Recombinant Human Cytochrome P450 Enzymes Research Articles

Improved preclinical drug metabolism and pharmacokinetics of pibothiadine (HEC121210), a novel hepatitis B virus capsid assembly modulator

Pibothiadine (PBD; HEC121120) is a novel hepatitis B virus capsid assembly modulator based on GLS4 (morphothiadine) and has inhibitory activities against resistant strains. To assess the overall preclinical drug metabolism and pharmacokinetics (DMPK) properties of PBD, in vivo pharmacokinetics studies in rats and dogs have been performed along with a series of in vitro metabolism assays. The oral bioavailability of PBD in rats and dogs might be related to its medium permeability in Caco-2 cells and largely be impacted by the pH-dependent solubility. PBD was highly distributed to the liver where the local exposure was 16.4 fold of the system exposure. PBD showed relatively low metabolic rate in recombinant human cytochrome P450 enzymes, whereas low to moderate in vitro clearance in liver microsomes and low (dog) to moderate (rat) in vivo clearance. Furthermore, β-oxidation and dehydrogenation were proposed as the primary metabolic pathways of PBD in rats. Compared to GLS4, the higher systemic exposure of PBD might be attributed to its improved oral absorption and metabolic stability. In addition, the enhanced liver/plasma exposure ratio could further increase the local exposure around the target. These improved DMPK properties might indicate better development of PBD in the clinical phase.

Anthraquinone biocolourant dermocybin is metabolized whereas dermorubin is not in in vitro liver fractions and recombinant metabolic enzymes.

Fungal anthraquinones dermocybin and dermorubin are attractive alternatives for synthetic dyes but their metabolism is largely unknown. We conducted a qualitative in vitro study to identify their metabolism using human liver microsomes and cytosol, as well as recombinant human cytochrome P450 (CYP), UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) enzymes. Additionally, liver microsomal and cytosolic fractions from rat, mouse and pig were used. Following incubations of the biocolourants with the enzymes in the presence of nicotinamide adenine dinucleotide phosphate, UDP-glucuronic acid, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) or S-adenosyl methionine (SAM) to enable CYP oxidation, glucuronidation, sulfonation or methylation, we observed several oxidation and conjugation metabolites for dermocybin but none for dermorubin. Human CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4 and 3A7 catalysed dermocybin oxidation. The formation of dermocybin glucuronides was catalysed by human UGT1A1, 1A3, 1A7, 1A8, 1A9, 1A10 and 2B15. Human SULT1B1, 1C2 and 2A1 sulfonated dermocybin. Dermocybin oxidation was faster than conjugation in human liver microsomes. Species differences were seen in dermocybin glucuronidation between human, rat, mouse and pig. In conclusion, many CYP and conjugation enzymes metabolized dermocybin, whereas dermorubin was not metabolized in human liver fractions in vitro. The results indicate that dermocybin would be metabolized in humans in vivo.

Evaluation of Lippia scaberrima Sond. and Aspalathus linearis (Burm.f.) R. Dahlgren extracts on human CYP enzymes and gold nanoparticle synthesis: implications for drug metabolism and cytotoxicity

BackgroundMetabolism is an important component of the kinetic characteristics of herbal constituents, and it often determines the internal dose and concentration of these effective constituents at the target site. The metabolic profile of plant extracts and pure compounds need to be determined for any possible herb-drug metabolic interactions that might occur.MethodsVarious concentrations of the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with fermented and unfermented Aspalathus linearis extract were used to determine the inhibitory potential on placental, microsomal and recombinant human hepatic Cytochrome P450 enzymes. Furthermore, the study investigated the synthesis and characterization of gold nanoparticles from the ethanolic extract of Lippia scaberrima as a lead sample. Confirmation and characterization of the synthesized gold nanoparticles were conducted through various methods. Additionally, the cytotoxic properties of the ethanolic extract of Lippia scaberrima were compared with the gold nanoparticles synthesized from Lippia scaberrima using gum arabic as a capping agent.ResultsAll the samples showed varying levels of CYP inhibition. The most potent inhibition took place for CYP2C19 and CYP1B1 with 50% inhibitory concentration (IC50) values of less than 0.05 µg/L for the essential oil tested and IC50-values between 0.05 µg/L-1 µg/L for all the other combinations and extracts tested, respectively. For both CYP1A2 and CYP2D6 the IC50-values for the essential oil, the extracts and combinations were found in the range of 1 – 10 µg/L. The majority of the IC50 values found were higher than 10 µg/L and, therefore, were found to have no inhibition against the CYP enzymes tested.ConclusionTherefore, the essential oil of Lippia scaberrima, the ethanolic extract of Lippia scaberrima alone and their combinations with Aspalathus linearis do not possess any clinically significant CYP interaction potential and may be further investigated for their adjuvant potential for use in the tuberculosis treatment regimen. Furthermore, it was shown that the cytotoxic potential of the Lippia scaberrima gold nanoparticles was reduced by twofold when compared to the ethanolic extract of Lippia scaberrima.

