Salem N, Wegher B, Mena P, Uauy R
Laboratory of Membrane Biochemistry and Biophysics, National Institute of Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, MD 20852, USA.
Proc Natl Acad Sci U S A. 1996 Jan 9;93(1):49-54. doi: 10.1073/pnas.93.1.49.
It is becoming clear that an adequate level of long-chain highly unsaturated fatty acids in the nervous system is required for optimal function and development; however, the ability of infants to biosynthesize long-chain fatty acids is unknown. This study explores the capacity of human infants to convert 18-carbon essential fatty acids to their elongated and desaturated forms, in vivo. A newly developed gas chromatography/negative chemical ionization/mass spectrometry method employing 2H-labeled essential fatty acids allowed assessment of this in vivo conversion with very high sensitivity and selectivity. Our results demonstrate that human infants have the capacity to convert dietary essential fatty acids administered enterally as 2H-labeled ethyl esters to their longer-chain derivatives, transport them to plasma, and incorporate them into membrane lipids. The in vivo conversion of linoleic acid (18:2n6) to arachidonic acid (20:4n6) is demonstrated in human beings. All elongases/desaturases necessary for the conversion of linolenic acid (18:3n3) to docosahexaenoic acid (22:6n3) are also active in the first week after birth. Although the absolute amounts of n-3 fatty acid metabolites accumulated in plasma are greater than those of the n-6 family, estimates of the endogenous pools of 18:2n6 and 18:3n3 indicate that n-6 fatty acid conversion rates are greater than those of the n-3 family. While these data clearly demonstrate the capability of infants to biosynthesize 22:6n3, a lipid that is required for optimal neural development, the amounts produced in vivo from 18:3n3 may be inadequate to support the 22:6n3 level observed in breast-fed infants.
越来越明显的是，神经系统中长链高度不饱和脂肪酸的充足水平是最佳功能和发育所必需的；然而，婴儿生物合成长链脂肪酸的能力尚不清楚。本研究探讨了人类婴儿在体内将18碳必需脂肪酸转化为其延长和去饱和形式的能力。一种新开发的采用2H标记必需脂肪酸的气相色谱/负离子化学电离/质谱方法能够以非常高的灵敏度和选择性评估这种体内转化。我们的结果表明，人类婴儿有能力将以2H标记乙酯形式经肠道给予的膳食必需脂肪酸转化为其长链衍生物，将它们转运到血浆中，并将它们纳入膜脂中。人类体内亚油酸（18:2n6）向花生四烯酸（20:4n6）的体内转化得到了证实。将亚麻酸（18:3n3）转化为二十二碳六烯酸（22:6n3）所需的所有延长酶/去饱和酶在出生后的第一周也具有活性。虽然血浆中积累的n-3脂肪酸代谢物的绝对量大于n-6家族的代谢物，但对18:2n6和18:3n3内源性库的估计表明，n-6脂肪酸的转化率高于n-3家族。虽然这些数据清楚地证明了婴儿生物合成22:6n3的能力，22:6n3是最佳神经发育所需的一种脂质，但由18:3n3在体内产生的量可能不足以支持母乳喂养婴儿中观察到的22:6n3水平。
