Hepatic Disposition of the Cytochrome P450 2E1 Marker Chlorzoxazone and its Hydroxylated Metabolite in Isolated Perfused Rat Livers

Bielectrode Strategy for Determination of CYP2E1 Catalytic Activity: Electrodes with Bactosomes and Voltammetric Determination of 6-Hydroxychlorzoxazone

We describe a bielectrode system for evaluation of the electrocatalytic activity of cytochrome P450 2E1 (CYP2E1) towards chlorzoxazone. One electrode of the system was employed to immobilize Bactosomes with human CYP2E1, cytochrome P450 reductase (CPR), and cytochrome b5 (cyt b5). The second electrode was used to quantify CYP2E1-produced 6-hydroxychlorzoxazone by its direct electrochemical oxidation, registered using square-wave voltammetry. Using this system, we determined the steady-state kinetic parameters of chlorzoxazone hydroxylation by CYP2E1 of Bactosomes immobilized on the electrode: the maximal reaction rate (Vmax) was 1.64 ± 0.08 min-1, and the Michaelis constant (KM) was 78 ± 9 μM. We studied the electrochemical characteristics of immobilized Bactosomes and have revealed that electron transfer from the electrode occurs both to the flavin prosthetic groups of CPR and the heme iron ions of CYP2E1 and cyt b5. Additionally, it has been demonstrated that CPR has the capacity to activate CYP2E1 electrocatalytic activity towards chlorzoxazone, likely through intermolecular electron transfer from the electrochemically reduced form of CPR to the CYP2E1 heme iron ion.

Cholesterol's inhibition effect on entering of chlorzoxazone into phosphatidylethanolamine bilayer: Relevance to cytochrome P450 drug metabolism at endoplasmic reticulum membranes

Many drugs are metabolized by cytochrome P450 (CYP) in the endoplasmic reticulum (ER) membrane. Recent studies have shown that CYP-substrate drugs reach the CYP active site after entering the lipid hydrophobic part of the ER membrane. To clarify the role of cholesterol (Chol) in the CYP-related drug metabolic process, we investigated the lipid bilayer entry of CYP-substrate drugs using a model membrane system as follows. The model membrane system comprised palmitoyl-oleoyl-phosphatidylethanolamine (POPE) and Chol. Phosphatidylethanolamine is the second major phospholipid component of ER membranes. Chlorzoxazone (CZX) was used as the CYP-substrate drug. Calorimetric measurements showed that the addition of CZX to POPE bilayers decreased the gel-liquid crystal phase transition temperature; X-ray diffraction indicated that CZX distributes into the liquid crystal phase bilayers but not practically the gel phase POPE bilayers. In the presence of Chol, dialysis and X-ray structural analyses showed that Chol inhibited CZX entry into the bilayer with an increase in Chol concentration. The Chol concentration in the ER membrane (5-10 mol%) is much lower than that in the plasma membrane (approximately 30 mol%). This fact may allow CYP-substrate drugs to enter the hydrophobic portion of the ER membrane more easily than other organelle membranes, yielding efficient drug metabolism.

Solar-Powered Whole-Cell P450 Catalytic Platform for C-Hydroxylation Reactions

Photobiocatalysis is a green platform for driving redox enzymatic reactions using solar energy, not needing high-cost cofactors and redox partners. Here, a visible light-driven whole-cell platform for human cytochrome P450 (CYP) photobiocatalysis was developed using natural flavins as a photosensitizer. Photoexcited flavins mediate NADPH/reductase-free, light-driven biocatalysis by human CYP2E1 both in vitro and in the whole-cell systems. In vitro tests demonstrated that the photobiocatalytic activity of CYP2E1 is dependent on the substrate type, the presence of catalase, and the acid type used as a sacificial electron donor. A protective effect of catalase was found against the inactivation of CYP2E1 heme by H₂ O₂ and the direct transfer of photo-induced electrons to the heme iron not by peroxide shunt. Furthermore, the P450 photobiocatalysis in whole cells containing human CYPs 1A1, 1A2, 1B1, and 3A4 demonstrated the general applicability of the solar-powered, flavin-mediated P450 photobiocatalytic system.

