Won-Ho Shin

Interleukin-13 and -4 induce death of activated microglia

When the brain suffers injury, microglia migrate to the damaged sites and become activated. These activated microglia are not detected several days later and the mechanisms underlying their disappearance are not well characterized. In this study, we demonstrate that interleukin (IL)‐13, an anti‐inflammatory cytokine, selectively induces cell death of activated microglia in vitro. Cell death was detected 4 days after the coaddition of IL‐13 with any one of the microglial activators, lipopolysaccharide (LPS), ganglioside, or thrombin. This cell death occurred in a time‐dependent manner. LPS, ganglioside, thrombin, or IL‐13 alone did not induce cell death. Among anti‐inflammatory cytokines, IL‐4 mimicked the effect of IL‐13, while TGF‐β did not. Cells treated with IL‐13 plus LPS, or IL‐13 plus ganglioside, showed the characteristics of apoptosis when analyzed by electron microscopy and terminal deoxynucleotidyl transferase‐mediated dUTP nick end labeling staining. Electron micrographs also showed microglia engulfing neighboring dead cells. We propose that IL‐13 and IL‐4 induce death of activated microglia, and that this process is important for prevention of chronic inflammation that can cause tissue damage. GLIA 38:273–280, 2002.

Induction of microglial toll-like receptor 4 by prothrombin kringle-2: a potential pathogenic mechanism in Parkinson’s disease

Microglia-mediated neuroinflammation may play an important role in the initiation and progression of dopaminergic (DA) neurodegeneration in Parkinson’s disease (PD), and toll-like receptor 4 (TLR4) is essential for the activation of microglia in the adult brain. However, it is still unclear whether patients with PD exhibit an increase in TLR4 expression in the brain, and whether there is a correlation between the levels of prothrombin kringle-2 (pKr-2) and microglial TLR4. In the present study, we first observed that the levels of pKr-2 and microglial TLR4 were increased in the substantia nigra (SN) of patients with PD. In rat and mouse brains, intranigral injection of pKr-2, which is not directly toxic to neurons, led to the disruption of nigrostriatal DA projections. Moreover, microglial TLR4 was upregulated in the rat SN and in cultures of the BV-2 microglial cell line after pKr-2 treatment. In TLR4-deficient mice, pKr-2-induced microglial activation was suppressed compared with wild-type mice, resulting in attenuated neurotoxicity. Therefore, our results suggest that pKr-2 may be a pathogenic factor in PD, and that the inhibition of pKr-2-induced microglial TLR4 may be protective against degeneration of the nigrostriatal DA system in vivo.

CB2 receptor activation prevents glial-derived neurotoxic mediator production, BBB leakage and peripheral immune cell infiltration and rescues dopamine neurons in the MPTP model of Parkinson’s disease

The cannabinoid (CB2) receptor type 2 has been proposed to prevent the degeneration of dopamine neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. However, the mechanisms underlying CB2 receptor-mediated neuroprotection in MPTP mice have not been elucidated. The mechanisms underlying CB2 receptor-mediated neuroprotection of dopamine neurons in the substantia nigra (SN) were evaluated in the MPTP mouse model of Parkinson’s disease (PD) by immunohistochemical staining (tyrosine hydroxylase, macrophage Ag complex-1, glial fibrillary acidic protein, myeloperoxidase (MPO), and CD3 and CD68), real-time PCR and a fluorescein isothiocyanate-labeled albumin assay. Treatment with the selective CB2 receptor agonist JWH-133 (10 μg kg−1, intraperitoneal (i.p.)) prevented MPTP-induced degeneration of dopamine neurons in the SN and of their fibers in the striatum. This JWH-133-mediated neuroprotection was associated with the suppression of blood–brain barrier (BBB) damage, astroglial MPO expression, infiltration of peripheral immune cells and production of inducible nitric oxide synthase, proinflammatory cytokines and chemokines by activated microglia. The effects of JWH-133 were mimicked by the non-selective cannabinoid receptor WIN55,212 (10 μg kg−1, i.p.). The observed neuroprotection and inhibition of glial-mediated neurotoxic events were reversed upon treatment with the selective CB2 receptor antagonist AM630, confirming the involvement of the CB2 receptor. Our results suggest that targeting the cannabinoid system may be beneficial for the treatment of neurodegenerative diseases, such as PD, that are associated with glial activation, BBB disruption and peripheral immune cell infiltration.

