EROD and MROD as Markers of Cytochrome P450 1A Activities in Hepatic Microsomes from Entire and Castrated Male Pigs

Modulation of Angiotensin II-Induced Cellular Hypertrophy by Cannflavin-C: Unveiling the Impact on Cytochrome P450 1B1 and Arachidonic Acid Metabolites

This research aimed to clarify the impacts of cannflavin-C on angiotensin II (Ang II)-induced cardiac hypertrophy and their potential role in modulating cytochrome P450 1B1 (CYP1B1) and arachidonic acid (AA) metabolites. Currently there is no evidence to suggest that cannflavin-C, a prenylated flavonoid, has any significant effects on the heart or cardiac hypertrophy. The metabolism of arachidonic acid (AA) into midchain hydroxyeicosatetraenoic acids (HETEs), facilitated by CYP1B1 enzyme, plays a role in the development of cardiac hypertrophy, which is marked by enlarged cardiac cells. Adult human ventricular cardiomyocyte (AC16) cell line was cultured and exposed to cannflavin-C in the presence and absence of Ang II. The assessment of mRNA expression pertaining to cardiac hypertrophic markers and cytochromes P450 (P450s) was conducted via real-time polymerase chain reaction (PCR), whereas the quantification of P450 protein levels was carried out through western blot analysis. Ang II induced hypertrophic markers myosin heavy chain (β/α-MHC), atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) and increased cell surface area, whereas cannflavin-C mitigated these effects. Gene and protein expression analysis revealed that cannflavin-C downregulated CYP1B1 gene expression, protein level, and enzyme activity assessed by 7-methoxyresorufin O-deethylase (MROD). Arachidonic acid metabolites analysis, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), demonstrated that Ang II increased midchain (R/S)-HETE concentrations, which were attenuated by cannflavin-C. This study provides novel insights into the potential of cannflavin-C in modulating arachidonic acid metabolites and attenuating Ang II-induced cardiac hypertrophy, highlighting the importance of this compound as potential therapeutic agents for cardiac hypertrophy. SIGNIFICANCE STATEMENT: This study demonstrates that cannflavin-C offers protection against cellular hypertrophy induced by angiotensin II. The significance of this research lies in its novel discovery, which elucidates a mechanistic pathway involving the inhibition of CYP1B1 by cannflavin-C. This discovery opens up new avenues for leveraging this compound in the treatment of heart failure.

Unravelling drug-drug interactions in pigs: Induction of hepatic cytochrome P450 1A (CYP1A) metabolism after the in-feed medication with the anthelmintic fenbendazole

The anthelmintic fenbendazole (FBZ) undergoes hepatic S‑oxygenation by monooxygenases belonging to the cytochrome P450 (CYP) and flavin-monooxygenase (FMO) families. The in-feed medication with FBZ induced CYP1A-dependent metabolism in pig liver. This fact may alter the metabolism of the anthelmintic itself, and of CYP1A substrates like aflatoxin B1 (AFB1). This work evaluated the effect of the in-feed administration of FBZ on CYP1A-dependent metabolism, on its own pattern of hepatic S‑oxygenation, and on the metabolism of AFB1. Landrace piglets remained untreated (n = 5) or received a pre-mix of FBZ (n = 6) in feed for 9 days. Pigs were slaughtered for preparation of liver microsomes used for: CYP content determination; monitoring the CYP1A-dependent enzyme activities, 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD); measurement of FBZ (50 μM) S‑oxygenation, and AFB1 (16 nM) disappearance from the incubation medium. In microsomes of FBZ-treated animals, EROD and MROD increased 19-fold (p = 0.002) and 14-fold (p = 0.003), respectively. An enhanced (3-fold, p = 0.004) participation of the CYP pathway in FBZ S‑oxygenation was observed in the liver of piglets treated with the anthelmintic (210 ± 69 pmol/min.nmol CYP) compared to untreated animals (68 ± 34 pmol/min.nmol CYP). AFB1 metabolism was 93% higher (p = 0.009) in the liver of FBZ-treated compared to untreated pigs. Positive and significant (p < 0.05) correlations were observed between CYP1A-dependent enzyme activities and FBZ or AFB1 metabolism. The sustained administration of FBZ caused an auto-induction of the CYP1A-dependent S‑oxygenation of this anthelmintic. The CYP1A induction triggered by the anthelmintic could amplify the production of AFB1 metabolites in pig liver, including the hepatotoxic AFB1-derived epoxide.+.

Biocompatibility of the oxygen carrier polymerized human hemoglobin towards HepG2/C3A cells

Hemoglobin (Hb) based oxygen carriers (HBOCs) are designed to minimize the toxicity of extracellular Hb, while preserving its high oxygen-carrying capacity for oxygen delivery to cells. Polymerized human Hb (PolyHb) is a novel type of nanosized HBOC synthesized via glutaraldehyde-mediated crosslinking of free Hb, and which preserves the predominant quaternary state during the crosslinking reaction (low oxygen affinity tense (T) quaternary state PolyHb is synthesized at 0% Hb oxygen saturation, and high oxygen affinity relaxed (R) quaternary state PolyHb is synthesized at 100% Hb oxygen saturation). Major potential applications for PolyHbs, and HBOCs in general, include oxygenation of bioreactor systems containing large liver cell masses, and ex-vivo perfusion preservation of explanted liver grafts. The toxicity of these compounds toward liver cells must be evaluated before testing their use in these complex systems for oxygen delivery. Herein, we characterized the effect of PolyHbs on the hepatoma cell line HepG2/C3A, used as a model hepatocyte and as a cell line used in some investigational bioartificial liver support devices. HepG2/C3A cells were incubated in cell culture media containing PolyHbs or unmodified Hb at concentrations up to 50 mg/mL and for up to 6 days. PolyHbs were well tolerated at a dose of 10 mg/mL, with no significant decrease in cell viability; however, proliferation was inhibited as much as 10-fold after 6 days of exposure at 50 mg/mL. Secretion of albumin, and urea, as well as glucose and ammonia removal were measured in presence of 10 mg/mL of PolyHbs or unmodified Hb. In addition, methoxy- and ethoxy-resorufin deacetylase (MROD and EROD) activities, which reflect cytochrome P450 metabolism, were measured. R-state PolyHb displayed improved or intact activity in 3 out of 7 functions compared to unmodified Hb. T-state PolyHb displayed improved or intact activity in 4 out of 7 functions compared to unmodified Hb. Thus, PolyHbs, both in the R-state and T-state, are safer to use at a concentration of 10 mg/mL as compared to unmodified Hb in static culture liver-related applications.

