A. Suzuki et al., ESTABLISHMENT OF A SALMONELLA TESTER STRAIN HIGHLY SENSITIVE TO MUTAGENIC HETEROCYCLIC AMINES, Cancer research, 58(9), 1998, pp. 1833-1838
Heterocyclic amines (HCAs) that are present in cooked foods require me
tabolic activation to exert their genotoxicity. They undergo activatio
n via N-hydroxylation by cytochrome P450 1A2 (CYP1A2), followed by O-e
sterification by O-acetyltransferase (OAT). To develop a Salmonella te
ster strain that is highly sensitive to mutagenic HCAs, we introduced
a coexpression plasmid (p1A2OR) carrying human CYP1A2 and NADPH-CYP re
ductase cDNAs and an expression plasmid (pOAT) carrying Salmonella OAT
to Salmonella typhimurium TA1538 to yield a TA1538/ARO strain. The TA
1538/ARO strain was proven to express the enzymes, as indicated by hig
h activities of 7-ethoxyresorufin O-deethylase and isoniazid N-acetyla
se. The TA1538/ARO strain exhibited very high sensitivity to mutagenic
HCAs 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3-methylimi
dazo[3,5-f]quinoline (IQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quino
xaline and a somewhat higher sensitivity to 2-amino-1-methyl-6-phenyli
midazo[4,5-b]pyridine compared with the parent Ames tester strain TA15
38. The minimum concentrations of 2-amino-3,3-dimethylimidazo[4,5-f]qu
inoline, IQ, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and 2-amin
o-1-methyl-6-phenylimidazo[4,5-b]pyridine giving positive results were
defined by evidence that the number of colonies increased in a dose-d
ependent manner and reached a number two times higher than that obtain
ed by vehicle alone as a control in the TA1538/ARO strain at concentra
tions of 0.3, 3, 30, and 1000 pM, respectively. When the membrane and
cytosol fractions prepared from TA1358/ARO were added to a mixture con
taining the parental TA1538, the sensitivity of TA1538 to IQ was much
lower than that seen with TA1538/ARO. These results indicate that the
intracellular expression of drug-metabolizing enzymes makes the establ
ished strain of Salmonella highly sensitive to mutagenic HCAs.