Protective effects of nicotine against aminochrome-induced toxicity in substantia nigra derived cells: implications for Parkinson's disease

Targets to Search for New Pharmacological Treatment in Idiopathic Parkinson's Disease According to the Single-Neuron Degeneration Model

One of the biggest problems in the treatment of idiopathic Parkinson's disease is the lack of new drugs that slow its progression. L-Dopa remains the star drug in the treatment of this disease, although it induces severe side effects. The failure of clinical studies with new drugs depends on the use of preclinical models based on neurotoxins that do not represent what happens in the disease since they induce rapid and expansive neurodegeneration. We have recently proposed a single-neuron degeneration model for idiopathic Parkinson's disease that requires years to accumulate enough lost neurons for the onset of motor symptoms. This single-neuron degeneration model is based on the excessive formation of aminochrome during neuromelanin synthesis that surpass the neuroprotective action of the enzymes DT-diaphorase and glutathione transferase M2-2, which prevent the neurotoxic effects of aminochrome. Although the neurotoxic effects of aminochrome do not have an expansive effect, a stereotaxic injection of this endogenous neurotoxin cannot be used to generate a preclinical model in an animal. Therefore, the aim of this review is to evaluate the strategies for pharmacologically increasing the expression of DT diaphorase and GSTM2-2 and molecules that induce the expression of vesicular monoamine transporter 2, such as pramipexole.

Nicotinic Acetylcholine Receptors in Glial Cells as Molecular Target for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by resting tremor, bradykinesia, rigidity, and postural instability that also includes non-motor symptoms such as mood dysregulation. Dopamine (DA) is the primary neurotransmitter involved in this disease, but cholinergic imbalance has also been implicated. Current intervention in PD is focused on replenishing central DA, which provides remarkable temporary symptomatic relief but does not address neuronal loss and the progression of the disease. It has been well established that neuronal nicotinic cholinergic receptors (nAChRs) can regulate DA release and that nicotine itself may have neuroprotective effects. Recent studies identified nAChRs in nonneuronal cell types, including glial cells, where they may regulate inflammatory responses. Given the crucial role of neuroinflammation in dopaminergic degeneration and the involvement of microglia and astrocytes in this response, glial nAChRs may provide a novel therapeutic target in the prevention and/or treatment of PD. In this review, following a brief discussion of PD, we focus on the role of glial cells and, specifically, their nAChRs in PD pathology and/or treatment.

Single-neuron neurodegeneration as a degenerative model for Parkinson's disease

The positive effect of levodopa in the treatment of Parkinson's disease, although it is limited in time and has severe side effects, has encouraged the scientific community to look for new drugs that can stop the neurodegenerative process or even regenerate the neuromelanin-containing dopaminergic nigrostriatal neurons. Successful preclinical studies with coenzyme Q10, mitoquinone, isradipine, nilotinib, TCH346, neurturin, zonisamide, deferiprone, prasinezumab, and cinpanemab prompted clinical trials. However, these failed and after more than 50 years levodopa continues to be the key drug in the treatment of the disease, despite its severe side effects after 4-6 years of chronic treatment. The lack of translated successful results obtained in preclinical investigations based on the use of neurotoxins that do not exist in the human body as new drugs for Parkinson's disease treatment is a big problem. In our opinion, the cause of these failures lies in the experimental animal models involving neurotoxins that do not exist in the human body, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 6-hydroxydopamine, that induce a very fast, massive and expansive neurodegenerative process, which contrasts with the extremely slow one of neuromelanin-containing dopaminergic neurons. The exceedingly slow progress of the neurodegenerative process of the nigrostriatal neurons in idiopathic Parkinson's patients is due to (i) a degenerative model in which the neurotoxic effect of an endogenous neurotoxin affects a single neuron, (ii) a neurotoxic event that is not expansive and (iii) the fact that the neurotoxin that triggers the neurodegenerative process is produced inside the neuromelanin-containing dopaminergic neurons. The endogenous neurotoxin that fits this degenerative model involving one single neuron at a time is aminochrome, since it (i) is generated within neuromelanin-containing dopaminergic neurons, (ii) does not cause an expansive neurotoxic effect and (iii) triggers all the mechanisms involved in the neurodegenerative process of the nigrostriatal neurons in idiopathic Parkinson's disease. In conclusion, based on the hypothesis that the neurodegenerative process of idiopathic Parkinson's disease corresponds to a single-neuron neurodegeneration model, we must search for molecules that increase the expression of the neuroprotective enzymes DT-diaphorase and glutathione transferase M2-2. It has been observed that the activation of the Kelch-like ECH-associated protein 1/nuclear factor (erythroid-derived 2)-like 2 pathway is associated with the transcriptional activation of the DT-diaphorase and glutathione transferase genes.

