Hyoung Chun Kim

Role of oxidative stress in epileptic seizures

Oxidative stress resulting from excessive free-radical release is likely implicated in the initiation and progression of epilepsy. Therefore, antioxidant therapies aimed at reducing oxidative stress have received considerable attention in epilepsy treatment. However, much evidence suggests that oxidative stress does not always have the same pattern in all seizures models. Thus, this review provides an overview aimed at achieving a better understanding of this issue. We summarize work regarding seizure models (i.e., genetic rat models, kainic acid, pilocarpine, pentylenetetrazol, and trimethyltin), oxidative stress as an etiologic factor in epileptic seizures (i.e., impairment of antioxidant systems, mitochondrial dysfunction, involvement of redox-active metals, arachidonic acid pathway activation, and aging), and antioxidant strategies for seizure treatment. Combined, this review highlights pharmacological mechanisms associated with oxidative stress in epileptic seizures and the potential for neuroprotection in epilepsy that targets oxidative stress and is supported by effective antioxidant treatment.

Synergistic depletion of astrocytic glutathione by glucose deprivation and peroxynitrite: correlation with mitochondrial dysfunction and subsequent cell death.

Abstract: Previously we reported that immunostimulated astrocytes were highly vulnerable to glucose deprivation. The augmented death was mimicked by the peroxynitrite (ONOO‐‐producing reagent 3‐morpholinosydnonimine (SIN‐1). Here we show that glucose deprivation and ONOO‐ synergistically deplete intracellular reduced glutathione (GSH) and augment the death of astrocytes via formation of cyclosporin A‐sensitive mitochondrial permeability transition (MPT) pore. Astrocytic GSH levels were only slightly decreased by glucose deprivation or SIN‐1 (200 μM) alone. In contrast, a rapid and large depletion of GSH was observed in glucose‐deprived/SIN‐1‐treated astrocytes. The depletion of GSH occurred before a significant release of lactate dehydrogenase (a marker of cell death). Superoxide dismutase and ONOO‐ scavengers completely blocked the augmented death, indicating that the reaction of nitric oxide with superoxide to form ONOO‐ was implicated. Furthermore, nitrotyrosine immunoreactivity (a marker of ONOO‐) was markedly enhanced in glucose‐deprived/SIN‐1‐treated astrocytes. Mitochondrial transmembrane potential (MTP) was synergistically decreased in glucose‐deprived/SIN‐1‐treated astrocytes. The glutathione synthase inhibitor L‐buthionine‐(S,R)‐sulfoximine markedly decreased the MTP and increased lactate dehydrogenase (LDH) releases in SIN‐1‐treated astrocytes. Cyclosporin A, an MPT pore blocker, completely prevented the MTP depolarization as well as the enhanced LDH releases in glucose‐deprived/SIN‐1‐treated astrocytes.

Silibinin attenuates cognitive deficits and decreases of dopamine and serotonin induced by repeated methamphetamine treatment

Cognitive deficits are a core feature of patients with methamphetamine (METH) abuse. It has been reported that repeated METH treatment impairs long-term recognition memory in the novel object recognition test (NORT) in mice. Recent studies indicate that silibinin, a flavonoid derived from the herb milk thistle, has potent neuroprotective effects in cell cultures and several animal models of neurological diseases. However, its effect on the cognitive deficit induced by METH remains unclear. In the present study, we attempt to clarify the effect of silibinin on impairments of recognition memory caused by METH in mice. Mice were co-administered silibinin with METH for 7 days and then cognitive function was assessed by NORT after 7-day withdrawal. Tissue levels of dopamine and serotonin as well as their metabolites in the prefrontal cortex and hippocampus were measured 1 day after NORT. Silibinin dose-dependently ameliorated the impairment of recognition memory caused by METH treatment in mice. Silibinin significantly attenuated the decreases in the dopamine content of the prefrontal cortex and serotonin content of the hippocampus caused by METH treatment. We also found a correlation between the recognition values and dopamine and serotonin contents of the prefrontal cortex and hippocampus. The effect of silibinin on cognitive impairment may be associated with an amelioration of decreases in dopamine and serotonin levels in the prefrontal cortex and hippocampus, respectively. These results suggest that silibinin may be useful as a pharmacological tool to investigate the mechanisms of METH-induced cognitive impairments.

