Pyranoflavones: a group of small-molecule probes for exploring the active site cavities of cytochrome P450 enzymes 1A1, 1A2, and 1B1.

Selective inhibition of P450 enzymes is the key to block the conversion of environmental procarcinogens to their carcinogenic metabolites in both animals and humans. To discover highly potent and selective inhibitors of P450s 1A1, 1A2, and 1B1, as well as to investigate active site cavities of these enzymes, 14 novel flavone derivatives were prepared as chemical probes. Fluorimetric enzyme inhibition assays were used to determine the inhibitory activities of these probes toward P450s 1A1, 1A2, 1B1, 2A6, and 2B1. A highly selective P450 1B1 inhibitor 5-hydroxy-4'-propargyloxyflavone (5H4'FPE) was discovered. Some tested compounds also showed selectivity between P450s 1A1 and 1A2. α-Naphthoflavone-like and 5-hydroxyflavone derivatives preferentially inhibited P450 1A2, while ß-naphthoflavone-like flavone derivatives showed selective inhibition of P450 1A1. On the basis of structural analysis, the active site cavity models of P450 enzymes 1A1 and 1A2 were generated, demonstrating a planar long strip cavity and a planar triangular cavity, respectively.

Co-administration of vismodegib with rosiglitazone or combined oral contraceptive in patients with locally advanced or metastatic solid tumors: a pharmacokinetic assessment of drug-drug interaction potential.

PURPOSE: Vismodegib, a first-in-class oral hedgehog pathway inhibitor, is an effective treatment for advanced basal cell carcinoma. Based on in vitro data, a clinical drug-drug interaction (DDI) assessment of cytochrome P450 (CYP) 2C8 was necessary; vismodegib's teratogenic potential warranted a DDI study with oral contraceptives (OCs). METHODS: This single-arm, open-label study included two cohorts of patients with locally advanced or metastatic solid malignancies [Cohort 1: rosiglitazone 4 mg (selective CYP2C8 probe); Cohort 2: OC (norethindrone 1 mg/ethinyl estradiol 35 µg; CYP3A4 substrate)]. On Day 1, patients received rosiglitazone or OC. On Days 2-7, patients received vismodegib 150 mg/day. On Day 8, patients received vismodegib plus rosiglitazone or OC. The effect of vismodegib on rosiglitazone and OC pharmacokinetic parameters (primary objective) was evaluated through pharmacokinetic sampling over a 24-h period (Days 1 and 8). RESULTS: The mean ± SD vismodegib steady-state plasma concentration (Day 8, N = 51) was 20.6 ± 9.72 µM (range 7.93-62.4 µM). Rosiglitazone AUC(0-inf) and C(max) were similar with concomitant vismodegib [≤8% change in geometric mean ratios (GMRs); N = 24]. Concomitant vismodegib with OC did not affect ethinyl estradiol AUC(0-inf) and C(max) (≤5% change in GMRs; N = 27); norethindrone C(max) and AUC(0-inf) GMRs were higher (12 and 23%, respectively) with concomitant vismodegib. CONCLUSIONS: This DDI study in patients with cancer demonstrated that systemic exposure of rosiglitazone (a CYP2C8 substrate) or OC (ethinyl estradiol/norethindrone) is not altered with concomitant vismodegib. Overall, there appears to be a low potential for DDIs when vismodegib is co-administered with other medications.

Genetic considerations.

Dual antiplatelet therapy with aspirin and a P2Y(12) receptor antagonist improves outcomes in patients with acute coronary syndrome and in those treated with percutaneous coronary intervention (PCI) and a coronary stent. Candidate gene and genome-wide association studies have found that common genetic polymorphisms of the cytochrome P450 (CYP) 2C19 isoenzyme that result in a loss of functional activity are associated with less exposure of clopidogrel active metabolite and a diminished antiplatelet effect. Meta-analyses of registries and genetic substudies of randomized clinical trials demonstrate that carriers of these polymorphisms who are treated with clopidogrel are at an increased risk of cardiovascular events, particularly stent thrombosis, compared with noncarriers. This deleterious effect appears to be attenuated in patients not treated with PCI. The influence of polymorphisms of other genes, such as ABCB1, is inconsistent across clinical studies. The clinical efficacy of the newer P2Y(12) antagonists prasugrel and ticagrelor do not appear to be affected by the CYP2C19 genotype, but these agents increase major bleeding not related to coronary artery bypass surgery. Although data from randomized clinical trials are currently lacking, these observations suggest that a pharmacogenomic-guided approach to antiplatelet therapy in acute coronary syndrome could potentially maximize ischemic benefit while minimizing bleeding risk.

