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T Yokoi

Publications and source records attributed to T Yokoi.

At least 37 records · Page 2Linked to original sources
PubMed2001

Interleukin-1beta induces the expression of lipocortin 1 mRNA in cultured rat cortical astrocytes.

Lipocortin 1 (LC1) has been shown to increase in neuronal damage and act as a neuroprotectant and a neurotrophic factor. IL-1beta acts as a mediator of inflammation and has been reported as a potent inducer of various neurotrophic factors including nerve growth factor and fibroblast growth factor. In this study, we investigated the relationship between LC1 and IL-1beta in cultured rat astrocytes. Time-and dose-dependent experiments of IL-1beta on rat cortical astrocytes in culture revealed that the expression of LC1 mRNA was significantly augmented by IL-1beta at 8 h, 10 ng/ml. In addition, IL-1beta evoked an extracellular secretion of LC1 without its cytotoxic effects. The effect of IL-1beta was completely abolished when we treated cells with inhibitor of mitogen-activated protein kinases (MAPKs) (PD98059) (25 microM), phospholipase A(2) inhibitor mepacrine (30 microM) and protein synthesis inhibitor cycloheximide (CHX) (10 microg/ml). This suggests that induction of LC1 by IL-1beta is through a MAPKs and phospholipaseA(2) pathway and requires protein synthesis. These results indicate that IL-1beta released in the central nervous system (CNS) injury can stimulate the transcription of the LC1 gene. Subsequent synthesis and release of LC1 may provide trophic support to neurons and modulate the action of IL-1beta in brain damage.

Animals↗
PubMed2001

Inhibitory effects of CYP3A4 substrates and their metabolites on P-glycoprotein-mediated transport.

It is generally known that the substrates and/or inhibitors of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp) overlap with each other. In intestinal epithelial cells, it is surmised that the metabolites coexist with their parent drug. However, most studies on P-gp did not take the effects of those metabolites into consideration. Therefore, in the present study, we investigated the inhibitory effects of five substrates of CYP3A4 (nifedipine, testosterone, midazolam, amiodarone, and azelastine) and their metabolites on the P-gp-mediated transcellular transport. The transcellular transports of [(3)H]daunorubicin or [(3)H]digoxin by monolayers of LLC-GA5-COL150 cells in which P-gp was overexpressed were measured in the presence or absence of the CYP3A4 substrates and their metabolites. Nifedipine, testosterone, midazolam, and their metabolites exhibited no effects on the P-gp-mediated transport of [(3)H]daunorubicin and [(3)H]digoxin. On the other hand, the transport of [(3)H]daunorubicin was strongly inhibited by amiodarone, desethylamiodarone, azelastine, and desmethylazelastine, with IC(50) values of 22.5, 15.4, 16.0 and 11.8 microM, respectively. The transport of [(3)H]digoxin was also strongly inhibited by these compounds, with IC(50) values of 45.6, 25.2, 30.0 and 41.8 microM, respectively. Another metabolite of azelastine, 6-hydroxyazelastine, exhibited no effects on these transports. It was suggested that the CYP3A4 metabolites of which their parent drug exhibited inhibition on the P-gp-mediated transport are possibly also inhibitors. It would be possible more complicated drug-drug interactions would be caused by the metabolites as well as their parent drugs in the liver and the intestine via the inhibition of CYP3A4 and P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Accumulation of the 1-methyl-4-phenylpyridinium ion in suncus (Suncus murinus) brain: implication for flavin-containing monooxygenase activity in brain microvessels.

