ELQ-331 as a prototype for extremely durable chemoprotection against malaria

Background

The potential benefits of long-acting injectable chemoprotection (LAI-C) against malaria have been recently recognized, prompting a call for suitable candidate drugs to help meet this need. On the basis of its known pharmacodynamic and pharmacokinetic profiles after oral dosing, ELQ-331, a prodrug of the parasite mitochondrial electron transport inhibitor ELQ-300, was selected for study of pharmacokinetics and efficacy as LAI-C in mice.

Methods

Four trials were conducted in which mice were injected with a single intramuscular dose of ELQ-331 or other ELQ-300 prodrugs in sesame oil with 1.2% benzyl alcohol; the ELQ-300 content of the doses ranged from 2.5 to 30 mg/kg. Initial blood stage challenges with Plasmodium yoelii were used to establish the model, but the definitive study measure of efficacy was outcome after sporozoite challenge with a luciferase-expressing P. yoelii, assessed by whole-body live animal imaging. Snapshot determinations of plasma ELQ-300 concentration ([ELQ-300]) were made after all prodrug injections; after the highest dose of ELQ-331 (equivalent to 30 mg/kg ELQ-300), both [ELQ-331] and [ELQ-300] were measured at a series of timepoints from 6 h to 5½ months after injection.

Results

A single intramuscular injection of ELQ-331 outperformed four other ELQ-300 prodrugs and, at a dose equivalent to 30 mg/kg ELQ-300, protected mice against challenge with P. yoelii sporozoites for at least 4½ months. Pharmacokinetic evaluation revealed rapid and essentially complete conversion of ELQ-331 to ELQ-300, a rapidly achieved (< 6 h) and sustained (4–5 months) effective plasma ELQ-300 concentration, maximum ELQ-300 concentrations far below the estimated threshold for toxicity, and a distinctive ELQ-300 concentration versus time profile. Pharmacokinetic modeling indicates a high-capacity, slow-exchange tissue compartment which serves to accumulate and then slowly redistribute ELQ-300 into blood, and this property facilitates an extremely long period during which ELQ-300 concentration is sustained above a minimum fully-protective threshold (60–80 nM).

Conclusions

Extrapolation of these results to humans predicts that ELQ-331 should be capable of meeting and far-exceeding currently published duration-of-effect goals for anti-malarial LAI-C. Furthermore, the distinctive pharmacokinetic profile of ELQ-300 after treatment with ELQ-331 may facilitate durable protection and enable protection for far longer than 3 months. These findings suggest that ELQ-331 warrants consideration as a leading prototype for LAI-C.

Alkoxycarbonate Ester Prodrugs of Preclinical Drug Candidate ELQ-300 for Prophylaxis and Treatment of Malaria

ELQ-300 is a preclinical antimalarial drug candidate that is active against liver, blood, and transmission stages of Plasmodium falciparum. While ELQ-300 is highly effective when administered in a low multidose regimen, poor aqueous solubility and high crystallinity have hindered its clinical development. To overcome its challenging physiochemical properties, a number of bioreversible alkoxycarbonate ester prodrugs of ELQ-300 were synthesized. These bioreversible prodrugs are converted to ELQ-300 by host and parasite esterase action in the liver and bloodstream of the host. One such alkoxycarbonate prodrug, ELQ-331, is curative against Plasmodium yoelii with a single low dose of 3 mg/kg in a murine model of patent malaria infection. ELQ-331 is at least as fully protective as ELQ-300 in a murine malaria prophylaxis model when delivered 24 h before sporozoite inoculation at an oral dose of 1 mg/kg. Here, we show that ELQ-331 is a promising prodrug of ELQ-300 with improved physiochemical and metabolic properties and excellent potential for clinical formulation.

Intestinal Metabolites Are Profoundly Altered in the Context of HLA-B27 Expression and Functionally Modulate Disease in a Rat Model of Spondyloarthritis

OBJECTIVE

HLA-B27-associated spondyloarthritides are associated with an altered intestinal microbiota and bowel inflammation. We undertook this study to identify HLA-B27-dependent changes in both host and microbial metabolites in the HLA-B27/β2 -microglobulin (β2 m)-transgenic rat and to determine whether microbiota-derived metabolites could impact disease in this major model of spondyloarthritis.

METHODS

Cecal contents were collected from Fischer 344 33-3 HLA-B27/β2 m-transgenic rats and wild-type controls at 6 weeks (before disease) and 16 weeks (with active bowel inflammation). Metabolomic profiling was performed by high-throughput gas and liquid chromatography-based mass spectrometry. HLA-B27/β2 m-transgenic rats were treated with the microbial metabolites propionate or butyrate in drinking water for 10 weeks, and disease activity was subsequently assessed.

RESULTS

Our screen identified 582 metabolites, of which more than half were significantly altered by HLA-B27 expression at 16 weeks. Both microbial and host metabolites were altered, with multiple pathways affected, including those for amino acid, carbohydrate, xenobiotic, and medium-chain fatty acid metabolism. Differences were even observed at 6 weeks, with up-regulation of histidine, tyrosine, spermidine, N-acetylmuramate, and glycerate in HLA-B27/β2 m-transgenic rats. Administration of the short-chain fatty acid propionate significantly attenuated HLA-B27-associated inflammatory disease, although this was not associated with increased FoxP3+ T cell induction or with altered expression of the immunomodulatory cytokines interleukin-10 (IL-10) or IL-33 or of the tight junction protein zonula occludens 1. HLA-B27 expression was also associated with altered host expression of messenger RNA for the microbial metabolite receptors free fatty acid receptor 2 (FFAR2), FFAR3, and niacin receptor 1.

CONCLUSION

HLA-B27 expression profoundly impacts the intestinal metabolome, with changes evident in rats even at age 6 weeks. Critically, we demonstrate that a microbial metabolite, propionate, attenuates development of HLA-B27-associated inflammatory disease. These and other microbiota-derived bioactive mediators may provide novel treatment modalities in HLA-B27-associated spondyloarthritides.

Longitudinal study on the use of dried blood spots for home monitoring in children after kidney transplantation

The use of DBSs for home monitoring has been limited due to unsatisfactory blood sampling and analytical difficulties. The aim of this longitudinal feasibility trial was to assess the utility of DBS to monitor TAC and Cr at home in transplant recipients. A total of 30 participants (2-21 years, mean±SD, 13.6±5.4 year) were enrolled over 12 months. Eighteen were males. Monthly DBS samples were obtained at home and mailed to the central laboratory for analysis of TAC and Cr. Nineteen patients completed the study, and 216 cards were received in the laboratory from a total of 279 cards expected, with 416/519 (80%) blood spots being suitable for analysis. We found a high correlation between blood TAC and Cr levels by DBS and the clinical laboratory, R² =.81 and .95, respectively. Fifteen parents and 15 youth completed measures of satisfaction with and preference for DBS testing. All but one parent/caregiver and youth reported satisfaction and preference for this method of testing over laboratory blood draws. We conclude that home DBS monitoring is a feasible method to monitor TAC and Cr in pediatric transplant recipients.

A comparison of salivary testosterone measurement using immunoassays and tandem mass spectrometry

Enzyme immunoassays (EIAs) are widely used to measure salivary testosterone. However, little is known about how accurately different EIAs assess testosterone, partially because estimates across various EIAs differ considerably. We compared testosterone concentrations across EIAs of three commonly used manufacturers (DRG International, Salimetrics, and IBL International) to liquid chromatography tandem mass spectrometry (LC-MS/MS). Relative to EIAs from Salimetrics and IBL International, EIAs supplied by DRG International provided the closest approximation to LC-MS/MS testosterone concentrations, followed closely by EIAs from Salimetrics, and then IBL. Additionally, EIAs tended to inflate estimates of lower testosterone concentrations in women. Examining our results and comparing them to existing data revealed that testosterone EIAs had decreased linear correspondence with LC-MS/MS in comparison to cortisol EIAs. Overall, this paper provides researchers with information to better measure testosterone in their research and more accurately compare testosterone measurements across different methods.

Diphenylether-Modified 1,2-Diamines with Improved Drug Properties for Development against Mycobacterium tuberculosis

New treatments for tuberculosis infection are critical to combat the emergence of multidrug- and extensively drug-resistant Mycobacterium tuberculosis (Mtb). We report the characterization of a diphenylether-modified adamantyl 1,2-diamine that we refer to as TBL-140, which has a minimal inhibitory concentration (MIC99) of 1.2 μg/mL. TBL-140 is effective against drug-resistant Mtb and nonreplicating bacteria. In addition, TBL-140 eliminates expansion of Mtb in cell culture infection assays at its MIC. To define the mechanism of action of this compound, we performed a spontaneous mutant screen and biochemical assays. We determined that TBL-140 treatment affects the proton motive force (PMF) by perturbing the transmembrane potential (ΔΨ), consistent with a target in the electron transport chain (ETC). As a result, treated bacteria have reduced intracellular ATP levels. We show that TBL-140 exhibits greater metabolic stability than SQ109, a structurally similar compound in clinical trials for treatment of MDR-TB infections. Combined, these results suggest that TBL-140 should be investigated further to assess its potential as an improved therapeutic lead against Mtb.

A role for adenine nucleotides in the sensing mechanism to purine starvation in Leishmania donovani

Purine salvage by Leishmania is an obligatory nutritional process that impacts both cell viability and growth. Previously, we have demonstrated that the removal of purines in culture provokes significant metabolic changes that enable Leishmania to survive prolonged periods of purine starvation. In order to understand how Leishmania sense and respond to changes in their purine environment, we have exploited several purine pathway mutants, some in which adenine and guanine nucleotide metabolism is uncoupled. While wild type parasites grow in any one of a variety of naturally occurring purines, the proliferation of these purine pathway mutants requires specific types or combinations of exogenous purines. By culturing purine pathway mutants in high levels of extracellular purines that are either permissive or non-permissive for growth and monitoring for previously defined markers of the adaptive response to purine starvation, we determined that adaptation arises from a surveillance of intracellular purine nucleotide pools rather than from a direct sensing of the extracellular purine content of the environment. Specifically, our data suggest that perturbation of intracellular adenine-containing nucleotide pools provides a crucial signal for inducing the metabolic changes necessary for the long-term survival of Leishmania in a purine-scarce environment.

