Kidneys play a central role in numerous disorders but current imaging methods have limited utility to probe renal metabolism. Hyperpolarized (HP) 13 C magnetic resonance imaging is uniquely suited to provide metabolite-specific information about key biochemical pathways and it offers the further advantage that renal imaging is practical in humans. This study evaluated the feasibility of hyperpolarization examinations in a widely used model for analysis of renal physiology, the isolated kidney, which enables isolation of renal metabolism from the effects of other organs and validation of HP results by independent measurements. Isolated rat kidneys were supplied with either HP [1-13 C]pyruvate only or HP [1-13 C]pyruvate plus octanoate. Metabolic activity in both groups was confirmed by stable renal oxygen consumption. HP [1-13 C]pyruvate was readily metabolized to [13 C]bicarbonate, [1-13 C]lactate, and [1-13 C]alanine, detectable seconds after HP [1-13 C]pyruvate was injected. Octanoate suppressed but did not eliminate the production of HP [13 C]bicarbonate from [1-13 C]pyruvate. Steady-state flux analyses using non-HP 13 C substrates validated the utilization of HP [1-13 C]pyruvate, as observed by HP 13 C NMR. In the presence of octanoate, lactate is generated from a tricarboxylic acid cycle intermediate, oxaloacetate. The isolated rat kidney may serve as an excellent model for investigating and establishing new HP 13 C metabolic probes for future kidney imaging applications. © 2022 John Wiley & Sons Ltd.

PURPOSE: [13 C]Bicarbonate formation from hyperpolarized [1-13 C]pyruvate via pyruvate dehydrogenase, a key regulatory enzyme, represents the cerebral oxidation of pyruvate and the integrity of mitochondrial function. The present study is to characterize the chronology of cerebral mitochondrial metabolism during secondary injury associated with acute traumatic brain injury (TBI) by longitudinally monitoring [13 C]bicarbonate production from hyperpolarized [1-13 C]pyruvate in rodents.; METHODS: Male Wistar rats were randomly assigned to undergo a controlled-cortical impact (CCI, n=31) or sham surgery (n=22). Seventeen of the CCI and 9 of the sham rats longitudinally underwent a 1 H/13 C-integrated MR protocol that includes a bolus injection of hyperpolarized [1-13 C]pyruvate at 0 (2h), 1, 2, 5, and 10days post-surgery. Separate CCI and sham rats were used for histological validation and enzyme assays.; RESULTS: In addition to elevated lactate, we observed significantly reduced bicarbonate production in the injured site. Unlike the immediate appearance of hyperintensity on T2 -weighted MRI, the contrast of bicarbonate signals between the injured region and the contralateral brain peaked at 24h post-injury, then fully recovered to the normal level at day 10. A subset of TBI rats demonstrated markedly increased bicarbonate in normal-appearing contralateral brain regions post-injury.; CONCLUSION: This study demonstrates that aberrant mitochondrial metabolism occurring in acute TBI can be monitored by detecting [13 C]bicarbonate production from hyperpolarized [1-13 C]pyruvate, suggesting that [13 C]bicarbonate is a sensitive in-vivo biomarker of the secondary injury processes. © 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.

Cellular redox is intricately linked to energy production and normal cell function. Although the redox states of mitochondria and cytosol are connected by shuttle mechanisms, the redox state of mitochondria may differ from redox in the cytosol in response to stress. However, detecting these differences in functioning tissues is difficult. Here, we employed C-13 magnetic resonance spectroscopy (MRS) and co- polarized [1-C-13] pyruvate and [1,3- C-13(2)] acetoacetate ([1,3-C-13(2)]AcAc) to monitor production of hyperpolarized (HP) lactate and beta-hydroxybutyrate as indicators of cytosolic and mitochondrial redox, respectively. Isolated rat hearts were examined under normoxic conditions, during low-flow ischemia, and after pretreatment with either aminooxyacetate (AOA) or rotenone. All interventions were associated with an increase in [P-i]/[ATP] measured by P-31 NMR. In well-oxygenated untreated hearts, rapid conversion of HP [1-C-13]pyruvate to [1-C-13]lactate and [1,3-C-13(2)]AcAc to [1,3-C-13(2)]beta-hydroxybutyrate ([1,3-C-13(2)]beta-HB) was readily detected. A significant increase in HP [1,3-C-13(2)]beta-HB but not [1-C-13]lactate was observed in rotenone-treated and ischemic hearts, consistent with an increase in mitochondrial NADH but not cytosolic NADH. AOA treatments did not alter the productions of HP [1-C-13]lactate or [1,3-C-13(2)]beta-HB. This study demonstrates that biomarkers of mitochondrial and cytosolic redox may be detected simultaneously in functioning tissues using co-polarized [1-C-13]pyruvate and [1,3-C-13(2)]AcAc and C-13 MRS and that changes in mitochondrial redox may precede changes in cytosolic redox.

