Toxicokinetics and metabolism.
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Animals↗
Biomedical subjects
Olavi Pelkonen
Publications and source records attributed to Olavi Pelkonen.
Reproductive and developmental toxicity.
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Abnormalities, Drug-Induced↗
In vitro screening of drug metabolism during drug development: can we trust the predictions?
Due to the importance of drug metabolism for drug action, side effects, interactions and interindividual differences, in vitro assays of drug metabolism are widely employed during drug development. Validation of the in vitro systems is still in a rather elementary stage, but some tentative conclusions about their performance for predicting various important in vivo characteristics of drugs can be attempted. So far, prediction of drug-drug interactions on the basis of in vitro screens has been advanced to a relatively reliable level. Prediction of other important characteristics, such as metabolic stability and consequent half-life and dosage schedule, or induction potential, is less reliable. Although metabolite profiles and participating enzymes are predicted quite accurately with advanced analytical techniques, an important problem here is the lack of reliable methods to detect reactive metabolites or products, which may be of significance regarding toxicity.
Animals↗
Regulation of Cyp2a5 transcription in mouse primary hepatocytes: roles of hepatocyte nuclear factor 4 and nuclear factor I.
The cytochrome P4502a5 (Cyp2a5) gene is expressed principally in liver and olfactory mucosa. In the present study, the transcriptional mechanisms of hepatocyte-specific expression of Cyp2a5 were studied in mouse primary hepatocytes. The Cyp2a5 5'-flanking region -3033 to +10 was cloned in front of a luciferase reporter gene and transfected into hepatocytes. Deletion analysis revealed two major activating promoter regions localized at proximal 271 bp and at a more distal area from -3033 to -2014 bp. The proximal activation region was characterized further by DNase I footprinting, and a single clear footprint was detected in the studied area centred over a sequence similar to the NF-I (nuclear factor I)-binding site. The binding of NF-I was confirmed using an EMSA (electrophoretic mobility-shift assay). A putative HNF-4 (hepatocyte nuclear factor 4)-binding site was localized at the proximal promoter by computer analysis of the sequence, and HNF-4alpha was shown to interact with the site using an EMSA. The functional significance of HNF-4 and NF-I binding to the Cyp2a5 promoter was evaluated by site-directed mutagenesis of the binding motifs in reporter constructs. Both mutations strongly decreased transcriptional activation by the Cyp2a5 promoter in primary hepatocytes, and double mutation almost completely abolished transcriptional activity. Also, the functionality of the distal activation region was found to be dependent on the intact HNF-4 and NF-I sites at the proximal promoter. In conclusion, these results indicate that HNF-4 and NF-I play major roles in the constitutive regulation of hepatic expression of Cyp2a5.
5' Flanking Region↗
Selective inhibition of CYP2B6-catalyzed bupropion hydroxylation in human liver microsomes in vitro.
Some inhibitory agents against CYP2B6 have been reported, but none of these has been extensively characterized or compared with others, as to the potency and selectivity of inhibition toward CYP2B6. The goal of this work was to find a selective and potent chemical in vitro inhibitor toward CYP2B6 using bupropion hydroxylation as a model reaction. At the initial screening of more than 30 substances, ticlopidine, triethylenethiophosphoramide (thioTEPA), metyrapone, xanthate C8, and benzylisothiocyanate displayed IC(50) values of <10 microM and were selected for a more detailed analysis. Metyrapone, xanthate C8, and benzylisothiocyanate inhibited several other cytochrome P450 activities rather effectively, some of them even more potently than CYP2B6, and consequently are unsuitable as CYP2B6-selective probes. Ticlopidine and thioTEPA were the most potent inhibitors of bupropion hydroxylation with K(i) values of 0.2 and 2.8 microM, respectively. The inhibition type of ticlopidine was found to be mixed type, with a component of mechanism-based inhibition, whereas thioTEPA inhibited CYP2B6 in a competitive manner. In addition to CYP2B6, ticlopidine also inhibited both mephenytoin 4-hydroxylation (CYP2C19) (IC(50), 2.7 microM) and dextromethorphan O-demethylation (CYP2D6) (IC(50), 4.4 microM). For thioTEPA the next sensitive P450 activity after CYP2B6 was coumarin 7-hydroxylation (IC(50), 256 microM). Thus, although both compounds proved to be relatively potent inhibitors of CYP2B6, thioTEPA was about 2 orders of magnitude more selective than ticlopidine. Thus, thioTEPA is a drug of choice when high CYP2B6 selectivity among major P450 enzymes is required. Ticlopidine is a useful alternative under a controlled experimental setup and when higher potency is needed.
