Biomedical subjects

Donato A Di Monte

Publications and source records attributed to Donato A Di Monte.

At least 19 recordsLinked to original sources

PubMed2007

Nicotine partially protects against paraquat-induced nigrostriatal damage in mice; link to alpha6beta2* nAChRs.

Epidemiological studies indicate that smoking is a negative, and exposure to pesticides, a positive risk factor for Parkinson's disease (PD). The purpose of this study was to assess the interplay between these two factors in a rodent model of nigrostriatal damage. To approach this, mice were administered nicotine, the agent in smoke implicated in neuroprotection. They were then treated for 3 weeks with the pesticide, paraquat, while nicotine was continued. Paraquat treatment decreased (25%) nigral dopaminergic neurons, consistent with previous results. Chronic nicotine administration significantly protected against nigral cell damage, with only a 16% decline in mice treated with both nicotine and paraquat. Paraquat treatment also decreased (14%) the striatal dopamine transporter, an effect that was partially prevented by nicotine. These changes in the striatal dopamine transporter paralleled those in a select striatal alpha6beta2* nicotinic receptor (nAChR) subtype. In contrast, striatal alpha4beta2* nAChRs were not decreased with paraquat treatment, suggesting they are on a differential subset of dopaminergic terminals. The results show that nicotine treatment partially protects against paraquat-induced declines in nigrostriatal dopaminergic neurons to which a select population of alpha6beta2* nAChRs are localized. Moreover, these data support epidemiological findings that environmental influences can elicit opposing effects on nigrostriatal dopaminergic integrity.

Analysis of Variance↗

PubMed2006

Effect of 4-hydroxy-2-nonenal modification on alpha-synuclein aggregation.

Several observations have implicated oxidative stress and aggregation of the presynaptic protein alpha-synuclein in the pathogenesis of Parkinson disease. alpha-Synuclein has been shown to have affinity for unsaturated fatty acids and membranes enriched in polyunsaturated fatty acids, which are especially sensitive to oxidation under conditions of oxidative stress. One of the most important products of lipid oxidation is 4-hydroxy-2-nonenal (HNE), which has been implicated in the pathogenesis of Parkinson disease. Consequently, we investigated the effects of the interaction of HNE with alpha-synuclein. Incubation of HNE with alpha-synuclein at pH 7.4 and 37 degrees C resulted in covalent modification of the protein, with up to six HNE molecules incorporated as Michael addition products. Fourier transform infrared and CD spectra indicated that HNE modification of alpha-synuclein resulted in a major conformational change involving increased beta-sheet. HNE modification of alpha-synuclein led to inhibition of fibrillation in an HNE concentration-dependent manner. This inhibition of fibrillation was shown to be due to the formation of soluble oligomers based on size exclusion high pressure liquid chromatography and atomic force microscope data. Small angle x-ray scattering analysis indicated that the HNE-induced oligomers were compact and tightly packed. Treatment with guanidinium chloride demonstrated that the HNE-induced oligomers were very stable with an extremely slow rate of dissociation. Addition of 5 mum HNE-modified oligomers to primary mesencephalic cultures caused marked neurotoxicity because the integrity of dopaminergic and GABAergic neurons was reduced by 95 and 85%, respectively. Our observations indicate that HNE modification of alpha-synuclein prevents fibrillation but may result in toxic oligomers, which could therefore contribute to the demise of neurons subjected to oxidative damage.

Aldehydes↗

PubMed2006

Microglial activation as a priming event leading to paraquat-induced dopaminergic cell degeneration.

