title: Evidence of a threshold-effect for 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline liver carcinogenicity in F344/DuCrj rats.
abstract: To estimate potential human risk of exposure to a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a 2-year carcinogenicity test was conducted using male F344 rats administered MeIQx-containing diet at doses of 0 (control), 0.001, 1, and 100 ppm. The lowest dose 0.001 ppm was established as equivalent to the daily intake of this carcinogen in humans (0.2 to 2.6 microg/man/day). Significant decreases of survival rate and body weight gain were observed in rats treated with 100 ppm MeIQx. Histopathological examination revealed significant induction of hepatocellular carcinomas, adenomas, and development of glutathione S-transferase placental form-positive foci with MeIQx at 100 ppm. Moreover, the incidences of Zymbal's glands carcinoma, mammary fibroadenoma, and subcutaneous fibroma were found significantly increased in a 100 ppm MeIQx group. However, no significant induction of altered preneoplastic hepatocellular foci was observed in 0.001 and 1 ppm groups as compared to the controls. 8-Hydroxy-2'-deoxyguanosine levels in the rat liver DNA of the 100 ppm-treated group were not elevated, but MeIQx-DNA adduct formation increased as compared with the 1 ppm case, albeit without significance. No significant induction of any other neoplastic lesions related to the carcinogen administration was found in MeIQx-administered groups except for 100 ppm. These results imply that 1 ppm may be a no-effect level for MeIQx carcinogenesis.
authors.affiliation: Developmental Research Laboratories, Shionogi & Co., Ltd. 3-1-1 Futaba-cho, Toyonaka, Osaka 561-0825, Japan.
authors.forename: Takshi
authors.initials: T
authors.lastname: Murai
authors.forename: Satoru
authors.initials: S
authors.lastname: Mori
authors.forename: Jin Seok
authors.initials: JS
authors.lastname: Kang
authors.forename: Keiichirou
authors.initials: K
authors.lastname: Morimura
authors.forename: Hideki
authors.initials: H
authors.lastname: Wanibuchi
authors.forename: Yukari
authors.initials: Y
authors.lastname: Totsuka
authors.forename: Shoji
authors.initials: S
authors.lastname: Fukushima
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D018248:Adenoma, Liver Cell / Q000139:chemically induced* / Q000473:pathology; D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D002273:Carcinogens / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced* / Q000473:pathology; D018736:DNA Adducts / Q000096:biosynthesis / Q000737:chemistry; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D008113:Liver Neoplasms / Q000139:chemically induced* / Q000473:pathology; D008136:Longevity / Q000187:drug effects; D008297:Male; D019055:No-Observed-Adverse-Effect Level; D011230:Precancerous Conditions / Q000139:chemically induced* / Q000201:enzymology / Q000473:pathology; D011810:Quinoxalines / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D011810:Quinoxalines; C036990:2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline; D000080242:8-Hydroxy-2'-Deoxyguanosine; D005982:Glutathione Transferase; D003849:Deoxyguanosine