Subcutaneous rotenone exposure causes highly selective dopaminergic degeneration and alpha-synuclein aggregation

The neurotoxicity of pesticides: Implications for Parkinson's disease

Parkinson's disease (PD) is the fastest-growing neurodegenerative disorder worldwide, and no effective cure is currently available. Neuropathologically, PD is characterized by the selective degeneration of dopaminergic neurons in the substantia nigra and by the accumulation of alpha-synuclein (aSyn)-rich proteinaceous inclusions within surviving neurons. As a multifactorial disorder, approximately 85 % of PD cases are sporadic with unknown etiology. Among the many risk factors implicated in PD, exposure to neurotoxic pesticides stands out as a significant contributor. While the effects of many are still uncharacterized, it has already been shown that rotenone, paraquat, maneb, and dieldrin affect critical cellular pathways, including mitochondrial and proteasomal dysfunction, aSyn aggregation, autophagy dysregulation, and disruption of dopamine metabolism. With the constant rise in pesticide usage to meet the demands of a growing human population, the risk of environmental contamination and subsequent PD development is also increasing. This review explores the molecular mechanisms by which pesticide exposure influences PD development, shedding light on their role in the pathogenesis of PD and highlighting the need for preventative measures and regulatory oversight to mitigate these risks.

Rotenone Exposure During Development Conditions Parkinsonian Phenotype in Young Adult Rats

Current studies suggest that environmental toxins may play a significant role in the fetal origins of Parkinson's disease (PD). Significant evidence from animal experiments has demonstrated that these toxins can disrupt fetal neurodevelopment. PD is a neurodegenerative disorder related to the loss of dopaminergic neurons in the substantia nigra pars compacta (S. nigra) and accumulation of α-synuclein (α-syn) in the brain. Parkinson's disease has long been associated with an idiopathic etiology, with environmental or ontogenetic factors as causes; however, the list of causal agents continues to expand as their effects are investigated at different stages of development. To explore the potential ontogenetic origins of PD, we exposed female rats subcutaneously (s.c.) to 1 mg/kg of the pesticide rotenone (ROT)-21 days during gestation, 21 days of breastfeeding, or 42 days in both periods-and assessed its long-term effects on their pups in adulthood. Our findings reveal that ROT exposure induces the degeneration of dopaminergic neurons in the S. nigra of adult rats. We administered ROT to dams during specific developmental stages and examined the nigrostriatal pathway and its functionality in offspring upon reaching young adulthood. Our results showed that perinatal ROT exposure led to (1) diminished motor skills, (2) greater concentrations of α-syn in the caudate nucleus (C. nucleus) and S. nigra, (3) reduced numbers of tyrosine hydroxylase immunoreactive neurons, and (4) hypomethylation of global 5-methylcytosine DNA compared to control rats at 60 days of age. The effects were more pronounced in rats exposed to ROT in utero and in both the in utero and breastfeeding periods, with fewer effects observed in those exposed only during breastfeeding. Thus, our findings suggest that exposure to ROT during the early developmental stages predisposes rats to Parkinsonian symptoms later in adulthood.

Xenotopic synthetic biology: Prospective tools for delaying aging and age-related diseases

Metabolic dysregulation represents one of the major driving forces in aging. Although multiple genetic and pharmacological manipulations are known to extend longevity in model organisms, aging is a complex trait, and targeting one's own genes may be insufficient to prevent age-dependent deterioration. An alternative strategy could be to use enzymes from other species to reverse age-associated metabolic changes. In this review, we discuss a set of enzymes from lower organisms that have been shown to affect various metabolic parameters linked to age-related processes. These enzymes include modulators of steady-state levels of amino acids (METase, ASNase, and ADI), NADPH/NADP+ and/or reduced form of coenzyme Q (CoQH2)/CoQ redox potentials (NDI1, AOX, LbNOX, TPNOX, EcSTH, RquA, LOXCAT, Grubraw, and ScURA), GSH (StGshF), mitochondrial membrane potential (mtON and mito-dR), or reactive oxygen species (DAAO and KillerRed-SOD1). We propose that leveraging non-mammalian enzymes represents an untapped resource that can be used to delay aging and age-related diseases.

Shikonin Ameliorates Rotenone-Induced Neurotoxicity Through Inhibition of Apoptosis via IGF-1R/PI3K/AKT Pathway in a Parkinson's Disease-Associated SH-SY5Y Cell Model

Parkinson's disease (PD) is the second most common multifactorial neurodegenerative disorder caused by several genetics and environmental factors. Rotenone a pesticide with mitotoxicity causes cytosolic proteopathy resulting in PD-associated apoptosis and modulations in cell survival pathways. Shikonin, a naphthoquinone compound extracted from the Lithospermum erythrorhizon herb, was investigated in this study for its neuroprotective properties and underlying molecular mechanisms against rotenone-induced cellular apoptosis and survival in SH-SY5Y cells. The molecular docking analysis of apoptotic proteins against Shikonin revealed that they showed a binding affinity with BAD. Shikonin effectively countered the loss of cell viability induced by rotenone, rescued annexin-positive apoptotic cells, and dose-dependently suppressed the generation of reactive oxygen species. Pre-treatment with Shikonin prevented the morphological aberrations like shrining of neurites leading to decreased LDH leakage and NO release caused due to the rotenone treatment. The α-synucleinopathy is a prime hallmark of PD, Shikonin mitigated the rotenone-induced aggregation of α-synuclein as seen from confocal imaging. Furthermore, Shikonin treatment reversed the rotenone-induced excessive production of reactive oxygen species, activation of caspases (-8 and -3), and mitochondrial dysfunction, as evidenced by the restoration of mitochondrial membrane potential and cellular ATP levels. Western blot and qPCR analysis revealed that Shikonin heightened the IGF1R/PI3K/AKT signaling associated with cell survival while concurrently downregulating rotenone-induced intrinsic apoptotic pathways. These findings underscore Shikonin as a promising candidate to prevent the onset of pesticide-induced Parkinson's disease and potentially other oxidative stress-related neurodegenerative disorders.

Monoamine Oxidase Inhibitors in Toxic Models of Parkinsonism

Monoamine oxidase inhibitors are widely used for the symptomatic treatment of Parkinson's disease (PD). They demonstrate antiparkinsonian activity in different toxin-based models induced by 6-hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and pesticides (rotenone and paraquat). In some models, such as MPTP-induced PD, MAO inhibitors prevent the formation of the neurotoxin MPP+ from the protoxin MPTP. Regardless of the toxin's nature, potent MAO inhibitors prevent dopamine loss reduction, the formation of hydrogen peroxide, hydrogen peroxide signaling, and the accumulation of hydrogen peroxide-derived reactive oxygen species responsible for the development of oxidative stress. It becomes increasingly clear that some metabolites of MAO inhibitors (e.g., the rasagiline metabolite 1-R-aminoindan) possess their own bio-pharmacological activities unrelated to the parent compound. In addition, various MAO inhibitors exhibit multitarget action, in which MAO-independent effects prevail. This opens new prospects in the development of novel therapeutics based on simultaneous actions on several prospective targets for the therapy of PD.

A rotenone organotypic whole hemisphere slice model of mitochondrial abnormalities in the neonatal brain

Mitochondrial abnormalities underscore a variety of neurologic injuries and diseases and are well-studied in adult populations. Clinical studies identify critical roles of mitochondria in a wide range of developmental brain injuries, but models that capture mitochondrial abnormalities in systems representative of the neonatal brain environment are lacking. Here, we develop an organotypic whole-hemisphere (OWH) brain slice model of mitochondrial dysfunction in the neonatal brain. We extended the utility of complex I inhibitor rotenone (ROT), canonically used in models of adult neurodegenerative diseases, to inflict mitochondrial damage in OWH slices from term-equivalent rats. We quantified whole-slice health over 6 days of exposure for a range of doses represented in ROT literature. We identified 50 nM ROT as a suitable exposure level for OWH slices to inflict injury without compromising viability. At the selected exposure level, we confirmed exposure- and time-dependent mitochondrial responses showing differences in mitochondrial fluorescence and nuclear localization using MitoTracker imaging in live OWH slices and dysregulated mitochondrial markers via RT-qPCR screening. We leveraged the regional structures present in OWH slices to quantify cell density and cell death in the cortex and the midbrain regions, observing higher susceptibilities to damage in the midbrain as a function of exposure and culture time. We supplemented these findings with analysis of microglia and mature neurons showing time-, region-, and exposure-dependent differences in microglial responses. We demonstrated changes in tissue microstructure as a function of region, culture time, and exposure level using live-video epifluorescence microscopy of extracellularly diffusing nanoparticle probes in live OWH slices. Our results highlight severity-, time-, and region-dependent responses and establish a complimentary model system of mitochondrial abnormalities for high-throughput or live-tissue experimental needs.