Purpose Previous cardiac imaging studies using hyperpolarized (HP) [1-C-13]pyruvate were acquired at end-diastole (ED). Little is known about the interaction between cardiac cycle and metabolite content in the myocardium. In this study, we compared images of HP pyruvate and products at end-systole (ES) and ED. Methods A dual-phase C-13 MRI sequence was implemented to acquire two sequential HP images within a single cardiac cycle at ES and ED during successive R-R intervals in an interleaved manner. Each healthy volunteer (N = 3) received two injections of HP [1-C-13]pyruvate for the dual-phase imaging on the short-axis and the vertical long-axis planes. Spatial distribution of HP C-13 metabolites at each cardiac phase was correlated to multiphase H-1 MRI to confirm the mechanical changes. Ratios of myocardial HP metabolites were compared between ES and ED. Segmental analysis was performed on the midcavity short-axis plane. Results In addition to mechanical changes, metabolic profiles of the heart detected by HP [1-C-13]pyruvate differed between ES and ED. The myocardial signal of [C-13]bicarbonate relative to [1-C-13]lactate was significantly smaller at ED than the ratio at ES (p < .05), particularly in mid-anterior and mid-inferoseptal segments. The distinct metabolic profiles in the myocardium likely reflect the technical aspects of the imaging approach such as the coronary flow in addition to the cyclical changes in metabolism. Conclusion The study demonstrates that metabolic profiles of the heart, measured by HP [1-C-13]pyruvate, are affected by the cardiac cycle in which that the data are acquired.

Purpose This study is to investigate time-resolved C-13 MR spectroscopy (MRS) as an alternative to imaging for assessing pyruvate metabolism using hyperpolarized (HP) [1-C-13]pyruvate in the human brain. Methods Time-resolved C-13 spectra were acquired from four axial brain slices of healthy human participants (n = 4) after a bolus injection of HP [1-C-13]pyruvate. C-13 MRS with low flip-angle excitations and a multichannel C-13/H-1 dual-frequency radiofrequency (RF) coil were exploited for reliable and unperturbed assessment of HP pyruvate metabolism. Slice-wise areas under the curve (AUCs) of C-13-metabolites were measured and kinetic analysis was performed to estimate the production rates of lactate and HCO3-. Linear regression analysis between brain volumes and HP signals was performed. Region-focused pyruvate metabolism was estimated using coil-wise C-13 reconstruction. Reproducibility of HP pyruvate exams was presented by performing two consecutive injections with a 45-minutes interval. Results [1-C-13]Lactate relative to the total C-13 signal (tC) was 0.21-0.24 in all slices. [C-13]HCO3-/tC was 0.065-0.091. Apparent conversion rate constants from pyruvate to lactate and HCO3- were calculated as 0.014-0.018 s(-1) and 0.0043-0.0056 s(-1), respectively. Pyruvate/tC and lactate/tC were in moderate linear relationships with fractional gray matter volume within each slice. White matter presented poor linear regression fit with HP signals, and moderate correlations of the fractional cerebrospinal fluid volume with pyruvate/tC and lactate/tC were measured. Measured HP signals were comparable between two consecutive exams with HP [1-C-13]pyruvate. Conclusions Dynamic MRS in combination with multichannel RF coils is an affordable and reliable alternative to imaging methods in investigating cerebral metabolism using HP [1-C-13]pyruvate.

