Modeling of presymptomatic and symptomatic stages of parkinsonism in mice

Effects of Age and MPTP-Induced Parkinson's Disease on the Expression of Genes Associated with the Regulation of the Sleep-Wake Cycle in Mice

Parkinson's disease (PD) is characterized by a long prodromal period, during which patients often have sleep disturbances. The histaminergic system and circadian rhythms play an important role in the regulation of the sleep-wake cycle. Changes in the functioning of these systems may be involved in the pathogenesis of early stages of PD and may be age-dependent. Here, we have analyzed changes in the expression of genes associated with the regulation of the sleep-wake cycle (Hnmt, Hrh1, Hrh3, Per1, Per2, and Chrm3) in the substantia nigra (SN) and striatum of normal male mice of different ages, as well as in young and adult male mice with an MPTP-induced model of the early symptomatic stage (ESS) of PD. Age-dependent expression analysis in normal mouse brain tissue revealed changes in Hrh3, Per1, Per2, and Chrm3 genes in adult mice relative to young mice. When gene expression was examined in mice with the MPTP-induced model of the ESS of PD, changes in the expression of all studied genes were found only in the SN of adult mice with the ESS model of PD. These data suggest that age is a significant factor influencing changes in the expression of genes associated with sleep-wake cycle regulation in the development of PD.

Pterostilbene alleviates MPTP-induced neurotoxicity by targeting neuroinflammation and oxidative stress

Pterostilbene (PTE), a naturally occurring phenolic compound primarily found in blueberries, demonstrates neuroprotective properties. However, the role of PTE in Parkinson's disease (PD) remains unclear. This study aimed to investigate the neuroprotective role of PTE in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD animal model. Our findings demonstrate that administering PTE effectively reversed the diminished levels of dopamine in the striatum, thereby ameliorating motor impairments in the MPTP model. Moreover, PTE administration mitigated the loss of dopaminergic (DA) neurons and reduced the upregulation of α-synuclein (α-syn) induced by MPTP. Mechanistic analysis revealed that PTE administration inhibited the activation of microglia and astrocytes, as well as pro-inflammatory factors such as TNF-α and IL-1β in the MPTP model. Additionally, PTE administration decreased MPTP-induced levels of reactive oxygen species (ROS) and malondialdehyde (MDA), while increasing total antioxidant capacity (TAOC) and superoxide dismutase (SOD) activity, thereby attenuating oxidative stress. Collectively, these findings demonstrate that PTE exerts neuroprotective effects in the MPTP mouse model of PD by suppressing neuroinflammation and oxidative stress. Thus, PTE holds promise as a therapeutic agent for PD.

Initial Molecular Mechanisms of the Pathogenesis of Parkinson's Disease in a Mouse Neurotoxic Model of the Earliest Preclinical Stage of This Disease

Studying the initial molecular mechanisms of the pathogenesis of Parkinson's disease (PD), primarily in the nigrostriatal dopaminergic system, is one of the priorities in neurology. Of particular interest is elucidating these mechanisms in the preclinical stage of PD, which lasts decades before diagnosis and is therefore not available for study in patients. Therefore, our main goal was to study the initial molecular mechanisms of the pathogenesis of PD in the striatum, the key center for dopamine regulation in motor function, in a mouse model of the earliest preclinical stage of PD, from 1 to 24 h after the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). It was shown that the content of tyrosine hydroxylase (TH), the first enzyme in dopamine synthesis, does not change within 6 h after the administration of MPTP, but decreases after 24 h. In turn, TH activity increases after 1 h, decreases after 3 h, remains at the control level after 6 h, and decreases 24 h after the administration of MPTP. The concentration of dopamine in the striatum gradually decreases after MPTP administration, despite a decrease in its degradation. The identified initial molecular mechanisms of PD pathogenesis are considered as potential targets for the development of preventive neuroprotective treatment.

Application of OpenArray Technology to Assess Changes in the Expression of Functionally Significant Genes in the Substantia Nigra of Mice in a Model of Parkinson's Disease

Studying the molecular mechanisms of the pathogenesis of Parkinson's disease (PD) is critical to improve PD treatment. We used OpenArray technology to assess gene expression in the substantia nigra (SN) cells of mice in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD and in controls. Among the 11 housekeeping genes tested, Rps27a was taken as the reference gene due to its most stable expression in normal and experimental conditions. From 101 genes encoding functionally significant proteins of nigrostriatal dopaminergic neurons, 57 highly expressed genes were selected to assess their expressions in the PD model and in the controls. The expressions of Th, Ddc, Maoa, Comt, Slc6a3, Slc18a2, Drd2, and Nr4a2 decreased in the experiment compared to the control, indicating decreases in the synthesis, degradation, and transport of dopamine and the impaired autoregulation of dopaminergic neurons. The expressions of Tubb3, Map2, Syn1, Syt1, Rab7, Sod1, Cib1, Gpx1, Psmd4, Ubb, Usp47, and Ctsb genes were also decreased in the MPTP-treated mice, indicating impairments of axonal and vesicular transport and abnormal functioning of the antioxidant and ubiquitin-proteasome systems in the SN. The detected decreases in the expressions of Snca, Nsf, Dnm1l, and Keap1 may serve to reduce pathological protein aggregation, increase dopamine release in the striatum, prevent mitophagy, and restore the redox status of SN cells.