The metabolism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was examined in an effort to evaluate the role of flavin-containing monooxygenase (FMO) expressed in the brain of suncus (Suncus murinus) and rats. MPTP was metabolized to generate both 1-methyl-4-phenylpyridinium ion (MPP(+)) and MPTP N-oxide by brain homogenates from rats. Although the level of MPP(+)-producing activity was similar in suncus and rats, a remarkable difference was found between the animal species in MPTP N-oxygenase activity, which was not detectable in brain homogenates from suncus. The concentrations of MPP(+) in suncus brain after a single ip administration of MPTP were markedly higher than that in rats, probably because of the lack of FMO activity in the suncus brain. The MPTP N-oxygenase activity of microvessel homogenates of rat brain was 21-fold greater than that of whole brain homogenates. These results suggest that FMO(s) plays a significant role in the detoxification of MPTP in cerebral endothelial cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2001

Piecemeal endoscopic aspiration mucosectomy for large superficial intramucosal tumors of the stomach.

BACKGROUND AND STUDY AIMS: As endoscopic techniques continue to develop, endoscopic mucosal resection is increasingly being used in the treatment of intramucosal gastric tumors. The aim of this study was to explore the feasibility of piecemeal endoscopic aspiration mucosectomy for large superficial intramucosal tumors of the stomach. PATIENTS AND METHODS: The study group consisted of five consecutive patients with large superficial intramucosal tumors of the stomach, 4 cm or more in diameter. Piecemeal endoscopic aspiration mucosectomy using a cap-fitted panendoscope was carried out. The initial resection was undertaken at the oral side of the lesion. Subsequent resections were carried out along the anal margin of the previous resection site, until the marks around the boundary of the tumor completely disappeared. RESULTS: The shape of the tumors was slightly elevated in four cases and slightly depressed in one. The mean diameter of the tumors was 4.8 cm. The diameters of the resected specimens ranged from approximately 1.0 cm to 2.3 cm. The numbers of piecemeal resection procedures needed per lesion ranged from five to 18 (mean 11). The visual field was well ensured by the cap, and the tumors were macroscopically completely resected without any complications in all patients. The final histological diagnoses in the specimens were adenoma in one case and mucosal carcinoma in adenoma in four. One patient had residual or recurrent tumor, and received full treatment with additional endoscopic procedures. CONCLUSIONS: Piecemeal endoscopic aspiration mucosectomy is a simple and very useful technique for treating large superficial intramucosal tumors of the stomach.

Adenoma↗
PubMed2001

Relationship between interindividual differences in nicotine metabolism and CYP2A6 genetic polymorphism in humans.

BACKGROUND: Nicotine is mainly metabolized to cotinine by cytochrome P450 (CYP) 2A6. Previously, we found that the CYP2A6 gene was deleted homozygously in one subject who was deficient in cotinine formation from nicotine. OBJECTIVE: Our objective was to clarify the relationship between interindividual differences in nicotine metabolism and CYP2A6 genetic polymorphism. METHODS: Nicotine was administered to 92 healthy Japanese subjects in the form of 1 piece of nicotine gum to investigate the potency of nicotine metabolism. The cotinine-nicotine ratio of the plasma concentration 2 hours after chewing was calculated as an index of nicotine metabolism. The genotypes of CYP2A6 gene, CYP2A6*1A, CYP2A6*1B, CYP2A6*2, CYP2A6*3, CYP2A6*4, and CYP2A6*5, were determined with polymerase chain reaction-restriction fragment length polymorphism. RESULTS: A large interindividual difference in nicotine metabolism was observed. Allele frequencies of CYP2A6*1A, CYP2A6*1B, and CYP2A6*4 were 42.4%, 37.5%, and 20.1%, respectively. The CYP2A6*2, CYP2A6*3, and CYP2A6*5 alleles were not found. Three subjects genotyped as CYP2A6*4/CYP2A6*4 were completely deficient in cotinine formation. The heterozygotes of the CYP2A6*4 allele tend to show lower capacities for cotinine formation. The subjects with CYP2A6*1A/CYP2A6*1B appeared to have higher capacities of cotinine formation than subjects with CYP2A6*1A/CYP2A6*1A, although the difference was not significant. The probit plot of the cotinine-nicotine ratio was not linear; this possibly indicated the existence of a novel mutation in the CYP2A6 gene genotyped as CYP2A6*1B/CYP2A6*4. CONCLUSIONS: The relationship between interindividual differences in nicotine metabolism and CYP2A6 genetic polymorphism in humans was proved.