Metabolite profiling and identification of enzymes responsible for the metabolism of hirsutine, a major alkaloid from Uncaria rhynchophylla

The in vitro metabolism of hirsutine was determined using liver microsomes and human recombinant cytochrome P450 enzymes. Under the current conditions, a total of 14 phase I metabolites were tentatively identified. Ketoconazole showed significant inhibitory effect on the metabolism of hirsutine. Human recombinant cytochrome P450 enzyme analysis revealed that metabolism of hirsutine was mainly catalysed by CYP3A4. Our data revealed that hirsutine was metabolised via mono-oxygenation, di-oxygenation, N-oxygenation, dehydrogenation, demethylation and hydrolysis. In glutathione (GSH)-supplemented liver microsomes, four GSH adducts were identified. Hirsutine underwent facile P450-mediated metabolic activation, forming reactive 3-methyleneindolenine and iminoquinone intermediates. This study provided valuable information on the metabolic fates of hirsutine in liver microsomes, which would aid in understanding the hepatotoxicity caused by hirsutine or hirsutine-containing herb preparation.

Metabolism and toxicity of usnic acid and barbatic acid based on microsomes, S9 fraction, and 3T3 fibroblasts in vitro combined with a UPLC-Q-TOF-MS method.

Introduction: Usnic acid (UA) and barbatic acid (BA), two typical dibenzofurans and depsides in lichen, have a wide range of pharmacological activities and hepatotoxicity concerns. This study aimed to clarify the metabolic pathway of UA and BA and illuminate the relationship between metabolism and toxicity. Methods: An UPLC-Q-TOF-MS method was developed for metabolite identification of UA and BA in human liver microsomes (HLMs), rat liver microsomes (RLMs), and S9 fraction (RS9). The key metabolic enzymes responsible for UA and BA were identified by enzyme inhibitors combined with recombinant human cytochrome P450 (CYP450) enzymes. The cytotoxicity and metabolic toxicity mechanism of UA and BA were determined by the combination model of human primary hepatocytes and mouse 3T3 fibroblasts. Results: The hydroxylation, methylation, and glucuronidation reactions were involved in the metabolic profiles of UA and BA in RLMs, HLMs, and RS9. CYP2C9, CYP3A4, CYP2C8, and UGT1A1 are key metabolic enzymes responsible for metabolites of UA and CYP2C8, CYP2C9, CYP2C19, CYP1A1, UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10 for metabolites of BA. UA and BA did not display evident cytotoxicity in human primary hepatocytes at concentrations of 0.01-25 and 0.01-100 µM, respectively, but showed potential cytotoxicity to mouse 3T3 fibroblasts with 50% inhibitory concentration values of 7.40 and 60.2 µM. Discussion: In conclusion, the attenuated cytotoxicity of BA is associated with metabolism, and UGTs may be the key metabolic detoxification enzymes. The cytotoxicity of UA may be associated with chronic toxicity. The present results provide important insights into the understanding of the biotransformation behavior and metabolic detoxification of UA and BA.

Investigation on the in vitro metabolism of bicyclol using liver microsomes, hepatocytes and human recombinant cytochrome P450 enzymes

In vitro metabolism of bicyclol was studied using liver microsomes, hepatocytes and human recombinant cytochrome P450 enzymes. Liquid chromatography-benchtop orbitrap mass spectrometry technique was utilised to identify the metabolites. A total of 19 metabolites, including 5 new metabolites (M2, M3, M4, M5 and M16) were tentatively identified. Among these metabolites, M6&M8 (demethylenation), M9&M10 (demethylation) and M19 (glucuronidation) were the major metabolites. In glutathione (GSH)-supplemented liver microsomes, 5 new GSH conjugates were found and tentatively identified. The formation was assumed to be through demethylenation of methylenedioxyphenyl to form catechol derivatives, which further underwent oxidation to form ortho-quinone intermediates, reacting with GSH to form stable adducts. CYP3A4 and 2C19 were demonstrated to be the major enzymes responsible for the bioactivation of bicyclol. This study provided valuable information on the metabolic fate of bicyclol in liver microsomes and hepatocytes, and the bioactivation pathways were reported for the first time, which would be helpful for us to understand the potential drug-drug interactions and the possible side effect of this drug.

