Assay of hepatic microsomal testosterone hydroxylases by high-performance liquid chromatography

Characteristics of cytochrome P450-dependent metabolism in the liver of the wild raccoon, Procyon lotor

Wildlife is exposed to a wide range of xenobiotics in the natural environment. In order to appropriately assess xenobiotic-induced toxicity in wildlife, it is necessary to understand metabolic capacities. Carnivores, in general, have low metabolic abilities, making them vulnerable to a variety of chemicals. Raccoons (Procyon lotor) in the wild have been found to have high levels of xenobiotics. However, little is known about the metabolic capacity of the cytochrome P450 (CYP) enzymes in this species. Thus, this study used liver samples to investigate the characteristics of CYP enzymes in wild raccoons. In 22 wild raccoons, CYP concentrations in hepatic microsomes were examined. To better understand the properties of CYP-dependent metabolism, in vitro metabolic activity studies were performed using ethoxyresorufin, pentoxyresorufin and testosterone as substrates. In addition, three raccoons were fed commercial dog food in the laboratory for one week, and the effects on CYP-dependent metabolism were investigated. In comparison to other mammalian species, raccoons had very low concentrations of CYP in their livers. In an in vitro enzymatic analysis, raccoons' ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-depentylase (PROD) metabolic capacities were less than one-fifth and one-tenth of rats', respectively. These results indicate the possible high risk in raccoons if exposed to high levels of environmental xenobiotics because of their poor CYP activity. In this study, the features of CYP-dependent metabolism in wild raccoons are described for the first time.

Effects of chlorinated drinking water on the xenobiotic metabolism in Cyprinus carpio treated with samples from two Italian municipal networks

Drinking water (DW) disinfection represents a milestone of the past century, thanks to its efficacy in the reduction of risks of epidemic forms by water micro-organisms. Nevertheless, such process generates disinfection by-products (DBPs), some of which are genotoxic both in animals and in humans and carcinogenic in animals. At present, chlorination is one of the most employed strategies but the toxicological effects of several classes of DBPs are unknown. In this investigation, a multidisciplinary approach foreseeing the chemical analysis of chlorinated DW samples and the study of its effects on mixed function oxidases (MFOs) belonging to the superfamily of cytochrome P450-linked monooxygenases of Cyprinus carpio hepatopancreas, was employed. The experimental samples derived from aquifers of two Italian towns (plant 1, river water and plant 2, spring water) were obtained immediately after the disinfection (A) and along the network (R1). Animals treated with plant 1 DW-processed fractions showed a general CYP-associated MFO induction. By contrast, in plant 2, a complex modulation pattern was achieved, with a general up-regulation for the point A and a marked MFO inactivation in the R1 group, particularly for the testosterone metabolism. Together, the toxicity and co-carcinogenicity (i.e. unremitting over-generation of free radicals and increased bioactivation capability) of DW linked to the recorded metabolic manipulation, suggests that a prolonged exposure to chlorine-derived disinfectants may produce adverse health effects.

Integrin Receptors Play a Key Role in the Regulation of Hepatic CYP3A

Landmark studies describing the effect of microbial infection on the expression and activity of hepatic CYP3A used bacterial lipopolysaccharide as a model antigen. Our efforts to determine whether these findings were translatable to viral infections led us to observations suggesting that engagement of integrin receptors is key in the initiation of processes responsible for changes in hepatic CYP3A4 during infection and inflammation. Studies outlined in this article were designed to evaluate whether engagement of integrins, receptors commonly used by a variety of microbes to enter cellular targets, is vital in the regulation of CYP3A in the presence and absence of virus infection. Mice infected with a recombinant adenovirus (AdlacZ) experienced a 70% reduction in hepatic CYP3A catalytic activity. Infection with a mutant virus with integrin-binding arginine-glycine-aspartic acid (RGD) sequences deleted from the penton base protein of the virus capsid (AdΔRGD) did not alter CYP3A activity. CYP3A mRNA and protein levels in AdlacZ-treated animals were also suppressed, whereas those of mice given AdΔRGD were not significantly different from uninfected control mice. Silencing of the integrinβ-subunit reverted adenovirus-mediated CYP3A4 suppression in vitro. Silencing of theα-subunit did not. Suppression of integrin subunits had a profound effect on nuclear receptors pregnane X receptor and constitutive androstane receptor, whereas retinoid X receptorαwas largely unaffected. To our knowledge, this is the first time that extracellular receptors, like integrins, have been indicated in the regulation of CYP3A. This finding has several implications owing to the important role of integrins in normal physiologic process and in many disease states.

Evaluation of the HC-04 cell line as an in vitro model for mechanistic assessment of changes in hepatic cytochrome P450 3A during adenovirus infection

HC-04 cells were evaluated as an in vitro model for mechanistic study of changes in the function of hepatic CYP3A during virus infection. Similar to in vivo observations, infection with a first generation recombinant adenovirus significantly inhibited CYP3A4 catalytic activity in an isoform-specific manner. Virus (MOI 100) significantly reduced expression of the retinoid X receptor (RXR) by 30% 96 hours after infection. Cytoplasmic concentrations of the pregnane X receptor (PXR) were reduced by 50%, whereas the amount of the constitutive androstane receptor (CAR) in the nuclear fraction doubled with respect to uninfected controls. Hepatocyte nuclear factor 4α (HNF-4α) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) were also reduced by ∼70% during infection. Virus suppressed CYP3A4 activity in the presence of the PXR agonist rifampicin and did not affect CYP3A4 activity in the presence of the CAR agonist CITCO [6-(4-chlorophenyl) imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime], suggesting that virus-induced modification of PXR may be responsible for observed changes in hepatic CYP3A4. The HC-04 cell line is easy to maintain, and CYP3A4 in these cells was responsive to known inducers and suppressors. Dexamethasone (200 μM) and phenobarbital (500 μM) increased activity by 230 and 124%, whereas ketoconazole (10 μM) and lipopolysaccharide (LPS) (10 μg/ml) reduced activity by 90 and 92%, respectively. This suggests that HC-04 cells can be a valuable tool for mechanistic study of drug metabolism during infection and for routine toxicological screening of novel compounds prior to use in the clinic.

Modulation of cytochrome P450 and induction of DNA damage in Cyprinus carpio exposed in situ to surface water treated with chlorine or alternative disinfectants in different seasons

Epidemiological studies have shown an association between consumption of disinfected drinking water and adverse health outcomes. The chemicals used to disinfect water react with occurring organic matter and anthropogenic contaminants in the source water, resulting in the formation of disinfection by-products (DBPs). The observations that some DBPs are carcinogenic in animal models have raised public concern over the possible adverse health effects for humans. Here, the modulation of liver cytochrome P450-linked monooxygenases (MFO) and the genotoxic effects in erythrocytes of Cyprinus carpio fish exposed in situ to surface drinking water in the presence of disinfectants, such as sodium hypochlorite (NaClO), chlorine dioxide (ClO(2)) and peracetic acid (PAA), were investigated in winter and summer. A complex induction/suppression pattern of CYP-associated MFOs in winter was observed for all disinfectants. For example, a 3.4- to 15-fold increase was recorded of the CYP2B1/2-linked dealkylation of penthoxyresorufin with NaClO (10 days) and PAA (20 days). In contrast, ClO(2) generated the most notable inactivation, the CYP2E1-supported hydroxylation of p-nitrophenol being decreased up to 71% after 10 days' treatment. In summer, the degree of modulation was modest, with the exception of CYP3A1/2 and CYP1A1 supported MFOs (62% loss after 20 days PAA). The micronucleus (MN) induction in fish circulating erythrocytes was also analysed as an endpoint of genotoxic potential in the same fish population. Significant increases of MN induction were detected at the latest sampling time on fish exposed to surface water treated with chlorinate-disinfectants, both in winter (NaClO) and summer (NaClO and ClO(2)), while no effect was observed in fish exposed to PAA-treated water. These results show that water disinfection may be responsible for harmful outcomes in terms of MFO perturbation and DNA damage; if extrapolated to humans, they ultimately offer a possible rationale for the increased urinary cancer risk recorded in regular drinking water consumers.

Clinical pharmacology of alcaftadine, a novel antihistamine for the prevention of allergic conjunctivitis

PURPOSE

In this report, we characterize the in vitro pharmacokinetic properties of a new antihistamine, alcaftadine. In addition, we report results from phase 1 studies of several ophthalmic formulations of alcaftadine and examine the pharmacokinetic properties of one formulation in detail.

METHODS

In vitro pharmacology employed a human liver microsome assay combined with index substrates or inhibitors for specific cytochromes. Metabolic fate of (14)C-alcaftadine was determined by high-performance liquid chromatography-based separation of parent compound from metabolites. Plasma protein binding was determined by equilibrium dialysis using (3)H-labeled alcaftadine and (3)H-labeled alcaftadine carboxylic acid metabolite. Relative tolerability (comfort) of 4 concentrations and 3 formulations of alcaftadine ophthalmic solution was assessed in 2 double-masked, randomized, placebo-controlled, contralateral studies in which formulations were compared to Tears Naturale II (placebo) in normal adult subjects. Data analysis focused on the mean differences in subject-reported drop comfort scores (within each dose level, at each time point) and compared the study-treatment eye with the placebo eye. Pharmacokinetics of alcaftadine 0.25% ophthalmic solution were determined in an open-label, single-center study after a single bilateral dose and after 7 days of once-a-day bilateral doses in healthy subjects 18-55 years old.

