Chelation of mitochondrial iron prevents seizure-induced mitochondrial dysfunction and neuronal injury

Silica Nanoparticles from Melon Seed Husk Abrogated Binary Metal(loid) Mediated Cerebellar Dysfunction by Attenuation of Oxido-inflammatory Response and Upregulation of Neurotrophic Factors in Male Albino Rats

Silica nanoparticles (SiNPs) have been touted for their role in the management of non-communicable diseases. Their neuroprotective benefits against heavy metal-induced neurotoxicity remain largely unexplored. This is a comparative evaluation of the oxido-inflammatory and neurotrophic effects of Ni, Al, and Ni/Al mixture on the cerebellum of male albino rats with or without treatment with SiNPs generated from melon seed husk. The study complied with the ARRIVE guidelines for reporting in vivo experiments. A total of 91, 7-9 week-old weight-matched male Sprague rats (to avoid sex bias) were randomly divided into 13 different dosing groups where Group 1 served as the control. Other groups received 0.2 mg/kg Ni, 1 mg/kg Al, and 0.2 mg/kg Ni + 1 mg/kg Al mixture with or without different doses of SiNP for 90 days. Rotarod performance was carried out. Oxidative stress markers, Ni, Al, Ca, Fe, Mg, neurotrophic factors, amyloid beta (Aβ-42), cyclooxygenase-2 (COX-2), and acetylcholinesterase (AChE) were determined in the cerebellum. SiNPs from melon seed husk caused a significant decrease in Aβ-42 level and activities of AChE and COX-2 and a significant increase in brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) mediated by Ni, Al, and Ni/Al mixture exposure in rats. Neurotoxicity of the Ni/Al mixture is via heightened neuronal lipoperoxidative damage, decreased Mg, and increased Fe, and co-administration of SiNPs from melon seed husk with the Ni/Al mixture attenuated some of these biochemical changes in the cerebellum.

Iron status and sarcopenia-related traits: a bi-directional Mendelian randomization study

Although serum iron status and sarcopenia are closely linked, the presence of comprehensive evidence to establish a causal relationship between them remains insufficient. The objective of this study is to employ Mendelian randomization techniques to clarify the association between serum iron status and sarcopenia. We conducted a bi-directional Mendelian randomization (MR) analysis to investigate the potential causal relationship between iron status and sarcopenia. MR analyses were performed using inverse variance weighted (IVW), MR-Egger, and weighted median methods. Additionally, sensitivity analyses were conducted to verify the reliability of the causal association results. Then, we harvested a combination of SNPs as an integrated proxy for iron status to perform a MVMR analysis based on IVW MVMR model. UVMR analyses based on IVW method identified causal effect of ferritin on appendicular lean mass (ALM, β = - 0.051, 95% CI - 0.072, - 0.031, p = 7.325 × 10-07). Sensitivity analyses did not detect pleiotropic effects or result fluctuation by outlying SNPs in the effect estimates of four iron status on sarcopenia-related traits. After adjusting for PA, the analysis still revealed that each standard deviation higher genetically predicted ferritin was associated with lower ALM (β = - 0.054, 95% CI - 0.092, - 0.015, p = 0.006). Further, MVMR analyses determined a predominant role of ferritin (β = - 0.068, 95% CI - 0.12, - 0.017, p = 9.658 × 10-03) in the associations of iron status with ALM. Our study revealed a causal association between serum iron status and sarcopenia, with ferritin playing a key role in this relationship. These findings contribute to our understanding of the complex interplay between iron metabolism and muscle health.

Clinical characteristics and risk factors of cerebral cavernous malformation-related epilepsy

PURPOSE

This study aimed to summarize the clinical characteristics and explore the risk factors for cerebral cavernous malformation (CCM)-related epilepsy (CRE).

METHODS

We retrospectively analyzed the clinical data of patients with CCM in our cerebral vascular malformations database. Descriptive statistics were used to present the clinical characteristics of CRE patients. Patients were divided into a CRE and a non-CRE group according to clinical presentation. Binary logistic regression analysis was used to analyze the risk factors of CRE.

RESULTS

A total of 199 patients with CCM confirmed by postoperative pathological examination were enrolled, 93 of whom were diagnosed with CRE, and 34 patients had drug-resistant epilepsy. The most common seizure type of CRE patients was focal to bilateral tonic-clonic seizure (FBTCS), followed by focal impaired awareness motor seizure. All CCM lesions were supratentorial, 97.8% of which involved the cerebral cortex, 86.0% of lesions had hemosiderin rim, and 50.5% of lesions were located in the temporal lobe. Binary logistic regression analysis indicated that CCM diagnosis age ≤ 44 years (odds ratio [OR] 2.79, p = 0.010), temporal lobe lesion location (OR = 9.07, p = 0.042), medial temporal lobe lesion (OR = 14.09, p = 0.002), cortical involvement of the lesion (OR = 32.77, p = 0.010), and hemosiderin rim around the lesion (OR = 16.48, p = 0.001) significantly increased the risk of CRE.

CONCLUSIONS

The most common seizure type of CRE was FBTCS. Those whose CCM diagnosis age was ≤ 44 years, having a temporal lobe lesion location, especially the medial temporal lobe lesion, cortical involvement, and hemosiderin rim around the lesion had a higher risk of developing CRE.

Causal Relationship of Genetically Predicted Serum Micronutrients Levels With Sarcopenia: A Mendelian Randomization Study

Objectives

Previous observational studies have suggested associations between concentrations of several circulating micronutrients and sarcopenia. However, the causality inferred from those studies was subjected to residual confounding and reverse causation. Therefore, we aimed to examine the causal effects of the levels of genetically predicted serum micronutrients on sarcopenia.

Methods

Single nucleotide polymorphisms (SNPs) were chosen from large-scale genome-wide association studies of participants only with European descent and were used as genetic instruments for the levels of 10 serum micronutrients (calcium, magnesium, selenium, copper, iron, zinc, Vitamin A, Vitamin B12, Vitamin D, and Vitamin E). Sarcopenia was defined by referencing to the 2019 definition given by the European Working Group on Sarcopenia in Older People (EWGSOP). A two-sample Mendelian randomization (MR) analysis was carried out to examine the associations between the levels of genetically predicted serum micronutrients and the risk of sarcopenia. Then, sensitivity analyses (including weighted median, MR-Egger and leave-one-out sensitivity analyses) were performed to evaluate the robustness of study findings. The estimates were presented as odds ratio (OR) with their 95% confidence intervals (CIs) per one standard deviation (SD) increase in the exposures.

