Miller R G, Keshen T H, Jahoor F, Shew S B, Jaksic T
Department of Surgery, Baylor College of Medicine and Texas Children's Hospital, Houston, Texas 77030, USA.
J Surg Res. 1996 Jun;63(1):199-203. doi: 10.1006/jsre.1996.0247.
The conversion of D-[U-13C]glucose to proline (Pro), aspartate (Asp), and cysteine (Cys) is limited in premature neonates, implying that these amino acids (AA) are conditionally essential. This study was performed to determine whether these findings resulted from an insufficient precursor dose or intracellular compartmentation of newly synthesized amino acids, rather than inadequate synthesis. In the first phase of this study, seven total parenteral nutrition-fed, premature neonates received IV D-[U-13C]glucose at 5 mg/kg/min for 4 hr. In the second phase, a separate cohort of eight patients received an identical infusion. Blood was obtained before and at the end of the infusion. Isotopic enrichments of the free plasma AA and glucose were measured using gas chromatography/mass spectrometry in both studies. In phase 2, the isotopic enrichments of the AA bound to the hepatically synthesized proteins, fibrinogen and VLDL-apolipoprotein B-100 (apo B-100), were measured. In phase 1, despite a glucose precursor enrichment greater than 66%, Pro, Asp, and Cys remained the least enriched of all amino acids studied (P < 0.05). Asp, but not Pro, demonstrated very high enrichments in apo B-100 (P < 0.001), reflecting distinct intracellular compartmentation. We conclude that the limited conversion Of D-[U-13C]glucose to Pro, Asp, and Cys did not result from low precursor glucose enrichment and that there is evidence of Asp compartmentation (intracellular) in premature neonates. However, the low Pro enrichment in the free plasma AA pool and the absence of intracellular Pro compartmentation suggest that Pro may be a conditionally essential AA for premature neonates.
早产新生儿将D-[U-13C]葡萄糖转化为脯氨酸（Pro）、天冬氨酸（Asp）和半胱氨酸（Cys）的能力有限，这意味着这些氨基酸（AA）为条件必需氨基酸。本研究旨在确定这些结果是由于前体剂量不足还是新合成氨基酸的细胞内分隔所致，而非合成不足。在本研究的第一阶段，7名接受全胃肠外营养的早产新生儿以5mg/kg/min的速度静脉输注D-[U-13C]葡萄糖，持续4小时。在第二阶段，另一组8名患者接受相同的输注。在输注前和输注结束时采集血液。在两项研究中均使用气相色谱/质谱法测量游离血浆氨基酸和葡萄糖的同位素富集情况。在第二阶段，测量与肝脏合成的蛋白质、纤维蛋白原和极低密度脂蛋白载脂蛋白B-100（apo B-100）结合的氨基酸的同位素富集情况。在第一阶段，尽管葡萄糖前体富集超过66%，但Pro、Asp和Cys在所有研究的氨基酸中仍然是富集最少的（P<0.05）。Asp（而非Pro）在apo B-100中表现出非常高的富集（P<0.001），反映出明显的细胞内分隔。我们得出结论，D-[U-13C]葡萄糖向Pro、Asp和Cys的有限转化并非由于前体葡萄糖富集不足，并且有证据表明早产新生儿存在Asp的分隔（细胞内）。然而，游离血浆氨基酸池中Pro的低富集以及细胞内不存在Pro分隔表明，Pro可能是早产新生儿的一种条件必需氨基酸。
