for youth who were diagnosed with type 2 diabetes, we extracted data from electronic medical records. Robust nonlinear models were parameterized to the equations describing height and weight versus age as defined by the Centers for Disease Control and Prevention (CDC). CDC z-scores were calculated using an internal program. The growth curves and z-scores were compared to CDC norms. Youth with type 2 diabetes were increasingly heavier than CDC norms from early childhood. Except for a period around puberty, youth with type 2 diabetes were, on average, shorter than CDC norms, resulting in shorter average adult height. Deviations in growth were apparent in youth who develop type 2 diabetes; such deviations may be expected for other conditions as well, and disease-specific growth curves should be considered during development of model-informed drug development for pediatric conditions.

Almost 50% of prescription drugs lack age-appropriate dosing guidelines and therefore are used "off-label." Only ~10% drugs prescribed to neonates and infants have been studied for safety or efficacy. Immaturity of drug metabolism in children is often associated with drug toxicity. This chapter summarizes data on the ontogeny of major human metabolizing enzymes involved in oxidation, reduction, hydrolysis, and conjugation of drugs. The ontogeny data of individual drug-metabolizing enzymes are important for accurate prediction of drug pharmacokinetics and toxicity in children. This information is critical for designing clinical studies to appropriately test pharmacological hypotheses and develop safer pediatric drugs, and to replace the long-standing practice of body weight- or surface area-normalized drug dosing. The application of ontogeny data in physiologically based pharmacokinetic model and regulatory submission are discussed.

The purpose of this study is to test the hypothesis that race and supplementation affect the concentration and correlation of various folate species in maternal and umbilical cord blood.This is a single-center, prospective, cross-sectional cohort of cord blood samples obtained from 40 uncomplicated term pregnancies as a pilot study, following a protocol approved by the Institutional Review Board. High performance liquid chromatography mass spectrometry quantitated the following concentrations in extracted plasma samples: 5-methyltetrahydrofolate (5MTHF), 5,10-methenyl-tetrahydrofolate (5,10-MeTHF), tetrahydrofolate (THF), and unmetabolized folic acid.Folate concentrations in the umbilical cord plasma were consistently higher than maternal samples for 5MTHF (5MTHF is the most prevalent folate in both cord and maternal plasma, and race and supplementation primarily affect variations in maternal and fetal 5MTHF concentrations and their correlation with each other. However, the greater concentration of THF in cord blood relative to maternal blood offers preliminary insight into the importance of how folate metabolism differs in the specific context of fetal development and physiology, with greater emphasis on DNA synthesis and stability. Furthermore, supplementation appeared to not have as great an impact on African American maternal or cord blood folates, suggesting a variable benefit of current repletion strategies to certain subsets of the population. Future studies that further elucidate these differences and their impact on birth outcomes may help inform supplementation protocols that are more personalized, with greater efficacy in promoting positive perinatal outcomes.

Purpose Poor adherence to dietary/behaviour modifications as interventions for hypercholesterolemia in paediatric patients often necessitates the initiation of statin therapy. The aim of this study was to develop a joint population pharmacokinetic model for simvastatin and four metabolites in children and adolescents to investigate sources of variability in simvastatin acid exposure in this patient population, in addition to SLCO1B1 genotype status. Methods Plasma concentrations of simvastatin and its four metabolites, demographic and polymorphism data for OATP1B1 and CYP3A5 were analysed utilising a population pharmacokinetic modelling approach from an existing single oral dose (10 mg C (rs4149056) on the pharmacokinetics of the active metabolite simvastatin acid in children/adolescents, consistent with adult data. In addition, age was identified as a covariate affecting elimination clearances of 6-hydroxymethyl simvastatin acid and 3, 5 dihydrodiol simvastatin metabolites. Conclusion The model developed describes the pharmacokinetics of simvastatin and its metabolites in children/adolescents capturing the effects of both c.521T>C and age on variability in exposure in this patient population. This joint simvastatin metabolite model is envisaged to facilitate optimisation of simvastatin dosing in children/adolescents. Electronic supplementary material The online version of this article (10.1007/s00228-019-02697-y) contains supplementary material, which is available to authorized users.