Comparative Metabolomic Profiling of the Metabolic Differences of Δ9-Tetrahydrocannabinol and Cannabidiol.

More than one hundred cannabinoids have been found in cannabis. Δ9-Tetrahydrocannabinol (THC) is the recognized addictive constituent in cannabis; however, the mechanisms underlying THC-induced toxicity remain elusive. To better understand cannabis-induced toxicity, the present study compared the metabolic pathways of THC and its isomer cannabidiol (CBD) in human and mouse liver microsomes using the metabolomic approach. Thirty-two metabolites of THC were identified, including nine undescribed metabolites. Of note, two glutathione (GSH) and two cysteine (Cys) adducts were found in THC's metabolism. Molecular docking revealed that THC conjugates have a higher affinity with GSH and Cys than with the parent compound, THC. Human recombinant cytochrome P450 enzymes, and their corresponding chemical inhibitors, demonstrated that CYP3A4 and CYP1B1 were the primary enzymes responsible for the formation of THC-GSH and THC-Cys, thus enabling conjugation to occur. Collectively, this study systematically compared the metabolism of THC with the metabolism of CBD using the metabolomic approach, which thus highlights the critical role of metabolomics in identifying novel drug metabolites. Moreover, this study also facilitates mechanistic speculation in order to expand the knowledge of drug metabolism and safety.

Identification of Optimal Urinary Biomarkers of Synthetic Cannabinoids BZO-HEXOXIZID, BZO-POXIZID, 5F-BZO-POXIZID, and BZO-CHMOXIZID for Illicit Abuse Monitoring.

The continuous introduction of new synthetic cannabinoid (SC) subtypes and analogues remains a major problem worldwide. Recently, a new "OXIZID" generation of SCs surfaced in seized materials across various countries. Hence, there is an impetus to identify urinary biomarkers of the OXIZIDs to detect their abuse. We adapted our previously reported two-pronged approach to investigate the metabolite profiles and disposition kinetics of 4 OXIZID analogues, namely, BZO-HEXOXIZID (MDA-19), BZO-POXIZID (5C-MDA-19), 5F-BZO-POXIZID (5F-MDA-19), and BZO-CHMOXIZID (CHM-MDA-19). First, bottom-up in vitro incubation experiments comprising metabolite identification, metabolic stability, and reaction phenotyping were performed using human liver microsomes and recombinant human cytochrome P450 enzymes. Second, top-down analysis of authentic urine samples from drug abusers was performed to corroborate the in vitro findings and establish a panel of urinary biomarkers. A total of 42 to 51 metabolites were detected for each OXIZID, and their major metabolic pathways included N-alkyl and phenyl hydroxylation, oxidative defluorination (for 5F-BZO-POXIZID), oxidation to ketone and carboxylate, amide hydrolysis, and N-dealkylation. The OXIZIDs were metabolically unstable, mainly metabolized by cytochromes P3A4, P3A5, and P2C9, and demonstrated mechanism-based inactivation of cytochrome P3A4. Integrating with the results of 4 authentic urine samples, the parent drug and both N-alkyl and phenyl mono-hydroxylated metabolites of each OXIZID were determined as suitable urinary biomarkers. Drug enforcement agencies worldwide may apply these biomarkers in routine monitoring procedures to identify abusers and counter the escalation of OXIZID abuse.

In vitro evaluation of fenfluramine and norfenfluramine as victims of drug interactions.

