Human extrahepatic cytochromes P450: function in xenobiotic metabolism and tissue-selective chemical toxicity in the respiratory and gastrointestinal tracts

CYP2A6 deletion polymorphism is associated with decreased susceptibility of lung cancer in Asian smokers: a meta-analysis

Cytochrome P450 2A6 (CYP2A6) is an enzyme involved in the metabolism of some tobacco carcinogens, which is an important risk factor of lung cancer. Among CYP2A6 allelic variants, CYP2A6*4 presents a whole gene deletion that accounts for the majority of poor metabolizer. In this study, a meta-analysis was performed to assess the association between CYP2A6*4 and risk of lung cancer. Literature searches were conducted to identify peer-reviewed manuscripts published up to December 20, 2012. Pooled odds ratios (ORs) and 95 % confidence intervals (95 % CIs) were calculated in a fixed-effects model and a random-effects model when appropriate. Eight eligible studies with 3,203 lung cancer cases and 2,839 controls were included in this study. Overall, no significant association was observed in CYP2A6*4 with the risk of lung cancer under any genetic model for all samples after correction. However, subgroup analysis showed that significant associations were observed in Asian with pooled OR (95 %CI) of 0.761 (0.672-0.861) for allele comparison, 0.769 (0.668-0.886) for dominant model, and 0.522 (0.359-0.760) for recessive model. Furthermore, after stratifying Asian samples according to smoking status, significant associations were only observed in smokers with pooled OR (95 %CI) of 0.713 (0.607-0.838) for allele comparison, 0.720 (0.596-0.869) for dominant model, and 0.444 (0.275-0.715) for recessive model. This meta-analysis suggests that the CYP2A6*4 polymorphism was associated with susceptibility of lung cancer for smokers in Asian. The whole gene deletion of CYP2A6 might decrease the risk of tobacco-related lung cancer in Asian.

The effect of rosmarinic acid on 1,2-dimethylhydrazine induced colon carcinogenesis

This study was carried out to investigate the chemopreventive potential of rosmarinic acid (RA) against 1,2-dimethylhydrazine (DMH) induced rat colon carcinogenesis by evaluating the effect of RA on tumour formation, antioxidant enzymes, cytochrome P450 content, p-nitrophenol hydroxylase and GST activities. Rats were divided into six groups and fed modified pellet diet for the entire experimental period. Group 1 served as control, group 2 received RA (10 mg/kgb.w.). Groups 3-6 were induced colon cancer by injecting DMH (20 mg/kgb.w.) subcutaneously once a week for the first four weeks (groups 3-6). In addition, RA was administered at the doses of 2.5, 5 and 10 mg/kgb.w. to groups 4-6 respectively. DMH treated rats showed large number of colonic tumours; decreased lipid peroxidation; decreased antioxidant status; elevated CYP450 content and PNPH activities; and decreased GST activity in the liver and colon. Supplementation with RA (5 mgkg/b.w.) to DMH treated rats significantly decreased the number of polyps (50%); reversed the markers of oxidative stress (21.0%); antioxidant status (38.55%); CYP450 content (29.41%); and PNPH activities (21.9%). RA at the dose of 5 mg/kgb.w. showed a most pronounced effect and could be used as a possible chemopreventive agent against colon cancer.

Biotransformation kinetics and sorption of cocaine and its metabolites and the factors influencing their estimation in wastewater

The quantitative analysis of human urinary metabolites as biomarkers in wastewater streams has been used to estimate the rates of illicit drug use in the wider community. The primary underlying assumption in such studies is that a sample of wastewater is equivalent to a cumulative sample of urine. Drug metabolism in humans is predominantly enzymatically mediated, but these processes are not exclusive to the human body, and are found to occur in the environment and the sewer network. Understanding what happens to drugs and their urinary metabolites in the sewer system between the point of excretion and sampling is particularly important since it is possible that in-sewer transformation may influence final biomarker concentration. The present study uses batch experiments to measure and assess the biotransformation processes of cocaine and its two major human metabolites, benzoylecgonine and ecgonine methyl ester. The activated sludge modelling framework for xenobiotic organic micro-pollutants (ASM-X) is used for model structure identification and calibration. Biotransformation was observed to follow pseudo first-order kinetics. The biodegradation kinetics of cocaine, benzoylecgonine and ecgonine methyl ester is not significantly affected by the availability of dissolved oxygen. Results obtained in this study show that omitting in-pipe biotransformation affects the accuracy of back-calculated cocaine use estimates. This varies markedly depending on the in-sewer hydraulic retention time, total biomass concentration and the relative concentration of each metabolite. However, back-calculated cocaine use estimates derived from wastewater concentrations of benzoylecgonine and ecgonine methyl ester do show very close agreement if ex-vivo biotransformation of these compounds is considered.

Pilot study of CYP2B6 genetic variation to explore the contribution of nitrosamine activation to lung carcinogenesis

We explored the contribution of nitrosamine metabolism to lung cancer in a pilot investigation of genetic variation in CYP2B6, a high-affinity enzymatic activator of tobacco-specific nitrosamines with a negligible role in nicotine metabolism. Previously we found that variation in CYP2A6 and CHRNA5-CHRNA3-CHRNB4 combined to increase lung cancer risk in a case-control study in European American ever-smokers (n = 860). However, these genes are involved in the pharmacology of both nicotine, through which they alter smoking behaviours, and carcinogenic nitrosamines. Herein, we separated participants by CYP2B6 genotype into a high- vs. low-risk group (*1/*1 + *1/*6 vs. *6/*6). Odds ratios estimated through logistic regression modeling were 1.25 (95% CI 0.68-2.30), 1.27 (95% CI 0.89-1.79) and 1.56 (95% CI 1.04-2.31) for CYP2B6, CYP2A6 and CHRNA5-CHRNA3-CHRNB4, respectively, with negligible differences when all genes were evaluated concurrently. Modeling the combined impact of high-risk genotypes yielded odds ratios that rose from 2.05 (95% CI 0.39-10.9) to 2.43 (95% CI 0.47-12.7) to 3.94 (95% CI 0.72-21.5) for those with 1, 2 and 3 vs. 0 high-risk genotypes, respectively. Findings from this pilot point to genetic variation in CYP2B6 as a lung cancer risk factor supporting a role for nitrosamine metabolic activation in the molecular mechanism of lung carcinogenesis.

Association of CYP2A6*4 with susceptibility of lung cancer: a meta-analysis

OBJECTIVES

To assess the association between the variant of Cytochrome P450 2A6 whole gene deletion (CYP2A6*4) polymorphism and risk of lung cancer.

