The high-affinity D2/D3 agonist D512 protects PC12 cells from 6-OHDA-induced apoptotic cell death and rescues dopaminergic neurons in the MPTP mouse model of Parkinson's disease

Fumaria vaillantii extract protects PC12 cells against neurotoxicity induced by 6-OHDA

BACKGROUND

Parkinson's disease is a neurological disorder caused by the loss of dopaminergic neurons in the midbrain. Various mechanisms are involved in the incidence of the disease including oxidative stress. Several herbs and natural products may interfere with the oxidative-stress pathway due to their antioxidant effects.

OBJECTIVE

Herein, we aimed to investigate the neuroprotective role of F. vaillantii extract on Parkinson's in vitro and in vivo model owing to the presence of the bioactive agents with antioxidant properties.

METHODS

In vitro experments showed that 6-hydroxydopamine could induce toxicity in PC12 cells. The impact of F. vaillantii extract on cell viability was measured by using MTT assay. Nuclear morphological changes were qualitatively evaluated employing Hoechst staining. The antioxidant activity of the extract was determined by ROS and lipid peroxidation assays. Tyrosine hydroxylase protein expression was measured by western blotting in PC12 cells. For in vivo study, movement parameters were evaluated.

RESULTS

The results indicated that 75 µΜ of 6-OHDA induced 50% toxicity in PC12 cells for 24 h. Following post-treatment with F. vaillantii extract (0.1 mg/ml) for 72 h, we observed that the extract effectively prevented cell toxicity induced by 6-OHDA and reduced the apoptotic cell population. Furthermore, the extract attenuated the ROS level, lipid peroxidation and increased protein expression of TH after 72 h of treatment. In addition, oral administration of 300 mg/kg of F. vaillantii extract for 14 days improved locomotor activity, catalepsy, bradykinesia, motor coordination and reduced the apomorphine-caused rotation in 6-OHDA- induced Parkinson's disease-like symptoms in male rats.

CONCLUSION

The present study suggests a protective role for the extract of F. vaillantii against oxidative stress-induced cell damage in the PC12 cells exposed to neurotoxin 6-OHDA which was verified in in vivo model by reducing the motor defects induced by 6-OHDA. This extract could be a promising therapeutic agent for the prevention of PD progression.

J24335 exerts neuroprotective effects against 6-hydroxydopamine-induced lesions in PC12 cells and mice

Parkinson's disease is the second most prevalent age-related neurodegenerative disease and disrupts the lives of people aged >60 years. Meanwhile, single-target drugs becoming inapplicable as PD pathogenesis diversifies. Mitochondrial dysfunction and neurotoxicity have been shown to be relevant to the pathogenesis of PD. The novel synthetic compound J24335 (11-Hydroxy-1-(8-methoxy-5-(trifluoromethyl)quinolin-2-yl)undecan-1-one oxime), which has been researched similarly to J2326, has the potential to be a multi-targeted drug and alleviate these lesions. Therefore, we investigated the mechanism of action and potential neuroprotective function of J24335 against 6-OHDA-induced neurotoxicity in mice, and in PC12 cell models. The key target of action of J24335 was also screened. MTT assay, LDH assay, flow cytometry, RT-PCR, LC-MS, OCR and ECAR detection, and Western Blot analysis were performed to characterize the neuroprotective effects of J24335 on PC12 cells and its potential mechanism. Behavioral tests and immunohistochemistry were used to evaluate behavioral changes and brain lesions in mice. Moreover, bioinformatics was employed to assess the drug-likeness of J24335 and screen its potential targets. J24335 attenuated the degradation of mitochondrial membrane potential and enhanced glucose metabolism and mitochondrial biosynthesis to ameliorate 6-OHDA-induced mitochondrial dysfunction. Animal behavioral tests demonstrated that J24335 markedly improved motor function and loss of TH-positive neurons and dopaminergic nerve fibers, and contributed to an increase in the levels of dopamine and its metabolites in brain tissue. The activation of both the CREB/PGC-1α/NRF-1/TFAM and PKA/Akt/GSK-3β pathways was a major contributor to the neuroprotective effects of J24335. Furthermore, bioinformatics predictions revealed that J24335 is a low toxicity and highly BBB permeable compound targeting 8 key genes (SRC, EGFR, ERBB2, SYK, MAPK14, LYN, NTRK1 and PTPN1). Molecular docking suggested a strong and stable binding between J24335 and the 8 core targets. Taken together, our results indicated that J24335, as a multi-targeted neuroprotective agent with promising therapeutic potential for PD, could protect against 6-OHDA-induced neurotoxicity via two potential pathways in mice and PC12 cells.

