Mitochondrial DNA damage and the involvement of antioxidant defense and repair system in hippocampi of rats with chronic seizures

APE1: A critical focus in neurodegenerative conditions

The global growth of the aging population has resulted in an increased prevalence of neurodegenerative diseases, characterized by the progressive loss of central nervous system (CNS) structure and function. Given the high incidence and debilitating nature of neurodegenerative diseases, there is an urgent need to identify potential biomarkers and novel therapeutic targets thereof. Apurinic/apyrimidinic endonuclease 1 (APE1), has been implicated in several neurodegenerative diseases, as having a significant role. Abnormal APE1 expression has been observed in conditions including Alzheimer's disease, stroke, amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, and epilepsy. However, whether this dysregulation is protective or harmful remains unclear. This review aims to comprehensively review the current understanding of the involvement of APE1 in neurodegenerative diseases.

N-acetylcysteine aggravates seizures while improving depressive-like and cognitive impairment comorbidities in the WAG/Rij rat model of absence epilepsy

N-acetylcysteine (NAC) is an antioxidant with some demonstrated efficacy in a range of neuropsychiatric disorders. NAC has shown anticonvulsant effects in animal models. NAC effects on absence seizures are still not uncovered, and considering its clinical use as a mucolytic in patients with lung diseases, people with epilepsy are also likely to be exposed to the drug. Therefore, we aimed to study the effects of NAC on absence seizures in the WAG/Rij rat model of absence epilepsy with neuropsychiatric comorbidities. The effects of NAC chronic treatment in WAG/Rij rats were evaluated on: absence seizures at 15 and 30 days by EEG recordings and animal behaviour at 30 days on neuropsychiatric comorbidities. Furthermore, the mechanism of action of NAC was evaluated by analysing brain expression levels of some possible key targets: the excitatory amino acid transporter 2, cystine-glutamate antiporter, metabotropic glutamate receptor 2, the mechanistic target of rapamycin and p70S6K as well as levels of total glutathione. Our results demonstrate that in WAG/Rij rats, NAC treatment significantly increased the number and duration of SWDs, aggravating absence epilepsy while ameliorating neuropsychiatric comorbidities. NAC treatment was linked to an increase in brain mGlu2 receptor expression with this being likely responsible for the observed absence seizure-promoting effects. In conclusion, while confirming the positive effects on animal behaviour induced by NAC also in epileptic animals, we report the aggravating effects of NAC on absence seizures which could have some serious consequences for epilepsy patients with the possible wider use of NAC in clinical therapeutics.

Fenofibrate protects the neurovascular unit and ameliorates plasma corticosterone levels in pentylenetetrazole-induced kindling seizure in mice

Epileptic seizures are the most common neurological diseases that change the function of neurovascular unit at molecular levels accompanied by activation of a wide variety of neurodegenerative cascades. Based on the pleiotropic functions of peroxisome proliferator-activated receptor-alpha (PPARα), the current study evaluated the neuroprotective effects of fenofibrate (an effective PPARα agonist) on the brain injuries induced by pentylenetetrazole (PTZ)-induced kindling seizure. Adult male NMRI mice were randomly assigned into four groups (n = 14) as follows; control, untreated kindled mice (PTZ) and two fenofibrate-treated kindled groups. Repeated intraperitoneal injections of PTZ (45 mg/kg) were used to develop kindling seizure every 48 h for 21 days. Treated mice were administered orally fenofibrate at doses of 30 and 50 mg/kg/day during the study. Plasma corticosterone and brain levels of brain-derived neurotrophic factor (BDNF), malondialdehyde (MDA) and mRNA transcription of p53, as well as blood-brain barrier (BBB) permeability, were determined at termination of the study. Fenofibrate considerably improved seizure latency and anxiety-like behaviors in treated kindled mice. Fenofibrate at doses of 30 and 50 mg/kg significantly (P < 0.001) decreased plasma corticosterone (56.88 ± 0.80 and 54.81 ± 0.29 ng/mL, respectively) compared to PTZ group (74.96 ± 1.60 ng/mL). It also significantly (P < 0.05) decreased BDNF levels in both treatment groups (8.13 ± 0.14 and 8.74 ± 0.09 ng/mL, respectively) compared to PTZ group (9.68 ± 0.20 ng/mL). Fenofibrate particularly at higher dose significantly (P < 0.01) decreased MDA content and mRNA expression levels of p53 in treated kindled mice by 67% and 28%, respectively, compared to PTZ group. Similarly, 50 mg/kg fenofibrate significantly (P < 0.05) decreased Evans blue extravasation into brain in treated kindled mice (8.72 ± 0.96 µg/g) compared to PTZ group (15.31 ± 2.18 µg/g). Our results revealed the anticonvulsive and neuroprotective effects of fenofibrate in PTZ-induced kindling seizure in mice. Fenofibrate also improved the neurovascular functions at molecular levels in kindling seizure that might be associated with ameliorating the seizure behaviors.

