Cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of 25% of clinically used drugs. Genetic polymorphisms cause substantial variation in CYP2D6 activity and serve as biomarkers guiding drug therapy. However, genotype–phenotype relationships remain ambiguous except for poor metabolizers carrying null alleles, suggesting the presence of yet unknown genetic variants. Searching for regulatory CYP2D6 polymorphisms, we find that a SNP defining the CYP2D6*2 allele, rs16947 [R296C, 17–60% minor allele frequency (MAF)], previously thought to convey normal activity, alters exon 6 splicing, thereby reducing CYP2D6 expression at least 2-fold. In addition, two completely linked SNPs (rs5758550/rs133333, MAF 13–42%) increase CYP2D6 transcription more than 2-fold, located in a distant downstream enhancer region (>100 kb) that interacts with the CYP2D6 promoter. In high linkage disequilibrium (LD) with each other, rs16947 and the enhancer SNPs form haplotypes that affect CYP2D6 enzyme activity in vivo. In a pediatric cohort of 164 individuals, rs16947 alone (minor haplotype frequency 28%) was associated with reduced CYP2D6 metabolic activity (measured as dextromethorphan/metabolite ratios), whereas rs5758550/rs133333 alone (frequency 3%) resulted in increased CYP2D6 activity, while haplotypes containing both rs16947 and rs5758550/rs133333 were similar to the wild-type. Other alleles used in biomarker panels carrying these variants such as CYP2D6*41 require re-evaluation of independent effects on CYP2D6 activity. The occurrence of two regulatory variants of high frequency and in high LD, residing on a long haplotype, highlights the importance of gene architecture, likely shaped by evolutionary selection pressures, in determining activity of encoded proteins.
The aim of this study was to establish reference intervals in healthy children for two novel urinary biomarkers of acute kidney injury, kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL).
Materials & Methods
Urinary biomarkers were determined in samples from children in the UK (n = 120) and the USA (n = 171) using both Meso Scale Discovery (MSD) and Luminex-based analytical approaches.
95% reference intervals for each biomarker in each cohort are presented and stratified by sex or ethnicity where necessary, and age-related variability is explored using quantile regression. We identified consistently higher NGAL concentrations in females than males (p < 0.0001), and lower KIM-1 concentrations in African–Americans than Caucasians (p = 0.02). KIM-1 demonstrated diurnal variation, with higher concentrations in the morning (p < 0.001).
This is the first report of reference intervals for KIM-1 and NGAL using two analytical methods in a healthy pediatric population in both UK and US-based populations.
KIM-1; nephrotoxicity; pediatric nephrology; proximal tubule
To determine the relationship between allelic variations in genes involved in fluticasone propionate (FP) metabolism and asthma control among children with asthma managed with inhaled FP.
The relationship between variability in asthma control scores and genetic variation in drug metabolism was assessed by genotyping nine single nucleotide polymorphisms (SNPs) in CYP3A4, CYP3A5, and CYP3A7. Genotype information was compared with asthma control scores (0 = well-controlled to 15 = poorly-controlled), determined by using a questionnaire modified from the National Heart Lung and Blood Institute Expert Panel 3 guidelines.
Our study cohort was comprised of 734 children with asthma (mean age 8.8 ± 4.3 years), who were predominantly male (61%) and non-Hispanic Whites (53%); 413 children (56%) were receiving inhaled glucocorticoids daily, of which FP was prescribed most frequently (65%). Among the children receiving daily FP, SNPs in the genes CYP3A5 and CYP3A7 were not associated with asthma control scores. In contrast, asthma control scores were significantly improved among 20 (7%) children with the CYP3A4*22 allele (median 3, range 0-6), as compared with the 201 patients without the CYP3A4*22 allele (median 4, range 0-15) (P=0.02). The presence of CYP3A4*22 was associated with improved asthma control scores by 2.1 points (95% CI: 0.5-3.8).
