Section Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel University, Am Botanischen Garten 18, Kiel 24118, Germany.
Pharmaceutical Institute, CAU Kiel, Gutenbergstr. 76, Kiel 24118, Germany.
Anal Chem. 2024 Oct 29;96(43):17135-17144. doi: 10.1021/acs.analchem.4c02419. Epub 2024 Oct 15.
Metabolic changes in an organism often occur much earlier than macroscopic manifestations of disease, such as invasive tumors. Therefore, noninvasive tools to monitor metabolism are fundamental as they provide insights into in vivo biochemistry. NMR represents one of the gold standards for such insights by observing metabolites. Using nuclear spin hyperpolarization greatly increases the NMR sensitivity, enabling μmol/L sensitivity with a time resolution of about one second. However, a metabolic phantom with reproducible, rapid, and human-like metabolism is needed to progress research in this area. Using baker's yeast as a convenient metabolic factory, we demonstrated in a single study that yeast cells provide a robust and rapidly metabolizing phantom for pyruvate and fumarate, including substrates with a natural abundance of C: we observed the production of ethanol, carbon dioxide, bicarbonate, lactate, alanine from pyruvate, malate, and oxaloacetate from fumarate. For observation, we hyperpolarized pyruvate and fumarate via the dissolution dynamic nuclear polarization (dDNP) technique to about 30% C polarization that is equivalent to 360,000 signal enhancement at 1 T and 310 K. Major metabolic pathways were observed using tracers at a natural abundance of C, demonstrating that isotope labeling is not always essential in vitro. Enriched [1-C]pyruvate revealed minor lactate production, presumably via the D-lactate dehydrogenase (DLD) enzyme pathway, demonstrating the sensitivity gain using a dense yeast solution. We foresee that yeast as a metabolic factory can find application as an abundant MRI phantom standard to calibrate and optimize molecular MRI protocols. Our study highlights the potential of using hyperpolarization to probe the metabolism of yeast and other microorganisms even with naturally abundant substrates, offering valuable insights into their response to various stimuli such as drugs, treatment, nourishment, and genetic modification, thereby advancing drug development and our understanding of biochemical processes.
生物体的代谢变化通常发生在疾病的宏观表现（如侵袭性肿瘤）之前。因此，监测代谢的非侵入性工具至关重要，因为它们提供了对体内生物化学的深入了解。NMR 通过观察代谢物来代表此类见解的黄金标准之一。通过核自旋超极化，大大提高了 NMR 的灵敏度，使其能够以约 1 秒的时间分辨率达到 μmol/L 的灵敏度。然而，需要具有可重复、快速且类似人类代谢的代谢体模来推进该领域的研究。使用面包酵母作为方便的代谢工厂，我们在一项研究中证明，酵母细胞为丙酮酸和富马酸提供了一个稳健且快速代谢的体模，包括具有 C 天然丰度的底物：我们观察到从丙酮酸生产乙醇、二氧化碳、碳酸氢盐、乳酸，从富马酸生产苹果酸和草酰乙酸。为了观察，我们通过溶解动态核极化（dDNP）技术将丙酮酸和富马酸超极化至约 30%的 C 极化，在 1 T 和 310 K 下等效于 360,000 倍的信号增强。使用 C 天然丰度的示踪剂观察到主要代谢途径，表明在体外并不总是需要同位素标记。富[1-C]丙酮酸显示出少量乳酸的产生，可能是通过 D-乳酸脱氢酶（DLD）酶途径，证明了使用密集酵母溶液的灵敏度增益。我们预计酵母作为代谢工厂可以作为丰富的 MRI 体模标准应用，用于校准和优化分子 MRI 协议。我们的研究强调了使用极化来探测酵母和其他微生物代谢的潜力，即使使用天然丰度的底物，也可以为它们对各种刺激（如药物、治疗、营养和遗传修饰）的反应提供有价值的见解，从而推进药物开发和我们对生化过程的理解。
