Biomaterial Database

In vitro metabolism of the biguanide antimalarials in human liver microsomes: evidence for a role of the mephenytoin hydroxylase (P450 MP) enzyme. 1990

N A Helsby, and S A Ward, and R E Howells, and A M Breckenridge

Department of Parasitology, Liverpool School of Tropical Medicine.

The metabolic activation of the arylbiguanide antimalarials proguanil (PG) and chlorproguanil (CPG) has been investigated in liver microsomes from three human livers. All three microsomal preparations activated the biguanides. The kinetic parameters for PG metabolism to cycloguanil (CG) were Km 21.8, 29.6 and 26.4 microM and Vmax 1.5, 5.9, and 8.2 pmol min-1 mg-1. The values for CPG conversion to chlorcycloguanil (CCG) were Km 12.9, 19.7 and 26.1 microM and Vmax 5.7, 4.8 and 3.6 pmol min-1 mg-1. The metabolic activation of both biguanides was competitively inhibited by the anticonvulsant mephenytoin. Sparteine and tolbutamide had no effect on biguanide metabolism. These data suggest an involvement of the mephenytoin hydroxylase enzyme, which exhibits a genetic polymorphism in man, in the metabolic activation of the biguanide antimalarials.

UI	MeSH Term	Description	Entries
D008617	Mephenytoin	An anticonvulsant effective in tonic-clonic epilepsy (EPILEPSY, TONIC-CLONIC). It may cause blood dyscrasias.	Methoin,Methyl Phenetoin,5-Ethyl-3-Methyl-5-Phenylhydantoin,Mefenetoin,Mesantoin,Phenantoin,5 Ethyl 3 Methyl 5 Phenylhydantoin,Phenetoin, Methyl
D008862	Microsomes, Liver	Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough.	Liver Microsomes,Liver Microsome,Microsome, Liver
D002727	Proguanil	A biguanide compound which metabolizes in the body to form cycloguanil, an anti-malaria agent.	Chlorguanid,Chloroguanide,Bigumal,Chloriguane,Chloroguanide Hydrochloride,Paludrin,Paludrine,Proguanil Hydrochloride,Hydrochloride, Chloroguanide,Hydrochloride, Proguanil
D003577	Cytochrome P-450 Enzyme System	A superfamily of hundreds of closely related HEMEPROTEINS found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (MIXED FUNCTION OXYGENASES). In animals, these P-450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (BIOTRANSFORMATION). They are classified, according to their sequence similarities rather than functions, into CYP gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the CYP1, CYP2, and CYP3 gene families are responsible for most drug metabolism.	Cytochrome P-450,Cytochrome P-450 Enzyme,Cytochrome P-450-Dependent Monooxygenase,P-450 Enzyme,P450 Enzyme,CYP450 Family,CYP450 Superfamily,Cytochrome P-450 Enzymes,Cytochrome P-450 Families,Cytochrome P-450 Monooxygenase,Cytochrome P-450 Oxygenase,Cytochrome P-450 Superfamily,Cytochrome P450,Cytochrome P450 Superfamily,Cytochrome p450 Families,P-450 Enzymes,P450 Enzymes,Cytochrome P 450,Cytochrome P 450 Dependent Monooxygenase,Cytochrome P 450 Enzyme,Cytochrome P 450 Enzyme System,Cytochrome P 450 Enzymes,Cytochrome P 450 Families,Cytochrome P 450 Monooxygenase,Cytochrome P 450 Oxygenase,Cytochrome P 450 Superfamily,Enzyme, Cytochrome P-450,Enzyme, P-450,Enzyme, P450,Enzymes, Cytochrome P-450,Enzymes, P-450,Enzymes, P450,Monooxygenase, Cytochrome P-450,Monooxygenase, Cytochrome P-450-Dependent,P 450 Enzyme,P 450 Enzymes,P-450 Enzyme, Cytochrome,P-450 Enzymes, Cytochrome,Superfamily, CYP450,Superfamily, Cytochrome P-450,Superfamily, Cytochrome P450