The presence of CYP3A4*22, which is associated with decreased hepatic CYP3A4 expression and activity, was accompanied by improved asthma control among FP treated children. Decreased CYP3A4 activity may improve asthma control with inhaled FP.
asthma; fluticasone; inhaled glucocorticoids; corticosteroids; children; pharmacogenetics
pathway; pharmacodynamics; pharmacogenomics; pharmacokinetics; valproic acid
High-resolution melt (HRM) analysis using ‘release-on-demand’ dyes, such as EvaGreen® has the potential to resolve complex genotypes in situations where genotype interpretation is complicated by the presence of pseudogenes or allelic variants in close proximity to the locus of interest. We explored the utility of HRM to genotype a SNP (785A>G, K262R, rs2279343) that is located within exon 5 of the CYP2B6 gene, which contributes to the metabolism of a number of clinically used drugs. Testing of 785A>G is challenging, but crucial for accurate genotype determination. This SNP is part of multiple known CYP2B6 haplotypes and located in a region that is identical to CYP2B7, a nonfunctional pseudogene. Because small CYP2B6-specific PCR amplicons bracketing 785A>G cannot be generated, we simultaneously amplified both genes. A panel of 235 liver tissue DNAs and five Coriell samples were assessed. Eight CYP2B6/CYP2B7 diplotype combinations were found and a novel variant 769G>A (D257N) was discovered. The frequency of 785G corresponded to those reported for Caucasians and African–Americans. Assay performance was confirmed by CYP2B6 and/or CYP2B7 sequence analysis in a subset of samples, using a preamplified CYP2B6-specific long-range-PCR amplicon as HRM template. Inclusion rather than exclusion of a homologous pseudogene allowed us to devise a sensitive, reliable and affordable assay to test this CYP2B6 SNP. This assay design may be utilized to overcome the challenges and limitations of other methods. Owing to the flexibility of HRM, this assay design can easily be adapted to other gene loci of interest.
CYP2B6; CYP2B7; genotyping; high-resolution melt analysis; HRM; SNPs
Rapid developments in molecular technology have yielded a large amount of high throughput genetic data to understand the mechanism for complex traits. The increase of genetic variants requires hundreds and thousands of statistical tests to be performed simultaneously in analysis, which poses a challenge to control the overall Type I error rate. Combining p-values from multiple hypothesis testing has shown promise for aggregating effects in high-dimensional genetic data analysis. Several p-value combining methods have been developed and applied to genetic data; see Dai et al. (2012b) for a comprehensive review. However, there is a lack of investigations conducted for dependent genetic data, especially for weighted p-value combining methods. Single nucleotide polymorphisms (SNPs) are often correlated due to linkage disequilibrium (LD). Other genetic data, including variants from next generation sequencing, gene expression levels measured by microarray, protein and DNA methylation data, etc. also contain complex correlation structures. Ignoring correlation structures among genetic variants may lead to severe inflation of Type I error rates for omnibus testing of p-values. In this work, we propose modifications to the Lancaster procedure by taking the correlation structure among p-values into account. The weight function in the Lancaster procedure allows meaningful biological information to be incorporated into the statistical analysis, which can increase the power of the statistical testing and/or remove the bias in the process. Extensive empirical assessments demonstrate that the modified Lancaster procedure largely reduces the Type I error rates due to correlation among p-values, and retains considerable power to detect signals among p-values. We applied our method to reassess published renal transplant data, and identified a novel association between B cell pathways and allograft tolerance.
generalized Fisher method (Lancaster procedure); weight function; correlated p-values; multiple hypothesis testing; high dimensional genetic data
To examine temporal trends of adverse drug reactions (ADRs) associated with trimethoprim-sulfamethoxazole (TMP-SMX) use in children.
We performed a retrospective observational study to characterize TMP-SMX ADRs in children between 2000 and 2009. We completed a chart review at our institution by identifying children diagnosed with TMP-SMX ADRs. To compare local trends to comparable institutions, we estimated the frequency of hospitalizations for TMP-SMX ADRs at 25 tertiary pediatric hospitals utilizing the Pediatric Health Information System database. To determine whether changes in outpatient prescribing rates occurred, we used the National Ambulatory Medical Care Survey/National Hospital Ambulatory Medical Care Survey.
At our institution, 109 children were diagnosed with a TMP-SMX ADR (5 cases from 2000 to 2004 as compared with 104 cases from 2005 to 2009). Fifty-eight percent had been treated for a skin and soft tissue infection (SSTI). A similar trend was observed nationally, where the incidence of TMP-SMX ADRs more than doubled from 2004 to 2009 at comparable pediatric hospitals (P < .001). Although national outpatient data revealed no change in overall TMP-SMX prescribing, the percentage of children prescribed TMP-SMX for SSTI sharply increased during the study period (0%–2% [2000-2004]; 9%–17% [2005–2009]).