Inhibition of USP15 Prevent Glutamate-Induced Oxidative Damage by Activating Nrf2/HO-1 Signaling Pathway in HT22 Cells

Oxidative stress has been identified as the significant mediator in epilepsy, which is a chronic disorder in central nervous system. About 30% of epilepsy patients are refractory to antiepileptic drug treatment. However, the underlying mechanism of oxidative damage in epilepsy needs further investigation. In our study, we first find that ubiquitin-specific peptidase 15 (USP15) expression was upregulated in a pentylenetetrazole (PTZ) kindled rat model of epilepsy. Silencing USP15 protected against glutamate-mediated neuronal cell death, and inhibited the high expression levels of cleaved caspase-3. Knockout of USP15 significantly reduced intracellular reactive oxygen species (ROS) levels and enhanced superoxide dismutase (SOD) activity in HT22 cells under the exposure to glutamate treatment. Furthermore, USP15 inhibition induced nuclear factor erythroid-derived 2-related factor2 (Nrf2) nuclear translocation and promoted protein expression level of heme oxygenase (HO-1). Taken together, our findings first reveal a role of USP15 in the pathogenesis of epilepsy, and silencing USP15 in vitro protects against glutamate-mediated cytotoxicity in HT22 cells. Pharmacological inhibition of USP15 may alleviate epileptic seizures via fighting against oxidative damage, providing a novel antiepileptic target.

Energy Metabolism and Redox State in Brains of Wistar Audiogenic Rats, a Genetic Model of Epilepsy

The Wistar Audiogenic Rat (WAR) strain is a genetic model of epilepsy, specifically brainstem-dependent tonic-clonic seizures, triggered by acute auditory stimulation. Chronic audiogenic seizures (audiogenic kindling) mimic temporal lobe epilepsy, with significant participation of the hippocampus, amygdala, and cortex. The objective of the present study was to characterize the mitochondrial energy metabolism in hippocampus and cortex of WAR and verify its relationship with seizure severity. Hippocampus of WAR naïve (no seizures) presented higher oxygen consumption in respiratory states related to the maximum capacities of phosphorylation and electron transfer system, elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl and lactate contents, compared with their Wistar counterparts. Audiogenic kindling had no adding functional effect in WAR, but in Wistar, it induced the same alterations observed in the audiogenic strain. In the cortex, WAR naïve presented elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl levels. Chronic acoustic stimulation in Wistar induced the same alterations in cortex and hippocampus. Mainly in the hippocampus, WAR naïve presented elevated mRNA expression of glucose, lactate and excitatory amino acids transporters, several glycolytic enzymes, lactate dehydrogenase, and Na⁺/K⁺ ATPase in neurons and in astrocytes. In vivo treatment with mitochondrial uncoupler 2,4-dinitrophenol (DNP) or N-acetylcysteine (NAC) in WAR had no effect on mitochondrial metabolism, but lowered oxidative stress. Unlike DNP, NAC downregulated all enzyme genes involved in glucose and lactate uptake, and metabolism in neurons and astrocytes. Additionally, it was able to reduce brainstem seizure severity in WAR. In conclusion, in WAR naïve animals, both cerebral cortex and hippocampus display elevated mitochondrial density and/or activity associated with oxidative damage, glucose and lactate metabolism pathways upregulation, and increased Na⁺/K⁺ ATPase mRNA expression. Only in vivo treatment with NAC was able to reduce seizure severity of kindled WARs, possibly via down regulation of glucose/lactate metabolism. Taken together, our results are a clear contribution to the field of mitochondrial metabolism associated to epileptic seizures.

Effect of Captopril on Brain Oxidative Damage in Pentylenetetrazole-Induced Seizures in Mice<br />

