Acetylcholinesterase inhibition by 1-methyl-4-phenylpyridinium ion, a bioactivated metabolite of MPTP

Biological interactions and attenuation of MPTP-induced toxicity in Drosophila melanogaster by Trans-astaxanthin

Trans-astaxanthin (TA) is a carotenoid with amphipathic chemical structure found in yeast, and aquatic organisms. It is known to possess both antioxidative and anti-inflammatory properties. This study was carried out to investigate the ameliorative action of TA on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity in Drosophila melanogaster (Fruit fly). The flies were orally treated with TA (2.5 mg/10 g diet) and/or MPTP (500 µM) for 5 days. Thereafter, we evaluated selected biomarkers of locomotor deficits (acetylcholinesterase (AChE) and negative geotaxis), oxidative stress (hydrogen peroxide (H2O2), protein carbonyls (PC)), antioxidants (total thiols (T-SH), non-protein thiols, glutathione-S-transferase (GST) and catalase), and inflammation (nitric oxide (nitrite/nitrate) in the flies. Furthermore, we investigated molecular docking analysis of TA against Kelch-like ECH-associated protein 1 (Keap1)) of Homo sapiens and D. melanogaster. The results indicated that TA increased MPTP-induced decreased activities of AChE, GST, and catalase, as well as levels of non-protein thiols and T-SH compared with MPTP-treated flies (p < 0.05). Furthermore, TA attenuated inflammation, and improved locomotor deficit in the flies. The molecular docking data showed that TA had docking scores for binding both the Human and Drosophila Keap1, nearly closer to or higher than the standard inhibitor. The attenuating effects of TA against MPTP-induced toxicity could arise from its antioxidative and anti-inflammatory properties as well as its chemical structure.

Neuroprotective effects of boron nitride nanoparticles in the experimental Parkinson's disease model against MPP+ induced apoptosis

Parkinson's disease (PD) is one of the most aggressive neurodegenerative diseases and characterized by the loss of dopamine-sensitive neurons in the substantia nigra region of the brain. There is no any definitive treatment to completely cure PD and existing treatments can only ease the symptoms of the disease. Boron nitride nanoparticles have been extensively studied in nano-biological studies and researches showed that it can be a promising candidate for PD treatment with its biologically active unique properties. In the present study, it was aimed to investigate ameliorative effects of hexagonal boron nitride nanoparticles (hBNs) against toxicity of 1-methyl-4-phenylpyridinium (MPP⁺) in experimental PD model. Experimental PD model was constituted by application of MPP⁺ to differentiated pluripotent human embryonal carcinoma cell (Ntera-2, NT-2) culture in wide range of concentrations (0.62 to 2 mM). Neuroprotective activity of hBNs against MPP⁺ toxicity was determined by cell viability assays including MTT and LDH release. Oxidative alterations by hBNs application in PD cell culture model were investigated using total antioxidant capacity (TAC) and total oxidant status (TOS) tests. The impacts of hBNs and MPP⁺ on nuclear integrity were analyzed by Hoechst 33258 fluorescent staining method. Acetylcholinesterase (AChE) enzyme activities were determined by a colorimetric assay towards to hBNs treatment. Cell death mechanisms caused by hBNs and MPP+ exposure was investigated by flow cytometry analysis. Experimental results showed that application of hBNs increased cell viability in PD model against MPP⁺ application. TAS and TOS analysis were determined that antioxidant capacity elevated after hBNs applications while oxidant levels were reduced. Furthermore, flow cytometric analysis executed that MPP⁺ induced apoptosis was prevented significantly (p < 0.05) after application with hBNs. In a conclusion, the obtained results indicated that hBNs have a huge potential against MPP⁺ toxicity and can be used in PD treatment as novel neuroprotective agent and drug delivery system.

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.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP⁺), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP⁺ (1.8-18 μg/mouse) in C57BL6 mice. MPP⁺ administration at high dose (18 μg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP⁺ administration at low dose (1.8 μg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP⁺ at doses of 1.8-18 μg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 μg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP⁺ administration (18 μg/mouse). At this highest dose, MPP⁺ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP⁺ at a dose of 18 μg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP⁺-induced striatal damage. MPP⁺ (18 μg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP⁺ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP⁺ (1.8-18 μg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP⁺ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP⁺ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

Cholinergic interneurons in the dorsal and ventral striatum: anatomical and functional considerations in normal and diseased conditions

Striatal cholinergic interneurons (ChIs) are central for the processing and reinforcement of reward-related behaviors that are negatively affected in states of altered dopamine transmission, such as in Parkinson's disease or drug addiction. Nevertheless, the development of therapeutic interventions directed at ChIs has been hampered by our limited knowledge of the diverse anatomical and functional characteristics of these neurons in the dorsal and ventral striatum, combined with the lack of pharmacological tools to modulate specific cholinergic receptor subtypes. This review highlights some of the key morphological, synaptic, and functional differences between ChIs of different striatal regions and across species. It also provides an overview of our current knowledge of the cellular localization and function of cholinergic receptor subtypes. The future use of high-resolution anatomical and functional tools to study the synaptic microcircuitry of brain networks, along with the development of specific cholinergic receptor drugs, should help further elucidate the role of striatal ChIs and permit efficient targeting of cholinergic systems in various brain disorders, including Parkinson's disease and addiction.

