Linked Life Data

10385214

Source:http://linkedlifedata.com/resource/pubmed/id/10385214

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
1999-8-3
pubmed:abstractText
We have clarified the contribution of the different enzymes involved in the N-debutylation of halofantrine in liver microsomes in man. The effect of ketoconazole and cytochrome P450 (CYP) 3A substrates on halofantrine metabolism has also been studied. The antimalarial drug halofantrine is metabolized into one major metabolite, N-debutylhalofantrine. In microsomes from nine livers from man, N-debutylation of halofantrine was highly variable with apparent Michaelis-Menten constant V(max) and K(m) values of 215+/-172 pmol min(-1) mg(-1) and 48+/-26 micromol L(-1), respectively, (mean+/-standard deviation). Formation of N-debutylhalofantrine was cytochrome P450 (CYP)-mediated. Studies using selective inhibitors of individual CYPs revealed the role of CYP 3As in the formation of N-debutylhalofantrine. alpha-Naphthoflavone, a CYP 3A activator, increased metabolite formation. In microsomes from 12 livers from man the rate of N-debutylation of halofantrine correlated strongly with CYP 3A4 relative levels (P = 0.002) and less strongly, but significantly, with CYP 2C8 levels (P = 0.025). To characterize CYP-mediated metabolism of halofantrine further, incubations were performed with yeast microsomes expressing specific CYP 3A4, CYP 3A5, CYP 2D6, CYP 2C8 and CYP 2C19 from man. The rate of formation of N-debutylhalofantrine was six- and twelvefold with CYP 3A4 than with CYP 3A5 and CYP 2C8, respectively. CYP 2D6 and CYP 2C19 did not mediate the N-debutylation of halofantrine, but, because in-vivo CYP 2C8 is present at lower concentrations than CYP 3A in the liver in man, the involvement of CYP 3As would be predominant. Diltiazem, erythromycin, nifedipine and cyclosporin (CYP 3A substrates) inhibited halofantrine metabolism. Similarly, ketoconazole inhibited, non-competitively, formation of N-debutylhalofantrine with an inhibition constant, K(i), of 0.05 microM. The theoretical percentage inhibition of halofantrine metabolism in-vivo by ketoconazole was estimated to be 99%. These results indicate that both CYP 3A4 and CYP 3A5 metabolize halofantrine, with major involvement of CYP 3A4. In-vivo, the other CYPs have a minor role only. Moreover, strong inhibition, and consequently increased halofantrine cardiotoxicity, might occur with the association of ketoconazole or other CYP 3A4 substrates.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
http://linkedlifedata.com/resource/pubmed/chemical/Aryl Hydrocarbon Hydroxylases, http://linkedlifedata.com/resource/pubmed/chemical/Benzoflavones, http://linkedlifedata.com/resource/pubmed/chemical/CYP2C19 protein, human, http://linkedlifedata.com/resource/pubmed/chemical/CYP3A protein, human, http://linkedlifedata.com/resource/pubmed/chemical/Cytochrome P-450 CYP2D6, http://linkedlifedata.com/resource/pubmed/chemical/Cytochrome P-450 CYP3A, http://linkedlifedata.com/resource/pubmed/chemical/Cytochrome P-450 Enzyme System, http://linkedlifedata.com/resource/pubmed/chemical/Isoenzymes, http://linkedlifedata.com/resource/pubmed/chemical/Ketoconazole, http://linkedlifedata.com/resource/pubmed/chemical/Mixed Function Oxygenases, http://linkedlifedata.com/resource/pubmed/chemical/Phenanthrenes, http://linkedlifedata.com/resource/pubmed/chemical/alpha-naphthoflavone, http://linkedlifedata.com/resource/pubmed/chemical/halofantrine
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0022-3573
pubmed:author
pubmed:issnType
Print
pubmed:volume
51
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
419-26
pubmed:dateRevised
2010-11-18
pubmed:meshHeading
pubmed:year
1999
pubmed:articleTitle
Halofantrine metabolism in microsomes in man: major role of CYP 3A4 and CYP 3A5.
pubmed:affiliation
Laboratoire de Pharmacie Clinique, Université de Paris XI, Chatenay-Malabry, France.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't