Exposure to potentially dangerous drug-drug interactions involving antipsychotics.

OBJECTIVE: Antipsychotic drug therapy is the cornerstone of treatment of persons with schizophrenia. Because most antipsychotics are metabolized by the hepatic cytochrome P450 system, concomitant use of an antipsychotic and medications that are competitively metabolized by the same system may cause a potentially harmful drug-drug interaction. This study used a large state's Medicaid claims database to examine the proportion of patients exposed to such interactions and the risk factors associated with exposure. METHODS: Claims from January 2000 through December 2003 for adult patients with a diagnosis of schizophrenia and at least one prescription for an antipsychotic (N=27,909) were examined for pairs of medications identified as potentially causing moderate or severe adverse drug effects. Logistic regression models were estimated to determine potential risk factors associated with exposure to the interaction pairs. RESULTS: A total of 6,417 (23%) patients were exposed to 14,213 potentially harmful interactions; 4,725 patients had at least one exposure from the same pharmacy, and 4,032 patients were exposed by the same physician. The greatest number of exposures (N=1,353) to potentially harmful combinations involved olanzapine and haloperidol. Patients prescribed risperidone were most likely to be exposed to an interaction (13.1%), followed by patients prescribed olanzapine (10.3%), quetiapine (3.3%), and clozapine (3.2%). A higher risk of exposure was associated with being female (odds ratio [OR]=.94), being white (OR=1.43), having depression (OR=1.21), or having impulse-control disorder (OR=1.98). CONCLUSIONS: Interventions by physicians and pharmacies to reduce the prescribing and dispensing of potentially harmful pairs of medications to patients with schizophrenia are recommended.

2,3,7,8-Tetrachlorodibenzo-p-dioxin activates the aryl hydrocarbon receptor and alters sex steroid hormone secretion without affecting growth of mouse antral follicles in vitro.

The persistent environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an ovarian toxicant. These studies were designed to characterize the actions of TCDD on steroidogenesis and growth of intact mouse antral follicles in vitro. Specifically, these studies tested the hypothesis that TCDD exposure leads to decreased sex hormone production/secretion by antral follicles as well as decreased growth of antral follicles in vitro. Since TCDD acts through binding to the aryl hydrocarbon receptor (AHR), and the AHR has been identified as an important factor in ovarian function, we also conducted experiments to confirm the presence and activation of the AHR in our tissue culture system. To do so, we exposed mouse antral follicles for 96 h to a series of TCDD doses previously shown to have effects on ovarian tissues and cells in culture, which also encompass environmentally relevant and pharmacological exposures (0.1-100 nM), to determine a dose response for TCDD in our culture system for growth, hormone production, and expression of the Ahr and Cyp1b1. The results indicate that TCDD decreases progesterone, androstenedione, testosterone, and estradiol levels in a non-monotonic dose response manner without altering growth of antral follicles. The addition of pregnenolone substrate (10 µM) restores hormone levels to control levels. Additionally, Cyp1b1 levels were increased by 3-4 fold regardless of the dose of TCDD exposure, evidence of AHR activation. Overall, these data indicate that TCDD may act prior to pregnenolone formation and through AHR transcriptional control of Cyp1b1, leading to decreased hormone levels without affecting growth of antral follicles.

Effects of capsaicin and dihydrocapsaicin on human and rat liver microsomal CYP450 enzyme activities in vitro and in vivo.

