Date Published: July 10, 2017
Publisher: Public Library of Science
Author(s): Kengo Sasaki, Daisuke Sasaki, Naoko Okai, Kosei Tanaka, Ryohei Nomoto, Itsuko Fukuda, Ken-ichi Yoshida, Akihiko Kondo, Ro Osawa, Mathias Chamaillard.
Accumulating evidence suggests that dietary taurine (2-aminoethanesulfonic acid) exerts beneficial anti-inflammatory effects in the large intestine. In this study, we investigated the possible impact of taurine on human colonic microbiota using our single-batch fermentation system (Kobe University Human Intestinal Microbiota Model; KUHIMM). Fecal samples from eight humans were individually cultivated with and without taurine in the KUHIMM. The results showed that taurine remained largely undegraded after 30 h of culturing in the absence of oxygen, although some 83% of the taurine was degraded after 30 h of culturing under aerobic conditions. Diversity in bacterial species in the cultures was analyzed by 16S rRNA gene sequencing, revealing that taurine caused no significant change in the diversity of the microbiota; both operational taxonomic unit and Shannon-Wiener index of the cultures were comparable to those of the respective source fecal samples. In addition, principal coordinate analysis indicated that taurine did not alter the composition of bacterial species, since the 16S rRNA gene profile of bacterial species in the original fecal sample was maintained in each of the cultures with and without taurine. Furthermore, metabolomic analysis revealed that taurine did not affect the composition of short-chain fatty acids produced in the cultures. These results, under these controlled but artificial conditions, suggested that the beneficial anti-inflammatory effects of dietary taurine in the large intestine are independent of the intestinal microbiota. We infer that dietary taurine may act directly in the large intestine to exert anti-inflammatory effects.
Taurine (2-aminoethanesulfonic acid) is a semi-essential amino acid and one of the most abundant free amino acids in mammalian tissues such as heart and brain . Taurine is known to play a wide range of critical roles in both human and animal physiology, including functions in antioxidation, osmoregulation, bile acid conjugation, regulation of blood pressure, maintenance of retinal and cardiac function, regulation of neuroendocrine activity, and prevention and treatment of fatty liver disease [2–8]. In addition, taurine may have anti-inflammatory effects, as demonstrated by the ability of dietary taurine to attenuate artificially induced colitis in mice . Consistent with this role, human intestinal epithelial Caco-2 cells grown in the presence of taurine exhibit enhanced expression of genes encoding proteins that protect against inflammation .
The NGS analysis revealed that KUHIMM is capable of reproducing the diversity and composition of the microbiota found in human intestinal tracts, where members of the phyla Firmicutes and Bacteroidetes typically dominate [33,34]. In addition, the PCoA indicated that the KUHIMM reproduced the unique individual composition of microbiota from each fecal donor. Furthermore, HPLC analyses confirmed that KUHIMM reproduced the composition of SCFAs in the large intestine, an environment that is characterized by the predominance of acetate, followed by propionate and butyrate . Our previous study successfully demonstrated that the bifidogenic properties of the oligosaccharides were reproduced in the KUHIMM, an observation consistent with reports from other studies [36,37]. This evidence indicates the reliable capacity of the KUHIMM for simulating individual human colonic microbiota, thereby allowing us to evaluate the fate of dietary taurine and speculate on its impact on human health as follows.