Compensatory Processes in Striatal Neurons Expressing the Tyrosine Hydroxylase Gene in Transgenic Mice in a Model of Parkinson's Disease

The mammalian striatum is known to contain non-dopaminergic neurons that express dopamine (DA)-synthesizing enzymes and produce DA, responsible for the regulation of motor function. This study assessed the expression of DA-synthesizing enzymes in striatal neurons and their role in DA synthesis in transgenic mice expressing the green fluorescent protein (GFP) gene under the tyrosine hydroxylase (TH) gene promoter in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease (PD). We showed that, in Parkinsonian animals, the number of neurons expressing the TH gene increased by 1.9 times compared with the control (0.9% NaCl), which indicates a compensatory response to the DAergic denervation of the striatum. This assumption is supported by a 2.5-fold increase in the expression of genes for TH and transcription factor Nurr1 and a 1.45-fold increase in the expression of the large amino acid transporter 1 gene. It is noteworthy that, in Parkinsonian mice, in contrast to the controls, DA-synthesizing enzymes were found not only in nerve fibers but also in neuronal cell bodies. Indeed, TH or TH and aromatic L-amino acid decarboxylase (AADC) were detected in GFP-positive neurons, and AADC was detected in GFP-negative neurons. These neurons were shown to synthesize DA, and this synthesis is compensatorily increased in Parkinsonian mice. The above data open the prospect of improving the treatment of PD by maintaining DA homeostasis in the striatum.

Behavioral, neural and ultrastructural alterations in a graded-dose 6-OHDA mouse model of early-stage Parkinson's disease

Studying animal models furthers our understanding of Parkinson's disease (PD) pathophysiology by providing tools to investigate detailed molecular, cellular and circuit functions. Different versions of the neurotoxin-based 6-hydroxydopamine (6-OHDA) model of PD have been widely used in rats. However, these models typically assess the result of extensive and definitive dopaminergic lesions that reflect a late stage of PD, leading to a paucity of studies and a consequential gap of knowledge regarding initial stages, in which early interventions would be possible. Additionally, the better availability of genetic tools increasingly shifts the focus of research from rats to mice, but few mouse PD models are available yet. To address these, we characterize here the behavioral, neuronal and ultrastructural features of a graded-dose unilateral, single-injection, striatal 6-OHDA model in mice, focusing on early-stage changes within the first two weeks of lesion induction. We observed early onset, dose-dependent impairments of overall locomotion without substantial deterioration of motor coordination. In accordance, histological evaluation demonstrated a partial, dose-dependent loss of dopaminergic neurons of substantia nigra pars compacta (SNc). Furthermore, electron microscopic analysis revealed degenerative ultrastructural changes in SNc dopaminergic neurons. Our results show that mild ultrastructural and cellular degradation of dopaminergic neurons of the SNc can lead to certain motor deficits shortly after unilateral striatal lesions, suggesting that a unilateral dose-dependent intrastriatal 6-OHDA lesion protocol can serve as a successful model of the early stages of Parkinson's disease in mice.

Whole Transcriptome Analysis of Substantia Nigra in Mice with MPTP-Induced Parkinsonism Bearing Defective Glucocerebrosidase Activity

Mutations in the GBA1 gene represent the major genetic risk factor for Parkinson's disease (PD). The lysosomal enzyme beta-glucocerebrosidase (GCase) encoded by the GBA1 gene participates in both the endolysosomal pathway and the immune response. Disruption of these mechanisms is involved in PD pathogenesis. However, molecular mechanisms of PD associated with GBA1 mutations (GBA-PD) are unknown today in particular due to the partial penetrance of GBA1 variants in PD. The modifiers of GBA1 penetrance have not been elucidated. We characterized the transcriptomic profiles of cells from the substantia nigra (SN) of mice with co-injection with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and selective inhibitor of GCase activity (conduritol-β-epoxide, (CBE)) to mimic PD bearing GCase dysfunction (MPTP+CBE), mice treated with MPTP, mice treated with CBE and control mice treated with injection of sodium chloride (NaCl) (vehicle). Differential expression analysis, pathway enrichment analysis, and outlier detection were performed. Functional clustering of differentially represented transcripts revealed more processes associated with the functioning of neurogenesis, inflammation, apoptosis and autophagy in MPTP+CBE and MPTP mice than in vehicle mice, with a more pronounced alteration of autophagy processes in MPTP+CBE mice than in MPTP mice. The PI3K-Akt-mTOR signaling pathway may be considered a potential target for therapy in PD with GCase dysfunction.

The Gene Expression of Proteins Involved in Intercellular Signaling and Neurodegeneration in the Substantia Nigra in a Mouse Subchronic Model of Parkinson's Disease

Given the limited access to clinical material for studying the pathogenesis of Parkinson's disease (PD), these studies should be carried out on experimental models. We have recently developed a subchronic model of the progressive development of PD with a gradual transition from the preclinical (asymptomatic) stage to the clinical (symptomatic) one. The aim of this study was to evaluate changes in the expression of a wide range of genes in the substantia nigra (SN), the central link in the regulation of motor function, in mice in our subchronic model of PD. We have found changes in the expression of a number of genes encoding enzymes involved in the synthesis and degradation of dopamine as well as proteins involved in the vesicular cycle, axonal transport, protein degradation in the proteasome system, neuroinflammation, and cell death in the SN of our mouse model of the clinical stage of PD. Similar changes in gene expression were previously demonstrated in patients (postmortem), indicating good reproducibility of PD in our model. Further analysis of the gene expression in the SN of mice has shown that the expression of some genes also changes in the model of the preclinical stage, when dopaminergic neurons have not yet died. Thus, this study opens up broad prospects for further evaluation of the molecular mechanisms of PD pathogenesis and the development of a test system for drug screening.

Modeling of the Progressive Degradation of the Nigrostriatal Dopaminergic System in Mice to Study the Mechanisms of Neurodegeneration and Neuroplasticity in Parkinson's Disease

The fight against neurodegenerative diseases, including Parkinson's disease (PD), is among the global challenges of the 21st century. The low efficiency of therapy is due to the late diagnosis and treatment of PD, which take place when there is already significant degradation of the nigrostriatal dopaminergic system, a key link in the regulation of motor function. We have developed a subchronic mouse model of PD by repeatedly administering 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at gradually increasing doses with a 24 h interval between injections, a period comparable to the time of MPTP metabolism and elimination from the body. This model reproduces the main hallmarks of PD: progressive degeneration of dopaminergic neurons; the appearance of motor disorders with a 70-80% decrease in the level of dopamine in the striatum; an increase in dopamine turnover in the striatum to compensate for dopamine deficiency. When comparing the degradation of the nigrostriatal dopaminergic system and motor disorders in mice in the acute and subchronic models of PD, it has turned out that the resistance of dopaminergic neurons to MPTP increases with its repeated administration. Our subchronic model of PD opens up broad prospects for studying the molecular mechanisms of PD pathogenesis and developing technologies for early diagnosis and preventive treatment.

