TY - JOUR
T1 - Depentylation of [3H-pentyl]methyl-n-amylnitrosamine by rat esophageal and liver microsomes and by rat and human cytochrome P450 isoforms
AU - Chen, Sheng C.
AU - Wang, Xiaojie
AU - Xu, Guoping
AU - Zhou, Lin
AU - Vennerstrom, Jonathan L.
AU - Gonzalez, Frank
AU - Gelboin, Harry V.
AU - Mirvish, Sidney S.
PY - 1999/1/1
Y1 - 1999/1/1
N2 - 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.
AB - 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.
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M3 - Article
C2 - 9892192
AN - SCOPUS:0032589899
SN - 0008-5472
VL - 59
SP - 91
EP - 98
JO - Cancer Research
JF - Cancer Research
IS - 1
ER -