Hydroxylated Metabolites Research Articles

CYP2J2 and CYP2C19 Are the Major Enzymes Responsible for Metabolism of Albendazole and Fenbendazole in Human Liver Microsomes and Recombinant P450 Assay Systems

Albendazole and fenbendazole are broad-spectrum anthelmintics that undergo extensive metabolism to form hydroxyl and sulfoxide metabolites. Although CYP3A and flavin-containing monooxygenase have been implicated in sulfoxide metabolite formation, the enzymes responsible for hydroxyl metabolite formation have not been identified. In this study, we used human liver microsomes and recombinant cytochrome P450s (P450s) to characterize the enzymes involved in the formation of hydroxyalbendazole and hydroxyfenbendazole from albendazole and fenbendazole, respectively. Of the 10 recombinant P450s, CYP2J2 and/or CYP2C19 was the predominant enzyme catalyzing the hydroxylation of albendazole and fenbendazole. Albendazole hydroxylation to hydroxyalbendazole is primarily mediated by CYP2J2 (0.34 μl/min/pmol P450, which is a rate 3.9- and 8.1-fold higher than the rates for CYP2C19 and CYP2E1, respectively), whereas CYP2C19 and CYP2J2 contributed to the formation of hydroxyfenbendazole from fenbendazole (2.68 and 1.94 μl/min/pmol P450 for CYP2C19 and CYP2J2, respectively, which are rates 11.7- and 8.4-fold higher than the rate for CYP2D6). Correlation analysis between the known P450 enzyme activities and the rate of hydroxyalbendazole and hydroxyfenbendazole formation in samples from 14 human liver microsomes showed that albendazole hydroxylation correlates with CYP2J2 activity and fenbendazole hydroxylation correlates with CYP2C19 and CYP2J2 activities. These findings were supported by a P450 isoform-selective inhibition study in human liver microsomes. In conclusion, our data for the first time suggest that albendazole hydroxylation is primarily catalyzed by CYP2J2, whereas fenbendazole hydroxylation is preferentially catalyzed by CYP2C19 and CYP2J2. The present data will be useful in understanding the pharmacokinetics and drug interactions of albendazole and fenbendazole in vivo.

Effects of cytochrome P450 inhibitors and inducers on the metabolism and pharmacokinetics of ospemifene

The objectives were to determine the cytochrome P450 (CYP) enzymes involved in the metabolism of ospemifene and its main hydroxylated metabolites and to examine the effects of CYP inhibitors and inducers on ospemifene pharmacokinetics. In vitro metabolism studies were conducted using human liver microsomes; CYP-selective inhibitors and CYP-specific substrates were used to determine the roles of nine CYP isoforms in ospemifene metabolism. Two Phase 1 clinical trials were conducted in healthy postmenopausal women; crossover designs examined the effects of pretreatment with the CYP modulators rifampicin, ketoconazole, fluconazole and omeprazole on ospemifene pharmacokinetics. Although several CYP inhibitors decreased the in vitro formation of ospemifene metabolites, none of them completely blocked metabolism. Roles for CYP3A4, CYP2C9, CYP2C19 and CYP2B6 in the metabolism of ospemifene and its two main metabolites, 4--hydroxyospemifene and 4'-hydroxyospemifene, were confirmed. The in vivo experiments demonstrated that ospemifene serum concentrations were decreased by rifampicin pretreatment, increased by ketoconazole or fluconazole pretreatment, and minimally affected by omeprazole pretreatment. The clinical pharmacokinetic findings and in vitro data suggest that CYP3A4 is important for ospemifene metabolism, but other CYP isoforms and metabolic pathways also contribute. Strong CYP3A or CYP2C9 inducers (e.g. rifampicin) would be expected to decrease the exposure to ospemifene. Ospemifene should be used with caution when coadministered with the modest CYP3A inhibitor ketoconazole and should not be coadministered with the potent CYP3A/CYP2C9/CYP2C19 inhibitor fluconazole. The potent CYP2C19 inhibitor omeprazole is unlikely to cause clinically significant changes in ospemifene pharmacokinetics.