Cytosolic sulfotransferases (SULTs), including SULT1A, SULT1B, SULT1E, and SULT2A isoforms, play noteworthy roles in xenobiotic and endobiotic metabolism. We quantified the protein abundances of SULT1A1, SULT1A3, SULT1B1, and SULT2A1 in human liver cytosol samples (n = 194) by liquid chromatography–tandem mass spectrometry proteomics. The data were analyzed for their associations by age, sex, genotype, and ethnicity of the donors. SULT1A1, SULT1B1, and SULT2A1 showed significant age-dependent protein abundance, whereas SULT1A3 was invariable across 0–70 years. The respective mean abundances of SULT1A1, SULT1B1, and SULT2A1 in neonatal samples was 24%, 19%, and 38% of the adult levels. Interestingly, unlike UDP-glucuronosyltransferases and cytochrome P450 enzymes, SULT1A1 and SULT2A1 showed the highest abundance during early childhood (1 to

Despite its widespread use, oral baclofen requires a critical review of the pharmacology to determine potential precision medicine applications to improve medication administration. Discussing the dose→exposure→response relationship of oral baclofen allows a conceptual framework in which designing clinical trials would become more successful. This paper seeks to examine some of the areas where variability in exposures can exist and lead to undesired clinical responses. Several factors are at play to implement precision medicine with oral baclofen in the pediatric patient with cerebral palsy. Variations in intestinal absorption, oral baclofen clearance, pharmacogenomic variants, and distribution of this medication into the cerebrospinal fluid cause differences in the amount of baclofen available at the GABA-B receptor site, causing a clinical response. Oral baclofen has significant variability in disposition and clinical response. Research to determine the causes for this variability and controlling for these factors would allow improvement in clinical outcomes.

Almost 50% of prescription drugs lack age-appropriate dosing guidelines and therefore are used "off-label." Only ~10% drugs prescribed to neonates and infants have been studied for safety or efficacy. Immaturity of drug metabolism in children is often associated with drug toxicity. This chapter summarizes data on the ontogeny of major human metabolizing enzymes involved in oxidation, reduction, hydrolysis, and conjugation of drugs. The ontogeny data of individual drug-metabolizing enzymes are important for accurate prediction of drug pharmacokinetics and toxicity in children. This information is critical for designing clinical studies to appropriately test pharmacological hypotheses and develop safer pediatric drugs, and to replace the long-standing practice of body weight- or surface area-normalized drug dosing. The application of ontogeny data in physiologically based pharmacokinetic model and regulatory submission are discussed.

Background: In utero smoke (IUS) exposure is associated with asthma susceptibility. Objective: We sought to test the hypothesis that changes in miRNA expression by IUS exposure during human lung development is associated with asthma susceptibility. Methods: Gene expression was profiled from 53 IUS unexposed and 51 IUS exposed human fetal lung tissues. We tested for the differential expression of miRNAs across post-conception age and by IUS using linear models with covariate adjustment. We tested the IUS-associated miRNAs for association with their gene expression targets using pair-wise inverse correlation. Using our mouse model, we investigated the persistence of the IUS-associated miRNA signature using RT-PCR from the lungs of mouse pups with and without IUS at postnatal day 14. MiRNAs were then tested for association with asthma and exacerbations using whole blood gene expression profiles from Asthma BRIDGE. Results: Five miRNAs were differentially expressed across post-conception age (adjusted p &lt, 0.0002) including two that were differentially expressed by IUS exposure in human fetal lung (p &lt, 0.05). MiR-15a was differentially expressed by post-conception age (p = 0.00002), IUS exposure in human fetal lung (p = 0.005), and in the post-natal mouse lung (p = 0.01). MiR-15a was also associated with the in utero expression of GSDMB (adjusted p = 0.0002), a known childhood asthma gene and with asthma exacerbations (p = 0.0009) in Asthma BRIDGE. Thus, miR-15a is expressed during human lung development, is impacted by IUS exposure, regulates the intrauterine expression of asthma genes, and is associated with asthma severity. Conclusions: These results provide evidence for the role of miR-15a in the fetal origin of asthma.

