[Antiangiogenic activity of thalidomide in vitro mediated by cytochrome CYP2C19]

This study was aimed to investigate the effect of metabolic system in human hepatic cell microsome on antiangiogenic in vitro activity of thalidomide used in treating multiple myeloma and to explore the role of cytochrome CYP2C19. Human umbilical cord vein endothelial cells (hUCVECs) were treated with thalidomide alone or thalidomide co-incubated with human hepatic cell microsome. Cell proliferation ability was assessed by MTT assay, cell cycle analysis and detection of apoptosis were carried out by flow cytometry (FCM), migration activity of hUCVECs was determined by modified Boyden chamber and differentiation of hUCVECs was assayed by tube formation test. The results showed that thalidomide alone had no obvious direct effect on hUCVEC viability or apoptosis, mild effect on cell migration and no effect on tube formation. However, when co-incubated with human hepatic cell microsome, thalidomide significantly inhibited the hUCVECs viability. At 100 microg/ml, thalidomide co-incubated with human hepatic cell microsome, the proliferation ability of hUCVECs decreased by (11.7 +/- 3.9)%, apoptosis cells increased by 27.2%, the cell migration was down-regulated significantly, and the tube formation was obviously inhibited. When omeprazole, a specific inhibitor of cytochrome CYP2C19, was added into the co-incubation mixture, the effects of thalidomide on cell proliferation ability, apoptosis, migration and tube formation decreased. It is concluded that effect of human hepatic cell microsome is required for thalidomide's antiangiogenic activity in vitro and cytochrome CYP2C19 may be involved in the antiangiogenic effect of thalidomide.

Contribution of age, body weight, and CYP2C9 and VKORC1 genotype to the anticoagulant response to warfarin: proposal for a new dosing regimen in Chinese patients

OBJECTIVE

The objective of this study was to assess the contribution of the VKORC1 and CYP2C9 genotypes and age, body size, and weight of the patients to the warfarin dose requirement in a Chinese population.

METHODS

Blood samples were collected from 178 Chinese patients with stable warfarin dose requirements and an international normalized ratio (INR) of the prothrombin time within the target range (1.5-3.0). The polymorphisms for the VKORC1 (-1639GA) and CYP2C9*3 genotypes, venous INR, and plasma concentration and unbound concentration of warfarin were then analyzed.

RESULTS

VKORC1 (-1639G>A) genotyping showed that 149 patients were homozygous AA, 28 were heterozygous GA, and one was homozygous for the GG genotype. CYP2C9*3 genotyping showed that 162 patients were *1/*1, and 16 patients were heterozygous *1/*3. Patients with the VKORC1(-1639 GG+GA) (3.32 +/- 1.02 mg/day) and CYP2C9*1/*1 (2.06 +/- 0.82 mg/day) genotypes required a significantly higher warfarin dose than those with the -1639 AA (1.76 +/- 0.57 mg/day; P < 0.001) or CYP2C9*1/*3 (1.60 +/- 1.29 mg/day; P < 0.001), genotype. The multiple linear regression model for warfarin dose indicated significant contributions from age (r (2) = 0.084; P < 0.001), weight (r (2) = 0.063; P < 0.001), VKORC1 genotype (r (2) = 0.494; P < 0.001), and age, weight, and CYP2C9 and VKORC1 genotype together (r (2) = 0.628; P < 0.001).

CONCLUSION

This study shows that age, weight and the VKORC1 and CYP2C9 polymorphism affect warfarin dose requirements in our sample of Chinese patients receiving long-term therapy and showing stable control of anticoagulation. It is anticipated that the use of dosing regimens modified by taking into account the contribution of age, weight, and the CYP2C9 and VKORC1 genotypes has the potential to improve the safety of warfarin therapy.

Rapid, non-destructive, cell-based screening assays for agents that modulate growth, death, and androgen receptor activation in prostate cancer cells

BACKGROUND

We developed non-invasive, cell-based screening assays to rapidly and biologically assess factors that modulate prostate cancer growth and affect androgen receptor (AR) activity.

METHODS

LNCaP cells, which stably express enhanced green fluorescent protein (EGFP) either constitutively or upon AR activation, were treated with a variety of agents, and then monitored by fluorescence and MTS assays for dose-dependent changes in cell number and AR activity.

RESULTS

The assays were validated for rapid, fluorescence-based, quantitative measurement for the presence of growth and AR modulators. Using these assays, we found that osteoblast conditioned media (CM) enhanced prostate cancer cell growth, but not AR activity. After priming with androgen (<1 nM R1881), forskolin or the pesticide dichlorvos enhanced AR activation, whereas interleukin-6 (IL-6) inhibited it.

CONCLUSION

These non-destructive, cell-based assays enable rapid systematic monitoring of the effects of drugs or complex mixtures on prostate cancer cell growth and/or AR activity.

Effect of Glimepiride and Glibenclamide on S-Warfarin 7-Hydroxylation by Human Liver Microsomes, Recombinant Human CYP2C9.1 and CYP2C9.3

The effect of glimepiride on metabolism of S-warfarin to 7-hydroxywarfarin was studied using human liver microsomes and recombinant cytochrome P450 2C9 microsomes (CYP2C9.1 and CYP2C9.3), and was compared with the results from the experiments using glibenclamide as an inhibitor. S-Warfarin 7-hydroxylation by recombinant CYP2C9.1 and CYP2C9.3 was inhibited by glimepiride competitively. The apparent K(i) value of glimepiride was lower at CYP2C9.3 than at CYP2C9.1. Glimepiride also inhibited 7-hydroxylation of S-warfarin in a competitive manner by microsomes from human liver which showed the genotypes of CYP2C9, as CYP2C9*1/*1 or CYP2C9*1/*3. The apparent K(i) value of glimepiride was lower than that of glibenclamide. These results may provide valuable information for optimizing the anticoagulant activity of warfarin when glimepiride is co-administered to patients.