Relationship between Genotypes Sult1a2 and Cyp2d6 and Tamoxifen Metabolism in Breast Cancer Patients

Tamoxifen is a pro-drug widely used in breast cancer patients to prevent tumor recurrence. Prior work has revealed a role of cytochrome and sulfotransferase enzymes in tamoxifen metabolism. In this descriptive study, correlations were examined between concentrations of tamoxifen metabolites and genotypes for CYP2D6, CYP3A4, CYP3A5, SULT1A1, SULT1A2 and SULT1E1 in 135 patients with estrogen receptor-positive breast cancer. Patients were genotyped using the Roche-AmpliChip® CYP450 Test, and Real-Time and conventional PCR-RFLP. Plasma tamoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen, endoxifen and tamoxifen-N-oxide were isolated and quantified using a high-pressure liquid chromatography-tandem mass spectrometry system. Significantly higher endoxifen levels were detected in patients with the wt/wt CYP2D6 compared to the v/v CYP2D6 genotype (p<0.001). No differences were detected in the remaining tamoxifen metabolites among CYP2D6 genotypes. Patients featuring the SULT1A2*2 and SULT1A2*3 alleles showed significantly higher plasma levels of 4-hydroxy-tamoxifen and endoxifen (p = 0.025 and p = 0.006, respectively), as likely substrates of the SULT1A2 enzyme. Our observations indicate that besides the CYP2D6 genotype leading to tamoxifen conversion to potent hydroxylated metabolites in a manner consistent with a gene-dose effect, SULT1A2 also seems to play a role in maintaining optimal levels of both 4-hydroxy-tamoxifen and endoxifen.

Metabolic Activation of Nonpolar Sediment Extracts Results in Enhanced Thyroid Hormone Disrupting Potency

Traditional sediment risk assessment predominantly considers the hazard derived from legacy contaminants that are present in nonpolar sediment extracts, such as polychlorinated biphenyls (PCBs), dioxins, furans (PCDD/Fs), and polyaromatic hydrocarbons (PAHs). Although in vivo experiments with these compounds have shown to be thyroid hormone disrupting (THD), in vitro their THD potency is not observed in nonpolar sediment extracts. This is hypothesized to be due to the absence of in vitro biotransformation which will result in bioactivation of the lipophilic compounds into THD hydroxyl metabolites. This study reveals that indeed metabolically activated nonpolar contaminants in sediments can competitively bind to thyroid hormone transport proteins. Sediment fractions were incubated with S9 rat microsomes, and the metabolites were extracted with a newly developed method that excludes most of the lipids to avoid interference in the applied nonradioactive 96-well plate TTR competitive binding assay. Metabolic activation increased the TTR binding potency of nonpolar fractions of POP-polluted sediments up to 100 times, resulting in potencies up to 240 nmol T4 equivalents/g sediment equivalent (nmol T4-Eq/g SEQ). This demonstrates that a more realistic in vitro sediment THD risk characterization should also include testing of both polar and medium polar sediment extracts for THD, as well as bioactivated nonpolar sediment fractions to prevent underestimation of its toxic potency.

Pharmacokinetics in Sprague-Dawley rats and Beagle dogs and in vitro metabolism of ZJM-289, a novel nitric dioxide donor

1. The aim was to evaluate the prodrug hypothesis by investigating the pharmacokinetics of ZJM-289 and its pharmacological metabolite 3-n-butylphthalide (NBP) in Sprague-Dawley rats and Beagle dogs following intravenous and intragastric administration of ZJM-289. The in vitro metabolic patterns in plasma and microsomal system were assessed to elucidate PK properties.2. In rats, ZJM-289 was eliminated rapidly (t1/2 = 19.2 ± 3.85 min), along with the fast formation of NBP (formation rate constant ka = 0.29 ± 0.092 min–1 for intravenous group, and ka = 0.16 ± 0.064 min−1 for intragastric group), accounting for about 47.4 ± 4.0% of ZJM-289. Both ZJM-289 (t1/2 = 239 ± 70.4 min) and NBP (t1/2 = 249 ± 39.0 min) were depleted slowly in Beagle dogs, with NBP formation rate constant at 0.12 ± 0.052 min−1 (ka = 0.15 ± 0.040 min−1 for intragastric group).3. In rat plasma, ZJM-289 was degraded rapidly (t1/2 = 24.3 ± 0.93 min) at 37 °C, but remained stable with almost no cleavage in dog and human plasma. In hepatic microsomes from rat, dog and human, the hydrolysis metabolites including the active metabolite NBP (M5), and their subsequent hydroxylation and conjugate metabolite, were all detected but varied greatly in the quantities.4. The findings testified the prodrug design hypothesis that ZJM-289 could be hydrolyzed to NBP. The pharmacokinetic profiles in both rats and dogs brought useful information in the pharmacokinetics prediction in human.