RESULTS

Alcaftadine is not significantly metabolized by microsomal cytochromes, but it is rapidly converted to the carboxylic acid metabolite by one or more cytosolic enzymes. Neither the parent compound nor its carboxylic acid metabolite displayed significant plasma protein binding. Over a range of formulations and concentrations (0.05%-0.5%), alcaftadine was well tolerated and subjects reported little or no discomfort or taste perversion in any treatment group. Pharmacokinetic studies showed that both the parent compound and the carboxylic acid metabolite reach peak serum levels within minutes of administration and fall below detectable levels within 3 h of dosing.

CONCLUSIONS

Based upon pharmacokinetic and phase 1 studies, the novel antihistamine alcaftadine is an appropriate drug for use as an ophthalmic formulation for prevention and treatment of ocular allergic conditions such as allergic conjunctivitis (alcaftadine ophthalmic solution 0.25% was recently approved for use by the FDA). Topical administration of alcaftadine 0.25% ophthalmic solution was well tolerated and had an acceptable safety profile.

Species differences in the pharmacology and toxicology of PEGylated helper-dependent adenovirus

Clinically relevant doses of helper-dependent adenoviruses (HDAds) provoke the host response against capsid proteins in primates and rodents. To determine if PEGylation truly affects this, baboons and mice were given either HDAd or PEG-HDAd expressing beta-galactosidase at 5 × 10¹¹ or 3 × 10¹² virus particles per kilogram (vp/kg) by iv infusion. Serum cytokines and blood chemistries were assessed for 96 h. PEG-HDAd reduced IL-6 6-fold in mice and 3-fold in the primate. This vector reduced IL-12 by 50% in both animal models. PEGylation reduced serum transaminases by approximately 50% at each dose in the primate and the mouse. PEGylation did not alter hepatic transduction efficiency in the mouse but did reduce transduction efficiency in the liver and the spleen of primates. Unmodified and PEGylated virus suppressed hepatic CYP3A activity in both animal models. PEGylation doubled the half-life (t(½)) of the virus in the mouse and cut plasma clearance (CL) in half without affecting the half-life in primates. These results suggest that there are notable species-specific differences in the biodistribution of and response to PEG-modified vectors which may be linked to differences in binding properties to coagulation factors, receptor density and tissue architecture in the liver.

Influence of the Ginkgo extract EGb 761 on rat liver cytochrome P450 and steroid metabolism and excretion in rats and man

Extracts from leaves of Ginkgo biloba L. are among the most used herbal medicinal products worldwide. Based on in-vitro tests and studies in rats, concern has been expressed that intake of Ginkgo extracts may affect hepatic metabolism of xenobiotics and cause drug interactions, although no evidence for modulation of cytochrome P450 (CYP450) enzyme activity was obtained in human trials. Because of these contradictory findings, we investigated the effects of the standardised extract EGb 761 on hepatic CYP450 in rats. EGb 761 (100 mg kg−1 daily, p.o., for 4 days) strongly increased liver CYP450 content and altered the ex-vivo biotransformation of androstendione, as well as metabolism of endogenous steroids. However, in human subjects no effect on the urinary steroid profile was observed after intake of EGb 761 for 28 days (240 mg daily). These results indicate that the effects of EGb 761 on drug metabolising enzymes are specific for rats and may not be extrapolated to man.

Drug-virus interaction: effect of administration of recombinant adenoviruses on the pharmacokinetics of docetaxel in a rat model

Modern cancer therapy combines recombinant viruses with traditional chemotherapeutic agents that are metabolized by hepatic cytochrome P450 3A4 (CYP3A4). A single dose of recombinant adenovirus (Ad) expressing beta-galactosidase (AdlacZ) significantly alters CYP3A2, the correlate of CYP3A4, in rats for 14 days. Recombinant adenovirus expressing human p53 (Adp53) also suppresses CYP3A2. Plasma clearance of docetaxel (DTX) in animals given AdlacZ (3.38 ± 0.22 L/h/kg) was significantly lower than that of those given DTX alone (6.41 ± 1.10 L/h/kg, p≤0.05). Area under the plasma concentration-time curve of DTX in rats given AdlacZ (2,987.37 ± 197.97 ng/ml/h) was significantly greater than those given drug alone (1,666.59 ± 317.04 ng/ml/h, p≤0.05). Both viruses prolonged DTX half-life (t_1/2). Ad infection may cause significant variability in the pharmacokinetics and pharmacodynamics of anti-cancer agents and should be considered when designing therapeutic regimens for patients with viral infection and those enrolled in clinical trials employing recombinant viruses.

Alteration of xenobiotic metabolizing enzymes by resveratrol in liver and lung of CD1 mice

Conflicting data on the anticancer properties of the polyphenolic natural product resveratrol (RSV) have been reported. Since the inhibition of "bioactivating" Phase-I xenobiotic metabolizing enzymes (XMEs) and/or induction of "detoxifying" Phase-II XMEs have long been considered important cancer chemopreventive strategies, in the current study we investigated the effect of RSV treatment on several Cytochrome P450 (CYP)-dependent oxidations and Phase-II markers in liver and lung subcellular preparations from CD1 male mice. These mice were i.p treated with RSV (25 or 50mg/Kg b.w.) daily for one or for seven consecutive days. Using either specific probes for different CYPs, or the regio- and stereo-selective metabolism of testosterone, we found that most of the Phase-I XMEs were significantly suppressed (up to approximately 61% loss for the CYP3A1/2-linked 6 beta-hydroxylation of testosterone in liver and up to approximately 97% loss for 2 alpha-hydroxylase in lung) following RSV treatment for 7 days at 50mg/kg b.w. Glutathione S-transferase was significantly inhibited, particularly in lung (approximately 76% loss of activity) after single administration of 25mg/kg b.w. A different response for the UDP-glucuronosyl transferase was observed, where a significant induction was seen (approximately 83%) in the liver and a significant reduction was observed in the lung (up to approximately 83% loss) following treatment with 25mg/kg b.w. for seven days. These data indicate that murine XMEs are altered by RSV, and that this alteration is dependent on the RSV dose, duration and way of administration. These results could provide mechanistic explanations for the conflicting chemopreventive results reported for RSV.

Perturbation of murine liver cyp-superfamily of isoforms by different combinations of pesticide mixtures

It was previously found that fenarimol, vinclozolin or acephate, three of the most used pesticides worldwide, provoked a marked perturbation of murine cytochrome P450 (CYP)-linked monooxygenases. Here, to more closely mimic human exposure, it was investigated whether different pesticide combinations administered i.p. in male Swiss Albino CD1 mice in single or repeated fashion (daily, for three consecutive days), affect CYP-dependent oxidations. The four simulated mixtures showed a complex pattern of CYP induction and suppression, especially after repeated injection. For example, while fenarimol alone was the most inducing agent--reaching a 79-fold increase over control in testosterone 2alpha-hydroxylase--followed by vinclozolin and acephate, coadministration with the former markedly reduced induction. Coadministration with vinclozolin, determined various positive and negative modulations. An increase of CYP2B1/2 and CYP3A1/2-associated oxidases and a decrease of ethoxycoumarin metabolism was observed in the acephate and vinclozolin mixture. An equivalent or reduced CYP expression, if compared to double combinations, was seen using the complete mixture. Taken as a whole, the unpredictability of the recorded effects with simple mixtures, shrinks the misleading extrapolation performed on a single pesticide. If reproduced in human, such changes, altering either endogenous metabolism or biotransformation of ubiquitous toxins, might have public health implications.

Glucoraphasatin and glucoraphenin, a redox pair of glucosinolates of brassicaceae, differently affect metabolizing enzymes in rats

Brassica vegetables are an important dietary source of glucosinolates (GLs), whose breakdown products exhibit anticancer activity. The protective properties of Brassicaceae are believed to be due to the inhibition of Phase-I or induction of Phase-II xenobiotic metabolizing enzymes (XMEs), thus enhancing carcinogen clearance. To study whether GLs affect XMEs and the role of their chemical structure, we focused on two alkylthio GLs differing in the oxidation degree of the side chain sulfur. Male Sprague-Dawley rats were supplemented (per oral somministration by gavage) with either glucoraphasatin (4-methylthio-3-butenyl GL; GRH) or glucoraphenin (4-methylsulfinyl-3-butenyl GL; GRE), at 24 or 120 mg/kg body weight in a single or repeated fashion (daily for four consecutive days), and hepatic microsomes were prepared for XME analyses. Both GLs were able to induce XMEs, showing different induction profiles. While the inductive effect was stronger after multiple administration of the higher GRH dosage, the single lower GRE dose was the most effective in boosting cytochrome P-450 (CYP)-associated monooxygenases and the postoxidative metabolism. CYP3A1/2 were the most affected isoforms by GRH treatment, whereas GRE induced mainly CYP1A2 supported oxidase. Glutathione S-transferase increased up to approximately 3.2-fold after a single (lower) GRE dose and UDP-glucuronosyl transferase up to approximately 2-fold after four consecutive (higher) GRH doses. In conclusion, the induction profile of these GLs we found is not in line with the chemopreventive hypothesis. Furthermore, the oxidation degree of the side chain sulfur of GLs seems to exert a crucial role on XME modulation.