Results

A total of 378,635 UK Biobank participants, including 572 participants who were identified with sarcopenia, were included in this study. The iron status was shown to have a clear effect on the risk of sarcopenia based on MR analyses. The per one SD increment in the genetically-determined serum iron level corresponded to a 53% increase in the risk of sarcopenia (OR = 1.53, 95% CI: 1.31-1.78, P = 0.001). The exclusion of SNPs of the circulating iron level (i.e., rs1799945 SNP, rs1800562 SNP or rs855791 SNP) did not attenuate the magnitude of the signal in MR analysis. There was little evidence supporting the associations between other remaining micronutrients and sarcopenia.

Conclusions

An increased risk of sarcopenia was observed with a genetically higher concentration of iron, suggesting that iron may play a role in the occurrence or development of sarcopenia.

Clinical phenotype modulates brain's myelin and iron content in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is associated with brain pathology extending beyond temporal lobe structures. We sought to look for informative patterns of brain tissue properties in TLE that go beyond the established morphometry differences. We hypothesised that volume differences, particularly in hippocampus, will be paralleled by changes in brain microstructure. The cross-sectional study included TLE patients (n = 25) from a primary care center and sex-/age-matched healthy controls (n = 55). We acquired quantitative relaxometry-based magnetic resonance imaging (MRI) data yielding whole-brain maps of grey matter volume, magnetization transfer (MT) saturation, and effective transverse relaxation rate R2* indicative for brain tissue myelin and iron content. For statistical analysis, we used the computational anatomy framework of voxel-based morphometry and voxel-based quantification. There was a positive correlation between seizure activity and MT saturation measures in the ipsilateral hippocampus, paralleled by volume differences bilaterally. Disease duration correlated positively with iron content in the mesial temporal lobe, while seizure freedom was associated with a decrease of iron in the very same region. Our findings demonstrate the link between TLE clinical phenotype and brain anatomy beyond morphometry differences to show the impact of disease burden on specific tissue properties. We provide direct evidence for the differential effect of clinical phenotype characteristics on processes involving tissue myelin and iron in mesial temporal lobe structures. This study offers a proof-of-concept for the investigation of novel imaging biomarkers in focal epilepsy.

Preadministration of high-dose alpha-tocopherol improved memory impairment and mitochondrial dysfunction induced by proteasome inhibition in rat hippocampus

Objective: The ubiquitin-proteasome system plays a key role in memory consolidation. Proteasome inhibition and free radical-induced neural damage were implicated in neurodegenerative states. In this study, it was tested whether alpha-tocopherol (αT) in low and high doses could improve the long-term memory impairment induced by proteasome inhibition and protects against hippocampal oxidative stress. Methods: Alpha-tocopherol (αT) (60, 200 mg/kg, i.p. for 5 days) was administered to rats with memory deficit and hippocampal oxidative stress induced by bilateral intra-hippocampal injection of lactacystin (32 ng/μl) and mitochondrial evaluations were performed for improvement assessments. Results: The results showed that lactacystin significantly reduced the passive avoidance memory performance and increased the level of malondialdehyde (MDA), reactive oxygen species (ROS) and diminished the mitochondrial membrane potential (MMP) in the rat hippocampus. Furthermore, Intraperitoneal administration of αT significantly increased the passive avoidance memory, glutathione content and reduced ROS, MDA levels and impaired MMP. Conclusions: The results suggested that αT has neuroprotective effects against lactacystin-induced oxidative stress and memory impairment via the enhancement of hippocampal antioxidant capacity and concomitant mitochondrial sustainability. This finding shows a way to prevent and also to treat neurodegenerative diseases associated with mitochondrial impairment.

In situ labeling of non-accommodating interneurons based on metabolic rates

Maintaining high frequency firing of narrow action potentials puts a large metabolic load on fast spiking (FS), perisomatic-inhibitory interneurons compared to their slow-spiking, dendrite targeting counterparts. Although the relationship of action potential (AP) firing and metabolism is firmly established, there is no single method to differentiate interneurons in situ based on their firing properties.

In this study, we explore a novel strategy to easily identify the metabolically active FS cells among different classes of interneurons.

We found that the oxidation of the fluorescent free radical marker 2,7-dichlorodihydrofluorescein (H₂DCF) preferentially occurs in interneurons both in slice cultures and acute brain slices. Despite their morphological heterogeneity, almost all DCF-positive (DCF+) neurons belonged to the cluster of non-accommodating FS interneurons. Furthermore, all FS interneurons expressing parvalbumin (PV) both in slice cultures and in acute slices from tdTomato-PVCre transgenic mice were also DCF+. However, only half of the recorded DCF + cells were also PV+, indicating that H₂DCF-oxidation occurs in different interneuron classes characterized by non-accomodating AP-firing. Comprehensively enhancing spontaneous neuronal activity led to mitochondrial oxidation of DCF in pyramidal cells as well as interneurons, suggesting that the apparent selectivity towards interneurons represents differences in the underlying metabolic load.

While radical-scavenging, inhibition of APs or NO-synthesis, and iron chelation had no effect on the staining pattern, exposure to the complex-I inhibitor, rotenone, prevented interneuronal DCF accumulation. We conclude that H₂DCF oxidation is independent of free radicals but correlates with the intensive oxidative energy metabolism and high mitochondrial mass in interneurons sharing the non-accommodating FS phenotype.

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Fast spiking non-adapting interneurons preferentially oxidize and accumulate H₂DCF.

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Labeling of interneurons correlates with mitochondrial mass and energy metabolism.

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Free radical formation does not contribute to DCF-labeling of interneurons.

New Insights into Oxidative Damage and Iron Associated Impairment in Traumatic Brain Injury

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Traumatic Brain Injury is considered one of the most prevalent causes of death around the world; more than seventy millions of individuals sustain the condition per year. The consequences of traumatic brain injury on brain tissue are complex and multifactorial, hence, the current palliative treatments are limited to improve patients’ quality of life. The subsequent hemorrhage caused by trauma and the ongoing oxidative process generated by biochemical disturbances in the in the brain tissue may increase iron levels and reactive oxygen species. The relationship between oxidative damage and the traumatic brain injury is well known, for that reason, diminishing factors that potentiate the production of reactive oxygen species have a promissory therapeutic use. Iron chelators are molecules capable of scavenging the oxidative damage from the brain tissue and are currently in use for ironoverload- derived diseases.