Alkyl protocatechuates as novel urinary biomarkers of exposure to p-hydroxybenzoic acid esters (parabens)

Human exposure to p-hydroxybenzoic acid esters (parabens) is a concern, owing to adverse health effects of these compounds. Parabens are metabolized and eliminated from the human bodies within a few hours of exposure. In this study, for the first time, methyl- and ethyl-protocatechuates (OH-MeP and OH-EtP) and their parent compounds, methyl- (MeP) and ethyl-parabens (EtP), were determined in urine samples collected from U.S. children and adults. Alkyl protocatechuates were found in almost all urine samples, with median concentrations of 11.8 (OH-MeP) and 2.90ng/mL (OH-EtP) in adults, and 5.43 (OH-MeP) and 0.85ng/mL (OH-EtP) in children. In adults, the concentrations of urinary OH-MeP and OH-EtP were higher than the corresponding concentrations of MeP and EtP. Significant correlation between OH-MeP/OH-EtP and MeP/EtP was observed. This is the first report to document hydroxylation of parabens in humans, and to propose hydroxylated metabolites (i.e., alkyl protocatechuates) as alternative biomarkers of exposure to parabens in human biomonitoring studies. The rates of transformation of parabens between children and adults appeared to be different, as evidenced from the slopes of regression between alkyl protocatechuates and parabens. In addition to alkyl protocatechuates, hydroxybenzoic acid (4-HB) and 3,4-dihydroxybenzoic acid (3,4-DHB) were found at considerable levels in the urine samples. The occurrence of a significant proportion of alkyl protocatechuates and 3,4-DHB suggests the need for inclusion of these derivatives in accurate estimation of human exposure to parabens and in epidemiological studies that associate paraben exposure to health outcomes in populations.

High-Performance Liquid Chromatography–Electrospray Ionization Tandem Mass Spectrometry for Metabolism Study of Timosaponin AIII

A sensitive method based on high-performance liquid chromatography-electrospray ionization tandem mass spectrometry was developed for the determination of timosaponin AIII (TA3) and its in vivo and in vitro metabolites. The rat plasma, urine, feces and tissue samples were collected after oral administration of TA3 at a single dose of 300 mg/kg. TA3 was incubated into artificial gastric juice and artificial intestinal juice. The in vivo and in vitro samples were purified by using liquid-liquid extraction. The structures of metabolites were elucidated by comparing their molecular weights, retention times and tandem mass spectrometric spectra with those of the parent drug. As a result, four metabolites (deglycosylated TA3, two hydroxylated TA3 and timosaponin BII) and the parent drug were found in in vivo and in vitro samples. In addition to the parent drug, one, one and two metabolites were identified in heart, urine and feces, respectively. Only the parent drug was detected in plasma, liver and kidney. One hydroxylation metabolite and TA3 were identified from incubation samples with AGJ, whereas two hydroxylation metabolites and TA3 were detected from the incubation with AIJ. This is the first systematic metabolism study of TA3. The biotransformation pathways of TA3 primarily included deglycosylation, hydroxylation and glycosylation.

Stereoselective excretion and first-pass metabolism of clausenamide enantiomers

Stereoselective differences in pharmacokinetics between clausenamide (CLA) enantiomers have been found after intravenous and oral administration of each enantiomer to rats. The differences could be associated with excretion and first-pass metabolism of two enantiomers. The data from this study demonstrated that (−)CLA was mainly excreted in feces with 13.9% of dose, whereas (+)CLA in bile with 17.2%. A large portion of CLA enantiomers could be transformed into hydroxyl metabolites. In the in vitro metabolic system using rat liver microsomes, it was found that (−)CLA was cleared more than its antipode with peak height ratios [(+)/(−)] from 1.0 to 1.8 at the corresponding substrate concentrations from 0.25 to 2mM. Further study in rabbits showed that two enantiomers underwent an intermediate degree of first-pass metabolism. (−)CLA had lower concentrations and AUC0–8h in the portal vein and heart than those of (+)CLA with rates of hepatic extraction 64.7% for (−)-isomer and 50.8% for (+)-isomer, and intrinsic metabolic clearances of (−) and (+)CLA being 186.3 and 107.2 (l/h), respectively. The first-pass metabolism was involved in CYP3A enzymes in the gut and liver, and different levels of CYP3A1 expression induced by (−)CLA or (+)CLA. Immunohistochemical analyses revealed that (−)-isomer significantly increased the expression of CYP3A1, while (+)-isomer had no obvious effects on it. Taken together, the results provided new evidence that stereoselective pharmacokinetics of CLA enantiomers could be resulted from their stereoselective excretion, first-pass metabolism and induction to metabolizing enzymes, which might be important in understanding the clinic pharmacology of active eutomer, (−)CLA, for treatment of Alzheimer’s disease.

