Yi Dan, Hou Yongqing, Wang Lei, Long Minhui, Hu Shengdi, Mei Huimin, Yan Liqiong, Hu Chien-An Andy, Wu Guoyao
Hubei Collaborative Innovation Center for Animal Nutrition and Feed Safety, Hubei Key Laboratory of Animal Nutrition and Feed Science, Wuhan Polytechnic University, Wuhan, 430023, China.
Department of Animal Science, Texas A&M University, College Station, TX, 77843, USA.
Amino Acids. 2016 Feb;48(2):523-33. doi: 10.1007/s00726-015-2105-z. Epub 2015 Oct 3.
Dietary supplementation with N-acetylcysteine (NAC) has been reported to improve intestinal health and treat gastrointestinal diseases. However, the underlying mechanisms are not fully understood. According to previous reports, NAC was thought to exert its effect through glutathione synthesis. This study tested the hypothesis that NAC enhances enterocyte growth and protein synthesis independently of cellular glutathione synthesis. Intestinal porcine epithelial cells were cultured for 3 days in Dulbecco's modified Eagle medium containing 0 or 100 μM NAC. To determine a possible role for GSH (the reduced form of glutathione) in mediating the effect of NAC on cell growth and protein synthesis, additional experiments were conducted using culture medium containing 100 μM GSH, 100 μM GSH ethyl ester (GSHee), diethylmaleate (a GSH-depletion agent; 10 μM), or a GSH-synthesis inhibitor (buthionine sulfoximine, BSO; 20 μM). NAC increased cell proliferation, GSH concentration, and protein synthesis, while inhibiting proteolysis. GSHee enhanced cell proliferation and GSH concentration without affecting protein synthesis but inhibited proteolysis. Conversely, BSO or diethylmaleate reduced cell proliferation and GSH concentration without affecting protein synthesis, while promoting protein degradation. At the signaling level, NAC augmented the protein abundance of total mTOR, phosphorylated mTOR, and phosphorylated 70S6 kinase as well as mRNA levels for mTOR and p70S6 kinase in IPEC-1 cells. Collectively, these results indicate that NAC upregulates expression of mTOR signaling proteins to stimulate protein synthesis in enterocytes independently of GSH generation. Our findings provide a hitherto unrecognized biochemical mechanism for beneficial effects of NAC in intestinal cells.
据报道，补充N-乙酰半胱氨酸（NAC）可改善肠道健康并治疗胃肠道疾病。然而，其潜在机制尚未完全明确。根据以往报道，NAC被认为是通过谷胱甘肽合成发挥作用。本研究检验了以下假设：NAC可独立于细胞谷胱甘肽合成增强肠上皮细胞生长和蛋白质合成。将猪肠道上皮细胞在含有0或100μM NAC的杜氏改良 Eagle培养基中培养3天。为确定谷胱甘肽（GSH，谷胱甘肽的还原形式）在介导NAC对细胞生长和蛋白质合成作用中的可能作用，使用含有100μM GSH、100μM GSH乙酯（GSHee）、马来酸二乙酯（一种GSH耗竭剂；10μM）或GSH合成抑制剂（丁硫氨酸亚砜胺，BSO；20μM）的培养基进行了额外实验。NAC增加细胞增殖、GSH浓度和蛋白质合成，同时抑制蛋白水解。GSHee增强细胞增殖和GSH浓度，但不影响蛋白质合成，但抑制蛋白水解。相反，BSO或马来酸二乙酯降低细胞增殖和GSH浓度，不影响蛋白质合成，同时促进蛋白质降解。在信号传导水平，NAC增加了IPEC-1细胞中总mTOR、磷酸化mTOR和磷酸化70S6激酶的蛋白质丰度以及mTOR和p70S6激酶的mRNA水平。总体而言，这些结果表明，NAC上调mTOR信号蛋白的表达，以独立于GSH生成刺激肠上皮细胞中的蛋白质合成。我们的研究结果为NAC在肠道细胞中的有益作用提供了一种迄今未被认识的生化机制。