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Here, we show an updated overview of the underlying mechanisms of the oxidative damage after traumatic brain injury. Later, we introduced the potential use of iron chelators as neuroprotective compounds for traumatic brain injury, highlighting the action mechanisms of iron chelators and their current clinical applications.

The role of astrocytes in seizure generation: insights from a novel in vitro seizure model based on mitochondrial dysfunction

Approximately one-quarter of patients with mitochondrial disease experience epilepsy. Their epilepsy is often severe and resistant towards conventional antiepileptic drugs. Despite the severity of this epilepsy, there are currently no animal models available to provide a mechanistic understanding of mitochondrial epilepsy. We conducted neuropathological studies on patients with mitochondrial epilepsy and found the involvement of the astrocytic compartment. As a proof of concept, we developed a novel brain slice model of mitochondrial epilepsy by the application of an astrocytic-specific aconitase inhibitor, fluorocitrate, concomitant with mitochondrial respiratory inhibitors, rotenone and potassium cyanide. The model was robust and exhibited both face and predictive validity. We then used the model to assess the role that astrocytes play in seizure generation and demonstrated the involvement of the GABA-glutamate-glutamine cycle. Notably, glutamine appears to be an important intermediary molecule between the neuronal and astrocytic compartment in the regulation of GABAergic inhibitory tone. Finally, we found that a deficiency in glutamine synthetase is an important pathogenic process for seizure generation in both the brain slice model and the human neuropathological study. Our study describes the first model for mitochondrial epilepsy and provides a mechanistic insight into how astrocytes drive seizure generation in mitochondrial epilepsy.

Inhibition of ferroptosis processes ameliorates cognitive impairment in kainic acid-induced temporal lobe epilepsy in rats

Hippocampal neuronal death plays a causal role in the cognitive impairment of temporal lobe epilepsy (TLE). Ferroptosis, a novel form of regulated cell death, is strongly linked to cognitive impairment. However, whether ferroptosis is associated with cognitive comorbidities of TLE is unknown. In this study, it was demonstrated that ferroptosis occurs in the hippocampus following kainic acid (KA)-induced TLE in rats. Treatment with ferrostatin-1, a specific inhibitor of ferroptosis, prevented the initiation and progression of ferroptosis in the hippocampus of KA-treated rats. This was through decreased expression of glutathione peroxidase 4, glutathione (GSH) depletion as well as lipid peroxides and iron accumulation. It was also found that ferrostatin-1 prevented hippocampal neuronal loss and rescued cognitive function in KA-induced TLE in rats. These results suggest that ferroptosis is involved in the cognitive impairment of KA-induced TLE in rats, and inhibition of ferroptosis processes ameliorates cognitive impairment in KA-induced TLE in rats.

Role of mitochondrial calcium uniporter-mediated Ca2+ and iron accumulation in traumatic brain injury

Previous studies have suggested that the cellular Ca²⁺ and iron homeostasis, which can be regulated by mitochondrial calcium uniporter (MCU), is associated with oxidative stress, apoptosis and many neurological diseases. However, little is known about the role of MCU‐mediated Ca²⁺ and iron accumulation in traumatic brain injury (TBI). Under physiological conditions, MCU can be inhibited by ruthenium red (RR) and activated by spermine (Sper). In the present study, we used RR and Sper to reveal the role of MCU in mouse and neuron TBI models. Our results suggested that the Ca²⁺ and iron concentrations were obviously increased after TBI. In addition, TBI models showed a significant generation of reactive oxygen species (ROS), decrease in adenosine triphosphate (ATP), deformation of mitochondria, up‐regulation of deoxyribonucleic acid (DNA) damage and increase in apoptosis. Blockage of MCU by RR prevented Ca²⁺ and iron accumulation, abated the level of oxidative stress, improved the energy supply, stabilized mitochondria, reduced DNA damage and decreased apoptosis both in vivo and in vitro. Interestingly, Sper did not increase cellular Ca²⁺ and iron concentrations, but suppressed the Ca²⁺ and iron accumulation to benefit the mice in vivo. However, Sper had no significant impact on TBI in vitro. Taken together, our data demonstrated for the first time that blockage of MCU‐mediated Ca²⁺ and iron accumulation was essential for TBI. These findings indicated that MCU could be a novel therapeutic target for treating TBI.

Is Iron Accumulation a Possible Risk Factor for Sarcopenia?

Sarcopenia has a high incidence among the elderly, with significant negative effects on the quality of life. The pathogenesis of sarcopenia is complex, and many factors are involved in its development and progression. Sarcopenia might be associated with iron accumulation given that (1) age-related iron accumulation was found in the skeletal muscle, (2) excess iron could cause skeletal muscle damage or atrophy, and (3) patients with sarcopenia showed higher levels of serum ferritin. Understanding the etiology and pathogenesis of sarcopenia would help to develop new treatment and preventive methods, thereby improving the quality of life of the elderly patients.

Unique Properties Associated with the Brain Penetrant Iron Chelator HBED Reveal Remarkable Beneficial Effects after Brain Trauma

Iron is postulated to contribute to secondary injury after brain trauma through various pathways including oxidative stress and inflammation. Therefore, one goal is to limit iron toxicity by either directly limiting iron activity, or limiting the secondary cascade mediated by iron, therefore rescuing the brain from damage after trauma. The N,N'-Di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid monohydrochloride (HBED) is a unique iron chelator that has the ability to cross the intact blood-brain barrier; it has a higher affinity to iron, and it has a longer half-life than most commonly used chelators. A controlled-cortical impact model of traumatic brain injury (TBI) was induced in mice. Mice were subcutaneously injected with HBED immediately after TBI, then at 12 h after, followed by a twice-a-day regimen until an end-point of 3 days. Neurobehavioral tests were performed daily. Cortical injury volume, hemispheric enlargement, and hippocampal swelling were quantified. Perls' iron immunostaining along with markers of gliosis, oxidative stress, and aquaporin (AQP) 4 were also performed. Data revealed that HBED treatment significantly decreases motor deficits and improves recovery after TBI. It also reduces cortical injury volume by 36.6 ± 6.8% (p < 0.001), hippocampal swelling by 23.4 ± 3.8% (p < 0.05), and total hemispheric volume by 13.3 ± 2.7% (p < 0.01). These effects are related to a reduction in microgliosis and oxidiative stress markers in the impacted corpus callosum area by 39.8 ± 7.3%, and by 80.5 ± 0.8% (p < 0.05), respectively. AQP4 staining is also attenuated in the hippocampus of HBED-treated mice. Therefore, our results suggest that HBED should be considered as a therapeutic tool to facilitate the recovery process following brain trauma.