Ospemifene metabolism in humans in vitro and in vivo: metabolite identification, quantitation, and CYP assignment of major hydroxylations

The metabolism of ospemifene, a novel nonsteroidal selective estrogen receptor modulator, was investigated as part of its development. Metabolite identification, tentative quantitation, and CYP assignment of ospemifene were performed in human liver microsomes or homogenate incubations and in plasma samples from volunteer humans. The potential contributions of CYP enzymes were determined by recombinant human CYPs. Metabolite identification and tentative quantification were performed by liquid chromatography-mass spectrometry. The relative abundances of metabolites produced were dependent on ospemifene concentration and liver preparation, but the largest quantities of 4- and 4'-hydroxy-ospemifene (and their glucuronides in smaller quantities) were produced in human liver microsomes at low ospemifene concentrations. Other metabolites were detected in in vitro incubation with human liver including a direct glucuronide of ospemifene and some metabolites with only minor abundance. In human plasma samples, 4-hydroxy-ospemifene was the most abundant metabolite, representing about 25% of the abundance of the parent compound. All the other metabolites detected in plasma, including 4'-hydroxy-ospemifene, represented <7% of the abundance of ospemifene. Several CYP enzymes participated in 4-hydroxylation, including CYP2C9, CYP2C19, CYP2B6, and CYP3A4, whereas CYP3A enzymes were the only ones to catalyze 4'-hydroxylation. In vitro incubations with liver preparations provided a rather reliable starting point in the search for potential metabolites in clinical settings. The in vitro metabolite profile is informative for the in vivo metabolite profile, especially regarding the major hydroxylated metabolites. However, it is anticipated that extended in vivo exposures may result in an increased production of more distal metabolites from major metabolites.

Abstract 4409: The characterization of isomerically stable fixed ring derivatives of tamoxifen metabolites 4-hydroxytamoxifen and 4-hydroxy-N-desmethyltamoxifen (endoxifen) in vitro.

Abstract Tamoxifen is the most widely used agent in the world for antihormonal therapy of Estrogen Receptor (ER)-positive breast cancer for both pre- and postmenopausal patients. Tamoxifen is a pro-drug and needs to be metabolically activated to a more potent antiestrogen with a higher affinity for the ER. Initially 4-hydroxytamoxifen (4OHT) was the active metabolite of interest, but more recently 4-hydroxy-N-desmethyltamoxifen (endoxifen) is also of significant interest. The role of endoxifen in therapy remains controversial, however both 4OHT and endoxifen exist in two isomeric forms- cis and trans. Previously, it was shown that cis-isomers of tamoxifen metabolites have weak anti-estrogenic properties using in vitro models available (Jordan VC et al, Endocrinology, 1987, 122(4); 1449-54). However, studies show that an increase of cis-isomers of 4OHT in animals and patients may contribute to tamoxifen resistance (Osborne CK et al, JNCI, 1991, 83; 1477-82; Osborne CK et al, J Clin Oncol, 1992, 10; 304-10). Thus, it is important to know the estrogenic properties of clinically relevant tamoxifen metabolites. To document the anti-estrogenic profiles of both geometric isomers of two major hydroxylated metabolites of tamoxifen, isomerically stable fixed-ring derivatives of 4OHT and endoxifen were synthesized. We have assessed the anti-estrogenic properties of these compounds using cell proliferation assays in selectively cloned hypersensitive ER-positive human breast cancer cell lines MCF-7:WS8 and T47D:A18. Also to assess to estrogenic/anti-estrogenic properties of synthesized compounds on transcriptional level, we have used real-time PCR of rat Prolactin (Prl) mRNA isolated from GH3 rat pituitary cell line. Our results indicate that the fixed-ring trans-4OHT and trans-Endoxifen are potent antiestrogens and equivalent to each other, and to their non-fixed-ring counterparts in both cell proliferation assays and Prl gene activity, as they do not possess any agonistic activities by themselves and are able to inhibit the estrogenic actions of 0,1nM 17β-estradiol (E2) completely (IC50 1nM). However, cis-isomers of the fixed-ring compounds are very weakly estrogenic by themselves but are very weak anti-estrogens in combination with 0,1nM E2 in all assays. Conclusions: the weak estrogen-like activity and low potency of the cis-isomers is unlikely to influence the growth of breast cancer during long-term therapy. The high potency of trans-endoxifen and 4OHT will dominate the control of the tumor growth. Support: This study (PYM) was supported by Susan G. Komen for the Cure International Postdoctoral Fellowship under award number SAC100009 (VCJ). Citation Format: Philipp Y. Maximov, Cynthia Myers, Daphne J. Fernandes, V. Craig Jordan. The characterization of isomerically stable fixed ring derivatives of tamoxifen metabolites 4-hydroxytamoxifen and 4-hydroxy-N-desmethyltamoxifen (endoxifen) in vitro. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4409. doi:10.1158/1538-7445.AM2013-4409

