Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized 13C magnetic resonance
Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized 13C magnetic resonance
复制标题
DOI：
10.1073/pnas.1111247108
复制
发表时间：
2011-11-22
影响因子：
11.1
通讯作者：
Burgess, Shawn C.
中科院分区：
文献类型：
--
作者：
Merritt, Matthew E.;Harrison, Crystal;Burgess, Shawn C.
在心脏中，超极化[1-C-13]丙酮酸盐给药后，通过磁共振（MR）检测到超极化[C-13]碳酸氢盐和（CO2）-C-13，仅由丙酮酸盐通过丙酮酸脱氢酶复合物（PDH）氧化脱羧引起。然而，肝线粒体具有[1-C-13]丙酮酸可进入的替代合成代谢途径，与其他组织相比，这可能允许超极化MR的诊断范围更广。在进食和禁食小鼠的离体灌注肝脏中监测三羧酸（TCA）循环中超极化[1-C-13]丙酮酸盐的代谢。超极化的[1-C-13]丙酮酸迅速转化为[1-C-13]乳酸、[1-C-13]丙氨酸、[1-C-13]苹果酸、[4-C-13]苹果酸、[1-C-13]天冬氨酸、[4-C-13]天冬氨酸和[C-13]碳酸氢盐。来自禁食动物的肝脏具有增加的乳酸：丙氨酸，与升高的NADH：NAD（+）一致。不对称富集的苹果酸和天冬氨酸的出现表明高速率的回补丙酮酸羧化酶活性和不完全平衡与富马酸。还检测到超极化[C-13]碳酸氢盐，与多种机制一致，包括[4-C-13]草酰乙酸通过磷酸烯醇丙酮酸羧激酶（PEPCK）的催化脱羧作用、[4-C-13]草酰乙酸在异柠檬酸脱氢酶处产生（CO2）-C-13的正向TCA循环通量或[1-C-13]丙酮酸通过PDH的脱羧作用。肝脏谷氨酸的同位素分析证实，回补是通过PDH流量的7倍。此外，在PEPCK KO小鼠的肝脏中，来自[4-C-13]苹果酸和[4-C-13]天冬氨酸的信号明显减弱，来自[C-13]碳酸氢盐的信号完全消失，表明超极化[1-C-13]丙酮酸进入肝脏TCA循环的主要途径是通过丙酮酸羧化酶，并且通过PEPCK的分解流是[C-13]碳酸氢盐的主要来源。我们得出结论，超极化TCA中间体和碳酸氢盐的MR检测是诊断丙酮酸羧化酶和PEPCK通量在肝脏中。
In the heart, detection of hyperpolarized [C-13] bicarbonate and (CO2)-C-13 by magnetic resonance (MR) after administration of hyperpolarized [1-C-13] pyruvate is caused exclusively by oxidative decarboxylation of pyruvate via the pyruvate dehydrogenase complex (PDH). However, liver mitochondria possess alternative anabolic pathways accessible by [1-C-13] pyruvate, which may allow a wider diagnostic range for hyperpolarized MR compared with other tissue. Metabolism of hyperpolarized [1-C-13] pyruvate in the tricarboxylic acid (TCA) cycle was monitored in the isolated perfused liver from fed and fasted mice. Hyperpolarized [1-C-13] pyruvate was rapidly converted to [1-C-13] lactate, [1-C-13] alanine, [1-C-13] malate, [4-C-13] malate, [1-C-13] aspartate, [4-C-13] aspartate, and [C-13] bicarbonate. Livers from fasted animals had increased lactate: alanine, consistent with elevated NADH:NAD(+). The appearance of asymmetrically enriched malate and aspartate indicated high rates of anaplerotic pyruvate carboxylase activity and incomplete equilibration with fumarate. Hyperpolarized [C-13] bicarbonate was also detected, consistent with multiple mechanisms, including cataplerotic decarboxylation of [4-C-13] oxaloacetate via phosphoenolpyruvate carboxykinase (PEPCK), forward TCA cycle flux of [4-C-13] oxaloacetate to generate (CO2)-C-13 at isocitrate dehydrogenase, or decarboxylation of [1-C-13] pyruvate by PDH. Isotopomer analysis of liver glutamate confirmed that anaplerosis was sevenfold greater than flux through PDH. In addition, signal from [4-C-13] malate and [4-C-13] aspartate was markedly blunted and signal from [C-13] bicarbonate was completely abolished in livers from PEPCK KO mice, indicating that the major pathway for entry of hyperpolarized [1-C-13] pyruvate into the hepatic TCA cycle is via pyruvate carboxylase, and that cataplerotic flux through PEPCK is the primary source of [C-13] bicarbonate. We conclude that MR detection of hyperpolarized TCA intermediates and bicarbonate is diagnostic of pyruvate carboxylase and PEPCK flux in the liver.