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D006899	Mixed Function Oxygenases	Widely distributed enzymes that carry out oxidation-reduction reactions in which one atom of the oxygen molecule is incorporated into the organic substrate; the other oxygen atom is reduced and combined with hydrogen ions to form water. They are also known as monooxygenases or hydroxylases. These reactions require two substrates as reductants for each of the two oxygen atoms. There are different classes of monooxygenases depending on the type of hydrogen-providing cosubstrate (COENZYMES) required in the mixed-function oxidation.	Hydroxylase,Hydroxylases,Mixed Function Oxidase,Mixed Function Oxygenase,Monooxygenase,Monooxygenases,Mixed Function Oxidases,Function Oxidase, Mixed,Function Oxygenase, Mixed,Oxidase, Mixed Function,Oxidases, Mixed Function,Oxygenase, Mixed Function,Oxygenases, Mixed Function
D000962	Antimalarials	Agents used in the treatment of malaria. They are usually classified on the basis of their action against plasmodia at different stages in their life cycle in the human. (From AMA, Drug Evaluations Annual, 1992, p1585)	Anti-Malarial,Antimalarial,Antimalarial Agent,Antimalarial Drug,Anti-Malarials,Antimalarial Agents,Antimalarial Drugs,Agent, Antimalarial,Agents, Antimalarial,Anti Malarial,Anti Malarials,Drug, Antimalarial,Drugs, Antimalarial
D001189	Aryl Hydrocarbon Hydroxylases	A large group of cytochrome P-450 (heme-thiolate) monooxygenases that complex with NAD(P)H-FLAVIN OXIDOREDUCTASE in numerous mixed-function oxidations of aromatic compounds. They catalyze hydroxylation of a broad spectrum of substrates and are important in the metabolism of steroids, drugs, and toxins such as PHENOBARBITAL, carcinogens, and insecticides.	Microsomal Monooxygenases,Xenobiotic Monooxygenases,Hydroxylases, Aryl Hydrocarbon,Monooxygenases, Microsomal,Monooxygenases, Xenobiotic
D001711	Biotransformation	The chemical alteration of an exogenous substance by or in a biological system. The alteration may inactivate the compound or it may result in the production of an active metabolite of an inactive parent compound. The alterations may be divided into METABOLIC DETOXICATION, PHASE I and METABOLIC DETOXICATION, PHASE II.
D013034	Sparteine	A quinolizidine alkaloid isolated from several FABACEAE including LUPINUS; SPARTIUM; and CYTISUS. It has been used as an oxytocic and an anti-arrhythmia agent. It has also been of interest as an indicator of CYP2D6 genotype.	7,14-Methano-2H,6H-dipyrido(1,2-a:1',2'-e)(1,5)diazocine, dodecahydro-, (7S-(7alpha,7aalpha,14alpha,14abeta))-,Lupinidin,Lupinidine,Pachycarpine,D-sparteine,Depasan Retard,Genisteine Alkaloid,L-Sparteine,Pachycarpine Sulfate (1:1), Pentahydrate, (7S-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Hydrochloride, (7R-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Hydrochloride, (7S-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Hydroiodide, (7R-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Monohydrochloride, (7R-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Monohydroiodide, (7R-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Sulfate,Sparteine Sulfate (1:1), (7S-(7alpha,7aalpha,14alpha,14aalpha))-Isomer,Sparteine Sulfate (1:1), (7S-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine Sulfate Anhydrous,Sparteine, (+)-Isomer,Sparteine, (-)-Isomer,Sparteine, (7R-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine, (7R-(7alpha,7abeta,14alpha,14abeta))-Isomer,Sparteine, (7S-(7alpha,7aalpha,14alpha,14aalpha))-Isomer,Sparteine, (7S-(7alpha,7aalpha,14alpha,14abeta))-Isomer,Sparteine, (7S-(7alpha,7abeta,14alpha,14abeta))-Isomer,alpha-Isosparteine,beta-Isosparteine,Anhydrous, Sparteine Sulfate,Sulfate Anhydrous, Sparteine,alpha Isosparteine,beta Isosparteine