Concurrent changes in ¹H MRS metabolites and antioxidant enzymes in the brain of C57BL/6 mouse short-termly exposed to cuprizone: possible implications for schizophrenia

Sulforaphane, an Nrf-2 Agonist, Modulates Oxidative Stress and Inflammation in a Rat Model of Cuprizone-Induced Cardiotoxicity and Hepatotoxicity

Cuprizone (CPZ) is a neurotoxic agent that is used to induce demyelination and neurotoxicity in rats. This study aimed to investigate the protective potential of sulforaphane (SF), nuclear factor E2 related factor (Nrf-2) activator, against CPZ-induced cardiotoxicity and hepatotoxicity. Male adult Wistar rats (n = 18) were fed with a regular diet or a CPZ-contained diet (0.2%) for four weeks. The rats were divided into three groups (n = 6): negative control rats, CPZ-exposed rats, and CPZ + SF treated rats. SF was intraperitoneally administrated (2 mg/kg/day) for two weeks. The anti-inflammatory and anti-oxidative functions of SF were investigated biochemically, histologically, and immunohistochemically. CPZ increased serum levels of cardiac troponin 1 (CTn1), aspartate amino transaminase (AST), alanine amino transaminase (ALT), and alkaline phosphatase (ALP). In addition, serum levels of inflammatory interferon-gamma (IFN-γ), and pro-inflammatory interleukin 1β (IL-1β) were significantly elevated. Moreover, CPZ administration provoked oxidative stress as manifested by declined serum levels of total antioxidant capacity (TAC), as well as, stimulated lipid peroxidation and decreased catalase activities in both cardiac and hepatic tissues. SF treatment reversed all these biochemical alterations through exerting anti-oxidative and anti-inflammatory activities, and this was supported by histopathological investigations in both cardiac and hepatic tissues. This SF-triggered modulation of oxidative stress and inflammation is strongly associated with Nrf-2 activation, as evidenced by activated immunoexpression in both cardiac and hepatic tissues. This highlights the cardioprotective and hepatoprotective activities of SF via Nrf-2 activation and enhancing catalase function.

Cognitive disturbances in the cuprizone model of multiple sclerosis

Cognitive problems frequently accompany neurological manifestations of multiple sclerosis (MS). However, during screening of preclinical candidates, assessments of behaviour in mouse models of MS typically focus on locomotor activity. In the present study, we analysed cognitive behaviour of 9 to 10-week-old female C57Bl/6J mice orally administered with the toxin cuprizone that induces demyelination, a characteristic feature of MS. Animals received 400 mg/kg cuprizone daily for 2 or 4 weeks, and their performance was compared with that of vehicle-treated mice. Cuprizone-treated animals showed multiple deficits in short touchscreen-based operant tasks: they responded more slowly to visual stimuli, rewards and made more errors in a simple rule-learning task. In contextual/cued fear conditioning experiments, cuprizone-treated mice showed significantly lower levels of contextual freezing than vehicle-treated mice. Diffusion tensor imaging showed treatment-dependent changes in fractional anisotropy as well as in axial and mean diffusivities in different white matter areas. Lower values of fractional anisotropy and axial diffusivity in cuprizone-treated mice indicated developing demyelination and/or axonal damage. Several diffusion tensor imaging measurements correlated with learning parameters. Our results show that translational touchscreen operant tests and fear conditioning paradigms can reliably detect cognitive consequences of cuprizone treatment. The suggested experimental approach enables screening novel MS drug candidates in longitudinal experiments for their ability to improve pathological changes in brain structure and reverse cognitive deficits.

