Josyula S, He Y H, Ruch R J, Schut H A
Department of Pathology, Medical College of Ohio, Toledo 43614-5806, USA.
Nutr Cancer. 1998;32(3):132-8. doi: 10.1080/01635589809514731.
The dietary mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mammary carcinogen in the female Fischer (F344) rat and a colon carcinogen in the male F344 rat. To exert its carcinogenicity, it is believed that 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 conjugated linoleic acid (CLA) inhibits chemical carcinogenesis in various experimental models. We have examined the effect of dietary CLA on PhIP-DNA adduct formation in female F344 rats. Four-week-old animals were maintained on AIN-76A diet without or with CLA (1%, 0.5%, and 0.1% wt/wt) for 57 days. PhIP 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 epithelial cells (MEC), colon, and white blood cells (WBC) was analyzed for PhIP-DNA adducts by 32P-postlabeling assays. On Day 43, CLA inhibited adduct formation in the liver (up to 58%) in a dose-dependent manner. CLA also inhibited hepatic adduct levels (29-39%) on Day 50 (at 1.0% and 0.5% CLA) and on Day 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 dietary CLA. On Day 57, adduct levels in MEC, liver, colon, and WBC were 0-30.3%, 8.6-41.7%, 21.5-50.7%, and 7.5-11.8%, respectively, of those on Day 43. Northern blot analysis of liver RNA showed that dietary CLA did not affect steady-state levels of CYP 1A1 or 1A2 mRNA. It is concluded that dietary CLA inhibits PhIP-DNA adduct formation in liver and WBC but that those in MEC and the colon are unaffected when a low-level dietary regimen of carcinogen and inhibitor was used. In inhibiting PhIP-DNA adduct formation, CLA does not appear to act by inhibiting CYP 1A1 or 1A2 expression.
膳食诱变剂2-氨基-1-甲基-6-苯基咪唑[4,5-b]吡啶（PhIP）是雌性Fischer（F344）大鼠的乳腺致癌物，也是雄性F344大鼠的结肠致癌物。据信，PhIP要发挥其致癌性，需要与DNA形成加合物，这一过程需要细胞色素P-450 1A1和/或1A2（CYP 1A1和/或1A2）将PhIP进行N-羟基化，以及对由此形成的羟胺进行进一步酯化。膳食共轭亚油酸（CLA）在各种实验模型中均可抑制化学致癌作用。我们研究了膳食CLA对雌性F344大鼠中PhIP-DNA加合物形成的影响。将四周龄的动物饲养在不含或含有CLA（1%、0.5%和0.1%重量/重量）的AIN-76A饮食中57天。从第14天至42天，在饮食中添加PhIP（0.04%重量/重量）。在第43天、50天和57天处死动物（每组4只）。通过32P后标记分析，对从肝脏、乳腺上皮细胞（MEC）、结肠和白细胞（WBC）中分离的DNA进行PhIP-DNA加合物分析。在第43天，CLA以剂量依赖的方式抑制肝脏中的加合物形成（高达58%）。CLA在第50天（1.0%和0.5%的CLA）和第57天（0.5%的CLA时为53%）也抑制肝脏加合物水平（29%-39%）。CLA在第50天显著降低白细胞中的加合物水平（63%-70%）。MEC和结肠中的加合物不受膳食CLA的影响。在第57天，MEC、肝脏、结肠和白细胞中的加合物水平分别为第43天时的0%-30.3%、8.6%-41.7%、21.5%-50.7%和7.5%-11.8%。对肝脏RNA进行的Northern印迹分析表明，膳食CLA不影响CYP 1A1或1A2 mRNA的稳态水平。得出的结论是，当采用低水平的致癌物和抑制剂饮食方案时，膳食CLA可抑制肝脏和白细胞中PhIP-DNA加合物的形成，但MEC和结肠中的加合物不受影响。在抑制PhIP-DNA加合物形成过程中，CLA似乎不是通过抑制CYP 1A1或1A2的表达来发挥作用的。