METHODS

Two investigators independently searched the PubMed, Elsevier, EMBASE, Web of Science, Wiley Online Library and Chinese National Knowledge Infrastructure (CNKI). Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) for CYP2A6*4 and lung cancer were calculated in a fixed-effects model (the Mantel-Haenszel method) and a random-effects model (the DerSimonian and Laird method) when appropriate.

RESULTS

This meta-analysis included seven eligible studies, which included 2524 lung cancer cases and 2258 controls (cancer-free). Overall, CYP2A6*4 was associated with the risk of lung cancer (allele*4 vs. allele non-*4, pooled OR  = 0.826, 95% CI  = 0.725-0.941, P-value  = 0.004). When stratifying for population, significant association was observed in Asian (additive model, pooled OR  = 0.794, 95% CI  = 0.694-0.909, P-value  = 0.001; dominant model, pooled OR  = 0.827, 95% CI  = 0.709-0.965, P-value  = 0.016; recessive model (pooled OR  = 0.444, 95% CI  = 0.293-0.675, P-value <0.0001). In the overall analysis, a comparably significant decrease in the frequency of *4/*4 genotype was detected between cases and controls in Asian while no *4/*4 genotype was detected in Caucasian in collected data.

CONCLUSION

This meta-analysis suggests that the CYP2A6*4 polymorphism is associated with susceptibility of lung cancer in Asian. The whole gene deletion of CYP2A6 may decrease the risk of lung cancer in Asian samples.

Severe acute nephrotoxicity in a kidney transplant patient despite low tacrolimus levels: a possible interaction between donor and recipient genetic polymorphisms

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus has a narrow therapeutic index and shows large interindividual variations in pharmacokinetics, which may be partly explained by genetic variability in metabolic enzymes of the cytochrome P450 (mainly CYP3A4 and CYP3A5) and transport P-glycoprotein (encoded by the ABCB1 gene). Genetic variability in the expression of biotransformation enzymes and drug transporters may also predispose individuals to tacrolimus-induced nephrotoxicity.

CASE SUMMARY

We report a case of severe biopsy-proven Tacrolimus (TAC) nephrotoxicity that occurred 1 month after renal transplantation despite persistently low TAC levels. The donor genotype was CYP3A5*3/*3 (loss-of-function genotype), whereas that of the recipient was CYP3A5*1/*3. The donor and recipient genotypes did not differ with respect to either CYP3A4 rs35599367C>T (both were CC homozygotes) or ABCB1 gene polymorphisms (both TT homozygotes for the 1236C>T polymorphism and CT heterozygotes for the 3435C>T polymorphism).

WHAT IS NEW AND CONCLUSION

This case study suggests that donor/recipient genetic mismatch in metabolic enzymes may have an important role in modulating tacrolimus nephrotoxicity. It provides a possible explanation for the intriguing observation that for a subset of patients, cumulative TAC doses appear to correlate better with nephrotoxicity than trough levels.

Genotoxic bioactivation of constituents of a diesel exhaust particle extract by the human lung

The ability of the human lung to catalyze genotoxic bioactivation of constituents of diesel exhaust particle (DEP) extract (DEPE) and the identity of the lung enzymes involved in the bioactivation were investigated using human lung tissues obtained from surgical resections. Genotoxicity was determined by lung S9-catalyzed mutagenicity of DEPE constituents to Salmonella typhimurium TA98NR in the Ames test and by DEPE-induced pneumocyte DNA damage response as determined by γH2Ax expression in ex vivo tissues. S9 was prepared from lung explants treated ex vivo with either DEPE to induce pulmonary enzymes (DEPE-S9) or vehicle only (CON-S9). TA98NR served as the tester strain for the purpose of enhancing and minimizing the contribution of lung S9 and Salmonella, respectively, to DEPE bioactivation. DEPE-S9 was 2.2-fold more active than CON-S9 or rat liver S9 in DEPE bioactivation and the bioactivation was inhibited 58, 45, 22, and 16% by α-naphthoflavone, dicumarol, ketoconazole, and ticlopidine, respectively. Alveolar S9 was less active than bronchioalveolar S9 in DEPE bioactivation. DEPE and diesel exhaust particles (DEP) induced γ-pH2Ax expression in pulmonary cells. Pulmonary CYP1A1 and NQO1 were induced by DEPE treatment, with the constitutive and induced CYP1A1 distributed throughout all peripheral lung regions, whereas NQO1 was limited in distribution to bronchiolar epithelium. The results show that the human lung is highly active in catalyzing genotoxic bioactivation of diesel emission constituents and that CYP1A and NQO1 play major roles in the reaction. The findings underscore the usefulness of human lung tissues in studies of the pneumotoxicity potential of chemicals to humans.

Odorant metabolism catalyzed by olfactory mucosal enzymes influences peripheral olfactory responses in rats

A large set of xenobiotic-metabolizing enzymes (XMEs), such as the cytochrome P450 monooxygenases (CYPs), esterases and transferases, are highly expressed in mammalian olfactory mucosa (OM). These enzymes are known to catalyze the biotransformation of exogenous compounds to facilitate elimination. However, the functions of these enzymes in the olfactory epithelium are not clearly understood. In addition to protecting against inhaled toxic compounds, these enzymes could also metabolize odorant molecules, and thus modify their stimulating properties or inactivate them. In the present study, we investigated the in vitro biotransformation of odorant molecules in the rat OM and assessed the impact of this metabolism on peripheral olfactory responses. Rat OM was found to efficiently metabolize quinoline, coumarin and isoamyl acetate. Quinoline and coumarin are metabolized by CYPs whereas isoamyl acetate is hydrolyzed by carboxylesterases. Electro-olfactogram (EOG) recordings revealed that the hydroxylated metabolites derived from these odorants elicited lower olfactory response amplitudes than the parent molecules. We also observed that glucurono-conjugated derivatives induced no olfactory signal. Furthermore, we demonstrated that the local application of a CYP inhibitor on rat olfactory epithelium increased EOG responses elicited by quinoline and coumarin. Similarly, the application of a carboxylesterase inhibitor increased the EOG response elicited by isoamyl acetate. This increase in EOG amplitude provoked by XME inhibitors is likely due to enhanced olfactory sensory neuron activation in response to odorant accumulation. Taken together, these findings strongly suggest that biotransformation of odorant molecules by enzymes localized to the olfactory mucosa may change the odorant’s stimulating properties and may facilitate the clearance of odorants to avoid receptor saturation.

