Binding of benzo[a]pyrene metabolites in the rat intestinal lumen by magnetic polyethyleneimine microcapsules following an intragastric dose of [14C]benzo[a]pyrene.

Semi-permeable magnetic polyethyleneimine (PEI) microcapsules have been developed to trap carcinogens and their metabolites in vivo and their time-dependent binding of a model carcinogen, [14C]benzo[a]pyrene [( 14C]BaP), is studied within the intestinal lumen. Overall, approximately 0.5% of an intragastric BaP dose was bound by these microcapsules recovered from faeces with specific binding of metabolites (nmol/10(6) recovered microcapsules) being similar in the 0-24-h and 24-48-h periods, but approximately 10-fold lower in the 48-72-h period. Successive extractions of microcapsules with ammoniacal methanol, 2.5 N HCl, methanol and dimethylsulfoxide released approximately 60% of bound radiolabeled and the unextracted radiolabel was presumed to have been bound covalently. By contrast, greater than 90% of bound radiolabel was extractable from the faeces of the treated animals and from microcapsules treated in vitro with [14C]7,8-dihydroxy-9,10-epoxytetrahydrobenzo[a]pyrene (BaPDE), indicating that the in vivo microcapsule-bound metabolites were not derived either from adsorbed faecal material or from [14C]BaPDE formed in situ. A time-dependent appearance of BaP 3,6-dione was found. Also the qualitative and quantitative patterns of metabolites trapped by microcapsules, as assayed by h.p.l.c., were consistent only with a unique set of BaP metabolites being bound within the intestinal lumen. Hence these carcinogen-binding microcapsules can be used to investigate the in situ formation of carcinogen metabolites within the intestinal tract.