Isolation of living dopaminergic neurons labeled with a fluorescent ligand of the dopamine transporter from mouse substantia nigra as a new tool for basic and applied research

Dopaminergic neurons (DNs) of the nigrostriatal system control the motor function, and their degeneration leads to the development of Parkinson's disease (PD). A stumbling block in the study of DNs in the whole substantia nigra (SN) is the lack of tools to analyze the expression of most of the genes involved in neurotransmission, neurodegeneration, and neuroplasticity, since they are also expressed in other cells of the SN. Therefore, this study aimed to develop a fluorescence-activated cell sorting method for isolating living DNs from the SN of wild-type mice using two fluorescent dyes, DRAQ5 (nuclear stain) and a dopamine uptake inhibitor GBR 12909 coupled to a fluorophore (DN stain). We have developed a method for selecting a population of DNs from the SN of mice, as evidenced by: (i) immunopositivity of 95% of the sorted cells for tyrosine hydroxylase, the first enzyme of dopamine synthesis; (ii) the sorted cells expressing the genes for specific proteins of the dopaminergic phenotype, tyrosine hydroxylase, the dopamine transporter, and vesicular monoamine transporter 2 and non-specific proteins, such as aromatic L-amino acid decarboxylase, non-specific enzyme of dopamine synthesis. We then compared the changes in gene expression found in the sorted DNs and in the SN homogenate in a PD model we developed, reproduced in mice by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Using quantitative PCR, we obtained evidence of the same changes in the expression of specific genes in the sorted DNs of SN and in the SN homogenate of a MPTP mouse model of PD, compared with the control. The undoubted advantage of our approach is the possibility of obtaining a large amount of readily available and relatively cheap primary material (SN) from wild-type mice, which can be used to solve both research and applied problems. In addition, this method can be easily adapted to the isolation of DNs from the SN in other animal species, including non-human primates.

HLDF-6 peptides exhibit neuroprotective effects in the experimental model of preclinical Parkinson's disease

The mechanisms of the neuroprotective action of the hexapeptides HLDF-6 encoded by the amino acid sequence 41-46 of Human Leukemia Differentiation Factor and its homoserine derivative HLDF-6H were studied in an experimental 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced model of Parkinson's disease (PD). C57Bl/6 mice received two intraperitoneal injections of 18 mg/kg MPTP-HCl, with an interval of 2 hours. MPTP-induced motor dysfunction was assessed using horizontal grid test. Our data show that chronic intranasal administration of peptides (3 weeks, 300 μg/kg/day) restored normal levels of dopamine and improved its turnover rates in the striatum. Furthermore, peptide administration increased serum estradiol levels and led to a significant improvement in motor functions in MPTP-treated mice. Additionally, peptide treatment increased the levels of mRNA encoding neurotrophin BDNF, but normalized the levels of mRNA encoding the inflammatory mediators TGFβ1, IL1β and IFNγ in the brain. Collectively, our behavioral and biochemical studies demonstrate that HLDF-6 peptides have a therapeutic potential for treating PD. We propose that HLDF-6 peptides may exert their neuroprotective mechanism, at least in part, by normalizing estradiol levels and modulating the expression of key factors involved in neurotrophic support and neuroinflammation.

Changes in Tyrosine Hydroxylase Activity and Dopamine Synthesis in the Nigrostriatal System of Mice in an Acute Model of Parkinson's Disease as a Manifestation of Neurodegeneration and Neuroplasticity

The progressive degradation of the nigrostriatal system leads to the development of Parkinson’s disease (PD). The synthesis of dopamine, the neurotransmitter of the nigrostriatal system, depends on the rate-limiting enzyme, tyrosine hydroxylase (TH). In this study, we evaluated the synthesis of dopamine during periods of neurodegradation and neuroplasticity in the nigrostriatal system on a model of the early clinical stage of PD. It was shown that the concentration of dopamine correlated with activity of TH, while TH activity did not depend on total protein content either in the SN or in the striatum. Both during the period of neurodegeneration and neuroplasticity, TH activity in SN was determined by the content of P19-TH, and in the striatum it was determined by P31-TH and P40-TH (to a lesser extent). The data obtained indicate a difference in the regulation of dopamine synthesis between DA-neuron bodies and their axons, which must be considered for the further development of symptomatic pharmacotherapy aimed at increasing TH activity.

Development of early diagnosis of Parkinson's disease on animal models based on the intranasal administration of α-methyl-p-tyrosine methyl ester in a gel system

The fight against neurodegenerative diseases, including Parkinson's disease (PD), is a global challenge of this century. The effectiveness of current PD therapy is limited, since it is diagnosed many years after the onset, following the death of most nigrostriatal dopaminergic neurons regulating motor function. PD treatment could be greatly improved if it was started at an early (preclinical) stage. For this purpose, it is necessary to develop an early diagnosis of PD, which is the goal of our study. We have developed an early diagnosis of PD on animal models using a provocative test by intranasal administration of α-methyl-p-tyrosine methyl ester (αMPTME), a reversible inhibitor of dopamine synthesis. First, we produced the provocative agent, αMPTME in gel, and showed its safety and penetration into the brain bypassing the blood-brain barrier. Then, the optimal dose of αMPTME and time after administration were selected, at which the level of dopamine in the striatum of intact animals decreases, but does not reach the 30% threshold for the appearance of motor disorders in PD patients. Finally, we proved on animal models that intranasal administration of αMPTME can serve as a diagnostic test for preclinical PD. Indeed, intranasal administration of αMPTME to mice in a model of PD at the preclinical stage reversibly reduced the dopamine level in the striatum to the 30% threshold causing short-term motor disorders. Thus, using animal models of PD, we have developed a provocative test for the preclinical diagnosis of PD, a fundamentally new technology in neurology.

