Human cytochrome P-450 enzymes

Effects of developmental exposures to Bisphenol-A and Bisphenol-S on hepatocellular function in male Long-Evans rats

Bisphenol-S (BPS) is a current substitute for Bisphenol-A (BPA) in various commercial products (paper, plastics, protective can-coatings, etc.) used by all age groups globally. The current literature indicates that a drastic surge in pro-oxidants, pro-apoptotic, and pro-inflammatory biomarkers in combination with diminished mitochondrial activity can potentially decrease hepatic function leading to morbidity and mortality. Consequently, there are increasing public health concerns that substantial Bisphenol-mediated effects may impact hepatocellular functions, particularly in newborns exposed to BPA and BPS postnatally. However, the acute postnatal impact of BPA and BPS and the molecular mechanisms affecting hepatocellular functions are unknown. Therefore, the current study investigated the acute postnatal effect of BPA and BPS on the biomarkers of hepatocellular functions, including oxidative stress, inflammation, apoptosis, and mitochondrial activity in male Long-Evans rats. BPA and BPS (5 and 20 microgram/Liter (μg/L) of drinking water) were administered to 21-day-old male rats for 14 days. BPS had no significant effect on apoptosis, inflammation, and mitochondrial function but significantly reduced the reactive oxygen species (51-60 %, **p < 0.01) and nitrite content (36 %, *p < 0.05), exhibiting hepatoprotective effects. As expected, based on the current scientific literature, BPA induced significant hepatoxicity, as seen by significant glutathione depletion (50 %, *p < 0.05). The in-silico analysis indicated that BPS is effectively absorbed in the gastrointestinal tract without crossing the blood-brain barrier (whereas BPA crosses the blood-brain barrier) and is not a substrate of p-Glycoprotein and Cytochrome P450 enzymes. Thus, the current in-silico and in vivo findings revealed that acute postnatal exposure to BPS had no significant hepatotoxicity.

Development and validation of a sensitive and specific LC-MS/MS cocktail assay for CYP450 enzymes: Application to study the effect of catechin on rat hepatic CYP activity

A sensitive and specific liquid chromatography tandem mass spectrometric (LC-MS/MS) method that enables the simultaneous quantification of probe substrates and metabolites of cytochrome P450 (CYP) enzymes was developed and validated. These substrates (metabolites)-coumarin (7-hydroxycoumarin), tolbutamide (4-hydroxytolbutamide), S-mephenytoin (4-hydroxymephenytoin), dextromethorphan (dextrorphan), and testosterone (6β-hydroxytestosterone)-were utilized as markers for the activities of the major human CYP enzymes CYP2A6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, respectively. Analytes were separated on Kinetex C₁₈ column (2.1 × 50 mm, 5 μm) using a binary gradient mobile phase of 0.1% formic acid in water and 0.1% formic acid in acetonitrile. Metabolites were detected and quantified by MS using multiple reaction monitoring at m/z 163 → 107.2 for 7-hydroxycoumarin, m/z 235 → 150.1 for 4-hydroxymephenytoin, m/z 287 → 171 for 4-hydroxytolbutamide, m/z 258 → 157.1 for dextrorphan, m/z 305 → 269 for 6β-hydroxytestosterone, and m/z 237 → 194 for the internal standard. The assay exhibited good linearity over a range of 10-500 ng/mL with acceptable accuracy and precision criteria. As a proof of concept, the developed cocktail assay was successfully used to examine the potential impact of catechin on the activity of the major rat liver CYP enzymes.

Structural Perspectives of the CYP3A Family and Their Small Molecule Modulators in Drug Metabolism

Cytochrome P450 enzymes function to catalyze a wide range of reactions, many of which are critically important for drug response. Members of the human cytochrome P450 3A (CYP3A) family are particularly important in drug clearance, and they collectively metabolize more than half of all currently prescribed medications. The ability of these enzymes to bind a large and structurally diverse set of compounds increases the chances of their modulating or facilitating drug metabolism in unfavorable ways. Emerging evidence suggests that individual enzymes in the CYP3A family play discrete and important roles in catalysis and disease progression. Here we review the similarities and differences among CYP3A enzymes with regard to substrate recognition, metabolism, modulation by small molecules, and biological consequence, highlighting some of those with clinical significance. We also present structural perspectives to further characterize the basis of these comparisons.

Circatidal gene expression in the mangrove cricket Apteronemobius asahinai

The mangrove cricket Apteronemobius asahinai is endemic to mangrove forest floors. It shows circatidal rhythmicity, with a 12.6-h period of locomotor activity under constant conditions. Its free-running activity also has a circadian component; i.e. it is more active during the subjective night than during the day. In this study, we investigated rhythmic gene expression under constant darkness by RNA sequencing to identify genes controlled by the biological clock. Samples collected every 3 h for 48 h were analysed (one cricket per time-point). We identified 284 significant circatidal cycling transcripts (period length 12–15 h). Almost half of them were annotated with known genes in the NCBI nr database, including enzymes related to metabolic processes and molecular chaperones. There were less transcripts with circadian rhythmicity than with circatidal rhythmicity, and the expression of core circadian clock genes did not show significant rhythmicity. This may reflect the nature of the mangrove cricket or may be due to the paucity of the sampling repeats: only two periods for circadian cycle with no replications. We evaluated for the first time the rhythmic transcriptome of an insect that shows circatidal rhythmic activity; our findings will contribute to future studies of circatidal clock genes.

Characterization of the Tissue Distribution of the Mouse Cyp2c Subfamily by Quantitative PCR Analysis

The CYP2C subfamily of the cytochrome P450 gene superfamily encodes heme-thiolate proteins that have a myriad of biologic functions. CYP2C proteins detoxify xenobiotics and metabolize endogenous lipids such as arachidonic acid to bioactive eicosanoids. We report new methods and results for the quantitative polymerase reaction (qPCR) analysis for the 15 members of the mouse Cyp2c subfamily (Cyp2c29, Cyp2c37, Cyp2c38, Cyp2c39, Cyp2c40, Cyp2c44, Cyp2c50, Cyp2c54, Cyp2c55, Cyp2c65, Cyp2c66, Cyp2c67, Cyp2c68, Cyp2c69, and Cyp2c70). Commercially available TaqMan primer/probe assays were compared with developed SYBR Green primer sets for specificity toward the mouse Cyp2c cDNAs and analysis of their tissue distribution. TaqMan primer/probe assays for 10 of the mouse Cyp2c isoforms were shown to be specific for their intended mouse Cyp2c cDNA; however, there were no TaqMan primer/probe assays specific for the mouse Cyp2c29, Cyp2c40, Cyp2c67, Cyp2c68, or Cyp2c69 transcripts. Each of the SYBR Green primer sets was specific for its intended mouse Cyp2c cDNA. The two qPCR methods confirmed similar patterns of Cyp2c tissue expression: Cyp2c37, Cyp2c38, Cyp2c39, Cyp2c44, Cyp2c50, Cyp2c54, and Cyp2c70 were most highly expressed in liver; Cyp2c55 was highly expressed in large intestine; Cyp2c65 was highly expressed in stomach, duodenum, and large intestine; and Cyp2c66 was highly expressed in both duodenum and jejunum. For isoforms without specific TaqMan primer/probe assays, the SYBR Green primer sets detected high level expression of Cyp2c29, Cyp2c40, Cyp2c67, Cyp2c68, and Cyp2c69 in the liver. Lower expression levels of the mouse Cyp2cs were also detected in other tissues.

