Stereotaxical infusion of rotenone: a reliable rodent model for Parkinson's disease

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

Neuroprotective effect of dexpanthenol on rotenone-induced Parkinson's disease model in rats

Parkinson's disease (PD) is the second most common and progressive neurodegenerative disease. This experimental study was designed to investigate the neuroprotective effects of dexpanthenol on antioxidant and anti-inflammatory processes in a rotenone-induced Parkinson's disease model in rats. Twenty-one male rats were randomly divided into 2 groups. The rotenone group (n = 14) was administered rotenone by intrastriatal injection, and the vehicle group (n = 7) was administered DMSO with the same application route. All animals underwent rotational movement testing with apomorphine injection 10 days later. Those with Parkinson's disease model were randomly divided into 2 groups. While 1 ml/kg of saline was applied to the saline group (n = 7), 500 mg/kg was administered to the dexpanthenol group intraperitoneally for 28 days. After 28 days, all rats were euthanized and brain tissue was removed. While striatal areas were evaluated immunohistochemically, brain MDA, TNF-α, and HVA levels were measured to evaluate their anti-oxidative and anti-inflammatory effects. In the dexpanthenol group, the total count (p < 0.001) and intensity (p < 0.001) of dopaminergic neurons in the striatal areas increased compared to the saline group. It was revealed that MDA (nmol/g) (p < 0.001) and TNF-α (pg/g) (p < 0.001) levels decreased in the dexpanthenol group, while HVA (ng/mg) levels increased (p < 0.01). This study suggests that dexpanthenol may have a neuroprotective effect by reducing neuronal loss, oxidative damage, and neuroinflammation in the striatum in rats.

Astragaloside IV Inhibits Rotenone-Induced α-syn Presentation and the CD4 T-Cell Immune Response

The increased α-synuclein (α-syn)-dependent activation of CD4 T cells leads to the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) in Parkinson's disease (PD). Astragaloside IV (AS-IV) protects DA neurons against neuroinflammation. The effects of AS-IV on CD4 T-cell-mediated immune responses in PD remain unknown. Rotenone (ROT) injected unilaterally into the substantia nigra pars compacta (SNc) of rats induced PD. AS-IV (20 mg/kg) was intraperitoneally injected once a day for 14 days. The limb hanging test and rotarod test were performed to evaluate the alteration of behavior at 4 and 6 weeks. Total gastrointestinal transit tests were performed at 4 weeks. Western blotting was used to detect the expression of proinflammatory cytokine proteins. Immunofluorescence staining was conducted to test the expression and localization of major histocompatibility complex class II (MHCII), cleaved caspase-1 and α-syn in astrocytes. Flow cytometry analysis, immunohistochemistry and immunofluorescence staining were used to measure the expression of CD4 T-cell subsets in the SN. The application of AS-IV protected against the loss of DA neurons and behavioral deficits in ROT-induced PD rat models. AS-IV administration inhibited the aggregation of α-syn in DA neurons and the expression of proinflammatory cytokines such as TNF-α, IL-18, IL-6 and IL-1β. AS-IV decreased the activation of CD4 T cells and three CD4 T-cell subsets: Tfh, Treg and Th1. AS-IV interrupted the ROT-induced interaction between astrocytes and CD4 T cells and the colocalization of MHCII and α-syn in astrocytes. AS-IV inhibited the expression of α-syn in astrocytes and the colocalization of α-syn and cleaved caspase-1 in astrocytes. AS-IV prevents the loss of DA neurons in PD by inhibiting the activation of α-syn-specific CD4 T cells, which is regulated by MHCII-mediated antigen presentation in astrocytes.

Lacosamide exhibits neuroprotective effects in a rat model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder that primarily affects the motor system. Although there are several treatments available to alleviate PD symptoms, there is currently no cure for the disease. Lacosamide, an anti-epileptic drug, has shown promising results in preclinical studies as a potential neuroprotective agent for PD. In this study, we aimed to investigate the neuroprotective effect of lacosamide in a murine model of PD.

METHODS

Twenty-one adult male rats were randomly divided into the following three groups (n = 7): 1 group received stereotaxical infusion of dimethyl sulfoxide (vehicle, group 1), and the others received stereotaxical infusion of rotenone (groups 2 and 3). The apomorphine-induced rotation test was applied to the rats after 10 days. Thereafter, group 2 was administered isotonic saline, whereas group 3 was administered lacosamide (20 mg/kg,i.p.) for 28 days. Apomorphine-induced rotation tests were performed to assess the effect of lacosamide on motor function. In addition, immunohistochemistry and biochemistry were used to assess the dopaminergic neuron loss in the substantia nigra and MDA, TNF-α and HVA levels, respectively.

RESULTS

In rats with Parkinson's disease induced by rotenone, levels of malondialdehyde and TNF-α significantly increased and HVA levels decreased, whereas in mice treated with lacosamide, levels of malondialdehyde and TNF-α significantly decreased and HVA levels increased. The apomorphine-induced rotation test scores of lacosamide-treated mice were lower compared with the untreated group. Furthermore, treatment with lacosamide significantly mitigated the degeneration of dopaminergic projections within the striatum originating from the substantia nigra and increased tyrosine hydroxylase (TH) immunofluorescence, indicative of preserved dopaminergic neuronal function.

CONCLUSION

In conclusion, our study provides evidence that lacosamide has a neuroprotective effect on the rat model of PD. Further studies are required to investigate the underlying mechanisms and evaluate the potential clinical use of lacosamide as a neuroprotective agent for PD.

Effects of ozone treatment to the levels of neurodegeneration biomarkers after rotenone induced rat model of Parkinson's disease

The study investigated the effects of ozone treatment on the neurodegeneration of stereotaxic rotenone-induced parkinson's disease (PD) model. The model was confirmed using the apomorphine rotation test. α-synuclein, amyloid-β, Tau, phosphorylated Tau, as well as tyrosine hydroxylase(+), nNOS(+), and glial cell counts were used to evaluate neurodegeneration in the substantia nigra pars compacta and ventral tegmental area. The experiment involved 48 Sprague-Dawley rats divided into four groups: dimethyl sulfoxide (DMSO), DMSO with ozone (O), DMSO/rotenone (R), and D/R/O. Ozone treatment significantly improved tissue α-synuclein level and TH+, nNOS+, and glial cell counts compared to the rotenone-only group. The study suggests that ozone treatment may have beneficial effects on PD biomarkers in the rotenone model. Further studies on ozone dosage, duration, and administration methods in humans could provide more evidence for its potential use in Parkinson's disease treatment.

4-Phenylbutyrate Mitigates the Motor Impairment and Dopaminergic Neuronal Death During Parkinson's Disease Pathology via Targeting VDAC1 Mediated Mitochondrial Function and Astrocytes Activation

Parkinson's disease (PD) is a progressive motor neurodegenerative disorder significantly associated with protein aggregation related neurodegenerative mechanisms. In view of no disease modifying drugs, the present study was targeted to investigate the therapeutic effects of pharmacological agent 4-phenylbutyric acid (4PBA) in PD pathology. 4PBA is an FDA approved monocarboxylic acid with inhibitory activity towards histone deacetylase and clinically treats urea cycle disorder. First, we observed the significant protective effects of 4PBA on PD specific neuromuscular coordination, level of tyrosine hydroxylase, α-synuclein level and neurotransmitter dopamine in both substantia nigra and striatal regions of the experimental rat model of PD. Further results revealed that treatment with 4PBA drug exhibited significant protection against disease related oxidative stress and augmented nitrite levels. The disease pathology-related depletion in mitochondrial membrane potential and augmented level of calcium as well as mitochondrion membrane located VDAC1 protein level and cytochrome-c translocation were also significantly attenuated with 4PBA administration. Inhibited neuronal apoptosis and restored neuronal morphology were also observed with 4PBA treatment as measured by level of pro-apoptotic proteins t-Bid, Bax and cleaved caspase-3 along with cresyl violet staining in both substantia nigra and striatal regions. Lastly, PD-linked astrocyte activation was significantly inhibited with 4PBA treatment. Altogether, our findings suggest that 4PBA exerts broad-spectrum neuroprotective effects in PD animal model.

