Pyruvate Magnetic Resonance Spectroscopy Research Articles

Hyperpolarized [1-13C]-pyruvate MRS evaluates immune potential and predicts response to radiotherapy in cervical cancer

BackgroundMonitoring pyruvate metabolism in the spleen is important for assessing immune activity and achieving successful radiotherapy for cervical cancer due to the significance of the abscopal effect. We aimed to explore the feasibility of utilizing hyperpolarized (HP) [1-13C]-pyruvate magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) to evaluate pyruvate metabolism in the human spleen, with the aim of identifying potential candidates for radiotherapy in cervical cancer.MethodsThis prospective study recruited six female patients with cervical cancer (median age 55 years; range 39–60) evaluated using HP [1-13C]-pyruvate MRI/MRS at baseline and 2 weeks after radiotherapy. Proton (1H) diffusion-weighted MRI was performed in parallel to estimate splenic cellularity. The primary outcome was defined as tumor response to radiotherapy. The Student t-test was used for comparing 13C data between the groups.ResultsThe splenic HP [1-13C]-lactate-to-total carbon (tC) ratio was 5.6-fold lower in the responders than in the non-responders at baseline (p = 0.009). The splenic [1-13C]-lactate-to-tC ratio revealed a 1.7-fold increase (p = 0.415) and the splenic [1-13C]-alanine-to-tC ratio revealed a 1.8-fold increase after radiotherapy (p = 0.482). The blood leukocyte differential count revealed an increased proportion of neutrophils two weeks following treatment, indicating enhanced immune activity (p = 0.013). The splenic apparent diffusion coefficient values between the groups were not significantly different.ConclusionsThis exploratory study revealed the feasibility of HP [1-13C]-pyruvate MRS of the spleen for evaluating baseline immune potential, which was associated with clinical outcomes of cervical cancer after radiotherapy.Trial registrationClinicalTrials.gov NCT04951921, registered 7 July 2021.Relevance statementThis prospective study revealed the feasibility of using HP 13C MRI/MRS for assessing pyruvate metabolism of the spleen to evaluate the patients’ immune potential that is associated with radiotherapeutic clinical outcomes in cervical cancer.Key points• Effective radiotherapy induces abscopal effect via altering immune metabolism.• Hyperpolarized 13C MRS evaluates patients’ immune potential non-invasively.• Pyruvate-to-lactate conversion in the spleen is elevated following radiotherapy.Graphical

Abstract 6165: Early detection of pancreatic cancer by hyperpolarized magnetic resonance

Abstract Introduction: Pancreatic cancer is difficult to diagnose due to its asymptomatic presentation at early stages. Therefore, there is an unmet need for non-invasive imaging markers that can help identify the aggressive pancreatic lesions at an early time point. One of the most promising imaging biomarkers is the conversion of hyperpolarized (HP) pyruvate to lactate1-3. With HP metabolic imaging, the conversion will be monitored among different premalignant models at different timepoints as well as tested against pancreatitis, a known confounder of pancreatic cancer in the clinic. Methods: HP [1-13C]pyruvate Magnetic Resonance Spectroscopy (MRS) was employed to study the metabolic processes in tamoxifen inducible genetically engineered mouse models (P48CreERT2;LSL-KrasG12D(iKC)) with pre-invasive pancreatic intraepithelial neoplasia (PanIN) precursor lesions, invasive pancreatic cancer model (P48CreERT2;LSL-KrasG12D; LSL-p53R172H (iKPC)) and control animals (P48CreERT2 (iC)) at 7T Bruker MRI scanner. These mice were imaged before tamoxifen induction at 10-, 20-, and 30-weeks post induction. For the pancreatitis model, iC and iKC mice they were treated with caerulein for three weeks, 7 weeks after tamoxifen induction. The pancreatitis mice were imaged 24 hours after the last caerulein injection. Results/Discussion: HP lactate-to-pyruvate ratio is increased in the cancer models compared to the control model. In the iKPC mouse model, at the 20-week post induction imaging there was a significant increase of the lactate-to-pyruvate ratio compared to the 10-weektime point after induction. The 20-week iKPC time point ratio compared to the iKC and control mouse models was significantly higher, indicating the aggressive nature of the disease. Even in the iKC model there is a slight increase of the lactate-to-pyruvate ratio at 20-weeks post induction compared to both previous time points, pre-induction and 10-week. No change in the lactate-to-pyruvate ratio was not observed with the pancreatitis phenotype. In the future, we plan on imaging at earlier timepoints or at smaller intervals in the iKPC model, to observe the exact moment the metabolism switches to lactate. Conclusion: Our data demonstrates that the metabolic flux to lactate is only increasing in the premalignant models of pancreatic cancer but not in the pancreatitis model, suggesting that the differentiation between early pancreatic cancer and pancreatitis can be achieved by hyperpolarized metabolic imaging. We are currently in the process of translating this in a clinical trial at MD Anderson Cancer Center. Citation Format: Paytience L. Smith, José S. Enriquez, Rian Howell, Olivereen Le Roux, Shivanand Pudakalakatti, Prasanta Dutta, Florencia Mcallister, Pratip Bhattacharya. Early detection of pancreatic cancer by hyperpolarized magnetic resonance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6165.

