Masatoshi Inden

Neurodegeneration of mouse nigrostriatal dopaminergic system induced by repeated oral administration of rotenone is prevented by 4-phenylbutyrate, a chemical chaperone.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by the degeneration of dopaminergic neurons in the nigrostriatal pathway. Previous studies have demonstrated that chronic systemic exposure of Lewis rats to rotenone produced many features of PD, and cerebral tauopathy was also detected in the case of severe weight loss. The present study was designed to assess the neurotoxicity of rotenone after daily oral administration for 28 days at several doses in C57BL/6 mice. In addition, we examined the protective effects of 4‐phenylbutyrate (4‐PBA) on nigral dopamine (DA) neurons in rotenone‐treated mice. 4‐PBA was injected intraperitoneally daily 30 min before each oral administration of rotenone. Chronic oral administration of rotenone at high doses induced specific nigrostriatal DA neurodegeneration, motor deficits and the up‐regulation of α‐synuclein in the surviving DA neurons. In contrast to the Lewis rat model, cerebral tauopathy was not detected in this mouse model. 4‐PBA inhibited rotenone‐induced neuronal death and decreased the protein level of α‐synuclein. These results suggest that this rotenone mouse model may be useful for understanding the mechanism of DA neurodegeneration in PD, and that 4‐PBA has a neuroprotective effect in the treatment of PD.

Nicotinic receptor stimulation protects nigral dopaminergic neurons in rotenone-induced Parkinson's disease models.

Parkinsons disease (PD) is the second most common neurodegenerative disease and is characterized by dopaminergic (DA) neuronal cell loss in the substantia nigra. Although the entire pathogenesis of PD is still unclear, both environmental and genetic factors contribute to neurodegeneration. Epidemiologic studies show that prevalence of PD is lower in smokers than in nonsmokers,. Nicotine, a releaser of dopamine from DA neurons, is one of the candidates of antiparkinson agents in tobacco. To assess the protective effect of nicotine against rotenone‐induced DA neuronal cell toxicity, we examined the neuroprotective effects of nicotine in rotenone‐induced PD models in vivo and in vitro. We observed that simultaneous subcutaneous administration of nicotine inhibited both motor deficits and DA neuronal cell loss in the substantia nigra of rotenone‐treated mice. Next, we analyzed the molecular mechanisms of DA neuroprotective effect of nicotine against rotenone‐induced toxicity with primary DA neuronal culture. We found that DA neuroprotective effects of nicotine were inhibited by dihydro‐β‐erythroidine (DHβE), α‐bungarotoxin (αBuTx), and/or PI3K‐Akt/PKB (protein serine/threonine kinase B) inhibitors, demonstrating that rotenone‐toxicity on DA neurons are inhibited via activation of α4β2 or α7 nAChRs‐PI3K‐Akt/PKB pathway or pathways. These results suggest that the rotenone mouse model may be useful for assessing candidate antiparkinson agents, and that nAChR (nicotinic acetylcholine receptor) stimulation can protect DA neurons against degeneration.

DJ-1 protects against neurodegeneration caused by focal cerebral ischemia and reperfusion in rats

Reactive oxygen species (ROS) is massively produced in the brain after cerebral ischemia and reperfusion. It reacts strongly with cellular components, which has detrimental effects and leads to neuronal cell death. DJ-1, which was found to be the causative gene of familial Parkinsons disease PARK7, is a multifunction protein, which plays a key role in transcriptional regulation, and a molecular chaperone. In this study, we investigated the neuroprotective effect of DJ-1 against neurodegeneration caused by ischemia/reperfusion injury. Cerebral ischemia was induced in rats by 120 mins of middle cerebral artery occlusion (MCAO) using an intraluminal introduction method. The intrastriatal injection of recombinant glutathione S-transferase-tagged human DJ-1 (GST-DJ-1) markedly reduced infarct size in 2,3,5-triphenyltetrazolium chloride staining at 3 days after MCAO. In addition, we performed a noninvasive evaluation of ischemic size using magnetic resonance imaging and found a significant reduction of infarct size with the administration of GST-DJ-1. In GST-DJ-1-treated rats, behavioral dysfunction and nitrotyrosine formation were significantly inhibited. Furthermore, GST-DJ-1 markedly inhibited H2O2-mediated ROS production in SH-SY5Y cells. These results indicate that GST-DJ-1 exerts a neuroprotective effect by reducing ROS-mediated neuronal injury, suggesting that DJ-1 may be a useful therapeutic target for ischemic neurodegeneration.

Possible involvement of both mitochondria- and endoplasmic reticulum-dependent caspase pathways in rotenone-induced apoptosis in human neuroblastoma SH-SY5Y cells.