The dextromethorphan analog dimemorfan attenuates kainate‐induced seizures via σ1 receptor activation: comparison with the effects of dextromethorphan

1 In a previous study, we demonstrated that a dextromethorphan analog, dimemorfan, has neuroprotective effects. 2 Dextromethorphan and dimemorfan are high‐affinity ligands at σ1 receptors. Dextromethorphan has moderate affinities for phencyclidine sites, while dimemorfan has very low affinities for such sites, suggesting that these sites are not essential for the anticonvulsant actions of dimemorfan. 3 Kainate (KA) administration (10 mg kg−1, i.p.) produced robust convulsions lasting 4–6 h in rats. Pre‐treatment with dimemorfan (12 or 24 mg kg−1) reduced seizures in a dose‐dependent manner. Dimemorfan pre‐treatment also attenuated the KA‐induced increases in c‐fos/c‐jun expression, activator protein (AP)‐1 DNA‐binding activity, and loss of cells in the CA1 and CA3 fields of the hippocampus. These effects of dimemorfan were comparable to those of dextromethorphan. 4 The anticonvulsant action of dextromethorphan or dimemorfan was significantly counteracted by a selective σ1 receptor antagonist BD 1047, suggesting that the anticonvulsant action of dextromethorphan or dimemorfan is, at least in part, related to σ1 receptor‐activated modulation of AP‐1 transcription factors. 5 We asked whether dimemorfan produces the behavioral side effects seen with dextromethorphan or dextrorphan (a phencyclidine‐like metabolite of dextromethorphan). Conditioned place preference and circling behaviors were significantly increased in mice treated with phencyclidine, dextrorphan or dextromethorphan, while mice treated with dimemorfan showed no behavioral side effects. 6 Our results suggest that dimemorfan is equipotent to dextromethorphan in preventing KA‐induced seizures, while it may lack behavioral effects, such as psychotomimetic reactions.

Oxidative damage causes formation of lipofuscin-like substances in the hippocampus of the senescence-accelerated mouse after kainate treatment.

We have demonstrated that seizures induced by kainic acid (KA) are, at least in part, mediated via oxidative stress in rats [Life. Sci. 61 (1997) PL373; Brain Res. 853 (2000) 215; Brain Res. 874 (2000) 15; Neurosci. Lett. 281 (2000) 65]. In order to extend our findings, we employed the rodent aging model in this study. After KA treatments (once a day for 5 days; 20,20,20,20 and 40 mg/kg, i.p.), several parameters reflecting neurotoxic behaviors, oxidative stress [malondialdehyde (MDA) and protein carbonyl] and aging (lipofuscin-like substances) were compared between senile-prone (P8) and resistant (R1) strains of 9-month-old male senescence-accelerated mice (SAM). KA-induced neurotoxic signs as shown by mortality and seizure activity were more accentuated in the SAM-P8 than in the SAM-R1. Levels of MDA and carbonyl are consistently higher in the hippocampus of SAM-P8 than that of SAM-R1. Significant increases in the values of MDA and carbonyl were observed 4 h or 2 days after the final KA administration. This finding was more pronounced in the SAM-P8 than in the SAM-R1. Although a significant loss of hippocampal neurons was observed 7 days post-KA, at this time the MDA and carbonyl content had returned to near control levels. In contrast, fluorescent lipofuscin-like substances and lipofuscin granules were significantly increased 7 days after KA treatments. Therefore, our data suggests that mice in the senescence model are more susceptible to KA-induced seizures/oxidative damage, and that oxidative damage could be one of the casual factors in the accumulation of lipofuscin.

Endogenous dynorphin protects against neurotoxin-elicited nigrostriatal dopaminergic neuron damage and motor deficits in mice

BackgroundThe striato-nigral projecting pathway contains the highest concentrations of dynorphin in the brain. The functional role of this opioid peptide in the regulation of mesencephalic dopaminergic (DAergic) neurons is not clear. We reported previously that exogenous dynorphin exerts potent neuroprotective effects against inflammation-induced dopaminergic neurodegeneration in vitro. The present study was performed to investigate whether endogenous dynorphin has neuroprotective roles in vivo.Methods1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and methamphetamine (MA), two commonly used neurotoxins in rodent models of Parkinson’s disease, were administered to wild-type (Dyn+/+) and prodynorphin-deficient mice (Dyn−/−). We examined dopaminergic neurotoxicity by using an automated video tracking system, HPLC, immunocytochemistry, and reverse transcription and polymerase chain reaction (RT-PCR).ResultsTreatment with MPTP resulted in behavioral impairments in both strains. However, these impairments were more pronounced in Dyn-l- than in Dyn+/+. Dyn−/− showed more severe MPTP-induced dopaminergic neuronal loss in the substantia nigra and striatum than Dyn+/+. Similarly, the levels of dopamine and its metabolites in the striatum were depleted to a greater extent in Dyn−/− than in Dyn+/+. Additional mechanistic studies revealed that MPTP treatment caused a higher degree of microglial activation and M1 phenotype differentiation in Dyn−/− than in Dyn+/+. Consistent with these observations, prodynorphin deficiency also exacerbated neurotoxic effects induced by MA, although this effect was less pronounced than that of MPTP.ConclusionsThe in vivo results presented here extend our previous in vitro findings and further indicate that endogenous dynorphin plays a critical role in protecting dopaminergic neurons through its anti-inflammatory effects.