In Vivo AAV1 Transduction With hRheb(S16H) Protects Hippocampal Neurons by BDNF Production

Recent evidence has shown that Ras homolog enriched in brain (Rheb) is dysregulated in Alzheimers disease (AD) brains. However, it is still unclear whether Rheb activation contributes to the survival and protection of hippocampal neurons in the adult brain. To assess the effects of active Rheb in hippocampal neurons in vivo, we transfected neurons in the cornu ammonis 1 (CA1) region in normal adult rats with an adeno-associated virus containing the constitutively active human Rheb (hRheb(S16H)) and evaluated the effects on thrombin-induced neurotoxicity. Transduction with hRheb(S16H) significantly induced neurotrophic effects in hippocampal neurons through activation of mammalian target of rapamycin complex 1 (mTORC1) without side effects such as long-term potentiation impairment and seizures from the alteration of cytoarchitecture, and the expression of hRheb(S16H) prevented thrombin-induced neurodegeneration in vivo, an effect that was diminished by treatment with specific neutralizing antibodies against brain-derived neurotrophic factor (BDNF). In addition, our results showed that the basal mTORC1 activity might be insufficient to mediate the level of BDNF expression, but hRheb(S16H)-activated mTORC1 stimulated BDNF production in hippocampal neurons. These results suggest that viral vector transduction with hRheb(S16H) may have therapeutic value in the treatment of neurodegenerative diseases such as AD.

Electrophysiological safety of novel fluoroquinolone antibiotic agents gemifloxacin and balofloxacin

Some fluoroquinolones have been reported to induce QT interval prolongation associated with the onset of torsades de pointes (TdP), resulting in a life-threatening ventricular arrhythmia. We investigated the cardiac electrophysiological effects of two new fluoroquinolones, gemifloxacin and balofloxacin, by using conventional microelectrode recording techniques in isolated rabbit Purkinje fiber and whole-cell patch-clamp techniques in human ether-á-go-go related gene (hERG)-transient transfected CHO cells. Gemifloxacin had no significant effects on the resting membrane potential, total amplitude, action potential, and Vmax of phase 0 depolarization at concentrations up to 30 μM, but gemifloxacin at 100 μM significantly decreased total amplitude (p < 0.01). These values of gemifloxacin (30 and 100 μM) were approximately 25- and 83-fold more than the free plasma concentration of 1.2 μM in a single therapeutic injection in humans. For IhERG, the IC50 value was about 300 μM. Balofloxacin had also no significant effects on the resting membrane potential, total amplitude, action potential duration, and Vmax of phase 0 depolarization at concentrations up to 30 μM, but balofloxacin at 100 μM significantly (p < 0.01) prolonged action potentials at both 50% repolarization (APD50) and 90% repolarization (APD90). These values of balofloxacin (30 and 100 μM) were approximately 6.8- and 23-fold more than the free plasma concentration of 4.4 μM in a single therapeutic injection in humans. For IhERG, the IC50 value was 214 ± 14 μM. Therefore, our data suggested that in the electrophysiological aspect, gemifloxacin and balofloxacin may have no torsadogenic potenties up to 30 μM.

Capsaicin prevents degeneration of dopamine neurons by inhibiting glial activation and oxidative stress in the MPTP model of Parkinson’s disease

The effects of capsaicin (CAP), a transient receptor potential vanilloid subtype 1 (TRPV1) agonist, were determined on nigrostriatal dopamine (DA) neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease (PD). The results showed that TRPV1 activation by CAP rescued nigrostriatal DA neurons, enhanced striatal DA functions and improved behavioral recovery in MPTP-treated mice. CAP neuroprotection was associated with reduced expression of proinflammatory cytokines (tumor necrosis factor-α and interleukin-1β) and reactive oxygen species/reactive nitrogen species from activated microglia-derived NADPH oxidase, inducible nitric oxide synthase or reactive astrocyte-derived myeloidperoxidase. These beneficial effects of CAP were reversed by treatment with the TRPV1 antagonists capsazepine and iodo-resiniferatoxin, indicating TRPV1 involvement. This study demonstrates that TRPV1 activation by CAP protects nigrostriatal DA neurons via inhibition of glial activation-mediated oxidative stress and neuroinflammation in the MPTP mouse model of PD. These results suggest that CAP and its analogs may be beneficial therapeutic agents for the treatment of PD and other neurodegenerative disorders that are associated with neuroinflammation and glial activation-derived oxidative damage.