Protective effects of dioscin against Parkinson's disease via regulating bile acid metabolism through remodeling gut microbiome/GLP-1 signaling

It is necessary to explore potent therapeutic agents via regulating gut microbiota and metabolism to combat Parkinson's disease (PD). Dioscin, a bioactive steroidal saponin, shows various activities. However, its effects and mechanisms against PD are limited. In this study, dioscin dramatically alleviated neuroinflammation and oxidative stress, and restored the disorders of mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). 16 S rDNA sequencing assay demonstrated that dioscin reversed MPTP-induced gut dysbiosis to decrease Firmicutes-to-Bacteroidetes ratio and the abundances of Enterococcus, Streptococcus, Bacteroides and Lactobacillus genera, which further inhibited bile salt hydrolase (BSH) activity and blocked bile acid (BA) deconjugation. Fecal microbiome transplantation test showed that the anti-PD effect of dioscin was gut microbiota-dependent. In addition, non-targeted fecal metabolomics assays revealed many differential metabolites in adjusting steroid biosynthesis and primary bile acid biosynthesis. Moreover, targeted bile acid metabolomics assay indicated that dioscin increased the levels of ursodeoxycholic acid, tauroursodeoxycholic acid, taurodeoxycholic acid and β-muricholic acid in feces and serum. In addition, ursodeoxycholic acid administration markedly improved the protective effects of dioscin against PD in mice. Mechanistic test indicated that dioscin significantly up-regulated the levels of takeda G protein-coupled receptor 5 (TGR5), glucagon-like peptide-1 receptor (GLP-1R), GLP-1, superoxide dismutase (SOD), and down-regulated NADPH oxidases 2 (NOX2) and nuclear factor-kappaB (NF-κB) levels. Our data indicated that dioscin ameliorated PD phenotype by restoring gut dysbiosis and regulating bile acid-mediated oxidative stress and neuroinflammation via targeting GLP-1 signal in MPTP-induced PD mice, suggesting that the compound should be considered as a prebiotic agent to treat PD in the future.

Reverses Motor Deficits and Reduces Accumulation of Human α-Synuclein Protein in Two Different Parkinson's Disease Animal Models

Aggregation of misfolded α-synuclein (α-syn) protein in the periphery and central nervous system (CNS) gives rise to a group of disorders, which are labeled collectively as synucleinopathies. These clinically distinct disorders are known as pure autonomic failure, Parkinson's disease (PD), Parkinson's disease dementia (PDD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). In the case of PD, it has been demonstrated that toxic aggregates of α-syn protein not only cause apoptosis of dopamine neurons but its accumulation in the neocortex and limbic area principally contributes to dementia. In our multifunctional drug discovery research for PD, we converted one of our catechol-containing lead dopamine agonist molecules D-520 into its prodrug D-685. The prodrug exhibited higher in vivo anti-Parkinsonian efficacy in a reserpinized PD animal model than the parent D-520 and exhibited facile brain penetration. In our study with an α-syn transgenic animal model (D line) for PD and dementia with Lewy bodies (DLB), we have shown that 1 month of chronic treatment with the compound D-685 was sufficient to reduce the accumulation of α-syn and phospho-α-syn in the cortex, hippocampus, and striatum areas significantly compared to the control tg mice. Furthermore, D-685 did not exhibit any deleterious effect in the CNS as was evident from the neuron and microglia studies. Future studies will further explore in depth the potential of D-685 to modify disease progression while addressing symptomatic deficits.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Biological Activity of Novel Pyrrole Derivatives as Antioxidant Agents Against 6-OHDA Induced Neurotoxicity in PC12 Cells

Background

Neuroinflammation and oxidative stress are critical factors involved in the pathogenesis of Parkinson's disease (PD), the second most common progressive neurodegenerative disease. Additionally, lipid peroxidation end products contribute to inflammatory responses by activating pro-inflammatory genes. Lipid peroxidation occurs as a result of either the overproduction of intracellular reactive oxygen species (ROS) or the reaction of cyclooxygenases (COXs).