Protective effects of cyclosporine A on neurodegeneration and motor impairment in rotenone-induced experimental models of Parkinson's disease

The development of neuroprotective drugs targeting mitochondria could be an important strategy in combating the progressive clinical course of Parkinson's disease. In the current study, we demonstrated that in SH-SY5Y cells (human dopaminergic neuroblastoma cell line), rotenone caused a dose-dependent (0.25-1 μM) and time-dependent (up to 48 h) loss of cell viability and a loss of cellular ATP content with mitochondrial membrane depolarization and an increased formation of reactive oxygen species; all these processes were markedly prevented by the mitochondrial permeability transition pore blocker cyclosporine A, which did not affect complex I inhibition by rotenone. The nuclear morphology of rotenone-treated cells for 48 h indicated the presence of both necrosis and apoptosis. We then examined the effects of cyclosporine A on the rotenone-induced model of Parkinson's disease in Wistar rats. Cyclosporine A significantly improved the motor deficits and prevented the loss of nigral dopaminergic neurons projecting into the striatum in rotenone-treated rats. Being a marketed immuno-suppressive drug, cyclosporine A should be further evaluated for its putative neuroprotective action in Parkinson's disease.

EMF promote BMSCs differentiation and functional recovery in hemiparkinsonian rats

Bone marrow mesenchymal stem cells (BMSCs) have self-renewal ability while maintaining the proliferation facility. The BMSCs reproducing ability could affect by electromagnetic fields (EMFs) as a physical inducing factor. We focused on the EMF (400 µT, 75 Hz) exposed multi-potential BMSCs which differentiated and successfully implanted in the substantia nigra pars compacta (SNpc) of Parkinson's disease rat model. The purified BMSCs are exposed to sinusoidal and square waveform EMF (1h/1 week or 7h/1 day) then injected into the left SNpc of Parkinson's rats. To evaluate the morphology of EMF exposed BMSCs, the cresyl violet staining labeled the Nissl bodies. After evaluation of the rat's activity by behavioral tests (open-field and rotarod tests), the brains were obtained for the preparation of SNpc blocks and carry out the cresyl violet staining. Cell morphology proved most cell differentiation to neurons in the sinusoidal EMF groups. In the sinusoidal EMF exposure groups, large and small neurons were seen with apparent synapses. Although in the square EMF exposed groups some neurons were seen, most of the differentiated cells were astrocytes, microglia, and oligodendrocyte. The results confirmed an improvement in locomotors' activity of BMSC alone and sinusoidal EMF exposed groups. We presented a low-frequency EMF (75 Hz) to promote the capability of BMSC proliferation, differentiation to neurons and glial cells, and motor coordination activity in the treatment of hemiparkinsonian rats.

Impact of eugenol on in vivo model of 6-hydroxydopamine-induced oxidative stress

Oxidative stress is involved in many pathological disturbs, such as neurodegenerative disorders. Eugenol (Eug) is a phenolic compound with antioxidant and neuroprotective activities. Then, this study was conducted to investigate the potential neuroprotective effects of Eug on oxidative stress model induced by 6-hydroxydopamine (6-OHDA) in rats. First, the in vivo oxidative stress model was performed by intrastriatal injection (int.) of 6-OHDA (21 µg), followed by the treatment of Eug (0.1, 1, and 10 mg/kg/7 d) per os (p.o.). On the 7 d, behavioral tests were performed. On the 8 d, all the animals were euthanasied and their cerebral areas were excised for neurochemical and transcriptional analyses. The results showed that the treatment with Eug promoted neuroprotective effects on in vivo through reducing of oxidative stress and modulation of genes related to antioxidant activity. Furthermore, animals treated with Eug demonstrated returning of behavioral performance and body weight gain to normal conditions. Thus, this study reports the neuroprotective effects of Eug against oxidative stress induced by 6-OHDA in rats.

Glial cells modulate retinal cell survival in rotenone-induced neural degeneration

Administration of the mitochondrial complex I inhibitor rotenone provides an excellent model to study the pathomechanism of oxidative stress-related neural degeneration diseases. In this study, we examined the glial roles in retinal cell survival and degeneration under the rotenone-induced oxidative stress condition. Mouse-derived Müller, microglial (BV-2), and dissociated retinal cells were used for in vitro experiments. Gene expression levels and cell viability were determined using quantitative reverse transcription-polymerase chain reaction and the alamarBlue assay, respectively. Conditioned media were prepared by stimulating glial cells with rotenone. Retinal ganglion cells (RGCs) and inner nuclear layer (INL) were visualized on rat retinal sections by immunohistochemistry and eosin/hematoxylin, respectively. Rotenone dose-dependently induced glial cell death. Treatment with rotenone or rotenone-stimulated glial cell-conditioned media altered gene expression of growth factors and inflammatory cytokines in glial cells. The viability of dissociated retinal cells significantly increased upon culturing in media conditioned with rotenone-stimulated or Müller cell-conditioned media-stimulated BV-2 cells. Furthermore, intravitreal neurotrophin-5 administration prevented the rotenone-induced reduction of RGC number and INL thickness in rats. Thus, glial cells exerted both positive and negative effects on retinal cell survival in rotenone-induced neural degeneration via altered expression of growth factors, especially upregulation of microglia-derived Ntf5, and proinflammatory cytokines.

Corynoxine Protects Dopaminergic Neurons Through Inducing Autophagy and Diminishing Neuroinflammation in Rotenone-Induced Animal Models of Parkinson's Disease

Recent studies have shown that impairment of autophagy is related to the pathogenesis of Parkinson's disease (PD), and small molecular autophagy enhancers are suggested to be potential drug candidates against PD. Previous studies identified corynoxine (Cory), an oxindole alkaloid isolated from the Chinese herbal medicine Uncaria rhynchophylla (Miq.) Jacks, as a new autophagy enhancer that promoted the degradation of α-synuclein in a PD cell model. In this study, two different rotenone-induced animal models of PD, one involving the systemic administration of rotenone at a low dosage in mice and the other involving the infusion of rotenone stereotaxically into the substantia nigra pars compacta (SNpc) of rats, were employed to evaluate the neuroprotective effects of Cory. Cory was shown to exhibit neuroprotective effects in the two rotenone-induced models of PD by improving motor dysfunction, preventing tyrosine hydroxylase (TH)-positive neuronal loss, decreasing α-synuclein aggregates through the mechanistic target of the rapamycin (mTOR) pathway, and diminishing neuroinflammation. These results provide preclinical experimental evidence supporting the development of Cory into a potential delivery system for the treatment of PD.

Generation of Mitochondrial Toxin Rodent Models of Parkinson's Disease Using 6-OHDA , MPTP , and Rotenone

Several animal models are employed to discover novel treatments for the symptoms of Parkinson's disease (PD). PD models can be divided into two models: neurotoxin models and genetic models. Among neurotoxins to produce PD models, 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and rotenone, which inhibit the mitochondrial complex I, are widely used. Animal models of PD using these neurotoxins are also known as mitochondrial toxin models. Here this chapter describes the preparation of these mitochondrial toxin models.