The majority of TMP-SMX ADRs at our institution occurred in conjunction with SSTI treatment. TMP-SMX ADRs have occurred more frequently coincident with increased prescribing for SSTI. Increased usage alone may explain the increasing trend of TMP-SMX ADRs in children; however drug–disease interaction may play a role and requires further investigation.
adverse drug reaction; trimethoprim-sulfamethoxazole; skin and soft tissue infections; pediatrics; physician practice patterns
To evaluate systematically in real clinical settings whether functional genetic variations in drug metabolizing enzymes influence optimized doses, efficacy, and safety of antipsychotic medications.
DNA was collected from 750 patients with chronic schizophrenia treated with five antipsychotic drugs (olanzapine, quetiapine, risperidone, ziprasidone and perphenazine) as part of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study. Doses for each of the medicines were optimized to 1, 2, 3, or 4x units in identically-appearing capsules in a double blind design. We analyzed 25 known functional genetic variants in the major and minor metabolizing enzymes for each medication. These variants were tested for association with optimized dose and other relevant clinical outcomes.
None of the tested variants showed a nominally significant main effect in association with any of the tested phenotypes in European-Americans, African-Americans or all patients. Even after accounting for potential covariates no genetic variant was found to be associated with dosing, efficacy, overall tolerability, or tardive dyskinesia.
There are no strong associations between common functional genetic variants in drug metabolizing enzymes and dosing, safety or efficacy of leading antipsychotics, strongly suggesting merely modest effects on the use of these medicines in most patients in typical clinical settings.
Pharmacogenetics; CYP 450; Drug Metabolizing Enzymes; Antipsychotics; Personalized Medicine
Multifactor Dimensionality Reduction (MDR) has been widely applied to detect gene-gene (GxG) interactions associated with complex diseases. Existing MDR methods summarize disease risk by a dichotomous predisposing model (high-risk/low-risk) from one optimal GxG interaction, which does not take the accumulated effects from multiple GxG interactions into account.
We propose an Aggregated-Multifactor Dimensionality Reduction (A-MDR) method that exhaustively searches for and detects significant GxG interactions to generate an epistasis enriched gene network. An aggregated epistasis enriched risk score, which takes into account multiple GxG interactions simultaneously, replaces the dichotomous predisposing risk variable and provides higher resolution in the quantification of disease susceptibility. We evaluate this new A-MDR approach in a broad range of simulations. Also, we present the results of an application of the A-MDR method to a data set derived from Juvenile Idiopathic Arthritis patients treated with methotrexate (MTX) that revealed several GxG interactions in the folate pathway that were associated with treatment response. The epistasis enriched risk score that pooled information from 82 significant GxG interactions distinguished MTX responders from non-responders with 82% accuracy.
The proposed A-MDR is innovative in the MDR framework to investigate aggregated effects among GxG interactions. New measures (pOR, pRR and pChi) are proposed to detect multiple GxG interactions.
A-MDR; Epistasis enriched risk score; Epistasis enriched gene network; pRR; pOR; pChi
carbamazepine; cytochrome P450 metabolizing enzymes; HLA-B; pharmacogenomics; pharmacokinetics
Despite the frequent utilization of biomarkers in medical practice, there is a relative paucity of information regarding validated pediatric biomarkers. Frequently, biomarkers found to be efficacious in adults are extrapolated to the pediatric clinical setting without considering that the pathogenesis of many diseases is distinctly different in children, and ontogeny directly influences disease evolution and therapeutic response in children. New and innovative approaches are necessary to provide reliable, validated biomarkers that can be used to improve and advance pediatric medical care.
biomarker; children; development; genomics; ontogeny; pediatrics; pharmacogenomics
CYP2C19; CYP2C9; HLA-B; pathway; pharmacogenomic; pharmacokinetics; phenytoin; SCN1A
Multifactor Dimensionality Reduction (MDR) is a popular and successful data mining method developed to characterize and detect nonlinear complex gene-gene interactions (epistasis) that are associated with disease susceptibility. Because MDR uses a combinatorial search strategy to detect interaction, several filtration techniques have been developed to remove genes (SNPs) that have no interactive effects prior to analysis. However, the cutoff values implemented for these filtration methods are arbitrary, therefore different choices of cutoff values will lead to different selections of genes (SNPs).
