Inhibition of DNA adduct formation of PhIP in female F344 rats by dietary conjugated linoleic acid

The dietary mutagen 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) is a mammary carcinogen in the female Fischer (F344) rat and a colon carci nogen in the male F344 rat. To exert its carcinogenicity, it is believed th at PhIP needs to form adducts with DNA, a process requiring N-hydroxylation of PhIP by cytochromes P-450 1A1 and/or 1A2 (CYP 1A1 and/or 1A2), as well as further esterification of the hydroxylamine thus formed. Dietary congreg ated linoleic acid (CLA) inhibits chemical carcinogenesis in various experi mental models. We have examined the effect of dietary CLA on PhIP-DNA adduc t formation in female F344 rats. Four-week-old animals were maintained on A IN-76A diet without or with CLA (1%, 0.5%, and 0.1% wt/wt) for 57 days. PhI P was added to the diets (0.04% wt/wt) from Days 14-42. Animals were killed (4/group) on Days 43, 50, and 57 DNA isolated from liver, mammary epitheli al cells (MEC), colon, and white blood cells (WBC) was analyzed for PhIP-DN A adducts by P-32-postlabeling assays. On Day 43, CLA inhibited adduct form ation in the liver (up to 58%) in a dose-dependent manner. CLA also inhibit ed hepatic adduct levels (29-39%) on Day 50 (at 1.0% and 0.5% CLA) and on D ay 57 (53% at 0.5% CLA). CLA significantly reduced adduct levels in the WBC on Day 50 (63-70%). Adducts in MEC and the colon were not affected by diet ary CLA. On Day 57 adduct levels in MEG, liver, colon, and WBC were 0-30.3% , 8.6-41.7%, 21.5-50.7%, and 75-11.8%, respectively, of those on Day 43. No rthern blot analysis of liver RNA showed that dietary CLA did not affect st eady-state levels of CYP 1A1 or 1A2 mRNA. It is concluded that dietary CLA inhibits PhIP-DNA adduct formation in liver and WBC hut that those in MEC a nd the colon are unaffected when a low-level dietary regimen of carcinogen and inhibitor was used. In inhibiting PhIP-DNA adduct formation, CLA does n ot appear to act by inhibiting CYP 1A1 or 1A2 expression.