Kj. Rich et al., DEVELOPMENTAL-CHANGES IN HEPATIC ACTIVATION OF 2-AMINO-3,8-DIMETHYLIMIDAZO[4,5-F] QUINOXALINE IN RABBIT, Carcinogenesis, 17(3), 1996, pp. 555-558
MeIQx, potent bacterial mutagen formed when meat is cooked, requires m
etabolic activation to exert its genotoxicity, a reaction catalysed pr
imarily by CYP1A2 in adult mammals, Little is known about mammalian de
velopmental changes in the mutagenic activation of compounds such as M
eIQx, In rabbits we have shown previously that expression of CYP1A2 in
creases with age and is inducible by 3-methylcholanthrene (MC) from as
early as 4 days pre-parturition. We have therefore investigated the e
ffect of age on rabbit liver activation of MeIQx (assessed in an Ames
test using Salmonella typhimurium TA98) before and after treatment of
the animals with MC, MeIQx activation could not be detected using hepa
tic microsomal fractions from rabbits of <17 days of age. Thereafter a
ctivation increased with age to peak in weanling animals, Following MC
treatment MeIQx activation was increased, being detectable in samples
from rabbits as young as 9-11 days, The inducibility of MeIQx activat
ion increased with age, reaching a plateau between 17 and 35 days, The
se rates of activation were broadly parallel to the changes in CYP1A2
specific content. These results indicate that the ability of rabbit li
ver to activate MeIQx is dependent on CYP1A2 activity, the expression
of which is developmentally regulated, Although it has been establishe
d that human activation of MeIQx is also CYP1A2 dependent, whether a s
imilar situation exists in infant humans has yet to be determined, alt
hough there is evidence that CYP1A2-dependent activity reaches a peak
in late childhood.