Scavenging reactive oxygen species inhibits status epilepticus-induced neuroinflammation

Inflammation has been identified as an important mediator of seizures and epileptogenesis. Understanding the mechanisms underlying seizure-induced neuroinflammation could lead to the development of novel therapies for the epilepsies. Reactive oxygen species (ROS) are recognized as mediators of seizure-induced neuronal damage and are known to increase in models of epilepsies. ROS are also known to contribute to inflammation in several disease states. We hypothesized that ROS are key modulators of neuroinflammation i.e. pro-inflammatory cytokine production and microglial activation in acquired epilepsy. The role of ROS in modulating seizure-induced neuroinflammation was investigated in the pilocarpine model of temporal lobe epilepsy (TLE). Pilocarpine-induced status epilepticus (SE) resulted in a time-dependent increase in pro-inflammatory cytokine production in the hippocampus and piriform cortex. Scavenging ROS with a small-molecule catalytic antioxidant decreased SE-induced pro-inflammatory cytokine production and microglial activation, suggesting that ROS contribute to SE-induced neuroinflammation. Scavenging ROS also attenuated phosphorylation of ribosomal protein S6, the downstream target of the mammalian target of rapamycin (mTOR) pathway indicating that this pathway might provide one mechanistic link between SE-induced ROS production and inflammation. Together, these results demonstrate that ROS contribute to SE-induced cytokine production and antioxidant treatment may offer a novel approach to control neuroinflammation in epilepsy.

Anticonvulsant and Antioxidant Effects of Pitavastatin Against Pentylenetetrazol-Induced Kindling in Mice

Purpose: The pleiotropic effects of statins (antioxidant and anti-inflammation) have been reported by previous studies. Therefore, we aimed to determine whether pitavastatin has protective effects against pentylenetetrazol (PTZ)-induced kindling in mice and also whether pitavastatin improves the brain antioxidant capacity and attenuates the oxidative injuries in kindled mice.

Methods: Twenty-four mice were randomly divided into four groups (each group n=6); control, PTZ-kindling and PTZ-kindled rats treated with pitavastatin (1&4 mg/kg). PTZ kindling seizures were induced by repetitive intraperitoneal injections of PTZ (65 mg/kg) every 48 hours till day twenty-one. Animals received daily oral pitavastatin for twenty-one days. Latency, score and duration of the seizures were recorded. The activities of catalase (CAT) ad superoxide dismutase (SOD), and likewise the contents of malondialdehyde (MDA) and nitrate were assessed in the brains of all rats.

Results: There was a progressive reduction in latency of the kindled rats in the next injections of PTZ. Pitavastatin reduced this value (latency) particularly at higher dose. Seizures duration and score also decreased in treatment groups. SOD and CAT activities significantly decreased in PTZ-kindling group by 62% and 64%, respectively, but pitavastatin did not significantly change the SOD and CAT activities. Brain MDA and nitrate significantly increased in PTZ-kindling group by 53% and 30%, respectively. Pitavastatin at higher dose significantly decreased the MDA and nitrate contents of PTZ-kindling rats by 45% and 32%, respectively.

Conclusion: Our findings revealed that pitavastatin can improve the behavioral expression of the PTZ-kindling rats and attenuate the seizure-induced oxidative/nitrosative damage.

SIRT5 Deficiency Enhances Susceptibility to Kainate-Induced Seizures and Exacerbates Hippocampal Neurodegeneration not through Mitochondrial Antioxidant Enzyme SOD2

Epilepsy is a common and serious neurological disorder characterized by occurrence of recurrent spontaneous seizures, and emerging evidences support the association of mitochondrial dysfunction with epilepsy. Sirtuin 5 (SIRT5), localized in mitochondrial matrix, has been considered as an important functional modulator of mitochondria that contributes to ageing and neurological diseases. Our data shows that SIRT5 deficiency strikingly increased mortality rate and severity of response to epileptic seizures, dramatically exacerbated hippocampal neuronal loss and degeneration in mice exposed to Kainate (KA), and triggered more severe reactive astrogliosis. We found that the expression of mitochondrial SIRT5 of injured hippocampus was relatively up-regulated, indicating its potential contribution to the comparably increased survival of these cells and its possible neuroprotective role. Unexpectedly, SIRT5 seems not to apparently alter the decline of antioxidant enzymes superoxide dismutase 2 (SOD2) and glutathione peroxidase (GPx) in hippocampus caused by KA exposure in our paradigm, which indicates the protective role of SIRT5 on seizures and cellular degeneration might through different regulatory mechanism that would be explored in the future. In the present study, we provided strong evidences for the first time to demonstrate the association between SIRT5 and epilepsy, which offers a new understanding of the roles of SIRT5 in mitochondrial functional regulation. The neuroprotection of SIRT5 in KA-induced epileptic seizure and neurodegeneration will improve our current knowledge of the nature of SIRT5 in central nervous system (CNS) and neurological diseases.

Reactive oxygen species mediate cognitive deficits in experimental temporal lobe epilepsy

Cognitive dysfunction is an important comorbidity of temporal lobe epilepsy (TLE). However, no targeted therapies are available and the mechanisms underlying cognitive impairment, specifically deficits in learning and memory associated with TLE remain unknown. Oxidative stress is known to occur in the pathogenesis of TLE but its functional role remains to be determined. Here, we demonstrate that oxidative stress and resultant processes contribute to cognitive decline associated with epileptogenesis. Using a synthetic catalytic antioxidant, we show that pharmacological removal of reactive oxygen species (ROS) prevents 1) oxidative stress, 2) deficits in mitochondrial oxygen consumption rates, 3) hippocampal neuronal loss and 4) cognitive dysfunction without altering the intensity of the initial status epilepticus (SE) or epilepsy development in a rat model of SE-induced TLE. Moreover, the effects of the catalytic antioxidant on cognition persisted beyond the treatment period suggestive of disease-modification. The data implicate oxidative stress as a novel mechanism by which cognitive dysfunction can arise during epileptogenesis and suggest a potential disease-modifying therapeutic approach to target it.

Oxidative stress associated with neuronal apoptosis in experimental models of epilepsy

Epilepsy is considered one of the most common neurological disorders worldwide. Oxidative stress produced by free radicals may play a role in the initiation and progression of epilepsy; the changes in the mitochondrial and the oxidative stress state can lead mechanism associated with neuronal death pathway. Bioenergetics state failure and impaired mitochondrial function include excessive free radical production with impaired synthesis of antioxidants. This review summarizes evidence that suggest what is the role of oxidative stress on induction of apoptosis in experimental models of epilepsy.