Expression of cytochrome P450 2A13 in human non-small cell lung cancer and its clinical significance

Lung cancer is one of the most important causes of cancer-related mortality worldwide. Human cytochrome P450 2A13 enzyme (CYP2A13) is predominantly expressed in the respiratory tract and could catalyze various carcinogens. In this study, we quantified CYP2A13 expression in non-small cell lung cancer (NSCLC) tissues and examined the relation between CYP2A13 and clinicopathologic factors. Thirty-five paired lung cancer and normal tissues were studied for the expression of the CYP2A13 gene by using real-time PCR and Western blotting assays. We also investigated the relationship between CYP2A13 expression and clinicopathologic factors such as age, gender, histology and lymph node status in tumor tissues. SPSS (17.0) statistical software was applied for data analysis. The real-time PCR results showed that there was no significant difference in the CYP2A13 mRNA transcript levels between tumor and paired normal tissues in the 35 samples and in 12 paired squamous cell carcinomas. In adenocarcinoma, the expression of CYP2A13 mRNA in tumor tissues was 12.5% of that in adjacent tissues (P < 0.05) and it was not associated with age, gender, histology and lymph node status of the patients. The amounts of CYP2A13 proteins detected by Western blotting assays correlated well with those of the corresponding mRNAs. In conclusion, the expression of CYP2A13 was downregulated in lung adenocarcinoma. CYP2A13 may be involved in the development and progression of lung adenocarcinoma.

Three-dimensional quantitative structure-activity relationship analysis of inhibitors of human and rat cytochrome P4503A enzymes

Cytochrome P450 3A4 (CYP3A4) is a member of the CYP family and is an important enzyme in drug metabolism. A compound that inhibits CYP3A4 activity could also affect the pharmacokinetics of other substrates, resulting in drug-drug interactions (DDIs) that could cause side effects. Pharmacokinetic data from drug-development studies in rats often determine the dosage used in human clinical trials. It is therefore useful to understand differences in metabolism in different species at an early stage in drug development. Human and rat CYP3A enzymes show different inhibition profiles with different drugs, although the mechanisms involved are not yet clear. Here we built three-dimensional quantitative structure-activity relationship (3D-QSAR) models using structure-based comparative molecular field analysis (CoMFA), to predict the direct inhibitory activity of ligands for human CYP3A4 and rat CYP3A1, based on computer-ligand docking. The alignment of the ligand docking poses suggested that key amino acid-ligand interactions (e.g., Thr309 in CYP3A4 and Pro310 in CYP3A1) characterized the different potencies with which the ligands inhibited CYP3A4 and CYP3A1. The 3D-QSAR models for human and rat CYP3A family inhibitors predicted the potency of inhibitors and could be useful for assessing DDIs at an early stage in drug discovery.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Evaluation of animal models for intestinal first-pass metabolism of drug candidates to be metabolized by CYP3A enzymes via in vivo and in vitro oxidation of midazolam and triazolam

1. To search an appropriate evaluation methodology for the intestinal first-pass metabolism of new drug candidates, grapefruit juice (GFJ)- and vehicle (tap water)-pretreated mice or rats were orally administered midazolam (MDZ) or triazolam (TRZ), and blood levels of the parent compounds and their metabolites were measured by liquid chromatography/MS/MS. A significant effect of GFJ to elevate the blood levels was observed only for TRZ in mice. 2. In vitro experiments using mouse, rat and human intestinal and hepatic microsomal fractions demonstrated that GFJ suppressed the intestinal microsomal oxidation of MDZ and especially TRZ. Substrate inhibition by MDZ caused reduction in 1'-hydroxylation but not 4-hydroxylation in both intestinal and hepatic microsomal fractions. The kinetic profiles of MDZ oxidation and the substrate inhibition in mouse intestinal and hepatic microsomal fractions were very similar to those in human microsomes but were different from those in rat microsomes. Furthermore, MDZ caused mechanism-based inactivation of cytochrome P450 3A-dependent TRZ 1'-hydroxylation in mouse, rat and human intestinal microsomes with similar potencies. 3. These results are useful information in the analysis of data obtained in mouse and rat for the evaluation of first-pass effects of drug candidates to be metabolized by CYP3A enzymes.

Biotransformation enzyme expression in the nasal epithelium of woodrats

When herbivores come in contact with volatile plant secondary compounds (PSC) that enter the nasal passages the only barrier between the nasal cavity and the brain is the nasal epithelium and the biotransformation enzymes present there. The expression of two biotransformation enzymes Cytochrome P450 2B (CYP2B) and glutathione-S-transferase (GST) was investigated in the nasal epithelia and livers of three populations of woodrats. One population of Neotoma albigula was fed juniper that contains volatile terpenes. Juniper caused upregulation of CYP2B and GST in the nasal epithelium and the expression of CYP2B and GST in the nasal epithelium was correlated to liver expression, showing that the nasal epithelia responds to PSC and the response is similar to the liver. Two populations of Neotoma bryanti were fed creosote that contains less volatile phenolics. The creosote naive animals upregulated CYP2B in their nasal epithelia while the creosote experienced animals upregulated GST. There was no correlation between CYP2B and GST expression in the nasal epithelia and livers of either population. The response of the nasal epithelium to PSC seems to be an evolved response that is PSC and experience dependent.

Dietary supplementation with vitamin D stimulates intestinal epithelial cell turnover after massive small bowel resection in rats

PURPOSE

While the endocrine action of the active metabolite 1,25-dihydroxyvitamin D (VtD) has been well characterized in relation to the maintenance of plasma calcium and phosphate homeostasis through regulation of intestinal absorption, recent research has focused on its autocrine and/or paracrine activities. Such activities have been best characterized in intestine, where VtD regulates cell differentiation and maturation. The purpose of this study was to evaluate the effect of VtD on enterocyte turnover in a rat model of short bowel syndrome (SBS).

METHODS

Male rats were divided into four groups: sham rats underwent bowel transection, sham-VtD rats underwent bowel transection and were treated oral VtD, SBS rats underwent a 75 % bowel resection, and SBS-VtD rats underwent bowel resection and were treated with VtD. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined at sacrifice. Illumina's digital gene expression (DGE) analysis was used to determine VtD pathway-related gene expression profiling. VtD receptor (VDR) and its promoter, Bax and Bcl-2 mRNA expression were determined using real-time PCR. Western blotting was used to determine p-ERK, Bax and β-catenin protein levels.

RESULTS

From the total of 20,000 probes, 11 genes related to VtD signaling were investigated. Of these genes, five were found to be up-regulated in SBS versus sham animals with a relative change in gene expression level of 20 %, five remained unchanged, and one was down-regulated. VtD treatment in sham and SBS rats resulted in significant up-regulation of the VDR gene and its promoter's expression. SBS-VtD rats demonstrated a significant increase in all intestinal mucosal parameters compared to SBS animals. A significant increase in cell proliferation in SBS-VtD rats was accompanied by increased β-catenin protein levels. A significant decrease in cell apoptosis in this group was correlated with lower Bax/Bcl-2 mRNA and protein levels.

CONCLUSION

In a rat model of SBS, dietary supplementation with VtD stimulates enterocyte turnover, which correlates with up-regulated VtD receptor expression in the remaining small intestine.

