Influence of reactive oxygen species production by monoamine oxidase activity on aluminum-induced mitochondrial permeability transition

Treatment of Ca2+-loaded mitochondria with both aluminum and tyramine results in a swelling of higher amplitude than with aluminum alone, while tyramine alone is ineffective. The phenomenon is accompanied by H2O2 production and thiol and pyridine nucleotide oxidation. Cyclosporin A, N-ethylmaleimide or dithioerythritol completely prevent these effects, while catalase exhibits a lower inhibition, pointing to the induction of the permeability transition (MPT) by an oxidative stress. Reactive oxygen species are generated by the interaction of aluminum with the inner membrane and the oxidation of tyramine by monoamine oxidase on the outer membrane. This different localization determines the oxidation of critical thiol groups located on both internal and external sides of pore-forming structures, resulting in MPT induction. The reduced effect by aluminum or the inefficacy by tyramine, when implied alone, can be attributable to the oxidation of thiol groups located only on the internal or external side, respectively. Ultrastructural observations show that aluminum plus tyramine induce the typical configuration of mitochondria that have undergone the MPT. Instead, with aluminum alone, the sensitive subpopulation, although swollen, preserves the outer membrane and shows an apparently orthodox configuration.