Clinical Guidelines for Psychiatrists for the Use of Pharmacogenetic Testing for CYP450 2D6 and CYP450 2C19

Pharmacogenetics has arrived in clinical psychiatric practice with the FDA approval of the AmpliChip CYP450 Test that genotypes for two cytochrome P450 2D6 (CYP2D6) and 2C19 (CYP2C19) genes. Other pharmacogenetic tests, including those focused on pharmacodynamic genes, are far from ready for clinical application. CYP2D6 is important for the metabolism of many antidepressants and antipsychotics, and CY2C19 is important for some antidepressant metabolism. Poor metabolizers (PMs), lacking the enzyme, account for up to 7% of Caucasians for CYP2D6 and up to 25% of East Asians for CYP2C19. Patients having three or more active CYP2D6 alleles (up to 29% in North Africa and the Middle East), are called CYP2D6 ultra-rapid metabolizers (UMs). CYP2D6 phenotypes (particularly PMs) are probably important in patients taking tricyclic antidepressants (TCAs), venlafaxine, typical antipsychotics, and risperidone. The CYP2C19 PM phenotype is probably important in patients taking TCAs and perhaps citalopram, escitalopram, and sertraline. On the basis of the literature and the authors' clinical experience, the authors provide provisional recommendations for identifying and treating CYP2D6 PMs, CYP2C19 PMs, and CYP2D6 UMs. The next few years will determine whether CYP2D6 genotyping is beneficial for patients taking the new drugs aripiprazole, duloxetine, and atomoxetine. Practical recommendations for dealing with laboratories offering CYP2D6 and CYP2C29 genotyping are provided.

Evidence for induced microsomal bilirubin degradation by cytochrome P450 2A5

Oxidative metabolism of bilirubin (BR) -- a breakdown product of haem with cytoprotective and toxic properties -- is an important route of detoxification in addition to glucuronidation. The major enzyme(s) involved in this oxidative degradation are not known. In this paper, we present evidence for a major role of the hepatic cytochrome P450 2A5 (Cyp2a5) in BR degradation during cadmium intoxication, where the BR levels are elevated following induction of haem oxygenase-1 (HO-1). Treatment of DBA/2J mice with CdCl(2) induced both the Cyp2a5 and HO-1, and increased the microsomal BR degradation activity. By contrast, the total cytochrome P450 (CYP) content and the expression of Cyp1a2 were down-regulated by the treatment. The induction of the HO-1 and Cyp2a5 was substantial at the mRNA, protein and enzyme activity levels. In each case, the up-regulation of HO-1 preceded that of Cyp2a5 with a 5-10h interval. BR totally inhibited the microsomal Cyp2a5-dependent coumarin hydroxylase activity, with an IC(50) approximately equal to the substrate concentration. The 7-methoxyresorufin 7-O-demethylase (MROD) activity, catalyzed mainly by the Cyp1a2, was inhibited up to 36% by BR. The microsomal BR degradation was inhibited by coumarin and a monoclonal antibody against the Cyp2a5 by about 90%. Furthermore, 7-methoxyresorufin, a substrate for the Cyp1a2, inhibited BR degradation activity by approximately 20%. In sum, the results strongly suggest a major role for Cyp2a5 in the oxidative degradation of BR. Secondly, the coordinated up-regulation of the HO-1 and Cyp2a5 during Cd-mediated injury implicates a network of enzyme systems in the maintenance of balancing BR production and elimination.

A virus-directed enzyme prodrug therapy (VDEPT) strategy for lung cancer using a CYP2B6/NADPH-cytochrome P450 reductase fusion protein

Virus-directed enzyme prodrug therapy (VDEPT) is an emerging strategy against cancer. Our approach is a P450-based VDEPT that consists of using cyclophosphamide (CPA) as a prodrug and a Cytochrome P450 2B6/NADPH cytochrome P450 reductase fusion protein (CYP2B6/RED) as a prodrug-activating enzyme. Due to the heterogenous expression of proteins in tumor cells, basal reductase activity may not be sufficient to supply CYP2B6 with electrons, the fusion protein should enable the expression of both proteins at high levels in tumor cells. CYP/RED fusion proteins have never been previously expressed in mammalian cells, to enable expression the fusion protein was cloned into an adenoviral vector and subsequently several pulmonary tumor cell lines were infected. The CYP2B6/RED fusion protein was detected by Western blot, its mRNA by Northern blot, and its heme incorporation into an active form by spectral analysis. Infection with the fusion gene increased RED activity in microsomes by a factor of 3 compared to the control. After infection and treatment with CPA, in cell lines with low endogenous RED, the fusion protein mediated significantly higher CPA-induced cytotoxicity compared to cells expressing solely CYP2B6. In conclusion, the fusion protein is functional for VDEPT by providing one protein for higher levels of CPA metabolism.

Metabolism of territrem B and C in liver microsomes from 14-wk-old Wistar rats is catalyzed by cytochrome P-450 3A

The metabolism of territrem B (TRB) and territrem C (TRC) in liver microsomes of 14-wk-old male and female Wistar rats was investigated. Metabolism of TRB to 4beta-hydroxylmethyl-4beta-demethylterritrem B (MB2), O-demethylation of the methoxy group of the aromatic moiety of TRB to form MB4 (same structure as TRC), and metabolism of TRC to 4beta-hydroxylmethyl-4beta-demethylterritrem C (MC) were observed in both genders. However, the amounts of MB2, MB4, and MC formed in females were much lower than in males. To investigate which cytochrome P-450 (CYP450) isoforms were involved in each step, four CYP450 isotype-specific inhibitors (furafylline, orphenadrine, cimetidine, and troleandomycin) and antibodies against CYP1A1, CYP2B1, CYP2C11, or CYP3A2 were used. Formation of MB2, MB4, and MC was markedly inhibited by cimetidine and troleandomycin, but less by furafylline and orphenadrine. Anti-CYP3A2 antibody completely inhibited MB, MB, and MC formation, while antibodies against CYP1A1, CYP2B1, or CYP2C11 produced no marked effect. Of the seven tested supersomes from baculovirus-transformed insect cells expressing rat CYP450 isoforms (1Al, 1A2, 2B1, 2C11, 2C12, 3A1, and 3A2), only those expressing CYP3A1 and CYP3A2 metabolized TRB and TRC. The amounts of MB2, MB4, and MC formed by male and female rat liver microsome preparations were related to the testosterone 6beta-hydroxylase activity and CYP3A1/2 protein content of the preparation. Immunoblotting showed that CYP3A1 was expressed in both genders, but at different levels, while CYP3A2 was only expressed in males. These results suggest that the formation of MB2, MB4, and MC in liver microsomes from 14-wk-old rats of either gender is mediated by CYP3A1 and CYP3A2.