Impact of valproic acid on busulfan pharmacokinetics: In vitro assessment of potential drug-drug interaction

Busulfan (Bu) is an alkylating agent commonly used at high doses in the preparative regimens of hematopoietic stem cell transplantation (HSCT). It has been shown that such high doses of Bu are associated with generalized seizures which are usually managed by prophylactic antiepileptic drugs (AEDs) such as valproic acid (VPA). Being a strong enzyme inhibitor, VPA may inhibit Bu metabolism and thus increase its potential toxicity. Despite its clinical relevance, the potential interaction between Bu and VPA has not yet been evaluated. The aim of the present study was to assess and evaluate the potential drug-drug interaction (DDI) between Bu and VPA. This study was carried out by incubating Bu in laboratory-prepared rat liver-subcellular fractions including S9, microsomes, and cytosol, alone or in combination with VPA. The liver fractions were prepared by differential centrifugation of the liver homogenate. Analysis of Bu was employed using a fully validated LC-MS/MS method. The validation parameters were within the proposed limits of the international standards guidelines. Bu metabolic stability was assessed by incubating Bu at a concentration of 8 μg/ml in liver fractions at 37°C. There were significant reductions in Bu levels in S9 and cytosolic fractions, whereas these levels were not significantly (P ˃ 0.05) changed in microsomes. However, in presence of VPA, Bu levels in S9 fraction remained unchanged. These results indicated, for the first time, the potential metabolic interaction of Bu and VPA being in S9 only. This could be explained by inhibiting Bu cytosolic metabolism by the interaction with VPA either by sharing the same metabolic enzyme or the required co-factor. In conclusion, the present findings suggest, for the first time, a potential DDI between Bu and VPA in vitro using rat liver fractions. Further investigations are warranted in human-derived liver fractions to confirm such an interaction.

Metabolism and in vitro assessment of the mutagenic activity of urinary extracts from rats after inhalation exposure to 1-methylnaphthalene

OBJECTIVES

1-Methylnaphthalene (1-MN) is composed of 2 benzene rings and belongs to polycyclic aromatic hydrocarbons. The metabolism of 1-MN in laboratory animals and bacteria leads to the formation of 1-naphthoic acid (1-NA).

MATERIAL AND METHODS

In this study the distribution of 1-NA in lung, liver, spleen, kidney and urinary excretion of 1-NA in rats after single and repeated inhalation exposure to 1-MN vapors were investigated. The activity of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and cytochrome were measured of the rats. Genotoxic effects were evaluated with the in vitro micronucleus test on V79 hamster fibroblasts.

RESULTS

The concentrations of 1-NA in the tissues of rats after single and repeated exposure to 1-MN were dependent on the exposure dose. High levels of 1-NA were found in kidneys of animals after the single and repeated exposure to 1-MN. With an increase of 1-MN dose, an increase in the activity of cytochrome P450 (CYP1A1 and CYP1A2) was observed in the liver of rats. Compared to control animals, significantly higher ALT activity was noted in serum of rats exposed to 1-MN. The micronuclei frequency in V79 cells exposed to 1-MN (in the range of analyzable concentrations; i.e., 5-25 μg/ml) did not differ significantly from the vehicle control, whereas urine extracts from rats exposed to 1-MN induced a significant increase in the frequency of micronuclei compared to urine extracts from the group of control animals.

CONCLUSIONS

Metabolism of 1-MN in rats after the inhalation exposure leading to 1-NA was mainly observed during the first day after the end of exposure. It is likely that 1-MN metabolites present in rat urine can induce the increased micronuclei frequency as was shown in V79 cells. Int J Occup Med Environ Health. 2022;35(6):731-46.

A novel approach to predict the comprehensive EROD potency: Mechanism-based curve fitting of CYP1A1 activity by PAHs

Cytochrome P450 1A1 (CYP1A1) plays critical roles in polycyclic aromatic hydrocarbon (PAH) toxicity, including DNA adduction and ROS generation. Therefore, CYP1A1 activity quantified by the 7-ethoxyresorufin-O-deethylase (EROD) assay (named EROD potency) has been considered a typical biomarker of PAH exposure and toxicity. The EROD dose-response curve always presents a biphasic style, increasing at low concentrations and decreasing at high concentrations of PAHs, but relative effect potency (REP) commonly used in PAH risk assessment is only involved in the increasing phase. In this study, a full bell-shaped EROD curve fitting formula Eq. (1) was obtained by considering both CYP1A1 mRNA induction and enzyme inhibition to completely assess the EROD potency of PAHs. Correspondingly, in silico models of QSAR and docking methods successfully predicted the full EROD curves of PAHs, and the structure-activity relationship indicated that PAHs with heavy molecular weight and large diameter showed stronger EROD potency. Further EROD potency with predicted curve parameters (EC_50,ind and area index) was confirmed by the reported REP (R² = 0.697-0.977) and experimental data from human and mouse cells (R² = 0.700-0.804). This study provides a novel curve fitting for the EROD dose-response relationship and a prediction model for PAH EROD potency.

Identification of Cytochrome P450 Isozymes Involved in Enantioselective Metabolism of Fipronil in Fish Liver: In Vitro Metabolic Kinetics and Molecular Modeling

Fipronil has been frequently detected in waterways worldwide at concentrations that threaten aquatic organisms, yet the metabolic behavior of fipronil enantiomers in aquatic organisms is largely unknown, which is of significance in enantioselective toxicity evaluation. We quantitatively identified the specific cytochrome P450 (CYP) isozymes involved in metabolizing fipronil enantiomers in tilapia by combining in vitro metabolic kinetic assays and molecular docking. Inhibition studies suggested that CYP1A enzyme was the main isoform catalyzing metabolism of fipronil and that CYP3A contributed in a limited way to the metabolism in fish liver S9. Both the dissipation rate constant and the maximum metabolic velocity of R-(-)-fipronil were greater than those of S-(+)-fipronil in tilapia liver S9, suggesting that tilapia selectively metabolized R-(-)-fipronil. The CYP1A1 isozyme exhibited the highest binding capacity to R-(-)-fipronil and S-(+)-fipronil (binding energy -9.39 and -9.17 kcal/mol, respectively), followed by CYP1A2 (-7.30 and -6.94 kcal/mol, respectively) and CYP3A4 (-7.16 and -6.91 kcal/mol, respectively). The results of in vitro metabolic assays and molecular docking were consistent, that is, CYP1A, specifically CYP1A1, exhibited a higher metabolic capacity to fipronil than CYP3A, and fish liver S9 selectively metabolized R-(-)-fipronil. The present study provides insight into the enantioselective metabolic behavior and toxicological implications of the in vitro metabolic kinetics of fipronil in fish. Environ Toxicol Chem 2022;41:230-239. © 2021 SETAC.

Stability investigations of cytochrome P450 (CYP) enzymes immediately after death in a pig model support the applicability of postmortem hepatic CYP quantification

Quantification of drug-metabolizing cytochrome P450 (CYP) isoforms using LC-MS/MS has been proposed as a potential way of estimating antemortem CYP levels using postmortem tissue, but the postmortem stability of CYP proteins is incompletely investigated. If one can use data obtained from the analysis of postmortem specimens to inform physiologically based pharmacokinetic (PBPK) models this greatly increases the access to rare specimens among special subpopulations. In this study, we developed and validated an LC-MS/MS method for targeted CYP protein quantification in a porcine animal model to study postmortem stability. We measured 19.9-28.3 pmol CYP1A2, 50.3-66.2 pmol CYP2D25, 132.9-142.7 pmol CYP2E1, and 16.8-48 pmol CYP3A29 protein per mg PLM in nondegraded tissue. In tissue stored at 4°C, we found that the CYP protein levels were unaffected by degradation after 72 h. At 21°C CYP1A2, CYP2D25, and CYP2E1 protein levels were nearly unaffected by degradation after 24 h, whereas a loss of approximately 50% was seen after 48 h. At 21°C CYP3A29 had a loss of 50% at 24 h and 70% at 48 h exhibiting less postmortem stability. In vitro enzyme activity measurements in the same tissue stored at 21°C showed a 50% decrease after 24 h and a complete loss of enzyme activity after 48 h. When stored at 4°C, the in vitro enzyme activity decreased to 50% activity after 96 h. In conclusion, measuring CYP levels by an LC-MS/MS approach was clearly less affected by postmortem changes than an activity-based approach. The found postmortem stability for 24 h at 21°C for 3 out of 4 CYP isoforms supports the use of properly stored postmortem tissue to inform PBPK models.