Fenfluramine (FFA) has potent antiseizure activity in severe, pharmacoresistant childhood‐onset developmental and epileptic encephalopathies (e.g., Dravet syndrome). To assess risk of drug interaction affecting pharmacokinetics of FFA and its major metabolite, norfenfluramine (nFFA), we conducted in vitro metabolite characterization, reaction phenotyping, and drug transporter−mediated cellular uptake studies. FFA showed low in vitro clearance in human liver S9 fractions and in intestinal S9 fractions in all three species tested (t1/2 > 120 min). Two metabolites (nFFA and an N‐oxide or a hydroxylamine) were detected in human liver microsomes versus six in dog and seven in rat liver microsomes; no metabolite was unique to humans. Selective CYP inhibitor studies showed FFA metabolism partially inhibited by quinidine (CYP2D6, 48%), phencyclidine (CYP2B6, 42%), and furafylline (CYP1A2, 32%) and, to a lesser extent (<15%), by tienilic acid (CYP2C9), esomeprazole (CYP2C19), and troleandomycin (CYP3A4/5). Incubation of nFFA with rCYP1A2, rCYP2B6, rCYP2C19, and rCYP2D6 resulted in 10%−20% metabolism and no clear inhibition of nFFA metabolism by any CYP‐selective inhibitor. Reaction phenotyping showed metabolism of FFA by recombinant human cytochrome P450 (rCYP) enzymes rCYP2B6 (10%–21% disappearance for 1 and 10 µM FFA, respectively), rCYP1A2 (22%−23%), rCYP2C19 (49%−50%), and rCYP2D6 (59%−97%). Neither FFA nor nFFA was a drug transporter substrate. Results show FFA metabolism to nFFA occurs through multiple pathways of elimination. FFA dose adjustments may be needed when administered with strong inhibitors or inducers of multiple enzymes involved in FFA metabolism (e.g., stiripentol).

Bulleyaconitine A is a sensitive substrate and competitive inhibitor of CYP3A4: One of the possible explanations for clinical adverse reactions

Bulleyaconitine A (BLA), a toxic Aconitum alkaloid, is a potent analgesic that is clinically applied to treat rheumatoid arthritis, osteoarthritis and lumbosacral pain. BLA-related adverse reactions occur frequently, but whether the underlying mechanism is related to its metabolic interplay with drug-metabolizing enzymes remains unclear. This study aimed to elucidate the metabolic characteristics of BLA and its affinity action and mechanism to drug-metabolizing enzymes to reveal whether BLA-related adverse reactions are modulated by enzymes. After incubation with human liver microsomes and recombinant human cytochrome P450 enzymes, we found that BLA was predominantly metabolized by CYP3A, in which CYP3A4 had an almost absolute advantage. In vitro, the CYP3A4 inhibitor ketoconazole noticeably suppressed the metabolism of BLA. In vivo, the AUC0-∞ values, cardiotoxicity and neurotoxicity of BLA in Cyp3a-inhibited mice were all obviously enhanced (P < 0.05) compared to those in normal mice. In the enzyme kinetics study, BLA was found to be a sensitive substrate of CYP3A4, and its characteristics were consistent with substrate inhibition (Km = 39.36 ± 10.47 μmol/L, Ks = 83.42 ± 19.65 μmol/L). BLA was further identified to be a competitive inhibitor of CYP3A4 with Ki = 53.64 μmol/L, since the intrinsic clearance (CLint) of midazolam, a selective CYP3A4 substrate, decreased significantly (P < 0.05) when incubated with BLA together in mouse liver microsomes. Overall, BLA is a sensitive substrate and competitive inhibitor of CYP3A4, and clinical adverse reactions of BLA may mechanistically related to the CYP3A4-mediated drug-drug interactions.

Elucidating a Complicated Enantioselective Metabolic Profile: A Study From Rats to Humans Using Optically Pure Doxazosin.

Doxazosin (DOX) is prescribed as a racemic drug for the clinical treatment of benign prostatic hyperplasia and hypertension. Recent studies found that the two enantiomers of DOX exhibit differences in blood concentration and pharmacological effects. However, the stereoselective metabolic characteristics and mechanisms for DOX are not yet clear. Herein, we identified 34 metabolites of DOX in rats based on our comprehensive and effective strategy. The relationship among the metabolites and the most discriminative metabolites between (−)-DOX and (+)-DOX administration was analyzed according to the kinetic parameters using state-of-the-art multivariate statistical methods. To elucidate the enantioselective metabolic profile in vivo and in vitro, we carefully investigated the metabolic characteristics of metabolites after optically pure isomers administration in rat plasma, rat liver microsomes (RLMs) or human liver microsomes (HLMs), and recombinant human cytochrome P450 (CYP) enzymes. As a result, the differences of these metabolites were found based on their exposure and elimination rate, and the metabolic profile of (±)-DOX was more similar to that of (+)-DOX. Though the metabolites identified in RLMs and HLMs were the same, the metabolic profiles of the metabolites from (−)-DOX and (+)-DOX were greatly different. Furthermore, four human CYP enzymes could catalyze DOX to produce metabolites, but their preferences seemed different. For example, CYP3A4 highly specifically and selectively catalyzed the formation of the specific metabolite (M22) from (−)-DOX. In conclusion, we established a comprehensive metabolic system using pure optical isomers from in vivo to in vitro, and the complicated enantioselectivity of the metabolites of DOX was clearly shown. More importantly, the comprehensive metabolic system is also suitable to investigate other chiral drugs.