Simultaneous itraconazole bioequivalence assessment and CYP3A phenotyping in South American subjects

OBJECTIVE

The present study evaluates the acute effect of a single-dose itraconazole administration on CYP3A phenotype, as measured by cortisol MR ratio in urine.

METHODS

Twenty-four healthy Uruguayan subjects recruited according to strict inclusion criteria participated in an open-label, randomized, two-period, crossover study designed to evaluate the bioequivalence of an itraconazole formulation (Traconal 100 mg, Achê Labs, São Paulo, Brazil). The study comprised two treatment periods separated by a wash-out period of 14 days. In each period a series of venous blood samples were drawn over 48 hours. Three urine samples were obtained for CYP3A phenotyping: pre-dose, 24 and 48 hours after dosing. Blood and urine samples were assayed for itraconazole, beta-hydroxycortisol and cortisol using a validated chromatographic method.

RESULTS

The ratio of the mean AUC0-inf. T/AUC0-inf. R was included in the bioequivalence range, however, due to high variability, the CI90% was not. It was found that the cortisol metabolic ratio (MR) showed inhibition relative to basal activity in a proportion of subjects 24 hours (68 +/- 6.1%, mean +/- CI95%) and 48 hours (80 +/- 7.3%, mean +/- CI95%) after ingestion of itraconazole. A significant correlation was found between itraconazole AUC0-inf. and normalized basal CYP3A MR for the reference (r = 0.62, t = 3.72, p = 0.001) and the test product (r = 0.74, t = 5.22, p = 0.00003). A good correlation existed between basal cortisol MR and the elimination half-life of itraconazole.

CONCLUSIONS

The findings are in line with the hypothesis that the determination of the bioavailability of highly variable CYP3A substrates might be improved by simultaneous non-interfering phenotyping. If this is confirmed, a new methodological paradigm may need to be developed in order to take account of metabolic variability in bioequivalence evaluation of this group of drugs.

A cytochrome P450 2B6 meditated gene therapy strategy to enhance the effects of radiation or cyclophosphamide when combined with the bioreductive drug AQ4N

BACKGROUND

AQ4N is metabolised in hypoxic cells by cytochrome P450s (CYPs) to the cytotoxin AQ4. Most solid tumours are known to contain regions of hypoxia whereas levels of CYPs have been found to vary considerably. Enhancement of CYP levels may be obtained using gene-directed enzyme prodrug therapy (GDEPT). We have therefore examined the potential of a CYP2B6-mediated GDEPT strategy to enhance the anti-tumour effect of the combination of AQ4N with radiation or cyclophosphamide (CPA).

METHODS

In vitro and in vivo transient transfection of human CYP2B6 +/- CYP reductase (CYPRED) was investigated in RIF-1 mouse tumours. Efficacy in vitro was assessed using the alkaline comet assay (ACA). In vivo, the time to reach 4x the treatment volume (quadrupling time; VQT) was used as the end point.

RESULTS

When CYP2B6 was transfected into RIF-1 cells and treated with AQ4N under hypoxic conditions there was a significant increase in DNA damage (measured by the ACA) compared with non-transfected cells. In vivo, a single intra-tumoural injection of a CYP2B6 vector construct significantly enhanced tumour growth delay in combination with AQ4N (100 mg/kg) and 10 Gy X-rays. AQ4N (100 mg/kg) and CPA (100 mg/kg) with CYP2B6 and CYPRED also enhanced tumour growth delay; this effect became significant when the schedule was repeated 14 days later (p = 0.0197).

CONCLUSIONS

The results show the efficacy of a CYP2B6-mediated GDEPT strategy for bioreduction of AQ4N; this may offer an additional approach to target radiation- and chemo-resistant hypoxic tumours that should enhance overall tumour control.

Evidence for concurrent effects of exposure to environmental cadmium and lead on hepatic CYP2A6 phenotype and renal function biomarkers in nonsmokers

We examined the interrelationships between phenotype of hepatic cytochrome P450 2A6 (CYP2A6), nephropathy, and exposure to cadmium and lead in a group of 118 healthy Thai men and women who had never smoked. Their urinary Cd excretion ranged from 0.05 to 2.36 microg/g creatinine, whereas their urinary Pb excretion ranged from 0.1 to 12 microg/g creatinine. Average age and Cd burden of women and men did not differ. Women, however, on average showed a 46% higher urinary Pb excretion (p < 0.001) and lower zinc status, suggested by lower average serum Zn and urinary Zn excretion compared with those in men. Cd-linked nephropathy was detected in both men and women. However, Pb-linked nephropathy was seen only in women, possibly because of higher Pb burden coupled with lower protective factors, notably of Zn (p < 0.001), in women compared with men. In men, Pb burden showed a negative association with CYP2A6 activity (adjusted beta = -0.29, p = 0.003), whereas Cd burden showed a positive association with CYP2A6 activity (adjusted beta = 0.38, p = 0.001), suggesting opposing effects of Cd and Pb on hepatic CYP2A6 phenotype. The weaker correlation between Cd burden CYP2A6 activity in women despite similarity in Cd burden between men and women is consistent with opposing effects of Pb and Cd on hepatic CYP2A6 phenotypic expression. A positive correlation between Cd-linked nephropathy (urinary N-acetyl-beta-D-glucosaminidase excretion) and CYP2A6 activity in men (r = 0.39, p = 0.002) and women (r = 0.37, p = 0.001) suggests that Cd induction of hepatic CYP2A6 expression and Cd-linked nephropathy occurred simultaneously.