Objectives

In this study, we examined the role of 1,5-diaryl pyrrole derivatives against the neurotoxic effects of 6-hydroxydopamine (6-OHDA) in a cellular model of PD.

Methods

PC12 cells were pre-treated with compounds 2-(4-chlorophenyl)-5-methyl-1-(4-(trifluoromethoxy)phenyl)-1H-pyrrole (A), 2-(4-chlorophenyl)-1-(4-methoxyphenyl)-5-methyl-1H-pyrrole (B), and 1-(2-chlorophenyl)-2-(4-chlorophenyl)-5-methyl-1H-pyrrole (C), respectively, 24 h before exposure to 6-OHDA. We conducted various assays, including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazoliumbromide (MTT), ROS, and lipid peroxidation assays, Hoechst staining, Annexin V/PI, Western blotting analysis and ELISA method, to assess the neuroprotective effects of pyrrole derivatives on 6-OHDA-induced neurotoxicity.

Results

Our results demonstrated that apoptosis induction was inhibited by controlling the lipid peroxidation process in the in vitro model following pre-treatment with compounds A, B, and, somehow, C. Furthermore, compounds A and C likely act by suppressing the COX-2/PGE2 pathway, a mechanism not attributed to compound B.

Conclusions

These findings suggest that the novel synthetic pyrrolic derivatives may be considered promising neuroprotective agents that can potentially prevent the progression of PD.

Thymol protects against 6-hydroxydopamine-induced neurotoxicity in in vivo and in vitro model of Parkinson's disease via inhibiting oxidative stress

Background

Parkinson’s disease (PD) is a multifactorial movement disorder with the progressive degeneration of the nigrostriatal system that impairs patients’ movement ability. Oxidative stress has been found to affect the etiology and pathogenesis of PD. Thymol, a monoterpenic phenol, is one of the most important dietary constituents in thyme species. It has been used in traditional medicine and possesses some properties including antioxidant, free radical scavenging, anti-inflammatory. In this study, in vitro and in vivo experiments were performed with the thymol in order to investigate its potential neuroprotective effects in models of PD.

Methods

The present study aimed to evaluate the therapeutic potential of thymol in 6-hydroxydopamine (6-OHDA)-induced cellular and animal models of PD. 

Results

Post-treatment with thymol in vitro was found to protect PC12 cells from toxicity induced by 6-OHDA administration in a dose-dependent manner by (1) increasing cell viability and (2) reduction in intracellular reactive oxygen species, intracellular lipid peroxidation, and annexin-positive cells. In vivo, post-treatment with thymol was protective against neurodegenerative phenotypes associated with systemic administration of 6-OHDA. Results indicated that thymol improved the locomotor activity, catalepsy, akinesia, bradykinesia, and motor coordination and reduced the apomorphine-caused rotation in 6-OHDA-stimulated rats. Increased level of reduced glutathione content and a decreased level of MDA (malondialdehyde) in striatum were observed in the 6-OHDA rats post-treated with thymol.

Conclusions

Collectively, our findings suggest that thymol exerts protective effects, possibly related to an anti-oxidation mechanism, in these in vitro and in vivo models of Parkinson’s disease.

Neurobiological and Pharmacological Perspectives of D3 Receptors in Parkinson’s Disease

The discovery of the D3 receptor (D3R) subtypes of dopamine (DA) has generated an understandable increase in interest in the field of neurological diseases, especially Parkinson’s disease (PD). Indeed, although DA replacement therapy with l-DOPA has provided an effective treatment for patients with PD, it is responsible for invalidating abnormal involuntary movements, known as L-DOPA-induced dyskinesia, which constitutes a serious limitation of the use of this therapy. Of particular interest is the finding that chronic l-DOPA treatment can trigger the expression of D1R–D3R heteromeric interactions in the dorsal striatum. The D3R is expressed in various tissues of the central nervous system, including the striatum. Compelling research has focused on striatal D3Rs in the context of PD and motor side effects, including dyskinesia, occurring with DA replacement therapy. Therefore, this review will briefly describe the basal ganglia (BG) and the DA transmission within these brain regions, before going into more detail with regard to the role of D3Rs in PD and their participation in the current treatments. Numerous studies have also highlighted specific interactions between D1Rs and D3Rs that could promote dyskinesia. Finally, this review will also address the possibility that D3Rs located outside of the BG may mediate some of the effects of DA replacement therapy.

