Abstract：
Age-induced osteoporosis is a global problem. Essential amino acids (EAAs) work as an energy source and a molecular pathway modulator in bone, but their functions have not been systematically reviewed in aging bone. This study aimed to discuss the contribution of EAAs on aging bone from in vitro, in vivo, and human investigations. In aged people with osteoporosis, serum EAAs were detected changing up and down, without a well-established conclusion. The supply of EAAs in aged people either rescued or did not affect bone mineral density (BMD) and bone volume. In most signaling studies, EAAs were proven to increase bone mass. Lysine, threonine, methionine, tryptophan, and isoleucine can increase osteoblast proliferation, activation, and differentiation, and decrease osteoclast activity. Oxidized L-tryptophan promotes bone marrow stem cells (BMSCs) differentiating into osteoblasts. However, the oxidation product of tryptophan called kynurenine increases osteoclast activity, and enhances the differentiation of adipocytes from BMSCs. Taken together, in terms of bone minerals and volume, more views consider EAAs to have a positive effect on aging bone, but the function of EAAs in bone metabolism has not been fully demonstrated and more studies are needed in this area in the future.
摘要：
年龄引起的骨质疏松症是一个全球性问题。必需氨基酸（EAAs）作为骨骼中的能量来源和分子途径调节剂，但是它们的功能尚未在老化的骨骼中得到系统的评估。本研究旨在从体外探讨EAA对衰老骨的贡献,在体内，和人类调查。在患有骨质疏松症的老年人中，检测到血清EAA上下变化，没有一个既定的结论。老年人的EAA供应可以挽救或不影响骨矿物质密度（BMD）和骨体积。在大多数信号研究中，EAA被证明可以增加骨量。赖氨酸,苏氨酸,蛋氨酸,色氨酸,异亮氨酸可以增加成骨细胞的增殖，激活,和差异化，并降低破骨细胞活性。氧化L-色氨酸促进骨髓干细胞（BMSCs）分化为成骨细胞。然而,色氨酸的氧化产物称为犬尿氨酸增加破骨细胞活性，促进BMSCs向脂肪细胞分化。一起来看,就骨矿物质和体积而言，更多的观点认为EAA对老化的骨骼有积极的影响，但是EAA在骨代谢中的作用尚未得到充分证实，未来需要在这方面进行更多的研究。
