title: Prenatal toxicity and lack of carcinogenicity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) following transplacental exposure.
abstract: Accumulating evidence from human and experimental animal studies indicates that consumption of heterocyclic amines (HA), derived from cooked meat and fish, may be associated with an increased incidence of cancer. Experiments were initiated to assess the role of one of these compounds, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), as a potential transplacental carcinogen, as well as to evaluate whether in utero exposure to IQ results in the induction of fetal cytochrome P4501A1 (Cyp1a1), P4501B1 (Cyp1b1), and/or glutathione S-transferase (GST). Inducible, or responsive, backcrossed fetuses resulting from a cross between congenic C57BL/6 (Ah(d)Ah(d)) nonresponsive female mice and C57BL/6 (Ah(b)Ah(b)) responsive male mice were transplacentally exposed to olive oil or 6.25, 12.5, or 25 mg/kg of IQ on day 17 of gestation. No macroscopically or microscopically visible liver, lung, or colon tumors were found in the transplacentally treated offspring by one year after birth. Ethoxyresorufin O-deethylase (EROD) and 1-chloro-2,4-dinitrobenzene assays were performed to evaluate whether transplacental exposure to IQ results in the induction of fetal Cyp1a1 and GST, respectively, in lung and liver tissues. Results showed levels of EROD and GST activity in tissues of IQ-treated mice to be very close, if not identical, to those of mice treated with olive oil. Similarly, ribonuclease protection assay data showed that the levels of Cyp1a1 and Cyp1b1 RNA in tissues of IQ-treated mice were not significantly different from those of oil-treated controls. Previous studies have shown that the developing organism expresses very low levels of Cyp1a2. Thus, in utero exposure to IQ does not lead to induction of Cyp1a1, Cyp1a2, or Cyp1b1 in the fetal compartment, thereby maintaining the low levels of these activating enzymes in the developing organism. Taken together, these data imply that, at least under the conditions employed for these experiments, IQ may not play an important role in transplacentally induced tumorigenesis.
authors.affiliation: Department of Physiology and Pharmacology, Comprehensive Cancer Center, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Gressani
authors.forename: S
authors.initials: S
authors.lastname: Leone-Kabler
authors.forename: M G
authors.initials: MG
authors.lastname: O'Sullivan
authors.forename: A J
authors.initials: AJ
authors.lastname: Townsend
authors.forename: M S
authors.initials: MS
authors.lastname: Miller
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001835:Body Weight / Q000187:drug effects; D015197:Carcinogenicity Tests; D002273:Carcinogens / Q000633:toxicity*; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics; D017931:DNA Primers / Q000737:chemistry; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D005333:Fetus / Q000187:drug effects / Q000201:enzymology; D005982:Glutathione Transferase / Q000096:biosynthesis; D007178:Inbreeding; D008098:Litter Size / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008168:Lung / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008431:Maternal-Fetal Exchange; D051379:Mice; D008810:Mice, Inbred C57BL; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D011804:Quinolines / Q000633:toxicity*; D012313:RNA / Q000378:metabolism; D015996:Survival Rate
chemical_list: D002273:Carcinogens; D017931:DNA Primers; D011804:Quinolines; C029216:2-amino-3-methylimidazo(4,5-f)quinoline; D012313:RNA; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D005982:Glutathione Transferase