Depentylation of [3H-pentyl]methyl-n-amylnitrosamine by rat esophageal and liver microsomes and by rat and human cytochrome P450 isoforms

Sheng C. Chen, Xiaojie Wang, Guoping Xu, Lin Zhou, Jonathan L. Vennerstrom, Frank Gonzalez, Harry V. Gelboin, Sidney S. Mirvish

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

Methyl-n-amylnitrosamine (MNAN) induces esophageal cancer in rats, probably involving activation by cytochromes P450. We studied the metabolic depentylation of MNAN. [3H-4,5-pentyl]-MNAN and [3H-2,3-pentyl]. MNAN were synthesized, purified, and incubated with rat esophageal microsomes (REM) or rat liver microsomes (RLM) to give [3H]pentaldehyde (depentylation), an indicator of MNAN activation. [3H]Pentaldehyde was determined by high- performance liquid chromatography of its 2,4-dinitrophenylhydrazone. Adding 5 mM semicarbazide to incubations increased the observed depentylation (except that due to CYP2E1) by >60%. MNAN depentylation by REM and uninduced and induced RLM showed K(m) values of 64, 610, and 170-330 μM, respectively (V(max): 20, 220, and 160-1270 pmol/mg protein/min, respectively). The depentylation of 100 μM MNAN by REM was inhibited 98% by CO and 65% by coumarin preincubated for 15 min with REM (K(i), 120 μM) but was unaffected by antibodies inhibitory to various P450s. MNAN inhibited coumarin 7- hydroxylation by RLM and CYP2A6 (K(i), 3000 and 320 μM, respectively). REM showed slight coumarin 7-hydroxylase activity. MNAN depentylation by RLM was 41% inhibited by an antibody to CYP2C11. K(m) for rat CYP2E1, human CYP2E1, and human CYP2A6 was 210, 115, and 17 μM, respectively (V(max:) 900, 570, and 120 pmol/nmol P450/min, respectively). We conclude that MNAN activation by REM is probably due to a P450 related to CYP2A3, a rodent nasal P450.

Original languageEnglish (US)
Pages (from-to)91-98
Number of pages8
JournalCancer Research
Volume59
Issue number1
StatePublished - Jan 1 1999

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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