Variability In Drug Metabolism Research Articles

Dose-linearity of the pharmacokinetics of an intravenous [14 C]midazolam microdose in children.

AimsDrug disposition in children may vary from adults due to age‐related variation in drug metabolism. Microdose studies present an innovation to study pharmacokinetics (PK) in paediatrics; however, they should be used only when the PK is dose linear. We aimed to assess dose linearity of a [14C]midazolam microdose, by comparing the PK of an intravenous (IV) microtracer (a microdose given simultaneously with a therapeutic midazolam dose), with the PK of a single isolated microdose.MethodsPreterm to 2‐year‐old infants admitted to the intensive care unit received [14C]midazolam IV as a microtracer or microdose, followed by dense blood sampling up to 36 hours. Plasma concentrations of [14C]midazolam and [14C]1‐hydroxy‐midazolam were determined by accelerator mass spectrometry. Noncompartmental PK analysis was performed and a population PK model was developed.ResultsOf 15 infants (median gestational age 39.4 [range 23.9–41.4] weeks, postnatal age 11.4 [0.6–49.1] weeks), 6 received a microtracer and 9 a microdose of [14C]midazolam (111 Bq kg−1; 37.6 ng kg−1). In a 2‐compartment PK model, bodyweight was the most significant covariate for volume of distribution. There was no statistically significant difference in any PK parameter between the microdose and microtracer, nor in the area under curve ratio [14C]1‐OH‐midazolam/[14C]midazolam, showing the PK of midazolam to be linear within the range of the therapeutic and microdoses.ConclusionOur data support the dose linearity of the PK of an IV [14C]midazolam microdose in children. Hence, a [14C]midazolam microdosing approach may be used as an alternative to a therapeutic dose of midazolam to study developmental changes in hepatic CYP3A activity in young children.

UPLC-MS/MS method for gemfibrozil determination in plasma with application to a pharmacokinetic study in healthy Brazilian volunteers

Gemfibrozil (GFZ) is a derivative of fibric acid and is used in the treatment of dyslipidemia. GFZ may affect the metabolism of various drugs, including statins, by inhibiting the sinusoidal influx transporter OATP1B1 and also CYP2C9 and CYP2C8 enzymes. This study presents the development and validation of a rapid, simple, sensitive and reproducible method of GFZ analysis in human plasma using UPLC-MS/MS. The method was applied in a pharmacokinetic study following administration of multiple doses of 600 mg GFZ every 12 h in healthy volunteers (n = 15). GFZ was separated on a C18 column using a mixture of 0.01% formic acid and acetonitrile (40:60, v/v) as the mobile phase at a flow rate of 0.4 mL/min. The method showed linearity in the range from 0.01 μg/mL to 100 μg/mL plasma. The coefficients of variation and the relative standard errors of the accuracy and precision analyses were <15%. The method allowed quantification of plasma concentrations of GFZ in the dose interval of the sixth day of administration of multiple oral doses of GFZ every 12 h. The pharmacokinetic parameters are presented as mean (95% CI): area under the plasma concentration versus time curve 88.84 (72.72–104.96) μg·h/mL, steady state mean plasma concentration 7.40 (6.06–8.75) μg/mL, minimum plasma concentration 1.24 (0.87–1.61) μg/mL, maximum plasma concentration 26.73 (21.31–32.15) μg/mL, time to reach maximum plasma concentration 2.28 (1.42–3.13) h, elimination half-life 2.81 (2.22–3.40) h, apparent total clearance 7.72 (5.85–9.58) L/h, apparent distribution volume 33.97 (18.41–49.53) L. In conclusion, the method for analysis of GFZ in human plasma showed sensitivity, linearity, precision and accuracy compatible with application in pharmacokinetic studies of multiple oral dose of 600 mg GFZ every 12 h.

Increased Clozapine Levels During Infection: more Frequent than Assumed?

Systemic infections are known to alter the metabolism of various drugs via inhibition of the cytochrome P450 family. Here, we report the cases of two patients with schizophrenic psychosis and highly elevated clozapine levels during pulmonary systemic infection, however without experiencing side effects. After antibiotic treatment and temporary reduction of clozapine dosage blood levels of clozapine normalized within a few days. These cases show that clozapine levels may be highly elevated without necessarily causing side effects and that intensified pharmacovigilance should be considered by the clinician in patients with systemic infections.

