Effect of dietary casein levels on activation of promutagens in the spiral Salmonella mutagenicity assay. II. Studies with induced rat liver S9.
In the previous study (Mutation Res., this issue), we showed that increased levels of dietary casein as the sole protein source for male F344 rats decreased the ability of the uninduced liver S9s to activate 2-aminoanthracene (2AN) to a mutagen in strain TA98 using the spiral Salmonella mutagenicity assay. No effects of dietary casein levels were noted for the ability of uninduced liver S9s to activate the promutagens aflatoxin B1 (AFB) and benzo[a]pyrene (BAP). In the present study, we have extended this study to include liver S9s induced with either Aroclor 1254, phenobarbital or 3-methylcholanthrene (3MC). S9s were derived from individual male F344 rats fed for 6 weeks on semisynthetic diets containing 8%, 12% or 22% methionine-supplemented casein as the sole source of protein (diets were made isocaloric by adjusting the corn starch content). Rats were housed in large, raised-bed cages by groups of three/diet/inducing agent. S9 activation mixtures were prepared at 5 mg of S9 protein/ml of S9 mix. Slopes from the linear portions of the mutagenicity dose-response curves were analyzed by ANOVA comparisons. Assays used to elucidate the phase I activities of microsomal preparations were cytochrome P-450 content, cytochrome-c reductase activity, flavin-containing monooxygenase activity, 7-ethoxyresorufin O-deethylation (EROD) activity, N-demethylation of benzphetamine, and para-nitrophenol O-deethylation. Phase II activities were assayed by estimating glutathione (GSH) content and measuring the metabolism of 1-chloro-2,4-dinitrobenzene (CDNB) by glutathione S-transferase in cytosolic preparations. None of the phase I or phase II endpoints were significantly affected by dietary casein levels. In general, increasing levels of dietary casein resulted in increased body and liver wet weight and amount of S9 protein. Aroclor-induced S9s from rats fed the 22% or 12% casein diet were most effective at activating AFB, depending on the lot of Aroclor used for induction; these divergent results were replicated with two groups of rats for each lot of Aroclor. The observed differences between Aroclor lots are assumed to arise from variation in the mix of PCB isomers. The Aroclor-induced S9s did not exhibit any casein-related effects for the activation of BAP or 2AN. For 3MC-induced S9s, the 12% casein diets produced S9s with the highest ability to activate AFB and BAP when standardized for protein content. Phenobarbital-induced S9s did not demonstrate any dietary casein-related effects on the activation of the three model promutagens. These results illustrate the complex interaction between dietary levels of casein, enzyme inducing agent and promutagen.
Woodall
G M
GM
Department of Toxicology, North Carolina State University, Raleigh 27695, USA.
Dauterman
W C
WC
DeMarini
D M
DM
D016604:Aflatoxin B1 / Q000493:pharmacokinetics; D000818:Animals; D000873:Anthracenes / Q000493:pharmacokinetics; D001564:Benzo(a)pyrene / Q000493:pharmacokinetics; D001711:Biotransformation; D001835:Body Weight; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D004798:Enzymes / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008297:Male; D009152:Mutagenicity Tests; D009153:Mutagens / Q000493:pharmacokinetics*; D009929:Organ Size; D051381:Rats; D011916:Rats, Inbred F344; D012475:Salmonella / Q000235:genetics*
D000873:Anthracenes; D002364:Caseins; D004044:Dietary Proteins; D004798:Enzymes; D009153:Mutagens; D001564:Benzo(a)pyrene; C006593:2-anthramine; D016604:Aflatoxin B1