Intra-intestinal kinetics and absorption mechanism of digestion-resisitant maclomolecular food components

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Egg albumin (ovalbumin:OVA) is resistant to proteolytic hydrolysis and known to be a major allergenic protein in egg allergy. By using egg albumin as a model macromoleculer food component, the absorption of OVA from mouse intestinal tract into body and the kinetics of OVA in circulating peripheral blood were investigated. After oral administration of OVA (10 mg) to mice, peripheral blood was collected and then serum was separated from coagulated blood. The OVA concentration in the serum was determined to be 10-50 ng/ml by EUSA, and the OVA in the serum was concentrated by immuno-affinity precipitation using anti-OVA antibodies coupled to Sepharose. In SDS-PAGE analysis, the OVA recovered from peripheral blood revealed a single major protein band with a molecular mass identical to intact OVA and a minor band with a slightly smaller molecular mass. No band corresponding to OVA fragments with smaller molecular masses, which had been demonstrated to be the major components of OVA antigens in the mouse small intestine. Furthermore, two-dimensional gel electrophoresis demonstrated that the OVA recovered from blood was composed of 4-6 protein spots with different pI but with the same molecular mass, and that the basic protein spots were dominant as compared with those of intacl OVA, suggesting that the pI of OVA was shifted to more basic ones during the intestinal absorption or the migration in circulating blood. Such a pI shift was not observed for OVA incubated in vitro with mouse serum. Taken together, it is suggested that a small portion of orally administered OVA could escape from intestinal proteolytic digestion and be absorbed as an intact form, but with a slight modification, across intestinal epithelium into the blood stream. Thus, it might be possible that orally administered bio-active proteins exert its biological function in peripheral tissues and organs.