Aryl Hydrocarbon Hydroxylases↗
In vitro methods in the prediction of kinetics of drugs: focus on drug metabolism.
The absorption, distribution, metabolism, excretion and toxicity (ADMET) properties of a candidate drug influence its final clinical success. These properties have traditionally been evaluated by using various in vivo animal approaches, but recently, a number of in vitro and in silico methods have been introduced to determine key ADMET features. Basic events, such as absorption through the gut wall, binding to plasma proteins, active and passive transfer through the blood-brain barrier, and various metabolic parameters, can now be screened with rapid in vitro and computer modelling methods. The focus in this short review is on the basic in vitro and in silico methods that are used for studying the metabolism properties of new drug molecules.
Absorption↗
Expression of CYP3A4 in human breast tumour and non-tumour tissues.
Cytochrome P450 3A4 (CYP3A4), a member of multigene superfamily of enzymes, plays a major role in the activation of procarcinogens such as polycyclic hydrocarbon dihydrodiols, aflatoxins and heterocyclic amines as well as of several drugs including tamoxifen which is used in breast cancer therapy. Using immunohistochemistry, the cellular distribution and the level of expression of CYP3A4 was assessed in breast tumour and surrounding tumour free (control) breast tissue in 25 pairs of samples obtained from females with infiltrating ductal carcinoma. Cells staining with the CYP3A4 antibody showed only cytoplasmic positivity with varying intensities in 100% (25/25) of tumours and 68% (17/25) of normal breast tissues. Cytoplasmic staining was present in invasive ductal carcinoma cells but not in tumour stroma. CYP3A4 was detected in normal epithelium and myoepithelium. Only focal staining was noted in some of the non-epithelial cells (e.g. endothelial cells) in normal breast tissues. When CYP3A4 staining was assessed semiquantitatively the mean staining score values of CYP3A4 were found to be significantly higher in tumours compared to that of normal breast tissues. These results show that CYP3A4 protein is expressed in both tumour and normal breast tissue with an increased expression in tumours.
Adult↗
Dual action of oestrogens on the mouse constitutive androstane receptor.
mCAR (mouse constitutive androstane receptor; NR1I3) controls the expression of cytochrome P450 as well as other enzymes involved in drug and steroid metabolism. The high basal activity of mCAR can be modulated by inhibitory steroids related to androstenol and by activating xenobiotic chemicals such as 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene and chlorpromazine. The ability of oestrogens and some other xenobiotics to activate mCAR is not clear. In the present study, co-transfection assays in HEK-293 cells indicated that oestrogens varied in their efficacy to activate mCAR, depending on variation at the steroid D-ring and position of hydroxy groups. In general, oestrogens were weaker activators of mCAR than 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene and chlorpromazine. Also, the induction of CYP2B10 mRNA by oestrogens was less pronounced in mouse primary hepatocytes. Yeast two-hybrid assays indicated that, unlike androstenol and the established activators, oestrogens attracted both nuclear receptor co-repressors and co-activators to the mCAR ligand-binding domain, thus limiting the extent of mCAR activation. This novel dual action is not limited to oestrogens, but is shared by some xenobiotic CYP2B inducers such as clotrimazole and methoxychlor. These findings offer an alternative explanation for the recently suggested nuclear activation step of mCAR.
Animals↗
Immunohistochemical demonstration of the expression of CYP2E1 in human breast tumour and non-tumour tissues.
