Formation of DNA adducts by the food mutagen 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (4,8-DiMeIQx) in vitro and in vivo. Identification of a N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx adduct.
The covalent binding of the mutagenic N2-hydroxy metabolite of the food mutagen 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (4,8-DiMeIQx) to 2'-deoxynucleosides and DNA was investigated in vitro and in vivo. N2-Hydroxy-4,8-DiMeIQx reacted to a small extent spontaneously with 2-deoxyguanosine. However, acetylation of N2-hydroxy-4,8-DiMeIQx with acetic anhydride to form the N2-acetoxy derivative prior to reaction with 2-deoxyguanosine resulted in much higher yield of adduct. N2-Acetoxy-4,8-DiMeIQx did not form adducts with 2'-deoxyadenosine, 2'-deoxycytidine or 2'-deoxythymidine. The adduct formed between the N2-OH metabolite of 4,8-DiMeIQx and 2-deoxyguanosine was analysed by mass spectrometry and NMR spectroscopy and the structure of the adduct was shown to be N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx. N2-Acetoxy-4,8-DiMeIQx reacted with calf thymus DNA and formed a covalently bound 4,8-DiMeIQx residue, which could not be removed by repeated precipitations or solvent extractions. The 4,8-DiMeIQx-DNA was hydrolysed enzymatically with nuclease P1/acid phosphatase and HPLC analysis showed that 70% of the bound mutagen was recovered as N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx. An additional minor adduct accounting for approximately 15% of the bound mutagen showed UV spectral characteristics similar to N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx and is probably an undigested oligomer. 32P-Postlabelling analysis of calf thymus DNA modified with 4,8-DiMeIQx in vitro and liver DNA from rats dosed with 50 mg/kg 4,8-DiMeIQx showed a similar adduct pattern. In both samples N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx accounted for 60-70% of the bound mutagen. Thus, these results show that 4,8-DiMeIQx similar to other heterocyclic amines form adducts with C-8 of guanine both in vitro and in vivo via its N2-OH metabolite.
Institute of Toxicology, National Food Agency, Søborg, Denmark.
H
H
Frandsen
S
S
Grivas
R J
RJ
Turesky
R
R
Andersson
L O
LO
Dragsted
J C
JC
Larsen
D000107:Acetylation; D000818:Animals; D001711:Biotransformation; D002273:Carcinogens / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts / Q000378:metabolism*; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000032:analysis; D008297:Male; D009153:Mutagens / Q000378:metabolism*; D011810:Quinoxalines / Q000032:analysis* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002273:Carcinogens; D018736:DNA Adducts; D009153:Mutagens; C090536:N(2)-(2'-deoxyguanosin-8-yl)-2-amino-3,4,8-trimethyl-3H-imidazo(4,5-f)quinoxaline; D011810:Quinoxalines; D004247:DNA; D003849:Deoxyguanosine; C045421:3,4,8-trimethylimidazo(4,5-f)quinoxalin-2-amine