We suggest incorporating a global test of p-values to filtration procedures to identify the optimal number of genes/SNPs for further MDR analysis and demonstrate this approach using a ReliefF filter technique. We compare the performance of different global testing procedures in this context, including the Kolmogorov-Smirnov test, the inverse chi-square test, the inverse normal test, the logit test, the Wilcoxon test and Tippett’s test. Additionally we demonstrate the approach on a real data application with a candidate gene study of drug response in Juvenile Idiopathic Arthritis.
Extensive simulation of correlated p-values show that the inverse chi-square test is the most appropriate approach to be incorporated with the screening approach to determine the optimal number of SNPs for the final MDR analysis. The Kolmogorov-Smirnov test has high inflation of Type I errors when p-values are highly correlated or when p-values peak near the center of histogram. Tippett’s test has very low power when the effect size of GxG interactions is small.
The proposed global tests can serve as a screening approach prior to individual tests to prevent false discovery. Strong power in small sample sizes and well controlled Type I error in absence of GxG interactions make global tests highly recommended in epistasis studies.
P-value; Global tests; ReliefF; Multifactor dimensionality reduction
Betaine-homocysteine methyltransferase (BHMT) catalyzes the remethylation of homocysteine. BHMT is highly expressed in the human liver. In the liver, BHMT catalyzes up to 50% of homocysteine metabolism. Understanding the relationship between BHMT genetic polymorphisms and function might increase our understanding of the role of this reaction in homocysteine remethylation and in S-adenosylmethionine-dependent methylation. To help achieve those goals, we measured levels of BHMT enzyme activity and immunoreactive protein in 268 human hepatic surgical biopsy samples from adult subjects as well as 73 fetal hepatic tissue samples obtained at different gestational ages. BHMT protein levels were correlated significantly (p<0.001) with levels of enzyme activity in both fetal and adult tissue, but both were decreased in fetal tissue when compared with levels in the adult hepatic biopsies. To determine possible genotype-phenotype correlations, 12 tag SNPs for BHMT and the closely related BHMT2 gene were selected from SNPs observed during our own gene resequencing studies as well as from HapMap data were used to genotype DNA from the adult hepatic surgical biopsy samples, and genotype-phenotype association analysis was performed. Three SNPs (rs41272270, rs16876512, and rs6875201), located 28 kb upstream, in the 5′-UTR and in intron 1 of BHMT, respectively, were significantly correlated with both BHMT activity (p=3.41E-8, 2.55E-9 and 2.46E-10, respectively) and protein levels (p=5.78E-5, 1.08E-5 and 6.92E-6, respectively). We also imputed 230 additional SNPs across the BHMT and BHMT2 genes, identifying an additional imputed SNP, rs7700790, that was also highly associated with hepatic BHMT enzyme activity and protein. However, none of the 3 genotyped or one imputed SNPs displayed a “shift” during electrophoretic mobility shift assays. These observations may help us to understand individual variation in the regulation of BHMT in the human liver and its possible relationship to variation in methylation.
Betaine-homocysteine methyltransferase; BHMT; BHMT2; single nucleotide polymorphisms; SNPs; genotype-phenotype correlation; hepatic tissue
Toll-like receptors (TLRs) are critical components of the innate immune system, acting as pattern recognition molecules and triggering an inflammatory response. TLR associated gene products are of interest in modulating inflammatory related pulmonary diseases of the neonate. The ontogeny of TLR related genes in human fetal lung has not been previously described and could elucidate additional functions and identify strategies for attenuating the effects of fetal inflammation. We examined the expression of 84 TLR related genes on 23 human fetal lung samples from three groups with estimated ages of 60 (57-59d), 90 (89-91d), and 130 (117-154d) days. Using a false detection rate algorithm, we identified 32 genes displaying developmental regulation with TLR2 having the greatest up-regulation of TLR genes (9.2 fold increase) and TLR4 unchanged. We confirmed the TLR2 up-regulation by examining an additional 133 fetal lung tissue samples with a fluorogenic polymerase chain reaction assay (TaqMan®) and found an exponential best-fit curve over the time studied. The best-fit curve predicts a 6.1 fold increase from 60d to 130d. We conclude that TLR2 is developmentally expressed from the early pseudoglandular stage of lung development to the canalicular stage.
