Abstract:Recent studies have shown that Fez+ increases the oxidation of monoamines such as serotonin, dopamine and related toxins and that the formed oxidation products can undergo co-valent binding to free sulphydryl groups of proteins such as actin and "serotonin binding proteins" which are present in soluble brain extracts. Here we have tested the ability of ferrous iron to induce [3H]dopamine association to cytoplasmic proteins and we have established that a similar oxidation mechanism evidenced in vitro studies could be applied in cell culture. When PC12 cells were incubated with ferrous iron (ferrocene), the binding of [3H]dopamine to proteins was found to be two fold increased with respect to control. The iron is likely to accelerate the oxidation of dopamine to produce quinones which covalently bind to proteins and induce high-molecular protein aggregates. We evidenced that dopaminehron combination induced cell death in undifferentiated PC12 cells via an active cellular process evaluated in terms of morphological and biochemical changes indicative of apoptosis. We also demonstrated induction of lipid peroxidation when dopamine and ferrocene were present in high concentrations. Moreover, ascorbic acid diminished apoptosis but not the lipid peroxidation process. It might indicate that ferrocene and dopamine could produce oxidative stress of a different nature. These results show that the actions of dopamine and iron are essential in the induction of apoptosis and lipid peroxidation. However, there is no necessary causual link between lipid peroxidation and apoptosis. Our data also suggest that iron is capable of increasing the cytotoxicity of dopamine merely by increasing its rate of oxidation and without intervention of the monoamine oxidase B enzyme and, hence, both phenomenons may occur independently from each other in rat pheochromocytoma PC12. These observations may have relevance to the understanding of the mechanism by which dopaminergic neurones are destroyed in some neurodegenerative disorders.The molecular mechanisms underlying neuronal cell death in degenerative disorders such as idiopathic Parkinson's disease are still poorly understood but dopamine has often been considered to be a contributing factor. Both the autoxidation of dopamine and its enzymatic catabolism by monoamine oxidase (MAO) is well known to produce hydrogen peroxide and oxyradicals. These reduced forms of oxygen are highly reactive and the "oxidative stress" which they produce has been held responsible for the loss of monoamine-containing neurones (Fahn and Cohen 1992). In addition, the autoxidation of dopamine produces semiquinones and quinones which are capable to bind covalently to proteins and to glutathione, one of the major cellular defence mechanisms against oxidative stress (Graham et al. 1978; Ito et al. 1988;Meister, 1988). The occurrence of 5-S-cysteinyl adducts of catechols in mammalian brains is thought to reflect the in vivo autoxidation of the catechols and the coupling of the resulting quinones to glutathione (...

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