Differential Susceptibility and Vulnerability of Brain Cells in C57BL/6 Mouse to Mitochondrial Dysfunction Induced by Short-Term Cuprizone Exposure

Cuprizone (CPZ) is a chemical chelator toxic to mitochondria of cells. While inducing oligodendrocyte (OL) loss and demyelination, CPZ caused no fatal damage to the other brain cells (neurons, astrocytes, and microglia) in previous studies, suggesting differential susceptibility and vulnerability of brain cells to the CPZ intoxication. To demonstrate this interpretation, C57BL/6 mice were fed rodent chow without or with CPZ (0.2%, w/w) for 7 days. One day later, mitochondrial function of brain cells was assessed by proton magnetic resonance spectroscopy (¹H-MRS) and biochemical analysis. Another batch of mice were processed to localize the CPZ-induced damage to mitochondrial DNA, label brain cells, and identify apoptotic cells. Compared to controls, CPZ-exposed mice showed significantly lower levels of N-acetyl-L-aspartate, phosphocreatine, and ATP detected by ¹H-MRS, indicating mitochondrial dysfunction in brain cells. Susceptibility analysis showed an order of OLs, microglia, and astrocytes from high to low, in terms of the proportion of 8-OHdG labeled cells in each type of these cells in corpus callosum. Vulnerability analysis showed the highest proportion of caspase-3 positive cells in labeled OLs in cerebral cortex and hippocampus, where neurons showed no caspase-3 labeling, but the highest proportion of 8-OHdG labeling, indicating a lowest vulnerability but highest susceptibility to CPZ-induced mitochondrial dysfunction. Immature OLs, microglia, and astrocytes showed adaptive changes in proliferation and activation in response to CPZ-exposure. These data for the first time demonstrated the CPZ-induced mitochondria dysfunction in brain cells of living mouse and specified the differential susceptibility and vulnerability of brain cells to the CPZ intoxication.

Five Decades of Cuprizone, an Updated Model to Replicate Demyelinating Diseases

INTRODUCTION

Demyelinating diseases of the central nervous system (CNS) comprise a group of neurological disorders characterized by progressive (and eventually irreversible) loss of oligodendrocytes and myelin sheaths in the white matter tracts. Some of myelin disorders include: Multiple sclerosis, Guillain-Barré syndrome, peripheral nerve polyneuropathy and others. To date, the etiology of these disorders is not well known and no effective treatments are currently available against them. Therefore, further research is needed to gain a better understand and treat these patients. To accomplish this goal, it is necessary to have appropriate animal models that closely resemble the pathophysiology and clinical signs of these diseases. Herein, we describe the model of toxic demyelination induced by cuprizone (CPZ), a copper chelator that reduces the cytochrome and monoamine oxidase activity into the brain, produces mitochondrial stress and triggers the local immune response. These biochemical and cellular responses ultimately result in selective loss of oligodendrocytes and microglia accumulation, which conveys to extensive areas of demyelination and gliosis in corpus callosum, superior cerebellar peduncles and cerebral cortex. Remarkably, some aspects of the histological pattern induced by CPZ are similar to those found in multiple sclerosis. CPZ exposure provokes behavioral changes, impairs motor skills and affects mood as that observed in several demyelinating diseases. Upon CPZ removal, the pathological and histological changes gradually revert. Therefore, some authors have postulated that the CPZ model allows to partially mimic the disease relapses observed in some demyelinating diseases.

CONCLUSION

for five decades, the model of CPZ-induced demyelination is a good experimental approach to study demyelinating diseases that has maintained its validity, and is a suitable pharmacological model for reproducing some key features of demyelinating diseases, including multiple sclerosis.

Adenosine Promotes the Recovery of Mice from the Cuprizone-Induced Behavioral and Morphological Changes while Effecting on Microglia and Inflammatory Cytokines in the Brain

Recent studies have shown that multiple sclerosis (MS) and schizophrenia share similarities in some respects, including white matter damage and neuroinflammation. On the other hand, adenosine was reported to promote oligodendrocyte precursor maturation and remyelinating while influencing microglia activation. The aim of the present study was to examine possible beneficial effects of adenosine on the recovery of cuprizone (CPZ)-exposed mouse which has been used as an animal model of MS and schizophrenia as the CPZ-exposed mouse presents demyelination, oligodendrocyte loss, microglia accumulation, as well as behavioral changes. As reported previously, C57BL/6 mice, after fed CPZ for 5 weeks, showed salient demyelination and oligodendrocyte loss in the cerebral cortex (CTX) and hippocampus, in addition to displaying anxiety-like behavior, spatial working memory deficit, and social interaction impairment. Administration of adenosine for 7 days during the recovery period after CPZ withdrawal promoted the behavioral recovery of CPZ-exposed mice and accelerated the remyelinating process in the brains of mice after CPZ withdrawal in a dose-dependent manner. In addition, the effective dose (10 mg/kg) of adenosine inhibited microglia activation and suppressed abnormal elevation of the pro-inflammatory cytokines IL-1β and TNF-α in CTX and hippocampus, but increased levels of the anti-inflammatory cytokines IL-4 or IL-10 in the same brain regions during the remyelinating process. These results provided an evidence-based rationale for the application of adenosine or its analogues as add-on therapy for schizophrenia.