Recently, it has been shown that rotenone, a specific inhibitor of mitochondrial complex I, is a useful tool in animal models of Parkinsons disease, but the mechanism of rotenone-induced neuronal death is not fully understood. In human neuroblastoma SH-SY5Y cells, rotenone induced the degradation of procaspases-12, -9 and -3, followed by cleavage of poly (adenosine diphosphate-ribose) polymerase, DNA fragmentation and cell death. Pretreatment with phorbol-12-myristate-13-acetate inhibited the rotenone-induced decrease in procaspases-9 and -3, but not that in procaspase-12. In contrast, benzyloxycarbonyl-Val-Ala-Asp(OCH(3))-CH(2)F inhibited the decrease in procaspase-12, but not those in procaspases-9 and -3 in this study. These results suggest that rotenone may induce activation of both mitochondria- and endoplasmic reticulum-dependent caspases in human SH-SY5Y cells.

DJ-1-binding compounds prevent oxidative stress-induced cell death and movement defect in Parkinson’s disease model rats

Parkinson’s disease (PD) is caused by neuronal cell death. Although a precursor of dopamine and inhibitors of dopamine degradation have been used for PD therapy, cell death progresses during treatment. DJ‐1, a causative gene product of a familial form of PD, PARK7, plays roles in transcriptional regulation and anti‐oxidative stress, and loss of its function is thought to result in the onset of PD. Superfluous oxidation of cysteine at amino acid 106 (C106) of DJ‐1 renders DJ‐1 inactive, and such oxidized DJ‐1 has been observed in patients with the sporadic form of PD. In this study, we isolated compounds that bind to the region at C106 by a virtual screening. These compounds prevented oxidative stress‐induced death of SH‐SY5Y cells, embryonic stem cell‐derived dopaminergic cells and primary neuronal cells of the ventral mesencephalon, but not that of DJ‐1‐knockdown cells of SH‐SY5Y and NIH3T3 cells, indicating that the effect of the compounds is specific to DJ‐1. These compounds inhibited production of reactive oxygen species and restored activities of mitochondrial complex I and tyrosine hydroxylase that had been compromised by oxidative stress. These compounds prevented dopaminergic cell death in the substantia nigra and restored movement abnormality in 6‐hydroxyldopamine‐injected PD model rats. One mechanism of action of these compounds is prevention of superfluous oxidation of DJ‐1, and the compounds passed through the blood–brain barrier in vitro. Taken together, the results indicate that these compounds should become fundamental drugs for PD therapy.

Improvement of focal ischemia-induced rat dopaminergic dysfunction by striatal transplantation of mouse embryonic stem cells.

Middle cerebral artery occlusion (MCAO) caused behavioral dysfunction with massive neuronal loss. Cell transplantation may recover this deficit by replacing damaged brain cells. In this study, we examined the effects of transplantation of mouse embryonic stem (ES) cells or ES cell-derived neuron-like (ES-N) cells on behavioral function in ischemic rats. Seven days after MCAO, ES or ES-N cells were transplanted into ipsilateral striata (but not the substantia nigra) of ischemic rats. Transplanted rats exhibited a gradual reduction in the number of rotations induced by methamphetamine compared to vehicle-injected rats. These rats also showed a significant improvement in rota-rod performance. At 15 weeks after transplantation, immunoreactivities for tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum were significantly recovered in rats grafted with ES or ES-N cells compared to vehicle-injected rats. These results suggest that intrastriatal-transplantation of ES or ES-N cells improved the dopaminergic function and subsequently recover behavioral dysfunction in focal ischemic rats.

The 6-hydroxydopamine-induced nigrostriatal neurodegeneration produces microglia-like NG2 glial cells in the rat substantia nigra.

Neuron/glial 2 (NG2)‐expressing cells are often referred to as oligodendrocyte precursor cells. NG2‐expressing cells have also been identified as multipotent progenitor cells. However, microglia‐like NG2 glial cells have not been fully examined in neurodegenerative disorders such as Parkinsons disease (PD). In the present study, we chose two rat models of PD, i.e., intranigral or intrastriatal injection of 6‐hydroxydopamine (6‐OHDA), since the cell bodies of dopamine (DA) neurons, which form a nigrostriatal pathway, are in the substantia nigra pars compacta (SNpc) while their nerve terminals are in the striatum. In the nigral 6‐OHDA‐injected model, activated NG2‐positive cells were detected in the SNpc but not in the striatum. In contrast, in the striatal 6‐OHDA‐injected model, these cells were detected in both the SNpc and the striatum. In both models, activated NG2‐positive cells were located close to surviving tyrosine hydroxylase (TH)‐positive neurons in the SNpc. In addition, activated NG2‐positive cells in the SNpc coexpressed ionized calcium‐binding adaptor molecule 1 (Iba1), a microglia/macrophage marker. Interestingly, these double‐positive glial cells coexpressed glial cell line‐derived neurotrophic factor (GDNF). These results suggest that microglia‐like NG2 glial cells may help protect DA neurons and may lead to new therapeutic targets in PD.