Weak intermolecular interactions in a series of biologically active 4'-methylthio-trans-stilbenes.

The crystal structures of nine methoxy-substituted 4'-methylthiostilbenes, which are potential inhibitors of human recombinant cytochrome P450 enzymes, were determined. These compounds included two mono-methoxy-substituted derivatives: 2-methoxy-4'-methylthio-trans-stilbene {systematic name: 1-[(E)-2-(2-methoxyphenyl)ethenyl]-4-(methylsulfanyl)benzene} (1) and 3-methoxy-4'-methylthio-trans-stilbene (2), both C16H16OS; four dimethoxy derivatives: 2,3-dimethoxy-4'-methylthio-trans-stilbene (3), 2,5-dimethoxy-4'-methylthio-trans-stilbene (4), 3,5-dimethoxy-4'-methylthio-trans-stilbene (5) and 2,4-dimethoxy-4'-methylthio-trans-stilbene (6), all C17H18O2S; and three trimethoxy compounds: 2,4,5-trimethoxy-4'-methylthio-trans-stilbene (7), 3,4,5-trimethoxy-4'-methylthio-trans-stilbene (8) and 2,4,6-trimethoxy-4'-methylthio-trans-stilbene (9), all C18H20O3S. The geometries of the compounds in the crystal structures were compared with those found during docking studies at the active site of the receptor, and some relevant differences were identified. Intermolecular interactions were analyzed using three different methods. First, the (3,-1) critical points of the gradient field of the electron density were identified, and then the appropriate contacts were analyzed using their geometrical characteristics and interaction energy calculations. The results confirmed the importance of weak delocalized interactions in the construction of the crystal structures, and the results of different methods (PIXEL and DFT) were comparable in the absence of strong well-defined intermolecular interactions.

Influence of verapamil on the pharmacokinetics of rotundic acid in rats and its potential mechanism

Context Rotundic acid (RA), a plant-derived pentacyclic triterpene acid, has been reported to possess extensive pharmacological activities. The poor bioavailability limits its further development and potential clinic application. Objective To clarify the potential mechanism for poor oral bioavailability. Materials and methods The single-dose pharmacokinetics of orally administered RA (10 mg/kg) in Sprague–Dawley rats without or with verapamil (25 or 50 mg/kg) were investigated. Additionally, MDCKII-MDR1 and Caco-2 cell monolayers, five recombinant human cytochrome P450 (rhCYP) enzymes (1A2, 2C8, 2C9, 2D6 and 3A4), and rat liver microsomes were also conducted to investigate its potential mechanism. Results Verapamil could significantly affect the plasma concentration of RA. Co-administered verapamil at 25 and 50 mg/kg, the AUC0–∞ increased from 432 ± 64.2 to 539 ± 53.6 and 836 ± 116 ng × h/mL, respectively, and the oral clearance decreased from 23.6 ± 3.50 to 18.7 ± 1.85 and 12.2 ± 1.85 L/h/kg, respectively. The MDCKII-MDR1 cell assay showed that RA might be a P-gp substrate. The rhCYPs experiments indicated that RA was mainly metabolized by CYP3A4. Additionally, verapamil could increase the absorption of RA by inhibiting the activity of P-gp, and slow down the intrinsic clearance of RA from 48.5 ± 3.18 to 12.0 ± 1.06 µL/min/mg protein. Discussion and conclusions These findings indicated that verapamil could significantly affect the pharmacokinetic profiles of RA in rats. It was demonstrated that P-gp and CYP3A were involved in the transport and metabolism of RA, which might contribute to the low oral bioavailability of RA.

Cytochrome P450 Mediated Bioactivation of Rutaevin, a Bioactive and Potentially Hepatotoxic Component of Evodia Rutaecarpa.

