Guo Xiaoze, Ran Chao, Zhang Zhen, He Suxu, Jin Min, Zhou Zhigang
Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, China; and.
Jangxi Academy of Agricultural Sciences, Nanchang, Jiangxi, China.
J Nutr. 2017 May;147(5):781-788. doi: 10.3945/jn.116.245506. Epub 2017 Mar 29.
Nucleotides have been used as functional nutrients to improve the growth and health of animals, including fish. The mechanism involved in the growth-promotion effect of nucleotides is still unclear. We investigated the bioenergetic mechanism underlying the growth-promotion effect of nucleotides in zebrafish and the associated roles played by the intestinal microbiota. Larval zebrafish were fed a control or a 0.1% mixed nucleotides-supplemented diet for 2 wk. Standard metabolic rate, the minimal rate of energy expenditure by animals at rest, was evaluated by oxygen consumption with the use of a respirometer. The expressions of fasting-induced adipose factor (Fiaf), inflammatory cytokines, and genes involved in fatty acid (FA) oxidation were tested by quantitative reverse transcriptase-polymerase chain reaction. The intestinal microbiota from the nucleotide-fed fish (NT fish) or control fish was transferred to 3-d postfertilization germ-free zebrafish in which oxygen consumption and expression of cytokines and were evaluated. Compared with controls, nucleotide supplementation at 0.1% increased the weight and energy gains of zebrafish by 10% and 25%, respectively ( < 0.01). Standard metabolic rate was 28% lower in NT fish than in controls ( < 0.001). Nucleotide supplementation downregulated the inflammatory tone in the head kidney of the fish. Moreover, NT fish had a 51% lower intestinal expression of than did controls ( < 0.05), which was consistent with decreased expression of key genes involved in FA oxidation [carnitine:palmitoyl transferase 1a () and medium-chain acyl coenzyme A dehydrogenase ()] in liver and muscle. Germ-free zebrafish colonized with microbiota from NT fish had a 25% lower standard metabolic rate than did those colonized by control microbiota ( < 0.01), whereas direct nucleotide feeding of germ-free zebrafish did not affect standard metabolic rate relative to germ-free controls that were not fed nucleotides. Furthermore, germ-free zebrafish colonized with nucleotide microbiota exhibited downregulated inflammatory tone and 33% lower expression compared with their control microbiota-colonized counterparts. The growth-promoting effect of dietary nucleotides in zebrafish involves 2 intestinal microbiota-mediated mechanisms that result in reduced standard metabolic rate: ) lower inflammatory tone and ) reduced FA oxidation associated with increased microbial suppression of intestinal .
核苷酸已被用作功能性营养素，以促进包括鱼类在内的动物的生长并改善其健康状况。核苷酸促进生长作用背后的机制仍不清楚。我们研究了斑马鱼中核苷酸促进生长作用的生物能量学机制以及肠道微生物群所起的相关作用。将幼体斑马鱼用对照饲料或添加0.1%混合核苷酸的饲料喂养2周。标准代谢率是动物在静息状态下的最低能量消耗率，通过使用呼吸计测量氧气消耗量来评估。通过定量逆转录聚合酶链反应检测禁食诱导脂肪因子（Fiaf）、炎性细胞因子以及参与脂肪酸（FA）氧化的基因的表达。将来自喂食核苷酸的鱼（NT鱼）或对照鱼的肠道微生物群转移到受精后3天的无菌斑马鱼中，评估其氧气消耗量以及细胞因子的表达。与对照组相比，添加0.1%的核苷酸使斑马鱼的体重和能量增加分别提高了10%和25%（P<0.01）。NT鱼的标准代谢率比对照组低28%（P<0.001）。添加核苷酸下调了鱼头部肾脏中的炎性状态。此外，NT鱼肠道中Fiaf的表达比对照组低51%（P<0.05），这与肝脏和肌肉中参与FA氧化的关键基因[肉碱：棕榈酰转移酶1a（cpt1a）和中链酰基辅酶A脱氢酶（mcad）]表达降低一致。用NT鱼的微生物群定殖的无菌斑马鱼的标准代谢率比用对照微生物群定殖的无菌斑马鱼低25%（P<0.01），而直接给无菌斑马鱼喂食核苷酸相对于未喂食核苷酸的无菌对照而言，对标准代谢率没有影响。此外，与用对照微生物群定殖的无菌斑马鱼相比用核苷酸微生物群定殖的无菌斑马鱼表现出炎性状态下调且Fiaf表达降低33%。日粮核苷酸对斑马鱼的促生长作用涉及两种肠道微生物群介导的机制，这些机制导致标准代谢率降低：（1）较低的炎性状态；（2）与肠道Fiaf微生物抑制增加相关的FA氧化减少。