Production of chlorzoxazone glucuronides via cytochrome P4502E1 dependent and independent pathways in human hepatocytes

CYP2E1 activity is measured in vitro and in vivo via hydroxylation of the Chlorzoxazone (CHZ) producing the 6-hydroxychlorzoxazone (OH-CHZ) further metabolized as a glucuronide excreted in urine. Thus, the quantification of the OH-CHZ following enzymatic hydrolysis of CHZ-derived glucuronide appears to be a reliable assay to measure the CYP2E1 activity without direct detection of this glucuronide. However, OH-CHZ hydrolyzed from urinary glucuronide accounts for less than 80% of the CHZ administrated dose in humans leading to postulate the production of other unidentified metabolites. Moreover, the Uridine 5'-diphospho-glucuronosyltransferase (UGT) involved in the hepatic glucuronidation of OH-CHZ has not yet been identified. In this study, we used recombinant HepG2 cells expressing CYP2E1, metabolically competent HepaRG cells, primary hepatocytes and precision-cut human liver slices to identify metabolites of CHZ (300 μM) by high pressure liquid chromatography-UV and liquid-chromatography-mass spectrometry analyses. Herein, we report the detection of the CHZ-O-glucuronide (CHZ-O-Glc) derived from OH-CHZ in culture media but also in mouse and human urine and we identified a novel CHZ metabolite, the CHZ-N-glucuronide (CHZ-N-Glc), which is resistant to enzymatic hydrolysis and produced independently of CHZ hydroxylation by CYP2E1. Moreover, we demonstrate that UGT1A1, 1A6 and 1A9 proteins catalyze the synthesis of CHZ-O-Glc while CHZ-N-Glc is produced by UGT1A9 specifically. Together, we demonstrated that hydrolysis of CHZ-O-Glc is required to reliably quantify CYP2E1 activity because of the rapid transformation of OH-CHZ into CHZ-O-Glc and identified the CHZ-N-Glc produced independently of the CYP2E1 activity. Our results also raise the questions of the contribution of CHZ-N-Glc in the overall CHZ metabolism and of the quantification of CHZ glucuronides in vitro and in vivo for measuring UGT1A activities.

Pharmacokinetic alterations in poloxamer 407-induced hyperlipidemic rats

1. Plasma lipid profile abnormalities in hyperlipidemia can potentially alter the pharmacokinetics of a drug in a complex manner. To evaluate these pharmacokinetic alterations in hyperlipidemia and to determine the underlying mechanism(s), poloxamer 407-induced hyperlipidemic rats (HL rats), a well-established animal model of hyperlipidemia have been used. 2. In this review, we summarize findings on the pathophysiological and gene expression changes in drug-metabolizing enzymes and transporters in HL rats. We discuss pharmacokinetic changes in drugs metabolized primarily via hepatic cytochrome P450 (CYPs) in terms of alterations in hepatic intrinsic clearance (CL^'_int), free fraction in plasma (f_u) and hepatic blood flow rate (Q_H), depending on the hepatic excretion ratio, as well as drugs eliminated primarily by mechanisms other than hepatic CYPs. 3. For lipoprotein-bound drugs, increased binding to lipoproteins resulted in lower f_u values and volumes of distribution, with some exceptions. Generally, slower non-renal clearance (or total body clearance) of drugs that are substrates of hepatic CYP3A and CYP2C is well explained by the following factors: alterations in CL^'_int (due to down-regulation of hepatic CYPs), decreased f_u and/or possible decreased Q_H. 4. These consistent findings across studies in HL rats suggest more studies are needed at the clinical level for optimal pharmacotherapies for hyperlipidemia.

Inhibition of mirtazapine metabolism by Ecstasy (MDMA) in isolated perfused rat liver model

Background

Nowadays MDMA (3,4-methylendioxymethamphetamine), known as ecstasy, is widely abused among the youth because of euphoria induction in acute exposure. However, abusers are predisposed to depression in chronic consumption of this illicit compound.

Mirtazapine (MRZ), an antidepressant agent, may be prescribed in MDMA-induced depression. MRZ is extensively metabolized in liver by CYP450 isoenzymes. 8-hydroxymirtazapine (8-OH) is mainly produced by CYP2D6. N-desmethylmirtazapine (NDES) is generated by CYP3A4.

MDMA is also metabolized by the mentioned isoenzymes and demonstrates mechanism-based inhibition (MBI) in association with CYP2D6. Several studies revealed that MDMA showed inhibitory effects on CYP3A4.

In the present study, our aim was to evaluate the impact of MDMA on the metabolism of MRZ in liver.

Therefore, isolated perfused rat liver model was applied as our model of choice in this assessment.

