PROTECTION BY CHLOROPHYLLIN AND INDOLE-3-CARBINOL AGAINST 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE (PHIP)-INDUCED DNA-ADDUCTS AND COLONIC ABERRANT CRYPTS IN THE F344 RAT

The most abundant heterocyclic amine in fried ground beef, 2-amino-1-m ethyl-6-phenylimidazo[4,5-b]pyridine (PhIP), induces colon carcinomas in the male F344 rat, The potential chemopreventive effects of two com pounds, namely, the 'interceptor molecule' chlorophyllin (CHL) and a m odulator of carcinogen activation, indole-3-carbinol (I3C), were exami ned in a PhIP colon carcinogenesis model, During weeks 3 and 4 of a 16 -week study, F344 rats were given PhIP by oral gavage (50 mg/kg body w eight, alternating days), Inhibitors were given either before and duri ng PhIP exposure, after PhIP treatment, or continuously for 16 weeks, Treatment of rats with 0.1% CHL in the drinking water inhibited the fo rmation of aberrant crypt foci (ACF) with greater than or equal to 4 c rypts/focus, from 1.4 +/- 0.9 in controls to 0.7 +/- 0.3 following pos t-initiation CHL treatment, and to 0.3 +/- 0.5 in rats given CHL conti nuously for 16 weeks (mean +/- SD; P < 0.05), Potent inhibition of PhI P-induced ACF occurred following initiation, postinitiation and contin uous exposure to 0.1% I3C in the diet, Using the initiation protocol, I3C completely inhibited the induction of ACF with greater than or equ al to 4 crypts/focus, In a separate experiment, rats were given 0.1% C HL in the drinking water or 0.1% I3C in the diet for 4 weeks, At the e nd of week 3, animals received 50 mg PhIP/kg body weight by single ora l gavage and PhIP-DNA adducts were quantified in the colon and several other tissues by P-32-postlabeling analysis, In addition, the urine a nd feces were collected to study the effects of inhibitor treatment on PhIP metabolism and excretion, No significant protection against PhIP -DNA adduct formation was detected in the colon after CHL dosing, nor was a consistent pattern of CHL inhibition observed in several other t issues, In contrast, I3C shifted the time-course of adducts in all tis sue; compared with controls, adducts were increased by I3C at 6 h but decreased at 24 h and 7 days following PhIP treatment, Analysis of uri ne metabolites revealed that I3C and CHL decreased the excretion of un metabolized PhIP and 4'-hydroxy-much less than PhIP but increased the phase II detoxification products PhIP-4'-O-glucuronide and PhIP-4'-sul fate, In the feces, the elimination of unmetabolized PhIP was increase d from 54,5% in controls to similar to 67% in CHL-treated rats and dec reased to 28% in rats given I3C (P < 0.05), These results support a pr otective role for CHL and I3C against PhIP-induced colon carcinogenesi s through mechanisms which alter the uptake or metabolism of the carci nogen, and by suppression in the post-initiation phase.