Characterization and Interspecies Scaling of rhTNF-α Pharmacokinetics with Minimal Physiologically Based Pharmacokinetic Models

Tumor necrosis factor-α (TNF-α) is a soluble cytokine and target of specific monoclonal antibodies (mAbs) and other biologic agents used in the treatment of inflammatory diseases. These biologics exert their pharmacological effects through binding and neutralizing TNF-α, and thus they prevent TNF-α from interacting with its cell surface receptors. The magnitude of the pharmacological effects is governed not only by the pharmacokinetics (PK) of mAbs, but also by the kinetic fate of TNF-α We have examined the pharmacokinetics of recombinant human TNF-α (rhTNF-α) in rats at low doses and quantitatively characterized its pharmacokinetic features with a minimal physiologically based pharmacokinetic model. Our experimental and literature-digitalized PK data of rhTNF-α in rats across a wide range of doses were applied to global model fitting. rhTNF-α exhibits permeability rate-limited tissue distribution and its elimination is comprised of a saturable clearance pathway mediated by tumor necrosis factor receptor binding and disposition and renal filtration. The resulting model integrated with classic allometry was further used for interspecies PK scaling and resulted in model predictions that agreed well with experimental measurements in monkeys. In addition, a semimechanistic model was proposed and applied to explore the absorption kinetics of rhTNF-α following s.c. and other routes of administration. The model suggests substantial presystemic degradation of rhTNF-α for s.c. and i.m. routes and considerable lymph uptake contributing to the overall systemic absorption through the stomach wall and gastrointestinal wall routes of dosing. This report provides comprehensive modeling and key insights into the complexities of absorption and disposition of a major cytokine.

Cytochrome P450 Organization and Function Are Modulated by Endoplasmic Reticulum Phospholipid Heterogeneity

Cytochrome P450s (P450s) comprise a superfamily of proteins that catalyze numerous monooxygenase reactions in animals, plants, and bacteria. In eukaryotic organisms, these proteins not only carry out reactions necessary for the metabolism of endogenous compounds, but they are also important in the oxidation of exogenous drugs and other foreign compounds. Eukaryotic P450 system proteins generally reside in membranes, primarily the endoplasmic reticulum or the mitochondrial membrane. These membranes provide a scaffold for the P450 system proteins that facilitate interactions with their redox partners as well as other P450s. This review focuses on the ability of specific lipid components to influence P450 activities, as well as the role of the membrane in P450 function. These studies have shown that P450s and NADPH-cytochrome P450 reductase appear to selectively associate with specific phospholipids and that these lipid-protein interactions influence P450 activities. Finally, because of the heterogeneous nature of the endoplasmic reticulum as well as other biologic membranes, the phospholipids are not arranged randomly but associate to generate lipid microdomains. Together, these characteristics can affect P450 function by 1) altering the conformation of the proteins, 2) influencing the P450 interactions with their redox partners, and 3) affecting the localization of the proteins into specific membrane microdomains.

Environmentally persistent free radical-containing particulate matter competitively inhibits metabolism by cytochrome P450 1A2

Combustion processes generate different types of particulate matter (PM) that can have deleterious effects on the pulmonary and cardiovascular systems. Environmentally persistent free radicals (EPFRs) represent a type of particulate matter that is generated after combustion of environmental wastes in the presence of redox-active metals and aromatic hydrocarbons. Cytochromes P450 (P450/CYP) are membrane-bound enzymes that are essential for the phase I metabolism of most lipophilic xenobiotics. The EPFR formed by chemisorption of 2-monochlorophenol to silica containing 5% copper oxide (MCP230) has been shown to generally inhibit the activities of different forms of P450s without affecting those of cytochrome P450 reductase and heme oxygenase-1. The mechanism of inhibition of rat liver microsomal CYP2D2 and purified rabbit CYP2B4 by MCP230 has been shown previously to be noncompetitive with respect to substrate. In this study, MCP230 was shown to competitively inhibit metabolism of 7-benzyl-4-trifluoromethylcoumarin and 7-ethoxyresorufin by the purified, reconstituted rabbit CYP1A2. MCP230 is at least 5- and 50-fold more potent as an inhibitor of CYP1A2 than silica containing 5% copper oxide and silica, respectively. Thus, even though PM generally inhibit multiple forms of P450, PM interacts differently with the forms of P450 resulting in different mechanisms of inhibition. P450s function as oligomeric complexes within the membrane. We also determined the mechanism by which PM inhibited metabolism by the mixed CYP1A2-CYP2B4 complex and found that the mechanism was purely competitive suggesting that the CYP2B4 is dramatically inhibited when bound to CYP1A2.

Inhibition of cytochrome P450 2B4 by environmentally persistent free radical-containing particulate matter

Combustion processes generate particulate matter (PM) that can affect human health. The presence of redox-active metals and aromatic hydrocarbons in the post-combustion regions results in the formation of air-stable, environmentally persistent free radicals (EPFRs) on entrained particles. Exposure to EPFRs has been shown to negatively influence pulmonary and cardiovascular functions. Cytochromes P450 (P450/CYP) are endoplasmic reticulum resident proteins that are responsible for the metabolism of foreign compounds. Previously, it was shown that model EPFRs, generated by exposure of silica containing 5% copper oxide (CuO-Si) to either dicholorobenzene (DCB230) or 2-monochlorophenol (MCP230) at ≥ 230 °C, inhibited six forms of P450 in rat liver microsomes (Toxicol. Appl. Pharmacol. (2014) 277:200-209). In this study, the inhibition of P450 by MCP230 was examined in more detail by measuring its effect on the rate of metabolism of 7-ethoxy-4-trifluoromethylcoumarin (7EFC) and 7-benzyloxyresorufin (7BRF) by the purified, reconstituted CYP2B4 system. MCP230 inhibited the CYP2B4-mediated metabolism of 7EFC at least 10-fold more potently than non-EPFR controls (CuO-Si, silica, and silica generated from heating silica and MCP at 50 °C, so that EPFRs were not formed (MCP50)). The inhibition by EPFRs was specific for the P450 and did not affect the ability of the redox partner, P450 reductase (CPR) from reducing cytochrome c. All of the PM inhibited CYP2B4-mediated metabolism noncompetitively with respect to substrate. When CYP2B4-mediated metabolism of 7EFC was measured as a function of the CPR concentration, the mechanism of inhibition was competitive. EPFRs likely inhibit CYP2B4-mediated substrate metabolism by physically disrupting the CPR·P450 complex.

Role of CYP3A in regulating hepatic clearance and hepatotoxicity of triptolide in rat liver microsomes and sandwich-cultured hepatocytes

Triptolide (TP) is an active component of Tripterygium wilfordii Hook. F and widely used to treat autoimmune and inflammatory diseases. It has been demonstrated that cytochrome P450 (CYP) are involved in the metabolism of TP. However, the underlying mechanisms of TP-induced toxicity mediated by hepatic CYP have not been well delineated. In this study, rat liver microsomes (RLM) and sandwich-cultured rat hepatocytes (SCRH) were used to identify the mechanism involving the CYP3A inhibition by TP and to evaluate TP-induced liver damage after CYP3A modulation by the known inhibitor, ketoconazole, and the known inducer, dexamethasone. The results showed that TP itself had a time- and concentration-dependent inhibitory effect on CYP3A. When the CYP3A inhibitor and inducer were added, the enzyme activity and hepatotoxicity changed significantly. The enzyme inducer increased CYP3A activity and decreased the metabolic half life (t1/2) of TP when compared to the control group, while the enzyme inhibitor had an opposite effect. Our findings reveal that TP is a weak CYP3A inhibitor involving the time-dependent inhibition mechanism. The induction or inhibition of CYP3A played an important role in TP-induced hepatotoxicity. Clinicians should be aware of the metabolic characteristics of TP to maximize therapeutic efficacy and reduce TP-induced toxicity.

