Xiuhe Zhao

Role of mitochondrial fission in neuronal injury in pilocarpine-induced epileptic rats

Mitochondrial fission has been reported to be involved in oxidative stress, apoptosis and many neurological diseases. However, the role of mitochondrial fission in seizures, which could induce oxidative stress and neuronal loss, remains unknown. In this study, we used pilocarpine to elicit seizures in rats. Meanwhile, we used mitochondrial division inhibitor 1 (mdivi-1), a selective inhibitor of mitochondrial fission protein dynamin-related protein1 (Drp1), to suppress mitochondrial fission in epileptic model of rats in vivo. We found that mitochondrial fission was increased after seizures and the inhibition of mitochondrial fission by mdivi-1 significantly attenuated oxidative stress and reduced neuronal loss after seizures, shown by the decreased 8-hydroxy deoxyguanosine (8-oHdG) content, the increased superoxide dismutase (SOD) activity, the reduced expression of cytochrome c and caspase3 and the increased surviving neurons in the hippocampus. These results indicated that mitochondrial fission is up-regulated after seizures and the inhibition of mitochondrial fission is protective against neuronal injury in seizures, the underlying mechanism may be through the mitochondria/reactive oxygen species (ROS)/cytochrome c pathway.

Resveratrol pre-treatment reduces early inflammatory responses induced by status epilepticus via mTOR signaling

Resveratrol is indicated to be involved in neuroprotection and anti-inflammation in epileptic rats. The molecular mechanism is still not fully understood. In this study, we investigated the role of resveratrol in nuclear factor-kappa B associated inflammatory responses induced by status epilepticus. Our data showed that seizures activated mammalian target of rapamycin (mTOR), increased the activity of nuclear factor-kappa B and promoted the expressions of inflammatory molecules including inducible nitric oxide synthase, cyclooxygenase-2 and interleukin-1β. Futhermore, resveratrol significantly inhibited the activation of nuclear factor-kappa B and the production of proinflammatory molecules via mTOR pathway. Additionally, we also proved that the inhibition of mTOR signal by resveratrol was mostly attributed to AMP-activated kinase (AMPK) activation. Altogether, our results suggest that resveratrol suppresses inflammatory responses induced by seizures partially via AMPK/mTOR pathway.

Autophagy is upregulated in rats with status epilepticus and partly inhibited by Vitamin E

Autophagy, a process of bulk degradation of cellular constituents through autophagosome-lysosomal pathway, is enhanced during oxidative stress. Whether autophagy is induced during status epilepticus (SE), which induces an excess production of reactive oxygen species (ROS) and leads to oxidative stress, is not established. We also sought to determine if pretreatment with Vitamin E reduced autophagy. We used pilocarpine to elicit SE in rats. The ratio of LC3 II to LC3 I and beclin 1 were used to estimate autophagy. We found that ratio of LC3 II to LC3 I and beclin 1 increased significantly at 2, 8, 16, 24 and 72 h, peaking at 24 h after SE onset. Pretreatment with Vitamin E partially inhibited autophagy by reducing LC3 II formation and de novo synthesis of beclin 1 at 24 h after seizures. These data show that autophagy is increased in rats with pilocarpine-induced SE, and Vitamin E have a partial inhibition on autophagy.

Ascorbic acid ameliorates seizures and brain damage in rats through inhibiting autophagy

Oxidative stress is a mechanism of cell death induced by seizures. Antioxidant compounds have neuroprotective effects due to their ability to inhibit free radical production. Autophagy is a process in which cytoplasmic components such as organelles and proteins are delivered to the lysosomal compartment for degradation, and plays an essential role in the maintenance of cellular homeostasis. The activity of autophagy is enhanced during oxidative stress. The objectives of this work were first to study the inhibitory action of antioxidant ascorbic acid on behavioral changes and brain damage induced by high doses of pilocarpine, then to study the effect of ascorbic acid on oxidative stress (MDA and SOD were used to estimate oxidative stress) and activated autophagy (beclin 1 was used to estimate autophagy) induced by seizures, aiming to further clarify the mechanism of action of this antioxidant compound. In order to determinate neuroprotective effects, we studied the effects of ascorbic acid (500 mg/kg, i.p.) on the behavior and brain lesions observed after seizures induced by pilocarpine (340 mg/kg, i.p., P340 model) in rats. Ascorbic acid injections prior to pilocarpine suppressed behavioral seizure episodes by increasing the latency to the first myoclonic, clonic and tonic seizure and decreasing the percentage of incidence of clonic and tonic seizures as well as the mortality rate. These findings suggested that oxidative stress can be produced and autophagy is increased during brain damage induced by seizures. In the P340 model, ascorbic acid significantly decreased cerebral damage, reduced oxidative stress and inhibited autophagy by reducing de novo synthesis of beclin 1. Antioxidant compound can exert neuroprotective effects associated with inhibition of free radical production and autophagy. These results highlighted the promising therapeutic potential of ascorbic acid in treatment for seizures.

Sirtuin 1 activation enhances the PGC-1α/mitochondrial antioxidant system pathway in status epilepticus

Sirtuin 1 (SIRT1) regulates numerous neuronal processes, including metabolism, antioxidation and aging, through activation of peroxisome proliferator-activated receptor coactivator 1-α (PGC-1α), an upstream regulator of mitochondrial biogenesis and function. However, the role of SIRT1 in the oxidative stress induced by seizures has yet to be elucidated. The present study aimed to investigate whether SIRT1 was involved in the activation of the PGC-1α/mitochondrial antioxidant system following status epilepticus (SE) in rats. The data demonstrated that SIRT1 expression and activity were enhanced in the rat hippocampus following SE. SIRT1 inhibition effectively blocked the SE-associated increase in PGC-1α and mitochondrial antioxidant enzymes, including superoxide dismutase 2 (SOD2) and uncoupling protein 2 (UCP2). Additionally, it was also demonstrated that the activation of SIRT1 enhanced mitochondrial electron transport chain complex I activity and increased ATP content. In conclusion, the present results suggest that SIRT1 activation may alleviate mitochondrial oxidative stress induced by seizures partially via PGC-1α signaling.