Adverse drug reactions are a concern for all clinicians who utilize medications to treat adults and children; however, the frequency of adult and pediatric adverse drug reactions is likely to be under-reported. In this age of genomics and personalized medicine, identifying genetic variation that results in differences in drug biotransformation and response has contributed to significant advances in the utilization of several commonly used medications in adults. In order to better understand the variability of drug response in children however, we must not only consider differences in genotype, but also variation in gene expression during growth and development, namely ontogeny. In this article, recommendations for systematically approaching pharmacogenomic studies in children are discussed, and several examples of studies that investigate the genomic and developmental contribution to adverse drug reactions in children are reviewed.
adverse drug reactions; genetic variants; methotrexate; pediatrics; pharmacogenomics
Little is known about the role of most asthma susceptibility genes during human lung development. Genetic determinants for normal lung development are not only important early in life, but also for later lung function.
To investigate the role of expression patterns of well-defined asthma susceptibility genes during human and murine lung development. We hypothesized that genes influencing normal airways development would be over-represented by genes associated with asthma.
Asthma genes were first identified via comprehensive search of the current literature. Next, we analyzed their expression patterns in the developing human lung during the pseudoglandular (gestational age, 7-16 weeks) and canalicular (17-26 weeks) stages of development, and in the complete developing lung time series of 3 mouse strains: A/J, SW, C57BL6.
In total, 96 genes with association to asthma in at least two human populations were identified in the literature. Overall, there was no significant over-representation of the asthma genes among genes differentially expressed during lung development, although trends were seen in the human (Odds ratio, OR 1.22, confidence interval, CI 0.90-1.62) and C57BL6 mouse (OR 1.41, CI 0.92-2.11) data. However, differential expression of some asthma genes was consistent in both developing human and murine lung, e.g. NOD1, EDN1, CCL5, RORA and HLA-G. Among the asthma genes identified in genome wide association studies, ROBO1, RORA, HLA-DQB1, IL2RB and PDE10A were differentially expressed during human lung development.
Our data provide insight about the role of asthma susceptibility genes during lung development and suggest common mechanisms underlying lung morphogenesis and pathogenesis of respiratory diseases.
Asthma; Development; Expression; Genetics; Lung
Rationale: Current understanding of the molecular regulation of lung development is limited and derives mostly from animal studies.
Objectives: To define global patterns of gene expression during human lung development.
Methods: Genome-wide expression profiling was used to measure the developing lung transcriptome in RNA samples derived from 38 normal human lung tissues at 53 to 154 days post conception. Principal component analysis was used to characterize global expression variation and to identify genes and bioontologic attributes contributing to these variations. Individual gene expression patterns were verified by quantitative reverse transcriptase–polymerase chain reaction analysis.
Measurements and Main Results: Gene expression analysis identified attributes not previously associated with lung development, such as chemokine-immunologic processes. Lung characteristics attributes (e.g., surfactant function) were observed at an earlier-than-anticipated age. We defined a 3,223 gene developing lung characteristic subtranscriptome capable of describing a majority of the process. In gene expression space, the samples formed a time-contiguous trajectory with transition points correlating with histological stages and suggesting the existence of novel molecular substages. Induction of surfactant gene expression characterized a pseudoglandular “molecular phase” transition. Individual gene expression patterns were independently validated. We predicted the age of independent human lung transcriptome profiles with a median absolute error of 5 days, supporting the validity of the data and modeling approach.