Background: Frequent seizure is followed by overproduction of free radicals and brain oxidative stress. Renin angiotensin system (RAS) has some effects on central nervous system. We designed this research to challenge the effect of captopril as an angiotensin converting enzyme (ACE) inhibitor against brain oxidative stress in pentylenetetrazole (PTZ) -induced seizures in mice. Methods: The groups were including (1) Control (saline); (2) PTZ (100 mg/kg, i.p.), (3-5) PTZ- captopril (Capto) that received three doses of Capto 10, 50 and 100 mg/kg 30 min before PTZ injection. Latency time in the onset minimal clonic seizures (MCS) and generalized tonic-clonic seizures (GTCS) were recorded. The level of malondialdehyde (MDA) and total thiol, as well as superoxide dismutase (SOD) and catalase (CAT) activity in the hippocampus and cortex were measured. Results: All doses of captopril postponed the onset of MCS and GTCS. Accumulation of MDA in the brain tissues of PTZ group was higher than control group, while total thiol content and CAT activity were lower. Pretreatment with captopril (100 mg/kg) diminished MDA concentration compared with PTZ group. Captopril (50 and 100 mg/kg) also increased the level of total thiol groups versus PTZ group. Captopril injection (50 and 100 mg/kg) elevated the activity of SOD and CAT in the brain tissues. In addition captopril administration diminished mortality rate caused by PTZ. Conclusion: Findings demonstrated that convulsions caused by PTZ were followed by oxidative stress status in the brain tissues. Pretreatment with captopril attenuated the effect of PTZ on brain tissue oxidative damage.<br />

Up-regulation of antioxidative proteins TRX1, TXNL1 and TXNRD1 in the cortex of PTZ kindling seizure model mice

Oxidative stress has been considered as one of pathogenesis of brain damage led by epilepsy. Reducing oxidative stress can ameliorate brain damage during seizures. However, expression levels of important antioxidative enzymes such as thioredoxin-1 (TRX1), thioredoxin-like 1 protein (TXNL1) and thioredoxin reductase 1 (TXNRD1) during seizures have not been investigated. In this study, we examined protein and mRNA expression levels of TRX1, TXNL1 and TXNRD1 in different brain regions in PTZ induced seizure model mice. We found that protein expression levels of TRX1, TXNL1 and TXNRD1 are simultaneously up-regulated by 2- or 3-fold in the cortex of both acute and chronic seizure model mice. But there is no unified expression pattern change of these enzymes in the hippocampus, cerebellum and diencephalon in the seizure model mice. Less extent up-regulation of mRNA expression of these enzymes were also observed in the cortex of seizure mice. These data suggest that antioxidative enzymes may provide a protective effect against oxidative stress in the cortex during seizures.

How oxygen gave rise to eukaryotic sex

How did full meiotic eukaryotic sex evolve and what was the immediate advantage allowing it to develop? We propose that the crucial determinant can be found in internal reactive oxygen species (ROS) formation at the start of eukaryotic evolution approximately 2 × 10⁹ years ago. The large amount of ROS coming from a bacterial endosymbiont gave rise to DNA damage and vast increases in host genome mutation rates. Eukaryogenesis and chromosome evolution represent adaptations to oxidative stress. The host, an archaeon, most probably already had repair mechanisms based on DNA pairing and recombination, and possibly some kind of primitive cell fusion mechanism. The detrimental effects of internal ROS formation on host genome integrity set the stage allowing evolution of meiotic sex from these humble beginnings. Basic meiotic mechanisms thus probably evolved in response to endogenous ROS production by the ‘pre-mitochondrion’. This alternative to mitosis is crucial under novel, ROS-producing stress situations, like extensive motility or phagotrophy in heterotrophs and endosymbiontic photosynthesis in autotrophs. In multicellular eukaryotes with a germline–soma differentiation, meiotic sex with diploid–haploid cycles improved efficient purging of deleterious mutations. Constant pressure of endogenous ROS explains the ubiquitous maintenance of meiotic sex in practically all eukaryotic kingdoms. Here, we discuss the relevant observations underpinning this model.

The anti-inflammatory role of extranuclear apurinic/apyrimidinic endonuclease 1/redox effector factor-1 in reactive astrocytes

Apurinic/apyrimidinic endonuclease 1 (APE1), a ubiquitous multipurpose protein, is also known as redox effector factor-1 (Ref-1). It is involved in DNA repair and redox signaling and, in turn, oxidative stress-induced neurodegeneration. Although previous studies have demonstrated that APE1/Ref-1 functions as a negative regulator of inflammatory response via several mechanisms in neuronal cells, little is known about the roles of APE1/Ref-1 in glial cells. In this study, we found that cytoplasmic APE1/Ref-1 expression was upregulated in reactive astrocytes of the kainic acid- or lipopolysaccharide (LPS)-injected hippocampus. Analysis of the inflammatory response induced by extranuclear APE1/Ref-1 (ΔNLS-Ref-1) in cultured primary astrocytes revealed that it markedly suppressed inducible nitric oxide synthase (iNOS) expression and tumor necrosis factor-α (TNF-α) secretion induced by LPS to a similar extent as did wild type APE1/Ref-1 (WT-Ref-1), supporting the concept an anti-inflammatory role of extranuclear APE1/Ref-1 in astrocytes. Additionally, overexpression of WT- and ΔNLS-Ref-1 suppressed the transcriptional activity of nuclear factor-κB (NF-κB), although it effectively enhanced activator protein 1 (AP-1) activity. The blunting effect of APE1/Ref-1 on LPS-induced NF-κB activation was not mediated by IκB kinase (IKK) activity. Instead, APE1/Ref-1 inhibited p300-mediated acetylation of p65 by suppressing intracellular reactive oxygen species (ROS) levels following LPS treatment. Taken together, our results showed that altered expression and/or subcellular distribution of APE1/Ref-1 in activated astrocytes regulated the neuroinflammatory response to excitotoxin and endotoxin insults used in model of neurodegenerative brain diseases.

