Pyruvate and acetate metabolism after TBI: implications for cerebral energy metabolism

治疗创伤性脑损伤患者的一个主要挑战是同时发生的复杂情况。 原发损伤后的继发性损伤过程。次要事件，如大脑 高糖酵解和线粒体衰竭在原发损伤后几分钟到几个月内发生，提供了 治疗干预的潜在机会之窗。如果及早进行干预，可能会阻止或 减少继发性脑损伤，直接影响患者的长期预后。因此，非侵入性 颅脑损伤患者急性期和亚急性期的病理生理检测及特征， 将对贫困风险最高的个体的早期诊断具有重要的临床意义 这对于确定和开发有效的治疗方法是至关重要的。虽然有一些人 颅脑损伤的病理改变是潜在的生物标志物，目前的临床影像检查都不敏感。 足以被常规用于检测有继发性损伤的脑子区域的代谢变化的细节。 超极化13C标记底物的磁共振光谱成像(MRSI)提供了独特的 体内关键动态代谢过程的非侵入性测量。特别是，丙酮酸占据了 脑能量代谢的关键节点，[1-13C]丙酮酸的命运之一是还原为乳酸AS 糖酵解的最终产物，在线粒体中转化为乙酰辅酶A和二氧化碳(检测为HCO3-) 丙酮酸脱氢酶(PDH)通量或逆丙酮酸羧化酶(PC)途径 磷酸化。另一方面，丙酮酸通过以下方式直接评估三羧酸(TCA)循环 检测[5-13C]谷氨酸的产生。虽然我们的初步数据显示乳酸和 超极化[1-13C]丙酮酸在大鼠颅脑损伤模型和急性脑损伤模型中HCO3-(碳酸氢盐)产生的减少 然而，作为TCA循环标志物的[13C]HCO3-作为TCA循环标志物的作用需要进一步验证，因为 丙酮酸羧化。脑损伤后的另一个关键代谢变化是脑组织醋酸盐氧化增加。 星形胶质细胞，发挥神经保护作用。增强的醋酸盐代谢与丙酮酸紧密地相互作用 代谢，因此，在解释[13C]丙酮酸代谢时应一并考虑。 这个项目的基本目标是了解脑外伤如何影响体内细胞代谢。 使用超极化13C磁共振脑成像作为脑外伤患者个性化治疗的一步。在这份提案中， 将使用大鼠脑外伤模型，通过比较活体内的 成像结果与体外组织分析。首先，我们将发展超极化的[2-13C]丙酮酸作为探针来 直接测量TBI中改变的TCA循环活性(目标1)。第二，我们将评估以下方面的贡献 在大鼠颅脑损伤模型中增加醋酸盐代谢为丙酮酸氧化(目标2)。活体纵向成像 数据(目标1和2)将通过冷冻夹脑的横截面体外核磁共振同位素分析来验证 纸巾。最后，我们将翻译这项技术来评估急性轻度脑外伤患者的代谢变化(目标3)。

A major challenge of treating traumatic brain injury (TBI) patients is the simultaneously occurring complex secondary injury processes following the primary injury. The secondary events such as cerebral hyperglycolysis and mitochondrial failure develop over minutes to months after the primary injury, providing a potential window of opportunity for therapeutic intervention. Given early, this intervention may prevent or reduce secondary brain damage, directly impacting long-term patient outcome. Therefore, the noninvasive detection and characterization of pathophysiology in TBI patients during the acute and early sub-acute stages, will have critical clinical implications for the early diagnosis of individuals with the highest risk of poor neurological outcomes and will be vital for identifying and developing effective therapies. While a number of pathological alternations in TBI are potential biomarkers, no current clinical imaging modalities are sensitive enough to be routinely used to detect the details of metabolic shifts in brain sub-regions with secondary injury. Magnetic resonance spectroscopic imaging (MRSI) of hyperpolarized 13C-labeled substrates provides unique noninvasive measurements of critical in vivo dynamic metabolic processes. In particular, pyruvate occupies a key nodal point in cerebral energy metabolism, among the fates of [1-13C]pyruvate are reduction to lactate as the end product of glycolysis, conversion in mitochondria to form acetyl-CoA and CO2 (detected as HCO3–) via pyruvate dehydrogenase (PDH) flux or anaplerotic pyruvate carboxylase (PC) pathway for oxidative phosphorylation. [2-13C]pyruvate, on the other hand, directly assess the tricarboxylic acid (TCA) cycle by detecting [5-13C]glutamate production. While our preliminary data demonstrated increased lactate and decreased HCO3– (bicarbonate) production from hyperpolarized [1-13C]pyruvate in a rat TBI model and acute TBI patients, however, the role of [13C]HCO3– as a TCA cycle marker needs further verification due to the high pyruvate carboxylation. Another key metabolic alteration following TBI is increased acetate oxidation in astrocytes, playing a neuro-protective role. The increased acetate metabolism tightly interacts with pyruvate metabolism, and thus, should be considered together when interpreting [13C]pyruvate metabolism. The fundamental goal of this project is to understand how TBI influences the in vivo cellular metabolism in the brain using hyperpolarized 13C MRSI as a step towards personalizing therapy for TBI patients. In this proposal, a comprehensive analysis of TBI metabolism will be performed using a rat TBI model by comparing the in vivo imaging results with ex vivo tissue analysis. First, we will develop hyperpolarized [2-13C]pyruvate as a probe to directly measure the altered TCA cycle activity in TBI (aim 1). Second, we will assess the contribution of increased acetate metabolism to pyruvate oxidation in a rat TBI model (aim 2). The longitudinal in vivo imaging data (aims 1&2) will be validated by cross-sectional ex vivo NMR isotopomer analysis of freeze-clamped brain tissues. Finally, we will translate the technique to assess metabolic changes in acute mild TBI patients (aim 3).