Unveiling the Therapeutic Potential of SGLT2 inhibitors and Oral Ketone Ester in Heart Failure with Preserved Ejection Fraction: A Comprehensive Exploration of Cardiac Function, Structure, and Metabolism in a Rat Model

BackgroundThis study investigated the potential efficacy of SGLT2 inhibitors empagliflozin and oral ketone supplementation as treatments for heart failure with preserved ejection fraction (HFpEF), which is often associated with obesity and type 2 diabetes mellitus. Methods20-week-old obese ZSF-1 rats were given different treatments for 12 weeks, including vehicle, empagliflozin, ketone ester (KE), or a combination of empagliflozin and KE. Cardiac magnetic resonance imaging (CMR) and hyperpolarized carbon-13 (13C) labeled pyruvate magnetic resonance spectroscopy imaging were used to evaluate cardiac function and metabolism, while histological and molecular markers of cardiac remodeling were assessed in the left ventricle. ResultsThe untreated HFpEF rats exhibited obesity, diabetes, cardiac hypertrophy, atrial enlargement, lung congestion, and increased cardiomyocyte size and cardiac expression of atrial natriuretic peptide (ANP) and fibrosis marker col1a1 and TIMP1. The treatment groups exhibited decreased body weight, increased circulating ketone levels, and reduced blood glucose levels. All treatment regimens significantly attenuated ventricular hypertrophy, atrial enlargement, and lung congestion. Furthermore, all treatments significantly reduced cardiomyocyte size and the expression of ANP and fibrosis marker. The combination of empagliflozin and KE showed the greatest improvement in diastolic function and cardiac ATP levels. Interestingly, hyperpolarized [1-13C] pyruvate detected a decrease in lactate/pyruvate ratio in the hearts treated with empagliflozin. ConclusionObese ZSF1 rats exhibit features of clinical HFpEF with predominant background of obesity and diabetes. A combination of empagliflozin and KE has greater benefits in treating HFpEF. Targeting cardiometabolic dysregulation may be a promising approach for HFpEF treatment.

Abstract 13962: Exploring the Therapeutic Potential of SGLT2 Inhibitors and Oral Ketone Ester in HFpEF: A Comprehensive Exploration of Cardiac Function, Structure, and Metabolism in a Rat Model

Introduction: This study aimed to assess the potential efficacy of the SGLT2 inhibitor empagliflozin and oral ketone ester supplementation as treatments for heart failure with preserved ejection fraction (HFpEF), which is commonly associated with obesity and type 2 diabetes mellitus. Methods: Twenty-week-old obese ZSF-1 rats were initially fed a high-fat diet (HFD) to establish and maintain the phenotype. Subsequently, the rats were randomly assigned to different treatment groups. These groups consisted of a control group receiving only the high-fat diet (HFD), as well as groups receiving empagliflozin, ketone ester (DeltaG®, KE), or a combination of both in addition to the HFD. Cardiac magnetic resonance imaging (CMR) and hyperpolarized carbon-13 (13C) labeled pyruvate magnetic resonance spectroscopy imaging were used to evaluate cardiac function and metabolism. Histological and molecular markers of cardiac remodeling were assessed in the left ventricle. Results: Untreated HFpEF rats exhibited obesity, diabetes, cardiac hypertrophy, atrial enlargement, lung congestion, increased cardiomyocyte size and fibrosis, as well as elevated expression of atrial natriuretic peptide (ANP), col1a1 (fibrosis marker), and TIMP1. The treatment groups displayed decreased body weight, increased circulating ketone levels, and reduced blood glucose levels. All treatment regimens significantly mitigated ventricular hypertrophy, atrial enlargement, and lung congestion. Furthermore, they reduced cardiomyocyte size, ANP expression, fibrosis marker expression, and increased cardiac ATP levels. CMR revealed that the combination of empagliflozin and KE resulted in improvement in diastolic function. Hyperpolarized [1-13C] pyruvate imaging revealed a decrease in lactate/pyruvate ratio in empagliflozin-treated hearts, indicating improved oxidative metabolism. Conclusions: The findings of this study suggest that targeting cardiometabolic dysregulation holds promise as an effective approach for the treatment of HFpEF. While both empagliflozin or KE alone demonstrated improvements in cardiac energetics and remodeling, the combination of empagliflozin and KE yielded the most notable benefits in enhancing cardiac diastolic function.

Abstract 3584: Early and non-invasive detection of radiation-induced cardiotoxicity in pre-clinical and clinical models