Administration, Oral↗
PubMed2001

Cooperativity of alpha-naphthoflavone in cytochrome P450 3A-dependent drug oxidation activities in hepatic and intestinal microsomes from mouse and human.

1. The effects of several CYP3A substrates (alpha-naphthoflavone (alphaNF), terfenadine, midazolam, erythromycin) on nifedipine oxidation and testosterone 6beta-hydroxylation activities were investigated in hepatic and intestinal microsomes from mouse and human. 2. alphaNF (10 microM) and terfenadine (100 microM) inhibited nifedipine oxidation activities (at substrate concentration of 100 microM) in mouse hepatic microsomes to approximately 50%, but not in mouse intestinal microsomes. alphaNF (30 microM) stimulated nifedipine oxidation activities in mouse and human intestinal microsomes and in human hepatic microsomes to approximately 1.3-1.8-fold. Inhibitory potencies (50% inhibition concentration, IC50) of midazolam and erythromycin for nifedipine oxidations were calculated to be approximately 90 microM in human intestinal microsomes. In contrast, testosterone (100 microM) stimulated the nifedipine oxidation activities approximately 1.5-fold in hepatic and intestinal microsomes from mouse and human. 3. alphaNF showed different effects on the kinetic parameters including the Hill coefficients of nifedipine oxidation and testosterone 6beta-hydroxylation catalysed by hepatic and intestinal microsomes from mouse and human. Cooperativity in nifedipine oxidation was increased by the addition of alphaNF to pooled human hepatic microsomes, but little effects of alphaNF could be observed in individual human intestinal microsomes. 4. These results suggest that CYP3A enzymes in liver and intestine might have different characteristics and that observations from hepatic microsomes should not be directly applicable to intestine metabolism in some cases. Studies of drug-drug interactions of CYP3A substrates are recommended to be performed using intestinal samples.

Animals↗
PubMed2001

Induction of cytochrome P450 1B1 in lung, liver and kidney of rats exposed to diesel exhaust.

We have shown previously that diesel exhaust particle (DEP) extracts (DEPE) and 1-nitropyrene were genotoxically activated by human cytochrome P450 1B1 in SOS/umu assay. In this study, the in vivo induction of P450 family 1 enzymes in rats by exposure to diesel exhaust was investigated with regard to mRNA levels, P450 enzyme content, drug oxidation activities in the microsomes and umu gene expression of typical P450 substrates and DEPE itself catalyzed by the microsomes. Male Fischer 344 rats (4 weeks old) were exposed to 0.3 and 3.0 mg/m(3) DEP for 12 h per day for 4 weeks; the former dose corresponded to the typical daily airborne particle concentration. The levels of mRNA of rat P450 1B1 and P450 1A1 in the lung and liver were significantly increased 1.1-1.4-fold by exposure to 0.3 mg/m(3) DEP. Diesel exhaust particle extracts induced umu gene expression in Salmonella typhimurium TA1535/pSK1002 in the absence of a functional P450 system and were further activated by human recombinant P450 1B1. Using an O-acetyltransferase overexpressing Salmonella strain, genotoxic activation of P450 1B1 marker chemicals (1-nitropyrene, 1-aminopyrene and DEPE) by lung, liver and kidney microsomes was increased 1.7-4.2-, 1.4-1.5- and 1.0-1.3-fold, respectively, by exposure to 0.3 mg/m(3) DEP. Activation of 3-amino-1,4-dimethyl-5H-pyrido [4,3-b]indole (Trp-P-1; marker for P450 1A1) by lung microsomes and the P450 1A2 content in liver microsomes were slightly increased by exposure to 3.0 mg/m(3) DEP. This is the first report to suggest that typical daily contaminant levels (0.3 mg particle/m(3)) of diesel exhaust can induce P450 1B1 in rats and that the induced P450 1B1 may catalyze the genotoxic activation of DEP.