Kolaviron protects against nigrostriatal degeneration and gut oxidative damage in a stereotaxic rotenone model of Parkinson's disease

The asymptomatic and clinical stages of Parkinson's disease (PD) are associated with comorbid non-motor symptoms including gastrointestinal (GI) dysfunction. Although the neuroprotective and gastroprotective roles of kolaviron (KV) have been reported independently, whether KV-mediated GI-protective capacity could be beneficial in PD is unknown. We therefore investigated the modulatory effects of KV on the loss of dopaminergic neurons, locomotor abnormalities, and ileal oxidative damage when rats are lesioned in the nigrostriatal pathway. KV treatment markedly suppressed the behavioral deficit and apomorphine-induced rotations associated with rotenone lesioning. KV attenuated the loss of nigrostriatal dopaminergic neurons and perturbations in the striatal glucose-regulated protein (GRP78) and X-box binding protein 1 (XBP1) levels. Ileal epithelial injury following stereotaxic rotenone infusion was associated with oxidative stress and marked inhibition of acetylcholine esterase activity and reduced expression of occludin in the crypt and villi. While KV treatment attenuated the redox imbalance in the gut and enhanced occludin immunoreactivity, acetylcholinesterase activity was not affected. Our data demonstrate ileal oxidative damage as a characteristic non-motor gut dysfunction in PD while showing the potential dual efficacy of KV in the attenuation of both neural defects and gut abnormalities associated with PD.

Behavioral Tests in Neurotoxin-Induced Animal Models of Parkinson's Disease

Currently, neurodegenerative diseases are a major cause of disability around the world. Parkinson's disease (PD) is the second-leading cause of neurodegenerative disorder after Alzheimer's disease. In PD, continuous loss of dopaminergic neurons in the substantia nigra causes dopamine depletion in the striatum, promotes the primary motor symptoms of resting tremor, bradykinesia, muscle rigidity, and postural instability. The risk factors of PD comprise environmental toxins, drugs, pesticides, brain microtrauma, focal cerebrovascular injury, aging, and hereditary defects. The pathologic features of PD include impaired protein homeostasis, mitochondrial dysfunction, nitric oxide, and neuroinflammation, but the interaction of these factors contributing to PD is not fully understood. In neurotoxin-induced PD models, neurotoxins, for instance, 6-hydroxydopamine (6-OHDA), 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-Methyl-4-phenylpyridinium (MPP+), paraquat, rotenone, and permethrin mainly impair the mitochondrial respiratory chain, activate microglia, and generate reactive oxygen species to induce autooxidation and dopaminergic neuronal apoptosis. Since no current treatment can cure PD, using a suitable PD animal model to evaluate PD motor symptoms' treatment efficacy and identify therapeutic targets and drugs are still needed. Hence, the present review focuses on the latest scientific developments in different neurotoxin-induced PD animal models with their mechanisms of pathogenesis and evaluation methods of PD motor symptoms.

Antioxidant and Neuroprotective Effects of Caffeine against Alzheimer's and Parkinson's Disease: Insight into the Role of Nrf-2 and A2AR Signaling

This paper reviews the results of studies conducted on the role of caffeine in the management of different neurological disorders, such as Parkinson's disease (PD) and Alzheimer's disease (AD). To highlight the potential role of caffeine in managing different neurodegenerative diseases, we identified studies by searching PubMed, Web of Science, and Google Scholar by scrutinizing the lists of pertinent publications. According to the collected overall findings, caffeine may reduce the elevated oxidative stress; inhibit the activation of adenosine A2A, thereby regulating the accumulation of Aβ; reduce the hyperphosphorylation of tau; and reduce the accumulation of misfolded proteins, such as α-synuclein, in Alzheimer's and Parkinson's diseases. The studies have suggested that caffeine has promising protective effects against different neurodegenerative diseases and that these effects may be used to tackle the neurological diseases and/or their consequences. Here, we review the ongoing research on the role of caffeine in the management of different neurodegenerative disorders, focusing on AD and PD. The current findings suggest that caffeine produces potent antioxidant, inflammatory, and anti-apoptotic effects against different models of neurodegenerative disease, including AD, PD, and other neurodegenerative disorders. Caffeine has shown strong antagonistic effects against the adenosine A2A receptor, which is a microglial receptor, and strong agonistic effects against nuclear-related factor-2 (Nrf-2), thereby regulating the cellular homeostasis at the brain by reducing oxidative stress, neuroinflammation, regulating the accumulation of α-synuclein in PD and tau hyperphosphorylation, amyloidogenesis, and synaptic deficits in AD, which are the cardinal features of these neurodegenerative diseases.

Nigral and ventral tegmental area lesioning induces testicular and sperm morphological abnormalities in a rotenone model of Parkinson's disease

Although sexual health is affected by Parkinson's disease (PD), the effect on testicular health and/or sperm quality is not well discussed. After 21 days of rotenone lesioning, we observed dopaminergic neuronal degeneration in the substantia nigra and hypothalamus. There were minimal SPACA-1-expressing epididymal spermatozoa with morphological abnormalities, scanty luminal spermatozoa and reduced testicular spermatids and post-meiotic germ cells indicating hypospermatogenesis. Occludin-expressing sertoli cells were dispersed over a wide area indicating compromised blood-testes barrier. Activated caspase-3 expression was intense while immunoreactivity of spermatogenic-enhancing SRY and GADD45 g was weak. Although serum follicle stimulating hormone level was not affected, the lesion was associated with reduced serum testosterone level, testicular oxidative damage and inhibition of acetylcholinesterase activity, even when rotenone was not detected in the testes. Together, dopaminergic lesions may mediate testicular and sperm abnormalities via the brain-hypothalamic-testicular circuit independent of the pituitary, thereby establishing a causal link between Parkinsonism and reproductive dysfunction.

Mechanistic evaluation of Ursolic acid against rotenone induced Parkinson's disease- emphasizing the role of mitochondrial biogenesis

Parkinson's disease (PD) is an age associated, progressive and a second most common neurodegenerative disease. It is caused due to degeneration of dopaminergic neurons in substantia nigra (SN). Various studies implicate mitochondrial dysfunction, oxidative stress, altered degradation of misfolded proteins in PD pathogenesis. Ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, is reported to possess a number of biological activities viz. anti-oxidant, anti-inflammatory etc. The focus of our study was to assess the neuroprotective potential of UA against the rotenone induced pathophysiological alterations. In this study rats were subjected to stereotaxic bilateral injection of rotenone (12 μg/μl) in SN. Further, they were treated per-orally with UA (5 and 10 mg/kg) for 30 days. During the study, neurobehavioral tests comprising Rota-rod, Open field and Barnes maze (BMT) were conducted. At the end of 30 days, the antioxidant (Reduced glutathione, superoxide dismutase, catalase and lipid peroxidation), inflammatory (TNF-α) parameters, mitochondrial complex I, mitochondrial biogenesis (MB) and immunohistochemical analysis (TH positive neurons, Glial Fibrillary Acidic Protein (GFAP)) was performed. The results exhibited significant amelioration in the motor deficits by UA which can be attributed to the protection of TH positive neurons from degeneration. A significant improvement in the cognitive function due to UA was observed in BMT. Biochemically, the oxidative stress and inflammation triggered by rotenone was significantly diminished by UA. It also significantly obviated the complex I inhibition and promoted MB. The preliminary results thus firmly advocate the neuroprotective potential of UA to prevent rotenone induced neurotoxicity in rats.

6-OH-BDE-47 exposure-induced Parkinson's disease pathology in Sprague Dawley rat

6-Hydroxy-BDE-47 (6-OH-BDE-47) is an important in vivo metabolite derived from 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a ubiquitous environmental pollutant. The chemical has been widely detected in environmental and biological samples. However, as a potential neurotoxin, whether 6-OH-BDE-47 could promote the development of typical neurodegenerative diseases such as Parkinson's disease (PD) is still unknown. Here, we tested the potential PD-related neurotoxic effect of 6-OH-BDE-47 in rat. The chemical with levels of 0.1, 1 and 10 µg was stereotaxically injected into the right midbrain regions of rat where contain abundant dopaminergic neurons. The resulting deteriorated motor function and decreased levels of striatal dopamine and nigrostriatal tyrosine hydroxylase indicate the dopaminergic neuron loss after the injection. Proteomics study revealed that protein degradation pathways were affected. Western blot analysis confirmed that 6-OH-BDE-47 could inhibit ubiquitination and autophagy, resulting in the increased formation of α-synuclein (α-syn) aggregate, an important pathological hallmark of PD. Overall, our study demonstrated that the 6-OH-BDE-47 administration could induce motor defect by impairing dopaminergic system and promote α-syn aggregation by inhibiting ubiquitination and autophagy, suggesting that the occurrence of 6-OH-BDE-47 in brain could be a risk for developing PD.

