The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform
Thomas Ebner - One of the best experts on this subject based on the ideXlab platform.
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Concept: The Use of Targeted Immunoaffinity Proteomics for Routine Assessment of In Vitro Enzyme Induction.
Journal of pharmaceutical sciences, 2017Co-Authors: Caroline Maclean, Frederik Weiß, Oliver Poetz, Thomas EbnerAbstract:In vitro investigations on Enzyme Induction are indispensable for assessing drug-drug interactions of drug candidates. Regulatory bodies require measurement of changes of mRNA in cultured human hepatocytes. However, such data provide only indirect assessments of effects of Enzyme Induction in vivo. We describe the quantification of cytochrome P450 (CYP) Enzyme protein levels by liquid chromatography-mass spectrometry for the routine assessment of Enzyme Induction. Protein concentration of CYP1A2, 2B6, 3A4, and 2C8 were measured in human hepatocytes after incubation with prototypical Enzyme inducers and drug candidate BI-X using an antibody-based capturing method. In addition, CYP mRNA levels and CYP Enzyme activities were determined. Except for CYP2B6, mRNA levels consistently showed more pronounced Induction effects than CYP activity or CYP protein concentration. Induction of CYP activities was better reflected on the level of CYP protein. The described method requires small sample amounts and can be integrated in routine in vitro Enzyme Induction studies using tissue culture in 48- and 96-well plates. Assessment of changes of Enzyme protein levels adds valuable information to conventional measurements of Enzyme Induction and can improve the use of in vitro data for the prediction of clinical outcomes.
Gregory L. Kedderis - One of the best experts on this subject based on the ideXlab platform.
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Extrapolation of in vitro Enzyme Induction data to humans in vivo
Chemico-biological interactions, 1997Co-Authors: Gregory L. KedderisAbstract:Enzyme Induction generally increases the rate and extent of xenobiotic metabolism in vitro, but physiological constraints can dampen these effects in vivo. Biotransformation kinetics determined in hepatocytes in vitro can be extrapolated to whole animals based on the hepatocellularity of the liver, since the initial velocity of an Enzyme-catalyzed reaction is directly proportional to the total Enzyme present in the cell. The biotransformation kinetics of various xenobiotics determined with isolated hepatocytes in vitro have been shown to accurately predict pharmacokinetics in whole animals. Analysis of the kinetic data, using physiologically based pharmacokinetics, allows extrapolation of xenobiotic biotransformation across dose routes and species in a biologically realistic context. Several fold variations were observed in the bioactivation of the hepatotoxicant furan by isolated human hepatocytes, due to Induction of cytochrome P450 2E1. Extrapolation of these data to humans in vivo showed that furan bioactivation was limited by hepatic blood flow delivery of the substrate. One important consequence of hepatic blood flow limitation is that the amount of metabolite formed in the liver is unaffected by increases in Vmax due to Enzyme Induction. Therefore, interindividual variations in cytochrome P450 2E1 among human populations would not affect the bioactivation of many rapidly metabolized hazardous chemical air pollutants. The hepatic blood flow limitation of biotransformation is also observed after oral bolus dosing of rapidly metabolized compounds. More slowly metabolized xenobiotics, such as therapeutic agents, are only partially limited by hepatic blood flow and other processes.
M Schütt - One of the best experts on this subject based on the ideXlab platform.
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The duration of Enzyme Induction in orocaecal transit time measurements.
European journal of clinical nutrition, 2007Co-Authors: Klaus D. Wutzke, M SchüttAbstract:In this study, the duration of Enzyme Induction provoked by unlabelled lactose ureide (LU) in orocaecal transit time (OCTT) measurements with lactose-[13C]ureide (13C-LU) was evaluated. Experimental study. University of Rostock, Children's Hospital, Research Laboratory. Fifteen healthy adults aged 19–54 years. One-half gram of 13C-LU was administered together with a continental breakfast. After 1 week, the test was repeated after pre-dosing of 5 × 100 mg LU on the day before the study began. The 13C-LU ingestion was repeated under identical conditions but without pre-dosing 1 and 3 weeks after pre-dosing. Expired air samples were taken over 14 h. 13CO2-enrichment was measured by isotope ratio mass spectrometry (SerCon, Crewe, UK). The OCTT was calculated from the interval between 13C-LU administration and the detection of a significant and sustained 13C-rise of 2 delta over baseline in breath. Without pre-dosing, an OCTT of 419±82 min was measured. The pre-dosing resulted in higher 13C-enrichments and caused a significant OCTT shortening of 311±99 min (P=0.028). One and 3 weeks after pre-dosing, the measured OCTT again increased to 404±124 and 379±103 min, respectively. Pre-dosing with LU before pulse labelling with 13C-LU led to an Induction of Enzyme activity and resulted in a definitive estimation of the OCTT when using a threshold of 2 delta over baseline. After 1 and 3 weeks, respectively, the OCTT was no longer significantly different to those without pre-dosing, indicating the disappearance of Enzyme Induction. Therefore, a pre-dosing with LU on the day before 13C-LU ingestion is essential for OCTT measurements.
