Oxley Anthony, Torstensen Bente E, Rustan Arild C, Olsen Rolf E
Institute of Marine Research, Matre Aquaculture Research Station, N-5984 Matredal, Norway.
Comp Biochem Physiol B Biochem Mol Biol. 2005 May;141(1):77-87. doi: 10.1016/j.cbpc.2005.01.012.
The substitution of fish oil with plant-derived oil in diets for carnivorous fish, such as Atlantic salmon, has previously revealed the potentially deleterious supranuclear accumulation of lipid droplets in intestinal cells (enterocytes) which may compromise gut integrity, and consequently, fish health. This suggests that unfamiliar dietary lipid sources may have a significant impact on intestinal lipid metabolism, however, the mode of lipid resynthesis is largely unknown in teleost fish intestine. The present study aimed at characterising three key lipogenic enzymes involved in the biosynthesis of triacylglycerol (TAG) and phosphatidylcholine (PC) in Atlantic salmon enterocytes: monoacylglycerol acyltransferase (MGAT), diacylglycerol acyltransferase (DGAT), and diacylglycerol cholinephosphotransferase (CPT). Furthermore, to investigate the dietary effect of plant oils on these enzymes, two experimental groups of fish were fed a diet with either capelin (fish oil) or vegetable oil (rapeseed oil:palm oil:linseed oil, 55:30:15 w/w) as the lipid source. The monoacylglycerol (MAG) pathway was highly active in the intestinal mucosa of Atlantic salmon as demonstrated by MGAT activity (7 nmol [1-(14)C]palmitoyl-CoA incorporated min(-1) mg protein(-1)) and DGAT activity (4 nmol [1-(14)C]palmitoyl-CoA incorporated min(-1) mg protein(-1)), with MGAT appearing to also provide adequate production of sn-1,2-diacylglycerol for potential utilisation in PC synthesis via CPT activity (0.4 nmol CDP-[(14)C]choline incorporated min(-1) mg protein(-1)). Both DGAT and CPT specific activity values were comparable to reported mammalian equivalents, although MGAT activity was lower. Nevertheless, MGAT appeared not to be the rate-limiting step in salmon intestinal TAG synthesis. The homology between piscine and mammalian enzymes was established by similar stimulation and inhibition profiles by a variety of tested cofactors and isomeric substrates. The low dietary n-3/n-6 PUFA ratio presented in the vegetable oil diet did not significantly affect the activities of MGAT, DGAT, or CPT under optimised assay conditions, or in vivo intestinal mucosa lipid class composition, when compared to a standard fish oil diet.
在肉食性鱼类（如大西洋鲑鱼）的日粮中用植物源油替代鱼油，此前已发现肠道细胞（肠上皮细胞）中脂滴出现潜在有害的核上积累，这可能会损害肠道完整性，进而影响鱼类健康。这表明不熟悉的日粮脂质来源可能对肠道脂质代谢有重大影响，然而，硬骨鱼肠道中脂质再合成的模式在很大程度上尚不清楚。本研究旨在表征参与大西洋鲑鱼肠上皮细胞中三酰甘油（TAG）和磷脂酰胆碱（PC）生物合成的三种关键脂肪生成酶：单酰甘油酰基转移酶（MGAT）、二酰甘油酰基转移酶（DGAT）和二酰甘油胆碱磷酸转移酶（CPT）。此外，为了研究植物油对这些酶的日粮影响，将两组实验鱼分别投喂以毛鳞鱼（鱼油）或植物油（菜籽油：棕榈油：亚麻籽油，55:30:15 w/w）为脂质来源的日粮。单酰甘油（MAG）途径在大西洋鲑鱼的肠黏膜中高度活跃，MGAT活性（7 nmol [1-(14)C]棕榈酰辅酶A掺入量min(-1) mg蛋白质(-1)）和DGAT活性（4 nmol [1-(14)C]棕榈酰辅酶A掺入量min(-1) mg蛋白质(-1)）证明了这一点，MGAT似乎还通过CPT活性（0.4 nmol CDP - [(14)C]胆碱掺入量min(-1) mg蛋白质(-1)）为PC合成中潜在利用的sn-1,2-二酰甘油提供了充足的产量。尽管MGAT活性较低，但DGAT和CPT的比活性值与报道的哺乳动物对应值相当。然而，MGAT似乎不是鲑鱼肠道TAG合成中的限速步骤。通过各种测试的辅因子和异构体底物的相似刺激和抑制曲线，确定了鱼类和哺乳动物酶之间的同源性。与标准鱼油日粮相比，植物油日粮中低的n-3/n-6多不饱和脂肪酸比例在优化的测定条件下或体内肠黏膜脂质类组成方面，并未显著影响MGAT、DGAT或CPT的活性。