Ion Mobility Spectrometry–Mass Spectrometry Analysis for the Site of Aromatic Hydroxylation

Hydroxylated metabolites often retain the pharmacological activity of parent compound, and the position of hydroxylation determines the formation of chemically reactive intermediates, such as quinones and analogs, from para- and/or ortho-hydroxylation of phenols or arylamines. Therefore, the identification of exact position of hydroxylation is often required at the early development stage of new drug candidates. In many cases, liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides identical MS/MS spectra among isomeric hydroxylated metabolites, and therefore, it alone cannot unequivocally identify the exact position(s) of hydroxylation. Ion mobility spectrometry (IMS), integrated with LC-MS/MS, recently showed the capability of separating isomeric species based on differences in their drift times from IMS, which are linearly proportional to the collision cross-section (CCS) reflecting physical size and shape. In the present study, a chemical derivatization of isomeric hydroxylated metabolites with 2-fluoro-N-methyl pyridinium p-toluenesulfonate was found to confer distinct theoretical CCS value on each isomer by forming corresponding N-methyl pyridine (NMP) derivative. The regression lines established by the comparison between theoretical CCS values and observed drift times from IMS for each set of parent compound (labetalol, ezetimibe, atorvastatin, and warfarin) and its MS/MS product ions accurately and selectively projected the actual drift times of NMP derivatives of corresponding aromatic or isomeric hydroxylated metabolites. The established method was used for the accurate assignment of predominant formation of 2-hydroxylated metabolite from imipramine in NADPH- fortified human liver microsomes. The present application expands the versatility of LC-IMS-MS technique to the structure identification of isomeric hydroxylated metabolites at the early stage for drug development.

Human metabolites of synthetic cannabinoids JWH-018 and JWH-073 bind with high affinity and act as potent agonists at cannabinoid type-2 receptors

K2 or Spice is an emerging drug of abuse that contains synthetic cannabinoids, including JWH-018 and JWH-073. Recent reports indicate that monohydroxylated metabolites of JWH-018 and JWH-073 retain high affinity and activity at cannabinoid type-1 receptors (CB1Rs), potentially contributing to the enhanced toxicity of K2 compared to marijuana. Since the parent compounds also bind to cannabinoid type-2 receptors (CB2Rs), this study investigated the affinity and intrinsic activity of JWH-018, JWH-073 and several monohydroxylated metabolites at human CB2Rs (hCB2Rs). The affinity of cannabinoids for hCB2Rs was determined by competition binding studies employing CHO-hCB2 membranes. Intrinsic activity of compounds was assessed by G-protein activation and adenylyl cyclase (AC)-inhibition in CHO-hCB2 cells. JWH-073, JWH-018 and several of their human metabolites exhibit nanomolar affinity and act as potent agonists at hCB2Rs. Furthermore, a major omega hydroxyl metabolite of JWH-073 (JWH-073-M5) binds to CB2Rs with 10-fold less affinity than the parent molecule, but unexpectedly, is equipotent in regulating AC-activity when compared to the parent molecule. Finally, when compared to CP-55,940 and Δ9-tetrahydrocannabinol (Δ9-THC), JWH-018, JWH-018-M5 and JWH-073-M5 require significantly less CB2R occupancy to produce similar levels of AC-inhibition, indicating that these compounds may more efficiently couple CB2Rs to AC than the well characterized cannabinoid agonists examined. These results indicate that JWH-018, JWH-073 and several major human metabolites of these compounds exhibit high affinity and demonstrate distinctive signaling properties at CB2Rs. Therefore, future studies examining pharmacological and toxicological properties of synthetic cannabinoids present in K2 products should consider potential actions of these drugs at both CB1 and CB2Rs.

