Short-term modulation of lipogenesis by macronutrients in rainbow trout (Oncorhynchus mykiss) hepatocytes

Rainbow trout (Oncorhynchus mykiss) hepatocytes were cultured under simulat ed conditions of varying nutritional status to explore the short-term modul ation by dietary substrates of the main lipogenic enzymes: glucose-6-phosph ate dehydrogenase (G6PD), malic enzyme (ME), ATP-citrate lyase (ACL), acety l-CoA carboxylase (ACoAC) and fatty acid synthetase (FAS). Primary cultures were individually exposed to varying amounts of glucose, hydrolysed casein and long-chain polyunsaturated fatty acids (PUFA) for 12 h. A second set o f experiments was designed to evaluate the effects of mixing different rela tive amounts of these macronutrients in the culture medium. Glucose concent rations of up to 20-25 mm showed a stimulatory effect on G6PD, ME, ACL and ACoAC activity (P<0.05) while an earlier inhibitory effect on FAS was obser ved at 10-20 mm glucose (P<0.05). The use of hydrolysed casein as a nutriti onal source of amino acids inhibited the activity of FAS and ME (P<0.05), a nd stimulated G6PD, ACoAC and ACL activity (P<0.05). Low levels of linoleni c acid exerted a stimulatory effect on all the lipogenic enzymes assayed (P <0.05) with the exception of FAS, and increased amounts showed some inhibit ion of lipogenic activities (P<0.05). Eicosapentaenoic acid and docosahexae noic acid showed a similar effect, although the former strongly inhibited F AS activity while the latter showed greater potential to inhibit ACoAC and G6PD. A complete change in the relative levels of glucose, hydrolysed casei n and PUFA in turn led to changes in the enzyme activity patterns observed. The present study shows the feasibility of exploring the direct regulation of lipogenesis in isolated fish cells by varying the relative amounts of m ain macronutrients, mimicking in vivo dietary conditions. It is felt that s uch an approach may serve to investigate the macronutrient regulation of ot her metabolic pathways.