Methods

The subjects of the study were categorized into two experimental groups. Rats in the control group received MRZ-containing Krebs-Henselit buffer (1 μg/ml). Rats in the treatment group received aqueous solution of 1 mg/ml MDMA (3 mg/kg) intraperitoneally 1 hour before receiving MRZ. Perfusate samples were analyzed by HPLC.

Results

Analyses of perfusate samples showed 80% increase in the parent drug concentrations and 50% decrease in the concentrations of both metabolites in our treatment group compared to the control group.

In the treatment group compared to the control group, AUC_(0–120) of the parent drug demonstrated 50% increase and AUC_(0–120) of 8-OH and NDES showed 70% and 60% decrease, respectively.

Observed decrease in metabolic ratios were 83% and 79% for 8-OH and NDES in treatment group compared to control group, respectively.

Hepatic clearance (CL_h) and intrinsic clearance (Cl_int) showed 20% and 60% decrease in treatment group compared to control group.

Conclusion

All findings prove the inhibitory effects of ecstasy on both CYP2D6 and CYP3A4 hepatic isoenzymes.

In conclusion, this study is the first investigation of MRZ metabolism in presence of MDMA in isolated perfused rat liver model.

Graphical abstract

Hepatic immunosuppressive effects of systemically administered novel dextran-methylprednisolone prodrugs with peptide linkers in rats

The hepatic immunosuppressive activities of two novel dextran prodrugs of methylprednisolone (MP) containing one (DMP1) or five (DMP5) amino acids as linkers were studied in rats. At various times (0-2 weeks) after intravenous administration of single 5 mg/kg (MP equivalent) doses of each prodrug or MP succinate (MPS), livers were isolated and immunologically stimulated ex vivo with lipopolysaccharide. The concentrations of tumor necrosis factor (TNF)-α in the outlet perfusate were then quantitated to assess immune response. Additionally, the concentrations of DMP1, DMP5, and/or MP were measured in the liver. MPS, DMP5, or DMP1 injections caused a maximum of 48.9%, 63.5%, or 85.7% decrease in the TNF-α secretion into the perfusate, with the time above the 50% inhibitory effect being <5, <24, or 120 h, respectively. Additionally, the area under the effect-time curve for DMP1 was 11-fold or fourfold higher than that after the administration of MPS or DMP5, respectively. Relatively high concentrations of DMP1 were present in the liver even at the last sampling time of 2 weeks. These data suggest that a single intravenous dose of DMP1 produces an intense and sustained immunosuppression in the liver for a relatively long time, which may be useful in liver transplantation.

Preclinical factors affecting the pharmacokinetic behaviour of tanshinone IIA, an investigational new drug isolated from Salvia miltiorrhiza for the treatment of ischaemic heart diseases

Tanshinone IIA (TSIIA) is a major active triterpenoid isolated from Salvia miltiorrhiza. The purposes of this study were to investigate various preclinical factors that determined the pharmacokinetics of TSIIA. After oral dosing at 6.7, 20, and 60 mg kg(-1), TSIIA was detected mainly as glucuronidated conjugate (TSIIAG) with only small amounts of the unchanged in the plasma. TSIIA was predominantly excreted into the bile and faeces as TSIIAG, and urine to a minor extent. The C(max) and AUC(0-)(t) of TSIIAG after i.p. administration were significantly lower than those after intragastric administration. The plasma concentration-time profiles of TSIIA following oral dosing of TSIIA showed multiple peaks. The C(max) and AUC(0-)(t) of TSIIA and its glucuronides in rats with intact bile duct were significantly lower than those of rats with bile duct cannulation. Studies from the linked-rat model and intraduodenal injection of bile containing TSIIA and its metabolites indicate that TSIIA glucuronides underwent hydrolysis and the aglycone was reabsorbed from the gut and excreted into the bile as conjugates. TSIIA had a wide tissue distribution, with a very high accumulation in the lung, but very limited penetration into the brain and testes. TSIIA was metabolized by rat CYP2C, 3A and 2D, as ticlopidine, ketoconazole and quinidine all inhibited TSIIA metabolism in rat liver microsomes. Taken collectively, these findings indicate that multiple factors play important roles in determining the pharmacokinetics of TSIIA.

