Pro-oxidant activity of Cu,Zn-superoxide dismutase

Hydrogen Peroxide and Amyotrophic Lateral Sclerosis: From Biochemistry to Pathophysiology

Free radicals are unstable chemical reactive species produced during Redox dyshomeostasis (RDH) inside living cells and are implicated in the pathogenesis of various neurodegenerative diseases. One of the most complicated and life-threatening motor neurodegenerative diseases (MND) is amyotrophic lateral sclerosis (ALS) because of the poor understanding of its pathophysiology and absence of an effective treatment for its cure. During the last 25 years, researchers around the globe have focused their interest on copper/zinc superoxide dismutase (Cu/Zn SOD, SOD1) protein after the landmark discovery of mutant SOD1 (mSOD1) gene as a risk factor for ALS. Substantial evidence suggests that toxic gain of function due to redox disturbance caused by reactive oxygen species (ROS) changes the biophysical properties of native SOD1 protein thus, instigating its fibrillization and misfolding. These abnormal misfolding aggregates or inclusions of SOD1 play a role in the pathogenesis of both forms of ALS, i.e., Sporadic ALS (sALS) and familial ALS (fALS). However, what leads to a decrease in the stability and misfolding of SOD1 is still in question and our scientific knowledge is scarce. A large number of studies have been conducted in this area to explore the biochemical mechanistic pathway of SOD1 aggregation. Several studies, over the past two decades, have shown that the SOD1-catalyzed biochemical reaction product hydrogen peroxide (H₂O₂) at a pathological concentration act as a substrate to trigger the misfolding trajectories and toxicity of SOD1 in the pathogenesis of ALS. These toxic aggregates of SOD1 also cause aberrant localization of TAR-DNA binding protein 43 (TDP-43), which is characteristic of neuronal cytoplasmic inclusions (NCI) found in ALS. Here in this review, we present the evidence implicating the pivotal role of H₂O₂ in modulating the toxicity of SOD1 in the pathophysiology of the incurable and highly complex disease ALS. Also, highlighting the role of H₂O₂ in ALS, we believe will encourage scientists to target pathological concentrations of H₂O₂ thereby halting the misfolding of SOD1.

Thiol oxidase ability of copper ion is specifically retained upon chelation by aldose reductase

Bovine lens aldose reductase is susceptible to a copper-mediated oxidation, leading to the generation of a disulfide bridge with the concomitant incorporation of two equivalents of the metal and inactivation of the enzyme. The metal complexed by the protein remains redox active, being able to catalyse the oxidation of different physiological thiol compounds. The thiol oxidase activity displayed by the enzymatic form carrying one equivalent of copper ion (Cu₁-AR) has been characterized. The efficacy of Cu₁-AR in catalysing thiol oxidation is essentially comparable to the free copper in terms of both thiol concentration and pH effect. On the contrary, the two catalysts are differently affected by temperature. The specificity of the AR-bound copper towards thiols is highlighted with Cu₁-AR being completely ineffective in promoting the oxidation of both low-density lipoprotein and ascorbic acid.

A review of the protective role of melatonin during phosphine-induced cardiotoxicity: focus on mitochondrial dysfunction, oxidative stress and apoptosis

OBJECTIVES

Acute poisoning with aluminium phosphide (AlP) is a major cause of mortality in developing countries. AlP mortality is due to cardiac dysfunction leading to cardiomyocyte death. The main mechanism is an inhibition of cytochrome c oxidase in the cardiomyocyte mitochondria, resulting in a decreased ATP production and oxidative stress. Unfortunately, the administration of exogenous drugs does not meet the desired requirements of an effective therapy. Melatonin is an amphiphilic molecule and can easily pass through all cellular compartments with the highest concentration recorded in mitochondria. It is known as a vigorous antioxidant, acting as a potent reactive oxygen species (ROS) scavenger. Our aim is to summarize the mechanisms by which melatonin may modulate the deteriorating effects of AlP poisoning on cardiac mitochondria.

KEY FINDINGS

Melatonin not only mitigates the inhibition of respiratory chain complexes, but also increases ATP generation. Moreover, it can directly inhibit the mitochondrial permeability transition pore (mPTP) opening, thus preventing apoptosis. In addition, melatonin inhibits the release of cytochrome c from mitochondria to hinder caspase activation leading to cell survival.

SUMMARY

Based on the promising effects of melatonin on mitochondria, melatonin may mitigate AlP-induced cardiotoxicity and might be potentially suggested as cardioprotective in AlP-intoxicated patients.