Butyrate protects and synergizes with nicotine against iron- and manganese-induced toxicities in cell culture: Implications for neurodegenerative diseases

Toxic exposures to heavy metals, such as iron (Fe) and manganese (Mn), can result in long-range neurological diseases and are therefore of significant environmental and medical concerns. We have previously reported that damage to neuroblastoma-derived dopaminergic cells (SH-SY5Y) by both Fe and Mn could be prevented by pre-treatment with nicotine. Moreover, butyrate, a short chain fatty acid (SCFA) provided protection against salsolinol, a selective dopaminergic toxin, in the same cell line. Here, we broadened the investigation to determine whether butyrate might also protect against Fe and/or Mn, and whether, if combined with nicotine, an additive or synergistic effect might be observed. Both butyrate and nicotine concentration-dependently blocked Fe and Mn toxicities. The ineffective concentrations of nicotine and butyrate, when combined, provided full protection against both Fe and Mn. Moreover, the effects of nicotine but not butyrate could be blocked by mecamylamine, a non-selective nicotinic antagonist. On the other hand, the effects of butyrate, but not nicotine, could be blocked by beta-hydroxy butyrate, a fatty acid-3 receptor antagonist. These results not only provide further support for neuroprotective effects of both nicotine and butyrate but indicate distinct mechanisms of action for each one. Furthermore, potential utility of the combination of butyrate and nicotine against heavy metal toxicities is suggested.

JM-20, a Benzodiazepine-Dihydropyridine Hybrid Molecule, Inhibits the Formation of Alpha-Synuclein-Aggregated Species

Studies showed that JM-20, a benzodiazepine-dihydropyridine hybrid molecule, protects against rotenone and 6-hydroxydopamine neurotoxicity. However, its protective effects against cytotoxicity induced by endogenous neurotoxins involved in Parkinson's disease (PD) pathogenesis have never been investigated. In this study, we evaluated the ability of JM-20 to inhibit alpha-synuclein (aSyn) aggregation. We also evaluated the interactions of JM-20 with aSyn by molecular docking and molecular dynamics and assessed the protective effect of JM-20 against aminochrome cytotoxicity. We demonstrated that JM-20 induced the formation of heterogeneous amyloid fibrils, which were innocuous to primary cultures of mesencephalic cells. Moreover, JM-20 reduced the average size of aSyn positive inclusions in H4 cells transfected with SynT wild-type and synphilin-1-V5, but not in HEK cells transfected with synphilin-1-GFP. In silico studies showed the interaction between JM-20 and the aSyn-binding site. Additionally, we showed that JM-20 protects SH-SY5Y cells against aminochrome cytotoxicity. These results reinforce the potential of JM-20 as a neuroprotective compound for PD and suggest aSyn as a molecular target for JM-20.

Evidence for Dopamine Abnormalities Following Acute Methamphetamine Exposure Assessed by Neuromelanin-Sensitive Magnetic Resonance Imaging

Background

Neuromelanin-sensitive magnetic resonance imaging (NM-MRI) is a newly developed MRI technique that provides a non-invasive way to indirectly measure of dopamine (DA) function. This study aimed to determine NM concentrations in brain regions following acute methamphetamine (MA) administration using NM-MRI and to explore whether NM-MRI can be used as a biomarker of DA function in non-neurodegenerative diseases.

Methods

Baseline NM-MRI, T1-weighted and T2-weighted images were acquired from 27 rats before drug/placebo injection. The control group (n = 11) received acute placebo (Normal saline), while the experimental group (n = 16) received acute MA. NM-MRI scans were performed 5, 30, 60 and 90 min after injection. Regions of interest (ROIs), including the caudate putamen (CP), nucleus accumbens (NAc), hippocampus (HIP), substantia nigra (SN) and crus cerebri (CC), were manually drawn by an experienced radiologist. NM-MRI signal intensity in five brain regions at different time points (baseline and 5, 30, 60, and 90 min) were analyzed.