Dopaminergic cells in the substantia nigra are highly vulnerable to the neurodegenerative process of Parkinson's disease. Therefore, mechanisms that enhance their susceptibility to injury bear important implications for disease pathogenesis. Repeated injections with the herbicide paraquat cause oxidative stress and a selective loss of dopaminergic neurons in mice. In this model, the first paraquat exposure, though not sufficient to induce any neurodegeneration, predisposes neurons to damage by subsequent insults. The purpose of this study was to elucidate the mechanisms underlying this "priming" event. We found that a single paraquat exposure was followed by an increase in the number of cells with immunohistochemical, morphological and biochemical characteristics of activated microglia, including induction of NADPH oxidase. If this microglial response was inhibited by the anti-inflammatory drug minocycline, subsequent exposures to the herbicide failed to cause oxidative stress and neurodegeneration. On the other hand, if microglial activation was induced by pre-treatment with lipopolysaccharide, a single paraquat exposure became capable of triggering a loss of dopaminergic neurons. Finally, mutant mice lacking functional NADPH oxidase were spared from neurodegeneration caused by repeated paraquat exposures. Data indicate that microglial activation and consequent induction of NADPH oxidase may act as risk factors for Parkinson's disease by increasing the vulnerability of dopaminergic cells to toxic injury.

Animals↗

PubMed2006

Nigrostriatal dopaminergic neurodegeneration in the weaver mouse is mediated via neuroinflammation and alleviated by minocycline administration.

The murine mutant weaver (gene symbol, wv) mouse, which carries a mutation in the gene encoding the G-protein inwardly rectifying potassium channel Girk2, exhibits a diverse range of defects as a result of postnatal cell death in several different brain neuron subtypes. Loss of dopaminergic nigrostriatal neurons in the weaver, unlike cerebellar granule neuronal loss, is via a noncaspase-mediated mechanism. Here, we present data demonstrating that degeneration of midbrain dopaminergic neurons in weaver is mediated via neuroinflammation. Furthermore, in vivo administration of the anti-inflammatory agent minocycline attenuates nigrostriatal dopaminergic neurodegeneration. This has novel implications for the use of the weaver mouse as a model for Parkinson's disease, which has been associated with increased neuroinflammation.

Analysis of Variance↗

PubMed2006

Comparison of the neurotoxic effects of proteasomal inhibitors in primary mesencephalic cultures.

Impairment of the ubiquitin-proteasome system (UPS) has been implicated in the pathogenesis of Parkinson's disease (PD). Because the neurodegenerative process of PD results in a severe loss of dopaminergic cells, previous in vitro studies have investigated the possibility that these neurons may be particularly vulnerable to proteasomal inhibition. Results of this earlier work are difficult to compare, however, since they were obtained using different proteasomal inhibitors at various concentrations and under diverse culture conditions. Here, four UPS inhibitors, i.e., lactacystin, PSI, epoxomicin and MG-132, were directly evaluated in terms of their ability to damage dopaminergic and GABAergic neurons in primary rat mesencephalic cultures. Using a broad range of concentrations and different incubation lengths, we found that proteasomal inhibitors consistently killed both dopaminergic and GABAergic neurons. The degree of toxicity was slightly different, however, between the two neuronal populations. When measurements of neurotransmitter uptake were used as indicators of neuronal cell viability, the extent of reduction of dopamine uptake caused by proteasomal inhibitors was slightly greater than the decrease in GABA uptake. With PSI the difference in reduction of dopamine vs. GABA uptake was less than 10% and did not reach statistical significance. With the other three inhibitors, dopaminergic cells were up to 20% more affected than GABAergic neurons; this difference reached statistical significance only at specific concentrations and time points. Preincubation of cultures with alpha-methyl-p-tyrosine, an inhibitor of dopamine synthesis, reduced dopamine concentration by 65% but failed to significantly change lactacystin- and MG-132-induced damage to dopaminergic neurons. Data indicate a modest preferential toxicity of proteasomal inhibitors toward dopaminergic cells and thus only in part support the hypothesis that a selective vulnerability to UPS dysfunction underlies the pathogenesis of nigrostriatal degeneration in PD.

Acetylcysteine↗

PubMed2006

Chronic oral nicotine treatment protects against striatal degeneration in MPTP-treated primates.

