Imaging glutathione depletion in the rat brain using ascorbate-derived hyperpolarized MR and PET probes.

Oxidative stress is a critical feature of several common neurologic disorders. The brain is well adapted to neutralize oxidative injury by maintaining a high steady-state concentration of small-molecule intracellular antioxidants including glutathione in astrocytes and ascorbic acid in neurons. Ascorbate-derived imaging probes for hyperpolarized 13C magnetic resonance spectroscopy and positron emission tomography have been used to study redox changes (antioxidant depletion and reactive oxygen species accumulation) in vivo. In this study, we applied these imaging probes to the normal rat brain and a rat model of glutathione depletion. We first studied hyperpolarized [1-13C]dehydroascorbate in the normal rat brain, demonstrating its robust conversion to [1-13C]vitamin C, consistent with rapid transport of the oxidized form across the blood-brain barrier. We next showed that the kinetic rate of this conversion decreased by nearly 50% after glutathione depletion by diethyl maleate treatment. Finally, we showed that dehydroascorbate labeled for positron emission tomography, namely [1-11C]dehydroascorbate, showed no change in brain signal accumulation after diethyl maleate treatment. These results suggest that hyperpolarized [1-13C]dehydroascorbate may be used to non-invasively detect oxidative stress in common disorders of the brain

Elevated Tumor Lactate and Efflux in High-grade Prostate Cancer demonstrated by Hyperpolarized 13C Magnetic Resonance Spectroscopy of Prostate Tissue Slice Cultures.

Non-invasive assessment of the biological aggressiveness of prostate cancer (PCa) is needed for men with localized disease. Hyperpolarized (HP) 13C magnetic resonance (MR) spectroscopy is a powerful approach to image metabolism, specifically the conversion of HP [1-13C]pyruvate to [1-13C]lactate, catalyzed by lactate dehydrogenase (LDH). Significant increase in tumor lactate was measured in high-grade PCa relative to benign and low-grade cancer, suggesting that HP 13C MR could distinguish low-risk (Gleason score ≤3 + 4) from high-risk (Gleason score ≥4 + 3) PCa. To test this and the ability of HP 13C MR to detect these metabolic changes, we cultured prostate tissues in an MR-compatible bioreactor under continuous perfusion. 31P spectra demonstrated good viability and dynamic HP 13C-pyruvate MR demonstrated that high-grade PCa had significantly increased lactate efflux compared to low-grade PCa and benign prostate tissue. These metabolic differences are attributed to significantly increased LDHA expression and LDH activity, as well as significantly increased monocarboxylate transporter 4 (MCT4) expression in high- versus low- grade PCa. Moreover, lactate efflux, LDH activity, and MCT4 expression were not different between low-grade PCa and benign prostate tissues, indicating that these metabolic alterations are specific for high-grade disease. These distinctive metabolic alterations can be used to differentiate high-grade PCa from low-grade PCa and benign prostate tissues using clinically translatable HP [1-13C]pyruvate MR

A Metabolite Specific 3D Stack-of-Spiral bSSFP Sequence for Improved Lactate Imaging in Hyperpolarized [1-13^{13}C]Pyruvate Studies on a 3T Clinical Scanner

Purpose: The balanced steady-state free precession sequence has been previously explored to improve the efficient use of non-recoverable hyperpolarized $^{13}$C magnetization, but suffers from poor spectral selectivity and long acquisition time. The purpose of this study was to develop a novel metabolite-specific 3D bSSFP ("MS-3DSSFP") sequence with stack-of-spiral readouts for improved lactate imaging in hyperpolarized [1-$^{13}$C]pyruvate studies on a clinical 3T scanner. Methods: Simulations were performed to evaluate the spectral response of the MS-3DSSFP sequence. Thermal $^{13}$C phantom experiments were performed to validate the MS-3DSSFP sequence. In vivo hyperpolarized [1-$^{13}$C]pyruvate studies were performed to compare the MS-3DSSFP sequence with metabolite specific gradient echo ("MS-GRE") sequences for lactate imaging. Results: Simulations, phantom and in vivo studies demonstrate that the MS-3DSSFP sequence achieved spectrally selective excitation on lactate while minimally perturbing other metabolites. Compared with MS-GRE sequences, the MS-3DSSFP sequence showed approximately a 2.5-fold SNR improvement for lactate imaging in rat kidneys, prostate tumors in a mouse model and human kidneys. Conclusions: Improved lactate imaging using the MS-3DSSFP sequence in hyperpolarized [1-$^{13}$C]pyruvate studies was demonstrated in animals and humans. The MS-3DSSFP sequence could be applied for other clinical applications such as in the brain or adapted for imaging other metabolites such as pyruvate and bicarbonate