An electrocardiographic, molecular and biochemical approach to explore the cardioprotective effect of vasopressin and milrinone against phosphide toxicity in rats

The present study was conducted to identify the protective effect of vasopressin (AVP) and milrinone on cardiovascular function, mitochondrial complex activities, cellular ATP reserve, oxidative stress, and apoptosis in rats poisoned by aluminum phosphide (AlP). Rats were divided into five groups (n = 12) including control, AlP (12.5 mg/kg), AlP + AVP (2.0 Units/kg), AlP + milrinone (0.25 mg/kg) and AlP + AVP + milrinone. After treatment, the animals were connected to an electronic cardiovascular monitoring device to monitor electrocardiographic (ECG) parameter. Finally, oxidative stress biomarkers, mitochondrial complex activities, ADP/ATP ratio and apoptosis were evaluated on the heart tissues. Results indicated that AlP administration induced ECG abnormalities along with a decline in blood pressure and heart rate. AVP and milrinone significantly ameliorated these changes in all treated groups. Considerable protective effects on oxidative stress biomarkers, complex IV activity, ADP/ATP ratio and caspase-3 and -9 activities in treated groups were also found. These findings were supported by flow cytometry assay of cardiomyocytes. In conclusion, administration of AVP and milrinone, not only improve cardiovascular functions in AlP poisoned rats in the short time, but after a long time can also restore mitochondrial function and ATP level and reduce the oxidative damage, which prevent cardiomyocytes from entering the apoptotic phase.

Diethyldithiocarbamate inhibits in vivo Cu,Zn-superoxide dismutase and perturbs free radical processes in the yeast Saccharomyces cerevisiae cells

Copper-zinc superoxide dismutase (Cu,Zn-SOD) and manganese superoxide dismutase (Mn-SOD) in some model experiments in vitro demonstrated antioxidant as well as pro-oxidant properties. In the present study, yeast Saccharomyces cerevisiae lacking Mn-SOD were studied using Cu,Zn-SOD inhibitor N-N'-diethyldithiocarbamate (DDC) as a model system to study the physiological role of the yeast Cu,Zn-SOD. Yeast treatment by DDC caused dose-dependent inhibition of SOD in vivo, with 75% inhibition at 10mM DDC. The inhibition of SOD by DDC resulted in modification of carbonylprotein levels, indicated by a bell-shaped curve. The activity of glutathione reductase, isocitrate dehydrogenase, and glucose-6-phosphate dehydrogenase (enzymes associated with antioxidant) increased, demonstrating a compensatory effect in response to SOD inhibition by different concentrations of DDC. A strong positive correlation (R2=0.97) was found between SOD and catalase activities that may be explained by the protective role of SOD for catalase. All observed effects were absent in the isogenic SOD-deficient strain that excluded direct DDC influence. The results are discussed from the point of view that in vivo Cu,Zn-SOD of S. cerevisiae can demonstrate both anti- and pro-oxidant properties.

Possible role of superoxide dismutases in the yeast Saccharomyces cerevisiae under respiratory conditions

We have analyzed the activity of antioxidant and tricarboxylic acid cycle enzymes as well as protein carbonyl content in budding yeast Saccharomyces cerevisiae cells grown in medium with glycerol using wild-strain cells and defective mutants in superoxide dismutases (SODs). The present report demonstrates that the activity of catalase, glucose-6-phosphate dehydrogenase, glutathione reductase, isocitrate dehydrogenase, succinate dehydrogenase, and malate dehydrogenase, on average, was lower in the strains lacking SODs than that in the parental strain. On the other hand, under conditions used in this study, the content of carbonyl groups in proteins was relatively higher in the wild type as compared with SOD-defective strains. It may be suggested that in vivo SOD can demonstrate protective as well as pro-oxidant properties, and the final result depends on particular conditions.

Retinoic acid reduces apoptosis and oxidative stress by preservation of SOD protein level

Retinoic acid (RA) has already been shown to exert antiapoptotic and antioxidative activity in various cells. In this study, we determined the effect of RA on the mRNA and protein levels of the Cu-,Zn-superoxide dismutase (SOD-1) and Mn-superoxide dismutase (SOD-2) during staurosporine-induced apoptosis in primary cultures from neonatal rat hippocampus. Exposure to staurosporine (300 nM, 24 h) increased the percentage of apoptotic neurons to 62% compared with 18% in controls. We determined an increase in the reactive oxygen species (ROS) content from 4 up to 48 h after the induction of the injury. Treatment with staurosporine did not significantly change the mRNA levels of SOD-1 and SOD-2. However, the SOD-1 and SOD-2 protein levels markedly decreased 24 and 48 h after the addition of staurosporine. Compared with staurosporine-exposed controls, RA (10 nM)-treated cultures showed a significant increase in neuronal survival, a reduced neuronal ROS content, and enhanced protein levels of SOD-1 and SOD-2 24 and 48 h after the start of the exposure to staurosporine. The results suggest that RA reduced staurosporine-induced oxidative stress and apoptosis by preventing the decrease in the protein levels of SOD-1 and SOD-2, and thus supported the antioxidant defense system.