Inhibition of dibenzo[a,l] pyrene-induced multi-organ carcinogenesis by dietary chlorophyllin in rainbow trout

Cancer chemoprevention by dietary chlorophyllin (CHL) was investigated in a rainbow trout multi-organ tumor model. In study 1, duplicate groups of 130 juvenile trout were treated for 2 weeks with control diet, 500 p.p.m. dibe nzo[a,l]pyrene (DB[a,l]P) or 500 p.p.m. DB[a,l]P + 2052 p.p.m. CHL, then re turned to control diet. DB[a,l]P alone proved somewhat toxic but induced hi gh tumor incidences in liver (61%), stomach (91%) and swimbladder (53%) 11 months after initiation. CHL co-feeding abrogated DB[a,l]P acute toxicity a nd reduced tumor incidences to 18% in liver, 34% in stomach and 3% in swimb ladder (P less than or equal to 0.01), A second tumor and DNA adduct study using a non-toxic initiation protocol (200 p.p.m. DB[a,l]P +/- 4000 p.p.m. CHL for 4 weeks) confirmed these results. Potential CHL inhibitory mechanis ms were investigated, Dietary CHL inhibited hepatic DB[a,l]P-DNA adducts in the two tumor studies by 89 and 76%, respectively. CHL was shown to comple x strongly with DB[a,l]P (K-d1,K-2 = 1.59 + 0.01 mu M, stoichiometry 2CHL:D B[a,l]P) and strongly inhibited DB[a,l]P mutagenesis in the Salmonella assa y, Significant inhibition occurred at CHL concentrations substantially less than stoichiometric with DB[a,l]P and thus not reflecting simple DB[a,l]P sequestration via complexation, These initial findings suggest that CHL che moprevention reflects complexation that might limit DB[a,l]P uptake in vivo , antimutagenic mechanisms such as catalytic degradation of the proximate e lectrophile in target cells, or both. These results demonstrate that dietar y CHL is a reproducibly effective chemopreventive agent for DB[a,l]P multi- organ tumorigenesis in trout and suggest that reduced DB[a,l]P-DNA adducts may be predictive biomarkers of CHL reduction of DB[a,l]P-initiated hepatic tumor.