Two independent radioimmunoassay techniques for the major phenobarbital-inducible cytochrome P-450 (PB P-450) of rat liver microsomal membranes are described. The first technique employs as the source of radiolabelled antigen the products of translation in vitro labelled with [35S]methionine. The second technique employs purified antigen labelled with 125I and is quicker, less expensive and mor...

Exogenously administered heme is incorporated into rat hepatic cytochrome P-450 in vivo (Correia, M. A., Farrell, G. C. Schmid, R. S., Ortiz de Montellano, P. R., Yost, G. S., and Mico, B. A. (1979) J. Biol. Chem. 254, 15-17). This was demonstrated in allylisopropylacetamide (AIA)-treated rats by the formation of a radioactive adduct derived from the porphyrin of the administered [3H]heme and A...

Electron transfer to rat liver microsomal cytochrome P-450 of 14 alpha-methyl group demethylation of 24,25-dihydrolanosterol (C30-sterol) has been studied with a new radio-high-performance liquid chromatography assay. The monooxygenase is dependent upon NADPH plus oxygen, insensitive to CN-, and sensitive to CO. Microsomal oxidation is also sensitive to trypsin digestion, and reactivation is de...

A systematic analysis of the heteroactivation of CYP3A-mediated carbamazepine 10,11-epoxidation has been investigated in three different in vitro systems, namely recombinant CYP3A4 and CYP3A5, human liver microsomes (HLMs) and cryopreserved human hepatocytes. The effect of 10 endogenous steroids and flavonoids was studied over a range of substrate and effector concentrations. A novel heteroacti...

Due to the importance of in vitro cytochrome P450 (P450) induction assay to assess the possible drug-drug interaction events, the recent US Food and Drug Administration draft guidance and European Medicines Agency guideline recommend to assess P450 induction using fresh or cryopreserved hepatocytes at mRNA level and/or enzyme activity level. Although cryopreserved hepatocytes are commercially a...

In addition to the known effects on drug metabolism and response, functional polymorphisms of genes coding for xenobiotic-metabolizing enzymes (XME) play a role in cancer. Genes coding for XME act as low-penetrance genes and confer modest but consistent and significant risks for a variety of cancers related to the interaction of environmental and genetic factors. Consistent evidence supports a ...

The effect of 4-(4-chlorobenzyl)pyridine (4-CBP) on rat hepatic microsomal cytochrome P450 (P450) and its molecular species (CYP2B1, 2E1, 3A2, 2C11, and 2C12), and on drug-metabolizing enzyme activities were examined in vivo and in vitro. Treatment of rats with 4-CBP resulted in the induction of P450 and drug-metabolizing enzymes in a dose-dependent manner, but it was markedly inhibitory at hig...

Due to the importance of in vitro cytochrome P450 (P450) induction assay to assess the possible drug-drug interaction events, the recent US Food and Drug Administration draft guidance and European Medicines Agency guideline recommend to assess P450 induction using fresh or cryopreserved hepatocytes at mRNA level and/or enzyme activity level. Although cryopreserved hepatocytes are commercially a...

Due to the importance of in vitro cytochrome P450 (P450) induction assay to assess the possible drug-drug interaction events, the recent US Food and Drug Administration draft guidance and European Medicines Agency guideline recommend to assess P450 induction using fresh or cryopreserved hepatocytes at mRNA level and/or enzyme activity level. Although cryopreserved hepatocytes are commercially a...

A procedure is described for isolating submicrosomal particles from the livers of rabbits treated with phenobarbital, without the use of proteolytic or lipolytic enzymes. The preparation contains 2.5 mpmoles of P-450 per mg of protein, whereas the content of P-420 and cytochrome bs is less than 1% of this. The preparation shows no distinct TPNHor DPNH-cytochrome c reductase activity, but DPNH-f...