Effect of Clebopride, Antidopaminergic Gastrointestinal Prokinetics, on Cardiac Repolarization

The inhibition of the potassium current I Kr and QT prolongation has been known to be associated with drug-induced torsades de pointes arrhythmias (TdP) and sudden cardiac death. In this study, the authors investigated the cardiac electrophysiological effects of clebopride, a class of antidopaminergic gastrointestinal prokinetic, that has been reported to prolong the QT interval by using the conventional microelectrode recording techniques in isolated rabbit Purkinje fiber and whole-cell patch clamp techniques in human ether-à-go-go-related gene (hERG)-stably transfected Chinese hamster ovarian (CHO) cells. Clebopride at 10 μM significantly decreased the V max of phase 0 depolarization (p < .05) and significantly prolonged the action potential duration at 90% repolarization (APD90) (p < .01), whereas the action potential duration at 50% repolarization (APD50) was not prolonged. For hERG potassium channel currents, the IC50 value was 0.62 ± 0.30 μM. Clebopride was found to have no effect on sodium channel currents. When these results were compared with C max (1.02 nM) of clinical dosage (1 mg, [p.o.]), it can be suggested that clebopride is safe at the clinical dosage of 1 mg from the electrophysiological aspect. These findings indicate that clebopride, an antidopaminergic gastrointestinal prokinetic drug, may provide a sufficient “safety factor” in terms of the electrophysiological threshold concentration. But, in a supratherapeutic concentration that might possibly be encountered during overdose or impaired metabolism, clebopride may have torsadogenic potency.

Upregulation of neuronal astrocyte elevated gene-1 protects nigral dopaminergic neurons in vivo

The role of astrocyte elevated gene-1 (AEG-1) in nigral dopaminergic (DA) neurons has not been studied. Here we report that the expression of AEG-1 was significantly lower in DA neurons in the postmortem substantia nigra of patients with Parkinson’s disease (PD) compared to age-matched controls. Similarly, decreased AEG-1 levels were found in the 6-hydroxydopamine (6-OHDA) mouse model of PD. An adeno-associated virus-induced increase in the expression of AEG-1 attenuated the 6-OHDA-triggered apoptotic death of nigral DA neurons. Moreover, the neuroprotection conferred by the AEG-1 upregulation significantly intensified the neurorestorative effects of the constitutively active ras homolog enriched in the brain [Rheb(S16H)]. Collectively, these results demonstrated that the sustained level of AEG-1 as an important anti-apoptotic factor in nigral DA neurons might potentiate the therapeutic effects of treatments, such as Rheb(S16H) administration, on the degeneration of the DA pathway that characterizes PD.

Beneficial Effects of Silibinin Against Kainic Acid-induced Neurotoxicity in the Hippocampus in vivo

Silibinin, an active constituent of silymarin extracted from milk thistle, has been previously reported to confer protection to the adult brain against neurodegeneration. However, its effects against epileptic seizures have not been examined yet. In order to investigate the effects of silibinin against epileptic seizures, we used a relevant mouse model in which seizures are manifested as status epilepticus, induced by kainic acid (KA) treatment. Silibinin was injected intraperitoneally, starting 1 day before an intrahippocampal KA injection and continued daily until analysis of each experiment. Our results indicated that silibinin-treatment could reduce seizure susceptibility and frequency of spontaneous recurrent seizures (SRS) induced by KA administration, and attenuate granule cell dispersion (GCD), a morphological alteration characteristic of the dentate gyrus (DG) in temporal lobe epilepsy (TLE). Moreover, its treatment significantly reduced the aberrant levels of apoptotic, autophagic and pro-inflammatory molecules induced by KA administration, resulting in neuroprotection in the hippocampus. Thus, these results suggest that silibinin may be a beneficial natural compound for preventing epileptic events.

Protection of nigral dopaminergic neurons by AAV1 transduction with Rheb(S16H) against neurotoxic inflammation in vivo

We recently reported that adeno-associated virus serotype 1 (AAV1) transduction of murine nigral dopaminergic (DA) neurons with constitutively active ras homolog enriched in brain with a mutation of serine to histidine at position 16 [Rheb(S16H)] induced the production of neurotrophic factors, resulting in neuroprotective effects on the nigrostriatal DA system in animal models of Parkinson’s disease (PD). To further investigate whether AAV1-Rheb(S16H) transduction has neuroprotective potential against neurotoxic inflammation, which is known to be a potential event related to PD pathogenesis, we examined the effects of Rheb(S16H) expression in nigral DA neurons under a neurotoxic inflammatory environment induced by the endogenous microglial activator prothrombin kringle-2 (pKr-2). Our observations showed that Rheb(S16H) transduction played a role in the neuroprotection of the nigrostriatal DA system against pKr-2-induced neurotoxic inflammation, even though there were similar levels of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β), in the AAV1-Rheb(S16H)-treated substantia nigra (SN) compared to the SN treated with pKr-2 alone; the neuroprotective effects may be mediated by the activation of neurotrophic signaling pathways following Rheb(S16H) transduction of nigral DA neurons. We conclude that AAV1-Rheb(S16H) transduction of neuronal populations to activate the production of neurotrophic factors and intracellular neurotrophic signaling pathways may offer promise for protecting adult neurons from extracellular neurotoxic inflammation.