Navigating the Neurobiology of Parkinson's: The Impact and Potential of α-Synuclein

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease worldwide; therefore, since its initial description, significant progress has been made, yet a mystery remains regarding its pathogenesis and elusive root cause. The widespread distribution of pathological α-synuclein (αSyn) aggregates throughout the body raises inquiries regarding the etiology, which has prompted several hypotheses, with the most prominent one being αSyn-associated proteinopathy. The identification of αSyn protein within Lewy bodies, coupled with genetic evidence linking αSyn locus duplication, triplication, as well as point mutations to familial Parkinson's disease, has underscored the significance of αSyn in initiating and propagating Lewy body pathology throughout the brain. In monogenic and sporadic PD, the presence of early inflammation and synaptic dysfunction leads to αSyn aggregation and neuronal death through mitochondrial, lysosomal, and endosomal functional impairment. However, much remains to be understood about αSyn pathogenesis, which is heavily grounded in biomarkers and treatment strategies. In this review, we provide emerging new evidence on the current knowledge about αSyn's pathophysiological impact on PD, and its presumable role as a specific disease biomarker or main target of disease-modifying therapies, highlighting that this understanding today offers the best potential of disease-modifying therapy in the near future.

Mapping the research of mitochondria and Parkinson's disease: a bibliometric analysis

Background

Parkinson's disease (PD) is a chronic, progressive neurodegenerative disorder primarily affecting the elderly. Relevant studies suggest a significant connection between the mitochondria and PD. Publications exploring this connection have steadily increased in recent years. This study employs a bibliometric approach to comprehensively analyze the current status and future directions of the research on mitochondria and PD.

Method

We retrieved data from the Web of Science database and used CiteSpace, VOSviewer, and "Bibliometrix" software to visually analyze various aspects of the research field. These aspects included the number of published papers, contributing countries and institutions, authors, publishing journals, cited references, and keywords.

Results

Our analysis identified a total of 3,291 publications involving 14,670 authors from 2,836 organizations across 78 countries. The publication volume exhibited a continuous upward trend from 1999 to 2023. The United States emerged as the leading force in this research area, contributing the highest number of high-quality publications. Notably, the United States collaborated extensively with Germany and the United Kingdom. The University of Pittsburgh stood out as the most prolific institution. Harvard University had the highest academic influence and closely cooperated with the University of Pittsburgh, Juntendo University, and McGill University. Dr. Hattori Nobutaka was identified as the most prolific author, while Dr. Youle, Richard J emerged as the most influential author based on the highest average citation frequency. The Journal of Neurochemistry was the most published journal. The most co-cited paper was titled "Hereditary early-onset Parkinson's disease caused by mutations in PINK1." The major keywords included oxidative stress, alpha-synuclein, pink1, mitophagy, and mitochondrial dysfunction. Mitofusin 2, ubiquitin, and mitochondrial quality control have been identified as new research hotspots in recent years.

Conclusion

Mitochondria-PD research is experiencing a steady increase in activity, fueled by increasing close collaboration between countries and different institutions. However, there is a need to further strengthen collaboration and communication between developed and developing nations. Current research has focused on the specific mechanisms of mitochondrial dysfunction and their relationship with PD. Mitofusin 2, ubiquitin, and mitochondrial quality control are positioned to be the hotspots and future research directions.

Construct, Face, and Predictive Validity of Parkinson's Disease Rodent Models

Parkinson's disease (PD) is the second most common neurodegenerative disease globally. Current drugs only alleviate symptoms without halting disease progression, making rodent models essential for researching new therapies and understanding the disease better. However, selecting the right model is challenging due to the numerous models and protocols available. Key factors in model selection include construct, face, and predictive validity. Construct validity ensures the model replicates pathological changes seen in human PD, focusing on dopaminergic neurodegeneration and a-synuclein aggregation. Face validity ensures the model's symptoms mirror those in humans, primarily reproducing motor and non-motor symptoms. Predictive validity assesses if treatment responses in animals will reflect those in humans, typically involving classical pharmacotherapies and surgical procedures. This review highlights the primary characteristics of PD and how these characteristics are validated experimentally according to the three criteria. Additionally, it serves as a valuable tool for researchers in selecting the most appropriate animal model based on established validation criteria.

Mitochondrial transfer of α-synuclein mediates carbon disulfide-induced mitochondrial dysfunction and neurotoxicity

Exposure to carbon disulfide (CS2) is a recognized risk factor in the pathogenesis of Parkinson's disease, yet the underlying mechanisms of deleterious effects on mitochondrial integrity have remained elusive. Here, through establishing CS2 exposure models in rat and SH-SY5Y cells, we demonstrated that highly expressed α-synuclein (α-Syn) is transferred to mitochondria via membrane proteins such as Tom20 and leads to mitochondrial dysfunction and mitochondrial oxidative stress, which ultimately causes neuronal injury. We first found significant mitochondrial damage and oxidative stress in CS2-exposed rat midbrain and SH-SY5Y cells and showed that mitochondrial oxidative stress was the main factor of mitochondrial damage by Mitoquinone intervention. Further experiments revealed that CS2 exposure led to the accumulation of α-Syn in mitochondria and that α-Syn co-immunoprecipitated with mitochondrial membrane proteins. Finally, the use of an α-Syn inhibitor (ELN484228) and small interfering RNA (siRNA) effectively mitigated the accumulation of α-Syn in neurons, as well as the inhibition of mitochondrial membrane potential, caused by CS2 exposure. In conclusion, our study identifies the translocation of α-Syn to mitochondria and the impairment of mitochondrial function, which has important implications for the broader understanding and treatment of neurodegenerative diseases associated with environmental toxins.

Neurotoxicology of dopamine: Victim or assailant?

Since the identification of dopamine as a neurotransmitter in the mid-20th century, investigators have examined the regulation of dopamine homeostasis at a basic biological level and in human disorders. Genetic animal models that manipulate the expression of proteins involved in dopamine homeostasis have provided key insight into the consequences of dysregulated dopamine. As a result, we have come to understand the potential of dopamine to act as an endogenous neurotoxin through the generation of reactive oxygen species and reactive metabolites that can damage cellular macromolecules. Endogenous factors, such as genetic variation and subcellular processes, and exogenous factors, such as environmental exposures, have been identified as contributors to the dysregulation of dopamine homeostasis. Given the variety of dysregulating factors that impact dopamine homeostasis and the potential for dopamine itself to contribute to further cellular dysfunction, dopamine can be viewed as both the victim and an assailant of neurotoxicity. Parkinson's disease has emerged as the exemplar case study of dopamine dysregulation due to the genetic and environmental factors known to contribute to disease risk, and due to the evidence of dysregulated dopamine as a pathologic and pathogenic feature of the disease. This review, inspired by the talk, "Dopamine in Durham: location, location, location" presented by Dr. Miller for the Jacob Hooisma Memorial Lecture at the International Neurotoxicology Association meeting in 2023, offers a primer on dopamine toxicity covering endogenous and exogenous factors that disrupt dopamine homeostasis and the actions of dopamine as an endogenous neurotoxin.

Alpha-pine self-emulsifying nano formulation attenuates rotenone and trichloroethylene-induced dopaminergic loss

AIM

The current investigation's goals are to pharmacologically evaluate the neurotherapeutic role of the bioactive compound Alpha Pinene (ALP)-loaded Self-emulsifying nano-formulation (SENF) in neurotoxin (Rotenone and the Industrial Solvent Trichloroethylene)- induced dopaminergic loss. It is believed that these models simulate important aspects of the molecular pathogenesis of Parkinson's disease.

MATERIAL AND METHODS

The ALP-nano-formulation's anti-Parkinson's activity was compared to ALP suspension in Wistar rats after rotenone and trichloro ethylene-induced dopaminergic loss. Neurobehavioral and motor performances were measured on the 14th, 21st, and 28th day in the rotenone model. However, in the trichloroethylene model, it was measured from the 4th to the 8th week.

RESULTS

Significant neurobehavioral improvement has been found in ALP-SENF treated animals then untreated and animals treated with plain ALP suspension. Furthermore, biochemical tests reveal marked expression of catalase, glutathione, and superoxide dismutase, which significantly combat the (Oxidative stress) OS-induced neurodegeneration.

CONCLUSION

The antioxidant effect of ALP-SENF likely includes free radicals neutralization and the activation of enzymes associated with antioxidant activity, leading to the enhancement of neurobehavioral abnormalities caused by rotenone and trichloroethylene.

