Ketamine Does Not Exert Protective Properties on Dopaminergic Neurons in the Lactacystin Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is an age-related neurodegenerative condition characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). A loss of proteasome function participates to the pathogenesis of PD, leading to the development of rodent models in which a proteasome inhibitor is applied to the nigrostriatal pathway. We recently characterized the intranigral lactacystin (LAC) mouse model, leading to nigrostriatal degeneration, motor dysfunction and alpha-synuclein accumulation. In the present study, we compared the effect of two commonly used anesthetics for generating animal models of PD—i.e., ketamine (KET) and isoflurane (ISO)—on the vulnerability of mouse dopaminergic neurons to proteasome inhibition-induced degeneration. Both anesthetics have the potential to affect the susceptibility of the nigrostriatal pathway for toxin-induced degeneration, and are known to modulate dopamine (DA) homeostasis. Yet, their impact on nigrostriatal degeneration in the proteasome inhibition model has not been evaluated. Unilateral injection with LAC in the SNpc of mice induced motor impairment and significantly reduced the number of dopaminergic cells to ~55%, irrespective of the anesthetic used. However, LAC-induced striatal DA depletion was slightly affected by the choice of anesthetic, resulting in a significant increase in DA turnover in the ISO- but not in KET-treated mice. These results suggest that the extent of nigrostriatal dopaminergic neural loss caused by LAC is not influenced by the choice of anesthetic, and that compared to other PD models, KET is not neuroprotective in the LAC model

Chronic sulfasalazine treatment in mice induces system xc- - independent adverse effects

Despite ample evidence for the therapeutic potential of inhibition of the cystine/glutamate antiporter system x(c) (−) in neurological disorders and in cancer, none of the proposed inhibitors is selective. In this context, a lot of research has been performed using the EMA- and FDA-approved drug sulfasalazine (SAS). Even though this molecule is already on the market for decades as an anti-inflammatory drug, serious side effects due to its use have been reported. Whereas for the treatment of the main indications, SAS needs to be cleaved in the intestine into the anti-inflammatory compound mesalazine, it needs to reach the systemic circulation in its intact form to allow inhibition of system x(c) (−). The higher plasma levels of intact SAS (or its metabolites) might induce adverse effects, independent of its action on system x(c) (−). Some of these effects have however been attributed to system x(c) (−) inhibition, calling into question the safety of targeting system x(c) (−). In this study we chronically treated system x(c) (−) - deficient mice and their wildtype littermates with two different doses of SAS (160 mg/kg twice daily or 320 mg/kg once daily, i.p.) and studied some of the adverse effects that were previously reported. SAS had a negative impact on the survival rate, the body weight, the thermoregulation and/or stress reaction of mice of both genotypes, and thus independent of its inhibitory action on system x(c) (−). While SAS decreased the total distance travelled in the open-field test the first time the mice encountered the test, it did not influence this parameter on the long-term and it did not induce other behavioral changes such as anxiety- or depressive-like behavior. Finally, no major histological abnormalities were observed in the spinal cord. To conclude, we were unable to identify any undesirable system x(c) (−)-dependent effect of chronic administration of SAS

Absence of system xc⁻ on immune cells invading the central nervous system alleviates experimental autoimmune encephalitis

Background: Multiple sclerosis (MS) is an autoimmune demyelinating disease that affects the central nervous system (CNS), leading to neurodegeneration and chronic disability. Accumulating evidence points to a key role for neuroinflammation, oxidative stress, and excitotoxicity in this degenerative process. System x(c)- or the cystine/glutamate antiporter could tie these pathological mechanisms together: its activity is enhanced by reactive oxygen species and inflammatory stimuli, and its enhancement might lead to the release of toxic amounts of glutamate, thereby triggering excitotoxicity and neurodegeneration. Methods: Semi-quantitative Western blotting served to study protein expression of xCT, the specific subunit of system x(c)-, as well as of regulators of xCT transcription, in the normal appearing white matter (NAWM) of MS patients and in the CNS and spleen of mice exposed to experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS. We next compared the clinical course of the EAE disease, the extent of demyelination, the infiltration of immune cells and microglial activation in xCT-knockout (xCT(-/-)) mice and irradiated mice reconstituted in xCT(-/-) bone marrow (BM), to their proper wild type (xCT(+/+)) controls. Results: xCT protein expression levels were upregulated in the NAWM of MS patients and in the brain, spinal cord, and spleen of EAE mice. The pathways involved in this upregulation in NAWM of MS patients remain unresolved. Compared to xCT(+/+) mice, xCT(-/-) mice were equally susceptible to EAE, whereas mice transplanted with xCT(-/-) BM, and as such only exhibiting loss of xCT in their immune cells, were less susceptible to EAE. In none of the above-described conditions, demyelination, microglial activation, or infiltration of immune cells were affected. Conclusions: Our findings demonstrate enhancement of xCT protein expression in MS pathology and suggest that system x(c)- on immune cells invading the CNS participates to EAE. Since a total loss of system x(c)- had no net beneficial effects, these results have important implications for targeting system x(c)- for treatment of MS