Environmental chemicals are one of the risk factors in breast cancer genesis. Cytochrome P450 2E1 (CYP2E1), a member of multigene superfamily of enzymes, plays a major role in the activation of some of these chemicals such as tobacco-derived N-nitrosamines. Using immunohistochemistry, the cellular distribution and the level of expression of CYP2E1 was assessed in breast tumour and surrounding tumour free (control) breast tissue in 25 pairs of samples obtained from females with infiltrating ductal carcinoma. Cells staining with the CYP2E1 antibody showed only cytoplasmic positivity with varying intensities in 100% (25/25) of tumours and 96% (24/25) of normal breast tissues. Cytoplasmic staining was present in invasive ductal carcinoma cells but not in tumour stroma. CYP2E1 was detected in normal epithelial, myoepithelial and to a lesser degree in some of the non-epithelial cells (e.g. endothelial cells). No positive staining was detected in other non-epithelial cells such as fibroblasts in normal breast tissues. When CYP2E1 staining was assessed semiquantitatively the mean staining score values of CYP2E1 was found to be significantly higher in tumours compared to that of normal breast tissues. These results show that CYP2E1 protein is expressed in both tumour and normal breast tissue with an increased expression in breast tumours.
Adult↗
Inhibition of cytochrome P450 2B6 activity by hormone replacement therapy and oral contraceptive as measured by bupropion hydroxylation.
AIM: Our objective was to study the effect of hormone replacement therapy and a combination oral contraceptive on the cytochrome P450 (CYP) 2B6 activity with bupropion (INN, amfebutamone) hydroxylation used as a probe reaction. METHODS: This was a 3-way crossover study with 12 healthy female volunteers. The first phase was a control phase, in which all subjects received a single 150-mg dose of bupropion (sustained release) without pretreatment. In the second and third phases, in randomized balanced crossover order, subjects received a 10-day pretreatment with either hormone replacement therapy, containing 2 mg estradiol valerate and 250 microg levonorgestrel, or an oral contraceptive, containing 30 microg ethinyl estradiol (INN, ethinylestradiol) and 150 microg desogestrel, and the bupropion dose was given 1 hour after the last hormone dose. The bupropion, hydroxybupropion, and hydrobupropion plasma concentrations were determined for up to 72 hours. RESULTS: The 10-day hormone replacement therapy pretreatment reduced the hydroxybupropion/bupropion area under the plasma concentration-time curve (AUC) ratio by 49% (P <.001; 95% confidence interval [CI], -58% to -40%) as a result of a marked 47% decrease (P <.001; 95% CI, -54% to -41%) in the AUC of hydroxybupropion. Moreover, the AUC of hydrobupropion was significantly (64%; P =.003; 95% CI, 22% to 106%) increased. The AUC of hydroxybupropion was also reduced after the oral contraceptive treatment but to a lesser extent (-31%; P <.001; 95% CI, -37% to -26%). However, the hydroxybupropion/bupropion AUC ratio was not significantly affected. CONCLUSIONS: Hormone replacement therapy markedly inhibited the CYP2B6-catalyzed hydroxylation of bupropion, whereas a combination oral contraceptive had only a modest effect on CYP2B6 activity. Patients receiving hormone replacement therapy or oral contraceptives may need dose adjustment when treated with drugs metabolized by CYP2B6.
Adult↗
Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers.
The Baltic Sea ecosystem has suffered from a heavy pollutant load for more than three decades. Persistent organic pollutants (POPs) and heavy metals have been of most concern due to their persistence and toxic properties. Ringed seals (Phoca hispida baltica) and grey seals (Halichoerus grypus) living in the Baltic Sea have been suffering from pathological impairments, including reproductive disturbances, which have resulted in a depressed reproductive capacity. We investigated several biochemical parameters as potential biomarkers for exposure to and effects of the contaminant load in the Baltic seals. Seals from less polluted areas were used as reference material in terms of the pollution load. In both Baltic seal populations, the levels of some biochemical parameters diverged from those in the reference seals, and some of these showed a clear correlation with the individual contaminant load. Of the potential bioindicators, we propose cytochrome P4501A activity and vitamin E levels, in blubber or plasma, as exposure biomarkers for polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in both species. The arylhydrocarbon receptor-mediated chemical-activated luciferase gene expression (CALUX) response reflects the whole PCB and DDT burden in ringed seals. Retinyl palmitate (vitamin A) levels showed a negative correlation with the individual POP load, and is proposed as potential effect biomarkers for the depletion of the vitamin A stores. As the nutritional levels of both vitamin A and E have an impact on the vitamin levels in the seals, more information on the dietary vitamin levels is needed before any conclusions can be drawn. As the relationship between biochemical parameters and contaminants varied between the two species, species-specific characteristics has to be considered when monitoring the health status and possible toxic effects of the contaminant load in ringed and grey seals.