Enzymatic Activities of CYP3A4 Allelic Variants on Quinine 3-Hydroxylation In Vitro.

Cytochrome P450 3A4 (CYP3A4) enzyme activity is known to show considerable ethnic heterogeneity and inter-individual differences, affecting the outcome of drug treatment. CYP3A4 genetic polymorphisms are believed to be one of the important causes, leading to inter-individual variability in drug metabolism. Quinine is an antipyretic drug with antimalarial properties that is metabolized primarily by CYP3A4. Quinine 3-hydroxylation has been proven as a biomarker reaction for evaluating CYP3A4 ability. Quinine has frequent adverse effects and there are distinct inter-individual differences in quinine sensitivity. The open reading frame for 30 CYP3A4 allelic variants were constructed from wild-type CYP3A4*1A by an overlap extension polymerase chain reaction. Recombinant CYP3A4 variants were expressed using baculovirus-insect cell expression system, and their catalytic activities towards quinine hydroxylation were determined and evaluated. Of the 30 CYP3A4 allelic variants, 23 variants exhibited significantly reduced intrinsic clearance towards quinine, 2 variants showed increased intrinsic clearance for quinine, 2 variants possessed no significant differences towards quinine, compared with CYP3A4*1A, and 3 variants had no detected expression and enzyme activity. Our assessment on the enzymatic activities of CYP3A4 variants towards quinine may contribute to laying an experimental foundation for further clinical studies so as to accelerate the process of determining the associations between genetic variations and clinical phenotypes.

Pharmacogenomics in Indigenous Populations

The integration of genomic technology into healthcare settings has the potential to transform health care through increased personalization of medical decisions. In particular, pharmacogenomic research on drug disposition and response can tailor and improve medication regimens for all patients by informing tests of function altering variation in drug metabolism and transport genes. Unfortunately, Indigenous peoples remain underrepresented in genomic and health research despite having a higher prevalence of heart disease, cancer, diabetes and stroke than any other population. Effective strategies to create research partnerships between tribal communities and genomic researchers are often lacking, yet such partnerships are needed for trustworthy research. As such, Indigenous populations are less likely to benefit from personalized medicine if they are not represented in studies that ascertain genotype‐phenotype relationships that can lead to improved drug treatment efficacy.We review what is currently known about pharmacogenetic variation in Indigenous populations and evaluate three case studies in which pharmacogenetic research with Indigenous populations were conducted. We highlight the importance of including Indigenous populations in future pharmacogenetic studies and discuss strategies for ethical engagement and collaboration in genomic research with Indigenous communities. The inclusion of Indigenous and other underrepresented communities in genomic research has the potential to expand our understanding of genomic influences on health and improve clinical approaches for all populations.Support or Funding InformationNIGMS F32 GM119237This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of Nucleosome Assembly on Alkylation by a Dynamic Electrophile.

Quinone methides are reactive electrophiles that are generated during metabolism of various drugs, natural products, and food additives. Their chemical properties and cellular effects have been described previously, and now their response to packaging DNA in a nucleosome core is described. A model bisquinone methide precursor (bisQMP) was selected based on its ability to form reversible adducts with guanine N7 that allow for their redistribution and transfer after quinone methide regeneration. Assembly of Widom's 601 DNA with the histone octamer of H2A, H2B, H3, and H4 from Xenopus laevis significantly suppressed alkylation of the DNA. This result is a function of DNA packaging since addition of the octamer without nucleosome reconstitution only mildly protected DNA from alkylation. The lack of competition between nucleophiles of DNA and the histones was consistent with the limited number of adducts formed by the histones as detected by tryptic digestion and ultraperformance liquid chromatography-mass spectrometry. Only three peptide adducts were observed after reaction with a monofunctional analogue of bisQMP, and only two peptide adducts were observed after reaction with bisQMP. Histone reaction was also suppressed when reconstituted into the nucleosome core particle. However, bisQMP was capable of cross-linking the DNA and histones in moderate yields (∼20%) that exceeded expectations derived from reaction of cisplatin, nitrogen mustards, and diepoxybutane. The core histones also demonstrated a protective function against dynamic alkylation by trapping the reactive quinone methide after its spontaneous regeneration from DNA adducts.