Pimozide is a dopamine receptor antagonist indicated for the treatment of Tourette syndrome. Prior in vitro studies characterized N-dealkylation of pimozide to 1,3-dihydro-1-(4-piperidinyl)-2H-benzimidazol-2-one (DHPBI) via CYP3A4 and, to a lesser extent, CYP1A2 as the only notable routes of pimozide biotransformation. However, drug-drug interactions between pimozide and CYP2D6 inhibitors and CYP2D6 genotype–dependent effects have since been observed. To reconcile these incongruities between the prior in vitro and in vivo studies, we characterized two novel pimozide metabolites: 5-hydroxypimozide and 6-hydroxypimozide. Notably, 5-hydroxypimozide was the major metabolite produced by recombinant CYP2D6 (K(m) ∼82 nM, V(max) ∼0.78 pmol/min per picomoles), and DHPBI was the major metabolite produced by recombinant CYP3A4 (apparent K(m) ∼1300 nM, V(max) ∼2.6 pmol/min per picomoles). Kinetics in pooled human liver microsomes (HLMs) for the 5-hydroxylation (K(m) ∼2200 nM, V(max) ∼59 pmol/min per milligram) and N-dealkylation (K(m) ∼3900 nM, V(max) ∼600 pmol/min per milligram) reactions were also determined. Collectively, formation of DHPBI, 5-hydroxypimozide, and 6-hydroxypimozide accounted for 90% of pimozide depleted in incubations of NADPH-supplemented pooled HLMs. Studies conducted in HLMs isolated from individual donors with specific cytochrome P450 isoform protein abundances determined via mass spectrometry revealed that 5-hydroxypimozide (r(2) = 0.94) and 6-hydroxypimozide (r(2) = 0.86) formation rates were correlated with CYP2D6 abundance, whereas the DHPBI formation rate (r(2) = 0.98) was correlated with CYP3A4 abundance. Furthermore, the HLMs differed with respect to their capacity to form 5-hydroxypimozide relative to DHPBI. Collectively, these data confirm a role for CYP2D6 in pimozide clearance via 5-hydroxylation and provide an explanation for a lack of involvement when only DHPBI formation was monitored in prior in vitro studies. SIGNIFICANCE STATEMENT: Current CYP2D6 genotype–guided dosing information in the pimozide label is discordant with available knowledge regarding the primary biotransformation pathways. Herein, we characterize the CYP2D6-dependent biotransformation of pimozide to previously unidentified metabolites. In human liver microsomes, formation rates for the novel metabolites and a previously identified metabolite were determined to be a function of CYP2D6 and CYP3A4 content, respectively. These findings provide a mechanistic basis for observations of CYP2D6 genotype–dependent pimozide clearance in vivo.

Pravastatin acid (PVA) can be isomerized to its inactive metabolite 3′α-iso-pravastatin acid (3αPVA) under acidic pH conditions. Previous studies reported interindividual differences in circulating concentrations of PVA and 3αPVA. This study investigated the functional consequences of PVA isomerization on OATP1B1-mediated transport. We characterized 3αPVA inhibition of OATP1B1-mediated PVA uptake into human embryonic kidney 293 cells expressing the four different OATP1B1 proteins (*1a, *1b, *5, and *15). 3αPVA inhibited OATP1B1-mediated PVA uptake in all four OATP1B1 gene products but with lower IC(50)/K(i) values for OATP1B1*5 and *15 than for the reference proteins (*1a and *1b). PVA and 3αPVA were transported by all four OATP1B1 proteins. Kinetic experiments revealed that maximal transport rates (V(max) values) for OATP1B1 variants *5 and *15 were lower than for *1a and *1b for both substrates. Apparent affinities for 3αPVA transport were similar for all four variants. However, the apparent affinity of OATP1B1*5 for 3αPVA was higher (lower K(m) value) than for PVA. These data confirm that PVA conversion to 3αPVA can have functional consequences on PVA uptake and impacts OATP1B1 variants more than the reference protein, thus highlighting another source variation that must be taken into consideration when optimizing the PVA dose-exposure relationship for patients. SIGNIFICANCE STATEMENT: 3′α-iso-pravastatin acid inhibits pravastatin uptake for all OATP1B1 protein types; however, the IC(50) values were significantly lower in OATP1B1*5 and *15 transfected cells. This suggests that a lower concentration of 3′α-iso-pravastatin is needed to disrupt OATP1B1-mediated pravastatin uptake, secondary to decreased cell surface expression of functional OATP1B1 in variant-expressing cells. These data will refine previous pharmacokinetic models that are utilized to characterize pravastatin interindividual variability with an ultimate goal of maximizing efficacy at the lowest possible risk for toxicity.