Bi-directional regulation of AIMP2 and its splice variant on PARP-1-dependent neuronal cell death; Therapeutic implication for Parkinson's disease

BACKGROUND

Parthanatos represents a critical molecular aspect of Parkinson's disease, wherein AIMP2 aberrantly activates PARP-1 through direct physical interaction. Although AIMP2 ought to be a therapeutic target for the disease, regrettably, it is deemed undruggable due to its non-enzymatic nature and predominant localization within the tRNA synthetase multi-complex. Instead, AIMP2 possesses an antagonistic splice variant, designated DX2, which counteracts AIMP2-induced apoptosis in the p53 or inflammatory pathway. Consequently, we examined whether DX2 competes with AIMP2 for PARP-1 activation and is therapeutically effective in Parkinson's disease.

METHODS

The binding affinity of AIMP2 and DX2 to PARP-1 was contrasted through immunoprecipitation. The efficacy of DX2 in neuronal cell death was assessed under 6-OHDA and H2O2 in vitro conditions. Additionally, endosomal and exosomal activity of synaptic vesicles was gauged in AIMP2 or DX2 overexpressed hippocampal primary neurons utilizing optical live imaging with VAMP-vGlut1 probes. To ascertain the role of DX2 in vivo, rotenone-induced behavioral alterations were compared between wild-type and DX2 transgenic animals. A DX2-encoding self-complementary adeno-associated virus (scAAV) was intracranially injected into 6-OHDA induced in vivo animal models, and their mobility was examined. Subsequently, the isolated brain tissues were analyzed.

RESULTS

DX2 translocates into the nucleus upon ROS stress more rapidly than AIMP2. The binding affinity of DX2 to PARP-1 appeared to be more robust compared to that of AIMP2, resulting in the inhibition of PARP-1 induced neuronal cell death. DX2 transgenic animals exhibited neuroprotective behavior in rotenone-induced neuronal damage conditions. Following a single intracranial injection of AAV-DX2, both behavior and mobility were consistently ameliorated in neurodegenerative animal models induced by 6-OHDA.

CONCLUSION

AIMP2 and DX2 are proposed to engage in bidirectional regulation of parthanatos. They physically interact with PARP-1. Notably, DX2's cell survival properties manifest exclusively in the context of abnormal AIMP2 accumulation, devoid of any tumorigenic effects. This suggests that DX2 could represent a distinctive therapeutic target for addressing Parkinson's disease in patients.

Polyvinylpyrrolidone-Capped Copper Oxide Nanoparticles-Anchored Pramipexole Attenuates the Rotenone-Induced Phenotypes in a Drosophila Parkinson's Disease Model

Parkinson's disease (PD) is a progressive, age-related neurodegenerative disease. The disease is characterized by the loss of dopaminergic neurons in the substantia nigra, pars compacta of the midbrain. Pramipexole (PPX) is a novel drug used for the treatment of PD. It has a high affinity for the dopamine (DA) D2 receptor subfamily and acts as a targeted mitochondrial antioxidant. It is less effective in the treatment of PD due to its short half-life, highly inconvenient dosing schedule, and long-term side effects. In recent years, PPX-loaded nanoformulations have been actively reported to overcome these limitations. In the current study, we focused on increasing the effectiveness of PPX by minimizing the dosing frequency and improving the treatment strategy for PD. Herein, we report the synthesis of biodegradable polyvinylpyrrolidone (PVP)-capped copper oxide nanoparticles (PVP-CuO NPs), followed by PPX anchoring on the surface of the PVP-CuO NPs (PPX-PVP-CuO NC), in a simple and inexpensive method. The newly formulated PPX-PVP-CuO NC complex was analyzed for its chemical and physical properties. The PPX-PVP-CuO NC was tested to protect against rotenone (RT)-induced toxicity in the Drosophila PD model. The in vivo studies using the RT-induced Drosophila PD model showed significant changes in negative geotaxis behavior and the level of DA and acetylcholinesterase. In addition, oxidative stress markers such as glutathione-S-transferase, total glutathione, thiobarbituric acid reactive species, and protein carbonyl content showed significant amelioration. The positive changes of PPX-PVP-CuO NC treatment in behavior, neurotransmitter level, and antioxidant level suggest its potential role in mitigating the PD phenotype. The formulation can be used for treatment or pharmacological intervention against PD.

Parkinson's disease: an update on preclinical studies of induced pluripotent stem cells

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease among adults worldwide. It is characterised by the death of dopaminergic neurons in the substantia nigra pars compacta and, in some cases, presence of intracytoplasmic inclusions of α-synuclein, called Lewy bodies, a pathognomonic sign of the disease. Clinical diagnosis of PD is based on the presence of motor alterations. The treatments currently available have no neuroprotective effect. The exact causes of PD are poorly understood. Therefore, more precise preclinical models have been developed in recent years that use induced pluripotent stem cells (iPSC). In vitro studies can provide new information on PD pathogenesis and may help to identify new therapeutic targets or to develop new drugs.

Viral-like TLR3 induction of cytokine networks and α-synuclein are reduced by complement C3 blockade in mouse brain

Inflammatory processes and mechanisms are of central importance in neurodegenerative diseases. In the brain, α-synucleinopathies such as Parkinson's disease (PD) and Lewy body dementia (LBD) show immune cytokine network activation and increased toll like receptor 3 (TLR3) levels for viral double-stranded RNA (dsRNA). Brain inflammatory reactions caused by TLR3 activation are also relevant to understand pathogenic cascades by viral SARS-CoV-2 infection causing post- COVID-19 brain-related syndromes. In the current study, following regional brain TLR3 activation induced by dsRNA in mice, an acute complement C3 response was seen at 2 days. A C3 splice-switching antisense oligonucleotide (ASO) that promotes the splicing of a non-productive C3 mRNA, prevented downstream cytokines, such as IL-6, and α-synuclein changes. This report is the first demonstration that α-synuclein increases occur downstream of complement C3 activation. Relevant to brain dysfunction, post-COVID-19 syndromes and pathological changes leading to PD and LBD, viral dsRNA TLR3 activation in the presence of C3 complement blockade further revealed significant interactions between complement systems, inflammatory cytokine networks and α-synuclein changes.

Neuroprotective Efficacy of a Nanomicellar Complex of Carnosine and Lipoic Acid in a Rat Model of Rotenone-Induced Parkinson's Disease

Oxidative stress, accompanied by mitochondrial dysfunction, is a key mechanism involved in the pathogenesis of Parkinson's disease (PD). Both carnosine and lipoic acid are potent antioxidants, the applicability of which in therapy is hindered by their limited bioavailability. This study aimed to evaluate the neuroprotective properties of a nanomicellar complex of carnosine and lipoic acid (CLA) in a rotenone-induced rat model of PD. Parkinsonism was induced via the administration of 2 mg/kg rotenone over the course of 18 days. Two doses of intraperitoneal CLA (25 mg/kg and 50 mg/kg) were administered alongside rotenone to assess its neuroprotective effect. At 25 mg/kg CLA decreased muscle rigidity and partially restored locomotor activity in animals that received rotenone. Furthermore, it caused an overall increase in brain tissue antioxidant activity, accompanied by a 19% increase in neuron density in the substantia nigra and increased dopamine levels in the striatum relative to animals that only received rotenone. Based on the acquired results, it may be concluded that CLA have neuroprotective properties and could potentially be beneficial in PD treatment when used in conjunction with the base therapy.

Gastrointestinal disorders in Parkinson's disease and other Lewy body diseases

Parkinson's disease (PD) is pathologically characterized by the abnormal accumulation of α-synuclein fibrils (Lewy bodies) in the substantia nigra and other brain regions, although the role of Lewy bodies remains elusive. Constipation usually precedes the motor symptoms in PD, which is in accordance with the notion that α-synuclein fibrils start from the intestinal neural plexus and ascend to the brain in at least half of PD patients. The gut microbiota is likely to be involved in intestinal and brain pathologies. Analyses of the gut microbiota in PD, rapid-eye-movement sleep behavior disorder, and dementia with Lewy bodies suggest three pathological pathways. First, Akkermansia, which is increased in PD, degrades the intestinal mucus layer and increases intestinal permeability, which triggers inflammation and oxidative stress in the intestinal neural plexus. Second, decreased short-chain fatty acids (SCFAs)-producing bacteria in PD reduce the number of regulatory T cells. Third, SCFAs also aggravate microglial activation with an unelucidated pathway. In addition, in dementia with Lewy bodies (DLB), which is another form of α-synucleinopathies, increased genera, Ruminococcus torques and Collinsella, may mitigate neuroinflammation in the substantia nigra by increasing secondary bile acids. Interventions for the gut microbiota and their metabolites may potentially delay or mitigate the development and progression of PD and other Lewy body diseases.