Role of estrogen receptor in regulation of polycyclic aromatic hydrocarbon metabolic activation in lung

Epidemiological and biochemical studies have indicated that females may be at greater risk of smoking associated lung cancer compared with males. Among lung cancer patients, female smokers have been found to have higher levels of PAH-related DNA adducts and CYP1A1 gene expression in their normal lung tissue compared to male smokers. A possible role of steroid hormones in these sex differences via interactions between aryl hydrocarbon receptor and estrogen receptor mediated cellular effects has been suggested. In the present study the impact of the estrogen receptor (ERalpha) on CYP1A1 and CYP1B1 gene expression was studied in vitro in human bronchial epithelial cells. Transient transfection of the BEP2D cell line with ERalpha influenced neither constitutive expression of CYP1A1 or CYP1B1 nor induction of these genes by TCDD as measured by real-time RT-PCR. ERalpha had no effect on the constitutive or TCDD-induced enzymatic activity of CYP1A1 (EROD). We also studied the effect of steroid hormones on lung PAH metabolic activation in A/J mice. Intact and ovariectomized female mice were orally exposed to a single dose of benzo[a]pyrene. Ovariectomy did not influence the levels of either benzo[a]pyrene-derived protein or DNA adducts in the lung tissue measured by HPLC and 32P-postlabeling, respectively. In conclusion, the present data do not support the hypothesis of a role of estrogen or the ERalpha in regulating the metabolic activation of polycyclic aromatic hydrocarbons in lung.

Anti-angiogenic effects of thalidomide: expression of apoptosis-inducible active-caspase-3 in a three-dimensional collagen gel culture of aorta

The anti-angiogenic properties of thalidomide have led to the use of the agent as a remedy for multiple myeloma. Nevertheless, the anti-angiogenic moiety of thalidomide remains unidentified. In this study we examined the anti-angiogenic effects of thalidomide in an in vitro model using a three-dimensional collagen gel culture. Angiogenesis was significantly inhibited when the culture was treated with thalidomide plus cytochrome P-450 (CYP2B4), and the migrating cells and tubules were positive for active-caspase-3 in an accompanying immunohistochemical investigation. Transmission electron microscopic observation also confirmed that active-caspase-3-positive cells demonstrated apoptotic characteristics. This study is the first to morphologically demonstrate the effect of thalidomide in directly inducing the apoptosis of new tubules and migrating cells on a three-dimensional collagen gel culture of aorta. Taken together with earlier findings, our new results indicate that the thalidomide-induced inhibition of angiogenesis involves apoptosis in addition to the suppression of TNF-alpha and inhibition of cell migration from aorta explants, i.e., the factors important for capillarogenesis.

The effect of methoxsalen on nicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism in vivo

Nicotine is metabolized to the inactive metabolite cotinine by cytochrome P450 2A6. NNK, or 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, is a potent procarcinogen shown to be activated to a reactive mutagenic metabolite by the enzyme CYP2A6. We studied the effect of inhibiting CYP2A6 on smoking behavior and metabolism of the procarcinogen NNK. In study 1, abstinent smokers (n=7) received methoxsalen (a potent CYP2A6 inhibitor), 30-50 mg orally, one-half hour before three subcutaneous nicotine injections (31 microg/kg) were given at hourly intervals. Methoxsalen increased mean plasma nicotine by 47% (p<.01) and mean nicotine area under the curve (AUC) by 63% (p<.0001); and decreased nicotine clearance by 39% (p<.0001), relative to placebo. In study 2, smokers (n=11) were told to maintain their same number of cigarettes smoked while receiving methoxsalen, 10 mg orally three times daily for 3 days. On day 3 of methoxsalen treatment, a 29% increase in plasma nicotine/expired-air CO (an index of smoke exposure) (p=0.03) was observed. Urinary levels of trans 3'-hydroxycotinine (metabolized by CYP2A6 from cotinine) also were decreased (p<.0001), and significantly more NNK was metabolized to the inactive NNAL-glucuronide (1.04+/-0.54 pmol/mg on day 1 to 1.37+/-0.74 pmol/mg on day 4, p<.01) relative to placebo. Thus, treatment with the CYP2A6 inhibitor methoxsalen in vivo increases the routing of NNK to the inactive NNAL-glucuronide and decreases smoking. CYP2A6 inhibition may have potential as an exposure reduction or cessation strategy in tobacco dependence.

Polymorphismes du cytochrome P450 2C9 (CYP2C9) et posologie à l’équilibre pour des patients âgés traités par warfarine

PURPOSE

Allelic variants of the gene coding for cytochrome P450 isoform 2C9 (CYP2C9), 2C9*2 and 2C9*3, were shown to increase sensitivity to warfarin in adults. In the elderly, the maintenance dose is influenced by acquired factors including comorbidities and polymedication. The aim of our purpose was to investigate whether a genetic factor, such as cyp2c9 genotype, does influence the warfarin maintenance dose in very elderly patients.

METHODS

In-patients treated with warfarin were recruited with the following inclusion criteria: i/ 75 years-old or over; ii/ a stable INR within the therapeutic range (INR 2.0-3.0). Genotypes were coded as numbers of alleles for each of the three polymorphisms, namely 2C9*1 (wild-type), 2C9*2, and 2C9*3.

RESULTS

CYP2C9 genotype was performed in 126 patients, mean age 87 +/-6 years (75-103), 29 males-97 females. The mean daily dose of warfarin was 3.0 +/-1.4 mg, with 3.1 mg in patients with the wild-type *1/*1 genotype (n =80), 2.7 mg in *1/*2 heterozygotes (n =20), 2.9 mg in *1/*3 heterozygotes (n =18), 1.2 mg in *2/*2 homozygotes (n =2), 2.3 mg in compound heterozygotes *2/*3 (n =6). The relationships between dose and potential factors were assessed using the correlation coefficient test for age and Fischer exact tests for the categorical variables. The only factors significantly linked to the dose were the numbers of 2C9*1 and 2C9*2 alleles.

CONCLUSION

In elderly patients, a genetic influence on response to warfarin does exist as in younger patients.