Contains fulltext : 220573.pdf (Publisher’s version ) (Open Access) The hepatic influx transporter OATP1B1 (SLCO1B1) plays an important role in the disposition of endogenous substrates and drugs prescribed to children. Alternative splicing increases the diversity of protein products from > 90% of human genes and may be triggered by developmental signals. As concentrations of several endogenous OATP1B1 substrates change during growth and development, with this exploratory study we investigated age-dependent alternative splicing of SLCO1B1 mRNA in 97 postmortem livers (fetus-adolescents). Twenty-seven splice variants were detected; 10 were confirmed by additional bioinformatic analyses and verified by quantitative polymerase chain reaction, and selected for detailed analysis based on relative abundance, association with age, and overlap with an adjacent gene. Two splice variants code for reference OATP1B1 protein, and eight code for truncated proteins. The expression of eight isoforms was associated with age. We conclude that alternative splicing of SLCO1B1 occurs frequently in children; although the functional consequences remain unknown, the data raise the possibility of a regulatory role for alternative splicing in mediating developmental changes in drug disposition.

Background: A major challenge in implementing personalized medicine in pediatrics is identifying appropriate drug dosages for children. The majority of drug dosing studies have been based on adult populations, often with modification of the dosing for children based on size and weight. However, the growth and development experienced by children between birth and adulthood represents a dynamically changing biological system, with implications for effective drug dosing, efficacy as well as potential drug toxicity. The purpose of this study was to apply a metabolomics approach to gain preliminary insights into the ontogeny of liver function from newborn to adolescent. Methods: Metabolites were measured in 98 post-mortem pediatric liver samples in two experiments 3 batches of samples, allowing for both technical and biological validation. After extensive quality control, imputation and normalization, non-parametric tests were used to determine which metabolite levels differ between the four age groups (AG) ranging in age from newborn to adolescent (AG1—children

Acetaminophen overdose is the most common cause of acute liver injury (ALI) or acute liver failure in the United States. Its pathogenetic mechanisms are incompletely understood. Additional studies are warranted to identify new genetic risk factors for more mechanistic insights and new therapeutic target discoveries. The objective of this study was to explore the role and mechanisms of nicotinamide phosphoribosyltransferase (NAMPT) in acetaminophen-induced ALI. C57BL/6 Nampt gene wild-type (Nampt(+/+)), heterozygous knockout (Nampt(+/−)), and overexpression (Nampt(OE)) mice were treated with overdose of acetaminophen, followed by histologic, biochemical, and transcriptomic evaluation of liver injury. The mechanism of Nampt in acetaminophen-induced hepatocytic toxicity was also explored in cultured primary hepatocytes. Three lines of evidence have convergently demonstrated that acetaminophen overdose triggers the most severe oxidative stress and necrosis, and the highest expression of key necrosis driving genes in Nampt(+/−) mice, whereas the effects in Nampt(OE) mice were least severe relative to Nampt(+/+) mice. Treatment of P7C3-A20, a small chemical molecule up-regulator of Nampt, ameliorated acetaminophen-induced mouse ALI over the reagent control. These findings support the fact that NAMPT protects against acetaminophen-induced ALI.

The major objective of this study was to investigate the association of genetic and nongenetic factors with variability in protein abundance and in vitro activity of the androgen-metabolizing enzyme UGT2B17 in human liver microsomes (n = 455). UGT2B17 abundance was quantified by liquid chromatography-tandem mass spectrometry proteomics, and enzyme activity was determined by using testosterone and dihydrotestosterone as in vitro probe substrates. Genotyping or gene resequencing and mRNA expression were also evaluated. Multivariate analysis was used to test the association of UGT2B17 copy number variation, single nucleotide polymorphisms (SNPs), age, and sex with its mRNA expression, abundance, and activity. UGT2B17 gene copy number and SNPs (rs7436962, rs9996186, rs28374627, and rs4860305) were associated with gene expression, protein levels, and androgen glucuronidation rates in a gene dose-dependent manner. UGT2B17 protein (mean ± S.D. picomoles per milligram of microsomal protein) is sparsely expressed in children younger than 9 years (0.12 ± 0.24 years) but profoundly increases from age 9 years to adults (∼10-fold) with ∼2.6-fold greater abundance in males than in females (1.2 vs. 0.47). Association of androgen glucuronidation with UGT2B15 abundance was observed only in the low UGT2B17 expressers. These data can be used to predict variability in the metabolism of UGT2B17 substrates. Drug companies should include UGT2B17 in early phenotyping assays during drug discovery to avoid late clinical failures.