Antidepressant therapy in patients with cardiovascular diseases

Depression is the most common form of mental illness in patients with cardiovascular diseases (CVD). Depression and CVD can worsen the clinical and dynamic characteristics of each other. The timely detection and adequate psychopharmacotherapy of depressive states in patients with CVD are of great clinical, therapeutic, and prognostic importance. Anti-antidepressant therapy promotes a more pronounced somatic stabilizing effect in patients with CVD. Adverse events to the use of antidepressants in patients with CVD may be associated with their negative effect on the hepatic cytochrome CYP450 isoenzymes involved in the metabolism of various drugs. The authors' own data of clinical psychopharmacotherapeutic studies and the results of meta-analyses indicate the high efficiency and good tolerability of agomelatine, an antidepressant with an innovative mechanism of action, in a wide range of patients

Pharmacogenomic Next-Generation DNA Sequencing: Lessons from the Identification and Functional Characterization of Variants of Unknown Significance in CYP2C9 and CYP2C19.

CYP2C9 and CYP2C19 are highly polymorphic pharmacogenes; however, clinically actionable genetic variability in drug metabolism due to these genes has been limited to a few common alleles. The identification and functional characterization of less-common open reading frame sequence variation might help to individualize therapy with drugs that are substrates for the enzymes encoded by these genes. The present study identified seven uncharacterized variants each in CYP2C9 and CYP2C19 using next-generation sequence data for 1013 subjects, and functionally characterized the encoded proteins. Constructs were created and transiently expressed in COS-1 cells for the assay of protein concentration and enzyme activities using fluorometric substrates and liquid chromatography- tandem mass spectrometry with tolbutamide (CYP2C9) and (S)-mephenytoin (CYP2C19) as prototypic substrates. The results were compared with the SIFT, Polyphen, and Provean functional prediction software programs. Cytochrome P450 oxidoreductase (CPR) activities were also determined. Positive correlations were observed between protein content and fluorometric enzyme activity for variants of CYP2C9 (P < 0.05) and CYP2C19 (P < 0.0005). However, CYP2C9 709G>C and CYP2C19 65A>G activities were much lower than predicted based on protein content. Substrate intrinsic clearance values for CYP2C9 218C>T, 343A>C, and CYP2C19 337G>A, 518C>T, 556C>T, and 557G>A were less than 25% of wild-type allozymes. CPR activity levels were similar for all variants. In summary, sequencing of CYP2C9 and CYP2C19 in 1013 subjects identified low-frequency variants that had not previously been functionally characterized. In silico predictions were not always consistent with functional assay results. These observations emphasize the need for high-throughput methods for pharmacogene variant mutagenesis and functional characterization.

Biochemical Analysis and Association of Butyrylcholinesterase SNPs rs3495 and rs1803274 with Substance Abuse Disorder.

Addiction is a complex mental and behavioral disorder that changes the neurochemistry and physiology of the brain. Genetics also plays a significant role in the pathophysiology of addiction. Butyrylcholinesterase (BChE), a cholinergic enzyme, has been implicated in the metabolism of various drugs, including cocaine, and an association between single-nucleotide polymorphisms (SNPs) of the butyrylcholinesterase gene (BCHE) and neuronal disorders has been reported. We report here the first investigation to be conducted on the status of BChE activity and the potential association of two BCHE gene SNPs, rs3495 (c.*189G > A) and rs1803274 (c.1699G>A, p.Ala567Thr, K-variant), with addiction vulnerability in heroin, hashish and polydrug users. Seventy-five individuals with an addiction to heroin, hashish and/or polydrug use were recruited to this study. BChE levels in the plasma were determined by Ellman's principle. SNPs were genotyped by standard procedures, followed by Sanger sequencing. Plasma BChE levels were found to be significantly higher (p ≤ 0.05) in addicts (mean ± standard error of the mean 0.031 ± 0.004μmol/L/min; 95% confidence interval [CI] 0.024-0.038) than in non-addicts (controls) (0.014 ± 0.001μmol/L/min; 95% CI 0.012-0.017). Statistical significant differences were also observed between the addicted cohorts. A statistically significant association for both SNPs (rs3495 and rs1803274) was not observed in addicted subjects tested in the dominant, recessive and allele genetic models, but trends of variations of the rs3495 risk G allele were noted. The authors conclude that BChE plays significant roles in addiction pathophysiology as increased BChE activity in blood samples obtained from the cohorts with addiction was evident. Further studies in this direction may provide novel approaches for the treatment of addiction, but studies with a larger sample size and different ethnic groups are warranted for broader conclusions to be drawn.