QUANTITATIVE CONTRIBUTION OF CYP2D6 AND CYP3A TO OXYCODONE METABOLISM IN HUMAN LIVER AND INTESTINAL MICROSOMES

Oxycodone undergoes N-demethylation to noroxycodone and O-demethylation to oxymorphone. The cytochrome P450 (P450) isoforms capable of mediating the oxidation of oxycodone to oxymorphone and noroxycodone were identified using a panel of recombinant human P450s. CYP3A4 and CYP3A5 displayed the highest activity for oxycodone N-demethylation; intrinsic clearance for CYP3A5 was slightly higher than that for CYP3A4. CYP2D6 had the highest activity for O-demethylation. Multienzyme, Michaelis-Menten kinetics were observed for both oxidative reactions in microsomes prepared from five human livers. Inhibition with ketoconazole showed that CYP3A is the high affinity enzyme for oxycodone N-demethylation; ketoconazole inhibited >90% of noroxycodone formation at low substrate concentrations. CYP3A-mediated noroxycodone formation exhibited a mean K(m) of 600 +/- 119 microM and a V(max) that ranged from 716 to 14523 pmol/mg/min. Contribution from the low affinity enzyme(s) did not exceed 8% of total intrinsic clearance for N-demethylation. Quinidine inhibition showed that CYP2D6 is the high affinity enzyme for O-demethylation with a mean K(m) of 130 +/- 33 microM and a V(max) that ranged from 89 to 356 pmol/mg/min. Activity of the low affinity enzyme(s) accounted for 10 to 26% of total intrinsic clearance for O-demethylation. On average, the total intrinsic clearance for noroxycodone formation was 8 times greater than that for oxymorphone formation across the five liver microsomal preparations (10.5 microl/min/mg versus 1.5 microl/min/mg). Experiments with human intestinal mucosal microsomes indicated lower N-demethylation activity (20-50%) compared with liver microsomes and negligible O-demethylation activity, which predict a minimal contribution of intestinal mucosa in the first-pass oxidative metabolism of oxycodone.

INCORPORATION OF AN OXYGEN FROM WATER INTO TROGLITAZONE QUINONE BY CYTOCHROME P450 AND MYELOPEROXIDASE

Troglitazone (TGZ) was the first glitazone used for the treatment of type II diabetes mellitus. TGZ undergoes an oxidative chroman ring-opening reaction to form a quinone product. Recently, cytochrome P450 (P450) was shown to be able to catalyze the formation of TGZ quinone. TGZ quinone was the major metabolite formed by dexamethasone-induced rat liver microsomes or myeloperoxidase (MPO) incubated with TGZ. The ultimate source for the quinone carbonyl oxygen atom of TGZ quinone was investigated using (18)O water in both enzyme reaction systems followed by liquid chromatography/tandem mass spectometry analysis of the TGZ quinone product. The resultant TGZ quinone formed by either liver microsomes or MPO contained a single atom of (18)O. The (18)O atom was determined to be the quinone carbonyl oxygen by collision-induced dissociation fragmentation of the (18)O-labeled TGZ quinone. The formation of TGZ quinone was inhibited approximately 90% by coincubation with ascorbic acid or cysteine in the MPO reaction system but only 10 to 20% in liver microsomes, which might reflect the difference in the mechanism by which TGZ quinone is formed by P450 and peroxidase. These results suggest that P450 catalyze an atypical reaction to form TGZ quinone, involving the incorporation of an oxygen from water into the quinone carbonyl position.

Effect of CYP2D6 and CYP2C9 genotypes on fluoxetine and norfluoxetine plasma concentrations during steady-state conditions

OBJECTIVES

CYP2D6 drug-metabolising enzyme has been shown to be involved in fluoxetine metabolism in vitro and in vivo. CYP2C9 has also been shown to influence the metabolism of fluoxetine in vitro; however, this relationship has not been studied in humans. The aim of the present study was to evaluate the influence of CYP2D6 and CYP2C9 genotypes on the plasma concentration of fluoxetine and norfluoxetine in psychiatric patients during steady-state conditions.

METHODS

White European psychiatric patients ( n=64) receiving antidepressant monotherapy with fluoxetine were studied. CYP2D6 and CYP2C9 genotypes were determined by polymerase chain reaction-specific methods. The plasma concentrations of fluoxetine and its metabolite, norfluoxetine, were measured by high-performance liquid chromatography.

RESULTS

The dose-corrected plasma concentrations of fluoxetine were related ( P<0.01, r=-0.36) to CYP2D6 genotypes (number of active genes). The fluoxetine/norfluoxetine ratio also correlated ( P<0.01, r=-0.39) with the number of active CYP2D6 genes. Among patients with two CYP2D6 active genes, the dose-corrected plasma concentrations of fluoxetine and active moiety (fluoxetine plus norfluoxetine) were significantly ( P<0.05) higher in the CYP2C9*1/*2 and CYP2C9*1/*3 genotype groups than in CYP2C9*1/*1. However, dose-corrected (C/D) plasma concentrations of fluoxetine, active moiety and fluoxetine/norfluoxetine ratios were not highly different in the individuals with two mutated alleles as compared with those heterozygous for *2 or *3.

CONCLUSION

The present results show that CYP2D6 and potentially CYP2C9 genotypes seem to influence fluoxetine plasma concentration during steady-state conditions in patients.

Involvement of cytochrome P450 2C9, 2E1 and 3A4 in trimethadione N-demethylation in human microsomes

BACKGROUND AND OBJECTIVES

Trimethadione (TMO), an antiepileptic drug, may be used as a candidate for estimating hepatic drug-oxidizing activity. While TMO metabolism is mainly catalysed by CYP2C9, CYP2E1 and CYP3A4 the contribution of the different isoforms is unclear. In this study, we determined the percentage contribution of the three CYPs (CYP2C9, CYP2E1 and CYP3A4) to TMO N-demethylation.

METHOD

We used human liver microsomes and human recombinant CYPs expressed in human B-lymphoblast cells and baculovirus-infected insect cells.

RESULTS

The mean Km, Vmax and Vmax/Km values of TMO N-demethylation in human microsomes were 3.66 (mm), 503 (pmol/min/mg) and 2.61 (mL/h/mg), respectively. In the microsomes from human B-lymphoblast cells or baculovirus-infected insect cells, CYP 2C9, CYP 2E1 and CYP3A4 exhibited similar Km and higher Vmax in baculovirus-infected insect cells than B-lymphoblast cells. In baculovirus-infected insect cells, CYP2C9, CYP2E1 and CYP3A4 exhibited activities of 32, 286 and 77 pmol/min/pmol CYP, respectively. No CYP activity catalysed by CYP1A2 and 2D6 were detected in the two human cDNA expressed CYP isoforms.

