IN-VIVO AFLATOXIN B-1 METABOLISM AND HEPATIC DNA ADDUCTION IN ZEBRAFISH (DANIO-RERIO)

The zebrafish (Danio rerio) is assuming prominence in developmental ge netics research. By comparison, little is known of tumorigenesis and n othing is known of carcinogen metabolism in this species. This study e valuated the ability of zebrafish to metabolize a well-characterized h uman carcinogen, aflatoxin B-1 (AFB(1)), to phase I and phase II metab olites and assessed hepatic AFB(1)-DNA adduction in vivo. Fish ip inje cted with 50-400 mu g [H-3]AFB(1)/kg body wt displayed a linear dose r esponse for hepatic DNA binding at 24 hr. AFB(1)-DNA adduct levels amo ng treatments showed no statistical difference over the period from 1 to 21 days after injection, suggesting poor adduct repair in this spec ies. DNA binding in female fish was 1.7-fold higher than that in males (p < 0.01). An in vitro AFB(1) metabolism assay verified that zebrafi sh liver extracts oxidize AFB(1) to the 8,9-epoxide proximate electrop hile (K-m = 79.0 +/- 16.4 mu M, V-max = 11.7 +/- 1.4 pmol/min/mg prote in at 28 degrees C). The excretion of AFB(1) and its metabolites was a lso examined by HPLC. As is typical of other fish studied, major metab olites excreted were aflatoxicol (AFL) and aflatoxicol-glucuronide (AF L-g), followed by unreacted AFB(1). AFL appeared as early as 5 min aft er injection, whereas AFL-g was a significant metabolite after 18 hr. This study shows that in vivo administration of AFB(1) to zebrafish re sults in moderate adduction of the carcinogen to liver DNA and that ze brafish have the capacity for both phase I and phase II metabolism of AFB(1). The approximate fourfold difference between rainbow trout and zebrafish AFB(1)-DNA covalent binding index appears insufficient to ex plain the relative resistance of zebrafish to dietary AFB(1) hepatocar cinogenicity. (C) 1997 Academic Press.