Capsaicin and dihydrocapsaicin, the two most abundant members of capsaicinoids in chili peppers, are widely used as food additives and for other purposes. In this study, we examined the inhibitory potentials of capsaicin and dihydrocapsaicin against CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4/5 activities in human liver microsomes. The effects of these two capsaicinoids on CYP450 enzymes were also evaluated in vivo in rats. The results demonstrated that capsaicin and dihydrocapsaicin moderately inhibited five isozymes (IC50) values ranging from 4.4 to 61.8 µM), with the exception of CYP2E1 (IC50 > 200 µM). Both capsaicinoids exhibited competitive, mixed, and noncompetitive inhibition on these isozymes (K (i) = 3.1 ± 0.5 - 78.6 ± 8.4 µM). Time-dependent inhibition of CYP3A4/5 by capsaicin was found. After multiple administrations of capsaicin and dihydrocapsaicin (1, 4, and 10 mg/kg) to rats, chlorzoxazone 6-hydroxylase activity and the expression of CYP2E1 were increased in liver microsomes. Our findings indicated that the possibility of food-drug interactions mediated by capsaicin and dihydrocapsaicin could not be excluded, and provided the useful information for evaluating the anticarcinogenic potentials of these two capsaicinoids.

Biomarkers and bioaccumulation of clam Ruditapes philippinarum in response to combined cadmium and benzo[α]pyrene exposure.

Biochemical and molecular biomarkers (the contents of metallothionein (MT), glutathione (GSH), the activities of aryl hydrocarbon hydroxylase (AHH), glutathione S-transferase (GST) and superoxide dismutase (SOD) and the mRNA expressions of GST-pi and Cu, Zn-SOD) were evaluated in clams Ruditapes philippinarum exposed to cadmium (Cd, 15 µg/L) and benzo[α]pyrene (BaP, 0.01 µg/L) individually and in combination (15 µg/L Cd+0.01 µg/L BaP) for 21 days. The accumulation of Cd, BaP and the biomarkers measured in the gills and digestive glands of the clam showed significant increase in combination treatment and it was significantly higher than the Cd or BaP treatment (P>0.05). The contents of MT increased in Cd and Cd+BaP treatment, while AHH activities were increased in Bap and Cd+BaP treatment (P>0.05). GSH levels enhanced in Cd group and declined significantly in Cd+BaP treatment (P>0.05). The activities of GST, SOD, and mRNA expressions of GST-pi, Cu, Zn-SOD increased remarkably in the clams exposed to combined pollutants. In this study, a significant interaction was observed for Cd and BaP accumulation in the clam and the current findings demonstrate the differences in antioxidant response of the biomarkers in clam to single contaminant and the mixtures.

Bioactivation of a novel 2-methylindole-containing dual chemoattractant receptor-homologous molecule expressed on T-helper type-2 cells/D-prostanoid receptor antagonist leads to mechanism-based CYP3A inactivation: glutathione adduct characterization and prediction of in vivo drug-drug interaction.

The 2-methyl substituted indole, 2MI [2-(4-(4-(2,4-dichlorophenylsulfonamido)-2-methyl-1H-indol-5-yloxy)-3-methoxyphenyl)acetic acid] is a potent dual inhibitor of 1) chemoattractant receptor-homologous molecule expressed on T-helper type-2 cells and 2) d-prostanoid receptor. During evaluation as a potential treatment for asthma and allergic rhinitis, 2MI was identified as a mechanism-based inactivator of CYP3A4 in vitro. The inactivation was shown to be irreversible by dialysis and accompanied by an NADPH-dependent increase in 2MI covalent binding to a 55- to 60-kDa microsomal protein, consistent with irreversible binding to CYP3A4. Two glutathione (GSH) adducts, G1 and G2, were identified in vitro, and the more abundant adduct (G1) was unambiguously determined via NMR to be GSH adducted to the 3-position of the 2-methylindole moiety. The potential for a clinical drug-drug interaction arising from mechanism-based inactivation of CYP3A4 by 2MI was predicted using a steady-state model, and a 4.3- to 7.5-fold increase in the exposure of midazolam was predicted at anticipated therapeutic concentrations. To better assess the potential for in vivo drug-drug interactions, the Sprague-Dawley rat was used as an in vivo model. An excellent in vitro-in vivo correlation was observed for the reduction in enzyme steady-state concentration (E'(ss/Ess)) as well as the change in the exposure of a prototypical CYP3A substrate, indinavir (area under the curve (AUC) for indinavir/AUC). In summary, 2MI was identified as a potent mechanism-based inactivator of CYP3A and was predicted to elicit a clinically relevant drug-drug interaction in humans at an anticipated therapeutic concentration.