The present studies were done to investigate the effect of long-term nicotine treatment against nigrostriatal damage in non-human primates. Monkeys were administered nicotine in drinking water for 6 months to provide chronic but intermittent delivery as with smoking. Plasma nicotine levels ranged from 10 to 15 ng/mL, which were within the range in cigarette smokers. Animals were then lesioned with low doses of the dopaminergic neurotoxin MPTP for several months while nicotine was continued. The results showed that levels of striatal tyrosine hydroxylase, dopamine transporter, vesicular monoamine transporter, dopamine and nicotinic receptors were greater in nicotine-treated MPTP-lesioned primates than in lesioned animals not receiving nicotine. Nicotine had no effect in unlesioned animals. Monoamine oxidase activity was similar in unlesioned and lesioned animals treated with or without nicotine, suggesting that nicotine did not exert its effects through changes in MPTP or dopamine metabolism. MPTP-induced cell loss in the substantia nigra was unaffected by nicotine treatment, indicating that nicotine acts at the striatal level to restore/maintain dopaminergic function. These data further support the possibility that nicotine contributes to the lower incidence of Parkinson's disease in smokers.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2006

Increased murine neonatal iron intake results in Parkinson-like neurodegeneration with age.

Iron elevation is well-documented in the Parkinsonian midbrain but its cause and contribution to subsequent neurodegeneration remain unknown. Mice administered iron at doses equivalent to those found in iron-fortified human infant formula during a developmental period equivalent to the first human year of life display progressive midbrain neurodegeneration and enhanced vulnerability to toxic injury. This may have major implications for the impact of neonatal iron intake as a potential risk factor for later development of Parkinson's disease (PD).

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2006

Lack of nigrostriatal pathology in a rat model of proteasome inhibition.

Systemic administration of ubiquitin-proteasome system inhibitors to rodents has been reported to induce certain behavioral and neuropathological features of Parkinson's disease. The goal of this study was to replicate these observations by administering a proteasome inhibitor (PSI) to rats using McNaught and colleagues' protocol. No alterations in locomotor activity or striatal dopamine and its metabolites were observed. Differences in nigral dopaminergic cell number between proteasome inhibitor- and vehicle-treated rats and inclusion bodies were not found. Extending the time of survival after administration and using different solvents failed to alter results, indicating this proteasome inhibitor does not consistently produce the selective toxicity and pathological hallmarks characterizing Parkinson's disease.

Animals↗

PubMed2005

Alpha-synuclein expression in the substantia nigra of MPTP-lesioned non-human primates.

Changes in the expression of alpha-synuclein are likely to underlie its normal function as well as its role in pathological processes. The relationship between toxic injury and alpha-synuclein expression was assessed in the substantia nigra of squirrel monkeys treated with a single injection of MPTP and sacrificed 1 week or 1 month later. At 1 week, when stereological cell counting revealed only a small decrease (-10%) in the number of dopaminergic neurons, alpha-synuclein mRNA and protein were markedly enhanced. Increased alpha-synuclein immunoreactivity was evident at the level of neuronal fibers whereas nigral cell bodies were devoid of detectable protein. At 1 month post-MPTP, neuronal loss rose to 40%. Both alpha-synuclein mRNA and protein remained elevated but, noticeably, a robust alpha-synuclein immunoreactivity characterized a significant number of cell bodies. Neuromelanin granules are hallmarks of dopaminergic neurons in primates. Therefore, the number of alpha-synuclein-positive cells that also contained neuromelanin was counted throughout the substantia nigra. At 1 month, the vast majority of alpha-synuclein-immunoreactive neurons contained neuromelanin, and approximately 80% of the dopaminergic cell bodies that survived MPTP toxicity stained positive for alpha-synuclein. The results indicate that a single toxic insult is capable of inducing a sustained alpha-synuclein up-regulation in the primate brain. They support a direct relationship between neuronal injury and enhanced alpha-synuclein expression, and suggest that protein elevation within cell bodies may be a late feature of neurons that have endured a toxic stress.

Animals↗

PubMed2005

The Webcam system: a simple, automated, computer-based video system for quantitative measurement of movement in nonhuman primates.

