Fatty acid metabolism in marine fish: Low activity of fatty acyl Δ5 desaturation in gilthead sea bream ( Sparus aurata ) cells

Marine fish are known to have an absolute dietary requirement for C20 and C22 highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in marine fish was either a deficiency in fatty acyl Δ5 desaturase or C18-20 elongase activity. Recently, Ghioni et al. (Biochim. Biophys. Acta, 1437, 170-181, 1999) presented evidence that in turbot cells there was low activity of C18-20 elongase whereas Δ5 desaturase had high activity. In the present study, the fatty acid desaturase/elongase pathway was investigated in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabelled polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-14C]18:2n-6 and [1-14C]18:3n-3), C18-20 elongase ([U-14C]18:4n-3), Δ5 desaturase ([1-14C]20:3n-6 and [U-14C]20:4n-3) and C20-22 elongase ([1-14C]20:4n-6 and [1-14C]20:5n-3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and there was substantial C18-20 elongase and C20-22 elongase activities. A deficiency in the desaturation/elongation pathway was clearly identified at the level of the fatty acyl Δ5 desaturase which was very low, particularly with 20:4n-3 as substrate. In comparison, the apparent activities of Δ6 desaturase, C18-20 elongase and C20-22 elongase were approximately 94-fold, 27-fold and 16-fold greater than that for Δ5 desaturase towards their respective n-3 polyunsaturated fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C20 and C22 highly unsaturated fatty acids in the marine fish, the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase activity

Lipídeos na nutrição de cães e gatos: metabolismo, fontes e uso em dietas práticas e terapêuticas Lipids in dogs and cats nutrition: metabolism, sources and application in practical and therapeutic diets

A partir do desenvolvimento de métodos mais precisos para a avaliação de lipídeos, diversos compostos têm sido descobertos e estudados como forma de enriquecer e melhorar dietas para atender às necessidades dos animais. O triglicerídeo é o principal componente lipídico da dieta e fonte de ácidos graxos que são utilizados para a síntese de outros lipídicos importantes como os fosfolípideos. Os ácidos graxos dos fosfolipídeos possuem papel fundamental na sinalização celular e são substratos das enzimas específicas durante o processo de produção de mediadores de respostas imunológicas. Diversos estudos têm evidenciado a participação de grupos de ácidos graxos das séries ômega 3 e 6 influenciando as respostas inflamatórias em cães e gatos. A deficiência de ácido araquidônico em gatos, por exemplo, pode ser suprida pelo acréscimo de AA pré formado ou pela inclusão de ácido &#947;-linolênico na dieta, que mostrou-se eficiente na sustentação dos níveis de ácido araquidônico exigidos por gatos adultos. Há evidências de que ácidos graxos de cadeia média (AGCM) proporcionam maior incremento calórico durante o processo de oxidação celular, sugerindo sua funcionalidade sobre o controle da obesidade. Outros compostos lipídicos têm sido avaliados quanto a sua participação no processo de controle de ganho de peso. A ausência de um AA nos diacilgliceróis (DAG) pode ser na posição sn 2 ou sn 3 do glicerol gerando DAGs diferentes. O 1,3 DAG quando comparado ao TAG resulta em diferentes efeitos metabólicos que suportam a hipótese de que o acréscimo de DAG na dieta aumenta a oxidação hepática ou intestinal de lipídeos, limitando a deposição de ácidos graxos em triglicerídeos junto ao tecido adiposo.<br>Following the development of more accurate methods for lipid evaluation, various compounds have been discovered and studied as a way to improve and enrich diets to meet the animal requirements. Triglycerides are the major lipid component of diets and source of fatty acids that are used in the synthesis of important compounds as phospholipids. The fatty acids from phospholipids play a fundamental role in cell signaling and are substrates for specific enzymes in the synthesis of immune response mediators. Several studies have shown the involvement of fatty acids, omega 3 and 6 series as influencing the inflammatory responses in dogs and cats. The deficiency of arachidonic acid in cats, for example, can be supplied by preformed arachidonic acid or by addition of &#947;-linolenic acid in the diet, which in turn can sustain the arachidonic acid levels required by adult cats. Evidences suggest that medium chain fatty acids (MCFAs) trigger greater energy expenditure during cellular oxidation, thus indicating their use as an aid for weight control in obesity. Other lipid compounds are under evaluation in their possible effects in the weight gain process in dogs and cats. This absence of one FA in the DAG can be at the sn2 or sn3 position in glycerol, and thus generating different DAGs. The 1,3 DAG when compared to TAG results in different metabolic effects which support the hypothesis that the addition of DAG in diets increases the hepatic or intestinal oxidation of lipids, thus limiting the deposition of fatty acids in adipose tissue triglycerides