Animals↗
Stability of sufentanil and levobupivacaine solutions and a mixture in a 0.9% sodium chloride infusion stored in polypropylene syringes.
We have evaluated the chemical and microbiological stability of sufentanil citrate, levobupivacaine hydrochloride and a mixture in a 0.9% sodium chloride infusion in order to provide background information on the storage of a sufentanil-levobupivacaine mixture in polypropylene (PP) syringes. Chemical assays were performed by HPLC on days 0, 1, 2, 3, 8, 14, 23, 28 and 30 after storage at 4, 21, and 36 degrees C. Microbiological stability was evaluated under aseptic conditions using a laminar air flow station, with a grade A environment and a B background. The samples taken for microbiological analysis were collected immediately after preparation of the solutions and then after 7, 14, 21 and 28 days storage. At 4 degrees C the sufentanil citrate solution was stable for 23 days. At 21 degrees C the sufentanil citrate solution maintained chemical stability for 3 days, but thereafter the concentration of sufentanil decreased 15% from day 3 to day 8. At 36 degrees C a similar decrease was noticed from day 1 to day 3. On the contrary, the levobupivacaine hydrochloride solution maintained chemical stability for 28 days at 4 and 21 degrees C and for 23 days at 36 degrees C. The sufentanil-levobupivacaine mixture maintained chemical stability for 28 days at 4, 21 and 36 degrees C. The sufentanil and levobupivacaine solutions and the mixture studied maintained microbiological stability for 28 days. According to the chemical and microbiological stability studies, the sufentanil-levobupivacaine mixture in PP syringes could be stored for 28 days at 4 and 21 degrees C.
Anesthetics, Intravenous↗
Cytochrome P450 enzyme activity in five herbivorous, non-passerine bird species.
We examined hepatic cytochrome P450 activity in wild and hand-reared grey partridges (Perdix perdix), capercaillies (Tetrao urogallus) and ring-necked pheasants (Phasianus colchicus), as well as the enzyme activity in a variety of tissues of hand-reared Japanese quails (Coturnix coturnix japonica) and pigeons (Columba livia). Post-mortem decrease in hepatic enzyme activity in the grey partridge was measured. Hepatic 7-ethoxyresorufin-O-deethylase activity was similar in wild and hand-reared grey partridges and pheasants, but the activity was significantly lower in wild than in hand-reared capercaillies, probably resulting from their phenolic-rich diet. In the tissues of both quails and pigeons 7-ethoxycoumarin-O-deethylase exhibited the highest and 7-pentoxyresorufin-O-deethylase the lowest activity. Hepatic enzyme activity was significantly higher than that in other tissues. In the small intestine some activity could be found, reflecting some intestinal detoxication capacity. Enzyme activity decreased by 34-69% during the 30-min sampling period, which confirmed the importance of equalising sampling time to obtain comparable data. Because the hand-reared birds in this study were fed the same commercial diets, we assumed that the enzyme activity values detected reflect species differences without any induction by dietary secondary compounds.
Animal Husbandry↗
Comparative studies on the cytochrome p450-associated metabolism and interaction potential of selegiline between human liver-derived in vitro systems.
