Murthy S, Albright E, Mathur S N, Davidson N O, Field F J
Department of Internal Medicine, University of Iowa, Iowa City 52242.
Arterioscler Thromb. 1992 Jun;12(6):691-700. doi: 10.1161/01.atv.12.6.691.
The regulation of apolipoprotein B (apo B) metabolism by eicosapentaenoic acid was investigated in CaCo-2 cells. Cells cultured on semipermeable membranes that separated an upper from a lower well were incubated for 48 hours with albumin alone or 1 mM eicosapentaenoic acid or oleic acid attached to albumin (4:1, mol/mol). Compared with cells incubated with oleic acid, cells incubated with eicosapentaenoic acid synthesized and secreted less [3H]glycerol-labeled triglycerides. Although both fatty acids increased cellular triglyceride mass compared with control cells, less triglycerides accumulated in cells incubated with the n-3 fatty acid. The secretion of triglyceride and apo B mass by cells incubated with eicosapentaenoic acid was less than that observed by cells incubated with oleate. The amount of apo B mass within cells, however, was not altered by either of the fatty acids and was similar to amounts found in control cells. Apo B mRNA abundance was decreased fourfold in cells exposed for 48 hours to eicosapentaenoic acid. In contrast, in cells incubated with oleic acid, apo B mRNA levels were not significantly altered. Pulse-chase experiments were performed to investigate the regulation of apo B synthesis and degradation by the fatty acids. In cells incubated with eicosapentaenoic acid, the synthesis and basolateral secretion of newly synthesized apo B-100 and apo B-48 were significantly less compared with control cells or cells incubated with oleic acid. In contrast, the synthesis and secretion of newly synthesized apo B in cells exposed to oleic acid were similar to control cells. Rates of apo A-I synthesis were similar in cells incubated with either of the fatty acids. Compared with control cells and cells incubated with eicosapentaenoic acid, the residence time of labeled apo B in cells incubated with oleic acid was prolonged. The percentage of newly synthesized apo B that was degraded was less in cells incubated with oleic acid. In contrast, residence times and the percentages of apo A-I and apo B-48 degraded were similar in control cells and cells incubated with the fatty acids. Thus, in CaCo-2 cells, compared with the effects of oleic acid, eicosapentaenoic acid impairs triglyceride transport in part by inhibiting apo B synthesis and secretion. The inhibition of apo B synthesis by eicosapentaenoic acid may be related to a decrease in gene transcription or a decrease in mRNA stability, as apo B mRNA levels were significantly decreased in cells incubated with this fatty acid.(ABSTRACT TRUNCATED AT 400 WORDS)
在CaCo-2细胞中研究了二十碳五烯酸对载脂蛋白B（apo B）代谢的调节作用。将培养在分隔上下孔的半透膜上的细胞，分别单独与白蛋白、或与附着有1 mM二十碳五烯酸或油酸的白蛋白（摩尔比4:1）一起孵育48小时。与用油酸孵育的细胞相比，用二十碳五烯酸孵育的细胞合成和分泌的[3H]甘油标记的甘油三酯较少。尽管与对照细胞相比，两种脂肪酸都增加了细胞内甘油三酯的含量，但在与n-3脂肪酸孵育的细胞中积累的甘油三酯较少。用二十碳五烯酸孵育的细胞分泌的甘油三酯和apo B含量低于用油酸孵育的细胞。然而，细胞内apo B的含量并未因任何一种脂肪酸而改变，且与对照细胞中的含量相似。暴露于二十碳五烯酸48小时的细胞中，apo B mRNA丰度降低了四倍。相比之下，在用油酸孵育的细胞中，apo B mRNA水平没有显著改变。进行脉冲追踪实验以研究脂肪酸对apo B合成和降解的调节作用。与对照细胞或用油酸孵育的细胞相比，用二十碳五烯酸孵育的细胞中新合成的apo B-100和apo B-48的合成和基底外侧分泌显著减少。相比之下，暴露于油酸的细胞中新合成的apo B的合成和分泌与对照细胞相似。用任何一种脂肪酸孵育的细胞中apo A-I的合成速率相似。与对照细胞和用二十碳五烯酸孵育的细胞相比，用油酸孵育的细胞中标记的apo B的停留时间延长。在用油酸孵育的细胞中，新合成的apo B被降解的百分比更低。相比之下，对照细胞和用脂肪酸孵育的细胞中apo A-I和apo B-48的停留时间以及降解百分比相似。因此，在CaCo-2细胞中，与油酸的作用相比，二十碳五烯酸部分地通过抑制apo B的合成和分泌来损害甘油三酯的转运。二十碳五烯酸对apo B合成的抑制可能与基因转录减少或mRNA稳定性降低有关，因为在用这种脂肪酸孵育的细胞中apo B mRNA水平显著降低。（摘要截短至400字）
