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 language||English (US)|
|Number of pages||8|
|State||Published - Jan 1 1999|
ASJC Scopus subject areas
- Cancer Research