Expression Analysis of Genes Involved in Transport Processes in Mice with MPTP-Induced Model of Parkinson’s Disease

Processes of intracellular and extracellular transport play one of the most important roles in the functioning of cells. Changes to transport mechanisms in a neuron can lead to the disruption of many cellular processes and even to cell death. It was shown that disruption of the processes of vesicular, axonal, and synaptic transport can lead to a number of diseases of the central nervous system, including Parkinson’s disease (PD). Here, we studied changes in the expression of genes whose protein products are involved in the transport processes (Snca, Drd2, Rab5a, Anxa2, and Nsf) in the brain tissues and peripheral blood of mice with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced models of PD. We detected changes in the expressions of Drd2, Anxa2, and Nsf at the earliest modeling stages. Additionally, we have identified conspicuous changes in the expression level of Anxa2 in the striatum and substantia nigra of mice with MPTP-induced models of PD in its early stages. These data clearly suggest the involvement of protein products in these genes in the earliest stages of the pathogenesis of PD.

Neurotoxicological Profiling of Paraquat in Zebrafish Model

Paraquat is a polar herbicide protecting plant products against invasive species, it requires careful manipulation and restricted usage because of its harmful potentials. Exposure to paraquat triggers oxidative damage in dopaminergic neurons and subsequently causes a behavioral defect in vivo. Thereby, persistent exposure to paraquat is known to increase Parkinson's disease risk by dysregulating dopaminergic systems in humans. Therefore, most studies have focused on the dopaminergic systems to elucidate the neurotoxicological mechanism of paraquat poisoning, and more comprehensive neurochemistry including histaminergic, serotonergic, cholinergic, and GABAergic systems has remained unclear. Therefore, in this study, we investigated the toxicological potential of paraquat poisoning using a variety of approaches such as toxicokinetic profiles, behavioral effects, neural activity, and broad-spectrum neurochemistry in zebrafish larvae after short-term exposure to paraquat and we performed the molecular modeling approach. Our results showed that paraquat was slowly absorbed in the brain of zebrafish after oral administration of paraquat. In addition, paraquat toxicity resulted in behavioral impairments, namely, reduced motor activity and led to abnormal neural activities in zebrafish larvae. This locomotor deficit came with a dysregulation of dopamine synthesis induced by the inhibition of tyrosine hydroxylase activity, which was also indirectly confirmed by molecular modeling studies. Furthermore, short-term exposure to paraquat also caused simultaneous dysregulation of other neurochemistry including cholinergic and serotonergic systems in zebrafish larvae. The present study suggests that this neurotoxicological profiling could be a useful tool for understanding the brain neurochemistry of neurotoxic agents that might be a potential risk to human and environmental health.

The Sphingolipid Asset Is Altered in the Nigrostriatal System of Mice Models of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease incurable due to late diagnosis and treatment. Therefore, one of the priorities of neurology is to study the mechanisms of PD pathogenesis at the preclinical and early clinical stages. Given the important role of sphingolipids in the pathogenesis of neurodegenerative diseases, we aimed to analyze the gene expression of key sphingolipid metabolism enzymes (ASAH1, ASAH2, CERS1, CERS3, CERS5, GBA1, SMPD1, SMPD2, UGCG) and the content of 32 sphingolipids (subspecies of ceramides, sphingomyelins, monohexosylceramides and sphinganine, sphingosine, and sphingosine-1-phosphate) in the nigrostriatal system in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models of the preclinical and clinical stages of PD. It has been shown that in PD models, the expression of five of the nine studied genes (CERS1, CERS5, ASAH1, ASAH2, and GBA1) increases but only in the substantia nigra (SN) containing dopaminergic cell bodies. Changes in the expression of enzyme genes were accompanied by an increase in the content of 7 of the 32 studied sphingolipids. Such findings suggest these genes as attractive candidates for diagnostic purposes for preclinical and clinical stages of PD.

Neuroinductive properties of mGDNF depend on the producer, E. Coli or human cells

The glial cell line-derived neurotrophic factor (GDNF) is involved in the survival of dopaminergic neurons. Besides, GDNF can also induce axonal growth and creation of new functional synapses. GDNF potential is promising for translation to treat diseases associated with neuronal death: neurodegenerative disorders, ischemic stroke, and cerebral or spinal cord damages. Unproductive clinical trials of GDNF for Parkinson's disease treatment have induced to study this failure. A reason could be due to irrelevant producer cells that cannot perform the required post-translational modifications. The biological activity of recombinant mGDNF produced by E. coli have been compared with mGDNF produced by human cells HEK293. mGDNF variants were tested with PC12 cells, rat embryonic spinal ganglion cells, and SH-SY5Y human neuroblastoma cells in vitro as well as with a mouse model of the Parkinson's disease in vivo. Both in vitro and in vivo the best neuro-inductive ability belongs to mGDNF produced by HEK293 cells. Keywords: GDNF, neural differentiation, bacterial and mammalian expression systems, cell cultures, model of Parkinson's disease.

