Participation of epoxygenase activation in saikogenin D-induced inhibition of prostaglandin E(2) synthesis.

We examined the effect of saikogenin D on arachidonic acid metabolism in C6 rat glioma cells to clarify its anti-inflammatory mechanism. Incubation of C6 cells with saikogenin D for 20 min resulted in the inhibition of prostaglandin E(2) production and the accumulation of an arachidonic acid metabolite that was found to be 11,12-dihydroxyeicosatrienoic acid, a metabolite of 11,12-epoxyeicosatrienoic acid. C6 cells expressed rat epoxygenase mRNAs, CYP1A1, CYP2B1 and CYP2J3, which converted arachidonic acid to epoxyeicosatrienoic acids. 11,12-Epoxyeicosatrienoic acid inhibited A23187-induced prostaglandin E(2) production and SKF-525A, an inhibitor of epoxygenase, attenuated the saikogenin D-induced inhibition of prostaglandin E(2) production in C6 cells. Furthermore, 11,12-epoxyeicosatrienoic acid and 11,12-dihydroxyeicosatrienoic acid, but not saikogenin D, inhibited the activity of cyclooxygenase in a cell-free condition. These data suggest that saikogenin D activates epoxygenases that rapidly convert arachidonic acid to epoxyeicosanoids and dihydroxyeicosatrienoic acids, and then the metabolites secondarily inhibit prostaglandin E(2) production.

Direct evidence for the formation of deoxyribonucleotide adducts from carcinogenic N-nitroso-N-methylaniline revealed by the 32P-postlabeling technique.

N-Nitroso-N-methylaniline (NMA) is an esophageal carcinogen in the rat. NMA forms a benzenediazonium ion (BDI) during microsomal cytochrome P-450 2B1 (CYP2B1) catalyzed metabolism. Using the nuclease P1-enhanced version of the 32P-postlabeling assay we investigated the formation of adducts by NMA with deoxyadenosine 3'-monophosphate (dAp) and deoxyguanosine 3'-monophosphate (dGp). 32P-postlabeling analysis of dAp and dGp, which were modified by NMA activated with microsomes of rats pretreated with phenobarbital (PB), and directly labeled resulted in each case in the appearance of one single adduct spot. Quantitative analysis of adducts revealed that the extent of dGp modification by activated NMA was more than 23 times greater than the extent of modification of dAp. The results suggest strongly that BDI, derived from NMA by CYP2B1 present in PB microsomes, participates in the formation of dAp and dGp adducts.

Toluene metabolism by cDNA-expressed human hepatic cytochrome P450.

The metabolism of toluene in human liver microsomes and by cDNA-expressed human cytochrome P450s (CYPs) was investigated. Toluene was metabolized mainly to benzyl alcohol and slightly to o- and p-cresol by human liver microsomes. Formation of o-cresol was elevated in microsomes from human livers derived from cigarette smokers, but the induced CYP isoforms were not clear. Of the eleven human CYP forms studied, CYP2E1 was the most active in forming benzyl alcohol, followed by CYP2B6, CYP2C8, CYP1A2, and CYP1A1, in that order. The activities of CYP2A6, CYP2C9, CYP2D6, CYP3A3, CYP3A4, and CYP3A5 were negligible. In addition, CYP2B6 and CYP2E1 catalyzed the formation of p-cresol (11-12% of total metabolites), and CYP1A2 catalyzed the formation of both o-(22%) and p-cresol (35%). The relationship between the amino acid sequence of rat CYP2B1 cDNA and the activity for toluene metabolism was investigated using variants, because of great differences in the forming of toluene ring products between CYP2B1 and CYP2B6. These results suggest that the structure of CYP2B1 at the site of Leu 58 rather than Ile-114 and Glu-282 plays an important role in the formation of toluene ring products, whereas in CYP2B1 Ile-114 plays an important role in the formation of benzyl alcohol. These results may explain, in part, the lower activity of CYP2B6, which has Phe at position 58 of the protein, for toluene ring oxidations than that of CYP2B1.