Abstract Background: Nearly half of all patients receive radiation therapy as a component of their cancer care. Despite the efficacy of radiation therapy as a cancer treatment, cardiotoxicity is a major concern in patients receiving chest radiotherapy. There are currently no standardized approaches for early detection of radiation-induced cardiotoxicity as a stage that offers potential for early intervention. In this study, we employ hyperpolarized 13C- pyruvate magnetic resonance spectroscopy to non-invasively characterize early metabolic changes in the heart in response to radiation. Methods: We established a pre-clinical model of radiation induced heart disease (RIHD) by performing whole heart irradiation (8Gy x 5) in rats. Echocardiography was used characterize mechanical changes in the heart following radiation. To non-invasively detect myocardial mitochondrial dysfunction following cardiac irradiation in vivo, we employed hyperpolarized 13C- pyruvate magnetic resonance spectroscopy (MRS) to track the fate of pyruvate, an intermediate of glucose metabolism, as it is metabolized in the heart. Hyperpolarized 13C- pyruvate MRS was also employed in a patient who received thoracic radiation for treatment of thymoma to non-invasively study changes in glucose metabolism in response to radiation. Results: We identified evidence of early cardiac mitochondrial dysfunction prior to onset of mechanical changes in the heart. Following cardiac irradiation, due to mitochondrial dysfunction, pyruvate was preferentially metabolized to lactate in the cytoplasm (as opposed to bicarbonate in the mitochondria in non-irradiated hearts). The ratio of products of 13C- pyruvate metabolism in the mitochondria and cytoplasm as ascertained by hyperpolarized 13C- pyruvate MRS served as a biomarker for metabolic dysfunction in the heart both in a pre-clinical rat model and in a patient who received thoracic radiation. Conclusions: We have developed a non-invasive approach for detection of cardiac mitochondrial dysfunction, which may serve as a biomarker for early detection of radiation-induced cardiotoxicity, and shown feasibility in a human patient. Clinical adoption of this approach may enable early identification of patients who are at high risk for future cardiac complications and may benefit from mitigation strategies. Citation Format: Taylor-Jade Higgins, Jayesh Sharma, Elizabeth R. Zhang-Velten, Sarah Elliott, Junjie Ma, Jun Chen, Gabriele Schiattarella, Chantal Vidal, Nan Jiang, Daniel Daou, Joseph Hill, Thomas Gillette, Craig Malloy, Vlad Zaha, Jae Mo Park, Prasanna Alluri. Early and non-invasive detection of radiation-induced cardiotoxicity in pre-clinical and clinical models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3584.

Hyperpolarized [1-13C]pyruvate Magnetic Resonance Spectroscopy Shows That Agmatine Increased Lactate Production in the Brain of Type 2 Diabetic Mice.

Type 2 diabetes mellitus (T2DM) is associated with a 2-fold increased risk of developing Alzheimer's disease. In earlier research, agmatine has been demonstrated to alleviate diabetes symptoms and increase cognitive performance. However, it is unclear whether the improvement of cognitive function is attributable to the reduction of diabetic symptoms or its direct influence on brain metabolism. Using hyperpolarized (HP) [1-13C]pyruvate magnetic resonance spectroscopy (MRS), this study intends to evaluate the influence of agmatine on brain metabolism. ICR mice were fed a high-fat diet and injected with streptozotocin to develop a T2DM animal model. During a 2-week period, T2DM mice were treated with normal saline or 100 mg/kg of agmatine, and brain HP [1-13C]pyruvate MRS was performed. The effect of agmatine on lactate generation and NADH/NAD+ redox state was investigated using C6 and neuro-2a (N2a) cells. As a perfusion marker, the total 13C signals in the brain of T2DM mice (p=0.07) and agmatine-treated mice (p<0.05) were reduced. The conversion constant (Kpl) from [1-13C]pyruvate to [1-13C]lactate was not distinguishable in the brains of T2DM mice but was significantly increased in the brains of agmatine-treated T2DM mice. Treating C6 and N2a cells with agmatine increased NADH/NAD+ratio and lactate generation. Agmatine influences the NADH/NAD+ redox state in the brains of T2DM mice, which may be connected with enhanced cognitive performance and increased conversion of HP [1-13C]pyruvate to HP [1-13C]lactate.

Abstract 3659: Early in vivo detection of radiation-induced cardiotoxicity

Abstract Background: Radiation-Induced Heart Disease (RIHD) is a major source of morbidity and mortality in patients receiving thoracic radiation, which is a common treatment for malignancies like lung cancer. There is currently no standardized program for follow-up of RIHD in cancer survivors. Therefore, there is an acute need for developing detection of RIHD at a stage that offers potential for early intervention and reversibility. The gold standard for detection of global cardiac dysfunction is echocardiography. However, this current paradigm detects cardiac changes in metrics such as Left Ventricular Ejection Fraction (LVEF), which are relatively late manifestations in the pathology of cardiotoxicity, decreasing the possibility of reversing such damage. We sought to assess radiation-induced changes significantly earlier than the current standard of care by measuring the efficiency of the tricarboxylic acid cycle in cardiac mitochondria; we hypothesized that radiation leads to impaired mitochondrial function, causing increased conversion of pyruvate to lactate in the cytosol and decreased conversion in the mitochondria. In order to non-invasively measure this impairment, we utilized Magnetic Resonance Spectroscopy (MRS) to track the fate of hyperpolarized (HP) C-13 pyruvate. Methods: Sprague-Dawley rats underwent baseline and post treatment echocardiography and HP C-13 pyruvate MRS at multiple timepoints. Half of the animals underwent image-guided cardiac radiation with cone-beam CT, to a total dose of 40 Gy in 5 fractions, a paradigm similar to a common dose given to lung cancer patients. Results: In the cardiac radiation group, C-13 pyruvate MRS demonstrated a statistically significant decrease in cardiac function (determined by bicarbonate-to-lactate ratio in myocardial mitochondria) compared to pre-radiation baseline (p=0.02, one-tailed paired t-test) as early as 1 week post treatment. No significant decrease in this ratio was observed in the non-irradiated, age matched controls (p=0.95). Comparatively, no significant changes in LVEF or global longitudinal strain were observed in either the cardiac irradiation or control group of rats until 2 months post treatment. Conclusion: Radiation-induced myocardial mitochondrial dysfunction is an early event that can be characterized and detected in vivo by hyperpolarized C-13 pyruvate MRS within 1 week after radiation prior to onset of echocardiographic changes. For the first time, we have demonstrated feasibility of employing HP C-13 pyruvate MRS for detecting radiation-induced myocardial mitochondrial metabolic changes in a pre-clinical rat model. This technology has the potential to serve as a platform for building radiation-focused cardio-oncology programs for early detection and mitigation of radiation-induced cardiac injury in hundreds of thousands of patients receiving thoracic radiation annually. Citation Format: Jayesh Sharma, Elizabeth Zhang, Xuliang Wang, Junjie Ma, Jun Chen, Gabriele Schiattarella, Joseph Hill, Jaemo Park, Craig Malloy, Vlad Zaha, Prasanna Alluri. Early in vivo detection of radiation-induced cardiotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3659.

