Distinct effects of intranigral L-DOPA infusion in the MPTP rat model of Parkinson's disease

Impact of Dopamine Oxidation on Dopaminergic Neurodegeneration

Parkinson's disease (PD) is the second most common neurodegenerative disease. The characteristic feature of PD is the progressive degeneration of the dopaminergic (DAergic) neurons in the substantia nigra (SN). DAergic neurons in the SN accumulate black and insoluble membrane structures known as neuromelanin during aging. The oxidation of dopamine (DA) to form neuromelanin generates many o-quinones, including DA o-quinones, aminochrome, and 5,6-indolequinone. The focus of this review is to discuss the role of DA oxidation in association with PD. The oxidation of DA produces oxidative products, inducing mitochondrial dysfunction, impaired protein degradation, α-synuclein aggregation into neurotoxic oligomers, and oxidative stress, in vitro. Recent studies have demonstrated that the DA content is critical for both DJ-1 knockout and A53T α-synuclein transgenic mice to develop PD pathological features, providing evidence for DA action in PD pathogenesis in vivo. The effects of L-DOPA, as the most effective anti-PD drug, are also briefly discussed.

Molecular Mechanisms behind Free Radical Scavengers Function against Oxidative Stress

Accumulating evidence shows that oxidative stress is involved in a wide variety of human diseases: rheumatoid arthritis, Alzheimer's disease, Parkinson's disease, cancers, etc. Here, we discuss the significance of oxidative conditions in different disease, with the focus on neurodegenerative disease including Parkinson's disease, which is mainly caused by oxidative stress. Reactive oxygen and nitrogen species (ROS and RNS, respectively), collectively known as RONS, are produced by cellular enzymes such as myeloperoxidase, NADPH-oxidase (nicotinamide adenine dinucleotide phosphate-oxidase) and nitric oxide synthase (NOS). Natural antioxidant systems are categorized into enzymatic and non-enzymatic antioxidant groups. The former includes a number of enzymes such as catalase and glutathione peroxidase, while the latter contains a number of antioxidants acquired from dietary sources including vitamin C, carotenoids, flavonoids and polyphenols. There are also scavengers used for therapeutic purposes, such as 3,4-dihydroxyphenylalanine (L-DOPA) used routinely in the treatment of Parkinson's disease (not as a free radical scavenger), and 3-methyl-1-phenyl-2-pyrazolin-5-one (Edaravone) that acts as a free radical detoxifier frequently used in acute ischemic stroke. The cell surviving properties of L-DOPA and Edaravone against oxidative stress conditions rely on the alteration of a number of stress proteins such as Annexin A1, Peroxiredoxin-6 and PARK7/DJ-1 (Parkinson disease protein 7, also known as Protein deglycase DJ-1). Although they share the targets in reversing the cytotoxic effects of H₂O₂, they seem to have distinct mechanism of function. Exposure to L-DOPA may result in hypoxia condition and further induction of ORP150 (150-kDa oxygen-regulated protein) with its concomitant cytoprotective effects but Edaravone seems to protect cells via direct induction of Peroxiredoxin-2 and inhibition of apoptosis.

Edaravone leads to proteome changes indicative of neuronal cell protection in response to oxidative stress

Neuronal cell death, in neurodegenerative disorders, is mediated through a spectrum of biological processes. Excessive amounts of free radicals, such as reactive oxygen species (ROS), has detrimental effects on neurons leading to cell damage via peroxidation of unsaturated fatty acids in the cell membrane. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) has been used for neurological recovery in several countries, including Japan and China, and it has been suggested that Edaravone may have cytoprotective effects in neurodegeneration. Edaravone protects nerve cells in the brain by reducing ROS and inhibiting apoptosis. To gain further insight into the cytoprotective effects of Edaravone against oxidative stress condition we have performed comparative two-dimensional gel electrophoresis (2DE)-based proteomic analyses on SH-SY5Y neuroblastoma cells exposed to oxidative stress and in combination with Edaravone. We showed that Edaravone can reverse the cytotoxic effects of H2O2 through its specific mechanism. We observed that oxidative stress changes metabolic pathways and cytoskeletal integrity. Edaravone seems to reverse the H2O2-mediated effects at both the cellular and protein level via induction of Peroxiredoxin-2.