Housekeeping Genes for Parkinson's Disease in Humans and Mice

A critical aspect of real-time PCR is the presence of housekeeping genes (HKGs) as an internal control for the normalization of expression data for genes of interest. It is necessary to select correct HKGs in the investigation of various pathologies. Thereby, we analyzed the stability of expression of the HKGs in Parkinson’s disease (PD). The work was carried out in the peripheral blood of patients with PD and in the brain tissues and peripheral blood of mice with MPTP-induced PD. As a result, Aars was the most stably expressed HKG in the mouse brain as a whole. However, different genes were more stably expressed in different parts of the brain. Polr2f was the most stably expressed in the cortex, Psmd6 was the most stably expressed in the cerebellum, and Psmd7 was the most stably expressed in the striatum and substantia nigra. HKGs were different in similar tissues of the studied organisms. Polr2f was the most stably expressed HKG in the peripheral blood of mice, whereas PSMD6 was the most stably expressed gene in humans. Thus, there is no universal HKG both for different brain tissues of one organism and for similar tissues of different organisms. Furthermore, the identified most stably expressed HKGs can be considered as such only under conditions in PD.

A Monoiodotyrosine Challenge Test in a Parkinson's Disease Model

Early (preclinical) diagnosis of Parkinson’s disease (PD) is a major challenge in modern neuroscience. The objective of this study was to experimentally evaluate a diagnostic challenge test with monoiodotyrosine (MIT), an endogenous inhibitor of tyrosine hydroxylase. Striatal dopamine was shown to decrease by 34% 2 h after subcutaneous injection of 100 mg/kg MIT to intact mice, with the effect not being amplified by a further increase in the MIT dose. The selected MIT dose caused motor impairment in a neurotoxic mouse model of preclinical PD, but not in the controls. This was because MIT reduced striatal dopamine to the threshold of motor symptoms manifestation only in PD mice. Therefore, using the experimental mouse model of preclinical PD, we have shown that a MIT challenge test may be used to detect latent nigrostriatal dysfunction.

A Pilot Study of Changes in the Level of Catecholamines and the Activity of α-2-Macroglobulin in the Tear Fluid of Patients with Parkinson's Disease and Parkinsonian Mice

Development of differential and early (preclinical) diagnostics of Parkinson’s disease (PD) is among the priorities in neuroscience. We searched for changes in the level of catecholamines and α-2-macroglobulin activity in the tear fluid (TF) in PD patients at an early clinical stage. It was shown that TF in patients is characterized by an increased level of noradrenaline mainly on the ipsilateral side of pronounced motor symptoms (72%, p = 0.049), a decreased level of adrenaline on both sides (ipsilateral—53%, p = 0.004; contralateral—42%, p = 0.02), and an increased α-2-macroglobulin activity on both sides (ipsilateral—53%, p = 0.03; contralateral—56%, p = 0.037) compared to controls. These changes are considered as potential biomarkers for differential diagnosis. Similar changes in the TF were found in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice when modeling clinical and preclinical stages of PD. These data show the adequacy of models to the pathogenesis of PD along the selected metabolic pathways, and also suggest that the found TF changes can be considered as potential biomarkers for preclinical diagnosis of PD. In Parkinsonian mice, the level of catecholamines also changes in the lacrimal glands, which makes it possible to consider them as one of the sources of catecholamines in the TF.

[Development of early diagnosis of Parkinson's disease and comprehensive economic analysis of the effect of its implementation]

The paper summarizes the literature and author's data on the development of early (preclinical) diagnosis of Parkinson's disease (PD). Implementation of this diagnosis will promote the use of preventive therapy and change investments in diagnosis and treatment of patients. The paper declares that at present the only approach to early diagnosis of PD is positron-emission tomography of the nigrostriatal dopaminergic system, but it cannot be used for preventive examination due to its high cost. The authors consider that a less specific, but more promising approach to the development of early diagnosis of PD is the search for markers in body fluids, mainly in the blood, in patients at the prodromal stage of PD. Indeed, a number of markers as changes in the level of metabolites of monoamines, sphingolipids, urates, and indicators of oxidative stress were found in patients selected for the risk group of the prodromal stage of PD, according to characteristic premotor symptoms. In addition, it is assumed that the search for blood markers at an earlier - pre-prodromal stage is possible only in animal models of PD at the early preclinical stage. This approach can also be used to verify blood markers identified in patients at the clinical stage of PD. It is also evident that the complex socio-economic factors influencing the incidence of PD is different in developed versus developing countries. The societal and medical costs of Parkinson's are huge and efforts to improve early preclinical diagnosis of PD will lead to considerable economical and societal benefits. For instance this will allow efficient selection of patients for preclinical diagnostic tests. To assess the effectiveness of this strategy considering the uncertainty of socio-economic issues, a modification of the «cost-utility» analysis is proposed. For the first time, a Markov model of PD including preclinical diagnostic tests and possible neuroprotective therapy was developed and studied. Analytical outcomes of this process suggest that the idea of developing a new multimodal strategy is promising from a socio-economic point of view.

Diffusion Tensor Imaging-Based Studies at the Group-Level Applied to Animal Models of Neurodegenerative Diseases

The understanding of human and non-human microstructural brain alterations in the course of neurodegenerative diseases has substantially improved by the non-invasive magnetic resonance imaging (MRI) technique of diffusion tensor imaging (DTI). Animal models (including disease or knockout models) allow for a variety of experimental manipulations, which are not applicable to humans. Thus, the DTI approach provides a promising tool for cross-species cross-sectional and longitudinal investigations of the neurobiological targets and mechanisms of neurodegeneration. This overview with a systematic review focuses on the principles of DTI analysis as used in studies at the group level in living preclinical models of neurodegeneration. The translational aspect from in-vivo animal models toward (clinical) applications in humans is covered as well as the DTI-based research of the non-human brains' microstructure, the methodological aspects in data processing and analysis, and data interpretation at different abstraction levels. The aim of integrating DTI in multiparametric or multimodal imaging protocols will allow the interrogation of DTI data in terms of directional flow of information and may identify the microstructural underpinnings of neurodegeneration-related patterns.

Development of early diagnosis of Parkinson's disease: Illusion or reality?

