Targeting deoxyhypusine hydroxylase activity impairs cap-independent translation initiation driven by the 5'untranslated region of the HIV-1, HTLV-1, and MMTV mRNAs

Replication of the human immunodeficiency virus type 1 (HIV-1) is dependent on eIF5A hypusination. Hypusine is formed post-translationally on the eIF5A precursor by two consecutive enzymatic steps; a reversible reaction involving the enzyme deoxyhypusine synthase (DHS) and an irreversible step involving the enzyme deoxyhypusine hydroxylase (DOHH). In this study we explored the effect of inhibiting DOHH activity and therefore eIF5A hypusination, on HIV-1 gene expression. Results show that the expression of proteins from an HIV-1 molecular clone is reduced when DOHH activity is inhibited by Deferiprone (DFP) or Ciclopirox (CPX). Next we evaluated the requirement of DOHH activity for internal ribosome entry site (IRES)-mediated translation initiation driven by the 5'untranslated region (5'UTR) of the full length HIV-1 mRNA. Results show that HIV-1 IRES activity relies on DOHH protein concentration and enzymatic activity. Similar results were obtained for IRES-dependent translation initiation mediated by 5'UTR of the human T-cell lymphotropic virus type 1 (HTLV-1) and the mouse mammary tumor virus (MMTV) mRNAs. Interestingly, activity of the poliovirus IRES, was less sensitive to the targeting of DOHH suggesting that not all viral IRESs are equally dependent on the cellular concentration or the activity of DOHH. In summary we present evidence indicating that the cellular concentration of DOHH and its enzymatic activity play a role in HIV-1, HTLV-1 and MMTV IRES-mediated translation initiation.

Influence of Various Phenolic Compounds on Phenol Hydroxylase Activity of a Trichosporon cutaneum Strain

The phenol-degrading strain Trichosporon cutaneum R57 utilizes various aromatic and aliphatic compounds as a sole carbon and energy source. The intracellular activities of phenol hydroxylase [EC 1.14.13.7] of a Trichosporon cutaneum R57 strain grown on phenol (0.5 g/l) were measured. Different toxic phenol derivatives (cresols, nitrophenols and hydroxyphenols) were used as substrates in the reaction mixture for determination of the enzyme activity. The data obtained showed that the investigated enzyme was capable to hydroxylate all applied aromatic substrates. The measured activities of phenol hydroxylase varied significantly depending on the aromatic compounds used as substrates. The rate of phenol hydroxylase activity with phenol as a substrate (1.0 U/mg total cell protein) was accepted as 100%.

Chromium-induced tropane alkaloid production and H6H gene expression in Atropa belladonna L. (Solanaceae) in vitro-propagated plantlets

Hyoscyamine and scopolamine tropane alkaloids found in several solanaceous plants are anticholinergic drugs. Hyoscyamine 6β-hydroxylase (H6H) catalyzes two consecutive oxidation reactions. The first reaction is the hydroxylation of hyoscyamine to 6β-hydroxyhyoscyamine and the second is epoxidation of 6β-hydroxyhyoscyamine yielding scopolamine that is the final metabolite in the tropane alkaloid biosynthetic pathway. The effects of trivalent chromium as KCr (SO4)(2) on the production of tropane alkaloids and the expression of hyoscyamine 6β-hydroxylase gene (h6h) were studied in micro-propagated Atropa belladonna L. plantlets. The results showed that chromium treatment decreased the growth parameters (weights and lengths of the plantlets) and chlorophyll contents and increased proline contents. Moreover, semiquantitave RT-PCR analysis showed that the transcript level of H6H increased under chromium treatment. This treatment also increased hyoscyamine and scopolamine contents as shown by HPLC analysis. Changes of scopolamine contents correlate with the expression levels of h6h gene under different concentrations of chromium.

In vivo and in vitro mixed-function oxygenase activity and vitellogenin induction in fish and in fish and rat liver cells by stilbenes isolated from scotch pine (Pinus sylvestris)

Many types of pulp and paper mill effluents have the ability to induce mixed-function oxygenase (MFO) activity and vitellogenin (VTG) protein in exposed male fish. The search for the compounds responsible for MFO induction has led to several classes of compounds, among them retene and stilbenes. The objective of this study was to investigate the biological activities of candidate stilbene compounds. Three stilbenes, 3,5-dihydroxystilbene (pinosylvin; P1), 3-hydroxy-5-methoxystilbene (P2), and 3,5-dimethoxystilbene (P3), were extracted from Scotch pine (Pinus sylvestris) and purified to evaluate their ability to induce MFO activity in vitro using ethoxyresorufin-O-deethylase (EROD) activity in a rat hepatoma cell line (H4IIE). As these compounds may be chlorinated during pulp bleaching, chlorination of P2 was undertaken, producing di- and trichlorinated isomers (Cl-P2), which were also tested. Compounds were tested for EROD-inducing ability in vivo by exposing juvenile rainbow tout (Oncorhynchus mykiss) to waterborne concentrations (0.010 to 1.0 mg/L) for 4 days. Compounds were also tested for their ability to induce VTG in trout primary liver cells in vitro. The stilbenes were weak inducers of EROD and VTG. H4IIE EROD was induced by all four compounds, with the most potent induction by P3, followed by P1, the Cl-P2 mixture, and then P2. Induction for all four stilbenes was from 3.13 × 10⁻³ to 3.57 × 10⁻⁴ as potent as retene and about 1.11 × 10⁻⁵ to 1.20 × 10⁻⁶ as potent as TCDD. Juvenile rainbow trout did not show EROD induction after exposures to P1, P2, or the Cl-P2 mixture, whereas P3 caused activity fourfold above that of controls. P1, P3, and Cl-P2 all weakly induced VTG in rainbow trout hepatocytes. The most potent inducer of VTG was Cl-P2, followed by P3 and P1. The results show the ability of wood-derived stilbenes to cause weak MFO induction in fish and in rat liver cells and to weakly induce vitellogenin in fish liver cells.

Comparative petroleum hydrocarbons levels and biochemical responses in mussels from hydrothermal vents (Bathymodiolus azoricus) and coastal environments (Mytilus galloprovincialis)

Aliphatic hydrocarbons and PAHs in the whole soft tissues of Bathymodiolus azoricus from three Mid-Atlantic Ridge hydrothermal vents (Menez-Gwen, Lucky Strike and Rainbow), and Mytilus galloprovincialis from three contaminated coastal sites in South Portugal were analysed, and its effects on the digestive gland microsomes mixed-function oxygenase system (MFO) were assessed. Aliphatic hydrocarbons levels were present in the same magnitude in both coastal and hydrothermal environments, while the UCM (unresolved complex mixture) for coastal mussels were higher than in vent mussels. In general, significantly higher PAHs concentrations were found in coastal mussels, compared to B. azoricus where low molecular weight PAHs (2-3 rings) represented the majority of PAHs contrarily to what was observed in M. galloprovincialis. The MFO components were present in both mussel species, and were detected in vent mussels for the first time. However this system seems to have different roles in species from these contrasting environments. In coastal mussels MFO responded to hydrocarbon contamination while response in hydrothermal organisms appeared to be related mainly to endogenous factors.

Protective effect of vitamin C towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay

The aim of this study was to investigate the protective effect of vitamin C towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay. None of the vitamin C concentrations tested (1-10 microM) in presence or absence of formamidopyrimidine-DNA glycosylase (Fpg enzyme) caused DNA damage per se. HepG2 cells simultaneously treated with vitamin C and N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosodibutylamine (NDBA) or N-nitrosopiperidine (NPIP) reduced the genotoxic effects of the N-nitrosamines in a dose-dependent manner. At concentrations of 1-5 microM vitamin C, the protective effect was higher towards NPYR-induced oxidative DNA damage (78-79%) than against NDMA (39-55%), NDBA (12-14%) and NPIP (3-55%), in presence of Fpg enzyme. However, a concentration of 10 microM vitamin C led to a maximum reduction in NDBA (94%), NPYR (81%), NPIP (80%) and NDMA (61%)-induced oxidative DNA damage, in presence of Fpg enzyme. The greatest protective effect of vitamin C (10 microM) was higher towards NDBA-induced oxidative DNA damage. One feasible mechanism by which vitamin C exerted its protective effect is that may interact with the enzyme systems catalyzing the metabolic activation of the N-nitrosamines, blocking the production of genotoxic intermediates. Vitamin C (10 microM) strongly reduced the coumarin hydroxylase (82%) activity. However, the p-nitrophenol hydroxylase and the ethoxyresorufine O-deethylation activities were slightly and weakly reduced (32-19%), respectively.