Formalization and Simulation of alpha-Synuclein Aggregation and Propagation under Different Pathobiological Conditions in PSMaude

PSMaude is a probabilistic extension of Maude that provides an expressive probabilistic strategy language to quantify the nondeterminism in probabilistic rewrite theories, allowing the user to specify different probabilistic strategies on top of a base model. In this paper we use PSMaude to define a formal, executable real-time model of the aggregation and interneuronal propagation of the alpha-synuclein (alpha-syn) protein causing Parkinson's disease (PD). To the best of our knowledge, this is the first effort to formally model the spatial, multicellular aspect of alpha-syn accumulation in detail, i.e., the propagation of the pathogenic aggregates through a neural network that is dynamically changing as a consequence of aggregation-induced neuronal death. We then define different probabilistic strategies on top of our model to formalize the aggregation and propagation of alpha-syn in three different scenarios: (i) in a healthy individual, (ii) in a predisposed individual with either the sporadic or the familial form of PD, and (iii) in a predisposed individual that is given some treatment with rapamycin. The strategies are time-dependent, since the brain becomes more predisposed to PD with aging. We then use PSMaude to simulate our model in these different scenarios

Oxidative Stress in Genetic Mouse Models of Parkinson’s Disease

There is extensive evidence in Parkinson’s disease of a link between oxidative stress and some of the monogenically inherited Parkinson’s disease-associated genes. This paper focuses on the importance of this link and potential impact on neuronal function. Basic mechanisms of oxidative stress, the cellular antioxidant machinery, and the main sources of cellular oxidative stress are reviewed. Moreover, attention is given to the complex interaction between oxidative stress and other prominent pathogenic pathways in Parkinson’s disease, such as mitochondrial dysfunction and neuroinflammation. Furthermore, an overview of the existing genetic mouse models of Parkinson’s disease is given and the evidence of oxidative stress in these models highlighted. Taken into consideration the importance of ageing and environmental factors as a risk for developing Parkinson’s disease, gene-environment interactions in genetically engineered mouse models of Parkinson’s disease are also discussed, highlighting the role of oxidative damage in the interplay between genetic makeup, environmental stress, and ageing in Parkinson’s disease

Acute versus long-term effects of 6-hydroxydopamine on oxidative stress and dopamine depletion in the striatum of mice

Oxidative stress is one of the mechanisms which may be important in the pathogenesis of Parkinson's disease. In the current study, the effects of 6-hydroxydopamine (6-OHDA) perfusion on hydroxyl radical formation in the mouse striatum were investigated using the in vivo salicylate trapping microdialysis technique. The latter uses salicylate as a trapping agent for hydroxyl radicals with formation of 2,3-dihydroxybenzoic acid (2,3-DHBA), which is measured by HPLC. Two different approaches of the technique were validated in mice. First, perfusion of the trapping agent salicylate (1 mM) via the probe in combination with 6-OHDA (5 μM) was used to screen for radical scavenging properties of compounds in mice. Alternatively, striatal administration of 6-OHDA in a concentration known to induce nigrostriatal denervation (1 mM), without the trapping agent, allowed to maximally challenge the neuronal microenvironment and as such to investigate both its acute and long-term effects. In the first method, as expected, glutathione (GSH) (1.5 mM) prevented the 6-OHDA-induced increase in 2,3-DHBA levels. In the second method, GSH prevented the hydroxyl radical formation, while depletion of GSH with 2-cyclohexen-1-one (CHO) resulted in significantly higher 2,3-DHBA levels than when 6-OHDA was perfused alone. Three weeks after the local 6-OHDA perfusion, the total striatal dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) content were reduced by 30%, compared to the intact striatum, accompanied by a reduction in striatal tyrosine hydroxylase (TH) immunoreactive (ir) nerve terminals. This suggests that the second method can be used to determine the acute as well as the long-term effects of 6-OHDA in the mouse striatum