Up-Regulated AKR1C2 is correlated with favorable prognosis in thyroid carcinoma.

Purpose: Aldo-keto reductase family 1, member C2 (AKR1C2) gene encodes for a member of the AKR superfamily and participates in the metabolism of various drugs. Moreover, tumor and normal tissues exhibit an evident difference in the expression level of this gene.Methods: We downloaded and analyzed AKR1C2 expression level and the data consisting of the clinicopathological features of 490 papillary thyroid carcinoma (PTC) tumor tissues and 59 normal thyroid tissues from The Cancer Genome Atlas (TCGA) cohort. Diverse statistical methods, such Chi-square test, univariate and multivariate Cox regression analyses, and Kaplan-Meier survival curves were used. We down-/up-regulated the expression of AKR1C2 and explored its specific role in thyroid cancer cell lines by utilizing the si-RNA and plasmid.Results: We divided all patients who were collected in TCGA data sets into under-expressed (n = 245) and over-expressed groups (n = 245). We subsequently analyzed the data and obtained the following findings: (a) AKR1C2 is down-regulated in papillary thyroid carcinoma (PTC) (p<0.001), (b) Kaplan-Meier result revealed that high expression level of AKR1C2 are correlated with favorable survival in PTC (p = 0.043), and (c) factors independently associated with recurrence-free survival are AKR1C2 expression (hazard ratio (HR 0.819) and American Joint Committee on Cancer (AJCC) stage (HR 1.534). We also analysed the relationship between AKR1C2 expression and clinicopathological features in the validated cohort. AKR12C under-expression correlated with lymph node metastasis (p = 0.009) and AJCC stage (p= 0.001) which might indicate AKR12C as a prognostic factor in PTC. The cell line experiment results showed that the knockdown and overexpression of AKR1C2 significantly enhance and weaken the abilities of migration and invasion in papillary thyroid carcinoma cell.Conclusion: Our results indicated that AKR1C2 exerts inhibitory effects on PTC oncogenesis and elevated AKR1C2 expression is associated with the favorable prognostic factors and recurrence free survival.

Cytochrome P450 1A1, 2C9, 2C19, and 3A4 Polymorphisms Account for Interindividual Variability of Toxicological Drug Metabolism in Cynomolgus Macaques.

Cytochromes P450 (P450s) and their genetic variants in humans are important drug-metabolizing enzymes partly accounting for interindividual variations in drug metabolism and toxicity. However, these genetic variants in P450s have not been fully investigated in cynomolgus macaques, a nonhuman primate species widely used in toxicological studies. In this study, genetic variants found in cynomolgus CYP1A1, CYP2C9 (formerly CYP2C43), CYP2C19 (CYP2C75), and CYP3A4 (CYP3A8) were assessed on functional importance. Resequencing of CYP1A1 in cynomolgus macaques found 18 nonsynonymous variants, of which M121I and V382I were located in SRSs, domains potentially important for P450 function. By further analyzing these two variants, V382I was significantly associated with lower drug-metabolizing activities in the liver for the heterozygotes than the wild types. Similarly, the heterozygotes or homozygotes of CYP2C9 variants (A82V and H344R) and CYP2C19 variant (A490V) showed significantly lower drug-metabolizing activities in the liver than the wild types. Moreover, the homozygotes of CYP3A4 variant (S437N) showed significantly higher activities than the wild type in the liver. Kinetic analyses using recombinant proteins revealed that CYP2C9 variants (A82V and H344R) showed substantially lower Ks values than the wild type, although CYP1A1 variant (V382I) showed kinetic parameters similar to the wild type. Likewise, CYP2C19 variant (A490V) showed substantially a lower Vmax/ Km value than the wild type, whereas CYP3A4 variant (S437N) showed a higher Vmax/ Km value than the wild type. These results suggest the toxicologically functional importance of CYP2C9 variants (A82V and H344R), CYP2C19 variant (A490V), and CYP3A4 variant (S437N) for hepatic drug metabolism in cynomolgus macaques.

