Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation. Pharmacol Ther. 2013;138:103-141. [PMID: 23333322 DOI: 10.1016/j.pharmthera.2012.12.007]

Genetic polymorphisms of phase I and phase II metabolic enzymes as modulators of lung cancer susceptibility

OBJECTIVES

Tobacco exposure remains the main etiologic factor for lung cancer (LC). Interactions between environment and individual genetic profile are particularly important for this disease. The aim of this study was to evaluate the contribution of CYP1A1*2A, CYP1A1*2C, CYP2D6*4, GSTP1, GSTM1, GSTT1 and NAT2 polymorphisms for the susceptibility to LC in a Portuguese population considering their demographic and clinical characteristics.

MATERIALS AND METHODS

A total of 200 LC and 247 controls subjects from the Centre of Portugal were studied. Clinical and demographic characteristics were collected from clinical files and by individual questionnaires. Polymorphisms of CYP1A1*2A, CYP1A1*2C, CYP2D6*4, GSTP1, GSTM1, GSTT1 and NAT2 were genotyped using PCR-RFLP, PCR multiplex, ARMS and real time.

RESULTS

Gender, family history of cancer, smoke cessation and alcohol consumption were independent risk factors (p < 0.05). Associations found between phases I and II genes and LC population reveal a sex dependent distribution. Logistic regression analysis demonstrates that enhanced activation by CYPs, associated by reduced or loss of function of phase II enzymes, can lead to a greater risk. GSTP1 and NAT2 polymorphisms studied have a significant contribution for the histological tumour types and the presence of metastases, at time of diagnosis, respectively, when males with smoking habits were considered.

CONCLUSION

Multiple interactions between environment and individual characteristics are clearly associated to this disease. Variants of the detoxification genes may act synergistically contributing to this disease and modifying the risk posed by smoking and sex. The GSTT1*0 and GSTP1 (Ile462Val) might contribute to the malignant phenotype through different mechanisms.

Associations Between CYP2B6 rs707265, rs1042389, rs2054675, and Hirschsprung Disease in a Chinese Population

BACKGROUND

Previous studies suggested that cytochrome P450 participated in the tumor metastasis and migration. CYP2B6 also acts as an important enzyme which metabolize partially or primarily metabolism of drugs, environmental contaminants, and mutagens. The objective of this study was to investigate the influence of CYP2B6 polymorphism on susceptibility of Hirschsprung disease.

METHODS

TaqMan assay was performed to determine the genotypes of CYP2B6 rs707265, rs1042389, rs2054675 in 262 cases and 290 control subjects. Logistic regression was used to assess the associations between these polymorphisms and HSCR.

RESULTS

We observed a significant association of CYP2B6 rs707265 (G>A) polymorphism and HSCR susceptibility (p < 0.001). Besides, rs707265 A presented a significant risk of HSCR (p < 0.001).

CONCLUSIONS

Our result suggested that CYP2B6 rs707265 modified the risk of HSCR.

Ethnic Differences in the Metabolism of Toluene: Comparisons between Korean and Foreign Workers Exposed to Toluene

The objectives of this study were to investigate the individual characteristics, lifestyle habits, exposure levels, and genetic diversity of xenobiotic-metabolizing enzymes involved in toluene metabolism in Korean and foreign workers exposed to toluene at a manufacturing plant. This study was conducted to determine the effects of culture or ethnicity on toluene metabolism. The results showed that blood and urinary toluene concentrations were dependent on the level of exposure to toluene. We analyzed the correlation between toluene metabolism and genetic diversity in glutathione S-transferase (GST) (M1), GSTT1, and cytochrome p-450 (CYP) 2E1*5 as well as lifestyle habits (smoking, drinking, and exercise habits). The results revealed significant correlations between toluene metabolism and GSTM1 and GSTT1 genetic diversity, as well as smoking and exercise.

Schisandrin B inhibits cell growth and induces cellular apoptosis and autophagy in mouse hepatocytes and macrophages: implications for its hepatotoxicity

A number of drugs and herbal compounds have been documented to cause hepatoxicity. Schisandrin B (Sch B) is an active dibenzocyclooctadiene isolated from Schisandrae fructus, with a wide array of pharmacological activities. However, the potential hepatotoxicity of Sch B is a major safety concern, and the underlying mechanism for Sch B-induced liver toxic effects is not fully elucidated. In the present study, we aimed to investigate the liver toxic effects and the molecular mechanisms of Sch B in mouse liver and macrophage cells. The results have shown that Sch B exhibits potent grow inhibitory, proapoptotic, and proautophagic effects in AML-12 and RAW 264.7 cells. Sch B markedly arrested cells in G₁ phase in both cell lines, accompanied by the down-regulation of cyclin dependent kinase 2 (CDK2) and cyclin D1 and up-regulation of p27 Kip1 and checkpoint kinase 1. Furthermore, Sch B markedly increased the apoptosis of AML-12 and RAW 264.7 cells with a decrease in the expression of B-cell lymphoma-extra-large and (Bcl-xl) B-cell lymphoma 2 (Bcl-2), but an increase in the expression of B-cell lymphoma 2-associated X protein (Bax). Sch B promoted the cleavage of caspase 3 and poly-adenosine diphosphate-ribose polymerase (PARP) in both cell lines. Additionally, Sch B significantly induced autophagy of AML-12 and RAW 264.7 cells. Sch B inhibited the activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, as indicated by their altered phosphorylation, contributing to the proautophagic effect of Sch B. Taken together, our findings show that the inducing effects of Sch B on cell cycle arrest, apoptosis, and autophagy may contribute to its liver toxic effects, which might provide a clue for the investigation of the molecular toxic targets and underlying mechanisms for Sch B-induced hepatotoxicity in herbal consumers. More studies are warranted to fully delineate the underlying mechanisms, efficacy, and safety of Sch B for clinical use.