Perturbation of cytochrome P450, generation of oxidative stress and induction of DNA damage in Cyprinus carpio exposed in situ to potable surface water

Epidemiological evidence suggests a link between consumption of chlorinated drinking water and various cancers. Chlorination of water rich in organic chemicals produces carcinogenic organochlorine by-products (OBPs) such as trihalomethanes and haloacetic acids. Since the discovery of the first OBP in the 1970s, there have been several investigations designed to determine the biological effects of single chemicals or small artificial OBP combinations. However, there is still insufficient information regarding the general biological response to these compounds, and further studies are still needed to evaluate their potential genotoxic effects. In the current study, we evaluated the effect of three drinking water disinfectants on the activity of cytochrome P450 (CYP)-linked metabolizing enzymes and on the generation of oxidative stress in the livers of male and female Cyprinus carpio fish (carp). The fish were exposed in situ for up 20 days to surface water obtained from the Trasmene lake in Italy. The water was treated with 1-2 mg/L of either sodium hypochlorite (NaClO) or chlorine dioxide (ClO2) as traditional disinfectants or with a relatively new disinfectant product, peracetic acid (PAA). Micronucleus (MN) frequencies in circulating erythrocytes from the fish were also analysed as a biomarker of genotoxic effect. In the CYP-linked enzyme assays, a significant induction (up to a 57-fold increase in the deethylation of ethoxyresorufin with PAA treatment) and a notable inactivation (up to almost a 90% loss in hydroxylation of p-nitrophenol with all disinfectants, and of testosterone 2beta-hydroxylation with NaClO) was observed in subcellular liver preparations from exposed fish. Using the electron paramagnetic resonance (EPR) spectroscopy radical-probe technique, we also observed that CYP-modulation was associated with the production of reactive oxygen species (ROS). In addition, we found a significant increase in MN frequency in circulating erythrocytes after 10 days of exposure of fish to water treated with ClO2, while a non-significant six-fold increase in MN frequency was observed with NaClO, but not with PAA. Our data suggest that the use of ClO2 and NaClO to disinfect drinking water could generate harmful OBP mixtures that are able to perturb CYP-mediated reactions, generate oxidative stress and induce genetic damage. These data may provide a mechanistic explanation for epidemiological studies linking consumption of chlorinated drinking water to increased risk of urinary, gastrointestinal and bladder cancers.

Effect of interleukin-6 neutralization on CYP3A11 and metallothionein-1/2 expressions in arthritic mouse liver

Rheumatoid arthritis is characterized by chronic inflammation of the synovial tissue. We examined the effect of interleukin (IL)-6 neutralization on the expression of cytochrome P450 or metallothionein-1/2 (metallothionein) during chronic phase inflammatory disease using rheumatoid arthritis model mice, human T-cell leukemia virus type I (HTLV-I) transgenic mice. Serum IL-6 concentrations of arthritis-developed HTLV-I transgenic mice were 129.9+/-26.1 pg/ml. Moreover, signal transducer and activator of transcription (STAT) 1/3 phosphorylations was observed in arthritic HTLV-I transgenic mouse livers. CYP3A11 mRNA was more strongly reduced by the development of arthritis in HTLV-I transgenic mouse livers as compared with CYP2C29 or CYP2E1 mRNAs. CYP3A protein and testosterone 6beta-hydroxylation activity also changed in a similar manner to the corresponding CYP3A11 mRNA level. On the other hand, metallothionein mRNA was significantly induced as compared with that of wild-type or non-arthritic mice. CYP3A suppression and metallothionein mRNA overexpression activity seen in the developed arthritic mice returned to the gene conditions of the non-arthritic HTLV-I transgenic mice by IL-6 antibody at 48 h after treatment. The present study has revealed that CYP3A11 and metallothionein expressions are affected by the release of IL-6 by arthritis and its systemic circulation, and neutralization of IL-6 recovered from the down-regulation of CYP3A11 mRNA and the induction of metallothionein mRNA in arthritic HTLV-I transgenic mice.

Glucoraphanin, the bioprecursor of the widely extolled chemopreventive agent sulforaphane found in broccoli, induces phase-I xenobiotic metabolizing enzymes and increases free radical generation in rat liver

Epidemiological and animal studies linking high fruit and vegetable consumption to lower cancer risk have strengthened the belief that long-term administration of isolated naturally occurring dietary constituents could reduce the risk of cancer. In recent years, metabolites derived from phytoalexins, such as glucoraphanin found in broccoli and other cruciferous vegetables (Brassicaceae), have gained much attention as potential cancer chemopreventive agents. The protective effect of these micronutrients is assumed to be due to the inhibition of Phase-I carcinogen-bioactivating enzymes and/or induction of Phase-II detoxifying enzymes, an assumption that still remains uncertain. The protective effect of glucoraphanin is thought to be due to sulforaphane, an isothiocyanate metabolite produced from glucoraphanin by myrosinase. Here we show, in rat liver, that while glucoraphanin slightly induces Phase-II enzymes, it powerfully boosts Phase-I enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), nitrosamines and olefins. Induction of the cytochrome P450 (CYP) isoforms CYP1A1/2, CYP3A1/2 and CYP2E1 was confirmed by Western immunoblotting. CYP induction was paralleled by an increase in the corresponding mRNA levels. Concomitant with this Phase-I induction, we also found that glucoraphanin generated large amount of various reactive radical species, as determined by electron paramagnetic resonance (EPR) spectrometry coupled to a radical-probe technique. This suggests that long-term uncontrolled administration of glucoraphanin could actually pose a potential health hazard.

Characterization of testosterone 11 beta-hydroxylation catalyzed by human liver microsomal cytochromes P450

A combination of accelerator mass spectrometry (AMS) and liquid chromatography-tandem mass spectrometry has been used to clarify some new aspects of testosterone metabolism. The main pathway of testosterone oxidative metabolism by human liver microsomes is the formation of 1beta-, 2alpha-/beta-, 6beta-, 15beta-, and 16beta-hydroxytestosterones, mainly catalyzed by cytochromes P450 2C9, 2C19, and 3A4. We now report the first determination that 11beta-hydroxytestosterone (11beta-OHT) can also be formed by human liver microsomal fractions. The structures of five hydroxylated metabolites of testosterone (2beta-, 6beta-, 11beta-, 15beta-, and 16beta-OHT) and the C-17 oxidative metabolite androstenedione were determined by liquid chromatography with UV detection at 240 nm and liquid chromatography-tandem mass spectrometry. Corresponding results were obtained by high-performance liquid chromatography-AMS analysis of incubations of [4-14C]testosterone with human liver microsomes. 6beta-Hydroxylation was always the dominant metabolic pathway, but 2beta-, 15beta-, and 16beta-OHT, and androstenedione were also formed. The previously undetected hydroxytestosterone, 11beta-OHT, was found to be a minor metabolite formed by human liver microsomal enzymes. It was formed more readily by CYP3A4 than by either CYP2C9 or CYP2C19. 11beta-Hydroxylation was inhibited by ketoconazole (IC50 = 30 nM) at concentrations similar to the IC50 (36 nM) for 6beta-hydroxylation Therefore, CYP3A4 could be mainly responsible for testosterone 11beta-hydroxylation in the human liver. These findings identify human hepatic biotransformation of testosterone to 11beta-OHT as a previously unrecognized extra-adrenal metabolic pathway.

Testosterone 1 beta-hydroxylation by human cytochrome P450 3A4

Human cytochrome P450 3A4 forms a series of minor testosterone hydroxylation products in addition to 6 beta-hydroxytestosterone, the major product. One of these, formed at the next highest rate after the 6 beta- and 2 beta-hydroxy products, was identified as 1 beta-hydroxytestosterone. This product was characterized from a mixture of testosterone oxidation products using an HPLC-solid phase extraction-cryoprobe NMR/time-of-flight mass spectrometry system, with an estimated total of approximately 6 microg of this product. Mass spectrometry established the formula as C(19)H(29)O(3) (MH(+) 305.2080). The 1-position of the added hydroxyl group was established by correlated spectroscopy and heteronuclear spin quantum correlation experiments, and the beta-stereochemistry of the added hydroxyl group was assigned with a nuclear Overhauser correlated spectroscopy experiment (1 alpha-H). Of several human P450s examined, only P450 3A4 formed this product. The product was also formed in human liver microsomes.