Rutaevin is one of the major bioactive constituents isolated from Evodia rutaecarpa, a well-known herbal medicine that has been widely prescribed for the treatment of gastrointestinal disorders in China. However, oral administration of rutaevin has been shown to cause hepatotoxicity in mice. Bioactivation was suggested to be involved in rutaevin-induced hepatotoxicity. The aim of this study was to investigate the bioactivation of rutaevin in rat and human liver microsomes fortified with NADPH. Rutaevin was metabolized into the reactive intermediate cis-butene-1,4-dial (BDA) that was dependent on NADPH. The rutaevin-derived BDA intermediate was trapped by nucleophiles such as glutathione (GSH), N-acetyl-lysine (NAL), and methoxylamine (MOA) in the microsomal incubation system. A total of 10 conjugates resulting from the conjugation of the intermediate with GSH, NAL, or MOA were detected and structurally characterized by liquid chromatography combined with high-resolution tandem mass spectrometry. M1, structurally confirmed by NMR spectroscopic analysis, was identified as a cyclic mono(GSH) conjugate of the BDA intermediate, which was also found in the biliary samples of rutaevin-treated rats. Further inhibitory experiments suggested that ketoconazole showed strong inhibitory effect on the formation of the rutaevin-derived BDA intermediate. CYP3A4 was demonstrated to be the major enzyme responsible for rutaevin bioactivation by using cDNA-expressed human recombinant cytochrome P450 enzymes. Additionally, it was found that rutaevin was a mechanism-based inactivator of CYP3A4, with inactivation parameters of KI = 15.98 μM, kinact = 0.032 min-1, and t1/2inact = 21.65 min. In summary, these findings are of great significance in understanding the bioactivation mechanism of rutaevin, the potential mechanism of rutaevin-caused hepatotoxicity, and the drug-drug interactions associated with rutaevin mainly via CYP3A4 inactivation.

Preference for O-demethylation reactions in the oxidation of 2′-, 3′-, and 4′-methoxyflavones by human cytochrome P450 enzymes

2′-, 3′-, and 4′-Methoxyflavones (MeFs) were incubated with nine forms of recombinant human cytochrome P450 (P450 or CYP) enzymes in the presence of an NADPH-generating system and the products formed were analyzed with LC-MS/MS methods.CYP1B1.1 and 1B1.3 were highly active in demethylating 4′MeF to form 4′-hydroxyflavone (rate of 5.0 nmol/min/nmol P450) and further to 3′,4′-dihydroxyflavone (rates of 2.1 and 0.66 nmol/min/nmol P450, respectively). 3′MeF was found to be oxidized by P450s to m/z 239 (M-14) products (presumably 3′-hydroxyflavone) and then to 3′,4′-dihydroxyflavone. P450s also catalyzed oxidation of 2′MeF to m/z 239 (M-14) and m/z 255 (M-14, M-14 + 16) products, presumably mono- and di-hydroxylated products, respectively.At least two types of ring oxidation products having m/z 269 fragments were formed, although at slower rates than the formation of mono- and di-hydroxylated products, on incubation of these MeFs with P450s; one type was products oxidized at the C-ring, having m/z 121 fragments, and the other one was the products oxidized at the A-ring (having m/z 137 fragments).Molecular docking analysis indicated the preference of interaction of O-methoxy moiety of methoxyflavones in the active site of CYP1A2.These results suggest that 2′-, 3′-, and 4′-methoxyflavones are principally demethylated by human P450s to form mono- and di-hydroxyflavones and that direct oxidation occurs in these MeFs to form mono-hydroxylated products, oxidized at the A- or B-ring of MeF.

Carbon-carbon Bond Cleavage Catalyzed by Human Cytochrome P450 Enzymes: α-ketol as the Key Intermediate Metabolite in Sequential Metabolism of Olanexidine.