Determination of cytochrome P450 enzymes involved in the metabolism of (-)-terpinen-4-ol by human liver microsomes

The in vitro metabolism of (-)-terpinen-4-ol was examined in human liver microsomes and recombinant enzymes. The biotransformation of (-)-terpinen-4-ol was investigated by gas chromatography-mass spectrometry. (-)-Terpinen-4-ol was found to be oxidized to (-)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol, major metabolic product by human liver microsomal P450 enzymes. The formation of metabolites of (-)-terpinen-4-ol was determined by relative abundance of mass fragments and retention times on GC. CYP2A6 in human liver microsomes was a major enzyme involved in the oxidation of (-)-terpinen-4-ol by human liver microsomes, based on the following lines of evidence. First, of 11 recombinant human P450 enzymes tested, CYP2A6 had the highest activity for oxidation of (-)-terpinen-4-ol. Second, oxidation of (-)-terpinen-4-ol was inhibited by (+)-menthofuran. Finally, there was a good correlation between CYP2A6 maker activity and (-)-terpinen-4-ol oxidation activities in liver microsomes of 10 human samples. Kinetic analysis showed that the V(max)/K(m) values for (-)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol catalysed by liver microsomes of human sample HH-18 was 2.49 μL/min/nmol. Human recombinant CYP2A6 catalysed (-)-(1S,2R,4R)-1,2-epoxy-p-menthan-4-ol with V(max) values of 13.9 nmol/min/nmol P450 and apparent K(m) values of 91 μM.

Metabolism of (+)-terpinen-4-ol by cytochrome P450 enzymes in human liver microsomes

We examined the in vitro metabolism of (+)-terpinen-4-ol by human liver microsomes and recombinant enzymes. The biotransformation of (+)-terpinen-4-ol was investigated by gas chromatography-mass spectrometry (GC-MS). (+)-Terpinen-4-ol was found to be oxidized to (+)-(1R,2S,4S)-1,2-epoxy-p-menthan-4-ol, (+)-(1S,2R,4S)-1,2-epoxy-p-menthan-4-ol, and (4S)-p-menth-1-en-4,8-diol by human liver microsomal P450 enzymes. The identities of (+)-terpinen-4-ol metabolites were determined through the relative abundance of mass fragments and retention times on GC-MS. Of 11 recombinant human P450 enzymes tested, CYP1A2, CYP2A6, and CYP3A4 were found to catalyze the oxidation of (+)-terpinen-4-ol. Based on several lines of evidence, CYP2A6 and CYP3A4 were determined to be major enzymes involved in the oxidation of (+)-terpinen-4-ol by human liver microsomes. First, of the 11 recombinant human P450 enzymes tested, CYP1A2, CYP2A6 and CYP3A4 catalyzed oxidation of (+)-terpinen-4-ol. Second, oxidation of (+)-terpinen-4-ol was inhibited by (+)-menthofuran and ketoconazole, inhibitors known to be specific for these enzymes. Finally, there was a good correlation between CYP2A6 and CYP3A4 activities and (+)-terpinen-4-ol oxidation activities in the 10 human liver microsomes.

Ritonavir inhibits the two main prasugrel bioactivation pathways in vitro: a potential drug-drug interaction in HIV patients

Prasugrel is an antiplatelet prodrug used in patients with acute coronary syndrome. Prasugrel is mainly bioactivated by cytochromes P450 3A4/5 and CYP2B6. HIV patients are at risk of cardiovascular disease, and the protease inhibitor ritonavir is a potent inhibitor of these 2 CYPs. The aim of this in vitro study was to determine the impact of ritonavir in prasugrel metabolism. Human liver microsomes (HLMs) and recombinant microsomes were used to identify the enzymes responsible for the bioactivation of prasugrel. Prasugrel concentrations of 5 to 200 μM were used for Km determination. Inhibition by ritonavir was characterized using HLMs at concentrations of 0.1 to 30 μM. Prasugrel active metabolite determination was performed with a validated liquid chromatography-mass spectrometry method. Using recombinant microsomes, prasugrel biotransformation was mainly performed by CYP2B6, CYP2D6, CYP2C19, CYP3A4, and CYP3A5. With specific inhibitors of CYP3A, CYP2B6, CYP2D6, CYP2C9, and CYP2C19, active metabolite production was decreased by 38% ± 15% with 4-(4-chlorobenzyl)pyridine (CYP2B6 inhibitor) and by 45 ± 16% with ketoconazole (CYP3A inhibitor). The Km value for prasugrel metabolism in HLMs was determined to be 92.5 μM. Ritonavir at 0.1 to 30 μM was shown to be a potent dose-dependent inhibitor of prasugrel. In this in-vitro study, we found a potent inhibition of prasugrel bioactivation by ritonavir compared to the specific inhibitors of CYP3A and CYP2B6 due to the simultaneous inhibition of CYP2B6 and CYP3A by ritonavir. This finding suggests a potential significant drug-drug interaction between these two drugs.

Metabolism of (+)- and (-)-menthols by CYP2A6 in human liver microsomes

The in vitro metabolism of (+)-(1S,3S,4R) and (-)-(1R,3R,4S)-menthol enantiomers was examined by incubation with human liver microsomes, and the oxidative metabolites thus formed were analyzed using gas chromatography-mass spectrometry (GC-MS). The (+)- and (-)-menthols were found to be oxidized to the respective (+)-(1S,3S,4S)- and (-)-(1R,3R,4R)-trans-p-menthane-3,8-diol derivatives by human liver microsomal P450 enzymes. Cytochrome P450 (CYP) 2A6 was determined to be the major enzyme involved in the hydroxylation of (+)- and (-)-menthols by human liver microsomes on the basis of the following lines of evidence. First, of 11 recombinant human P450 enzymes tested, CYP2A6 catalyzed the oxidation of (+)- and (-)-menthols. Second, oxidation of (+)- and (-)-menthols was inhibited by (+)-menthofuran and anti-CYP2A6 antibody. Finally, (+)- and (-)-menthol activities were found to correlate with contents of CYP2A6 in liver microsomes of 9 human samples.

Evaluation of impairment of DNA integrity in marine gastropods (Cronia contracta) as a biomarker of genotoxic contaminants in coastal water around Goa, West coast of India

The measurement of the impairment of DNA in marine gastropod (Cronia contracta) provides an insight into the genotoxic effects of contaminants on marine organisms along the Goa coast. The impact of genotoxic contaminants on Goan coastal environment was evaluated in terms of the loss of DNA integrity (expressed as the value of 'I') in marine snails with respect to those from the reference site (Palolem) over a period from April 2004 to May 2005 using the technique of alkaline unwinding assay. The DNA integrity in marine snails was found to be significantly damaged at Dona Paula (58%), Vasco (73.5%), and Velsao (48.5%) during the monsoon period (July-August 2004). Similar trend in the loss of DNA integrity in marine gastropods was also detected during the post-monsoon (November-December 2004) and the pre-monsoon (April-May 2005) periods. The low integrities of DNA in marine gastropods at these sites can be attributed to exposure to genotoxic contaminants especially polycyclic aromatic hydrocarbons (PAHs) and toxic heavy metals (Pb, Cd, Cu, Fe, and Mn) prevalent in the marine environment as evident by their accumulation in the tissues of the marine snails inhabiting different sites along the Goa coast. The contaminant-induced DNA strand breaks in marine snails increased significantly at Dona Paula, Vasco, and Velsao clearly indicating the levels of contamination of the sites by genotoxic compounds in those regions. The genotoxic effects of contaminants were further substantiated by detection of the impairment (39%) of DNA integrity in marine snails in a field experiment in which the same species of marine snails (C. contracta) collected from the reference site, Palolem, were deployed at Dona Paula and caged for 25 days for exposure to ambient marine pollutants. The impairment of DNA integrity in marine gastropods along the Goa coast can thus act as a biomarker for marine pollution monitoring of genotoxic contaminants.