CONCLUSION

TMO is metabolized not only by CYP2E1 but also CYP3A4 and CYP2C9. The order of this metabolism is as follows: CYP2E1 >> CYP3A4 > CYP2C9.

Polymorphisms in the CYP1B1 gene are associated with increased risk of prostate cancer

CYP1B1 has been evaluated as a candidate gene for various cancers because of its function in activating environmental procarcinogens and catalysing the conversion of oestrogens to genotoxic catechol oestrogens. To test the hypothesis that genetic polymorphisms in the CYP1B1 gene may associate with the risk for prostate cancer (CaP), we compared the allele, genotype, and haplotype frequencies of 13 single nucleotide polymorphisms (SNPs) of CYP1B1 among 159 hereditary prostate cancer (HPC) probands, 245 sporadic CaP cases, and 222 unaffected men. When each of the SNPs was analysed separately, marginally significant differences were observed for allele frequencies between sporadic cases and controls for three consecutive SNPs (−1001C/T, −263G/A, and −13C/T, P=0.04–0.07). Similarly, marginally significant differences between sporadic cases and controls in the frequency of variant allele carriers were observed for five consecutive SNPs (−1001C/T, −263G/A, −13C/T, +142C/G, and +355G/T, P=0.02–0.08). Interestingly, when the combination of these five SNPs was analysed using a haplotype approach, a larger difference was found (P=0.009). One frequent haplotype (C-G-C-C-G of −1001C/T, −263G/A, −13C/T, +142C/G, and +355G/T) was associated with an increased risk for CaP, while the other frequent haplotype (T-A-T-G-T) was associated with a decreased risk for CaP. These findings suggest that genetic polymorphisms in CYP1B1 may modify the risk for CaP.

Discovery of cytochrome P450 1B1 inhibitors as new promising anti-cancer agents

Human cytochrome P450 (CYP)1B1 is a major enzyme for carcinogenic estrogen metabolism and involved in the metabolic activation of procarcinogens of the polycyclic aromatic hydrocarbons (PAHs). CYP1B1 is known to be expressed at a high frequency in various human cancers, but not in normal tissues. It also plays an important role in the metabolism of various anti-cancer drugs. These findings suggest inhibition of CYP1B1 as a new oncological therapeutic strategy. Several natural and synthetic compounds have been studied in an effort to find the isoform-specific inhibitors of the CYP1 subfamily. A survey of the inhibitors of CYP1B1 and other related inhibitors of the CYP1 subfamily is provided in this review.

Formation of benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene adducts in vascular endothelia of cytochrome P4501A-induced chicken embryos

Polycyclic aromatic hydrocarbons (PAHs) are widespread in the environment and birds may be exposed to PAHs via diet, from preening feathers contaminated with oil, or through contamination of the eggshell during embryo development. In the present study, tissue distribution and the cell-specific binding of two labeled PAHs, benzo[a]pyrene ([3H]BaP) and 7,12-dimethylbenz[a]anthracene ([3H]DMBA), were examined in chicken embryos exposed in ovo to CYP1A inducers. Tape-section autoradiograms revealed high concentrations of radioactivity in the bile, liver, kidneys, heart, and leptomeninges. Light microscopy autoradiography of solvent-extracted tissue slices showed a high and selective binding in endothelial cells in certain blood vessels in brain, heart, lung, and chest muscle. Binding was also observed in blood vessel endothelial cells in the chorioallantoic membrane (CAM), an extraembryonal tissue lining the eggshell. Endothelial binding was confirmed in CAM exposed in vitro, implying that tissue-binding metabolites were formed in situ. The CYP1A inhibitor ellipticine abolished bleeding in the target endothelial cells in CAM. It is thus concluded that blood vessel endothelia in various tissues in birds can bioactivate environmental contaminants and be targets for their toxicity. In view of its critical position beneath the shell, the CAM could be an important target for toxicants following external exposure in oviparous species.

Cytochrome P-4503A1 catalyzes the formation of MA1 from territrem a in liver microsomes of 7-week-old female Wistar rats

Liver microsomal territrem A (TRA) metabolism was studied in 7-wk-old female Wistar rats. Pretreatment with phenobarbital (PB) or dexamethasone (DEX) resulted in a significant increase in 4 beta-hydroxymethyl-4 beta-demethylterritrem A (MA1) production. SKF 525A (0.025 and 0.05 mM), a general cytochrome P-450 (CYP450) inhibitor, blocked MA1 formation in liver microsomes from PB-pretreated female rats. Anti-CYP2B antibody had no marked effect on MA1 formation, although orphenadrine (0.5 mM), which inhibits CYP2B, blocked MA1 formation in liver microsomes from PB-treated female rats. An immunoinhibition study showed that anti-CYP3A2 antibody reduced MA1 formation to nondetectable levels in liver microsomes from PB-treated female rats. Furthermore, immunoblotting showed that CYP3A1 protein was expressed in 7-wk-old female rat and only MA1 was formed from TRA using supersomes from CYP3A1-expressing baculovirus-infected insect cells. Further, Western blot analysis indicated that CYP3A2 protein was expressed in 2-wk-old rats of both sexes and 7-wk-old male rats, and 3 metabolites of TRA, such as MA1, MAX, and MA2, were formed using supersomes from CYP3A2-expressing baculovirus-infected insect cells. These results suggest that MA1 formation in liver microsomes of 7-wk-old female Wistar rats is mediated by CYP3A1.

Epoxygenase-driven angiogenesis in human lung microvascular endothelial cells

Angiogenesis is one of the most recent physiological functions attributed to products of cytochrome P-450 (CYP450) enymes. To test this at a molecular level in human cells, we used a cloned cDNA for the human endothelial enzyme CYP450 2C9 (CYP2C9) to study growth as well as differentiation of human microvascular endothelial cells from the lung (HMVEC-L). Using adenoviral vectors overexpressing mRNA for CYP2C9, we show that the presence of CYP2C9 doubles thymidine incorporation and stimulates proliferation of primary cultures of endothelial cells compared with Ad5-GFP (control) in 24 h. In addition, there is a significant increase of tube formation in Matrigel after infection of HMVEC-L with Ad5-2C9 than with Ad5-GFP. More interestingly, Ad5-2C9 expressing the antisense product of CYP2C9 (2C9AS) inhibited tube formation compared with both Ad5-GFP as well as the Ad5-2C9 constructs. Finally, we tested the most abundant arachidonic acid metabolite of CYP2C9, 14,15-epoxyeicosatrienoic acid, which induced angiogenesis in vivo when embedded in Matrigel plugs and implanted in adult rats. These data support an important role for CYP2C9 in promoting angiogenesis.