Results

In both the control and experimental groups, at each time point (baseline and 5, 30, 60, and 90 min), the SN exhibited significantly higher NM-MRI signal intensity than the other brain regions (P < 0.05). In addition, acute MA administration resulted in a continuous upward trend in NM-MRI signal intensity in each brain region over time. However, there was no such trend over time in the control group. The NM-MRI signal intensity of SN in the experimental group was significantly higher at the 60 and 90 min compared with that in the control group (P values were 0.042 and 0.042 respectively). Within experimental group, the NM-MRI signal intensity of SN was significantly higher at the 60 and 90 min compared with that before MA administration (P values were 0.023 and 0.011 respectively). Increased amplitudes and rates of NM-MRI signal intensity were higher in the SN than in other brain regions after MA administration.

Conclusion

Our results indicated that NM was mainly deposited in the SN, and the conversion of DA to NM was most significant in the SN after acute MA exposure. Increased DA release induced by acute MA exposure may lead to increased accumulation of NM in multiple brain regions that can be revealed by NM-MRI. NM-MRI may serve as a powerful imaging tool that could have diverse research and clinical applications for detecting pathological changes in drug addiction and related non-neurodegenerative diseases.

A pharmacological review of dicoumarol: An old natural anticoagulant agent

Dicoumarol is an oral anticoagulant agent prescribed in clinical for decades. It is a natural hydroxycoumarin discovered from the spoilage of Melilotus officinalis (L.) Pall and is originally discovered as a rodenticide. Due to its structural similarity to that of vitamin K, it significantly inhibits vitamin K epoxide reductase and acts as a vitamin K antagonist. Dicoumarol is mainly used as an anticoagulant to prevent thrombogenesis and to cure vascular thrombosis. Other biological activities besides anticoagulants such as anticancer, antimicrobial, antiviral, etc., have also been documented. The side effects of dicoumarol raise safety concerns for clinical application. In this review, the physicochemical property, the pharmacological activities, the side effects, and the pharmacokinetics of dicoumarol were summarized, aiming to provide a whole picture of the "old" anticoagulant.

Neurotoxicity of e-cigarettes

It appears that electronic cigarettes (EC) are a less harmful alternative to conventional cigarette (CC) smoking, as they generate substantially lower levels of harmful carcinogens and other toxic compounds. Thus, switching from CC to EC may be beneficial for smokers. However, recent accounts of EC- or vaping-associated lung injury (EVALI) has raised concerns regarding their adverse health effects. Additionally, the increasing popularity of EC among vulnerable populations, such as adolescents and pregnant women, calls for further EC safety evaluation. In this state-of-the-art review, we provide an update on recent findings regarding the neurological effects induced by EC exposure. Moreover, we discuss possible neurotoxic effects of nicotine and numerous other chemicals which are inherent both to e-liquids and EC aerosols. We conclude that in recognizing pertinent issues associated with EC usage, both government and scientific researchers must address this public health issue with utmost urgency.

Development of a Competition-Binding Assay to Determine Binding Affinity of Molecules to Neuromelanin via Fluorescence Spectroscopy

Neuromelanin, the polymeric form of dopamine which accumulates in aging neuronal tissue, is increasingly recognized as a functional and critical component of a healthy and active adult human brain. Notorious in plant and insect literature for their ability to bind and retain amines for long periods of time, catecholamine polymers known colloquially as 'melanins' are nevertheless curiously absent from most textbooks regarding biochemistry, neuroscience, and evolution. Recent research has brought attention to the brain pigment due to its possible role in neurodegeneration. This linkage is best illustrated by Parkinson's disease, which is characterized by the loss of pigmented dopaminergic neurons and the 'white brain' pathological state. As such, the ability to determine the binding affinity of neurotoxic agents, as well as any potential specific endogenous ligands to neuromelanin are of interest and potential value. Neuromelanin has been shown to have saturable binding interactions with nicotine as monitored by a fluorimeter. This interaction provides a signal to allow for a competition-binding assay with target molecules which do not themselves produce signal. The current report establishes the viability of this competition assay toward three compounds with central relevance to Parkinson's disease. The K_d of binding toward neuromelanin by methyl-phenyl-pyridinium ion (MPP+), dopamine, and 6-hydroxydopamine were found to be 1 mM, 0.05 mM, and 0.1 mM, respectively in the current study. In addition, we demonstrate that 6-hydroxydopamine polymerizes to form neuromelanin granules in cultured dopaminergic neurons that treated with 2,4,5-trihydroxy-l-phenylalanine. Immunohistochemical analysis using fluor-tagged anti-dopamine antibodies suggests that the incorporation of 6-hydroxydopamine (following internalization and decarboxylation analogous to levodopa and dopamine) alters the localized distribution of bound dopamine in these cells.