A Conspectus: Hepatotoxicity Caused by Drug’s

Liver is the principle organ for metabolism of various drugs, endotoxins. Hepatotoxicity is one of the reversible conditions. Drugs are an vital cause of liver injury. Drug-induced injury to the liver can mimic any form of acute or chronic liver disease. The action of cytochrome P450 can induce acute injury to liver, through which drug will break down into electrophiles or free radicals. These spontaneous metabolites can covalently bind to protein and unsaturated fatty acids or induce lipid peroxidation, respectively. The clinical presentation of liver damage may be either cytolytic or cholestatic. Systemic hypersensitivity reaction against the applied agent may be one of the major causes of liver damage. Drug- or toxin-induced liver damage includes vascular damage, induction of liver tumours and development of liver cirrhosis. The most important pre-emptive measure is judicious drug used by the prescribing physician. Early recognition of hepatotoxicity and termination of the offending agent is essential for treatment. The diagnosis may be confirmed by additional diagnostic measures (e. g. liver biopsy) or the clinical course after exposure to the causing agent has been stopped. Therefore, the main aim is to prevent chronic liver damage through early and correct diagnosis. Due to the extensive variety of possibly liver toxic drugs and chemical agents this aspect is a major challenge to physicians. Taking into account the significance of drug-induced hepatotoxicity as a key cause of liver damage, this review pitch light on various drugs which induce hepatotoxicity, with their mechanism of liver damage and clinical scenario.

Thiopurine Optimization Through Combination With Allopurinol in Children With Inflammatory Bowel Diseases.

Thiopurines are commonly used in the maintenance of remission for children with inflammatory bowel diseases (IBDs). Variation in drug metabolism may affect hepatotoxicity or therapeutic effect. We aimed to describe our center's experience with thiopurine optimization through the use of reduced thiopurine dosing in combination with allopurinol upon hepatotoxicity, drug metabolite levels, and clinical outcomes in children with IBD. Patients aged 2 to 21 years with IBD treated with the combination of thiopurines/allopurinol between 2008 and 2015 were retrospectively reviewed. Patients previously treated with antitumor necrosis factor therapy were excluded. Demographic data, transaminase levels (aspartate transaminase, alanine transaminase), drug metabolites levels (6-thioguanine [6-TG], 6-methylmercaptopurine), physician global assessment, and corticosteroid use were recorded at baseline, 6, and 12 months. Fifty-two patients (29 girls, 56%) met inclusion criteria. Thirty-two of 52 (62%) remained on the combination for 12 months. In those remaining on the thiopurine/allopurinol combination, median alanine transaminase and aspartate transaminase levels were reduced (P < 0.001) and median 6-TG levels were increased (P < 0.001) at both 6 and 12 months. Corticosteroid use was decreased at both 6 (P < 0.001) and 12 months (P < 0.001) compared to use at baseline. Remission rates also improved at both 6 (P = 0.013) and 12 months (P = 0.003). Twenty of the 52 patients (38%) had discontinued the thiopurine/allopurinol combination within 12 months of initiation with 17 of 52 (33%) initiating antitumor necrosis factor therapy. Low-dose thiopurines in combination with allopurinol improved hepatotoxicity and increased 6-TG levels in children with IBD. Corticosteroid use was reduced and remission rates improved in those patients remaining on this combination for 1 year. However, approximately 40% of patients required a change in therapy within 12 months.