N-acetylcysteine attenuates the cuprizone-induced behavioral changes and oligodendrocyte loss in male C57BL/7 mice via its anti-inflammation actions

Previous animal studies have linked white matter damage to certain schizophrenia-like behaviors in cuprizone (CPZ)-exposed mouse. Mitochondrial dysfunction, oxidative stress, neuroinflammation, and oligodendrocyte loss coexist in the brain of such mice. The aim of this study was to examine effects of the antioxidant N-acetylcysteine (NAC) on CPZ-induced behavioral changes and concurrent oligodendrocyte loss, oxidative stress, and neuroinflammation in these animals. Male C57BL/6 mice were given intraperitoneal saline or NAC at doses of 100, 200, and 400 mg/kg/day for 2 weeks; animals were fed a CPZ-containing diet (0.2%, w/w) during days 5-14. During days 15-17, the mice were examined in open-field, social recognition, and Y-maze tests (1 test per day). Six mice in each group were then used for biochemical and enzyme-linked immunosorbent assay analyses, while the remaining animals were used for immunohistochemical and immunofluorescence staining. The mice exposed to CPZ for 10 days showed significantly lower spontaneous alternation in the Y-maze, lower activity of total superoxide dismutase, and glutathione peroxidase, but higher levels of malondialdehyde in the cerebral cortex and hippocampus, elevated concentrations of interleukin-1β and tumor necrosis factor-α in the brain regions mentioned above and caudate putamen, and a decreased number of mature oligodendrocytes, but increased number of microglia in all the brain regions examined. These changes, however, were not seen or effectively alleviated in NAC-treated mice at all three doses. These results demonstrate that NAC protected mature oligodendrocytes against the toxic effects of CPZ, likely via its antioxidant and anti-inflammatory actions.

Myricetin alleviates cuprizone-induced behavioral dysfunction and demyelination in mice by Nrf2 pathway

Multiple sclerosis (MS) is a demyelinating disease occurring in the central nervous system. In the present study, we evaluated the function of myricetin on the alleviation of behavioral dysfunction and myelin protection in the cuprizone-induced demyelination model. Mice were daily fed with fodder including 0.2% cuprizone and were administrated myricetin (100 mg kg^-1) by gavage administration for 5 weeks. The treatment of myricetin ameliorated hyper-locomotion and behavior impairment induced by cuprizone toxicity. With the administration of myricetin, the demyelinating lesion was lessened via increasing the LFB staining area and myelin phosphatide protein (MBP) expression. In addition, myricetin evidently promoted Nrf2 translocation in the nuclear fraction and enhanced the HO-1 and NQO1 expression levels. Our data revealed that myricetin may be a potential candidate for mitigating motor defects and demyelination in a cuprizone-induced mouse model via activating the Nrf2 pathway.

Evaluation of neuron-glia integrity by in vivo proton magnetic resonance spectroscopy: Implications for psychiatric disorders

Proton magnetic resonance spectroscopy (¹H-MRS) has been widely applied in human studies. There is now a large literature describing findings of brain MRS studies with mental disorder patients including schizophrenia, bipolar disorder, major depressive disorder, and anxiety disorders. However, the findings are mixed and cannot be reconciled by any of the existing interpretations. Here we proposed the new theory of neuron-glia integrity to explain the findings of brain ¹H-MRS stuies. It proposed the neurochemical correlates of neuron-astrocyte integrity and axon-myelin integrity on the basis of update of neurobiological knowledge about neuron-glia communication and of experimental MRS evidence for impairments in neuron-glia integrity from the authors and the other investigators. Following the neuron-glia integrity theories, this review collected evidence showing that glutamate/glutamine change is a good marker for impaired neuron-astrocyte integrity and that changes in N-acetylaspartate and lipid precursors reflect impaired myelination. Moreover, this new theory enables us to explain the differences between MRS findings in neuropsychiatric and neurodegenerative disorders.