The methoxylated flavones eupatorin and cirsiliol induce CYP1 enzyme expression in MCF7 cells.

Flavonoids have often been associated with cancer prevention and activity of the human cytochrome P450 enzymes CYP1A1 and CYP1B1 with the occurrence of cancer. The flavones eupatorin (1) and cirsiliol (2) enhanced CYP1 enzyme activity in a concentration-dependent manner in MCF7 human breast adenocarcinoma cells. In the range of 0-2.5 microM, 2 caused a dose-dependent increase in CYP1B1 mRNA levels and an increase in CYP1A1 mRNA. Compound 1 caused an increase in CYP1A1 and CYP1B1 mRNA at higher doses (approximately 5 microM). Both CYP1B1 and CYP1A1 catalyzed the conversion of 2 into an as yet unidentified compound. Application of the CYP1 family inhibitor, acacetin, significantly increased the IC(50) value of 2 in MCF7 cells, but did not significantly affect the action of 1. The data suggest that 2 induces CYP1 enzyme expression in cancer cells and is subsequently converted by CYP1B1 or CYP1A1 into an antiproliferative agent.

Repression of activated aryl hydrocarbon receptor-induced transcriptional activation by 5alpha-dihydrotestosterone in human prostate cancer LNCaP and human breast cancer T47D cells.

Polycyclic aromatic hydrocarbons (PAHs) and dioxins are ubiquitous environmental pollutants and activate the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor. It has been reported that testosterone represses 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced transcription of the cytochrome P450 (CYP) 1A1 gene in LNCaP cells. In this study, we investigated the mechanism for the repression of 3-methylcholanthrene (3MC)-induced transcription of AhR-regulated genes, CYP1A1, CYP1A2, CYP1B1, and AhR repressor (AhRR), by 5alpha-dihydroteststerone (DHT) in LNCaP and T47D cells, which are androgen receptor (AR)- and AhR-positive. Real-time PCR analysis showed that DHT repressed 3MC-induced mRNA expression of the CYP1 family and AhRR genes. DHT repressed 3MC-induced luciferase activity in an AhR response element-driven luciferase reporter assay in LNCaP and T47D cells. The inhibitory effect of DHT was abolished by knockdown of AR protein with siRNA. The protein levels of AhR and AhR nuclear translocator (Arnt), the AhR-dimerizing partner, were not affected by DHT. Co-immunoprecipitation assay showed that DHT significantly facilitated the complex formation between AR and AhR in 3MC-treated cells. These results suggest that complex formation between activated AR and AhR plays an important role in the suppression of 3MC-induced transcription of CYP1 family genes by DHT.

Cytochrome P450 2C9 variants influence response to celecoxib for prevention of colorectal adenoma.