Identifying the Metabolic Signatures of PPARD-Overexpressing Gastric Tumors.

Peroxisome proliferator-activated receptor delta (PPARD) is a nuclear receptor known to play an essential role in regulation of cell metabolism, cell proliferation, inflammation, and tumorigenesis in normal and cancer cells. Recently, we found that a newly generated villin-PPARD mouse model, in which PPARD is overexpressed in villin-positive gastric progenitor cells, demonstrated spontaneous development of large, invasive gastric tumors as the mice aged. However, the role of PPARD in regulation of downstream metabolism in normal gastric and tumor cells is elusive. The aim of the present study was to find PPARD-regulated downstream metabolic changes and to determine the potential significance of those changes to gastric tumorigenesis in mice. Hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, and liquid chromatography-mass spectrometry were employed for metabolic profiling to determine the PPARD-regulated metabolite changes in PPARD mice at different ages during the development of gastric cancer, and the changes were compared to corresponding wild-type mice. Nuclear magnetic resonance spectroscopy-based metabolomic screening results showed higher levels of inosine monophosphate (p = 0.0054), uracil (p = 0.0205), phenylalanine (p = 0.017), glycine (p = 0.014), and isocitrate (p = 0.029) and lower levels of inosine (p = 0.0188) in 55-week-old PPARD mice than in 55-week-old wild-type mice. As the PPARD mice aged from 10 weeks to 35 weeks and 55 weeks, we observed significant changes in levels of the metabolites inosine monophosphate (p = 0.0054), adenosine monophosphate (p = 0.009), UDP-glucose (p = 0.0006), and oxypurinol (p = 0.039). Hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy performed to measure lactate flux in live 10-week-old PPARD mice with no gastric tumors and 35-week-old PPARD mice with gastric tumors did not reveal a significant difference in the ratio of lactate to total pyruvate plus lactate, indicating that this PPARD-induced spontaneous gastric tumor development does not require glycolysis as the main source of fuel for tumorigenesis. Liquid chromatography-mass spectrometry-based measurement of fatty acid levels showed lower linoleic acid, palmitic acid, oleic acid, and steric acid levels in 55-week-old PPARD mice than in 10-week-old PPARD mice, supporting fatty acid oxidation as a bioenergy source for PPARD-expressing gastric tumors.

Metabolic Effects of Doxorubicin on the Rat Liver Assessed With Hyperpolarized MRI and Metabolomics.

Doxorubicin (DOX) is a successful chemotherapeutic widely used for the treatment of a range of cancers. However, DOX can have serious side-effects, with cardiotoxicity and hepatotoxicity being the most common events. Oxidative stress and changes in metabolism and bioenergetics are thought to be at the core of these toxicities. We have previously shown in a clinically-relevant rat model that a low DOX dose of 2 mg kg–1 week–1 for 6 weeks does not lead to cardiac functional decline or changes in cardiac carbohydrate metabolism, assessed with hyperpolarized [1-13C]pyruvate magnetic resonance spectroscopy (MRS). We now set out to assess whether there are any signs of liver damage or altered liver metabolism using this subclinical model. We found no increase in plasma alanine aminotransferase (ALT) activity, a measure of liver damage, following DOX treatment in rats at any time point. We also saw no changes in liver carbohydrate metabolism, using hyperpolarized [1-13C]pyruvate MRS. However, using metabolomic analysis of liver metabolite extracts at the final time point, we found an increase in most acyl-carnitine species as well as increases in high energy phosphates, citrate and markers of oxidative stress. This may indicate early signs of steatohepatitis, with increased and decompensated fatty acid uptake and oxidation, leading to oxidative stress.

Early In Vivo Detection of Radiation-Induced Cardiotoxicity With Hyperpolarized C-13 Pyruvate Magnetic Resonance Spectroscopy