Animals↗
PubMed2001

Nicotine metabolism and CYP2A6 allele frequencies in Koreans.

CYP2A6 is a major catalyst of nicotine metabolism to cotinine. Previously, we demonstrated that the interindividual difference in nicotine metabolism is related to a genetic polymorphism of the CYP2A6 gene in Japanese. To clarify the ethnic differences in nicotine metabolism and frequencies of CYP2A6 alleles, we studied nicotine metabolism and the CYP2A6 genotype in 209 Koreans. The cotinine/nicotine ratio of the plasma concentration 2 h after chewing one piece of nicotine gum was calculated as an index of nicotine metabolism. The genotypes of CYP2A6 gene (CYP2A6*1A, CYP2A6*1B, CYP2A6*2, CYP2A6*3, CYP2A6*4 and CYP2A6*5) were determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism or allele specific (AS)-PCR. There were ethnic differences in the allele frequencies of CYP2A6*1A, CYP2A6*1B, CYP2A6*4 and CYP2A6*5 between Koreans (45.7%, 42.8%, 11.0% and 0.5%, respectively) and Japanese (42.4%, 37.5%, 20.1% and 0%, respectively, our previous data). Similar to the Japanese, no CYP2A6*2 and CYP2A6*3 alleles were found in Koreans. The homozygotes of the CYP2A6*4 allele (four subjects) were completely deficient in cotinine formation, being consistent with the data among Japanese. The heterozygotes of CYP2A6*4 tended to possess a lower metabolic ratio (CYP2A6*1A/CYP2A6*4, 4.79 +/- 3.17; CYP2A6*1B/CYP2A6*4, 7.43 +/- 4.97) than that in subjects without the allele (CYP2A6*1A/CYP2A6*1A, 7.42 +/- 6.56; CYP2A6*1A/CYP2A6*1B, 9.85 +/- 16.12; CYP2A6*1B/CYP2A6*1B, 11.33 +/- 9.33). The subjects who possess the CYP2A6*1B allele appeared to show higher capabilities of cotinine formation. It was confirmed that the interindividual difference in nicotine metabolism was closely related to the genetic polymorphism of CYP2A6. The probit plot of the metabolic ratios in Koreans (8.73 +/- 11.88) was shifted to a higher ratio than that in the Japanese (3.78 +/- 3.09). In each genotype group, the Korean subjects revealed significantly higher metabolic ratios than the Japanese subjects. The ethnic difference in cotinine formation might be due to environmental and/or diet factors as well as genetic factors.

Adult↗
PubMed2001

Gastric-mucous membrane protection activity of coptisine derivatives.

Coptisine and 8-oxocoptisine were isolated as principles of the gastric-mucous membrane protection from Coptidis rhizoma. The two compounds showed stronger activity than cimetidine and sucralfate. We prepared several derivatives having a partial structure of coptisine from commercially available starting materials. The compounds obtained were tested for gastric-mucous membrane protective activity and a correlation between activity and structure was studied. Our results suggest that the partial charge of the catechol skeleton is related to activity.

Animals↗
PubMed2001

Decreases in phenytoin hydroxylation activities catalyzed by liver microsomal cytochrome P450 enzymes in phenytoin-treated rats.