Carbon-carbon bond cleavage of a saturated aliphatic moiety is rarely seen in xenobiotic metabolism. Olanexidine (Olanedine®), containing an n-octyl (C8) side chain, was mainly metabolized to various shortened side chain (C4 to C6) acid-containing metabolites in vivo in preclinical species. In liver microsomes and S9, the major metabolites of olanexidine were from multi-oxidation on its n-octyl (C8) side chain. However, the carbon-carbon bond cleavage mechanism of n-octyl (C8) side chain, and enzyme(s) responsible for its metabolism in human remained unknown. A pair of regioisomers of α-ketol-containing C8 side chain olanexidine analogs (3,2-ketol olanexidine and 2,3-ketol olanexidine) were synthesized, followed by incubation in human liver microsomes, recombinant human cytochrome P450 enzymes or human hepatocytes, and subsequent metabolite identification using LC/UV/MS. Multiple shortened side chain (C4 to C6) metabolites were identified, including C4, C5 and C6- acid and C6-hydroxyl metabolites. Among 19 cytochrome P450 enzymes tested, CYP2D6, CYP3A4 and CYP3A5 were identified to catalyze carbon-carbon bond cleavage. 3,2-ketol olanexidine and 2,3-ketol olanexidine were confirmed as the key intermediates in carbon-carbon bond cleavage. Its mechanism is proposed that a nucleophilic addition of iron-peroxo species, generated by CYP2D6 and CYP3A4/5, to the carbonyl group caused the carbon-carbon bond cleavage between the adjacent hydroxyl and ketone groups. As results, 2,3-ketol olanexidine formed a C6 side chain acid metabolite. While, 3,2-ketol olanexidine formed a C6 side chain aldehyde intermediate, which was either oxidized to a C6 side chain acid metabolite or reduced to a C6 side chain hydroxyl metabolite.

Metabolism of Benzalkonium Chlorides by Human Hepatic Cytochromes P450.

Benzalkonium chlorides (BACs) are widely used as disinfectants in cleaning products, medical products, and the food processing industry. Despite a wide range of reported toxicities, limited studies have been conducted on the metabolism of these compounds in animal models and none in human-derived cells or tissues. In this work, we report on the metabolism of BACs in human liver microsomes (HLM) and by recombinant human hepatic cytochrome P450 (CYP) enzymes. BAC metabolism in HLM was NADPH-dependent and displayed apparent half-lives that increased with BAC alkyl chain length (C10 < C12 < C14 < C16), suggesting enhanced metabolic stability of the more lipophilic, longer chain BACs. Metabolites of d7-benzyl labeled BAC substrates retained all deuteriums and there was no evidence of N-dealkylation. Tandem mass spectrometry fragmentation of BAC metabolites confirmed that oxidation occurs on the alkyl chain region. Major metabolites of C10-BAC were identified as ω-hydroxy-, (ω-1)-hydroxy-, (ω, ω-1)-diol-, (ω-1)-ketone-, and ω-carboxylic acid-C10-BAC by liquid chromatography-mass spectrometry comparison with synthetic standards. In a screen of hepatic CYP isoforms, recombinant CYP2D6, CYP4F2, and CYP4F12 consumed substantial quantities of BAC substrates and produced the major microsomal metabolites. The use of potent pan-CYP4 inhibitor HET0016, the specific CYP2D6 inhibitor quinidine, or both confirmed major contributions of CYP4- and CYP2D6-mediated metabolism in the microsomal disappearance of BACs. Kinetic characterization of C10-BAC metabolite formation in HLM demonstrated robust Michaelis-Menten kinetic parameters for ω-hydroxylation (Vmax = 380 pmol/min/mg, Km = 0.69 μM) and (ω-1)-hydroxylation (Vmax = 126 pmol/min/mg, Km = 0.13 μM) reactions. This work illustrates important roles for CYP4-mediated ω-hydroxylation and CYP2D6/CYP4-mediated (ω-1)-hydroxylation during the hepatic elimination of BACs, an environmental contaminant of emerging concern. Furthermore, we demonstrate that CYP-mediated oxidation of C10-BAC mitigates the potent inhibition of cholesterol biosynthesis exhibited by this short-chain BAC.

Cytotoxicity of safrole in HepaRG cells: studies on the role of CYP1A2-mediated ortho-quinone metabolic activation

