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

Abstract

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. Within the 0 – 100 μ M range thioridazine did not reduce the free radical 1,1‐diphenyl‐2‐picryl‐hydrazyl (DPPH) nor did it chelate iron. However, at 10 μ M thioridazine showed important antioxidant activity on mitochondria, characterized by inhibition of accumulation of mitochondria‐generated O 2 •− , assayed as lucigenin‐derived chemiluminescence, inhibition of Fe 2+ /citrate‐mediated lipid peroxidation of the mitochondrial membrane (LPO), assayed as malondialdehyde generation, and inhibition of Ca 2+ / t ‐butyl hydroperoxide ( t ‐BOOH)‐induced mitochondrial permeability transition (MPT)/protein‐thiol oxidation, assayed as mitochondrial swelling. 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). The inhibition of LPO and MPT onset correlated well with the inhibition of cytochrome c release from mitochondria. 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 . British Journal of Pharmacology (2002) 136 , 136–142; doi: 10.1038/sj.bjp.0704672