Novel Synthetic Analogues of 19(S/R)-Hydroxyeicosatetraenoic Acid Exhibit Noncompetitive Inhibitory Effect on the Activity of Cytochrome P450 1A1 and 1B1

BACKGROUND AND OBJECTIVES

Cytochrome P450 (CYP) 1A1 and CYP1B1 enzymes play a significant role in the pathogenesis of cancer and cardiovascular diseases (CVD) such as cardiac hypertrophy and heart failure. Previously, we have demonstrated that R- and S-enantiomers of 19-hydroxyeicosatetraenoic acid (19-HETE), an arachidonic acid endogenous metabolite, enantioselectively inhibit CYP1B1. The current study was conducted to test the possible inhibitory effect of novel synthetic analogues of R- and S-enantiomers of 19-HETE on the activity of CYP1A1, CYP1A2, and CYP1B1.

METHODS

The O-dealkylation rate of 7-ethoxyresorufin (EROD) by recombinant human CYP1A1 and CYP1B1, in addition to the O-dealkylation rate of 7-methoxyresorufin (MROD) by recombinant human CYP1A2, were measured in the absence and presence of varying concentrations (0-40 nM) of the synthetic analogues of 19(R)- and 19(S)-HETE. Also, the possible inhibitory effect of both analogues on the catalytic activity of EROD and MROD, using RL-14 cells and human liver microsomes, was assessed.

RESULTS

The results showed that both synthetic analogues of 19(R)- and 19(S)-HETE exhibited direct inhibitory effects on the activity of CYP1A1 and CYP1B1, while they had no significant effect on CYP1A2 activity. Nonlinear regression analysis and comparisons showed that the mode of inhibition for both analogues is noncompetitive inhibition of CYP1A1 and CYP1B1 enzymes. Also, nonlinear regression analysis and Dixon plots showed that the R- and S-analogues have K_I values of 15.7 ± 4.4 and 6.1 ± 1.5 nM for CYP1A1 and 26.1 ± 2.9 and 9.1 ± 1.8 nM for CYP1B1, respectively. Moreover, both analogues were able to inhibit EROD and MROD activities in a cell-based assay and human liver microsomes.

CONCLUSIONS

Therefore, the synthetic analogues of 19-HETE could be considered as a novel therapeutic approach in the treatment of cancer and CVD.

Tissue-specific expression and activity of cytochrome P450 1A and 3A in rainbow trout (Oncorhynchus mykiss)

Piscine cytochrome P450 (CYP) enzymes play an important role in the metabolism of xenobiotics. Xenobiotics often act as inducers of CYP1A1 and CYP3A expression and activity in fish. We compared constitutive mRNA expression of CYP1A1, CYP3A27, and CYP3A45 and catalytic activity of CYP1A (7-ethoxyresorufin-O-deethylation, EROD) and CYP3A-like (benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylation, BFCOD) enzymes in the following six rainbow trout tissues: liver, gill, heart, brain, intestine, and gonad. mRNA expression and activity were present in all investigated tissues. The CYP1A1 mRNA expression was higher in the liver, gill, heart, and brain compared to gonad and intestine. The intestine was the main site of CYP3A27 and CYP3A45 expression. The highest EROD and BFCOD activity was observed in liver tissue followed in descending order by heart, brain, gill, intestine, and gonad. Such differences might be related to the role of CYP physiological functions in the specific tissue. Rainbow trout exposure to 50 mg/kg of β-naphthoflavone for 48 h resulted in a 7.5- and 5.9-fold increase in liver EROD and BFCOD activity, respectively. In vitro EROD activity inhibition with ellipticine showed tissue-specific inhibition, while ketoconazole decreased BFCOD activity by 50-98 % in all tissues. Further studies are needed to identify all CYP isoforms that are responsible for these activities and modes of regulation.

Induction of Cyp450 enzymes by 4-thiazolidinone-based derivatives in 3T3-L1 cells in vitro

4-Thiazolidinones and related derivatives are regarded as privileged structures in medicinal chemistry and a source of new drug-like compounds. To date it is known that thiazolidinones are able to induce CYP1A1 activity in 3T3-L1 cells. Therefore, to extend the knowledge of the mechanism of thiazolidinones in the cell, four chemically synthesized heterocycles were tested on 3T3-L1 cells. The 3T3-L1 cells were exposed to Les-2194, Les-3640, Les-5935, and Les-6166. Our study showed that 1 μM βNF, Les-2194, and Les-6166 decreased the expression of Ahr mRNA. In turn, βNF, Les-2194, and Les-3640 increased the Cyp1a1 mRNA expression at the same time interval. On the other hand, Les-5935 was found to decrease the Cyp1a1 mRNA expression. Interestingly, the expression of Cyp1a2 mRNA was activated only by βNF and Les-2194. The expression of Cyp1b1 mRNA in the 3T3 cell line increased after the βNF and Les-2194 treatment but declined after the exposure to Les-5935 and Les-6166. Moreover, the Les-2194 and Les-5935 compounds were shown to increase the activity of EROD, MROD, and PROD. Les-3640 increased the activity of EROD and decreased the activity of PROD. In turn, the treatment with Les-6166 resulted in an increase in the activity of EROD and a decrease in the activity of MROD and PROD in the 3T3-L1 cells.

Digital Microfluidics-Enabled Analysis of Individual Variation in Liver Cytochrome P450 Activity

The superfamily of hepatic cytochrome P450 (CYP) enzymes is responsible for the intrinsic clearance of the majority of therapeutic drugs in humans. However, the kinetics of drug clearance via CYPs varies significantly among individuals due to both genetic and external factors, and the enzyme amount and function are also largely impacted by many liver diseases. In this study, we developed a new methodology, based on digital microfluidics (DMF), for rapid determination of individual alterations in CYP activity from human-derived liver samples in biopsy-scale. The assay employs human liver microsomes (HLMs), immobilized on magnetic beads to facilitate determination of the activity of microsomal CYP enzymes in a parallelized system at physiological temperature. The thermal control is achieved with the help of a custom-designed, inkjet-printed microheater array modularly integrated with the DMF platform. The CYP activities are determined with the help of prefluorescent, enzyme-selective model compounds by quantifying the respective fluorescent metabolites based on optical readout in situ. The selectivity and sensitivity of the assay was established for four different CYP model reactions, and the diagnostic concept was validated by determining the interindividual variation in one of the four model reaction activities, that is, ethoxyresorufin O-deethylation (CYP1A1/2), between five donors. Overall, the developed protocol consumes only about 15 μg microsomal protein per assay. It is thus technically adaptable to screening of individual differences in CYP enzyme function from biopsy-scale liver samples in an automated fashion, so as to support tailoring of medical therapies, for example, in the context of liver disease diagnosis.