Protective Effects of Crude Plant Extracts against Aminochrome-induced toxicity in Human Astrocytoma Cells: Implications for Parkinson's Disease

BACKGROUND/AIMS

Aminochrome, an endogenous compound formed during dopamine oxidation can induce neurotoxicity under certain aberrant conditions and induce Parkinson-like syndrome. Glutathione transferase M2 (GSTM2) activity of astrocytes by catalysing the conjugation of aminochrome with glutathione, can offer protection against aminochrome toxicity. Some medicinal toxicity through this plants may exert protective effect against aminochrome mechanism.

METHODS

In the present study, extracts from plants native to Cameroon, such as Alchornea laxiflora (leaves), Dacryodes edulis (barks), Annona muricata (seeds), Annona senegalensis (barks) were evaluated for their protection against aminochrome-induced toxicity in human glioblastoma/ astrocytoma U373MG wild type and U373MGsiGT6 cells in which GSTM2 expression was 74% silenced. The cells were pre-incubated with the plant extracts for 2 hr before addition of aminochrome (75 μM) and measurement of cell death/viability by flow cytometry after 24 hr incubation.

RESULTS

The extract of A. laxiflora (1 μg/ml), D. edulis (25 μg/ml), A. muricata (25 μg/ml) and A. senegalensis (25μg/ml) significantly decreased aminochrome-induced toxicity in U373siGST6 and U373MG cells. However, only A. laxiflora and A. muricata significantly increased the mitochondria membrane potential in U373siGST6 cells following aminochrome treatment.

CONCLUSION

The results indicate that extracts of some Cameroon plants can provide protection against aminochrome-induced toxicity and mitochondria dysfunction in human glioblastoma/astrocytoma cells. Although further identification of active components of these extracts is needed, potential usefulness of these compounds in Parkinson's disease may be suggested.

Aminochrome decreases NGF, GDNF and induces neuroinflammation in organotypic midbrain slice cultures

Recent evidence shows that aminochrome induces glial activation related to neuroinflammation. This dopamine derived molecule induces formation and stabilization of alpha-synuclein oligomers, mitochondria dysfunction, oxidative stress, dysfunction of proteasomal and lysosomal systems, endoplasmic reticulum stress and disruption of the microtubule network, but until now there has been no evidence of effects on production of cytokines and neurotrophic factors, that are mechanisms involved in neuronal loss in Parkinson's disease (PD). This study examines the potential role of aminochrome on the regulation of NGF, GDNF, TNF-α and IL-1β production and microglial activation in organotypic midbrain slice cultures from P8 - P9 Wistar rats. We demonstrated aminochrome (25 μM, for 24 h) induced reduction of GFAP expression, reduction of NGF and GDNF mRNA levels, morphological changes in Iba1⁺ cells, and increase of both TNF-α, IL-1β mRNA and protein levels. Moreover, aminochrome (25 μM, for 48 h) induced morphological changes in the edge of slices and reduction of TH expression. These results demonstrate neuroinflammation, as well as negative regulation of neurotrophic factors (GDNF and NGF), may be involved in aminochrome-induced neurodegeneration, and they contribute to a better understanding of PD pathogenesis.

