ゼブラフィッシュからヒト臨床へ：ラムナン硫酸の腸内細菌叢変化を伴う便秘改善作用

抄録

Rhamnan sulfate (RS) is a sulfate polysaccharide composed of L-rhamnose and sulfated L-rhamnose found in green algae such as Monostroma nitidum. It has been reported to have anticoagulant and antiviral effects in the last decade. In 2015, our group discovered the anti-obesity effect of RS using the diet-induced obesity model of zebrafish (Zang L, et al. J Funct Foods. 2015;17:364-370). In this study, we first administrated RS (0.25 mg/g food volume) orally to high-fat diet-treated mice for 4 weeks. RS increased fecal volume and calorie excretion with suppression of body weight increase, and decreased plasma lipids and fasting blood glucose levels, which was consistent with the results of our zebrafish study. Noting the increased excretion by RS, we administrated RS (100 mg/day) to subjects with low defaecation frequencies (3–5 times/week) for 2 weeks in a double-blind placebo-controlled manner. As a result, Firmicutes tended to decrease, while Bacteroides increased. It is known that the obese population has more Firmicutes and fewer Bacteroides depending on their body mass index. Thus, RS improved the intestinal microflora in the direction of anti-obesity. In addition, clostridia (Firmicutes), which produce medium-chain fatty acids that increase the absorption of water in the intestine (one of the causes of constipation), were reduced by the intake of RS. Furthermore, Metagenomics profiling using PICRUSt and KEGG pathway showed that RS intake activated the "cytochrome p450-mediated excretion of foreign substances" pathway, "biological defense against invasive bacteria," and the "biomolecular NAD synthesis" pathway, which has already been reported to have a therapeutic effect on constipation, suggesting a possible mechanism for the ameliorating effect of RS.