High-Meat-Protein High-Fat Diet Induced Dysbiosis of Gut Microbiota and Tryptophan Metabolism in Wistar Rats

Meat-diet-induced changes in gut microbiota are often accompanied with the development of various metabolic and inflammatory disorders. The exact biochemical mechanism underlying these effects is not well elucidated. This study aims to evaluate how meat proteins in high-fat diets affect tryptophan metabolism in rats. The high-chicken-protein (HFHCH) or high-pork-protein (HFHP) diets increased levels of skatole and indole in cecal and colonic contents, feces, and subcutaneous adipose tissue. The HFHCH and HFHP diets also increased the abundance of Lactobacillus, the Family XIII AD3011 group, and Desulfovibrio in the cecum and colon, which may be involved in the production of skatole and indole. Additionally, high-meat-protein diets induced lower activity of skatole- and indole-metabolizing enzyme CYP2E1 in liver compared with low-meat-protein diets. This work highlights the negative impact of high meat proteins on physiological responses by inducing dysbiosis of gut microbiota and tryptophan metabolism.

Quality screening of the Lagos lagoon sediment by assessing the cytotoxicity and toxicological responses of rat hepatoma H4IIE and fish PLHC-1 cell-lines using different extraction approaches

In this study, sediment samples from Makoko and Ikorodu sites of the Lagos lagoon (Nigeria) were screened for toxicological responses on mammalian and fish cell lines using different extraction methods. Rat hepatoma H4IIE and fish PLHC-1 cell-lines were exposed to serial dilutions of the elutriate, polar and non-polar extracts. We evaluated exposed cells for cytotoxicity and aryl hydrocarbon receptor (AhR)-mediated toxicity. Cells exposed to polar and water extracts from Makoko and Ikorodu showed viability percentage of >80% at 48 h. On the other hand, exposure to the non-polar extracts exhibited cell viability of 50-60% at all tested dilutions. For both cell lines, a significant concentration-dependent induction of cyp1a mRNA was observed after exposure to the different extracts from both sites. Interestingly, the extracts affected functional enzymes differently for both cell lines. For H4IIE cells, while EROD activity paralleled cyp1a mRNA expression patterns, MROD showed significant concentration-specific reduction in cells exposed to polar and water extracts. On the contrary, while the MROD activity paralleled cyp1a mRNA, EROD activity was significantly inhibited in PLHC-1 cells exposed to water-, polar and non-polar extracts from both sites. These observations paralleled sediments PAH contamination burden from the study sites as revealed by co-relation analysis. In conclusion, although the different extracts did not exert high cytotoxic effects (except the non-polar) at the tested concentrations, they significantly modulated phase I biotransformation responses, showing that the studied sediments contain complex chemical mixture in the different extracts, with potential for overt physiological and general health consequences.

Neurovascular Drug Biotransformation Machinery in Focal Human Epilepsies: Brain CYP3A4 Correlates with Seizure Frequency and Antiepileptic Drug Therapy

Pharmacoresistance is a major clinical challenge for approximately 30% of patients with epilepsy. Previous studies indicate nuclear receptors (NRs), drug efflux transporters, and cytochrome P450 enzymes (CYPs) control drug passage across the blood-brain barrier (BBB) in drug-resistant epilepsy. Here, we (1) evaluate BBB changes, neurovascular nuclear receptors, and drug transporters in lesional/epileptic (EPI) and non-lesional/non-epileptic (NON-EPI) regions of the same brain, (2) examine regional CYP expression and activity, and (3) investigate the association among CYP brain expression, seizure frequency, duration of epilepsy, and antiepileptic drug (AED) combination. We used surgically resected brain specimens from patients with medically intractable epilepsy (n = 22) where the epileptogenic loci were well-characterized by invasive and non-invasive methods; histology confirmed distinction of small NON-EPI regions from EPI tissues. NRs, transporters, CYPs, and tight-junction proteins were assessed by western blots/immunohistochemistry, and CYP metabolic activity was determined and compared. The relationship of CYP expression with seizure frequency, duration of epilepsy, and prescribed AEDs was evaluated. Decreased BBB tight-junction proteins accompanied IgG leakage in EPI regions and correlated with upregulated NR and efflux transporter levels. CYP expression and activity significantly increased in EPI compared to NON-EPI tissues. Change in EPI and NON-EPI CYP3A4 expression increased in patients taking AEDs that were CYP substrates, was downregulated when CYP- and non-CYP-substrate AEDs were given together, and correlated with seizure frequency. Our studies suggest focal neurovascular CYP-NR-transporter alterations, as demonstrated by the relationship of seizure frequency and AED combination to brain CYP3A4, might together impact biotransformation machinery of human pharmacoresistant epilepsy.

4-n-nonylphenol degradation by the genus Metarhizium with cytochrome P450 involvement

In this study, the ability of 4-n-nonylphenol (4-n-NP) elimination by fungal species belonging to the genus Metarhizium was investigated. The occurrence of 35 metabolites from 4-n-NP degradation was confirmed. For the first time, based on the obtained results, the 4-n-NP biodegradation pathway distinctive for the genus Metarhizium was proposed. Principal Component Analysis (PCA) indicated that despite the similar elimination pathway in all the examined Metarhizium species, there are significant differences in the kinetics of degradation of 4-n-NP. Oxidation of the terminal methyl group of the aliphatic chain leading to the formation of carboxylic acids coupled with the removal of terminal carbon is characteristic of M. robertsii and M. guizhouense, whereas metabolites with a hydroxyl group in the distal part of the nonyl chain distinguish M. lepidiotae and M. majus. Additionally, this study verified the participation of cytochrome P450 in the elimination of the xenobiotic by Metarhizium as experimentally proven for M. robertsii.

Evaluation of the bioaccumulation potential of selected alternative brominated flame retardants in marine fish using in vitro metabolic transformation rates

The global consumption of alternative brominated flame retardants (BFRs) has increased with the restriction of the first generation BFRs such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). However, many alternative BFRs are suspected to be persistent in the environment and possibly bioaccumulative after their release into the environment because of their chemical properties, which are similar to those of the already banned BFRs. In this study, the bioaccumulation potential of selected alternative BFRs (1,2-bis(2,4,6‑tribromophenoxy)ethane (BTBPE), 1,2,3,4,5,6‑hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), 2,3,4,5,6‑pentabromotoluene (PBT), 2‑ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and 2,3,4,5‑tetrabromo-6-chlorotoluene (TBCT)) was evaluated. The in vitro depletion rate constants (k_depl) were measured for the alternative BFRs using liver S9 fractions isolated from five marine fish species (Epinephelus septemfasciatus, Konosirus punctatus, Lateolabrax japonicus, Mugil cephalus, and Sebastes schlegelii) that inhabit the oceans off the Korean coast. The measured k_depl values were converted to in vitro intrinsic clearance rate constants (CL_{in vitro}) to estimate whole-body metabolic rate constants (k_MET) using an in vitro to in vivo extrapolation (IVIVE) model. Finally, the bioconcentration factors (BCF) were determined using a one-compartment model. The transformation kinetics for obtaining k_depl agreed well with first-order chemical kinetics, regardless of initial BFR concentrations. The values of CL_{in vitro} were lower in the selected marine fish species than those in freshwater fish species, implying slower metabolic transformation. The derived BCF values based on the total concentration in water (BCF_TOT) ranged from 16 (TBB in M. cephalus) to 27,000 (HBB in K. punctatus). The BCF values for HBB and PBT were >2000 except for those in M. cephalus suggesting further investigation of BCF values of BFRs whose log K_OW is between 6 and 7.