A phase II study of sulforaphane-rich broccoli sprout extracts in men with recurrent prostate cancer

INTRODUCTION

Diets high in cruciferous vegetables are associated with lower risk of incidence of prostate cancer, including aggressive forms of this disease. Human intervention studies with cruciferous vegetable-rich diets also demonstrate modulation of gene expression in important pathways in prostate cells.

PURPOSE

Sulforaphane is a constituent of these foods postulated to harbor the anti-neoplastic activity based on multiple tumor models. Our own work demonstrates that sulforaphane inhibits AR signaling in prostate cancer cells. Here, we report results from the first clinical trial of sulforaphane-rich extracts in men with prostate cancer.

METHODS

We treated 20 patients who had recurrent prostate cancer with 200 μmoles/day of sulforaphane-rich extracts for a maximum period of 20 weeks and determined the proportion of patients with ≥50% PSA declines, the primary endpoint. Only one subject experienced a ≥50% PSA decline. Thus, the primary endpoint was not achieved. Seven patients experienced smaller PSA declines (<50%). There was also a significant lengthening of the on-treatment PSA doubling time (PSADT) compared with the pre-treatment PSADT [6.1 months pre-treatment vs. 9.6 months on-treatment (p = 0.044)]. Finally, treatment with sulforaphane-rich extracts was safe with no Grade 3 adverse events.

CONCLUSIONS

Treatment with 200 μmoles/day of sulforaphane-rich extracts did not lead to ≥50% PSA declines in the majority of patients. However, because of the safety of treatment and the effects on PSADT modulation, further studies, including those with higher doses, may be warranted to clarify the role of sulforaphane as a prevention agent or treatment agent.

Sulforaphane treatment in men with recurrent prostate cancer

5017

Background: Diets high in cruciferous vegetables are strongly associated with lower prostate cancer risk. Sulforaphane is a constituent of these foods postulated to harbor the anti-neoplastic activity based on pre-clinical evidence in multiple tumor models. Our own work demonstrates that sulforaphane inhibits HDAC function and suppresses AR signaling in prostate cancer cells (Gibbs, et al PNAS 2009). However, the anti-tumor efficacy and safety of sulforaphane in men with prostate cancer was unknown. Methods: In this single arm study, we treated patients with biochemical (PSA)-recurrence of prostate cancer with 200 µmol of sulforaphane extracts for up to 20 weeks. The primary endpoint was PSA response rate (>50% decline in PSA). Other efficacy endpoints included: maximal PSA decline and percent change in PSA from baseline to end of study. We also analyzed PSA doubling time changes using a mixed effects model. Genotyping for GSTM1 that contributes to sulforaphane metabolism, sulforaphane pharmacokinetics (PK), and pharmacodynamic (PD) measurements of HDAC inhibition in mononuclear cells (MCs) were also performed. Results: Twenty patients were enrolled, and 16/20 (80%) completed the pre-planned 20 weeks of treatment. One patient experienced a PSA decline >50%. Thirty-five percent of patients had lesser PSA declines (3% to 20%), and 15% of patients had a final PSA lower than baseline. There was a significant reduction in PSA doubling time (6 months pre-study vs. 9.4 months on-study, p=.013). Of note, testosterone levels remained non-castrate in all subjects. PK analysis demonstrated that GSTM1 null genotype correlated with longer sulforaphane T1/2 (half-life) (2.6 hours for GSTM1 null vs. 2.1 hours for GSTM1 intact, p=0.04). Sulforaphane treatment also increased histone acetylation in PD assays in MCs. Finally, no grade three adverse events were seen, and only one patient discontinued study treatment for toxicity (grade one GI discomfort). Conclusions: Treatment with 200 µmol per day of sulforaphane is feasible, safe, and inhibits HDAC function. This combined with the preliminary observation of PSA modulation, which may indicate biologic activity, provides the basis for dose escalation studies of sulforaphane in men with prostate cancer. Clinical trial information: NCT01228084.

Analysis of tacrolimus and creatinine from a single dried blood spot using liquid chromatography tandem mass spectrometry

Long term therapeutic drug monitoring and assessment of renal function are required in renal transplant recipients on immunosuppressant therapy such as tacrolimus. Dry blood spots (DBS) have been used successfully in the clinic for many years and offers a convenient, simple and non-invasive method for repeated blood tests. We developed and performed a preliminary validation of a method for the analysis of tacrolimus and creatinine from a single DBS using liquid chromatography-tandem mass spectrometric (LC-MS/MS). Tacrolimus and creatinine were extracted from a 6mm punch with a mixture of methanol/acetonitrile containing ascomycin and deuterated creatinine as internal standards. A 10 μl aliquot of the extract was analyzed directly after dilution for creatinine with normal phase high performance liquid chromatography and multiple reaction monitoring. The remainder of the extract was processed and analyzed for tacrolimus. The lower limit of quantification for tacrolimus was 1 ng/ml with accuracy of 0.34% bias and precision (CV) of 11.1%. The precision ranged from 1.33% to 7.68% and accuracy from -4.44% to 11.6% bias for the intra- and inter-day analysis. The lower limit of quantification of creatinine was 0.01 mg/dL with precision of 7.94%. Accuracy was based on recovery of additional creatinine spiked into whole blood samples and ranged from -2.45% bias at 5 mg/dL to 3.75% bias at 0.5 mg/dL. Intra- and inter-day precision was from 3.48 to 4.11%. The assay was further validated with DBS prepared from pediatric renal transplant recipients. There was excellent correlation between the levels of tacrolimus and creatinine obtained from the clinical laboratory and the DBS method developed. After additional validation, this assay may have a significant impact on compliance with medication intake as well as potentially lowering the cost associated with intravenous blood draws in clinical laboratories.

Threshold levels of ABL tyrosine kinase inhibitors retained in chronic myeloid leukemia cells determine their commitment to apoptosis

The imatinib paradigm in chronic myelogenous leukemia (CML) established continuous BCR-ABL inhibition as a design principle for ABL tyrosine kinase inhibitors (TKI). However, clinical responses seen in patients treated with the ABL TKI dasatinib despite its much shorter plasma half-life and the apparent rapid restoration of BCR-ABL signaling activity following once-daily dosing suggested acute, potent inhibition of kinase activity may be sufficient to irrevocably commit CML cells to apoptosis. To determine the specific requirements for ABL TKI-induced CML cell death for a panel of clinically important ABL TKIs (imatinib, nilotinib, dasatinib, ponatinib, and DCC-2036), we interrogated response of CML cell lines and primary CML cells following acute drug exposure using intracellular fluorescence-activated cell sorting and immunoblot analyses of BCR-ABL signaling, apoptosis measurements, liquid chromatography/tandem mass spectrometry of intracellular drug levels, and biochemical TKI dissociation studies. Importantly, significant intracellular TKI stores were detected following drug washout, levels of which tracked with onset of apoptosis and incomplete return of BCR-ABL signaling, particularly pSTAT5, to baseline. Among TKIs tested, ponatinib showed the most robust capacity for apoptotic commitment showing sustained suppression of BCR-ABL signaling even at low intracellular levels following extensive washout, consistent with high-affinity binding and slow dissociation from ABL kinase. Together, our findings suggest commitment of CML cells to apoptosis requires protracted incomplete restoration of BCR-ABL signaling mediated by intracellular retention of TKIs above a quantifiable threshold. These studies refine our understanding of apoptotic commitment in CML cells and highlight parameters important to design of therapeutic kinase inhibitors for CML and other malignancies.

The effects of nitrogen-heme-iron coordination on substrate affinities for cytochrome P450 2E1

A descriptor based computational model was developed for cytochrome P450 2E1 (CYP2E1) based on inhibition constants determined for inhibition of chlorzoxazone, or 4-nitrophenol, metabolism. An empirical descriptor for type II binding was developed and tested for a series of CYP2E1 inhibitors. Inhibition constants where measured for 51 different compounds. A fast 2-dimensional predictive model was developed based on 40 compounds, and tested on 8 compounds of diverse structure. The trained model (n=40) had an r(2) value of 0.76 and an RMSE of 0.48. The correlation between the predicted and actual pK(i) values of the test set of compounds not included in the model gives an r(2) value of 0.78. The features that described binding include heme coordination (type II binding), molecular volume, octanol/water partition coefficient, solvent accessible surface area, and the sum of the atomic polarizabilities. The heme coordination parameter assigns an integer between 0 and 6 depending on structure, and is a new descriptor, based on simple quantum chemical calculations with correction for steric effects. The type II binding parameter was found to be important in obtaining a good correlation between predicted and experimental inhibition constants increasing the r(2) value from 0.38 to 0.77.

Interstrain differences in the liver effects of trichloroethylene in a multistrain panel of inbred mice

Trichloroethylene (TCE) is a widely used industrial chemical and a common environmental contaminant. It is a well-known carcinogen in rodents and a probable carcinogen in humans. Studies utilizing panels of mouse inbred strains afford a unique opportunity to understand both metabolic and genetic basis for differences in responses to TCE. We tested the hypothesis that strain- and liver-specific toxic effects of TCE are genetically controlled and that the mechanisms of toxicity and susceptibility can be uncovered by exploring responses to TCE using a diverse panel of inbred mouse strains. TCE (2100 mg/kg) or corn oil vehicle was administered by gavage to 6- to 8-week-old male mice of 15 mouse strains. Serum and liver were collected at 2, 8, and 24 h postdosing and were analyzed for TCE metabolites, hepatocellular injury, and gene expression of liver. TCE metabolism, as evident from the levels of individual oxidative and conjugative metabolites, varied considerably between strains. TCE treatment-specific effect on the liver transcriptome was strongly dependent on genetic background. Peroxisome proliferator-activated receptor-mediated molecular networks, consisting of the metabolism genes known to be induced by TCE, represent some of the most pronounced molecular effects of TCE treatment in mouse liver that are dependent on genetic background. Conversely, cell death, liver necrosis, and immune-mediated response pathways, which are altered by TCE treatment in liver, are largely genetic background independent. These studies provide better understanding of the mechanisms of TCE-induced toxicity anchored on metabolism and genotype-phenotype correlations that may define susceptibility or resistance.

