L. Patrice McDaniel

Chemoprotection against the formation of colon DNA adducts from the food-borne carcinogen 2-amino-1 -methyl-6-phenylimidazo[4,5-b ]pyridine (PhIP) in the rat

The mutagenic heterocyclic aromatic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), is a pyrolysis product in cooked foods that has been shown to be a rat colon carcinogen and has been implicated in the etiology of human colon cancer. In order to identify chemoprotection strategies that could be carried out in humans, a pilot study was conducted in which PhIP-DNA-adduct levels were quantified in the colons of male F344 rats that had been subjected to 16 different putative chemoprotection regimens, followed by a gavage of PhIP (50 mg/kg) and sacrifice 24 h later. The 16 treatments (Oltipraz, benzylisothiocyanate, diallyl sulfide, garlic powder, ethoxyquin, butylated hydroxyanisole, glutathione, indole-3-carbinol, alpha-angelicalactone, kahweol/cafestol palmitates, quercetin, green tea, black tea, tannic acid, amylase-resistant starch, and physical exercise) comprised sulfur-containing compounds, antioxidants, flavonoids, diterpenes, polyphenols, high dietary fiber, etc. The strongest inhibition of PhIP-DNA adduct formation in the colon was observed upon pretreatment with black tea, benzylisothiocyanate, and a mixture (1:1) of kahweol:cafestol palmitates, which resulted in 67, 66, and 54% decreases in colon PhIP-DNA adduct levels, as compared with controls. Preliminary studies on their mechanism of action indicated that only kahweol:cafestol caused a substantial induction of glutathione S-transferase isozymes (GSTs) that are thought to be important in the detoxification of PhIP. Notably, this induction occurred in the liver rather than in the colon.

Mutagenicity and DNA adduct formation by aristolochic acid in the spleen of Big Blue® rats †

Aristolochic acid (AA) is a potent human nephrotoxin and carcinogen. We previously reported that AA treatment resulted in DNA damage and mutation in the kidney and liver of rats. In this study, we have determined the DNA adducts and mutations induced by AA in rat spleen. Big Blue® transgenic rats were gavaged with 0, 0.1, 1.0, and 10.0 mg AA/kg body weight five‐times/week for 3 months. Three DNA adducts, [7‐(deoxyadenosin‐N6‐yl)‐aristolactam I, 7‐(deoxyadenosin‐N6‐yl)‐aristolactam II and 7‐(deoxyguanosin‐N2‐yl)‐aristolactam I], were identified by 32P‐postlabeling. Over the dose range studied, there were strong linear dose‐responses for AA‐DNA adduct formation in the treated rat spleens, ranging from 4.6 to 217.6 adducts/108 nucleotides. Spleen cII mutant frequencies also increased in a dose‐dependent manner, ranging from 32.7 to 286.2 × 10−6 in the treated animals. Mutants isolated from the different treatment groups were sequenced; analysis of the resulting spectra indicated that there was a significant difference between the pattern of mutation in the 10 mg/kg AA‐treated and the vehicle control rats. A:T → T:A transversion was the major type of mutation in AA‐treated rats, whereas G:C → A:T transition was the main type of mutation inthe vehicle controls. These results indicate that AA is genotoxic in the spleen of rats exposed under conditions that result in DNA adduct formation and mutation induction in kidney and liver. Environ. Mol. Mutagen., 2012.