Curcumin protects against rotenone-induced Parkinson's disease in mice by inhibiting microglial NLRP3 inflammasome activation and alleviating mitochondrial dysfunction

Parkinson's disease (PD) is a common neurodegenerative disorder worldwide. Currently, treatment options can only relieve symptoms but cannot prevent, slow, or halt the neurodegenerative process of PD. Much evidence has suggested that microglia-mediated neuroinflammation is involved in the pathophysiology of PD. As an anti-inflammatory agent, curcumin may exert a neuroprotective effect on PD. However, its mechanism has yet to be demonstrated clearly. Our results indicated that curcumin alleviated rotenone-induced behavioral defects, dopamine neuron loss, and microglial activation. Besides, the NF-κB signaling pathway, the NLRP3 inflammasome, and pro-inflammatory cytokines, including IL-18 and IL-1β, contributed to the microglia-mediated neuroinflammation in PD. Furthermore, Drp1-mediated mitochondrial fission causing mitochondrial dysfunction also had an etiological role in the process. This study suggests that curcumin protects against rotenone-induced PD by inhibiting microglial NLRP3 inflammasome activation and alleviating mitochondrial dysfunction in mice. Thus, curcumin may be a neuroprotective drug with promising prospects in PD.

Roflumilast escalates α-synuclein aggregate degradation in rotenone-induced Parkinson's disease in rats: Modulation of the ubiquitin-proteasome system and endoplasmic reticulum stress

Perturbation of the protein homeostasis circuit is one of the principal attributes associated with many neurodegenerative disorders, such as Parkinson's disease (PD). This study aimed to explore the neuroprotective effect of roflumilast (ROF), a phosphodiesterase-4 inhibitor, in a rotenone-induced rat model of PD and investigate the potential underlying mechanisms. Interestingly, ROF (1 mg/kg, p.o.) attenuated motor impairment, prevented brain lesions, and rescued the dopaminergic neurons in rotenone-treated rats. Furthermore, it reduced misfolded α-synuclein burden. ROF also promoted the midbrain cyclic adenosine monophosphate level, which subsequently enhanced the 26S proteasome activity and the expression of the 20S proteasome. ROF counteracted rotenone-induced endoplasmic reticulum stress, which was demonstrated by its impact on activating transcription factor 6, glucose-regulated protein 78, and C/EBP homologous protein levels. Moreover, ROF averted rotenone-induced oxidative stress, as evidenced by its effects on the levels of nuclear factor erythroid 2-related factor 2, heme oxygenase-1, reduced glutathione, and lipid peroxides with a significant anti-apoptotic activity. Collectively, this study implies repurposing of ROF as a novel neuroprotective drug owning to its ability to restore normal protein homeostasis.

First Insight into the Neuroprotective and Antibacterial Effects of Phlorotannins Isolated from the Cell Walls of Brown Algae Fucus vesiculosus and Pelvetia canaliculata

Phaeophyceae (brown algae) essentially contribute to biotopes of cold and temperate seas. Their thalli are rich in biologically active natural products, which are strongly and universally dominated with phlorotannins—polyphenols of complex and diverse structure based on multiple differently arranged phloroglucinol units and well known as strong antioxidants with a broad spectrum of biological activities. In the algal cells, phlorotannins can either accumulate in the cytoplasm or can be secreted into the cell wall (CW). The biological activities of extractable intracellular phlorotannins have been comprehensively characterized, whereas the properties of the CW-bound polyphenol fraction are still mostly unknown. Recently, we identified dibenzodioxin bonding as the principal structural feature of the CW-bound phlorotannins in fucoid algae, whereas soluble intracellular phlorotannins rely on aryl and ether bonds. However, profiles of biological activity associated with these structural differences are still unknown. Therefore, to the best of our knowledge, for the first time we address the antioxidant, cytotoxic, neuroprotective, and antibacterial properties of the CW-bound phlorotannin fractions isolated from two representatives of the order Fucales—Fucus vesiculosus and Pelvetia canaliculata. The CW-bound phlorotannins appeared to be softer antioxidants, stronger antibacterial agents and were featured with essentially less cytotoxicity in comparison to the intracellular fraction. However, the neuroprotective effects of both sub-cellular phlorotannin fractions of F. vesiculosus and P. canaliculata were similar. Thus, due to their lower cytotoxicity, CW-bound phlorotannins can be considered as promising antioxidants and neuroprotectors.

UBA52 Attunes VDAC1-Mediated Mitochondrial Dysfunction and Dopaminergic Neuronal Death

Mitochondrial homeostasis regulates energy metabolism, calcium buffering, cell function, and apoptosis. The present study has been conducted to investigate the implications of the ubiquitin-encoding gene UBA52 in mitochondrial physiology. Transient expression of Myc-UBA52 in neurons significantly inhibited the rotenone-induced increase in reactive oxygen species generation, nitrite level, and depleted glutathione level. Mass spectrometric and coimmunoprecipitation data suggested the profound interaction of UBA52 with mitochondrial outer membrane channel protein, VDAC1 in both the wild-type and Myc-α-synuclein overexpressed neuronal cells and in the Parkinson's disease (PD)-specific substantia nigra and striatal region of the rat brain. In vitro ubiquitylation assay revealed that UBA52 participates in the ubiquitylation of VDAC1 through E3 ligase CHIP. Myc-UBA52 overexpression in neurons further improved the mitochondrial functionality and cell viability by preventing the alteration in mitochondrial membrane potential, mitochondrial complex I activity, and translocation of cytochrome c and p-Nrf2 along with the effect on intracellular calcium uptake, thus collectively inhibiting the opening of mitochondrial permeability transition pore. Additionally, Myc-UBA52 expression in neuronal cells offered protection against apoptotic and autophagic cell death. Altogether, our findings delineate a functional association between UBA52 and mitochondrial homeostasis, providing new insights into the deterrence of dopaminergic cell death during acute PD pathogenesis.

Barbigerone Potentially Alleviates Rotenone-Activated Parkinson's Disease in a Rodent Model by Reducing Oxidative Stress and Neuroinflammatory Cytokines

BACKGROUND

Parkinson's disease (PD) is a common age-related and slowly progressive neurodegenerative disease that affects approximately 1% of the elderly population. In recent years, phytocomponents have aroused considerable interest in the research for PD treatment as they provide a plethora of active compounds including antioxidant and anti-inflammatory compounds. Herein, we aimed to investigate the anti-Parkinson's effect of barbigerone, a natural pyranoisoflavone possessing antioxidant activity in a rotenone-induced rat model of PD.

METHODS

To evaluate antioxidant activity, a 0.5 mg/kg dose of rotenone was injected subcutaneously into rats. Barbigerone (10 and 20 mg/kg) was administered to rats for 28 days 1 h prior to rotenone. All behavioral parameters were assessed before sacrificing the rats. On the 29th day, all of the rats were humanely killed and assessed for biochemical changes in antioxidant enzymes (superoxide dismutase, glutathione, malondialdehyde, and catalase), neurotransmitter levels (dopamine, 5-hydroxyindoleacetic acid, serotonin, dihydroxyphenylacetic acid, and homovanillic acid levels), and neuroinflammatory cytokines [interleukin (IL)-1β, tumor necrosis factor-α, nuclear factor kappa B, and IL-6].

RESULTS

The data presented in this study has shown that barbigerone attenuated rotenone-induced motor deficits including the rotarod test, catalepsy, akinesia, and open-field test. Additionally, barbigerone has shown improvements in the biochemical and neuroinflammatory parameters in the rotenone-induced rat model of PD.

CONCLUSION

The results demonstrated that barbigerone exhibits antioxidant and anti-inflammatory actions via reducing oxidative stress and inflammatory cytokines. Altogether, these findings suggest that barbigerone could potentially be utilized as a therapeutic agent against PD.

Benefits of p-coumaric acid in mice with rotenone-induced neurodegeneration

The paper examines the use of natural antioxidant and anti-inflammation substances as therapeutic candidates for brain disease. Para-coumaric acid (pCA), a phenolic compound with a variety of medicinal properties, was used against deterioration caused by various diseases. Recently, pCA has gained attention for use against cardiovascular disease but less so for neurodegenerative disease (i.e., Parkinson's disease). Therefore, the present study intended to investigate the effect of pCA against rotenone-induced Parkinson's disease-like pathology in mice. Thirty male institute of cancer research (ICR) mice were randomly divided into three experimental groups: Sham-veh, Rot-veh, and Rot-pCA100. Rotenone (Rot) 2.5 mg/kg was subcutaneously injected every 48 h in the rotenone groups. Alternately, a 100 mg/kg pCA dose was given every 48 h via intragastric gavage to the Rot-pCA100 group for 6 weeks. Motor ability was assessed at the second, fourth, and sixth week before brain collection for biochemical and histological analyses. Results indicated significant motor deficits appeared from the second to sixth week after rotenone injection. Brain analysis detected a significant effect of rotenone in the increase of malondialdehyde and tumor necrosis factor-alpha (TNF-α). This result was observed in accordance with a reduction of tyrosine hydroxylase (TH) and an increase of neuronal degeneration in the substantia nigra par compacta (SNc) and striatum. However, pCA was able to reverse all of the deterioration (i.e., reduced malondialdehyde and TNF-α) rotenone had caused, and it protected against TH and neuronal loss in the SNc and striatum. Therefore, the present study has depicted the neuroprotective effect of pCA against rotenone-induced Parkinson's disease-like pathology in mice. Benefits of pCA include anti-lipid peroxidation and anti-inflammatory effects, inhibition of neurodegeneration, and a nurturing effect on the TH level in the SNc and striatum, leading to mitigation of motor deficits.