Induction of cytochrome P450 1B1 in MDA-MB-231 human breast cancer cells by non-ortho-substituted polychlorinated biphenyls

The effects of 12 non-ortho-substituted polychlorinated biphenyl (PCB) congeners on the induction of human cytochrome P450 1B1 (CYP1B1), an estradiol 4-hydroxylase, were investigated in MDA-MB-231 breast cancer cells. Three independent quantitative assays were used, in which the rates of estrogen metabolism, the levels of the CYP1B1 and CYP1A1 mRNAs, and luciferase activities under the control of the CYP1B1 promoter were measured. Of the congeners investigated, 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,4',5-trichlorobiphenyl (PCB 39) and 3,3',4,5-tetrachlorobiphenyl (PCB 78) were the most potent in each assay, causing four to 10-fold increases in response. Exposure to 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) resulted in elevated CYP1B1 mRNA and increased CYP1B1-promoter driven luciferase activity, but caused depressed rather than elevated rates of E(2) metabolism due to inhibition of CYP1B1. The relative magnitudes of CYP1B1 induction by the PCB congeners, as determined by the three assays, were in close agreement, with the exception noted for PCB 169. These results indicate that PCB structure-activity relationships for the induction of human CYP1B1 are similar to those observed for human CYP1A1, but differ somewhat from what has been reported for induction of rat CYP1A1.

Amiodarone N-deethylation by CYP2C8 and its variants, CYP2C8*3 and CYP2C8 P404A

Amiodarone is a potent Class III antiarrhythmic drug. The N-deethylation of amiodarone to desethylamiodarone is known to be catalyzed by cytochrome P450 (CYP) 2C8. In the present study, amiodarone N-deethylation by the CYP2C8s, CYP2C8*1 (wild-type), CYP2C8*3, and CYP2C8 P404A (Pro404Ala substitution in exon 8), was investigated by their transient expression in Hep G2 cells. The expression levels of CYP2C8*1 and CYP2C8*3 were similar, whereas the level of CYP2C8 P404A was 55.6% of that of CYP2C8*1. The kinetic parameters of amiodarone N-deethylation were obtained by means of Lineweaver-Burk analysis. The intrinsic clearance (Vmax/Km, per mg of microsomal protein) of amiodarone by CYP2C8 P404A but not CYP2C8*3 was significantly (48.7%) less than that of CYP2C8*1. These results suggest that CYP2C8 P404A but not CYP2C8*3 is less effective in the N-deethylation of amiodarone.

Altering cytochrome P4501A activity affects polycyclic aromatic hydrocarbon metabolism and toxicity in rainbow trout (Oncorhynchus mykiss)

The polycyclic aromatic hydrocarbons (PAHs) phenanthrene and retene (7-isopropyl-1-methyl phenanthrene) are lethal to rainbow trout (Oncorhynchus mykiss) larvae during chronic exposures. Phenanthrene is a low-toxicity, non-cytochrome P4501A (CYP1A)-inducing compound that accumulates in fish tissues during exposure to lethal concentrations in water. Retene is a higher toxicity CYP1A-inducing compound that is not detectable in tissue at lethal exposure concentrations. The metabolism, excretion, and toxicity of retene and phenanthrene were examined in juvenile and larval rainbow trout during coexposure to the model CYP1A inducer beta-naphthoflavone (betaNF), or to the inducer-inhibitor piperonyl butoxide to determine if modulating CYP1A activity affected PAH metabolism and toxicity. Phenanthrene metabolism, excretion rate, and toxicity increased with coexposure to betaNE Piperonyl butoxide inhibited phenanthrene metabolism and reduced the excretion of all phenanthrene metabolites. As a consequence, embryo mortality rates increased but rates of sublethal effects did not. Coexposure of trout to retene and betaNF caused no change in retene metabolism and excretion, but retene toxicity increased, perhaps due to additivity. Piperonyl butoxide inhibited retene metabolism, decreased the excretion of some retene metabolites while increasing the excretion of others, and increased the toxicity of retene. These results support the role of CYP1A activity in PAH metabolism and excretion, and the role ofthe CYP1A-generatedmetabolites of PAHs in chronic toxicity to larval fish.

Cytochrome P450 1B1 determines susceptibility to dibenzo[a,l]pyrene-induced tumor formation

Metabolic activation, DNA binding, and tumorigenicity of the carcinogenic polycyclic aromatic hydrocarbon dibenzo[a,l]pyrene (DB[a,l]P) catalyzed by murine cytochrome P450 (P450) enzymes were investigated. DNA binding of DB[a,l]P in human mammary carcinoma MCF-7 and human P450-expressing Chinese hamster V79 cell lines was previously shown to occur preferentially with metabolically generated fjord region DB[a,l]P-11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE). To elucidate different capabilities of murine P450 1A1 and 1B1 for metabolic activation of DB[a,l]P, V79 cell cultures stably expressing P450s 1A1 or 1B1 from mice were exposed to 10 or 100 nM DB[a,l]P. Both cell lines transformed DB[a,l]P to DNA binding intermediates. As with V79 cells expressing the corresponding human P450 enzyme [Luch et al. (1998) Chem. Res. Toxicol. 11, 686-695], murine P450 1B1-catalyzed metabolism and DNA binding proceeded exclusively through generation of fjord region DB[a,l]PDE. In addition, only DB[a,l]PDE-derived DNA adducts were found in V79 cells expressing P450 1A1 from mice. This is in contrast to our recent findings with V79 cells expressing P450 1A1 from humans or rats which catalyzed the formation of both highly polar DNA adducts as well as nonpolar DB[a,l]PDE-DNA adducts. To establish the role of P450 1B1 in DB[a,l]P-induced tumor formation in vivo, we treated P450 1B1-null and wild-type mice intragastrically and monitored survival rates and appearance of neoplasias in various organs. All wild-type mice (n = 17) used in this study developed at least one tumor at one site (tumor rate of 100%). In contrast, 5 of 13 P450 1B1-null mice were observed to be free from any tumor (tumor rate of 62%). The organ sites of tumor formation and the dignity of tumors were different between wild-type and P450 1B1-null mice. Wild-type mice were diagnosed with both benign and malignant tumors of the ovaries, lymphoid tissues, as well as with skin and endometrial hyperplasias, whereas P450 1B1-null mice developed only lung adenomas and endometrial hyperplasias. DNA binding studies using embryonic fibroblasts isolated from these animals provided further evidence that P450 1B1-catalyzed formation of fjord region DB[a,l]PDE-DNA adducts is the critical step in DB[a,l]P-mediated carcinogenesis in mice, and probably also in man.