Hyperbilirubinemia protects against focal ischemia in rats

Heme oxygenase‐1 (HO1) catalyzes oxidation of the heme molecule in concert with NADPH‐cytochrome P450 reductase following the specific cleavage of heme into carbon monoxide, iron, and biliverdin, which is rapidly metabolized to bilirubin. HO1 is a stress‐inducible protein that protects cells against oxidative injury, but its protective mechanism is not fully understood. The Eizai hyperbilirubinemic rat (EHBR), a mutant strain derived from the Sprague‐Dawley rat (SDR), has a mutation in the gene for the canalicular multispecific organic anion transporter, which results in a phenotype of hyperbilirubinemia, and thus is a model of Dubin‐Johnson syndrome in humans. In this study, we compared EHBR and SDR with regard to neuronal death induced by 2 hr of occlusion of the middle cerebral artery and reperfusion. In EHBR, the area that was immunoreactive for microtubule‐associated protein‐2 was significantly reduced, and the HO1‐immunoreactive area was smaller than that in SDR. These results suggest that bilirubin has essentially a neuroprotective effect against focal ischemia and may participate in HO1‐induced neuroprotection.

Neuroprotective effect of the antiparkinsonian drug pramipexole against nigrostriatal dopaminergic degeneration in rotenone-treated mice.

Pramipexole, an agonist for dopamine (DA) D2/D3-receptors, has been used to treat both early and advanced Parkinsons disease (PD). In this study, we examined the effect of pramipexole on DA neurons in a PD model of C57BL/6 mice, which were treated with rotenone (30 mg/kg, p.o.) daily for 28 days. Pramipexole (1 mg/kg, i.p.) was injected daily 30 min before each oral administration of rotenone. Chronic oral administration of rotenone caused a loss of DA neurons in the substantia nigra pars compacta (SNpc), motor deficits and the up-regulation of alpha-synuclein immunoreactivity in some surviving DA neurons. Pramipexole inhibited rotenone-induced DA neuronal death and motor deficits, and reduced immunoreactivity for alpha-synuclein. In addition, pramipexole inhibited the in vitro oligomerization of human wild-type alpha-synuclein by H(2)O(2)plus cytochrome c. To examine the neuroprotective effect of pramipexole against oxidative stress, we used a DJ-1-knockdown SH-SY5Y cell line and electron spin resonance (ESR) spectrometry. Simultaneous treatment with H(2)O(2) and pramipexole resulted in the significant protection of DJ-1-knockdown cells against cell death in a concentration-dependent manner. A high concentration of pramipexole directly scavenged hydroxyl radical (*OH) generated from H(2)O(2) and Fe(2+). Furthermore, pramipexole increased Bcl-2 immunoreactivity in DA neurons in the SNpc. These results suggest that pramipexole may protect DA neurons against exposure to rotenone by chronic oral administration, and this effect is mediated by multiple functions including scavenging of *OH and induction of Bcl-2 protein.

Serofendic acid prevents 6-hydroxydopamine-induced nigral neurodegeneration and drug-induced rotational asymmetry in hemi-parkinsonian rats.

Serofendic acid was recently identified as a neuroprotective factor from fetal calf serum. This study was designed to evaluate the neuroprotective effects of an intranigral microinjection of serofendic acid based on behavioral, neurochemical and histochemical studies in hemi‐parkinsonian rats using 6‐hydroxydopamine (6‐OHDA). Rats were injected with 6‐OHDA in the presence or absence of serofendic acid, or were treated with serofendic acid on the same lateral side, at 12, 24 or 72 h after 6‐OHDA lesion. Intranigral injection of 6‐OHDA alone induced a massive loss of tyrosine hydroxylase (TH)‐immunopositive neurons in the substantia nigra pars compacta (SNpc). Either simultaneous or 12 h post‐administration of serofendic acid significantly prevented both dopaminergic neurodegeneration and drug‐induced rotational asymmetry. Immunoreactivities for oxidative stress markers, such as 3‐nitrotyrosine (3‐NT) and 4‐hydroxy‐2‐nonenal (4‐HNE), were markedly detected in the SNpc of rats injected with 6‐OHDA alone. These immunoreactivities were markedly suppressed by the co‐administration of serofendic acid, similar to the results in vehicle‐treated control rats. In addition, serofendic acid inhibited 6‐OHDA‐induced α‐synuclein expression and glial activation in the SNpc. These results suggest that serofendic acid protects against 6‐OHDA‐induced SNpc dopaminergic neurodegeneration in a rat model of Parkinsons disease.