Abstract
Brain ischemia leads to a decrease in pHo. We have shown previously in synaptosomes that the extracellular acidification induces depolarization of mitochondria followed by synthesis of superoxide anions and oxidative stress. Here, we investigated the effects of lowered pHo on oxidative stress and membrane potentials in synaptosomes treated by the iron chelator deferoxamine and zinc chelator TPEN. We demonstrated that chelating of metals has no impact on superoxide anion synthesis and intrasynaptosomal mitochondria depolarization. Meanwhile, deferoxamine was able to inhibit oxidative stress induced by low pHo and hydrogen peroxide application. Compared to deferoxamine, TPEN was less effective but it decreased the DCF fluorescence induced by pHo 6.0 which had no effects in other oxidative stress models. We found that the chelators were able to inhibit slightly plasma membrane depolarization. Synaptosomes preincubation at low pHo caused no effects on the reduced glutathione level. Depletion of glutathione by CDNB produced no additional increase in the DCF fluorescence induced by pHo 7.0. Our results suggest that free iron is crucial for the development of oxidative stress elicited by acidification in synaptosomes. Chelating of this metal seems to be a promising strategy for protecting the neuronal presynaptic terminals against oxidative stress developed at stroke.
Highlights
Stroke is associated with acidification reaching pHo of 5.3 in certain cases, for instance, in hyperglycemia (Thorn and Heitmann 1954; Crowell and Kaufman, 1961; Kraig and Chesler 1990; Tombaugh and Sapolsky 1993; Isaev et al 2008)
Paper we investigated an impact of the membrane permeable iron chelator deferoxamine and membrane permeable zinc chelator N,N,N’,N’-tetrakis(2pyridylmethyl)ethylenediamine (TPEN) on free radical formation in rat brain synaptosomes at low pHo
Oxidative stress was inhibited by the iron chelator deferoxamine (100 μM) and zinc chelator TPEN (5 μM), with deferoxamine being even more effective than ionol (Figure 1b)
Summary
Stroke is associated with acidification reaching pHo of 5.3 in certain cases, for instance, in hyperglycemia (Thorn and Heitmann 1954; Crowell and Kaufman, 1961; Kraig and Chesler 1990; Tombaugh and Sapolsky 1993; Isaev et al 2008). The main cause of pH lowering is a metabolic shift to predominance of glycolysis (Tombaugh and Sapolsky 1993; Isaev et al 2008; Obara et al 2008). Lowering of pH down to 6.0 can induce neuronal death (Nedergaard et al 1991; Isaev et al 2010). The main cause of acid-induced neuronal death is thought to be activation of the acid sensitive ion channels (ASICs) (Krishtal and Pidoplichko 1981; Xiong et al 2004; Isaev et al 2008; Wemmie et al 2013). At least in some cases, damage of neurons under low pH was associated rather with an acidification-induced increase in cytosolic zinc levels than ASIC activity (Isaev et al 2010; Kiedrowski 2011). It was suggested that the mitochondria depolarization followed by oxidative stress plays a key role in development of this phenomenon (Isaev et al 2010)
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