The influence of sex, ethnicity, and CYP2B6 genotype on bupropion metabolism as an index of hepatic CYP2B6 activity in humans

The effects of sex, ethnicity, and genetic polymorphism on hepatic CYP2B6 (cytochrome P450 2B6) expression and activity were previously demonstrated in vitro. Race/ethnic differences in CYP2B6 genotype and phenotype were observed only in women. To identify important covariates associated with interindividual variation in CYP2B6 activity in vivo, we evaluated these effects in healthy volunteers using bupropion (Wellbutrin SR GlaxoSmithKline, Research Triangle Park, NC) as a CYP2B6 probe substrate. A fixed 150-mg oral sustained-release dose of bupropion was administered to 100 healthy volunteers comprising four sex/ethnicity cohorts (n = 25 each): Caucasian men and Caucasian, African American, and Hispanic women. Blood samples were obtained at 0 and 6 hours postdose for the measurement of serum bupropion (BU) and hydroxybupropion (HB) concentrations. Whole blood was obtained at baseline for CYP2B6 genotyping. To characterize the relationship between CYP2B6 activity and ethnicity, sex, and genotype when accounting for serum BU concentrations (dose-adjusted log(10)-transformed), analysis of covariance model was fitted in which the dependent variable was CYP2B6 activity represented as the log(10)-transformed, metabolic ratio of HB to BU concentrations. Several CYP2B6 polymorphisms were associated with CYP2B6 activity. Evidence of dependence of CYP2B6 activity on ethnicity or genotype-by-ethnicity interactions was not detected in women. These results suggest that CYP2B6 genotype is the most important patient variable for predicting the level of CYP2B6 activity in women, when measured by the metabolism of bupropion. The bupropion metabolic ratio appears to detect known differences in CYP2B6 activity associated with genetic polymorphism, across different ethnic groups. Prospective studies will be needed to validate the use of bupropion as a probe substrate for clinical use.

Animal models of toxicology testing: the role of pigs

INTRODUCTION

In regulatory toxicological testing, both a rodent and non-rodent species are required. Historically, dogs and non-human primates (NHP) have been the species of choice of the non-rodent portion of testing. The pig is an appropriate option for these tests based on metabolic pathways utilized in xenobiotic biotransformation.

AREAS COVERED

This review focuses on the Phase I and Phase II biotransformation pathways in humans and pigs and highlights the similarities and differences of these models. This is a growing field and references are sparse. Numerous breeds of pigs are discussed along with specific breed differences in these enzymes that are known. While much available data are presented, it is grossly incomplete and sometimes contradictory based on methods used.

EXPERT OPINION

There is no ideal species to use in toxicology. The use of dogs and NHP in xenobiotic testing continues to be the norm. Pigs present a viable and perhaps more reliable model of non-rodent testing.

Cytochrome P450s and cytochrome P450 reductase in the olfactory organ of the cotton leafworm Spodoptera littoralis

Cytochrome P450 enzymes (P450s) are involved in many physiological functions in insects, such as the metabolism of signal molecules, adaptation to host plants and insecticide resistance. Several P450s have been reported in the olfactory organs of insects, the antennae, and have been proposed to play a role in odorant processing and/or xenobiotic metabolism. Despite recent transcriptomic analyses in several species, the diversity of antennal P450s in insects has not yet been investigated. Here, we report the identification of 37 putative P450s expressed in the antennae of the pest moth Spodoptera littoralis, as well as the characterization of a redox partner, cytochrome P450 reductase (CPR). Phylogenetic analysis revealed that S. littoralis P450s belong to four clades defined by their conservation with vertebrate P450s and their cellular localization. Interestingly, the CYP3 and CYP4 clans, which have been described to be mainly involved in the metabolism of plant compounds and xenobiotics, were largely predominant. More surprisingly, two P450s related to ecdysteroid metabolism were also identified. Expression patterns in adult and larval tissues were studied. Eight P450s appeared to be specific to the chemosensory organs, ie the antennae and proboscis, suggesting a specific role in odorant and tastant processing. Moreover, exposure of males to a plant odorant down-regulated the transcript level of CPR, revealing for the first time the regulation of this gene by odorants within insect antennae. This work suggests that the antennae of insects are a key site for P450-mediated metabolism of a large range of exogenous and endogenous molecules.

Pharmacokinetic interaction study of sulphasalazine in healthy subjects and the impact of curcumin as an in vivo inhibitor of BCRP

BACKGROUND AND PURPOSE An ATP-binding cassette (ABC) transporter, breast cancer resistance protein (BCRP)/ABCG2, limits oral bioavailability of sulphasalazine. Here we examined the effect of curcumin, the principal curcuminoid of turmeric, on oral bioavailability of microdoses and therapeutic doses of sulphasalazine in humans. EXPERIMENTAL APPROACH Effects of curcumin were measured on the ATP-dependent sulphasalazine uptake by hBCRP-expressing membrane vesicles and on oral bioavailability of sulphasalazine in wild-type and Bcrp(-/-) mice. Eight healthy Japanese subjects received an oral dose of sulphasalazine suspension (100 µg) or tablets (2 g) alone or after curcumin tablets (2 g). Uptake of sulphasalazine was studied in HEK293 cells transfected with the influx transporter (OATP)2B1. KEY RESULTS Curcumin was a potent hBCRP inhibitor in vitro (K(i) 0.70 ± 0.41 µM). Curcumin increased the area under the curve (AUC)(0-8) of plasma sulphasalazine eightfold in wild-type mice at 300 and 400 mg·kg(-1), but not in Bcrp(-/-) mice. Curcumin increased AUC(0-24) of plasma sulphasalazine 2.0-fold at microdoses and 3.2-fold at therapeutic doses in humans. Non-linearity of the dose-exposure relationship was observed between microdoses and therapeutic doses of sulphasalazine. Sulphasalazine was a substrate for OATP2B1 (K(m) 1.7 ± 0.3 µM). Its linear index (dose/K(m)) at the therapeutic dose was high and may saturate OATP2B1. CONCLUSIONS AND IMPLICATIONS Curcumin can be used to investigate effects of BCRP on oral bioavailability of drugs in humans. Besides the limited dissolution, OATP2B1 saturation is a possible mechanism underlying non-linearity in the dose-exposure relationship of sulphasalazine.