Tetrachlorobenzoquinone exposure triggers ferroptosis contributing to its neurotoxicity

Halogenated quinones are representative metabolites of persistent organic pollutants. Tetrachlorobenzoquinone (TCBQ) is a reactive metabolite of the widely used fungicide hexachlorobenzene (HCB) and wood preservative pentachlorophenol (PCP). Our previous studies have demonstrated that TCBQ induced neuron-like cell apoptosis in a reactive oxygen species (ROS)-dependent manner. Here, we found that TCBQ caused lipid peroxidation and cellular morphological changes including shrinked mitochondrial size, suggesting the involvement of a recently uncovered form of programmed cell death (PCD), ferroptosis. Indeed, we then identified that ferroptosis is a novel PCD driven by TCBQ, which was correlated with a decrease in glutathione peroxidase 4 (GPX4) level and iron accumulation by altering iron metabolism. Notably, nuclear factor erythroid-derived 2-like 2 (Nrf2) is a negative regulator in modulating the outcomes of ferroptosis as an adaptive cellular defense response. Nrf2 activation enhanced iron storage capacity and GPX4 activity by elevating ferritin heavy chain 1 (FTH1) expression and glutathione (GSH) level, respectively. On the contrary, Nfe2l2 (Nrf2) deficiency enhanced PC12 cells susceptibility to ferroptosis.

Recent advances in dopaminergic strategies for the treatment of Parkinson's disease

Parkinson's disease (PD) is the second most common progressive neurodegenerative disease worldwide. However, there is no available therapy reversing the neurodegenerative process of PD. Based on the loss of dopamine or dopaminergic dysfunction in PD patients, most of the current therapies focus on symptomatic relief to improve patient quality of life. As dopamine replacement treatment remains the most effective symptomatic pharmacotherapy for PD, herein we provide an overview of the current pharmacotherapies, summarize the clinical development status of novel dopaminergic agents, and highlight the challenge and opportunity of emerging preclinical dopaminergic approaches aimed at managing the features and progression of PD.

Activation of CB2R with AM1241 ameliorates neurodegeneration via the Xist/miR-133b-3p/Pitx3 axis

Activation of cannabinoid receptor type II (CB2R) by AM1241 has been demonstrated to protect dopaminergic neurons in Parkinson's disease (PD) animals. However, the specific mechanisms of the action of the CB2R agonist AM1241 for PD treatment have not been characterized. Wild-type (WT), CB1R knockout (CB1-KO), and CB2R knockout (CB2-KO) mice were exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 1 week to obtain a PD mouse model. The therapeutic effects of AM1241 were evaluated in each group. Behavioral tests, analysis of neurotransmitters, and immunofluorescence results demonstrated that AM1241 ameliorated PD in WT animals and CB1-KO animals. However, AM1241 did not ameliorate PD symptoms in CB2-KO mice. RNA-seq analysis identified the lncRNA Xist as an important regulator of the protective actions of AM1241. Specifically, AM1241 allowed WT and CB1-KO animals treated with MPTP to maintain normal expression of Xist, which affected the expression of miR-133b-3p and Pitx3. In vitro, overexpression of Xist or AM1241 protected neuronal cells from death induced by 6-hydroxydopamine and increased Pitx3 expression. The CB2 receptor agonist AM1241 alleviated PD via regulation of the Xist/miR-133b-3p/Pitx3 axis, and revealed a new approach for PD treatment.

Targeting alpha synuclein and amyloid beta by a multifunctional, brain-penetrant dopamine D2/D3 agonist D-520: Potential therapeutic application in Parkinson's disease with dementia

A significant number of people with Parkinson’s disease (PD) develop dementia in addition to cognitive dysfunction and are diagnosed as PD with dementia (PDD). This is characterized by cortical and limbic alpha synuclein (α-syn) accumulation, and high levels of diffuse amyloid beta (Aβ) plaques in the striatum and neocortical areas. In this regard, we evaluated the effect of a brain-penetrant, novel multifunctional dopamine D2/D3 agonist, D-520 on the inhibition of Aβ aggregation and disintegration of α-syn and Aβ aggregates in vitro using purified proteins and in a cell culture model that produces intracellular Aβ-induced toxicity. We further evaluated the effect of D-520 in a Drosophila model of Aβ_1-42 toxicity. We report that D-520 inhibits the formation of Aβ aggregates in vitro and promotes the disaggregation of both α-syn and Aβ aggregates. Finally, in an in vivo Drosophila model of Aβ_1-42 dependent toxicity, D-520 exhibited efficacy by rescuing fly eyes from retinal degeneration caused by Aβ toxicity. Our data indicate the potential therapeutic applicability of D-520 in addressing motor dysfunction and neuroprotection in PD and PDD, as well as attenuating dementia in people with PDD.