α-Arbutin Protects Against Parkinson's Disease-Associated Mitochondrial Dysfunction In Vitro and In Vivo

Parkinson's disease (PD), the most common neurodegenerative movement disorder, is characterized by the progressive loss of dopaminergic neurons in substantia nigra. The underlying mechanisms of PD pathogenesis have not been fully illustrated and currently PD remains incurable. Accumulating evidences suggest that mitochondrial dysfunction plays pivotal role in the dopaminergic neuronal death. Therefore, discovery of novel and safe agent for rescuing mitochondrial dysfunction would benefit PD treatment. Here we demonstrated for the first time that α-Arbutin (Arb), a natural polyphenol extracted from Ericaceae species, displayed significant protective effect on the rotenone (Rot)-induced mitochondrial dysfunction and apoptosis of human neuroblastoma cell (SH-SY5Y). We further found that the neuroprotective effect of Arb was associated with ameliorating oxidative stress, stabilizing of mitochondrial membrane potential, and enhancing adenosine triphosphate production. To investigate the underlying mechanism, we checked the AMP-activated protein kinase and autophagy pathway and we found that both were involved in the neuroprotection of Arb. Moreover, we explored the protective effect of Arb in drosophila PD model and found that Arb rescued parkin deficiency-induced motor function disability and mitochondrial abnormality of drosophila. Taken together, our study demonstrated that Arb got excellent neuroprotective effect on PD models both in vitro and in vivo and Arb might serve as a potent therapeutic agent for the treatment of PD.

Animal models of olfactory dysfunction in neurodegenerative diseases

Olfactory dysfunction seems to occur earlier than classic motor and cognitive symptoms in many neurodegenerative diseases, including Parkinson's disease (PD) and Alzheimer's disease (AD). Thus, the use of the olfactory system as a clinical marker for neurodegenerative diseases is helpful in the characterization of prodromal stages of these diseases, early diagnostic strategies, differential diagnosis, and, potentially, prediction of treatment success. The use of genetic and neurotoxin animal models has contributed to the understanding of the mechanisms underlying olfactory dysfunction in a number of neurodegenerative diseases. In this chapter, we provide an overview of behavioral and neurochemical alterations observed in animal models of different neurodegenerative diseases (such as genetic and Aβ infusion models for AD and neurotoxins and genetic models of PD), in which olfactory dysfunction has been described.

Pharmacological Properties, Molecular Mechanisms, and Pharmaceutical Development of Asiatic Acid: A Pentacyclic Triterpenoid of Therapeutic Promise

Asiatic acid (AA) is a naturally occurring aglycone of ursane type pentacyclic triterpenoids. It is abundantly present in many edible and medicinal plants including Centella asiatica that is a reputed herb in many traditional medicine formulations for wound healing and neuropsychiatric diseases. AA possesses numerous pharmacological activities such as antioxidant and anti-inflammatory and regulates apoptosis that attributes its therapeutic effects in numerous diseases. AA showed potent antihypertensive, nootropic, neuroprotective, cardioprotective, antimicrobial, and antitumor activities in preclinical studies. In various in vitro and in vivo studies, AA found to affect many enzymes, receptors, growth factors, transcription factors, apoptotic proteins, and cell signaling cascades. This review aims to represent the available reports on therapeutic potential and the underlying pharmacological and molecular mechanisms of AA. The review also also discusses the challenges and prospects on the pharmaceutical development of AA such as pharmacokinetics, physicochemical properties, analysis and structural modifications, and drug delivery. AA showed favorable pharmacokinetics and found bioavailable following oral or interaperitoneal administration. The studies demonstrate the polypharmacological properties, therapeutic potential and molecular mechanisms of AA in numerous diseases. Taken together the evidences from available studies, AA appears one of the important multitargeted polypharmacological agents of natural origin for further pharmaceutical development and clinical application. Provided the favorable pharmacokinetics, safety, and efficacy, AA can be a promising agent or adjuvant along with currently used modern medicines with a pharmacological basis of its use in therapeutics.

Demethoxycurcumin, a Natural Derivative of Curcumin Abrogates Rotenone-induced Dopamine Depletion and Motor Deficits by Its Antioxidative and Anti-inflammatory Properties in Parkinsonian Rats

Background:

Parkinson's disease (PD) is a progressive neurodegenerative disorder (NDD) associated with the loss of dopaminergic neurons in the substantia nigra and subsequently has an effect on motor function and coordination. The pathology of PD is multifactorial, in which neuroinflammation and oxidative damage are the two of the main protagonists.

Objectives:

The present study aims to assess the potential antioxidant and anti-inflammatory effects of demethoxycurcumin (DMC), a natural derivative of curcumin, against rotenone-induced PD in rats.

Materials and Methods:

Rats were randomized and divided into six groups: control, rotenone (0.5 mg/kg/day, intraperitoneal in sunflower oil) treated for 7 days, rotenone and DMC (5, 10, and 20 mg/kg b.w) cotreated, and DMC (20 mg/kg b.w) alone treated groups.

Results:

Based on the dopamine concentration and biochemical estimations, the effective dose of DMC was selected and the chronic study was performed. At the end of the experimental period, behavioral studies and protein expression patterns of inflammatory markers were analyzed. Rotenone treatment led to motor dysfunctions, neurochemical deficits, and oxidative stress and enhanced expressions of inflammatory markers, whereas oral administration of DMC attenuated all the above.

Conclusion:

Even though further research is needed to prove its efficacy in clinical trial, the results of our study showed that DMC may offer a promising and new therapeutic lead for the treatment of NDDs including PD.

SUMMARY

Curcumin and their derivatives have been shown to be potent neuroprotective effect

Demethoxycurcumin (DMC) amolerated the rotenone induced behavioural alterations

DMC abrogated the rotenone induced dopamine deficits

DMC attenuated the rotenone induced oxidative stress

DMC diminished the rotenone mediated inflammation.

Abbreviations used: COX-2: Cyclooxygenase-2; DA: Dopamine; DMC: Demethoxycurcumin; DMRT: Duncan's multiple range test; GSH: Reduced glutathione; GPx: Glutathione peroxidase; IL-1 β: Interleukin-1 β; IL-6: Interleukin-6; iNOS: Inducible nitric oxide synthase; PD: Parkinson's disease; SN: Substantia nigra; SOD: Superoxide dismutase; TBARS: Thiobarbituric acid reactive substances; TNF-α: Tumor necrosis factor-α.

Neuroprotective Effects of Eexenatide in a Rotenone-Induced Rat Model of Parkinson's Disease

BACKROUND

Several studies suggest an association between Parkinson's disease (PD) and type 2 diabetes mellitus; these 2 diseases are both known to affect the common molecular pathways. As a synthetic agonist for the glucagon-like peptide 1 receptor, exenatide has been evaluated as a neuroprotective agent in multiple animal models. Rotenone models of PD have great potential for the investigation of PD pathology and motor and nonmotor symptoms, as well as the role of gene-environment interactions in PD causation and pathogenesis. Therefore, in this study, the neurochemical, behavioral and histologic effects of exenatide on a rotenone-induced rat model of PD were examined.

MATERIALS AND METHODS

Eighteen adult male rats were randomly divided into the following 3 groups (n = 6): 1 group received stereotaxical infusion of dimethyl sulfoxide (vehicle, group 1) and the others received stereotaxical infusion of rotenone (groups 2 and 3). Apomorphine-induced rotation test was applied to the rats after 10 days. Thereafter, group 2 was administered isotonic saline, whereas group 3 was administered exenatide for 28 days.