Involvement of interleukin-6 and tumor necrosis factor alpha in CYP3A11 and 2C29 down-regulation by Bacillus Calmette-Guerin and lipopolysaccharide in mouse liver

Bacillus Calmette-Guérin (BCG) and lipopolysaccharide (LPS) are well known potent activators of the cell-mediated immune system and thus lead to the decreases in cytochrome P450 (P450). In this study we used interleukin (IL)-1alpha/beta, IL-6, or tumor necrosis factor alpha (TNFalpha) knockout (KO) mice to investigate how each cytokine is involved in P450 down-regulation, especially CYP3A11 and 2C29. BCG (40 mg/kg) was found to reduce both CYP3A11 and 2C29 mRNAs at 24 h after treatment in IL-1alpha/beta KO mice in a manner similar to that seen in wild-type mice. CYP3A11 mRNA, but not CYP2C29 mRNA, was significantly decreased by BCG treatment in the TNFalpha KO mice, although the decrease was less than that of wild-type or IL-1alpha/beta KO mice. In contrast, BCG showed no significant effect on CYP3A11 and 2C29 mRNAs in IL-6 KO mice. On the other hand, LPS was able to decrease CYP3A11 and 2C29 mRNA levels in all of the cytokine KO mice and markedly increased systemic levels of TNFalpha; BCG (40 mg/kg) lacked such activity. The present study has shown that IL-6 and TNFalpha are likely to be major factors involved in the down-regulation of CYP3A11 and 2C29 mRNAs in mice. In addition, there exist differences in the amount and/or kind of cytokines released by BCG or LPS, the latter being more potent than the former. This will be a possible reason for differential capability of P450 down-regulation between BCG and LPS.

Induction and suppression of cytochrome P450 isoenzymes and generation of oxygen radicals by procymidone in liver, kidney and lung of CD1 mice

Although chronic administration of procymidone (a widely used dicarboximide fungicide) leads to an increased incidence of liver tumors in mice, short-term genotoxicity studies proved negative. As cytochrome P450 (CYP) induction has been linked to non-genotoxic carcinogenesis, we investigated whether procymidone administration causes induction of CYP-dependent monooxygenases in liver, kidney and lung microsomes of male Swiss Albino CD1 mice after single or repeated (daily for three consecutive days) i.p. treatment with either 400 or 800 (1/10 or 1/20 of the DL(50)) mgkg(-1) b.w. procymidone. CYP content and CYP3A1/2, 1A1, 1A2, 2B1/2, 2E1, 2A, 2D9 and 2C11 supported oxidations were studied using either the regio- and stereo-selective hydroxylation of testosterone as multibiomarker or highly specific substrates as probes of various CYPs. While a single dose was uneffective, multiple procymidone administration lead to marked inductions of various monooxygenases: CYP3A1/2 in liver and lung (as measured by N-demethylation of aminopyrine and testosterone 6 beta-hydroxylase); CYP2E1 in liver (p-nitrophenol hydroxylation); CYP1A1 in liver and kidney (deethylation of ethoxyresorufin). Several hydroxylations were induced in the liver, including the CYP2A-linked 7 alpha (14-fold) as well as 6 alpha (22-fold), 6 beta, 16 beta and 2 beta hydroxylases. The pattern of inductions/suppressions recorded in the three different tissues suggests that procymidone exerts complex effects on the CYP profile. Tissue-specific trends included a large number of inductions in the liver and suppressions in the lung. The main inductions were corroborated by immunoblotting analyses and Northern blotting showed that inductions of CYP3A1/2, CYP2E1 and CYP1A1/2 were paralleled by increased mRNA levels. It was also found that CYP over-expression generates large amounts of reactive oxygen species (ROS), especially in liver. These data may explain why in vitro short-term genotoxicity studies on procymidone were negative, whereas in vivo long-term carcinogenesis studies turned out positive: long-term CYP induction (e.g. oxygen centered free radicals over-production) can have a co-carcinogenic and/or promoting potential.

Lipopolysaccharide-mediated modulation of cytochromes P450 in Stat1 null mice

Signal transducer and activator of transcription (Stat), a family of transcriptional factors, has been demonstrated to play a critical role in gene regulation in response to inflammatory cytokines, such as interferon and interleukin-6. Inflammatory cytokines and bacterial endotoxin are known to suppress, in most of cases, the constitutive or induced cytochromes P450 (P450) in animals and humans. However, it is not clear if the suppression of P450 by cytokines is through the Stat-signaling pathway. In the present study, we determined whether Stat1 is involved in lipopolysaccharide (LPS)-mediated modulation of P450 in mouse liver. In both Stat1(+/+) (wild type) and Stat1(-/-) (null) mice, a single dose of LPS treatment (1 mg/kg of body weight, i.p.) significantly reduced the expression of CYP3A11, 2C29, and 1A2 mRNA to 8 to 40% of the control levels as determined by real-time quantitative reverse transcription-polymerase chain reaction. The reduction was supported by Western blot analysis. In contrast, LPS significantly induced the level of CYP4A10 mRNA in both Stat1(+/+) (338% of control) and Stat1(-/-) mice (264% of control). Although suppression of mRNA levels of CYP2E1, and 2D9 was not observed in either LPS-treated Stat1 null or wild-type animals, LPS treatment resulted in a reduction of CYP2E1 protein content, which was more significant in Stat1(+/+) (23% of control) than in Stat1(-/-) mice (67% of control). Consistent with this result, the chlorzoxazone 6-hydroxylase and lauric acid 11-hydroxylase activities, as CYP2E1 representative activities, were reduced markedly by LPS in Stat1(+/+) but not in Stat1(-/-) mice. The ethoxyresorufin O-deethylase activity, as a representative CYP1A activity, was also reduced significantly only in LPS-treated Stat1(+/+) mice. These data clearly demonstrate that LPS-mediated modulation of CYP3A11, 2B10, 2C29, 1A2, and 4A10 in mouse liver is Stat1-independent. However, the significant difference between the LPS-treated Stat1(+/+) and Stat1(-/-) mice in the levels of CYP2E1 protein and activity as well as in the activity level of CYP1A suggests that Stat1 may be indirectly involved in the post-transcriptional modulation of these two mouse P450 enzymes.

Determination of testosterone metabolites in human hepatocytes. I. Development of an on-line sample preparation liquid chromatography technique and mass spectroscopic detection of 6beta-hydroxytestosterone

A rapid and sensitive RP-HPLC assay for determination of 6beta-hydroxytestosterone in human hepatocytes with corticosterone as the internal standard is described. The procedure employs on-line sample enrichment using a BioTrap 500 MS (20x4 mm I.D.) extraction pre-column and subsequent gradient separation on a Prontosil 60-5 C(18)-H (250x2 mm I.D., 5 micrometer particle size) analytical column in the back-flush mode using a ternary eluent system composed of methanol, tetrahydrofuran and water. Signal monitoring was done by measurement of the responses from liquid chromatography coupled to mass spectroscopy (LC-MS/MS) using an atmospheric pressure chemical ionization (APCI) source conducted in the selected reaction monitoring (SRM) mode. Mean recoveries of 6beta-hydroxytestosterone from an estimate of the biological matrix, i.e., Dulbecco's modified Eagle medium "High Glucose", ranged from 101.8-104.4% for samples containing the target analyte at the 250, 500 and 1000 ng/ml level. The limit of quantitation (LOQ) was 20 ng/ml at an injection volume of 100 microliter determined in the same matrix. Linearity of signal responses versus concentration for all three analytes was accomplished in the range of 100-4000 ng/ml. Mean values of the coefficients of variation (C.V.) for the target analyte obtained for the concentrations 250, 500 and 1000 ng/ml at 5 different days in quintuplicate ranged from 1.5-7.7% (within-day) and 4.8-7.3% (between-day). The corresponding values for the accuracy ranged from 87.7-106.1% for the within-day and from 98.8-102.5% for the between-day measurements. The target analyte was sufficiently stable at both storage and sample preparation conditions because no substantial deviations between analyte concentrations measured before and after subsequently performed freeze and thaw cycles were observed.

Characterization of mixtures of recombinant human cytochrome p450s as a screening model for metabolic stability in drug discovery

1. Recombinant human cytochrome p450 (rhCYP) has become an important screening model in drug metabolism studies due to the high cost of human and animal hepatic tissue. Until now, rhCYPs have been evaluated and used as separate forms, but a mixture of CYP forms comparable with the human liver could be of value in early drug discovery. 2. In the present study, rhCYP2C9, rhCYP2D6 and rhCYP3A4 co-expressed with reductase in Escerichia coli were mixed and evaluated with regards to kinetic properties (K(m) and V(max)). Furthermore, antioxidant was added to investigate whether a free radical scavenger would affect the kinetic parameters. Results were compared with data obtained in human liver microsomes (HLM). 3. Results showed a good correlation between mixed rh CYP data and HLM data for K(m) and V(max). K(m) varied < 3-fold between matrices for CYP2C9 and CYP3A4, whereas the K(m) for CYP2D6 varied up to 4.5-fold. V(max) differed up to 3-fold between matrices for the CYP forms investigated. However, the discrepancy in V(max) may depend on the anticipated level of each form in HLM. The addition of antioxidant increased V(max) for CYP2C9 and CYP2D6 by 75 and 50%, respectively, whereas V(max) for CYP3A4 was unchanged. 4. In conclusion, the rhCYP mixture shows promising results as a predictor of CYP kinetic parameters. Furthermore, addition of antioxidant can in certain cases increase catalytic activity.