Clinical Outcomes from Tamoxifen Drug-herb Interactions

Background: Tamoxifen is an important drug in chemotherapy being part of various protocols in cancer treatment, but is not universally effective even when used before surgery or in preventing recurrence. Pharmacogenetic variability in drug metabolism is one possible mechanism of treatment failure. We hypothesize that Drug-Herb Interactions (DHI) contribute in disease outcomes, nevertheless the functional single nucleotide polymorphisms in drug metabolizing enzymes that activate cytochrome enzymes. Methods: We performed a retrospective study in the last 9 years of clinical cases enrolled in follow up of Observatory of Drug-Herb Interactions, University of Coimbra - Portugal (www.oipm.uc.pt), and the data collected will be discussed in this paper. Data obtained from PubMed and from PubChem Compounds with preference given to the data obtained during the last 10 years, was also obtained. The search terms were varied depending of the Clinical situation. Results: From our experience, in order to avoid the major predictable DHI more observational trials should be carried out for therapeutic protocols associated to tamoxifen. The most consumed, fruits and vegetables, medicinal plants and other natural products associated to the intake of tamoxifen were, for example, Orange and Better juice, Aloe, Geranium, Saint John Wort leaves and flowers, roots as Astragalus, Curcuma, Ginger, Ginseng, Rehmanniae and Valeriana, mushrooms as Coriolus, Maitake, Shiitake and Reishi. Conclusions: Based on the major compounds involved in those products will be predictable how to advice patients doing this kind of treatment and follow a possible therapy failure, or even a toxic event. Our group did a flyer with the main possible interactions selected for DHI with Tamoxifen. This it will be given to patients doing therapy with tamoxifen, helping them to be a aware of the situation and involving all in the resolution for a better outcome (it will be available in our website as other materials for download already posted there).

1H NMR based pharmacometabolomics analysis of metabolic phenotype on predicting metabolism characteristics of losartan in healthy volunteers

Inter-individual variability in drug metabolism and disposition is common in both preclinical and clinical researches. Losartan and its active metabolite EXP3174 present a high degree of inter-individual differences in blood concentrations that affect drug efficacy and side effect. Pharmacometabolomics has been increasingly applied on predicting the drug responses by analyzing the differences in metabolic profile. A pre-dose metabolic phenotype was investigated to interpret inter-individual variations in the metabolism characteristics of losartan. 1H Nuclear Magnetic Resonance (NMR) spectroscopy-based metabolic profiles were performed on 36 healthy Chinese male volunteers by measuring their pre-dose plasma samples. After oral administration of losartan, the concentrations of losartan and its bioactive metabolite EXP3174 were monitored by liquid chromatography-mass spectrometry (LC-MS). Orthogonal partial least-squares (O-PLS) model was conducted to select potential biomarkers that substantially contributed to the inter-individual variations in the metabolism features via analyzing the ratio of pharmacokinetics (PK) parameters of its metabolite to parent drug. Potential metabolites such as glycine, phosphorylcholine, choline, creatine, creatinine, lactate, citrate, α-glucose, and lipids showed strong correlations with metabolism features of losartan. In addition, the pathway analysis revealed that baseline lipid metabolism, the glycine, serine and threonine pathway, and glycolysis or gluconeogenesis metabolism pathway were significantly associated with the ratio of PK parameters of EXP3174 to losartan. Step-wise multiple linear regression (MLR) was constructed to investigate the potential roles of the selected biomarkers in predicting individualized metabolism characteristics of losartan. These results showed that the pre-dose individual metabolic traits may be a useful approach for characterizing individual differences in losartan metabolism characteristics and therefore for expediting personalized dose-setting in further clinical studies.

Age‐ and genotype‐dependent UGT2B7 and UGT2B17 proteomics data explain the inter‐individual variability in metabolism of codeine and MK‐7246