Hyperpolarized C-13 Magnetic Resonance Imaging for Assessing Tissue Metabolism and Microenvironment: Technical Development, Preclinical Validation, and Clinical Translation

Hyperpolarized (HP) C-13 magnetic resonance (MR) is an emerging molecular imaging technique that has shown the potential to assess metabolic and microenvironmental alterations in various diseases. MR spectroscopic imaging methods can monitor the distribution and biochemical conversion of injected HP C-13 labeled probes. These quantitative imaging markers could address the unmet clinical needs of non-invasive evaluation of cancer aggressiveness, disease burden, and early therapeutic response or resistance. This dissertation focuses on developing HP C-13 MR probes and techniques to evaluate cellular redox capacity, glycolytic metabolism, as well as tissue perfusion and microenvironment. Chapter 1 introduces the fundamental principles of MR, hyperpolarization techniques, and their biological and clinical applications. Chapter 2 describes using ascorbate-derived MR and Positron Emission Tomography probes to interrogate in vivo redox capacity of the brain. Chapter 3 reports the preclinical validation of the combined HP C-13 pyruvate and urea MR as a simultaneous metabolic and perfusion imaging technique to evaluate early and dose-dependent tumor response to radiation therapy in a prostate cancer mouse model. The results of Chapter 3, combined with other prior preclinical evidence, motivated the clinical translation of this dual-probe imaging technique. Chapter 4 describes the technical development (including co-polarization system development, probe characterizations, and imaging methodology development) and non-clinical studies (including impurity characterizations, toxicology study, and imaging feasibility study) required to translate the combined C-13 pyruvate and urea MR for clinical investigations. This work has led to the regulatory approval of this combined metabolic and perfusion imaging technique for investigational use to aid prostate cancer diagnosis in patients

In Vivo Hyperpolarized Carbon-13 Diffusion Weighted MRI Measures Lactate Metabolism and Transport in Prostate Cancer

Prostate cancer is a heterogeneous group of tumors ranging from clinicallyinsignificant to lethally malignant. The clinical management of prostate cancer is challenging due to the lack of accurate assessment of cancer aggressiveness. Hyperpolarized magnetic resonance imaging (MRI) has enabled real-time measurement of metabolism, and has shown great promise for cancer diagnosis, staging and assessing treatment response in both pre- clinical and clinical studies. Aggressive prostate cancer overproduces lactate and overexpresses MCT4, the transporter primarily responsible for lactate efflux, resulting in acidification of the extracellular space and conferring a poor prognosis. In this pilot study, hyperpolarized diffusion weighted MRI was used to elucidate the intra- and extracellular distribution of metabolites, which can infer lactate efflux, and tumor microstructural environment. Transgenic adenocarcinoma mouse prostate (TRAMP) models of different stages were injected with hyperpolarized pyruvate; then pyruvate and lactate were excited with a single- band spectral-spatial RF pulse, followed by a single-shot, double spin-echo flyback echo planar imaging (EPI) readout. Four b-values were acquired per metabolite, ranging from 25-1000 s • mm^-2. Data were corrected for RF utilization and fit voxel-wise to a monoexponential decay to generate apparent diffusion coefficient (ADC) maps for each metabolite. We found that the in vivo lactate ADC is close to the ex vivo extracellular ADC, rather than the intracellular ADC. We also found lactate ADC in late-stage tumors (0.65 ± 0.11 mm • s^−1 , n=4) is higher than early-stage (0.46 mm^2 • s^−1 , n=1), indicating there is increased lactate efflux in aggressive cancer. In conclusion, we demonstrated that hyperpolarized diffusion weighted MRI can provide insight into metabolite compartmentalization and lactate efflux in the prostate tumor, and potentially assess cancer aggressiveness and therapeutic changes in a rapid, non-invasive manner

