Ratiometric Fluorescent Sensors Illuminate Cellular Magnesium Imbalance in a Model of Acetaminophen-Induced Liver Injury

Magnesium(II) plays catalytic, structural, regulatory, and signaling roles in living organisms. Abnormal levels of this metal have been associated with numerous pathologies, including cardiovascular disease, diabetes, metabolic syndrome, immunodeficiency, cancer, and, most recently, liver pathologies affecting humans. The role of Mg²⁺ in the pathophysiology of liver disease, however, has been occluded by concomitant changes in concentration of interfering divalent cations, such as Ca²⁺, which complicates the interpretation of experiments conducted with existing molecular Mg²⁺ indicators. Herein, we introduce a new quinoline-based fluorescent sensor, MagZet1, that displays a shift in its excitation and emission wavelengths, affording ratiometric detection of cellular Mg²⁺ by both fluorescence microscopy and flow cytometry. The new sensor binds the target metal with a submillimolar dissociation constant─well suited for detection of changes in free Mg²⁺ in cells─and displays a 10-fold selectivity against Ca²⁺. Furthermore, the fluorescence ratio is insensitive to changes in pH in the physiological range, providing an overall superior performance over existing indicators. We provide insights into the metal selectivity profile of the new sensor based on computational modeling, and we apply it to shed light on a decrease in cytosolic free Mg²⁺ and altered expression of metal transporters in cellular models of drug-induced liver injury caused by acetaminophen overdose.