The effects of sewage treatment plant effluents on hepatic and intestinal biomarkers in common carp (Cyprinus carpio)

Sewage treatment plants (STPs) are one of the major source of pharmaceuticals and personal care products in the aquatic environment. Generally, the effects of individual chemicals on fish are studied under laboratory conditions, which leads to results that are potentially not realistic regarding the effects of these chemicals under environmental conditions. Therefore, in this study, common carps were held in exposed pond that receive water from STP effluents for 360 days under natural conditions. Elimination of xenobiotics starts in the fish intestine, in which the microbial community strongly influences its function. Moreover, the fish intestine functions as crucial organ for absorbing lipids and fatty acids (FA), with consequent transport to the liver where their metabolism occurs. The liver is the primary organ performing xenobiotic metabolism in fish, and therefore, the presence of pollutants may interact with the metabolism of FA. The catalytic activity of CYP1A and CYP3A-like enzymes, their gene expression, FA composition and intestinal microbiome consortia were measured. The catalytic activity of enzymes and their gene and protein expression, were induced in hepatic and intestinal tissues of fish from the exposed pond. Also, fish from the exposed pond had different compositions of FA than those from the control pond: concentration of 18:1 n-9 and 18:2 n-6 were significantly elevated and the longer chain n-3 FA 20:5 n-3, 22:5 n-3 and 22:6 n-3 were significantly lowered. There were clear differences among microbiome consortia in fish intestines across control and exposed groups. Microbiome taxa measured in exposed fish were also associated with those found in STP activated sludge. This study reveals that treated STP water, which is assumed to be clean, affected measured biomarkers in common carp.

CYP1A1 activity in rainbow trout is inhibited by the environmental pollutant p-cresol

Naturally- and anthropogenically-produced cresols could pose serious risks to fish health. In this study, three piscine CYP isoforms were investigated for their abilities to interact with p-cresol. Therefore, the activity of 7-ethoxyresorufin-O-deethylase (EROD), 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylase (BFCOD), and p-nitrophenol hydroxylase (PNPH) were evaluated in the hepatic microsomes of juvenile rainbow trout. Results showed that EROD activity was inhibited in a competitive manner, BFCOD activity was inhibited in presence the highest tested p-cresol concentration and PNPH activity was not affected. These results indicate that p-cresol might affect the ability of fish to metabolize numerous aromatic hydrocarbons and dioxin compounds, which are present in the aquatic environment.

Effect of human pharmaceuticals common to aquatic environments on hepatic CYP1A and CYP3A-like activities in rainbow trout (Oncorhynchus mykiss): An in vitro study

This study examined the ability of several human pharmaceuticals to modulate hepatic piscine CYP-mediated monooxygenase activities. Effects of six pharmaceuticals: diclofenac, sulfamethoxazole, tramadol, carbamazepine, venlafaxine and nefazodone, were investigated in vitro in rainbow trout hepatic microsomes. The reactions of 7-ethoxyresorufin-O-deethylase (EROD) and benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylase (BFCOD), were used as markers for hepatic CYP1A and CYP3A-like activities, respectively. Our results showed that EROD and BFCOD activities were both affected by nefazodone. Nefazodone inhibited EROD in a dose dependent manner and was found to be a potent non-competitive inhibitor of EROD with a K_i value of 6.6 μM. BFCOD activity was inhibited non-competitively in the presence of nefazadone with K_i value of 30.7 μM. BFCOD activity was slightly reduced only by the highest concentration of carbamazepine. Diclofenac, sulfamethoxazole, tramadol, and venlafaxine did not affect the activity of either EROD or BFCOD. We further exposed microsomal fraction to mixtures of six pharmaceuticals to investigate potential inhibition. The results showed that EROD and BFCOD activity was inhibited on 94% and 80%, respectively at higher tested concentration. To our knowledge, this is the first report to demonstrate an inhibitory effect of nefazodone on hepatic CYP1A and CYP3A-like proteins in rainbow trout.

In vitro effects of diosmin, naringenin, quercetin and indole-3-carbinol on fish hepatic CYP1A1 in the presence of clotrimazole and dexamethasone

Phytochemicals are widely present in fruits, vegetables and other plants and have great health benefits owing to their antioxidant properties. They are naturally found in the aquatic environment as well as discharged from sewage treatment plants after their large consumption. Little is known about their impact on fish; particularly in light of their interactions with pharmaceuticals. Therefore, this study was designed to determine the effects of diosmin, naringenin, quercetin and idole-3-carbinol on CYP1A-dependent 7-ethoxyresorufin-O-deethylase (EROD) activity on rainbow trout hepatic microsomes in the presence of two pharmaceuticals: clotrimazole and dexamethasone. The interactions between the phytochemicals and pharmaceuticals used in this study were determined using a combination index. Hepatic microsomes were exposed to two concentrations (1-or 50 μM) of phytochemicals and pharmaceuticals separately and in combinations. Singly, clotrimazole inhibited EROD activity 40% and 90% of control, while dexamethasone did not. Naringenin and diosmin inhibited EROD activity alone up to 90% and 55% respectively, but activities were further inhibited in the presence of either pharmaceutical. The preliminary study of combinations of clotrimazole with phytochemicals primarily showed synergistic effects. While EROD activity was not inhibited in the presence of quercetin or indole-3-carbinol, significant and synergistic inhibition was detected when either of these was combined with clotrimazole or dexamethasone.

Nanofractionation Platform with Parallel Mass Spectrometry for Identification of CYP1A2 Inhibitors in Metabolic Mixtures

With early assessment of inhibitory properties of drug candidates and their circulating metabolites toward cytochrome P450 enzymes, drug attrition, especially later in the drug development process, can be decreased. Here we describe the development and validation of an at-line nanofractionation platform, which was applied for screening of CYP1A2 inhibitors in Phase I metabolic mixtures. With this platform, a metabolic mixture is separated by liquid chromatography (LC), followed by parallel nanofractionation on a microtiter well plate and mass spectrometry (MS) analysis. After solvent evaporation, all metabolites present in the nanofractionated mixture are assayed utilizing a fluorescence CYP1A2 inhibition bioassay performed on the plate. Next, a bioactivity chromatogram is constructed from the bioassay results. By peak shape and retention time correlation of the bioactivity peaks with the obtained MS data, CYP1A2-bioactive inhibiting metabolites can be identified. The method correctly evaluated the potency of five CYP1A2 inhibitors. Mixtures comprising potent inhibitors of CYP1A2 or in vitro-generated metabolites of ellipticine were evaluated for their inhibitory bioactivities. In both cases, good LC separation of all compounds was achieved and bioactivity data could be accurately correlated with the parallel recorded MS data. Generation and evaluation of Phase II metabolites of hydroxylated ellipticine was also pursued.