BACKGROUND & AIMS: Variants in the cytochrome P450 2C9 (CYP2C9) gene are associated with impaired metabolism of celecoxib. We examined the influence of CYP2C9*2 (R144C) and CYP2C9*3 (I359L) variants on dose-related response or toxicity in a randomized trial of celecoxib. METHODS: We identified individuals with CYP2C9*2 and CYP2C9*3 genotypes (>or=1 variant allele) in the Adenoma Prevention with Celecoxib trial. Following adenoma removal, patients were assigned randomly to groups given placebo or low-dose (200 mg twice daily) or high-dose (400 mg twice daily) celecoxib and underwent follow-up colonoscopies at 1 and/or 3 years. RESULTS: Among 1660 patients, 21% were CYP2C9*2, and 12% were CYP2C9*3 genotypes. Overall, celecoxib was associated with a dose-dependent reduction in adenoma, compared with placebo, with relative risks (RR) of 0.65 (95% confidence interval [CI]: 0.56-0.76) for the low-dose and 0.54 (95% CI: 0.46-0.63) for the high-dose groups. However, the additional protective effect of the high dose, compared with the low-dose, was observed only in those with CYP2C9*3 genotypes (RR, 0.51; 95% CI: 0.30-0.87). The high dose, compared with low dose, was not associated with significant risk reduction among those with CYP2C9*2 (RR, 0.83; 95% CI: 0.57-1.21) or wild-type (RR, 0.89; 95% CI: 0.72-1.11) genotypes. Compared with placebo, a higher incidence of cardiovascular events was associated with both doses among patients with wild-type genotypes but only with the high dose among patients with variant genotypes. CONCLUSIONS: The greater efficacy of high-dose celecoxib, compared with the low-dose, in preventing colorectal adenoma appears confined to individuals with slow metabolizer (CYP2C9*3) genotypes. Genetic variability influences susceptibility to the potential benefits and hazards of celecoxib.

Chemopreventive effects of fermented brown rice and rice bran against 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis in female A/J mice.

The most common cause of human lung cancer is suggested to be exposure to the carcinogens in tobacco smoke. Among the multiple chemicals in tobacco smoke, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) has been regarded as one of the important agents for generation of lung cancers. Previously, our studies proved that fermented brown rice and rice bran (FBRA) has chemopreventive effects against carcinogenesis of the colon, liver, stomach, bladder and esophagus. In the present study, we examined possible chemopreventive effects of FBRA on the NNK-induced lung tumorigenesis in mice. Six-week-old female A/J mice were divided into 8 groups, and groups 1-5 were given NNK (10 mmol) by i.p. injection at week 7. Groups 2 and 3 were fed with diet containing 5 and 10% FBRA during the initiation phase, respectively. Groups 4 and 5 were fed with 5% and 10% FBRA during the post-initiation phase. Groups 1 and 6 were given control diet throughout the experiment. Groups 7 and 8 were given the diet containing 5 and 10% FBRA throughout the experiment, respectively. In both initiation (group 3) and post-initiation phase (group 5), 10% FBRA exposure significantly reduced the multiplicity of lung tumor (group 3, 2.35+/-2.13; group 5, 3.00+/-1.52; group 1, 4.08+/-1.85; p<0.006 and 0.04, respectively). Furthermore, administration of FBRA during the post-initiation phase significantly decreased the tumor size in comparison with that of control mice (0.66+/-0.32 vs. 0.77+/-0.33 mm). Treatment of 10% FBRA significantly reduced the mRNA expression levels of cytochrome P450 2A5 (Cyp2a5), which is known to be closely related to the human CYP2A6 enzyme that is involved in the mutagenic activation of NNK, in the lung but not liver tissues. A significantly reduced index of Ki67 positivity of lung tumors in group 5 was confirmed when compared with tumors of the control group (0.065+/-0.016 vs. 0.114+/-0.025). These findings suggest that FBRA has inhibitory effects on NNK-induced pulmonary tumorigenesis in A/J mice in both during initiation and post-initiation treatment, which is possibly associated with the induction of Cyp2a5 in the lung and the reduced proliferation rate of tumor cells. FBRA may be a promising chemopreventive agent for human lung cancers.

Effects of atrazine on hepatic metabolism and endocrine homeostasis in rainbow trout (Oncorhynchus mykiss).