Thalamus Degeneration and Inflammation in Two Distinct Multiple Sclerosis Animal Models

There is a broad consensus that multiple sclerosis (MS) represents more than an inflammatory disease: it harbors several characteristic aspects of a classical neurodegenerative disorder, i.e., damage to axons, synapses, and nerve cell bodies. While several accepted paraclinical methods exist to monitor the inflammatory-driven aspects of the disease, techniques to monitor progression of early and late neurodegeneration are still in their infancy and have not been convincingly validated. It was speculated that the thalamus with its multiple reciprocal connections is sensitive to inflammatory processes occurring in different brain regions, thus acting as a "barometer" for diffuse brain parenchymal damage in MS. To what extent the thalamus is affected in commonly applied MS animal models is, however, not known. In this article we describe direct and indirect damage to the thalamus in two distinct MS animal models. In the cuprizone model, we observed primary oligodendrocyte stress which is followed by demyelination, microglia/astrocyte activation, and acute axonal damage. These degenerative cuprizone-induced lesions were found to be more severe in the lateral compared to the medial part of the thalamus. In MOG35-55-induced EAE, in contrast, most parts of the forebrain, including the thalamus were not directly involved in the autoimmune attack. However, important thalamic afferent fiber tracts, such as the spinothalamic tract were inflamed and demyelinated on the spinal cord level. Quantitative immunohistochemistry revealed that this spinal cord inflammatory-demyelination is associated with neuronal loss within the target region of the spinothalamic tract, namely the sensory ventral posterolateral nucleus of the thalamus. This study highlights the possibility of trans-neuronal degeneration as one mechanism of secondary neuronal damage in MS. Further studies are now warranted to investigate involved cell types and cellular mechanisms.

The cuprizone-induced changes in (1)H-MRS metabolites and oxidative parameters in C57BL/6 mouse brain: Effects of quetiapine

Cuprizone is a copper-chelating agent and able to induce oligodendrocyte loss and demyelination in C57BL/6 mouse brain. Recent studies have used the cuprizone-fed mouse as an animal model of schizophrenia to examine putative roles of altered oligodendrocytes in this mental disorder. The present study reported the effects of cuprizone on the brain metabolites and oxidative parameters with the aim of providing neurochemical evidence for the application of the cuprizone mouse as an animal model of schizophrenia. In addition, we examined effects of quetiapine on the cuprizone-induced changes in brain metabolites and oxidative parameters; this atypical antipsychotic was shown to ameliorate the cuprizone-induced demyelination and behavioral changes in previous studies. C57BL/6 mice were fed a standard rodent chow without or with cuprizone (0.2% w/w) for four weeks during which period they were given sterilized saline or quetiapine in saline. The results of the proton magnetic resonance spectroscopy (1H-MRS) showed that cuprizone-feeding decreased (1)H-MRS signals of N-acetyl-l-aspartate (NAA), total NAA (NAA + NAAG), and choline-containing compounds (phosphorylcholine and glycerophosphorylcholine), suggestive of mitochondrial dysfunction in brain neurons. Biochemical analyses showed lower activities of catalase and glutathione peroxidase, but higher levels of malondialdehyde and H2O2 in the brain tissue of cuprizone-fed mice, indicative of an oxidative stress. These cuprizone-induced changes were effectively relieved in the mice co-administered with cuprizone and quetiapine, although the antipsychotic alone showed no effect. These findings suggest the toxic effects of cuprizone on mitochondria and an antioxidant capacity of quetiapine, by which this antipsychotic relieves the cuprizone-induced mitochondrial dysfunction in brain cells.