Use of Polyetheretherketone as a Material for Solid Phase Extraction of Hydroxylated Metabolites of Polycyclic Aromatic Hydrocarbons in Human Urine

In this study, a novel application of polyetheretherketone (PEEK) tubing for solid phase extraction (SPE) of urinary hydroxylated metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) is presented. The use of PEEK tubing for extracting nine OH-PAHs (2-5 rings) from different matrixes (e.g., urine, acid/enzymatic hydrolysis solution) was demonstrated; a facile method for fast (<2 min) quantification of urinary 1-hydroxypyrene (1-OHPyr) was also developed by the use of PEEK tubing extraction coupled to electrospray ionization tandem mass spectrometry (ESI-MS/MS). Although no optimization was performed for the extraction process, a limit of detection (LOD) as low as 0.01 μg L(-1) was obtained, and the ratio of signal intensity of 1-OHPyr to that of 1-OHPyr-d9 (internal standard) was linearly related with the 1-OHPyr concentration over the range of 0.05-5.00 μg L(-1) (R(2) = 0.9995). Satisfactory recoveries (87-91%) were achieved, and less than 2 min was required to carry out the whole analytical procedure including sample pretreatment and mass spectrometric detection. In a biomonitoring study, the PEEK tubing extraction based method was successfully applied to the quantification of 1-OHPyr in eight human urine samples, further confirming the potential of PEEK tubing for SPE of organic compounds.

Microbial transformation of cycloastragenol

The microbial transformation of cycloastragenol by the fungi Cunninghamella blakesleeana NRRL 1369 and Glomerella fusarioides ATCC 9552, and the bacterium Mycobacterium sp. NRRL 3805 were investigated. Both fungi mainly provided hydroxylated metabolites together with products formed by cyclization, dehydrogenation and Baeyer-Villiger oxidation resulting in a ring cleavage. The bacteria yielded only a single oxidation product, namely, 3-oxo-cycloastragenol. Structures of the metabolites were elucidated by 1-D ((1)H,(13)C), 2-D NMR (COSY, HMBC, HMQC) and HRMS analyses.

Is meconium useful to predict fetal exposure to organochlorines and hydroxylated PCBs?

The objective of this study is to compare meconium and maternal serum as biomarkers of fetal exposure to organochlorines (OCs). A subset of 40 meconium samples and complementary maternal sera from the Northern Norway Mother-and-Child Contaminant Cohort Study (MISA) were selected. Meconium samples were collected at the earliest opportunity (median 9.0 hours postpartum, range 0-61) and maternal serum in the 2nd trimester (median 19.0 gestational weeks, range 13-34) and analysed for OC contaminants selected from the Arctic Monitoring and Assessment Programme's (AMAP) suite of OCs and selected hydroxylated metabolites. Eight compounds with detection frequencies ≥70% in both media (criterion for inclusion) were included in the statistical analyses. Median concentration ratios for p,p'-DDE, HCB, trans-nonachlor and cis-nonachlor favoured meconium, and PCB 138 and 153 and OH-PCB 146 and 172 were higher in maternal serum. All inter-media correlations were significant (Spearman's rho) for wet-weight concentrations and improved when concentrations in a small subset of 15 meconium and serum samples were both lipid-adjusted; only OH-PCB 146 slightly favoured maternal serum. Multivariable linear regression modelling confirmed that maternal serum was the most consistent predictor of meconium concentrations, with gestational age and time of meconium sampling improving the models. Although more challenging to analyse, the lipid-adjusted OC concentration in meconium is viewed as a sensitive and informative fetal exposure index when taking into account the gestational age and its postpartum sampling time.

In Vitro Biotransformation Studies of 2-Oxo-clopidogrel: Multiple Thiolactone Ring-Opening Pathways Further Attenuate Prodrug Activation