Traumatic brain injury: oxidative stress and neuroprotection

SIGNIFICANCE

A vast amount of circumstantial evidence implicates high energy oxidants and oxidative stress as mediators of secondary damage associated with traumatic brain injury. The excessive production of reactive oxygen species due to excitotoxicity and exhaustion of the endogenous antioxidant system induces peroxidation of cellular and vascular structures, protein oxidation, cleavage of DNA, and inhibition of the mitochondrial electron transport chain.

RECENT ADVANCES

Different integrated responses exist in the brain to detect oxidative stress, which is controlled by several genes termed vitagens. Vitagens encode for cytoprotective heat shock proteins, and thioredoxin and sirtuins.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This article discusses selected aspects of secondary brain injury after trauma and outlines key mechanisms associated with toxicity, oxidative stress, inflammation, and necrosis. Finally, this review discusses the role of different oxidants and presents potential clinically relevant molecular targets that could be harnessed to treat secondary injury associated with brain trauma.

Differences in vulnerability to nicotine-induced kindling between female and male periadolescent rats

RATIONALE

It has recently been reported that chronic nicotine administration at subconvulsive doses causes seizures, a phenomenon referred to as kindling. Evidence points to the involvement of oxidative stress in pharmacological and electrical kindling, sex is known to influence the brain's response to nicotine.

OBJECTIVES

This study investigated the sex differences in vulnerability to nicotine-induced kindling and the involvement of oxidative stress in this phenomenon.

METHODS

Male and female periadolescent Wistar rats received repeated injections of a subconvulsive dose of nicotine (hemisulfate salt; 2 mg/kg, i.p.) every weekday for up to 25 days. To better understand the influence of oxidative stress in nicotine kindling, the antioxidant vitamin E (200 and 400 mg/kg, p.o.) was administered prior to nicotine administration. The levels of gluthatione (GSH), superoxide dismutase (SOD) activity, and lipid peroxidation were determined in the hippocampus (HC), prefrontal cortex (PFC), and striatum.

RESULTS

Female animals developed kindling more rapidly than male rats. In female rats, kindling was associated with decreases in antioxidant defenses, including GSH levels in the HC and striatum and SOD activity in the PFC and striatum, and increased lipid peroxidation in all brain areas studied. By contrast, male kindled animals presented only with a decrease in the GSH in the HC. Vitamin E prevented the occurrence of kindled seizures by 80 % and 75 % in male and female rats, respectively.

CONCLUSION

These novel findings indicate that female periadolescent rats develop nicotine-kindled seizures earlier than their male counterparts. Differences in the oxidative balance may be involved in this mechanism.

Progress of elemental anomalies of hippocampal formation in the pilocarpine model of temporal lobe epilepsy--an X-ray fluorescence microscopy study

In the present paper, X-ray fluorescence microscopy was applied to follow the processes occurring in rat hippocampal formation during the post-seizure period. In the study, one of the status epilepticus animal models of epilepsy was used, namely the model of temporal lobe epilepsy with pilocarpine-induced seizures. In order to analyze the dynamics of seizure-induced elemental changes, the samples taken from seizure-experiencing animals 3 h and 1, 4, and 7 days after proconvulsive agent administration were analyzed. The obtained results confirmed the utility of X-ray fluorescence microscopy in the research of mechanisms involved in the pathogenesis and progress of epilepsy. The topographic and quantitative elemental analysis of hippocampal formations from different periods of epileptogenesis showed that excitotoxicity, mossy fibers sprouting, and iron-induced oxidative stress may be the processes responsible for seizure-induced neurodegenerative changes and spontaneous recurrent seizures occurring in the chronic phase of the pilocarpine model. The analysis of correlations between the recorded elemental anomalies and quantitative parameters describing animal behavior in the acute period of pilocarpine-induced status epilepticus showed that the areal densities of selected elements measured in the latent period strongly depend on the progress of the acute phase. Especially important seem to be the observations done for Ca and Zn levels which suggest that the intensity of the pathological processes such as excitotoxicity and mossy fibers sprouting depend on the total time of seizure activity. These results as well as dependencies found between the levels of S, K, and Cu and the intensity of maximal seizures clearly confirm how important it is to control the duration and intensity of seizures in clinical practice.