Carvacrol Protects Against 6-Hydroxydopamine-Induced Neurotoxicity in In Vivo and In Vitro Models of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder characterized by selective loss of dopaminergic neurons that project from the substantia nigra pars compacta to the striatum. Evidence from human and animal studies has suggested that oxidative damage critically contributes to neuronal loss in PD. Carvacrol (CAR), a monoterpenic phenol, is the main constituents in the essential oil of many aromatic plants and possesses some properties including anti-inflammatory and anti-oxidant effects. In this study, in vitro and in vivo experiments were performed with the CAR in order to investigate its potential neuroprotective effects in models of PD. Post-treatment with CAR in vitro was found to protect rat adrenal pheochromocytoma PC12 cells from toxicity induced by 6-hydroxydopamine (6-OHDA) administration in a dose-dependent manner by (1) increasing cell viability and (2) reduction in intracellular reactive oxygen species, intracellular lipid peroxidation, and annexin-positive cells. In vivo, post-treatment with CAR (15 and 20 mg/kg) was protective against neurodegenerative phenotypes associated with systemic administration of 6-OHDA. Results indicated that CAR improved the locomotor activity, catalepsy, akinesia, bradykinesia, and motor coordination and reduced the apomorphine-caused rotation in 6-OHDA-stimulated rats. Increased level of reduced glutathione content and a decreased level of MDA (malondialdehyde) were observed in the 6-OHDA rats post-treated with CAR. These findings suggest that CAR exerts protective effects, possibly related to an anti-oxidation mechanism, in these in vitro and in vivo models of Parkinson's disease.

Partial decortication ameliorates dopamine depletion‑induced striatal neuron lesions in rats

The balance between glutamate (cortex and thalamus) and dopamine (substantia nigra) inputs on striatal neurons is of vital importance. Dopamine deficiency, which breaks this balance and leads to the domination of cortical glutamatergic inputs, plays an important role in Parkinson's disease (PD). However, the exact impact on striatal neurons has not been fully clarified. Thus, the present study aimed to characterize the influence of corticostriatal glutamatergic inputs on striatal neurons after decortication due to dopamine depletion in rats. 6-Hydroxydopamine was injected into the right medial forebrain bundle to induce dopamine depletion, and/or ibotenic acid into the primary motor cortex to induce decortication. Subsequently, the grip strength test and Morris water maze task indicated that decortication significantly shortened the hang time and the latency that had been increased in the rats subjected to dopamine depletion. Golgi staining and electron microscopy analysis showed that the total dendritic length and dendritic spine density of the striatal neurons were decreased in the dopamine-depleted rats, whereas decortication alleviated this damage. Immunohistochemistry analysis demonstrated that decortication decreased the number of caspase-3-positive neurons in the dopamine-depleted rats. Moreover, reverse transcription-quantitative PCR and western blot analyses showed that decortication offset the upregulation of caspase-3 at both the protein and mRNA levels in the dopamine-depleted rats. In conclusion, the present study demonstrated that a relative excess of cortical glutamate inputs had a substantial impact on the pathological processes of striatal neuron lesions in PD.

Design, Synthesis, and Pharmacological Characterization of Carbazole Based Dopamine Agonists as Potential Symptomatic and Neuroprotective Therapeutic Agents for Parkinson's Disease

