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O Pelkonen

Publications and source records attributed to O Pelkonen.

At least 127 records · Page 7Linked to original sources
PubMed1992

Human and mouse liver coumarin 7-hydroxylases do not metabolize warfarin in vitro.

1. The contribution of human P450 2A6 and mouse P450 2a-5 isoenzymes, both highly active in coumarin 7-hydroxylation, to the metabolism of warfarin was studied in several in vitro systems with human and mouse liver preparations. 2. The reconstituted P450 2a-5 purified from DBA/2 mouse liver did not metabolize warfarin. 3. An anti-P450 2a-5 antibody did not consistently inhibit any of the warfarin biotransformation reactions catalyzed by human or mouse liver microsomes, although coumarin 7-hydroxylation was inhibited by over 90%. 4. In some human microsomal samples, 4- and 8-hydroxylations of warfarin were inhibited to some extent by the anti-P450 2a-5 antibody. 5. Warfarin (less than 1 mM) did not inhibit coumarin 7-hydroxylation by human or mouse liver microsomes in vitro. 6. We conclude that mouse and human coumarin 7-hydroxylases do not oxidise warfarin.

Adult↗
PubMed1992

7-Alkoxyquinoline O-dealkylation by microsomes from human liver and placenta.

1. The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsomes and the effect of maternal cigarette smoking on placental 7-alkoxyquinoline metabolism was studied. 2. None of several monoclonal antibodies to isoenzymes of cytochrome P450 had a clear effect on metabolism of the compounds by liver microsomes. 3. Maternal cigarette smoking induced the O-dealkylation of all of the 7-alkoxyquinoline derivatives, being greatest for 7-butoxy- and 7-benzyloxyquinoline. 4. Placental 7-alkoxyquinoline metabolism induced by smoking was partially inhibited by the monoclonal antibody 1-7-1 raised against 3-methylcholanthrene-induced rat liver P450. 5. None of the 7-alkoxyquinoline O-dealkylations could be assigned specifically to any known P450 isoenzyme in human liver or placenta.

Animals↗
PubMed1992

Carcinogen metabolism and individual susceptibility.

Many chemical carcinogens need activation by drug metabolizing enzymes, principally cytochrome P450 enzymes, to become capable of binding to deoxyribonucleic acid and initiating the carcinogenic process. The activity and inducibility of drug metabolizing enzymes are regulated by interplay between genetic, host, and environmental factors. Consequently, individual differences in cancer susceptibility might be explained somewhat by genetic differences in metabolic activation. Three examples, the induction of aryl hydrocarbon (benzo[a]pyrene) hydroxylase by polycyclic aromatic hydrocarbons, polymorphic debrisoquine/sparteine oxidation, and polymorphic acetylation, are briefly reviewed. Despite useful animal models and promising early human findings, no consensus has been reached about the significance of genetically based differences in drug metabolism in cancer etiology. It is expected that, with the use of molecular biological methods, the genetic background of study subjects can be investigated without bias caused by the disease, age, treatment, or other factors which have plagued investigations thus far.

Acetylation↗
PubMed1992

Debrisoquine hydroxylation phenotypes of patients with high versus low to normal serum antidepressant concentrations.

Debrisoquine hydroxylation phenotype was determined in 22 psychiatric patients who had previously developed exceptionally high serum antidepressant (AD) concentrations, and in 22 sex-, age-, and dose-matched counterparts who had low to normal serum AD levels. The patients were recruited from 641 subjects in whom serum AD levels were monitored. In each AD level group, 16 patients had been treated with tricyclic antidepressants (amitriptyline, doxepin, trimipramine, imipramine, clomipramine) and 6 with mianserin. Eight poor metabolizer (PM) phenotypes (debrisoquine/hydroxydebrisoquine ratio in 6-hour urine greater than or equal to 41.5) were identified in the high AD level group, but only two in the group with low to normal AD level (p = 0.03, Fisher's test). Comedications in the two study groups did not differ markedly from ach other and could not, therefore, explain the greater frequency of PMs among the patients with high serum AD levels. Three of 6 mianserin patients, who had developed high serum AD levels, were PMs. This high proportion of PMs raises the question of a possible involvement of the same metabolic pathway (cytochrome P-450IID6 isoenzyme) also in mianserin hydroxylation. The results suggest further that during AD therapy with standard dosage, PM phenotypes are at special risk for high serum AD concentrations and, consequently, for clinical symptoms of toxicity.

Antidepressive Agents↗
PubMed1991

Comparative studies on coumarin and testosterone metabolism in mouse and human livers. Differential inhibitions by the anti-P450Coh antibody and metyrapone.