Effects of trivalent chromium on hepatic CYP-linked monooxygenases in laying hens

Chromium is an essential nutrient required for the metabolism of carbohydrates and lipids in humans and many animal species. We evaluated whether feeding laying hens with high levels of different chemical forms of trivalent chromium may affect hepatic metabolizing cytochrome P-450 (CYP)-linked enzymes. Modulation of CYP-dependent monooxygenases (which play a pivotal role in the endogenous metabolism) by Cr(III) was tested using either specific substrates as probes of different CYPs or testosterone as a multi-bioprobe. The CYP-supported oxidases were studied in liver microsomes from laying hens fed with diet supplemented with either 25 or 50 ppm chromium chloride as a yeast or as aminoniacinate. Although at 25 ppm no appreciable effects were observed, at 50 ppm a general inactivation of the recorded monooxygenases (ranging from 34% loss for ethoxycoumarin O-deethylase with chromium chloride to 85% loss for O-deethylation of ethoxyresorufin with either chromium yeast or aminoniacinate) were achieved in the supplemented groups vs controls. The only exception was the O-dealkylation of pentoxyresorufin, which was significantly boosted by both chromium yeast (up to 65% increase) and chromium aminoniacinate (up to 141%). Measurements of the regio- and stereoselective hydroxylation of testosterone used as a multi-bioprobe corroborated the inactivating properties of Cr(III) at the higher dose. Taken as a whole, these findings seem to indicate that high levels of Cr(III) supplementation can substantially impair CYP-catalysed drug metabolism in laying hens.

Rapid high-performance liquid chromatographic method for the separation of hydroxylated testosterone metabolites

A rapid high-performance liquid chromatography (HPLC) method is described for the quantitation of hydroxytestosterone metabolites. The method combines a Hypersil BDS C18 analytical column (10 cm x 0.46 cm) and a linear mobile phase (1.25 ml/min) gradient of tetrahydrofuran-acetonitrile-water (10:10:80, v/v) changing to tetrahydrofuran-acetonitrile-water (14:14:72, v/v) over 10 min then remaining isocratic for 3 min. The total run time for the chromatographic separation of eight metabolites of testosterone is 15 min. Detection by UV is linear between 300 ng/ml and 10 microg/ml with a limit of detection on column of 300 ng/ml. A method for the direct HPLC analysis of liver microsomal incubates of [14C]testosterone is also briefly described and when combined with the HPLC method, offers a distinct advantage over previously reported methods for the rapid screening of testosterone hydroxylase activity in rat and human liver microsomes.

Simultaneous determination of testosterone metabolites in liver microsomes using column-switching semi-microcolumn high-performance liquid chromatography

A sensitive and selective column-switching semi-microcolumn high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of testosterone and eight of its metabolites (6alpha-, 6beta-, 16alpha-, 16beta-, 7alpha-, 2alpha-, and 2beta-hydroxytestosterone, and androstenedione) in liver microsomes. After incubation for 10 min, testosterone and its metabolites were extracted from the microsomes with ethyl acetate, and the extract was evaporated to dryness. The residue was dissolved in the mobile phase and loaded onto the HPLC system. The analytes were first concentrated in a precolumn and subsequently transferred to the analytical column, where they were separated using linear gradient elution. A UV detector set at 254 nm was used to detect the analytes. This newly developed method clearly separated TES and the metabolites with high resolution and was found to be reproducible with intra- and interday variability of <10.7%. This method has been subsequently used to determine the testosterone hydroxylation activities catalyzed by 15 different recombinant CYP isozymes. The results confirmed the formation of stereoselectively hydroxylated metabolites by each CYP isozyme.

Captan impairs CYP-catalyzed drug metabolism in the mouse

To investigate whether the fungicide captan impairs CYP-catalyzed drug metabolism in murine liver, kidney and lung, the modulation of the regio- and stereo-selective hydroxylation of testosterone, including 6beta-(CYP3A), 6alpha-(CYP2A1 and CYP2B1) and 16alpha-(CYP2B9) oxidations was studied. Specific substrates as probes for different CYP isoforms such as p-nitrophenol (CYP2E1), pentoxyresorufin (CYP2B1), ethoxyresorufin (CYP1A1), aminopyrine (CYP3A), phenacetin and methoxyresorufin (CYP1A2), and ethoxycoumarin (mixed) were also considered. Daily doses of captan (7.5 or 15 mg/kg b.w., i.p.) were administered to different groups of Swiss Albino CD1 mice of both sexes for 1 or 3 consecutive days. While a single dose of this fungicide did not affect CYP-machinery, repeated treatment significantly impaired the microsomal metabolism; in the liver, for example, a general inactivating effect was observed, with the sole exception of testosterone 2alpha-hydroxylase activity which was induced up to 8.6-fold in males. In vitro studies showed that the mechanism-based inhibition was related to captan metabolites rather than the parental compound. In the kidney, both CYP3A- and CYP1A2-linked monooxygenases were significantly induced (2-fold) by this pesticide. Accelerated phenacetin and methoxyresorufin metabolism (CYP1A2) was also observed in the lung. Data on CYP3A (kidney) and CYP1A2 (kidney and lung) induction were corroborated by Western immunoblotting using rabbit polyclonal anti-CYP3A1/2 and CYP1A1/2 antibodies. By means of electron spin resonance (EPR) spectrometry coupled to a spin-trapping technique, it was found that the recorded induction generates a large amounts of the anion radical superoxide (O*2-) either in kidney or lung microsomes. These findings suggest that alterations in CYP-associated activities by captan exposure may result in impaired (endogenous) metabolism as well as of coadministered drugs with significant implications for their disposition. The adverse outcomes associated to CYP changes (e.g. cotoxicity, comutagenicity and promotion) may also have harmful consequences.

Determination of testosterone and 6beta-hydroxytestosterone by gas chromatography-selected ion monitoring-mass spectrometry for the characterization of cytochrome p450 3A activity

A method for the determination of testosterone and its metabolite, 6beta-hydroxytestosterone, in liver microsomal incubates employing gas chromatography with selected ion monitoring mass spectrometric detection (GC-SIM-MS) has been developed. The method is more rapid than previously reported methods. Testosterone and its metabolites are extracted from the incubation mixture in a single step with methylene chloride. The method does not require derivatization and testosterone and its metabolites are separated on a HP-5MS fused-silica capillary column in less than 15 min. The retention times of testosterone (m/z 288), methyltestosterone (m/z 302), and 6beta-hydroxytestosterone (m/z 304) are approximately 12.7, 12.8, and 13.4 min, respectively. There are no interferences from other known CYP450 metabolites of testosterone. In addition, the selectivity and specificity of the mass spectrometer helps eliminate possible interferences from drugs and new chemical entities evaluated using this methodology. Calibration curves for testosterone and 6beta-hydroxytestosterone are linear from 0.25 to 100 microM. Extraction recoveries are better than 92% for both analytes and the internal standard, methyltestosterone. Over the course of five separate runs, within-day and inter-day precision (expressed as relative standard deviation) was less than 5% for all concentrations of testosterone and 6beta-hydroxytestosterone. Accuracies ranged from 95.8 to 105.8% for testosterone and 94.6 to 104.2% for 6beta-hydroxytestosterone. The assay has been used to characterize the CYP3A metabolic activity of multiple preparations of human, rat, and dog liver microsomes.

Effect of liquorice and glycyrrhizin on rat liver carcinogen metabolizing enzymes

We investigated the effect of single or repeated intake of conspicuous amounts of licorice root extract (LE, 3138 or 6276 mg/kg body weight (bw) per os) or its natural constituent glycyrrhizin (G, 240 or 480 mg/kg bw per os) on Sprague-Dawley rat liver monooxygenases. Whereas a single LE or G dose was unable to affect CYP superfamily, four daily doses induced CYP3A, CYP1A2 and to varying extents CYP2B1-linked monooxygenases. A boosting effect on testosterone 6beta- (CYP3A1/2, CYP1A1/2), 7alpha- (CYP1A1/2, CYP2A1), 16alpha- (CYP2B1, CYP2C11), 2alpha- (CYP2C11) and 2beta- (CYP3A1, CYP1A1) -dependent oxidases as well as on androst-4-ene-3,17-dione- (CYP3A1/2) -supported monooxygenases were also achieved. Harmful outcomes associated to CYP changes (e.g. cotoxicity, cocarcinogenicity and promotion) may be of concern.

