Martin Stangel

Cortical demyelination is prominent in the murine cuprizone model and is strain-dependent.

The cuprizone model of toxic demyelination in the central nervous system is commonly used to investigate the pathobiology of remyelination in the corpus callosum. However, in human demyelinating diseases such as multiple sclerosis, recent evidence indicates a considerable amount of cortical demyelination in addition to white matter damage. Therefore, we have investigated cortical demyelination in the murine cuprizone model. To induce demyelination, C57BL/6 mice were challenged with 0.2% cuprizone feeding for 6 weeks followed by a recovery phase of 6 weeks with a cuprizone-free diet. In addition to the expected demyelination in the corpus callosum, the cortex of C57BL/6 mice was completely demyelinated after 6 weeks of cuprizone feeding. After withdrawal of cuprizone the cortex showed complete remyelination similar to that in the corpus callosum. When C57BL/6 mice were fed cuprizone for a prolonged period of 12 weeks, cortical remyelination was significantly delayed. Because interstrain differences have been described, we also investigated the effects of cuprizone on cortical demyelination in BALB/cJ mice. In these mice, cortical demyelination was only partial. Moreover, cortical microglia accumulation was markedly increased in BALB/cJ mice, whereas microglia were absent in the cortex of C57BL/6 mice. In summary, our results show that cuprizone feeding is an excellent model in which to study cortical demyelination and remyelination, including contributing genetic factors represented by strain differences.

Astrocytes regulate myelin clearance through recruitment of microglia during cuprizone-induced demyelination

Recent evidence suggests that astrocytes play an important role in regulating de- and remyelination in multiple sclerosis. The role of astrocytes is controversial, and both beneficial as well as detrimental effects are being discussed. We performed loss-of-function studies based on astrocyte depletion in a cuprizone-induced rodent model of demyelination. This led to strong astrogliosis accompanied by microgliosis and demyelination in C57BL/6 wild-type mice. Ablation of astrocytes in glial fibrillary acidic protein-thymidine kinase transgenic mice was associated with a failure of damaged myelin removal and a consecutive delay in remyelination. Despite oligodendrocyte death, myelin was still present, but ultrastructual investigations showed that the myelin structure was loosened and this damaged myelin did not protect axons. These alterations were associated with a decrease in microglial activation. Thus, our results show that astrocyte loss does not prevent myelin damage, but clearance of damaged myelin through recruitment of microglia is impaired. Further studies suggest that this process is regulated by the chemokine CXCL10. As a consequence of the delayed removal of myelin debris, remyelination and oligodendrocyte precursor cell proliferation were impaired. Experiments omitting the influence of myelin debris demonstrated an additional beneficial effect of astrocytes on oligodendrocyte regeneration during remyelination. In conclusion, these data demonstrate for the first time in vivo that astrocytes provide the signal environment that forms the basis for the recruitment of microglia to clear myelin debris, a process required for subsequent repair mechanisms. This is of great importance to understanding regenerative processes in demyelinating diseases such as multiple sclerosis.

Drug Insight: the use of intravenous immunoglobulin in neurology—therapeutic considerations and practical issues

Over the past few years, we have achieved increasing success in the treatment of a number of autoimmune-mediated disorders affecting nerves and muscles. This success is partly attributable to the use of high-dose polyclonal intravenous immunoglobulin (IVIg), which has dramatically changed our treatment options. On the basis of results from controlled, but non-FDA-approved, clinical trials, IVIg is now the treatment of choice for Guillain–Barré syndrome, chronic idiopathic inflammatory demyelinating polyneuropathy and multifocal motor neuropathy; IVIg offers rescue therapy for patients with rapidly worsening myasthenia gravis, and is a second-line therapy for dermatomyositis, stiff-person syndrome, and pregnancy-associated or postpartum multiple sclerosis attacks. The ability of IVIg to treat such immunologically diverse disorders effectively, coupled with its excellent safety profile, has led clinicians to use the drug more liberally, even in diseases for which the data are weak and not evidence-based and in patients with coexisting conditions. Use of IVIg for such indications can increase the risk of complications while raising the cost of the drug. Practical issues regarding dosing and frequency of infusions generate dilemmas in clinical practice. In this article, we review the current indications for IVIg treatment, address practical issues related to the use and costs of the drug, and summarize its mechanisms of action.

Remyelinating strategies for the treatment of multiple sclerosis

Demyelination is the pathological hallmark of multiple sclerosis (MS) lesions. The concept of remyelination has gained acceptance in recent years, but naturally occurring remyelination is incomplete. To improve repair processes, a number of strategies have been explored experimentally and clinical trials are being carried out. In principle, remyelination can be achieved by either promoting endogenous repair mechanisms or by providing an exogenous source of myelinating cells via transplantation. Both approaches have been successful in animal models of demyelination. Besides, many studies have elucidated principal mechanisms of oligodendrocyte biology and remyelination in the central nervous system (CNS). This progress in knowledge also allowed for more specific interventions. First clinical trials to enhance endogenous remyelination have been performed, unfortunately with disappointingly negative results. This illustrates that experimental data cannot be easily transferred to human disease, and more detailed knowledge on the regulatory mechanisms of remyelination in MS is required. Recently, the first MS patient received a transplant of autologous Schwann cells. Many other cell types are being studied experimentally, including stem cells. Despite the ethical problems associated with an embryonic cell source, new developments in stem cell biology indicate that adult stem cells or bone marrow-derived cells may substitute for embryonic cells in the future. In this review, we describe the current views on oligodendrocyte biology, myelination and remyelination, and focus on recent developments leading to reconstructing, remyelinating strategies in MS.