The fight against neurodegenerative diseases, Alzheimer disease and Parkinson's disease (PD), is a challenge of the 21st century. The low efficacy of treating patients is due to the late diagnosis and start of therapy, after the degeneration of most specific neurons and depletion of neuroplasticity. It is believed that the development of early diagnosis (ED) and preventive treatment will delay the onset of specific symptoms. This review evaluates methodologies for developing ED of PD. Since PD is a systemic disease, and the degeneration of certain neurons precedes that of nigrostriatal dopaminergic neurons that control motor function, the current methodology is based on searching biomarkers, such as premotor symptoms and changes in body fluids (BF) in patients. However, all attempts to develop ED were unsuccessful. Therefore, it is proposed to enhance the current methodology by (i) selecting among biomarkers found in BF in patients at the clinical stage those that are characteristics of animal models of the preclinical stage, (ii) searching biomarkers in BF in subjects at the prodromal stage, selected by detecting premotor symptoms and failure of the nigrostriatal dopaminergic system. Moreover, a new methodology was proposed for the development of ED of PD using a provocative test, which is successfully used in internal medicine.

Expression analysis of genes involved in mitochondrial biogenesis in mice with MPTP-induced model of Parkinson's disease

The mitochondrion is an extremely important organelle that performs various functions in the cell: e.g. energy production, regulation of respiration processes and maintenance of calcium homeostasis. Disruption of the biogenesis and functioning of this organelle can lead to cell damage and cell death. Mitochondrial dysfunction has been shown to possibly be involved in the pathogenesis of Parkinson's disease. However, the role of genes associated with mitochondrial biogenesis in the early stages of disease remains poorly understood. The objective of the present study was to analyze changes in the expression of activator (Nrf1, Ppargc1a, Prkn, and Kif1b) and repressor (Zfp746 and Mybbp1a) genes of mitochondrial biogenesis in the early stages of the development of neurodegeneration in an MPTP-induced model of presymptomatic and early symptomatic stages of PD. Statistically significant changes in expression at the mRNA level were detected for all studied genes. There was mainly a decrease in the expression of activator genes (Nrf1, Ppargc1a, Prkn, and Kif1b) at all stages of neurodegeneration, which seemed to be associated with impaired mitochondrial biogenesis and the development of neurodegeneration processes. A predominant decrease in the expression was detected for the Zfp746 and Mybbp1a repressor genes of mitochondrial biogenesis. However, in this case, it was associated with the emergence of compensatory mechanisms during the development of Parkinson's disease. The largest number of statistically significant changes was detected for the Nrf1 activator gene and the Mybbp1a repressor gene. Apparently, these two genes play the most important role in this disease.

Mice deficient in GM1 manifest both motor and non-motor symptoms of Parkinson's disease; successful treatment with synthetic GM1 ganglioside

Parkinson's disease (PD) is a major neurodegenerative disorder characterized by a variety of non-motor symptoms in addition to the well-recognized motor dysfunctions that have commanded primary interest. We previously described a new PD mouse model based on heterozygous disruption of the B4galnt1 gene leading to partial deficiency of the GM1 family of gangliosides that manifested several nigrostriatal neuropathological features of PD as well as movement impairment. We now show this mouse also suffers three non-motor symptoms characteristic of PD involving the gastrointestinal, sympathetic cardiac, and cerebral cognitive systems. Treatment of these animals with a synthetic form of GM1 ganglioside, produced by transfected E. coli, proved ameliorative of these symptoms as well as the motor defect. These findings further suggest subnormal GM1 to be a systemic defect constituting a major risk factor in sporadic PD and indicate the B4galnt1(+/-) (HT) mouse to be a true neuropathological model that recapitulates both motor and non-motor lesions of this condition.

Proteins of the Vesicular Cycle as a Marker of Neuroplasticity of Dopaminergic Neurons in the Substantia Nigra of the Brain

Nigrostriatal dopaminergic neurons (DNs), involved in the regulation of motor function, are characterized by a high plasticity. Indeed, at the death of up to 50% of DNs in Parkinson's disease, the survived neurons provide normal regulation. This study was aimed to determine whether the vesicle cycle proteins, syntaxin Ia (Syn Ia), synaptotagmin I (Syt I), Rab5a, and complexins I and II (Cmpx I and II) are involved in the mechanisms of neuroplasticity in the substantia nigra, which mainly contains cell bodies and processes of the DNs. In the neurotoxic models of Parkinson's disease in mice, it was shown that, at the degeneration of up to 50% of DNs, the content of Syt I, Syn Ia, and Cmpх I and II, involved in vesicle exocytosis, does not change in the substantia nigra as a whole but is compensatorily increased in individual survived DNs. Thus, the data obtained in this study suggest that the impairment of motor behavior, which occurs at the death of half of the nigrostriatal DNs, is not caused by the impairment of the production of vesicle cycle proteins in the survived DNs.

VCP expression decrease as a biomarker of preclinical and early clinical stages of Parkinson's disease

Valosin-containing human protein (VCP) or p97 performs enzyme functions associated with the maintenance of protein homeostasis and control of protein quality. Disruption of its normal functioning might be associated with the development of Parkinson’s disease (PD). Tissues of mice with toxin-induced presymptomatic and early symptomatic stages of PD, as well as 52 treated and untreated patients with newly diagnosed PD and nine patients with a “predicted” form of PD, were investigated. Significant changes in Vcp gene expression were observed in almost all studied mouse tissues. A significant decrease in VCP expression specific for PD was also detected at both the late preclinical and the early clinical stages of PD in untreated patients. Thus, a decrease in VCP expression is important for changes in the function of the nervous system at early stages of PD. Analysis of changes in VCP expression in all patients with PD and in Vcp in the peripheral blood of mice used as models of PD revealed significant decreases in expression specific for PD. These data suggest that a decrease in the relative levels of VCP mRNA might serve as a biomarker for the development of pathology at the early clinical and preclinical stages of human PD.