Quetiapine mitigates the neuroinflammation and oligodendrocyte loss in the brain of C57BL/6 mouse following cuprizone exposure for one week

This study aimed at examining effects of quetiapine (QTP), an atypical antipsychotic, on the behaviors of mice which had consumed cuprizone (CPZ)-containing diet for one week and on inflammatory reactions and oligodendrocyte (OL) loss in brains of them. Young adult C57BL/6 mice, after fed CPZ-containing diet (0.2%, w/w) for one week, showed an increase in the locomotor activity in the open-field, and a decreased exploration time in the novel object recognition (NOR) test compared to controls. But, these changes were not seen in mice co-administered with QTP and CPZ. All mice in the four groups showed comparable performances in Y-maze test. After the behavioral tests, mice were killed and their brains were processed for immunohistochemical and immunofluorescence staining to examine OLs, astrocytes and microglia. The levels of proinflammatory cytokines TNF-α and IL-6 in certain brain regions were also evaluated by ELISA method. Mice in the NS+CPZ group showed fewer OLs, more activated astrocytes and microglia with higher immunofluorescence intensity in the examined brain regions of the corpus callosum, caudate putamen, cerebral cortex, and hippocampus. The levels of TNF-α and IL-6 in some of these brain regions were also increased. But these changes were completely blocked or effectively ameliorated in the QTP+CPZ group. These results demonstrated an anti-inflammatory effect of QTP in CPZ-exposed mice and this action may contribute to its protection on OLs and beneficial effects on the CPZ-induced behavioral changes in these mice.

Brain metabolite changes in subcortical regions after exposure to cuprizone for 6 weeks: potential implications for schizophrenia

Cuprizone is a copper chelating agent able to selectively damage the white matter in the mouse brain. Recent studies have reported behavioral abnormalities relevant to some of schizophrenia symptoms. While associating white matter damage to the behavioral abnormalities, these previous studies did not rule out the possible impairment in neuronal functions in cuprizone-exposed mice. The aim of this study was to examine brain metabolites of the cuprizone-exposed mice by proton magnetic resonance spectroscopy ((1)H-MRS). The examined brain regions were the caudoputamen, midbrain, and thalamus; these subcortical regions showed different susceptibilities to cuprizone in terms of demyelination and oligodendrocyte loss in previous studies. Young C57BL/6 mice were fed a standard rodent chow without or with cuprizone (0.2 %) for 6 weeks. At the end, open-field and Y-maze tests were performed to measure the emotional and cognitive behaviors of the animals, followed by (1)H-MRS procedure to evaluate the brain metabolites. Cuprizone-exposure increased anxiety levels and impaired spatial working memory. The same treatment increased T2 signal intensity in the cerebral cortex, hippocampus, and caudoputamen, but not in the thalamus. Cuprizone-exposure decreased the concentrations of NAA and NAA+NAAG in caudoputamen, but not in thalamus and midbrain. It decreased levels of Cr+PCr, GPC+PCh and myo-inositol in all the three brain regions. These results provided neurochemical evidence for the impairment in neuronal functions by cuprizone treatment.

Changes in proinflammatory cytokines and white matter in chronically stressed rats

Although the pathogenesis of depression, an incapacitating psychiatric ailment, remains largely unknown, previous human and animal studies have suggested that both proinflammatory cytokines and altered oligodendrocytes play important roles in the condition. This study examined these two factors in the brains of rats following unpredictable chronic mild stress for 4 weeks, with the hypothesis that chronic stress may affect oligodendrocytes and elevate proinflammatory cytokines in the brain. After suffering unpredictable stressors for 4 weeks, the rats showed depression-like behaviors, including decreased locomotion in the open field, increased immobility time in the forced swim test, and decreased sucrose consumption and less sucrose preference when compared with controls. Immunohistochemical staining of brain sections showed higher immunoreactivity of proinflammatory cytokines in certain brain regions of stressed rats compared with controls; lower immunoreactivity of myelin basic protein and fewer mature oligodendrocytes were seen in the prefrontal cortex, but no demyelination was detected. These results are interpreted and discussed in the context of recent findings from human and animal studies.