Detecting non-allelic homologous recombination from high-throughput sequencing data

Non-allelic homologous recombination (NAHR) is a common mechanism for generating genome rearrangements and is implicated in numerous genetic disorders, but its detection in high-throughput sequencing data poses a serious challenge. We present a probabilistic model of NAHR and demonstrate its ability to find NAHR in low-coverage sequencing data from 44 individuals. We identify NAHR-mediated deletions or duplications in 109 of 324 potential NAHR loci in at least one of the individuals. These calls segregate by ancestry, are more common in closely spaced repeats, often result in duplicated genes or pseudogenes, and affect highly studied genes such as GBA and CYP2E1.

Prevention of Aflatoxin B1 Hepatoxicity by Dietary Selenium Is Associated with Inhibition of Cytochrome P450 Isozymes and Up-Regulation of 6 Selenoprotein Genes in Chick Liver

BACKGROUND

The involvement of cytochrome P450 (CYP450) isozymes and the selenogenome in selenium-mediated protection against aflatoxin B1 (AFB1)-induced adverse effects in broilers remains unclear.

OBJECTIVE

This study was designed first to determine whether selenium could reduce AFB1-induced hepatotoxic effects and then to determine whether these effects were due to changes in the CYP450 isozymes and selenogenome expression in the liver of chicks.

METHODS

Male avian broilers (aged 120 d) were allocated to 4 groups with 5 replicates of 6 birds to be included in a 2-by-2 factorial trial in which the main factors included supplementation of AFB1 (<5 compared with 100 μg/kg) and selenium (0.2 compared with 0.5 mg/kg) in a corn/soybean-based diet for 4 wk. Serum biochemistry, hepatic histology, and mRNA and/or activities of hepatic antioxidant enzymes, CYP450 isozymes, and 26 selenoproteins were analyzed at week 2 and/or 4.

RESULTS

Administration of AFB1 induced liver injury, decreasing (P < 0.05) total protein and albumin concentrations by 33.3-43.8% and increasing (P < 0.05) alanine aminotransferase and aspartate aminotransferase activities by 26.0-33.8% in serum, and induced hepatic necrosis and bile duct hyperplasia at week 2. AFB1 also decreased (P < 0.05) hepatic activities of glutathione peroxidase (GPX), thioredoxin reductase (TXNRD), and catalase, and the glutathione concentration by 13.1-59.9% and increased (P < 0.05) malondialdehyde, 8-hydroxydeoxyguanosine and exo-AFB1-8,9-epoxide (AFBO) DNA concentrations by 17.9-1200%. In addition, the mRNA and activity of enzymes responsible for the bioactivation of AFB1 into AFBO, which included CYP450 A1, 1A2, 2A6, and 3A4, were significantly induced (P < 0.05) by 29.2-271% in liver microsomes after 2-wk exposure to AFB1. These alterations induced by AFB1 were prevented by selenium supplementation. Dietary selenium supplementation increased (P < 0.05) mRNA and/or activities of 6 selenoprotein genes (Gpx3, Txnrd1, Txnrd2, Txnrd3, iodothyronine deiodinase 2, and selenoprotein N) in the liver of AFB1-treated groups at week 2.

CONCLUSIONS

Dietary selenium protected chicks from AFB1-induced liver injury, potentially through the synergistic actions of inhibition of the pivotal CYP450 isozyme-mediated activation of AFB1 to toxic AFBO, and increased antioxidant capacities by upregulation of selenoprotein genes coding for antioxidant proteins.

Confounding factors and genetic polymorphism in the evaluation of individual steroid profiling

In the fight against doping, steroid profiling is a powerful tool to detect drug misuse with endogenous anabolic androgenic steroids. To establish sensitive and reliable models, the factors influencing profiling should be recognised. We performed an extensive literature review of the multiple factors that could influence the quantitative levels and ratios of endogenous steroids in urine matrix. For a comprehensive and scientific evaluation of the urinary steroid profile, it is necessary to define the target analytes as well as testosterone metabolism. The two main confounding factors, that is, endogenous and exogenous factors, are detailed to show the complex process of quantifying the steroid profile within WADA-accredited laboratories. Technical aspects are also discussed as they could have a significant impact on the steroid profile, and thus the steroid module of the athlete biological passport (ABP). The different factors impacting the major components of the steroid profile must be understood to ensure scientifically sound interpretation through the Bayesian model of the ABP. Not only should the statistical data be considered but also the experts in the field must be consulted for successful implementation of the steroidal module.

Functional characterization of 20 allelic variants of CYP1A2

Genetic variations in cytochrome P450 1A2 (CYP1A2) are associated with interindividual variability in the metabolism and efficacy of many medications. Twenty CYP1A2 variants harboring amino acid substitutions were analyzed for functional changes in enzymatic activity. Recombinant CYP1A2 variant proteins were heterologously expressed in COS-7 cells. Enzyme kinetic analyses were performed with two representative CYP1A2 substrates, phenacetin and 7-ethoxyresorufin. Among the 20 CYP1A2 allelic variants, CYP1A2*4, CYP1A2*6, CYP1A2*8, CYP1A2*15, CYP1A2*16, and CYP1A2*21 were inactive toward both substrates. CYP1A2*11 showed markedly reduced activity, but the changes in Km were different between the substrates. CYP1A2*14 and CYP1A2*20 exhibited increased activity compared to the wild-type enzyme, CYP1A2*1. This comprehensive in vitro assessment provided insight into the specific metabolic activities of CYP1A2 proteins encoded by variant alleles, which may to be valuable when interpreting the results of in vivo studies.

Evaluating a physiologically based pharmacokinetic model for prediction of omeprazole clearance and assessing ethnic sensitivity in CYP2C19 metabolic pathway

PURPOSE

The purpose of this study is to evaluate the ethnicity-specific population models in the SimCYP Simulator® for prediction of omeprazole clearance with attention to differences in the CYP2C19 metabolic pathway.

