Thallium(III)-mediated changes in membrane physical properties and lipid oxidation affect cardiolipin-cytochrome c interactions

Trivalent thallium (TI(III)) is a highly toxic heavy metal through not completely understood mechanisms. Previously, we demonstrated that TI(III) causes mitochondrial depolarization in PC12 cells leading to a decrease in cell viability. Given the role of the phospholipid cardiolipin (CL) in mitochondrial events, we evaluated in vitro the short- (2 min) and long- (60 min) time effects of TI(III) (1-75 mu M) on CL-containing membranes physical properties, and the consequences on cytochrome c binding to CL. After 2 min of incubation, TI(111) significantly decreased liposome surface potential, lipid packing, and hydration of phosphatidylcholine:CL liposomes, while CL pK(2) decreased from 9.8 to 8.2. The magnitude of these changes was even higher after 60 min of incubation. While no TI(III) was found bound to membranes, TI(I) was present in the samples. Accordingly, significant oxidative damage to both CL fatty acids and polar headgroup was observed. Cytochrome c binding to CL was decreased in TI(III)-treated liposomes. The present results indicate that TI(III) interaction with CL-containing membranes affected their physical properties, caused lipid oxidation and CL hydrolysis, and resulted in a decrease of cytochrome c binding. If occurring in vivo, these effects of TI(III) could partially account for mitochondrial dysfunction in cells exposed to this metal. (C) 2008 Elsevier B.V. All rights reserved.