CYP2B6 genotype alters abstinence rates in a bupropion smoking cessation trial

BACKGROUND

CYP2B6 is the primary enzyme involved in bupropion (Zyban; GlaxoSmithKline, Research Triangle Park, North Carolina) metabolism. Genetic polymorphisms in CYP2B6, such as CYP2B6*6, can alter bupropion metabolism and may affect bupropion treatment outcome.

METHODS

Subjects participated in a smoking cessation clinical trial of bupropion versus placebo. The main outcome was a 7-day point prevalence abstinence rate measured 10 weeks after the start of treatment (i.e., end of treatment) and at the 6-month follow-up; secondary outcomes were severity of adverse effects, withdrawal, and urge to smoke. Subjects were haplotyped for the CYP2B6*6 variants.

RESULTS

Among smokers in the CYP2B6*6 group (CYP2B6*1/*6 or CYP2B6*6/*6 genotype, n = 147, 45% of the population), bupropion produced significantly higher abstinence rates than placebo at the end of treatment (32.5% vs. 14.3%, p = .01) and at the 6-month follow-up (31.2% vs. 12.9%, p = .008). In contrast, bupropion was no more effective than placebo for smokers in the CYP2B6*1 group (CYP2B6*1/*1, n = 179) at the end of treatment (31.0% vs. 31.6%, p = .93) or at the 6-month follow-up (22.0% vs. 21.5%, p = .94). There was a significant genotype by treatment interaction at the end of treatment (odds ratio [OR] = 2.97, confidence interval [CI] = 1.05-8.40, p = .04), which was similar at 6-month follow-up (OR = 2.98, CI = .98-9.06, p = .05).

CONCLUSIONS

These data suggest that smokers with the CYP2B6*6 genotype have a higher liability to relapse on placebo and that they may be good candidates for bupropion treatment for smoking cessation.

Effects of eleven isothiocyanates on P450 2A6- and 2A13-catalyzed coumarin 7-hydroxylation

Many isothiocyanates (ITCs), both naturally occurring and synthetic, are potent and selective inhibitors of carcinogenesis in animal models and are now viewed as a class of promising chemopreventive agents. We have investigated the ability of 11 ITCs to inhibit and/or inactivate P450 2A6- and 2A13-mediated coumarin 7-hydroxylation. Two of these 11 ITCs, phenylpropyl isothiocyanate (PPITC) and phenylhexyl isothiocyanate (PHITC), were potent inhibitors of P450 2A13. The K I values for the inhibition of P450 2A13-mediated coumarin 7-hydroxylation by PPITC and PHITC were approximately 0.14 and 1.1 microM, respectively. P450 2A6 was also inhibited by these two ITCs; however, the K I values indicated they were approximately 10-20-fold less potent for P450 2A6 than for P450 2A13. Most of the ITCs tested, including PPITC and PHITC, showed some degree of inactivation of both P450s; however, only one compound, tert-butyl isothiocyanate (tBITC), showed significant inactivation of P450 2A13 at a concentration of 10 microM. None of the ITCs caused significant inactivation of P450 2A6 at this concentration. tBITC inactivated P450 2A13 with an apparent K I of 4.3 microM and a k inact of 0.94 min (-1). Inactivation of P450 2A6 by tBITC was observed only at high concentrations and long incubation times. The observed differences in inhibition and/or inactivation of P450 2A6 and 2A13 by a few of the isothiocyanates suggest that these compounds may be useful for structure-function studies.

VKORC1: molecular target of coumarins

The genetic diagnosis of a single family with combined vitamin K-dependent clotting factor deficiency (VKCFD2, OMIM #607473) finally led to the identification and molecular characterization of vitamin K epoxide reductase (VKORC1). VKORC1 is the key enzyme of the vitamin K cycle and the molecular target of coumarins, which represent the most commonly prescribed drugs for therapy and prevention of thromboembolic conditions. However, coumarins are known to have a narrow therapeutic window and a considerable risk of bleeding complications caused by a broad variation of intra- and inter-individual drug requirement. Now, 3 years after its identification, VKORC1 has greatly improved our understanding of the vitamin K cycle and has led to the translation of basic research into clinical practise in at least three directions: (i) Mutations within VKORC1 have been shown to cause a coumarin-resistant phenotype and a single SNP (rs9923231) within the VKORC1 promoter region has been identified as the major pharmacodynamic determinant of coumarin dose. Together with the previously described CYP2C9 variants and other dose-influencing factors, such as age, gender and weight, individualized dosing algorithms have become available. (ii) Preliminary studies indicate that concomitant application of low-dose vitamin K (80-100 microg day(-1)) and warfarin significantly improves INR stability and time of INR within the therapeutic range. (iii) Co-expression studies of FIX and FX with VKORC1 have shown that VKOR activity is the rate-limiting step in the synthesis of biologically active vitamin K-dependent factors. Thus, co-expression of VKORC1 leads to a more efficient production of recombinant vitamin K-dependent coagulation factors such as FIX and FVII. This could improve production of recombinant factor concentrates in the future.

Influence of rabeprazole and lansoprazole on the pharmacokinetics of tacrolimus in relation to CYP2C19, CYP3A5 and MDR1 polymorphisms in renal transplant recipients

The objective of this study was to evaluate whether genetic polymorphisms of CYP2C19, CYP3A5 and MDR1 significantly impact the interaction between tacrolimus and rabeprazole or lansoprazole. Seventy-three recipients were randomly assigned after renal transplantation to receive repeated doses of tacrolimus for 28 days with a regimen of either 20 mg of rabeprazole or 30 mg of lansoprazole. Blood concentrations of tacrolimus were measured by microparticle enzyme immunoassay. The mean daily dose and the dose-adjusted area under the plasma concentration-time curves from 0 to 12 h (AUC(0-12)) of tacrolimus coadministered with rabeprazole or lansoprazole were the lowest and highest, respectively, in CYP2C19 poor metabolizers (PMs) having the CYP3A5*3/*3 genotype (0.084 and 0.112 mg/kg/day and 1.269 and 1.033 ng.h/ml/mg/kg, respectively). On the other hand, the mean dose-adjusted AUC(0-12) of tacrolimus coadministered with rabeprazole or lansoprazole were the highest in CYP2C19 PMs having the MDR13435CC+CT genotype, but not significantly. The present study indicates that there are significant interactions between tacrolimus and rabeprazole or lansoprazole in CYP2C19 PM renal transplant recipients bearing the CYP3A5*3/*3 genotypes. For recipients having these genetic polymorphisms, lower dosages of tacrolimus are required to achieve the target therapeutic index.

CYP2A6 genotype, phenotype, and the use of nicotine metabolites as biomarkers during ad libitum smoking

CYP2A6 inactivates nicotine to cotinine and cotinine to 3-hydroxycotinine. We investigated which of plasma nicotine and metabolites were most related to CYP2A6 genotype and smoking levels. We assessed demographic and smoking histories in 152 Caucasian ad libitum smokers, measured breath carbon monoxide (CO) levels, and determined plasma nicotine, cotinine, and 3-hydroxycotinine by high-performance liquid chromatography and CYP2A6 genotypes by PCR. Cigarettes per day was most closely related to CO (r = 0.60, P < 0.001) followed by plasma cotinine (r = 0.53, P < 0.001), whereas plasma cotinine was most strongly correlated with CO levels (r = 0.74, P < 0.001), confirming that cotinine is a good indicator of smoking levels; this was not limited by CYP2A6 variants. 3-Hydroxycotinine/cotinine is reported to be a good marker of CYP2A6 activity, and we found that the 3-hydroxycotinine/(cotinine + nicotine) ratio was most correlated with CYP2A6 genotype (r = 0.38, P < 0.001). Inclusion of the CYP2A6*12A allele strengthened the correlation (r = 0.46, P < 0.001), suggesting that the identification of novel alleles will continue to improve this relationship. Nicotine metabolism is slower in smokers, and we have shown that CYP2A6 is reduced by nicotine treatment in monkeys. Here, we found that plasma nicotine levels were inversely correlated with CYP2A6 activity (3-hydroxycotinine/cotinine, r = -0.41, P < 0.001) among those without CYP2A6 variants, suggesting a reduction in metabolism with higher nicotine levels. Together, these findings (a) confirm the use of plasma cotinine and CO as indicators of Caucasians' smoking levels, and that this is not limited by CYP2A6 genetic variation; (b) indicate that 3-hydroxycotinine/cotinine and 3-hydroxycotinine/(cotinine + nicotine) are moderately good indicators of the CYP2A6 genotype; and (c) support that nicotine exposure may reduce its own metabolism.