Generation and characterization of a novel Cyp2a(4/5)bgs-null mouse model

Knockout mouse models targeting various cytochrome P450 (P450 or CYP) genes are valuable for determining P450's biologic functions, including roles in drug metabolism and chemical toxicity. In this study, a novel Cyp2a(4/5)bgs-null mouse model was generated, in which a 1.2-megabase pair genomic fragment containing nine Cyp genes in mouse chromosome 7 (including, sequentially, Cyp2a5, 2g1, 2b19, 2b23, 2a4, 2b9, 2b13, 2b10, and 2s1) are deleted, through Cre-mediated recombination in vivo. The resultant mouse strain was viable and fertile, without any developmental deficits or morphologic abnormalities. Deletion of the constitutive genes in the cluster was confirmed by polymerase chain reaction analysis of the genes and the mRNAs in tissues known to express each gene. The loss of this gene cluster led to significant decreases in microsomal activities toward testosterone hydroxylation in various tissues examined, including olfactory mucosa (OM), lung, liver, and brain. In addition, systemic clearance of pentobarbital was decreased in Cyp2a(4/5)bgs-null mice, as indicated by >60% increases in pentobarbital-induced sleeping time, compared with wild-type (WT) mice. This novel Cyp2a(4/5)bgs-null mouse model will be valuable for in vivo studies of drug metabolism and chemical toxicities in various tissues, including the liver, lung, brain, intestine, kidney, skin, and OM, where one or more of the targeted Cyp genes are known to be expressed in WT mice. The model will also be valuable for preparation of humanized mice that express human CYP2A6, CYP2A13, CYP2B6, or CYP2S1, and as a knockout mouse model for five non-P450 genes (Vmn1r184, Nalp9c, Nalp4a, Nalp9a, and Vmn1r185) that were also deleted.

The genes of all seven CYP3A isoenzymes identified in the equine genome are expressed in the airways of horses

In the present study, we examined the gene expression of cytochrome P450 3A (CYP3A) isoenzymes in the tracheal and bronchial mucosa and in the lung of equines using TaqMan probes. The results show that all seven CYP3A isoforms identified in the equine genome, that is, CYP3A89, CYP3A93, CYP3A94, CYP3A95, CYP3A96, CYP3A97 and CYP3A129, are expressed in the airways of the investigated horses. Though in previous studies, CYP3A129 was found to be absent in equine intestinal mucosa and liver, this CYP3A isoform is expressed in the airways of horses. The gene expression of the CYP3A isoenzymes varied considerably between the individual horses studied. However, in most of the horses CYP3A89, CYP3A93, CYP3A96, CYP3A97 and CYP3A129 were expressed to a high extent, while CYP3A94 and CYP3A95 were expressed to a low extent in the different parts of the airways. The CYP3A isoenzymes present in the airways may play a role in the metabolic degradation of inhaled xenobiotics. In some instances, the metabolism may, however, result in bioactivation of the xenobiotics and subsequent tissue injury.

Metabolic and Pharmacokinetic Differentiation of STX209 and Racemic Baclofen in Humans

STX209 is an exploratory drug comprising the single, active R-enantiomer of baclofen which is in later stage clinical trials for the treatment of fragile x syndrome (FXS) and autism spectrum disorders (ASD). New clinical data in this article on the metabolism and pharmacokinetics of the R- and S-enantiomers of baclofen presents scientific evidence for stereoselective metabolism of only S-baclofen to an abundant oxidative deamination metabolite that is sterically resolved as the S-enantiomeric configuration. This metabolite undergoes some further metabolism by glucuronide conjugation. Consequences of this metabolic difference are a lower C_max and lower early plasma exposure of S-baclofen compared to R-baclofen and marginally lower urinary excretion of S-baclofen after racemic baclofen administration. These differences introduce compound-related exposure variances in humans in which subjects dosed with racemic baclofen are exposed to a prominent metabolite of baclofen whilst subjects dosed with STX209 are not. For potential clinical use, our findings suggest that STX209 has the advantage of being a biologically defined and active enantiomer.

Intestinal cytochromes P450 regulating the intestinal microbiota and its probiotic profile

Cytochromes P450 (CYPs) enzymes metabolize a large variety of xenobiotic substances. In this vein, a plethora of studies were conducted to investigate their role, as cytochromes are located in both liver and intestinal tissues. The P450 profile of the human intestine has not been fully characterized. Human intestine serves primarily as an absorptive organ for nutrients, although it has also the ability to metabolize drugs. CYPs are responsible for the majority of phase I drug metabolism reactions. CYP3A represents the major intestinal CYP (80%) followed by CYP2C9. CYP1A is expressed at high level in the duodenum, together with less abundant levels of CYP2C8-10 and CYP2D6. Cytochromes present a genetic polymorphism intra- or interindividual and intra- or interethnic. Changes in the pharmacokinetic profile of the drug are associated with increased toxicity due to reduced metabolism, altered efficacy of the drug, increased production of toxic metabolites, and adverse drug interaction. The high metabolic capacity of the intestinal flora is due to its enormous pool of enzymes, which catalyzes reactions in phase I and phase II drug metabolism. Compromised intestinal barrier conditions, when rupture of the intestinal integrity occurs, could increase passive paracellular absorption. It is clear that high microbial intestinal charge following intestinal disturbances, ageing, environment, or food-associated ailments leads to the microbial metabolism of a drug before absorption. The effect of certain bacteria having a benefic action on the intestinal ecosystem has been largely discussed during the past few years by many authors. The aim of the probiotic approach is to repair the deficiencies in the gut flora and establish a protective effect. There is a tentative multifactorial association of the CYP (P450) cytochrome role in the different diseases states, environmental toxic effects or chemical exposures and nutritional status.

Differential distribution of CYP2A6 and CYP2A13 in the human respiratory tract

BACKGROUND

Human CYP2A6 and CYP2A13 play important roles in metabolic activation of many pulmonary carcinogens and thus their expression and distribution may determine the pulmonary susceptibility to metabolically activated carcinogens and the following lung cancer development. Because of the 93.5% of amino acid identity between CYP2A6 and CYP2A13, generation of antibodies specific to CYP2A6 or CYP2A13 has limited immunohistochemical (IHC) analysis of CYP2A6 and CYP2A13 levels in the respiratory tract.

OBJECTIVES

This study aimed to determine the differential distribution of CYP2A6 and CYP2A13 in human respiratory tissue with IHC analysis.

METHODS

With computer-aided protein sequence analyses, candidate epitopes of 15 amino acids in the C-terminal domains of CYP2A6 and CYP2A13 were selected for antibody generation. Specificity of these two antibodies was confirmed with immunoblot and immunofluorescence analyses. With these two selective antibodies, the differential distribution of CYP2A6 and CYP2A13 in human respiratory tissues, including tracheae, bronchi, bronchioles and alveoli, was determined.

RESULTS

IHC results showed that both CYP2A6 and CYP2A13 were markedly expressed in epithelial cells of tracheae and bronchi and that only CYP2A6 was detected in bronchiolar epithelial cells of peripheral lungs. A limitation of the present study is the cross-reactivity of our CYP2A6 antibody to the functional inactive CYP2A7.