METHODS

The SimCYP® models incorporating Caucasian, Chinese, and Japanese population-specific demographic, physiological, and enzyme data were applied to simulate omeprazole pharmacokinetics. Published pharmacokinetic data of omeprazole after intravenous or oral administration in Caucasian, Chinese, and Japanese were used for the evaluation.

RESULTS

Following oral administration, the ratio of the predicted to observed geometric mean of omeprazole clearance in Caucasian extensive metabolizers (EMs) was 0.88. The ratios in Chinese EMs were 1.16 and 0.99 after intravenous and oral administration, respectively. The ratios in Japanese EMs were 0.88 and 0.71 after intravenous and oral administration, respectively. Significant differences (2-fold) in the observed oral clearance of omeprazole were identified between Caucasian and Asian (Chinese and Japanese) EMs while the observed oral and intravenous clearances of omeprazole were similar between Chinese and Japanese EMs. Physiologically based pharmacokinetics (PBPK) models within SimCYP accurately predicted the difference in the observed oral clearance between Caucasian and Chinese EMs but overpredicted the difference between Caucasians and Japanese EMs due to under-prediction of oral clearance in Japanese EMs.

CONCLUSIONS

The PBPK model within SimCYP adequately predicted omeprazole clearance in Caucasian, Chinese, and Japanese EMs and the 2-fold differences in clearance of omeprazole between Caucasian and Asian EMs. This may lead to early identification of ethnic sensitivity in clearance and the need for different dosing regimens in a specific ethnic group for substrates of CYP2C19 which can support the rational design of bridging clinical trials.

Nonalcoholic steatohepatitis in precision medicine: Unraveling the factors that contribute to individual variability

There are numerous factors in individual variability that make the development and implementation of precision medicine a challenge in the clinic. One of the main goals of precision medicine is to identify the correct dose for each individual in order to maximize therapeutic effect and minimize the occurrence of adverse drug reactions. Many promising advances have been made in identifying and understanding how factors such as genetic polymorphisms can influence drug pharmacokinetics (PK) and contribute to variable drug response (VDR), but it is clear that there remain many unidentified variables. Underlying liver diseases such as nonalcoholic steatohepatitis (NASH) alter absorption, distribution, metabolism, and excretion (ADME) processes and must be considered in the implementation of precision medicine. There is still a profound need for clinical investigation into how NASH-associated changes in ADME mediators, such as metabolism enzymes and transporters, affect the pharmacokinetics of individual drugs known to rely on these pathways for elimination. This review summarizes the key PK factors in individual variability and VDR and highlights NASH as an essential underlying factor that must be considered as the development of precision medicine advances. A multifactorial approach to precision medicine that considers the combination of two or more risk factors (e.g. genetics and NASH) will be required in our effort to provide a new era of benefit for patients.

Variability in bioavailability of small molecular tyrosine kinase inhibitors

Small molecular tyrosine kinase inhibitors (smTKIs) are in the centre of the very quickly expanding area of personalized chemotherapy and oral applicability thereof. The number of drugs in this class is rapidly growing, with twenty current approvals by both the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The drugs are, however, generally characterized by a poor oral, and thus variable, bioavailability. This results in significant variation in plasma levels and exposure. The cause is a complex interplay of factors, including poor aqueous solubility, issued permeability, membrane transport and enzymatic metabolism. Additionally, food and drug-drug interactions can play a significant role. The issues related with an impaired bioavailability generally receive little attention. To the best of our knowledge, this article is the first to provide an overview of the factors that determine the bioavailability of the smTKIs.

Targeted label-free approach for quantification of epoxide hydrolase and glutathione transferases in microsomes

The aim of this study was to investigate the expression and organ distribution of cytochrome P450 (CYP450) enzymes, microsomal epoxide hydrolase (MEH), and microsomal glutathione-S-transferase (MGST 1, 2, 3) in human liver, lung, intestinal, and kidney microsomes by targeted peptide-based quantification using nano liquid chromatography-tandem multiple reaction monitoring (nano LC-MRM). Applying this method, we analyzed 16 human liver microsomes and pooled lung, kidney, and intestine microsomes. Nine of the CYP450s (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, 3A5) could be quantified in liver. Except for CYP3A4 and 3A5 existing in intestine, other CYP450s had little content (<0.1 pmol/mg protein) in extrahepatic tissues. MEH and MGSTs could be quantified both in hepatic and in extrahepatic tissues. The highest concentrations of MEH and MGST 1, 2 were found in liver; conversely MGST 3 was abundant in human kidney and intestine compared to liver. The targeted proteomics assay described here can be broadly and efficiently utilized as a tool for investigating the targeted proteins. The method also provides novel CYP450s, MEH, and MGSTs expression data in human hepatic and extrahepatic tissues that will benefit rational approaches to evaluate metabolism in drug development.

Overview of the biochemical and genetic processes in malignant mesothelioma

Malignant mesothelioma (MM) is a highly aggressive form of cancer, has a long latency period, and is resistant to chemotherapy. It is extremely fatal, with a mean survival of less than one year. The development of MM is strongly correlated with exposure to asbestos and with other factors, such as erionite and simian virus 40 [corrected]. Although various countries have banned the use of asbestos, MM has proven to be difficult to control and there appears to be a trend toward an increase in its incidence in the years to come. In Brazil, MM has not been widely studied from a genetic or biochemical standpoint. In addition, there have been few epidemiological studies of the disease, and the profile of its incidence has yet to be well established in the Brazilian population. The objective of this study was to review the literature regarding the processes of malignant transformation, as well as the respective mechanisms of tumorigenesis, in MM.

