LAUSR

Abstract Cationic manganese(III) ortho N‐substituted pyridylporphyrins (MnP) act as efficient antioxidants catalyzing superoxide dismutation and accelerating peroxynitrite reduction. Importantly, MnP can reach mitochondria offering protection against reactive species in different animal models of disease. Although an LC‐MS/MS‐based method for MnP quantitation and subcellular distribution has been reported, a direct method capable of evaluating both the uptake and the redox state of MnP in living cells has not yet been developed. In the present work we applied resonance Raman (RR) spectroscopy to analyze the intracellular accumulation of two potent MnP‐based lipophilic SOD mimics, MnTnBuOE‐2‐PyP5+ and MnTnHex‐2‐PyP5+ within endothelial cells. RR experiments with isolated mitochondria revealed that the reduction of Mn(III)P was affected by inhibitors of the electron transport chain, supporting the action of MnP as efficient redox active compounds in mitochondria. Indeed, RR spectra confirmed that MnP added in the Mn(III) state can be incorporated into the cells, readily reduced by intracellular components to the Mn(II) state and oxidized by peroxynitrite. To assess the combined impact of reactivity and bioavailability, we studied the kinetics of Mn(III)TnBuOE‐2‐PyP5+ with peroxynitrite and evaluated the cytoprotective capacity of MnP by exposing the endothelial cells to nitro‐oxidative stress induced by peroxynitrite. We observed a preservation of normal mitochondrial function, attenuation of cell damage and prevention of apoptotic cell death. These data introduce a novel application of RR spectroscopy for the direct detection of MnP and their redox states inside living cells, and helps to rationalize their antioxidant capacity in biological systems. Graphical abstract Figure. No caption available. HighlightsRaman Resonance was utilized to reveal the redox state of Mn‐porphyrins (MnP) in cells.Mn(III)P are readily reduced intracellularly to the Mn(II) state.Intramitochondrial oxidation of a peroxynitrite‐sensitive probe is inhibited by MnP.The cytotoxicity of peroxynitrite is neutralized by MnP via a catalytic redox cycle.