Ubiquitin-dependent proteasomal degradation of human liver cytochrome P450 2E1: identification of sites targeted for phosphorylation and ubiquitination

Human liver CYP2E1 is a monotopic, endoplasmic reticulum-anchored cytochrome P450 responsible for the biotransformation of clinically relevant drugs, low molecular weight xenobiotics, carcinogens, and endogenous ketones. CYP2E1 substrate complexation converts it into a stable slow-turnover species degraded largely via autophagic lysosomal degradation. Substrate decomplexation/withdrawal results in a fast turnover CYP2E1 species, putatively generated through its futile oxidative cycling, that incurs endoplasmic reticulum-associated ubiquitin-dependent proteasomal degradation (UPD). CYP2E1 thus exhibits biphasic turnover in the mammalian liver. We now show upon heterologous expression of human CYP2E1 in Saccharomyces cerevisiae that its autophagic lysosomal degradation and UPD pathways are evolutionarily conserved, even though its potential for futile catalytic cycling is low due to its sluggish catalytic activity in yeast. This suggested that other factors (i.e. post-translational modifications or "degrons") contribute to its UPD. Indeed, in cultured human hepatocytes, CYP2E1 is detectably ubiquitinated, and this is enhanced on its mechanism-based inactivation. Studies in Ubc7p and Ubc5p genetically deficient yeast strains versus corresponding isogenic wild types identified these ubiquitin-conjugating E2 enzymes as relevant to CYP2E1 UPD. Consistent with this, in vitro functional reconstitution analyses revealed that mammalian UBC7/gp78 and UbcH5a/CHIP E2-E3 ubiquitin ligases were capable of ubiquitinating CYP2E1, a process enhanced by protein kinase (PK) A and/or PKC inclusion. Inhibition of PKA or PKC blocked intracellular CYP2E1 ubiquitination and turnover. Here, through mass spectrometric analyses, we identify some CYP2E1 phosphorylation/ubiquitination sites in spatially associated clusters. We propose that these CYP2E1 phosphorylation clusters may serve to engage each E2-E3 ubiquitination complex in vitro and intracellularly.

Optimization of endochin-like quinolones for antimalarial activity

Our prior work on tricyclic acridones combined with a desire to minimize the tricyclic system led to an interest in antimalarial quinolones and a reexamination of endochin, an experimental antimalarial from the 1940's. In the present article, we show that endochin is unstable in the presence of murine, rat, and human microsomes which may explain its relatively poor antimalarial activity in mammalian systems. We also profile the structure-activity relationships of ≈ 30 endochin-like quinolone (ELQ) analogs and highlight features that are associated with enhanced metabolic stability, potent antiplasmodial activity against multidrug resistant strains of Plasmodium falciparum, and equal activity against an atovaquone-resistant clinical isolate. Our work also features an ELQ construct containing a polyethylene glycol carbonate pro-moiety that is highly efficacious by oral administration in a murine malaria model. These findings provide compelling evidence that development of ELQ therapeutics is feasible.

Pharmacokinetic study of lipoic acid in multiple sclerosis: comparing mice and human pharmacokinetic parameters

Lipoic acid is a natural antioxidant available as an oral supplement from a number of different manufacturers. Lipoic acid administered subcutaneously is an effective therapy for murine experimental autoimmune encephalomyelitis, a model of multiple sclerosis. The aim of this study was to compare serum lipoic acid levels with oral dosing in patients with multiple sclerosis with serum levels in mice receiving subcutaneous doses of lipoic acid. We performed serum pharmacokinetic studies in patients with multiple sclerosis after a single oral dose of 1200 mg lipoic acid. Patients received one of the three different racemic formulations randomly: tablet (Formulation A) and capsules (Formulations B and C). Mice pharmacokinetic studies were performed with three different subcutaneous doses (20, 50 and 100 mg/kg racemic lipoic acid). The pharmacokinetic parameters included Maximum Serum Concentrations (C(max) in microg/ml) and area under the curve (0-infinity) (AUC ( 0-infinity) in microg*min/ml). We found mean C(max) and AUC (0-infinity) in patients with multiple sclerosis as follows: group A (N = 7) 3.8 +/- 2.6 and 443.1 +/- 283.9; group B (N = 8) 9.9 +/- 4.5 and 745.2 +/- 308.7 and group C (N = 8) 10.3 +/- 3.8 and 848.8 +/- 360.5, respectively. Mean C(max) and AUC (0-infinity) in the mice were: 100 mg/kg lipoic acid: 30.9 +/- 2.9 and 998 +/- 245; 50 mg/kg lipoic acid: 7.6 +/- 1.4 and 223 +/- 20; 20 mg/kg lipoic acid: 2.7 +/- 0.7 and 119 +/- 33. We conclude that patients taking 1200 mg of lipoic acid from two of the three oral formulations achieved serum C(max) and AUC levels comparable to that observed in mice receiving 50 mg/kg subcutaneous dose of lipoic acid, which is a highly therapeutic dose in experimental autoimmune encephalomyelitis. A dose of 1200 mg oral lipoic acid can achieve therapeutic serum levels in patients with multiple sclerosis.

Mechanism for prevention of alcohol-induced liver injury by dietary methyl donors

Alcohol-induced liver injury (ALI) has been associated with, among other molecular changes, abnormal hepatic methionine metabolism, resulting in decreased levels of S-adenosylmethionine (SAM). Dietary methyl donor supplements such as SAM and betaine mitigate ALI in animal models; however, the mechanisms of protection remain elusive. It has been suggested that methyl donors may act via attenuation of alcohol-induced oxidative stress. We hypothesized that the protective action of methyl donors is mediated by an effect on the oxidative metabolism of alcohol in the liver. Male C57BL/6J mice were administered a control high-fat diet or diet enriched in methyl donors with or without alcohol for 4 weeks using the enteral alcohol feeding model. As expected, attenuation of ALI and an increase in reduced glutathione:oxidized glutathione ratio were achieved with methyl donor supplementation. Interestingly, methyl donors led to a 35% increase in blood alcohol elimination rate, and while there was no effect on alcohol metabolism in the stomach, a profound effect on liver alcohol metabolism was observed. The catalase-dependent pathway of alcohol metabolism was induced, yet the increase in CYP2E1 activity by alcohol was blunted, which may be mitigating production of oxidants. Additional factors contributing to the protective effects of methyl donors in ALI were increased activity of low- and high-K(m) aldehyde dehydrogenases leading to lower hepatic acetaldehyde, maintenance of the efficient mitochondrial energy metabolism, and promotion of peroxisomal beta-oxidation. Profound changes in alcohol metabolism represent additional important mechanism of the protective effect of methyl donors in ALI.

Soluble epoxide hydrolase gene deletion is protective against experimental cerebral ischemia

BACKGROUND AND PURPOSE

Cytochrome P450 epoxygenase metabolizes arachidonic acid to epoxyeicosatrienoic acids (EETs). EETs are produced in the brain and perform important biological functions, including vasodilation and neuroprotection. However, EETs are rapidly metabolized via soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs). We tested the hypothesis that sEH gene deletion is protective against focal cerebral ischemia through enhanced collateral blood flow.

METHODS

sEH knockout (sEHKO) mice with and without EETs antagonist 14, 15 epoxyeicosa-5(Z)-enoic acid (EEZE) were subjected to 2-hour middle cerebral artery occlusion (MCAO), and infarct size was measured at 24 hours of reperfusion and compared to wild-type (WT) mice. Local CBF rates were measured at the end of MCAO using iodoantipyrine (IAP) autoradiography, sEH protein was analyzed by Western blot and immunohistochemistry, and hydrolase activity and levels of EETs/DHETs were measured in brain and plasma using LC-MS/MS and ELISA, respectively.

RESULTS

sEH immunoreactivity was detected in WT, but not sEHKO mouse brain, and was localized to vascular and nonvascular cells. 14,15-DHET was abundantly present in WT, but virtually absent in sEHKO mouse plasma. However, hydrolase activity and free 14,15-EET in brain tissue were not different between WT and sEHKO mice. Infarct size was significantly smaller, whereas regional cerebral blood flow rates were significantly higher in sEHKO compared to WT mice. Infarct size reduction was recapitulated by 14,15-EET infusion. However, 14,15-EEZE did not alter infarct size in sEHKO mice.

CONCLUSIONS

sEH gene deletion is protective against ischemic stroke by a vascular mechanism linked to reduced hydration of circulating EETs.

Effect of Pregnancy on the Pharmacokinetics of Paclitaxel: A Case Report

Breast cancer during pregnancy is increasingly common as women delay childbearing until later in life. Safe administration of adjuvant chemotherapy during pregnancy has been reported. Physiologic and metabolic changes during pregnancy could alter the pharmacokinetics of these agents. This is a pilot study to prospectively study the pharmacokinetics of chemotherapeutic agents during pregnancy. Herein, we report the initial results with paclitaxel in the first patient.

