Effects of indole-3-carbinol on lung tumorigenesis and DNA methylation induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and on the metabolism and disposition of NNK in A/J mice.
The effects of indole-3-carbinol (I3C) on lung neoplasia induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were assessed in an A/J mouse pulmonary adenoma bioassay. Mice were administered corn oil or I3C (25 or 125 mumol/mouse/day) by gavage for 4 consecutive days. Two h after the final pretreatment, mice were administered a single dose of NNK (10 mumol/mouse) i.p. Pulmonary adenomas were quantitated 16 wk after NNK dosing. Mice pretreated with corn oil developed 10.7 tumors/mouse; I3C pretreatment at either dose level inhibited tumor multiplicity by approximately 40%. The effects of I3C on NNK-induced DNA methylation in the lungs and livers of A/J mice were assessed using the same dosing regimen as in the bioassay. Both dose levels of I3C inhibited pulmonary O6-methylguanine formation by at least 50%, but enhanced hepatic DNA methylation at 2 or at 6 h after NNK administration. The effects of I3C pretreatment on NNK metabolism were also investigated. Hepatic microsomes of I3C-pretreated mice showed increased formation of alpha-hydroxylation products, while no significant effect of I3C pretreatment was observed in pulmonary microsomes. The effects of I3C on [5-3H]NNK disposition were also evaluated. I3C pretreatment produced lower levels of total radioactivity in the lung when compared with controls. Additionally, lower proportions of NNK and its carcinogenic metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol were found in the lungs of I3C-pretreated mice. These results demonstrate that I3C inhibits NNK-induced lung neoplasia in A/J mice and suggest that the basis of this inhibition is the decrease in O6-methylguanine formation in A/J lung caused by I3C pretreatment. This decrease in lung DNA methylation appears to be due to the decreased bioavailability of NNK and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in the lungs of I3C-treated mice which, in turn, may be a result of increased metabolic alpha-hydroxylation of NNK by the liver.
Morse
M A
MA
Section of Nucleic Acid Chemistry, Naylor Dana Institute for Disease Prevention, American Health Foundation, Valhalla, New York.
LaGreca
S D
SD
Amin
S G
SG
Chung
F L
FL
D000236:Adenoma / Q000139:chemically induced; D000818:Animals; D002273:Carcinogens / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008175:Lung Neoplasms / Q000139:chemically induced*; D008745:Methylation; D051379:Mice; D009602:Nitrosamines / Q000378:metabolism* / Q000633:toxicity
D002273:Carcinogens; D007211:Indoles; D009602:Nitrosamines; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D004247:DNA; C016517:indole-3-carbinol