The herbicide atrazine (ATZ) is one of the most widely used pesticides in the world and is now under scrutiny for its alleged capacity to disrupt the endocrine system. Exhibiting negligible interaction with the estrogen receptor (ER), ATZ's mode of action remains to be elucidated. ATZ may act as an inducer of the enzyme aromatase, which converts androgens to estrogens, although other mechanisms should also be taken into consideration such as impairment of hepatic metabolism. Therefore we administered juvenile rainbow trout (Oncorhynchus mykiss) a dose of either 2 or 200 microg ATZ/kg, or of carrier control phosphate buffered saline (PBS) and we measured plasma concentrations of testosterone (T), 17beta-estradiol (E2) and vitellogenin (Vtg) 6 days after exposure. Simultaneously we analyzed hepatic gene expression of cytochrome P450 (CYP) 1A and pi-class glutathione S-transferase (GST-P), and catalase (CAT) activity. Although sex steroid levels showed no significant alterations, we found a dose-dependent increase in Vtg and a concomitant decrease in CYP1A. There was no effect of ATZ on GST-P mRNA levels but GST-P was positively correlated with CYP1A. Also, CYP1A was negatively correlated with liver CAT and E2, and varied with T concentrations in a hormetic manner. The results showed that ATZ can alter hepatic metabolism, induce estrogenic effects and oxidative stress in vivo, and that these effects are linked.

Induction of cytochrome P450 2B6 activity by the herbal medicine baicalin as measured by bupropion hydroxylation.

PURPOSE: This study investigated the effect of the herbal medicine baicalin on bupropion hydroxylation, a probe reaction for CYP2B6 activity related to different CYP2B6 genotype groups. METHOD: Seventeen healthy male volunteers (6 CYP2B6*1/*1, 6 CYP2B6*1/*6, and 5 CYP2B6*6/*6) received orally administered bupropion alone and during daily treatment with baicalin. Blood samples were taken up to 72 h after each bupropion dose, and pharmacokinetics profiles were determined on days 1 and 25 for bupropion and hydroxybupropion. RESULT: Baicalin administration increased hydroxybupropion maximum plasma concentration (C(max)) by 73% [90% confidence interval (CI), 44-108%; P < 0.01] and the area under the concentration time curve extrapolated to infinity (AUC(0-infinity)) of hydroxybupropion by 87% (90% CI, 48-137%; P < 0.01), with no change in the elimination half-life of hydroxybupropion. Baicalin increased the AUC(0-infinity) ratio of hydroxybupropion to bupropion by 63% (90% CI, 38-92%; P < 0.01). CONCLUSION: Baicalin significantly induced CYP2B6-catalyzed bupropion hydroxylation, and the effects of baicalin on other CYP2B6 substrate drugs deserve further investigation.

Efavirenz induces CYP2B6-mediated hydroxylation of bupropion in healthy subjects.

OBJECTIVE: To characterize the effect of efavirenz on bupropion hydroxylation as a marker of cytochrome P450 (CYP) 2B6 activity in healthy subjects. METHODS: Thirteen subjects received a single oral dose of bupropion SR 150 mg before and after 2 weeks of efavirenz administration for comparison of bupropion and hydroxybupropion pharmacokinetics. Efavirenz plasma concentrations were also assessed. Subjects were genotyped for CYP2B6 (G516T, C1459T, and A785G), CYP3A4 (A-392G), CYP3A5 (A6986G), and multidrug resistance protein 1 (C3435T). RESULTS: The area under the concentration vs. time curve ratio of hydroxybupropion:bupropion increased 2.3-fold after efavirenz administration (P=0.0001). Bupropion area under the concentration vs. time curve and Cmax decreased by 55% and 34%, respectively (P<0.002). None of the CYP2B6 or CYP3A genotypes evaluated were associated with a difference in bupropion or efavirenz clearance. The 2 individuals homozygous for multidrug resistance protein 1 3435-T/T had 2.5- and 1.8-fold greater bupropion and efavirenz clearance, respectively, relative to C/C and C/T individuals (P<0.05). CONCLUSIONS: Our results confirm that efavirenz induces CYP2B6 enzyme activity in vivo, as demonstrated by an increase in bupropion hydroxylation after 2 weeks of efavirenz administration.