Neuroprotective Effect of Phloretin in Rotenone-Induced Mice Model of Parkinson's Disease: Modulating mTOR-NRF2-p62 Mediated Autophagy-Oxidative Stress Crosstalk

BACKGROUND

Parkinson's disease (PD) is an age-related progressive multifactorial, neurodegenerative disease. The autophagy and Keap1-Nrf2 axis system are both implicated in the oxidative-stress response, metabolic stress, and innate immunity, and their dysregulation is associated with pathogenic processes in PD. Phloretin (PLT) is a phenolic compound reported possessing anti-inflammatory and antioxidant activities.

OBJECTIVE

To evaluate the neuroprotective potential of PLT in PD via modulating the autophagy-antioxidant axisMethods:The neuroprotective effect of PLT was evaluated in vitro using rotenone (ROT) exposed SH-SY5Y cell line and in vivo using ROT administered C57BL/6 mice. Mice were administered with PLT (50 and 100 mg/kg, p.o.) concomitantly with ROT (1 mg/kg, i.p) for 3 weeks. Locomotive activity and anxiety behaviors were assessed using rotarod and open field tests respectively. Further apoptosis (Cytochrome-C, Bax), α-Synuclein (α-SYN), tyrosine hydroxylase (TH), antioxidant proteins (nuclear factor erythroid 2-related factor 2 (NRF2), heme oxygenase-1 (HO-1) and autophagic (mTOR, Atg5,7, p62, Beclin,LC3B-I/II) protein activity were evaluated both in in vitro and in vivo.

RESULTS

PLT improved locomotive activity and anxiety-like behavior in mice. Further PLT diminished apoptotic cell death, α-SYN expression and improved the expression of TH, antioxidant, and autophagic regulating protein.

CONCLUSION

Taken together, present data deciphers that the PLT effectively improves motor and non-motor symptoms via modulating the mTOR/NRF2/p62 pathway-mediated feedback loop. Hence, PLT could emerge as a prospective disease-modifying drug for PD management.

The Treatment of Parkinson's Disease with Sodium Oxybate

Sodiun Oxybate (SO) has a number of attributes that may mitigate the metabolic stress on the substantia nigra pars compacta (SNpc) dopaminergic (DA) neurons in Parkinson's disease (PD). These neurons function at the borderline of energy sufficiency. SO is metabolized to succinate and supplies energy to the cell by generating ATP. SO is a GABAB agonist and, as such, also arrests the high energy requiring calcium pace-making activity of these neurons. In addition, blocking calcium entry impedes the synaptic release and subsequent neurotransmission of aggregated synuclein species. As DA neurons degenerate, a homeostatic failure exposes these neurons to glutamate excitotoxicity, which in turn accelerates the damage. SO inhibits the neuronal release of glutamate and blocks its agonistic actions. Most important, SO generates NADPH, the cell's major antioxidant cofactor. Excessive free radical production within DA neurons and even more so within activated microglia are early and key features of the degenerative process that are present long before the onset of motor symptoms. NADPH maintains cell glutathione levels and alleviates oxidative stress and its toxic consequences. SO, a histone deacetylase inhibitor also suppresses the expression of microglial NADPH oxidase, the major source of free radicals in Parkinson brain. The acute clinical use of SO at night has been shown to reduce daytime sleepiness and fatigue in patients with PD. With long-term use, its capacity to supply energy to DA neurons, impede synuclein transmission, block excitotoxicity and maintain an anti-oxidative redox environment throughout the night may delay the onset of PD and slow its progress.

Advances in NURR1-Regulated Neuroinflammation Associated with Parkinson's Disease

Neuroinflammation plays a crucial role in the progression of neurodegenerative disorders, particularly Parkinson's disease (PD). Glial cell activation and subsequent adaptive immune involvement are neuroinflammatory features in familial and idiopathic PD, resulting in the death of dopaminergic neuron cells. An oxidative stress response, inflammatory mediator production, and immune cell recruitment and activation are all hallmarks of this activation, leading to chronic neuroinflammation and progressive neurodegeneration. Several studies in PD patients' cerebrospinal fluid and peripheral blood revealed alterations in inflammatory markers and immune cell populations that may lead to or exacerbate neuroinflammation and perpetuate the neurodegenerative process. Most of the genes causing PD are also expressed in astrocytes and microglia, converting their neuroprotective role into a pathogenic one and contributing to disease onset and progression. Nuclear receptor-related transcription factor 1 (NURR1) regulates gene expression linked to dopaminergic neuron genesis and functional maintenance. In addition to playing a key role in developing and maintaining neurotransmitter phenotypes in dopaminergic neurons, NURR1 agonists have been shown to reverse behavioral and histological abnormalities in animal PD models. NURR1 protects dopaminergic neurons from inflammation-induced degeneration, specifically attenuating neuronal death by suppressing the expression of inflammatory genes in microglia and astrocytes. This narrative review highlights the inflammatory changes in PD and the advances in NURR1-regulated neuroinflammation associated with PD. Further, we present new evidence that targeting this inflammation with a variety of potential NURR1 target therapy medications can effectively slow the progression of chronic neuroinflammation-induced PD.

Neuronal Oxidative Stress Promotes α-Synuclein Aggregation In Vivo

Both genetic and environmental factors increase risk for Parkinson's disease. Many of the known genetic factors influence α-synuclein aggregation or degradation, whereas most of the identified environmental factors produce oxidative stress. Studies using in vitro approaches have identified mechanisms by which oxidative stress can accelerate the formation of α-synuclein aggregates, but there is a paucity of evidence supporting the importance of these processes over extended time periods in brain. To assess this issue, we evaluated α-synuclein aggregates in brains of three transgenic mouse strains: hSyn mice, which overexpress human α-synuclein in neurons and spontaneously develop α-synuclein aggregates; EAAT3^-/- mice, which exhibit a neuron-specific impairment in cysteine uptake and resultant neuron-selective chronic oxidative stress; and double-transgenic hSyn/EAAT3^-/- mice. Aggregate formation was evaluated by quantitative immunohistochemistry for phosphoserine 129 α-synuclein and by an α-synuclein proximity ligation assay. Both methods showed that the double transgenic hSyn/EAAT3^-/- mice exhibited a significantly higher α-synuclein aggregate density than littermate hSyn mice in each brain region examined. Negligible aggregate formation was observed in the EAAT3^-/- mouse strain, suggesting a synergistic rather than additive interaction between the two genotypes. A similar pattern of results was observed in assessments of motor function: the pole test and rotarod test. Together, these observations indicate that chronic, low-grade neuronal oxidative stress promotes α-synuclein aggregate formation in vivo. This process may contribute to the mechanism by which environmentally induced oxidative stress contributes to α-synuclein pathology in idiopathic Parkinson's disease.

Neuroprotective Effect of Swertiamarin in a Rotenone Model of Parkinson's Disease: Role of Neuroinflammation and Alpha-Synuclein Accumulation

Parkinson's disease (PD) is a progressive neurodegenerative disease with no permanent cure affecting around 1% of the population over 65. There is an urgency to search for a disease-modifying agent with fewer untoward effects. PD pathology involves the accumulation of toxic alpha-synuclein (α-syn) and neuronal inflammation leading to the degeneration of dopaminergic (DAergic) neurons. Swertiamarin (SWE), a well-studied natural product, possesses a strong anti-inflammatory effect. It is a secoiridoid glycoside isolated from Enicostemma littorale Blume. SWE showed a reversal effect on the α-syn accumulation in the 6-hydroxydopamine (6-OHDA)-induced Caenorhabditis elegans model of PD. However, there are no reports in the literature citing the effect of SWE as a neuroprotective agent in rodents. The present study aimed to evaluate the anti-inflammatory activity of SWE against lipopolysaccharide (LPS)-induced C6 glial cell activation and its neuroprotective effect in the intrastriatal rotenone mouse PD model. SWE treatment showed a significant reduction in interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) levels in LPS-induced C6 glial cell activation. Further, our studies demonstrated the suppression of microglial and astroglial activation in substantia nigra (SN) after administration of SWE (100 mg/kg, intraperitoneally) in a rotenone mouse model. Moreover, SWE alleviated the rotenone-induced α-syn overexpression in the striatum and SN. SWE ameliorated the motor impairment against rotenone-induced neurotoxicity and mitigated the loss of DAergic neurons in the nigrostriatal pathway. Therefore, SWE has the potential to develop as an adjunct therapy for PD, but it warrants further mechanistic studies.