Conclusions: This study extends our knowledge of key gene expression patterns and bioontologic attributes underlying early human lung developmental processes. The data also suggest the existence of molecular phases of lung development.
microarrays; surfactant; principal component analysis
Polymorphic expression of CYP2D6 contributes to the wide range of activity observed for this clinically important drug metabolizing enzyme. In this report we describe novel CYP2D7/2D6 hybrid genes encoding non-functional and functional CYP2D6 protein and a CYP2D7 variant that mimics a CYP2D7/2D6 hybrid gene. Five-kilobyte-long PCR products encompassing the novel genes were entirely sequenced. A quantitative assay probing in different gene regions was employed to determine CYP2D6 and 2D7 copy number variations and the relative position of the hybrid genes within the locus was assessed by long-range PCR. In addition to the previously known CYP2D6*13 and *66 hybrids, we describe three novel non-functional CYP2D7-2D6 hybrids with gene switching in exon 2 (CYP2D6*79), intron 2 (CYP2D6*80), and intron 5 (CYP2D6*67). A CYP2D7-specific T-ins in exon 1 causes a detrimental frame shift. One subject revealed a CYP2D7 conversion in the 5′-flanking region of a CYP2D6*35 allele, was otherwise unaffected (designated CYP2D6*35B). Finally, three DNAs revealed a CYP2D7 gene with a CYP2D6-like region downstream of exon 9 (designated CYP2D7[REP6]). Quantitative copy number determination, sequence analyses, and long-range PCR mapping were in agreement and excluded the presence of additional gene units. Undetected hybrid genes may cause over-estimation of CYP2D6 activity (CYP2D6*1/*1 vs *1/hybrid, etc), but may also cause results that may interfere with the genotype determination. Detection of hybrid events, “single” and tandem, will contribute to more accurate phenotype prediction from genotype data.
CYP2D6; hybrid genes; CYP2D6*35B; CYP2D6*67; CYP2D6*79; CYP2D6*80; CYP2D6 poor metabolizer
Although methotrexate is widely used in clinical practice there remains significant lack of understanding of its mechanisms of action and the factors that contribute to the variability in toxicity and response seen clinically. In addition to differences in drug administration, factors that affect pharmacokinetics and pharmacodynamics such as genetic variation may explain individual differences in drug biotransformation. However, the pediatric population has an additional factor to consider, namely the ontogeny of gene expression which may result in variation throughout growth and development. We review the current understanding of methotrexate biotransformation and the concept of ontogeny, with further discussion of how to implement a developmental pharmacogenomics approach in future studies.
Carbamazepine (CBZ) is a widely prescribed anticonvulsant whose use is often associated with idiosyncratic hypersensitivity. Sera of CBZ-hypersensitive patients often contain anti-CYP3A antibodies, including those to a CYP3A23 K-helix peptide that is also modified during peroxidative CYP3A4 heme-fragmentation. We explored the possibility that cytochromes P450 (P450s) such as CYP3A4 bioactivate CBZ to reactive metabolite(s) that irreversibly modify the P450 protein. Such CBZ-P450 adducts, if stable in vivo, could engender corresponding serum P450 autoantibodies. Incubation with CBZ not only failed to inactivate functionally reconstituted, purified recombinant CYP3A4 or CYP3A4 Supersomes in a time-dependent manner, but the inclusion of CBZ (0–1 mM) also afforded a concentration-dependent protection to CYP3A4 from inactivation by NADPH-induced oxidative uncoupling. Incubation of CYP3A4 Supersomes with 3H-CBZ resulted in its irreversible binding to CYP3A4 protein with a stoichiometry of 1.58 ± 0.15 pmol 3H-CBZ bound/pmol CYP3A4. Inclusion of glutathione (1.5 mM) in the incubation reduced this level to 1.09. Similar binding (1.0 ± 0.4 pmol 3H-CBZ bound/pmol CYP3A4) was observed after 3H-CBZ incubation with functionally reconstituted, purified recombinant CYP3A4(His)6. The CBZ-modified CYP3A4 retained its functional activity albeit at a reduced level, but its testosterone 6β-hydroxylase kinetics were altered from sigmoidal (a characteristic profile of substrate cooperativity) to near-hyperbolic (Michaelis-Menten) type, suggesting that CBZ may have modified CYP3A4 within its active site.
