Multi-spin Redox Sensor for Electron Paramagnetic Resonance Studies of Tissue Redox State In Vivo: Validation of Data With a Conventional Spin Probe

Redox imaging is one of the fastest growing areas in diagnostics of pathologies accompanied by redox imbalance. We describe a multi-spin redox sensor (RS) and its application for redox imaging in mice using electron paramagnetic resonance (EPR) spectroscopy. The probe is composed of a quantum dot functionalized with a cyclodextrin shell, conjugated with nitroxide residues (TEMPO) and triphenylphosphonium to achieve intracellular delivery. The data were validated with a conventional spin probe, mito-TEMPO. Nitroxide probe (RS or mito-TEMPO) was injected intravenously in mice under anesthesia. Blood samples were collected from the tail vein at four time intervals within 2 hours and subjected immediately to analysis using EPR spectroscopy. Two hours after injection, mice were sacrificed, five organs were isolated, and tissue homogenates were prepared and subjected to EPR analysis. RS had the same EPR contrast and significantly higher MRI contrast compared to mito-TEMPO. RS circulated longer in the bloodstream than mito-TEMPO, with both substances undergoing reduction in the blood. The distribution of RS and mito-TEMPO in different organs was equal, except for the brain. No adverse side effects were found in mice at the selected dose. Using a non-toxic nanoparticle in the chemical structure of RS as a carrier of nitroxide residues would enhance its translational relevance.