Metabolism of (−)-fenchone by CYP2A6 and CYP2B6 in human liver microsomes

The in vitro metabolism of (-)-fenchone was examined in human liver microsomes and recombinant enzymes. The biotransformation of (-)-fenchone was investigated by gas chromatography-mass spectrometry. (-)-Fenchone was found to be oxidized to 6-exo-hydroxyfenchone, 6-endo-hydroxyfenchone and 10-hydroxyfenchone by human liver microsomal P450 enzymes. The formation of metabolites was determined by the relative abundance of mass fragments and retention times on gas chromatography (GC). CYP2A6 and CYP2B6 were major enzymes involved in the hydroxylation of (-)-fenchone by human liver microsomes, based on the following lines of evidence. First, of 11 recombinant human P450 enzymes tested, CYP2A6 and CYP2B6 catalysed the oxidation of (-)-fenchone. Second, oxidation of (-)-fenchone was inhibited by thioTEPA and (+)-menthofuran. Finally, there was a good correlation between CYP2A6, CYP2B6 contents and (-)-fenchone hydroxylation activities in liver microsomes of 11 human samples. CYP2A6 may be more important than CYP2B6 in human liver microsomes. Kinetic analysis showed that the Vmax/Km values for (-)-fenchone 6-endo-, 6-exo- and 10-hydroxylation catalysed by liver microsomes of human sample HG-03 were 24.3, 44.0 and 1.3nM(-1)min(-1) , respectively. Human recombinant CYP2A6 and CYP2B6 catalysed (-)-fenchone 6-exo-hydroxylation with Vmax values of 2.7 and 12.9 nmol min(-1) nmol(-1) P450 and apparent Km values of 0.18 and 0.15 mM and (-)-fenchone 6-endo-hydroxylation with Vmax values of 1.26 and 5.33nmolmin(-l) nmol(-1) P450 with apparent Km values of 0.29 and 0.26mM. (-)-Fenchone 10-hydroxylation was catalysed by CYP2B6 with Km and Vmax values of 0.2 mM and 10.66 nmol min(-1) nmol(-1) P450, respectively.

The induction of cytochrome P450 1A1 by sudan dyes

Azo dyes form a major class of chemically related compounds that are ubiquitous in foods, paints, printing inks, cosmetics, and also used as biological stains in histological and histopathological laboratories and clinics. Sudan I, sudan III, and sudan IV have been classified as category 3 carcinogens by International Agency for Research on Cancer. In this study, we investigated the difference between these three sudan dyes in induction of CYP1A1. We intraperitoneally treated Wistar rats with each of the three sudan dyes (I, III, and IV) for 3 days. Treatment of Wistar rats with sudan I produced the highest induction of CYP1A1 protein and mRNA whereas treatment of Wistar rats with sudan III produced about two third of CYP1A1 protein and mRNA than induced by sudan I. Furthermore, treatment of Wistar rats with sudan IV produced the lowest induction of CYP1A1 protein and mRNA which is about two third of that induced with sudan III treatment. We further investigated the effect of these sudan dyes on CYP1A1 transcription through investigating the xenobiotic response element (XRE) reporter activity in HepG2. The XRE reporter activity study showed the same trend of activity of sudan dyes comparable to the effects on CYP1A1 mRNA and protein. Immunohistochemical study revealed a differential pattern of distribution of CYP1A1 protein in rat liver among the three sudan dyes, apparent in the centrilobular and midzonal region with sudan III, progressing to panlobular with sudan I, whereas sudan IV showed a reversal of pattern of induction with the most intense staining in the periportal region. Our results suggest that there is an inverse relationship between the molecular size of the three sudan dyes and their ability to induce CYP1A1.

Effect of sodium ozagrel on the activity of rat CYP2D6

The aim of the study was to investigate the influence of sodium ozagrel on CYP2D6 (cytochromeP450 2D6) activity. The studies were performed with rat urine and liver microsomes and chemical inhibitors. The metabolism of dextromethorphan (dextrophan/dextromethorphan, dextrophan is a metabolite of dextromethorphan) and phenacetin (paracetamol/phenacetin, paracetamol is a metabolites of phenacetin) was used as probe to measure CYP2D6 and CYP1A2 (cytochromeP450 1A2) activity, respectively, determined by high-performance liquid chromatography (HPLC). The results showed that the metabolism of dextrophan/dextromethorphan in the sodium ozagrel-treated group (37 mg/kg) was higher than that of the control (P<0.05/6) in both in vivo and in vitro studies (r=0.9811). The rate of dextromethorphan metabolism was inhibited by sodium ozagrel and cimetidine in rat liver microsomes prepared from sodium ozagrel-treated rats and control rats group (sodium ozagrel IC(50)=26.5 microM, cimetidine IC(50)=86.3 microM in sodium ozagrel-treated group; sodium ozagrel IC(50)=13.9 microM, cimetidine IC(50)=24.8 microM in control group). The inhibitory effect of sodium ozagrel on CYP2D6 activity was noncompetitive with dextromethorphan with a K(i) of 324.94 microM. Kinetic parameters of the reactions were established by using Lineweaver-Burk with K(m)=0.67 mM and V(max)=2.13 pm/min/mg protein for the sodium ozagrel-treated group and K(m)=0.29 mM, and V(max)=0.91 pm/min/mg protein for the control group, respectively. The expression of CYP2D6 protein in the treated group was higher than that of the control group, as determined by Western blotting. The activity and expression of CYP1A2 did not show obvious differences in the control group and sodium ozagrel treated group. In conclusion, sodium ozagrel metabolism in rats is mediated primarily through CYP2D6, and sodium ozagrel can induce CYP2D6 activity.

A variant in the cytochrome p450 oxidoreductase gene is associated with breast cancer risk in African Americans

Variation in the cytochrome P450 oxidoreductase (POR) gene, a key regulator of type II cytochrome P450 enzymes, may affect exposure to endogenous steroid hormones and breast cancer risk. We sequenced the POR locus and tested candidate polymorphisms G5G and A503V for association with breast cancer risk among women in the Multiethnic Cohort Study (1,615 cases and 1,962 controls). The single nucleotide polymorphism (SNP) A503V was common in all racial/ethnic populations (minor allele frequency, > or =0.05) but was not associated with risk. SNP G5G (A --> G nucleotide change), which lies in a suggestive exonic splicing enhancer motif in exon 1, was common only in African Americans (minor allele frequency, 0.21) and the homozygous state was modestly associated with increased breast risk among all cases [345 cases and 426 controls; odds ratio (OR), 1.64; 95% confidence interval (CI), 0.89-3.04; P = 0.12] and among cases with advanced disease (95 cases: OR, 3.08; 95% CI, 1.42-6.70; P = 0.005). In an attempt to replicate this association, we genotyped SNP G5G in additional African American case-control studies (747 cases and 468 controls). Nonsignificant positive associations were noted with the GG genotype class in all studies. In the pooled analysis (1,038 cases and 877 controls with genotype data), the association was statistically significant among all cases (OR, 1.58; 95% CI, 1.04-2.41; P = 0.03) and stronger in those with advanced disease (411 cases and 877 controls; OR, 2.60; 95% CI, 1.56-4.34; P = 0.0002). These data suggest that African Americans harbor an allele at the POR locus that may increase breast cancer risk.

Urinary profile of 6 beta-hydroxycortisol in workers exposed to aluminum

The aim of the present study was to evaluate whether aluminum exposure may cause alterations of cytochrome P4503A4 by measuring the urinary excretion of 6 beta-hydroxycortisol as biomarker. There is a positive correlation between urinary 6 beta-hydroxycortisol and aluminum excretion (p < 0.05). The correlations between occupational duration, smoking habits, and age were also evaluated. The increased excretion of the biomarker suggests that this element may induce formation of cytochrome P 450 in exposed individuals.

Influences of 3-methylcholanthrene, phenobarbital and dexamethasone on xenobiotic metabolizing-related cytochrome P450 enzymes and steroidogenesis in human fetal adrenal cortical cells

AIM

To explore the influence and possible mechanism of xenobiotics on adrenal steroidogenesis during fetal development.