CONCLUSIONS

The differential distribution patterns of CYP2A6 and CYP2A13 in the respiratory tract are of importance in considering the pulmonary susceptibility to carcinogens and the following lung cancer development.

Selective expression of CYP2A13 in human pancreatic α-islet cells

Exposure to cigarette smoke is an etiological factor of human pancreatic cancer and has been associated with an increased risk of pancreatic diseases, including pancreatitis and diabetes. The toxicants in cigarette smoke can reach pancreatic tissue, and most of the toxicants require cytochrome P450 (P450)-mediated metabolic activation to exert their toxicity. Among all the human P450 enzymes, CYP2A13 is the most efficient enzyme in the metabolic activation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major tobacco-specific toxicant and a suspected human carcinogen. It also metabolically activates 4-aminobiphenyl, another toxicant in cigarette smoke. Immunohistochemical analysis in this study demonstrated that CYP2A13 was selectively expressed in the islets but not in the exocrine portion of adult human pancreas. Further study using dual immunofluorescence labeling technique showed that CYP2A13 protein was mainly expressed in the α-islet but not in β-islet cells. The selective expression of CYP2A13 in human pancreatic α-islet cells suggests that these islet cells could be damaged by the toxicants existing in cigarette smoke through CYP2A13-mediated in situ metabolic activation. Our result provides a mechanistic insight for human pancreatic diseases that have been associated with cigarette smoke exposure.

Identification of significant pathways in gastric cancer based on protein-protein interaction networks and cluster analysis

Gastric cancer is one of the most common and lethal cancers worldwide. However, despite its clinical importance, the regulatory mechanisms involved in the aggressiveness of this cancer are still poorly understood. A better understanding of the biology, genetics and molecular mechanisms of gastric cancer would be useful in developing novel targeted approaches for treating this disease. In this study we used protein-protein interaction networks and cluster analysis to comprehensively investigate the cellular pathways involved in gastric cancer. A primary immunodeficiency pathway, focal adhesion, ECM-receptor interactions and the metabolism of xenobiotics by cytochrome P450 were identified as four important pathways associated with the progression of gastric cancer. The genes in these pathways, e.g., ZAP70, IGLL1, CD79A, COL6A3, COL3A1, COL1A1, CYP2C18 and CYP2C9, may be considered as potential therapeutic targets for gastric cancer.

Stress is a critical player in CYP3A, CYP2C, and CYP2D regulation: role of adrenergic receptor signaling pathways

Stress is a critical player in the regulation of the major cytochrome P-450s (CYPs) that metabolize the majority of the prescribed drugs. Early in life, maternal deprivation (MD) stress and repeated restraint stress (RS) modified CYP expression in a stress-specific manner. In particular, the expression of CYP3A1 and CYP2C11 was increased in the liver of MD rats, whereas RS had no significant effect. In contrast, hepatic CYP2D1/2 activity was increased by RS, whereas MD did not affect it. The primary effectors of the stress system, glucocorticoids and epinephrine, highly induced CYP3A1/2. Epinephrine also induced the expression of CYP2C11 and CYP2D1/2. Further investigation indicated that AR-agonists may modify CYP regulation. In vitro experiments using primary hepatocyte cultures treated with the AR-agonists phenylephrine, dexmedetomidine, and isoprenaline indicated an AR-induced upregulating effect on the above-mentioned CYPs mediated by the cAMP/protein kinase A and c-Jun NH₂-terminal kinase signaling pathways. Interestingly though, in vivo pharmacological manipulations of ARs using the same AR-agonists led to a suppressed hepatic CYP expression profile, indicating that the effect of the complex network of central and peripheral AR-linked pathways overrides that of the hepatic ARs. The AR-mediated alterations in CYP3A1/2, CYP2C11, and CYP2D1/2 expressions are potentially connected with those observed in the activation of signal transducer and activator of transcription 5b. In conclusion, stress and AR-agonists may modify the expression of the major CYP genes involved in the metabolism of drugs used in a wide range of diseases, thus affecting drug efficacy and toxicity.

Knockdown of Cytochrome P450 2E1 Inhibits Oxidative Stress and Apoptosis in the cTnT R141W Dilated Cardiomyopathy Transgenic Mice

Cytochrome P450 2E1 (CYP2E1) is a cytochrome P450 enzyme that catalyzes the metabolism of toxic substrates. CYP2E1 is upregulated in heart disease, including the dilated cardiomyopathy (DCM) mouse model. Here, knockdown of CYP2E1 significantly ameliorated the dilated left ventricle, thin wall, and dysfunctional contraction in the cTnT R141W and adriamycin-induced DCM mouse models. Interstitial fibrosis, poorly organized myofibrils, and swollen mitochondria with loss of cristae were improved in the myocardium of α-myosin heavy chain (MHC)-cTnT R141W ×CYP2E1-silence double-transgenic mice when compared with the cTnT R141W transgenic mice. Oxidative stress, the activation of caspase 3 and caspase 9, the release of cytochrome c , and the apoptosis in the myocardium were significantly decreased in double-transgenic mice compared with the cTnT R141W transgenic mice. In summary, the expression of CYP2E1 is upregulated in heart disease and might be induced by hypoxemia in cardiomyopathy. The overexpression of CYP2E1 can enhance the metabolism of endogenous ketones to meet the energy demand of the heart in certain disease states, but the overexpression of CYP2E1 can also increase oxidative stress and apoptosis in the DCM heart. Knockdown or downregulation of CYP2E1 might be a therapeutic strategy to control the development of DCM after mutations of cTnT R141W or other factors, because DCM is the third most common cause of heart failure and the most frequent cause of heart transplantation.

Toxic hepatitis in occupational exposure to solvents

The liver is the main organ responsible for the metabolism of drugs and toxic chemicals, and so is the primary target organ for many organic solvents. Work activities with hepatotoxins exposures are numerous and, moreover, organic solvents are used in various industrial processes. Organic solvents used in different industrial processes may be associated with hepatotoxicity. Several factors contribute to liver toxicity; among these are: species differences, nutritional condition, genetic factors, interaction with medications in use, alcohol abuse and interaction, and age. This review addresses the mechanisms of hepatotoxicity. The main pathogenic mechanisms responsible for functional and organic damage caused by solvents are: inflammation, dysfunction of cytochrome P450, mitochondrial dysfunction and oxidative stress. The health impact of exposure to solvents in the workplace remains an interesting and worrying question for professional health work.

