Slobodan Rendić

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Interaction of ranitidine with liver microsomes

1. Ranitidine interacts with liver microsomes from rats pretreated with different inducers of cytochrome P-450 to produce substrate difference optical spectra with a peak at 426-429 nm and a trough at 390-400 nm. 2. Cytochrome P-450 reduced with dithionite in the presence of ranitidine produced substrate difference spectra with a peak at 447 nm. 3. Ks values for the interaction of ranitidine with cytochrome P-450 (not reduced), calculated from double reciprocal plots, were in the range 1.4-2.8 mM. 4. The O-dealkylation of 7-ethoxycoumarin and of p-nitroanisole was inhibited by the presence of ranitidine and the inhibition was of a mixed type. Kii and Kis values were: for inhibition of 7-ethoxycoumarin dealkylation, 0.8 to 9 mM, and 0.16 to 0.67 mM, respectively; for inhibition of p-nitroanisole dealkylation, 5.8 to 13.7 mM, and 1 to 4.5 mM, respectively. 5. The I50 values for 7-ethoxycoumarin dealkylation was 1.8 mM and for p-nitroanisole dealkylation about 7.2 mM (microsomes from phenobarbital-pretreated rats). 6. The e.p.r. spectra of cytochrome P-450 from phenobarbital-pretreated rats, in the presence of ranitidine, reveal two types of interaction depending on the ranitidine concentration. At lower concentrations of ranitidine, a ligand exchange reaction with an oxygen atom is indicated, and at higher concentrations are with nitrogenous or thioether ligand of ranitidine.

Circular dichroism and gel filtration study of binding of prochiral and chiral 1,4-benzodiazepin-2-ones to human serum albumin.

Abstract Combining circular dichroism (c.d.) and gel filtration method in studying the binding of chiral ((S)/R)- 1 ) and prochiral ( 2 . diazepam and 3 . desmethyldiazepam) benzodiazepines to human serum albumin (HSA), the following results were obtained: c.d. measurements revealed that both enantiomers of 1 are bound by HSA with different affinities. Gel filtration measurements revealed the following data on binding; (a) the HSA affinity for ( S)- 1 is about 40 times higher than for ( R)- 1 , (b) for ( S)- 1 exist two independent and nonequivalent sites of high affinity and for ( R)- 1 two independent equivalent sites of low affinity, (c) at equimolar concentrations of 1 and HSA, (S)-enantiomer is bound up to 5 3 per cent, but (R)-enantiomer up to 18 per cent only; at the same ratio of ligand to protein prochiral 3 was bound up to 56 per cent.

Metabolism of anabolic steroids by recombinant human cytochrome P450 enzymes. Gas chromatographic-mass spectrometric determination of metabolites.

Metabolism of steroid hormones with anabolic properties was studied in vitro using human recombinant CYP3A4, CYP2C9 and 2B6 enzymes. The enzyme formats used for CYP3A4 and CYP2C9 were insect cell microsomes expressing human CYP enzymes and purified recombinant human CYP enzymes in a reconstituted system. CYP3A4 enzyme formats incubated with anabolic steroids, testosterone, 17alpha-methyltestosterone, metandienone, boldenone and 4-chloro-1,2-dehydro-17alpha-methyltestosterone, produced 6beta-hydroxyl metabolites identified as trimethylsilyl (TMS)-ethers by a gas chromatography-mass spectrometry (GC-MS) method. When the same formats of CYP2C9 were incubated with the anabolic steroids, no 6beta-hydroxyl metabolites were formed. Human lymphoblast cell microsomes expressing human CYP2B6 incubated with the steroids investigated produced traces of 6beta-hydroxyl metabolites with testosterone and 17alpha-methyltestosterone only. We suggest that the electronic effects of the 3-keto-4-ene structural moiety contribute to the selectivity within the active site of CYP3A4 enzyme resulting in selective 6beta-hydroxylation.

General approach to chiroptical characterization of binding of prochiral and chiral 1,4-benzodiazepin-2-ones to human serum albumin.

Abstract General interpretation of chiroptical characteristics of binding process of prochiral (Z) and chiral (Z ∗ ) 1,4-benzodiazepin-2-ones to human serum albumin (HSA) is presented. Interpretation of binding of Z studied by circular dichroism (CD) measurements allows us to conclude that the CD within the bands of bound Z is mainly due to the chirality of the first sphere and that the greatest part of 3 is bound in the M-conformation. For Z ∗ we conclude that ( S )-1 binds on both binding sites of HSA in the M-conformation, while ( R )-1 binds on two different binding sites in opposite conformations. Furthermore we conclude that binding via two nitrogens of the benzodiazepine, i.e. at two ends of the chromophoric system is rather more probable than via ring A.

Toxic effects and a structure-property study of organic explosives, propellants, and related compounds

(1994). Toxic Effects and a Structure-Property Study of Organic Explosives, Propellants, and Related Compounds. Drug Metabolism Reviews: Vol. 26, No. 4, pp. 717-738.

STEREOSELECTIVE IN VITRO AROMATIC OXYGENATION OF CHIRAL 1,4-BENZODIAZEPIN-2-ONES

Publisher Summary This chapter focuses on stereoselective in vitro aromatic oxygenation of chiral 1,4-benzodiazepin-2-ones. Biotransformation pathways and pharmacology of drugs belonging to the group of l,4-benzodiazepin-2-ones are being extensively investigated. In these investigations, structure-activity relationships are of special interest. The most frequent in vivo biotransformations of 1,4-benzodiazepine derivatives are N(l)-dealkylation, hydroxylation of the heterocyclic and aromatic rings, hydrolysis of the lactam and azomethyne bonds, and N(4)-oxidation and formation of O-glucuronides. Actual metabolism depends on the substituents. Stereoselectivity in oxidative metabolism, presumably residing in cytochrome P-450, has been repeatedly reported for various drugs. The chapter describes a study in which stereoselectivity in biotransformation of enantiomeric 7-chloro-l,3-dihydro-3methyl-5-phenyl-2H-l,4-benzodiazepin-2-ones and their N(1)-methyl derivatives was analyzed. These experiments were carried out in vitro, using postmitochondrial and microsomal fractions of rat liver as enzyme sources. Results suggested that oxygenases involved in aromatic oxygenation of chiral 1,4-benzodiazepin-2-ones in vitro act stereoselectively on the S-form. Hydroxylation in position C(3), however, was found to be nonstereoselective. Hydroxylation in position C(3) and hydroxylation of aromatic rings should be catalyzed by different species of cytochrome P-450.