Centella asiatica accelerates nerve regeneration upon oral administration and contains multiple active fractions increasing neurite elongation in-vitro

Axonal regeneration is important for functional recovery following nerve damage. Centella asiatica Urban herb, also known as Hydrocotyle asiatica L., has been used in Ayurvedic medicine for centuries as a nerve tonic. Here, we show that Centella asiatica ethanolic extract (100 microg mL-1) elicits a marked increase in neurite outgrowth in human SH-SY5Y cells in the presence of nerve growth factor (NGF). However, a water extract of Centella was ineffective at 100 microg mL-1. Sub-fractions of Centella ethanolic extract, obtained through silica-gel chromatography, were tested (100 microg mL-1) for neurite elongation in the presence of NGF. Greatest activity was found with a non-polar fraction (GKF4). Relatively polar fractions (GKF10 to GKF13) also showed activity, albeit less than GKF4. Thus, Centella contains more than one active component. Asiatic acid (AA), a triterpenoid compound found in Centella ethanolic extract and GKF4, showed marked activity at 1 microM (microg mL-1). AA was not present in GKF10 to GKF13, further indicating that other active components must be present. Neurite elongation by AA was completely blocked by the extracellular-signal-regulated kinase (ERK) pathway inhibitor PD 098059 (10 microM). Male Sprague-Dawley rats given Centella ethanolic extract in their drinking water (300-330 mg kg-1 daily) demonstrated more rapid functional recovery and increased axonal regeneration (larger calibre axons and greater numbers of myelinated axons) compared with controls, indicating that the axons grew at a faster rate. Taken together, our findings indicate that components in Centella ethanolic extract may be useful for accelerating repair of damaged neurons.

Alcohol metabolism's damaging effects on the cell: a focus on reactive oxygen generation by the enzyme cytochrome P450 2E1

Alcohol metabolism's various processes create harmful compounds that contribute to cell and tissue damage. In particular, the enzyme cytochrome P450 2E1 (CYP2E1) plays a role in creating a harmful condition known as oxidative stress. This condition is related to oxygen's ability to accept electrons and the subsequent highly reactive and harmful byproducts created by these chemical reactions. CYP2E1's use of oxygen in alcohol metabolism generates reactive oxygen species, ultimately leading to oxidative stress and tissue damage.

Steatohepatitis induced by intragastric overfeeding in mice

Nonalcoholic steatohepatitis is prevalent among obese individuals with excessive caloric intake, insulin resistance, and type II diabetes. However, no animal models exist that recapitulate this important association. This study produced and characterized steatohepatitis (SH) caused by intragastric overfeeding in mice. C57BL/6, tumor necrosis factor (TNF) type I receptor-deficient, and genetically matched wild type mice were fed via an implanted gastrostomy tube a high-fat diet for 9 weeks in the increasing amount up to 85% in excess of the standard intake. Animals were examined for weight gain, insulin sensitivity, and histology and biochemistry of liver and white adipose tissue (WAT). Overfed C57BL/6 mice progressively became obese, with 71% larger final body weights. They had increased visceral WAT, hyperglycemia, hyperinsulinemia, hyperleptinemia, glucose intolerance, and insulin resistance. Of these mice, 46% developed SH with increased plasma alanine aminotransferase (121 +/- 27 vs. 13 +/- 1 U/L), neutrophilic infiltration, and sinusoidal and pericellular fibrosis. Obese WAT showed increased TNFalpha and leptin expression and reciprocally reduced adiponectin expression. The expression of lipogenic transcription factors (SREBP-1c, PPARgamma, LXRalpha) was increased, whereas that of a lipolytic nuclear factor PPARalpha was reduced in SH. SH was associated with reduced cytochrome P450 (Cyp)2e1 but increased Cyp4a. TNF type I receptor deficiency did not prevent obesity and SH. In conclusion, forced overfeeding with a high-fat diet in mice induces obesity, insulin resistance, and SH in the absence of TNF signaling or Cyp2e1 induction.

Cytochrome P450 CYP2E1, but not nicotinamide adenine dinucleotide phosphate oxidase, is required for ethanol-induced oxidative DNA damage in rodent liver

The occurrence of malignant tumors of the upper gastrointestinal tract and liver is, based largely on epidemiological evidence, causally related to the consumption of ethanol. It is widely recognized that oxidants play a key role in alcohol-induced liver injury; however, it is unclear how oxidants may be involved in DNA damage. We asked whether nicotinamide adenine dinucleotide phosphate oxidase, cytochrome P450 CYP2E1, or both are responsible for the production of DNA damage. The rodent Tsukamoto-French model of intragastric ethanol infusion was used. Wistar rats, Cyp2e1-, p47(phox)-null, and hCyp2e1 transgenic mice were used. The abundance of oxidative DNA adducts, mutagenic apurinic/apyrimidinic sites, and expression of base excision DNA repair genes was determined. In rats and wild-type mice, ethanol treatment for 4 weeks led to an increase in oxidative DNA damage and induction of expression of the base excision DNA repair genes that are known to remove oxidative DNA lesions. No increase in either of the endpoints was observed in ethanol-treated Cyp2e1-null mice, whereas the magnitude of response in p47(phox)-null mice and transgenic hCyp2e1 was identical to that in wild types. The increase in expression of DNA repair genes was completely abolished by treatment with the P450 inhibitor 1-aminobenzotriazole. In conclusion, the data support the hypothesis that oxidative stress to DNA is induced in liver by ethanol. Furthermore, although it was shown that nicotinamide adenine dinucleotide phosphate oxidase-derived oxidants are critical for the development of ethanol-induced liver injury, CYP2E1 is required for the induction of oxidative stress to DNA, and thus may play a key role in ethanol-associated hepatocarcinogenesis.

A phase I study of 5-fluorouracil, leucovorin, and celecoxib in patients with incurable colorectal cancer

A phase I study of fixed-dose 5-fluorouracil (FU) and leucovorin (LCV), with excalating doses of the selective cyclooxygenase-2 (COX-2) inhibitor celecoxib, was conducted in 16 patients with advanced colorectal adenocarcinoma. At doses typically used to treat arthritis patients (100-200 mg po BID), celecoxib did not increase toxicities expected from the chemotherapy alone. 5-FU and leucovorin did not affect COX-2 inhibition by celecoxib. Preliminary data suggest it is safe to combine celecoxib with standard chemotherapeutic agents, in treatment of patients with colorectal cancer.

Proteasome-dependent degradation of cytochromes P450 2E1 and 2B1 expressed in tetracycline-regulated HeLa cells

The degradation of ethanol-inducible cytochrome P450 2E1 (CYP2E1) and phenobarbital-inducible cytochrome P450 2B1 (CYP2B1) expressed in tetracycline (Tc)-inducible HeLa cell lines was characterized. A steady-state pulse-chase analysis was used to determine a half-life of 3.8 h for CYP2E1 while the half-life of CYP2B1 was 2.3-fold greater in the same cell line. In contrast, NADPH cytochrome P450 reductase which is constitutively expressed in Tc-HeLa cells had a half-life of about 30 h. Lactacystin and other selective proteasome inhibitors including N-benzyloxycarbonyl-leucyl-leucyl-leucinal (MG132) and N-benzyloxycarbonyl-L-leucyl-L-leucyl-L-norvalinal (MG115) significantly inhibited both CYP2E1 and CYP2B1 degradation. The turnover of CYP2E1 was slightly inhibited by calpain inhibitors while CYP2B1 turnover was not altered. Inhibitors of lysosomal proteolysis had no effect on the degradation of either protein. Treatment of cells with brefeldin A did not alter the degradation of either P450 which suggested the degradation occurred in the endoplasmic reticulum (ER). Even in the presence of proteasome inhibitors high molecular weight ubiquitin conjugates were not observed. Mutagenesis of two putative ubiquitination sites (Lys 317 and 324) did not alter the degradation of CYP2E1. The role of ubiquitination in the degradation of CYP2E1 was also examined in a Chinese hamster mutant cell line E36ts20 that contains a thermolabile ubiquitin-activating enzyme (E1). The turnover of CYP2E1 was not significantly different at the nonpermissive temperature in the ts20 when compared to the control E36 cells. Furthermore, the addition of the hsp90 inhibitors geldanamycin, herbimycin, and radicicol had no effect on the turnover of CYP2E1, differentiating the degradation of CYP2E1 from other substrates for proteasome-dependent degradation.

ω-Hydroxylation of farnesol by mammalian cytochromes P450

Studies have shown that mammalian cytochromes p450 participate in the metabolism of terpenes, yet their role in the biotransformation of farnesol, an endogenous 15-carbon isoprenol, is unknown. In this report, [(14)C]-farnesol was transformed to more polar metabolites by NADPH-supplemented mammalian microsomes. In experiments with microsomes isolated from acetone-treated animals, the production of one polar metabolite was induced, suggesting catalysis by CYP2E1. The metabolite was identified as (2E, 6E, 10E)-12-hydroxyfarnesol. In studies with purified CYP2E1, 12-hydroxyfarnesol was obtained as the major product of farnesol metabolism. Among a series of available human p450 enzymes, only CYP2C19 also produced 12-hydroxyfarnesol. However, in individual human microsomes, CYP2E1 was calculated to contribute up to 62% toward total 12-hydroxyfarnesol production, suggesting CYP2E1 as the major catalyst. Mammalian cells expressing CYP2E1 demonstrated further farnesol metabolism to alpha,omega-prenyl dicarboxylic acids. Since such acids were identified in animal urine, the data suggest that CYP2E1 could be an important regulator of farnesol homeostasis in vivo. In addition, CYP2E1-dependent 12-hydroxyfarnesol formation was inhibited by pharmacological alcohol levels. Given that farnesol is a signaling molecule implicated in the regulation of tissue and cell processes, the biological activity of ethanol may be mediated in part by interaction with CYP2E1-dependent farnesol metabolism.