Microencapsulated, CYP2B1-transfected cells activating ifosfamide at the site of the tumor: the magic bullets of the 21st century.

BACKGROUND: Conventional chemotherapy of pancreatic carcinoma is only marginally effective. This is in part due to the severity of side effects following systemic administration of the cytostatic drug. The aim was to create a therapeutic tool allowing the targeting of the conversion site of a cytotoxic prodrug to the site of the tumor. This was realized by transfection of the CYP2B1 gene, the major ifosfamide-converting P450 enzyme, in cells with subsequent microencapsulation and administration of these microcapsules to or into the tumor. The enzyme activity (resorufin assay) remained stable for weeks in vitro and in vivo within the microencapsulated CYP2B1-expressing cells. We demonstrated a significant antitumor effect of the intratumorally injected capsules against xenotransplanted human pancreatic carcinomas in the nude mouse. Angiographic experiments in the pig confirmed the feasibility of an intraarterial placement of the capsules into the pancreas. A clinical protocol was established and approved. PATIENTS, MATERIAL AND METHODS: L293 cells were transfected with the CYP2B1 gene, microencapsulated (diameter 0.7 mm) under GCP conditions and packed sterile. Patients with confirmed inoperable adenocarcinoma of the pancreas underwent angiography, and capsules were injected into a vessel leading into the tumor. The patients were monitored for 48 h to exclude allergic reactions or pancreatitis. A day later, ifosfamide was administered for three consecutive days to be repeated on days 21-23. The patients were followed up for 5 months. RESULTS: A total of 17 patients were enrolled. The patients tolerated the procedure without any complications. No allergic reactions or pancreatitis were encountered. Chemotherapy was uneventful. All patients had stable disease, and two patients a partial remission. The median survival was 44 weeks which compared favorably with that of a historical control group (22 weeks). CONCLUSIONS: The intraarterial administration of microcapsules for targeted chemotherapy was well tolerated. Control of local tumor growth was achieved.

Role of cytochrome P450 2B1 in puromycin aminonucleoside-induced cytotoxicity to glomerular epithelial cells.

Puromycin aminonucleoside (PAN)-induced glomerular injury in rats mimics minimal-change nephrotic syndrome (NS) in humans. We have demonstrated an important role of cytochrome P450 (CYP) as a significant source of catalytic iron in this model of NS. The current study was designed to identify CYP isozyme(s) present in the rat glomerular epithelial cells (GEC) and to explore the role of the specific CYP isozyme in PAN-induced cytotoxicity. CYP2B1 was identified in GEC by immunocytochemistry and Western blot. Treatment of GEC with PAN resulted in a marked generation of hydrogen peroxide (H(2)O(2)) and reduction of CYP2B1 content associated with significant increase in catalytic iron and hydroxyl radical formation. Preincubating GEC with CYP2B1 inhibitors (piperine and cimetidine) and H(2)O(2) scavenger (pyruvate) significantly reduced H(2)O(2 )generation, preserved CYP2B1 content, prevented the increase in catalytic iron and hydroxyl radical formation including PAN-induced cytotoxicity. We also observed the induction of heme oxygenase (HO-1) in PAN-treated GEC, and this up-regulation was reduced by pretreatment of the CYP inhibitors and pyruvate. Our data thus indicate an important role of CYP2B1 in PAN-induced cytotoxicity by serving as a site of reactive oxygen metabolite generation and a significant source of catalytic iron.

Effects of paving asphalt fume exposure on genotoxic and mutagenic activities in the rat lung.

