Thioridazine interacts with the membrane of mitochondria acquiring antioxidant activity toward apoptosis - potentially implicated mechanisms

1 We evaluated the effects of the phenothiazine derivative thioridazine on mechanisms of mitochondria potentially implicated in apoptosis, such as those involving reactive oxygen species (ROS) and cytochrome c release, as well as the involvement of drug interaction with mitochondrial membrane in these effects. 2 Within the 0-100 muM range thioridazine did not reduce the free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) nor did it chelate iron. 3 However, at 10 muM thioridazine showed important antioxidant activity on mitochondria, characterized by inhibition of accumulation of mitochondria-generated O-2(.-), assayed as lucigenin-derived chemiluminescence, inhibition of Fe2-/citrate-mediated lipid peroxidation of the mitochondrial membrane (LPO), assayed as malondialdehyde generation, and inhibition of Ca2-/t-butyl hydroperoxide (t-BOOH)-induced mitochondrial permeability transition (MPT)/protein-thiol oxidation, assayed as mitochondrial swelling. 4 Thioridazine respectively increased and decreased the fluorescence responses of mitochondria labelled with 1-aniline-8-naphthalene sulfonate (ANS) and 1-(4-trimethylammonium phenyl)-6 phenyl 1,3,5-hexatriene (TMA-DPH). 5 The inhibition of LPO and MPT onset correlated well with the inhibition of cytochrome c release from mitochondria. 6 We conclude that thioridazine interacts with the inner membrane of mitochondria, more likely close to its surface, acquiring antioxidant activity toward processes with potential implications in apoptosis such as O-2(.-) accumulation, as well as LPO, MPT and associated release of cytochrome c.