We have developed a series of carbazole-derived compounds based on our hybrid D₂/D₃ agonist template to design multifunctional compounds for the symptomatic and disease-modifying treatment of Parkinson's disease (PD). The lead molecules (-)-11b (D-636), (-)-15a (D-653), and (-)-15c (D-656) exhibited high affinity for both D₂ and D₃ receptors and in GTPγS functional assay, the compounds showed potent agonist activity at both D₂ and D₃ receptors (EC₅₀ (GTPγS); D₂ = 48.7 nM, D₃ = 0.96 nM for 11b, D₂ = 0.87 nM, D₃ = 0.23 nM for 15a and D₂ = 2.29 nM, D₃ = 0.22 nM for 15c). In an animal model of PD, the test compounds exhibited potent in vivo activity in reversing hypolocomotion in reserpinized rats with a long duration of action compared to the reference drug ropinirole. In a cellular antioxidant assay, compounds (-)-11b, (-)-15a, and (-)-15c exhibited potent activity in reducing oxidative stress induced by neurotoxin 6-hydroxydopamine (6-OHDA). Also, in a cell-based PD neuroprotection model, these lead compounds significantly increased cell survival from toxicity of 6-OHDA, thereby producing a neuroprotective effect. Additionally, compounds (-)-11b and (-)-15a inhibited aggregation and reduced toxicity of recombinant alpha synuclein protein in a cell based in vitro assay. These observations suggest that the lead carbazole-based dopamine agonists may be promising multifunctional molecules for a viable symptomatic and disease-modifying therapy of PD and should be further investigated.

Induction of ferroptosis and mitochondrial dysfunction by oxidative stress in PC12 cells

Neurodegenerative diseases (NDD) are typically associated with neuron loss in nervous system areas. Interventions with related death mechanisms may ameliorate NDD progression. Oxidative stress plays an important role in NDD cell death routines. However, tert-butylhydroperoxide (t-BHP), a widely used oxidative stress stimulus, induces neural cell death through a mechanism that remains elusive. In our study, the ferroptosis marker events occurred after co-treatment with 100 μM t-BHP for 1 h, all of which were reversed in the presence of the ferroptosis inhibitor ferrostatin-1 (Fer-1) and the iron chelator deferoxamine, implying the occurrence of ferroptosis. Moreover, mitochondrial dysfunction accompanied by a decreased in membrane potential and ATP production, increased mitochondrial ROS generation. Furthermore, this mitochondrial dysfunction could be reversed by Fer-1. In addition, JNK1/2 and ERK1/2 were activated upstream of the ferroptosis and mitochondrial dysfunction. In summary, these data suggest that ferroptosis, coupled with mitochondrial dysfunction, was involved in t-BHP-induced PC12 death. JNK1/2 and ERK1/2 played important roles in t-BHP-induced cell death. Overall, this study might provide clues to the oxidative stress-based strategies for cell protection in NDD.

D-512, a novel dopamine D2/3 receptor agonist, demonstrates greater anti-Parkinsonian efficacy than ropinirole in Parkinsonian rats

BACKGROUND AND PURPOSE

Symptoms of Parkinson's disease are commonly managed using selective dopamine D_2/3 receptor agonists, including ropinirole. While D_2/3 agonists are useful in early-stage Parkinson's disease, they tend to lose efficacy in later disease stages and do not appear to modify disease progression. We have recently developed a novel 'multifunctional' compound, D-512: a high-affinity D_2/3 receptor agonist with antioxidant and other neuroprotective properties that may limit Parkinson's disease progression. This study sought to compare the anti-Parkinsonian properties of the clinically used compound, ropinirole, with those of the novel compound, D-512.

EXPERIMENTAL APPROACH

A rat model of Parkinson's disease was created by unilaterally infusing 6-hydroxydopamine, a dopamine neurotoxin, into the medial forebrain bundle. D-512 was compared with ropinirole for ability to stimulate spontaneous motor activity and reverse Parkinsonian akinesia. These beneficial effects were compared against each drug's liability to provoke dyskinesia, a common motor side effect.

KEY RESULTS

Both compounds increased spontaneous movement, but D-512 showed a longer duration of action. Only D-512 was able to significantly reverse forelimb akinesia. Drug-induced dyskinesia was similar for equivalent doses.

CONCLUSIONS AND IMPLICATIONS

Compared with ropinirole, D-512 showed greater peak-dose efficacy and a longer duration of action, despite a similar side-effect profile. Our results add to earlier data showing that D-512 is superior to available D_2/3 agonists and could merit clinical investigation.