Molecular modelling and enzymatic studies of acetylcholinesterase and butyrylcholinesterase recognition with paraquat and related compounds

The potent herbicide paraquat and three other analogues MPP+, MPDP+ and MPTP have a known toxicological profile linked to the ability to damage dopaminergic neurons. Other biological effects were recently addressed to this class of compounds, including the ability to interact with enzymatic targets involved in the Central Nervous System, such as the acetylcholinesterase (AChE) and the butyrylcholinesterase (BuChE). A combined molecular modelling and enzymatic study focusing onto their interaction against the AChE and BuChE is reported. The former study was performed by docking techniques using target known co-crystallographic models. The latter study was carried out by the widely adopted Ellman's method. In both studies the anti-Alzheimer FDA approved drug tacrine was used as reference inhibitor. Our results indicate that paraquat, MPTP, MPDP+ and MPP+ recognize both enzymatic cleft in a similar fashion compared to the reference inhibitor. A structure-activity correlation was found with the net charge of the ligands, indicating a major role of the electrostatic term in the recognition and inhibition of these compounds. Our data completed their enzymatic profile, added new information on the molecular mechanisms underlying their neurotoxicity useful for the rational design of new cholinesterase inhibitors.

Intrastriatal infusion of the Parkinsonian neurotoxin, MPP+, induces damage of striatal cell nuclei in Sprague–Dawley rats

The potent Parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine is known to destroy dopaminergic neurons of the basal ganglia. Its neurotoxically active metabolite, 1-methyl-4-phenyl pyridinium (MPP(+)), has been examined in the present study to verify whether administration of the neurotoxin that depletes about 70% of the striatal dopamine (DA) can cause damage to nuclear components of the cells at the terminal region, the striatum. Unilateral intrastriatal infusion of MPP(+) (100 and 200 nmol in 4 microl saline) caused a dose-dependent depletion of striatal DA (69 and 92%, respectively), as measured employing HPLC electrochemistry. It also resulted in the loss of tyrosine hydroxylase (TH) immunoreactivity in the striatum and in the perikarya at substantia nigra pars compacta (SNpc) and acetylcholinesterase histoenzymological staining in the striatum. Specific nuclear staining employing Hoechst 33342 and acridine orange revealed distorted and spindle shaped nuclei, and perinuclear positioning of nucleolus, respectively, for the former and latter dyes in several of the cell populations in the ipsilateral striatum compared to the contralateral side. Existence of a widened lateral ventricle at the side that received the neurotoxin, as well as denser cellular population, as compared to the contralateral side under transmission electron microscope evidenced general shrinkage of the striatum. Extensive damage of the nuclei was visible in the cell bodies in the treated side. These results demonstrate non-specific damage extending to the cellular groups including cholinergic neurons in addition to dopaminergic neurons in the striatum to intrastriatal administration of the Parkinsonian neurotoxin, MPP(+).

Inactivation of acetylcholinesterase by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride

The neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to reversibly inhibit the activity of acetylcholinesterase. The inactivation of the enzyme was detected by monitoring the accumulation of yellow color produced from the reaction between thiocholine and dithiobisnitrobenzoate ion. The kinetic parameter, Km for the substrate (acetylthiocholine), was found to be 0.216 mM and Ki for MPTP inactivation of acetylcholinesterase was found to be 2.14 mM. The inactivation of enzyme by MPTP was found to be dose-dependent. It was found that MPTP is neither a substrate of AChE nor the time-dependent inactivator. The studies of reaction kinetics indicate the inactivation of AChE to be a linear mixed-type inhibition. The dilution assays indicate that MPTP is a reversible inhibitor for AChE. These data suggest that once MPTP enters the basal ganglia of the brain, it can inactivate the acetylcholinesterase enzyme and thereby increase the acetylcholine level in the basal ganglia of brain, leading to potential cell dysfunction. It appears that the nigrostriatal toxicity by MPTP leading to Parkinson's disease-like syndrome may, in part, be mediated via the acetylcholinesterase inactivation.

Differential release of acetylcholinesterase in vivo, from the guinea pig substantia nigra compared to the caudate putamen following dopamine depletion

In the substantia nigra acetylcholinesterase may have a novel role unrelated to acetylcholine but linked instead to dopamine. Using a sensitive chemiluminescent system, we have investigated the effects of dopamine depletion on the vivo release of acetylcholinesterase in both the substantia nigra and the caudate putamen. Dopamine levels in the caudate putamen were significantly depleted compared to the non-lesioned side, using either of two different toxins for dopaminergic nigrostriatal cells: 6-hydroxydopamine ( 1 or 3 weeks prior to study) or N-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (1 week prior to study). Spontaneous release of acetylcholinesterase from the substantia nigra was significantly reduced following all three pretreatments; however, in the caudate putamen a significant reduction in the spontaneous release of acetylcholinesterase, compared to controls, was only seen in animals studied 1 week after the administration of 6-hydroxydopamine. In all control groups, application of potassium ions (60 mM) evoked a significant release of acetylcholinesterase in the substantia nigra (p < 0.05) and this effect persisted in the surviving neurones following a partial lesion by neurotoxin pre-treatment. The results from this study are discussed in the light of a regulatory mechanism for acetylcholinesterase release from the striatum, which may come into operation depending on the extent of destruction of dopaminergic nigrostriatal neurones.