Gardner M L
School of Biomedical Sciences, University of Bradford, West Yorkshire, England.
Annu Rev Nutr. 1988;8:329-50. doi: 10.1146/annurev.nu.08.070188.001553.
There is now no reasonable doubt that small quantities of intact proteins do cross the gastrointestinal tract in animals and adult humans, and that this is a physiologically normal process required for antigen sampling by subepithelial immune tissue in the gut. It is too small to be nutritionally significant in terms of gross acquisition of amino-nitrogen, but since it has important implications relating to dietary composition it must receive consideration from nutritionists. The process of intact protein absorption occurs without eliciting harmful consequences for most individuals, but it appears likely that a small number of people absorbing these "normal" amounts may react idiosyncratically; also, some individuals may absorb excessive amounts, and they may suffer clinically significant consequences. Likewise, individuals with diminished absorption of intact protein may be at risk. Normal absorption probably occurs predominantly by transcellular endocytosis with some possible contribution by a route between cells; increased net entry of protein to the circulation may reflect (a) increased paracellular (intercellular) passage, (b) increased transcellular passage, and/or (c) decreased lysosomal proteolysis. Tests to distinguish among these possibilities are strongly desirable. Intact protein absorption may be involved in the pathogenesis of inflammatory bowel disease, "food allergies," and other diseases, including even major psychiatric disorders, but the current evidence is mainly indirect and suggestive. Great caution and careful objective studies are needed to establish whether such relationships with disease do exist and to unravel the underlying basic physiological mechanisms. Now that interest has developed in the assessment of intestinal permeability to small- and medium-sized molecules, it is hoped that equally simple methods for studying macromolecular permeability will be developed and applied. Therapeutic methods for enhancing intact polypeptide absorption would be valuable for vaccine and peptide drug administration by the oral route. Therapeutic reduction of the process may be relevant in food-sensitive patients.
现在毫无疑问，少量完整蛋白质确实会穿过动物和成年人体内的胃肠道，而且这是肠道上皮下免疫组织进行抗原采样所需的生理正常过程。就氨基氮的总体获取而言，其数量过少，在营养方面无显著意义，但由于它与饮食组成有重要关联，营养学家必须予以考虑。完整蛋白质吸收过程对大多数个体而言不会引发有害后果，但似乎少数吸收这些“正常”量蛋白质的人可能会出现特异反应；此外，一些个体可能吸收过量，从而遭受具有临床意义的后果。同样，完整蛋白质吸收能力下降的个体可能面临风险。正常吸收可能主要通过跨细胞内吞作用发生，细胞间途径可能也有一定作用；蛋白质进入循环的净量增加可能反映出（a）细胞旁（细胞间）通道增加，（b）跨细胞通道增加，和/或（c）溶酶体蛋白水解减少。非常需要能够区分这些可能性的检测方法。完整蛋白质吸收可能与炎症性肠病、“食物过敏”及其他疾病（甚至包括主要精神障碍）的发病机制有关，但目前证据主要是间接的且具有提示性。需要极其谨慎并进行细致客观的研究，以确定与疾病的这种关系是否确实存在，并阐明潜在的基本生理机制。鉴于目前已对评估肠道对中小分子的通透性产生兴趣，希望能开发并应用同样简单的方法来研究大分子通透性。增强完整多肽吸收的治疗方法对于口服疫苗和肽类药物给药将具有重要价值。对食物敏感患者而言，减少这一过程的治疗方法可能具有相关性。