Radiation therapy is commonly used for treatment of patients with intrathoracic malignancies, such as lung cancer, esophageal cancer, and lymphoma. Radiation-Induced Heart Disease (RIHD) is a major source of morbidity and mortality in patients receiving thoracic radiation. Therefore, there is an acute need for development of non-invasive approaches for detection of RIHD at a stage that offers potential for early intervention and reversibility. Cardiac mitochondrial dysfunction is a hallmark of radiation-induced cardiac injury. During aerobic respiration, pyruvate enters the tricarboxylic acid cycle and is metabolized into bicarbonate in mitochondria. We hypothesized that radiation-induced mitochondrial dysfunction results in decreased conversion of pyruvate to bicarbonate in the mitochondria and increased conversion to lactate in cytosol. We sought to non-invasively assess radiation-induced changes in mitochondrial myocardial metabolism by tracking the fate of hyperpolarized (HP) C-13 pyruvate utilization using Magnetic Resonance Spectroscopy (MRS).Sprague-Dawley rats (n = 10) underwent baseline echocardiography and HP C-13 pyruvate MRS. Rats in the cardiac radiation group (n = 5) underwent image-guided cardiac radiation with cone-beam CT, to a total dose of 40 Gy in 5 fractions. All rats underwent repeat echocardiography and hyperpolarized C-13 pyruvate MRS one week later.For the first time, we have demonstrated feasibility of employing HP C-13 pyruvate MRS for detecting radiation-induced myocardial mitochondrial metabolic changes in a pre-clinical rat model. In the cardiac radiation group, C-13 pyruvate MRS demonstrated a statistically significant decrease in cardiac bicarbonate-to-lactate ratio compared to pre-radiation baseline (P = 0.02, one-tailed paired t-test), suggesting increased metabolism of pyruvate into lactate in the cytoplasm (at the expense of metabolism into bicarbonate in the mitochondria) due to mitochondrial dysfunction. No significant decrease in this ratio was observed in the non-irradiated, age matched controls (P = 0.90). No significant changes in left ventricular ejection fraction or global longitudinal strain were observed in either the cardiac irradiation or control group of rats at this time point.Radiation-induced myocardial mitochondrial dysfunction is an early event and can be detected in vivo by hyperpolarized C-13 pyruvate MRS within 1 week after radiation, and prior to onset of echocardiographic changes. Due to its non-invasive nature, this technology has the potential to serve as a platform for building radiation-focused cardio-oncology programs for early detection and mitigation of radiation-induced cardiac injury in hundreds of thousands of patients receiving thoracic radiation annually.

Remodeling after myocardial infarction and effects of heart failure treatment investigated by hyperpolarized [1-13 C]pyruvate magnetic resonance spectroscopy.

Hyperpolarized [1-13 C]pyruvate MRS can measure cardiac metabolism in vivo. We investigated whether [1-13 C]pyruvate MRS could predict left ventricular remodeling following myocardial infarction (MI), long-term left ventricular effects of heart failure medication, and could identify responders to treatment. Thirty-five rats were scanned with hyperpolarized [1-13 C]pyruvate MRS 3 days after MI or sham surgery. The animals were re-examined after 30 days of therapy with β-blockers and ACE-inhibitors (active group, n = 12), placebo treatment (placebo group, n = 13) or no treatment (sham group, n = 10). Furthermore, heart tissue mitochondrial respiratory capacity was assessed by high-resolution respirometry. Metabolic results were compared between groups, over time and correlated to functional MR data at each time point. At 30 ± 0.5 days post MI, left ventricular ejection fraction (LVEF) differed between groups (sham, 77% ± 1%; placebo, 52% ± 3%; active, 63% ± 2%, P < .001). Cardiac metabolism, measured by both hyperpolarized [1-13 C]pyruvate MRS and respirometry, neither differed between groups nor between baseline and follow-up. Three days post MI, low bicarbonate + CO2 /pyruvate ratio was associated with low LVEF. At follow-up, in the active group, a poor recovery of LVEF was associated with high bicarbonate + CO2 /pyruvate ratio, as measured by hyperpolarized MRS. In a rat model of moderate heart failure, medical treatment improved function, but did not on average influence [1-13 C]pyruvate flux as measured by MRS; however, responders to heart failure medication had reduced capacity for carbohydrate metabolism.

Multimodality In Vivo Imaging of Perfusion and Glycolysis in a Rat Model of C6 Glioma.

Chemical exchange saturation transfer MRI using an infusion of glucose (glucoCEST) is sensitive to the distribution of glucose in vivo; however, whether glucoCEST is more related to perfusion or glycolysis is still debatable. We compared glucoCEST to computed tomography perfusion (CTP), [18F] fluorodeoxyglucose positron emission tomography (FDG-PET), and hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy imaging (MRSI) in a C6 rat model of glioma to determine if glucoCEST is more strongly correlated with measurements of perfusion or glycolysis. 106 C6 glioma cells were implanted in Wistar rat brains (n = 11). CTP (including blood volume, BV; blood flow, BF; and permeability surface area product, PS) and FDG-PET standardized uptake value (SUV) were acquired at 11 to 13 days post-surgery. GlucoCEST measurements (∆CEST) were acquired the following day on a 9.4 T MRI before and after an infusion of glucose solution. This was followed by MRSI on a 3.0 T MRI after the injection of hyperpolarized [1-13C] pyruvate to generate regional maps of the lactate:pyruvate ratio (Lac:Pyr). Pearson's correlations between glucoCEST, CTP, FDG-PET, and Lac:Pyr ratio were evaluated. Tumors had significantly higher SUV, BV, and PS than the contralateral brain. Tumor ∆CEST was most strongly correlated with CTP measurements of BV (ρ = 0.74, P = 0.01) and PS (ρ = 0.55, P = 0.04). No significant correlation was found between glycolysis measurements of SUV or Lac:Pyr with tumor ∆CEST. PS significantly correlated with SUV (ρ = 0.58, P = 0.005) and Lac:Pyr (ρ = 0.75, P = 0.005). BV significantly correlated with Lac:Pyr (ρ = 0.57, P = 0.02), and BF significantly correlated with SUV (ρ = 0.49, P = 0.02). This study determined that glucoCEST is more strongly correlated to measurements of perfusion than glycolysis. GlucoCEST measurements have additional confounds, such as sensitivity to changing pH, that merit additional investigation.