Asphalt fumes are complex mixtures of aerosols and vapors containing various organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Previously, we have demonstrated that inhalation exposure of rats to asphalt fumes resulted in dose-dependent induction of CYP1A1 with concomitant down-regulation of CYP2B1 and increased phase II enzyme quinone reductase activity in the rat lung. In the present study, the potential genotoxic effects of asphalt fume exposure due to altered lung microsomal enzymes were studied. Rats were exposed to air or asphalt fume generated under road paving conditions at various concentrations and sacrificed the next day. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage and examined for DNA damage using the comet assay. To evaluate the systemic genotoxic effect of asphalt fume, micronuclei formation in bone marrow polychromatic erythrocytes (PCEs) was monitored. Lung S9 from various exposure groups was isolated from tissue homogenates and characterized for metabolic activity in activating 2-aminoanthracene (2-AA) and benzo[a]pyrene (BaP) mutagenicity using the Ames test with Salmonella typhimurium YG1024 and YG1029. This study showed that the paving asphalt fumes significantly induced DNA damage in AM, as revealed by DNA migration in the comet assay, in a dose-dependent manner, whereas the micronuclei formation in bone marrow PCEs was not detected even at a very high exposure level (1733 mg h/m3). The conversion of 2-AA to mutagens in the Ames test required lung S9-mediated metabolic activation in a dose-dependent manner. In comparison to the controls, lung S9 from rats exposed to asphalt fume at a total exposure level of 479+/-33 mg h/m3 did not significantly enhance 2-AA mutagenicity with either S. typhimurium YG1024 or YG1029. At a higher total asphalt fume exposure level (1150+/-63 mg h/m3), S9 significantly increased the mutagenicity of 2-AA as compared to the control. However, S9 from asphalt fume-exposed rats did not significantly activate the mutagenicity of BaP in the Ames test. These results show that asphalt fume exposure, which significantly altered both phases I and II metabolic enzymes in lung microsomes, is genotoxic to AM and enhances the metabolic activation of certain mutagens through altered S9 content.

Propofol metabolism is enhanced after repetitive ketamine administration in rats: the role of cytochrome P-450 2B induction.

BACKGROUND: In a series of ex vivo and in vivo studies we investigated the ability of repetitive ketamine administration to alter the metabolism and anaesthetic effect of propofol and the role of ketamine-mediated P-450 2B induction in rats. METHODS: Male Wistar rats were pretreated with 80 mg kg(-1) ketamine i.p. twice daily for 4 days. Pentoxyresorufin O-dealkylation (PROD), P-450 2B protein and mRNA were determined. Residual propofol concentration was measured after incubating hepatic microsomes with 100 muM propofol. Sleeping times induced by i.p. 80 mg kg(-1) propofol were determined. Orphenadrine, a P-450 2B inhibitor, was added in both ex vivo and in vivo studies. Finally, serial whole blood propofol concentrations were determined after i.v. infusion of 15 mg kg(-1) propofol. RESULTS: Ketamine pretreatment produced 5.4-, 3.4- and 1.7-fold increases in hepatic PROD activity, P-450 2B protein and mRNA, respectively. Residual propofol concentration was 46% lower after incubation with microsomes from ketamine-pretreated rats than in the control group. The addition of orphenadrine to ketamine-pretreated microsomes produced an increase in residual propofol concentration in a concentration-dependent manner. Ketamine pretreatment reduced propofol sleeping time to 12% of the control, which was reversed by orphenadrine. The whole blood propofol concentration in ketamine-pretreated rats was significantly lower than that of control rats at 1, 2, 4 and 8 min after cessation of propofol infusion. CONCLUSIONS: Repetitive ketamine administration enhances propofol metabolism and reduces propofol sleeping time in rats. We suggest that P-450 2B induction may produce ketamine-propofol interaction in anaesthetic practice.

Combined therapy of experimental pancreatic cancer with CYP2B1 producing cells: low-dose ifosfamide and local tumor irradiation.