We have studied coumarin 7-hydroxylase (COH) and testosterone 15 alpha-hydroxylase (15 alpha OH) activities in human liver microsomes and compared them with corresponding activities catalysed by members of the P450IIA sub-family in DBA/2N mouse liver microsomes. Human liver contained low levels of 15 alpha OH (about 5-30 pmol/min/mg protein) when compared with control mouse liver microsomes (about 200 pmol/min/mg protein). The anti-P450Coh antibody efficiently inhibited mouse liver 15 alpha OH, also 7 alpha OH (which is a member of the P450IIA sub-family), but it did not inhibit human 15 alpha OH or other testosterone hydroxylases. In mouse liver microsomes, metyrapone preferentially inhibited 15 alpha OH, but in human liver microsomes it inhibited all testosterone hydroxylations measured, including 15 alpha OH (IC50 = 2.0-5.0 microM). Metyrapone clearly inhibited COH in mouse liver microsomes, but interestingly it had no effect on COH activity in human liver microsomes, although these two isozymes have earlier been shown to be immunologically similar. On the basis of available evidence human and mouse P450Coh isozymes seem to be orthologous enzymes whereas the present results indicate that the human 15 alpha OH is different from the mouse P45015 alpha.

Animals↗
PubMed1991

Comparison between cobalt and pyrazole in the increased expression of coumarin 7-hydroxylase in mouse liver.

The data in this report show that administration of both cobalt and pyrazole results in an elevation in the amount of hepatic mRNA encoding for microsomal P45015 alpha/P450Coh, an increase in the amount of P450Coh protein, and an activation of COH and to a lesser extent testosterone 15 alpha-hydroxylase in two inbred strains of mice. Considerable quantitative differences between the two compounds and the two mouse strains in the response suggest that the effects of cobalt and pyrazole are mediated, at least partly, through different mechanisms. It is of interest that human hepatic COH resembles very closely that in the mouse liver.

Animals↗
PubMed1991

Distribution and effects on cytochrome P450 system of two hexachlorobiphenyl isomers in the rat.

Tissue distribution and effects induced by 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB) on cytocrome P450 isozymes were compared with those of 2,2',3,3',6,6'-hexacholorobiphenyl (236-HCB). Male Wistar rats were given a single intragastric dose (23 mg/kg body wt) of either isomer, and killed after 72 h. At termination the tissue concentrations of 245-HCB were considerably higher than those of 236-HCB, suggesting a more effective metabolism of the latter. The binding affinity of 236-HCB to cytochrome P450 was higher and the magnitude of binding greater than of 245-HCB. 245-HCB-treatment elevated the hepatic concentration of cytochrome P450 and also the activities of 7-pentoxyresorufin O-depentylase (50-fold), aniline p-hydroxylase (2-fold) and 7-ethoxycoumarin O-deethylase (2-fold), a response typical of phenobarbital-type inducers. In the Western immunoblot of liver microsomes from 245-HCB treated rats, an increased amount of P450IIB 1/2 was detected by a monoclonal antibody 2-66-3, which specifically detects phenobarbital inducible isoenzymes. The minimum molecular mass of the P450 isozyme induced was 52 kDa. After 236-HCB administration, a weak inducing effect was observed.

Animals↗
PubMed1991

The cerium-induced liver injury and oxidative drug metabolism in DBA/2 and C57BL/6 mice.

The influence of the known hepatotoxic agent, cerium (Ce) on the activity of liver microsomal monoxygenases, especially coumarin 7-hydroxylase (COH) was investigated in two inbred strains of male mice, DBA/2N and C57BL/6N. Ce was injected intravenously in three doses (0.5, 1.0 and 2.0 mg/kg body wt) and the animals were killed 24 or 72 h later. On the basis of histological assessment of the liver, C57BL/6N mice are apparently more resistant to the hepatotoxic effect of Ce. At 24 h, COH activity was increased in a dose-dependent manner in DBA/2 animals, whereas no change was seen in C57BL/6N animals. A significant increase in all other enzymes studied, cytochrome P-450 (P450), ethoxycoumarin O-deethylase and ethoxyresorufin O-deethylase, was seen in DBA/2 mice injected with the highest dose of Ce. At 72 h Ce increased CON activity, as well as other enzymes, in C57BL/6N mice in a dose-dependent manner, whereas in DBA/2 mice the increase was only seen after the two lower doses, the highest dose causing severe morphological changes in the liver structure and a clear decrease in COH and other activities. The distribution studies with Ce-141 showed that C57BL/6N livers contained more Ce than DBA/2 livers after the highest dose.

Animals↗
PubMed1991

Comparative effects of medetomidine enantiomers on in vitro and in vivo microsomal drug metabolism.