Differential expression of microRNAs in early-stage neoplastic transformation in the lungs of F344 rats chronically treated with the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

While numerous microRNAs (miRNAs) have been reported to alter their expression levels in human lung cancer tissues compared with normal tissues, the function of these miRNAs and their contribution to the long process of lung cancer development remains largely unknown. We applied a tobacco-specific carcinogen-induced cancer model to investigate the involvement of miRNAs in early lung cancer development, which could also provide information on potential, early biomarkers of lung cancers. Male F344 rats were first chronically treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogen present in tobacco products, for up to 20 weeks. The expression profiles of miRNAs in rat lungs were then determined. As measured by miRNA microarrays and confirmed by Northern blot and real-time polymerase chain reaction analyses, NNK treatment reduced the expression of a number of miRNAs, such as miR-101, miR-126*, miR-199 and miR-34. Significantly, these miRNAs overlap with previously published reports on altered miRNA expression in human lung cancer samples. These miRNAs might, therefore, represent early-response miRNAs that signify the molecular changes associated with pulmonary tumorigenesis. Moreover, we identified cytochrome P450 (CYP) 2A3, a critical enzyme in rat lungs that activates NNK to render it carcinogenic, as a potential target of miR-126*. NNK treatment in rats repressed miR-126* but induced CYP2A3 expression, a mechanism that may potentiate the oncogenic effects of NNK.

Life-threatening serotonin toxicity due to a citalopram-fluconazole drug interaction: case reports and discussion.

OBJECTIVE: To discuss two cases of life-threatening serotonin toxicity due to a drug interaction between citalopram and fluconazole and to review the pertinent literature. METHODS: A Medline search without date limitation was conducted using the terms serotonin syndrome, serotonin toxicity, fluconazole and citalopram. RESULTS AND DISCUSSION: Fluconazole inhibits CYP2C19. Citalopram is a substrate for 2C19 and inhibition of its metabolism may result in serotonin toxicity. Serotonin toxicity in oncology patients may not present with the classic constellation of signs typically described in the literature. Delirium may be the only presenting feature. Current level of evidence for treatment of serotonin toxicity is level 4 or 5 (case series and expert opinion). Nevertheless, there is a strong theoretical basis for treating serotonin toxicity in medical patients with a 5H(2A) blocker such as cyproheptadine. CONCLUSIONS: Consultation-liaison psychiatrists and oncologists should be aware of this preventable and underrecognized interaction. Citalopram should be stopped or substituted prior to the concurrent administration of fluconazole, and in the event of toxicity, treatment with cyproheptadine has a favorable risk-benefit ratio despite a lack of randomized controlled data to support its use.

Tetrahydro anthranilic acid as a surrogate for anthranilic acid: application to the discovery of potent niacin receptor agonists.

The design, synthesis, and biological activity of a series of cycloalkene acid-based niacin receptor agonists are described. This led to the discovery that tetrahydro anthranilic acid is an excellent surrogate for anthranilic acid. Several compounds were identified that were potent against the niacin receptor, had enhanced cytochrome P450 selectivity against subtypes CYP2C8 and CYP2C9, and improved oral exposure in mice.

Roles of nitric oxide in inflammatory downregulation of human cytochromes P450.

The purpose of this study was to determine the role of nitric oxide (NO) in the downregulation of human cytochrome P450 (CYP) enzymes and mRNAs by an inflammatory stimulus in cultured human hepatocytes. We focused on CYP2B6 because previous studies showed that rat CYP2B proteins undergo an NO-dependent degradation in response to inflammatory stimuli. To ensure high-level expression of CYP2B6, the inducer phenytoin was present at all times. Stimulation of cells with a mixture of tumor necrosis factor-alpha, interleukin-1, and interferon-gamma (ILmix) downregulated CYP2B6 mRNA and protein to 9 and 19% of control levels. The NO donor NOC-18 downregulated CYP2B6 protein to 30% of control, with only a small effect on CYP2B6 mRNA. Nitric oxide synthase inhibitors attenuated the downregulation of CYP2B6 protein but not mRNA by ILmix. These findings demonstrate that the posttranscriptional NO-dependent downregulation of CYP2B enzymes, observed previously in rat hepatocytes, is conserved in human CYP2B6. This mechanism is specific for CYP2B6 among the enzymes tested. No evidence was found for regulation of CYP2E1 mRNA or protein by NO. NOC-18 treatment downregulated CYP3A4 mRNA to 50% of control. However, NOS inhibitors failed to block the effects of ILmix on CYP3A4 expression.