Iron chelation and multiple sclerosis

Histochemical and MRI studies have demonstrated that MS (multiple sclerosis) patients have abnormal deposition of iron in both gray and white matter structures. Data is emerging indicating that this iron could partake in pathogenesis by various mechanisms, e.g., promoting the production of reactive oxygen species and enhancing the production of proinflammatory cytokines. Iron chelation therapy could be a viable strategy to block iron-related pathological events or it can confer cellular protection by stabilizing hypoxia inducible factor 1α, a transcription factor that normally responds to hypoxic conditions. Iron chelation has been shown to protect against disease progression and/or limit iron accumulation in some neurological disorders or their experimental models. Data from studies that administered a chelator to animals with experimental autoimmune encephalomyelitis, a model of MS, support the rationale for examining this treatment approach in MS. Preliminary clinical studies have been performed in MS patients using deferoxamine. Although some side effects were observed, the large majority of patients were able to tolerate the arduous administration regimen, i.e., 6-8 h of subcutaneous infusion, and all side effects resolved upon discontinuation of treatment. Importantly, these preliminary studies did not identify a disqualifying event for this experimental approach. More recently developed chelators, deferasirox and deferiprone, are more desirable for possible use in MS given their oral administration, and importantly, deferiprone can cross the blood-brain barrier. However, experiences from other conditions indicate that the potential for adverse events during chelation therapy necessitates close patient monitoring and a carefully considered administration regimen.

Combined therapy of iron chelator and antioxidant completely restores brain dysfunction induced by iron toxicity

Background

Excessive iron accumulation leads to iron toxicity in the brain; however the underlying mechanism is unclear. We investigated the effects of iron overload induced by high iron-diet consumption on brain mitochondrial function, brain synaptic plasticity and learning and memory. Iron chelator (deferiprone) and antioxidant (n-acetyl cysteine) effects on iron-overload brains were also studied.

Methodology

Male Wistar rats were fed either normal diet or high iron-diet consumption for 12 weeks, after which rats in each diet group were treated with vehicle or deferiprone (50 mg/kg) or n-acetyl cysteine (100 mg/kg) or both for another 4 weeks. High iron-diet consumption caused brain iron accumulation, brain mitochondrial dysfunction, impaired brain synaptic plasticity and cognition, blood-brain-barrier breakdown, and brain apoptosis. Although both iron chelator and antioxidant attenuated these deleterious effects, combined therapy provided more robust results.

Conclusion

In conclusion, this is the first study demonstrating that combined iron chelator and anti-oxidant therapy completely restored brain function impaired by iron overload.

Mitochondrial involvement and oxidative stress in temporal lobe epilepsy

A role for mitochondria and oxidative stress is emerging in acquired epilepsies such as temporal lobe epilepsy (TLE). TLE is characterized by chronic unprovoked seizures arising from an inciting insult with a variable seizure-free "latent period." The mechanism by which inciting injury induces chronic epilepsy, known as epileptogenesis, involves multiple cellular, molecular, and physiological changes resulting in altered hyperexcitable circuitry. Whether mitochondrial and redox mechanisms contribute to epileptogenesis remains to be fully clarified. Mitochondrial impairment is revealed in studies from human imaging and tissue analysis from TLE patients. The collective data from animal models suggest that steady-state mitochondrial reactive oxygen species and resultant oxidative damage to cellular macromolecules occur during different phases of epileptogenesis. This review discusses evidence for the role of mitochondria and redox changes occurring in human and experimental TLE. Potential mechanisms by which mitochondrial energetic and redox mechanisms contribute to increased neuronal excitability and therapeutic approaches to target TLE are delineated.

A delicate balance: Iron metabolism and diseases of the brain

Iron is the most abundant transition metal within the brain, and is vital for a number of cellular processes including neurotransmitter synthesis, myelination of neurons, and mitochondrial function. Redox cycling between ferrous and ferric iron is utilized in biology for various electron transfer reactions essential to life, yet this same chemistry mediates deleterious reactions with oxygen that induce oxidative stress. Consequently, there is a precise and tightly controlled mechanism to regulate iron in the brain. When iron is dysregulated, both conditions of iron overload and iron deficiencies are harmful to the brain. This review focuses on how iron metabolism is maintained in the brain, and how an alteration to iron and iron metabolism adversely affects neurological function.

Brain iron accumulation in aging and neurodegenerative disorders

Over the decades, various studies have established an association between accumulation of iron and both aging and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Excess levels of iron can lead to increased oxidative stress through Fenton chemistry, and depletion of iron can similarly have deleterious effects. In addition, metal ions are known to be involved in both Alzheimer's disease and Parkinson's disease protein aggregation. Metal ion chelators have been extensively investigated in preclinical models, and may prove to be appropriate for modulating brain iron levels in age-related neurodegenerative disorders. Investigating age-related iron deposition is vital, and can possibly aid in determining at-risk groups and diagnosing neurodegenerative diseases at an early stage. Novel imaging methods have enabled researchers to examine iron deposition in vivo, and offer a noninvasive method of monitoring the progression of accumulation, and possible therapeutic effects of chelating compounds.

Mitochondrial calcium uniporter blocker effectively prevents brain mitochondrial dysfunction caused by iron overload

AIMS

Although iron overload induces oxidative stress and brain mitochondrial dysfunction, and is associated with neurodegenerative diseases, brain mitochondrial iron uptake has not been investigated. We determined the role of mitochondrial calcium uniporter (MCU) in brain mitochondria as a major route for iron entry. We hypothesized that iron overload causes brain mitochondrial dysfunction, and that the MCU blocker prevents iron entry into mitochondria, thus attenuating mitochondrial dysfunction.

MAIN METHODS

Isolated brain mitochondria from male Wistar rats were used. Iron (Fe(2+) and Fe(3+)) at 0-286 μM were applied onto mitochondria at various incubation times (5-30 min), and the mitochondrial function was determined. Effects of MCU blocker (Ru-360) and iron chelator were studied.

KEY FINDINGS

Both Fe(2+) and Fe(3+) entered brain mitochondria and caused mitochondrial swelling in a dose- and time-dependent manner, and caused mitochondrial depolarization and increased ROS production. However, Fe(2+) caused more severe mitochondrial dysfunction than Fe(3+). Although all drugs attenuated mitochondrial dysfunction caused by iron overload, only an MCU blocker could completely prevent ROS production and mitochondrial depolarization.