Nicotinic Receptor Intervention in Parkinson's Disease: Future Directions

Sufficient preclinical and epidemiological data are available to justify nicotinic intervention in Parkinson's disease (PD). Although use of nicotine patch has been suggested in some neurodegenerative disorders, including PD, the key for success with nicotinic intervention, particularly in PD, appears to rely not only on the dose but also on the mode of nicotine administration. Our aim in this short review is to provide justification for such contention. Thus, following a short introduction of nicotinic receptor pharmacology, the potential of nicotine in alleviating not only the motor symptoms, but also the mood disorders (e.g. depression) and mild cognitive impairments that are commonly co-morbid with PD will be presented. Moreover, since current PD therapy is associated with dyskinesia, the effectiveness of nicotine in ameliorating levodopa (L-Dopa)-induced dyskinesia will also be discussed. It is suggested that pulsatile nicotine administration (e.g. via inhalation or nasal spray) may be the optimal route in nicotinic intervention in PD.

Duality of Antidepressants and Neuroprotectants

The co-morbidity of neuropsychiatric disorders, particularly major depressive disorder (MDD) with neurodegenerative diseases, in particular Parkinson's disease (PD) is now well recognized. Indeed, it is suggested that depressive disorders, especially in late life, may be an indication of latent neurodegeneration. Thus, it is not unreasonable to expect that deterrents of MDD may also deter the onset and/or progression of the neurodegenerative diseases including PD. In this review, examples of neuroprotective efficacy of established as well as prospective antidepressants are provided. Conversely, mood-regulating effects of some neuroprotective drugs are also presented. Thus, in addition to currently used antidepressants, ketamine, nicotine, curcumin, and resveratrol are discussed for their dual efficacy. In addition, potential neurobiological substrates for their actions are presented. It is concluded that pharmacological developments of mood-regulating or neuroprotective drugs can have cross benefit in co-morbid conditions of neuropsychiatric and neurodegenerative disorders and that inflammatory and neurotrophic factors play important roles in both conditions.

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.

Antipsychotic medication and tobacco use among outpatients with schizophrenia: a cross-sectional study

BACKGROUND

Many studies have shown that the prevalence of smoking in schizophrenia is higher than in the general population. Biological, psychological and social factors influence smoking in patients with schizophrenia.

METHODS

The study was carried out in psychiatry outpatient clinics in a tertiary care hospital in Sri Lanka. Every third patient was selected using systematic sampling from patients diagnosed with schizophrenia according to ICD-10 clinical criteria. Smoking behaviours were assessed using self-reports. Severity of illness was assessed using Brief Psychiatric Rating Scale (BPRS). Fagerstrom Test for Nicotine Dependence assessed level of dependence. Readiness to Change Questionnaire assessed motivation to change smoking behaviour.

RESULTS

The sample consisted of 306 patients with schizophrenia. Mean age was 38.93 years (SD 10.98). There were 148 males (48.4%). Mean duration of illness was 12.63 years (SD 8.38). Current medication was oral atypical antipsychotics 103, clozapine 136, oral typicals 29 and depot typicals 38. Prevalence of tobacco use among males was 30.41% (95% CI 22.91 to 37.90) and among females 1.90% (95% CI -0.25 to 4.05). Prevalence of current smoking among males was 20.27% (95% CI 13.72 to 26.82). None of the females smoked. Prevalence of smokeless tobacco use among males was 10.14 (95% CI 5.22 to 15.05) and among females 1.90 (95% CI -0.03 to 4.05). When patients treated with clozapine were excluded from the analysis, prevalence of tobacco use was 41.6% among males and 3.2% among females and prevalence of smoking was 29.9% among males. Prevalence of tobacco use was lowest in patients treated with clozapine 18.31 (95% CI 9.09 to 27.53) and highest in those treated with depot antipsychotics 47.83 (95% CI 25.74 to 69.91).

CONCLUSIONS

Prevalence of smoking was less than in many countries. This is influenced by prevalence in the general population and low affordability. Risk of tobacco use was significantly less among patients treated with clozapine.

Neurodegeneration in Parkinson's disease: interactions of oxidative stress, tryptophan catabolites and depression with mitochondria and sirtuins