METHODS

Primary human fetal adrenal cortical cells were prepared, cultured and treated with 3-methylcholanthrene, phenobarbital and dexamethasone. The activities of 7-ethoxyresorufin O-dealkylase, benzphetamine, aminopyrine and erythromycin N-demethylases were measured by enzyme assays. At the same time, quantitative analysis of steroid hormones cortisol, aldosterone, testosterone and progesterone were carried out in cultural medium by radioimmunoassays.

RESULTS

The activities of benzphetamine and aminopyrine N-demethylase were increased in the cultural fetal adrenal cells treated with phenobarbital (0.25-1 mmol/L) for 24 h. Dexamethasone (25-100 micromol/L) also increased the activity of erythromycin N-demethylase. The activity of 7-ethoxyresorufin O-dealkylase was undetected in the cells treated without and with 3-methylcholanthrene (0.5-2 micromol/L). Meanwhile, the contents of medium cortisol, aldosterone and progesterone were decreased after treatment with 3-methylcholanthrene. Cortisol, aldosterone and progesterone concentrations were also slightly decreased with phenobarbital. Dexamethasone enhanced the productions of cortisol and progesterone remarkably. The trend of testosterone concentration was uncertain after 3-methylcholanthrene, phenobarbital or dexamethasone treatment.

CONCLUSION

3-Methylcholanthrene, phenobarbital or dexamethasone could interfere with the synthesis of cortisol, aldosterone and progesterone in primary human fetal adrenal cortical cells, which likely act through xenobiotic metabolizing-related cytochrome P450 isoform activation.

Metabolism of (+)-Fenchone by CYP2A6 and CYP2B6 in Human Liver Microsomes

The in vitro metabolism of (+)-fenchone was examined in human liver microsomes and recombinant enzymes. Biotransformation of (+)-fenchone was investigated by gas chromatography-mass spectrometry. (+)-Fenchone was found to be oxidized to 6-exo-hydroxyfenchone, 6-endo-hydroxyfenchone and 10-hydroxyfenchone by human liver microsomal P450 enzymes. The formation of metabolite of (+)-fenchone was determined by relative abundance of mass fragments and retention time with GC. CYP2A6 and CYP2B6 in human liver microsomes were major enzymes involved in the hydroxylation of (+)-fenchone, based on the following lines of evidence. First, of eleven recombinant human P450 enzymes tested, CYP2A6 and CYP2B6 catalyzed oxidation of (+)-fenchone. Second, oxidation of (+)-fenchone was inhibited by thioTEPA, (+)-menthofuran anti-CYP2A6 and anti-CYP2B6 antibodies. Finally, there was a good correlation between CYP2A6, CYP2B6 contents and (+)-fenchone hydroxylation activities in liver microsomes of 8 human samples.

Prostaglandin E2 down-regulation of cytochrome P-450 2B1 expression induced by phenobarbital is through EP2 receptor in rat hepatocytes

Cytochrome P-450 is an important bioactivation-detoxification system in vivo. Its expression is regulated by foreign chemicals and dietary factors, and lipids have been found to regulate its gene expression. We showed previously that prostaglandin E(2) (PGE(2)), a fatty acid metabolite, down-regulates cytochrome P-450 2B1 (CYP 2B1) expression induced by phenobarbital. The objective of the present study was to determine whether PGE(2) type 2 receptor (EP(2))-which is coupled to Gs-protein when bound by PGE(2), leading to cAMP production-is involved in this down-regulation. We also determined the possible roles of EP(2) downstream pathways in this down-regulation. We used a primary rat hepatocyte culture model in which EP(2) was shown to be present to study this question. The intracellular cAMP concentration in primary rat hepatocytes was significantly higher after treatment with 1microM PGE(2) than after treatment with 0, 0.01, or 0.1microM PGE(2). Butaprost, an EP(2) agonist, down-regulated CYP 2B1 expression in a dose-dependent manner. SQ22536, an adenylate cyclase inhibitor, reversed the down-regulation by PGE(2) as did H-89, a protein kinase A inhibitor. These results suggest that EP(2) and the downstream pathways of cAMP and protein kinase A are involved in the down-regulation of CYP 2B1 expression by PGE(2) in the presence of phenobarbital.

Risk of coronary artery disease associated with polymorphism of the cytochrome P450 epoxygenase CYP2J2

BACKGROUND

Cytochrome P450 (CYP) 2J2 is expressed in the vascular endothelium and metabolizes arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs). The EETs are potent endogenous vasodilators and inhibitors of vascular inflammation. However, it is not known whether genetic polymorphisms of CYP2J2 are associated with increased cardiovascular risks.

METHODS AND RESULTS

All 9 exons of the CYP2J2 gene and its proximal promoter were sequenced in 132 patients to identify potential variants. Functional consequence of a single nucleotide polymorphism (SNP) in the promoter of CYP2J2 was further evaluated by use of transcription factor-binding and reporter assays. A total of 17 polymorphisms were identified. One of the most relevant polymorphisms in terms of frequency and functional importance is located at -50 (G-50T) in the proximal promoter of CYP2J2. Screening of 289 patients with coronary artery disease and 255 control subjects revealed 77 individuals with the G-50T SNP (17.3% of coronary artery disease patients, 10.6% of control subjects; P=0.026). The association of the G-50T polymorphism remained significant after adjustment for age, gender, and conventional cardiovascular risk factors (OR, 2.23; 95% CI, 1.04 to 4.79). The G-50T mutation resulted in the loss of binding of the Sp1 transcription factor to the CYP2J2 promoter and resulted in a 48.1+/-2.4% decrease in CYP2J2 promoter activity (P<0.01). Plasma concentrations of stable EET metabolites were significantly lower in individuals with the G-50T SNP.

CONCLUSIONS

A functionally relevant polymorphism of the CYP2J2 gene is independently associated with an increased risk of coronary artery disease.

Role of hepatocyte nuclear factor 3γ in the expression of human CYP2C genes

Hepatocyte nuclear factor 3 gamma (HNF-3 gamma) is an important transcription factor for the maintenance of specific liver functions. However, its relevance in the expression of human cytochrome P450 (CYP) genes has not yet been explored. Several HNF3 putative binding sites can be identified in human CYP2C 5'-flanking regions. Gene reporter experiments with proximal promoters revealed that HNF-3 gamma transactivated CYP2C8, CYP2C9, and CYP2C19 (25-, 4-, and 4-fold, respectively), but it did not transactivate CYP2C18. However, overexpression of HNF-3 gamma in hepatoma cells by means of a recombinant adenovirus induced CYP2C9, CYP2C18, and CYP2C19 mRNA (4.5-, 20-, and 50-fold, respectively) but did not activate endogenous CYP2C8. The lack of effect of HNF-3 gamma on endogenous CYP2C8 could be reversed by treating cells with the deacetylase inhibitor, trichostatin A, suggesting the existence of chromatin condensation around functional HNF3 elements in this gene. We conclude that HNF3 gamma is an important transcription factor for the hepatic-specific expression of human CYP2C genes. Our results also evidence that efficient transfection tools, such as adenoviral vectors, may be decisive for assessing the role of transcription factor on chromatin organized genes.

Effects of Malnutrition on Cytochrome P450 1A2 Activity in Elderly Patients

Little is known of the influence of nutritional status on cytochrome P450 (CYP) 1A2 activity in elderly patients. Thirty elderly institutionalised patients with malnutrition (group A, aged 88 +/- 5 years) and 24 without (group B, aged 81 +/- 9 years) were included. Malnutrition was defined as weight loss of >10% over the previous 6 months and/or a body mass index (BMI) <21 kg/m2 and albuminaemia < or = 32 g/L. CYP1A2 activity was evaluated by the plasma paraxanthine/caffeine (PAX/CAF) metabolic ratio. The plasma PAX/CAF metabolic ratio was similar in both groups regardless of nutritional status (0.34 +/- 0.13 [A] versus 0.30 +/- 0.11 [B]; p = 0.11). The CYP1A2 metabolic ratio was not correlated to either BMI, serum albumin or renal clearance. CYPI A2 activity, as measured by the plasma PAX/CAF ratio, was not influenced by nutritional status in elderly patients.

