Trapping of chemical carcinogens with magnetic polyethyleneimine microcapsules: I. Microcapsule preparation and in vitro reactivity of encapsulated nucleophiles.

In this paper we describe the synthesis and characterization of magnetic microcapsules, intended for use in vivo, and which contain polyethyleneimine nucleophilic targets capable of trapping electrophilic carcinogens. The microcapsules, 15-50 microns in diameter, consist of a semipermeable cross-linked nylon membrane surrounding core polyethyleneimine and magnetite. These microcapsules can be readily manipulated and extracted from aqueous suspensions by magnetic fields. Core polyethyleneimine was released after membrane rupture by sonication. Magnetic hemoglobin microcapsules were also prepared but were unsuitable due to precipitation of hemoglobin within the core. Treatment by proteolytic enzymes that are present in the gastrointestinal tract caused microcapsule damage resulting in protein release, whereas polyethyleneimine microcapsules remained unaffected. After incubation with N-[methyl-14C]-N-nitrosourea, (1) the microcapsules retained covalently bound radiolabel, both in core polyethyleneimine and the microcapsule membrane. The efficiency of the binding of 1 was investigated by varying the polymer concentration during microcapsule manufacture. These type of microcapsules appear to have the desired properties for investigating carcinogen exposure in the mammalian gastrointestinal tract. They can be prepared easily and reproducibly, contain sufficient magnetite to allow their facile recovery from aqueous suspensions, are easily broken to release soluble core polyethyleneimine, and are stable to hydrolytic enzymes (trypsin) in vitro.