CYP2E1 overexpression alters hepatocyte death from menadione and fatty acids by activation of ERK1/2 signaling

Chronic oxidative stress induced by overexpression of the cytochrome P450 isoform 2E1 (CYP2E1) has been implicated in hepatocyte injury and death. However, the mechanism by which CYP2E1 overexpression may promote cell death is unknown. Acute oxidative stress activates mitogen-activated protein kinases (MAPK), suggesting that chronic oxidant generation by CYP2E1 may regulate cellular responses through these signaling pathways. The effect of CYP2E1 overexpression on MAPK activation and their function in altering death responses of CYP2E1-overexpressing hepatocytes were investigated. Chronic CYP2E1 overexpression led to increased extracellular signal-regulated kinase 1/2 (ERK1/2) activation constitutively and in response to oxidant stress from the superoxide generator menadione. CYP2E1-overexpressing cells were resistant to menadione toxicity through an ERK1/2-dependent mechanism. Similar to menadione, the polyunsaturated fatty acid (PUFA) arachidonic acid (AA) induced an increased activation of ERK1/2 in hepatocytes that overexpressed CYP2E1. However, CYP2E1-overexpressing cells were sensitized to necrotic death from AA and the PUFA gamma-linolenic acid, but not from saturated or monounsaturated fatty acids. Death from PUFA resulted from oxidative stress and was blocked by inhibition of ERK1/2, but not p38 MAPK or activator protein-1 signaling. CYP2E1 expression induced ERK1/2 activation through increased epidermal growth factor receptor (EGFR)/c-Raf signaling. Inhibition of EGFR signaling reversed CYP2E1-induced resistance to menadione and sensitization to AA toxicity. In conclusion, chronic CYP2E1 overexpression leads to sustained ERK1/2 activation mediated by EGFR/c-Raf signaling. This adaptive response in hepatocytes exposed to chronic oxidative stress confers differential effects on cellular survival, protecting against menadione-induced apoptosis, but sensitizing to necrotic death from PUFA.

The CYP inhibitor 1-aminobenzotriazole does not prevent oxidative stress associated with alcohol-induced liver injury in rats and mice

Cytochrome P450 (CYP) 2E1 is induced by ethanol and is postulated to be a source of reactive oxygen species during alcoholic liver disease. However, there was no difference in liver pathology and radical formation between wild-type and CYP2E1 knockout mice fed ethanol. Other CYP isoforms may contribute these effects if CYP2E1 is inhibited or absent. The purpose of this study was, therefore, to determine if blocking most of the P450 isoforms with 1-aminobenzotriazole (ABT; 100 mg/kg i.g.), has any effect on liver damage and oxidative stress due to alcohol in rats and mice. Male C57BL/6 mice and Wistar rats were fed either high-fat control or ethanol-containing enteral diet for 4 weeks. ABT had a significant inhibitory effect on many P450 isoforms independent of concomitant alcohol administration. However, ABT did not protect against liver damage due to alcohol in either species. Indices of oxidative stress and inflammation were also similar in livers from vehicle-treated and ABT-treated animals fed ethanol. In summary, suppression of P450 activity with ABT had no apparent effect on oxidative stress caused by alcohol in both rats and mice. These data support the hypothesis that oxidative stress and liver damage can occur independently of CYP activities in both rats and mice during early alcohol-induced liver injury.

Rat hepatic CYP2E1 is induced by very low nicotine doses: an investigation of induction, time course, dose response, and mechanism

CYP2E1 is an ethanol- and drug-metabolizing enzyme that can also activate procarcinogens and hepatotoxicants and generate reactive oxygen species; it has been implicated in the pathogenesis of liver diseases and cancer. Cigarette smoke increases CYP2E1 activity in rodents and in humans and we have shown that nicotine (0.1-1.0 mg/kg s.c. x 7 days) increases CYP2E1 protein and activity in the rat liver. In the current study, we have shown that the induction peaks at 4 h postnicotine (1 mg/kg s.c. x 7 days) treatment and recovers within 24 h. No induction was observed after a single injection, and 18 days of treatment did not increase the levels beyond that found at 7 days. We found that CYP2E1 is induced by very low doses of chronic (x 7 days) nicotine with an ED50 value of 0.01 mg/kg s.c.; 0.01 mg/kg in a rat model results in peak cotinine levels (nicotine metabolite) similar to those found in people exposed to environmental tobacco smoke (passive smokers; 2-7 ng/ml). Previously, we have shown no change in CYP2E1 mRNA, and our current mechanistic study indicates that nicotine does not regulate CYP2E1 expression by protein stabilization. We postulated that a nicotine metabolite could be causing the induction but found that cotinine (1 mg/kg x 7 days) did not increase CYP2E1. Our findings indicate that nicotine increases CYP2E1 at very low doses and may enhance CYP2E1-related toxicity in smokers, passive smokers, and people treated with nicotine (e.g., smokers, patients with Alzheimer's disease, ulcerative colitis or Parkinson's disease).

Analysis of differential substrate selectivities of CYP2B6 and CYP2E1 by site-directed mutagenesis and molecular modeling

Human CYP2B6 and CYP2E1 were used to investigate the extent to which differential substrate selectivities between cytochrome P450 subfamilies reflect differences in active-site residues as opposed to distinct arrangement of the backbone of the enzymes. Reciprocal CYP2B6 and CYP2E1 mutants at active-site positions 103, 209, 294, 363, 367, and 477 (numbering according to CYP2B6) were characterized using the CYP2B6-selective substrate 7-ethoxy-4-trifluoromethylcoumarin, the CYP2E1-selective substrate p-nitrophenol, and the common substrates 7-ethoxycoumarin, 7-butoxycoumarin, and arachidonic acid. This report is the first to study the active site of CYP2E1 by systematic site-directed mutagenesis. One of the most intriguing findings was that substitution of CYP2E1 Phe-477 with valine from CYP2B6 resulted in significant 7-ethoxy-4-trifluoromethylcoumarin deethylation. Use of three-dimensional models of CYP2B6 and CYP2E1 based on the crystal structure of CYP2C5 suggested that deethylation of 7-ethoxy-4-trifluoromethylcoumarin by CYP2E1 is impeded by van der Waals overlaps with the side chain of Phe-477. Interestingly, none of the CYP2B6 mutants acquired enhanced ability to hydroxylate p-nitrophenol. Substitution of residue 363 in CYP2E1 and CYP2B6 resulted in significant alterations of the metabolite profile for the side chain hydroxylation of 7-butoxycoumarin. Probing of CYP2E1 mutants with arachidonic acid indicated that residues Leu-209 and Phe-477 are critical for substrate orientation in the active site. Overall, the study revealed that differences in the side chains of active-site residues are partially responsible for differential substrate selectivities across cytochrome P450 subfamilies. However, the relative importance of active-site residues appears to be dependent on the structural similarity of the compound to other substrates of the enzyme.

Cytochrome P450 2E1 expression induces hepatocyte resistance to cell death from oxidative stress

Increased expression of cytochrome P450 2E1 (CYP2E1) occurs in alcoholic liver disease, and leads to the hepatocellular generation of toxic reactive oxygen intermediates (ROI). Oxidative stress created by CYP2E1 overexpression may promote liver cell injury by sensitizing hepatocytes to oxidant-induced damage from Kupffer cell-produced ROI or cytokines. To determine the effect of CYP2E1 expression on the hepatocellular response to injury, stably transfected hepatocytes expressing increased (S-CYP15) and decreased (AN-CYP10) levels of CYP2E1 were generated from the rat hepatocyte line RALA255-10G. S-CYP15 cells had increased levels of CYP2E1 as demonstrated by Northern blot analysis, immunoblotting, catalytic activity, and increased cell sensitivity to death from acetaminophen. Death in S-CYP15 cells was significantly decreased relative to that in AN-CYP10 cells following treatment with hydrogen peroxide and the superoxide generator menadione. S-CYP15 cells underwent apoptosis in response to these ROI, whereas AN-CYP10 cells died by necrosis. This differential sensitivity to ROI-induced cell death was partly explained by markedly decreased levels of glutathione (GSH) in AN-CYP10 cells. However, chemically induced GSH depletion triggered cell death in S-CYP15 but not AN-CYP10 cells. Increased expression of CYP2E1 conferred hepatocyte resistance to ROI-induced cytotoxicity, which was mediated in part by GSH. However, CYP2E1 overexpression left cells vulnerable to death from GSH depletion.

Effects of Ginkgo biloba extract (EGb 761) and quercetin on lipopolysaccharide-induced signaling pathways involved in the release of tumor necrosis factor-alpha

Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages induces tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine. Pretreatment with Ginkgo biloba extract (EGb 761) inhibited the in vivo production of TNF-alpha (measured by ELISA) after challenge with LPS. To begin to understand the mechanism of this inhibition, we evaluated the in vitro effects of EGb 761 and its flavonoid component, quercetin, on LPS-treated RAW 264.7 macrophages. Pretreatment with EGb 761 or quercetin concentration-dependently inhibited TNF-alpha release, as measured by the L929 fibroblast assay. Northern blotting demonstrated that quercetin inhibited LPS-induced TNF-alpha mRNA, but did not alter its half-life. Activation of mitogen-activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1), are key events in the signal transduction pathways mediating TNF-alpha induction. Phosphorylation of extracellular signal-related kinases 1 and 2 (ERK 1/2), p38 MAPK, and Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), members of the MAPK family, was analyzed by western blotting. Our results suggest that quercetin is unique in its ability to inhibit TNF-alpha transcription by inhibiting the phosphorylation and activation of JNK/SAPK and, therefore, suppressing AP-1-DNA binding [assessed by electrophoretic mobility shift analysis (EMSA)]. Results from western analysis, EMSA, and transient transfections suggest that EGb 761 diminishes LPS-induced NF-kappaB but has no effect on LPS-induced TNF-alpha transcription. Both EGb 761 and quercetin inhibited ERK1/2 phosphorylation and p38 MAPK activity, which are important in the post-transcriptional regulation of TNF-alpha mRNA.

