EPR signal reduction kinetic of several nitroxyl derivatives in blood in vitro and in vivo

Abstract

Abstract. The present study is focused on the mechanism(s) of electron-paramagnetic resonance (EPR) signal reduction kinetic of several nitroxyl radicals and nitroxyl-labeled anticancer drugs in physiological solutions in the context of their application for evaluation of oxidation/reduction status of blood and tissues -an important step in biomedical diagnostics and planning of therapy of many diseases. The nitroxyl derivatives were characterized with different size and water-solubility. Some of them are originally synthesized. In buffer, in the absence of reducing and oxidizing equivalents, the EPR signal intensity of all nitroxyls was constant with the time. In serum and cell cultured medium, in an absence of cells and in a negligible amount of reducing and oxidizing equivalents, there was no significant EPR signal reduction, too. In vitro (in freshly isolated blood samples), the EPR signal intensity was characterized with slow decrease within 30 min, presumably as a result of interaction between the nitroxyl derivative and blood cells. The EPR spectrum of hydrophobic nitroxyls showed a slight anisotropy in cell-containing solutions and it did not changed in non-cell physiological solutions. This suggests for a limited motion of more hydrophobic nitroxyls through their preferable location in cell membranes. In vivo (in the bloodstream of mice under anesthesia), the EPR signal reduction kinetic was characterized by two phases: i) a rapid enhancement within 30 s as a result of increasing of nitroxyl concentration in the bloodstream after its intravenous injection, followed by ii) a rapid decrease (~80-100%) within 2-5 min, presumably as a result of transportation of nitroxyl in the tissues. The hydrophobic nitroxyls were characterized with stronger and faster decrease in EPR signal intensity in the blood in vivo, as a result of their higher cell permeability, rapid clearance from the bloodstream and/or transportation in the surrounding tissues. The hydrophilic nitroxyls persist in the bloodstream (in their radical form) for a comparatively long time.The data suggest that the hydrophobic cell-permeable nitroxyl derivatives are most appropriate for evaluation of cell and tissue oxidation/reduction status, while the hydrophilic nitroxyls (impermeable for cell membranes or with very slow cell permeability) are most appropriate for evaluation of oxidation/reduction status of blood using EPR imaging.

Tissue Redox Activity as a Hallmark of Carcinogenesis: From Early to Terminal Stages of Cancer

“…Nitrosoureas are well-known DNA-annealing agents, penetrating cellular and even nuclear membranes (35,40). Thus, the dynamics of the nitroxide-enhanced MRI signal using SLENU (Figs.…”

“…[31][32][33][34][35]. The comparative analysis of the results, obtained using both imaging techniques, gives accurate information about the TRA in vivo.…”

“…The MRI/EPR signal dynamics is a result of various factors and processes that occur simultaneously in the following 4 areas: (i) the lifetime of the nitroxide in the circulation, depending on its water solubility (35,36), (ii) the reduction/oxidation of the nitroxide in the bloodstream, which is expected to be low in the plasma but sufficiently high in blood cells (if it penetrates cell membranes; refs. 35,36), (iii) the penetration and accumulation of the nitroxide in the EES and its reduction/oxidation, which is expected to be negligible, and (iv) the penetration and accumulation of the nitroxide in the cells of the tissue and its intracellular reduction/oxidation, which is expected to be substantial in comparison with the bloodstream and EES (20,37). TRA is a combination of the redox capacity of the extracellular (EES) and intracellular space of the tissue.…”

Molecular Probes for Evaluation of Oxidative Stress by In Vivo EPR Spectroscopy and Imaging: State-of-the-Art and Limitations

“…Most studies in this field have focused on cyclic tetramethyl-substituted nitroxides. Depending on the structure, nitroxide elimination in vivo principally occurs through renal excretion and reduction to hydroxylamine in tissues, while reduction in the blood is negligible [55][56][57][58][59][60][61][62][63][64][65]. Other pathways could play a minor role for some structures, such as the transformation of the six-membered ring of TEMPO, (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl, to a five-membered ring by cytochrome P450 in the liver [64,66].…”

Survival benefit with PCI for chronic total occlusions: The Jury is still out

“…On the other hand, the magnetic resonance relaxivity and electron paramagnetic resonance (EPR) property have endowed the nitroxyl radical‐containing materials with the potential application as bioimaging probes. Much attentions have been paid on the development of the nitroxyl radical‐based magnetic resonance imaging (MRI) probes because they have lower toxicity in comparison with the commercially gadolinium derivatives agents 22–24. However, the MR relaxivities of the nitroxyl radical are relatively lower.…”