LDH and PDH Activities in the Ischemic Brain and the Effect of Reperfusion—An Ex Vivo MR Study in Rat Brain Slices Using Hyperpolarized [1-13C]Pyruvate

Abstract

Ischemic stroke is a leading cause for neurologic disability worldwide, for which reperfusion is the only available treatment. Neuroimaging in stroke guides treatment, and therefore determines the clinical outcome. However, there are currently no imaging biomarkers for the status of the ischemic brain tissue. Such biomarkers could potentially be useful for guiding treatment in patients presenting with ischemic stroke. Hyperpolarized 13C MR of [1-13C]pyruvate is a clinically translatable method used to characterize tissue metabolism non-invasively in a relevant timescale. The aim of this study was to utilize hyperpolarized [1-13C]pyruvate to investigate the metabolic consequences of an ischemic insult immediately during reperfusion and upon recovery of the brain tissue. The rates of lactate dehydrogenase (LDH) and pyruvate dehydrogenase (PDH) were quantified by monitoring the rates of [1-13C]lactate and [13C]bicarbonate production from hyperpolarized [1-13C]pyruvate. 31P NMR of the perfused brain slices showed that this system is suitable for studying ischemia and recovery following reperfusion. This was indicated by the levels of the high-energy phosphates (tissue viability) and the chemical shift of the inorganic phosphate signal (tissue pH). Acidification, which was observed during the ischemic insult, has returned to baseline level following reperfusion. The LDH/PDH activity ratio increased following ischemia, from 47.0 ± 12.7 in the control group (n = 6) to 217.4 ± 121.3 in the ischemia-reperfusion group (n = 6). Following the recovery period (ca. 1.5 h), this value had returned to its pre-ischemia (baseline) level, suggesting the LDH/PDH enzyme activity ratio may be used as a potential indicator for the status of the ischemic and recovering brain.

Real-Time Non-Invasive and Direct Determination of Lactate Dehydrogenase Activity in Cerebral Organoids—A New Method to Characterize the Metabolism of Brain Organoids?

“…For [ 13 C]bicarbonate acquisition the sinc pulse was centered 214 Hz down-field from the [ 13 C]bicarbonate resonance frequency, yielding a [1- 13 C]pyruvate-to-[ 13 C]bicarbonate excitation ratio of 0.12. A detailed description regarding the calibration of the RF pulses used in the current study has been previously published [ 17 ]. Using the selective product excitation, the hyperpolarized product signal was fully sampled upon each excitation and thus nulled prior to the next repetition time.…”

“…It is also important to note that studies with hyperpolarized [1- 13 C]pyruvate are translational as it is the lead agent for clinical use [13]. One of the most observed metabolic conversions when administering hyperpolarized [1- 13 C]pyruvate to mammalian tissues in vivo or ex vivo is the production of hyperpolarized [1- 13 C]lactate, which is due to the incell activity of lactate dehydrogenase (LDH) [14][15][16][17][18][19][20][21][22]. Previously, the metabolic properties of organoids were studied mostly by mass spectroscopy-based methods [23][24][25].…”

Accumulation of 3‐aminopropylphosphonate in the ex vivo brain observed by phosphorus‐31 nuclear magnetic resonance

“…Tissue slices and organs were prepared and perfused in the NMR spectrometer as previously described for mouse liver 6,7 (n = 2), breast cancer xenograft tumors 8 (n = 7), mouse heart 9 (n = 4), and rat cerebrum [10][11][12] (n = 4).…”

“…The tissue was placed inside a 10-mm NMR tube and connected to the perfusion system as previously described. [6][7][8][9][10][11][12] The spectra were acquired using a nutation angle of 50 and a repetition time of 1.1 s. Each spectrum was obtained using 820 scans (total scan time of 15 min).…”

A beneficial role for elevated extracellular glutamate in Amyotrophic Lateral Sclerosis and cerebral ischemia

“…This metabolic shift from pyruvate to glutamate oxidation is proposed to occur in ALS and cerebral ischemia; however, there is currently a lack of support for its activity in the former as little is known concerning the expression of EAAT3/EAAC1, the quantity of acetyl CoA or activity of PDH, PDK1, or GOT in ALS tissue. There is more support for the metabolic shift in cerebral ischemia as this condition is associated with an increase in the expression of EAAT3/EAAC1, [124] a decrease in the activity of PDH [125] and an increase in the activity of GOT. [68,69] There is, however, a lack of information regarding the quantity of acetyl CoA.…”