The role of Fe 2þ -induced lipid peroxidation in the initiation of the mitochondrial permeability transition Vladimir Gogvadze, 1 Patrick B. Walter, 2 and Bruce N. Ames * Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA Received 7 November 2002 Abstract Iron and iron complexes stimulate lipid peroxidation and formation of malondialdehyde (MDA). We have studied the effects of Fe 2þ and ascorbate on mitochondrial permeability transition induced by phosphate and Ca 2þ . Iron is necessary for detectable MDA formation, but only Ca 2þ and phosphate are necessary for the induction of membrane potential loss ðDwÞ and Ca 2þ release. Keeping the iron at a constant concentration and varying the Ca 2þ level changed the mitochondrial Ca 2þ retention times, but not the amount of MDA formation. The antioxidant butylated hydroxytoluene at low concentrations prevented MDA formation, but not mito- chondrial Ca 2þ release. Preincubation of mitochondria with Fe 2þ decreased Ca 2þ retention time in a concentration-dependent manner and facilitated Ca 2þ -stimulated MDA accumulation. Thus, Ca 2þ phosphate-induced mitochondrial permeability transition (MPT) can be separated mechanistically from MDA accumulation. Lipid peroxidation products do not appear to participate in the initial phase of the permeability transition, but sensitize mitochondria toward MPT. Ó 2003 Elsevier Science (USA). All rights reserved. Keywords: Calcium; Iron; Aging Iron and iron complexes stimulate lipid peroxidation in cells. Induction of lipid peroxidation in mitochondria, both in vivo and in vitro, is associated with an irre- versible decrease in membrane potential, release of mi- tochondrial Ca 2þ , and mitochondrial swelling [1–5], which are characteristics of the mitochondrial perme- ability transition. Elevated cytosolic Ca 2þ potentiates prooxidant-in- duced damage of mitochondria [6,7]. The mechanism of this potentiation, however, is still poorly understood. The Ca 2þ -induced exacerbation of oxygen free radical injury is likely to be due in part to activation of phos- pholipase A 2 , since the effect of Ca 2þ can be significantly suppressed by EGTA, ruthenium red, or inhibitors of mitochondrial phospholipase A 2 [6,7]. Similar changes occur in mitochondria exposed to supraphysiological concentrations of Ca 2þ . The sensitivity of mitochondria to Ca 2þ is greatly increased by adenine nucleotide de- pletion, elevated phosphate concentration, or low membrane potential (Dw) [8–10]. The similarity between the effects of calcium and those of lipid peroxidation on mitochondrial function suggests that the effect of Ca 2þ is conditioned by Ca 2þ - stimulated electron leakage from the respiratory chain, which increases the mitochondrial production of reac- tive oxygen species [11,12]. It has been proposed that mitochondrial damage induced by inorganic phosphate, uncouplers, or prooxidants such as t-butyl hydroper- oxide and diamide, is caused by the Ca 2þ -stimulated production of oxidants by the respiratory chain at the level of the coenzyme Q [13]. Some authors, however, did not observe the rise in lipid peroxidation products during Ca 2þ phosphate-stimulated damage of mito- chondria [14,15]. Furthermore, the accumulation of li- pid peroxidation products in mitochondria has a delay, which starts when the respiratory capacities of mito- chondria are decreased and intramitochondrial gluta- thione is depleted [16]. Archives of Biochemistry and Biophysics 414 (2003) 255–260 www.elsevier.com/locate/yabbi ABB * Corresponding author. Present address: ChildrenÕs Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA. Fax: 1-510-597-7128. E-mail address: bnames@chori.org (B.N. Ames). 1 Present address: Institute of Theoretical and Experimental Biophysics, Pushchino 142290, Russia. 2 Present address: Biology Department, University of Victoria, P.O. Box 3020, Victoria, Canada V8W 3N5. 0003-9861/03/$ - see front matter Ó 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0003-9861(02)00750-6