Caroline Maclean - One of the best experts on this subject based on the ideXlab platform.
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Concept: The Use of Targeted Immunoaffinity Proteomics for Routine Assessment of In Vitro Enzyme Induction.
Journal of pharmaceutical sciences, 2017Co-Authors: Caroline Maclean, Frederik Weiß, Oliver Poetz, Thomas EbnerAbstract:In vitro investigations on Enzyme Induction are indispensable for assessing drug-drug interactions of drug candidates. Regulatory bodies require measurement of changes of mRNA in cultured human hepatocytes. However, such data provide only indirect assessments of effects of Enzyme Induction in vivo. We describe the quantification of cytochrome P450 (CYP) Enzyme protein levels by liquid chromatography-mass spectrometry for the routine assessment of Enzyme Induction. Protein concentration of CYP1A2, 2B6, 3A4, and 2C8 were measured in human hepatocytes after incubation with prototypical Enzyme inducers and drug candidate BI-X using an antibody-based capturing method. In addition, CYP mRNA levels and CYP Enzyme activities were determined. Except for CYP2B6, mRNA levels consistently showed more pronounced Induction effects than CYP activity or CYP protein concentration. Induction of CYP activities was better reflected on the level of CYP protein. The described method requires small sample amounts and can be integrated in routine in vitro Enzyme Induction studies using tissue culture in 48- and 96-well plates. Assessment of changes of Enzyme protein levels adds valuable information to conventional measurements of Enzyme Induction and can improve the use of in vitro data for the prediction of clinical outcomes.
Yuichi Sugiyama - One of the best experts on this subject based on the ideXlab platform.
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the quantitative prediction of in vivo Enzyme Induction caused by drug exposure from in vitro information on human hepatocytes
Drug Metabolism and Pharmacokinetics, 2005Co-Authors: Motohiro Kato, Koji Chiba, Masato Horikawa, Yuichi SugiyamaAbstract:There have been no reports of the quantitative prediction of Induction for drug-metabolizing Enzymes in humans. We have tried to predict such Enzyme Induction in humans from in vitro data obtained using human hepatocytes. The in vitro and in vivo data on Enzyme Induction by inducers, such as rifampicin, phenobarbital and omeprazole, were collected from the published literature. The degree of Enzyme Induction in humans was compared with that predicted from in vitro data on human hepatocytes. Using the in vivo data, we calculated the hepatic intrinsic clearance of typical CYP substrates, such as midazolam and caffeine, before and after inducer treatment and estimated the Induction ratios of hepatic intrinsic clearance following treatment. In the in vitro studies, the amount of mRNA or Enzyme and Enzyme activity in human hepatocytes, with or without an inducer, were compared and the Induction ratios were estimated. The unbound mean concentration was taken as an index of drug exposure and the Induction ratios in the in vivo and in vitro studies were compared. The unbound mean concentrations of inducers used in the in vitro studies were higher than those in the in vivo studies. The maximum Induction ratios by inducers in the in vitro studies were higher than those in the in vivo studies. The Induction ratio for rifampicin, omeprazole, troglitazone, dexamethasone and phenobarbital increased as the unbound mean concentration increased to reach a constant value. The Induction of CYP3A and 1A was analyzed by the Emax model. The maximum Induction ratio (Emax) and the concentration at half maximum Induction (EC50) for rifampicin, omeprazole, troglitazone, dexamethasone and phenobarbital were 12.3, 0.847 micromol/L, 2.36, 0.225 micromol/L, 6.86, 0.002 micromol/L, 8.30, 9.32 micromol/L, and 7.62, 58.4 micromol/L, respectively. The Emax and EC50 of omeprazole for CYP1A were 12.02 and 0.075 micromol/L, respectively. The predicted Induction ratio of all those inducers, except for omeprazole, based on the Emax and EC50 values obtained from the in vitro data were similar to the observed values. On the whole, a good correlation between the observed and predicted Induction ratio of omeprazole was observed (r=0.768, p<0.05), although the predicted Induction ratio was higher than the observed value. In conclusion, the present study suggests that it is possible to predict quantitatively the CYP3A Enzyme Induction from hepatocyte data.