Karelson Gunnar, Ziegler André, Künnecke Basil, Seelig Joachim
Department of Biophysical chemistry, Biozentrum, University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland.
NMR Biomed. 2003 Oct-Nov;16(6-7):413-23. doi: 10.1002/nbm.845.
Using in vivo (13)C-NMR spectroscopy, the energy metabolism in rat brain has commonly been studied via infusion of (13)C-labeled substrates on a minute to hour time scale. In the present study, as a novel approach, (13)C-enriched animal chow was administered over several days and compared with a 2 h infusion of [U-(13)C(6)]-glucose. Rats received chow containing either [U-(13)C(6)]-glucose or [U-(13)C]-biomass (a mixture of proteins, lipids, DNA, and carbohydrates) during 3 to 5 days. During feeding with (13)C-labeled glucose and biomass, in vivo (13)C-NMR spectroscopy was carried out daily and revealed slow but successive label incorporation into a large number of metabolites. Lipids and proteins were not significantly (13)C-enriched during a 2 h infusion of (13)C-labeled glucose, but became the most prominent resonances in the (13)C feeding experiment. Likewise, feeding with (13)C-enriched biomass led to additional (13)C-label incorporation into creatine, urea carbons and glycogen. Finally, only the acetyl moiety of N-acetyl-aspartate (NAA) became significantly enriched during the 2 h infusion experiment, whereas the aspartyl moiety remained at natural abundance levels. In the feeding experiments, however, label incorporation into all carbons of NAA could be observed. Moreover, isotopomer analysis of brain extracts revealed that the acetyl moiety of NAA in feeding experiments was always more strongly (13)C-enriched than its aspartyl moiety, suggesting that the turnover of the acetyl moiety is faster than that of the aspartyl moiety. The different enrichment kinetics of acetyl and aspartyl moiety could be explained by the existence of two different metabolic pathways reflecting the compartmentalised synthesis of NAA.
利用体内¹³C核磁共振波谱技术，通常通过在分钟至小时的时间尺度上输注¹³C标记的底物来研究大鼠大脑中的能量代谢。在本研究中，作为一种新方法，在数天内给予富含¹³C的动物饲料，并与输注[U-¹³C₆]-葡萄糖2小时进行比较。大鼠在3至5天内接受含有[U-¹³C₆]-葡萄糖或[U-¹³C]-生物质（蛋白质、脂质、DNA和碳水化合物的混合物）的饲料。在用¹³C标记的葡萄糖和生物质喂养期间，每天进行体内¹³C核磁共振波谱分析，结果显示标记物缓慢但持续地掺入大量代谢物中。在输注¹³C标记的葡萄糖2小时期间，脂质和蛋白质的¹³C富集不显著，但在¹³C喂养实验中成为最显著的共振峰。同样，用富含¹³C的生物质喂养导致额外的¹³C标记掺入肌酸、尿素碳和糖原中。最后，在2小时输注实验期间，只有N-乙酰天门冬氨酸（NAA）的乙酰部分显著富集，而天门冬氨酰部分保持在自然丰度水平。然而，在喂养实验中，可以观察到标记物掺入NAA的所有碳中。此外，对脑提取物的同位素异构体分析表明，在喂养实验中，NAA的乙酰部分的¹³C富集总是比其天门冬氨酰部分更强，这表明乙酰部分的周转速度比天门冬氨酰部分快。乙酰和天门冬氨酰部分不同的富集动力学可以通过存在反映NAA分区合成的两种不同代谢途径来解释。