Effect of .GAMMA.-Oryzanol on Cytochrome P450 Activities in Human Liver Microsomes

The effects of gamma-oryzanol, a drug mainly used for the treatment of hyperlipidaemia, on several cytochrome P450 (CYP) specific reactions in human liver microsomes were investigated to predict drug interactions with gamma-oryzanol in vivo from in vitro data. The following eight CYP catalytic reactions were used in this study: CYP1A1/2-mediated 7-ethoxyresorufin O-deethylation, CYP2A6-mediated coumarin 7-hydroxylation, CYP2B6-mediated 7-benzyloxyresorufin O-debenzylation, CYP2C8/9-mediated tolbutamide methylhydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated bufuralol 1'-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, and CYP3A4-mediated testosterone 6beta-hydroxylation. gamma-Oryzanol had little inhibitory effects on CYP activities, indicating that this compound would not be expected to cause clinically significant interactions with other CYP-metabolized drugs at expected therapeutic concentrations.

Effect of probucol on cytochrome P450 activities in human liver microsomes

The effects of probucol, a cholesterol-lowering agent, on several cytochrome P450 (CYP) isoform-specific reactions in human liver microsomes were investigated to predict drug interactions with probucol in vivo from in vitro data. The following eight CYP catalytic reactions were used in this study: CYP1A1/2-mediated 7-ethoxyresorufin O-deethylation, CYP2A6-mediated coumarin 7-hydroxylation, CYP2B6-mediated 7-benzyloxyresorufin O-debenzylation, CYP2C8/9-mediated tolbutamide methylhydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated bufuralol 1'-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, and CYP3A4-mediated testosterone 6beta-hydroxylation. Probucol had neither stimulatory nor inhibitory effects on CYP1Al/2, 2A6, 2B6, 2C8/9, 2C19, 2D6, 2E1, and 3A4 activities at concentrations up to 300 microM, indicating that probucol, at the expected therapeutic concentrations, would not be predicted to cause clinically significant interactions with other CYP-metabolized drugs.

Inhibition of human drug metabolizing cytochrome P450 by buprenorphine

The effects of buprenorphine, a powerful mixed agonist/antagonist analgesic, on several cytochrome P450 (CYP) isoform specific reactions in human liver microsomes were investigated to predict drug interaction of buprenorphine in vivo from in vitro data. The following eight CYP-catalytic reactions were used in this study: CYPlA1/2-mediated 7-ethoxyresorufin O-deethylation, CYP2A6-mediated coumarin 7-hydroxylation, CYP2B6-mediated 7-benzyloxyresorufin O-debenzylation, CYP2C8/9-mediated tolbutamide methylhydroxylation, CYP2C19-mediated S-mephenytoin 4-hydroxylation, CYP2D6-mediated bufuralol 1'-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, and CYP3A4-mediated testosterone 6beta-hydroxylation. Buprenorphine strongly inhibited the CYP3A4- and CYP2D6-catalyzed reactions with Ki values of 14.7 microM and 21.4 microM, respectively. The analgesic also weakly inhibited specific reactions catalyzed by CYP1A1/2 (Ki=132 microM), CYP2B6 (Ki=133 microM), CYP2C19 (Ki=146 microM), CYP2C8/9 (IC50>300 microM), and CYP2E1 (IC50>300 microM), but not CYP2A6 mediated pathway. In consideration of the Ki values obtained in this study and the therapeutic concentration of buprenorphine in human plasma, buprenorphine would not be predicted to cause clinically significant interactions with other CYP-metabolized drugs.

Role of chiral chromatography in therapeutic drug monitoring and in clinical and forensic toxicology

Advances in chiral chromatographic separations have given pharmacologists and toxicologists the tools to examine unexpected clinical results involving chiral drugs. The ability to unravel complex phenomena associated with drug transport and drug metabolism is presented in this manuscript. The relation between the chirality of the drug mefloquine and the intracellular concentrations of the drug cyclosporine is illustrated by examining the effect of the enantiomers of mefloquine on the transport activity of P-glycoprotein (Pgp). These studies were conducted using a liquid chromatographic column containing immobilized Pgp. The results demonstrated that (+)-mefloquine competitively displaced the Pgp substrate cyclosporine whereas (-)-mefloquine had no effect on cyclosporine-Pgp binding. The data suggest that cyclosporine cellular and CNS concentrations can be increased through the concomitant administration of (+)-mefloquine. The use of chirality in clinical and forensic situations is also illustrated by the metabolism of the enantiomers of ketamine (KET). The plasma concentrations of (+)-KET and (-)-KET and the norketamine metabolites (+)-NK and (-)-NK were measured in rat plasma using enantioselective gas chromatography. The separations were accomplished using a gas chromatography chiral stationary phase based on beta-cyclodextrin. The pharmacokinetic profiles of (+)-, (-)-KET and (+)-, (-)-NK were determined in control and protein-calorie malnourished (PCM) rats to determine the effect of PCM on ketamine metabolism and clearance. The results indicate that PCM produced a significant and stereoselective decrease in KET and NK metabolism. The data suggest that the effects of environmental factors (smoking, alcohol use, diet) and drug interactions (coadministered agents) can be measured using the changes in stereochemical metabolic and pharmacokinetic patterns of KET and similar drugs.

Involvement of steroids and cytochromes P(450) species in the triggering of immune defenses

In vertebrates the wide variety of cytochromes P(450) (P(450)) is a key for elimination of low molecular weight xenobiotics and for the production and metabolism of steroid hormones. In contrast, xenobiotics of large molecular weight are processed and eliminated after the immune response. The suppression of immune response by native P(450)-produced glucocorticoid (GC) hormones constitutes a first link between P(450) and immunity. In the last decade, mechanisms and molecules responsible for the triggering of immune response were investigated and results showed that many tissues and organs transform native 3beta-hydroxysteroids into 7-hydroxylated metabolites that trigger immunity. Present data suggest that 7-hydroxysteroids are native anti-GCs that block the GC-induced immunosuppression. Because specific P(450) are responsible for the production of 7-hydroxylated steroids resulting into increased immunity, a second link exists between P(450) and immunity. Taken together, these findings support the proposal that P(450) are keys to all of the known defense mechanisms of vertebrates against all xenobiotic forms.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Inhibitory effect of short-term bile duct ligation on hepatic cytochrome P450 of bile acid-depleted rats

In this study we analyzed the effect resulting from a short-term (1 h) bile duct obstruction in bile acid-depleted or taurocholate-replenished rats on liver cytochrome P450 enzyme system activity. Rats were depleted of endogenous bile acids and then subjected to a biliary obstruction for 1 h. Some of these depleted-obstructed rats were replenished previously to the obstruction with exogenous taurocholic acid (TC) and the others were treated with the solvent alone. To study the isolated effect of the bile acid, other rats were also previously depleted and then replenished with TC but they were obstructed briefly (20 min). CYP3A2-linked activity was evaluated in vivo with the aminopyrine breath test and in vitro by the measurement of nifedipine oxidase microsomal activity. The results suggested that bile flow suppression per se might inhibit this CYP-linked activity and that bile acid retention is not involved at least as a sole determinant.