Tear Fluid Catecholamines As Biomarkers of the Parkinson's Disease: A Clinical and Experimental Study

An important approach to an early diagnosis of Parkinson's disease (PD) is screening for peripheral biomarkers in patients at the early clinical stage. In this study, we evaluated catecholamine concentration changes in the tear fluid of untreated PD patients as biomarkers. Norepinephrine and dopamine concentrations in the tear fluid of patients were found to increase compared to those in age controls, which was especially pronounced on the side where motor symptoms appeared. On the contrary, the epinephrine concentration in the tear fluid of patients was reduced bilaterally. Since there was no reason to consider the markers found in the clinical stage of PD as markers of the preclinical stage, we additionally studied the tear fluid composition in mouse neurotoxic models of PD preclinical and clinical stages. The norepinephrine concentration in the tear fluid of mice from the clinical stage model was found to be higher than that in controls; in the preclinical stage model, the norepinephrine concentration had a tendency to increase. Therefore, both PD patients and mice from PD preclinical and clinical stage models manifest unidirectional changes in their tear fluid compositions, which may be considered as promising biomarkers for the development of early diagnosis.

Moxibustion Exerts a Neuroprotective Effect through Antiferroptosis in Parkinson's Disease

The objective of this study was to explore the neuroprotective effect of moxibustion on rats with Parkinson's disease (PD) and its mechanism. A Parkinson's disease model was established in rats using a two-point stereotactic 6-hydroxydopamine injection in the right substantia nigra (SN) and ventral tegmental area. The rats received moxibustion at the Baihui (GV20) and Sishencong (EX-HN1) acupoints for 20 minutes, six times a week, for 6 weeks. The right SN tissue was histologically and immunohistochemically examined. Differentially expressed genes (DEGs) were identified through RNA sequencing. In addition, the levels of tyrosine hydroxylase (TH), glutathione peroxidase 4 (GPX4), and ferritin heavy chain 1 (FTH1) in SN were measured. In comparison to the model group, the moxibustion group showed a significantly greater TH immunoreactivity and a higher behavioural score. In particular, moxibustion led to an increase in the number and morphological stability of SN neural cells. The functional pathway analysis showed that DEGs are closely related to the ferroptosis pathway. GPX4 and FTH1 in the SN were significantly overexpressed in the moxibustion-treated rats with PD. Moxibustion can effectively reduce the death of SN neurons, decrease the occurrence of ferroptosis, and increase the TH activity to protect the neurons in rats with PD. The protective mechanism may be associated with suppression of the ferroptosis.

An investigation of the single and combined effects of hypogravity and ionizing radiation on brain monoamine metabolism and rats' behavior

BACKGROUND

Ionizing radiation and hypogravity can cause central nervous system (CNS) dysfunctions. This is a key limiting factor for deep space missions. Up until now, the mechanisms through which they affect the neural tissue are not completely understood.

OBJECTIVES

We studied how the combination of hypogravity (antiorthostatic suspension model, AS) and ionizing radiations (γ-quanta and ¹H⁺ together, R) affects the CNS.

METHODS

We applied separately and in combination AS and R to determine the influence of these factors on behavior and metabolism of monoamines in Wistar rat's brain.

RESULTS

We found out that R has a slight effect on both the behavior and metabolism of monoamines. However, when applied in combination with AS the former was able to reduce the negative effects of the latter. The combined effect of ionizing radiation and hypogravity led to the recovery of locomotor activity, orientation and exploratory behavior, and long-term context memory impaired under the impact of hypogravity only. These changes came together with an increase in the serotonin and dopamine turnover in all of the brain structures that were studied.

CONCLUSIONS

We received the first evidence of interferential interaction between the effects of ionizing radiation and hypogravity factors with regard to a behavior and monoamine turnover in the brain. Further studies with heavy nuclei at relevant doses (<0.5 Gy) are needed.

[Circadian changes in the structure of cardiac rhythm during pre-symptomatic and symptomatic stages of Parkinson's disease]

AIM

To study circadian regulation of heart rhythm during the pre-symptomatic (PS) and early symptomatic (ESS) stages of Parkinson's disease (PD) and determine the functionally most unfavorable periods during which there is a risk of life-threatening arrhythmias.

MATERIAL AND METHODS

The studies were performed on C57BL/6 mice. ECG monitoring was performed in online mode using a wireless telemetry system (ADInstruments Australia).

RESULTS

Characteristics of circadian changes heart rate during PS and ESS of PD were detected. During PS changes in the autonomic regulation of the heart occur at night. The increase at this time of the parasympathetic tone indicates compensatory mechanisms that prevent changes in the total power spectrum. However, they can't prevent the high risk of life-threatening arrhythmias. The early symptomatic stage leads to the changes in mechanisms of not only sympathetic, but also parasympathetic regulation of the heart, increase in sympathetic tone and disturbed structure of the heart rhythm over most of the day. The decrease in the total power of the spectrum indicates a decrease in the adaptive capacity of the cardiovascular system. The increase in the intervals of QT, QTc and Tpeak Tend, indicates a risk of life-threatening arrhythmias.

CONCLUSION

PD predetermines complications of circadian autonomic regulation of the heart during PS and ESS, which can become the pathogenetic basis for severe cerebrocardial disorders.