Expression and activity of the cytochrome P450 2E1 in patients with nonalcoholic steatosis and steatohepatitis

BACKGROUND/AIMS

Nonalcoholic steatohepatitis (NASH) and nonalcoholic fatty liver (NAFL) have a different prognosis and should be dealt with differently. The pathogenesis of NASH implicates the overexpression of cytochrome P450 2E1 (CYP2E1). We investigated whether the noninvasive determination of CYP2E1 activity could replace a liver biopsy in order to differentiate NASH from NAFL.

METHOD

Forty patients referred for suspicion of NASH underwent liver biopsy. In these patients, CYP2E1 activity was determined noninvasively by the 6-hydroxychlorzoxazone/chlorzoxazone (CHZ) ratio (CHZ test). Expression of CYP2E1 on liver slides was assessed by immunohistochemistry, and immunostaining for smooth muscle actin was used to assess the activation of hepatic stellate cells (HSC).

RESULTS

Thirty patients with NASH were compared with 10 subjects with NAFL. No statistically significant difference could be identified for the clinical and biochemical parameters between the two groups. In the histology, steatosis was more important in NASH than in NAFL (P<0.0001). There was no difference either in the activity (CHZ test) or in the expression of CYP2E1 (immunohistochemistry) between patients with NASH and patients with NAFL. The degree of HSC activation was also comparable between the two groups. A positive and significant correlation was found between the activity of CYP2E1 and body mass index (P<0.001) as well as with the degree of steatosis (P=0.008).

CONCLUSION

For patients suspected to have NASH, noninvasive tests including the determination of the CYP2E1 activity are unable to distinguish them from patients with steatosis.

Circadian rhythm of cytochrome P4502E1 and its effect on disposition kinetics of chlorzoxazone in rats

The aim of this report is to study the circadian rhythm of cytochrome P4502E1 (CYP2E1) and its effect on the disposition kinetics of chlorzoxazone in male Wistar rats. The rats were housed under a 12-h light/dark cycle (lights from 9:00 to 21:00) with food and water ad libitum for 3 months. It was found that the expression of microsomal CYP2E1 mRNA in the liver during the dark phase was significantly lower than during the light phase, whereas the content of CYP2E1 protein and its hydroxylation activity were significantly higher. Therefore, chlorzoxazone 20 mg/kg was intravenously administered at 12:00 (light phase group) or 24:00 (dark phase group) to determine the effect on the disposition kinetics. The value of the area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) of chlorzoxazone showed no significant difference between the two groups. However, the value of chlorzoxazone half-life in plasma of the light phase group was significant longer than the dark phase group. The AUC(0-8 h) of 6-hydroxychlorzoxazone, a metabolite formed from chlorzoxazone mainly by CYP2E1, was significantly higher in the dark phase than in the light phase. In conclusion, microsomal CYP2E1 shows a substantial circadian variation in rats, and this was associated with a decrease of chlorzoxazone half life, and an increase of 6-hydroxychlorzoxazone production. Therefore, the temporal variations of therapeutic response and toxicological effects may have to be taken into consideration for other xenobiotics that are predominantly metabolized by CYP2E1, particularly those with a short half-life.

Obesity-induced increase of CYP2E1 activity and its effect on disposition kinetics of chlorzoxazone in Zucker rats

This study was designed to investigate the induction of CYP2E1 in obese Zucker rats and its effect on the disposition kinetics of chlorzoxazone (CZX). CZX 20mg/kg was administered to three groups of rats: normal Zucker rats fed a normal diet (ND), normal Zucker rats fed a high-fat diet (HF), and genetically obese Zucker rats fed a normal diet (OB). The values of the area under the plasma concentration-time curve from 0 to infinity (AUC(infinity)) of CZX were in the order of ND>HF>OB rats. The AUC(infinity) values of total 6-hydroxychlorzoxazone (6OHCZX-T), which is considered to be a CYP2E1 metabolic marker, were in the opposite order. The values of the AUC(infinity) ratio (6OHCZX-T/CZX) in ND, HF and OB rats were approximately 0.2, 0.3 and 0.4, respectively. The CZX concentration in fat was much higher than the concentrations in plasma, liver and kidney in all groups. Induction of CYP2E1 protein was greater in both liver and fat of OB rats than in those of HF rats. Microsomal activity of CYP2E1 in liver and fat was also in the order of OB>HF>NM rats. These results suggest that CYP2E1 may be induced in liver and fat of obese patients, thereby potentially altering the disposition kinetics of not only CZX, but also other lipophilic drugs metabolized by CYP2E1.