RS-Predictor models augmented with SMARTCyp reactivities: robust metabolic regioselectivity predictions for nine CYP isozymes

RS-Predictor is a tool for creating pathway-independent, isozyme-specific, site of metabolism (SOM) prediction models using any set of known cytochrome P450 (CYP) substrates and metabolites. Until now, the RS-Predictor method was only trained and validated on CYP 3A4 data, but in the present study, we report on the versatility the RS-Predictor modeling paradigm by creating and testing regioselectivity models for substrates of the nine most important CYP isozymes. Through curation of source literature, we have assembled 680 substrates distributed among CYPs 1A2, 2A6, 2B6, 2C19, 2C8, 2C9, 2D6, 2E1, and 3A4, the largest publicly accessible collection of P450 ligands and metabolites released to date. A comprehensive investigation into the importance of different descriptor classes for identifying the regioselectivity mediated by each isozyme is made through the generation of multiple independent RS-Predictor models for each set of isozyme substrates. Two of these models include a density functional theory (DFT) reactivity descriptor derived from SMARTCyp. Optimal combinations of RS-Predictor and SMARTCyp are shown to have stronger performance than either method alone, while also exceeding the accuracy of the commercial regioselectivity prediction methods distributed by Optibrium and Schrödinger, correctly identifying a large proportion of the metabolites in each substrate set within the top two rank-positions: 1A2 (83.0%), 2A6 (85.7%), 2B6 (82.1%), 2C19 (86.2%), 2C8 (83.8%), 2C9 (84.5%), 2D6 (85.9%), 2E1 (82.8%), 3A4 (82.3%), and merged (86.0%). Comprehensive datamining of each substrate set and careful statistical analyses of the predictions made by the different models revealed new insights into molecular features that control metabolic regioselectivity and enable accurate prospective prediction of likely SOMs.

Intranasal drug delivery: an efficient and non-invasive route for systemic administration: focus on opioids

Intranasal administration is a non-invasive route for drug delivery, which is widely used for the local treatment of rhinitis or nasal polyposis. Since drugs can be absorbed into the systemic circulation through the nasal mucosa, this route may also be used in a range of acute or chronic conditions requiring considerable systemic exposure. Indeed, it offers advantages such as ease of administration, rapid onset of action, and avoidance of first-pass metabolism, which consequently offers for example an interesting alternative to intravenous, subcutaneous, oral transmucosal, oral or rectal administration in the management of pain with opioids. Given these indisputable interests, fentanyl-containing formulations have been recently approved and marketed for the treatment of breakthrough cancer pain. This review will outline the relevant aspects of the therapeutic interest and limits of intranasal delivery of drugs, with a special focus on opioids, together with an in-depth discussion of the physiological characteristics of the nasal cavity as well as physicochemical properties (lipophilicity, molecular weight, ionisation) and pharmaceutical factors (absorption enhancers, devices for application) that should be considered for the development of nasal drugs.

Generation and characterization of a CYP2A13/2B6/2F1-transgenic mouse model

CYP2A13, CYP2B6, and CYP2F1, which are encoded by neighboring cytochrome P450 genes on human chromosome 19, are active in the metabolic activation of many drugs, respiratory toxicants, and chemical carcinogens. To facilitate studies on the regulation and function of these human genes, we have generated a CYP2A13/2B6/2F1-transgenic (TG) mouse model (all *1 alleles). Homozygous transgenic mice are normal with respect to gross morphological features, development, and fertility. The tissue distribution of transgenic mRNA expression agreed well with the known respiratory tract-selective expression of CYP2A13 and CYP2F1 and hepatic expression of CYP2B6 in humans. CYP2A13 protein was detected through immunoblot analyses in the nasal mucosa (NM) (∼100 pmol/mg of microsomal protein; similar to the level of mouse CYP2A5) and the lung (∼0.2 pmol/mg of microsomal protein) but not in the liver of the TG mice. CYP2F1 protein, which could not be separated from mouse CYP2F2 in immunoblot analyses, was readily detected in the NM and lung but not the liver of TG/Cyp2f2-null mice, at levels 10- and 40-fold, respectively, lower than that of mouse CYP2F2 in the TG mice. CYP2B6 protein was detected in the liver (∼0.2 pmol/mg of microsomal protein) but not the NM or lung (with a detection limit of 0.04 pmol/mg of microsomal protein) of the TG mice. At least one transgenic protein (CYP2A13) seems to be active, because the NM of the TG mice had greater in vitro and in vivo activities in bioactivation of a CYP2A13 substrate, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (a lung carcinogen), than did the NM of wild-type mice.

Cytochrome P450-mediated metabolism and DNA binding of 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline and its carcinogenic isomer 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in mice

2-Amino-1,7-dimethylimidazo[4,5-g]quinoxaline (MeIgQx) is a recently discovered heterocyclic aromatic amine (HAA) that is formed during the cooking of meats. MeIgQx is an isomer of 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), a rodent carcinogen and possible human carcinogen that also occurs in cooked meats. MeIgQx is a bacterial mutagen, but knowledge about its metabolism and carcinogenic potential is lacking. Metabolism studies on MeIgQx and MeIQx were conducted with human and mouse liver microsomes, and recombinant human P450s. DNA binding studies were also investigated in mice to ascertain the genotoxic potential of MeIgQx in comparison to MeIQx. Both HAAs underwent comparable rates of N-oxidation to form genotoxic N-hydroxylated metabolites with mouse liver microsomes (0.2-0.3 nmol/min/mg protein). The rate of N-oxidation of MeIQx was 4-fold greater than the rate of N-oxidation of MeIgQx with human liver microsomes (1.7 vs 0.4 nmol/min/mg protein). The rate of N-oxidation, by recombinant human P450 1A2, was comparable for both substrates (6 pmol/min/pmol P450 1A2). MeIgQx also underwent N-oxidation by human P450s 1A1 and 1B1 at appreciable rates, whereas MeIQx was poorly metabolized by these P450s. The potential of MeIgQx and MeIQx to form DNA adducts was assessed in female C57BL/6 mice given [(14)C]-MeIgQx (10 μCi, 9.68 mg/kg body wt) or [(14)C]-MeIQx (10 μCi, 2.13 mg/kg body wt). DNA adduct formation in the liver, pancreas, and colorectum was measured by accelerator mass spectrometry at 4, 24, or 48 h post-treatment. Variable levels of adducts were detected in all organs. The adduct levels were similar for both HAAs, when adjusted for dose, and ranged from 1 to 600 adducts per 10(7) nucleotides per mg/kg dose. Thus, MeIgQx undergoes metabolic activation and binds to DNA at levels that are comparable to MeIQx. Given the high amounts of MeIgQx formed in cooked meats, further investigations are warranted to assess the carcinogenic potential of this HAA.