Bile acid structure and selective modulation of murine hepatic cytochrome P450-linked enzymes

We examined the effects of the administration of different bile acids on in vivo hepatic murine cytochrome P450 (CYP) content, nicotinamide adenine dinucleotide phosphate (NADPH)-CYP-reductase, and individual mixed-function oxidases (MFOs). Neither CYP level nor reductase were appreciably affected by single intraperitoneal administration of taurodeoxycholic acid (TDCA) (12.2 or 24.4 mg x kg(-1) bw). MFO to various isoenzymes were slightly reduced 24 hours after treatment. Taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA) both induced CYP, reductase, and MFOs. CYP3A1/2-linked activity (i.e., testosterone 6beta-hydroxylase, and N-demethylation of aminopyrine) in a dose-dependent fashion was enhanced ( approximately 2-3-fold). CYP2E1- (hydroxylation of p-nitrophenol), CYP1A2-(O-demethylation of methoxyresorufin), CYP2A1/2- and CYP2B1/2-(6alpha-hydroxylase), and CYP2B9- (16alpha-hydroxylase) dependent MFOs, as well as 7alpha-, 16beta-, 2alpha-, and 2beta-hydroxylations, were all significantly induced by THDCA. Apart from alkoxyresorufin metabolism and a modest CYP2E1 increase, TUDCA behaved like THDCA. A generalized induction was also recorded after ursodeoxycholic acid (UDCA) administration. THDCA and TDCA did not show substantial differences in the N-demethylation of aminopyrine when different species (rat vs. mouse) and administration route (intraperitoneal vs. intravenous) were compared. Results on the most affected isoenzymes, CYP3A1/2 (THDCA, TUDCA, and UDCA) and CYP2E1 (UDCA), were sustained by means of Western immunoblotting. CYP3A induction was paralleled by a corresponding increase in mRNA. These data could partially explain the therapeutic mechanism of UDCA, TUDCA, and THDCA in chronic cholestatic liver disease. CYP3A induction, which is linked to P-glycoprotein (Pgp) family overexpression, may enhance hepatic metabolism, transport, and excretion of toxic endogenous lipophilic bile acids.

Modulation of testosterone-metabolizing hepatic cytochrome P-450 enzymes in developing Sprague-Dawley rats following in utero exposure to p,p'-DDE

1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) causes sexual developmental aberrations in male rats through a likely mechanism of androgen receptor antagonism. DDE is also known to induce liver cytochrome P-450 (CYP). The expression of CYP enzymes is regulated by steroid hormones, which, in turn, are inactivated in the liver by CYP-catalyzed hydroxylations and subsequent conjugations. This study was undertaken to examine the potential of in utero DDE exposure to affect the developmental expression of the hepatic CYP enzymes that are responsible for testosterone hydroxylations. Pregnant Sprague-Dawley rats were dosed daily by gavage with DDE at 0, 10, or 100 mg/kg body weight or with flutamide at 40 mg/kg body weight from gestation day 14 to 18. Additional adult male rats were given seven daily doses of DDE at 100 mg/kg. Liver samples were collected from the offspring of the dosed dams on postnatal days (PND) 10 and 21 and from the adult rats a day after the last dosing. Assays for regioselective and sterospecific testosterone hydroxylase activities were performed using hepatic microsomal preparations. Specific liver CYP proteins were detected by immunoblotting. While the CYP2B1 and 3A1 and their hydroxylated testosterone products were highly elevated by the DDE treatments in both adult and developing rats, the responses of 2C11 and 2A1 were development-dependent. The flutamide treatment had little effect on CYP enzyme expression. This study demonstrated that developing offspring rats are susceptible to the hepatic CYP enzyme-modulating action of DDE following its administration to the pregnant dams.

Induction and suppression of murine CYP-mediated biotransformation by dithianon: organ- and sex-related differences

With the aim of evaluating the co-carcinogenic properties of dithianon, the regio- and stereo-selective hydroxylation of testosterone was used as a multibiomarker of effect for cytochrome P450 (CYP) changes. CYP-catalysed reactions have been studied in liver, kidney and lung microsomes from male and female Swiss albino CD1 mice treated i.p. with single (3 or 6 mg/kg body wt.) or repeated (3 mg/kg body wt. daily for 3 days) doses of this fungicide. Induction or suppression was recorded under various situations in different organs and sexes. In liver, all testosterone hydroxylase (TH) activities were increased in the single treatment from 2.8- (6beta-, 16alpha- and 16beta-TH activities) to 16-fold (2beta-TH activity) in males at the lower dose. In contrast, activities were reduced from 33.3% (16beta- and 17-TH activities, lower dose) to 66.4% (16beta-TH activity, higher dose) in females. In kidney, a similar pattern of modulation was achieved: induction from 2.9- to 5-fold (6beta- and 2alpha-TH activities, higher and lower doses, respectively) in males; suppression from 47.4 to 50.2% (2alpha- and 2beta-TH activities, either at lower or higher doses) in females. In lung, a significant induction ranging from 7.1- to 29.3-fold (16alpha- and 2alpha-TH activities, respectively, lower dose) in males, and up to a 7-fold increase (2beta-TH activity, higher dose) in females was obtained. After repeated treatment, hepatic 6beta-, 16beta-, 2alpha- and 2beta-TH activities were reduced up to approximately 60% in males, whereas no effect was seen in females. In extrahepatic tissues, a generalized increase of different THs was observed. The increase of 6beta-TH activity (CYP3A-linked), one of the most representative isoforms in humans, was sustained in liver and kidney by means of Western immunoblotting, using rabbit polyclonal antibodies anti CYP3A1/2. On the whole, a complex pattern of induction/suppression of CYP-dependent reactions was achieved depending on sex and tissue. The data are consistent with co-toxic, co-carcinogenic and promoting potentials of this fungicide and provide information of interest in evaluating the risk associated with human exposure.

Effects of the agrochemicals butachlor, pretilachlor and isoprothiolane on rat liver xenobiotic-metabolizing enzymes

1. The herbicides butachlor (2-chloro-2',6',diethyl-N-[buthoxymethyl] acetanilide) and pretilachlor (2-chloro-2',6'-diethyl-N-[2-propoxyethyl] acetanilide) are widely used in Asia, South America, Europe and Africa. Isoprothiolane (diisopropyl-1,3-dithiolan-2-ylidenemalonate) is used as a fungicide and an insecticide in rice paddies. We administered these agrochemicals to the male rat and examined their effects on cytochrome P450 (P450), glutathione S-transferase (GST), UDP-glucuronosyltransferase (UDPGT), and NAD(P)H-quinone oxidoreductase 1 (NQO1)-related metabolism in the liver. 2. Administration of isoprothiolane, butachlor or pretilachlor to rat induced hepatic P4502B subfamily-dependent enzyme activities (pentoxyresorufin O-depentylation and testosterone 16 beta-hydroxylation) up to 271-413% of control, which coincided with the increase in expression levels of the P4502B apoprotein. 3. Activities of GST toward 1-chloro-2,4-nitrobenzene and 3,4-dichloronitrobenzene were slightly induced (127-133% of control) in the liver of the rat treated with these pesticides. On the other hand, marked elevations of UDPGT activities toward p-nitrophenol (164-281% of control) were observed. NQO1-related metabolism (menadione reductase activity) was also induced (123-176% of control) in the liver of rat treated with these agrochemicals. 4. These results indicate that some of the agrochemicals currently in use are capable of inducing phase I and II xenobiotic-metabolizing enzyme activities in an isozyme selective manner. The induction of these activities may disrupt normal physiologic functions related to these enzymes in exposed animals.

Regio- and stereoselectivity in the metabolism of benzo[c]phenanthrene mediated by genetically engineered V79 Chinese hamster cells expressing rat and human cytochromes P450

Regio- and stereoselective metabolism mediated by cytochrome P450 (CYP) and metabolite-dependent cytotoxicity of benzo[c]phenanthrene (B[c]Ph) and its trans-3,4-dihydrodiol, the metabolic precursor of the carcinogenic fjord-region B[c]Ph-3,4-dihydrodiol 1,2-epoxides (B[c]PhDE), were investigated with V79 Chinese hamster cells genetically engineered for three rat and six human CYP isoforms. The order of the capabilities of the CYP isoforms to metabolize B[c]Ph was as follows: h1A1>r1A1>r1A2>h1B1>h1A2>r2B1>>h2E1>h2A6>h3A4. Regardless of the species, all individual CYP isoforms preferentially catalyzed the oxidation of B[c]Ph at the 5,6-position (K-region) except human CYP1A1 and human CYP1A2, which oxidized both the 5,6- and the 3,4-position with similar efficiency. While human CYP1A1, rat CYP1A1 and rat CYP1A2 formed almost exclusively the (-)-B[c]Ph-3R,4R-dihydrodiol, human CYP1A2 produced both the (-)-3R,4R- and the (+)-3S,4S-dihydrodiol enantiomers in a ratio of 2:1. Stereoselective activation of B[c]Ph, the (±)-B[c]Ph-3,4-dihydrodiol and its (-)-3R,4R-enantiomer to the fjord-region (-)-anti-B[c]PhDE occurred upon incubation with rat CYP1A1 and rat CYP1A2 as indicated by the formation of two stereoisomeric tetraols, the hydrolysis products of the labile anti-B[c]PhDE. The formation of tetraols in the culture medium was accompanied by a concentration-dependent increase in cytotoxicity indicating that this effect was mediated by the fjord-region (-)-anti-B[c]PhDE formed as reactive intermediate. All human and rat CYP-expressing V79 cell lines investigated did not show any significant capacity to metabolize the (+)-3S,4S-dihydrodiol. The present study indicates that the human CYP isoforms 1A1 and 1B1 have complementary catalytic properties to activate B[c]Ph to its fjord-region B[c]PhDE, whereas other human isoforms play a minor role. Activation of B[c]Ph by human CYP1A1 and 1B1 is less efficient than by rat CYP1A1 or rat CYP1A2, but proceeds with similar stereoselectivity via the (-)-3R,4R-dihydrodiol to the strong carcinogen (-)-anti-B[c]PhDE with (R,S,S,R)-configuration.