The biological underpinnings to the etiology and course of neurodegeneration in Parkinson's disease are an area of extensive research that has yet to produce an early biological marker or disease-slowing or preventative treatment. Recent conceptualizations of Parkinson's disease have integrated immuno-inflammation and oxidative and nitrosative stress occurring in depression, somatization and peripheral inflammation into the course of Parkinson's disease. We review the data showing the importance of immuno-inflammatory processes and oxidative and nitrosative stress in such classically conceived 'comorbidities', suggesting that lifetime, prodromal and concurrent depression and somatization may be intricately involved in the etiology and course of Parkinson's disease, rather than psychiatric comorbidities. This produces a longer term developmental perspective of Parkinson's disease, which incorporates tryptophan catabolites (TRYCATs), lipid peroxidation, sirtuins, cyclic adenosine monophosphate, aryl hydrocarbon receptor, and circadian genes. This integrates wider bodies of data pertaining to neuronal loss in Parkinson's disease, emphasizing how these interact with susceptibility genes to drive changes in mitochondria, blood-brain barrier permeability and intercellular signalling. We review this data here in the context of neurodegeneration in Parkinson's disease and to the future directions indicated for slowing disease progression.

One-electron reduction of 6-hydroxydopamine quinone is essential in 6-hydroxydopamine neurotoxicity

6-Hydroxydamine has widely been used as neurotoxin in preclinical studies related on the neurodegenerative process of dopaminergic neurons in Parkinson's disease based on its ability to be neurotoxic as a consequence of free radical formation during its auto-oxidation to topaminequinone. We report that 50-µM 6-hydroxydopamine is not neurotoxic in RCSN-3 cells derived from substantia nigra incubated during 24 h contrasting with a significant sixfold increase in cell death (16 ± 2 %; P < 0.001) was observed in RCSN-3NQ7 cells expressing a siRNA against DT-diaphorase that silence the enzyme expression. To observe a significant cell death in RCSN-3 cells induced by 6-hydroxydopamine (24 ± 1 %; P < 0.01), we have to increase the concentration to 250 μm while a 45 ± 2 % cell death (P < 0.001) was observed at this concentration in RCSN-3NQ7 cells. The cell death induced by 6-hydroxydopamine in RCSN-3NQ7 cells was accompanied with a (i) significant increase in oxygen consumption (P < 0.01), (ii) depletion of reduced glutathione and (iii) a significant decrease in ATP level (P < 0.05) in comparison with RCSN-3 cells. In conclusion, our results suggest that one-electron reduction of 6-hydroxydopamine quinone seems to be the main reaction responsible for 6-hydroxydopamine neurotoxic effects in dopaminergic neurons and DT-diaphorase seems to play an important neuroprotective role by preventing one-electron reduction of topaminequinone.

Neuroinflammation, neurodegeneration, and depression

Neurodegeneration and depression are two common co-morbid conditions, particularly within the aging population. Research has linked neuroinflammation as a major contributing factor to both of these diseases. The key to neuroinflammation effects on neurodegeneration and depression appears to lie within the dysregulation of the control and release of pro- and anti-inflammatory cytokines. This can come from an internal or external insult to the system, or from changes in the individual due to aging that culminate in immune dysregulation. The need to reduce neuroinflammation has led to extensive research into neuroprotectants. We discuss the efficacy found with nicotine, alcohol, resveratrol, curcumin, and ketamine. Our main focus will be on what research tells us about the connections between neuroinflammation, neurodegeneration, and depression, and the hope that neuroprotectants research gives people suffering from neurodegeneration and depression stemming from neuroinflammation. We will conclude by making suggestions for future research in this area.

Dopamine oxidation and autophagy

The molecular mechanisms involved in the neurodegenerative process of Parkinson's disease remain unclear. Currently, there is a general agreement that mitochondrial dysfunction, α-synuclein aggregation, oxidative stress, neuroinflammation, and impaired protein degradation are involved in the neurodegeneration of dopaminergic neurons containing neuromelanin in Parkinson's disease. Aminochrome has been proposed to play an essential role in the degeneration of dopaminergic neurons containing neuromelanin by inducing mitochondrial dysfunction, oxidative stress, the formation of neurotoxic α-synuclein protofibrils, and impaired protein degradation. Here, we discuss the relationship between the oxidation of dopamine to aminochrome, the precursor of neuromelanin, autophagy dysfunction in dopaminergic neurons containing neuromelanin, and the role of dopamine oxidation to aminochrome in autophagy dysfunction in dopaminergic neurons. Aminochrome induces the following: (i) the formation of α-synuclein protofibrils that inactivate chaperone-mediated autophagy; (ii) the formation of adducts with α- and β-tubulin, which induce the aggregation of the microtubules required for the fusion of autophagy vacuoles and lysosomes.