RESULTS

Malondialdehyde and tumor necrosis factor alpha levels increased in the rats with PD induced by rotenone, whereas malondialdehyde and tumor necrosis factor alpha levels markedly decreased in the rats treated with exenatide. The apomorphine-induced rotation test scores of exenatide-treated rats were determined to be lower compared with the untreated group. Additionally, treatment with exenatide significantly reduced the loss of dopaminergic neurons in striatum.

CONCLUSIONS

These results have shown that exenatide has neuroprotective, anti-inflammatory and antioxidant effects in a rotenone-induced rat model of PD.

Asiaticoside: Attenuation of rotenone induced oxidative burden in a rat model of hemiparkinsonism by maintaining the phosphoinositide-mediated synaptic integrity

Asiaticoside (AS), a triterpenoid saponin isolated from the Indian medicinal herb Centella asiatica is known to exert a neuroprotective effect by attenuating the neurobehavioral, neurochemical and pathological changes in animal models. However, its potential neuroprotection in rotenone-induced hemiparkinsonism which implicates phospholipid-mediated neurotransmission remains unclear. Therefore, we have investigated the neuroprotective effects of AS in rat model of ROT-infused hemiparkinsonism with respect to phosphoinositides-assisted cytodynamics and synaptic function. Adult male Sprague-Dawley rats (250-300g) were distributed randomly into 6 groups, with 6 rats in each group: Sham control, Vehicle control (DMSO-0.1%), ROT-infused group (6μg/μl/kg), AS-treated group (50mg/kg/day), Drug (AS) control and Levodopa (l-DOPA)-treated group (6mg/kg/day). At the end of the experimental period, the rats were sacrificed after performing behavioral analyses and the striatum regions were dissected out. Phosphoinositides (PI) are involved in intrinsic membrane signals that regulate intracellular membrane trafficking vesicle and endocytosis. We have assessed mRNA and protein expressions of genes involved in PI-mediated signaling and also in synaptic function (PI3K, PDK 1, PEBP, Stx 1A and TH) in addition to the levels of neurotransmitters and the enzymatic antioxidant profile. AS caused an improved working memory and motor co-ordination in the ROT group. It alters the levels of neurotransmitters (p<0.01), the expression of mRNA and protein assessed which were significantly affected (P<0.001) by rotenone, thus exhibiting its intervention in the progression of neurodegeneration. We demonstrate that AS can mediate distinct function in PI-assisted vesicle endocytosis, cytoprotective signaling and in the synaptic function thereby mitigating the ROT-infused hemiparkinsonism, however, its specific regulatory role remains to be unraveled.

Intranasal Administration of Rotenone to Mice Induces Dopaminergic Neurite Degeneration of Dopaminergic Neurons in the Substantia Nigra

Exposure to environmental neurotoxins is suspected to be a risk factor for sporadic progressive neurodegenerative diseases. Parkinson's disease has been associated with exposure to the pesticide rotenone, a mitochondrial respiration inhibitor. We previously reported that intranasal administration of rotenone in mice induced dopaminergic (DA) neurodegeneration in the olfactory bulb (OB) and reduced olfactory functions. In the present study, we investigated the DA neurons in the brains of mice that were administered rotenone intranasally for an extended period. We found that the olfactory function of mice was attenuated by rotenone administration. Electrophysiological analysis of the mitral cells, which are output neurons in the OB, revealed that the inhibitory input into the mitral cells was retarded. In the immunohistochemical analysis, neurite degeneration of DA neurons in the substantia nigra was observed in rotenone-administered mice, indicating that rotenone progressively initiated the degeneration of cerebral DA neurons via the nasal route.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has a neuroprotective function in dopamine-based neurodegeneration in rat and snail parkinsonian models

Pituitary adenylate cyclase-activating polypeptide (PACAP) rescues dopaminergic neurons from neurodegeneration and improves motor changes induced by 6-hydroxy-dopamine (6-OHDA) in rat parkinsonian models. Recently, we investigated the molecular background of the neuroprotective effect of PACAP in dopamine (DA)-based neurodegeneration using rotenone-induced snail and 6-OHDA-induced rat models of Parkinson's disease. Behavioural activity, monoamine (DA and serotonin), metabolic enzyme (S-COMT, MB-COMT and MAO-B) and PARK7 protein concentrations were measured before and after PACAP treatment in both models. Locomotion and feeding activity were decreased in rotenone-treated snails, which corresponded well to findings obtained in 6-OHDA-induced rat experiments. PACAP was able to prevent the behavioural malfunctions caused by the toxins. Monoamine levels decreased in both models and the decreased DA level induced by toxins was attenuated by ∼50% in the PACAP-treated animals. In contrast, PACAP had no effect on the decreased serotonin (5HT) levels. S-COMT metabolic enzyme was also reduced but a protective effect of PACAP was not observed in either of the models. Following toxin treatment, a significant increase in MB-COMT was observed in both models and was restored to normal levels by PACAP. A decrease in PARK7 was also observed in both toxin-induced models; however, PACAP had a beneficial effect only on 6-OHDA-treated animals. The neuroprotective effect of PACAP in different animal models of Parkinson's disease is thus well correlated with neurotransmitter, enzyme and protein levels. The models successfully mimic several, but not all etiological properties of the disease, allowing us to study the mechanisms of neurodegeneration as well as testing new drugs. The rotenone and 6-OHDA rat and snail in vivo parkinsonian models offer an alternative method for investigation of the molecular mechanisms of neuroprotective agents, including PACAP.

Summary: PACAP has a neuroprotective effect in different toxin-induced rat and snail parkinsonian models, acting partially through the same mechanisms.

Amelioration of apoptotic events in the skeletal muscle of intra-nigrally rotenone-infused Parkinsonian rats by Morinda citrifolia--up-regulation of Bcl-2 and blockage of cytochrome c release

Parkinson's disease is a progressive neurodegenerative movement disorder with the cardinal symptoms of bradykinesia, resting tremor, rigidity, and postural instability, which lead to abnormal movements and lack of activity, which in turn cause muscular damage. Even though studies have been carried out to elucidate the causative factors that lead to muscular damage in Parkinson's disease, apoptotic events that occur in the skeletal muscle and a therapeutical approach to culminate the muscular damage have not been extensively studied. Thus, this study evaluates the impact of rotenone-induced SNPc lesions on skeletal muscle apoptosis and the efficacy of an ethyl acetate extract of Morinda citrifolia in safeguarding the myocytes. Biochemical assays along with apoptotic markers studied by immunoblot and reverse transcription-polymerase chain reaction in the current study revealed that the supplementation of Morinda citrifolia significantly reverted alterations in both biochemical and histological parameters in rotenone-infused PD rats. Treatment with Morinda citrifolia also reduced the expression of pro-apoptotic proteins Bax, caspase-3 and caspase-9 and blocked the release of cytochrome c from mitochondria induced by rotenone. In addition, it augmented the expression of Bcl2 both transcriptionally and translationally. Thus, this preliminary study paves a way to show that the antioxidant and anti-apoptotic activities of Morinda citrifolia can be exploited to alleviate skeletal muscle damage induced by Parkinsonism.

Morinda citrifolia mitigates rotenone-induced striatal neuronal loss in male Sprague-Dawley rats by preventing mitochondrial pathway of intrinsic apoptosis

OBJECTIVES

Parkinson disease (PD) is a neurodegenerative disorder affecting mainly the motor system, as a result of death of dopaminergic neurons in the substantia nigra pars compacta. The present scenario of research in PD is directed to identify novel molecules that can be administered individually or co-administered with L-Dopa to prevent the L-Dopa-Induced Dyskinesia (LID) like states that arise during chronic L-Dopa administration. Hence, in this study, we investigated whether Morinda citrifolia has therapeutic effects in rotenone-induced Parkinson's disease (PD) with special reference to mitochondrial dysfunction mediated intrinsic apoptosis.