Vulnerability of marsh frog Pelophylax ridibundus to the typical wastewater effluents ibuprofen, triclosan and estrone, detected by multi-biomarker approach

Pharmaceutical and personal care products (PPCPs) are the environmental pollutants of growing concern. The aim of this study was to indicate the effects of typical PPCPs on the marsh frog Pelophylax ridibundus. We treated male frogs with waterborne ibuprofen (IBU, 250ng·L^-1), triclosan (TCS, 500ng·L^-1), or estrone (E1, 100ng·L^-1) for 14days. Common vulnerability of the frogs was detected from dramatic decrease of Zn, total and metalated metallothionein (MT) concentrations, Zn/Cu ratio, the elevation of activity of glutathione-S-transferase, cathepsin D and DNA instability in the liver, the depletion of cholinesterase in the brain and cortisol in the blood plasma in all exposures. Nevertheless, lipofuscin concentration in the liver was always decreased. The groups were best distinguished by cytochrome P450 (CYP450) activity determined by ELISA. The exposure to IBU caused lesser damage, but elevated the levels of oxyradicals and glutathione (GSH and GSSG) and lysosomal membrane instability. Exposures to TCS and E1 provoked the endocrine disturbance (increased levels of vitellogenin and thyrotropin in blood plasma), decreased lactate dehydrogenase activity and increased level of pyruvate in the liver. TCS caused the increase of GSSG by 7.3 times and lactate levels. Only E1 lead to decrease of deiodinase activity in the liver, activation of CYP450 and caspase-3 and efflux of cathepsin D from lysosomes. Spectrophotometric and ELISA assays of MTs and CYP450 gave distinct results in E1-group. Broad disruption of the hormonal pathways caused by E1 could be of concern for the health status of frogs in their habitats.

Skatole metabolites in urine as a biological marker of pigs with enhanced hepatic metabolism

Boar taint is a quality defect in meat, related to accumulation of skatole and androstenone in male pigs. The levels of skatole and its main metabolites in plasma and urine samples were measured with a validated liquid chromatography-MS method and related to activity of hepatic cytochrome P450 (CYP450) in order to identify 'fast metabolizing' pigs. Urine (n=46), blood (n=12), liver (n=25) and adipose tissue (n=46) were sampled from a total of 46 entire male pigs. Skatole levels in fat were negatively correlated to CYP2E1 activity and positively to 3-hydroxy-3-methyloxindole (HMOI), indole-3-carboxylic acid (ICA) and 2-aminoacetophenone in urine. HMOI and ICA levels in urine were the best predictors of high skatole levels in fat. In summary, the present study provided further evidence for the key role of CYP2E1 in skatole metabolism and suggested that measurement of HMOI and/or ICA in urine might provide information about skatole levels in live pigs.

Effect of taurine on chronic and acute liver injury: Focus on blood and brain ammonia

Hyperammonemia is associated with chronic and acute liver injury. There is no promising therapeutic agent against ammonia-induced complications. Hence, finding therapeutic molecules with safe profile of administration has clinical value. The present study was conducted to evaluate the role of taurine (TA) administration on plasma and brain ammonia and its consequent events in different models of chronic and acute liver injury and hyperammonemia. Bile duct ligated (BDL) rats were used as a model of chronic liver injury. Thioacetamide and acetaminophen-induced acute liver failure were used as acute liver injury models. A high level of ammonia was detected in blood and brain of experimental groups. An increase in brain ammonia level coincided with a decreased total locomotor activity of animals and significant changes in the biochemistry of blood and also liver tissue. TA administration (500 and 1000 mg/kg, i.p), effectively alleviated liver injury and its consequent events including rise in plasma and brain ammonia and brain edema. The data suggested that TA is not only a useful and safe agent to preserve liver function, but also prevented hyperammonemia as a deleterious consequence of acute and chronic liver injury.

Pigs in Toxicology

Both a rodent and a nonrodent species are required for evaluation in nonclinical safety studies conducted to support human clinical trials. Historically, dogs and nonhuman primates have been the nonrodent species of choice. Swine, especially the miniature swine or minipigs, are increasingly being used in preclinical safety as an alternate nonrodent species. The pig is an appropriate option for these toxicology studies based on metabolic pathways utilized in xenobiotic biotransformation. Both similarities and differences exist in phase I and phase II biotransformation pathways between humans and pigs. There are numerous breeds of pigs, yet only a few of these breeds are characterized with regard to both xenobiotic-metabolizing enzymes and background pathology findings. Some specific differences in these enzymes based on breed and sex are known. Although swine have been used extensively in biomedical research, there is also a paucity of information in the current literature detailing the incidence of background lesions and differences between commonly used breeds. Here, the xenobiotic-metabolizing enzymes are compared between humans and pigs, and minipig background pathology changes are reviewed with emphasis on breed differences.

2-Aminoacetophenone Is the Main Volatile Phase I Skatole Metabolite in Pietrain × Baden-Württemberg Hybrid Type Boars

Skatole metabolites have been considered as putative contributors to boar taint. Recently, 2-aminoacetophenone, a volatile phase I skatole metabolite, was identified in back fat samples from boars of Pietrain × Baden-Württemberg hybrid type. This paper addresses the question of the physiological origin of the observed 2-aminoacetophenone in these pigs. Microsomal fractions from nine boars were isolated, and formation of skatole metabolites was subsequently analyzed by stable-isotope dilution analysis (SIDA) using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS). Significant breed-related differences in phase I skatole metabolism were observed, explaining the high levels of 2-aminoacetophenone in Pietrain × Baden-Württemberg hybrid type boars.

In vitro gender-dependent inhibition of porcine cytochrome p450 activity by selected flavonoids and phenolic acids

We investigated gender-related differences in the ability of selected flavonoids and phenolic compounds to modify porcine hepatic CYP450-dependent activity. Using pools of microsomes from male and female pigs, the inhibition of the CYP families 1A, 2A, 2E1, and 3A was determined. The specific CYP activities were measured in the presence of the following selected compounds: rutin, myricetin, quercetin, isorhamnetin, p-coumaric acid, gallic acid, and caffeic acid. We determined that myricetin and isorhamnetin competitively inhibited porcine CYP1A activity in the microsomes from both male and female pigs but did not affect the CYP2A and CYP2E1. Additionally, isorhamnetin competitively inhibited CYP3A in both genders. Noncompetitive inhibition of CYP3A activity by myricetin was observed only in the microsomes from male pigs, whereas CYP3A in female pigs was not affected. Quercetin competitively inhibited CYP2E1 and CYP1A activity in the microsomes from male pigs and irreversibly CY3A in female pigs. No effect of quercetin on CYP2E1 was observed in the microsomes from female pigs. Neither phenolic acids nor rutin affected CYP450 activities. Taken together, our results suggest that the flavonoids myricetin, isorhamnetin, and quercetin may affect the activities of porcine CYP1A, CYP3A, and CYP2E1 in a gender-dependent manner.