Advances and challenges in the search for D2 and D3 dopamine receptor-selective compounds

Compounds that target D2-like dopamine receptors (DRs) are currently used as therapeutics for several neuropsychiatric disorders including schizophrenia (antagonists) and Parkinson's disease (agonists). However, as the D₂R and D₃R subtypes are highly homologous, creating compounds with sufficient subtype-selectivity as well as drug-like properties for therapeutic use has proved challenging. This review summarizes the progress that has been made in developing D₂R- or D₃R-selective antagonists and agonists, and also describes the experimental conditions that need to be considered when determining the selectivity of a given compound, as apparent selectivity can vary widely depending on assay conditions. Future advances in this field may take advantage of currently available structural data to target alternative secondary binding sites through creating bivalent or bitopic chemical structures. Alternatively, the use of high-throughput screening techniques to identify novel scaffolds that might bind to the D₂R or D₃R in areas other than the highly conserved orthosteric site, such as allosteric sites, followed by iterative medicinal chemistry will likely lead to exceptionally selective compounds in the future. More selective compounds will provide a better understanding of the normal and pathological functioning of each receptor subtype, as well as offer the potential for improved therapeutics.

A novel iron (II) preferring dopamine agonist chelator D-607 significantly suppresses α-syn- and MPTP-induced toxicities in vivo

Here, we report the characterization of a novel hybrid D₂/D₃ agonist and iron (II) specific chelator, D-607, as a multi-target-directed ligand against Parkinson's disease (PD). In our previously published report, we showed that D-607 is a potent agonist of dopamine (DA) D₂/D₃ receptors, exhibits efficacy in a reserpinized PD animal model and preferentially chelates to iron (II). As further evidence of its potential as a neuroprotective agent in PD, the present study reveals D-607 to be protective in neuronal PC12 cells against 6-OHDA toxicity. In an in vivo Drosophila melanogaster model expressing a disease-causing variant of α-synuclein (α-Syn) protein in fly eyes, the compound was found to significantly suppress toxicity compared to controls, concomitant with reduced levels of aggregated α-Syn. Furthermore, D-607 was able to rescue DAergic neurons from MPTP toxicity in mice, a well-known PD neurotoxicity model, following both sub-chronic and chronic MPTP administration. Mechanistic studies indicated that possible protection of mitochondria, up-regulation of hypoxia-inducible factor, reduction in formation of α-Syn aggregates and antioxidant activity may underlie the observed neuroprotection effects. These observations strongly suggest that D-607 has potential as a promising multifunctional lead molecule for viable symptomatic and disease-modifying therapy for PD.

Novel multifunctional dopamine D2/D3 receptors agonists with potential neuroprotection and anti-alpha synuclein protein aggregation properties

Our ongoing drug development endeavor to design compounds for symptomatic and neuroprotective treatment of Parkinson's disease (PD) led us to carry out a structure activity relationship study based on dopamine agonists pramipexole and 5-OHDPAT. Our goal was to incorporate structural elements in these agonists in a way to preserve their agonist activity while producing inhibitory activity against aggregation of α-synuclein protein. In our design we appended various catechol and related phenol derivatives to the parent agonists via different linker lengths. Structural optimization led to development of several potent agonists among which (-)-8a, (-)-14 and (-)-20 exhibited potent neuroprotective properties in a cellular PD model involving neurotoxin 6-OHDA. The lead compounds (-)-8a and (-)-14 were able to modulate aggregation of α-synuclein protein efficiently. Finally, in an in vivo PD animal model, compound (-)-8a exhibited efficacious anti-parkinsonian effect.

Development of a Highly Potent D2/D3 Agonist and a Partial Agonist from Structure-Activity Relationship Study of N(6)-(2-(4-(1H-Indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine Analogues: Implication in the Treatment of Parkinson's Disease

Our structure-activity relationship studies with N(6)-(2-(4-(1H-indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine derivatives led to development of a lead compound (-)-21a which exhibited very high affinity (Ki, D2 = 16.4 nM, D3 = 1.15 nM) and full agonist activity (EC50 (GTPγS); D2 = 3.23 and D3 = 1.41 nM) at both D2 and D3 receptors. A partial agonist molecule (-)-34 (EC50 (GTPγS); D2 = 21.6 (Emax = 27%) and D3 = 10.9 nM) was also identified. In a Parkinson's disease (PD) animal model, (-)-21a was highly efficacious in reversing hypolocomotion in reserpinized rats with a long duration of action, indicating its potential as an anti-PD drug. Compound (-)-34 was also able to elevate locomotor activity in the above PD animal model significantly, implying its potential application in PD therapy. Furthermore, (-)-21a was shown to be neuroprotective in protecting neuronal PC12 from toxicity of 6-OHDA. This report, therefore, underpins the notion that a multifunctional drug like (-)-21a might have the potential not only to ameliorate motor dysfunction in PD patients but also to modify disease progression by protecting DA neurons from progressive degeneration.