Differential alteration of drug-metabolizing enzyme activities after cyclophosphamide/adriamycin administration in breast cancer patients

Cyclophosphamide (CPA) and adriamycin (ADR) are widely used drugs for cancer chemotherapy. It has been reported that CPA and ADR singly or in combination could alter activities of a variety of drug-metabolizing enzymes in animals via multiple mechanisms. However, the effects of CPA/ADR on drug metabolism are largely unknown in human beings. Losartan metabolism has been suggested as a marker for determination of CYP2C9 activity. Caffeine is a commonly used probe to assess the metabolic activities of CYP1A2, CYP2A6, N-acetyltransferase 2 (NAT2) and xanthine oxidase (XO). The present study was designed to analyze the effects of CPA/ADR on these drug-metabolizing enzymes by using losartan and caffeine as probe drugs. A single oral dose of 25 mg losartan and a cup of instant coffee was given to 15 breast cancer patients on three occasions (before, and 2-4 h and 3 weeks after the adjuvant CPA/ADR chemotherapy [600 mg CPA/m2/day, 60 mg ADR/m2/day]). Losartan, caffeine and their metabolites were analyzed by using high-pressure liquid chromatography. When compared with baseline, CYP1A2 activity was increased by 20% and CYP2C9 activity was decreased by 315% 3 weeks after the administration of CPA/ADR chemotherapy (p = 0.05). The chemotherapy did not change the activities of CYP2A6, NAT2 or XO. CPA/ADR treatment caused a differential effect on drug-metabolizing enzyme activities, and this may contribute to predicting the efficacy and toxicity of chemotherapeutics, as well as understanding the drug-drug interactions.

Selectivity and Affinity Determinants for Ligand Binding to the Aromatic Amino Acid Hydroxylases

Hydroxylation of the aromatic amino acids phenylalanine, tyrosine and tryptophan is carried out by a family of non-heme iron and tetrahydrobiopterin (BH4) dependent enzymes, i.e. the aromatic amino acid hydroxylases (AAHs). The reactions catalyzed by these enzymes are important for biomedicine and their mutant forms in humans are associated with phenylketonuria (phenylalanine hydroxylase), Parkinson's disease and DOPA-responsive dystonia (tyrosine hydroxylase), and possibly neuropsychiatric and gastrointestinal disorders (tryptophan hydroxylase 1 and 2). We attempt to rationalize current knowledge about substrate and inhibitor specificity based on the three-dimensional structures of the enzymes and their complexes with substrates, cofactors and inhibitors. In addition, further insights on the selectivity and affinity determinants for ligand binding in the AAHs were obtained from molecular interaction field (MIF) analysis. We applied this computational structural approach to a rational analysis of structural differences at the active sites of the enzymes, a strategy that can help in the design of novel selective ligands for each AAH.

Warfarin dose and the pharmacogenomics of CYP2C9 and VKORC1 - rationale and perspectives

Warfarin is the most widely prescribed oral anticoagulant, but there is greater than 10-fold interindividual variability in the dose required to attain a therapeutic response. Information from pharmacogenomics, the study of the interaction of an individual's genotype and drug response, can help optimize drug efficacy while minimizing adverse drug reactions. Pharmacogenetic analysis of two genes, the warfarin metabolic enzyme CYP2C9 and warfarin target enzyme, vitamin K epoxide reductase complex 1 VKORC1, confirmed their influence on warfarin maintenance dose. Possession of CYP2C9*2 or CYP2C9*3 variant alleles, which result in decreased enzyme activity, is associated with a significant decrease in the mean warfarin dose. Several single nucleotide polymorphisms (SNPs) in VKORC1 are associated with warfarin dose across the normal dose range. Haplotypes based on these SNPs explain a large fraction of the interindividual variation in warfarin dose, and VKORC1 has an approximately three-fold greater effect than CYP2C9. Algorithms incorporating genetic (CYP2C9 and VKORC1), demographic, and clinical factors to estimate the warfarin dosage, could potentially minimize the risk of over dose during warfarin induction.

Genetic influences on the response to warfarin

PURPOSE OF REVIEW

Warfarin has a narrow therapeutic index and there is wide interindividual variability in the drug dose requirement. Uncertainty of response renders currently used loading regimens inaccurate as they fail to take into account individual patient factors that have a major influence on anticoagulation response. This review focuses on recent research findings demonstrating the impact of genetics on warfarin sensitivity and dose requirement and the issues concerning the clinical utility of individualized therapy.

RECENT FINDINGS

Single-nucleotide polymorphisms in cytochrome P450 2C9 and vitamin K epoxide reductase have been shown to make significant contributions to the variability in warfarin dose requirements. Polymorphisms in other genes that mediate the actions of warfarin make little or no contribution to the variability. Racial and cultural differences influence dose requirements, which can be explained at least in part by genetic and dietary factors.

SUMMARY

Individualization of therapy based on genetic and environmental factors has the potential to reduce the adverse effects associated with the commencement of warfarin therapy. Prospective studies that incorporate both CYP2C9 and VKORC1 genes and environmental factors in warfarin dose calculation will be required to demonstrate the safety, cost-effectiveness, and feasibility of individualized dosing regimens.

Acid-suppressive effects of generic omeprazole: comparison of three brands of generic omeprazole with original omeprazole

BACKGROUND

Generic omeprazole contains the same active ingredient as original omeprazole and require verification of the bioequivalence with original omeprazole. However, very few clinical studies have been reported.

AIMS

A prospective, randomised, open-label, crossover study to compare acid-suppressive effect of generic omeprazole with that of original omeprazole.

SUBJECTS

Seven healthy Helicobacter pylori-negative subjects of CYP2C19 extensive metaboliser.

METHODS

Intragastric pH was measured for 24 h without medications (placebo) and on day 7 of repeated administration of 10 mg once daily after breakfast of original omeprazole, Omeprazon, or three brands of generic omeprazole, Omeprazole-Towa, Ovulanze or Omerap.

RESULTS

Median values of intragastric pH and percentages of time with pH>4 for 24 h were significantly higher with administration of any omeprazole formulation compared with placebo (P<0.05, Wilcoxon signed-rank test). Whereas, during the night-time period (20:00-08:00 h), percentages of time with pH>4 with Omeprazole-Towa and Omerap were not significantly higher than placebo. Compared with Omeprazon, these two parameters for 24 h showed significantly greater inter-subject variations with Omeprazole-Towa (P<0.05 and P<0.01, F-test) and Ovulanze (P<0.05).

CONCLUSIONS

Acid-suppressive effects of some brands of generic omeprazole are not the same as original omeprazole. These differences might be reflected in clinical outcomes.

Carbon monoxide orchestrates a protective response through PPARgamma

Carbon monoxide (CO) suppresses proinflammatory responses in macrophages reacting to LPS. We hypothesize that CO acts by inducing a molecule(s) that suppresses the inflammatory response to subsequent stress. Exposure of macrophages to CO alone in vitro produced a brief burst of mitochondrial-derived ROS, which led to expression of PPARgamma. PPARgamma expression proved essential for mediating the anti-inflammatory effects of CO. Blocking the CO-mediated increase in ROS generation prevented PPARgamma induction, and blocking PPARgamma prevented CO's anti-inflammatory effects. In a model of acute lung injury in mice, CO blocked expression of Egr-1, a central mediator of inflammation, and decreased tissue damage; inhibition of PPARgamma abrogated both effects. These data identify the mitochondrial oxidases as an (perhaps the) initial cellular target of CO and demonstrate that CO upregulates expression of PPARgamma via the mitochondria, which assures that a subsequent stress stimulus will lead to a cytoprotective as opposed to a proinflammatory phenotype.

Isoflavones inhibit nicotine C-oxidation catalyzed by human CYP2A6

The inhibitory effects of isoflavones (daidzein, genistein, and glycitein) on human cytochrome P450 (CYP) 2A6 activities were investigated. Daidzein, genistein, and glycitein uncompetitively inhibited nicotine C-oxidation catalyzed by recombinant CYP2A6 expressed in baculovirus-infected insect cells with Ki values of 1.3 +/- 0.3 microM, 0.7 +/- 0.2 microM, and 5.2 +/- 0.8 microM, respectively, but not coumarin 7-hydroxylation. Effects of the intake of soy isoflavones on in vivo nicotine metabolism were investigated with 7 healthy Japanese homozygotes of CYP2A6*1. The cotinine/nicotine ratio of the plasma concentrations 2 hours after chewing 1 piece of nicotine gum under the basal condition (after abstaining from soy foods for 1 week) was 8.8 +/- 2.6 (4.4-11.4). The ratio was significantly (P < .05) reduced to 6.7 +/- 1.6 (4.0-8.2) after consumption of a soy isoflavone supplement (60 mg of total isoflavones/d) for 5 days. The authors found that isoflavone contained in soy products significantly decreased nicotine metabolism.