Effects of Ginkgo biloba extract (EGb 761) and quercetin on lipopolysaccharide-induced release of nitric oxide

Administration of bacterial lipopolysaccharide (LPS) to laboratory animals and cultured macrophages is known to induce the production of nitric oxide (NO) from inducible nitric oxide synthase (iNOS). Here we show that pre-treatment with Ginkgo biloba extract (EGb 761) suppresses the in vivo production of NO (measured by the Griess reaction) after challenge with LPS. In order to begin to understand the mechanism of this inhibition, we evaluated in vitro effects of EGb 761 and its flavonoid component, quercetin, on LPS-treated RAW 264.7 macrophages. Pre-treatment with EGb 761 or quercetin dose-dependently inhibited NO release. Both substances scavenged NO generated from the decomposition of sodium nitroprusside. Western analysis showed that EGb 761 and quercetin inhibited LPS-induced levels of iNOS protein. Northern blotting demonstrated that EGb 761 and quercetin decreased LPS-induced iNOS mRNA levels without altering the half-life. Activation of mitogen activated protein kinases (MAPKs) and the redox-sensitive transcription factors, nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) are key events in the signal transduction pathways mediating iNOS induction. In our studies, both EGb 761 and quercetin inhibited p38 MAPK activity, which is necessary for iNOS expression in LPS-stimulated RAW 264.7 macrophages. However, differences in the response of NF-kappaB, AP-1, and Jun N-terminal kinase/stress activated protein kinase (JNK/SAPK) and its downstream substrates to EGb 761 and quercetin suggest that quercetin is not the sole component responsible for the in vivo inhibition of LPS-induced iNOS activation by EGb 761.

Attenuation of CCl(4)-induced hepatic fibrosis by GdCl(3) treatment or dietary glycine

The role of Kupffer cells in CCl(4)-induced fibrosis was investigated in vivo. Male Wistar rats were treated with phenobarbital and CCl(4) for 9 wk, and a group of rats were injected with the Kupffer cell toxicant gadolinium chloride (GdCl(3)) or were fed glycine, which inactivates Kupffer cells. After CCl(4) alone, the fibrosis score was 3.0 +/- 0.1 and collagen protein and mRNA expression were elevated, but GdCl(3) or glycine blunted these parameters. Glycine did not alter cytochrome P-450 2E1, making it unlikely that glycine affects CCl(4) metabolism. Treatment with GdCl(3) or glycine prevented CCl(4)-induced increases in transforming growth factor (TGF)-beta 1 protein levels and expression. CCl(4) treatment increased alpha-smooth muscle actin staining (score 3.0 +/- 0.2), whereas treatment with GdCl(3) and glycine during CCl(4) exposure blocked this effect (1.2 +/- 0.5); there was no staining with glycine treatment. These results support previous in vitro data and demonstrate that treatment of rats with the selective Kupffer cell toxicant GdCl(3) prevents stellate cell activation and the development of fibrosis.

CYP2E1 is not involved in early alcohol-induced liver injury

The continuous intragastric enteral feeding protocol in the rat was a major development in alcohol-induced liver injury (ALI) research. Much of what has been learned to date involves inhibitors or nutritional manipulations that may not be specific. Knockout technology avoids these potential problems. Therefore, we used long-term intragastric cannulation in mice to study early ALI. Reactive oxygen species are involved in mechanisms of early ALI; however, their key source remains unclear. Cytochrome P-450 (CYP)2E1 is induced predominantly in hepatocytes by ethanol and could be one source of reactive oxygen species leading to liver injury. We aimed to determine if CYP2E1 was involved in ALI by adapting the enteral alcohol (EA) feeding model to CYP2E1 knockout (-/-) mice. Female CYP2E1 wild-type (+/+) or -/- mice were given a high-fat liquid diet with either ethanol or isocaloric maltose-dextrin as control continuously for 4 wk. All mice gained weight steadily over 4 wk, and there were no significant differences between groups. There were also no differences in ethanol elimination rates between CYP2E1 +/+ and -/- mice after acute ethanol administration to naive mice or mice receiving EA for 4 wk. However, EA stimulated rates 1.4-fold in both groups. EA elevated serum aspartate aminotransferase levels threefold to similar levels over control in both CYP2E1 +/+ and -/- mice. Liver histology was normal in control groups. In contrast, mice given ethanol developed mild steatosis, slight inflammation, and necrosis; however, there were no differences between the CYP2E1 +/+ and -/- groups. Chronic EA induced other CYP families (CYP3A, CYP2A12, CYP1A, and CYP2B) to the same extent in CYP2E1 +/+ and -/- mice. Furthermore, POBN radical adducts were also similar in both groups. Data presented here are consistent with the hypothesis that oxidants from CYP2E1 play only a small role in mechanisms of early ALI in mice. Moreover, this new mouse model illustrates the utility of knockout technology in ALI research.

Retention of nociceptor responses during deep barbiturate anesthesia in frogs

Bullfrogs (Rana catesbeiana) anesthetized with a large dose of thiopental (42.8 mg/kg) retained movement responses to nociceptor stimuli despite an average plasma drug level of 51 mg/l, of which 63% was bound to plasma proteins. This concentration, when corrected to include only unbound and uncharged drug, was 2-fold greater than those reported to abolish nociceptor response (NR) during surgical anesthesia in man. The median anesthetic dose (AD50) for loss of the righting reflex was 11.2 mg/kg by s.c. injection into the abdominal lymph sac; however, at 54.0 mg/kg, all frogs retained NRs, although otherwise deeply anesthetized. The ratio of NR-blocking dose to light AD was thus > 4.8, as compared to < 2 in mammalian studies. Whole body levels of thiopental determined at 3 h after intralymphatic injection showed that about half the injected drug had been eliminated by this time and that termination of anesthesia was chiefly due to drug elimination. Even though the pharmacokinetics of thiopental appears to differ markedly in frogs and men, the poor analgesia seen in the present study frequently has been reported during clinical barbiturate anesthesia. Since this deficiency is much more pronounced in the bullfrog than in man, its neurophysiological basis might profitably be studied using the bullfrog as a model; however, the high mortality associated with deep thiopental anesthesia in the frog should preclude its use as a practical anesthetic in amphibia.

Effects of the wine polyphenolics quercetin and resveratrol on pro-inflammatory cytokine expression in RAW 264.7 macrophages

The beneficial effects of moderate red wine consumption have been attributed, in part, to the presence of antioxidant components. Oxidant stress is an activating stimulus for the NF (nuclear factor)-KB/Rel family of transcription factors, which have binding sites in the promoter regions of many genes involved in inflammatory and immune responses. The effect of lipopolysaccharide (LPS)-stimulated activation of NF-KB and the subsequent production of tumor necrosis factor alpha (TNF-alpha) and NO was determined in the macrophage cell line RAW 264.7. Unexpectedly, the wine polyphenolics quercetin and resveratrol and the antioxidant N-acetylcysteine (NAC) did not inhibit LPS-induced activation of the NF-KB complex p50/65, as determined by mobility shift. Quercetin inhibited LPS-induced p50/50. Northern blot analysis indicated that quercetin (0.1 and 0.2 mM) inhibited LPS-dependent production of inducible nitric oxide synthase (iNOS) mRNA and decreased NO release, as measured by the Griess reaction. This flavonoid had no effect on LPS-induced TNF-alpha mRNA, but decreased LPS-stimulated TNF-alpha release, as measured by ELISA. Resveratrol (0.05 and 0.1 mM) posttranscriptionally decreased LPS-induced nitrite release. It increased basal levels of TNF-alpha mRNA and protein and enhanced LPS-induced TNF-alpha mRNA and cytokine release. Our results do not support the view that wine antioxidants inhibit LPS-induced NF-KB activation but instead that they have a more selective action on genes activated by LPS.

Tightly regulated and inducible expression of rabbit CYP2E1 using a tetracycline-controlled expression system

A tetracycline (Tc)-controlled gene expression system that quantitatively controls gene expression in eukaryotic cells () was used to express cytochrome P-450 2E1 (CYP2E1) in HeLa cells in culture. The rabbit CYP2E1 cDNA was subcloned into the Tc-controlled expression vector (pUHD10-3) and transfected into a HeLa cell line constitutively expressing the Tc-controlled transactivator, a positive regulator of expression in the absence of Tc. The expression of CYP2E1 was tightly regulated. There was a time-dependent induction of CYP2E1 after removal of Tc. In the absence of Tc, the enzyme was induced more than 100-fold and expressed about 18 pmol of CYP2E1/mg microsomal protein. At maximal levels of expression the enzyme catalyzed the formation of 158 pmol 6-hydroxychlorzoxazone/min/mg total cellular protein. In addition, the level of the enzyme could be modulated by the concentration of Tc in the media. In the absence of Tc, exposure of cells to N-nitrosodimethylamine caused a significant dose-dependent decrease in cell viability. In contrast, menadione, a redox cycling toxicant, was less toxic to the cells after induction of CYP2E1 when compared with noninduced cells. Pulse-chase studies conducted 72 h after removal of Tc indicated a rapid turnover of CYP2E1 with a half-life of 3.9 h. Addition of the ligand, 4-methylpyrazole, and the suicide substrate, 1-aminobenzotrizole, decreased the degradation of CYP2E1. This cell line offers a useful system to examine the role of CYP2E1 in the cytotoxicity of xenobiotics and to investigate post-translational regulation of the enzyme.