Characterization of human cytochrome P450s involved in the bioactivation of tri-ortho-cresyl phosphate (ToCP)

Tri-ortho-cresyl phosphate (ToCP) is a multipurpose organophosphorus compound that is neurotoxic and suspected to be involved in aerotoxic syndrome in humans. It has been reported that not ToCP itself but a metabolite of ToCP, namely, 2-(ortho-cresyl)-4H-1,2,3-benzodioxaphosphoran-2-one (CBDP), may be responsible for this effect as it can irreversibly bind to human butyrylcholinesterase (BuChE) and human acetylcholinesterase (AChE). The bioactivation of ToCP into CBDP involves Cytochrome P450s (P450s). However, the individual human P450s responsible for this bioactivation have not been identified yet. In the present study, we aimed to investigate the metabolism of ToCP by different P450s and to determine the inhibitory effect of the in vitro generated ToCP-metabolites on human BuChE and AChE. Human liver microsomes, rat liver microsomes, and recombinant human P450s were used for that purpose. The recombinant P450s 2B6, 2C18, 2D6, 3A4 and 3A5 showed highest activity of ToCP-bioactivation to BuChE-inhibitory metabolites. Inhibition experiments using pooled human liver microsomes indicated that P450 3A4 and 3A5 were mainly involved in human hepatic bioactivation of ToCP. In addition, these experiments indicated a minor role for P450 1A2. Formation of CBDP by in-house expressed recombinant human P450s 1A2 and 3A4 was proven by both LC-MS and GC-MS analysis. When ToCP was incubated with P450 1A2 and 3A4 in the presence of human BuChE, CBDP-BuChE-adducts were detected by LC-MS/MS which were not present in the corresponding control incubations. These results confirmed the role of human P450s 1A2 and 3A4 in ToCP metabolism and demonstrated that CBDP is the metabolite responsible for the BuChE inactivation. Interindividual differences at the level of P450 1A2 and 3A4 might play an important role in the susceptibility of humans in developing neurotoxic effects, such as aerotoxic syndrome, after exposure to ToCP.

Conversions of tricyclic antidepressants and antipsychotics with selected P450s from Sorangium cellulosum So ce56

Human cytochromes P450 (P450s) play a major role in the biotransformation of drugs. The generated metabolites are important for pharmaceutical, medical, and biotechnological applications and can be used for derivatization or toxicological studies. The availability of human drug metabolites is restricted and alternative ways of production are requested. For this, microbial P450s turned out to be a useful tool for the conversion of drugs and related derivatives. Here, we used 10 P450s from the myxobacterium Sorangium cellulosum So ce56, which have been cloned, expressed, and purified. The P450s were investigated concerning the conversion of the antidepressant drugs amitriptyline, clomipramine, imipramine, and promethazine; the antipsychotic drugs carbamazepine, chlorpromazine, and thioridazine, as well as their precursors, iminodibenzyl and phenothiazine. Amitriptyline, chlorpromazine, clomipramine, imipramine, and thioridazine are efficiently converted during the in vitro reaction and were chosen to upscale the production by an Escherichia coli-based whole-cell bioconversion system. Two different approaches, a whole-cell system using M9CA medium and a system using resting cells in buffer, were used for the production of sufficient amounts of metabolites for NMR analysis. Amitriptyline, clomipramine, and imipramine are converted to the corresponding 10-hydroxylated products, whereas the conversion of chlorpromazine and thioridazine leads to a sulfoxidation in position 5. It is shown for the first time that myxobacterial P450s are efficient to produce known human drug metabolites in a milligram scale, revealing their ability to synthesize pharmaceutically important compounds.

Transcriptional analysis identifies key genes involved in metabolism, fibrosis/tissue repair and the immune response against Fasciola hepatica in sheep liver

BACKGROUND

Although fascioliasis has been relatively well studied, little is known about the molecular basis of this disease. This is particularly relevant, considering the very different response that sheep have to Fasciola hepatica relative to cattle. The acute phase of this disease is severe in sheep, whereas chronic fascioliasis is more common in cattle.

METHODS

To begin to explore the host-response to Fasciola in sheep and improve the understanding of the host-pathogen interactions during the parasite's migration through liver parenchyma to the bile duct, we used RNA sequencing (RNA-seq) to investigate livers from sheep infected for eight weeks compared with those from uninfected controls.

RESULTS

This study identified 572 and 42 genes that were up- and down-regulated, respectively, in infected livers relative to uninfected controls. Our molecular findings provide significant new insights into the mechanisms linked to metabolism, fibrosis and tissue-repair in sheep, and highlight the relative importance of specific components of immune response pathways, which appear to be driven toward a suppression of inflammation.

CONCLUSIONS

This study is, to our knowledge, the first detailed investigation of the transcriptomic responses in the liver tissue of any host to F. hepatica infection. It defines the involvement of specific genes associated with the host's metabolism, immune response and tissue repair/regeneration, and highlights an apparent overlapping function of many genes involved in these processes.

New insights into the use of currently available non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs), which act via inhibition of the cyclooxygenase (COX) isozymes, were discovered more than 100 years ago. They remain a key component of the pharmacological management of acute and chronic pain. The COX-1 and COX-2 isozymes have different biological functions; analgesic activity is primarily (although not exclusively) associated with inhibition of COX-2, while different side effects result from the inhibition of COX-1 and COX-2. All available NSAIDs, including acetaminophen and aspirin, are associated with potential side effects, particularly gastrointestinal and cardiovascular effects, related to their relative selectivity for COX-1 and COX-2. Since all NSAIDs exert their therapeutic activity through inhibition of the COX isozymes, strategies are needed to reduce the risks associated with NSAIDs while achieving sufficient pain relief. A better understanding of the inhibitory activity and COX-1/COX-2 selectivity of an NSAID at therapeutic doses, based on pharmacokinetic and pharmacodynamic properties (eg, inhibitory dose, absorption, plasma versus tissue distribution, and elimination), and the impact on drug tolerability and safety can guide the selection of appropriate NSAIDs for pain management. For example, many NSAIDs with moderate to high selectivity for COX-2 versus COX-1 can be administered at doses that maximize efficacy (~80% inhibition of COX-2) while minimizing COX-1 inhibition and associated side effects, such as gastrointestinal toxicity. Acidic NSAIDs with favorable tissue distribution and short plasma half-lives can additionally be dosed to provide near-constant analgesia while minimizing plasma concentrations to permit recovery of COX-mediated prostaglandin production in the vascular wall and other organs. Each patient’s clinical background, including gastrointestinal and cardiovascular risk factors, should be taken into account when selecting appropriate NSAIDs. New methods are emerging to assist clinicians in the selection of appropriate NSAIDs and their doses/schedules, such as biomarkers that may predict the response to NSAID treatment in individual patients.

