Hubei International Scientific and Technological Cooperation Base of Animal Nutrition and Gut Health, Wuhan Polytechnic University, Wuhan, China.
Feed Research Institute, Newhope Liuhe Feeds Inc., Chengdu, Sichuan, China.
Adv Exp Med Biol. 2020;1265:21-37. doi: 10.1007/978-3-030-45328-2_2.
The liver plays a central role in amino acid (AA) metabolism in humans and other animals. In all mammals, this organ synthesizes many AAs (including glutamate, glutamine, alanine, aspartate, asparagine, glycine, serine, and homoarginine), glucose, and glutathione (a major antioxidant). Similar biochemical reactions occur in the liver of birds except for those for arginine and glutamine hydrolysis, proline oxidation, and gluconeogenesis from AAs. In contrast to mammals and birds, the liver of fish has high rates of glutamate and glutamine oxidation for ATP production. In most animals (except for cats and possibly some of the other carnivores), the liver produces taurine from methionine or cysteine. However, the activity of this pathway is limited in human infants (particularly preterm infants) and is also low in adult humans as compared with rats, birds and livestock species (e.g., pigs, cattle and sheep). The liver exhibits metabolic zonation and intracellular compartmentation for ureagenesis, uric acid synthesis, and gluconeogenesis, as well as AA degradation and syntheses. Capitalizing on these extensive bases of knowledge, dietary supplementation with functional AAs (e.g., methionine, N-acetylcysteine, and glycine) to humans and other animals can alleviate or prevent oxidative stress and damage in the liver. Because liver diseases are common problems in humans and farm animals (including fish), much research is warranted to further both basic and applied research on hepatic AA metabolism and functions.
肝脏在人类和其他动物的氨基酸（AA）代谢中起着核心作用。在所有哺乳动物中，肝脏合成多种 AA（包括谷氨酸、谷氨酰胺、丙氨酸、天冬氨酸、天冬酰胺、甘氨酸、丝氨酸和同型精氨酸）、葡萄糖和谷胱甘肽（一种主要的抗氧化剂）。除了精氨酸和谷氨酰胺水解、脯氨酸氧化和 AA 生成葡萄糖之外，鸟类的肝脏中也会发生类似的生化反应。与哺乳动物和鸟类不同，鱼类肝脏具有较高的谷氨酸和谷氨酰胺氧化率，用于产生 ATP。在大多数动物（猫除外，可能还有一些其他肉食动物）中，肝脏会从蛋氨酸或半胱氨酸产生牛磺酸。然而，该途径的活性在人类婴儿（尤其是早产儿）中受到限制，与大鼠、鸟类和家畜物种（如猪、牛和羊）相比，成人的活性也较低。肝脏表现出尿素生成、尿酸合成和葡萄糖生成的代谢分区和细胞内区室化，以及 AA 的降解和合成。利用这些广泛的知识基础，对人类和其他动物进行功能性 AA（如蛋氨酸、N-乙酰半胱氨酸和甘氨酸）的膳食补充可以减轻或预防肝脏的氧化应激和损伤。由于肝脏疾病在人类和农场动物（包括鱼类）中很常见，因此有必要进行更多的研究，以进一步开展肝脏 AA 代谢和功能的基础和应用研究。