Background and ObjectiveUGT abundance and activity are associated with age and genetic polymorphisms. The aims of this project were to apply our previously generated quantitative UGT proteomics data i) to predict the effect of UGT2B7 ontogeny on the pharmacokinetics (PK) of morphine (an active metabolite) in breastfed neonate of a codeine‐prescribed mother, and ii) to predict age‐ and genotype‐dependent variability in the PK of MK‐7246 (MK; a UGT2B17 substrate) using physiologically‐based PK (PBPK) modeling.MethodsFirst an adult PBPK model was constructed and validated against the observed PK data following single oral dose of codeine (30 mg) and MK (1 mg) using Simcyp simulator. The simulation trial size was consisted of 10 trials of 10 subjects. The predicted adult codeine and morphine concentrations were validated by comparing literature data from adults with different CYP2D6 genotypes (i.e., poor, extensive and ultra‐rapid metabolizers, PM, EM, UM, respectively) and in breast‐feeding mother. We then predicted PK of codeine and morphine in neonates by integrating average milk intake, steady‐state milk‐to‐plasma ratio (2.5) and UGT2B7 ontogeny data into the PBPK model. Likewise, disposition of MK was predicted in children (age 0–18) and subjects carrying UGT2B17*2/*2, *1/*2 vs. reference allele (*1/*1) by integrating UGT2B17 proteomics data in the liver and intestine into the model. The models were evaluated by visual predictive checks and by comparison of predicted (mean and 5–95 % confidence intervals (CIs)) data with the observed PK parameters.ResultsThe predicted codeine mean AUC (ng/ml.hr) values in CYP2D6 PM, EM and UM adults were 211, 194 and 180 vs. 180, 191, and 192 (observed1), respectively. Similarly, the predicted morphine AUC (ng/ml.hr) values after codeine dose in adults were 0 (PM), 9.5 (EM), and 17 (UM), which were within the range of the observed data1 (Fig 1A). The normal neonatal morphine levels were closely predicted, i.e., &lt; 2 ng/ml; however, the reported toxic levels linked to death of a neonate2 were only predicted accurately (54 vs. 70 ng/ml) when UGT2B7 activity was limited or not considered in mother and neonates. The predicted MK AUC (ng/ml.hr) also correlate the observed values in the adults (61.3 vs. 61.7; 4.8 vs. 6.1; 3.6 vs. 2.5) in case of carriers of UGT2B17 *2*2 (deletion), *1*2 and wild type *1*1 alleles3 (Fig 1B). We then predicted that MK clearance could be highly variable across age, e.g., 2 (neonates) to 85 (adults) ml/min/kg in the *1*1 individuals.DiscussionAge‐ and genotype‐dependent UGT abundance data are useful in predicting inter‐individual variability in drug metabolism. Consideration of variability in UGT2B7 mediated morphine metabolism after its formation from codeine could predict morphine toxicity, which is not fully explained by CYP2D6 variability alone2. Unprecedented variability in UGT2B17 protein abundance and its higher protein abundance in the intestine could be associated with larger age‐ and genotype‐dependent PK of its substrates as demonstrated for MK‐7246.Support or Funding InformationNIH R01 HD081299This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Towards a System Approach to the Human Cytochrome P450 Ensemble: A New Strategy for Studying the Network of P450‐P450 Interactions in Human Liver Microsomes

The composition of the human cytochrome P450 ensemble is commonly recognized as a key factor determining the interindividual variability in drug metabolism. However, recent studies on a large selection of human liver microsomes (HLM) demonstrated the lack of a direct correlation between the composition of the cytochrome P450 ensemble and the profile of drug metabolism. At the same time, there is an emerging recognition of the functional importance of interactions between multiple cytochrome P450 species co‐localized in the microsomal membrane. A change in the content of any particular P450 enzyme alters the landscape of protein‐protein interactions and thus affects drug metabolism in a complex, hard‐to‐predict manner. Therefore, a systematic exploration of the network of P450‐P450 interactions and identification of their functional consequences represents an issue of emerging importance for revealing the interrelationships between the profile of P450 expression and the profile of drug metabolism. In a search for a model system suitable for these studies we introduced a method based on incorporation of purified cytochromes P450 into the microsomes. Here we demonstrate high potential of this approach for creating preparations of HLM with altered composition of the P450 ensemble. An important characteristic of this strategy is its adaptability for incorporating genetically or chemically modified proteins. This includes the incorporation of proteins bearing fluorescent probes and light‐activating crosslinkers. Therefore, this strategy may be used for monitoring protein‐protein interactions in HLM with a variety of biophysical techniques, as well as for searching the partners of P450 protein‐protein interactions with the technique of molecular fishing.Here we report the use of our new approach for studying the effect of enriching the HLM with ethanol‐inducible CYP2E1, one of the the most populated P450 species in human liver. Incorporation of CYP2E1 into HLM results in an increase in the rate of metabolism of CYP2E1‐specific substrates, which is proportional to the amount of the incorporated enzyme up to its content of 0.3 nmol per mg protein (or ~50% of CYP2E1 in the total P450 content). Our studies with a series of substrates of drug‐metabolizing P450s showed that CYP2E1 incorporation results in pronounced alterations in the metabolism of substrates of several other P450 species present in HLM. In particular, we observed over 2‐fold increase in the rate of metabolism and a substantial decrease in the apparent KM observed with 3‐cyano‐7‐etoxycoumarin (CEC), the substrate of CYP1A2 and CYP2C19. This finding may indicate that the increase in CYP2E1 concentration results in redirecting the main route of CEC metabolism from CYP2C19 to CYP1A2, which is characterized with lower KM and higher turnover numbers with this substrate. Similarly, increase in CYP2E1 content causes an important changes in the function of CYP3A enzymes, which is revealed in a compromised homotropic cooperativity, decreased affinity and increased Vmax, observed with 7‐benzyloxyquinoline, a selective substrate of CYP3A4 and CYP3A5.Support or Funding InformationThis research was supported by grant R01‐GM114369 from NIH.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pharmacogenomics in Critical Care.

