Lin Yu Hong, Llanos Adolfo, Mena Patricia, Uauy Ricardo, Salem Norman, Pawlosky Robert J
Laboratory of Membrane Biochemistry and Biophysics and Laboratory of Metabolic Control, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, USA.
Am J Clin Nutr. 2010 Aug;92(2):284-93. doi: 10.3945/ajcn.2009.28779. Epub 2010 Jun 9.
During early postnatal development, the nervous system accretes docosahexaenoic acid (DHA; 22:6n-3), a highly unsaturated n-3 (omega-3) fatty acid (FA) used in the formation of neural cell membranes. DHA, which is present in human breast milk, may also be biosynthesized from n-3 FAs such as 18:3n-3 [alpha-linolenic acid (ALA)] or 20:5n-3 [eicosapentaenoic acid (EPA)]. An important concern is to what extent these precursors can supply DHA to the developing infant.
We analyzed measurements of fractional percentages of plasma (2)H(5)-ALA and (13)C-U-EPA directed toward the synthesis of labeled 22:6n-3 in 11 newborn infants by using compartmental modeling procedures.
One-week-old infants received doses of (2)H(5)-ALA and (13)C-U-EPA ethyl esters enterally. We drew blood from the infants periodically and analyzed the plasma for endogenous and labeled n-3 FAs. From the time-course concentrations of the labeled FAs, we determined rate constant coefficients, fractional synthetic rates, and plasma turnover rates of n-3 FAs.
In infants, approximately 0.04% of the (2)H(5)-ALA dose converted to plasma (2)H(5)-EPA. Plasma (2)H(5)-EPA and (2)H(5)-22:5n-3 [docosapentaenoic acid (DPA)] efficiently converted to (2)H(5)-DPA and (2)H(5)-DHA, respectively. The percentage of plasma (13)C-U-EPA directed toward the synthesis of (13)C-DHA was lower than the percentage of plasma (2)H(5)-EPA that originated from (2)H(5)-ALA.
Endogenously synthesized EPA was efficiently converted to DHA. In comparison, preformed EPA was less efficiently used for DHA biosynthesis, which suggests a differential metabolism of endogenous EPA compared with exogenous EPA. However, on a per mole basis, preformed EPA was 3.6 times more effective toward DHA synthesis than was ALA. Newborns required an intake of approximately 5 mg preformed DHA. kg(-1) x d(-1) to maintain plasma DHA homeostasis.
在出生后的早期发育阶段，神经系统会积累二十二碳六烯酸（DHA；22:6n-3），这是一种高度不饱和的n-3（欧米伽-3）脂肪酸（FA），用于形成神经细胞膜。存在于人乳中的DHA也可由n-3脂肪酸如18:3n-3[α-亚麻酸（ALA）]或20:5n-3[二十碳五烯酸（EPA）]生物合成。一个重要的问题是这些前体能够在多大程度上为发育中的婴儿提供DHA。
我们通过使用房室模型程序分析了11名新生儿血浆中（2）H（5）-ALA和（13）C-U-EPA转化为标记的22:6n-3的合成的分数百分比测量值。
一周大的婴儿经肠道接受（2）H（5）-ALA和（13）C-U-EPA乙酯剂量。我们定期从婴儿身上采集血液，并分析血浆中的内源性和标记的n-3脂肪酸。根据标记脂肪酸的时间进程浓度，我们确定了n-3脂肪酸的速率常数系数、分数合成率和血浆周转率。
在婴儿中，约0.04%的（2）H（5）-ALA剂量转化为血浆（2）H（5）-EPA。血浆（2）H（5）-EPA和（2）H（5）-22:5n-3[二十二碳五烯酸（DPA）]分别有效转化为（2）H（5）-DPA和（2）H（5）-DHA。血浆中（13）C-U-EPA转化为（13）C-DHA的百分比低于血浆中源自（2）H（5）-ALA的（2）H（5）-EPA的百分比。
内源性合成的EPA有效转化为DHA。相比之下，预先形成的EPA用于DHA生物合成的效率较低，这表明内源性EPA与外源性EPA的代谢存在差异。然而，以每摩尔计算，预先形成的EPA对DHA合成的效果比ALA高3.6倍。新生儿需要摄入约5mg预先形成的DHA·kg（-1）·d（-1）以维持血浆DHA稳态。
