Laboratory of Aquaculture Nutrition and Environmental Health (LANEH), School of Life Sciences, East China Normal University, Shanghai, China.
Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China.
Sci Rep. 2017 Jan 19;7:40815. doi: 10.1038/srep40815.
Excess fat accumulation has been observed widely in farmed fish; therefore, efficient lipid-lowering factors have obtained high attention in the current fish nutrition studies. Dietary L-carnitine can increase fatty acid β-oxidation in mammals, but has produced contradictory results in different fish species. To date, the mechanisms of metabolic regulation of L-carnitine in fish have not been fully determined. The present study used zebrafish to investigate the systemic regulation of nutrient metabolism by dietary L-carnitine supplementation. L-carnitine significantly decreased the lipid content in liver and muscle, accompanied by increased concentrations of total and free carnitine in tissues. Meanwhile, L-carnitine enhanced mitochondrial β-oxidation activities and the expression of carnitine palmitoyltransferase 1 mRNA significantly, whereas it depressed the mRNA expression of adipogenesis-related genes. In addition, L-carnitine caused higher glycogen deposition in the fasting state, and increased and decreased the mRNA expressions of gluconeogenesis-related and glycolysis-related genes, respectively. L-carnitine also increased the hepatic expression of mTOR in the feeding state. Taken together, dietary L-carnitine supplementation decreased lipid deposition by increasing mitochondrial fatty acid β-oxidation, and is likely to promote protein synthesis. However, the L-carnitine-enhanced lipid catabolism would cause a decrease in glucose utilization. Therefore, L-carnitine has comprehensive effects on nutrient metabolism in fish.
养殖鱼类中普遍存在脂肪过度积累的现象；因此，高效的降脂因子在当前鱼类营养研究中受到高度关注。膳食左旋肉碱可以增加哺乳动物的脂肪酸β氧化，但在不同鱼类中产生了相反的结果。迄今为止，左旋肉碱在鱼类中的代谢调节机制尚未完全确定。本研究使用斑马鱼来研究膳食左旋肉碱补充对营养代谢的系统调节。左旋肉碱显著降低了肝脏和肌肉中的脂质含量，同时组织中的总肉碱和游离肉碱浓度增加。同时，左旋肉碱增强了线粒体β氧化活性，显著上调肉碱棕榈酰转移酶 1 mRNA 的表达，而下调与脂肪生成相关的基因的 mRNA 表达。此外，左旋肉碱在禁食状态下引起更高的糖原沉积，并分别增加和降低与糖异生和糖酵解相关的基因的 mRNA 表达。左旋肉碱还增加了摄食状态下肝脏中 mTOR 的表达。综上所述，膳食左旋肉碱补充通过增加线粒体脂肪酸β氧化来减少脂肪沉积，可能促进蛋白质合成。然而，左旋肉碱增强的脂肪分解会导致葡萄糖利用率降低。因此，左旋肉碱对鱼类的营养代谢有全面的影响。