Genetic variants in nuclear-encoded mitochondrial proteins are associated with oxidative stress in obsessive compulsive disorders

Obsessive compulsive disorder is a common psychiatric disorder defined by the presence of obsessive thoughts and repetitive compulsive actions. The mutations or polymorphic variants in mitochondrial DNA-encoded genes or nuclear genes result in oxidative stress, which has recently been associated with various psychiatric disorders. In order to understand the association of mitochondrial disorders with oxidative stress in obsessive compulsive disorder, we examined genetic variants of manganese superoxide dismutase and uncouple-2 antioxidant genes and malondialdehyde and glutathione, markers of oxidative stress. The study sample comprised 104 patients with OCD and 110 healthy controls. For manganese superoxide dismutase, the frequencies of CT (Ala/Val) genotype (p < 0.01) in patients were significantly lower than those of controls. In contrast, CC (Ala/Ala) genotype was significantly more frequent in patients than controls (p < 0.05). For uncouple-2 I/D, the frequencies of ID genotype (p < 0.01) and I allele (p < 0.05) were lower in patients as compared with controls. In contrast, DD genotype was more prevalent in patients than controls (p < 0.01). While whole blood glutathione was significantly diminished (p < 0.0001), serum malondialdehyde was significantly elevated in patients compared with controls (p < 0.0001). Malondialdehyde levels were significantly elevated in subjects with DD genotype of UCP-2 I/D (p < 0.05) and CC genotype of manganese superoxide dismutase (p < 0.05) as compared with II or ID and TT or CT genotype, respectively. Malondialdehyde levels in patients carrying CC (p < 0.05) or CT (p < 0.05) genotype were significantly higher than those of carrying TT genotype. In conclusion, CC genotype of manganese superoxide dismutase or DD genotype of UCP-2 might result in mitochondrial disorders by increasing oxidative stress in obsessive compulsive disorders.

Impaired mitochondrial biogenesis in hippocampi of rats with chronic seizures

Mitochondrial dysfunction has been suggested to be a contributing factor of epilepsy, but the underlying mechanisms are not completely explored. Mitochondrial biogenesis is involved in regulation of mitochondrial content, morphology, and function. In the current study, we show mitochondrial biogenesis severely impaired in hippocampi of rats with chronic seizures induced by pilocarpine, as evidenced by decreased mitochondrial DNA (mtDNA) content and decreased mtDNA-encoded protein level. Furthermore, we show mtDNA transcription and replication reduced in rats with chronic seizures. These defects were independent of downregulation of mitochondrial biogenesis-related factors, such as peroxisome proliferator-activated receptor gamma coactivator-1α, nuclear respiratory factor-1, and mitochondrial transcription factor A (Tfam), but depended on reduced Tfam-DNA binding activity. The present study suggests novel mechanisms for mitochondrial dysfunction during chronic seizures.

Conserved toxic responses across divergent phylogenetic lineages: a meta-analysis of the neurotoxic effects of RDX among multiple species using toxicogenomics

At military training sites, a variety of pollutants such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), may contaminate the area originating from used munitions. Studies investigating the mechanism of toxicity of RDX have shown that it affects the central nervous system causing seizures in humans and animals. Environmental pollutants such as RDX have the potential to affect many different species, therefore it is important to establish how phylogenetically distant species may respond to these types of emerging pollutants. In this paper, we have used a transcriptional network approach to compare and contrast the neurotoxic effects of RDX among five phylogenetically disparate species: rat (Sprague-Dawley), Northern bobwhite quail (Colinus virginianus), fathead minnow (Pimephales promelas), earthworm (Eisenia fetida), and coral (Acropora formosa). Pathway enrichment analysis indicated a conservation of RDX impacts on pathways related to neuronal function in rat, Northern bobwhite quail, fathead minnows and earthworm, but not in coral. As evolutionary distance increased common responses decreased with impacts on energy and metabolism dominating effects in coral. A neurotransmission related transcriptional network based on whole rat brain responses to RDX exposure was used to identify functionally related modules of genes, components of which were conserved across species depending upon evolutionary distance. Overall, the meta-analysis using genomic data of the effects of RDX on several species suggested a common and conserved mode of action of the chemical throughout phylogenetically remote organisms.