Environmental induction of CYP1A-, CYP2M1- and CYP2K1-like proteins in tropical fish species by produced formation water on the northwest shelf of Australia

Normal operation of oil well platforms results in the discharge of "produced formation water" (PFW). The expression of CYP1A, CYP2M1- and 2K1-like proteins was examined for use as possible biomarkers of PFW exposure. A pilot study at the Harriet A production platform, on the Northwest Shelf of Australia, had indicated that PFW contamination possibly contributes to induction of CYP1A- and 2K1/2M1-like proteins in Gold-Spotted Trevally (Carangoides fulvoguttatus). In a subsequent caged fish study in the same location, Stripey seaperch (Lutjanus carponotatus) were caught at a clean site, then distributed to three caging sites: A (near-field), B (far-field) and C (a non-impacted reference site). Fish were sampled at time T = 0, 3 and 10 days. Significant increases of CYP1A, one CYP2K1- and two CYP2M1-like proteins were noted at Site A at T = 10. For another CYP2K1-like protein, a significant increase was observed at Site A only at T = 3. Prevailing winds changed between days 6 and 8 of sampling, moving the surface water plume directly west, possibly impacting in situ PFW exposure. The results indicate that tropical fish CYP1A protein is sensitive to PFW exposure. Importantly, statistically significant environmental induction of both CYP2M1- and CYP2K1-like proteins in tropical fish due to PFW exposure had not previously been described and CYP2 family induction may represent possible new biomarkers (other than CYP1A) of PFW exposure. In addition, the novel fraction-specific response of CYP2K-like proteins requires further verification but offers promise for improved monitoring of sub-lethal responses in marine organisms. (Supported by Australian Institute of Marine Science, Apache Energy Ltd. and the Environmental Toxicology Research Program at The University of Mississippi).

Use of omeprazole sulfone in a single plasma sample as a probe for CYP3A4

OBJECTIVE

The hydroxylation of omeprazole, measured as the ratio of omeprazole/5-hydroxyomeprazole in a plasma sample taken 3 h after an oral dose, is an established method to determine CYP2C19 activity, and the ratio of omeprazole AUC/omeprazole sulfone AUC has been used for assessing CYP3A4 activity. The aim of this study was to determine whether the latter ratio from a single 3-h sample can also be used for CYP3A4 phenotyping.

METHODS

Plasma levels of omeprazole and omeprazole sulfone were analyzed by reversed-phase high-performance liquid chromatography in a blood sample drawn 3 h after intake of a single oral 20-mg dose of omeprazole by 22 healthy subjects and five patients with newly diagnosed epilepsy. The procedure was repeated on the 4th day of 200 mg of ketoconazole intake (10 subjects), after 3 weeks of 150-200 mg twice-daily carbamazepine (five patients), and on the 6th day of 4 mg twice-daily tolterodine (12 subjects). Five subjects also took 100 mg and 50 mg of ketoconazole for 3 days before concomitant intake with omeprazole.

RESULTS

The mean log10(omeprazole/omeprazole sulfone) ratio was 0.18 3 h after intake of omeprazole alone. After concomitant intake of ketoconazole, the corresponding value was 1.38 (p<0.001); after intake of carbamazepine it was -0.42 (p<0.05); and after tolterodine it was 0.29 (not significant). In the five subjects taking increasing doses of ketoconazole, the ratio was 0.11, 0.79, 1.2, and 1.5 after 0, 50, 100, and 200 mg of ketoconazole, respectively. The correlation between the metabolic ratios from the AUC((0-6h)) and from the single 3-h samples was very good, with a correlation coefficient of 0.92 (p<0.001).

CONCLUSIONS

A single blood sample taken 3 h after intake of 20 mg of omeprazole can be reliably used to phenotype for both CYP2C19 and CYP3A4 activity.

Effects of clarithromycin and verapamil on rabeprazole pharmacokinetics between CYP2C19 genotypes

OBJECTIVE

Rabeprazole as a proton pump inhibitor (PPI) is mainly reduced to rabeprazole thioether via a nonenzymatic pathway, with minor CYP2C19 and CYP3A4 involvement. The aim of this study was to compare possible effects of clarithromycin and verapamil as inhibitors of CYP3A4 on the pharmacokinetics of rabeprazole among CYP2C19 genotypes.

METHODS

A three-way randomized, double-blind, placebo-controlled crossover study was performed. Nineteen volunteers, of whom six were homozygous extensive metabolizers (EMs), eight were heterozygous EMs, and five were poor metabolizers (PMs) for CYP2C19, received three 6-day courses of either daily 800 mg clarithromycin, 240 mg verapamil, or placebo in a randomized fashion, with a single oral dose of 20 mg rabeprazole on day 6 in all cases. Plasma concentrations of rabeprazole and rabeprazole thioether were monitored up to 24 h after the dosing.

RESULTS

In the control phase, the AUC(0-infinity) values for rabeprazole and rabeprazole thioether were 1,005+/-366 and 412+/-149 ng.h/ml in homozygous EMs, 1,108+/-340 and 491+/-245 ng.h/ml in heterozygous EMs, and 2,697+/-364 and 2,116+/-373 ng.h/ml in PMs, respectively. There were significant differences (p<0.001) in the AUC(0-infinity) of rabeprazole and rabeprazole thioether among three different CYP2C19 genotypes. In the clarithromycin and verapamil phases, no significant differences were found in the pharmacokinetic parameters of rabeprazole compared with those in the control phase irrespective of CYP2C19 genotypes, whereas the AUC(0-infinity) of rabeprazole thioether was significantly increased 2.8-fold and 2.3-fold in homozygous EMs (p<0.01), 2.0-fold and 2.0-fold in heterozygous EMs (p<0.05), and 1.6-fold and 1.9-fold in PMs (p<0.05), respectively. In each genotype group for CYP2C19, there were no statistical differences in the percent increase in those pharmacokinetic parameters between the clarithromycin and verapamil pretreatment phases.

CONCLUSION

The pharmacokinetic parameters of rabeprazole were not altered by clarithromycin or verapamil irrespective of the CYP2C19 genotypes. However, this result shows that both clarithromycin and verapamil significantly influence the disposition of rabeprazole by inhibiting the oxidation of the thioether, since the AUC(0-infinity) of rabeprazole thioether that has no effect on acid secretion increased. Therefore, the pharmacokinetic interactions between rabeprazole and CYP3A4 or P-glycoprotein inhibitors have limited clinical significance.

Dose dependent inhibitory effects of dietary 8-methoxypsoralen on NNK-induced lung tumorigenesis in female A/J mice

We have reported that pretreatment by stomach tube with 8-methoxypsoralen (methoxsalen; 8-MOP), a potent human CYP2A6 inhibitor, strongly suppresses lung tumorigenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female A/J mice (Cancer Res. 2003). Here, we examined inhibitory effects with administration in the diet. When the mice were 7 weeks of age, they received dietary supplementation with 8-MOP at concentrations of 1, 10 or 100 ppm for 3 days prior to a single dose of NNK (2mg/0.1 ml saline/mouse, i.p.) or an equal volume of saline (vehicle control). The experiment was terminated 16 weeks after the first 8-MOP treatment and lung proliferative lesions were analyzed. The incidences and multiplicities in the 8-MOP 100 ppm-treated group were significantly reduced as compared with values for the NNK alone group (P<0.001). Multiplicities of NNK-induced lung proliferative lesions were also reduced in a dose dependent manner (Spearman rank correlation coefficient; rho=-0.806, correction P<0.0001). Mouse CYP2A4 and CYP2A5 differ from each other only 11 amino acids, and are closely related to the human CYP2A6. One hour after the last of three daily doses of 8-MOP (0.5, 5 or 50mg/kg body weight in 0.2 ml corn oil, given by stomach tube) or an equal volume of corn oil (vehicle control), given to the mice at 7 weeks of age, isolation of lung and liver RNAs demonstrated no effects on CYP2A4 and CYP2A5 mRNA levels with 8-MOP. In conclusion, the results of this study showed that clear dose response inhibitory effects of 8-MOP on NNK-induced lung tumorigenesis in female A/J mice fed diets containing 8-MOP, due to inhibition of enzyme activity of CYP2A4 and CYP2A5, rather than their gene expression.

Impact of CYP2A6 genotype on pretreatment smoking behaviour and nicotine levels from and usage of nicotine replacement therapy

We investigated the effect of slow metabolism of nicotine, predicted by CYP2A6 genotypes resulting in less than or equal to 50% activity, on baseline smoking behaviours and treatment variables in an open-label nicotine replacement therapy (NRT) clinical trial. Caucasian smokers with CYP2A6 slow vs normal metabolism had lower metabolic activity, indicated by the 3-hydroxycotinine/cotinine ratio (0.23+/-0.17 vs 0.45+/-0.22, P<0.01, respectively). CYP2A6 slow metabolizers also smoked fewer cigarettes per day compared to normal metabolizers (20+/-7 vs 24+/-10, respectively, P<0.04). With nicotine patch use, slow metabolizers had higher nicotine plasma levels compared to normal metabolizers (22.8+/-4.6 vs 15.8+/-7.6 ng/ml, respectively, P=0.02) while using the same numbers of patches/week. With nicotine spray use, where like in smoking the nicotine intake can be easily adjusted to adapt to rates of metabolism, slow metabolizers achieved similar nicotine levels compared to normal metabolizers (5.8+/-4.1 vs 8.0+/-9.1 ng/ml, P=0.82), by using fewer doses of nicotine spray/day (4.8+/-3.6 vs 10.5+/-8.0, respectively, P<0.02). These findings indicate that CYP2A6 genotype influences smoking behaviour in a Caucasian treatment-seeking population and that CYP2A6 genotype affects plasma levels obtained from, and usage of, NRT.

