Effects of dietary conjugated linoleic acid on DNA adduct formation of PhIP and IQ after bolus administration to female F344 rats

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Abstract
Meats cooked at high temperatures contain mutagenic heterocyclic amines such as 2‐amino‐l‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) and 2‐amino‐3‐methylimidazo[4,5‐f]quinoline (IQ). In female Fischer 344 rats, IQ is a multiorgan carcinogen, whereas PhIP induces mammary adenocarcinomas. For IQ and PhIP, N‐hydroxylation, catalyzed by microsomal cytochrome P‐450 1A1 and/or 1A2, and then esterification, especially O‐acetylation, are the principal steps leading to DNA adduct formation. Conjugated linoleic acid (CLA) is a mixture of conjugated linoleic acid isomers found in various meat and dairy products. We have examined the effect of dietary CLA on DNA adduct formation by PhIP and IQ in female Fischer 344 rats. Four‐week‐old animals were maintained on AIN‐76A diet without or with CLA (4% wt/wt) and treated with IQ or PhIP (50 mg/kg by gavage) after two weeks. Animals were killed (4/group) one, four, and eight days later. DNA isolated from mammary epithelial cells, liver, colon, and white blood cells was analyzed for carcinogen‐DNA adducts by 32P‐postla‐beling assays. On Day 1, dietary CLA significantly inhibited adduct formation (82.0%) in mammary epithelial cells in IQ‐but not in PhIP‐treated rats. In the colon, dietary CLA significantly inhibited PhIP‐DNA adduct formation (18.7%) on Day 8 but increased IQ‐DNA adduct formation (30.5%) on Day 8. Dietary CLA had no effect on adduct levels in liver or white blood cells. Calf thymus DNA was incubated with N‐hydroxy‐PhIP or ‐IQ in the presence of acetyl‐CoA. Enzymatic activation was catalyzed by liver or mammary cytosol. A two‐week pretreatment with 2% (wt/wt) dietary CLA had no effect on O‐acetyltransferase‐catalyzed IQ‐ or PhIP‐DNA adduct formation. It is concluded, under certain conditions, that dietary CLA can lower IQ‐ and PhlP‐DNA adduct formation. Overall, however, the major mode of action of CLA is probably by a mechanism other than the inhibition of the N‐hydroxylation and subsequent O‐acetylation of PhIP or IQ.

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