METHODS

Male Sprague-Dawley rats were stereotaxically infused with rotenone (3 µg in both SNPc and VTA) and co-treated with the ethyl acetate extract of Morinda citrifolia and levodopa.

RESULTS

The results revealed that rotenone-induced cell death was reduced by MCE treatment as measured by decline in the levels of pro-apoptotic proteins. Moreover, MCE treatment significantly augmented the levels of anti-apoptotic Bcl2 and blocks the release of cytochrome c, thereby alleviating the rotenone-induced dopaminergic neuronal loss, as evidenced by tyrosine hydroxylase (TH) immunostaining in the striatum.

DISCUSSION

Taken together, the results suggest that Morinda citrifolia may be beneficial for the treatment of neurodegenerative diseases like PD.

Sulforaphane protects against rotenone-induced neurotoxicity in vivo: Involvement of the mTOR, Nrf2, and autophagy pathways

Sulforaphane, a naturally occurring compound found in cruciferous vegetables, has been shown to be neuroprotective in several neurological disorders. In this study, we sought to investigate the potential protective effects and associated molecular mechanisms of sulforaphane in an in vivo Parkinson's disease (PD) model, based on rotenone-mediated neurotoxicity. Our results showed that sulforaphane inhibited rotenone-induced locomotor activity deficiency and dopaminergic neuronal loss. Additionally, sulforaphane treatment inhibited the rotenone-induced reactive oxygen species production, malondialdehyde (MDA) accumulation, and resulted in an increased level of total glutathione and reduced glutathione (GSH): oxidized glutathione (GSSG) in the brain. Western blot analysis illustrated that sulforaphane increased the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H quinone oxidoreductase (NQO1), the latter two of which are anti-oxidative enzymes. Moreover, sulforaphane treatment significantly attenuated rotenone-inhibited mTOR-mediated p70S6K and 4E-BP1 signalling pathway, as well as neuronal apoptosis. In addition, sulforaphane rescued rotenone-inhibited autophagy, as detected by LC3-II. Collectively, these findings demonstrated that sulforaphane exert neuroprotective effect involving Nrf2-dependent reductions in oxidative stress, mTOR-dependent inhibition of neuronal apoptosis, and the restoration of normal autophagy. Sulforaphane appears to be a promising compound with neuroprotective properties that may play an important role in preventing PD.

Thiol Oxidation by Diamide Leads to Dopaminergic Degeneration and Parkinsonism Phenotype in Mice: A Model for Parkinson's Disease

AIMS

This study investigates the role of thiol homeostasis disruption in Parkinson's disease (PD) pathogenesis using a novel animal model. A single unilateral administration of the thiol oxidant, diamide (1.45 μmol) into substantia nigra (SN) of mice leads to locomotor deficits and degeneration of dopaminergic (DA) neurons in SN pars compacta (SNpc).

RESULTS

Diamide-injected mice showed hemiparkinsonian behavior, measured as spontaneous contralateral body rotations, poor grip strength, and impaired locomotion on a rotarod. We observed a significant loss of DA neurons in ipsilateral but not contralateral SNpc and their striatal fibers. This was accompanied by increased Fluoro-Jade C-positive cells and a loss of NeuN-positive neurons, indicative of neurodegeneration. Importantly, diamide injection led to α-synuclein aggregation in ipsilateral SNpc, a hallmark of PD pathology not often seen in animal models of PD. On investigating putative mechanism(s) involved, we observed a loss of glutathione, which is essential for maintaining protein thiol homeostasis (PTH). Concomitantly, the redox-sensitive ASK1-p38 mitogen-activated protein kinase (MAPK) death signaling pathway was activated in the ipsilateral but not contralateral ventral midbrain through dissociation of ASK1-Trx1 complex. In Neuro-2a cells, diamide activated ASK1-p38 cascade through Trx1 oxidation, leading to cell death, which was abolished by ASK1 knockdown.

INNOVATION

Since diamide selectively disrupts PTH, DA neurons appear to be vulnerable to such perturbations and even a single insult with a thiol oxidant can result in long-lasting degeneration.

CONCLUSION

Identification of the role of PTH dysregulation in neurodegeneration, especially in early PD, not only facilitates an understanding of novel regulatory features of molecular signaling cascades but also may aid in developing disease-modifying strategies for PD. Antioxid. Redox Signal. 25, 252-267.

Levetiracetam attenuates rotenone-induced toxicity: A rat model of Parkinson's disease

Levetiracetam (LEV), a second-generation anti-epileptic drug, is used for treatment of both focal and generalized epilepsy. Growing body of evidence suggests that LEV may have neuroprotective effects. The present study was undertaken to investigate the neuroprotective effects of LEV on rotenone-induced Parkinson's disease (PD) in rats. Twenty-four adult Sprague-Dawley rats were infused with rotenone (3 μg/μl in DMSO) or vehicle (1 μl DMSO) into the left substantia nigra pars compacta (SNc) under stereotaxic surgery. PD model was assessed by rotational test ten days after drug infusion. The valid PD rats were randomly distributed into two groups; Group 1 (n=8) and Group 2 (n=8) were administered saline (1 ml/kg/day, i.p.) and LEV (600 mg/kg/day, i.p.) through 21 days, respectively. The effects of LEV treatment were evaluated by behavioral (rotation score), biochemical (brain homovalinic acid level and oxidant/antioxidant status) and immunohistochemical (tyrosine hydroxylase) parameters. Apomorphine-induced rotations in PD rats were significantly suppressed by LEV treatment. While unilateral rotenone lesion induced a dramatic loss of dopaminergic neurons both in the striatum and SNc, LEV treatment significantly attenuated the degenerative changes in dopaminergic neurons. Furthermore, LEV significantly decreased lipid peroxide levels, a marker of lipid peroxidation, and induced glutathione levels, catalase and superoxide dismutase activity in PD rats compared with saline group. We conclude that LEV may have beneficial effects on dopaminergic neurons against rotenone-induced injury. The underlying mechanism may be associated with the attenuation of oxidative stress.

Evaluation of Models of Parkinson's Disease

Parkinson's disease is one of the most common neurodegenerative diseases. Animal models have contributed a large part to our understanding and therapeutics developed for treatment of PD. There are several more exhaustive reviews of literature that provide the initiated insights into the specific models; however a novel synthesis of the basic advantages and disadvantages of different models is much needed. Here we compare both neurotoxin based and genetic models while suggesting some novel avenues in PD modeling. We also highlight the problems faced and promises of all the mammalian models with the hope of providing a framework for comparison of various systems.

Lithium protects dopaminergic cells from rotenone toxicity via autophagy enhancement

Background

Previous studies have indicated that enhancement of autophagy lysosome pathway may be beneficial for Parkinson’s disease (PD), in which aberrant accumulation of aggregated/misfolded proteins and mitochondrial dysfunction are considered as crucial pathogenesis. Recently, a number of studies have suggested the neuroprotective effects of lithium in models of several neurodegenerative diseases including PD. However, the exact mechanisms underlying this neuroprotection remain unclear. In our study, rotenone-exposed SH-SY5Y cells were used as an in vitro parkinsonian model to assess the autophagy-enhancing effect of lithium and the underlying mechanisms were further investigated.

Results

Similar to the common used autophagy enhancer rapamycin (Rap, 0.2 μM), lithium (LiCl, 10 mM) significantly recovered the shrinkage of SH-SY5Y cells, and alleviated rotenone-induced cell apoptosis, mitochondrial membrane potential reduction and reactive oxygen species accumulation. Furthermore, the protective effects induced by LiCl were partially blocked by the co-treatment of autophagy inhibitors such as 3-methyladenine (3-MA, 10 mM) or chloroquine (CHL, 10 μM). Moreover, 3-MA or Chl suppressed LiCl-induced autophagy in the immunoblot assay. In addition, the co-localization of LC3 and mitochondria and the preservation of mitochondrial function within LiCl-treated cells were observed, confirming that the damaged mitochondria were cleared through autophagy (mitophagy).