SIGNIFICANCE

Our findings indicated that iron overload caused brain mitochondrial dysfunction, and that an MCU blocker effectively prevented this impairment, suggesting that MCU could be the major portal for brain mitochondrial iron uptake.

Post-translational oxidative modification and inactivation of mitochondrial complex I in epileptogenesis

Mitochondrial oxidative stress and damage have been implicated in the etiology of temporal lobe epilepsy, but whether or not they have a functional impact on mitochondrial processes during epilepsy development (epileptogenesis) is unknown. One consequence of increased steady-state mitochondrial reactive oxygen species levels is protein post-translational modification (PTM). We hypothesize that complex I (CI), a protein complex of the mitochondrial electron transport chain, is a target for oxidant-induced PTMs, such as carbonylation, leading to impaired function during epileptogenesis. The goal of this study was to determine whether oxidative modifications occur and what impact they have on CI enzymatic activity in the rat hippocampus in response to kainate (KA)-induced epileptogenesis. Rats were injected with a single high dose of KA or vehicle and evidence for CI modifications was measured during the acute, latent, and chronic stages of epilepsy. Mitochondrial-specific carbonylation was increased acutely (48 h) and chronically (6 week), coincident with decreased CI activity. Mass spectrometry analysis of immunocaptured CI identified specific metal catalyzed carbonylation to Arg76 within the 75 kDa subunit concomitant with inhibition of CI activity during epileptogenesis. Computational-based molecular modeling studies revealed that Arg76 is in close proximity to the active site of CI and carbonylation of the residue is predicted to induce substantial structural alterations to the protein complex. These data provide evidence for the occurrence of a specific and irreversible oxidative modification of an important mitochondrial enzyme complex critical for cellular bioenergetics during the process of epileptogenesis.

Impaired iron status in aging research

Aging is associated with disturbances in iron metabolism and storage. During the last decade, remarkable progress has been made toward understanding their cellular and molecular mechanisms in aging and age-associated diseases using both cultured cells and animal models. The field has moved beyond descriptive studies to potential intervention studies focusing on iron chelation and removal. However, some findings remain controversial and inconsistent. This review summarizes important features of iron dyshomeostasis in aging research with a particular emphasis on current knowledge of the mechanisms underlying age-associated disorders in rodent models.

Characterization of tannery effluent wastewater by proton-induced X-ray emission (PIXE) analysis to investigate their role in water pollution

INTRODUCTION

Over the last few decades, the chromium-based tanning industry has shown rapid growth in Pakistan. However, the rules and regulations promulgated by the government are not strictly followed for processing the effluent discharge from the tanneries. Consequently, tannery effluents have become a great source of water pollution in surrounding areas.

MATERIALS AND METHODS

In this case study, characterization of tannery effluent wastewater (TW), shallow groundwater (SW), and deep groundwater (DW) samples was carried out to determine the source of water pollution in the district of Kasur, Pakistan.

RESULTS

The concentrations of calcium (Ca), chlorine (Cl), chromium (Cr), iron (Fe), potassium (K), Mg, sulfur (S), silicon (Si), and Sr in TW were significantly higher than SW and DW, which also exceeded the international limits. In addition, increased concentrations of major toxic elements (Cl, Cr, Fe, K, Ni, and Si) were also observed in SW, which were higher in comparison to DW. Strikingly, the concentrations of Cr and Si in various DW samples were also beyond World Health Organization (WHO) safe limit, which reinforced the trend that water pollution in the area is directly linked to the distance from the source (TW). The particle-induced X-ray emission (PIXE) indices also suggested that TW is a main contributory source of water-based pollution in the area, which is imposing great threat to local inhabitants due to known hazardous and carcinogenic potential of these elements.

CONCLUSION

Protecting the water resources will be a formidable challenge in the study area, which requires modernization of tannery industry, thereby improving the recovery and recycling of TW. Moreover, PIXE analysis presented here as a successful tool, could serve as landmark for the contemporary research in environmental toxicology.

Reduction of mitoferrin results in abnormal development and extended lifespan in Caenorhabditis elegans

Iron is essential for organisms. It is mainly utilized in mitochondria for biosynthesis of iron-sulfur clusters, hemes and other cofactors. Mitoferrin 1 and mitoferrin 2, two homologues proteins belonging to the mitochondrial solute carrier family, are required for iron delivery into mitochondria. Mitoferrin 1 is highly expressed in developing erythrocytes which consume a large amount of iron during hemoglobinization. Mitoferrin 2 is ubiquitously expressed, whose functions are less known. Zebrafish with mitoferrin 1 mutation show profound hypochromic anaemia and erythroid maturation arrests, and yeast with defects in MRS3/4, the counterparts of mitoferrin 1/2, has low mitochondrial iron levels and grows poorly by iron depletion. Mitoferrin 1 expression is up-regulated in yeast and mouse models of Fiedreich's ataxia disease and in human cell culture models of Parkinson disease, suggesting its involvement in the pathogenesis of diseases with mitochondrial iron accumulation. In this study we found that reduced mitoferrin levels in C. elegans by RNAi treatment causes pleiotropic phenotypes such as small body size, reduced fecundity, slow movement and increased sensitivity to paraquat. Despite these abnormities, lifespan was increased by 50% to 80% in N2 wild type strain, and in further studies using the RNAi sensitive strain eri-1, more than doubled lifespan was observed. The pathways or mechanisms responsible for the lifespan extension and other phenotypes of mitoferrin RNAi worms are worth further study, which may contribute to our understanding of aging mechanisms and the pathogenesis of iron disorder related diseases.