Investigations using models of neurologic disease frequently involve quantifying animal motor activity. We developed a simple method for measuring motor activity using a computer-based video system (the Webcam system) consisting of an inexpensive video camera connected to a personal computer running customized software. Images of the animals are captured at half-second intervals and movement is quantified as the number of pixel changes between consecutive images. The Webcam system allows measurement of motor activity of the animals in their home cages, without devices affixed to their bodies. Webcam quantification of movement was validated by correlation with measures simultaneously obtained by two other methods: measurement of locomotion by interruption of infrared beams; and measurement of general motor activity using portable accelerometers. In untreated squirrel monkeys, correlations of Webcam and locomotor activity exceeded 0.79, and correlations with general activity counts exceeded 0.65. Webcam activity decreased after the monkeys were rendered parkinsonian by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), but the correlations with the other measures of motor activity were maintained. Webcam activity also correlated with clinical ratings of parkinsonism. These results indicate that the Webcam system is reliable under both untreated and experimental conditions and is an excellent method for quantifying motor activity in animals.

Animals↗

PubMed2005

Dyskinesias in normal squirrel monkeys induced by nomifensine and levodopa.

The mechanisms underlying levodopa-induced dyskinesias are unclear. They might involve impairment of the buffering capacity for dopamine, resulting from loss of nigral dopaminergic cells and the subsequent degeneration of their terminals in striatum. This study investigated the role of striatal buffering in the development of dyskinesias. We used nomifensine, a selective dopamine reuptake blocker, to pharmacologically impair presynaptic buffering capacity in normal squirrel monkeys. Dyskinesias were assessed at 30-min intervals for 4 h after twice-daily treatment with drug. As previously reported by our group, animals receiving levodopa alone (15 mg/kg) exhibited dyskinetic behavior. Treatment with nomifensine alone (3 mg/kg) also induced dyskinesias. Furthermore, combining levodopa with nomifensine significantly increased dyskinesias. Over 4 weeks of treatment, the animals developed tolerance to the dyskinesia-inducing effect of nomifensine. The development of tolerance was prevented by concurrent treatment with levodopa. These results show that impairing buffering by preventing dopamine reuptake can induce dyskinesias and can also augment levodopa-induced dyskinesias. Thus, this study suggests that diminished buffering capacity for dopamine could play a role in the development of dyskinesias, and that an endogenous mechanism might exist that ameliorates dyskinesias.

Animals↗

PubMed2005

Redox cycling of the herbicide paraquat in microglial cultures.

Mechanisms involved in paraquat neurotoxicity that selectively target nigrostriatal dopaminergic neurons remain relatively unknown. In this study, we tested the hypotheses that paraquat exposure leads to the production of reactive oxygen species (ROS) through a process of redox cycling and that microglia represent an important site for the initiation of redox cycling reactions. Addition of paraquat to N9 microglial cultures resulted in a dose- and time-dependent release of superoxide radicals. Other agents that share with paraquat the property of redox cycling, i.e., benzyl viologen and diquat, also induced a marked production of superoxide radicals by microglia. The ability of paraquat, benzyl viologen, and diquat to induce superoxide release was correlated to their one-electron reduction potentials and thus their tendency to redox cycle. Nitric oxide synthase and NADPH oxidase were identified as enzymatic sources of electrons that triggered paraquat redox cycling by microglia. Taken together, these data provide evidence in favor of a new mechanism by which microglia could play a role in oxidative injury during neurodegenerative processes. Microglial NOS and NADPH oxidase could promote the generation of ROS via the redox cycling of paraquat-like toxicants.

Acetophenones↗

PubMed2005

Role of oxidative stress in paraquat-induced dopaminergic cell degeneration.