Conclusions

These findings suggested that lithium exerted neuroprotection against rotenone-induced injuries partially through the autophagy pathway. Pharmacologically induction of autophagy by lithium may represent a novel therapeutic strategy as a disease-modifier in PD.

Tianma Gouteng Yin, a Traditional Chinese Medicine decoction, exerts neuroprotective effects in animal and cellular models of Parkinson's disease

Tianma Gouteng Yin (TGY) is a traditional Chinese medicine (TCM) decoction widely used to treat symptoms associated with typical Parkinson’s disease (PD). In this study, the neuroprotective effects of water extract of TGY were tested on rotenone-intoxicated and human α-synuclein transgenic Drosophila PD models. In addition, the neuroprotective effect of TGY was also evaluated in the human dopaminergic neuroblastoma SH-SY5Y cell line treated with rotenone and the rotenone intoxicated hemi-parkinsonian rats. In rotenone-induced PD models, TGY improved survival rate, alleviated impaired locomotor function of Drosophila, mitigated the loss of dopaminergic neurons in hemi-parkinsonian rats and alleviated apoptotic cell death in SH-SY5Y cells; in α-synuclein transgenic Drosophila, TGY reduced the level of α-synuclein and prevented degeneration of dopaminergic neurons. Conclusively, TGY is neuroprotective in PD models both in vivo and in vitro.

Animal models of Parkinson's disease: An updated overview

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology, besides a minority of genetic cases, is still largely unknown. Animal models have contributed to elucidate PD etiology and pathogenesis, as well as its cellular and molecular mechanisms, leading to the general hypothesis that this neurological disorder is due to complex interactions between environmental and genetic factors. However, the full understanding of PD is still very far from being achieved, and new potential treatments need to be tested to further improve patients' quality of life and, possibly, slow down the neurodegenerative process. In this context, animal models of PD are required to address all these issues. "Classic" models are based on neurotoxins that selectively target catecholaminergic neurons (such as 6-hydroxydopamine, 1-methyl-1,2,3,6-tetrahydropiridine, agricultural pesticides, etc.), while more recent models employ genetic manipulations that either introduce mutations similar to those find in familial cases of PD (α-synuclein, DJ-1, PINK1, Parkin, etc.) or selectively disrupt nigrostriatal neurons (MitoPark, Pitx3, Nurr1, etc.). Each one of these models has its own advantages and limitations, thus some are better suited for studying PD pathogenesis, while others are more pertinent to test therapeutic treatments. Here, we provide a critical and updated review of the most used PD models.

X-box-binding protein 1-modified neural stem cells for treatment of Parkinson's disease

X-box-binding protein 1-transfected neural stem cells were transplanted into the right lateral ventricles of rats with rotenone-induced Parkinson's disease. The survival capacities and differentiation rates of cells expressing the dopaminergic marker tyrosine hydroxylase were higher in X-box-binding protein 1-transfected neural stem cells compared to non-transfected cells. Moreover, dopamine and 3,4-dihydroxyphenylacetic acid levels in the substantia nigra were significantly increased, α-synuclein expression was decreased, and neurological behaviors were significantly ameliorated in rats following transplantation of X-box-binding protein 1-transfected neural stem cells. These results indicate that transplantation of X-box-binding protein 1-transfected neural stem cells can promote stem cell survival and differentiation into dopaminergic neurons, increase dopamine and 3,4-dihydroxyphenylacetic acid levels, reduce α-synuclein aggregation in the substantia nigra, and improve the symptoms of Parkinson's disease in rats.

The neuroprotective effect of erythropoietin on experimental Parkinson model in rats

Dopaminergic neuronal loss in Parkinson's disease (PD) results from oxidative stress, neuroinflammation and excitotoxicity. Because erythropoietin (EPO) has been shown to have antioxidant, anti-inflammatory and neuroprotective effects in many previous studies, present study was designed to evaluate the effect of EPO on rotenone-induced dopaminergic neuronal loss. The rats in which PD was induced by stereotaxical infusion of rotenone showed increased MDA and TNF-alpha levels and decreased HVA levels. On the other hand, EPO treatment resulted in markedly decreased MDA and TNF-alpha levels and increased HVA levels. EPO treatment in rotenone-infusion group resulted in improvement of striatal neurodegeneration and a significant increase in decreased total number of neurons and immunohistochemical TH positive neurons. Results of the present study demonstrate the neuroprotective, anti-inflammatory and antioxidant effects of EPO in a rotenone-induced neurodegenerative animal model.

Fenpropathrin, a Widely Used Pesticide, Causes Dopaminergic Degeneration

Fenpropathrin is one of the widely used pyrethroids in agriculture and household and also reported to have neurotoxic effects in rodent models. In our Parkinson's disease (PD) clinic, there was a unique patient with a history of daily exposure to fenpropathrin for 6 months prior to developing Parkinsonian symptoms progressively. Since whether fenpropathrin is related to any dopaminergic degeneration was unknown, we aimed in this study to evaluate the neurotoxic effects of fenpropathrin on the dopaminergic system and associated mechanisms in vitro and in vivo. In cultured SH-SY5Y cells, fenpropathrin caused cell death, reactive oxygen species generation, Lewy body-associated proteins aggregation, and Lewy body-like intracytoplasmic inclusions formation. In rodent animals, two different injections of fenpropathrin were used for administrations, intraperitoneal (i.p), or stereotaxical (ST). The rats exhibited lower number of pokes 60 days after first i.p injection, while the rats in ST group showed a significant upregulation of apomorphine-evoked rotations 60 days after first injection. Decreased tyrosine hydroxylase (TH) and vesicular monoamine transporter 2 (VMAT2) immunoreactivity, while increased dopamine transporter (DAT) immunoreactivity were observed in rats of either i.p or ST group 60 days after the last exposure to fenpropathrin. However, the number of TH-positive cells in the substantia nigra was more reduced 120 days after the first i.p injection than those of 60 days. Our data demonstrated that exposure to fenpropathrin could mimic the pathologic and pathogenetic features of PD especially in late onset cases. These results imply fenpropathrin as a DA neurotoxin and a possible environmental risk factor for PD.

Parkinson's disease: animal models and dopaminergic cell vulnerability

Parkinson's disease (PD) is a neurodegenerative disorder that affects about 1.5% of the global population over 65 years of age. A hallmark feature of PD is the degeneration of the dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the consequent striatal DA deficiency. Yet, the pathogenesis of PD remains unclear. Despite tremendous growth in recent years in our knowledge of the molecular basis of PD and the molecular pathways of cell death, important questions remain, such as: (1) why are SNc cells especially vulnerable; (2) which mechanisms underlie progressive SNc cell loss; and (3) what do Lewy bodies or α-synuclein reveal about disease progression. Understanding the variable vulnerability of the dopaminergic neurons from the midbrain and the mechanisms whereby pathology becomes widespread are some of the primary objectives of research in PD. Animal models are the best tools to study the pathogenesis of PD. The identification of PD-related genes has led to the development of genetic PD models as an alternative to the classical toxin-based ones, but does the dopaminergic neuronal loss in actual animal models adequately recapitulate that of the human disease? The selection of a particular animal model is very important for the specific goals of the different experiments. In this review, we provide a summary of our current knowledge about the different in vivo models of PD that are used in relation to the vulnerability of the dopaminergic neurons in the midbrain in the pathogenesis of PD.

