Electron paramagnetic resonance monitoring of ischemia-induced myocardial oxygen depletion and acidosis in isolated rat hearts using soluble paramagnetic probes.

A new low-field electron paramagnetic resonance approach for noninvasive measurements of myocardial oxygen tension and tissue acidity was developed. The approach was applied to monitor myocardial pO(2) and pH in a model of global no-flow ischemia (30 min) and reperfusion in isolated perfused rat hearts. The myocardial oxygen measurements were performed using deuterated Finland trityl radical probe. A rapid decrease in myocardial pO(2) from 160 mmHg to about 2 ± 1 mmHg was observed within the first minute of ischemia followed by incomplete restoration of pO(2) to 50 mmHg during 30 min of reperfusion. The lower oxygen concentration after ischemia was attributed to the 50% reduction in coronary flow after ischemia as a consequence of myocardial ischemia and reperfusion damage. Myocardial pH measurements using a specially designed imidazoline pH-sensitive nitroxide showed severe myocardial acidification to pH 6.25 during 30 min of ischemia. Preconditioning of the hearts with two 5-min periods of ischemia significantly reduced the acidification of myocardial tissue during sustained ischemia. Noninvasive electron paramagnetic resonance monitoring of myocardial oxygenation and pH may provide important insights into the mechanisms of ischemia and reperfusion injury and a background for development of new therapeutic approaches.

In vivo monitoring of pH, redox status, and glutathione using L-band EPR for assessment of therapeutic effectiveness in solid tumors.

Approach for in vivo real-time assessment of tumor tissue extracellular pH (pH(e)), redox, and intracellular glutathione based on L-band EPR spectroscopy using dual function pH and redox nitroxide probe and disulfide nitroxide biradical, is described. These parameters were monitored in PyMT mice bearing breast cancer tumors during treatment with granulocyte macrophage colony-stimulating factor. It was observed that tumor pH(e) is about 0.4 pH units lower than that in normal mammary gland tissue. Treatment with granulocyte macrophage colony-stimulating factor decreased the value of pH(e) by 0.3 units compared with PBS control treatment. Tumor tissue reducing capacity and intracellular glutathione were elevated compared with normal mammary gland tissue. Granulocyte macrophage colony-stimulating factor treatment resulted in a decrease of the tumor tissue reducing capacity and intracellular glutathione content. In addition to spectroscopic studies, pH(e) mapping was performed using recently proposed variable frequency proton-electron double-resonance imaging. The pH mapping superimposed with MRI image supports probe localization in mammary gland/tumor tissue, shows high heterogeneity of tumor tissue pH(e) and a difference of about 0.4 pH units between average pH(e) values in tumor and normal mammary gland. In summary, the developed multifunctional approach allows for in vivo, noninvasive pH(e), extracellular redox, and intracellular glutathione content monitoring during investigation of various therapeutic strategies for solid tumors.