The lung HETEs (and EETs) up

Arachidonic acid metabolites of the cyclooxygenase and lipoxygenase pathways have a variety of important lung functions. Recent observations indicate that cytochrome P-450 (P-450) monooxygenases are also expressed in the lung, localized to specific pulmonary cell types (e.g., epithelium, endothelium, and smooth muscle), and may modulate critical lung functions. This review summarizes recent data on the presence and biological activity of P-450-derived eicosanoids in the pulmonary vasculature and airways, including effects on pulmonary vascular and bronchial smooth muscle tone and airway epithelial ion transport. We hypothesize a number of potential functions of P-450-derived arachidonate metabolites in the lungs such as contribution to hypoxic pulmonary vasoconstriction, regulation of bronchomotor tone, control of the composition of airway lining fluid, and limitation of pulmonary inflammation. Finally, we describe a number of emerging technologies, including congenic and transgenic strains of experimental animals, P-450 isoform-specific inhibitors and inhibitory antibodies, eicosanoid analogs, and vectors for delivery of P-450 cDNAs and antisense oligonucleotides. These tools will facilitate further studies on the contribution of endogenously formed P-450 eicosanoid metabolites to lung function, under both normal and pathological conditions.

Alterations of prostate biomarker expression and testosterone utilization in human LNCaP prostatic carcinoma cells by garlic-derived S-allylmercaptocysteine

BACKGROUND

This study determined the effects of S-allylmercaptocysteine (SAMC), a phytoconstituent from garlic, on the expression of androgen-responsive biomarkers, prostate specific antigen (PSA), and prostate specific membrane antigen (PSMA), in human prostatic carcinoma cells (LNCaP).

METHODS

Secretion of PSA was determined as well as the activity of PSMA measured as a function of its ability to hydrolyze poly-gamma-glutamated folate and N-acetylaspartylglutamate (NAAG). Folate hydrolase capacity was also determined in SAMC-treated cells grown in charcoal stripped fetal calf serum (CS-FCS). In addition, testosterone disappearance was measured from culture media of SAMC-treated LNCaP and PC-3 cells as well as from cell free lysates.

RESULTS

PSA secretions were significantly decreased compared to control values at 1 day (8.4 +/- 2.6 vs. 18.9 +/- 1.7, P < 0.01), 4 days (18.9 +/- 5.3 vs. 73.8 +/- 4. 4, P < 0.001), and 6 days (35.6 +/- 2.1 vs. 96.5 +/- 17.9 ng/10(5) cells, P < 0.01; mean +/- SD). By contrast, PSMA activity measured as either folate hydrolase or NAAG dipeptidase (NAALADase) activity increased in cells treated with SAMC. PSMA-folate hydrolase activity in SAMC-treated cells grown in CS-FCS increased beyond that observed in cells grown in CS-FCS alone. Pre-exposure of LNCaP cells to SAMC resulted in enhanced rate of testosterone disappearance from culture media at 6 hr (P < 0.01) and at 48 hr (P < 0.001) compared to media from cells not previously exposed to SAMC. Results similar to these were also observed in androgen-independent PC-3 cells treated with SAMC. In lysates of SAMC-treated LNCaP cells, the rate of testosterone catabolism was twice that from phosphate buffered saline (PBS)-treated cells. SAMC-treated LNCaP cells grown in media supplemented with testosterone temporarily exhibited enhanced growth over a 2 day period but cell numbers declined later to levels similar to those of SAMC treatment.

CONCLUSIONS

These results show that SAMC exhibits differential effects on recognized biomarkers for LNCaP cells similar to those produced by androgen deprivation and strongly suggests that this effect may be mediated, in part, by diminishing the trophic effects of testosterone, likely by converting it to metabolites less reactive toward androgen receptors.

High-performance liquid chromatography determination of N- and O-demethylase activities of chemicals in human liver microsomes: application of postcolumn fluorescence derivatization using Nash reagent

Formaldehyde is liberated in the process of cytochrome P450 (CYP) mediated demethylation of a wide variety of compounds containing the CH(3)N or CH(3)O functionality. A highly sensitive method using a high-performance liquid chromatography (HPLC) system with postcolumn derivatization was developed to measure the liberated formaldehyde as N- and O-demethylase activity of drugs in human liver microsomes. Following the chromatographic separation of formaldehyde on a C18 column, the formaldehyde was reacted with the Nash reagent in the postcolumn reactor at 100 degrees C and detected by the fluorescence method. The results showed that the present method has excellent precision and accuracy. The intra- and interassay variances of this method were less than 10%. The newly developed HPLC method was found to be about 80-fold more sensitive than the colorimetric method in detection of formaldehyde. The N-demethylase activity of sertraline in rat liver microsomes determined by the present method did not differ from those detected by previous methods quantifying produced desmethyl metabolite. The present method has been successfully applied to determine the N-demethylase activities of several drugs, including aminopyrine, erythromycin, fluoxetine, S-mephenytoin, and sertraline, in human liver microsomes. This assay should be useful for generic analysis of N- and O-demethylase activities of xenobiotic and endobiotic chemicals by CYP enzymes.

A discordance of the cytochrome P450 2C19 genotype and phenotype in patients with advanced cancer

AIMS

To examine the relationship between cytochrome P450 2C19 (CYP2C19) genotype and expressed metabolic activity in 16 patients with advanced metastatic cancer.

METHODS

Individual CYP2C19 genotypes were determined by PCR-based amplification, followed by restriction fragment length analysis, and compared with observed CYP2C19 metabolic activity, as determined using the log hydroxylation index of omeprazole.

RESULTS

All 16 patients had an extensive metabolizer genotype. However, based on the antimode in a distribution of log omeprazole hydroxylation indices from healthy volunteers, four of the patients had a poor metabolizer phenotype and there was a general shift of the remaining 12 patients towards a slower metabolic phenotype. This suggests a reduction in metabolic activity for all patients relative to healthy volunteers. A careful analysis of patient medical records failed to reveal any drug interactions or other source for the observed discordance between genotype and phenotype.

CONCLUSIONS

There are no previous reports of a 'discordance' between genotype and expressed enzyme activity in cancer patients. Such a decrease in enzyme activity could have an impact on the efficacy and toxicity of chemotherapeutic agents and other drugs, used in standard oncology practice.

Effects of imidazole antimycotics on the liver microsomal cytochrome P450 isoforms in rats: comparison of in vitro and ex vivo studies

We have studied the effects of three imidazole derivatives, clotrimazole (CLO), ketoconazole (KET) and miconazole (MIC) on the liver microsomal diazepam (DZ) metabolism. In in vitro experiments using rats and human liver microsomes, significant inhibition of CYP3A in terms of DZ-3-hydroxylase activity was observed. The inhibition of DZ metabolism was seen 1 h after CLO dosing. On the other hand, the induction of certain cytochrome P450 (CYP) isozymes was observed in in vivo studies 24 h after dosing. That is, CYP1A, CYP2B and CYP3A2, but not CYP2E, were observed 24 h after CLO or KET or MIC treatment. Under these conditions, CLO was the most potent inducer of CYP3A and MIC was a more potent inducer of CYP1A and CYP2B. KET induced CYP1A and CYP2B whereas the inducibility of KET was less than those of CLO and MIC. All of the imidazole derivatives tested here showed significant inhibition of CYP isozymes which overcame the induction of the CYP isozymes by those drugs in the data of Western blot analysis.

Human brain cytochrome P450 1B1: immunohistochemical localization in human temporal lobe and induction by dimethylbenz(a)anthracene in astrocytoma cell line (MOG-G-CCM)

CYP1B1, a new member of human cytochrome P450 family 1, is involved in the xenobiotic detoxification metabolism and possibly activation of numerous procarcinogens and promutagens. Localization of CYP1B1 in human temporal lobe and its induction in astrocytoma cell line (MOG-G-CCM) by 7,12-dimethylbenz(a)anthracene (DMBA) was investigated using antibodies against human CYP1B1. A single band of approximately 58 kDa size in both human temporal lobe and in MOG-G-CCM was detected by Western blot analysis. Treatment of MOG-G-CCM cells with DMBA resulted in approximately 2.8-fold induction of CYP1B1. CYP1B1 immunoreactivity was detected at the blood-brain interface areas of the temporal lobe as evidenced by co-localization with CD34 antigen. These results suggest that this enzyme may be important in brain xenobiotic metabolism acting as an enzymatic barrier.

