Williard D E, Kaduce T L, Harmon S D, Spector A A
Department of Biochemistry, University of Iowa, Iowa City 52242, USA.
J Lipid Res. 1998 May;39(5):978-86.
Human skin fibroblasts can convert arachidonic acid to 14- and 16-carbon polyunsaturated fatty acid products by peroxisomal beta-oxidation. The purpose of this study was to determine whether similar products are formed from eicosapentaenoic acid (EPA) and whether EPA and arachidonic acid compete for utilization by this oxidative pathway. Three radiolabeled metabolites with shorter retention times than EPA on reverse-phase high-performance liquid chromatography accumulated in the medium during incubation of fibroblasts with [5,6,8,9,11,12,14,15,17,18-3H] EPA ([3H]EPA). These metabolites, which were not formed from [1-14C]EPA and were not detected in the cells, were identified as tetradecatrienoic acid (14:3n-3), hexadecatetraenoic acid (16:4n-3), and octadecatetraenoic acid (18:4n-3). The most abundant product under all of the conditions tested was 16:4n-3. [3H]EPA was converted to 16:4n-3 and 14:3n-3 by fibroblasts deficient in mitochondrial long-chain acyl CoA dehydrogenase, but not by Zellweger syndrome or acyl CoA oxidase mutants that are deficient in peroxisomal beta-oxidation. Competition studies indicated that 16:4n-3 formation from 5 microM [3H]EPA was reduced by 60% when 10 microM arachidonic acid was added, but the conversion of [3H]arachidonic acid to its chain-shortened products was not decreased by the addition of 10 microM EPA. These findings demonstrate that as in the case of arachidonic acid, chain-shortened polyunsaturated fatty acid products accumulate when EPA undergoes peroxisomal beta-oxidation. While EPA does not reduce arachidonic acid utilization by this pathway, it is possible that some biological actions of EPA may be mediated by the formation of the corresponding EPA products, 16:4n-3 and 14:3n-3.
人皮肤成纤维细胞可通过过氧化物酶体β-氧化将花生四烯酸转化为14碳和16碳的多不饱和脂肪酸产物。本研究的目的是确定二十碳五烯酸（EPA）是否能形成类似产物，以及EPA和花生四烯酸是否会竞争该氧化途径的利用。在用[5,6,8,9,11,12,14,15,17,18-3H]EPA（[3H]EPA）培养成纤维细胞的过程中，三种在反相高效液相色谱上保留时间比EPA短的放射性标记代谢产物在培养基中积累。这些代谢产物不是由[1-14C]EPA形成的，且在细胞中未检测到，它们被鉴定为十四碳三烯酸（14:3n-3）、十六碳四烯酸（16:4n-3）和十八碳四烯酸（18:4n-3）。在所有测试条件下，最丰富的产物是16:4n-3。[3H]EPA被线粒体长链酰基辅酶A脱氢酶缺陷的成纤维细胞转化为16:4n-3和14:3n-3，但过氧化物酶体β-氧化缺陷的 Zellweger 综合征或酰基辅酶A氧化酶突变体则不能。竞争研究表明，当添加10μM花生四烯酸时，5μM[3H]EPA形成16:4n-3的量减少了60%，但添加10μM EPA并未降低[3H]花生四烯酸向其链缩短产物的转化。这些发现表明，与花生四烯酸的情况一样，当EPA进行过氧化物酶体β-氧化时，链缩短的多不饱和脂肪酸产物会积累。虽然EPA不会通过该途径降低花生四烯酸的利用，但EPA的一些生物学作用可能是由相应的EPA产物16:4n-3和14:3n-3的形成介导的。