Hyperpolarized C-13 Magnetic Resonance Imaging for Assessing Tissue Metabolism and Microenvironment: Technical Development, Preclinical Validation, and Clinical Translation

Hyperpolarized (HP) C-13 magnetic resonance (MR) is an emerging molecular imaging technique that has shown the potential to assess metabolic and microenvironmental alterations in various diseases. MR spectroscopic imaging methods can monitor the distribution and biochemical conversion of injected HP C-13 labeled probes. These quantitative imaging markers could address the unmet clinical needs of non-invasive evaluation of cancer aggressiveness, disease burden, and early therapeutic response or resistance. This dissertation focuses on developing HP C-13 MR probes and techniques to evaluate cellular redox capacity, glycolytic metabolism, as well as tissue perfusion and microenvironment. Chapter 1 introduces the fundamental principles of MR, hyperpolarization techniques, and their biological and clinical applications. Chapter 2 describes using ascorbate-derived MR and Positron Emission Tomography probes to interrogate in vivo redox capacity of the brain. Chapter 3 reports the preclinical validation of the combined HP C-13 pyruvate and urea MR as a simultaneous metabolic and perfusion imaging technique to evaluate early and dose-dependent tumor response to radiation therapy in a prostate cancer mouse model. The results of Chapter 3, combined with other prior preclinical evidence, motivated the clinical translation of this dual-probe imaging technique. Chapter 4 describes the technical development (including co-polarization system development, probe characterizations, and imaging methodology development) and non-clinical studies (including impurity characterizations, toxicology study, and imaging feasibility study) required to translate the combined C-13 pyruvate and urea MR for clinical investigations. This work has led to the regulatory approval of this combined metabolic and perfusion imaging technique for investigational use to aid prostate cancer diagnosis in patients

The impact of preoperative parameters on postoperative foveal displacement in idiopathic macular hole

Abstract This study examined the effect of vitrectomy combined with internal limiting membrane (ILM) peeling on foveal displacement in 42 eyes with idiopathic macular hole (IMH). A retrospective analysis was conducted to measure various macular hole parameters before surgery, including basal diameter, minimum diameter, hole height, and areas affected by traction such as macular hole area (MHA), macular hole cystoid space area (MHCSA), macular hole retinal area (MHRA), and total area (TA). The results showed a postoperative shift of the fovea towards the optic disc in all cases. Notably, the extent of foveal displacement was significantly linked to the preoperative basal diameter (r s  = 0.405, P = 0.008) but not to other preoperative parameters or postoperative visual acuity. Furthermore, the study found that the temporal side of the macular hole was more affected by traction than the nasal side preoperatively, leading to greater postoperative displacement (All P < 0.05)

Deuterium Metabolic Imaging-Rediscovery of a Spectroscopic Tool.

The growing demand for metabolism-specific imaging techniques has rekindled interest in Deuterium (2H) Metabolic Imaging (DMI), a robust method based on administration of a substrate (glucose, acetate, fumarate, etc.) labeled with the stable isotope of hydrogen and the observation of its metabolic fate in three-dimensions. This technique allows the investigation of multiple metabolic processes in both healthy and diseased states. Despite its low natural abundance, the short relaxation time of deuterium allows for rapid radiofrequency (RF) pulses without saturation and efficient image acquisition. In this review, we provide a comprehensive picture of the evolution of DMI over the course of recent decades, with a special focus on its potential clinical applications