申請者らの先行研究により、複数の天然物由来機能性物質を代謝疾患モデルに投与したところ、二次胆汁酸であるデオキシコール酸（deoxycholic acid：DCA）が糞便中で劇的に低下する天然物由来機能性物質を発見したが、これら機能性物質の代謝疾患の改善程度も他と比較し顕著であった。胆汁酸投与によるミトコンドリアクリステの増加や、胆汁酸応答シグナルがミトコンドリア活性を促進することから、本年度は、これまでの研究を発展させ、二次胆汁酸合成菌を殺菌する抗生物質投与有無での天然物由来機能性物質の代謝制御機能の評価をミトコンドリア機能活性を中心に検討した。代謝疾患の表現型の検討後、1)腸内細菌叢、胆汁酸組成（約30種類）解析を行った。2)遺伝子網羅的発現解析を行った。特に腸管の胆汁酸受容体であるTGR5、FXR下流に存在する遺伝子に注目した。3)ミトコンドリア機能解析を行い、腸内細菌・胆汁酸代謝相互作用を検討した。二次胆汁酸が強いリガンドとなるTGR5を介し褐色脂肪での熱産生を促進することが申請者らの研究によって明らかとなっているが、二次胆汁酸合成菌を含むグラム陰性菌を殺菌するVCM投与群においては褐色脂肪でのミトコンドリアでの熱産生系遺伝子発現の低下が見られた。一方、天然物由来機能性物質をVCM投与群に合わせて投与したところ、その低下がRescueされた。二次胆汁酸は褐色脂肪のミトコンドリアの活性を高めるが、一方で細胞毒性も指摘されている。今回、申請者らが検討した複数の天然物由来機能性物質は二次胆汁酸を増やさないが、褐色脂肪中のミトコンドリアでの熱産生系遺伝子発現の上昇が確認されており、ミトコンドリア機能改善に対する直接作用を有していることが確認された。本研究の一部の成果は海外国際学術誌にアクセプトされた。
In our previous study, we found that deoxycholic acid (DCA), a secondary bile acid, was dramatically reduced in feces when several natural product-derived functional substances were administered to a metabolic disease model. In addition, the degree of amelioration of metabolic diseases by these natural product-derived functional substances was also remarkable compared to others. Since bile acid administration increases mitochondrial cristae and bile acid response signals promote mitochondrial activity, in this year, we extended our previous studies to evaluate the metabolic regulatory functions of natural product-derived functional substances in the presence and absence of antibiotics that kill secondary bile acid synthesizing bacteria, focusing on mitochondrial functional activity. After examining the phenotypes of metabolic diseases, 1) analysis of intestinal microflora and bile acid composition (about 30 kinds) was conducted. 2) comprehensive gene expression analysis was conducted. 3) Mitochondrial function analysis was performed to examine the interaction between intestinal bacteria and bile acid metabolism. It has been shown by the applicants that secondary bile acids promote energy expenditure in brown adipose tissue via TGR5, which is a strong ligand. However, in the VCM-treated group in which Gram-negative bacteria, including secondary bile acid synthesizing bacteria, were sterilized, there was a decrease in the expression of energy expenditure related genes in mitochondria in brown adipose tissue. On the other hand, when a natural product-derived functional substance was administered along with the VCM-treated group, these decreases were rescued. Secondary bile acids increase the activity of mitochondria in brown adipose tissue, but they are also known to be cytotoxic. In this study, we found that several natural product-derived functional substances did not increase secondary bile acids, but increased the expression of energy expenditure related genes in mitochondria of brown adipose tissue, indicating that they have a direct effect on improving mitochondrial function. Some of the results of this study have been accepted for publication in an international scientific journal.