Exposure to polycyclic aromatic hydrocarbons: bulky DNA adducts and cellular responses

Environmental and dietary carcinogens such as polycyclic aromatic hydrocarbons (PAHs) have been intensively studied for decades. Although the genotoxicity of these compounds is well characterized (i.e., formation of bulky PAH-DNA adducts), molecular details on the DNA damage response triggered by PAHs in cells and tissues remain to be clarified. The conversion of hazardous PAHs into carcinogenic intermediates depends on enzyme-catalyzed biotransformation. Certain cytochrome P450-dependent monooxygenases (CYPs) play a pivotal role in PAH metabolism. In particular, CYP1A1 and 1B1 catalyze oxidation of PAHs toward primary epoxide species that can further be converted into multiple follow-up products, both nonenzymatically and enzymatically. Distinct functions between these major CYP enzymes have only been appreciated since transgenic animal models had been derived. Electrophilic PAH metabolites are capable of forming stable DNA adducts or to promote depurination at damaged nucleotide sites. During the following DNA replication cycle, bulky PAH-DNA adducts may be converted into mutations, thereby affecting hot spot sites in regulatory important genes such as Ras, p53, and others. Depending on the degree of DNA distortion and cell cycle progression, PAH-DNA adducts trigger nucleotide excision repair (NER) and various DNA damage responses that might include TP53-dependent apoptosis in certain cell types. In fact, cellular responses to bulky PAH-DNA damage are complex because distinct signaling branches such as ATM/ATR, NER, TP53, but also MAP kinases, interact and cooperate to determine the overall outcome to cellular injuries initiated by PAH-DNA adducts. Further, PAHs and other xenobiotics can also confer DNA damage via an alternative route of metabolic activation, which leads to the generation of PAH semiquinone radicals and reactive oxygen species (ROS). One-electron oxidations mediated by peroxidases or other enzymes can result in PAH radical cations that mainly form unstable DNA adducts subjected to depurination. In addition, generation of ROS can also trigger multiple cellular signaling pathways not directly related to mutagenic or cytotoxic effects, including those mediated by NFκB, SAPK/JNK, and p38. In recent years, it became clear that PAHs may also be involved in inflammatory diseases, autoimmune disorders, or atherosclerosis. Further research is under way to better characterize the significance of such newly recognized systemic effects of PAHs and to reconsider risk assessment for human health.

Prediction of sites of metabolism in a substrate molecule, instanced by carbamazepine oxidation by CYP3A4

In drug discovery process, improvement of ADME/Tox properties of lead compounds including metabolic stability is critically important. Cytochrome P450 (CYP) is one of the major metabolizing enzymes and the prediction of sites of metabolism (SOM) on the given lead compounds is key information to modify the compounds to be more stable against metabolism. There are two factors essentially important in SOM prediction. First is accessibility of each substrate atom to the oxygenated Fe atom of heme in a CYP protein, and the other is the oxidative reactivity of each substrate atom. To predict accessibility of substrate atoms to the heme iron, conventional protein-rigid docking simulations have been applied. However, the docking simulations without consideration of protein flexibility often lead to incorrect answers in the case of very flexible proteins such as CYP3A4. In this study, we demonstrated an approach utilizing molecular dynamics (MD) simulation for SOM prediction in which multiple MD runs were executed using different initial structures. We applied this strategy to CYP3A4 and carbamazepine (CBZ) complex. Through 10 ns MD simulations started from five different CYP3A4-CBZ complex models, our approach correctly predicted SOM observed in experiments. The experimentally known epoxidized sites of CBZ by CYP3A4 were successfully predicted as the most accessible sites to the heme iron that was judged from a numerical analysis of calculated ΔG(binding) and the frequency of appearance. In contrast, the predictions using protein-rigid docking methods hardly provided the correct SOM due to protein flexibility or inaccuracy of the scoring functions. Our strategy using MD simulation with multiple initial structures will be one of the reliable methods for SOM prediction.

Development of cocaine-induced interstitial lung damage in two CYP2C and VKORC1 variant allele carriers

BACKGROUND

Often, the connection between drug use and the development of related inflammatory damage or idiosyncratic toxicities is hard to recognize and objectify. The presence of cytochrome P450 (CYP) variant genotypes appears to be a substantial susceptibility risk factor in the development of drug-induced pulmonary adverse events. We hypothesized that the presence of variant alleles may be associated with serious complications of illicit drug use.

CASE REPORT

We report the cases of two cocaine users who developed a 'flu-like' syndrome with diffuse interstitial infiltrates after cocaine abuse. Genotyping for CYP (CYP2C9, CYP2C19) and vitamin K epoxide reductase complex 1 (VKORC1) allelic variants (-1639G/A and 1173C/T) was performed in these two patients. Both cases were heterozygous for VKORC1 variant alleles, and both possessed a CYP2C polymorphism (case 1: CYP2C19*1/*2; case 2: CYP2C9*1/*3).

CONCLUSIONS

The described drug abuse cases suggest that an association between the presence of CYP2C and VKORC1 allelic variants and cocaine-induced interstitial lung damage is highly likely. It is assumed that these polymorphisms contribute to intra-individual variability in drug response and toxicity, including cocaine response and toxicity. Moreover, the importance of including pharmacogenomics in the work-up of patients with suspected drug-induced (lung) toxicity, such as alveolar hemorrhage, is highlighted by these cases.

Plasma caffeic acid is associated with statistical clustering of the anticolitic efficacy of caffeic acid in dextran sulfate sodium-treated mice

We hypothesized that interindividual variability in the bioavailability of caffeic acid (CA) would influence its anticolitic efficacy and that mice may be appropriate for modeling human gut microbial metabolism of CA, which is thought to influence CA bioavailability. Anaerobic human fecal and mouse cecal sample mixtures were incubated with CA derivatives from Echinacea purpurea and compound disappearance rates were measured, which were similar in both sample types. CA metabolism, including formation of its main metabolite, m-hydroxyphenylpropionate, in the mouse cecum may usefully model human gut metabolism of this compound. Ten-week-old CD-1/IGS female mice were fed 120 mg CA/kg (n = 36) or control diet for 7 d (n = 12); one-half of each group then drank 1.25% dextran sulfate sodium (DSS) in water for 5 d. DSS-treated mice fed CA showed lessened colitic damage than did mice given DSS alone, with longer colons, greater body weight, and colonic Cyp4b1 expression. Cluster analysis of the cecal histopathological score showed that mice with severe cecal damage (mean cecal score = 8.5; n = 11) also had greater myeloperoxidase (MPO) activity and lower plasma CA compared with mice showing mild cecal damage (mean cecal score = 4.5; n = 4) (P < 0.05). Cecal score was positively correlated with colonic MPO activity (r = 0.72; P < 0.05) and negatively correlated with plasma CA (r = -0.57; P < 0.05). These studies indicated that the anticolitic efficacy of CA was related to variability in CA bioavailability, which may be influenced by gut microbial metabolism of this compound.