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

In this study, we demonstrated a decreased level of mitochondrial DNA (mtDNA) with a large number of oxidized bases in hippocampi of rats with epilepsy induced by pilocarpine. In order to verify the underlying mechanism of mtDNA impairment, we detected the response of antioxidant defense system and mitochondrial base excision repair (mtBER) pathway. Superoxide dismutase2 (SOD-2) and glutathione (GSH) were significantly decreased in the experimental group, manifesting a decreased capacity of scavenging free radicals. Mitochondrial base excision repair (mtBER) pathway, which is the main repair pathway for the removal of oxidative base modifications, displayed unbalanced expression in epileptic group. DNA polymeraseγ (polγ) increased, while apurinic/apyrimidinic endonuclease (APE1), one of mtBER initiators, decreased in mitochondria in the chronic phase of epileptogenesis. In conclusion, mtDNA was impaired during chronic recurrent seizures, whereas the endogenous antioxidants and the mtBER pathway failed to respond to the elevated mtDNA damage.

Cellular NAD depletion and decline of SIRT1 activity play critical roles in PARP-1-mediated acute epileptic neuronal death in vitro

Intense poly(ADP-ribose) polymerase-1 (PARP-1) activation was implicated as a major cause of caspase-independent cell death in the hippocampal neuronal culture (HNC) model of acute acquired epilepsy (AE). The molecular mechanisms are quite complicated. The linkage among neuronal death, cellular nicotinamide adenine dinucleotide (NAD) levels, apoptosis-inducing factor (AIF) translocation, SIRT1 expression and activity were investigated here. The results showed that PARP-1 over-activation caused by Mg²⁺-free stimuli led to cellular NAD depletion which could block AIF translocation from mitochondria to nucleus and attenuate neuronal death. Also, SIRT1 deacetylase activity was reduced by Mg²⁺-free treatment, accompanied by elevated ratio of neuronal death, which could be rescued by NAD repletion. These data demonstrated that cellular NAD depletion and decline of SIRT1 activity play critical roles in PARP-1-mediated epileptic neuronal death in the HNC model of acute AE.

Clinical and EEG characteristics of benign rolandic epilepsy in Chinese patients.

We retrospectively evaluated the clinical and electroencephalogram (EEG) characteristics of benign rolandic epilepsy (BRE) in Chinese children. Two hundred and seventy-six patients with BRE were enrolled in this study. All patients had their first seizure between the ages of 3 and 12 years. 39.5% (109 cases) of patients ceased to have further BRE seizures by the age of 6 years, 93.1% (257 cases) recovered by the age of 12 years and 96.7% (267 cases) recovered by the age of 18 years. Two hundred and twenty-seven patients suffered only simple partial seizures, whereas 49 patients suffered generalized seizures from onset of BRE. The EEG scans of 239 patients showed repetitive diphasic spikes or sharp waves with high amplitude, which were most dominant in the central or centrotemporal areas. The spikes were confined to one hemisphere in 180 patients and occurred bilaterally in 59 patients. Ninety-eight patients were treated with antiepileptic drugs (AEDs): carbamazepine (CBZ) or valproate (VPA). The study showed that, in Chinese children, BRE is remarkably characteristic in its clinical and EEG presentation. Although BRE is usually benign in terms of ease of control with AEDs and spontaneous seizure remission, for those patients with a high frequency of seizures, AEDs should be prescribed positively.

Alternating Hemiplegia of Childhood in Chinese Following Long-Term Treatment With Flunarizine or Topiramate

ABSTRACT Objective: Alternating hemiplegia of childhood (AHC) is a rare and intractable disorder. The etiology and standard therapy of AHC remain unknown. The long-term effects of flunarizine or topiramate on patients with AHC are still not clear. Methods: Fifteen patients were investigated in this study. Their neurological disturbance and mental retardation after drug therapy were evaluated. Results: Nine patients treated with flunarizine therapy and three children with topimarate treatment presented with shorter duration or less frequency of the hemiplegic attacks. These drug responsive patients also showed improvements on neurological disturbance including eye movement disorder, choreoathetotic movements, dystonia, and ataxia. However, seizure episodes and cognitive impairments were not alleviated in AHC with long-term drug therapy. Conclusions: The findings from the present study support flunarizine or topitamate as the rational treatment for AHC.

Diazoxide preconditioning against seizure-induced oxidative injury is via the PI3K/Akt pathway in epileptic rat.

Diazoxide (DZ), a highly selective opener of the mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel, has neuroprotective effects against neuronal cell death by reducing oxidative stress. However, the mechanism of DZ protecting hippocampal neurons against seizure-induced oxidative injury is unknown. In this study, we investigated DZ attenuating neuronal loss caused by pilocarpine-induced seizures in rat hippocampus. DZ attenuated oxidative stress injury by upregulating superoxide dismutase (SOD) activity and downregulating malondialdehyde (MDA) level, which could be abolished with 5-hydroxydecanoic acid, an inhibitor of mitoK(ATP). In addition, wortmannin, an inhibitor of phosphatidylinositol-3-kinase (PI3K), attenuated the changes in MDA and SOD levels after seizures. DZ could reduce oxidative injury induced by seizures by suppressing the activity of MDA and increasing the level of SOD in part by the PI3K/Akt pathway.