Response to a drug often differs widely among individual patients. This variability is frequently observed not only with respect to effective responses but also with adverse drug reactions. Matching patients to the drugs that are most likely to be effective and least likely to cause harm is the goal of effective therapeutics. Pharmacogenomics (PGx) holds the promise of precision medicine through elucidating the genetic determinants responsible for pharmacological outcomes and using them to guide drug selection and dosing. Here, we survey the US landscape of research programs in PGx implementation, review current advances and clinical applications of PGx, summarize the obstacles that have hindered PGx implementation, and identify the critical knowledge gaps and possible studies needed to help to address them.

Supplemental Digital Content is available in the text., Objectives The majority of drug dosing studies are based on adult populations, with modification of the dosing for children based on size and weight. This rudimentary approach for drug dosing children is limited, as biologically a child can differ from an adult in far more aspects than just size and weight. Specifically, understanding the ontogeny of childhood liver development is critical in dosing drugs that are metabolized through the liver, as the rate of metabolism determines the duration and intensity of a drug’s pharmacologic action. Therefore, we set out to determine pharmacogenes that change over childhood development, followed by a secondary agnostic analysis, assessing changes transcriptome wide. Materials and methods A total of 47 human liver tissue samples, with between 10 and 13 samples in four age groups spanning childhood development, underwent pair-end sequencing. Kruskal–Wallis and Spearman’s rank correlation tests were used to determine the association of gene expression levels with age. Gene set analysis based on the pathways in KEGG utilized the gamma method. Correction for multiple testing was completed using q-values. Results We found evidence for increased expression of ‘very important pharmacogenes’, for example, coagulation factor V (F5) (P=6.7×10−7), angiotensin I converting enzyme (ACE) (P=6.4×10−3), and solute carrier family 22 member 1 (SLC22A1) (P=7.0×10−5) over childhood development. In contrast, we observed a significant decrease in expression of two alternative CYP3A7 transcripts (P=1.5×10−5 and 3.0×10−5) over development. The analysis of genome-wide changes detected transcripts in the following genes with significant changes in mRNA expression (P

Background Reduced telomere length, or its accelerated attrition, has been implicated in aging, mortality, and several human diseases, including respiratory diseases. Age dependent manifestation of telomere-mediated disease during life span indicates the role of developmental stage in these diseases and highlights the importance of fetal developmental process in utero and at earlier life stages. Environmental determinants during developmental and later stages of life could affect telomere length. Smoke exposure as one of these significant determinants have been investigated in association with telomere length in neonates at time of delivery, children and adults. Objective We sought to investigate whether intrauterine fetal exposure to tobacco smoking characterized by placenta cotinine levels during early weeks of pregnancy might be associated with shorter relative telomere length (T/S ratio) as compared to fetuses without exposure to tobacco smoking. Study design 207 Human placenta and epithelial lung samples were used for both fetal lung telomere length assessment and measurement of placental cotinine levels. Tissues were obtained from two NICHD–supported tissue retrieval programs with registries for elective abortions, the University of Washington Center for Birth Defects Research (Seattle, WA) and the University of Maryland Brain and Tissue Bank for Developmental Disorders (Baltimore, MD). Cotinine levels (ng/g total placental tissue) were determined in whole cell extracts prepared from human placenta samples to characterize and confirm the cotinine exposure status associated with maternal smoking. Relative telomere length (T/S ratio) in genomic DNA extracted from fetal lung tissue was measured by use of quantitative real-time polymerase chain reaction. Multivariable linear regression was used to investigate the relationship between fetal Telomere-to-Single Copy (T/S) ratio and tobacco exposure. Results The estimated post-conception ages for included samples in the study ranged from 54 to 137 days (7–19 weeks of gestation); 47.37% of fetal samples had female sex. Of the samples included in the analysis 96 and 111 fetal samples with and without intrauterine tobacco smoking exposure were distinguished. While T/S ratio was not different between those with and without smoking exposure (1.24 ± 0.41 and 1.27 ± 0.48, respectively; P = 0.70), a significant effect modification of post-conception age on the relationship of intrauterine smoke exposure on fetal T/S ratio was observed (adjusted coefficient = −0.008, 95% CI: −0.016, −0.0004). The smoke exposure status was associated with T/S ratio after 93-day post conception (adjusted coefficient = −0.29, 95% CI: −0.53, −0.052). Conclusions Our results demonstrate a significant association of smoke exposure in utero at early pregnancy with shortened fetal relative telomere length in the developing lung and suggest that the detrimental effect of smoking exposure on future disease sequelae may start at the early stages of pregnancy.

