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

蛋清蛋白（ovalbumin:OVA）是一种抗水解蛋白，是引起鸡蛋过敏的主要致敏蛋白。以鸡蛋白蛋白为模型大分子食物成分，研究了卵清蛋白在小鼠肠道内的吸收及卵清蛋白在外周血循环中的动力学。小鼠口服OVA （10 mg）后，采集外周血，从凝血中分离血清。用EUSA法测定血清中OVA浓度为10 ~ 50 ng/ml，用Sepharose偶联抗OVA抗体免疫亲和沉淀法浓缩血清中的OVA。在SDS-PAGE分析中，从外周血中回收的OVA显示单个主要的蛋白带，其分子质量与完整的OVA相同，而一个次要的蛋白带的分子质量略小。没有与分子质量较小的OVA片段对应的条带，这些片段已被证明是小鼠小肠中OVA抗原的主要成分。此外，双向凝胶电泳显示，从血液中回收的OVA由4-6个不同pI但分子量相同的蛋白点组成，与完整OVA相比，碱性蛋白点占主导地位，这表明OVA在肠道吸收或在循环血液中迁移过程中pI向更碱性的pI转移。在体外与小鼠血清孵育的OVA中未观察到这种pI移位。综上所述，这表明一小部分口服OVA可以从肠道蛋白水解消化中逃脱，并以完整的形式被吸收，但经过轻微的修饰，穿过肠上皮进入血流。因此，口服生物活性蛋白可能在外周组织和器官中发挥其生物学功能。

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.