Conversion of the carbamazepine metabolite, 3-hydroxycarbamazepine (3-OHCBZ), to the catechol, 2,3-dihydroxycarbamazepine (2,3-diOHCBZ), followed by subsequent oxidation to a reactive o-quinone species has been proposed as a possible bioactivation pathway in the pathogenesis of carbamazepine-induced hypersensitivity. Initial in vitro phenotyping studies implicated CYP3A4 as a primary catalyst of 2,3-diOHCBZ formation: 2-hydroxylation of 3-OHCBZ correlated significantly (r2≥0.929, P<0.001) with CYP3A4/5 activities in a panel of human liver microsomes (n=14) and was markedly impaired by CYP3A inhibitors (>80%), but not by inhibitors of other cytochrome P450 enzymes (≤20%). However, in the presence of troleandomycin, the rate of 2,3-diOHCBZ formation correlated significantly with CYP2C19 activity (r2=0.893, P<0.001) in the panel of human liver microsomes. Studies with a panel of cDNA-expressed enzymes revealed that CYP2C19 and CYP3A4 were high (S50=30 μM) and low (S50=203 μM) affinity enzymes, respectively, for 2,3-diOHCBZ formation and suggested that CYP3A4, but not CYP2C19, might be inactivated by a metabolite formed from 3-OHCBZ. Subsequent experiments demonstrated that preincubation of 3-OHCBZ with human liver microsomes or recombinant CYP3A4 led to decreased CYP3A4 activity, which was both preincubation time- and concentration-dependent, but not inhibited by inclusion of glutathione or N-acetylcysteine. CYP3A4, CYP3A5, CYP3A7, CYP2C19 and CYP1A2 converted [14C]3-OHCBZ into protein-reactive metabolites, but CYP3A4 was the most catalytically active enzyme. The results of this study suggest that CYP3A4-dependent secondary oxidation of 3-OHCBZ represents a potential carbamazepine bioactivation pathway via formation of reactive metabolites capable of inactivating CYP3A4, potentially generating a neo-antigen that may play a role in the etiology of carbamazepine-induced idiosyncratic toxicity.
With the recent development of microarray technologies, the comparability of gene expression data obtained from different platforms poses an important problem. We evaluated two widely used platforms, Affymetrix U133 Plus 2.0 and the Illumina HumanRef-8 v2 Expression Bead Chips, for comparability in a biological system in which changes may be subtle, namely fetal lung tissue as a function of gestational age.
We performed the comparison via sequence-based probe matching between the two platforms. "Significance grouping" was defined as a measure of comparability. Using both expression correlation and significance grouping as measures of comparability, we demonstrated that despite overall cross-platform differences at the single gene level, increased correlation between the two platforms was found in genes with higher expression level, higher probe overlap, and lower p-value. We also demonstrated that biological function as determined via KEGG pathways or GO categories is more consistent across platforms than single gene analysis.
We conclude that while the comparability of the platforms at the single gene level may be increased by increasing sample size, they are highly comparable ontologically even for subtle differences in a relatively small sample size. Biologically relevant inference should therefore be reproducible across laboratories using different platforms.
CYP2J2 metabolizes arachidonic acid to 20-HETE and EETs which play a critical role in the regulation of renal, pulmonary, cardiac and vascular function. However, the contribution of CYP2J2 to EET formation in the liver remains poorly characterized. Similarly, information is sparse regarding the extent and variability of CYP2J2 expression during human development. This investigation was undertaken to characterize the variability of CYP2J2 expression in fetal liver, heart, kidney, lung, intestine and brain and postnatal liver samples. CYP2J2 mRNA expression was measured using quantitative PCR, and immunoreactive CYP2J2 was examined using two anti-CYP2J2 antibodies. CYP2J2 mRNA was ubiquitously expressed in pre- and postnatal samples. Fetal hepatic mRNA expression varied 127-fold (1351 ± 717 transcripts/ng total RNA), but this variation was reduced to 8-fold after exclusion of four samples with extremely low levels of mRNA. Amounts of immunoreactive protein also varied substantially among samples without an apparent relationship with transcript number or genotype. Western blot analysis revealed a different protein pattern between prenatal and postnatal liver samples. DNA resequencing of selected subjects identified a single novel SNP (CYP2J2*10), which was found in only one subject and therefore did not explain the large variability in CYP2J2 protein content. In vitro expression suggests that the protein product of CYP2J2*10 confers reduced enzymatic activity. Aberrant splicing produces three minor transcripts which were present in all samples tested. Due to premature termination codons none encodes functional protein. The mechanisms leading to variable amounts of immunoreactive protein and distinct pre- and postnatal CYP2J2 protein patterns warrant further investigation.