Selegiline was used as a model compound in a project aimed at comparing, evaluating, and integrating different in vitro approaches for the prediction of cytochrome p450 (p450)-catalyzed hepatic drug metabolism in humans (EUROCYP). Metabolic predictions were generated using homology modeling, cDNA-expressed p450 enzymes, human liver microsomes, primary cultured human hepatocytes, and precision-cut human liver slices. All of the in vitro systems correctly indicated the formation of two dealkylated metabolites, desmethylselegiline and methamphetamine. The metabolic instability of selegiline was demonstrated by all of the in vitro systems studied. Estimates of clearance varied from 16 l/h to 223 l/h. With the exception of one approach, all systems underpredicted the in vivo clearance in humans (236 l/h). Despite this, all approaches successfully classified selegiline as a high clearance compound. Homology modeling suggested the participation of CYP2B6 in the demethylation of selegiline and of CYP2D6 in the depropargylation of the drug. Studies with recombinant expressed enzymes and with human hepatic microsomal fraction supported the involvement of CYP2B6 but not of CYP2D6. These techniques also suggested the involvement of CYP1A2, CYP2C8, and CYP2C19 in the biotransformation of selegiline. In vitro, CYP2B6 was the most active form of p450 involved in selegiline metabolism. Metabolism by several enzymes operating in parallel implies a low interaction potential for the drug. None of the techniques alone was able to predict all aspects of the metabolic and kinetic behavior of selegiline in vivo. However, when used as an integrated package, all significant characteristics were predictable.
Cells, Cultured↗
Regulation of CYP3A5 by glucocorticoids and cigarette smoke in human lung-derived cells.
CYP3A5 is the major CYP3A form in the human lung, and it is inducible by dexamethasone in the human A549 lung adenocarcinoma cell line. In the present study, we characterized the nature and mechanism of this induction process. The induction of CYP3A5 mRNA was assessed by quantitative reverse transcriptase-polymerase chain reaction in A549 cells. About 4-fold induction was detected by nanomolar concentrations of dexamethasone and also by budenoside and beclomethasone dipropionate, glucocorticoids used for the inhalation treatment of bronchial asthma, whereas the CYP3A4 inducers mifepristone (RU486), rifampicin, clotrimazole, and nifedipine were without effect. The glucocorticoid induction was blocked by the glucocorticoid receptor (GR) antagonist RU486. In transient transfection assays to A549 cells, CYP3A5 5' regulatory region was activated by the dexamethasone treatment. In contrast, dexamethasone was unable to induce CYP3A5 transcription in GR-deficient COS-1 cells, but the induction could be achieved after GR cotransfection. The CYP3A5 expression was measured in alveolar macrophages from patients with respiratory diseases. The CYP3A5 expression level was decreased by smoking, but glucocorticoid therapy had no statistically significant effect. In conclusion, CYP3A5 is induced in the A549 cells by glucocorticoids through a GR-mediated pathway, whereas smoking may be able to depress CYP3A5 expression.
Analysis of Variance↗
[Anti-inflammatory agent and liver damage].
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Anti-Inflammatory Agents, Non-Steroidal↗
[Are old medications abandoned for nothing?].
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Cardiovascular Diseases↗
Lack of association between CYP2A5 induction and apoptosis in mouse primary hepatocytes.
Upregulation of mouse hepatic cytochrome P450 2A5 (CYP2A5) is a process closely associated with hepatocellular damage and formation of liver tumours. 2-Aminopurine, a protein kinase inhibitor modulating cell cycle control, was recently shown to strongly induce CYP2A5 in mouse hepatocytes. The objective of this study was to determine the association between CYP2A5 induction and apoptosis in mouse primary hepatocytes. Five well-characterised CYP2A5 inducers were tested for their ability to affect apoptosis rate, determined by immunohistochemical in situ 3'-end-labelling technique, in a primary mouse hepatocyte model. Transforming growth factor beta (TGFbeta) was used as a positive (proapoptotic) control. Phenobarbital, pyrazole and the mitogen-activated protein kinase inhibitor PD98059 did not significantly affect apoptosis rate in hepatocytes. Norcocaine induced apoptosis at 6 hr (1.8-fold) and 2-aminopurine 12 hr (1.4-fold) after treatment, which is considerably earlier than peaks in the amount of CYP2A5 mRNA. TGFbeta reduced CYP2A5 marker activity, coumarin 7-hydroxylase by 74%. These results indicate that in a primary hepatocyte model (a) there is no systematic correlation between apoptosis and CYP2A5 induction; (b) phenobarbital does not significantly affect the rate of apoptosis; and (c) the induction of apoptosis caused by the chemicals tested occurs considerable earlier than elevation of CYP2A5 expression. Thus, no causal link appears to exist between induction of CYP2A5 and apoptotic rate.
2-Aminopurine↗