Vegusdal A, Gjøen T, Berge R K, Thomassen M S, Ruyter B
AKVAFORSK, Institute of Aquaculture Research, NO-1432 As, Norway.
Lipids. 2005 May;40(5):477-86. doi: 10.1007/s11745-005-1407-z.
We have studied the effects of dietary FA on the accumulation and secretion of [3H]glycerolipids by salmon hepatocytes in culture. Atlantic salmon were fed diets supplemented with either 100% soybean oil (SO) or 100% fish oil (FO), and grew from an initial weight of 113 +/- 5 g to a final weight of 338 +/- 19 g. Hepatocytes were isolated from both dietary groups and incubated with [3H]glycerol in an FA-free medium; a medium supplemented with 0.75 mM of one of three FA-18:1 n-9, 20:5n-3, or 22:6n-3--or a medium supplemented with 0.75 mM of the sulfur-substituted FA analog tetradecylthioacetic acid (TTA), which cannot undergo beta-oxidation. Incubations were allowed to proceed for 1, 2, 6, or 24 h. The rate of the secretion of radioactive glycerolipids with no FA added was 36% lower from hepatocytes isolated from fish fed the FO diet than it was from hepatocytes isolated from fish fed the SO diet. Hepatocytes incubated with 18:1 n-9 secreted more [3H]TAG than when incubated with no FA, whereas hepatocytes incubated with 20:5n-3 or TTA secreted less labeled TAG than when incubated with no FA. This observation was independent of the feeding group. Hepatocytes incubated with 22:6n-3 secreted the highest amounts of total [3H]glycerolipids compared with the other treatments, owing to increased secretion of phospholipids and mono- and diacylglycerols (MDG). In contrast, the same amounts of [3H]TAG were secreted from these cells as from cells incubated in an FA-free medium. The lipid-lowering effect of FO is thus independent of 22:6n-3, showing that 20:5n-3 is the FA that is responsible for the lipid-lowering effect. The ratio of TAG to MDG in lipids secreted from hepatocytes to which 20:5n-3 or TTA had been added was lower than that in lipids secreted from hepatocytes incubated with 18:1 n-9 or 22:6n-3, suggesting that the last step in TAG synthesis was inhibited. Morphometric measurements revealed that hepatocytes incubated with 20:5n-3 accumulated significantly more cellular lipid than cells treated with 18:1n-9, 22:6n-3, TTA, or no treatment. The area occupied by mitochondria was also greater in these cells. The present study shows that dietary FO reduces TAG secretion from salmon hepatocytes and that 20:5n-3 mediates this effect.
我们研究了日粮脂肪酸（FA）对培养的鲑鱼肝细胞中[3H]甘油脂质积累和分泌的影响。给大西洋鲑投喂分别添加100%大豆油（SO）或100%鱼油（FO）的日粮，鱼的初始体重为113±5克，最终体重增长至338±19克。从两个日粮组中分离出肝细胞，在无脂肪酸的培养基中与[3H]甘油一起孵育；培养基中添加0.75 mM的三种脂肪酸之一——18:1 n-9、20:5n-3或22:6n-3——或者添加0.75 mM的硫取代脂肪酸类似物十四烷基硫代乙酸（TTA），后者不能进行β-氧化。孵育时间为1、2、6或24小时。未添加脂肪酸时，从投喂FO日粮的鱼中分离出的肝细胞分泌放射性甘油脂质的速率比从投喂SO日粮的鱼中分离出的肝细胞低36%。与未添加脂肪酸孵育相比，用18:1 n-9孵育的肝细胞分泌更多的[3H]甘油三酯（TAG），而用20:5n-3或TTA孵育的肝细胞分泌的标记TAG比未添加脂肪酸孵育时少。这一观察结果与投喂组无关。与其他处理相比，用22:6n-3孵育的肝细胞分泌的总[3H]甘油脂质量最高，这是由于磷脂以及单酰甘油和二酰甘油（MDG）的分泌增加。相反，这些细胞分泌的[3H]TAG量与在无脂肪酸培养基中孵育的细胞相同。因此，FO的降脂作用与22:6n-3无关，表明20:5n-3是导致降脂作用的脂肪酸。添加20:5n-3或TTA的肝细胞分泌的脂质中TAG与MDG的比例低于用18:1 n-9或22:6n-3孵育的肝细胞分泌的脂质中的比例，这表明TAG合成的最后一步受到抑制。形态学测量显示，用20:5n-3孵育的肝细胞比用18:1n-9、22:6n-3、TTA孵育或未处理的细胞积累了更多的细胞脂质。这些细胞中线粒体所占面积也更大。本研究表明，日粮FO可降低鲑鱼肝细胞中TAG的分泌，且20:5n-3介导了这一作用。