Mitochondrial oxidative stress and epilepsy in SOD2 deficient mice: attenuation by a lipophilic metalloporphyrin

Epileptic seizures are a common feature associated with inherited mitochondrial diseases. This study investigated the role of mitochondrial oxidative stress in epilepsy resulting from mitochondrial dysfunction using cross-bred mutant mice lacking mitochondrial manganese superoxide dismutase (MnSOD or SOD2) and a lipophilic metalloporphyrin catalytic antioxidant. Video-EEG monitoring revealed that in the second to third week of postnatal life (P14-P21) B6D2F2 Sod2(-/-) mice exhibited frequent spontaneous motor seizures providing evidence that oxidative stress-induced mitochondrial dysfunction may contribute to epileptic seizures. To confirm the role of mitochondrial oxidative stress in epilepsy a newly developed lipophilic metalloporphyrin, AEOL 11207, with high potency for catalytic removal of endogenously generated reactive oxygen species was utilized. AEOL 11207-treated Sod2(-/-) mice showed a significant decrease in both the frequency and duration of spontaneous seizures but no effect on seizure severity. A significant increase in the average lifespan of AEOL 11207-treated Sod2(-/-) mice compared to vehicle-treated Sod2(-/-) mice was also observed. Indices of mitochondrial oxidative stress and damage (aconitase inactivation, 3-nitrotyrosine formation, and depletion of reduced coenzyme A) and ATP levels affecting neuronal excitability were significantly attenuated in the brains of AEOL 11207-treated Sod2(-/-) mice compared to vehicle-treated Sod2(-/-) mice. The occurrence of epileptic seizures in Sod2(-/-) mice and the ability of catalytic antioxidant therapy to attenuate seizure activity, mitochondrial dysfunction, and ATP levels suggest that ongoing mitochondrial oxidative stress can contribute to epilepsy associated with mitochondrial dysfunction and disease.

Tryptamine-gallic acid hybrid prevents non-steroidal anti-inflammatory drug-induced gastropathy: correction of mitochondrial dysfunction and inhibition of apoptosis in gastric mucosal cells

We have investigated the gastroprotective effect of SEGA (3a), a newly synthesized tryptamine-gallic acid hybrid molecule against non-steroidal anti-inflammatory drug (NSAID)-induced gastropathy with mechanistic details. SEGA (3a) prevents indomethacin (NSAID)-induced mitochondrial oxidative stress (MOS) and dysfunctions in gastric mucosal cells, which play a pathogenic role in inducing gastropathy. SEGA (3a) offers this mitoprotective effect by scavenging of mitochondrial superoxide anion (O(2)(·-)) and intramitochondrial free iron released as a result of MOS. SEGA (3a) in vivo blocks indomethacin-mediated MOS, as is evident from the inhibition of indomethacin-induced mitochondrial protein carbonyl formation, lipid peroxidation, and thiol depletion. SEGA (3a) corrects indomethacin-mediated mitochondrial dysfunction in vivo by restoring defective electron transport chain function, collapse of transmembrane potential, and loss of dehydrogenase activity. SEGA (3a) not only corrects mitochondrial dysfunction but also inhibits the activation of the mitochondrial pathway of apoptosis by indomethacin. SEGA (3a) inhibits indomethacin-induced down-regulation of bcl-2 and up-regulation of bax genes in gastric mucosa. SEGA (3a) also inhibits indometacin-induced activation of caspase-9 and caspase-3 in gastric mucosa. Besides the gastroprotective effect against NSAID, SEGA (3a) also expedites the healing of already damaged gastric mucosa. Radiolabeled ((99m)Tc-labeled SEGA (3a)) tracer studies confirm that SEGA (3a) enters into mitochondria of gastric mucosal cell in vivo, and it is quite stable in serum. Thus, SEGA (3a) bears an immense potential to be a novel gastroprotective agent against NSAID-induced gastropathy.

Regulation of quinolinic acid neosynthesis in mouse, rat and human brain by iron and iron chelators in vitro

Several lines of evidence indicate that excess iron may play an etiologically significant role in neurodegenerative disorders. This idea is supported, for example, by experimental studies in animals demonstrating significant neuroprotection by iron chelation. Here, we tested whether this effect might be related to a functional link between iron and the endogenous excitotoxin quinolinic acid (QUIN), a presumed pathogen in several neurological disorders. In particular, the present in vitro study was designed to examine the effects of Fe(2+), a known co-factor of oxygenases, on the activity of QUIN's immediate biosynthetic enzyme, 3-hydroxyanthranilic acid dioxygenase (3HAO), in the brain. In crude tissue homogenate, addition of Fe(2+) (2-40 μM) stimulated 3HAO activity 4- to 6-fold in all three species tested (mouse, rat and human). The slope of the iron curve was steepest in rat brain where an increase from 6 to 14 μM resulted in a more than fivefold higher enzyme activity. In all species, the Fe(2+)-induced increase in 3HAO activity was dose-dependently attenuated by the addition of ferritin, the main iron storage protein in the brain. The effect of iron was also readily prevented by N,N'-bis(2-hydroxybenzyl) ethylenediamine-N,N'-diacetic acid (HBED), a synthetic iron chelator with neuroprotective properties in vivo. All these effects were reproduced using neostriatal tissue obtained postmortem from normal individuals and patients with end-stage Huntington's disease. Our results suggest that QUIN levels and function in the mammalian brain might be tightly controlled by endogenous iron and proteins that regulate the bioavailability of iron.

Mitochondrial dysfunction in epilepsy

Mitochondrial dysfunction has been identified as one potential cause of epileptic seizures. Impaired mitochondrial function has been reported for the seizure focus of patients with temporal lobe epilepsy and Ammon's horn sclerosis and of adult and immature animal models of epilepsy. Since mitochondrial oxidative phosphorylation provides the major source of ATP in neurons and mitochondria participate in cellular Ca(2+) homeostasis and generation of reactive oxygen species, their dysfunction strongly affects neuronal excitability and synaptic transmission. Therefore, mitochondrial dysfunction is proposed to be highly relevant for seizure generation. Additionally, mitochondrial dysfunction is known to trigger neuronal cell death, which is a prominent feature of therapy-resistant epilepsy. For this reason mitochondria have to be considered as promising targets for neuroprotective strategies in epilepsy.

Mitochondrial dysfunction and oxidative stress: a contributing link to acquired epilepsy?

Mitochondrial dysfunction and oxidative stress contribute to several neurologic disorders and have recently been implicated in acquired epilepsies such as temporal lobe epilepsy (TLE). Acquired epilepsy is typically initiated by a brain injury followed by a "latent period" whereby molecular, biochemical and other cellular alterations occur in the brain leading to chronic epilepsy. Mitochondrial dysfunction and oxidative stress are emerging as factors that not only occur acutely as a result of precipitating injuries such as status epilepticus (SE), but may also contribute to epileptogenesis and chronic epilepsy. Mitochondria are the primary site of reactive oxygen species (ROS) making them uniquely vulnerable to oxidative damage that may affect neuronal excitability and seizure susceptibility. This mini-review provides an overview of evidence suggesting the role of mitochondrial dysfunction and oxidative stress as acute consequences of injuries that are known to incite chronic epilepsy and their involvement in the chronic stages of acquired epilepsy.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.