Assessment of Protective Role of Multifunctional Dopamine Agonist D-512 Against Oxidative Stress Produced by Depletion of Glutathione in PC12 Cells: Implication in Neuroprotective Therapy for Parkinson's Disease

Oxidative stress has been strongly implicated in the progression of Parkinson's disease (PD). Depletion of cytoplasmic glutathione levels is one of the indications of oxidative stress, which occur in the substantia nigra of PD patients at an early stage of the disease process. It has been shown that glutathione depletion causes the inhibition of mitochondrial complex I, thus affecting mitochondrial function leading to oxidative stress via production of reactive oxygen species. Studies were carried out to investigate the role of D-512, a potent multifunctional neuroprotective D2/D3 receptor agonist, in protecting dopaminergic PC12 cells treated with buthionine sulfoximine (BSO), an inhibitor of key enzyme in glutathione synthesis and 6-hydroxydopamine (6-OHDA), a widely used neurotoxin. D-512 was able to restore level of glutathione against BSO/6-OHDA-mediated glutathione depletion. D-512 also showed significant neuroprotection in PC12 cells against toxicity induced by combined treatment of BSO and 6-OHDA. Furthermore, D-512 was able to restore both phospho-extracellular signal-regulated kinase and phospho-Jun N-terminal kinase levels upon treatment with 6-OHDA providing an evidence on the possible mechanism of action for neuroprotection by modulating mitogen-activated protein kinases. We have further demonstrated the neuroprotective effects of D-512 against oxidative insult produced by BSO and 6-OHDA in PC12 cells.

Carriers of a common variant in the dopamine transporter gene have greater dementia risk, cognitive decline, and faster ventricular expansion

INTRODUCTION

Genetic variants in DAT1, the gene encoding the dopamine transporter (DAT) protein, have been implicated in many brain disorders. In a recent case-control study of Alzheimer's disease (AD), a regulatory polymorphism in DAT1 showed a significant association with the clinical stages of dementia.

METHODS

We tested whether this variant was associated with increased AD risk, and with measures of cognitive decline and longitudinal ventricular expansion, in a large sample of elderly participants with genetic, neurocognitive, and neuroimaging data from the Alzheimer's Disease Neuroimaging Initiative.

RESULTS

The minor allele-previously linked with increased DAT expression in vitro-was more common in AD patients than in both individuals with mild cognitive impairment and healthy elderly controls. The same allele was also associated with poorer cognitive performance and faster ventricular expansion, independently of diagnosis.

DISCUSSION

These results may be due to reduced dopaminergic transmission in carriers of the DAT1 mutation.

Cortex Fraxini (Qingpi) Protects Rat Pheochromocytoma Cells against 6-Hydroxydopamine-Induced Apoptosis

Parkinson's disease (PD) is a chronic neurodegenerative disorder having close relationship with oxidative stress induced by reactive oxygen species (ROS). Cortex Fraxini (QP) is a kind of traditional Chinese medicinal herb with antioxidant properties. It may be a potential candidate for preventing the development of chronic neurodegenerative diseases. Thus, the key objective of the current study was to investigate the neuroprotective effect of QP water extract on 6-hydroxydopamine (6-OHDA) induced apoptosis in rat pheochromocytoma (PC12) cells. It was found that QP water extract possesses strong antioxidant property with SC₅₀ = 0.15 mg/mL. Total phenolic content of QP water extract was found to be 200.78 ± 2.65 mg GAE/g. QP water extract's free radical scavenging capacity was demonstrated by reversing the increased level of intracellular ROS induced by 6-OHDA, using 2′,7′-dichlorodihydrofluorescein diacetate. Moreover, QP water extract (0.5 mg/mL) could remarkably increase the viability of PC12 cells treated with 6-OHDA. The protective effect of QP water extract was found to be via inhibiting MEK/ERK pathway and reversing PI3-K/Akt/GSK3β pathway. The current results suggest that QP might be a potential candidate for preventing the development of neurodegenerative diseases, such as PD.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.