Hyperpolarized 13C pyruvate magnetic resonance spectroscopy for in vivo metabolic phenotyping of rat HCC

The in vivo assessment of tissue metabolism represents a novel strategy for the evaluation of oncologic disease. Hepatocellular carcinoma (HCC) is a high-prevalence, high-mortality tumor entity often discovered at a late stage. Recent evidence indicates that survival differences depend on metabolic alterations in tumor tissue, with particular focus on glucose metabolism and lactate production. Here, we present an in vivo imaging technique for metabolic tumor phenotyping in rat models of HCC. Endogenous HCC was induced in Wistar rats by oral diethyl-nitrosamine administration. Peak lactate-to-alanine signal ratios (L/A) were assessed with hyperpolarized magnetic resonance spectroscopic imaging (HPMRSI) after [1-13C]pyruvate injection. Cell lines were derived from a subset of primary tumors, re-implanted in nude rats, and assessed in vivo with dynamic hyperpolarized magnetic resonance spectroscopy (HPMRS) after [1-13C]pyruvate injection and kinetic modelling of pyruvate metabolism, taking into account systemic lactate production and recirculation. For ex vivo validation, enzyme activity and metabolite concentrations were spectroscopically quantified in cell and tumor tissue extracts. Mean peak L/A was higher in endogenous HCC compared to non-tumorous tissue. Dynamic HPMRS revealed higher pyruvate-to-lactate conversion rates (kpl) and lactate signal in subcutaneous tumors derived from high L/A tumor cells, consistent with ex vivo measurements of higher lactate dehydrogenase (LDH) levels in these cells. In conclusion, HPMRS and HPMRSI reveal distinct tumor phenotypes corresponding to differences in glycolytic metabolism in HCC tumor tissue.

Organ-specific metabolic profiles of the liver and kidney during brain death and afterwards during normothermic machine perfusion of the kidney.

We investigated metabolic changes during brain death (BD) using hyperpolarized magnetic resonance (MR) spectroscopy and ex vivo graft glucose metabolism during normothermic isolated perfused kidney (IPK) machine perfusion. BD was induced in mechanically ventilated rats by inflation of an epidurally placed catheter; sham‐operated rats served as controls. Hyperpolarized [1‐13C]pyruvate MR spectroscopy was performed to quantify pyruvate metabolism in the liver and kidneys at 3 time points during BD, preceded by injecting hyperpolarized[1‐13C]pyruvate. Following BD, glucose oxidation was measured using tritium‐labeled glucose (d‐6‐3H‐glucose) during IPK reperfusion. Quantitative polymerase chain reaction and biochemistry were performed on tissue/plasma. Immediately following BD induction, lactate increased in both organs (liver: eµd0.21, 95% confidence interval [CI] [−0.27, −0.15]; kidney: eµd0.26, 95% CI [−0.40, −0.12]. After 4 hours of BD, alanine production decreased in the kidney (eµd0.14, 95% CI [0.03, 0.25], P < .05). Hepatic lactate and alanine profiles were significantly different throughout the experiment between groups (P < .01). During IPK perfusion, renal glucose oxidation was reduced following BD vs sham animals (eµd0.012, 95% CI [0.004, 0.03], P < .001). No differences in enzyme activities were found. Renal gene expression of lactate‐transporter MCT4 increased following BD (P < .01). In conclusion, metabolic processes during BD can be visualized in vivo using hyperpolarized magnetic resonance imaging and with glucose oxidation during ex vivo renal machine perfusion. These techniques can detect differences in the metabolic profiles of the liver and kidney following BD.

Metabolic alterations in acute myocardial ischemia-reperfusion injury and necrosis using in vivo hyperpolarized [1-13C] pyruvate MR spectroscopy

This study aimed to investigate real-time early detection of metabolic alteration in a rat model with acute myocardial ischemia-reperfusion (AMI/R) injury and myocardial necrosis, as well as its correlation with intracellular pH level using in vivo hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy (MRS). Hyperpolarized 13C MRS was performed on the myocardium of 8 sham-operated control rats and 8 rats with AMI/R injury, and 8 sham-operated control rats and 8 rats with AMI-induced necrosis. Also, the correlations of levels of [1-13C] metabolites with pH were analyzed by Spearman’s correlation test. The AMI/R and necrosis groups showed significantly higher ratios of [1-13C] lactate (Lac)/bicarbonate (Bicar) and [1-13C] Lac/total carbon (tC), and lower ratios of 13C Bicar/Lac + alanine (Ala), and 13C Bicar/tC than those of the sham-operated control group. Moreover, the necrosis group showed significantly higher ratios of [1-13C] Lac/Bicar and [1-13C] Lac/tC, and lower ratios of 13C Bicar/Lac + Ala and 13C Bicar/tC than those of the AMI/R group. These results were consistent with the pattern for in vivo the area under the curve (AUC) ratios. In addition, levels of [1-13C] Lac/Bicar and [1-13C] Lac/tC were negatively correlated with pH levels, whereas 13C Bicar/Lac + Ala and 13C Bicar/tC levels were positively correlated with pH levels. The levels of [1-13C] Lac and 13C Bicar will be helpful for non-invasively evaluating the early stage of AMI/R and necrosis in conjunction with reperfusion injury of the heart. These findings have potential application to real-time evaluation of cardiac malfunction accompanied by changes in intracellular pH level and enzymatic activity.