Background Pharmacogenomic variability can contribute to differences in pharmacokinetics and clinical responses. Pediatric patients with cerebral palsy with genetic variations have not been studied for these potential differences. Objective To determine the genetic sources of variation in oral baclofen clearance and clinical responses. Design Pharmacogenomic add-on study to determine variability in oral baclofen clearance and clinical responses. Setting Multicenter study based in academic pediatric cerebral palsy clinics. Participants A total of 49 patients with cerebral palsy who had participated in an oral baclofen pharmacokinetic/pharmacodynamic study. Methods or Interventions Of 53 participants in a pharmacokinetic/pharmacodynamic trial, 49 underwent genetic analysis of 307 key genes and 4535 single-nucleotide polymorphisms involved in drug absorption, distribution, metabolism, and excretion. Associations between genotypes and phenotypes of baclofen disposition (weight-corrected and allometrically scaled clearance) and clinical endpoints (improvement from baseline in mean hamstring Modified Tardieu Scale scores from baseline for improvement of R1 spastic catch) were determined by univariate analysis with correction for multiple testing by false discovery rate. Main Outcome Measurements Primary outcome measures were the genotypic and phenotypic variability of oral baclofen in allometrically scaled clearance and change in the Modified Tardieu Scale angle compared to baseline. Results After univariate analysis of the data, the SNP of ABCC9 (rs11046232, heterozygous AT versus the reference TT genotype) was associated with a 2-fold increase in oral baclofen clearance (mean 0.51 ± standard deviation 0.05 L/h/kg for the AT genotype versus 0.25 ± 0.07 L/h/kg for the TT genotype, adjusted P ABCC12 , SLC28A1 , and PPARD . Conclusions Genetic variation in ABCC9 affecting oral baclofen clearance highlights the need for continued studies of genetic polymorphisms to better characterize variable drug response in children with cerebral palsy. Single-nucleotide polymorphisms in ABCC12 , SLC28A1 , and PPARD were associated with varied responses, which warrants further investigation to determine their effect on spasticity. Level of Evidence II

Hepatic flavin-containing mono-oxygenase 3 (FMO3) metabolizes a broad array of nucleophilic heteroatom (e.g., N or S)-containing xenobiotics (e.g., amphetamine, sulindac, benzydamine, ranitidine, tamoxifen, nicotine, and ethionamide), as well as endogenous compounds (e.g., catecholamine and trimethylamine). To predict the effect of genetic and nongenetic factors on the hepatic metabolism of FMO3 substrates, we quantified FMO3 protein abundance in human liver microsomes (HLMs; n = 445) by liquid chromatography-tandem mass chromatography proteomics. Genotyping/gene resequencing, mRNA expression, and functional activity (with benzydamine as probe substrate) of FMO3 were also evaluated. FMO3 abundance increased 2.2-fold (13.0 ± 11.4 pmol/mg protein vs. 28.0 ± 11.8 pmol/mg protein) from neonates to adults. After 6 years of age, no significant difference in FMO3 abundance was found between children and adults. Female donors exhibited modestly higher mRNA fragments per kilobase per million reads values (139.9 ± 76.9 vs. 105.1 ± 73.1; P < 0.001) and protein FMO3 abundance (26.7 ± 12.0 pmol/mg protein vs. 24.1 ± 12.1 pmol/mg protein; P < 0.05) compared with males. Six single nucleotide polymorphisms (SNPs), including rs2064074, rs28363536, rs2266782 (E158K), rs909530 (N285N), rs2266780 (E308G), and rs909531, were associated with significantly decreased protein abundance. FMO3 abundance in individuals homozygous and heterozygous for haplotype 3 (H3), representing variant alleles for all these SNPs (except rs2066534), were 50.8% (P < 0.001) and 79.5% (P < 0.01), respectively, of those with the reference homozygous haplotype (H1, representing wild-type). In summary, FMO3 protein abundance is significantly associated with age, gender, and genotype. These data are important in predicting FMO3-mediated heteroatom-oxidation of xenobiotics and endogenous biomolecules in the human liver.