Acute versus long-term effects of 6-hydroxydopamine on oxidative stress and dopamine depletion in the striatum of mice

Oxidative stress is one of the mechanisms which may be important in the pathogenesis of Parkinson's disease. In the current study, the effects of 6-hydroxydopamine (6-OHDA) perfusion on hydroxyl radical formation in the mouse striatum were investigated using the in vivo salicylate trapping microdialysis technique. The latter uses salicylate as a trapping agent for hydroxyl radicals with formation of 2,3-dihydroxybenzoic acid (2,3-DHBA), which is measured by HPLC. Two different approaches of the technique were validated in mice. First, perfusion of the trapping agent salicylate (1mM) via the probe in combination with 6-OHDA (5μM) was used to screen for radical scavenging properties of compounds in mice. Alternatively, striatal administration of 6-OHDA in a concentration known to induce nigrostriatal denervation (1mM), without the trapping agent, allowed to maximally challenge the neuronal microenvironment and as such to investigate both its acute and long-term effects. In the first method, as expected, glutathione (GSH) (1.5mM) prevented the 6-OHDA-induced increase in 2,3-DHBA levels. In the second method, GSH prevented the hydroxyl radical formation, while depletion of GSH with 2-cyclohexen-1-one (CHO) resulted in significantly higher 2,3-DHBA levels than when 6-OHDA was perfused alone. Three weeks after the local 6-OHDA perfusion, the total striatal dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) content were reduced by 30%, compared to the intact striatum, accompanied by a reduction in striatal tyrosine hydroxylase (TH) immunoreactive (ir) nerve terminals. This suggests that the second method can be used to determine the acute as well as the long-term effects of 6-OHDA in the mouse striatum.status: publishe

Lack of effect of Theiler's murine encephalomyelitis virus infection on system xc⁻.

Changes in the expression of xCT, the specific subunit of system xc(-) or the cystine/glutamate antiporter, have been associated with several neurological disorders and system xc(-) was recently proposed as a potential target for the development of new treatment strategies for multiple sclerosis (MS). In this study we used Theiler's murine encephalomyelitis virus (TMEV) infection, both in vitro and in vivo, as a model to further evaluate the involvement of system xc(-) in MS. Protein levels of xCT, as well as activity of system xc(-) were unaffected in RAW264.7 macrophages after infection with the demyelinating DA strain of TMEV. Also, protein expression of xCT remained stable in spinal cord and brain of FVB mice 1-2 and 6 weeks after intracranial injection of the DA strain of TMEV. These results demonstrate that TMEV infection of macrophages or FVB mice has no effect on system xc(-) and as such cannot be used as a model to study the involvement of system xc(-) in MS

The cystine-glutamate exchanger (xCT, Slc7a11) is expressed in significant concentrations in a subpopulation of astrocytes in the mouse brain.

The cystine-glutamate exchanger (xCT) promotes glutathione synthesis by catalyzing cystine uptake and glutamate release. The released glutamate may modulate normal neural signaling and contribute to excitotoxicity in pathological situations. Uncertainty, however, remains as neither the expression levels nor the distribution of xCT have been unambiguously determined. In fact, xCT has been reported in astrocytes, neurons, oligodendrocytes and microglia, but most of the information derives from cell cultures. Here, we show by immunohistochemistry and by Western blotting that xCT is widely expressed in the central nervous system of both sexes. The labeling specificity was validated using tissue from xCT knockout mice as controls. Astrocytes were selectively labeled, but showed greatly varying labeling intensities. This astroglial heterogeneity resulted in an astrocyte domain-like labeling pattern. Strong xCT labeling was also found in the leptomeninges, along some blood vessels, in selected circumventricular organs and in a subpopulation of tanycytes residing the lateral walls of the ventral third ventricle. Neurons, oligodendrocytes and resting microglia, as well as reactive microglia induced by glutamine synthetase deficiency, were unlabeled. The concentration of xCT protein in hippocampus was compared with that of the EAAT3 glutamate transporter by immunoblotting using a chimeric xCT-EAAT3 protein to normalize xCT and EAAT3 labeling intensities. The immunoblots suggested an xCT/EAAT3 ratio close to one (0.75 ± 0.07; average ± SEM; n = 4) in adult C57BL6 mice. CONCLUSIONS: xCT is present in select blood/brain/CSF interface areas and in an astrocyte subpopulation, in sufficient quantities to support the notion that system xc- provides physiologically relevant transport activity