Proteome analysis reveals roles of L-DOPA in response to oxidative stress in neurons

Background

Parkinson’s disease (PD) is the second most common neurodegenerative movement disorder, caused by preferential dopaminergic neuronal cell death in the substantia nigra, a process also influenced by oxidative stress. L-3,4-dihydroxyphenylalanine (L-DOPA) represents the main treatment route for motor symptoms associated with PD however, its exact mode of action remains unclear. A spectrum of conflicting data suggests that L-DOPA may damage dopaminergic neurons due to oxidative stress whilst other data suggest that L-DOPA itself may induce low levels of oxidative stress, which in turn stimulates endogenous antioxidant mechanisms and neuroprotection.

Results

In this study we performed a two-dimensional gel electrophoresis (2DE)-based proteomic study to gain further insight into the mechanism by which L-DOPA can influence the toxic effects of H₂O₂ in neuronal cells. We observed that oxidative stress affects metabolic pathways as well as cytoskeletal integrity and that neuronal cells respond to oxidative conditions by enhancing numerous survival pathways. Our study underlines the complex nature of L-DOPA in PD and sheds light on the interplay between oxidative stress and L-DOPA.

Conclusions

Oxidative stress changes neuronal metabolic routes and affects cytoskeletal integrity. Further, L-DOPA appears to reverse some H₂O₂-mediated effects evident at both the proteome and cellular level.

Behavioral, neurochemical and histological alterations promoted by bilateral intranigral rotenone administration: a new approach for an old neurotoxin

Rotenone exposure in rodents provides an interesting model for studying mechanisms of toxin-induced dopaminergic neuronal injury. However, several aspects remain unclear regarding the effects and the accuracy of rotenone as an animal model of Parkinson's disease (PD). In order to counteract these limitations, this study characterized a precise neurotoxin-delivery strategy employing the bilateral intranigral administration protocol of rotenone as a reliable model of PD. We performed bilateral intranigral injections of rotenone (12 μg) and subsequent general activity (1, 10, 20, and 30 days after rotenone) and cognitive (7, 8, 15, and 30 days after rotenone) evaluations followed by neurochemical and immunohistochemical tests. We have observed that rotenone was able to produce a remarkable reduction on the percentage of tyrosine hydroxylase immunoreactive neurons (about 60%) within the substantia nigra pars compacta. Dopamine (DA) was severely depleted at 30 days after rotenone administration, similarly to its metabolites. In addition, an increase in DA turnover was detected at the same time-point. In parallel, striatal serotonin and its metabolite were found to be increased 30 days after the neurotoxic insult, without apparent modification in the serotonin turnover. Besides, motor behavior was impaired, mainly 1 day after rotenone. Furthermore, learning and memory processes were severely disrupted in different time-points, particularly at the training and test session (30 days). We now provide further evidence of a time-dependent neurodegeneration associated to cognitive impairment after the single bilateral intranigral administration of rotenone. Thus, it is proposed that the current rotenone protocol provides an improvement regarding the existing rotenone models of PD.

The neurobiology of the substantia nigra pars compacta: from motor to sleep regulation

Clinical characteristics of Parkinson's disease (PD) are the result of the degeneration of the neurons of the substantia nigra pars compacta (SNpc). Several mechanisms are implicated in the degeneration of nigrostriatal neurons such as oxidative stress, mitochondrial dysfunction, protein misfolding, disturbances of dopamine (DA) metabolism and transport, neuroinflammation, and necrosis/apoptosis. The literature widely explores the neurotoxic models elicited by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA). Because of the models, it is known that basal ganglia, particularly substantia nigra, have been related to a diversity of functions, from motor to sleep regulation. Nevertheless, a current debate concerning the role of DA on the sleep-wake cycle is in progress. In summary, it is suggested that the dopaminergic system is implicated in the physiology of sleep, with particular regard to the influence of the SNpc neurons. The understanding of the functioning and connectivity of the SNpc neurons has become fundamental to discovering the neurobiology of these neurons.