Phenytoin, 5,5-diphenylhydantoin, is a widely used anticonvulsant agent with a variety of toxicities, including drug interactions. The formation of four oxidative metabolites, 4'-hydroxylated (4'-HPPH), 3'-hydroxylated (3'-HPPH), a catechol (3',4'-diHPPH), and the 3',4'-dihydrodiol form of phenytoin was examined in rat liver microsomes. In 11 cDNA-expressed rat P450 enzymes tested, CYP2C6 had the highest activities in 4'- and 3'-HPPH formation from phenytoin, followed only by CYP2C11. In contrast, CYP2C11 had high activity for 3',4'-diHPPH formation from 4'-HPPH, followed by CYP2C6. The rates of 4'-HPPH and 3',4'-diHPPH formation from phenytoin in liver microsomes in the presence of NADPH were significantly decreased by oral administration of phenytoin (300 mg/kg for 20 days) to rats, despite the increase in P450 contents. However, the cumene hydroperoxide-supported formation of 3',4'-dihydrodiol and 4'-HPPH from phenytoin was induced by phenytoin administration. Hydrogen peroxide formation in reaction mixtures with NADPH was induced by the administration of phenytoin; however, the coupling ratio of phenytoin oxidation was decreased in phenytoin-induced liver microsomal P450 systems. These results suggested that phenytoin could not stimulate its own apparent oxidative metabolism by liver P450s induced with phenytoin administration. The increase of unmetabolized phenytoin and byproducts of oxygen generated in the phenytoin-induced liver microsomal P450 system may be involved in phenytoin-related drug toxicity.

Animals↗
PubMed2001

Involvement of microsomal cytochrome P450 and cytosolic thymidine phosphorylase in 5-fluorouracil formation from tegafur in human liver.

Recently, we have reported that tegafur, an anticancer agent, is biotransformed into active drug 5-fluorouracil (5-FU) by cytochromes P450 1A2, 2A6, and 2C8 in human liver microsomes (T. Komatsu et al., Drug Metab. Dispos, 28: 1457-1463, 2000). Because the conversion of tegafur into 5-FU has also been reported to be catalyzed by cytosolic thymidine phosphorylase (dThdPase), the involvement of human liver microsomes and cytosol and individual differences in 5-FU formation from tegafur were investigated. In 14 human samples, the mean rates of 5-FU formation in liver microsomes were 5-fold and 2-fold higher than those in liver cytosol at substrate concentrations of 100 microM and 1 mM tegafur, respectively. In the presence of 5-chloro-2,4-dihydroxypyridine, a dihydropyrimidine dehydrogenase inhibitor, the rates of 5-FU formation by the combination of liver microsomes and cytosol showed 5- and 3-fold interindividual differences at 100 microM and 1 mM tegafur, respectively. Kinetic analysis of human liver cytosolic 5-FU formation indicated an apparent higher Km value (16 +/- 4 mM) than that of liver microsomes (1.8 +/- 0.3 mM) with similar Vmax values. Human liver cytosolic 5-FU formation was confirmed to be catalyzed by dThdPase with correlation and chemical inhibition studies. These results suggested that 5-FU formation from tegafur in human liver was mainly catalyzed by microsomal P450 at low concentrations of tegafur, but the contribution of cytosolic 5-FU formation by dThdPase would be important at high concentrations.

Antimetabolites, Antineoplastic↗
PubMed2001

A missense mutation, A156T, in the alpha-galactosidase A gene causes typical Fabry disease.

AIMS: Fabry disease is a rare but important cause of end-stage renal disease. Recent molecular investigations on alpha-galactosidase A (alpha-Gal A) have proven the existence of atypical variants in Fabry disease, making genotype assessment of each phenotype indispensable. We report here a missense mutation, which causes a typical form of Fabry disease. MATERIAL AND METHODS: The proband, a 45-year-old man, presented with acroparesthesias, hypohidrosis, left ventricular hypertrophy, renal involvement (proteinuria and renal insufficiency) with typical microscopic findings and extremely reduced plasma alpha-Gal A activity, indicating the typical form of the disease. Total RNA was isolated from the proband's cultured fibroblasts, reverse-transcribed and amplified for direct sequencing of alpha-Gal A. Genomic DNA of the proband's mother and 75 controls (50 males and 25 females) living in the same area as the proband was also examined. RESULTS: Sequencing of the cDNA revealed a substitution of G to A in codon 156 of alpha-Gal A, resulting in a single amino acid change from alanine to threonine (A156T). The mutation can be detected with PCR-RFLP with SfaNI digestion. This technique revealed that the mother was a heterozygote of A156T with no A156T noted in the 100 haplotypes of the controls. With a vigorous search of the same mutation in the literature, no previous description was found other than one case listed in several review papers as a classic phenotype without any other information. In our study, we examined A156T in a pedigree and demonstrated that the mutation was not a polymorphic variant in our area. CONCLUSION: Taken together, the present results strongly suggest that the missense mutation, A156T, in the alpha-Gal A gene causes typical Fabry disease.