Biotransformation of xenobiotics in the human colon and rectum and its association with colorectal cancer

In humans, the liver is generally considered to be the major organ contributing to drug metabolism, but studies during the last years have suggested an important role of the extra-hepatic drug metabolism. The gastrointestinal tract (GI-tract) is the major path of entry for a wide variety of compounds including food, and orally administered drugs, but also compounds - with neither nutrient nor other functional value - such as carcinogens. These compounds are metabolized by a large number of enzymes, including the cytochrome P450 (CYP), the glutathione S-transferase (GST) family, the uridine 5'-diphospho- glucuronosyltransferase (UDP-glucuronosyltransferase - UGT) superfamily, alcohol-metabolizing enzymes, sulfotransferases, etc. These enzymes can either inactivate carcinogens or, in some cases, generate reactive species with higher reactivity compared to the original compound. Most data in this field of research originate from animal or in vitro studies, wherein human studies are limited. Here, we review the human studies, in particular the studies on the phenotypic expression of these enzymes in the colon and rectum to get an impression of the actual enzyme levels in this primary organ of exposure. The aim of this review is to give a summary of currently available data on the relation between the CYP, the GST and the UGT biotransformation system and colorectal cancer obtained from clinical and epidemiological studies in humans.

Tamoxifen metabolism predicts drug concentrations and outcome in premenopausal patients with early breast cancer

Tamoxifen is the standard-of-care treatment for estrogen receptor-positive premenopausal breast cancer. We examined tamoxifen metabolism via blood metabolite concentrations and germline variations of CYP3A5, CYP2C9, CYP2C19 and CYP2D6 in 587 premenopausal patients (Asians, Middle Eastern Arabs, Caucasian-UK; median age 39 years) and clinical outcome in 306 patients. N-desmethyltamoxifen (DM-Tam)/(Z)-endoxifen and CYP2D6 phenotype significantly correlated across ethnicities (R(2): 53%, P<10(-77)). CYP2C19 and CYP2C9 correlated with norendoxifen and (Z)-4-hydroxytamoxifen concentrations, respectively (P<0.001). DM-Tam was influenced by body mass index (P<0.001). Improved distant relapse-free survival (DRFS) was associated with decreasing DM-Tam/(Z)-endoxifen (P=0.036) and increasing CYP2D6 activity score (hazard ratio (HR)=0.62; 95% confidence interval (CI), 0.43-0.91; P=0.013). Low (<14 nM) compared with high (>35 nM) endoxifen concentrations were associated with shorter DRFS (univariate P=0.03; multivariate HR=1.94; 95% CI, 1.04-4.14; P=0.064). Our data indicate that endoxifen formation in premenopausal women depends on CYP2D6 irrespective of ethnicity. Low endoxifen concentration/formation and decreased CYP2D6 activity predict shorter DRFS.

Stratified medicine for the use of antidiabetic medication in treatment of type II diabetes and cancer: where do we go from here?

At present, the global diabetes epidemic is affecting 347 million individuals, 90% of whom are diagnosed with type II diabetes mellitus (T2DM). T2DM is commonly treated with more than one type of therapy, including oral antidiabetic drugs (OADs) and agents used in the treatment of diabetic complications. Several pharmacological classes of OADs are currently available for the treatment of T2DM, of which insulin secretagogues (i.e. sulphonylureas and meglitinides), insulin sensitizers [thiazolidinediones (TZDs)] and biguanides are the most commonly prescribed. Although many of these OADs have been used for more than half a century in the treatment of T2DM, the pharmacogenomic characteristics of these compounds have only recently been investigated, primarily in retrospective studies. Recent advances in pharmacogenomics have led to the identification of polymorphisms that affect the expression and function of drug-metabolizing enzymes and drug transporters, as well as drug targets and receptors. These polymorphisms have been shown to affect the therapeutic response to and side effects associated with OADs. The aim of this review was to provide an up-to-date summary of some of the pharmacogenomic data obtained from studies of T2DM treatment, with a focus on polymorphisms in genes affecting pharmacokinetics, pharmacodynamics and treatment outcome of the most commonly prescribed OADs. In addition, the implications of pharmacogenomics in the use of the OAD metformin in cancer will be briefly discussed. Finally, we will focus on recent advances in novel 'omics' technologies and discuss how these might aid in the personalized management of T2DM.

Investigation of the dominant positive effect of porcine farnesoid X receptor (FXR) splice variant 1

Pigs are well recognized as a model for humans in research studies due to similarities in metabolism and physiology between the two species. The potential for pigs to model humans in studying metabolic diseases is highly dependent on similarities in hepatic metabolism between the two species, including similarities in the farnesoid X receptor (FXR; NR1H4) which regulate bile acid homeostasis. During initial cloning of porcine FXR (pFXR), an alternative splice variant (pFXR-SV1) was isolated which contained a four amino acid (MYTG) insert that exerted a dominant positive effect on the wild type receptor (pFXR-WT). The current study investigated the role of this insert in the dominant positive effect. Individual point mutations were made to the first three amino acids of the MYTG insert. Mutations of the methionine (M) or threonine (T) to alanine (A) reduced the dominant positive effect, while mutation of the tyrosine (Y) to either A or phenylalanine (F) completely abolished the dominant positive effect. Treatment with the tyrosine phosphatase inhibitor sodium orthovanadate (Na3VO4) increased the dominant positive effect of pFXR-SV1 by about 30%. These results suggest that the dominant positive effect may be dependent on the phosphorylation status of the tyrosine in the MYTG insert. The human variant hFXRα+ has the same MYTG insert as pFXR-SV1, but did not cause a dominant positive effect on hFXR-WT and significantly reduced the activity of hFXR-WT. Thus, although the MYTG insert is conserved in both human and pig, the effects of this insert are different in the two species.