The biotransformation of clopidogrel has been under extensive investigation to address the observed high clinical variability and resistance of its antithrombotic prodrug therapy. Clopidogrel (M0) is first activated to its thiolactone intermediate, 2-oxo-clopidogrel (M2), by hepatic cytochrome P450 (P450) enzymes. Subsequent P450-catalyzed S-oxidation is followed by thioester hydrolysis, which cleaves the thiolactone ring and yields a sulfenic acid intermediate (M12); this intermediate is reduced to the final active metabolite (M13). The aim of the present study is to characterize the metabolic fates of M2 more comprehensively with focus on the thiolactone ring-opening pathways. It was found that the bioactivating S-oxidation confers on the thiolactone moiety not only one electrophilic site at the carbonyl C-atom (Site A), but also a second one at the allylic bridge C-atom (Site B). Both sites can react with H2O or other nucleophiles, like glutathione (GSH), leading to different thiolactone ring-opening pathways. In addition to the pharmacologically desired A-H2O pathway leading to M13 formation, the A-GSH pathway leads to the formation of a glutathione conjugate (GS-3), the B-H2O pathway leads to the formation of a desulfurized hydroxyl metabolite (M17), and the B-GSH pathway leads to the formation of a desulfurized glutathione conjugate (GS-2). These results demonstrate the reactive nature of the electrophilic thiolactone S-oxide intermediate (M11) and suggest that M13 formation from M2 might be accompanied by more attenuating pathways than previously reported. The research presented here may facilitate future studies exploring the clinical antithrombotic response to clopidogrel as well as the susceptibility to the adverse effect of clopidogrel and its close prodrug analogues.

Effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites: exploration of a novel CYP2B6 phenotyping index

To evaluate the effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites in relation to the CYP2B6*6 genotype and explore potential phenotyping indices for CYP2B6 activity in vivo using a low dose of oral efavirenz. We conducted a randomized three phase crossover study in 17 healthy Korean subjects pre-genotyped for the CYP2B6*6 allele (CYP2B6*1/*1, n = 6; *1/*6, n = 6; *6/*6, n = 5). Subjects were pretreated with clopidogrel (75 mg day(-1) for 4 days), itraconazole (200 mg day(-1) for 6 days), or placebo and then given a single dose of efavirenz (200 mg). The plasma (0-120 h) and urine (0-24 h) concentrations of efavirenz and its metabolites (7- and 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz) were determined by LC/MS/MS. This study is the first to delineate quantitatively the full (phase I and II) metabolic profile of efavirenz and its three hydroxyl metabolites in humans. Clopidogrel pretreatment markedly decreased AUC(0,48 h), C(max) and Ae(0,24 h) for 8,14-dihydroxyefavirenz, compared with placebo; 95% CI of the ratios were 0.55, 0.73, 0.30, 0.45 and 0.25, 0.47, respectively. The 8,14-dihydroxyefavirenz : efavirenz AUC(0,120 h) ratio was significantly correlated with the weight-adjusted CL/F of efavirenz (r(2) ≈ 0.4, P < 0.05), differed with CYP2B6*6 genotype and was affected by clopidogrel pretreatment (P < 0.05) but not by itraconazole pretreatment. The disposition of 8,14-dihydroxy-EFV appears to be sensitive to CYP2B6 activity alterations in human subjects. The 8,14-dihydroxyefaviremz : efavirenz AUC(0,120 h) ratio is attractive as a candidate phenotyping index for CYP2B6 activity in vivo.

Novel and Distinct Metabolites Identified Following a Single Oral Dose of α- or γ-Hexabromocyclododecane in Mice

The metabolism of α- and γ-hexabromocyclododecane (HBCD) was investigated in adult C57BL/6 female mice. α- or γ-[(14)C]HBCD (3 mg/kg bw) was orally administered with subsequent urine and feces collection for 4 consecutive days; a separate group of mice was dosed and sacrificed 3 h postexposure to investigate tissue metabolite levels. Extractable and nonextractable HBCD metabolites were quantitated in liver, blood, fat, brain, bile, urine, and feces and characterized by LC/MS (ESI-). Metabolites identified were distinct between the two stereoisomers. In mice exposed to α-HBCD, four hydroxylated metabolites were detected in fecal extracts, and one of these metabolite isomers was consistently characterized in liver, brain, and adipose tissue extracts. In contrast, fecal extracts from mice exposed to γ-HBCD contained multiple isomers of monohydroxy-pentabromocyclododecene, dihydroxy-pentabromocyclododecene, and dihydroxy-pentabromocyclododecadiene, while in liver and adipose tissues extracts only a single monohydroxy-pentabromocyclododecane metabolite was observed. Both stereoisomers were transformed to metabolites which formed covalent bonds to proteins and/or lipids in the gut as suggested by high fecal nonextractables. The presence of tissue- and excreta-specific metabolic products after in vivo exposure to the two main HBCD stereoisomers supports previous toxicokinetic studies indicating that these two stereoisomers are biologically distinct. The distinct metabolic products identified in this study have the potential to aid in the identification of stereoisomer-specific HBCD exposures in future biomonitoring studies.