The role of biotransformation in dietary (anti)carcinogenesis

The fact that dietary compounds influence the susceptibility of human beings to cancer, is widely accepted. One of the possible mechanisms that is responsible for these (anti)carcinogenic effects is that dietary constituents may modulate biotransformation enzymes, thereby affecting the (anti)carcinogenic potential of other compounds. This ambiguous theme is the basis for the present paper. The possible effects of enzymatic bioactivation and detoxification of dietary constituents are discussed using two representative examples of phase I and phase II biotransformation enzymes i.e., cytochrome P450 and glutathione S-transferase. Furthermore, the impact of genetic polymorphisms of these two enzyme systems is considered. Although it is very difficult on the basis of the enzyme inducing or inhibiting properties of dietary compounds, especially to characterize them as anticarcinogenic, for certain constituents it is acknowledged that they have anticarcinogenic properties. As such, this provides for an important mechanistic substantiation of the established cancer chemopreventive effect of a diet rich in fruits and vegetables.

P450 subfamily CYP2J and their role in the bioactivation of arachidonic acid in extrahepatic tissues

Historically, there has been intense interest in P450 metabolic oxidation, peroxidation, and reduction of xenobiotics. More recently, there has been a growing appreciation for the role of P450s in the oxidation of lipophilic endobiotics, such as bile acids, fat-soluble vitamins, and eicosanoids. This review details the emerging CYP2J subfamily of P450s and their role as catalysts of arachidonic acid metabolism.

Cytochrome P450 1B1 mRNA in the human central nervous system

AIMS

To study the expression of CYP1B1 in a variety of human and rat cell lines as a means of identifying a new tool for the investigation of gene regulation. In addition, to identify the expression of cytochrome P450 1B1 (CYP1B1) in different regions of the central nervous system (CNS).

METHODS

Reverse transcription-polymerase chain reaction followed by cloning and sequencing were used to detect the expression of CYP1B1 in human cell lines. Poly A+ mRNA from the human spinal cord and from different brain regions was analysed using a CYP1B1 probe labelled with 32PdCTP.

RESULTS

Expression of CYP1B1 was shown in a human astrocytoma cell line (MOG-G-CCM). CYP1B1 mRNA was expressed in a variety of regions of the CNS but with a distinct regional specificity. Expression was highest in the putamen.

CONCLUSIONS

The expression of CYP1B1 in a human astrocytoma enables this cell line to be used in further studies of regulation and function of this gene. The demonstration that CYP1B1 mRNA is expressed in a variety of regions of the CNS suggests a role for this gene in brain and spinal cord metabolism. The regional specificity of expression might explain the focal damage of certain human neurodegenerative diseases.

Liver damage induced by bile duct ligation affects CYP isoenzymes differently in rats

We examined the influence of liver damage induced by bile duct ligation on the activity and the expression of hepatic cytochrome P450 (CYP) 1A, 2B, 2C6, 2C11, 2E1 and 3A2 in male Sprague-Dawley rats. In the ligation group, testosterone 2 alpha-, 16 alpha-, and 6 beta-hydroxylase activities were severely decreased, whereas ethoxyresorufin O-deethylase and progesterone 21-hydroxylase activities relatively remained. Pentoxyresorufin O-deethylase and chlorzoxazone 6-hydroxylase activities were reduced to approximately one thirds those of control. The protein contents of these isoenzymes expressed in hepatic microsomes of the ligation group were decreased to 45%, 32%, 79%, 13%, 58%, and 23% of control for CYP1A, 2B, 2C6, 2C11, 2E1 and 3A2, respectively. The rank order of magnitude of the influence of bile duct ligation on CYP isoenzymes, assessed by the reduction in the enzyme activity and the protein content, corresponded with each other except CYP1A. The reduction of the enzyme activities significantly correlated with the reduction in the protein contents of different isoenzymes. These results suggested that bile duct ligation affected CYP isoenzyme activities and contents with different extent.

In vitro approaches to predicting drug interactions in vivo

In vitro metabolic models using human liver microsomes can be applied to quantitative prediction of in vivo drug interactions caused by reversible inhibition of metabolism. One approach utilizes in vitro Ki, values together with in vivo values of inhibitor concentration to forecast in vivo decrements of clearance caused by coadministration of inhibitor. A critical limitation is the lack of a general scheme for assigning intrahepatic exposure of enzyme to inhibitor or substrate based only on plasma concentration; however, the assumption that plasma protein binding necessarily restricts hepatic uptake is not tenable. Other potential limitations include: flow-dependent hepatic clearance, "mechanism-based" chemical inhibition, concurrent induction, or a major contribution of gastrointestinal P450-3A isoforms to presystemic extraction. Nonetheless, the model to date has provided reasonably accurate forecasts of in vivo inhibition of clearance of several substrates (desipramine, terfenadine, triazolam, alprazolam, midazolam) by coadministration of selective serotonin reuptake-inhibitor antidepressants and azole antifungal agents. Such predictive models deserve further evaluation, since they may ultimately yield more cost-effective and expeditious screening for drug interactions, with reduced human drug exposure and risk.

CYP26, a novel mammalian cytochrome P450, is induced by retinoic acid and defines a new family

A novel member of the cytochrome P450 superfamily, CYP26, which represents a new family of cytochrome P450 enzymes, has been cloned. CYP26 mRNA is up-regulated during the retinoic acid (RA)-induced neural differentiation of mouse embryonic stem cells in vitro and is transiently expressed by embryonic stem cells undergoing predominantly non-neural differentiation. CYP26 transcript is detectable as early as embryonic day 8.5 in mouse embryos, suggesting a function for the gene in early development. CYP26 is expressed in mouse and human liver, as expected for a cytochrome P450, and is also expressed in regions of the brain and the placenta. Acute administration of 100 mg/kg all-trans-RA increases steady-state levels of transcript in the adult liver, but not in the brain. CYP26 is highly homologous to a Zebrafish gene, CYPRA1, which has been proposed to participate in the degradation of RA, but is minimally homologous to other mammalian cytochrome P450 proteins. Thus, we report the cloning of a member of a novel cytochrome P450 family that is expressed in mammalian embryos and in brain and is induced by RA in the liver.

Halothane inhalation inhibits the metabolism of chlorzoxazone, a substrate for CYP2E1, in rabbits

We demonstrated the inhibitory effect of halothane (HAL) inhalation on the metabolism of chlorzoxazone (CZZ), a substrate for CYP2E1, in a bolus and a continuous injection study in rabbits receiving artificial ventilation. In a bolus injection study, the inhalation of 1.0% HAL significantly increased the half-life and the area under the curve and decreased the clearance of CZZ compared with those variables in midazolam administration. In a continuous injection study, the effect of various concentrations of inhaled HAL on plasma CZZ concentration at steady state was compared. Systolic and diastolic arterial blood pressure were decreased dose-dependently after 0.5%, 1.0%, or 2.0% HAL was inhaled. Although the plasma concentration of CZZ was increased 2.5-fold after 3 h of HAL inhalation, there was no significant difference in mean plasma concentrations among the groups treated with 0.5%, 1.0%, or 2.0% HAL. In contrast, the plasma concentration of lidocaine, a substrate for CYP3A, remained unchanged after 1.0% HAL was inhaled. These results suggest that general anesthesia obtained with HAL inhalation will affect the metabolism of drugs administered concomitantly when the drug is a substrate for CYP2E1.