Regulation of porcine hepatic cytochrome p450 - implication for boar taint

Cytochrome P450 (CYP450) is the major family of enzymes involved in the metabolism of several xenobiotic and endogenous compounds. Among substrates for CYP450 is the tryptophan metabolite skatole (3-methylindole), one of the major contributors to the off-odour associated with boar-tainted meat. The accumulation of skatole in pigs is highly dependent on the hepatic clearance by CYP450s. In recent years, the porcine CYP450 has attracted attention both in relation to meat quality and as a potential model for human CYP450. The molecular regulation of CYP450 mRNA expression is controlled by several nuclear receptors and transcription factors that are targets for numerous endogenously and exogenously produced agonists and antagonists. Moreover, CYP450 expression and activity are affected by factors such as age, gender and feeding. The regulation of porcine CYP450 has been suggested to have more similarities with human CYP450 than other animal models, including rodents. This article reviews the available data on porcine hepatic CYP450s and its implications for boar taint.

Comparable constitutive expression and activity of cytochrome P450 between the lobes of the porcine liver

Due to limited availability of human liver tissue for the study of cytochrome P450 (CYP450), porcine liver tissue has been suggested as an alternative source to prepare microsomes and hepatocytes. The porcine liver is made by four different lobes. The present study investigated the expression and activity of specific CYP450 isoforms in the four lobes, with the purpose to examine if one lobe of the porcine liver resembles the human more than others. Samples from the four major lobes were taken from female pigs and mRNA expression and activity of CYP1A, 2A, 2C, 2D, 2E and 3A determined. The results showed no differences in specific mRNA expression and activity of any of the investigated CYP450 isoforms. In conclusion, the study shows that all parts of the porcine liver are equally useful as model tissue.

Clotrimazole, but not dexamethasone, is a potent in vitro inhibitor of cytochrome P450 isoforms CYP1A and CYP3A in rainbow trout

The effects of clotrimazole (CLO) and dexamethasone (DEX), both detected in the aquatic environment, were assessed on inhibition of cytochrome P450 (CYP450) in hepatic microsomes of rainbow trout. Activity of three CYP450 isoforms: ethoxyresorufin O-deethylase (EROD; CYP1A), 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylase (BFCOD; CYP3A) and p-nitrophenol hydroxylase (PNPH; CYP2E1-like protein) was investigated in the presence of four concentrations of CLO and DEX. Clotrimazole in a concentration range of 1-100μM decreased the activity of EROD and BFCOD. The inhibition was reversible, as pre-incubation of the microsomes with CLO, before addition of the substrate, had no effect. EROD activity was non-competitively inhibited with a Ki of 0.5μM, and BFCOD activity revealed competitive inhibition with a Ki of 0.04μM. The relatively low Ki for CLO inhibition of EROD and BFCOD activity may indicate that the ability of CYP1A and CYP3A to metabolize xenobiotics is reduced in the presence of CLO. PNPH activity was not affected by CLO. DEX showed no inhibitory potency on any investigated reaction. CLO, but not DEX, inhibited EROD and BFCOD activity by different mechanisms.

Simultaneous determination of cytochrome P450 1A, 2A and 3A activities in porcine liver microsomes

The aim of this study was to develop a robust method for the simultaneous determination of the activities of three porcine CYP450 enzymes in hepatic microsomes. A cocktail consisting of three selective CYP450 probe substrates, 7-ethoxyresorufin (CYP1A), coumarin (CYP2A) and 7-benzyloxy-4-trifluoromethylcoumarin (BFC; CYP3A), was incubated with porcine liver microsomes. The presence of 7-ethoxyresorufin appears to significantly influence the kinetics of coumarin hydroxylation and BFC O-debenzylation. These results indicate that the use of 7-ethoxyresorufin in substrate cocktails together with coumarin and BFC should be avoided.

Expression and activities of hepatic cytochrome P450 (CYP1A, CYP2A and CYP2E1) in entire and castrated male pigs

This study aimed to provide further insights into the mechanism of in vivo regulation of cytochrome P450 (CYP450) 1A, 2A and 2E1 activities in pigs with different levels of testicular steroids. Hepatic mRNA and protein expression and enzymatic activity of CYP1A, CYP2A and CYP2E1 were compared between entire male and castrated pigs. Castration was performed either surgically or immunologically. The pigs were divided into four groups. In the first group, piglets were surgically castrated without anaesthesia. Immunological castration was performed by vaccination with Improvac® (Pfizer Ltd). Vaccinated pigs were subdivided into two groups according to the vaccination regimen: early and standard vaccination. Pigs in the early vaccination group were vaccinated when aged 11 and 15 weeks. Pigs in the standard vaccination group were vaccinated when aged 17 and 21 weeks. In the control group, pigs remained intact throughout the study. Hepatic CYP450 mRNA expression, measured by real-time RT-PCR, differed significantly between groups for all isoforms measured: CYP1A2 (P = 0.002), 2A (P = 0.000) and 2E1 (P = 0.002). Lower CYP450 mRNA in entire male pigs suggests suppression of CYP1A2, CYP2A and CYP2E1 by testicular steroids at the transcriptional level. However, this suppression was not always reflected in decreased protein expression and activities of these isoforms, suggesting that at least some CYP450s (e.g. CYP2E1) are regulated by a post-transcriptional mechanism.

Verapamil does not modify catalytic activity of CYP450 in rainbow trout after long-term exposure

Little is known about the effects of the cardiovascular drug verapamil (VRP) on metabolic processes in fish. Most calcium channel blockers including VRP are metabolized by cytochrome P450 (CYP450) enzymes. In this study we investigated the in vivo effect of VRP on some CYP450-mediated reactions in juvenile rainbow trout (Oncorhynchus mykiss). Fish were exposed to sublethal concentrations of VRP (0.5, 27 and 270 μg l(-1)) for 0, 21, and 42 day. The following CYP450-mediated reactions were studied in hepatic microsomes: O-dealkylation of ethoxyresorufin, methoxyresorufin, and pentoxyresorufin, hydroxylation of coumarin, tolbutamide, and p-nitrophenol, and O-debenzylation of 7-benzyloxy-4-trifluoromethylcoumarin. The amounts of products of these reactions did not differ among fish exposed to different levels of VRP and control fish. This suggests that the levels of VPR used did not alter catalytic activity of the selected CYP450 enzymes. In conclusion, none of the investigated CYP450-mediated reactions has potential as a biomarker to monitor VRP contamination of the aquatic environment.

Para-nitrophenol hydroxylation by fish liver microsomes: kinetics and effect of selective cytochrome P450 inhibitors

The study investigated the kinetics of p-nitrophenol hydroxylase (PNPH) in hepatic microsomes obtained from Atlantic salmon (Salmo salar). The selective inhibitors for some major mammalian cytochrome P450 (CYP450) were used to investigate the potential inhibitory effect on enzymes involved in p-nitrophenol hydroxylation. The following inhibitors were used: α-naphtoflavone (CYP1A), ellipticine (CYP1A1), furafylline (CYP1A2), 8-methoxypsoralen (8MOP, CYP2A6), 4-methylpyrazole (4MP, CYP2A6/2E1), diallyl sulfide (DAS, CYP2E1), and ketoconazole (CYP3A4). Additionally, the natural steroids 17-beta-oestraiol (E2) and testosterone were investigated as potential inhibitors of PNPH activity. It was found that formation of 4-nitrocatechol from p-nitrophenol followed monophasic kinetics with K(m) = 0.17 ± 0.03 mM and V(max) = 21.8 ± 1.05 pmol/min/mg. PNPH activity was competitively inhibited by diallyle sulfide with the K(i) value of 285.1 ± 94.2 μM μM and uncompetitively by ellipticine with K(i) value of 65.7 ± 7.8 μM. Moreover, E2 showed an ability to reduce PNPH activity through the mechanism-based inhibition mode. Our results suggest that hepatic microsomes from Atlantic salmon possess CYP2E1-like activity. However, specific isoform-mediated PNPH activity should be identified.