Background: Pyruvate dehydrogenase (PDH) and lactate dehydrogenase are essential for adenosine triphosphate production in skeletal muscle. At the onset of exercise, oxidation of glucose and glycogen is quickly enabled by dephosphorylation of PDH. However, direct measurement of PDH flux in exercising human muscle is daunting, and the net effect of covalent modification and other control mechanisms on PDH flux has not been assessed.Purpose: To demonstrate the feasibility of assessing PDH activation and changes in pyruvate metabolism in human skeletal muscle after the onset of exercise using carbon 13 (C-13) MRI with hyperpolarized (HP) [1-C-13]-pyruvate.Materials and Methods: For this prospective study, sedentary adults in good general health (mean age, 42 years +/- 18 [standard deviation]; six men) were recruited from August 2019 to September 2020. Subgroups of the participants were injected with HP [1-C-13]-pyruvate at resting, during plantar flexion exercise, or 5 minutes after exercise during recovery. In parallel, hydrogen 1 arterial spin labeling MRI was performed to estimate muscle tissue perfusion. An unpaired t test was used for comparing C-13 data among the states.Results: At rest, HP [1-C-13]-lactate and [1-C-13]-alanine were detected in calf muscle, but [C-13]-bicarbonate was negligible. During moderate flexion-extension exercise, total HP C-13 signals (tC) increased 2.8-fold because of increased muscle perfusion (P = .005), and HP [1-C-13]-lactate-to-tC ratio increased 1.7-fold (P = .04). HP [C-13]-bicarbonate-to-tC ratio increased 8.4-fold (P = .002) and returned to the resting level 5 minutes after exercise, whereas the lactate-to-tC ratio continued to increase to 2.3-fold as compared with resting (P = .008).Conclusion: Lactate and bicarbonate production from hyperpolarized (HP) [1-carbon 13 {C-13}]-pyruvate in skeletal muscle rapidly reflected the onset and the termination of exercise. These results demonstrate the feasibility of imaging skeletal muscle metabolism using HP [1-C-13]-pyruvate MRI and the sensitivity of in vivo pyruvate metabolism to exercise states. (C) RSNA, 2021

Transient disruption of the blood-brain barrier (BBB) with focused ultrasound (FUS) is an emerging clinical method to facilitate targeted drug delivery to the brain. The focal noninvasive disruption of the BBB can be applied to promote the local delivery of hyperpolarized substrates. In this study, we investigated the effects of FUS on imaging brain metabolism using two hyperpolarized C-13-labeled substrates in rodents: [1-C-1(3)]-pyruvate and [1-C-1(3)]glycerate. The BBB is a rate-limiting factor for pyruvate delivery to the brain, and glycerate minimally passes through the BBB. First, cerebral imaging with hyperpolarized [1-C-1(3)]pyruvate resulted in an increase in total C-13 signals (p = 0.05) after disrupting the BBB with FUS. Significantly higher levels of both [1-C-1(3)]lactate (lactate/total C-13 signals, p = 0.01) and [C-13]bicarbonate (p = 0.008) were detected in the FUS-applied brain region as compared to the contralateral FUS-unaffected normal-appearing brain region. The application of FUS without opening the BBB in a separate group of rodents resulted in comparable lactate and bicarbonate productions between the FUS-applied and the contralateral brain regions. Second, C-13 imaging with hyperpolarized [1-C-13]glycerate after opening the BBB showed increased [1-C-1(3)]glycerate delivery to the FUS-applied region (p = 0.04) relative to the contralateral side, and [1-C-1(3)]lactate production was consistently detected from the FUS-applied region. Our findings suggest that FUS accelerates the delivery of hyperpolarized molecules across the BBB and provides enhanced sensitivity to detect metabolic products in the brain; therefore, hyperpolarized C-13 imaging with FUS may provide new opportunities to study cerebral metabolic pathways as well as various neurological pathologies.