Enzymatic determinants of the substrate specificity of CYP2C9: role of B'-C loop residues in providing the pi-stacking anchor site for warfarin binding

Previous modeling efforts have suggested that coumarin ligand binding to CYP2C9 is dictated by electrostatic and pi-stacking interactions with complementary amino acids of the protein. In this study, analysis of a combined CoMFA-homology model for the enzyme identified F110 and F114 as potential hydrophobic, aromatic active-site residues which could pi-stack with the nonmetabolized C-9 phenyl ring of the warfarin enantiomers. To test this hypothesis, we introduced mutations at key residues located in the putative loop region between the B' and C helices of CYP2C9. The F110L, F110Y, V113L, and F114L mutants, but not the F114Y mutant, expressed readily, and the purified proteins were each active in the metabolism of lauric acid. The V113L mutant metabolized neither (R)- nor (S)-warfarin, and the F114L mutant alone displayed altered metabolite profiles for the warfarin enantiomers. Therefore, the effect of the F110L and F114L mutants on the interaction of CYP2C9 with several of its substrates as well as the potent inhibitor sulfaphenazole was chosen for examination in further detail. For each substrate examined, the F110L mutant exhibited modest changes in its kinetic parameters and product profiles. However, the F114L mutant altered the metabolite ratios for the warfarin enantiomers such that significant metabolism occurred for the first time on the putative C-9 phenyl anchor, at the 4'-position of (R)- and (S)-warfarin. In addition, the Vmax for (S)-warfarin 7-hydroxylation decreased 4-fold and the Km was increased 13-fold by the F114L mutation, whereas kinetic parameters for lauric acid metabolism, a substrate which cannot interact with the enzyme by a pi-stacking mechanism, were not markedly affected by this mutation. Finally, the F114L mutant effected a greater than 100-fold increase in the Ki for inhibition of CYP2C9 activity by sulfaphenazole. These data support a role for B'-C helix loop residues F114 and V113 in the hydrophobic binding of warfarin to CYP2C9, and are consistent with pi-stacking to F114 for certain aromatic ligands.

Role of human CYP4F2 in hepatic catabolism of the proinflammatory agent leukotriene B4

Leukotriene B4 (LTB4), an arachidonic acid derivative, is a potent proinflammatory agent whose actions are terminated by catabolism via a microsomal omega-hydroxylation pathway. Although the liver serves as the principal site for LTB4 clearance from the systemic circulation, the attributes of hepatic LTB4 metabolism are ill defined in humans. Thus, we examined metabolism of LTB4 to its omega-hydroxylated metabolite 20-hydroxyleukotriene B4 (20-OH LTB4) by human liver microsomes and also purified the hepatic P450 enzyme underlying this reaction. Liver microsomes from 10 different subjects converted LTB4 to 20-OH LTB4 at similar rates (1.06 +/- 0.3 nmol/min/nmol P450; 0.25 +/- 0.1 nmol/min/mg protein). Analysis of the microsomal LTB4 20-hydroxylation reaction revealed kinetic parameters (apparent Km of 74.8 microM with a VMAX of 2.42 nmol/min/nmol P450) consistent with catalysis by a single P450 enzyme. Conventional chromatography combined with immunochemical screening with rat CYP4A1 antibodies was then used to isolate a P450 enzyme from human liver microsomes with a molecular weight of 57,000 and an NH2-terminal amino acid sequence 94% homologous (12Trp --> 12Gly) over the first 17 residues with the human CYP4F2 cDNA-derived sequence. Upon reconstitution with P450 reductase and phospholipid, CYP4F2 converted LTB4 to 20-OH LTB4 at a turnover rate of 392 pmol/min/nmol P450, whereas the other human liver P450s tested, including CYP4A11, exhibited neglible LTB4 omega-hydroxylase activity. Polyclonal antibodies to CYP4F2 were found to markedly inhibit (91.9 +/- 5%; n = 5) LTB4 20-hydroxylation by human liver microsomes. Microsomal 20-OH LTB4 formation was also inhibited 30% by arachidonic acid, a known CYP4F2 substrate, and 50% by prostaglandin A1 but was unaffected by lauric acid, palmitic acid, and PGF2alpha. Finally, a strong correlation (r = 0.86; P < 0.002; n = 10) was observed between CYP4F2 content and LTB4 20-hydroxylase activity in the human liver samples. Our results indicate that CYP4F2 is the principle LTB4 omega-hydroxylating enzyme expressed in human liver and, as such, may play an important role in regulating circulating as well as hepatic levels of this powerful proinflammatory eicosanoid.

Cyclosporine suppresses rat hepatic cytochrome P450 in a time-dependent manner

BACKGROUND

Cyclosporine is a potent immunosuppressant know to selectively suppress specific cytochrome P450 (P450) isoforms following chronic therapy in the rat. Cyclosporine undergoes significant hepatic metabolism in the rat, primarily due to P450 3A isoforms. Hence, alterations in hepatic metabolism of cyclosporine may lead to changes in drug pharmacokinetics or pharmacodynamics. The purpose of this study was to examine the temporal effect of chronic cyclosporine dosing on P450 protein expression and metabolic activity in a rat model of chronic cyclosporine nephropathy.

METHODS

Adult male rats were administered cyclosporine 15 mg/kg/day or vehicle 1 ml/kg/day by subcutaneous injection for up to 28 days. To examine whether or not metabolic activity recovered following drug removal, additional rats were administered cyclosporine for 28 days followed by vehicle for up to an additional 15 days. Hepatic P450 protein expression and microsomal metabolic activity were measured by Western blot analysis and in vitro steroid hydroxylation, respectively.

RESULTS

Cyclosporine trough levels progressively increased over the 28 days period and were still measurable for up to 15 days after discontinuation. Immunoblot analysis indicated that chronic cyclosporine treatment suppressed P450 3A2 expression and in vitro steroid hydroxylation in a time-dependent manner. Fifteen days following discontinuation of cyclosporine dosing, hepatic metabolic activity and microsomal P450 3A2 levels returned to near pre-dosing levels.

CONCLUSIONS

We conclude that the time-dependent P450 suppression by cyclosporine may at least partially explain the variability in cyclosporine pharmacokinetics. These studies support the hypothesis that hepatic isoforms other than P450 3A2 may be responsible for cyclosporine metabolism during chronic treatment in the rat.

Oxidation of 1,3-butadiene to (R)- and (S)-butadiene monoxide by purified recombinant cytochrome P450 2E1 from rabbit, rat and human

1,3-Butadiene (BD) is a gas used widely in the rubber and plastics industry as an intermediate in production processes and has been detected in automobile exhaust and cigarette smoke. BD requires metabolic activation to exert toxicity and has been shown to be carcinogenic in rodents. IARC has classified BD as a group 2A (probably carcinogenic to humans) carcinogen. The initial oxidation of BD to butadiene monoxide (BMO) occurs primarily via cytochrome P450 2E1 and two stereoisomers of BMO (R and S) can be formed. (R) and (S)-BMO are metabolized differently and demonstrate markedly different toxicities in isolated rat hepatocytes. This work examined the generation of (R) and (S)-BMO from BD by cytochrome P450 2E1 from rabbit, rat and human. BMO level was measured by GC-MS analysis and enantiomeric composition was determined by GC-FID. The greatest rate of formation of BMO from BD was obtained with rabbit cytochrome P4502E1 followed by human and then by rat. Enantiomeric distribution of R and S-BMO produced by the three species demonstrated no significant differences.

Cytochrome P450-dependent desaturation of lauric acid: isoform selectivity and mechanism of formation of 11-dodecenoic acid

Cytochrome P450-catalyzed desaturation reactions have been reported infrequently in the literature. Previously, we documented the formation of the terminal olefinic metabolite of valproic acid by various members of the CYP2B and CYP4B sub-families. However, despite the extensive use of fatty acid substrates in drug metabolism studies, other examples of terminal desaturation at non-activated carbon centers are lacking. The goals of the present studies were to determine whether the archetypal P450 substrate, lauric acid (dodecanoic acid; DDA), also undergoes desaturation reactions, identify specific rabbit P450 isoforms which catalyze this reaction and examine its mechanism. A highly sensitive, capillary GC/MS assay was developed to separate and quantitate the trimethylsilyl derivatives of 11-ene-DDA, cis- and trans-10-ene-DDA and cis- and trans-9-ene-DDA. Among all of these potential olefinic metabolites, only 11-ene-DDA was formed at a significant rate by rabbit liver microsomes. The formation of 11-ene-DDA was NADPH-dependent, and was induced markedly by acetone pre-treatment, but not by phenobarbital, rifampin or Arochlor 1254. Studies with seven purified, reconstituted rabbit P450 isoforms showed that the most rapid rates of desaturation were obtained with CYP2E1, CYP4A5/7 and CYP4B1. Non-competitive, intermolecular isotope effect experiments, conducted with [12,12,12-2H3]DDA and [11,11-2H2]DDA, demonstrated further that CYP4B1-mediated terminal desaturation of DDA is initiated by removal of a hydrogen atom from the omega-1 rather than the omega position.

Gadolinium chloride blocks alcohol-dependent liver toxicity in rats treated chronically with intragastric alcohol despite the induction of CYP2E1

Hepatic CYP2E1 is induced in several models of alcohol administration, but clinically relevant pathology is only observed in rats in a model involving the continuous intragastric administration of an ethanol-containing, corn oil-based, high-fat diet. The level of CYP2E1 correlates with the degree of liver pathology in the intragastric feeding model, which leads to the hypothesis that radical production by CYP2E1 is responsible for the pathology. Destruction of the Kupffer cells with gadolinium chloride (GdCl3) prevented the development of ethanol-dependent pathology and decreased the production of radicals that appeared in the bile of intragastrically alcohol-fed rats. If the induction of CYP2E1 and subsequent formation of oxidant species by the enzyme is causative in the ethanol-dependent hepatic pathology, then protection by GdCl3 could be due an inhibition of CYP2E1 induction. In the current study, ethanol-administration for 4 wk produced marked steatosis, necrosis, and inflammation not seen in control rats. Immunochemically, CYP2E1 was induced 5- to 6-fold in microsomes from the ethanol-treated animals. Rates of p-nitrophenol and chlorzoxazone hydroxylation were elevated approximately 3-fold, consistent with CYP2E1 induction. When GdCl3 was administered with ethanol, there was a decrease of approximately 80% in Kupffer cell receptor expression, and there was a significant decrease in hepatic pathology, which confirms previous studies. However, in the ethanol and GdCl3-treated animals, there was no significant decrease in the induction of CYP2E1. CYP2E1 was elevated approximately 5-fold, as estimated by immunoblot analysis, and rates of p-nitrophenol and chlorzoxazone hydroxylation were elevated 3- to 4-fold in ethanol + GdCl3-treated rats. Thus, these results clearly dissociate the induction of CYP2E1 by intragastric infusion of ethanol from the generation of early alcohol-induced liver disease. It is concluded that Kupffer cells rather than CYP2E1 play the major role in the initiation of hepatocyte damage caused by alcohol.