Hyperpolarized [1-13C]lactate flux increased in the hippocampal region in diabetic mice

Increasing evidence suggests there is a relationship between cognitive impairment and metabolic dysfunction. Diabetes is a chronic disease, and metabolic factors affecting brain metabolisms, such as serum glucose, insulin, and glucagon, are altered according to disease progression. In our previous study, we applied hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy in prediabetic mice after feeding them a 60% high-fat diet (HFD) for 6 months. Ultimately, we detected significantly increased [1-13C]lactate conversion in the whole brain and an almost five-fold increased [1-13C]lactate/pyruvate ratio in the hippocampal region. In the present study, we induced diabetes in mice by injecting streptozotocin and feeding them an HFD for 6 months. Unlike in prediabetic mice, [1-13C]lactate conversion in the diabetic mice did not differ from that in the control group, but [1-13C]lactate/total 13C ratio showed an almost 1.4-fold increase in the hippocampal region. We measured the amount of the lactate and mRNA levels of glucose transporters from isolated hippocampus and cortex samples. In the hippocampus, significantly decreased GLUT1 mRNA levels and increased lactate were detected, suggesting an inconsistency between glucose and pyruvate metabolism. Pyruvate can be produced from oxaloacetate as well as glucose. We investigated ATP citrate lyase (ACLY) because it cleaves citrate into oxaloacetate and acetyl CoA. Phosphorylated ACLY (Ser455), the active form, was increased in both hippocampus and cortex samples of mice injected with streptozotocin and fed an HFD. Also, phosphorylated ACLY/total ACLY showed a positive correlation with lactate amount in the hippocampus. Our results suggest that the brain has different responses to diabetic progression, but, in the hippocampus, maintains metabolic alteration toward increasing lactate production from the prediabetic to the diabetic stage. We suggest that ACLY-mediated pyruvate be used to support lactate levels in the hippocampus in cases of limited glucose availability.

Hyperpolarized [1-13C] pyruvate MR spectroscopy detect altered glycolysis in the brain of a cognitively impaired mouse model fed high-fat diet

Higher dietary intakes of saturated fatty acid increase the risk of developing Alzheimer’s disease and dementia, and even in people without diabetes higher glucose levels may be a risk factor for dementia. The mechanisms causing neuronal dysfunction and dementia by consuming high-fat diet degrading the integrity of the blood-brain barrier (BBB) has been suggested but are not yet fully understood, and metabolic state of the brain by this type of insult is still veiled. The objective of this study was to investigate the effect of high-fat diet on the brain metabolism by a multimodal imaging method using the hyperpolarizedcarbon 13 (13C)-pyruvate magnetic resonance (MR) spectroscopy and dynamic contrast-enhanced MR imaging in conjunction with the biochemical assay and the behavior test in a mouse model fed high-fat diet (HFD). In mice were fed 60% HFD for 6 months, hyperpolarized [1-13C] pyruvate MR spectroscopy showed decreased perfusion (p < 0.01) and increased conversion from pyruvate to lactate (p < 0.001) in the brain. The hippocampus and striatum showed the highest conversion ratio. The functional integrity of the blood-brain barrier tested by dynamic contrast-enhanced MR imaging showed no difference to the control. Lactate was increased in the cortex (p < 0.01) and striatum (p < 0.05), while PDH activity was decreased in the cortex (p < 0.01) and striatum (p < 0.001) and the phosphorylated PDH was increased in the striatum (p < 0.05). Mice fed HFD showed less efficiency in learning memory compared with control (p < 0.05). To determine whether hyperpolarized 13C-pyruvate magnetic resonance (MR) spectroscopy could detect a much earier event in the brain. Mice fed HFD for 3 months did not show a detectable cognitive decline in water maze based learning memory. Hyperpolarized [1-13C] pyruvate MR spectroscopy showed increased lactate conversion (P < .001), but no difference in cerebral perfusion. These results suggest that the increased hyperpolarized [1-13C] lactate signal in the brain of HFD-fed mice represent that altered metabolic alteration toward to glycolysis and hypoperfusion by the long-term metabolic stress by HFD further promote to glycolysis. The hyperpolarized [1-13C] pyruvate MR spectroscopy can be used to monitor the brain metabolism and will provide information helpful to understand the disease process.

Empagliflozin reduces myocardial ketone utilization while preserving glucose utilization in diabetic hypertensive heart disease: A hyperpolarized 13 C magnetic resonance spectroscopy study.