Accelerated hemolysis and neurotoxicity in neuron-glia-blood clot co-cultures

A growing body of experimental evidence suggests that an intracerebral hematoma is toxic to neighboring cells. However, injury mechanisms remain largely undefined, due in part to conflicting results from in vivo studies. In order to investigate blood toxicity in a more controlled environment, murine clots were co-cultured on porous membrane inserts with primary neurons and glia. Erythrocyte lysis was apparent within 48 h, but was reduced by almost 80% in cultures lacking neurons, and by over 90% in the absence of both neurons and glial cells. By 72 h, most released hemoglobin had oxidized to methemoglobin or its hemichrome degradation products. At this time point, approximately 50% of neurons were non-viable, as detected by propidium iodide staining; glia were not injured. Deferoxamine, Trolox and the NMDA receptor antagonist MK-801 prevented most neuronal death, but had no effect on hemolysis at neuroprotective concentrations. The 27-fold increase in culture malondialdehyde and 5.8-fold increase in heme oxygenase-1 expression were also attenuated by deferoxamine and Trolox, but not by MK-801. These results suggest that hemoglobin release from clotted blood is accelerated by adjacent neurons and glia. Subsequent neurotoxicity is mediated by both iron-dependent and excitotoxic injury pathways.

The emerging role of iron dyshomeostasis in the mitochondrial decay of aging

Recent studies show that cellular and mitochondrial iron increases with age. Iron overload, especially in mitochondria, increases the availability of redox-active iron, which may be a causal factor in the extensive age-related biomolecular oxidative damage observed in aged organisms. Such damage is thought to play a major role in the pathogenesis of iron overload diseases and age-related pathologies. Indeed, recent findings of the beneficial effects of iron manipulation in life extension in Caenorhabditis elegans, Drosophila and transgenic mice have sparked a renewed interest in the potential role of iron in longevity. A substantial research effort now focuses on developing and testing safe pharmacologic interventions to combat iron dyshomeostasis in aging, acute injuries and in iron overload disorders.

Mitochondria, oxidative stress, and temporal lobe epilepsy

Mitochondrial oxidative stress and dysfunction are contributing factors to various neurological disorders. Recently, there has been increasing evidence supporting the association between mitochondrial oxidative stress and epilepsy. Although certain inherited epilepsies are associated with mitochondrial dysfunction, little is known about its role in acquired epilepsies such as temporal lobe epilepsy (TLE). Mitochondrial oxidative stress and dysfunction are emerging as key factors that not only result from seizures, but may also contribute to epileptogenesis. The occurrence of epilepsy increases with age, and mitochondrial oxidative stress is a leading mechanism of aging and age-related degenerative disease, suggesting a further involvement of mitochondrial dysfunction in seizure generation. Mitochondria have critical cellular functions that influence neuronal excitability including production of adenosine triphosphate (ATP), fatty acid oxidation, control of apoptosis and necrosis, regulation of amino acid cycling, neurotransmitter biosynthesis, and regulation of cytosolic Ca(2+) homeostasis. Mitochondria are the primary site of reactive oxygen species (ROS) production making them uniquely vulnerable to oxidative stress and damage which can further affect cellular macromolecule function, the ability of the electron transport chain to produce ATP, antioxidant defenses, mitochondrial DNA stability, and synaptic glutamate homeostasis. Oxidative damage to one or more of these cellular targets may affect neuronal excitability and increase seizure susceptibility. The specific targeting of mitochondrial oxidative stress, dysfunction, and bioenergetics with pharmacological and non-pharmacological treatments may be a novel avenue for attenuating epileptogenesis.

Oxidative inactivation of mitochondrial aconitase results in iron and H2O2-mediated neurotoxicity in rat primary mesencephalic cultures

BACKGROUND

Mitochondrial oxidative stress is a contributing factor in the etiology of numerous neuronal disorders. However, the precise mechanism(s) by which mitochondrial reactive oxygen species (ROS) modify cellular targets to induce the death of neurons remains unknown. The goal of this study was to determine if oxidative inactivation of mitochondrial aconitase (m-aconitase) resulted in the release of redox-active iron (Fe2+) and hydrogen peroxide (H2O2) and whether this contributes to cell death.

METHODOLOGY/PRINCIPAL FINDINGS

Incubation of rat primary mesencephalic cultures with the redox cycling herbicide paraquat (PQ2+) resulted in increased production of H2O2 and Fe2+ at times preceding cell death. To confirm the role of m-aconitase as a source of Fenton reagents and death, we overexpressed m-aconitase using an adenoviral construct thereby increasing the target available for inactivation by ROS. Co-labeling studies identified astrocytes as the predominant cell type expressing transduced m-aconitase although neurons were identified as the primary cell type dying. Oxidative inactivation of m-aconitase overexpressing cultures resulted in exacerbation of H2O2 production, Fe2+ accumulation and increased neuronal death. Increased cell death in m-aconitase overexpressing cultures was attenuated by addition of catalase and/or a cell permeable iron chelator suggesting that neuronal death occurred in part via astrocyte-derived H2O2.

CONCLUSIONS

These results suggest a role of ROS-sensitive m-aconitase as a source of Fe2+ and H2O2 and as a contributing factor to neurotoxicity.

Mitochondrial death effectors: relevance to sarcopenia and disuse muscle atrophy

Accelerated apoptosis in skeletal muscle is increasingly recognized as a potential mechanism contributing to the development of sarcopenia of aging and disuse muscle atrophy. Given their central role in the regulation of apoptosis, mitochondria are regarded as key players in the pathogenesis of myocyte loss during aging and other atrophying conditions. Oxidative damage to mitochondrial constituents, impaired respiration and altered mitochondrial turnover have been proposed as potential triggering events for mitochondrial apoptotic signaling. In addition, iron accumulation within mitochondria may enhance the susceptibility to apoptosis during the development of sarcopenia and possibly acute muscle atrophy, likely through exacerbation of oxidative stress. Mitochondria can induce myocyte apoptosis via both caspase-dependent and independent pathways, although the apoptogenic mediators involved may be different depending on age, muscle type and specific atrophying conditions. Despite the considerable advances made, additional research is necessary to establish a definite causal link between apoptotic signaling and the development of sarcopenia and acute atrophy. Furthermore, a translational effort is required to determine the role played by apoptosis in the pathogenesis of sarcopenia and disuse-induced muscle loss in human subjects.