Fabry Disease↗
PubMed2001

Rat cytochrome p450 1A and 3A enzymes involved in bioactivation of tegafur to 5-fluorouracil and autoinduced by tegafur in liver microsomes.

Tegafur, an anticancer prodrug, is reported to be bioactivated to 5-fluorouracil (5-FU) by cytochrome P450 (P450) enzymes. Liver microsomal P450 enzymes involved in the biotransformation of tegafur into 5-FU in rats and the effect of tegafur in vivo on P450 levels in rats were investigated. Of 12 cDNA-expressed rat P450 enzymes tested, CYP1A2, CYP3A1, and CYP2C11 had high 5-FU formation rates from 100 microM and 1.0 mM tegafur concentrations. The contributions of CYP1A, CYP2C, and CYP3A enzymes to 5-FU formation in male rat liver microsomes were supported by immunoinhibition studies. 5-FU formation from tegafur, at substrate concentrations of 100 microM and 1.0 mM, was increased by intraperitoneal treatment of tegafur (50 mg/kg for 5 days) as well as by beta-naphthoflavone, phenobarbital, and dexamethasone. Orally administered tegafur (100 mg/kg daily for 20 days) caused the induction of CYP2B (5-fold) and of CYP1A and CYP3A (approximately 2-fold) and of 5-FU formation (approximately 2-fold) in rat liver microsomes. These results suggest that CYP1A and CYP3A enzymes, autoinduced by tegafur, have important roles in 5-FU formation from tegafur in rat liver microsomes. Coadministration of tegafur and P450-inducing drugs could markedly enhance the biotransformation of tegafur into 5-FU via P450 induction.

Animals↗
PubMed2001

Effect of prolonged low-dose methylprednisolone therapy in acute exacerbation of idiopathic pulmonary fibrosis.

We report on a 74-year-old man with an acute exacerbation of idiopathic pulmonary fibrosis (IPF) who was successfully treated with prolonged low-dose methylprednisolone, initiated at a loading dose of 2 mg/kg, followed by 2 mg/kg per day for 14 days. The dose was then tapered. The exacerbation observed on the chest radiograph and high-resolution computed tomography was found to have abated after the treatment. This successful case suggests the feasibility of this methylprednisolone treatment protocol for patients with IPF accompanied by accelerated deterioration. Furthermore, this case suggests possible similarities between acute exacerbation of IPF and late acute respiratory distress syndrome, as the same treatment protocol was previously proved to be beneficial for patients with late acute respiratory distress syndrome.

Acute Disease↗
PubMed2001

Inhibition and inactivation of human cytochrome P450 isoforms by phenethyl isothiocyanate.