Differential inductive and suppressive effects of endotoxin and particulate irritants on hepatic and renal cytochrome P-450 expression

Inflammatory stimuli such as bacterial lipopolysaccharide (LPS) have been shown to down-regulate the mRNA and protein expression of hepatic cytochrome P-450 (P-450) isozymes 2C11, 2C12, 2E1 and 3A2 and to induce the mRNA expression of the P-450 4A subfamily. In this study, we examined the effects of irritants on the hepatic and renal expression of P-450 2C11, 2E1 and 3A2 and the 4A subfamily in the rat. Fischer 344 rats were administered doses of SiO2 (Celite), BaSO4, kaolin and LPS intraperitoneally and killed after different times for hepatic and renal RNA and microsome isolation. The administration of each irritant was found to suppress hepatic P-450 2C11 mRNA and protein and to induce P-450 4A1, 4A2 and 4A3 mRNA expression while having no significant effect on P-450 2E1 or 3A2. P-450 4A2, 4A3 and 2E1 mRNAs were all induced in the kidney cortices of the irritant- and LPS-treated rats. The effects of BaSO4 and SiO2 were found to be dose dependent. Chlorzoxazone-6-hydroxylase activity increased in the kidneys of irritant-treated rats, which is consistent with an increased expression of P-450 2E1. All irritants were found to induce the mRNA for the acute-phase protein fibrinogen; however, in contrast to LPS treatment, none of the irritants that were tested induced hepatic inducible nitric oxide synthase mRNA expression. These findings demonstrate the induction of renal P-450 isozymes after irritant and LPS administration. The findings of this study also suggest that different inflammatory stimuli affect the individual P-450 isozymes differentially.

Epoxidation of C18 unsaturated fatty acids by cytochromes P4502C2 and P4502CAA

The regioselective epoxidation of oleic, linoleic, alpha-linolenic, and gamma-linolenic acid by cytochromes P4502CAA and P4502C2 was characterized. Epoxide metabolites for all fatty acids were resolved by normal phase HPLC and identified by gas chromatography and mass spectrometry. Both isoforms epoxidized the single double bond in oleic acid and both double bonds in linoleic acid. The ratio of the two epoxides produced with linoleic acid (1.6:1 for the 12,13- and 9,10-epoxides) was similar for both enzymes. When alpha-linolenic acid was the substrate, all three epoxides were produced in about equal ratios with both enzymes. In contrast for the omega-6 fatty acid, gamma-linolenic acid, both enzymes produced only the 9,10- and 12,13-epoxides. Furthermore, the ratio of the metabolites produced by each enzyme was significantly different. The ratios of 12,13-epoxide to 9,10-epoxide for gamma-linolenic were 11.0 +/- 0.19 and 5.8 +/- 1.2 for P4502CAA and P4502C2, respectively. These results suggest that there may be subtle differences in the structure of 2C2 and 2CAA and also indicate that P450 may be important in the generation of potentially active epoxide metabolites of unsaturated fatty acids other than arachidonic acid.

Selective suppression of rat hepatic microsomal activity during chronic cyclosporine nephrotoxicity

Cyclosporine is an immunosuppressant that undergoes extensive hepatic biotransformation to hydroxylated and demethylated metabolites. At present, the CYP3A gene family is thought to be the primary enzyme system responsible for cyclosporine metabolism. The effect of chronic cyclosporine therapy on the suppression of drug metabolism was studied in male and female rats maintained on a low-salt diet. After 28 days of subcutaneous cyclosporine dosing 15 mg/kg, cyclosporine-treated rats had significant renal dysfunction as compared with gender-matched control rats. Creatinine clearance in male cyclosporine-treated rats was reduced by 47% (P < .01) as compared with male controls. Female rats demonstrated a 38% (P < .01) decrease in creatinine clearance as a result of chronic cyclosporine therapy. Despite similar nephrotoxicity, female rats had whole blood cyclosporine levels 48% (P < .01) less than male rats. Immunoblot analysis of hepatic microsomal proteins indicated that chronic cyclosporine treatment decreased the protein levels of P450 3A2 in male rats. This loss was paralleled by reduced production of 6 beta-hydroxytestosterone, the primary product of P450 3A activity, by hepatic microsomes from cyclosporine-treated male rats by 76% (P < .001). In addition, cyclosporine treatment of male rats also reduced the formation of 2 alpha-hydroxytestosterone and 16 alpha-hydroxytestosterone by 81% (P < .01) and 84% (P < .001), respectively. At the end of the study period, steroid 5 alpha-reductase activity in control male rats was only 4% (P < .001) of female counter-parts; however, cyclosporine treatment increased steroid 5 alpha-reductase activity in male rats to 79% (P < .001) of female values. These alterations in testosterone metabolism are consistent with the suppression of the predominately male-associated P450 3A2, P450 2C11 and P450 2C13 isoforms. Levels of 6 alpha-hydroxytestosterone and 7 alpha-hydroxytestosterone were not statistically different between rat groups. Taken together, the steady-state blood levels and metabolism studies suggest that, after chronic cyclosporine treatment, isoforms other than those from the CYP3A family or unidentified members of the CYP3A family are likely responsible for cyclosporine metabolism.

Endotoxemia in rats is associated with induction of the P4504A subfamily and suppression of several other forms of cytochrome P450

Bacterial lipopolysaccharide (LPS) has been previously shown to down-regulate the mRNA and protein expression of the hepatic cytochrome P450 (P450) isozymes 2C11 and 2C12. In this study, we examined the effects of LPS on the constitutive expression of P4503A2, P4502E1, and the P4504A subfamily in the rat. Fischer 344 and Sprague-Dawley rats were each administered 1 mg/kg LPS intraperitoneally and killed for hepatic RNA and microsome isolation at different times. LPS treatment was found to suppress P4502C11, P4503A2, and P4502E1 protein and mRNA expression in both strains of rat. Total microsomal P450 levels decreased by 30%, which was smaller than the effects on the levels of individual isozymes. The magnitude of suppression exhibited in the Sprague-Dawley rats, however, seemed to be more variable than that in the F344 strain. The mRNAs of all three of the P4504A subfamily members were induced 2- to 6-fold in the F344 rat livers after LPS administration. P4504A3 protein expression increased 2-fold, whereas P4504A1/2 protein levels decreased by 30%. Lauric acid omega-hydroxylase activity increased 1.6-fold in LPS-treated Fischer 344 rats and omega-1-hydroxylase activity decreased by 38%. In the Sprague-Dawley strain, however, decreases were seen in both omega- and omega-1-hydroxylase activities after LPS treatment. Our data demonstrate that LPS administration induces P4504A subfamily mRNA and P4504A3 protein expression. Furthermore, our findings also suggest strain differences in both suppression and induction of P450s between the Sprague-Dawley and F344 rats.

Rabbit P450 2E1 expressed in CHO-K1 cells has a short half-life

Rabbit P450 2E1 was stably expressed in Chinese hamster ovary cells after cotransfection with pRC/CMV-2E1 and pFR400 which expresses murine dihydrofolate reductase with a single arginine to leucine substitution at position 22. This mutation permits amplification of expression with increasing methotrexate concentrations in CHO-K1 cells that are not dihydrofolate reductase deficient. After amplification with 1 microM methotrexate, a representative clone expressed about 15 pmol of P450 2E1/mg microsomal protein. Cells from a single 35-mm plate catalyzed the formation of 1.02 nmol 6-hydroxychlorzoxazone/10(6) cells/h or about 127 pmol/mg total cell protein/min. The enzyme was rapidly labeled when pulsed with [35S]-methionine. Initial pulse-chase experiments indicate that the expressed protein has a half-life of 4.8 h.

Regio- and stereoselective epoxidation of arachidonic acid by human cytochromes P450 2C8 and 2C9

In the present study, the regio- and stereoselective epoxidation of arachidonic acid by cytochromes P450 2C8 and 2C9, two members of the CYP2C gene subfamily expressed in human liver, was determined. Purified P450 isozymes, reconstituted with NADPH:P450 oxidoreductase, cytochrome b5 and lipid, or microsomes isolated from human liver, were incubated with [1-14C]-arachidonic acid. For regioselective analysis, the epoxide metabolites formed, 14,15-, 11,12- and 8,9-epoxyeicosatrienoic acids (EETs), were resolved by reverse-phase high-performance liquid chromatography. P450 2C8 produces only the 14,15- and 11,12-EETs in a 1.25:1.00 ratio. The two epoxides represent 68% of the total metabolites. P450 2C9 produces 14,15-, 11,12- and 8,9-EETs in a 2.3:1.0:0.5 ratio. The three epoxides represent 69% of the total metabolites. Neither P450 isoform catalyzes the formation of 5,6-EET. For chiral analysis, the two major epoxide metabolites, 14,15- and 11,12-EETs, were derivatized to methyl and pentafluorbenzyl esters, respectively. Enantiomers of 14,15- and 11,12-EET esters were subsequently resolved on Chiralcel OB and OD columns (J.T. Baker, Phillipsburg, PA), respectively. Both P450 2C8 and 2C9 are stereoselective at the 14,15- position, preferentially producing 14(R), 15(S)-EET with 86.2% and 62.5% selectivity, respectively. Both enzymes are also stereoselective at the 11,12-position but have the opposite selectivity. P450 2C8 is 81.1% selective for 11(R), 12(S)-EET; P450 2C9 is 69.4% selective for the 11(S), 12(R)-EET. Immunoinhibition studies performed with anti-2C9 immunoglobulin G (which also reacts with P450 2C8) and hepatic microsomes indicate that these two P450s are important arachidonic acid epoxygenases in human liver.