Systemic treatment of mice with the herbicide paraquat causes the selective loss of nigrostriatal dopaminergic neurons, reproducing the primary neurodegenerative feature of Parkinson's disease. To elucidate the role of oxidative damage in paraquat neurotoxicity, the time-course of neurodegeneration was correlated to changes in 4-hydroxy-2-nonenal (4-HNE), a lipid peroxidation marker. When mice were exposed to three weekly injections of paraquat, no nigral dopaminergic cell loss was observed after the first administration, whereas a significant reduction of neurons followed the second exposure. Changes in the number of nigral 4-HNE-positive neurons suggest a relationship between lipid peroxidation and neuronal death, since a dramatic increase in this number coincided with the onset and development of neurodegeneration after the second toxicant injection. Interestingly, the third paraquat administration did not cause any increase in 4-HNE-immunoreactive cells, nor did it produce any additional dopaminergic cell loss. Further evidence of paraquat-induced oxidative injury derives from the observation of nitrotyrosine immunoreactivity in the substantia nigra of paraquat-treated animals and from experiments with ferritin transgenic mice. These mice, which are characterized by a decreased susceptibility to oxidative stress, were completely resistant to the increase in 4-HNE-positive neurons and the cell death caused by paraquat. Thus, paraquat exposure yields a model that emphasizes the susceptibility of dopaminergic neurons to oxidative damage.

Aldehydes↗

PubMed2004

Effect of the D3 dopamine receptor partial agonist BP897 [N-[4-(4-(2-methoxyphenyl)piperazinyl)butyl]-2-naphthamide] on L-3,4-dihydroxyphenylalanine-induced dyskinesias and parkinsonism in squirrel monkeys.

Although l-3,4-dihydroxyphenylalanine (L-dopa) is one of the most effective therapies for Parkinson's disease, continued treatment may result in excessive involuntary movements known as L-dopa-induced dyskinesias (LIDs). Because LIDs can become dose-limiting, there is great interest in finding ways to ameliorate or prevent this troubling side effect of L-dopa therapy. It was recently reported that the D3 receptor partial agonist BP897 [N-[4-(4-(2-methoxyphenyl)piperazinyl)butyl]-2-naphthamide] reduces LIDs without diminishing antiparkinsonian effects of L-dopa in macaques. In the present study, we tested the effects of BP897 on LIDs in squirrel monkeys, a nonhuman primate particularly prone to dyskinesias. Parkinsonism was induced using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Animals were then gavaged with L-dopa/carbidopa (7.5 or 15 mg/kg/dose) without and with BP897. The effects of BP897 treatment were evaluated on several components of LIDs, including time course, peak dyskinesias, and area under the curve (AUC), a measure that encompasses both peak and duration of the response. Analyses of the time course and overall dyskinetic response (AUC) showed that BP897 significantly reduced LIDs but at the expense of the antiparkinsonian effect of L-dopa. BP897 had no significant effect on peak dyskinesias. Correlation studies showed that beneficial effects of BP897 on dyskinesias were linked to a decline in the antiparkinsonian action of L-dopa. Analyses of a subgroup of animals with mild/moderate parkinsonism yielded comparable results. Thus, in squirrel monkeys in contrast to macaques, BP897 fails to exert an antidyskinetic effect without diminishing the antiparkinsonian effects of L-dopa. These results suggest that BP897 may be less effective than originally anticipated for treating LIDs in Parkinson's disease.

Animals↗

PubMed2004

Aging of the nigrostriatal system in the squirrel monkey.

Increasing incidence of Parkinson's disease with advancing age suggests that age-related processes predispose the nigrostriatal dopaminergic system to neurodegeneration. Several hypotheses concerning the effects of aging on nigrostriatal neurons were assessed in this study using a non-human primate model. First, we examined the possibility that the total number of dopaminergic neurons decline in the substantia nigra as a function of age. Stereological counting based on both tyrosine hydroxylase immunoreactivity (TH-ir) and neuromelanin (NM) content revealed no difference in cell number between young, middle-aged and old squirrel monkeys. We then determined whether advancing age changed the relative proportion of neurons characterized by 1) TH-ir in the absence of NM, 2) the presence of both TH-ir and NM, or 3) NM without TH-ir. Indeed, a progressive age-related depletion of TH only cells was paralleled by an increase in NM only neurons. The possibility that these changes could underlie a functional impairment of the nigrostriatal system was supported by striatal dopamine measurements showing a decrease in older monkeys. Finally, we tested the hypotheses that aging may enhance cell vulnerability to injury and that different dopaminergic subpopulations display varying degrees of susceptibility. When monkeys were exposed to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, cell loss was markedly more pronounced in older animals, and the ranking of vulnerability was TH only < TH/NM < NM only cells. The data indicate that, even in the absence of an overall neuronal loss, changes in the characteristics of dopaminergic cells reflect functional deficits and increased vulnerability to injury with age. NM content appears to be an important marker of these age-related effects.