Response of rainbow trout (Oncorhynchus mykiss) D-11 cell line to 3-methylcholanthrene (3MC) exposure

The rainbow trout cytochrome P4501A gene subfamily consists of two members, CYP1A1 and CYP1A3, which are induced by polycyclic aromatic hydrocarbons (PAHs). In this study, we investigated the induction of cytochrome P4501A3 in the rainbow trout (Onchorhynchus mykiss) D-11 cell line after 3-methylcholanthrene (3MC) exposure by generating chimeric constructs in which a 2.3 kb fragment or portion of the 5'-flanking region of the trout cytochrome CYP1A3 gene was fused to the firefly luciferase (Luc) gene. The constructs were then transiently transfected into the trout D-11 cells and their transcriptional activity measured by luciferase assay after treatment with different 3MC concentrations. Maximal induction following exposure to 2 microM 3MC was 2.2-fold after 72 h. Deletion of the region specifying the 5' untranslated region (5'UTR) of the mRNA encoding the CYP1A3 gene increased unstimulated luciferase activity but also led to a loss of response to 3MC treatment. This finding suggests that the region specifying the 5'UTR contains a negative element that is also involved in the transcriptional response to 3MC.

Short-term responses of Oryzias latipes (Pisces: Adrianichthyidae) and Macrobrachium nipponense (Crustacea: Palaemonidae) to municipal and pharmaceutical waste water in Beijing, China: survival, behaviour, biochemical biomarkers

Whole effluent toxicity was assessed for the fish Oryzias latipes and the prawn Macrobrachium nipponense for 18 h in a dilution series (0-66%) of the inflow and effluent of a municipal waste water treatment plant as well as waste water from a teramycin producing pharmaceutical industry, before, during and after a pilot laboratory purification process. The waste waters caused acute toxicity as measured by inhibition of light emission in the luminiscent bacterium Vibrio qingaiensis sp. nov. (Q67). EROD and aryl hydrocarbon hydroxylase activity in in vitro carp liver-cells showed a dose-dependent toxic response to the municipal waste water. Behavioural responses and time-to-death of fish and prawn, recorded online with the "Multispecies Freshwater Biomonitor" proved to be concentration- and time-dependent sensitive toxicity indicators in both types of waste water. Behaviour changed stepwise from normal activity to (increased or decreased) activity to more time spent on ventilation and finally to increased morbidity at higher concentration and time of exposure. The municipal waste water treatment plant managed to reduce toxicity to bacteria (Q67), prawn and fish. The pharmaceutical waste water treatment process still has to be improved, in order to reduce toxicity for fish and prawn.

Biomarkers of carcinogenic contaminants in Baltic flounder (Platichthys flesus): temporal changes in urban and non-urban sites in Tallinn bay

In order to study effects of environmental contamination, a suite of biomarkers were measured over the period 1996 to 1999 in livers of flounder (Platichthys flesus) from two urban embayments and one non-urban reference site of the Gulf of Finland in the vicinity of Tallinn, Estonia. Total cytochrome P450 (CYP) level, aryl hydrocarbon hydroxylase (AHH), 5-aminolevulinic acid synthetase (ALA-S), and heme synthetase (HEM-S) activities were quantified by means of spectrophotometry. These data were compared to results obtained in 1994 for the same biomarkers at one of the urban embayments and the non-urban site, as measured by the same protocols. For the flounder collected from the non-urban site, changes occurred in AHH activity and the total CYP level, which were significantly lower in 1996 and 1999 compared with 1994 (p < 0.05). Activity of ALA-S decreased slightly over this same period. The activity of HEM-S increased between 1996 and 1999. In the urban site first investigated in 1994, the activities of AHH and ALA-S, as well as the total level of CYP in flounder liver were significantly higher compared with 1999 (p < 0.05). HEM-S activities did not show any significant changes over this time period. AHH activities of flounder collected in another urban site decreased slightly between 1996 and 1999, in contrast to data on the total CYP level which diminished drastically over these years (p < 0.05). Activities of HEM-S increased significantly (p < 0.05) during the period investigated, while activities of ALA-S remained unchanged. These findings suggest that contamination of the marine environments by PAHs has gone down everywhere in the Tallinn area during the last 3 to 5 years. However, the results indicate that the area is still contaminated, as indicated by elevated heme synthesis enzymes and the total CYP content, and that monitoring of contaminants and their effects should be continued in this region.

Interaction of chemical carcinogens and drug-metabolizing enzymes in primary cultures of hepatic cells from the rat

The experiments described in this paper have demonstrated that hepatocytes cultured on floating collagen membranes for periods of 10 days retain their ability to respond to the inducers of drug-metabolizing enzymes, phenobarbital and methylcholanthrene, by increases in cytochromes of the cytochrome P-450 complex. Since the regulation of these cytochromes is the rate-controlling factor in the metabolism of drugs and carcinogens in hepatocytes, such experiments indicate that hepatocytes cultured on floating collagen membranes retain those functions of the liver cell responsible for the metabolism and "activation" of carcinogenic substances. The data support this hypothesis and further indicate that this system may have potential application both in the investigation of hepatocarcinogenesis by chemicals in vitro and as a screening system for the detection of substances truly carcinogenic for the mammalian organism.