Mammalian colonic contribution of amino acids to whole-body homeostasis

The colon is an effective bioreactor with auxotrophic microbiota that can serve by hydrolyzing dietary and endogenous protein, as well as by synthesizing essential amino acids through nitrogen salvage. Due to assumed negligible amino acid absorption, this colonic contribution was thought to be minimal, but this may not be true.

Several studies that examined the colonic environment in health and disease, show the presence of proteases in the colonic lumen, which are of both host and microbial origin, along with indirect evidence of amino acid transporters in the colonic epithelium. There are also amino acid biosynthetic pathways in the microflora, and the contribution of colonic amino acid to host amino acid nutrition has been shown in wild animals. Yet, current direct and quantitative evidence on amino acid absorption in human colon is minimal.

Although amino acid absorption in colon is not very well established, current studies show that substantial amounts of amino acid could possibly be contributed to the host by the colon. There is a need for assessing this contribution quantitatively using direct isotopic methods under different nutritional conditions, dietary intakes, and clinical conditions.