Aging↗

PubMed2004

Dopamine and L-dopa disaggregate amyloid fibrils: implications for Parkinson's and Alzheimer's disease.

Protein deposition diseases involve the aggregation of normally soluble proteins, leading to both fibrillar and amorphous deposits. The aggregation of alpha-synuclein is associated with Parkinson's disease, and the aggregation of the Abeta peptide is associated with Alzheimer's disease. Here we show that L-dopa, dopamine, and other catecholamines dissolve fibrils of alpha-synuclein and Abeta peptide generated in vitro. The catecholamines also inhibited the fibrillation of these proteins. In addition, intraneuronal alpha-synuclein deposits formed in a mouse model were dissolved by incubation of tissue slices with L-dopa. These catecholamines are susceptible to oxidative breakdown, and we show that oxidation products are more effective than the parent compounds in inhibition. The ability to dissolve fibrils provides a new approach for studying mechanisms and consequences (e.g., the relationship between fibril formation and neurodegeneration) of protein aggregation. It is also likely to help in the development of strategies for the prevention and treatment of protein deposition diseases.

Alzheimer Disease↗

PubMed2003

Nuclear localization of alpha-synuclein and its interaction with histones.

The aggregation of alpha-synuclein is believed to play an important role in the pathogenesis of Parkinson's disease as well as other neurodegenerative disorders ("synucleinopathies"). However, the function of alpha-synuclein under physiologic and pathological conditions is unknown, and the mechanism of alpha-synuclein aggregation is not well understood. Here we show that alpha-synuclein forms a tight 2:1 complex with histones and that the fibrillation rate of alpha-synuclein is dramatically accelerated in the presence of histones in vitro. We also describe the presence of alpha-synuclein and its co-localization with histones in the nuclei of nigral neurons from mice exposed to a toxic insult (i.e., injections of the herbicide paraquat). These observations indicate that translocation into the nucleus and binding with histones represent potential mechanisms underlying alpha-synuclein pathophysiology.

Cell Nucleus↗

PubMed2003

Alpha-synuclein overexpression protects against paraquat-induced neurodegeneration.

Alpha-synuclein is likely to play a role in neurodegenerative processes, including the degeneration of nigrostriatal dopaminergic neurons that underlies Parkinson's disease. However, the toxicological properties of alpha-synuclein remain relatively unknown. Here, the relationship between alpha-synuclein expression and neuronal injury was studied in mice exposed to the herbicide paraquat. Paraquat neurotoxicity was compared in control animals versus mice with transgenic expression of human alpha-synuclein driven by the tyrosine hydroxylase (TH) promoter. In control mice, paraquat caused both the formation of alpha-synuclein-containing intraneuronal deposits and the degeneration of nigrostriatal neurons, as demonstrated by silver staining and a reduction of the counts of TH-positive and Nissl-stained cells. Mice overexpressing alpha-synuclein, either the human wild-type or the Ala53Thr mutant form of the protein, displayed paraquat-induced protein aggregates but were completely protected against neurodegeneration. These resistant animals were also characterized by increased levels of HSP70, a chaperone protein that has been shown to counteract paraquat toxicity in other experimental models and could therefore contribute to neuroprotection in alpha-synuclein transgenic mice. The results indicate a dissociation between toxicant-induced alpha-synuclein deposition and neurodegeneration. They support a role of alpha-synuclein against toxic insults and suggest that its involvement in human neurodegenerative processes may arise not only from a gain of toxic function, as previously proposed, but also from a loss of defensive properties.

Animals↗