Local therapy of pancreatic cancer with microencapsulated CYP2B1-producing cells and ifosfamide showed an effect both on the primary tumor and on distant metastatases. This possibly represents a consequence of the activation of immune response. Other studies have demonstrated that local tumor irradiation leads to the activation of the intratumoral lymphocyte infiltration. The aim of our study was to investigate the efficacy of the combined therapy with low-dose irradiation, ifosfamide and CYP2B1-producing cells. Syngenic pancreatic cancer was induced in 38 Lewis-rats by subcutaneous inoculation of 1 x 10(6) (DSL6A) tumor cells. Microencapsulated CYP2B1-producing cells were injected peritumorally 10--12 weeks after tumor implantation. Animals were randomized to the following groups: 1) control (NaCl, 1 ml i.p.), 2) ifosfamide (50 mg/kg, i.p., (3x/week), 3) local irradiation with 5 Gy and 4) ifosfamide plus irradiation. The tumor growth was monitored for 3 weeks. The tumor infiltration with CD4+, CD8+, NK-cells, microvessel density and proliferation rates were investigated by immunohistochemistry. Cytokine plasma level for TNF-alpha were measured by ELISA. Seven of 9 animals in the group of combined therapy showed an objective response to the therapy. The therapy with ifosfamide or radiation alone showed 5 and 3 responders, respectively. The mean tumor volume was significantly reduced after combined ifosfamide plus radiation therapy in the first week, whereas monotherapy with ifosfamide or radiation significantly decreased tumor growth earliest after 2 and 3 weeks, respectively. The high plasma level of TNF-alpha in the control group was significantly reduced after combined ifosfamide/irradiation treatment. The lymphocyte infiltration and tumor proliferation were not significantly different between the groups. Microvascular density was significantly increased after ifosfamide and ifosfamide plus irradiation therapy. The combination of ifosfamide/CYP2B1-producing cells and irradiation showed an earlier therapeutical effect on the growth of rat pancreatic cancer than the irradiation or ifosfamide alone. There was no evidence of late activation of lymphocyte infiltration and PCNA-positive tumor cells.

Roles of human CYP2A6 and 2B6 and rat CYP2C11 and 2B1 in the 10-hydroxylation of (-)-verbenone by liver microsomes.

(-)-Verbenone, a monoterpene bicyclic ketone, is a component of the essential oil from rosemary species such as Rosmarinus officinalis L., Verbena triphylla, and Eucalyptus globulus and is used for an herb tea, a spice, and a perfume. In this study, (-)-verbenone was found to be converted to 10-hydroxyverbenone by rat and human liver microsomal cytochrome p450 (p450) enzymes. The product formation was determined by high-performance liquid chromatography with UV detection at 251 nm. There was a good correlation between activities of coumarin 7-hydroxylation and (-)-verbenone 10-hydroxylation catalyzed by liver microsomes of 16 human samples, indicating that CYP2A6 is a principal enzyme in (-)-verbenone 10-hydroxylation in humans. Human recombinant CYP2A6 and CYP2B6 catalyzed (-)verbenone 10-hydroxylation at Vmax values of 15 and 21 nmol/min/nmol p450 with apparent Km values of 16 and 91 microM, respectively. In contrast, rat CYP2A1 and 2A2 did not catalyze (-)-verbenone 10-hydroxylation at all, suggesting that there were species-related differences in the catalytic properties of human and rat CYP2A enzymes in the metabolism of (-)-verbenone. In the rat, recombinant CYP2C11, CYP2B1, and CYP3A2 catalyzed (-)-verbenone 10-hydroxylation with Vmax and Km ratios (ml/min/nmol p450) of 0.73, 0.20, and 0.03, respectively. Male-specific CYP2C11 was a major enzyme in (-)-verbenone 10-hydroxylation by untreated rat livers, and CYP2B1 catalyzed this reaction in liver microsomes of phenobarbital-treated rats. Rat CYP2C12, a female-specific enzyme, did not catalyze (-)verbenone 10-hydroxylation. These results suggest that human CYP2A6 and rat CYP2C11 are the major catalysts in the metabolism of (-)-verbenone by liver microsomes and that there are species-related differences in human and rat CYP2A enzymes and sex-related differences in male and female rats in the metabolism of (-)-verbenone.