Long read nanopore sequencing for detection of HLA and CYP2D6 variants and haplotypes

Haplotypes are often critical for the interpretation of genetic laboratory observations into medically actionable findings. Current massively parallel DNA sequencing technologies produce short sequence reads that are often unable to resolve haplotype information. Phasing short read data typically requires supplemental statistical phasing based on known haplotype structure in the population or parental genotypic data. Here we demonstrate that the MinION nanopore sequencer is capable of producing very long reads to resolve both variants and haplotypes of HLA-A, HLA-B and CYP2D6 genes important in determining patient drug response in sample NA12878 of CEPH/UTAH pedigree 1463, without the need for statistical phasing. Long read data from a single 24-hour nanopore sequencing run was used to reconstruct haplotypes, which were confirmed by HapMap data and statistically phased Complete Genomics and Sequenom genotypes. Our results demonstrate that nanopore sequencing is an emerging standalone technology with potential utility in a clinical environment to aid in medical decision-making.

Long read nanopore sequencing for detection of HLA and CYP2D6 variants and haplotypes

Haplotypes are often critical for the interpretation of genetic laboratory observations into medically actionable findings. Current massively parallel DNA sequencing technologies produce short sequence reads that are often unable to resolve haplotype information. Phasing short read data typically requires supplemental statistical phasing based on known haplotype structure in the population or parental genotypic data. Here we demonstrate that the MinION nanopore sequencer is capable of producing very long reads to resolve both variants and haplotypes of HLA-A, HLA-B and CYP2D6 genes important in determining patient drug response in sample NA12878 of CEPH/UTAH pedigree 1463, without the need for statistical phasing. Long read data from a single 24-hour nanopore sequencing run was used to reconstruct haplotypes, which were confirmed by HapMap data and statistically phased Complete Genomics and Sequenom genotypes. Our results demonstrate that nanopore sequencing is an emerging standalone technology with potential utility in a clinical environment to aid in medical decision-making.

Nuclear Receptors in Drug Metabolism, Drug Response and Drug Interactions

Orally delivered small-molecule therapeutics are metabolized in the liver and intestine by phase I and phase II drug-metabolizing enzymes (DMEs), and transport proteins coordinate drug influx (phase 0) and drug/drug-metabolite efflux (phase III). Genes involved in drug metabolism and disposition are induced by xenobiotic-activated nuclear receptors (NRs), i.e. PXR (pregnane X receptor) and CAR (constitutive androstane receptor), and by the 1α, 25-dihydroxy vitamin D3-activated vitamin D receptor (VDR), due to transactivation of xenobiotic-response elements (XREs) present in phase 0-III genes. Additional NRs, like HNF4-α, FXR, LXR-α play important roles in drug metabolism in certain settings, such as in relation to cholesterol and bile acid metabolism. The phase I enzymes CYP3A4/A5, CYP2D6, CYP2B6, CYP2C9, CYP2C19, CYP1A2, CYP2C8, CYP2A6, CYP2J2, and CYP2E1 metabolize >90% of all prescription drugs, and phase II conjugation of hydrophilic functional groups (with/without phase I modification) facilitates drug clearance. The conjugation step is mediated by broad-specificity transferases like UGTs, SULTs, GSTs. This review delves into our current understanding of PXR/CAR/VDR-mediated regulation of DME and transporter expression, as well as effects of single nucleotide polymorphism (SNP) and epigenome (specified by promoter methylation, histone modification, microRNAs, long non coding RNAs) on the expression of PXR/CAR/VDR and phase 0-III mediators, and their impacts on variable drug response. Therapeutic agents that target epigenetic regulation and the molecular basis and consequences (overdosing, underdosing, or beneficial outcome) of drug-drug/drug-food/drug-herb interactions are also discussed. Precision medicine requires understanding of a drug's impact on DME and transporter activity and their NR-regulated expression in order to achieve optimal drug efficacy without adverse drug reactions. In future drug screening, new tools such as humanized mouse models and microfluidic organs-on-chips, which mimic the physiology of a multicellular environment, will likely replace the current cell-based workflow.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

A current review for biological monitoring of manganese with exposure, susceptibility, and response biomarkers

People can be easily exposed to manganese (Mn), the twelfth most abundant element, through various exposure routes. However, overexposure to Mn causes manganism, a motor syndrome similar to Parkinson disease, via interference of the several neurotransmitter systems, particularly the dopaminergic system in areas. At cellular levels, Mn preferentially accumulates in mitochondria and increases the generation of reactive oxygen species, which changes expression and activity of manganoproteins. Many studies have provided invaluable insights into the causes, effects, and mechanisms of the Mn-induced neurotoxicity. To regulate Mn exposure, many countries have performed biological monitoring of Mn with three major biomarkers: exposure, susceptibility, and response biomarkers. In this study, we review current statuses of Mn exposure via various exposure routes including food, high susceptible population, effects of genetic polymorphisms of metabolic enzymes or transporters (CYP2D6, PARK9, SLC30A10, etc.), alterations of the Mn-responsive proteins (i.e., glutamine synthetase, Mn-SOD, metallothioneins, and divalent metal trnsporter1), and epigenetic changes due to the Mn exposure. To minimize the effects of Mn exposure, further biological monitoring of Mn should be done with more sensitive and selective biomarkers.

Gambogic acid suppresses cytochrome P450 3A4 by downregulating pregnane X receptor and up-regulating DEC1 in human hepatoma HepG2 cells

Gambogic acid suppresses cytochrome P450 3A4 by downregulating pregnane X receptor and up-regulating DEC1 in human hepatoma HepG2 cells.

Electrocatalytic cycle of P450 cytochromes: the protective and stimulating roles of antioxidants

This study reports the investigation of the catalytic activity of isolated cytochromes from the cytochrome P450 superfamily. Electrochemically driven CYP reactions may have practical relevance, providing a useful tool for drug assay studies.