Effects of benzyl and phenethyl isothiocyanate on P450s 2A6 and 2A13: potential for chemoprevention in smokers

Isothiocyanates have been shown to be potent inhibitors of carcinogenesis in animals exposed to a number of chemical carcinogens including the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In this study the effects of benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), two naturally occuring isothiocyanates, on P450 2A6 and 2A13 were investigated. P450s 2A6 and 2A13 are thought to be the primary human P450 enzymes responsible for the in vivo metabolism of nicotine and NNK, respectively. In vitro, BITC and PEITC efficiently inhibited P450 2A6- and 2A13-mediated coumarin 7-hydroxylation. The inhibition of P450 2A6 and 2A13 by BITC was non-competitive with KI's of 4.1 and 1.3 microM, respectively. PEITC was a more potent inhibitor of both enzymes than BITC, with a KI of 0.37 microM for P450 2A6 and 0.03 microM for P450 2A13. P450 2A6-mediated metabolism of nicotine and P450 2A13-mediated alpha-hydroxylation of NNK were also inhibited significantly by these two isothiocyanates. Both BITC and PEITC were able to inactivate P450 2A6 and 2A13 in an NADPH-dependent manner potentially through the formation of adducts to the apoprotein. The potent inhibition of P450 2A6- and 2A13-mediated metabolisms together with the ability of BITC and PEITC to inactivate the enzymes suggests the possibility that these isothiocyanates could be developed as chemopreventive agents to protect smokers who are unwilling or unable to quit smoking against lung cancer.

Effects of dichloroethene isomers on the induction and activity of butane monooxygenase in the alkane-oxidizing bacterium "Pseudomonas butanovora"

We examined cooxidation of three different dichloroethenes (1,1-DCE, 1,2-trans DCE, and 1,2-cis DCE) by butane monooxygenase (BMO) in the butane-utilizing bacterium "Pseudomonas butanovora." Different organic acids were tested as exogenous reductant sources for this process. In addition, we determined if DCEs could serve as surrogate inducers of BMO gene expression. Lactic acid supported greater rates of oxidation of the three DCEs than the other organic acids tested. The impacts of lactic acid-supported DCE oxidation on BMO activity differed among the isomers. In intact cells, 50% of BMO activity was irreversibly lost after consumption of approximately 20 nmol mg protein(-1) of 1,1-DCE and 1,2-trans DCE in 0.5 and 5 min, respectively. In contrast, a comparable loss of activity required the oxidation of 120 nmol 1,2-cis DCE mg protein(-1). Oxidation of similar amounts of each DCE isomer ( approximately 20 nmol mg protein(-1)) produced different negative effects on lactic acid-dependent respiration. Despite 1,1-DCE being consumed 10 times faster than 1,2,-trans DCE, respiration declined at similar rates, suggesting that the product(s) of oxidation of 1,2-trans DCE was more toxic to respiration than 1,1-DCE. Lactate-grown "P. butanovora" did not express BMO activity but gained activity after exposure to butane, ethene, 1,2-cis DCE, or 1,2-trans DCE. The products of BMO activity, ethene oxide and 1-butanol, induced lacZ in a reporter strain containing lacZ fused to the BMO promoter, whereas butane, ethene, and 1,2-cis DCE did not. 1,2-trans DCE was unique among the BMO substrates tested in its ability to induce lacZ expression.

Opposite effects of short-term and long-term St John’s wort intake on voriconazole pharmacokinetics

OBJECTIVES

Constituents of St John's wort (SJW) in vivo induce the cytochrome P450 (CYP) isozymes 3A4, 2C9, and 2C19 but in vitro were shown to inhibit them. This study investigates both short- and long-term effects of SJW on the antifungal voriconazole, which is metabolized by these enzymes.

METHODS

In a controlled, open-label study, single oral doses of 400 mg voriconazole were administered to 16 healthy men stratified for CYP2C19 genotype before and on day 1 and day 15 of concomitant SJW intake (300 mg LI 160 3 times daily). Plasma and urine concentrations of voriconazole were determined by liquid chromatography with mass-spectrometric detection.

RESULTS

During the initial 10 hours of the first day of SJW administration, the area under the voriconazole plasma concentration-time curve was increased by 22% compared with control (15.5 +/- 6.84 h . microg/mL versus 12.7 +/- 4.16 h . microg/mL, P = .02). After 15 days of SJW intake, the area under the plasma concentration-time curve from hour 0 to infinity was reduced by 59% compared with control (9.63 +/- 6.03 h . microg/mL versus 23.5 +/- 15.6 h . microg/mL, P = .0004), with a corresponding increase in oral voriconazole clearance (CL/F) from 390 +/- 192 to 952 +/- 524 mL/min (P = .0004). The baseline CL/F of voriconazole and the absolute increase in CL/F were smaller in carriers of 1 or 2 deficient CYP2C19*2 alleles compared with wild-type individuals (P < .03).

CONCLUSIONS

Coadministration of SJW leads to a short-term but clinically irrelevant increase followed by a prolonged extensive reduction in voriconazole exposure. SJW might put CYP2C19 wild-type individuals at highest risk for potential voriconazole treatment failure.

Common genetic variants of microsomal epoxide hydrolase affect warfarin dose requirements beyond the effect of cytochrome P450 2C9

BACKGROUND

Warfarin dose response is partially explained by the polymorphisms in the cytochrome P450 (CYP) 2C9 gene, affecting S -warfarin clearance, as well as by age and body weight. We examined the influence on warfarin dose requirements of candidate genes encoding microsomal epoxide hydrolase (mEH), as well as glutathione S -transferase A1 (GSTA1) components of vitamin K epoxide reductase and the gamma-glutamylcarboxylase (GGCX) gene.

METHODS

We studied the effects of CYP2C9, mEH, GSTA1, and GGCX genotypes on warfarin maintenance doses, accounting for age, weight, vitamin K plasma concentrations and concurrent medications, in 100 patients undergoing therapeutic anticoagulation.

RESULTS

Allele frequencies were 76.5%, 12.5%, and 11% for CYP2C9*1 , *2 , and *3 , respectively; 75% and 25% for mEH T 612 C; 75.8% and 24.2% for mEH A 691 G; 73.5% and 26.5% for GSTA1 T 631 G; and 70.5% and 29.5% for GGCX G 8762 A. Warfarin doses differed among the CYP2C9 ( 2C9*1 , 2C9*2 , and 2C9*3 ) genotype groups: 6.3 +/- 1.9 mg/d, 5.3 +/- 1.8 mg/d, and 3.8 +/- 1.7 mg/d, respectively (F = 4.83, P < .01). There were no differences in any of the other genotype groups. Among the 62 wild-type CYP2C9 patients, variant mEH T 612 C homozygotes required higher doses than heterozygotes and wild-type patients (7.5 +/- 2.9 mg/d, 6.5 +/- 4.2 mg/d, and 6.0 +/- 2.6 mg/d, respectively [F = 3.57, P = .03]). The odds ratio for requiring greater than 7 mg/d in variant mEH T 612 C patients versus wild-type patients was 3.14 (95% confidence interval, 1.47-6.67), accounting for CYP2C9.

CONCLUSIONS

Variant mEH T 612 C genotypes are associated with warfarin doses of greater than 50 mg/wk beyond the effect of CYP2C9.

Effect of picroliv administration on hepatic microsomal mixed function oxidases and glutathione-conjugating enzyme system in cholestatic rats

The effect of Picroliv on hepatic microsomal mixed-function oxidases (MFO) and glutathione conjugating enzyme system in cholestatic rats was studied. Bile duct ligation in male rats for one weeks caused significant increase in both serum sorbitol dehydrogenase activity and serum bile acide concentration indicating cholestatic liver injury. Furthermore, a rise in the hepatic hydroxyproline level indicating collagen accumulation was observed. As a result of these alterations, the hepatic microsomal MFO system was imparied as evidenced by a decrease in cytochrome P-450 system content and in the activities of NADPH-cytochrome C reductase and aminopyrine demethylase. While the hepatic glutathione content remained unaffected, the cytosolic glutathione S-transferase activity was clearly suppressed due to subchronic cholestasis. Oral administration of Picroliv (25 mg/kg/day for 21 days)--a standardized irioid glycoside fraction of Picrorhiza kurroa in bile ligation induced cholestatic rats, singnificantly prevented the biochemical changes induced in liver and serum of cholestatic rats. These results suggested that picroliv has anti-cholestatic activity which may be attributed to antioxidant property or it's specific role in protein synthesis.