1. Safrole is a natural compound categorized as a group 2B carcinogen extracted from sassafras oil or certain other essential oils. The hepatotoxicity of safrole has always been highly concerned. So, the purpose of this study was to evaluate the role of cytochrome P450 (CYP450)-mediated reactive metabolites (RMs) formation and its induced cytotoxicity in HepaRG cells.2. Safrole belongs to the methylenedioxyphenyl structure which could be activated to RMs. Two metabolites (M1, M2) and three new glutathione conjugates (M3–M5) of safrole ortho-oquinone RMs were found in HepaRG cells. Using human recombinant CYP450 enzymes and chemical inhibitor method, the metabolism of safrole RMs was predominantly carried out through the CYP1A2 with minor contributions by CYP2E1.3. Induction of CYP1A2 by omeprazole (OME) enhanced safrole-induced cytotoxicity, compared with treatment with safrole alone, whereas inhibition of CYP1A2 by alpha-naphthoflavone (α-NAP) decreased the cytotoxicity. The cytotoxicity of cell induced by safrole was related to the amount of RMs formation. Besides, pretreatment with L-buthionine sulfoximine (BSO) to deplete intracellular GSH markedly enhanced safrole-induced cytotoxicity. OME induced the safrole-induced GSH exhaustion, and GSH depletion by safrole was not via oxidation of GSH and occurred prior to the increase in ROS. Furthermore, mitochondrial membrane potential (ΔΨm) could be aggravated by the inducer of CYP1A2 together with safrole. Collectively, these data suggest that the ortho-quinone RM may mediate safrole hepatotoxicity, and CYP1A2 was the core enzyme in ortho-quinone RMs-mediated safrole hepatotoxicity.

Pharmacokinetics, excretion and metabolites analysis of DL0410, a dual‑acting cholinesterase inhibitor and histamine‑3 receptor antagonist.

DL0410, a dual-action cholinesterase inhibitor and histamine-3 receptor antagonist with a novel structural scaffold, may be a potential candidate for the treatment of Alzheimer's disease (AD). To the best of the authors' knowledge, this is the first study to demonstrate a reliable method for the measurement of DL0410 in rat plasma, brain, bile, urine and feces samples, and identification of its primary metabolites. The pharmacokinetic properties of DL0410 were analyzed by liquid chromatography-mass spectrometry at oral doses of 25, 50 and 100 mg/kg and intravenous dose of 5 mg/kg. The investigation of the excretion and metabolism of DL0410 was determined following liquid-liquid extraction for biliary, urinary and fecal samples. Finally, the cytochrome (CY)P450 isoforms involved in the production of DL0410 metabolites with recombinant human cytochrome P450 enzymes were characterized. The results suggested that DL0410 was not well absorbed; however, was distributed to the entorhinal cortex and hippocampus of the brain. A total of two common metabolites of the reduction of DL0140 in the bile, urine and feces were identified and CYP2D6 was involved in this reaction. The pharmacokinetic results of DL0410 provided information for the illustration of its pharmacodynamic properties, mechanism of action and promoted its continued evaluation as a therapeutic agent for AD treatment.

The Toll-like receptor agonist imiquimod is metabolized by aryl hydrocarbon receptor-regulated cytochrome P450 enzymes in human keratinocytes and mouse liver.

The Toll-like receptor 7 agonist imiquimod (IMQ) is an approved drug for the topical treatment of various skin diseases that, in addition, is currently tested in multiple clinical trials for the immunotherapy of various types of cancers. As all of these trials include application of IMQ to the skin and evidence exists that exposure to environmental pollutants, i.e., tobacco smoke, affects its therapeutic efficacy, the current study aims to elucidate the cutaneous metabolism of the drug. Treatment of human keratinocytes with 2.5µM benzo[a]pyrene (BaP), a tobacco smoke constituent and aryl hydrocarbon receptor (AHR) agonist, for 24h induced cytochrome P450 (CYP) 1A enzyme activity. The addition of IMQ 30min prior measurement resulted in a dose-dependent inhibition of CYP1A activity, indicating that IMQ is either a substrate or inhibitor of CYP1A isoforms. Incubation of 21 recombinant human CYP enzymes with 0.5µM IMQ and subsequent LC-MS analyses, in fact, identified CYP1A1 and CYP1A2 as being predominantly responsible for IMQ metabolism. Accordingly, treatment of keratinocytes with BaP accelerated IMQ clearance and the associated formation of monohydroxylated IMQ metabolites. A co-incubation with 5µM 7-hydroxyflavone, a potent inhibitor of human CYP1A isoforms, abolished basal as well as BaP-induced IMQ metabolism. Further studies with hepatic microsomes from CD-1 as well as solvent- and β-naphthoflavone-treated CYP1A1/CYP1A2 double knock-out and respective control mice confirmed the critical contribution of CYP1A isoforms to IMQ metabolism. Hence, an exposure to life style-related, dietary, and environmental AHR ligands may affect the pharmacokinetics and, thus, treatment efficacy of IMQ.