100 research outputs found
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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
Imaging Active Infection in vivo Using D-Amino Acid Derived PET Radiotracers.
Occult bacterial infections represent a worldwide health problem. Differentiating active bacterial infection from sterile inflammation can be difficult using current imaging tools. Present clinically viable methodologies either detect morphologic changes (CT/ MR), recruitment of immune cells (111In-WBC SPECT), or enhanced glycolytic flux seen in inflammatory cells (18F-FDG PET). However, these strategies are often inadequate to detect bacterial infection and are not specific for living bacteria. Recent approaches have taken advantage of key metabolic differences between prokaryotic and eukaryotic organisms, allowing easier distinction between bacteria and their host. In this report, we exploited one key difference, bacterial cell wall biosynthesis, to detect living bacteria using a positron-labeled D-amino acid. After screening several 14C D-amino acids for their incorporation into E. coli in culture, we identified D-methionine as a probe with outstanding radiopharmaceutical potential. Based on an analogous procedure to that used for L-[methyl-11C]methionine ([11C] L-Met), we developed an enhanced asymmetric synthesis of D-[methyl-11C]methionine ([11C] D-Met), and showed that it can rapidly and selectively differentiate both E. coli and S. aureus infections from sterile inflammation in vivo. We believe that the ease of [11C] D-Met radiosynthesis, coupled with its rapid and specific in vivo bacterial accumulation, make it an attractive radiotracer for infection imaging in clinical practice
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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
Determination of myoglobin concentration in blood-perfused tissue
金沢大学人間社会研究域人間科学系The standard method for determining the myoglobin (Mb) concentration in blood-perfused tissue often relies on a simple but clever differencing algorithm of the optical spectra, as proposed by Reynafarje. However, the underlying assumptions of the differencing algorithm do not always lead to an accurate assessment of Mb concentration in blood-perfused tissue. Consequently, the erroneous data becloud the understanding of Mb function and oxygen transport in the cell. The present study has examined the Mb concentration in buffer and blood-perfused mouse heart. In buffer-perfused heart containing no hemoglobin (Hb), the optical differencing method yields a tissue Mb concentration of 0.26 mM. In blood-perfused tissue, the method leads to an overestimation of Mb. However, using the distinct 1H NMR signals of MbCO and HbCO yields a Mb concentration of 0.26 mM in both buffer- and blood-perfused myocardium. Given the NMR and optical data, a computer simulation analysis has identified some error sources in the optical differencing algorithm and has suggested a simple modification that can improve the Mb determination. Even though the present study has determined a higher Mb concentration than previously reported, it does not alter significantly the equipoise PO2, the PO2 where Mb and O2 contribute equally to the O2 flux. It also suggests that any Mb increase with exercise training does not necessarily enhance the intracellular O2 delivery. © Springer-Verlag 2008
Palmitate interaction with physiological states of myoglobin
BackgroundPrevious studies have shown that palmitate (PA) can bind specifically and non-specifically to Fe(III)MbCN. The present study has observed PA interaction with physiological states of Fe(II)Mb, and the observations support the hypothesis that Mb may have a potential role in facilitating intracellular fatty acid transport.Methods1H NMR spectra measurements of the Mb signal during PA titration show signal changes consistent with specific and non-specific binding.ResultsPalmitate (PA) interacts differently with physiological states of Mb. Deoxy Mb does not interact specifically or non-specifically with PA, while the carbonmonoxy myoglobin (MbCO) interaction with PA decreases the intensity of selective signals and produces a 0.15ppmupfield shift of the PAmethylene peak. The selective signal change upon PA titration provides a basis to determine an apparent PA binding constant,which serves to create a model comparing the competitive PA binding and facilitated fatty acid transport of Mb and fatty acid binding protein(FABP).ConclusionsGiven contrasting PA interaction of ligated vs. unligated Mb, the cellular fatty acid binding protein(FABP) and Mb concentration in the cell, the reported cellular diffusion coefficients, the PA dissociation constants from ligated Mb and FABP, a fatty acid flux model suggests that Mb can compete with FABP transporting cellular fatty acid.General significanceUnder oxygenated conditions and continuous energy demand, Mb dependent fatty acid transport could influence the cell's preference for carbohydrate or fatty acid as a fuel source and regulate fatty acid metabolism
Interaction of myoglobin with oleic acid
Previous studies have shown that palmitate (PA) can interact with myoglobin (Mb). The present study has investigated the interaction of the more soluble unsaturated fatty acid, oleic acid (OA). Indeed, (1)H NMR measurements of the Mb signal during OA titration also show signal changes consistent with specific and non-specific binding. At OA:Mb ratio<4:1, OA perturbs selectively the 8-heme methyl signal, consistent with a local and specific fatty acid-protein interaction. As OA:Mb ratio increases from 4:1 to 40:1, all hyperfine shifted MbCN signals decrease, consistent with a non-selective, global perturbation of the protein. The pH titration analysis indicates that the observed OA methylene signal in the presence of Mb reflects a non-specific interaction and does not originate from a shift in the lamella-micelle equilibrium. Given the OA interaction with Mb, a fatty acid flux model suggests that Mb can play a fatty acid transport role under certain physiological conditions
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