Hydroxylation index of omeprazole in relation to CYP2C19 polymorphism and sex in a healthy Iranian population

BACKGROUND

Polymorphism of CYP2C19 gene is one of the important factors in pharmacokinetics of CYP2C19 substrates. Omeprazole is a proton pump inhibitor which is mainly metabolized by cytochrome P450 2C19 (CYP2C19). The aim of present study was to assess omeprazole hydroxylation index as a measure of CYP2C19 activity considering new variant allele (CYP2C19*17) in Iranian population and also to see if this activity is sex dependent.

METHODS

One hundred and eighty healthy unrelated Iranian individuals attended in this study. Blood samples for genotyping and phenotyping were collected 3 hours after administration of 20 mg omeprazole orally. Genotyping of 2C19 variant alleles *2, *3 and *17 was performed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and semi-nested PCR methods. Plasma concentrations of omeprazole and hydroxyomeprazole were determined by high performance liquid chromatography (HPLC) technique and hydxroxylation index (HI) (omeprazole/ hydroxyomeprazole) was calculated.

RESULTS

The CYP2C19*17 was the most common variant allele in the studied population (21.6%). Genotype frequencies of CYP2C19*17*17, *1*17, and *2*17 were 5.5%, 28.8% and 3.3% respectively. The lowest and the highest median omeprazole HI was observed in *17*17 and *2*2 genotypes respectively (0.36 vs. 13.09). The median HI of omeprazole in subjects homozygous for CYP2C19*1 was 2.16-fold higher than individuals homozygous for CYP2C19*17 (P < 0.001) and the median HI of CYP2C19*1*17 genotype was 1.98-fold higher than CYP2C19 *17*17 subjects (P < 0.001). However, subjects with CYP2C19*2*17 (median HI: 1.74) and CYP2C19*1*2 (median HI: 1.98) genotypes and also CYP2C19*1*17 (median HI: 0.71) and CYP2C19*1*1 (mean HI: 0.78) did not show any significantly different enzyme activity. In addition, no statistically significant difference was found between women and men in distribution of CYP2C19 genotypes. Furthermore, the hydroxylation index of Omeprazole was not different between women and men in the studied population.

CONCLUSION

Our data point out the importance of CYP2C19*2 and CYP2C19*17 variant alleles in metabolism of omeprazole and therefore CYP2C19 activity. Regarding the high frequency of CYP2C19*17 in Iranian population, the importance of this new variant allele in metabolism of CYP2C19 substrates shall be considered.

Prediction of tamoxifen outcome by genetic variation of CYP2D6 in post-menopausal women with early breast cancer

The question of whether genetic polymorphisms of CYP2D6 can affect treatment outcome in patients with early post-menopausal oestrogen receptor (ER)-positive breast cancer has been a matter of debate over the past few years. In this article we revisit the hypothesis of CYP2D6 being a potential tamoxifen outcome predictor and provide detailed insight into the ongoing controversy that prevented the CYP2D6 marker from being accepted by the scientific and clinical community. We summarize the available pharmacokinetic, pharmacodynamic and pharmacogenetic evidence and resolve the controversy based on the recognized methodological and statistical issues. The cumulative evidence suggests that genotyping for CYP2D6 is clinically relevant in post-menopausal women. This is important, because the clarification of this issue has the potential to resolve a clinical management question that is relevant to hundreds of thousands of women diagnosed with ER-positive breast cancer each year, who should not be denied effective endocrine therapy.

Pharmacological management of hypertension in pregnancy

Hypertension in pregnancy remains a significant public health problem. Pharmacological management of blood pressure in pregnancy is impacted by changes in maternal drug disposition and by the pharmacodynamic effects of specific agents. This article will review the impact of pregnancy on pathways of drug elimination and the associated clinical implications, the pharmacodynamic effects of specific drugs and classes of drugs in pregnancy, and the data to date on the impact of antihypertensive therapy on mothers and their fetuses.

Molecular mechanisms of the microsomal mixed function oxidases and biological and pathological implications

The cytochrome P450 mixed function oxidase enzymes play a major role in the metabolism of important endogenous substrates as well as in the biotransformation of xenobiotics. The liver P450 system is the most active in metabolism of exogenous substrates. This review briefly describes the liver P450 (CYP) mixed function oxidase system with respect to its enzymatic components and functions. Electron transfer by the NADPH-P450 oxidoreductase is required for reduction of the heme of P450, necessary for binding of molecular oxygen. Binding of substrates to P450 produce substrate binding spectra. The P450 catalytic cycle is complex and rate-limiting steps are not clear. Many types of chemical reactions can be catalyzed by P450 enzymes, making this family among the most diverse catalysts known. There are multiple forms of P450s arranged into families based on structural homology. The major drug metabolizing CYPs are discussed with respect to typical substrates, inducers and inhibitors and their polymorphic forms. The composition of CYPs in humans varies considerably among individuals because of sex and age differences, the influence of diet, liver disease, presence of potential inducers and/or inhibitors. Because of such factors and CYP polymorphisms, and overlapping drug specificity, there is a large variability in the content and composition of P450 enzymes among individuals. This can result in large variations in drug metabolism by humans and often can contribute to drug–drug interactions and adverse drug reactions. Because of many of the above factors, especially CYP polymorphisms, there has been much interest in personalized medicine especially with respect to which CYPs and which of their polymorphic forms are present in order to attempt to determine what drug therapy and what dosage would reflect the best therapeutic strategy in treating individual patients.

●

The CYP P450 system is important in metabolism of endogenous substrates and drugs.

●

About 150 forms of CYPs have been identified and they are grouped into families.

●

CYPs catalyze a wide variety of reactions and are among the most diverse catalysts known.

●

Electrons are passed to the CYP via NADPH+NADPH-cytochrome P450 reductase.

●

Metabolism of certain compounds by CYPs generate reactive intermediates which are toxic.

