Linked Life Data

2539558

Source:http://linkedlifedata.com/resource/pubmed/id/2539558

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
1989-5-23
pubmed:abstractText
Certain toxic effects of phenytoin are thought to result from its cytochrome P-450-catalyzed bioactivation to a reactive arene oxide intermediate that binds covalently to proteins. Using an in vitro system, we examined an alternative hypothesis based upon the cooxidation of phenytoin to a reactive free radical intermediate by prostaglandin synthetase (PGS), horseradish peroxidase, or thyroid peroxidase. Microsomes from hepatic, thyroid, seminal vesicular, or pulmonary tissues, or PGS or horseradish peroxidase, were incubated with the appropriate enzymatic cofactors to study activities of cytochromes P-450 (NADPH), PGS (arachidonic acid), thyroid peroxidase (guiaicol, H2O2), and horseradish peroxidase (H2O2). The production of potentially teratogenic, reactive phenytoin intermediates during in vitro incubations was estimated by the amount of radiolabeled phenytoin bound covalently to microsomal protein or bovine serum albumin and by the detection of a free radical intermediate using ESR spectrometry. Arachidonic acid-dependent bioactivation of phenytoin was demonstrated for purified PGS and ram seminal vesicles (RSV), as well as for liver, lung, and kidney. Optimal arachidonate concentrations varied substantially for different tissues. Arachidonate-dependent binding of phenytoin with PGS and RSV was reduced to baseline levels by coincubation with the cyclooxygenase inhibitor indomethacin. Hydrogen peroxide-dependent covalent binding of phenytoin was observed with thyroid peroxidase and horseradish peroxidase, and binding was significantly reduced in these systems and in PGS and RSV by coincubation with the peroxidase inhibitor methimazole. Glutathione, the antioxidants caffeic acid and butylated hydroxyanisole, and the free radical trapping agent alpha-phenyl-N-t-butylnitrone (PBN) all significantly reduced arachidonate-dependent phenytoin binding. Oxygen uptake was increased in a dose-dependent manner by the arachidonate-dependent bioactivation of phenytoin by PGS. ESR spin-trapping techniques using PBN indicated the generation of a free radical intermediate during the metabolism of phenytoin by PGS. These results suggest that the hydroperoxidase component of PGS, as well as thyroid peroxidase and other peroxidases, can bioactivate phenytoin to a reactive free radical intermediate, which may be toxicologically relevant.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0026-895X
pubmed:author
pubmed:issnType
Print
pubmed:volume
35
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
504-11
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1989
pubmed:articleTitle
In vitro bioactivation of phenytoin to a reactive free radical intermediate by prostaglandin synthetase, horseradish peroxidase, and thyroid peroxidase.
pubmed:affiliation
Faculty of Pharmacy, University of Toronto, Canada.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't