Upgraded Methodology for the Development of Early Diagnosis of Parkinson's Disease Based on Searching Blood Markers in Patients and Experimental Models

Numerous attempts to develop an early diagnosis of Parkinson's disease (PD) by searching biomarkers in biological fluids were unsuccessful. The drawback of this methodology is searching markers in patients at the clinical stage without guarantee that they are also characteristic of either preclinical stage or prodromal stage (preclinical-prodromal stage). We attempted to upgrade this methodology by selecting only markers that are found both in patients and in PD animal models. HPLC and RT-PCR were used to estimate the concentration of amino acids, catecholamines/metabolites in plasma and gene expression in lymphocytes in 36 untreated early-stage PD patients and 52 controls, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice at modeling the clinical ("symptomatic") stage and preclinical-prodromal ("presymptomatic") stage of PD. It was shown that among 13 blood markers found in patients, 7 markers are characteristic of parkinsonian symptomatic mice and 3 markers of both symptomatic and presymptomatic mice. According to our suggestion, the detection of the same marker in patients and symptomatic animals indicates adequate reproduction of pathogenesis along the corresponding metabolic pathway, whereas the detection of the same marker in presymptomatic animals indicates its specificity for preclinical-prodromal stage. This means that the minority of markers found in patients-decreased concentration of L-3,4-dihydroxyphenylalanine (L-DOPA) and dihydroxyphenylacetic acid (DOPAC) and increased dopamine D3 receptor gene expression-are specific for preclinical-prodromal stage and are suitable for early diagnosis of PD. Thus, we upgraded a current methodology for development of early diagnosis of PD by searching blood markers not only in patients but also in parkinsonian animals.

[Changes in characteristics of sleep-wake cycle and motor activity at the preclinical stage of Parkinson's disease in old rats]

AIM

To assess the changes in temporal characteristics and total motor activity (MA) during the sleep-wake cycle in old rats in the model of the preclinical stage of Parkinson's disease (PD).

MATERIAL AND METHODS

Progressing inhibition of proteasome system and prolonged (up to the 21st day) development of the preclinical stage of PD in 19-20-month Wistar rats was caused by the specific proteasomal inhibitor lactacystin administered twice with a week interval. Telemetric monitoring of sleep-wake cycle was performed along with the video recording of MA. Dopamine level in the dorsal striatum was measured by high-performance liquid chromatography.

RESULTS

During the 13-21st days, the preclinical stage of PD in old rats was characterized by the following features: 1) increased drowsiness in the active (dark) phase of day that can be compared with the excessive daytime sleepiness in patients with PD; 2) growth of delta-activity indicating presumably a compensatory increase in the deep slow-wave sleep (SWS) stage; 3) decreased MA during SWS and drowsiness, which was coupled with the lowered dopamine level in the dorsal striatum typical for the preclinical stage of PD.

CONCLUSION

Both increased drowsiness and reduced MA during sleep, reflecting dopamine deficit in the nigrostriatal system, may be recommended for using in clinical research as inexpensive early markers of the preclinical stage of PD.

[Ophthalmic disorders as a manifestation of Parkinson's disease]

Parkinson's disease is a severe neurodegenerative disease accompanied with the degeneration of dopaminergic neurons in the central and peripheral nervous system. The diagnosis of Parkinson's disease can still be made only on the stage of irreversible and nearly total degeneration of the nigrostriatum dopaminergic system and exhaustion of brain compensatory mechanisms that explains the low efficacy of therapy. Ophthalmic pathology is one of the nonmotor symptoms of Parkinson's disease. This can be explained firstly by the fact that eye is a 'peripheral part of brain' and secondly by the involvement of dopaminergic neurons (dopamine-producing cells) that are subject to the selective degeneration during Parkinson's disease in the regulation of visual function in the eye and brain. Dopaminergic neurons and dopamine receptors are present in all structures of the eye. Parkinson's disease cause abnormalities not only in the retina but in the whole optic tract and can be considered as peripheral manifestations of the disease that precede the well-known motor dysfunctions. This review describes ophthalmological symptoms of Parkinson's disease, possible pathophysiological mechanisms of their development, optical disorders in experimental models of Parkinson's disease and also the perspectives of experimental and clinical studies of visual disorders for the development of preclinical diagnosis of Parkinson's disease.

Short- and long-term effects induced by repeated 6-OHDA intraventricular administration: A new progressive and bilateral rodent model of Parkinson's disease

The pathological hallmark of Parkinson's disease (PD) is the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), and the resulting striatal dopamine deficiency, which are responsible for the classic motor features. Although a diagnosis of PD relies on the clinical effects of dopamine deficiency, this disease is also associated with other neurotransmitter deficits that are recognized as causing various motor and non-motor symptoms. However, the cause of dopaminergic nigral neurodegeneration in PD and the underlying mechanisms remain unknown. While animal models are considered valuable tools with which to investigate dopaminergic cell vulnerability, rodent models usually fail to mimic the neurodegeneration progression that occurs in human PD. To find a convenient rat model for studying the progression of dopaminergic cell degeneration and motor signs, we have developed a progressive rodent model using a repeated daily, intraventricular administration of the neurotoxin 6-hydroxydopamine (6-OHDA) (100µg/day) in awakened rats for 1 to 10 consecutive days. The short- (6-day) and long-term (32-day) progression of motor alterations was studied. This model leads to a bilateral and progressive increase in catalepsy (evident from the 3rd infusion in the short-term groups (p<0.01) and from the 7th infusion in the long-term groups (p<0.01), which was associated with a progressive nigrostriatal dopaminergic deficit. All together this makes the new model an interesting experimental tool to investigate the mechanisms involved in the progression of dopaminergic neurodegeneration.

Structural and Functional State of Erythrocyte Membranes in Mice at Different Stages of Experimental Parkinson's Disease Induced by Administration of 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP)

We studied some structural and functional parameters of erythrocyte membranes in mice at the late presymptomatic and early symptomatic stages of experimental Parkinson's disease induced by administration of MPTP (hemolysis, microviscosity of different regions of the lipid bilayer, LPO intensity, activity of antioxidant enzymes, and kinetic properties of acetylcholinesterase). At the presymptomatic stage, significant deviations of the studied parameters from the normal were observed; they were similar in direction and magnitude to those in humans with Parkinson's disease. At the early symptomatic stage, most parameters tended to normal. Microviscosity of bulk lipids increased at the presymptomatic stage and decreased after appearance of clinical symptoms. This dynamics probably reflects activation of compensatory mechanisms aimed at inhibition of oxidative stress triggered by the development of the pathological process.