AimTo investigate the effects of the sodium‐glucose co‐transporter‐2 inhibitor empagliflozin on myocardial ketone body utilization in diabetic, obese rats with spontaneously hypertensive heart failure (SHHF), after 6 months of treatment.Materials and MethodsMyocardial ketone body utilization was measured in vivo real time using a novel ketone probe (hyperpolarized [3‐13C]acetoacetate) and magnetic resonance spectroscopy (MRS). Myocardial glucose utilization and cardiac function were also determined in vivo using hyperpolarized [1‐13C]pyruvate MRS and magnetic resonance imaging (MRI), respectively. Myocardial fatty acid uptake and liver ketogenesis were assessed via protein expression.ResultsAt baseline, myocardial ketone and glucose utilization were both higher in SHHF compared with control rats. Six months of empagliflozin treatment in SHHF rats was associated with less obesity, lower blood pressure, reduced blood glucose and insulin levels, and increased fasting blood β‐hydroxybutyrate levels, as expected. Contrary to the hypothesis, myocardial ketone body utilization was lower in empagliflozin‐treated SHHF rats, while glucose utilization and cardiac function were unaltered and hepatic congestion was reduced, compared with vehicle‐treated SHHF rats.ConclusionsIn diabetic hypertensive heart disease, empagliflozin reduces afterload without altering myocardial function and glucose utilization in the face of falling blood glucose levels, but does not enhance myocardial ketone utilization despite increased circulating levels.

Noninvasive Immunometabolic Cardiac Inflammation Imaging Using Hyperpolarized Magnetic Resonance.

Current cardiovascular clinical imaging techniques offer only limited assessment of innate immune cell-driven inflammation, which is a potential therapeutic target in myocardial infarction (MI) and other diseases. Hyperpolarized magnetic resonance (MR) is an emerging imaging technology that generates contrast agents with 10- to 20 000-fold improvements in MR signal, enabling cardiac metabolite mapping. To determine whether hyperpolarized MR using [1-13C]pyruvate can assess the local cardiac inflammatory response after MI. We performed hyperpolarized [1-13C]pyruvate MR studies in small and large animal models of MI and in macrophage-like cell lines and measured the resulting [1-13C]lactate signals. MI caused intense [1-13C]lactate signal in healing myocardial segments at both day 3 and 7 after rodent MI, which was normalized at both time points after monocyte/macrophage depletion. A near-identical [1-13C]lactate signature was also seen at day 7 after experimental MI in pigs. Hyperpolarized [1-13C]pyruvate MR spectroscopy in macrophage-like cell suspensions demonstrated that macrophage activation and polarization with lipopolysaccharide almost doubled hyperpolarized lactate label flux rates in vitro; blockade of glycolysis with 2-deoxyglucose in activated cells normalized lactate label flux rates and markedly inhibited the production of key proinflammatory cytokines. Systemic administration of 2-deoxyglucose after rodent MI normalized the hyperpolarized [1-13C]lactate signal in healing myocardial segments at day 3 and also caused dose-dependent improvement in IL (interleukin)-1β expression in infarct tissue without impairing the production of key reparative cytokines. Cine MRI demonstrated improvements in systolic function in 2-DG (2-deoxyglucose)-treated rats at 3 months. Hyperpolarized MR using [1-13C]pyruvate provides a novel method for the assessment of innate immune cell-driven inflammation in the heart after MI, with broad potential applicability across other cardiovascular disease states and suitability for early clinical translation.

Combined hyperpolarized 13C-pyruvate MRS and 18F-FDG PET (hyperPET) estimates of glycolysis in canine cancer patients

13C Magnetic Resonance Spectroscopy (MRS) using hyperpolarized 13C-labeled pyruvate as a substrate offers a measure of pyruvate-lactate interconversion and is thereby a marker of the elevated aerobic glycolysis (Warburg effect) generally exhibited by cancer cells. Here, we aim to compare hyperpolarized [1-13C]pyruvate MRS with simultaneous 18F-2-fluoro-2-deoxy-d-glucose (FDG) PET in a cross-sectional study of canine cancer patients. MethodsCanine cancer patients underwent integrated PET/MRI using a clinical whole-body system. Hyperpolarized [1-13C]pyruvate was obtained using dissolution-DNP. 18F-FDG PET, dynamic 13C MRS, 13C MRS Imaging (MRSI) and anatomical 1H MRI was acquired from 17 patients. Apparent pyruvate-to-lactate rate constants were estimated from dynamic 13C MRS. 18F-FDG Standard Uptake Values and maximum [1-13C]lactate-to-total-13C ratios were obtained from tumor regions of interest. Following inspection of data, patients were grouped according to main cancer type and linear regression between measures of lactate generation and 18F-FDG uptake were tested within groups. Between groups, the same measures were tested for group differences. ResultsThe main cancer types of the 17 patients were sarcoma (n = 11), carcinoma (n = 5) and mastocytoma (n = 1). Significant correlations between pyruvate-to-lactate rate constants and 18F-FDG uptake were found for sarcoma patients, whereas no significant correlations appeared for carcinoma patients. The sarcoma patients showed a non-significant trend towards lower 18F-FDG uptake and higher lactate generation than carcinoma patients. However, the ratio of lactate generation to 18F-FDG uptake was found to be significantly higher in sarcoma as compared to carcinoma. The results were found both when lactate generation was estimated as an apparent pyruvate-to-lactate rate constant from dynamic 13C MRS and as an [1-13C]lactate to total 13C ratio from 13C MRSI. ConclusionsA comparison of hyperpolarized [1-13C]pyruvate MRS with simultaneous 18F-FDG PET indicate that lactate generation and 18F-FDG uptake in cancers can be related and that their relation depend on cancer type. This finding could be important for the interpretation and eventual clinical implementation of hyperpolarized 13C. In addition, the differences between the two modalities may allow for better metabolic phenotyping performing hybrid imaging in the form of hyperPET.