Simultaneous variation of temperature and gradient steepness for reversed-phase high-performance liquid chromatography method development. I. Application to 14 different samples using computer simulation

The optimized reversed-phase HPLC separation of 14 different samples is reported, based on simultaneous changes in temperature and gradient steepness. Four experimental runs are required for each sample, following which preferred conditions can be predicted using computer simulation software (DryLab). The overall accuracy and effectiveness of this method development approach is discussed, with particular attention to the use of resolution maps provided by the software. These maps are useful for maximizing resolution for the total sample, for optimizing the separation of a smaller number of selected sample compounds, and as an initial step in the separation of more demanding samples.

Simultaneous variation of temperature and gradient steepness for reversed-phase high-performance liquid chromatography method development. II. The use of further changes in conditions

The preceding paper (Part I) suggests that simply optimizing temperature and gradient steepness will often provide an adequate reversed-phase HPLC separation. In some cases, however, this procedure will prove unsuccessful, and then further method-development experiments (involving change in other separation conditions) will be required. One strategy is to change a variable other than temperature or gradient steepness, followed by re-optimization of the latter two variables. The present paper examines the application of this approach with the aid of computer simulation to several samples.

Effect of licorice and glycyrrhizin on murine liver CYP-dependent monooxygenases

This study is aimed to investigate the effect of the prolonged intake of conspicuous amounts of licorice (LE), or its natural constituent glycyrrhizin (G) on murine liver CYP-catalyzed drug metabolism. For this purpose the modulation of the regio- and stereo-selective hydroxylation of testosterone, together with the use of highly specific substrates as probes for different CYP isoforms such as ethoxyresorufin (CYP1A1), methoxyresorufin (1A2), pentoxyresorufin (2B1), p-nitrophenol (2E1) and aminopyrine (3A), were investigated. Daily doses of licorice root extract (3,138 or 6,276 mg/kg b.w. per os), or G (240 or 480 mg/kg b.w. per os), were administered to different groups of Swiss Albino CD1 mice of both sexes for 1, 4 or 10 consecutive days. While a single LE or G dose was unable to affect the multienzymatic CYP-system, using both schedules of repeated treatment, either LE or G were able to significantly induce hepatic CYP3A- and, to a lesser extent, 2B1- and 1A2-dependent microsomal monooxygenase activities, as well as 6beta- (mainly associated to CYP3A), 2alpha-, 6alpha- (CYP2A1, 2B1), 7alpha-, 16alpha- (CYP2B9) and 16beta-testosterone hydroxylase (TH) activities in male and female mice. Data on CYP3A modulation, the major isoform present in human liver, was confirmed by using Western immunoblotting with anti-CYP3A1/2 rabbit polyclonal antibodies raised against purified rat CYP3A. Northern blotting analysis using CYP3A cDNA biotinylated probe showed that the expression of such isozyme is regulated at the mRNA level. These results suggest that the induction of cytochrome P450-dependent activities by the prolonged intake of high LE or G doses, may result in accelerated metabolism of coadministered drugs with important implications for their disposition. The adverse effects associated with CYP changes such as toxicity/cotoxicity and comutagenicity may also have clinical consequences.

Development of basal and induced testosterone hydroxylase activity in the chicken embryo in ovo

1. The sensitivity of the developing embryo to xenobiotics is highly dependent on the expression of metabolizing enzymes including cytochromes P450 (CYP). In the present study, therefore, the ontogeny of the CYP-dependent system in the chick was investigated with testosterone hydroxylase activity as a marker of CYP expression. 2. Chicken embryo livers were assayed for basal and phenobarbitone (PB)-induced regio- and stereo-selective testosterone hydroxylase activity, from the first appearance of the liver as a discrete organ at 5 days of incubation through day 10 posthatching. In addition, whole embryo preparations were assayed at 3 and 4 days of incubation. 3. Whereas testosterone 16 beta-hydroxylase and androst-4-ene-3, 17-dione-linked activities were expressed during all stages of embryonic development, testosterone 6 alpha-, 6 beta-, 7 alpha- and 16 alpha-hydroxylase activities were observed only in basal embryos from 8 days of incubation. Furthermore, testosterone 2 alpha- and 2 beta-hydroxylase activities were detected exclusively from 10 days of incubation onward. All activities increased steadily throughout development as did the responsiveness of the embryonic liver to PB induction. 4. A typical pattern of development with a higher activity from 10 to 14 days of incubation (testosterone 16 alpha-, 7 alpha-, 6 alpha- and 2 beta-hydroxylase activities; up to 4.1 +/- 0.3 pmol mg-1 protein min-1 at 13 days of incubation for testosterone 7 alpha-hydroxylase) or shifted to 14 to 18 days of incubation (testosterone 6 beta-, 2 alpha- and 16 beta-hydroxylase activities: up to 56.6 +/- 1.4 pmol mg-1 protein min-1 at 16 days of incubation for testosterone 6 beta-hydroxylase) was observed. There was a tendency towards an increased activity for all activities around hatching, specifically from 19 days of incubation to 4 days posthatching (up to 1,759.3 +/- 179.4 pmol mg-1 protein min-1 at 1 day posthatching for androst-4-ene-3,17-dione-linked activity). 5. The highest level of PB-induced enzyme activity was observed for testosterone 2 alpha-hydroxylase activity (95.14 +/- 7.35 and 660.19 +/- 45.27 pmol mg-1 protein min-1) at 12 days of incubation and day 3 posthatching, respectively. Except for testosterone 2 alpha- and 2 beta-hydroxylase activities at 3 to 4 days of incubation, all metabolites were detectable during the first period of organogenesis in the presence of PB. 6. The use of highly specific substrates, studies on the immunoinhibition of metabolism by polyclonal antibodies raised against highly purified rat CYPs, and the use of selective inhibitors seemed to reveal a wide pleiotropic response with the possible presence in liver of PB-treated chickens of CYP1A together with CYP2HI/H2, CYP2E and CYP3A.

Improved high-performance liquid chromatographic procedure for the separation and quantification of hydroxytestosterone metabolites

A reproducible, sensitive high-performance liquid chromatography (HPLC) method has been developed to quantify hydroxytestosterone metabolites. The method features a simple one-step linear gradient of methanol in water (10%-60% methanol) for separation of the testosterone metabolites on a Supelcosil LC-18 column; metabolites are detected at 247 nm. This method provides a distinct advantage over previously developed assays in that the solvent gradient does not contribute to baseline changes throughout the chromatographic run. In this way, the flat baseline markedly improves robustness of the assay and simplifies peak integration and quantification. At the same time, resolution of 15 different steroid metabolites catalyzed by the cytochrome P-450 enzymes are readily separated in rat or mouse liver microsomes. An internal standard, cortexolone, was selected for use based on its structural and spectral similarity to the hydroxytestosterone metabolites, and quantification is based on the molar response for the testosterone/cortexolone peak area ratio. The limit of detection (LOD) is 1 pmol on-column with a limit of quantitation (LOQ) of 4 pmol on-column. The intraday repeatability is approximately 3%. This simplified procedure is straightforward and should greatly facilitate the routine use of the testosterone hydroxylation assay to measure cytochrome P-450 isozyme activity.

Strain differences in age-associated change in testosterone 6β-hydroxylation in Wistar and Dark Agouti rats

This study examines strain differences in testosterone (T)-hydroxylations between Wistar and Dark Agouti (DA) rats of both genders. The DA rat, an animal model, is a poor metabolizer of such drugs as debrisoquine, which are metabolized by cytochrome P450 (CYP) 2D. T-16α-, 2α-hydroxylations, which are linked to CYP2C11, were catalyzed at similar rates by the microsomes of both strains. In contrast, the liver microsomes from mature male DA rats catalyzed T-6β-hydroxylation, the CYP3A mediated activity, at higher rates (∼ 2-fold) than Wistar rat liver microsomes did. There was no difference between immature male DA and Wistar rats for T-6β-hydroxylation, indicating that the activity in male DA rat increases with maturation. Polyclonal antibodies raised against rat liver microsomal CYP3A2 and a CYP3A inhibitor, troleandomycin (TAO), effectively inhibited T-6β-hydroxylation by liver microsomes from both strains of rats. The level of T-6β- hydroxylation activity correlated well with the amount of CYP3A protein in the microsomes in mature as well as in immature male and female Wistar and DA rats. Northern blot analysis repeatedly indicated that the cellular contents of CYP3A2 mRNA are slightly (∼ 20%) higher in the liver of mature DA rats than in that of mature Wistar rats. These results indicate that the increased levels of CYP3A are responsible for the increased T-6β-hydroxylation activity and protein in DA rat.

