Coumarin metabolism by rat esophageal microsomes and cytochrome P450 2A3.
Coumarin metabolism by rat esophageal microsomes and cytochrome P450 2A3.
复制标题
大鼠食管微粒体和细胞色素 P450 2A3 的香豆素代谢。
DOI：
10.1021/tx010065v
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发表时间：
2001
影响因子：
4.1
通讯作者：
Murphy,SE
中科院分区：
文献类型：
--
作者：
vonWeymarn,LB;Murphy,SE
The rat esophagus is strikingly sensitive to tumor induction by nitrosamines, and it has been hypothesized that this tissue contains cytochrome P450 enzymes (P450s) which catalyze the metabolic activation of these carcinogens. The metabolic capacity of the esophagus is not well characterized. In the study described here, the products of14C-coumarin metabolism by rat esophageal microsomes were identified and quantified. Metabolite characterization was by LC/MS/MS and GC/MS and comparison to standards, quantification was by radioflow HPLC. The coumarin metabolites formed by rat esophageal microsomes were compared to those formed by P450 2A3. The major metabolites formed by esophageal microsomes were 8-hydroxycoumarin,o-hydroxyphenylacetaldehyde (o-HPA), ando-hydroxyphenylacetic acid (o-HPAA). A smaller amount of 5-hydroxycoumarin, about one-third the 8-hydroxycoumarin, was also formed.o-HPA ando-HPAA are products of coumarin 3,4-epoxidation. The relative rates of coumarin 8-hydroxylation and 3,4-epoxidation were similar. Coumarin 8-hydroxylation has not previously been reported as a major pathway in any tissue, and no P450s have yet been reported to catalyze this reaction. P450 2A3 catalyzed both the 7-hydroxylation and 3,4-epoxidation of coumarin. P450 2A3 was previously characterized as a coumarin 7-hydroxylase, however, in this study, we report that it catalyzes the formation ofo-HPA more efficiently. TheKmandVmaxwere 1.3 ± 0.35 μM and 0.65 ± 0.06 nmol/min/nmol P450 for coumarin 7-hydroxylation and 1.4 ± 0.58 μM and 3.1 ± 0.46 nmol/min/nmol P450 foro-HPA formation.