Effects of amitraz on cytochrome P450-dependent monooxygenases and estrogenic activity in MCF-7 human breast cancer cells and immature female rats

This study investigated the ability of amitraz, a formamidine insecticide, to induce cytochrome P450-dependent monooxygenases and to disrupt estrogenic activity in human breast cancer MCF-7 cells and immature female rats. In MCF-7 cells, treatment with 10 microM amitraz for 24 h increased 7-ethoxyresorufin O-deethylase activity in cell homogenate. Treatment of MCF-7 cells with 1 and 10 microM amitraz for 3 h replaced previously bound [(3)H]17beta-estradiol (E(2)) from estrogen receptors. Treatment with 0.1 and 1 microM amitraz for 2 days inhibited [(3)H]thymidine incorporation into the DNA of MCF-7 cells while the inhibition was blocked in cells co-treated with 1 nM E(2) and amitraz. In immature female rats, treatment with 50 mg/kg amitraz intraperitoneally for 3 days increased cytochrome P450 content, 7-ethoxyresorufin, methoxyresorufin and pentoxyresorufin O-dealkylases, and benzo[a]pyrene hydroxylase activities in liver microsomes. The results of immunoblot analysis revealed that amitraz induced liver microsomal CYP1A1/2, 2B1/2B2, and 3A proteins. Treatment with 10 and 25 mg/kg amitraz for 3 days dose-dependently decreased uterine weight and peroxidase activity in immature female rats while the decreases were blocked in rats co-treated with 10 microg/kg E(2) and 10 or 25 mg/kg amitraz. These in vitro and in vivo findings suggest that amitraz induces multiple forms of P450 and exerts weak antiestrogenic activity.

Alosetron repeat dose pharmacokinetics, effects on enzyme activities, and influence of demographic factors

AIM

To assess the pharmacokinetics of alosetron, its effect on in vivo enzyme activities, and influence of demographic factors during repeated dosing.

METHODS

Thirty healthy men and women received 1 mg oral alosetron twice-daily for 29.5 days and a single oral dose of a metabolic probe cocktail before and on the last day of alosetron dosing. Serum alosetron concentrations were measured on days 1, 8, 15, 22 and 29. Probe-substrate and metabolite concentrations were measured after each cocktail dose.

RESULTS

Alosetron accumulation in serum was negligible. Exposure to alosetron did not alter probe-metabolite/substrate ratios associated with CYP2C19, 2E1, 2C9, or 3A4 activity, but modestly decreased those associated with CYP1A2 and N-acetyltransferase activity. Systemic exposure to alosetron was higher in women, positively correlated with age and body mass index, and negatively correlated with CYP1A2 activity. Incidence of constipation was higher in women, but not associated with alosetron concentration.

CONCLUSIONS

Single dose data can reliably predict the pharmacokinetics of alosetron after repeated doses. Alosetron exhibits limited potential for inhibition of cytochrome P450-mediated metabolism. Interindividual differences in alosetron pharmacokinetics associated with demographic factors may be related to strong dependence on metabolism by CYP1A2.

Polymorphism of interleukin-1beta affects the eradication rates of Helicobacter pylori by triple therapy

BACKGROUND AND AIMS

Polymorphism in interleukin-1beta (IL-1beta) is associated with intragastric pH levels in Helicobacter pylori-positive subjects. Intragastric pH levels affect the activity of antibiotics against H. pylori in the stomach. The aim of this study was to investigate whether IL-1beta polymorphism is associated with eradication rates of H. pylori by triple therapy with a proton pump inhibitor (PPI), amoxicillin, and clarithromycin.

METHODS

Three hundred thirty-six patients infected with H. pylori completed treatment with omeprazole, 20 mg, or lansoprazole, 30 mg twice daily; clarithromycin, 200 mg 3 times daily; and amoxicillin, 500 mg 3 times daily, for 1 week. IL-1beta-511 and CYP2C19 genotypes of patients and sensitivity of H. pylori to clarithromycin and amoxicillin were determined.

RESULTS

Logistic regression analysis showed that the IL-1beta-511 polymorphism, as well as CYP2C19 genotype of patients and clarithromycin-resistance of H. pylori, was associated with successful eradication. Eradication rates for H. pylori were 77.3% (75 of 97; 95% confidence interval, 67.5-84.6), 89.6% (147 of 164; 95% confidence interval, 83.9-93.1), and 94.7% (95% confidence interval, 86.9-98.5) in patients with the C/C, C/T, and T/T genotypes of IL-1beta-511, respectively (P = 0.0014).

CONCLUSIONS

IL-1beta-511 polymorphism is one of the determinants of successful eradication of H. pylori using triple therapy with a PPI, amoxicillin, and clarithromycin, together with CYP2C19 genotype and bacterial resistance to clarithromycin.

Formation of plant cuticle: evidence for the occurrence of the peroxygenase pathway

Cuticle plays a major role as a protective barrier in plants. Despite its physiological importance, the mode of formation of this complex structure remains poorly understood. In particular, none of the putative enzymes involved in the biosynthesis of the cutin, the matrix of cuticle, have been cloned. We have shown previously that peroxygenase is able to catalyze in vitro the epoxidation step required for the biosynthesis of C18 cutin monomers. In the present work, we have confirmed in planta that this oxidase is indeed a key enzyme involved in the formation of cutin. Thus, in maize leaves, the specific inactivation of peroxygenase by organophosphorothioates resulted in a dramatic decrease of cuticular epoxide content, as visualized by a specific histochemical technique that was accompanied by a reduced thickness of the cuticle. A strict correlation could also be established between the extent of inhibition of the peroxygenase and the modification of the cuticle triggered by a family of structurally related inhibitors. Importantly, these effects were restricted to plants that contain a cutin originating from C18 monomers. The altered cuticle of maize, treated with the peroxygenase inhibitor, was characterized by an increased permeability to pesticides. In addition, such plants became largely susceptible to infection by fungi, implying that the cuticle represents a crucial target for the modulation of the response in plant-pathogen interactions.

Expression of CYP2A3 mRNA and its regulation by 3-methylcholanthrene, pyrazole, and beta-ionone in rat tissues

Cytochrome P450 (CYP) 2A enzymes are involved in the metabolism of numerous drugs and hormones and activate different carcinogens. Human CYP2A6, mouse CYP2A5 and rat CYP2A3 are orthologous enzymes that present high similarity in their amino acid sequence and share substrate specificities. However, different from the human and mouse enzyme, CYP2A3 is not expressed in the rat liver. There are limited data about expression of CYP2A3 in extrahepatic tissues and its regulation by typical CYP inducers. Therefore, the objective of the present study was to analyze CYP2A3 mRNA expression in different rat tissues by RT-PCR, and to study the influence of 3-methylcholanthrene, pyrazole and -ionone treatment on its expression. Male Wistar rats were divided into four groups of 5 rats each, and were treated ip for 4 days with 3-methylcholanthrene (25 mg/kg body weight), pyrazole (150 mg/kg body weight), -ionone (1 g/kg body weight), or vehicle. Total RNA was extracted from tissues and CYP2A3 mRNA levels were analyzed by semiquantitative RT-PCR. CYP2A3 mRNA was constitutively expressed in the esophagus, lung and nasal epithelium, but not along the intestine, liver, or kidney. CYP2A3 mRNA levels were increased in the esophagus by treatment with 3-methylcholanthrene and pyrazole (17- and 7-fold, respectively), in lung by pyrazole and -ionone (3- and 4-fold, respectively, although not statistically significant), in the distal part of the intestine and kidney by 3-methylcholanthrene and pyrazole, and in the proximal part of the intestine by pyrazole. CYP2A3 mRNA was not induced in nasal epithelium, liver or in the middle part of the intestine. These data show that, in the rat, CYP2A3 is constitutively expressed in several extrahepatic tissues and its regulation occurs through a complex mechanism that is essentially tissue specific.