An update on the rotenone models of Parkinson's disease: their ability to reproduce the features of clinical disease and model gene-environment interactions

Parkinson's disease (PD) is the second most common neurodegenerative disorder that is characterized by two major neuropathological hallmarks: the degeneration of dopaminergic neurons in the substantia nigra (SN) and the presence of Lewy bodies in the surviving SN neurons, as well as other regions of the central and peripheral nervous system. Animal models have been invaluable tools for investigating the underlying mechanisms of the pathogenesis of PD and testing new potential symptomatic, neuroprotective and neurorestorative therapies. However, the usefulness of these models is dependent on how precisely they replicate the features of clinical PD with some studies now employing combined gene-environment models to replicate more of the affected pathways. The rotenone model of PD has become of great interest following the seminal paper by the Greenamyre group in 2000 (Betarbet et al., 2000). This paper reported for the first time that systemic rotenone was able to reproduce the two pathological hallmarks of PD as well as certain parkinsonian motor deficits. Since 2000, many research groups have actively used the rotenone model worldwide. This paper will review rotenone models, focusing upon their ability to reproduce the two pathological hallmarks of PD, motor deficits, extranigral pathology and non-motor symptoms. We will also summarize the recent advances in neuroprotective therapies, focusing on those that investigated non-motor symptoms and review rotenone models used in combination with PD genetic models to investigate gene-environment interactions.

Cell cycle regulation of DNA polymerase beta in rotenone-based Parkinson's disease models

In Parkinson's disease (PD), neuronal cells undergo mitotic catastrophe and endoreduplication prior to cell death; however, the regulatory mechanisms remain to be defined. In this study, we investigated cell cycle regulation of DNA polymerase β (poly β) in rotenone-based dopaminergic cellular and animal models. Incubation with a low concentration (0.25 µM) of rotenone for 1.5 to 7 days resulted in a flattened cell body and decreased DNA replication during S phase, whereas a high concentration (2 µM) of rotenone exposure resulted in enlarged, multi-nucleated cells and converted the mitotic cycle into endoreduplication. Consistently, DNA poly β, which is mainly involved in DNA repair synthesis, was upregulated to a high level following exposure to 2 µM rotenone. The abrogation of DNA poly β by siRNA transfection or dideoxycytidine (DDC) treatment attenuated the rotenone-induced endoreduplication. The cell cycle was reactivated in cyclin D-expressing dopaminergic neurons from the substantia nigra (SN) of rats following stereotactic (ST) infusion of rotenone. Increased DNA poly β expression was observed in the substantia nigra pars compacta (SNc) and the substantia nigra pars reticulate (SNr) of rotenone-treated rats. Collectively, in the in vitro model of rotenone-induced mitotic catastrophe, the overexpression of DNA poly β promotes endoreduplication; in the in vivo model, the upregulation of DNA poly β and cell cycle reentry were also observed in the adult rat substantia nigra. Therefore, the cell cycle regulation of DNA poly β may be involved in the pathological processes of PD, which results in the induction of endoreduplication.

Puerarin protects dopaminergic neurons in Parkinson's disease models

It has been acknowledged that oxidative stress, resulting in the apoptosis of dopaminergic neurons, is a key mechanism in the pathogenesis of Parkinson's disease (PD). Puerarin, extracted from the root of pueraria lobata, has been clinically used for ischemic heart disease and cerebrovascular diseases as an oxygen free radical scavenger. In this study, we aimed to explore the effect of puerarin on dopaminergic cell degeneration in vitro and in vivo and its possible underlying mechanisms. In SH-SY5Y cells, the reduction of cell viability, apoptosis rate and average DCFH-DA fluorescence intensity of puerarin-treated (0, 10, 50, 100 and 150 μM) cells were significantly lower than control group. In rotenone-based rodent models, puerarin treatment for 7 days ameliorated apomorphine-induced rotations significantly in Pue-50 and Pue-100 group by 45.65% and 53.06% in the first week, by 44.60% and 48.45% in the second week. Moreover, compared to control group, puerarin increased tyrosine hydroxylase (TH) expression in the substantia nigra by 85.52% and 84.26% in Pue-50 group and Pue-100 group, and upregulated the vesicular monoamine transporter 2 (VMAT2) by 41.24% in Pue-50 group and 35.20% in Pue-100 group, and decreased ubiquitin expression by 47.55% in Pue-50 group and 69.15% in Pue-100 group. These data indicated that puerarin alleviated the oxidative stress and apoptosis in a PD cellular model, protected the dopaminergic neurons against rotenone toxicity and decreased the abnormal protein overexpressing in PD animal models. These findings suggest that puerarin may develop into a neuroprotective alternative for patients with PD.

Dopamine Cytotoxicity Involves Both Oxidative and Nonoxidative Pathways in SH-SY5Y Cells: Potential Role of Alpha-Synuclein Overexpression and Proteasomal Inhibition in the Etiopathogenesis of Parkinson's Disease

Background. The cytotoxic effects of dopamine (DA) on several catecholaminergic cell lines involve DA oxidation products like reactive oxygen species (ROS) and toxic quinones and have implications in the pathogenesis of sporadic Parkinson's disease (PD). However, many molecular details are yet to be elucidated, and the possible nonoxidative mechanism of dopamine cytotoxicity has not been studied in great detail. Results. Cultured SH-SY5Y cells treated with DA (up to 400 μM) or lactacystin (5 μM) or DA (400 μM) plus N-acetylcysteine (NAC, 2.5 mM) for 24 h are processed accordingly to observe the cell viability, mitochondrial dysfunctions, oxidative stress parameters, proteasomal activity, expression of alpha-synuclein gene, and intracellular accumulation of the protein. DA causes mitochondrial dysfunction and extensive loss of cell viability partially inhibited by NAC, potent inhibition of proteasomal activity marginally prevented by NAC, and overexpression with accumulation of intracellular alpha-synuclein partially preventable by NAC. Under similar conditions of incubation, NAC completely prevents enhanced production of ROS and increased formation of quinoprotein adducts in DA-treated SH-SY5Y cells. Separately, proteasomal inhibitor lactacystin causes accumulation of alpha-synuclein as well as mitochondrial dysfunction and cell death. Conclusions. DA cytotoxicity includes both oxidative and nonoxidative modes and may involve overexpression and accumulation of alpha-synuclein as well as proteasomal inhibition.

Neuroprotection by valproic acid in an intrastriatal rotenone model of Parkinson's disease

Rotenone, which is used as a pesticide and insecticide, has been shown to cause systemic inhibition of mitochondrial complex I activity, with consequent degeneration of dopaminergic neurons within the substantia nigra and striatum, as observed in Parkinson's disease. A novel intrastriatal rotenone model of Parkinson's disease was used to examine the neuroprotective effects of valproic acid (VPA), which is known to upregulate neurotrophic factors and other protective proteins in the brain. Sham or lesioned rats were treated with either vehicle or VPA at a dose of 4mg/mL in drinking water. The right striatum was lesioned by infusion of rotenone at three sites (2μg/site) along its rostro-caudal axis. A forelimb asymmetry (cylinder) test indicated a significant (p<0.01) decrease in use of the contralateral forelimb in rotenone-lesioned animals, in the third week post-lesioning, which was abolished by VPA treatment. Similarly, a significant (p<0.01) and persistent increase in use of the ipsilateral forelimb in lesioned animals over the 4weeks of testing, was not seen in animals treated with VPA. Results of the asymmetry test illustrate that intrastriatal infusion of rotenone causes contralateral motor dysfunction, which is blocked by VPA. The significant increase in ipsilateral forelimb use has not been documented previously, and presumably represents a compensatory response in lesioned animals. Six weeks post-surgery, animals were sacrificed by transcardial perfusion. Subsequent immunohistochemical examination revealed a decrease in tyrosine hydroxylase immunoreactivity within the striatum and substantia nigra of rotenone-lesioned animals. VPA treatment attenuated the decrease in tyrosine hydroxylase in the striatum and abolished it in the substantia nigra. Stereological cell counting indicated a significant (p<0.05) decrease in tyrosine hydroxylase-positive dopamine neurons in the substantia nigra of rotenone-lesioned animals, which was confirmed by Nissl staining. Importantly, this loss of dopamine neurons in rotenone-lesioned animals, was blocked by chronic VPA treatment. These findings strongly support the therapeutic potential of VPA in Parkinson's disease.