The inhibition and mechanism-based inactivation potencies of phenethyl isothiocyanate (PEITC) for human cytochrome P450 (CYP) activities were investigated using microsomes from baculovirus-infected insect cells expressing specific human CYP isoforms. PEITC competitively inhibited phenacetin O-deethylase activity catalyzed by CYP1A2 (K(i) = 4.5 +/- 1.0 microM) and coumarin 7-hydroxylase activity catalyzed by CYP2A6 (K(i) = 18.2 +/- 2.5 microM). Benzyloxyresorufin O-dealkylase activity catalyzed by CYP2B6 was most strongly and noncompetitively inhibited (K(i) = 1.5 +/- 0.0 microM). Paclitaxel 6alpha-hydroxylase activity catalyzed by CYP2C8 was not affected by PEITC up to 100 microM. PEITC noncompetitively inhibited S-warfarin 7-hydroxylase activity catalyzed by CYP2C9 (K(i) = 6.5 +/- 0.9 microM), S-mephenytoin 4'-hydroxylase activity catalyzed by CYP2C19 (K(i) = 12.0 +/- 3.2 microM), bufuralol 1'-hydroxylase activity catalyzed by CYP2D6 (K(i) = 28.4 +/- 7.9 microM), and chlorzoxazone 6-hydroxylase activity catalyzed by CYP2E1 (K(i) = 21.5 +/- 3.4 microM). The inhibition for testosterone 6beta-hydroxylase activity catalyzed by CYP3A4 was a mixed-type of competitive (K(i) = 34.0 +/- 6.5 microM) and noncompetitive (K(i) = 63.8 +/- 12.5 microM) inhibition. Furthermore, PEITC is a mechanism-based inactivator of human CYP2E1. The k(inact) value was 0.339 min(-1) and K(i) was 9.98 microM. Human CYP1A2, CYP2A6, CYP2B6, CYP2D6, and CYP3A4 were not inactivated. The present study directly proved that the chemopreventive effects of PEITC for nitrosamine-induced carcinogenesis are due to the inhibition of CYP by an in vitro study. The possibility that PEITC would affect the pharmacokinetics of clinically used drugs that are metabolized by these CYP isoforms was also suggested.

Binding, Competitive↗
PubMed2000

Bioactivation of diesel exhaust particle extracts and their major nitrated polycyclic aromatic hydrocarbon components, 1-nitropyrene and dinitropyrenes, by human cytochromes P450 1A1, 1A2, and 1B1.

The genotoxicities of four samples of diesel exhaust particle (DEP) extracts (DEPE) and nine nitroarenes found in DEPE were investigated after activation catalyzed by human cytochrome P450 (P450) family 1 enzymes co-expressed with NADPH-cytochrome P450 reductase (NPR) in Escherichia coli membranes. The DEPE samples induced umu gene expression in Salmonella typhimurium TA1535/pSK1002 without any P450 system and were further activated by human P450 1B1/NPR membranes. Moderate activation of the DEPE sample by P450 1A2/NPR membranes was also observed, but not by either P450 1A1/NPR or NPR membranes. 1-Nitropyrene (1-NP) was strongly activated by human P450 1B1/NPR membranes. 1,8-Dinitropyrene (1,8-DNP) was most highly activated by P450 1A1 and 1B1 systems for the three DNPs tested. In contrast, 1, 3-DNP was inactivated by P450 1A1/NPR, 1A2/NPR, and 1B1/NPR systems and slightly activated by NPR membranes. 2-Nitrofluoranthene (2-NF) and 3-nitrofluoranthene (3-NF) showed activities similar to 1-NP after bioactivation by P450 1B1/NPR membranes. However, the genotoxicities of 6-nitrochrysene, 7-nitrobenz[a]anthracene, and 6-nitrobenzo[a]pyrene were all weak in the present assay system. Apparent genotoxic activities of DEPE were very low compared with standard nitroarenes in the presence of P450s, possibly because unknown component(s) of DEPE had inhibitory effects on the bioactivation of 1-NP and 1,8-DNP catalyzed by human P450 1B1. These results suggest that environmental chemicals existing in airborne DEP, in addition to 1-NP, 1,6-DNP, 1,8-DNP, 2-NF, and 3-NF, can be activated by human P450 1B1. Biological actions of air pollutants such as nitroarenes to human extrahepatic tissues may be of concern in tissues in which P450 1B1 is expressed.

Aryl Hydrocarbon Hydroxylases↗