In Vivo Hyperpolarized Carbon-13 Magnetic Resonance Spectroscopy Reveals Increased Pyruvate Carboxylase Flux in an Insulin-Resistant Mouse Model
In Vivo Hyperpolarized Carbon-13 Magnetic Resonance Spectroscopy Reveals Increased Pyruvate Carboxylase Flux in an Insulin-Resistant Mouse Model
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DOI：
10.1002/hep.26028
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发表时间：
2013-02-01
期刊：
影响因子：
13.5
通讯作者：
Radda, George K.
中科院分区：
文献类型：
--
作者：
Lee, Philip;Leong, Waifook;Radda, George K.
2型糖尿病的发病机制的特征在于胰岛素作用受损和肝葡萄糖产生（HGP）增加。尽管肝代谢异常在糖尿病发展中的重要性，但目前还没有分子探针可以在体内以非侵入性方式测量肝代谢异常途径。在这项研究中，我们使用超极化碳13（C-13）标记的丙酮酸磁共振波谱（MRS），以确定在高脂饮食（HFD）诱导的2型糖尿病小鼠模型的肝再生的变化。与普通饲料喂养的小鼠相比，HFD喂养的小鼠显示出更高水平的草酰乙酸、天冬氨酸和苹果酸，沿着超极化[1-C-13]丙酮酸及其下游代谢物[1-C-13]苹果酸和[1-C-13]天冬氨酸之间的C-13标记交换率增加。使用肝脏提取物的生化分析显示，在HFD喂养的小鼠中，苹果酸脱氢酶活性上调，但天冬氨酸转氨酶活性未上调。此外，[1-C-13]丙酮酸和[1-C-13]天冬氨酸之间的C-13标记交换率（k（pyr->asp））与肝细胞中致肝细胞坏死的丙酮酸羧化酶（PC）活性具有明显的相关性。最后，通过天冬氨酸信号和k（pyr->asp）的增加检测到胰高血糖素刺激上调的HGP，而用二甲双胍处理2周的HFD小鼠显示出天冬氨酸和苹果酸的产生较低，以及丙酮酸和苹果酸之间的k（pyr->asp）和C-13-标记交换率降低，与下调的胚胎发生一致。结论：两者合计，我们表明，增加PC流量是一个重要的途径，负责增加HGP在糖尿病的发展，和胆固醇诱导的代谢变化，具体到肝脏可以在体内检测到超极化C-13-生物分子探针。超极化C-13 MRS和代谢物交换率的测定可以纵向监测疾病发展中的肝功能。（肝脏学2013;57：515-524）
The pathogenesis of type 2 diabetes is characterized by impaired insulin action and increased hepatic glucose production (HGP). Despite the importance of hepatic metabolic aberrations in diabetes development, there is currently no molecular probe that allows measurement of hepatic gluconeogenic pathways in vivo and in a noninvasive manner. In this study, we used hyperpolarized carbon 13 (C-13)-labeled pyruvate magnetic resonance spectroscopy (MRS) to determine changes in hepatic gluconeogenesis in a high-fat diet (HFD)-induced mouse model of type 2 diabetes. Compared with mice on chow diet, HFD-fed mice displayed higher levels of oxaloacetate, aspartate, and malate, along with increased C-13 label exchange rates between hyperpolarized [1-C-13] pyruvate and its downstream metabolites, [1-C-13] malate and [1-C-13] aspartate. Biochemical assays using liver extract revealed up-regulated malate dehydrogenase activity, but not aspartate transaminase activity, in HFD-fed mice. Moreover, the C-13 label exchange rate between [1-C-13] pyruvate and [1-C-13] aspartate (k(pyr->asp)) exhibited apparent correlation with gluconeogenic pyruvate carboxylase (PC) activity in hepatocytes. Finally, up-regulated HGP by glucagon stimulation was detected by an increase in aspartate signal and k(pyr->asp), whereas HFD mice treated with metformin for 2 weeks displayed lower production of aspartate and malate, as well as reduced k(pyr->asp) and C-13-label exchange rate between pyruvate and malate, consistent with down-regulated gluconeogenesis. Conclusion: Taken together, we demonstrate that increased PC flux is an important pathway responsible for increased HGP in diabetes development, and that pharmacologically induced metabolic changes specific to the liver can be detected in vivo with a hyperpolarized C-13-biomolecular probe. Hyperpolarized C-13 MRS and the determination of metabolite exchange rates may allow longitudinal monitoring of liver function in disease development. (HEPATOLOGY 2013;57:515-524)