Regional differences between grey and white matter in cuprizone induced demyelination

Cuprizone feeding is a commonly used model to study experimental de- and remyelination, with the corpus callosum being the most frequently investigated white matter tract. We have previously shown that demyelination is also extensive in the cerebral cortex in the cuprizone model. In the current study, we have performed a detailed analysis of the dynamics of demyelination in the cortex in comparison to the corpus callosum. Prominent and almost complete demyelination in the corpus callosum was observed after 4.5-5 weeks of 0.2% cuprizone feeding, whereas complete cortical demyelination was only observed after 6 weeks of cuprizone feeding. Interestingly, remyelination in the corpus callosum occurred even before the termination of cuprizone administration. Accumulation of microglia in the corpus callosum started as early as week 3 reaching its maximum at week 4.5 and was still significantly elevated at week 6 of cuprizone treatment. Within the cortex only a few scattered activated microglial cells were found. Furthermore, the intensity of astrogliosis, accumulation of oligodendrocyte progenitor cells and nestin positive cells differed between the two areas investigated. The time course and dynamics of demyelination differ in the corpus callosum and in the cortex, suggesting different underlying pathomechanisms.

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Towards the implementation of ‘no evidence of disease activity’ in multiple sclerosis treatment: the multiple sclerosis decision model

Objective: The introduction of new and potent therapies for the treatment of relapsing remitting multiple sclerosis (MS) has increased the desire for therapeutic success. There is growing doubt that the mere reduction of relapse rate, Expanded Disability Status Scale (EDSS) progression and magnetic resonance imaging (MRI) markers are exclusive and appropriate factors to monitor the new aim of ‘no evidence of disease activity’ (NEDA). However, there is no generally accepted definition so far. Methods: To achieve the therapeutic aim of NEDA, a panel of MS experts searched the available literature on clinical and paraclinical outcomes to propose a test battery that is sensitive to detect disease activity in an everyday clinical setting. Results: The panel proposed to include, besides relapse rate, disability progression and MRI, neuropsychological outcome measures such as cognitive status, fatigue, depression and quality of life. To standardize the examinations in an economic and schematic way, a multifactorial model [multiple sclerosis decision model (MSDM)] that includes the domains ‘relapse’, ‘disability progression’, ‘MRI’, and ‘neuropsychology’ is proposed. The scheme reflects the complexity of the disease even in the early stages when scales such as the EDSS are not able to distinguish low levels of progression. Conclusion: The MSDM aims to support early treatment decisions and uncover timely treatment failure. Prospective investigations are required to prove that such a disease-monitoring concept leads to an early and effective silencing of disease activity.

Fumaric acid and its esters: an emerging treatment for multiple sclerosis with antioxidative mechanism of action.

Fumaric acid was originally therapeutically used in psoriasis. Several lines of evidence have demonstrated immunomodulatory but also neuroprotective effects for FAE. Clinical studies in psoriasis showed a reduction of peripheral CD4+ and CD8+ T-lymphocytes due to the ability of FAE to induce apoptosis. In vitro studies with the ester dimethylfumarate (DMF) described an inhibitory effect on nuclear factor kappa B (NF-κB)-dependent transcription of tumor necrosis factor-alpha (TNF-α) induced genes in human endothelial cells. Animal experiments in the mouse model of central nervous system demyelination, MOG-induced experimental autoimmune encephalomyelitis, revealed a clear preservation of myelin and axonal density in the plaque. Molecular studies showed that this is based on the antioxidative mechanism of action via induction of the transcription factor Nrf-2. A phase II clinical trial in relapsing-remitting multiple sclerosis (RRMS) patients with dimethylfumarate showed a significant reduction in the number of gadolinium enhancing lesions after 24weeks.

Intravenous immunoglobulin treatment of neurological autoimmune diseases

Intravenous immunoglobulin (IVIg) has been widely used in neurological diseases during the last decade. The current indications of IVIg in neurological diseases are reviewed and discussed on the basis of the available experimental data and clinical trials. Compared to other immunomodulating treatments used in neurological diseases, IVIg has only few side effects with a small risk of transmission of infectious agents. Good clinical evidence for the effectiveness is available for Guillain-Barré-Syndrome, chronic inflammatory demyelinating polyneuropathy and multifocal motor neuropathy. In conditions like myasthenia gravis and myositis favourable effects of IVIg were reported, but future studies have to be awaited. For all other neurological conditions where IVIg has been administered, there is currently no support for the use of IVIg other than in controlled trials. In conclusion, IVIg is a promising immunomodulary therapy that has been shown to be effective in some neurological autoimmune diseases. Routine use in neurological practice should be restricted to diseases for which a positive effect has been proven in controlled trials. For all other conditions no definite recommendations can presently be made.

The utility of cerebrospinal fluid analysis in patients with multiple sclerosis

Diagnosis of multiple sclerosis (MS) requires the exclusion of other possible diagnoses. For this reason, the cerebrospinal fluid (CSF) should be routinely analysed in patients with a first clinical event suggestive of MS. CSF analysis is no longer mandatory for diagnosis of relapsing–remitting MS, as long as MRI diagnostic criteria are fulfilled. However, caution is required in diagnosing MS in patients with negative MRI findings or in the absence of CSF analysis, as CSF investigation is useful to eliminate other causes of disease. The detection of oligoclonal IgG bands in CSF has potential prognostic value and is helpful for clinical decision-making. In addition, CSF analysis is important for research into the pathogenesis of MS. Pathophysiological and neurodegenerative findings of inflammation in MS have been derived from CSF investigations. Novel CSF biomarkers, though not yet validated, have been identified for diagnosis of MS and for ascertaining disease activity, prognosis and response to treatment, and are likely to increase in number with modern detection techniques. In this Review, we summarize CSF findings that shed light on the differential diagnosis of MS, and highlight the potential of novel biomarkers for this disease that could advance understanding of its pathophysiology.