The effects of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, and its levo enantiomer (MPV-1441), on in vitro microsomal P450-dependent drug-metabolizing activities as well as on in vivo aminopyrine elimination and hexobarbital sleeping time were studied. Both enantiomers inhibited the oxidative metabolism of several model substrates and testosterone in rat liver microsomal incubations. Microsomal activities derived from control animals or rats pretreated with phenobarbital were more sensitive to inhibitory effects of dexmedetomidine than those from rats treated with 3-methylcholanthrene. Enzyme activities in human liver microsomes were also inhibited by dexmedetomidine. Retardation of the elimination of aminopyrine was dose-dependent; elimination was marginally retarded with doses up to 100 micrograms/kg (from 17 to 23 min.; both enantiomers). Higher doses of the levo enantiomer prolonged aminopyrine half-life to 78 (1 mg/kg) and 162 min. (10 mg/kg). The hexobarbital sleeping time was prolonged by the dose of 1 mg/kg of the levo enantiomer (128 min. versus 20 min. in controls), while the dose of 0.1 mg/kg had no effect (23 versus 20 min.). These studies indicate that both enantiomers of medetomidine are inhibitors of microsomal drug metabolism in vitro, but significant effects on aminopyrine elimination or hexobarbital sleeping time are apparent only at doses, which do not allow the use of dexmedetomidine because of excessive sedative effect.

Adrenergic alpha-Agonists↗
PubMed1990

Immunochemical detection of human liver cytochrome P450 forms related to phenobarbital-inducible forms in the mouse.

Polyclonal antibodies generated to four distinct mouse liver phenobarbital-inducible cytochrome P450 isoforms were used to analyse related forms in human liver. N-terminal sequence analysis and biochemical properties of the P450s used as antigens suggest that they belong to P450 subfamilies IIB (P450PBI), IA (P450PBII), IIC (P450PBIII) and IIA (P450Coh). In immunoblot analysis, anti-P450PBII detected a single protein presumed to be P450IA2 in all the human livers tested. No proteins corresponding with P450IA1 could be detected. Anti-PBIII and anti-P450Coh antibodies each detected one band (54 and 48 kDa, respectively) in the liver samples. No bands were revealed by anti-P450PBI antibody. Protein dot-immunobinding analysis showed that P450s immunodetectable by anti-P450PBII, anti-P450PBIII and anti-P450Coh antibodies are expressed in human liver (range 9 to 69 pmol P450/mg protein). In immunoinhibition experiments the activity of 7-ethoxyresorutin O-deethylase (EROD) was blocked up to 90% by the anti-P450PBII antibody. Aryl hydrocarbon hydroxylase (AHH) was inhibited only by anti-P450PBIII, and coumarin 7-hydroxylase (COH) only by anti-P450Coh antibody. Testosterone hydroxylations in positions 6 beta, 7 alpha, 15 alpha and 16 alpha were not affected significantly by any of the antibodies. These data suggest that the human liver P450IA2 is responsible for most of the elevated EROD activity, P450s in the IIC subfamily for constitutive AHH and P450s in the IIA subfamily for all of COH activity.

Adult↗
PubMed1990

Immunochemical and molecular biological studies on human placental cigarette smoke-inducible cytochrome P-450-dependent monooxygenase activities.

The induction of specific forms of cytochrome P-450 and P-450-associated xenobiotic-metabolizing monooxygenase activities by maternal cigarette smoking was characterized in human placenta employing polyclonal and monoclonal antibodies and recombinant DNA probes. The anti-BNF-B2 (prepared against rat liver P-450 induced by beta-naphthoflavone) inhibited about 60 per cent of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufin O-deethylase activities (ERDE) in placental tissues from smoking mothers, whereas the anti-PB-B2 (to phenobarbital-induced rat liver P-450) was without significant inhibitory effect. Inhibition of 7-ethoxycoumarin O-deethylase (ECDE) by the anti-BNF-B2 was dependent on maternal smoking: the enzyme from non-smokers was not significantly inhibited, whereas the enzyme from smokers was variably inhibited by 15-60 per cent. The monoclonal antibodies towards the major 3-methylcholanthrene-inducible and phenobarbital-inducible rat liver P-450s (Mab 1-7-1 and 2-66-3, respectively) behaved similarly, except the inhibition was somewhat stronger if present. Antibody raised against rat liver NADPH-cytochrome P-450 oxido-reductase did not inhibit any activity studied. In immunoblotting experiments, the anti-reductase recognized the protein in human placental microsomes. However, neither anti-BNF-B2, anti-PB-B2 or Mab 1-7-1 or Mab 2-66-3 detected any proteins in human placental microsomes, regardless of smoking status. Northern blot hybridization analysis of placental RNA samples showed that only P-450IA1 mRNA existed in the placentas of smoking mothers with detectable ERDE activity. Despite the discrepancy between protein blotting and immunoinhibition data all other findings support the conclusion that maternal cigarette smoking induces the expression of the CYPIA1 gene (and not CYPIA2), resulting in an increased synthesis of P-450IA1 protein and increased AHH, ERDE and ECDE activities in human placenta.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1990

Cytochrome P450 isozyme induction by methyl ethyl ketone and m-xylene in rat liver.