Fenofibrate promotes neuroprotection in a model of rotenone-induced Parkinson's disease

Parkinson's disease is a neurodegenerative disease, the etiology of which remains unknown, but some likely causes include oxidative stress, mitochondrial dysfunction and neuroinflammation. Peroxisome-proliferator-activated receptor (PPAR) agonists have been studied in animal models of Parkinson's disease and have shown neuroprotective effects. In this study, we aimed to (1) confirm the neuroprotective effects of PPAR-alpha agonist fenofibrate. To this end, male rats received fenofibrate (100 mg/kg) orally for 15 days, 5 days before the intraperitoneal injections of rotenone (2.5 mg/kg for 10 days). After finishing the treatment with rotenone and fenofibrate, animals were subjected to the open field, the forced swim test and the two-way active avoidance task. Subsequently, rats were euthanized for measurement of dopamine and metabolites levels in the striatum and quantification of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta (SNpc). In addition, we aimed to (2) evaluate the neuroprotective effects of fenofibrate on the accumulation of α-synuclein aggregates. Here, rats were treated for 5 days with fenofibrate continuing for over 28 days with rotenone. Then, animals were perfused for immunohistochemistry analysis of α-synuclein. The results showed that fenofibrate reduced depressive-like behavior and memory impairment induced by rotenone. Moreover, fenofibrate diminished the depletion of striatal dopamine and protected against dopaminergic neuronal death in the SNpc. Likewise, the administration of fenofibrate attenuated the aggregation of α-synuclein in the SNpc and striatum in the rotenone-lesioned rats. Our study confirmed that fenofibrate exerted neuroprotective effects because parkinsonian rats exhibited reduced behavioral, neurochemical and immunohistochemical changes, and importantly, a lower number of α-synuclein aggregates.

Time-dependent alterations in the rat nigrostriatal system after intrastriatal injection of fibrils formed by α–Syn and tau fragments

Introduction

Accurate demonstration of phosphorylated α-synuclein aggregation and propagation, progressive nigrostriatal degeneration and motor deficits will help further research on elucidating the mechanisms of Parkinson’s Disease. α-synucleinN103 and tauN368, cleaved by activated asparagine endopeptidase in Parkinson’s Disease, robustly interacted with each other and triggered endogenous α-synuclein accumulation in a strong manner. However, the detailed pathophysiological process caused by the complex remains to be established.

Methods

In this study, rats were unilaterally inoculated with 15 or 30 μg of this complex or vehicle (phosphate buffered saline, PBS). Over a 6-month period post injection, we then investigated the abundance of pSyn inclusions, nigrostriatal degeneration, and changes in axonal transport proteins to identify the various dynamic pathological changes caused by pSyn aggregates in the nigrostriatal system.

Results

As expected, rats displayed a dose-dependent increase in the amount of α-synuclein inclusions, and progressive dopaminergic neurodegeneration was observed throughout the study, reaching 30% at 6 months post injection. Impairments in anterograde axonal transport, followed by retrograde transport, were observed prior to neuron death, which was first discovered in the PFFs model.

Discussion

The current results demonstrate the value of a novel rat model of Parkinson’s disease characterized by widespread, “seed”-initiated endogenous α-Syn pathology, impaired axonal transport, and a neurodegenerative cascade in the nigrostriatal system. Notably, the present study is the first to examine alterations in axonal transport proteins in a PFF model, providing an appropriate foundation for future research regarding the mechanisms leading to subsequent neurodegeneration. As this model recapitulates some essential features of Parkinson’s disease, it provides an important platform for further research on specific pathogenic mechanisms and pre-clinical evaluations of novel therapeutic strategies.

UBA52 Is Crucial in HSP90 Ubiquitylation and Neurodegenerative Signaling during Early Phase of Parkinson's Disease

Protein aggregation is one of the major pathological events in age-related Parkinson's disease (PD) pathology, predominantly regulated by the ubiquitin-proteasome system (UPS). UPS essentially requires core component ubiquitin; however, its role in PD pathology is obscure. This study aimed to investigate the role of ubiquitin-encoding genes in sporadic PD pathology. Both cellular and rat models of PD as well as SNCA C57BL/6J-Tg (Th-SNCA*A30P*A53T)39 Eric/J transgenic mice showed a decreased abundance of UBA52 in conjunction with significant downregulation of tyrosine hydroxylase (TH) and neuronal death. In silico predictions, mass spectrometric analysis, and co-immunoprecipitation findings suggested the protein-protein interaction of UBA52 with α-synuclein, HSP90 and E3-ubiquitin ligase CHIP, and its co-localization with α-synuclein in the mitochondrion. Next, in vitro ubiquitylation assay indicated an imperative requirement of the lysine-63 residue of UBA52 in CHIP-mediated HSP90 ubiquitylation. Myc-UBA52 expressed neurons inhibited alteration in PD-specific markers such as α-synuclein and TH protein along with increased proteasome activity in diseased conditions. Furthermore, Myc-UBA52 expression inhibited the altered protein abundance of HSP90 and its various client proteins, HSP75 (homolog of HSP90 in mitochondrion) and ER stress-related markers during early PD. Taken together, the data highlights the critical role of UBA52 in HSP90 ubiquitylation in parallel to its potential contribution to the modulation of various disease-related neurodegenerative signaling targets during the early phase of PD pathology.

Inhibition of Calpain Attenuates Degeneration of Substantia Nigra Neurons in the Rotenone Rat Model of Parkinson's Disease

In the central nervous system (CNS), calcium homeostasis is a critical determinant of neuronal survival. Calpain, a calcium-dependent neutral protease, is widely expressed in the brain, including substantia nigra (SN) dopaminergic (DA) neurons. Though calpain is implicated in human Parkinson's disease (PD) and corresponding animal models, the roles of specific ubiquitous calpain isoforms in PD, calpain-1 and calpain-2, remain poorly understood. In this study, we found that both isoforms are activated in a nigrostriatal pathway with increased phosphorylated synuclein following the administration of rotenone in Lewis rats, but calpain isoforms played different roles in neuronal survival. Although increased expression of calpain-1 and calpain-2 were detected in the SN of rotenone-administered rats, calpain-1 expression was not altered significantly after treatment with calpain inhibitor (calpeptin); this correlated with neuronal survival. By contrast, increased calpain-2 expression in the SN of rotenone rats correlated with neuronal death, and calpeptin treatment significantly attenuated calpain-2 and neuronal death. Calpain inhibition by calpeptin prevented glial (astroglia/microglia) activation in rotenone-treated rats in vivo, promoted M2-type microglia, and protected neurons. These data suggest that enhanced expression of calpain-1 and calpain-2 in PD models differentially affects glial activation and neuronal survival; thus, the attenuation of calpain-2 may be important in reducing SN neuronal loss in PD.

Non-Reproducibility of Oral Rotenone as a Model for Parkinson's Disease in Mice

Oral rotenone has been proposed as a model for Parkinson’s disease (PD) in mice. To establish the model in our lab and study complex behavior we followed a published treatment regimen. C57BL/6 mice received 30 mg/kg body weight of rotenone once daily via oral administration for 4 and 8 weeks. Motor functions were assessed by RotaRod running. Immunofluorescence studies were used to analyze the morphology of dopaminergic neurons, the expression of alpha-Synuclein (α-Syn), and inflammatory gliosis or infiltration in the substantia nigra. Rotenone-treated mice did not gain body weight during treatment compared with about 4 g in vehicle-treated mice, which was however the only robust manifestation of drug treatment and suggested local gut damage. Rotenone-treated mice had no deficits in motor behavior, no loss or sign of degeneration of dopaminergic neurons, no α-Syn accumulation, and only mild microgliosis, the latter likely an indirect remote effect of rotenone-evoked gut dysbiosis. Searching for explanations for the model failure, we analyzed rotenone plasma concentrations via LC-MS/MS 2 h after administration of the last dose to assess bioavailability. Rotenone was not detectable in plasma at a lower limit of quantification of 2 ng/mL (5 nM), showing that oral rotenone had insufficient bioavailability to achieve sustained systemic drug levels in mice. Hence, oral rotenone caused local gastrointestinal toxicity evident as lack of weight gain but failed to evoke behavioral or biological correlates of PD within 8 weeks.