Inactivation of JAK2/STAT3 signaling axis and downregulation of m1 mAChR cause cognitive impairment in klotho mutant mice, a genetic model of aging

We previously reported cognitive dysfunction in klotho mutant mice. In the present study, we further examined novel mechanisms involved in cognitive impairment in these mice. Significantly decreased janus kinase 2 (JAK2) and signal transducer and activator of transcription3 (STAT3) phosphorylation were observed in the hippocampus of klotho mutant mice. A selective decrease in protein expression and binding density of the M1 muscarinic cholinergic receptor (M1 mAChR) was observed in these mice. Cholinergic parameters (ie, acetylcholine (ACh), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE)) and NMDAR-dependent long-term potentiation (LTP) were significantly impaired in klotho mutant mice. McN-A-343 (McN), an M1 mAChR agonist, significantly attenuated these impairments. AG490 (AG), a JAK2 inhibitor, counteracted the attenuating effects of McN, although AG did not significantly alter the McN-induced effect on AChE. Furthermore, AG significantly inhibited the attenuating effects of McN on decreased NMDAR-dependent LTP, protein kinase C βII, p-ERK, p-CREB, BDNF, and p-JAK2/p-STAT3-expression in klotho mutant mice. In addition, k252a, a BDNF receptor tyrosine kinase B (TrkB) inhibitor, significantly counteracted McN effects on decreased ChAT, ACh, and M1 mAChR and p-JAK2/p-STAT3 expression. McN-induced effects on cognitive impairment in klotho mutant mice were consistently counteracted by either AG or k252a. Our results suggest that inactivation of the JAK2/STAT3 signaling axis and M1 mAChR downregulation play a critical role in cognitive impairment observed in klotho mutant mice.

Dextromethorphan modulates the AP-1 DNA-binding activity induced by kainic acid.

We have recently reported that dextromethorphan attenuates the neurotoxicity induced by kainic acid in a dose-related fashion. Pretreatments with dextromethorphan (50 mg/kg, p.o. x2) significantly reduced the activator protein-1 DNA-binding activity and the Fos-related antigen-immunoreactive protein induced by kainic acid (10 mg/kg, i.p.) in the CA1, but not the CA3 or the dentate gyrus sector of the rat hippocampus. Paradoxically, dextromethorphan itself caused an elevated activator protein-1 DNA-binding activity and Fos-related antigen-immunoreactive protein in the CA1 region which lasted for at least 4 days. The results suggest that the CA1 area is the critical site for mediating the putative neuroprotective effect induced by dextromethorphan.

Protection by a manganese porphyrin of endogenous peroxynitrite-induced death of glial cells via inhibition of mitochondrial transmembrane potential decrease

In the cerebral ischemic penumbra, progressive metabolic deterioration eventually leads to death of glial cells. The exact mechanism for the death of glial cells is unclear. Here we report that under glucose‐deprived conditions immunostimulated glial cells rapidly underwent death via production of large amounts of peroxynitrite. The cell‐permeable Mn(III)tetrakis(N‐methyl‐4′‐pyridyl)porphyrin (MnTMPyP) caused a concentration‐dependent attenuation of the increased death in glucose‐deprived immunostimulated glial cells. The structurally related compound H2TMPyP, which lacks metals, did not attenuate this augmented cell death. MnTMPyP prevented the elevation in nitrotyrosine immunoreactivity (a marker of ONOO−) in glucose‐deprived immunostimulated glial cells. In glucose‐deprived glial cells, MnTMPyP also completely blocked the augmented death and nitrotyrosine immunoreactivity induced by the ONOO−‐producing reagent 3‐morpholinosydnonimine (SIN‐1). The mitochondrial transmembrane potential (MTP), as measured using the dye JC‐1, was rapidly decreased in immunostimulated or SIN‐1‐treated glial cells deprived of glucose. MnTMPyP, but not H2TMPyP, blocked the depolarization of MTP in those glial cells. The present data, at least in part, provide evidence for how glial cells die in the postischemic and/or recurrent ischemic brain. GLIA 31:155–164, 2000.

Control of neurite outgrowth by RhoA inactivation

J. Neurochem. (2012) 120, 684–698.