Regulation of hepatic lipogenesis by dietary protein/energy in juvenile European seabass (Dicentrarchus labrax)

Abstract A growth trial was conducted with groups of European seabass having an initial weight of 6 g to study the lipogenic action of dietary protein and non-protein energy supplies. Six experimental diets were formulated to contain one of two crude protein levels (43 and 52%) with digestible protein (DP) to digestible energy (DE) ratios ranging from 19 to 26 mg/kJ. At the end of the growth trial (12 weeks), the activities of liver glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49), malic enzyme (ME, EC 1.1.1.40), ATP citrate lyase (ACL, EC 4.1.3.8), acetyl-CoA carboxylase (ACoAC, EC 6.4.1.2) and fatty acid synthetase (FAS, EC 2.3.1.38) were measured. Digestibility of main dietary components was also determined over a three-week period. At each protein level, an increase in dietary DE led to improved growth performance, protein efficiency, daily N deposition and to a reduction of N loss. Best results were achieved at 40% DP and a DP/DE ratio of 19–20 mg/kJ. G6PD, ME and ACoAC were found to be the key regulatory enzymes in the lipogenic pathway, with G6PD being the main NADPH-generating enzyme. Activities of G6PD, ME, ACL and FAS were reduced with increasing fat intake. Activities of G6PD, ME and ACL were increased with increasing starch intake. ACoAC activity was negatively correlated with starch intake and positively with fat intake.