Purpose: To develop a noninvasive prognostic imaging biomarker related to hypoxia to predict SABR tumor control. Methods and Materials: A total of 145 subcutaneous syngeneic Dunning prostate R3327-AT1 rat tumors were focally irradiated once using cone beam computed tomography guidance on a small animal irradiator at 225 kV. Various doses in the range of 0 to 100 Gy were administered, while rats breathed air or oxygen, and tumor control was assessed up to 200 days. Oxygen-sensitive magnetic resonance imaging (MRI) (T-1-weighted, Delta R-1, Delta R-2*) was applied to 79 of these tumors at 4.7 T to assess response to an oxygen gas breathing challenge on the day before irradiation as a probe of tumor hypoxia. Results: Increasing radiation dose in the range of 0 to 90 Gy enhanced tumor control of air-breathing rats with a TCD50 estimated at 59.6 +/- 1.5 Gy. Control was significantly improved at some doses when rats breathed oxygen during irradiation (eg, 40 Gy; P0.922 with O-2-gas breathing challenge showed significantly better control at 40 Gy during irradiation while breathing oxygen (75% vs 0%, P0.922 revealed different survival curves, with TCD50 = 36.2 +/- 3.2 Gy for tumors responsive to oxygen gas breathing challenge; this was significantly less than the 54.7 +/- 2.4 Gy for unresponsive tumors (P<.005), irrespective of the gas inhaled during tumor irradiation. Conclusions: Oxygen-sensitive MRI allowed stratification of tumors in terms of local control at 40 Gy, indicating its use as a potential predictive imaging biomarker. Increasing dose to 50 Gy overcame radiation resistance attributable to hypoxia in 50% of tumors. (C) 2021 Elsevier Inc. All rights reserved.

De novo lipogenesis (DNL) is disrupted in a wide range of human disease. Thus, quantification of DNL may provide insight into mechanisms and guide interventions if it can be performed rapidly and noninvasively. DNL flux is commonly measured by H-2 incorporation into fatty acids following deuterated water ((H2O)-H-2) administration. However, the sensitivity of this approach is limited by the natural abundance of C-13, which masks detection of H-2 by mass spectrometry. Here we report that high-resolution Orbitrap gas-chromatography mass-spectrometry resolves H-2 and C-13 fatty acid mass isotopomers, allowing DNL to be quantified using lower (H2O)-H-2 doses and shorter experimental periods than previously possible. Serial measurements over 24-hrs in mice detects the nocturnal activation of DNL and matches a H-3-water method in mice with genetic activation of DNL. Most importantly, DNL is detected in overnight-fasted humans in less than an hour and is responsive to feeding during a 4-h study. Thus, H-2 specific MS provides the ability to study DNL in settings that are currently impractical. Fat synthesis is necessary for normal physiology, but its dysregulation contributes to the pathology of many diseases. Here, the authors report a high-resolution mass spectrometry approach that quantifies fat synthesis flux in humans and mice following a brief and low dose of deuterated water.

Guanosine diphosphate mannose (GDP-Man) is the donor substrate required for mannosylation in the synthesis of glycoproteins, glycolipids and the newly discovered glycoRNA. Normal GDP-Man biosynthesis plays a crucial role in support of a variety of cellular functions, including cell recognition, cell communication and immune responses against viruses. Here, we report the detection of GDP-Man in human brain for the first time, using P-31 MRS at 7 T. The presence of GDP-Man is evidenced by the detection of a weak P-31 doublet at -10.7 ppm that can be assigned to the phosphomannosyl group (P beta) of the GDP-Man molecule. This weak but well-resolved signal lies 0.9 ppm upfield of UDP(G) P beta-multiplet from a mixture of UDP-Glc, UDP-Gal, UDP-GlcNAc and UDP-GalNAc. In reference to ATP (2.8 mM), the concentration of GDP-Man in human brain was estimated to be 0.02 +/- 0.01 mM, about 15-fold lower than the total concentration of UDP(G) (0.30 +/- 0.04, N = 17) and consistent with previous reports of UDP-Man in cells and brain tissue extracts measured by high-performance liquid chromatography. The reproducibility of the measured GDP-Man between test and 2-week retest was 21% +/- 15% compared with 5% +/- 4% for UDP(G) (N = 7). The measured concentrations of GDP-Man and UDP(G) are linearly correlated ([UDP(G)] = 4.3 [GDP-Man] + 0.02, with R = 0.66 and p = 0.0043), likely reflecting the effect of shared sugar precursors, which may vary among individuals in response to variation in nutritional intake and consumption. Given that GDP-Man has another set of doublet (P alpha) at -8.3 ppm that overlaps with NAD(H) and UDP(G)-P alpha signals, the amount of GDP-Man could potentially interfere with the deconvolution of these mixed signals in composition analysis. Importantly, this new finding may be useful in advancing our understanding of glycosylation and its role in the development of cancer, as well as infectious and neurodegenerative diseases.