Druggable transcriptomic pathways revealed in Parkinson's patient-derived midbrain neurons

Complex genetic predispositions accelerate the chronic degeneration of midbrain substantia nigra neurons in Parkinson’s disease (PD). Deciphering the human molecular makeup of PD pathophysiology can guide the discovery of therapeutics to slow the disease progression. However, insights from human postmortem brain studies only portray the latter stages of PD, and there is a lack of data surrounding molecular events preceding the neuronal loss in patients. We address this gap by identifying the gene dysregulation of live midbrain neurons reprogrammed in vitro from the skin cells of 42 individuals, including sporadic and familial PD patients and matched healthy controls. To minimize bias resulting from neuronal reprogramming and RNA-seq methods, we developed an analysis pipeline integrating PD transcriptomes from different RNA-seq datasets (unsorted and sorted bulk vs. single-cell and Patch-seq) and reprogramming strategies (induced pluripotency vs. direct conversion). This PD cohort’s transcriptome is enriched for human genes associated with known clinical phenotypes of PD, regulation of locomotion, bradykinesia and rigidity. Dysregulated gene expression emerges strongest in pathways underlying synaptic transmission, metabolism, intracellular trafficking, neural morphogenesis and cellular stress/immune responses. We confirmed a synaptic impairment with patch-clamping and identified pesticides and endoplasmic reticulum stressors as the most significant gene-chemical interactions in PD. Subsequently, we associated the PD transcriptomic profile with candidate pharmaceuticals in a large database and a registry of current clinical trials. This study highlights human transcriptomic pathways that can be targeted therapeutically before the irreversible neuronal loss. Furthermore, it demonstrates the preclinical relevance of unbiased large transcriptomic assays of reprogrammed patient neurons.

Methanolic Extract of Boswellia serrata Gum Protects the Nigral Dopaminergic Neurons from Rotenone-Induced Neurotoxicity

Boswellia serrata gum is a natural product that showed beneficial effects on neurodegenerative diseases in recent studies. In this study, we investigated the effects of Boswellia serrata resin on rotenone-induced dopaminergic neurotoxicity. Firstly, we attempted to see if the resin can induce AMP-activated protein kinase (AMPK) signaling pathway which has been known to have broad neuroprotective effects. Boswellia increased AMPK phosphorylation and reduced phosphorylation of mammalian target of rapamycin (p-mTOR) and α-synuclein (p-α-synuclein) in the striatum while increased the expression level of Beclin1, a marker for autophagy and brain-derived neurotrophic factor. Next, we examined the neuroprotective effects of the Boswellia extract in the rotenone-injected mice. The results showed that Boswellia evidently attenuated the loss of the nigrostriatal dopaminergic neurons and microglial activation caused by rotenone. Moreover, Boswellia ameliorated rotenone-induced decrease in the striatal dopamine and impairment in motor function. Accumulation of α-synuclein meditated by rotenone was significantly ameliorated by Boswellia. Also, we showed that β-boswellic acid, the active constituents of Boswellia serrata gum, induced AMPK phosphorylation and attenuated α-synuclein phosphorylation in SHSY5 cells. These results suggest that Boswellia protected the dopaminergic neurons from rotenone neurotoxicity via activation of the AMPK pathway which might be associated with attenuation of α-synuclein aggregation and neuroinflammation. Further investigations are warranted to identify specific molecules in Boswellia which are responsible for the neuroprotection.

Nardosinone regulates the slc38a2 gene to alleviate Parkinson's symptoms in rats through the GABAergic synaptic and cAMP pathways

In a rotenone-induced Parkinson's disease (PD) rat model, behavioral investigation, pathological examination, inflammatory factor analysis, and mitochondrial structure and function investigation verified the anti-PD efficacy of nardosinone. A combined transcriptome and proteome analysis proposed that the anti-PD target of nardosinone is the slc38a2 gene and may involve the GABAergic synaptic pathway and cAMP-signaling pathway. Analysis of targeted slc38a2 knockout cells and expression of key enzyme-encoding genes in both pathways verified the target and pathways proposed by the 'omics analysis. This further confirms that nardosinone can regulate the slc38a2 gene, a potential new target for the treatment of Parkinson's disease, and plays an anti-PD role through the GABAergic synaptic and cAMP pathways.

Neuroprotective Effects of VEGF in the Enteric Nervous System

Although the enteric nervous system (ENS) functions largely autonomously as part of the peripheral nervous system (PNS), it is connected to the central nervous system (CNS) via the gut–brain axis. In many neurodegenerative diseases, pathological changes occur in addition to gastrointestinal symptoms, such as alpha-synuclein aggregates in Parkinson’s disease, which are found early in the ENS. In both the CNS and PNS, vascular endothelial growth factor (VEGF) mediates neuroprotective and neuroregenerative effects. Since the ENS with its close connection to the microbiome and the immune system is discussed as the origin of neurodegenerative diseases, it is necessary to investigate the possibly positive effects of VEGF on enteric neurons. Using laser microdissection and subsequent quantitative RT-PCR as well as immunohistochemistry, for the first time we were able to detect and localize VEGF receptor expression in rat myenteric neurons of different ages. Furthermore, we demonstrate direct neuroprotective effects of VEGF in the ENS in cell cultures. Thus, our results suggest a promising approach regarding neuroprotection, as the use of VEGF (may) prevent neuronal damage in the ENS.

Rotenone induces regionally distinct α-synuclein protein aggregation and activation of glia prior to loss of dopaminergic neurons in C57Bl/6 mice

Rotenone is a naturally occurring insecticide that inhibits mitochondrial complex I and leads to neurochemical and neuropathological deficits closely resembling those in Parkinson's disease (PD). Deficits include loss of dopaminergic neurons (DAn) in the substantia nigra pars compacta (SNpc), decreased dopamine levels and aggregation of misfolded alpha-synuclein (p129). In rat models of rotenone-induced parkinsonism, the progression of neuronal injury has been associated with activation of microglia and astrocytes. However, these neuroinflammatory changes have been challenging to study in mice, in part because the systemic rotenone exposure model utilized in rats is more toxic to mice. To establish a reproducible murine model of rotenone-induced PD, we therefore investigated the progression of neuroinflammation, protein aggregation and DAn loss in C57Bl/6 mice by exposing animals to 2.5 mg/kg/day rotenone for 14 days, followed by a two-week period where neuroinflammation is allowed to progress. Our results indicate that initial cellular dysfunction leads to increased formation of proteinase K-resistant p129 aggregates in the caudate-putamen and SNpc. Clearance of these aggregates was region- and cell type-specific, with the early appearance of reactive astrocytes coinciding with accumulation of p129 in the SNpc. Phagocytic microglial cells containing p129 aggregates were observed proximal to p129+ DAn in the SNpc. The majority of neuronal loss in the SNpc occurred during the two-week period after rotenone exposure, subsequent to the peak of microglia and astrocyte activation, as well as the peak of p129 aggregation. A secondary peak of p129 coincided with neurodegeneration at later timepoints. These data indicate that systemic exposure to rotenone in C57Bl/6 mice causes progressive accumulation and regional spread of p129 aggregates that precede maximal loss of DAn. Thus, activation of glial cells and aggregation of p129 appear to drive neuronal loss following neurotoxic stress imposed by exposure to rotenone.

Early Forms of α-Synuclein Pathology Are Associated with Neuronal Complex I Deficiency in the Substantia Nigra of Individuals with Parkinson’s Disease

Idiopathic Parkinson’s disease (iPD) is characterized by degeneration of the dopaminergic substantia nigra pars compacta (SNc), typically in the presence of Lewy pathology (LP) and mitochondrial respiratory complex I (CI) deficiency. LP is driven by α-synuclein aggregation, morphologically evolving from early punctate inclusions to Lewy bodies (LBs). The relationship between α-synuclein aggregation and CI deficiency in iPD is poorly understood. While studies in models suggest they are causally linked, observations in human SNc show that LBs preferentially occur in CI intact neurons. Since LBs are end-results of α-synuclein aggregation, we hypothesized that the relationship between LP and CI deficiency may be better reflected in neurons with early-stage α-synuclein pathology. Using quadruple immunofluorescence in SNc tissue from eight iPD subjects, we assessed the relationship between neuronal CI or CIV deficiency and early or late forms of LP. In agreement with previous findings, we did not observe CI-negative neurons with late LP. In contrast, early LP showed a significant predilection for CI-negative neurons (p = 6.3 × 10⁻⁵). CIV deficiency was not associated with LP. Our findings indicate that early α-syn aggregation is associated with CI deficiency in iPD, and suggest a double-hit mechanism, where neurons exhibiting both these pathologies are selectively lost.