The rat hepatic cytochrome P450 induction pattern caused by administration of a high peroral dose of methyl ethyl ketone (MEK, 1.4 ml/kg once daily for 3 consecutive days) and m-xylene (1.0 ml/kg X 3) was studied by catalytic activity and immunoblotting techniques. MEK caused a marked increase in the amount of P450 isozymes belonging to the phenobarbital- and ethanol-inducible P450 subfamilies P450IIB and P450IIE, respectively. Catalytic activities linked with these isozymes, pentoxyresorufin O-depentylase (P450IIB), aniline hydroxylase, and N-nitrosodimethylamine N-demethylase (P450IIE), were also increased (18.0-, 5.4-, and 2.4-fold, respectively). The activity of ethoxyresorufin O-deethylase, which is predominantly linked with the polycyclic aromatic hydrocarbon-inducible P450 isozymes, was also increased 2.3-fold without an apparent increase in the amount of the respective P450 protein (P450IA). m-Xylene caused a similar induction pattern with less effect on P450IIE. Simultaneous administration of MEK and m-xylene resulted in an additive or, in the case of pentoxyresorufin O-depentylase, a potentiating effect on P450-linked catalytic activities. These data indicate that MEK and m-xylene elicit a qualitatively similar induction of P450 isozymes, which may play a role in the metabolic interactions of these compounds.

Animals↗
PubMed1990

Differential expression and regulation of members of the cytochrome P450IA gene subfamily in human tissues.

Cigarette smoking increases phenacetin O-deethylase (POD) activity in both the liver and placenta in man, but aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity is increased only in the placenta. Whilst there was no correlation between hepatic POD and AHH activities (rs = 0.42, P greater than 0.1), there was a highly significant correlation between these two activities in placenta (rs = 0.76, P less than 0.02). On Western blotting of human liver samples with an antibody specific to cytochrome P450IA2 in the rat, only the orthologue of P450IA2 could be detected. This antibody inhibited greater than 70% of hepatic high-affinity POD activity but had no effect on the placental activity. Furafylline, a methylxanthine that acts as a highly specific inhibitor of P450IA2-dependent activities in man, inhibited all of the high-affinity component of POD activity in human liver, but was at least three orders of magnitude less potent an inhibitor of placental POD and of both hepatic and placental AHH activities. As previously shown in the rat, exposure of man to polycyclic aromatic hydrocarbons, present in cigarette smoke, differentially induces P450IA2 in the liver and P450IA1 in extrahepatic tissues, at least in the placenta. Again, as in the rat, POD activity in the liver is catalysed by P450IA2, but in the placenta of women exposed to polycyclic aromatic hydrocarbons in cigarette smoke POD activity is catalysed by another isoenzyme, most likely P450IA1. Thus, tissue-dependent induction and substrate specificity of members of the P450IA family in man, at least in the placenta, appear to be the same as previously shown in the rat.

Adolescent↗
PubMed1990

Species variation in the response of the cytochrome P-450-dependent monooxygenase system to inducers and inhibitors.

1. In the safety evaluation of drugs and other chemicals it is important to evaluate their possible inducing and inhibitory effects on the enzymes of drug metabolism. 2. While many similarities exist between species in their response to inducers and inhibitors, there are also important differences. Possible mechanisms of such variation are considered, with particular reference to the cytochrome P-450 system. 3. Differences in inhibition may be due to differences in inhibitory site of the enzyme involved, which is not always the active site of the enzyme, in competing pathways or in the pharmacokinetics of the inhibitor. 4. Differences in induction could be due to differences in the nature of the induction mechanism, in the isoenzyme induced, in tissue- or age-dependent regulation, in competing pathways for the substrate or its products, or in the pharmacokinetics of the inducing agent. 5. Examples of each of these possible differences are considered, often from our own work on the P450 IA subfamily, and results in animals are compared with those in humans, where possible. 6. At present, the differences between species in their response to inducers and inhibitors make extrapolation to humans from the results of animal studies difficult, so that ultimately such effects should be studied in the species of interest, humans.

Allosteric Regulation↗