Neuroprotective effects of fluorophore-labelled manganese complexes: Determination of ROS production, mitochondrial membrane potential and confocal fluorescence microscopy studies in neuroblastoma cells

Abstract

In this work, four manganese(II) complexes derived from the ligands H₂L¹-H₂L⁴, that incorporate dansyl or tosyl fluorescent dyes, have been investigated in term of their antioxidant properties. Two of the manganese(II) complexes have been newly prepared using the asymmetric half-salen ligand H₂L² and the thiosemicarbazone ligand H₂L³. The four organic strands and the manganese complexes have been characterized by different analytical and spectroscopic techniques. The study of the antioxidant behaviour of these two new complexes and other two fluorophore-labelled analogues was tested in SH-SY5Y neuroblastoma cells. These four model complexes 1-4 were found to protect cells from oxidative damage in this human neuronal model, by reducing the release of reactive oxygen species. Complexes 1-4 significantly improved cell survival, with levels between 79.1 ± 0.8% and 130.9 ± 4.1%. Moreover, complexes 3 and 4 were able to restore the mitochondrial membrane potential at 1 μM, with 4 reaching levels higher than 85%, similar to the percentages obtained by the positive control agent cyclosporin A. The incorporation of the fluorescent label in the complexes allowed the study of their ability to enter the human neuroblastoma cells by confocal microscopy.

Keywords: Fluorophore; Manganese; Neuroprotection; Oxidative stress; Schiff bases; Superoxide dismutase.