Since the successful completion of the Human Genome Project in 2003, extensive genomic research has continued to alter pathophysiology at the molecular level. This research includes investigation of the specific receptors and metabolizing enzymes in drug pharmacodynamics and pharmacokinetics, specifically the cytochrome P450 system located primarily in the liver. In this article, pharmacogenomics and the role of the cytochrome P450 system in metabolism of various drugs are discussed. Specifically, drugs that are used in the critical care setting and are of clinical significance to the bedside critical care nurse are examined.

Physiological Regulation of Drug Metabolism and Transport: Pregnancy, Microbiome, Inflammation, Infection, and Fasting

This article is a report on a symposium entitled "Physiological Regulation of Drug Metabolism and Transport" sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 2017 meeting in Chicago, IL. The contributions of physiologic and pathophysiological regulation of drug-metabolizing enzymes and transporters to interindividual variability in drug metabolism are increasingly recognized but in many cases are not well understood. The presentations herein discuss the phenomenology, consequences, and mechanism of such regulation. CYP2D6 transgenic mice were used to provide insights into the mechanism of regulation of this enzyme in pregnancy, via hepatocyte nuclear factor 4α, small heterodimer partner, and retinoids. Regulation of intestinal and hepatic drug-processing enzymes by the intestinal microbiota via tryptophan and its metabolites was investigated. The potential impact of parasitic infections on human drug metabolism and clearance was assessed in mice infected with Schistosoma mansoni or Plasmodium chabaudi chabaudi AS, both of which produced widespread and profound effects on murine hepatic drug-metabolizing enzymes. Finally, the induction of Abcc drug efflux transporters by fasting was investigated. This was demonstrated to occur via a cAMP, protein kinase A/nuclear factor-E2-related factor 2/Sirtuin 1 pathway via antioxidant response elements on the Abcc genes.

Genetic Parameter Estimates for Metabolizing Two Common Pharmaceuticals in Swine.

In livestock, the regulation of drugs used to treat livestock has received increased attention and it is currently unknown how much of the phenotypic variation in drug metabolism is due to the genetics of an animal. Therefore, the objective of the study was to determine the amount of phenotypic variation in fenbendazole and flunixin meglumine drug metabolism due to genetics. The population consisted of crossbred female and castrated male nursery pigs (n = 198) that were sired by boars represented by four breeds. The animals were spread across nine batches. Drugs were administered intravenously and blood collected a minimum of 10 times over a 48 h period. Genetic parameters for the parent drug and metabolite concentration within each drug were estimated based on pharmacokinetics (PK) parameters or concentrations across time utilizing a random regression model. The PK parameters were estimated using a non-compartmental analysis. The PK model included fixed effects of sex and breed of sire along with random sire and batch effects. The random regression model utilized Legendre polynomials and included a fixed population concentration curve, sex, and breed of sire effects along with a random sire deviation from the population curve and batch effect. The sire effect included the intercept for all models except for the fenbendazole metabolite (i.e., intercept and slope). The mean heritability across PK parameters for the fenbendazole and flunixin meglumine parent drug (metabolite) was 0.15 (0.18) and 0.31 (0.40), respectively. For the parent drug (metabolite), the mean heritability across time was 0.27 (0.60) and 0.14 (0.44) for fenbendazole and flunixin meglumine, respectively. The errors surrounding the heritability estimates for the random regression model were smaller compared to estimates obtained from PK parameters. Across both the PK and plasma drug concentration across model, a moderate heritability was estimated. The model that utilized the plasma drug concentration across time resulted in estimates with a smaller standard error compared to models that utilized PK parameters. The current study found a low to moderate proportion of the phenotypic variation in metabolizing fenbendazole and flunixin meglumine that was explained by genetics in the current study.