Dietary sodium lactate promotes protein and lipid deposition through increasing energy supply from glycolysis in Nile tilapia (Oreochromis niloticus)

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Although lactate is previously considered as a waste product of glucose metabolism, accumulating evidences had revaluated its pivotal role in regulating diverse biological processes. In the present study, we investigated the effects of dietary sodium lactate on growth performance and systematic energy metabolism in juvenile Nile tilapia (Oreochromis niloticus). During an 8-week feeding trial, Nile tilapia was fed diets containing three sodium lactate concentrations (0%, 1% and 3%). The results revealed that the fish fed dietary sodium lactate (1% and 3%) exhibited a better growth performance. In addition, the fish fed dietary sodium lactate (3%) significantly promoted whole fish total protein and lipid deposition, but reduced its liver glycogen content. Further results showed that the dietary sodium lactate-fed tilapia exhibited higher triglycerides and free fatty acids contents in liver and serum than those of the control group. The hepatic Ampk (AMP-activated protein kinase), Pparα (peroxisome proliferator-activated receptor α) and Cpt1a (carnitine palmitoyl transferase 1a) protein, lipolysis and proteolysis process-related gene expressions were significantly inhibited in the fish fed dietary sodium lactate. Moreover, the targeted metabolome analysis also showed that dietary sodium lactate reduced the carnitine content, but caused the accumulation of amino acids and fatty acids in liver. In addition, pyruvate and lactate levels in the serum and liver of tilapia fed dietary sodium lactate were significantly higher than those of control fish. Furthermore, dietary sodium lactate treatment increased hepatic mct1 (lactate transport 1), ldhb (lactate dehydrogenase B chain), glycolysis and gluconeogenesis-related gene expressions, but decreased the contents of most metabolic intermediates in TCA cycle in the liver of fish. These results demonstrated that the Nile tilapia fed dietary sodium lactate (3%) exhibited a better growth performance with high protein and lipid deposition through the inhibition of proteolysis and lipolysis. To maintain the energy homeostasis, dietary lactate increased conversion of lactate to glucose and thereby largely stimulated glycolysis pathway fueled by the lactate- and glycogen-derived glucose. Therefore, lactate plays an essential role in maintaining energy homeostasis in fish.