Alpha-Synuclein Aggregation Pathway in Parkinson's Disease: Current Status and Novel Therapeutic Approaches

Following Alzheimer’s, Parkinson’s disease (PD) is the second-most common neurodegenerative disorder, sharing an unclear pathophysiology, a multifactorial profile, and massive social costs worldwide. Despite this, no disease-modifying therapy is available. PD is tightly associated with α-synuclein (α-Syn) deposits, which become organised into insoluble, amyloid fibrils. As a typical intrinsically disordered protein, α-Syn adopts a monomeric, random coil conformation in an aqueous solution, while its interaction with lipid membranes drives the transition of the molecule part into an α-helical structure. The central unstructured region of α-Syn is involved in fibril formation by converting to well-defined, β-sheet rich secondary structures. Presently, most therapeutic strategies against PD are focused on designing small molecules, peptides, and peptidomimetics that can directly target α-Syn and its aggregation pathway. Other approaches include gene silencing, cell transplantation, stimulation of intracellular clearance with autophagy promoters, and degradation pathways based on immunotherapy of amyloid fibrils. In the present review, we sum marise the current advances related to α-Syn aggregation/neurotoxicity. These findings present a valuable arsenal for the further development of efficient, nontoxic, and non-invasive therapeutic protocols for disease-modifying therapy that tackles disease onset and progression in the future.

Kunitz-Type Peptides from Sea Anemones Protect Neuronal Cells against Parkinson's Disease Inductors via Inhibition of ROS Production and ATP-Induced P2X7 Receptor Activation

Parkinson’s disease (PD) is a socially significant disease, during the development of which oxidative stress and inflammation play a significant role. Here, we studied the neuroprotective effects of four Kunitz-type peptides from Heteractis crispa and Heteractis magnifica sea anemones against PD inductors. The peptide HCIQ1c9, which was obtained for the first time, inhibited trypsin less than other peptides due to unfavorable interactions of Arg17 with Lys43 in the enzyme. Its activity was reduced by up to 70% over the temperature range of 60–100 °C, while HCIQ2c1, HCIQ4c7, and HMIQ3c1 retained their conformation and stayed active up to 90–100 °C. All studied peptides inhibited paraquat- and rotenone-induced intracellular ROS formation, in particular NO, and scavenged free radicals outside the cells. The peptides did not modulate the TRPV1 channels but they affected the P2X7R, both of which are considered therapeutic targets in Parkinson’s disease. HMIQ3c1 and HCIQ4c7 almost completely inhibited the ATP-induced uptake of YO-PRO-1 dye in Neuro-2a cells through P2X7 ion channels and significantly reduced the stable calcium response in these cells. The complex formation of the peptides with the P2X7R extracellular domain was determined via SPR analysis. Thus, these peptides may be considered promising compounds to protect neuronal cells against PD inductors, which act as ROS production inhibitors and partially act as ATP-induced P2X7R activation inhibitors.

Crocin Protects Malathion-Induced Striatal Biochemical Deficits by Inhibiting Apoptosis and Increasing α-Synuclein in Rats' Striatum

Long-term exposure to organophosphates might result in neurodegenerative diseases, comprising Parkinson's disease. Malathion is an organophosphate pesticide with high neurotoxicity. Oxidative stress, apoptosis, and α-synuclein accumulation are important underlying mechanisms in Parkinson's disease. According to studies, crocin, an active constituent of saffron, has anti-apoptotic, anti-inflammatory, and antioxidant properties. Thus, the effect of crocin on malathion-induced striatal biochemical deficits in rats was investigated in this study. Six groups of male Wistar rats were used: 1. control (normal saline); 2. malathion (100 mg/kg/day, i.p.); 3. crocin (10 mg/kg/day, i.p.) + malathion; 4. levodopa (10 mg/kg/day, i.p.) + malathion; 5. crocin (40 mg/kg/day, i.p.); and 6. polyethylene glycol (PEG) (vehicle of levodopa) groups. The drugs were administered for 28 days. The amounts of Bcl-2, Bax, and caspases 3, 8, and 9 proteins in the striatum were measured by western blotting. Also, the amounts of protein and mRNA level of the α-synuclein in striatum tissue were measured by western blotting and RT-qPCR methods. Malathion induced apoptosis by increasing the amount of Bax/Bcl2 ratio and caspases 3 and 9 proteins in rat striatum tissue. It also increased the protein and mRNA level of α-synuclein in striatal tissue. Co-administration of crocin or levodopa with malathion inhibited the toxic effects of malathion on striatal tissue. Crocin ameliorates the neurotoxic effect of malathion by its anti-apoptotic activity and regulating the expression of proteins involved in Parkinson's disease pathogenesis. As a result, crocin has the potential to be used as a treatment for malathion-induced neurotoxicity.

Gene therapy of yeast NDI1 on mitochondrial complex I dysfunction in rotenone-induced Parkinson’s disease models in vitro and vivo

Purpose

Parkinson's disease (PD) is the second most common neurodegenerative disease without cure or effective treatment. This study explores whether the yeast internal NADH-quinone oxidoreductase (NDI1) can functionally replace the defective mammalian mitochondrial complex I, which may provide a gene therapy strategy for treating sporadic PD caused by mitochondrial complex I dysfunction.

Method

Recombinant lentivirus expressing NDI1 was transduced into SH-SY5Y cells, or recombinant adeno-associated virus type 5 expressing NDI1 was transduced into the right substantia nigra pars compacta (SNpc) of mouse. PD cell and mouse models were established by rotenone treatment. The therapeutic effects of NDI1 on rotenone-induced PD models in vitro and vivo were assessed in neurobehavior, neuropathology, and mitochondrial functions, by using the apomorphine-induced rotation test, immunohistochemistry, immunofluorescence, western blot, complex I enzyme activity determination, oxygen consumption detection, ATP content determination and ROS measurement.

Results

NDI1 was expressed and localized in mitochondria in SH-SY5Y cells. NDI1 resisted rotenone-induced changes in cell morphology, loss of cell viability, accumulation of α-synuclein and pS129 α-synuclein, mitochondrial ROS production and mitochondria-mediated apoptosis. The basal and maximal oxygen consumption, mitochondrial coupling efficiency, basal and oligomycin-sensitive ATP and complex I activity in cell model were significantly increased in rotenone + NDI1 group compared to rotenone + vector group. NDI1 was efficiently expressed in dopaminergic neurons in the right SNpc without obvious adverse effects. The rotation number to the right side (NDI1-treated side) was significantly increased compared to that to the left side (untreated side) in mouse model. The number of viable dopaminergic neurons, the expression of tyrosine hydroxylase, total and maximal oxygen consumption, mitochondrial coupling efficiency and complex I enzyme activity in right substantia nigra, and the content of dopamine in right striatum were significantly increased in rotenone + NDI1 group compared to rotenone + vector group.

Conclusion

Yeast NDI1 can rescue the defect of oxidative phosphorylation in rotenone-induced PD cell and mouse models, and ameliorate neurobehavioral and neuropathological damages. The results may provide a basis for the yeast NDI1 gene therapy of sporadic PD caused by mitochondrial complex I dysfunction.

Time Course of Neurobehavioral Disruptions and Regional Brain Metabolism Changes in the Rotenone Mice Model of Parkinson’s Disease

Parkinson’s disease (PD) is characterized by slow progression with a long prodromal stage and the gradual evolution of both neuropsychological symptoms and subtle motor changes, preceding motor dysfunction. Thus, in order for animal models of PD to be valid, they should reproduce these characteristics of the disease. One of such models, in which neuropathology is induced by chronic injections of low doses of mitochondrial toxin rotenone, is well established in rats. However, data on this model adapted to mice remain controversial. We have designed the study to describe the timecourse of motor and non-motor symptoms during chronic subcutaneous administration of rotenone (4 mg/kg daily for 35 days) in C57BL/6 mice. We characterize the underlying neuropathological processes (dopaminergic neuron degeneration, regional brain metabolism, monoamine neurotransmitter and lipid peroxidation changes) at different timepoints: 1 day, 2 weeks and 5 weeks of daily rotenone exposure. Based on the behavioral data, we can describe three stages of pathology: cognitive changes from week 2 of rotenone exposure, subtle motor changes in week 3–4 and motor dysfunction starting roughly from week 4. Neuropathological changes in this model include a general decrease in COX activity in different areas of the brain (acute effect of rotenone) and a more specific decrease in midbrain (chronic effect), followed by significant neurodegeneration in SNpc but not VTA by the 5th week of rotenone exposure. However, we were unable to find changes in the level of monoamine neurotransmitters neither in the striatum nor in the cortex, nor in the level of lipid peroxidation in the brainstem. Thus, the gradual progression of pathology in this model is linked with metabolic changes, rather than with oxidative stress or tonic neurotransmitter release levels. Overall, this study supports the idea that a low-dose rotenone mouse model can also reproduce different stages of PD as well as rats.