Marine invertebrate xenobiotic-activated nuclear receptors: their application as sensor elements in high-throughput bioassays for marine bioactive compounds

Developing high-throughput assays to screen marine extracts for bioactive compounds presents both conceptual and technical challenges. One major challenge is to develop assays that have well-grounded ecological and evolutionary rationales. In this review we propose that a specific group of ligand-activated transcription factors are particularly well-suited to act as sensors in such bioassays. More specifically, xenobiotic-activated nuclear receptors (XANRs) regulate transcription of genes involved in xenobiotic detoxification. XANR ligand-binding domains (LBDs) may adaptively evolve to bind those bioactive, and potentially toxic, compounds to which organisms are normally exposed to through their specific diets. A brief overview of the function and taxonomic distribution of both vertebrate and invertebrate XANRs is first provided. Proof-of-concept experiments are then described which confirm that a filter-feeding marine invertebrate XANR LBD is activated by marine bioactive compounds. We speculate that increasing access to marine invertebrate genome sequence data, in combination with the expression of functional recombinant marine invertebrate XANR LBDs, will facilitate the generation of high-throughput bioassays/biosensors of widely differing specificities, but all based on activation of XANR LBDs. Such assays may find application in screening marine extracts for bioactive compounds that could act as drug lead compounds.

Endocannabinoid metabolism by cytochrome P450 monooxygenases

The endogenous cannabinoid system was first uncovered following studies of the recreational drug Cannabis sativa. It is now recognized as a vital network of signaling pathways that regulate several physiological processes. Following the initial discovery of the cannabinoid receptors 1 (CB1) and 2 (CB2), activated by Cannabis-derived analogs, many endogenous fatty acids termed "endocannabinoids" are now known to be partial agonists of the CB receptors. At present, the most thoroughly studied endocannabinoid signaling molecules are anandamide (AEA) and 2-arachidonylglycerol (2-AG), which are both derived from arachidonic acid. Both AEA and 2-AG are also substrates for the eicosanoid-synthesizing pathways, namely, certain cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes. In the past, research in the endocannabinoid field focused on the interaction of AEA and 2-AG with the COX and LOX enzymes, but accumulating evidence also points to the involvement of CYPs in modulating endocannabinoid signaling. The focus of this review is to explore the current understanding of CYP-mediated metabolism of endocannabinoids.

Cytochrome P450-mediated bioactivation of mefenamic acid to quinoneimine intermediates and inactivation by human glutathione S-transferases

Mefenamic acid (MFA) has been associated with rare but severe cases of hepatotoxicity, nephrotoxicity, gastrointestinal toxicity, and hypersensitivity reactions that are believed to result from the formation of reactive metabolites. Although formation of protein-reactive acylating metabolites by phase II metabolism has been well-studied and proposed to be the cause of these toxic side effects, the oxidative bioactivation of MFA has not yet been competely characterized. In the present study, the oxidative bioactivation of MFA was studied using human liver microsomes (HLM) and recombinant human P450 enzymes. In addition to the major metabolite 3'-OH-methyl-MFA, resulting from the benzylic hydroxylation by CYP2C9, 4'-hydroxy-MFA and 5-hydroxy-MFA were identified as metabolites resulting from oxidative metabolism of both aromatic rings of MFA. In the presence of GSH, three GSH conjugates were formed that appeared to result from GSH conjugation of the two quinoneimines formed by further oxidation of 4'-hydroxy-MFA and 5-hydroxy-MFA. The major GSH conjugate was identified as 4'-OH-5'-glutathionyl-MFA and was formed at the highest activity by CYP1A2 and to a lesser extent by CYP2C9 and CYP3A4. Two minor GSH conjugates resulted from secondary oxidation of 5-hydroxy-MFA and were formed at the highest activity by CYP1A2 and to a lesser extent by CYP3A4. Additionally, the ability of seven human glutathione S-transferases (hGSTs) to catalyze the GSH conjugation of the quinoneimines formed by P450s was also investigated. The highest increase of total GSH conjugation was observed with hGSTP1-1, followed by hepatic hGSTs hGSTA2-2 and hGSTM1-1. The results of this study show that, next to phase II metabolites, reactive quinoneimines formed by oxidative bioactivation might also contribute to the idiosyncratic toxicity of MFA.

Epigenetic modification of histone 3 lysine 27: mediator subunit MED25 is required for the dissociation of polycomb repressive complex 2 from the promoter of cytochrome P450 2C9

The Mediator complex is vital for the transcriptional regulation of eukaryotic genes. Mediator binds to nuclear receptors at target response elements and recruits chromatin-modifying enzymes and RNA polymerase II. Here, we examine the involvement of Mediator subunit MED25 in the epigenetic regulation of human cytochrome P450 2C9 (CYP2C9). MED25 is recruited to the CYP2C9 promoter through association with liver-enriched HNF4α, and we show that MED25 influences the H3K27 status of the HNF4α binding region. This region was enriched for the activating marker H3K27ac and histone acetyltransferase CREBBP after MED25 overexpression but was trimethylated when MED25 expression was silenced. The epigenetic regulator Polycomb repressive complex (PRC2), which represses expression by methylating H3K27, plays an important role in target gene regulation. Silencing MED25 correlated with increased association of PRC2 not only with the promoter region chromatin but with HNF4α itself. We confirmed the involvement of MED25 for fully functional preinitiation complex recruitment and transcriptional output in vitro. Formaldehyde-assisted isolation of regulatory elements (FAIRE) revealed chromatin conformation changes that were reliant on MED25, indicating that MED25 induced a permissive chromatin state that reflected increases in CYP2C9 mRNA. For the first time, we showed evidence that a functionally relevant human gene is transcriptionally regulated by HNF4α via MED25 and PRC2. CYP2C9 is important for the metabolism of many exogenous chemicals including pharmaceutical drugs as well as endogenous substrates. Thus, MED25 is important for regulating the epigenetic landscape resulting in transcriptional activation of a highly inducible gene, CYP2C9.