Correlation between atmospheric polycyclic aromatic hydrocarbons exposure and urinary hydroxyl metabolites of polycyclic aromatic hydrocarbons in elderly population in Tianjin, China

To identify suitable hydroxyl polycyclic aromatic hydrocarbons (OH-PAHs) for co-evaluation of internal exposure level of PAHs by simultaneous determination of a variety of OH-PAHs in urine. The 24-h individual particulate matter and morning urine samples of 112 subjects were collected during June 2011. PAHs carried by individual particulate matter samples and OH-PAHs in urine samples were detected by gas chromatography-mass spectrometry. Seven OH-PAHs were detected in urine samples, among which 1-hydroxy-naphthalene (1-OHNap) concentration was the highest [(20.54 ± 28.94) µmol/mol Cr], while 1-hydroxy-pyrene (1-OHP) concentration was the lowest [(0.73 ± 0.63) µmol/mol Cr]. The concentrations of these seven OH-PAHs decreased in the following order: 1-hydroxy-naphthalene (1-OHNap) > 9-hydroxy-fluorene (9-OHFlu) > 2-hydroxy-naphthalene (2-OHNap) > 3-hydroxy-fluorene (3-OHFlu) > 2-hydroxy-fluorene (2-OHFlu) > 6-hydroxy-chrysene (6-OHChr) > 1-hydroxy-pyrene (1-OHP). The effects of gender and smoking upon the contents of OH-PAHs in urine samples were not significant. There was a good correlation between total hydroxy-naphthalene (ΣOHNap) and 1-OHNap (r = 0.948), and a good correlation was also showed between total hydroxy-fluorene (ΣOHFlu) and 9-OHFlu (r = 0.975). Naphthalene carried by atmospheric particulate matters demonstrated better correlation with 1-OHNap than 2-OHNap, while fluorene carried by atmospheric particulate matters showed better correlation with 9-OHFlu than 3-OHFlu and 2-OHFlu. The correlation coefficients of ΣOHNap, ΣOHFlu and 6-OHChr with 1-OHP were 0.427, 0.543 and 0.655, respectively, and the correlations were not strong. It cannot reflect internal exposure level of PAHs to use 1-OHP as the only biomarker, while 1-OHNap and 9-OHFlu can be well predictive of the exposure levels of corresponding total OH-PAHs, suggesting that simultaneous determination of 1-OHNap, 9-OHFlu and 1-OHP can be more accurate and comprehensive in evaluating the internal exposure level of PAHs.

Cytochrome P450-mediated oxidative metabolism of abused synthetic cannabinoids found in K2/Spice: identification of novel cannabinoid receptor ligands.

Abuse of synthetic cannabinoids (SCs), such as [1-naphthalenyl-(1-pentyl-1H-indol-3-yl]-methanone (JWH-018) and [1-(5-fluoropentyl)-1H-indol-3-yl]-1-naphthalenyl-methanone (AM2201), is increasing at an alarming rate. Although very little is known about the metabolism and toxicology of these popular designer drugs, mass spectrometric analysis of human urine specimens after JWH-018 and AM2201 exposure identified monohydroxylated and carboxylated derivatives as major metabolites. The present study extends these initial findings by testing the hypothesis that JWH-018 and its fluorinated counterpart AM2201 are subject to cytochrome P450 (P450)-mediated oxidation, forming potent hydroxylated metabolites that retain significant affinity and activity at the cannabinoid 1 (CB(1)) receptor. Kinetic analysis using human liver microsomes and recombinant human protein identified CYP2C9 and CYP1A2 as major P450s involved in the oxidation of the JWH-018 and AM2201. In vitro metabolite formation mirrored human urinary metabolic profiles, and each of the primary enzymes exhibited high affinity (K(m) = 0.81-7.3 μM) and low to high reaction velocities (V(max) = 0.0053-2.7 nmol of product · min(-1) · nmol protein(-1)). The contribution of CYP2C19, 2D6, 2E1, and 3A4 in the hepatic metabolic clearance of these synthetic cannabinoids was minimal (f(m) = <0.2). In vitro studies demonstrated that the primary metabolites produced in humans display high affinity and intrinsic activity at the CB(1) receptor, which was attenuated by the CB(1) receptor antagonist (6aR,10aR)-3-(1-methanesulfonylamino-4-hexyn-6-yl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran (O-2050). Results from the present study provide critical, missing data related to potential toxicological properties of "K2" parent compounds and their human metabolites, including mechanism(s) of action at cannabinoid receptors.