BIOAVAILABILITY AND TOXICITY STUDIES OF MICROENCAPSULATED CHEMICALS

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The National Toxicology Program is exploring the feasibility of adopting microencapsulation as an alternative means of incorporating volatile, reactive, and/or unpalatable chemicals into animal feed for toxicologic studies. Oral (dosed-feed) toxicology studies are performed on those chemicals which are demonstrated to be adequately stabilized in the microcapsules, but released into the gastrointestinal tract to allow biological availability. The absorption of trichloroethylene (TCE), stabilized in gelatin- sorbitol microcapsules, was equivalent to that of neat TCE dissolved in corn oil when administered by gavage to Fischer 344 rats. In a 14-day repeated-dose study in F344 rats, similar toxic effects were produced by microencapsulated TCE given in feed as TCE dissolved in corn oil administered by gavage. These studies indicate that microencapsulation can provide an excellent alternative method for studying the oral toxicological properties of volatile chemicals in laboratory animals. 2-Ethylhexanol (2- EH) was stabilized in a starch matrix-type microcapsule. Bioequivalence studies have demonstrated that 2-EH is similarly absorbed after gavage administration of corn oil suspensions of microencapsulated 2-EH or neat 2-EH dissolved in corn oil. Future work will involve bioequivalence studies and toxicologic characterization of other microencapsulated chemicals.