Ith Michael, Stettler Christoph, Xu Jian, Boesch Chris, Kreis Roland
University Institute of Diagnostic, Interventional and Pediatric Radiology, University and Inselspital Bern, Switzerland.
NMR Biomed. 2014 Nov;27(11):1285-92. doi: 10.1002/nbm.3186. Epub 2014 Sep 2.
(1) H-MRS is regularly applied to determine lipid content in ectopic tissue - mostly skeletal muscle and liver - to investigate physiological and/or pathologic conditions, e.g. insulin resistance. Technical developments also allow non-invasive in vivo assessment of cardiac lipids; however, basic data about methodological reliability (repeatability) and physiological variations are scarce. The aim of the presented work was to determine potential diurnal changes of cardiac lipid stores in humans, and to put the results in relation to methodological repeatability and normal physiological day-to-day variations. Optimized cardiac- and respiratory-gated (1) H-MRS was used for non-invasive quantification of intracardiomyocellular lipids (ICCL), creatine, trimethyl-ammonium compounds (TMA), and taurine in nine healthy young men at three time points per day on two days separated by one week. This design allowed determination of (a) diurnal changes, (b) physiological variation over one week and (c) methodological repeatability of the ICCL levels. Comparison of fasted morning to post-absorptive evening measurements revealed a significant 37 ± 19% decrease of ICCL during the day (p = 0.0001). There was a significant linear correlation between ICCL levels in the morning and their decrease during the day (p = 0.015). Methodological repeatability for the ICCL/creatine ratio was excellent, with a coefficient of variance of ~5%, whereas physiological variation was found to be considerably higher (22%) in spite of a standardized physiological preparation protocol. In contrast, TMA levels remained stable over this time period. The proposed (1) H-MRS technique provides a robust way to investigate relevant physiological changes in cardiac metabolites, in particular ICCL. The present results suggest that ICCL reveal a diurnal course, with higher levels in the morning as compared to evening. In addition, a considerable long-term variation of ICCL levels, in both the morning and evening, was documented. Given the high methodological repeatability, these effects should be taken into account in studies investigating the metabolic role of ICCL.
（1）氢磁共振波谱（H-MRS）常用于测定异位组织（主要是骨骼肌和肝脏）中的脂质含量，以研究生理和/或病理状况，如胰岛素抵抗。技术的发展也使得能够对心脏脂质进行非侵入性的体内评估；然而，关于方法可靠性（可重复性）和生理变异的基础数据却很匮乏。本研究的目的是确定人类心脏脂质储备的潜在昼夜变化，并将结果与方法的可重复性和正常生理日常变异联系起来。采用优化的心脏和呼吸门控氢磁共振波谱（H-MRS）技术，对9名健康年轻男性在相隔一周的两天里每天三个时间点进行心肌细胞内脂质（ICCL）、肌酸、三甲铵化合物（TMA）和牛磺酸的非侵入性定量分析。这种设计能够确定：（a）昼夜变化；（b）一周内的生理变异；以及（c）ICCL水平的方法可重复性。空腹早晨与吸收后傍晚测量值的比较显示，白天ICCL显著下降37±19%（p = \alpha）。早晨的ICCL水平与其白天下降幅度之间存在显著的线性相关性（p = \beta）。ICCL/肌酸比值的方法可重复性极佳，变异系数约为5%，而尽管采用了标准化的生理准备方案，生理变异仍明显更高（22%）。相比之下，TMA水平在此时间段内保持稳定。所提出的氢磁共振波谱（H-MRS）技术为研究心脏代谢物尤其是ICCL的相关生理变化提供了一种可靠的方法。目前的结果表明，ICCL呈现昼夜变化过程，早晨水平高于傍晚。此外，记录到早晨和傍晚的ICCL水平均存在相当大的长期变异。鉴于方法的高可重复性，在研究ICCL的代谢作用时应考虑这些影响。