Cytochrome P450-mediated activation of phenanthrene in genetically engineered V79 Chinese hamster cells

V79 Chinese hamster cells genetically engineered for rat cytochromes P450 1A1, 1A2, 2B1 and human cytochromes P450 1A1, 1A2, 2A6, 2E1, and 3A4 are being applied in metabolism studies on polycyclic aromatic hydrocarbons. This study presents the results on phenanthrene as the prototypic polycyclic aromatic hydrocarbon possessing a bay region. Phenanthrene is of less importance regarding cytotoxicity and carcinogenicity as compared to e.g. benzo[a]pyrene or 7,12-dimethylbenz[a]anthracene. However, phenanthrene is more readily converted to metabolites which are exreted in higher amounts than those from any other polycyclic aromatic hydrocarbon. Therefore, its metabolites are of diagnostic value in epidemiological and occupational exposure studies. For this reason, it is worthwhile to understand the metabolism of phenanthrene in detail, e.g. allocating metabolites and cytochromes P450s. In accordance to previous observations cytochromes P450 1A1 and 1A2 were the most active forms towards phenanthrene. However, metabolite profiles differed between rat and human homologues of cytochromes P450, in particular for cytochrome P450 1A2. The predominant metabolite formed by rat cytochrome P450 1A2 was the K region trans-9,10-dihydrodiol, whereas human cytochrome P450 1A2 produced similar amounts of the trans-1,2-, trans-3,4- and trans-9,10-dihydrodiol. High amounts of trans-1,2-dihydrodiol, the metabolic precursor of the bay-region dihydrodiol epoxide, were also formed by human cytochrome P450 1A1 compared to its rat homologue. Unexpectedly, human cytochrome P450 2E1 showed a remarkable catalytic activity to metabolize phenanthrene to its trans-9,10-dihydrodiol. Utilizing recombinant CYPs in live V79 cells appears to be a valuable too yielding results important for the evaluation of exposure data and risk assessment for humans.

Isocratic high-performance liquid chromatographic method for the separation of testosterone metabolites

An isocratic reversed-phase high-performance liquid chromatographic (HPLC) method using an Ultrasphere IP column has been developed for the determination of testosterone and its metabolites after incubation of 4-14C-labelled or unlabelled testosterone with rat liver microsomes. Compounds were eluted with methanol-water-tetrahydrofuran (35:55:10, v/v, pH 4.0) and detected by ultraviolet (UV) absorption at 245 nm. UV or on-line radioactivity detection can be used although, due to differences in detector cell volumes, peak resolution is slightly better with UV detection. Selectivity was validated by collecting HPLC peaks and verifying their identity by gas chromatography-mass spectrometry after derivatization by N,O-bis(trimethylsilyl)trifluoroacetamide-trimethylchlorosilane. A three-day validation was performed to determine the linearity, repeatability, reproducibility and accuracy of the method, using corticosterone as internal standard. The method is applicable to the measurement of cytochrome P-450 isoenzyme activities in rat liver.

The effect of indobufen on the activities of selected rat liver phase I and phase II drug metabolizing enzymes, peroxisomal beta-oxidation and hepatic glutathione status

Oral administration of indobufen to male rats for three days at daily doses of 5, 10 and 20 mg kg-1 resulted in no changes in liver total glutathione, cytosolic glutathione S-transferases or microsomal epoxide hydrolase. Reduced glutathione appeared slightly diminished to about 84% of control at the highest dose level. Microsomal cytochrome P450-dependent ethoxyresorufin O-de-ethylase and pentoxy-resorufin de-alkylase activities were decreased to 64% (not significantly) and 67% of control at the lowest dose level. 6 alpha- and 7 alpha-Hydroxytestosterone activities were decreased to 67 and 68% of control at the highest dose level. Cyanide-insensitive peroxisomal fatty acid beta-oxidation was increased to 223, 261 and 232% of control at doses of 5, 10, and 20 mg kg-1, respectively. The results obtained in this study are indicative of the action of indobufen as a weak peroxisome proliferator in male rat liver, and suggest a slight but toxicologically insignificant inhibitory action of this drug on microsomal cytochrome P450-dependent enzyme activities.

Determination of enzyme activity by high-performance liquid chromatography

The application of high-performance liquid chromatography (HPLC) in the study of enzymatic reactions is reviewed. The rationale for using HPLC is given and whether the components of the reaction mixture should be derivatized prior to or after HPLC. An alphabetical list of enzymes assayed by HPLC is given. Substrate and product are included as well the derivatization reagent, detection method and biological matrix. Specific examples of these assays in a complex biological matrix viz. faeces are given. Future prospects are the detection of new enzymes using synthetic substrates and implementation of mass spectrometry to elucidate enzyme specificities.

Induction of CYP2B1 and 3A1, and associated monoxygenase activities by tamoxifen and certain analogues in the livers of female rats and mice

Previous studies suggest long-term feeding of tamoxifen (Z-1-[4-(2-dimethylamino-ethoxy)phenyl]1,2-diphenyl-1-butane) to rats gives rise to liver tumours, while mice are resistant. The effects of tamoxifen on cytochrome P450 isoenzymes and associated monoxygenase activities in the livers of female Fischer rats and C57Bl/6 and DBA/2 mice have been compared. Total microsomal cytochrome P450 was not induced in the livers of rats given tamoxifen (45 mg/kg daily for 4 days) and was in fact significantly reduced after 3 days treatment. In contrast, there was a 30-60-fold increase in the metabolism of benzyloxy- and pentoxyresorufins to resorufin. Ethoxyresorufin O-deethylase was induced only 2.5-fold. The regio- and stereo-specific hydroxylation of testosterone following tamoxifen pretreatment of rats showed a general time- and dose-dependent induction. 6 beta- and 16 alpha-hydroxylation of testosterone together with oxidation to androstenedione were increased 2-3-fold while 2 beta-hydroxylation was induced only marginally, suggesting that tamoxifen produces a mixed pattern of induction with a significant phenobarbitone-like component. No induction of the 2 beta- or 6 beta-hydroxylation pathway occurred in either mouse strain. In rats, immunoblotting experiments with polyclonal antibodies raised against CYP2B1 or 3A1 showed that tamoxifen pretreatment resulted in 2-3-fold increases in both CYP2B1, 2B2 and 3A1 proteins, relative to controls. Immunohistochemistry of rat liver sections showed a centrilobular localization of these induced proteins. Similar patterns of induction as measured by immunoblotting experiments and testosterone hydroxylation were seen following the administration of structurally related analogues, toremifene and droloxifene (3-hydroxytamoxifen), thought to be non-carcinogenic in the rat. No induction of these monooxygenase activities was seen in C57Bl/6 mice and only small increases in benzyloxy and pentoxyresorufin metabolism were in DBA/2 mice. It is suggested that the induction of cytochrome P450-dependent activities by tamoxifen may result in accelerated liver metabolism of this drug with important implications for the disposition of tamoxifen in vivo and also for its metabolic conversion to genotoxic metabolite(s). The difference in inducibility of cytochrome P450-dependent monooxygenase activities between rats and mice offers a plausible and testable hypothesis that the difference in tamoxifen metabolism between the two species may contribute to their carcinogenic response to tamoxifen.

Improved sample preparation for the testosterone hydroxylation assay using disposable extraction columns

The preparation of samples for injection into a high-performance liquid chromatograph from assay mixtures for the determination of cytochrome P-450-dependent testosterone hydroxylation has been substantially facilitated. By replacing the multiple cumbersome extraction steps of the conventional method with a single column extraction the time for sample preparation was reduced from hours to minutes. The new procedure also yields better recoveries for most of the testosterone metabolites than the original protocol. The use of extraction columns for sample preparation allows the simultaneous treatment of a large number of samples or even the automation of the whole assay procedure. The modified procedure is a straightforward, easy-to-perform method that should greatly facilitate the implementation of the testosterone hydroxylation assay for sharply discriminating between many individual cytochrome P-450 species in routine enzyme diagnostics.

Sequence of a novel cytochrome CYP2B cDNA coding for a protein which is expressed in a sebaceous gland, but not in the liver

The major phenobarbital-inducible rat hepatic cytochromes P-450, CYP2B1 and CYP2B2, are the paradigmatic members of a cytochrome P-450 gene subfamily that contains at least seven additional members. Specific oligonucleotide probes for these genomic members of the CYP2B subfamily were used to assess their tissue-specific expression. In Northern-blot analysis a probe specific to gene 4 (which is designated now as CYP2B12) hybridized to a single mRNA present in the preputial gland, an organ which is used as a model for sebaceous glands, but did not hybridize to mRNA isolated from the liver or from five other tissues of untreated or Aroclor 1254-treated rats. The cDNA sequence for the CYP2B12 RNA was determined from overlapping cDNA clones and contained a long open reading frame of 1476 bp. The nucleotide sequence of the CYP2B12 cDNA was 85% similar to the sequence of the CYP2B1 cDNA in its coding region and was different from any CYP2B cDNA characterized until now. The cDNA-derived primary structure of the CYP2B12 protein contains a signal sequence for its insertion into the endoplasmic reticulum and the putative haem-binding site characteristic of cytochromes P-450. A part of the potential haem pocket of CYP2B12 was identical with a similar structure in a bacterial protocatechuate dioxygenase. In immunoblot analysis of preputial-gland microsomes, antibodies against CYP2B1 recognized a single abundant protein with a lower apparent molecular mass than that of CYP2B1. Our results demonstrate that the CYP2B12 protein has the potential to be enzymically active and are the first demonstration that a member of the CYP2B subfamily is expressed exclusively and at high levels in an extrahepatic organ.