Gender-related differences in cytochrome P450 in porcine liver--implication for activity, expression and inhibition by testicular steroids

In pigs, the hepatic cytochrome P450 (CYP) 1A2, 2A and 2E1 activity is important in the regulation of skatole accumulation in adipose tissue. This study investigated gender-related differences in CYP1A2, 2A and 2E1 dependent activity, protein and mRNA expression. This study also investigated the gonadal steroid dependent inhibition of CYP activity in relation to gender and dietary composition. Microsomes were prepared from the liver of female and entire male pigs (Landrace × Yorkshire sire and Duroc boars) reared under similar conditions and slaughtered at an age of 164 days. A group of entire male pigs fed dried chicory root for 16 days prior to slaughter were included in the study. CYP activities were assessed by the use of probe substrates, whilst mRNA and protein expression were analysed by RT-PCR and Western blotting. Furthermore inhibition of CYP dependent activity by gonadal steroids was assessed in vitro. Microsomes from female pigs had greater CYP1A2 and 2A activity, as well as mRNA expression compared to entire male pigs. The antibodies used did not detected differences in protein expression. In vitro inhibition by 17β-oestradiol, oestrone, androstenone and 3β-OH androstenol of CYP2E1 activity in microsomes from entire male pigs as well as inhibition of CYP1A activity in chicory fed entire male pigs was observed. Apart from that no effect of steroids was shown. In conclusion, female pigs show greater CYP activity and mRNA expression. Including chicory in the diet for 16 days changed the gonadal steroid dependent inhibition of CYP activity in entire male pigs.

In vitro inhibition of porcine cytochrome P450 by 17β -estradiol and 17α-estradiol

Sexually mature pigs are known to possess high concentrations of testicular steroids, which have been shown to change the activities of cytochrome P450 in vitro. The aim of the present study was to evaluate the regulation of CYP1A and CYP2E1 activity by the steroids dihydrotestosterone (DHT), 3β-androstenol, 17β-estradiol and 17α-estradiol. Catalytic activities of 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD) were used as markers of CYP1A activities, while p-nitrophenol hydroxylase (PNPH) was used as a marker of CYP2E1 activities. Of the steroids tested, only 17β-estradiol and 17α-estradiol inhibited EROD and MROD activities. This inhibition was observed when a steroid concentration of 100 µM was used, while lower concentrations showed no inhibitory effect. PNPH activities were inhibited only by 100 µM of 17β-estradiol. The significance of these results in vivo is unknown because inhibition was only found when concentrations of estrogens higher than physiological levels were used. Nevertheless, the results provided further evidence on the important role of estrogens in regulation of porcine cytochrome P450 activities.

Hepatic ethoxy-, methoxy- and pentoxyresorufin O-dealkylase activities in Landrace and Duroc pigs stimulated with HCG

The effect of human chorionic gonadotropin (hCG) stimulation on the activities of ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD) and pentoxyresorufin O-depentylase (PROD) was studied in intact male pigs of purebred Landrace and Duroc breeds. Pigs were divided into four groups: two control groups of each breed, without hCG stimulation (n = 20 for each breed), and two experimental groups (n = 18 for each breed), with hCG stimulation (Pregnyl(®); N.V. Organon, Oss, The Netherlands, 30 IU/kg live weight). Pigs were slaughtered 3 days after hCG stimulation and enzyme activities were measured in hepatic microsomes using two approaches. First, only one substrate concentration was used for the analysis of each enzyme activity. We found that EROD activity was suppressed by hCG-stimulation in Landrace (p = 0.004), but not Duroc pigs (p > 0.05). Generally, EROD activity was higher in Duroc pigs compared with Landrace (p = 0.017). Methoxyresorufin O-demethylase and PROD activities did not differ between groups (p > 0.05). To further characterize EROD, MROD and PROD, enzyme kinetic studies were performed. V(max) values for EROD and MROD in both breeds were lower after hCG stimulation (p < 0.001 for Landrace and p < 0.05 for Duroc). Additionally, V(max) values for EROD significantly differed between Landrace and Duroc pigs being higher in Duroc pigs (p < 0.05). We concluded that both hCG stimulation and breed differences may be important in the regulation of EROD and MROD activities. This study provides the first data on the effect of hCG stimulation and thus high testicular steroids, on EROD, MROD and PROD activities. Further studies are needed to investigate individual CYP450 enzymes and their regulation in porcine tissues.

In vivo effect of dried chicory root (Cichorium intybus L.) on xenobiotica metabolising cytochrome P450 enzymes in porcine liver

Cytochrome P450 (CYP) enzymes are widely studied for their involvement in metabolism of drugs and endogenous compounds. In porcine liver, CYP1A2, 2A and 2E1 are important for the metabolism of skatole. Feeding chicory roots to pigs is known to decrease the skatole concentration in plasma and fat. In the present study we investigated the effect of chicory on CYP mRNA and protein expression, as well as their activity. Male pigs were feed dried chicory root for 16 days before liver samples were collected. By the use of RT-PCR and Western blotting we showed that the mRNA and protein expression of CYP1A2 and 2A were increased in chicory fed pigs. The mRNA expression of CYP2E1 was increased, while there was no effect on protein expression. Activity of CYP1A2 and 2A were increased in chicory feed pigs; this was not the case for CYP2E1 activity. In conclusion; oral administration of chicory root for 16 days to pigs increased the mRNA expression of CYP1A2, 2A and 2E1; and the protein expression of CYP1A2 and 2A. The activities of CYP1A2 and 2A were increased.

Comparison of cytochrome P450 concentrations and metabolic activities in porcine hepatic microsomes prepared with two different methods

In the present study, porcine liver microsomes prepared by a conventional ultracentrifugation method were compared with microsomes prepared by a calcium aggregation method. Protein concentrations and activities of several cytochrome P450 enzymes were measured. It was concluded that using a calcium aggregation method for microsome preparation resulted in lower activities of porcine 7-ethoxyresorufin O-deethylase (EROD), 7-methoxyresorufin O-demethylase (MROD), 7-pentoxyresorufin O-depentylase (PROD) and p-nitrophenol hydroxylase (PNPH), compared to ultracentrifugation. Protein concentrations of CYP1A2 and CYP2E1, measured by Western blot, were similar in the microsomes prepared by the two methods, whereas CYP2A protein concentrations were significantly lower in the microsomes prepared by the calcium aggregation method. The choice of homogenization buffer (TRIS with addition of either 250 mM sucrose or 2mM EDTA) did not affect either individual CYP450 protein concentration or the rates of CYP450-mediated reactions. Freeze/thawing of microsomes did not affect the activities of EROD, MROD, COH and PNPH in the microsomes, indicating the stability of the measured isoforms following three cycles of freezing/thawing. A reduction in the activity of PROD was observed after the third freeze/thawing cycles of the microsomes prepared by both methods.