Induction of liver monooxygenases by annatto and bixin in female rats

Annatto or urucum is an orange-yellow dye obtained from Bixa orellana seeds. It has been used as a natural dye in a variety of food products, drugs and cosmetics, and also in Brazilian cuisine as a condiment ('colorau'). Bixin, a carotenoid devoid of provitamin A activity, is the main pigment found in annatto. Some carotenoids (canthaxanthin, astaxanthin and beta-Apo-8'-carotenal) are known to be potent inducers of CYP1A1, a property not shared by others (beta-carotene, lycopene and lutein). Little is known, however, about the CYP1A1-inducing properties of bixin and annatto. The present study was performed to determine the effects of an annatto extract (28% bixin) and bixin (95% pure) on rat liver monooxygenases. Adult female Wistar rats were treated by gavage with daily doses of annatto (250 mg/kg body weight, which contains approximately 70 mg bixin/kg body weight), bixin (250 mg/kg body weight) or the vehicle only (corn oil, 3.75 g/kg body weight) for 5 consecutive days, or were not treated (untreated control). The activities of aniline-4-hydroxylase (A4H), ethoxycoumarin-O-deethylase (ECOD), ethoxy- (EROD), methoxy- (MROD), pentoxy- (PROD) and benzyloxy- (BROD) resorufin-O-dealkylases were measured in liver microsomes. Annatto (250 mg/kg containing 70 mg bixin/kg) induced EROD (3.8x), MROD (4.2x), BROD (3.3x) and PROD (2.4x). Bixin (250 mg/kg) was a weaker inducer of EROD (2.7x), MROD (2.3x) and BROD (1.9x) and did not alter PROD, A4H or ECOD activities. These results suggest that constituents of the extract other than bixin play an important role in the induction of CYP1A and CYP2B observed with annatto food colorings.

Auxin regulation of the gibberellin pathway in pea

The auxin indole-3-acetic acid (IAA) has been shown to promote the biosynthesis of the active gibberellin (GA(1)) in shoots of pea (Pisum sativum). We used northern analysis to investigate the timing of IAA-induced changes in transcript levels of PsGA3ox1 (Mendel's LE), PsGA2ox1, PsGA2ox2, and PsGA20ox1, key genes for the later stages of GA(1) biosynthesis and metabolism in pea. Rapid (2-4 h) changes occurred in the transcript levels of PsGA3ox1, PsGA2ox1, and PsGA2ox2 after treatment with IAA. [(14)C]GA(1) metabolism studies in decapitated shoots indicated that IAA inhibits GA(1) deactivation, consistent with the suppression of PsGA2ox1 (SLN) transcript levels by IAA. Studies with the sln mutant also indicated that PsGA2ox1 activity is involved in GA(1) deactivation in decapitated shoots. Culture of excised internode tissue in the presence of auxin clearly demonstrated that internode tissue is a site of GA(1) biosynthesis per se. Excised internode tissue cultured in the presence/absence of cycloheximide showed that de novo protein synthesis is required for IAA-induced increases in PsGA3ox1 transcript levels. Auxin dose response studies indicated that IAA concentration is a critical determinant of GA(1) biosynthesis over 1 to 2 orders of magnitude, and a range of auxins was shown to affect the GA pathway.

Influence of CYP2C9 and CYP2C19 genetic polymorphisms on warfarin maintenance dose and metabolic clearance

OBJECTIVE

Our objective was to determine the influence of cytochrome P450 (CYP) 2C9 and CYP2C19 genetic polymorphisms on warfarin dose requirement and metabolic clearance.

METHODS

The study population consisted of 93 Italian outpatients receiving long-term warfarin anticoagulant therapy (international normalized ratio values, 2-3), divided into 3 dose groups: low (<26.25 mg/wk; n = 37), medium (26.25-43.75 mg/wk; n = 32), and high (>43.75 mg/wk; n = 24). Steady-state unbound plasma concentrations of S- and R-warfarin were measured by HPLC and equilibrium dialysis, and corresponding unbound oral clearance (CL(free)) values were calculated. Allelic variants of CYP2C9 (CYP2C9(*)2 and CYP2C9(*)3) and CYP2C19 (CYP2C19(*)2) were identified by polymerase chain reaction, followed by restriction enzyme analysis.

RESULTS

Fifty-four patients carried no CYP2C9 mutated alleles ((*)1/(*)1), 31 carried one ((*)1/(*)2, n = 15; and (*)1/(*)3, n = 16), and 8 carried two ((*)2/(*)2, n = 2; (*)3/(*)3, n = 2; and (*)2/(*)3, n = 4). Two subjects were homozygous and 19 were heterozygous for the CYP2C19(*)2 allele variant. The frequencies of CYP2C9 mutated alleles were 72% in the low-dose group, 36% in the medium-dose group, and 4% in the high-dose group; the corresponding mean S-warfarin CL(free) values were 307.5 mL/min, 480.3 mL/min, and 881.3 mL/min. The mean S-warfarin CL(free) values varied significantly among the CYP2C9 genotype groups (P <.0001), although most patients (72%) with no mutated alleles showed S-warfarin CL(free) values in the same range as those carrying mutated alleles (58-777 mL/min). No relationship was found between S-warfarin CL(free) and CYP2C19 genotype or between R-warfarin CL(free) and either CYP2C9 or CYP2C19 genotype.

CONCLUSION

CYP2C9 genetic polymorphisms markedly influence warfarin dose requirements and metabolic clearance of the S-warfarin enantiomer, although nongenetic factors may also contribute to their large interindividual variability.

Effects of St. John's wort on irinotecan metabolism

St. John's wort (SJW), a widely used herbal product, has been implicated in drug interactions resulting from the induced expression of the cytochrome P450 CYP3A4 isoform. In this study, we determined the effect of SJW on the metabolism of irinotecan, a pro-drug of SN-38 and a known substrate for CYP3A4. Five cancer patients were treated with irinotecan (350 mg/m(2), intravenously) in the presence and absence of SJW (900 mg daily, orally for 18 days) in an unblinded, randomized crossover study design. The plasma levels of the active metabolite SN-38 decreased by 42% (95% confidence interval [CI] = 14% to 70%) following SJW cotreatment with 1.0 micro M x h (95% CI = 0.34 micro M x h to 1.7 micro M x h) versus 1.7 micro M x h (95% CI = 0.83 micro M x h to 2.6 micro M x h) (P =.033, two-sided paired Student's t test). Consequently, the degree of myelosuppression was substantially worse in the absence of SJW. These findings indicate that patients on irinotecan treatment should refrain from taking SJW because plasma levels of SN-38 were dramatically reduced, which may have a deleterious impact on treatment outcome.

What limits production of unusual monoenoic fatty acids in transgenic plants?

Unusual monounsaturated fatty acids are major constituents (greater than 80%) in seeds of Coriandrum sativum L. (coriander) and Thunbergia alata Bojer, as well as in glandular trichomes (greater than 80% derived products) of Pelargonium x hortorum (geranium). These diverged fatty acid structures are produced via distinct plastidial acyl-acyl carrier protein (ACP) desaturases. When expressed in Arabidopsis thaliana (L.) Heynh. under strong seed-specific promoters the unusual acyl-ACP desaturases resulted in accumulation of unusual monoene fatty acids at 1-15% of seed fatty acid mass. In this study, we have examined several factors that potentially limit higher production of unusual monoenes in transgenic oilseeds. (i) Immunoblots indicated that the introduced desaturases were expressed at levels equivalent to or higher than the endogenous delta9 18:0-ACP desaturase. However, the level of unusual fatty acid produced in transgenic plants was not correlated with the level of desaturase expression. (ii) The unusual desaturases were expressed in several backgrounds, including antisense 18:0-ACP desaturase plants, in fab1 mutants, and co-expressed with specialized ACP or ferredoxin isoforms. None of these experiments led to high production of expected products. (iii) No evidence was found for degradation of the unusual fatty acids during seed development. (iv) Petroselinic acid added to developing seeds was incorporated into triacylglycerol as readily as oleic acid, suggesting no major barriers to its metabolism by enzymes of glycerolipid assembly. (v) In vitro and in situ assay of acyl-ACP desaturases revealed a large discrepancy of activity when comparing unusual acyl-ACP desaturases with the endogenous delta9 18:0-ACP desaturase. The combined results, coupled with the sensitivity of acyl-ACP desaturase activity to centrifugation and low salt or detergent suggests low production of unusual monoenes in transgenic plants may be due to the lack of, or incorrect assemble of, a necessary multi-component enzyme association.

Topiramate and phenytoin pharmacokinetics during repetitive monotherapy and combination therapy to epileptic patients

PURPOSE

To evaluate the potential pharmacokinetic interactions between topiramate (TPM) and phenytoin (PHT) in patients with epilepsy by studying their pharmacokinetics (PK) after monotherapy and concomitant TPM/PHT treatment.

METHODS

Twelve patients with epilepsy stabilized on PHT monotherapy were enrolled in this study, with 10 and seven patients completing the phases with 400 and 800 mg TPM daily doses, respectively. TPM was added at escalating doses, and after stabilization at the highest tolerated TPM dose, PHT doses were tapered. Serial blood and urine samples were collected for PK analysis during the monotherapy phase or the lowest PHT dose after taper and the concomitant TPM/PHT phase. Potential metabolic interaction between PHT and TPM also was studied in vitro in human liver microsomal preparations.