Hepatic cytosolic alcohol and aldehyde dehydrogenases (ADHs and ALDHs) catalyze the biotransformation of xenobiotics (e.g., cyclophosphamide and ethanol) and vitamin A. Because age-dependent hepatic abundance of these proteins is unknown, we quantified protein expression of ADHs and ALDH1A1 in a large cohort of pediatric and adult human livers by liquid chromatography coupled with tandem mass spectrometry proteomics. Purified proteins were used as calibrators. Two to three surrogate peptides per protein were quantified in trypsin digests of liver cytosolic samples and calibrator proteins under optimal conditions of reproducibility. Neonatal levels of ADH1A, ADH1B, ADH1C, and ALDH1A1 were 3-, 8-, 146-, and 3-fold lower than the adult levels, respectively. For all proteins, the abundance steeply increased during the first year of life, which mostly reached adult levels during early childhood (age between 1 and 6 years). Only for ADH1A protein abundance in adults (age > 18 year) was ∼40% lower relative to the early childhood group. Abundances of ADHs and ALDH1A1 were not associated with sex in samples with age > 1 year compared with males. Known single nucleotide polymorphisms had no effect on the protein levels of these proteins. Quantification of ADHs and ALDH1A1 protein levels could be useful in predicting disposition and response of substrates of these enzymes in younger children.

Aims Aprepitant and fosaprepitant, commonly used for the prevention of chemotherapy-induced nausea and vomiting, alter cytochrome P450 activity. This systematic review evaluates clinically significant pharmacokinetic drug interactions with aprepitant and fosaprepitant and describes adverse events ascribed to drug interactions with aprepitant or fosaprepitant. Methods We systematically reviewed the literature to September 11, 2016 to identify articles evaluating drug interactions involving aprepitant/fosaprepitant. The clinical significance of each reported pharmacokinetic drug interaction was evaluated based on the United States Food and Drug Administration guidance document on conducting drug interaction studies. The probability of an adverse event reported in case reports being due to a drug interaction with aprepitant/fosaprepitant was determined using the Drug Interaction Probability Scale. Results 4377 publications were identified. Of these, 64 met inclusion eligibility criteria: 34 described pharmacokinetic drug interactions and 30 described adverse events ascribed to a drug interaction. Clinically significant pharmacokinetic interactions between aprepitant/fosaprepitant and bosutinib PO, cabazitaxel IV, cyclophosphamide IV, dexamethasone PO, methylprednisolone IV, midazolam PO/IV, oxycodone PO and tolbutamide PO were identified as were adverse events resulting from an interaction between aprepitant/fosaprepitant and alcohol, anthracyclines, ifosfamide, oxycodone, quetiapine, selective serotonin reuptake inhibitors/serotonin-norepinephrine reuptake inhibitors and warfarin. Conclusions The potential for a drug interaction with aprepitant and fosaprepitant should be considered when selecting antiemetic therapy.

Owing to its highly polymorphic nature and major contribution to the metabolism and bioactivation of numerous clinically used drugs, CYP2D6 is one of the most extensively studied drug-metabolizing enzymes and pharmacogenes. CYP2D6 alleles confer no, decreased, normal, or increased activity and cause a wide range of activity among individuals and between populations. However, there is no standard approach to translate diplotypes into predicted phenotype. We exploited CYP2D6 allele-frequency data that have been compiled for Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines (>60,000 subjects, 173 reports) in order to estimate genotype-predicted phenotype status across major world populations based on activity score (AS) assignments. Allele frequencies vary considerably across the major ethnic groups predicting poor metabolizer status (AS = 0) between 0.4 and 5.4% across world populations. The prevalence of genotypic intermediate (AS = 0.5) and normal (AS = 1, 1.5, or 2) metabolizers ranges between 0.4 and 11% and between 67 and 90%, respectively. Finally, 1 to 21% of subjects (AS >2) are predicted to have ultrarapid metabolizer status. This comprehensive study summarizes allele frequencies, diplotypes, and predicted phenotype across major populations, providing a rich data resource for clinicians and researchers. Challenges of phenotype prediction from genotype data are highlighted and discussed. Genet Med 19 1, 69–76.