RESULTS

In nine of the 12 patients, PHT plasma concentrations remained stable, with a mean (+/-SD) area under the curve (AUC) ratio (combination therapy/monotherapy) of 1.13 +/- 0.17 (range, 0.89-1.23). Three patients had AUC ratios of 1.25, 1.39, and 1.55, respectively, and with the addition of TPM (800, 400, and 400 mg daily, respectively), their peak PHT plasma concentrations increased from 15 to 21 mg/L, 28 to 36 mg/L, and 27 to 41 mg/L, respectively. Human liver microsomal studies with S-mephenytoin showed that TPM partially inhibited CYP2C19 at very high concentrations of 300 microM (11% inhibition) and 900 microM (29% inhibition). Such high plasma concentrations would correspond to doses in humans that are 5 to 15 times higher than the recommended dose (200-400 mg). TPM clearance was approximately twofold higher during concomitant TPM/PHT therapy

CONCLUSIONS

This study provides evidence that the addition of TPM to PHT generally does not cause clinically significant PK interaction. PHT induces the metabolism of TPM, causing increased TPM clearance, which may require TPM dose adjustments when PHT therapy is added or is discontinued. TPM may affect PHT concentrations in a few patients because of inhibition by TPM of the CYP2C19-mediated minor metabolic pathway of PHT.

Alteration of the biochemical properties of female gonads and vitellins in the clam Mya arenaria at contaminated sites in the Saguenay Fjord

Vitellins (Vn) are the major egg yolk proteins that constitute an important energy reserve for mollusc embryos. The purpose of the present study was to examine whether the relative levels of sugars, lipids, phosphates, and labile IIb metals and calcium normally associated with Vn would differ in clam populations living at contaminated sites. Softshell clams (Mya arenaria) were collected at three sites in the area of the Saguenay Fjord: a marina, a municipal sewer outfall zone, and a reference site. The condition factor (weight:length ratio), metallothionein-like proteins, cytochrome P450 1A1 activity and DNA damage were all determined in the clam's digestive gland. Levels of total sugars, lipids, alkali-labile phosphates, proteins, and labile zinc and calcium were determined in female gonad homogenates and in purified Vn. The results show that clam gonads at the contaminated site by a marina displayed a lower index of gonad activity than the reference site. In addition, the condition factor was significantly lower at the marina site as compared to the reference site, with a concomitant increase in DNA damage and metallothionein (MT) induction. In fact, the condition factor was significantly correlated with DNA damage (R = -0.413, P = 0.045) and MT levels (R = -0.622, P = 0.03). Homogenates of female gonads were found to contain higher levels of labile IIb metals and calcium, with lower lipid content at the marina site compared to the reference site, and much higher levels of alkali-labile phosphates (ALP) and calcium at the municipal outfall site. Vn from the marina site were significantly higher in labile IIb metals but lipid content appeared to be somewhat lower than at the reference site. Vn from the municipal site were found to be highly phosphorylated, with higher levels of lipids and calcium. These results suggest that the chemical composition of the gonads and Vn are altered in contaminated sites.

Effects of intrinsic fluorescence and quenching on fluorescence-based screening of natural products

To evaluate the effects of intrinsic (natural) fluorescence and quenching as confounding variables in fluorescence-based enzyme inhibition assays of natural products, we measured the fluorescence and quenching properties of 25 components of popular herbal products. The analyses were performed under conditions typically employed in drug-drug interaction studies that use c-DNA-derived P450 isoforms and surrogate fluorogenic substrates. Four of the 25 compounds tested (isorhamnetin, quercetin, vitexin, and yangonin) fluoresced or quenched sufficiently to interfere with these assays. Intrinsic fluorescence had a greater effect on these assays than quenching and for one compound, yangonin, was sufficient to mask inhibition and potentially produce a false negative result. Quenching had less of an effect on these assays, but was significant enough for one compound, quercetin, to mimic "weak" inhibition. Therefore, because intrinsic fluorescence or quenching could render some natural products unsuitable for testing in certain fluorometric assays, it would be prudent to include an evaluation of these properties in experimental protocols.

Effect of alachlor on hepatic cytochrome P450 enzymes in rats

Alachlor ((2-chloro-N-methoxymethyl)-N-(2,6-diethylphenyl)acetamide) is a widely used preemergence herbicide which has been classified by the USEPA as a probable human carcinogen. The herbicide has been suggested to be metabolized by hepatic cytochrome P450 system. We examined the effects of alachlor on cytochrome P450 enzymes in rat liver microsomes. Rats were treated intraperitoneally with alachlor daily for 5 days, at doses of 25, 50 and 100 mg/kg. Among the cytochrome P450-dependent monooxygenase activities, 7-pentoxyresorufin O-depentylase, which is associated with CYP2B1, was dose-dependently increased by alachlor. The induction relative to control activity was 1.7-4.2-fold. The activities of CYP1A-dependent monooxygenases such as 7-ethoxy-resorufin O-deethylase and acetanilide 4-hydroxylase were also significantly increased by alachlor at doses of 50 and 100 mg/kg (1.7-2.1-fold). Furthermore, immunoblotting showed that alachlor significantly increased CYP2B1/2 and CYP1A1/2 protein levels by 4.2-6.3- and 1.8-fold, respectively. Although 7-ethoxycoumarin O-deethylase, bufuralol 1'-hydroxylase and 4-nitrophenol 2-hydroxylase activities were significantly increased by alachlor at higher doses (> or = 50 mg/kg), the induction ratios were less than 1.6-fold. The activities of other cytochrome P450-dependent monooxygenases, namely testosterone 7 alpha-hydroxylase, testosterone 2 alpha-hydroxylase, testosterone 6 beta-hydroxylase and lauric acid omega-hydroxylase, were not affected by alachlor at any dose. In addition, there was no significant change in the protein levels of CYP2C11/6, CYP2D1, CYP2E1, CYP3A2/1 and CYP4A1/2/3. These results suggest that alachlor selectively induces cytochrome P450 isoforms of the CYP1A and CYP2B subfamilies in rat liver microsomes, and that the expression of these isoforms is closely related to the toxicity of alachlor.

The paradoxical effect of acetaminophen on CYP3A4 activity and content in transfected HepG2 cells

HepG2 cell lines that constitutively and stably express human CYP3A4 were constructed in order to study enzyme interactions with CYP3A4 as the only P450 present. CYP3A4 activity and content were assessed by the metabolism of fentanyl, a CYP3A substrate, and Western blots. Northern blots were used to examine the effects of acetaminophen (APAP) on CYP3A4-mRNA. The HepG2 cell lines' CYP3A4 activity was stable over time. High concentrations of APAP inhibited CYP3A4 activity. At lower concentrations, APAP produced a dose-dependent increase in CYP3A4 activity and content. No increases in CYP3A4-mRNA were seen. Incubation with cycloheximide caused a decrease in fentanyl metabolism secondary to a decrease in P450 levels that was prevented by the coincubation with APAP. Additionally, human microsomal CYP3A4 was stabilized by APAP against cytosol-mediated degradation. In our models, APAP appears to increase CYP3A4 activity. This increase appears to be via substrate stabilization. This is the first report that APAP can increase CYP3A4 activity and content in transfected HepG2 cells.

Cloning of gibberellin 3 beta-hydroxylase cDNA and analysis of endogenous gibberellins in the developing seeds in watermelon

We have isolated Cv3h, a cDNA clone from the developing seeds of watermelon, and have demonstrated significant amino acid homology with gibberellin (GA) 3 beta-hydroxylases. This cDNA clone was expressed in Escherichia coli as a fusion protein that oxidized GA(9) and GA(12) to GA(4) and GA(14), respectively. The Cv3h protein had the highest similarity with pumpkin GA 2 beta,3 beta-hydroxylase, but did not possess 2 beta-hydroxylation function. RNA blot analysis showed that the gene was expressed primarily in the inner parts of developing seeds, up to 10 d after pollination (DAP). In the parthenocarpic fruits induced by treatment with 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU), the embryo and endosperm of the seeds were undeveloped, whereas the integumental tissues, of maternal origin, showed nearly normal development. Cv3h mRNA was undetectable in the seeds of CPPU-treated fruits, indicating that the GA 3 beta-hydroxylase gene was expressed in zygotic cells. In our analysis of endogenous GAs from developing seeds, GA(9) and GA(4) were detected at high levels but those of GA(20) and GA(1) were very low. This demonstrates that GA biosynthesis in seeds prefers a non-13-hydroxylation pathway over an early 13-hydroxylation pathway. We also analyzed endogenous GAs from seeds of the parthenocarpic fruits. The level of bioactive GA(4 )was much lower there than in normal seeds, indicating that bioactive GAs, unconnected with Cv3h, exist in integumental tissues during early seed development.